Compositions comprising responsive dyes and method of using thereof

Abstract

Disclosed are compositions and systems comprising responsive dyes, as well as methods of using thereof.

Description

[0001] Attorney Docket No.11196-099WO1 Compositions Comprising Responsive Dyes and Method of Using Thereof CROSS-REFERENCE TO RELATED APPLICATIONS This application claims benefit of priority U.S. Provisional Application No. 63 / 639,635, filed April 27, 2024, which is hereby incorporated herein by reference in its entirety. BACKGROUND Counterfeiting and anti-counterfeiting measures have been a part of human society since ancient times. Forgery, also known as “the second oldest profession,” has been recorded as far back as Ancient Egypt and Greece. Today, due to the high profits from counterfeiting and illegal information decryption, these criminal activities have become widespread and even deadly. Information encryption and anti-counterfeiting play a crucial role in protecting goods, luxury merchandise, and confidential documents. Advances in technology have led to more sophisticated optical methods for information encryption and anti-counterfeiting. Due to the ease of use and clear visualization, photoluminescent materials stand out and have been commonly used in anti- counterfeiting and information encryption demonstrations. However, fluorescence-based encryption implementation methods have limitations, such as the need for special paper without fluorescence interference (usually originated from the optical brighteners in papers) and the presence of ink traces under daylight or UV light. Stimuli-responsive optical materials have the potential to provide extra layers of security, but current stimuli-responsive photoluminescent materials, although extensively applied in anti-counterfeiting and information encryption, still have issues with background fluorescence and ink traces. pH indicators, which change color based on acid or base stimuli, are widely known and used, but they only provide two-state switching and limit the number of color combinations. The security of optical information encryption and anti-counterfeiting can be enhanced by having more color options. However, the photoluminescence-based methods (emissive methods) provide high contrast in a dark environment but work poorly under daylight or bright ambient light. Whereas the pH indicator-based methods (reflective / transmissive methods) perform better under daylight and ambient light but work Attorney Docket No.11196-099WO1 poorly in a dark environment. Therefore, current encryption implementation methods have their own inherent limitations. Accordingly, improved compositions and methods for use in security and anti- counterfeiting applications are needed. SUMMARY Provided herein are compositions for forming markings on a surface. These compositions can comprise a dye and a carrier. The dye can comprise a responsive dye that exhibits a change in photophyical properties upon exposure to an external stimulus, such as a change in temperature, a change in pH, exposure to a nucleophile or an electrophile, exposure to light, or a combination thereof. In some embodiments, the dye is pH responsive that is transitionable between a first chemical form exhibiting a first set of photophysical properties and a second chemical form exhibiting a second set of photophysical properties in response to a change in pH; and upon exposure to a nucleophile, the dye is transitionable to a third chemical form exhibiting a third set of photophysical properties. In some embodiments, the dye is halochromic. In some embodiments, the dye is halofluorochromic. In some embodiments, the first chemical form comprises a substantially colorless leuco form. In some embodiments, the first chemical form exhibits a fluorescence quantum yield of less than 0.5% in acetonitrile. In some embodiments, the second chemical form exhibits a visible color. In some embodiments, the second chemical form exhibits a λmaxabsorption that is bathochromically shifted relative to a λmax absorption of the first form. In some embodiments, the second chemical form exhibits a λmaxabsorption of from 390 nm to 550 nm. In some embodiments, the second chemical form exhibits a λmax emission of from 390 nm to 550 nm. In some embodiments, the second chemical form exhibits a fluorescence quantum yield of from 2% to 60% in acetonitrile. In some embodiments, the third chemical form exhibits a λmaxabsorption that is hypsochromically shifted relative to a λmax absorption of the second chemical form. In some embodiments, the third chemical form comprises a substantially colorless leuco form. In some embodiments, the third chemical form exhibits a λmaxemission that is hypsochromically shifted relative to a λmax emission of the second chemical form. In some Attorney Docket No.11196-099WO1 embodiments, the third chemical form exhibits a fluorescence quantum yield of from 2% to 60% in acetonitrile. In some embodiments, the dye comprises a six-membered anhydride ring. In some embodiments, the dye is defined by the formula below wherein R1, R2, R3, and R4are each independently chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; or wherein R1and R2, R2and R3, and / or R3and R4, together with the atoms to which they are attached, forms a fused cycloalkyl, heterocycloalkyl, ary, heteroaryl, each optionally substituted with one or more substituents individually chosen from RA; R5is chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl; alkylthio; haloalkylthio; alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, dialkylaminocarbonyl, and heterodialkylaminocarbonyl. In some embodiments, R1, R2, R3, and R4are each independently chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, C1-C6 alkylamino, C1-C6 dialkylamino, C1- C6alkyl, C1-C6haloalkyl, C1-C6alkylthio, C1-C6haloalkylthio, C1-C6alkoxy, C1-C6haloalkoxy, C2-C6 alkenyl, C2-C6 haloalkenyl, C2-C6 alkynyl, C2-C6 haloalkynyl, a 3-7 membered cycloalkyl ring, a 3-7 membered heterocycloalkyl ring, a 5-7 membered ary ring, Attorney Docket No.11196-099WO1 a 5-7 membered heteroaryl ring, C1-C6alkylsulfinyl, C1-C6haloalkylsulfinyl, C1-C6alkylsulfonyl, C1-C6 haloalkylsulfonyl, C1-C6 alkylcarbonyl, C1-C6 haloalkylcarbonyl, C1-C6 alkoxycarbonyl, C1-C6haloalkoxycarbonyl, C1-C6alkylaminocarbonyl, C1-C6heteroalkylaminocarbonyl, and C1-C6 dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; R5is chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, C1-C6 alkylamino, C1-C6 dialkylamino, C1-C6 alkyl, C1-C6 haloalkyl, C1-C6 alkylthio, C1-C6 haloalkylthio, C1-C6 alkoxy, C1-C6 haloalkoxy, C2-C6 alkenyl, C2-C6 haloalkenyl, C2-C6 alkynyl, C2-C6 haloalkynyl, a 3-7 membered cycloalkyl ring, a 3-7 membered heterocycloalkyl ring, a 5-7 membered ary ring, a 5-7 membered heteroaryl ring, C1-C6alkylsulfinyl, C1-C6haloalkylsulfinyl, C1-C6alkylsulfonyl, C1-C6haloalkylsulfonyl, C1-C6 alkylcarbonyl, C1-C6 haloalkylcarbonyl, C1-C6 alkoxycarbonyl, C1- C6haloalkoxycarbonyl, C1-C6alkylaminocarbonyl, C1-C6heteroalkylaminocarbonyl, and C1-C6 dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; and and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, C1-C6 alkylamino, C1-C6 dialkylamino, C1-C6 alkyl, C1-C6 haloalkyl; C1-C6 alkylthio; C1-C6haloalkylthio; C1-C6alkoxy, C1-C6haloalkoxy, C2-C6alkenyl, C2-C6haloalkenyl, C2-C6 alkynyl, C2-C6 haloalkynyl, C1-C6 alkylsulfinyl, C1-C6 haloalkylsulfinyl, C1-C6 alkylsulfonyl, C1-C6haloalkylsulfonyl, C1-C6alkylcarbonyl, C1-C6haloalkylcarbonyl, C1-C6alkoxycarbonyl, C1-C6 haloalkoxycarbonyl, C1-C6 alkylaminocarbonyl, C1-C6 heteroalkylaminocarbonyl, C1-C6 dialkylaminocarbonyl, and C1-C6 heterodialkylaminocarbonyl. In some embodiments, R1, R2, R3, and R4are each independently chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, C1-C6alkylamino, C1-C6dialkylamino, C1-C6 alkyl, C1-C6 haloalkyl, C1-C6 alkylthio, C1-C6 haloalkylthio, C1-C6 alkoxy, C1-C6 haloalkoxy, C2-C6alkenyl, C2-C6haloalkenyl, C2-C6alkynyl, C2-C6haloalkynyl, a 3-7 membered cycloalkyl ring, a 3-7 membered heterocycloalkyl ring, a 5-7 membered ary ring, a 5-7 membered heteroaryl ring, C1-C6alkylsulfinyl, C1-C6haloalkylsulfinyl, C1-C6alkylsulfonyl, C1-C6 haloalkylsulfonyl, C1-C6 alkylcarbonyl, C1-C6 haloalkylcarbonyl, C1-C6 alkoxycarbonyl, C1-C6haloalkoxycarbonyl, C1-C6alkylaminocarbonyl, C1-C6heteroalkylaminocarbonyl, and C1-C6 dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; R5is chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, C1-C4alkylamino, C1-C4dialkylamino, C1-C4alkyl, C1-C4 haloalkyl, C1-C4 alkylthio, C1-C4 haloalkylthio, C1-C4 alkoxy, C1-C4 haloalkoxy, C2-C4 alkenyl, C2-C4haloalkenyl, C2-C4alkynyl, C2-C4haloalkynyl, C1-C4alkylsulfinyl, C1-C4 Attorney Docket No.11196-099WO1 haloalkylsulfinyl, C1-C4alkylsulfonyl, C1-C4haloalkylsulfonyl, C1-C4alkylcarbonyl, C1-C4haloalkylcarbonyl, C1-C4 alkoxycarbonyl, C1-C4 haloalkoxycarbonyl, C1-C4 alkylaminocarbonyl, C1-C4heteroalkylaminocarbonyl, and C1-C4dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, C1-C6alkylamino, C1-C6dialkylamino, C1-C6 alkyl, C1-C6 haloalkyl; C1-C6 alkylthio; C1-C6 haloalkylthio; C1-C6 alkoxy, C1-C6 haloalkoxy, C2-C6 alkenyl, C2-C6 haloalkenyl, C2-C6 alkynyl, C2-C6 haloalkynyl, C1-C6 alkylsulfinyl, C1-C6 haloalkylsulfinyl, C1-C6 alkylsulfonyl, C1-C6 haloalkylsulfonyl, C1-C6 alkylcarbonyl, C1-C6 haloalkylcarbonyl, C1-C6 alkoxycarbonyl, C1- C6haloalkoxycarbonyl, C1-C6alkylaminocarbonyl, C1-C6heteroalkylaminocarbonyl, C1-C6dialkylaminocarbonyl, and C1-C6 heterodialkylaminocarbonyl. In some embodiments, R1, R2, R3, and R4are each independently chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, C1-C6 alkylamino, C1-C6 dialkylamino, C1- C6alkyl, C1-C6haloalkyl, C1-C6alkylthio, C1-C6haloalkylthio, C1-C6alkoxy, C1-C6haloalkoxy, C2-C6 alkenyl, C2-C6 haloalkenyl, C2-C6 alkynyl, C2-C6 haloalkynyl, a 3-7 membered cycloalkyl ring, a 3-7 membered heterocycloalkyl ring, a 5-7 membered ary ring, a 5-7 membered heteroaryl ring, C1-C6 alkylsulfinyl, C1-C6 haloalkylsulfinyl, C1-C6 alkylsulfonyl, C1-C6haloalkylsulfonyl, C1-C6alkylcarbonyl, C1-C6haloalkylcarbonyl, C1-C6alkoxycarbonyl, C1-C6 haloalkoxycarbonyl, C1-C6 alkylaminocarbonyl, C1-C6 heteroalkylaminocarbonyl, and C1-C6 dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; R5is hydrogen; and and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, C1-C6 alkylamino, C1-C6 dialkylamino, C1-C6alkyl, C1-C6haloalkyl; C1-C6alkylthio; C1-C6haloalkylthio; C1-C6alkoxy, C1-C6haloalkoxy, C2-C6 alkenyl, C2-C6 haloalkenyl, C2-C6 alkynyl, C2-C6 haloalkynyl, C1-C6 alkylsulfinyl, C1-C6haloalkylsulfinyl, C1-C6alkylsulfonyl, C1-C6haloalkylsulfonyl, C1-C6alkylcarbonyl, C1-C6 haloalkylcarbonyl, C1-C6 alkoxycarbonyl, C1-C6 haloalkoxycarbonyl, C1-C6alkylaminocarbonyl, C1-C6heteroalkylaminocarbonyl, C1-C6dialkylaminocarbonyl, and C1-C6 heterodialkylaminocarbonyl. In certain embodiments, the dye is defined by the formula below . In some embodiments, the dye is pH responsive such that the dye is transitionable between a first chemical form exhibiting a first set of photophysical properties at a first pH Attorney Docket No.11196-099WO1 and a second chemical form exhibiting a second set of photophysical properties at a second pH. In some embodiments, the first pH is 6.0 or less and the second pH is greater than 6.0. In some embodiments, the first pH is 6.5 or less and the second pH is greater than 6.5. In some embodiments, the first pH is 7.0 or less and the second pH is greater than 7.0. In some embodiments, the first pH is 7.5 or less and the second pH is greater than 7.5. In some embodiments, a change in pH from the first pH to the second pH can be induced by contacting the dye with a base. In some embodiments, the base comprises a nucleophilic base, such as triethylamine, sodium hydroxide, potassium hydroxide, potassium tert-butoxide, sodium tert-butoxide, 2-amino-2-methyl-1-propanol, or any combination thereof. In other embodiments, the base comprises a non-nucleophilic base (i.e., a sterically hindered organic base), such as N,N-Diisopropylethylamine (DIPEA, also called Hünig's Base), 1,8-Diazabicycloundec-7-ene (DBU), 1,5-Diazabicyclo(4.3.0)non-5- ene (DBN), 2,6-Di-tert-butylpyridine, phosphazene bases, such as t-Bu-P4, lithium diisopropylamide (LDA), silicon-based amides, such as sodium and potassium bis(trimethylsilyl)amide (NaHMDS and KHMDS, respectively), lithium tetramethylpiperidide (LiTMP or harpoon base), or any combination thereof. In some embodiments, upon exposure to a nucleophile, the dye irreversibly transitions to the third chemical form exhibiting the third set of photophysical properties. In some embodiments, the carrier comprises a fluid carrier, such as a volatile fluid carrier. In some embodiments, the carrier comprises water, ethanol, acetone, acetonitrile, pentane, hexane, heptane, mineral oil, benzene, toluene, xylene, or any combination thereof. In some embodiments, the carrier comprises a polymer or an oligomer. In some embodiments, the carrier comprises a curable material. In some embodiments, the dye is present in the carrier in an amount of from 0.1% by weight to 10% by weight, based on the total weight of the composition. In some embodiments, the dye is present in the carrier as a concentration of from 1 micromolar to 800 millimolar, such as a concetrantion of from 10 micromolar to 750 millimolar, a concentration of from 50 micromolar to 600 millimolar, or a concentration of from 100 micromolar to 500 millimolar. Also provided herein are systems for forming markings on a surface. These systems can comprise a first ink composition comprising a first dye that exhibits an indigo, blue, or green color; a second ink composition comprising a second dye that exhibits an orange, red, or magenta color; and a third ink composition comprising a third dye that exhibits a yellow Attorney Docket No.11196-099WO1 color. At least one of the first dye, the second dye, and the third dye can be responsive such that it is transitionable between a substantially colorless leuco form and a colored form. In some embodiments, at least one of the first dye, the second dye, and the third dye is pH responsive such that it is transitionable between a substantially colorless leuco form and a colored form in response to a change in pH. In some embodiments, the first dye comprises a leuco dye transitionable between a substantially colorless leuco form and a second chemical form that exhibits an indigo, blue, or green color in response to a change in pH. In some embodiments, first dye comprises a cyan dye. In some embodiments, the first dye comprises α-naphtholphthalein (NaPh). In some embodiments, the second dye comprises a leuco dye transitionable between a substantially colorless leuco form and a second chemical form that exhibits an orange, red, or magenta color in response to a change in pH. In some embodiments, the second dye comprises a magenta dye. In some embodiments, the second dye comprises phenophthalein. In some embodiments, the third dye comprises a leuco dye transitionable between a substantially colorless leuco form and a second chemical form that exhibits a yellow color in response to a change in pH. In some embodiments, upon exposure to a nucleophile, the third dye is transitionable to a third chemical form exhibiting a third set of photophysical properties. In some embodiments, the third dye comprises a six-membered anhydride ring. In some embodiments, the third dye is defined by the formula below wherein R1, R2, R3, and R4are from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; or wherein R1and R2, R2and R3, and / or R3and R4, together with the atoms to which they are attached, forms a Attorney Docket No.11196-099WO1 fused cycloalkyl, heterocycloalkyl, ary, heteroaryl, each optionally substituted with one or more substituents individually chosen from RA; R5is chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl; alkylthio; haloalkylthio; alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, dialkylaminocarbonyl, and heterodialkylaminocarbonyl. In some embodiments, the third dye is defined by the formula below . Also provided herein are systems for forming markings on a surface that comprise a first ink composition comprising a first leuco dye transitionable between a substantially colorless leuco form and a second chemical form that exhibits an indigo, blue, or green color in response to a change in pH; a second ink composition comprising a second leuco dye transitionable between a substantially colorless leuco form and a second chemical form that exhibits an orange, red, or magenta color in response to a change in pH; and a third ink composition comprising a dye that is pH responsive such that it is transitionable between a substantially colorless leuco form and a second chemical form that exhibits a yellow color in response to a change in pH. In some embodiments, the first dye comprises a cyan dye. In some embodiments, the first dye comprises α-naphtholphthalein (NaPh). In some embodiments, the second dye comprises a magenta dye. In some embodiments, the second dye comprises phenophthalein. In some embodiments, upon exposure to a nucleophile, the third dye is transitionable to a third chemical form exhibiting a third set of photophysical properties. Attorney Docket No.11196-099WO1 In some embodiments, the third dye comprises a six-membered anhydride ring. In some embodiments, the third dye is defined by the formula below wherein R1, R2, R3, and R4are each from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; or wherein R1and R2, R2and R3, and / or R3and R4, together with the atoms to which they are attached, forms a fused cycloalkyl, heterocycloalkyl, ary, heteroaryl, each optionally substituted with one or more substituents individually chosen from RA; R5is chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl; alkylthio; haloalkylthio; alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, dialkylaminocarbonyl, and heterodialkylaminocarbonyl. In certain embodiments, the third dye is defined by the formula below . The principles and methods can be used to generate functional inks (including for security and anti-counterfeiting applications) and paints, as well as sensors. Attorney Docket No.11196-099WO1 For example, provided herein are methods for marking a surface. These methods can comprise applying a composition described herein or one or more inks of a system described herein to an article. In some embodiments, the method further comprises exposing the article to an acid or a base (e.g., to induce a change in the appearance of a pH responsive dye present in the composition or system). Also provided herein are articles comprising a marking formed a composition described herein or one or more inks of a system described herein. DESCRIPTION OF DRAWINGS Figs.1A-1D. Halofluorochromism behavior of HA. (Fig.1A) pH-induced color change (halochromism) behavior of HA. Upon base addition, the colorless HA solution turns to yellow color. (Fig.1B) Upon base addition, the absorption peak of HA shifts from 283 nm to 433 nm. (Fig.1C) pH-induced turn-on fluorescence behavior of HA. Upon base addition, the colorless HA solution emanentes yellow-green fluorescence under UV light. (Fig.1D) Upon base addition, the HA solution exhibits complete “turn-on” fluorescence and emits a pronounced yellow-green fluorescence with a peak wavelength at 534 nm. Figs.2A-2F. Self-destruction behavior of HA. (Fig.2A) Photos of decay progress of HA after adding TEA. Upon addition of nucleophilic base, TEA, the yellow color and yellow-green fluorescence diminished over time (The blue fluorescence originates from the ester formed in the subsequent reaction, which will be discussed in later sections, we only focus on the yellow-green fluorescence from HAehere). (Fig.2B) Photos of decay progress of HA after adding DBU. Upon addition of non-nucleophilic base, DBU, the yellow color and yellow-green fluorescence decayed much slower. (Fig.2C) Proposed mechanisms of the halofluorochromism and self-destruction behaviors of HA. (Fig.2D) Single-crystal unit cell of HAk (C: brown balls, O: red balls, and H: white balls). (Fig.2E) Stick model of HAk (the out-of-plane structure is manifested by the 3.5º C4-C7-C8-O9, 7.8º C5-C10-O9-C8 and 8.5º C7-C8-O9-C10 dihedral angles). (Fig.2F) Scheme illustrating the duality of bases on keto-enol tautomerization and anhydride ring opening of HA. Figs.3A-3E. Mechanistic studies and structure characterizations of HA upon adding different bases. (Fig.3A) Fluorescence emission spectra of HA right after and after 2 h of adding TEA (λex = 430 nm) and the intensity change profile over time plot (λex = 430 nm, λem= 530 nm). (Fig.3B) Fluorescence emission spectra of HA right after and after 2 h of adding DBU (λex = 430 nm) and the intensity change profile over time plot (λex = 430 nm, Attorney Docket No.11196-099WO1 λem= 530 nm). (Fig.3C) FTIR spectra of HA before, after 7 s, and after 30 min of adding DBU. (Fig.3D) NMR spectra of HA before and after adding DBU. (Fig.3E) The calculated bandgap and electron distribution for the HOMO and LUMO of HAk and HAe. Figs.4A-4D. Information encryption by applying the CMY palette system. (Fig. 4A) Schematic of encryption and security printing / writing procedures. (Fig.4B) A China Dragon image printed by exploiting the CMY palette system. After printing, no ink traces could be observed under either ambient or UV light, while once the base was applied, the colored pattern appeared instantaneously. Dragon image used with permission. (Fig.4C) “Burn after reading” and time dimensional encryption demonstration. Taking advantage of the metastable characteristic of HAe, the HA (yellow) parts gradually disappeared after applying the nucleophilic base. (Fig.4D) Gradient encryption demonstration. Sequentially applying the bases with the pH between the color transition points of HA, PhPh, and NaPh gradually revealed the information encrypted by the three colorants. Fig.5. Absolute and relative quantum yield of the enolate form of HA. (a) Absolute quantum yield (QY) of the enolate form of HA was obtained from a spectrofluorometer equipped with an integration sphere. Left: excitation photon counts, right: emission photon counts. (b) Relative quantum yield of the enolate form of HA was obtained using Coumarin 153 (C153) as a reference. Left: emission spectra of C153 and the enolate form of HA, right: emission spectra of C153 and the enolate form of HA with a Y-axis break Fig. 6. Normalized absorption and PL spectra of HA in different solvents. Red lines are acetonitrile (ACN) which possesses high polarity, blue lines are tetrahydrofuran (THF) which has medium polarity, and green lines represent toluene which possesses low polarity. Fig.7. Normalized kinetic absorption spectra of HA after addition of different bases. The recorded wavelength was fixed at 430 nm and the measurement duration was 2 hr. Fig.8. Integrated plot of normalized kinetic absorption and fluorescence spectra of HA after addition of different bases. The fluorescence and absorption decay profiles of DBU matched well while the absorption decay profile of TEA mismatched its fluorescence decay profile indicating more complicated reactions occurred with TEA addition compared to DBU. The recorded wavelength was fixed at 430 nm (absorption) or 530 nm (fluorescence) and the measurement duration was 2 h. Fig.9. FTIR spectra of HA before and after adding DBU. Spectra span the whole fingerprint region; the spectrum of HA before adding base is shown in blue, the green spectrum shows HA immediately after base addition, subsequent spectra are shown in red Attorney Docket No.11196-099WO1 color going from dark red to light red in 7s intervals after base addition (right); absorbance profile of peak 2 (left). Fig.10. FTIR spectra of HA before and after adding TEA. Spectra span the whole fingerprint region (right); zoomed-in range showing details of characteristic peaks of the keto form and the enolate form of HA (middle); absorbance profile at 1699.5 cm-1(left). Fig.11. FTIR spectra on DBU-related comparison. Orange line represents pure DBU, blue line refers to HA sample and green line is 1.75 min after adding DBU into HA sample. The black dashed line-covered area contains the peaks of interest, showing that DBU does not overlap with two structures of HA. Fig.12. FTIR spectra on TEA-related comparison. Orange line represents pure TEA, blue line refers to HA sample and green line is 3.4 min after adding TEA into HA sample. The black dashed line-covered area contains the peaks of interest, showing that TEA does not overlap with two structures of HA. Fig.13.1H NMR (500 MHz, CD3CN) spectrum of HA sample before adding base. Showing the major component is homophthalic anhydride (HA) and the minor species is the ring-opening product, homophthalic acid. Green brackets with number labels are peak integration Fig.14. Kinetic1H NMR (500 MHz, CD3CN) spectra of HA after adding TEA. The measurements started right after TEA addition and lasted for 2 h with the same time interval between each measurement. Fig.15. Superimposed1H NMR (500 MHz, CD3CN) spectra of HA before and after spiking experiment. The HA 5 days after adding TEA was measured (thick red line) followed by adding homophthalic acid into the sample and measuring again (thin blue line). The increased peaks clearly showed which peaks should be assigned to homophthalic acid. Fig.16. Kinetic1H NMR (500 MHz, CD3CN) spectra of HA after adding DBU. The measurements started right after DBU addition and lasted for 3 h with the same time interval between each measurement. Fig.17.1H NMR (500 MHz, CD3CN) spectrum of HA right after adding DBU. Showing the enolate form of HA, homophthalate and DBU co-exist in the sample. Green and red brackets with number labels are peak integration. Fig.18.13C NMR (850 MHz, CD3CN) spectrum of HA right after adding DBU. Showing the enolate form of HA and DBU co-exist in the sample. Attorney Docket No.11196-099WO1 Fig.19.2D NMR (HSQC and HMBC, 850 MHz, CD3CN) spectra of HA right after adding DBU. The dark red contour map is HSQC and the green contour map represents HMBC. Fig.20. DEPT NMR (500 MHz, CD3CN) spectra of HA 5 days after adding TEA. Dark red spectra are decoupled13C (normal13C) showing all types of carbon signals (primary, secondary, tertiary and quaternary carbons), blue spectra are DEPT-90 only showing CH signals (CH2 and CH3 signals apparently decreased but are still observable) and green spectra are DEPT-135 showing positive CH and CH3 signals and negative CH2 signals. Fig.21. Stacked1H NMR (500 MHz, CD3CN) spectra of HA 5 days after adding TEA before and after column chromatography purification. The sample before column chromatography purification (blue line) and the sample after column chromatography purification (red line) were measured. Note that the purification process also removed TEA and therefore changed the pH and further results in some peak shifts. Fig.22.1H NMR (500 MHz, CD3CN) spectrum of HA 5 days after adding TEA prior to column chromatography purification (pristine). Showing more than one components exist in the sample. Green brackets with number labels are peak integration. Fig.23.1H NMR (500 MHz, CD3CN) spectrum of HA 5 days after adding TEA followed by column chromatography purification. Showing only one main component exist in the sample. Green brackets with number labels are peak integration. Fig. 24. Fluorescence spectra of the ester from the subsequent reaction after adding TEA into HA solution. The ester product exhibits blue fluorescence (λem = 430 nm) under the excitation of UV light (λexc = 367 nm). Fig.25. Scheme of whole reaction mechanisms between HA and TEA (nucleophilic base) or DBU (non-nucleophilic base). HA (a) reacts with a nucleophilic base, such as TEA, producing a mixture of the enolate form of HA (b) and the ring-opening product, homophthalic acid (c), followed by two simultaneous reactions: the ring opening of the enolate form of HA to form homophthalic acid (b to c) and the esterification of the enolate form of HA and homophthalic acid (b + c to d). While HA (a) reacts with a non- nucleophilic base, such as DBU, only affording the enolate form of HA (b), and the enolate form of HA undergoes a ring opening to afford homophthalic acid (c) slowly (b slowly to c). Attorney Docket No.11196-099WO1 Fig.26. Normalized absorption spectra of PhPh and NaPh lactone form. Before adding the base, PhPh and NaPh ethanol solutions exhibited no absorbance in the visible range (above 400 nm). Fig.27. Comparison between ThPh and NaPh. The normalized absorption spectra and colors of 100 mM ThPh and NaPh ethanol solutions after adding base are shown. ThPh has an absorption maximum at 603 nm and exhibits more blue color while NaPh possesses an absorption peak at 655 nm and shows a more cyan color. Fig.28. Comparison between HA and 4-NP. The images of a piece of printer paper written with HA and 4-NP under ambient light and UV light without applying the base are shown. HA did not show any noticeable ink traces while 4-NP exhibited apparent ink traces under daylight and UV light. Fig.29. Basis of CMY color tuning system. (a) Complementary color theory for CMY color system. (b) Comparison of 4-nitrophenol (4-NP) and homophthalic anhydride (HA). The dash lines are absorption spectra before adding the base and the solid lines are after adding the base; the blue lines are absorption spectra of 4-NP and the red lines are HA. (c) Structural changes and color changes of HA, PhPh, and NaPh upon base addition. (d) Absorption spectra of HA, PhPh, and NaPh after adding the base in solution. Fig.30. CMY palette system. (a) Illustration of CMY color tuning method. Yellow (Y), magenta (M), and cyan (C) comprise the three primaries in the subtractive color mixing system and can generate seamlessly and continuously changed colors by varying their ratios. (b) Representative colors generated from the CMY palette system. The left side image in each group is the sample before adding the base, while the right side is after adding the base. (c) CIE 1931 chromaticity diagram showing the simulated gamut of the CMY palette system plus the chromaticity coordinates of HA’s turn-on fluorescence Fig.31. Continuous and seamless color tuning demonstration. The images of a multi-well plate containing different ratios of CMY colorant solutions before and after adding the base. Fig.32. Color-related characterizations of three samples prepared from PhPh + HA. (a) Images of three samples before (left) and after (right) adding the base, (b) Absorption spectra of the three samples, (c) Chromaticity coordinates of the three colors on a CIE 1931 chromaticity diagram. Fig.33. Color-related characterizations of three samples prepared from NaPh + HA. (a) Images of three samples before (left) and after (right) adding the base, (b) Absorption Attorney Docket No.11196-099WO1 spectra of the three samples, (c) Chromaticity coordinates of the three colors on a CIE 1931 chromaticity diagram. Fig.34. Color-related characterizations of three samples prepared from NaPh + PhPh. (a) Images of three samples before (left) and after (right) adding the base, (b) Absorption spectra of the three samples, (c) Chromaticity coordinates of the three colors on a CIE 1931 chromaticity diagram. Fig.35. Encryption and security printing demonstration. (a) The printed area before applying the base under ambient light; no ink traces can be observed, (b) The China Dragon image appeared right after applying the base, (c) The China Dragon image right after applying the base under UV light; the yellow part exhibited bright yellow-green fluorescence, the yellow predominant area also showed some fluorescence while areas with traces of yellow or no yellow color did not exhibit fluorescence. Fig.36. Performance of the palette system on various substrates. (a) Filter paper, (b) Kimwipe, (c) Hand towel, (d) Paper towel, (e) Laminated paper, (f) Cardboard, (g) Cotton cloth, (h) Drywall. On each panel, the left side refers to before applying the base and the right side represents after applying the base. Fig.37. Human skin encryption demonstration. “P” was written with HA, “S” was written with PhPh, and “U” was written with NaPh; after writing and followed by a water rinse, the encrypted information could still be revealed by applying the base (AMP water solution); under UV light, the yellow-green fluorescence from HA was bright and striking; once the base was applied, it was easy to wash away the written information with water. Fig.38. Performance of nucleophilic base versus non-nucleophilic base on the palette system. The “TB” was written with HA and “BL” was written with NaPh. After applying the nucleophilic base, NaOH water solution, the yellow color of the HA part rapidly decayed and completely disappeared within 10 minutes whereas after applying the non-nucleophilic base, DBU, the yellow color of the HA part decayed slowly (no apparent difference up to 10 minutes and there were still noticeable traces even up to 24 h). In contrast to HA, the NaPh part showed no appreciable difference between NaOH and DBU. Fig.39. Gradient encryption demonstration on filter paper. “P” was written with HA, “S” was written with PhPh, and “U” was written with NaPh; after the three different pH solutions were applied sequentially, the encrypted information was gradually revealed. Fig.40. Schematic illustration and real-world images of an exemplary case of anti- counterfeiting application. The coding step is to use individual or combined colorants to write / print the information. In this case, different strokes of “9” were written with Attorney Docket No.11196-099WO1 individual HA, PhPh, and NaPh inks while “2” and “3” were written using combined inks. The verification processes can involve multiple dimensions such as conventional 2D patterns, time, pH, and nucleophilicity and consist of information decryption and checking with authorization information. In this case, all possible combinations upon applying various operations under ambient and UV light are shown. Fig.41. Long-term storage test of HA, PhPh, and NaPh solutions. “P” was written with HA, “S” was written with PhPh, and “U” was written with NaPh; the upper “PSU” was written with solutions stored for 3 months while the lower “PSU” was written with freshly made solutions. Fig.42. Stability of CMY colorants solutions stored for 3 months before writing. (a) Absorption spectra of freshly made HA solution and HA solution stored for 3 months after adding the base, (b) Absorption spectra of freshly made PhPh solution and PhPh solution stored for 3 months after adding the base, (c) Absorption spectra of freshly made NaPh solution and NaPh solution stored for 3 months after adding the base. Fig.43. Stability test of HA, PhPh, and NaPh on paper surface. “P” was written with HA, “S” was written with PhPh, and “U” was written with NaPh; the paper was placed in ambient environment and the same information was written on printer paper 3 weeks, 2 weeks, 1 week, and right before imaging; under ambient light and UV light, no ink traces were visible in any groups before applying the base; after applying the base, PhPh (“S”) and NaPh (“U”) appeared in all groups without significant difference in color while for HA (“P”), right before (“0” group in the figure) showed normal color, the 1 week group only exhibited faint yellow “P”, and no yellow “P” could be observed in the “2 weeks” or “3 weeks” groups. Fig.44. Chemical structure of cellulose with hydrogen-bonded water molecules. Fig.45. FTIR spectra of printer paper with different treatments. The orange line (“Blank”) represents the paper without heating. The 1780 and 1750 cm-1peaks are assigned to two HA carbonyl groups, while the 1644 cm-1peak is attributed to the adsorbed water, and the 3700–3000 cm-1band is related to both cellulose and adsorbed water. Fig.46. FTIR spectra of heated printer paper at different time points. The orange line (“Blank”) represents the paper without heating. Fig.47. Stability test of HA on paper surface. “P” was written with HA and the concentration of HA increased to 500 mM; the paper was placed in ambient environment and the same information was written on a printer paper 2 weeks, 1 week, and right before imaging; under ambient light and UV light, no visible ink traces were observed; the yellow Attorney Docket No.11196-099WO1 “P” also appeared in “1 week” and “2 weeks” groups with only a slightly lighter color compared to that in the right before (“0”) group. Fig.48. Scheme and summary of encryption workflow and features of the palette system. Fig.49. Crystal structure of homophthalic acid. Showing single-crystal unit cell of homophthalic acid (C: brown balls, O: red balls, H: white balls, and hydrogen bonds: dashed lines). Fig.50. HR-MS spectrum of HAe. Calculated (top) and found (bottom) m / z. Fig.51. HR-MS spectrum of Homophthalate. Calculated (top) and found (bottom) m / z. Fig.52. HR-MS spectrum of the ester product. Calculated (top) and found (bottom) m / z. Fig.53. The optimized structures and their transition dipole (Debye) of HAk and HAe. The white, brown, and red balls denote H, C, and O atoms, respectively. λ is vertical excited wavelength (nm). Fig.54. The HOMO and LUMO plots and their orbital energies (eV) for HAkand HAe. The red and cyan colors denote positive and negative orbital phases whose isovalue is 0.05. Fig.55. The excited charge density difference between S0 and S1 for HAk and HAe. The red and cyan colors are charge density concentration and depletion whose isovalue is 0.002 e / Bohr3. Fig.56. “PSU” was written with Alizarin, Congo Red and their mix (molar ratio of Alizarin : Congo Red = 1 : 1), respectively (middle). Upon the addition of acid (1 M H2SO4), “P” disappeared, “S” and “U” turned to blue but with slight differences (left); while after adding a base (1 M NaOH), “P” showed purple color, “S” remained red and “U” exhibited a pink-red color that is different from its original color before adding the base (right). The results indicated that 1) the proposed system can exhibit various outputs in response to different stimuli, providing diverse options of stimuli for encryption; 2) multiple colors can be tuned using the proposed system with single or mixed pH indicators. Fig.57. The Crystal Violet lactone ethanol solutions were added into four glass tubes. The first tube served as the control group with nothing added and showed a transparent and colorless appearance. H2SO4, Cu(NO3)2and Fe(NO3)3were added into the second, third and fourth tubes, respectively. The second and third tubes showed a blue color while the fourth tube exhibited a dark purple color. The results indicated that the Crystal Attorney Docket No.11196-099WO1 Violet lactone is sensitive to Fe3+and can be added into the proposed system to provide an additional stimulus (ion-responsive) type and increase the security level of encryption. Fig.58. (a) POC (poly(1,8-octanediol-co-citrate)) prepolymer was mixed with HA and crosslinked at 80ºC for 3 days resulting in a POC-HA film. Before immersing into the base solution, the film was transparent and colorless. However, right after immersing into the base solution (1 M NaOH), the surface of the film and the liquid attached to it turned yellow. (b) POC prepolymer was mixed with PhPh and crosslinked at 80ºC for 3 days resulting in a POC-PhPh film. Before immersing into the base solution, the film was transparent and colorless. However, right after being immersed into the base solution (1 M NaOH), the surface of the film and the liquid attached to it turned magenta. After wiping away the attached liquid and a short period of time (seconds), the film became transparent and colorless again. The color change can happen again once the film was dipped into the base solution. (c) POC prepolymer was mixed with ThPh and crosslinked at 80ºC for 3 days, resulting in a POC-ThPh film. Before immersing into the base solution, the film was transparent and colorless. However, right after immersing into the base solution (1 M NaOH), the surface of the film and the liquid attached to it turned blue. The above results indicated that 1) the proposed color tuning system can be integrated in a polymer potentially for device / product fabrication; 2) the products can be used multiple times by simply wiping away the colored liquid attached to the device / product surface. Fig.59. (a) A CUPE (cross-linked urethane-doped polyester) scaffold was soaked in HA in acetone solution shaken overnight. Before being immersed into the base solution, the scaffold was white (left). After being immersed into the base solution, the scaffold turned yellow (right). (b) A CUPE (cross-linked urethane-doped polyester) scaffold was soaked in PhPh in ethanol solution and shaken overnight. Before being immersed into the base solution, the scaffold was white (left). After being immersed into the base solution, the scaffold turned magenta (right). (c) A CUPE (cross-linked urethane-doped polyester) scaffold was soaked in NaPh in ethanol solution and shaken overnight. Before being immersed into the base solution, the scaffold was white (left). After being immersed into the base solution, the scaffold turned blue (right). (d) A CUPE (cross-linked urethane-doped polyester) scaffold was soaked in HA-PhPh-NaPh mixed solution shaking overnight. Before being immersed into the base solution, the scaffold was white (left). After being immersed into the base 1 solution (1 M, pH 7.6 Tris-HCl buffer), the scaffold exhibited a yellow color (middle left). After being immersed into the base 2 solution (0.25 M 2-amino-2-methyl-1- propanol acetonitrile solution), the scaffold turned to a greenish blue (middle right). After Attorney Docket No.11196-099WO1 dipping into the base 3 solution (1 M NaOH water solution), the scaffold showed a fuchsia color (right). The results indicated that 1) the proposed color tuning system can be integrated with a polymer potentially for device / product fabrication; 2) after immersing with polymer scaffold, the proposed system still exhibited gradient color change ability. Fig.60. Individual Bromothymol Blue (BB) or Phenol Red (PR), or their mix was added into 9 cuvettes containing PBS buffer solution with pH ranging from 5.6 to 8.0. (a) Only BB was added, and the color changes were observed; (b) Only PR was added and the color changes were observed; (c) A BB-PR mix (molar ratio of BB : PR = 2 : 1) was added and the color changes were observed; (d) A BB-PR mix (molar ratio of BB : PR = 1 : 1) was added and the color changes were observed; (e) A BB-PR mix (molar ratio of BB : PR = 1 : 2) was added and the color changes were observed. It can be observed that (c), (d), (e) exhibited color change patterns that are different from (a) and (b) and different from each other. The above results indicated that by tuning the ratio of different colorants, more color could be generated, showing that when the initial color of the system does not need to be colorless, the system can have more color changes. The color tuning system showed tunable colors encompassing the physiological pH, suggesting its potential applications in physiological pH sensing for various disease or physiological conditions. Fig.61. Before being soaked into pH indicator solutions, the POC porous scaffold was white (left). After being soaked into BB-PR mix solution (molar ratio of BB : PR = 1 : 1) and shaken overnight, the POC scaffold turned yellow-orange. The scaffold was cut into nine pieces and put in nine EP tubes containing PBS buffer solution with pH ranging from 5.6 to 8.0. After gently shaking and a couple of seconds, the solution showed different colors. The scaffold mimics medical patches or tapes, such as wound dressing, and the PBS solutions mimic the interstitial fluids in the interacting area. The results indicated that the proposed system has the potential to be integrated into medical patches or tapes to measure the local pH or to indicate the presence of specific substances that cause pH changes. DETAILED DESCRIPTION Provided herein are compositions for forming markings on a surface. These compositions can comprise a dye and a carrier. The dye can comprise a responsive dye that exhibits a change in photophyical properties upon exposure to an external stimulus, such as a change in temperature, a change in pH, exposure to a nucleophile or an electrophile, exposure to light, or a combination thereof. Suitable dyes are described in more detail below. Attorney Docket No.11196-099WO1 In some embodiments, the dye is pH responsive that is transitionable between a first chemical form exhibiting a first set of photophysical properties and a second chemical form exhibiting a second set of photophysical properties in response to a change in pH; and upon exposure to a nucleophile, the dye is transitionable to a third chemical form exhibiting a third set of photophysical properties. In some embodiments, the dye is halochromic. In some embodiments, the dye is halofluorochromic. In some embodiments, the first chemical form comprises a substantially colorless leuco form. In some embodiments, the first chemical form exhibits a fluorescence quantum yield of less than 0.5% in acetonitrile. In some embodiments, the second chemical form exhibits a visible color. In some embodiments, the second chemical form exhibits a λmaxabsorption that is bathochromically shifted relative to a λmax absorption of the first chemical form. In some embodiments, the second chemical form exhibits a λmaxabsorption of from 390 nm to 550 nm. In some embodiments, the second chemical form exhibits a λmax emission of from 390 nm to 550 nm. In some embodiments, the second chemical form exhibits a fluorescence quantum yield of from 2% to 60% in acetonitrile. In some embodiments, the third chemical form exhibits a λmaxabsorption that is hypsochromically shifted relative to a λmax absorption of the second chemical form. In some embodiments, the third chemical form comprises a substantially colorless leuco form. In some embodiments, the third chemical form exhibits a λmaxemission that is hypsochromically shifted relative to a λmax emission of the second chemical form. In some embodiments, the third chemical form exhibits a fluorescence quantum yield of from 2% to 60% in acetonitrile. In some embodiments, the dye comprises a six-membered anhydride ring. In some embodiments, the dye is defined by the formula below wherein R1, R2, R3, and R4are each from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, Attorney Docket No.11196-099WO1 haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; or wherein R1and R2, R2and R3, and / or R3and R4, together with the atoms to which they are attached, forms a fused cycloalkyl, heterocycloalkyl, ary, heteroaryl, each optionally substituted with one or more substituents individually chosen from RA; R5is chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl; alkylthio; haloalkylthio; alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, dialkylaminocarbonyl, and heterodialkylaminocarbonyl. In some embodiments, R1, R2, R3, and R4are each independently chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, C1-C6 alkylamino, C1-C6 dialkylamino, C1- C6 alkyl, C1-C6 haloalkyl, C1-C6 alkylthio, C1-C6 haloalkylthio, C1-C6 alkoxy, C1-C6 haloalkoxy, C2-C6alkenyl, C2-C6haloalkenyl, C2-C6alkynyl, C2-C6haloalkynyl, a 3-7 membered cycloalkyl ring, a 3-7 membered heterocycloalkyl ring, a 5-7 membered ary ring, a 5-7 membered heteroaryl ring, C1-C6alkylsulfinyl, C1-C6haloalkylsulfinyl, C1-C6alkylsulfonyl, C1-C6 haloalkylsulfonyl, C1-C6 alkylcarbonyl, C1-C6 haloalkylcarbonyl, C1-C6 alkoxycarbonyl, C1-C6haloalkoxycarbonyl, C1-C6alkylaminocarbonyl, C1-C6heteroalkylaminocarbonyl, and C1-C6 dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; R5is chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, C1-C6 alkylamino, C1-C6 dialkylamino, C1-C6 alkyl, C1-C6haloalkyl, C1-C6alkylthio, C1-C6haloalkylthio, C1-C6alkoxy, C1-C6haloalkoxy, C2-C6alkenyl, C2-C6 haloalkenyl, C2-C6 alkynyl, C2-C6 haloalkynyl, a 3-7 membered cycloalkyl ring, a 3-7 membered heterocycloalkyl ring, a 5-7 membered ary ring, a 5-7 membered heteroaryl ring, C1-C6alkylsulfinyl, C1-C6haloalkylsulfinyl, C1-C6alkylsulfonyl, C1-C6haloalkylsulfonyl, C1-C6 alkylcarbonyl, C1-C6 haloalkylcarbonyl, C1-C6 alkoxycarbonyl, C1- C6haloalkoxycarbonyl, C1-C6alkylaminocarbonyl, C1-C6heteroalkylaminocarbonyl, and Attorney Docket No.11196-099WO1 C1-C6dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; and and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, C1-C6alkylamino, C1-C6dialkylamino, C1-C6alkyl, C1-C6haloalkyl; C1-C6alkylthio; C1-C6 haloalkylthio; C1-C6 alkoxy, C1-C6 haloalkoxy, C2-C6 alkenyl, C2-C6 haloalkenyl, C2- C6alkynyl, C2-C6haloalkynyl, C1-C6alkylsulfinyl, C1-C6haloalkylsulfinyl, C1-C6alkylsulfonyl, C1-C6 haloalkylsulfonyl, C1-C6 alkylcarbonyl, C1-C6 haloalkylcarbonyl, C1-C6 alkoxycarbonyl, C1-C6 haloalkoxycarbonyl, C1-C6 alkylaminocarbonyl, C1-C6 heteroalkylaminocarbonyl, C1-C6 dialkylaminocarbonyl, and C1-C6 heterodialkylaminocarbonyl. In some embodiments, R1, R2, R3, and R4are each independently chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, C1-C6 alkylamino, C1-C6 dialkylamino, C1- C6alkyl, C1-C6haloalkyl, C1-C6alkylthio, C1-C6haloalkylthio, C1-C6alkoxy, C1-C6haloalkoxy, C2-C6 alkenyl, C2-C6 haloalkenyl, C2-C6 alkynyl, C2-C6 haloalkynyl, a 3-7 membered cycloalkyl ring, a 3-7 membered heterocycloalkyl ring, a 5-7 membered ary ring, a 5-7 membered heteroaryl ring, C1-C6 alkylsulfinyl, C1-C6 haloalkylsulfinyl, C1-C6 alkylsulfonyl, C1-C6haloalkylsulfonyl, C1-C6alkylcarbonyl, C1-C6haloalkylcarbonyl, C1-C6alkoxycarbonyl, C1-C6 haloalkoxycarbonyl, C1-C6 alkylaminocarbonyl, C1-C6 heteroalkylaminocarbonyl, and C1-C6dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; R5is chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, C1-C4 alkylamino, C1-C4 dialkylamino, C1-C4 alkyl, C1-C4haloalkyl, C1-C4alkylthio, C1-C4haloalkylthio, C1-C4alkoxy, C1-C4haloalkoxy, C2-C4alkenyl, C2-C4 haloalkenyl, C2-C4 alkynyl, C2-C4 haloalkynyl, C1-C4 alkylsulfinyl, C1-C4 haloalkylsulfinyl, C1-C4alkylsulfonyl, C1-C4haloalkylsulfonyl, C1-C4alkylcarbonyl, C1-C4haloalkylcarbonyl, C1-C4 alkoxycarbonyl, C1-C4 haloalkoxycarbonyl, C1-C4 alkylaminocarbonyl, C1-C4heteroalkylaminocarbonyl, and C1-C4dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, C1-C6alkylamino, C1-C6dialkylamino, C1-C6 alkyl, C1-C6 haloalkyl; C1-C6 alkylthio; C1-C6 haloalkylthio; C1-C6 alkoxy, C1-C6haloalkoxy, C2-C6alkenyl, C2-C6haloalkenyl, C2-C6alkynyl, C2-C6haloalkynyl, C1-C6 alkylsulfinyl, C1-C6 haloalkylsulfinyl, C1-C6 alkylsulfonyl, C1-C6 haloalkylsulfonyl, C1-C6 alkylcarbonyl, C1-C6 haloalkylcarbonyl, C1-C6 alkoxycarbonyl, C1- C6haloalkoxycarbonyl, C1-C6alkylaminocarbonyl, C1-C6heteroalkylaminocarbonyl, C1-C6dialkylaminocarbonyl, and C1-C6 heterodialkylaminocarbonyl. Attorney Docket No.11196-099WO1 In some embodiments, R1, R2, R3, and R4are each independently chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, C1-C6 alkylamino, C1-C6 dialkylamino, C1- C6alkyl, C1-C6haloalkyl, C1-C6alkylthio, C1-C6haloalkylthio, C1-C6alkoxy, C1-C6haloalkoxy, C2-C6 alkenyl, C2-C6 haloalkenyl, C2-C6 alkynyl, C2-C6 haloalkynyl, a 3-7 membered cycloalkyl ring, a 3-7 membered heterocycloalkyl ring, a 5-7 membered ary ring, a 5-7 membered heteroaryl ring, C1-C6 alkylsulfinyl, C1-C6 haloalkylsulfinyl, C1-C6 alkylsulfonyl, C1-C6 haloalkylsulfonyl, C1-C6 alkylcarbonyl, C1-C6 haloalkylcarbonyl, C1-C6 alkoxycarbonyl, C1-C6 haloalkoxycarbonyl, C1-C6 alkylaminocarbonyl, C1-C6 heteroalkylaminocarbonyl, and C1-C6 dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; R5is hydrogen; and and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, C1-C6 alkylamino, C1-C6 dialkylamino, C1-C6alkyl, C1-C6haloalkyl; C1-C6alkylthio; C1-C6haloalkylthio; C1-C6alkoxy, C1-C6haloalkoxy, C2-C6 alkenyl, C2-C6 haloalkenyl, C2-C6 alkynyl, C2-C6 haloalkynyl, C1-C6 alkylsulfinyl, C1-C6haloalkylsulfinyl, C1-C6alkylsulfonyl, C1-C6haloalkylsulfonyl, C1-C6alkylcarbonyl, C1-C6 haloalkylcarbonyl, C1-C6 alkoxycarbonyl, C1-C6 haloalkoxycarbonyl, C1-C6alkylaminocarbonyl, C1-C6heteroalkylaminocarbonyl, C1-C6dialkylaminocarbonyl, and C1-C6 heterodialkylaminocarbonyl. In certain embodiments, the dye is defined by the formula below . In some embodiments, the such that the dye is transitionable between a first chemical form exhibiting a first set of photophysical properties at a first pH and a second chemical form exhibiting a second set of photophysical properties at a second pH. In some embodiments, the first pH is 6.0 or less and the second pH is greater than 6.0. In some embodiments, the first pH is 6.5 or less and the second pH is greater than 6.5. In some embodiments, the first pH is 7.0 or less and the second pH is greater than 7.0. In some embodiments, the first pH is 7.5 or less and the second pH is greater than 7.5. In some embodiments, a change in pH from the first pH to the second pH can be induced by contacting the dye with a base. In some embodiments, the base comprises a nucleophilic base, such as triethylamine, sodium hydroxide, potassium hydroxide, potassium tert-butoxide, sodium tert-butoxide, 2-amino-2-methyl-1-propanol, or any combination thereof. In other embodiments, the base comprises a non-nucleophilic base (i.e., a sterically hindered organic base), such as N,N-Diisopropylethylamine (DIPEA, also Attorney Docket No.11196-099WO1 called Hünig's Base), 1,8-Diazabicycloundec-7-ene (DBU), 1,5-Diazabicyclo(4.3.0)non-5- ene (DBN), 2,6-Di-tert-butylpyridine, phosphazene bases, such as t-Bu-P4, lithium diisopropylamide (LDA), silicon-based amides, such as sodium and potassium bis(trimethylsilyl)amide (NaHMDS and KHMDS, respectively), lithium tetramethylpiperidide (LiTMP or harpoon base), or any combination thereof. In some embodiments, upon exposure to a nucleophile, the dye irreversibly transitions to the third chemical form exhibiting the third set of photophysical properties. In some embodiments, the carrier comprises a fluid carrier, such as a volatile fluid carrier. In some embodiments, the carrier comprises water, ethanol, acetone, acetonitrile, pentane, hexane, heptane, mineral oil, benzene, toluene, xylene, or any combination thereof. In some embodiments, the carrier comprises a polymer or an oligomer. In some embodiments, the carrier comprises a curable material. In some embodiments, the dye is present in the carrier in an amount of from 0.1% by weight to 10% by weight, based on the total weight of the composition. In some embodiments, the dye is present in the carrier as a concentration of from 1 micromolar to 800 millimolar, such as a concetrantion of from 10 micromolar to 750 millimolar, a concentration of from 50 micromolar to 600 millimolar, or a concentration of from 100 micromolar to 500 millimolar. Also provided herein are systems for forming markings on a surface. These systems can comprise a first ink composition comprising a first dye that exhibits an indigo, blue, or green color; a second ink composition comprising a second dye that exhibits an orange, red, or magenta color; and a third ink composition comprising a third dye that exhibits a yellow color. At least one of the first dye, the second dye, and the third dye can be responsive such that it is transitionable between a substantially colorless leuco form and a colored form. In some embodiments, at least one of the first dye, the second dye, and the third dye is pH responsive such that it is transitionable between a substantially colorless leuco form and a colored form in response to a change in pH. In some embodiments, the first dye comprises a leuco dye transitionable between a substantially colorless leuco form and a second chemical form that exhibits an indigo, blue, or green color in response to a change in pH. In some embodiments, first dye comprises a cyan dye. In some embodiments, the first dye comprises α-naphtholphthalein (NaPh). Attorney Docket No.11196-099WO1 In some embodiments, the second dye comprises a leuco dye transitionable between a substantially colorless leuco form and a second chemical form that exhibits an orange, red, or magenta color in response to a change in pH. In some embodiments, the second dye comprises a magenta dye. In some embodiments, the second dye comprises phenophthalein. In some embodiments, the third dye comprises a leuco dye transitionable between a substantially colorless leuco form and a second chemical form that exhibits a yellow color in response to a change in pH. In some embodiments, upon exposure to a nucleophile, the third dye is transitionable to a third chemical form exhibiting a third set of photophysical properties. In some embodiments, the third dye comprises a six-membered anhydride ring. In some embodiments, the third dye is defined by the formula below wherein R1, R2, R3, and R4are each from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; or wherein R1and R2, R2and R3, and / or R3and R4, together with the atoms to which they are attached, forms a fused cycloalkyl, heterocycloalkyl, ary, heteroaryl, each optionally substituted with one or more substituents individually chosen from RA; R5is chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl; alkylthio; haloalkylthio; alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, Attorney Docket No.11196-099WO1 alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, dialkylaminocarbonyl, and heterodialkylaminocarbonyl. In some embodiments, the third dye is defined by the formula below . Also provided herein are systems for forming markings on a surface that comprise a first ink composition comprising a first leuco dye transitionable between a substantially colorless leuco form and a second chemical form that exhibits an indigo, blue, or green color in response to a change in pH; a second ink composition comprising a second leuco dye transitionable between a substantially colorless leuco form and a second chemical form that exhibits an orange, red, or magenta color in response to a change in pH; and a third ink composition comprising a dye that is pH responsive such that it is transitionable between a substantially colorless leuco form and a second chemical form that exhibits a yellow color in response to a change in pH. In some embodiments, the first dye comprises a cyan dye. In some embodiments, the first dye comprises α-naphtholphthalein (NaPh). In some embodiments, the second dye comprises a magenta dye. In some embodiments, the second dye comprises phenophthalein. In some embodiments, upon exposure to a nucleophile, the third dye is transitionable to a third chemical form exhibiting a third set of photophysical properties. In some embodiments, the third dye comprises a six-membered anhydride ring. In some embodiments, the third dye is defined by the formula below wherein R1, R2, R3, and R4are each from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, Attorney Docket No.11196-099WO1 alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; or wherein R1and R2, R2and R3, and / or R3and R4, together with the atoms to which they are attached, forms a fused cycloalkyl, heterocycloalkyl, ary, heteroaryl, each optionally substituted with one or more substituents individually chosen from RA; R5is chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl; alkylthio; haloalkylthio; alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, dialkylaminocarbonyl, and heterodialkylaminocarbonyl. In certain embodiments, the third dye is defined by the formula below . Dyes As discussed above, the compositions and systems described herein can include one or more dyes. A wide variety of dyes can be utilized. Examples of dyes are discussed below. In some embodiments, one or more of the dyes can comprise a leuco dye. A leuco dye (from the Greek word LEUKOS=WHITE) is a dye whose molecule can acquire at least two chemical forms, one of which is substantially colorless. As already briefly said above in general for all dyes, also leuco dyes are often classified according to the different chemical mechanisms that cause the change of the dye molecule from its substantially colorless (LEUCO) form to a colorful form. Therefore in literature it is possible to find leuco dyes classified in families like for example thermochromic leuco dyes, in which the color change from a colorless to a colorful state (or vice versa) is caused by a temperature variation; photochromic leuco dyes in which the change from a colorless to a Attorney Docket No.11196-099WO1 colorful state (or vice versa) is caused by light; solvatochromic leuco dyes in which the change from a colorless to a colorful state (or vice versa) is caused by the contact with specific solvents and especially with a solvent of a certain well defined polarity; biochromic leuco dyes in which the change from a colorless to a colorful state (or vice versa) is caused by the contact with specific biological entities or components; redox leuco dyes in which the change from a colorless to a colorful state (or vice versa) is caused by chemical oxidation or reduction; electrochromic leuco dyes whose change from a colorless to a colorful state (or vice versa) is caused by the passage of an electric current; ionochromic leuco dyes in which the change from a colorless to a colorful state (or vice versa) is caused by the interaction with specific ions and / or by a variation in their concentration; halochromic leuco dyes in which the change from a colorless to a colorful state (or vice versa), according to the original literal meaning of the word (from the Greek word HALOS=SALT), is caused by the interaction with specific salts etc. The term “halochromic” is often used for dyes and leuco dyes that change from an initial color (which is a colorless state, for leuco dyes) to a different colorful state due to a variation in the concentration of hydrogen ions. In this slightly different meaning, therefore, halochromic leuco dyes form a subset of the more general ionochromic leuco dyes, when the ions whose variation in concentration causes the change of the leuco dye from a colorless to a colorful state or vice versa, are hydrogen ions. A number of leuco dyes are known in the art. One example leuco dye is crystal violet lactone, a phthalide based colorant (spirolactone) abbreviated as CVL and chemically named as 3,3-Bis (p-dimethylaminophenyl)-6-dimethylaminophthalide or 6- (Dimethylamino)-3,3-bis [p-(dimethylamino) phenyl] phthalide, also identified by the CAS Number 1552-42-7. Other phthalide dyes, especially the ones having the same basic molecular structure of CVL may change from a colorless to a strongly colored state. Leuco dyes of such type are for example heterocyclic analogues of CVL, in particular the ones with indole and pyridine rings, an example of which is 3-(1,2-Dimethyl-3-indolyl)-3- [4-(diethylamino)-2-methylphenyl]phthalide, identified also with the CAS number 36499- 49-7 and also commercially known with the trade dye name of NC BLUE 3. Other types of leuco dyes include the leuco-quinone class of leuco dyes, leuco derivatives of the oxazine, thiazine, and phenazine dyes, thymolphthalein, alpha- naphtholphthalein, 4,5,6,7-tetrabromo-phenolphthalein, 3′,3″,5′,5″-tetrabromo- phenolphthalein, o-cresolphthalein, phenolphthalein, xylenolphthalein, guiacolphthalein, ethyl bis (2,4-dinitrophenyl) acetate, bis-[9-(diethylamino)-5H-benzo[a]phenoxazin-5- Attorney Docket No.11196-099WO1 iminium] sulfate (Nile Blue A), Quinoline Blue, Heptamethoxy Red, 3-nitrophenol, pinachrome, other phthalide leuco dyes, triarylmethane leuco dyes, thiazine, oxazine and phenazine leuco dyes; leuco quinones; fluoran leuco dyes, triarylmethane-based leuco dyes, e.g.3,3-bis(p-dimethylaminophenyl)phthalide, 3-(p-dimethylaminophenyl)-3-(1,2- dimethylindol-3-yl) phthalide, 3-(pdimethylaminophenyl)-3-(2-methyl-indol-3-yl) phthalide, 3,3-bis(1,2-dimethylindo1-3-yl)-5-dimethyl-aminophthalide, 3,3-bis(1,2- dimethylindol-3-yl)-6-dimethyl-amino-phthalide, 3,3-bis(9-ethylcarbazol-3-yl)-6- dimethylaminophtha-lide, 3,3-bis(2-phenylindol-3-yl)-6-dimethylamino phthalide, 3- pdimethyl-aminophenyl-3-(1-methylpyrrol-3-yl)-6-dimethylaminophtha-lide, etc; diphenylmethane-based dyes, e.g., 4,4′-bisdimethyl-aminobenzhydryl benzyl ether, N- halophenylleucoauramine, N-2,4,5-trichlorophenyl-leucoauramine, etc.; lactam-based dyes, e.g., rhodamine-B-anilinolactam, rhodamine-(p-nitroanilino)lactam,rhodamine-(o- nitroanilino)lactam, etc.; fluoran-based dyes, e.g., 3-dimethylamino-7-methoxy fluoran, 3- diethylamino-6-methoxyfluoran, 3-di-ethylamino-7-methoxy fluoran, 3-diethylamino-7- chloro fluoran, 3-diethylamino-6-methyl-7-chloro fluoran, 3-di-ethylamino-6,7-dimethyl fluoran, 3-(N-ethyl-p-toluidino)-7-methyl fluoran, 3-diethylamino-7-(N-acetyl-N- methylamino) fluoran, 3-diethylamino-7(N-methylamino) fluoran, 3-diethylamino-7- dibenzylamino fluoran, 3-diethylamino-7-(N-methyl-N-benzylamino) fluoran, 3- diethylamino-7-(N-chloroethyl-N-methylamino) fluoran, 3-diethylamino-7-N-diethylamino fluoran, 3-(N-ethyl-p-toluidino)-6-methyl-7-phenylamino fluoran, 3-(N-ethyl-p-toluidino)- 6-methyl-7-(p-toluidino) fluoran, 3-diethylamino-6-methyl-7-phenylamino fluoran, 3- dibutylamino-6-methyl-7-phenylamino fluoran, 3-diethylamino-7-(2 carbomethoxy-phenyl- amino) fluoran, 3-(N-cyclohexyl-N-methylamino)-6-methyl-7-phenylamino fluoran, 3- pyrrolidino-6-methyl-7-phenylamino fluoran, 3-piperidino-6-methyl-7-phenylamino fluoran, 3-diethylamino-6-methyl-7-(2,4-dimethylamino) fluoran, 3-diethylamino-7-(o- chlorophenylamino) fluoran, 3-dibutylamino-7-(o-chlorophenylamino) fluoran, 3- pyrrolidino-6-methyl-7-(p-butylphenylamino) fluoran, 3-(N-methyl-N-n-amylamino)-6- methyl-7-phenylaminofluoran, 3-(N-ethyl-N-n-amylamino)-6-methyl-7-phenylamino fluoran, 3-(N-ethyl-N isoamylamino)-6-methyl-7-phenylamino fluoran, 3-(N-methyl-N-n- hexylamino)-6-methyl-7-phenylamino fluoran, 3-(N-ethyl-N-n-hexylamino)-6-methyl-7- phenylamino fluoran, 3-(N-ethyl-N-[3-ethylhexylamino)-6-methyl-7-phenylamino fluoran, etc.; Malachite Green Lactone, Leuco Indigo, Leuco Methylene Blue, Benzoyl Leuco Methylene Blue etc. Other responsive dyes include those described below. Attorney Docket No.11196-099WO1 Dye Low pH Transition low Transition High pH color end high end color l R 1 ll et et et et Attorney Docket No.11196-099WO1 phenylene-diamine monohydrochloride R i Bl d 45 6 bl Photochromic dyes, such as triarylmethanes, stilbenes, azastilbenes, nitrones, fulgides, spiropyrans, naphthopyrans, spiro-oxazines, quinones, and crystal violet lactone Attorney Docket No.11196-099WO1 Thermochromic dyes, such as spiroheterocyclic compounds (e.g., spiropyrans and spirooxazines), Schiff bases and related nitrogen-containing molecules, and bianthrones and other overcrowded ethenes. Articles and Methods of Use The compositions and systems described herein can be used to apply markings, printings, images, and / or security features to any surface. Accordingly provided herein are methods for marking a surface. These methods can comprise applying a composition described herein or one or more inks of a system described herein to an article. In some embodiments, the method further comprises exposing the article to an acid or a base (e.g., to induce a change in the appearance of a pH responsive dye present in the composition or system). Also provided herein are articles comprising a marking formed a composition described herein or one or more inks of a system described herein. In some embodiments, the compositions and systems can be employed to provide authentication of articles (e.g., as a security and anti-counterfeiting feature to identify and distinguish authentic products from counterfeit products) and / or to provide visual enhancement of manufactured articles and packaging. The compositions and systems can be employed in many fields of use and applications. Examples include: Government and defense applications—whether Federal, State or Foreign (such as Passports, ID Cards, Driver's Licenses, Visas, Birth Certificates, Vital Records, Voter Registration Cards, Voting Ballots, Social Security Cards, Bonds, Food Stamps, Postage Stamps, and Tax Stamps); currency—whether Federal, State or Foreign (such as security threads in paper currency, features in polymer currency, and features on paper currency); documents (such as Titles, Deeds, Licenses, Diplomas, and Certificates); financial and negotiable instruments (such as Certified Bank Checks, Corporate Checks, Personal Checks, Bank Vouchers, Stock Certificates, Travelers' Checks, Money Orders, Credit cards, Debit cards, ATM cards, Affinity cards, Prepaid Phone cards, and Gift Cards); confidential information (such as Movie Scripts, Legal Documents, Intellectual Property, Medical Records / Hospital Records, Prescription Forms / Pads, and “Secret Recipes”); Attorney Docket No.11196-099WO1 product and brand protection, including Fabric & Home Care (such as Laundry Detergents, fabric conditioners, dish care, household cleaners, surface coatings, fabric refreshers, bleach, and care for special fabrics); beauty care (such as Hair care, hair color, skin care & cleansing, cosmetics, fragrances, antiperspirants & deodorants, feminine protection pads, tampons and pantiliners); baby and family care (such as Baby diapers, baby and toddler wipes, baby bibs, baby change & bed mats, paper towels, toilet tissue, and facial tissue); health care (such as Oral care, pet health and nutrition, prescription pharmaceuticals, over-the counter pharmaceuticals, drug delivery and personal health care, prescription vitamins and sports and nutritional supplements; prescription and non-prescription eyewear; Medical devices and equipment sold to Hospitals, Medical Professionals, and Wholesale Medical Distributors (e.g., bandages, equipment, implantable devices, surgical supplies); food and beverage packaging; dry goods packaging; electronic equipment, parts & components; apparel and footwear, including sportswear clothing, footwear, licensed and non- licensed upscale, sports and luxury apparel items, fabric; biotech pharmaceuticals; aerospace components and parts; automotive components and parts; sporting goods; tobacco Products; software; compact disks, DVDs, and Blu-Ray discs; explosives; novelty items (such as gift wrap and ribbon) books and magazines; school products and office supplies; business cards; shipping documentation and packaging; notebook covers; book covers; book marks; Attorney Docket No.11196-099WO1 event and transportation tickets; gambling and gaming applications (such as Lottery tickets, game cards, casino chips and items for use at or with casinos, raffle and sweepstakes); home furnishing (such as towels, linens, and furniture); flooring and wallcoverings; jewelry & watches; handbags; art, collectibles and memorabilia; toys; food (e.g., on the surface candies including chocolate); displays (such as Point of Purchase and Merchandising displays); and product marking and labeling (such as labels, hangtags, tags, threads, tear strips, over-wraps, securing a tamperproof image applied to a branded product or document for authentication or enhancement, as camouflage, and as asset tracking). In certain embodiments, the compositions and systems can be applied to a document or packaging for a document. The document can be, for example, a banknote, a check, a money order, a passport, a visa, a vital record (e.g., a birth certificate), an identification card, a credit card, an atm card, a license, a tax stamp, a postage stamp, a lottery ticket, a deed, a title, a certificate, or a legal document. In some embodiments, the substrates can be employed to provide visual enhancement of an article, such as coinage, CDs, DVDs, or Blu- Ray Discs, or packaging, such as aluminum cans, bottles (e.g., glass or plastic bottles), plastic film, or foil wrappers. In some embodiments, compositions and systems can be used as a coating composition which can be applied to articles. The compositions and systems can be applied uniformly over a surface, or in a pattern to aesthetically enhance an article and / or to provide for a method of authentication. EXAMPLES The invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of non- critical parameters which can be changed or modified to yield essentially the same results. Attorney Docket No.11196-099WO1 Example 1. Harnessing the Duality of Bases Toward Controlled Color and Fluorescence—Halofluorochromism of HA and resulting dynamic CMY palette. Overview Halofluorochromism of homophthalic anhydride was discovered, and used to generate a highly dynamic palette for encryption. Bases can promote keto-enol tautomerism, a prevalent form of prototropic tautomerism, and facilitate the ring-opening of anhydride ring structures. The intrinsic chemical distinctions between these processes provide an opportunity to modulate these seemingly parallel reactions. However, this potential remains largely unexplored. In this work, we report homophthalic anhydride, the first molecule exhibiting simultaneous halochromism, turn-on fluorescence (halofluorochromism), and subsequent self-destruction. Through comprehensive spectroscopic analysis and theoretical calculations, we unravel the mechanisms underlying these phenomena, emphasizing the pivotal roles of the basicity and nucleophilicity of the base. Our findings reveal that by modulating the basicity and nucleophilicity of the base, we can achieve controlled durations of color change and turn-on fluorescence. Capitalizing on these intriguing properties, we develop a highly dynamic CMY (Cyan-Magenta-Yellow) palette, ideal for entity encryption and anti-counterfeiting applications. Our work reshapes the understanding of the relationship between the basicity and nucleophilicity of bases, enriching the comprehension of the six-membered anhydride ring, keto-enol tautomerism, and homophthalic anhydride chemistry. It paves the way for the design and development of stimuli-responsive dynamic molecules, sophisticated entity encryption, anti-counterfeiting systems, and beyond. Introduction Keto-enol tautomerism stands as a cornerstone in organic chemistry, denoting the equilibrium between ketones (or aldehydes) and their isomeric enol counterparts. Facilitated by a hydrogen atom adjacent to a carbonyl group, this equilibrium hinges on intramolecular proton transfer(1, 2). The position of this equilibrium can be influenced by factors such as solvent, pH, temperature, and the nature of the substituents(1, 3-8). This tautomerism finds applications in pharmaceutical design, elucidation of enzymatic reaction mechanisms, and synthesis of intricate organic compounds(1, 2, 9-14). For instance, the enol form acts as a nucleophile in the aldol reaction, a fundamental step in many synthetic pathways(15-17). Moreover, the tautomeric equilibrium has been extensively studied in relation to the stability and reactivity of biomolecules like DNA bases and proteins, highlighting the biological significance of this phenomenon(10-12, 18-20). Six-membered anhydride ring Attorney Docket No.11196-099WO1 structures, distinct from the more commonly encountered five-membered cyclic anhydrides, are rarer in nature and synthesis due to their unique reactivity, offer insights into ring size effects on chemical stability and reactivity(21-23). When the six-membered anhydride ring and keto-enol tautomerism encounter bases, they both undergo a structural change but with distinct chemical natures. For keto-enol tautomerism, a base abstracts the α-hydrogen and facilitates the transition from keto form to enol form, depending on its basicity, whereas for breaking up anhydride ring, the base attacks at the carbonyl carbon as a nucleophile. This leaves a space to control the tautomerization and ring opening separately. However, there is currently a lack of studies on the correlation between the duality of bases and the keto-enol tautomerism and six-membered anhydride ring related structural changes. In this work, we elucidate the underlying mechanisms of the pH-induced color change and turn-on fluorescence (together termed halofluorochromism) as well as self-destruction of a model molecule, homophthalic anhyride (HA), and investigate how the basicity and nucleophilicity of a base affect the corresponding structural changes. By decoupling the basicity and nucleophilicity, we achieved controlled duration of halofluorochromism or, in other words, self-destruction time. Empowered by the intriguing characteristics of HA and the duality of bases on HA, we develop a CMY palette with dynamic multidimensional and multimode optical encryption features for information encryption and anti-counterfeiting. Our findings thereby contribute to the design of dynamic molecules and materials with tunable color and fluorescence changes, and more potential fields. Results Halofluorochromism and tunable self-destruction of HA. The pH-induced color change (halochromism) phenomenon of HA was observed serendipitously during our organic synthesis trials with HA and basic compounds accompanied by the subsequent discovery of its turn-on fluorescence. As depicted in Fig.1A-D, HA displayed a halofluorochromic behavior. In the absence of a base, the HA solution remained colorless, showing neither absorption nor fluorescence emission in the visible spectrum. However, upon base addition, prominent peaks emerged at 433 nm for absorption (yellow color) and 534 nm for fluorescence, marking a stark transition from “off” to “on”. Intriguingly, both the yellow color and the yellow-green fluorescence of the solution were transient, diminishing over time (Fig.2A and 2B; the blue fluorescence observed in Fig.2A originates from the ester formed in the subsequent reaction, which will be discussed in later sections). Attorney Docket No.11196-099WO1 To explain this behavior, we put forth a mechanism, which is rooted in the chemical structure of HA, as illustrated in part of Fig.2C. HA before adding the base (the keto form of HA, HAk) features a benzene ring in tandem with a six-membered anhydride ring, which is not fully conjugated. We surprisingly found that there is a lack of single crystal data of HAkin literature or any database. So, we conducted single crystal X-ray diffraction experiment on HAk and deposited it in Cambridge Crystallographic Data Centre (CCDC) under a new CCDC number: 2206140. The single crystal X-ray diffraction data clearly present a non-planar configuration for the anhydride ring of HAk. In detail, the dihedral angles are 3.5º for C4-C7-C8-O9, 7.8º for C5-C10-O9-C8 and 8.5º for C7-C8-O9-C10 in contrast to those from the benzene ring (all less than 0.5º), confirming its non-conjugated structure (Fig.2D, 2E and Table 1). As a result, the absorption of HAk falls into the UV range and no fluorescence can be observed. When a base is introduced, the α-methylene ketone moiety of HA undergoes keto-enol tautomerization, transforming into an enolate (the enolate form of HA, HAe). This transition engenders a fully conjugated ring structure, yielding a D-π-A push-pull structure where the remaining carbonyl group works as the electron-withdrawing group (EWG) and the newly formed enolate is a strong electron- donating group (EDG). The rigid planar structure endows HAe with bright fluorescence, and both conjugated system extension and the newly formed D-π-A push-pull structure are attributed to the bathochromic shift of absorption and fluorescence of HA. Furthermore, it is worth noting that the base serves a dual role: it aids in α-hydrogen abstraction, driving keto- enol tautomerization, and also partakes in nucleophilic attacks on the carbonyl carbon on the other side of the anhydride ring (Fig.2F). This dual action, on the one hand, leads to a keto-to-enolate transformation that endows HA with a yellow color and yellow-green turn- on fluorescence; on the other hand, induces ring opening, which causes the color and fluorescence to wane over time. To dissect the underlying mechanisms of the halofluorochromic behavior and the associated fading, we sought to obtain relative long-lived yellow-colored molecular species for some characterizations such as UV-vis, fluorescence and nuclear magnetic resonance (NMR) spectroscopies. Given that the enolization and deprotonation of the α-methylene ketone part of HA resulting in the color change are contingent on the basicity of the base, while the ring opening that brings self-destructive behavior hinges on the nucleophilicity, it is interesting to investigate whether the halofluorochromic and the self-destructive behavior of HA could be decoupled and controlled by adjusting the basicity and nucleophilicity of the base. In most cases, the base with stronger basicity also possesses stronger Attorney Docket No.11196-099WO1 nucleophilicity. However, there are several non-nucleophilic bases that exist (Supplementary Note 1, both nucleophilic and non-nucleophilic bases used or mentioned in this work are summarized in Table 2). Thus, we predicted that the non-nucleophilic base could still convert HA from the keto form to its enolate form by abstracting the α-hydrogen, meanwhile effectively preventing the ring opening from the nucleophilic attack. In other words, the persistence of HAe, along with its yellow hue and turn-on fluorescence, can be modulated by manipulating the base’s nucleophilicity while maintaining strong enough basicity. Upon adding a non-nucleophilic base, 1,8-Diazabicyclo(5.4.0)undec-7-ene (DBU), both the yellow color and the turn-on fluorescence exhibited a significantly prolonged duration compared to that of nucleophilic counterpart, as shown in Fig.2A and 2B. This observation supports our hypothesis that the halofluorochromism and self-destruction of HA can be independently controlled by harnessing of the duality of bases. Therefore, the complete hypothesis was HAk can be converted to HAe, which possesses both yellow color and turn-on fluorescence, by adding either nucleophilic or non-nucleophilic bases; whereas HAkand HAecan only transform into the ring-opening form, homophthalate, upon the addition of nucleophilic bases, resulting in the loss of both the yellow hue and the yellow- green fluorescence (Fig.2C). UV-vis and fluorescence spectroscopies were then conducted to interrogate the photophysical properties of HA. The spectroscopic features have been mentioned above. Just note that the large absorption redshift (150 nm) indicated the existence of another mechanism besides conjugated system extension, such as intramolecular charge transfer (ICT), which further extends the absorption wavelength. Furthermore, the quantum yield of HAe in acetonitrile was determined to be around 5.51% (Supplementary Note 2 and Fig.5) and solvent polarity effect on photophysical properties of HAe was also investigated (Fig. 6). Next, the absorption and fluorescence decay profiles with different base addition were recorded at fixed wavelengths to monitor the dynamic change of the chromogenic / fluorogenic species in the solution. Upon adding a nucleophilic base, triethylamine (TEA), the absorption and fluorescence emission intensity decreased rapidly, while after adding DBU, the decay rates were much slower (Fig.3A, 3B and Fig.7). Of note, the absorption and fluorescence decay curves of HA after adding DBU matched well, and after 2 hours, there was 44.3% of the original absorbance (at 430 nm) and 42.5% of fluorescence intensity (at 530 nm) remaining, which are close to each other, indicating the same chemical species contributed prominently to the yellow color and fluorescence. In Attorney Docket No.11196-099WO1 contrast, the absorption decay curve of HA after adding TEA was apparently above the fluorescence decay curve, and after 2 hours there was 25.6% of the original absorbance but only 9.8% of fluorescence intensity remaining (Fig.8). Besides, the absorption and fluorescence decay profiles show that the degradation of HAe may have different reaction orders and merits for a further investigation. The above results imply that more complicated chemical reactions occurred in the solution when adding TEA than after adding DBU, and some chemical species only formed in the solution with TEA, contributing to the difference between absorbance and fluorescence intensity reduction. Kinetic measurements of Fourier-transform infrared (FTIR) spectroscopy were then applied. As shown in Fig.3C, before adding the base, two peaks were observed at 1803 and 1754 cm-1, which correspond to the two carbonyls of the keto form of HA, and the shoulder at 1728 cm-1is consistent with the carboxylic C=O of homophthalic acid(24), indicating a small degree of conversion of HA to the diacid. Upon addition of DBU, the two anhydride C=O peaks rapidly diminished then disappeared, and a peak at 1693 cm-1appeared, which is assigned to C=O vibration from the enolate form of HA. This C=O peak reached its maximum in seconds then continued to decrease, indicating that the degradation of the enolate form of HA was proceeding. The detailed data analysis and additional FTIR spectra can be found in the Supplementary Materials (Supplementary Note 3 and Figs.9-12). Nuclear magnetic resonance (NMR) spectroscopy was exploited to further investigate the detailed chemical structure information and reaction mechanisms. Based on the1H spectra of HA shown in Fig.3D, the group of small peaks (green and magenta arrows in Fig.3D) were assigned to the ring-opening form, homophthalic acid, indicating that there was small portion of HA already hydrolyzed before adding the base, probably due to the air moisture as confirmed by the FTIR results. Comparing the1H spectra of HA before and after adding the base, almost every peak shifted upfield except one; the overall shifts could be ascribed to the pH effect while the peak at 4.17 ppm was contrary to the trend and shifted downfield to 4.56 ppm. This proposed enolic CH exhibited chemical shifts of 4.56 ppm (1H) and 73.69 (13C) ppm, which are between the conjugated vinylic and saturated proton / carbon chemical shift range. These chemical shifts clearly showed that the proposed enolate part of HA is ambident, referring to the negative charge being delocalized over the α-carbon and the oxygen, endowing all bonds among the enolate region partial double bond character, which is in accordance with the literature for similar molecules and common chemical knowledge(25, 26). The chemical shifts are also convincing evidence showing that HAk was converted to HAe. Although mentioned explicitly or vaguely in Attorney Docket No.11196-099WO1 previous literature on HA(27-29), our NMR results are the first definite evidence of the formation of an enolate structure from HA in basic environments. The1H and13C chemical shifts combined with 2D spectra of HA right after adding DBU provides solid proof of the structural change from HAk to HAe. While in the solution with added TEA, HAe can react with homophthalate, either from the small amount in the starting materials or from the ring opening of HA by nucleophilic attack of TEA, to form an ester, resulting in the aforementioned rapid decrease of absorbance and yellow-green fluorescence intensity. All NMR spectra, the detailed analysis, and discussions are in Supplementary Note 4 and Fig. 13-23. Putting the spectroscopic data together, the commercial HA sample used as received initially contains a small portion of homophthalic acid. The addition of nucleophilic base, TEA, results in the enolate form and ring-opening form of HA followed by rapid esterification, and thus the enolate form as well as the yellow color and yellow-green fluorescence quickly depletes. The formed ester exhibits a certain degree of blue fluorescence (Fig.24), as previously mentioned. The addition of non-nucleophilic base, DBU, makes the enolate form of HA much stabler and it lasts for a much longer time, and the enolate part of HA exhibits a partial double-bond characteristic where the negative charge is delocalized over the α-carbon and the oxygen (Fig.25). High Resolution Mass Spectrometry (HRMS) spectra of HAe, homophthalate and the ester were successfully collected (Figs.50-52) further supporting the above mechanisms. A scheme of proposed whole reaction mechanisms between HA and TEA (nucleophilic base) or DBU (non- nucleophilic base) is shown in Fig.25. To better understand the photophysical changes and reaction mechanisms, we performed first-principles calculations based on density functional theory (DFT) (Fig.3E, 53-55 and Supplementary Note 5). The calculated HOMO (the highest occupied molecular orbital)- LUMO (the lowest unoccupied molecular orbital) gap and the calculated absorption wavelength (271.59 nm) for HAkand (412.65 nm) for HAeare in agreement with our experimentally measured absorption maxima at 283 and 433 nm, respectively. The calculated electron density distribution diagrams of HOMO and LUMO align with the hypothesized structural alteration. The results support the fact that HAe has a higher degree of conjugation. The transition from HAk to HAe markedly elevates the electron charge density in the right-side ring, accompanied by a denser electron clouds correlation at the enolate part, signifying the augmented conjugation of the ring and electron delocalization across the enolate moiety. Notably, the transition dipole calculated for HAe(2.523 Debye) is Attorney Docket No.11196-099WO1 significantly higher than that of HAk(1.437 Debye), combined with their excited charge density difference between the ground state (S0) to the first excited state (S1), indicate a larger dipole moment from HAeupon photoexcitation and support the proposed ICT process. Dynamic CMY palette for encryption and anti-counterfeiting. An information encryption system can be simplified as three integrated components: the input, the material, and the output(30, 31). The fewer materials integrated, the simpler and more reliable the system is, whereas the more diverse the combination of inputs and outputs, the more secure the encryption system is. By leveraging the halofluorochromism and controlled self- destruction properties of HA, we developed a highly dynamic CMY palette for entity encryption and anti-counterfeiting. Two leuco dyes, phenolphthalein (PhPh) and α- naphtholphthalein (NaPh), were chosen as magenta and cyan colorants, while HA served as the yellow colorant. The rationale behind the choice was discussed in Supplementary Note 6. In theory, by altering the concentration and ratios of C, M and Y colorants, just like a real palette, any color within the color gamut of the system can be obtained, and a continuous and seamless color tuning can be achieved. The continuous color tunability was tested and the potential color gamut was simulated (Supplementary Note 7, 8 and Fig.29-34). We subsequently applied the palette system we developed to inkjet printing and handwriting, which are the two major implementations in information encryption applications (Fig.4A). When colorants are deposited onto a substrate, the situation is different from when in solution, since in solution, the molecules are surrounded by solvent molecules, whereas deposited on a substrate, the molecules are more like solid-state and interact with the substrate surface to some extent. Generally, conventional organic fluorophores, which exhibit bright fluorescence in dilute solution, suffer from aggregation- caused quenching (ACQ) in their solid state(32, 33), hindering their applications in anti- counterfeiting and information encryption. Intriguingly, HAe exhibits bright turn-on fluorescence in both solution and solid-state (on the substrate surface), which differs from conventional organic fluorophores and enables another layer of encryption. A computer-designed China Dragon image was first printed on printer paper using an inkjet printer by loading pure HA (Y), PhPh (M), and NaPh (C) solutions into the corresponding chambers of a customized CMY ink cartridge (Fig.4B). Right after printing, the solvent in the ink drops was evaporated in seconds leaving no noticeable ink traces under daylight and UV light. After applying the base, the image with the expected colors appeared instantly. The China Dragon image was then printed on a non-fluorescent inkjet Attorney Docket No.11196-099WO1 paper to avoid strong background fluorescence, and it also showed the invisible feature and only the HA (yellow)-dominant portions displayed fluorescence under UV after applying the base (Fig.35). The palette system’s performance was further assessed on various substrates, with consistent results (Supplementary Note 9, Fig.36 and 37). Besides the normal reflective and emissive modes of encryption, the self-destruction of HA enables an extra type of security feature: “burn after reading” and time-dimensional encryption, which means that the information or color parts written by HA will disappear after a certain amount of time after applying the base (Fig.4C). This allows the creation of self- destructive information suitable for time-sensitive application scenarios, such as cashing bank checks within the validity period. As shown in Fig.4C, three letters were written with yellow (HA), magenta (PhPh), and green (HA-NaPh 1 : 1 mix) respectively. Right after applying the base, the yellow “P”, magenta “S”, and green “U” appeared and after 10 minutes, the yellow parts (the whole “P” and yellow color of “U”) had already completely disappeared, leaving the magenta “S” and cyan “U”. It is worth noting that by tuning the nucleophilicity of the base, the persistence of HA (yellow) parts can be manipulated (Fig. 38). Furthermore, the different color transition points of the C, M, Y colorants enable gradient encryption (Fig.4D and Fig.39). By applying base 1, the yellow parts showed up; after applying base 2, the cyan parts appeared; and when base 3, which is strongest among the three bases, was applied, the magenta parts showed and the whole “PSU” could be observed. These demonstrations proved that our palette system can also be used to encode the encryption information in multiple domains. Moreover, an exemplary case to show how to exploit our palette system in anti-counterfeiting is presented in Fig.40 and Supplementary Note 10. For the potential commercialization, we tested the ink’s stability under two conditions, (a) before writing and (b) after writing but before applying the base on printer paper. Before writing (condition (a)), the solutions of three colorants were stored for three months, and their performance was compared by writing with inks that had been stored for three months or freshly prepared after applying the base, and monitoring the degradation using UV-vis spectroscopy. To test the stability of the CMY ink solutions under condition (a), 100 mM HA in acetone, and 10 mM PhPh and 2.5 mM NaPh in ethanol were stored in capped 15 mL tubes for 3 months. Two groups of characters, “P”, “S”, “U”, were written using HA, PhPh, and NaPh solutions, respectively. In Fig.41, the upper characters were written with solutions stored for 3 months while the lower ones were written with freshly made solutions. Upon base addition, the two groups of “S” and “U” showed no appreciable Attorney Docket No.11196-099WO1 difference while the yellow (HA) part, i.e., “P” made from the group stored for 3 months exhibited a slightly lighter color than the freshly made group, which indicated some degree of degradation (Fig.41). Thus, to further quantitatively investigate the stability, UV-vis spectroscopy was applied to measure the absorption change of the three ink solutions after 3 months. As shown in Fig.42, after adding the base, the absorption of PhPh and NaPh hardly changed from freshly made to 3 months’ storage, showing excellent stability of PhPh and NaPh in solution, whereas the absorption of HA decreased to around 50% after 3 months, indicating that the HA molecules were slowly degrading in solution and corresponding to the results on paper writing. The above results showed that PhPh and NaPh possess excellent stability in solution whereas the stability of HA in solution is moderate. Therefore, there is room to improve the stability of HA solution for long term storage purposes. On the other hand, since the coloration of the HA ink before and after storage for 3 months didn’t show a significant difference, for some application scenarios that do not require restricted coloration effects, the long-term stored HA solution is also acceptable. In other words, the acceptable threshold of long-term storage results of HA solution depends on the specific application. Moreover, removing the moisture and air combined with sealing the container of the HA solution, increasing HA concentration, adding protective ingredients, changing the solvent, or choosing another form of HA such as dry powder, might all help improve the stability of HA solution and prolong the duration of its storage. To assess the colorant stability after being written on paper (condition (b)), the magenta (PhPh) and cyan (NaPh) parts exhibited no significant difference up to 3 weeks, while the yellow (HA) parts were quite dim after one week and further disappeared completely within the second week (Fig.43). Sealing the writing area with a tape, placing the paper in a desiccator and even putting the paper in a glovebox right after writing did not make any difference. By heating the paper to remove moisture and with the help of ATR- FTIR spectroscopy, we confirmed that the adsorbed water / moisture from the cellulose (paper) plays a major role in the degradation of HA. The details are discussed below. It is well known that the main component of common paper is cellulose, which is a polysaccharide consisting of repeating β-1,4 linked D-glucose units. Due to its abundant hydroxyl groups in the cellulosic fiber, the surface of paper appears hydrophilic. The hydrogen bonding is attributed to the water / moisture absorption and retention from the air(34). Taking oxygen atoms from intra- and intermolecular C-O-C bonds into account, the number of hydrogen bonding acceptors is more than that of hydrogen bonding donors, which enables water molecules to adsorb and be stabilized on the paper surface(35) (Fig. Attorney Docket No.11196-099WO1 44). There are some other factors that can also appreciably affect the water adsorption capability of cellulosic fibers, including temperature of surroundings and humidity of air(34, 36, 37), and we utilized these two factors to help us investigate the interactions between water and HA on the paper surface. Owing to the surface and in situ measurement capability, ATR-FTIR spectroscopy is the ideal technique to investigate the chemical changes of HA degradation on the paper surface. The 1644 cm-1OH bending peak is suitable for analyzing the water content of cellulose and is usually well-visible considering the cellulose spectrum(35, 38). Meanwhile, the OH stretching absorption band between 3700–3000 cm-1, which is assigned to the intra- and intermolecular hydrogen bonding, might also provide some information on water content change(35). Since 2 weeks after writing, no yellow color appeared on the paper when we applied the base, we speculated that the moisture in the air might have reacted with HA and hydrolyzed the anhydride ring, resulting in the loss of color change ability. A desiccator with bench vacuum and an argon gas glovebox were used respectively. However, as mentioned in the main text, putting the paper in either the desiccator or glovebox did not help at all. This reminded us that there might be interactions between HA and something already on the paper surface. Considering the hydrophilic nature of cellulosic fibers, the adsorbed water on the paper surface becomes the most possible factor. Shown in Fig.45, we first measured a blank printer paper surface. The appreciable water signal centered at 1644 cm-1indicated the existence of adsorbed water on the paper surface. Then, a cotton swab tipped with 100 mM HA acetone solution was used to write on the paper. Shortly after the solvent evaporated, the paper was measured. Two new distinct peaks around 1780 cm-1and 1750 cm-1were assigned to two carbonyl groups of HA correspondingly, while the water peak still showed up. In contrast, the written paper after 2 weeks exhibited no HA carbonyl peaks, indicating the full degradation of HA, corresponding to the observation that no yellow color appeared when applying the base. Since putting the paper in the glovebox did not prevent HA degradation, meaning that the hydrogen bonds between adsorbed water and cellulosic fibers were strong enough to withstand the extraction force from the atmosphere in the glovebox, another attempt, heating the paper to remove the adsorbed water, was exploited to prevent the hydrolysis of HA. The influence of heating on the paper was investigated (Fig.46). The paper was heated at 110ºC in an oven for 10 hours. Compared to the blank, the paper right after heating showed a clear decrease of the 1644 cm-1water peak and after 10 minutes in the ambient environment, the water peak intensity increased but remained lower than that of the blank. Attorney Docket No.11196-099WO1 After 20 minutes, results showed no apparent difference compared to the 10 minutes results and the 1644 cm-1peak further increased after 30 minutes but was still lower than that of the blank (Fig.46). The 3700–3000 cm-1band did not exhibit an informative trend. Since this broad band comprises both -OH from cellulose and water, it might result from the -OH perturbations from cellulose after the water was removed / reduced. Therefore, in agreement with the literature, we believe that the 1644 cm-1peak brings more reliable and solid evidence of the water content changes. We also wrote on the heated paper and placed it in the ambient environment for 2 weeks. There was no yellow color after applying the base, and the FTIR spectrum also showed the disappearance of the two HA peaks, quite similar to that without heating (Fig.45). These results showed that (1) the heating can effectively reduce / remove the adsorbed water on the paper surface; (2) once the paper is taken out of the oven, it will slowly absorb water / moisture again. Back to the HA degradation mechanisms study, since we know heating can effectively reduce / remove the adsorbed water on the paper surface, this time we used a heated paper written right after putting into the glovebox and expected it to retain color change capability after 2 weeks. The experimental results perfectly met our expectations: after applying the base, the written information turned to yellow color and the two HA peaks were conspicuous, while the adsorbed water peak remained lower than the blank (Fig.45). Conclusively, with the adsorbed water removal / reduction, the HA degradation was effectively slowed down, and this strongly supports that the adsorbed water on the paper surface plays a crucial role in the HA degradation before applying the base. Based on above results, we predicted that by increasing the HA concentration in the ink, the effective time of steganographic information could be prolonged. After increasing the HA concentration from 100 mM to 500 mM, the yellow color was still quite noticeable after 2 weeks even though slightly dimmer (Fig.47). To sum up, the C, M, and Y inks are quite stable in solution; C and M colorants are also stable for up to 3 weeks after being written on the printer paper, while Y colorant (HA) keeps decaying over time once being written on the paper. This results in an effective time of the information before applying base and it can be manipulated by tuning the concentration of HA. Furthermore, we developed a smartphone app to enhance anti-counterfeiting measures, enabling the detection of subtle color variations often overlooked by the human eye, thereby leveraging the continuous color tuning capability of our palette system. Finally, putting the aforementioned capabilities of the palette system all together, a schematic Attorney Docket No.11196-099WO1 illustration of the workflow and all encryption features of the palette system are given in Fig.48. Discussion Currently, we have only investigated and observed that as the amount of the base added increases within a certain range, the time for color / fluorescence fading decreases. This observation is understandable since we have noted that the non-nucleophilic bases still possess a certain degree of nucleophilicity; therefore, an excessive amount of base will accelerate the ring-opening process, resulting in more rapid self-destruction. In future work, we are keen on conducting detailed and quantitative kinetic studies to explore how the amount of base added, pH and nucleophilicity affect the halofluorochromic behavior of HA and to delve deeper into this chemistry. The mechanisms of the halofluorochromism and self-destruction of HA we reveal provide fresh insights into chemical and photophysical perspectives of the intriguing and versatile molecule, HA, deepen our understanding of six-membered anhydride rings with enolizable α-hydrogen(s) and the keto-enol tautomerism and might inspire the molecular design strategy of dual-mode optical switching materials with tunable duration. By harnessing the halofluorochromism and self-destruction properties of HA and the duality of bases, we achieve controlled color and fluorescence duration, and develop a CMY palette with unparalleled highly dynamic, multidimensional and multimodal optical encryption capabilities. With the pH-responsive and self-destructive features, HA-derived systems hold unprecedented promise in constructing pH-responsive drug delivery systems owing to the diverse pH values of tissues at various physiological and pathological conditions. For future studies, it will also be of interest to expand the applications of HA and the CMY palette, as well as to design and develop more novel molecules and materials exhibiting halofluorochromism with a broader range of colors and dynamic features. Materials and Methods Materials. Homophthalic anhydride (HA) was purchased from Acros Organics, all other chemicals were purchased from Sigma Aldrich, and all were used as received. UV-vis and fluorescence spectroscopies measurements. The steady-state UV-vis spectra and absorption decay profiles (kinetic measurements) of sample solutions were recorded on a PerkinElmer Lambda 950 UV-Vis-NIR spectrometer. The steady-state fluorescence spectra and intensity decay profiles (kinetic measurements) of sample solutions were collected on a Horiba FluoroMax-4 fluorometer. Quartz cuvettes with a 10 mm path-length and a PTFE stopper were used for UV-Vis and fluorescence measurements. Attorney Docket No.11196-099WO1 HA was dissolved in acetonitrile, and PhPh and NaPh were dissolved in ethanol. For UV- vis measurements of PhPh and NaPh, 20 μL freshly made 1 M tBuOK ethanol solution was added to 2.5 mL of PhPh or NaPh solution, respectively. For both UV-vis and fluorescence measurements, 2.5 mL HA solution (100 μM in acetonitrile) was added into the cuvette, 20 μL of pure TEA or DBU was added quickly with thorough mixing, and the measurement was started as quickly as possible. The long-term storage test of HA solution was conducted in acetone at high concentration (100 mM) while the UV-vis measurement required diluted solution in acetonitrile; thus, the HA solution stored for 3 months was diluted with acetonitrile to 100 μM for the UV-vis measurement. Quantum yield determination of the enolate form of HA. Absolute quantum yield measurement was conducted on a Horiba FluoroMax-4 fluorometer equipped with a Quanta-φ F-3029 integrating sphere. Relative quantum yield was calculated using the method in Supplementary Note 2. HA was dissolved in acetonitrile and Coumarin 153 (C153) was dissolved in ethanol. A small portion of the HA solution was taken out, DBU was added and the absorbance was measured, and then the rest of the portion was diluted until the required absorbance was reached. The ODs of HA after adding DBU and C153 were measured using a PerkinElmer Lambda 950 UV-Vis-NIR spectrometer and adjusted to around 0.1. The fluorescence emission spectra were recorded on a Horiba FluoroMax-4 fluorometer. For HA, 2.5 mL HA solution was added into the cuvette, 20 μL of pure DBU was added quickly and mixed thoroughly, and the measurement was started as quickly as possible. The quantum yield of C153 in ethanol (0.53%) was obtained from the literature1,47as a reference standard in this work. FTIR measurements and data processing for HA color change mechanisms study. Fourier transform infrared (FTIR) spectra were collected on a Bruker vertex 80 spectrometer equipped with a liquid nitrogen cooled mercury cadmium telluride (MCT) detector. All spectra were measured in attenuated total reflection (ATR) mode using a Harrick scientific horizon multiple bounce ATR accessory with a Zinc Selenide (ZnSe) liquid sampling cell. Kinetic (time resolved) measurements were performed during which a total of 6 scans were averaged per spectrum at a resolution of 6 cm-1resulting in one spectrum every 7 seconds. This was done to capture any spectral changes during the initial stages after the addition of base. For non-time resolved experiments, a total of 400 scans were averaged per spectrum and the absorbance was calculated by referencing to the clean ZnSe crystal. Attorney Docket No.11196-099WO1 NMR measurements. The NMR spectra were recorded on Bruker Avance 500 MHz and 850 MHz spectrometers. The1H measurements were conducted using 10 mg / mL HA in CD3CN unless specified,13C measurements including DEPT measurements were conducted using 40 mg / mL HA in CD3CN, and HSQC and HMBC measurements were conducted using 10 mg / mL HA in CD3CN. HRMS measurements. The UPLC-HRMS measurements were conducted on a Waters I-Class Plus / Syanpt-XS system. Mobile phase A: H2O (0.1% FA); B: ACN (0.1% FA); ESI source: negative mode; infused by 0.3ml / min A1:B1=70:30. Spectra of HAe and homophthalate were collected from the sample (5 mL 100 mM HA + 200 μL DBU after 5 days then diluted 40 times with DI water) with injection volume of 0.1 μL. Spectrum of the ester was collected from the sample (5 mL 100 mM HA + 200 μL TEA after 5 days then diluted 40 times with DI water) with injection volume of 0.1 μL. ATR-FTIR measurements and data processing for adsorbed water on the paper surface study. To record the FTIR spectra, the aforementioned Bruker vertex 80 spectrometer equipped with a liquid nitrogen cooled mercury cadmium telluride (MCT) detector was used, and measurements were made in ATR mode using a Harrick DiaMax accessory with a germanium (Ge) crystal. A total of 400 scans were averaged per spectrum at 6 cm-1resolution and the absorbance was calculated by referencing to the clean Ge crystal. All the FTIR spectra were subjected to baseline correction and normalized with the 1030 cm-1peak which was assigned to C-O stretching at C6 of cellulose. The 2894 cm-1peak assigned to C-H stretching of cellulose also showed consistency after normalization, which supports our normalization method. For experiments that required removal of water from the air, an argon gas glovebox was used, whose water content was below 0.5 ppm. Photos of decay progress of HA (Fig.2A and 2B).100 μL pure TEA or DBU was added into 2.5 mL HA solution (1 mM in acetonitrile) with quick mixing, followed by photo shooting at the initial point and at 10, 20, 30, and 40-minute time points. Preparation of various representative color samples (Fig.30). Seven colors (yellow, magenta, cyan, blue, green, red and black) from the CMY palette system after adding a base are shown in Fig.30 to demonstrate the continuous color tuning capability of the system. To prepare CMY primaries’ solutions, HA was dissolved in acetone to obtain 100 mM HA solution, while PhPh and NaPh were dissolved into ethanol to obtain 1 and 5 mM PhPh solutions and 100 and 500 μM NaPh solutions, respectively. Potassium tert- butoxide (tBuOK) was dissolved in ethanol to obtain 1M tBuOK base solution. The yellow Attorney Docket No.11196-099WO1 sample contained 2.5 mL 100 mM HA + 20 μL TEA; the magenta sample contained 2.5 mL 5 mM PhPh + 20 μL 1M tBuOK; the cyan sample contained 2.5 mL 100 μM NaPh + 20 μL 1M tBuOK; the blue sample contained 1.25 mL 500 μM NaPh + 1.25 mL 1 mM PhPh + 20 μL 1M tBuOK; the green sample contained 1.25 mL 100 mM HA + 1.25 mL 100 μM NaPh + 200 μL 1M tBuOK; the red sample contained 1.25 mL 100 mM HA + 1.25 mL 5 mM PhPh + 200 μL 1M tBuOK; and the black sample contained 0.833 mL 100 mM HA + 0.833 mL 500 μM NaPh + 0.833 mL 5 mM PhPh + 200 μL 1M tBuOK. Continuous color tuning demonstration using a multiwell plate (Fig.31). The mother solutions of CMY colorants used were: 50 mM HA in acetonitrile, 10 mM PhPh in ethanol, and 100 μM NaPh in ethanol. Each well contained 0.5 mL liquid in total. The formulas of each well in the well plate are shown in Table 3 correspondingly. Inkjet printing of the China Dragon image (Fig.4B and Fig.35). The inks used were 500 mM HA acetone solution (Y), 40 mM PhPh ethanol solution (M), and 10 mM NaPh ethanol solution (C); the base used was 1 M NaOH water solution; the papers used were normal printer paper (Fig.4B) and Red River Paper Palo Duro Baryta Fiber 300 inkjet paper (reverse side; Fig.35). The base was sprayed onto the paper surface after a short wait (several seconds) for the solvent to evaporate, and the images appeared immediately. Tests on various substrates (Fig.36). The inks used were 100 mM HA acetone solution, 10 mM PhPh ethanol solution, and 2.5 mM NaPh ethanol solution, and 1 M NaOH water solution was used as the base. Human skin encryption test (Fig.37). The “P”, “S”, and “U” were written using a cotton swab on the arm with HA (100 mM, acetone), PhPh (10 mM, ethanol) and NaPh (2.5 mM, ethanol) solution, respectively. Then, 1 M 2-amino-2-methyl-1-propanol (AMP) water solution was applied on the writing area with or without a water rinse. Immediately after application of AMP, a 365 nm UV flashlight was used (only for a few seconds) to excite the turn-on fluorescence from the character “P”. The writing areas were thoroughly washed after the experiment to insure there was no residual ink remaining. Nucleophilic vs. non-nucleophilic base demonstration (Fig.38). The inks used were 100 mM HA acetone solution (for “TB”) and 2.5 mM NaPh ethanol solution (for “BL”); 1 M NaOH water solution was used as the base for the upper part while pure DBU was used for the lower part. “Burn after reading” and time dimensional encryption demonstration (Fig. 4C). The inks used were 100 mM HA acetone solution (Y), 10 mM PhPh ethanol solution Attorney Docket No.11196-099WO1 (M), and 100 mM HA acetone solution mixed with 2.5 mM NaPh ethanol solution (1 : 1 volumetric ratio; G = C + Y). The base used was 1 M NaOH water solution. The “PSU” was written using cotton swabs with corresponding inks (“P”–Y, “S”–M and “U”–G), and then the base was applied. Over time, the yellow part gradually disappeared. After 10 mins, the yellow parts (the whole “P” and yellow color of “U”) completely disappeared. Therefore, the previous “PSU” (“U” was green) was converted to “SU” (“U” was cyan). Gradient encryption demonstration (Fig.4D and Fig.39). All the letters were written on the inkjet paper (Fig.4D) and the filter paper (Fig.39) using cotton swabs; the “P”, “S”, and “U” were written by HA (500 mM, acetone), PhPh (10 mM, ethanol), and NaPh (2.5 mM, ethanol) solution, respectively; 1 M, pH 7.6 Tris-HCl buffer was used as the base 1; 0.25 M 2-amino-2-methyl-1-propanol (AMP) acetonitrile solution was used as the base 2; 1 M NaOH water solution was used as the base 3; the papers used were Red River Paper Palo Duro Baryta Fiber 300 inkjet paper (reverse side; Fig.4D) and normal filter paper (Fig.39). Exemplary anti-counterfeiting demonstration (Fig.40). The digital numbers “9”, “2”, and “3” were written using, individually or in combination, 100 mM HA acetone solution, 10 mM PhPh ethanol solution, and 2.5 mM NaPh ethanol solution; 1 M, pH 7.6 Tris-HCl buffer was used as base 1; 0.25 M 2-amino-2-methyl-1-propanol (AMP) acetonitrile solution was used as base 2; 1 M NaOH water solution was used as base 3; pure 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) was used as base 3′; the papers used were Red River Paper Palo Duro Baryta Fiber 300 inkjet paper (reverse side). After writing and before applying the base, there was no ink trace under ambient light. Under UV no fluorescence or only faint blue fluorescence (which may be due to the interactions between HA and the inkjet paper surface) was observed. After applying the base 1, the digital number “123” with yellow color appeared; meanwhile, under UV light, an apparent “123” with fluorescence could be observed. After applying the base 2, the cyan parts appeared and the number changed to “723” (“2” was a green color); meanwhile, under UV light, the number “13” with yellow-green fluorescence was observed. After applying the base 3, which is a nucleophilic base, the magenta parts appeared resulting in the number “923”; meanwhile, under UV light, the fluorescence of HA only had parts (i.e., “1”) which could be observed. After 10 mins followed by applying base 3, the yellow parts completely disappeared and under UV light, no yellow-green fluorescence from HA could be observed. For the base 3′, which is a non-nucleophilic base, there was no significant difference between the colors and fluorescence right after applying the base and after 10 mins. Of note, Attorney Docket No.11196-099WO1 after applying the base 3′, under UV light, the “1” showed yellow-green fluorescence from HA but the “2” and “3” still showed some weak fluorescence. We are currently working on investigating the reason and optimizing the formula to avoid such minor interference, although the weak interference fluorescence from “2” and “3” can be distinguished from the bright yellow-green fluorescence from “1” by the naked eye. Smartphone app for anti-counterfeiting application demonstration. An anti- counterfeiting demonstration app was developed based on the iOS system for a smartphone. The app is used in conjunction with the palette system. The app allows the user to either access the camera to capture the image or upload the already-captured image of appeared encrypted information. The software will analyze the color of the image. If the color is too faint, it will remind “Color too faint, please apply more solution”; if the color is incorrect, it will output “False”; if the color is in the acceptable range, it will output “True” and direct to our lab website. Color image printing demo. The inks used were 500 mM HA acetone solution (Y), 40 mM PhPh ethanol solution (M), and 10 mM NaPh ethanol solution (C); the base used was 1 M NaOH water solution; and the paper used was normal printer paper. After the fast evaporation of the solvent and before the base application, the printed image was completely invisible under ambient light and UV light. Once the base was sprayed onto the paper surface, the colored image appeared immediately. Color QR code printing demo. The inks used were 500 mM HA acetone solution (Y), 40 mM PhPh ethanol solution (M), and 10 mM NaPh ethanol solution (C); the base used was 1 M NaOH water solution; and the paper used was normal printer paper. After the fast evaporation of the solvent and before the base application, the printed QR code was completely invisible under ambient light and UV light. Once the base was sprayed onto the paper surface, the colored QR code appeared immediately and was easily recognized by the smartphone. Time dimensional encryption demo. The inks used were 100 mM HA acetone solution (Y), 10 mM PhPh ethanol solution (M), and 100 mM HA acetone solution mixed with 2.5 mM NaPh ethanol solution (1 : 1 volumetric ratio; C + Y = G, green); the base used was 1 M NaOH water solution. The original information was written using cotton swabs with different inks. The false information appeared right after applying the base. Over time, the yellow part gradually disappeared. After less than 10 mins, the yellow parts completely disappeared. Therefore, the false information was replaced by the true information (“I LOVE PSU”). Attorney Docket No.11196-099WO1 Anti-counterfeiting smartphone app demo. The inks used were 100 mM HA acetone solution (Y) and 10 mM PhPh ethanol solution (M); the bases used were 1 M NaOH water solution (for PhPh) and pure DBU (for HA). The app can analyze the image taken from the camera. The area before applying the base gave a “Color too faint, please apply more solution” reminder on the app and didn’t direct to our lab website. Once the base was sprayed on the PhPh written area, the area turned to magenta color and gave a “False” output on the app since the RGB value doesn’t fall into the preset acceptable range. Then the DBU was applied by a cotton swab and the color which appeared was in the acceptable range; the app, therefore, gave an output of “True” and directed to our lab website. Supplementary Notes Supplementary Note 1. Overview of the basicity and nucleophilicity The bases discussed in this paper are Lewis bases that are capable of donating one or more non-bonding electron pairs. Both basicity and nucleophilicity represent the ability to donate the lone pair electrons of the compound. However, basicity measures the affinity to protons, while nucleophilicity defines the ability to attack the electrophiles. Thus, in most cases, basicity is a subset of nucleophilicity, i.e., the stronger the basicity, the stronger the nucleophilicity. Intriguingly, several non-nucleophilic bases exist. The underlying principle of non-nucleophilic base is a steric hinderance effect: they usually contain bulky groups shielding the lone pair of electrons of the donating atom, and therefore the bulky electrophiles cannot reach the non-bonding electron pairs, but a small steric proton still can be abstracted, resulting in moderate or high basicity but poor nucleophilicity. Since the keto-enolate conversion of HA originates from the abstraction of α- hydrogen in the methylene ketone structure, the higher basicity the base possesses, the higher the conversion efficiency. The conversion from both keto form and enolate form of HA to homophthalate (i.e., ring-opening form) relies on the nucleophilic attack of the base to the carbonyl carbon. Therefore, the keto-enolate conversion and ring opening are accompanied by each other in nucleophilic base cases, whereas the non-nucleophilic bases which have appreciable basicity but poor nucleophilicity can separate the two above- mentioned processes, i.e., allowing the keto-enolate tautomerization but prevent the ring opening. Supplementary Note 2. Quantum yield determination and solvent polarity test of the enolate form of HA Attorney Docket No.11196-099WO1 The quantum yield determination methods can be divided into absolute and relative methods. Simply speaking, the absolute method starts from the definition of quantum yield of photoluminescence: the ratio of the number of photons emitted to the number of photons absorbed. By measuring how many photons are absorbed by the sample and how many photons are emitted, the absolute quantum yield can be calculated. In this work, the absolute quantum yield of the enolate form of HA was obtained using a commercial fluorometer equipped with quantum yield measurement accessories. In contrast, the relative method uses a dye of known quantum yield as a reference to calculate the quantum yield. In this work, we referred to the protocol from the literature1to obtain the relative quantum yield of the enolate form of HA, aiming to cross-reference absolute and relative quantum yields to ensure reliable and accurate results. For relative quantum yield determination, the equations below are applied: Fƒ^ n^ ^= ^^ ·F · ·^ n^^(S1)Where ^ is the quantum reference dye, F and F^are integral emission or photon flux of the sample and the reference dye, respectively, ƒ and ƒ^are the absorption factor of the sample and the reference dye, respectively, n is the refractive index of solvent of the sample solution, n^is the refractive index of solvent of the reference dye solution, and d(^^^) denotes the optical density at the excitation wavelength. It is noted that the lower and upper limits of the integration should cover the corresponding emission wavelength range of the sample fluorescence and the reference fluorescence; and to be more accurate, the refractive indices applied should be at the mean or average emission wavelength, which are often difficult to obtain; instead, the values given for the standard wavelengths are usually used. In this work, the reference dye used was Coumarin 153 (C153) in ethanol and the HA sample was dissolved in acetonitrile, thus the refractive indices applied were 1.3441 (acetonitrile) and 1.3614 (ethanol), which are the ratio of the velocity of light (sodium D line) in air to the velocity of light in the solvent (at 20°C). As shown in Fig.5, the quantum yield from the absolute method is 5.33%, while from the relative method is 5.51%. Because the enolate form of HA slowly degrades in the non-nucleophilic base, DBU, and both absolute and relative methods take some time from the moment the base is added into the solution until the detection is completed, the actual quantum yield of the enolate form of HA should be higher than the obtained values. Since the relative method takes less time Attorney Docket No.11196-099WO1 than the absolute method, we believe that 5.51% should be closer to and slightly lower than the actual quantum yield of the enolate form of HA. The experimental details can be found in the “Materials and Methods” section. The absorption, fluorescence excitation and emission spectra of the enolate form of HA in different solvents were recorded. Three solvents, acetonitrile (ACN), tetrahydrofuran (THF) and toluene, with high, medium and low polarity, respectively, were used to dissolve HA followed by DBU addition. As shown in Fig.6, the absorption spectra matched well with the excitation spectra. The spectra from THF and toluene matched each other. Compared to THF and toluene, the absorption and excitation spectra from ACN shifted to the longer wavelength (red shift) while the emission spectra overlapped perfectly. The red shift of absorption in high polarity solvent in contrast to medium-low polarity solvents supported ICT occurred in the enolate form of HA, whereas the fluorescence emission did not show dependence on solvent polarity which is rarely observed from common ICT molecules and needs further investigation. Supplementary Note 3. FTIR spectroscopy analysis to explore the chemical structure of the enolate form of HA Kinetic measurements of HA upon DBU addition. Similar to Fig.3C but giving more spectra after the base addition with a 7 s interval, Fig.9 shows the spectra of a 100 mM solution of HA in acetonitrile before, during, and after the addition of DBU. Before the addition of DBU, two peaks were observed at 1803 cm-1and 1754 cm-1(peaks 1 and 2), which correspond to the two anhydride C=O groups, and a shoulder at 1728 cm-1is ascribed to the carboxylic C=O of homopthalic acid2, which indicates a small amount of HA was converted to the diacid. Upon addition of base, the two anhydride C=O peaks rapidly diminished and disappeared at around 35 s, and a peak at 1693cm-1appeared, which can be ascribed to the enolate form C=O vibration (peak 3). The C=N peaks of DBU at 1614 cm-1(peak 5) and 1315cm-1(peak 7) also decreased accompanied by a corresponding appearance of C=NH+peaks at 1646 cm-1(peak 4) and 1324 cm-1(peak 6), which are indicative of proton abstraction by DBU3. The C=C peak is expected at ~1620–1650 cm-1which overlaps with DBU C=N vibrations and hence is not directly observable in Fig.9; however, it is expected that conjugation will result in the redshift of the C=O frequency, which is consistent with our observation of a C=O peak at 1693 cm-1 4. Kinetic measurements of HA upon TEA addition. The changes of a 100 mM solution of HA in acetonitrile before, during, and after the addition of TEA are shown in Attorney Docket No.11196-099WO1 Fig.10. Similar to DBU, after adding TEA, the two anhydride C=O peaks at 1803 and 1754 cm-1rapidly decreased while, to the contrary, the enolate form C=O peak at 1699.5 cm-1rose. The left panel in Fig.10 shows the formation and kinetic change of the enolate form of HA (enolate form C=O): upon the addition of TEA, the enolate form of HA rapidly formed (green dot) and reached the maximum in the first 14 s, then gradually decreased. Additionally, new peaks were observed at 1662 and 1546 cm-1. The precise assignment of these peaks is still unclear, however, the NMR data presented in this manuscript suggests a more complicated reaction with TEA. One peak at ~1706 cm-1, which is ascribed to C=O, was observed in spectra after adding either DBU or TEA. The NMR data clearly showed that the enolate part of HA possessed a partial double bond characteristic. This explains the origin of the extra C=O peak. Additionally, Fig.11 and 12 put the pure DBU and TEA FTIR spectra with the corresponding sample spectra together to show that DBU and TEA do not have overlaps with the main peaks of interest. Supplementary Note 4. NMR spectroscopy analysis to investigate the chemical structures and the reaction mechanisms of HA after adding bases HA before adding the base. NMR spectroscopy is the most powerful tool to determine organic chemical structures. The first thing we did was to figure out the composition of the starting materials. The commercial HA powder was dissolved in CD3CN, since the photophysical characterizations of HA were all done in acetonitrile, obtaining the HA sample. The1H NMR spectrum of the HA sample (Fig.13) clearly showed that there are two chemical species: a major one with much higher peak intensity and a small proportion of a minor species. The major component was assigned to homophthalic anhydride (the keto form of HA), while the minor one was attributed to the hydrolyzed product, homophthalic acid, which is highly possible owing to the hygroscopic nature of anhydride and the resultant hydrolysis from water in the air. This also matches the FTIR results. Kinetic measurements of HA sample after adding TEA and DBU. The kinetic measurements were conducted right after adding TEA (for 2 h) or DBU (for 3 h). Equal time elapsed between scans, and only a few of the spectra are presented in Fig.14 and 16, including the first and last spectrum for each experiment. Compared to the DBU spectra, those of TEA contain more peaks indicating more chemical species and more complicated reactions (Fig.14). For TEA, even the first Attorney Docket No.11196-099WO1 spectrum shows many peaks originating from not a single source, especially in aromatic regions. Based on the composition of the starting HA sample, we predicted that there should be homophthalate (the deprotonated form of homophthalic acid) in the sample. If we can preclude the peaks from homophthalate, the resultant spectra will be cleaner. Note that since the pH of the sample had been changed and the homophthalic acid, whose peaks had already been assigned, was deprotonated, the peaks shifted. Therefore, a spiking experiment was conducted by adding pure homophthalic acid powder into the sample of HA 5 days after adding TEA. The increased peaks were then assigned to homophthalate with TEA addition. As shown in Fig.15, the aromatic proton peaks at around 7.73, 7.35, and 7.30- 7.25 ppm apparently increased as well as a saturated aliphatic proton peak at 3.70 ppm which increased significantly, with no change in other peaks, making clear to us all the peak positions of homophthalate protons. Going back to the kinetic spectra of TEA, homophthalate peaks didn’t change much among the measurement duration. Since the nucleophilic base, TEA, can open the ring structure and continue generating homophthalate, the results imply other reaction(s) consuming the homophthalate. The DBU spectra were relatively clean (Fig.16). The first spectrum shows that only one major component was present in the sample, and it kept decreasing and took a predominant proportion to the end (3 h). Thus, this component is very likely to be the enolate form of HA based on our proposed reaction mechanisms and the observation of absorption and fluorescence change. Considering the relatively clear components of the DBU group versus the relatively complex components of the TEA group, we chose the first spectrum of the DBU group to further study the exact chemical structure of the enolate form of HA, while the reaction mechanisms and some main components for TEA were investigated later and will be discussed in later sections. HA right after adding DBU. We conducted both 500 (in the kinetic measurements) and 850 MHz1H measurements of HA right after DBU addition and got the same results. We chose 500 MHz1H (Fig.17) and 850 MHz13C (Fig.18) spectra as representatives to analyze the structure of the products in this work. In the1H spectrum, there were two apparent chemical species, and the minor component is known to be homophthalate. The four aromatic proton peaks of the main component were located at around 7.68, 7.14, 6.81 and 6.56 ppm; one more peak in the upfield region was at around 4.56 ppm. Interestingly, the 4.56 ppm chemical shift of the proton was between that of conjugated vinylic hydrogen and saturated aliphatic hydrogen. We noted that the broad band in the1H spectrum and the Attorney Docket No.11196-099WO1 kinetic spectra of DBU is ascribed to the N-proton of the protonated DBU, which corresponds to the FTIR data. Then we turned to the13C spectrum. Similarly, the most intriguing chemical shift was 73.69 ppm of a carbon, which is exactly in the middle of vinylic carbon and saturated aliphatic carbon. Furthermore, the 2D results (HSQC and HMBC) helped us correlate and assign all the hydrogen and carbon atoms of the enolate form of HA (Fig.19). These results indicated that the bond between C7 and C8 of the enolate form of HA was actually between single bond and double bond; in other words, it possessed a partial double bond character, and these experimental data corresponded perfectly to the enolate-related knowledge from textbooks and the literature5-8. As shown in Fig.25, there are two resonance structures and the negative charge is delocalized among the whole carbon-carbon-oxygen (C7-C8-O12) region and the bonds between them are partially double-bond, making both the C end and O end nucleophilic (so called “ambident”). HA after adding TEA. Returning to TEA, since there was a complex composition, the sample was measured after 5 days to let the reaction complete and have a stable composition. Broad-band decoupled13C (i.e., normal13C) and Distortionless Enhancement by Polarization Transfer (DEPT) experiments were first conducted to give a brief understanding of the carbon backbones of the main components in the sample. DEPT spectroscopy applies proton pulses with different flip angles (θ = 45º, 90º and 135º) to determine the multiplicities of carbon atoms substituted with hydrogens (i.e., distinguish CH, CH2and CH3)9-11. In detail, DEPT-45 yields CH, CH2and CH3all positive phase while only CH signals can be observed in DEPT-90, and DEPT-135 gives positive-phased CH and CH3signals and negative-phased CH2signals. However, the quaternary carbon atoms are invisible in all DEPT spectra. Combining with the normal13C spectrum where all carbons including the quaternary carbons can be observed, carbons with all types of multiplicities (primary, secondary, tertiary and quaternary carbons) are identified. Since the information given by normal13C covers that from DEPT-45, only normal13C, DEPT-90, and DEPT-135 were used in this work (Fig.20). After excluding solvent and TEA peaks, there remained 5 carbonyl groups (not aldehyde), 1 single hydrogen-substituted alkene (C=CH), ~18 aromatic carbons (including 6 quaternary carbons) and 2 methylene (CH2) groups. The1H NMR spectrum of HA 5 days after adding TEA seemed to show at least 2 main components (one of them was confirmed to be homophthalate) with some trace byproducts (Fig.21, pristine and 22). Therefore, column chromatography was applied to separate the unknown main component(s) from homophthalate and purify the unknown component(s). After column chromatography purification, the fraction containing unknown Attorney Docket No.11196-099WO1 product(s) was measured with NMR spectroscopy (Fig.21, column chromatography purified and 23). Compared to the spectrum of pristine, that of after purification looked very neat and clearly shows that the homophthalate peak at 3.7 ppm had disappeared (the aromatic peaks were difficult to determine due to the shift resulting from the pH change (TEA removal) and some overlap with peaks of the unknown component) indicating that no homophthalate existed in the purified sample. The integration of all peaks indicated that there was only one compound with 8 aromatic protons, 1 vinyl proton, and 1 aliphatic proton (Fig.23). Combining the information from DEPT and13C and1H spectra of HA 5 days after adding TEA, the structure and reaction mechanisms of the unknown main component became clear: the newly formed enolate form of HA reacted with homophthalate instantaneously to link the enolate O and the aliphatic carboxyl group on homophthalate forming an ester (the structure can be found in Fig.23 and 25) where TEA works as the catalyst. The excess homophthalate remained there with the ester and they were the two main chemical species in the sample. The ester possesses 2 benzene rings (each of them has 2 substituents), 3 carbonyls, 1 C=CH, 1 CH2,and homophthalate contains 1 benzene ring with 2 substituents, 2 carbonyls, 1 CH2; putting all together yields 18 aromatic C (6 of them are quaternary), 5 carbonyls, 1 C=CH and 2 CH2, which is in perfect accordance with the NMR data. It is noted that after reacting with homophthalate to form the ester, the α- carbon and α-hydrogen of the enolate form of HA shifted downfield to 103.32 and 6.22 ppm, respectively, which are both in typical alkene chemical shift regions, confirming the resonance structure and ambident nature of the enolate form of HA on the other side. Summary. So far, with the powerful tool of NMR spectroscopy, the whole picture of the reaction mechanisms between HA and TEA or DBU has been essentially elucidated. As shown in Fig.25, when HA reacts with TEA, both the enolate form of HA and homophthalate form, and the enolate form of HA can undergo nucleophilic attack from TEA to form homophthalate as well. The enolate form of HA and homophthalate further participate in an esterification catalyzed by TEA. While HA reacts with DBU, the non- nucleophilic nature of DBU makes the enolate form of HA much more stable in the solution. However, the so-called “non-nucleophilic base” doesn’t mean there is no nucleophilicity at all but rather poor nucleophilicity. Therefore, in the presence of traces of water, the ring opening still proceeds but in a quite slow manner. The above reaction mechanisms might be able to be extended to other nucleophilic and non-nucleophilic base reactions with HA. Attorney Docket No.11196-099WO1 Supplementary Note 5. DFT calculations The electronic structures for C^H^O^and C^H^O^^ were studied by density functional theory (DFT), where the structure was optimized via Gaussian 16 C.0212at B3LYP functional13,14and the def2-TZVPD15,16basis set extracted from Basis Set Exchange17. Harmonic frequency was performed at the same level to confirm that all geometries have no imaginary frequency, viz. they locate at the minima of the potential energy surface. The vertical excited calculations were performed at TD18,19-B3LYP- D3(BJ) / def2-TZVPD level of theory. The HOMO (Highest occupied molecular orbital), LUMO (Lowest unoccupied molecular orbital), excited charge density difference, and transition dipole were calculated by Multiwfn 3.8 (dev)20, whose input files were extracted from Gaussian formatting checkpoint files, and plotted by VMD 1.9.321. In addition, all above calculations were considered the acetonitrile as implicit solvent by the polarizable continuum model using the integral equation formalism variant (IEFPCM)22,23. The optimized structures and their transition dipole moment of studied molecules are shown in Fig.53, the HOMO and LUMO plots as well as their orbital energies (eV) for studied molecules are presented in Fig.3E and Fig.54 and diagrams of the excited charge density difference between S0 and S1 for studied molecules are illustrated in Fig.55. Supplementary Note 6. CMY and complementary color theory and rationale of colorant selection CMY and complementary color theory. Vision is probably the most important sensation for humankind. For example, there were more studies on visual memory than studies on the auditory, gustatory, olfactory and tactile / haptic memory combined in PsycINFO database24. In the human eye, photoreceptor cells are vanguards in capturing the incoming light. There are two types of photoreceptor cells, rod cells (rods) and cone cells (cones) contributing to human vision. The rods are highly sensitive to light but cannot generate color vision, while there are three different types of cones which are sensitive to various ranges of light with peaks centered at relatively short, middle, and long wavelengths, respectively25-28. These three types of cones lay the foundation for the trichromacy of human color vision. The light whose wavelength falls into the sensitive range of the cones stimulates the cones followed by transmission of nerve impulses to the brain. The sensitive spectral distributions of cones are called color matching functions (CMFs). The same light might stimulate more than one type of cone cell depending on the wavelength(s) and the resulting neural signals transduce and process to produce the color vision (visual phototransduction). Attorney Docket No.11196-099WO1 The most sensitive light wavelength of the above mentioned short-, middle-, and long-type cones are 420, 534, and 564 nm, which correspond to blue (B), green (G), and red (R) light, respectively29. Starting with Isaac Newton, who first described complementary colors, although without using the term30, many scientists have developed and refined the complementary color theory. Among them, Helmholtz experimentally found the first pair of complementary colors, yellow and blue31, Grassman first demonstrated the existence of complementary colors mathematically32, Thompson coined the term “complementary color”33, Maxwell brought a chromaticity diagram showing the three pairs of additive complementary colors, R-C, G-M and B-Y. RGB are additive color mixture primaries, while their complementary colors CMY became utilized as subtractive color mixture primaries34. In colorimetry, complementary color stimuli are defined as pairs of color stimuli that, when additively mixed in suitable proportion, match to an agreed achromatic or white color stimulus35,36. A pair of complementary color stimuli can both be monochromatic, one monochromatic and the other heterochromatic, or both be heterochromatic37. A phenomenon called “metamerism”, says that a broad spectral distribution of light generates exactly the same color perceived as a spectrally monochromatic light if they have the same stimulation values on the short-, middle-, and long-type of cone cells based on the corresponding CMFs, and vice versa. The complementary color concept is a special case of metamerism, where the two stimuli generate not the same but opposite colors. The aforementioned metamerism and RGB primaries theories are also the basis of modern screen display, and the CMY primaries theory of subtractive color mixing lays the foundation for color printing including this work. In detail, for an object which emanates light itself, such as a computer screen, assuming that it is in a dark environment and ignoring the reflectance, its color depends on the wavelength(s) of light it emits. By tuning the proportion of R, G, and B in each tiny pixel, we can perceive most colors in the spectrum. In contrast, for an object which doesn’t emanate light itself, its color comes from the light it transmits (if it is transparent) or reflects (if it is non-transparent). That is to say, the color is based on the external illuminant (the color of light given) and its own absorption spectrum (the color of light absorbed). Achromatic or white light, such as sunlight or incandescent light, is the most common light in our daily life. So, for non-emissive objects illuminated under white light, one straightforward way to generate a full spectrum of colors is also to achieve RGB reflectance / transmittance by absorbing the complementary colors of RGB, i.e., CMY. The organic dyes or pigments usually have a single peak of absorption only covering a small Attorney Docket No.11196-099WO1 portion of the visible spectral range. Combined with metamerism theory, the resulting spectral color after absorption is equivalent to the complementary color of its absorbed color of light. Rationale of colorant selection. For a particular non-transparent object, since the reflectivity is determined, its color depends on the wavelengths of light it absorbs, i.e., its absorption spectrum. Similarly, when the dyes are applied onto a substrate, such as a piece of paper, the absorption of the dyes will determine the color of the strokes. To create a CMY color-tuning system for encryption and anti-counterfeiting, the absorption spectrum of each colorant before and after color change needs to be carefully selected and the invisibility of the stroke is crucial. Therefore, the materials applied without external stimuli should not show noticeable ink traces under daylight, ambient light, or even UV light. This requires the materials to have no absorption of visible light and negligible fluorescence under UV light before applying the external stimuli. Meanwhile, as mentioned in section 1.1, a CMY color system is a subtractive color system, which means that after applying the external stimuli, the cyan (C), magenta (M) and yellow (Y) colorants should have maximal absorption at their complementary color regions, which are red (R), green (G) and blue (B), respectively. Considering the above prerequisites, phthalein dyes are a good choice for encryption and anti-counterfeiting among common pH indicators due to their ideal color transition (usually from colorless to colored) and well-understood color change mechanisms38. Speaking of phthalein dye, phenolphthalein (PhPh) is the first to come to mind. It is so commonly used and well-known that even elementary school students know it turns from colorless to magenta when it encounters a base. By searching the phthalein dye library, we selected α-naphtholphthalein (NaPh) as the cyan colorant. The color change mechanisms of PhPh and NaPh were well understood. Briefly, the two phenol and α-naphthol groups are not conjugated in their neutral state (lactone form), resulting in low visible wavelength range absorbance (Fig.26). When a base is added, one of the phenol and α-naphthol groups is converted to phenolate and α-naphtholate, resulting in a conjugation length extension, a D-π-A push-pull structure and a bathochromic shift of absorption (Fig.29). Additionally, unlike their highly fluorescent xanthene dye counterparts, such as fluorescein, the conjugated systems of PhPh and NaPh after adding a base are flexible and lack sufficient rigidity. As a result, large non-radiative decay rates are predominant in the colored forms of PhPh and NaPh, and the fluorescence is negligible. It is noted that another commonly used phthalein dye, thymolphthalein (ThPh), exhibits a bluer color than cyan in basic solution Attorney Docket No.11196-099WO1 compared to NaPh, which is not ideal for creating a CMY color tuning system and led us to NaPh (Fig.27). It should be noted that selecting a yellow (Y) colorant to construct the pH- responsive CMY color-tuning system is challenging. The organic pH indicators that transit from colorless to yellow are limited and most of them are nitrophenol isomers or derivatives. Among them, 4-nitrophenol (4-NP) is the most commonly used. However, the fatal flaw of 4-NP in encryption is that before adding the base, besides the main absorption peak at 308 nm, 4-NP also shows a minor absorption peak at 429 nm, which makes its ink trace visible under ambient light and even more pronounced under UV light (Fig.28), and this will ruin the security of the hidden information. In contrast, HA, the commercially available but largely underexplored compound, shows an absorption peak at 283 nm with negligible absorption above 300 nm in its non-colored form before adding a base, which results in its colorlessness under ambient light. After adding a base, HA turns into a colored form and its absorption peaks at 433 nm (Fig.1B and Fig.29), which results in its bright yellow color. Therefore, HA was an ideal leuco dye to construct the pH-responsive CMY palette. Furthermore, it is the halofluorochromism and controllable self-destruction behaviors of HA that empower the pH-responsive CMY palette for multidimensional and multimode optical encryption, as discussed in the main text. Supplementary Note 7. CMY palette system color tunability studies For proof-of-concept, we first tested the color tunability of our CMY palette system. The individual HA, PhPh and NaPh solutions were prepared, and more samples were obtained by mixing two or three colorants with different ratios. Then, the base was added into each sample with gentle mixing. As shown in Fig.30(b) and Fig.31: before adding the base, all the solutions were colorless and transparent, while right after the base was added, various colors were generated. The CMY, three primaries system enables a yield of a large chromaticity gamut with continuous tunability. The simulated color gamut of our CMY palette system is presented on a CIE 1931 chromaticity diagram (Fig.30(c)). Additionally, the absorption spectra and CIE 1931 coordinates of 9 solutions of intermediate colors between CM, CY and MY (3 of each) were collected and calculated (Fig.32-34). The resultant absorption spectra matched the superposition of the component absorption spectra from corresponding individual colorants, indicating no significant interactions or interference between different colorants. Supplementary Note 8. CIE 1931 chromaticity coordinates calculation and CMY gamut simulation Attorney Docket No.11196-099WO1 CIE 1931 chromaticity coordinates calculation. The CMY color system is a subtractive color mixing system, in which white light passes through the layer of dyes / inks and only certain wavelengths of light can reach the eye while the rest is absorbed. As mentioned above, human color vision is subjective, difficult to quantify, and varies from person to person. When one says “red”, other people can think of vastly different colors. The most straightforward way to distinguish and visualize different colors is to arrange them together and give each of them an identification number. Several color spaces have been established and CIE 1931 color space is one of the most well-known and widely used. It was created by the International Commission on Illumination (CIE) in 193139,40based on a series of color physiological experiments among different observers to average the variation of different people41,42. All the human perceivable colors are displayed on a tongue-shaped / horseshoe-shaped diagram and every point is a color with its unique Cartesian coordinates (identification number). The chromaticity coordinates (x,y) can be obtained from equation S343: x= XìX + Y + Z) Where X, Y and Z are wavelength-sensitive types of human cone cells, respectively, and are derived from the corresponding spectral sensitivity function. You may notice that although there are x, y and z, three coordinate components, we use only x and y. The reason is that the model allows us to simply consider that any color can be decomposed into a mixture of red, green and bluein different proportions and x, y and z are the proportion values. Thus, x + y + z = 1, and ifwe know x and y, z can be easily obtained (z = 1 − x − y).For reflective or transmissive systems (e.g., in this work, the security printing part is reflective and when the colorants are dissolved in solution, they are transmissive), the tristimulus values can be calculated using equation S4 below: Attorney Docket No.11196-099WO1 ìX = K+x,(^)S(^)R(^)d^(^)S(^)R(^)d^(S4) (^)S(^)R(^)d^100.y,(^)R(^)d^ Where K is a scaling for a given reference illuminant, x,(^), y,(^), and z,(^) are color matching functions for short-, middle-, and long-type cone cells, respectively, S(^) refers to spectral reflectance (or transmittance), and R(^) is spectral power distribution of a reference illuminant. In this work, CIE 19312º color matching functions (CMFs) and CIE standard illuminant E (SE) were used. S(^) was obtained from the UV-Vis absorption spectra of C (NaPh), M (PhPh), and Y (HA) colorants. For an emissive system, such as the case of fluorescence from the enolate form of HA, since it emanates light itself, no external illuminant is required. Therefore, the S(^)R(^) term in a reflective / transmissive system should be replaced with an equivalent term, spectral power distribution P(^), which is the emission spectrum of the emission source; the scaling factor constant K is also no longer needed, and the new tristimulus value equation is given by: ìX = +x,(^)P(^)d^CMY gamut simulation. system where the physical behavior of color mixing is a linear superposition of emission spectral power distribution, the CMY color system, a subtractive color mixing system, has more complex physical behavior of color mixing. For the RGB color system (usually emissive mode), if there is more than one separate emission source, since within a certain range, the sensitivity of the human eye to the superposition of energy is linear, the relationship between total spectral power distribution (3(^)) and spectral power distribution of each emission source (34(^)) is depicted by equation S6 below: 3(^) = (^) Attorney Docket No.11196-099WO1 Therefore, in the CIE 1931 chromaticity diagram, the coordinates of the three primaries (R, G, B) do not change with emission intensity / power and the gamut keeps constant as a triangle (only the brightness of colors, which is not presented in the 2D chromaticity diagram, changes) In contrast, for the CMY color system (usually reflectance / transmittance mode and from a dye system), the relationship between the amount of dye applied and the transmittance is negative logarithmic. Additionally, when the amount of dye applied increases or decreases, the primaries’ (CMY) coordinates move and the gamut boundary changes at different rates, resulting in non-regular polygonal rather than triangular boundaries. The amount of dye applied or the concentration of the dye is positively correlated to the absorbance or optical density. Optical density (OD) is defined as negative decadic logarithm of light transmittance, as shown in equation S7: >78 = −9:;<=> (S7)=where I0 is the incident light outcoming light after going through linearly additive, as shown is equation S8: @(^) = 5@4(^) (S8)where @(^) is total optical spectral distribution of a single dye. The chromaticity coordinates or gamut calculation is based on the spectral transmittance / reflectance times spectral power distribution of a reference illuminant (equivalent to spectral power distribution which is an energy-related term) in the CMY color system. Thus: 1. it depends on the reference illuminant: if the reference illuminant changes, the chromaticity coordinates and the gamut change as well; 2. the absorption spectra need to be converted to spectral transmittance / reflectance to calculate the chromaticity coordinates and the gamut. Therefore, from absorption spectra based on OD to spectral transmittance of a single dye (B4(^)), the equation S9 is applied: >B (^) ^CD ^EF(^)4 = = 10 = 10 (S9)Then, combining B(^) = HB4(^) (S10)where S(^) is total spectral reflectance / transmittance and B4(^) is spectral reflectance / transmittance of a single dye. That is to say, the total spectral transmittance is equal to the product of the spectral transmittances of each dye, which are not linearly Attorney Docket No.11196-099WO1 superposable. This is the reason for the movement of primaries’ (CMY) coordinates and the non-triangular and irregular change of the gamut boundary. In this work, CIE standard illuminant E (SE) was chosen as the reference illuminant as mentioned in section 2.1, and the three spectral transmittances converted from absorption spectra of C (NaPh), M (PhPh), and Y (HA) colorants were applied to simulate the color gamut through Python by adjusting their ratio and applying the aforementioned methods. It is noted that the real boundary is not a perfectly straight line and to simplify and better quantify the gamut, we chose the characteristic boundary points of C (cyan), M (magenta), Y (yellow), R (red), G (green), and B (blue) with straight line linkage to represent the simulated color gamut region.3 OD of absorbance (i.e.,<<===of light can pass through) was chosen as the maximum optical density (@IJ^) value colorant. Supplementary Note 9. Human skin tests To test the performance of the palette system on human skin, the “P”, “S”, and “U” were written with HA, PhPh, and NaPh, respectively. No ink traces could be observed under either ambient or UV light. Then, a safer base, 2-amino-2-methyl-1-propanol (AMP) water solution, which is used in cosmetics44, was applied on the writing area. After applying AMP, the written “PSU” appeared and under 365 nm UV light, the bright yellow-green fluorescence was observed from the character “P”. We then used water to wash the writing area, followed by wiping with tissue or paper towel a couple of times, and no traces could be seen anymore. It is noted that there were still observable color change and fluorescence on the skin when the AMP concentration was down to 0.1 M. Thus, the trade-off between a safer concentration and a better coloration on the skin can be further explored in the future. In a real-world application, water is a common factor that the encrypted information will encounter. To investigate the performance of our system encountering water, we first wrote “PSU” on the arm on the same way. Once the solvent evaporated, we rinsed the writing area with some water followed by drying the area gently with a piece of tissue. Then the AMP solution was applied, and the information appeared as before. Under UV light, the fluorescence intensity showed no significant difference. Hereafter, we rinsed the information with water again followed by wiping with tissue, and this time, the information was easily washed away (Fig.37). This indicated that the three colorants on skin have good water resistance before applying the base, which attributes to their relatively hydrophobic nature, while after applying the base, the colored forms of the three colorants exhibit higher hydrophilicity due to the ionic structures, which make them easily cleaned by water. This Attorney Docket No.11196-099WO1 “hard to lose, easy to clean” feature renders it excellent utility and practicality, and this demonstration expands the application scenarios of the palette system to human skin. Supplementary Note 10. An exemple case of anti-counterfeiting application exploiting our CMY palette Combining the available encryption features from our palette system, a schematic illustration of a real-world demonstration is presented in Fig.40 as an exemplary case to show how to exploit our palette system in anti-counterfeiting. After the information was written or printed, it cannot be recognized under either ambient light or UV light; with the three bases orderly applied, a yellow “123” with fluorescence first appeared and then changed to “723” with corresponding CY-related colors (and under UV, it showed “13” with yellow-green fluorescence) followed by turning to “923” with CMY-related colors (only “1” showed obvious fluorescence under UV light); if a nucleophilic base (base 3) was applied, after some time, the yellow parts disappeared, leaving changed information and no yellow-green fluorescence remaining under UV light as well; while if a non-nucleophilic base was used as base 3, the color, the fluorescence and the information did not change after the same period of time. Without instructions, the location of encrypted information, the proper type of stimulus, the choice or the order in which the different bases should be applied, the real information or information combinations are all unknown. In other words, only if the authorized instructions are received and followed will the real information show up (the deciphering process for encryption ends here). And if the appeared information matches the verification information from pre-agreed, pre-stored, or other sources, the item will be confirmed not a forgery (anti-counterfeiting ends here). Supplementary Note 11. Single crystal X-ray diffraction The single-crystal X-ray diffraction data sets were collected on a Rigaku MicroMax007 copper rotating-anode generator equipped with HyPix-Arc 150 detector and Oxford cryosystem for cooling the crystal (as in the case of the homophthalic anhydride). The data collection and data-processing (integration, scaling, and absorption corrections) were performed using the CrysAlis software (CrysAlisPro 1.171.41.109a (Rigaku Oxford Diffraction, 2021)). In each of the two cases, structure solution was achieved by dual-space (XHELXT; Sheldrick, G.M. (2015) Acta Cryst. A71, 3-8.45) algorithm. Full-matrix least- squares refinement and graphical visualization of the structure was done using Olex2 and SHELX software suites45,46. The non-hydrogen atoms were refined anisotropically while the hydrogen atom positions were calculated and refined isotropically using the riding-model. The crystallographic details are available in Table 1. Attorney Docket No.11196-099WO1 Table 1. Structure data of homophthalic anhydride (HA keto form) and homophthalic acid single crystals. Compound Homophthalic anhydride (HA keto form) Homophthalic acid Attorney Docket No.11196-099WO1 Table 2. Nucleophilic and non-nucleophilic bases used or mentioned in this example. Name StructureBasicitystrength

[0002] Attorney Docket No.11196-099WO1 Table 3. The formulas of each well in well plate. 1 2 3 4 5 6 1 e erences 1. D. U. Andrews et al., Photo-Tautomerization of Acetaldehyde to Vinyl Alcohol: A Potential Route to Tropospheric Acids. Science 337, 1203-1206 (2012). 2. S. Liu et al., A Rh(II)-catalyzed multicomponent reaction by trapping an α- amino enol intermediate in a traditional two-component reaction pathway. Science Advances 3, e1602467 (2017). 3. A. SchÖNberg, A. Mustafa, W. Asker, Thermochromism and Keto-Enol Tautomerism of Solutions of 1 : 3-Diketo-2-phenyl-5-bromoindan. Nature 171, 222-222 (1953). 4. P. Zuman, J. Michl, Role of Keto-Enol Tautomerism in the Polarographical Reduction of Some Carbonyl Compounds. Nature 192, 655-657 (1961). 5. B. R. Heazlewood et al., Near-threshold H / D exchange in CD3CHO photodissociation. Nature Chemistry 3, 443-448 (2011). 6. C. Tang et al., Voltage-driven control of single-molecule keto-enol equilibrium in a two-terminal junction system. Nature Communications 14, 3657 (2023). 7. Y. Chiang, A. J. Kresge, Enols and Other Reactive Species. Science 253, 395-400 (1991). Attorney Docket No.11196-099WO1 8. P. Naumov, M. Kochunnoonny, Spectral−Structural Effects of the Keto−Enol−Enolate and Phenol−Phenolate Equilibria of Oxyluciferin. Journal of the American Chemical Society 132, 11566-11579 (2010). 9. C. A. Taatjes et al., Enols Are Common Intermediates in Hydrocarbon Oxidation. Science 308, 1887-1889 (2005). 10. D. L. Boger, When sugar is not so sweet. Science 350, 275-276 (2015). 11. C. Draghici, T. Wang, D. A. Spiegel, Concise total synthesis of glucosepane. Science 350, 294-298 (2015). 12. T. A. Mollner et al., Reductive site-selective atypical C,Z- type / N2-C2 cleavage allows C-terminal protein amidation. Science Advances 8, eabl8675 (2022). 13. X. Zhang et al., Divergent synthesis of complex diterpenes through a hybrid oxidative approach. Science 369, 799-806 (2020). 14. F. G. Cantú Reinhard et al., Keto–Enol Tautomerization Triggers an Electrophilic Aldehyde Deformylation Reaction by a Nonheme Manganese(III)-Peroxo Complex. Journal of the American Chemical Society 139, 18328-18338 (2017). 15. N. Yoshikawa, Y. M. A. Yamada, J. Das, H. Sasai, M. Shibasaki, Direct Catalytic Asymmetric Aldol Reaction. Journal of the American Chemical Society 121, 4168-4178 (1999). 16. J. M. O'Connor, R. Uhrhammer, A. L. Rheingold, D. M. Roddick, Keto-enol tautomerization in metal-acyl complexes: the enolization properties of bimetallic .mu.- malonyl compounds. Journal of the American Chemical Society 113, 4530-4544 (1991). 17. D. A. Evans, J. S. Clark, R. Metternich, V. J. Novack, G. S. Sheppard, Diastereoselective aldol reactions using .beta.-keto imide derived enolates. A versatile approach to the assemblage of polypropionate systems. Journal of the American Chemical Society 112, 866-868 (1990). 18. F. Velazquez Escobar et al., A protonation-coupled feedback mechanism controls the signalling process in bathy phytochromes. Nature Chemistry 7, 423-430 (2015). 19. W. T. Astbury, D. M. Wrinch, Intramolecular Folding of Proteins by Keto- Enol Interchange. Nature 139, 798-798 (1937). 20. S. Liu et al., Structural basis of antagonizing the vitamin K catalytic cycle for anticoagulation. Science 371, eabc5667 (2021). 21. S. Borsley, E. Kreidt, D. A. Leigh, B. M. W. Roberts, Autonomous fuelled directional rotation about a covalent single bond. Nature 604, 80-85 (2022). Attorney Docket No.11196-099WO1 22. M. González-López, J. T. Shaw, Cyclic Anhydrides in Formal Cycloadditions and Multicomponent Reactions. Chemical Reviews 109, 164-189 (2009). 23. I. Atodiresei, I. Schiffers, C. Bolm, Stereoselective Anhydride Openings. Chemical Reviews 107, 5683-5712 (2007). 24. G. Dey, A. Chakraborty, Tautomers of homophthalic anhydride in the ground and excited electronic states: analysis through energy, hardness and vibrational signatures. Journal of Molecular Modeling 26, 173 (2020). 25. C. G. Seitz, H. Zhang, Y. Mo, J. M. Karty, Why Do Enolate Anions Favor O-Alkylation over C-Alkylation in the Gas Phase? The Roles of Resonance and Inductive Effects in the Gas-Phase SN2 Reaction between the Acetaldehyde Enolate Anion and Methyl Fluoride. The Journal of Organic Chemistry 81, 3711-3719 (2016). 26. G. Moss, P. Smith, D. Tavernier, Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995). Pure and applied chemistry 67, 1307-1375 (1995). 27. Y. Tamura, M. Sasho, K. Nakagawa, T. Tsugoshi, Y. Kita, Strong base induced cycloaddition of homophthalic anhydrides leading to peri-hydroxy polycyclic compounds. The Journal of Organic Chemistry 49, 473-478 (1984). 28. Y. Tamura, A. Wada, M. Sasho, Y. Kita, Cycloaddition of homophthalic anhydride: A new and simple route to linearly condensed phenolic compoumds. Tetrahedron Letters 22, 4283-4286 (1981). 29. R. Jangir, Homophthalic anhydride derivatives to bioactive natural products. (2016). 30. J. Andréasson, U. Pischel, Molecules for security measures: from keypad locks to advanced communication protocols. Chemical Society Reviews 47, 2266-2279 (2018). 31. S. Liu, X. Liu, J. Yuan, J. Bao, Multidimensional Information Encryption and Storage: When the Input Is Light. Research 2021, 7897849 (2021). 32. S. A. Jenekhe, J. A. Osaheni, Excimers and Exciplexes of Conjugated Polymers. Science 265, 765-768 (1994). 33. G. Bünau, J. Birks, Photophysics of Aromatic Molecules. Wiley- Interscience, London 1970.704 Seiten. Preis: 210s. Ber. Bunsenges. Phys. Chem.74, 1294- 1295 (1970). Attorney Docket No.11196-099WO1 34. P. Sahu, M. Gupta, Water absorption behavior of cellulosic fibres polymer composites: A review on its effects and remedies. Journal of Industrial Textiles 51, 7480S- 7512S (2022). 35. S. Cichosz, A. Masek, IR Study on Cellulose with the Varied Moisture Contents: Insight into the Supramolecular Structure. Materials 13, 4573 (2020). 36. H. M. Akil, C. Santulli, F. Sarasini, J. Tirillò, T. Valente, Environmental effects on the mechanical behaviour of pultruded jute / glass fibre-reinforced polyester hybrid composites. Composites Science and Technology 94, 62-70 (2014). 37. Z. N. Azwa, B. F. Yousif, A. C. Manalo, W. Karunasena, A review on the degradability of polymeric composites based on natural fibres. Materials & Design 47, 424- 442 (2013). 38. A.-M. Olsson, L. Salmén, The association of water to cellulose and hemicellulose in paper examined by FTIR spectroscopy. Carbohydrate Research 339, 813- 818 (2004). Supplementary References 1 Würth, C., Grabolle, M., Pauli, J., Spieles, M. & Resch-Genger, U. Relative and absolute determination of fluorescence quantum yields of transparent samples. Nature Protocols 8, 1535-1550, doi:10.1038 / nprot.2013.087 (2013). 2 Dey, G. & Chakraborty, A. Tautomers of homophthalic anhydride in the ground and excited electronic states: analysis through energy, hardness and vibrational signatures. Journal of Molecular Modeling 26, 173, doi:10.1007 / s00894-020-04411-7 (2020). 3 Khokarale, S. G. & Mikkola, J.-P. Hydrogen sulfide gas capture by organic superbase 1,8-diazabicyclo-[5.4.0]-undec-7-ene through salt formation: salt synthesis, characterization and application for CO2 capture. RSC Advances 8, 18531-18541, doi:10.1039 / C8RA02993H (2018). 4 Song, J., Lei, Y. X. & Rappoport, Z. The First Solid Enols of Anhydrides. Structure, Properties, and Enol / Anhydride Equilibria1. The Journal of Organic Chemistry 72, 9152-9162, doi:10.1021 / jo071206m (2007). 5 Seitz, C. G., Zhang, H., Mo, Y. & Karty, J. M. Why Do Enolate Anions Favor O-Alkylation over C-Alkylation in the Gas Phase? The Roles of Resonance and Inductive Effects in the Gas-Phase SN2 Reaction between the Acetaldehyde Enolate Anion and Methyl Fluoride. The Journal of Organic Chemistry 81, 3711-3719, doi:10.1021 / acs.joc.6b00351 (2016). Attorney Docket No.11196-099WO1 6 Guedira, N. E. & Beugelmans, R. Ambident behavior of ketone enolate anions in SNAr substitutions on fluorobenzonitrile substrates. The Journal of Organic Chemistry 57, 5577-5585, doi:10.1021 / jo00047a008 (1992). 7 Moss, G., Smith, P. & Tavernier, D. Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995). Pure and applied chemistry 67, 1307-1375 (1995). 8 McMurry, J. E. Organic Chemistry. 841-855 (Cengage Learning, 2008). 9 Atta ur, R., Choudhary, M. I. & Atia tul, W. in Solving Problems with NMR Spectroscopy (Second Edition) (eds Rahman Atta ur, Muhammad Iqbal Choudhary, & Wahab Atia tul) 133-190 (Academic Press, 2016). 10 Gemmecker, G. & Kessler, H. in Carbon-13 NMR Spectroscopy of Biological Systems (ed Nicolau Beckmann) 7-64 (Academic Press, 1995). 11 Claridge, T. D. W. in High-Resolution NMR Techniques in Organic Chemistry (Third Edition) (ed Timothy D. W. Claridge) 133-169 (Elsevier, 2016). 12 Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery Jr, J. A.; Peralta, J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J.; Brothers, E. N.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A. P.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, N. J.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J., Gaussian 09, Revision E.01; Gaussian, Inc., Wallingford CT, 2013. 13 Becke, A. D. Density‐functional thermochemistry. III. The role of exact exchange. J. Chem. Phys.98, 5648-5652, doi:10.1063 / 1.464913 (1993). 14 Lee, C., Yang, W. & Parr, R. G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Physical Review B 37, 785-789, doi:10.1103 / PhysRevB.37.785 (1988). Attorney Docket No.11196-099WO1 15 Weigend, F. & Ahlrichs, R. Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy. Physical Chemistry Chemical Physics 7, 3297-3305, doi:10.1039 / B508541A (2005). 16 Weigend, F. Accurate Coulomb-fitting basis sets for H to Rn. Physical Chemistry Chemical Physics 8, 1057-1065, doi:10.1039 / B515623H (2006). 17 Pritchard, B. P., Altarawy, D., Didier, B., Gibson, T. D. & Windus, T. L. New Basis Set Exchange: An Open, Up-to-Date Resource for the Molecular Sciences Community. Journal of Chemical Information and Modeling 59, 4814-4820, doi:10.1021 / acs.jcim.9b00725 (2019). 18 Furche, F. & Ahlrichs, R. Adiabatic time-dependent density functional methods for excited state properties. The Journal of Chemical Physics 117, 7433-7447, doi:10.1063 / 1.1508368 (2002). 19 Liu, J. & Liang, W. Analytical Hessian of electronic excited states in time- dependent density functional theory with Tamm-Dancoff approximation. The Journal of Chemical Physics 135, doi:10.1063 / 1.3605504 (2011). 20 Lu, T. & Chen, F. Multiwfn: A multifunctional wavefunction analyzer. Journal of Computational Chemistry 33, 580-592, doi:https: / / doi.org / 10.1002 / jcc.22885 (2012). 21 Humphrey, W., Dalke, A. & Schulten, K. VMD: Visual molecular dynamics. Journal of Molecular Graphics 14, 33-38, doi:https: / / doi.org / 10.1016 / 0263-7855(96)00018- 5 (1996). 22 Cancès, E., Mennucci, B. & Tomasi, J. A new integral equation formalism for the polarizable continuum model: Theoretical background and applications to isotropic and anisotropic dielectrics. The Journal of Chemical Physics 107, 3032-3041, doi:10.1063 / 1.474659 (1997). 23 Mennucci, B., Cancès, E. & Tomasi, J. Evaluation of Solvent Effects in Isotropic and Anisotropic Dielectrics and in Ionic Solutions with a Unified Integral Equation Method:  Theoretical Bases, Computational Implementation, and Numerical Applications. The Journal of Physical Chemistry B 101, 10506-10517, doi:10.1021 / jp971959k (1997). 24 Hutmacher, F. Why is there so much more research on vision than on any other sensory modality? Frontiers in psychology 10, 2246 (2019). 25 Hecht, S., Shlaer, S. & Pirenne, M. H. Energy, quanta, and vision. The Journal of general physiology 25, 819-840 (1942). Attorney Docket No.11196-099WO1 26 Baylor, D. A., Lamb, T. & Yau, K.-W. Responses of retinal rods to single photons. The Journal of physiology 288, 613-634 (1979). 27 Wald, G. Human vision and the spectrum. Science 101, 653-658 (1945). 28 Ebrey, T. & Koutalos, Y. Vertebrate Photoreceptors. Progress in Retinal and Eye Research 20, 49-94, doi:https: / / doi.org / 10.1016 / S1350-9462(00)00014-8 (2001). 29 Bowmaker, J. K. & Dartnall, H. Visual pigments of rods and cones in a human retina. The Journal of physiology 298, 501-511 (1980). 30 Newton, S. Opticks: Or, A Treatise of the Reflexions, Refractions, Inflexions and Colours of Light. Also Two Treaties of the Species and Magnitude of Curvilinear Figures.[The Advertisement Signed: IN, Ie Sir Isaac Newton]. (Sam. Smith & Benj. Walford, 1704). 31 Helmholtz, H. v. Über die Theorie der zusammengesetzten Farben. Annalen der Physik 163, 45-66 (1852). 32 Grassmann, H. On the theory of compound colors. Phil. Mag 7, 254-264 (1854). 33 von Rumford, B. G. The Complete Works of Count Rumford. Vol.1 (Macmillan, 1876). 34 Maxwell, J. C. IV. On the theory of compound colours, and the relations of the colours of the spectrum. Philosophical Transactions of the Royal Society of London, 57- 84 (1860). 35 CIE. (2018). 36 Wyszecki, G. & Stiles, W. S. Color science. Vol.8 (Wiley New York, 1982). 37 Pridmore, R. W. Complementary colors: A literature review. Color Research & Application 46, 482-488, doi:https: / / doi.org / 10.1002 / col.22576 (2021). 38 Sabnis, R. W. in Kirk‐Othmer Encyclopedia of Chemical Technology 1- 21. 39 CIE, C. Commission internationale de l’eclairage proceedings, 1931. Cambridge University, Cambridge (1932). 40 Smith, T. & Guild, J. The CIE colorimetric standards and their use. Transactions of the optical society 33, 73 (1931). 41 Wright, W. D. A re-determination of the trichromatic coefficients of the spectral colours. Transactions of the Optical Society 30, 141 (1929). Attorney Docket No.11196-099WO1 42 Guild, J. The colorimetric properties of the spectrum. Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a Mathematical or Physical Character 230, 149-187 (1931). 43 Hunt, R. W. G. & Pointer, M. R. Measuring colour. (John Wiley & Sons, 2011). 44 Aminomethyl Propanol, <https: / / www.cosmeticsinfo.org / ingredients / aminomethyl-propanol / > (2023). 45 Sheldrick, G. M. SHELXT–Integrated space-group and crystal-structure determination. Acta Crystallographica Section A: Foundations and Advances 71, 3-8 (2015). 46 Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. & Puschmann, H. OLEX2: a complete structure solution, refinement and analysis program. Journal of applied crystallography 42, 339-341 (2009). 47 Würth, C., Grabolle, M., Pauli, J., Spieles, M. & Resch-Genger, U. Comparison of Methods and Achievable Uncertainties for the Relative and Absolute Measurement of Photoluminescence Quantum Yields. Analytical Chemistry 83, 3431-3439, doi:10.1021 / ac2000303 (2011). The compositions, systems, and methods of the appended claims are not limited in scope by the specific compositions and methods described herein, which are intended as illustrations of a few aspects of the claims. Any compounds, compositions, systems, and methods that are functionally equivalent are intended to fall within the scope of the claims. Various modifications of the compounds, compositions, systems, and methods in addition to those shown and described herein are intended to fall within the scope of the appended claims. Further, while only certain representative compounds, components, compositions, systems, and method steps disclosed herein are specifically described, other combinations of the compounds, components, compositions, systems, and method steps also are intended to fall within the scope of the appended claims, even if not specifically recited. Thus, a combination of steps, elements, components, or constituents may be explicitly mentioned herein or less, however, other combinations of steps, elements, components, and constituents are included, even though not explicitly stated. The term “comprising” and variations thereof as used herein is used synonymously with the term “including” and variations thereof and are open, non-limiting terms. Although the terms “comprising” and “including” have been used herein to describe various Attorney Docket No.11196-099WO1 embodiments, the terms “consisting essentially of” and “consisting of” can be used in place of “comprising” and “including” to provide for more specific embodiments of the invention and are also disclosed. Other than where noted, all numbers expressing geometries, dimensions, and so forth used in the specification and claims are to be understood at the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, to be construed in light of the number of significant digits and ordinary rounding approaches. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Methods and materials are described herein for use in the present invention; other, suitable methods and materials known in the art can also be used. The materials, methods, and examples are illustrative only and not intended to be limiting. All publications, patent applications, patents, sequences, database entries, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control.

Claims

Attorney Docket No.11196-099WO1 WHAT IS CLAIMED IS:

1. A composition for forming markings on a surface, the composition comprising a dye and a carrier, wherein the dye is pH responsive that is transitionable between a first chemical form exhibiting a first set of photophysical properties and a second chemical form exhibiting a second set of photophysical properties in response to a change in pH; and wherein upon exposure to a nucleophile, the dye is transitionable to a third chemical form exhibiting a third set of photophysical properties.

2. The composition of claim 1, wherein the first chemical form comprises a substantially colorless leuco form.

3. The composition of any one of claims 1-2, wherein the second chemical form exhibits a visible color.

4. The composition of any one of claims 1-3, wherein the second chemical form exhibits a λmax absorption that is bathochromically shifted relative to a λmax absorption of the first chemical form.

5. The composition of any one of claims 1-4, wherein the second chemical form exhibits a λmax absorption of from 390 nm to 550 nm.

6. The composition of any one of claims 1-5, wherein the dye is halochromic.

7. The composition of any one of claims 1-6, wherein the dye is halofluorochromic.

8. The composition of any one of claims 1-7, wherein the first chemical form exhibits a fluorescence quantum yield of less than 0.5% in acetonitrile.

9. The composition of any one of claims 1-8, wherein the second chemical form exhibits a λmaxemission of from 390 nm to 550 nm.Attorney Docket No.11196-099WO1 10. The composition of any one of claims 1-9, wherein the second chemical form exhibits a fluorescence quantum yield of from 2% to 60% in acetonitrile.

11. The composition of any one of claims 1-10, wherein the third chemical form exhibits a λmaxabsorption that is hypsochromically shifted relative to a λmaxabsorption of the second chemical form.

12. The composition of any one of claims 1-11, wherein the third chemical form comprises a substantially colorless leuco form.

13. The composition of any one of claims 1-12, wherein the third chemical form exhibits a λmaxemission that is hypsochromically shifted relative to a λmaxemission of the second chemical form.

14. The composition of any one of claims 1-13, wherein the third chemical form exhibits a fluorescence quantum yield of from 2% to 60% in acetonitrile.

15. The composition of any one of claims 1-14, wherein the dye comprises a six- membered anhydride ring.

16. The composition of any one of claims 1-15, wherein the dye is defined by the formula below whereinR1, R2, R3, and R4are each independently chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; or wherein R1andAttorney Docket No.11196-099WO1 R2, R2and R3, and / or R3and R4, together with the atoms to which they are attached, forms a fused cycloalkyl, heterocycloalkyl, ary, heteroaryl, each optionally substituted with one or more substituents individually chosen from RA; R5is chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl; alkylthio; haloalkylthio; alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, dialkylaminocarbonyl, and heterodialkylaminocarbonyl.

17. The composition of claim 16, wherein R1, R2, R3, and R4are each independently chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, C1-C6 alkylamino, C1-C6 dialkylamino, C1-C6 alkyl, C1-C6 haloalkyl, C1- C6alkylthio, C1-C6haloalkylthio, C1-C6alkoxy, C1-C6haloalkoxy, C2-C6alkenyl, C2-C6haloalkenyl, C2-C6 alkynyl, C2-C6 haloalkynyl, a 3-7 membered cycloalkyl ring, a 3-7 membered heterocycloalkyl ring, a 5-7 membered ary ring, a 5-7 membered heteroaryl ring, C1-C6 alkylsulfinyl, C1-C6 haloalkylsulfinyl, C1-C6 alkylsulfonyl, C1-C6 haloalkylsulfonyl, C1-C6alkylcarbonyl, C1-C6haloalkylcarbonyl, C1-C6alkoxycarbonyl, C1-C6haloalkoxycarbonyl, C1-C6 alkylaminocarbonyl, C1-C6 heteroalkylaminocarbonyl, and C1-C6 dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; R5is chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, C1-C6alkylamino, C1-C6 dialkylamino, C1-C6 alkyl, C1-C6 haloalkyl, C1-C6 alkylthio, C1-C6 haloalkylthio, C1-C6 alkoxy, C1-C6 haloalkoxy, C2-C6 alkenyl, C2-C6 haloalkenyl, C2-C6 alkynyl, C2-C6haloalkynyl, a 3-7 membered cycloalkyl ring, a 3-7 membered heterocycloalkyl ring, a 5-7 membered ary ring, a 5-7 membered heteroaryl ring, C1-C6 alkylsulfinyl, C1-C6haloalkylsulfinyl, C1-C6alkylsulfonyl, C1-C6haloalkylsulfonyl, C1-C6Attorney Docket No.11196-099WO1 alkylcarbonyl, C1-C6haloalkylcarbonyl, C1-C6alkoxycarbonyl, C1-C6haloalkoxycarbonyl, C1-C6 alkylaminocarbonyl, C1-C6 heteroalkylaminocarbonyl, and C1-C6 dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, C1-C6alkylamino, C1-C6dialkylamino, C1-C6 alkyl, C1-C6 haloalkyl; C1-C6 alkylthio; C1-C6 haloalkylthio; C1-C6 alkoxy, C1-C6 haloalkoxy, C2-C6 alkenyl, C2-C6 haloalkenyl, C2-C6 alkynyl, C2-C6 haloalkynyl, C1-C6 alkylsulfinyl, C1-C6 haloalkylsulfinyl, C1-C6 alkylsulfonyl, C1-C6 haloalkylsulfonyl, C1-C6 alkylcarbonyl, C1-C6 haloalkylcarbonyl, C1-C6 alkoxycarbonyl, C1- C6haloalkoxycarbonyl, C1-C6alkylaminocarbonyl, C1-C6heteroalkylaminocarbonyl, C1-C6dialkylaminocarbonyl, and C1-C6 heterodialkylaminocarbonyl.

18. The composition of any one of claims 16-17, wherein R1, R2, R3, and R4are each independently chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, C1-C6 alkylamino, C1-C6 dialkylamino, C1-C6 alkyl, C1-C6 haloalkyl, C1- C6alkylthio, C1-C6haloalkylthio, C1-C6alkoxy, C1-C6haloalkoxy, C2-C6alkenyl, C2-C6haloalkenyl, C2-C6 alkynyl, C2-C6 haloalkynyl, a 3-7 membered cycloalkyl ring, a 3-7 membered heterocycloalkyl ring, a 5-7 membered ary ring, a 5-7 membered heteroaryl ring, C1-C6 alkylsulfinyl, C1-C6 haloalkylsulfinyl, C1-C6 alkylsulfonyl, C1-C6 haloalkylsulfonyl, C1-C6 alkylcarbonyl, C1-C6 haloalkylcarbonyl, C1-C6 alkoxycarbonyl, C1-C6 haloalkoxycarbonyl, C1-C6alkylaminocarbonyl, C1-C6heteroalkylaminocarbonyl, and C1-C6dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; R5is chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, C1-C4 alkylamino, C1-C4dialkylamino, C1-C4alkyl, C1-C4haloalkyl, C1-C4alkylthio, C1-C4haloalkylthio, C1-C4 alkoxy, C1-C4 haloalkoxy, C2-C4 alkenyl, C2-C4 haloalkenyl, C2-C4 alkynyl, C2-C4haloalkynyl, C1-C4alkylsulfinyl, C1-C4haloalkylsulfinyl, C1-C4alkylsulfonyl, C1-C4 haloalkylsulfonyl, C1-C4 alkylcarbonyl, C1-C4 haloalkylcarbonyl, C1-C4 alkoxycarbonyl, C1-C4haloalkoxycarbonyl, C1-C4alkylaminocarbonyl, C1-C4heteroalkylaminocarbonyl, and C1-C4 dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, C1-C6alkylamino, C1-C6dialkylamino, C1-C6 alkyl, C1-C6 haloalkyl; C1-C6 alkylthio; C1-C6 haloalkylthio; C1-C6 alkoxy, C1-C6haloalkoxy, C2-C6alkenyl, C2-C6haloalkenyl, C2-C6alkynyl, C2-C6Attorney Docket No.11196-099WO1 haloalkynyl, C1-C6alkylsulfinyl, C1-C6haloalkylsulfinyl, C1-C6alkylsulfonyl, C1-C6haloalkylsulfonyl, C1-C6 alkylcarbonyl, C1-C6 haloalkylcarbonyl, C1-C6 alkoxycarbonyl, C1- C6haloalkoxycarbonyl, C1-C6alkylaminocarbonyl, C1-C6heteroalkylaminocarbonyl, C1-C6dialkylaminocarbonyl, and C1-C6 heterodialkylaminocarbonyl.

19. The composition of any one of claims 16-18, wherein R1, R2, R3, and R4are each independently chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, C1-C6 alkylamino, C1-C6 dialkylamino, C1-C6 alkyl, C1-C6 haloalkyl, C1- C6 alkylthio, C1-C6 haloalkylthio, C1-C6 alkoxy, C1-C6 haloalkoxy, C2-C6 alkenyl, C2-C6 haloalkenyl, C2-C6alkynyl, C2-C6haloalkynyl, a 3-7 membered cycloalkyl ring, a 3-7 membered heterocycloalkyl ring, a 5-7 membered ary ring, a 5-7 membered heteroaryl ring, C1-C6alkylsulfinyl, C1-C6haloalkylsulfinyl, C1-C6alkylsulfonyl, C1-C6haloalkylsulfonyl, C1-C6 alkylcarbonyl, C1-C6 haloalkylcarbonyl, C1-C6 alkoxycarbonyl, C1-C6 haloalkoxycarbonyl, C1-C6alkylaminocarbonyl, C1-C6heteroalkylaminocarbonyl, and C1-C6dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; R5is hydrogen; and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, C1-C6alkylamino, C1-C6dialkylamino, C1-C6 alkyl, C1-C6 haloalkyl; C1-C6 alkylthio; C1-C6 haloalkylthio; C1-C6 alkoxy, C1-C6 haloalkoxy, C2-C6 alkenyl, C2-C6 haloalkenyl, C2-C6 alkynyl, C2-C6 haloalkynyl, C1-C6alkylsulfinyl, C1-C6haloalkylsulfinyl, C1-C6alkylsulfonyl, C1-C6haloalkylsulfonyl, C1-C6 alkylcarbonyl, C1-C6 haloalkylcarbonyl, C1-C6 alkoxycarbonyl, C1- C6haloalkoxycarbonyl, C1-C6alkylaminocarbonyl, C1-C6heteroalkylaminocarbonyl, C1-C6dialkylaminocarbonyl, and C1-C6 heterodialkylaminocarbonyl.

20. The composition of any one of claims 1-19, wherein the dye is defined by the formula below .

21. The composition of any of claims 1-14, wherein the dye is pH responsive such that the dye is transitionable between a first chemical form exhibiting a first set of photophysicalAttorney Docket No.11196-099WO1 properties at a first pH and a second chemical form exhibiting a second set of photophysical properties at a second pH.

22. The composition of claim 21, wherein the first pH is 6.0 or less and the second pH is greater than 6.

0.

23. The composition of claim 21, wherein the first pH is 6.5 or less and the second pH is greater than 6.

5.

24. The composition of claim 21, wherein the first pH is 7.0 or less and the second pH is greater than 7.

0.

25. The composition of claim 21, wherein the first pH is 7.5 or less and the second pH is greater than 7.

5.

26. The composition of any one of claims 21-25, where a change in pH from the first pH to the second pH can be induced by contacting the dye with a base.

27. The composition of claim 26, wherein the base comprises a nucleophilic base, such as triethylamine, sodium hydroxide, potassium hydroxide, potassium tert-butoxide, sodium tert-butoxide, 2-amino-2-methyl-1-propanol, or any combination thereof.

28. The composition of claim 26, wherein the base comprises a non-nucleophilic base (i.e., a sterically hindered organic base), such as N,N-Diisopropylethylamine (DIPEA, also called Hünig's Base), 1,8-Diazabicycloundec-7-ene (DBU), 1,5-Diazabicyclo(4.3.0)non-5- ene (DBN), 2,6-Di-tert-butylpyridine, phosphazene bases, such as t-Bu-P4, lithium diisopropylamide (LDA), silicon-based amides, such as sodium and potassium bis(trimethylsilyl)amide (NaHMDS and KHMDS, respectively), lithium tetramethylpiperidide (LiTMP or harpoon base), or any combination thereof.

29. The composition of any one of claims 1-28, wherein upon exposure to a nucleophile, the dye irreversibly transitions to the third chemical form exhibiting the third set of photophysical properties.Attorney Docket No.11196-099WO1 30. The composition of any one of claims 1-29, wherein the carrier comprises a fluid carrier.

31. The composition of any one of claims 1-30, wherein the carrier comprises a volatile fluid carrier.

32. The composition of any one of claims 1-31, wherein the carrier comprises water, ethanol, acetone, acetonitrile, pentane, hexane, heptane, mineral oil, benzene, toluene, xylene, or any combination thereof.

33. The composition of any one of claims 1-32, wherein the carrier comprises a polymer or an oligomer.

34. The composition of any one of claims 1-33, wherein the carrier comprises a curable material.

35. The composition of any one of claims 1-34, wherein the dye is present in the carrier in an amount of from 0.1% by weight to 10% by weight, based on the total weight of the composition.

36. The composition of any one of claims 1-35, wherein the dye is present in the carrier as a concentration of from 1 micromolar to 800 millimolar, such as a concetrantion of from 10 micromolar to 750 millimolar, a concentration of from 50 micromolar to 600 millimolar, or a concentration of from 100 micromolar to 500 millimolar.

37. A system for forming markings on a surface, the system comprising a first ink composition comprising a first dye that exhibits an indigo, blue, or green color; a second ink composition comprising a second dye that exhibits an orange, red, or magenta color; and a third ink composition comprising a third dye that exhibits a yellow color; wherein at least one of the first dye, the second dye, and the third dye is responsive such that it is transitionable between a substantially colorless leuco form and a colored form.Attorney Docket No.11196-099WO1 38. The system of claim 37, wherein at least one of the first dye, the second dye, and the third dye is pH responsive such that it is transitionable between a substantially colorless leuco form and a colored form in response to a change in pH.

39. The system of any one of claims 37-38, wherein the the first dye comprises a leuco dye transitionable between a substantially colorless leuco form and a second chemical form that exhibits an indigo, blue, or green color in response to a change in pH.

40. The system of any one of claims 37-39, wherein the first dye comprises a cyan dye.

41. The system of any one of claims 37-40, wherein the first dye comprises α- naphtholphthalein (NaPh).

42. The system of any one of claims 37-41, wherein the second dye comprises a leuco dye transitionable between a substantially colorless leuco form and a second chemical form that exhibits an orange, red, or magenta color in response to a change in pH.

43. The system of any one of claims 37-42, wherein the second dye comprises a magenta dye.

44. The system of any one of claims 37-43, wherein the second dye comprises phenophthalein.

45. The system of any one of claims 37-44, wherein the third dye comprises a leuco dye transitionable between a substantially colorless leuco form and a second chemical form that exhibits a yellow color in response to a change in pH.

46. The system of claim 45, wherein upon exposure to a nucleophile, the third dye is transitionable to a third chemical form exhibiting a third set of photophysical properties.

47. The system of any one of claims 37-46, wherein third dye comprises a six- membered anhydride ring.Attorney Docket No.11196-099WO1 48. The system of any one of claims 37-47, wherein the third dye is defined by the formula below wherein 12 3 4R , R , R , and R are each from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; or wherein R1and R2, R2and R3, and / or R3and R4, together with the atoms to which they are attached, forms a fused cycloalkyl, heterocycloalkyl, ary, heteroaryl, each optionally substituted with one or more substituents individually chosen from RA; R5is chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl; alkylthio; haloalkylthio; alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, dialkylaminocarbonyl, and heterodialkylaminocarbonyl.

49. The system of any one of claims 37-48, wherein the third dye is defined by the formula belowAttorney Docket No.11196-099WO1 .

50. A system for forming on a the system comprising a first ink composition comprising a first leuco dye transitionable between a substantially colorless leuco form and a second chemical form that exhibits an indigo, blue, or green color in response to a change in pH; a second ink composition comprising a second leuco dye transitionable between a substantially colorless leuco form and a second chemical form that exhibits an orange, red, or magenta color in response to a change in pH; and a third ink composition comprising a dye that is pH responsive such that it is transitionable between a substantially colorless leuco form and a second chemical form that exhibits a yellow color in response to a change in pH.

51. The system of claim 50, wherein the first dye comprises a cyan dye.

52. The system of any one of claims 50-51, wherein the first dye comprises α- naphtholphthalein (NaPh).

53. The system of any one of claims 50-52, wherein the second dye comprises a magenta dye.

54. The system of any one of claims 50-53, wherein the second dye comprises phenophthalein.

55. The system of any one of claims 50-54, wherein upon exposure to a nucleophile, the third dye is transitionable to a third chemical form exhibiting a third set of photophysical properties.

56. The system of any one of claims 50-55, wherein third dye comprises a six- membered anhydride ring.Attorney Docket No.11196-099WO1 57. The system of any one of claims 50-56, wherein the third dye is defined by the formula below wherein 12 3 4R , R , R , and R are each from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; or wherein R1and R2, R2and R3, and / or R3and R4, together with the atoms to which they are attached, forms a fused cycloalkyl, heterocycloalkyl, ary, heteroaryl, each optionally substituted with one or more substituents individually chosen from RA; R5is chosen from hydrogen, halogen, hydroxyl, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl, alkylthio, haloalkylthio, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, cloalkyl, heterocycloalkyl, aryl, heteroaryl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, and dialkylaminocarbonyl, each optionally substituted with one or more substituents individually chosen from RA; and RAis chosen from hydroxy, halogen, -CN, -NO2, amino, alkylamino, dialkylamino, alkyl, haloalkyl; alkylthio; haloalkylthio; alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkynyl, haloalkynyl, alkylsulfinyl, haloalkylsulfinyl, alkylsulfonyl, haloalkylsulfonyl, alkylcarbonyl, haloalkylcarbonyl, alkoxycarbonyl, haloalkoxycarbonyl, alkylaminocarbonyl, heteroalkylaminocarbonyl, dialkylaminocarbonyl, and heterodialkylaminocarbonyl.

58. The system of any one of claims 50-57, wherein the third dye is defined by the formula belowAttorney Docket No.11196-099WO1 .

59. A method for marking a surface comprising applying the composition of any of claims 1-36 or one or more inks of the system of any of claims 37-58 to an article.

60. The method of claim 59, wherein the method further comprises exposing the article to an acid or a base.

61. An article comprising a marking formed by the composition of any of claims 1-36 or one or more inks of the system of any of claims 37-58.

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