Spiro-benzodioxole photobase generators for polyimide formation

Abstract

The present disclosure relates to photobase generators including a spiro-benzodioxole moiety, a visible light absorbing moiety, and a linker complex. Application of visible light to the photobase generator may provide a basic entity for manufacturing a polyimide.

Description

[0001] SPIRO-BENZODIOXOLE PHOTOBASE GENERATORS FOR POLYIMIDE FORMATION

[0002] Inventors: Jeffrey R. Hammaker, Shijun Zheng, Tissa Sajoto, Kota Nishino, and Kumpei Otsuka

[0003] CROSS-REFERENCE TO RELATED APPLICATIONS

[0004] This application claims priority to U.S. Provisional Application No. 63 / 570,233, filed March 26, 2024, which is incorporated by reference in its entirety.

[0005] FIELD

[0006] The present disclosure relates to photobase generator compounds which may be used for polyimide formation.

[0007] BACKGROUND

[0008] Photobase Generators (PBGs) typically include three parts: a chromophore, responsible for light absorption, and thus transforming the energy of photons into chemical energy, a latent base, which is the moiety that releases the actual base upon application of light, and a linker that connects the base with the chromophore. PBGs release amine bases upon light irradiation and are being explored in the areas of photoinitiated polymerization, photoinduced crosslinking of polymers, photo-patterning, adhesives, and lithography. However, photobase generators are less developed than photoacid generators. PBGs are based on both non-ionic and ionic types. A wide range of materials has been used as chromophores for the absorption of light, including those limited to absorption in the ultra-violet region. Typical PBG linkers include carbamates, O- acyloximes, ammonium salts, sulfonamides, formamides, nifedipines, and a- aminoketones. By way of example, O-acyloximes require water to release the base so they may not be ideal in polymeric substrates that are sensitive to water. Overall, carbamate linker based PBGs are efficient and synthetically versatile.

[0009] Polyimides have been widely used as protection and insulation layers in microelectronics due to their excellent chemical, mechanical stability, and electrical properties. Photosensitive polyimides (PSPIs) may be attractive for microelectronics because they can be patterned by direct exposure and developed without a photoresist. PSPIs may find applications in various electronic, electro-optic, waveguide, and nonlinear optical materials. A photosensitive polyimide system typically includes a polyimide precursor and a photobase generator as an accelerator to form a polyimide by photoreaction. However, a polyimide precursor with an aromatic ring as a basic skeleton typically has a broad absorption band in the ultraviolet (UV) region of wavelengths below 400 nm. Therefore, when ultraviolet light is applied, the photochemical reaction may not proceed effectively in the exposed area because the light is predominantly absorbed by the polyimide precursor, which results in low sensitivity and deterioration of the pattern shape.

[0010] Most PBGs have minimal absorption above 400 nm, so the base generation can only be triggered by UV light. Compared to visible-light initiators, UV responsive catalysts require high photon energy, often achieve reduced curing depths, and may also cause irreversible damage to UV-sensitive materials. Moreover, existing photobase generators also show high thermal residue, and low photolytic base release efficiency, which are undesirable for improving the photosensitive polyimide-based electronic device efficiency. Thus, there is a need for additional contributions in this area of technology.

[0011] SUMMARY

[0012] Photobase generator compounds described herein may be used to provide good absorption in the visible spectral region, efficient photolytic base release efficiency under photo-irradiation, and / or low thermal residue. In some embodiments, a photobase generator may absorb light of a first wavelength and emit light of a second, higher wavelength than the first wavelength. The photobase generators disclosed herein may be utilized in methods of making polyimide film for use in microelectronics, printed circuit boards, and / or optical devices, amongst other things. In some aspects, a polyimide film described herein may exhibit high thermal and mechanical stability properties.

[0013] In one embodiment, a photobase generator compound includes a light absorbing spiro-benzodioxole derivative, a linker group, and an amine base moiety. The amine base moiety may be a secondary or tertiary amine which, when released from the photobase generator compound, provides a primary or secondary amine. In some forms, the linker group may covalently link the spiro-benzodioxole derivative and the amine base moiety. In some forms, the spiro-benzodioxole derivative may absorb light energy of a first excitation wavelength and transfer energy to the linker group, and upon heterolytic cleavage the base moiety is releasable from the linker group.

[0014] In another embodiment, a photobase generator may be a compound according to formula (1):

[0015] In formula (1), n may represent 1 or 2, R1represents H, an alkyl, or a cyclic alkyl group, and R2and R3independently represent H, an alkyl, or a cyclic alkyl group.

[0016] In some forms, R1represents H, a methyl, a C2-C4 alkyl, or . In some forms, R2and R3independently represent a C3-C8 alkyl or a cyclic alkyl.

[0017] In another embodiment, a method for making a polyimide includes providing a photobase generator (PBG) compound as described herein and a polyimide precursor dispersion in a dispersant; applying the PBG compound and the polyimide precursor to a substrate; applying visible light to the substrate; and heating the substrate to accomplish at least one of removing the dispersant from the covering and curing the covered substrate. In some forms, the method may further include masking portions of the covered substrate to selectively apply visible light to unmasked portions of the substrate.

[0018] In a further embodiment, a method for measuring the base release efficiency of a photobase generator compound includes dissolving a photobase generator compound described herein in acetonitrile; measuring the pH of a solution including the photobase generator compound and acetonitrile; exposing the solution to visible light; and measuring the pH of the solution following exposure to visible light.

[0019] In one aspect, a photobase generator compound described herein may exhibit excellent absorption in the visible spectral region, low thermal residue upon heating up to 450 °C, and / or base moiety separation. In another aspect, a method for manufacturing polyimide films including use of a photobase generator compound described herein is provided. These and other embodiments are described in greater detail below.

[0020] BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 is a graph depicting the poly imidization efficiency of an embodiment described herein.

[0022] FIG. 2 is a graph depicting the UV-visible spectra of an embodiment described herein.

[0023] DETAILED DESCRIPTION

[0024] The current disclosure relates to photobase generator compounds and their uses in generating reactive precursors for polyimide generation. A photobase generator may be used for the formation of a polyimide under light irradiation conditions, which in turn may be useful for fabrication of efficient microelectronic devices. In some forms, the photobase generator may absorb light in the visible region, for example from about 380 nm to about 440 nm, exhibit high photobase release activity, and / or may have a very low thermal residue upon heating above 400 °C.

[0025] In one aspect, a photobase generator compound may absorb light energy of a first wavelength and on heterolytic cleavage, utilizes a photoreleasing mechanism by (1) a photinduced H-atom transfer (HAT*) leading to primary aci-nitro intermediates, and (2) ground state cyclization of the aci-nitro intermediates to benzo[c]isoxazol-1(3H)-ols in which the carbamate group is cleaved and an amine base is released. In addition, the cleaved base compounds may act as catalysts for formation of a polyimide from a polyimide precursor.

[0026] The term “bond”, “bonded”, “direct bond” or “single bond” as used herein means a chemical bond between two atoms or to two moieties when the atoms joined by the bond are considered to be part of a larger structure.

[0027] The term “moiety” as used herein refers to a specific segment or functional group of a molecule. Chemical moieties are often recognized as chemical entities embedded in or appended to a molecule.

[0028] The term “spiro-benzodioxole” as used herein refers to a chemical moiety having a spiro that may be varied from a 5-membered ring to a 6-membered ring with the following structures:

[0029] In one embodiment, a photobase generator compound includes a light absorbing spiro-benzodioxole derivative, a linker group, and an amine base. The amine base moiety may be a secondary or tertiary amine which, when released from the photobase generator compound, provides a primary or secondary amine. In some forms, the linker group may covalently link the spiro-benzodioxole derivative and the amine base, and the spiro- benzodioxole derivative may absorb light energy of a first excitation wavelength and transfer energy to the linker group. The amine base may be releasable from the linker group upon cleavage.

[0030] In one embodiment, a photobase generator includes a compound according to formula (1):

[0031] In formula (1), n may be 1 or 2, R1represents H, an alkyl, or a cyclic alkyl group, and R2and R3independently represent H, an alkyl, or a cyclic alkyl group.

[0032] In some forms, R1represents H, a methyl, a C2-C4 alkyl, or . In some forms, R2and R3independently represent a C3-C8 alkyl or cyclic alkyl.

[0033] More particular but non-limiting compounds according to formula (1) include the following:

[0034] In another embodiment, a method for making a polyimide includes providing the photobase generator (PBG) compound as described herein and a polyimide precursor dispersion in a dispersant; applying the PBG compound and the polyimide precursor to a substrate; applying visible light to the substrate; and heating the substrate to accomplish at least one of removing the dispersant from the covering and curing the covered substrate. In some forms, the method may further include masking portions of the substrate to selectively apply visible light to unmasked portions of the substrate. In a further embodiment, a method for measuring the base release efficiency of a photobase generator compound includes dissolving a photobase generator compound described herein in acetonitrile; measuring the pH of a solution including the photobase generator compound and the acetonitrile; exposing the solution to visible light; and measuring the pH of the solution following exposure to visible light.

[0035] In another embodiment, a method for measuring the base release efficiency of a photobase generator compound includes dissolving a photobase generator compound in a polar solvent such as acetonitrile. However, different polar solvents may be used. The method further includes measuring the pH of the solution including the photobase generator and acetonitrile, and exposing the solution to visible light (e.g., about 600 mJ / cm2). The method further includes measuring the pH of the solution after exposure to visible light. By comparing the pH before and after exposure, the change in pH can be indicative of the amount of basic moiety released and thus the release efficiency of the photobase generator compound.

[0036] In The photobase generator compounds described herein may exhibit a high photosensitivity or high quantum yield for release of the base moiety upon exposure to the desired wavelength radiation. By way of example, the photosensitivity may be demonstrated by a change in pH before and after exposure to the radiation. In some forms, the pH change may be greater than about 0.2, about 0.4, about 0.8, about 1.5, and / or about 2.2 In some forms, the release quantum yield may be greater than about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.8, about 0.9, about 1.0, about 1.5 and / or about 2.2. Base release efficiency may be measured by dividing the pH of a photobase generator solution after exposure to light of certain energy by the pH of the same solution before light exposure, which is equivalent to the release efficiency of the PBG moiety. In various forms, the PBG moiety may have a release efficiency greater than about 2.2. In some forms, the base release efficiency may be greater than about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, about 0.9, about 1.0, about 1.25, about 1.5, about 2.0 and / or about 2.2 The pH change measurements in solution can be made by mercury lamp such as a Dymax UV curing conveyor with 5000- EC lamps.

[0037] In some forms, a UV-Vis light absorbing photobase generator compound described herein may have a peak absorption maximum between about 370 nm to about 440 nm wavelength. In some forms, the peak absorption may be in the range of about 370 nm, about 375 nm, about 380 nm, about 390 nm, about 395 nm, about 400 nm, about 410 nm, about 420 nm, about 430 nm, and about 440 nm to about 410 nm, about 420 nm, about 430 nm, and about 440 nm, and / or any permutation of the aforementioned values, e.g., about 365 nm, about 405 nm, and / or about 436 nm.

[0038] Other embodiments include a photobase generator where the spatial distance between a UV-Vis light absorbing spiro-benzodioxole derivative and an amine base (which when released from the photobase generator provides a primary or secondary amine) is optimized through a linker complex, for formation of a carbamate anion, and then to photo-release an amine base.

[0039] In one embodiment, a photobase generator compound (PBGC) includes a UV-vis light absorbing spiro-benzodioxole derivative, a linker complex, and an amine base (which when released from the photobase generator provides a primary or secondary amine) including those having a hexylamine structure or partial structure. In some forms, the linker complex may covalently link the visible light absorbing spiro-benzodioxole derivative and the amine base. The spiro-benzodioxole derivative absorbs light energy of a first excitation wavelength and transfers energy to the linker complex, which leads to cleavage of a carbamate group. The carbamate undergoes photodecarboxylation to release a desired amine base moiety, such as a dihexylamine. In these forms, the released base pH change may be greater than about 0.2, and the released base compound may act as a catalyst for formation of a polyimide from a polyimide precursor.

[0040] In some embodiments, the linker complex covalently links the UV-vis light absorbing spiro-benzodioxole derivative with an amine base. When the amine base is released, it may be primary or secondary amine base, but when it is linked to the o- nitrobenzylic derivative it may be a secondary or tertiary amine base. The linker complex can be tuned to optimize the quick release of the primary or secondary amine base. By optimizing the linker complex, the efficiency of base release may be tuned.

[0041] In forms, the linker complex may include a stabilizing substitution, such as a methyl, cyclopropyl, cyclopentyl or cyclohexyl group, just to provide a few non-limiting examples. The linker complex may include a carbonyl bond between the spiro- benzodioxole derivative and the amine base.

[0042] In some forms, the linker complex may include an unsubstituted or substituted ester group. When the linker complex includes an unsubstituted ester group, the linker complex may include one of the following structures:

[0043] In some forms, the linker complex may include an optically substituted C2-C7 ester group. When the linker complex includes a substituted ester group, the linker complex may have one of the following structures:

[0044] In a further embodiment, a method for making a polyimide includes providing a photobase generator compound as described herein and a polyimide precursor dispersion. The PBG compound and polyimide precursor may be dispersed within a solvent and / or a dispersant. The polyimide precursor may be polyamidic acid and the dispersant may be an aprotic / polar / non-polar solvent such as n-methyl pyrrolidone (NMP). In some forms, the method may also include applying visible light to a PBG and polyimide precursor covered substrate, e.g., about 600 mJ / cm2. In some forms, the method may also include heating the covered substrate to remove the dispersant from the covering. This heating may be performed at about 120 °C for at least 10 minutes, although variations are possible. In some forms, the method also includes heating the covered surface to cure, polymerize, and / or harden the covered substrate surface. This heating may be performed at about 185 °C for about 5 minutes, although variations are possible. In some forms, the method may include masking portions of the dispersant covered substrate to restrict, minimize or reduce the exposure of the precursor dispersant to the enabling visible light.

[0045] EXAMPLES

[0046] It has been discovered that photobase generator compounds described herein showed improved photobase release performance. These benefits are further demonstrated by the following examples, which are intended to be illustrative of the disclosure but are not intended to limit the scope or underlying principles in any way.

[0047] The following examples are synthesis procedures of many embodiments of the spiro-benzodioxole photobase generators as described herein: General synthesis procedure of compound PBG1 o

[0048] Compound PBG1.1 (spiro[benzo[d][1,3]dioxole-2,1'-cyclopentane]):

[0049] Cyclopentanone (100.0 mmol, 8.85 mL) and catechol (200.0 mmol, 22.022 g) were stirred in dry benzene (100 mL) under argon at reflux (120 °C) with a Dean-Stark trap for three hours. The reaction mixture was cooled to 0 °C, then treated with ~75 mL of saturated sodium bicarbonate solution. The layers were separated, the aqueous layer extracted with EtOAc (2 X 50 mL), and the combined organic layers dried over magnesium sulfate, filtered, and evaporated to dryness in vacuo. The mixture was taken up in a small volume of hexanes and loaded onto ~45g of flash silica gel packed into a loader. It was then purified by flash chromatography on silica gel (220g, isocratic DCM). Fractions containing product were evaporated to dryness in vacuo to give a colorless liquid, 2799 mg (16% yield). MS (APCI): calculated for Chemical Formula: C11H12O2 (M+H) = 177 found: 177. 1 H NMR (400 MHz, CDCI3) 5 6.88 - 6.66 (m, 4H), 2.20 - 2.05 (m, 4H), 1.89 - 1.78 (m, 4H).

[0050] Compound PBG1.2 (1-(spiro[benzo[d][1,3]dioxole-2,1'-cyclopentan]-5- yl)ethan-1-one): Compound PBG1.1 (7.037 mmol, 1240 mg) and acetic anhydride (14.07 mmol, 1 .33 mL) were stirred at room temperature. TFA (7.5 mL) was added to the mixture and the mixture was stirred at room temperature for five minutes. The mixture was then transferred to a large flask with EtOAc (100 mL) and carefully quenched to pH ~8 with saturated sodium bicarbonate solution. The mixture was diluted with brine (100 mL) and the layers separated. The aqueous layer was extracted with EtOAc (2 X 100 mL), and the combined organic layers dried over magnesium sulfate, filtered, and evaporated to dryness in vacuo. The crude product was diluted with DCM / hexanes and loaded onto ~40g of flash silica gel packed into a loader. It was then purified by flash chromatography on silica gel (120g, 0% DCM / hexanes (2 CV) 100% (5 CV) isocratic DCM). Fractions containing product were evaporated to dryness in vacuo to give an oil, 1436 mg (94% yield). MS (APCI): calculated for Chemical Formula: C13H14O3 (M+H) = 219 found: 219. 1 H NMR (400 MHz, TCE) 5 7.52 (dd, J = 8.1 , 1.8 Hz, 1 H), 7.34 (d, J = 1.7 Hz, 1 H), 6.79 (d, J = 8.1 Hz, 1 H), 2.52 (s, 3H), 2.21 - 2.07 (m, 4H), 1.93 - 1.77 (m, 4H).

[0051] Compound PBG1.3 (1 -(5-nitrospiro[benzo[d][1 ,3]dioxole-2,1 '-cyclopentan]- 6-yl)ethan-1-one): Compound PBG1.2 (20.93 mmol, 4569 mg) was dissolved in nitromethane (20 mL) and cooled to 0 °C. The reaction mixture was stirred and treated with 70% nitric acid (20 mL), with the acid being added dropwise over a few minutes. The mixture was stirred at 0 °C for 30 minutes, then transferred to a 1 L flask, diluted with 200 mL of ethyl acetate, and carefully neutralized to pH ~8 with saturated sodium bicarbonate solution. The mixture was treated with brine (-200 mL) and the layers were separated. The aqueous layer was extracted with EtOAc (2 X 200 mL). The combined organic layers were dried over magnesium sulfate, filtered, and evaporated to dryness in vacuo. The mixture was diluted with DCM / hexanes and loaded onto ~45g of flash silica gel packed into a loader. It was purified by flash chromatography on silica gel (120g, 50% DCM / hexanes (2 CV) 100% (10 CV)). Fractions containing product were evaporated to dryness in vacuo to give an oil, 4091 mg (74% yield). MS (APCI): calculated for Chemical Formula: C13H13NO5 (M+H) = 264 found: 264. 1 H NMR (400 MHz, TCE) 5 7.46 (s, 1 H), 6.66 (s, 1 H), 2.49 (s, 3H), 2.24 - 2.09 (m, 4H), 1.94 - 1.80 (m, 4H).

[0052] Compound PBG1.4 (1 -(5-nitrospiro[benzo[d][1 ,3]dioxole-2,1 '-cyclopentan]- 6-yl)ethan-1-ol): NaBH4 (62.16 mmol, 2358 mg) was suspended in dry THF (50 mL) and dry I PA (25 mL) mL and stirred under argon at room temperature. The mixture was carefully treated with HOAc (15.54 mmol, 0.89 mL). When bubbling had ceased (-5 min), Compound PBG1.3 (5.540 mmol, 4091 mg) was added, followed by 25 mL of dry THF. The mixture was stirred at room temperature for two hours. The crude reaction mixture was then transferred to a large flask and carefully quenched with sat. ammonium chloride solution to pH -8. The reaction mixture was extracted with ethyl acetate (2 X 100 mL), and the combined organics dried over magnesium sulfate, filtered, and evaporated to dryness. It was then dissolved in DCM and loaded onto ~45g flash silica gel packed into a loader, purified by flash chromatography on silica gel (120g, 0% EtOAc / DCM (2 CV) 10% (15 CV)). Fractions containing product were evaporated to dryness in vacuo to give an off-white solid, 4030 mg (98% yield). MS (APCI): calculated for Chemical Formula: C13H15NO5 (M+H) = 266 found: 266. 1 H NMR (400 MHz, TCE) 5 7.38 (s, 1 H), 7.16 (s, 1 H), 5.41 (qd, J = 6.3, 3.6 Hz, 1 H), 2.33 (d, J = 3.7 Hz, 1 H), 2.22 - 2.09 (m, 4H), 1.94 - 1.78 (m, 4H), 1.53 (d, J = 6.3 Hz, 3H). Compound PBG1.5 (4-nitrophenyl (1-(5-nitrospiro[benzo[d][1,3]dioxole-2,1'- cyclopentan]-6-yl)ethyl) carbonate): Compound PBG1.4 (15.19 mmol, 4030 mg) was dissolved in dry DCE (50 mL) and stirred at room temperature under argon. 4-nitrophenyl carbonochloridate (22.79 mmol, 4594 mg) and triethylamine (37.98 mmol, 5.3 mL) were added to the reaction. The mixture was stirred at room temperature for sixty minutes, wrapped in foil. The crude reaction mixture was evaporated to dryness in vacuo, diluted with DCM, and evaporated onto ~45g of flash silica gel in vacuo and packed into a loader. It was purified by flash chromatography on silica gel (120g, 0% DCM / hexanes (2 CV) 100% DCM (5 CV). Fractions containing product were evaporated to dryness in vacuo to give a light yellow solid, 5221 mg (80% yield). MS (APCI): calculated for Chemical Formula: C20H18N2O9 (M+H) = 431 found: 431. 1 H NMR (400 MHz, TCE) 5 8.32 - 8.16 (m, 2H), 7.44 (s, 1 H), 7.42 - 7.35 (m, 2H), 7.06 (s, 1 H), 6.41 (q, J = 6.3 Hz, 1 H), 2.23 - 2.11 (m, 4H), 1.94 - 1.82 (m, 4H), 1.76 (d, J = 6.4 Hz, 3H).

[0053] Compound PBG1 (1-(5-nitrospiro[benzo[d][1,3]dioxole-2,1'-cyclopentan]-6- yl)ethyl dihexylcarbamate): Compound PBG1.5 (12.13 mmol, 5220 mg) was stirred in dry DCE (50 mL) at room temperature under argon. Dihexylamine (18.19 mmol, 4.2 mL) was added to the flask. The reaction mixture was heated to 60 °C for three hours. The reaction mixture was then cooled to room temperature, reduced in volume in vacuo, and loaded onto ~45g of flash silica gel packed into a loader. It was purified by flash chromatography on silica gel (120g, 0% DCM / hexanes (2 CV) - 100% (5 CV) - 100% iso DCM). Fractions containing product were evaporated to dryness in vacuo (shielded from light). This compound was stored in an amber vial to give a light-yellow oil, 4852 mg (84% yield). MS (APCI): calculated for Chemical Formula: C26H40N2O6 (M+H) = 477 found: 477. 1 H NMR (400 MHz, TCE) 5 7.33 (s, 1 H), 6.81 (s, 1 H), 6.16 (q, J = 6.4 Hz, 1 H), 3.37 - 2.95 (m, 4H), 2.15 - 1.95 (m, 4H), 1.77 (td, J = 8.6, 4.9 Hz, 4H), 1.48 (d, J = 6.4 Hz, 7H), 1.29 - 1.06 (m, 12H), 0.91 - 0.69 (m, 6H).

[0054] General synthesis procedure of compound PBG2

[0055] Compound PBG2.1 (5-bromospiro[benzo[d][1,3]dioxole-2,1'-cyclohexane]): 4-bromobenzene-1 ,2-diol (75.00 mmol, 14.176 g), cyclohexanone (112.5 mmol, 11.7 mL), and pTsOH.H2O (1.973 mmol, 375 mg) were stirred in dry benzene (120 mL) at 140 °C with a jacketed Dean-Stark trap overnight. The reaction mixture was cooled to room temperature, diluted with 100 mL of ethyl acetate, and quenched with ~50 mL of saturated sodium bicarbonate solution. Brine (-100 mL) was added to the mixture and the layers separated. The aqueous layer was extracted with ethyl acetate (2 X 100 mL), and the combined organic layers dried over magnesium sulfate, filtered, and evaporated to dryness in vacuo. The crude material was diluted with hexanes and loaded onto ~45g of flash silica gel packed into a loader. It was purified by flash chromatography on silica gel (330g, 50% DCM / hexanes (2 CV) 100% (10 CV)). Fractions containing product were evaporated to dryness in vacuo to give an oil, -80% purity, 17.30 g (86% yield). MS (APCI): calculated for Chemical Formula: Ci2Hi3BrO2 (M+H) = 269 found: 269. 1 H NMR (400 MHz, TCE) 56.92 - 6.83 (m, 2H), 6.59 (d, J = 8.0 Hz, 1 H), 1.98 - 1 .82 (m, 5H), 1.80 - 1.63 (m, 4H), 1.54 - 1 .45 (m, 2H).

[0056] Compound PBG2.2 (1-(spiro[benzo[d][1,3]dioxole-2,1'-cyclohexan]-5- yl)ethan-1-one): Compound PBG2.1 (25.00 mmol, 6729 mg) was stirred in dry THF (75 mL) under argon and cooled to -78 °C (dry ice / acetone). The mixture was treated with nBuLi (2.5M / hex, 50.00 mmol, 20.0 mL) over a period of three minutes with stirring. The reaction mixture was stirred at -78 °C for forty-five minutes, then N-methoxy-N- methylacetamide (75.00 mmol, 8.0 mL) was added over a few minutes with stirring. The reaction mixture was stirred at -78 °C and allowed to warm to room temperature slowly overnight. The mixture was diluted with 100 mL of ethyl acetate and quenched with 100 mL of saturated ammonium chloride solution. 100 mL of brine was added, and the layers were separated and the aqueous layer was extracted with ethyl acetate (2 X 100 mL). The combined organic layers were dried over magnesium sulfate, filtered, and evaporated to dryness in vacuo. The crude product was taken up in hexanes and loaded onto ~45g of flash silica gel packed into a loader. It was purified by flash chromatography on silica gel (220g, 0% EtOAc / hexanes (2 CV) 15% (15 CV)). Fractions containing product were evaporated to dryness in vacuo, loaded onto ~45g of flash silica gel, and repurified (330g, 30% (10 CV)). Fractions containing product were evaporated to dryness in vacuo to give an oil, 3173 mg (55% yield). MS (APCI): calculated for Chemical Formula: CI4HI6O3(M+H) = 233 found: 233. 1 H NMR (400 MHz, TCE) 5 7.50 (dd, J = 8.1 , 1.8 Hz, 1 H), 7.34 (d, J = 1.8 Hz, 1 H), 6.79 (d, J = 8.2 Hz, 1 H), 2.52 (s, 3H), 1.97 - 1.87 (m, 4H), 1.81 - 1.68 (m, 4H), 1.56 - 1.44 (m, 2H).

[0057] Compound PBG2.3 (1-(5-nitrospiro[benzo[d][1,3]dioxole-2,T-cyclohexan]-6- yl)ethan-1-one): Compound PBG2.2 (13.66 mmol, 3173 mg) was dissolved in nitromethane (10 mL) and stirred at 0 °C. 70% nitric acid (7.5 mL) was added over a period of four minutes. The reaction was stirred at 0 °C for one hour, then 4 mL of 70% nitric acid was added. After stirring an additional 30 minutes, another 5 mL of 70% nitric acid was added and the reaction stirred at 0 °C for another 30 minutes. The mixture was transferred to a large flask with ethyl acetate (150 mL) and carefully quenched with saturated sodium bicarbonate solution to pH ~8. 150 mL of brine was added, and the layers were separated, extracted 2 X 100 mL ethyl acetate, dried over magnesium sulfate, filtered, and evaporated to dryness in vacuo. It was dissolved in hexanes / DCM and loaded onto ~45g flash silica gel packed into a loader and purified by flash chromatography on silica gel (120g, 50% DCM / hexanes (2 CV) - 100% (10 CV)). Fractions containing product were evaporated to dryness in vacuo to give an oil, 2809 mg (74% yield). MS (APCI): calculated for Chemical Formula: C14H15NO5 (M+H) = 278 found: 278. 1 H NMR (400 MHz, TCE) 5 7.47 (s, 1 H), 6.67 (s, 1 H), 2.49 (s, 3H), 2.04 - 1.89 (m, 4H), 1.84 - 1.67 (m, 4H).

[0058] Compound PBG2.4 (1-(5-nitrospiro[benzo[d][1,3]dioxole-2,T-cyclohexan]-6- yl)ethan-1-ol): NaBH4(40.51 mmol, 1536 mg) was stirred in dry THF (50 mL) and dry IPA (25 mL) at room temperature. This was treated carefully with HOAc (10.13 mmol, 0.58 mL). After bubbling had ceased (~5 minutes), Compound PBG2.3 (10.13 mmol, 2808 mg) was added, followed by 25 mL of dry THF. The reaction mixture was stirred at room temperature for four hours, wrapped in foil. The mixture was transferred to a large flask with ethyl acetate (100 mL) and carefully quenched with saturated ammonium acetate to pH ~8 and diluted with brine (100 mL), and the layers were separated, extracted with ethyl acetate (2 X 100 mL), dried over magnesium sulfate, filtered, and evaporated to dryness in vacuo. The crude product was diluted with DCM and loaded onto ~45g of flash silica gel packed into a loader. It was purified by flash chromatography on silica gel (120g, 0% EtOAc / DCM (2 CV) 10% (20 CV)). Fractions containing product were evaporated to dryness in vacuo to give a whitish solid, 2842 mg (quantitative). MS (APCI): calculated for Chemical Formula: C14H17NO5 (M+H) = 280 found: 280. 1 H NMR (400 MHz, DMSO) 5 7.46 (s, 1 H), 7.20 (s, 1 H), 5.42 (d, J = 4.4 Hz, 1 H), 5.13 (qd, J = 6.2, 4.3 Hz, 1 H), 1.93 (q, J = 6.1 Hz, 4H), 1.66 (p, J = 5.7 Hz, 4H), 1.48 (p, J = 6.0 Hz, 2H), 1.34 (d, J = 6.2 Hz, 3H).

[0059] Compound PBG2.5 (4-nitrophenyl (1-(5-nitrospiro[benzo[d][1,3]dioxole-2,1'- cyclohexan]-6-yl)ethyl) carbonate): Compound PBG2.4 (10.18 mmol, 2842 mg) was dissolved in dry DCE (50 mL) and stirred at room temperature under argon. 4-nitrophenyl carbonochloridate (15.26 mmol, 3077 mg) and triethylamine (25.44 mmol, 3.55 mL) were added to the reaction. The mixture was stirred at room temperature for sixty minutes, wrapped in foil. The crude reaction mixture was evaporated to dryness in vacuo, diluted with DCM, and evaporated onto ~45g of flash silica gel in vacuo and packed into a loader. It was purified by flash chromatography on silica gel (120g, 0% DCM / hexanes (2 CV) 100% (10 CV) isocratic 100%). Fractions containing product were evaporated to dryness in vacuo to give a light-yellow solid, 3130 mg (69% yield). MS (APCI): calculated for Chemical Formula: C21H20N2O9 (M+H) = 445 found: 445. 1 H NMR (400 MHz, TCE) 5 8.31 - 8.23 (m, 2H), 7.45 (s, 1 H), 7.42 - 7.35 (m, 2H), 7.07 (s, 1 H), 6.41 (q, J = 6.3 Hz, 1 H), 2.05 - 1.92 (m, 4H), 1.84 - 1.67 (m, 7H), 1.58 - 1.45 (m, 2H).

[0060] Compound PBG2 (1-(5-nitrospiro[benzo[d][1,3]dioxole-2,1'-cyclohexan]-6- yl)ethyl dihexylcarbamate): Compound PBG2.5 (7.043 mmol, 3130 mg) was stirred in dry DCE (50 mL) at room temperature under argon. Dihexylamine (14.09 mmol, 3.3 mL) was added to the flask. The reaction mixture was heated to 60 °C for three hours. The reaction mixture was then cooled to room temperature, reduced in volume in vacuo, and loaded onto ~45g of flash silica gel packed into a loader. It was purified by flash chromatography on silica gel (120g, 0% EtOAc / hexanes (2 CV) - 20% (15 CV)). Fractions containing product were evaporated to dryness in vacuo to give 2314 mg (67% yield). MS (APCI): calculated for Chemical Formula: C27H42N2O6 (M+H) = 491 found: 491. 1 H NMR (400 MHz, TCE) 5 7.42 (s, 1 H), 6.90 (s, 1 H), 6.26 (q, J = 6.3 Hz, 1 H), 3.41 - 3.02 (m, 4H), 2.00 - 1.87 (m, 4H), 1.80 - 1.71 (m, 4H), 1.57 (d, J = 6.4 Hz, 9H), 1.38 - 1.11 (m, 12H), 0.89 (dt, J = 17.5, 5.1 Hz, 6H). General synthesis procedure of compound PBG3

[0061] PBG3.5 PBG3

[0062] Compound PBG3.1 (spiro[benzo[d][1,3]dioxole-2,1'-cyclohexane]): Catechol (200.0 mmol, 22.022 g), cyclohexanone (340.0 mmol, 35.2 mL), and pTsOH.H2O (5.260 mmol, 1001 mg) were combined in dry benzene (60 mL) and refluxed with a vacuum- jacketed Dean-Stark trap overnight (heat block = 140 °C). The reaction mixture was cooled in an ice bath and carefully quenched with saturated sodium bicarbonate solution (25 mL). Brine (100 mL) and ethyl acetate (100 mL) were added to the reaction, and the layers separated. The reaction was further extracted with 2 X 100 mL ethyl acetate, and the combined organic layers were dried over magnesium sulfate, filtered, and evaporated to dryness in vacuo. The crude product was loaded onto flash silica gel in hexanes and purified by flash chromatography on silica gel (330g, 0% EtOAc / hexanes (2 CV) 10% EtOAc / hexanes (20 CV)). Fractions containing product were evaporated to dryness in vacuo to give a light-yellow oil, 29.77 g (78% yield). MS (APCI): calculated for Chemical Formula: C12H14O2 (M+H) = 191 found: 191. 1 H NMR (400 MHz, CDCI3) 5 6.79 - 6.71 (m, 4H), 6.71 - 6.61 (m, 1 H), 1 .90 (dd, J = 7.4, 5.0 Hz, 4H), 1.78 - 1 .69 (m, 4H), 1 .55 - 1.44 (m, 2H).

[0063] Compound PBG3.2 (cyclopentyl(spiro[benzo[d][1,3]dioxole-2,1'- cyclohexan]-5-yl)methanone): Compound PBG3.2 was synthesized from Compound PBG3.1 (17.86 mmol, 3397 mg), Compound 1742-29 (35.72 mmol, 7510 mg) and TFA (10 mL). It was purified by flash chromatography on silica gel (120g, 0% EtOAc / hexanes (2 CV) 5% EtOAc / hexanes (15 CV)). Fractions containing product were evaporated to dryness in vacuo to give an oil 3690 mg (72% yield). It contained an impurity that is difficult to remove, so it was carried to the next step without further purification attempts. MS (APCI): calculated for Chemical Formula: C18H22O3 (M+H) = 287 found: 287. 1 H NMR (400 MHz, TCE) 5 7.53 (dd, J = 8.2, 1.8 Hz, 1 H), 7.37 (d, J = 1.7 Hz, 1 H), 6.79 (d, J = 8.2 Hz, 1 H), 3.71 - 3.50 (m, 1 H), 1.50 (p, J = 6.1 Hz, 2H).

[0064] Compound PBG3.3 (cyclopentyl(5-nitrospiro[benzo[d][1,3]dioxole-2,1'- cyclohexan]-6-yl)methanone): Compound PBG3.3 (17.86 mmol, 3397 mg) was treated with 70% nitric acid (12 mL) in nitromethane (15 ml) at 0 °C. The crude product was purified by flash chromatography on silica gel (120g, 0% DCM / hexanes (2 CV) 100% DCM (10 CV)). Fractions containing product were evaporated to dryness in vacuo to give an oil, 2592 mg (61% yield). The impurity from the previous step was no longer present. MS (APCI): calculated for Chemical Formula: C18H21NO5 (M+H) = 332 found: 332. 1 H NMR (400 MHz, TCE) 5 7.49 (s, 1 H), 6.63 (s, 1 H), 3.12 (p, J = 8.1 Hz, 1 H), 2.04 - 1.92 (m, 4H), 1.91 - 1.81 (m, 4H), 1.81 - 1.67 (m, 6H), 1.66 - 1.55 (m, 2H), 1.55 - 1.42 (m, 2H).

[0065] Compound PBG3.4 (cyclopentyl(5-nitrospiro[benzo[d][1,3]dioxole-2,1'- cyclohexan]-6-yl)methanol): Compound PBG3.4 (7.822 mmol, 2592 mg), sodium borohydride (31.29 mmol, 1187 mg) and HOAc (7.822 mmol, 0.45 mL) were reacted. The crude product was purified by flash chromatography on silica gel (120g, 0% DCM / hexanes (2 CV) 100% DCM (10 CV)). Fractions containing product were evaporated to dryness in vacuo to give 1620 mg (62% yield). MS (APCI): calculated for Chemical Formula: C18H23NO5 (M+H) = 334 found: 334. 1 H NMR (400 MHz, DMSO) 5 7.43 (s, 1 H), 7.13 (s, 1 H), 5.42 (d, J = 4.9 Hz, 1 H), 4.94 (dd, J = 6.2, 4.9 Hz, 1 H), 2.09 (q, J = 7.6 Hz, 1 H), 1.98 - 1 .86 (m, 4H), 1.74 - 1.62 (m, 4H).

[0066] Compound PBG3.5 (cyclopentyl(5-nitrospiro[benzo[d][1,3]dioxole-2,1'- cyclohexan]-6-yl)methyl (4-nitrophenyl) carbonate): Compound PBG3.5 (4.859 mmol, 1620 mg), 4-nitrophenyl carbonochloridate (7.289 mmol, 1469 mg), and triethylamine (12.15 mmol, 1.7 mL) were reacted. The product was purified by flash chromatography on silica gel (120g, 0% DCM / hexanes (2 CV) 100% (10 CV)). Fractions containing product were evaporated to dryness in vacuo to give 1596 mg (65% yield). MS (APCI): calculated for Chemical Formula: C25H26N2O9 (M+H) = 499 found: 499. 1 H NMR (400 MHz, TCE) 5 8.32 - 8.15 (m, 2H), 7.40 (s, 1 H), 7.39 - 7.34 (m, 2H), 7.00 (s, 1 H), 6.33 (d, J = 7.5 Hz, 1 H), 2.48 (p, J = 7.9 Hz, 1 H), 2.02 - 1.92 (m, 4H), 1.92 - 1.81 (m, 1 H), 1.81 - 1.68 (m, 6H), 1.67 - 1.41 (m, 8H).

[0067] Compound PBG3 (cyclopentyl(5-nitrospiro[benzo[d][1,3]dioxole-2,1'- cyclohexan]-6-yl)methyl dihexylcarbamate): Compound PBG3.5 (3.202 mmol, 1596 mg) and dihexylamine (6.403 mmol, 1.5 mL) were reacted similarly to Compound 1742- 42. The product was purified by flash chromatography on silica gel (120g, 0% DCM / hexanes (2 CV) 100% (10 CV)). Fractions containing product were evaporated to dryness in vacuo to give an off-white solid, 1589 mg (91% yield). MS (APCI): calculated for Chemical Formula: C31H48N2O6 (M+H) = 545 found: 545. 1 H NMR (400 MHz, TCE) 5 7.41 (s, 1 H), 6.83 (s, 1 H), 6.24 (d, J = 5.6 Hz, 1 H), 3.35 - 3.04 (m, 4H), 2.33 (p, J = 7.6 Hz, 1 H), 1.99 - 1.86 (m, 4H), 1.80 - 1.70 (m, 4H), 1.67 (d, J = 4.2 Hz, 4H), 1.60 - 1.39 (m, 10H), 1.38 - 1.16 (m, 12H), 0.98 - 0.78 (m, 6H).

[0068] General synthesis procedure of compound PBG4

[0069] Compound PBG4.1 (cyclopentanecarboxylic anhydride):

[0070] Cyclopentanecarboxylic acid (100.0 mmol, 11.414 g) was stirred in dry DCE (100 mL) under argon. The reaction was treated with DMAP.pTsOH salt (5.000 mmol, 1472 mg) and EDC.HCI (75.00 mmol, 14.378 g). The reaction mixture was stirred at room temperature under argon for one hour. The reaction mixture was diluted with DCM (100 mL), washed water (100 mL), saturated sodium bicarbonate (100 mL), and 1 N HCI (100 mL). The product was dried over magnesium sulfate, filtered, and evaporated to dryness in vacuo to give a light-yellow oil, 11.806 g (112% yield). It was used as-is in subsequent steps. 1 H NMR (400 MHz, CDCI3) 52.92 - 2.80 (m, 2H), 2.00 - 1 .80 (m, 8H), 1.79 - 1 .67 (m, 4H), 1.66 - 1.51 (m, 4H).

[0071] Compound PBG-4.2 (cyclopentyl(spiro[benzo[d][1,3]dioxole-2,T- cyclopentan]-5-yl)methanone): Compoundl 733-40 (10.00 mmol, 1762 mg) was stirred with Compound PBG4.1 (20.00 mmol, 4205 mg) and TFA (7.5 mL) at room temperature, capped loosely for one hour. The mixture was transferred to an Erlenmeyer flask with 100 mL of ethyl acetate and carefully quenched with saturated sodium bicarbonate solution to pH ~8. The mixture was diluted with 100 mL brine and the layers separated. Extracted 2 X 100 mL ethyl acetate, dried over magnesium sulfate, filtered, and evaporated to dryness in vacuo. The product was purified by flash chromatography on silica gel (120g, 30% DCM / hexanes (2 CV) 100% DCM (10 CV)). Fractions containing product were evaporated to dryness in vacuo to give an oily product, 2553 mg (94% yield). MS (APCI): calculated for Chemical Formula: C17H20O3 (M+H) = 273 found: 273. 1 H NMR (400 MHz, TCE) 5 7.54 (dd, J = 8.2, 1.7 Hz, 1 H), 7.37 (d, J = 1.7 Hz, 1 H), 6.79 (d, J = 8.2 Hz, 1 H), 3.74 - 3.51 (m, 1 H), 2.17 - 2.06 (m, 4H), 1.96 - 1.78 (m, 8H), 1.78 - 1.64 (m, 4H).

[0072] Compound PBG4.3 (cyclopentyl(5-nitrospiro[benzo[d][1,3]dioxole-2,1'- cyclopentan]-6-yl)methanone): Compound PBG4.2 (9.371 mmol, 2552 mg) was stirred in nitromethane (15 mL) at 0 °C and treated with 70% nitric acid (10 mL) and stirred for 20 minutes. The mixture was transferred to an Erlenmeyer flask with ethyl acetate (100 mL) and carefully quenched with saturated sodium bicarbonate solution to pH ~8. Brine (100 mL) was added and the layers separated, extracted with ethyl acetate (2 X 100 mL), dried over magnesium sulfate, filtered, and evaporated to dryness in vacuo. The product was [purified by flash chromatography on silica gel (120g, 30% DCM / hexanes (2 CV) 100% DCM (10 CV) isocratic DCM)). Fractions containing product were evaporated to dryness in vacuo to give a light-yellow solid, 1991 mg (67% yield). MS (APCI): calculated for Chemical Formula: C17H19NO5 (M+H) = 318 found: 318. 1 H NMR (400 MHz, TCE) 5 7.49 (s, 1 H), 6.62 (s, 1 H), 3.12 (p, J = 8.1 Hz, 1 H), 2.22 - 2.07 (m, 4H), 1.97 - 1.82 (m, 9H), 1.81 - 1.68 (m, 2H), 1.67 - 1.52 (m, 2H).

[0073] Compound PBG4.4 (cyclopentyl(5-nitrospiro[benzo[d][1,3]dioxole-2,1'- cyclopentan]-6-yl)methanol): Sodium borohydride (25.10 mmol, 952 mg) was stirred in 50 mL of dry THF and 25 mL of dry isopropanol under argon and treated with acetic acid (6.724 mmol, 0.36 mL) dropwise, then stirred for about 10 minutes until all bubbling had ceased. Compound PBG4.3 (6.274 mmol, 1991 mg) was dissolved in 25 mL of dry THF and added to the reaction mixture. The reaction mixture was stirred at room temperature for two hours, transferred to an Erlenmeyer flask with 100 mL of ethyl acetate, and quenched with saturated ammonium chloride solution until all bubbling had ceased. 100 mL brine was added, and the layers were separated, extracted 2 X 100 mL EtOAc, dried over magnesium sulfate, filtered, and evaporated to dryness. The product was purified by flash chromatography on silica gel (120g, 0% DCM / hexanes (2 CV) - 100% DCM (5 CV) isocratic DCM)). Fractions containing product were evaporated to dryness in vacuo to give a light-yellow solid, 1512 mg (75% yield). MS (APCI): calculated for Chemical Formula: C17H21NO5 (M+H) = 320 found: 320. 1 H NMR (400 MHz, CDCI3) 5 7.31 (s, 1 H), 7.05 (s, 1 H), 5.07 (dd, J = 7.6, 4.0 Hz, 1 H), 2.43 (d, J = 4.1 Hz, 1 H), 2.30 (h, J = 8.0 Hz, 1 H), 1.93 - 1.82 (m, 4H), 1.83 - 1.43 (m, 7H), 1.23 - 1.11 (m, 1 H).

[0074] Compound PBG4.5 (cyclopentyl(5-nitrospiro[benzo[d][1,3]dioxole-2,1'- cyclopentan]-6-yl)methyl (4-nitrophenyl) carbonate): Compound PBG4.4 (4.697 mmol, 1511 mmol) was dissolved in dry DCE (25 mL) and treated with 4-nitrophenyl carbonochloridate (7.045 mmol, 1420 mg) and triethylamine (11.74 mmol, 1.64 mL). The reaction mixture was stirred at room temperature under argon for 45 minutes, then heated to 50 °C for one hour. The crude reaction mixture was loaded onto silica gel and purified by flash chromatography on silica gel (120g, 0% DCM / hexanes (2 CV) 100% (10 CV) isocratic DCM)). Fractions containing product were evaporated to dryness in vacuo to give a light yellow solid, 1635 mg (72% yield). MS (APCI): calculated for Chemical Formula: C24H24N2O9 (M+H) = 485 found: 485. 1 H NMR (400 MHz, TCE) 5 8.30 - 8.18 (m, 2H), 7.39 (s, 1 H), 7.39 - 7.32 (m, 2H), 6.99 (s, 1 H), 6.33 (d, J = 7.4 Hz, 1 H), 2.48 (h, J = 8.0 Hz, 1 H), 2.24 - 2.08 (m, 4H), 1.95 - 1.81 (m, 4H), 1.80 - 1.36 (m, 8H).

[0075] Compound PBG4 (cyclopentyl(5-nitrospiro[benzo[d][1,3]dioxole-2,1'- cyclopentan]-6-yl)methyl dihexylcarbamate): Compound PBG4.5 (3.375 mmol, 1635 mg) was dissolved in dry DCE (25 mL) and stirred at room temperature under argon. Dihexylamine (6.750 mmol, 1 .6 mL) was added to the reaction. The reaction mixture was heated to 60 °C and stirred overnight. The crude reaction mixture was loaded onto silica gel and purified by flash chromatography on silica gel (120g, 0% EtOAc / toluene (2 CV) isocratic 2%)). Fractions containing product were evaporated to dryness in vacuo to give an off-white solid, 1534 mg (86% yield). MS (APCI): calculated for Chemical Formula: C30H46N2O6 (M+H) = 531 found: 531. 1 H NMR (400 MHz, TCE) 5 7.40 (s, 1 H), 6.82 (s, 1 H), 6.24 (d, J = 5.6 Hz, 1 H), 3.40 - 3.04 (m, 4H), 2.33 (q, J = 7.5 Hz, 1 H), 2.21 - 2.07 (m, 4H), 1.95 - 1.77 (m, 4H), 1.75 - 1.38 (m, 13H), 1.38 - 1.11 (m, 12H), 1.05 - 0.74 (m, 6H).

[0076] PBG base release efficiency measurements pH Change studies of the PBG compounds were performed in MeCN solvent with a 1 mg / mL concentration. In an amber vial, weighed ~6 mg of a PBG compound and then ~6 mL acetonitrile was added to dissolve the PBG compound. Initial pH (before exposure) was measured using a pH meter (after 3 pH Calibrations at pH 4.0, 7.0 and 10.0). Then, the solution containing the PBG compound was exposed to -600 mJ / cm2 mercury lamp using a Dymax UV curing conveyor. pH after exposure was then measured using the same pH meter. pH Change was calculated by subtracting the pH after exposure with the initial pH. The pH Change results are shown in Table 1. Solution base release experiments of PBG compounds were performed in MeCN solvent with a 1 mg / mL concentration. In a transparent glass vial, -1 mg of a PBG compound was added and then -1 mL acetonitrile was added to the PBG compound. Then, the solution containing the PBG compound was exposed to a -600 mJ / cm2 mercury lamp using a Dymax UV curing conveyor. Analysis of photo products, and efficiency was carried out using Shimadzu LC / MS.

[0077] TGA Data of spiro-benzodioxole PBGs

[0078] TGA measurements were taken from 25 °C to 590 °C under nitrogen with a flow rate of 25 mL / min using the method with the ramp rate of 10 °C / min by TA instrument TGA550. The TGA data of the spiro-benzodioxole PBGs are presented in Table 1.

[0079] Table 1. Efficiency of base-release under light, and TGA of PBG compounds Standard Polyimide formation method

[0080] Selected PBGs (i.e. PBG2 and PBG3) and a polyimide precursor (polyamidic acid) were weighed into a container / jar (j.e. 30 mg of PBG in 3 g of PI Varnish), then mixed by using Thinky (2000 rpm for 3 min, added more mixing time as needed until all fully dissolved). The mixed solution was then spin-coated on Steel Use Stainless (SUS) 304 substrates taped on rigid glass plate (main spin-coating rate: 1100 rpm for 30 sec). (SUS304 is a Japanese JIS Standard and one of the most frequently used stainless steels, including 18% Cr and 8% Ni). Then, it was baked at 120 °C for 10 min to remove N-methyl-2-pyrrolidone (NMP) solvent. After that, a 600 mJ / cm2mercury lamp was exposed on the sample masking on various portions thereof (using Dymax UV curing conveyor). Afterwards, the post-exposure baking was conducted at 200 °C for 7 min. As the final step, FT-IR (Thermo Nicolet iS50) measurements of the exposed and the unexposed area of the sample were performed to obtain imidization contrast ratios. (Imidization rate % = Corrected height of imide peak (1777cnv1) / Corrected height of benzene peak (1489 cm-1) x 100). The imidization contrast ratio is the ratio of the imidization rate % of the exposed area to the imidization rate % of the unexposed area. PBG2 and PBG3 exhibit an imidization contrast ratio of 1.17 and 1.13, respectively. Related results are illustrated in FIG. 1.

[0081] Absorbance of Representative PBGs (FIG.2)

[0082] Additional optical properties of PBG1 , PBG2, PBG3 and PBG4 are graphically illustrated in FIG. 2. Absorbance spectra of the PBGs were measured in N- methylpyrrolidone (NMP) solvent using Shimadzu UV3600 spectrometer. The normalized absorption spectra of the PBGs are shown in FIG. 2.

[0083] Use of the term “may” or “may be” or “can” should be construed as shorthand for “is” or “is not” or, alternatively, “does” or “does not” or “will” or “will not,” etc. For example, the statement “a thermally conductive composite may further include a backing layer” should be interpreted as, for example, “In some embodiments, a thermally conductive composite further includes a backing layer,” or “In some embodiments, a thermally conductive composite does not further include a backing layer.”

[0084] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties, such as, molecular weight, reaction conditions, and so forth used in the specification and embodiments are to be understood as being modified in all instances by the term “about.” The term “about” as used herein, can include any numerical value that can vary without changing the basic function of that value. When used with a range, “about” also discloses the range defined by the absolute values of the two endpoints. The term “about” may refer to plus or minus 10% of the indicated number.

[0085] Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached embodiments are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt to limit the application of the doctrine of equivalents. To the scope of the embodiments, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0086] For the processes and / or methods disclosed, the functions performed in the processes and methods may be implemented in differing order, as may be indicated by context. Furthermore, the outlined steps and operations are only provided as examples, and some of the steps and operations may be optional, combined into fewer steps and operations, or expanded into additional steps and operations.

[0087] This disclosure may sometimes illustrate different components contained within, or connected with, different other components. Such depicted architectures are merely examples, and many other architectures can be implemented which achieve the same or similar functionality.

[0088] The terms used in this disclosure, and in the appended embodiments, are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including, but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes, but is not limited to,” etc.). In addition, if a specific number of elements is introduced, this may be interpreted to include at least the recited number, as may be indicated by context (e.g., the bare recitation of "two recitations," without other modifiers, includes at least two recitations, or two or more recitations). As used in this disclosure, any disjunctive word and / or phrase presenting two or more alternative terms should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”

[0089] The terms and words used are not limited to the bibliographical meanings but are merely used to enable a clear and consistent understanding of the disclosure. The terms “a,” “an,” “the” and similar referents used in the context of describing the present disclosure (especially in the context of the following embodiments) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of any and all examples, or representative language (e.g., “such as”) provided herein is intended merely to better illuminate the present disclosure and does not pose a limitation on the scope of any embodiments. No language in the specification should be construed as indicating any non-embodied element essential to the practice of the present disclosure.

[0090] Groupings of alternative elements or embodiments disclosed herein are not to be construed as limitations. Each group member may be referred to and embodied individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and / or patentability. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended embodiments.

[0091] Certain embodiments are described herein, including the best mode known to the inventors for carrying out the present disclosure. Of course, variations on these described embodiments, will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the present disclosure to be practiced otherwise than specifically described herein. Accordingly, the embodiments include all modifications and equivalents of the subject matter recited in the embodiments as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is contemplated unless otherwise indicated herein or otherwise clearly contradicted by context. In closing, it is to be understood that the embodiments disclosed herein are illustrative of the principles of the embodiments. Other modifications that may be employed are within the scope of the embodiments. Thus, by way of example, but not of limitation, alternative embodiments may be utilized in accordance with the teachings herein. Accordingly, the embodiments are not limited to the embodiments precisely as shown and described.

[0092] By the term "substantially" it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those skilled in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0093] Aspects of the present disclosure may be embodied in other forms without departing from its spirit or essential characteristics. The described aspects are to be considered in all respects illustrative and not restrictive. The embodied subject matter is indicated by the appended embodiments rather than by the foregoing description. All changes, which come within the meaning and range of equivalency of the embodiments, are to be embraced within their scope.

Claims

CLAIMSWhat is claimed is:1 . A compound according to formula (1):wherein n is 1 or 2;R1represents H, an alkyl, or a cyclic alkyl group; andR2and R3independently represent H, an alkyl or a cyclic alkyl group.

2. The compound of claim 1 , wherein R1representsH, a methyl, a C2-C4 alkyl,3. The compound of claim 1 , wherein R2and R3independently represent a C3-C8 alkyl or cyclic alkyl.

4. The compound of claim 1 , having the following structure:

5. The compound of claim 1 , having the following structure:

6. The compound of claim 1 , having the following structure:

7. The compound of claim 1, having the following structure:

8. A method for making a polyimide including: providing a compound according to any one of claims 1-7 and a polyimide precursor dispersion in a dispersant; applying the compound and the polyimide precursor to a substrate; applying visible light to the compound and the polyimide precursor on the substrate; and heating the substrate to accomplish at least one of removing the dispersant and curing the covered substrate.

9. The method of claim 8, further including masking portions of the substrate to selectively apply visible light to unmasked portions of the substrate.

10. A method for measuring the base release efficiency of a photobase generator compound including: dissolving a compound according to any one of claims 1-7 in acetonitrile; measuring the pH of a solution including the compound and the acetonitrile; exposing the solution to visible light; and measuring the pH of the solution following exposure to visible light.

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