Anthracene-based solid-state systems and use for thermal energy storage and release

Abstract

A dianthracene of Formula (II), wherein each R is the same or different, and R is a substituent wherein [4+4] cycloreversion of the dianthracene of Formula (II) to corresponding donor- acceptor anthracenes discharges energy in an amount from 80 kJ / mol to 200 kJ / mol, or 90 to 150 kJ / mol, or 90 to 130 kJ / mol, and / or R is a substituent wherein reversion of the dianthracene of Formula (II) to donor-acceptor anthracenes of Formula (I) is self-activating, and / or R is C1-4 alkyl, C1-4 alkoxy, or a combination thereof; uses, methods of storing thermal energy, and thermal energy systems including the dianthracene.

Description

(2024-051-02)ANTHRACENE-BASED SOLID-STATE SYSTEMS AND USE FOR THERMAL ENERGY STORAGE AND RELEASECROSS-REFERENCE TO RELATED APPLICATIONThis application is based on and claims the benefit of U.S. Provisional Application Serial No. 63 / 637,326, Filed April 22, 2024, the entire contents of which are hereby incorporated by reference.STATEMENT OF GOVERNMENT SUPPORT

[0001] This invention was made with government support from the National Science Foundation under Grant No. DMR-2142887, and the Air Force Office of Scientific Research under Grant No. AFRL / IF FA9550-22- 1-0254). The U.S. government has certain rights in this invention.BACKGROUND

[0002] Disclosed herein are solid-solid phase change anthracene-based systems, methods of their manufacture, and uses thereof, in particular for thermal energy storage and release.

[0003] Photo-induced molecular transformations, in particular reversible photochemical reactions / isomerizations, have attracted significant attention as a potential method for harnessing solar energy. A particular class of molecules, referred to as molecular solar thermal storage (MOST) systems, respond to light conformational and energetic changes. MOST molecules present an opportunity to store photon energy in constrained chemical bonds, and then upon triggering release the energy in the form of heat. MOST systems can accordingly be used as a heat-storage material for use in heat-storage devices such as thermal batteries.

[0004] The concept of MOST energy storage has been largely demonstrated with molecular photoswitches including norbornadienes, azo(hetero) arenes, hydrazones, dihydroazulenes, and fulvalene diruthenium derivatives that store photon energy in their metastable photoisomers. Many of these systems have been primarily investigated in solution state. However, enabling the energy storage and release processes in condensed liquid or solid phases is desirable to provide MOST systems with maximized gravimetric energy densities.

[0005] In this effort, various azo(hetero)arenes and hydrazone derivatives have been designed to undergo photo-induced structural changes in solids and transform into liquids,(2024-051-02) harnessing the additional energy storage from the phase transition. Recently, another class of MOST compounds has emerged, which stores photon energy via solid-state photochemical reactions, as illustrated by the intermolecular [2+2] photocycloaddition among styrylpyryliums. The strong donor- acceptor design of styrylpyrylium structures allowed for the favorable head-to- tail stacking of molecules in crystals and the facile [2+2] cycloaddition upon the absorption of a broad range of visible light as well as a natural solar spectrum. Also, both UV-induced and thermally-activated cycloreversion of cyclobutanes to styrylpyryliums were successful, releasing the stored energy as heat.

[0006] These solid-state intermolecular photochemical reactions demonstrated potential for MOST energy storage, but there were limitations of the styrylpyrylium-based systems. First, the maximum energy storage density of 42 kJ / mol per cyclobutane and gravimetric energy density of 51 J / g are suboptimal compared to the conventional MOST systems such as azo(hetero)arenes and norbomadienes that offer the energy storage densities over 100 kJ / mol and 300 J / g. Second, the activation energy (Ea) of 121 -122 kJ / mol for the thermally-activated cycloreversion process is far greater than the released energy of 42 kJ / mol, which necessitates the continuous heating of the metastable cyclobutaenes at temperatures above 131 °C for the complete cycloreversion and heat release. Therefore, the energy release could be monitored only on a few-milligram scale using differential scanning calorimetry (DSC), while it was challenging to detect any sizable temperature increase of the solid MOST compounds outside the thermally-insulated environment of DSC. Still further, the small energy released from the solids quickly dissipates to the air and substrates, leading to negligible temperature changes of the compounds that are in a thermal equilibrium with the heat source.

[0007] Effective and potent energy sources (fuels) have the ability to self-ignite upon the initial triggering, which allows the external energy supply to be limited to a short-term initiation, and maximizes the efficiency of energy release. For example, the self-ignition of hydrocarbons enables the complete and spontaneous combustion of the fuels after the initial compression- or electrical discharge-induced triggering of the exothermic reactions. Frontal polymerizations have also leveraged exothermic reactions to self-propagate the polymer growth. These irreversible self-activating reactions generate products such as carbon dioxide, water, and polymers. However, we are unaware of any significant self-activated energy release from MOST systems. This may be due to a number of reasons. In a solution state, the heat dissipation to the large volume of solvent is prominent and restricts the effective heat transfer to the unreacted metastable isomers. Even in a solid state, thin films or powders have large surface areas where the released heat quickly dissipates to the environment, limiting the heat transfer between(2024-051-02) molecules. Lastly, the activation energy (Ea) for thermal reversion is generally much greater than the released energy per molecule, which fundamentally prevents the cascade of exothermic reactions.

[0008] Accordingly, there remains a need in the art for MOST systems that operate in solvent-free conditions, store a large quantity of energy (AHstorage), comparable to or greater than the Eaof reversion, that are scalable, and / or that self-activate the heat release and propagation.SUMMARY

[0009] Disclosed herein is thermal storage system including a donor- acceptor anthracene of Formula (I), a dianthracene compound of Formula (II), or a combination thereof,(I) (II) wherein each R is the same or different, and is a Ci-4 alkyl, Ci-4 alkoxy, or a combination thereof.

[0010] Also disclosed are compositions including the donor-acceptor anthracene of Formula (I), the dianthracene compound of Formula (II), or a combination thereof. In particular, a composition comprises, consists of, or consists essentially of, the donor-acceptor anthracene of Formula (I), the dianthracene compound of Formula (II), or a combination thereof, preferably wherein the composition is a solid composition.

[0011] A composite structure comprising a porous structural component and the donoracceptor anthracene of Formula (I), the dianthracene compound of Formula (II), or a combination thereof are described.

[0012] A method of storing energy includes providing an energy storage device comprising the donor- acceptor anthracene of Formula (I), and optionally the dianthracene compound of Formula (11); photoirradiating the donor- acceptor anthracene of the compound of Formula (II) to produce the dianthracene of Formula I via [4+4] cycloaddition; and storing dianthracene of Formula (II) for a period of time. The method can further include inducing the dianthracene of Formula (II) to convert back to the donor-acceptor anthracene of Formula (I), to release energy stored during the photoirradiating.(2024-051-02)

[0013] A thermal storage system is described that includes the donor-acceptor anthracene of Formula (I), the dianthracene compound of Formula (II), or a combination thereof.

[0014] The above described and other features are exemplified by the following figures, detailed description, examples, and claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The following Figures are exemplary embodiments, which are provided to illustrate the present disclosure. The Figures are not intended to limit compositions, systems, or devices made in accordance with the disclosure to the materials, conditions, or process parameters set forth herein.

[0016] FIG. 1A is a schematic illustration of photon energy storage in dianthracenes and triggered release of energy during their cycloreversion to anthracenes.

[0017] FIG. IB shows reversible [4+4] cycloaddition of anthracene derivatives 1-4(A) to form a dianthracene 1-4(D).

[0018] FIG. 1C shows solid-state UV-vis spectra of 3-A and 3-D obtained from irradiation and thermal reversion.

[0019] FIG. ID shows solution-state UV-vis spectra of anthracene 3-A and dianthracene 3-D in dichloromethane. Anthracene 3-A is obtained from the thermal reversion of anthracene 3- D in solution.

[0020] FIG. 2A shows solid-state NMR spectra of anthracene 3-A and dianthracene 3-D and the corresponding chemical structures.

[0021] FIG. 2B shows DSC thermograms of anthracene 3-A and dianthracene 3-D measured during the first heating (black) and cooling (blue) cycle.

[0022] FIG. 2C shows DSC thermographs of dianthracenes 1-D, 2-D, and 4-D, measured during the first heating cycle. Red highlighted areas represent the exotherms of cycloreversion (AHstorage). Tm-A: melting point of anthracene, TC-A: crystallization point of anthracene, Trev: peak temperature of thermal reversion, TOnset: onset temperature of thermal reversion.

[0023] FIG. 3A shows simulated and refined structures of anthracene 3-A and dianthracene 3-D, showing head-to-tail stacking of anthracenes and the shortened distance between reactive carbons upon bond formation.

[0024] FIG. 3B shows simulated and refined packing structures of anthracene 3-A displaying crystal-to-crystal transformation and 0.3% volume increase upon dimerization.(2024-051-02)

[0025] FIG. 3C shows simulated and refined packing structures of dianthracene 3-D displaying crystal-to-crystal transformation and 0.3% volume increase upon dimerization.

[0026] FIG. 4A is a schematic of experimental setup composed of a heating block and a solid pellet of compound.

[0027] FIG. 4B shows temperature profiles of a solid pellet measured over time at five positions (a-e) for anthracene 3-A.

[0028] FIG. 4C shows temperature profiles of a solid pellet measured over time at five positions (a-e) for dianthracene 3-D.

[0029] FIG. 4D shows the corresponding images showing the color and temperature change of a pellet over time for anthracene 3-A.

[0030] FIG. 4E shows the corresponding images showing the color and temperature change of a pellet over time for dianthracene 3-D.

[0031] FIG. 5 A shows optical and IR images showing the color and temperature change of a pellet of dianthracene 3-D during the heat propagation.

[0032] FIG. 5B shows net temperature increases of the pellet over time.

[0033] FIG. 5C shows the kinetics of spatial heat propagation. Ad (x-a) is the distance between a position on the pellet (b-e) and the position a.

[0034] FIG. 5D shows IR-laser triggered cycloreversion and heat cascade for a pellet of dianthracene 3-D.

[0035] FIG. 5E shows optical and IR images showing the melting process of a pellet of dianthracene 1-D upon cycloreversion.

[0036] FIG. 5F shows temperature profiles of a solid pellet measured over time at five positions (a-e) for 1-A

[0037] FIG. 5G shows temperature profiles of a solid pellet measured over time at five positions (a-e) for dianthracene 1-D.

[0038] FIG. 6 A shows the DFT calculation results on [4+4] cycloaddition and reversion of anthracene derivatives, showing energy level changes surveyed as the distance between two cofacial anthracenes was varied, calculated at the B3LYP-D3 / 6-31+G(d,p) level of theory.

[0039] FIG. 6B is a table summarizing the calculation results. AGCaic: calculated energy storage density, AG*Caic: calculated activation energy, d (C9-C10*)D: distance between a 9- position of an anthracene and a 10-position of the counterpart in a dimer, d (C9-C 10*)TS: distance between a 9-position of an anthracene and a 10-position of the counterpart in a transition state.(2024-051-02)

[0040] FIG. 7A shows relative energy profiles recorded as a function of C9-C10* distance between two anthracenes, calculated at the B3LYP-D3 / 6-31+G(d,p) level of theory. The energy level of 9-CN anthracene at 3.4 A was selected as the reference (0).

[0041] FIG. 7B is a table summarizing the calculation results.

[0042] FIG. 8 shows energy diagrams of frontier orbitals of 9-CN anthracene, 1-CN anthracene, 2-CN anthracene, and their dimers, calculated at the B3LYP-D3 / 6-31+G(d,p) level of theory.

[0043] FIG. 9 shows the lowest unoccupied molecular orbital of 9-CN, 1-CN, and 2-CN anthracene dimers calculated at the B3LYP-D3 / 6-31+G(d,p) level of theory

[0044] FIG. 10 shows the photographs of the ball-mixing setup and the procedure of the ball-mixing method.

[0045] FIG. 11 shows the DSC thermograms of dianthracene 1-D, dianthracene 2-D, and dianthracene 3-D prepared by the ball mixing method.

[0046] FIG. 12A shows powder XRD patterns of anthracene 1 -A (orange) measured after the mixing with balls and dianthracene 1-D (gray) upon the irradiation of ball-mixed anthracene 1-A.

[0047] FIG. 12B shows powder XRD patterns of anthracene 2- A (orange) measured after the mixing with balls and dianthracene 2-D (gray) upon the irradiation of ball-mixed anthracene 2- A.

[0048] FIG. 12C shows powder XRD patterns of anthracene 3-A (orange) measured after the mixing with balls and dianthracene 3-D (gray) upon the irradiation of ball-mixed anthracene 3-A.

[0049] FIG. 12D shows powder XRD patterns of anthracene 4- A (orange) measured after the mixing with balls and dianthracene 4-D (gray) upon the irradiation of ball-mixed anthracene 4-A (top) and anthracene 4-A after irradiation (bottom, i.e. no reaction).

[0050] FIG. 13A, FIG. 13B, and FIG. 13C shows the UV-vis absorption spectra of the monomers and dimers in thin films. Monomers 1 -3 were melt-pressed between two glass slides to form thin films of uniform thickness. The monomer films were irradiated to obtain thin films of dimers.

[0051] FIG. 13D shows that the monomer 4 could not undergo photo-dimerization in films, the diffuse reflectance spectra of anthracene 4-A and dianthracene 4-D were obtained along with the thin film absorption spectrum of anthracene 4-A (dotted line).

[0052] FIG. 14A shows the thickness profile of a film of 1-A.

[0053] FIG. 14B shows the optical microscope image of the measure area of FIG. 14A.(2024-051-02)

[0054] FIG. 14C shows 3D topography of the measured area of FIG. 14A. The glass slide surface area is highlighted in blue, film area is in yellow, and the difference between the two areas is the thickness of film. Eight different areas were measured to get the average thickness of 0.13 pm.

[0055] FIG. 15A shows the measured thickness profile of a film of anthracene 2-A.

[0056] FIG. 15B shows the optical microscope image of the measured area of FIG. 15 A.

[0057] FIG. 15C shows 3D topography of the measured area of FIG. 15A. The glass slide surface area is highlighted in blue, film area is in yellow, and the difference between the two areas is the thickness of film. Eight different areas were measured to get the average thickness of 0.502 pm.

[0058] FIG. 16A shows thickness profile of a film of anthracene 3-A.

[0059] FIG. 16B shows the optical microscope image of the measured area of FIG. 16A.

[0060] FIG. 16C shows 3D topography of the measured area of FIG. 16A. The glass slide surface area is highlighted in blue, film area is in yellow, and the difference between the two areas is the thickness of film. Eight different areas were measured to get the average thickness of 0.721 pm.

[0061] FIG. 17 shows UV-vis absorption spectra of the monomers and dimers in dichloromethane (DCM). The concentration of dimers was 2.5xl0-5M, and their reversion to monomers in solution was monitored until the full conversion was achieved.

[0062] FIG. 18 shows solid state13C NMR spectra of anthracene 1-A (bottom) and dianthracene 1-D (top). Dashed line: spectra after dipolar dephasing, documenting that the carbon resonating at 135 ppm is bonded to hydrogen. The arrow indicates the disappearance of the monomer peak upon irradiation.

[0063] FIG. 19 shows the solid state13C NMR spectra of anthracene 2-A (bottom) and dianthracene 2-D (top). Dashed lines are the spectrum after dipolar dephasing. The arrows indicate the disappearance of monomer peaks upon irradiation.

[0064] FIG. 20 shows the solid state13C NMR spectra of anthracene 3-A and dianthracene 3-D. Dashed: spectrum after dipolar dephasing. The arrows indicate the disappearance of monomer peaks upon irradiation.

[0065] FIG. 21 shows the solid state13C NMR spectra of anthracene 4-A and dianthracene 4-D. The arrows indicate the disappearance of monomer peaks upon irradiation.

[0066] FIG. 22A shows the TGA plot for anthracene 1-A, FIG. 22B shows the TGA plot for anthracene 2-A, FIG. 22C shows the TGA plot for anthracene 3-A, and FIG. 22D shows the TGA plot for anthracene 4-A, measured at a heating rate of 20 °C / min, demonstrating the onset(2024-051-02) temperatures of thermal decomposition: 1-A at 200 °C, anthracene 2-A at 215 °C, anthracene 3- A at 185 °C, and anthracene 4- A at 205 °C.

[0067] FIG. 23A shows the DSC plots of anthracene 1-A and dianthracene 1-D; FIG. 23B shows the DSC plots of anthracene 2-A and dianthracene 2-D; FIG. 23C shows the DSC plots of anthracene 3-A and dianthracene 3-D; and FIG. 23D shows the DSC plots of anthracene 4-A and dianthracene 4-D. The highlighted areas are integrated to obtain AGstorage values. Trcv: peak temperature of D— >2A thermal reversion. Tm: melting temperature of monomer. Tc: crystallization temperature of monomer.

[0068] FIG. 24A shows a single crystal structure of anthracene 2-A (50% probability for thermal ellipsoids, hydrogen atoms are omitted for clarity), wherein crystallographically independent molecular units distinguished by color (A- J); FIG. 24B shows a top view of the stacked anthracene 2-A dimer; and FIG. 24C shows bird’s eye view and the interatomic distance between C9 and CIO* positions.

[0069] FIG. 25A shows the comparison of experimental and simulated PXRD patterns of dianthracene 2-D.

[0070] FIG. 25B shows the comparison of experimental and simulated PXRD patterns of anthracene 3-A.

[0071] FIG. 25C shows the comparison of experimental and simulated PXRD patterns of dianthracene 3-D.

[0072] FIG. 25D shows the comparison of experimental and simulated PXRD patterns of anthracene 4-A.

[0073] FIG. 25E shows the comparison of experimental and simulated PXRD patterns of dianthracene 4-D.

[0074] FIG. 26A shows a simulated and refined crystal structure of anthracene 2-A based on powder XRD pattern and single crystal structure of anthracene 2-A (50% probability for thermal ellipsoids, hydrogen atoms omitted for clarity), where crystallographically independent molecular units distinguished by color (A-J); FIG. 26B shows a top view of stacked anthracene 2-A dimer; and FIG. 26C shows a bird’s eye view and the interatomic distance between C9 and CIO* positions of stacked anthracene 2-A dimer.

[0075] FIG. 27A shows a simulated and refined crystal structure of anthracene 3-A based on powder XRD pattern and crystal structure of anthracene 2-A (50% probability for thermal ellipsoids, hydrogen atoms omitted for clarity, cubic shape atoms do not contain information on anisotropic and isotropic temperature factors), where crystallographically independent molecular units distinguished by color (A-J); FIG. 27B shows a top view of stacked(2024-051-02) anthracene 3- A dimer; and FIG. 27C shows bird’s eye view and the interatomic distance between C9 and CIO* positions of stacked anthracene 3- A dimer.

[0076] FIG. 28A shows a simulated and refined crystal structure of anthracene 4-A based on powder XRD pattern and crystal structure of anthracene 2-A (50% probability for thermal ellipsoids, hydrogen atoms omitted for clarity, cubic shape atoms do not contain information on anisotropic and isotropic temperature factors), where crystallographically independent molecular units distinguished by color (A-J); FIG. 28B shows a top view of stacked anthracene 4-A dimer; and FIG. 28C shows a bird’s eye view and the interatomic distance between C9 and CIO* positions of stacked anthracene 4-A dimer.

[0077] FIG. 29A shows a simulated and refined crystal structure of dianthracene 2-D based on powder XRD pattern and crystal structure of anthracene 2-A (50% probability for thermal ellipsoids, hydrogen atoms omitted for clarity), where crystallographically independent molecular units distinguished by color (A-F); FIG. 29B shows a bird’s eye view and the distance between C9 and CIO* positions of dianthracene 2-D.

[0078] FIG. 30A shows a simulated and refined crystal structure of dianthracene 3-D based on powder XRD pattern and crystal structure of anthracene 2-A (50% probability for thermal ellipsoids, hydrogen atoms omitted for clarity, cubic shape atoms do not contain information on anisotropic and isotropic temperature factors.). Crystallographically independent molecular units distinguished by color (A-F).

[0079] FIG. 30B shows bird’s eye view and the distance between C9 and CIO* positions of dianthracene 3-D.

[0080] FIG. 31A shows simulated and refined crystal structure of dianthracene 4-D based on powder XRD pattern and crystal structure of anthracene 2-A (50% probability for thermal ellipsoids, hydrogen atoms omitted for clarity, cubic shape atoms do not contain information on anisotropic and isotropic temperature factors.). Crystallographically independent molecular units distinguished by color (A-F).

[0081] FIG. 31B shows bird’s eye view and the distance between C9 and CIO* positions of dianthracene 4-D.

[0082] FIG. 32 shows simulated and refined packing structures of anthracene 2-A and dianthracene 2-D. Hydrogen atoms are omitted for clarity.

[0083] FIG. 33 shows simulated and refined packing structures of anthracene 4-A and dianthracene 4-D. Hydrogen atoms are omitted for clarity.

[0084] FIG. 34A shows the conversion of dianthracene 1-D at 130 °C, 135 °C, and 140 °C. The conversion at each temperature was fitted to an exponential function. The fitted(2024-051-02) parameters were used to obtain the Arrhenius and Eyring plots. The thermal half-life of dianthracene 1-D at 25 °C was determined via the extrapolation of the Arrhenius plot.

[0085] FIG. 34B shows the corresponding Arrhenius plots for the conversion of dianthracene 1-D at 130 °C, 135 °C, and 140 °C.

[0086] FIG. 34C shows the corresponding Eyring plots for the conversion of dianthracene 1-D at 130 °C, 135 °C, and 140 °C.

[0087] FIG. 35A shows the conversion of dianthracene 2-D at 50 °C, 55 °C, and 60 °C. The conversion at each temperature was fitted to an exponential function. The fitted parameters were used to obtain the Arrhenius and Eyring plots. The thermal half-life of dianthracene 2-D at 25 °C was determined via the extrapolation of the Arrhenius plot.

[0088] FIG. 35B shows the corresponding Arrhenius plots the conversion of dianthracene 2-D at 50 °C, 55 °C, and 60 °C.

[0089] FIG. 35C shows the corresponding Eyring plots for the conversion of dianthracene 2-D at 50 °C, 55 °C, and 60 °C.

[0090] FIG. 36A shows the conversion of dianthracene 3-D at 55 °C, 65 °C, and 70 °C. The conversion at each temperature was fitted to an exponential function. The conversion at each temperature was fitted to an exponential function. The fitted parameters were used to obtain the Arrhenius and Eyring plots. The thermal half-life of dianthracene 3-D at 25 °C was determined via the extrapolation of the Arrhenius plot.

[0091] FIG. 36B shows the corresponding Arrhenius plot for the conversion of dianthracene 3-D at 55 °C, 65 °C, and 70 °C.

[0092] FIG. 36C shows the corresponding Eyring plots for the conversion of dianthracene 3-D at 55 °C, 65 °C, and 70 °C.

[0093] FIG. 37A shows the conversion of dianthracene 4-D at 50 °C, 55 °C, and 60 °C. The conversion at each temperature was fitted to an exponential function. The fitted parameters were used to obtain the Arrhenius and Eyring plots. The thermal half-life of dianthracene 4-D at 25 °C was determined via the extrapolation of the Arrhenius plot.

[0094] FIG. 37B shows the corresponding Arrhenius plots for the conversion of dianthracene 4-D at 50 °C, 55 °C, and 60 °C.

[0095] FIG. 37C shows the corresponding Eyring plots for the conversion of dianthracene 4-D at 50 °C, 55 °C, and 60 °C.

[0096] FIG. 38A shows optical and IR images showing the color and temperature change of dianthracene 2-D over 240 seconds.(2024-051-02)

[0097] FIG. 8B shows optical and IR images showing the color and temperature change of dianthracene 2-D during the heat propagation.

[0098] FIG. 39A shows optical and IR images showing the color and temperature change of dianthracene 4-D over 270 seconds.

[0099] FIG. 39B shows optical and IR images showing the color and temperature change of dianthracene 4-D during the heat propagation.

[0100] FIG. 40A shows temperature profiles of anthracene 2-A; FIG. 40B shows temperature profiles of dianthracene 2-D; FIG. 40C shows temperature profiles of anthracene 4- A and dianthracene 4-D, each at point a (0, -4 mm), point b (0, -2 mm), point c (0, 0 mm), point d (0, 2 mm), and point e (0, 4 mm) with respect to the center (0, 0) of each pellet. Compound 2 was heated to 90 °C and compound 4 to 80 °C. The results show that dianthracene pellets 2-D and 4-D have significant heat release due to the cycloreversion D— >A.

[0101] FIG. 41 A shows net temperature increases of dianthracene pellet 1-D; FIG. 4 IB shows net temperature increases of dianthracene pellet 2-D; and FIG. 41C shows net temperature increases of dianthracene pellet 4-D.

[0102] FIG. 42A shows kinetics of spatial heat propagation of dianthracene 2-D and FIG. 42B shows kinetics of spatial heat propagation of dianthracenes 4-D.

[0103] FIG. 43 is shows the results of varying the method of forming films, in particular conversion (%) of anthracene 1-A to dianthracene 1-D using different irradiation methods as determined by *H NMR.DETAILED DESCRIPTION

[0104] Disclosed herein are engineered anthracene-based compounds designed to optimize energy storage and release in solid-state environments. The compounds represent a significant advancement in MOST energy storage technology, and are a notable improvement over previous MOST systems, which as described above, are less efficient.

[0105] In particular, the system is based on novel anthracene derivatives, chemically modified at the 10-position of a 9-cy anoanthracene molecule. The anthracene derivatives are donor- acceptor substituted anthracenes that undergo visible light-induced [4+4] cycloaddition, producing metastable cycloadducts (dianthracenes with quaternary carbons), and storing photon energy. The triggered cycloreversion of dianthracenes to anthracenes discharges the stored energy on the order of 100 kJ / mol (200 J / g). The series of compounds displays remarkable selfheating, or cascading heat release, upon the initial triggering. Such self-activated energy release is enabled by the large energy storage in dianthracenes, low activation energy for their thermal(2024-051-02) reversion, and effective heat transfer to unreacted molecules in the solid state. This process mirroring the self-ignition of fossil fuels opens up opportunities to use dianthracenes as effective and renewable solid-state fuels that can release energy rapidly and completely upon initial activation.

[0106] In particular, the strategic modification of 9-cyanoanthracene directly addresses the limitations observed in prior systems, such as those based on styrylpyrylium, which suffered from high activation energy for the thermal reversion process that exceeded the energy actually released. The use of anthracene derivatives significantly lowers the activation energy required for the energy release phase, allowing for a more efficient and practical energy release process. This ensures that the stored energy can be released without the need for continuous external heating, vastly improving the system's operational efficiency and practical applicability.

[0107] The anthracene-based MOST system further introduces a self-activated energy release mechanism that spontaneously releases the stored energy upon the initial triggering. The initial triggering by short thermal activation leads to the self-activation of heat release from the remaining fuels. This feature marks a significant advancement, as it enhances the system's efficiency and reduces the dependency on external energy inputs.

[0108] Furthermore, the specific design of the 9-cy anoanthracenes aids in separating the melting points from the temperatures at which thermal reversion occurs. This distinction is important because it can prevent the overlapping of thermal processes, a common issue in traditional anthracene derivatives, where melting and exothermic reversion overlapped, which significantly hindered heat release. The design described herein allows precise measurement of the heat storage enthalpy (AHstOrage) in solid states and maximized energy release from the system.

[0109] As described above, in order to improve the AHstorage, a small and neutral aromatic molecule, anthracene, is used as a scaffold for the MOST compounds. The molecular weight of anthracene (178 g / mol) is significantly smaller than that of styrylpyryliums (412-474 g / mol) bearing two / Bu groups and heavy counter-anions ranging from BF4- and CIOT to CFvSOr. The solid-state photodimerization of anthracenes have been largely studied for their photomechanical responses in crystals, particularly with those bearing a methyl (Me) or a - COOH group on the 9-position of anthracene. Anthracenes have also been incorporated into the building blocks of covalent organic frameworks and metal organic frameworks, displaying reversible dimerization in solid state. The potential of anthracene derivatives for MOST energy storage has been only studied at a fundamental level. Anthracenes bearing a functional group (- CHO, -CHgOH, Me, and longer alkyls) on the 9-position or two groups (OMe and COOR) on(2024-051-02)2,6-positions were photodimerized in solutions, and their thermal reversion was monitored either in solutions or in molten liquid states, recording AHstorage values of 20-30 kJ / mol, which are small.

[0110] However, Donati, et al. (1972) reported that dimers of 9-CN-anthracene and 9- CN, 10-acetyl (AcO)-anthracene can undergo solid-state thermal cycloreversion to anthracenes, releasing 74 and 82 kJ / mol, respectively. (Donati, et al. “Thermal Behaviour and Monomerization Kinetics of 9-CN Anthracene and 9-CN, 10- Acetoxy Anthracene Dimers in the Solid State.” Mol. Cryst. Liq. Cryst. 17, 187-195. h. QZ208083J 67. The temperatures of thermal reversion were lower than the melting points of the corresponding anthracenes, enabling the measurement of the enthalpy associated with the solid-to-solid transition. It has been discovered by the inventors hereof that 9-CN-anthracene with specific functionalizations at the 10- position are good candidates for MOST energy storage, where the 10-position functionalization can be used to fine-tune the relative scale of Eaof thermal reversion and AHstorage. The successful discovery of the structure-property relationship would enable the self-activated energy release from dianthracenes in solid state.

[0111] To understand the significance of substituents on anthracenes for energy storage, a theoretical investigation of AGstorage among the anthracene derivatives bearing various electron-donating and -withdrawing functional groups (Me, MeO, Br, CN, and NO2) at the 9- position was performed. Density functional theory (DET) calculation results suggested that there is a large gap between the AGstorage of 9-CN-anthracene (106 kJ / mol) and the rest of anthracene derivatives (51-65 kJ / mol) (Table 3). Additionally, varying the functional group position on anthracene resulted in a larger AGstorage value for 9-CN than 1-CN and 2-CN (54 and 42 kJ / mol, respectively) (FIG. 7-FIG. 9).

[0112] Based on these results, and without being bound by theory, it is believed that that the 9-CN functionalization significantly stabilizes the anthracene structure via effective electron delocalization, relative to dearomatized dianthracene counterpart with considerably less electron delocalization, increasing the energy gap between two states. Thus, anthracene derivatives with donor- acceptor structures, which would further enhance the electron delocalization over the anthracene structures and potentially increase AGstorage, were next investigated.

[0113] As shown in FIG. 1A, functionalized anthracenes undergo [4+4] photodimerization in the solid state when the distance between two neighboring, cofacial reactive units is within 4.2 A, according to the Schmidt’s principle. The resulting dianthracenes are metastable, storing the energy difference between the thermodynamically-stable anthracene pairs and dianthracenes (AGstorage). Upon thermal or photochemical triggering, the(2024-051-02) cycloreversion to anthracenes occurs, releasing the stored energy as heat (AHstorage). The 9-CN- anthracene derivatives were investigated by functionalizing the 10-position with H (compound 1-A, R = H), Me (compound 2-A, R = -CH3), MeO (compound 3-A, R = -OCH3), and AcO (compound 4- A, R = -OC(=O)CH3) (FIG. IB). In addition to increasing the electron delocalization over anthracenes, the donor- acceptor structures can facilitate a head-to-tail stacking of monomers in crystals, which increases the chance of dimerization and yielding single isomer of photodimer.

[0114] Thus, photodimers of compounds 1-3 via the irradiation of 405 nm LED in solid state were prepared. The anthracenes were mixed and stirred with small stainless-steel balls in a stainless-steel jar, assisted by magnetic stirring. The ball-mixed solid-state photodimerization was quantitative and generally more effective when stirred than when irradiated in thin films or in ethanol suspensions, while the reaction rate varied among the derivatives (FIG. 10-FIG. 12; FIG. 43). Compound 4- A was able to photodimerize only in ether suspension, indicating the less favorable packing of anthracenes and limited conformational freedom in crystals. For compound 4, diffuse reflectance spectra were acquired instead, due to the difficulty of obtaining uniform films for the dianthracene (FIG. 13). In solutions, the dianthracenes rapidly revert to anthracenes even at room temperature (FIG. ID), and the photocycloaddition of anthracenes in solution was not performed because it could produce a mixture of head-to-head and head-to-tail dimers. All UV-vis absorption spectra of solution-state compounds are illustrated in FIG. 17. This data showed reversible dimerization upon photoirradiation and thermal reversion.

[0115] The purity of dianthracenes was confirmed by the solid-state NMR spectroscopy (FIG. 2A). Since the dissolution of dianthracenes in organic solvents readily reverts to the monomer anthracenes, it is difficult to identify the chemical composition of the dianthracenes as synthesized by photodimerization using solution-state NMR. The solid-state13C NMR spectra of all dianthracenes show greater than 97% dimer content with negligible monomer residue, and the chemical shifts of reactive carbon atoms changing before and after the dimerization are clearly monitored (FIG. 18-FIG. 21).

[0116] Thermal properties of the anthracenes and dianthracenes were investigated using differential scanning calorimetry (DSC) in the range from -90 °C to around 200 °C, below their decomposition temperatures (FIG. 22). The anthracenes exhibit clear melting and crystallization, and the dianthracenes undergo exothermic thermal cycloreversion to generate corresponding anthracenes, allowing for the measurement of AHstoragcthat serves as an approximation for AGstorage (FIG. 2B, FIG. 23). The heating curves of all dianthracenes are illustrated in FIG. 2B and 2C, showing multiple exothermic events occurring simultaneously. Typical energy release(2024-051-02) from metastable MOST compounds such as azo(hetero)arenes, hydrazones, Lewis acid- coordinated azo compounds, and styrylpyryliums appear as a broad exotherm resembling a Gaussian curve. The presence of sharp peaks in addition to the broad exotherm indicates that additional exothermic process(es) accompanies the thermal cycloreversion. Without being bound by theory, it is hypothesized that crystal-to-crystal phase transition occurs during the cycloreversion, which contributes to the large AHstorage values of 9-CN-anthracene derivatives.

[0117] Crystal structures of certain compounds were obtained by the combination of single-crystal X-ray diffraction (anthracene 1-A, dianthracene 1-D, and anthracene 2- A) and simulated PXRD data, refined by the Pawley method (dianthracene 2-D, anthracene 3-A, dianthracene 3-D, anthracene 4-A, and dianthracene 4-D) (Table 5-Table 6, FIG. 24-FIG. 25). FIG. 3A shows the head-to-tail stacked anthracene 3-A pairs displaying short distances between the reactive carbon atoms below 4.2 A, fulfilling the Schmidt’s principle. The photoirradiation of anthracene 3-A crystals generates head-to-tail dimer dianthracene 3-D, with about 0.3% of unit cell volume increase upon dimerization. The crystal structures of all monomers and dimers of compounds 2-4 are illustrated in FIG. 26-FIG. 33, documenting unit cell volume changes of 4% (compound 2) and 3% (compound 4) upon dimerization. Compound 1 undergoes the most significant structural changes from 1-A (head-to-head paired) to dianthracene 1-D (head-to-tail dimer) and the space group change, indicating the rotation of anthracenes under photoirradiation during the dimerization process. Based on the changes of the molecular packing for compounds 1-4 upon dimerization, the contribution of the solid-state phase transition enthalpies to the overall energy storage densities of MOST systems is shown.

[0118] Table 1 summarizes the important thermal parameters relevant to the cycloreversion process of compounds 1-4 and a comparison styrylpyrylium that exhibited the greatest energy storage for the [4+4] cycloaddition-based MOST system. Table 1. Thermal parameters for cycloreversion process.Tm-A: melting point of anthracene monomerTonset: onset temperature of cycloreversionAGstorage: energy storage densityAG*: Gibbs free energy of activation ti / 2: thermal half-life of dianthracene at room temperature in solid state(2024-051-02)

[0119] First, the melting points of anthracenes (Tm_A) and the onset temperature for thermal cycloreversion (Tonset) by DSC were compared. For all compounds, Tm-A is higher than Tonset, which is important for achieving a net exothermic process of cycloreversion. If Tm.A is similar to or lower than TonSet, the released heat is reabsorbed during the melting process of the generated anthracenes, significantly reducing the overall energy release. We notice that Tonset values of donor- cceptor structures 2-4 are substantially lower than that of 9-CN-anthracene (1), which favorably increases the temperature gap between Tonset and Tm-A and prevents the reabsorption of thermal energy by the melting of anthracene. The lower Tonset values also indicate the smaller AG* of cycloreversion for compounds 2-4, achieved by the functionalization at the 10-position.

[0120] All compounds 1 -4 display substantial energy storage densities (AGstorage), both per molecule and per mass, comparable to those of norbornadienes and phase-transition MOST compounds based on azo(hetero)arenes. These values of up to 102 kJ / mol and 221 J / g, significantly larger than those of styrylpyryliums (max. 42 kJ / mol and 51 J / g), are attributed to the intrinsically weaker C-C bonds of dianthracenes and the additional exothermic events associated with solid-state phase transitions. Gibbs free energy of activation (AG*) and half-lives for the thermal cycloreversion of dianthracenes were measured using DSC (FIG. 34-FIG. 37, Table 7). Notably, the AG* and AGstorage values of dianthracenes were nearly identical for dianthracene 4-D and similar for dianthracene 2-D and dianthracene 3-D (Table 1), in contrast to styrylpyryliums that exhibit much greater AG* than AGstorage (about 3 times). Thus, without being bound by theory, it is believed that this modest difference between AG* and AGstorage allows self-activated cycloreversion upon the initial triggering of dianthracenes, as long as the released heat is effectively transferred to the neighboring unreacted dianthracenes.

[0121] To verify this hypothesis, local thermal triggering experiments were performed on compact solid pellets of the compounds (FIG. 4A). The temperature profiles of anthracenes (exemplified with anthracene 3-A in FIG. 4B) represent the slow and stagnating heat conduction through the solid organic compounds. In contrast, the pellet of dianthracene 3-D undergoes a rapid temperature increase within 2 minutes of local thermal triggering at position a, and the released heat is quickly transferred to positions b-e, resulting in the sharp increase of temperature throughout the whole pellet and reaching the maximum temperature of 165 °C. After the heat release process, the pellet spontaneously cooled to the baseline temperatures, via heat dissipation to the environment, consistent to those of the pellet of anthracene 3-A. The abrupt increase of temperature for the pellet of dianthracene 3-D, far exceeding the baseline temperatures, is thus attributed to the exothermic process of [4+4] cycloreversion of(2024-051-02) dianthracenes. It is believed that this is the first experimental observation of such a cascade of thermally-triggered exothermic process throughout MOST compounds. A prior report on a solid-state MOST system consisting of an azobenzene polymer, illustrated the thermal triggering experiment for a polymer pellet, which requires heating the entire pellet up to 150 °C using an external heat source. The released heat from the polymer yields relatively small temperature differences (max. 10 °C) from the baseline, due to the small AHstorage (less than 100 J / g) and fast thermal equilibrium with the heat source set at the high temperature. Most importantly, no heat cascade had been observed, which makes the donor-acceptor 9-CN-anthracene derivatives a unique class of MOST compounds that can self-activate the heat release from the entire solid materials upon the initial triggering. The optical and IR images of the pellets anthracene 3-A and dianthracene 3-D are shown in FIG. 4D and FIG. 4E, corresponding to the temperature profiles in FIG. 4B and FIG. 4C.

[0122] To investigate the rapid heat cascade process, the propagation of heat front on the pellet was analyzed (FIG. 5 A). The bottom of the pellet (position a) starts to release heat at 100 sec, and the heat transfer to the top of the pellet (position e) is completed in 10 seconds (FIG. 5B). The net temperature change of the pellet, achieved by the exothermic cycloreversion, is shown as AT (D-A) that is as large as 120 °C, underlining the high potential of the MOST system as a renewable heating material for a thermal battery application. The rate of spatial heat propagation (vprop) through the solid pellet is measured to be 0.7 mm / s for compound 3 (FIG. 5C). The successful observation of self-activated heat release for compounds 2-4 is summarized in Table 2 and illustrated in detail in FIG. 38-FIG. 42.Table 2. Thermal parameters for the self-activated heat cascade process.Trev: peak temperature of cycloreversionTtrig: triggering temperature set for the heat source tind: induction period for thermal triggeringVprop : rate of spatial heat propagationTmax: maximum temperature detected on each pelletTm-A: melting point of anthracene monomerAG storage: energy storage density

[0123] It was found that the induction period for thermal triggering (tmd) is even shorter and Vprop is higher for compound 4, due to its lower AG* value for cycloreversion and more facile(2024-051-02) heat release compared to 3. For compound 2, its low TOnset and large AGstorage enable a rapid cascade of reversion throughout the pellet, desipte its high AG* value. The maximum temperature detected on each pellet (Tmax) is also higher for compounds 2 and 4 than compound 3, highlighting the tunability of the temperature profile and heat release kinetics by molecular design. Since there are significant gaps between the thermal reversion temperature (Trev) and Tm~ A for compounds 2-4, the released heat from cycloreversion is not reabsorbed by the melting process of the resulting anthracenes. The pellets of compounds and 2 and 4 undergo noticeable shape changes to vertical ovals upon the self-activated heat release (FIG. 38- FIG. 39), which is attributed to the larger volume change of compounds 2 and 4 (4% and 3%, respectively) than compound 3 (0.3%) during the cycloreversion.

[0124] Infrared (IR)-laser triggering experiments were designed using pellets of dianthracene 3-D (FIG. 5D) to confirm that a short-term triggering of a smaller area on the pellets can lead to heat propagation. An IR-laser (A, of 1200 nm, power of 630 mW, and approximate spot size of 29 pm) was used to trigger an off-center position of the pellet of dianthracene 3-D for 6-8 seconds, which resulted in the radial propagation of heat front and the completion of heat release in less than 20 seconds. The similarity in the heat propagation kinetics triggered by the transient laser irradiation and by the heat conduction from a localized heat source indicate that only localized thermal triggering is necessary to convert a small portion of MOST materials above a threshold, which is followed by the self-cascading heat transfer and complete conversion. The optimization and mechanistic studies of the scale, triggering threshold, and geometry of solid materials are the subjects of ongoing research. It is notable that compound 1, unlike compounds 2-4, fails to undergo self- activated heat release, due to the small gap between Trevand TmA (Table 2), which led to the melting of anthracenes by the released heat (FIG. 5E). The temperature profiles of the pellet of dianthracene 1-D do not display any peaks or heat propagation features similar to those of 1-A (FIG. 5F), as a result of the reabsorption of heat by melting of anthracene (FIG. 5G). Based on the contrast between the unsuccessful (compound 1 ) and successful (compounds 2-4) heat release experiments, the temperature gap between Tievand Tm-A should be at least 80 °C to prevent the undesirable melting of anthracenes, for the size of pellets tested (300 mg, 1 cm in diameter).

[0125] Lastly, a theoretical investigation of the energetic changes during the cycloreversion of dianthracenes was performed. First, d (C9-C10*) was defined as the distance between a 9-position of an anthracene and a 10-position of the counterpart in a dimer or monomer pair. While changing the d (C9-C10*) by 0.1 A in the range from 1.5 A to 3.4 A, a structural optimization of the paired molecules was performed (FIG. 6A). The most energetically(2024-051-02) stable structure within this range was obtained at d (C9-C10*) of 3.4 A for each compound, so the energy of this structure was used as a reference point. Compounds 1-4 display the maximum relative energy when d (C9-C10*) equals 2.4 A, and the corresponding structures were assigned to the approximated transition states. The results suggest that the introduction of 9-CN and electron donating groups on the 10-position increases AGstorage and decreases the AG of thermal cycloreversion, corroborating the experimental observations (FIG. 6B). Consistent with the observation of the relative AGstorage among 1-CN, 2-CN, and 9-CN anthracenes (FIG. 7-FIG. 9), compounds 2-A, 3-A, and 4-A that undergo a large reduction in the effective conjugation upon dimerization display larger AGstorage compared to anthracene and compound 1. Without being bound by theory, it is hypothesized that the relatively destabilized dimers 2-4 would undergo facile thermal cycloreversion, exhibiting lower AG* values.

[0126] A solid-solid system has been discovered where the donor-acceptor anthracene of Formula (I) produces a dianthracene compound of Formula (II) via a [4+4] photocycloaddition in the solid state. The dianthracene compound of Formula (II) can revert to the donor-acceptor anthracene of Formula (I), to release energy in the solid state.(I) (II)

[0127] In Formulas (I) and (II), each is independently Ci-4 alkyl, Ci-4 alkoxy, or a combination thereof. In an aspect, each R is the same. In another aspect, each R is the same, and is methyl or methoxy.

[0128] In an embodiment a composition comprises, consists of, or consists essentially of, the donor-acceptor anthracene of Formula (I), the dianthracene compound of Formula (II), or a combination thereof. The composition can consist of the donor-acceptor anthracene of Formula (I), the dianthracene compound of Formula (II), or the combination thereof in a substantially pure form, such as at least about 95% pure, at least about 97% pure, at least about 98% pure, or at least about 99% pure.

[0129] Preferably the composition is a solid composition. The solid composition can be of any configuration. Examples of configurations that can be used include, but are not limited to, powders, disks, pellets, fibers, and the like. The solid compositions are especially use in thermal(2024-051-02) storage devices as described below. As used herein, a “solid composition” does not substantially melt or flow under conditions of ordinary use, for example in a thermal storage device. For example, the composition does not substantially melt or flow at a temperature of 200 °C or less, or 180 °C or less, or 150 °C or less, or 120 °C or less.

[0130] Exemplary components include, without limitation, trace amounts of organic solvents as well as organic phase-change materials (PCM), provided that the type or amount of any additional solvent or PCM does not significantly adversely affect the solid state of the composition as a whole.

[0131] Exemplary PCMs include higher molecular weight alkanes (aliphatic hydrocarbons), fatty acids, fatty alcohols, fatty acid esters, paraffin waxes, polyethylene glycols, sugar alcohols, salts of fatty acid, and combinations thereof. They can have an origin derived from animal fat, animal grease, vegetable oil, vegetable wax, synthetic compounds, or a combination thereof.

[0132] In certain embodiments, the organic phase-change material comprises one or more of aliphatic hydrocarbons, fatty acids, fatty alcohols, or combinations thereof. The aliphatic hydrocarbons, fatty acid, and fatty alcohol phase change those having a C12-30 hydrocarbon chain. The hydrocarbon chain can be saturated or unsaturated, although it is preferably saturated. Suitable fatty acids include those occurring naturally in triglycerides as well as synthetic fatty acids. Fatty acids can be obtained from the hydrolysis of triglycerides, as is well known in the art. Exemplary fatty acids include, but are not limited to oleic acid, palmitic acid, linoleic acid, palmitoleic acid, stearic acid, tridecanoic acid, pentadecanoic acid, heptadecanoic acid, nonadecanoic acid, caprylic acid, capric acid, and lauric acid as well as combinations of two or more thereof. Frequently available fatty acids can be hydrates and hydrogenated acids of any of the preceding acids.

[0133] The fatty acid esters can be formed with alcohols, diols, and / or polyols, including mono-, di- or triglycerides of glycerol, esters of pentaerythritol, polyesters of polyhydric alcohols, esters of methanol, ethanol, propanol, butanol, isobutanol, pentanol, hexanol, cyclohexanol, esters or diesters of ethylene glycol and / or combinations of two or more thereof. The fatty acid esters can be mono-, di- or triglycerides of glycerol, and / or combinations thereof. Additionally, the fatty acid esters can be ester of higher fatty acids with higher monohydric alcohols. Esters of fatty acids can be formed by a variety of methods known in the art including transesterification or hydrolysis followed by esterification. The advantage of this approach is that relatively pure components having targeted melting point temperatures can be synthesized. For example, a multitude of esters of oleic acid can be formed by complete esterification with(2024-051-02) methanol, ethanol, propanol, butanol, isobutanol, pentanol, hexanol, cyclohexanol, phenol, ethylene glycol, glycerin, diethylene glycol, and many more. To a first approximation, the oleate esters formed with each of these esters will result in different melting point temperatures. Furthermore, mixtures of two of the esters have the potential to form mixtures having relatively narrow and useful melting point temperature ranges.

[0134] Exemplary fatty alcohols for use as PCMs include, but are not limited to, dodecanol (lauryl alcohol), tetradecanol (myristyl alcohol), hexadecanol (cetyl alcohol), and octadecanol (stearyl alcohol).

[0135] In another aspect, the phase change material is a long chain alkane or alkene with minimal branching, or no branching; of these, long chain alkanes with minimal branching are preferred. These hydrocarbons are able to solidify at temperatures above 0 °C, and can absorb heat. Alkanes ranging in carbon length from Cis-30 may be useful. Exemplary alkane PCMs of the present application include, but are not limited to long chain aliphatic such as tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, icosane, henicosane, docosane, tricosane, tetracosane, pentacosane, hexacosane, heptacosane, octacosane, nonacosane, and triacontane.

[0136] Other PCMS that can be used include natural or synthetic polymers such as poly(tert-butyl acrylate), poly(isopropyl methacrylamide), hydroxypropyl cellulose, hydroxymethyl cellulose, poly(oxazoline), and poly(organophosphazenes). Sugar alcohols can be used, such as xylitol, pentraerythritol, trimethylolethane, erythrite, mannitol, neopentyl glycol, or a combination thereof.

[0137] The optional organic PCM can be present, if used, in an amount of about 1 to about 30 weight percent (based on the total weight of the composition), again provided that the composition as a whole remains solid. For example, the organic phase-change material can be present in the composition in an amount of about 5 to about 20 weight percent, or about 5 to about 15 weight percent.

[0138] In another aspect, the composition can further comprise a natural or synthetic polymer in which the compound of Formula (II), specifically Formula (la), is dispersed. The polymer is preferably selected to also be a solid that does not substantially melt or flow under conditions of ordinary use, for example in a thermal storage device, such as at a temperature of 200 °C or less, or 180 °C or less, or 150 °C or less, or 120 °C or less. The polymer is further selected to allow the transmission of light, in particular visible light or sunlight when in the form used, for example a film.(2024-051-02)

[0139] The polymer can be, for example, a polyolefin, a polyacrylate, a poly methacrylate, a polymethyl methacrylate, a polyester, a polystyrene, a polyamide, a polyurethane, a polypropylene, a polyethylene, a polytetrafluoroethylene, polychlorotrifluoroethylene, a copolymer of the foregoing or a combination thereof. Such compositions can be used as functional coatings or functional fabrics. Polymer-based molecular solar thermal system (MOST) can be realized by compounding into existing polymer matrices of the types described above. Further substituents, like carbazole or benzophenones may be attached to the polymer to facilitate the photoisomerization process.

[0140] The composition can further comprise other components, provided that such components do not substantially adversely affect the desired properties of the composition, for example transparency to sunlight or visible light. Other components can be, for example, antioxidants, thermal stabilizers, mold release agents, or the like.

[0141] The compounds and compositions as described herein can be used to form thermal storage devices, as well as components for thermal storage devices. Although one goal of the compounds and compositions is to eliminate a need for encapsulation or a support, composite structures may be used to form subcomponents of thermal storage devices. In an aspect, a composite structure includes a porous structural component and the donor-acceptor anthracene of Formula (I), the dianthracene compound of Formula (II), or the combination thereof. Exemplary porous structural components include an aerogel, a xerogel, a nanotube, metal organic framework, covalent organic framework, zeolite, graphene, graphene oxide, graphite, transition metal dichalcogenide, or hexagonal boron nitride.

[0142] In another embodiment, a thermal storage system includes the composition or the composite structure. Again, preferably the composition is a solid composition, and more. Optionally, the thermal storage system can include a plurality of the compositions, a plurality of the composites, a plurality of the light sources, or a combination thereof. In accordance with yet another embodiment, the thermal-storage device may include the donor-acceptor anthracene of Formula (I), the dianthracene compound of Formula (II), or the combination thereof as described herein, where the compound or composition is retained on a substrate. The substrate may optionally include a thermal conducting element to facilitate heat transfer from the compound or composition to another article or the ambient environment during exothermic phase change, as discussed herein. Thermal storage devices / systems that include a compound or composition as described herein can take any of a variety of configurations.

[0143] In an exemplary thermal storage system, the composition or the composite structure can be enclosed by compartment comprising an optically transparent portion (e.g., a(2024-051-02) polymer or a glass) to allow the transmission of sunlight or light in the visible range to impinge on the composition or the composite structure. In accordance with another embodiment, a thermal conducting element forms a portion of the enclosure or the porous structural component.

[0144] The thermal storage system can further include one or more of a light source that emits a wavelength of light effective to induce [4+4] cycloaddition of the compound of Formula (I); a switch that controls operation of the light source; and either a power source or a connector adapted for connecting the thermal storage system to a power source. The switch can be a thermo-sensitive switch or a manually operable switch. The power source can be a battery.

[0145] The thermal-storage device may optionally include a light source, as well as accompanying circuitry controls, to allow the light source to illuminate the donor- acceptor anthracene of Formula (I), and thereby induce the cycloaddition.

[0146] In accordance with one embodiment, a thermal-storage device may include a plurality of composition structures and a plurality of light sources. In an embodiment, the light source(s) are LED light source(s).

[0147] An example of a thermal storage device is a device that is configured to facilitate heat transfer to engine oil or to stored water in accordance with the embodiments described and / or illustrated in PCT Application Publ. No. WO 2020 / 227227, which is hereby incorporated by reference in its entirety.

[0148] Another example of a thermal-storage device is a solar energy collector, which can optionally include a wavelength converter or an energy converter. Non-limiting examples of energy storage devices, including solar energy storage devices, are described in International Application Publication Nos. WO 2019 / 106029 Al and WO 2016 / 097199 Al; U.S. Application Publication No. 2018 / 0355234 Al; Moth-Poulsen et al., “Molecular Solar Thermal (MOST) Energy Storage and Release System,” Energy Environ. Sci.5:8534-8537 (2012); and Kashyap et al., “Full Spectrum Solar Thermal Energy Harvesting and Storage by a Molecular and Phase- Change Hybrid Material,” loule 3( 12):3100-3111 (2019), each of which is hereby incorporated by reference in its entirety.

[0149] In these systems, it can be desirable to move the composition within the system from a location where the donor-acceptor anthracene of Formula (I) is exposed to photoenergy, to a separate location where the dianthracene compound of Formula (II) can be stored and, later, converted to donor- acceptor anthracene of Formula (I) when harvesting the stored energy. Movement of the compounds or compositions can be carried out using conveyers, belts, and the like.(2024-051-02)

[0150] The donor-acceptor anthracene of Formula (I), the dianthracene of Formula (II), or the combination thereof, or the composite structure can be used as a thermal-storage material. In particular, a method of storing energy includes providing an energy storage device comprising the donor- acceptor anthracene of Formula (I) as a thermal-storage material; activating, preferably photoirradiating the donor- acceptor anthracene of Formula (I) to produce the dianthracene of Formula (II); and storing the dianthracene of Formula (II) for a period of time.

[0151] The activating by photoirradiating, includes exposing the donor-acceptor anthracene of Formula (I) of the energy storage device to sunlight or light having a wavelength in the visible spectrum.

[0152] The light energy stored during the activation, i.e., the photoirradiation, can be released as thermal energy by inducing the dianthracene compound of Formula (II) to revert back to donor- acceptor anthracene of Formula (I), to release energy stored during the photoirradiation. At least two cycles of the photoirradiating, storing, and inducing can be performed.

[0153] By including one or more compounds of Formula (I), it is possible to use a wider range of wavelengths when irradiating the system. Activating is by heat and / or photoirradiation, which can involve photon absorption, such as by using sunlight or fluorescent light. Photoirradiation is preferred, with or without the application of heat. Depending on the compound(s) included in the system, the optimal wavelength of the irradiation can be determined and then utilized. Regardless of the manner of activation, the step involves solid-to- liquid phase change of the compound or composition described herein.

[0154] The period of energy storage may be cyclical, such as on a daily cycle where the storage period may be several hours (e.g., up to 12 or 18 hours), but it may be desirable to extend the period of storage such that it is acyclical (e.g., for as long as a user desires). As indicated in the examples, several of the compounds can store energy for long periods of time over several days, several weeks, and over several months. In an embodiment, storing can be carried out for a period of time exceeding 12 hours. For example, storing is carried out for a period of time exceeding 24 hours, 36 hours, 48 hours, or 72 hours. Alternatively, storing can be carried out for a period of time from about 1 day up to about 21 days, about 2 days up to about 18 days, about 2 days up to about 14 days, about 3 days up to about 14 days, about 3 days up to about 10 days, or about 3 days up to about 7 days.

[0155] Having stored the energy for later use, the method also includes inducing the dianthracene of Formula (II) to revert back to the donor-acceptor anthracene of Formula (I),(2024-051-02) thereby releasing energy stored during the photoirradiation. The energy released can be collected and / or transferred, if desired.

[0156] The inducing step can optionally be by application of appropriate energy, for example heat, infra-red exposure, or a combination thereof.

[0157] In an embodiment, the induced energy release by the compounds of Formula (II) is at least 80 kJ / mol, or at least 100 kJ / mol, or at least 120 kJ / mol, up to 200 kJ / mol. For example, the induced energy release by the compounds of Formula (II) can be at least 90 kJ / mol, or at least 100 kJ / mol, up to 150 kJ / mol, or up to 1400 kJ / mol, or up to 130 kJ / mol. In another aspect, reversion of the dianthracene of Formula (II) to the donor- acceptor anthracenes of Formula (I) discharges energy in an amount from 80 kJ / mol to 200 kJ / mol, or 90 to 150 kJ / mol, or 90 to 130 kJ / mol.

[0158] Based on the foregoing, it should be apparent that it is contemplated that the method can be carried out repeatedly, with multiple cycles of the activating (preferably photoirradiating), storing, and inducing steps.

[0159] The compounds of Formulas (I) and (II) have a ground state (OFF state) that is a solid. Due to exposure to light of appropriate wavelength or high temperature, the compounds of formula (I) react via [4+4] cycloaddition, and irradiation (using light of appropriate wavelength) changes the switch to a metastable state (ON state) and “locks” the dianthracene form. The step of irradiation can be carried out for a period of time sufficient to lock the dianthracene form in the metastable state; typically, this is from several minutes to several hours depending on the compound, the light source, and the intensity of the light. The stabilized dianthracene form can then be stored for a desired period of time and allowed to cool to ambient temperature, and it can optionally be moved from one location (where it was activated to the ON state) to another location, such as a reservoir or a location where release and heat recovery occurs. For the release, irradiation and / or heat induces a chemical transformation that reverts the compound to the initial state, e.g., where the dianthracene compound reverts to the donor-acceptor anthracenes (i.e., turning off the switch).

[0160] In addition to the foregoing utilities described above, organic photoswitches that undergo reversible changes upon light irradiation have been integrated into various materials for applications, including light-driven actuation, drug delivery, sensing, and optical memory (Han et al., “Optically-controlled Long-term Storage and Release of Thermal Energy in Phase-change Materials,” Nature Communications 8:1446 (2017), which is hereby incorporated by reference in its entirety). These additional utilities are also contemplated for the compounds and compositions described herein.(2024-051-02)

[0161] The system including the donor- acceptor anthracene of Formula (I), the dianthracene compound of Formula (II), or the combination thereof as described herein on has immediate commercial applications in several areas due to its enhanced energy storage capabilities and efficient heat propagation features. The technology is well-suited for use in thermal batteries, where its rapid and efficient heat release can be employed to deliver controlled thermal energy on demand. This makes it particularly valuable in sectors such as electric vehicles, where thermal management is crucial for battery efficiency and cabin heating. Additionally, its ability to store and release heat efficiently positions it as an innovative solution for renewable energy systems, enhancing the utility of solar energy by storing excess heat during peak sunlight hours and releasing it as needed.

[0162] The system including the donor- acceptor anthracene of Formula (I), the dianthracene compound of Formula (II), or the combination thereof as described herein further has potential in smart buildings for climate control. The thermal batteries could be used for heating the space and water of buildings, particularly during the energy demand peak hours in the evening. Furthermore, the self-activating heat release also opens opportunities for developing portable heating devices, providing on-the-go warmth for food heating, outdoor activities, emergency situations, or in environments where traditional energy sources are unavailable.

[0163] The systems as described herein provide a number of advantages over the art, including enhanced energy storage densities. The system significantly improves energy storage densities, both per molecule and per mass. The derivatized 9-cyanoanthracene compounds demonstrate maximum energy storage capacities of 102 kJ / mol and 221 J / g. These figures are notably higher than those observed in styrylpyrylium-based systems, which have maximum values of 42 kJ / mol and 51 J / g. The increased energy storage capacities in the derivatized 9- cyanoanthracene compounds can be attributed to the intrinsically weaker C-C bonds in dianthracenes and the additional exothermic events associated with solid-state phase transitions. This advancement places the derivatized 9-cyanoanthracene compounds on par with or superior to established MOST compounds, such as norbornadienes and azo(hetero)arene-based phasetransition systems.

[0164] Another advantage relates to optimized activation energy and reaction kinetics. The detailed measurements of the Eaand half-lives for the thermal cycloreversion of dianthracenes using DSC as described above show that the Eavalues for the compounds are similar to their AHstorage, unlike the values seen in styrylpyrylium systems, where Easignificantly exceeds AHstorage. This unique characteristic suggests that derivatized 9-cyanoanthracene(2024-051-02) compounds can achieve self-activated cycloreversion upon initial triggering, provided that the released heat is efficiently transferred to the neighboring unreacted dianthracenes. This feature allows a more efficient and potentially autonomous thermal response, enhancing the practical utility and efficiency of the energy release process.

[0165] The systems further provide rapid and efficient heat propagation for thermal applications. The above-described investigations into the heat propagation within the pellets showed rapid heat transfer, completing within seconds, and achieving significant temperature increases (up to 120 °C), demonstrating the potential of the anthracene-based MOST system as a renewable heating material for thermal battery applications. This rapid spatial propagation, measured at a rate of 0.7- 1.2 mm / s, is important for applications requiring quick and efficient heat distribution. Furthermore, IR-laser triggering experiments confirmed that minimal initial thermal input can initiate comprehensive heat release across the material, underlining the efficiency and effectiveness of the molecular design of the anthracene-based system in practical applications.

[0166] The invention is further illustrated by the following examples, which are nonlimiting.1. Material and Methods a. General materials

[0167] Commercial sources provided all reagents and initial materials, which were used as received unless specified otherwise. Deuterated solvents were acquired from Cambridge Isotope Laboratories, Inc. and were utilized without any modifications.1H and13C NMR spectra were collected using a Varian INOVA 400 spectrometer and an AVANCE NEO 400 NMR, both operating at frequencies of 400 MHz for1H NMR and 100 MHz fornC NMR. Chemical shifts are expressed in parts per million (ppm) with respect to tetramethylsilane (TMS), employing the solvent's residual peak as a secondary reference. ESI mass spectra were performed on a Waters Quattro II ESI mass spectrometer. LEDs were sourced from Thorlabs, Inc., including the models M365L3 (365 nm,14.4 pW / mm2, 1290 mW); M405L4 (405 nm, 14.53 pW / mm2, 1300 mW). b. UV-vis absorption spectroscopy in solution

[0168] UV-Vis absorption spectra for compounds 1-A to anthracene 4-A and dianthracene 1-D to dianthracene 4-D were recorded using a Cary 60 Bio UV-Vis spectrophotometer, employing a UV Quartz cuvette with a 10 mm path length. Dimers were dissolved in dichloromethane (DCM), allowing for the observation of their gradual conversion back to monomers. The concentration was maintained at approximately 5 xl0‘5M for 1-A to anthracene 4-A and 2.5 x 10'5M for the dimers dianthracene 1-D to dianthracene 4-D.(2024-051-02) c. UV-vis absorption spectroscopy in solid

[0169] Thin-film samples of compounds 1-3 were prepared by adding 0.5 mg of their monomers on clean glass slides (2.5 x 2.5 cm2) and heating them to molten samples. Then the melted samples were covered by another glass slide to spread. The films were slowly cooled to room temperature for solid state UV-Vis characterization. The thickness of thin films was measured using Zeta-20 Optical Profilometer. d. Solid state NMR

[0170] Solid-state NMR experiments were conducted on a Bruker Neo Avance 400WB spectrometer at resonance frequencies of 400 MHz for1H and 100 MHz for13C, using a 4 mm magic-angle spinning (MAS) double resonance probe head. 50-60 mg of each sample was packed in a 4 mm outer diameter zirconia rotor with a 3 mm tall glass spacer at the bottom and a Kel-F cap at the top. The JI / 2 pulse length on]H was 3.6 ps and on13C was 4 ps. A rotation- synchronized Hahn echo was used before detection to avoid baseline distortions caused by deadtime. Protons were decoupled with TPPM at |yB 1 | / 2?r = 95 kHz before and with SPINAL-64 at |yB 1 | / 2TI = 85 kHz after signal detection.13C chemical shifts were externally referenced to13COO of a-glycine at 176.49 ppm.13C NMR spectra of all samples were acquired at 14 kHz using 'H-^C composite pulse multiple cross polarization (multiCP) with 4 blocks of 1.1 ms of ramped CP separated by 5 s ofrepo larization time for a more quantitative transfer of 1H magnetization to13C. All experiments were conducted in ~50 °C from friction heating of 14 kHz MAS.

[0171] Due to long1H spin-lattice relaxation time of all samples, 30 s instead of the usual 4 x Tin was used as recycle delays for all dimer samples (except for the slightly faster relaxing CHs-deriv ati ve with 10 s recycle delay), in order to minimize dimer reversion during signal averaging. Each dimer spectrum was signal averaged for 30 minutes for minimal dimer reversion and reasonable signal- to-noise ratio. The monomers were generated directly in the NMR rotors after their corresponding dimers completely reverted after > 10 h. For the monomers, a recycle delay of 120 s was used, with 10-12 h signal averaging. For the monomers, spectra were also measured after recoupled dipolar dephasing achieved by two periods of 30 ps without]H dipolar decoupling flanking the n pulse of the Hahn echo, to distinguish signals of carbons not bonded to hydrogen (little dephasing, to >90%) and CH3 groups (dephasing to 57%) from those of C-H moieties, which undergo nearly complete dephasing. e. Differential scanning calorimetry (DSC)

[0172] DSC analysis was conducted using a DSC 250 instrument from TA Instruments, which was equipped with an RSC 90 cooling component. The samples underwent a protocol(2024-051-02) where they were initially heated to a temperature range between 180-220 °C, then cooled down to -90 °C at a rate of 10 °C / min. An exception was made for compound dianthracene 2-D, which was processed differently; it was run at a slower rate of 2 °C / min throughout the cooling and heating cycle. f. Thermal reversion kinetics by DSC

[0173] Thermal D^A reversion kinetics were determined using established isothermal DSC methods. Under isothermal conditions, the degree of an exothermic reaction is directly proportional to the amount of heat evolved.

[0174] i indicates incremental measurements, a indicates fractional conversion or extent of the reaction, AH,- indicates partial heat generated, and \Hmindicates the total heat of the reaction. AHrxnis used as an approximation of AGrafor the solid-state reaction.

[0175] In isothermal DSC, partial heat AH, is obtained from the area under the exothermic peak.(Equation 2)dH / dt indicates heat flow, and / is time in seconds.

[0176] Dianthracenes 1-4 (3.532 ± 0.008 mg) was hermetically sealed in an aluminum pan. The DSC cell was pre-heated to the target isothermal temperature and stabilized for at least 5 minutes. The dianthracenes sample was then quickly loaded into the cell and data collection was immediately initiated. In the case of dianthracene 1-D, the DSC cell was pre-heated to 100 °C, the highest standby temperature available for this instrument. After loading the sample and initiating the data collection, the sample was quickly ramped to the target isothermal temperature, and the isothermal experiment proceeded as normal. The reversion of dianthracenes 1-4 was monitored at three different isothermal temperatures.

[0177] From the isothermal DSC curve, heat flow dH / dt was obtained as a function of time, then integrated to calculate the partial heat AH, (Equation 2). The total heat AHrxn was derived from the non- isothermal DSC curve2 at heating rates of 2 °C / min for dianthracene 1-D, and 10 °C / min for dianthracene 2-D, dianthracene 3-D, and dianthracene 4-D. Subsequently, fractional conversion a of each compound at three different temperatures was calculated using Equation 1.

[0178] An exponential fit of fractional conversion a as a function of time was performed to determine the experimental rate constant k of the reversion. The activation energy Eaof the reversion was obtained from the Arrhenius plot of In k versus the reciprocal of temperature(2024-051-02)(Equation 3) wherein k indicates the rate constant, Eais the activation energy, R is the molar gas constant (8.314 J / K-mol), T is the temperature at which the compounds were measured, and A is the preexponential factor or Arrhenius factor.

[0179] Additionally, the Gibbs free energy of activation AG* of the reversion was determined from the Eyring plot of In (k / T) versus the reciprocal of temperature(Equation 4) wherein AH* is the enthalpy of activation, ke is the is the Boltzmann’s constant (1.381 x 10‘23J / K), h is Planck's constant (6.626 x 10'34J s), and A.S'2is the entropy of activation. The enthalpy of activation AH* and the entropy of activation AS* were determined from the slope and intercept of the linear fit, respectively.

[0180] The Gibbs free energy of activation was then obtained from Equation 5(Equation 5) wherein AG* is the Gibbs free energy of activation.

[0181] The thermal half-life rl / 2 of dianthracenes 1-4 was determined by first extrapolating the rate constant k at T = 298 K from the Arrhenius plot (Equation 3). The rate constant k was then applied to the exponential fit of fractional conversion a as a function of time at a = 0.5 to give rl / 2 at T = 298 K. g. IR thermal imaging analysis

[0182] IR imaging was performed using an infrared camera (Nippon Avionics Co., LTD.) to monitor heat release from heated pellets of anthracenes 1-4 and their respective dianthracenes. The thermal imaging videos were analyzed with InfReC Analyzer NS9500 software. Five points on the surface of each pellet — defined by their coordinates relative to the center point (0, 0) of the pellet: point a (0, -4 mm), point b (0, -2 mm), point c (0, 0 mm), point d (0, 2 mm), and point e (0, 4 mm) — were selected for analysis. The temperatures at these points were recorded and plotted as a function of time.

[0183] To decouple the effects of heating, the temperature differences AT (D-A) between anthracenes 1-4 and their corresponding dianthracenes were plotted over time. Additionally, to assess spatial heat propagation vprOp through the solid pellets, the vertical distances from point a to each subsequent position were plotted against the time taken for those points to reach(2024-051-02) specified temperature differences. Three distinct temperatures (30 °C, 60 °C , and 90 °C ) were chosen for this analysis. Each temperature data set was fitted to a linear model, where the slope of each line represents the rate of heat propagation. The average of these slopes was calculated to provide the rate of heat propagation vpropfor each compound. h. IR-laser triggered cycloreversion

[0184] A pellet of compound dianthracene 3-D (300 mg, 1 cm in diameter) was irradiated with a femtosecond laser (Light Conversion Carbide CB3-40W with an Orpheus-HP- SH optical parametric amplifier) tuned to a wavelength of 1200 nm. The beam was focused to a spot size of r = 29 m using a gold coated off-axis parabolic mirror (RFL = 76.2 mm), and the sample was placed upon a stage with the focal point of the beam approximately hitting the front surface of the pellet. The power was gradually increased using a neutral density filter wheel until just high enough to trigger a response within the sample, approximately 630 mW. A fresh pellet of dianthracene 3-D was then irradiated using this power at an off-center position while monitoring the heat release with IR imaging (Nippon Avionics Co., LTD.). Heat propagation was manually observed after 6-8 seconds of exposure and the beam was immediately blocked. The heat release was completed within 20 seconds. After allowing the sample to cool back down to room temperature, the resulting pellet of anthracene 3- A was then irradiated again with the same conditions, and no heat propagation was observed. i. Computational methods

[0185] All density functional theory (DFT) calculations were performed using Becke’s three-parameter hybrid exchange functionals, the Lee- Yang-Paar correlation functional, and Grimme’s D3 dispersion force correction method (B3LYP-D3)3,4 with the 6-31 + G** basis set implemented in the Gaussianl6 Revision B.015suite of programs with default thresholds and algorithms. Geometry optimization of anthracenes and anthracene dimers were performed in vacuum under standard conditions. The stationary points were optimized without any symmetry assumptions and characterized by frequency analysis at the same level of theory (the number of imaginary frequencies, NIMAG, was 0).

[0186] Optimization of the local minimum structure was performed under constraint conditions fixing the distance between C9-C10*. Among the local minimum structures optimized at 0. 1 A intervals within the range of 1.5 to 3.4 A, the most unstable structure was approximately considered as the transition state structure. The zero-point corrected Gibbs Free energy calculated by frequency analysis of the optimized structure was used as the relative energy value. AGcaic was defined as the energy difference between the optimized structure with a C9-C10* distance of 3.4 A and the optimized anthracene dimer. AG*Caic was defined as the(2024-051-02) energy difference between the optimized transition state structure and the optimized anthracene dimer. Cartesian coordinates (A) of all optimized structures are available in a separate attachment (.txt). j. Powder X-ray diffraction (PXRD) measurements

[0187] Powder X-ray diffraction (PXRD) patterns were obtained using a Broker D8 diffractometer with a Copper X-ray source (X, = 1.5418 A) at 40 kV and 40 mA. Prior to PXRD analysis, the sample was ground carefully to produce even powders.2. Computational Studies

[0188] Table 3. AGcalc(kJ / mol) and C9-C10* distance (A) of anthracene dimer calculated at theB3LYP- D3 / 6-31+G(d,p) level of theory.3. Synthesis procedures of monomer and dimer

[0189] The reagent 1-A, which is purchased directly from Sigma- Aldrich, is used for dimerization studies.

[0190] ‘H NMR (400 MHz, CDC13) 5 8.68 (s, lHa), 8.44 (d, J = 8.7 Hz, 2Hb), 8.09 (d, J = 8.5 Hz, 2HC), 7.72 (t, J = 8.6 Hz, 2Hd), 7.59 (t, J = 7.6 Hz, 2He), 1.55 (s, H2O).

[0191] 13C NMR (101 MHz, CDCh) 5 133.32 (Ca), 132.75 (Cb), 130.64 (Cc), 128.98 (Cd), 128.96 (Ce), 126.37 (Cf), 125.31 (Cg), 117.29 (Ch), 105.45 (Ci).

[0192] HRMS (ESI-TOF) m / z: [M + H]+Calcd for C15H10N 204.0735; Found 204.0807.(2024-051-02)Synthesis of anthracene 2-AScheme 1. Synthesis of anthracene 2-A.

[0193] The cyanation at the 10-position of anthracene was adapted and modified from Lohaus et. a!6. In a flame-dried round-bottom flask, 6 g (31.21 mmol) of 9-methylanthracene was added. Dry toluene (200 mL) was then added under a nitrogen atmosphere. Chlorosulfonyl isocyanate (5.45 mL, 62.42 mmol) was added dropwise. The progress of the reaction was monitored by TLC. After the complete consumption of all 9-methylanthracene, the reaction mixture was filtered. The solid residue was dried under vacuum and directly used for the subsequent step. DMF (12.04 mL, 156.09 mmol) was added to the solid residue, and the mixture was sonicated for 5 minutes. The reaction mixture was extracted with ethyl acetate and water, followed by a brine wash, and then dried over sodium sulfate. Silica gel column chromatography was used to purify the product. The eluent used was a mixture of 2% ethyl acetate and 98% hexane (v / v). The overall yield after two steps was 39%.

[0194] *H NMR (400 MHz, CDCh) 3 8.47 (d, J = 8.6, 2Ha), 8.38 (d, J = 8.7, 2Hb), 7.73 (t, J = 8.6 Hz, 2HC), 7.64 (t, J = 8.9 Hz, 2Hd), 3.18 (s, 3He), 1.54 (s, H2O).

[0195] 13C NMR (101 MHz, CDC13) 6 138.16 (Ca), 132.87 (Cb), 129.40 (Cc), 128.36 (Cd), 126.19 (Ce), 126.07 (Cf), 125.38 (Cg), 117.74 (Cb), 104.29 (Ci), 14.83 (Cj).

[0196] HRMS (ESI-TOF) m / z: [M + H]+Calcd for CI6HI2N 218.0891; Found 218.0971.Synthesis of anthracene 3-AScheme 2. Synthesis of anthracene 3-A.

[0197] The synthesis of 9-methoxyanthracene was derived from a reported procedure 7, and its identity was confirmed by comparing the obtained 1H NMR spectra with the spectra(2024-051-02) published in the literature. The synthesized 9-methoxyanthracene was used directly for the cyanation reaction.

[0198] In a flame-dried round-bottom flask, 500 mg (2.40 mmol) of 9- methoxyanthracene was added. Dry toluene (20 mL) was then added under a nitrogen atmosphere. Chlorosulfonyl isocyanate (419.48 pL, 4.80 mmol) was added dropwise. The progress of the reaction was monitored by TLC. After the complete consumption of all 9- methoxyanthracene, the reaction mixture was filtered. The solid residue was dried under vacuum and directly used for the subsequent step. DMF (925 pL, 11.99 mmol) was added to the solid residue, and the mixture was sonicated for 5 minutes. The reaction mixture was extracted with ethyl acetate and water, followed by a brine wash, and then dried over sodium sulfate. Silica gel column chromatography was used to purify the product. The eluent used was a mixture of 6% ethyl acetate and 94% hexane (v / v). The overall yield after three steps was 21%.

[0199] !H NMR (400 MHz, CDCh) 5 8.45 (d, J = 8.7 Hz, 2Ha), 8.39 (d, J = 8.7 Hz, 2Hb), 7.73 (t, J = 7 Hz, 2HC), 7.63 (t, J = 7.6 Hz, 2Hd), 4.21 (s, 3He), 1.56 (s, H2O).

[0200] 1C NMR (101 MHz, CDCh) 8 157.72 (Ca), 134.69 (Cb), 129.11 (Cc), 126.18 (Cd), 125.75 (Ce), 124.18 (Cf), 123.15 (Cg), 117.46 (Ch), 101.27 (Ci), 64.11 (Cj).

[0201] HRMS (ESI-TOF) m / z: [M + H]+Calcd for CeHnNO 234.0841; Found 234.0915.Synthesis of anthracene 4-A4-Scheme 3. Synthesis of anthracene 4-A.

[0202] The synthesis of 9- acetoxy anthracene was derived from a reported procedure 8, and its identity was confirmed by comparing the obtained 1H NMR spectra with the spectra(2024-051-02) published in the literature. The synthesized 9-acetoxyanthracene was used directly for the cyanation reaction.

[0203] In a flame-dried round-bottom flask, 2.35 g (9.95 mmol) of 9-acetoxyanthracene was added. Then, 50 mL of dry acetonitrile was added under a nitrogen atmosphere. Chlorosulfonyl isocyanate (1.74 mL, 19.89 mmol) was added dropwise. The progress of the reaction was monitored by TLC. After the complete consumption of the 9-acetoxyanthracene, the reaction mixture was filtered. The solid residue was dried under vacuum and directly used for the subsequent step. To the solid residue, 3.84 mL (49.76 mmol) of dry DMF was added, and the mixture was sonicated for 5 minutes. Water was then added to the reaction mixture, and a workup was performed using ethyl acetate and water, followed by a brine wash. The mixture was then dried over sodium sulfate. The organic layer was dried under vacuum to obtain 9- hydroxy-10-cyanoanthracene of dark yellow color. Its identity was confirmed by comparing the obtained1H NMR spectra with the spectra published in the literature9.

[0204] 9-Hydroxy-10-cyanoanthracene exhibits instability when exposed to air, so we immediately proceeded with its use in the acetylation process to preserve its quality.

[0205] In a round-bottom flask, 200 mg (912.23 pmol) of 9-hydroxy-10- cyanoanthracene was combined with 862.30 pL (9. 12 mmol) of acetic anhydride, followed by the addition of 7.31 p l . (91.22 pmol) of pyridine. The reaction mixture was stirred for 30 minutes, then quenched with NaHCOv Subsequently, a workup was performed using ethyl acetate and water, followed by a brine wash. The organic layer was dried under vacuum and purified via silica gel column chromatography. The eluent used was a mixture of 8% ethyl acetate and 92% hexane (v / v) The combined yield after four steps was 11%.

[0206] !H NMR (400 MHz, CDCh) 5 8.43 (d, J = 8.7 Hz, 2Ha), 8.03 (d, J = 8.7 Hz, 2Hb), 7.73 (t, J= 6.6, 2HC), 7.61 (t, J= 7.8, 2Hd), 2.67 (s, 3He).

[0207] 13C NMR (101 MHz, CDCh) 8 168.83 (Ca), 147.08 (Cb), 133.94 (Cc), 129.17 (Cd), 127.18 (Ce), 125.69 (Cf), 123.64 (Cg), 122.31 (Ch), 116.93 (Ci), 104.12 (Q), 20.75 (Ck).

[0208] HRMS (ESI-TOF) m / z: [M + H]+Calcd for C17H12NO2 262.0790; Found 262.0864.4. Dimerization of anthracenes

[0209] To find an efficient photocharging method for anthracene derivatives, the three types of photoirradiation methods described below were compared.(2024-051-02) a. Sandwiched powder

[0210] 50 mg of 1-A powder was spread between two 10 cm xlO cm glass slides. 365 nm LED light was irradiated from the top of the sandwiched powder for 4 h.Suspension

[0211] 50 mg of 1-A and 5 ml of ethanol were added to a glass vial with an inner diameter of 25 mm. A 405 nm LED light was irradiated from the side of the vial for 4 h, while stirring the suspension with a magnetic stirrer. The irradiated solids were collected by filtration. This method was also applied for the dimerization of compounds 2 and 3. Compound 4 was irradiated in an ether suspension, according to the following procedure.

[0212] 300 mg of anthracene 4- A was suspended in 15 mL of diethyl ether, and the suspension was stirred for 5-6 hours under a 405 nm LED light. Over time, a white precipitate formed. This solid white precipitate, identified as a dimer, was subsequently filtered out using vacuum filtration. Unless otherwise mentioned, dimers ( 1-dianthracene 4-D) prepared by this method were used for various spectroscopic and thermal analysis.

[0213] !H NMR (400 MHz, CD2C12) 5 7.57 (d, J = 7.4 Hz, 4HA), 7.08 (m, 8HB,c), 6.87 (d, J = 7.5 Hz, 4HD), 2.46 (s, 6HE), 1.49 (s, H2O). b. Ball mixing

[0214] A stainless-steel jar with an inner diameter of 38 mm was charged with 50 mg of 1-A and 50 stainless-steel balls of diameter 5 mm. After pre-mixing the powder and balls with a spatula, a cross-shaped magnetic stir bar was placed in the steel jar. The stainless-steel jar was irradiated with 365 nm LED light from the top for 4 h, while stirring at 60 rpm. The irradiated solids were dispersed in ethanol and recovered by filtration. The details of the instrument setup are shown in FIG. 10.

[0215] This method was also applied to anthracene 2- A and anthracene 3-A with the irradiation at 405 nm for 20 h. The DSC results and the powder XRD after irradiation are shown in FIG. 11 and FIG. 12. For anthracene 4-A, the progress of the reaction was not observed in the powder XRD results (FIG. 12D).

[0216] Dianthracene 1-D::H NMR (400 MHz, CDCh) 57.46 (dd, J = 7.1, 1.5 Hz, 4Ha), 7.07 (m, 12Hb,c.d), 4.92 (s, 2He), 1.55 (s, H2O).

[0217] 13C NMR (101 MHz, CDCh) 6 138.09 (Ca), 138.04 (Cb), 128.49 (Cc), 127.80 (Cd), 127.45 (Ce), 125.58 (Cf), 121.00 (Cg), 60.92 (Ch), 54.17 (Ci).

[0218] Dianthracene 2-D: *H NMR (400 MHz, CDCh) 57.47 (d, J = 7. 1, 4HA), 7.25 (d, J=9 Hz, 4HB), 7.05 (m, 8HC,D), 2.39 (s, 6HE), 1.53 (s, H2O).(2024-051-02)

[0219] Dianthracene 3-D: *H NMR (400 MHz, CDCh) 8 7.57 (m, 4HA), 7.13 (m, 4HB), 7.03 (m, 8HC,D), 3.30 (s, 6HE), 1.56 (s, H2O), 1.25 (s, H-grease).Table 4. Conversion (%) of 1-A to dianthracene 1-D using different irradiation methods as determined by1H NMR.5. Crystal structure analysis a. Single-crystal X-ray diffraction (SC-XRD) measurements

[0220] Intensity data were collected from a single crystal X-ray diffractometer equipped with a Bruker X8 Dual imuS APEX2 detector with MoK« radiation ( = 0.71073) for anthracene 2- A. The structures were solved SHLEXT-2018 / 2 and refined by the full-matrix least-squares on SHELXL-2O19 / 310,11. All non-hydrogen atoms were refined anisotropically, and all hydrogen atoms were placed using AFIX instructions. Olex2 1.512was used as the GUI for these analyses.Table 5. Crystallographic data of anthracene 2-A.b. Structure simulation from powder X-ray diffraction (PXRD) data(2024-051-02)

[0221] The simulated structures were constructed using Materials Studio and we optimized the geometry and unit cell by Forcite method. Then, we refined the experimental PXRD patterns against Pawley fit, using Materials Studio, until Rwpvalue fell below 10%. As shown in Table 6, Pawley refinement revealed that experimental PXRD patterns match well with the simulated crystal structures.Table 6. Pawley fit results of 2-D, anthracene 3-A, dianthracene 3-D, anthracene 4- A, and dianthracene 4-D.Table 7. Summary of Arrhenius activation energy, Eyring activation energy parameters, and the

[0222] This disclosure further encompasses the following aspects.

[0223] Aspect 1: A dianthracene of Formula (II)(2024-051-02) wherein each R is the same or different, and R is a substituent wherein [4+4] cycloreversion of the dianthracene of Formula (II) to corresponding donor- acceptor anthracenes discharges energy in an amount from 80 kJ / mol to 200 kJ / mol, or 90 to 150 kJ / mol, or 90 to 130 kJ / mol, and / orR is a substituent wherein reversion of the dianthracene of Formula (II) to donoracceptor anthracenes of Formula (I) is self-activating, and / or R is CM alkyl, Ci-4 alkoxy, or a combination thereof.

[0224] Aspect 2: The compound of aspect 1, wherein each R is the same.

[0225] Aspect 3: The compound of aspect 1 or aspect 2, wherein R is methyl or methoxy.Aspect 4: A composition for thermal storage, the composition comprising, consisting of, or consisting essentially of, a donor-acceptor anthracene of Formula (I), a dianthracene compound of Formula (II), or a combination thereof,wherein in each of Formula II) and Formula (II), each R is the same or different, and R is a substituent wherein reversion of the dianthracene of Formula (II) to the donor-acceptor anthracenes of Formula (I) discharges energy in an amount from 80 kJ / mol to 200 kJ / mol, or 90 to 150 kJ / mol, or 90 to 130 kJ / mol, and / or R is a substituent wherein reversion of the dianthracene of Formula (II) to the donor- acceptor anthracenes of Formula (I) is self-activating, and / or R is Ci-4 alkyl, Ci-4 alkoxy, or a combination thereof.

[0226] Aspect 5: The composition of aspect 4, wherein each R is the same.

[0227] Aspect 6: The composition of aspect 4 or aspect 5, wherein R is methyl or methoxy.

[0228] Aspect 7: The composition of any one of aspects 4-6, wherein the composition is a solid composition.

[0229] Aspect 8: Use of the composition of any one of aspects 4-7 as a thermal storage material.(2024-051-02)

[0230] Aspect 9: A method of storing energy comprising providing a composition, preferably in an energy-storage device, the composition comprising the donor-acceptor anthracene of Formula (I), and optionally the dianthracene compound of Formula (II)(I) (II) wherein each R is the same or different, and R is a substituent wherein reversion of the dianthracene of Formula (II) to the donor- acceptor anthracenes of Formula (I) discharges energy in an amount from 80 kJ / mol to 200 kJ / mol, or 90 to 150 kJ / mol, or 90 to 130 kJ / mol, and / or R is a substituent wherein reversion of the dianthracene of Formula (II) to the donor- acceptor anthracenes of Formula (I) is self-activating, and / or R is Ci-4 alkyl, Ci-4 alkoxy, or a combination thereof; activating, preferably by photoirradiating, the donor- acceptor anthracenes of Formula (I) to produce the dianthracene of Formula (II) via [4+4] cycloaddition; and storing dianthracene of Formula (II) for a period of time.

[0231] Aspect 10: The method of aspect 9, wherein the activating is by photoirradiation and comprises exposing the donor-acceptor anthracenes of Formula (I) of the energy storage device to light energy, preferably sunlight or light having a wavelength in the visible spectrum.

[0232] Aspect 1 1 : The method of aspect 9 or aspect 10, further comprising: inducing the dianthracene of Formula (II) to revert to the donor- acceptor anthracenes of Formula (I), to release energy stored during the activating.

[0233] Aspect 12: The method of aspect 11, wherein the inducing is by exposing the dianthracene of Formula (II) to light or heat energy, for example infrared irradiation.

[0234] Aspect 13: The method of aspect 11 or aspect 12, wherein the dianthracene of Formula (II) is self-activating.

[0235] Aspect 14: The method of any one of aspects 11-13, comprising at least two cycles of the activating, storing, and inducing.

[0236] Aspect 15: A thermal storage system comprising the compounds of any one of aspects 1-3 or the composition of any one of aspects 4-7, and a light source that emits a wavelength of light effective to induce [4+4] cycloaddition of the donor- acceptor anthracenes of(2024-051-02)Formula (I) to provide the dianthracene of Formula (II). change of the compound of formula (II) or (la).

[0237] Aspect 16: A thermal storage system comprising the compounds of any one of aspects 1-3 or the composition of any one of aspects 4-7, and a compartment comprising an optically transparent portion at least partially enclosing the compounds or the composition.

[0238] Aspect 17: The thermal storage system of aspect 16 or aspect 17, comprising a light source of aspect 13 and the compartment of aspect 15, and further comprising a switch that controls operation of the light source, and either a power source or a connector adapted for connecting the thermal storage system to a power source.

[0239] Aspect 18: The thermal storage system according to any one of aspects 15-17, comprising a plurality of the compositions, a plurality of the composites, a plurality of the light sources, or a combination thereof.

[0240] The compositions, methods, and articles can alternatively comprise, consist of, or consist essentially of, any appropriate materials, steps, or components herein disclosed. The compositions, methods, and articles can additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any materials (or species), steps, or components, which are otherwise not necessary to the achievement of the function or objectives of the compositions, methods, and articles.

[0241] The terms “a” and “an” and “the” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. For example, the term “the compound of Formula (II)” means one compound or more than one compound of Formula (II). The term “or” means “and / or” unless clearly indicated otherwise by context. Reference throughout the specification to “an aspect”, means that a particular element (e.g., feature, structure, step, or characteristic) described in connection with the aspect is included in at least one aspect described herein, and may or may not be present in other aspects. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various aspects.

[0242] The compositions, methods, and articles can alternatively comprise, consist of, or consist essentially of, any ingredients, steps, or components herein disclosed. The compositions, methods, and articles can additionally, or alternatively, be formulated, conducted, or manufactured so as to be devoid, or substantially free, of any ingredients, steps, or components not necessary to the achievement of the function or objectives of the present claims.(2024-051-02)

[0243] Unless specified to the contrary herein, all test standards are the most recent standard in effect as of the filing date of this application, or, if priority is claimed, the filing date of the earliest priority application in which the test standard appears.

[0244] The endpoints of all ranges directed to the same component or property are inclusive of the endpoints, are independently combinable, and include all intermediate points and ranges. For example, ranges of “up to 25 wt%, or 5 to 20 wt%” is inclusive of the endpoints and all intermediate values of the ranges of “5 to 25 wt%,” such as 10 to 23 wt%, etc.

[0245] The term “combination” is inclusive of blends, mixtures, alloys, reaction products, and the like. Also, “at least one of’ means that the list is inclusive of each element individually, as well as combinations of two or more elements of the list, and combinations of at least one element of the list with like elements not named.

[0246] The term "alkyl" means an aliphatic hydrocarbon group which may be straight or branched having a recited number of carbon atoms in the chain. Branched means that one or more lower alkyl groups such as methyl, ethyl or propyl are attached to a linear alkyl chain. Exemplary alkyl groups include methyl, ethyl, n- propyl, i-propyl, n-butyl, t-butyl, n-pentyl, and 3 -pentyl.

[0247] The term “alkoxy” means groups of carbon atoms of a straight, branched, or cyclic configuration and combinations thereof attached to the parent structure through an oxygen. Examples include methoxy, ethoxy, propoxy, isopropoxy, butoxy, cyclopropyloxy, cyclohexyloxy, and the like. Alkoxy also includes methylenedioxy and ethylenedioxy in which each oxygen atom is bonded to the atom, chain, or ring from which the methylenedioxy or ethylenedioxy group is pendant so as to form a ring.

[0248] The term "halogen" means fluoro, chloro, bromo, or iodo.

[0249] The term “substituted” or “substitution” of an atom means that one or more hydrogen on the designated atom is replaced with a selection from the indicated group, provided that the designated atom’s normal valency is not exceeded.

[0250] “Unsubstituted” atoms bear all of the hydrogen atoms dictated by their valency. When a substituent is keto (i.e., =0), then two hydrogens on the atom are replaced. Combinations of substituents and / or variables are permissible only if such combinations result in stable compounds; by “stable compound” or “stable structure” is meant a compound that is sufficiently robust to survive isolation to a useful degree of purity from a reaction mixture.

[0251] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this invention belongs.(2024-051-02)

[0252] All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

[0253] While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.

Claims

(2024-051-02)CLAIMSWhat is claimed is:

1. A dianthracene of Formula (II)wherein each R is the same or different, andR is a substituent wherein [4+4] cycloreversion of the dianthracene of Formula (II) to corresponding donor-acceptor anthracenes discharges energy in an amount from 80 kJ / mol to 200 kJ / mol, or 90 to 150 kJ / mol, or 90 to 130 kJ / mol, and / orR is a substituent wherein reversion of the dianthracene of Formula (II) to donoracceptor anthracenes of Formula (I) is self- activating, and / orR is Ci-4 alkyl, Ci-4 alkoxy, or a combination thereof.

2. The compound of claim 1, wherein each R is the same.

3. The compound of claim 1 or claim 2, wherein R is methyl or methoxy.

4. A composition for thermal storage, the composition comprising, consisting of, or consisting essentially of, a donor- acceptor anthracene of Formula (I), a dianthracene compound of Formula (II), or a combination thereof,(2024-051-02) wherein in each of Formula (II) and Formula (II), each R is the same or different, andR is a substituent wherein reversion of the dianthracene of Formula (II) to the donoracceptor anthracenes of Formula (I) discharges energy in an amount from 80 kJ / mol to 200 kJ / mol, or 90 to 150 kJ / mol, or 90 to 130 kJ / mol, and / orR is a substituent wherein reversion of the dianthracene of Formula (II) to the donoracceptor anthracenes of Formula (I) is self-activating, and / orR is Ci^ alkyl, Ci-4 alkoxy, or a combination thereof.

5. The composition of claim 4, wherein each R is the same.

6. The composition of claim 4 or claim 5, wherein R is methyl or methoxy.

7. The composition of any one of claims 4-6, wherein the composition is a solid composition.

8. Use of the composition of any one of claims 4-7 as a thermal storage material.

9. A method of storing energy comprising providing a composition, preferably in an energy-storage device, the composition comprising the donor- acceptor anthracene of Formula (I), and optionally the dianthracene compound of Formula (II)(I) (II) wherein each R is the same or different, andR is a substituent wherein reversion of the dianthracene of Formula (II) to the donoracceptor anthracenes of Formula (I) discharges energy in an amount from 80 kJ / mol to 200 kJ / mol, or 90 to 150 kJ / mol, or 90 to 130 kJ / mol, and / orR is a substituent wherein reversion of the dianthracene of Formula (II) to the donoracceptor anthracenes of Formula (I) is self-activating, and / or(2024-051-02)R is C1-4 alkyl, CM alkoxy, or a combination thereof; activating, preferably by photoirradiating, the donor- acceptor anthracenes of Formula (I) to produce the dianthracene of Formula (II) via [4+4] cycloaddition; and storing dianthracene of Formula (II) for a period of time.

10. The method of claim 9, wherein the photoirradiating comprises exposing the donor- acceptor anthracenes of Formula (I) of the energy storage device to light energy, preferably sunlight or light having a wavelength in the visible spectrum.

11. The method of claim 9 or claim 10, further comprising: inducing the dianthracene of Formula (II) to revert to the donor-acceptor anthracenes of Formula (I), to release energy stored during the photoirradiation.

12. The method of claim 1 1 , wherein the inducing is by exposing the dianthracene of Formula (II) to light energy, heat energy, or a combination thereof, for example infrared irradiation.

13. The method of claim 11 or claim 12, wherein the dianthracene of Formula (II) is self-activating.

14. The method of any one of claims 11-13, comprising at least two cycles of the activating, storing, and inducing.

15. A thermal storage system comprising the compounds of any one of claims 1-3 or the composition of any one of claims 4-7, and a light source that emits a wavelength of light effective to induce [4+4] cycloaddition of the donor-acceptor anthracenes of Formula (I) to provide the dianthracene of Formula (II). change of the compound of formula (II) or (la).

16. A thermal storage system comprising the compounds of any one of claims 1-3 or the composition of any one of claims 4-7, and a compartment comprising an optically transparent portion at least partially enclosing the compounds or the composition.(2024-051-02)17. The thermal storage system of claim 15 or claim 16, comprising a light source of claim 13 and the compartment of claim 15, and further comprising a switch that controls operation of the light source, and either a power source or a connector adapted for connecting the thermal storage system to a power source.

18. The thermal storage system according to any one of claims 15-17, comprising a plurality of the compositions, a plurality of the composites, a plurality of the light sources, or a combination thereof.

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