Energy Storage Hot Paper Azopyridine Polymers in Organic Phase Change Materials for High Energy Density Photothermal Storage and Controlled Release Rihui Liang, Bo Yuan, Fei Zhang, and Wei Feng* Abstract: Azo-compounds molecules and phase change materials offer potential applications for sustainable energy systems through the storage and controllable release photochemical and phase change energy. Devel- opingnovelandhighlyefficientAzo-basedsolarthermal fuels (STFs) for photothermal energy storage and synergistic cooperation with organic phase change materials present significant challenges. Herein, three typesof(ortho-, meta-,and para-) azopyridine polymers hingedwithflexiblealkylchainaresynthesized,inwhich meta-azopyridine polymer exhibits striking photother- mal storage capacity of 430J/g, providing a feasibility solution for developing high energy density Azo-based STFs. Furthermore, a stable two-phase hybrid system was innovatively constructed by combining the meta- azopyridine polymer with organic phase change materi- als leveraging hydrogen bonds and van der Waals interactions to collectively harness phase change energy and photothermal energy. The organic phase change materialnotonlysuppliesadditionalphasechangelatent heat but also serves as a solvent, offering abundant free volume for the photo-induced isomerization of the azopyridine chromophores, which successfully circum- vents the low charging efficiency in the condensed state and reliance on solvent-assisted charging in traditional Azo-based STFs. This study demonstrates the energy distributionandutilizationforhouseholdconsumersand the photothermal-assisted insulation strategy, achieving moreextensivepotentialimplementationforSTFs. Introduction Efficient utilization of solar energy has become one of the significant measures to alleviate the consumption of tradi- tional fossil fuels and mitigate the environmental pollution. The most representative methods are photoelectric conver- sion (photovoltaic [1] and photothermal power generation [2] ) and photothermal conversion. Photothermal conversion typicallyemploysphasechangematerials(PCMs)toconvert absorbed light energy into stored thermal energy, whereas, the PCMs are significantly influenced by the surrounding ambient temperature and can only store thermal energy above the phase change temperature, which severely limits theutilizationofsolarthermalenergy. [3] Another novel method for utilizing solar thermal energy has attracted widespread attention in recent years, as is known to solar thermal fuels (STFs) or molecular solar thermal (MOST) energy storage which leverages photo- active molecules with unique photo-responsiveness and photo-switches transform stable into metastable configura- tion accompanying with storing photothermal energy into chemical bonds under light of specific wavelengths excita- tion, and the storage photothermal energy is released upon external stimulation (such as light, heat, or catalysts), in where the entire cyclical procedure occurs the identical molecular site. [4] At present, photochromics including nor- bornadiene-quadricyclane (NBD-QC), [5] fulvalene-diruthe- nium complexes, [6] dihydroazulenes [7] and azobenzene, [8] etc, have been widely employed in STFs. Among photo-switch- ing molecules, the NBD-QC is plagued by the restriction of lightexcitationofspecificwavelength(typicallywithoptimal absorption around 230nm) during the photoisomerization process, complex synthesis and easy degradation of prod- ucts.Dihydroazuleneswithrelativelylowenergydensityand significant spectral optical overlap between two isomers, as well as fulvalene-diruthenium complexes is confronted with large-scaleproductiondifficultiesbytheuseofnoblemetals, which severely limits practical application in solar energy storage and conversion. azobenzene has been extensively studiedduetoitssimplestructureandadaptablefunctional- ization. As the most crucial performance for STFs, energy density and half-life determine the photothermal energy storage capacity and stability, respectively. To improve the above-mentioned performance, researchers have proposed several effective strategies, including azobenzene molecules modifications, [9] carbon nano-templates, [10] polymer- templates [4c,8b,11] and phase change composites. [12] Despite theseadvances,azobenzene-basedSTFscontinuetoencoun- ter challenges, including low energy density and reliance on solvent-assisted charging, which restrict practical applica- tionsinthermalmanagement. The development of new types of heterocyclic azo compounds to replace traditional azobenzene-based STFs [*] R. Liang, B. Yuan, Prof. W. Feng Beijing University of Chemical Technology Institute of Advanced Technology and Equipment Beijing, 100029, China E-mail: weifeng@tju.edu.cn F. Zhang Institute of Flexible Electronics Technology of Tsinghua University, Zhejiang, 314000, China Prof. W. Feng Tianjin University, School of Materials Science and Engineering and Tianjin Key Laboratory of Composite and Functional Materials Tianjin, 300072, China Angewandte Chemie Forschungsartikel www.angewandte.org Zitierweise: Angew. Chem. Int. Ed. 2025, 64, e202419165 doi.org/10.1002/anie.202419165 Angew. Chem. 2025, 137, e202419165 (1 of 13) © 2024 Wiley-VCH GmbH