Graduate Student Ryann Kemmerling

"Azo-based Photo-switchable Compounds: Controlled Storage and Triggered Heat Release"

Solar energy is one of the most important renewable energy sources to date. Specifically, it is crucial for solar energy to be captured, stored, and released efficiently.1 Solar thermal fuels, ones whose molecules have chemical bonds with high photochemical activity, are a class of latent energy storage materials which are designed to collect solar energy and release thermal energy.2 Molecular solar thermal (MOST) materials store photon energy, and release energy upon triggering in the form of heat.3
Yuran Shi et al. explored azobenzene based molecular photoswitches that harvest sunlight photon energy and convert it into chemical energy through the isomerization and phase change of the stable ground-state isomers to high-energy metastable isomers.4 By ortho-substitution of azobenzene units, the activation of photo-switches by long wavelengths is achieved. The sunlight-activated liquid phase exhibits a long heat storage time without crystallization of two months.
Xingtang Xu et al. address the hinderance of visible light storage for solar thermal fuels and exhibit outstanding energy conversion and stable storage by presenting an arylazopyrazole (AAP) containing dendrimer.5 The excellent energy storage and conversion are attributed to the absorbance of visible wavelengths by para -substituted AAP groups, and the stability of cis isomers. The half-life can reach up to 12.9 days and the heat release can be triggered by light and heat, providing an avenue to fabricate visible light storage solar thermal fuels.

References:
1. C.-L. Sun, C. Wang, R. Boulatov. Applications of Photoswitches in the Storage of Solar energy. ChemPhotoChem 2019, 3, 268.
2. Zhang, B., Feng, Y. & Feng, W. Azobenzene-Based Solar Thermal Fuels: A Review. Nano-Micro Lett. 2022, 14, 138.
3. Xu. X, Wang. G. Molecular Solar Thermal Systems towards Phase Change and Visible Light Photon Energy Storage. Small 2022, 18, 2107473.
4. Shi. Y, et al. Sunlight-activated phase change materials for controlled heat storage and triggered release. J. Mater. Chem. A, 2021, 9, 9798.
5. Xu. X, et al. Arylazopyrazole-Based Dendrimer Solar Thermal Fuels: Stable Visible Light Storage and Controllable Heat Release. ACS Appl. Mater. Interfaces. 2021, 13, 22655-22663.