Arylazopyrazoles for Long-Term Thermal Energy Storage and Optically Triggered Heat Release below 0 °C
Mihael A. Gerkman, Rosina S. L. Gibson, Joaquín Calbo, Yuran Shi, Matthew J. Fuchter, Grace G. D. Han
Abstract
Arylazopyrazole derivatives based on four core structures (4pzMe, 3pzH, 4pzH, and 4pzH-F2) and functionalized with a dodecanoate group were demonstrated to store thermal energy in their metastable Z isomer liquid phase and release the energy by optically triggered crystallization at −30 °C for the first time. Three heat storage–release schemes were discovered involving different activation methods (optical, thermal, or combined) for generating liquid-state Z isomers capable of storing thermal energy. Visible light irradiation induced the selective crystallization of the liquid phase via Z-to-E isomerization, and the latent heat stored in the liquid Z isomers was preserved for longer than 2 weeks unless optically triggered. Up to 92 kJ/mol of thermal energy was stored in the compounds, demonstrating remarkable thermal stability of Z isomers at high temperatures and liquid-phase stability at temperatures below 0 °C.