Phase-change azobenzene derivatives for upgraded photon energy storage and release via molecular design

Abstract

Photo-liquefiable azobenzene derivatives enable the simultaneous storage of photon energy and phase-change energy, with the ability to release the stored energy in a controllable manner. However, a contradiction exists between the superior properties of azobenzene derivatives and photo-induced phase changes. To address this, two azobenzene derivatives featuring photo-liquefiable phase-change properties were designed. By optimizing their molecular structures and intermolecular interactions, these derivatives effectively overcome the challenge of concurrently storing photon energy and latent heat. The designed tri-azobenzene derivative exhibits an impressive total energy density of up to 525 kJ mol⁻¹, encompassing both isomerization enthalpy and phase-change energy. This significantly surpasses the 160 kJ mol⁻¹ of long-alkyl-substituted azobenzene derivatives. Notably, the molar isomerization enthalpy of the tri-azobenzene derivative is more than 10 times that of pristine azobenzene. Furthermore, in a distributed energy utilization device operating at room or low temperatures, these phase-change azobenzene derivatives can achieve a temperature rise of 7.0 °C through blue light-induced synchronous heat release. This work proposes an innovative molecular design strategy, laying a foundation for the development of high-performance phase-change azobenzene-based energy storage materials.