Multi‐azo Photoswitches for Improved Molecular Solar Thermal Energy Storage

Molecular solar thermal energy storage (MOST) based on photoisomerization represents a novel approach for the capture, conversion, and storage of solar energy. Azo photoswitches can store energy by isomerization from their thermodynamically stable E isomers to higher energy metastable Z isomers. Enhancing the energy density through molecular structural design represents a central research focus in the field of MOST. A straightforward approach to enhance the energy density is to design multi-azo photoswitches. This allows multiple azobenzene units to share a common framework while keeping the molecular weight as small as possible. In particular, when two azobenzene units are connected via a phenyl ring in a meta orientation, it facilitates efficient isomerization, thereby maximizing the energy density of the azo photoswitches (392 J g−1). This paper provides a brief overview of the development of multi-azo photoswitches and highlights their outstanding performance as a MOST system. It also offers prospects for their future advancements in the field. We propose that, to further improve the energy density of multi-azo photoswitches, one approach is to design wide spectrum of light photoisomerization of multi-azo photoswitches. Additionally, introducing photo-induced phase changes to multi-azo photoswitches enables the simultaneous storage of both photon energy and ambient heat.