Utilisation of photo-thermal energy and bond enthalpy based on optically triggered formation and dissociation of coordination bonds

The closed cycle utilisation of photo-thermal energy faces two main challenges: increasing the ability of energy storage and controlling the heat output. However, in solid-state media, these aspects are greatly restricted by a low energy gap and limited structural transformation. Herein, we introduce a novel reversible dynamic bond into a nano graphene-templated azobenzene (G-Azo) hybrid for crosslinking via coordination bonds formed between Mg metal ions and sulphonate. The optically triggered solid-state formation and dissociation of coordination bonds enlarge the molecular energy gap by lowering energy level of trans-isomer and accelerate reversion by increasing that of cis-isomer. As a result, G-Azo-Mg self-assembly film exhibits a maximum energy density of 720.1 kJ kg−1 with photo-thermal energy and bond enthalpy. We also demonstrate that the G-Azo-Mg assembly is an excellent solid-state integrable heat source to reversibly harvest, store, release, and deliver photo-thermal energy and bond energy for distributed utilisation.