Optically Controlled Solid-to-Liquid Phase Transition Materials Based on Azo Compounds

Phase transition materials can be utilized in a varietyof functionalizationscenarios, benefiting from the photoinduced changes in their physicochemicalproperties. Among them, small molecular crystals or liquid-crystallinepolymers containing azobenzene moieties that show phototunable meltingpoints or glass transition temperatures, respectively, have provento be significant in optically controlled functional materials. Inrecent years, they have been successfully used in reversible mechanicalactuation, adhesion, energy storage, self-healing, athermal nanoimprinting,and other applications, which has attracted the attention of morescientists and engineers. In this review, azobenzene-containing materialswith photoinduced phase transition capabilities are systematicallydiscussed in terms of molecular design strategies, phase change mechanisms,performance control, methods of preparation of materials, and potentialapplications. Existing problems and future challenges are also discussed.We hope to provide some inspiration for the development of photocontrolledphase transition materials.