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

Phase transition materials can be utilized in a variety of functionalization scenarios, benefiting from the photoinduced changes in their physicochemical properties. Among them, small molecular crystals or liquid-crystalline polymers containing azobenzene moieties that show phototunable melting points or glass transition temperatures, respectively, have proven to be significant in optically controlled functional materials. In recent years, they have been successfully used in reversible mechanical actuation, adhesion, energy storage, self-healing, athermal nanoimprinting, and other applications, which has attracted the attention of more scientists and engineers. In this review, azobenzene-containing materials with photoinduced phase transition capabilities are systematically discussed in terms of molecular design strategies, phase change mechanisms, performance control, methods of preparation of materials, and potential applications. Existing problems and future challenges are also discussed. We hope to provide some inspiration for the development of photocontrolled phase transition materials.