Developing intelligent control of photoresponsive materials: from switch-type to multi-mode.

Most photoresponsive materials are controllably switched between two functional states with contrary relationship, which is defined as switch-type control logic. However, the world is not black and white. When facing real-world applications, the photoresponsive materials are working under complex stimuli. Therefore, developing the control logic of photoresponsive materials from switch-type to multi-mode is essential, meaning the materials could switch among multiple (n > 2) functional states by varying light conditions. In this tutorial review, the light-switchable optical, electrical, chemical, mechanical and morphological properties of photoresponsive materials with switch-type control logic is introduced. The multi-mode control of photoresponsive materials is discussed from two aspects: (1) switching between multiple stationary states, termed as multi-stable control and (2) switching between multiple nonequilibrium states, termed as multi-stage control. The potential applications and future challenges are envisioned to encourage further and continuous developments for the multi-mode photoresponsive materials.