Multistate photoswitches beyond on and off

Molecular photoswitches are compounds that undergo isomerization between at least two distinct states upon light irradiation, accompanied by pronounced changes in their physicochemical properties. The incorporation of photoswitches into material systems enables light-triggered switching of material properties. Multistate photoswitches are attracting considerable attention because of their manipulation of light-controllable states and wider application when compared to traditional binary photoswitches. In this Perspective, we discuss the rapidly advancing field of multistate photoswitches, exploring the evolution of the field, fundamental principles, key design strategies, representative examples, diverse emerging applications, as well as the current challenges and future research directions. Multistate photoswitches are an interesting class of photochromic materials which exhibit complex stimulus response. This Perspective explores this rapidly advancing field discussing design strategies, applications, and the current challenges facing researchers.