Thermally Bistable Stiff Stilbene Photoswitches and Polymer Applications.

Photoresponsive molecular switches (photoswitches) enable reversible control of molecular structures and properties using light, offering powerful opportunities for functional materials. However, their practical use in polymeric systems has long been constrained by thermal instability, which also hampers mechanistic understanding and precise control. This Personal Account summarizes recent progress in thermally stable photoswitches, with particular emphasis on stiff stilbene (SS) and sterically hindered stiff stilbene (HSS) photoswitches, largely based on our own studies. After outlining the fundamental characteristics of rare thermally stable photoswitches, it is shown how HSS photoswitches combine large structural changes with exceptional thermal bistability and well-balanced photoisomerization yields. These unique features have led to diverse polymer applications, including mechanochemical studies, reversible control of single-chain conformations, and consequent switching of inter- and intrachain interactions, solubility, and surface wettability. Finally, future prospects for thermally stable photoswitches in polymer science are briefly discussed.