Sterically Hindered Stiff-Stilbene Photoswitch Offers Large Motions, 90% Two-Way Photoisomerization, and High Thermal Stability

Molecular photoswitches have been widely used as molecular machines in various fields due to the small structures and simple motions generated in reversible isomerization. However, common photoswitches, as represented by azobenzene (AB), cannot combine both large motions and high thermal stability, which are critically important for some practical applications in addition to high photoisomerization yields. Here, we focus on a promising photoswitch, stiff stilbene (SS), and its derivative, sterically hindered SS (HSS). The detailed investigation of their performance with a comparison to AB demonstrated that HSS is an outstanding photoswitch offering larger motions than AB and SS, ca. 90% photoisomerization in both E-to-Z and Z-to-E directions, and significantly high thermal stability with a half-life of ca. 1000 years at room temperature. The superior performance of HSS promises its use in various applications, even where previous photoswitches have troubles and are unavailable.