Visible-light-triggered exclusive bistable E/Z photoswitching based on sterically frustrated dicyanostilbene derivatives.

Developing photoswitches with precise control over reaction pathways, visible-light responsiveness, and robust thermal stability remains a significant challenge in photoresponsive materials. Here we report a class of sterically frustrated dicyanostilbene-based molecular photoswitches that achieve exclusive, efficient, and robust visible-light-triggered E/Z photoisomerization in both solution and aggregated states. They function as bistable switches with thermal half-lives reaching up to 1817 years. Furthermore, their pronounced polarity and solubility differences between isomers, together with photofluorochromic behavior, enable facile separation, real-time switching monitoring, and photonic encryption demonstrations. Single-crystals and theoretical calculation elucidates the dual steric control mechanism: in solution, molecular distortion of the Z-isomer suppresses intramolecular photocyclization while stabilizing the Z-conformation to enable ultralong thermal half-lives; in the aggregated state, isolated and loosely packed molecules inhibit intermolecular photocycloaddition and concurrently provide the free volume required for isomerization. This work advances the design of bistable dicyanostilbene photoswitches, offering a versatile platform for green chemistry and smart materials.