Controlling the isomerization of photoresponsive molecules through a limiting tautomerization strategy

Controlling the multistage photoresponsivity remains a challenge, in part, due to the spontaneous tautomerization between isomers. Herein, we present a strategy to access three independent states (linear, cyclic keto, and cyclic enolate) of crown ether (CE)-substituted donor–acceptor Stenhouse adducts (DASAs) by limiting the tautomerization of the closed isomers. The linear–cyclic keto isomerization is reversibly triggered by treatment with metal ions (Na+ or K+) and CE, while the linear–cyclic enolate isomerization is induced by green light and heat. Density functional theory and molecular dynamics calculation results suggest that the steric effect and supramolecular interaction between the electron-donating and electron-withdrawing moieties play an important role in hindering the tautomerization between cyclic keto and cyclic enolate DASA-CE. The strategy to influence key steps in the photoswitching process inspires well-controlled multistage isomerization of photoresponsive molecules.