Design of crystal packings of styryl heterocycles and regularities of [2+2] photocycloaddition in their single crystals 8. Topochemical [2+2] autophotocycloaddition and back reaction in styryl dye of the benzothiazole series

Controllable photomechanical bending of metal-organic rotaxane crystals facilitated by regioselective confined-space photodimerization

Molecular machines based on mechanically-interlocked molecules (MIMs) such as (pseudo) rotaxanes or catenates are known for their molecular-level dynamics, but promoting macro-mechanical response of these molecular machines or related materials is still challenging. Herein, by employing macrocyclic cucurbit[8]uril (CB[8])-based pseudorotaxane with a pair of styrene-derived photoactive guest molecules as linking structs of uranyl node, we describe a metal-organic rotaxane compound, U-CB[8]-MPyVB, that is capable of delivering controllable macroscopic mechanical responses. Under light irradiation, the ladder-shape structural unit of metal-organic rotaxane chain in U-CB[8]-MPyVB undergoes a regioselective solid-state [2 + 2] photodimerization, and facilitates a photo-triggered single-crystal-to-single-crystal (SCSC) transformation, which even induces macroscopic photomechanical bending of individual rod-like bulk crystals. The fabrication of rotaxane-based crystalline materials with both photoresponsive microscopic and macroscopic dynamic behaviors in solid state can be promising photoactuator devices, and will have implications in emerging fields such as optomechanical microdevices and smart microrobotics.

Features of styryl dye crystal packings and their influence on [2 + 2] photocycloaddition reaction with single crystal retention

Only in two of three crystal modifications the initial dye is subjected to the SC–SC [2 + 2]-photocycloaddtion under visible light irradiation.