A reversibly photoresponsive halogen bonding receptor as a photoswitchable catalyst for an anion abstraction reaction and cationic polymerization

Abstract

Exploring new noncovalent interaction motifs with photoswitchable binding strength is crucial for the development of photoresponsive supramolecular assembly systems and materials with attractive spatiotemporally controlled properties and functions. This paper describes a distinct azobenzene-derived photoresponsive halogen bonding (XB) receptor that can act as an efficient photoswitchable organocatalyst for XB-mediated catalysis of an anion abstraction reaction and cationic polymerization. Upon alternating yellow (>550 nm) and purple (400 nm) light irradiation, the reversible Z/E photoisomerization of the azo core of the XB receptor could be triggered to switch between the monodentate (E) and bidentate (Z) isomers, with the latter showing stronger halide anion binding affinity and better performance (with the reaction rate enhanced up to 730-fold) in the XB-mediated anion abstraction of the Friedel–Crafts benchmark reaction. Remarkably, the receptor could also be applied as an efficient organocatalyst for realizing unprecedented photocontrolled XB-mediated cationic polymerization. Such a reversibly photoresponsive XB system not only delivers a spatiotemporally controllable and environmentally benign supramolecular catalytic methodology for molecular synthesis, but also provides new opportunities for fabricating appealing photoresponsive XB-mediated functional supramolecular assemblies and materials.