A light-powered stretch–contraction supramolecular system based on cobalt coordinated [1]rotaxane

Abstract

A mechanically switchable bistable [1]rotaxane, constituted of azobenzene modified cyclodextrins (CyDs) and a Schiff base bridged by a metallosalen unit, was designed and synthesized. ¹H NOESY NMR and ICD spectra were investigated to characterize the movement process of this stretch–contraction supramolecular system. The geometries of [1]rotaxane before and after irradiation by UV light were optimized and calculated. Coordinated with cobalt(III) ion, the rotaxane becomes more rigid and linear, which is seen from the more obvious signals in the induced circular dichroism (ICD) and ¹H NMR spectra. This type of light-powered [1]rotaxane has favourable repeatability and exhibits a novel approach to elaborate the transformation of a light-driven molecular machine.