Synthesis and characterization of spin-labelled [2]rotaxanes containing tetrathiafulvalene and 1,5-dioxynaphthalene molecular stations

Abstract

The central component of one of the most studied programmable molecular switches reported by Stoddart and Heath is a [2]rotaxane, which consists of a cyclobis(paraquat-p-phenylene) shuttle (CBPQT⁴⁺)(PF₆⁻)₄ (the ring) encircling a finger and moving between two molecular stations, tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP). In order to employ ESR spectroscopy for understanding the mechanism of this switch, we report here the synthesis and characterization of [2]rotaxanes having persistent nitroxide radicals as the stopper units and TTF or DNP as molecular stations. Isolation of the rotaxanes was successful when bulky nitroxide radicals containing cyclohexyl substituents at 2 and 6 positions of the piperidine-N-oxyl ring were used as terminal stoppers.