A Molecular Chameleon: Chromophoric Sensing by a Self-Complexing Molecular Assembly.

A color change from purple to green takes place on addition of tetrathiafulvalene (TTF) to the macrobicyclic receptor 14+ , which is composed of a cyclobis(paraquat-p-phenylene) tetracation that shares one of its paraphenylene rings with a 1,5-naphthoparaphenylene-[36]crown-10 macrocycle. The TTF molecule forces the macrobicycle to turn inside out (see schematic drawing below) and displaces the self-complexed 1,5-dioxynaphthalene ring system from the center of the tetracationic cyclophane.