Persistent mixed-valence [(TTF)2]+* dyad of a chiral bis(binaphthol)-tetrathiafulvalene (TTF) derivative.
Résumé
Mixed-valence dyadic [(TTF)(2)](+*) (TTF=tetrathiafulvalene) species--the elementary building blocks of organic conductors--are usually too weakly associated to be observed in solution, unless covalently bound in dimers or physically constrained into a cage structure. We demonstrate here that a novel chiral tetrathiafulvalene functionalised with two 1,1'-binaphthol units (1) is able to associate in solution into persistent mixed-valence [(TTF)(2)](+*) dyadic moieties through a stereospecific recognition pattern. This redox active molecule exhibits different electrochemical and spectroscopic responses, as enantiopure RR, SS or meso isomers, a rare example of a chiral system in which different diastereoisomers do not exhibit the same electrochemical features, with a selective formation of the mixed-valence species in the enantiopure (RR)-1 or (SS)-1 isomers only, whereas the meso form does not show this association ability. A rationale for the selective self-association of the RR and SS enantiomers upon oxidation is provided, based on the different molecular geometries and accessibility of the TTF core toward the formation of the mixed-valence species.