New materials based on highly-functionalised tetrathiafulvalene derivatives

Tetrathiafulvalene (TTF) 1 is famous as a π-electron donor molecule that forms low-dimensional organic metals and organic semiconductors upon complexation with a range of π—electron acceptor species, e.g tetracyano-p-quinodimethane (TCNQ) and inorganic and organometallic anions, e.g halogens and metal (dmit)2 [1]. Some derivatives of TTF, notably bis(ethylenedithio)-TTF (BEDT-TTF) form cation radical salts which are organic superconductors, with current Tc values as high as 12K [2]. The significance of functionalised electroactive molecules [e.g quinone, metal(bipyridyl) and ferrocene derivatives] in the wider context of supramolecular chemistry [3] and molecular electronics [4] is well recognised and TTF offers tremendous potential as a versatile building block in this respect [5]. The relevant properties of the TTF ring system are: (i) oxidation of TTF to the radical cation species occurs reversibly at a relatively low potential (ca. +0.34 V, vs. Ag/AgCI for unsubstituted TTF 1) which can be finely tuned by the attachment of substituents; (ii) TTF+ is thermodynamically a very stable species; (iii) oxidised TTF units readily form highly ordered arrays with close intermolecular interactions involving both π—π overlap and non-bonded S--S contacts.