A new series of π-extended tetrathiafulvalene derivatives incorporating fused furanodithiino and thienodithiino units: a joint experimental and theoretical study

Abstract

A new family of tetrathiafulvalenes has been prepared. The materials exhibit complex redox behaviour related to the electronic influence of the 1,4-dithiin moieties embedded within the framework of the molecules. The X-ray crystal structure of compound 4 reveals an unusual non-planar conformation of the heterocyclic compound, with the TTF fragment adopting a boat conformation. Theoretical calculations, performed at the DFT level (B3P86/6-31G*), confirm the boatlike structure (C_2v symmetry) as the most stable conformation for this family of tetrathiafulvalenes. Upon oxidation, electrons are extracted from the whole molecule and the radical cations and dications remain highly distorted from planarity. For the dications, the 1,4-dithiin units present foldings of ∼40° suggesting the possibility of reaching higher oxidation states in agreement with experimental results. For the tetracations, both the TTF nucleus and the 1,4-dithiin units are singly-charged and become planar. The tetracations therefore present fully-planar, π-delocalised structures and are stabilised by the gain of aromaticity of the TTF and 1,4-dithiin electron-donor units.