Syntheses and properties of a new series of tetrathiafulvalene derivatives incorporating fused ethyleneoxymethylene and ethylenethiomethylene units, and their charge–transfer complexes

• TTF derivatives incorporating fused ethyleneoxymethylene (EOM) and ethylenethiomethylene (ETM) units were newly synthesized.
• Crystal structure of neutral donors was determined by X-ray crystal structure analyses.
• Electrochemical properties of these donors were investigated by cyclic voltammetry.
• Molecular orbital calculations were carried out using density functional theory.
• The CT complex of EOMMDT-TTF (5) with TCNQ is metallic down to 102 K.

Nine tetrathiafulvalene (TTF) derivatives incorporating fused ethyleneoxymethylene (EOM) and ethylenethiomethylene (ETM) units were newly synthesized by self-coupling or cross-coupling reactions. Unsymmetrical ETMEDT-TTF (4) was also synthesized by a Wittig-type reaction. Crystal structural analysis of these neutral donors revealed specific intermolecular interactions between donors, and many S⋯S, O⋯H, and S⋯H short contacts. Electrochemical properties of these donors were investigated by cyclic voltammetry under two different measurement conditions. Electronic spectra of neutral donors in chloroform and some cation radicals in methanol and on KBr pellets were measured and discussed. A distribution of the highest occupied molecular orbital (HOMO) around the EOM and ETM moieties of these donors was not found. The introduction of EOM and ETM groups to the TTF skeleton only slightly modulated the HOMO energy. Some charge–transfer (CT) complexes of these donors with tetracyanoquinodimethane (TCNQ) derivatives were prepared. A needle crystal of the CT complex of EOMMDT-TTF (5) with TCNQ was metallic down to 102 K with a high σRT value of 169 S cm−1. TTF derivatives incorporating fused EOM groups were more effective in conductivity than those incorporating fused ETM groups.

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