Synthesis of highly functionalized BEDT-TTF analogues incorporating 1,4-dithiin rings from 1,8-diketones

Employment of 1,8-diketone ring formation reaction led to the synthesis of tetrathiafulvalene derivatives having diphenyl-1,4-dithiin ring together with dihydroxyl, dimethyl, MEM and diphenylthiophene groups. Spectroelectrochemistry of ET and its fully unsaturated analogue 4 was compared. While both displayed nearly similar behaviours, ET started to precipitate as the second oxidation potential is reached. CV studies indicated that the fully unsaturated 4 and tetraphenyldithiophene 20 have the highest oxidation potentials, while diphenyldithiindimethylthio 16 displayed the lowest oxidation potentials. CV measurements indicated that the combination of dithiin and hydroxyl groups help lowering the oxidation potentials. It is surprising that while the presence of dithiin ring results in higher oxidation potentials, hydroxyl groups lower the potentials. Single crystal structure of 13, having both dithiin and 1,4-dithiepine rings, was examined and it was observed that dithiin and dithiepine rings form angles of 20.52° and 25.65° with the planar TTF core in cis form as both rings bent about their S⋯S axis to give a boat conformation.

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