Synthesis and properties of novel heterocycle-fused TTF-type electron donors: Bis(propylenethio)tetrathiafulvalene (BPT-TTF), bis(propyleneseleno)tetrathiafulvalene (BPS-TTF), and their tetraselenafulvalene analogues (BPT-TSF and BPS-TSF)

A series of novel heterocycle-fused TTF-type electron donors, bis(propylenethio)tetrathiafulvalene (BPT-TTF, 5), bis(propyleneseleno)tetrathiafulvalene (BPS-TTF, 6), and their tetraselenafulvalene analogues (BPT-TSF, 7 and BPS-TSF, 8) have been effectively synthesized from a common starting compound, THP-protected pent-4-yn-1-ol. The solution electrochemistry reveals that all the new donors have good electron donating properties. Formation of their radical cation salts by electrocrystallization technique has been successfully achieved. All the radical salts derived from the TTF derivatives (5 and 6) are insulating owing to the complete charge transfer. On the other hand, the TSF derivatives (7 and 8) afford different types of highly conductive radical cation salts. Of these, 7·PF₆, 7·AsF₆ and 7·FeCl₄ remain metallic down to liquid helium temperature.