A sulfur-rich π-electron acceptor derived from 5,5′-bithiazolidinylidene: charge-transfer complex vs. charge-transfer salt

Abstract

Novel π-electron acceptors are still highly desirable for the formation of conducting salts or as n-dopable semiconductors. We describe here two synthetic approaches to substitute a dicyanovinylidene group, CC(CN)₂ to a thioketone (CS) in the recently described DEBTTT acceptor where DEBTTT stands for (E)-3,3′-diethyl-5,5′-bithiazolidinylidene-2,4,2′,4′-tetrathione. These electron withdrawing groups enhance the electron accepting ability as demonstrated through electrochemical investigations, without hindering the formation of short intra- and intermolecular S⋯S contacts in the solid state. Association of this acceptor 1 with tetramethyltetrathiafulvalene (TMTTF) and decamethylferrocene (Fe(Cp*)₂) afforded 1 : 1 adducts which were analyzed by single crystal X-ray diffraction. Combined with vibrational and magnetic properties, it appears that [TMTTF][1] behaves as a neutral charge-transfer complex while [Fe(Cp*)₂][1] is an ionic salt. The concentration of the spin density on the exocyclic sulfur atoms in 1⁻˙ favors the setting of direct antiferromagnetic interactions in [Fe(Cp*)₂][1].