Synthesis, Structures and Properties of Molecular Conductors Based on Bis-Fused Donors Composed of (Thio)Pyran-4-ylidene-1,3-dithiole and Tetraselenafulvalene

Abstract

Bis-fused donors composed of (thio)pyran-4-ylidene-1,3-dithiole and tetraselenafulvalene (1a, 2a) and their bis(methylthio) derivatives (1b, 2b) were synthesized. Cyclic voltamograms of all the donors consisted of four pairs of one-electron redox waves, and it was suggested that a positive charge of 1+• and 2+• distributed mainly on the (thio)pyran-4-ylidene-1,3-dithiole moiety. X-ray structure analysis revealed that (1b)PF6(C6H5Cl)0.5 and (2b)PF6(C6H5Cl) formed one-dimensional conducting stacks in which the donors were dimerized or tetramerized. In those salts, intramolecular charge disproportionation of the donors was suggested by X-ray structure analysis and density functional theory (DFT) calculation with UB3LYP/6-31G(d) basis function. A tight-binding band calculation suggested that these materials were band insulators. All the donors gave highly conducting TCNQ (7,7,8,8-tetracyanoquinodimethane) complexes and I3− salts (σrt = 0.3–19 S cm−1 on a compressed pellet) with very low activation energies of 0.017–0.040 eV, while single crystals of (1b)PF6(C6H5Cl)0.5 and (2b)PF6(C6H5Cl) exhibited semiconductive behavior with large activation energies (Ea = 0.16–0.22 eV).

Keywords

• molecular conductor
• tetrathiapentalene
• pyran
• thiopyran
• tetraselenafulvalene
• cyclic voltammetry
• X-ray structure analysis
• band calculation
• electrical conductivity
• intramolecular charge disproportionation