Highly Conducting Ion-Radical Salts of Tetrathiotetracene

The electrical resistivity and thermoelectric power of the organic semiconductor tetrathiotetracene (TTT) and its chloride, bromide, iodide, and thiocyanate salts are reported as a function of temperature. The ion–radical salts, of nearly 1:1 stoichiometry, were discovered to be highly conducting organic semiconductors and have resistivity values at room temperature ranging from 2.3 × 103 Ω·cm for TTT–chloride to 0.71 Ω·cm for TTT–iodide. The sign of the Seebeck coefficient of TTT–chloride corresponds to an n-type semiconductor, while for TTT and the other salts it indicates p-type behavior. Infrared absorption spectra of the solids, uv–visible spectra of solutions, preliminary x-ray powder patterns and density measurements are correlated with electrical properties. The influence of constitution of the ion–radical salts on the electrical resistivity and possible mechanisms of conduction are discussed.