PHASE-TRANSITION OF TETRAKIS(OCTYLTHIO)TETRATHIAFULVALENE (TTC8-TTF) AND CRYSTAL-STRUCTURE ANALYSIS

Tetrakis(octylthio)tetrathiafulvalene (TTC8-TTF) crystallizes into two different phases (Forms I and II). Form I undergoes a slightly endothermic, phase transition at ca. 33-degrees-C with a steep increase in the resistivity and a decrease in the drift mobility. Powder X-ray diffraction confirms that this transition is the result of a structural transformation from Form I to Form II. The microscopic origin of the phase transition is ascribed to a subtle repulsive motion in the nearest-neighbour octyl chains which results in the decrease in the transfer integrals between the neighbouring pi-electron moieties of TTC8-TTF molecules within a segregated column.