Phase transition of tetrakis(octylthio)tetrathiafulvalene (TTC8–TTF) and crystal structure analysis

Abstract

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 °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 π-electron moieties of TTC₈–TTF molecules within a segregated column.