Pressure-induced charge transfer phase transition in crystalline C60*C10H12Se4*2(CS2) molecular complex studied by Raman spectroscopy

The Raman spectra of the molecular neutral state complex C60*C10H12Se4*2(CS2) [C10H12Se4, tetramethyl-tetra-selenafulvalene (TMTSF)] have been measured as a function of pressure up to 9.5 GPa at room temperature. The pressure dependence of the frequencies of almost all intramolecular phonon modes exhibits irreversible changes at 5.0±0.5 GPa. These changes include splitting and softening of various modes, the most characteristic being the irreversible softening by 9 cm−1 of the Ag(2) pentagon-pinch (PP) mode, observed upon total release of pressure. This softening is the same as in the case of the potassium-doped fullerene KC60. These observations are attributed to a pressure-induced irreversible phase transition, associated with the transfer of one electron from TMTSF donor to C60 acceptor molecule.