Photoinduced dissociation of donor–acceptor pairs in non‐magnetic phase of organic charge‐transfer crystal of tetrathiafulvalene–tetrabromo‐1,4‐benzoquinone

We have studied 532 nm laser‐induced changes in the infrared reflection of a charge‐transfer (CT) crystal of tetrathiafulvalene (TTF) and tetrabromo‐1,4‐benzoquinone (BA) at 4 K. The spectra of the fractional change (Δ R / R ) were characterized by dips situated in proximity to the structures ascribed to the a g ‐mode vibrations of TTF + and BA – at low excitation intensity. However, the excitation above 0.2 W cm –2 gave structures characterized by the inverted shape of the a g ‐mode structures, indicating that the laser excitation reduced the intensity of the a g ‐mode structures. The appearance of the a g ‐mode structures is associated with loss of the inversion centre of the crystal due to the dimerization of TTF + and BA – ; hence, the intensity reduction of the a g ‐mode structures is ascribed to dissociation of TTF + ‐BA – pairs. We found that Δ R / R increased super‐linearly with enhancing excitation intensity. The result suggests that the dissociation involves a multi‐quantum process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)