TETRAMETHYLBENZIDINE-TCNQ - STUDIES OF THE NEUTRAL-IONIC TRANSITION BY TIME-RESOLVED NONDEGENERATE 4-WAVE-MIXING

Y. Iwasa et al. reported recently experimental evidence for the occurr ence of a temperature-induced neutral-ionic transition (TINT) in a new mixed stack charge transfer (CT) compound consisting of 3,3',5,5' tet ramethyl benzidine (TMB) as the donor and TCNQ as the acceptor (T-c = 205 +/- 5K). We have used femtosecond laser pulses and the technique o f time resolved non degenerate four-wave mixing to measure the third o rder susceptibility chi((3)) of thin films of TMB-TCNQ, and the corres ponding temporal response function of temperature above and below the neutral-ionic transition. The change of the decay time of different co ntributions to chi((3)) with T will be discussed in connection with th e physical process related to this neutral-ionic phase transition. We point out the importance of the electron-phonon interactions in this p hase transition.