Initial dynamics of photo-induced ionic (I) to neutral (N) phase transition in tetrathiafulvalene-p-chloranil (TTF-CA) was investigated by femtosecond reflection spectroscopy with various excitation intensities. A charge transfer excitation in the I phase produces N donor (D0)-acceptor (A 0) strings within 2 ps. For a weak excitation intensity, these initial N states decay with a life time of 300 ps at 4 K., but rather multiply leading to macroscopic I-N conversion within 20 ps at 77 K just below the N-I transition temperature TNI. Near TNI, we also found the coherent motion of the macroscopic N-I domain boundary with a period of 85 ps.
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