Ultrafast optical switching from an ionic ( I) to a neutral ( N) state in TTF-CA was observed in femtosecond reflection spectroscopy. Charge transfer excitation in the I phase produces N donor ( D0) acceptor ( A0) strings within 2 ps. These initial N states decay with a lifetime 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 T(NI). Near T(NI), we also found the evidence for the coherent motion of the macroscopic N-I domain boundary with a period of 85 ps.

Ferroelectricity in an organic charge-transfer compound, tetrathiafulvalene-p-chloranil ͑TTF-CA͒, originating from the one-dimensional valence and lattice instabilities, has been investigated by an electroreflectance ͑ER͒ method. Microscopic ER spectroscopy in the visible region enables real-space observations of both ferroelectric domain structures with a few hundred micrometers in size and depinning of the domain walls under strong electric fields. In addition, from ER spectroscopy in the infrared molecular-vibration region, we demonstrate that field-induced changes in the dimeric molecular displacement as well as charge transfer between TTF and CA molecules play an important role in the large dielectric response in TTF-CA.

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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 (D 0 )-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 T NI . Near T NI , we also found the coherent motion of the macroscopic N-I domain boundary with a period of 85 ps.