Ultrafast laser multihoton-gated reaction of photochromic molecules.

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The instant property change in photochromic systems has been attracting muuch attention not only from the viewpoint of the fundamental chemical reaction processes but also from the application to optoelectronic devices such as rewritable optical memory and switches. Recently, we reported laser-induced enhancement(more than 50 times)of cycloreversion reaction in a photochromic diarylethene derivatives with a low reaction yield under the steady-state light irradiation. The excitation intensity and pulse duration effects of the reaction profiles revealed that higher excited states attained by multiphoton absorption could open the effective photochromic reaction channel. This multiphoton-gated reaction may provide a new approach to erasable memory media with non-destructive readout capability.In order to elucidate the detailed mechanisms and to confirm the generality of the multiphoton-gated cycloreversion reaction, we have investigated the reaction dynamics of various diarylethene derivat … More ives in solutions and in polymer matrices by means of nanosecond, picosecond, and femtosecond pulsed laser excitation. From these results, it was revealed that all of the diarylethene derivatives examined here underwent the multiphoton cycloreversion by picosecond laser pulsed excitation and this reaction also took place in polymer matrices. In addition, direct one photon excitation with two-photon energy of the visible light did not lead to the efficient cycloreversion. This result indicates that the specific excited state regulated by the optical absorption selection rule takes an important role for the efficient reaction to take place.In addition to the picosecond incoherent multiphoton excitation, we have investigated the coherent multiphoton excitation by means of the femtosecond double pulse excitation. As a result of this investigation, we have observed the modulation of the reaction yield dependent on the phase of the low frequency coherent vibrations. The dynamics and mechanisms of multiphoton-gated photochromic reaction were comprehensively discussed. Less