Ultrafast laser multihoton-gated reaction of photochromic molecules.

光致变色系统的瞬时性质变化不仅从基本化学反应过程的角度，而且从可重写光存储器和开关等光电器件的应用角度都受到了广泛的关注。最近，我们报道了一种低产率的光致变色二乙烯衍生物在稳态光照射下的环还原反应增强（超过50倍）。反应谱的激发强度和脉冲持续时间效应表明，通过多光子吸收获得的高激发态可以打开有效的光致变色反应通道。这种多光子门控反应可能为具有非破坏性读出能力的可擦存储器介质提供一种新的途径。为了阐明多光子门控环可逆反应的详细机理和确认其普遍性，我们利用纳秒、皮秒和飞秒脉冲激光激发，研究了不同二乙烯衍生物在溶液和聚合物基体中的反应动力学。从这些结果可以看出，在皮秒激光脉冲激发下，所有的二乙烯衍生物都发生了多光子环还原反应，这种反应也发生在聚合物基体中。此外，用可见光的双光子能量直接激发单光子并不能导致有效的循环逆转。这一结果表明，受光吸收选择规则调控的特定激发态对有效反应的发生起着重要作用。除了皮秒非相干多光子激发外，我们还研究了飞秒双脉冲激发的相干多光子激发。研究的结果是，我们观察到低频相干振动的相位对反应产率的调制。全面讨论了多光子门控光致变色反应的动力学和机理。少

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