FEMTOSECOND SPECTROSCOPIC STUDY ON SOME PHOTOCHROMIC AND ELECTROCHROMIC REACTIONS AND THEIR RESPONSE AT THE INTERFACE

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Photochromic and electrochromic reactions of some diarylethene derivatives, salicylidene aniline (SA) derivatives, and Rh- and Ru-complexes conjugated with azobenzene derivatives have been investigated by femtosecond laser spectroscopy, semi-empirical molecular orbital calculation, and electrochemical methods. Photochromic reaction of a spiropyran derivative on the solid interface has been also examined by AFM and time-resolved fluorescence SNOM.It was found that the proton transfer of SA took place with a time constant of 200 〜 300 fs followed by the structural change. The solvent dependence of the rate was negligibly small at R.T.indicating the efficient photochromic reaction in the solid phase. In diarylethene derivatives, the ring closure reaction was firstly confirmed to take place without any intermediates according to the Woodward-Hoffmann rule. The activation energy of the reaction was also found to be negligibly small. In addition, the large structural change in the excited si … More nglet state reduces the quantum yield of the photochromic reaction.In azobenzene derivatives, the trans-cis isomerization was found to occur from S1 state with a time constant of 1 〜 10 ps depending on the solvent viscosity through the inversion mechanism even in the excitation to the S2 state. Rh-complexes with azobenzene show trans-cis isomerization although their redox behaviors are irreversible, whereas Ru-complexes show ultrafast excitation energy transfer from azobenzene to MLCT state without any isomerization although their redox behaviors are reversible.Photochromic response at the solid interface was examined by scanning probe microscopy. The formation of merocyanine from spiropyran was confirmed to be almost no displacement of the molecules on the solid interface. However, the J-aggregate was formed through the large displacement of a few 100 nm to μm of molecules actrivated by the thermal energy.These results are considered to be indispensable to develop new photochromic and electrochromic materials and nanosized photo- and electro-responsive devices. Less