A theoretical study on the relationship between the excited states and the photochemical behavior of stilbene and its derivatives

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The photochemical behavior of stilbene and its derivatives has been of great interest in photochemistry. In spite of much effort to elucidate it both experimentally and theoretically, there is no widely accepted picture. In this research project, we examined the electronic structures and dynamics in the excited states of stilbene and its derivatives (stilbenoids) by means of ab initio molecular orbital (MO) method. We reduced the computational labor of complete. active space self-consistent field calculations based on preliminary configuration interaction calculations.1) the photochemical behavior of stilbene in the Franck-Condon (FC) region of teans-stilbeneWe calculated the potential energy surfaces in the FC region to know the initial process of trans-stilbene. Right after electronic excitation of S_0-S_3 which is main transition in the first excited manifold, a planar delocalized quinoid structure is preferable so as for the photoisomerization to take place.2) the photochemical behavior of stvreneWe globally scanned the potential energy surfaces of styrene including the important ingredients of the S_1/S_0- and S_2/S_1-conical intersections (CIXs) so as to present a new and reasonable picture of the photochemistry of styrene.3)the S_1/S_0-CIX_s of styrene derivativesWe calculated the S_1/S_0-CIX_s of styrene derivatives. It is found that they are characterized by a crossing region between zwitterionic and covalent diradical states.4) the photochemical behavior of 4-dimethylamino. 4'-cyanostilbene (DCS)We calculated the free energy surface of DCS in polar solvent to discuss the formation mechanism of the twisted internal charge transfer state. We also calculated the S_1/S_0-CIX for the photosiomerization.