Time Resolved Resonance Raman Spectroscopic and Laser Flash Photolysis Studies on Typical Significant Stock-Shifted large π System

It is concluded that the behavior of singlet transients is barely altered by the acidity and the polarity since the photochemical features are almost identical in both nanosecond and femtosecond domain aside from the insignificant of lifetime (within several nanoseconds). More importantly, the ns-TR3 results of in acetonitrile shows the concrete and direct evidence that the transition from ground state to singlet state gives rise to the structural and electronic changes. In the excited state, the C–C bonds on the oxepin ring have a larger double bond character than for the ground state leading to smaller torsion angles thus transferred to a planar structure from the original saddle-shaped structure with a more continuous electron delocalization than the ground state. In conclusion, this direct experimental findings could shed light on fundamental mechanism studies of the phototrigger reactions of the large conjugated systems.