Nonadiabatic decay dynamics of phthalide from the light‐absorbing S ₃3 (ππ*) state‐resonance Raman spectroscopy and CASSCF study

摘要

> Conical intersection or curve‐crossing is well known to be an efficient dynamic funnel for nonadiabatic transition between two different potential energy surfaces in chemical dynamics. Tremendous efforts have been made in the direct experimental probing of conical intersection. However, the direct following‐up of the dynamic process initiated from the Franck–Condon (FC) region toward a curve‐crossing point is still challenging. With the aid of complete active space self‐consistent field calculations, the resonance Raman spectroscopy has been applied to face challenges. Herein, the nonadiabatic decay dynamics of phthalide initiated from the light‐absorbing S ₃ (ππ*) state were studied. The UV and vibrational spectra were assigned with the aid of the density functional theory calculations and normal‐mode analysis. The minima of the six lowest electronic excited states (S ₁ , S ₂ , S ₃ , T ₁ , T ₂ , and T ₃ ) and the corresponding minimum‐energy intersections were fully optimized at the complete active space self‐consistent field level. The B‐band resonance Raman spectra in acetonitrile were simulated by using the time‐dependent wave‐packet theory in a simple model to obtain the dimensionless normal‐mode displacements, and the results were compared with the relative changes of the geometric structural parameters between the curve‐crossing points and S ₀ so as to help determine the decay channels initiated from the FC region. Two nonadiabatic decay channels were discovered, and that one of these had not been previously observed. The results provided general insights into the ultrafast decay dynamics initiated from the FC region of the light‐absorbing excited state to the nearby conical intersection or curve‐crossing points for organic molecules in solution. Copyright ? 2017 John Wiley & Sons, Ltd.