Structural Dynamics of Phenyl Azide in Light-Absorbing Excited States: Resonance Raman and Quantum Mechanical Calculation Study

Abstract

The excited state structural dynamics of phenyl azide (PhN3) after excitation to the light absorbing S2(A′), S3(A′), and S6(A′) states were studied using the resonance Raman spectroscopy and complete active space self-consistent field calculations. The vibrational spectra and the UV absorption bands were assigned on the basis of the Fourier transform (FT)-Raman, FT-infrared measurements, the density-functional theory computations and the normal mode analysis. The A-, B-, and C-bands resonance Raman spectra in cyclohexane, acetonitrile, and methanol solvents were, respectively, obtained at 273.9, 252.7, 245.9, 228.7, 223.1, and 208.8 nm excitation wavelengths to probe the corresponding structural dynamics of PhN3. The results indicated that the structural dynamics in the S2(A′), S3(A′), and S6(A′) states were significantly different. The crossing points of the potential energy surfaces, S2S1(1) and S2S1(2), were predicted to play a key role in the low-lying excited state decay dynamics, in accordance with Kasha's rule, and N7=N8 dissociation. Two decay channels initiated from the Franck-Condon region of the S2(A′) state were predicted: the radiative S2,min→S0 radiative decay and the S2→S1 internal conversion through the crossing points S2S1(1)/S2S1(2).