Density functional theory calculation of molecular structure and vibrational spectra of dibenzothiophene in the ground and the lowest triplet state

The molecular geometries and harmonic vibrational frequencies of the ground and the lowest triplet state of dibenzothiophene have been calculated using the Becke-3-Lee-Yang-Parr (B3LYP) density functional methods with the 6-31G* basis set. A structural change occurs from a benzene-like to a planar, quinone-like form upon the excitation to the first excited state. Scaled vibrational frequencies for the ground state obtained from the B3LYP calculation show good agreement with experiment. On the basis of the calculated and experimental vibrational frequencies, a few vibrational fundamentals for both states are newly assigned and the spectral position of some missing lines are predicted.