Geometry changes upon S0 → S1 electronic excitation of aniline derivatives

Molecular geometries of some substituted benzenes in their lowest singlet excited state are evaluated using ab initio quantum mechanical calculation and compared with the intensity distributions in the LIF excitation spectra. The geometry changes that occur upon electronic excitation are investigated for benzene derivatives containing the following molecular groups: –NH2, –OH, –COOH, –COOCH3, –CN and –CH3. The intensity distributions in the LIF excitation spectra have been analyzed using multidimensional FC factors, taking into account the displacements of the normal mode coordinates, frequency changes and normal mode mixing. All these quantities were derived from HF/6-31++G**and CIS/6-31++G** calculations.