Photoinduced intramolecular charge transfer process of betaine pyridinium: A theoretical spectroscopic study

Using Time-Dependent Density Functional Theory and taking into account bulk solvent effects, we investigate the absorption and emission spectra of a betaine pyridinium molecule, the 2-(1-pyridinio) benzimidazolate (SBPa). This molecule exhibits strong photoinduced intramolecular charge transfer (ICT). We have identified two different electronic states involved, respectively, in the strong bathochromic ICT absorption band (S2) and in the moderate emission band (S1). The ICT process is analyzed in terms of charge distribution and dipole moment evolutions upon photoexcitation. These results are compared with steady-state spectroscopic measurements.