Anharmonic Franck-Condon simulation of the absorption and fluorescence spectra for the low-lying S1 and S2 excited states of pyrimidine

► Dynamic shift of spectra is equal to difference of reorganization energy. ► Intensity enhancement of absorption is against intensity weakening of fluorescence. ► The CASSCF method provides good accuracy for simulation of geometry difference. ► The first-order anharmonic correction is leading contribution to vibronic spectra.