Absorption and fluorescence spectra of the neutral and anionic green fluorescent protein chromophore: Franck-Condon simulation

► 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.