Non-Condon effects in one- and two-photon absorption spectra of the green fluorescent protein
We report calculations of one and two photon absorption (OPA and TPA, respectively) spectra of the green fluorecent protein chromophore using the double-harmonic parallel-mode approximation and including explicit dependence of the electronic transition moments on nuclear geometry. The non-Condon effects are found to be more significant for TPA. They change the shape of the spectra and result in a blue shift of 500 cm-1 of the TPA spectra relative to OPA. The computed shift is in excellent agreement with the experimentally observed 700 cm-1.