Electronic spectra of coumarin-151 in polar solvents: Linear response free energy approach

We calculate the absorption and fluorescence spectra of coumarin-151 in polar solvents by using the linear response free energy method, which provides the nonequilibrium solvation free energy for the final state. We compare the solvent effects on the bandwidths and shifts with those observed by experiments. The results show that the spectral feature of coumarin-151 is dominated by the relative stability of intramolecular charge transfer (ICT) to local excitation (LE) states. The ICT state stabilization is essential for spectral difference between polar and nonpolar solvents.