TD-DFT study of the for coumarins

The excited state acid dissociation constants ( pK a ∗ ) of a panel of five coumarins have been studied using several PCM–TD-DFT protocols including both vibrational and state-specific (SS) effects. The pK a ∗ have been calculated using the excited state thermodynamical cycle and the Förster cycle. For this set of compounds the addition of explicit water molecules does not improve the computed acidity constants computed with the thermodynamical cycle. However, the addition of explicit water molecules to the PCM model apparently improves the quality of the optical spectra and hence the Förster estimates. State specific effects do not bring significant improvements in this case.