PCM/TD-DFT study of the two lowest excited states of uracil derivatives in solution: The effect of the functional and of the cavity model

The Vertical Excitation Energies of the two lowest energy excited electronic states of uracil and 5,fluoro-uracil have been computed in water and acetonitrile at the PCM/TD-DFT level by using four different density functionals and different PCM models. PBE0, LC-ωPBE, CAM-B3LYP, and M05-2X functionals provide similar results, and agree in predicting that a fluoro substituent stabilizes the spectroscopic state, a π → π∗ transition, with respect to the lowest energy dark excited state, with n → π∗ character. State-Specific PCM/TD-DFT calculations are confirmed to provide a more reliable estimate of solvent effect than Linear Response PCM/TD-DFT calculations. Finally, the energy difference between the excited electronic states noticeably depends on the size of the solute cavity used in the PCM calculations.