Absorption and emission spectra in gas-phase and solution using TD-DFT: Formaldehyde and benzene as case studies

The first vertical and relaxed singlet excited states of formaldehyde and benzene have been computed using time-dependent density functional theory in conjunction with the hybrid PBE0 functional. Absorption, adiabatic and fluorescence transition energies have been determined. In addition to a basis set study, we have assessed the bulk solvent effects using the polarizable continuum model. It turns out that 6-311+G(d,p) provides converged results for all investigated spectroscopic characteristics, although 6-31G(d,p) could be sufficient for determining the ground and excited structures of benzene. The solvent effects are quite small (0.1 eV variations) and, in first approximation, can be neglected during the excited-state optimization.