A TDDFT study of the electronic spectrum of s-tetrazine in the gas-phase and in aqueous solution

Time-dependent density functional theory (TDDFT) is applied to calculate vertical excitation energies of s-tetrazine, both in the gas-phase and in aqueous solution. The model density functional (PBE0) is obtained by combining the Perdew–Burke–Erzenrhof (PBE) generalized gradient functional with a predetermined amount of exact exchange, while the polarizable continuum model (PCM) is used to mime solvent effects on electronic transitions. Our results in the gas-phase show that the PBE0 functional provides accurate excitations both to valence and to low-lying Rydberg states. At the same time, the experimental solvent shifts in aqueous solution are well reproduced when the solute and the first solvation shell are embedded by a continuum solvent. These results show the potentialities of the combined TDDFT/PCM approach for the study of UV spectra of aromatic compounds.