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 gasphase 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. (C) 2000 Elsevier Science B.V. All rights reserved.