Insights into the photoinduced degradation of terbuthylazine from aqueous solution: The synergic effects generated from hydrogen-bond interactions

In this work, we examined the stability of terbuthylazine (TBA) as well as the mechanisms related to its photoinduced degradation considering two conditions: i) when exposed (solely) to UV radiation and ii) when exposed to UV radiation in presence of H2O2. Ground state properties (such as bond lengths, hydrogen-bond interactions, and relative energetics) as well as excited state parameters (vertical excitation energies and generalized oscillator strengths, GOS) were determined through the use of standard and well documented density functional theory based electronic structure methods and, subsequently, explored for accomplishing the purpose of the work; results were obtained considering both the gas-phase and a (water) solvent environment. In terms of ground state, the presence of the additional hydrogen-bond interaction when the H2O2 molecule is nearing the N atom located in the opposite side to the Cl atom in TBA suggested the system to be more stable (for instance, 9.93 kJ/mol at the CAM-B3LYP/aug-cc-pVTZ level of theory in water) than its counterpart with the H2O2 molecule neighboring the N and Cl atoms. The excitation energies determined considering solvation were found to be in fairly good agreement when compared to the corresponding obtained in the gas-phase. Interestingly and more important, a different situation is observed in terms of GOS when solvation is considered. In this case, two excited states (versus no state in the gas-phase) were found to have considerably large GOS and, thus, are expected to be accessible at the UV region. Therefore, the interactions between TBA, H2O2, and water molecules (from the solvent environment) play an important role in regards to the excited states to be accessed. By coexisting with the UV photolysis of the H2O2 molecules in aqueous solution, the synergic effects from the TBA-H2O2-H2O interactions may add to the enhancement in the yield of the photoinduced degradation of TBA.