Phenol Photostatic Spectra and Quantum-Classical Photodynamic Deprotonation

The spectral-luminescence properties and photochemical conversions of phenol were analyzed for an isolated molecule as well as in water solvents in a continuum implicit model and explicit atomistic surroundings. This involved employing cut-edge hybrid quantum-classical methodologies to generate static optical spectra and the excited dissipative crossing potential energy curves. A combination of electronic excitations, gradient calculations, and embedding electrostatic potential fitting charges on quantum-classical molecular dynamic propagation trajectories provided statistically averaged absorption spectra. The mixed-reference spin-flip multiconfigurational linear response method based on reference triplet preprocessed in the time-dependent density-functional theory was utilized to determine conical intersections between the lowest excited and ground states, as well as two-stage transitions from the second excitation to the ground state. Non-adiabatic quantum-classical molecular dynamics defined photodissipative trajectories of excited states, their lifetimes, and crossing points through trajectory surface hopping together with the mixed-reference spin-flip and embedding electrostatic potential fitting approaches. Dyson orbitals of the extended Koopmans' theorem were applied to reveal the nature of molecular states at conical intersections and key points on photodynamic trajectories. Potential hydroxyl group cleavage predicted with conical intersections searching turns to “swift” OH deprotonation through |π→${\sigma }_{\mathrm{OH}}^{*}$⟩ transition along photodynamic propagations in contrast with “long” processes leading to benzene ring deformation with stable OH bond.