Abstract
The analysis of the absorption spectrum and density of states of a cluster of phenol solvated with 15 water molecules indicates that the reorganization of the water molecules, facilitating the formation of solvated electrons, is a plausible mechanism in the photodissociation of phenol. Using quantitative wavefunction analysis, we demonstrate that while charge-transfer states involving electron transfer from phenol to water are mainly dark, a considerable number of them exists below the maximum of the ππ* absorption band and could be populated by internal conversion. These low-lying charge-transfer states do not show extended O-H distances, but are found for large electron-hole separations at which several water molecules can solvate and stabilize the transferred electron. Thus, charge-transfer states in solvated phenol can be stabilized by two factors: (i) elongation of the O-H bond, as was extensively discussed in the past, and (ii) reorganization of solvent molecules, as it is shown here.
Highlights
IntroductionBased on theoretical calculations,[6,7,8,9] it has been proposed that after excitation to the bright first excited state of pp* character, a conical intersection can be reached upon O–H elongation to populate a charge-transfer (CT) state of ps* character with low oscillator strength
Inclusion of just one water molecule leads to a red-shift of 0.11 eV compared to the calculated gas-phase spectrum, and a blue-shift of 0.16 eV compared to the experimental spectrum in aqueous solution
This conclusion is drawn from the characterization of the absorption spectrum and density of states (DOS) of phenol solvated with 15 water molecules
Summary
Based on theoretical calculations,[6,7,8,9] it has been proposed that after excitation to the bright first excited state of pp* character, a conical intersection can be reached upon O–H elongation to populate a charge-transfer (CT) state of ps* character with low oscillator strength. This state is dissociative with respect to the O–H bond, leading to the hydrogen atom and phenoxyl radical PhO products. In aqueous solution this orbital is located in the solvent and, upon excitation of solvated phenol a concerted proton and electron transfer from phenol to the solvent has been postulated[6] to take place
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