Microhydration effects on the electronic properties of protonated phenol: A theoretical study

Abstract

The CC2 (second-order approximate coupled cluster method) has been employed to investigate microhydration effect on electronic properties of protonated phenol (PhH+) According to the CC2 calculation results on electronic excited states of microhydrated PhH+, for the S1 and S2 electronic states, which are of 1ππ* nature and belong to the A′ representation of molecular Cs point group, a significant blue shift effect on the S1 and S2 electronic states, which are of 1ππ* nature and belong to the A′ representation of molecular Cs point group, in comparison to corresponding transitions on bare cation (PhH+), has been predicted. Nevertheless, for the S3-S0 (1A′′, 1σπ*) transition, a large red shift effect has been predicted. Furthermore, it has been found that the lowest 1σπ* state plays a prominent role in the photochemistry of these systems. In the bare protonated phenol, the 1σπ* state is a bound state with a broad potential curve along the OH stretching coordinate, while it is dissociative in microhydrated species. This indicates to a predissociation of the S 1(1ππ*) state by a low-lying 1σπ* state, which leads the excited system to a concerted proton-transfer reaction from protonated chromophore to the solvent. The dissociative 1σπ* state in monohydrated PhH + has small barrier, while increasing the solvent molecules up to three removes the barrier and consequently expedites the proton-transfer reaction dynamics. © 2013 American Chemical Society.