Photodecomposition of bromophenols

Abstract

Photodecomposition of bromophenols (BPs) represents a potent channel of debromination and elimination of these species in the environment. From this perspective, the present contribution reports geometrical parameters, electronic absorption spectra and excited states of the complete series of BPs in their ground state (S0), as well as their first singlet exited state (S1). We calculate excitation energies for S0 → S1 transition within the framework of the time-dependent density functional theory (TDDFT). We estimate and discuss charges on bromine atoms and HOMO-LUMO energy gaps (E(H-L)) as molecular descriptors for the photoreactivity of BPs and photo-induced debromination mechanism of BPs. Spectral patterns reveal that, as the degree of bromination increases, peaks of absorption spectra red-shift toward wavelengths near 300 nm, for the pentabrominated phenol. Based on the analysis of optimised geometries and Hirshfeld's atomic charges, photodebromination of BPs commences via the loss of an ortho Br atom. The excitation energies decrease linearly with increasing number of bromine atoms. This indicates that, higher brominated congeners of BPs photodecompose more readily than lower brominated congeners.

Keywords: Bromophenols; Electronic properties; Photodecomposition; Reductive debromination reactions; TDDFT calculations.