Optical properties of β-brominated meso-tetraphenylporphyrins: Comparative experimental and computational studies

Abstract

The UV-vis and fluorescence spectra of a series of [Formula: see text]-brominated derivatives of meso-tetraphenylporphyrin (H[Formula: see text]TPPBr[Formula: see text]; [Formula: see text] 0, 2, 4, 5, 6, 7, 8) were used to investigate the steroelectronic effects of bromine atoms on the optical properties of H[Formula: see text]TPP. The wavelength and intensity of the absorption and emission bands were found to be influenced by the bromine atoms. The degree of configuration interaction between the S[Formula: see text] and S[Formula: see text] excited states and fluorescence quantum yield and their dependence on the bromine atoms were also studied. Computational studies based on density functional theory and time-dependent density functional approach (DFT and TD-DFT) support and provide an explanation for the spectral changes associated with the bromination of H[Formula: see text]TPP. Furthermore, the solvent effect on the spectral properties of higher degrees of [Formula: see text]-bromination was attributed to the formation of relatively strong hydrogen bonds between their saddle-distorted porphyrin cores and the solvent molecules.