Novel Two-Photon Singlet Oxygen Photosensitizers: Experimental and Theoretical Studies of Numbers of Bromine Atoms Effect

This article prepared a variety of novel singlet oxygen photosensitizers containing different numbers of bromine atoms, which could be divided into two groups (G1, G2) according to parent chemical structural characteristics. Effects of numbers of substituted bromine atoms on one- and two-photon optical properties of singlet oxygen photosensitizers were surveyed experimentally and theoretically. One-photon fluorescence emission spectra of the photosensitizers were affected more remarkably by numbers of substituted bromine atoms than one-photon absorption spectra. Two-photon absorption (TPA) properties of these photosensitizers were determined under 700~880nm near-infrared laser frequencies at 20nm step tuning. The photosensittizers with two substituted bromine atoms showed the largest TPA cross sections in two groups respectively. The generation of singlet oxygen by these photosensitizers under one- and twophoton irradiation was confirmed by photochemical methods and ESR (electron spin resonance) experiments. Singlet oxygen quantum yields of these photosensitizers were improved with increasing substituted bromine atoms, but the enhancement extents were different between G1 and G2. Molecular geometry optimization was performed to analyze further the fundamental reasons of influence of number of substituted bromine atoms on the ground and excited states of various photosensitizers.