In this study, a series of beta-brominated meso-tetraphenylporphyrins, H2TPPBrx (x = 2, 4, 6 and 8) with remarkably red shifted absorption bands towards the longer wavelengths of the visible light known as therapeutic window and their diprotonated analogues were used as photosensitizers in the aerobic oxidation of cyclooctene to investigate the influence of degree of 1 bromination on the photocatalytic activity and oxidative stability of H2TPP. Furthermore, the 1 brominated porphyrins showed significantly decreased fluorescence quantum yields (phi(F)) and radiative decay rate constants but increased nonradiative decay rate constants. The highest catalytic activity was observed in the case of the partially brominated porphyrins, H2TPPBr2 and H2TPPBr4. While, H2TPPBr2 and H2TPPBr4 were as stable as H2TPP, the oxidative degradation of H2TPPBr6 and H2TPPBr8 was remarkably higher than that of the non-brominated porphyrin. A good correlation was observed between the photocatalytic activity of H2TPPBrx and their diprotonated species and the singlet oxygen quantum yields (phi(Delta) = 0.02-0.21 and 0.12 to 0.59, respectively), determined chemically through the reaction of singlet oxygen with 1,3-diphenylisobenzofuran (DPBF). In order to examine the effects of steric hindrance on the photocatalytic properties of the brominated porphyrins, 1 tetra-brominated derivative of meso-tetra(2-methylphenyl) porphyrin, H2T(2-Me)PPBr4 with bulky methyl substituents at the ortho positions was prepared and compared with H2TPPBr4. The steric hindrance caused by the presence of four methyl groups could improve the oxidative stability of the photosensitizer by 30 to 50% at the cost of significant loss of photocatalytic activity. On the other hand, diprotonation of H2TPPBrx with weak and strong acids (CH2ClCOOH and CF3COOH) was found to be an efficient approach to overcome the extensive oxidative degradation of these photosensitizers, with concomitant red shift of the absorption bands to 451-490 and 674-743 nm, in the Soret and Q band regions, respectively. (C) 2019 Elsevier Inc. All rights reserved.