A series of thioporphyrazines have been synthesized via cocondensation from 2,3-dicyano-1,4-dithiin (A) and 2,3-bis(butylthio) maleonitrile (B) and thoroughly characterized with UV-vis, H-1 NMR and MALDI-TOF MS. Through modulation of peripheral substituents of thioporphyrazines, both symmetrical and asymmetrical molecular structures in thioporphyrazines including B-4, cis-A(2)B(2), trans-A(2)B(2) and AB(3) were obtained, and were further used to react with cobalt acetate to form metal complexes, cobalt thioporphyrazines. Moreover, they were loaded on Al2O3 to form biomimetic catalysts for photocatalytic activation of dioxygen, whose efficiencies were assessed by photodegradation of Rhodamine B (RhB) in an aerated suspension under simulating sunlight irradiation. Importantly, it was found that the lower on the molecular symmetry of thioporphyrazine delivers the better on the photocatalytic activity. Electrochemical and theoretical studies demonstrated that lowering the molecular symmetry of the cobalt thioporphyrazines moderately decreased the HOMO-LUMO energy gap and increased the contribution of S atom in substitiuents to HOMO so as to enhance the photocatalytic activity. A possible mechanism to predict this reaction pattern was proposed through both detailed analysis of degradation products by HPLC and detection of the main reactive oxygen species (ROS) by ESR, indicating both energy transfer (major) and electron transfer (minor) to dioxygen to exist in the heterogeneous light photocatalytic system. (C) 2016 Elsevier B.V. All rights reserved.