Bisphenazine-Based Porous Aromatic Frameworks for Photocatalytic and Electrocatalytic Oxygen Activation

Abstract

Two closely related bisphenazine-based porous aromatic frameworks (PAFs), incorporating either phenyl (PAF-Phen) or benzothiadiazole (PAF-Phen-BT) linkers, were synthesized and investigated as metal-free nanostructured materials for photocatalytic and electrocatalytic oxygen activation. Both frameworks were comprehensively characterized using spectroscopic, structural, and surface techniques, and their optical and electronic properties were evaluated. The photocatalytic performance of the materials was assessed in aerobic oxidation reactions under visible-light irradiation, while their electrocatalytic activity toward the oxygen reduction reaction (ORR) was examined under electrochemical conditions. Density functional theory calculations were performed to characterize the excited-state properties underlying the photocatalytic behavior and to compute the vertical ionization energies, electron attachment energies, and O2 adsorption energies related to the electrocatalytic activity. The combined experimental and computational results show that PAF-Phen exhibits superior photocatalytic activity, operating predominantly through energy-transfer-mediated photosensitization of molecular oxygen, whereas PAF-Phen-BT displays enhanced electrocatalytic performance toward oxygen reduction. These contrasting behaviors are associated with framework-dependent electronic structure, excited-state dynamics, and oxygen–material interactions, which selectively bias the materials toward energy-transfer or electron-transfer-dominated pathways.