Photocatalyst with annulated binuclear thioporphyrazine-enhancing photocatalytic performance by expansion of a π-electron system

Abstract

A novel planar binuclear zinc hexa(2,3-bis(butylthio)) porphyrazine (bi-ZnPz(SBu)₆) sharing one benzene ring has been synthesized. In order to assess the photocatalytic activity of bi-ZnPz(SBu)₆, it was loaded on neutral Al₂O₃ to form a composite photocatalyst bi-ZnPz(SBu)₆@Al₂O₃, then the degradation of rhodamine B (RhB) in an aerated suspension under simulated sunlight was carried out. It was discovered that the photocatalytic activity of bi-ZnPz(SBu)₆ is two times higher than that of its mononuclear counterpart. A possible mechanism was proposed through theoretical calculation by density functional theory (DFT) and detection of reactive oxygen species by electron spin resonance (ESR) technology. The results show that the HOMO–LUMO energy gap (ΔE_H–L) of bi-ZnPz(SBu)₆ is much smaller than that of its mononuclear counterpart, which is beneficial to the excitation of energy and electron under irradiation of light. Super-powerful signals of singlet oxygen (¹O₂) formed by bi-ZnPz(SBu)₆ indicated that the energy transfer capacity of bi-ZnPz(SBu)₆ was enhanced significantly under irradiation of light while the electron transfer capacity was decreased due to the weakening of the contribution from the active S atoms in the thiobutyl groups in the periphery to the HOMO. This work introduces a novel and promising biomimetic antenna molecule, whose excellent light-harvesting capacity will be favored and admired in the field of solar cells, photocatalysis and photodynamic therapy.