Intramolecular charge transfer modulation of zinc porphyrin-melamine complexes for efficient reactive oxygen species photogeneration on TiO2 nanoparticles

Two zinc porphyrin-melamine complexes are designed for photocatalysis. • The two TiO 2 composites show similar morphology and light harvesting ability. • TPA-surpasses TPTZ-substituted samples for photocurrent and degradation. • All h + , .•OH and •O 2 − are the reactive oxygen species for photodegradation. • Cascade superiors competitive charge transfer for ROS generation. The generation efficiency of reactive oxygen species (ROS) typically governs the photodegradation performance. This work aims to compare two molecular design protocols in ROS photogeneration on TiO 2 nanoparticles. To this end, two zinc porphyrin-melamine conjugated complexes are designed, denominated as tri-TPTZ-ZnP-mel and tri-TPA-ZnP-mel, bearing triphenyltriazine (TPTZ) and triphenylamine (TPA) as the substituents, respectively. Our results demonstrate that the electron-withdrawing, planar tri-TPTZ-ZnP-mel induces intramolecular competitive electron transfer and accelerates charge recombination. In contrast, the electron-donating, three-dimensional structured tri-TPA-ZnP-mel suppresses molecular aggregation, promotes cascade charge transfer, and delivers significantly higher photocurrent, lower interfacial charge-transfer resistance, and superior photodegradation activity toward organic dyes. Mechanistic studies clarify the distinct roles of holes (h + ), hydroxyl radical (•OH) and superoxide radical (•O 2 − ) governed by substituent-driven charge transfer behaviours. Download: Download high-res image (309KB) Download: Download full-size image