Photoinduced Aerobic Oxidation Driven by Phosphorescence Ir(III) Complex Anchored to Mesoporous Silica

A series of photocatalysts with the [Ir(Mebib)(ppy)Cl] (Mebib: bis(N-methylbenzimidazolyl)pyridine, ppy: phenylpyridine) complex anchored to (3-aminopropyl)trimethoxysilane-modified mesoporous silica materials (SBA-15, MCM-48, and MCM-41) were successfully synthesized. At room temperature, the anchored Ir(III) complex exhibits a strong phosphorescence emission at nearly 530 nm due to triplet metal-to-ligand charge transfer ((MLCT)-M-3) transitions. The intensity of the emission increases in the sequence of MCM-41 < MCM-48 < SBA-15, which follows the photocatalytic activity in the selective oxidation using molecular oxygen (O-2) under visible light irradiation (lambda > 420 nm). Scavenging experiments suggest that singlet oxygen (O-1(2)) is the main reactive species. It is assumed that the enhanced excitation rate and quantum efficiency of the anchored Ir complex increase the energy-transfer from the excited (MLCT)-M-3 to O-2, leading to an increase in photooxidation activity.