Anchoring of Pt(II) Pyridyl Complex to Mesoporous Silica Materials: Enhanced Photoluminescence Emission at Room Temperature and Photooxidation Activity using Molecular Oxygen

Chloro(2,2′:6′,2′′-terpyridine)platinum(II) ([Pt(tpy)Cl]Cl) complex was successfully anchored to a series of (3-aminopropyl)trimethoxysilane-modified mesoporous silica materials (MCM-41, SBA-15, and MCM-48). Pt L III -edge X-ray absorption fine structure (XAFS) measurements reveal that the Pt complex reacts with amino groups anchored on the mesoporous silica to create a new Pt−N bond. Upon anchoring, the nonemissive Pt(II) complex exhibits strong photoluminescence at room temperature, which is maximized near 530 nm due to ligand-centered ( 3 LC) and/or metal-to-ligand charge transfer ( 3 MLCT) transitions. The intensities of the emission increase in the order of MCM-41 < SBA-15 < MCM-48. In the case of MCM-48, the emission intensity is the highest at 0.42 wt % Pt loading, while concentration quenching is observed accompanied with a new emission due to the metal−metal-to-ligand charge-transfer ( 3 MMLCT) transition at high Pt loading. These results correspond well with the photocatalytic activities in the selective oxidation of styrene derivatives using molecular oxygen (O 2 ). It can be supposed that the enhanced excitation rate and quantum efficiency of the anchored Pt complex, due to the differences in nanoconfinement, increase the energy and/or electron transfer to O 2, which ultimately enhances the photooxidation activity. The 3D-connected channel structure of the MCM-48 silica also accounts for the high photocatalytic activity, where the diffusion of O 2 toward the anchored Pt complex occurs smoothly compared to the one-dimensional MCM-41 and SBA-15 silicas, as demonstrated by the quenching rate constants obtained from Stern−Volmer plots.