Hybrid mesoporous-silica materials functionalized by Pt(II) complexes: correlation between the spatial distribution of the active center, photoluminescence emission, and photocatalytic activity.

[Pt(tpy)Cl]Cl (tpy: terpyridine) was successfully anchored to a series of mesoporous-silica materials that were modified with (3-aminopropyl)triethoxysilane with the aim of developing new inorganic-organic hybrid photocatalysts. Herein, the relationship between the luminescence characteristics and photocatalytic activities of these materials is examined as a function of Pt loading to define the spatial distribution of the Pt complex in the mesoporous channel. At low Pt loading, the Pt complex is located as an isolated species and exhibits strong photoluminescence emission at room temperature owing to metal-to-ligand charge-transfer ((3)MLCT) transitions (at about 530 nm). Energy- and/or electron-transfer from (3)MLCT to O(2) generate potentially active oxygen species, which are capable of promoting the selective photooxidation of styrene derivatives. On the other hand, short Pt···Pt interactions are prominent at high loading and the metal-metal-to-ligand charge-transfer ((3)MMLCT) transition is at about 620 nm. Such Pt complexes, which are situated close to each other, efficiently catalyze H(2)-evolution reactions in aqueous media in the presence of a sacrificial electron donor (EDTA) under visible-light irradiation. This study also investigates the effect of nanoconfinement on anchored guest complexes by considering the differences between the pore dimensions and structures of mesoporous-silica materials.