Homogeneous-like photocatalysis: covalent immobilization of an iridium() complex onto polystyrene brushes grafted on SiO2 nanoparticles as a mass/charge transfer-enhanced platform

Current heterogeneous photocatalysis faces the major bottlenecks of limited mass transfer, charge recombination and tedious immobilization of expensive photocatalysts. In this work, fac-Ir(ppy)(3) is directly anchored at a low cost via covalent linkage to poly(4-vinyl benzyl chloride) (PVBC) brushes grafted on SiO2 nanoparticles (PVBC@SiO2 NPs) via Friedel-Crafts alkylation, affording PVBC@SiO2 NP-supported fac-Ir(ppy)(3) with high luminous efficacies such as emission lifetime and quantum yield. In the reductive cross-coupling of benzaldehydes/acetophenones with 1,4-dicyanobenzene (1,4-DCB), the as-fabricated photocatalyst affords benzhydrols in the same yields as homogeneous fac-Ir(ppy)(3), except for o-substituted benzaldehydes/acetophenones. In terms of the same yields as homogeneous fac-Ir(ppy)(3), a new catalytic model, named homogeneous-like photocatalysis, is proposed. In this catalytic model, the open stretching of PVBC brushes in DMSO enables the anchored fac-Ir(ppy)(3) to catalyse the reaction in a similar manner as homogeneous fac-Ir(ppy)(3), effectively avoiding charge recombination and mass transfer limitation. Furthermore, no significant decrease in yield (<5%) is observed over eight catalytic cycles, due to the good chemical and mechanical stabilities of PVBC@SiO2 NP-supported fac-Ir(ppy)(3). Overall, the immobilization of fac-Ir(ppy)(3) onto the PVBC brushes grafted on SiO2 NPs provides a mass/charge transfer-enhanced platform for supported photocatalysts.