Donor–Acceptor Mixed-Naphthalene Diimide-Porphyrin MOF for Boosting Photocatalytic Oxidative Coupling of Amines

Abstract

Integrating electron donor and acceptor chromophores as ligands within one MOF for light harvesting and photocatalysis appears to be a major synthesis challenge. Meanwhile, high-efficiency and selective aerobic oxidative coupling of amines to imines under mild conditions is highly desirable for scientific and industrial fields. Herein, via a facile one-pot synthetic strategy, an electron donor porphyrin ligand 5,15-di(p-benzoato)porphyrin (H2DPBP) was successfully integrated into a naphthalene diimide (electron acceptor)-based Zr-MOF (Zr-NDI) to construct a mixed-ligand MOF (Zr-NDI-H2DPBP) benefiting from the two ligands with similar geometry and connectivity. When utilized as a heterogeneous photocatalyst for aerobic oxidative coupling of benzylamine at room temperature, the prepared mixed-ligand Zr-NDI-H2DPBP exhibited a boosted imine generation rate (136 mmol g–1 h–1) far exceeding those of other noble-metal-free MOF photocatalysts and can be successfully applied to various benzylamine derivatives. Furthermore, from the results of the experiments and density functional theory calculations, the photocatalytic performance of Zr-NDI-H2DPBP is attributed to the photoinduced electron transfer from the donor H2DPBP to the acceptor NDI and the energy transfer facilitated by the photosensitized H2DPBP under irradiation, which effectively improve the electron–hole separation efficiency to generate abundant reactive active species of superoxide radical (O2•–) and singlet oxygen (1O2), respectively. This work provides an avenue to construct electron donor and acceptor chromophore-based light-harvesting systems by utilizing mixed-ligand MOFs as platforms to boost the solar-energy conversion.