A Stable Triphenylamine-Based Zn(II)-MOF for Photocatalytic H 2 Evolution and Photooxidative Carbon-Carbon Coupling Reaction.

Efficient charge transfer has always been a challenge in heterogeneous MOF-based photoredox catalysis due to the poor electrical conductivity of the MOF photocatalyst, the toilless electron-hole recombination, and the uncontrollable host-guest interactions. Herein, a propeller-like tris(3'-carboxybiphenyl)amine ( H 3 TCBA ) ligand was synthesized to fabricate a 3D Zn 3 O cluster-based Zn(II)-MOF photocatalyst, Zn 3 (TCBA) 2 (μ 3 -H 2 O)H 2 O ( Zn-TCBA ), which was applied to efficient photoreductive H 2 evolution and photooxidative aerobic cross-dehydrogenation coupling reactions of N -aryl-tetrahydroisoquinolines and nitromethane. In Zn-TCBA , the ingenious introduction of the meta-position benzene carboxylates on the triphenylamine motif not only promotes Zn-TCBA to exhibit a broad visible-light absorption with a maximum absorption edge of 480 nm but also causes special phenyl plane twists with dihedral angles of 27.8-45.8° through the coordination to Zn nodes. The semiconductor-like Zn clusters and the twisted TCBA 3- antenna with multidimensional π interaction sites facilitate photoinduced electron transfer to render Zn-TCBA a good photocatalytic H 2 evolution efficiency of 27.104 mmol·g -1 ·h -1 in the presence of [Co(bpy) 3 ]Cl 2 under visible-light illumination, surpassing many non-noble-metal MOF systems. Moreover, the positive enough excited-state potential of 2.03 V and the semiconductor-like characteristics of Zn-TCBA endow Zn-TCBA with double oxygen activation ability for photocatalytic oxidation of N -aryl-tetrahydroisoquinoline substrates with a yield up to 98.7% over 6 h. The durability of Zn-TCBA and the possible catalytic mechanisms were also investigated by a series of experiments including PXRD, IR, EPR, and fluorescence analyses.