Large π-Conjugated Metal–Organic Frameworks for Infrared-Light-Driven CO2 Reduction

It remains challenging to excite traditional photocatalysts through near-infrared (NIR) light. Attempts to use NIR-light-response materials for photochemical reduction usually suffer from inapposite band position due to extremely narrow band gaps. Here, we report that large π-conjugated organic semiconductor engineered metal-organic framework (MOF) can result in NIR-light-driven CO2 reduction catalyst with high photocatalytic activity. A series of mesoporous MOFs, with progressively increased macrocyclic π-conjugated units, were synthesized for tuning the light adsorption range and catalytic performance. Attainment of these MOFs in single-crystal form revealed the identical topology and precise spatial arrangements of constituent organic semiconductor units and metal clusters. Furthermore, the ultrafast spectroscopic studies confirmed the formation of charge separation state and the mechanism underlying photoexcited dynamics. This combined with X-ray photoelectron spectroscopy and in situ electron paramagnetic resonance studies verified the photoinduced electron transfer pathway within MOFs for NIR-light-driven CO2 reduction. Specifically, tetrakis(4-carboxybiphenyl)naphthoporphyrin) MOF (TNP-MOF) photocatalyst displayed an unprecedentedly high CO2 reduction rate of over 6630 μmol h-1 g-1 under NIR light irradiation, and apparent quantum efficiencies (AQE) at 760 and 808 nm were over 2.03% and 1.11%, respectively. The photocatalytic performance outperformed all the other MOF-based photocatalysts, even visible-light-driven MOF-based catalysts.