Single-chromophore single-molecule photocatalyst for the production of dihydrogen using low-energy light

Single-chromophore single-molecule photocatalysts for the conversion and storage of solar energy into chemical bonds are rare, inefficient and do not use significant portions of the visible spectrum. Here we show a new, air-stable bimetallic scaffold that acts as a single-chromophore photocatalyst for hydrogen-gas generation and operates with irradiation wavelengths that span the ultraviolet to the red/near-infrared. Irradiation in acidic solutions that contain an electron donor results in the catalytic production of hydrogen with 170 ± 5 turnovers in 24 hours and an initial rate of 28 turnovers per hour. The catalysis proceeds through two stepwise excited-state redox events—atypical of the currently known homogeneous photocatalysis—and features the storage of multiple redox equivalents on a dirhodium catalyst enabled by low-energy light. Homogeneous photocatalysts for the conversion and storage of solar energy typically feature separate sensitizer–catalyst assemblies, whereas previous examples of single-chromophore single-molecule photocatalysts are inefficient and do not use significant portions of the visible spectrum. Now a dirhodium single-chromophore single-molecule catalyst has been developed that generates hydrogen using low-energy light through a previously unobserved mechanism.