An Adaptable Blueprint for Non-Metal Near-Infrared Organic Photo-catalysts by Aromatic Sulfones

We present a versatile approach for designing and utilizing high-performance near-infrared (NIR) organic photo-catalysts based on aromatic sulfones. Our sulfone-rosamine-based photo-catalyst 3 demonstrates exceptional capabilities, including high photo-oxidation ability for metal-free photo-oxidative bromination, intrinsically oxygen-independent redox reactions, and remarkable photo-stability with a turnover number (TON) exceeding 2800. We showcase the photo-catalyst's efficacy in photo-oxidative bromination of aromatic compounds under 738 nm illumination. The reaction mechanism is elucidated through a combination of electrochemical studies, time-resolved spectral measurements, and DFT calculations. Transient absorption measurements using the randomly interleaved pulse train (RIPT) method reveal the photo-excited state of 3 approximately 1 ns post-excitation, demonstrating electron transfer from the substrate to excited 3 as the initial step. 3 demonstrated its photocatalytic ability for several aromatic substances, including those that exhibit strong light absorption below 500 nm, which overlaps with the absorption of certain conventional organic photo-catalysts. This aromatic sulfone-based approach offers a robust blueprint for developing NIR organic non-metal photo-catalysts with superior photo-oxidation ability and stability, addressing key limitations of conventional organic NIR-photocatalysts.