Expanding the Color Space in the Two-Color Heterogeneous Photocatalysis of Ullmann C-C Coupling Reactions

The Ullmann reaction can be heterogeneously photo catalyzed by UV excitation of Pd@TiO2. While a similar dose of visible light does not initiate the reaction, combination with UV light enhances activity and selectivity toward cross-combination products. The reaction involves photoresponsive intermediates, likely associated with the catalyst, where Pd nanostructures can absorb visible radiation and TiO2, the UV component. Hence, a single hybrid-photoresponsive material can have different reactivity upon two-wavelength irradiation enabling direct tuning of yields and selectivity. This color-space expansion promises unprecedented uses in organic chemistry, where improvement in catalytic activity and selectivity will impact the development of catalytic processes with long-term multicycle performance.