Photocatalysis has emerged as a highly valuable and economic method that was used extensively in the last few decades for the synthesis of important organic molecules and facilitating crucial bond formations such as C-C, C-N, and C-O bonds.[1-3] Although significant development has been made in the field, conventional photocatalysts usually comprise expensive transition metals such as Ru[4], Ir[5], or Au[6], and are often hard-to-prepare, require air-free conditions for obtaining high conversion rates, and may be of limited reusability. A promising alternative for solar- or LED-driven photocatalysis lies in lead halide perovskite quantum dots (LHP-QD) as recent developments highlighted their strong and broadly tunable absorption with high coefficients (~10⁶ M^-1cm^-1), near unity quantum yields (>90%)[7], highly dynamic and accessible surface, and low electron-hole binding energy causing facile charge generation/transfer. These properties overall indicate the high potential of lead halide perovskites as sustainable heterogeneous photocatalysts.   

In this work, we showcase the use of LHP-QDs as efficient photocatalysts in various organic transformations. First, we demonstrate the impact of designer ligands on the catalytic activity at extremely low catalyst loadings (<10*10^-6 mol%, <100 ppb) for α-, and γ- bromination of the β-ketoesters, ketones, and various benzyl derivatives reaching turnover numbers over 9,000,000. Investigating the effect of solvent on the performance as well as doing a comprehensive mechanistic study allowed us to rationalize the catalyst properties. Next, we show the development of thin-inorganic coatings (AlO_x, TiO_x, and ZrO_x) on LHP QDs for efficient photocatalysis. We explore the dimerization of benzyl bromide derivatives as model systems using surface-engineered LHP-QDs, achieving high conversions to the desired products in short reaction times (<4h) and with low catalyst loadings. Our findings confirm that a properly designed surface passivation and balancing of the oxidation and reduction reaction rates can successfully resolve the stability issues anticipated for such ionic compounds in reaction conditions. Photocatalysts can be separated from the reaction mixture, regenerated, and still exhibit >95% conversion efficiency during the second cycle of the reaction.

Overall, our efforts reveal that LHP QDs enable photocatalyzed transformations that are otherwise not achievable with the established photocatalysts, and we believe the engineering of the surface in these materials will allow the community to advance in the context of photoredox catalysis.