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Abstract

The selective oxidative coupling of phenol derivatives, involving carbon-carbon (C-C) and carbon-oxygen (C-O) bond formation, has emerged as a critical approach in the synthesis of natural products. However, achieving precise control over the selectivity in coupling reactions of unsubstituted phenols utilizing solar light as the driving force remains a big challenge. In this study, we report a series of porous Cs₃Bi₂X₉ (X = Cl, Br, I) photocatalysts with tailored bandgaps and compositions engineered for efficient solar-light-driven oxidative phenol coupling. Notably, p-Cs₃Bi₂Br₉ exhibited about 73 % selectivity for C-C coupling, displaying a high formation rate of 47.3 μmol g_cat.⁻¹ h^‑1 under solar radiation. Furthermore, this approach enables control of the site-selectivity for phenol derivatives on Cs₃Bi₂X₉, enhancing C-C coupling. The distinctive porous structure and appropriate band-edge positions of Cs₃Bi₂Br_{9 facilitated efficient charge separation, and} surface interaction/activation of phenolic hydroxyl groups, resulting in the kinetically preferred formation of C-C over C-O bond. Mechanistic insights into the reaction pathway, supported by comprehensive control experiments, unveiled the crucial role of interfacial charge transfers and Lewis acid Bi sites in stabilizing phenolic intermediates, thereby directing the regioselectivity of diradical couplings and resulting in the formation of unsymmetrical biphenols.