Photocatalytic Molecular Oxygen Activation by Regulating Excitonic Effects in Covalent Organic Frameworks

Excitonic effects caused by Coulomb interactions between electrons and holes play subtle and significant roles on photocatalysis, yet have been long ignored. Herein, porphyrinic covalent organic frameworks (COFs, specifically DhaTph-M), in the absence or presence of different metals in porphyrin centers, have been shown as ideal models to regulate excitonic effects. Remarkably, the incorporation of Zn2+' in the COF facilitates the conversion of singlet to triplet excitons, whereas the Ni2+ introduction promotes the dissociation of excitons to hot carriers under photoexcitation. Accordingly, the discriminative excitonic behavior of DhaTph-Zn and DhaTph-Ni enables the activation of O-2 to O-1(2) and O-2(center dot-), respectively, under visible light irradiation, resulting in distinctly different activity and selectivity in photocatalytic terpinene oxidation. Benefiting from these results, DhaTph-Ni exhibits excellent photocatalytic activity in O-2(center dot-)-engaged hydroxylation of boronic acid, while DhaTph-Zn possesses superior performance in O-1(2)-mediated selective oxidation of organic sulfides. This work provides indepth insights into molecular oxygen activation and opens an avenue to the regulation of excitonic effects based on COFs.