Reducing the Exciton Binding Energy of Covalent Organic Framework Through π‐Bridges to Enhance Photocatalysis

Abstract The pronounced exciton binding energy ( E b ) in covalent organic frameworks (COFs) results in significant energy loss, thereby constraining the photocatalytic efficiency of COFs. Herein, triphenylamine is employed as an electron donor, while triphenyltriazine served as an acceptor; benzene, naphthalene, and anthracene are utilized as π‐bridges with progressively increasing conjugation to synthesize a series of D‐π‐A structured COFs photocatalysts (COF‐1, COF‐2, and COF‐3). The correlation between π‐bridge structures and E b is systematically examined through the removal of hexavalent uranium U(VI) from tailings wastewater under visible light irradiation as a model reaction. Notably, an increase in π‐bridge conjugation initially enhanced and then diminished the photocatalytic properties of these three catalysts. This phenomenon can be attributed to the fact that coplanarity within the COFs frameworks does not consistently improve with greater π‐bridge conjugations; specifically, COF‐2 featuring a naphthalene π‐bridge exhibited the smallest dihedral angle. The reduced dihedral angle facilitated a more planar and delocalized electron transport pathway between donor and acceptor moieties, leading to decreased E b and inhibited exciton recombination. Consequently, COF‐2 demonstrated exceptional photocatalytic reduction of U(VI), achieving efficiencies 1.8 times and 1.5 times greater than those of COF‐1 and COF‐3, respectively. This approach offers novel insights into mitigating E b in COFs‐based photocatalysts.