Biomimetic D-A1-A2 Organic Cages with Recombination-Suppressed Sequential Charge Transfer for Hydrogen Peroxide Photosynthesis.
Abstract
Photocatalytic synthesis of hydrogen peroxide (H2O2) offers a sustainable route toward green oxidation and environmental remediation, yet its efficiency is fundamentally constrained by rapid backward charge recombination, underscoring the synthetic challenge of creating molecular architectures capable of enforcing directional and recombination-suppressed charge transfer. Inspired by the stepwise electron transfer within the compartmentalized reaction centers of thylakoid membranes in natural photosynthesis, we design here biomimetic donor-acceptor 1-acceptor 2 (D-A1-A2) organic cages, where donors and acceptors are orderly positioned along an energy gradient to achieve a recombination-suppressed sequential charge transfer (RS-SCT) process, thereby promoting photocatalytic H2O2 production. Two single crystals of D-A1-A2 organic cages, BNC-O and BNC-S, are successfully constructed from in situ generated ditopic boronated monomers and C3-symmetric monomers via B-N dative bonds. Both cages show the RS-SCT process from electron-rich triphenylamines as the D through coordinated pyridines as A1 to more electron-deficient benzoxadiazoles or benzothiadiazoles as A2, which enable sequential charge migration and suppress backward charge recombination with prolonged excited-state lifetimes. As a result, the self-assembled two-dimensional crystalline cages featuring well-organized active sites exhibit significantly enhanced photocatalytic H2O2 production performance, achieving a rate of 4.15 mmol g-1 h-1 for crystalline BNC-O, which is markedly higher than those of the corresponding components lacking RS-SCT, including the individual D, A1, A2, and D-A systems. Furthermore, these D-A1-A2 organic cages are implemented in a photocatalytic microflow reactor for controllable in situ H2O2 generation under sunlight, which is further integrated into a cascade phenol-containing wastewater treatment system.