Selective Generation\nof Reactive Oxygen Species in\nPhotocatalytic Oxidation by Tuning Porphyrin-Based COFs’ Dimensionality

Regulating the selective generation of reactive oxygen\nspecies\n(ROS) is a significant challenge in the field of photocatalytic oxidation,\nwith successful approaches still being limited. Herein, we present\na strategy to selectively generate singlet oxygen (<sup>1</sup>O<sub>2</sub>) and superoxide radicals (O<sub>2</sub><sup>•–</sup>) by tuning the dimensionality of porphyrin-based covalent organic\nframeworks (COFs). The transformation of COFs from three-dimensional\n(3D) solids to two-dimensional (2D) sheets was achieved through the\nreversible protonation of the imine bond. Upon irradiation, both bulk\nand thin-layer COF-367 can transfer energy to O<sub>2</sub> to generate <sup>1</sup>O<sub>2</sub>. However, thin-layer COF-367 exhibited a superior\nperformance compared to its bulk counterpart in activating O<sub>2</sub> to form the O<sub>2</sub><sup>•–</sup> radicals via\nelectron transfer. After excluding the influences of the band structure,\nO<sub>2</sub> adsorption energy, and frontier orbital composition\nattributed to the dimensionality of the COFs, it is reasonably speculated\nthat the variance in ROS generation arises from the differential exposure\nratios of the active surfaces, leading to distinct reaction pathways\nbetween the carrier and O<sub>2</sub>. This study is the first to\nexplore the modulation mechanism of COF dimensionality on the activation\nof the O<sub>2</sub> pathway, underscoring the importance of considering\nCOF dimensionality in photocatalytic reactions.