Single-Atom Fe-N4 sites promote the triplet-energy transfer process of g-C3N4 for the photooxidation

Polymeric carbon nitride materials show intriguing prospects in numerous light-to-energy conversion applications, but seldom studies focus on their triplet energy transfer, leading to the insufficient lifetime for the photochemical process. Inspired by the porphyrin molecular photocatalyst, single-atom sites (Fe-N 4 ) as triplet sensitizing sites were fabricated in g-C 3 N 4 for the preparation of Fe-g-C 3 N 4 , which processes a long-lived triplet emissive state (τ PH  = 4.93 μs). But under realistic condition for the large-scale production of catalyst, single atoms are inevitable to sinter, resulting in the formation of other metal species. Therefore, the photooxidation of 1,5-dihydroxynaphthalene (1,5-DHN) and the photocatalytic E-Z Isomerization of stilbene were selected as the model reactions to evaluate the influence of various Fe species on the triplet energy transfer. It was found that Fe-N 4 sites promote the triplet energy transfer process, while Fe nanoclusters (Fe 0 ) promote the electron transfer and inhibit triplet energy transfer. This finding provides guidance for the rational design of photocatalysts to efficiently improve triplet energy transfer process and its application.