Charge‐Transfer State Enabled by Ionic‐Active‐Site Design in Polymeric Carbon Nitride for Visible‐Light‐Driven Benzylic C‒H Fluorination

ABSTRACT Semiconductor‐based photocatalysis enables high‐value organic chemical synthesis, whereas the role of photocatalyst–substrate interactions in regulating excited‐state properties and catalytic performance has long been neglected. Herein, we propose designing ionic active sites in polymeric carbon nitride (CN) to strengthen catalyst–Selectfluor bonding for promoting photocatalytic Selectfluor activation. We demonstrate that light‐induced potassium release exposes negatively charged bridging nitrogen sites in semicrystalline cyanamide‐functionalized potassium‐doped carbon nitride (K‐CN), which could accommodate the cation species of Selectfluor. The notable K‐CN–Selectfluor interaction results in the formation of charge‐transfer states, endowing the system with notable visible‐light response and effective electron transfer. Besides, semicrystallinity‐related exciton dissociation and cyanamide‐group‐related electron trapping synergistically promote Selectfluor activation. Benefiting from these features, K‐CN exhibits excellent activity in triggering benzylic C‒H fluorination. Taking ethylbenzene fluorination for example, K‐CN gave a 1‐fluoroethylbenzene yield rate of ∼47.5 mmol g − 1 h − 1 , which is 47 times higher than pristine CN.