Cutting COF‐like C4N to Give Colloidal Quantum Dots: Towards Optical Encryption and Bidirectional Sulfur Chemistry via Functional Group and Edge Effects

Abstract Herein, we report the first synthesis of colloidal C 4 N quantum dots (QDs) and their functional composites and explore their optical activities and edge‐selective polysulfide adsorption‐catalysis. As‐obtained C 4 NQDs are rich in carbonyl groups and edges, allowing good solution processability and facile assembly with other moieties for creating functionalities. While C 4 NQDs show normal fluorescence (FL), the QD/poly(vinyl alcohol) (PVA) composites give FL/room‐temperature‐phosphorescence (RTP) dual‐mode emission, enabling the corresponding solution to be used as an encryption ink. The QDs anchored onto carbon nanotubes can be used as a barrier layer to decorate commercial separators, endowing a Li−S cell with excellent cycling stability, high rate capability, and large areal capacity. Computation and experiment studies show that edge sites in C 4 N favor polysulfide adsorption and catalysis and the enriched edges and carbonyl groups in QDs synergically promotecatalytic conversion of sulfur species.