Bromoacetyl Bromide‐Derived CsPbBr3 Quantum Dots: Robust Water Stability for Aqueous‐Phase Photocatalysis

Abstract Cesium lead bromide (CsPbBr 3 ) perovskites are promising photocatalysts for organic transformations, offering a cost‐effective and recyclable alternative to conventional catalysts. However, their scope is limited to nonpolar solvents due to instability in aqueous environments. Here, bromoacetyl bromide (BABr) as a novel precursor for the one‐step synthesis of highly water stable, size‐controlled CsPbBr 3 quantum dots (QDs), is introduced. BABr reacts with oleylamine (OAm) to generate bromide ions for crystallization while forming a unique passivating ligand, [ 2 ‐bromo‐ N ‐(octadec‐ 9 ‐en‐ 1 ‐yl) acetamide] (BOAM), which strongly coordinates to the QD surface via a carbonyl C─O group and a sacrificial bromine atom, as confirmed by FTIR, NMR, XPS, and DFT studies. This strategy yields high‐quality size‐tunable (emission ≈475–521 nm, PLQY ≈95–100%) CsPbBr 3 QDs at mild temperatures (≈60–140 °C). Additionally, the protonated polar amide group in the ligand imparts a positive zeta potential (+56 mV), ensuring high dispersibility and unprecedented stability (>2 months, photoluminescence (PL) retention ≈78%) in aqueous media. Leveraging this, the first example of CsPbBr 3 QDs as recyclable photocatalysts for the azide‐alkyne “click reaction” in water under visible light, achieving ≈100% yields at room temperature is demonstrated. Combining synthetic simplicity, mechanistic insights, and functional demonstration, this work paves the way for aqueous‐phase photocatalysis with CsPbBr 3 perovskite QDs.