Bromoacetyl Bromide‐Derived CsPbBr ₃ Quantum Dots: Robust Water Stability for Aqueous‐Phase Photocatalysis

Cesium lead bromide (CsPbBr₃) 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 CsPbBr₃ 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%) CsPbBr₃ 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 CsPbBr₃ 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 CsPbBr₃ perovskite QDs.