Aqueous‐Phase Preparation of Core–Shell Perovskite Nanorods Encapsulated in Polydopamine with Ultrahigh Water Stability

All‐inorganic perovskite CsPbBr 3 (CPB) nanocrystals (NCs) are not widely applied in aqueous environments due to their readily decomposable nature. Therefore, the aqueous‐phase preparation of CPB NCs has been a considerable challenge. In this work, a feasible method is proposed for preparing aqueous‐phase core–shell CPB nanorods (NRs) encapsulated with polydopamine (PDA) by employing a multifunctional additive cesium trifluoroacetate (Cs‐TFA). Highly luminescent TFA‐CPB NRs are obtained via a chemical transformation of Cs 4 PbBr 6 NCs in water. Subsequently, PDA constitutes a robust shell on the surface of TFA‐CPB NRs through the covalent oxidative polymerization, which effectively reduces the original dynamic properties of surface ligands, retards the decomposition of ligands and inhibits the leakage of Pb 2+ ions. The results demonstrate that the fluorescence intensity of TFA‐CPB@PDA NRs maintains 49.3% of the initial intensity after 136 days. Meanwhile, the NRs exhibit low cytotoxicity, and the cell viability remains at 80% when the concentration of the NRs is 200 μg mL −1 . The reliable preparation of aqueous‐phase core–shell perovskite NRs (PNRs) will facilitate their development in many fields, such as materials science, biology, medicine, and their applications in aqueous environments.