Size-Homogenizedand Strongly Confined Stable Dion–JacobsonPhase CsPbBr₃ Quantum Wells Achieved by Diquaternary Ammonium-ModifiedBODIPY

Ruddlesden–Popper (RP) phase perovskite quantum wells (QWs) offer the potential for achieving deep blue emission. However, the RP perovskite consists of bilayers of monovalent alkylammonium ions arranged back-to-back between the separated perovskite octahedral layers. The weak van der Waals interactions between these bilayers cause an inherent tendency for dissociation, facilitating the generation of mixed phases and promoting the decomposition of the perovskite. Herein, we propose a spacer molecule management strategy to achieve size-homogenized and strongly confined stable Dion-Jacobson (DJ) phase CsPbBr₃ QWs, using BODIPY (BDP) containing diquaternary ammonium salt as a cospacer organic molecule (QWs-BDP). The gap is bridged by the short dications BDP with steric hindrance in QWs-BDP, which increases the rigidity of the structure and shortens the layer spacing, reducing both their thickness and lateral size. The BDP interacts strongly with [PbBr₆]^4–, forming a stable structural domain with <i>n</i> = 3. Moreover, BDP as a cospacer organic facilitates singlet-state energy transfer. Notably, QWs-BDP demonstrates significant phase stability under polar solvents and high-temperature thermal stimuli. Based on their external stimuli-responsive nature, the prepared anticounterfeiting labels enable both encryption and decryption of information. The rational design of spacer molecule structures offers a new approach to controlling the dimensions and phase of perovskite QWs.