Dual functional phosphate-ester BODIPY regulation achieved stable CsPbBr3 nanocrystals for optical anti-counterfeiting

Abstract

Colloidally synthesized cesium lead bromine (CsPbBr₃) nanocrystals are considered as one of the most promising luminescent materials due to their excellent photoelectric properties. However, the ligands binding to CsPbBr₃ are prone to being detached from the surface due to proton exchange, which leads to the formation of high-density defects, thus reducing their stability significantly. Herein, it is proposed to synthesize stable CsPbBr₃ using a dual functional phosphate-ester BODIPY (BDPPO) as an alternative to the traditional oleic acid ligand (BDPPO–CsPbBr₃). The PO and –F groups in BDPPO act as a double passivation system, which allows the coordination with unsaturated sites (Cs⁺ or Pb²⁺), thus effectively managing the defects of CsPbBr₃. Notably, the hard base (PO) shows an intense interaction with the hard acid (Cs⁺) according to the soft–hard–acid–base theory, which ensures high efficiency in stabilizing the BDPPO ligand capped on CsPbBr₃. Moreover, the BDPPO substitute can be used to create an acid-free environment, which eliminates the possibility of proton transfer, thus enhancing the hydrogen-bonding interaction between the Br terminal in CsPbBr₃ and the ammonium groups of oleylamine. Consequently, the obtained BDPPO–CsPbBr₃ exhibits better performance than CsPbBr₃ in terms of operational stability. By taking advantage of the different responses of CsPbBr₃ and BDPPO–CsPbBr₃ to environmental stimuli in combination, a variety of luminescent anti-counterfeiting labels are prepared to achieve the encryption and decryption of information. Therefore, stable CsPbBr₃ can be obtained innovatively through a reasonable design of the unique proton-free ligand capable of facilitating capping ligands to bind tightly on CsPbBr₃.