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.