Fluorine-Induced Anomalous Optical Stability and Pressure-Enhanced Emission Property of 0D Lead Perovskite Derivatives

Low-dimensional metal halides, especially zero-dimensional (0D) compounds, are important derivative members of the halide perovskite family primarily due to their highly emissive properties. Here, we report two highly luminescent 0D lead bromides, (BPP)₂PbBr₄ and (BPPF)₂PbBr₄·2H₂O, abbreviated as BPP-0D and BPPF-0D (BPP = benzyltriphenylphosphonium, BPPF = (4-fluorobenzyl)triphenylphosphonium). Both compounds share mutual seesaw inorganic units [PbBr₄]^2– separated by bulky organic cations. BPP-0D and BPPF-0D emit yellow and green lights, respectively, with photoluminescence (PL) quantum yields (PLQYs) of ∼15 and ∼55% at ambient conditions. Both compounds show excellent environmental stability and practical applications in light-emitting diodes. Upon compression, BPP-0D experiences a rapid decrease in PL intensity, accompanied by an obvious change in its emissive color from yellow to blue. In contrast, BPPF-0D demonstrates excellent optical stability, retaining its green emission, while the PL increases by ∼1.7 times at 0.8 GPa and the PLQY increases to 93%. For BPPF-0D, the presence of an extra highly electronegative fluoride group adds many more noncovalent interactions, such as C–H···F hydrogen bond and F···F interactions. These interactions strengthen the structural and optical stabilities of BPPF-0D, maintaining its emission peak position with elevated pressure. The straightforward comparison between two similar compounds and their optical properties under pressure modulation underscores the importance of engineering organic cations to control and optimize their properties.