Pressure-Driven Circularly Polarized Luminescence Enhancement and Chirality Amplification

Achieving ultrahigh-color-purity circularly polarized luminescence (CPL) in low-dimensional chiral perovskites is challenging due to strong electron-phonon coupling caused by lead halide octahedral distortion. Herein, the circularly polarized piezoluminescence behaviors of six novel chiral perovskites, (S/R-3-XPEA)₂PbBr₄ (PEA = phenethylamine; X = F, Cl, Br), were systematically investigated. Upon compression, (S/R-3-ClPEA)₂PbBr₄ exhibits significant piezofluorochromic behaviors, transforming from yellow CPL to ultrahigh-color-purity deep-blue CPL. At 2.5 GPa, the deep-blue CPL intensity increases by an order of magnitude and its luminescence asymmetry factors (g_lum) are amplified from the initial ±0.03 to ±0.1. (S/R-3-BrPEA)₂PbBr₄ presents a similar piezochromic response, realizing deep-blue CPL at 1.7 GPa, while (S/R-3-FPEA)₂PbBr₄ retains a yellow CPL under high pressure. High-pressure structural characterization and theoretical calculations confirm that pressure-enhanced halogen bonds reduce the penetration depth of S/R-3-BrPEA⁺ and S/R-3-ClPEA⁺ into the [PbBr₆]^4- frameworks, significantly suppressing electron-phonon coupling and increasing magnetic transition dipole moment in (S/R-3-BrPEA)₂PbBr₄ and (S/R-3-ClPEA)₂PbBr₄, which are responsible for the ultrahigh-purity deep-blue CPL and chirality amplification, respectively.