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) 2 PbBr 4 (PEA = phenethylamine; X = F, Cl, Br), were systematically investigated. Upon compression, ( S / R -3-ClPEA) 2 PbBr 4 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) 2 PbBr 4 presents a similar piezochromic response, realizing deep-blue CPL at 1.7 GPa, while ( S / R -3-FPEA) 2 PbBr 4 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 [PbBr 6 ] 4– frameworks, significantly suppressing electron–phonon coupling and increasing magnetic transition dipole moment in ( S / R -3-BrPEA) 2 PbBr 4 and ( S / R -3-ClPEA) 2 PbBr 4, which are responsible for the ultrahigh-purity deep-blue CPL and chirality amplification, respectively.