Pressure-Induced Conglomerate to Racemate Transformation in a One-Dimensional Disulfide-Based Lead Halide

Abstract

Controlling the molecular chirality under external pressure is particularly challenging in low-dimensional hybrid halides, as the constrained structure and strong hydrogen bonding hinder significant conformational changes in bulky organic molecules. Here, by incorporating flexible disulfide-based molecules into the one-dimensional (1D) PbI₅ framework, the chiral hybrid halide [NH₃(CH₂)₂S–S(CH₂)₂NH₃]PbI₅·H₃O undergoes a transformation from conglomerate to racemate at a hydrostatic pressure of approximately 0.10 GPa. This reversible acentric-to-centric transformation is accompanied by the second-harmonic generation (SHG) “on–off” switching and significant conformational changes in the cystamine cations within the structure. In the high-pressure racemic phase, two enantiomers with left- and right-handed conformers (M- and P-helicity) coexist within the lattice structure and their deformations under compression resemble those of a compressed mechanical spring, ultimately leading to considerable distortions of the 1D zigzag PbI₅ chains through strong organic–inorganic H···I interactions. Furthermore, both experimental and theoretical results reveal that the unique phase transformation induces minor alterations in the electronic structures and optical bandgaps. Our findings provide insights into the manipulation of molecular chirality and SHG properties in hybrid halides by introducing flexible organic molecules into inorganic frameworks.