Sculpting Low-Dimensional Hybrid Lead Halides via Pressure-Induced Polymerization

Pressure is a powerful tool to modulate hybrid metal halides (HMHs), but its effects are often reversed upon decompression. Here, using the unsaturated m-aminophenylacetylene (m-APA) cation, we report pressure-induced polymerization (PIP) as a strategy for irreversible band-structure engineering in three heterostructures as HMH crystals: (m-APA)₂Pb₃I₈, (m-APA)₂PbBr₄, and (m-APA)PbCl₃. Distinct polymerization pathways yield novel ambient-stable phases with narrowed band gaps and reconfigured band alignments. The resulting polymeric cations exhibit varied sp²/sp³-C ratios, which significantly tune the electronic coupling across organic-inorganic interfaces. Specifically, P-(m-APA)₂Pb₃I₈ retains type I alignment with gap narrowing driven by chemical pressure on the inorganic sublattice, while P-(m-APA)₂PbBr₄ undergoes a type I to type II transition, and P-(m-APA)PbCl₃ transforms from type II to reversed-type I via organic band-edge reconstruction. This work demonstrates PIP as a novel and general approach to permanently tailor the electronic structures of HMHs, enabling functional design through the controlled covalent transformation of organic cations under high pressure.