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) 2 Pb 3 I 8, ( m -APA) 2 PbBr 4, and ( m -APA)PbCl 3 . Distinct polymerization pathways yield novel ambient-stable phases with narrowed band gaps and reconfigured band alignments. The resulting polymeric cations exhibit varied sp 2 /sp 3 -C ratios, which significantly tune the electronic coupling across organic–inorganic interfaces. Specifically, P-( m -APA) 2 Pb 3 I 8 retains type I alignment with gap narrowing driven by chemical pressure on the inorganic sublattice, while P-( m -APA) 2 PbBr 4 undergoes a type I to type II transition, and P-( m -APA)PbCl 3 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.