Crucial Impact of Degrees of Freedom on Pressure-induced Optical Properties of Water-stable 1D Perovskites

Abstract

One-dimensional (1D) organic-inorganic hybrid perovskites exhibit excellent water stability when incorporating rigid π-conjugated hydrophobic organic cations, however, their suboptimal optical properties impede practical applications. While applying pressure can significantly enhance the optical performance of these perovskites, sustaining such improvements under ambient conditions poses a considerable challenge. Herein, we investigate the influence of structural degrees of freedom (DOF) on the optical performance of 1D hybrid perovskites in aqueous environments under pressure. Our results reveal that 4-(3-phenylpropyl)pyridine (4PPY), characterized by high DOF, strengthens organic-inorganic binding interactions, transforming the originally non-emissive (4PPY)₈Pb₈I₂₄ into a broad-band luminescent material with emission spanning 450-800 nm. In contrast, the low DOF 4,4'-trimethylenedipyridine (4,4'-TMDP) induces rapid structural distortion in (4,4'-TMDP)Pb₂I₆, resulting in a significant optical absorption edge shift from 430 nm to 650 nm under ambient pressure, corresponding to a remarkable 34% reduction in bandgap, the highest modulation efficiency reported for halide perovskites to date. These findings provide critical insights that will inform the design, development, and application of stable and efficient hybrid perovskites.