Continuous blueshift of self-trapped exciton emission upon compression and decompression in one-dimensional (C4H8N)2PbCl4.

Pressure engineering is a powerful approach for tuning the properties of materials, yet the induced responses are typically reversible. Here, we demonstrate a rare counterexample in the 1D hybrid metal halide (C4H8N)2PbCl4, where self-trapped exciton emission exhibits irreversibility upon compression and decompression. The irreversible emission-energy increase of 0.40 eV arises from distinct governing mechanisms along the two pressure pathways. During compression, the blueshift is dominated by a reduction in lattice distortion energy, whereas upon decompression it is sustained by a persistently widened bandgap and a recovery of exciton binding energy. These effects originate from pressure-driven structural modifications of the inorganic [PbCl4]2- chains, cooperatively coupled with reactions of the confined organic cations. By revealing an unconventional pathway that couples exciton dynamics with lattice reconstruction and organic chemical reactivity, this work demonstrates that pressure engineering can transcend simple lattice compression and provides a viable strategy for achieving irreversible optoelectronic modulation in hybrid materials.