Pressure-Induced Single-Molecule Deformation Enables 208-Fold Photoluminescence-Intensity Enhancement in...

Hybrid metal halides exhibit diverse excited-state behaviors, yet the molecular-level origin of pressure-induced emission enhancement (PIEE) remains elusive. Here, we develop a rational molecular design strategy to isolate pressure-induced single-molecule deformation as the key factor of PIEE in 0D copper iodide hybrids. By systematically tuning the alkyl-chain length of quaternary phosphonium cations, we construct a series of single crystals, (EtPPh₃)₂Cu₂I₄, (PrPPh₃)₂Cu₂I₄, and (BuPPh₃)₂Cu₂I₄, which exhibit distinct crystal-packing modes and distortions while preserving a [Cu₂I₄] emissive core. In this work, "single-molecule deformation" refers to the pressure-induced geometric evolution of an individual discrete [Cu₂I₄]^2- emissive unit within the crystal lattice. Pressure-dependent structural, spectroscopic, kinetic, and theoretical analyses show that crystal packing and intermolecular interactions govern pressure transmission and suppress nonradiative relaxation, while deformation of the initially pre-distorted [Cu₂I₄]^2- unit in (PrPPh₃)₂Cu₂I₄ drives excited-state reconfiguration and activates radiative decay. Consequently, its photoluminescence (PL) intensity reaches 208-fold the ambient-pressure value at 2.6 GPa, and the absolute photoluminescence quantum yield (PLQY) rises from 0.68% to 84.59%. These results identify single-molecule deformation as the predominant structural origin of its high PIEE. Moreover, we demonstrate a power-free preload-sensing gasket and multilevel pressure-encoded optical encryption, underscoring the application potential of pressure-responsive luminescence.