Distinct Responses to Anisotropic Grinding and Isotropic Compression in Piezochromic Luminescence of 1,1'-Bipyrene

Abstract

Piezochromic luminescent (PCL) materials are essential components for intelligent photonic systems due to their ability to dynamically modulate luminescence under external mechanical stimuli. However, investigations into their responses to combined multiple mechanical stimuli remain scarce, particularly for materials exhibiting distinct PCL behaviors under anisotropic mechanical grinding and isotropic hydrostatic pressure. In this work, we investigate a chemically-bonded pyrene dimer, 1,1'-bipyrene (BP), to explore the structure-property relationship governing differential PCL responses, using parent pyrene (PY) as a reference compound. Single-crystal X-ray diffraction analysis reveals that BP adopts a twisted conformation between its two PY units, forming a uniform network of weak intermolecular C-H•••π interactions. Notably, BP exhibits opposing PCL responses to mechanical grinding and hydrostatic pressure, which enables full-visible-spectrum emission modulation. Grinding induces a blueshift in emission from green to blue due to the disruption of C-H•••π interactions without forming new π-π stacking interactions, while hydrostatic pressure (up to 7.6 GPa) leads to a redshift from green to red owing to the strengthening of these interactions. In contrast, PY, with strong π-π stacking interactions in its crystal structure, shows an inert response to grinding and only a slight redshift under hydrostatic pressure. This study not only demonstrates BP as a promising PCL material with multifunctional potential but also provides critical mechanistic insights into how intermolecular interactions govern differential PCL responses to mechanical stimuli in organic aggregates.