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Dimensionality-Dependent Pressure-Induced Emission Memory in Covalent Organic Frameworks.

Junxia Ren1, Yixuan Wang2, Yaozu Liu1

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Covalent organic frameworks (COFs) show a pressure-induced emission memory effect, retaining luminescence after pressure release. This discovery in 1D COFs opens new avenues for optical data storage and pressure sensors.

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Area of Science:

  • Materials Science
  • Supramolecular Chemistry
  • Photophysics

Background:

  • Stimuli-responsive luminescent materials with memory effects are crucial for optical data storage and pressure sensing.
  • Crystalline covalent organic frameworks (COFs) offer tunable properties for advanced material design.

Purpose of the Study:

  • To investigate the pressure-induced emission memory effect in a series of tetraphenylethylene-based COFs with varying dimensionality (1D, 2D, 3D).
  • To establish the structure-dimensionality-function relationship governing photophysical responses under hydrostatic pressure.

Main Methods:

  • Synthesis of 1D (JUC-730, JUC-731), 2D (JUC-732), and 3D (JUC-733) COFs.
  • Systematic investigation of photophysical responses under hydrostatic pressure.
  • In situ FT-IR, powder X-ray diffraction (PXRD), and DFT analyses to elucidate the mechanism.

Main Results:

  • The first observation of a pressure-induced emission memory effect in crystalline COFs, specifically in 1D frameworks like JUC-730.
  • JUC-730 exhibited a persistent 2.4-fold fluorescence enhancement after pressure release (PIEE).
  • The memory effect in JUC-730 is attributed to anisotropic unit-cell contraction and conformational locking of aryl-O-aryl linkages, stabilizing the emissive state.

Conclusions:

  • Framework dimensionality critically influences photophysical responses and the manifestation of emission memory effects in COFs.
  • 1D COFs demonstrate significant potential for mechanically programmable luminescent materials.
  • The findings provide a design strategy for developing novel pressure-responsive materials with tailored optical memory capabilities.