Fluorescence-Enhanced Covalent Organic Frameworks via Integration of Structural Locking with Electron Modulation for...

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Two-dimensional imine-linked covalent organic frameworks (COFs) are challenging to synthesize with high emission due to nonradiative decay.
• Strong interlayer π-π stacking and intramolecular rotation often lead to fluorescence quenching in COFs.

Purpose of the Study:

• To design and synthesize novel pyrene-based COFs with enhanced solid-state photoluminescence.
• To investigate the structure-property relationships governing the luminescence of these COFs.
• To evaluate the potential of the synthesized COFs as luminescent sensors for metal ions.

Main Methods:

• Synthesis of three isostructural pyrene-based COFs.
• Characterization of their photoluminescence properties, including photoluminescence quantum yield (PLQY).
• Investigation of the role of hydroxyl groups and hydrogen bonding in modulating fluorescence.
• Evaluation of selectivity and sensitivity for metal ion detection using dual N,O chelation sites.

Main Results:

• The hydroxy-functionalized COF (OH-COF) demonstrated the strongest solid-state photoluminescence with a PLQY of 12.15%.
• Superior fluorescence in OH-COF is attributed to electronic modulation by hydroxyl groups and structural locking via hydrogen bonding, suppressing nonradiative transitions.
• OH-COF exhibited high selectivity for metal ions, with a low detection limit of 0.14 μM for Fe³⁺ and a fast response time.

Conclusions:

• Synergistic effects of electronic modulation and structural locking are crucial for designing highly emissive imine COFs.
• The developed OH-COF shows promise as a high-performance luminescent sensor for Fe³⁺.
• This study offers valuable insights for the rational design of advanced luminescent materials based on COFs.