Ultrafine Spatial Modulation of Diazapyrene-Based Two-Dimensional Conjugated Covalent Organic Frameworks

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Organic Chemistry

Background:

• Covalent Organic Frameworks (COFs) offer tunable properties through tailored synthesis.
• High crystallinity is crucial for COF performance.
• Pyrene-based COFs are known for their ordered crystalline structures.

Purpose of the Study:

• To synthesize and characterize novel two-dimensional (2D) COF layers using 2,7-diazapyrene building blocks.
• To investigate the impact of diazapyrene substitution on COF structure, electronic properties, and conductivity.
• To evaluate the potential of these materials for electrical and proton conduction applications.

Main Methods:

• Bottom-up synthesis of COFs using functionalized building blocks.
• Structural characterization to determine topology and crystallinity.
• Spectroscopic analysis to determine optical bandgaps.
• Microwave conductivity measurements to assess electrical properties.
• Proton conductivity measurements.

Main Results:

• Diazapyrene substitution led to nearly "flat" 2D COF layers with controlled torsional angles.
• Achieved ordered face-to-face (slipped AA) stacking arrangements with high thermodynamic stability (∼500 °C).
• Extended electrical conjugation across 2D frames with modest optical bandgaps (∼2.1 eV).
• Demonstrated significant microwave conductivity and a maximum proton conductivity of 10⁻² S cm⁻¹.
• Nitrogen centers in diazapyrene units act as active sites for proton transfer.

Conclusions:

• Tetragonal COFs based on diazapyrene are highly crystalline 2D materials.
• These materials possess unique electrical and proton-conducting capabilities.
• The planar structure and nitrogen centers contribute to their enhanced conductivity.
• Diazapyrene-based COFs show promise for applications requiring efficient charge and proton transport.