Electronic Structure of a Semiconducting Imine-Covalent Organic Framework

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Organic Chemistry

Background:

• Covalent organic frameworks (COFs) are crystalline porous polymers with tunable properties.
• Schiff base chemistry offers a versatile route for COF synthesis.
• Understanding structure-property relationships is crucial for designing advanced materials.

Purpose of the Study:

• To synthesize and characterize imine COFs using Schiff base reaction between p-phenylenediamine (PDA) and benzene-1,3,5-tricarboxaldehyde (TCA).
• To investigate the influence of reactant molar ratios and water presence on COF morphology.
• To determine the electronic properties and stability of the synthesized imine COF.

Main Methods:

• Preparation of imine COF on a HOPG-air interface.
• Characterization using probe microscopies (e.g., STM, AFM).
• Electronic property analysis via tunneling spectroscopy and dispersion-corrected density functional theory (DFT) calculations.

Main Results:

• Smooth imine COF domains (up to a few μm) were formed with a high TCA to PDA molar ratio (>2).
• Microscopic roughness of the imine COF is significantly affected by water presence during synthesis.
• The imine COF exhibits semiconducting behavior with a band gap of approximately 1.8 eV.
• Frontier orbitals are delocalized across the entire framework.
• Calculated cohesive energy indicates stability comparable to graphene.

Conclusions:

• The study demonstrates a controlled synthesis of imine COFs with tunable morphology.
• Water plays a critical role in the Schiff base reaction influencing COF structure.
• The synthesized imine COF possesses favorable electronic and stability properties for potential applications.