Covalently Doped and Highly Oriented Covalent Organic Framework Thin Films

Area of Science:

• Materials Science
• Organic Chemistry
• Solid-State Physics

Background:

• 2D covalent organic frameworks (COFs) are promising for microelectronics but challenging to process into thin films due to insolubility.
• Controlling crystallographic orientation and band structure is key for high-performance COF-based devices.

Purpose of the Study:

• To develop a strategy for controlled covalent doping of imine COF thin films.
• To investigate the effect of thiophene linker incorporation on COF crystallinity and electronic properties.

Main Methods:

• Liquid-solid synthesis of COF thin films using varying ratios of terephthalaldehyde (PDA) and 2,5-thiophenedicarboxaldehyde (TDA) with 1,3,5-tris(4-aminophenyl)benzene (TAPB).
• Characterization of crystallographic ordering, band gap, work function, and valence band maximum.

Main Results:

• Highly crystalline and uniformly oriented TAPB-PDA-TDA COF thin films were successfully synthesized with up to 20% TDA incorporation.
• Thiophene doping minimally disrupted crystallographic ordering while reducing the band gap and increasing the work function.
• Covalent doping enhanced π-conjugation and electron delocalization, demonstrating p-type semiconductor behavior.

Conclusions:

• Controlled covalent doping of 2D COF thin films with thiophene linkers is achievable.
• This doping strategy offers a pathway to tune the electronic properties of COFs for advanced microelectronic applications.
• Enhanced crystallinity and π-conjugation in doped COFs improve charge transport properties.