Structure Directing Acid-Amine Salt Films for Imine-Linked Covalent Organic Framework Films by Chemical Vapor...

Area of Science:

• Materials Science
• Nanotechnology
• Chemical Engineering

Background:

• Chemical vapor deposition (CVD) is a promising technique for high-quality metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) films.
• Existing strategic approaches for synthesizing COF films via CVD are limited.
• Acids are known catalysts for imine condensation in solution but their role in vapor-phase reactions is less understood.

Purpose of the Study:

• To develop a new strategic approach for synthesizing imine-linked COF films using CVD.
• To investigate the role of acid-amine salt films in the CVD synthesis of COFs.
• To explore the influence of acids on the crystallinity and orientation of COF films.

Main Methods:

• Synthesis of COF-LZU1 thin films using p-phenylenediamine and 1,3,5-triformylbenzene via CVD.
• Inclusion of p-toluenesulfonic acid to form acid-amine salt films.
• Structural analysis using grazing-incidence wide-angle X-ray scattering (GIXAS).

Main Results:

• Highly crystalline and smooth COF-LZU1 films were obtained only in the presence of p-toluenesulfonic acid.
• Amorphous films with a face-on orientation were obtained in the absence of acid.
• Using benzenesulfonic acid resulted in COF-LZU1 films with an edge-on orientation, demonstrating acid-modulated structure.
• Control experiments with benzoic acid and succinic acid showed that acid-amine salt formation is crucial for CVD synthesis of imine-linked COF films.

Conclusions:

• Acid-amine salt formation is critical for the successful CVD synthesis of imine-linked COF films.
• The study explains the limited types of active acids for vapor-phase imine condensation.
• This approach expands the facile synthesis of highly crystalline COF films via CVD and allows for structural control.