Layered 3D Covalent Organic Framework Films Based on Carbon-Carbon Bonds

The development of covalent organic frameworks (COFs)during thepast decades has led to a variety of promising applications withingas storage, catalysis, drug delivery, and sensing. Even though mostdescribed synthesis methods result in powdery COFs with uncontrolledgrain size, several approaches to grow COF films have recently beenexplored. However, in all COFs so far presented, the isolated materialsare chemically homogeneous, with all functionalities homogeneouslydistributed throughout the entire material. Strategies to syntheticallymanipulate the spatial distribution of functionalities in a singlefilm would be game changing. Specifically, this would allow for theintroduction of local functionalities and even consecutive functionsin single frameworks, thus broadening their synthetic versatilityand application potential. Here, we synthesize two 3D crystallineCOF films. The frameworks, the ionic B-based and neutral C-basedCOFs, have similar unit cell parameters, which enables their epitaxialstacking in a layered 3D COF film. The film growth was monitored inreal time using a quartz crystal microbalance, showing linear growthwith respect to reaction time. The high degree of polymerization wasconfirmed by chemical analysis and vibrational spectroscopy. Theirpolycrystalline and anisotropic natures were confirmed with grazingincidence X-ray diffraction. We further expand the scope of the conceptby making layered films from COF-300 and its iodinated derivative.Finally, the work presented here will pave the path for multifunctionalCOF films where concurrent functionalities are embedded in the samecrystalline material.

Automated summary

The development of covalent organic frameworks (COFs) has led to promising applications in gas storage, catalysis, drug delivery, and sensing. However, current COFs are chemically homogeneous and lack control over the spatial distribution of functionalities. This study successfully synthesized two 3D crystalline COF films that allowed for the epitaxial stacking of frameworks with similar unit cell parameters. The films showed linear growth and confirmed their high degree of polymerization and anisotropic nature.