A highly soluble, crystalline covalent organic framework compatible with device implementation

Abstract

We report a soluble yet crystalline covalent organic framework (COF) by regulation of inter-layer interactions, which endows the COF with remarkable solubility and processability of thin films for optoelectronic devices that exhibit high yet anisotropic conductivities and outperform all the other COF-based semiconductors.

Acid Exfoliation of Imine‐linked Covalent Organic Frameworks Enables Solution Processing into Crystalline Thin Films

“…This strategy provides freestanding films, but thickness control requires significant reoptimization for every network, and films with poor or no crystallinity are often obtained, especially when they are thinner than 50 nm . Finally, a third method, exfoliation and reconstitution of COF powders, has been explored . This strategy is highly desirable because it provides a direct route to the film morphology from abundant microcrystalline powders, which are simpler to synthesize, and the film dimensions can be precisely tuned by changing the suspension concentration and substrate surface area …”

“…Although numerous COF powder exfoliation methods have been reported, very few of these studies demonstrate the ability to reconstitute the resulting nanosheets into large‐area COF films . Most reported methods involve either sonicating the powders in organic solvents or mechanically grinding the powders prior to dispersion, but due to challenges with re‐aggregation and sedimentation at high concentrations, these strategies typically produce dilute suspensions (≤0.2 mg mL −1 ) that are not conducive to large‐scale film fabrication .…”

“…Although Tsuru and co‐workers demonstrated that thin films can be prepared from a dilute suspension (0.15 mg mL −1 ) of COF‐1 powder prepared through sonication in dichloromethane, the fabrication process required repeated drop‐casting/drying cycles to form a continuous film, and therefore lacks scalability and practicality . More recently, charge‐mediated and chemical exfoliation strategies have been developed, which produce more concentrated suspensions (≥0.5 mg mL −1 ) that can be drop‐cast to produce large‐area films . However, these strategies have thus far made use of intentionally incorporated functional groups that are not generalizable across broad classes of COF networks .…”

“…More recently, charge‐mediated and chemical exfoliation strategies have been developed, which produce more concentrated suspensions (≥0.5 mg mL −1 ) that can be drop‐cast to produce large‐area films . However, these strategies have thus far made use of intentionally incorporated functional groups that are not generalizable across broad classes of COF networks . For example, Banerjee and co‐workers demonstrated that an anthracene‐based 2D COF powder could be chemically exfoliated through a Diels–Alder reaction between the anthracene units and N ‐hexylmaleimide .…”

“…For example, Banerjee and co‐workers demonstrated that an anthracene‐based 2D COF powder could be chemically exfoliated through a Diels–Alder reaction between the anthracene units and N ‐hexylmaleimide . Furthermore, Ma and co‐workers synthesized a 2D COF containing cationic viologen units, such that the resulting sheets were easily separated due to electrostatic repulsion …”