Crystallizing Sub 10 nm Covalent Organic Framework Thin Films via Interfacial–Residual Concomitance

Abstract

Synthesis of covalent organic framework (COF) thin films on different supports with high crystallinity and porosity is crucial for their potential applications. We have designed a new synchronized methodology, residual crystallization (RC), to synthesize sub 10 nm COF thin films. These residual crystallized COF thin films showcase high surface area, crystallinity, and conductivity at room temperature. We have used interfacial crystallization (IC) as a rate-controlling tool for simultaneous residual crystallization. We have also diversified the methodology of residual crystallization by utilizing two different crystallization pathways: fiber-to-film (F−F) and sphere-to-film (S−F). In both cases, we could obtain continuous COF thin films with high crystallinity and porosity grown on various substrates (the highest surface area of a TpAzo COF thin film being 2093 m 2 g −1 ). Precise control over the crystallization allows the synthesis of macroscopic defect-free sub 10 nm COF thin films with a minimum thickness of ∼1.8 nm. We have synthesized two COF thin films (TpAzo and TpDPP) using F−F and S−F pathways on different supports such as borosilicate glass, FTO, silicon, Cu, metal, and ITO. Also, we have investigated the mechanism of the growth of these thin films on various substrates with different wettability. Further, a hydrophilic support (glass) was used to grow the thin films in situ for four-probe system device fabrication. All residual crystallized COF thin films exhibit outstanding conductivity values. We could obtain a conductivity of 3.7 × 10 −2 mS cm −1 for the TpAzo film synthesized by S−F residual crystallization.

Landscaping Covalent Organic Framework Nanomorphologies

“…In the case of COF nanospheres, the free −NH 2 and −CHO functionalities initiate the assembly of the COF crystallites via Schiff base condensation to generate crystalline and porous COF thin films (Figure c) . The minimization of the surface energy via covalent self-assembly guides the transmutation of the COF morphologies from 0-D to 2-D. On the contrary, the covalent self-assembly of identical COF nanospheres at the solid–liquid interface eventuates through the protrusion of the 1-D nanofibers at the COF nanosphere’s surface (Figure d). , Over time, COF nanospheres transform into 1-D COF nanofibers exclusively, and these further assemble in two dimensions to transmute into thin films.…”

Electroactive Covalent Organic Framework Enabling Photostimulus-Responsive Devices

“…The continuity and uniformity of the COF film have a significant influence on the performance and stability of the device . Here, BDFamide-Tp COF films were prepared using interfacial synthesis (Figure S8), which is a widely reported method for the fabrication of COF films. − After optimization of synthetic conditions (Table S3 and Figure S9), a BDFamide-Tp film with high quality was obtained at the liquid–liquid interface. Synthesized films of several millimeters in size can be transferred to desired substrates without rupturing for further characterization and device construction.…”

Weaving microscale wool ball-like hollow covalent organic polymers from nanorods for efficient adsorption and sensing

“…It can be concluded that on the interface, (i) a reversible dissolution process happened to produce oligomers or monomers, and they recondensed to construct a stable keto structure, or (ii) the enol structure was irreversibly tautomerized into a more stable keto structure. 17,18 Also, in PXRD studies, the increased wide peak indicated the continuous covalent assembly for elongated π–π stacking (Fig. 2).…”

“…The process was driven by the reduced interfacial energy, 9 which can promote the dynamic covalent chemistry process on the interface. 17,18 Then, an in situ interfacial dissolution-recondensation process happened to fabricate microscale wool ball-like hollow COPs (MWH-COPs) (Fig. S1d, ESI †).…”