Heterogeneous catalysis in water has not been explored beyond certain advantages like recyclability and recovery of the catalysts from the reaction medium. In doing so, they often fail to address other authentic pitfalls of homogeneous catalysis. Moreover, poor yield, extremely low selectivity, and active catalytic sites' deactivation further underrate the heterogeneous catalysis in water. On the other hand, most of the synthetically useful homogeneous catalysts are either water intolerant or remain catalytically inactive in water. Considering these facts, we have rationally designed and synthesized solution dispersible porous covalent organic framework (COF) nano-spheres to utilize their distinctive morphology and dispersibility to bridge between homogeneous and heterogeneous catalysis. The success has further been extended in fabricating catalyst immobilized COF thin-lms via covalent self-assembly for the very rst time. We have used these catalyst immobilized COF thin-lms to develop a general methodology for the C-H functionalization of organic substrates in water. This unique covalent self-assembly occurs through the protrusion of the bers/threads at the interface of two nano-spheres, transmuting the catalytic spheres into lms without any leaching of catalyst molecules, which was hitherto unheard of. The catalyst immobilized porous COF thin-lms' chemical functionality and hydrophobic environment stabilizes the high valent transient active oxoiron(V) intermediate in water and restricts the active catalytic site's deactivation. An elevated catalytic yield and high selectivity (3°:2°) have been achieved in open-air conditions at room temperature, accompanying the elemental feature of heterogeneous catalysis, i.e., the recyclability. These COF lms functionalized the unactivated C-H bonds in water with a high catalytic yield (45-99%) and with a high degree of selectivity (cis:trans=155:1; 3°:2°=257:1 in case of cis-1,2dimethylcyclohexane). To establish the "practical implementation" of this approach, we conducted the in ow catalysis (Turnover Number = 355±5) using catalyst immobilized COF lms fabricated on a macroporous polymeric support.

The synthesis of homogeneous covalent organic framework (COF) thin films on a desired substrate with decent crystallinity, porosity, and uniform thickness has great potential for optoelectronic applications. We have used a solution-processable sphere transmutation process to synthesize 300 ± 20 nm uniform COF thin films on a 2 × 2 cm 2 TiO 2 -coated fluorine-doped tin oxide (FTO) surface. This process controls the nucleation of COF crystallites and molecular morphology that helps the nanospheres to arrange periodically to form homogeneous COF thin films. We have synthesized four COF thin films (TpDPP, TpEtBt, TpTab, and TpTta) with different functional backbones. In a close agreement between the experiment and density functional theory, the TpEtBr COF film showed the lowest optical band gap (2.26 eV) and highest excited-state lifetime (8.52 ns) among all four COF films. Hence, the TpEtBr COF film can participate in efficient charge generation and separation. We constructed optoelectronic devices having a glass/FTO/TiO 2 /COF-film/Au architecture, which serves as a model system to study the optoelectronic charge transport properties of COF thin films under dark and illuminated conditions. Visible light with a calibrated intensity of 100 mW cm −2 was used for the excitation of COF thin films. All of the COF thin films exhibit significant photocurrent after illumination with visible light in comparison to the dark. Hence, all of the COF films behave as good photoactive substrates with minimal pinhole defects. The fabricated out-of-plane photodetector device based on the TpEtBr COF thin film exhibits high photocurrent density (2.65 ± 0.24 mA cm −2 at 0.5 V) and hole mobility (8.15 ± 0.64 ×10 −3 cm 2 V −1 S −1 ) compared to other assynthesized films, indicating the best photoactive characteristics.

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.

Covalent organic frameworks (COFs) are ideal host matrices for biomolecule immobilization and biocatalysis due to their high porosity, various functionalities, and structural robustness. However, the porosity of COFs is limited...

No abstract