Covalent organic frameworks

Abstract

Two-dimensional covalent organic frameworks (2D COFs) are emerging crystalline 2D organic material comprising planar and covalent networks with long-ranging structural order. Benefiting from their intrinsic porosity, crystallinity, and electrical properties, 2D COFs have displayed great potential for separation, energy conversion, and electronic fields. For the most of these applications, large-area and highly-ordered 2D COFs thin films are required. As such, considerable efforts have been devoted to exploring the fabrication of 2D COF thin films with controllable architectures and properties. In this chapter, we aim to provide the recent advances in the fabrication of 2D COF thin films and highlight the advantages and limitations of different methods focusing on chemical bonding, morphology, and crystal structure.

Post-synthetic Transformation of Imine- into Nitrone-linked Covalent Organic Frameworks for Atmospheric Water Harvesting at Decreased Humidity

“…Likewise, oxaziridines pointing into the interlayer space, towards the neighboring layers, would cause an expansion of the interlayer stacking distance, which is in stark contrast to the observed reduction of the stacking distance in the nitrone (Figure 2a). The absence of any aliphatic carbon signals in the 13 C ssNMR spectrum (Figure 2b) and nitrogen signals in the 15 N ssNMR spectrum (Figure 2c) relating to oxaziridine formation supports our hypothesis that, in the sterically crowded COF pore, oxidation likely occurs through an electrophilic attack of mCPBA on the nitrogen, 31 as similarly observed for sterically hindered small molecule N-alkyl imines. 32 The electrophilic attack mechanism involves an equatorial advance of the mCPBA reagent towards the linkage nitrogen, i. e. from within the pores, perpendicular to the stacking direction of the layers.…”

“…After synthesizing NO-PI-3-COF and handling it in ambient air, we noticed a broad signal centered at ν ≈ 3350 cm -1 in the FT-IR spectrum (Figure S2), which disappeared after extensive drying of the material under reduced pressure. Likewise, an intense signal at δ = 4.5 ppm in the 1 H ssNMR spectrum of NO-PI-3-COF, as well as minor intensity changes in the 13 C ssNMR spectrum around δ = 150 and 119 ppm were visible, referring to carbons in close proximity to the nitrone center (Figure 2b). Due to the characteristic vibration in the FT-IR spectrum, we attributed the signal to water in NO-PI-3-COF, which was captured from ambient air.…”

“…10 The structural diversity of COF building blocks and linkages, coupled with their regular ordering in the crystalline material, also allow for almost infinite variation and optimization possibilities, and provide the basis for application-targeted engineering of these materials. 11,12,13,14 Despite this adaptability of their structures, water capture in many evaluated COFs systems, especially in those with pore diameters larger than 1.5 nm, is typically characterized by high uptake pressures and large hysteresis, limiting their potential for application as water harvesting materials. 15 Thus, several approaches have been made to improve the sorption properties of COFs.…”

“…To demonstrate the generality of our post-synthetic oxidation method, we apply this novel approach to the synthesis of two hexagonal COFs with different pore diameters, namely NO-PI-3-COF (1.6 nm) and NO-TTI-COF (2.1 nm), from their imine-linked parent materials (Figure 1b-c). We characterize changes in the material by utilizing a comprehensive suite of analytical techniques including Fourier transform infrared (FT-IR) spectroscopy, 13 C and 15 N solid-state nuclear magnetic resonance spectroscopy (ssNMR), and X-ray powder diffraction (XRPD) and correlate the COFs' ability of adsorbing water vapor, assessed by water vapor sorption experiments, to the targeted modification of the linkage chemistry.…”

Three-Dimensional Covalent Organic Frameworks with pts Topology for Controlled Anticancer Drug Delivery

“…Covalent organic frameworks (COFs) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] represent a new class of extended crystalline solids characterized by open frameworks, that encompass void spaces (pores) and are composed of organic building blocks held together by robust covalent bonds. Attributed to their molecular designability, unique pore environments, and functional modularity, COFs have become increasingly important in a wide array of applications including catalysis, 16,17 gas storage and separation, 18,19 sensing, 20,21 energy conversion and storage, 22,23 and biomedicine [24][25][26] .…”