Conjugated organic framework with three-dimensionally ordered stable structure and delocalized π clouds

Abstract

Covalent organic frameworks are a class of crystalline organic porous materials that can utilize π–π-stacking interactions as a driving force for the crystallization of polygonal sheets to form layered frameworks and ordered pores. However, typical examples are chemically unstable and lack intrasheet π-conjugation, thereby significantly limiting their applications. Here we report a chemically stable, electronically conjugated organic framework with topologically designed wire frameworks and open nanochannels, in which the π conjugation-spans the two-dimensional sheets. Our framework permits inborn periodic ordering of conjugated chains in all three dimensions and exhibits a striking combination of properties: chemical stability, extended π-delocalization, ability to host guest molecules and hole mobility. We show that the π-conjugated organic framework is useful for high on-off ratio photoswitches and photovoltaic cells. Therefore, this strategy may constitute a step towards realizing ordered semiconducting porous materials for innovations based on two-dimensionally extended π systems.

Mercury nano-trap for effective and efficient removal of mercury(II) from aqueous solution

“…1) that features high surface area with densely populated yet highly accessible Hg(II) binding sites thereby affording high Hg(II) adsorption capacity; strong Hg(II) chelating groups that are well dispersed throughout the single-walled pore surface thus rendering high affinity for Hg(II) and efficient utilization of Hg(II) binding sites; large yet tunable pore size to enable fast yet controllable kinetics of Hg(II) adsorption; Hg(II) chelating groups that are covalently anchored to the backbone thus avoiding the leaching of binding sites; exceptional water/chemical stability facilitating regeneration/recyclability. Such mercury 'nano-trap' can be targeted by grafting desired Hg(II) chelating groups to the highly robust porous organic polymers (POPs) [35][36][37][38][39][40][41][42][43][44] that exhibit high surface areas, tunable pore sizes and high water/ chemical stabilities, via stepwise post-synthetic modification 45 of the phenyl rings of their structural components using various established organic reactions. Herein we demonstrate such a POP-based mercury 'nano-trap' that exhibits an exceptional mercury saturation uptake capacity of over 1,000 mg g À 1 and can effectively reduce Hg(II) concentration from 10 p.p.m.…”

Intensified synthesis and post-synthetic modification of covalent organic frameworks using a continuous flow of microdroplets technique

“…Note that the broadness of the PXRD peaks for the β-ketoenamine-linked COFs is a well-established phenomenon, which likely originates from stacking faults or dislocations, displaying an inter-layer distance estimated at~3.4 Å. 40 It is also noteworthy that this series of COFs has not yet shown very high crystallinity in comparison to COFs with reversible imine or boronateester linkages. 41 The high-resolution TEM images revealed parallelaligned, stacked sheets 40 composed of crystalline domains with sizes of 10-40 nm (Supplementary Figures S5 and S6).…”

“…40 It is also noteworthy that this series of COFs has not yet shown very high crystallinity in comparison to COFs with reversible imine or boronateester linkages. 41 The high-resolution TEM images revealed parallelaligned, stacked sheets 40 composed of crystalline domains with sizes of 10-40 nm (Supplementary Figures S5 and S6). Accordingly, we observed improved nanoscale crystallinity with slightly enhanced short-range ordering, when compared to the β-ketoenamine-linked COFs obtained by conventional solvothermal methods.…”

Recent Progress in the Fabrication of Low Dimensional Nanostructures via Surface-Assisted Transforming and Coupling

“…Unlike the reaction that occurred in solution, fabricating low dimensional COF at the liquid/solid or gas/solid interface through self-condensation of boronic acids is a novel method to form a series of nanomaterials equipped with functional characteristics such as sensing [38,39], energy storage [40], optoelectronic devices [41,42], and catalysis [43,44]. The building blocks of the condensation equipped with more than two functional groups, hydroxide radical, is a basic precondition to trigger the reaction, and the ambient environment around the reaction monomers can obviously decide the quality of the surface covalent organic framework (SCOF).…”