From Highly Crystalline to Outer Surface-Functionalized Covalent Organic Frameworks—A Modulation Approach

Abstract

Crystallinity and porosity are of central importance for many properties of covalent organic frameworks (COFs), including adsorption, diffusion, and electronic transport. We have developed a new method for strongly enhancing both aspects through the introduction of a modulating agent in the synthesis. This modulator competes with one of the building blocks during the solvothermal COF growth, resulting in highly crystalline frameworks with greatly increased domain sizes reaching several hundreds of nanometers. The obtained materials feature fully accessible pores with an internal surface area of over 2000 m2 g–1. Compositional analysis via NMR spectroscopy revealed that the COF-5 structure can form over a wide range of boronic acid-to-catechol ratios, thus producing frameworks with compositions ranging from highly boronic acid-deficient to networks with catechol voids. Visualization of an −SH-functionalized modulating agent via iridium staining revealed that the COF domains are terminated by the modulator. Using functionalized modulators, this synthetic approach thus also provides a new and facile method for the external surface functionalization of COF domains, providing accessible sites for post-synthetic modification reactions. We demonstrate the feasibility of this concept by covalently attaching fluorescent dyes and hydrophilic polymers to the COF surface. We anticipate that the realization of highly crystalline COFs with the option of additional surface functionality will render the modulation concept beneficial for a range of applications, including gas separations, catalysis, and optoelectronics.

Photoactive and Conducting Covalent Organic Frameworks

“…The wellknown boronate ester COF-5 formed larger crystalline domain sizes and exhibited improved porosity by including a competitor molecule into the reaction mixture. [19] Here, slowing down the reaction rate resulted in significantly reduced structural defects. Recently, Bein and co-workers investigated the dual-pore COF platform for the realization of highly crystalline, robust frameworks.…”

Defective 2D Covalent Organic Frameworks for Postfunctionalization

“…Therefore, it seems that rationally introducing defects into COFs may be a good strategy for broadening COFs functionalities and applications. However, up to now, reported works about defects in COFs are relatively limited, and most of these reported defective COFs are focused on regulate defects for enhancing the crystalline quality to obtain the perfect COFs . Dichtel's and Bein's groups employed monomer‐truncation strategy to create defects for functionalization of COFs.…”

“…However, up to now, reported works about defects in COFs are relatively limited, and most of these reported defective COFs are focused on regulate defects for enhancing the crystalline quality to obtain the perfect COFs . Dichtel's and Bein's groups employed monomer‐truncation strategy to create defects for functionalization of COFs. Meanwhile, Yaghi's, Lotsch's, Loh's, and Dong's groups constructed defective COFs via precise controlling the reaction solvent and conditions.…”

Kovalente organische Netzwerke und Käfigverbindungen: Design und Anwendungen von polymeren und diskreten organischen Gerüsten

“…Cooper und Mitarbeiter konnten füre ine Reihe von Käfignanopartikeln zeigen, dass Fehlordnungen und amorphe Phasen in erheblichem Umfang zur Mikroporositätd ieser Materialien beitragen kçnnen, obwohl sie für Standardanalysemethoden wie PXRD nahezu unsichtbar sind. [213] Als einen Meilenstein der COF-Charakterisierung präsentierten Beaudoin et al [118] die ersten Einkristallstrukturanalysen füre ine Serie von kovalenten Nitroso-Polymernetzwerken. Propellerfçrmige Bausteine kçnnen als molekulare Andockstellen [211] fungieren und so zu einem synchronisierten Stapelungsversatz führen.…”