title: 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 m(2) 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.
authors.affiliation: Department of Chemistry and Center for NanoScience (CeNS), University of Munich (LMU) , Butenandtstrasse 5-13, 81377 Munich, Germany.
authors.forename: Mona
authors.initials: M
authors.lastname: Calik
authors.affiliation: Department of Chemistry and Center for NanoScience (CeNS), University of Munich (LMU) , Butenandtstrasse 5-13, 81377 Munich, Germany.
authors.forename: Torben
authors.initials: T
authors.lastname: Sick
authors.affiliation: Department of Chemistry and Center for NanoScience (CeNS), University of Munich (LMU) , Butenandtstrasse 5-13, 81377 Munich, Germany.
authors.forename: Mirjam
authors.initials: M
authors.lastname: Dogru
authors.affiliation: Department of Chemistry and Center for NanoScience (CeNS), University of Munich (LMU) , Butenandtstrasse 5-13, 81377 Munich, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Döblinger
authors.affiliation: Department of Chemistry and Center for NanoScience (CeNS), University of Munich (LMU) , Butenandtstrasse 5-13, 81377 Munich, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Datz
authors.affiliation: Department of Chemistry and Center for NanoScience (CeNS), University of Munich (LMU) , Butenandtstrasse 5-13, 81377 Munich, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Budde
authors.affiliation: Department of Chemistry and Center for NanoScience (CeNS), University of Munich (LMU) , Butenandtstrasse 5-13, 81377 Munich, Germany.
authors.forename: Achim
authors.initials: A
authors.lastname: Hartschuh
authors.affiliation: Department of Chemistry and Center for NanoScience (CeNS), University of Munich (LMU) , Butenandtstrasse 5-13, 81377 Munich, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Auras
authors.affiliation: Department of Chemistry and Center for NanoScience (CeNS), University of Munich (LMU) , Butenandtstrasse 5-13, 81377 Munich, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Bein