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Emissive Single-Crystalline Boroxine-Linked Colloidal Covalent Organic Frameworks

preprint
submitted on 17.08.2019 and posted on 19.08.2019 by Austin Evans, Ioannina Castano, Alexandra Brumberg, Lucas R. Parent, Amanda Corcos, Rebecca Li, Nathan C. Flanders, David J. Gosztola, Nathan Gianneschi, Richard Schaller, William Dichtel
The synthesis of periodic two-dimensional (2D) polymers and characterization of their optoelectronic behaviors are challenges at the forefront of polymer chemistry and materials science. Recently, we showed that layered 2D polymers known as 2D covalent organic frameworks (COFs) can be synthesized as single crystals by preparing COF particles as colloidal suspensions. Here we expand this approach from the condensation of boronic acids and catechols to the dehydrative trimerization of polyboronic acids. The resulting boroxine-linked colloids are the next class of 2D COFs to be obtained as single‑crystalline particles, as demonstrated here for four 2D COFs and one 3D COF. Colloidal stabilization enables detailed structural analysis by synchrotron X-ray diffraction and high-resolution transmission electron microscopy. Solution fluorescence spectroscopy revealed that the COF crystallites are highly emissive compared to their respective monomer solutions. Excitation‑emission matrix fluorescence spectroscopy indicated that the origin of this enhanced emission can be attributed to through-space communication of chromophores between COF sheets. These observations will motivate the development of colloidal COF systems as a platform to organize functional aromatic systems into precise and predictable assemblies with emergent properties.

Funding

ARO W911NF-15-1-0447

NSF DGE-1324585

NSF DMREF-1629383

DOE DE AC02-06CH11357

NIH F32EB021859

NSF DGE-1842165

NSF ECCS-1542205

NSF DMR-1720139

NCI CCSG P30 CA060553

History

Email Address of Submitting Author

wdichtel@northwestern.edu

Institution

Northwestern University

Country

United States

ORCID For Submitting Author

0000-0002-3635-6119

Declaration of Conflict of Interest

The authors note no conflict of interest.

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