Colloidal Covalent Organic Frameworks.
Covalent organic frameworks (COFs) are two- or three-dimensional (2D or 3D) polymer networks with designed topology and chemical functionality, permanent porosity, and high surface areas. These features are potentially useful for a broad range of applications, including catalysis, optoelectronics, and energy storage devices. But current COF syntheses offer poor control over the material's morphology and final form, generally providing insoluble and unprocessable microcrystalline powder aggregates. COF polymerizations are often performed under conditions in which the monomers are only partially soluble in the reaction solvent, and this heterogeneity has hindered understanding of their polymerization or crystallization processes. Here we report homogeneous polymerization conditions for boronate ester-linked, 2D COFs that inhibit crystallite precipitation, resulting in stable colloidal suspensions of 2D COF nanoparticles. The hexagonal, layered structures of the colloids are confirmed by small-angle and wide-angle X-ray scattering, and kinetic characterization provides insight into the growth process. The colloid size is modulated by solvent conditions, and the technique is demonstrated for four 2D boronate ester-linked COFs. The diameter of individual COF nanoparticles in solution is monitored and quantified during COF growth and stabilization at elevated temperature using in situ variable-temperature liquid cell transmission electron microscopy imaging, a new characterization technique that complements conventional bulk scattering techniques. Solution casting of the colloids yields a free-standing transparent COF film with retained crystallinity and porosity, as well as preferential crystallite orientation. Collectively this structural control provides new opportunities for understanding COF formation and designing morphologies for device applications.
Department of Chemistry and Chemical Biology and Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, United States; Department of Chemistry, Bucknell University, Lewisburg, Pennsylvania 17837, United States.
Brian J
BJ
Smith
Department of Chemistry & Biochemistry and Materials Science & Engineering, University of California, San Diego , La Jolla, California 92093, United States.
Lucas R
LR
Parent
Department of Chemistry and Chemical Biology and Department of Materials Science and Engineering, Cornell University , Ithaca, New York 14853, United States.
Anna C
AC
Overholts
Department of Chemistry and Chemical Biology and Department of Materials Science and Engineering, Cornell University , Ithaca, New York 14853, United States.
Peter A
PA
Beaucage
Department of Chemistry and Chemical Biology and Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, United States; Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
Ryan P
RP
Bisbey
Department of Chemistry and Chemical Biology and Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, United States; Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
Anton D
AD
Chavez
Department of Chemistry and Chemical Biology and Department of Materials Science and Engineering, Cornell University , Ithaca, New York 14853, United States.
Nicky
N
Hwang
Department of Industrial and Manufacturing Engineering, Florida State University , Tallahassee, Florida 32306, United States.
Chiwoo
C
Park
Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.
Austin M
AM
Evans
Department of Chemistry & Biochemistry and Materials Science & Engineering, University of California, San Diego, La Jolla, California 92093, United States; Department of Chemistry & Biochemistry and Materials Science & Engineering, University of California, San Diego, La Jolla, California 92093, United States.
Nathan C
NC
Gianneschi
Department of Chemistry and Chemical Biology and Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, United States; Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
William R
WR
Dichtel