Single-crystal x-ray diffraction structures of covalent organic frameworks

TLDR

Covalent organic frameworks (COFs) are difficult to characterize structurally because they tend to form powders or amorphous materials, and recent work has examined three‑dimensional imine‑linked COFs. The authors describe a two‑step growth process in which nanoscale boronate ester–linked 2D COF seeds are expanded into micrometer‑scale single crystals by using a solvent that suppresses additional nucleation. Adding aniline inhibits nucleation, enabling the growth of large single crystals suitable for X‑ray diffraction, and transient‑absorption spectroscopy shows that these crystallites exhibit superior charge transport compared with conventional COF powders. Ma et al.

Abstract

Covalent organic frameworks writ large Covalent organic framework (COF) materials have been difficult to characterize structurally and to exploit because they tend to form powders or amorphous materials. Ma et al. studied a variety of three-dimensional COFs based on imine linkages (see the Perspective by Navarro). They found that the addition of aniline inhibited nucleation and allowed the growth of crystals large enough for single-crystal x-ray diffraction studies. Evans et al. describe a two-step process in which nanoscale seeds of boronate ester–linked two-dimensional COFs can be grown into micrometer-scale single crystals by using a solvent that suppresses the nucleation of additional nanoparticles. Transient absorption spectroscopy revealed superior charge transport in these crystallites compared with that observed in conventional powders. Science , this issue p. 48 , p. 52 ; see also p. 35