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 Micrometer-scale single crystals of two-dimensional boronate ester–linked frameworks can be grown in a two-step process. Polymerization of monomers into periodic two-dimensional networks provides structurally precise, layered macromolecular sheets that exhibit desirable mechanical, optoelectronic, and molecular transport properties. Two-dimensional covalent organic frameworks (2D COFs) offer broad monomer scope but are generally isolated as powders comprising aggregated nanometer-scale crystallites. We found that 2D COF formation could be controlled using a two-step procedure in which monomers are added slowly to preformed nanoparticle seeds. The resulting 2D COFs are isolated as single-crystalline, micrometer-sized particles. Transient absorption spectroscopy of the dispersed COF nanoparticles revealed improvement in signal quality by two to three orders of magnitude relative to polycrystalline powder samples, and suggests exciton diffusion over longer length scales than those obtained through previous approaches. These findings should enable a broad exploration of synthetic 2D polymer structures and properties.

中文翻译：

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单晶二维共价有机骨架的种子生长

共价有机骨架写大 共价有机骨架 (COF) 材料难以在结构上表征和开发，因为它们倾向于形成粉末或无定形材料。马等人。研究了基于亚胺键的各种三维 COF（参见 Navarro 的观点）。他们发现加入苯胺会抑制成核，并允许晶体生长足够大以进行单晶 X 射线衍射研究。埃文斯等人。描述了一个两步过程，其中硼酸酯连接的二维 COF 的纳米级种子可以通过使用抑制额外纳米粒子成核的溶剂生长成微米级单晶。与在常规粉末中观察到的相比，瞬态吸收光谱显示这些微晶中的电荷传输更优。科学，这个问题 p。48 页。52; 另见第。二维硼酸酯连接骨架的 35 微米级单晶可以通过两步法生长。单体聚合成周期性二维网络提供了结构精确的层状大分子片，表现出理想的机械、光电和分子传输特性。二维共价有机骨架 (2D COF) 提供了广泛的单体范围，但通常被分离为包含聚集纳米级微晶的粉末。我们发现可以使用两步程序控制 2D COF 的形成，其中将单体缓慢添加到预先形成的纳米粒子种子中。所得的 2D COF 被分离为单晶、微米级颗粒。与多晶粉末样品相比，分散的 COF 纳米颗粒的瞬态吸收光谱显示信号质量提高了两到三个数量级，并表明激子扩散的长度比通过以前的方法获得的更长。这些发现应该能够对合成的 2D 聚合物结构和特性进行广泛的探索。