Two-Dimensional Covalent Organic Framework Solid Solutions

作者：Rebecca L. Li, Anna Yang, Nathan C. Flanders, Michael T. Yeung, Daylan T. Sheppard, William R. Dichtel · 发表于：Journal of the American Chemical Society · 年份：2021 · DOI：10.1021/jacs.1c01683 · 被引用次数：56 · 研究领域：Covalent Organic Framework Applications、Metal-Organic Frameworks: Synthesis and Applications、Luminescence and Fluorescent Materials

Covalent organic frameworks (COFs) generally leverage one or two monomers with specific sizes and shapes to access highly symmetric and periodic polymer networks. Almost all reported COFs employ the minimum sets of monomers needed for the polymerization (usually two, sometimes one) and crystallize in high-symmetry topologies. COFs synthesized from more than two monomers usually employ mixtures with different pendant functionalities to distribute these groups statistically throughout the structure, or monomers with different sizes in ratios targeting lower symmetry topologies. Here, we demonstrate that mixtures of monomers with different lengths generate single-phase, hexagonal two-dimensional covalent organic framework (2D COF) solid solutions at continuously variable feed ratios. X-ray diffraction measurements, Fourier-transform infrared spectroscopy, and Pawley refinement indicate that both monomers distribute randomly within the same lattice, and the lattice parameters continuously increase as more of the larger linker is incorporated. Furthermore, COF solid solutions are accessed directly by polymerizing a mixture of monomers but not via linker exchange from a preformed COF. As strain develops from the lattice accommodating monomers with different sizes, the nonlinear relationship between the monomer incorporation and the COF's lattice parameters suggests that bond-bending of the monomers plays a role in incorporating monomers of different lengths into the solid solutions...