Johnson Kristen N, Hurlock Matthew J, Zhang Qiang, Hipps K W, Mazur Ursula
Department of Chemistry , Washington State University , Pullman , Washington 99163-4630 , United States.
Materials Science & Engineering Program , Washington State University , Pullman , Washington 99163-2711 , United States.
Langmuir. 2019 Apr 16;35(15):5271-5280. doi: 10.1021/acs.langmuir.9b00204. Epub 2019 Apr 4.
This study explores directed noncovalent bonding in the self-assembly of nonplanar aromatic carboxylic acids on gold and graphite surfaces. It is the first step in developing a new design strategy to create two-dimensional surface metal-organic frameworks (SURFMOFs). The acid molecules used are tetraphenylethene-based and are typically employed in the synthesis of three-dimensional (3D) MOF crystalline solids. They include tetraphenylethene tetracarboxylic acid, tetraphenylethene bisphenyl carboxylic acid, and tetraphenylethene tetrakis-phenyl carboxylic acid. The two-dimensional structures formed from these molecules on highly ordered pyrolytic graphite (HOPG) and Au(111) are studied by scanning tunneling microscopy in a solution environment. The process of monolayer formation and final surface linker structures are found to be strongly dependent on the combination of the molecule and substrate used and are discussed in terms of intermolecular and molecule-substrate interactions, bonding geometry, and symmetry of the acid molecules. In the case of linker self-assembly on HOPG, the molecule-substrate interactions play a significant role in the resulting surface structure. When the acid molecules are adsorbed on Au(111), the intermolecular interactions tend to dominate over the weaker molecule-substrate bonding. Additionally, the interplay of π-π interactions and hydrogen bonding that directs the surface self-assembly on different supports can be modified by varying the linker concentration. This is particularly applicable for the case of the acid molecules adsorbing on the Au(111) substrate. Precise control over predesigned surface structures and orientation of the nonplanar aromatic carboxylic linkers open up an exciting prospect for manipulating the direction of SURFMOF growth in two dimensions and potentially in 3D.
本研究探索了非平面芳香族羧酸在金和石墨表面自组装过程中的定向非共价键合。这是开发一种新的设计策略以创建二维表面金属有机框架（SURFMOFs）的第一步。所使用的酸分子基于四苯乙烯，通常用于合成三维（3D）MOF晶体固体。它们包括四苯乙烯四羧酸、四苯乙烯双苯基羧酸和四苯乙烯四（苯基）羧酸。通过在溶液环境中使用扫描隧道显微镜研究了这些分子在高度有序热解石墨（HOPG）和Au(111)上形成的二维结构。发现单层形成过程和最终的表面连接体结构强烈依赖于所使用的分子和底物的组合，并根据分子间和分子 - 底物相互作用、键合几何形状以及酸分子的对称性进行了讨论。在连接体在HOPG上自组装的情况下，分子 - 底物相互作用在所得表面结构中起重要作用。当酸分子吸附在Au(111)上时，分子间相互作用往往比较弱的分子 - 底物键合占主导地位。此外，通过改变连接体浓度可以改变指导不同载体上表面自组装的π - π相互作用和氢键的相互作用。这在酸分子吸附在Au(111)底物的情况下尤其适用。对预先设计的表面结构和非平面芳香族羧酸连接体取向的精确控制为在二维甚至潜在的三维中操纵SURFMOF生长方向开辟了令人兴奋的前景。
