Self-assembly of hydrogen-bonded two-dimensional quasicrystals

摘要

The process of molecular self-assembly on solid surfaces is essentially one of crystallization in two dimensions, and the structures that result depend on the interplay between intermolecular forces and the interaction between adsorbates and the underlying substrate. Because a single hydrogen bond typically has an energy between 15 and 35 kilojoules per mole, hydrogen bonding can be a strong driver of molecular assembly; this is apparent from the dominant role of hydrogen bonding in nucleic-acid base pairing, as well as in the secondary structure of proteins. Carboxylic acid functional groups, which provide two hydrogen bonds, are particularly promising and reliable in creating and maintaining surface order, and self-assembled monolayers of benzoic acids produce structure that depends on the number and relative placement of carboxylic acid groups. Here we use scanning tunnelling microscopy to study self-assembled mono-layers of ferrocenecarboxylic acid (FcCOOH), and find that, rather than producing dimeric or linear structures typical of carboxylic acids, FcCOOH forms highly unusual cyclic hydrogen-bonded pen-tamers, which combine with simultaneously formed FcCOOH dimers to form two-dimensional quasicrystallites that exhibit local five-fold symmetry and maintain translational and rotational order (without periodicity) for distances of more than 400 angstroems.%在其中观察到非周期性准晶序的系统范围还在继续扩大，小分子自组装单层材料现在也进入了这一范畴。具体来讲，Natalie Wasio及同事发现，二茂铁羧酸的氢键模式驱动这些分子组装成不寻常的环形五聚物，其五倍对称性有助于形成一个二维准晶排列。作者预测，很多不同新型准晶超分子聚合体有可能基于这一分子框架而形成。