College of Materials Science and Engineering, South China University of Technology, Guangzhou, China.
Chem Asian J. 2013 May;8(5):926-33. doi: 10.1002/asia.201201229. Epub 2013 Feb 27.
The 2D self-assembly of various 2-hydroxy-7-alkoxy-9-fluorenone (HAF) molecules has been investigated by scanning tunneling microscopy (STM) at the liquid/solid interface. A systematic study revealed that HAF molecules with different numbers of carbon atoms in their alkoxy chains could form two or three different kinds of nanostructures, that is, less-ordered, flower-like, and zig-zag patterns, owing to the formation of different types of intermolecular hydrogen bonds. The observed structural transition was found to be driven by molecular thermodynamics, surface diffusion, and the voltage pulse that was applied to the STM tip. The zig-zag pattern was the most stable of these configurations. An odd-even effect on the flower-like structure, as induced by the odd and even number of carbon atoms in the side chain, was observed by STM. The influence of the odd-even effect on the melting point has a close relationship with the molecular self-assembled pattern. Our results are significant for understanding the influence of hydrogen-bonding interactions on the dominant adsorption behavior on the surface and provide a new visual approach for observing the influence of the odd-even effect on the phase transition.
通过在液体/固体界面处的扫描隧道显微镜（STM）研究了各种 2-羟基-7-烷氧基-9-芴酮（HAF）分子的二维自组装。系统研究表明，由于形成了不同类型的分子间氢键，烷氧基链中碳原子数不同的 HAF 分子可以形成两种或三种不同的纳米结构，即较无序的花状和锯齿状图案。观察到的结构转变是由分子热力学、表面扩散和施加在 STM 尖端的电压脉冲驱动的。这些构型中，锯齿状图案是最稳定的。通过 STM 观察到侧链中碳原子数为奇数和偶数时对花状结构的奇偶效应。通过分子自组装模式，观察到奇偶效应对熔点的影响。我们的结果对于理解氢键相互作用对表面主要吸附行为的影响具有重要意义，并为观察奇偶效应对相变的影响提供了一种新的直观方法。
