利用掃描式電子穿隧顯微鏡探討吡唑及含吡唑液晶分子於金(111)電極上之吸附結構

In Situ Scanning Tunneling Microscopy of Pyrazole and Pyrazole Liquid Crystal Molecules Adsorbed on Au(111) Electrode

黃雅郁(Ya-yu Huang)

指導教授 ： 姚學麟

國立中央大學/理學院/化學系/碩士(2011年)

摘要

液晶分子的物性及化性與分子間吸引力有相當大的關係，藉由掃描式電子穿隧顯微鏡可以更深入的對分子內部結構及分子間的作用力進行研究。因此本研究將利用掃描式電子穿隧顯微鏡就吡唑及含吡唑液晶分子5-(dodecyloxy)-2- (5-(4-(pentyloxy)phenyl)-1H-pyrazol-3-yl)phenol (簡稱為Pyph-5,12與Pyph-8,12)針對電位變化進行探討。
吡唑分子因分子間氫鍵以二聚體的形式吸附於金(111)電極上，且吸附結構受電位與電解液的改變所影響。在過氯酸系統下，吡唑分子於0.5 V[VS. RHE]前後結構皆為(5 × √13)，隨著電位調整，吸附結構發生改變，使得覆蓋度從0.1上升0.2。當電位由0.8 V往正調至0.85 V時，金(111)表面由重排轉變為(1 × 1)，吡唑的吸附結構也會隨之改變從(5 × √13)轉變為(√13 × √39)。除此之外，當電解液由過氯酸替換成硫酸時，推測硫酸根會與吡唑分子共吸附於金(111)電極上，但硫酸根與吡唑是否確實有共吸附的現象還有賴其他的實驗證明。
含有吡唑液晶分子Pyph-5,12與Pyph-8,12不同於單純吡唑分子會因分子間氫鍵而形成二聚體，吸附結構是由分子間烷氧基鏈的凡德瓦力主導著。分子會堆疊成層狀，且分子為Smetic 液晶相，分子長軸的方向與層狀分子互相垂直，由高解像STM圖確實可得到此層狀的結構。當電位較正時則得到另一個不同的吸附結構，且此結構轉換是可逆的，故藉由調控電位可以得到不同的吸附結構。

關鍵字

吡唑 ； 液晶分子 ； 掃描式電子穿隧顯微鏡

並列摘要

The physical and chemical properties of liquid crystals (LC) owe a great deal to their intermolecular interactions and the devise of STM has yielded insights into how molecules interact with one another. In this study, STM was employed to examine the spatial structures of pyrazole and pyrazole derivatives 5-(dodecyloxy)-2- (5-(4-(pentyloxy)phenyl)-1H-pyrazol-3-yl)phenol (Pyph-5,12 and Pyph-8,12) molecules adsorbed on Au(111) electrode in an electrochemical environment.
In theory, it is possible that the N-H moieties of pyrazole could form dimers through N---H－N(hydrogen-bonding), and the structure of pyrazole onto Au(111) electrode varied with concentration and supporting electrolyte. Molecular-resolution STM imaging in 0.1mM pyrazole/0.1 M HClO4 revealed highly ordered structures of (5 × √13) adsorbed on the reconstructed Au(111) electrode between 0.2 and 0.9 V [vs. RHE]. However, the structure and coverag varied with potential. Increasing the potential to E > 0.85 V lifted the reconstructed Au(111) surface and the ordered pyrazole structure of (√13 × √39) appeared simultaneously. Ordered pyrazole structures of (5 × √13) could be restored by applying potentials negative enough to reinforce the reconstructed Au(111). In addition, the electrolyte replaced by the sulfuric acid, the structure changed, due to the sulfate and pyrazole coadsorbed on Au(111) electrode.
These molecules could form smectic phases, where molecules are stacked in layers with their long axis aligned perpendicularly to the layer. High-quality STM images were obtained to reveal that indeed Pyph-5,12 and 8,12 could be adsorbed in a lamellar phase which resembles closely to the expected layered structure of these molecules in the bulk liquid crystal. Results obtained also show the formation of another chained phase at more positive potentials. Real-time STM imaging revealed transitions between these ordered phases in response to the modulation of potential. The van der Waals interactions between alkoxy chains of Pyph-5,12 appeared to predominate their lateral structures, whereas intermolecular hydrogen bonds formed by pyrazole mesogens could be secondary.

並列關鍵字

STM ； Pyrazole ； Liquid crystal

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