Weidner Tobias, Bretthauer Frauke, Ballav Nirmalya, Motschmann Hubert, Orendi Horst, Bruhn Clemens, Siemeling Ulrich, Zharnikov Michael
Angewandte Physikalische Chemie, Universitat Heidelberg, 69120 Heidelberg, Germany.
Langmuir. 2008 Oct 21;24(20):11691-700. doi: 10.1021/la802454w. Epub 2008 Sep 27.
We have compared the structural and photoisomerization properties of self-assembled monolayers (SAMs) comprising either the trans or cis isomers of azobenzene terminated dithiolane with in-chain amide unit, viz., 4-(phenyldiazenyl)phenyl-4-(1,2-dithiolane-3-yl)-butylcarboxamide ( 1). These films were prepared on Au(111) from solutions of both isomers. Structure and composition of the SAMs were studied by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The photoresponse of the films was monitored in real time by ellipsometry. SAMs fabricated from the trans isomer were found to be densely packed and highly ordered. These films did not show any discernible photoresponse upon irradiation with UV light, which, under favorable conditions, triggers the trans- cis isomerization. In contrast, films prepared from solutions containing predominantly the cis isomer were loosely packed and mostly disordered but exhibited reversible photoreactivity. The results confirm that steric effects, i.e., available free volume, play a dominant role for the photoresponse of aliphatic SAMs bearing the photoactive azobenzene group. The crystal structure of 1 ( trans isomer) exhibits a row-like aggregation of neighboring molecules by weak hydrogen bonds and can be taken as a model for the arrangement of 1 in the monolayer films. Further, in addition to the surface coordination behavior, we have also mimicked the chemisorption of the 1,2-dithiolane moiety onto the gold substrate in molecular coordination chemistry in oxidative addition reactions with the zero-valent platinum complex [Pt(PPh 3) 4].
我们比较了由链内酰胺单元的偶氮苯封端二硫杂环戊烷的反式或顺式异构体组成的自组装单分子层（SAMs）的结构和光异构化性质，即4-(苯基重氮基)苯基-4-(1,2-二硫杂环戊烷-3-基)-丁基甲酰胺（1）。这些薄膜是在Au(111)上由两种异构体的溶液制备的。通过X射线光电子能谱和近边X射线吸收精细结构光谱研究了SAMs的结构和组成。通过椭偏仪实时监测薄膜的光响应。发现由反式异构体制造的SAMs紧密堆积且高度有序。在用紫外光照射时，这些薄膜没有显示出任何可察觉的光响应，而在有利条件下，紫外光会引发反式-顺式异构化。相比之下，由主要含有顺式异构体的溶液制备的薄膜堆积松散且大多无序，但表现出可逆的光反应性。结果证实，空间效应，即可用自由体积，对带有光活性偶氮苯基团的脂肪族SAMs的光响应起主导作用。1（反式异构体）的晶体结构通过弱氢键呈现相邻分子的行状聚集，并且可以作为1在单分子层薄膜中排列的模型。此外，除了表面配位行为，我们还在分子配位化学中通过与零价铂配合物[Pt(PPh₃)₄]的氧化加成反应模拟了1,2-二硫杂环戊烷部分在金基底上的化学吸附。
