CEA, IRAMIS, SPCSI Chemistry of Surfaces and Interfaces Group, F-91191, Gif-sur-Yvette, France.
Langmuir. 2012 Aug 14;28(32):11767-78. doi: 10.1021/la3011103. Epub 2012 Aug 1.
The spontaneous reaction of diazonium salts on various substrates has been widely employed since it consists of a simple immersion of the substrate in the diazonium salt solution. As electrochemical processes involving the same diazonium salts, the spontaneous grafting is assumed to give covalently poly(phenylene)-like bonded films. Resistance to solvents and to ultrasonication is commonly accepted as indirect proof of the existence of a covalent bond. However, the most relevant attempts to demonstrate a metal-C interface bond have been obtained by an XPS investigation of spontaneously grafted films on copper. Similarly, our experiments give evidence of such a bond in spontaneously grafted films on nickel substrates in acetonitrile. In the case of gold substrates, the formation of a spontaneous film was unexpected but reported in the literature in parallel to our observations. Even if no interfacial bond was observed, formation of the films was explained by grafting of aryl cations or radicals on the surface arising from dediazoniation, the film growing later by azo coupling, radical addition, or cationic addition on the grafted phenyl layer. Nevertheless, none of these mechanisms fits our experimental results showing the presence of an Au-N bond. In this work, we present a fine spectroscopic analysis of the coatings obtained on gold and nickel substrates that allow us to propose a chemical structure of such films, in particular, their interface with the substrates. After testing the most probable mechanisms, we have concluded in favor of the involvement of two complementary mechanisms which are the direct reaction of diazonium salts with the gold surface that accounts for the observed Au-N interfacial bonds as well as the formation of aryl cations able to graft on the substrate through Au-C linkages.
自反应性的重氮盐在各种基质上的反应已经得到了广泛的应用，因为它只需要将基质浸入重氮盐溶液中。作为涉及相同重氮盐的电化学过程，自发接枝被认为能得到共价键合的聚（亚苯基）类似的键合膜。对溶剂和超声处理的抗性通常被认为是共价键存在的间接证据。然而，通过对铜基质上自发接枝膜的 XPS 研究，最相关的尝试是证明金属-C 界面键的存在。同样，我们的实验在乙腈中镍基质上自发接枝膜中也证明了这种键的存在。在金基质的情况下，自发膜的形成是出乎意料的，但在文献中与我们的观察结果平行报道。即使没有观察到界面键，也可以通过芳基阳离子或自由基在表面上的接枝来解释膜的形成，这些自由基是脱重氮反应产生的，随后膜通过偶氮偶联、自由基加成或接枝的苯基层上的阳离子加成生长。然而，这些机制都不符合我们的实验结果，实验结果表明存在 Au-N 键。在这项工作中，我们对金和镍基质上获得的涂层进行了精细的光谱分析，这使我们能够提出这些薄膜的化学结构，特别是它们与基质的界面结构。在测试了最可能的机制后，我们得出结论，支持两种互补机制的参与，即重氮盐与金表面的直接反应，这解释了观察到的 Au-N 界面键，以及能够通过 Au-C 键合接枝到基质上的芳基阳离子的形成。
