Genorio Bostjan, He Tao, Meden Anton, Polanc Slovenko, Jamnik Janko, Tour James M
Department of Chemistry, Smalley Institute for Nanoscale Science and Technology, Rice University, MS-222, 6100 Main Street, Houston, Texas 77005, USA.
Langmuir. 2008 Oct 21;24(20):11523-32. doi: 10.1021/la802197u. Epub 2008 Sep 24.
Self-assembled monolayers (SAMs) provide a simple route to functionalize electrode surfaces with organic molecules. Herein we use cavity-containing derivatives of calix[4]arenes in SAMs. Bound to noble metal surface, the assembled molecules are candidates to serve as molecular sieves for H 2 molecules and H (+) ions, which could have relevance for fuel cell applications. Tetra- O-alkylated calix[4]arenes with thiolacetate and thiolamide wide-rim anchoring groups in cone and partial-cone conformations were designed, synthesized and self-assembled onto Au, Pt, and Pd surfaces. The resulting SAMs were systematically examined. Single crystal X-ray diffraction of 5,11,17,23-tetrakis(thioacetyl)-25,26,27,28-tetra- i-propoxycalix[4]arene confirmed the cone conformation and revealed the cavity dimensions of the SAMs that were formed by immersing noble metal substrates (Au, Pt and Pd deposited on Si-wafers) in solutions of calix[4]arenes. Surface characterization techniques including ellipsometry, cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) were used, indicating that the metal surface is terminated with a monomolecular layer. Experimental thicknesses obtained from the ellipsometry are consistent with the calculated values. CV results showed 50 to 80% physical passivation against the Fe(CN) 6 (3-/4-) couple, implying an overall relatively low concentration of defects and pinholes in the films. The binding energies of the S2p core level in the XPS were consistent with the literature values and revealed that up to 3.2 out of four anchoring groups were bonded to the noble metal surface.
自组装单分子层（SAMs）为利用有机分子对电极表面进行功能化提供了一条简单途径。在此，我们在SAMs中使用了含杯[4]芳烃的含腔衍生物。结合到贵金属表面后，组装的分子有望用作H₂分子和H⁺离子的分子筛，这可能与燃料电池应用相关。设计、合成了具有硫代乙酸酯和硫代酰胺宽边锚定基团且呈锥式和部分锥式构象的四-O-烷基化杯[4]芳烃，并将其自组装到金、铂和钯表面。对所得的SAMs进行了系统研究。5,11,17,23-四（硫代乙酰基）-25,26,27,28-四-i-丙氧基杯[4]芳烃的单晶X射线衍射证实了锥式构象，并揭示了通过将贵金属基底（沉积在硅片上的金、铂和钯）浸入杯[4]芳烃溶液中形成的SAMs的腔尺寸。使用了包括椭偏仪、循环伏安法（CV）和X射线光电子能谱（XPS）在内的表面表征技术，表明金属表面以单分子层终止。由椭偏仪获得的实验厚度与计算值一致。CV结果表明，对Fe(CN)₆(³⁻/⁴⁻)电对有50%至80%的物理钝化，这意味着薄膜中缺陷和针孔的总体浓度相对较低。XPS中S2p核心能级的结合能与文献值一致，表明四个锚定基团中多达3.2个与贵金属表面键合。
