Self-Assembled Monolayers on Gold of Thiols Incorporating Conjugated Terminal Groups

Abstract

Thiols 3, 6, and 14 incorporating ω-attached conjugated aromatic groups form self-assembled monolayers (SAMs) on polycrystalline gold. The thicknesses of the films as measured by optical ellipsometry correspond well to the expected thickness of monolayer films in which the components are oriented roughly perpendicular to the Au surface. Cyclic voltammetry measurements of K4Fe(CN)6 in aqueous KCl solution on a SAM modified gold electrode show that these monolayers are densely packed and attenuate electron transfer between the gold and the solution electrophore. Grazing angle reflectance−Fourier transform infrared spectroscopy (GAR−FTIR) shows that the conjugated arenes of 3, 6, and 14, as well as the C6 chains of thiols 6 and 14, are roughly perpendicular to the plane of the Au surface. Fluorescence spectroscopy indicates that the terminal arenes in SAMs of 6 and of 11 interact, causing red-shifted, structured emission in the SAM relative to that observed for the same species in dilute homogeneous solution.