Relative stability of thiol and selenol based SAMs on Au(111) — exchange experiments

Abstract

Two fully analogue homologue series of thiol and selenol based aromatic self-assembled monolayers (SAMs) on Au(111) in the form of CH₃–(C₆H₄)₂–(CH₂)_n–S–Au(111) (BPnS/Au(111), n = 2–6) and CH₃–(C₆H₄)₂–(CH₂)_n–Se–Au(111) (BPnSe/Au(111), n = 2–6), respectively, have been used to elucidate the relative stability of the S–Au(111) and Se–Au(111) bonding by monitoring their exchange by alkanethiol and alkaneselenol molecules from their respective solutions. The exchange process was monitored using infrared reflection absorption spectroscopy (IRRAS). Two main results obtained by these study are: (1) the selenium-based BPnSe/Au(111) series is significantly more stable than their sulfur analogues; (2) a clear odd–even effect exists for the stability of both BPnS/Au(111) and BPnSe/Au(111) SAMs towards exchange processes with the even-numbered systems being less stable. The results obtained are discussed in view of previously reported microscopic and spectroscopic data of the same SAMs addressing the issue of the relative stability of S–Au(111) and Se–Au(111) bonding, which is an important factor for the rational design of SAMs.