Ordered self-assembled monolayers of 4,4′-biphenyldithiol on polycrystalline silver: Suppression of multilayer formation by addition of tri-n-butylphosphine

Ulrike Weckenmann, Silvia Mittler, Kai Naumann, Roland A. Fischer

Research output: Contribution to journalArticlepeer-review

52 Scopus citations

Abstract

Self-assembled monolayers (SAMs) of 4-biphenylthiol (BT) and 4,4′-biphenyldithiol (BDT) formed on polycrystalline silver substrates were characterized by surface plasmon resonance spectroscopy (SPR), reflection absorption infrared spectroscopy (RAIRS), and X-ray photoelectron spectroscopy (XPS). The RAIRS measurements reveal that the molecules in a BT-SAM are oriented perpendicular to the surface whereas the adsorption of BDT results in the formation of multilayers due to the oxidative coupling of the terminal thiol groups forming disulfide-bridged species. The process of multilayer formation was monitored by SPR and RAIRS indicating that BDT initially forms a monolayer which exhibits a structure similar to the one found for BT and that disorder is introduced by the rapid oxidation of the exposed thiol groups resulting in the formation of a multitayer. The addition of tri-n-butylphosphine to the self-assembly solution of 4,4′-biphenyldithiol prevents the formation of multilayers and allows the generation of well-ordered monolayers of the dithiol in which the molecules adopt a standing-up orientation as observed for 4-biphenylthiol. The existence of free thiol groups at the surface of the dithiol SAM was proven by quantitative XPS measurements.

Original languageEnglish
Pages (from-to)5479-5486
Number of pages8
JournalLangmuir
Volume18
Issue number14
DOIs
StatePublished - 9 Jul 2002
Externally publishedYes

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