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

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Mittler,  Silvia
MPI for Polymer Research, Max Planck Society;

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Weckenmann, U., Mittler, S., Naumann, K., & Fischer, R. A. (2002). Ordered self-assembled monolayers of 4,4 '-biphenyldithiol on polycrystalline silver: Suppression of multilayer formation by addition of tri-n-butylphosphine. Langmuir, 18(14), 5479-5486.


Cite as: http://hdl.handle.net/11858/00-001M-0000-000F-659B-4
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 RAMS 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 multilayer. 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.