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Vibrational Stark Effect of the Electric-Field Reporter 4-Mercaptobenzonitrile as a Tool for Investigating Electrostatics at Electrode/SAM/Solution Interfaces
Technische Universität Berlin, Insitut für Chemie, Sekr. PC14, Straße des 17, Juni 135, Berlin, D-10623, Germany
Biomolecular Spectroscopy, LaserLaB Amsterdam, Vrije Universiteit Amsterdam, De Boelelaan 1083, Amsterdam, NL-1081 HV, The Netherlands
Department of Chemistry, North Carolina State University, Box 8204, Raleigh, NC 27695, USA
* Author to whom correspondence should be addressed.
Received: 9 May 2012; in revised form: 6 June 2012 / Accepted: 11 June 2012 / Published: 18 June 2012
Abstract: 4-mercaptobenzonitrile (MBN) in self-assembled monolayers (SAMs) on Au and Ag electrodes was studied by surface enhanced infrared absorption and Raman spectroscopy, to correlate the nitrile stretching frequency with the local electric field exploiting the vibrational Stark effect (VSE). Using MBN SAMs in different metal/SAM interfaces, we sorted out the main factors controlling the nitrile stretching frequency, which comprise, in addition to external electric fields, the metal-MBN bond, the surface potential, and hydrogen bond interactions. On the basis of the linear relationships between the nitrile stretching and the electrode potential, an electrostatic description of the interfacial potential distribution is presented that allows for determining the electric field strengths on the SAM surface, as well as the effective potential of zero-charge of the SAM-coated metal. Comparing this latter quantity with calculated values derived from literature data, we note a very good agreement for Au/MBN but distinct deviations for Ag/MBN which may reflect either the approximations and simplifications of the model or the uncertainty in reported structural parameters for Ag/MBN. The present electrostatic model consistently explains the electric field strengths for MBN SAMs on Ag and Au as well as for thiophenol and mercaptohexanoic acid SAMs with MBN incorporated as a VSE reporter.
Keywords: interfaces; self-assembled monolayer; electrode; vibrational Stark effect; surface enhanced Raman; surface enhanced infrared; potential of zero-charge
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Schkolnik, G.; Salewski, J.; Millo, D.; Zebger, I.; Franzen, S.; Hildebrandt, P. Vibrational Stark Effect of the Electric-Field Reporter 4-Mercaptobenzonitrile as a Tool for Investigating Electrostatics at Electrode/SAM/Solution Interfaces. Int. J. Mol. Sci. 2012, 13, 7466-7482.
Schkolnik G, Salewski J, Millo D, Zebger I, Franzen S, Hildebrandt P. Vibrational Stark Effect of the Electric-Field Reporter 4-Mercaptobenzonitrile as a Tool for Investigating Electrostatics at Electrode/SAM/Solution Interfaces. International Journal of Molecular Sciences. 2012; 13(6):7466-7482.
Schkolnik, Gal; Salewski, Johannes; Millo, Diego; Zebger, Ingo; Franzen, Stefan; Hildebrandt, Peter. 2012. "Vibrational Stark Effect of the Electric-Field Reporter 4-Mercaptobenzonitrile as a Tool for Investigating Electrostatics at Electrode/SAM/Solution Interfaces." Int. J. Mol. Sci. 13, no. 6: 7466-7482.