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Infrared Ellipsometric Study of Hydrogen-Bonded Long-Chain Thiolates on Gold: Towards Resolving Structural Details
Institute of Organic Chemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Block 9, Sofia 1113, Bulgaria
Leibniz-Institut für Analytische Wissenschaften–ISAS–e.V, Department Berlin, Albert-Einstein-Str. 9, Berlin 12489, Germany
* Authors to whom correspondence should be addressed.
Received: 29 April 2011; in revised form: 18 June 2011 / Accepted: 19 June 2011 / Published: 22 June 2011
Abstract: A set of newly synthesized aryl-substituted amides of 16-mercaptohexadecanoic acid (R = 4-OH; 3,5-di-OH) are self-assembled on Au(111) substrate. Self assembled monolayers (SAMs) formed by these molecules are studied by ellipsometry from infrared to visible spectral range. Best fit calculations based on the three-phase optical model are employed in order to determine the average tilt angle of the hydrocarbon chains. The data revealed that the SAMs reside in a crystalline-like environment as the long methylene chains predominantly exist in all-trans conformation. The calculated tilt angle of the hydrocarbon chain is decreased by approximately 12° in comparison with the one for the correspondent long-chain n-alkyl thiols. Strong hydrogen bonded networks were detected between the amide proton and the carbonyl oxygen as well as between hydroxyl groups in the end aryl substituents. The transition dipole moments of the C=O, N-H and O-H modes are oriented almost parallel to the gold surface.
Keywords: IR ellipsometry; aryl-substituted long-chain thiols; hydrogen bonds
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Tsankov, D.; Philipova, I.; Kostova, K.; Hinrichs, K. Infrared Ellipsometric Study of Hydrogen-Bonded Long-Chain Thiolates on Gold: Towards Resolving Structural Details. Micromachines 2011, 2, 306-318.
Tsankov D, Philipova I, Kostova K, Hinrichs K. Infrared Ellipsometric Study of Hydrogen-Bonded Long-Chain Thiolates on Gold: Towards Resolving Structural Details. Micromachines. 2011; 2(2):306-318.
Tsankov, Dimiter; Philipova, Irena; Kostova, Kalina; Hinrichs, Karsten. 2011. "Infrared Ellipsometric Study of Hydrogen-Bonded Long-Chain Thiolates on Gold: Towards Resolving Structural Details." Micromachines 2, no. 2: 306-318.