Dresden 2006 – wissenschaftliches Programm
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O: Oberflächenphysik
O 14: Poster session I (Adsorption, Epitaxy and growth, Phase transitions, Surface reactions, Organic films, Electronic structure, Methods) (sponsored by Omicron Nanotechnology GmbH)
O 14.50: Poster
Montag, 27. März 2006, 18:00–21:00, P2
Azobenzene containing ligands for photoresponsive self-assembled monolayers on gold — •M. Trojtza1, B. Krohn1, T. Weidner1, M. Meier2, F. Bretthauer2, D. Enders3, U. Siemeling2, and F. Träger1 — 1Institut für Physik, Universität Kassel, Kassel — 2Institut für Chemie, Universität Kassel, Kassel — 3Kirchhoff Institut für Physik, Universität Heidelberg, Heidelberg
The new azobenzene-derivatized 1,2-dithiolanes (1) (a five membered ring with two sulfur and three carbon atoms) was synthesised and used for the preparation of self-assembled monolayers (SAM) on gold. Azobenzene derivatives can be switched between their "cis" and "trans" isomers by irradiation with light and represent the most widely studied building blocks for photoresponsive SAMs. However, in SAMs based on thiols and disulfides on gold, the chromophores are densely packed and show little free volume to allow photoisomerisation. The binding unit of 1 with its two attachment points and increased size should lead to considerable void space between the individual "azo" units which protrude from the surface. Photoswitching was confirmed by IR-spectroscopy. The results were compared to azobenzene containing disulfides (2), which showed no evidence for photoresponsive behaviour. In addition, the kinetics of film formation of 1 and 2 have been compared by in situ optical second harmonic generation. The adsorption of 1 is best described by first order Langmuir kinetics at an adsorption rate of 2.2· 10−4 s−1. For 2 the data reveal second order Langmuir kinetics at a rate of 9.0· 10−3 s−1. Film thickness of (11± 1) Å for 1 and (12± 1) Å for 2 were obtained from spectroscopic ellipsometry in accord with monolayer formation.