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O: Fachverband Oberflächenphysik
O 29: Organic/bio Molecules on Metal Surfaces III
O 29.6: Vortrag
Dienstag, 12. März 2013, 11:45–12:00, H38
Photo-switching of diluted azobenzene-based SAMs on Au(111) — •Thomas Moldt1, Daniel Brete1, Daniel Przyrembel1, Joel R. Goldman2, Rafal Klajn2, Cornelius Gahl1, and Martin Weinelt1 — 1Freie Universität Berlin, Department of Physics, Arnimallee 14, 14195 Berlin — 2Weizmann Institute of Science, Department of Organic Chemistry, 76100 Rehovot, Israel
Photoisomerization of azobenzene within densely packed self-assembled monolayers (SAMs) of azobenzene-terminated alkanethiols is strongly suppressed.[1,2]. This is attributed to steric hindering [2] and/or excitonic coupling [3] among the chromophores. In this work we examine SAMs of 11-[(4-phenylazo)phenoxy]-undecane-1-thiol diluted with dodecane-1-thiol prepared by co-adsorption from solution. By differential reflectance spectroscopy (DRS) we demonstrate that the molecules self-assemble at the Au(111) surface whereby the azobenzene concentration is adjustable through the relative concentrations in solution. The azobenzene chromophores form aggregates with the excitonic shift of the S2 absorption band decreasing with dilution. In addition near-edge X-ray absorption fine structure spectroscopy (NEXAFS) reveals changes of the orientation of the azobenzene photoswitch in the pure and mixed SAMs. In contrast to the pure azobenzene SAM, the mixed SAMs can be optically switched with high quantum efficiency.
[1] Evans et al., Langmuir, 1998, 14, 6436-6440
[2] Wang et al., J. Electroanal. Chem., 1997, 438, 213-219
[3] Gahl et al., J. Am. Chem. Soc., 2010, 132, 1831-1838