Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 44: Poster Session II (Semiconductors; Oxides and Insulators: Adsorption, Clean Surfaces, Epitaxy and Growth; Surface Chemical Reactions and Heterogeneous Catalysis; Surface or Interface Magnetism; Solid-Liquid Interfaces; Organic, Polymeric, Biomolecular Films; Particles and Clusters; Methods: Atomic and Electronic Structure; Time-resolved Spectroscopies)
O 44.25: Poster
Mittwoch, 28. März 2007, 17:00–19:30, Poster C
Geometric and electronic structure of azobenze - alkanethiols on gold — •Daniel Brete1,2, Roland Schmidt1,2, Sanja Korika1, Cornelius Gahl1, and Martin Weinelt1,2 — 1Max-Born-Institut, Max-Born-Str. 2A, 12489 Berlin — 2Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin
Azobenzene is a conformational photo-switch. Upon optical excitation at 350 nm and 430 nm geometric changes of the chromophore occur on a sub-picosecond to picosecond timescale. This ultrafast dynamics suggests that switching may even occur when azobenzene is bound to a surface, where charge transfer into the substrate efficiently quenches electronic excitations. Associated with the geometric change of the azobenzene molecule from trans to cis conformation is a shift of the optical π to π∗ transition.
We have investigated self-assembled monolayer of azobenzene - alkanethiols adsorbed on gold and their potential as a molecular switch by X-ray absorption as well as by X-ray and VUV photoemission spectroscopy. The molecules are well oriented at 100 K and the azobenzene entity is sufficiently decoupled from the substrate by the alkane chain. The occupied frontier orbitals of non-bonding n and of π character are identified by angle-resolved photoemission and autoionization spectroscopy at the N1s and C1s absorption edges. Their energetics and oscillator strengths are substantially modified by substituants attached to the azobenzene entity. Resultant implications for the switching efficiency will be discussed.