Regensburg 2007 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 16: Organic, Polymeric, and Biomolecular Films I
O 16.8: Vortrag
Montag, 26. März 2007, 16:00–16:15, H42
A photooptical switch - azobenzene carrying alkanethiols on gold — Daniel Brete1,2, Wolfgang Freyer1, Cornelius Gahl1, Sanja Korica1,2, •Roland Schmidt1,2, and Martin Weinelt1,2 — 1Max-Born-Institut, Max-Born-Str. 2A, 12489 Berlin — 2Freie Univerität Berlin, Fachberecih Physik, Arnimallee 14, 14195 Berlin
The photoisomeric switch azobenzene can be linked to gold surfaces by alkanethiols forming self-assembled monolayers (SAMs, Au-S-(CH2)n-O-C6H4-N-N-C6H5). Sufficient decoupling of the azobenzene group from the surface is thereby necessary to maintain its ability to photo-isomerize. Using the core-hole-clock technique and Resonant-Raman-Auger Spectroscopy we prove that the decay of the N1s-LUMO excitation is independent of chain lengths down to n=3. The resonance lifetime of ≥ 20 fs falls in the timescale of trans-cis conformational photo-isomerization. Functionalizing the azobenzene entity with an electronegative CF3 endgroup leads to a shift of the HOMO and HOMO-1 orbitals and modifies the oscillator strength of the corresponding transitions. This may be relevant for the switching process. All SAMs are well oriented with the azobenzene entity adopting the trans-isomerization. Admixture of alkanes to the layer does not affect the molecular orientation. NEXAFS spectra show clear indication for optical switching of the molecules upon optical excitation at 350 nm.