DPG Phi
Verhandlungen
Verhandlungen
DPG

Berlin 2008 – scientific programme

Parts | Days | Selection | Search | Downloads | Help

O: Fachverband Oberflächenphysik

O 34: Metal Substrates: Adsorption of Organic/Bio Molecules II

O 34.6: Talk

Tuesday, February 26, 2008, 15:00–15:15, MA 043

Why a ’decoupled’ switch doesn’t switch. Self-assembled monolayers of Azobenzenethiol on gold — •Roland Schmidt1, Daniel Brete1,2, Wolfgang Freyer1, Cornelius Gahl1, and Martin Weinelt1,21Max-Born-Institut, Max-Born-Straße 2A, 12489 Berlin — 2FU-Berlin, Arnimallee 14, 14195 Berlin

We have investigated well oriented, self-assembled monolayers of alkanethiols on gold, functionalized by the molecular switch azobenzene (HS−(CH2)nOC6H4−N2C6H4CF3, n=3,6,10). Using X-ray absorption spectroscopy the tilt angle between the backbone of the azobenzene group and the surface normal was shown to be ∼ 15, with only slight dependence on the length of the alkane chain n. The evaluation of autoionization spectra of the N1s−1π∗ +1 state in terms of the core-hole-clock approach gave a charge-transfer time τCT of the LUMO of several 10 fs. Also τCT showed no significant dependence on the length of the alkane chain n. Hence the switches are significantly decoupled from the substrate. However, a strong quenching of the SAM’s π−π-excitation is observed in UV-Vis spectroscopy, pointing out that lateral interactions among the azobenzene chromophores in the crystal-like layer dominate both the charge transfer and the geometrical structur of the SAM. This is supported by the energy dependence of τCT that is atypical for tunnelling into the substrate. We suppose that the ultrafast delocalization of the S2 excitation causes the observed inefficiency of photochemical switching of alkanethiol based SAMs.

100% | Mobile Layout | Deutsche Version | Contact/Imprint/Privacy
DPG-Physik > DPG-Verhandlungen > 2008 > Berlin