Publications (2)3.26 Total impact
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Article: Electronic structure of the molecular switch tetra-tert-butyl-azobenzene adsorbed on Ag(111)
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ABSTRACT: Occupied and unoccupied electronic states in tetra-tert-butyl-azobenzene (TBA) absorbed on Ag(111) have been investigated by one-photon and two-photon photoemission spectroscopy. These measurements allow the quantitative determination of energetic positions of the highest occupied (HOMO) and the lowest unoccupied molecular orbital (LUMO) as well as the n=1 image potential state. The assignment of the electronic states are supported by quantum chemical calculations. Experimentally a HOMO–LUMO gap of 2.85eV is observed, whereas the gap obtained from the calculated molecular orbital energies is 0.92eV larger. This discrepancy can be explained by image charge screening. Furthermore, two unoccupied final states located 0.18 and 0.43eV above the vacuum level, respectively, have been identified.Applied Physics A 04/2012; 88(3):465-472. · 1.63 Impact Factor -
Article: Kinetic analysis of the photochemically and thermally induced isomerization of an azobenzene derivative on Au (111) probed by two-photon photoemission
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ABSTRACT: Two-photon photoemission (2PPE) spectroscopy is employed to quantify the photochemically and thermally induced trans cis isomerization of the molecular switch tetra-tert-butyl-azobenzene (TBA) adsorbed on an Au(111) surface. The isomerization of TBA is accompanied by sig-nificant changes in the electronic structure, namely differ-ent energetic positions of the lowest unoccupied molecu-lar orbital of both isomers and the appearance of an unoc-cupied final state for cis-TBA. A quantitative analysis of these effects allows the calculation of cross sections for the reversible isomerization and determination of the ratio between both isomers in the photostationary state, where 55 ± 5% of the molecules are switched to cis-TBA. The cross section for the photoinduced trans → cis isomeriza-tion is 3.3 ± 0.5 × 10 −22 cm 2 , while for the back reaction, a value of 2.7 ± 0.5 × 10 −22 cm 2 is obtained. Furthermore a pronounced reduction of the activation energy by a factor of four compared to the free molecule is found for the ther-mally activated cis → trans isomerization of the surface-adsorbed TBA. This demonstrates that the potential energy landscape of the adsorbed TBA is remarkably different from the liquid phase.Applied Physics A 01/2008; 9320:253-260. · 1.63 Impact Factor
