Regensburg 2016 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 5: Dynamics of Molecules on Surfaces

O 5.4: Vortrag

Montag, 7. März 2016, 11:15–11:30, S053

Direct Observation of Photo-Induced Tautomerization in Single Porphycene Molecules at a Metal Surface — •Hannes Böckmann¹, Shuyi Liu¹, Johannes Mielke¹, Sylvester Gawinkowski³, Jacek Waluk^3,4, Leonhard Grill^1,2, Martin Wolf¹, and Takashi Kumagai¹ — ¹FHI of the MPG, Berlin, Germany — ²University of Graz, Graz, Austria — ³Polish Academy of Sciences, Warsaw, Poland — ⁴Cardinal Stefan Wyszyński University, Warsaw, Poland

Molecular switches are of fundamental importance in nature, and photoexcitation is an important stimulus to selectively drive the switching process. However, the local dynamics of these molecules remain far from being completely understood at the single-molecule level. Here we report the direct observation of photo-induced tautomerization in single porphycene molecules on a Cu(111) surface using a combination of LT STM and laser excitation in the near-IR to UV regime. It is found that the thermodynamically stable trans porphycene is converted to the metastable cis form in a unidirectional fashion by photoirradiation. The wavelength dependence of the tautomerization cross section exhibits a steep onset around 2 eV that corresponds to the energy of the d-band edge of the Cu substrate, indicating a surface mediated excitation mechanism. Additionally, a giant isotope effect (about 100) is observed upon substitution with deuterium. Furthermore, we examined the influence of the local environment on the tautomerization by varying the intermolecular interactions via the molecular density and found a decrease in the cross section at high coverage.