Dresden 2011 – scientific programme

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O: Fachverband Oberflächenphysik

O 75: Metal substrates: Adsorption of organic / bio molecules VIII

O 75.8: Talk

Thursday, March 17, 2011, 16:45–17:00, PHY C213

Electronic Structure of a Spiropyran Derived Molecular Switch in Direct Contact with the Au(111) Surface — •Christopher Bronner, Gunnar Schulze, Katharina J. Franke, José Ignacio Pascual, and Petra Tegeder — Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany

As nanometer scale phenomena advance into the grasp of technological application, the potential building blocks of molecular electronics and sensorics are studied in detail. Surface-bound molecular switches are of particular interest, since the functionality of the substrate/adsorbate system can be switched by an external stimulus.

We present combined two-photon photoemission (2PPE) and scanning tunneling spectroscopy (STS) investigations of a nitro-spiropyran derivative's occupied and unoccupied electronic states at the Au(111) surface in both its open and closed form. Both forms exhibit significant differences in the electronic structure which allows following a potential ring-opening/closure reaction. Resonant electron tunneling from the STM tip into the LUMO of the adsorbate molecule induced ring-opening, while the corresponding photon driven process via transfer of electrons from the substrate to the adsorbate turned out to be inefficient. The loss of the molecule's functionality is attributed to a strong electronic coupling between adsorbate and metallic substrate and accordingly to short lifetimes of molecular excited states.