X-ray spectroscopic investigations of adsorbed switchable molecules
Prof. Dr. Wolfgang Kuch (Institut für Experimentalphysik, FU Berlin)

Molecules that exist in two metastable states can be envisioned as building blocks for future molecular electronics. Several molecules are known to undergo reversible switching between metastable states in solution or in the gas phase, however, stabilization on a solid surface significantly changes the situation and may sensitively affect the switching.

I will present X-ray spectroscopic investigations of photoswitchable dimetacyano-azobenzene molecules on Bi(111). After illumination with intense X rays tuned to the photon energy of the azo N 1s → LUMO transition, the spectra change significantly, indicating a switching of at least 20% of the molecules from the trans to the cis conformation. The process is reversible, as waiting for 1 h in darkness at 110 K restores the initial spectral properties, indicating a thermally induced back reaction.

Switching the magnetic properties of paramagnetic molecules is a promising route towards molecular spin-electronics. I will show how the magnetic coupling between adsorbed paramagnetic Fe porphyrin molecules and a ferromagnetic substrate can stabilize the magnetic moments of the molecules against thermal fluctuations. The strength and also the sign of the coupling can be controlled by insertion layers like oxygen or graphene, which mediate the coupling between the molecules and the metallic ferromagnetic substrate. The magnetic molecule—substrate interaction can further be switched reversibly by attaching and detaching NO. This constitutes an important step towards the realization of room-temperature surface-mounted molecular spintronic devices.