High resolution electron energy loss spectroscopy is employed to analyze the adsorption geometry and the photoisomerization ability of the molecular switch carboxy-benzylideneaniline (CBA) adsorbed on Au(111). CBA adopts on the Au(111) surface a planar (trans) configuration in the first monolayer (ML) as well as for higher coverages (up to 6 ML), contrary to the geometry in solution, which is strongly non-planar. Illumination with UV light of CBA in direct contact with the Au(111) surface (≤ 1 ML) caused no changes in the vibrational structure, whereas at higher coverages ( > 1 ML) pronounced modifications of vibrational features are observed, which we assign to a trans → cis isomerization. Thermal activation induced the back reaction to trans-CBA. We propose that the photoisomerization is driven by a direct (intramolecular) electronic excitation of the adsorbed CBA molecules in the second ML (and above) analogous to CBA in the liquid phase.
The original publication is available at J. Chem. Phys. by link DOI: 10.1063/1.3460647