Reversible changes in the vibrational structure of tetra-tert-butylazobenzene on a Au(111) surface induced by light and thermal activation

High-resolution electron energy loss spectroscopy (HREELS) is employed to analyze reversible changes in the geometrical structure of the molecular switch tetra-tert-butylazobenzene (TBA) adsorbed on Au(111), which are induced by UV-light and thermal activation. In the submonolayer regime, TBA adsorbs in the planar trans configuration. UV-light exposure at 3.5 eV leads to pronounced changes in the vibrational structure of the TBA molecules in direct contact with the Au(111) surface, which we assign to a trans to cis isomerization. The-reverse process, that is, the cis to trans isomerization, can be stimulated by thermal activation. An intensity decrease of vibrational modes as a function of photon dose allows calculation of an effective cross section of sigma(eff) approximate to 2 x 10(-21) cm(2) for the trans to cis isomerization.