Irreversible isomerization of the azobenzene derivate Methyl Orange on Au(1 1 1)

Isolated molecules of 4-dimethylaminoazobenzene-4-sulfonic acid, an azobenzene derivate called Methyl Orange, are adsorbed on the Au(1 1 1) surface at 18 K and investigated with scanning tunneling microscopy at 5 K. Methyl Orange adsorbs in both trans- and cis-configuration on the substrate. The cis-configuration largely dominates in contrast to the gas phase where the trans-configuration is energetically preferred. Electron-induced manipulation with electron energies of 900 meV allows to switch the trans- into the cis-configuration while the inverse process is not possible below the fragmentation of the molecule at electron energies of 1000 meV.