The cis-trans isomerization of azobenzene has many uses in materials technologies. Among forecasted applications are molecular switches for nanoscale devices. Chemisorbed and physisorbed azobenzenes can switch between their two isomers, with different charge-conduction properties. Here, we examine the switching behavior of N-(2-mercaptoethyl)-4-phenylazobenzamide, chemisorbed on Au (111) in an upright conformation. We considered the effects of electric fields and charging processes on the isomerization process. Cationic and anionic isomerization mechanisms presented lower barriers than neutral ground state isomerization. This effect was moderated on metallic substrates, due to charge delocalization into the surface. The relationships between observed barriers and frontier orbitals are also discussed. (C) 2011 Elsevier B.V. All rights reserved.