M-TBA (4-methoxy-3,30,5,50-tetra-tert-butylazobenzene) adsorbed on a gold (111) surface was found to form four different polymorphs, two of which isomerizable at −1.7 V, but with a low propensity for further isomerisation of nearby molecules (C. Dri, M. V. Peters, J. Schwarz, S. Hecht, L. Grill, Nat. Nanotechnol., 2008, 3, 649–653). Atomistic simulations investigate the origin of the effects.