The substituent effect on the adsorption behaviors of four halogen/pseudohalogen-terminated biphenyls (X-BP-X, with X = F, Br, land CN) on a Au(111) surface in 0.1 M HClO4 solution has been investigated by electrochemical scanning tunneling microscopy (ECSTM) and cyclic voltammetry (CV). All the four molecules could form ordered adlayers at adsorption potentials. From F-BP-F, Br-BP-Br to I-BP-I, the molecular adsorption configuration varies from upright, alternating upright and flat-lying to totally flat-lying. In contrast, a trimer motif connected via CN-Au coordination interaction is found as the building unit for the adlayer of CN-BP-CN on Au(111) electrode. The adlayer structures and configurations are regulated by the properties of the substituted groups. (C) 2012 Elsevier B.V. All rights reserved.