Electrochemical characterization in monolayer assemblies formed by covalent linkage of synthesized 1,1'-[1,4-phenylenebis(methylene)]bis(2-carboxyethyl)-4,4'-bipyridium (PBB) to cystamine, chemisorbed onto gold electrodes, were examined. The surface coverage of PBB corresponded to r = 2.4 x 10(-10) mol cm(-2). The equilibrium binding constants of charge-transfer complexes formed by the receptor, resulting in a redox-active monolayer surface with five aromatic compounds (tiron, hydroquinone sulfonic acid, and three kinds of ferrocene derivative) and sodium hexachloroiridate (III), were measured in aqueous media using the differential pulse voltammetric method. The values obtained from tiron were K-o = 330 000 M-1 of PBB4+-modified electrode and K-gamma= 4200 M-1 of PBB2+-modified electrode. Furthermore K-o values of the three kinds of ferrocene derivative were increased in order of negative charge number. The coulomb force between host and guest was influenced by host-guest interaction. On the other hand, the value obtained from monocationic (ferrocenylmethyl) trimethylammonium ion repulsed positively charged PBB-modifed electrode was K-r/K-o = 0.019. The reduction of tetracationic PBB to dicationic one decreased the pi -acceptor character of the receptor PBB-modified electrode.