Electrochemically Polymerized N,N-Dimethylaniline Films Containing Tris-(Bathophenanthroline Disulfonato)Iron(II/III) Complexes

The electropolymerization of N, N-dimethylaniline (DMA) was carried out in an aqueous CF₃COONa solution (pH 1.0) containing DMA in the presence of tris(bathophenanthroline disulfonato)iron(II), Fe(bphen)₃ ^4-. Poly(N, N-dimethylanilinium trifluoroacetate) (PDMA) film was formed on electrode surfaces and, at the same time, Fe(bphen)₃ ^4- ions were stably confined in the formed PDMA film by electrostatic interaction between them and the positively charged quaternary ammonium sites of the PDMA film. The PDMA-Fe(bphen)₃ ^4-/3- film thus prepared displayed well-defined reversible electroactivity and electrochromic properties ascribable to those of the Fe(bphen)₃ ^4-/3- couple confined in the film. The PDMA-Fe(bphen)₃ ^4- film is red, and the PDMA-Fe(bphen)₃ ^3- film is colorless. The response rate of the color change to a potential pulse was found to be correlated with the kinetic parameters characterizing the rate of the overall charge-transfer reaction at the PDMA-Fe(bphen)₃ ^4-/3- film-coated electrode, that is, the apparent diffusion coefficient (D _app) for the homogeneous charge-transport process within the film and the standard rate constant (k) of the heterogeneous electron-transfer reaction at the electrode/film interface. For the PDMA-Fe(bphen)₃ ^4-/3- film with larger k° and D _app values, the response rate of the color change was larger, Further, k°, D _app, and response rate depended on the concentration (C°) of the Fe(bphen)₃ ^4- (or Fe(bphen)₃ ^3-) confined in the PDMA film; and at a given film thickness, the lower C°, the higher were k°, D _app, and response rate. At a given C°, the thinner the film thickness, the greater was the response rate.