Ionic Self-Assembled Redox-Active Polyelectrolyte−Ferrocenyl Surfactant Complexes:  Mesomorphous Structure and Electrochemical Behavior

Abstract

Redox-active polyelectrolyte−surfactant complexes (PSC) were prepared via the ionic self-assembly of sodium poly(styrenesulfonate) (PSS) and ferrocenyl surfactant, n -alkyl (ferrocenylmethyl)ammonium bromide (Fc n, n = 8, 12, 16, where n is the carbon number of the alkyl chain), in solution. The PSS−Fc n complex exhibited an ordered lamellar mesomorphous structure with the long period of d = 2.49, 2.94, and 3.74 nm for PSS−Fc8, PSS−Fc12, and PSS−Fc16, respectively. With increasing the length of surfactant alkyl chain, the stacking order was improved. Interestingly, in the solid complex, the ferrocenyl moieties formed H-aggregation showing an increase in the π−π* energy transfer of cyclopentadienes in the ferrocene moieties as known from the blue shift in the UV spectrum. These complexes showed higher thermal stability compared with their components due to the ionic interaction. Cyclic voltammogram (CV) measurements indicated that the electrode process of these redox-active complex films was diffusion-controlled and almost reversible or quasi-reversible at scan rates ranging from 0.02 to 4 V/s. Though the reversibility of the electrode process became worse for the PSS−Fc12 and PSS−Fc16 films than that for the PSS−Fc8, the redox peak current | i p | increased with increasing surfactant tail length in the complex because the more ordered packing in the complex film formed by longer surfactant tails was more favorable for the electrolyte diffusion and charge transfer as judged on values of the surface charge-transfer coefficient α n α, standard rate constant K s, and apparent diffusion coefficient D app reflecting the electrode kinetics. The present results demonstrate that the electrochemical activity of the redox-active poly(styrenesulfonate)−ferrocenyl surfactant complex can be easily tuned by changing the surfactant tail length. Our work provides a simple and facile approach to the preparation of redox-active polymers with ordered mesomorphous structure by the ionic self-assembly.