Electrochemically Assisted Sol−Gel Process for the Synthesis of Polysiloxane Films Incorporating Phenothiazine Dyes Analogous to Methylene Blue. Structure and Ion-Transport Properties of the Films via Spectroscopic and Electrochemical Characterization

Abstract

A sol−gel process is directed toward an electrode surface via electrochemical manipulation of the solubility of trimethoxysilyl group-modified methylene blue in an aqueous environment. The process lasts for 2−3 h and results in electrode derivatization with a polysiloxane network incorporating methylene blue. Cross-linking (curing) is completed by drying the films at room temperature for 2 days. The concentration of the phenothiazine moieties in the resulting xero films was calculated at ∼3.9 M, and the film density at ∼2.6 g/cm3. The average distance between phenothiazine moieties is <5 Å allowing interactions between their π-systems. The narrow pores between monomer units restrict movement of hydrated charge-compensating ions, so that the redox switching of the films depends upon the chemical identity of both the cation and anion of the supporting electrolyte. The films retain the electrochromic and electrocatalytic properties of the parent dye; for example, gold electrodes derivatized with the film mediate reduction of cytochrome c at potentials close to its standard electrochemical potential.