Controlled release of dyes from chemically polymerised conducting polymers

The hydroxytriarylmethane family of dyes (sub-category sulfonphthaleins, e.g. phenol red) has shown sufficient chemical stability to remain unchanged when exposed to the oxidative environment required for chemical polymerisation of inherently conducting polymers (ICPs). This oxidative stability allows these dyes to be incorporated as counter-ions in polypyrrole or poly(3,4-ethylenedioxythiophene), and then later released when the ICP is reduced, either by change in potential or change in pH. The polypyrrole-dye composite can be applied to paper or plastic films by inkjet printing a dye-oxidant mixture which is then dried and used as a template for vapour phase polymerisation. For poly(3,4-ethylenedioxythiophene)-dye composites, polymerisation can be conveniently conducted in a single step in the liquid phase, using a volatile organic base as a retardant during application.