Polyelectrolyte multilayers prepared from water-soluble poly(alkoxythiophene) derivatives

Electronically conducting polyanion and polycation based on poly(alkoxythio phene) derivatives, poly-3-(3'-thienyloxy)propanesulfonate (P3TOPS) and pol y-3-(3'-thienyloxy)propyltriethylammonium (P3TOPA) have been synthesized. B oth polymers are water-soluble and exhibit high conjugation length in solut ion and in the solid state. These polyelectrolytes were used to prepare con ducting and electroactive polyelectrolyte multilayers by the sequential lay er-by-layer adsorption technique. In aqueous solutions multilayers of P3TOP S with inactive polyelectrolytes (e.g., poly(diallyldimethylammonium chlori de), PDADMA) displayed electrochemical and optical behavior similar to poly thiophene films prepared in organic media. Their in-plane conductivity was low (ca. 1.6 x 10(-5) S cm(-1)). The conductivity could, however, be increa sed by a factor of ca. 40 in "all-thiophene" films, in which P3TOPA was sub stituted for the inactive polycation (PDADMA). The interpenetration of laye rs is of prime importance in films containing conducting components. The in terpenetration of P3TOPS was studied by measuring the charge-transfer rate across an insulating polyelectrolyte multilayer between the substrate and t he P3TOPS layer with modulated electroreflectance. The extent of interpenet ration was 8-9 polyelectrolyte layers, the length scale (7-15 nm) depending on the nature of the insulating layer and, especially, on the ionic streng th of the solution used for the adsorption of P3TOPS.