Multiple Adsorption of Polythiophene Layers on ITO/Glass Electrodes and Their Optical, Electrochemical, and Conductive Properties

Polyelectrolyte multilayers containing electrochemically active polythiophenes have been constructed on ITO/glass substrates using the layer-by-layer adsorption deposition technique. Electrochemically active layers of poly(cyclopentadithiophene sulfonate), poly(cyclopentadithiophene trimethylammonium) and a,w-bis(carboxyhexyl)sexithiophene were deposited with non-electroactive layers of polyallylamine and polystyrenesulfonate. The first sequential adsorption of multilayers in which both the polycation and the polyanion are based on the same polythiophene is reported. Uv-vis spectroscopy and cyclic voltammetry indicate a linear dependence of the amount of deposited polymer on the number of deposition cycles. The rate of deposition depends on the oxidation state of the polythiophene being 3 times lower for the oxidized polycationic polymer. Atomic force microscopy characterization of the layers has shown that flat monolayers are deposited with a progressive increase of roughness. Interposition of multiple non-electroactive layers between the electrode and a single external electroactive polythiophene layer has allowed to determine by cyclic voltammetry that each polythiophene layer interpenetrates the confining layers up to a three-layer distance. The conductivities of the multilayers along the surface and perpendicular to it are anisotropic depending on the layer alternation. The photoluminescence properties of the a,w-bis(carboxyhexyl)sexithiophene multilayers are the same for vacuum-deposited polycrystalline layers.