Assembly of Electroactive Ordered Multilayer Films of Cobalt Phthalocyanine Tetrasulfonate and Polycations

Films with alternating layers of the anion cobalt phthalocyanine tetrasulfonate (CoIIPcTS4-) and cationic polydimethyldiallylammonium chloride (PDDA) were prepared by electrostatic layer-by-layer adsorption. Quartz crystal microbalance and optical studies demonstrated formation of smooth ultrathin films with a linear increase in thickness with the number of deposition steps. Films containing 1, 2, 3, 4, and 5 bilayers of CoIIPcTS4-/PDDA on a gold electrode gave reversible, reproducible steady state cyclic voltammetry for the CoII/CoI redox couple with midpoint potential at -0.28 V vs a saturated calomel reference electrode. Voltammetry was controlled predominantly by charge transport processes in the film, even for films containing only a bilayer of PDDA/CoIIPcTS4-. The peak reduction current increased with the number of layers and showed a tendency to saturation after a deposition of 4-5 bilayers. Copyright 1999 Academic Press.