Assembly of electroactive ordered multilayer films of cobalt phthalocyanine tetrasulfonate and polycations

Films with alternating layers of the anion cobalt phthalocyanine tetrasulfonate ((CoPcTS4-)-Pc-II) 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 (CoPcTS4-)-Pc-II/PDDA on a gold electrode gave reversible, reproducible steady state cyclic voltammetry for the Co-II/Co-I 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/(CoPcTS4-)-Pc-II. The peak reduction current increased with the number of layers and showed a tendency to saturation after a deposition of 4-5 bilayers, (C) 1999 Academic Press.