Electrostatically Self-assembled Multilayers of Novel Symmetrical Rigid-Rod Polyanionic and Polycationic Polythiophenes on ITO/Glass and Gold Electrodes

Anodic coupling of 4,4-bis-butanesulfonate cyclopentadithiophene occurs in acetonitrile after the addition of 1:1 HClO 4 to yield water-soluble polyanionic poly(1). 4,4-Bis-hexyltrimethylammonium cyclopentadithiophene is polymerized in acetonitrile to acetonitrile-soluble polycationic poly(2) which is converted to the water-soluble hydroxide form by anion exchange. These novel water-soluble polythiophenes, characterized by a rigid-rod symmetrical shape of the chain, display a high conjugation length (λ max = 560−575 nm) and a good solubility in water (>10 gL - 1 ). MALDI and UV−vis spectroscopy assign these polymers a degree of polymerization of 5−6. The polymers form stable monolayers (storing a redox charge of 10 μC cm - 2 ) on ITO/glass and gold electrodes. Subsequent electrostatic self-assembly (ESA) of poly(1) and poly(2), both between them and each with a non-electroactive polycation or polyanion, proceeds with a linear growth rate monitored by cyclic voltammetry (10 μC cm - 2 bilayer - 1 ) and UV−vis spectroscopy. No effect of ionic strength was observed in contrast with ESA of conventional polyionic polymers. IRRAS and XRD analysis of the multilayers agree with a regular disposition of the polythiophene chains in the layers.