In situ conductivity of poly-(3-methylthiophene) and (3-methylthiophene) x-[Ru(2,2'-bipyridine) 2(3-{pyrrol-1-ylmethyl}pyridine) 2] 2+

Abstract

The in situ electronic conductivities of poly(3-methylthiophene) and (3-methylthiophene) x-[Ru(bp) 2 (pmp) 2](ClO 4) 2 copolymers (bp = 2,2'-bipyridine, pmp = 3-(pyrrol-1-ylmethyl)pyridine) have been investigated by dual (sandwich) electrode voltammetry and rotating disc voltammetry. The experimental data have been treated using an ohmic conductivity model which takes into account the variation in conductivity across the film. The conductivity of the methylthiophene homopolymer increases exponentially with a slope of 96 mV/decade from ca. 10 −8 Ω −1 cm −1 at 0 V vs. SSCE to ca. 1 Ω −1 cm −1 at +0.8 V. Significant hysteresis is observed in the conductivity vs potential data; the conductivity of the polymer is generally higher during reduction than during oxidation at the same potential. Copolymerization of the Ru complex with 3-methylthiophene results in films with a much lower conductivity at all potentials. In terms of an electron hopping model the Ru sites lead to a substantial decrease in the electron hopping rate between oxidized poly(3-methylthiophene) sites. The maximum conductivity of the copolymer films decreases exponentially with increasing Ru concentration as predicted by such a model. A secondary effect of the Ru sites is to increase the average redox potential of the poly(3-methylthiophene) so that higher potentials are required to produce charge carriers (oxidized sites).