Electropolymerisation dynamics of a highly conducting metallopolymer: poly-[Os(4 ′-(5-(2,2 ′-bithienyl))-2,2 ′:6 ′,2 ″-terpyridine) 2] 2+

Abstract

The potential, time, and concentration dependence of the potentiostatic electropolymerisation of the thienyl-substituted transition metal complex [Os(bttpy) 2 2+] onto platinum disk microelectrodes is reported, bttpy is 4 ′-(5-(2,2 ′-bithienyl))-2,2 ′:6 ′,2 ″-terpyridine. Oxidative electropolymerisation of the thienyl bridges is highly efficient with an electropolymerisation efficiency of 36 ± 3% being observed across a wide range of potentials and monomer concentrations. The osmium centres are oxidised when polymerisation proceeds and the deposited polymer is highly conducting allowing high surface coverage films, up to 6 × 10 −7 mol cm −2, to be deposited within 60 s. SEM imaging reveals that smooth films can be produced using moderate overpotentials for electrodeposition. Significantly, diffusional mass transport controls the rate of film deposition allowing the radial diffusion field found at microelectrodes to be exploited to favour film growth co-planar with the electrode surface. The electropolymerisation rate increases approximately linearly with increasing monomer concentration from approximately 8 to 400 μM and this first-order dependence likely arises from mass transport limitations. The rate of homogeneous charge transport through potentiostatically deposited films, characterised by D 1/2 C, where D is the apparent charge transport diffusion coefficient and C is the concentration of osmium centres, is 3.5 ± 0.5 × 10 −7 mol cm −2 s −1/2 and is largely insensitive to the deposition potential, and is very similar to that previously observed for potentiodynamically deposited films. This charge transport parameter is approximately two orders of magnitude larger than those found for non-conjugated bridges and is interpreted in terms of resonant superexchange across the quaterthienyl bridge.