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

The potential, time, and concn. dependence of the potentiostatic electropolymn. of the thienyl-substituted transition metal complex [Os(bttpy)22+] onto platinum disk microelectrodes is reported, bttpy is 4'-(5-(2,2'-bithienyl))-2,2':6',2''-terpyridine. Oxidative electropolymn. of the thienyl bridges is highly efficient with an electropolymn. efficiency of 36 ± 3% being obsd. across a wide range of potentials and monomer concns. The osmium centers are oxidized when polymn. 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 favor film growth co-planar with the electrode surface. The electropolymn. rate increases approx. linearly with increasing monomer concn. from approx. 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, characterized by D1/2C, where D is the apparent charge transport diffusion coeff. and C is the concn. of osmium centers, 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 obsd. for potentiodynamically deposited films. This charge transport parameter is approx. two orders of magnitude larger than those found for non-conjugated bridges and is interpreted in terms of resonant superexchange across the quaterthienyl bridge.