CHEMICALLY MODIFIED ELECTRODES: SYNTHESIS AND ELECTRON TRANSFER PROPERTIES (INORGANIC, POLYMER, ELECTROCHEMISTRY).

摘要

The synthesis and electropolymerization of a number of vinyl containing metal poly-pyridyl complexes has been achieved. Two of the most useful electropolymerizable ligands are vpy (4-vinylpyridine) and vbpy (4-vinyl-4'-methyl-2,2'-bipyridine). Iron, ruthenium, osmium complexes with these ligands can be reductively electropolymerized from acetonitrile solutions to form adherent, relatively pinhole-free, electroactive films on Pt. The stability and well-behaved electrochemistry of these thin film electrodes make them ideal candidates for permeation and electron transfer studies.; Thin films of poly-{lcub}(bpy)(,2)Os(vpy)(,2){rcub}('2+/3+) (bpy = 2,2'-bipyridine) are impermeable to bulky, cationic species like {lcub}(bpy)(,3)Ru{rcub}('2+) (PD(,s,pol) (LESSTHEQ) 1.4 x 10('-12) cm('2)/s; P and D(,s,pol) are the substrate partition coefficient into and diffusion coefficient within the polymer film), while highly permeable to small anions like Cl('-) (PD(,s,pol) = 3.5 x 10('-7) cm('2)/s).; The rate of charge transport for several polymers has been measured. Representative values for the charge transport diffusion coefficient, D, in acetonitrile are: poly-{lcub}(bpy)(,2)Os(vpy)(,2){rcub}('2+/3+), D (,(TURN))6.4 x 10('-9) cm('2)/s; poly-{lcub}(vbpy)(,3)Ru{rcub}('2+/3+), D (,(TURN))1.2 x 10('-9) cm('2)/s; poly-{lcub}(vbpy)(,3)Fe{rcub}('2+/3+), D (,(TURN))1.4 x 10('-9) cm('2)/s.; Quantitation of the low permeability and high charge transport rate within films like poly-{lcub}(bpy)(,2)Os(vpy)(,2){rcub}('2+/3+), indicates that electron transfer reactions between the polymer film and dissolved metal complexes in acetonitrile occur exclusively at the polymer/solution interface. The interfacial electron transfer rate constants for thermodynamically unfavorable reactions (i.e., equilibrium constant < 1) are measurable and correlate with the Marcus relations for outer sphere reactions in homogeneous solution. Furthermore, the self exchange rates obtained for the polymer sites at the polymer/solution interface agree well with those reported for analogous {lcub}(bpy)(,3)M{rcub}('2+/3+) complexes in acetonitrile.; Charge trapping rates in spatially segregated redox polymer bilayer electrodes have been investigated. For thermodynamically favorable reactions the initial rates are limited by the charge transport rates within the inner film; the interfacial electron transfer rates are too fast to measure in these particular bilayers. Rotated disk experiments have been developed to study thermodynamically unfavorable bilayer trapping reactions. The results indicate that charge transport effects are not completely absent in the reactions, but it is possible to assign a lower limit to the polymer/polymer electron transfer rate constant. Remarkably, this value is within a factor of ca. 25 of that calculated for the analogous solution reaction.