A previously reported laser-based spatially resolved absorption spectroelectrochemical technique was extended to the visible wavelength range by substitution of the laser with a xenon arc source. The modified instrument permits acquisition of concentration vs. distance profiles of optically absorbing reactants and products of electrode reactions, resolved in space, time, and wavelength. The spatial resolution along the axis perpendicular to the electrode plane is ca. 5 ~m, while the time resolution is 10-100 ms, depending on the magnitude of the absorbance. The spatially resolved spectrum of chloropromazine cation radical was obtained, as were the concentration profiles for both electrogenerated and electroconsumed Fe(CN)C ~. The method was used to determine the effect of electrode orientation on diffusion layer thickness for electroconsumed Fe(CN)C ~. At times below 20s after a potential step, vertical or horizontal diffusion produced identical concentration profiles, with no evidence of density driven convection. At times longer than 20s, erratic profiles resulted, with slightly thicker boundary layers observed for horizontal diffusion. While density driven convection cannot be ruled out from these results, there is no apparent effect on experiments with typical electroanalytical time scales. Finally, the method was applied to a twin working electrode thin layer geometry, with a linear profile of Fe(CN)C 3 observed at steady state.
ABSTRACTCommercially available, thermally cyclized, poly(4,4'-oxydiphenylenepyromellitimide) displays ohmic charge transport when suitably doped through an aqueous interfacial electron transfer reaction. The normally highly insulating polymer increases in conductivity by approximately 11 to 13 orders of magnitude becoming an air-sensitive semiconductor with bulk conductivities ranging from 10 -~ to 10 -7 Yt -1 cm-'. The mechanism of conduction appears to be based upon interchain electron hopping.
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