| Abstract
| - The micro-optical ring electrode (MORE) is a photoelectrochemical device based on a ring microelectrodethat uses the insulating material interior to the ring electrode as a light guide. In this paper, we describe thepreparation and characterization of very thin ring MOREs with (ring inner radius)/(ring outer radius) > 0.99.Theoretically, we derive asymptotic analytical expressions for the time dependence of the diffusion-limitedtransient light-on photocurrent generated by two general types of photoelectrochemical systems: (a) the PE(photophysical−electrochemical) system, wherein the photoexcited species itself is directly detected on thering; (b) the PCE (photophysical−chemical−electrochemical) system, wherein the photoexcited speciesundergoes a homogeneous electron transfer reaction prior to electrochemical detection. Experimentally, weestablish that it is possible to use such MOREs to study the wavelength dependence of photocurrents derivedfrom photoelectrochemically active systems, such as the Ru(bipy)32+/Fe3+ PCE system, demonstrating thepotential utility of the MORE as a selective electroanalytical probe. We also use our expressions for the timedependence of photocurrents at the MORE to derive values for the photoelectrochemical kinetic parametersof this system, including the rate coefficient for the back reaction of photogenerated Ru(bipy)33+ (0.115 s-1)and the quantum efficiency for the primary redox products, Ru(bipy)33+ and Fe2+, escaping cage recombination,φCE = 0.099.
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