The Micro-Optical Ring Electrode (MORE) is a novel photoelectrochemical device based on a ring microelectrode and using the insulating material interior to the ring electrode as a light guide. Thin rings exhibit high rates of material flux to the electrode surface, facilitating the detection of short lived photogenerated solution intermediates. To exploit this advantage, we have prepared MOREs with (ring inner radius)/(ring outer radius) values in excess of 0.999. Such MOREs have been used in a study of the photoelectrochemical behaviour of (Ru(bipy)32+ ) in the presence of Fe3+ quenching agent. The spectral dependence of the MORE photocurent response has been investigated and found to correspond to the singlet-to-singlet, metal-to-ligand charge transfer band of the UV-visible spectrum of Ru(bipy)32+. A value of the Stern-Volmer constant for the quenching of photoexcited Ru(bipy)32+ by Fe3+ has been obtained using the MORE. The value obtained (1.59 m3 mol-1 ) compares favourably with the value obtained from fluorescence measurements (0.9 m3 mol-1).