The Micro-Optical Ring Electrode (MORE), a novel photoelectrochemical device capable of delivering light via a fibre optic light guide directly to the region of electrochemical measurement. Based on a ring microelectrode and using the insulating material interior to the ring electrode as a light guide, the MORE can therefore be used to conduct microelectrochemical studies of systems with complex photochemistry. Most recently, the MORE has been used in a preliminary study of the photoelectrochemical behaviour of tris(2,2'-bipyridine)ruthenium(II) (Ru(bipy)(3)(2+)) in the presence of the oxidising quenching agent, Fe3+. Chronoamperograms have been recorded at the MORE using increasing concentrations of Fe3+. A direct correlation has been established between the recorded photocurrent and [Fe3+]. A value of the Stern-Volmer constant (k(st)) for the homogeneous quenching of photoexcited Ru(bipy)(3)(2t) by Fe3+ has been obtained from electrochemical measurements conducted using the MORE. The value of k(st) so obtained (0.4 m(3) mol(-1)) compares favourably with the value of the Stern-Volmer constant for the same reaction obtained from fluorescence measurements (0.9 m(3) mol(-1)).