PHOTOPROCESSES AT THE LIQUID LIQUID INTERFACE .3. CHARGE-TRANSFER DETAILS FOR PHOTOACTIVE METAL-COMPLEXES

Earlier we reported the occurrence of a photoeffect at the liquid-liquid interface for a single component colored species rationalized as a photothermal effect. Simultaneously we reported an electron transfer process occurring at the liquid-liquid interface deriving from the quenching of excited state [Ru(bpy)3]2+ (bpy is 2,2'-bipyridyl) by methylviologen (MV2+) each in distinct phases. The results reported and discussed here are an expansion of the previous work done to clarify questions raised by the previous work. These measurements were done with a redesigned optical system to increase the sensitivity. The absence of a photocurrent for the single-component [Fe(bpy)3]2+ system, whose absorbance properties are identical to the [Ru(bpy)3]2+ but does not have the redox capability of [Ru(bpy)3]2+, made questionable the previous "photothermal" rationale of the photoeffect. Subsequent examination of the effect of O2 upon this measurement made it apparent that quenching of the [Ru(bpy)3]2+ by O2 is likely the origin of the photoeffect. The quenching of the [Ru(bpy)3]2+ by MV2 (as well as other quenchers) to produce an electron transfer current was verified by these results. Further homogeneous phase reactions between the excited-state species and these quenchers did not produce a measureable photocurrent, thus demonstrating that the interfacial current can only be an electron current and not another reaction product produced by the photoredox reaction. Impedance measurements on the irradiated interface enabled estimation of a rate constant of 10(2)-10(3) for the interfacial charge transfer process, substantially higher than those constants measured for ion species crossing this same interface. Comparision of this measured value to the calculated value for this interfacial process suggests that efficiency of the interfacial quenching reaction is large.