Inverted Region Electron Transfer Demonstrated by Electrogenerated Chemiluminescence at the Liquid/Liquid Interface

We describe several transinterface electron-transfer processes occurring at the benzonitrile (PhCN)/water interface that produce excited states. When an electrode was moved very close to the interface or even through the interface to produce an electrode/thin layer organic phase/aqueous solution configuration, the electrogenerated radical species formed in the PhCN phase (C12-Ru(bpy)3, DPA+, or TH+) diffused to the liquid/ liquid interface to react with (oxidize) a coreactant (C2O4) soluble only in the aqueous solution, leading to the formation of a strongly reducing radical species (CO2). The electron transfer from CO2 in the aqueous solution to the oxidized species in the organic phase across the liquid/liquid interface produced an electronically excited state which then emitted light. The appearance of an ECL signal in these systems supports the suggestion of Marcus inverted region behavior in very exothermic heterogeneous electron-transfer reactions at the liquid/ liquid interface.