Photoinduced electron transfer across a water–oil boundary as a model for redox reaction separation

Abstract

THE creation of artificial solar energy conversion and storage systems that mimic the photosynthetic pathway has evoked great interest in recent years¹. One approach to the photolysis of water involves the mediation of two photosystems in the generation of reduced and oxidised species that are the active components in the decomposition of water^2,3. However, homogeneous (aqueous) solutions of these components suffer from the basic limitation that the reducing and oxidising agents can react with each other and thus no net reaction can be observed. Several kinds of synthetic ‘photosynthetic membranes’ have been suggested as a means of separating the two redox units and overcoming these fundamental difficulties³. Recently, photo-sensitised electron transfer across vesicle walls has been demonstrated and suggested as a means for generating oxidising and reducing agents in separate water compartments⁴. We report here a photochemical electron transfer across the interface of a water-in-toluene microemulsion, and propose this system as a model for the separation of oxidised and reduced species. It is well known that surfactant molecules aggregate to reversed micelles in organic solvents⁵. Reversed micelles entrap water to form ‘water pools’ in a continuous oil phase. The proposed general model for the compartmentalisation of two water phases and its utilisation in the photolysis of water is shown in Fig. 1.