Roles of organized molecular assemblies in artificial photosyntheses

Abstract

As has been verified in biological photosynthesis, organized molecular assemblies (OMAs) are capable of controlling photochemical energy conversion. Charge separation of photoactivated species has bee attempted using type I OMAs such as micelles, microemulsions, bilayer membranes and polysoaps. The charge separation is enhanced by molecular diffusion which is aided by local electric field and segregation effects due to microenvironmental compartmentalization. The transport of electrons across the membrane wall of vesicles has been studied in an effort to achieve up-hill energy conversion. The attempts were successful in principle, but in practice considerable improvement of the membrane is required. However, new synthetic amphiphiles have been developed which form bilayers, and stable membranes with variable thicknesses (of he order of 50 Å - 10 μm) have become available. Geometric structures of the membrane may also be modified easily. Both energy transfer and electron transport systems can be constructed using the new bilayer membranes with appropriately immobilized elements. Linked donor-acceptor systems, as represented by porphyrin-quinone, may serve as good photoreaction centres when they are installed on these type II OMAs with immobilized elements. The development of type III OMAs is required for efficient coupling of elementary processes in artificial photo-synthesis. The construction of charge pools in OMAs seems to be one of the solutions, as has been demonstrated in several examples such as the cooperative activation of two photoredox systems by the use of OMAs with electron pools. © 1985.