PHOTOCURRENT GENERATION IN METAL BISPHOSPHONATE MULTILAYER THIN-FILMS

Attempts to mimic the highly efficient process of photosynthesis(1-3) are of considerable interest, the goal being to design artificial syst ems for the efficient conversion of solar energy into chemical or elec trical energy(4-14). In both natural and artificial systems, the under lying process is photoinduced charge separation, typically involving a redox reaction between a photoexcited donor molecule and an acceptor molecule. Through careful choice of the molecular arrangement, and the redox potentials of the donors, intermediate charge carriers and acce pters, it is possible to minimize the reverse electron transfer proces s and thereby obtain stable photoinduced charge separation. In this co ntext, photochemical electron accepters based on methylviologen and it s derivatives have been widely studied(5,6,8-12,14-19). Here we descri be the synthesis and characterization of metal biphosphonate multilaye r thin films composed of viologen-based acceptor layers and donor laye rs of p-phenylenediamine. Our method of film growth provides control o ver both the structure and composition of the multilayer films, leadin g to efficient photoinduced charge separation and directional electron transport. These films generate photocurrents when irradiated with ul traviolet and visible light.