To make the altered nanotubes, Dirk M. Guldi of the University of Notre Dame and his colleagues attached molecules of ferrocene to their walls. Made up of two flat rings of five carbon atoms each that sandwich an iron atom, ferrocene is known for its tendency to give up its electrons. The scientists determined that when they exposed their altered nanotubes to light in the visible range, carbon atoms in the walls of the tubes accept the electrons originally associated with the ferrocene molecules. "This separation of charge is sufficiently long-lived for us to divert and use the electrons," Guldi notes.
This is the first time hybrid nanotube complexes have been shown to undergo such photoinduced electron transfer. And it didn't take much: the researchers added just one ferrocene group for every 100 carbon atoms in the nanotubes. The results, Guldi remarks, meet "the first criteria for the development of solar cells based on modified carbon nanotubes."