Laser Spectroscopy of New Fullerene and Metallofullerene Optical Materials

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Abstract 9632993 Wright This research is concerned with understanding the relationship between the different kinds of fullerenes, their nonlinear properties, and their electronic structure. The proposed work will involve creating examples of the new derivatives and materials that can be probed to understand how the interaction with other moieties changes the electronic and optical properties. It is clear that the neutral fullerenes do not have interesting nonlinearities and that the most interesting members of the fullerene and fullerene derivatives family are the charged ions, charge transfer complexes, and the endohedral metallofullerenes. The proposed research will continue to have two important parts: synthesis, purification, preparation, and characterization of new fullerene-based materials and measurement of the novel optical properties of these materials. The heart of the optical measurements will concentrate on using the capabilities of multi-resonant four wave mixing spectroscopy to identify the states that are responsible for the nonlinearities, to probe the transitions and coupling between electronic states, and to determine the character and usefulness of the new states that are caused by having endohedral metals or external moieties that allow charge transfer transitions. %%% There is great interest in the optical properties of materials that are based on fullerenes and metallofullerenes because of their stability, nonlinear properties, charge transfer characteristics and the ability to manipulate their properties through changes in the valence state, the size of the cage, the number and type of endohedral ions. the derivatization, and the linking with other fullerenes. The possible materials include charge transfer salts, nano-scale surface structures and films, zeolytes, and polymeric materials. Development of new optical materials requires an understanding of how changes in the nature of the fullerene affect the material's optical and electr on transfer properties. Work during a prior grant period has made it clear that the neutral fullerenes will not be the magic nonlinear material that will make the field of photonics competitive. Their nonlinearities are much smaller than the workers in the field had hoped for and measured. Nevertheless, the nonlinearities of the anions are substantial and they may be improved considerably by the ideas presented here and by forming derivatives that accentuate the polarizability. The fullerenes are also unusual and intriguing materials because of the ability to engineer their electronic structures by manipulating the number of carbons in the cage, the valence state, the endohedral metal ion and by forming fullerene derivatives. In addition to their promise for nonlinear materials, the normal electronic and charge transfer states of fullerenes are central to many interesting potential uses including photorefractive, photoconductive, photovoltaic, hole burning storage, and laser materials. The program during this grant period will focus on the electronic structures characteristic of the different valence states of the charged fullerenes and the endohedral metallofullerenes.