Research Project
2605400
DESCRIPTION: The objective of this work is to develop methods for the synthesis and characterization of a series of monodisperse nanoscale (n)phenancene derivatives (with n up to 127) that are solubilized by alkyl substituents. The parent (n)phenancenes have n benzene rings fused in an extended phenanthrene-like structural motif, and are related structurally to graphite as ribbons are related to sheets. Organic chemists are giving increasing attention to the synthesis of monodisperse compounds with molecular sizes in the nanoscale regime, the regime that lies beyond the range of traditional organic chemistry but includes many biologically important molecules and organisms. The proposed work should contribute to the growing body of knowledge about what modifications may be required in the conventional experimental methods of synthesis, purification, and molecular structure proof in order to deal effectively with nanoscale compounds. In addition, the work should reveal informative trends in the spectral properties (especially electronic absorption and fluorescence spectra) and physical properties (especially solubilities and deviations of the aromatic ring systems from planarity) of the (n) phenancenes as a function of n. Ultimately, these graphite-like compounds could be found to possess interesting and potentially practical properties as electrical conductors or as nonlinear optical materials. The work also will provide valuable laboratory training and experience in organic synthesis that will prepare a number of graduate and undergraduate research students for professional careers in bio-organic chemistry or biomedical chemistry. The proposed syntheses follow a divergent-convergent iterative strategy in which each four step iteration converts a phenancene with n rings to one with 2n + 1 rings. In the first iteration, 2-bromo-4-tert-butyltoluene is transformed separately into two compounds: reaction of the ring methyl substituent with NBS followed by Ph3P produces a benzylic triphenylphosphomium salt; and the reaction of the bromo substituent with BuLi followed by DMF produces an aldehyde. A Wittig reaction involving these two compounds yields a stilbene derivative, which is then photocyclized to give 1-bromo-3, 5-di-tert- butyl-8-methylphenanthrene. In the second iteration, the bromo and methyl substituents of this phenanthrene derivative are similarly transformed to produce both a phosphonium salt and an aldehyde, and the Wittig coupling of these two intermediates yields a diphenanthrylethylene that is photocyclized to give a (7)phenancene derivation with bromo, methyl, and four tert-butyl substituents. Subsequent iterations should give (n)phenancene derivatives with n=15, 31, 63 and 127.
