Unusual aromaticity and organic semiconductor performance John D. Tovar, Department of Chemistry, Johns Hopkins University PRF-45738-G7: February 2007 - September 2009 Unusual -topologies that display aromatic properties have been a subject of intense research in physical organic chemistry, but their evaluation as useful materials has not been as well-developed. These materials, although elaborate and synthetically non-trivial, could facilitate the formation of the quinoidal electronic structures often invoked as the key elements in charge transport. Work supported by the PRF has resulted in the synthesis of new molecular systems and new electroactive polymers that incorporate unusual aromatic rings: shown below are examples of materials built from methano[10]annulene and dibenzo[b,f]borepin. From competing 10 -electron circuits: [10]annulene vs naphthalene … Polymer cyclic voltammetry (a,b) and spectroelectrochemistry (c,d) suggest that the annulene provides for a greater extent of delocalization upon oxidation, a process that in the present case leads to the formation of a conductive plastic. This study shows how unusual aromatics can help to extend the effective conjugation length, an important parameter for organic electronic materials. Annulene: delocalized Naphthalene: localized … to vacant p-orbitals: borepins with fused arenes UV-vis Our synthetic design of the borepins allows for the inclusion of halide groups (R = Cl, Br) para to the boron center … can these handles be used for further functionalization? Emerging questions currently under examination: How do the -electrons partition themselves? How will Lewis bases affect the electronics?