Department of Chemistry
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Item Cyclization of Oxa-Bicyclic Alkenes with β-Iodo-(Z)-propenoates and o-Iodobenzoate Catalyzed by Nickel Complexes: A Simple Efficient Route to Annulated Coumarins(ACS, 2003) Shukla, ParitoshIn the presence of Ni(dppe)Br2 and Zn powder in acetonitrile at 80 °C, oxa-bicyclic olefins undergo cyclization with o-iodobenzoate and with β-iodo-(Z)-propenoates to give the benzocoumarin derivatives in moderate to good yields. This methodology offers a simple efficient way for the synthesis of structurally complicate coumarins in one pot.Item Facile β-Alkyl and β-Hydride Elimination in the Nickel-Catalyzed Annulation of o-Iodophenyl Ketones and Aldehydes with Bicyclic Alkenes(ACS, 2006-05-26) Shukla, Paritosho-Iodoaryl aldehydes react with bicyclic alkenes in the presence of NiBr2(dppe) and Zn powder in acetonitrile at 80 °C undergoing annulation to give polycyclic ketone derivatives. Surprisingly, o-iodoaryl alkyl ketones also react with bicyclic alkenes to form polycyclic ketones with structures the same as those from the corresponding o-iodoaryl aldehydes.Item Diazapentacene Derivatives as Thin-Film Transistor Materials: Morphology Control in Realizing High-Field-Effect Mobility(ACS, 2009) Shukla, Paritosh5,7,12,14-Tetrachloro-6,13-diaza-6,13-dihydropentacene (TCDAHP) and 5,7,12,14-tetrachloro-6,13-diazapentacene (TCDAP) were synthesized and assessed as the active channel materials for thin-film transistor applications. Analyses of the crystal structures of these molecules revealed that both exhibited slipped π−π stacking of the long and fused aromatic moiety. Although the packing features of the two compounds are basically identical, their highest occupied molecular orbitals, which are relevant to hole transport, are very different. Better mobility was predicted for TCDAHP over TCDAP based on the dimeric structure in the X-ray coordinates. The morphologies of thin films of TCDAHP and TCDAP prepared by thermal evaporation depend critically on the substrate on which the molecules were deposited: from the amorphous state on a SiO2/Si surface to the crystalline state on a pentacene buffer layer surface. The performance of thin-film transistors prepared on various substrate surfaces was studied. While no field-effect mobility was observed for these films deposited on SiO2/Si, a high mobility of 1.4 cm2/(V s) for the TCDAHP film was achieved when deposited on a pentacene buffer layer prepared on a rubbed monolayer of n-nonyltrichlorosilane on a SiO2/Si surface. A similar device prepared from TCDAP gave a mobility of 0.13 cm2/(V s).