Zn 3 N 2 polycrystalline films with n+-type conductivity have been grown by metalorganic chemical vapor deposition and rf-molecular beam epitaxy with carrier concentration in the range between 1019 and ∼1020cm−3. Oxygen contamination without an intentional doping was found to be a cause of high electron concentration, leading to a larger band-gap energy due to Burstein-Moss shift. The significant blue shift of the optical band gap Eopt with increasing carrier concentration ne obeys the relation Eopt=1.06+1.30×10−14ne2∕3. This evaluation enables the conclusion that the actual band-gap energy of Zn3N2 is 1.06eV. Electron effective mass m* for Zn3N2 has been deduced from Fourier transform infrared reflectivity measurements to be (0.29±0.05)mo.

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Helicenes and helicene-like molecules have long attracted much attention because of their potential applications to optical or electronic functional materials.[1] Therefore, flexible as well as convenient methods for their syntheses are highly desired for structural alterations and supply of sufficient quantities.[2] The most frequently employed method for the synthesis of helicenes is the oxidative photocyclization of stilbene-type precursors, however this procedure cannot be conducted on a large scale because of the highly dilute reaction conditions.[3] Several non-photochemical methods for the synthesis of [6]-and [7]helicenes and helicene-like molecules have been developed to date.[4] As such, transition metal mediated intramolecular [2+2+2] cycloadditions of triynes are useful methods for the synthesis of [6]-and [7]helicene-like molecules through the formation of three successive rings. [5,6] Starµ and co-workers pioneered this strategy by using cobalt-or nickel-mediated or catalyzed [2+2+2] cycloadditions.[5] Following this pioneering work, we recently reported a cationic rhodium(I)/chiral bisphosphine complex, which catalyzed the intramolecular [2+2+2] cycloadditions of 2-naphthol-linked triynes, leading to enantioenriched [7]helicene-like molecules (Scheme 1). [6,7] Notably, non-photochemical methods that can furnish higher ordered (! [8]) helicenes and helicene-like molecules are rare. [8] To access sterically more demanding [9]helicene-like molecules [9] starting from commercially available 2-naphthol, we designed an intermolecular double [2+2+2] cycloaddition between a 2-naphthol-linked tetrayne and a dialkynylketone, [10] which forms five successive rings (Scheme 2). This method would furnish various [9]helicene-like molecules, containing a densely substituted fluorenone core, by changing substituents of each cycloaddition partner.The 2-naphthol-linked tetraynes 4 were readily prepared by a three-step sequence starting from a known terminal alkyne 1 [7] as shown in Scheme 3. A copper-mediated Scheme 3. Syntheses of tetraynes 4 a and 4 b. DMAP = 4-dimethylaminopyridine, DCC = dicyclohexylcarbodiimide.

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[structure: see text]. A cationic rhodium(I)/dppb complex catalyzed direct intermolecular hydroacylation of N,N-dialkylacrylamides with both aliphatic and aromatic aldehydes has been achieved through the stabilization of acylrhodium intermediates by alkene chelation to rhodium. This method represents a versatile new route to gamma-ketoamides in view of the high atom economy and commercial availability of substrates.