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The reaction kinetics of 1,3-dipolar cycloaddition of 1,2-diphenylcyclopropenes to C-aryl, N-aryl (or N-methyl) nitrones with the formation of bicyclic isoxazolidine products is reported. The substitution at the [C.sup.3] position of cyclopropenes by an electron acceptor group decreases the reactivity of cyclopropenes.

The scope of 1,3-dipolar cycloaddition of carbonyl ylides generated from diazo-carbonyl precursors with strained C,C double bonds of such cyclopropenes as 1,2-diphenylcyclopropenes substituted at the [C.sup.3] position and sterically hindered 3,3-disubstituted cyclopropenes is demonstrated. The highly stereoselective formation of polycyclic frameworks containing a condensed cyclopropane fragment proceed in most cases with good to excellent yields

A systematic study of the preparation of porphyrins with extended conjugation by meso, β-fusion with polycyclic aromatic hydrocarbons (PAHs) is reported. The meso-positions of 5,15-unsubstituted porphyrins were readily functionalized with PAHs. Ring fusion using standard Scholl reaction conditions (FeClj, dichloromethane) occurs for perylene-substituted porphyrins to give a porphyrin β meso annulated with perylene rings (0.7:1 ratio of syn and anti isomers). The naphthalene, pyrene, and coronene derivatives do not react under Scholl conditions but are fused using thermal cydodehydrogenation at high temperatures, giving mixtures of syn and anti isomers of the meso β-fused porphyrins. For pyrenyl-substituted porphyrins, a thermal method gives synthetically acceptable yields (>30%). Absorption spectra of the fused porphyrins undergo a progressive bathochromic shift in a series of naphthyl λmax = 730 nm), coronenyl (λmax = 780 nm), pyrenyl (λmax = 815 nm), and perylenyl (λmax = 900 nm) annulated porphyrins. Despite being conjugated with unsubstituted fused PAHs, the P,me$o-fused porphyrins are more soluble and processable than the parent nonfused precursors. Pyrenyl-fused porphyrins exhibit strong fluorescence in the near-infrared (NIR) spectral region, with a progressive improvement in luminescent efficiency (up to 13% with λmax = 829 nm) with increasing degree of fusion. Fused pyrenyl-porphyrins have been used as broadband absorption donor materials in photovoltaic cells, leading to devices that show comparatively high photovoltaic efficiencies. [ABSTRACT FROM AUTHOR]

The carbonyl ylide dipoles generated by the dirhodium tetra-acetate-catalyzed decomposition of diazocarbonyl precursors 1, 5, and 8 cycloadd to 3-substituted 1,2-diphenylcyclopropenes 3a-e and 3,3-disubstituted cyclopropenes 13, 14, 19, and 20 to give polycyclic compounds with 8-oxatricyclo[3.2.1.02,4]octane and 9-oxatricyclo[3.3.1.02,4]nonane frameworks. Generally, reactions proceed stereoselectively to give adducts of exo stereochemistry with the approach of the carbonyl ylide dipoles from the less-hindered face of cyclopropenes. The electronic properties of the substituent at the C³ position of cyclopropenes play an important role in governing the reactivity of cyclopropenes: when the C³ position is substituted by electron-acceptors such as the methoxycarbonyl or cyano groups, the yields of adducts are decreased significantly or no adducts can be detected at all. Relative reactivities of cyclopropenes were quantified by competition experiments to give the best correlation with σF-Taft constants. Both measured photoelectron spectra and ground-state calculations of a series of 1,2-diphenylcyclopropenes indicate considerable lowering of cyclopropene π-HOMO energies by substitution with an acceptor group. Such changes in electronic structures of cyclopropenes may cause the inversion of frontier molecular orbital (FMO) interactions from HOMOcyclopropene-LUMOylide to LUMOcyclopropene-HOMOylide type. In terms of philicity, nucleophilic properties of acceptor-substituted cyclopropenes are diminished to such an extent that these species are no longer good nucleophiles in the reaction with carbonyl ylides, and neither are they good electrophiles, being unreactive. This was shown by the B3LYP calculations of addends. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate organic heterojunction photodetectors sensitive to wavelengths λ >1500nm based on a solution processed Zn–porphyrin-dimer donor layer that includes phenyl-C61-butyric acid methyl ester (PCBM) and/or 4,4′-bipyridyl (Bipy) additives, and an evaporated C60 acceptor layer. The inclusion of PCBM results in up to a 20-fold increase in differential resistance, while the inclusion of Bipy results in up to a 100% increase in external quantum efficiency (EQE) compared to devices lacking additives. The devices have peak specific detectivities of D ∗ =8.8±0.2×1011 Jones (EQE =3.6±0.1%) at λ =1130nm, and D ∗ =8.2±0.2×1010 Jones (EQE =10.5±0.2%) at λ =1400nm. The maximum external quantum efficiency at λ =1400nm is 13.5±0.3%, approximately double that of previously reported organic near infrared detectors. [Copyright &y& Elsevier]