Acenes can be thought of as one-dimensional strips of graphene and they have the potential to be used in the next generation of electronic devices. However, because acenes larger than pentacene have been found to be unstable, it was generally accepted that they would not be particularly useful materials under normal conditions. Here, we show that, by using a physical vapour-transport method, platelet-shaped crystals of hexacene can be prepared from a monoketone precursor. These crystals are stable in the dark for a long period of time under ambient conditions. In the crystal, the molecules are arranged in herringbone arrays, quite similar to that observed for pentacene. A field-effect transistor made using a single crystal of hexacene displayed a hole mobility significantly higher than that of pentacene. This result suggests that it might be instructive to further explore the potential of other higher acenes.
Photoinduced color change of naphthalene diimides (NDIs) bearing alkylamine moieties has been observed in the solid state. The color change is attributed to the generation of a NDI radical-anion species, which may be formed through a photoinduced electron-transfer process from the alkylamine moiety to the NDI. The photosensitivity of NDIs is highly dependent on the structures of the alkylamine moieties. Crystallographic analysis, kinetic analysis, UV/Vis/NIR spectroscopic measurements, and analysis of the photoproduct suggested that a radical anion was formed through an irreversible process initiated by proton abstraction between an amine radical cation and the neutral amine moiety. The radical anions formed stacks including mixed-valence stacks and radical-anion stacks, as shown by the broad absorption bands in near-IR spectra. These photosensitive NDIs also showed crystal bending upon photoirradiation, which may be associated with a change in the intermolecular distance of the NDI stacks by the formation of monomeric radical anions, mixed-valence stacks, and radical-anion stacks.
Octyl-and nonylphenols in the environment have been proposed to function as estrogens. To gain insight into their structural essentials in binding to the estrogen receptor, a series of phenols with saturated alkyl groups at the para position, HO-C 6 H 4 -C n H 2n+1 (n = 0±12), were examined for their ability to displace [ 3 H]17b-estradiol in the recombinant human estrogen receptor, which was expressed in Sf9 cells using the vaculovirus expression system. All tested para-alkylphenols were found to bind fully to the estrogen receptors in a dose-dependent manner. The interaction of alkylphenols with the receptor became stronger with increase in the number of the alkyl carbons and the activity was maximized with n = 9 of nonylphenol. Phenol (n = 0) exhibited weak but full binding to the receptor, whereas anisole with a protected phenolic hydroxyl group was completely inactive. Also, alkanes such as n-octane, 2,2,4-trimethylpentane corresponding to tert-octane, and n-nonane exhibited no binding. The results indicate that the binding of para-alkylphenols to the estrogen receptor is due to the effect of covalent bonding of two constituents of the phenol and alkyl groups, which correspond to the A-ring and hydrophobic moiety of the steroid structure, respectively. When alkylphenols were examined for their receptor binding conformation by 1 H-NMR measurements and ab initio molecular orbital calculations, it was suggested that nonbranched alkyl groups are in an extended conformation, while branched alkyl groups are in a folded conformation. These results suggest that branched and nonbranched alkyl moieties of alkylphenols interact differently with the lipophilic ligand binding cavity of the estrogen receptor when compared to the binding of 17b-estradiol.
The syntheses, conformational study, and transannular π-π interaction of multibridged [3 n ]cyclophanes including the ultimate member of this series, [3 6 ](1,2,3,4,5,6)cyclophane 1, are described. The stepwise construction of trimethylene bridges starting from [3 3 ](1,3,5)cyclophane 6 led to the synthesis of 1 by way of four-and fivebridged cyclophanes 7 and 8. The variable-temperature (VT) 1 H NMR study (CD 2 Cl 2 ) and molecular mechanics calculations (MM3) of five-bridged 8 revealed the most stable conformer, the relative stability order of the three stable isomers, and energy barriers for the trimethylene bridge inversion. A similar VT 1 H NMR study (toluene-d 8 ) of 1 suggests the presence of the trimethylene bridge inversion process between two C 6h conformers. The charge transfer (CT) bands of the complexes of multibridged [3 n ]cyclophanes with tetracyanoethylene (TCNE) show significant bathochromic shifts with the increase in the number of the bridges, and this is mainly attributed to the effective hyperconjugation between the benzyl hydrogens and the benzene rings. The CT band of the TCNE-1 complex (728 nm) is the longest wavelength among those of the TCNE complexes of [m.n]cyclophanes and multibridged benzenophanes.
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