- Extremely efficient and reversible visible-light photochromism and accompanying switch of electronic communication in N-phenylcarbazole-appended diethynylethene
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Photoisomerization: N-phenylcarbazole-conjugated dimethyl 2,3-diethynylfumarate/maleate, E/Z-4, shows highly efficient and reversible visible-light E/Z photoisomerization (φtotal=0.40) upon excitation with an intramolecular charge-transfer band. This photochromism induces switching of electronic communication between the two N-phenylcarbazole moieties in the one-electron oxidized mixed-valent state (see scheme). Copyright
- Hayashi, Mikihiro,Sakamoto, Ryota,Nishihara, Hiroshi
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supporting information; experimental part
p. 8610 - 8613
(2012/08/27)
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- Synthesis and properties of metal-ligand complexes with endohedral amine functionality
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A series of tetracationic M2L4 palladium-pyridyl complexes with endohedral amine functionality have been synthesized. The complexes were analyzed by NMR techniques (including Diffusion NMR and 2D NOESY), electrospray ionization (ESI) mass spectrometry, and X-ray crystallography. The solid state analysis shows a large change in crystal morphology upon introduction of the endohedral amine groups, caused by deleterious interactions between the amines and the triflate counterions from the coordination process. Combination of different ligands allows analysis of ligand exchange rates via NMR analysis, with half-lives on the order of 3 h, independent of the donor properties of the ligand. Self-sorting behavior is observed, with more electron-rich ligands being favored. The amine-containing and extended complexes are strongly fluorescent, giving quantum yields of up to 83%.
- Johnson, Amber M.,Moshe, Orly,Gamboa, Ana S.,Langloss, Brian W.,Limtiaco, John F. K.,Larive, Cynthia K.,Hooley, Richard J.
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p. 9430 - 9442
(2011/11/04)
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- Javelin-, hockey stick-, and boomerang-shaped liquid crystals. Structural variations on p-quinquephenyl
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The ramifications of changing molecular geometry in a series of all-aromatic liquid crystals derived from p-quinquephenyl are reported. Substituting heterocyclic rings such as thiophene, oxadiazole, oxazole, or 1,3-phenylene into the p-quinquephenylene core affects molecular shape changes via the substituent's exocyclic bond angle. In general, we found that introducing nonlinearity into molecules depresses the melting transition temperature. The symmetric (boomerang-shaped) molecules, 2,5-bisbiphenyl-4-yl-1,3,4-oxadiazole, 2,5-bisbiphenyl-4-yl-oxazole, and 1,3-bisbiphenyl-4-yl-benzene, melt into isotropic phases showing small monotropic mesophases. By contrast, the asymmetric (hockey stick-shaped) mesogens, 2-terphenyl-4-yl-5-phenyl thiophene and 2-terphenyl-4-yl-5-phenyl-1,3,4-oxadiazole, exhibit more stable enantiotropic liquid crystalline phases. The hockey stick-shaped mesogens exhibit a smectic phase as well as a nematic phase. High-temperature X-ray determination of the smectic layer spacing gives an unambiguous picture of interdigitated, bilayerlike supramolecular architecture in the smectic phase. There are associated changes in the mesogen's electrostatic profile when a heterocycle is introduced into the quinquiphenylene framework (e.g., conjugation is perturbed). Our findings suggest that steric packing considerations dominate the phase preferences (nematic versus smectic phases). However, electronic considerations (conjugation) appear to control the range of mesomorphism in this new family of nonlinear liquid crystals.
- Dingemans, Theo J.,Murthy, N. Sanjeeva,Samulski, Edward T.
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p. 8845 - 8860
(2007/10/03)
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- Detection of Aryl Radicals in Hydrodediazoniations
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Iodoacetic acid, an effective aryl radical trapping agent, was employed to investigate the reactive intermediates in several hydrodediazoniations. Isolation of an aryl iodide constitutes a positive result in the test for aryl radicals. Equally as important is the lower yield of the reduction product when the trap diverts radicals from their usual reaction path. Hydrodediazoniations performed in MeOH, EtOH, i-PrOH, benzyl alcohol, THF, tetramethylurea, formamide, and hypophosphorous acid all involve aryl radical intermediates. Ferrocene was found to be an effective initiator in most of these reactions; through its action as an electron donor, it serves to shorten reaction times and to improve yields of hydrodediazoniation products. All hydrodediazoniations examined, whether initiated or not, involve radical intermediates.
- Wassmundt, Frederick W.,Kiesman, William F.
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p. 8304 - 8308
(2007/10/03)
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