- Turning-on the quenched fluorescence of azomethines through structural modifications
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A series of fluorene azomethines were prepared to examine the effect of structural modification on the absolute fluorescence quantum yields (Φfl). The change in fluorescence occurring upon reversing the orientation of the azomethine bond, the number of fluorene units, and alkylation at the 9,9′-positions of fluorene was examined. It was found that Φfl could be tailored with these structural modifications with 0.05 ≤ Φfl ≤ 0.45. The highest Φfl was measured for the trimer derived from 2,7-diamino fluorene with each fluorene being alkylated at the 9,9′-positions. The fluorescence quantum yields did not increase at 77 K, implying the absence of fluorescence quenching modes involving internal conversion. Fluorescence enhancement was also not observed upon protonating the imine with trifluoroacetic acid. This confirms that Waldon inversion and isomerization are not fluorescence deactivation modes. Additionally, no photoisomerization was observed either at room temperature or at 77 K when the fluorene derivatives were irradiated at 354 nm. In contrast, the Z photoisomer of a N-benzylideneaniline analogue was spectroscopically detected both by absorbance and by 1H NMR spectroscopy. The absolute fluorescence quantum yield of conjugated azomethines was increased to 45 % by structural modifications and adjusting the orientation of the azomethines. Copyright
- Barik, Satyananda,Skene, William G.
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- Solid-state intermolecular contacts involving the nitrile group in p-cyano-N-(p-cyanobenzylidene)aniline and 4,4′-(azinodimethylidyne)bis- benzonitrile
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As part of an investigation of the solid-state intermolecular contacts in which the nitrile group participates, the crystal structures of p-cyano-N-(p-cyanobenzylideneaniline), C15H9N3 (CN/CN) and 4,4′-(azinodimethylidyne)
- Ojala, Charles R.,Ojala, William H.,Britton, Doyle
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- Systematic studies on mechanochemical synthesis: Schiff bases from solid aromatic primary amines and aldehydes
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A versatile and robust mechanochemical route to Aldehyde–Schiff base conversions has been established for a broad range of aldehydes via a simple cogrinding in mortar with a pestle under a solvent-free, as well as solvent-assisted, environment. The extent
- Tigineh, Getinet Tamiru,Liu, Ling-Kang
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p. 1729 - 1737
(2019/06/21)
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- Visible-Light Photocatalytic Synthesis of Amines from Imines via Transfer Hydrogenation Using Quantum Dots as Catalysts
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CdSe/CdS core/shell quantum dots (QDs) can be used as stable and highly active photoredox catalysts for efficient transfer hydrogenation of imines to amines with thiophenol as a hydrogen atom donor. This reaction proceeds via a proton-coupled electron transfer (PCET) from the QDs conduction band to the protonated imine followed by hydrogen atom transfer from the thiophenol to the α-aminoalkyl radical. This precious metal free transformation is easy to scale up and can be carried out by a one-pot protocol directly from aldehyde, amine, and thiophenol. Additional advantageous features of this protocol include a wide substrate scope, high yield of the amine products, extremely low catalyst loading (0.001 mol %), high turnover number (105), and the mild reaction conditions of using visible light or sun light at room temperature in neutral media.
- Xi, Zi-Wei,Yang, Lei,Wang, Dan-Yan,Pu, Chao-Dan,Shen, Yong-Miao,Wu, Chuan-De,Peng, Xiao-Gang
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p. 11886 - 11895
(2018/09/25)
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- Effects of molecular conformation on the spectroscopic properties of 4,4′-disubstituted benzylideneanilines
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The relationship between the molecular conformation and spectroscopic properties of unsymmetrical 4,4′-disubstituted benzylideneanilines, was explored by the combination of experiment and reference data. Crystal structure information and spectroscopic beh
- Fang, Zhengjun,Wu, Feng,Yi, Bing,Cao, Chenzhong,Xie, Xin
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- Synthesis of optically pure vic-sulfanyl amines mediated by a remote sulfinyl group
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Enantiomerically pure syn-1,2-diaryl-1,2-sulfanylamine derivatives can be obtained in a completely stereoselective manner by reaction of the benzylcarbanion Li-(S)-1 with N-phenyl (or PMP)-arylidene aldimines and further desulfinylation with t-BuLi. Theoretical studies at the DFT (mPW1PW91) level with the CPCM model, by using the Gaussian09 program, provide a good explanation for the stereochemical results.
- Arroyo, Yolanda,Sanz-Tejedor, M. Ascension,Alonso, Ines,Garcia-Ruano, Jose L.
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supporting information; experimental part
p. 4534 - 4537
(2011/10/09)
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- Substituent cross-interaction effects on the electronic character of the C=N bridging group in substituted benzylidene anilines - Models for molecular cores of mesogenic compounds. A 13C NMR study and comparison with theoretical results
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13C NMR chemical shifts δc(C=N) were measured in CDCl 3 for a wide set of mesogenic molecule model compounds, viz. the substituted benzylidene anilines P-X-C6H4CH=NC 6H4-p-Y (X = NO2, CN, CF3, F, Cl, H, Me, MeO, or NMe2; Y = NO2, CN, F, Cl, H, Me, MeO, or NMe2). The substituent dependence of δc(C=N) was used as a tool to study electronic substituent effects on the azomethine unit. The benzylidene substituents X have a reverse effect on δc(C=N): electron-withdrawing substituents cause shielding, while electron-donating ones behave oppositely, the inductive effects clearly predominating over the resonance effects. In contrast, the aniline substituents Y exert normal effects: electron-withdrawing substituents cause deshielding, while electron-donating ones cause shielding of the C=N carbon, the strengths of the inductive and resonance effects being closely similar. Additionally, the presence of a specific cross-interaction between X and Y could be verified. The electronic effects of the neighboring aromatic ring substituents systematically modify the sensitivity of the C=N group to the electronic effects of the benzylidene or aniline ring substituents. Electron-withdrawing substituents on the aniline ring decrease the sensitivity of δc(C=N) to the substitution on the benzylidine ring, while electron-donating substituents have the opposite effect. In contrast, electron-withdrawing substituents on the benzylidene ring increase the sensitivity of δc(C=N) to the substituent on the aniline ring, while electron-donating substituents act in the opposite way. These results can be rationalized in terms of the substituent-sensitive balance of the electron delocalization (mesomeric effects). The present NMR characteristics are discussed as regards the computational literature data. Valuable information has been obtained on the effects of the substituents on the molecular core of the mesogenic model compounds.
- Neuvonen, Helmi,Neuvonen, Kari,Fueloep, Ferenc
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p. 3141 - 3148
(2007/10/03)
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- SUBSTITUENT EFFECTS ON THE 31P, 13C, AND 1H NMR CHEMICAL SHIFTS OF SUBSTITUTED DIPHENYL 1-PHENYLAMINO-1-PHENYLMETHANEPHOSPHONATES AND THEIR ANIONS
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For a series of thirty-five novel diphenyl 1-phenylamino-1-phenylmethanephosphonates, substituted in the meta and para positions on the anilino and/or aryl ring, 31P chemical shifts show a good linear correlation with Hammett ?n and Taft ?0 parameters, the 31P nucleus being better shielded in the case of electron withdrawing substituents.The same pattern is observed for the phosphonate anions, except when para phenyl substituents can interact with the phosphorus atom by direct resonance.This inverse relationship is due to a field effect of the substituent dipole which polarizes ?-electron clouds in the molecule.A corresponding shift in ?-electron density is likewise observed for 13C resonances of the two diastereotopic phenoxy groups, the phenylamino and phenyl moieties.Vicinal CH-NH coupling is shown to be dependent on the rate of NH proton exchange as influenced by resonance, temperature and solvent effects.
- Smith, Scott J.,Zimmer, Hans,Fluck, Ekkehard,Fischer, Peter
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p. 105 - 120
(2007/10/02)
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- DIPOLE MOMENTS, ESCA, THEORETICAL CALCULATIONS AND GAS-LIQUID CHROMATOGRAPHIC STUDIES ON SOME P-P prime -DERIVATIVES OF BENZYLIDENE ANILINE.
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Pairs of nematic liquid crystals of the Schiff's base type that are identical in length-to-breadth ratios, but differ in the location of the atoms in the central linkage were synthesized. Combined ESCA and theoretical calculations revealed that the nature
- Janini,Hovakeemian,Katrib,Fitzpatrick,Attari
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p. 271 - 280
(2007/10/02)
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