- Synthetic, Optical and Theoretical Study of Alternating Ethylenedioxythiophene–Pyridine Oligomers: Evolution from Planar Conjugated to Helicoidal Structure towards a Chiral Configuration
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A series of alternating 3,4-ethylenedioxythiophene–alkynylpyridine oligomers (DA)n with increased solubility are synthesized and their photophysical properties and nonlinear optical properties are investigated. Their quadratic polarizabilities are determined from hyper-Rayleigh scattering experiments to obtain information on their conformations in solution. These chromophores, based on the alternation of electron-rich (D) and electron-deficient (A) moieties, exhibit optical properties that arise from the combination of dipolar and helicoidal features in the (DA)n homologue series where n=1–4. The transition from dipolar conjugated planar structures (n=1, 2) to helicoidal structures (n=3, 4) is clearly evidenced by results from symmetry-sensitive second-order nonlinear optical experiments. This suggests an approach towards highly efficient chiral chromophores for second-order nonlinear optics. Interestingly, this structural evolution also has significant impact on the photophysical properties: both absorption and fluorescence emission show bathochromic and hyperchromic shifts with increasing number of repeating units in the dipolar planar derivatives (n=1–2) but show saturation effects in the helicoidal structures (n=2–4). In addition, the helicoidal structures show sizeable two-photon absorption at 700–750 nm (40–100 GM) for compounds lacking either electron-donating or electron-withdrawing substituents.
- Chevallier, Floris,Charlot, Marina,Mongin, Florence,Champagne, Beno?t,Franz, Edith,Clays, Koen,Blanchard-Desce, Mireille
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p. 4090 - 4101
(2016/12/23)
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- Deprotonative metalation of chloro- and bromopyridines using amido-based bimetallic species and regioselectivity-computed CH acidity relationships
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A series of chloro- and bromopyridines have been deprotometalated by using a range of 2,2,6,6-tetramethylpiperidino-based mixed lithium-metal combinations. Whereas lithium-zinc and lithium-cadmium bases afforded different mono- and diiodides after subsequent interception with iodine, complete regioselectivities were observed with the corresponding lithium-copper combination, as demonstrated by subsequent trapping with benzoyl chlorides. The obtained selectivities have been discussed in light of the CH acidities of the substrates, determined both in the gas phase and as a solution in THF by using the DFT B3LYP method.
- Snegaroff, Katia,Nguyen, Tan Tai,Marquise, Nada,Halauko, Yury S.,Harford, Philip J.,Roisnel, Thierry,Matulis, Vadim E.,Ivashkevich, Oleg A.,Chevallier, Floris,Wheatley, Andrew E. H.,Gros, Philippe C.,Mongin, Florence
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experimental part
p. 13284 - 13297
(2012/02/03)
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- Deprotonation of chloropyridines using lithium magnesates
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Chloropyridines are deprotonated using lithium magnesates. 4-Chloropyridine was deprotonated on treatment with 1/3 equiv of the highly coordinated magnesate Bu3(TMP)MgLi2 in THF at -10°C, as evidenced by trapping with I2. The use of Bu(TMP)2MgLi in Et 2O allowed the reaction of 2-chloropyridine, giving the 3-functionalized derivative as the main product. Mixtures of 3- and 4-functionalized derivatives were obtained when 2,6-dichloropyridine was involved in the reaction. Performing the reaction on 3-chloropyridine with lithium magnesates in THF, either the 4,4′-dimer or the 4-iodo derivative was formed after quenching by I2, the former using 1/3 equiv of Bu2(TMP)MgLi and the latter using 1 equiv of (TMP)3MgLi. Similar results were observed with 3,5-dichloropyridine, 2,5-dichloropyridine and 3-chloro-2-fluoropyridine. 1,2-Migration of the lithium arylmagnesate formed by deprotonation was proposed to justify the dimers formation.
- Awad, Ha?an,Mongin, Florence,Trécourt, Fran?ois,Quéguiner, Guy,Marsais, Francis
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p. 7873 - 7877
(2007/10/03)
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