Stability and solid-state polymerization reactivity of imidazolyl- and benzimidazolyl-substituted diacetylenes: pivotal role of lattice water

International audience1,6-Bis(1-imidazolyl)-2,4-hexadiyne (1) and1,6-bis(1-benzimidazolyl)-2,4-hexadiyne (5) have beenpreparedby a novel method that consists in refluxing excess imidazole and benzimidazole with 2,4-hexadiyne-1,6-diol bis(p-toluenesulfonate),pTS (3). This procedure is a viable alternative to the widely used Hay coupling protocol in case the target diyne possesses substituents capable of deactivating the copper catalyst by complexation. Diyne1crystallizes as a hydrate,1?H2O(2). For this compound, water is essential toachieve a crystalline material, and attempts to obtain crystals without included solvent were unsuccessful. In the structure of2, the organic fragments organize around the water molecule and interact with it through a dense network of hydrogen bonds. The CMC-CMC moieties are not oriented suitably for topochemical polymerization, and when trying to alter the organizationof the crystal by heating so as to induce polymerization, water is lost in an abrupt fashion that leads to instantaneous decomposition into polyaromatic-like species. Similar results were observed when water was removedin vacuo at room temperature. The benzimidazole-containing compound can be crystallized with water molecules (4)orwithout(5). X-ray crystallography shows that the structure of 5is organized by numerous C-H...N, C-H...p,andimidazolyl...imidazolyl p-p interactions. The diacetylene molecules almost have the right arrangement for topochemical polymerization, withpossibly reactingCMC-CMC fragments not beingparallel, a rare situation indiacetylene chemistry. Yet, experiments showthat topochemical polymerizationdoes not occur. Incorporationofwater in the lattice of5leads toa solvate that is topochemically reactive. Unlike2, however, water molecules in 4are not isolated but are organized as ribbons. Spectroscopic characterization of the polymer of4indicates that it is a blue phase polymer, with water coordinated to it. This study shows that it is possible to use water, and more generally solvent molecules, to transform a nonreactive diacetylene into a reactive one, even though this approach is less predictable than the cocrystal approach developed by Fowler, Lauher, and Goroff. The solvate approach is simple to implement, quite versatile because of the large rangeof solvents available, andonedoes not face theproblemof having to remove the host in case one needs to recover the polymer. Previous studies describing a similar approach are scarce

Azole-functionalized diacetylenes as precursors for nitrogen-doped graphitic carbon materials

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Size-Based Characterization of an Ionic Polydiacetylene by Taylor Dispersion Analysis and Capillary Electrophoresis

International audienceThis work focuses on the size-based characterization of a water-soluble ionic polydiacetylene with a polycationic structure, poly-[(1,6-bis(N-methylimidazolium)hexa-2,4-diyne)dibromide]. This polymer could not be characterized using classical analytical techniques such as size-exclusion chromatography and MALDI−TOF mass spectrometry due to problems of purification, low quantities available, and difficult laser desorption. The work presented here demonstrates the interest and the complementarity of two independent analytical methods, Taylor dispersion analysis (TDA) and capillary electrophoresis (CE), that require only very small amounts of sample (only a few nanoliters are injected) and that can be easily implemented on commercially available capillary electrophoresis apparatus. TDA is a nonseparative method that allows the absolute determination of the average hydrodynamic radius of the polymer. This method does not require the determination of the polymer concentration in the sample and is not perturbed by the presence of residual monomer. Since the average hydrodynamic radius determined by this method is a weight average value, it also gives information complementary to the average value derived from dynamic light scattering measurements. Simple hydrodynamic modeling allows estimation of a minimal value for the average degree of polymerization. Free solution CE can be used for monitoring the polymerization process and quantifying the degree of conversion. Furthermore, entangled polymer solution CE was used as a size-based separation technique for the characterization of the molar mass distribution using calibration with polyvinylpyridine standards. Number and weight molar mass distributions of the sample were obtained relative to this calibration

Guanidinium Alkynesulfonates with Single-Layer Stacking Motif: Interlayer Hydrogen Bonding Between Sulfonate Anions Changes the Orientation of the Organosulfonate R Group from “Alternate Side” to “Same Side”

International audienceHydrolyses of HCCSO3SiMe3 (1) and CH3CCSO3SiMe3 (2) lead to the formation of acetylenic sulfonic acids HCCSO3H·2.33H2O (3) and CH3CCSO3H·1.88H2O (4). These acids were reacted with guanidinium carbonate to yield [+C(NH2)3][HCCSO3] (5) and [+C(NH2)3][CH3CCSO3] (6). Compounds 1–6 were characterized by spectroscopic methods, and the X-ray crystal structures of the guanidinium salts were determined. The X-ray results of 5 show that the guanidinium cations and organosulfonate anions associate into 1D ribbons through R22(8) dimer interactions, whereas association of these ions in 6 is achieved through R22(8) and R12(6) interactions. The ribbons in 5 associate into 2D sheets through R22(8) dimer interactions and R36(12) rings, whereas those in 6 are connected through R12(6) and R22(8) dimer interactions and R46(14) rings. Compound 6 exhibits a single-layer stacking motif similar to that found in guanidinium alkane- and arenesulfonates, that is, the alkynyl groups alternate orientation from one ribbon to the next. The stacking motif in 5 is also single-layer, but due to interlayer hydrogen bonding between sulfonate anions, the alkynyl groups of each sheet all point to the same side of the sheet

Molecular Assemblies from Imidazolyl-Containing Haloalkenes and Haloalkynes: Competition between Halogen and Hydrogen Bonding

International audience1-(3-Iodopropargyl)imidazole and 1-(2,3,3-triiodoallyl)imidazole self-assemble to give polymeric chains as a result of N...I halogen bonding. However, these interactions are not sufficiently strong to compete with hydrogen bonding. N-H...O and N-H...N interactions govern the molecular arrangement in the 1:1 cocrystal of 1-(2,3,3-triiodoallyl)imidazole and morpholinium iodide

H-1, C-13, and N-15 Solid-State NMR Studies of Imidazole- and Morpholine-Based Model Compounds Possessing Halogen and Hydrogen Bonding Capabilities

The halogen and hydrogen bonding interactions present in solid 1-(2,3,3-triiodoallyl)imidazole (1), morpholinium iodide (2), the 1:1 cocrystal 1-(2,3,3-triiodoallyl)imidazole-morpholinium iodide (3), morpholine (4), imidazole (5), and 1-(3-iodopropargyl)imidazole (6) have been investigated by solid-state H-1, C-13, and N-15 NMR spectroscopies. Comparison of the N-15 CP MAS NMR spectrum of 3 with that of 2 indicates that protonated morpholine is present in solid 3, but this conclusion must be taken with caution as GIPAW calculations predict a N-15 chemical shift for morpholine similar to that of the morpholinium cation. Conclusive evidence for the presence of a morpholinium cation in crystalline 3 was obtained by recording the static N-15 NMR spectrum of this host-guest complex and comparing the morpholiniun/morpholine part of the spectrum with the static spectra of 3 and 4 as obtained from ab initio calculations of NMR parameters based on the X-ray structures of these compounds. Concerning the imidazolyl group, N-15 NMR spectroscopy has proven quite valuable to identify changes in the bonding situation of the C-N = C nitrogen on passing from 1 to 3. In addition, slight differences are observed between the N-15 chemical shifts of 1 and 6 that are ascribed to differences in halogen bond strengths between the two compounds. Attempts have also been made to study halogen bonding by C-13 NMR spectroscopy, but this method did not provide exploitable results as signals corresponding to the sp and sp(2) carbon atoms bonded to iodine could not be observed experimentally. H-1 NMR spectroscopy is a powerful tool to study hydrogen bonding interactions of moderate energies such as +NH2 center dot center dot center dot X (X = N, O, I). Indeed, we have found that the chemical shifts of the NH hydrogens were quite sensitive to the nature of X and to the N-H center dot center dot center dot X distance. This is demonstrated by the fact that the chemical shifts of the +NH2 protons of the morpholinium cation in 2 and 3 are noticeably different

Stark effect and Franz-Keldysh effect of a quantum wire realized by conjugated polymer chains of a diacetylene 3NPh2

International audienceConjugated polymer chains diluted in monomer single crystals of a diacetylene, 1,10-bis(diphenylamino)-4,6-decadiyne, represent quantum wires of long-range coherence. They differ from most polydiacetylenes by their repeat unit that consists of two C4 units with twisted molecular planes. The resulting modification of exciton and band states is studied by electroabsorption which resolves an increase in the exciton transition energy to 2.399 eV and of the free-electron gap to 3.158 eV. The Stark shift of the exciton reveals a significant reduction in the exciton radius by about 40% to 61 Å which is consistent with a similar increase in the exciton binding energy to 759 meV. The line shape of electroabsorption spectra at the free-electron gap is for fields larger than 30 kV/cm in accordance with the one-dimensional Franz-Keldysh effect and yields a reduced mass of 0.07m0 larger than in other polydiacetylene (PDA). Spectra at smaller fields are distorted by contributions of a weak dipole allowed and a forbidden exciton 38 and 12 meV, respectively, below the band gap. Coherent coupling of free electrons and vibrational modes leads to replicas of the Franz-Keldysh effect. Since light polarized parallel to the conjugated chain excites two propagating modes in the monomer crystals the quantitative analysis was restricted to electroabsorption spectra taken with perpendicular polarization in samples which transmit only the weakly absorbed polariton mode

Exciton spectroscopy of red polydiacetylene chains in single crystals

International audienceThe absorption and emission properties of excitons are investigated in a pure “red” phase of luminescent polydiacetylene wires. The values of the binding energy (Eb = 0.556 eV) and Bohr radius (r ~ 14 Å) make the “red” exciton similar to the one of the extensively studied “blue” phase, so the conformational modifications which lead to a reordering of excited states and luminescent emission do not strongly affect the exciton structure. The opening of a thermally activated non radiative channel leads to an efficient quenching of the intense luminescence observed at low temperature