Sylvain G. Dutremez

Polymorphs and colors of polydiacetylenes: a first principles study.

Polydiacetylenes (PDAs) are exceptional polymeric materials with pi-conjugated backbones. Several of them can undergo chromogenic transitions under a wide range of external stimuli. Herein we investigate the electronic structure and the resulting properties of model and experimental PDAs, by means of first principles condensed matter calculations. It is shown that torsional isomers with a twist of the lateral groups can be formed at small energetic costs. We also show the relationship that exists between these twists and the observed changes in the electronic and physical properties. In particular, the calculated changes in the absorption, Raman and NMR spectra agree with the color and property changes as observed experimentally. Therefore, these isomers are excellent models for the structures involved in the chromogenic transitions.

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

A novel strategy for the preparation of nitrogen-doped carbon is presented that is based on the use of azole-functionalized diacetylenic precursors (imidazole and benzimidazole). As demonstrated by thermal analyses (TGA, DSC) and spectroscopic measurements (IR, 13C solid-state NMR), these diacetylenic molecules undergo exothermic polyaromatization at low temperature. This process is independent of the intrinsic ability of the diacetylenes to undergo solid-state topochemical polymerization. At 800 °C, graphite-like structures incorporating nitrogen are obtained, as proven by XPS measurements. The nitrogen contents of the residues resulting from thermolysis at 800 °C are fairly high, 7.4 and 8.4 wt%, and these percentages amount to about 4 wt% at 1100 °C. This study also shows that mixing these diacetylenes with small amounts of FeCl2 prior to pyrolysis at 800 °C leads to porous carbon materials with relatively high surface areas, 253 and 281 m2 g−1. TEM photographs indicate that these porous carbon materials form graphitic nanostructures. Polydiacetylenes also decompose into graphite-like materials, and the degree of graphitization of these materials and their nitrogen contents are comparable to those of the residues obtained by pyrolysis of the diacetylene monomers. Thus, low molecular weight diacetylenic monomers are effective precursors to access graphite-like materials, and this process does not require the prior preparation of a polymer.

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

Hydrolyses of HC[triple bond]CSO3SiMe3 (1) and CH3C[triple bond]CSO3SiMe3(2) lead to the formation of acetylenic sulfonic acids HC[triple bond]CSO3H.2.33H2O (3)and CH3C[triple bond]CSO3H.1.88H2O (4). These acids were reacted with guanidinium carbonate to yield [+C(NH2)3][HC[triple bond]CSO3] (5) and [+C(NH2)3][CH3C[triple bond]CSO3] (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 R2(2)(8) dimer interactions,whereas association of these ions in 6 is achieved through R2(2)(8) and R1(2)(6) interactions. The ribbons in 5 associate into 2D sheets through R2(2)(8) dimer interactions and R3(6)(12) rings, whereas those in 6 are connected through R1(2)(6)and R2(2)(8) dimer interactions and R4(6)(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.

DIETHYL ETHYNYLPHOSPHONATE: A VERSATILE SYNTHON FOR THE PREPARATION OF 1-ALKYNYL- AND 1,3-BUTADIY NE-1,4-DIYLPHOSPHONATES

Abstract The cross-coupling reaction between diethyl ethynylphosphonate (1) and several aromatic iodides under the Sonogashira conditions (Cl2Pd(PPh3)2/CuI/Et3N) gives only minute amounts of the expected 1-alkynylphosphonates. Yields of about 20% are achieved upon using Pd(OAc)2/2PPh3/Et3N in place of the previous catalytic system. Side-reactions involving 1 and the mine are shown to be responsible for these low yields. Metalation of 1 with EtMgBr and t-BuLi has been carried out and the M-C≡C-P(O)(OEt)2 (M = MgBr, Li) derivatives have been characterized via reaction with Me3SiCl or Ph3iCl. The easy access to the organolithium compound has made possible the synthesis of the zinc analog (M = ZnCl) which reacts with aromatic iodides (C6H5I, p-MeOC6H41, p-O2NC6H4I, p-1C6H4I, 2-iodothiophene), in the presence of Pd(PPh3)4, to give diethyl 1-alkynylphosphonates in reasonable yields. Oxidative dimerization of 1 under the Hay conditions (CuCl/TMEDA:acetone/air) gives the symmetrical diacetylenic diphosphonate (EtO)2(O)P-C≡C-C≡C-P(O)(OEt)2 in high yield.

Diacetylenes with Ionic‐Liquid‐Like Substituents: Associating a Polymerizing Cation with a Polymerizing Anion in a Single Precursor for the Synthesis of N‐Doped Carbon Materials

Imidazolium- and benzimidazolium-substituted diacetylenes with bromide or nitrogen-rich dicyanamide and tricyanomethanide anions were synthesized and used as precursors for the preparation of N-doped carbon materials. On pyrolysis under argon at 800 °C both halide precursors afforded graphite-like structures with nitrogen contents of about 8.5%. When the dicyanamide and tricyanomethanide precursors were thermolyzed at the same temperature, graphite-like structures were obtained that exhibit nitrogen contents in the range 17-20 wt%; thereby, the benefit of associating a polymerizing cation with a polymerizing anion in a single precursor was demonstrated. On pyrolysis at 1100 °C the nitrogen contents of the latter pyrolysates remain high (ca. 6 wt%). Adsorption measurements with krypton at 77 K indicated that the materials are nonporous. The highest electrical conductivity was observed for a pyrolysate with one of the lowest nitrogen contents, which also has the highest degree of graphitization. Thus, the quest for N-rich carbons with high electrical conductivities should include both maximization of the nitrogen content and optimization of the degree of graphitization. Crystallographic investigation of the precursors and spectroscopic characterization of the pyrolysates prepared by heating at 220 °C indicate that construction of the final carbon framework does not involve the intermediate formation of a polydiacetylene.

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

1,6-Bis(1-imidazolyl)-2,4-hexadiyne (1) and 1,6-bis(1-benzimidazolyl)-2,4-hexadiyne (5) have been prepared by 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. Diyne 1 crystallizes as a hydrate, 1·H2O (2). For this compound, water is essential to achieve a crystalline material, and attempts to obtain crystals without included solvent were unsuccessful. In the structure of 2, the organic fragments organize around the water molecule and interact with it through a dense network of hydrogen bonds. The CC–CC moieties are not oriented suitably for topochemical polymerization, and when trying to alter the organization of 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 removed in vacuo at room temperature. The benzimidazole-containing compound can be crystallized with water molecules (4) or without (5). X-ray crystallography shows that the structure of 5 is organized by numerous C–H⋯N, C–H⋯π, and imidazolyl⋯imidazolyl π–π interactions. The diacetylene molecules almost have the right arrangement for topochemical polymerization, with possibly reacting CC–CC fragments not being parallel, a rare situation in diacetylene chemistry. Yet, experiments show that topochemical polymerization does not occur. Incorporation of water in the lattice of 5 leads to a solvate that is topochemically reactive. Unlike 2, however, water molecules in 4 are not isolated but are organized as ribbons. Spectroscopic characterization of the polymer of 4 indicates 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 range of solvents available, and one does not face the problem of having to remove the host in case one needs to recover the polymer. Previous studies describing a similar approach are scarce.

A Flexible Diacetylene-Based Mixed-Linker MOF with Two Low-Temperature Phase Transitions and Colossal Positive and Negative Thermal Expansions

Solvothermal reaction in N,N-dimethylformamide (DMF) between 1,6-bis(1-imidazolyl)-2,4-hexadiyne monohydrate (L1⋅H2 O), isophthalic acid (H2 L2), and Zn(NO3 )2 ⋅6 H2 O gives the diacetylene-based mixed-ligand coordination polymer {[Zn(L1)(L2)](DMF)2 }n (UMON-44) in 38 % yield. Combination of DSC with variable-temperature single-crystal X-ray diffraction revealed the occurrence of two phase transitions spanning the ranges 129-144 K and 158-188 K. Furthermore, the three structurally similar phases of UMON-44 show giant negative and/or colossal positive thermal expansions. These unusual phenomena exist without any change in the contents of the unit cell. DFT calculations using the PBE+D3 dispersion scheme were able to distinguish between these polymorphs by accurately reproducing their salient structural features, although corrections in the size of the unit cell turned out to be necessary for the high-temperature phase to account for its large thermal expansion. In addition, the infrared spectra (vibration frequencies and peak intensities) of these theoretical models were calculated, allowing for univocal identification of the corresponding polymorphs. Last, the limits of our computational method were tested by calculating the phase transition temperatures and their associated enthalpies, and the derived figures compare favorably with the values determined experimentally.