Irina A. Khotina

Tetrahexylsexithiophene: crystal structure and molecular mechanics calculations

SUMMARY: The synthesis, crystal structure and detailed molecular mechanics calculations, including crystal packing interactions, of tetrahexylsubstituted sexithienylene are presented. Unexpectedly the molecule, which arranges in the P-1 space group, displays no herringbone arrangement, thienylenic rings are far from coplanarity and the alkylic side chains present different conformations. Molecular mechanics fully accounts for these findings. From crystal packing computations it is derived that different arrangements are unable to lower the packing energy, due to the closeness of two alkyl chains on the same side of the thienylenic backbone, which prevents interspersion of non-parallel molecules.

Aromatic Symmetric Cyclotrimers and Poly(arylenevinylene)s with Branched Aromatic Substituents in Vinylene Groups. Synthesis and Optical Properties

New poly(arylenevinylene)s were realized by Ni 0 -catalyzed polymerization of aromatic dibromides, containing vinylene groups substituted completely with branched oligophenylenes. The monomers were synthesized by acylation of 1,3,5-triphenylbenzene or 1,3,5-tri-diphenylyl)benzene with 4-bromobenzoyl chloride followed by the McMurry homocondensation in the presence of TiCl 4 and Zn. Model cyclotrimers with 1,3,5-trisubstituted benzene core were synthesized and characterized. Their molar extinction coefficients and luminescence quantum yields were in the ranges (0.5-1.5) . 10 5 M -1 . cm -1 and 29-72%, respectively. The highest quantum yield 92% promising for further photophysical investigation was found for the cyclotrimer with tolan as substitutent. The quantum yield of the cyclotrimers depended on both the symmetry of molecules and the amount of benzene rings in the ambience. The incorporation of the substituents of three-dimensional structure instead of benzene rings led the polymers to become rather highly emissive with fluorescence quantum yields of 22-23% in comparison to the value of 1% of polymer with benzene rings.

Platinum nanoparticles generated in functionality-enhanced reaction media based on polyoctadecylsiloxane with long-chain functional modifiers.

Functionality-enhanced nanostructured matrices generated by intercalating polyoctadecylsiloxane (PODS) with octadecene (ODC) or octadecylamine (ODA) are employed as reaction media in which to grow Pt nanoparticles. Small-angle X-ray scattering (SAXS) signatures confirm that the amphiphilic PODS matrix orders into lamellae with a periodicity (d) of 5.24 nm, which corresponds to the siloxy bilayer and a double layer of alkyl tails. The regular packing of the hydrophobic tails becomes distorted upon introduction of ODC or ODA. Incorporation of K[(C2H4)PtCl3].H2O (a Zeise salt) into the PODS/ODC matrix, followed by reduction of the Pt ions by NaBH4 or H2, results in the localization of Pt compounds and nanoparticles along the siloxy bilayers, which remain dimensionally unchanged. Electron density profiles deduced from PODS/ODA, however, provide evidence for considerable structural reorganization upon metalation with H2PtCl6.6H2O. In this case, the siloxy bilayers broaden due to the presence of PtCl62- ions, and the hydrophobic layers become distorted due to the formation of (PtCl62-)(ODAH+)2 complexes. Subsequent reduction by NaBH4 restores the inherent PODS organization, while H2 reduction partially preserves the distorted matrix, indicating that some Pt nanoparticles form in close proximity to the siloxy bilayer. Transmission electron microscopy reveals that relatively monodisperse Pt nanoparticles measuring approximately 1 nm in diameter are located along the siloxy bilayers, whereas anomalous SAXS further indicates that nanoparticles form aggregates of comparable size to d within the PODS double layers.

Preparation and characterizations of soluble regularly alternating polyazomethines from oligothienylenes

The preparation and characterization of oligothienylene dialdehydes and related soluble copolymers in which thenylenic segments regularly alternate with phenylenic portions linked by azomethine moieties is presented. The polymer series with three, six and eight thienylenic residues showed interesting evidences of electronic confinement in low-gap segments (thienylenic). Self-assembled structures of oligomers can be obtained either by evaporation in high vacuum or by a proper thermal treatment of spin coated films, depending on the molecule length. Polymers prepared by different synthetic routes show different thermal and structural properties as a function of the ratio of two possible isomers at imino linkage. The order degree also influences the optical properties in fact luminescence data are strictly related to the percentage of the two isomers.

Synthesis and Characterization of New Poly(arylene ethynylene)s Based on 3-Hexyl Multisubstituted Oligothiophene Blocks

A series of new regioregular poly(arylene ethynylene)s were prepared by Pd-catalyzed condensation of 3-hexyl multisubstituted oligothiophene derivatives with either benzene or anthracene compounds. The NMR characterization of the starting materials and model compounds lead to a thorough investigation of the corresponding macromoleculs. Both small and large molecules were characterized by optical methods. The former, particularly when containing anthracene moieties, display noticeable photoluminescence quantum yields. In the polymers, the photoluminescence quantum yields is lower than that of the starting materials when anthracene is present, while the polymers containing benzene show higher quantum yields.

Synthesis and crystal structure of 1,3,5-tris [4-(phenylethynyl)phenyl]benzene

The crystal structure of 1,3,5-tris[4-(phenylethynyl)phenyl]benzene (1) has been investigated. Compound1 represents a model of the repeating unit of the most typical polyphenylene, which contains 1,3,5-trisubstituted benzene rings (chain centers) and acetylenic groups (complex-forming and cross-linking centers) in the main chain. The acetylene groups of neighboring molecules have a tendency to close mutual arrangement, which is favorable for their topochemical interaction. However, the relative conformational rigidity of molecules1 restricts not only the possibility of the optimal adjustment of the reactive sites of neighboring molecules to one another, but also hampers the close packing of molecules in the crystal, which contains channels filled by the solvent molecules (chloroform).

Synthesis of new aryl and hetaryl dibromides and diiodides, the monomers for preparation of polyarylene ethynylenes

Dibromides and diiodides with quinoxaline, phenylimidazole, and hexa- or pentaphenylarylene fragments were synthesized from dihalotolans obtained from chloral. Oligoarylene ethynylenes were synthesized by the reaction of the monomers with equimolar amounts of diethynyl aromatic compounds in the presence of the PdII complex. Oligomers with imidazole and hexa(penta)arylbenzene cycles are soluble in amide organic solvents and their reduced viscosities do not exceed 0.09 dL g−1.

Synthesis of novel bis- and polyarylene ethynylenes by cross-coupling catalyzed by palladium complexes

A novel carborane-containing compound with ethynyl groups, 1,2-bis[4-(4′-ethynylphenoxy)phenyl]-o-carborane, was synthesized. Cross-linking with 4-iodo- and 4,4′-diiododiphenyl ethers catalyzed by Pd complexes afforded the model bis-arylene ethynylenes and the corresponding polymers. The introduction of a carborane nucleus into the structure of the model compounds and polymers was shown to render these systems soluble.

Branched oligophenylenes containing octylphenotiazine and dioctylfluorene groups and phen-1,3,5-triyl branching center

A series of branched oligophenylenes containing the dioctylfluorene and octylphenothiazine moieties was synthesized using the Suzuki reaction applied within the framework of the A2 + B2 + B3 approach. 1,3,5-tris(7-Bromo-9,9-di-n-octylfluoren-2-yl)benzene and 1,3,5-tris- (4-bromophenyl)benzene were used as the branching co-monomers. It was shown that the fluorescence spectra of co-oligomers containing phenothiazine moieties are shifted to the longwavelength region as compared to the spectra of that without such moieties.

Study of structural aspects of thermochemical conversions of compounds modeling oligophenylenes containing acenaphthylenyl and acenaphthenyl groups

With the aim of elucidating the mechanism of the thermochemical conversion of oligophenylenes containing acenaphthylenyl groups, the thermolysis of model compounds: l,3,5-tris(5-acenaphthylenyl)benzene (1), 1,3,5-tris(5-acenaphthenyl)benzene (2), acenaphthylene, and acenaphthene, was studied by differential thermal analysis (DTA), dynamic thermogravimetric analysis (TGA), and mass spectrometry. Compounds1 and2 were studied by X-ray structural analysis. A scheme for the formation of secondary structures was suggested. Optimum temperature conditions were found for preparing thermostable, heat-resistant, and stable to thermooxidation polymers based on compounds containing the acenaphthylenyl groups.