Self-assembling phenylpropyl ether dendronized helical polyphenylacetylenes

The first example of a self-assembling phenylpropyl ether based dendronized polymer has been reported and its preferred helical handedness has been determined. Dendronized polymer poly(10) and its nondendritic analogue poly(8) are high-cis-content polyphenylacetylenes (PPAs) prepared by using [Rh(nbd)Cl]2/NEt3 (nbd: 2,5-norbornadiene). Both polymers possess a stereocenter in their side chain, which selects a preferred helical handedness. Based on negative exciton chirality observed in the CD spectra of poly(10), we have designated this molecule as a right-handed helical polymer, which persists over a wide temperature range. Poly(10) self-organizes into both Phiioh and Phih lattices in bulk. The Phiioh-to-Phih transition is associated with thermoreversible cis-cisoidal to cis-transoidal isomerization of the helical PPA, accompanied by a dramatic decrease in the column diameter and a decrease in the pi-stacking correlation length along the column. A model for the right-handed helical dendronized PPA has been proposed wherein dendrons from adjacent column strata interdigitate to effectively fill space.     

A bridge between pillared-layer and helical structures: a series of three-dimensional pillared coordination polymers with multiform helical chains

Rational self-assembly of a long V-shaped 3,3',4,4'-benzophenonetetracarboxylate (bptc) ligand and metal salts in the presence of linear bidentate ligand yield a series of novel pillared helical-layer complexes, namely, [Cu2(bptc)(bpy)2] (1), [M3(Hbptc)2(bpy)3(H2O)4].2 H2O (M = Fe(2) and Ni(3)), [Co2(bptc)(bpy)(H2O)].0.5 bpy (4), [Cd2(bptc)(bpy)(H2O)2].H2O (5), [Mn2(bptc)(bpy)1.5(H2O)3] (6) and [M2(bptc)(bpy)0.5(H2O)5].0.5 bpy (M = Mn(7), Mg(8) and Co(9), bpy=4,4'-bipyridine). Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric (TG) analyses. The structure of 1 consists of two types of chiral layers, one left-handed and the other right-handed, which are connected by bpy pillars to generate a novel 3D open framework featuring four distinct helical chains. Compounds 2 and 3 are isostructural and feature 3D structures formed from the interconnection of arm-shaped helical layers with bpy pillars. Compound 4 is a pillared helical double-layer complex containing four different types of helices, among which the nine-fold interwoven helices constructed from triple-stranded helical motifs are unprecedented. Compound 5 exhibits a novel 3D covalent framework which features nanosized tubular channels. These channels are built from helical layers pillared by bptc ligands. The structure of 6 is constructed from {Mn(bptc)(H2O)}n2n- layers, which consist of left- and right-handed helical chains, pillared by [Mn2(bpy)3(H2O)4]4+ complexes into a 3D framework. To the best of our knowledge, compounds 1-6 are the first examples of pillared helical-layer coordination polymers. Compounds 7-9 are isostructural and exhibit interesting 2D helical double-layer structures, which are constructed from {M(bptc)(H2O)2}n2n- ribbons cross-linked by [M2(bpy)(H2O)6]4+ complexes. Furthermore, the 3D supramolecular structures of 7-9 are similar to the 3D structure of 6, and the 2D structure of 7 can be transformed into the 3D structure of 6 at higher reaction temperature. By inspection of the structures of 1-9, it is believed that the V-shaped bptc ligand and V-shaped phthalic group of the bptc ligand are important for the formation of the helical structures. The magnetic behavior of compounds 1, 2, 4, 6, and 9 was studied and indicated the existence of antiferromagnetic interactions. Moreover, compound 5 shows intense photoluminescence at room temperature.     

Synthesis, structural analysis, and visualization of a library of dendronized polyphenylacetylenes

A library of eleven high cis-content cis-transoidal polyphenylacetylenes (PPAs) dendronized with self-assembling dendrons was prepared from a library of fifteen convergently synthesized macromonomers. Using [Rh(C triple bond CPh)(nbd)(PPh(3))(2)] (nbd=2,5-norbornadiene) in the presence of 10 equiv of N,N-dimethylaminopyridine, predictive control over molecular weight and narrow molecular weight distribution are obtained. The PPA backbone serves as a helical scaffold for the self-assembling dendrons. The dendron primary structure dictates the diameter of the cylindrical PPAs in bulk, both in the self-organized hexagonal columnar (Phi(h)) lattice determined by X-ray diffraction (XRD) and in monolayers on highly ordered pyrolytic graphite (HOPG) and mica visualized by atomic force microscopy (AFM). Thermal and bulk phase characteristics of the cylindrical PPAs reinforces the generality that flexible polymer backbones adopt a helical conformation within the cylindrical macromolecules generated by polymers jacketed with self-assembling dendrons.     

Optically active helical polymer from radical polymerization of menthyl vinyl ketone

Menthyl vinyl ketone (MVK) was radically polymerized to obtain a polymer with excess of one‐handed helical sense. Like as the anionically polymerized poly‐MVK, the radically polymerized poly‐MVK also kept stable one‐handed helical conformation in solvent. The optical rotation and the circular dichroism signal intensity of the radically polymerized poly‐MVK were larger than that of the anionically polymerized poly‐MVK. The molecular weight of the radically polymerized poly‐MVK was much larger than that of the THF‐soluble part of the anionically polymerized poly‐MVK. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

A thermally stable polymer molecular composite

A molecular composite of rigid-rod poly(p-phenylene benzobisthiazole) and flexible-coil poly(benzimidazobenzophenantroline) has been prepared, characterized, and shown to be thermally stable to at least 300°C. These results suggest that stable miscible blends of rodlike and coil-like polymers can be prepared by controlling the glass transition temperature of the flexible-coil polymer. © 1995 John Wiley & Sons, Inc.     

Synthesis,structural, and retrostructural analysis of helical dendronized poly(1‐naphthylacetylene)s

Structural and retrostructural analysis of chiral, nonracemic ( poly [(3,4,5)dm8G1‐1EN] ), and achiral ( poly[(3,4,5)12G1‐1EN] ) poly(1‐naphthylacetylene)s demonstrates new design principles for helical dendronized polyarylacetylenes. The oblate cylindrical dendronized polymers self‐organize in a c2mm centered rectangular columnar (Φ_r‐c) lattice. An all cis‐polyene backbone microstructure with very high cisoid character is introduced to rationalize features from small‐ and wide‐angle X‐ray diffraction experiments. More compact helical conformations are ideal for efficient communication or amplification of chirality over long distances. Peripheral chiral tails select a preferred helical screw sense of the polyene backbone. In solution, the preferred helical conformation persists over a wide temperature range. In bulk, the naphthyl moiety facilitates a longer correlation length for helical order compared to an analogous minidendritic poly(phenylacetylene). These attributes suggest that the naphthyl moiety may be better suited for expressing helical chirality in monolayer domains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4974–4987, 2007     

Determination of the helical screw sense and side-group chirality of a synthetic chiral polymer from Raman optical activity

Splitting it up: Excellent agreement between the experimental and the quantum-chemically simulated Raman optical activity (ROA) spectrum of (+)-poly(trityl methacrylate) shows that the polymer backbone adopts a left-handed helical conformation while the trityl side groups display a left-handed propeller conformation. Thus ROA can be used to determine the complete structure of synthetic chiral polymers in solution.     

Solvent‐induced helical conformation observed from a conjugated polymer poly(N‐octylcarbazole ethylene)

The formation of a cylinder‐like helical conformation induced by solvation was observed from a conjugated polymer poly(N‐octylcarbazole ethylene). The polymer was synthesized by McMurry condensation using N‐octyl‐3,6‐diformylcarbazole as monomer, in which the alkylcarbazolyl group was functioned as a turn angle. IR analysis indicated that the double bond in the polymer chain mainly takes a cis‐ conformation. Computer simulation revealed that the polymer could form into a hollow tubular nano‐structure with a cavity of less than 1 nm in diameter by folding its strand. The helical conformation formed by solvent induction was further proved by the measurements of circular dichroism (CD) spectrum, specific rotatory power and fluorescent (FL) spectra. Copyright © 2006 John Wiley & Sons, Ltd.     

Spontaneous resolution through helical assembly of a conformationally chiral molecule with an unusual zwitterionic structure

A conformationally chiral zwitterionic molecule forms mutually orthogonal helical superstructures in the crystal. This is achieved through a network of hydrogen bond pathways, and electrostatic interactions in crystals formed with and without water of crystallization. A systematic protocol for the computation of charge distribution on the 'molecule-in-the-crystal' is presented; the computed charges provide an insight into the origin of the intermolecular electrostatic interactions. The coexisting orthogonal helical formations lead to the homochiral assembly, and spontaneous resolution observed in the crystals. This material facilitates an appraisal of the molecular level interactions, which form the basis for the persistent spontaneous resolution of a conformationally chiral molecule in the solid state.     

Covalent connection of individualized, neutral, dendronized polymers on a solid substrate using a scanning force microscope

The synthesis of a neutral, high-molar-mass, acrylamide-based, third-generation dendronized polymer (denpol) with a defined number of azide groups at its periphery is reported. An attach-to route is used in which a first-generation denpol is reacted with second-generation (G2) dendrons. The degree of structure perfection of the resulting denpol is quantified as 99.8 %. This value was obtained after the introduction of a fluorescence label at the sites that remained unaffected by the dendronization. The high coverage was independently confirmed for the dendronization of another first-generation polymer and a closely related G2 dendron. The third-generation denpol resulting from the first dendronization experiment was spin-coated as a sub-monolayer onto highly oriented graphite precoated with an ultrathin layer of C12H25NH2, which was introduced to provide a well-defined substrate for denpol adsorption and manipulation. Scanning force microscopy revealed single denpols, which could be moved across the surface and "welded" by covalent cross-linking induced by photochemical decomposition of the azides into highly reactive nitrenes. The successful formation of covalent bonds between two denpols was confirmed by mechanically challenging the link with the scanning force microscope (SFM) tip. This is the second reported case of a move-connect-prove sequence using polymers and the SFM, which for the first time employs noncharged denpols, thus widening the applicability of this method significantly.     

The conformation of poly(3-dodecyl thiophene) within methacrylic polymer matrix

Blends of poly(3-dodecyl thiophene) (PDDT) with poly(methyl methacrylate), poly(butyl methacrylate) (PBMA), and poly(methyl methacrylate-co-butyl methacrylate) (PMMA/PBMA) were studied by polarization optical microscopy, atomic-force microscopy, and absorption spectroscopy and were modeled using molecular dynamics (MD) simulations. The observed thermochromic transitions are shown to be host-matrix dependent, with PDDT/PBMA absorption spectra differing substantially from pristine PDDT. The dispersion of PDDT within PBMA matrix is observed to be greater than in the other host polymers. MD calculations of both individual PDDT molecules and molecular aggregates suggest that the distribution of dihedral angles present in the PDDT backbone is the narrowest for aggregates of PDDT embedded within a polymer matrix. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2909–2917, 1999     

Lanthanide class of a trinuclear enantiopure helical architecture containing chiral ligands: synthesis, structure, and properties

The pinene-bipyridine carboxylic derivatives (+)- and (-)-HL, designed to form configurationally stable lanthanide complexes, proved their effectiveness as chiral building blocks for the synthesis of lanthanide-containing superstructures. Indeed a self-assembly process takes place with complete diastereoselectivity between the enantiomerically pure ligand L(-) and Ln(III) ions (La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er), thus leading to the quantitative formation of a trinuclear supramolecular architecture with the general formula [Ln(3)(L)(6)(mu(3)-OH)(H(2)O)(3)](ClO(4))(2) (abbreviated as tris(Ln[L](2))). This class of C(3)-symmetrical compounds was structurally characterized in the solid state and solution. Electrospray (ES) mass spectrometric and (1)H NMR spectroscopic analyses indicated that the trinuclear species are maintained in solution (CH(2)Cl(2)) and are stable in the investigated concentration range (10(-2)-10(-6) m). The photophysical properties of the ligand HL and its tris(Ln[L](2)) complexes were studied at room temperature and 77 K, thus demonstrating that the metal-centered luminescence is well sensitized both for the visible and near-IR emitters. The chiroptical properties of tris(Ln[L](2)) complexes were investigated by means of circular dichroism (CD) and circularly polarized luminescence (CPL). A high CD activity is displayed in the region of pi-pi* transitions of bipyridine. CPL spectra of tris(Eu[(+)-L](2)) and tris(Tb[(+)-L](2)) present large dissymmetry factors g(em) for the sensitive transitions of Eu(III) ((5)D(0)-->(7)F(1), g(em)=-0.088) and Tb(III) ((5)D(4)-->(7)F(5), g(em)=-0.0806). The self-recognition capabilities of the system were tested in the presence of artificial enantiomeric mixtures of the ligand. (1)H NMR spectra identical to those of the enantiomerically pure complexes and investigations by CD spectroscopic analysis reveal an almost complete chiral self-recognition in the self-assembly process, thus leading to mixtures of homochiral trinuclear structures.     

Synthesis of optically active poly(N‐propargylsulfamides) with helical conformation

A novel chiral N‐propargylsulfamide monomer ( 1a ) and its enantiomer ( 1b ) were synthesized and polymerized with (nbd)Rh⁺B^?(C₆H₅)₄ as a catalyst providing poly(1) (poly( 1a ) and poly( 1b )) in high yields (≥99%). Poly(1) could take stable helices in less polar solvents (chloroform and THF), demonstrated by strong circular dichroism signals and UV–vis absorption peaks at about 415 nm and the large specific rotations; but in more polar solvents including DMF and DMSO, poly(1) failed to form helix. Quantitative evaluation with anisotropy factor showed that the helical screw sense had a relatively high thermal stability. These results together with the IR spectra measured in solvents showed that hydrogen bonding between the neighboring sulfamide groups is one of the main driving forces for poly(1) to adopt stable helices. In addition, copolymerization of monomer 1a and monomer 2 was conducted, the solubility of poly(1) was improved drastically. However, the copolymerization had adverse effects on the formation of stable helices in the copolymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 500–508, 2007