Fine structural analysis,formation of interfacial particle films,and accurate estimation of orientation in polyguanamine derivatives with a high refractive index

Precise analyses of the molecular arrangement of three‐dimensional crystals, two‐dimensional molecular films, and interfacial particle layers of polyguanamine derivatives with a high refractive index have been performed. The high refractive index of the polyguanamine derivatives is not due to the chemical structure of the molecule, but is based on the packing of molecular chains or the refraction of transmitted light due to the difference in electron density between the crystalline and amorphous regions. A highly crystalline polymer has been produced by polycondensation of guanamine derivatives bearing a triazine ring and phenyl rings. The packing models of molecular chains in the three‐dimensional crystal have been determined using wide‐angle X‐ray diffraction measurements and reciprocal lattice analysis. Highly hydrophobic polyguanamine derivatives undergo a transition from monolayer to single particle layer at the air/water interface. The π‐conjugated molecular plane in the two‐dimensional films is densely stacked. Multiparticle layers are formed with a highly ordered layered structure. Polymer nanoparticles are formed by the integration of units of the collapsed polymer monolayer folded along the height direction. Since this folding occurs within the amorphous region, formation of fine particles with a high refractive index and their integrated films with densely packed π‐conjugated planes is feasible. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 999–1009     

Unraveling Inter‐ and Intrachain Electronics in Polythiophene Assemblies Mediated by Coordination Nanospaces

Strong interchain interactions render unsubstituted polythiophene un‐fusible, non‐melting, and insoluble. Therefore, control of the packing structure, which has a profound effect on the optical and electronic properties of the polymer, has never been achieved. Unsubstituted polythiophene was prepared in the one‐dimensional channels of [La(1,3,5‐benzenetrisbenzoate)]_n, where polymer chains form unprecedented assembly structures mediated by the host framework. It is noteworthy that the emission and carrier transport properties were drastically changed by varying the number of chains within a particular assembly. The response of the composite to additional guests is also examined as a method to use the composites as low‐concentration sensors. Our findings show that the encapsulation of polymer chains in host materials is a facile method for understanding the intrinsic properties of conjugated polymers, along with controlling and enhancing their functions.     

Molecular mobility and structuring in textured films of the ferroelectric copolymer of vinylidene fluoride with tetrafluoroethylene

The processes of molecular mobility in vinylidene fluoride–tetrafluoroethylene ferroelectric copolymer–based films textured via uniaxial drawing are studied. It is found that the cooperative mobility in the amorphous regions of the copolymer is described by the Vogel–Fulcher equation, whose parameters are sensitive to the drawing conditions. It is shown that a decrease in the drawing temperature causes a reduction in the effective activation energy of the above-mentioned motion. In accordance with the X-ray diffraction data, this circumstance may be explained by an increase in the packing density of chains in interlamellar spaces. This effect is partially provided by deformation-induced processes of formation of small and defective crystals of the paraelectric or antiferroelectric phase in spaces between neighboring lamellar crystals at the primary stage of crystallization. The relationship between the value of the orientational polarization in oriented films and the topology of structure formation in microfibrils is discussed. It is observed that enlargement of the interlamellar space (filled with a liquidlike amorphous phase) between neighboring crystals in microfibrils promotes an increase in the orientational polarization of chains in the amorphous phase.     

Interpreting molecular crystal disorder in plumbocene,Pb(C5H5)2: insight from theory

Plane-wave density functional theory has been applied in a novel way to help interpret the molecular crystal structure disorder observed in the orthorhombic zigzag phase of plumbocene, Pb(C5H5)2. A crystal lattice comprising uniformly staggered C5H5 rings was found to be lower in energy by 2.8 kJ mol-1 per unit cell, compared to a uniformly eclipsed packing arrangement. This energy difference has been attributed to the difference in the strength of intermolecular interactions between the Pb(C5H5)2 chains for the two different lattices. The calculations performed allowed the determination of the crystallographic occupancy factors by a quantum mechanical technique for the first time.     

Prediction of the Crystalline Structure of a Novel Polythiophene Using Molecular Dynamics Simulations

A novel polythiophene, poly(3-acetamido-undecanoic-succinimidyl-thiophene), has been synthesized and characterized by using IR, RMN, X-ray, DSC, and density measurements. Powder X-ray analysis shows that the polymer crystallizes in a distinct lamellar structure with a spacing of ～23 Å. Fine details at large diffraction angles indicated the presence of a three-dimensional crystalline structure although the data were insufficient to resolve the exact form of this structure. DSC measurements showed two distinct melting peaks a few degrees apart, which are possibly linked to a liquid-crystal intermediate phase. In a second stage, molecular dynamics (MD) simulations have been used in an attempt to predict the crystal structure and to shed light on the double melting peak behavior. Based on the initial assumption that the polymer backbones are parallel and the aliphatic side chains are linear (all trans), three trial starting configurations have been generated, energy minimized, and then allowed to relax by using constant pressure-constant temperature MD. Two of these systems have been followed for over 1 ns of elapsed time. Although both of these latter systems maintain a linear ordering of the polymer backbones, one shows a low degree of order in the arrangement of the side chains, whereas the other shows a high degree of order. Comparisons are made between the properties of the two systems and model X-ray diffractograms are presented and compared with experimental data.     

Monte Carlo simulations of a liquid crystal copolymer in the solid state

The condensed phase of the alternating copolyester of p-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) is investigated by studying the room temperature packing arrangement of the copolymer chains. A molecular modeling methodology is employed with a Monte Carlo sampling of the configurational phase space. Realistic poly(HBA-alt-HNA) polymer chains are represented by an explicit atom representation of the HBA/HNA dimers. States are sampled from the NVT ensemble using a sampling scheme consisting of (1) valence and torsional variations, (2) rigid body rotations of the chain about the chain axis, and (3) rigid body translations of the chain. The effect of chain packing on the conformation of chains, as well as the relative intra- and intermolecular orientations of aromatic rings, is investigated. Correlation of chain positioning along the chain axis is dominated by aromatic rings maintaining a center-to-center plane of registry. These layers of aromatic units pack with a preference for edge-to-face orientations in a herringbone-type pattern and have an intermolecular ring angle between the pairs of aromatic rings in the unit cell that is ca. 68°. The aromatic rings, on average, are rotated 38° out from the b–c plane. The phenylene rings of these copolyesters are less restricted in their relative orientation in comparison to the naphthalene rings. Intramolecular orientational probability density distributions indicate a preference for staggering the successive aromatic rings along the chain, with a staggering angle of ca. 66°. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 727–741, 1998     

Electrochromic properties of polythiophene polyrotaxane film

The electrochromic properties of a polythiophene polyrotaxane film consisting of a polythiophene backbone wrapped by the tetra-cationic cyclophane, cyclobis(paraquat-p-phenylene), were characterized. A naked reference polythiophene film, i.e., polythiophene without tetra-cationic cyclophane, was also characterized. The surface morphology and thickness of the film (L) were observed by atomic force microscopy. The surface of the naked reference polythiophene film has micrometer-scale polythiophene aggregates, which causes the darker color of the film and smaller color contrast in the electrochromic process. The polythiophene polyrotaxane gives a more homogeneous and brighter colored film owing to the suppression of molecular interactions between the polythiophene chains by the tetra-cationic cyclophanes. Potential-step chronoamperometric measurement provided the area density of the oxidizable sites (Γ) and the apparent diffusion coefficient of the charge transport in the film. From linear relationship between L and Γ, the concentrations of the oxidizable sites in the polythiophene polyrotaxane and naked reference polythiophene films were calculated to be 1.3 and 2.4 mmol cm(-3), respectively. Interestingly, the polythiophene polyrotaxane film afforded a significantly larger apparent diffusion coefficient than the naked reference polythiophene film. This result suggests that the rate-determining step of the charge transport is not the electron hopping between the polythiophene chains but the transport of charge-compensating counterions from the solvent into the polythiophene. We believe that the counteranions of the tetra-cationic cyclophane provide a pathway allowing the charge-compensating counteranions to migrate from the solvent to polythiophene. The polythiophene polyrotaxane film showed faster color change than the naked reference polythiophene film in the electrochromic reaction. These results indicate that our polythiophene polyrotaxane is a better electrochromic material than the naked reference polythiophene.     

Highly Ordered Columnar Structures from Hexa-peri-hexabenzocoronenes—Synthesis,X-ray Diffraction,and Solid-State Heteronuclear Multiple-Quantum NMR Investigations

Improved long-range ordering in the columnar mesophase of hexa(para-n-dodecylphenyl)hexabenzocoronene 1 has been achieved by inserting phenyl rings between the extended aromatic core of hexabenzocoronene and the alkyl side chains, which are needed to form liquid crystalline phases. The long-range hexagonal order of the columns is demonstrated by X-ray scattering, while the improved packing of the aromatic cores within the columns and the molecular mobility is probed by a newly developed heteronuclear multiple-quantum MAS NMR technique.     

Structural characteristics of some metallo-organic discogens

We have recently analysed the crystal and molecular structures of six metalloorganic discogens with substituted β-diketone ligands. The molecules consist of a rigid 11 atom core and a fringe made up of four phenyl rings substituted with alkyl/alkoxy chains. In complex (i), with four octyloxy chains, there are four oxygen atoms around the core. Complex (ii) is asymmetrically substituted with two heptyloxy and two heptyl chains and therefore has two oxygen atoms and complexes (iii) to (vi) have only alkyl chains and hence no oxygen atoms around the core. The metal atom used for coordination has been chosen as Cu/Pd/Ni. Determination of the crystal and molecular structures of these discogens has led to the identification of the following similarities: (1) All the six discogens crystallize in the triclinic space group P1. The recurrence of the space group may be correlated with the structural requirements for efficient packing of the molecules in the crystal lattice. (2) The coordination around the metal atom is square planar. (3) The 11 atom core is only nearly planar. (4) The phenyl rings and the chains are tilted with respect to the core. (5) The molecular conformation in the crystal confers a nearly rectangular shape to these discogens. (6) The chains are fully extended in an all trans conformation. (7) The molecular arrangement is tilted columnar except for the crystal structure of complex (ii).

In addition to the similarities, distinct differences in the crystal structural characteristics have also been observed. For example, when oxygen atoms are present in the fringe, the molecules have no crystallographic symmetry and they tend to pair. In the crystal structure of (i) where the repeat unit along the column is a molecular pair, the metal atoms are distributed in a zig-zag fashion. In the other crystals with columnar arrangement, the metal atoms are stacked one over another. Complex (ii) has a layer-like molecular arrangement in the crystalline phase.     

Odd and even model self-assembled monolayers: links between friction and structure

The friction between an amorphous carbon tip and two n-alkane monolayers has been examined using classical molecular dynamics simulations. The two monolayers have the same packing density, but the chains comprising each monolayer differ in length by one -CH2- unit. The simulations show that the monolayers composed of C13 chains have higher friction than those composed of C14 chains when sliding in the direction of chain cant; the difference in friction becomes more pronounced as the load is increased. Examination of the contact forces between the chains and the tip, along with conformational differences between the two chain types, lends insight into the friction differences.     

A self-threading polythiophene: defect-free insulated molecular wires endowed with long effective conjugation length

Herein, we report on a self-threading polythiophene whose conjugated molecular wire is sheathed within its own cyclic side chains. The defect-free insulating layer prevents electronic cross-communication between the adjacent polythiophene backbone even in the solid film. Notably, the covalently linked cyclic side chains extend the effective conjugation length of the interior polythiophene backbone, which results in an excellent intrawire hole mobility of 0.9 cm(2) V(-1) s(-1).     

Twisting of conjugated oligomers and polymers: case study of oligo- and polythiophene

Interring twisting (change in the dihedral angle between conjugated rings) of polythiophene was studied theoretically using periodic boundary conditions (PBC) at the B3LYP/6-31G(d) level. We find that the band gap of polymers is strongly dependent on the interring twist angle; yet twisting requires very little energy. A twist of 30 degrees increases the band gap by 0.75 eV in polythiophene, while requiring only 0.41 kcal mol(-1) per monomer unit. Such a small energetic value is of the order of crystal packing or van der Waals forces. These results are compared with calculations performed on model oligomers. Sexithiophene, its radical cations, and its dication are optimized at 0-180 degrees end-to-end twist angles (which correspond to 0-36 degrees interring dihedral angles) using the B3LYP/6-31G(d) method. The theoretical results suggest that the HOMO-LUMO gap, ionization potential, and charge distribution of oligomers are strongly dependent on twisting, whereas, similar to the case of polythiophene, twisting of neutral oligothiophenes costs very little energy. In the case of the radical cation, the lowest energy transition is shifted to a longer wavelength region on twisting, while the second-lowest energy transition is shifted to a shorter wavelength region. This implies that twisted, doped conducting polymers (modeled here by an oligomer radical cation), in contrast to planar, doped polymers, should be transparent within a certain optical window (in the far-visible region, at approximately 1.5 eV). This observation is explained on the basis of changes in the shape and overlap of the frontier molecular orbitals.     

Study of temperature transitions in solid poly(oxymethylene) by thermal analysis methods

Poly(oxymethylene)s with different molecular mass and chemical structure were studied using DSC, dynamic mechanical relaxation, thermomechanical analysis, and thermogravimetry.Molecular mobilities of two types were found in the amorphous phase of poly(oxymethylene). Unconstrained chains of poly(oxymethylene) soften at –70°C and then amorphous chains with different restraints from the crystalline phase are successively activated in a wide temperature interval.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayThis work has been supported by DuPont Company     

Ethylene–chlorotrifluoroethylene copolymers. II. Effects of structure on resistance to thermal stress cracking

Copolymers of ethylene and chlorotrifluoroethylene that contain small amounts of units derived from perfluorohexylethylene show improved resistance of thermal stress cracking. This is a consequence of effects of these units on structural parameters of both the crystalline and amorphous phases. Those of the crystalline phase entail growth and organization of lamellae, whereas those of the amorphous phase are related to conformation and packing of polymer chains. The crystalline phase consists exclusively of alternately arranged units of ethylene and chlorotrifluoroethylene. The amorphous phase is characterized by chain segments composed of randomly distributed units derived from ethylene, chlorotrifluoroethylene, pairs of these two units, and units derived from perfluorohexylethylene.     

Synthesis of Self‐Threading Bithiophenes and their Structure–Property Relationships Regarding Cyclic Side‐Chains with Atomic Precision

We have recently reported a self‐threading polythiophene as a new family of insulated molecular wires. Herein, we focused on the structure–property relationships of the unique three‐dimensional architecture of the monomer. We have synthesized nine self‐threading bithiophene monomers that have cyclic side‐chains of different size and flexibility: i.e., 21‐, 22‐, 23‐, 24‐, 26‐, and 30‐membered rings composed of paraffinic, olefinic, or alkynic chains. To investigate their structure–property relationships, ¹H NMR spectroscopy, UV absorption, and fluorescence spectroscopy measurements were conducted. We found that cyclic side‐chains define the movable range of the dihedral angle of the bithiophene backbone, thereby affecting its photophysical properties. Therefore, the ability to design a structure with atomic precision as described herein would lead to the fine‐tuning of the electronic properties of insulated molecular wires.     

Amylose‐grafted Curdlan: A New Class of Semi‐artificial Branched Polysaccharides for Hierarchical Polymeric Superstructures Created by the Action of “Orthogonal” Binding Sites

The semi‐artificial branched‐polysaccharides, amylose‐grafted curdlans, were synthesized utilizing an enzymatic polymerization. Both a curdlan main chain and amylose side chains on the polysaccharides maintain the original helical structure as well as the molecular binding ability. Thanks to the difference in their molecular recognition properties between β‐1,3‐glucan chain and α‐1,4‐glucan chain, the amylose‐grafted curdlans can provide two different orthogonal binding sites within one polymeric system. When a water‐soluble polythiophene was mixed with the amylose‐grafted curdlan, the polythiophene was twisted in two different modes and therein, fluorescence energy of the polythiophene wrapped by the amylose side chains was successfully transferred to the polythiophene wrapped by the curdlan main chain. We thus concluded that in the dendritic superstructure of this polysaccharide, a self‐organized “Janus‐type FRET system” was successfully constructed.     

Self-assembly of amphiphilic hexapyridinium cations at the air/water interface and on HOPG surfaces.

Mono- and multilayers of a novel amphiphilic hexapyridinium cation with six eicosyl chains (3) are spread at the air/water interface as well as on highly ordered pyrolytic graphite (HOPG). On water, the monolayer of 3 is investigated by recording surface pressure/area and surface potential/area isotherms, and by Brewster angle microscopy (BAM). Self-organized tubular micelles with an internal edge-on orientation of molecules form at the air/water interface at low surface pressure whereas multilayers are present at high surface pressure, after a phase transition. Packing motifs suggesting a tubular arrangement of the constituting molecules were gleaned from atomic force microscopy (AFM) investigations of Langmuir-Blodgett (LB) monolayers being transferred on HOPG at different surface pressures. These LB film structures are compared to the self-assembled monolayer (SAM) of 3 formed via adsorption from a supersaturated solution, which is studied by scanning tunnelling microscopy (STM). On HOPG the SAM of 3 consists of nanorods with a highly ordered edge-on packing of the aromatic rings and an arrangement of alkyl chains which resembles the packing of molecules at the air/water interface at low surface pressure. Additional details of the molecular packing were gleaned from single-crystal X-ray structure analysis of the hexapyridinium model compound 2b, which possesses methyl instead of eicosyl residues.     

LOW POTENTIAL ELECTROPOLYMERIZATION OF ANISOTROPIC CONDUCTIVE POLYTHIOPHENE FILMS AND FABRICATION OF ELECTRICAL DEVICES

The complexation of thiophene with a Lewis acid with moderate acidity as a solvent, such as BF_3-ethyl ether (BFEE) remarkedly lowered the electrochemical polymerization potential. The positively chargedmetal surface of electrode in the process of electrochemical deposition enhanced the coordination interactionbetween π-electrons of thiophene unit and the metal, which makes thiophene rings lie parallel to the surfaceof electrode, resulting in a highly ordered polymeric structure. Because of the large intra-chain transferintegrals, the transport of charge is believed to be principally along the conjugated chains, which is muchgreater than the inter-chain hopping. The specific electrical resistance across the polythiophene film thicknessis more than 10~4 times than that along the surface plane of the film. In this paper we review the recentdevelopment of polymerization technique by low potential electrochemical method performed in our lab andseveral electrical devices in which the compact polythiophene films, such as anionic and cationic sieves, andlaminate film junction of undoped polythiophene derivatives were used.     

RADIAL DISTRIBUTION FUNCTION OF cis-1,4-POLYBUTADIENE BY ELECTRON DIFFRACTION

The interatomic distance function of rareearth catalyzed cis-1,4-polybutadiene was studied by" radial distribution function (RDF) derived from electron diffraction. Two intramolecular peaks and three interrnolecular peaks have been found on the RDF. The appearance of such a number of intermolecular maxima on the RDF can be explained by the local parallel packing of long molecular chains of the amorphous polymers.     

The molecular structure of poly(biphenyl dianhydride-p-phenylenediamine) polyimide thin films by infrared spectroscopy: Thickness dependence of structure in the nano- to micrometer range

The molecular structure of poly[biphenyl dianhydride-p-phenylenediamine] (BPDA–PDA) polyimide in ultrathin (3–300 nm) films on silicon has been characterized by polarized infrared spectroscopy in conjunction with ellipsometry and X-ray reflectivity measurements. In spite of the high degree of crystalline packing of the polymer chains, the results show that an unexpected and significant content of imide rings exhibit local structural perturbations, including out-of-plane twisting. Further, the fraction of perturbed rings increases with increasing film thickness while, in contrast, the high degree of in-plane uniaxial film symmetry and planar stacking of the chains remain constant with thickness. These results reveal a new structural aspect of localized ring disorder that arises within the otherwise well-ordered, chain-stacked structure of BPDA–PDA polyimide films. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1247–1260, 1998