Liquid crystalline supramolecular crosslinked polymer complexes of ditopic rylenebisimides and P4VP

Perylenebisimide and naphthalenebisimide (PBI‐PDP and NBI‐PDP) end functionalized with pentadecyl phenol is designed as ditopic hydrogen bonding acceptors to form supramolecular crosslinked network with poly(4‐vinyl pyridine) (P4VP). The pristine PBI‐PDP has been grown as single crystals from DCM‐MeOH (dichloromethane‐methanol) mixture at room temperature, which revealed a P21 space group. Noticeably, the pentadecyl alkyl chain shields the aromatic perylene core on both sides resulting in the absence of π–π interaction in single‐crystal assembly. The naphthalenebisimide derivative exhibits thermotropic liquid crystalline behavior, while both the molecules exhibits lyotropic liquid crystalline phases in tetrahydrofuran (THF), which were characterized using a combination of differential scanning calorimeter, X‐ray diffraction, and polarized light microscopy. The hydrogen‐bonded complex of both the rylenebisimides with P4VP preserves the mesomorphic properties in THF. The electron transport mobility measured by space charge limited current measurements reveals a two orders of magnitude increase in the charge transport in the P4VP complex compared to that of the pristine molecule. The average electron mobility obtained is μ _e,avg: 10^?3 cm²/Vs for P4VP‐PBI compared to μ _e,avg: 10^?5 cm²/Vs for pristine PBI derivative. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 951–959     

Synthesis and characterisation of main-chain hydrogen-bonded supramolecular liquid crystalline complexes formed by azo-containing compounds

A series of azopyridine-containing hydrogen bonding acceptors (4a-c) with flexible spacers of oligo(methylene) were synthesised. Hydrogen-bonded polymeric complexes 4/5 and trimeric complexes 4/6₂ , where 5 and 6 are aromatic dicarboxylic acids and monocarboxylic acids, respectively, were prepared and their liquid crystallinity was examined using differential scanning calorimetry and polarising optical microscopy. The study showed that most of the complexes displayed reversible thermotropic nematic phase. The isotropic to nematic phase transition temperatures of polymeric complexes 4/5 and trimeric complexes 4/6₂ in general decreased with the increase in length of spacers and terminal groups in the corresponding proton acceptors 4 and the proton donors 5 and 6, respectively. Hydrogen bonding interactions in complexes 4/5 and 4/6₂ were studied by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.     

Simple and supramolecular copper complexes as precursors in the HRTEM induced formation of crystalline copper nanoparticles

In the HRTEM investigations of copper(I) bisphenanthroline nanoscaffolds and simple precursor complexes, nanoparticles were generated that upon closer inspection turned out to be pure crystalline copper nanoparticles.     

Asymmetric halogenation and hydrohalogenation oftrans-cinnamic acid in crystalline cyclodextrin complexes

Asymmetric halogenation and hydrohalogenation oftrans-cinnamic acid have been achieved in the microcrystals of cyclodextrin complexes. The bromination of the organic acid in the cavity of -cyclodextrin gave theerythro-dibromide in 40 % optical yield which was much larger than that from the resolution treatment of the racemic dibromide with -cyclodextrin and the absolute configuration was opposite in sign. The asymmetric induction in the gas-solid reaction was not due to optical resolution but to the reaction itself which was influenced by the chiral frame of cyclodextrin. The reaction shows the molecular size effect that the acid in the cavity of -cyclodextrin reacted with smaller hydrogen bromide but did not with larger bromine and chlorine. In contrast, the guest molecule in the wider cavity of -cyclodextrin reacted with bromine and chlorine as well as hydrogen bromide. The stereospecificities of the gas-solid halogenations of the acid in -cyclodextrin were similar to those of the both reactions in the solid state and in carbon tetrachloride solution without -cyclodextrin: bromination of the acid yieldederythro-2, 3-dibromo-3-phenylpropionic acid stereospecifically in 100 % in three different conditions, but chlorination gave an excess ofthreo-2, 3-dichloro-3-phenylpropionic acid to theerythro-isomer in 7287 % yields.     

Hydrogen-bonded supramolecular complexes formed between isophthalic acid and pyridine-based derivatives

Two types of supramolecular liquid crystals were prepared through the formation of double hydrogen-bonded complexes between isophthalic acid (A) and two different groups of pyridine-based derivatives ( I n and I _a-e ). The first group of the base, I n (molecular formula 4-C_nH_2n+1OC₆H₄COOC₆H₄-N=N-C₅H₄N) homologues differ from each other by the number of carbon atoms (n) in the alkoxy chain, which varies between 8, 10, 12 and 14 carbons. The second group of the pyridine-based derivatives, I _a-e (molecular formula 4-X-C₆H₄COOC₆H₄-N=N-C₅H₄N) analogues differ from each other by the terminal polar substituent, X, that changes between OCH₃, CH₃, H, NO₂ and Br groups. In this manner two different groups of complexes are formed, one of them is A : 2I n, (Group A ), and the other is A : 2I _a-e , (Group B ). All complexes were investigated for their mesophase behaviour by differential scanning calorimetry and polarised light microscopy. The formation of 1:2 hydrogen-bonded complexes was confirmed by FTIR spectroscopy and binary phase diagrams. Most complexes A and B show nematic and/or SmA phases. X-ray diffraction of the SmA phase of a representative complex of type A indicates a layer distance corresponding to only half of the length of the H-bonded complexes which is interpreted by a phase structure where these complexes adopt a U-shape which intercalate and form non-polar SmA phases.     

Effect of the site of hydrogen-bonding on the liquid crystalline behaviour of supramolecular complexes

Two series of hydrogen-bonded side-chain liquid crystal polymers have been prepared by mixing components containing carboxyl acid and pyridyl-based fragments. We have focused our attention on the effect that the position of the hydrogen bond donor or acceptor site attached to the side-chain backbone has on the hydrogen-bonding interactions and liquid crystalline phase transitions of the system. The liquid crystalline behaviour of the complexes is studied using Fourier transform infrared spectroscopy, differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The results indicate that the phase transition temperatures of the complexes are influenced by the site of hydrogen-bonding.     

Octupole-like supramolecular aggregates of conical iron fullerene complexes into a three-dimensional liquid crystalline lattice

The installation of three structural features into a fullerene molecule, a conical shape, a polar iron-ferrocene complex, and long alkyl chains, allowed dipolar molecules 1 and 2 to undergo microphase separation and to form a three-dimensional lattice in a crystalline and a thermotropic liquid crystalline phase. The key feature is a tetrameric octupole-like aggregate, in which four dipoles are arranged supramolecularly to cancel the molecular polarity, forming a sphere. In addition to this lattice formation mechanism, the molecules incorporate noteworthy features, such as redox active C(60)/ferrocene and luminescent cyclophenacene.     

Selectivity in supramolecular host-guest complexes

The background of possible selectivity-affinity correlations and their limitations is reviewed, with typical crown ether and cryptand complexes, ionic associations, hydrogen bonded complexes and complexes driven by van der Waals, stacking or hydrophobic interactions, with some additional topics including associations based on metal coordination as supplementary material. This tutorial review is addressed to students and researchers interested in molecular recognition, and relates to the design of sensors, of discriminators for separation processes, of supramolecular devices and of drug compounds. A theoretical analysis of selectivity in supramolecular host-guest complexes, defined as a difference in binding free energies for structurally related guests, as a function of total binding free energy shows that for certain types of intermolecular interactions one may observe a correlation between selectivity and affinity. Such correlation fails however if the selectivity is due to additional interactions at a secondary binding sites, which is expected in complexes with anisotropic guest molecules. Several clear examples of theoretically expected selectivity-affinity correlations are found. The influence of reaction conditions on the experimentally observed selectivity, defined as a difference in complexation degrees with different guests in the presence of added receptor, is illustrated. The importance of often neglected solvent effects on selectivity is exemplified with ionophore and hydrogen bonded complexes.     

pH-dependent assembly of Keggin-based supramolecular architecture

Three Keggin-based supramolecular architectures were synthesized on the basis of same molecular building units, showing that the pH value of the reaction plays a crucial role in controlling the topological structures of the supramolecular architectures.     

Solubilization of single-walled carbon nanotubes by supramolecular complexes of barbituric acid and triaminopyrimidines

In this letter, we report that single-walled carbon nanotubes (SWNTs) can be dissolved in organic solvents through the formation of admixtures with barbituric acid.triaminopyrimidine (BA.TP) complexes using mechanochemical high-speed vibration milling (HSVM) and sonication methods. In contrast, neither BA nor TP alone were capable of solubilizing SWNTs. Moreover, the glutarimide (GI).TP complex was also found to be incapable of solubilizing SWNTs because the two carbonyl groups and one imino group of GI are located on only one side of the molecule such that the GI.TP complex cannot form the desired hydrogen-bonding network. These results strongly suggest that the formation of a hydrogen-bonding network makes possible the formation of multipoint interactions with the surfaces of the SWNTs.     

Electrospinning of supramolecular polymer complexes

Supramolecular polymer complexes with small molecules are self-assembled through non-covalent interactions and have been proposed for a wide variety of applications in materials science and nanoscience.Our research group has recently shown the possibility of forming highly ordered nanofibers of supramolecular complexes in their thermodynamically stable state using the electrospinning technique.The ultrafast solvent evaporation rate of electrospinning made possible the in-depth characterization of complexes that had never been prepared in their pure state before because of kinetic issues associated with their formation by conventional approaches.The improved understanding of the formation mechanism allowed us to extend the concept to other techniques featuring a fast solvent evaporation rate,such as electrospray and spin-coating.In this article,we review our most significant contributions in this research field.     

Room-temperature ferroelectricity and gigantic dielectric susceptibility on a supramolecular architecture of phenazine and deuterated chloranilic acid

Ferroelectricity and large dielectric constant at room temperature have been demonstrated for cocrystals of phenazine and anilic acids constructing supramolecular assemblies. Deuteration of the anilic acids gives rise to an increase by more than 50 K in the transition temperature, which exceeds room temperature for the deuterated chloranilic acid. At room temperature in air, the crystals show a clear polarization hysteresis with a small coercive field. Application of hydrostatic pressure and halogen substitution in the anilic acids bring about the structural effect on the transition temperature in a parallel way, whereas the deuterium substitution does this in a distinct way. The observed large deuteration effect cannot be elucidated by the geometric change of the hydrogen bond, which has been considered as the possible mechanism of ferroelectricity in the conventional hydrogen-bonded with double-well potential.     

Two supramolecular complexes based on 4-hydroxybenzoic acid and triethanolamine: Synthesis and structure

Two new copper and nickel complexes with triethanolamine (TEA) and 4-hydroxybenzoic acid (L) have been synthesized within the framework of systematic studies into the formation of mixed-ligand metal complexes on the basis of commercially available compounds with the simplest structure, such as ethanolamines and benzoic acid monoderivatives (hydroxy-, amino-, and nitrobenzoic acids). According to X-ray diffraction data, the complexes have the compositions [Cu₂(L)₂(TEA)₂] · [Cu(TEA)₂] · 2H₂O (I) and [Ni(TEA)₂] · 2L (II). Compound I is a mixed-ligand complex, while complex II is a supramolecular compound consisting of a nickel–TEA monoligand complex anion and non-coordinated L. TEA molecules in complex I are coordinated in both tetradentate and tridentate mode, while only tridentate coordination is typical for complex II. The coordination polyhedra of metal atoms are tetragonal bipyramids elongated due to the Jahn–Teller effect in complex I and octahedra in complex II. In both crystals, structural units are linked into 2D associates via hydrogen bonds.     

Spontaneous resolution in a halogen bonded supramolecular architecture

The halogen bonding driven self-assembly of 1,8-diiodoperfluorooctane and N,N,N',N'-tetramethyl-p-phenylenediamine induces the formation of a chiral and enantiopure co-crystal wherein the fluorinated chains adopt an unusual gauche arrangement.     

Tetrahedral zinc complexes with liquid crystalline and luminescent properties: interplay between nonconventional molecular shapes and supramolecular mesomorphic order

Novel metallomesogens with luminescent properties and liquid crystalline behavior at room temperature have been achieved by the preparation of zinc complexes with polycatenar pyrazole and bis(pyrazolyl)methane ligands. Their molecular structures do not have a conventional shape in that they are far from the typical rod-like and flat disc-like geometries of common liquid crystals. They consist of a nonplanar nucleus due to the methylene spacer and/or the coordination to the tetrahedral center, as confirmed by single crystal analysis of the cores. The different numbers and positions of side chains in the pyrazole ligand enabled us to access lamellar and columnar mesophases and, of particular interest, to obtain columnar arrangements at room temperature. Supramolecular models for the organization of the molecules in the mesophases are proposed on the basis of the small-angle XRD diffractograms. The zinc complexes display luminescence in the near UV-blue region with large Stokes shifts. An interplay between non-conventional molecular shapes (due to the tetrahedral core) and the supramolecular mesomorphic order (due to the ligand design) led to materials that interestingly embody two rather opposite properties, a columnar self-organizational ability and luminescence with weak intermolecular interactions.     

The chirality of dendrimer-based supramolecular complexes

Boc-protected L-phenylalanine has been connected to a spacer-armed ureido-acetic acid derivative, which can form multiple supramolecular complexes with urea-adamantyl modified poly(propylene imine) dendrimers in chloroform. Complexes of this guest with several generations of urea-adamantyl dendrimers were prepared. The dendrimer-guest complexes were characterized in detail by (1)H-NMR, (1)H-(1)H-NOESY spectroscopy and mass spectrometry to prove their formation. Optical rotation experiments performed on different generations of dendrimer-guest complexes showed a constant positive value. These observations indicate that, though guest molecules decrease the flexibility at the periphery of the dendrimer upon binding, the amino acid at the terminus of the guest molecule retains its high local conformational freedom. This is in agreement with values found for covalently modified spacer-armed dendrimers.     

Photochemical properties of mixed-metal supramolecular complexes

We have prepared a series of mixed-metal trimetallic complexes of the form {[(bpy)₂Ru(BL)]₂MCl₂}ⁿ⁺(bpy 2,2′-bipyridine; BL 2,3-bis(2-pyridyl)pyrazine (dpp), 2,3-bis(2-pyridyl)quinoxaline (dpq) or 2,3-bis(2-pyridyl)-benzoquinozaline (dpb); M Ir(III), Rh(III) or Os(II). This new class of trimetallic complexes can be prepared with a good yield, often as high as 95%, using our building block strategy. The central rhodium and iridium fragments of these trimetallic, namely [M(BL)₂Cl₂]⁺, have been shown in our laboratory to be capable of delivering multiple electrons, “stored” on the bridging ligand π* orbitals, to a substrate as they functioned as electrocatalysts for the reduction of carbon dioxide to formate. The two terminal ruthenium metals are good light absorbers designed to give rise to photochemical activity. These bichromophoric systems should be capable of absorbing two photons of light, each giving rise to a desired photochemical reaction, namely excited-state electron transfer. Thus these systems form the basis of a molecular device for photoinitiated electron collection. The properties of these supramolecular complexes have been tuned by variation in the central metal and bridging ligand. Comparison of this array of nine complexes is described herein.     

Effect of auxiliary ligand on the crystalline architectures of copper(II)-sparfloxacin complexes via coordinative and supramolecular interactions

Reactions of sparfloxacin (Hsf) with Cu(II), in the absence or presence of auxiliary ligands (bpy, 2,2′-bipyridine; dmbpy, 4,4′-dimethyl-2,2′-bipyridine) under similar conditions, afforded three coordination complexes, [Cu(Hsf)₂(ClO₄)](ClO₄)(CH₃OH)₂(H₂O)_3.75 (1), [Cu(Hsf)(bpy)(ClO₄)](ClO₄)(H₂O) (2), and [Cu₂(Hsf)₂(dmbpy)₂(ClO₄)₃](ClO₄)(C₂H₅OH)₃(H₂O)_0.75 (3). All three complexes have been structurally characterized by single-crystal X-ray diffraction. In their crystal structures, distinct extended metallosupramolecular architectures, specifically 3D (for 1), 2D (for 2), and 2D + 1D (for 3), are constructed with the aid of secondary interactions involving H-bonding and aromatic stacking.     

Photocontrol of supramolecular architecture in azopolymers: Achiral and chiral aggregation

The absorption spectra and circular dichroism responses upon irradiation with 488 nm circularly polarized light (CPL) have been studied on polymeric films processed from two nematic copolymers containing azobenzene chromophores. Influence of the aggregation and orientation of azobenzenes on the photoinduced chiroptical properties has been analyzed. Moreover, polymeric films and 4 μm planar cells filled with the copolymers were studied by polarized optical microscopy (POM) with the aim of investigating the change of macroscopic optical properties and textures of azopolymers upon irradiation with CPL.     

Two 3-D supramolecular architecture based on the linkages of Co(II) complexes and lattice water molecules

Two new 3-D supramolecular compounds [Co(phen)(tdc)(H₂O)₃]·5H₂O (1) and [Co(phen)(Htdc)(H₂O)₃]·(Htdc)·2H₂O (2, phen = 1,10-phenanthroline, H₂tdc = thiophene-2,5-dicarboxylate) have been hydrothermally synthesized and structurally characterized. In 1, the neutral [Co(phen)(tdc)(H₂O)₃] complexes behave as pillars to join the water layers to make an overall 3-D supramolecular architecture by H-bond interactions. In 2, similar 2-D water layer is not observed, which could be due to one uncoordinated Htdc ligand instead of three lattice water molecules of 1. The thermal stabilities of 1 and 2 were investigated by thermogravimetric measurements.