Hierarchical supramolecular fullerene architectures with controlled dimensionality

Self-assembly of a fullerene derivative with long alkyl chains in different solvents results in the formation of hierarchically-ordered supramolecular assemblies with well-defined 1, 2 and 3D architectures such as vesicles, fibers, discs and cones, whose fundamental structural sub-unit consists of bilayers.     

Diversification of self-organized architectures in supramolecular dye assemblies

Upon complexation with bismelamine receptors (BMn) featuring different alkyl linker lengths (number of methylene groups (n) = 5-12), a barbituric acid merocyanine dye (1) can be loaded into diverse self-organized superstructures through multiple hydrogen-bonding interactions. UV/vis, dynamic light scattering, and NMR studies in cyclohexane demonstrate that the diversification of the primarily formed hydrogen-bonded species in solution occurs by varying the linker length of BMn. Hierarchical organization of the hydrogen-bonded species is achieved by slow evaporation of the solvent (forming solvent-free films), and the resulting superstructures are evaluated by polarized optical microscopy, X-ray diffraction, SEM, and AFM techniques. The formation of columnar structures with and without two-dimensional ordering are revealed for shorter (n = 5-7) and longer (n = 11, 12) linker bis(melamines), respectively. On the contrary, in the cases of n = 8-10, the formation of lamellar structures is unveiled. Several assemblies (n = 5, 7, 11) indicate the formation of a liquid crystalline mesophase in POM and DSC analyses. Hierarchical organization is also achieved in solution by prolonged aging, affording phase-separated crystalline nanofibers (n = 5, 7) and soft nanofibrils agglomerating into wormlike objects (n = 8), gel-forming continuous globular networks (n = 10), and nanofibers (n = 11, 12). These superstructural and morphological diversifications are an outcome of the variation in the primarily formed hydrogen-bonded supramolecular architectures. Using this strategy, diverse self-assembled materials will be obtained from a single dye component.     

Synthesis and properties of crystalline fullerene hydrides

The interaction of crystalline fullerence C₆₀ with highly pure hydrogen, which was evolved from hydrides of intermetallic compounds of rear-earth metals and nickel, was studied. Crystalline fullerene hydrides containing from 10 to 30 hydrogen atoms per fullerene molecule were synthesized (1.0–2.5 MPa and 300–673 K). Crystalline hydrides release hydrogen at 800 K with retention of the structure of the fullerene molecule. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2093–2096, October, 1998.     

Anisotropic adsorption of molecular assemblies on crystalline surfaces

Orientational order of surfactant micelles and proteins on crystalline templates has been observed but, given that the template unit cell is significantly smaller than the characteristic size of the adsorbate, this order cannot be attributed to lattice epitaxy. We interpret the template-directed orientation of rodlike molecular assemblies as arising from anisotropic van der Waals interactions between the assembly and crystalline surfaces where the anisotropic van der Waals interaction is calculated using the Lifshitz methodology. Provided the assembly is sufficiently large, substrate anisotropy provides a torque that overcomes rotational Brownian motion near the surface. The probability of a particular orientation is computed by solving a Smoluchowski equation that describes the balance between van der Waals and Brownian torques. Torque aligns both micelles and protein fibrils; the interaction energy is minimized when the assembly lies perpendicular to a symmetry axis of a crystalline substrate. Theoretical predictions agree with experiments for both hemi-cylindrical micelles and protein fibrils adsorbed on graphite.     

Single crystals and two-dimensional crystalline assemblies of block copolymers

Block copolymer single crystals (BCPSCs) have attracted widespread attentions due to their unique two-dimensional (2D) structure, good controllability, and great potential applications in recent years. In this paper, the morphology, surface structure of BCPSCs and the related influencing factors are reviewed. We also summarize the studies of 2D crystalline assemblies of block copolymers (BCPs) driven by crystallization and intermolecular π–π interaction. Moreover, the functionalization and properties of BCPSCs and 2D crystalline assemblies of BCPs are introduced. Finally, we put forward some unsolved problems in this field.     

Multiple photosynthetic reaction centres composed of supramolecular assemblies of zinc porphyrin dendrimers with a fullerene acceptor

Multiple photosynthetic reaction centres have successfully been constructed using supramolecular complexes of zinc porphyrin dendrimers [D(ZnP)(n): n = 4, 8, 16] with fulleropyrrolidine bearing a pyridine ligand (C(60)py). Efficient energy migration occurs completely between the ZnP units of dendrimers prior to the electron transfer with increasing the generation of dendrimers to attain an extremely long charge-separation lifetime.     

Solution behavior of two liquid crystalline polymers of different architectures

Solutions of two different liquid crystalline polymers of high molecular weight are investigated by static and dynamic light scattering (LS), membrane osmometry and size-exclusion chromatography (SEC). Measurements in dilute solution in different solvents showed no specific behavior as formation of aggregates or chain stiffening. Large discrepancies between the LS results and the results from osmometry and SEC show that the latter methods are in the present cases not suitable for molecular weight determination. In semi-dilute solution the osmotic modulus and the time correlation function were studied. Behavior of flexible chains was observed. In one system a slight aggregation of small molecules onto longer chains was found causing less interpenetration of the chains in that solvent. At moderately high concentrations cluster formation was observed from i) a small angle excess scattering, ii) a downturn of the osmotic modulus, and iii) the appearance of a slow motion in the time-correlation function.     

One-pot synthesis of highly crystalline mesoporous TiO2 nanoparticle assemblies with enhanced photocatalytic activity

We report an unprecedented formation of mesoporous titania via a surfactant-assisted aggregating assembly of TiO(2) nanoparticles. These mesostructures possess a highly crystalline anatase phase, large and accessible pore surface area, and exhibit superior photocatalytic performance.     

Crystal engineering of metalloporphyrin assemblies. New supramolecular architectures mediated by bipyridyl ligands

Targeted synthesis of new supramolecular motifs of metalloporphyrins in crystals by a concerted mechanism of molecular recognition in three dimensions, aided by organic ligands, is presented; it involves induced assembly of [tetrakis(4-hydroxyphenyl)porphyrinato]zinc species by a combination of axial coordination through bridging bipyridyls and of lateral hydrogen bonding.     

Self-organized anisotropic wrinkling of molecularly aligned liquid crystalline polymer

Anisotropic wrinkling which utilizes the anisotropic nature of liquid crystalline polymer (LCP) is demonstrated as a means of physical self-assembly to produce periodic microstructures. Through the plasma treatment on the molecularly aligned LCP film surface, one-dimensionally ordered wrinkle pattern was spontaneously formed on glass substrates without employing external thin-film deposition or prestrain control of the system. Experimental results indicate that the directionality of the wrinkle pattern can be tailored by the structural ordering of LCP molecules in the bilayer system of a hard skin layer on a soft substrate. Studies on process variables, such as the plasma treatment time and the film thickness, were conducted to figure out the effect on the wrinkling morphology. Due to its spatial periodicity over a large area and undemanding requirement of the process, this approach can be a candidate for the microfabrication in various applications.     

Novel crystalline supramolecular assemblies of amorphous polypyrrole nanoparticles through surfactant templating

A lamellar-structured crystalline polypyrrole (PPy) supramolecular assembly was prepared by surfactant templating, and the regularly linked amorphous PPy nanoparticles with tunable window sizes could play the role of crystalline lattices in the supramolecular assembly.     

Liquid crystalline thermosets based on anisotropic phases of cellulose nanocrystals

A new class of liquid crystalline thermosets (LCTs) was successfully produced containing lyotropic cellulose nanocrystals (CNCs) as the primary mesogenic component (up to 72 wt%) by the addition of non-mesogenic epoxy monomers. Cellulose-based LCTs were produced by totally aqueous processing methods and ultimately cured at elevated temperatures to produce ordered networks of ‘frozen’ liquid crystalline (LC) phases. Various degrees of birefringence were obtained via self-assembly of CNCs into oriented phases as observed by polarized optical microscopy and transmission electron microscopy. X-ray diffraction measurements highlighted the effects of texture of CNCs within LCT films compared to lyophilized CNCs. Cellulose-based LCT films uniquely exhibited thermo-mechanical properties of both traditional LCTs and LC elastomers, such as high elastic modulus (~1 GPa) under ambient conditions and low glass transition temperature (~?25 °C), respectively. The development of LCTs based on CNCs and aqueous processing methods provides a renewable pathway for designing high performance composites with ordered network structures and unique optical properties.     

The scattering of light by correlated assemblies of anisotropic rods in two dimensions

The scattering from an assembly of anisotropic rods having correlated orientation is calculated in terms of a correlation function expressing the probability of parallelism of orientation of their optic axes as a function of their separation. The scattering is dependent upon the product of a form factor for the scattering from an individual rod and an interference factor dependent upon this correlation function.     

Hydrogen-bond-directed 2-D sheet assemblies of sulfamide derivatives: formation of giant vesicles with patchwork-like surface pattern

Sulfamide derivatives showed high ability to form hydrogen-bond-directed two-dimensional (2-D) sheet assemblies of nanometer thickness. Further, fine-tuning of the side chain structures and preparation conditions allowed for the formation of micrometer-sized giant vesicles of 4b in water by the simple injection method. IR and XRD studies indicated that 4b having tetradecyl and oxyethylene-terminated alkyl side chains formed hydrogen-bond-directed 2-D nanosheet pairs. SEM, AFM, and TEM observation of the dried vesicles revealed that the vesicle membrane was composed of several lamellar-stacked layers of 2-D nanosheets and showed a characteristic patchwork-like pattern on the surface.     

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.     

Supramolecular nanostructured assemblies of different types of porphyrins with fullerene using TiO2 nanoparticles for light energy conversion

TiO₂ nanoparticles were modified with porphyrin derivatives, 5-[4-benzoic acid]-10,15,20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (Ar-H₂P-COOH), 5-[4-benzoic acid]-10,20-tris[3,5-di-tert-butylphenyl]-21H,23H-porphyrin (H-H₂P-COOH), and 5,10,15,20-tetra[4-benzoic acid]-21H,23H-porphyrin (H₂P-4COOH). The porphyrin-modified TiO₂ nanoparticles were deposited on nanostructured OTE/SnO₂ electrode together with nanoclusters of fullerene (C₆₀) in acetonitrile-toluene (3/1, v/v) using an electrophoretic deposition technique to afford the porphyrin-modified TiO₂ composite electrode denoted as OTE/SnO₂/(porphyrin-modified TiO₂ nanoparticle+C₆₀)_n. The porphyrin-modified TiO₂ composite electrodes have efficient light absorbing properties in the visible region, exhibiting the photoactive response under visible light excitation using redox couple. The incident photon-to-photocurrent efficiency (IPCE) values of supramolecular nanostructured electrodes of porphyrin-modified TiO₂ nanoparticles with fullerene [OTE/SnO₂/(Ar-H₂P-COO-TiO₂+C₆₀)_n, OTE/SnO₂/(H-H₂P-COO-TiO₂+C₆₀)_n, and OTE/SnO₂/(H₂P-4COO-TiO₂+C₆₀)_n] are much larger than those of the reference systems of porphyrin-modified TiO₂ nanoparticles without C₆₀ [OTE/SnO₂/(Ar-H₂P-COO-TiO₂)_n, OTE/SnO₂/(H-H₂P-COO-TiO₂)_n, and OTE/SnO₂/(H₂P-4COO-TiO₂)_n]. In particular, the maximum IPCE value (41%) is obtained for OTE/SnO₂/(H-H₂P-COO-TiO₂+C₆₀)_n under the bias potential of 0.2 V versus SCE. This indicates that the formation of supramolecular complexes between porphyrins and fullerene on TiO₂ nanoparticles plays an important role in improvement of the light energy conversion properties.     

Principles of hierarchical meso- and macropore architectures by liquid crystalline and polymer colloid templating

The generation of porous silica with hierarchically organized bimodal mesoporosity of adjustable size and well-defined shape was investigated by using surfactant mixtures and the nanocasting procedure (liquid crystalline templating). A systematic study of combinations of various block copolymers (Pluronics F127, KLE (poly(omega-hydroxypoly(ethylene-co-butylene)-co-poly(ethylene oxide))) and SE (PS-co-PEO)) with smaller surfactants (Pluronics P123, C16mimCl, and CTAB) revealed that hierarchical bimodal mesopore architectures could only be obtained by the usage of block copolymers with a strong hydrophilic-hydrophobic contrast, such as KLE and SE, giving rise to pores between 6 and 22 nm. Furthermore, the ionic liquid (IL) C16mimCl appeared to have advantageous templating properties, resulting in 2-3-nm pores being located between the block copolymer mesopores, whereas phase separation was observed for Pluronics and CTAB as small templates. Thereby, the study provided also general insights into the mixing and co-self-assembly behavior of block copolymers and ionic surfactants in water and confirmed the special templating properties of ILs, as recently proposed. In addition to the bimodal mesoporosity, additional tunable macroporosity was created by the presence of poly(styrene) or poly(methyl methacrylate) spheres, leading to well-defined trimodal hierarchical pore architectures with the small pores being located in the walls of the respective larger pores. As a major improvement, due to the pore hierarchy, these large-pore materials showed relatively large surface areas and pore volumes, and the size of densely packed macropores could even be decreased down to 90 nm. The materials were characterized by electron microscopy, small-angle X-ray scattering, and nitrogen sorption using a proper NLDFT (nonlocal density functional theory) approach for calculations of the pore size distribution in the entire range of micro- and mesopores.     

Extraction of fullerene mixture from fullerene soot with organic solvents

Investigation of extraction of fullerene mixture from the fullerene soot obtained by plasma erosion of graphite rod in helium atmosphere with different solvents such as α-chloronaphthalene, o-dichlorobenzene, o-xylene, toluene, benzene, carbon tetrachloride, and n-hexane at 25°C was carried out. Completeness and effectiveness of extraction as well as relative content of light (C₆₀, C₇₀) and heavy (C₇₆, C₇₈, C₈₄) fullerenes in the extract were evaluated.     

Investigation of a flat sheet membrane desolvator for aqueous solvent removal with inductively coupled plasma atomic emission spectrometry

Results obtained from a preliminary investigation of the performance of a flat sheet membrane desolvator (FSMD) utilizing dual hydrophobic polypropylene membranes with an average pore size of 0.05 mum and a 50 +/- 5 mum thickness are reported. The membranes have a desolvation area of 241 cm(2). The volume-to-surface area ratio is 0.3 cm. Using the FSMD with an ultrasonic nebulizer (USN), aqueous solvent desolvation efficiencies of greater than 99.9% were obtained at all nebulizer gas flow rates investigated (0.8, 1.2, and 1.8 l min(-1)). This efficient desolvation occurred when the countercurrent gas flow rate was equal to or slightly greater than the applied nebulizer gas flow rate. Under these conditions preconcentration factors of 18, 44, and 590 were observed with flows of 0.8, 1.2 and 1.8 l min(-1), respectively. Operating with countercurrent gas flow rates much higher than the nebulizer gas flow rates leads to a significant reduction in analyte flux, thus increasing detection limits. Depending on the nebulizer and countercurrent gas flow rate conditions, the FSMD contributed between 10-40% to the overall analyte loss in the system. The lowest detection limit observed for aqueous copper with the USN-FSMD system is 0.4 ppb at nebulizer and countercurrent gas flow rates of 1.2 and 1.4 l min(-1), respectively. At this nebulizer gas flow rate, replacing the FSMD in the system with a commercial tubular membrane desolvator, MDX100, gave a lowest Cu detection limit of 0.2 ppb at a countercurrent gas flow rate of 1.2 l min(-1). These detection limits represents improvements over the 0.7 and 8 ppb obtained with USN and pneumatic nebulization, respectively.