Paul A. Heiney

Self-organization of supramolecular helical dendrimers into complex electronic materials

The discovery of electrically conducting organic crystals and polymers has widened the range of potential optoelectronic materials, provided these exhibit sufficiently high charge carrier mobilities and are easy to make and process. Organic single crystals have high charge carrier mobilities but are usually impractical, whereas polymers have good processability but low mobilities. Liquid crystals exhibit mobilities approaching those of single crystals and are suitable for applications, but demanding fabrication and processing methods limit their use. Here we show that the self-assembly of fluorinated tapered dendrons can drive the formation of supramolecular liquid crystals with promising optoelectronic properties from a wide range of organic materials. We find that attaching conducting organic donor or acceptor groups to the apex of the dendrons leads to supramolecular nanometre-scale columns that contain in their cores π-stacks of donors, acceptors or donor–acceptor complexes exhibiting high charge carrier mobilities. When we use functionalized dendrons and amorphous polymers carrying compatible side groups, these co-assemble so that the polymer is incorporated in the centre of the columns through donor–acceptor interactions and exhibits enhanced charge carrier mobilities. We anticipate that this simple and versatile strategy for producing conductive π-stacks of aromatic groups, surrounded by helical dendrons, will lead to a new class of supramolecular materials suitable for electronic and optoelectronic applications.

Self-assembly of amphiphilic dendritic dipeptides into helical pores

Natural pore-forming proteins act as viral helical coats and transmembrane channels, exhibit antibacterial activity and are used in synthetic systems, such as for reversible encapsulation or stochastic sensing. These diverse functions are intimately linked to protein structure. The close link between protein structure and protein function makes the design of synthetic mimics a formidable challenge, given that structure formation needs to be carefully controlled on all hierarchy levels, in solution and in the bulk. In fact, with few exceptions, synthetic pore structures capable of assembling into periodically ordered assemblies that are stable in solution and in the solid state have not yet been realized. In the case of dendrimers, covalent and non-covalent coating and assembly of a range of different structures has only yielded closed columns. Here we describe a library of amphiphilic dendritic dipeptides that self-assemble in solution and in bulk through a complex recognition process into helical pores. We find that the molecular recognition and self-assembly process is sufficiently robust to tolerate a range of modifications to the amphiphile structure, while preliminary proton transport measurements establish that the pores are functional. We expect that this class of self-assembling dendrimers will allow the design of a variety of biologically inspired systems with functional properties arising from their porous structure.

Structure, dynamics and ordering transition of solid C60

Abstract Solid C60 forms a face-centered-cubic structure at room temperature, in which the molecules exhibit dynamic orientational disorder. At 255 K the molecules develop orientational order via a first order phase transition, lowering the space group symmetry to Pa 3 in a simple cubic lattice. Even in the ordered phase, short-range disorder persists to the lowest temperatures. The Pa 3 structure is stabilized by both Lennard-Jones atomic pair potentials and by Coulombic forces arising from excess charge in the double bonds. The low temperature dynamics are primarily characterized by jump rotational diffusion between equivalent orientations superimposed on small amplitude librational oscillations. The behavior at the phase transition is strongly influenced by trace impurities and solvent. Similar effects are seen in C60O and in C70.

Modular synthesis of amphiphilic Janus glycodendrimers and their self-assembly into glycodendrimersomes and other complex architectures with bioactivity to biomedically relevant lectins

The modular synthesis of 7 libraries containing 51 self-assembling amphiphilic Janus dendrimers with the monosaccharides D-mannose and D-galactose and the disaccharide D-lactose in their hydrophilic part is reported. These unprecedented sugar-containing dendrimers are named amphiphilic Janus glycodendrimers. Their self-assembly by simple injection of THF or ethanol solution into water or buffer and by hydration was analyzed by a combination of methods including dynamic light scattering, confocal microscopy, cryogenic transmission electron microscopy, Fourier transform analysis, and micropipet-aspiration experiments to assess mechanical properties. These libraries revealed a diversity of hard and soft assemblies, including unilamellar spherical, polygonal, and tubular vesicles denoted glycodendrimersomes, aggregates of Janus glycodendrimers and rodlike micelles named glycodendrimer aggregates and glycodendrimermicelles, cubosomes denoted glycodendrimercubosomes, and solid lamellae. These assemblies are stable over time in water and in buffer, exhibit narrow molecular-weight distribution, and display dimensions that are programmable by the concentration of the solution from which they are injected. This study elaborated the molecular principles leading to single-type soft glycodendrimersomes assembled from amphiphilic Janus glycodendrimers. The multivalency of glycodendrimersomes with different sizes and their ligand bioactivity were demonstrated by selective agglutination with a diversity of sugar-binding protein receptors such as the plant lectins concanavalin A and the highly toxic mistletoe Viscum album L. agglutinin, the bacterial lectin PA-IL from Pseudomonas aeruginosa, and, of special biomedical relevance, human adhesion/growth-regulatory galectin-3 and galectin-4. These results demonstrated the candidacy of glycodendrimersomes as new mimics of biological membranes with programmable glycan ligand presentations, as supramolecular lectin blockers, vaccines, and targeted delivery devices.

Nanomechanical function from self-organizable dendronized helical polyphenylacetylenes.

Self-organizable dendronized helical polymers provide a suitable architecture for constructing molecular nanomachines capable of expressing their motions at macroscopic length scales. Nanomechanical function is demonstrated by a library of self-organized helical dendronized cis-transoidal polyphenylacetylenes ( cis-PPAs) that possess a first-order phase transition from a hexagonal columnar lattice with internal order (varphi h (io)) to a hexagonal columnar liquid crystal phase (varphi h). These polymers can function as nanomechanical actuators. When extruded as fibers, the self-organizable dendronized helical cis-PPAs form oriented bundles. Such fibers have been shown capable of work by displacing objects up to 250-times their mass. The helical cis-PPA backbone undergoes reversible extension and contraction on a single molecule length scale resulting from cisoid-to-transoid conformational isomerization of the cis-PPA. Furthermore, we clarify supramolecular structural properties necessary for the observed nanomechanical function.

Compressibility of M3C60 Fullerene Superconductors: Relation Between Tc and Lattice Parameter

X-ray diffraction and diamond anvil techniques were used to measure the isothermal compressibility of K3C60 and Rb3C60, the superconducting, binary alkali-metal intercalation compounds of solid buckminsterfullerene. These results, combined with the pressure dependence of the superconducting onset temperature Tc measured by other groups, establish a universal first-order relation between Tc and the lattice parameter a over a broad range, between 13.9 and 14.5 angstroms. A small secondorder intercalate-specific effect was observed that appears to rule out the participation of intercalate-fullerene optic modes in the pairing interaction.

Self-Assembly of Dendritic Crowns into Chiral Supramolecular Spheres

The synthesis and structural and retrostructural analysis of a library of dendronized cyclotriveratrylene containing seven nonchiral and seven chiral self-assembling dendrons is reported. These dendronized cyclotriveratrylenes exhibit a crown conformation that we named dendritic crown. Selected examples of dendritic crowns self-assemble into helical pyramidal columns that self-organize into columnar crystals or into 2-D columnar hexagonal lattices with intracolumnar order. A second group of dendritic crowns self-assembles into helical pyramidal columns and spherical supramolecular dendrimers that self-organize into cubic and tetragonal lattices. A third group of dendritic crowns self-assembles only in spherical supramolecular dendrimers. The helical pyramidal columns and spherical supramolecular dendrimers assembled from dendronized cyclotriveratrylene containing nonchiral dendrons are chiral but racemic while those generated from chiral dendrons exhibit amplified chirality. Structural analysis by a combination of X-ray diffraction methods and CD experiments demonstrated a new mechanism for the assembly of chiral supramolecular spheres that involves an intramolecular structure containing short fragments of helical pyramidal columns.

Order and disorder in fullerene and fulleride solids

Abstract A review is given of crystal structures and order/disorder phenomena in the fullerene solids C 60 , C 60 O and C 70 and in the alkali metal intercalation compounds of C 60 . Recent results on orientational melting and quenched orientational disorder in the pristine solids are summarized, and the effect of small perturbations on the quasi-spherical molecular shape are described. The intercalation properties of C 60 are discussed in the context of other host lattices such as graphite. The variety of orientational correlations in fullerenes and fullerides is rationalized in terms of competing contributions to the orientational potentials. Structural properties of alkali fullerides are correlated with electronic properties and superconductivity, and an updated binary phase diagram is described.

Molecular Structure of Helical Supramolecular Dendrimers

The molecular structure of helical supramolecular dendrimers generated from self-assembling dendrons and dendrimers and from self-organizable dendronized polymers was elucidated for the first time by the simulation of the X-ray diffraction patterns of their oriented fibers. These simulations were based on helical diffraction theory applied to simplified atomic helical models, followed by Cerius2 calculations based on their complete molecular helical structures. Hundreds of samples were screened until a library containing 14 supramolecular dendrimers and dendronized polymers provided a sufficient number of helical features in the X-ray diffraction pattern of their oriented fibers. This combination of techniques provided examples of single-9(2) and -11(3) helices, triple-6(1), -8(1), -9(1), and -12(1) helices, and an octa-32(1) helix that were assembled from crownlike dendrimers, hollow and nonhollow supramolecular crownlike dendrimers, hollow and nonhollow supramolecular disklike dendrimers, and hollow and nonhollow supramolecular and macromolecular helicene-like architectures. The method elaborated here for the determination of the molecular helix structure was transplanted from the field of structural biology and will be applicable to other classes of synthetic helical assemblies. The determination of the molecular structure of helical supramolecular assemblies is expected to provide an additional level of precision in the design of helical functional assemblies resembling those from biological systems.

Self-Assembly of Dendronized Perylene Bisimides into Complex Helical Columns

The synthesis of perylene 3,4:9,10-tetracarboxylic acid bisimides (PBIs) dendronized with first-generation dendrons containing 0 to 4 methylenic units (m) between the imide group and the dendron, (3,4,5)12G1-m-PBI, is reported. Structural analysis of their self-organized arrays by DSC, X-ray diffraction, molecular modeling, and solid-state (1)H NMR was carried out on oriented samples with heating and cooling rates of 20 to 0.2 °C/min. At high temperature, (3,4,5)12G1-m-PBI self-assemble into 2D-hexagonal columnar phases with intracolumnar order. At low temperature, they form orthorhombic (m = 0, 2, 3, 4) and monoclinic (m = 1) columnar arrays with 3D periodicity. The orthorhombic phase has symmetry close to hexagonal. For m = 0, 2, 3, 4 ,they consist of tetramers as basic units. The tetramers contain a pair of two molecules arranged side by side and another pair in the next stratum of the column, turned upside-down and rotated around the column axis at different angles for different m. In contrast, for m = 1, there is only one molecule in each stratum, with a four-strata 2(1) helical repeat. All molecules face up in one column, and down in the second column, of the monoclinic cell. This allows close and extended π-stacking, unlike in the disruptive up-down alteration from the case of m = 0, 2, 3, 4. Most of the 3D structures were observed only by cooling at rates of 1 °C/min or less. This complex helical self-assembly is representative for other classes of dendronized PBIs investigated for organic electronics and solar cells.