An optically-active liquid-crystalline hexa-adduct of [60]fullerene which displays supramolecular helical organization

Functional Chirality: From Small Molecules to Supramolecular Assemblies

Many structures in nature look symmetric, but this is not completely accurate, because absolute symmetry is close to death. Chirality (handedness) is one form of living asymmetry. Chirality has been extensively investigated at different levels. Many rules were coined in attempts made for many decades to have control over the selection of handedness that seems to easily occur in nature. It is certain that if good control is realized on chirality, the roads will be ultimately open towards numerous developments in pharmaceutical, technological, and industrial applications. This tutorial review presents a report on chirality from single molecules to supramolecular assemblies. The realized functions are still in their infancy and have been scarcely converted into actual applications. This review provides an overview for starters in the chirality field of research on concepts, common methodologies, and outstanding accomplishments. It starts with an introductory section on the definitions and classifications of chirality at the different levels of molecular complexity, followed by highlighting the importance of chirality in biological systems and the different means of realizing chirality and its inversion in solid and solution-based systems at molecular and supramolecular levels. Chirality-relevant important findings and (bio-)technological applications are also reported accordingly.

An Ultra-Long-Lived Triplet Excited State in Water at Room Temperature: Insights on the Molecular Design of Tridecafullerenes

Suitably engineered molecular systems exhibiting triplet excited states with very long lifetimes are important for high-end applications in nonlinear optics, photocatalysis, or biomedicine. We report the finding of an ultra-long-lived triplet state with a mean lifetime of 93 ms in an aqueous phase at room temperature, measured for a globular tridecafullerene with a highly compact glycodendrimeric structure. A series of three tridecafullerenes bearing different glycodendrons and spacers to the C60 units have been synthesized and characterized. UV/Vis spectra and DLS experiments confirm their aggregation in water. Steady-state and time-resolved fluorescence experiments suggest a different degree of inner solvation of the multifullerenes depending on their molecular design. Efficient quenching of the triplet states by O2 but not by waterborne azide anions has been observed. Molecular modelling reveals dissimilar access of the aqueous phase to the internal structure of the tridecafullerenes, differently shielded by the glycodendrimeric shell.

Tuning the Liquid Crystallinity of Cholesteryl-o-Carborane Dyads: Synthesis, Structure, Photoluminescence, and Mesomorphic Properties

A set of mesomorphic materials in which the o-carborane cluster is covalently bonded to a cholesteryl benzoate moiety (mesogen group) through a suitably designed linker is described. The olefin cross-metathesis between appropriately functionalized styrenyl-o-carborane derivatives and a terminal alkenyl cholesteryl benzoate mesogen (all type I terminal olefins) leads to the desired trans-regioisomer, which is the best-suited configuration to obtain mesomorphic properties in the final materials. The introduction of different substituents (R = H (M2), Me (M3), or Ph (M4)) to one of the carbon atoms of the o-carborane cluster (Ccluster) enables the tailoring of liquid crystalline properties. Compounds M2 and M3 show the chiral nematic (N*) phase, whereas M4 do not show liquid crystal behavior. Weaker intermolecular interactions in the solid M3 with respect to those in M2 may allow the liquid crystallinity in M3 to be expressed as enantiotropic behavior, whereas breaking the stronger intermolecular interaction in the solid state of M2 leads directly to the isotropic state, resulting in monotropic behavior. Remarkably, M3 also displays the blue phase, which was observed neither in the chiral nematic precursor nor in the styrenyl-cholesterol model (M5) without an o-carborane cluster, which suggests that the presence of the cluster plays a role in stabilizing this highly twisted chiral phase. In the carborane-containing mesogens (M2 and M3), the o-carborane cluster can be incorporated without destroying the helical organization of the mesophase.

3D supramolecular self-assembly of [60]fullerene hexaadducts decorated with triarylamine molecules

A clickable fullerene hexa-adduct scaffold has been functionalized with twelve triarylamine subunits. The light-triggered self-assembly of this molecular unit leads to 3D honeycomb-like structures with inner pores of around 10 nm diameter. Multiple grafting of triarylamine subunits onto a hard-core C₆₀ unit increases the dimensionality of the self-assembly process by reticulating the 1D nanowires typically obtained from the supramolecular polymerization of triarylamine monomers.

Fullerene hexa-adduct scaffolding for the construction of giant molecules

Hexa-substituted fullerenes are unique scaffolds for the fast construction of globular dendrimers. Efficient synthetic methodologies based on the post-functionalization of pre-constructed fullerene hexa-adduct derivatives have been reported in recent years and dendrimers difficult or even impossible to prepare by classical fullerene chemistry are now easily accessible. Fullerodendrimers for various applications have been thus prepared. Examples include liquid crystalline materials, non-viral gene delivery systems and bioactive glycoclusters. On the other hand, fullerene hexa-adduct building blocks have been used for the ultra-fast synthesis of giant dendrimers. Indeed, the resulting dendrimers of first generation are already surrounded by 120 peripheral functional groups. This strategy has been used to prepare giant glycoclusters with anti-viral activity and multivalent glycosidase inhibitors.

Conformational Preferences and the Phase Stability of Fullerene Hexa-adducts

Molecular conformation and the assembly structure determine the spatial arrangements of the constituent units and the functions of a molecule. Although, fullerene hexa-adducts (FHAs) have been known as functional materials with great versatility, their conformational preferences and phase stability remain a complicate issue. By choosing bithiophene (T2 ) and dodecyl bithiophene (C12 T2 ) as the peripheral units of FHA, and using microscopic, scattering and diffraction characterizations, our study reveals how the intramolecular interaction and environmental stimulus affects the conformational preferences and phase stability of FHAs.

Cyclooctyne [60]fullerene hexakis adducts: a globular scaffold for copper-free click chemistry

The synthesis of a new highly symmetric hexakis adduct of C₆₀ appended with 12 cyclooctyne moieties has been carried out.

Self-organisation of dodeca-dendronized fullerene into supramolecular discs and helical columns containing a nanowire-like core

Twelve chiral and achiral self-assembling dendrons have been grafted onto a [60]fullerene hexa-adduct core by copper-catalyzed alkyne azide "click" cycloaddition. The structure adopted by these compounds was determined by the self-assembling peripheral dendrons. These twelve dendrons mediate the self-organisation of the dendronized [60]fullerene into a disc-shaped structure containing the [60]fullerene in the centre. The fullerene-containing discs self-organise into helical supramolecular columns with a fullerene nanowire-like core, forming a 2D columnar hexagonal periodic array. These unprecedented supramolecular structures and their assemblies are expected to provide new developments in chiral complex molecular systems and their application to organic electronics and solar cells.

Synthesis of highly functionalized C60 fullerene derivatives and their applications in material and life sciences

Highly functionalized fullerenes can be efficiently constructed by various techniques.

Synthesis and study of hybrid hydrogen-bonded bent-core liquid crystal complexes containing C60- and Si-based proton donors

Mesophasic and electro-optical properties can be manipulated via the ratio of Si- and C₆₀-based moieties in H-bonded bent-core LC complexes.

Twisted and frustrated states of matter

The World, and much of Nature that we see within it, experiences an environment of reduced symmetries. For example, living organisms are dependent on asymmetric or dissymmetric structures for their life processes. In the solid state, a large number of space groups are chiral. Conversely, in liquids, the effects of reduced symmetries are smeared out owing to the dynamical fluctuations of the constituent molecules, atoms or ions. Thus, on progressing from the strongly ordered solid to the amorphous liquid state, the effects of reduced symmetries weaken as the molecular or atomic correlations and penetration lengths fall. Between these two states of matter, the fourth state of organized fluids can be markedly affected by chirality, and over substantial length scales, owing to both the fluidity and partial ordering of the molecules. In effect, complex fluids can amplify the effects of chirality at the molecular level. Broken symmetries in self-organizing systems can lead to the formation of novel phases of matter and to the creation of structured liquids, and to the generation of nonlinear properties such as heli-, ferro-, ferri- and antiferro-electricity, and electroclinism, which can be harnessed in a wide range of applications including thermal sensors, imaging devices and information displays, to name but a few.

Transfer, amplification, and inversion of helical chirality mediated by concerted interactions of C3-supramolecular dendrimers

The synthesis, structural, and retrostructural analysis of two libraries containing 16 first and second generation C(3)-symmetric self-assembling dendrimers based on dendrons connected at their apex via trisesters and trisamides of 1,3,5-benzenetricarboxylic acid is reported. A combination of X-ray diffraction and CD/UV analysis methods demonstrated that their C(3)-symmetry modulates different degrees of packing on the periphery of supramolecular structures that are responsible for the formation of chiral helical supramolecular columns and spheres self-organizable in a diversity of three-dimensional (3D) columnar, tetragonal, and cubic lattices. Two of these periodic arrays, a 3D columnar hexagonal superlattice and a 3D columnar simple orthorhombic chiral lattice with P222(1) symmetry, are unprecedented for supramolecular dendrimers. A thermal-reversible inversion of chirality was discovered in helical supramolecular columns. This inversion is induced, on heating, by the change in symmetry from a 3D columnar simple orthorhombic chiral lattice to a 3D columnar hexagonal array and, on cooling, by the change in symmetry from a 2D hexagonal to a 2D centered rectangular lattice, both exhibiting intracolumnar order. A first-order transition from coupled columns with long helical pitch, to weakly or uncorrelated columns with short helical pitch that generates a molecular rotator, was also discovered. The torsion angles of the molecular rotator are proportional to the change in temperature, and this effect is amplified in the case of the C(3)-symmetric trisamide supramolecular dendrimers forming H-bonds along their column. The structural changes reported here can be used to design complex functions based on helical supramolecular dendrimers with different degree of packing on their periphery.

Nanoparticles in liquid crystals and liquid crystalline nanoparticles

Combinations of liquid crystals and materials with unique features as well as properties at the nanoscale are reviewed. Particular attention is paid to recent developments, i.e., since 2007, in areas ranging from liquid crystal-nanoparticle dispersions to nanomaterials forming liquid crystalline phases after surface modification with mesogenic or promesogenic moieties. Experimental and synthetic approaches are summarized, design strategies compared, and potential as well as existing applications discussed. Finally, a critical outlook into the future of this fascinating field of liquid crystal research is provided.

Sequential copper catalyzed alkyne-azide and thiol-ene click reactions for the multiple functionalization of fullerene hexaadducts

A fullerene hexakis-adduct incorporating complementary reactive centres with very different and selective reactivity has been prepared and functionalized with three different peripheral groups by successive alkyne-azide and thiol-ene click reactions.

Liquid−Crystalline Janus-Type Fullerodendrimers Displaying Tunable Smectic−Columnar Mesomorphism

Janus-type liquid-crystalline fullerodendrimers were synthesized via the 1,3-dipolar cycloaddtition of two mesomorphic dendrons and C60. By assembling poly(aryl ester) dendrons functionalized with cyanobiphenyl groups, displaying lamellar mesomorphism, with poly(benzyl ether) dendrons carrying alkyl chains, which display columnar mesomorphism, we could tailor by design the liquid-crystalline properties of the title compounds as a function of each dendron size. The liquid-crystalline properties were examined by polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction. Depending on the dendrimer generations, smectic (SmC and/or SmA phases) or columnar (Colr-c2mm or Colr-p2gg phases) mesomorphism was obtained. The supramolecular organization is governed by (1) the adequacy of the cross-sectional area of the dendrons, (2) the microsegregation of the dendrimer, (3) the deformation of the dendritic core, and (4) the dipolar interactions between the cyanobiphenyl groups. Comparison of the mesomorphic properties of two fullerodendrimers with those of model compounds (fullerene-free analogues) indicated that the C60 unit does not influence the type of mesophase that is formed. Molecular properties determined in solution (permanent dipole moment, specific dielectric polarization, molar Kerr constant) confirm that microsegregation persists in solution and strengthen the models proposed for the structure of the mesophases.

Synthesis and Liquid Crystalline Properties of Mono-, Di- and Tri-O-alkyl Pentaerythritol Derivatives Bearing Tri-, Di- or Monogalactosyl Heads: The Effects of Curvature of Molecular Packing on Mesophase Formation

Self-organisation and self-assembly are critical to the stability of synthetic and biological membranes. Of particular importance is consideration of the packing arrangements of the various molecular species. Both phospho- and glycolipids can pack in ways in which curvature can be introduced into self-organised or self-assembled systems. For instance, it is known that the degree of curvature can affect the structures of any condensed phases that are formed. In this article we report on a systematic study in which we have varied the shapes of glycolipids and examined the condensed phases that they form. In doing so, we have also unified the shape dependency of lyotropic liquid crystals with those of thermotropic liquid crystals. In order to undertake this systematic study a range of different pentaerythritol derivatives was synthesized, which covers combinations of one to three alkyl chains of different lengths (6,7,9,10,11,12,14,16 carbon atoms) and three to one galactosyl heads. Mono- and di-O-galactosyl derivatives were prepared directly by glycosylation of the corresponding alcohols using 2,3,4,6-tetra-O-benzoyl or acetyl-alpha-D-galactopyranosyl trichloroacetimidate or bromide as the donors; the tri-O-galactosyl derivatives were synthesized from O-alkyl-O-benzyl di-O-galactosyl pentaerythritol intermediates, followed by de-O-benzylation and glycosylation steps. All of the fully deprotected products were obtained by standard methods, and their self-organising and self-assembling properties examined.