Grafting Dendrons onto Pillar[5]Arene Scaffolds.

With their ten peripheral substituents, pillar[5]arenes are attractive compact scaffolds for the construction of nanomaterials with a controlled number of functional groups distributed around the macrocyclic core. This review paper is focused on the functionalization of pillar[5]arene derivatives with small dendrons to generate dendrimer-like nanomaterials and bioactive compounds. Examples include non-viral gene vectors, bioactive glycoclusters, and liquid-crystalline materials.

Supramolecular Arene-Ruthenium Metallacycle with Thermotropic Liquid-Crystalline Properties.

Functionalization of 1,4-di(4-pyridinyl)benzene with poly(arylester) dendrimers bearing cyanobiphenyl end-groups gives a bidentate dendromesogenic ligand (L) that exhibits thermotropic liquid-crystalline properties. Combination of the diruthenium complex [Ru2(p-cymene)2(donq)][DDS]2 (M) with L, by coordination-driven self-assembly, affords the discrete and well-defined metallacycle M2L2. Like L, this supramolecular dendritic system displays mesomorphic properties above 50 °C. Both compounds L and M2L2 show smectic phases, characterized by a multilayered organization of the multiple components.

Liquid-Crystalline Tris[60]fullerodendrimers.

Liquid-crystalline tris[60]fullerodendrimers based on first- and second-generation poly(arylester)dendrons carrying cyanobiphenyl mesogens were synthesized for the first time by the olefin cross-metathesis reaction between type I (terminal) and type II (α,ß-unsaturated carbonyl) olefinic precursors, using a second-generation Grubbs or Hoveyda-Grubbs catalyst. The modular synthetic approach developed here also allowed the selective preparation of the [60]fullerene-free, mono[60]fullerodendrimer, and bis[60]fullerodendrimer derivatives from the appropriate precursors. As revealed by polarized optical microscopy, differential scanning calorimetry, and small-angle X-ray scattering, all of the materials displayed liquid-crystalline properties. In agreement with the nature of the dendritic building blocks, the emergence of lamellar mesophases (smectic C and/or smectic A phases), with the segregation of the various constitutive parts, was systematically observed. The small variation of the mesomorphic temperature range and of the mesophase stability suggested that the mesomorphism is essentially dominated by the dendrimer itself and is regulated by a subtle adaptive mechanism, in which the proportion of monolayering and bilayering arrangements of the multisegregated lamellar mesophases is modified in order to compensate the space requirements of each of the elementary building blocks, namely, the [60]fullerene units, the cyanobiphenyl mesogens, and the dendritic matrix.

Preparation of Pillar[5]arene-Based [2]Rotaxanes by a Stopper-Exchange Strategy.

A pillar[5]arene-containing rotaxane building block bearing exchangeable stoppers has been prepared in multigram scale quantities with high yields from the reaction of 2,4-dinitrophenol (DNP) with the inclusion complex resulting from the association of dodecanedioyl chloride with 1,4-diethoxypillar[5]arene. Stopper exchange reactions have been achieved by treatment of the resulting DNP diester with various amines through an addition-elimination mechanism preventing the unthreading of the axle component during the reaction and thus preserving the [2]rotaxane structures. The resulting diamide [2]rotaxane derivatives have thus been obtained in good to excellent yields. Importantly, [2]rotaxanes difficult or impossible to prepare by direct introduction of the two stoppers in a single synthetic step are now easily available.

Design, Synthesis, and Self-Assembly Behavior of Liquid-Crystalline Bis-[60]Fullerodendrimers.

Bis-[60]fullerodendrimers were synthesized by assembling [60]fullerene-containing type I (terminal olefin) and type II (α,ß-unsaturated carbonyl olefin) olefins through the olefin cross-metathesis reaction. The synthetic modular approach developed in this study allowed the preparation of mono-[60]fullerodendrimers and their [60]fullerene-free analogues. First- and second-generation poly(aryl ester) dendrons carrying cyanobiphenyl mesogens were used as liquid-crystalline promoters. The liquid-crystalline properties were studied by polarized optical microscopy, differential scanning calorimetry, and small-angle X-ray scattering. In agreement with the nature and structure of the dendrimers, nematic, smectic, and multisegregated lamellar phases were observed. Owing to its versatility and tolerance towards many functional groups, olefin cross-metathesis proved to be a reaction of choice for the elaboration of molecular materials with complex architectures.

From Pillar[n]arene Scaffolds for the Preparation of Nanomaterials to Pillar[5]arene-containing Rotaxanes.

Pillar[n]arenes are a new class of macrocycles that are efficiently prepared from readily available building blocks. In this particular field, our research teams became interested in the use of a pillar[5]arene core as a compact scaffold for the synthesis of nanomaterials with a controlled distribution of functional groups on both rims of the macrocyclic framework. Such compounds have found applications in biology as multivalent ligands for specific lectines or as polycationic compounds for gene delivery. Liquid-crystalline derivatives have been prepared by grafting mesogenic subunits on the pillar[5]arene core. On the other hand, we also became interested in the preparation of pillar[5]arene-containing [2]rotaxanes. In particular, we have shown that pillar[5] arene-based [2]rotaxanes can be obtained from the reaction of amine stoppers with pseudo-rotaxanes resulting from the association of a pillar[5]arene derivative with a diacyl chloride reagent. Finally, amphiphilic [2]rotaxanes have been prepared and incorporated in thin ordered films at the air-water interface.

Piling Up Pillar[5]arenes To Self-Assemble Nanotubes.

New liquid-crystalline pillar[5]arene derivatives have been prepared by grafting first-generation Percec-type poly(benzylether) dendrons onto the macrocyclic scaffold. The molecules adopt a disc-shaped structure perfectly suited for self-organization into a columnar liquid-crystalline phase. In this way, the pillar[5]arene cores are piled up, thus forming a nanotubular wire encased within a shell of peripheral dendrons. The capability of pillar[5]arenes to form inclusion complexes has been also exploited. Specifically, detailed binding studies have been carried out in solution with 1,6-dicyanohexane as the guest. Inclusion complexes have also been prepared in the solid state. Supramolecular organization into the Colh mesophase has been deduced from X-ray diffraction data and found to be similar to that observed within the crystal lattice of a model inclusion complex prepared from 1,4-dimethoxypillar[5]arene and 1,6-dicyanohexane.

NMR spectroscopy and DFT calculations of a self-assembled arene ruthenium rectangle obtained from a combination of coordination and hydrogen bonds.

The hydrogen-bonded arene ruthenium metalla-rectangle, [(p-cymene)2Ru2(OO∩OO)(UPy)2]2(4+), obtained from 1-(4-oxo-6-undecyl-1,4-dihydropyrimidin-2-yl)-3-(pyridin-4-ylmethyl)urea (UPy) and the dinuclear arene ruthenium clip (p-cymene)2Ru2(OO∩OO)Cl2 (OO∩OO = 2,5-dioxido-1,4-benzoquinonato), is investigated by means of solution-phase NMR spectroscopy. Rotating frame nuclear Overhauser effect measurements are used to probe the H-bond network that drives the UPy self-assembly as well as the full rectangular supramolecular system. An effective distance that takes into account both intra- and intermolecular polarization-transfer pathways is utilised for data analysis. The experimental findings are corroborated by DFT calculations of NMR parameters and internuclear distances, thus confirming the formation of a very stable tetranuclear metalla-assembly.

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.

Designing supramolecular liquid-crystalline hybrids from pyrenyl-containing dendrimers and arene ruthenium metallacycles.

The association of the arene ruthenium metallacycle [Ru4(p-cymene)4(bpe)2(donq)2][DOS]4 (bpe = 1,2-bis(4-pyridyl)ethylene, donq = 5,8-dioxydo-1,4-naphtoquinonato, DOS = dodecyl sulfate) with pyrenyl-functionalized poly(arylester) dendrimers bearing cyanobiphenyl end-groups is reported. The supramolecular dendritic systems display mesomorphic properties as revealed by polarized optical microscopy, differential scanning calorimetry and small-angle X-ray scattering measurements. The multicomponent nature of the dendrimers and of the corresponding host-guest supramolecules (i.e., end-group mesogens, dendritic core, pyrene unit, aliphatic spacers, and metallacycle) leads to the formation of highly segregated mesophases with a complex multilayered structure due to the tendency of the various constitutive building-blocks to separate in different organized zones. The pyrenyl dendrimers exhibit a multilayered smectic A-like phase, thereafter referred to as LamSmA phase to emphasize this unaccustomed morphology. As for the corresponding Ru4-metallacycle adducts, they self-organize into a multicontinuous thermotropic cubic phase with the Im3̅m space group symmetry. This represents a unique example of liquid-crystalline behavior observed for such large and complex supramolecular host-guest assemblies. Models of their supramolecular organizations within both mesophases are proposed.

Building liquid crystals from the 5-fold symmetrical pillar[5]arene core.

Comparison of the liquid-crystalline properties of a pillar[5]arene core functionalized with 10 mesogenic cyanobiphenyl units with those of a corresponding model compound revealed the strong influence of the macrocyclic pillar[5]arene core on the mesomorphic properties.

Enhancement of cytotoxicity by combining pyrenyl-dendrimers and arene ruthenium metallacages.

Three generations of pyrenyl bis-MPA dendrimers with two different end-groups, acetonide (pyr(Gn)) or alcohol (pyr(Gn-OH)) (n = 1-3), were synthesized, and the pyrenyl group of the dendritic molecules was encapsulated in the arene ruthenium metallacages, [Ru(6)(p-cymene)(6)(OO∩OO)(3)(tpt)(2)](6+) (OO∩OO = 5,8-dioxydo-1,4-naphtaquinonato (donq) [1](6+) and 6,11-dioxydo-5,12-naphtacenedionato (dotq) [2](6+); tpt =2,4,6-tri(pyridin-4-yl)-1,3,5-triazine). The host-guest properties of [guest⊂1](6+) and [guest⊂2](6+) were studied in solution by NMR and UV-vis spectroscopic methods, thus allowing the determination of the affinity constants. Moreover, the cytotoxicity of these water-soluble host-guest systems and the pyrenyl-dendrimers was evaluated on human ovarian cancer cells.

Design of liquid-crystalline gold nanoparticles by click chemistry.

Mesomorphic alkyne-based first- and second-generation dendrons were grafted onto gold nanoparticles carrying azide groups under click reaction conditions. The nanoparticles decorated with the dendrons displayed liquid-crystalline properties and good thermal stability.

Encapsulation of pyrene-functionalized poly(benzyl ether) dendrons into a water-soluble organometallic cage.

Two generations of lipophilic pyrenyl functionalized poly(benzyl ether) dendrimers (P(1) and P(2)) have been synthesized. The thermal properties of the two functionalized dendrimers have been investigated, and the pyrenyl group of the dendritic molecules encapsulated in the arene-ruthenium metalla-cage, [Ru(6)(p-cymene)(6)(tpt)(2)(donq)(3)](6+) ([1](6+)) (tpt=2,4,6-tri(pyridin-4-yl)-1,3,5-triazine; donq=5,8-dioxydo-1,4-naphthoquinonato). The host-guest properties of [P(1)⊂1](6+) and [P(2)⊂1](6+) were studied in solution by NMR and UV/Vis spectroscopic methods, thus allowing the determination of the affinity constants. Moreover, the cytotoxicity of these water-soluble host-guest systems was evaluated on human ovarian cancer cells.

Double targeting of tumours with pyrenyl-modified dendrimers encapsulated in an arene-ruthenium metallaprism.

The self-assembly of 2,4,6-tris(pyridin-4-yl)-1,3,5-triazine (tpt) triangular panels with p-cymene-ruthenium building blocks and 5,8-dioxido-1,4-naphthoquinonato (donq) bridges, in the presence of pyrenyl-containing dendrimers of different generations (P(0), P(1) and P(2)), affords the triangular prismatic host-guest compounds [P(n)⊂Ru(6)(p-cymene)(6)(tpt)(2)(donq)(3)](6+) ([P(n)⊂1](6+)). The host-guest nature of these systems, with the pyrenyl moiety being encapsulated in the hydrophobic cavity of the cage and the dendritic functional group pointing outwards, was confirmed by NMR spectroscopy ((1)H, 2D and DOSY). The host-guest properties of these systems were studied in solution by NMR and UV/Vis spectroscopic methods, allowing the determination of their affinity constants (K(a)). Moreover, the ability of these water-soluble host-guest systems to carry the pyrenyl-containing dendrimers into cancer cells was evaluated on human ovarian cancer cells. The host-guest systems are all more cytotoxic than the empty cage [1][CF(3)SO(3)](6) (IC(50)≈4 µM), with the most active compound, [P(0)⊂1][CF(3)SO(3)](6), being an order of magnitude more cytotoxic.

Accordion-optimized DEPT experiments.

In this contribution, a pulse sequence is described for recording accordion-optimized DEPT experiments. The proposed ACCORDEPT experiment detects a wide range of one-bond coupling constants using accordion optimization. As a proof of concept, this strategy has been applied to a mesogen containing a large range of one-bond (1)J(CH) coupling constants associated with the various structural elements. The ACCORDEPT experiment afforded significant enhancements for the resonances with the larger (1)J(CH) couplings, similar SNR for aliphatic resonances, but reduced SNR for aliphatic resonances as compared with the standard DEPT experiment. In addition, the ACCORDEPT is straightforward to implement, does not require any supplementary calibration procedures and can be used under automated conditions without difficulty by inexperienced users.

Optically active liquid-crystalline fullerodendrimers from enantiomerically pure fulleropyrrolidines.

A synthetic methodology based on the 1,3-dipolar cycloaddition reaction was developed to design enantiomerically pure liquid-crystalline fullerodendrimers.

Diastereoisomerically pure fulleropyrrolidines as chiral platforms for the design of optically active liquid crystals.

Incorporation of [60]fullerene (C(60)) within self-organizing systems is conceptually challenging but allows us to obtain materials which combine the characteristics (anisotropy, organization) of condensed mesophases with the properties of C(60) (photo- and electrochemical activity). Here, we report on the synthesis, characterization, and liquid-crystalline properties of four optically active fullerodendrimers, which are chiral at the point of conjunction between the fullerene scaffold and the mesogenic moieties. Thus, the novelty of this study is to take advantage of the asymmetric carbon atom created during the 1,3-dipolar cycloaddition reaction on C(60) in order to induce mesoscopic chirality in the materials. Four diastereoisomeric fulleropyrrolidines ((R,S)-1, (R,R)-1, (S,R)-1, and (S,S)-1) were synthesized and associated with a second-generation nematic (N) dendron to give fullerodendrimers ((R,S)-2, (R,R)-2, (S,R)-2, and (S,S)-2) which display chiral nematic (N*) phases. The absolute configurations of the stereogenic centers were determined by X-ray crystallography, 1D and 2D NMR experiments, and circular dichroism (CD) spectroscopy. The liquid-crystalline properties of the fullerodendrimers were studied by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The fulleropyrrolidine derivatives 2 exhibit supramolecular helicoidal organizations with a right-handed helix for the (R,S)-2 and (R,R)-2 diastereoisomers and a left-handed helix for the (S,R)-2 and (S,S)-2 diastereoisomers. This result suggests that the self-organization of such supermolecular materials can be controlled at the molecular level by the introduction of only one chiral center.

[60]Fullerene-based liquid crystals acting as acid-sensitive fluorescent probes.

Functionalization of [60]fullerene with liquid-crystalline dendrimers and a dibutylaniline-based phenylenevinylene moiety leads to supramolecular materials, the fluorescence of which responds to acid-base stimuli.

High-resolution characterization of liquid-crystalline [60]fullerenes using solid-state nuclear magnetic resonance spectroscopy.

Liquid-crystalline materials containing fullerenes are valuable in the development of supramolecular switches and in solar cell technology. In this study, we characterize the liquid-crystalline and dynamic properties of fullerene-containing thermotropic compounds using solid-state natural abundance (13)C NMR experiments under stationary and magic angle spinning sample conditions. Chemical shifts spectra were measured in isotropic, liquid-crystalline nematic and smectic A and crystalline phases using one-dimensional (13)C experiments, while two-dimensional separated local-field experiments were used to measure the (1)H- (13)C dipolar couplings in mesophases. Chemical shift and dipolar coupling parameters were used to characterize the structure and dynamics of the liquid-crystalline dyads. NMR data of fullerene-containing thermotropic liquid crystals are compared to that of basic mesogenic unit and mesomorphic promoter compounds. Our NMR results suggest that the fullerene-ferrocene dyads form highly dynamic liquid-crystalline phases in which molecules rotate fast around the symmetry axis on the characteristic NMR time scale of approximately 10 (-4) s.