Hexabenzocoronene Graphitic Nanocoils Appended with Crown Ethers: Supramolecular Chirality Induced by Host-Guest Interaction.

We have designed and synthesized two new achiral hexa-peri-hexabenzocoronene (HBC) derivatives, HBCCE and HBCTEG-CE , which bear the crown ether as the pendant for the amino acid binding site. The HBCCE self-assembled into a racemic mixture of P- and M-handed helical nanocoils, however, in the presence of chiral amino acid guests, it formed helical nanocoils with one-handed screw sense. The effects of the concentration, type and configuration of the guests on the induced circular dichroism (ICD) during the co-assembly of HBCCE with chiral amino acids were also investigated. Additionally, after complete removal of the chiral guests, the optically active nanocoils did not racemize, even in the presence of excess amino acids with the opposite configuration. In contrast, HBCTEG-CE with a long triethylene glycol (TEG) chain between the crown ether group and the HBC unit did not exhibit ICD during the co-assembly with chiral amino acids.

Helix Sense-Selective Supramolecular Polymerization Seeded by a One-Handed Helical Polymeric Assembly.

Helix sense-selective supramolecular polymerization was achieved using a one-handed helical nanotubular polymeric assembly as a seed. First, bipyridine (BPY)-appended achiral hexabenzocoronene ((BPY)HBC) was copolymerized noncovalently with chiral (BPY)HBC(S) (or (BPY)HBC(R)) at a molar ratio of 9:1, which, via the sergeants-and-soldiers effect, afforded a P-helical (or M-helical) nanotube, which was then treated with Cu(2+) to transform into structurally robust ((BPY)Cu)NT(P) (or ((BPY)Cu)NT(M)) with a Cu(2+)/BPY coordination polymer shell. Helical seeds ((BPY)Cu)NT(P) and ((BPY)Cu)NT(M) brought about the controlled assembly of fluorinated chiral FHBC(S) and FHBC(R) as well as achiral FHBC to yield one-handed helical nanotubular supramolecular block copolymers, in which the helical senses of the newly formed block segments were solely determined by those of the helical seeds employed. Noteworthy, FHBC(S) and FHBC(R) alone without the helical seeds form ill-defined agglomerates. Attempted supramolecular polymerization of a racemic mixture of FHBC(S) and FHBC(R) from ((BPY)Cu)NT(P) (or ((BPY)Cu)NT(M)) resulted in its chiral separation, affording P-helical (or M-helical) diastereomeric block segments composed of FHBC(S)and FHBC(R) with different thermodynamic properties.

Size-selective recognition by a tubular assembly of phenylene-pyrimidinylene alternated macrocycle through hydrogen-bonding interactions.

Study of artificial tubular assemblies as a useful host scaffold for size-selective recognition and release of guest molecules is an important subject in host-guest chemistry. We describe well-defined self-assembled nanotubes (NT6mer) formed from π-conjugated m-phenylene-pyrimidinylene alternated macrocycle 16mer that exhibit size-selective recognition toward a specific aromatic acid. In a series of guest molecules, a size-matched trimesic acid (G3) gives inclusion complexes (NT6mer⊃G3) in dichloromethane resulting in an enhanced and red-shifted fluorescence. (1)H nuclear magnetic resonance (NMR) titration experiments indicated that the complex was formed in a 1:1 molar ratio. Density functional theory (DFT) calculations and the binding constant value (K = 1.499 × 10(5) M(-1)) of NT6mer with G3 suggested that the complex involved triple hydrogen-bonding interactions. The encapsulated guest G3 molecules can be readily released from the tubular channel through the dissociation of hydrogen bonding by the addition of a polar solvent such as dimethylsulfoxide (DMSO). In contrast, 16mer could not form self-assembled nanotubes in CHCl3 or tetrahydrofuran (THF) solution, leading to weak or no size-selective recognizability, respectively.

Selective synthesis of single- and multi-walled supramolecular nanotubes by using solvophobic/solvophilic controls: stepwise radial growth via "coil-on-tube" intermediates.

Novel hexa-peri-hexabenzocoronene (HBC) derivatives, (F) HBC and (F) HBC*, which carry perfluoroalkyl segments on one side of the HBC core and long alkyl tails on the other, were synthesized. Their perfluoroalkyl segments are highly solvated in C6 F6 (solvophilic effect) and do not assemble, whereas in CH2 Cl2 , they are excluded (solvophobic effect) and assemble together consequently. For example, the use of C6 F6 and CH2 Cl2 as assembling media for (F) HBC leads to the selective formation of single- and multi-walled nanotubes, respectively. When a higher monomer concentration is applied in CH2 Cl2 , multi-walled nanotubes with a larger number of walls result. (F) HBC in CH2 Cl2 self-assembles rather slowly, thereby allowing for the observation of coil-on-tube structures, which are possible intermediates for the stepwise radial growth of the nanotubular wall. Casting of the multi-walled nanotubes onto a quartz plate yields a superhydrophobic thin film with a water contact angle of 161±2°.

Dynamic or nondynamic? Helical trajectory in hexabenzocoronene nanotubes biased by a detachable chiral auxiliary.

When ether vapor was allowed to diffuse into a CH(2)Cl(2) solution of an enantiomer of a hexa-peri-hexabenzocoronene (HBC) derivative carrying a chiral (BINAP)Pt(II)-appended coordination metallacycle (HBC(Py)([(R)-Pt]) or HBC(Py)([(S)-Pt])), screw-sense-selective assembly took place to give optically active nanotubes (NT(Py)([(R)-Pt]) or NT(Py)([(S)-Pt])) with helical chirality, which were enriched in either left-handed (M)-NT(Py)([(R)-Pt]) or right-handed (P)-NT(Py)([(S)-Pt]), depending on the absolute configuration of the (BINAP)Pt(II) pendant. When MeOH was used instead of ether for the vapor-diffusion-induced assembly, nanocoils formed along with the nanotubes. As determined by scanning electron microscopy, the diastereomeric excess of the nanocoils was 60% (80:20 diastereomeric ratio). Removal of the (BINAP)Pt(II) pendants from NT(Py)([(R)-Pt]) or NT(Py)([(S)-Pt]) with ethylenediamine yielded metal-free nanotubes (NT(Py)) that remained optically active even upon heating without any change in the circular dichroism spectral profile. No helical inversion took place when NT(Py) derived from HBC(Py)([(R)-Pt]) or HBC(Py)([(S)-Pt]) was allowed to complex with (BINAP)Pt(II) with an absolute configuration opposite to the original one.

2-[3-Meth-oxy-5-(pyrimidin-2-yl)phen-yl]pyrimidine.

The title compound, C15H12N4O, was synthesized by a standard Suzuki cross-coupling reaction. The terminal pyrim-idine rings are rotated at dihedral angles of 12.06 (4) and -13.13 (4)° with respect to the central benzene ring. In the crystal, the mol-ecules are connected by two kinds of C-H⋯N hydrogen bonds, forming zigzag chains along the c axis. Weak π-π inter-actions between the benzene and one of the pyrimidine rings are also found and stack the mol-ecules along the b axis [centroid-centroid distance = 4.112 (3) Å].

Ambipolar-transporting coaxial nanotubes with a tailored molecular graphene-fullerene heterojunction.

Despite a large steric bulk of C(60), a molecular graphene with a covalently linked C(60) pendant [hexabenzocoronene (HBC)-C(60); 1] self-assembles into a coaxial nanotube whose wall consists of a graphite-like pi-stacked HBC array, whereas the nanotube surface is fully covered by a molecular layer of clustering C(60). Because of this explicit coaxial configuration, the nanotube exhibits an ambipolar character in the field-effect transistor output [hole mobility (micro(h)) = 9.7 x 10(-7) cm(2) V(-1) s(-1); electron mobility (micro(e)) = 1.1 x 10(-5) cm(2) V(-1) s(-1)] and displays a photovoltaic response upon light illumination. Successful coassembly of 1 and an HBC derivative without C(60) (2) allows for tailoring the p/n heterojunction in the nanotube, so that its ambipolar carrier transport property can be optimized for enhancing the open-circuit voltage in the photovoltaic output. As evaluated by an electrodeless method called flash-photolysis time-resolved microwave conductivity technique, the intratubular hole mobility (2.0 cm(2) V(-1) s(-1)) of a coassembled nanotube containing 10 mol % of HBC-C(60) (1) is as large as the intersheet mobility in graphite. The homotropic nanotube of 2 blended with a soluble C(60) derivative [(6,6)-phenyl C(61) butyric acid methyl ester] displayed a photovoltaic response with a much different composition dependency, where the largest open-circuit voltage attained was obviously lower than that realized by the coassembly of 1 and 2.

Trichlorido[4-meth-oxy-2,6-bis-(2-pyrimidin-2-yl-κN)phenyl-κC(1)]platinum(IV) acetonitrile monosolvate.

In the title complex, [Pt(C(15)H(11)N(4)O)Cl(3)]·CH(3)CN, the Pt(IV) ion adopts a distorted octa-hedral coordination geometry defined by a tridentate cyclo-metalated NCN ligand and three Cl atoms. In the crystal, individual mol-ecules are aggregated into a three-dimensional network by C-H⋯Cl hydrogen-bonding inter-actions and π-π stacking inter-actions between the tridentate ligands, the shortest ring centroid-centroid distance being 3.613 Å.

Metal-ion-coated graphitic nanotubes: controlled self-assembly of a pyridyl-appended gemini-shaped hexabenzocoronene amphiphile.

The assembly line: Hexabenzocoronene amphiphiles appended with pyridyl-terminated triethylene glycol side chains, in combination with trans-[Pt(PhCN)(2)Cl(2)], lead to the formation of graphitic nanotubes. The structural features and dimensions of the nanotubes depend on the assembly conditions. A platinum(II)-bridged cyclic dimer having two HBC units self-assembles into a nanotubular structure.

Systematic studies on structural parameters for nanotubular assembly of hexa-peri-hexabenzocoronenes.

Thirteen different hexa-peri-hexabenzocoronenes (HBCs) I-III were newly synthesized, and their self-assembling behaviors were investigated. Taking into account also the reported behaviors of amphiphilic HBCs, some structural parameters of HBC essential for the tubular assembly were revealed. Points to highlight include (1) the importance of two phenyl groups attached to one side of the HBC unit, (2) essential roles of long paraffinic side chains on the other side of the phenyl groups, and (3) no necessity of hydrophilic oligo(ethylene glycol) side chains. The hierarchical nanotubular structure, rendered by virtue of a synchrotron radiation technique, was virtually identical to our previous proposal, where the nanotubes are composed of helically coiled bilayer tapes with a tilting angle of approximately 45 degrees. Each tape consists of pi-stacked HBC units, where the inner and outer HBC layers are connected by interdigitation of paraffinic side chains. The coiled structure is most likely caused by a steric congestion of the phenyl groups attached to the HBC unit, whose tilting direction may determine the handedness of the helically chiral nanotube.

Reversible transformation of self-assemblies and fluorescence by protonation-deprotonation in pyrimidinylene-phenylene macrocycles.

We describe herein that the self-assembled nanoobjects based on pyrimidinylene-phenylene macrocycles, 1 and 2, which possess the capability to respond to acid-stimuli by proton binding, can undergo reversible transformation of self-assemblies and fluorescence switching by protonation-deprotonation.

Highly selective and sensitive colorimetric probe for hydrogen sulfide by a copper (II) complex of azo-dye based on chemosensing ensemble approach.

A copper (II) complex of azo-dye (Cu-1) has been synthesized by the reaction of 1-(2-pyridylazo)-2-naphthol (1) with copper (II) chloride. The complex Cu-1 is able to selectively sense hydrogen sulfide over other anions followed by the release of compound 1 to give a remarkable change of UV-vis absorption at neutral pH in aqueous solution.

Supramolecular linear heterojunction composed of graphite-like semiconducting nanotubular segments.

One-dimensionally connected organic nanostructures with dissimilar semiconducting properties are expected to provide a reliable platform in understanding the behaviors of photocarriers, which are important for the development of efficient photon-to-electrical energy conversion systems. Although bottom-up supramolecular approaches are considered promising for the realization of such nanoscale heterojunctions, the dynamic nature of molecular assembly is problematic. We report a semiconducting nanoscale organic heterojunction, demonstrated by stepwise nanotubular coassembly of two strategically designed molecular graphenes. The dissimilar nanotubular segments, thus connected noncovalently, were electronically communicable with one another over the heterojunction interface and displayed characteristic excitation energy transfer and charge transport properties not present in a mixture of the corresponding homotropically assembled nanotubes.

Formation of water-dispersible nanotubular graphitic assembly decorated with isothiouronium ion groups and its supramolecular functionalization.

A newly designed Gemini-shaped hexabenzocoronene amphiphile (1), carrying an isothiouronium ion-appended side chain, self-assembles in CH2Cl2 to form a nanotubular object, whose graphitic wall is densely covered by a positively charged molecular layer of isothiouronium ion pendants. The graphitic nanotube can be dispersed uniformly in aqueous media owing to effective hydration as well as electrostatic repulsion. Post-supramolecular functionalization of the nanotube surface is possible, without disruption of the tubular morphology, by taking advantage of a specific interaction of the isothiouronium ion pendants with oxoanion guests. Mixing with sodium poly(4-styrenesulfonate) results in wrapping of the nanotube, while complexation with an electron-accepting oxoanion such as anthraquinone carboxylate allows photoinduced electron transfer from the graphitic wall to the bound guest molecules.

Stabilization of a kinetically favored nanostructure: surface ROMP of self-assembled conductive nanocoils from a norbornene-appended hexa-peri-hexabenzocoronene.

Newly designed norbornene-appended hexabenzocoronene 1 self-assembles, upon diffusion of an Et(2)O vapor into its CH(2)Cl(2) solution, to form either graphitic nanocoils or nanotubes, depending on the self-assembling conditions. The coiled assembly, selectively formed at 15 degrees C, is a kinetic intermediate for the tubular assembly and transforms into nanotubes on standing at 25 degrees C. However, post-ring-opening metathesis polymerization of the norbornene pendants of 1 enhances the thermal stability of the coiled assembly as well as the tubular one and disables a thermodynamic coil-to-tube transition. The polymerized nanocoils show an electroconductivity of 1 x 10(-)(4) S cm(-)(1) upon doping with I(2), while the nonpolymerized nanocoils are disrupted upon being doped.

Self-assembled graphitic nanotubes with one-handed helical arrays of a chiral amphiphilic molecular graphene.

Self-assembly of a Gemini-shaped, chiral amphiphilic hexa-peri-hexabenzocoronene having two chiral oxyalkylene side chains, along with two lipophilic side chains, yields graphitic nanotubes with one-handed helical chirality. The nanotubes are characterized by an extremely high aspect ratio of >1,000 and have a uniform diameter of 20 nm and a wall thickness of 3 nm. The nanotubes with right- and left-handed helical senses were obtained from the (S)- and (R)-enantiomers of the amphiphile, respectively, due to an efficient translation of point chirality into supramolecular helical chirality. The (S)- and (R)-enantiomers coassemble at varying mole ratios to give nanotubes, whose circular dichroism profiles are almost unchanged over a wide range of the enantiomeric excess of the amphiphile (100-20%). The high level of chirality amplification thus observed indicates a long-range cooperativity in the self-assembling process. In sharp contrast, a hexabenzocoronene amphiphile with chiral lipophilic side chains did not form nanotubular assemblies. The present work demonstrates the majority rule in noncovalent systems and also may provide a synthetic strategy toward realization of molecular solenoids.

Controlled self-assembly triggered by olefin metathesis: cross-linked graphitic nanotubes from an amphiphilic hexa-peri-hexabenzocoronene.

Acyclic diene metathesis (ADMET) in CH2Cl2 of a Gemini-shaped nonionic hexabenzocoronene amphiphile (2), bearing triethylene glycol chains with terminal allylic functionalities, resulted in spontaneous formation of graphitic nanotubes with a cross-linked surface. Without ADMET, 2 did not self-assemble to form a tubular structure due to a high solubility in CH2Cl2. Although 2 formed nanotubes in THF, ADMET on the surface of the preformed nanotubes in THF proceeded only sluggishly and resulted in partial disruption of the tubular structure. The cross-linked nanotubes showed a softening temperature (244 degrees C) higher than that of the uncross-linked version (195 degrees C) and preserved their hollow structure much longer upon heating.

Self-assembled hexa-peri-hexabenzocoronene graphitic nanotube.

An amphiphilic hexa-peri-hexabenzocoronene self-assembles to form a pi-electronic, discrete nanotubular object. The object is characterized by an aspect ratio greater than 1000 and has a uniform, 14-nanometer-wide, open-ended hollow space, which is an order of magnitude larger than those of carbon nanotubes. The wall is 3 nanometers thick and consists of helical arrays of the pi-stacked graphene molecule, whose exterior and interior surfaces are covered by hydrophilic triethylene glycol chains. The graphitic nanotube is redox active, and a single piece of the nanotube across 180-nanometer-gap electrodes shows, upon oxidation, an electrical resistance of 2.5 megohms at 285 kelvin [corrected]. This family of molecularly engineered graphite with a one-dimensional tubular shape and a chemically accessible surface constitutes an important step toward molecular electronics.