1D Supramolecular Assemblies That Crystallize and Form Gels in Response to the Shape-Complementarity of Alcohols.

N-9-Fluorenylmethyloxycarbonyl (Fmoc)- and C-tertiary butyl (t-Bu)-protected glutamate (L-2), bearing a phenanthroline moiety at the side residue, forms 1D supramolecular assemblies via H-bonding as well as undergoing π-stacking interactions to afford crystals or gels that depend on the shape-complementarity of coexisting alcohols, as demonstrated by structural analyses on these assemblies by means of single-crystal X-ray diffractometry and supplemented with small- and wide-angle X-ray scattering data. Moreover, the rheological measurements on the gels help to define a model for when gels and crystals are expected and found. These observations and conclusions highlight an important, but not very appreciated, aspect of solute-solvent interactions within supramolecular assemblies that can allow the constituent-aggregating molecules in some systems to exhibit high selectivity toward the structures of their solvents. The consequences of this selectivity, as demonstrated here by single-crystal and powder X-ray diffraction data, can lead to self-assembled structures which alter completely the bulk phase properties and morphology of the materials. In that regard, rheological measurements have helped to develop a model to explain when gels and phase-separated mixtures of crystals and solvents are expected.

Mixed Conductive, Injectable, and Fluorescent Supramolecular Eutectogel Composites.

Eutectogels are an emerging family of soft ionic materials alternative to ionic liquid gels and organogels, offering fresh perspectives for designing functional dynamic platforms in water-free environments. Herein, the first example of mixed ionic and electronic conducting supramolecular eutectogel composites is reported. A fluorescent glutamic acid-derived low-molecular-weight gelator (LMWG) was found to self-assemble into nanofibrillar networks in deep eutectic solvents (DES)/poly(3,4-ethylenedioxythiophene) (PEDOT): chondroitin sulfate dispersions. These dynamic materials displayed excellent injectability and self-healing properties, high ionic conductivity (up to 10-2  S cm-1 ), good biocompatibility, and fluorescence imaging ability. This set of features turns the mixed conducting supramolecular eutectogels into promising adaptive materials for bioimaging and electrostimulation applications.

A Glutathione-Responsive Short Sequence of Metal-Organic Complex Array.

A short metal-organic complex array (MOCA) containing a sequence of RPtRRu (1Cl ) was found to exhibit unique responses to a major biothiol, glutathione (GSH). Upon binding of GSH to 1Cl , the resultant 1:1 complex (1GS ) formed nanofibrous assemblies that suggested supramolecular polymerization through the double-salt-bridge structure formation. The binding behavior of this MOCA sequence to calf thymus DNA was also dependent on GSH; a larger conformational change of DNA was observed upon binding with 1GS , relative to that with 1Cl .

Platinum(II) Terpyridine Complex That Switches Its Photochemical Reactivity in Response to Its Chromic Behavior in the Crystalline State.

A platinum(II) terpyridine complex having an enantiopure lactate anion afforded hydrated crystals l- or d-1hyd containing infinite chains of interacting Pt centers, while their dehydration induced crystal-to-crystal transformation into l- or d-1dehyd, respectively, exhibiting less significant Pt-Pt and/or ligand-ligand interactions. That transformation was accompanied by changes in the color as well as the photochemical reactivity of the crystals, where l-1dehyd showed higher reactivity than l-1hyd in the presence of amines under visible-light irradiation.

Modular synthesis of metal-organic complex arrays containing precisely designed metal sequences.

A modular synthetic approach is reported for the synthesis of heterometallic metal-organic complex arrays (MOCAs). Modules of four metal centers containing three different metals copper(II), nickel(II), platinum(II), or ruthenium(II) are prepared using a solid-phase polypeptide synthesis technique and then linked in solution to make MOCAs of eight metal centers as linear, T-branched, and H-branched compounds. The MOCA molecular topologies thus have specific unique linear and branched sequences of metals along the peptide backbone.

Coassembly-Directed Fabrication of an Exfoliated Form of Alternating Multilayers Composed of a Self-assembled Organoplatinum(II) Complex-Fullerene Dyad.

The self-assembly of covalently linked dyad 1a of cyclometalated organoplatinum(II) complex and fullerene afforded alternating multilayers of electron-rich and -deficient molecular components. On the other hand, the coassembly of 1a with organoplatinum(II) complex 2 having no fullerene moiety gave an exfoliated form of the multilayers, by inhibiting the interdigitation of organoplatinum(II) complex moieties of 1a. The coassembled 1a/2 transports both of the photogenerated holes and electrons, while the self-assembled 1a allows only the transportation of electrons under the same conditions.

Functional oligo- and polypeptide assemblies for photochemical, optical and electronic applications.

The primary and secondary structures of peptides are useful as scaffolds to sequentially arrange functional groups of molecules. In this review, we review self-assembled functional peptides, whereby peptides with appropriate amino acid sequences can assemble using functional groups on their side chains. First, we apply our design strategies for the synthesis of peptide-based materials with sequenced side chains with polar moieties, organic dyes and metal complexes. The synthetic oligopeptides thus obtained exhibit inherent photoinduced charge separation and electrochemical redox activities, as well as responses to bio-sequences. Next, catalytic and photocatalytic oxidation reduction reactions and hydrogen evolution reactions are shown by utilizing the peptides with separated functionalities on both sides of ß-sheets by hybridizing with electro- and photoactive graphene oxide and metal nanoparticles. Finally, the self-assembled natural proteins that form micrometre-scale spherical geometry and fibres are utilized for optical and electronic applications. The silk fibroin forms well-defined microspheres with smooth surface morphology, leading to properties suitable for use in optical resonators, which can sense external humidity because of the hygroscopic nature of silk fibroin. Dragline silk fibres can act as optical waveguides that can perform intermediate natural polymer-based optical logic operations. These functional peptides are utilizable for various applications in catalysis, optics and electronics.

Selective supramolecular fullerene-porphyrin interactions and switching in surface-confined C60-Ce(TPP)2 dyads.

The control of organic molecules, supramolecular complexes and donor-acceptor systems at interfaces is a key issue in the development of novel hybrid architectures for regulation of charge-carrier transport pathways in nanoelectronics or organic photovoltaics. However, at present little is known regarding the intricate features of stacked molecular nanostructures stabilized by noncovalent interactions. Here we explore at the single molecule level the geometry and electronic properties of model donor-acceptor dyads stabilized by van der Waals interactions on a single crystal Ag(111) support. Our combined scanning tunneling microscopy/spectroscopy (STM/STS) and first-principles computational modeling study reveals site-selective positioning of C(60) molecules on Ce(TPP)(2) porphyrin double-decker arrays with the fullerene centered on the π-system of the top bowl-shaped tetrapyrrole macrocycle. Three specific orientations of the C(60) cage in the van der Waals complex are identified that can be reversibly switched by STM manipulation protocols. Each configuration presents a distinct conductivity, which accounts for a tristable molecular switch and the tunability of the intradyad coupling. In addition, STS data evidence electronic decoupling of the hovering C(60) units from the metal substrate, a prerequisite for photophysical applications.

Isomers of metal-organic complex arrays.

Three metal-organic complex arrays (MOCAs) with a specific sequence of metal centers as well as that of amino acid units were synthesized. These MOCAs are also isomers exhibiting a gelation capability dependent on the location of the metal complexes in the arrays.

Gelation of a π-Decorated Glutamate as a Homochiral Selective Self-assembly to Obtain Macroscopic Chiral Symmetry Breaking.

An N-Fmoc and C-tBu-protected glutamate (1) bearing a phenanthrene moiety at the side residue crystalizes and gels to afford hetero- and homochiral assemblies, respectively, depending on its optical purity or solvent. When a non-stoichiometric mixture of enantiomers of 1 in acetonitrile was treated with the conditions that leave a mixture of gel and supernatant, it exhibited the self-disproportionation of enantiomers with an enrichment of the major enantiomer in the gel. Under similar conditions, a racemic mixture of 1 also provided a gel/supernatant mixture, where the gel was enriched in either of L or D-form of 1 stochastically as the result of macroscopic chiral symmetry breaking in its gelation process.

Synthesis of metal−organic complex arrays.

The Merrifield solid-phase peptide synthesis technique has been adapted to the synthesis of homo- and heterometallic metal−organic complex arrays (MOCAs). A terpyridine-appended and Fmoc-protected L-tyrosine derivative was metalated with Pt(II), Rh(III), or Ru(II) ions in solution and sequentially coupled at the surface of functionalized polymeric resin to give a metal complex triad (Rh−Pt−Ru), tetrad (Ru−Rh−Pt−Pt), pentad (Rh−Pt−Ru−Pt−Rh), and hexad (Rh−Pt−Ru−Pt−Rh−Pt) with specific metal sequence arrangements. These were cleaved from the resin, and their character was confirmed by mass spectrometry.

Ferromagnetic spin coupling between endohedral metallofullerene La@C82 and a cyclodimeric copper porphyrin upon inclusion.

The cyclic host cyclo-[P(Cu)](2) carrying two covalently connected Cu(II) porphyrin units can accommodate La@C(82), a paramagnetic endohedral metallofullerene, in its cavity to form the inclusion complex cyclo-[P(Cu)](2)⊃La@C(82), which can be transformed into the caged complex cage-[P(Cu)](2)⊃La@C(82) by ring-closing olefin metathesis of its side-chain olefinic termini. On the basis of electron spin resonance (ESR) and electron spin transient nutation (ESTN) studies, cyclo-[P(Cu)](2)⊃La@C(82) is the first ferromagnetically coupled inclusion complex featuring La@C(82), whereas cage-[P(Cu)](2)⊃La@C(82) is ferrimagnetic.

Electron- or hole-transporting nature selected by side-chain-directed π-stacking geometry: liquid crystalline fused metalloporphyrin dimers.

Novel liquid crystalline (LC) semiconductors were prepared from the copper complex of a fused porphyrin dimer as the electroactive core by attaching to its periphery dodecyl and semifluoroalkyl side chains site-specifically (P≡P(hetero)) and semifluoroalkyl side chains alone (P≡P(homo)). The former and latter formed rectangular columnar and orthorhombic LC mesophases, respectively, where the stacking geometries of the π-conjugated core are quite different from one another. Although the π-electronic properties of the core units in P≡P(hetero) and P≡P(homo) in solution are substantially identical to one another, transient photocurrent profiles of their LC states under time-of-flight conditions clearly showed that P≡P(hetero) behaves as an n-type semiconductor, whereas P≡P(homo), in contrast, behaves as a p-type semiconductor.

One-pot enantioselective extraction of chiral fullerene C76 using a cyclic host carrying an asymmetrically distorted, highly pi-basic porphyrin module.

Optical resolution of nonsubstituted chiral fullerenes such as C(76) is one of the most challenging subjects in host-guest chemistry. The novel cyclic host 1(2H), which bears a meso-diaryl-beta-octaethylporphyrin (P(2H)) unit on one side and its chiral N-2-acetoxyethyl derivative (P(N-EtOAc)) on the other, traps C(76) enantioselectively in its cavity and furnishes 7% enantiomeric excess in a single extraction. Control experiments using reference hosts indicated the importance of the high pi-basicity and large asymmetric distortion of the chiral N-substituted porphyrin unit (P(N-EtOAc)) in 1(2H) for the enantioselection of C(76).

Chiroselective assembly of a chiral porphyrin-fullerene dyad: photoconductive nanofiber with a top-class ambipolar charge-carrier mobility.

Upon slow admission of MeOH, the enantiomerically pure form of chiral amphiphilic porphyrin-fullerene dyad 1 in CH(2)Cl(2) self-assembles at 25 degrees C into nanofibers with a built-in donor/acceptor heterojunction, while its racemic form, under identical conditions, self-assembles into submicrometer-sized spheres with a donor/acceptor arrangement essentially different from that in the nanofiber assembly. Although a cast film of the latter hardly shows a photoconducting profile on micrometer-gap electrodes, the former sample clearly displays photoconduction with an ambipolar charge-transporting character. The electron and hole mobilities under zero electric field, as estimated from time-of-flight profiles, are 0.14 and 0.10 cm(2) V(-1) s(-1), respectively, which are comparable to or even better than those reported for top-class organic materials with a donor/acceptor heterojunction.

Amyloid-like Nanofibrillation of Metal-Organic Complex Arrays Ruled by Their Precisely Designed Metal Sequences.

Self-assembly of a series of dimetallic sequences constructed on a backbone with two successive tyrosine moieties (Fmoc-M1 -M2 -CO2 H) revealed that the resultant morphology is clearly dependent on the metal sequence, where Re-containing sequences such as homometallic Fmoc-Re-Re-CO2 H specifically afforded amyloid-like nanofibers. These findings further allowed to achieve the fibrillation of a longer metal sequence containing three different metals (Fmoc-Rh-Pt-Re-Re-CO2 H). Cyclic voltammetry of the fibrillated Fmoc-Re-Re-CO2 H demonstrated that the redox activity of the metal complexes in the sequence is preserved in the nanofibrous forms.

Liquid crystalline corannulene responsive to electric field.

An amide-appended corannulene derivative (3) with tribranched paraffinic side chains self-assembles into a hexagonal columnar liquid crystalline (LC) mesophase over a wide temperature range from 154 to -10 degrees C. In contrast with columnar LC assemblies of planar polycyclic aromatic hydrocarbons, the LC assembly of nonplanar 3 responds to an applied electric field and can align homeotropically to the electrode surface. Even after the electric field is switched off, this alignment is memorized for a long period of time unless the material is heated above the clearing temperature.

Prominent electron transport property observed for triply fused metalloporphyrin dimer: directed columnar liquid crystalline assembly by amphiphilic molecular design.

A triply fused copper porphyrin dimer, when site-specifically modified on its periphery with hydrophobic and hydrophilic wedges (1C12/TEG), self-assembles into a columnar liquid crystalline (LC) mesophase over a wide-temperature range from -17 to 99 degrees C but gives rise to an amorphous solid when modified with only hydrophobic (1C12/C12) or hydrophilic wedges (1TEG/TEG). A LC film of 1C12/TEG displays at 16 degrees C a top-class one-dimensional electron mobility (0.27 cm2/V x s), as evaluated from its maximum flash-photolysis time-resolved microwave conductivity.

Synthesis of a Water-soluble Metal-Organic Complex Array.

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as Ru(II), Pt(II), and Rh(III). The compound, named as a water-soluble metal-organic complex array (WSMOCA), is obtained through 1) the conventional solution-chemistry-based preparation of the corresponding metal complex monomers having a 9-fluorenylmethyloxycarbonyl (Fmoc)-protected amino acid moiety and 2) their sequential coupling together with other water-soluble organic building units on the surface-functionalized polymeric resin by following the procedures originally developed for the solid-phase synthesis of polypeptides, with proper modifications. Traces of reactions determined by mass spectrometric analysis at the representative coupling steps in stage 2 confirm the selective construction of a predetermined sequence of metal centers along with the peptide backbone. The WSMOCA cleaved from the resin at the end of stage 2 has a certain level of solubility in aqueous media dependent on the pH value and/or salt content, which is useful for the purification of the compound.