Ion-based materials derived from positively and negatively charged chloride complexes of π-conjugated molecules

Ion-Pairing Assemblies of Anion-Responsive π-Electronic Systems Bearing Triazole Moieties Introduced by Click Chemistry

In this study, the diverse derivatives of dipyrrolyldiketone boron complexes as anion-responsive π-electronic systems were synthesized via the Huisgen cycloaddition of an ethynyl-substituted anion receptor and azide derivatives. The obtained triazole-substituted anion receptors showed effective anion-binding behaviors and ion-pairing assemblies comprising receptor-anion complexes and countercations. Solid-state ion-pairing structures were modulated according to the introduced azide moieties along with coexisting bulky and π-electronic cations.

Supramolecular Assemblies of Dipyrrolyldiketone CuII Complexes

Dipyrrolyldiketones are essential building units of anion-responsive π-electronic molecules and ion-pairing assemblies. Here, we demonstrated that they form complexes with CuII characterized by planar geometries. The solid-state stacking assembled structures, as revealed by single-crystal X-ray analysis, were modulated by the substitution of pyrrole units. The rectangular shapes of the CuII complexes resulted in the formation of mesophases upon introduction of aliphatic chains.

Dipyrrolyldiketonato Titanium(IV) Complexes from Monomeric to Multinuclear Architectures: Synthesis, Stability, and Liquid-Crystal Properties

Dipyrrolyldiketone ligands (dpkH) are used with Ti(OⁱPr)₄ to afford monomeric titanium(IV) complexes displaying the general formula C₂-[Ti(dpk)₂(OⁱPr)₂]. The dpkH ligands employed consist of two dipyrrolyldiketone compounds (2H and 3H) and three diphenyl-substituted analogues (4H-6H). The behavior of these octahedral [Ti(dpk)₂(OⁱPr)₂] species in solution was investigated by ¹H NMR at variable temperatures. Dynamic phenomena were evidenced, and the activation parameters associated with these processes (ΔH^⧧, ΔS^⧧, and ΔG^⧧) were retrieved. [Ti(dpk)₂(OⁱPr)₂] complexes are precursors for the formation of high-nuclearity aggregates whose structures depend on the substituents on the diketone backbone. The crystal structures of monomeric ([Ti(1)₂(OⁱPr)₂]; 1 is the 1,3-diphenyl-1,3-propanedionato ligand) and [Ti(2)₂(OEt)₂]), dimeric ([Ti₂(1)₄(μ₂-O)₂]), and tetrameric ([Ti₄(4)₈(μ₂-O)₄]) species have been established, and the origin of this structural diversity is discussed. The solid-state optical properties of several complexes were determined and interpreted with the help of DFT calculations. Finally, the dinuclear complex [Ti(6)₂(μ₂-O)₂] was synthesized, where ligand 6 incorporates six long alkyl chains (C₁₆H₃₃). This complex shows rich mesomorphic properties, with an original room-temperature plastic crystal phase followed by a hexagonal columnar liquid-crystalline phase.

Arylethynyl Groups That Modulate Anion-Binding and Assembling Modes of Rod- and Fan-Shaped π-Electronic Systems

The introduction of arylethynyl moieties at the pyrrole α- and β-positions of dipyrrolyldiketone BF₂ complexes as anion-responsive π-electronic molecules was investigated. The arylethynyl-substituted derivatives formed a variety of anion complexes with planar [1+1]- and interlocked [2+1]-type structures in solution and in the solid state. The derivatives with long alkyl chains in the introduced arylethynyl groups also formed mesophases in the form of ion pairs of the anion complexes and a counter cation. The geometries of the constituent anion complexes affected the packing modes of the dimension-controlled assemblies.

Ion-Pairing Assemblies of Porphyrin-AuIII Complexes in Combination with π-Electronic Receptor-Anion Complexes

Anion complexes of anion-responsive π-electronic molecules can behave as pseudo π-electronic anions providing various ion pairs in combination with countercations. In this study, single crystals of ion-pairing assemblies comprising porphyrin-Au^III complexes and Cl^- complexes of dipyrrolyldiketone BF₂ complexes were prepared from 1:1 mixtures of anion receptors and the Cl^- salts of cationic porphyrins in solution. In the solid state, the ion pairs formed characteristic assemblies, depending on the substituents of the anion receptors and porphyrin-Au^III complexes. Theoretical calculations on the ion pairs revealed that the stacking structures are stabilized by compensating positive and negative charges as well as π-π interactions.

Computational simulation of anion binding association mechanisms contributing toward rotation of pyrrole rings in dipyrrolyldiketone BF2 complexes

Dipyrrolyldiketone BF₂ complexes have a characteristic association mechanism with anions; an anion is tightly captured by the NH bonding of the two rotated pyrrole rings and the CH bonding of the backbone.

Arylpyrrolyldiketone Boron Complexes Exhibiting Various Anion-Binding Modes Based on Dynamic Conformation Changes

Arylpyrrolyldiketone boron complexes as anion-responsive π-electronic molecules were synthesized by Claisen condensations of acetylpyrrole and corresponding aryl esters. The synthesized π-electronic molecules exhibited anion-binding behavior with various binding modes including pyrrole-inverted and non-inverted [1+1]-type anion complexes as well as [2+1]-type complexes owing to the presence of only a single pyrrole ring. Furthermore, solid-state ion-pairing assemblies, comprising receptor-anion complexes and countercations, were constructed based on fairly planar [2+1]-type complexes.

Liquid Crystals Comprising π-Electronic Ions from Porphyrin-AuIII Complexes

Porphyrin–Au^III complexes were found to act as π-electronic cations, which can combine with various counteranions, including π-electronic anions. Single-crystal X-ray analyses revealed the formation of assemblies with contributions of charge-by-charge and charge-segregated assemblies, depending on the geometry and electronic state of the counteranions. Porphyrin–Au^III complexes possessing aliphatic alkyl chains formed dimension-controlled ion-pairing assemblies as thermotropic liquid crystals, whose ionic components were highly organized by π–π stacking and electrostatic interactions.

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Ion pairs based on porphyrin–Au^III complexes as π-electronic cations were prepared

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Porphyrin–Au^III complexes formed ion-pairing assemblies in combination with anions

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Aliphatic substituents in the cations provided liquid crystalline mesophases

Supramolecular alternate donor-acceptor copolymers mediated by PtPt metal-metal interactions and their photocatalytic applications

Precise arrangement of the aromatic donor-acceptor units is of paramount importance to dictate the performance of multi-component π-functional materials. Herein a novel strategy has been developed toward alternate donor-acceptor copolymers, by incorporating Pt(ii)Pt(ii) metal-metal interactions for the hetero-complexation process. The proximity of Pt atoms endows the resulting supramolecular copolymers with metal-metal-to-ligand charge-transfer transitions in the visible/NIR region. The signals have been further applied for low-energy visible-light photo-catalysis that is unattainable for the individual species. More interestingly, "on-demand" photo-catalytic efficiency can be achieved by manipulating the reversibility of the supramolecular copolymerization process. Hence, the current work demonstrates the efficiency of fabricating multi-component π-functional materials via the elaborate manipulation of non-covalent driving forces.

Dynamic Polymorph Formation during Evaporative Crystallization from Solution: The Key Role of Liquid-Like Clusters as "Crucible" at Ambient Temperature

Understanding the polymorph phenomenon for organic crystals is essential for the development of organic solid materials. Here, the fluorescence study of the evaporative crystallization of 1,3-dipyrrol-2-yl-1,3-propanedione boron difluoride complex (1), which has three polymorphs showing different emission profiles, is reported. The droplet of 1 in 1,2-dichloroethane showed blue emission just after dropping. Solids with bluish-green emission were observed. As time elapsed, a solid with red or orange emission was observed around the droplet. Time evolution of the fluorescence spectra, observed for the first time, implied that the molten state of 1 was observed by emission of an intermediate, even at ambient temperature. These findings suggested that the liquid-like cluster incidentally forms an ordered array as the crystallites nucleate. The liquid-like cluster can be considered as the "crucible" in the nucleation of polymorphs.

Two-component supramolecular metallogels with the presence of Pt–Pt metal–metal interactions

Two-component supramolecular metallogels have been successfully constructed with the involvement of heteromeric Pt(ii)⋯Pt(ii) metal–metal interactions, which display low-energy emissions in the near-infrared region.

Pyrrole N-H Anion Complexes

Synthetic pyrrole-based anion receptors date back to the 1990s. They have been extensively developed in the context of macrocyclic systems as expanded porphyrins and calixpyrroles, and related systems. The chemistry of open-chain pyrrolic systems is, in many respects, no less venerable. It also has more direct analogy to naturally occurring pyrrole-based anion binding motifs. However, it has not been the subject of a comprehensive review. Presented herein is a summary of efforts devoted to the creation of de novo pyrrole-based receptors, as well as the anion recognition chemistry of naturally occurring pyrrolic systems as prodigiosins and their synthetic analogues.

Dimension-controlled ion-pairing assemblies based on π-electronic charged species

This feature article summarizes the recent progress in the study of ion-pairing assemblies based on π-electronic ion pairs, including anion complexes of π-electronic molecules.

Dimension-controlled assemblies of anion-responsive π-electronic systems bearing aryl substituents with fan-shaped geometries

Pyrrole-4-aryl-substituted dipyrrolyldiketone BF₂ complexes showed fan-shaped and rod-shaped geometries for anion-free states and receptor–anion complexes, respectively, as building units of dimension-controlled assemblies.

[C-H···anion] interactions mediate the templation and anion binding properties of topologically non-trivial metal-organic structures in aqueous solutions

Two synthetic approaches-temperature variation and anion templation-allowed for the selective formation of a [2]catenane ([2]C4+ ) or a trefoil knot (TK6+ ), or for the enhanced formation of a Solomon link (SL8+ ), all from a simple set of starting materials (Zn(ii) acetate, diformylpyridine (DFP) and a diamino-2,2'-bipyridine (DAB)) in mixed aqueous solutions. The catenane formed exclusively at 90 °C in a 1 : 1 mixed solvent of D2O and MeOD. In the presence of bromide ion as template, TK6+ formed exclusively at 50 °C in the same solvent. In the solid state, TK6+ hosts two bromide ions in its central cavity by forming six Csp2 -H hydrogen bonds. In D2O, TK6+ , which was originally prepared as a trifluoroacetate (TFA) salt, was found to exchange two TFA counterions for two monovalent anions of different sizes and shapes, which lodged within the knot's central cavity. In contrast to bromide, the larger triflate anion (CF3SO3-) promoted the formation of SL8+ , which was characterized by 1H NMR spectroscopy and mass spectrometry. Two dimensional heteronuclear 19F-1H-HOSEY NMR experiments detected CH···F interactions inside the cavity of SL8+ . Thus, the product distribution of this dynamic link forming system is sensitive to temperature and the size and shape of the anion template, and one of the products, TK6+ , is capable of binding a variety of monovalent anions in D2O with high affinity (with log β2 values of 4 to 6 being typical).

Dipyrrolyphenol as a precursor of π-electronic anion that forms ion pairs with cations

A nitro-substituted dipyrrolylphenol was synthesized as a precursor of a π-electronic anion, whose phenolate (phenoxide) moiety upon deprotonation was stabilized by the hydrogen-bond-donating pyrrole NH, thus forming solid-state ion pairs with various cationic species.

Ionic Liquid Crystals: Versatile Materials

This Review covers the recent developments (2005-2015) in the design, synthesis, characterization, and application of thermotropic ionic liquid crystals. It was designed to give a comprehensive overview of the "state-of-the-art" in the field. The discussion is focused on low molar mass and dendrimeric thermotropic ionic mesogens, as well as selected metal-containing compounds (metallomesogens), but some references to polymeric and/or lyotropic ionic liquid crystals and particularly to ionic liquids will also be provided. Although zwitterionic and mesoionic mesogens are also treated to some extent, emphasis will be directed toward liquid-crystalline materials consisting of organic cations and organic/inorganic anions that are not covalently bound but interact via electrostatic and other noncovalent interactions.

Anion coordinated capsules and pseudocapsules of tripodal amide, urea and thiourea scaffolds

This review provides a detailed and comparative account of the solid- and solution-states anion (halides and oxyanions) binding affinities of hydrogen bonding tripodal scaffolds.

Fused π-conjugated imidazolium liquid crystals: synthesis, self-organization, and fluorescence properties

Fused π-conjugated imidazolium compounds bearing two or three long alkoxy chains and various counter anions were systematically prepared following our reported synthetic route.

β-Perfluoroalkyl-substituted pyrrole as an anion-responsive π-electronic system through a single NH moiety

A pyrrole derivative possessing two perfluorohexyl (C₆F₁₃) chains at the β-positions was synthesized. The significant electron-withdrawing properties of the β-perfluoroalkyl chains induced fascinating anion-binding behaviour.

Dipyrrolylpyrimidines as anion-responsive π-electronic systems

Dipyrrolylpyrimidines synthesized by coupling reactions exhibited anion-binding abilities with the inversion of pyrrole rings. In the solid state, anion complexes of dipyrrolylpyrimidines formed charge-by-charge columnar structures in combination with counter cations.

Charge carrier mobility in organic molecular materials probed by electromagnetic waves

Charge carrier mobility is an essential parameter providing control over the performance of semiconductor devices fabricated using a variety of organic molecular materials. Recent design strategies toward molecular materials have been directed at the substitution of amorphous silicon-based semiconductors; accordingly, numerous measurement techniques have been designed and developed to probe the electronic conducting nature of organic materials bearing extremely wide structural variations in comparison with inorganic and/or metal-oxide semiconductor materials. The present perspective highlights the evaluation methodologies of charge carrier mobility in organic materials, as well as the merits and demerits of techniques examining the feasibility of organic molecules, crystals, and supramolecular assemblies in semiconductor applications. Beyond the simple substitution of amorphous silicon, we have attempted to address in this perspective the systematic use of measurement techniques for future development of organic molecular semiconductors.

Modulation of physical properties of supramolecular hydrogels based on a hydrophobic core

We demonstrate herein the variation in viscoelastic properties of supramolecular hydrogels (SMG) composed of two amphiphiles, N-Palmitoyl-Gly-His (PalGH) and sodium palmitate (PalNa).

Synthesis, X-ray characterization and DFT studies of bis-N-imidazolylpyrimidine salts: the prominent role of hydrogen bonding and anion–π interactions

Five new compounds have been synthesized and characterized by elemental analysis, IR, NMR and single-crystal X-ray diffraction. They present interesting assemblies in the solid state dominated by H-bonding and anion–π interactions.

Transition metal ion induced hydrogelation by amino-terpyridine ligands

Hydrogelation behavior of a new class of terpyridine based metallogelators are explored. The gelation and the gel morphology was found to be critically dependent on divalent metal ions, anions and on subtle structural changes on the gelator molecule.

Neutral CH and cationic CH donor groups as anion receptors

Neutral and cationic CH hydrogen bond donors have been actively used in various shape persistent macrocycles, foldamers and “molecular machines”.