Anion-dependent ion-pairing assemblies of triazatriangulenium cation that interferes with stacking structures.

Ion pairs of N-(2,6-dimethylphenyl)-substituted triazatriangulenium (TATA+) cation with various counteranions were synthesized to investigate the interactions for the bulky cation. Single-crystal X-ray analysis of the TATA+ ion pairs revealed solid-state ion-pairing assemblies without stacking at the cationic π-planes. The TATA+ cation showed counteranion-dependent assembly structures, with smaller counteranions located at the top of TATA+ and bulkier counteranions displaced from the TATA+ plane to interact with the surrounding TATA+.

Ion-Pairing Chromonic Liquid Crystals via Alternately Stacked Assembly of Amphiphilic Charged π-Electronic Systems.

In this study, a new assembly strategy for lyotropic chromonic liquid crystals (LCLCs) is proposed using iπ-iπ interactions, mainly comprising electrostatic and dispersion forces, between charged π-electronic systems to form stacking structures supported by the hydration of triethylene glycol (TEG) units.  Meso-TEG-aryl-substituted porphyrin AuIII complex, an amphiphilic π-electronic cation, showed diverse states and assembly modes in ion pairs depending on the coexisting counteranions.  The PCCp- ion pair formed a hexagonal columnar (Colh) LC phase based on a charge-by-charge assembly, suggesting the formation of an ordered arrangement of charged p-electronic systems through iπ-iπ interactions, with reduced interactions between the TEG chains.  Furthermore, in the presence of water, LCLC behaviors in the Colh and nematic columnar phases according to the amount of water were observed for the PCCp- ion pair via iπ-iπ interactions.  Magnetic-field-induced orientation of the charge-by-charge columnar structures upon dehydration was observed.  Furthermore, single-stranded charge-by-charge columnar structures, as components of the LCLCs, were observed using transmission electron microscopy (TEM).

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On-surface Synthesis of Triaza[5]triangulene through Cyclodehydrogenation and its Magnetism.

Triangulenes as neutral radicals are becoming promising candidates for future applications such as spintronics and quantum technologies. To extend the potential of the advanced materials, it is of importance to control their electronic and magnetic properties by multiple graphitic nitrogen doping. Here, we synthesize triaza[5]triangulene on Au(111) by cyclodehydrogenation, and its derivatives by cleaving C-N bonds. Bond-resolved scanning tunneling microscopy and scanning tunneling spectroscopy provided detailed structural information and evidence for open-shell singlet ground state. The antiferromagnetic arrangement of the spins in positively doped triaza[5]triangulene was further confirmed by density function theory calculations. The key aspect of triangulenes with multiple graphitic nitrogen is the extra pz electrons composing the π orbitals, favoring charge transfer to the substrate and changing their low-energy excitations. Our findings pave the way for the exploration of exotic low-dimensional quantum phases of matter in heteroatom doped organic systems.

Ion-Pairing Assemblies of Anion-Responsive π-Electronic Systems That Have Noncovalently Assisted Expanded Planar Region.

Arylethynyl-substituted dipyrrolyldiketone BF2 complexes as anion-responsive π-electronic molecules exhibited characteristic electronic properties derived from conformation changes upon anion binding, which caused an increase in UV/vis absorption and associated two-photon absorption. The anion complexes showed expanded planar regions assisted by intramolecular interactions, resulting in charge-by-charge ion-pairing assemblies in the solid state.

Norcorroles as antiaromatic π-electronic systems that form dimension-controlled assemblies.

Norcorrole derivatives with 3,4,5-trialkoxyphenyl moieties at the meso positions were synthesized to form various stacking assemblies in single crystals and thermotropic liquid crystals (LCs) depending on aliphatic chain lengths. Triple-decker stacking structures were formed via the interactions between the antiaromatic systems formed for the butoxy and dodecyloxy derivatives in the single-crystal and LC states, respectively. In particular, the LC state exhibited discotic columnar structures comprising triple deckers to exhibit high electric conductivity, as supported by molecular dynamics simulations.

Substitution-pattern- and counteranion-dependent ion-pairing assemblies of heteroporphyrin-based π-electronic cations.

Metal complexation and peripheral modifications of thiaporphyrins have been investigated for preparing polarized π-electronic cations with anion-dependent ion-pairing assembling modes, including charge-segregated structures exhibiting electric conductive properties.

Ion-pairing assemblies of π-extended anion-responsive organoplatinum complexes.

PtII complexes of π-extended dipyrrolyldiketones were synthesized as anion-responsive π-electronic molecules. The dipyrrolyldiketone PtII complexes exhibited red-shifted absorption and photoluminescence properties. In the solid state, [1 + 1]-type anion complexes formed charge-by-charge ion-pairing assemblies when combined with countercations. Detailed theoretical studies of the packing structures revealed favorable interactions between the planar anion complexes and π-electronic cations.

Pt^II complexes of π-extended dipyrrolyldiketones, introducing arylethynyl substituents, in the form of anion complexes exhibited the formation of charge-by-charge assemblies with π-electronic cations via ⁱπ­ⁱπ interactions.

Enhanced solid-state phosphorescence of organoplatinum π-systems by ion-pairing assembly.

Anion binding and ion pairing of dipyrrolyldiketone PtII complexes as anion-responsive π-electronic molecules resulted in photophysical modulations, as observed in solid-state phosphorescence properties. Modifications to arylpyridine ligands in the PtII complexes significantly impacted the assembling behaviour and photophysical properties of anion-free and anion-binding (ion-pairing) forms. The PtII complexes, in the presence of guest anions and their countercations, formed various anion-binding modes and ion-pairing assembled structures depending on constituents and forms (solutions and crystals). The PtII complexes emitted strong phosphorescence in deoxygenated solutions but showed extremely weak phosphorescence in the solid state owing to self-association. In contrast, the solid-state ion-pairing assemblies with tetraalkylammonium cations exhibited enhanced phosphorescence owing to the formation of hydrogen-bonding 1D-chain PtII complexes dispersed by stacking with aliphatic cations. Theoretical studies revealed that the enhanced phosphorescence in the solid-state ion-pairing assembly was attributed to preventing the delocalisation of the electron wavefunction over PtII complexes.

π-Electronic ion pairs: building blocks for supramolecular nanoarchitectonics viaiπ-iπ interactions.

The pairing of charged π-electronic systems and their ordered arrangement have been achieved by iπ-iπ interactions that are derived from synergetically worked electrostatic and dispersion forces. Charged π-electronic systems that provide ion pairs as building blocks for assemblies have been prepared by diverse strategies for introducing charge in the core π-electronic systems. One method to prepare charged π-electronic systems is the use of covalent bonding that makes π-electronic ions and valence-mismatched metal complexes as well as protonated and deprotonated states. Noncovalent ion complexation is another method used to create π-electronic ions, particularly for anion binding, producing negatively charged π-electronic systems. Charged π-electronic systems afford various ion pairs, consisting of both cationic and anionic π-systems, depending on their combinations. Geometries and electronic states of the constituents in π-electronic ion pairs affect the photophysical properties and assembling modes. Recent progress in π-electronic ion pairs has revealed intriguing characteristics, including the transformation into radical pairs through electron transfer and the magnetic properties influenced by the countercations. Furthermore, the assembly states exhibit diversity as observed in crystals and soft materials including liquid-crystal mesophases. While the chemistry of ion pairs (salts) is well-established, the field of π-electronic ion pairs is relatively new; however, it holds great promise for future applications in novel materials and devices.

Bidipyrrin AuIII Complex as a Helical Charged π-Electronic System.

A series of ion pairs based on a bidipyrrin-AuIII complex that acts as a stable helical π-electronic cation have been prepared via ion-pair metathesis. The helical cation, which exhibits NIR absorption and phosphorescence emission, formed solid-state ion-pairing assemblies, whose assembling modes depended on the properties of coexisting counteranions.

Ion-Pairing Assemblies of Dithienylnitrophenol-Based π-Electronic Anions Stabilized by Intramolecular Interactions.

Dithienylnitrophenols were synthesized as precursors of π-electronic anions, which were stabilized by intramolecular chalcogen bonding, forming various ion pairs in combination with cations. The modes of solid-state charge-by-charge assemblies, along with solution-state stacking and photoinduced electron transfer behaviors, were modulated by the constituent ionic species.

Deprotonation-Induced and Ion-Pairing-Modulated Diradical Properties of Partially Conjugated Pyrrole-Quinone Conjunction.

Quinoidal molecules based on dipyrrolyldiketone boron complexes (QPBs), in which pyrrole units were connected by a partially conjugated system as a singlet spin coupler, were synthesized. QPB, which was stabilized by the introduction of a benzo unit at the pyrrole ß-positions, formed a closed-shell tautomer conformation that showed near-infrared absorption. The deprotonated species, monoanion QPB- and dianion QPB2-, showing over 1000 nm absorption, were formed by the addition of bases, providing ion pairs in combination with countercations. Diradical properties were observed in QPB2-, whose hyperfine coupling constants were modulated by ion-pairing with π-electronic and aliphatic cations, demonstrating cation-dependent diradical properties. VT NMR and ESR along with a theoretical study revealed that the singlet diradical was more stable than the triplet diradical.

Anion-Responsive Boron-Spiro-Centered π-Electronic Systems That Form Ion-Pairing Assemblies.

A variety of naphthalenediolates were orthogonally introduced to the boron unit of dipyrrolyldiketone boron complexes, exhibiting electronic properties that depended on the substituting positions of the naphthyl moieties. Combining the anion complexes with countercations resulted in the formation of ion-pairing assemblies with supporting stacking interactions of the naphthyl units.

Substituent-Dependent Photoexcitation Processes of π-Stacked Ion Pairs.

Porphyrin ion pairs, the charge of which is delocalized in core units, form tightly associated structures through i π-i π interactions. 5,10,15-Triphenyl-substituted porphyrin-AuIII complex, which is favorable for forming stacked structures in the form of a stable ion, has been synthesized. Ion-pair metathesis based on the hard and soft acids and bases theory enabled combination with porphyrin anions possessing electronic states controlled by electron-donating and electron-withdrawing groups. Transient absorption spectroscopy suggested that the lifetimes of the radical pairs generated by photoinduced electron transfer of the ion pairs could be controlled by a judicious combination of the anions and cations.

Charge-Segregated Stacking Structure with Anisotropic Electric Conductivity in NIR-Absorbing and Emitting Positively Charged π-Electronic Systems.

Squarylium-based π-electronic cation with an augmented dipole was synthesized by methylation of zwitterionic squarylium. The cation formed various ion pairs in combination with anions, and the ion pairs exhibited distinct photophysical properties in the dispersed state, ascribed to the formation of J- and H-aggregates. The ion pairs provided solid-state assemblies based on cation stacking. It is noteworthy that complete segregation of cations and anions was observed in a pseudo-polymorph of the ion pair with pentacyanocyclopentadienide as a π-electronic anion. In the crystalline state, the ion pairs exhibited photophysical properties and electric conductivity derived from cation stacking. In particular, the charge-segregated ion-pairing assembly induces an electric conductive pathway along the stacking axis. The charge-segregated mode and fascinating properties were derived from the reduced electrostatic repulsion between adjacent π-electronic cations via dipole-dipole interactions.

π-Stacked Ion Pairs: Tightly Associated Charged Porphyrins in Ordered Arrangement Enabling Radical-Pair Formation.

π-Electronic ion pairs are of interest for fabricating electronic materials that use intermolecular interactions based on electrostatic and dispersion forces, defined as iπ-iπ interactions, to provide dimension-controlled assemblies. Porphyrin ions, whose charge is delocalized in the core units, are suitable for ordered arrangement and assemblies by ion pairing. Herein, charged porphyrins were found to form solid-state assemblies and solution-state stacked ion pairs according to the peripheral electron-donating groups (EDGs) and electron-withdrawing groups (EWGs). The concentration-dependent 1H NMR signal shifts of a porphyrin ion pair, comprising a meso-EWG cation and a meso-EWG anion, provided a hetero-dimerization constant of 2.8 × 105 M-1 in CD2Cl2 at 20 °C. In the ion pair of a meso-EWG cation and a meso-EDG anion, the electron transfer in the steady and excited states according to solvent polarity and photoexcitation, respectively, produced the radical pairs. The electron spin resonance analysis in frozen toluene revealed the formation of a heterodiradical in a closely stacked structure by the antiferromagnetic dipolar interaction and temperature-dependent spin transfer behavior.

Ion-pairing assemblies of heteroporphyrin-based π-electronic cation with various counteranions.

Various counteranions of the thiaporphyrin-NiII complex as a π-electronic cation were exchanged for preparing stable ion pairs. The ion-pairing assembling modes, which included contributions of charge-by-charge and charge-segregated modes, and properties depended on the geometries and electronic states of the counteranions.

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.

Electron-donating curved π-electronic systems that complex with buckyballs.

Modifications in curved π-electronic systems, dipyrrolylbenzodiazepines, resulted in various derivatives with modulated electronic properties and assembly behaviour. The electron-rich pyrrole-based curved π-system exhibited C60 complexation in the form of a hydrogen-bonding cyclic hexamer, giving rise to solid-state photo-induced electron transfer as elucidated by transient absorption spectroscopy.