Protonic Conductivity and Hydrogen Bonds in (Haloanilinium)(H₂PO₄) Crystals

Brønsted acid–base reactions between phosphoric acid (H₃PO₄) and haloanilines in alcohols formed 1:1 proton-transferred ionic salts of (X-anilinium⁺)­(H₂PO₄^–) and 2:1 ones of (X-anilinium⁺)₂(HPO₄^2–) (X = F, Cl, Br, and I at o, m, and p positions of anilinium). Only the former 1:1 single crystals showed proton conductivity under the N₂ condition, and the latter 2:1 crystals became protonic insulators. In crystals, diverse hydrogen-bonding structures from 1D to 2D networks were achieved by modification of the molecular structure of X-anilinium cations. The protonic conductivity was associated with the connectivity of H₂PO₄^– anions in the hydrogen-bonding networks. The hydrogen-bonding ladder chains in (<i>o</i>-cloroanilinim)­(H₂PO₄^–) and (<i>o</i>-bromoanilinim)­(H₂PO₄^–) resulted in the highest protonic conductivity of ∼10^–3 S cm^–1. The protonic conductivity of the ladder-chain (H₂PO₄^–) arrangements was higher than that of 2D sheets. The motional freedom of protons was analyzed by difference Fourier analysis of the single-crystal X-ray structure. The 2D layer, including (H₂PO₄^–)₂ dimers and (H₂PO₄^–)₄ tetramers, showed relatively low protonic conductivity, and the activation energy for proton conductivity was lowered by increasing the hydrogen-bonding connectivity and uniformity between H₂PO₄^– anions

Collective In-Plane Molecular Rotator Based on Dibromoiodomesitylene π‑Stacks

Interest in artificial solid-state molecular rotator systems is growing as they enable systems to be designed for achieving specific physical functions. The phase transition behavior of four halomesitylene crystals indicated dynamic in-plane molecular rotator characteristics in dibromoiodomesitylene, tribromomesitylene, and dibromomesitylene crystals. Such molecular rotation in diiodomesitylene crystals was suppressed by effective I···I intermolecular interactions. The in-plane molecular rotation accompanied by a change in dipole moment resulted in dielectric phase transitions in polar dibromoiodomesitylene and dibromomesitylene crystals. No dielectric anomaly was observed for the in-plane molecular rotation of tribromomesitylene in the absence of this dipole moment change. Typical antiferroelectric–paraelectric phase transitions were observed in the dibromomesitylene crystal, whereas the dielectric anomaly of dibromoiodomesitylene crystals was associated with the collective in-plane molecular rotation of polar π-molecules in the π-stack. We found that the single-rope-like collective in-plane molecular rotator was dominated by intermolecular I···I interactions along the π-stacking column of polar dibromoiodomesitylene

Carrier Concentration Dependent Conduction in Insulator-Doped Donor/Acceptor Chain Compounds

On the basis of the concept that the design of a mixed valence system is a key route to create electronic conducting frameworks, we propose a unique idea to rationally produce mixed valency in an ionic donor/acceptor chain (i.e., D⁺A^– chain). The doping of a redox-inert (insulator) dopant (P) into a D⁺A^– chain in place of neutral D enables the creation of mixed valency A⁰/A^– domains between P units: P–(D⁺A^–)_<i>n</i>A⁰–P, where <i>n</i> is directly dependent on the dopant ratio, and charge transfer through the P units leads to electron transport along the framework. This hypothesis was experimentally demonstrated in an ionic DA chain synthesized from a redox-active paddlewheel [Ru₂^II,II] complex and TCNQ derivative by doping with a redox-inert [Rh₂^II,II] complex

Carrier Concentration Dependent Conduction in Insulator-Doped Donor/Acceptor Chain Compounds

On the basis of the concept that the design of a mixed valence system is a key route to create electronic conducting frameworks, we propose a unique idea to rationally produce mixed valency in an ionic donor/acceptor chain (i.e., D⁺A^– chain). The doping of a redox-inert (insulator) dopant (P) into a D⁺A^– chain in place of neutral D enables the creation of mixed valency A⁰/A^– domains between P units: P–(D⁺A^–)_<i>n</i>A⁰–P, where <i>n</i> is directly dependent on the dopant ratio, and charge transfer through the P units leads to electron transport along the framework. This hypothesis was experimentally demonstrated in an ionic DA chain synthesized from a redox-active paddlewheel [Ru₂^II,II] complex and TCNQ derivative by doping with a redox-inert [Rh₂^II,II] complex

Carrier Concentration Dependent Conduction in Insulator-Doped Donor/Acceptor Chain Compounds

On the basis of the concept that the design of a mixed valence system is a key route to create electronic conducting frameworks, we propose a unique idea to rationally produce mixed valency in an ionic donor/acceptor chain (i.e., D⁺A^– chain). The doping of a redox-inert (insulator) dopant (P) into a D⁺A^– chain in place of neutral D enables the creation of mixed valency A⁰/A^– domains between P units: P–(D⁺A^–)_<i>n</i>A⁰–P, where <i>n</i> is directly dependent on the dopant ratio, and charge transfer through the P units leads to electron transport along the framework. This hypothesis was experimentally demonstrated in an ionic DA chain synthesized from a redox-active paddlewheel [Ru₂^II,II] complex and TCNQ derivative by doping with a redox-inert [Rh₂^II,II] complex

Carrier Concentration Dependent Conduction in Insulator-Doped Donor/Acceptor Chain Compounds

On the basis of the concept that the design of a mixed valence system is a key route to create electronic conducting frameworks, we propose a unique idea to rationally produce mixed valency in an ionic donor/acceptor chain (i.e., D⁺A^– chain). The doping of a redox-inert (insulator) dopant (P) into a D⁺A^– chain in place of neutral D enables the creation of mixed valency A⁰/A^– domains between P units: P–(D⁺A^–)_<i>n</i>A⁰–P, where <i>n</i> is directly dependent on the dopant ratio, and charge transfer through the P units leads to electron transport along the framework. This hypothesis was experimentally demonstrated in an ionic DA chain synthesized from a redox-active paddlewheel [Ru₂^II,II] complex and TCNQ derivative by doping with a redox-inert [Rh₂^II,II] complex

Structural and Spectroscopic Study of 6,7-Dicyano-Substituted Lumazine with High Electron Affinity and Proton Acidity

The introduction of cyano groups into lumazine (pteridine-2,4-(1<i>H</i>,3<i>H</i>)­dione) at the C6 and C7 positions enhances its electron affinity, proton acidity, and solubility in solvents. As a result, 6,7-dicyanolumazine (DCNLH₂) forms charge transfer (CT) complexes with donors such as tetrathiafulvalene, 2,3,5,6-tetramethyl-1,4-phenylenediamine, and 3,3′,5,5′-tetramethylbenzidine and readily dissociates a proton from the N1 nitrogen to form a monoanionic salt with tetrabutylammonium (TBA⁺). Crystal structures of the CT complexes consist of mixed stacks in which DCNLH₂ interacts with donors in face-to-face configurations, but they form intermolecular hydrogen bonds differently depending on the donor type. In the TBA⁺ salt, two deprotonated DCNLH^– monoanions form a unique dianionic dimer connected by two centrosymmetric hydrogen bonds, N3–H···O–C2, which is electronically isolated by the presence of bulky TBA⁺ countercations and the absence of a proton at the N1 hydrogen-bonding site. This dimer fluoresces yellowish green (fluorescence quantum yield Φ = 0.04). Because the DCNLH^– anion only shows weak blue fluorescence in aqueous solution (Φ < 0.01), we suggest that the dimer formation is responsible for the fluorescence enhancement with a large emission band shift to the low-energy side

Structural and Spectroscopic Study of 6,7-Dicyano-Substituted Lumazine with High Electron Affinity and Proton Acidity

The introduction of cyano groups into lumazine (pteridine-2,4-(1<i>H</i>,3<i>H</i>)­dione) at the C6 and C7 positions enhances its electron affinity, proton acidity, and solubility in solvents. As a result, 6,7-dicyanolumazine (DCNLH₂) forms charge transfer (CT) complexes with donors such as tetrathiafulvalene, 2,3,5,6-tetramethyl-1,4-phenylenediamine, and 3,3′,5,5′-tetramethylbenzidine and readily dissociates a proton from the N1 nitrogen to form a monoanionic salt with tetrabutylammonium (TBA⁺). Crystal structures of the CT complexes consist of mixed stacks in which DCNLH₂ interacts with donors in face-to-face configurations, but they form intermolecular hydrogen bonds differently depending on the donor type. In the TBA⁺ salt, two deprotonated DCNLH^– monoanions form a unique dianionic dimer connected by two centrosymmetric hydrogen bonds, N3–H···O–C2, which is electronically isolated by the presence of bulky TBA⁺ countercations and the absence of a proton at the N1 hydrogen-bonding site. This dimer fluoresces yellowish green (fluorescence quantum yield Φ = 0.04). Because the DCNLH^– anion only shows weak blue fluorescence in aqueous solution (Φ < 0.01), we suggest that the dimer formation is responsible for the fluorescence enhancement with a large emission band shift to the low-energy side

Cation–Anion Dual Sensing of a Fluorescent Quinoxalinone Derivative Using Lactam–Lactim Tautomerism

A quinoxalinone derivative capable of lactam–lactim tautomerization was designed as a new fluorescence probe for sensing of cation (M⁺ = Li⁺ and Na⁺) and anion (X^– = F^–, Cl^–, Br^–, and CH₃COO^–) in organic solvents. In THF, the minor lactam tautomer exhibited a weak fluorescence band at 425 nm with a typical Stokes shift of ∼4400 cm^–1, whereas the major lactim tautomer exhibited an intense fluorescence band at 520 nm with large Stokes shift of ∼8900 cm^–1 due to excited-state intramolecular proton transfer (ESIPT). The presence of either cations or anions was found to promote lactim-to-lactam conversion, resulting in the lowering of the ESIPT fluorescence. The lone pairs on the alkylamide oxygen and the quinoxalinone ring nitrogen of the lactam were found to bind Li⁺ to form a 1:2 coordination complex, which was confirmed by single crystal X-ray structural analysis and fluorescent titrations. In addition, the N–H bond of the lactam was able to recognize anions via N–H···X hydrogen bonding interactions. Where X = F^– or CH₃COO^–, further addition of these anions caused deprotonation of the lactam to generate an anionic state, consistent with the crystal structure of the anion prepared by mixing tetrabutylammonium fluoride and the quinoxalinone derivative in THF. Dual cation–anion-sensing responses were found to depend on the ion-recognition procedure. The anionic quinoxalinone derivative and its Li⁺ complex, which are formed by the addition of CH₃COO^– and Li⁺, respectively, displayed different fluorescence enhancement behavior due to the two anions exchanging with each other

Carrier Concentration Dependent Conduction in Insulator-Doped Donor/Acceptor Chain Compounds

On the basis of the concept that the design of a mixed valence system is a key route to create electronic conducting frameworks, we propose a unique idea to rationally produce mixed valency in an ionic donor/acceptor chain (i.e., D⁺A^– chain). The doping of a redox-inert (insulator) dopant (P) into a D⁺A^– chain in place of neutral D enables the creation of mixed valency A⁰/A^– domains between P units: P–(D⁺A^–)_<i>n</i>A⁰–P, where <i>n</i> is directly dependent on the dopant ratio, and charge transfer through the P units leads to electron transport along the framework. This hypothesis was experimentally demonstrated in an ionic DA chain synthesized from a redox-active paddlewheel [Ru₂^II,II] complex and TCNQ derivative by doping with a redox-inert [Rh₂^II,II] complex