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

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

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

Supramolecular Rotators of (Aniliniums)([18]crown-6) in Electrically Conducting [Ni(dmit)₂] Crystals

Supramolecular assemblies of anilinium (Ani⁺) and fluoroanilinium derivatives (FAni⁺) with [18]­crown-6 were introduced into electrically conducting [Ni­(dmit)₂] crystals (dmit^2– is 2-thioxo-1,3-dithiole-4,5-dithiolate). The crystal structures, electrical conductivities, and magnetic susceptibilities of four new crystals of (Ani⁺)­([18]­crown-6)­[Ni­(dmit)₂]₃ (<b>1</b>), (<i>o</i>-FAni⁺)­([18]­crown-6)­[Ni­(dmit)₂]₃ (<b>2</b>), (<i>m</i>-FAni⁺)­([18]­crown-6)­[Ni­(dmit)₂]₃ (<b>3</b>), and (<i>p</i>-FAni⁺)­([18]­crown-6)­[Ni­(dmit)₂]₃ (<b>4</b>) were examined from the viewpoint of dynamic supramolecular rotator structures within the crystals. The crystal structures, electrical conduction, and magnetic properties were classified into group-<b>I</b> (crystals <b>1</b> and <b>4</b>) and group-<b>II</b> (crystals <b>2</b> and <b>3</b>). The hydrogen-bonding interaction between -NH₃⁺ and the oxygen atoms of [18]­crown-6 formed the stand-up configuration of rotator-stator structures of (Ani⁺)­([18]­crown-6) and (FAni⁺)­([18]­crown-6) supramolecules. The potential energy barriers for the 2-fold flip-flop motion of phenyl- and <i>p</i>-fluorophenyl-rings in crystals <b>1</b> and <b>4</b> had a relatively small magnitude of ∼150 kJmol^–1, suggesting that rotations of Ani⁺ and <i>p</i>-FAni⁺ cations around the C-NH₃⁺ axis occurred in the crystals. In contrast, a large magnitude of the potential energy barriers for the rotations of <i>o</i>-FAni⁺ and <i>m</i>-FAni⁺ cations in crystals <b>2</b> and <b>3</b> (>600 kJmol^–1) resulted in static supramolecular cationic structures. The cation:anion ratio of 1:3 in these crystals yielded a trimer π-stack of [Ni­(dmit)₂] with a semiconductor-like temperature dependence. The magnetic susceptibilities of the static crystals <b>2</b> and <b>3</b> were reproduced by the one-dimensional antiferromagnetic linear Heisenberg chain through the one-dimensional linear trimer arrangement. The magnetic susceptibilities of dynamic crystals <b>1</b> and <b>4</b> enhanced electron delocalization through the intratrimer and intertrimer interactions within the trimer stack, where the molecular rotations of Ani⁺ and <i>p</i>-FAni⁺ cations played an important role