Graphene, a two-dimensional layer of sp(2)-hybridized carbon atoms, can be viewed as a sheet of benzene rings fused together. Three benzene rings can be combined in three different ways, to yield ...linear anthracene and angular phenanthrene, where the rings share two C-C bonds, and the phenalenyl structure where three C-C bonds are shared between the rings. This third structure contains an uneven number of carbon atoms and, hence, in its neutral state, an uneven number of electrons--that is, it is a radical. All three structures may be viewed as being sections of graphene. Extension of this concept leads to an entire family of phenalenyl derivatives--'open-shell graphene fragments'--that are of substantial interest from the standpoint of fundamental science as well as in view of their potential applications in materials chemistry, in particular quantum electronic devices. Here we discuss current trends and challenges in this field.
Abstract
The transcription factor IRF5 has been implicated as a therapeutic target for the autoimmune disease systemic lupus erythematosus (SLE). However, IRF5 activation status during the disease ...course and the effects of IRF5 inhibition after disease onset are unclear. Here, we show that SLE patients in both the active and remission phase have aberrant activation of IRF5 and interferon-stimulated genes. Partial inhibition of IRF5 is superior to full inhibition of type I interferon signaling in suppressing disease in a mouse model of SLE, possibly due to the function of IRF5 in oxidative phosphorylation. We further demonstrate that inhibition of IRF5 via conditional
Irf5
deletion and a newly developed small-molecule inhibitor of IRF5 after disease onset suppresses disease progression and is effective for maintenance of remission in mice. These results suggest that IRF5 inhibition might overcome the limitations of current SLE therapies, thus promoting drug discovery research on IRF5 inhibitors.
Luminescence from a gold(I) complex with an N‐heterocycliccarbene‐based ligand, 1+⋅NTf2−, increased rapidly upon the application of one‐shot needlestick‐stimulus. The weakly orange‐emitting ...solid‐state of 1+⋅NTf2− was prepared by cooling its melted liquid to 90 °C. Upon applying a weak pinpoint stimulus with a needle, this weakly orange‐emitting solid state transformed into an intensively violet‐blue‐emitting state on a timescale of seconds. The emission after applying the stimulus could be visualized upon UV excitation even under ambient room light. This sequential phase transition from a stable solid to a liquid and then to a metastable solid could occur repeatedly without any measurable degradation of the complex. Various shapes could be prepared by casting the liquid‐state complex into molds of different designs. This rapid response is thought to be triggered by the flexible intermolecular interactions in the kinetically generated aggregates formed upon cooling the liquid state, and by the strong Au–Au interactions in the thermodynamically stable crystals after applying the needlestick‐stimulus.
Luminescence from a bis(trifluoromethanesulfonyl)imide salt of gold(I) complex with an N‐heterocyclic carbene‐based ligand increased rapidly upon application of a needlestick‐stimulus. Upon stimulation under UV‐light irradiation, the weakly orange‐emitting solid state rapidly transformed into an intensively violet‐blue‐emitting state on a timescale of seconds.
A liquescent dihydrophenazine radical cation, 1.+⋅NTf2−, showed drastic changes in near‐infrared (near‐IR) transparency and opaqueness through hysteretic phase transitions with no measurable ...degradation of the compound even under aerated conditions. During the heating and slow cooling process (0.5 K min−1), its electronic and magnetic properties were altered clearly and repeatedly changed between solid and liquid states. The liquid state was transparent to near‐IR light (940 nm), but the solid state was opaque, despite both samples exhibiting a similar green color under room light. Additionally, the liquid state was changed to a glass state under a fast cooling process (2–10 K min−1). UV/Vis/near‐IR and electron spin‐resonance spectroscopy revealed that these drastic changes were attributable to the dynamic dissociation and association of a π‐dimer structure for 1.+ accompanying with the solid–liquid phase transitions even under the neat conditions.
Temperature‐dependent hysteretic changes in near‐infrared transparency were achieved for a liquescent bis(trifluoromethanesulfonyl)imide‐(dihydrophenazine radical cation) salt. These hysteretic changes were attributed to dynamic dissociation and association of a dimer structure for the radical cations, which accompanied the solid–liquid phase transitions even under neat conditions with no measurable degradation of the compound.
We have developed a method for the arylation of nitronyl nitroxide without using its transition metal complex as a nucleophile. Various nitronyl nitroxide-substituted π-electronic compounds can be ...obtained from the parent nitronyl nitroxide and the corresponding aryl iodides using a combination of zero-valent palladium catalysts and a 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl ligand in the presence of sodium tert-butoxide. The utility of the method has been demonstrated by the direct synthesis of open-shell compounds with giant π-electronic systems, such as 10P.
Formation of a partially charge-transfer or partially oxidized/reduced state has been one of the most important requirements for the development of highly conducting molecular materials, such as ...organic metals and superconductors. This requirement has been fulfilled by combining appropriate electron-donor and acceptor molecules to construct multi-component molecular complexes/salts, such as (TTF+0.59)(TCNQ–0.59) and (BEDT-TTF+0.5)2X–, where TTF = tetrathiafulvalene, TCNQ = tetracyanoquinodimethane, BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene, and X = monovalent inorganic anion. Here, we propose a methodology to fulfill this requirement by a single neutral molecule; namely, we have connected two TTF+0.5-type partially oxidized π-skeletons through a boron anion to design a purely organic zwitterionic neutral radical {(PDT-TTF-Cat) 2 + B – } • . This molecule was successfully obtained as air-stable crystals containing solvent tetrahydrofuran (THF) molecules. Measurements of electrical resistivity, magnetic susceptibility, and X-ray diffraction reveal that the partially oxidized state is certainly formed, which enables realization of a 3/4-filled electron band. Furthermore, this system has intramolecular charge degrees of freedom, attributable to the two TTF+0.5 π-skeletons introduced into the molecule. The resulting interplay of intra- and intermolecular charge degrees of freedom (or simply, intra- and intermolecular electronic interactions) has led to multi-step phase transitions and crossover, providing unique strongly correlated electron properties, such as the formation of a three-dimensional charge-ordered dimer-Mott insulating state and its melting triggered by disorder–order transformation of the co-crystallized solvent THF molecules at low temperatures.
A triplet ground‐state diradical molecule, bis(nitronyl nitroxide)‐substituted diphenyldihydrophenazine (1..), that can be converted into a one‐electron oxidized species, 1…+, in the quartet ground ...state has been developed. Surprisingly, these species, 1.. and 1…+, can be used under ambient conditions because they are reasonably stable under aerobic conditions, even in solution. The temperature‐dependent magnetic susceptibilities reveal that 1.. and 1…+ are in the triplet state, with a weak exchange interaction (J1/kB = +3.1 K) and quartet ground state with a strong exchange interaction (J2/kB = +160 K), respectively. The interconversion between the neutral and one‐electron oxidized species can be realized through electrochemical reactions. Significantly different absorption bands in the near‐IR region newly appeared in the electronic spectra acquired during electrochemical oxidation/reduction.
Higher order exchange coupling: Oxidation of a diradical bis(nitronyl nitroxide)‐substituted diphenyldihydrophenazine introduces an additional electronic spin at the dihydrophenazine core, which results in a cationic quartet ground‐state species with stronger ferromagnetic coupling in comparison with that of the neutral triplet‐state species. Reversible conversion between the two species is confirmed from the electronic spectra acquired during electrochemical reactions.
Open-shell π-electronic molecules exhibit spin and magnetic properties, facile redox properties, and unique photophysical properties derived from their unpaired electron(s) and the presence of ...singly-occupied molecular orbital(s). Especially, stable open-shell π-electron molecules are continuously attracting attention in interdisciplinary research areas as promising components of magnetic, electric, and related materials. Among them, radical cation species generated by oxidation of π-electron molecules with superior electron donating ability are one of the promising components of the materials because their physical properties and functionality of molecular entities and assemblies are able to be controlled by substituents and counter anions. Here, we have introduced detailed molecular structures and intriguing physical properties of highly stable radical cations based on phenothiazine, dihydrophenazine, and phenoxiazine π-electronic systems, such as controls of magnetic, near-IR absorption, and liquescent properties, that have been elucidated as results of our continuous research.
A series of novel azacyclophanes consisting of 2,7-anthrylene and phenylene units were designed and synthesized by the Buchwald–Hartwig coupling reaction to investigate their unique electronic ...properties in multiple oxidized states. Cyclic voltammetry showed that the p-phenylene derivative exhibited three reversible oxidation waves, whereas the o- and m-phenylene derivatives showed two quasi-reversible oxidation waves due to the complicated intramolecular interaction between the oxidized units and neutral units. Moreover, the absorption spectra of the p-phenylene derivative in different oxidation states showed absorption bands at 865 and 1025 nm, which were attributed to intramolecular charge–transfer interactions. The photophysical and electrochemical properties of the p-phenylene analog were also compared with those of the o- and m-phenylene derivatives based on theoretical calculations for further evaluation of the intramolecular electronic interactions.
In this research, phase transformation process under different thermal cycles corresponding to a low and a high heat input welding in the heat-affected zone of low-carbon boron-treated steel is ...systematically investigated by a high temperature laser scanning confocal microscopy. The effect of thermal cycles on the phase transformation process is quantified by measuring the transformation start temperature of each transformation product and the average number of nucleation sites of intragranular acicular ferrite.
PDF
