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The donor–acceptor–π-conjugated (D–π–)2A fluorescent dyes OUY-2, OUK-2 and OUJ-2 with two (diphenylamino)carbazole thiophene units as D (electron-donating group)–π (π-conjugated bridge) moiety and a pyridine, pyrazine or triazine ring as electron-withdrawing group (electron-accepting group, A) have been designed and synthesized. The photophysical and electrochemical properties of the three dyes were investigated by photoabsorption and fluorescence spectroscopy, Lippert–Mataga plots, cyclic voltammetry and density functional theory calculations. The photoabsorption maximum (λmax,abs) and the fluorescence maximum (λmax,fl) for the intramolecular charge-transfer characteristic band of the (D–π–)2A fluorescent dyes show bathochromic shifts in the order of OUY-2 < OUK-2 < OUJ-2. Moreover, the photoabsorption bands of the (D–π–)2A fluorescent dyes are nearly independent of solvent polarity, while the fluorescence bands showed bathochromic shifts with increasing solvent polarity (i.e., positive fluorescence solvatochromism). The Lippert–Mataga plots for OUY-2, OUK-2 and OUJ-2 indicate that the Δμ (= μe − μg) value, which is the difference in the dipole moment of the dye between the excited (μe) and the ground (μg) states, increases in the order of OUY-2 < OUK-2 < OUJ-2. Therefore, the fact explains our findings that OUJ-2 shows large bathochromic shifts of the fluorescence maxima in polar solvents, as well as the Stokes shift values of OUJ-2 in polar solvents are much larger than those in nonpolar solvents. The cyclic voltammetry of OUY-2, OUK-2 and OUJ-2 demonstrated that there is little difference in the HOMO energy level among the three dyes, but the LUMO energy levels decrease in the order of OUY-2 > OUK-2 > OUJ-2. Consequently, this work reveals that for the (D–π–)2A fluorescent dyes OUY-2, OUK-2 and OUJ-2 the bathochromic shifts of λmax,abs and λmax,fl and the lowering of the LUMO energy level are dependent on the electron-withdrawing ability of the azine ring, which increases in the order of OUY-2 < OUK-2 < OUJ-2.

Graphite intercalation compounds are a new class of electronic materials that are classified as graphite-based host guest systems.They have specific structural features based on the alternating stacking of graphite and guest intercalate sheets.

Graphene oxide, a two-dimensional aromatic scaffold decorated by oxygen-containing functional groups, possesses rich chemical properties and may present a green alternative to precious metal catalysts. Graphene oxide-based carbocatalysis has recently been demonstrated for aerobic oxidative reactions. However, its widespread application is hindered by the need for high catalyst loadings. Here we report a simple chemical treatment that can create and enlarge the defects in graphene oxide and impart on it enhanced catalytic activities for the oxidative coupling of amines to imines (up to 98% yield at 5 wt% catalyst loading, under solvent-free, open-air conditions). This study examines the origin of the enhanced catalytic activity, which can be linked to the synergistic effect of carboxylic acid groups and unpaired electrons at the edge defects. The discovery of a simple chemical processing step to synthesize highly active graphene oxide allows the premise of industrial-scale carbocatalysis to be explored. Graphene oxide has been proposed as an alternative to precious metals for the catalysis of aerobic oxidative reactions; however, high catalyst loadings are needed. Here a simple base and acid treatment is shown to enhance its catalytic activity for the oxidative coupling of amines under ambient conditions.

The donor–acceptor–π-conjugated (D–π–) 2 A fluorescent dyes OUY - 2 , OUK-2 and OUJ-2 with two (diphenylamino)carbazole thiophene units as D (electron-donating group)–π (π-conjugated bridge) moiety and a pyridine, pyrazine or triazine ring as electron-withdrawing group (electron-accepting group, A) have been designed and synthesized. The photophysical and electrochemical properties of the three dyes were investigated by photoabsorption and fluorescence spectroscopy, Lippert–Mataga plots, cyclic voltammetry and density functional theory calculations. The photoabsorption maximum (λ max,abs ) and the fluorescence maximum (λ max,fl ) for the intramolecular charge-transfer characteristic band of the (D–π–) 2 A fluorescent dyes show bathochromic shifts in the order of OUY-2 < OUK-2 < OUJ-2 . Moreover, the photoabsorption bands of the (D–π–) 2 A fluorescent dyes are nearly independent of solvent polarity, while the fluorescence bands showed bathochromic shifts with increasing solvent polarity (i.e., positive fluorescence solvatochromism). The Lippert–Mataga plots for OUY - 2 , OUK-2 and OUJ-2 indicate that the Δμ (= μ e − μ g ) value, which is the difference in the dipole moment of the dye between the excited (μ e ) and the ground (μ g ) states, increases in the order of OUY-2 < OUK-2 < OUJ-2 . Therefore, the fact explains our findings that OUJ-2 shows large bathochromic shifts of the fluorescence maxima in polar solvents, as well as the Stokes shift values of OUJ-2 in polar solvents are much larger than those in nonpolar solvents. The cyclic voltammetry of OUY - 2 , OUK-2 and OUJ-2 demonstrated that there is little difference in the HOMO energy level among the three dyes, but the LUMO energy levels decrease in the order of OUY-2 > OUK - 2 > OUJ - 2 . Consequently, this work reveals that for the (D–π–) 2 A fluorescent dyes OUY - 2 , OUK-2 and OUJ-2 the bathochromic shifts of λ max,abs and λ max,fl and the lowering of the LUMO energy level are dependent on the electron-withdrawing ability of the azine ring, which increases in the order of OUY-2 < OUK-2 < OUJ-2 .

Nano-structured graphene has recently attracted extraordinary attention due to its potential use as an electronic or spintronic material. We investigated the electrical conductivities of antidot and Ar-sputtered graphene samples under a magnetic field in terms of the carrier density. Antidot samples exhibit conductivity that is well explained by charged impurity scattering, which is associated with intravalley scattering. This suggestion is supported by the low intensity of the Raman D band, which is related to intervalley scattering induced by structural defects. In contrast, Ar-sputtered samples show a strong D band and conductivity that is affected by defect scattering. The difference in the main scattering mechanism between the two types of samples appears as Shubnikov-de Haas oscillations at high magnetic fields, which are observed in antidot samples but not in Ar-sputtered samples. Furthermore, an analysis of weak localization effects in both samples at low fields reveals that intra- and intervalley scatterings play significant roles in antidot and Ar-sputtered samples, respectively.

Graphene, a single sheet of graphite, has an unconventional electronic structure that can be described in terms of massless Dirac Fermions. This interesting electronic feature is not only an important fundamental issue in condensed matter physics but also holds future promise in post-Si electronic/spintronics device applications.

Randomly networked nanographene sheets have been studied by electron spin resonance (ESR) technique at 20 GHz (K-band) and 35 GHz (Q-band). Nanographene has spin-polarized non-bonding π-electron states (edge-state spins) localized in the zigzag edge region. We have investigated the temperature dependence of an ESR signal of activated carbon fibers at two different microwave powers for each frequency. The signal intensity smoothly increases with decreasing temperature at any microwave power. The line width of ESR signal with a Lorentzian line shape decreases linearly upon cooling, and then increases steeply after taking a minimum at about 20 K irrespective of microwave power. The former is interpreted as the Korringa relation in the localized edge spins and conduction π carriers. The latter may be caused by inhomogeneous line broadening of the ESR signal from randomly distributed nanographene sheets with different sizes due to the suppression of electron hopping between nanographene sheets, i.e. electron localization. The discontinuous line broadening and the signal intensity drop at around 20 K reported in the previous X-band ESR at 1 μW were not observed, probably because of either higher microwave power than 1 μW or some amount of oxygen adsorption in our sample in the present study.

The electronic structure of a nanographene sheet depends on the shape of its edges. In zigzag‐shaped edges, a nonbonding edge state of π‐electron origin is created in spite of the absence of such a state in armchair‐shaped edges. As the edge state is strongly spin polarized, the edge‐state spin is an important building block in creating carbon‐based molecular magnets. In addition, defect of σ‐dangling bond can be another instance of magnetic origin. The magnetic structure of nanographene and its unconventional magnetic phenomena are reviewed. Edge‐state spins strongly interact with each other through exchange interaction in contrast to the isolated feature of σ‐dangling bond spins. In a zigzag edge, strong intra‐zigzag‐edge ferromagnetic interaction arranges the edge‐state spins in parallel. In an arbitrarily shaped nanographene sheet, with its periphery being a combination of zigzag and armchair edges, the cooperation of strong ferromagnetic intra‐zigzag‐edge interaction and intermediate‐strength inter‐zigzag‐edge antiferromagnetic/ferromagnetic interaction makes the magnetic structure ferrimagnetic with a nonzero net magnetic moment remaining. In nanographene‐based nanoporous carbon, mechanical compression of nanographite domains (a stack of three to four nanographene sheets) by guest molecules condensed physisorptively into the nanopores brings about a magnetic switching phenomenon between high‐ and low‐spin states on adsorption/desorption processes. Huge helium condensation into the nanopores accelerates the spin‐lattice relaxation rate of the edge‐state spin through the collisional process. This suggests that edge‐state spins can be utilized as a probe for helium sensor.

The pressure-induced conducting behavior of the charge-transfer salts (BDA-TTP)2X [BDA-TTP = 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene; X = ClO4·H2O, ClO4, BF4·H2O, BF4, and I3] has been investigated. With increasing pressure, the transition temperature to insulator observed in the ClO4·H2O, ClO4, BF4·H2O, and BF4 salts increases. On the other hand, the resistance of the I3 salt as a function of temperature at 10.0 kbar shows a drop attributable to a superconducting transition with an onset at 4.5 K. The superconducting transition temperature (Tc) can reach 8.2 K by applying a pressure of 10.3 kbar, but gradually decreases with further increases in the pressure.