Heteropoly compounds as octahedral high valence complex. Spectrochemical properties of Waugh-structure enneamolybdonickelate(IV) and enneamolybdomanganate(IV) ions

Electronic absorption and magnetic circular dichroism (MCD) spectra in UV-vis region of Waugh-structure [XMo₉O₃₂]^6?(X = Ni(IV), Mn(IV)) ion in aqueous solution and solid IR spectra have been measured. The Ni(IV) ion in the polyanion has a low-spin d⁶ electronic configuration and the Mn(IV) ion has a d³ configuration. Visible absorption spectrum of the nickelate(IV) polyanion is interpreted to be mainly governed by charge-transfer transitions of the “ligand”, Mo₉O₃₂, to Ni(IV) ion, rather than d-d transitions, while visible absorption of the manganate(IV) polyanion is governed, to a great extent, by d-d transitions. It is indicated by the MCD spectrum that the splitting of the first d-d absorption in the manganate(IV) polyanion is due to a contribution of the spin-forbiden transition, rather than from a trigonal splitting of the spin-allowed transition. Absorption and MCD spectra in UV region are due to charge-transfer transition within a common “ligand”, which are less influenced by the kind of heteroatom, Ni(IV) or Mn(IV). The MCD pattern by the intra-ligand charge-transfer is especially characteristic of the Waugh-structure polyanions.     

Tunable design strategy for fluorescence probes based on 4-substituted BODIPY chromophore: improvement of highly sensitive fluorescence probe for nitric oxide

4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) is a well-known fluorophore, with a high molar extinction coefficient and high fluorescence quantum efficiency (Phi(fl)). Furthermore, its structure can be modified to change its excitation and emission wavelengths. However, little work has been done on the structural modification of fluorines at the B-4 position with other functional groups. We synthesized 4-methoxy-substituted BODIPY derivatives in satisfactory yields, and found that they exhibited improved solubility in aqueous solution. Moreover, their oxidation and reduction potentials were greatly decreased without any change in their absorbance and fluorescence properties. These features of 4-substituted BODIPYs may be useful for developing novel fluorescence probes based on the intramolecular photoinduced electron transfer (PeT) mechanism, because it is possible to optimize the PeT process precisely by modulating the electrochemical properties of the fluorophore. The value of this approach is exemplified by its application to the development of a highly sensitive and pH-independent fluorescence probe for nitric oxide.     

Study of γ d → π + π − d Reaction in an Energy Region of 0.67 ≤ E γ ≤ 1.08 GeV

Double charged pion photoproductions from the deuteron have been studied at Research Center for Electron Photon Science (ELPH), Tohoku University. Tagged photon beams in an energy range of 0.67 ≤ E _γ ≤ 1.08 GeV were impinged on the liquid deuteron target. Produced charged particles were observed with the Neutral Kaon Spectrometer2 (NKS2). The γ d → π ⁺ π ^? d process was clearly separated among the three charged tracks. We obtained the photon energy dependence of the normalized yields of this process.     

Study of Strangeness Photoproduction on the Neutron in the Threshold Region

Photoproduction of the neutral kaon on the deuteron has been investigated at the Research Center for Electron Photon Science, Tohoku University. We constructed the Neutral Kaon Spectrometer-2 for the detection of charged particles from the decay of the neutral kaon and the hyperon. We obtained a momentum distribution of K ⁰ with the inclusive measurement. It was consistent with the previous measurement. The total cross section of γ + d → K ⁰ + Λ + p was estimated from the measured integral cross section of γ + d → Λ + X. The total cross section with respect to the photon energy was compared with the theoretical calculations. It favored the Saclay-Lyon A model calculation with the ratio of the neutral to charged coupling constants of the axial-vector meson, K ₁, as ~ ?1.5. The energy dependence and the magnitude of the total cross section were similar to the total cross section of γ + p → K ⁺ Λ.     

Study of Neutron-Rich Hypernuclei by the (π −, K +) Reaction at J-PARC

We are planning to perform an experiment at J-PARC and produce new neutron-rich Λ hypernuclei by using the (π ^?, K ⁺) reaction (J-PARC E10). As the first step, we are planning to produce ${^6_{\Lambda}{\rm H}}$ hypernuclei with a ⁶Li target. To conduct this experiment, we are developing new detectors, those are scintillating fiber tracker, and silicon strip detector, for high rate operation to aim at increasing beam intensity up to 10⁷/spill. As a result of beam test in Jun 2012, we are going to use high-rate beam at least 10⁷/spill.     

Theoretical investigation of Mn adsorbates aside self-organised Bi nanolines on hydrogenated Si(0 0 1) surface

We have theoretically investigated the atomic structure, magnetic behaviour, and electronic properties of Mn adsorbates on hydrogen passivated self-organised Bi nanolines on the Si(0 0 1)surface. It is found that the most stable geometry for monolayer (ML) coverage of Mn is just underneath the first Si(0 0 1) surface layer. The Mn atoms in the optimised configuration are seven-fold coordinated with their neighbouring Si atoms. Total energy calculations suggest that the Mn adsorbates form a degenerate state of ferromagnetic and anti-ferromagnetic lines parallel and adjacent to the self-assembled Bi lines. The density functional band structure calculation within the local-spin density approximation shows that the ferromagnetic system behaves like a metal in both spin channels. On the other side, the anti-ferromagnetic phase exhibits a half-metallic phenomenon with semiconducting character for the majority spin channel and semi-metallic character for the minority spin channel.     

Dual Emission from Precious Metal-Free Luminophores Consisting of C,H, O,Si, and S/P at Room Temperature

Fluorescence–phosphorescence dual-emissive compounds are valuable tools for ratiometric luminescence sensing. Herein, it is reported that 2,5-bis(phenylsulfonyl)- and 2,5-bis[bis(4-methoxyphenyl)phosphinyl]-1,4-disiloxybenzenes exhibit dual emission with emission peaks that were easily identified without performing time-gated measurement. The disiloxybenzenes in powder simultaneously fluoresced and phosphoresced at 358–374 and 457–470 nm, respectively, under vacuum. The intensity ratios of the phosphorescence/fluorescence maxima of the disiloxybenzenes in powder and in a thin film of poly(methyl methacrylate) were sensitive to temperature and molecular oxygen, respectively. The plots of the relative intensity versus temperature or partial pressure of molecular oxygen were well fitted with calibration curves defined by an exponential approximation with excellent correlation coefficients R² (0.9708–0.9921), demonstrating the high potential of the disiloxybenzenes as precious metal-free probes applicable to ratiometric luminescence sensing.     

Synthesis and optoelectronic properties of conjugated polymers based on a dithienobenzimidazole unit in the main chain

Three conjugated polymers with the dithienobenzimidazole (DTBIm) unit ( P1 , P3 , and P4 ) and one conjugated polymer with the dithienobenzoxazole unit ( P2 ) were synthesized by the cross‐coupling polymerization. The absorption maxima showed a red‐shift in the order of P3 (406 nm), P2 (426 nm), P1 (438 nm), and P4 (450 nm), which was studied in detail using the frontier molecular orbital calculation of the model compounds. The energy levels of the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the DTBIm unit‐containing conjugated polymers were estimated by the cyclic voltammetry. The transformation from DTBIm ( P4 ) to dithienobenzimidazolium ( P4' ) was also carried out to shift the absorption maxima of P4' (454 nm) by promoting the intramolecular charge transfer between the DTBIm and thiophene units. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 401–409