The photoexcited spin-aligned state of high-density exciton magnetic polarons and the effect of magnetic field in semimagnetic semiconductor Cd(0.8)Mn(0.2)Te

In Cd(0.8)Mn(0.2)Te, nonlinear photoluminescence (PL) appears only when localized excitons are selectively excited to high-density states. Here, the effect of a magnetic field is compared between nonlinear PL and PL due to localized magnetic polarons. Nonlinear PL shows a shift towards lower energy under an applied magnetic field, whereas PL of a localized magnetic polaron band shows a slight shift towards higher energy. The experimental results support the hypothesis that the origin of the nonlinear PL is a spin-aligned state of high-density exciton magnetic polarons. In the spin-aligned state, most spins of electrons (holes) in many magnetic polarons point in the same direction. In this new high-density photoexcited state, the s, p-d exchange interaction between photoexcited electrons (holes) and magnetic ions plays an important role.     

Temperature dependence of the emission spectra of p-benzoquinone in a p-dichlorobenzene matrix

Emission and excitation spectra of p-benzoquinone have been measured in a partially translucent p-dichlorobenzene host matrix at different temperatures from 77 up to 323 K. Successive occurrence of the T₁(n,π^?) and T₂(n,π^?) phosphorescence and S₁(n,π^?) fluorescence has been observed for p-benzoquinone upon increasing temperature. The S₁–T₂ and T₂–T₁ energy separations determined from the temperature dependence of the emission intensities agreed well with those obtained from the locations of the T₁ and T₂ phosphorescence and S₁ fluorescence origins. Occurrence of the emission from S₁ and T₂ is brought by the thermal population from the T₁ state. The symmetries of the T₁ and T₂ states were determined to be B_1g and A_u, respectively, based on the spectral data.     

Oxygen partial pressure dependence of in situ X-ray absorption spectroscopy at the Co and Fe K edges for (La0.6Sr0.4)(Co0.2Fe0.8)O3−δ

The oxygen partial pressure (P(O₂)) dependence of in situ X-ray absorption spectroscopy (XAS) at the Co and Fe K edges was measured simultaneously and continuously at 900 and 1000 K. These experiments, which were performed during reduction, changing P(O₂) from 1 to 10^?4 atm, were used to investigate each valence related to Co and Fe in (La_0.6Sr_0.4)(Co_0.2Fe_0.8)O_3?δ (LSCF). The absorption edge shift of the Co K edge was more than twice that of the Fe K edge at 1000 K during reduction. For quantitative analysis, X-ray absorption near-edge structure spectroscopy was carried out at the Co and Fe K edges; the results indicated that the Co valence decreased more easily than the Fe valence; that is, the oxygen preferentially left from the oxygen sites around Co.     

NiII(TPA) as an efficient catalyst for alkane hydroxylation with m-CPBA

A simple Ni(II)(TPA) complex [TPA = tris(2-pyridylmethyl)amine] has been demonstrated to act as an efficient turnover catalyst for alkane hydroxylation with m-CPBA (m-chloroperbenzoic acid), in which contribution of a NiO(+) (nickel-oxo) type active oxygen species is suggested.     

Modeling the mononuclear, dinuclear, and trinuclear copper(I) reaction centers of copper proteins using pyridylalkylamine ligands connected to 1,3,5-triethylbenzene spacer

The structure and O2-reactivity of copper(I) complexes supported by novel ligands, Pye2 (1,3,5-triethyl-2,4-bis((N-benzyl-N-(2-(pyridin-2-yl)ethyl)-)aminomethyl)benzene), Pye3 (1,3,5-triethyl-2,4,6-tris((N-benzyl-N-(2-(pyridin-2-yl)ethyl))aminomethyl)benzene), MePym2 (1,3,5-triethyl-2,4-bis((N-benzyl-N-(6-methylpyridin-2-ylmethyl))aminomethyl)benzene), and MePym3 (1,3,5-triethyl-2,4,6-tris((N-benzyl-N-(6-methylpyridin-2-ylmethyl))aminomethyl)benzene) have been examined. The ligands are designed to construct mono-, di-, and trinuclear copper(I) complexes by connecting two or three pyridylalkylamine metal-binding sites to a 1,3,5-triethylbenzene spacer. Thus, the reaction of the ligands with [CuI(CH3CN)4]X (X = PF6, CF3SO3) or CuICl gave the expected mononuclear copper(I) complexes [CuI(Pye2)(CF3SO3)] (1) and [CuI(Pye3)](CF3SO3) (2), dinuclear copper(I) complex [CuI2(MePym2)(Cl)]CuICl2 (3), and trinuclear copper(I) complex [CuI3(MePym3)(CH3CN)3](CF3SO3)3 (4), the structures of which were determined by X-ray crystallographic analysis. The mononuclear copper(I) complexes, 1 and 2, exhibit a distorted three-coordinate T-shape structure and a trigonal planar structure, respectively, which are very close to the coordination geometry of the CuA site of PHM (peptidylglycine alpha-hydroxylating monooxygenase) and the CuB site of CcO (cytochrome c oxidase). Notably, 1 and 2 showed a significantly high oxidation potential (990 mV vs SCE), thus showing virtually no reactivity toward O2. On the other hand, the metal centers of the dinuclear and trinuclear copper(I) complexes, 3 and 4, exhibit a distorted trigonal planar geometry and a trigonal pyramidal geometry, respectively. In contrast to the mononuclear copper(I) complexes, these dinuclear and trinuclear copper(I) complexes reacted with O2 to induce an aromatic ligand hydroxylation reaction involving an NIH-shift of one of the ethyl substituents on the benzene spacer. The NIH-shift of the alkyl substituent on the aromatic ring is strong evidence of the electrophilic aromatic substitution mechanism, although the active oxygen intermediate could not be directly detected during the course of the reaction. The biological relevance of the copper(I) complexes is also discussed on the basis of structure and O2-reactivity.     

Infrared spectra of p-, m- and o-fluorobenzaldehyde in low temperature argon matrices

Three structural isomers of fluorobenzaldehyde (p-, m- and o-forms) have been investigated in detail with matrix-isolation infrared spectroscopy, in the 700-3000 cm⁻¹ region, combined with the UV photoexcitation and the density functional calculations. Two rotamers (syn and anti) were identified for m- and o-fluorobenzaldehyde upon the photoexcitation and most of the bands of each rotamer were assigned. It is shown that the formation of the intramolecular C-H?F hydrogen bond for the anti rotamer of o-FB results in the shortening of the aldehyde C-H bond length and that the C-F and/or CO bond lengths are shortened for the syn rotamer of o-FB presumably due to the repulsion between the aldehyde O and F atoms.     

Two new dioxopiperazine derivatives, arestrictins A and B, isolated from Aspergillus restrictus and Aspergillus penicilloides

In the course of searching for bioactive substances, two new dioxopiperazine derivatives, arestrictins A (1) and B (2), were isolated along with the known dioxopiperazine, cristatin A (3), and the known peptide, asperglucide (4), from the organic extract of the xerophilic fungi, Aspergillus restrictus and Aspergillus penicilloides. The absolute structures of 1 and 2, except for the configuration of the secondary alcohol in 1, were established by spectroscopic and chemical investigation. The absolute configuration of cristatin A (3) was also determined.     

Numerical Radius Norms on Operator Spaces

We introduce a numerical radius operator space (X, W_n). Theconditions to be a numerical radius operator space are weakerthan Ruan's axiom for an operator space (X, O_n). Let w(·)be the numerical radius on B(H). It is shown that, if X admitsa norm W_n(·) on the matrix space M_n(X) which satisfiesthe conditions, then there is a complete isometry, in the senseof the norms W_n(·) and w_n(·), from (X, W_n) into(B(H), w_n). We study the relationship between the operator space(X, O_n) and the numerical radius operator space (X, W_n). Thecategory of operator spaces can be regarded as a subcategoryof numerical radius operator spaces.