Synthesis of pyrrolophenanthridone alkaloid kalbretorine from indolecarboxylic acids via hypervalent iodine(III) mediated halodecarboxylation and reduction

The treatment of 8,9,10-trimethoxy-7H-pyrrolo[3,2,1-de]phenanthridine-4,5-dicarboxylic acid with phenyliodine diacetate and potassium iodide in tetrahydrofuran gave the corresponding 4,5-diiodo derivative, which was converted to kalbretorine via reduction, demethylation, followed by alkylation.     

Effect of aggregation on the excited-state electronic structure of perylene studied by transient absorption spectroscopy

The effect of aggregation on the excited-state electronic structure of perylene was studied through transient absorption measurements of isolated molecules, excimers, monomeric crystals (beta-perylene), and dimeric crystals (alpha-perylene). Changes of electronic state were clearly identified from the changes in transient absorption spectra. A detailed investigation was made by combining the obtained results with previous measurements of ground-state absorption and fluorescence spectra. The energy level of the ion-pair state in alpha-perylene crystals was estimated, and the results are compared with previous photoconductivity results. Moreover, the relaxation processes of excited states in alpha-perylene crystals were studied by femtosecond transient absorption measurements.     

Conformation-controlled luminescent properties of lanthanide clusters containing p-tert-butylsulfonylcalix[4]arene

Dinuclear and cubane-shaped lanthanide cluster complexes containing EuIII)and TbIII were synthesized by step-by-step construction using p-tert-butylsulfonylcalix[4]arene as a cluster-forming ligand. The sulfonylcalixarene adopts a pinched-cone conformation in the dinuclear complexes and a cone conformation in the cubane complexes. Because the calixarene has a large pi-conjugate system expanding over the entire molecule, it behaves as a good antenna chromophore for UV and near-UV light, and a slight conformational change of the calixarene (from cone to pinched-cone and vice versa) has an effect on the energy levels of excited S1 and T1 states. As a result, selectivity is observed in the luminescent properties of dinuclear and cubane-shaped systems of EuIII and TbIII.     

Reversible dimerization of decaniobate

Three different solvates of TBA₆[Nb₁₀O₂₈] (TBA = tetra-n-butylammonium) were structurally characterized. The results revealed that two water molecules are hydrogen-bonded to the terminal oxygens of the [Nb₁₀O₂₈]⁶⁻ anion in the same manner in all of the solvates. Decaniobate [Nb₁₀O₂₈]⁶⁻ dimerizes by the action of HCl to form icosaniobate [Nb₂₀O₅₄]⁸⁻, while icosaniobate breaks up into decaniobate [Nb₁₀O₂₈]⁶⁻ by the action of TBAOH. Decaniobate also dimerizes spontaneously to form icosaniobate [Nb₂₀O₅₄]⁸⁻ in CH₂Cl₂ even if no acid is added to the solution. The reaction was followed by IR spectroscopy, and the results suggested the reaction is second order with respect to the concentration of [Nb₁₀O₂₈]⁶⁻.     

Application of approximations for joint cumulative k-distributions for mixtures to FSK radiation heat transfer in multi-component high temperature non-LTE plasmas

Approximations for joint cumulative k-distribution for mixtures are efficient for full spectrum k-distribution (FSK) computations. These approximations provide reduction of the database that is necessary to perform FSK computation when compared to the direct approach, which uses cumulative k-distributions computed from the spectrum of the mixture, and also less computational expensive when compared to techniques in which RTE's are required to be solved for each component of the mixture. The aim of the present paper is to extend the approximations for joint cumulative k-distributions for non-LTE media. For doing that, a FSK to non-LTE media formulation well-suited to be applied along with approximations for joint cumulative k-distributions is presented. The application of the proposed methodology is demonstrated by solving the radiation heat transfer in non-LTE high temperature plasmas composed of N, O, N₂, NO, N₂⁺ and mixtures of these species. The two more efficient approximations, that is, the superposition and multiplication are employed and analyzed.     

Auger-free luminescence due to interatomic p–d transition and self-trapped exciton luminescence in Rb2ZnCl4 crystals

It is reported that Auger-free (AF) luminescence appears with two bands at 4.5 and 6.3 eV in Rb₂ZnCl₄. This luminescence originates from a radiative transition of the Cl 3p valence electrons into the Zn 3d outermost-core holes. The present work is the first observation of AF luminescence due to interatomic p–d transitions in halide crystals. The appearance of two AF luminescence bands suggests the existence of two types of AF transitions following core hole creation. A largely Stokes-shifted luminescence band is also found to appear at 1.9 eV. This band has an excitation threshold at the fundamental absorption edge, and is ascribed to the radiative decay of a self-trapped exciton.     

Syntheses of 2‐alkylthio‐1,3‐thiazine derivatives from S‐alkyldithiocarbamates and α,β‐unsaturated ketones

Various 2‐alkylthio‐1,3‐thiazine derivatives were synthesized by the reactions of S‐alkylthiocarbamates with α,β‐unsaturated ketones in the presence of BF₃ · Et₂O. The thiazine was converted into two isomeric dehydrated products in the presence of a Lewis acid. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:377–379, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10055