- Control of the white-light emission in the mixed two-dimensional hybrid perovskites (C6H11NH3)2[PbBr4?xIx]
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The control of the composition of mixed organic-inorganic hybrid perovskites by solid-state alloying is a very efficient tool to tune the band gap of the material, leading to enhanced optical performances. At this end, we have elaborated a series of mixed-halide two-dimensional hybrid perovskites (C6H11NH3)2[PbBr4?xIx], with 0 ≤ x ≤ 4, for which we studied the composition-dependence of the structural parameters and their effect on the white-light luminescence properties at room temperature. The structural analysis revealed the existence of a composition-induced structural phase transition occurring in the range 2 a change between Cmc21and Pbca space groups. The optical properties, investigated using optical absorption and photoluminescence measurements, have shown that bromine (Br) to iodine (I) halogen ion substitution redshifts the excitonic optical absorption band, as a result of the hybridization of the valence band structure, built from np orbitals of Br and/or I halogens and 6s orbitals of lead. When iodine was predominant (x > 2), the photoluminescence spectra showed a sharp peak with a relatively small Stokes shift (less than 0.2 eV) attributed to free or bound excitons emissions. In contrast, when the bromide is majority (x a broadband white-light emission with a very large Stokes shift (between 1.2 eV and 0.3 eV), attributed to self-trapped excitons activated by a strong structural distortion of the inorganic sheets. Confronting optical and structural data highlighted the effect of the structure in monitoring the optical properties, since the intensity of the white-light emission increases with the bromine content and was found to excellently correlate with the change of the angular distortion of inorganic octahedra PbX6(X = I/Br).
- Yangui, Aymen,Pillet, Sebastien,Lusson, Alain,Bendeif, El-Eulmi,Triki, Smail,Abid, Younes,Boukheddaden, Kamel
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- EFFECT OF THE STRUCTURE OF AMINES ON RATE AND MECHANISM OF THEIR REACTIONS WITH 2-(β,β-DIBROMOVINYL)-5-NITROFURAN IN ACETONITRILE
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The kinetics of the reaction of 2-(β,β-dibromovinyl)-5-nitrofuran with alkylamines of various types (primary, secondary, and tertiary) in acetonitrile at 55 deg C were studied.It was shown that enamines are formed quantitatively in the case of the reactions with secondary amines.At the same time the products from the reactions with primary amines are the corresponding amidines.Here the monosubstitution product is formed at the first stage, as in the case of the reactions with secondary amines, and rearranges to the imidoyl halide with subsequent substitution of the halogen atom at the imidoyl carbon atom.A quantitative assessment is made of the effect of the structure of the enamine on the rate of the processes.
- Kravchenko, V. V.,Kotenko, A. A.,Popov, A. F.,Kostenko, L. I.,Vegh, D.,Kovac, J.
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p. 2140 - 2143
(2007/10/02)
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- OPTICALLY ACTIVE TRIORGANOSILYL ESTERS OF PHOSPHORUS. SYNTHESIS AND STRUCTURE
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We report this synthesis of the first optically active silyl esters of phosphorus having two centres of chirality : one on silicon and the other on phosphorus.Compounds are obtained of general formula : t-BuPhP(X)YSiαNpPhMe X,Y=O, O(1); S, O(2); Se, O(3); S, S(4); doublet, O(5) including 1 and 3 with optical activity located on Si, 2 and 5 with the activity on Si or P and on both these centres, 4 only racemic.Absolute configurations are determined. 31P and 29Si NMR spectra of these models and their trimethylsilyl analogues are reported.The triorganosilyl group is always preferentially bound to phosphorus through oxygen atom.Surprisingly, diastereotopic NMR chemical shifts exclude the fast 1,3 migration in esters 1 and 4. 29Si NMR spectra correspond to a tetracoordinate silicon atom.
- Chojnowski, J.,Cypryk, M.,Michalski, J.,Wozniak, L.,Corriu, R.,Lanneau, G.
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p. 385 - 398
(2007/10/02)
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- KINETICS OF THE REACTIONS OF 2-HALOGENOPYRIDINIUM SALTS WITH PRIMARY AND SECONDARY AMINES IN ACETONITRILE
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The kinetics of the reactions of 2-halogeno-N-alkylpyridinium salts with primary and secondary aliphatic amines in acetonitrile at 25 deg C were investigated.The reactions obey second-order relationships.In the reaction of 2-bromo-N-ethylpyridinium bromide with aliphatic amines the effect of electronic and steric factors on the reactivity of the amines was examined.
- Litvinenko, L. M.,Titskii, G. D.,Mitchenko, E. S.
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p. 1731 - 1736
(2007/10/02)
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- OXALSAEUREDERIVATE DURCH OXIDATIVE KUPPLUNG VON KOHLENMONOXID AN NICKEL
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Carbon monoxide is oxidatively coupled by ligand nickel(II) compounds with secondary, primary amines and with alkali alkoxides to give oxalic acid derivatives.In the case of secondary amines the CO coupling can be run catalytically by adding oxidants like copper(II) salts.The yield of oxalic esters depends on the types of ligands and anions.
- Hoberg, Heinz,Fananas, F. Javier,Riegel, Hans Josef
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p. 267 - 272
(2007/10/02)
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