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101.
Lee LF Adronov A Schaller RD Fréchet JM Saykally RJ 《Journal of the American Chemical Society》2003,125(2):536-540
Near-field scanning optical microscopy (NSOM) has been used to investigate the photophysical characteristics of first- to fourth-generation (G1 to G4) light-harvesting dendrimer thin films containing coumarin-343 and coumarin-2 as the core and peripheral chromophores, respectively. Thin film photoluminescence (PL) spectra exhibit a significant red shift in the lower generations (G1, G2, and G3) as compared to their respective solution PL spectra, implying the formation of excimers. Spatially resolved PL NSOM images exhibit pronounced nanoscopic domains in G1, which become more homogeneous in higher generations due to site-isolation of the core chromophore. G4 exhibits complete site-isolation for these light-harvesting dendrimer films. 相似文献
102.
The stereochemistry of the reaction of silver benzoates on chiral di-O-aroyl-1,2 iododeoxy-3-sn-glycerols has been reinvestigated. The reaction proceeds either with or without neighbouring group participation, depending on : - possible electrophilic assistance by the silver ion to the ionisation of the substrate (occuring only with dissociated silver salts), - ability of substituants R1 and R2 on the substrates to stabilize a positive charge. Rearrangements are at minimum with R1 and R2 electronreleasing groups in the substrate, silver salts un-or weakly dissociated and bearing a good nucleophile. For one case, a regio- and stereo specific reaction is observed. 相似文献
103.
Broussy S Bernardes-Génisson V Gornitzka H Bernadou J Meunier B 《Organic & biomolecular chemistry》2005,3(4):666-669
An ortho-metallation-electrophilic substitution sequence was employed as a key step to build the 4-benzoylpyridine framework. It was found that 4-benzoylpyridine-3-carboxamide and an N-pyridyl alkylated derivative both exist in a unique cyclized hemiamidal structure, not in the usually expected keto-amide open form. These structures represent fragment models of the Isoniazid-NAD adducts involved in the mechanism of action of the antituberculous drug Isoniazid. 相似文献
104.
Jean Michel Brunel 《Tetrahedron》2007,63(18):3899-3906
A new and efficient mild Pd/P(t-Bu)3 catalyst for selective reduction of various alkenes under transfer hydrogen conditions has been developed leading to the corresponding saturated derivatives in chemical yields varying from 65 to 98%. Mechanistic rationale of this reaction has been also demonstrated. 相似文献
105.
According to the subsequent treatment, azepines , , or 1,2-dihydro derivatives and are obtained in the photolysis in basic medium of β-anthracenic azides and and provide strong evidence for the intermediate formation of bicyclic aziridines. 相似文献
106.
Natural Occurrence of C(15)-Epimeric Coleons C and D and its Significance to the Stereochemistry of the Formation of a Spirocyclopropanring In a previous paper some evidence was presented for a predominant occurrence of epimeric coleons ((15S)-coleon C ((15 S)- 1a ), and (15S)-coleon D ((15S)- 2a )) in Plectranthus lanuginosus [1], The proposed structures have now been proven by careful comparison of their physical data with those of the already described C(15)-epimers whose structures were deduced by X-ray analysis of a derived cis-diketone 3 [5], Examination of the epimeric purity of coleons possessing a 2-hydroxy-1-methylethyl side-chain (coleons C , D , H , I , I ′ and derivatives) isolated from seven different species (Coleus, Plectranthus and Solenostemon) has shown that these coleons always occur as a mixture of C(15)-epimers, although in most cases with one predominant epimer. The consequences for the stereochemistry of the postulated in vivo formation of the methyl-substituted spirocyclopropane substructure is discussed. 相似文献
107.
Jacqueline Ficini Jean dAngelo Arnaud Eman Anne Marie Touzin 《Tetrahedron letters》1976,17(9):683-686
108.
109.
Enrico Borgarello Jean Desilvestro Michael Grtzel Ezio Pelizzetti 《Helvetica chimica acta》1983,66(6):1827-1834
Conduction band electrons produced by band gap excitation of TiO2-particles reduce efficiently thiosulfate to sulfide and sulfite. \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm 2e}_{{\rm cb}}^ - ({\rm TiO}_{\rm 2}) + {\rm S}_{\rm 2} {\rm O}_3^{2 - } \longrightarrow {\rm S}^{2 - } + {\rm SO}_3^{2 - } $\end{document} This reaction is confirmed by electrochemical investigations with polycrystalline TiO2-electrodes. The valence band process in alkaline TiO2-dispersions involves oxidation of S2O to tetrathionate which quantitatively dismutates into sulfite and thiosulfate, the net reaction being: \documentclass{article}\pagestyle{empty}\begin{document}$ 2{\rm h}^{\rm + } ({\rm TiO}_{\rm 2}) + 0.5{\rm S}_{\rm 2} {\rm O}_{\rm 3}^{{\rm 2} - } + 1.5{\rm H}_{\rm 2} {\rm O} \longrightarrow {\rm SO}_3^{2 - } + 3{\rm H}^{\rm + } $\end{document} This photodriven disproportionation of thiosulfate into sulfide and sulfite: \documentclass{article}\pagestyle{empty}\begin{document}$ 1.5{\rm H}_{\rm 2} {\rm O } + 1.5{\rm S}_{\rm 2} {\rm O}_{\rm 3}^{{\rm 2} - } \mathop \to \limits^{h\nu} 2{\rm SO}_3^{2 - } + {\rm S}^{{\rm 2} - } + 3{\rm H}^{\rm + } $\end{document} should be of great interest for systems that photochemically split hydrogen sulfide into hydrogen and sulfur. 相似文献
110.
Turbiez M Frère P Allain M Videlot C Ackermann J Roncali J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(12):3742-3752
Hybrid oligothiophenes based on a various combinations of thiophene and 3,4-ethylenedioxythiophene (EDOT) groups have been synthesized. UV/Vis absorption spectra show that the number and relative positions of the EDOT groups considerably affect the width of the HOMO-LUMO gap and the rigidity of the conjugated system. Analysis of the crystallographic structure of two hybrid quaterthiophenes confirms that insertion of two adjacent EDOT units in the middle of the molecule leads to a self-rigidification of the conjugated systems by intramolecular SO interactions. Cyclic voltammetry data shows that the first oxidation potential of the oligomers decreases with increasing chain length and increasing number of EDOT groups for a given chain length. Electrochemical studies and theoretical calculations show that the positions of the EDOT units in the conjugated chain control the potential difference (DeltaE(p)) between the first and second oxidation steps. Moving the EDOT groups from the outer to the inner positions of the conjugated system increases DeltaE(p). Theoretical calculations confirm that this phenomenon reflects an increase of the intramolecular coulombic repulsion between positive charges in the dication. A thin-film field-effect transistor was fabricated by vacuum sublimation of a pentamer with alternating thiophene-EDOT structure, and the hole mobility was determined. 相似文献