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1Author    HansE. Wilhelm, Horst Gebert, Wolfgang RegensteinRequires cookie*
 Title    Effect of Substituents on the Viscosity Dependence of Fluorescence and on the S l -T l Energy Gap of Donor-Acceptor Substituted Trans-Stilbenes  
 Abstract    The dependence of fluorescence quantum yields and Sj-lifetimes of donor-acceptor substituted trans-stilbenes on temperature was measured in the temperature range from 298 to 100 K, using solutions of stilbenes in 3-methylpentane (3-MP). Measurements of fluorescence and phosphores-cence spectra show that the triplet energy is almost independent of the acceptor. The S[-energy and the S r Ti energy gap decrease with increasing acceptor strength. For all compounds intersystem crossing (ISC) S, —» T, is negligible. 
  Reference    Z. Naturforsch. 52a, 837—842 (1997); received November 18 1997 
  Published    1997 
  Keywords    Stilbenes, Fluorescence, Phosphorescence, Singlet-Triplet Energy Gap, Rate Constants 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0837.pdf 
 Identifier    ZNA-1997-52a-0837 
 Volume    52 
2Author    Shozi Yamashita, Mizuki Yoshida, Giiti TomitaRequires cookie*
 Title    Photoionization of Indole in Alkaline Aqueous Solutions at 77 °K  
 Abstract    The photoionization process of indole in alkaline aqueous solutions at 77 °K and the recombination process of trapped electron with its mother molecule were investigated. The fluorescence spectrum of indole in these glassy media depended on the NaOH concentration; the disappearance of the 325 nm band at the NaOH concentrations higher than 5 M with the appearance of a fluorescence band at 375 nm. The latter emission is possibly ascribed to the fluorescence of indole anion formed by proton dissociation in the excited singlet state of indole. The intensities of the 375 nm band and the ESR signal due to trapped electrons were dependent on the NaOH concentration and increased steeply with increasing the NaOH concentration. There was a parallel relation between the indole anion concentration and the trapped electron density to some extent. The dependence of the ESR signal intensity on irradiation intensity suggested that the photoionization of indole in alkaline aqueous solution occurred through a two photon process. The presence of a photoactive intermediate for absorbing the second photon was further investigated with simultaneous irradiation of two different wavelength lights. The trapped electron was detrapped with the irradiation of visible light (e.g. 580 nm), and its recombination with mother molecule caused an emission with the same spectrum as indole phosphorescence. The molecular species of the photoactive intermediate in alkaline aqueous solutions seems to be the indole anion. The photoionization in NaOH aqueous solution at 77 °K was also compared with that in methanolic glassy solution. 
  Reference    (Z. Naturforsch. 31b, 361—366 [1976]; received April 28/July 22 1975) 
  Published    1976 
  Keywords    Photoionization, Phosphorescence, ESR, Trapped Electron, Indole 
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 TEI-XML for    default:Reihe_B/31/ZNB-1976-31b-0361.pdf 
 Identifier    ZNB-1976-31b-0361 
 Volume    31 
3Author    I. Timtcheva, P. Nikolov, St Minchevand, N. SofronievRequires cookie*
 Title    Luminescence Properties of Some 4-or 5-Aminosubstituted Indan-13-Diones  
 Abstract    The photophysical characteristics of some 4(5)-amino-2-aryl-and 4(5)-amino-2-aryl-2-carboxy-methyl-l,3-indandiones have been studied in solvents of different polarity at room temperature and at 77 °K. In contrast to the 2-arylindan-l,3-diones unsubstituted in the phthaloyl fragment, the compounds investigated are photostable and fluoresce in the region 25 000-18 000 cm -1 with fluorescence quantum yields between 0.1 and 0.5. 
  Reference    Z. Naturforsch. 42a, 289—292 (1987); received October 22 1986 
  Published    1987 
  Keywords    4-and 5-amino indan-l, 3-diones, absorption, fluorescence, phosphorescence 
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 TEI-XML for    default:Reihe_A/42/ZNA-1987-42a-0289.pdf 
 Identifier    ZNA-1987-42a-0289 
 Volume    42 
4Author    J. Krzystek, H.J U C Von Schütz, Wolf, R.-D Stigler, J. J. StezowskiRequires cookie*
 Title    Characterization of the Phenanthrene-Tetrachlorophthalic Anhydride (P/TCPA) 1:1 Charge-Transfer Crystal: Spectroscopic and Structural Investigations  
 Abstract    The 1:1 phenanthrene-tetrachlorophthalic anhydride (P/TCPA) charge-transfer complex crystalizes with monoclinic symmetry, space group P2,, with two magnetically inequivalent stacks in the unit cell. The noncentrosymmetric space group is very unusual for CT-complexes. The optical emission spectra at low temperature are characterized by a strong CT phospho-rescence and a weak CT fluorescence and delayed fluorescence. The S, band lies at 22 800 ± 100 cm" 1 , the T, band at 21 200 ± 100 cm" 1 . Above 15 K triplet excitons, moving along the stacks are revealed by ESR. They have a CT character of about 30%, coinciding with that of the shallow X-traps found by ODMR at jow temperatures. A further trap, with zero-field-splitting (zfs) parameters of £> = ±0.0617, E = + 0.0116 cm" 1 has a much larger CT character of 50% as found in the isolated complex in low-temperature glass [1]. A structural model is proposed. 
  Reference    Z. Naturforsch. 42a, 622—630 (1987); received February 28 1987 
  Published    1987 
  Keywords    Charge-transfer crystal, crystal structure, fluorescence, phosphorescence, triplet excitons 
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 TEI-XML for    default:Reihe_A/42/ZNA-1987-42a-0622.pdf 
 Identifier    ZNA-1987-42a-0622 
 Volume    42 
5Author    Shan-Yuan Yang, S. S. BrodyRequires cookie*
 Title    Effect of ß-Carotene on Delayed Light Emission from Aggregated Chlorophyll  
 Abstract    Delayed light emission (DLE) from aggregated chlorophyll is used to probe energy transfer between aggre­ gated chlorophyll and ß-carotene. Preilluminated ß-carotene when injected into a dark chamber containing aggregated chlorophyll, induces DLE from aggregated chlorophyll. If the dark chamber contains only monomeric chlorophyll, there is no DLE. The intensity of DLE is de­ pendent on the time of illumination of ß-carotene. The decay of energy stored by the carotene is not a first order process. The first half life is about 2 min, the next about 1 0 min. 
  Reference    Z. Naturforsch. 45c, 132—134 (1990); received February 6 /August 15 1989 
  Published    1990 
  Keywords    ß-Carotene, Delayed Light Emission, Chlorophyll Aggre­ gates, Fluorescence, Phosphorescence 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-0132_n.pdf 
 Identifier    ZNC-1990-45c-0132_n 
 Volume    45