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  • 1985-1989  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 3571-3576 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This work is concerned with the theory of concentration self-quenching of luminescence due to incoherent energy transfer between randomly distributed molecules. A simple model of self-quenching is considered, in which luminescent molecules within a critical distance of each other act as perfect traps. Due to the statistical nature of these traps, few practical results can be obtained from systematic or formal theories. We demonstrate, however, that within the framework of hopping theories for energy transfer an exact and a simple intuitive treatment of the donor and trap distributions differ only very little in their results for the quantum yield and emission anisotropy.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 3577-3582 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present high accuracy Monte Carlo simulations on the steady state fluorescence quantum yield and anisotropy for systems in which concentration self-quenching due to incoherent energy transfer between randomly distributed molecules occurs. A simple model of self-quenching is considered, in which luminescent molecules within a critical distance of each other act as perfect traps. The simulations are based on the complete solution of the coupled rate equations for a randomly chosen distribution of molecules in a finite box. Finite size effects are systematically investigated. The results are used to assess the validity of simple analytic theories, such as Burshtein's theory of hopping transfer, which is found to give a good semiquantitative description of the fluorescence quantities. Furthermore, we show that truncating the transfer rate in such a way that, on the average, 10–20 molecules are within reach of an excitation residing on a given molecule, induces large deviations in the yield. We point out that this is a serious source of error in previous simulations.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 4438-4441 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The incorporation is studied of the orientation factor occurring in the complete Förster rate of incoherent energy transfer, into the theory of concentration self-quenching by statistical pairs of luminescent molecules. Within Burshtein's theory of hopping transport, exact results for the steady state donor fluorescence yield and emission anisotropy are obtained for three-dimensional systems. Two opposite limits to treat the orientations of the molecular transition dipoles within statistical pairs are considered, and it appears that in both cases the fluorescence yield is substantially influenced by inclusion of the orientation factor into the transfer kinetics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 2990-2997 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theory is presented that incorporates the effect of orientational correlations between luminescent molecules on the fluorescence depolarization due to incoherent energy transfer. The luminescent molecules are embedded in a homogeneous two- or three-dimensional medium which is in an axially symmetric phase with the xy plane as a symmetry plane, and consists of axially symmetric molecules. For the general orientational singlet distribution and the general form of orientational correlations consistent with these symmetries, we derive analytical expressions for the anisotropy of fluorescence emission. In a no back transfer model, numerical results are evaluated for a simple choice of correlations that tend to align nearby molecules. In a pure donor system, the anisotropy of fluorescence is found to be strongly dependent on these correlations. By ignoring them, the critical transfer distance, as obtained from depolarization experiments, may be drastically underestimated. In a system where donors are surrounded by a huge majority of traps, the critical transfer distance can be determined from the intensity of trap fluorescence. Its anisotropy also strongly depends on correlations and may thus give an indication of the correlation length scale.
    Type of Medium: Electronic Resource
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