Rapid fluorescence quenching of S2-xanthione by 3,3-diethylpentane in perfluorohydrocarbons

Abstract

Rapid fluorescence quenching of S2-xanthione by 3,3-diethylpentane has been studied in three perfluorohydrocarbons of different viscosities. The donor fluorescence decay in the presence of a quencher was fitted using the Smoluchowski-Collins-Kimball (SCK) model. The molecular parameters, R (the sum of the molecular radii), D (the sum of diffusion coefficients), and the specific rate constant of the process, kappa, were determined. The values of parameter D for all systems studied differed from the sum of the macroscopic diffusion coefficients Dx measured independently. This behavior is explained by the dependence of the molecular diffusion coefficient (as determined from the SCK model) on the distance traveled by the donor and quencher molecules during the excited donor lifetime.

Fluorescence and Phosphorescence from Higher Excited States of Organic Molecules

“…242 Krystkowiak also fitted the S 2 fluorescence quenching of xanthione by dimethylpentane in perfluoroalkanes to the SCK model. 243 Milewski et al investigated the emission properties of the complexes of 4H-1-benzopyran-4-thione with β-cyclodextrin and alcohols. They showed that the S 2 fluorescence and the T 1 phosphorescence were enhanced due to the shielding effect imposed on the thioketone from water molecules, when the thioketone molecule was trapped in βcyclodextrin.…”

“…investigated the solvent quenching effect on the S 2 fluorescence of seven aromatic thioketones, and the results were rationalized using the SCK model . Krystkowiak also fitted the S 2 fluorescence quenching of xanthione by dimethylpentane in perfluoroalkanes to the SCK model . Milewski et al investigated the emission properties of the complexes of 4 H -1-benzopyran-4-thione with β-cyclodextrin and alcohols.…”

Diffusion-Facilitated Direct Determination of Intrinsic Parameters for Rapid Photoinduced Bimolecular Electron-Transfer Reactions in Nonpolar Solvents

“…Time-resolved fluorescence spectroscopy has been shown to be an effective tool for studying the kinetics of fast bimolecular reactions occurring in dilute fluid solutions . The theoretical framework to account for the influence of diffusion on reaction kinetics is now highly developed, and a variety of commercial instrumentation and analysis software required for high-precision time-resolved fluorescence measurements on a nanosecond time scale are in use in many laboratories around the world. ,,,,, Recent work using ultrafast time resolution has focused on the use of complicated analytical functions that comprehensively describe the fluorescence decay kinetics. , This type of approach offers the potential for more directly probing the quenching reaction kinetics, although data analysis invariably necessitates fixing the magnitude of some key parameters, such as reaction distances and/or diffusion coefficients, using estimated rather than experimentally determined values, which can undermine the usefulness of this methodology.…”

“…For example, for the analysis of fluorescence decay data on ultrashort time scales according to the more complex functions, the magnitude of D is usually fixed at a value calculated from the van der Waals radii of the reactants (the sum of which is also sometimes used as a fixed estimate for the encounter distance, R ). However, significant discrepancies have emerged in the limited number of systems in which values of D obtained from fluorescence decay curve analysis have been compared with experimentally determined values of ( D F + D Q ). ,,,− In many cases, the magnitude of D is found to be of the order of only 30–60% that of ( D F + D Q ); one contributing factor to this difference could be that the former includes the diffusion coefficient of the electronically excited fluorophore, whereas the latter reflects the diffusion coefficient of the fluorophore in the ground electronic state. A more significant difference is that the magnitude of D reflects the diffusion coefficient when the fluorophore and the quencher are sufficiently close to react, whereas that of ( D F + D Q ) reflects the bulk relative diffusion coefficient when the fluorophore–quencher separation is much larger than the reaction distance.…”