Time-resolved fluorescence Stokes shift

FIG. 4 Time-resolved fluorescence Stokes shift of coumarin 343 in Aerosol OT reverse micelles, (a) normalized time-correlation functions, C i) = v(t) — v(oo)/v(0) — v(oo), and (b) unnormalized time-correlation functions, S i) = v i) — v(oo), showing the magnitude of the overall Stokes shift in addition to the dynamic response, wq = 1.1 ( ), 5 ( ), 7.5 ( ), 15 ( ), and 40 (O) and for bulk aqueous Na solution (A)- Points are data and lines that are multiexponential fits to the data. (Reprinted from Ref 38 with permission from the American Chemical Society.)... 

We found by NMR measurement that the fluidity of the AOT monolayer is parallel to the mobility of the water in the interface of the monolayer [19]. The appearance of longer relaxation times of water in the reversed micelles has been studied also by time-resolved fluorescence Stokes shift [37]. The mobility of water inside the AOT reversed micelles was revealed to be substantially reduced regardless of the kinds of counterions... 

Unie resolved ground state hole spectra of cresyl violet in acetonitrile, methanol, and ethanol at room temperature have been measured in subpicosecond to picosecond time region. The time correlation function of the solvent relaxation expressed by the hole width was obtained. The main part of the correlation function decayed much slower compared with that of the reported correlation function observed in time dependent fluorescence Stokes shift. Some possible mechanisms are proposed for understanding of the time depencences of the spectral broadening under the condition with the distribution of the relaxation times in fluid solution based on the entropy term in the solvent orientation as well as the site dependent response of the solvent. 

The time taken for reorganization of the solvent molecules around an instantly created dipole is termed as solvation time or solvent relaxation time (r, ) [72]. As the ILs are polar, time-resolved fluorescence studies on dipolar fluorescent molecules provide valuable information on the timescales of reorganization of the constituents of the ILs around a photoexcited molecule. The timescale of solvation depends on the viscosity, temperature, and molecular structure of the surrounding solvent [72]. As ILs are highly viscous, the solvation in ILs is a much slow process compared with that in less viscous conventional solvents. The dynamics of solvation is commonly studied by monitoring the time-dependent fluorescence Stokes shift of a dipolar molecule following its excitation by a short pulse (Scheme 7.2). This phenomenon is called dynamic fluorescence Stokes shift [73], and the solvation dynamics in several ILs has been studied by this method using various fluorescent probes. 

In time-resolved fluorescence, rare earths are frequently used as fluorescent labels. The fluorophores have large Stokes shifts, ie, shifts of the emitted light to a higher wavelength relative to the absorption wavelength, and comparatively long decay times, approximately 0.5 ms. This simplifies the optical... 

We have done a study by time-resolved hole-burning spectroscopy for dye molecules in polar solvents and found that the time correlation function of the hole width decays much slower than that of the peak shift of the hole, which occurs very rapidly, as you observed in the case of the fluorescence Stokes shift [K. Nishiyama, Y. Asano, N. Hashimoto, and T. Okada, J. Mol. Liquids 65/66, 41 (1995)]. 

Laitala V, Hemmila L. Homogeneous assay based on low quan- 83. turn yield Sm(lll)-donor and anti-Stokes shift time-resolved fluorescence resonance energy-transfer measurement. Analyt. Chim. 

In order to understand the dynamics of the solvent fluctuation, many experimental as well as theoretical efforts have been made intensively in the last decade. One of the most convenient methods to observe solvent reorganization relaxation processes within the excited state molecule is time resolved fluorescence spectroscopy. By using time resolved techniques a time dependent fluorescence peak shift, so ( ed dynamic Stokes shift, has been detected in nanosecond picosecond >, and femtosecond time regions. Another method to observe solvent relaxation processes is time resolved absorption spectroscopy. This method is suitable for the observation of the ground state recovery of the solvent orientational distribution surrounding a solute molecule. 

Heterogeneous fluorescent immunoassays for T4 based on lanthanide rare earth ions and time-resolved fluorescence were also developed. The use of europium chelates as fluorescent probes is particularly attractive because of their extraordinarily long Stokes shifts and long fluorescence decay times. Thus the sharp emission peak of europium (613 nm) can be easily separated fr om scattering caused by excitation light (340 nm) or by interfering substances in... 

The technique of transient grating spectroscopy has been reviewed, with particular emphasis on its application to monitoring non-radiative deactivation. A unified theory of time-resolved fluorescence anisotropy and Stokes shift spectroscopy has appeared. A separate review has considered the chemical and photophysical events occurring from upper excited states as accessed by multiphoton absorption techniques. ... 

However, time-resolved optical spectroscopy is perhaps the premier method for learning about the dynamics of a complex system, especially on nanosecond or picosecond time scales. Some DNA dynamics data from NMR spectroscopy are presented in Table 4.3. Time-resolved emission decays, time-resolved fluorescence anisotropy, and time-resolved Stokes shifts measurements of probe molecules in DNA have been described (and see below) and fast components in the time decays assigned to various DNA motions. The dynamics as a function of sequence are incompletely mapped and provide an exciting area for future investigations. 

As dynamic fluorescence Stokes shift studies can also provide information on the structural heterogeneity of a medimn, the solvation dynamics of C-153 is studied imder isoviscous ( / = 130cP) conditions in several morphohnium ILs. The time-resolved... 

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