Time-dependent fluorescence

Tao T 1969 Time-dependent fluorescence depolarization and Brownian rotational diffusion coefficients of macromolecules Biopolymers 8 609-32... 

Figure C 1.5.5. Time-dependent fluorescence signals observed from liquid solutions of rhodamine 6G by confocal fluorescence microscopy. Data were obtained with 514.5 mn excitation and detected tlirough a 540-580 nm...

To perform structural research on a food stuff into which a colorant is incorporated, special properties of fluorescing molecules are exploited fluorescence efficiency, fluorescence lifetime, fluorescence quenching, radiationless energy (Foerster) transfer, stationary or time-dependent fluorescence polarization and depolarization." Generally, if food colorants fluoresce, they allow very sensitive investigations which in most cases cannot be surpassed by other methods. 

This approximation requires that cos. This behavior in fact follows from a Debye dielectric continuum model of the solvent when it is coupled to the solute nuclear motion [21,22] and then xs would be proportional to the longitudinal dielectric relaxation time of the solvent indeed, in the context of time dependent fluorescence (TDF), the Debye model leads to such an exponential dependence of the analogue... 

C.H. Lochmiiller and S.S. Saavedra, Conformational changes in a soil fulvic acid measured by time-dependent fluorescence depolarization, Anal. Chem., 58... 

Time-dependent fluorescence measurements have been made on tyrosine in calf thymus nucleosome core particles by Ashikawa et al. S7) Based on the salt dependence of the decay data, the tyrosines were divided into two classes. At 20 to 400 mM salt, about half of the tyrosine residues appear to be partially quenched, possibly by resonance energy transfer to DNA bases. The other half are thought to be statically quenched, possibly by hydrogen bonds this quenching is partially eliminated at about 2 M salt. In view of the number of tyrosines per nucleosome core particle (estimated at 30), it is impossible to make a more detailed analysis of the decay data. 

G. van der Zwan and J. T. Hynes, Time-dependent fluorescence solvent shifts, dielectric friction and nonequilibrium solvation in polar solvents, J. Phys. Chem. 89, 418M188 (1985). 

L. A. Chen, R. E. Dale, S. Roth, and L. Brand, Nanosecond time-dependent fluorescence depolarization of diphenylhexatriene in dimyristoyllecithin vesicles and the determination of microviscosity, J. Biol. Chem. 252, 2163-2169 (1977). 

Fig. 4 Time-dependent fluorescence intensity of 12 upon exposure to TNT vapor at 0,10,30, 60,120,180,300, and 600 s (top to bottom), and fluorescence quenching (%) as a function of time (inset). (Reprinted with permission from Ref. [18]. Copyright 1998 American Chemical Society)...

This problem does not exist with time-dependent fluorescence polarization measurements where the decay of the emission anisotropy r(t) is obtained by determining the decay of Iz and Ix according to eq 12. 

Time-resolved fluorescence from sub-picosecond to the nanosecond time-scale of dye molecules like coumarins has been widely used to study solvation dynamics in liquids [1], As the dye is photoexcited, its dipole moment abruptly changes. Then by monitoring the time-dependent fluorescence energy one can have access to the solvent dynamical response to the charge reorganization in the dye. The microscopic interpretation of these experiments has greatly benefited from Molecular Dynamics (MD) studies [2], Recently, few experimental [3-5] and theoretical [6,7] works have been performed on solvation dynamics in liquid mixtures. A number of new phenomena can arise in mixtures which are not present in pure solvents, like association, mutual diffusion and preferential solvation [6]. We present here a... 

Molecular Dynamics study of the time-dependent fluorescence of coumarin 153 (C153 - see Fig. 1) in benzene-acetonitrile and benzene-methanol mixtures. The solvation dynamics in benzene-acetonitrile mixtures will be analyzed by inspection of the time-dependent local populations of the two constituents around the coumarin dye. 

Finally time dependent fluorescence spectra and kinetics can be obtained from the rate matrix and the spectrum of each eigenstate, fi. The time dependent fluorescence, F(t), can be written in terms of the eigenvalues and eigenvectors of the rate matrix K ... 

Fig. 5. Time dependent fluorescence spectra and spectral shift correlation fiiction for ferulic acid analogue.

In the case of electron transfers in solution there appears to be a greater cohesiveness of views, and the need for vibrational assistance is well established for reactions accompanied by vibrational changes (e.g., changes in bond lengths). A detailed analysis of the experiments could be made because of the existence of independent data, which include X-ray crystallography, EXAFS, resonance Raman spectra, time-dependent fluorescence Stokes shifts, among others. 

One may inquire as to what this experience with solutions suggests for the study of reactions in clusters. In the case of electron transfers supplementary information, such as time-dependent fluorescence Stokes shift in clusters, would again be helpful. Equation (2.3) can be modified to include a D(t), as in the isothermal case, if needed from the results of such data. For isomerizations, also, it would be useful to have, for solutions or clusters, detailed analogous data such as the above Stokes shift. However, because of the low intensity of such a fluorescence in this case, such data appear to be absent or scarce. 

In order to make this a realistic simulation, we have used the ab-initio Na2 curves of Meyer et al. [14] to calculate the df i dipole matrix-elements. Given these matrix elements, the simulated preparation coefficients, a , are obtained from Eq. (4) and the time-dependent fluorescence signal, F(t)—from Eq. (7). 

Time-resolved fluorescence spectroscopy of polar fluorescent probes that have a dipole moment that depends upon electronic state has recently been used extensively to study microscopic solvation dynamics of a broad range of solvents. Section II of this paper deals with the subject in detail. The basic concept is outlined in Figure 1, which shows the dependence of the nonequilibrium free energies (Fg and Fe) of solvated ground state and electronically excited probes, respecitvely, as a function of a generalized solvent coordinate. Optical excitation (vertical) of an equilibrated ground state probe produces a nonequilibrium configuration of the solvent about the excited state of the probe. Subsequent relaxation is accompanied by a time-dependent fluorescence spectral shift toward lower frequencies, which can be monitored and analyzed to quantify the dynamics of solvation via the empirical solvation dynamics function C(t), which is defined by Eq. (1). 

The Practical Determination of C(0- The time-dependent fluorescence Stokes shift of the spectrum should manifest itself as (i) a rapid decay in the fluorescence intensity on the blue edge of the fluorescence spectrum, (ii) a... 

TABLE 2 Low Temperature Solvation Dynamics Determined from Time-Dependent Fluorescence Stokes Shift Measurements... 

E. A. Carter and J. T. Hynes, Solvation dynamics of an ion pair in a polar solvent time-dependent fluorescence and photochemical charge transfer, J. Chem. Phys., 94 (1991) 5961-79. 

I. Benjamin, Chemical reactions and solvation at liquid interfaces a microscopic perspective, Chem. Rev. (Washington, D. C.), 96 (1996) 1449-75 I. Benjamin, Theory and computer simulations of solvation and chemical reactions at liquid interfaces, Acc. Chem. Res., 28 (1995) 233-9 L. R. Martins, M. S. Skaf and B. M. Ladanyi, Solvation dynamics at the water/zirconia interface molecular dynamics simulations, J. Phys. Chem. B, 108 (2004) 19687-97 J. Faeder and B. M. Ladanyi, Solvation dynamics in reverse micelles the role of headgroup-solute interactions, J. Phys. Chem. B, 109 (2005) 6732 10 W. H. Thompson, Simulations of time-dependent fluorescence in nano-confined solvents, J. Chem. Phys., 120 (2004) 8125-33. 

A more direct way of exploring the dynamics of polar solvent in the presence of a solute is by the optical excitation of a solute to an intramolecular charge transfer state and then observing the time-dependent fluorescence, as shown in Fig. 1.7 [47, 52]. To follow the time-dependent fluorescence at short times, faster than the usual fluorescent lifetime of nanoseconds, lasers plus an up-conversion technique were used. A quantity frequently measured is the dynamic Stokes shift S(r),... 

In the following subsections we will review simulation studies we have performed aiming at investigating the dielectric behavior of SCW and solvation dynamics of excess electrons, making a close connection to recent pulse radiolysis and time-dependent fluorescence experiments. 

Pair in a Polar Solvent Time-Dependent Fluorescence and Photochemical Charge Transfer. 

Dielectric friction is the measure of the dynamic interaction of a charged or dipolar solute molecule with the surrounding polar solvent molecules. This concept has been applied, by Hynes et al. [339] and others [486], to solvent- and time-dependent fluorescence shifts resulting from the electronic absorption by a solute in polar solvents. If the solvent molecules are strongly coupled to the charge distribution in ground- and excited-state molecules, the relatively slow solvent reorientation can lead to an observable time evolution of the fluorescence spectrum in the nano- to picosecond range. This time-dependent fluorescence (TDF) has been theoretically analysed in terms of dynamic... 

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