Time-dependent fluorescence decay

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. 

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. 

The internal rotational relaxation times of 1-pyrene carboxaldehyde in sulfonate systems may offer some indication of the extent of probe binding to the inverted micelle. In the absence of any background fluorescence interference to the time-dependent anisotropy decay profile, the internal rotational relaxation time should correlate with the strength of binding with the polar material in the polar core. However, spectral interference from the aromatic moieties of sulfonates is substantial, so that the values of internal rotational relaxation time can only be used for qualitative comparison. 

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... 

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. 

Where solvent relaxation is slow compared with the decay time of the fluorescent molecule, time-dependent fluorescence spectra will be observed. 

The plane-polarized light pulses characteristic of mode-locked lasers also provide an ideal excitation source for time-dependent fluorescence depolarization studies although conventional excitation sources can be used. If the rotational relaxation time of the excited molecule is comparable to its fluorescence decay time, then the vertical (I ) and horizontal (Ix) components of the fluorescence decay observed through suitable polarizers following excitation by polarized li t pulses, may be analysed to provide information concerning the size and motion of die molecule and Sect. 5. However, if only the true fluorescence decay characteristics are of interest it is necessary to compensate for these emission anisotropy effects Perhaps the simplest technique is to analyse only that component of fluorescence emitted at 54.7° to the direction of pdarization of the excitation source, the so-called magic-angle ... 

We also measured picosecond time-resolved TFD-IR images from —10 to 50ps. Figure 29.9 shows the picosecond time-resolved TFD-IR images obtained around a 0 ps delay time. For these TFD-IR images, the population decay of the vibrationally excited Rhodamine-6G molecule in a cell is demonstrated as the delay-time dependent fluorescence. At a — 5 ps delay time, when visible light is applied before IR light,... 

A plot of the temperature-dependent fluorescence decay time as a function of 3 MeV proton fluence is shown in Fig. The error bars shown in Fig. 12... 

Typically, in measurements of time-resolved luminescence in the time regime of tens of picoseconds, data obtained from 10 to 20 laser shots are averaged to improve the signal-to-noise ratio and to minimize the effects of shot-to-shot variations in the laser pulse energy and shape. Once the reliability of the data has been ensured by application of the corrections described above and made necessary by detector-induced distortions, the time-resolved fluorescence data is analyzed in terms of a kinetic model which assumes that the emitting state is formed with a risetime, xR, and a decay time, Tp. Deconvolution of the excitation pulse from the observed molecular fluorescence is performed numerically. The shape of the excitation pulse to be removed from the streak camera data is assumed to be the same as the prepulse shape, and therefore the prepulse is generally used for the deconvolution procedure. Figure 6 illustrates the quality of the fit of the time-dependent fluorescence data which can be achieved. 

Re-examination of what are generally considered to be well established theories are needed for extension of photophysics into new areas. For example, the theory of concentration quenching of fluorescence in 1, 2 and 3 dimensional media has been examined by Sienicki and the time dependence of decay and fluorescence quenching in a one dimensional lattice analysed by Dudkiewicz and Twardowski. ... 

Alkylpyrenylsilanes Chemically Bound to Silica. Loch-miiller et al. reported on time-dependent fluorescence studies with the alkylpyrenylsilanes PPS and PDS chemically bound to microparticulate silica (41-43). These compounds undergo intermolecular excimer formation in contact with a number of solvents such as tetrahydrofuran and methanol. For all solvents, at different surface concentrations of PPS and PDS, the monomer fluorescence decays ij (t) could be fitted with three exponentials. The excimer decays were also found to be triple-exponential, although only the excimer rise times, having values comparable with the shortest monomer decay times Tg, were reported. 

We recognized that these pH sensors could be excited with conveniently simple lasers, such as the 543 nm HeNe laser. Additionally, we suspected that the spectral shifts could be accompanied by a change in lifetime. Hence, we measured the pH-dependent fluorescence decay times of the few SNAFL and SNARF probes. The detailed chemical and spectral properties of these probes are in (86),... 

A rather simple experimental teehnique involving measurement of the time-dependent fluorescence Stokes shift (TDFSS) after an initial exeitation has been applied to measure SD in a large number of liquids. TDFSS oceurs due to dipolar solvation of the excited probe and thus gives an estimate of the solvation timeseales. In an important paper, Jimenez et al. reported the results of SD of the exeited state of the dye coumarin 343 (C343) in liquid water [14]. Their result is shown in Figure 3.13. The initial part of the solvent response of water was found to be extremely fast (few tens of femtoseconds) and it constituted more than 60% of the total solvation energy relaxation. The subsequent relaxation was found to occur in the picosecond timescale. The decay of the solvation time correlation function, S t)y was fitted to a function of the following form... 

A map of the singlet-singlet excitation and photoisomerization potential energy surface for tetraphenylethylene in alkane solvents were prepared using fluorescence and picosecond optical calorimetry (Figure 3.4) [4]. The line shapes of the vertical and relaxed exdted-state emissions at 294 K in methylcyclohexane were obtained from the steady-state emission spectrum, the wavelength dependence of the time-resolved fluorescence decays, and the temperature dependence of the vertical and relaxed state emission quantum yields and of the time-resolved fluorescence decays. 

The time-dependent fluorescence from these coherently excited states shows, besides the exponential decay exp(—t/tsp), a beat period ATqb = fi/( a — Eb) due to the different frequencies coj and... 

However, even in the absence of a physical model, which would justify the use of a particular model, sum of exponentials or stretched exponential functions, relevant information can be obtained from time-resolved fluorescence decays of complex systems. For example. Fig. 15.21 shows the temperature dependence of the migration rate constant (obtained using a sum of exponential functions) in the non-dispersive regime for a polyfluorene copolymer film. At room temperature, the migration shows an activated regime with an energy barrier of 23 meV, turning... 

Fig. 6. Time-dependent fluorescence anisotropy decays for GOPl, G1P4, G3P16 and G5P64 measured at an emission wavelength of 655 nm when excited at 595 nm in an EPA glass...

Figure 7 Wavelength-dependent fluorescence decay profiles (a) and time-dependent dynamic fluorescence Stokes shift (b) of dipolar probe C-153 in [MorjJfTfjN] IL at xc = 405nm and /=130cP. Reproduced from Khara and Samanta [49] with permission from the American Chemical Society.

Noiu diative excitation energy transfer affects the time-resolved fluorescence decay and shortens the experimental values of the average fluorescence lifetime of the donor. In a macroscopic system, the shape of the decay curve depends on the... 

In ERET experiments, the time-dependent fluorescence intensity decay (as described in Section 25.2.3) of the donor is usually measured. By fitting the experimental results with a theoretical decay that takes into account the energy transfer process, it is possible to obtain morphological information on the interface, such as the width of the interface between two polymers. 

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