Time-resolved fluorescence decays

Fig. 23 Time-resolved fluorescence decay of diCN-HBO in various solvents monitored at the normal emission (PC )...

Figure 3.5 Time-resolved fluorescence decay measured by time-correlated singlephoton counting, which involves counting the number of photons that arrive within a given time interval after excitation. The results are stored in a number of channels, each channel corresponding to a particular time interval. When displayed, the results are not continuous, but by using a large number of channels the output approximates to a continuous decay curve...

A single tyrosine is in the C-terminal portion of the transcription factor 1 (TF1), a type II procaryotic DNA binding protein encoded by Bacillus subtilis phage SPOl. Time-resolved fluorescence decay measurements yielded... 

J. R. Lakowicz and A. Baiter, Resolution of initially excited and relaxed states of tryptophan fluorescence by differential-wavelength deconvolution of time-resolved fluorescence decays, Biophys. Chem. 15, 353-360 (1982). 

Itaya et al,(99) have described a TIR system for obtaining time-resolved fluorescence decay curves induced by laser flash illumination of polymer films in a microscope configuration. Presumably, use of this configuration can be extended to studies on biological cells. 

When using DCE as quencher (Fig.3a), the second deactivation channel remains open until Ati=l ns. The small free ion yield for this system indicates that charge recombination is much more efficient and therefore much more rapid than charge separation. Furthermore, we know from time resolved fluorescence decay measurements that electron transfer quenching is still not finished at At =lns. Consequently the absorbance should be dominated by fresh geminate ion pairs, over the whole timescale investigated. Thus, the GSR dynamics of Pe + in presence of DCE should be independent of Ati, which is confirmed by our experimental observations. 

Figure 8 shows a pair of typical time-resolved fluorescence decay traces for 100 / M pyrene in supercritical CO2 (Tr = 1.02 pr = 1.17). Note that the ordinate is logarithmic. The upper and lower panels show results for selective observation in the monomer (400 +. 10 nm) and excimer (460 + 10 nm) regions of the pyrene emission spectrum. Several interesting features are apparent from these traces. First, both decay processes are not single exponential. Second, the excimer emission has a significant contribution from a species that "grows in" between 30 - 75 ns this is a result of the excimer taking time to form (i.e., k in Figure 1). Third, the fits between the experimental data and the model shown in Figure 1 are good. Detailed analysis of these decay traces (10,11,21-26) yields the entire ensemble of photophysical kinetic parameters for the pyrene excimer in supercritical C02.

Figure 8. Time-resolved fluorescence decay traces for 100 fiM pyrene in supercritical C02. Tr = 1.02 pr = 1.17. Upper and lower panels represent monomer (400 nm) and excimer (460 nm) emission, respectively.

Figure 13.5 Time-resolved fluorescence decay spectrum of 2AP8-IRE at 27 °C in 30 mM NaCl, 10 mM potassium phosphate, pH 7.0.

Fig. 21. Typical picosecond time resolved fluorescence decays of a 5 X 10-3 M solution of irons-stilbene at (a) 14 C and (b) 0 C, with the corresponding semi-logarithmic plots (c) and (d), respectively. (After ref. 69.)...

Figure 1.13. Time-resolved fluorescence decays of P-CIP4 with fits at 600 nm and 700 nm detection wavelengths. The upper panel shows the weighted distribution of residuals (Rt) and the lower panel represents the autocorrelation (ac) function for the decays. Inset reports on a shorter time scale.

Table 1 Decay times and amplitudes obtained from time-resolved fluorescence decays of PF2/6 and PFO...

The time-resolved fluorescence decay of donors without and in the presence of acceptor molecules in various concentrations were simulated by using Eq. [51, 16], and [7]. The goodness of... 

Figure 4. Time-resolved fluorescence decay curves of two differently concentrated R-6G solutions. The initial sharp peak is due to the excitation pulse. The time window during which fluorescence counts are accumulated in time-gate detection is also shown. (Adopted from [30].)...

The Caussian distribution model was applied to the decay profiles at various concentrations of oxygen. Time-resolved fluorescence decay... 

Fig. 5.98 Wavelength- and time-resolved fluorescence decay of the light-harvesting complex of a plant cell recorded by a delay-line PMT and two TCSPC cards...

Figure 6.5 Time-resolved fluorescence decays for an excitation wavelength of 360nm (recorded at maximum emission) of allylamine-grafted Si NPs synthesized by reduction with NaBH4 and LiAlH. ...

Fig. 50 Time-resolved fluorescence decay spectra of g-C3N4, Bi2MoOe as well as Bi2MoOg/g-C3N4. Reproduced from ref. 101. Copyright (2014), with permission from...

Fig. 2. Time-resolved fluorescence decays of whole cells of Rb. capsulatus. In each sample, the reaction center quinones west reduced with sodium dithionite. Excitation was at 870 nm, detection at 900 nm. For each decay, the instrument response function is also shown. Top decay wild type reaction center operon. Middle decay chimera 15 (yery similar decays w e observed for 4 and 32 as well). Bottom decay chimera 5 (vay similar decays. , -. .. wereobserv for and 2aswell).

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 lifetimes of the first excited state of substituted stilbenes in solvents of different polarities were detected. An example of the time-resolved fluorescence decay profile is shown in Figure 11.6. 

The analysis of time-resolved fluorescence decay curves, using a sum of discrete exponential functions to fit the experimental data, is based on a simple assumption the number of different exponential terms used has to be equal to the number of kinetically different excited state species present in the molecular system. While this assumption has the advantage of providing a clear physical meaning for the fitting parameters, decay times and pre-exponential coefficients, the identification of the different kinetic species is frequently not evident, particularly in more complex systems like polymers and proteins, and this approach has been questioned [85]. 

The MEM analysis of time-resolved fluorescence decays of several copolymers is shown in Fig. 15.18a. For the homopolymer PF2/6, only a narrow distribution is observed around 360 ps. However, for copolymers PF/FLx, with different fractions of fluorenone residues, distributed randomly along the polymer chain, the distribution at 360 ps is accompanied by two additional peaks. These are observed around 20 and 100 ps as a result of quenching of polyfluorene emission, due to energy transfer from the fluorene to the fluorenone sinks. Figure 15.18b shows the fluorescence decay of the copolymer labelled with 25 % of fluorenone groups, analysed with a sum of three exponential functions. Note the good agreement between MEM and multiexponential analysis [91]. 

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... 

There are thus several different models able to describe time-resolved fluorescence decays, all of them equally valid but giving origin to different physical meanings of the fitting parameters. The choice of an appropriate model is crucial and should rely on our knowledge of the system under investigation and the underlying physical phenomena involved. 

H-NMR spectra of the procyanidins, like most other proanthocyanidins, show restricted rotation about the interflavanoid bond under normal temperature conditions (91, 98, 352, 382). The phenolic forms of procyanidins with a 2,3-cis-3A-trans upper unit give broadened but first order spectra until the temperature is reduced to 0 C where two rotational isomers become apparent (98). It is very important to establish the presence and relative proportions of rotational isomers in the free phenols at physiological temperature conditions. It is not possible to resolve these rotamers by NMR because of the comparatively slow time scale. The presence of two rotamers of the dimeric procyanidins as free phenols, and in proportions similar to those found for the locked methyl ether or acetate derivatives, has recently been shown by time-resolved fluorescence decay methods... 

Keywords Steady-state fluorescence spectra Time-resolved fluorescence decays Fluorescence anisotropy Huorescence quenching Nonradiative excitation energy transfer Solvent relaxation Excimer J and H aggregates... 

First, we will describe the fluorescence kinetics after excitation with an ultrafast excitation pulse that can be approximated by a 5-pulse in the absence of nonradiative processes that could deplete the excited state (idealized case of time-resolved fluorescence decay measurements) [11, 12]. In a system of equivalent fluorophores (embedded in a homogeneous medium and interacting equally with the microenvironment), all the excited molecules have the same probability of emission of a photon but, due to the stochastic nature of the spontaneous emission, only the relationships concerning large numbers of fluorophores can be formulated. It is obvious that the number of photons released per unit time (rate of emission, or fluorescence intensity, F (xdNp/dt) in the system without competing nonradiative processes equals the total rate of de-excitation (depletion of the excited state), —dN/dt, which is proportional to the number of fluorophores excited at a given time, N t). Hence, we can write — dN/dt = N(t), where is the rate constant of... 

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