Lifetimes fitting

For fluorescence decay curves of the J-aggregate LB films of [CI-MC] mixed with various matrix agents, measured with a picosecond time-resolved single photon counting system, three components of the the lifetimes fitting to exponential terms in the following equation ... 

Pyrene excimer formation still continues to be of interest and importance as a model compound for various types of study. Recent re-examinations of the kinetics have been referred to in the previous section. A non a priori analysis of experimentally determined fluorescence decay surfaces has been applied to the examination of intermolecular pyrene excimer formation O. The Kramers equation has been successfully applied to the formation of intermolecular excimer states of 1,3-di(l-pyrenyl) propane . Measured fluorescence lifetimes fit the predictions of the Kramer equation very well. The concentration dependence of transient effects in monomer-excimer kinetics of pyrene and methyl 4-(l-pyrenebutyrate) in toluene and cyclohexane have also been studied . Pyrene excimer formation in polypeptides carrying 2-pyrenyl groups in a-helices has been observed by means of circular polarized fluorescence" . Another probe study of pyrene excimer has been employed in the investigation of multicomponent recombination of germinate pairs and the effect on the form of Stern-Volmer plots ". 

Figure 8. Distributional fluorescence lifetime fit for Ru (16-mer)3-AEDANS. One hundred exponentials were used, yielding x values of 0.94 and 0.82 for experiments run in 6 M urea (circles) or trifluoroethanol (squares), respectively. These fits yielded better values than attempts using two or three exponentials.

However maquettes for the design of redox proteins were proposed, based on a three helix bundle with a capping Co(III) (bipyridine)3 electron acceptor at the N-terminus and an electron donor at the C-terminus (199, 200). These proteins were tested for LRET. The a-helical percent was adjusted by addition of urea or trifluoroethanol (201, 202). Intriguingly, studies of one of the proteins (l6-mer-three helix bundle) shows a 2-fold higher LRET rate constant when the percent of helicity is 77% than when it is 0% (denatured in urea). However authors indicate that the kinetics is not a simple first-order one in the presence of urea. They interprete these data as coming from different donor-acceptor distances. The distribution of distances was determined by fluorescence lifetimes fit. Both when helicity is 0% or 77%, distributions peak around 18 A for the Ru(II) (16-mer)3-A (where A=5-((((2-acetyl)amino]ethyl)amino)-naphthalene-l sulfonic acid). Actually the distance appears 0.7A shorter for a-helix which is found consistent with the increased rate constant, by the authors. 

The aging effect on the intensity of the bands and the preexponential values of the two fluorescence lifetimes fitting the decay of the TICT band. 

Fig. 5.138 Double-exponential lifetime fit to the data of Fig. 5.137 in a time window indicated by the cursor lines. Fluorescence, scattering, and convolution of scattering curve with calculated decay function. Lower part Residuals of the fit...

Figure 4.20 CompEirison of the distribution of lifetimes as a function of lifetime fitting the emission decay traces for 66 (...), 64 (—), and 61 (...) in the solid state at 298 K [55]...

Figure Cl.5.2. Fluorescence excitation spectra (cps = counts per second) of pentacene in /i-teriDhenyl at 1.5 K. (A) Broad scan of the inhomogeneously broadened electronic origin. The spikes are repeatable features each due to a different single molecule. The laser detuning is relative to the line centre at 592.321 nm. (B) Expansion of a 2 GHz region of this scan showing several single molecules. (C) Low-power scan of a single molecule at 592.407 nm showing the lifetime-limited width of 7.8 MHz and a Lorentzian fit. Reprinted with pennission from Moemer [198]. Copyright 1994 American Association for the Advancement of Science.

Lifetimes were fitted to a single exponential (dotted curves) with decay times of 2.56 ns y = 1.05) in (C) and 3.20... 

Figure C1.5.12.(A) Fluorescence decay of a single molecule of cresyl violet on an indium tin oxide (ITO) surface measured by time-correlated single photon counting. The solid line is tire fitted decay, a single exponential of 480 5 ps convolved witli tire instmment response function of 160 ps fwiim. The decay, which is considerably faster tlian tire natural fluorescence lifetime of cresyl violet, is due to electron transfer from tire excited cresyl violet (D ) to tire conduction band or energetically accessible surface electronic states of ITO. (B) Distribution of lifetimes for 40 different single molecules showing a broad distribution of electron transfer rates. Reprinted witli pennission from Lu andXie [1381. Copyright 1997 American Chemical Society.

Since fatigue cracks often start at a random surface imperfection, considerable scatter occurs in fatigue data, increasing with the increasing lifetime wherever crack initiation occupies most of the fatigue life of a specimen. When a line of the best fit is drawn from the available data points on an S-N curve, this represents the mean life expected at any given stress level or the stress that would cause, say, 50% of the product failures in a given number of cycles. 

Figure 12.10 Typical time traces of (a) emission intensityand (b) lifetime, measured from a single DMPBI nanocrystal, (c) Photon correlation histogram obtained from the time trace of the emission intensity (a). The lifetimes were obtained by fitting a single exponential function to the decay curves constructed for every 2000...

Figure 3.18. Time dependence of the peak position of the 1570 cm Raman band of Sj trans-stilbene in chloroform solution (filled triangle). The time dependence of the anti-Stokes/Stokes intensity ratio is also shown with open circles. The best fit of the peak position change with a single-exponential function is shown with a solid curve, while the best fit of the anti-Stokes/Stokes intensity ratio is shown with a dotted curve. The obtained lifetime for both single-exponential decay functions was 12ps. (Reprinted with permission from reference [78]. Copyright (1997) American Chemical Society.)...

Much less is known about excited-state dynamics of carotenoid J-aggregates, as only zeaxanthin J-aggregates have been studied to date. Only two decay components of -5 and 30ps were needed to fit the kinetics recorded at the maximum of the Sj-S band, Figure 8.8. Since no annihilation studies were carried out, the origin of these components is not known. It is likely that the 5ps lifetime is due to annihilation whereas the 30 ps component corresponds to the. S, lifetime, which is even longer than that of the H-aggregates. 

In the trajectory study of Cl-—CHjCl complex formation by Cl" + CH3C1 association, the number of complexes with a lifetime t, i.e. N(t), was evaluated for different Cl" + CH3C1 initial conditions.36,37 The resulting plots of N(t) are highly nonexponential and plots of N(t)/N(0) were fit with the biexponential function... 

Steady-state behavior and lifetime dynamics can be expected to be different because molecular rotors normally exhibit multiexponential decay dynamics, and the quantum yield that determines steady-state intensity reflects the average decay. Vogel and Rettig [73] found decay dynamics of triphenylamine molecular rotors that fitted a double-exponential model and explained the two different decay times by contributions from Stokes diffusion and free volume diffusion where the orientational relaxation rate kOI is determined by two Arrhenius-type terms ... 

With some further assumptions, it is possible to use single frequency FLIM data to fit a two-component model, and calculate the relative concentration of each species, in each pixel [16], To simplify the analysis, we will assume that in each pixel of the sample we have a mixture of two components with single exponential decay kinetics. We assume that the unknown fluorescence lifetimes, iq and r2, are invariant in the sample. In each pixel, the relative concentrations of species may be different and are unknown. We first seek to estimate the two spatially invariant lifetimes, iq and t2. We make a transformation of the estimated phase-shifts and demodulations as follows ... 

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