Fluorescence decay fitting

Table 1. Results of the fluorescence decay fit with two exponentials (ti, t2, A, A2), average time r, and observed decay constant kob., for AgBr grains of different size and surface type.

Tao and Frank [45] found that 2-vinylnaphthalene homopolymer fluorescence decays fit the FF model under conditions of relatively low temperature. However, they noted that at higher temperatures the model breaks down, probably because of the breakdown of one of the assumptions below ... 

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.

Figure 21.23 exhibits the room-temperature fluorescence decay profiles of Ba3BP30i2 Eu powders. The experimental decay curve can be fitted by an equation with two exponential terms corresponding to two decay times of 20 ns (98.97%) and 522 ns (1.03%), respectively. 

Lifetime heterogeneity can be analyzed by fitting the fluorescence decays with appropriate model function (e.g., multiexponential, stretched exponential, and power-like models) [39], This, however, always requires the use of additional fitting parameters and a significantly higher number of photons should be collected to obtain meaningful results. For instance, two lifetime decays with time constants of 2 ns, 4 ns and a fractional contribution of the fast component of 10%, requires about 400,000 photons to be resolved at 5% confidence [33],... 

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 ... 

In media of fractal structure, non-integer d values have been found (Dewey, 1992). However, it should be emphasized that a good fit of donor fluorescence decay curves with a stretched exponential leading to non-integer d values have been in some cases improperly interpreted in terms of fractal structure. An apparent fractal dimension may not be due to an actual self-similar structure, but to the effect of restricted geometries (see Section 9.3.3). Another cause of non-integer values is a non-random distribution of acceptors. 

Figure 12.14. Fluorescence decay (+++), excitation pulse (-- ), fitted function (—) for IR-140 in acetone excited at 750 run using (he argon-hydrogen flashlamp. The decay was measured in 4 min. The fluorescence lifetime is 1.2 nsec. The weighted residuals are shown at (he bottom of the figure. (From Ref. 55.)...

The fluorescence decay parameters of tyrosine and several tyrosine analogues at neutral pH are listed in Table 1.2. Tyrosine zwitterion and analogues with an ionized a-carboxyl group exhibit monoexponential decay kinetics. Conversion of the a-carboxyl group to the corresponding amide results in a fluorescence intensity decay that requires at least a double exponential to fit the data. While not shown in Table 1.2, protonation of the carboxyl group also results in complex decay kinetics.(38)... 

Permyakov et alS32) have compared the effects of calcium binding upon the steady-state and time-resolved fluorescence of two different species of fish parvalbumin, one with a single tryptophan (whiting) and one with a single tyrosine (pike). The fluorescence decays of both proteins were best fit by double exponentials either in the presence or absence of calcium. We focus here on the tyrosine results from pike parvalbumin. Calcium binding causes a 50% increase in the tyrosine steady-state fluorescence quantum yield and... 

Haas et al.(m) have examined the fluorescence decay of tyrosine due to different Tyr-Pro conformations in small peptides to elucidate further the nature of the fluorescence change associated with Tyr-92. These peptides have acetyl groups at the amino terminus and /V-mcthylamidc groups at the carboxyl terminus. They found that whereas the dipeptide fluorescence decay requires a double-exponential fit, that of the tripeptide Tyr-Pro-Asn can be fit by a single exponential. By comparison of the average fluorescence decay time and steady-state quantum yield of the peptide to that of A-acetyltyrosine-A-methylamide, they found a relatively greater reduction in the steady-state quantum yield of the peptides. This is attributed to static quenching, which increased from 5 % in the dipeptide to 25 % in the tripeptide. The conformations of these peptides were also examined by NMR, but the results could be interpreted in terms of either cis-trans isomerization or other conformational isomerizations. 

Lakowicz et al.(]7] VB) examined the intensity and anisotropy decays of the tyrosine fluorescence of oxytocin at pH 7 and 25 °C. They found that the fluorescence decay was best fit by a triple exponential having time constants of 80, 359, and 927 ps with respective amplitudes of 0.29, 0.27, and 0.43. It is difficult to compare these results with those of Ross et al,(68) because of the differences in pH (3 vs. 7) and temperature (5° vs. 25 °C). For example, whereas at pH 3 the amino terminus of oxytocin is fully protonated, at pH 7 it is partially ionized, and since the tyrosine is adjacent to the amino terminal residue, the state of ionization could affect the tyrosine emission. The anisotropy decay at 25 °C was well fit by a double exponential with rotational correlation times of 454 and 29 ps. Following the assumptions described previously for the anisotropy decay of enkephalin, the longer correlation time was ascribed to the overall rotational motion of oxytocin, and the shorter correlation time was ascribed to torsional motion of the tyrosine side chain. 

Satisfactory fits of the fluorescence decays for ethidium bound to yeast tRNAPhe and E. coli tRNA al require (at least) two exponentials in the sum response S(t) [cf. Eq. (4.56)] under all conditions studied.0 870 88) The normalized amplitudes and lifetimes for tRNA 1 (extrapolated to zero concentration) are S° = 0.917, r, = 25.6ns and S02 = 0.082, t2 = 5.6 ns.(187) The results for tRNAPhe are similar.(188) This requirement for two (or more) exponentials is unequivocal evidence for at least two ethidium binding sites. The dominant component has a lifetime similar to, but slightly longer than, that of ethidium intercalated in DNA and is taken to represent ethidium... 

Schneider et al. [63] investigated the photochemistry of the spiro-oxazine merocyanines pumping and probing at 570 nm in acetonitrile. The found that the solution bleached within the <5-psec pulse duration. The bleached state recovered with at least a biexponential behavior, and from their fluorescence decay measurements, three exponentials were required to fit the decay. They attribute these findings to the possibility of three merocyanine isomers that are in equilibrium. Their compounds feature geminal ethyl groups on the indoline moieties and this may influence the system as compared to NOSIl. 

Figure 4. Observed fluorescence decay profiles (points) and theoretical fits (solid lines), calculated by the deconvolution program according to Equation 2, using v as an adjustable parcuneter in the fit, for (A) H2TPP and (B) MgTPP in BuCl containing CBr at 77 K, following excitation at 515 nm and 424 nm, respectively. The concentration of CBr was (a) 0, (b) 0.4, emd (c) 0.8 mol/L. The parauaeters used in the fits were, for H2TPP, To=14.5 ns, L/2=0.83 A and v=l,4 x 10 s"-, and for MgTPP, To=15.5 ns, L/2=0.83 A and...

Conventional EPR techniques have been successfully used to measure the D and E values of matrix-isolated carbenes in the ground triplet state because the steady-state concentration of triplet species is sufficiently high in the system. The technique cannot be used, however, for excited species having triplet hfetimes of the order of 10-100 ns, since their steady-state concentration is too low. The D parameters are estimated from the external magnetic field effect on the T—T fluorescence decay in a hydrocarbon matrix at low temperamre. The method is based on the effect of the Zeeman mixing on the radiative and nonradiative decay rates of the T -Tq transition in the presence of a weak field. The D values are estimated by fitting the decay curve with that calculated for different D values. The D T ) values estimated for nonplanar DPC (ci symmetry) is 0.20... 

The effect of exciplex dissociation (process MC) on the over-all kinetics of molecular fluorescence decay has been examined by Ware and Richter34 for the system perylene-dimethylaniline in solvents with dielectric constants (e) varying from 2.3 to 37. In low dielectric media (e = 2.3-4) the perylene fluorescence response may be fitted to a two-component exponential curve and exciplex emission is also observed, whereas in more polar solvents (e > 12) exciplex fluorescence is absent (at ambient temperatures) and the molecular fluorescence decays exponentially. These observations are consistent with both an increase in exciplex stability toward molecular dissociation with solvent polarity (Eq. 13) and the increased probability of dissociation into solvated ions... 

Fig. 11.5 Measurement of lifetime of anthracene in solution by single photon time correlation technique. Fluorescence decay curve of 8 X10-4 M anthracene in cyclohexane in the absence (A) and presence (B) of 0.41 M CC14. Points experimental data Line best fitting single exponential decay convoluted with instrumental response function (C) Time scale 0.322 nsec per channel. (Ref. 13).

In each case, the fluorescence of the acceptor was strongly quenched due to ET (r/i 4 ns in chlorobenzene in absence of quencher). Typical fluorescence decays and best multiexponential fits are shown in Fig. 2 and Table 1. The two major observations are [4] the fluorescence decay is about 10 times faster with PeCN than with the other electron acceptors and the decays are highly non-exponential. 

Amplitudes, A, and time constants, Xj, obtained from a triexponential fit to the fluorescence decay of the acceptors in DMA and average lifetime, Tav. 

Double exponential fit of the fluorescence decay and single exponential fit of the anisotropy. 

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