Fluorescence decay curves

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 ... 

Figure 20. Fluorescence decay curves of J-aggregate ([CI-MC] [AA] = 1 2) in LB films combined with spacer and acceptor layers.

Figure 26. Fluorescence decay curves of the donor layer separated by the spacer (Cp) from the acceptor (a)Cl2NC12 and (b)C18NC8, observed at 470 nm.

Figure 39. Fluorescence decay curves of the excimer observed at 480 nm for the multilayers of L-PyrAla-C1 s prepared at different conditions.

Fluorescence Rise and Decay Curves. Both monomer and excimer fluorescence decay curves of the unirradiated film are nonexponential and the excimer fluorescence shows a slow rise component. This behavior is quite similar to the result reported for the PMMA film doped with pyrene. (23) A delay in the excimer formation process was interpreted as the time taken for the two molecules in the ground state dimer to form the excimer geometry. Dynamic data of the ablated area observed at 375 no (monomer fluorescence) and 500 nm (exciner fluorescence) are shown in Figure 5. When the laser fluence increased, the monomer fluorescence decay became slower. The slow rise of the excimer fluorescence disappeared and the decay became faster. 

Fig. B4.3.2. Fluorescence decay curves for pyranine in various aqueous environments. See text for the meaning of A, B, C and D (reproduced with permission from Gutman et al.b ).

Knutson J. M., Beechem J. M. and Brand L. (1983) Simultaneous Analysis of Multiple Fluorescence Decay Curves A Global Approach, Chem. Phys. Lett. 102, 501-507. 

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 8.8. Examples of nonexponential fluorescence decay curves 9,10-diphenyl-anthracene on alumina for chromatographic purposes (Uhl.Oelkrug, unpublished results) (unnumbered curves time profiles of the excitation pulse, 2 - 360 nm). Upper left effect of environment (1) high vacuum, (2) liquid n-hexane. c=3/tmol g"1,2 =440 nm. Upper right effect of fluorescence wavelength (1) 2 = 500 nm, (2) 440 nm, (3) 406 nm c=3 /tmol g 1. Lower left effect of surface loading (1) 3 /rmol g (2) 0.13 mol g , (3) 0.02/r mol g"1 2e=440. Lower right effect of sample thickness (l) d - . (2) d - 0 c - 3 /tmol g 1, 2 = 440 nm.

Some methods of quantitative analysis of nonexponential fluorescence decay curves will be shortly described in Section 6.6. 

Figure 8.15. Distortion of fluorescence decay curves by time-of-flight dispersion in a scattering sample with r - 50 ps, d = l cm, 1C - 1 cm-1, = = 100 cm-1. Linear left) and semi logarithmic (right)...

Single-photon silicon APDs possess a quantum efficiency ofca. 20-40% between 700 and 900 nm which compares very favorably with ca. 3% at best expected from an S20R or SI photocathode over this range. The lack of late-pulsing in an APD response as compared with a linear focused photomultiplier also has some virtues in the reconvolution analysis of fluorescence decay curves. 

In protein molecules with two or more tryptophan residues, it is necessary to obtain first the fluorescence decay curves for the individual residues. For this purpose, additional spectroscopic information is necessary. One can use the dependence of the decay curves on emission wavelength, apply selective fluorescence quenchers, or selectively modify one of the tryptophan residues. The results of Brochon et al. for the lac repressor(44) and those of Beechem et al. for alcohol dehydrogenase(45) provide evidence in favor of such approaches. 

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. 

Table II presents the vadues of v, the rate constant for the electron transfer reaction with the donor and acceptor in contact, calculated by deconvolution of the fluorescence decay curves for a number of excited porphyrin-cOkyl halide systems. It appears that the rate parauneter depends strongly on the calculated exothermicity for these reactions. Parauneter i/ contadns information about the Framck-Condon factor of the electron-tramsfer reaction, which is in itself dependent on the reaction exothermicity and reorgauiization energy (22.23). Whether the rate constauit for the electron-transfer reactions depends on the exothermicity in the manner predicted by theory, that is with a simple Gaussian dependence (22), cannot be ainswered at present because of the uncertainties in the energetics of the particular reactions studied here.

In the absence of detailed analyses of fluorescence decay curves (Section II.D), limiting values for the photoassociation equilibrium constants Ka may be obtained from the experimental quantities [Q]y2, r, and r which are related by the expression (cf. Eq. 12)... 

The introduction of reversible photoassociation at higher fluor (or quencher) concentrations invalidates the analysis of fluorescence decay curves of either emitting species in terms of a single decay constant since these species do not relax independently accordingly the decay curves each represent the sum of two exponential components and the corresponding decay constants Ax and A2 are related to the photoassociation rate constants kDM and kMD and to the lifetimes rp and t of both emitting species. The treatment given below follows that of Birks, Dyson, and Munro.1... 

Weller24 has estimated enthalpies of exciplex formation from the energy separation vg, — i>5 ax of the molecular 0"-0 and exciplex fluorescence maximum using the appropriate form of Eq. (27) with ER assumed to have the value found for pyrene despite the doubtful validity of this approximation the values listed for AHa in Table VI are sufficiently low to permit exciplex dissociation during its radiative lifetime and the total emission spectrum of these systems may be expected to vary with temperature in the manner described above for one-component systems. This has recently been confirmed by Knibbe, Rehm, and Weller30 who obtain the enthalpies and entropies of photoassociation of the donor-acceptor pairs listed in Table XI. From a detailed analysis of the fluorescence decay curves for the perylene-diethyl-aniline system in benzene, Ware and Richter34 find that... 

Lifetimes t°(C are available from analyses of fluorescence decay curves as described in Section II.D where, to a good approximation, 1/t (C is given as the experimental parameter Ax describing terminal decay for a system exhibiting excimer (exciplex) fluorescence only. 

Huffman (87) studied the transient emissions from terbium in a vinylic resin matrix. His compound was Tb tris-[4,4,4-trifluoro-l-(2-thienyl)-1,3-butaneodione] in polymethylmethacrylate. This may be conveniently abbreviated as TbTTA in PMMA. The compound EuTTA in PMM A had previously been reported by Wolff and Pressley (99) to give laser oscillation. Working with small fibers at 77°K, Huffman found distortions from the normal fluorescent decay curves when the optical pumping was large. He interprets this as evidence for stimulated emission. A comparison of these distorted decays with EuTTA in PMMA indicated a similar behavior, thus tending to substantiate his hypothesis. 

As one might then expect, the fluorescent-decay curves for the pure chelates are smooth exponential functions, whereas those of the impure compounds have a number of components. 

Figure 52. Fluorescent-decay curves of the 4/9/2 >4fi5/2 transition of CaF2i(0.1 Er3+). In (a) the ion is excited with 2550-A monochromatic radiation emitted by a 50-/xsec xenon flash lamp. The curve is resolvable into the difference of two exponentials with r = 400 50 and r2 = 200 50 / sec. In (b) the ion is excited with 2537-A radiation from an electronically chopped low-pressure mercury lamp. The steady state of fluorescence was established each time before the mercury lamp was switched off electronically. The afterglow in the lamp was of the order of 10 / sec [from Ref. (762)].

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).

Abstract Ultrafast photoreactions in PNS of PYP have been studied by means of fs fluorescence up conversion method. Conclusions obtained are (a) Photoreaction in PNS (chromophore twisting) occurs from vibrationally unrelaxed fluorescence state and coherent oscillations in the fluorescence decay curves have been observed for the first time, (b) Comparative studies on fluorescence dynamics of mutants and w.-t. PYP have proved that the w.-t. PYP is best engineered for the ultrafast reaction, (c) The coherent oscillations in the fluorescence decay completely disappeared and the reaction was much slower in the denatured state, demonstrating the supremely important role of PNS for the photoreaction. 

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