Fluorescence-time curves

A non-linear regression allows calculation of the parameters / j to for fluorescence-time curves. These equations correlate with eq. (5.141) in the case of the simple mechanism Under such conditions eq. (5.148)... 

Fig. 5.48. Fluorescence-time curve for the photoreaction of carbol in oxygen free methanolic solution. The symbols represents the points of measurements for two wavelength of observation. (—) is the theoretically calculated curve to determine the kinetic parameters. Irradiation took place at 254 nm. Intensity /rt=1.37 x I0 Einstein cm" s ...

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 ... 

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. 

For the determination of the dissociation constant in the excited state, several methods have been used the Forster cycle,(109 m) the fluorescence titration curve/113 the triplet-triplet absorbance titration curve,014 but all involve the assumption that the acid-base equilibrium may be established during the lifetime of the excited state, which is by no means a common occurrence. A dynamic analysis using nanosecond or picosecond time-resolved spectroscopy is therefore often needed to obtain the correct pK a values.1(n5)... 

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nonexponential fluorescence decay curves 9,10-diphenyl-anthracene on alumina for chromatographic purposes (Uhl.Oelkrug, unpublished results) (unnumbered curves time profiles of the excitation pulse, 2 - 360 nm).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.

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)...

Collection of multiple data sets for each time span, with frequent alternation of the polarization, is an essential feature of our protocol. This provides some protection against the effects of drifts in laser power, photomultiplier quantum yield, and absolute calibration of the TAC, photochemical decomposition of the dye, and any other long-term processes that may alter the measured fluorescence response curves. Separate analysis of each data set is necessary to provide an indication of the uncertainty in run-to-run reproducibility and to detect and delete the rare spurious data set. 

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. 

Bhaumik (148) measured the rise time of the red fluorescence in some europium chelates. His data were collected with a stroboscopic instrument having a time-resolution capability of around 0.2 /xsec. Figure 40 shows the fluorescence-rise curve of the sDq- >1F2 transition in the piperidine adduct of the four-ligand europium dibenzoylmethide chelate. Data were collected at 77°K. 

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. 

At T = 77 K in MTHF, the kinetics of fluorescence decay of P-L-Q with a bridge containing one bicyclo[2.2.2]octyl is of a non-exponential character. This effect can be explained by the coexistence in the frozen solution of several rotational conformations of the P-L-Q molecule (rotation of the porphyrin fragment around the a bond in its meso position is meant here). The characteristic time of the fluorescence decay for the predominant portion of the P-L-Q particles at 77 K, r 1.1 x 10 1°s, virtually coincides with the value of r = l/k(e1 at 298 K, i.e. the rate of tunneling from P to Q is independent of temperature. The exponential character of the fluorescence decay curve at 298 K indicates that, at this temperature, the rate of rotation exceeds k(e1. ... 

Fig. 2.17. Fluorescence decay curves of 2,5-dimethylpyrrolidinobenzonitrile at — 108°C in n-butyl chloride, excited by synchrotron radiation from BESSY and observed at (a) 360 nm and (b) 460 nm (A band).50 The computed lines are mono- to biexponential fits [decay time in (a) 1.04 ns, rise time in (b) 0.91 ns]. 

Figure 15 Representative fluorescence decay curves of single CV molecules on a PMMA film. Data accumulation time was 180 s. These curves are fitted to single exponential functions (A) for a strong fluorescent spot (1.92 ns), and (B) for a weak fluorescent spot (0.44 ns) in the bimodal histogram of Fig. 14A. (From Refs. 1, 15.)...

We further carried out time-resolved fluorescence measurement on a single fluorescent spot of the individual enzyme-TNP-ATP complexes. Figure 24A and B shows a representative fluorescence decay curve and fluorescence spectrums of single enzyme-TNP-ATP complexes. The fluorescence spectrum varied from spot to spot, as an indication of fluorescence from individual complexes. The decay curve cannot be fitted to a single exponential, but was well fitted to a... 

TNP-ATP complex obtained by the single-molecule time-resolved spectroscopy, together with a fluorescence decay curve of TNP-ATP obtained by a bulk measurement. Both curves were well fitted to biexponential functions. The instrument-response function in 195-ps fwhm is also displayed. (B) Representative fluorescence spectrums of two individual enzyme-TNP-ATP complexes showing different emission peaks. A fluorescence spectrum of TNP-ATP obtained from a bulk measurement is also displayed for comparison. All spectrums were normalized to unity at their maximum. (From Ref. 18.)... 

Figure 8.9 Time-resolved fluorescent lifetime analysis of Cy3 attached to double-stranded DNA (Iqbal et al., 2008b). Fluorescent decay curve for Cy3 attached to a 16 bp DNA duplex, showing the experimental data and the instrument response function (IRF), and the fit to three exponential functions (line). The decay curve was generated using time-correlated single-photon counting, after excitation by 200 fs pulses from a titanium sapphire laser at 4.7 MHz.

Time resolved A state fluorescence is measured with a transient recorder-signal averager, as described previously.(6J A typical fluorescence decay curve is shown in Figure 3. It is composed of at least three exponentials, independent of excitation wavelength. The short component lifetime is extracted by fitting approximately the first third of the decay to the expression. 

Fig. 9. (i) Fluorescence decay curve (solid lines) for Rhodamine B (1 X 10 6 M, room temperature) (a) linear (b) semi-log. (ii) fluorescence decay curves (solid lines) for Rhodamine B (1 X 1CT6 M, room temperature) in the presence of 1.2 M KI (a) linear, (b) semi-log. The laser excitation pulse profile is shown by the broken lines. The time scale calibration of 64.1 ps per channel was derived from the 13.020 ns spacing between the mode-locked laser pulses. (After ref. 54.)... 

For an experimental demonstration of the capabilities of this system, Taylor et al. [69] studied the dual fluorescence decay of frans-stilbene as a function of temperature between —10 and 30° C. The fluorescence comprised two components, a short one varying between 125 and 64 ps and a longer one varying from 690 to 1450 ps over the range of temperatures studied. Typical fluorescence decay curves are shown in Fig. 21. The fluorescence decay curves were recorded over a total integration time of 2 s which represented a summation of 3 x 108 fluorescence decay profiles. The fluorescence profile of a single-shot would not be observable above the noise level. 

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