Fluorescence rise and decay curves

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. 

Figure 5. Fluorescence rise and decay curves of EPy in PMMA before and after laser ablation.

Fig. 7.10. Fluorescence rise and decay curves of band M (monomer) and band E (excimer) (at 365 and 420 nm, respectively) recorded at two different channel widths. 2exc 297 nm. The instrumental response function for the excitation laser pulse is shown in figure a. (Reprinted with permission from ref. [22]). 

A more detailed picture of the energy-transfer sequence was revealed by additional kinetic analysis. Mimuro et al. obtained rise and decay curves for the individual chromophores by deconvolution ofthe time-resolved fluorescence spectra based on the relative intensities obtained by photon counting. The time-resolved fluorescence spectra could be computer-fitted to the reported emission spectra of nine major chromophores four belonging to the rod PC and the remaining five to the APC-core complex. 

Fig. 11. Rise and decay curve of the excimer fluorescence of (A) 1Py(3)1Py adsorbed on Si-C- 8 (3 x 10 6 mol/g) and (B) Py adsorbed on Si-C- 8 (5-5 10 5 mol/g), fitted to three exponentials. The excitation pulse (337 nm) is also depicted in each case. The values for the decay parameters A 1 (in ns) and their amplitudes are given (see text). The weighted deviations in units of a (expected de- viation), the autocorrelation function (A-C), and the value for x " are also indicated. (Reprinted with permission from the Journal of Physical Chemistry, 86 (1985) 3521, our ref. (38), Copyright (1985) American Chemical Society).

Fig. 2. Time-resolved fluorescence spectra of P. tamarensis at —196°C (A), their deconvoluted patterns (B) and rise and decay curves of individual fluorescence components (C). In (A), each time-resolved spectrum was shown after normalization to the maximum intensity. In (C), vertical line shows the time zero and broken lines, pulse profile. Small bars over the decay curves indicate the time when the maximum intensity was observed.

Fig. 2 Rise and decay patterns of the fluorescence components resolved by deconvolution of the spectra as shown in Fig. ID. Each point was calculated by the relative height in the spectrum and actual counts of photons. Broken line the excitation pulse profile. The bar over each curve indicates the maximum point of intensity.

By fluorescence analyses just upon laser ablation and of ablated surface, Molecular aspects of ablation echanisa were elucidated and a characterization of ablated Materials was perforaed. Laser fluence dependence of poly(N-vinylcarbazole) fluorescence indicates the iaportance of Mutual interactions between excited singlet states. As the fluence was increased, a plasna-like eaission was also observed, and then fluorescence due to diatonic radicals was superinposed. While the polyner fluorescence disappeared Mostly during the pulse width, the radicals attained the naxinun intensity at 100 ns after irradiation. Fluorescence spectra and their rise as well as decay curves of ablated surface and its nearby area were affected to a great extent by ablation. This phenonenon was clarified by probing fluorescence under a Microscope. 

For EPy-doped PMMA film, a 308 nm excimer laser (Lumonics TE 430T-2, 6ns) was used as as exposure source. We used a tine-correlated single photon counting systen (18) for measuring fluorescence spectra and rise as well as decay curves of a snail ablated area. The excitation was a frequency-doubled laser pulse (295 nm, lOps) generated from a synchronously punped cavity-dumped dye laser (Spectra Physics 375B) and a CW mode-locked YAG laser (Spectra Physics 3000). Decay curves under a fluorescence microscope were measured by the same systen as used before (19). 

CMS and Polystyrene Solutions in Cyclohexane. Both monomer and excimer fluorescences were observed in the pulse radiolysis of polystyrene solution in cyclohexane. The decay curves of monomer and excimer fluorescences at 287 and 360 nm are shown in Figures 7(a) and (b), respectively. Energy migration on the polymer chain has been discussed elsewhere (15). The dependences of the decay of monomer fluorescence and the rise of excimer fluorescence on the... 

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]. 

Because of the spectral relaxation due to the appearance of a high dipole moment in the charge-transfer state, the dynamics of the TICT state formation has been studied by following the fluorescence rise in the whole A band. In Fig. 5.6 are plotted, in the 10 ns time range, the experimental curve iA(t) at -110°C in propanol (tj = 1.5 x 103 cp) and the decay of the B emission at 350 nm. The solid curve representing the evolution of the TICT state expected in a constant reaction rate scheme shows a slower risetime with respect to that of the recorded A emission. To interpret the experimental iA(t) curves, the time dependence of the reaction rate kliA(t) should be taken into account. From the coupled differential equations for the populations nB(t) and nA(t) of the B and A states (remembering that the reverse reaction B <—A is negligible at low temperatures) ... 

Experimental results for a micellar phase consisting of rod-like micelles and of an a-lamellar phase in the same system are compared in Fig. 20.8. Fluorescence decay curves are presented as logarithmic plots. The deviations from exponentiality in the micellar system (Fig. 20.8 a) are evident as all traces are curved even for long times except for the system containing no quencher (top trace). Evidently, the decay is faster in the a-lamellar phase (Fig. 20.8 b) when comparing runs at the same quencher concentration. This result meets the intuitive expectation that the approach of quenchers from all sides within a lamellar plane should give rise to a faster decay as compared to one-dimensional random walk within a cylindrical or rod-like micelle. 

Since the radiative lifetime is nearly independent of v (852), it can be seen that the measured decay rate 1/t is proportional to kp, which in turn is proportional to the quantum yield of I atom production. Therefore, the wavelength dependence of decay rate follows approximately the quantum yield curve shown in Fig. V-22, that is, the decay rate is faster when the quantum yield of atom production is larger. However, the exact correspondence may not be expected, since both the B3n and ln states contribute to the 1 atom production, while only the B3n state gives rise to fluorescence. Then the percent absorption due to a transition to the B3fl state must be known at each wavelength. 

Solvation dynamics are measured using the more reliable energy relaxation method after a local perturbation [83-85], typically using a femtosecond-resolved fluorescence technique. Experimentally, the wavelength-resolved transients are obtained using the fluorescence upconversion method [85], The observed fluorescence dynamics, decay at the blue side and rise at the red side (Fig. 3a), reflecting typical solvation processes. The molecular mechanism is schematically shown in Fig. 5. Typically, by following the standard procedures [35], we can construct the femtosecond-resolved emission spectra (FRES, Stokes shifts with time) and then the correlation function (solvent response curve) ... 

Fig. 9. A tracing of a calcium response to GPCR activation in cells is shown. The curve shape can be quite variable, but generally involves a rapid rise followed by a gradual decay in fluorescent signal. The lag is rather short and is mixing and diffusion limited.

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