Time-resolved fluorescence decay traces

Figure 8 shows a pair of typical time-resolved fluorescence decay traces for 100 / M pyrene in supercritical CO2 (Tr = 1.02 pr = 1.17). Note that the ordinate is logarithmic. The upper and lower panels show results for selective observation in the monomer (400 +. 10 nm) and excimer (460 + 10 nm) regions of the pyrene emission spectrum. Several interesting features are apparent from these traces. First, both decay processes are not single exponential. Second, the excimer emission has a significant contribution from a species that "grows in" between 30 - 75 ns this is a result of the excimer taking time to form (i.e., k in Figure 1). Third, the fits between the experimental data and the model shown in Figure 1 are good. Detailed analysis of these decay traces (10,11,21-26) yields the entire ensemble of photophysical kinetic parameters for the pyrene excimer in supercritical C02.

Figure 8. Time-resolved fluorescence decay traces for 100 fiM pyrene in supercritical C02. Tr = 1.02 pr = 1.17. Upper and lower panels represent monomer (400 nm) and excimer (460 nm) emission, respectively.

Figure 5. Time-resolved fluorescence of pyranine at the wavelength of maximum

StudiN of DNA by fluorescence can be traced to the use of dyes lo stain chromatin for fluorescence microscopy. The use of time-resolved fluorescence for DNA dynamics originated with the measurement of anisotropy decays of EB bound to DNA. " These early studies showed an unusual anisotropy decay, similar to that found for DPH in membranes, in which the anisotropy at long times did not decay to zero (Figure 11,24). At that time, the results were interpreted in terms of the angle through which the EB could rotate within the DNA helix. However, more recent... 

Time-resolved emission spectra were reconstructed from a set of multifrequency phase and modulation traces acquired across the emission spectrum (37). The multifrequency phase and modulation data were modeled with the help of a commercially available global analysis software package (Globals Unlimited). The model which offered the best fits to the data with the least number of fitting parameters was a series of bi-exponential decays in which the individual fluorescence lifetimes were linked across the emission spectrum and the pre-exponential terms were allowed to vary. 

Figure 10.5 Picosecond time resolved emission after photodissociation of trans-stilbene-He dimers. Excitation at 198 cm is followed by both decay of the reagent (top trace) and the appearance of product stilbene (bottom trace). The reference trace at zero energy is of the dimer, which is characterized by an instrumentally limited rise time of 20 ps and the fluorescence decay (2.67 ns) of the dimer. At an excitation energy of 95 cm , the rate is monitored by the appearance of ground state stilbene and vibrationally excited stilbene. The excited product is formed more rapidly than can be measured, while the ground state product is formed slowly (45 ps). Furthermore, the rates are faster at 95 cm than they are at 198 cm " excitation energies. These findings show that this reaction is not statistical. Taken with some modification from Semmes et al. (1987).

Fig.3. Time resolved, low temperature (80K) spectroscopy on RCs from the Dll niutant of Rb. capsulatus. (a) Decay of difference absorption monitored at 525nm. Insert Difference absorption spectrum after 80ps (upper trace) and 3ns (lower trace), (b) Decay of fluorescence.

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