Time-integrated fluorescence spectra

The time-integrated fluorescence spectra and time profiles of the fluorescence intensities of these components, which were obtained by varying the delay time x in steps of 0.02 ns and then averaging in each area of — P3 (see Figure 32.10b), were plotted in Figure 32.11a and b, respectively. It should be mentioned that the fluorescence properties of the short- and long-wavelength components in elicitor-... 

Figure 32.11 (a) Time-integrated fluorescence spectra and (b) time profiles of the fluorescence intensities. The lines are results experimentally observed and the symbols are the components extracted by PARAFAC. The fluorescence spectra and the time profiles were drawn with appropriate shifts in a vertical direction for comparison. 

Figure 2 portrays time integrated fluorescence spectra of 3HF that reveal the dual fluorescence bands of this molecule (12-15). Spectra are presented for methanol solvent and Dj-Methanol solvent for which the 3HF alcoholic proton is exchanged with a deuteron. Kinetic traces recorded by method A for 3HF are shown in Figure 3. Each trace was acquired in 500 sec. of instrument time, i.e., 5000 laser pulses.

Case 2. Time-integrated fluorescence spectra Now consider experiments in which one spectrally resolves time-integrated fluorescence so as to relate spectral features to IVR rates. In such a case one is interested in [a b]/[ab ], where the bars denote integration over time. This ratio gives the ratio of fluorescence intensity from the ab y states relative to that from the a by states, and can be obtained by integrating Eqs. (2.1) and (2.2) over time ... 

Second, we considered the mid-wavelength component, which was only observed in the elicitor-treated cells. This suggests the possibility that the component is associated with avenanthramides. It was reported that avenanthramide A is a major component of induced avenanthramides and reaches a maximum at 36-48 h after treatment with the elidtor [32].We measured the time-resolved fluorescence spectrum of avenanthramide A in aqueous solution (pH. 7.0) in vitro. The time-integrated fluorescence spectrum is broad and centered at 510 nm (Figure 32.11a). The spectral shape is, in part, similar to that of P2 and very similar to that of Component II. The... 

Being mainly interested in the dynamics associated with the conical intersection of the and S2 excited electronic states, we focus in the following on the excited-state contribution to the pump-probe spectrum. Figures 2 and 3 compare three different excited-state pump-probe signals, namely the integral stimulated-emission spectrum (2b), the time-resolved fluorescence spectrum (3a), and the dispersed stimulated-emission spectrum (3b). As has been discussed above, the integral stimulated-emission spectrum and the time-resolved fluorescence spectrum are rather similar. Because of the... 

Figure 7.5 Ultrafast spectrally resolved dynamics of two CdS tSei x nanobelts. The fluorescence image is shown in the upper left corner. Note that the broad, time-integrated photoluminescence spectrum shown on the left consists of two distinct features centered at 628 and 636 nm with vastly different dynamics that is clearly discernible in the 2D map.

Figure 23 Fluorescence spectrum of DMP measured at 100 nsec after e. Energy of / V532, 130 mJ. Inset a plot of the integrated fluorescence intensity of DMP as a function of the delay time of hv532 relative to eT (open circle) is superimposed with a plot of AO.D.575 (solid circle).

Figure 29. Time-dependent fluorescence spectra of a lipophilic carbocyanine molecule, excited by the optical near field of an aperture probe. Time averaged spectrum integrated over 17 min, wavelength shifted spectrum recorded during the eighteenth minute, after spontaneous irreversible photobleaching the background spectrum was recorded (twentieth minute). (Adopted from [96].)...

Fig. 3.15 (Right) Time-gated fluorescence spectra of a film of polyfluorene PF2/6 after optical excitation at 3.35 eV at low temperature (15 K). The spectra were time integrated from 0-2, 8-10, 35-57, 134-136, 329-331, 822-824 and 1770-1850 ps, respectively. The arrow indicates the excitation energy. (Left) Low-temperature (80 l<) absorption spectrum of the film. The dashed line is a fit of a Gaussian curve to the red edge of absorption spectrum. Reprinted from [73], copyright 2001, with permission from Elsevier.

In order to obtain the spectrum of the emitted field, the probe pulse is frequency resolved by a spectrometer after it has passed the sample (see, e.g. Ref. 54). Because the PP signal is measured as the time-integrated energy rate (cf. Eq. (7)), the corresponding spectrum may be considered as stationary, although it inherently depends on the delay time At. Contrary to the case of time-resolved fluorescence (see next Section), the effects of the spectrometer therefore need not to be considered in the theoretical description, and we may define the dispersed PP signal as the intensity of the Fourier transform of the total emitted field (6), 3uelding °di... 

The above section has outlined the physical parameters that describe the fluorescence process. One can measure the fluorescence spectrum, P(X), the singlet excited state lifetime, xs, and determine the Tliese parameters can be interpreted in terms of the structure, environment and ( mamics of the molecule of interest. In this section, the different optical and electronic components comprising an instrument that can measure Fl( ) and will be described. This instrument is generally known as a steady state fluorescence spectrometer, since it integrates the fluorescence intensity over a given time period. Time-resolved fluorescence instrumentation that is used to measure the excited singlet state decay times is described in Chapter 3. 

Fig. Ila-c Spectral fluctuations of single tetramethylrhodamine (TMR)-labeled myosin molecules a fluorescence images of single TMR-myosin molecules. Arrow represents the fluorescence spot analyzed b a series of fluorescence spectra from a single TMR-myosin arrow in a) with time. Spectra were taken sequentially every 0.61 s with the collection time of 0.5 s for each spectrum c fluctuations in the fluorescence spectrum of single TMR-myosin. The spectral mean was plotted as a function of time, inset) Total fluorescence intensity obtained by integrating fluorescence intensity for wavelengths from 540 to 600 nm for each spectrum...

Here pis the quantum efficiency of the sensitizer (ti = Tp/xp = l/3forpentacene)in the O4 site of p-terphenyl at 4 K, n is the index of refraction (n = 1.7 for the p-terphenyl crystal), and Na is the Avogadro s number. The integral in (H9) is calculated from the normalized fluorescence spectrum/(v) and the decadic molar extinction coefficient e(v) of pentacene at O4 site. The critical interaction distance is the sensitizer-activator separation for which the transfer rate is equal to the intrinsic decay time. Although derived for low temperatures. Equation H9 is also vaUd for arbitrary temperatures. In fact, the temperature dependence of the resonant energy transfer rate is contained in the spectral overlap integral. 

The analysis of the fluorescence emission spectra under high frequency modulated light provides, in addition to the time integrated spectrum Fc ( i.e. at the zero frequency ),two supplementary spectra s Re and Im (respectively the real and imaginary part of the fluorescence at the frequency of modulation ). If Fc is a linear combination of a basis of elementary components 9 Re and Xm must be also a linear combination of the same basis. By repiting the experiment at n different fx equencies spectra can be obtained. To evidence lifetime values Re and Im can be remplaced by two others parametres defined as follows... 

There is another important difference between direct absorption and LIF spectroscopies. This difference reflects a fundamental distinction between direct and indirect detection schemes. In a direct absorption spectrum, the signal integrated over the absorption line is determined by a fundamental molecular property, the integrated absorption cross section, oA (see Eqs. 6.1.11 and 6.1.13), times the number density (molecules/cm3) of molecules in the lower level of the absorption transition. In an LIF spectrum, the detected signal is reduced by the product of the fluorescence quantum yield... 

---