Emission spectra fluorescence analysis

TGA, iodometric, mid-IR, luminescence (fluorescence and phosphorescence) and colour formation (yellowness index according to standard method ASTM 1925) were all employed in a study of aspects of the thermal degradation of EVA copolymers [67], Figure 23 compares a set of spectra from the luminescence analysis reported in this work. In the initial spectra (Figure 23(a)) of the EVA copolymer, two excitation maxima at 237 and 283 nm are observed, which both give rise to one emission spectrum with a maximum at 366 nm weak shoulders... 

An increase in sensitivity and reliability of chip analysis can also be achieved by using fluorescence resonance energy transfer (FRET). For this purpose both the probe and the target are labeled with a fluorophor. When the emission spectrum of the donor, e.g. Cy5, overlaps with the absorption spectrum of the acceptor, e.g. Cy5.5, and the donor and the acceptor are at a certain distance from each other, energy is transferred from the donor to the acceptor on excitation of the donor fluorophor. 

The fluorescence emission spectrum of TIN in PS and PMMA films is dominated by a blue emission with a maximum at approximately 400 nm. The fluorescence excitation spectrum, monitoring this emission, corresponds to the absorption band of TIN(non-planar) obtained from the PCOMP analysis indicating that it is this form that leads to the observed emission. 

The quantification of fluorescent particles in cellular systems is difficult because several aspects such as autofluorescence, bleaching (see below), and quenching hamper analysis. Keep in mind that many fluorophores show a pH-dependent change in emission spectrum and intensity fluorescein-labeled dextrans (FITC-dextran) and calcein are strongly quenched upon acidification. If available, one should read the fluorescence intensity at its isosbestic point, where the intensity is not pH dependent. 

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... 

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.

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. 

Hayashi J, Kuroiwa Y Sato H, et al. Transadventitial localization of atheromatous plaques by fluorescence emission spectrum analysis of mono-L-aspartyl chlorin e6. Cardiovasc Res 1993 27 1943-1947. 

Electronic Spectrum. Acetone is the simplest ketone and thus has been one of the most thoroughly studied molecules. The it n absorption spectrum extends from 350 nm and reaches a maximum near 270 nm (125,175). There is some structure observable below 295 nm, but no vibrational and rotational analysis has been possible. The fluorescence emission spectrum starts at about 380 nm and continues to longer wavelengths (149). The overlap between the absorption and the fluorescence spectra is very poor, and the 0-0 band has been estimated to be at - 330 nm (87 kcal/mol). The absorption spectra, emission spectra, and quantum yields of fluorescence of acetone and its symmetrically methylated derivatives in the gas phase havbe been summarized recently (101). The total fluorescence quantum yield from vibrationally relaxed acetone has been measured to be 2.1 x 10 j (105,106), and the measurements for other ketones and aldehydes are based on this fluorescence standard. The phosphorescence quantum yield is -0.019 at 313 nm (105). 

B, then the fluorescence of A would be dominated by the acceptor emission spectrum and that of B by the donor spectrum. Thus, the reaction would cause a blue shift, which, if it were big enough, would enable a cross-correlation measurement. The reverse process with FRET large for B and small for A, would work equally well. For the bimolecular reaction A 4- L B, the flux could be measured if the binding caused a large enough shift in the fluorescence spectrum of A. The analysis for the bimolecular reaction is the same as given earlier in a steady state, the concentration of L is constant and so can be absorbed into a pseudo-first-order rate constant. 

As a typical example of polyene spectroscopy, absorption and fluorescence spectra of frons,frans-l,3,5,7-octatetraene in hexane at 23 °C are shown in Figure 3. An absorption band with several peaks is observed in Figure 3a. It should be noted that the positions of electronic absorption bands strongly depend on solvents . This absorption band is dipole allowed, because the molar absorption coefficient of this band is very large (Table 1). This band is attributed to the transition from the 1 kg ground state to the 1 feu excited state (tt-tt transition). Although the absorption peaks are due to vibrational transitions, a precise vibrational analysis cannot be made because of the broad band widths. The position of the observed emission spectrum (Figure 3b) shows a considerable red shift in... 

Fluorescence spectroscopy is not considered a major structural or qualitative analysis tool, because molecules with subtle structural differences often have similar fluorescence spectra. Also, fluorescence bands in solution are relatively broad at room temperature. However, fluorescence has proved to be a valuable tool in oil spill identification. The source of an oil spill can often be identified by comparing the fluorescence emission spectrum of the spill sample with that of a suspected source. The vibrational structure of polycyclic hydrocarbons present in the oil makes this type of identification possible. 

Polymers in Rigid Solution. The emission spectrum of PCVA in 2-methy1tetrahydrofuran (MTHF) at 77 K consists of prominent delayed fluorescence and phosphorescence bands(19). For this reason it was decided to investigate the rate of triplet exciton decay in these rigid solutions and to treat the data in terms of concurrent first and second order processes. For systems in which an equilibrium distribution of potential reactants may be assumed, eq 1 may be employed for data analysis. It is not clear, however, that such a distribution is valid for polymer solutions especially in light of evidence suggesting that T-T annihilations occur principally by intra-coil processes(14-15). 

Figure 1. Decay-associated fluorescence emission spectrum for ca. 1 X 10 M triad 2 in benzonitrile following excitation at 590 nm. The spectrum was obtained from a global analysis of data at the six indicated wavelengths ( = 1.14) analyzed as four exponentials. The major component has the lifetime of 55 ps ( . ...

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