Decay, monoexponential

Poly(541) pristine films of this polymer exhibited a photoinduced transient absorption band at around 700 nm. The transient signal decayed monoexponentially with a lifetime of 7 (is under Ar atmosphere, accelerating to 1.5 (is under O2 atmosphere. These transient bands are assigned to Ti > T transitions of polymer triplet excitons (3P ) formed in the amorphous polymer pristine films. 

The temperature dependent thermal reaction constants describe both the decay of the n-mer molecules, and by the addition step to DR +i, the generation of the n+l-mer molecules. Consequently in Figs. 18 and 19 only the dimer molecules (I) decay monoexponentially. The trimer and tetramer molecules etc. (I, II, etc.) are first produced from their precursors before decaying. Their time dependencies are described by two or more exponential functions. 

The appearance of the new, red, long-lived exciplex emission becomes even more obvious when plotting three-dimensional, time-resolved emission spectra (TRES). Figure 2.12 shows that the PL emission of the pure polymers decays monoexponentially with no spectral changes throughout their lifetime, whereas the blend PL evolves into the red exciplex peak. 

This behavior is consistent with experimental data. For high-frequency excitation, no fluorescence rise-time and a biexponential decay is seen. The lack of rise-time corresponds to a very fast internal conversion, which is seen in the trajectory calculation. The biexponential decay indicates two mechanisms, a fast component due to direct crossing (not seen in the trajectory calculation but would be the result for other starting conditions) and a slow component that samples the excited-state minima (as seen in the tiajectory). Long wavelength excitation, in contrast, leads to an observable rise time and monoexponential decay. This corresponds to the dominance of the slow component, and more time spent on the upper surface. 

An alternative graphical solution makes use of the biphasic exponential nature of the plasma concentration function ineq. (39.16). At larger time values, when the effect of absorption has decayed, the function behaves approximately as monoexponential. Under these conditions, and after replotting the concentration data on a (decimal) logarithmic scale, one obtains a straight line for the later part of the curve (Fig. 39.8a). This line represents the P-phase of the plasma concentration and is denoted by C ... 

Kinetics recorded at the maxima of the Sj-S bands, monitoring dynamics of the lowest excited state, have revealed further differences, Figure 8.8. Although monoexponential decays have been observed for monomeric carotenoids (9ps for zeaxanthin and 24 ps for ACOA), aggregates exhibit more complicated decay patterns. The Sx decay of the H-aggregate requires at least four decay... 

Broos J, Maddalena F, Hesp BH (2004) In vivo synthesized proteins with monoexponential fluorescence decay kinetics. J Am Chem Soc 126 22-23... 

The only unknowns in these equations are the two fluorescence lifetimes, which considerably reduces the complexity of the problem. Figure 2.3 shows a plot of N versus D for all possible monoexponential decays, and for all possible mixtures of two monoexponential species with lifetimes equal to 2.5 and 1 ns. The half-circle though (0,0) and (0,1) represents the values of N and D that correspond to all possible monoexponential decay kinetics [13, 16, 43], All the values of /V, and D, for a mixture of two species he on a straight line connecting the two points on the half-circle that correspond to the lifetimes of the two species. The offset and the slope of this straight line are given by Eq. (2.21). 

We can apply the quantitative analysis of two-component mixtures to the FRET data from Fig. 2.4 [20]. In this case, the two lifetimes are equal to the lifetimes of the donor in the absence and presence of acceptor. Figure 2.5a shows the results for EGFR-GFP. It can be seen that in the control sample, the relative concentrations of the short-lifetime component are not equal to zero, as would be expected for a monoexponential donor in the absence of FRET. Indeed, if we look at the plot of Nt versus D, for a subset of the pixels of the EGFR-GFP data, we see that the data for the control are not centered on a point on half-circle of monoexponential decays. In contrast, if we look at the results of EGFR-YFP (Fig. 2.5b), we find that the relative concentrations of the short-lifetime component are indeed much closer to zero. Indeed, the plot of Ni versus Dt shows that the data for the control are centered on a... 

Fluorescence Examples Nile Red 0.7 (dioxane) Cy3 0.04 (phosphate buffer) Alexa 0.12 (phosphate buffer) IR125 0.04 (MeOH) 1-10 ns, monoexponential decay CdSe 0.65-0.85 CdTe 0.3-0.75 PbSe 0.12-0.81 CuInS2 0.2-0.3 10-100 ns, typically... 

Fig. 2 Comparison of the luminescence decays of QDs and organic dyes. InP and CdTe QDs decay multiexponentially with a mean lifetime (ii/e) of 17 and 6 ns, respectively. The organic dye Cy5 shows monoexponential decay with tf of 1.5 ns...

Typically, a series of several 2D spectra are recorded with various relaxation delays, ranging from very short to the longest delays, which usually correspond to 1.5-2 relaxation times. The delay values are usually selected so that they are uniformly distributed over this time interval or so that the signal values are uniformly spread. Another sparse sampling strategy proposed in [12] is based on an optimal sampling scheme for a monoexponential decay function a five-point variant of this strategy uses one measurement at a very short relaxation delay and four measurements at 1.3 T2 (or 7 i). 

It will be seen that, as in the case of the LED, control of the bias voltage gives simple modulation of the laser output intensity. This is particularly useful in phase-modulation fluorometry. However, a measure of the late awareness of the advantages of IR techniques in fluorescence is that only recently has this approach been applied to the study of aromatic fluorophores. Thompson et al.(51) have combined modulated diode laser excitation at 670 and 791 nm with a commercial fluorimeter in order to measure the fluorescence lifetimes of some common carbocyanine dyes. Modulation frequencies up to 300 MHz were used in conjunction with a Hamamatsu R928 photomultipler for detecting the fluorescence. Figure 12.18 shows typical phase-modulation data taken from their work, the form of the frequency response curves is as shown in Figure 12.2 which describes the response to a monoexponential fluorescence decay. 

The fluorescence decay parameters of tyrosine and several tyrosine analogues at neutral pH are listed in Table 1.2. Tyrosine zwitterion and analogues with an ionized a-carboxyl group exhibit monoexponential decay kinetics. Conversion of the a-carboxyl group to the corresponding amide results in a fluorescence intensity decay that requires at least a double exponential to fit the data. While not shown in Table 1.2, protonation of the carboxyl group also results in complex decay kinetics.(38)... 

Pharmacokinetics When administered intravenously, ICG rapidly binds to plasma proteins and is exclusively cleared by the liver, and subsequently secreted into the bile [8]. This forms the basis of the use of ICG for monitoring hepatic blood flow and function. Two pharmacokinetics models, a monoexponential decay, which describes the initial rapid clearance of ICG with a half-life of about 3 minutes (Eq. (1)) and a bi-exponential model, which incorporates the secondary phase clearance with a longer half-life (Eq. (2)), describe total clearance of ICG from plasma [ 132]. For real-time measurements by continuous organ function monitoring, the mono-exponential decay is preferred. 

A number of studies on the fluorescence decay of tyrosine, tyrosine derivatives, and small tyrosyl peptides have been carried out. 36-38 Whereas the tyrosine zwitterion and tyrosine derivatives with an ionized a-carboxy group exhibited monoexponential fluorescence decay (x = 3.26-3.76 ns), double- or triple-exponential decay was observed in most other cases. As in the case of the tryptophan model compounds, the complex decay kinetics were again interpreted in terms of rotamer populations resulting from rotation around the C —Cp bond. There is evidence to indicate that the shorter fluorescence lifetimes may arise from rotamers in which the phenol ring is in close contact with a hydrated carbonyl group 36 37 and that a charge-transfer mechanism may be implicated in this quenching process. 39 ... 

Just after CT excitation of the DACs, the TG spectrum consists of a band centred at 670 nm (see Figure 3) and due to the radical anion of PMDA. Its decay, which can be reasonably well reproduced with a monoexponential function, is due to CR to the neutral ground state. 

A digressing result concerning the Trp fluorescence decay has been reported by Sarkar and Song [109] for 114/118-kDa phytochrome the decay at 293 K was found to be monoexponential with a nanosecond lifetime in the case of Pr, and biexponential with lifetimes around 2 and 5 ns in the case of Pfr. Since the degraded phytochrome possesses only eight Trp residues [110],... 

Fig. 5.16. Nonexponential decay curves of crystal violet (excited with synchrotron radiation from BESSY) in glycerol at six different temperatures. Within experimental error limits, the decays can be fitted by a biexponential model. The two lifetime components at 13°C are 330 and 850 ps, respectively. Upon reducing the temperature, both fitted decay times increase, as well as the relative weight of the slower decay component. At -72°C, a monoexponential decay is observed (2.71 ns).

It is probably appropriate to note at this point that Stern-Volmer type of analysis of luminescence data obtained using modern gated spectrometers (such as the Perkin-Elmer LS5) follows different mathematical expressions than those used for data obtained under continuous irradiation conditions. This is true even for homogeneous systems where the excited state decays with simple monoexponential behaviour. 

The inclusion of 5 wt% PCBM [l-(3-methoxycarbonyl)propyl-l-phe-nyl-[6,6]C6i] in the spin-coating solutions resulted in efficient polymer emission quenching for all the polythiophenes studied. The transient absorption spectra of the amorphous poly(541)/PCBM blend film. At 10 ps exhibited an absorption peak around 700 nm, similar to that observed for the poly(541) pristine film. The shape of the transient spectrum varied with time, with the absorption peak shifting from 700 nm at 10 is to 900 nm for time delays >100 (is, demonstrating the formation of two distinct transient species in the blend film. The monoexponential lifetime was t = 8 (is under Ar atmosphere and significantly shortened under 02 atmosphere. Monoexponential phase is therefore assigned to the decay of poly(541) triplet excitons. 

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