Fluorescence decay measurements

Figure 3.5 Time-resolved fluorescence decay measured by time-correlated singlephoton counting, which involves counting the number of photons that arrive within a given time interval after excitation. The results are stored in a number of channels, each channel corresponding to a particular time interval. When displayed, the results are not continuous, but by using a large number of channels the output approximates to a continuous decay curve...

Streak cameras and multianode microchannel plate photomultipliers (MCP-PMs) interfaced to a polychromator also permit multiwavelength fluorescence decay measurements, the spectral response of both being determined by the photocathode composition. 

Figure 12.6. Multiplexed single-photon counting arrangement for parallel fluorescence decay measurements (from Ref. 29.)...

W. R. Ware, M. Pratinidhi and R. K. Bauer, Performance characteristics of a small side-window photomultiplier in laser single-photon fluorescence decay measurements, Rev. Sci. Instrum. 54, 1148-1156 (1983). 

A single tyrosine is in the C-terminal portion of the transcription factor 1 (TF1), a type II procaryotic DNA binding protein encoded by Bacillus subtilis phage SPOl. Time-resolved fluorescence decay measurements yielded... 

Fluorescence decay measurements have also allowed one to propose a qualitative model of film occupancy in which both amorphous sites and crystal-line-amorphous interfaces would be occupied by ester molecules, with predominance of the former ones [291]. 

Schneider et al. [63] investigated the photochemistry of the spiro-oxazine merocyanines pumping and probing at 570 nm in acetonitrile. The found that the solution bleached within the <5-psec pulse duration. The bleached state recovered with at least a biexponential behavior, and from their fluorescence decay measurements, three exponentials were required to fit the decay. They attribute these findings to the possibility of three merocyanine isomers that are in equilibrium. Their compounds feature geminal ethyl groups on the indoline moieties and this may influence the system as compared to NOSIl. 

A large number of fluorescence decay measurements have been performed with proteins.127 Studies on the fluorescence decay of tyrosine and tryptophan and their derivatives, and on biologically active peptides containing intrinsic or extrinsic fluorophores have also been carried out and a few illustrative examples will be reviewed here. 

There are also a few more recent papers in which a casual fluorescent-decay measurement was made during the course of other experiments. Often no analysis is included, and sometimes the data are simply repetitious. Some discretion has been exercised concerning the inclusion of these, and no pretense is made that every recent fluorescent-lifetime measurement is included. 

When using DCE as quencher (Fig.3a), the second deactivation channel remains open until Ati=l ns. The small free ion yield for this system indicates that charge recombination is much more efficient and therefore much more rapid than charge separation. Furthermore, we know from time resolved fluorescence decay measurements that electron transfer quenching is still not finished at At =lns. Consequently the absorbance should be dominated by fresh geminate ion pairs, over the whole timescale investigated. Thus, the GSR dynamics of Pe + in presence of DCE should be independent of Ati, which is confirmed by our experimental observations. 

Fujiwara T, Lim EC (2006), unpublished results based on fluorescence decay measurement. 

The operation of an oscilloscope can best be described by reference to Fig. 5, which shows a simplified layout of the controls of a commercial (Tektronix) digital instrument. The signal to be measured is applied to the input connector (BNC) of one of the vertical amplifier channels and must not exceed an upper limit of, typically, 400 volts if the scope input impedance is one megaohm and 5 volts for 50-ohm input impedance. The latter impedance is necessary for signal changes that occur rapidly, such as in the fluorescence decay measurements of Exps. 40 and 44. The lower limit of sensitivity is about 1 mV/division, so preamplification is sometimes needed if very low signal levels are to be measured. 

Since the electron transfer from the conduction band into the surface state (Eq. 67) can be very fast and the corresponding rate may be determined by the thermal velocity of electrons toward the surface, it has to be assumed that the initial chemical etching reaction (66) is even faster. However, it is not clear whether this assumption is correct. Very recently it has been found that also the reduction of protons (H2-formation) at n-GaAs is a very fast reaction. The current potential dependence can actually be described by the thermionic emission model (see Eq. (65)) [142]. This result indicates that the electron transfer can occur at much higher rates if the electron acceptor is adsorbed on the surface. This assumption is supported by recent results reported by Nozik [143]. He repeated his fluorescence decay measurements by using nitrobenzene as an electron acceptor and found a much lower rate than for ferrocence. Nozik assumed that the high rate constant for ferrocence may also be due to adsorption. 

Para-substituted Carbon Core Dendrimers Table 1.1 shows that the lifetimes of p-C IP , p-C IP3, and p-C1P4 are identical with the fluorescence decay measured for an adequate model containing a peryleneimide chromo-phore. A representative plot of the fluorescence decay of the first generation para-substituted dendrimers is given in Figure 1.13 for p-CIP4. 

Fluorescence and Chemiluminescence Spectroscopy. - The fluorescence excitation spectrum of PF3 at 9-13 eV, using monochromatised synchrotron radiation, has been examined to resolve the pyramidal geometry of the X Ai ground state of the PFs" cation, which was also confirmed by ab initio calculations. Dimethylamino-substituted triphenylphosphines exhibit dual fluorescence in polar solvents, and fluorescence-decay measurements have shown that the photo-induced intramolecular charge-transfer process occurs in a few picoseconds, even in weakly-polar solvents. 

Photoinduced electron transfer in fullerene based supramolecular systems has been described in Section 7.3.5 as an example of process that can be followed both by time-resolved fluorescence and transient absorption, and reaction time on the picosecond time scale was calculated from fluorescence decay measurements. Transient absorption with subpicosecond or picosecond resolution allows the characterization of the product formed while fluorescence is quenched. On a longer time-scale it provides information on the lifetime of the photoproduct. The porphyrin-fullerene (H2P-C60) diads in which the two chromophores are linked... 

Exciplex Formation in Cvclopentane. This section begins on a cautionary note. Fluorescence decay measurements on the two lowest molecular weight samples of DMT-PS-Py [M = 3000, 5000] give data that differ in one key respect from the predictions in Scheme I. 

Emission spectra and absorption spectra were recorded on a Perkin-Elmer 650-iOS Fluorescence Spectrophotometer and a Perkin-Elmer 320 tn/ Spectrophotometer, respectively. Fluorescence decay data were obtained on a single-photon-counting apparatus from Photochemical Research Associates. The samples were bubbled witli nitrogen for the steady-state fluorescence spectra and the fluorescence decay measurements. In some cases, front face spectra were taken. The data were analyzed by a software package from PRA based on the iterative convolution method. NMR spectra were obtained on a JEOL FX90Q, and FTIR spectra were recorded on a Nicolet 5DX. The elemental analyses were conducted by M-H-W Laboratories of Phoenix, AZ. 

Heterogeneous Molecular Environments Probed by Fluoro-phores Bonded to Chemically Modified Silica Gel Fluorescence Decay Measurements under a Microscope (Satoshi Hirayama, Takashi Kubo, and Hirohisa Yamasaki)... 

Spectroscopic techniques based on the optical microscope are being used with increasing success in photophysics. Microscopic fluorescence decay measurements have been made on both thin liquid films and droplets of concentrated dye solutions.Illustrative data are given for rhodamine B in 20 pm films. A luminescence lifetime microscope spectrometer based on time-correlated single photon counting with an avalanche diode detector has measured... 

The fluorescence of 1-8 derives from the porphyrin moiety and is essentially indistinguishable from that of the porphyrin model except for a reduction in quantum yield. Fluorescence decay measurements of 1-8 were obtained in dichloromethane, chloroform, and benzonitrile with laser excitation at 590 nm. Table I presents the fluorescence lifetimes and initial amphtudes for triads 1-4 in these solvents. The decays were measured at six wavelengths in the 650-750 nm region and analyzed globally. In the case of triad 2, for example, a satisfac-... 

S-20 spectral response operating in the photon counting mode. Fluorescence decay measurements were performed on approximately 1 X 10 M solutions using the time-correlated single photon counting method described previously... 

Criteria for evaluating the degree of fit between measured fluorescence decay curves and trial decay functions have been discussed.In some instances plots of weighted residuals were found to be sufficient, but a generalized statistical test was proposed for all other cases. An analysis of the statistical distribution of noise in fluorescence decay measurements by SPC has shown, as expected, that Poisson statistics dominate. A method for obtaining decay information from pulse fluorimetry without the need for consideration of the excitation pulse, has been described. ... 

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