Lifetime measurement

Lifetime measurements have elements in eommon with both eounting and time-of-flight experiments [4, 5]. In a lifetime experiment there is an initiating event that produees the system tliat subsequently deeays witli the emission of radiation, partieles or both. Deeay is statistieal in eharaeter taking as an example luielear deeay. 

Demas J N 1983 Excited State Lifetime Measurements (New York Aoademio)... 

Wilkerson C W Jr, Goodwin P M, Ambrose W P, Martin J C and Keller R A 1993 Detection and lifetime measurement of single molecules in flowing sample streams by laser-induced fluorescence Appl. Phys. Lett. 62 2030-2... 

Pirotta M, Guttler F, Gygax FI, Renn A, Sepiol J and Wild U P 1993 Single molecule spectroscopy fluorescence lifetime measurements of pentacene in p-terphenyl Chem. Phys. Lett. 208 379-84... 

Dunn R C, Holtom G R, Mets L and Xie X S 1994 Near-field fluorescence imaging and fluorescence lifetime measurement of light harvesting complexes in intact photosynthetic membranes J. Chem. Phys. 98 3094-8... 

Cline-Love L J and Shaver L A 1976 Time correlated single photon technique fluorescence lifetime measurements Anal. Chem. 48 370A-371A... 

Figure 22. (a) Comparison of stationary PMC peak at positive potentials and (b) peak in PMC transient lifetime, measured for n-ZnO single crystals.25... 

Otherwise, the effect of electrode potential and kinetic parameters as contained in the relevant expression for the PMC signal (21), which controls the lifetime of PMC transients (40), may lead to an erroneous interpretation of kinetic mechanisms. The fact that lifetime measurements of PMC transients largely match the pattern of PMC-potential curves, showing peaks in accumulation and depletion of the semiconductor electrode and a minimum at the flatband potential [Figs. 13, 16-18, 34, and 36(b)], demonstrates that kinetic constants are accessible via PMC transient measurements, as indicated by the simplified relation (40) derived for the depletion layer of an n-type electrode. 

Luminescence lifetime spectroscopy. In addition to the nanosecond lifetime measurements that are now rather routine, lifetime measurements on a femtosecond time scale are being attained with the intensity correlation method (124), which is an indirect technique for investigating the dynamics of excited states in the time frame of the laser pulse itself. The sample is excited with two laser pulse trains of equal amplitude and frequencies nl and n2 and the time-integrated luminescence at the difference frequency (nl - n2 ) is measured as a function of the relative pulse delay. Hochstrasser (125) has measured inertial motions of rotating molecules in condensed phases on time scales shorter than the collision time, allowing insight into relaxation processes following molecular collisions. 

After extraction, each phase may be studied independently in order to obtain a useful qualitative evaluation of the components in the original sample. The selectivity and specificity of fluorescence analysis can be especially beneficial in identification of PAHs. For example, some components could be identified by examining the fluorescence spectra of the organic and aqueous phases. Characteristic peak shapes may reveal identities of the components. For more complicated systems in which the spectra overlap, lifetime measurements may be used to identify components (27). 

Fluorescence lifetime measurements can increase the analytical specificity when analyzing mixtures (1-4) and can indicate changes in chemical binding of the fluorophores under various environmental conditions (5). 

Demas, J.N. Excited State Lifetime Measurements Academic New York, 1983 ... 

Quantitative analysis of the results obtained has shown that a single eosin guest is sufficient to completely quench the fluorescence of any excited dansyl unit of the hosting dendrimer. Fluorescence lifetime measurements indicated that the dye molecules can occupy two different sites (or two families of substantially different sites) in the interior of the dendritic structure. 

Figure 12.10 Typical time traces of (a) emission intensityand (b) lifetime, measured from a single DMPBI nanocrystal, (c) Photon correlation histogram obtained from the time trace of the emission intensity (a). The lifetimes were obtained by fitting a single exponential function to the decay curves constructed for every 2000...

During the course of these studies, it was found that fluorescence intensity from the polymeric films rapidly decreased on continued excitation in a fluorescence spectrophotometer (ca. 30% loss in 1 min for L). Herein, we (1) elaborate further upon the fluorescence loss studies, (2) provide direct evidence for RET from fluorescence lifetime measurements, and (3) present preliminary findings on the photochemistry of model compounds for polymer 1. The results support the conclusion, from previous studies, that the effectiveness of added stabilizer decreases with time due to formation of a photoproduct(s) from the polymer which competes in RET, and is less able to dissipate the resulting excitation energy.1... 

Ultraviolet absorption spectra were obtained from a Cary 118C Spectrophotometer. Luminescence measurements were obtained from a Perkin-Elmer Model MPF-3 Fluorescence Spectrophotometer equipped with Corrected Spectra, Phosphorescence and Front Surface Accessories. A Tektronix Model 510N Storage Oscilloscope was used for luminescence lifetime measurements. Fiber irradiation photolyses were carried out in a Rayonet Type RS Model RPR-208 Preparative Photochemical Reactor equipped with a MGR-100 Merry-go-Round assembly. 

Additionally, note that the polarity of the solvent significantly affects not only the positions of absorption and fluorescence spectra but also the fluorescence quantum yields. The largest difference in quantum yield is observed for G19 (eight times larger in toluene) [86]. The effect of solvent polarity on quantum yield and fluorescence lifetime was investigated in mixtures of toluene and ACN (polarity range 0.013-0.306). Polarity dependent quantum yield and lifetime measurements are presented in Fig. 22. 

The measurement of fluorescent decay dynamics, i.e., fluorescence lifetime measurements, promise to overcome several of the challenges discussed above. Most importantly, lifetime and quantum yield are directly related through (11),... 

A strong decrease in relaxivity (from 12.8mM-1s-1 to 2mM-1s-1) between pH 6 and 11 has been reported for a positively charged macrocyclic Gdm complex (Scheme 10), which was explained by the successive deprotonation of the coordinated water molecules.167 Luminescence lifetime measurements of a Yb111 analogue proved that the complex possesses three bound waters at pH 5.5. Above pH 11, a di-oxo-bridged dimer is formed that has no more bound water or OH groups. 

The second chapter by Peter Verveer and Quentin Hanley describes frequency domain FLIM and global analysis. While the frequency domain technique for fluorescence lifetime measurement is sometimes counterintuitive, the majority of the 10 most cited papers using FLIM have taken advantage of the frequency domain method as stated by these authors. The global analysis of lifetime data in the frequency domain, resolving both E and /d has contributed significantly to this advantage. 

Examination of Eqs. (2.9-2.11) suggests that having frequency domain lifetimes measured at a variety of frequencies is desirable, as it will allow a mixture of fluorophores to be determined. With this in mind, two approaches may be taken to obtain multifrequency results. The first of these is simply to make a series of FLIM measurements while stepping through a predetermined set of frequencies. In practice, this is of limited utility for biological systems because of photo-induced damage to the specimen. 

At the end of the 1980s and early 1990s, first experiments were carried out to combine fluorescence lifetime measurements with imaging using both time domain [1-4] and frequency domain [5-7] based approaches. This chapter will deal exclusively with time domain based fluorescence lifetime imaging methods. For the frequency domain based methods, refer Chapter 2. 

The performance of a lifetime detection system can be conveniently quantified by a figure-of-merit F, which is defined as the ratio of the SNR in a lifetime measurement and the SNR in an intensity measurement both carried out with the same number of photons. Based on this definition, F can be written as ... 

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