Fluorescence quenching time resolved spectroscopy

Time-resolved spectroscopy establishes that the fluorescence of the excited (singlet) anthracene ( ANT ) is readily quenched by maleic anhydride (MA), which leads to the formation of the ion pair ANT+, MA via diffusional electron transfer (see Fig. 12), i.e.,... 

Besides fluorescence spectroscopy, time-resolved spectroscopy can rely on the measurement of excited (singlet or triplet) state absorption. Similarly to ground-state absorption, the spectral and absorbance properties may be altered by CyD complexation and yield information about the behavior of the complex in the excited state in addition, the time dependence (formation and decay) of the excited state absorption yields information about the kinetics and dynamics of the system. This is illustrated by the behavior of the lowest triplet state of naphthalene as measured by nanosecond spectroscopy using a Q-switched Nd YAG laser at 266 nm for excitation [21]. The triplet-triplet absorption spectra were measured in neat solvents (water and ethanol) and in the presence of a- and -CyD (Fig. 10.3.3). The spectra in ethanol and H2O had the same absorption maximum, but the transition was considerably weaker and broadened in H2O. Both CyDs induced a red shift, and a-CyD additionally narrowed the main band considerably. Fig. 10.3.4 shows the effect of a-CD concentration on the time evolution of the triplet-triplet absorption at 416 nm in the microsecond range. Triplet decay was caused by O2 quenching a detailed kinetic analysis of the time dependence yielded two main components which could be assigned to the free guest and the 1 2 complex, in full... 

Weller [21-23] has pointed out the competition between the rates of proton transfer and the deactivation in the excited state. In fact, it has been shown that proton-induced fluorescence quenching competitive with the proton-transfer reaction is present in the excited state of naphthylamines, that is, simple acid-base equilibrium cannot be accomplished in the excited state of aromatic amines, and that a dynamic analysis containing the quenching process is, therefore, needed in order to obtain the correct values [32,33]. The dynamic analyses by means of nanosecond time-resolved spectroscopy with fluorimetry have been applied to 1-aminopyrene [34,35], 1-aminoanthracene [36], phenanthrylamine [37,38], and naphthols [39]. This method to determine the values of naphthylamines has been used by Hafner et al. [40], and similar experiments for excited naphthols have been carried out by Harris and Selinger [41]. On the other hand, establishment of prototropic equilibrium has been reported in the case of 2-hydroxynaphthalene-6,8-disulfonate [42]. 

Time-resolved fluorescence spectroscopy is widely used as a research tool in biochemistry and biophysics. These uses of fluorescence have resulted in extensive knowledge of the structure and dynamics of biological macromolecules. This information has been gained by studies of phenomena that affect the excited state, such as the local environment, quenching processes, and energy transfer. 

Increasing the solvent polarity results in a red shift in the -t -amine exciplex fluorescence and a decrease in its lifetime and intensity (113), no fluorescence being detected in solvents more polar than tetrahydrofuran (e = 7.6). The decrease in fluorescence intensity is accompanied by ionic dissociation to yield the t-17 and the R3N" free radical ions (116) and proton transfer leading to product formation (see Section IV-B). The formation and decay of t-17 have been investigated by means of time resolved resonance Raman (TR ) spectroscopy (116). Both the TR spectrum and its excitation spectrum are similar to those obtained under steady state conditions. The initial yield of t-1 is dependent upon the amine structure due to competition between ionic dissociation and other radical ion pair processes (proton transfer, intersystem crossing, and quenching by ground state amine), which are dependent upon amine structure. However, the second order decay of t-1" is independent of amine structure... 

The application of vb-DMASP to MIPs was continued in subsequent works [64, 65], In these investigations, time-resolved fluorescence spectroscopy was applied to study bulk fluorescent MIP. The imprinted polymer fluorescence quenching with increasing concentrations of aqueous cAMP was determined from the fluorescence lifetime parameters. Two components in the fluorescence decays were identified and assigned to two different types of cavities present in the polymer matrix. One was accessible and open to binding, whereas the other was inaccessible, being buried inside the bulk polymer. The fluorescence lifetime decreased due to the increase in the concentration of the initial target analyte. However, the accessible... 

The fluorescence lifetime of a fluorophore is highly sensitive to its molecular environment. Many macromolecular events, such as rotational diffusion, resonance-energy transfer, and dynamic quenching, occur on the same timescale as the fluorescence decay. Thus, time-resolved fluorescence spectroscopy can be used to investigate these processes and gain insight into the chemical surroundings of the fluorophore. 

The properties of the flavin are exploited for flavoenzyme characterization. Absorbance spectroscopy (under anaerobisis, as needed) can be used for binding studies, redox titrations, and rapid-reaction kinetics (Note the relevant articles in the See Also section). Other useful techniques include fluorescence spectroscopy (at equilibrium or time-resolved, although in most cases the flavin fluorescence is quenched in the holoen-zyme), EPR, and NMR. Several of these techniques have been developed early on (also) thanks to research on fiavoproteins. 

Time-resolved Raman spectroscopy also provides valuable mechanistic information on quenching reactions of molecules such as trans-stilbene [123]. The fluorescence of trans-stilbene can be quenched by tertiary amines. TR spectra measured 60 ns after excitation contained peaks that could be assigned to the transient anion radical of trans-stilbene [123]. 

The dynamics of both static and dynamic quenching of the fluorescent singlet states of diazapyrenium salts by nucleotides has been investigated by Brun and Harriman using sub-nanosecond time-resolved transient absorption spectroscopy [88]. Observation of the reduced acceptor DAP+ (Table 5) supports an electron transfer mechanism for fluorescence quenching. Diffusion-controlled rate constants were observed for quenching of DAP + by all four deoxynucleotides. Excitation of... 

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