Inherent fluorescence lifetime

For details, see Michl, J. Bonacic-Koutecky, V. Electronic Aspects of Organic Photochemistry Wiley-Interscience New York, 1990 p. 74. In general, weak absorptions predict long inherent lifetimes, while strong absorptions are associated with high fluorescence rate constants and short inherent fluorescence lifetimes. 

It is important to note that if a mixture of fluorophores with different fluorescence lifetimes is analyzed, the lifetime computed from the phase is not equivalent to the lifetime computed from the modulation. As a result, the two lifetimes are often referred to as apparent lifetimes and should not be confused with the true lifetime of any particular species in the sample. These equations predict a set of phenomena inherent to the frequency domain measurement. 

In Scheme 10 electron transfer to singlet state is portrayed. The plots obtained are also consistent for a process which involves electron transfer to the triplet state. However, using the values of the (slope)/(intercept) for plots of l/4> vs. 1/[A] for 17,18 and 19 in the exciplex dominant region and the values of the triplet lifetimes obtained from phosphorescence measurements (112, 36, and 29 ms), values of kex 10 - 102M 1s 1 are obtained which are too low. Estimating the inherent radiative lifetime from the molar absorptivity, kisc must be 109 - 1010 s 1, since no detectable fluorescence was observed. The slope over the intercept using Eq. 16 now yields values 109 — 1010 M "1 s 1 for kex which is more reasonable [39]. 

Measurements of fluorescence lifetime ofa chromophore can enhance the potential offluorescence microscopy [1,2,5-8]. Fluorescence lifetime is an inherent property of a chromophore, and thus is independent of chromophore concentration, photo-bleaching and, excitation intensity, but highly dependent on pH, ion concentration, and local environment that affects the non-radiative rate of a chromophore. This makes fluorescence lifetime imaging (FLIM) a powerful tool for quantitative imaging of cellular conditions as well as the circumstances around the fluorescent dyes. 

Compared to type I fluorescent polymers, the conjugated polymer backbone is the active chromophore. The monomer units that make up the polymer might not be inherently fluorescent. The absorption and emission of photons involve electronic transitions between a ground-state singlet (So) and a excited-state singlet (typically Si) as shown in Fig. 1.3. Radiative (kT) and nonradiative (km) transitions result in relaxation to the ground state and the observed kinetic lifetime t of these systems is governed by the relationship... 

Photophysics of 1-Aminopyrene on Various Silica Gel Surfaces. Figure 2 presents the fluorescence spectra of 1-AP adsorbed on MCB and FS-662 silica gel in cyclohexane. The fluorescence spectrum of MCB-bound 1-AP is quite typical of 1-APH+, whereas the fluorescence spectrum of FS-662-bound 1-AP is quite typical of 1-AP. The surface-bound 1-APH+ decays with an inherent unimolecular lifetime of 135 2 ns, and the surface-bound 1-AP decays with an inherent unimolecular lifetime of 4.9 0.1 ns. The different photophysical behavior of the 1-AP indicates that the adsorption sites for 1-AP are different on these silica gel samples at the given probe loadings. 

The vast majority of single-moleeule optieal experiments employ one-photon excited spontaneous fluorescence as the speetroseopie observable beeause of its relative simplicity and inherently high sensitivity. Many molecules fluoresee with quantum yields near unity, and spontaneous fluorescence lifetimes for chromophores with large oseillator strengths are a few nanoseeonds, implying that with a sufficiently intense excitation source a single... 

Our previous approaches to detect endogenous complexes of dynamin and auxilin using co-immunoprecipitation approaches were unsuccessful, so we turned to fluorescence lifetime imaging microscopy (FLIM). While fluorescence microscopy provides two- or three-dimensional information about fiuorophore concentration, FLIM can reveal spatial differences in fluorophore population lifetimes that are independent of concentration. Besides being useful in fiuorophore identification, which transcends issues of spectral overlap, FLIM inherently observes lifetime truncations on a pixel by pixel basis that are induced by fluorescence resonance energy... 

All nonradiative processes that contribute to the depletion of the excited state shorten the fluorescence lifetime and weaken the emission intensity. Some of them arise as inherent features of the fluorophore (e.g., internal conversion) and their effect depends on its interactirm with solvent and on temperature. They predetermine the natural fluorescence lifetime, Tpo, which is defined as the lifetime in the absence of additional components that can quench the fluorescence. 

The quantum yields of fluorescence of the different systems have also been determined relative to a single crystal of neodymium-doped YAG for which a quantum yield of unity has been assumed (Heller, 1968a). The quantum yields obtained, even if they are accurate only within a factor of two, follow the same trend as for the lifetimes, with the highest values for the acidic solutions 0.70 and >0.75 in presence of S11CI4 and SbCls, respectively. Neutral and basic solutions are less luminescent and have quantum yields of 0.5 and 0.4, respectively. Identical measurements performed on a sodium-compensated neodymium-doped calcium tungstate crystal lead to a value of 0.5. The high quantum efficiency and the low threshold (between 2 and 40 J) of these Nd3+ SeOCl2 systems clearly demonstrate that liquids are not inherently inferior to solids as laser materials. 

The time resolution of the electronics in a single photon counting system can be better than 50 ps. A problem arises because of the inherent dispersion in electron transit times in the photomultiplier used to detect fluorescence, which are typically 0.1—0.5 ns. Although this does not preclude measurements of sub-nanosecond lifetimes, the lifetimes must be deconvoluted from the decay profile by mathematical methods [50, 51]. The effects of the laser pulsewidth and the instrument resolution combine to give an overall system response, L(f). This can be determined experimentally by observing the profile of scattered light from the excitation source. If the true fluorescence profile is given by F(f) then the... 

The emission lifetimes of the bipy and phen complexes of ruthenlum(II) at 77°K are generally in the range t = 0.5-10 ps. (Table 7). Since these values are intermediate to those generally observed for the fluorescence and phosphorescence of organic compounds, the radiative transition in the ruthenium complexes was suggested to be a heavy-atom perturbed spin-forbidden process (168,169). From a determination of the absolute quantum yields as well as lifetimes of a series of ruthenium(II) and osmium(II) complexes, the associated radiative lifetimes were calculated (170). The variations in these inherent lifetimes within the series could be rationalized with a semi-emipirical spin-orbit coupling model thus affording further evidence that the radiative transitions are formally spin forbidden in these systems. 

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