Phosphorescence time dependence

Fig. 13. Semilogarithmic plot of the phosphorescence time dependence of the stereoregular phenylcyclosiloxanes [PhSiO(OSiMe3)] where n = 4, 6, 8, and 12, measured together with the tetraphenyl-l,3-disiloxanediol, all measurement conditions as described in the legend to Fig. 12 above, except for the emission wavelength...

Figure 8. Phosphorescence time dependence of the emission from the stereoregular phenylcyclosiloxanes, [PhSi(0SiMe3)0], = 4, 6, 8, 12, together with the linear tetraphenyl-l,3-siloxanediol, measured (in powder form), at the temperature of liquid nitrogen, T = 77 K. Excitation wavelength 320 nm, emission wavelength 380 nm, spectral bandwidth ca 8 nm, edge filter (370 nm). Excitation flash duration (at half maximum) 3 ps, delay time increment 5 ps, sampling window size 10 ps, cumulative emission from 10 flashes per data point.

Phosphorescence quenching la 35 -, detection limits la 15 -, time dependance la 34 Phosphoric acid la 179,185,242,278,430 Phosphoric acid esters la 44,170 Phosphoric acid insecticides lb 115,332, 339,340... 

The major reasons for using intrinsic fluorescence and phosphorescence to study conformation are that these spectroscopies are extremely sensitive, they provide many specific parameters to correlate with physical structure, and they cover a wide time range, from picoseconds to seconds, which allows the study of a variety of different processes. The time scale of tyrosine fluorescence extends from picoseconds to a few nanoseconds, which is a good time window to obtain information about rotational diffusion, intermolecular association reactions, and conformational relaxation in the presence and absence of cofactors and substrates. Moreover, the time dependence of the fluorescence intensity and anisotropy decay can be used to test predictions from molecular dynamics.(167) In using tyrosine to study the dynamics of protein structure, it is particularly important that we begin to understand the basis for the anisotropy decay of tyrosine in terms of the potential motions of the phenol ring.(221) For example, the frequency of flips about the C -C bond of tyrosine appears to cover a time range from milliseconds to nanoseconds.(222)... 

G. B. Strambini and W. C. Galley, Time-dependent phosphorescence anisotropy... 

For times shorter than this, the rate coefficient may be expected to be time-dependent. For instance, with A 108 s 1, L 0.14 nm and D 10"18 m2 s 1, Reff 1 nm and > 0.3 s. This would require a long-lived phosphorescent state, such as of phenanthrene (r0 4 s), for time dependence to be observed. Since the residual time dependence of eqn. (96) contains no dependence on the radial co-ordinate, r, the time-dependent rate coefficient, eqns. (73)—(75), is simply... 

Pauli principle, 45-47,178-182, 284-287 Pauli spin matrices, 96 P branch, 171-173,218,303 Peanuts, 320 Perpendicular band, 259, 265 Perturbation, spectroscopic, 283 Perturbation theory, 35-38,102 degenerate, 36-38 for nuclear motion, 149-159 time-dependent, 110-114 Phase, 13 Phenol, 225 Phosphorescence, 128 Phosphorous trichloride, structure of, 222, 223... 

Reticulum ATPase [105,106], Owing to the long-lived nature of the triplet state, Eosin derivatives are suitable to study protein dynamics in the microsecond-millisecond range. Rotational correlation times are obtained by monitoring the time-dependent anisotropy of the probe s phosphorescence [107-112] and/or the recovery of the ground state absorption [113— 118] or fluorescence [119-122], The decay of the anisotropy allows determination of the mobility of the protein chain that cover the binding site and the rotational diffusion of the protein, the latter being a function of the size and shape of the protein, the viscosity of the medium, and the temperature. 

Figure 3. Time dependence of the phosphorescence intensity of K-phenylpropiophenone (Aem=450 nm) with varying conditions.

Patemo-Buchi reactions, 238-255 Pauli s exclusion principle, 19,24,31,40 Perturbation, external heavy atom, 145 Perturbation theory time dependent, 53 Phantom triplet, 229 Phase-shift method, 309, 311 a-phosphorescence, 129 -phosphorescence, 157 Phosphorescence... 

Application of the microwave pulse with a frequency of 2886 MHz to Pd(2-thpy)2 leads to a strong increase of the phosphorescence intensity, when monitored at the electronic origin at 18,418 cm E The recovery signal (after the pulse) is depicted in Fig. 9b. Its time dependence is best fit by a biexponential function... 

The quantum yields of fluorescence and phosphorescence, 4>f and d>p, may be determined experimentally by means of a fluorescent standard such as a rhodamine B solution whose independent of the exciting wavelength within a wide range. Lifetimes rp and rp are also experimentally accessible through time-resolved fluorescence measurements (phase method or single-photon counting) or by measuring the time dependence of phosphorescence. (Cf. Rabek, 1982.) In Table 5.2 the observable quantities and their relationship to rate constants are collected. 

Therefore, the relaxation is proportional to the width of the DOS, a. Furthermore, the time dependent relaxation of the phosphorescence can be measured to actually determine the true width of the triplet DOS of polyfluorene as shown in Fig. 17. 

Non-exponential phosphorescence decay is frequently observed for various aromatic chromophores molecularly dispersed in polymer matrices. Various possible mechanisms for non-exponential decay are reviewed, and a dynamic quenching mechanism by polymer matrices including the effect of a time-dependent transient term in the rate coefficient is discussed in some detail. The biphotonic triplet-triplet annihilation mechanism is also introduced for the non-exponential decay under high-intensity and/or repeated laser irradiation. 

Time-Dependent Phosphorescence Spectra of Polymers. Although a strong similarity exists between phosphorescence spectra of vinyl aromatic polymers and the corresponding monomeric analogues, it is interesting to focus attention upon the differences which exist between these spectra. A sample comparison is provided in Figure 1 between NEC and PVCA both as dilute solutions in MTHF at 77 K (23). Both spectra are recorded using comparable conditions and instrument parameters. 

For low excitation conditions, i. e. where the monomolecular decay prevails 7tta[ ]2<< / o[T ]> time dependence of the phosphorescence intensity derived from Eq. (16) is ... 

Turkey and Galley (201) have shown that the phosphorescence band in LADH around 400 nm is split at low temperatures into separate peaks at 405 and 410 nm. From the time dependence of the bromide quenching, they concluded that the 410 peak arises from a tryptophan in a more hydrophobic environment than that responsible for the 405 nm peak. The 410 nm peak can, thus, in all probability, be assigned to Trp-314 which is buried deep in the hydrophobic subunit interaction area, whereas Trp-15 is exposed to the solvent (Section II,C). 

From magnetic resonance spectroscopy [49] it is well-known that IB effects are adequately circumvented by the tricks of a spin echo experiment. For instance, in a two-pulse echo experiment, IB effects are averaged out and one probes spin dephasing determined by time-dependent fluctuations characteristic of HB only (and not IB). More specifically, a nll-r-n microwave pulse sequence is applied, where the first nil pulse creates a coherent superposition state for which a la = 1 and the n pulse, applied at time r after the first pulse, generates a spin coherence (the echo) at time 2r after the initial pulse. The echo amplitude is traced with r. The echo amplitude decay time is characteristic of the pure dephasing dynamics. For phosphorescent triplet states it is possible to make the echo optically detectable by means of a final nil probe pulse applied at time f after the second pulse [44]. In Fig. 3b, the optically detected echo amplitude decay for the zero-field transition at 2320 MHz of... 

With these and similar experiments in zero field and also from the time dependence of the Zeeman components of the phosphorescence spectra in high magnetic fields (Bo = 5 T) [30], the decay rates fe , their radiative contributions fe[, and the relative occupation probabiUties s could be determined. Table 7.4 contains the... 

Suitable molecules covering the range of interest were investigated by measuring the emission and excitation spectra of the steady-state photoluminescence and of its phosphorescence component (at a fixed time delay after excitation with a pulsed light source) as well as the time dependence of the phosphorescence in the time regime above ca. 5 ps. 

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