Phosphorescence decays

Starting C cells (brown) = 0 (So for the phosphorescence decay path) Starting C" cells (yellow) = 0 (So for the nonradiative decay from state Ti)... 

In principle, measurement of the phosphorescence characteristics of samples obtained after extraction of polymers with organic solvents may also yield useful information regarding the nature and concentration of the additives present. Parker and Hatchard [157] have examined the possibilities of phosphorescence measurements for V-phenyl-2-naphthylamine. Although it should be possible to determine various analytes simultaneously by correct choice of ex and em wavelengths and phosphorescence decay, no pertinent reports are available. Phosphorescence finds limited application for the direct determination of additives in polymers (without prior extraction). 

Determined by phosphorescence decay at 77°K unless otherwise noted. 

Possibly the most easily observable process is the phosphorescence decay.<17) While at 77°K the decay is exponential, at 1.6°K the observed decay for compounds like pyrazine is nonexponential and is composed of three first-order decays. Thus one can determine the values of kx, ky, and kz from this decay. Typical values are shown in Table 6.2. 

For pyrazine three exponential decays of lifetime 6, 130, and 400 msec can be extracted. From these three values the 77°K rate constant for phosphorescence decay can be calculated ... 

Griseofulvin exhibits both fluorescence and luminescence. A report by Neely et al., (7) gives corrected fluorescence excitation (max. 295 nm) and emission (max. 420 nm) spectra, values for quantum efficiency of fluorescence (0.108) calculated fluorescence lifetime (0.663 nsec) and phosphorescence decay time (0.11 sec.). The fluorescence excitation and emission spectra are given in Figure 7. 

Another large band-gap electron transport host is 3-phenyl-4-(l -naphthyl)-5-phenyl-1,2,4-triazole (TAZ), which has a HOMO (-6.6 eV) and LUMO (-2.6 eV). Using TAZ1 (109) as the host, a maximum EQE (ext) of 15.5% and a luminous power efficiency of 40 lm/W can be achieved in a phosphorescent OLED the value of excited state lifetime [174]. 

From the practical point of view, the radiative decay rate kr may be assumed to be independent of the external parameters surrounding the excited sensor molecule. Its value is determined by the intrinsic inability of the molecule to remain in the excited state. The radiative decay rate kr is a function of the unperturbed electronic configuration of the molecule. In summary, for a given luminescent molecule, its unperturbed fluorescent or phosphorescent decay rate (or lifetime) may be regarded to be only a function of the nature of the molecule. 

The transient response of luminescent substances to pulsed excitation can be captured in the time domain by sampling enough data points within the time span of the decay. For example, fast digitizers are commonly employed to store phosphorescence decays. If fast digitizers are unavailable, time-correlated single-photon counting can be used to monitor fluorescence decays. 

D. J. Morantz and J. W. Wigley, The contrasting phosphorescence decay kinetics of diacetyl and aromatic ketone phosphors in polymeric matrices, Polymer Communication 26, 170-171 (1985). 

The phosphorescence decays of phenol, tyrosine, and related compounds, which had been examined extensively during the 1960s, have been reviewed by... 

Becker.(49) The lifetimes were all reported as being single-exponential. Rousslang and his collaborators have recently reexamined a number of these compounds at pH 3 and 5.(50) In general, the phosphorescence decays are biexponential, but are dominated by a longer lived component of about 3 s which comprises 98 % or more of the decay. 

Essentially nothing is known about tyrosine phosphorescence at ambient temperatures. In frozen solution, tyrosine residues have a phosphorescence decay of seconds. We would expect, however, a decay of milliseconds or shorter at ambient temperature. Observation of tyrosine phosphorescence from proteins in liquid solution will undoubtedly require efficient removal of oxygen. Nevertheless, it could be fruitful to explore ambient temperature measurements, since the phosphorescence decay could extend the range of observation of excited-state dynamics into the microsecond, or even millisecond, time range. 

T.-T. Co, J. Hoover, and A. H. Maki, Dynamics of the tyrosine triplet state from magnetic resonance saturated phosphorescence decay measurements, Chem. Phys. Lett. 27, 5-9 (1974). 

Vanderkooi et al.(m) examined the phosphorescence from tryptophan in sarcoplasmic reticulum vesicles and the purified Ca transport ATPase at room temperature in deoxygenated solutions. The phosphorescence decay is multiexponential the lifetime of the long-lived component of phosphorescence is 22 ms. Addition of ATP or vanadate decreased the phosphorescence yield. The Ca2+-ATPase of the sarcoplasmic reticulum alternates between two conformations, called Ei and E2, during Ca2+ transport. The observations were interpreted to indicate that either the binding of vanadate or phosphate to the phosphorylation site of the ATPase or the induced shift in the conformation from the i to the E2 state produced the phosphorescence quenching. 

Berger and Vanderkooi(88) studied the depolarization of tryptophan from tobacco mosaic virus. The major subunit of the coat protein contains three tryptophans. The phosphorescence decay is non-single-exponential. At 22°C the lifetime of the long component decays with a time constant of 22 ms, and at 3°C the lifetime is 61 ms. The anisotropy decay is clearly not singleexponential and was consistent with the known geometry of the virus. 

The lifetime of triplet acetone at 25° in the vapor phase, as measured from the rate of decay of phosphorescence, is 0.0002 sec,318 so that the rate of decay is 5 x 103 sec-1. This figure represents the sum of the rates of all decay processes. Since the data at 40° 308 indicate that decomposition and internal conversion of triplet acetone occur approximately 40 times as fast as emission, the radiative lifetime must be on the order of 0.01 sec. Measurements of the rate of phosphorescence decay from solid acetone at 77°K, where all activated fragmentation and most radiationless decay normally disappear, have actually yielded values approximately one-tenth as large as that obtained in the gas phase at room temperature.319 The most recent measurements of the lifetime of triplet acetone at 77°K in frozen glasses does indeed yield an estimate of 0.01 sec for the radiative lifetime of triplet acetone.318... 

Electron transfer kinetics from the triplet excited state of TMPD to PA in polystyrene has been monitored by phosphorescence emission decay in ref. 85. The rate constant has been found to be invariant over the temperature interval 77-143 K. Parameters ae and ve calculated from the phosphorescence decay using eqn. (12) were found to be ae = 3.46 A and vc = 104 s 1. 

Sj - S0, the interconversion into the triplet state Tlf is also possible. The characteristic time of the phosphorescence decay of MP, on the other hand, is rather large and amounts to 10-2 s. (For a review of the physical and chemical properties of MP, see, for example, ref. 52.)... 

The phosphorescence decay kinetics of the triplet excited states of CuP molecules (Fig. 18) is adequately described by the equation... 

Fig. 18. The kinetics [63] of the phosphorescence decay of tetramethyl ether of copper hemato-IX porphyrin (CuP) in the presence of various concentrations of C(N02)4 1, 0 M 2, 0.3 M and 3, 0.6 M. The points represent the experiment and the solid lines reflect the calculation using eqn. (12) of Chap. 7.

Several authors have reported that in polar solvents the overall phosphorescence decay of some phenyl alkyl ketones has a long- and a short-lived component they attribute this to simultaneous emission from 3(77,77 ) and 3(77,77 ) states that are not in equilibrium with each other. This interpretation assumes that phosphorescence, a spin-forbidden process, occurs more rapidly than internal conversion from T2 to 7 and therefore seems improbable. It is more likely that one of the phosphorescent species is a photochemical product of the original ketone.13,14... 

T-6T have been determined (95CP(201)309). A computational work in this field appeared (02JCC(23)824). Two photon absorption in thiophene and bithiophene induces triplet formation with a phosphorescence decay within about 20 ps (99SM(101)624). 

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