Rate constant of phosphorescence

The formation of product C, on the other hand, proceeds in two steps with the efficiencies 1 r/isc. (Equation 3.32) and 3rjc 3/cr/(3/cr I 3/qsc I 3/cph + 3kqcq) where 3kr refers to the reaction from the lowest triplet state Ti leading to the photoproduct C, 3/cph is the rate constant of phosphorescence, 3/cisc that of intersystem crossing to the ground state and 3/cq is the second-order rate constant for quenching of I) by a quencher q. The overall quantum yield for the formation of product C is equal to the product of the efficiencies of the two reaction steps, (I visc Vc- Many authors do not distinguish between... 

SPP, basicity, SB, and acidity, SA, of solvent. The variation of rate constant of phosphorescence, kp, in solvents mixtures is described by the equation ... 

Several fundamental luminescence parameters were calculated for the anion of p-aminobenzoic acid on sodium acetate (11). The triplet formation efficiency (( ), the rate constant for phosphorescence... 

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 ... 

Other groups may cause shortening of the lifetime. The phosphorescence of parvalbumin is quenched by free tryptophan with a quenching rate constant of about 10s M i s l (D. Calhoun, unpublished results). A more extensive survey of proteins or model compounds with known distances between tryptophans is needed to study how adjacent tryptophans affect the lifetime. It should be noted that at low temperature the phosphorescence lifetime of poly-L-tryptophan is about the same as that of die monomer.(12) This does not necessarily mean that in a fluid solution tryptophan-tryptophan interaction could not take place. Thermal fluctuations in the polypeptide chain may transiently produce overlap in the n orbitals between neighboring tryptophans, thus resulting in quenching. 

Fig. 14. Schematic representation of energy levels and transitions for fluorescence and related processes kic, rate constant for interval conversion fcF, rate constant for fluorescence fcISC, rate constant for intersystems crossing fc[cp> rate constant for internal conversion from triplet state kp, rate constant for phosphorescence S, energy level for the first excited singlet state after solvent rearrangement for a polarity probe in a polar solvent.

In aromatic hydrocarbons, the radiationless transitions from the triplet to the ground state are dominated by CH stretching vibrational modes. In these hydrocarbons perdeuteration reduces kJsc and consequently enhances kp, the rate constant for phosphorescence emission. The lifetime rp, is considerably reduced. The reduction of kjsc (T, 5,) which... 

Spin, Mossbauer, fluorescent and phosphorescent labels were introduced into the various portions of the system being studied. They were covalently bound to the RC surface groups, adsorbed by the hydrophobic segments of the protein and membrane, and 57Fe atoms were incorporated by way of biosynthesis into iron-containing proteins. Then, in the same samples, the dependence on temperature, moisture content and viscosity was measured for the label mobility and the rate constant of electron transfer... 

The differences observed in the temperature dependences of luminescence for europium and terbium(III) clathrochelates can also be due to the absence of back energy transfer from encapsulated Eu cation to the clathrochelate ligand. The expression for the rate constant of metal-to-ligand back transfer contains the AE value, which is the energy difference between the triplet level of the bipyridine fragment and the metal ion phosphorescence level. The back transfer rate for the europium (III) ion is much less than that for the terbium(III) ion. This process is essential for the terbium(III) ion, and this is confirmed by differences in the temperature dependence of excited-state lifetimes for europium and terbium (III) clathrochelates in D5O the luminescence of the terbium(III) complex at 77 K is approximately an order of magnitude higher than that at 300 K, whereas for the europium(III) complex, it does not depend on temperature. 

From the above estimate of the lifetime of a singlet state the rate constant of fluorescence kf - I/tq is obtained as kf = W-IO s , depending on the value of the oscillator strength /. Phosphorescence, on the other hand, is a spin-forbidden process with a much smaller rate constant, k - I0 -I0 ... 

Table 2. Spectral-Luminescence groups and types of organic molecules and some of their characteristics (Molar absorptivity of the longest wavelength band - emax Rate constants of fluorescence -kfl, phosphorescence - kph, intersystem crossing - kisc Lifetimes of fluorescence - zih phosphorescence - Tph)...

Temperature, pressure and deuterium effects on the phosphorescence decay-rate constant of naphthalene in single crystals of durene show that photo-induced hydrogen abstraction... 

TABLE 5 Quantum Yields and Lifetimes t of Phosphorescence aud Oxygen Quenching Rate Constants of 1-Bromonaphthalene-Glucosyl-p-CD-alcohol Complexes in Water ... 

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