Phosphorescence self-quenching

Once again, the most recent developments have been in the area of green phosphorescent materials where phenomenal efficiencies are now beginning to be coupled with good device lifetimes. The prototypical emitter of this type is iridium-tris-2-phenylpyridine (Ir(ppy)3) used as a dopant (Scheme 3.98), usually diluted into a carbazole type host, because it is prone to serious self-quenching problems. 

In Section XIII.A this process was responsible for the delayed fluorescence. Here the self-quenching of triplets, following their electrochemical generation, lowers their quantum yield and resulting phosphorescence. 

Self-quenching of the phosphorescence supports the second-order decomposition... 

F. Kwong. H. L. Zheng. H. Che. C. M. (2001). Reduction of Self-Quenching Effect in Organic Electrophosphorescence Emitting Devices via the Use of Sterically Hindered Spacers in Phosphorescence Molecules. Advanced Materials, vol. 13, no. 16,1245-1248. 

One main reason for our limited information comes from a fact that this molecule does not phosphoresce under any conditions and the transient absorption is very weak. By applying the TG method, a remarkably shortened triplet lifetime of about 100 ns was measured in many solvents at room temperature [85] (at a lower temperature, the lifetime is 3 jrs from the TL studies [94]). Compared with the lifetimes of about a few 10 ms for pyrazine and pyrimidine at a lower temperature, the observed lifetime is quite short. The short lifetime is neither due to the self-quenching nor to the quenching by 02, but is intrinsic. The quantum yield of the triplet formation (r/)isc) was determined from the relative intensity of the two rising components, Qs/Qtot, and the energy balance relation of Eq. (34) to be 0.1, which is much smaller than that at the lower temperature. These temperature-dependent lifetimes and isc could well be explained by a model of... 

Several reviews have been written concerning the phosphorescence of intrinsic indole probes [201] and the use of triplet excited states to probe proteins [202]. Triplet tryptophan can be used to probe proteins, but its photophysics is complex, because in a homogeneous solution, the decays of the excited triplet tryptophan or indole derivatives do not usually follow first-order kinetics, due to protonation, triplet-triplet annihilation, or self-quenching [203,204]. In ad-... 

The zero pressure lifetimes and the self-quenching rate constants k, of fluorescence and phosphorescence are given in Table 6 (Kuttner et ai, 1977b). The difference in the zero pressure lifetimes of fluorescence and phosphorescence for the two isotope species is due to the normal deuterium... 

Scheme 7.2 Fluorescence (F) and phosphorescence (P). Normal fluorescence (F) arises from Sj (independently from which singlet has been initially reached, and thus its shape is not affected by the energy of the wavelength used, provided that this has been absorbed. This is the Vavilov rule, rationalized by Kasha as due to the fact that internal conversion among states of the same multiplicity is always the fastest process, see Chap. 3). Delayed fluorescence may involve triple-triplet annihilation, in which self-quenching of the triplet leads back to the singlet Sj, with the usual fluorescence spectrum but the triplet lifetime...

Phosphorescent inclusion complex can be used to probe heme accessibihty in heme proteins [27]. The phosphorescence lifetime of 6-bromo-2-naphthyl sulfate (BNS) is several hundred microseconds and is self-quenched. Quenching of BNS phosphorescence does not occur for the non-heme protein lysoz3me and apomyoglobin but occurs by a dynamic mechanism with a quenching constant of 12 X lO M s for cytochrome c and myoglobin and with a quenching constant of 6.2 x 10 s for protoporphyrin IX. The phosphorescence of... 

Chromatographic agents, solvents, and samples can frequently reduce the luminous output produced by interactions between the radioactive sample and the fluor of the scintillation fluid. This effect, known as quenching, directly reduces the counting efficiency of the system and can result in significant quantitation errors if not taken into account. In addition to quenching, other interfering processes such as chemiluminescence, phosphorescence, and efficiency losses due to self-adsorption of labeled compounds on the TLC adsorbent can affect quantitative measurement (5,49,50,51). 

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