NO self-quenching

In an earlier work Basco, Callear, and Norrish22 measured approximate quenching constants. There appears to be an error in Table 4 of ref. 22 which lists the radius of electronic quenching. If we assume that the quenching constants are proportional to the electronic radius (as opposed to the square of the radius) and use a proportionality constant from the data quoted in ref. 78, we can obtain reasonable values. Apparently this was done in ref. 78 when referring to the data of ref. 22. Furthermore, values of Basco, Callear, and Norrish are too low, because correction for the NO self-quenching was not made. As the NO pressures were 2-5 torr, the self-quenching was more effective than emission. 

The behavior of the triplet state has been examined to a limited extent. The radiative lifetime must be long since in a glassy matrix it is 10 sec or more.5 For a molecule of the high symmetry of benzene there is no reason to expect that it would be appreciably less in the gaseous phase. The lifetime of the lB2u state is about 5 x 10"7 sec55 and there is probably no self-quenching in benzene. 

Callear and Smith monitored the emission from all three spectroscopic levels. When the 8 bands were monitored, NO pressures from 2 to 12 torr were used. The variation in pressure had little effect as the half-pressure for the self-quenching is >15 torr. When the y bands... 

Precisely why the alkali atoms exhibit self quenching behavior so different from the rare gases is not fully understood, although it is no doubt due to the longer range interaction of the alkali atom with the Rydberg electron, and perhaps the Rydberg ion core as well. 

The fluorescent properties of TRITC (mixed isomers) include an absorbance maximum at about 544 nm and an emission wavelength of 570 nm. Fluorescent quenching of the molecule is possible. Under concentrated conditions, rhodamine-to-rhodamine interactions result in self-quenching, which reduces its luminescence yield. This phenomenon can occur with TRITC-tagged molecules, as well. If derivatization of a protein is done at too high a level, the resultant quantum yield of the conjugate will be depressed from expected values. Typically, modifications of proteins involve adding no more than 8-10 rhodamine molecules per molecule of protein, with a 4-5 substitution level considered optimal. 

The anthracenylmethyl lariat ether shown as (10) was reported by de Silva and coworkers (1986) as a crown that is useful for fluorescence sensing. Binding of K+ resulted in a detectable fluorescence emission signal. Recent advances in this area include the development of compounds that can sense ion pairs. The anthracenyl crown shown as (11) was designed to simultaneously sense sodium and phosphate ions (de Silva, 2003). Excitation of the complex with ultraviolet radiation results in a fluorescent output only when Na+ is complexed in the crown and the ammonium groups are bound to the anion. The complex self-quenches in the case when either no or only one of the ions is present. 

An important aspect of the photophysics of the Pt(diimine)(dithiolate) photochemistry that has received increasing attention is the ability of the excited-state complexes to undergo self-quenching. Initial work by Connick and Gray (111) showed that the lifetime of the complex Pt(bpy)(bdt) (bdt = benzene-1,2-dithiolate, 31) decreased with increasing solution concentration. The bimolecular self-quenching rate constant, calculated from a Stem-Volmer quenching analysis, was found to be 9.5 x 109 A/-1 s-1 in acetonitrile and 4 x 109 M 1 s 1 in chloroform. However, no evidence of excimer formation... 

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. 

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