Quenching of triplet state oxygen

The oxygen quenching of triplet state molecules has been the subject of numerous experimental and theoretical studies [Refs. 60, 81, 326, 331, 332,379,486,654]. The processes expected to be involved in the quenching of triplet state molecules are... 

OXYGEN QUENCHING OF TRIPLET STATES IN ISOLATED PHOTOSYSTEM 2 REACTION CENTRES A MECHANISM FOR PHOTODAMAGE. 

Oxygen Quenching of Triplet States in Isolated Photosystem 2 Reaction Centres A... 

Gamer, A., Wilkinson, F., Quenching of Triplet States by Molecular Oxygen and Role of Charge transfer Interactions, Chem. Phys. Lett. 1977, 45, 432 435. 

Phosphorescence is associated with formally spin-forbidden transitions such as T,—> Sq. It occurs rarely in fluid solution due to efficient quenching of triplet states by oxygen. Phosphorescence is usually observed from molecules that are frozen in glassy solvents or adsorbed on a solid substrate such as filter paper—so-called room-temperature phosphorescence. 

In the theory outlined above we assumed a weak collision complex between the triplet state of the organic molecule and the triplet state of oxygen, and we were able to account for the rate of quenching of triplet states by O2 on this basis. Further investigation into the nature of this interaction indicates that it is not necessarily weak (7). 

Equation (9) is included because it probably accounts for the efficient quenching of triplet states by oxygen or nitric oxide. 

Moreover, carotenoids may quench electronically excited states and scavenge free radicals formed in the retina, and therefore protect biomolecules from oxidative damage. Due to the low energy level of the first excited triplet state ( Car), carotenoids (Car) can act as efficient acceptors of triplet state energy from photosensitizers (S) (Equation 15.1), such as all-tra .s-retinal, the photosensitizers of lipofuscin (Rozanowska et al., 1998), or singlet oxygen C02) (Equation 15.2) (Cantrell et al., 2003) ... 

Fig. 34 Photosensitized singlet oxygen production 1/ r is the general (radiative and non-radiative) rate constant of the transition Si So fcsi is the rate constant of singlet-triplet conversion tt is the lifetime of the triplet, T1, electronic state of PS kj is the second-order rate constant of singlet oxygen quenching of the Ti state of PS tl and nr are the radiative lifetime and rate constant of all intramolecular nonradiative energy relaxation processes of O2 ( Ag)...

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