Eosin triplet lifetimes

Triplet Lifetimes and Triplet Formation Efficiencies of Eosin Di-Aniona... 

We have performed laser flash photolysis experiments in ethyl acetate/20% methanol under conditions in which triplet-triplet annihilation is not important. We achieve these conditions by using Eosin concentrations higher than 1 x 10 5 M and low pulse energies in order to obtain clean exponential decays for the triplet. Determination of the triplet lifetime at different Eosin and amine concentrations allows us to obtain the rate constants collected in Table 5. A summary of our observations is as follows ... 

Thermal repopulation, where the triplet level is close enough to the singlet level that the singlet state can be thermally populated from the triplet. Sometimes called E-type delayed fluorescence, after the compound eosin (4.4) which exhibits this behaviour. The lifetime of E-type delayed fluorescence is equal to the triplet lifetime. Other materials which exhibit E-type delayed fluorescence are palladium porphyrins (5.4) and thiocarbonyls (11.21). 

The triplet lifetime depends on the access of Op to a given binding site of eosin isothiocyanate in the host profein. Thus, the triplet lifetime reflects the proximity of a binding site to the bulk medixim and/or the flexibility of protein chains which cover a binding site. 

The spectroscopic details of the eosin probe were reviewed elsewhere (5,9). Fig.1 shows a typical trace for the time-course of the absorption changes at 515 nm of eosin-SCN when bound to isolated CF1 after excitation with a short (10 ns FMWH) flash from a Nd-YAG-Laser. The rapid rise of absorption is due to ground state depletion of eosin and the decay to its subsequent repopulation from the excited states. The decay of laser induced eosin absorption changes is a measure of the triplet lifetime. It depends on the oxygen pressure. Binding of eosin-SCN to CF1 can provide a partial... 

The delayed fluorescence produced by triplet-triplet quenching is to be sharply differentiated from that observed with eosin or proflavine hydrochloride. The latter type has the same lifetime as the triplet and its intensity is proportional to the first power of the rate of light absorption. It is produced by thermal activation of molecules from the triplet level to the excited singlet level and can occur with any substance for which... 

Photosensitized electron injection in colloidal TiOz has been reported by Moser and Gratzel as part of a scheme to photoreduce water [155], Moser et al. [156] and Rosetti and Brus [157] saw the formation of semioxidized Eosin by monitoring its absorption in the visible and by Raman spectroscopy. No oxidation of the triplet of Eosin adsorbed in Ti02 is observed, the lifetime... 

B. Phosphorescence lifetimes are typicaUy near l-IO ms. Assume that the nahiral fifetime for phosphores cence emission of these compounds is 10 ms and that the nonra< ative dec rates of the two compomds are the same for the triplet state as for the singlet state. Estim e the phosphorescence quantum yields of eosin and Er B at room tempoature. 

Examples of heavy-atom enhanced intersystem crossing to the triplet state can be found in the halogen substituted derivatives of fluorescein (F1) in aqueous solution. Using the streak camera system, the fluorescence lifetimes of fluorescein (F1,. 6 ns), eosin Y (Fl.Brj, 1.2 ns), tetrachlorotetraiodofluorescein (Fl.Cl. Ii, 1.10 ns) and erythrosin Y (Fl.I/j, 0.11 ns) have been... 

E-type delayed fluorescence. As defined by the lUPAC Gold book [2], this is the process in which the first excited singlet state becomes populated by a thermally activated radiationless transition from the first excited triplet state. Since in this case the populations of the singlet and triplet states are in thermal equilibrium, the lifetimes of delayed fluorescence and the concomitant phosphorescence are equal. This process takes its name from eosin and is typically observed with dyes, where the Si-Ti gap is small. 

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