โ Scribed by Maria V. Encinas; Carlos M. Previtali; Marcelo H. Gehlen; Miguel G. Neumann
No coin nor oath required. For personal study only.
The photophysics of the excited states of safranine T and its reactions with aliphatic amines were studied in aqueous solution. The fluorescence lifetime of the singlet state was found to be 1.3 ns at 20 ยฐC in water, and increases in non-hydroxylic solvents. This state is quenched by trialkylamines with nearly diffusional rate constants. In addition to the intense absorption of the monoprotonated form of the triplet state at 820 nm, a weaker absorption at 420 nm was detected. The non-protonated form also has a residual absorption at 820 rim. The lifetime of the non-protonated triplet was found to be around 15 p.s. The monoprotonated triplet state of the dye is quenched by amines with rate constants of about 1 X 109 M-~ s-~, too high to be ascribed to a charge transfer mechanism. Similar to the reaction in organic solvents, this reaction proceeds by a proton transfer mechanism, leading to the non-protonated form of the triplet state. This form is then quenched by another amine molecule to give the corresponding semireduced species.
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