The interaction of aliphatic amines with safranine T in aqueous solution

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 degrees C 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 nm. The lifetime of the non-protonated triplet was found to be around 15 mu s. The monoprotonated triplet state of the dye is quenched by amines with rate constants of about 1 X 10(9) M(-1) s(-1), 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.