Photophysics and photochemistry of phenosafranin dye in aqueous and acetonitrile solutions

Abstract

The singlet and triplet excited state properties of phenosafranin dye were characterized in aqueous and acetonitrile solutions. The singlet excited state exhibited an absorption maximum at ∼ 430 nm and a lifetime of 930 ps in aqueous medium. The transient absorption spectra of the protonated and unprotonated forms of excited triplet were investigated by the laser flash photolysis technique. The protonated phenosafranin triplet had absorption maxima at 380 nm (ϵ = 11 000 M −1 cm −1), 615 nm (ϵ = 9700 M −1 cm −1) and 665 nm (ϵ = 10 800 M −1) and the unprotonated phenosafranin triplet had absorption maxima at 410 nm (ϵ = 8800 M −1 cm −1), 700 nm (ϵ = 6900 M −1 cm −1) and 790 nm (ϵ = 11 600 M −1 cm −1) in aqueous medium. The p K a of the protonated triplet phenosafranin was found to be 7.25. Diffusion-controlled quenching of the excited phenosafranin triplet by amines led to the reduction of the dye. The absorption spectra of the semireduced phenosafranin, which was characterized in acetonitrile, exhibited absorption maxima at 440 nm (ϵ = 29 000 M −1 cm −1) and 870 nm (ϵ = 19 000 M −1 cm −1).