Photophysical properties of safranine O in protic solvents

MARÍA L. GÓMEZ; CARLOS M. PREVITALI; HERNÁN A. MONTEJANO

SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY.

Elsevier B.V.

Año: 2004 vol. 60 p. 2433 - 2439

1386-1425

Spectroscopic and photophysical properties of safranine O (Sf) were investigated in binary water/solvent mixtures. It was found that these properties are strongly solvent-dependent. A blue shift is observed for both the ground-state absorption and the triplet?triplet main absorption band when the solvent polarity augments. At the same time a red shift of the fluorescence emission band takes place. These facts are interpreted in terms of higher dipole moment of the dye molecule in the S1 state as compared with the S0 state, while a decrease in the dipole moment of the triplet state Tn with respect to the triplet state T1 occurs. The Stokes? shift and the fluorescence lifetime shows a linear correlation with the ET(30) parameter, while a non-linear behavior is observed when a correlation with models of a continuous dielectric solvent is attempted. These results suggest the operation of strong specific interactions of Sf with solvent molecules, most likely hydrogen bonding. From fluorescence lifetime and quantum yield determinations, as well as intersystem-crossing quantum yields, the solvent dependence of the photophysical kinetic parameters were obtained. The radiative fluorescence rate constant can be adequately reproduced by calculations based on the UV-Vis absorption and emission spectra, as given by the Strickler?Berg equation.