THIONINE-TRIETHYLAMINE INTERACTIONS IN MIXED-SOLVENTS

Addition of triethylamine (TEA) to thionine (Th+) solutions in CH3CN/H2O(9:1, v/v) and CH3OH/H2O (9:1, v/v) solvents leads to shift in absorption maxima from 597 nm to 500 nm and from 600 nm to 515 nm respectively. The spectral changes with various TEA concentrations have isosbestic points at 533 nm and 544 nm. Various types of interactions have been analysed to show that the charge transfer initiated redox disproportionation of the dye does not explain the observed data and the interaction in fact involves 1:1 complexation of the lewis acid/base type with K = 2.60 x 10(2) mol-1dm3 in CH3CN/H2O and 0.33 x 10(2) mol-1dm3 in CH3OH/H2O solvent.