Effects of urea and thiourea on the absorption and fluorescence behaviours of the dye safranine T in micellar medium

The absorption and fluorescence extents of the dye Safranine T (ST) are influenced by micellar solution. The critical micellar concentration (CMC), aggregation number and micelle-ST binding constant of ionic surfactant, sodium dodecylsulphate (SDS) and nonionic surfactants polyoxyethylene (20) sorbitan -monolaurate, -monopalmitate, -monostearate and -monooleate (Tween-20, Tween-40, Tween-60 and Tween-80) respectively have been determined by exploiting the spectral behaviours of ST in presence of urea and thiourea. The CMC and the aggregation number of the micelles have been found to increase and decrease respectively in presence of the additives urea and thiourea. While thiourea has greater CMC increasing effect than urea, it diminishes the aggregation number of the micelles efficiently than urea. The dye-micelle binding constant has been found to decrease in presence of urea and thiourea. Thiourea also quenches the fluorescence of ST in aqueous as well as in micellar medium.