Effect of salt and solvents on the ionic solvation of p-toluidinonaphthalene sulfonate

Abstract

Fluorescence properties of p-toluidinonaphthalene sulfonate (TNS) are studied in the presence of tetra-n-butylammonium bromide (TBBr) in different solvents. In the presence of TBBr, in solvents of low polarity (tetrahydrofuran, THF), the fluorescence decay of TNS at the blue end (395 nm) is distinctly faster than that at the red end (500 nm). This is attributed to the formation of ionic aggregates involving negatively charged TNS and positively charged tetrabutylammonium ions. From the difference in the lifetimes at the red and blue ends, the ionic relaxation rates are obtained. In solvents of moderately high polarity (dimethylformamide, DMF) no such aggregates are detected and the decay at the red end is very similar to that at the blue end. In highly polar aqueous media, however, micellar aggregates of TBBr are formed, but there is no difference in the decay at the red and blue ends. The micellar aggregates in aqueous media remain unaffected in the presence of 3 mol dm^–3 urea.