Spectroscopic study of the dimerization of rhodamine 6G in water and different organic solvents

Abstract

The self-association or aggregation of rhodamine 6G (R6G) in aqueous and aqueous solutions containing primary alcohols, urea and tetraethylammonium bromide has been studied by using spectrophotometry. The concentration range from ~1×10−5M to ~2×10−4M was selected to avoid trimer and higher aggregate formation. The observed spectra were processed by chemometric technique to get the dimer dissociation constant and individual monomer-dimer spectra. The geometry of dimer, the twisted angle and the interaction energy between the molecules of rhodamine 6G in the dimeric species have been explained by employing molecular exciton theory. The effect of solvent has been checked by measuring the absorbance in the aqueous solutions of different solvents such as ethanol (10−1M to 10−4M), propan-1-ol (10−1M to 10−4M) and butan-1-ol (10−1M to 10−4M) and the properties evaluated have been explained in terms of the role of low concentration of solvent molecules in dye aggregation and there by affecting degree of association, interaction energy, dipole moments in monomer and dimer forms. Similar experiments were made on the aqueous dye solutions containing urea (~0.1M–0.4M) and tetraethylammonium bromide (~0.005M–0.1M). Also we have studied the concentration and solvent effects on the fluorescence emission spectra of rhodamine 6G (R6G) dye. The number of different pure organic solvents such as methanol, ethanol, propan-1-ol, butan-1-ol and chloroform along with water as well as mixtures of organic solvents/urea/tetraethylammonium bromide (TEAB) in water has been used. The results have been explained in terms of bonding between dye molecule and solvents which affects the arrangement of molecules there by affecting extent of aggregation.