The self-aggregation of Rhodamine-6G [1 x 10-6 to 4 x 10-4] in water and in aqueous solution of urea (0.1-0.3M) has been investigated by recording electronic spectra in the wavelength range 460 to 600nm. Analysis of the spectral data yielded the dimer dissociation constant, individual characteristic monomer and dimer spectra. By applying the excitaton model for the first time, the interaction energy between the Rhodamine-6G molecules in dimer species has been evaluated. Further information about the dimer geometry and twist angle between the dipoles of the Rh-6G molecules has been obtained. Similarly, data have also been obtained for aqueous solution of Rh-6G in urea. The significant observation is the change in dimer geometry from sandwich type to end-onend type in the presence of urea. It is observed that the contribution to the interaction energy is mainly from van der Waal’s type and dispersion forces in addition to short-range forces involving multi poles. However, the contribution from hydrogen bonding interaction between Rh-6G and water molecules is found to be significantly low. It is proposed that water structural effects and hydrophobic interactions are the major factors in the phenomenon of aggregation.
