Study of preferential solvation of 2,6-diaminoanthraquinone in binary mixtures by absorption and fluorescence studies

The role of solute–solvent and solvent–solvent interaction on the preferential solvation characteristics of 2,6-diaminoanthraquinone (DAAQ) has been analysed by monitoring the optical absorption and fluorescence emission spectra. Binary mixtures consist of dimethylformamide (DMF)–ethanol (EtOH), DMF–dimelthylsulfoxide (DMSO), benzene (BZ)–DMF and acetonitrile (ACN)–DMF. The optical absorption spectra maximum and emission spectra maximum of DAAQ show the changes with varying the solvents and change in the composition in the case of binary mixtures. Non-ideal solvation characteristics are observed in all binary mixtures. It is found that at certain concentrations two mixed solvents interact to form a common structure with a ν12 (wave number in cm−1) value not always intermediate (ν1 and ν2) between the values of the solvents mixed. Synergistic effect is observed in the case of DMF–EtOH mixtures. The preferential solvation parameters local mole fraction X2L, solvation index δS2, exchange constant K12 are calculated in all binary mixtures expect in the case of DMF–BZ mixture and DMF–EtOH mixture in the ground state. We have also monitored excitation wavelength effect on the probe molecule in aprotic polar and protic polar solvents.