Spectral investigations of preferential solvation and solute-solvent interactions of 1,4-dimethylamino anthraquinone in CH2Cl2/C2H5OH mixtures

The optical absorption and IR spectra of 1,4-dimethylamino anthraquinone (1,4-DMAAQ) in CH2Cl2/C2H5OH mixtures have been investigated. The preferential solvation of 1,4-DMAAQ in CH2Cl2/C2H5OH mixed solvents has been studied by monitoring the charge transfer band of 1,4-DMAAQ. The optical absorption spectral study indicates that 1,4-DMAAQ is preferentially solvated by CH2Cl2 in CH2Cl2/C2H5OH mixtures. This can be confirmed by the observed index of preferential solvation value (δs1) as well as higher mole fraction of CH2Cl2 in the solvation microsphere (x1L) than in the bulk solvent (x1). The CH2Cl2 molecules become more available to enter the solvation shell of 1,4-DMAAQ because of the hydrogen bonded clusters formed by ethanol molecules. This is also evident from the non-linear behavior of the transition energy (E12) as well as the absence of synergistic behavior. IR spectral studies show that the observed shifts in the ν(CO) and ν(NH) of 1,4-DMAAQ are due to the dipole-dipole interaction between the 1,4-DMAAQ and the associated ethanol.