Photophysical Properties of Amino- and Dimethylamino Salicylates in Neat and Binary Solvent Mixtures

The solvation characteristic of 2-methoxy-4-aminobenzoic acid methyl ester (MABAE) and 2methoxy-4-dimethylaminobenzoic acid methyl ester (MDABAE) in the S0, S1(LE) and S1(ICT) states has been determined by means of solvatochromic shifts in neat and binary solvent mixtures. The multiple linear regression analysis of Kamlet et al. indicates that non-specific dielectric dipoledipole and specific hydrogen-bonding interactions play almost an equal role in defining the position of the absorption and fluorescence maxima. On the basis of the performed analysis of normalized solvatochromic shifts, it has been shown that both solutes are preferentially solvated. For cyclohexane-ethanol (CH-EtOH) binary mixtures the preferential solvation characteristics in the S0, S1(LE) and S1(ICT) states are determined predominantly by the hydrogen-bonding interactions. For both molecules under study the electric dipole moment in the S0, S1(LE) and S1(ICT) states as well as the outer-sphere solvent reorganization energy (λout), intramolecular reorganization energy (λin), and destabilization energy (Edest.) have been determined.