Solvation in highly nonideal solutions: A study of aqueous 1-propanol using the coumarin 153 probe

We have investigated the anomalous behavior of aqueous 1-propanol binary solutions using a typical fluorescence probe molecule, coumarin 153. We present data on the fluorescence lifetimes, fluorescence anisotropies, and solvent reorganization dynamics, as well as the steady-state absorption and emission spectra of coumarin 153 in the binary solutions. The rotational diffusion and solvation time constants depend strongly on the content of 1-propanol, especially at low 1-propanol mole fractions. Spectroscopic results presented here are consistent with prior light scattering [G. H. Grossmann and K. H. Ebert, Ber. Bunsenges. Phys. Chem. 85, 1026 (1981)], small angle x-ray scattering [H. Hayashi, K. Nishikawa, and T. Iijima, J. Phys. Chem. 94, 8334 (1990)], and dielectric relaxation [S. Mashimo, T. Umehara, and H. Redlin, J. Chem. Phys. 95, 6257 (1991)] data. The anomalous dynamics features likely arise from the effect of the preferential solvation due to the 1-propanol clustering. (C) 2000 American Institute of Physics. [S0021-9606(00)50605-9].