Picosecond Spectroscopy in Solutions: The Excited-State Solvation Dynamics of 9,9'-Bianthryl

摘要

Details of the systems used for obtaining from samples excited with a single laser pulse were measured in 10 nm bandwidths with 6 ps resolution using a computer-controlled streak camera system. Absorption measurements made with the same system measured, with a resolution of .01 OD, the time-dependent attenuation of the emission from a dye solution by a second sample. Limited results from a Raman spectrometer in a pump-probe configuration are also described, as are the limitations inherent in such measurements. The applicability of coherent Raman techniques to solution measurements is discussed. Measurements of the solvation dynamics of 9,9'-bianthryl in alcohol, deuterated alcohols and alcohol-alkane mixtures at several temperatures are described. Complex triexponential decays were observed, correlating with dielectric relaxation, alcohol concentration and solvent viscosity. No dynamics were observed in nonhydrogen-bonding solvents irrespective of polarity. These results combined with evidence of excited-state proton transfer suggest that BA initially (approx.20-50 ps) forms an unsolvated charged transfer state which then forms hydrogen bonds to the solvent (approx.50-500 ps, increasing with viscosity). Other interpretations are discussed. (ERA citation 11:036396)