Determination of solvatochromic solvent parameters for the characterization of gas-expanded liquids

Solvatochromic shifts of six probe indicators {4-nitroaniline, 4-nitroanisole, 4-nitrophenol, N,N-dimethyl-4-nitroaniline, 4-(2,4,6-triphenylpyridinium)-2,6-diphenylphenoxide and 2,6-dichloro-4-(2,4,6-triphenyl-1-pyridinio)phenolate} have been measured in binary mixtures of carbon dioxide with acetone and methanol at 35 and 40 °C over the entire range of solvent composition. The indicators were used to specify the solvatochromic solvent parameters (ET(30), α, β, and π*), which were calculated from the solvatochromic shifts of the maximum absorbance peak ( ν max ) observed by means of UV–vis spectroscopy.