The Hammett acidity function H0 in trifluoroacetic acid–dichloromethane mixtures

The acidity function (H0) of solutions of trifluoroacetic acid (TFA) in dichloromethane was measured by the indicator method at 298 K in the whole concentration range. The H0 value for the most acidic solution studied (12.93 M trifluoroacetic acid) is −3.09. The equation describing the dependence of H0 on the acid concentration was determined. The obtained quantitative data were used for a spectrophotometric study of the basicity of 2,9,16,23-tetra-tert-butylphthalocyanine. Two forms with different UV/vis spectra were observed and their stability constants determined.