The Py scale of solvent polarities

The relative intensities I 1 /I 3 of the vibronic bands of pyrene fluorescence in 94 solvents and the vapor phase are reported. These values, ranging from 0.47 (vapor) to 1.95 (dimethyl sulfoxide) form the Py scale of solvent polarities. This scale is compared to other scales of solvent polarity, particularly the π* scale of Kamlet and Taft in order to assess the contributions of various factors (dipolarity/polarizability, hydrogen bonding, etc.) to the solute–solvent interaction.