This paper is dedicated to Professor Peter

Abstract— Pyrene fluorescence spectra have been run in 62 solvents of widely differing solvent polarity. As has been noted previously, the intensity ratio of the first (the 0–0 band) and third bands in vibronic fine structure of these spectra are very sensitive to solvent polarity. These I1/I3 values, however, are not sensitive to hydrogen bonding aspects of solvent‐solute interactions. Correlations are reported with Winstein's Y values and with Dimrotb's ET values. On this basis the I1/I3 values for pyrene fluorescence are suggested as the basis for a new empirical scale of solvent polarity, called the Py scale, which offers certain conveniences over other scales of solvent polarity.

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The diol 2 was converted by treatment with potassium iodide in polyhydrogen fluoride – pyridine into a mixture of the diiodide and homohypostrophene 6. The diol 10 under the same conditions gave the ether 14. Treatment of the mixture of 5 and 6 with sodium in boiling tetrahydrofuran gave an easily-separable mixture of 6 and 7.

The bromo compounds 3-11, 13, and 14 have been prepared and characterized by analysis, IR and NMR.