Syntheses and UV–visible spectroscopic properties of new ‘fluorophilic’ fluorine‐ and perfluoroalkyl‐substituted solvatochromic pyridinium N ‐phenolate betaine dyes

Syntheses and negative solvatochromism of three new ‘fluorophilic’ fluorine‐ and perfluoroalkyl‐substituted pyridinium N ‐phenolate betaine dyes 3 – 5 are described in order to obtain new zwitterionic dyes which should be less basic and better soluble in perfluorinated solvents than the solvatochromic standard betaine dyes 1 and 2 , used to establish an empirical scale of solvent polarity, called the E T ( 30 ) or $E_{T}^{N}$ scale. The new betaine dyes 3 – 5 were designed to allow an extension of the existing E T ( 30 ) scale to new solvents. Copyright © 2001 John Wiley & Sons, Ltd.