Syntheses and UV-visible spectroscopic properties of new ‘fluorophilic’ fluorine- and perfluoroalkyl-substituted solvatochromic pyridinium<i>N</i>-phenolate betaine dyes
Syntheses and negative solvatochromism of three new ‘fluorophilic’ fluorine- and perfluoroalkyl-substituted pyridinium N-phenolate betainedyes 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 betainedyes 1 and 2, used to establish an empirical scale of solvent polarity, called the ET