SYNTHESIS AND CHARACTERIZATION OF NEW TYPES OF 4-[2-(2-HYDROXYARYL)ETHENYL]PYRIDINIUM BETAINE DYES

Two types of pyridinium betaine dyes, 4-[4-(2-arylethenyl)-l-pyridinio ]phenolates and 2-[2-(1-aryl-4-pyridinio)ethenyl]phenolates, which hav e a chromophore either of ET-30 type or the stilbazolium betaine type, have been synthesized. Both types of dyes show negative solvatochromi sm in various solvents, the intensity of chromism depending upon the p olarity of the solvent. Betaines (11a-c) have the possibility of two b etaine structures, the ET-30 or the stilbazolium betaine types. The tr ansition energies of 11a-c as well as 11g-i are linear with the same s lope against the E(T) (30) scale of solvent polarity. Therefore, the s tilbazolium betaine structure of 11a-c contributes to the negative sol vatochromism. The dyes prepared could be an indicator of solvent polar ity.