Solvatochromic and halochromic properties of some phosphonioarylimino- and phosphonioarylazo-phenolate betaine dyes

Abstract

The synthesis and characterisation of two new solvatochromic phosphonium betaine systems is reported. Both 4-N-(o-triorganophosphoniobenzylidene) aminophenolate and 4-(o-triphenylphosphoniophenylazo)phenolate betaine dyes exhibit negative solvatochromism, consistent with a transition to a significantly less polar excited state. The solvatochromic properties of these compounds are compared with those of a related series of pyridinium iminophenolate betaines, and also with those of the Reichardt betaine dye. Cation-induced halochromism is also observed on treating acetonitrile solutions of the phosphonium betaine dyes with alkali halides.