The novel functional chromophores based on squarylium dyes

. They are two principal types: the 1,2-bisdonorsubstituted derivatives, and the 1,3-bisdonor-substituted derivatives. The former are essentially merocyanines and have no distinctive properties, whereasthe latter represent a unique type of chromophore, which is neither a merocyanines nor cyanine and hasexceptional light absorption characteristics. They also have many func tional applications based on their specialproperties. Thus it was the objective of this research project to synthesize a range of 1,3-squarylium dyes ofwidely differing structural types, and to investigate th eir light absorption and fluorescence properties in general,and the color change properties of appropriate examples in particular. Also in this study, the various pH-induced colour change processes were examined.