ABSTRACT
Cationic polymethines have been subdivided on the basis of the nature of the acceptor and donor groups. In the dyes most used in biology and medicine, acceptor and donor groups are nitrogen. According to whether both, one, or neither nitrogens are components of rings, the dyes are respectively called cyanines, hemicyanines or streptocyanines. Some names of dyes are derived from the name of the heterocycle containing an acceptor/donor nitrogen, as with benzimidazole and indolenine dyes. A dye such as indocyanine green has a cationic cyanine chromophore but carries two sulfonate substituents, so is an anion under usage conditions. This chapter describes dyes using the headings cyanines, oxonols, benzimidazoles and indolenines, and azamethines. Within each of these groups the usual sequence of anions, cations, and reactive dyes is followed when appropriate. Within each subgroup dyes are listed in order of increasing formula weight.
