ABSTRACT
Polyene dyes and fluorochromes contain linked methine groups forming a chain of trans-oriented conjugated carbon-carbon double bonds, as shown below in structure a. In the naturally occurring carotenoids these are lipophilic alicyclic or aliphatic groups (as in lycopene) or hydrophilic groups such as hydroxy or carboxyl (as in crocetin). The polyene category so specified subsumes various traditional dye classes. These include carotenoids, the stilbenes, and two-methine polyenes with end-groups other than phenyl; the latter have been discussed elsewhere as ethylene derivatives. Some anionic dyes are salts of strong acids (sulfonates, e.g. calcofluor white M2R), some of weak acids (carboxylic, e.g. crocetin). The carotenoids are natural products, and saffron and lycopene are still extracted from plant material. The term saffron describes the naturally occurring yellow material present in the flowers and fruit of various plants. The yellow compounds are crocins; mono- and diglycosyl esters of the dicar-boxylic acid crocetin.
