A note on some old and some possible new redox indicators

Summary Starting with the frequently used dye 2,6-dichloroindophenol some of the chemical properties of the quinonimide class of dyes are described. Consideration of the effects of completing a hetero-six-membered ring, as in the azine, thiazine and oxazine classes, on the properties of the compounds is suggested as a lead towards the development of some redox indicators perhaps more desirable than the indophenols. This approach developed from a study of the Liebermann nitroso-reaction for phenols. Some properties of the redox indicators which resulted from that work are described in relation to energy transduction in the chloroplast.