Structure and Properties of Carotenoid Cations

Abstract

Naturally occurring carotenoids are familiar as yellow, orange or red pigments with λmax below 600 nm in organic solvents. Carotenoids with short polyene chains, such as the triene phytoene (44) and the pentaene phytofluene (42), absorb light only in the UV region and are colourless. Compounds that absorb light in the near infrared (NIR) region above ca. 900 nm are also colourless, unless they also absorb light in the 600–900 nm region, in which case they appear blue. True carotenoproteins (Chapter 6) are purple-blue and absorb light above 600 nm.