Siphonaxanthin and siphonein are two keto-carotenoids. Upon anthracene-sensitizing, triplet excitation dynamics of these two carotenoids were studied in n-hexane and in methanol, respectively, by ns flash photolysis spectroscopy. In n-hexane, bleaching of the ground state absorption (GSB) and the excitation triplet ((3)Car*) absorption were observed. In methanol, upon the decay of the (3)Car*, the cation dehydrodimer of carotenoid, (#)[Car]2*, generated by the same rate, while an additional GSB generated synchronously, a polar solvent assisted and anthracene-sensitized mechanism was addressed based on the discussion. The environment-sensitive triplet excitation dynamics imply their potential role in photo-protection in vivo. (C) 2015 Elsevier B.V. All rights reserved.