Visible light induced photo-oxidation of highly branched isoprenoid (HBI) alkenes: Significant dependence on the number and nature of double bonds

► Visible light-induced photooxidation of C25 HBI alkenes in solution investigated. ► Degradation rate dependent on number of trisubstituted double bonds. ► High photoreactivity of some HBIs in dead cells of diatoms confirmed. ► HBI with trisubstituted double bonds should be strongly photo-altered in the ocean. ► Results support the apparent good preservation of monoene IP25 in sediments.