Photochemical formation of singlet molecular oxygen ((1)O2) in illuminated 6-methylcoumarin solutions

Use of the fragrance 6-methylcoumarin (6-MC) in cosmetic products has declined significantly due to numerous reports of photoallergic contact dermatitis associated with its use. We have determined that 6-MC undergoes direct photolysis with an estimated half-life of 83 minutes when illuminated with mid-latitude U.S., noon-centered, equinox sunlight and a quantum yield for photolysis at 313 nm of phi = 3 x 10(-3). The work presented here also provides evidence that singlet molecular oxygen ((1)O2) is formed in illuminated solutions containing 6-MC. An estimated value of phi = 0.01 is reported for the (1)O2 quantum yield at 313 nm. Formation of (1)O2 is significant because it is known to react with a variety of biomolecules and it is possible that (1)O2 formation is at least partially responsible for reports of 6-MC photoallergenicity and phototoxicity.