The Photochemical Quantum Yield for the Self‐sensitized Photooxidation of Bilirubin. Evidence for Oxygen‐induced Intersystem Crossing at High Oxygen Concentrations

The in vitro self‐sensitized photooxygenation of bilirubin has been studied as a function of oxygen and bilirubin concentrations in a variety of solvents. The results which have been interpreted in terms of a singlet oxygen reaction indicate bilirubin triplet yields of 0.05–0.08 and further show that oxygen induced intersystem crossing is appreciable at high oxygen concentrations. The results also show that the quantum efficiency of the photochemical reaction would be of the order of 1% at the bilirubin and oxygen concentrations typical for the in vivo treatment of neonatal jaundice.