The project aims to prepare novel probes to advance our understanding of chemistry and biology of the clinically important heme degradation product bilirubin during hyperbilirubinemia phototherapy. The pursued approach will combine innovative synthetic chemistry to provide bilirubin, and many of its known degradation products, in isotope-labeled form. In-dept photochemical studies will be used to deliver a detailed mechanistic picture regarding the formation and behavior of the bilirubin fragments generated during phototherapy. Resulting well-characterized probes will be invaluable for biomedical research in the context of hyperbilirubinemia phototherapy.