Abstract—The use of competitive methods with rubrene as reference acceptor provides values of the rate constants kBQ= 2.3 times 109/ mol‐1s‐1and kvq= 3.3 times 109mol‐1s‐1for the physical quenching of O21δg, by bilirubin (in CCl4) and biliverdin (in CHCl3) respectively attributed to electron and energy transfer processes.The rate constant kBR= 1.7 times 108/ mol‐1s‐1for bilirubin reaction with O21δg is considerably greater than that kvR3 times 108mol‐s‐1for the reaction of biliverdin which has identical O21δa, acceptor sites, and is attributed to a primary Type I oxidation process followed by a slower Type II addition of O21δg to