The excited states of photoporphyrin IX.

Abstract Pulse radiolysis of protoporphyrin IX dimethyl ester in benzene solution produces an emitting state of lifetime 23 ns and a non-emitting state of lifetime > 240 μs. The relative lifetimes and oxygen quenching rates show the emitting state to be a singlet and the non-emitting state a triplet. Other quenching measurements on the triplet are reported. CNDO/S calculations on the conjugated system of protoporphyrin IX support the assigned multiplicities.