Efficient Photodissociation of O2 from Synthetic Heme and Heme/M (M = Fe, Cu) Complexes

Single wavelength excitation (λex = 355 or 532 nm) of low-temperature stabilized (198 K) synthetic heme−dioxygen and heme−dioxygen/M complexes, where M = copper or iron in a non-heme environment, results in the dissociation of dioxygen as indicated by the generation of the ferrous heme (Soret band, 427 nm) and the bleaching of the ferric-superoxide (FeIII(O2 -)) 410-nm Soret band in the transient absorption difference spectrum. Dioxygen rebinds to the four heme complexes studied with comparable rate constants (∼6−9 × 105 M-1 s-1). However, the quantum yield for complete dissociation of O2 from our simplest heme−O2 complex (F8)FeIII(O2 -) (φ = 0.60) is higher than the other complexes measured (φ = ∼0.2−0.3) as well as that for oxy-myoglobin (φ = 0.3).