Femtosecond Dynamics of Dioxygen - Picket-Fence Cobalt Porphyrins: Ultrafast Release of O_2 and the Nature of Dative Bonding

Abstract

The ultrafast release of O_2 from the O_2 adduct of picket-fence cobalt porphyrin (see picture) has been probed in real time, and has a total reaction time of 2 ps, without subsequent recombination over several nanoseconds. The dynamics of this ultrafast release of O_2 shows that relaxation within the porphyrin system (200 fs) precedes porphyrin-to-metal electron transfer, but the latter occurs at an enhanced rate (500 fs as opposed to the more usual 1 – 2 ps) because of the dative bonding of cobalt and O_2, which gives the adduct ground state significant Co^(III)−O_2^− character.