Femtosecond Dynamics of Dioxygen - Picket-Fence Cobalt Porphyrins: Ultrafast Release of O(2) and the Nature of Dative Bonding

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.