51321-48-3Relevant academic research and scientific papers
Picosecond Photolysis of Axial Ligands on Cobalt(II) and Cobalt(III) Porphyrins
Tait, C. Drew,Holten, Dewey,Gouterman, Martin
, p. 6653 - 6659 (2007/10/02)
Excited-state photoprocesses of cobalt(II) octaethylporphyrin (OEP), cobalt(II) tetraphenylporphyrin (TPP), CoIII(OEP)(CN), and CoII(OEP)(CN)(γ-picoline) in noncomplexing solvents and in the presence of coordinating species Me2SO and piperidine have been studied.The transient absorption spectra suggest that the excited-state relaxation of cobalt(II) porphyrins proceeds via the tripdoublet, 2T(?,?*), and the 2(?, dz2) charge-transef (CT) states and that rapid deactivation of the latter state competes favorably with axial ligand release, accounting for the low yield for photodissociation.When five-coordinate CoIII(OEP)(CN) is excited, the transient spectra suggest that the initial (?,?*) and (?,d) CT excited states decay to 3(d?, dz2), followed by ligand loss to produce four-coordinate III(OEP)>+.However, when six-coordinate III(OEP)L2>+ systems are excited, the transient spectra suggest that both five-coordinate III(OEP)L>+ and four-coordinate III(OEP)>+ are produced, both presumably from 3(d?, dz2), which is not observed.In 1-4 M ligating solvents III(OEP)L>+ rebinds a ligand in 250 ps to 1.4 ns, whereas III(OEP)>+ is stable for >/=1 ns.This difference in stablity is attributed to the five-coordinate species having a singlet ground state, while the four-coordinate species is a triplet ligand-field (d, d) state.
