Laser photolysis of complexes of etioporphyrin I with rare-Earth elements

Photophysics of Lanthanide Triple Decker Porphyrin Sandwich Complexes

“…Similar reasoning can help explain the apparent <200 fs time constant for T‘ formation in Eu 2 (OEP) 3 , if there is sufficient spin coupling of the metal-f and macrocycle-π electrons. This mechanism together with the spin−orbit effect of the two heavy metal ions probably also leads to a yield of the triplet manifold of ∼1 for Eu 2 (OEP) 3 , as has been suggested for the monomeric Eu(III) porphyrins . This framework also provides an assignment for the small-amplitude 20 ps kinetic component found for Eu 2 (OEP) 3 found in the blue-green region of the spectrum (Figure B).…”

“…The enhanced intersystem crossing 1 Q‘(π,π*) ↔ 3 T‘(π,π*) in this triple decker undoubtedly arises from the spin−orbit effect of the two heavy La(III) ions in the complex ( Z = 57). Similar reasoning has been proposed to explain the finding of short 1 (π,π*) lifetimes (<50 ps), high 3 (π,π*) yields (>90%), and weak or no fluorescence from lanthanum tetrabenzylporphyrin (TBP) and a number of other monomeric lanthanoid porphyrins, − as well as thorium(IV) bisporphyrinates. 4c,e …”

“…Ultrafast absorption experiments suggest that the sing-doublet decays to the triplet− doublet in the copper porphyrin monomers in <350 fs . A similarly rapid formation of the “triplet” state of U(OEP) 2 has been observed,4f and for paramagnetic lanthanoid monoporphyrins such as EuTBP can be inferred from time resolved absorption data and the weakness or absence of fluorescence. 19a,c In all of these cases the rapid rate of “internal conversion” from the excited sing-multiplet state to the corrresponding trip-multiplet state has been ascribed to the coupling of the metal and ring electron spins and the concomitant relaxation of the spin forbiddeness of what would otherwise be the 1 (π,π*) → 3 (π,π*) intersystem crossing process.…”

“…Excited State Deactivation Rates and Pathways. The importance of the metal ion in determining the relaxation rates and pathways in monomeric transition metal porphyrins has been well-documented. 15b,− A principal means by which this occurs is if ligand-field or metal ↔ ring CT states lie below the normally emissive (π,π*) states of the macrocycle, opening new routes for deactivation. For paramagnetic metalloporphyrins, a second way that the metal influences the photophysical behavior is through coupling of unpaired metal spin(s) with those of the porphyrin (π,π*) states, giving rise to “sing-multiplet” and “trip-multiplet” states and transitions having altered spin selection rules .…”

“…For paramagnetic metalloporphyrins, a second way that the metal influences the photophysical behavior is through coupling of unpaired metal spin(s) with those of the porphyrin (π,π*) states, giving rise to “sing-multiplet” and “trip-multiplet” states and transitions having altered spin selection rules . Both mechanisms, in addition to heavy-atom enhancement of intersystem crossing rates, have been proposed to contribute to the luminescence properties and excited state deactivation behavior of lanthanoid monoporphyrins, including trivalent La, Eu, and Ce complexes. − Additionally, low-energy metal-centered excited states are thought to facilitate ultrafast deactivation of tervalent Ce and U porphyrin double deckers. 4a,b,f …”