Excited state emission and absorption decay measurements were made on the cage-type cryptate complexes [M .cntnd. bpy.bpy.bpy]n+, where Mn+ = Na+, La3+, Eu3+, Gd3+ or Tb3+ and [bpy.bpy.bpy] is a tris-bipyridine macrobicyclic cryptand. Excitation performed in the high intensity 1ππ→ cryptand band with max. at ∼300 nm. Expts. were carried out in H2O or D2O solns. and at 300 and 77 K to evaluate the rate consts. of radiative and nonradiative decay processes. For Mn+ = Na+, La3+, and Gd3+ the lowest excited state of the cryptate is a 3ππ→ level of the cryptand which decays in the μs time scale at room temp. in H2O soln. and in the 2nd ms time scale at 77 K in MeOH-EtOH. For Mn+ = Eu3+, the lowest excited state is the luminescent 5D0Eu3+ level which in H2O soln. is populated with 10% efficiency and decays to the ground state with rate consts. 2.9 × 103 s-1 at room temp. and 1.2 × 103 s-1 at 77 K. The relatively low efficiency of 5D0 population upon 1ππ→ decays directly to the ground state. For Mn+ = Tb3+ the lowest excited state is the luminescent 5D4Tb3+ level. The process of 5D4 population upon 1ππ→ excitation is ∼100% efficient, but at room temp. it is followed by a high efficiency, activated back energy transfer from the 5D4 Tb3+ level to the 3ππ→ ligand level because of the relatively small energy gap between the 2 levels (1200 cm-1) and the intrinsically long lifetime of 5D4. At 77 K, back energy transfer cannot take place and the 5D4 Tb3+ level deactivates to the ground state with rate const. 5.9 × 102 s-1 (H2O soln.). The relevance of these results toward the optimization of Eu3+ and Tb3+ cryptates as luminescent probes is discussed. [on SciFinder(R)]
Antenna effect in luminescent lanthanide cryptates: a photophysical study
PERATHONER, Siglinda;
1990-01-01
Abstract
Excited state emission and absorption decay measurements were made on the cage-type cryptate complexes [M .cntnd. bpy.bpy.bpy]n+, where Mn+ = Na+, La3+, Eu3+, Gd3+ or Tb3+ and [bpy.bpy.bpy] is a tris-bipyridine macrobicyclic cryptand. Excitation performed in the high intensity 1ππ→ cryptand band with max. at ∼300 nm. Expts. were carried out in H2O or D2O solns. and at 300 and 77 K to evaluate the rate consts. of radiative and nonradiative decay processes. For Mn+ = Na+, La3+, and Gd3+ the lowest excited state of the cryptate is a 3ππ→ level of the cryptand which decays in the μs time scale at room temp. in H2O soln. and in the 2nd ms time scale at 77 K in MeOH-EtOH. For Mn+ = Eu3+, the lowest excited state is the luminescent 5D0Eu3+ level which in H2O soln. is populated with 10% efficiency and decays to the ground state with rate consts. 2.9 × 103 s-1 at room temp. and 1.2 × 103 s-1 at 77 K. The relatively low efficiency of 5D0 population upon 1ππ→ decays directly to the ground state. For Mn+ = Tb3+ the lowest excited state is the luminescent 5D4Tb3+ level. The process of 5D4 population upon 1ππ→ excitation is ∼100% efficient, but at room temp. it is followed by a high efficiency, activated back energy transfer from the 5D4 Tb3+ level to the 3ππ→ ligand level because of the relatively small energy gap between the 2 levels (1200 cm-1) and the intrinsically long lifetime of 5D4. At 77 K, back energy transfer cannot take place and the 5D4 Tb3+ level deactivates to the ground state with rate const. 5.9 × 102 s-1 (H2O soln.). The relevance of these results toward the optimization of Eu3+ and Tb3+ cryptates as luminescent probes is discussed. [on SciFinder(R)]Pubblicazioni consigliate
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