the 5DJ level of the Eu3+ ion generates pure red emission. However,
in the other four systems, mixed emission was observed because
of the incomplete energy transfer from the excited MLCT state
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3
to the triplet energy levels of 2a–2d, as well as possible reverse
transfer. Therefore, the triplet energy level of the linking ligand is
important, because it behaves as a channel for ET in the above
Ir–Eu dyads. Complete ET will occur only when the triplet energy
level of the linking ligand is suitably lower than the 3MLCT level
5
of the Ir moiety and higher than the DJ levels of the Eu3+ ion,
resulting in efficient sensitization.
Conclusions
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The synthesis and characterization of Ir(III) complexes of a series
of NŸN,OŸO-chelating linking ligands based on substituted 1-
(pyridin-2-yl)-3-methyl-5-pyrazolone was reported. The ET pro-
cess between these iridium complexes and europium ions in
solution was investigated. The triplet energy level of the linking
ligand is a key factor in terms of the ET process between the two
emission centers. Only when the triplet energy level of the linking
3
ligand is sufficiently lower than the MLCT energy levels of the
Ir moiety and higher than the 5DJ energy levels of the Eu(III) ion
will complete ET occur and pure emission from the Eu(III) ion
be observed (for example, 4e). If the triplet energy level of the
linking ligand is higher or close to the 3MLCT energy levels of the
Ir moiety, mixed emission from both the Ir moiety and the Eu(III)
moiety (4a–4d) is obtained. These findings could be helpful in the
design of linking ligands for sensitizing europium ions.
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Acknowledgements
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1551.
The authors thank the National Basic Research Pro-
gram (2006CB601103) and the NNSFC (90922004, 20971006,
20821091, and 50772003) for financial support as well as beamline
BL14W (Shanghai Synchrotron Radiation Facility) for providing
the beam time.
36 S. J. A. Pope, B. J. Coe, S. Faulkner, E. V. Bichenkova, X. Yu and K. T.
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