C.R. De Silva et al. / Inorganica Chimica Acta 360 (2007) 3543–3552
3551
Radiative lifetimes (sR), intrinsic quantum yields of the
Acknowledgements
lanthanide luminescence step (ULn), and sensitization effi-
ciencies (gsens) of the five Eu(III) complexes are calculated
using Eqs. (1)–(3). These parameters along with the exper-
imentally determined luminescence lifetimes (sobs) and
overall quantum yields (Utot) are summarized in Table 3.
The overall photoluminescence quantum yields (Utot) of
Eu(tta)3(dmbipy), Eu(btfac)3(dmbipy), Eu(hfac)3(dmbipy)-
(H2O), Eu(tta)3(dmphen), and Eu(hfac)3(dmphen)(EtOH)
were found to be 0.23, 0.18, 0.48, 0.34, and 0.39, respec-
tively. Clearly the hfac ligand-bearing complexes display
higher quantum yields than the other complexes.
This work was supported by NSF CAREER Grant No.
CHE-0238790. Acknowledgment is also made to the Do-
nors of The Petroleum Research Fund, administered by
the American Chemical Society, for partial support of this
research. The authors greatly appreciate the lifetime mea-
surements by Professor S. Petoud and Mr. J. Zhang of Uni-
versity of Pittsburg. We thank Professor K. Miranda for
the use of fluorometers. The CCD-based X-ray diffractom-
eter was purchased through an NSF Grant (CHE-
96103474, USA).
Intrinsic quantum yields of Eu(tta)3dmbipy, Eu(btfac)3-
dmbipy, and Eu(tta)3dmphen are similar to one another
due to their comparable coordination environments. These
values are larger than those calculated for Eu(hfac)3dmbi-
py(H2O) and Eu(hfac)3(dmphen)(EtOH). The lumines-
cence lifetime (sobs) observed for Eu(hfac)3dmbipy(H2O)
is the shortest among the five complexes. It is understand-
able that the presence of the O–H oscillators in the close
proximity of Eu(III) center effectively quenches the lumi-
nescence via vibrational relaxations [38]. As such, Eu(hfac)3-
dmbipy(H2O) exhibits a relatively low intrinsic quantum
yield value (ULn). A similar behavior was observed for
Eu(hfac)3(dmphen)(EtOH). Thus, the observed higher over-
all quantum yields (Utot) of Eu(hfac)3dmbipy(H2O) and
Eu(hfac)3(dmphen)(EtOH) must be due to the high efficien-
cies of ligand-to-metal energy transfer processes prior to
lanthanide-centered luminescence, indicated by the sensiti-
zation efficiencies summarized in Table 3. The relatively high
overall quantum yields suggest the potential applications of
these complexes in electroluminescent devices. Our studies
along this more technological line of research will be
reported elsewhere.
Appendix A. Supplementary material
CCDC Nos. 618404, 618405, 618406, 618407 and
618408 contain the supplementary crystallographic data
for Eu(tta)3(dmbipy), Eu(btfac)3(dmbipy), Eu(hfac)3(dmbi-
py)(H2O), Eu(tta)3(dmphen) and Eu(hfac)3(dmphen)-
(EtOH). These data can be obtained free of charge via
the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-
033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary
data associated with this article can be found, in the online
References
[1] (a) I. Hemmila, V. Laitala, J. Fluoresc. 15 (2005) 529;
(b) H. Maas, A. Currao, C. Gion, Angew. Chem. Int. Ed. 41 (2002)
2495;
(c) C.H. Huang, F.Y. Li, W. Huang, Introduction to Organic Light-
Emitting Materials and Devices, Fudan Press, Shanghai, China, 2005.
[2] (a) J. Kido, Y. Okamoto, Chem. Rev. 102 (2002) 2357;
(b) H. You, J. Fang, Y. Xuan, D. Ma, Mater. Sci. Eng. B131 (2006)
252.
4. Conclusions
[3] (a) F.S. Richardson, Chem. Rev. 82 (1982) 541;
(b) J. Yuan, G. Wang, J. Fluoresc. 15 (2005) 559.
[4] (a) J.G. Bunzli, Acc. Chem. Res. 39 (2006) 53;
(b) J.P. Leonard, T. Gunnlaugsson, J. Fluoresc. 15 (2005) 585.
[5] C. Go¨rller-Walrand, in: K. Binnemans, K.A. Gschneidner Jr., L.
Eyring (Eds.), Spectral Intensities of f–f Transitions in Handbook on
the Physics and Chemistry of Rare Earths, vol. 25, North-Holland,
Amsterdam, 1998.
[6] (a) S.I. Weissman, J. Chem. Phys. 10 (1942) 214;
(b) E.B. van der Tol, H.J. van Ramesdonk, J.W. Verhoeven, F.J.
Steemers, E.G. Kerver, W. Verboom, D.N. Reinhoudt, Chem. Eur. J.
4 (1998) 2315;
Several new europium complexes with fluorinated b-
diketonate ligands and nitrogen p,p0-disubstituted bipyri-
dine and phenanthroline ligands were synthesized and their
structures established by single-crystal X-ray diffraction. It
has been shown that the lanthanide coordination behavior
is significantly influenced by the b-diketonate ligands uti-
lized, and to a much less extent, by the neutral ligands.
The disparity of bond distance and coordination number
can be rationalized in terms of the electronic and steric
properties of the ligands. This work not only provides some
luminescent lanthanide complexes, it also offers some much
needed supporting evidence for drawing the conclusions
elaborated above, that is, subtle but significant change in
the coordination behavior can be achieved by judiciously
chosen ligands. Photoluminescence studies show that exci-
tation of the complexes is ligand based, and that the emis-
sion is characteristic of trivalent europium ion. The
differences in overall quantum yields of the title complexes
were evaluated in terms of their intrinsic quantum yields
and the efficiencies of ligand sensitization.
(c) A.P. Bassett, S.W. Magennis, P.B. Glover, D.J. Lewis, N. Spencer,
S. Parsons, R.M. Williams, L. De Cola, Z. Pikramenou, J. Am.
Chem. Soc. 126 (2004) 9413.
[7] (a) G.A. Crosby, R.E. Whan, J.J. Freeman, J. Phys. Chem. 66 (1962)
2493;
(b) R.E. Whan, G.A. Crosby, J. Mol. Spectrosc. 8 (1962) 315;
(c) F.J. Steemers, W. Verboom, D.N. Reinhoudt, E.B. van der Tol,
J.W. Verhoeven, J. Am. Chem. Soc. 117 (1995) 9408.
[8] K. Binnemans, Rare-earth beta-diketonates, in: K.A. Gschneidner
Jr., J.-C.G. Bunzli, V.K. Pecharsky (Eds.), Handbook on the Physics
¨
and Chemistry of Rare Earths, vol. 35, Elsevier, 2005.
[9] (a) Y. Hasegawa, M. Yamamuro, Y. Wada, N. Kanehisha, Y. Kai, S.
Yanagida, J. Phys. Chem. A 107 (2003) 1697;