C O M M U N I C A T I O N S
Table 1. Speciation Data of Ln(III)(NO3)3 with ThPybox in
ligand emission, which, as mentioned above, is not completely
quenched by the Tb(III) and overlaps with the transitions of the
metal ion.
Acetonitrile Obtained by Absorption and Emission Titrationsa
Ln(III)
method
log â11
log â21
log â31
In summary, ThPybox is a highly efficient sensitizer of Eu(III)
and Tb(III) luminescence, as reflected in the high emission quantum
yields of luminescence, which in the case of Eu(III) is up to three
times as high as previously reported for other complexes. Further,
the versatile chemistry of these ligands allows tuning of the
sensitization ability and tailoring of the Ln(III) complex properties
for specific applications. As such, Pybox and its derivatives show
extreme promise as a new class of antennas for lanthanide ion
emission.
Eu
absorption
emission
average
absorption
emission
average
5.70 ( 0.07
5.15 ( 0.18
5.43 ( 0.19
5.01 ( 0.17
4.75 ( 0.09
4.88 ( 0.19
10.70 ( 0.20
10.09 ( 0.11
10.40 ( 0.23
9.10 ( 0.11
9.09 ( 0.07
9.10 ( 0.13
15.38 ( 0.10
14.34 ( 0.20
14.86 ( 0.22
13.38 ( 0.14
12.10 ( 0.20
12.74 ( 0.24
Tb
a Values are the average of at least three measurements with each
technique. Sample absorption titration shown in Figure S5, Supporting
Information.
Table 2. Photophysical Characterization of Ln(III)(NO3)3 with
Acknowledgment. We acknowledge the donors of the Petro-
leum Research Fund (Grant 43347-AC3) administered by the
American Chemical Society, NSF-REU for summer support to AR,
and NSF-CHE 0621664 for support of this work. We thank Dr.
Andrei Poloukhtine for experimental support.
ThPybox in Acetonitrile in 3:1 Stoichiometrya
complex
ThPyboxEu
ThPyboxTb
Φ[%]b
76.2 ( 6.6
2.097 ( 0.081
58.6 ( 4.1
τ[ms]
0.367 ( 0.032
0.019 ( 0.002
1S[cm-1
]
]
28310 (28,610)
21080 (21,080)
Supporting Information Available: Experimental details of the
synthesis and spectroscopic characterization and X-ray crystallographic
files in CIF. This material is available free of charge via the Internet at
.html (or from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK;
fax: +44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk). CCDC
658540 contains the supplementary crystallographic data for the
complex described in this paper.
c
c
3T[cm-1
a [L] ) 3[Ln(III)] ≈ 1 × 10-6 M. b Average of at least three measure-
ments with different experimental conditions. c Measured in a solution with
Ln ) Gd at 77 K,24 data in parenthesis is uncoordinated ligand.
moieties of the oxazoline or thiophene rings and F-O shorts
contacts22,23 are present in this structure (Figure S2).
These complexes, as well as others with similar Pybox ligands
described elsewhere,11,12 are highly luminescent in the solid state,
as shown by the characteristic red or green color seen when the
crystals are held under a handheld UV lamp (λ ) 254 nm). When
dissolved in methanol or acetonitrile luminescent solutions are
obtained. While to date only a 2:1 complex was isolated in the
solid state, other species are present in solution. To characterize
these species ThPybox was titrated with Ln(III) nitrate in acetonitrile
and the absorption and emission spectra of the resulting solutions
were measured. Results of these speciation studies are summarized
in Table 1 and are consistent with the formation of 1:1, 2:1 and
3:1 species in solution. The stability constants were obtained through
independent absorption and emission titrations and are similar for
both ions, with the Eu(III) species being slightly more stable.
Through the use of speciation diagrams (Figure S3), conditions for
the photophysical measurements were chosen to ensure that the
main species in solution was the 3:1 species.
References
(1) Lanthanide Probes in Life, Chemical and Earth Sciences - Theory and
Practice; Bu¨nzli, J.-C. G., Choppin, G. R., Eds.; Elsevier: Amsterdam,
1989.
(2) Reinhard, C.; Gu¨del, H. U. Inorg. Chem. 2002, 41, 1048-1055.
(3) Chauvin, A.-S.; Gumy, F.; Imbert, D.; Bu¨nzli, J.-C. G. Spectroscopy Lett.
2004, 37, 517-532.
(4) Jensen, T. B.; Scopelliti, R.; Bu¨nzli, J.-C. G. Inorg. Chem. 2006, 45, 7806-
7814.
(5) Moore, E. G.; Xu, J.; Jocher, C. J.; Werner, E. J.; Raymond, K. N. J. Am.
Chem. Soc. 2006, 128, 10648-10649.
(6) Aspinall, H. C.; Bickley, J. F.; Greeves, N.; Kelly, R. V.; Smith, P. M.
Organometallics 2005, 24, 3458-3467.
(7) Aspinall, H. C.; Dwyer, J. L. M.; Greeves, N.; Smith, P. M. J. Alloys
Compds. 2000, 303-304, 173-177.
(8) Aspinall, H. C.; Greeves, N. J. Organomet. Chem. 2002, 647, 151-157.
(9) Desimoni, G.; Faita, G.; Filippone, S.; Mella, M.; Zampori, M. G.; Zema,
M. Tetrahedron 2001, 57, 10203-10212.
(10) Desimoni, G.; Faita, G.; Quadrelli, P. Chem. ReV. 2003, 103, 3119-3154.
(11) de Bettencourt-Dias, A.; Viswanathan, S.; Rollett, A. Unpublished work,
2007.
(12) de Bettencourt-Dias, A.; Viswanathan, S.; USPTO, #11565272, 2006.
(13) Chen, X.-Y.; Bretonniere, Y.; Pecaut, J.; Imbert, D.; Bu¨nzli, J.-C.;
Mazzanti, M. Inorg. Chem. 2007, 46, 625-637.
Absorption, excitation, and emission spectra for both metal ion
complexes (Figure S4) show that the excitation spectra closely
follow the absorption spectrum of the ligand. Further, the emission
spectra of both Eu(III) and Tb(III) solutions show the characteristic
(14) Edwards, A.; Claude, C.; Sokolik, I.; Chu, T. Y.; Okamoto, Y.; Dorsinville,
R. J. Appl. Phys. 1997, 82, 1841-1846.
(15) Petoud, S.; Muller, G.; Moore, E. G.; Xu, J.; Sokolnicki, J.; Riehl, J. P.;
Le, U. N.; Cohen, S. M.; Raymond, K. N. J. Am. Chem. Soc. 2007, 129,
77-83.
transitions 5D0
f f
7FJ (J ) 1-4) and 5D4 7FJ (J ) 6-2),
(16) Charbonnie`re, L. J.; Ziessel, R. HelV. Chim. Acta 2003, 86, 3402-3410.
(17) Comby, S.; Imbert, D.; Chauvin, A.-S.; Bu¨nzli, J.-C. G.; Charbonnie`re,
L. J.; Ziessel, R. F. Inorg. Chem. 2004, 43, 7369-7379.
(18) Chatterton, N.; Bretonniere, Y.; Pecaut, J.; Mazzanti, M. Angew. Chem.,
Int. Ed. 2005, 44, 7595-7598.
respectively. As a result of almost complete quenching of the ligand
centered emission in the case of the Tb(III) an increased background
in the 450 to 500 nm region is seen. This translates into a quantum
yield of emission of 58.6% (Table 2). This quantum yield is lower
than the emission efficiency of 76.2% determined for Eu(III).
However, both values are high and are accompanied by long
luminescence lifetimes of ∼2 ms for the Eu(III) and 367 µs for the
Tb(III) species. The lifetime of the red emission could be determined
from a single-exponential fitting of the decay curve and is consistent
with the presence of one major luminescent species. In the case of
the green emission, a double exponential had to be utilized. Closer
inspection of the triplet emission spectrum of the ligand (Figure
S6) reveals that the second component corresponds to residual
(19) Charbonnie`re, L. J.; Balsiger, C.; Schenk, K. J.; Bu¨nzli, J.-C. G. J. Chem.
Soc., Dalton Trans. 1998, 505-510.
(20) Petoud, S.; Bu¨nzli, J.-C. G.; Schenk, K. J.; Piguet, C. Inorg. Chem. 1997,
36, 1345-1353.
(21) Desiraju, G.; Steiner, T. The Weak Hydrogen Bond In Structural Chemistry
and Biology; Oxford University Press: New York, 1999; Vol. 9.
(22) Patroniak, V.; Baxter, P. N. W.; Lehn, J.-M.; Hnatejko, Z.; Kubicki, M.
Eur. J. Inorg. Chem. 2004, 2379-2384.
(23) Cantuel, M.; Bernardinelli, G.; Muller, G.; Riehl, J. P.; Piguet, C. Inorg.
Chem. 2004, 43, 1840-1849.
(24) Crosby, G. A.; Whan, R. E.; Alire, R. M. J. Chem. Phys. 1961, 34,
743-748.
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