Design of dipicolinic acid ligands for the two-photon sensitized luminescence of europium complexes with optimized cross-sections

Article abstract of DOI:10.1021/ic8012975

The multistep synthesis of an extensive series of push-pull donor-π-conjugated dipicolinic acid ligands is described. The charge transfer character of the ligand can be tuned by changing the donor group (CH ₂R, OR, SR, or NR₂) or the nature of the conjugated backbone (phenyl, phenylethynyl, naphtylethynyl, bis(phenylethynyl), or chalcone). The photophysical properties of related D₃ symmetric europium complexes (absorption and luminescence) were measured. Experiments using two-photon sensitized luminescence of a Eu^III complex reveal large two-photon absorption (TPA) cross-section values (775 GM at 740 nm) in dichloromethane. Furthermore, some structure-property relationships can be derived from this systematic study, allowing an optimization of TPA properties of lanthanide complexes.

Full text of DOI:10.1021/ic8012975

Inorg. Chem. 2008, 47, 10269-10279
Design of Dipicolinic Acid Ligands for the Two-Photon Sensitized
Luminescence of Europium Complexes with Optimized Cross-Sections
Anthony D’Ale´o,† Alexandre Picot,† Patrice L. Baldeck,‡ Chantal Andraud,†,* and Olivier Maury†,*
UniVersite´ de Lyon, Laboratoire de Chimie, CNRS - Ecole Normale Supe´rieure de Lyon,
UMR 5182, 46 alle´e d’Italie, 69007 Lyon, France, and Laboratoire de Spectrome´trie Physique,
UniVersite´ Joseph Fourier, CNRS - UMR 5588, BP 87 F-38402 Saint Martin d’He`res, France
Received July 10, 2008
The multistep synthesis of an extensive series of push-pull donor-π-conjugated dipicolinic acid ligands is described.
The charge transfer character of the ligand can be tuned by changing the donor group (CH2R, OR, SR, or NR2)
or the nature of the conjugated backbone (phenyl, phenylethynyl, naphtylethynyl, bis(phenylethynyl), or chalcone).
The photophysical properties of related D3 symmetric europium complexes (absorption and luminescence) were
measured. Experiments using two-photon sensitized luminescence of a EuIII complex reveal large two-photon
absorption (TPA) cross-section values (775 GM at 740 nm) in dichloromethane. Furthermore, some structure-property
relationships can be derived from this systematic study, allowing an optimization of TPA properties of lanthanide
complexes.
Introduction
Zn2+,14...) applications. This technique is based on the two-
photon excited fluorescence phenomenon that consists of the
simultaneous absorption of two photons of longer wavelength
(TPA; a third-order nonlinear optical phenomenon) followed
by the classical emission of a fluorescence photon. The
spatial confinement of two-photon laser excitation presents
several intrinsic advantages: three-dimensional resolution and
reduced photobleaching and photodamage due to the absence
of out-of-focus absorption. In addition, longer-wavelength
near-infrared (NIR) light (typically 800 nm) used for TPA
excitation is less scattered by biological tissue, allowing
deeper penetration.15 This technique requires the presence
of fluorescent probes that can be either an endogenous dye
or commercially available fluoro-probes featuring a generally
low two-photon absorption cross-section (σ2 < 50 GM).16
For a decade, chromophores have been specially optimized
for such applications with a high σ2 value comprised between
750 and 1500 GM for organic dyes17-23 and up to 50 000
GM for quantum dots or dendrimers.24,25
Since the pioneering work of Webb in the early 1990s,1
two-photon excited microscopy has evolved as an alternative
to conventional techniques for in vivo, in vitro, or in cellulo
biological imaging2-5 or sensing6-10 (pH,11 Mg2+,12,13
* Author to whom correspondence should be addressed. E-mail:
olivier.maury@ens-lyon.fr.
†
Universite´ de Lyon.
Universite´ Joseph Fourier.
‡
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On the other hand, lanthanide complexes have been widely
and successfully used for bioimaging,26-30 taking benefit
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10.1021/ic8012975 CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 22, 2008 10269
Published on Web 10/21/2008

D’Ale´o et al.
from the very characteristic luminescence properties of these
metal ions31-35 (sharp transitions with a large Stokes shift
located in the visible or in the NIR spectral range, insensitiv-
ity to oxygen, and sensitivity to the local environment) and
particularly from their long excited-state lifetime. This latter
property triggered the development of time-gated microscopy
in order to eliminate any parasitic short-lived luminescence
coming from the scattering or autofluorescence of endog-
enous chromophores or other molecular probes.30,36-40 In
order to combine the advantages of both rare earths and
nonlinear microscopy, our project was to design a new
generation of lanthanide complexes stable in biological media
and featuring optimized two-photon cross-sections. In the
early 2000s, the groups of Lakowicz and Thompson,
respectively, demonstrated the proof-of-concept of a two-
photon antenna effect in a biological medium with complexes
exhibiting very low (generally not measured) TPA cross-
sections.41,42 Recently, sensitization of europium(III) was
achieved by the two-photon antenna effect, using either
Michler’s ketone,43 2-(diethylanilin-4-yl)-4,6-bis(3,5-dim-
ethylpyrazolyl)-triazine,44,45 or functionalized pyridine-di-
46
carboxamide (L2A, Chart 1).
In all cases, σ2 values are
significant, comprised between 100 and 300 GM, but these
complexes are only stable in organic solvents and not
compatible with water and therefore are not suitable for any
practical applications as biological probes. To overcome this
limitation, we focused on tris-dipicolinate lanthanide com-
plexes Ln(DPA)33- (DPA ) 2,6-pyridine-dicarboxylic acid,
Chart 1) known to present sufficient stability in water for
spectroscopic applications,47,48 and we described the first
two-photon microscopy experiment of a Tb(DPA)33- derived-
protein crystal.49 On the other hand, Wong et al. described
the sensitization of terbium by the three-photon antenna effect
to image biological cells.50 In addition, Palsson et al. reported
two-photon excited time-resolved luminescence spectroscopy
experiments using a cavity dumped Ti-sapphire laser
source.51 This important result opens the way for the
development of time-gated two-photon microscopy imaging
techniques. It is important to note that all of these complexes
used for nonlinear microscopy bioimaging present a rather
low two- (respectively three-) photon cross-section (for
instance, with a TPA cross-section < 5 GM), which is a
main drawback for practical applications. In this context,
functionalization of the DPA ligand by (i) a π-conjugated
TPA antenna and (ii) hydrosolubilizing groups (L2G, Chart
1) has allowed the synthesis of the europium complex
Na3[Eu(L2G)3] featuring significant σ2 in water (92 GM at
700 nm) and suitable for two-photon microscopy imaging
of fixed human cancer cells.52 To further optimize the
properties of this class of complexes, it is important to
increase the TPA cross-section of the probe at the bioimaging
operating wavelengths that are comprised between 700 and
1000 nm for Ti-Sapphire fs-laser and more precisely in the
750-800 spectral range usually used for practical imaging
experiments.
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10270 Inorganic Chemistry, Vol. 47, No. 22, 2008

Design of Dipicolinic Acid Ligands
Chart 1. Chemical Structure and Abbreviation Name of the Studied Ligand and Related EuIII Complexes
alkoxy, and alkylthio) as well as the length of the π-conju-
gated backbone (phenyl, phenylethynyl, naphtylethynyl,
bis(phenylethynyl), and chalcone) could be tuned (Chart 1).
Part 1 of this series of papers illustrated that the europium
luminescence can be efficiently sensitized from a relaxed
charge transfer (CT) excited state and that high quantum
yields can been obtained (up to 40%) only when the CT
excited-state energy lies above a limit estimated between
18 400 and 17 500 cm-1. For this reason, this process can
not occur in the case of the [NBu4]3[Eu(L6)3] for which CT
relaxed state energy is below this range. The second part of
this work described in the present paper, consists in the
systematic study of TPA properties of this family of
europium complexes [NBu4]3[Eu(L1-9)3] (Chart 1) in order
(i) to red-shift the maximal TPA wavelength (λTPA) and (ii)
to enhance the TPA cross-section.
Results
1. Synthesis. All of the ligands, L1-L9, are dipolar
compounds in which an acceptor moiety, namely, dipicolic
acid, is linked to various donor fragments, alkoxy, alkylthio,
and dialkylamino, via a different π-conjugated skeleton. The
synthesis involves as key steps palladium-catalyzed aryl/
ethynyl Sonogashira or aryl/aryl Suzuki cross-coupling
reactions. All of the syntheses started with the alkylation of
commercially available compounds (4-iodophenol, 4-iodot-
hiophenol, 6-bromo-2-naphtol, 2,6-dimethyl-4-bromoaniline,
and 4-iodoaniline) with a [2-(2-(2-methoxyethoxy)ethoxy)-
ethyl] group. This polyether chain was chosen to ensure the
solubility of the ligand in water in order to carry out
efficiently the final complexation step. Alkylation was
performed in a basic medium using 2-(2-(2-methoxyethoxy)-
Inorganic Chemistry, Vol. 47, No. 22, 2008 10271

D’Ale´o et al.
Scheme 1. Synthesis of the Conjugated Donor Groups 1-5c and 8c
Scheme 2. Elongation of the π-Conjugated System
Scheme 3. Syntheses of the Chalcone-Acetylide Moieties
ethoxy)ethylmethylsulfonate or 1-chloro-2-(2-(2-methoxy-
ethoxy)ethoxy)ethane. The first synthons featuring phenyle-
nethynyl moieties 1-5c and 8c were obtained in two steps
(Scheme 1): first, a Sonogashira cross-coupling reaction with
trimethylsilylacetylene using standard experimental condi-
tions (THF/triethylamine at 45 °C for the iodo derivatives
and DMF/triethylamine at 100 °C for the bromo ones)
yielded 1-5b and 8b in good yield. The trimethylsilyl
protecting group (TMS) was further cleaved with potassium
carbonate. Extension of conjugation by the incorporation of
an additional phenylenethynylene unit (9c) was performed
by two subsequent Sonogashira cross-coupling reactions with
(i) bromo-iodobenzene and (ii) TMS-acetylene followed by
deprotection of the TMS moieties (Scheme 2). Finally,
chalcone derivative 6a was prepared by the condensation of
dialkylaminobenzaldehyde and 4-bromoacetophenone fol-
lowing literature procedures. Addition of the ethynylene
fragment in 6c was then realized as described above for the
other systems (Scheme 3). Cross-coupling of all of these
donor-π-conjugated-acetylide synthons (1-6c and 8-9c)
with dimethyl-4-iodo-pyridine-2,6-dicarboxylate, whose large-
scale synthesis has been previously reported,53 gave 1-6d
and 8-9d in moderated to good yields after purification by
(53) Picot, A.; Feuvrie, C.; Barsu, C.; Malvolti, F.; Le Guennic, G.; Le
Bozec, H.; Andraud, C.; Toupet, L.; Maury, O. Tetrahedron 2008,
64, 399–411.
10272 Inorganic Chemistry, Vol. 47, No. 22, 2008

Design of Dipicolinic Acid Ligands
Scheme 4. Ligands Synthesis
Scheme 5. Preparation of L7
column chromatography (Scheme 4). Final saponification of
the ester moieties by sodium hydroxide led to the formation
of the tridendate ligands L1-L6 and L8-L9 in excellent
yields. The synthesis of L7, featuring a simple phenyl link
between donor and acceptor fragments, involved a Suzuki
cross-coupling between dimethyl-4-(pinacolatoboronic ester)-
2,6-dicarboxylate and 5a catalyzed with PdCl2(dppf) (dppf
) diphenylferrocenyl-phosphine) in DMF at 100 °C followed
by saponification of the ester moieties (Scheme 5). It is
important to note that all of the syntheses were carried out
on a large scale (few hundreds of milligrams to several
grams) and that the intermediates as well as the ligands are
isolated as sticky oils (except for L8 and L9), which makes
the synthesis uncomfortable. All of the molecules were fully
characterized by 1H NMR, 13C NMR, and mass spectrometry.
In addition, final ligands L1-L9 give satisfactory mi-
croanalyses. Their photophysical properties were thoroughly
described in the preceding paper. Finally, the corresponding
europium complexes [A]3[EuL1-93] (A stands for NBu4,
Chart 1) were prepared in water by mixing 3 equiv of ligands
with hydrated lanthanide chloride in the presence of NBu4OH
acting as base and counterion, followed by extraction with
dichloromethane. The resulting complexes are isolated as oils
(except for L8 and L9). 1H and 13C NMR spectra reveal only
one set of signals in agreement with the 3-fold symmetry of
the complexes, and the dipicolinate proton chemical shifts
are in agreement with data reported in the literature.54 In
addition, all europium complexes present elemental analyses
corresponding to the formation of dichloromethane solvate.
2. Photophysical Properties. All of the complexes present
broad intense transitions in the UV/visible spectrum (Figure
1 and Table 1) assigned to intraligand CT transitions on the
basis of time-dependent density functional theory calculations
(vide part 1 paper). It is worth noting that the absorption
bands of complexes [A]3[EuL1 ] and [A]3[EuL2 ] present a
3
3
shoulder corresponding to the overlap between the local
excited state and the CT transitions. As shown in part 1,
increasing the strength of the donor from -CH2OR, -OR,
-SR, or -NR2 results in a strong bathochromic shift of the
CT band from 312 to 370 nm (∆λ ) 60 nm, Table 1). On
the other hand, lengthening the π-conjugated backbone in
the series [A]3[EuL2,8,93] featuring an alkoxy donor group
induces a less-pronounced red-shift (∆λ ) 14 nm) but a
significant hyperchromic effect and broadening of the
absorption band (Figure 1).8,55,56 A similar effect is observed
in the series [A]3[EuL7,5,63] featuring dialkylamino donor
group. In addition, [A]3[EuL6 ] featuring dialkylaminochal-
3
cone moieties exhibits the most red-shifted transition centered
at 427 nm. All complexes, except [A]3[Eu(L6)3], exhibit the
classical emission profile of europium tris-dipicolinate, with
5
7
a very intense hypersensitive D0 f F2 transition (Figure
2).47-49 The quantum yields vary from 5.9% to 43% and
the lifetimes from 0.45 to 1.9 ms, depending on the nature
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D’Ale´o et al.
Figure 1. UV/visible absorption spectra in dichloromethane of [A]3[EuL2 ] (black), [A]3[EuL3 ] (blue), [A]3[EuL8 ] (red), and [A]3[EuL9 ] (green) (left)
3
3
3
3
and [A]3[EuL4 ] (purple), [A]3[EuL5 ] (green), [A]3[EuL6 ] (orange), and [A]3[EuL7 ] (aqua) (right).
3
3
3
3
Table 1. Photophysical and Two-Photon Absorption Data in
broad ligand-centered CT fluorescence is observed without
any europium luminescence, as detailed in part 1 (Figure
3). This result can be explained by the too low energy level
of the antenna ligand L6 for the sensitization of europium.
3. Two-Photon Absorption Properties. The two-photon
absorption cross-sections (σTPA) have been determined in
dichloromethane solution using the two-photon excited
fluorescence technique in the 700-900 nm wavelength range
with a femtosecond Ti-Sapphire pulsed laser source, accord-
ing to the experimental protocol described by Xu and
Webb.60 The quadratic dependence of the europium lumi-
nescence intensity versus incident laser power has been
checked, and an example is depicted in the case of
Dichloromethane Solution
max
max
λ
εmax
λ
τLn
σ2
λTPA
abs
em
(nm) (L mol-1 cm-1
)
(nm)
φL
(ms) (GM) (nm)a
[A]3[EuL1 ] 312
61300
92000
79000
58500
89200
94000
63600
86000
131000
613 0.059 0.86
3
[A]3[EuL2 ] 321
613 0.15
613 0.43
613 0.27
1.90
1.42
1.81
14
53
96
700
700
740
740
840
730
700
700
3
[A]3[EuL3 ] 322
3
[A]3[EuL4 ] 318
3
[A]3[EuL5 ] 370
613 0.070 0.85 775
3
[A]3[EuL6 ] 427
565 0.070b
613 0.28
173
3
[A]3[EuL7 ] 364
1.75 193
3
[A]3[EuL8 ] 335
613 0.090 0.90 110
613 0.036 0.45 218
3
[A]3[EuL9 ] 335
3
a λTPA stated for the wavelength of which the maximum two-photon cross-
section has been measured within the laser spectral range (700-900 nm).
b Emission from the CT state.
[A]3[EuL5 ] (Figure 4). In that case, the experimental
3
of the antenna ligand (donor group and conjugation length;
Table 1). Detailed studies of the luminescence properties of
[A]3[Eu(L1-6)3], reported in the part 1 paper, indicate that
europium luminescence is sensitized directly from the CT
state for these complexes.57-59 In the part 1 paper, it was
demonstrated that the global efficiency of the sensitization
process (in terms of luminescence quantum yield) presents
a maximum depending on (i) the relative position between
the energy levels of the CT donating state and the europium
regression coefficient is estimated at about 1.8 (th: 2),
indicating that, in the experimental laser power range, no
saturation or photodegradation occurs and unambiguously
confirming that the luminescence arises from a two-photon
absorption process. The two-photon excitation spectra were
calibrated using coumarin-307 as a standard60 (see the
Experimental Section for details). For all compounds, the
two-photon excitation spectra match the wavelength-doubled
scale single-photon one (Figures 5, 6, and 7 in the cases of
[A]3[EuL5 ], [A]3[EuL9 ], and [A]3[EuL6 ], respectively).
5
5D1 and D0 accepting states and (ii) the intrinsic antenna
3
3
3
quantum yield. In addition, for a given alkoxy donor group,
lengthening the conjugated pathway from phenylethynyl (L2),
naphtylenthynyl (L8), and bis-phenylethynyl (L9) results in
a regular decrease of both quantum yield and lifetime. This
tendency indicates a less efficient energy transfer to EuIII
that is in agreement with the presence of a residual CT broad
emission band centered at 402 nm in the case of
This good correlation is in agreement with the two-photon
selection rules and is characteristic for noncentrosymmetric
derivatives such as, for example, the D3 symmetric octupolar
complexes described in the present study.55,61-63 It indicates
that the lowest excited state in energy, here a CT state, is
one- and two-photon-allowed and confirms that the europium
luminescence (except for [A]3[EuL6 ]) is induced by a two-
3
[A]3[Eu(L9 )] (Figure 2). It is worth noting that this new
3
photon antenna effect with a similar photophysical sensitiza-
sensitization processes through the CT state allows for
reaching high quantum yield efficiency (43% in the case of
[A]3[Eu(L2)3]). Finally, in the case of [A]3[Eu(L6)3], featuring
the most red-shifted absorption band (Table 1), only the
(60) Xu, C.; Webb, W. W. J. Opt. Soc. Am. B 1996, 13, 481–491.
(61) Bhaskar, A.; Ramakrishna, G.; Lu, Z.; Twieg, R.; Hales, J. M.; Hagan,
D. J.; Van Stryland, E.; Goodson, T., III. J. Am. Chem. Soc. 2006,
128, 11840–11849.
(62) Mazzucato, S.; Fortunati, I.; Scolaro, S.; Zerbetto, M.; Ferrante, C.;
Signorini, R.; Bozio, R.; Locatelli, D.; Righetto, S.; Roberto, D.; Ugo,
R.; Abbotto, A.; Archetti, G.; Beverina, L.; Ghezzi, S. Phys. Chem.
Chem. Phys. 2007, 9, 2999–3005.
(63) Rumi, M.; Ehrlich, J. E.; Heikal, A. A.; Perry, J. W.; Barlow, S.; Hu,
Z.; McCord-Maughon, D.; Parker, T. C.; Ro¨ckel, H.; Thayumanavan,
S.; Marder, S. R.; Beljonne, D.; Bre´das, J.-L. J. Am. Chem. Soc. 2000,
122, 9500–9510.
(57) Werts, M. H. V.; Jukes, R. T. F.; Verhoeven, J. W. Phys. Chem. Chem.
Phys. 2002, 4, 1542–1548.
(58) Yang, C.; Fu, L. M.; Wang, Y.; Zhang, J. P.; Wong, W. T.; Ai, X. C.;
Qiao, Y. F.; Zou, B. S.; Gui, L. L. Angew. Chem., Int. Ed. 2004, 43,
5010–5013.
(59) Kim, Y. H.; Baek, N. S.; Kim, H. K. ChemPhysChem 2006, 7, 213–
221.
10274 Inorganic Chemistry, Vol. 47, No. 22, 2008

Design of Dipicolinic Acid Ligands
Figure 2. Room temperature emission spectra in DCM solution of [A]3[Eu(L9)3], inset: emission of residual CT state zoom × 10 (λexc) 340nm) (left).
Room temperature emission spectra in DCM solution of [A]3[Eu(L5)3], inset: emission of residual CT state zoom × 100 (λexc) 340 nm) (right).
Figure 5. Two-photon excitation spectrum of [A]3[EuL5 ] in dichlo-
3
Figure 3. Room temperature emission spectrum in DCM solution of
romethane solution (9, lower abscissa). Superimposed on this plot is the
[A]3[Eu(L6)3].
single-photon absorption spectrum in wavelength doubled scale (-, upper
abscissa).
The maximal two-photon absorption cross-section (σ2) and
the maximal TPA wavelength (λTPA) are summarized in Table
1. In the cases of [A]3[EuL2 ] and [A]3[EuL3 ], featuring
3
3
weak alkoxy or alkylthio donor groups, the maximal TPA
wavelength is located out of the laser range, and only a weak
tail corresponding to the red edge of the band is detected
(Figure 8). Similarly, it was not possible to record any TPA
excitation spectrum in the case of [A]3[EuL1 ] in the
3
700-900 nm range because its absorption is located at too
high an energy, and the remaining TPA cross-section in the
experimental range was too low. Although increasing the
length of the conjugated backbone with a naphtyl linker (in
[A]3[EuL8 ]) should allow a red-shift of the TPA band, as is
3
the case for the UV/visible absorption band, the TPA
maximum remains out of the spectral range. However, at
700 nm, the two-photon cross-section is now about 110 GM,
which is as high as other values found in the literature for
other europium complexes.43-46 When extending the con-
Figure 4. Plot of the europium emission intensity at 613 nm versus incident
laser power for [A]3[EuL5 ] (λex ) 800 nm) on a log/log scale. The fit of
3
the experimental data is shown in black, and the corresponding equation
and standard deviation are reported in the inset.
tion process, namely, two-photon absorption in the antenna
CT state followed by a direct energy transfer to the metal
jugated backbone as for [A]3[EuL9 ], the λTPA value is found
3
ion (Scheme 6). In the particular case of [A]3[EuL6 ], no
to be at 700 nm, twice the single absorption wavelength of
the shoulder at 354 nm (Figure 6) with a high TPA cross-
section of 218 GM. The 2-fold increase of the σ2 from
3
europium sensitization occurs, so only the CT emission is
observed upon one- or two-photon excitation (Scheme 6).
Inorganic Chemistry, Vol. 47, No. 22, 2008 10275

D’Ale´o et al.
Figure 6. Two-photon excitation spectrum of [A]3[EuL9 ] in dichlo-
romethane solution (9, lower abscissa). Superimposed on this plot is the
single-photon absorption spectrum in wavelength doubled scale (-, upper
abscissa).
3
Figure 8. Two-photon excitation spectra of [A]3[Eu(L2)3] (red 2),
[A]3[Eu(L3)3] (blue b), [A]3[Eu(L8)3] (purple 9), and [A]3[Eu(L9)3] (orange
1) in dichloromethane solution.
Figure 9. Two-photon excitation spectra of [A]3[Eu(L4)3] (purple 9),
[A]3[Eu(L5)3] (green 2), and [A]3[Eu(L7)3] (aqua b) in dichloromethane
solution.
Figure 7. Two-photon excitation spectrum of [A]3[EuL6 ] in dichlo-
romethane solution (9, lower abscissa). Superimposed on this plot is the
single-photon absorption spectrum in wavelength doubled scale (-, upper
abscissa).
3
Finally, replacing the alkoxy by a stronger amino donor
group induces a strong enhancement of the two-photon cross-
section accompanied by a large red-shift of the maximum
TPA wavelength (775 GM at 740 nm), which is the highest
value ever reported for a Eu complexes.43-46 In this series,
reducing the conjugation either by shortening or by twisting
the π skeleton in [A]3[EuL7 ] and [A]3[EuL4 ], respectively,
Scheme 6. Schematic Representation of the Two-Photon Excited
Photophysical Process
3
3
results in a significant decrease of σ2 (193 and 96 GM,
respectively; Figure 9).
Furthermore, in the case of the amino-donor-containing
complexes, the two-photon cross-section remains significant
in the spectral range where the nonlinear microscopy imaging
experiments are generally performed (750-800 nm). For
instance, at 780 nm, a TPA cross-section of about 315 GM
is obtained for [A]3[EuL5 ], more than 1 order of magnitude
3
higher than that of our benchmark complex Na3[Eu(L2G)3]
(σ2 (760) ) 19 GM and σ2 (780) ) 5 GM).52 Keeping in
mind that most of the intensity of the Eu emission is
concentrated in the sharp hypersensitive D0 f F2 band
(70% of the emission area), these complexes are interesting
[A]3[EuL8 ] to [A]3[EuL9 ] can be related to the hyperchro-
mic effect observed in one-photon absorption spectra, and a
similar enhancement of σ2 by lengthening the π-squeleton
are classically observed for organic chromophores.55,61,63
3
3
5
7
10276 Inorganic Chemistry, Vol. 47, No. 22, 2008

Design of Dipicolinic Acid Ligands
with a lens (focal length 10 cm) at the middle of the fluorescence
cell (10 mm). The fluorescence, collected at 90° to the excitation
beam, was focused into an optical fiber (diameter 600 µm)
connected to an Ocean Optics S2000 spectrometer. The incident
beam intensity was adjusted to 50 mW in order to ensure an
intensity-squared dependence of the fluorescence over the whole
spectral range. The detector integration time was fixed to 1 s.
Calibration of the spectra was performed by comparison with
the published 700-900 nm Coumarin-307 two-photon absorption
spectrum60 (Coumarin-307 quantum yield 0.56 in ethanol). The
measurements were done at room temperature in dihloromethane
and at a concentration of 10-4 M.
candidates for two-photon imaging applications. Interestingly,
the remarkable σ2 value reached in the case of [A]3[EuL5 ]
3
(775 GM at 740 nm) can be considered close to the upper
limit that can be reached for this family of complexes.
Indeed, although higher σ2 values should be expected by
further extension of the π system, for example, the resulting
lower gap between the antenna ground state and the Eu
excited state will prohibit any energy transfer to the metal
as in [A]3[Eu(L6)3]. This upper limit depends of course on
the nature of the lanthanide and on its sensitization process.
As a consequence, a higher σ2 could be obtained using more
conjugated ligands, for NIR-emitting lanthanides (Yb, Nd,
or Er), whereas lower limit values are expected with weakly
conjugated systems for Tb or Dy, for which accepting excited
states lie at higher energy.
General Procedure. NMR spectra (1H and 13C) were recorded
at room temperature on a BRUKER AC 200 operating at 200.13
1
and 50.32 MHz for H and 13C, respectively. Data are listed in
parts per million (ppm) and are reported relative to tetramethylsilane
(1H and 13C); residual solvent peaks of the deuterated solvents were
used as an internal standard. UV/vis absorption measurements were
recorded on a JASCO V550 absorption spectrometer. Low-
resolution mass spectrometry was carried out on an Agilent 1100
Series LC/MSD apparatus. High-resolution mass spectrometry
measurements and elemental analyses were performed at the Service
Central d’Analyze du CNRS (Vernaison, France).
Conclusion
In conclusion, we designed a new versatile family of
chromophore-based ligands able to induce europium emission
by a two-photon antenna effect. Tuning the strength of the
donor as well as the length of the π-conjugated backbone
allows optimization of the TPA cross-section, 775 GM at
General Procedure for Sonogashira Cross-Coupling Reac-
tions. In a 100 mL Schlenk flask, dimethyl-4-iodopyridine-2,6-
dicarboxylate (1 equiv) was dissolved in a mixture a THF and
triethylamine (15 mL/15 mL). The solution was thoroughly
degassed by argon bubbling for 20 min and an acetylene derivative,
copper iodide (0.2 equiv), and (Ph3P)PdCl2 (0.l equiv) were added
under a flux of argon. The reaction was stirred at 40 °C for 14 h.
The solution was evaporated under a vacuum, and the resulting oil
was dissolved in ethylacetate and extracted with a NH4Cl aqueous
solution and with brine. The crude was purified by column
chromatography on silica.
740 nm for [A]3[EuL5 ], and a shift of the maximal TPA
3
wavelength to the red. In the spectral region of interest
(750-800 nm), this latter compound conserves a very
significant TPA cross-section. These results emphasize the
high potentialities of this class of compounds: (i) the high
σ2 values are promising for the sensitization of NIR emitters
such as ytterbium and neodymium, and (ii) their stability in
water is of prime importance for the further design of a new
family of bioprobes with enhanced water solubility. These
results combined with two-photon excited time-gated spec-
troscopy experiments recently demonstrated51 open the way
to an improved biological imaging technique: biphotonic
time-gated microscopy, combining the advantage of both
lanthanides and two-photon microscopy.
1d. Transparent oil (68%) from 1c (835 g), chromatography
1
conditions: ethyl acetate. H NMR (200.13 MHz, CDCl3): δ 8.28
(s, 2H), 7.59 (d, 3J ) 8.1 Hz, 2H), 7.32 (d, 3J ) 8.1 Hz, 2H), 4.53
(s, 2H), 3.96 (s, 6H), 3.60 (m, 10H), 3.50 (m, 2H), 3.30 (s, 3H).
13C NMR (50.332 MHz, CDCl3): 164.81, 148.57, 140.70, 134.60,
132.23, 129.71, 127.73, 120.50, 97.03, 85.45, 72.73, 72.06, 70.75,
70.66, 69.94, 59.12, 53.39. EI-MS: [M + H]+, 472; [M + Na]+,
494.
Experimental Section
2d. Transparent oil (84%) from 2c (1.84 g), chromatography
Luminescence Measurements: Luminescence. The lumines-
cence spectra were measured using a Horiba-Jobin Yvon Fluo-
rolog-3 spectrofluorimeter (see the preceding article for details).
Phosphorescence lifetimes (>30 µs) were obtained by pulsed
excitation using an FL-1040 UP xenon lamp. Luminescence decay
curves were fitted by least-squares analysis using Origin. Fluores-
cence quantum yields, Q, were measured in a diluted solution with
an optical density lower than 0.1 using the following equation: Qx/
1
conditions: dichloromethane/ethyl acetate (9/1). H NMR (200.13
3
MHz, CDCl3): δ 8.29 (s, 2H), 7.43 (d, J ) 8.8 Hz, 2H), 6.87 (d,
3
3J ) 8.8 Hz, 2H), 4.13 (t, J ) 4.9 Hz, 2H), 3.99 (s, 6H), 3.86 (t,
3J ) 4.5 Hz, 2H), 3.64 (m, 6H), 3.52 (m, 2H), 3.34 (s, 3H). 13C
NMR (50.332 MHz, CDCl3): δ 165.0, 160.4, 148.6, 135.1, 134.0,
129.7, 115.2, 113.7, 97.7, 84.9, 72.2, 71.1, 70.9, 70.8, 69.8, 67.8,
59.3, 53.5. EI-MS: [M + H]+, 458; [M + Na]+, 480. Elem anal.
calcd for C24H27NO8: C, 63.01; H, 5.95; N, 3.06. Found: C, 62.76;
H, 5.84; N, 2.92.
2
Qr ) [Ar(λ)/Ax(λ)][nx /nr2][Dx/Dr], where A is the absorbance at the
excitation wavelength (λ), n is the refractive index, and D is the
integrated luminescence intensity. The “r” and “x” stand for
reference and sample. Here, references are the quinine bisulfate in
1 N sulfuric acid in aqueous solution (Qr ) 0.546)64 and Ru(bpy)3
2Cl complexes in a water solution (Qr ) 0.028)65 for each complex.
Two-Photon Excited Luminescence Measurements. The TPA
cross-section spectra were obtained by up-conversion fluores-
cence using a Ti:sapphire femtosecond laser in the range
700-900 nm. The excitation beam (5 mm diameter) is focalized
3d. Transparent oil (59%) from 3c (620 mg), chromatography
1
conditions: ethyl acetate. H NMR (200.13 MHz, CDCl3): δ 8.28
(s, 2H), 7.41 (d, 3J ) 8.3 Hz, 2H), 7.27 (d, 3J ) 8.4 Hz, 2H), 3..98
3
(s, 6H), 3.86 (t, J ) 4.5 Hz, 2H), 3.59 (m, 8H), 3.50 (m, 2H),
3
3.32 (s, 3H), 3.13 (t, J ) 6.8 Hz, 2H). 13C NMR (50.332 MHz,
CDCl3): δ 164.8, 148.6, 139.9, 134.6, 133.5, 129.7, 127.8, 118.3,
96.9, 85.9, 72.1, 70.7, 70.7, 69.8, 59.2, 53.4, 32.2. EI-MS: [M +
Na]+, 474; [M + Na]+, 496.
4d. Orange oil (87%) from 4c (300 mg), chromatography
conditions: chloroform/diethylether (3/1). 1H NMR (200.13 MHz,
CDCl3): δ 8.28 (s, 2H), 7.19 (s, 2H), 3.99 (s, 6H), 3.50 (m, 20H),
(64) Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991–1024.
(65) Nakamaru, K. Bull. Chem. Soc. Jpn. 1982, 55, 2697–2705.
Inorganic Chemistry, Vol. 47, No. 22, 2008 10277

D’Ale´o et al.
3
3.33 (s, 6H), 3.25 (t, J ) 5.8 Hz, 4H), 2.26 (s, 6H). 13C NMR
70.6, 70.0, 67.4, 59.0. EI-MS: [M + H]+, 430; [M + Na]+, 452.
Elem anal. calcd for C22H23NO8: C, 61.53; H, 5.40; N, 3.26. Found:
C, 61.57; H, 5.35; N, 3.13.
(50.332 MHz, CDCl3): δ 165.0, 150.2, 148.6, 138.2, 135.1, 132.7,
129.7, 117.4, 97.9, 85.0, 72.1, 70.8, 70.7, 70.5, 59.2, 53.7, 53.4,
19.3. EI-MS: [M + H]+, 631; [M + Na]+, 653.
5d. Orange oil (86%) from 5c (370 mg), chromatography
conditions: ethyl acetate. H NMR (200.13 MHz, CDCl3): δ 8.19
L3. White solid (96%). 1H NMR (200.13 MHz, CDCl3): δ 9.83
(b, 2H), 8.31 (s, 2H), 7.35 (d, 3J ) 7.7 Hz, 2H), 7.17 (d, 3J ) 7.8
3
1
Hz, 2H), 3.66 (m, 8H), 3.57 (m, 2H), 3.35 (s, 3H), 3.11 (t, J )
6.3 Hz, 2H). 13C NMR (50.332 MHz, CDCl3): 164.53, 146.48,
140.21, 135.89, 132.51, 129.48, 127.11, 117.79, 98.06, 85.73, 71.83,
70.49, 70.44, 70.38, 69.45, 58.93, 31.91. EI-MS: [M + Na]+, 446
(s, 2H), 7.21 (d, 3J ) 8.7 Hz, 2H), 6.61 (d, 3J ) 8.9 Hz, 2H), 3.93
(s, 6H), 3.46 (m, 24H), 3.28 (s, 6H). 13C NMR (50.332 MHz,
CDCl3): δ 164.9, 150.0, 148.2, 135.4, 133.7, 111.5, 107.4, 95.6,
84.5, 71.9, 70.7, 70.5, 68.3, 59.0, 53.1, 50.8. Elem anal. calcd for
C31H42N2O10: C, 61.78; H, 7.02; N, 4.65. Found: C, 61.44; H, 6.96;
N, 4.62.
(446); [M
+
Na]+, 468 (468). Elem anal. calcd for
C22H23NO7S·H2O: C, 57.01; H, 5.44; N, 3.02. Found: C, 56.89;
H, 5.47; N, 2.84.
L4. Orange solid (84%). 1H NMR (200.13 MHz, CDCl3): δ 8.99
(b, 2H), 8.29 (s, 2H), 6.99 (s, 2H), 3.50 (m, 20H), 3.29 (m, 10H),
2.21 (s, 6H). 13C NMR (50.332 MHz, CDCl3): 164.33, 149.99,
146.37, 137.62, 136.13, 132.59, 129.16, 117.03, 98.49, 85.37, 71.85,
70.42, 70.29, 58.89, 53.37, 18.99. Elem anal. calcd for
C31H42N2O10 ·H2O: C, 59.99; H, 7.15; N, 4.51. Found: C, 58.98;
H, 6.91; N, 4.30.
6d. Orange solid (85%) from 6c (115 mg), chromatography
conditions: ethyl acetate/methanol (95/5). 1H NMR (200.13 MHz,
CDCl3): δ 8.38 (s, 2H), 8.02 (d, J ) 8.2 Hz, 2H), 7.78 (d, J )
3
3
3
3
15.4 Hz, 1H), 7.67 (d, J ) 8.2 Hz, 2H), 7.29 (d, J ) 15.4 Hz,
3
1H), 6.71 (d, J ) 8.8 Hz, 2H), 4.03 (s, 6H), 3.56 (m, 32H), 3.35
(s, 6H). 13C NMR (50.332 MHz, CDCl3): δ 189.36, 164.63, 150.25,
148.55, 146.42, 139.75, 134.03, 132.17, 130.79, 129.68, 128.43,
124.88, 122.43, 116.19, 111.71, 96.02, 87.52, 71.92, 70.76, 70.61,
70.51, 68.38, 50.02, 53.34, 50.94.
L5. Orange solid (99%). 1H NMR (200.13 MHz, CDCl3): δ 8.20
(s, 2H), 7.12 (d, 3J ) 8.5 Hz, 2H), 6.48 (d, 3J ) 8.5 Hz, 2H), 3.49
(m, 24H), 3.30 (s, 6H). 13C NMR (50.332 MHz, CDCl3): δ 164.4,
149.0, 146.1, 136.8, 133.7, 111.6, 107.4, 100.8, 85.0, 71.8, 70.6,
70.6, 70.4, 68.3, 58.9, 50.5. EI-MS: [M + H]+, 575; [M + Na]+,
597. Elem anal. calcd for C29H38N2O10 ·H2O: C, 58.77; H, 6.80;
N, 4.73. Found: C, 58.74; H, 6.80; N, 4.58.
8d. White oil (83%) from 8c (1.82 g), chromatography condi-
1
tions: ethyl acetate. H NMR (200.13 MHz, CDCl3): δ 8.29 (s,
3
2H), 7.95 (s, 1H), 7.64 (m, 2H), 7.47 (d, J ) 8.3 Hz, 1H), 7.13
(m, 2H), 4.19 (m, 2H), 3.97 (s, 6H), 3.86 (m, 2H), 3.63 (m, 6H),
3.50 (m, 2H), 3.30 (s, 3H). 13C NMR (50.332 MHz, CDCl3): δ
164.7, 158.2, 148.4, 134.9, 134.6, 132.5, 129.6, 129.5, 128.6, 128.3,
127.2, 120.1, 116.1, 106.8, 97.9, 85.3, 71.9, 70.9, 70.7, 70.6, 69.6,
67.5, 59.0, 53.3. EI-MS: [M + H]+, 508; [M + Na]+, 530.
9d. White solid (70%) from 9c (310 mg), chromatography
conditions: dichloromethane/diethylether (9/1) to dichloromethane/
diethylether (4/1). 1H NMR (200.13 MHz, CDCl3): δ 8.26 (s, 2H),
L6. Orange solid (99%). 1H NMR (200.13 MHz, CDCl3): δ 8.33
3
3
(s, 2H), 7.92 (d, J ) 7.4 Hz, 2H), 7.71 (d, J ) 15.0 Hz, 1H),
7.53 (d, 3J ) 7.4 Hz, 2H), 7.38 (d, 3J ) 7.4 Hz, 2H), 7.21 (d, 3J )
15.0 Hz, 1H), 6.61 (d, J ) 7.4 Hz, 2H), 3.60 (m, 32H), 3.33 (s,
3
6H). 13C NMR (50.332 MHz, CDCl3): δ 189.12, 164.43, 150.22,
146.90, 146.51, 139.44, 135.03, 132.23, 130.80, 129.41, 128.40,
124.76, 122.44, 115.81, 111.70, 96.69, 87.58, 71.87, 70.58, 70.53,
70.42, 68.40, 58.98, 50.75. EI-MS: [M + H]+, 793; [M + Na]+,
815. Elem anal. calcd for C42H52N2O13 ·2H2O: C, 60.86; H, 6.81;
N, 3.38. Found: C, 60.03; H, 6.74; N, 3.44.
3
7.37 (m, 6H), 6.82 (d, J ) 8.9 Hz, 2H), 4.07 (m, 2H), 3.95 (s,
3
6H), 3.78 (t, J ) 5.0 Hz, 2H), 3.57 (m, 6H), 3.47 (m, 2H), 3.30
(s, 3H). 13C NMR (50.332 MHz, CDCl3): δ 164.6, 159.2, 148.4,
134.2, 133.1, 132.0, 131.5, 129.5, 129.3, 120.5, 114.9, 114.7, 96.6,
92.5, 87.6, 86.9, 71.9, 70.8, 70.6, 70.5, 69.6, 67.5, 59.0, 53.3. EI-
MS: [M + H]+, 558; [M + Na]+, 580.
L7. Orange-yellow solid (99%). 1H NMR (200.13 MHz,
(CD3)2CO): δ 8.25 (b, 2H), 7.82 (b, 2H), 6.94 (b, 2H), 3.58 (m,
24H), 3.26 (s, 6H). 13C NMR (50.332 MHz, (CD3)2CO): δ 164.2,
152.0, 150.3, 147.1, 128.2, 122.5, 121.6, 112.3, 71.8, 70.5, 70.4,
70.3, 68.4, 57.9, 50.8. Elem anal. calcd for C27H38N2O10 ·H2O: C,
57.03; H, 7.09; N, 4.93. Found: C, 56.51; H, 7.08; N, 4.54.
L8. White solid (96%). 1H NMR (200.13 MHz, CDCl3): δ 7.78
(s, 2H), 7.74 (s, 1H), 7.49 (s, 2H), 7.38 (d, 3J ) 9.2 Hz, 1H), 7.02
General Procedure for the Ligand Deprotection. In a 100 mL
round-bottom flask, the ligand diester precursor 1-10d was
dissolved in 15 mL of methanol; a solution of NaOH (4-5 equiv)
in water (20 mL) wad added, and the reaction was stirred at room
temperature for 1 h. The methanol was evaporated; the water phase
was extended to 100 mL, and the aqueous phase was extracted
with ethyl acetate (two times). The water was acidified with HCl
(10%) until the pH was 1-2, and the aqueous phase was extracted
three times with dichloromethane. The organic phases were
regrouped and dried over sodium sulfate. After evaporation of the
organic solvents, the white solid was dried at room temperature
under a vacuum for 1 h.
3
(dd, J ) 9.2 Hz, 1H), 6.76 (s, 1H), 4.21 (m, 2H), 3.96 (m, 2H),
3.79 (m, 4H), 3.63 (m, 2H), 3.54 (m, 2H), 3.25 (s, 3H). 13C NMR
(50.332 MHz, CDCl3): δ 164.1, 157.5, 145.4, 134.9, 134.3, 132.6,
129.6, 129.2, 128.3, 128.0, 127.1, 119.7, 116.6, 106.0, 98.4, 85.1,
71.6, 70.7, 70.3, 69.9, 67.0, 58.7. Elem anal. calcd for
C26H25NO8 ·H2O: C, 62.77; H, 5.47; N, 2.82. Found: C, 63.10; H,
5.28; N, 2.73.
L1. White solid (93%). 1H NMR (200.13 MHz, CDCl3): δ 10.00
(bs, 2H), 8.27 (s, 2H), 7.31 (d, 3J ) 8.0 Hz, 2H), 7.19 (d, 3J ) 8.0
Hz, 2H), 4.49 (s, 2H), 3.66 (m, 8H), 3.55 (m, 2H), 3.45 (m, 2H),
3.25 (s, 3H). 13C NMR (50.332 MHz, CDCl3): 164.1, 146.2, 140.0,
135.7, 132.1, 129.2, 127.7, 120.2, 97.6, 85.6, 72.7, 71.7, 70.6, 70.5,
70.4, 70.3, 70.0, 58.8. Elem anal. calcd for C23H25NO8 ·2H2O: C,
57.61; H, 6.10; N, 2.92. Found: C, 57.86; H, 5.35; N, 2.89.
L2. White solid (97%). 1H NMR (200.13 MHz, CDCl3): δ 8.14
(s, 2H), 7.23 (d, 3J ) 8.7 Hz, 2H), 6.60 (d, 3J ) 8.7 Hz, 2H), 3.99
(m, 2H), 3.88 (m, 2H), 3.78 (s, 4H), 3.64 (m, 2H), 3.52 (m, 2H),
3.22 (s, 3H). 13C NMR (50.332 MHz, CDCl3): δ 164.28, 159.7,
146.1, 136.2, 134.1, 129.1, 114.6, 113.7, 98.5, 85.3, 71.9, 70.9,
L9. White solid (83%).1H NMR (200.13 MHz, CDCl3): δ 8.22
(s, 2H), 7.28 (m, 4H), 7.19 (d, 3J ) 8.6 Hz, 2H), 6.59 (d, 3J ) 8.6
Hz, 2H), 4.02 (m, 2H), 3.92 (m, 2H), 3.83 (m, 4H), 3.68 (m, 2H),
3.55 (m, 2H), 3.26 (s, 3H). 13C NMR (50.332 MHz, CDCl3): δ
164.24, 158.48, 146.00, 135.43, 132.78, 131.88, 131.21, 128.94,
125.08, 120.23, 115.10, 114.05, 97.21, 91.95, 88.59, 87.05, 71.68,
70.73, 70.21, 70.13, 69.86, 66.86, 58.77. EI-MS: [M + H]+, 530;
[M + Na]+, 552. Elem anal. calcd for C30H27NO8.H2O: C, 65.81;
H, 5.34; N, 2.56. Found: C, 66.03; H, 5.09; N, 2.51.
General Procedure for the Synthesis of the Complexes. In a
100 mL round-bottom flask, Li (i ) 1-9, 3 equiv) and tetrabuty-
lammonium hydroxide (40% in methanol, 6 equiv) were dissolved
10278 Inorganic Chemistry, Vol. 47, No. 22, 2008

Design of Dipicolinic Acid Ligands
3
3
in water (15 mL), and EuCl3 ·6H2O (1.05 equiv) was added. The
solution was stirred at room temperature for 1 h. This aqueous
mixture was extracted with dichloromethane (5 × 100 mL). The
organic phases were combined, concentrated up to 40 mL, washed
several times with water (5 × 100 mL), dried over magnesium
sulfate, and evaporated under a vacuum. The products were obtained
as hygroscopic light yellow or orange oils.
Hz, 6H), 7.32 (d, J ) 15.2 Hz, 3H), 7.18 (d, J ) 8.1 Hz, 6H),
3
6.75 (d, J ) 8.6 Hz, 6H), 4.53 (bs, 6H), 3.57 (m, 96H), 3.36 (m,
42H), 1.69 (m, 24H), 1.43 (m, 24H), 1.02 (t, J) 7.1 Hz, 36H).
Elem anal. calcd for C174H258N9O39Eu·6CH2Cl2: C, 59.90; H, 7.74;
N, 3.49. Found: C, 59.45; H, 7.62; N, 3.37.
3
[NBu4]3[Eu(L7)3]. Orange oil, yield: 61%. 1H NMR (200.13 MHz,
CD3OD): δ 6.23 (m, 12H), 4.12 (bs, 6H), 3.68 (m, 24H), 3.35 (m,
72H), 3.16 (s, 18H), 1.95 (m, 24H), 1.62 (m, 24H), 1.06 (t, 3J ) 7.0
Hz, 36H). 13C NMR (50.332 MHz, CD3OD): δ 164.4, 161.6, 149.3,
137.3 128.1, 118.5, 110.8, 71.4, 70.1, 69.9, 68.2, 58.6, 50.2, 23.8, 19.6,
12.8. Elem anal. calcd for C129H216N9O30Eu·3CH2Cl2: C, 57.03; H,
8.05; N, 4.53. Found: C, 56.59; H, 8.27; N, 4.26.
1
[NBu4]3[Eu(L1)3]. Colorless oil, yield: 67%. H NMR (200.13
MHz, CDCl3): δ 7.17 (b, 2H), 6.99 (b, 2H), 5.10 (b, 2H), 4.46 (b,
2H), 3.30 (m, 23H), 1.73 (b, 8H), 1.48 (b, 8H), 1.05 (b, 12H). Elem
anal. calcd for C117H177N6O24Eu·7CH2Cl2: C, 53.23; H, 6.83; N,
3.00. Found: C, 53.61; H, 6.74; N, 2.93.
[Bu4N]3[EuL2 ]. Light yellow oil, yield: 49%. 1H NMR (200.13
3
[Bu4N]3[EuL8 ]. White oil, yield: 85%. NMR (200.13 MHz,
3
3
3
MHz, CDCl3): 6.89 (d, J ) 8.7 Hz, 6H), 6.65 (d, J ) 8.7 Hz,
6H), 5.56 (m, 24H), 4.95 (s, 6H), 3.98 (m, 6H), 3.75 (m, 18H),
3.57 (m, 6H), 3.44 (m, 6H), 3.29 (s, 9H), 2.88 (m, 24H), 2.00 (m,
24H), 1.11 (t, 3J ) 6.9 Hz, 36H). Elem anal. calcd for
CDCl3): 7.46 (m, 9H), 7.05 (m, 9H), 5.15 (bs, 6H), 4.65 (m, 24H),
4.16 (m, 6H), 3.85 (m, 6H), 3.64 (m, 18H), 3.51 (m, 6H), 3.32 (s,
9H), 2.37 (m, 24H), 1.76 (m, 24H), 1.02 (m, 36H). Elem anal. calcd
for C126H177N6O24Eu·2CH2Cl2: C, 61.95; H, 7.35; N, 3.39. Found:
C, 61.89; H, 7.95; N, 3.39.
C
114H171N6O24Eu·CH2Cl2: C, 61.48; H, 7.76; N, 3.16. Found: C,
61.80; H, 8.05; N, 3.79.
[Bu4N]3[Eu(L3)3]. Yellow oil, yield: 67%. H NMR (200.13
1
[Bu4N]3[EuL9 ]. White oil, yield: 55% NMR (200.13 MHz,
3
3
3
CDCl3): 7.35 (d, 3J ) 8.9 Hz, 6H), 7.27 (d, 7.30 (m, 6H), 6.96 (d,
MHz, CDCl3): δ 7.09 (d, J ) 8.0 Hz, 6H), 6.92 (d, J ) 7.9 Hz,
3J ) 8.3 Hz, 6H), 6.82 (d, J ) 8.9 Hz, 6H), 5.76 (b, 24H), 5.04
3
6H), 5.30 (b, 6H), 4.78 (m, 24H), 3.49 (m, 24H), 3.28 (s, 9H),
3
(s, 6H), H), 4.10 (m, 6H), 3.81 (t, 3J ) 5.0 Hz, 6H), 3.60 (m, 18H),
3.53 (m, 6H), 3.30 (s, 9H), 2.98 (b, 24H), 2.08 (b, 24H), 1.15 (t, 3J
) 6.7 Hz, 36H). Elem anal. calcd for C138H183N6O24Eu·2CH2Cl2:
C, 63.89; H, 7.16; N, 3.19. Found: C, 64.05; H, 7.72; N, 3.17.
3.01 (t, J ) 6.6 Hz, 6H), 2.43 (b, 24H), 1.76 (b, 24H), 1.00 (b,
36H). 13C NMR (50.332 MHz, CDCl3): 165.78, 143.32, 141.68,
138.61, 132.78, 127.45, 117.77, 95.83, 85.12, 80.95, 71.85, 70.51,
70.40, 69.62, 60.33, 58.98, 32.32, 24.94, 20.23, 13.94. Elem anal.
calcd for C114H171N6O21S3Eu ·3CH2Cl2: C, 57.02; H, 7.24; N, 3.41.
Found: C, 57.38; H, 8.03; N, 3.28.
[Bu4N]3[Eu(L4)3]. Orange oil, yield: 76%. 1H NMR (200.13
MHz, CD3OD): δ 6.61 (s, 6H), 4.15 (bs, 6H), 3.45 (m, 84H), 3.21
Acknowledgment. The authors are grateful to the French
Agence Nationale de la Recherche (ANR LnOnL NT05-
3_42676) for financial support. The authors also would
like J. Bernard for technical assistance and Dr. M. Allali
for help.
3
(s, 18H), 3.11 (m, 12H), 2.12 (s, 18H), 1.82 (m, 24H), 1.52 (q, J
3
) 7.1 Hz, 24H), 1.04 (t, J ) 7.1 Hz, 36H). Elem anal. calcd for
C141H228EuN9O30 ·4CH2Cl2: C, 57.65; H, 7.87; N, 4.17. Found: C,
57.35; H, 7.87; N, 4.17.
[Bu4N]3[EuL5 ]. Orange oil, yield: 64%. NMR (200.13 MHz,
3
3
3
CD3OD): 6.78 (d, J ) 8.3 Hz, 6H), 6.49 (d, J ) 8.3 Hz, 6H),
Supporting Information Available: Comparison of TPA
spectra of Na3EuL2G3 in water and DCM solution, photophysical
and two-photon data for Eu complexes, and detailed synthesis
procedures of the intermediate compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
4.24 (b, 6H), 3.38 (m, 114H), 1.75 (m, 24H), 1.47 (m, 24H), 1.03
3
(t, J ) 7.1 Hz, 36H). Elem anal. calcd for C135H216N9O30Eu ·
4CH2Cl2: C, 56.85; H, 7.69; N, 4.29. Found: C, 56.58; H, 7.76; N,
4.23.
[Bu4N]3[EuL6 ]. Yield: 67%. NMR (200.13 MHz, CD3OD): 7.85
3
(d, 3J ) 8.1 Hz, 6H), 7.64 (d, 3J ) 15.2 Hz, 3H), 7.50 (d, 3J ) 8.6
IC8012975
Inorganic Chemistry, Vol. 47, No. 22, 2008 10279