Synthesis and photoluminescence properties of heteroleptic europium(III) complexes with appended carbazole units

Article abstract of DOI:10.1002/ejic.200701257

Two europium complexes {Eu·dbm·carb·phen = tris[1-{[6-(9H-carbazol-9-yl)hexoxy]phenyl}-3-{[6-(9H-carbazol-9-yl)-hexoxy] phenyl}propane-1,3-dione](1,10-phenanthroline)-europium(III), Eu·dbm·carb·bath = tris[1-{[6-(9H-carbazol-9-yl)hexoxy] phenyl}-3-{[6-(9H-carbazol-9-yl)hexoxy]phenyl}-propane-1,3-dione] (bathophenanthroline)europium(III)} and their reference compounds were synthesized and characterized. Each complex contains three different chromophores: carbazole (carb), phenanthroline (phen) (or bathophenanthroline, bath) and dibenzoylmethane (dbm) units. The luminescence properties investigated in dichlorometh-ane solution and in solid matrix show that the carbazole moiety is a better sensitizer for the metal-centred emitting states of the Eu ^III ion compared to the dibenzoylmethane and phenanthroline units. Furthermore, the charge-transporting properties of the carbazole moieties appear to be appealing when integrated into the emitting units. Finally, the high number of appended carbazole units confers a strong light-harvesting character to the structure. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200701257

FULL PAPER
DOI: 10.1002/ejic.200701257
Synthesis and Photoluminescence Properties of Heteroleptic Europium(III)
Complexes with Appended Carbazole Units
Youxuan Zheng,[a][‡] Francois Cardinali,[a] Nicola Armaroli,[a] and Gianluca Accorsi*[a]
Keywords: Europium / Photoluminescence / Carbazoles / Chromophores
Two europium complexes {Eu·dbm·carb·phen = tris[1-{[6-
(9H-carbazol-9-yl)hexoxy]phenyl}-3-{[6-(9H-carbazol-9-yl)-
hexoxy]phenyl}propane-1,3-dione](1,10-phenanthroline)-
europium(III), Eu·dbm·carb·bath = tris[1-{[6-(9H-carbazol-9-
yl)hexoxy]phenyl}-3-{[6-(9H-carbazol-9-yl)hexoxy]phenyl}-
propane-1,3-dione](bathophenanthroline)europium(III)} and
their reference compounds were synthesized and charac-
terized. Each complex contains three different chromo-
phores: carbazole (carb), phenanthroline (phen) (or batho-
phenanthroline, bath) and dibenzoylmethane (dbm) units.
The luminescence properties investigated in dichlorometh-
ane solution and in solid matrix show that the carbazole moi-
ety is a better sensitizer for the metal-centred emitting states
of the EuIII ion compared to the dibenzoylmethane and phen-
anthroline units. Furthermore, the charge-transporting prop-
erties of the carbazole moieties appear to be appealing when
integrated into the emitting units. Finally, the high number
of appended carbazole units confers a strong light-harvesting
character to the structure.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
Introduction
Organic light-emitting diodes (OLEDs)[1] are extensively
studied for their potential application in next generation
full-colour flat panel displays and light sources.[2–12] EuIII
complexes are suitable luminescent materials for red
OLEDs[13–16] owing to their quasimonochromatic red-light
emission. Furthermore, the multiplet nature of the elec-
tronic transitions (f–f) leads to an efficient energy conver-
sion in electroluminescence.[17] However, in spite of the ex-
cellent photoluminescence (PL) properties of EuIII materi-
als, bright-red europium-containing electroluminescent
(EL) devices with satisfying performance are hardly obtain-
able because of the poor charge-transporting ability of the
lanthanide complexes and the luminescence quenching by
matrix vibrations through nonradiative pathways.[18,19] To
improve the charge-transporting properties of EuIII com-
plexes to be used in electroluminescent devices, a suitable
strategy would involve doping with electron/hole-trans-
porting molecules, such as biphenyl-p-(tert-butyl)phenyl-
1,3,4-oxadiazole (PBD), N,NЈ-diphenyl-N,NЈ-bis(3-meth-
ylphenyl)-1,1Ј-biphenyl-4,4Ј-diamine (TPD) or 4,4Ј-N,NЈ-
[a] Molecular Photoscience Group, Istituto per la Sintesi Organica
e la Fotoreattività, Consiglio Nazionale delle Ricerche (CNR-
ISOF),
Via P. Gobetti 101, 40129 Bologna, Italy
E-mail: gianluca.accorsi@isof.cnr.it
[‡] Current address: State Key Laboratory of Coordination Chem-
istry, Nanjing University,
210093 Nanjing, P. R. China
E-mail: yxzheng@nju.edu.cn
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Scheme 1. Chemical structures of the studied compounds.
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2075
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Y. Zheng, F. Cardinali, N. Armaroli, G. Accorsi
FULL PAPER
dicarbazolebiphenyl (CBP). Unfortunately, this method first reported by Bauer et al.[23] and is now commercially
usually leads to phase separation during device manufactur- available.
ing, (i.e. sublimation). An alternative approach is given by
We developed an approach in which two carbazole units
covalent linking of charge-transporting moieties with lan- were appended to the dibenzoylmethane[24] unit through a
thanide complexes, as proposed by Zheng et al.,[20] Bazan synthetic method described in Scheme 2. Carbazole was
et al.,[21] Tian et al.[7] and Huang et al.,[22] who reported treated with 1,6-dibromohexane in the presence of potas-
efficient OLEDs by using oxadiazole- or carbazole-func- sium carbonate to give 6-(9H-carbazol-9-yl)-1-bromohex-
tionalized lanthanide complexes. In contrast, to enhance ane. This product was then treated on the one hand with
the molar extinction coefficients of the complex and limit ethyl 4-hydroxybenzoate to give the corresponding ether
the vibronic luminescence quenching by the matrix, light- through classical conditions (potassium carbonate, NaI),
harvesting multichromophoric ligands have been pro- and on the other hand, 6-(9H-carbazol-9-yl)-1-bromohex-
posed.[7] These systems have the ability to collect and trans- ane was treated with 1-(4-hydroxyphenyl)ethanone to give
fer the excitation energy from the periphery of the complex the corresponding ether. Reaction of the two building
to the emitting lanthanide ion core and, at the same time, blocks in the presence of a strong base (NaH) yielded
protect the central ion by parasite quenching processes.
the desired ligand 1-{[6-(9H-carbazol-9-yl)hexoxy]phenyl}-
In this paper, the synthesis and photophysical properties 3-{[6-(9H-carbazol-9-yl)hexoxy]phenyl}propane-1,3-dione
of two multichromophoric europium complexes and their (cpcpd). This synthetic route provided the ligand in gram-
reference compounds (Scheme 1) are described. The ap- scale quantities, which was essential for the purpose of
pended carbazole moieties, which widen the absorption further preparative scale up. The two complexes involving
profile and act as light-harvesting units, are expected to im- three units of cpcpd with europium and the nitrogen-bear-
prove the hole-transporting ability, prevent the crystalli- ing ligands 1,10-phenanthroline and bathophenanthroline
zation of complexes and increase the solubility in common were then prepared through classical conditions.[25]
organic solvents.
Absorption and Emission Properties
Results and Discussion
The electronic absorption spectra of Eu·dbm·carb·phen,
Eu·dbm·carb·bath and those of related reference com-
Synthesis
The structural basis and model complex of the present pounds (i) Eu·dbm·phen [tris(dibenzoylmethane)mono-
study was the strongly luminescent complex (1,10-phenan- (1,10-phenanthroline)europium(III)], (ii) Br·carb {[9-(6-
throline)tris(dibenzoylmethanato)europium(III), which was bromohexyl)-9H-carbazole]} and (iii) Hdbm (1,3-diketone
Scheme 2. Synthetic route to the Eu·dbm·carb·phen complex (an identical process was used for Eu·dbm·carb·bath).
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Heteroleptic Europium(III) Complexes with Appended Carbazole Units
dibenzoylmethane) were recorded in CH2Cl2 solution (Fig- luminescence intensity from Eu·dbm·phen was detected in
ure 1). Five peaks at 240, 264, 294, 332 and 347 nm were solvents bearing –OH quenching groups,[19] such as
attributed to π–π* transitions of the carbazole moieties by CH3OH (Table 1), which suggests that the phen and dbm
comparison with Br·carb. The electronic transitions of the coordinating ligands do not provide efficient shielding of
β-diketonate (peak at ca. 350 nm) and the phenanthroline the metal core towards external quenching.
(peak at ca. 230 and 260 nm) units are overlapped with the
much stronger carbazole features.[26] However, although in
the high-energy spectral region (λ Ͻ 300 nm) carbazole-
selective excitation may be accomplished (Ͼ90%, Figure 1),
the light partitioning around 350 nm is approximately 65
and 35% for the carbazole and β-diketonate moieties,
respectively.
Figure 2. Luminescence spectra of Eu·dbm·carb·phen (– – –) and
Eu·dbm·phen (–––) obtained at room temperature in CH2Cl2 (O.D.
= 0.2, λexc = 350 nm) under the same experimental conditions. The
radiative transitions from the emitting (5D0) to the ground (7FJ)
states were assigned and depicted.
Measurements in solid state matrices (6% doped poly-
Figure 1. UV/Vis electronic absorption spectra recorded in CH2Cl2
carbonate) were performed for Eu·dbm·phen, Eu·dbm·
carb·phen and Eu·dbm·carb·bath (Table 1). A remarkable
enhancement in the luminescence intensity relative to that
in solution was detected. This shows that the quenching
observed in solution, mainly attributable to –OH and –CH
vibrations of the solvent molecules, is severely limited in the
rigid solid medium. In polycarbonate matrix, the absolute
emission quantum yields are difficult to assess with accept-
able accuracy, but the measured lifetimes (consistent with
values reported in the literature for EuIII complexes in rigid
media)[27] can provide quantitative information. Indeed, it
is possible to evaluate the emission quantum yield by means
of Equation (1), where τobs and τ0 are the observed and the
radiative[18,28,29] lifetimes, respectively. Notably, quantum
yields as high, as 0.18 and 0.14 are estimated for
Eu·dbm·carb·phen and Eu·dbm·carb·bath, respectively.
solution. Left: Eu·dbm·carb·phen (–––), Eu·dbm·carb·bath (᭺) and
Eu·dbm·phen (– – –). Right: Br·carb (–––) and Hdbm (– – –).
For both Eu·dbm·carb·bath and Eu·dbm·carb·phen, the
typical EuIII ion luminescence spectrum peak at 612 nm was
detected in dichloromethane solution upon exciting at 264
and 350 nm (Table 1), respectively. For these two com-
pounds, which also exhibit the same emission quantum
yield, the lack of residual carbazole fluorescence (peak at
340 and 360 nm, Φem = 0.24) suggests an efficient energy-
transfer (EnT) process between the appended fragment and
the central metal ion. By contrast, Eu·dbm·phen can be se-
lectively excited on both the phenanthroline (≈ 260 nm) and
the β-diketonate (≈350 nm) moieties. In the first case, a rela-
tively intense metal-centred (MC) luminescence was de-
tected (Φ = 0.05), whereas the excitation at 350 nm afforded
an almost 10-fold weaker emission spectrum (Table 1, Fig-
ure 2), which points to an inefficient sensitization of the
EuIII excited states by the dbm units (Table 1). Even lower Φem = τobs/τ0
(1)
Table 1. Photophysical data collection (CH2Cl2, room temp.) and rigid matrix and solid state.
MC Luminescence (CH2Cl2, 298 K)
Spin-coated thin film[d]
[a]
[a]
λmax [nm]
Φem [%]
τ [ms]
λmax [nm]
Φem [%][e]
τ [ms]
0.5[b]
0.06[c]
0.02[c,f]
1.0[c]
1.0[b]
Eu·dbm·phen
614
0.1[c]
612
10
0.5
[c,f]
0.08
0.6[c]
0.50[b]
Eu·dbm·carb·phen
Eu·dbm·carb·bath
614
614
612
612
18
14
0.9
0.7
1.0[b]
[a] Emission maxima from uncorrected spectra. [b] λexc = 264 nm. [c] λexc = 350 nm. [d] 6% in polycarbonate. [e] Estimated by Equa-
tion (1), see text. [f] CH3OH solution.
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Y. Zheng, F. Cardinali, N. Armaroli, G. Accorsi
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The emitting states of the EuIII complexes involving π- between the lowest triplet ligand centred donor level and
conjugated ligands are usually populated by intramolecular the acceptor level of the lanthanide ion (5D0 for EuIII) fav-
EnT process through the triplet excited state of the li- ours an efficient EnT process,[32] which prevents the forma-
gand(s).[30,31] For EuIII and lanthanide complexes in gene- tion of a thermal equilibrium (back-energy-transfer pro-
ral, the intramolecular energy migration efficiency from the cess) between the involved levels. In order to determine the
chelating and/or appended ligands to the central Ln3+ ion ligand-centred triplet energy levels of the dbm and carb-
is the most important step influencing their luminescence azole subunits in the complexes, 77 K phosphorescence
output.[30] The intersystem-crossing efficiency and the in- spectra of Hdbm and Br·carb reference fragments were re-
trinsic luminescence quantum yield of the LnIII ion are the corded (Figure 3).
other steps regulating the overall efficiency of LnIII-sensi-
The maxima of the highest-energy emission features are
tized emission. Generally, a large (Ͼ1500 cm–1) energy gap located at 19500 (Hdbm) and 24000 (Br·carb) cm–1. Thus,
the energy gap between the EuIII core (5D0 ≈ 17500 cm–1)
[30]
and the donor ligand units turns out to be ca. 2000
and ca. 6500 cm–1 for Hdbm and Br·carb, respectively. This
suggests that although the triplet state of the carbazole unit
is energetically compatible with an efficient EnT process,
the lower-lying dbm level may undergo thermal back-en-
ergy transfer from the central core.[19] Furthermore, the 5D1
EuIII emitting state, located at approximately 18800 cm–1,
is critically close to the triplet energy level of dbm
(19500 cm–1). A schematic representation of ligand-centred
and metal-centred energy levels is depicted in Figure 4.
For Eu·dbm·carb·phen and Eu·dbm·carb·bath, the ap-
parently large distance between the carbazole units and the
central ion due to the alkyl spacer chains (Scheme 1) would
seem to suggest a Förster-type mechanism[33] for the energy-
transfer process. However, in solution, the floppy nature of
the spacer is likely to allow close vicinity between the carba-
zole and the metal centre, which supports a short-distance
Figure 3. Normalized phosphorescence spectra of Br·carb (left, λexc
= 294 nm) and Hdbm (right, λexc = 350 nm) in 77 K rigid matrix
(CH2Cl2).
mechanism (Dexter)[34] for the sensitization process.
Figure 4. Energy level diagram of Br·carb, dbm and EuIII and radiative (–––) and nonradiative (·····) deactivation pathways in related
complexes investigated here.
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Heteroleptic Europium(III) Complexes with Appended Carbazole Units
layer was washed with water and dried with Na2SO4. Solvent was
removed by evaporation, and then the resulting residue was puri-
fied by chromatography (SiO2; dichloromethane/hexane, 2:3) to ob-
tain the product (10.3 g, 52%). M.p. 50–51 °C. 1H NMR
(400 MHz, CDCl3): δ = 1.32–1.45 (m, 4 H, CH2), 1.72–1.87 (m, 4
H, CH2), 3.32 (t, J = 6.67 Hz, 2 H, -CH2Br), 4.46 (t, J = 7.08 Hz,
2 H, -NCH2-), 7.22 (t, J = 7.52 Hz, 2 H, ArH), 7.36 (d, J = 8.23 Hz,
2 H, ArH), 7.45 (t, J = 7.54 Hz, 2 H, ArH), 8.01 (d, J = 7.62 Hz,
2 H, ArH) ppm. C18H20BrN (330.27): calcd. C 65.46, H 6.10, N
4.24; found C 64.92, H 6.13, N 4.31.
Conclusions
We synthesized two multichromophoric europium com-
plexes containing appended carbazole units. These com-
pounds contain three different types of chromophores,
namely phenanthroline (phen), dibenzoylmethane (dbm)
and carbazole itself (carb); an almost selective excitation
(≈90%) was possible only for the latter moiety. The PL
properties of Eu·dbm·carb·phen in solution in comparison
to those of Eu·dbm·phen showed that an efficient popula-
tion of the EuIII emitting states by energy transfer occurs
from the carbazole units. In contrast, the dbm units turned
out to be poor sensitizers for the metal centre, which points
to the importance of the relative position of the ligand low-
est triplet levels relative to the metal-centred accepting state
(5D0). Notably, in both cases, a strong enhancement in the
MC luminescent intensity was detected in solid matrix,
which provides evidence for the limited action of the
vibrational quenchers under these conditions.
Ethyl 6-(9H-Carbazol-9-yl)hexoxybenzoate: A mixture of 9-(4-bro-
mohexyl)-9H-carbazole (3.3 g, 10 mmol), ethyl 4-hydroxybenzo-
ate (1.66 g, 10 mmol), potassium carbonate (1.52 g, 11 mmol) and
NaI (1 g) in anhydrous acetone (60 mL) was stirred vigorously and
heated at reflux for 48 h under the protection of a nitrogen atmo-
sphere. The solvent was removed by evaporation, and the resulting
solid was recrystallized from ethanol to give white needles (2.91 g,
1
70.1%). M.p. 107–108 °C. H NMR (500 MHz, CDCl3): δ = 1.37
(m, 3 H, CH3), 1.85–2.12 (m, 8 H, CH2), 3.98 (m, 2 H, -OCH2),
4.32 (m, 2 H, -NCH2), 4.40 (m, 2 H, -OCH2), 6.84 (d, J = 8.8 Hz,
2 H, ArH), 7.23 (t, J = 7.0 Hz, 2 H, ArH), 7.43 (d, J = 8.1 Hz, 2
H, ArH), 7.47 (t, J = 7.2 Hz, 2 H, ArH), 7.96 (d, J = 8.7 Hz, 2 H,
ArH), 8.10 (d, J = 7.6 Hz, 2 H, ArH) ppm. C27H29NO3 (415.53):
calcd. C 78.04, H 7.04, N 3.37; found C 77.95, H 7.07, N 3.42.
The ability of the carbazole units to act as light-harvest-
ing systems, sensitize and protect the metal emitting states,
together with their intrinsic charge-transporting capability,
make such molecules potentially interesting for the fabrica-
tion of electroluminescent devices.[35,36]
6-(9H-Carbazol-9-yl)hexoxyphenone: A mixture of 9-(4-bromo-
hexyl)-9H-carbazole (3.3 g, 10 mmol), 4-hydroxyacetophenone
(1.36 g, 10 mmol), potassium carbonate (1.52 g, 11 mmol) and NaI
(1 g) in anhydrous acetone (60 mL) was stirred vigorously and
heated at reflux for 48 h under the protection of a nitrogen atmo-
sphere. The solvent was removed by evaporation, and the resulting
solid was recrystallized from ethanol to give white needles (3.18 g,
85.3%). 1H NMR (500 MHz, CDCl3): δ = 1.35 (m, 3 H, CH3),
1.84–2.11 (m, 8 H, CH2), 4.30 (m, 2 H, -NCH2), 4.37 (m, 2 H,
-OCH2), 6.84 (d, J = 8.8 Hz, 2 H, ArH), 7.23 (t, J = 7.0 Hz, 2 H,
ArH), 7.43 (d, J = 8.1 Hz, 2 H, ArH), 7.47 (t, J = 7.2 Hz, 2 H,
ArH), 7.96 (d, J = 8.7 Hz, 2 H, ArH), 8.10 (d, J = 7.6 Hz, 2 H,
ArH) ppm. C26H27NO2 (385.51): calcd. C 81.00, H 7.06, O 8.30,
N 3.63; found C 79.54, H 7.09, O 8.35, N 3.68.
Experimental Section
General Information: Carbazole, 1,6-dibromohexane, K2CO3, ethyl
4-hydroxybenzoate, NaI, NaH, 4-hydroxyacetophenone, dimeth-
oxyethane, EuCl3·6H2O, 1,10-phenanthroline and bathophen-
anthroline were commercially available and used without further
purification. Elemental analysis was carried out with a CE-440 and
Carlo Erba Elemental Analysers.
Spectroscopic Measurements: Absorption spectra were recorded
with a Perkin–Elmer λ9 spectrophotometer. For luminescence ex-
periments, the samples were placed in fluorimetric 1-cm path cu-
vettes and, when necessary, purged from oxygen by bubbling with
argon. Uncorrected emission spectra were obtained with an Edin-
burgh FLS920 spectrometer equipped with a Peltier-cooled Hama-
matsu R928 photomultiplier tube (185–850 nm). Corrected spectra
were obtained by a calibration curve supplied with the instrument.
Luminescence quantum yields (Φem) obtained from spectra on a
wavelength scale (nm) were measured according to the approach
described by Demas and Crosby[37] by using air-equilibrated
[Ru(bpy)3Cl2] in water solution, Φem = 0.028,[38] as standard. The
luminescence lifetimes in the microsecond-millisecond scales were
measured by using a Perkin–Elmer LS-50B spectrofluorometer
equipped with a pulsed xenon lamp with variable repetition rate
and elaborated with standard software fitting procedures (Origin
6.1). To record the 77-K luminescence spectra, the samples were
put in glass tubes (2 mm diameter) and inserted into a special
quartz dewar filled up with liquid nitrogen. Experimental uncer-
tainties are estimated to be Ϯ8% for lifetime determinations,
Ϯ20% for emission quantum yields and Ϯ2 nm and Ϯ5 nm for
absorption and emission peaks, respectively.
1-{[6-(9H-Carbazol-9-yl)hexoxy]phenyl}-3-{[6-(9H-carbazol-9-yl)-
hexoxy]phenyl}propane-1,3-dione (cpcpd): Ethyl 6-(9H-carbazol-
9-yl)hexoxybenzoate (1.68 g, 4.05 mmol), 6-(9H-carbazol-9-yl)-
hexoxyphenone (1.53 g, 4.1 mmol) and NaH (0.12 g, 5 mmol) were
put in a dry flask. Dry dimethoxyethane (30 mL) was added, and
the solution was heated at reflux for 24 h. Then, the solution was
poured into water and acidified to pH ~2 by using HCl solution.
The solid collected was purified by column chromatography (SiO2;
acetone/hexane, 1:8) to obtain a white solid (0.9 g, 29.5%). 1H
NMR (400 MHz, CDCl3): δ = 1.49 (m, 8 H, CH2), 1.77 (m, 4 H,
CH2), 1.93 (m, 4 H, CH2), 3.96 (t, J = 6 Hz, 4 H, CH2), 4.34 (t, J
= 6 Hz, 4 H, CH2), 6.88 (d, J = 8.4 Hz, 4 H, ArH), 7.23 (m, 6 H,
ArH and diketonate CH2), 7.45 (m, 8 H, ArH), 8.04 (d, J = 8 Hz,
4 H, ArH), 8.11 (d, J = 8 Hz, 4 H, ArH) ppm. C51H50N2O4
(754.97): calcd. 81.13, H 6.68, O 8.48, N 3.71; found C 81.01, H
6.71, O 8.39, N 3.75.
Eu(cpcpd)3phen (Eu·dbm·carb·phen): The cpcpd ligand (0.45 g,
0.6 mmol) and 1,10-phenanthroline (0.036 g, 0.2 mmol) were dis-
solved in hot ethanol (15 mL, 60 °C). A solution of NaOH (1 ,
0.6 mL) was added to neutralize the cpcpd ligand. Then,
EuCl3·6H2O (0.073 g, 0.2 mmol) was dissolved in ethanol (2 mL)
and added dropwise to the above solution. The solution was stirred
at 60 °C for 5 h. Then, the solvent was removed under reduced
pressure, and the solid was washed with water several times. After
9-(6-Bromohexyl)-9H-carbazole (Br·carb): A mixture of carbazole
(10.0 g, 0.06 mol), 1,6-dibromohexane (58.6 g, 0.24 mol) and
K2CO3 (25.0 g, 0.18 mol) in dimethylformamide (DMF; 100 mL)
was stirred at room temperature for 24 h before pouring into water.
After extraction with dichloromethane (3ϫ15 mL), the organic
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M.p. 99–100 °C. C165H155EuO12N8 (2594.05): calcd. C 76.39, H
6.02, O 7.40, N 4.32; found C 76.31, H 6.13, O 7.46, N 4.47.
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Received: November 22, 2007
Eu(cpcpd)3bath (Eu·dbm·carb·bath): The same procedure as that
above was followed by replacing 1,10-phenanthroline with batho-
phenanthroline. Yield: 67%. M.p. 108–109 °C. C177H163EuO12N8
(2746.25): calcd. C 77.41, H 5.98, O 6.99, N 4.08; found C 77.02,
H 6.06, O 7.08, N 4.29.
[19]
[20]
Supporting Information (see footnote on the first page of this arti-
1
cle): H NMR spectrum of the cpcpd ligand.
[21]
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[24]
Acknowledgments
We thank the EC (IST-2002-004607, OLLA) and the CNR
(PM.P04.010, MACOL) for financial support; we also thank
Roberto Cortesi for technical help.
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Published Online: March 4, 2008
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