Synthesis and photoluminescence properties of asymmetrical europium(III) complexes involving carbazole, phenanthroline and bathophenanthroline units

Article abstract of DOI:10.1016/j.ica.2009.02.014

Three novel europium complexes, Eu(CCHPD)₃Phen = Tris[1-(9H-carbazol-9-yl)-3-[(6-(9H- carbazol-9-yl)hexoxy)-phenyl]-1,3-dione](1,10-phenanthroline) europium(III), Eu(CCHPD)₃Bath = Tris[1-(9H-carbazol-9-yl)-3-[(6-(9H-carbazol-9-yl)hex

Full text of DOI:10.1016/j.ica.2009.02.014

Inorganica Chimica Acta 362 (2009) 3181–3186
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis and photoluminescence properties of asymmetrical europium(III)
complexes involving carbazole, phenanthroline and bathophenanthroline units
a
a
a,
Qian Ma b, Youxuan Zheng a,b, , Nicola Armaroli , Margherita Bolognesi , Gianluca Accorsi
*
*
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
b State Key Laboratory of Coordination Chemistry, Nanjing University, 210093 Nanjing, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 August 2008
Received in revised form 27 January 2009
Accepted 14 February 2009
Available online 25 February 2009
Three novel europium complexes, Eu(CCHPD)3Phen = Tris[1-(9H-carbazol-9-yl)-3-[(6-(9H- carbazol-9-
yl)hexoxy)-phenyl]-1,3-dione](1,10-phenanthroline) europium(III), Eu(CCHPD)3Bath = Tris[1-(9H-car-
bazol-9-yl)-3-[(6-(9H-carbazol-9-yl)hexoxy)-phenyl]-1,3-dione](bathophenanthroline)
europium(III)
and Eu(CPD)3Phen = Tris[1-(9H-carbazol-9-yl)-3-phenylpropane]-1,3-dione](1,10-phenanthroline) euro-
pium(III), have been synthesized and characterized (Scheme 1). Involved ligands consist of different che-
lating and non-chelating units: appended carbazole (Br-Carb), phenanthroline (Phen),
bathophenanthroline (Bath) and 1-(9H-carbazol-9-yl)-3-phenylpropane]-1,3-dione (CPD). The lumines-
cence properties show that the carbazole moiety is a better sensitizer for the metal centred (MC) emitting
states relative to Phen and Bath. Moreover, its charge-transporting properties make such complexes
appealing for their application in electroluminescent devices.
Keywords:
Europium
Luminescence
Carbazole
Phenanthroline
Bathophenanthroline
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
charge-transporting fragments to the ligand framework, as pro-
posed by Zheng and co-workers [17], Bazan and co-workers [18],
Organic light-emitting diodes (OLEDs) [1,2] are one of the most
promising next generation low cost and full color flat panel dis-
plays and also hold great promise for a variety of lighting applica-
tions [3–8]. Nowadays, organic fluorescent molecules, polymers
and phosphorescent coordination compounds are widely used as
active materials in OLEDs [9,10]. Among phosphorescent materials,
emitting lanthanide complexes are well suited for lighting applica-
tions [11] due to their high color purity and efficient energy con-
version in electroluminescence [12]. In particular, red-emitting
Eu(III) complexes have been extensively used [13,14] but, in spite
of their excellent photoluminescence (PL) properties, efficient de-
vices containing these compounds are hardly obtainable owing to
their poor charge carrier-transporting ability and the occurrence
of efficient luminescence quenching processes by the matrix layer
via non-radiative vibrational pathways [15,16]. In order to improve
the charge-transporting properties of Eu(III) complexes, incorpora-
tion of electron/hole-transporting chelating ligands has been pro-
posed [3,12]. Unfortunately, this method usually leads to phase
separation during manufacturing (i.e. sublimation) and functioning
of the device, significantly affecting the OLEDs lifetime and effi-
ciency. An alternative approach involves covalent linking of
Tian and co-workers [19] and Huang and co-workers [20] who re-
ported efficient OLEDs using oxadiazole or carbazole functional-
ized lanthanide complexes. On the other hand, in order to
enhance the molar extinction coefficients of the complexes and
limit vibronic luminescence quenching by the matrix, organic li-
gands, acting as ‘‘antennas” have been proposed [21]. These sys-
tems can collect and transfer the excitation energy from the
periphery of the complex to the metal core and protect it by para-
site quenching processes. Thus, the synthesis of complexes inte-
grating both charge-transporting moieties and antenna structures
seems to be particularly appealing [22].
In this paper, we report the synthesis and photophysical prop-
erties of three novel europium complexes (Scheme 1) with ap-
pended carbazole units which widen the absorption profile and
act as light-harvesting chromophores. Carbazoles are also expected
to improve the hole-transporting ability, prevent the crystalliza-
tion of complexes and increase the solubility in common organic
solvents.
2. Results and discussion
2.1. Synthesis
* Corresponding authors. Address: 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 addresses: yxzheng@nju.edu.cn (Y. Zheng), gianluca.accorsi@isof.cnr.it
(G. Accorsi).
The novel b-diketone ligands with carbazole moieties were syn-
thesized under Claisen condensation conditions described in
Scheme 2. Carbazole reacted with 1,6-dibromohexane in presence
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.02.014

3182
Q. Ma et al. / Inorganica Chimica Acta 362 (2009) 3181–3186
O
O
O
O
O(CH )
N
N
N
2 6
CPD
CCHPD
N
N
N
N
Bath
Phen
N
N
O
N
N
O
N
N
Eu
Eu
Eu
O
O
O
O
O(CH )
N
N
O(CH )
N
2 6
2 6
N
N
3
3
3
Eu(CCHPD)3Bath
Eu(CCHPD)3Phen
Eu(CPD)3Phen
Scheme 1. Chemical structures of the studied complexes and related reference compounds.
O
O
O
O
i
Br(CH2)6Br
ii
+
NH
N
(CH2)6Br
N
(CH2)6Br
+
O
(CH2)6
N
OH
O
O
O
O
O
iii
O
(CH2)6
N
+
N
O(CH2)6
N
N
N
N
Eu
O
N
O
O
O
iv
O(CH2)6
N
O(CH2)6
N
N
3
Eu(CCHPD)3Phen
CCHPD
N
N
O
Eu
O
N
O
O
O
O
O
v
+
N
vi
N
3
CPD
Eu(CPD)3Phen
Scheme 2. Synthetic route to the complex Eu(CCHPD)3Phen (an identical process has been used for Eu(CCHPD)3Bath) and Eu(CPD)3Phen. i: K2CO3, anhydrous DMF, RT 24 h,
yield: 52%; ii: K2CO3, NaI, anhydrous acetone, reflux 48 h, yield: 70.1%; iii: NaH, anhydrous dimethoxyethane, reflux 24 h, yield: 54.5%; iv: Phen, NaOH, EuCl3.6H2O, ethanol,
60 °C 2 h, yield: 57%; v: NaH, anhydrous dimethoxyethane, reflux 24 h, yield: 26%; and vi: Phen, NaOH, EuCl3 Á 6H2O, ethanol, 60 °C 2 h, yield: 54%.

Q. Ma et al. / Inorganica Chimica Acta 362 (2009) 3181–3186
3183
of potassium carbonate to give 9-(6-bromohexyl)-9H-carbazole
(Br-Carb). This product was then reacted with ethyl 4-hydroxyben-
zoate to give the corresponding ether through classical conditions
(potassium carbonate, NaI). Reaction of the ethyl 6-(9H-carbazol-
9-yl)-hexoxy- benzoate and 9-acetylcarbazole (9-Ace-Carb) in the
presence of a strong base (NaH) yielded the desired ligand 1-(9H-
carbazol-9-yl)-3-[(6-(9H-carbazol-9-yl)hexoxy)-phenyl]-1,3-dione]
(CCHPD) [18]. In the same way, the ligand 1-(9H-carbazol-9-yl)-3-
phenylpropane]-1,3-dione (CPD) was obtained by reacting 9-ace-
tylcarbazole and methylbenzoate in the presence of NaH. The
corresponding europium complexes involving three units of dike-
tone ligands and one nitrogen-bearing ligand 1,10-phenanthroline
or bathophenanthroline were then prepared through classical
methods [23].
cause of the lack of the alkyl carbazole units. The matching be-
tween free ligand and complex absorption profiles show the
negligible influence of the triply charged central ion on the
electronic properties of the chelating organic units [24]. The elec-
tronic absorption spectra of Phen and Bath peak at ca. 264
(e
ꢀ 34000 MÀ1 cmÀ1) and 274 (
e
ꢀ 62000 MÀ1 cmÀ1) nm, respec-
tively, and are overlapped with that of carbazole. Accordingly, for
all complexes, selective excitation of the carbazole units (>90%)
is achievable only by exciting at 294 nm. Elsewhere (i.e. 264 nm,
Table 1), the light partitioning between carbazole and Phen (or
Bath) moieties is less selective, especially for Eu(CPD)3Phen
(roughly 50%). Light excitation at wavelengths longer than
ꢀ300 nm leads to weak emission intensities because of the low
extinction coefficient of the carbazole moiety in this spectral win-
dow and the relatively low emission quantum yields of the com-
plexes in solution.
2.2. Absorption and emission properties
Eu(CCHPD)3Phen and Eu(CCHPD)3Bath show the typical Eu(III)
narrow luminescence bands with the most intense peak located
at 612 nm in dichloromethane solution, upon excitation at both
264 and 294 nm (Fig. 2). The emission bands at 580 and 650 nm
are very weak because their corresponding transitions 5D0–7F0,3
are forbidden both for magnetic and electric dipole. The intensity
of the emission band at 592 nm (5D0–7F1) is relatively strong and
independent on the coordination environment due to its magnetic
nature. On the contrary, the 5D0–7F2 transition is of induced
electric dipole character and its corresponding intense emission
at ꢀ612 nm is very sensitive to the coordination environment
[25]. Regarding the emission spectra of Eu(CCHPD)3Phen and
Eu(CCHPD)3Bath, the lack of the residual carbazole fluorescence
(peaked at 340 and 360 nm, Uem = 0.24) suggests an efficient en-
ergy-transfer (EnT) process between the appended fragment and
the central metal ion. CCHPD-containing complexes showed the
best luminescence performances when excited at 294 nm
The electronic absorption spectra of Eu(CCHPD)3Phen,
Eu(CCHPD)3Bath, Eu(CPD)3Phen and those of related reference
compounds CPD, CCHPD, Bath and Phen were recorded in CH2Cl2
solution (Fig. 1). Eu(CCHPD)3Phen and Eu(CCHPD)3Bath profiles
show five peaks at around 240, 264, 294, 332 and 350 nm that
can be attributed to the p–p* transitions of carbazole moieties by
comparison with that of Br-Carb [22]. The absorption maxima of
Eu(CPD)3Phen are blue-shifted (its spectral profile matches with
that of CPD), relative to those of CCHPD-containing complexes, be-
(b)
(a)
14
12
10
8
50
40
30
20
10
0
(U = 1.4%, s = 1.0 ms and U = 4.9%, s = 1.1 ms for Eu(CCHPD)3Phen
and Eu(CCHPD)3Bath, respectively). On the other hand, excitation
at 264 nm leads to weaker emission intensities in both cases (Table
1). Due to the different light partition between the involved
chromophores (see above), this indicates a better sensitization
ability of the carbazole moiety relative to Phen or Bath. Further-
more, the comparison of the PL properties of Eu(CCHPD)3Phen and
Eu(CCHPD)3Bath with those of similar symmetrical Eu(III) com-
plexes reported in our previous work (in which only alkyl carba-
zole units were involved) [22], indicates slight improvement of
the emission intensities, which is likely to be related to the closer
distance between the sensitizer and the metal ion. In principle,
Eu(CPD)3Phen is a suitable reference sample for Eu(CCHPD)3Phen
and Eu(CCHPD)3Bath because the central core of the complex is the
same. However, Eu(CPD)3Phen exhibits a rather weak emission spec-
trum which is most probably related to dissociation/photobleaching
6
4
2
0
240 270 300 330 360 390
240 270 300 330 360
λ / nm
Fig. 1. UV–Vis electronic absorption spectra recorded in CH2Cl2 solution. (a): Phen
(empty circles), CCHPD (short dashed line), Bath (solid line) and CPD (dotted line);
(b) Eu(CPD)3Phen (dotted line), Eu(CCHPD)3Phen (short dashed line) and
Eu(CCHPD)3Bath (solid line).
Table 1
Photophysical data at room temperature in CH2Cl2 solution and solid state.
298 K MC luminescence, CH2Cl2
Solid state (as powder)
a
a
e
kmax (nm)
Uem (%)
sobs (ms)
kmax (nm)
Uem (%)
sobs (ms)
d
d
Eu(CPD)3Phen
Eu(CCHPD)3Phen
Eu(CCHPD)3Bath
a
614
614
614
10b
12c
0.5b
0.6c
614
614
0.6b
1.4c
1.2b
4.9c
0.6b
1.0c
0.7b
1.1c
614
614
12b
18c
10b
12c
0.6b
0.9c
0.5b
0.6c
614
614
614
614
Emission maxima from uncorrected spectra.
kexc = 264 nm.
b
c
kexc = 294 nm.
d
e
Not detected due to a progressive dissociation/photobleaching under UV irradiation (see text).
Estimated by Uem s0, where sobs and s0 are the observed and radiative [15,25,37] lifetimes, respectively.
=
sobs/

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Q. Ma et al. / Inorganica Chimica Acta 362 (2009) 3181–3186
5D0
7FJ
(b)
(a)
J = 2
I
J = 1
J = 4
J = 0
J = 3
580
600
620
640
660
680
700
720
400 450 500 550 600
450
500
550
600
λ / nm
λ / nm
Fig. 2. Photoluminescence spectra of Eu(CCHPD)3Phen (solid line) and
Eu(CCHPD)3Bath (dotted line) obtained at room temperature in CH2Cl2 (OD = 0.2,
kexc = 294 nm) under the same experimental conditions. MC transitions are also
indicated.
Fig. 3. Normalized phosphorescence spectra of (a) Gd(CCHPD)3 Á 2H2O (dashed line,
= 2.4 ms), CPD (solid gray line, = 3.0 s) and Br-Carb (solid black line, = 2.8 s)
obtained at 77 K rigid matrix (CH2Cl2), kexc = 294 nm; (b) Bath (solid line, = 2.1 ms)
and Phen (dotted line, = 1.7 ms) obtained at 77 K in ethylene iodide rigid matrix in
s
s
s
s
s
order to enhance the singlet-triplet intersystem crossing (isc) due to heavy atom
effect, kexc = 264 and 274 nm, respectively.
processes in solution [26]. Indeed, upon UV irradiation in CH2Cl2
solution a progressive decrease of the luminescence intensity
(around 20%) is recorded for Eu(CPD)3Phen, while Eu(CCHPD)3Phen
and Eu(CCHPD)3Bath didn’t show any spectral/intensity changes
under the same conditions. By contrast, in the solid state, all of
the compounds turn out to be stable under irradiation and a
remarkable enhancement of the luminescence intensity is de-
tected, also for Eu(CPD)3Phen, compared to solution samples (Table
1). This suggests that the quenching observed in solution, mainly
attributable to –CH vibrations of solvent molecules [24], is severely
limited in the rigid solid medium. Under these conditions, all com-
plexes show better luminescence properties when excited at
Br-Carb
CPD
CCHPD
E / 103 cm-1
Phen
Bath
Eu(III)
S1
S1
30
S1
T1
25
20
15
294 nm (
U
= 10%,
s
= 0.5 ms for Eu(CPD)3Phen;
U = 18%, s = 0.9
T1
T1
EnT
for Eu(CCHPD)3Phen;
U
= 12%, = 0.6 ms for Eu(CCHPD)3Bath).
s
Also excitation at 264 nm leads to appreciable PL performances
(Table 1).
As it is well known, the emitting states of Eu(III) complexes
involving p-conjugated ligands are usually populated, by the trip-
5D1
5D0
let excited state of the ligand(s) via intramolecular EnT process
[27]. In this case, the sensitization process of the lanthanide ions
generally consists of three steps: excitation of the singlet excited
state of the ligand, subsequent intersystem crossing to its triplet
state and energy transfer from the triplet state to the emission lan-
thanide ion [28,29] (although direct energy transfer from the sin-
glet levels of the ligands has been also observed [29–31]). For
lanthanide complexes, the intramolecular energy migration effi-
ciency from the chelating and/or appended ligands to the central
Ln3+ ion is the most important step influencing their luminescence
output [24]. The intersystem crossing efficiency and the intrinsic
luminescence quantum yield of the Ln(III) ion represent the other
steps regulating the overall efficiency of Ln(III)-sensitized emis-
7FJ J= 6
0
Ground states
Scheme 3. Energy level diagram of Br-Carb, Phen, Bath, Eu(III) and related radiative
(solid lines) and non-radiative (dotted lines) deactivation pathways. Upon exciting
the antenna units, an intersystem crossing process occurs from singlet to triplet
ligand excited states. This is followed by the EnT process to the Eu(III) emitting
levels. The energy gap between Eu(III) and donor excited state turns out to be at
least >3400 cmÀ1, indicating that the triplet levels of all involved ligands are
energetically compatible with an efficient EnT process.
sion. Generally, the larger the energy gap (at least >1500 cmÀ1
)
between the lowest triplet ligand-centred donor level and the
acceptor level of the lanthanide ion (5D0 for Eu(III)), the more effi-
cient is the EnT process [32], preventing the formation of thermal
equilibrium between involved levels (back energy transfer pro-
cess). In order to determine the ligand-centred (LC) triplet energy
levels, 77 K phosphorescence spectra of Br-Carb, Gd(CCHPD)3 Á
2H2O, CPD, Bath and Phen have been recorded (Fig. 3). The lowest
MC excited state of the Gd3+ ion is known to be located at much
higher energy (around 31000 cmÀ1) [16] than that of the sensitiz-
ing units. This rules out the possibility of observing MC emission
from Gd3+ complexes allowing the detection of the ligand-centred
(LC) phosphorescence. The maxima of the highest energy emission
features are located at ꢀ24000 cmÀ1 for all carbazole-containing
samples (even higher value for CCHPD) while those of Bath and
Phen lie at 20900 cmÀ1 and 22100 cmÀ1, respectively. Thus, the
energy gap between the Eu(III) core (5D0 ꢀ 17500 cmÀ1) [27] and
donor units turns out to be energetically compatible (around
3400 and 6400 cmÀ1 for phenanthroline and carbazole derivatives,
respectively) with an efficient EnT process. A schematic represen-
tation of the ligand and metal centred energy levels is depicted
in Scheme 3.

Q. Ma et al. / Inorganica Chimica Acta 362 (2009) 3181–3186
3185
with Na2SO4. Solvent was removed by evaporation, and then the
resulting residue was purified by chromatography (SiO2; dichloro-
methane/hexane, 2:3) to obtain the product (10.3 g, yield: 52%,
M.p. 50–51 °C). 1H NMR (400 MHz, CDCl3, ppm): d = 1.32–1.45
(m, 4 H, CH2), 1.72–1.87 (m, 4H, CH2), 3.32 (t, J = 6.67 Hz, 2H, –
CH2Br), 4.46 (t, J = 7.08 Hz, 2H, –NCH2–), 7.22 (t, J = 7.52 Hz, 2H,
ArH), 7.36 (d, J = 8.23 Hz, 2H, ArH), 7.45 (t, J = 7.54 Hz, 2H, ArH),
8.00 (d, J = 7.62 Hz, 2H, ArH). Anal. Calc. for C18H20BrN (330.27):
C, 65.46; H, 6.10; N, 4.24. Found: C, 64.92; H, 6.13; N, 4.31%.
3. Conclusion
Three novel asymmetric europium complexes involving carba-
zole units have been synthesized and photophysically investigated.
The complexes contain three different chromophores, namely Phen
(or Bath), CPD and alkyl carbazole. An almost selective excitation
(>90%) is possible only for the latter moiety. The PL properties of
Eu(CCHPD)3Phen and Eu(CCHPD)3Bath both in solution and in solid
state, show that the most efficient population of the Eu(III) emit-
ting states, via energy transfer process, occurs from the carbazole
units. Their ability to act as light-harvesting units, sensitize and
protect the metal emitting states together with the intrinsic
charge-transporting capability, makes such molecules potentially
interesting for the fabrication of electroluminescent devices
[33,34].
4.3.2. Ethyl 6-(9H-carbazol-9-yl)hexoxy-benzoate
A mixture of 9-(4-bromohexyl)-9H-carbazole (3.3 g, 10 mmol),
ethyl 4-hydroxybenzoate (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 pro-
tection of a nitrogen atmosphere. The solvent was removed by
evaporation, and the resulting solid was recrystallized from etha-
nol to give white needles (2.91 g, yield: 70.1%, M.p. 107–108 °C).
1H NMR (500 MHz, CDCl3, ppm): d = 1.37 (m, 3H, CH3), 1.85–
2.12 (m, 8H, CH2), 3.98 (m, 2H, –OCH2), 4.32 (m, 2H, –NCH2),
4.40 (m, 2H, –OCH2), 6.84 (d, J = 8.8 Hz, 2H, ArH), 7.23 (t,
J = 7.0 Hz, 2H, ArH), 7.43 (d, J = 8.1 Hz, 2H, ArH), 7.47 (t,
J = 7.2 Hz, 2H, ArH), 7.96 (d, J = 8.7 Hz, 2H, ArH), 8.10 (d,
J = 7.6 Hz, 2H, ArH). Anal. Calc. for C27H29NO3 (415.53): C, 78.04;
H, 7.04; N, 3.37. Found: C, 77.95; H, 7.07; N, 3.42%.
4. Experiment
4.1. General information
Carbazole, 1,6-dibromohexane, K2CO3, ethyl 4-hydroxybenzo-
ate, NaI, NaH, 9-acetylcarbazole, dimethoxyethane, EuCl3 Á 6H2O,
1,10-phenanthroline and bathophenanthroline were commercial
and used without further purification. Elemental analysis was car-
ried out with a CE-440 and Carlo Erba Elemental Analysers.
4.3.3. 1-(9H-carbazol-9-yl)-3-[(6-(9H-carbazol-9-yl)hexoxy)phenyl]-
1,3-dione (CCHPD)
4.2. Spectroscopic measurements
1.996 g ethyl 6-(9H-carbazol-9-yl)hexoxy-benzoate (4.8 mmol)
and 0.837 g 9-acetyl-carbazole (4 mmol), 0.12 g NaH (5 mmol)
were put into the dry flask. 30 mL dry dimethoxyethane was
added and the solution was refluxed for 24 h. Then, the solution
was poured into water and acidified to pH about 2 using diluted
HCl solution. The solid collected was purified by column chroma-
tography with aceton/hexane = 1:8 as the eluent to get the white
solid (1.26 g, yield: 54.5%, M.p.: 174–175 °C). 1H NMR (400 MHz,
CDCl3, ppm): d = 1.28–1.97 (t, 8H, –CH2–), 3.99 (t, 2H, CH2,
–NCH2–), 4.36 (t, 2H, –OCH2–), 6.91 (d, J = 8.4 Hz, 2H, ArH), 7.25
(m, 6H, ArH and diketone CH2), 7.44 (d, J = 8 Hz, 4H, ArH), 7.48
(d, J = 8 Hz,4H, ArH), 7.99 (d, J = 8 Hz, 2H, ArH), 8.03 (d, J = 8 Hz,
2H, ArH), 8.13 (d, J = 8 Hz, 2H, ArH). Anal. Calc. for C39H34N2O3
(578.71): C, 80.94; H, 5.92; N, 4.84; O, 8.29. Found: C, 79.85;
H, 6.04; N, 4.76; O, 8.47%.
Absorption spectra were recorded with a Perkin–Elmer k9 spec-
trophotometer. For luminescence experiments, the samples were
placed in fluorimetric 1-cm path cuvettes. Uncorrected emission
spectra were obtained with an Edinburgh FLS920 spectrometer
equipped with a Peltier-cooled Hamamatsu R928 photomultiplay-
er tube (185–850 nm). Corrected spectra were obtained via a cali-
bration curve supplied with the instrument. Luminescence
quantum yields (Uem) obtained from spectra on a wavelength scale
(nm) were measured according to the approach described by De-
mas and Crosby [35] using air-equilibrated [Ru(bpy)]3Cl2 in water
solution Uem = 0.028] [36] as standard. QY of the solid state sam-
ples were evaluated by exploiting known photophysical parame-
ters for the Eu(III)-based emission. This approach is based on the
fact that the luminescence lifetime of an emitter is governed by
radiative (r) and non-radiative (nr) processes,
s = 1/(kr + knr), and
that for a Eu(III) centre the intrinsic radiative rate constant is mod-
erately affected by the environment, kr = 90–170 sÀ1[37]. This al-
4.3.4. 1-(9H-carbazol-9-yl)-3-phenylpropane]-1,3-dione (CPD)
0.836 g 9-acetylcarbazole (4 mmol) and 0.654 g methylbenzo-
ate (4.8 mmol), 0.12 g NaH (5 mmol) were put into the dry flask.
Thirty microliters dry dimethoxyethane was added and the solu-
tion was refluxed for 24 h. Then, the solution was poured into
water and acidified to pH about 2 using diluted HCl solution. The
solid collected was purified by column chromatography with ace-
tone/hexane = 1:8 as the eluent to get the white solid (0.325 g,
yield: 26%, M.p.:145–146 °C). Anal. Calc. for C51H50O4N2: C,
80.49; H, 4.82; N, 4.47. Found: C, 80.58; H, 4.80; N, 4.39%.
lows evaluation of kr and knr from the observed value of s, and
the luminescence efficiency is in turn evaluated on the basis of
Uem = kr/(kr + knr) [38]. The luminescence lifetimes in the microsec-
ond-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 fit-
ting procedures (Origin 6.1). To record the 77 K luminescence spec-
tra, the samples were put in glass tubes (2 mm diameter) and
inserted in a special quartz dewar, filled up with liquid nitrogen.
Experimental uncertainties are estimated to be 8% for lifetime
determinations, 20% for emission quantum yields, 2 nm and
5 nm for absorption and emission peaks, respectively.
4.3.5. Eu(CCHPD)3Phen
0.347 g CCHPD (0.6 mmol) and 0.024 g Phen (0.2 mmol) were
dissolved in 15 mL hot ethanol (60 °C). 0.6 mL (1 N) NaOH solution
was added to neutralize the CCHPD. Then, 0.073 g EuCl3 Á 6H2O
(0.2 mmol) was dissolved in 2 mL ethanol and added dropwise to
the above solution. The solution was stirred at 60 °C for 2 h. Then,
the solid was filtered and washed with water and ethanol several
times. After drying, the solid was dissolved in 5 mL hot chloroform
and then a lot of hexane was added by the wall of the flask
carefully. After one day, the light-brown solid (Eu(CCHPD)3Phen)
crystallized (0.67 g, yield: 57%, M.p.: 124–125 °C). Anal. Calc. for
4.3. Synthesis
4.3.1. 9-(6-Bromohexyl)-9H-carbazole (Br-Carbazole)
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 dimethylform-
amide (DMF, 100 mL) was stirred at room temperature for 24 h be-
fore pouring into water. After extraction with dichloromethane
(3 Â 15 mL), the organic layer was washed with water and dried

3186
Q. Ma et al. / Inorganica Chimica Acta 362 (2009) 3181–3186
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Found: C, 73.31; H, 5.59; O, 7.61; N, 5.28%.
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4.3.6. Eu(CCHPD)3Bath
The same procedure as above was followed, replacing 1,10-phe-
nanthroline by bathophenanthroline, to give Eu(CCHPD)3Bath
(yield: 61%, M.p. 130–131 °C). Anal. Calc. for EuC132H113O9N8
(2107.35): C, 75.23; H, 5.40; O, 6.83; N, 5.32. Found: C, 75.02; H,
5.51; O, 7.16; N, 5.14%.
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4.3.7. Eu(CPD)3Phen
0.188 g CPD (0.6 mmol) and 0.024 g Phen (0.2 mmol) were dis-
solved in 15 mL hot ethanol (60 °C). 0.6 mL (1 N) NaOH solution
was added to neutralize the CPD. Then, 0.073 g EuCl3 Á 6H2O
(0.2 mmol) was dissolved in 2 mL ethanol and added dropwise to
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the solid was filtered and washed with water and ethanol several
times. After drying, the solid was dissolved in 5 mL hot chloroform
and then a lot of hexane was added by the wall of the flask
carefully. After 1 day, the light-redish solid (Eu(CPD)3phen) crystal-
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Eu(CPD)3phen EuC75H50O6N5 (1269.21): C, 70.98; H, 3.97; O,
7.56; N, 5.52. Found: C, 70.64; H, 4.02; O, 7.78; N, 5.34%.
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Acknowledgements
We thank the EC (IST-2002-004607, OLLA), the CNR
(PM.P04.010, MACOL), the National Natural Science Foundation
of China (20701019), the National Basic Research Program of China
(973 Program, 2007CB925103), the Major State Basic Research
Development Program (2006CB806104) for financial support, and
Roberto Cortesi for technical help.
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