Antenna-functionalized dendritic β-diketonates and europium complexes: synthetic approaches to generation growth

Article abstract of DOI:10.1016/j.tet.2006.03.052

Six dendritic β-diketonates and their corresponding europium complexes were synthesized. These dendritic β-diketonate ligands consist of dibenzoylmethane cores, Fre?chet-type poly(aryl ether) dendrons, and the carbazole-grafted peripheral functional groups. The designs of dendrimers are on the basis of high light-harvesting capability and dendron functionalization in virtue of the high extinction coefficient and carrier-injection adjustment of carbazole units. Different approaches to generation growth were utilized: the first generation europium complexes through etheral connectivity were developed via convergent synthetic approach; the second and third generation dendrons through esteral connectivity were developed by a hyperbranch core approach containing the advantages of convergent and divergent approaches. Their chemical structures were well characterized. Preliminary results show that the dendron-functionalized carbazole units not only tune the carrier-transporting capability, but also exhibit strong light-harvesting potential, resulting in a strong intense emission from the central Eu(III) ion via sensitization.

Full text of DOI:10.1016/j.tet.2006.03.052

Tetrahedron 62 (2006) 5035–5048
Antenna-functionalized dendritic b-diketonates and europium
complexes: synthetic approaches to generation growth
*
Shangfeng Li, Weihong Zhu, Zhongyu Xu, Jianfeng Pan and He Tian
*
Labs for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology,
Shanghai 200237, PR China
Received 24 January 2006; revised 15 March 2006; accepted 17 March 2006
Available online 17 April 2006
Abstract—Six dendritic b-diketonates and their corresponding europium complexes were synthesized. These dendritic b-diketonate ligands
´
consist of dibenzoylmethane cores, Frechet-type poly(aryl ether) dendrons, and the carbazole-grafted peripheral functional groups. The de-
signs of dendrimers are on the basis of high light-harvesting capability and dendron functionalization in virtue of the high extinction coeffi-
cient and carrier-injection adjustment of carbazole units. Different approaches to generation growth were utilized: the first generation
europium complexes through etheral connectivity were developed via convergent synthetic approach; the second and third generation den-
drons through esteral connectivity were developed by a hyperbranch core approach containing the advantages of convergent and divergent
approaches. Their chemical structures were well characterized. Preliminary results show that the dendron-functionalized carbazole units
not only tune the carrier-transporting capability, but also exhibit strong light-harvesting potential, resulting in a strong intense emission
from the central Eu(III) ion via sensitization.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
their corresponding Eu(III) complexes developed through
diverse approaches (see Scheme 1). The dendritic b-diketo-
´
Due to the extreme narrow-width emission band, europium
complexes have attracted considerable interest for the design
of laser materials,1 organic light-emitting diodes,2–5 and
fluorescent probes.6–9 However, the luminescence efficiency
is suffered from the low extinction coefficient and non-
radiative deactivation of Eu(III) ion.10–13 Up to now, little
work was concerned about modifying the light harvesting of
b-diketonate ligand except the pursuit of novel second
ligands.3,14–17
nates consist of dibenzoylmethane cores, Frechet-type poly
(aryl ether) dendrons, and carbazole (CZ) peripheral
functional groups. Once they were chelated with Eu(III)
ions, such dendritic ligands were expected to create encapsu-
lating cages, thus reducing the self-quenching process and
environmental influence. In virtue of high extinction coeffi-
cient of the terminated carbazole units, more photons could
be efficiently harvested and then transferred to the focal ion.
Due to the acceptable yield of Claisen condensation, con-
vergent synthetic approach was utilized to achieve the first
generation europium complexes. The second and third
generation dendrons were synthesized via hypercore syn-
thetic approach28 to circumvent the weak reactivity of senior
generation esters. These complexes ranging from the first
generation to the third generation are denoted by [xCaz-
Gy]3-Eu, where [xCaz] refers to the number of carbazole
units incorporated into dendron and [Gy] denotes the genera-
tion number (y¼1, 2, 3).
Dendrimers have attracted much interest because of their
unique structures and properties.18–22 The globular shape
of dendrimers provides a large surface area that can be deco-
rated with chromophores,23–25 resulting in a large absorption
cross section and efficient capture of photons. Another inter-
esting properties of dendritic molecules are the site-isolation
effect of dendrons to create a micro-environment to prevent
the intermolecular interaction and avoid self-quenching
effect.11
On the basis of our earlier work,26,27 here we report a series
of novel carbazole-terminated dendritic b-diketonates and
2. Results and discussion
2.1. b-Diketonate as core
Keywords: Europium complexes; Dendrimers; Synthesis.
* Corresponding authors. Tel.: +86 21 64252756; fax: +86 21 64252288;
e-mail addresses: whzhu@ecust.edu.cn; tianhe@ecust.edu.cn
In order to obtain different generations of dendritic
b-diketonates, it is necessary to synthesize the branched
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.03.052

5036
S. Li et al. / Tetrahedron 62 (2006) 5035–5048
N
N
O
N
N
N
N
O
O
O
O
O
N
N
O
O
N
N
N
N
O
O
O
O
Eu
Eu
Eu
3
3
3
[Caz-G1]3-Eu
[3Caz-G1]3-Eu
[2Caz-G1]3-Eu
N
N
N
N
N
N
N
N
O
O
O
N
O
N
O
O
O
O
O
O
O
O
O
O
O
O
O
O
N
N
N
O
O
Eu
Eu
N
O
O
3
3
[4Caz-G2]3-Eu
[6Caz-G2]3-Eu
N
N
N
N
N
N
O
O
O
O
N
N
O
O
O
O
O
O
O
O
O
O
O
O
3
N
O
O
Eu
N
[8Caz-G3]3-Eu
Scheme 1. Chemical structures of six target dendritic europium complexes.

S. Li et al. / Tetrahedron 62 (2006) 5035–5048
5037
MeO
HO
HO
HO
HO
MeO
MeO
O
O
O
O
O
O
a
b
c
OMe
OMe
MeO
1
2
3
4
Scheme 2. Divergent synthesis of focal b-diketonate 4. Reagents and conditions: (a) CH3I, acetone, K2CO3, reflux, 48 h, 92%; (b) NaH, acetophenone, THF,
60 ꢀC, 72 h, 22%; (c) BBr3, CH2Cl2, ꢁ78 ꢀC for 0.5 h, then rt, overnight, 84%.
dibenzoylmethane derivatives. Phenolate 4 (Scheme 2) is an
ideal intermediate with two phenolic hydroxyl groups on
which convergent carboxylate dendrons can be incorporated
to form a higher generation derivatives. As shown in Scheme
2, phenolate 4 was synthesized via three steps with good
overall yield, that was, O-alkylation of methyl 3,5-dihydroxy-
benzoate (1) with methyl iodide, Claisen condensation be-
tween methyl 3,5-dimethoxybenzoate (2) and acetophenone,
and finally the methyl deprotection by BBr3.
contrast, treatment of 9-(4-bromobutyl)-9H-carbazole with
phenolate 4 via the divergent way yielded several byproducts
owning to three active sites (a, b, and c indicated in Scheme
4), which was a time-consuming work to determine and
purify the target ligands.
RO
O
Acetophenone
RO
RO
O
O
OMe
Convergent approach
RO
2.2. The first generation dendron via convergent
approach
[2Caz-G1]-COOMe
O
a
O
[2Caz-G1]-L
HO
There are two basic approaches to construct dendrimers: the
divergent approach and convergent approach.29 The synthe-
sis of first generation (8) was very straightforward without
any group protection and deprotection via convergent ap-
proach with acceptable yield. In Scheme 3, the alkylation
of phenol group of ethyl 4-hydroxybenzoate (5) with 9-(4-
bromobutyl)-9H-carbazole underwent smoothly in the pres-
ence of anhydrous potassium carbonate and 18-crown-6 in
acetone under reflux. Then, the resulting intermediate 6
reacted with acetophenone via Claisen condensation in the
presence of sodium hydride to give 7, followed by chelating
with europium ion.
c
OH
b
R =
N
(CH2)4
RBr
Scheme 4. Procedure for designing the first generation dendritic ligand
[2Caz-G1]-L.
Dendritic europium complexes with the first generation den-
dron of AB2 and AB3 type were synthesized in convergent
approach, which were identical to that of AB type 7 (Scheme
5). Furthermore, since b-diketonates 11a and 11b have
green-yellowish fluorescence, the reaction can be monitored
easily by TLC, and the target b-diketonates were separated
smoothly by column chromatography.
In the synthesis of first generation dendrons (11a and 11b),
Claisen condensation became the crucial step and was ac-
companied with many side reactions, such as aldol conden-
sation and hydrolysis. Once the steric hindrance of the ester
(10a and 10b) was increased, the resulting yield of Claisen
condensation dropped dramatically. Therefore, we attempted
to synthesize the first generation derivatives in two paths to
optimize the reaction procedures. Taking the synthesis of
[2Caz-G1]-L as an example shown in Scheme 4, the first
approach was convergent one in which [2Caz-G1]-COOMe
was coupled with acetophenone in an acceptable yield. In
2.3. The second and third generation dendrons via
hypercore approach
Although the convergent approach seemed to be very helpful
during the syntheses of the first generation dendrons, many
unexpected problems took place during the preparation of
OR
O
O
O
O
OEt
6, [Caz-G1]-COOEt
N
N
c
O
O
b
a
RO
HO
RO
Eu
OEt
3
5, [OH-G1]-COOEt
7, [Caz-G1]-L
8, [Caz-G1]3-Eu
R =
N
-
(CH2)4
Scheme 3. Convergent synthesis of the first generation complex [Caz-G1]3-Eu. Reagents and conditions: (a) 9-(4-bromobutyl)-9H-carbazole, acetone, K2CO3,
reflux, 56 h, 66%; (b) NaH, acetophenone, THF, 60 ꢀC, 90 h, 16%; (c) EuCl3$6H2O, phenanthroline$H2O, NaOH, THF, ethanol, 60 ꢀC, 4 h, 76%.

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S. Li et al. / Tetrahedron 62 (2006) 5035–5048
R'
RO
OR
HO
R'
HO
RO
R'
RO
RO
RO
O
O
O
O
N
N
c
b
O
O
a
R'
Eu
OMe
OMe
R =
N
(CH2)4
3
9, [xOH-G1]-COOMe
10, [xCaz-G1]-COOMe
11, [xCaz-G1]-L
12, [xCaz-G1]3-Eu
a R'=H, x=2
b R'=OH, x=3
a R'=H, x=2
b R'=OR, x=3
a R'=H, x=2
b R'=OR, x=3
a R'=H, x=2
b R'=OR, x=3
Scheme 5. Convergent synthesis of the first generation dendrimer. Reagents and conditions: (a) 9-(4-bromobutyl)-9H-carbazole, acetone, K2CO3, reflux, 56 h,
70–90%; (b) NaH, acetophenone, THF, 60 ꢀC, 90 h, 19–30%; (c) EuCl3$6H2O, phenanthroline$H2O, NaOH, THF, ethanol, 60 ꢀC, 4 h, 45–75%.
the second generation dendrons. When the generation of
corresponding methyl benzoxylate [4Caz-G2]-COOMe was
increased, Claisen condensation between the ester and
acetophenone became very difficult, and little corresponding
ligand [4Caz-G2]-L0 was obtained (Scheme 6).
shown in Scheme 6, we firstly attempted to use ether bond
as the dendritic wedge bridge between [2Caz-G1]-Br with
4, but the yields were unacceptable with many byproducts,
which were similar to the aforementioned O-alkylation in
Scheme 4. Fortunately, the esterification could be preceded
smoothly with the assistance of dicyclohexylcarbodiimide
(DCC) at room temperature with a fairly good yield when
esteral connectivity was chosen as the dendritic wedge. As
a case shown in Scheme 7, the dendron propagation was
started with the saponification of 10. Then the dendritic
wedge 13 containing focal carboxylic group was esterified
with 4 to give the corresponding dendritic b-diketonate 14
with around 55% yield. Treatment of compound 13 with 4
could achieve the second generation dendron 14, which
was a rapid generation-growth approach with respect to
To solve the problem, a hypercore (hyperbranch core) syn-
thetic approach28 containing the advantages of convergent
and divergent approaches was introduced. It involved the
pre-assembly of oligomeric species, which could then be
linked together to give dendrimers in a short route and
high yields. In our design, phenolate 4 containing two reac-
tive phenolic hydroxyl groups at its extremity was utilized
for divergent growth by attaching other preformed dendritic
wedges through their single focal point reactive group. As
RO
OR
RO
RO
OR
O
Acetophenone
O
RO
RO
Convergent approach
Very low yield
O
OMe
O
O
O
O
O
RO
a
O
[4Caz-G2]-COOMe
HO
c
OH
RO
RO
b
[4Caz-G2]-L'
Br
[2Caz-G1]-Br
OR
O
RO
OR
RO
HO
O
O
RO
O
O
O
HO
Hypercore approach
O
OH
RO
[2Caz-G1]-COOH
O
O
R =
N
(CH2)4
[4Caz-G2]-L
Scheme 6. Procedure for designing the second dendritic ligands.

S. Li et al. / Tetrahedron 62 (2006) 5035–5048
5039
R'
RO
R'
R'
R'
RO
OR
O
RO
OR
RO
OR
RO
OR
c
b
R'
RO
OH
O
O
O
O
O
O
O
O
O
O
O
O
N
13, [xCaz-G1]-COOH
Eu
a R'=H, x=2
b R'=OR, x=3
N
3
a
14, [xCaz-G2]-L
10, [xCaz-G1]-COOMe
15, [xCaz-G2]3-Eu
R =
N
(CH2)4
a R'=H, x=2
b R'=OR, x=3
a R'=H, x=4
b R'=OR, x=6
a R'=H, x=4
b R'=OR, x=6
Scheme 7. Hypercore synthesis of the second dendritic complexes. Reagents and conditions: (a) NaOH, THF, H2O, reflux, 8 h, w93%; (b) 4, DCC, DPTS,
CH2Cl2, rt, 24 h,w55%; (c) EuCl3$6H2O, phenanthroline$H2O, triethylamine, THF, ethanol, 60 ꢀC, 4 h,w80%.
the convergent synthesis from the reaction of [4Caz-G2]-
COOMe and acetophenone.
simple synthetic transformations were used for synthesizing
dendrons: (1) selective alkylation of phenolic hydroxyl
groups, and (2) conversion of a benzylic alcohol to a benzylic
bromide to generate a reactive focal moiety (Scheme 8).
Herein, O-alkylation was the repetitive steps for the synthe-
The third generation dendrimer was also obtained via hyper-
core approach with multiple steps consisting O-alkylation,
bromo-substitution, hydrolysis, and esterification. Two
´
sis of higher generation of Frechet-type poly(aryl ether)
RO
OR
RO
OR
OR
O
RO
OR
RO
e
RO
HO
HO
RO
O
O
O
O
O
O
a
c
RO
RO
OH
X
X
RO
O
O
16, X = OH
O
O
b
RO
18, X = OMe
19, X = OH
17, X = Br
O
O
d
RO
OR
RO
OR
RO
OR
RO
OR
20, [8Caz-G3]-L
O
O
O
O
O
O
f
O
O
3
N
N
O
O
Eu
R =
N
(CH2)4
21, [8Caz-G3]3-Eu
Scheme 8. Hypercore synthesis of the third dendritic complexes. Reagents and conditions: (a) 9-(4-bromobutyl)-9H-carbazole, acetone, K2CO3, reflux, 56 h,
83%; (b) PPh3, CBr4, CH2Cl2, rt, 5 h, 92%; (c) methyl 3,5-dihydroxyl benzoate, 18-crown-6, acetone, K2CO3, reflux, 56 h, 81%; (d) NaOH, THF, H2O, reflux,
5 h, 93%; (e) 4, DCC, DPTS, CH2Cl2, rt, 24 h, 17%; (f) EuCl3$6H2O, phenanthroline$H2O, triethylamine, THF, ethanol, 60 ꢀC, 4 h, 87%.

5040
S. Li et al. / Tetrahedron 62 (2006) 5035–5048
dendrons. The O-alkylation of 9-(4-bromobutyl)-9H-carba-
zole and 3,5-dihydroxyl benzyl alcohol afforded the first
generation of benzyl alcohol 16, which was facile to be pu-
rified via recrystallization. Then the corresponding dendritic
benzyl bromide 17 was prepared by the combinatorial bro-
mination reagents of PPh3 and CBr4, followed by phenolic
alkylation of methyl 3,5-dihydroxyl benzoate to yield the
second generation of methyl benzoate 18. Treatment of
product 19 with 4 in the presence of DCC/DPTS gave the
third generation of desirable dendritic ligand 20. The third
generation dendrimer of Eu(III) complex 21 was finally ob-
tained by the treatment of the corresponding ligand with
EuCl3$6H2O in the mixing solvents of ethanol and THF
kept in oil bath at 60 ꢀC. The coordination was easily ob-
served by instantaneous color change of the reaction mixture
upon addition of Eu(III) salt.
ligand, 1,10-phenanthroline, usually observed at 1610 cmꢁ1
,
is difficult to be distinguished due to the overlapping with the
vibration peak of double bond. Another peak at 1340 cmꢁ1 is
attributed to the stretching vibration of C–N bond.5,30 Two
spectra both contain two sharp and strong absorption peaks
at 726 and 747 cmꢁ1, associated with the characteristic ab-
sorption of the carbazole moieties. All demonstrate a suc-
cessful coordination between [2Caz-G1]-L and Eu(III) ion.
To date, most europium complexes haven’t been character-
ized by H NMR spectrum due to the Eu(III) paramagnet-
1
ism.3,17,31,32 Although NMR signals for the second- and
third-generation Eu(III) dendrimers are too complicated
and broad, H NMR spectra of dendritic ligands and their
1
first generation europium complexes provide useful infor-
mation and solid evidences for Eu(III) coordination. As a
result of the ring current effect between phenanthroline
and b-diketonate, the proton chemical shifts of ligands in
the complexes have a dramatic change with respect to that
of corresponding free ligands. For Eu(III) complexes, pro-
tons of phenanthroline are deshielded while protons linking
2.4. Structure characterization
All dendrimers were recrystallized from acetone for several
times. Further purification of the obtained Eu(III) coordi-
nated dendrimers by silica gel column chromatography
failed, only yielding the corresponding starting dendrons.
This might be the result of ligand exchange reaction between
the coordinated dendrimers and surface silanol groups
(Si–OH) of silica gel, resulting in the adsorption of Eu(III)
onto the silica gel.11 Dendritic b-diketonates and their euro-
pium complexes were well characterized. In order to assign
functional groups in detail, the IR spectra of [2Caz-G1]-L
and [2Caz-G1]3-Eu are illustrated in Figure 1. The ligand
[2Caz-G1]-L (Fig. 1a) has a broad vibration band at 3300–
3600 cmꢁ1 assigned to hydroxyl group of enol form of b-di-
ketonates, which almost disappeared after the coordination
with Eu(III) (complex [2Caz-G1]3-Eu, Fig. 1b). A single
peak at 3051 cmꢁ1 and a doublet at about 2855 and
2930 cmꢁ1 are corresponding to the C–H stretching vibra-
tion of aryl ring and alkyl chain. The C]O and C]C
stretching vibrations of ligand in the complex [2Caz-G1]3-
Eu (Fig. 1b) appear at about 1551 and 1592 cmꢁ1, respec-
tively, whereas these vibrations in ligand [2Caz-G1]-L
(Fig. 1a) are at 1600 cmꢁ1. The ring vibration of the second
1
to b-diketonates are shielded. As a typical example, the H
NMR spectra of [2Caz-G1]-L and [2Caz-G1]3-Eu are shown
in Figure 2. Owing to the ligand of [2Caz-G1]-L existing in
enol form,13,33 each of the protons (Hh, Hi, and Hj) in [2Caz-
G1]-L is characteristic of single peak. Comparing with the
assignment of the proton signals of [2Caz-G1]-COOMe,
the chemical shift of Hg in [2Caz-G1]-L is shifted downfield
to 7.97 ppm due to the adjacent electron-withdrawing effect
of carbonyl group, indicating that the form of enol-1 is more
favorable as shown in Scheme 9. Thermodynamically, the
conjugation state of enol-1 is more stable than that of
enol-2. Upon coordination with Eu(III) ion, 1H NMR spec-
trum of [2Caz-G1]3-Eu becomes complicated. Due to
[2Caz-G1]-L existing in anionic form, the protons of the
focal b-diketonate in the complex are shielded so that dra-
matic changes are observed for the chemical shifts of He,
Hf, Hg, Hh, Hi, and Hj, which are shifted from 7.55, 7.49,
7.97, 6.75, 7.04, and 6.53 ppm to approximately 7.53, 7.26,
7.40, 6.00, 6.61, and 5.67 ppm, respectively. In contrast, due
to the deshield effect, Ha, Hb, Hc, and Hd signals of phenan-
throline ligand appear at the downfield of 10.71, 7.97, 10.42,
and 8.53 ppm.
1
With the dendron-generation growth, H NMR signals be-
a
come more complicated and difficult to discern structures.
To assess more clearly the identity of chemical structures,
further characterization has been performed by MALDI-
TOF mass spectroscopy. This technique provides macro-
molecular mass determinations for intact molecular ions of
nonvolatile species, and is particularly useful for structural
characterization of high molecular weight dendrimers.
MALDI-TOF results of the ligand dendrons and their corre-
sponding europium complex dendrimers are shown in Section
4. Some signals observed are either potassium or sodium ad-
ducts of the molecular ions, depending on the matrix used.
The MALDI-TOF spectra of the second-and third-generation
b-diketonate ligands are shown in Figure 3. The MALDI-
TOF spectra of the europium dendrimers for the first- and
second-generation derivativesarepresentedinFigure4. These
peaks occurred at m/z values consistently within 0.2% of the
theoretical values. Thus, the MALDI-TOF data provided
additional support for the identity of these dendrimers.
b
3500
3000
1500
Wavelength (cm-1
1000
500
)
Figure 1. IR spectra of [2Caz-G1]-L (a) and [2Caz-G1]3-Eu (b).

S. Li et al. / Tetrahedron 62 (2006) 5035–5048
5041
Figure 2. 1H NMR spectra (500 MHz, CDCl3, 25 ꢀC) of (A) [2Caz-G1]3-L and (B) [2Caz-G1]3-Eu.
RO
RO
j
RO
j'
i
g
i'
g'
O
OH
O
O
O
OH
h
RO
RO
RO
enol-1
-diketonate
enol-2
Scheme 9. Tautomers of [2Caz-G1]-L. Note: NMR spectra suggest that the form of enol-1 is more favorable.
2.5. Light-harvesting effect of the peripheral carbazole
units in europium complexes
transfer from ‘light-harvesting antenna’ ligand (donor) to
central lanthanide ion. Excitation mechanism of the central
metal ion also differs widely from that of organic fluorescent
compounds. For Eu(III) complexes with p-conjugated li-
gands such as b-diketonate, Eu(III) ions are excited via intra-
molecular energy transfer from the triplet excited states of
Generally, because the central Eu(III) ion shows little or no
absorption in the visible light region, the luminescence of
lanthanide complexes is critically dependent on the energy

5042
S. Li et al. / Tetrahedron 62 (2006) 5035–5048
Figure 3. MALDI-TOF mass spectra of [4Caz-G2]-L, [6Caz-G2]-L, and [8Caz-G3]-L.
the ligands.2 To improve the energy transfer to Eu(III) ions,
the triplet states of ligands must be closely matched to or
slightly above the emitting resonance levels of center Eu(III)
ions.
When excited at the absorption wavelength of the grafted
carbazole units, all dendritic europium complexes in
CH2Cl2 or solid film emit a characteristic sharp lumines-
cence peak at 615 nm with four shoulders ascribed to
Figure 4. MALDI-TOF mass spectra of [3Caz-G1]3-Eu ([M+]), top) and [4Caz-G2]3-Eu ([M++Na], [M++K], bottom).

S. Li et al. / Tetrahedron 62 (2006) 5035–5048
5043
transitions between 4f states of Eu(III) ion. All five peaks at
586, 591, 615, 651, and 702 nm are corresponding to Eu(III)
characteristic transitions (5D0/7Fj, j¼0–4).
Notably, with respect to carbazole, the emission of periph-
eral donor carbazole unit in the system of the synthesized eu-
ropium dendrimers is almost completely quenched under the
direct excitation of 331 nm (curve c, Fig. 5). As can be seen
in Figure 5 (curves a and b), the luminescence of carbazole
units is overlapped with the absorption of [3Caz-G1]3-Eu to
a certain extent, thus an efficient Forster-resonance energy
¨
transfer in the complex system can take place from the
singlet excited state of the grafted carbazole to the singlet
excited state of b-diketonate ligand, and followed by the
intersystem crossing to the excited triplet state of b-diketo-
nate, where it is finally transferred to the central Eu(III)
ion. The efficient energy transfer is further confirmed by
the excitation spectrum of [3Caz-G1]3-Eu (Fig. 6), indicat-
ing that the peripheral carbazole units in such complexes
can exhibit efficient light-harvesting potential. Thus, it is
possible to obtain a strong intense emission from the central
Eu(III) when excited via sensitization from a large light-
harvesting antenna. Moreover, the site isolation of dendrons
can also be favorable to enhance luminance. For comparing
the relative luminescence quantum yields, we normalized
the spectra of the absorption peak at b-diketonate region
(360 nm), and compared the relative intensity of lumines-
cence. As a result of the carbazole light harvesting and the
site isolation of dendrons, in comparison with the lumines-
cence intensity of reference complex Eu(BPPD)3Phen26 in
solid film excited at 331 nm (carbazole absorption maxi-
mum), the relative luminescence quantum yields of [Caz-
G1]3-Eu, [2Caz-G1]3-Eu, and [3Caz-G1]3-Eu are 3.3, 7.9,
and 4.5 folds, respectively. It should be noted that the lumi-
nescence of [3Caz-G1]3-Eu containing three carbazole units
is unexpectedly weaker than that of [2Caz-G1]3-Eu contain-
ing two carbazole units, which might be attributed to the
spatial hindrance of three neighboring carbazole units incor-
porated into one side of ligand and leading to a less effective
energy transfer between carbazole and b-diketonate. The de-
tailed studies of energy transfer, luminescence dynamics,
and photo-physical properties with these dendrimers are
now undergoing, and will be reported elsewhere. Notably,
300
350
400
450
500
Wavelength (nm)
Figure 6. Absorption spectrum (solid line) and excitation spectrum (dash
dot line) of [3Caz-G1]3-Eu monitored at 615 nm. The excitation spectrum
is normalized at the absorption peak at b-diketonate region (360 nm). All
measurements are in CH2Cl2 (1.2ꢂ10ꢁ6 mol Lꢁ1).
preliminary results show that white light electrolumines-
cence (CIE: 0.333, 0.348) using a complex [3Caz-G1]3-Eu
can be achieved,27 indicating that modifying ligands can
not only tune the carrier-transporting properties of com-
plexes, but also provide a useful clue to use electroplex or
exciplex to realize a broad or even white electrolumi-
nescence.
3. Conclusions
Several dendritic b-diketonates and corresponding europium
complexes were designed and synthesized based on the fol-
lowing consideration: (1) high light-harvesting capability
and efficient energy transfer to the focal ion in virtue of
high extinction coefficient of the terminated carbazole units,
(2) dendron functionalization to incorporate carbazole units
to realize the carrier-injection adjustment, and (3) avoiding
core luminescence quenching by the means of the dendron
to enhance core luminescence. Their dendritic b-diketonate
´
ligands consist dibenzoylmethane cores, Frechet-type poly
(aryl ether) dendrons, and the grafted carbazole (CZ) periph-
eral functional groups. Due to the acceptable yield of Claisen
condensation, convergent synthetic approach through etheral
connectivity was utilized to achieve the first generation
europium complexes. For the second and third generation
dendrons, a hyperbranch core synthetic approach containing
the advantages of convergent and divergent approaches was
introduced. Preliminary results showed that the peripheral
carbazole units in such complexes can not only tune the
carrier-transporting capability, but also exhibit strong light-
harvesting potential, thus resulting in a strong intense emis-
sion from the central Eu(III) via the sensitization.
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
b
c
a
4. Experimental
4.1. General
300
400
500
Wavelength (nm)
600
700
Figure 5. Absorption spectrum of [3Caz-G1]3-Eu in CH2Cl2 (2.0ꢂ10ꢁ5
mol Lꢁ1, curve a), and PL spectra excited at 331 nm in CH2Cl2 (2.0ꢂ10ꢁ5
mol Lꢁ1) of carbazole (curve b) and [3Caz-G1]3-Eu (curve c).
THF was dried from metal sodium. Sodium hydride was
purchased from J&K, kept in a vacuum drier at room

5044
S. Li et al. / Tetrahedron 62 (2006) 5035–5048
temperature. EuCl3$6H2O (99.9%) and carbazole were ob-
tained from Aldrich. Acetophenone from Aldrich was dried
with MgSO4 and redistilled prior to usage. All other starting
materials and reagents were of analytic purity without treat-
ment. Melting points were measured on X4 Micro-melting
point apparatus. 1H NMR and 13C NMR spectra were
recorded on a Brucker AM-500 spectrometer. TMS was
used as internal reference for all the compounds. MS were
recorded on FAB or MALDI-TOF mass spectroscopy. IR
spectra of thin films on KBr plates were recorded on a Nexus
470 FTIR spectrometer. Elemental analyses were obtained
on a Perkin–Elmer 240C elemental analyzer.
4.1.4. Ethyl 4-[4-(9H-carbazol-9-yl)butoxy]benzoate
([Caz-G1]-COOEt, 6). A mixture of 9-(4-bromobutyl)-
9H-carbazole (2.00 g, 6.62 mmol), 5 (1.43 g, 8.61 mmol),
potassium carbonate (1.30 g, 9.42 mmol), and 18-crown-6
(0.13 g, 4.72 mmol) in anhydrous acetone (60 mL) was
heated at reflux and stirred vigorously under nitrogen for
56 h. The mixture was allowed to cool and evaporated to dry-
ness under reduced pressure. The residue was washed with
water and a large amount of precipitate appeared followed
by filtration. After recrystallization, a white needle-like crys-
1
tal was obtained (1.71 g), yield 66%. Mp: 80–82 ꢀC. H
NMR (500 MHz, CDCl3): d ppm, 1.37 (t, 3H, J¼6.2 Hz,
–CH3), 1.87–1.91 (m, 2H, –CH2), 2.10–2.14 (m, 2H,
–CH2), 3.98 (t, 2H, J¼6.2 Hz, –OCH2), 4.32 (t, 2H,
J¼6.0 Hz, –OCH2), 4.40 (t, 2H, J¼7.0 Hz, –NCH2), 6.84
(d, 2H, J¼8.8 Hz, Ph–H), 7.23 (t, 2H, J¼7.0, 8.2 Hz, Ph–
H), 7.43 (d, 2H, J¼8.1 Hz, Ph–H), 7.47 (t, 2H, J¼7.2,
8.3 Hz, Ph–H), 7.96 (d, 2H, J¼8.8 Hz, Ph–H), 8.10 (d, 2H,
J¼7.6 Hz, Ph–H). MS (FAB): m/z 389.2 [M++2], 388.2
[M++1], 387.2 [M+] (100%). Anal. Calcd for C25H25NO3:
C, 77.49; H, 6.50; N, 3.61. Found: C, 77.28; H, 6.32; N, 3.75.
4.1.1. Synthesis of methyl 3,5-dimethoxybenzoate ([2Me-
G1]-COOMe, 2). To a 100 mL flask were added methyl
iodide (9.0 g, 63.4 mmol), methyl 3,5-dihydroxybenzoate
(5.0 g, 29.5 mmol), potassium carbonate (8.6 g,
62.3 mmol), and anhydrous acetone (60 mL). The mixture
was heated at reflux and stirred vigorously under argon for
48 h. Then it was allowed to cool and evaporate to dryness
under reduced pressure. The residue was washed with water.
After filtration and recrystallization, pink crystals were
obtained (5.3 g), yield 92%. Mp: 55–57 ꢀC. 1H NMR
(500 MHz, CDCl3): d ppm, 3.82 (s, 6H, –OCH3), 3.89 (s,
3H, –OCH3), 6.54 (s, 1H, Ph–H), 7.14 (s, 2H, Ph–H). MS
(FAB): m/z 197.1 [M++1], 196.1 [M+] (100%).
4.1.5. 1-[4-[4-(9H-Carbazol-9-yl)butoxy]phenyl]-3-
phenylpropane-1,3-dione ([Caz-G1]-L, 7). To a dry flask
containing a solution of acetophenone (0.37 g, 3.08 mmol)
and 6 (1.20 g, 3.09 mmol) in THF (60 mL) was added
quickly 60% sodium hydride (0.30 g, 7.5 mmol). The reac-
tion mixture was heated under argon at 60 ꢀC for 90 h.
The solution was then acidified with dilute HCl and ex-
tracted with CH2Cl2. After solvent removal, the solid residue
was separated over a silica gel column (CH2Cl2/CCl4, 1:2/
v:v) and a light yellow solid was obtained (0.23 g), yield
16.2%. Mp: 159–162 ꢀC. 1H NMR (500 MHz, CDCl3):
d ppm, 1.89–1.92 (m, 2H, CH2), 2.11–2.15 (m, 2H, CH2),
4.01 (t, 2H, J¼6.1 Hz, –OCH2), 4.43 (t, 2H, J¼7.0 Hz,
–NCH2), 6.79 (s, 1H, ]CH), 6.91 (d, 2H, J¼5.2 Hz, Ph–
H), 7.25 (d, 2H, J¼6.5 Hz, Ph–H), 7.42 (d, 2H, J¼8.1 Hz,
Ph–H), 7.44–7.50 (m, 4H, Ph–H), 7.53 (t, 1H, J¼1.4,
1.2 Hz, Ph–H), 7.93–7.97 (m, 4H, Ph–H), 8.11 (d, 2H,
J¼7.6 Hz, Ph–H). MS (FAB): m/z 463 [M++2], 462
[M++1], 461 [M+]. Anal. Calcd for C31H27NO3: C, 80.67;
H, 5.90; N, 3.03. Found: C, 80.38; H, 5.69; N, 3.13.
4.1.2. 1-(3,5-Dimethoxyphenyl)-3-phenylpropane-1,3-di-
one ([2Me-G1]-L, 3). To a dry flask containing a solution
of acetophenone (1.2 g, 10.2 mmol) and
2 (2.0 g,
10.2 mmol) in THF (60 mL) was added quickly 60% sodium
hydride (0.4 g, 10.0 mmol). The reaction mixture was heated
under argon at 60 ꢀC for 72 h. The solution was then acidi-
fied with dilute HCl and extracted with CH2Cl2. After re-
moval of solvent, the pure product was obtained (0.63 g)
as a yellow solid over a silica gel column (CH2Cl2/CCl4,
1
1:5/v:v), yield 21.7%. Mp: 62–63 ꢀC. H NMR (500 MHz,
CDCl3): d ppm, 3.83 (s, 6H, –OCH3), 6.65 (t, 1H,
J¼2.0 Hz, Ph–H), 6.80 (s, 1H, ]CH), 7.12 (d, 2H,
J¼2.0 Hz, Ph–H), 7.48 (t, 2H, J¼7.4, 7.3 Hz, Ph–H), 7.55
(t, 1H, J¼7.3 Hz, Ph–H), 7.97 (d, 2H, J¼7.4 Hz, Ph–H);
MS (FAB): m/z 286.1 [M++2], 285.1 [M++1], 284.1 [M+]
(100%).
4.1.6. Tris[1-[4-[4-(9H-carbazol-9-yl)butoxy]phenyl]-3-
phenylpropane-1,3-dione](1,10-phenanthroline) euro-
pium (III) ([Caz-G1]3-Eu, 8). To a solution of 7 (120 mg,
0.26 mmol) and 1,10-phenanthroline monohydrate (18 mg,
4.1.3. 1-(3,5-Dihydroxyphenyl)-3-phenylpropane-1,3-
dione ([2OH-G1]-L, 4). To a solution of 2 (1.6 g,
5.63 mmol) in dry CH2Cl2 (50 mL) at ꢁ78 ꢀC was slowly
syringed BBr3 (1.6 mL), and after stirring at ꢁ78 ꢀC for
0.5 h, the solution was allowed to warm to room temperature
90.9 mmol) in THF (10 mL), aqueous NaOH (1 mol Lꢁ1
,
0.2 mL) was syringed dropwise, followed by aqueous
EuCl3 hexahydrate (31.7 mg, 87.4 mmol). Under the protec-
tion of argon, the mixture was stirred at 60 ꢀC for 4 h and
then cooled. The product was collected by filtration and
washed with deionized water twice before crystallization
with acetone and vacuum drying (112 mg), yield 75.5%.
Mp: 110–113 ꢀC. 1H NMR (500 MHz, CDCl3): d ppm,
1.72 (br, 6H, CH2), 2.17 (br, 6H, CH2), 3.77 (br, 6H,
–OCH2), 4.35 (br, 6H, –NCH2), 5.59 (br, 6H, ]CH, Ph–
H), 5.95 (br, 6H, Ph–H), 6.20 (br, 6H, Ph–H), 6.61–6.78
(m, 12H, Ph–H), 7.26–7.46 (m, 15H, Ph–H), 8.11 (br, 9H,
Ph–H), 8.97 (br, 2H, phenanthroline–H), 9.90 (br, 2H, phen-
anthroline–H), 10.64 (br, 2H, phenanthroline–H), 11.01 (br,
2H, phenanthroline–H). MS (FAB): m/z 1752.6 [M++K],
1736.7 [M++Na], 1714 [M+] (100%). Anal. Calcd for
and left overnight. A dilute solution of NaOH (1 mol Lꢁ1
,
5 mL) was then added at 0 ꢀC. The mixture was extracted
with ethyl acetate to remove the unreacted reagent and the
remaining aqueous solution was neutralized with hydro-
chloric acid (2 mol Lꢁ1). Large amount of yellow solid
was precipitated and filtered. The crude product was purified
by chromatography on silica gel (CH2Cl2/acetone, 10:1/v:v).
The total yield was 84% (1.3 g). 1H NMR (500 MHz,
CDCl3): d ppm, 6.60 (s, 1H, Ph–H), 6.78 (s, 1H, ]CH),
7.10 (s, 2H, Ph–H), 7.48 (t, 2H, J¼7.4, 7.8 Hz, Ph–H),
7.55 (t, 1H, J¼7.3 Hz, Ph–H), 7.97 (d, 2H, J¼7.1 Hz, Ph–
H). MS (FAB): m/z 257 [M++1], 256 [M+] (100%), 255
[M+ꢁ1], 239 [M+ꢁOH].

S. Li et al. / Tetrahedron 62 (2006) 5035–5048
5045
C105H86EuN5O9: C, 73.59; H, 5.06; N, 4.09. Found: C,
73.21; H, 4.69; N, 4.38.
]CH), 6.00 (br, 6H, Ph–H), 6.61–6.78 (m, 9H, Ph–H),
7.26–7.45 (m, 12H, Ph–H), 7.40–7.76 (m, 30H, Ph–H),
7.97 (br, 2H, phenanthroline–H), 8.10 (br, 15H, Ph–H),
8.53 (br, 2H, phenanthroline–H), 10.42 (br, 2H, phenanthro-
line–H), 10.71 (br, 2H, phenanthroline–H); MALDI-TOF
MS m/z: 2425 [M+]. Anal. Calcd for C153H131EuN8O12: C,
75.76; H, 5.44; N, 4.62. Found: C, 75.28; H, 5.07; N, 4.85.
4.1.7. Methyl 3,5-bis[4-(9H-carbazol-9-yl)butoxy]ben-
zoate ([2Caz-G1]-COOMe, 10a). A mixture of 9-(4-bromo-
butyl)-9H-carbazole (3.00 g, 9.93 mmol), 9a (0.78 g,
4.64 mmol), potassium carbonate (1.82 g, 13.1 mmol), and
18-crown-6 (0.13 g, 4.7 mmol) in anhydrous acetone
(100 mL) was heated at reflux and stirred vigorously under
nitrogen for 56 h. The mixture was allowed to cool and evap-
orated to dryness under reduced pressure. The residue was
washed with water and a large amount of precipitate ap-
peared followed by filtration. After recrystallization with
ethanol, a white powder was obtained (2.5 g), yield 88.3%.
Mp: 124–127 ꢀC. 1H NMR (500 MHz, CDCl3): d ppm,
1.82–1.87 (m, 4H, CH2), 2.05–2.11 (m, 4H, CH2), 3.88 (s,
3H, –OCH3), 3.94 (t, 4H, J¼6.1 Hz, –OCH2), 4.39 (t, 4H,
J¼7.0 Hz, –NCH2), 6.54 (s, 1H, Ph–H), 7.14 (s, 2H, Ph–
H), 7.23 (t, 4H, J¼7.2, 7.4 Hz, Ph–H), 7.42 (d, 4H,
J¼8.1 Hz, Ph–H), 7.46 (t, 4H, J¼7.4 Hz, 7.8 Hz, Ph–H),
8.10 (d, 4H, J¼7.8 Hz, Ph–H). MALDI-TOF MS (FAB):
m/z 612.5 [M++2], 611.5 [M++1], 610.5 [M+] (100%).
Anal. Calcd for C40H38N2O4: C, 78.66; H, 6.27; N, 4.59.
Found: C, 78.40; H, 6.00; N, 4.82.
4.1.10. Methyl 3,4,5-tris[4-(9H-carbazol-9-yl)butoxy]-
benzoate ([3Caz-G1]-COOMe, 10b). A mixture of 9-(4-
bromobutyl)-9H-carbazole (3.00 g, 9.93 mmol), methyl
3,4,5-trihydroxy benzoate (0.60 g, 3.31 mmol), potassium
carbonate (1.51 g, 10.9 mmol), and 18-crown-6 (0.13 g,
4.7 mmol) in anhydrous acetone (60 mL) was stirred vigor-
ously, and refluxed for 56 h under the protection of nitrogen.
After cooling, solvents under reduced pressure were re-
moved, the resulting solid was filtrated, and recrystallized
from ethanol to give a white needle-like crystal (2.13 g),
1
yield 75%. Mp: 86–88 ꢀC. H NMR (500 MHz, CDCl3):
d ppm 1.55–1.60 (m, 2H, –CH2), 1.72–1.75 (m, 4H,
–CH2), 1.92–1.98 (m, 6H, –CH2), 3.84–3.88 (m, 5H,
–OCH3, –CH2), 3.91 (t, 4H, J¼6.1 Hz, –CH2), 4.10 (t, 2H,
J¼7.1 Hz, –CH2), 4.21 (t, 4H, J¼7.0 Hz, –CH2), 7.17 (s,
2H, Ph–H), 7.19–7.21 (m, 6H, Ph–H), 7.24 (t, 2H, J¼1.3,
7.2 Hz, Ph–H), 7.29 (d, 4H, J¼8.2 Hz, Ph–H), 7.36–7.42
(m, 6H, Ph–H), 8.05 (d, 2H, J¼7.7 Hz, Ph–H), 8.06 (d,
4H, J¼5.0 Hz, Ph–H). MALDI-TOF MS (FAB): m/z 847.9
[M++1], 846.9 [M+]. Anal. Calcd for C56H53N3O5: C,
79.31; H, 6.30; N, 4.95. Found: C, 79.08; H, 6.11; N, 5.20.
4.1.8. 1-[3,5-Bis[4-(9H-carbazol-9-yl)butoxy]phenyl]-3-
phenylpropane-1,3-dione ([2Caz-G1]-L, 11a). To a dry
flask containing a solution of acetophenone (0.39 g,
3.3 mmol) and 10a (2.00 g, 3.28 mmol) in THF (80 mL)
was added quickly 60% sodium hydride (0.20 g,
5.0 mmol). The reaction mixture was heated under argon
at 60 ꢀC for 90 h. The solution was then acidified with dilute
HCl and extracted with CH2Cl2. After solvent removal, the
solid residue was separated over a silica gel column
(CH2Cl2/CCl4, 1:5/v:v) and a light yellow solid was ob-
tained (0.43 g), yield 19.0%. Mp: 57–59 ꢀC. 1H NMR
(500 MHz, CDCl3): d ppm, 1.88–1.91 (m, 4H, CH2), 2.06–
2.10 (m, 4H, CH2), 3.98 (t, 4H, J¼6.1 Hz, –OCH2), 4.41
(t, 4H, J¼7.0 Hz, –NCH2), 6.53 (s, 1H, Ph–H), 6.75 (s,
1H, ]CH), 7.04 (s, 2H, Ph–H), 7.25 (t, 4H, J¼7.2 Hz,
Ph–H), 7.42–7.51 (m, 10H, Ph–H), 7.55 (t, 1H, J¼7.2,
7.0 Hz, Ph–H), 7.97 (d, 2H, J¼7.6 Hz, Ph–H), 8.11 (d, 4H,
J¼7.7 Hz, Ph–H). 13C NMR (CDCl3): d ppm, 26.5, 27.6,
43.4, 68.5, 94.0, 106.0, 106.4, 109.3, 119.6, 121.1, 123.6,
126.4, 127.8, 129.3, 133.1, 136.0, 138.4, 141.1, 160.9,
185.9, 186.6. MS (FAB): m/z 700 [M++2], 699 [M++1],
698 [M+]. Anal. Calcd for C47H42N2O4: C, 80.78; H, 6.06;
N, 4.01. Found: C, 80.50; H, 5.85; N, 4.23.
4.1.11. 1-[3,4,5-Tris[4-(9H-carbazol-9-yl)butoxy]phenyl]-
3-phenylpropane-1,3-dione ([3Caz-G1]-L, 11b). To a dry
flask containing a solution of acetophenone (0.21 g,
1.76 mmol) and 10b (1.50 g, 1.76 mmol) in THF (60 mL)
was added quickly 60% sodium hydride (0.10 g,
2.5 mmol). The reaction mixture was heated at 60 ꢀC for
90 h under argon. The solution was then acidified with dilute
HCl, and extracted with CH2Cl2. After solvent removal, the
solid residue was purified via a silica gel column (CH2Cl2/
CCl4, 1:2/v:v), a light yellow oil was obtained (0.49 g), yield
1
29.7%. Mp: 71 ꢀC. H NMR (500 MHz, CDCl3): d ppm,
1.60–1.65 (m, 2H, –CH2), 1.74–1.78 (m, 4H, –CH2), 1.94–
2.03 (m, 6H, –CH2), 3.88 (t, 2H, J¼6.1 Hz, –CH2), 3.94 (t,
4H, J¼7.2 Hz, –CH2), 4.12 (t, 2H, J¼6.1 Hz, –CH2), 4.22
(t, 4H, J¼7.1 Hz, –CH2), 6.65 (s, 1H, ]CH), 7.08 (s, 2H,
Ph–H), 7.17–7.21 (m, 6H, Ph–H), 7.25–7.28 (m, 2H, Ph–
H), 7.30 (d, 4H, J¼8.2 Hz, Ph–H), 7.37–7.41 (m, 6H, Ph–
H), 7.47 (t, 2H, J¼7.8, 7.5 Hz, Ph–H), 7.54 (t, 1H, J¼7.8,
7.7 Hz), 7.92 (d, 2H, J¼7.2 Hz), 8.07 (t, 6H, J¼7.6,
6.8 Hz, Ph–H). MS (FAB): m/z 974.4 [M++K], 958.4
[M++Na]. Anal. Calcd for C63H57N3O5: C, 80.83; H, 6.14;
N, 4.49. Found: C, 80.58; H, 5.87; N, 4.70.
4.1.9. Tris[1-[3,5-bis[4-(9H-carbazol-9-yl)butyloxy]-
phenyl]-3-phenylpropane-1,3-dione](1,10-phenanthro-
line) europium (III) ([2Caz-G1]3-Eu, 12a). To a solution of
11a (0.10 g, 0.14 mmol) and 1,10-phenanthroline mono-
hydrate (11.3 mg, 57.2 mmol) in THF (10 mL), aqueous
NaOH (1 mol Lꢁ1, 0.20 mL) was syringed dropwise
followed by aqueous EuCl3 hexahydrate (17.5 mg,
48.2 mmol). Under the protection of argon, the mixture
was stirred at 60 ꢀC for 4 h and then cooled. The product
was collected by filtration and washed with deionized water
twice before crystallization with acetone and vacuum drying
4.1.12. Tris[1-[3,4,5-tris[4-(9H-carbazol-9-yl)butoxy]-
phenyl]-3-phenyl-propane-1,3-dione](1,10-phenanthro-
line) europium (III) ([3Caz-G1]3-Eu, 12b). To a solution of
11b (226 mg, 240 mmol) and 1,10-phenanthroline mono-
hydrate (16 mg, 81 mmol) in THF (10 mL), aqueous NaOH
(mol Lꢁ1, 0.38 mL) was syringed dropwise, followed by
aqueous EuCl3$6H2O (29.4 mg, 80 mmol). The mixture
was stirred at 60 ꢀC for 4 h under the protection of nitrogen.
After cooling, the product was filtrated, washed with de-
ionized water, and recrystallized from acetone to give light
1
(57 mg), yield 49%. Mp: 89–92 ꢀC. H NMR (500 MHz,
CDCl3): d ppm, 1.56 (br, 12H, CH2), 1.86 (br, 12H, CH2),
3.51 (br, 12H, CH2), 4.24 (br, 12H, CH2), 5.67 (br, 3H,

5046
S. Li et al. / Tetrahedron 62 (2006) 5035–5048
yellow powder (180 mg), yield 71.6%. Mp: 84–87 ꢀC.
MALDI-TOF MS m/z: 3143.6 [M+]. Anal. Calcd for
C201H176EuN11O15: C, 76.94; H, 5.65; N, 4.91. Found: C,
76.58; H, 5.28; N, 5.16.
4.1.16. 3,4,5-Tris[4-(9H-carbazol-9-yl)butoxy]benzoic
acid ([3Caz-G1]-COOH, 13b). Similar to 13a to get white
1
solid in 95% yield. Mp: 85–86 ꢀC. H NMR (500 MHz,
CDCl3): d ppm, 1.58–1.62 (m, 2H, CH2), 1.76–1.81 (m,
4H, CH2), 1.97–2.02 (m, 6H, CH2), 3.88 (t, 2H, J¼6.0 Hz,
–OCH2), 3.92 (t, 4H, J¼6.0 Hz, –OCH2), 4.13 (t, 2H,
J¼7.2 Hz, –NCH2), 4.22 (t, 4H, J¼7.0, 7.0 Hz, –NCH2),
7.20–7.22 (m, 8H, Ph–H), 7.23–7.25 (m, 2H, Ph–H), 7.29
(d, 4H, J¼8.1 Hz, Ph–H), 7.39–7.44 (m, 6H, Ph–H), 8.08–
8.12 (m, 6H, Ph–H). MALDI-TOF MS (FAB): m/z 835.4
[M++1], 834.4 [M+], 833.4 [M+ꢁ1]. Anal. Calcd for
C55H51N3O5: C, 79.21; H, 6.16; N, 5.04. Found: C, 79.04;
H, 6.01; N, 5.20.
4.1.13. 3,5-Bis[4-(9H-carbazol-9-yl)butoxy]benzoic acid
([2Caz-G1]-COOH, 13a). To a solution of 12a (3.0 g,
4.92 mmol) in THF (60 mL) was added NaOH (0.4 g,
10 mmol) aqueous solution (20 mL) and the solution was
heated to reflux with stirring for 8 h. When the solution
was cooled to room temperature, it was poured into dilute
HCl solution. The precipitate was filtrated and dried to get
1
a white solid (2.7 g) in 93% yield. Mp: 179–181 ꢀC. H
NMR (500 MHz, CDCl3): d ppm, 1.72–1.76 (m, 4H, CH2),
2.10–2.15 (m, 4H, CH2), 3.90 (t, 4H, J¼6.0 Hz, –OCH2),
4.40 (t, 4H, J¼7.0 Hz, –NCH2), 6.54 (s, 1H, Ph–H), 7.17
(s, 2H, Ph–H), 7.22 (t, 4H, J¼6.9 Hz, Ph–H), 7.38–7.50
(m, 8H, Ph–H), 8.10 (d, 4H, J¼7.4 Hz, Ph–H). MALDI-
TOF MS (FAB): m/z 597.2 [M++1], 596.2 [M+] (100%),
595.2 [M+ꢁ1]. Anal. Calcd for C39H36N2O4: C, 78.50; H,
6.08; N, 4.69. Found: C, 78.23; H, 5.80; N, 4.83.
4.1.17. 1-[3,5-Bis[3,4,5-tri[4-(9H-carbazol-9-yl)butoxy]-
benzoyloxy]phenyl]-3-phenylpropane-1,3-dione ([6Caz-
G2]-L, 14b). Similar to 14a to get light yellow solid in
1
60% yield. Mp: 93–95 ꢀC. H NMR (500 MHz, CDCl3):
d ppm, 1.55–1.61 (m, 4H, CH2), 1.69–1.74 (m, 8H, CH2),
1.89–1.98 (m, 12H, CH2), 3.88 (t, 4H, J¼6.1, 6.2 Hz,
CH2), 3.91 (t, 8H, J¼6.1 Hz, CH2), 4.10 (t, 4H, J¼7.0 Hz,
CH2), 4.21 (t, 8H, J¼7.1 Hz, CH2), 6.80 (s, 1H, ]CH),
7.16–7.21 (m, 13H, Ph–H), 7.25–7.31 (m, 10H, Ph–H),
7.30 (d, 8H, J¼6.6 Hz, Ph–H), 7.37 (t, 12H, J¼7.1,
7.4 Hz, Ph–H), 7.46 (t, 2H, J¼7.5, 8.1 Hz, Ph–H), 7.62 (t,
1H, J¼7.4, 7.7 Hz, Ph–H), 7.85 (d, 2H, J¼7.7 Hz, Ph–H),
8.04 (d, 8H, J¼5.3 Hz, Ph–H), 8.07 (d, 4H, J¼7.8 Hz, Ph–
H). 13C NMR (CDCl3): d ppm, 25.6, 25.7, 27.0, 27.8, 42.5,
68.8, 72.9, 93.4, 108.6, 118.0, 118.8, 119.7, 120.4, 122.8,
123.4, 125.6, 127.3, 128.7, 132.8, 135.1, 137.9, 140.3,
142.8, 151.6, 152.6, 164.2, 183.4, 186.2. MALDI-TOF MS
m/z: 1890.4 [M++2], 1889.4 [M++1], 1888.4 [M+], 1887.4
[M+ꢁ1]. Anal. Calcd for C125H110N6O12: C, 79.51; H,
5.87; N, 4.45. Found: C, 79.33; H, 5.68; N, 4.68.
4.1.14. 1-[3,5-Bis[3,5-bis[4-(9H-carbazol-9-yl)butoxy]
benzoyloxy]phenyl]-3-phenylpropane-1,3-dione ([4Caz-
G2]-L, 14a). To a solution of 13a (0.28 g, 0.47 mmol), 4
(55 mg, 0.21 mmol) in dry CH2Cl2 (50 mL) was added 4-
(dimethylamino)-pyridinium p-toluenesulphonate (DPTS)
(25 mg, 0.08 mmol). The mixture was stirred at 25 ꢀC for
15 min under nitrogen atmosphere. Dicyclohexylcarbo-
diimide (DCC) (0.10 g, 0.48 mmol) was then added and
stirred at room temperature for 24 h. The reaction mixture
was filtered and the filtrate was evaporated to dryness under
reduced pressure. Pure product was obtained (0.16 g) via
column chromatograph eluting with initially CH2Cl2 and
then a mixture of CH2Cl2/acetone (4:1). The yield was
1
55%. Mp: 62–64 ꢀC. H NMR (500 MHz, CDCl3): d ppm,
4.1.18. Tris[1-[3,5-bis[3,4,5-tri[4-(9H-carbazol-9-yl)butoxy]-
benzoyloxy]phenyl]-3-phenylpropane-1,3-dione](1,10-
phenanthroline) europium (III) ([6Caz-G2]3-Eu, 15b).
Similar to 15a to get light yellow solid in 85% yield. Mp:
83–85 ꢀC. MALDI-TOF MS m/z: 5989.2 [M+ꢁ4]. Anal.
Calcd for C387H335EuN20O36: C, 77.55; H, 5.63; N, 4.67.
Found: C, 77.16; H, 5.36; N, 4.96.
1.89 (m, 8H, CH2), 2.11–2.15 (m, 8H, CH2), 3.99 (t, 8H,
J¼6.1 Hz, –OCH2), 4.41 (t, 8H, J¼7.1 Hz, –NCH2), 6.61
(s, 2H, Ph–H), 6.84 (s, 1H, ]CH), 7.21 (t, 8H, J¼7.4,
7.2 Hz, Ph–H), 7.26 (d, 4H, J¼5.7 Hz, Ph–H), 7.34 (s, 1H,
Ph–H), 7.41 (t, 8H, J¼8.0, 7.8 Hz, Ph–H), 7.44 (d, 8H,
J¼7.5 Hz), 7.46 (t, 2H, J¼8.0, 8.2 Hz, Ph–H), 7.56 (t, 1H,
J¼7.4, 7.9 Hz, Ph–H), 7.74 (d, 2H, J¼2.0 Hz, Ph–H), 7.98
(d, 2H, J¼7.8 Hz, Ph–H), 8.10 (d, 8H, J¼7.7 Hz, Ph–H).
MALDI-TOF MS m/z: 1412.7 [M+], 1411.7 [M+ꢁ1].
Anal. Calcd for C93H80N4O10: C, 79.01; H, 5.70; N, 3.96.
Found: C, 78.75; H, 5.56; N, 4.23.
4.1.19. 3,5-Bis[4-(9H-carbazol-9-yl)butoxy]benzyl alco-
hol ([2Caz-G1]-OH, 16). A mixture of 9-(4-bromobutyl)-
9H-carbazole (4.40 g, 14.5 mmol), 3,5-dihydroxybenzyl
alcohol (1.00 g, 7.1 mmol), potassium carbonate (3.40 g,
60 mmol), and 18-crown-6 (0.38 g, 1.42 mmol) in anhy-
drous acetone (50 mL) was heated at reflux and stirred vig-
orously under nitrogen for 56 h. The mixture was allowed to
cool and evaporated to dryness under reduced pressure. The
residue was partitioned between CH2Cl2 and water, and the
aqueous layer was extracted with CH2Cl2 (40 mLꢂ3). The
combined extracts were dried with anhydrous MgSO4 and
evaporated. The product was purified by column chromato-
graphy on silica gel eluting with CH2Cl2 to give 16 as pale
yellow crystalline solid (3.5 g, yield 83%). Mp: 118–
4.1.15. Tris[1-[3,5-bis[3,5-bis[4-(9H-carbazol-9-yl)butoxy]-
benzoyloxy]phenyl]-3-phenylpropane-1,3-dione](1,10-
phenanthroline) europium (III) ([4Caz-G2]3-Eu, 15a). To
a solution of 14a (0.15 g, 106 mmol) and 1,10-phenanthro-
line monohydrate (7.1 mg, 35.8 mmol) in THF (10 mL), tri-
ethylamine (0.10 mL) was syringed dropwise, followed by
a solution of EuCl3 hexahydrate (12.9 mg, 35.3 mmol) in eth-
anol (4 mL). After injection of argon repeatedly, the mixture
was stirred at 60 ꢀC for 4 h and then cooled. The product was
collected by filtration and washed with deionized water
twice before crystallization with acetone and vacuum drying
(0.12 g), yield 74.4%. Mp: 60–62 ꢀC. MALDI-TOF MS m/z:
4590.3 [M++Na], 4606.4 [M++K]. Anal. Calcd for
C291H245EuN14O30: C, 76.48; H, 5.40; N, 4.29. Found: C,
76.09; H, 5.13; N, 4.50.
1
120 ꢀC. H NMR (500 MHz, CDCl3): d ppm, 1.83–1.88
(m, 4H, CH2), 2.14–2.19 (m, 4H, CH2), 3.85 (t, 4H,
J¼6.1 Hz, –OCH2), 4.37 (t, 4H, J¼7.1 Hz, –NCH2), 4.71
(s, 2H, –CH2OH), 6.25 (s, 1H, Ph–H), 6.54 (s, 2H, Ph–H),
7.21 (t, 4H, J¼6.8, 1.0 Hz, Ph–H), 7.42 (d, 4H, J¼8.0 Hz,
Ph–H), 7.48 (t, 4H, J¼7.9, 1.0 Hz, Ph–H), 8.23 (d, 4H,

S. Li et al. / Tetrahedron 62 (2006) 5035–5048
5047
J¼7.8 Hz, Ph–H). MS (FAB): m/z 597.7 [M++1], 596.6 [M+]
4.1.23. 1-[3,5-Bis[3,5-bis[3,5-bis[4-(9H-carbazol-9-yl)bu-
toxy]benzyloxy]benzoyloxy]phenyl]-3-phenyl propane-
1,3-dione ([8Caz-G3]-L, 20). To a solution of 19 (0.60 g,
0.47 mmol), 4 (55 mg, 0.22 mmol) in dry dichloromethane
(50 mL) was added 4-(dimethylamino)-pyridinium p-toluene-
sulphonate (DPTS) (50 mg, 0.17 mmol). The contents
were stirred at 25 ꢀC for 15 min under nitrogen atmosphere.
Dicyclohexylcarbodiimide (DCC) (0.20 g, 0.97 mmol) was
then added and stirring continued at room temperature for
24 h, during this time a precipitate of dicyclohexyl urea
appeared. The reaction mixture filtered and the filtrate evap-
orated to dryness under reduced pressure, pure product
(0.15 g) was obtained via column chromatograph eluting
with initially CH2Cl2 and then a mixture of CH2Cl2/acetone
(4:1), yield 17%. Mp: 68–70 ꢀC. 1H NMR (500 MHz,
CDCl3): d ppm, 1.89–1.95 (m, 16H, CH2), 2.05–2.13 (m,
16H, CH2), 3.99 (t, 16H, J¼6.2 Hz, –OCH2), 4.37 (t, 16H,
J¼7.2 Hz, –NCH2), 4.98 (s, 8H, –OCH2), 5.30 (s, 1H, Ph–
H), 6.32 (s, 4H, Ph–H), 6.51 (s, 8H, Ph–H), 6.73 (s, 1H,
Ph–H), 6.78 (s, 1H, Ph–H), 6.83 (s, 1H, ]CH), 7.19 (t,
16H, J¼7.3 Hz, Ph–H), 7.38–7.48 (m, 40H, Ph–H), 7.54
(tꢂd, 1H, J¼7.8 Hz, 1.2 Hz, Ph–H), 7.95 (d, 2H,
J¼7.6 Hz, Ph–H), 8.07 (d, 16H, J¼7.8 Hz, Ph–H).
MALDI-TOF MS m/z: 2788.2 [M++1]. Anal. Calcd for
C185H164N8O18: C, 79.72; H, 5.93; N, 4.02. Found: C,
79.32; H, 5.75; N, 4.35.
(100%).
4.1.20. 3,5-Bis[4-(9H-carbazol-9-yl)butoxy]benzyl bro-
mide ([2Caz-G1]-Br, 17). A mixture of compound 16
(1.00 g, 1.68 mmol), CBr4 (0.57 g, 1.72 mmol) in dry
CH2Cl2 (20 mL) was cooled to 0 ꢀC. Triphenylphosphine
(0.48 g, 1.72 mmol) was then slowly added and stirred for
5 h. After removal of CH2Cl2, the product was purified by
column chromatography on silica gel using CH2Cl2 as eluent
to give pale yellow powder (1.02 g), yield 92.1%. Mp: 163–
164 ꢀC. 1H NMR (500 MHz, CDCl3): d ppm, 1.83–1.87 (m,
4H, CH2), 2.15–2.19 (m, 4H, CH2), 3.85 (t, 4H, J¼6.1 Hz,
–OCH2), 4.22 (s, 2H, –CH2Br), 4.37 (t, 4H, J¼7.1 Hz,
–NCH2), 6.30 (s, 1H, Ph–H), 6.45 (s, 2H, Ph–H), 7.22 (t,
4H, J¼7.3 Hz, Ph–H), 7.4 (d, 4H, J¼8.0 Hz, Ph–H), 7.48
(t, 4H, J¼7.8 Hz, 1.0 Hz, Ph–H), 8.21 (d, 4H, J¼7.8 Hz,
Ph–H). MS (FAB): m/z 659.6 [M+2]+, 657.6 [M+] (100%),
579.8 [M+ꢁBr]. Anal. Calcd for C39H37BrN2O2: C, 72.55;
H, 5.78; N, 4.34. Found: C, 72.32; H, 5.62; N, 4.53.
4.1.21. Methyl 3,5-bis[3,5-bis[4-(9H-carbazol-9-yl)butoxy]-
benzyloxy]benzoate ([4Caz-G2]-COOMe, 18). A mixture
of 17 (3.00 g, 4.64 mmol), methyl 3,5-dihydroxybenzoate
(0.40 g, 2.38 mmol), potassium carbonate (1.00 g, 7.25 mmol),
and 18-crown-6 (0.13 g, 4.7 mmol) in anhydrous acetone
(100 mL) was heated at reflux and stirred vigorously under
nitrogen for 56 h. The mixture was allowed to cool and evap-
orated to dryness under reduced pressure. The residue was
washed with water and a large amount of precipitate ap-
peared followed by filtration. After column chromatography
on silica gel using CH2Cl2 as eluent, a white powder was
obtained (2.5 g), yield 81%. Mp: 75–77 ꢀC. 1H NMR
(500 MHz, CDCl3): d ppm, 1.89–1.93 (m, 8H, CH2), 2.05–
2.09 (m, 8H, CH2), 3.88 (s, 3H, –OCH3), 3.99 (t, 8H,
J¼6.0 Hz, –OCH2), 4.37 (t, 8H, J¼7.1 Hz, –NCH2), 4.92
(s, 4H, –OCH2Br), 6.25 (s, 2H, Ph–H), 6.40 (s, 5H, Ph–H),
6.51 (s, 2H, Ph–H), 7.23 (t, 8H, J¼7.8, 1.0 Hz, Ph–H),
7.42 (d, 8H, J¼8.1 Hz, Ph–H), 7.46 (t, 8H, J¼7.9, 1.0 Hz,
Ph–H), 8.20 (d, 8H, J¼7.8 Hz, Ph–H). Anal. Calcd for
C86H80N4O8: C, 79.60; H, 6.21; N, 4.32. Found: C, 79.42;
H, 6.02; N, 4.25.
4.1.24. Tris[1-[3,5-bis[3,5-bis[3,5-bis[4-(9H-carbazol-9-
yl)butoxy]benzyloxy]benzoyloxy]phenyl]-3-phenylpro-
pane-1,3-dione](1,10-phenanthroline) europium (III)
([8Caz-G3]3-Eu, 21). Similar to 15 in yield 87.4%. Mp:
81–82 ꢀC. MALDI-TOF MS m/z: 8722.2 [M++Na]. Anal.
Calcd for C567H497EuN26O54: C, 78.36; H, 5.76; N, 4.19.
Found: C, 77.95; H, 5.44; N, 4.31.
Acknowledgments
This work was supported by NSFC/China (20576035), the
Scientific Committee and Education Committee of Shang-
hai. W.H. Zhu also thanks the foundation for National excel-
lent dissertation of PR China (Project No.: 200143), the
Ministry of Education (No. 104082), and the Laboratory of
Organic Solids, Institute of Chemistry (CAS/China).
4.1.22. 3,5-Bis[3,5-bis[4-(9H-carbazol-9-yl)butoxy]benz-
yloxy]benzoic acid ([4Caz-G2]-COOH, 19). To a solution
of 18 (1.27 g, 0.985 mmol) in THF (30 mL) was once added
sodium hydroxide aqueous solution (0.20 g, 10 mL). The so-
lution was heated to reflux for 5 h prior to concentration. The
residue was washed with water and filtered. The crude prod-
uct was column chromatographed eluting with initially
dichloromethane and then with chloroform/ethanol (25:1)
to give 19, and it was further purified by recrystallization
from ethanol as a white solid (1.10 g) in 93% yield. Mp:
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