Highly luminescent lanthanide complexes with novel bis-β-diketone ligand: Synthesis, characterization and photoluminescent properties

Article abstract of DOI:10.1016/j.saa.2012.05.078

A biphenyl-linked bis-β-diketone ligand, 3,3′-bis(3-phenyl-3- oxopropanol)biphenyl (BPB) has been prepared for the syntheses of a series of dinuclear lanthanide complexes. The ligand bears two benzoyl β-diketonate sites linked by a 3,3'-biphenyl spacer. Reaction of the doubly negatively charged bis-bidenate ligand with lanthanide ions forms triple-stranded dinuclear complexes Ln₂(BPB)₃ (Ln = Nd (1), Sm (2), Eu (3), Yb (4) and Gd (5)). Electrospray mass spectrometry is used to identify the formation of the triple-stranded dinuclear complexes 1-5, which have been further characterized by various spectroscopic techniques. The complexes display strong visible and NIR luminescence upon excitation at ligands bands around 360 nm, depending on the choice of the lanthanides, and the emission quantum yields and luminescence lifetimes of 2-3 have been determined. It shows that the biphenyl-linked ligand BPB is a more efficient sensitizer than the monodiketone ligand DBM (dibenzoylmethane), through the comparisons of Ln₂(BPB) ₃ and Ln(DBM)₃ on their photoluminescent properties.

Full text of DOI:10.1016/j.saa.2012.05.078

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 197–201
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Highly luminescent lanthanide complexes with novel bis-b-diketone ligand:
Synthesis, characterization and photoluminescent properties
⇑
Hong-Feng Li, Guang-Ming Li, Peng Chen, Wen-Bin Sun, Peng-Fei Yan
Key Laboratory of Functional Inorganic Material Chemistry (Heilongjiang University), Ministry of Education, School of Chemistry and Materials Science, Heilongjiang University,
Harbin 150080, PR China
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
A bis-b-diketone ligand BPB has been
prepared.
"
A series of BPB lanthanide complexes
have been prepared and
characterized.
"
"
The photoluminescent behaviors of
BPB lanthanide complexes are
investigated.
Bis-b-diketone is more efficient to
sensitize lanthanide than the mono-
b-diketone.
a r t i c l e i n f o
a b s t r a c t
A biphenyl-linked bis-b-diketone ligand, 3,30-bis(3-phenyl-3-oxopropanol)biphenyl (BPB) has been pre-
pared for the syntheses of a series of dinuclear lanthanide complexes. The ligand bears two benzoyl b-
diketonate sites linked by a 3,3’-biphenyl spacer. Reaction of the doubly negatively charged bis-bidenate
ligand with lanthanide ions forms triple-stranded dinuclear complexes Ln2(BPB)3 (Ln = Nd (1), Sm (2), Eu
(3), Yb (4) and Gd (5)). Electrospray mass spectrometry is used to identify the formation of the triple-
stranded dinuclear complexes 1–5, which have been further characterized by various spectroscopic tech-
niques. The complexes display strong visible and NIR luminescence upon excitation at ligands bands
around 360 nm, depending on the choice of the lanthanides, and the emission quantum yields and lumi-
nescence lifetimes of 2–3 have been determined. It shows that the biphenyl-linked ligand BPB is a more
efficient sensitizer than the monodiketone ligand DBM (dibenzoylmethane), through the comparisons of
Ln2(BPB)3 and Ln(DBM)3 on their photoluminescent properties.
Article history:
Received 24 February 2012
Received in revised form 18 May 2012
Accepted 29 May 2012
Available online 8 June 2012
Keywords:
Lanthanides
Bis-b-diketone
Ligand design
Triple-stranded dinuclear structure
Photoluminescence
Crown Copyright Ó 2012 Published by Elsevier B.V. All rights reserved.
Introduction
infrared light (0.3–3 lm). However, suitable sensitizer is required
as the antenna to excite the lanthanide center, in respective to
the fact that 4f–4f transitions in lanthanide ions are spin- and par-
ity-forbidden [5].
On account of the unique optical properties of lanthanide (Ln)
ions, lanthanide complexes with organic ligands continue to re-
ceive increasing attention because of their potential application
in disparate fields such as optoelectronic device [1], telecommuni-
cation [2], bioassays [3], and sensors [4]. The luminescence from
Ln(III) ions is featured by high color purity, long-lived excited life-
times and the emission ranges from ultraviolet to visible and near
The b-diketone is one of the most studied ligands due to their
chemical stability, highly molar extinction coefficiency and high
energy transfer efficiency from the ligand to the Ln(III) ions [6].
Up to date, hundreds of different b-diketone ligands have been
documented, among which dibenzoylmethane (DBM) and its
derivatives are extensively studied due to their strong absorption
and high ligand-to-metal energy transfer efficiency [7]. The triplet
energy level of DBM is 20300 cmꢀ1 [8], which is 3050 cm–1 higher
⇑
Corresponding author.
E-mail address: yanpf@vip.sina.com (P.-F. Yan).
1386-1425/$ - see front matter Crown Copyright Ó 2012 Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.05.078

198
H.-F. Li et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 197–201
than the 5D0 energy level of Eu(III) ion (17250 cmꢀ1). According to
theoretical calculations and experimental data [9], it is widely ac-
cepted that energy transfer could take place effectively if the triplet
energy level of ligand is 2000–5000 cmꢀ1 higher than the 5D0 res-
onance level of the Eu(III) ion. Thus the ligand DBM has suitable
energy level for sensitizing the luminescence of Eu(III) ion. Indeed,
many DBM Eu(III) complexes and related electroluminescent de-
vices have been studied extensively [10]. For example, Huang
and coworkers reported a Eu(III) complex Eu(DBM)2(c-DBM)(bath)
as the electroluminescent material and its maximum luminance
was found to be 2797 cd mꢀ2 at 14 V [11]. However, the energy
gap between the triplet energy level of DBM and the excited state
level of NIR-emissive Ln(III) ion (such as Nd, Er, Yb) is too large to
make the energy transfer efficient. One feasible approach that can
decrease the energy gap is to incorporate a conjugated group into
the phenyl of DBM. Several Nd(III), Er(III), and Yb(III) complexes
with DBM containing condensed aromatic group or a conjugated
polyene chain have been reported with excellent NIR luminescence
[12].
Recently, lanthanide complexes of bis-b-diketones have at-
tracted attention due to their highly efficient photoluminescence,
visible light sensitization and chirality as well [13,14]. Pikramenou
et al. have reported a dinuclear samarium complex based on a
bis-b-diketone ligand 1,3-bis(3-phenyl-3-oxopropanoyl)benzene
which could be seen as a derivative of DBM. The photoluminescent
studies show that luminescence signal is more intense (about 11
times) than the corresponding DBM complex, although the two
ligands possess the similar triplet state levels [13b]. The increase
of the luminescence quantum yields of the dinuclear complexes
was attributed to the effect of an additional Ln(III) lumophore in
the dinuclear complexes. Recently, we have reported a series of
triple-stranded dinuclear complexes Ln2(BTB)3 assembled about a
bis-b-diketone ligand 3,30-bis(4,4,4-trifluoro-1,3-dioxobutyl)
biphenyl (BTB) which bears two trifluoroacetyl b-diketonate sites
linked by a 3,30-biphenyl spacer [15]. The complex Eu2(BTB)3 dis-
plays 1.33 times luminescence signal intensity than the mononu-
clear complex Eu(BTFA)3. The result prompts us to synthesize a
new bis-b-diketone ligand 3,30-bis(3-phenyl-3-oxopropanol)
biphenyl (BPB) which could be looked upon as coupling of the
two mono-b-diketone DBM at the meta-position of benzene ring
(Scheme S1). The triplet state energy levels of BPB should be close
to those of DBM, because the meta-connection could interrupt the
of 4000–370 cmꢀ1. UV spectra were recorded on a Perkin-Elmer
Lambda 25 spectrometer. The 1H NMR spectra were recorded on
a Bruker Avance III 400 MHz spectrometer in CDCl3 solution. Elec-
tron ionization (EI) and Electrospray TOF (ESI–TOF) mass spectra
were recorded on Agilent 5973 N and Bruker maXis mass spec-
trometers, respectively. Excitation and emission spectra were mea-
sured with an Edinburgh FLS 920 fluorescence spectrophotometer.
Luminescence lifetimes were recorded on a single photon counting
spectrometer from Edinburgh FLS 920 fluorescence spectropho-
tometer with microsecond pulse lamp as the excitation. The data
were analyzed by software supplied by Edinburgh Instruments.
Luminescence quantum yields for Eu(III) and Sm(III) complexes
were measured according to the method reported by Nakamura
using [Ru(2,20–bipyridyl)3]Cl2 (
dard [17].
U = 0.028 in aerated H2O) as a stan-
Syntheses of 3,30-bis(3-phenyl-3-oxopropanol)biphenyl, BPB
A solution of 3,30-diacetylbiphenyl (1.0 g, 4.2 mmol) in 20 mL
ethyl benzoate was added dropwise to a stirred suspension of
NaH (60% dispersion in mineral oil) (0.336 g, 8.4 mmol) in
20 mL methyl benzoate at 60 °C. The reaction mixture was stirred
at 60 °C for 2 h, and then kept overnight at room temperature
(Scheme S2). The resulting yellow precipitate was filtered and
washed thoroughly with toluene. The powered solid was sus-
pended in 30 mL glacial acetic and stirred for 2 h. The product
was filtered and washed with water, and recrystallization from
acetone gave white needle crystals (0.6 g, 32%). Anal. Calc. for
C30H22O4: C, 80.70; H, 4.97; O, 14.33. Found: C, 80.65; H, 5.05;
O, 14.28. IR (KBr, cm–1): 3427, 3059, 1600, 1541, 1478, 1421,
1318, 1286, 1261, 1229, 1218, 1065, 999, 892, 753, 683, 618.
1H NMR (CDCl3, 400 MHz): 15.01 (s, 2H, Hi), 8.26 (t, J = 1.6 Hz,
2H, Ha), 8.03–8.05 (m, 6H, Hd, Hf), 7.86 (d, J = 8 Hz, 2H, Hb),
7.51–7.66 (m, 8H, Hh, Hc, Hg), 6.95 (s, 2H, He). ESI–MS m/z 469
[M + Na]+.
Syntheses of the complexes Ln2(BPB)3
A solution of LnCl3ꢁ6H2O (2.0 mmol) in 20 mL MeOH was added
dropwise to a stirred solution of BPB (1.34 g, 3.0 mmol) in 50 mL
CHCl3, resulting in a pale yellow solution. A solution of NEt3
(0.61 g, 6.0 mmol) in 5 mL MeOH was added dropwise to this solu-
tion and stirred overnight at room temperature. The product was
filtered and washed with CHCl3 (2 ꢂ 10 mL), MeOH (2 ꢂ 10 mL),
H2O (2 ꢂ 10 mL) and dried under vacuum to give the desired prod-
uct Ln2(BPB)3 (Ln = Nd, Sm, Eu, Gd, and Yb) (yields 48–65%).
Ln(DBM)3 complexes were prepared according to the process
described in the literature [18].
p
-electron conjugation of two DBM which makes the triple state
localized at each structure [16]. The synthesized ligand has been
utilized for the syntheses series of lanthanide complexes
a
Ln2(BPB)3 (Ln = Nd (1), Sm (2), Eu (3), Yb (4) and Gd (5)). To exam-
ine the effect of the bis-b-diketone ligand on sensitizing the lumi-
nescence of Ln(III) ions, the photoluminescent properties of the
lanthanide complexes are compared with the corresponding
Ln(DBM)3 complexes.
Results and discussion
Experimental
1H NMR spectrum
Materials and instruments
The 1H NMR spectrum of BPB obtained at 400 MHz in CDCl3 is
shown in Fig. 1. The observed broad single peak, 2H at d 15.01
shows the characteristic Henol protons (Hi), and the singlet, 2H at
d 6.95 is assigned to methine Hketo protons (He). By integrating
the areas corresponding to both species, it is found that the ligand
exists completely in the enolic form in CDCl3. A single peak, 2H
observed at d 8.26 is assigned to the protons Ha due to the absence
of direct coupling with neighboring protons. Doublet, 2H, Hb is ob-
served at d 7.86 due to the coupling of Hc protons. Protons Hd, Hf
appear as two unresolved doublet peaks at d 8.03–8.05 and cor-
rectly integrate for six protons. Multiple signals in the range of d
The commercially available chemicals were analytical reagent
grade and used without further purification. LnCl3ꢁ6H2O was pre-
pared according to the literature by dissolving 99.99% oxide in a
slight excess of hydrochloric acid. The solution was evaporated
and the precipitate was recrystallized from water. 3,30-diacetylbi-
phenyl was prepared according to the process described in the
literature [15].
Elemental analyses were performed on an Elementar Vario EL
cube analyzer. FT-IR spectra were obtained on a Perkin-Elmer
Spectrum One spectrophotometer by using KBr disks in the range

H.-F. Li et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 197–201
199
Fig. 1. 400 MHz 1H NMR spectrum of BPB in CDCl3.
Fig. 2. Expanded regions of the ESI–TOF–MS of Eu2(BPB)3 in acetone.
1395–1412 cmꢀ1 in complexes 1–5. Moreover, the absorbance fre-
quency due to vC@C of benzene rings at 1540, 1465 cmꢀ1 of the li-
gands are split into two peaks at 1514–1553 cmꢀ1 and 1451–
1484 cmꢀ1, respectively, in the complexes.
7.51–7.66 are attributed to the methine protons Hh, Hc, Hg, inte-
grating for eight protons.
ESI–TOF mass spectrum
The mass spectra and elemental analysis data of the complexes
are summarized in Table 1. In view of the soft ionization of the
sample provided by ESI–TOF mass spectrometry, which avoids
destructive fragmentation of the complexes, we have resorted to
this technique to ascertain the formation of the dinuclear com-
plexes. The patterns of mass spectra show characteristic mass dis-
tribution of the complexes 1–5. Taking 3 as an example (Fig. 2), the
peak centered at m/z 1659.24 is attributed to [Eu2(BPB)3 + Na]+,
confirming its formation. The results of elemental analyses are in
agreement with the calculated values from molecular formulae as-
signed to these complexes.
UV–Vis and phosphorescent spectra
UV–Vis absorption spectra of the ligands DBM, BPB and their
corresponding Eu(III) complexes in acetone are shown in Fig. 3.
The maximum absorption bands at 342 and 348 nm for DBM and
BPB are attributed to the singlet–singlet p–
pꢃ electronic transition
in the diketones. The absorption maxima is slightly red-shifted
about 10 nm and 12 nm in complexes Eu(DBM)3 and Eu(BPB)3
compared with the free ligands, as a result of the enlargement of
the conjugate structure of the ligand subsequent to coordination
to the Eu(III) ions. In comparison with DBM, the maximum absorp-
tion peak is red-shifted about 5 nm for BPB, indicating a slight in-
crease of conjugation of the ligand. The spectral patterns of Eu(III)
complexes in acetone are similar to that of the free ligands, indicat-
ing that the coordination to the lanthanide ions do not significantly
influence the energy of the singlet states of the diketone. The single
IR spectra
The characteristic FT-IR spectral data of the ligand and their cor-
responding Ln(III) complexes are given in Table 2. The IR spectral
data of the ligands are compared with those of the lanthanide com-
plexes in order to ascertain the formation of the complexes. The
broad bands at 3559–3144 cmꢀ1 are ascribed to the presence of
the intra-molecular H-bondings in ligands (enol forms) and inter-
molecular H-bondings in the complexes (solvent molecules). The
free ligand shows a strong band at 1600 cmꢀ1, which is the charac-
teristic frequency of the diketone vC@O stretching vibrations. The
vC@O bands are shifted to the lower frequency and appear around
1592–1596 cmꢀ1 in all the complexes, indicating the coordination
of the oxygen atoms to the lanthanide ions. This coordination is
further supported by the appearance of bands in the range of
431–439 cmꢀ1 due to vLnAO stretching vibrations. The ligand is
indicated to be in the enolic form by the presence of a band at
1421 cmꢀ1 of a vC@CAO stretching vibration, which is shifted to
state energy (1 pꢃ) levels of DBM and BPB can be estimated by
p–
referring to their wavelengths of UV–Vis absorbance edges, which
are 26110 cmꢀ1 (383 nm) and 25773 cmꢀ1 (388 nm), respectively.
It is well-known that the energy-level match between the triple
states of the ligand and excited levels of Ln(III) ions in lanthanide
complexes plays an important role in determining the luminescent
properties of the lanthanide complexes. On account of the diffi-
culty in observing the phosphorescence of the ligand, the emission
spectrum of the Gd(III) complex at 77 K is used to estimate the
triplet state energy level, because the lowest excited energy level
of Gd3+ ion (6P7/2) is too high to accept energy from the ligand
[19]. As shown in Fig. 4, the triplet energy levels of DBM and
BPB, which correspond to their lower wavelength emission, are
20300 cmꢀ1 (492 nm) and 20000 cmꢀ1 (500 nm), respectively.
Table 1
Elemental analysis and mass spectrum data of Ln(III) complexes of BPB.
Complex
Mw. (M ꢀ solvent + Na) found (cal.)
Elemental analysis found% (cal.%)
C
H
O
Nd2(BPB)3(CH3OH)2(H2O)2 (1)
Sm2(BPB)3(CH3OH)2(H2O)2 (2)
Eu2(BPB)3(CH3OH)2(H2O)2 (3)
Yb2(BPB)3(CH3OH)2(H2O)2 (4)
Gd2(BPB)3(CH3OH)2(H2O)2 (5)
1643.52 (1644.91)
1657.24 (1657.14)
1659.24 (1660.35)
1702.36 (1702.53)
1671.13 (1670.92)
64.22(64.17)
63.80(63.71)
63.68(63.60)
62.14(62.09)
63.15(63.21)
4.20(4.21)
4.08(4.18)
4.09(4.18)
4.01(4.08)
4.15(4.15)
14.77(14.87)
14.75(14.76)
14.61(14.73)
14.36(14.38)
14.72(14.64)

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H.-F. Li et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 197–201
Table 2
Characteristic IR bands (cmꢀ1) of the ligand and the corresponding complexes.
Compounds
v(OAH)
v(C@O)
v(C@C)
v(C@C)
v(C@CAO)
v(LnAO)
BPB
3427
3414
3414
3415
3414
3412
1600
1592
1592
1592
1590
1593
1541
1478
1421
1410
1411
1412
1411
1410
–
Nd2(BPB)3(CH3OH)2(H2O)2 (1)
Sm2(BPB)3(CH3OH)2(H2O)2 (2)
Eu2(BPB)3(CH3OH)2(H2O)2 (3)
Yb2(BPB)3(CH3OH)2(H2O)2 (4)
Gd2(BPB)3(CH3OH)2(H2O)2 (5)
1552/1514
1550/1515
1552/1515
1552/1517
1553/1515
1483/1451
1482/1451
1484/1452
1483/1452
1484/1452
431
431
432
435
432
of the complexes Eu(BPB)3 and Eu(DBM)3 are shown in Fig. 5a,
which display a series of characteristic narrow band emission of
Eu(III) ion at 579, 593, 612, 650, and 693 nm, corresponding to
the 5D0 ? 7FJ (J = 0–4) transitions. Among them, the 5D0 ? 7F2 tran-
sition at k = 612 nm is the most strong transition that is an induced
electric dipole transition, whose intensity is sensitive to the coor-
dination environment [20]. Instead, the 5D0 ? 7F1 transition is a
magnetic dipole transition whose intensity is independent of the
coordination environment [21]. Thus, the intensity ratio of the
5D0 ? 7F2 transition to the 5D0 ? 7F1 transition (I7F2/I7F1) reflects
the nature and symmetry of the first coordination sphere. The
intensity ratios of I7F2/I7F1 are 21.4 and 17.4 for complexes Eu(BPB)3
and Eu(DBM)3, respectively revealing the decrease of the symme-
try around Eu(III) ion in complex Eu(BPB)3 by the formation of tri-
ple-stranded dinuclear structure. The luminescence lifetimes of
complexes Eu(BPB)3 and Eu(DBM)3 in acetone are determined at
room temperature under direct intra-4f6 excitation by monitoring
the emission decay curves within the 5D0 ? 7F2 transition at
612 nm. Each of the decay curves is well-reproduced by single-
exponential functions, which suggests that only one species exists
in the excited state in the two complexes. The lifetimes observed
Fig. 3. UV–Visible absorption spectra of DBM, BPB and complexes Eu(BPB)3 and
Eu(DBM)3 in acetone.
for complexes Eu(DBM)3 and Eu(BPB)3 are 238 ls and 284 ls,
respectively. In addition to the lifetime measurements, the lumi-
nescence quantum yields of the complexes in acetone are also
measured to be 1.1% and 1.8% for Eu(DBM)3 and Eu(BPB)3,
respectively.
The excitation and emission spectra of complexes Sm(BPB)3 and
Sm(DBM)3 in acetone are shown in Fig. 5b. Upon excitation at
360 nm, complexes Sm(BPB)3 and Sm(DBM)3 show characteristic
narrow band emissions of Sm(III) ion corresponding to the
4G5/2 ? 6HJ (J = 5/2,7/2,9/2,11/2) transitions. The four expected
peaks for the 4G5/2 ? 6H5/2–11/2 transitions are well resolved. The
most intense peak is the hypersensitive transition 4G5/2 ? 6H9/2
at 648 nm. The quantum yields of Sm(BPB)3 and Sm(DBM)3 are
measured to be 0.026% and 0.015% and their lifetimes are found
to be 18.7
ls and 7.6 ls, respectively.
Fig. 4. Phosphorescence spectra of Gd(DBM)3 and Gd2(BPB)3 at 77 K.
Considering the higher triple state energy of the ligands than
the energy levels of Nd(III) (4F3/2, 11527 cmꢀ1) and Yb(III) (2F5/2
,
10000 cmꢀ1) luminescent excited state, the suitability of the li-
gands as a sensitizer for Nd(III) and Yb(III) luminescence are exam-
ined. As shown in Fig. 5c, the emission spectra of complexes
Nd(BPB)3 and Nd(DBM)3 consist of three bands at 873, 1057, and
The triplet energy level of BPB is 300 cmꢀ1 lower than that of DBM,
which indicates that the coupling of the two DBM moieties at the
meta-position of the benzene ring does not significantly affect
the triple state of the ligand.
1330 nm, which are attributed to the f–f transitions 4F3/2 ? 4I9/2
,
4F3/2 ? 4I11/2 and 4F3/2 ? 4I13/2
, respectively. For complexes
Luminescence properties
Yb(BPB)3 and Yb(DBM)3, the emission spectra contain one band
corresponding to the 2F5/2 ? 2F7/2 transition (Fig. 5d). This band
is split into two components that the strongest is centered at
972 nm and a shoulder at 1002 nm. The luminescent intensities
of the dinuclear complexes Nd(BPB)3 and Yb(BPB)3 are 1.8 and
2.4 times higher than that of mononuclear complexes Nd(DBM)3
and Yb(DBM)3 in the isoabsorptive solutions. It proposes that
BPB could be a better candidate on sensitizing luminescence of
the Ln(III) ions than DBM, which might be attributed to the rigidity
of the triple-stranded helicate. The rigid structure restricts the
thermal vibration of the ligands and reduces the energy loss by
the radiativeless decay.
The excitation and emission spectra of the isoabsorptive solu-
tions of complexes 1–4 and the corresponding DBM complexes in
acetone are shown in Fig. 5. All the complexes show characteristic
Ln(III) emission upon excitation under the absorbance wavelengths
of the ligands. The excitation spectra of Eu(III) and Sm(III) com-
plexes are recorded by monitoring the strongest emission bands
of their corresponding lanthanide ions in each case. They all show
a broad bands between 260 nm and 430 nm with an excitation
maximum at approximately 360 nm, which can be assigned to
the p–
pꢃ electronic transition of the ligands. The emission spectra

H.-F. Li et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 197–201
201
Fig. 5. Excitation and emission spectra of isoabsorptive solutions (A = 0.1) of complexes 1–4 and corresponding complexes Ln(DBM)3 in acetone.
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In summary, we have reported a novel bis-b-diketone, 3,30-
bis(3-phenyl-3-oxopropanol)biphenyl (BPB) featured by the cou-
pling of two mono-b-diketone dibenzoylmethanate (DBM) at the
meta-position of the benzene ring. The reaction of BPB with Ln(III)
ions in a 3:2 ratio results in the formation of triple-strand dinuclear
complexes. The lower triple state energy level enables BPB to sen-
sitize the metal-centered luminescence of Nd(III), Sm(III), Eu(III)
and Yb(III) ions. Notably, the luminescence quantum yield experi-
ments show that dinuclear complexes have higher luminescent
intensities than that of corresponding mono-b-diketone com-
plexes. Better photoluminescent behavior of Ln2(BPB)3 complexes
ensures their potential applications as emitting layers in light-
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& 21072050 &
51102081 & 21102039), Heilongjiang Province (No. 2010td03)
and Heilongjiang University (2010hdtd-08 and 2010hdtd-11).
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