Promoting near-infrared emission of neodymium complexes by tuning the singlet and triplet energy levels of β-diketonates

Article abstract of DOI:10.1039/b601160h

A series of neodymium complexes with various modified β-diketonates and their corresponding gadolinium complexes have been synthesized and characterized. The singlet and triplet energy levels of the coordinated ligands were measured and compared. These co

Full text of DOI:10.1039/b601160h

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PAPER
www.rsc.org/njc | New Journal of Chemistry
Promoting near-infrared emission of neodymium complexes by tuning the
singlet and triplet energy levels of b-diketonates
Lifen Yang,a Zeliang Gong,a Daobo Nie,a Bin Lou,a Zuqiang Bian,a Min Guan,a
Chunhui Huang,*a Hyun Joo Leeb and Woo Phil Baikb
Received (in Montpellier, France) 26th January 2006, Accepted 10th March 2006
First published as an Advance Article on the web 28th March 2006
DOI: 10.1039/b601160h
A series of neodymium complexes with various modified b-diketonates and their corresponding
gadolinium complexes have been synthesized and characterized. The singlet and triplet energy
levels of the coordinated ligands were measured and compared. These complexes emit
characteristic Nd31 light at about 880, 1060, 1330 nm with long-lived lifetimes. The relationship
between the structure and photophysical properties has been discussed and the energy transfer
process in these complexes has been studied.
transition and consequently has been targeted for its ability to
sensitize the luminescence of the Ln31 ions; (2) the ability of
Introduction
Lanthanide ions have attracted considerable attentions due to
the diketonate and lanthanide ions to form an adduct is
their intense, line-like and long-lived emissions, which cover a
strong. (3) the b-diketonate lanthanide complexes are stable
enough for practical usage.
spectral range from the near-UV to the visible and even the
near-infrared (NIR) region. The NIR, especially 800–1700 nm,
luminescence from lanthanide ions such as PrIII, NdIII, ErIII
In this study, a series of neodymium b-diketonate complexes
formed by various modification of the b-diketonate ligands
have been synthesized and characterized. The singlet and
and YbIII is of particular interest due to its electronic and
optical applications, especially for optical communications,
triplet energy levels of the ligands have been determined.
biological and sensor applications.1 For fundamental pur-
The relationship between the structure and the photophysical
poses, research efforts are often focused on the following
properties has been compared and the energy transfer process
areas: (1) design of ligands with large steric hindrance or other
in the complexes has been discussed.
methods to avoid relaxation of energy through resonance
vibration;2 (2) adjustment of the triplet energy level of the
ligand to match the lowest unoccupied orbital of the central
ion;3 (3) improvement of the energy transfer by synthesis of
heterobimetallic compounds or introducing a functional group
into the emitting molecule or combining the electronic con-
ductive material directly with the emitting material, such as
conductive polymers etc., to promote the transport of the
electrons and holes.4 However for the near-infrared ions, their
lowest excited states and their ground states are very close in
energy, therefore the emission often occurs in the infrared
region and their intensities are weaker by several orders of
magnitude (jpl E 10ꢀ4–10ꢀ6) compared to that of visible
emission based on europium and terbium complexes. Further-
more, their deactivation process often occurs easily through a
non-radiative transition and energy transfer problems exist
between the ligand and the central ion. Therefore, to choose
appropriate ligands for sensitization the near-infrared ion is
important.
Experimental
Materials and reagents
All the materials and reagents were used as purchased without
further purification except otherwise stated. Dibenzoyl-
methane (HDBM) was purchased from Merck Company.
Phenanthroline (phen), 4,7-diphenyl-1,10-phenanthroline
(bath), naphthyle, naphthyl acetate and 4-tert-butylbenzoyl
chloride were purchased from Acros Chemical Co. Di-
naphthoylmethane (HDNM) was synthesized by Claisen con-
densation between naphthyl acetate and 2-acetylnaphthalene.
The reagents were dried using appropriate methods before use.
Instrument
Corrected visible (400–800 nm) and near-IR (800–1600 nm)
photoluminescence spectra were measured on an Edinburgh
Instrument (EI) FLS 920 spectrometer. For the latter, a liquid-
nitrogen cooled Ge detector with a standard lock-in technique
was used. Decay curve measurements in the visible region were
carried out using an EI Life-Spec-red instrument, while the
NIR region ones were performed on an EI FL920 time-
resolved spectrometer by monitoring at about 1060 nm lumi-
nescence decay after excitation with a 100 ps pulse of a PDL
800-B laser. The phosphorescence spectra of Gd complexes
were measured on an EI FLS 920 spectrometer at 77 K and
b-Diketones are popular ligands for lanthanide ions,5 which
have the following advantages: (1) the diketone ligand has
strong absorption within a large wavelength range for its p–p*
a State Key Laboratory of Rare Earth Materials Chemistry and
Applications, Peking University, Beijing, 100871, P.R. China.
E-mail: chhuang@pku.edu.cn; Fax: þ86(10)62757156;
Tel: þ86(10)62757156
b Department of Chemistry, Myong Ji University, Yong in City Kyong
Kido, 449-728, Korea
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an Elementar Vario EL instrument (Germany). FT-IR spectra
were taken on a Nicolet MAGNA-IR 750 spectrometer.
Synthesis
Previously, we have synthesized the carbazole-modified
HDBMs, i.e. Carz-HDBM and CBO-HDBM respectively for
coordinating with EuIII ions.6 In this paper, we have synthe-
sized the neodymium complexes with these ligands and other
newly synthesized ligands. Nd(DBM)3(phen), Nd(DBM)3
(bath) and Nd(DNM)3(bath) were also synthesized and char-
acterized for comparison. The chemical structures of the b-
diketone ligands used in this paper are shown in Scheme 1.
The oxadiazole-modified b-diketone ligand t-HONBM was
synthesized through a multi-step method as shown in Scheme
2, and another tert-butyl modified b-diketone ligand HNBM
was synthesized by the Claisen condensation method as shown
in Scheme 3.
Synthesis of ethyl 4-(2H-tetrazol-5-yl)benzoate (1). Ethyl 4-
cyanobenzoate (5.2 g, 30 mmol), NaN3 (2.93 g, 45 mmol) and
NH4Cl (2.4 g, 45 mmol) were dissolved in 30 mL DMF, and
the mixture was refluxed below 100 1C for 24 h. After cooling
to room temperature, it was poured into 400 mL distilled
water and carefully acidified with dilute HCl and then filtered.
The white powder obtained was dried and weighed (yield
72%). 1H NMR (CDCl3), d (ppm): 8.26–8.24 (d, 2H),
8.22–8.20 (d, 2H), 4.47–4.41 (q, 2H), 1.45–1.42 (t, 3H).
Synthesis of ethyl 4-(5-(4-tert-butylphenyl)-1,3,4-oxadiazol-
2-yl)benzoate (2). Under N2 protection, 11 mL (0.055 mol)
4-tert-butylbenzoyl chloride was added dropwise to 50 mL
pyridine containing 10.9 g (0.05 mol) of compound 1. The
Scheme 1 The chemical structures of the b-diketone ligands used in
this paper.
their lifetimes were determined simultaneously using a micro-
second lamp as the excitation source.
1H NMR spectra were recorded on a Bruker 400 MHz
spectrometer. Mass spectra were taken on a ZAB-HS Micro-
mass instrument (UK). Elemental analyses were performed on
Scheme 3 Synthetic route to HNBM.
Scheme 2 Synthetic route to t-HONBM.
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mixture was allowed to react for 10 h at 80–90 1C. After most
of the solvent was removed by rotary evaporation, the mixture
was poured into 400 mL distilled water and a brown precipi-
tate was obtained. This was filtered off, dried and weighed
(yield: 97%).
1016w, 1001vw, 970vw, 916vw, 852vw, 832vw, 804vw, 804vw,
791vw, 767w, 749w, 723w, 701, 673w.
Nd(CBO-DBM)3(bath) Calcd. for C117H94N5O9Nd ꢂ -
C2H5OH (M = 1904.374), C: 75.05, H: 5.29, N: 3.68; Found:
C: 74.96, H: 5.02, N: 3.54%. FT-IR (cmꢀ1): 3054w, 2940w,
2875w, 1592vs, 1548vs, 1522s, 1498vs, 1483vs, 1452vs, 1423s,
1398vs, 1348w, 1326w, 1304w, 1252m, 1218m, 1172m, 1154w,
1129vw, 1121vw, 1109vw, 1090vw, 1070w, 1058w, 1025w,
1001w, 969vw, 938vw, 926vw, 844w, 803w, 768m, 750m,
723m, 702w, 665vw.
Synthesis of 1-(4-(5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl)
phenyl)-3-(naphthalen-2-yl)propane-1,3-dione
(t-HONBM).
This compound was prepared by Claisen condensation with
equimolar quantities of compound 2 (14 g, 0.04 mol) and
1-(naphthalen-2-yl)ethanone (6.8 g, 0.04 mol) in the presence
of NaH. The reaction was allowed to proceed in dry dimethyl-
benzene for 24 h at room temperature then for 72 h at 40 1C.
After that it was poured into 400 mL water and HCl was
added dropwise to it until pH = 2–3. Then the mixture was
extracted with CHCl3 and the product recrystallized from
absolute alcohol. The yellow powder obtained was dried in a
vacuum oven at 60 1C (yield: 23%). 1H NMR (CDCl3), d
(ppm): 16.91 (s, 1H), 8.58 (s, 1H), 8.29–8.27 (d, 2H), 8.20–8.18
(d, 2H), 8.11–8.09 (d, 2H), 8.06–8.04 (m, 1H), 8.02–8.00 (d,
1H), 7.96–7.94 (d, 1H), 7.91–7.89 (d, 1H), 7.64–7.57 (m, 4H),
7.07 (s, 1H), 1.39 (s, 9H). m/z: 474. FT-IR (cmꢀ1): 3057w,
2962m, 2903w, 2868w, 1934vw, 1613s, 1602s, 1579s, 1557vs,
1528s, 1492vs, 1462m, 1431w, 1417w, 1389w, 1366w, 1299w,
1271w, 1253vw, 1213w, 1195w, 1161vw, 1122w, 1098w,
1071w, 1014w, 995vw, 964w, 953vw, 921vw, 858w, 841w,
826w, 792s, 756m, 714m, 688w. Elemental analysis (%): Calcd.
for C31H26N2O3 (M = 474.55), C: 78.46, H: 5.52, N, 5.90;
Found: C: 77.92, H: 5.57, N: 5.93%.
Nd(NBM)3(bath): Calcd. for C93H82N2O6Nd (M
=
1464.903), C: 76.25, H: 5.44, N: 1.91; Found: C: 76.79, H:
5.27, N: 2.24%. FT-IR (cmꢀ1): 1599m, 1587s, 1547s, 1521vs,
1496s, 1463w, 1440m, 1418vs, 1393m, 1363w, 1344w, 1309w,
1297w, 1269w, 1235vw, 1193w, 1121w, 1091vw, 1063vw,
1015w, 961vw, 933vw, 851w, 832w, 788m, 763w, 741w,
702w, 686w.
Nd(t-ONBM)3(bath): Calcd. for C119H91N8O9Nd ꢂ 2.5-
C2H5OH (M = 2036.4965), C: 73.13, H: 5.25, N: 5.50; Found:
C: 72.77, H: 4.92, N: 5.81%. FT-IR (cmꢀ1): 3056w, 2963w,
2903w, 2868w, 1599s, 1590s, 1561s, 1517vs, 1486vs, 1462m,
1441s, 1422s, 1396s, 1344w, 1296w, 1271w, 1235vw, 1194w,
1153w, 1117w, 1096w, 1068w, 1015w, 962w, 859w, 843w,
789w, 759w, 741w, 717w, 703w, 677w.
Synthesis of the Gd complexes. For measurement of the
triplet energy level of the ligand, gadolinium complexes were
synthesized accordingly. The procedures were as follows:
To a 50 mL ethanol solution containing 1 mmol of
GdCl3 ꢂ 6H2O, a solution of 3 mmol b-diketone in THF and
1.0 mol Lꢀ1 NaOH (aq) was added dropwise under stirring.
Then it was refluxed for 5 h and rotary evaporated. The
obtained solid was washed with water several times. Finally
it was recrystallized from THF–ethanol and the precipitate
was filtered and dried.
Synthesis of 1-(4-tert-butylphenyl)-3-(naphthalen-2-yl)pro-
pane-1,3-dione (HNBM). This compound was synthesized by
reacted methyl 4-tert-butylbenzoate with 1-(naphthalen-2-
yl)ethanone in the dry dimethylbenzene using NaH as the
activator at room temperature for more than 72 h, the
Gd(DBM)3(H2O)2: Calcd. for C45H37O8Gd (M = 863.033),
C: 62.63, H: 4.32; Found: C: 61.91, H: 3.83%.
1
procedure was similar to the one above. H NMR (CDCl3),
(d ppm): 17.0 (s, 1H), 8.55 (s, 1H), 8.04–7.89 (m, 6H),
7.60–7.57 (m, 2H), 7.56–7.52 (d, 2H), 7.00 (s, 1H), 1.38 (s,
9H). m/z: 330. FT-IR (cmꢀ1): 1628w, 1599s, 1580s, 1524vs,
1503vs, 1463m, 1431w, 1387vw, 1367w, 1299w, 1267w,
1251vw, 1212w, 1193m, 1126w, 1111w, 1061vw, 1015w,
949vw, 911vw, 866vw, 846w, 822w, 794m, 757w, 696w. Ele-
mental analysis (%): Calcd. for C23H22O2 (M = 330.42), C:
83.60, H: 6.71; Found: C: 83.41, H: 6.66%.
Gd(DNM)3(H2O)2: Calcd. for C69H49O8Gd (M
=
1163.393), C: 71.24, H: 4.25; Found: C: 71.24, H: 4.00%.
Gd(CBO-DBM)3(H2O)2: Calcd. for C93H82N3O11Gd (M =
1574.66), C: 70.93, H: 5.25, N: 2.67; Found: C: 71.27, H: 5.15,
N: 2.67%.
Gd(NBM)3(H2O)2: Calcd. for C69H67O8Gd (M = 1181.52),
C: 70.14, H: 5.72; Found: C: 70.01, H: 5.86%.
Gd(Carz-DBM)3(H2O)2: Calcd. for C81H58N3O8Gd (M =
1358.59), C: 71.61, H: 4.30, N: 3.09; Found: C: 71.32, H: 4.53,
N: 3.11%.
General procedures for the preparation of NdIII and GdIII
complexes. Nd complexes were synthesized according to the
conventional method, described as follows:
Gd(t-ONBM)3(H2O)2: Calcd. for C93H79N6O11Gd (M =
1613.91), C: 69.21, H: 4.93, N: 5.21; Found: C: 69.02, H: 5.10,
N: 5.14%.
A mixture of b-diketone (3.0 mmol), bath or phen (1.00
mmol) and NaOH (3.00 mmol) in 30 mL of THF was slowly
added to 10 mL of NdCl3 ꢂ 6H2O (0.389 g, 1.00 mmol) ethanol
solution under stirring. After being refluxed for 3 h, a yellow
precipitate formed. It was filtered and recrystallized from 30
mL of THF and EtOH (1 : 1, v/v). The yields are about 85%.
Nd(Carz-DBM)3(bath) Calcd. for C105H70N5O6Nd ꢂ 3-
C2H5OH (M = 1780.191), C: 74.89, H: 4.30, N: 3.93, Found:
C: 74.62, H: 4.62, N: 3.96%. FT-IR (cmꢀ1): 1597m, 1548m,
1502s, 1480s, 1451vs, 1421m, 1396m, 1362w, 1335w, 1314w,
1228w, 1228w, 1170w, 1120w, 1104w, 1071w, 1058w, 1026w,
Results and discussion
UV-Vis and photoluminescent (PL) spectra of the free ligands
and corresponding neodymium complexes
The UV-Vis absorption spectra of the free ligands in 1,2-
dichloromethane are shown in Fig. 1(a). The maximum ab-
sorptions as well as their molar absorption coefficients are
summarized in Table 1. It can be seen that the free ligands
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gesting that the coordination of the Nd31 does not have a
significant influence on the 1pp* state energy (0–0 transition).7
The PL spectra of the free ligands were measured using thin
films on quartz at room temperature. All of them exhibit
intense, short-lived fluorescence. The emissions are due to
the deactivation of the lowest electronic singlet states. The
maximum emissions of the six free ligands are in the order of
CBO-HDBM E HDBM o HDNM o Carz-HDBM o
HNBM o t-HONBM, and range from 433 nm (CBO-
HDBM) to 507 nm (t-HONBM), showing that the singlet
energy level of the ligand can be lowered by extending the
conjugation of the ligand or by the introduction of an electron
donor or acceptor group. The maximum emission of CBO-
HDBM is close to that of HDBM, which can be attributed to
the fact that introduction of a donor group (carbazole) to
HDBM through a flexible chain does not have an important
influence on the p system of the molecule. The red shifted PL
wavelengths of the other free ligands can be ascribed to the
enlarged p system. The emissions of the complexes in the UV-
Vis region were also measured using thin films on quartz at
298 K. It was found that the complexes can emit broad weak
bands in the visible region. By comparing the emission in-
tensities of the complexes to those of their corresponding free
ligands, it was found that the ligand luminescence is greatly
suppressed, showing that ligand-to-metal energy transfer takes
place.8 The PL spectra of free ligands and corresponding
complexes are given in Fig. 2.
Lifetime of the free ligands
Lifetime experiments show that the decay curves of the free
ligands can be fitted to a biexponential decay, except for that
of t-HONBM (which can be fitted to a monoexponential decay
format). The average lifetimes of them are in the nanosecond
timescale within the range of 1.0–7.0 ns (Table 1). This
indicates that the main energy transfer process in the present
complexes may be through the triplet state of the ligands.
Fig. 1 UV-Vis absorption of the free ligands (a) and corresponding
neodymium(III) complexes (b) in 1,2-dichloromethane.
have strong absorptions between 300–400 nm with extinction
coefficients of the order of 104
M
ꢀ1cmꢀ1 magnitude, which
mainly arise from the intramolecular p–p* transition. The
absorptions of the new ligands Carz-HDBM and t-HONBM
have the longest wavelengths (about 375 nm, ca. 26 700 cmꢀ1),
which are red-shifted about 33 nm compared to HDBM due to
the extended conjugation system. The UV-Vis absorption
spectra of the NdIII complexes were also obtained in 1,2-
dichloromethane, and these are illustrated in Fig. 1(b). It is
found that these complexes can also absorb strongly in the
UV-Vis region with extinction coefficients of the same order as
the free ligands. Comparing Fig. 1(a) with Fig. 1(b), it is clear
that the shapes of the absorption spectra of the free ligands
and those of their corresponding complexes are similar, sug-
Triplet energy level of the coordinated ligands
Since the band gap between the ground state and the first
excited state of gadolinium is very large due to its half-full
electronic configuration, the energy absorbed by the ligand can
Table 1 Photophysical data of the free ligands
l
max/nm
(e/Mꢀ1cmꢀ1
Singlet
lemmax/nm energy/cmꢀ1 ta/ns
Ligand
HDBM
)
342 (2.35 ꢃ 104) 434
B23 041
B21 413
B20 284
B23 095
B20 619
B19 724
1.20
4.76
6.50
2.83
6.94
5.26
CBO-HDBM 347 (3.32 ꢃ 104) 433
HDNM
HNBM
Carz-HDBM
t-HONBM
371 (3.28 ꢃ 104) 467
359 (2.71 ꢃ 104) 493
375 (2.06 ꢃ 104) 485
375 (3.85 ꢃ 104) 507
a
t: lifetime.
Fig. 2 PL spectra of the free ligands.
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Sensitized NIR emission
Fig. 4 illustrates emissions in the NIR region from the com-
plexes upon excitation of the antenna chromophore. All of the
synthesized complexes show the characteristic emission bands
of the Nd31 ion in the NIR region, which are assigned to the
4
4
4
4
4F3/2 - I9/2 (880 nm), F3/2 - I11/2 (1060 nm) and F3/2
-
4I13/2 (1330 nm) transitions, respectively. Among them, the
band at 1060 nm is dominant and is most important because it
is potentially applicable to laser emission. The unsymmetrical
multiple components and the different relative intensities of
three characteristic bands may be ascribed to the various
coordination environments of Nd31 in amorphous solid ma-
trices13 and the unsymmetrical nature of the ligands.14
Decay curves of these complexes could be fitted biexponen-
tially by monitoring at about 1060 nm in the powder form with
a domain lifetime of the order of ms, as shown in Table 3. The
shortest lifetime corresponds most probably to a hydrated
species (the complexes are quite hygroscopic). Therefore only
the longer lifetime has been taken into consideration. It can be
seen from Table 3 that Nd(CBO-DBM)3(bath) has the shortest
lifetime (14.0 ms) while Nd(t-ONBM)3(bath) has the longest
one (24.9 ms), the latter are almost twice that of the former. By
comparing our results with the terphenyl15 or polydentate
terphenylene-functionalized14 NdIII complex in both the
DMSO (1.2 ms for the former and 1.4 ms for the latter) and
DMSO-d6 (both are 2.5 ms) media, it can be concluded that by
direct coordination of the antenna chromophore to the lantha-
nide ion, the lifetime can be greatly improved. The longer
lifetimes are beneficial in the optical amplification process.
Since the observed rate constant k is the sum of the natural
radiative rate constant (k0) and the non-radiative rate constant
knr, and as the k0 for Nd31 is 4000 sꢀ1, it is obvious that for the
near-IR emitting ions, k is dominated by non-radiative deac-
tivation of the luminescent state. It can be inferred that the
non-radiative deactivation rate constant of the complexes are
in the order: Nd(CBO-DBM)3(bath) 4 Nd(DBM)3(bath) 4
Nd(DBM)3(phen) 4 Nd(Carz-DBM)3(bath) 4 Nd(DNM)3
(bath) 4 Nd(t-ONBM)3(bath).
Fig. 3 PL spectra of Gd complexes in the solid state at 77 K.
not be transferred to the central ion. In this case, the phos-
phorescence observed should be belonged to the coordinated
ligand and consequently the triplet energy of the coordinated
ligand can be estimated.9 The phosphorescent spectra of the
Gd complexes from thin films on quartz at 77 K show strong
emissions composed of two distinct bands (Fig. 3), corre-
sponding to the emission from the lowest two triplet states
of b-diketonate ligand molecules.7 The long lifetime values
measured (typically 470 ms) are consistent with emission from
a characteristic triplet state.10 To estimate the triplet energy
level, we take 0–0 transition as a measurement. From the
energy vibration feature of the phosphorescence bands of the
Gd31 complexes, the triplet energy state of the ligands has
been estimated to be in the range of 20 410–18 520 cmꢀ1 (Table
2). According to Dexter’s theory,11 the suitability of the energy
difference DE = EL ꢀ ELn between the first excited energy
level of the Ln31 ion ELn(11 500 cmꢀ1 for Nd13 4F3/2) and the
triplet state energy level of the ligand EL is a critical factor for
efficient energy transfer. If the triplet state energy level of the
ligand is too high, then the energy transfer rate constant will
decrease due to the diminishing in the overlap between the
donor and the acceptor. On the other hand, if the energy level
of the ligand is too low, energy back transfer from the central
ion to the ligand will take place.
As many papers have suggested, the intrinsic quantum yield
(jint) can be estimated from eqn (1),16 in which t is the
In the case of these complexes, energy transfer takes place
from the triplet excited state, because the singlet state of the
ligands is depopulated very fast to the triplet state and Dexter-
type energy transfer is the dominant mechanism.12 Applying
these considerations to the b-diketonates, it can be expected
that t-HONBM will be the best ligand for sensitizing Nd31
emission.
Table 2 Triplet energy levels of the coordinated ligands
Complex
lem/nm
T1/cmꢀ1
DEa/cmꢀ1
Gd(DBM)3(H2O)2
535
20 410
19 080
18 280
18 870
18 980
18 520
8910
7580
6780
7370
7480
7020
Gd(CBO-DBM)3(H2O)2
Gd(DNM)3(H2O)2
Gd(NBM)3(H2O)2
Gd(Carz-DBM)3(H2O)2
Gd(t-ONBM)3(H2O)2
548, 585
564, 606
554, 589
550, 589
570, 609
Fig. 4 NIR photoluminescence of synthesized complexes in the solid
a
DE = T1 ꢀ 11 500(4F3/2).
state.
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Table 3 Lifetime and intrinsic quantum efficiency data of the com-
plexes
Acknowledgements
The authors want to thank the Physics Department of Xiamen
University for NIR lifetime measurement. Also we would like
to thank the national basic research 973 program
(2006CB601103), NNSFC (20221011, 20471004, 50372002
and 90401028), China education foundation for doctorial pro-
gram (20030001065) and the RRC program of Korea ministry
of commerce, industry and energy for financial supports.
Complex
t/ms (at 1060 nm) jinta/10ꢀ2 k/104 sꢀ1
Nd(DBM)3(phen)
0.707 ꢄ 0.002
(62.9%)
8.6 ꢄ 0.2
4.7 ꢄ 0.1
21.5 ꢄ 0.6
(37.1%)
0.670 ꢄ 0.003
(52.3%)
Nd(DBM)3(bath)
8.1 ꢄ 0.1
4.94 ꢄ 0.09
20.2 ꢄ 0.4
(47.7%)
Nd(CBO-DBM)3(bath) 0.803 ꢄ 0.004
5.60 ꢄ 0.03 7.14 ꢄ 0.04
9.81 ꢄ 0.09 4.08 ꢄ 0.04
(28.6%)
14.0 ꢄ 0.1
(71.4%)
References
1 (a) W. D. Horrocks Jr, J. P. Bolender, W. D. Smith and R. M.
Supkowski, J. Am. Chem. Soc., 1997, 119, 5972; (b) V. Vicinelli, P.
Ceroni, M. Maestri, V. Balzani, M. Gorka and F. Vogtle, J. Am.
Chem. Soc., 2002, 124, 6461; (c) S. I. Klink, G. A. Hebbink, L.
Grave, F. G. A. Peters, F. C. J. M. van Veggel, D. N. Reinhoudt
and J. W. Hofstraat, Eur. J. Org. Chem., 2000, 1923; (d) V.
Vicinelli, P. Ceroni, M. Maestri, V. Balzani, M. Gorka and F.
Vogtle, J. Am. Chem. Soc., 2002, 124, 646; (e) A. Dossing, Eur. J.
¨
Inorg. Chem., 2005, 1425; (f) J.-C. G. Bunzli and C. Piguet, Chem.
¨
Soc. Rev., 2005, 34, 1048.
2 B. S. Harrison, T. J. Foley, M. Bouguettaya, J. M. Boncella, J. R.
Reynolds, K. S. Schanze, J. Shim, P. H. Holloway, G. Padmana-
ban and S. Ramakrishnan, Appl. Phys. Lett., 2001, 79, 3770.
3 (a) D. Imbert, M. Cantuel, J. C. G. Bunzli, G. Bernardinelli and C.
Piguet, J. Am. Chem. Soc., 2003, 125, 15698; (b) J. Zhang, P. D.
Badger, S. J. Geib and S. Petoud, Angew. Chem., Int. Ed., 2005, 44,
2508; (c) H. Wang, G. Qian, M. Wang, J. Zhang and Y. Luo, J.
Phys. Chem. B, 2004, 108, 8084.
Nd(DNM)3(bath)
0.845 ꢄ 0.005
(11.6%)
24.5 ꢄ 0.2
(88.4%)
—
¨
Nd(NBM)3(bath)
—
—
Nd(Carz-DBM)3 (bath) 0.864 ꢄ 0.005
9.69 ꢄ 0.09 4.13 ꢄ 0.04
(7.8%)
24.2 ꢄ 0.2
(92.2%)
0.994 ꢄ 0.008
(6.7%)
Nd(t-ONBM)3 (bath)
9.95 ꢄ 0.07 4.02 ꢄ 0.03
24.9 ꢄ 0.2
(93.3%)
a
j
int: intrinsic quantum yield = t/t0, t0 = 0.25 ms.
4 (a) S. Torelli, D. Imbert, M. Cantuel, G. Bernardinelli, S. Dela-
haye, A. Hauser, J. C. G. Bunzli and C. Piguet, Chem.-Eur. J.,
2005, 11, 3228; (b) N. M. Shavaleev, L. P. Moorcraft, S. J. A. Pope,
Z. R. Bell, S. Faulkner and M. D. Ward, Chem. Commun., 2003,
1134.
5 (a) R. Reyes, M. Cremona, E. E. S. Teotonio, H. F. Brito and O. L.
Malta, Chem. Phys. Lett., 2004, 396, 54; (b) X. H. Zhu, L. H.
Wang, J. Ru, W. Huang, J. F. Fang and D. G. Ma, J. Mater.
Chem., 2004, 14, 2732; (c) K. Binnemans, in Handbook on the
Physics and Chemistry of Rare Earths, Elsevier, Amsterdam, 2005,
ch. 225, vol. 35, pp. 107–272.
observed emission lifetime and t0 is the radiative or natural
lifetime (0.25 ms from the literature), but this refers only to the
quantum yield of the lanthanide-based emission process and
takes no account of the factors such as intersystem crossing
and energy-transfer process.
jint = t/t0
(1)
The intrinsic quantum yields of the title complexes are listed in
Table 3, and are in the reverse order to that of the non-radiative
deactivation rate constants of the complexes. Obviously, Nd
(t-ONBM)3(bath) has achieved the lowest non-radiative deac-
tivation rate constant and the highest intrinsic QE.
6 C. H. Huang, Z. Q. Bian, M. Guan, F. Y. Li and H. Xin, China
Patent, No.: ZL 03142611.5, 2003.
7 F. Goncalves e Silva, O. L. Malta, C. Reinhard, H.-U. Gudel, C.
¨
¨
Piguet, J. E. Moser and J.-C. G. Bunzil, J. Phys. Chem. A, 2002,
106, 1670.
8 X. P. Yang, B. S. Kang, W. K. Wong, C. Y. Su and H. Q. Liu,
Inorg. Chem., 2003, 42, 169.
9 (a) L. M. Ying, A. C. Yu, X. S. Zhao, Q. Li, D. J. Zhou, C. H.
Huang, S. Umetani and M. Matasai, J. Phys. Chem., 1996, 100,
18387; (b) H. Xin, M. Shi, X. C. Gao, Y. Y. Huang, Z. L. Gong, D.
B. Nie, H. Cao, Z. Q. Bian, F. Y. Li and C. H. Huang, J. Phys.
Chem. B, 2004, 108, 10796.
Conclusion
We have synthesized a series of neodymium complexes con-
sisting of electron-donating or withdrawing moieties. The PL
spectra of these complexes show characteristic emission in the
NIR region with unsymmetrical profiles and different relative
intensities. The singlet energy levels as well as the triplet levels
of the ligands have been estimated. The new complexes have
lifetimes on the ms timescale and Nd(t-ONBM)3(bath) com-
plex has the longest lifetime and thus the highest intrinsic
efficiency. It may be related to the fact that the lowest triplet
10 S. S. Braga, R. A. Sa Ferreira, I. S. Goncalves, M. Pillinger, J.
´
Rocha, J. J. C. Teixeira-Dias and L. D. Carlos, J. Phys. Chem. B,
2002, 106, 11430.
11 D. L. Dexter, J. Chem. Phys., 1953, 21, 836.
12 G. A. Hebbink, L. Grave, L. A. Woldering, D. N. Reinhoudt and
F. C. J. M. van Veggel, J. Phys. Chem. A, 2003, 107, 2483.
13 S. Yanagida, Y. Hasegawa, K. Murakoshi, Y. Wada, N. Naka-
shima and T. Yamanaka, Coord. Chem. Rev., 1998, 171, 461.
14 S. I. Klink, L. Grave, D. N. Reinhoudt, F. C. J. M. van Veggel, M.
H. V. Werts, F. G. A. Geurts and J. W. Hofstraat, J. Phys. Chem.
A, 2000, 104, 5457.
15 S. I. Klink, G. A. Hebbink, L. Grave, F. G. A. Peters, F. C. J. M.
van Veggel, D. N. Reinhoudt and J. W. Hofstraat, Eur. J. Org.
Chem., 2000, 1923.
16 N. M. Shavaleev, L. P. Moorcraft, S. J. A. Pope, Z. R. Bell, S.
Faulkner and M. D. Ward, Chem.-Eur. J., 2003, 9, 5283.
4
energy level of the t-HONBM ligand is closer to F3/2 of the
Nd31 ion compared to the other ligands, therefore it can have
good energy transfer to the central ion. This fact indicates the
near infrared emission of neodymium complexes can be
promoted by modifying the ligand and consequently tuning
the singlet and triplet energy levels.
ꢁc
796 | New J. Chem., 2006, 30, 791–796 This journal is the Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2006