Photophysical properties of novel lanthanide (Tb3+, Dy3+, Eu3+) complexes with long chain para-carboxyphenol ester p-L-benzoate (L = dodecanoyloxy, myristoyloxy, palmitoyloxy and stearoyloxy)

Article abstract of DOI:10.1016/j.saa.2006.02.047

In this paper, a series of 12 binary luminescent lanthanide coordination compounds with long chain p-carboxyphenol ester were assembled. Both elemental analysis and infrared spectroscopy allowed to determine the complexes formula: LnL₃, where L

Full text of DOI:10.1016/j.saa.2006.02.047

Spectrochimica Acta Part A 66 (2007) 236–242
Photophysical properties of novel lanthanide (Tb3+, Dy3+, Eu3+)
complexes with long chain para-carboxyphenol ester p-L-benzoate
(L = dodecanoyloxy, myristoyloxy, palmitoyloxy and stearoyloxy)
Bing Xu, Bing Yan∗
Department of Chemistry, Tongji University, Shanghai 200092, PR China
Received 30 November 2005; accepted 22 February 2006
Abstract
In this paper, a series of 12 binary luminescent lanthanide coordination compounds with long chain p-carboxyphenol ester were assem-
bled. Both elemental analysis and infrared spectroscopy allowed to determine the complexes formula: LnL3, where Ln = Tb, Dy, Eu; L = p-
dodecanoyloxybenzoate (12-OBA), p-myristoyloxybenzoate (14-OBA), p-palmitoyloxybenzoate (16-OBA) and p-stearoyloxybenzoate (18-OBA),
respectively. The photophysical properties of these complexes were studied in detail with various of spectroscopies such as ultraviolet–visible
absorption spectra, low temperature phosphorescence spectra and fluorescent spectra. The ultraviolet–visible absorption spectra showed that some
bands shift with the different chain length of p-carboxyphenol ester. From the low temperature phosphorescent emission, the triplet state energies
for these four ligands were determined to be around 24,242 cm−1 (12-OBA), 24,612 cm−1 (14-OBA), 24,084 cm−1 (16-OBA) and 24,125 cm−1
(18-OBA), respectively, suggesting they are suitable for the sensitization of the above lanthanide ions, especially for Tb3+ and Dy3+. The fluo-
rescence excitation and emission spectra for these lanthanide complexes of the four ligands take agreement with the above predict from energy
match.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Lanthanide complexes; Long chain p-carboxyphenol ester; Photophysical property; Energy transfer; Spectroscopy
1. Introduction
intersystem crossing quantum yield, the antenna-lanthanide dis-
tance and the overlap between the energy levers of donor and
acceptor are the three main factors, in which the energy trans-
fer – usually an organic chromophore – plays an essential role.
Only when organic chromophore absorbs light strongly in the
UV region to overcome the difficulty of direct excitation into
the parity then transfers it to the lanthanide ion efficiently, and
at the same time protects central cation from solvent molecules
that can quench the central metal emission can it be selected.
Therefore, the encapsulation of the lanthanide ion in an organic
ligand has been become fascinating areas of research, because it
improves not only the processibility of lanthanide ions in organic
matrices but also its optical properties, as the ligand shields the
lanthanide ion from its environment. For binary complexes, it
was found that most ␤-diketone derivatives are more suitable for
luminescence of Eu3+ [9–13] while most aromatic carboxylic
acids are more suitable for the luminescence of Tb3+ [14–18].
We also have studied the energy match and intramolecular
energy transfer mechanism in ternary lanthanide complexes with
aromatic carboxylic acids and 1,10-phenanthroline in details
The study of the trivalent rare earth ions (RE3+) com-
plexes continues to be an active research area, which may be
attributed to the luminescent properties of these compounds
and their applications as optical signal amplifiers, electrolumi-
nescent devices and luminescent probes or labels in biological
systems [1–4]. Considerable studies have been focused on the
design and assembly of lanthanide complexes with organic lig-
ands such as aromatic carboxylic acids, ␤-diketones, cryptands,
calixarenes, heterocyclic ligands, etc. [5–8]. In fact, the photo-
physical properties of lanthanide compounds markedly depend
on their environment. Unless very intense irradiation is used for
direct excitation of the weak lanthanide f–f transitions, emission
has to be sensitized by energy transfer from a suitable adjacent
chromophore. To get an efficient cation emission, the antenna
∗
Corresponding author. Tel.: +86 21 65984663; fax: +86 21 65982287.
E-mail address: byan@tongji.edu.cn (B. Yan).
1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.02.047

B. Xu, B. Yan / Spectrochimica Acta Part A 66 (2007) 236–242
237
Scheme 1. Synthesis of long chain phenol ester by modification of para-
hydroxybenzoic acid with L-chloride (L = 1-dodecanoyl, 1-myristoyl, 1-
palmitoyl and 1-stearoyl) (n = 10, 12, 14, 16).
[19,20], indicating there still exist intramolecular energy trans-
fer mechanism between ligands (i.e. from aromatic carboxylic
acids and 1,10-phenanthroline). On account of the energy match
and energy transfer mechanism, it can be realized to predict the
luminescent properties of lanthanide complexes. Phthalate and
aminobenzoate derivative have been found to exhibit favorable
properties of luminescence and film formation [21,22], but the
hydroxybenzoate derivatives has not been investigated.
In this context, using para-hydroxybenzoic acid as origi-
nal material, four kinds of long chain p-carboxyphenol ester
were achieved, i.e. p-dodecanoyloxybenzoate (12-OBA), p-
myristoyloxybenzoate (14-OBA), p-palmitoyloxybenzoate (16-
OBA) and p-stearoyloxybenzoate (18-OBA), respectively. The
corresponding lanthanide (Tb3+, Dy3+ and Eu3+) complexes
with these ligands were synthesized and characterized. The pho-
tophysical properties for these long carboxyphenol ester and
their lanthanide complexes were studied in detail, which can be
expected to have practical application to fabricate the Langmuir-
Blodgett films.
Scheme 2. Synthesis of lanthanide complexes with long chain carboxyphenol
ester (Ln = Eu, Tb, Dy; n = 10, 12, 14, 16).
2.2. Synthesis of lanthanide complexes with long chain
p-carboxyphenol ester
The lanthanide oxides (Eu2O3, Tb4O7 and Dy2O3) were con-
verted to their nitrates by treatment with concentrated nitric acid.
p-L-oxybenzoic acid (0.318 g for 12-OBA, 0.344 g for 14-OBA,
0.374 g for 16-OBA and 0.403 g for 18-OBA; 1.0 mmol) was
dissolved into the aqueous solution of Na2CO3 (0.1 mol L−1).
Then aqueous solution of lanthanide nitrate (Ln(NO3)3·6H2O,
L = Eu, Tb, Dy; 0.33 mmol) was added very slowly to above
mixed solution with vigorous stirring, resulting in white solid
products (Scheme 2). After stirring for 1 h, the product was fil-
tered, washed with ethanol and water repeatedly and dried in
desiccator. The compositions of the complexes were confirmed
by elemental analysis: Ln(L)3, Ln = Eu, Tb, Dy; L = 12-OBA,
14-OBA, 16-OBA and 18-OBA. Anal. Calcd. for C57H84O12Eu:
C, 61.68; H, 7.57; Found: C, 61.92; H, 7.16. For C63H93O12Eu:
C, 63.37; H, 7.80; Found: C, 63.07; H, 7.42. For C69H105O12Eu:
C, 64.84; H, 8.22; Found: C, 65.21; H, 7.89. For C75H117O12Eu:
C, 66.13; H, 8.60; Found: C, 66.40; H, 8.18. For C57H84O12Tb:
C, 61.29; H, 7.26; Found: C, 61.03; H, 7.01. For C63H93O12Tb:
C, 63.00; H, 7.75; Found: C, 63.26; H, 7.44. For C69H105O12Tb:
C, 64.48; H, 8.18; Found: C, 64.19; H, 7.93. For C75H117O12Tb:
C, 65.79; H, 8.55; Found: C, 65.97; H, 8.20. For C57H84O12Dy:
C, 61.10; H, 7.50; Found: C, 61.40; H, 7.12. For C63H93O12Dy:
C, 62.82; H, 7.73; Found: C, 63.14; H, 7.47. For C69H105O12Dy:
C, 64.31; H, 8.16; Found: C, 64.60; H, 7.88. For C75H117O12Dy:
C, 65.62; H, 8.53; Found: C, 65.35; H, 8.23.
2. Experimental
2.1. Synthesis of p-carboxyphenol ester by the modification
of p-hydroxybenzoic acid
Para-hydroxybenzoic acid (1.37 g) was dissolved into ace-
tone, equimolar amount of long chain L-chloride (1-dodecanoyl
chloride (2.18 g), 1-myristoyl chloride (2.46 g), 1-palmitoyl
chloride (2.74 g) and 1-stearoyl chloride (3.03 g)) was added into
the acetone solution slowly. Then the mixture was placed in a
waterbathatthetemperature65–70 ◦Candreactfor10 h. Finally
thesampleswererecrystallizedwithethanolthreetimestoafford
the products (Scheme 1). The compositions of the aim products
were confirmed by elemental analysis: Calcd. for C19H28O4: C,
71.25; H, 8.75; Found: C, 71.65; H, 9.00. H NMR δ 7.98 (2H),
7.25 (2H), 3.74 (2H), 2.34 (2H), 1.63 (2H), 1.27 (14H), 0.88
(3H), 10.50 ( COOH). For C21H32O4: C, 72.41; H, 9.20; Found:
C, 72.95; H, 9.59. H NMR δ 7.98 (2H), 7.37 (2H), 3.88 (2H),
2.34 (2H), 1.72 (2H), 1.25 (18H), 0.89 (3H), 10.62 ( COOH).
For C23H36O4: C, 73.40; H, 9.57; Found: C, 73.61; H, 9.85. H
NMR δ 8.01 (2H), 7.59 (2H), 4.12 (2H), 2.15 (2H), 1.27 (24H),
0.88 (3H), 10.50 ( COOH). For C25H40O4: C, 74.26; H, 9.90;
Found: C, 74.61; H, 10.01. H NMR δ 7.97 (2H), 7.55 (2H), 3.54
(2H), 3.01 (2H), 1.38 (28H), 0.87 (3H), 10.59 ( COOH).
2.3. Physical measurements
Elemental analyses (C, H) were carried out by the Elemen-
tar Cario EL elemental analyzer. Infrared spectroscopy with
KBr pellets was performed on a Nicolet Nexus 912 AO446
model spectrophotometer in the 4000–400 cm−1. Ultraviolet
absorption spectra were obtained with an Agilent 8453 spec-
trophotometer. Lowtemperaturephosphorescencespectrumwas
determined Perkin-Elmer LS-55 spectrophotometer at 77 K.
The fluorescence (excitation and emission) spectra were deter-
mined with Perkin-Elmer LS-55 spectrophotometer: excitation
slit width = 10 nm, emission slit width = 5 nm.

238
B. Xu, B. Yan / Spectrochimica Acta Part A 66 (2007) 236–242
3. Results and discussion
All the IR spectra of these lanthanide complexes show the
similar features. For example, in the IR spectra of Ln(12-OBA)3
system, the characteristic absorption peaks of the carboxylic
group appear at 1548, 1548, 1548 cm−1 for ␯ (COO ) and
as
1442, 1442, 1466 for ␯s (COO ), respectively, while there does
not exist for free 12-OBA ligand, suggesting that the oxygen
atoms of 12-OBA carbonyl group are coordinated with Ln3+.
The characteristic absorption band of the carbonyl group shifts
from high wave number of 1702.45 cm−1 for 12-OBA to a lower
value of 1671.75 cm−1 for Ln(12-OBA)3 and the absorption
intensity is weaker for complexes than that of 12-OBA, sug-
gesting there still exist one carboxyl group in the long chain
carboxyphenol ester and these carbonyl groups coordinated with
Ln ions. For the IR spectra of Ln(14-OBA)3 system, the charac-
teristic absorption peaks of the carboxylic group emerge at 1548,
Fig. 1. Ultraviolet–visible absorption spectra of long chain carboxyphenol
esters.
1544, 1552 cm−1 for ␯ (COO ) and 1470, 1433, 1470 cm−1
as
for ␯s (COO ), respectively, while it is not observed in the spec-
tra of free 14-OBA ligand, indicating that the oxygen atoms of
14-OBA carbonyl group are coordinated with Ln3+. Both the
free ligand and its complexes show the characteristic absorp-
tion bands of carbonyl group (1703.52 cm−1 (s) for 14-OBA
and 1671.79 cm−1 for Ln(14-OBA)3) except for the weaker
absorption intensity for complexes than that of 14-OBA, which
indicates that there still exist one carbonyl group in the long
chain carboxyphenol ester which also take part in coordina-
tion with Ln ions. In the IR spectra of Ln(16-OBA)3 system,
the characteristic absorption peaks of the carboxylic group are
there still exists one carboxyl group of long chain carboxyphenol
ester. In the IR spectra of Ln(18-OBA)3 system, the characteris-
tic absorption peaks of the carboxylic group are located at 1544,
1527, 1548 cm−1 for ␯ (COO ) and 1413, 1380, 1413 cm−1
as
for ␯ (COO ), respectively. While these peaks are not present
s
for free 18-OBA ligand, which indicate that the oxygen atoms
of mono 18-OBA carbonyl group are coordinated with Ln3+.
The characteristic absorption bands of the carbonyl group for
complexes (1671.74 cm−1) show blue shift compared with their
corresponding ligand (1705.54 cm−1, strong), suggesting that
there still exist one carboxyl group of long chain carboxyphenol
ester which also coordinate with lanthanide ions (Table 1).
Fig. 1 shows the representative ultraviolet–visible absorption
spectra for the four long chain ligands (12-OBA, 14-OBA, 16-
OBA and 18-OBA). They all exhibit domain absorption peaks in
the ultraviolet region of 200–400 nm, and the maximum absorp-
tion peaks are located at 252 nm (12-OBA), 248 nm (14-OBA),
244 nm (16-OBA) and 243 nm (18-OBA), respectively, which
shown at 1552, 1531, 1552 cm−1 for ␯ (COO ) and 1470,
as
1470, 1470 cm−1 for ␯ (COO ), respectively, while they are
s
not present for free 16-OBA ligand, which illuminates that the
oxygen atoms of mono 16-OBA carbonyl group are coordinated
with Ln3+. The free ligand and its complexes show the charac-
teristic absorption bands of the carbonyl group at 1704.42 cm−1
(strong) and 1744.38 cm−1, respectively, and the intensity of
the latter is much weaker than that of complexes, verifying that
Table 1
The IR spectra data and band assignments of the lanthanide complexes
Complex
νs CH
νas CH
␯
C
␯
s COO
␯
␯
s C
␯
as C
O
as COO
O
C
O C
3
3
12-OBA
2847.67
2847.67
2847.67
2851.76
2917.14
2917.14
2917.14
2917.14
1702.45
1671.75
1671.75
1671.75
1111.01
1111.01
1111.01
1111.01
1249.94
1239.64
1239.64
1239.64
Dy-12-OBA
Eu-12-OBA
Tb-12-OBA
1548.24
1548.24
1548.24
1442.00
1442.00
1466.52
14-OBA
2847.67
2847.67
2847.67
2848.67
2917.14
2917.14
2917.14
2921.23
1703.52
1671.79
1671.79
1671.79
1172.60
1106.92
1106.92
1111.01
1286.72
1284.72
1284.72
1284.72
Dy-14-OBA
Eu-14-OBA
Tb-14-OBA
1548.24
1544.15
1552.33
1470.60
1433.83
1470.60
16-OBA
2847.67
2847.67
2847.67
2847.67
2917.14
2921.23
2921.2
1704.42
1744.38
1744.38
1744.38
1098.75
1111.01
1115.10
1111.01
1298.98
1287.38
1287.38
1287.38
Dy-16-OBA
Eu-16-OBA
Tb-16-OBA
1552.33
1531.90
1552.33
1470.60
1470.60
1470.60
2917.14
18-OBA
2851.89
2851.76
2843.59
2847.67
2916.76
2917.14
2917.14
2917.14
1705.54
1671.74
1671.74
1671.74
1074.59
1106.92
1111.01
1111.01
1288.65
1285.65
1285.65
1285.65
Dy-18-OBA
Eu-18-OBA
Tb-18-OBA
1544.15
1527.81
1548.24
1413.39
1380.70
1413.39

B. Xu, B. Yan / Spectrochimica Acta Part A 66 (2007) 236–242
239
Fig. 2. Ultraviolet–visible absorption spectra of long chain carboxyphenol and its lanthanide complexes: (a) 12-OBA and Ln(12-OBA)3; (b) 14-OBA and Ln(14-
OBA)3; (c) 16-OBA and Ln(16-OBA)3; (d) 18-OBA and Ln(18-OBA)3.
are ascribed to the characteristic absorption peaks of phenyl
ring with long chain substituted groups. The little distinction
of band position and intensity is due to the different chain
length (12-OBA-14OBA-16OBA-18OBA). Besides, it can be
observed that the maximum absorption bands exhibit small blue
shifts with the increase of chain length, suggesting the increase
of substituted chain length influences the electron distribution
in along the phenyl ring. Fig. 2(a–d) exhibits the absorption
spectra of Ln-12-OBA, Ln-14-OBA, Ln-16-OBA and Ln-18-
OBA (Ln = Tb, Dy), respectively. All of them show blue shifts
compared with the corresponding free ligands: 242 nm for
Ln-12-OBA, 242.5 nm for Ln-14-OBA, 242 nm for Ln-16-OBA
and 241 nm for Ln-18-OBA separately, it is estimated that
during the process of complexation, lanthanide ions may
hinder the conjugating effect of double bonds (C C and C O)
and enlarge the energy difference levels among the electron
transitions.
We further measured the low temperature phosphorescence
spectra of the four long chain ligands at 77 K. From the
maximum phosphorescent emission band (412.5 nm for 12-
OBA, 406 nm for 14-OBA, 415 nm for 16-OBA and 414.5 nm
for 18-OBA, respectively), the triplet state energies can be
determined as 24,242 cm−1 (12-OBA), 24,612 cm−1 (14-OBA),
24,084 cm−1 (16-OBA) and 24,125 cm−1 (18-OBA), separately.
The energy differences between the triplet state of the four
ligands (12-OBA, 14-OBA, 16-OBA and 18-OBA) and the res-
onance energy levels of Eu3+ (5D0, 17,265 cm−1), Tb3+ (5D4,
20,500 cm−1) and Dy3+ (4F9/2, 21,000 cm−1) can be calculated
and the detailed data have been shown in Table 2. According to
the intramolecular energy mechanism [23–26], the intramolec-
ular energy transfer efficiency depends chiefly on two energy
transfer processes: the first one leads from the triplet level of
ligands to the emissive energy level of the Ln3+ ion by Dexter’s
resonant exchange interaction [27]; the second one is just an
inverse energy transfer by a thermal deactivation mechanism.
Both energy transfer rate constants depend on the energy differ-
ences between the triplet level of the ligands and the resonant
emissive energy of Ln3+. Intramolecular energy transfer effi-
ciency in lanthanide complexes conforms to Dexter’s exchange
energy transfer theory [27]:
ꢀ
ꢁ
ꢄ
ꢂ ꢃ
2πZ2
r
KET
=
exp
Fd(E)Fa(E) dE
(1)
R
l
where KET is the rate constant of energy transfer, r the inter-
molecular distance between the energy donor and acceptor
atoms, l the van der Waals radius, the integral represents the
Table 2
The phosphorescence spectra data of aromatic carboxylic acids
Ligands Triplet state
energies (cm−1
ꢀE(Tr-Eu3+
)
ꢀE(Tr-Tb3+
)
ꢀE(Tr-Dy3+
)
(cm−1
)
)
(cm−1
)
(cm−1
)
12-OBA 24242
14-OBA 24612
16-OBA 24084
18-OBA 24125
6977
7347
6819
6860
3742
4112
3584
3625
3242
3612
3084
3125

240
B. Xu, B. Yan / Spectrochimica Acta Part A 66 (2007) 236–242
overlap between the luminescence spectrum of the ligands and
the absorption spectrum of Ln3+ (Fd(E): the luminescence spec-
trum of energy donor (ligand), Fa(E): absorption spectrum of
energy acceptor (Ln3+)), and 2πZ2/R is a constant relating to
the mutual distance between Ln3+ and coordinated atom. r and
l are both considered to be constant for intramolecular energy
transfer processes. From Eq. (1), KET increases with decreasing
energy difference ꢀE(Tr-Ln3+) between the triplet state energy
of ligands and the resonance emission energy of Eu3+ and Tb3+.
Thus, ligands with a large energy difference cannot sensitize rare
earth ions effectively. On the other hand, there exists an inverse
energy transfer process which affects luminescence intensity by
temperature (k(T) [28]: rate constant of inverse energy trans-
fer process (thermal deactivation process), A: pre-exponential
factor):
ꢀ
ꢁ
ꢀE(Tr-Ln3+
RT
)
k(T) = A exp
−
(2)
It can be seen that the activation energy is approximately
equal to ꢀE(Tr-Ln3+) in the inverse energy transfer process;
therefore, a decreasing energy difference increases k(T).
Based on this evidence, the conclusion can be drawn that
ꢀE(Tr-Ln3+) is of opposite influence on the two energy transfer
processes and an optimal value can be assumed to exist (around
3000 500 cm−1). From the data in Table 2, it can be primarily
predicted that the energy transfer process will occur from the
long ligands to the three Ln ions, especially for Tb3+ and Dy3+.
Fig. 3(a–c) gives the excitation spectra of Tb, Dy and Eu
solid complexes with the four ligands. The excitation bands for
Tb complexes under the green emission of 545 nm mainly take
place in the narrow range from 210 to 300 nm and some apparent
peaks are shown: 223 and 241 nm for Tb-12-OBA, 222, 241, 256
and 267 nm for Tb-14-OBA, 223 and 241 nm for Tb-16-OBA
and 222, 241 and 257 nm for Tb-18-OBA. Under the blue emis-
sion of 484 nm, the excitation bands for Dy complexes exhibit
obvious peaks: 237, 255, 269 and 339 nm for Dy-12-OBA, 237,
256 and 267 nm for Dy-14-OBA, 241, 255 and 333 nm for Dy-
16-OBA and 237 and 255 nm for Dy-18-OBA. The excitation
bands for Eu complexes under the red emission of 613 nm show
broad excitation bands and the maximum excitation peaks are
located around 241 nm for Eu-12-OBA, 241 nm for Eu-14-OBA
and 241 nm for Eu-16-OBA, respectively. The excitation spec-
trum of Eu-18-OBA shows some differences from the above
three Eu complexes, which exhibit three apparent peaks at 241,
255 and 276 nm. We further measured the corresponding emis-
sion spectra by selective excitation with the different excitation
wavelengths, they show the similar emission position except for
different luminescent intensities.
Fig. 3. Excitation spectra of lanthanide complexes with long chain carboxyphe-
nol ester: (a) Tb(L)3, (b) Dy(L)3 and (c) Eu(L)3 (L = 12-OBA, 14-OBA, 16-OBA
and 18-OBA).
green emission. For Dy complexes, two apparent emission peaks
under the excitation of 256 nm are observed: one is at 482 nm
for Dy-12-OBA, 482 nm for Dy-14-OBA, 484.5 nm for Dy-16-
OBA and 483.5 nm for Dy-18-OBA; the other is at 578 nm for
Dy-12-OBA, 579 nm for Dy-14-OBA, 575 nm for Dy-16-OBA
and 574.5 nm for Dy-18-OBA separately, which correspond
Figs. 4–6 show the selected emission spectra of Tb, Dy and
Eu complexes with these four ligands. For Tb complexes, all
of which exhibit similar behavior. The emission spectra under
the excitation of 241 nm show two apparent emission peaks
at 489 and 544 nm attributed to be the characteristic emission
7
4
6
5D4 → FJ (J = 6, 5) transition of Tb3+ ion, indicating that the
to the characteristic F9/2 → HJ (J = 15/2, 13/2) transition of
Dy3+ ion, suggesting that the energy transition goes smoothly
from triplet state of the four ligands to emissive energy level of
four long ligands are good sensitizers for the Tb3+ lumines-
5
7
cence. Among the D4 → F5 transition exhibits the strongest

B. Xu, B. Yan / Spectrochimica Acta Part A 66 (2007) 236–242
241
Dy3+ ion. For europium complexes, the spectrum for europium
complexes were not ideal, two peaks of the emission spectra
7
corresponding to the emissions originated from 5D0 → FJ tran-
sitions (J = 1, 2) of Eu3+ ion have not been divided absolutely
and they are located at 593, 593, 594, 596 nm and 613, 613,
615, 614 nm for Eu-12-OBA, Eu-14-OBA, Eu-16-OBA and Eu-
18-OBA separately. The overlap of the two transitions suggests
that the long chain carboxyphenol ester is not suitable for the
sensitization of the Eu3+ ion, which has a good agreement with
the data from Table 2.
4. Conclusions
Four long chain carboxyphenol ester ligands have been syn-
thesized and their 12 complexes with lanthanide ions (Tb3+,
Dy3+ and Eu3+) have been prepared. The photophysical prop-
erties of them have been studied with ultraviolet spectra, low
temperature phosphorescent spectra, excitation and emission
spectra. The triplet state energy of the four long chain lig-
ands are determined to be 24,242 cm−1 (12-OBA), 24,612 cm−1
(14-OBA), 24,084 cm−1 (16-OBA)and24,125 cm−1 (18-OBA),
respectively, with the phosphorescence spectra. The energy
match between the long chain ligands and lanthanide ions (Tb3+,
Dy3+ and Eu3+) has been studied to predict that the optimum
energy transfer exists between the ligand and Ln3+.
Fig. 4. Emission spectra of Tb complexes with long chain carboxyphenol ester.
Acknowledgement
This work was supported by the National Natural Science
Foundation of China (20301013).
References
[1] Y.X. Ci, Y.Z. Li, W.B. Chang, Anal. Chim. Acta 248 (1991) 589.
[2] L.K. Scott, W.D. Horrocks, J. Inorg. Biochem. 46 (1992) 193.
[3] J. Kido, Y. Okamoto, Chem. Rev. 102 (2002) 2357.
[4] R. Reyes, E.N. Hering, M. Cremona, C.F.B. Silva, H.F. Brito, C.A. Achete,
Thin Solid Films 23 (2002) 420.
Fig. 5. Emission spectra of Dy complexes with long chain carboxyphenol ester.
[5] Y.S. Yang, M.L. Gong, Y.Y. Li, H.Y. Lei, S.L. Wu, J. Alloys Compd.
207/208 (1994) 112.
[6] C.J. Feng, Q.H. Luo, C.Y. Duan, J. Chem. Soc., Dalton Trans. (1998) 377.
[7] T. Gunnlaugsson, A.J. Harte, J.P. Leonard, M. Nieuwenhuyzen, Chem.
Commun. (2002) 2135.
[8] B. Yan, Y.S. Song, J. Fluoresc. 14 (2004) 289.
[9] G.A. Crosby, J. Chem. Phys. 34 (1961) 743.
[10] M.L. Bhaumid, L.J. Nugent, J. Chem. Phys. 43 (1965) 1680.
[11] A.A. Lamola, G.S. Hamond, J. Chem. Phys. 43 (1965) 2129.
[12] Y. Matsuda, Bull. Chem. Soc. Jpn. 42 (1968) 1513.
[13] J.J. Milkula, J. Chem. Phys. 45 (1966) 2140.
[14] H.J. Zhang, B. Yan, S.B. Wang, J.Z. Ni, J. Photochem. Photobiol. A Chem.
109 (1997) 223.
[15] B. Yan, H.J. Zhang, S.B. Wang, J.Z. Ni, Spectrosc. Lett. 31 (1998) 603.
[16] B. Yan, H.J. Zhang, S.B. Wang, J.Z. Ni, Monatsh. Chem. 129 (1998) 151.
[17] B. Yan, H.J. Zhang, S.B. Wang, J.Z. Ni, Monatsh. Chem. 129 (1998) 567.
[18] B. Yan, H.J. Zhang, S.B. Wang, J.Z. Ni, Chem. Pap. 52 (1998) 199.
[19] B. Yan, H.J. Zhang, S.B. Wang, J.Z. Ni, J. Chin. Chem. Soc. 44 (1997) 567.
[20] B. Yan, H.J. Zhang, S.B. Wang, J.Z. Ni, J. Photochem. Photobiol. A Chem.
116 (1998) 209.
[21] B. Li, H.J. Zhang, J.F. Ma, S.B. Wang, J.Z. Ni, Chin. Sci. Bull. 42 (1996)
825.
[22] H.J. Zhang, B. Li, J.F. Ma, J.Z. Ni, Thin Solid Films 310 (1997) 274.
Fig. 6. Emission spectra of Eu complexes with long chain carboxyphenol ester.

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B. Xu, B. Yan / Spectrochimica Acta Part A 66 (2007) 236–242
[23] S. Sato, M. Wada, Bull. Chem. Soc. Jpn. 43 (1970) 1955.
[24] B. Yan, H.J. Zhang, J.Z. Ni, Chin. J. Mol. Sci. 15 (1997) 20.
[25] B. Yan, H. Shao, H.J. Zhang, S.B. Wang, J.Z. Ni, Chin. J. Inorg. Chem. 14
(1998) 407.
[26] B. Yan, H.J. Zhang, J.Z. Ni, Chem. Res. Chin. Univ. 14 (1998) 245.
[27] D.L. Dexter, J. Chem. Phys. 21 (1953) 836.
[28] C.R.S. Dean, T.M. Shepherd, J. Chem. Soc., Faraday Trans. II 71 (1975)
146.