Synthesis and luminescence properties of 2-(benzylcarbamoyl)phenyl derivatives and their europium complexes

Article abstract of DOI:10.1002/bio.2378

Six novel 2-(benzylcarbamoyl)phenyl derivatives were synthesized and characterized by ¹H-NMR, mass spectrometry, infrared spectra and elemental analysis. Their europium complexes were prepared and characterized by elemental analysis, EDTA titri

Full text of DOI:10.1002/bio.2378

Research article
Received: 27 December 2011,
Revised: 12 March 2012,
Accepted: 01 April 2012
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/bio.2378
Synthesis and luminescence properties of
2-(benzylcarbamoyl)phenyl derivatives and
their europium complexes
Dongcai Guo*, Wei He, Bang Liu, Lining Gou and Ruixia Li
ABSTRACT: Six novel 2-(benzylcarbamoyl)phenyl derivatives were synthesized and characterized by 1H-NMR, mass spectrom-
etry, infrared spectra and elemental analysis. Their europium complexes were prepared and characterized by elemental
analysis, EDTA titrimetric analysis, IR and UV spectra as well as molar conductivity measurements. The luminescence
properties of these complexes were investigated and results show that 2-(benzylcarbamoyl)phenyl derivatives possess
high selectivity and good coordination with the europium ion. Complex Eu-2-(benzylcarbamoyl)phenyl-2-phenylacetate
showed green luminescence that was emitted by the ligand of 2-(benzylcarbamoyl)phenyl-2-phenylacetate, while other
complexes showed the characteristic red luminescence of europium ion and also possessed high luminescence intensity.
Copyright © 2012 John Wiley & Sons, Ltd.
Keywords: amide ligand; rare earth; complex; synthesis; luminescence properties
Introduction
Experimental
Methods
Rare earth complexes are currently attracting considerable
attention due to their special physical and chemical properties;
i.e. electric, magnetic and catalytic attributes (1–3). Since rare
earth complexes can show narrow emission bands and hyper-
sensitivity to coordination environments, researchers have paid
particular attention to their luminescence properties (4). The
luminescence intensity of rare earth complexes is strongly
dependent on the absorption efficiency of ligands in the UV
region, the efficiency of ligand-to-metal energy transfer and
the efficiency of rare earth luminescence (5,6). Because of its
ring-like coordination structure and terminal group effects (7),
the amide compounds have a variable coordination style for rare
earth ions. Many studies have reported in recent years on the
synthesis of amide rare earth complexes. Ercules et al. (8) synthe-
sized N-(methylpyridyl)acetamide and reported the influence of
N-(methylpyridyl)acetamide ligands on the photoluminescent
properties of Eu-perchlorate complexes. Liu et al. (9) synthesized
a series of ether-amide-type multipodal ligands and their
europium complexes. Song et al. (10) synthesized 2,2’-bipydine
derivative and its rare earth complexes and investigated their
luminescence properties. Luo et al. (11) designed and synthe-
sized novel mono-substituted b-diketone ligands and their rare
earth complexes. In this study, six novel 2-(benzylcarbamoyl)
phenyl derivatives as well as their intermediates were synthe-
sized and characterized by 1H nuclear magnetic resonance
spectroscopy (1H-NMR), mass and infrared spectroscopy
(MS & IR) and elemental analysis. Their europium complexes
were also prepared and characterized by elemental analysis,
ethylenediaminetetraacetic acid (EDTA) titration analysis, IR
and UV spectra as well as molar conductivity measurements.
The luminescence properties and coordination modes of these
complexes were investigated. The synthesis route for the
2-(benzylcarbamoyl)phenyl derivatives (L1-6) is shown in Scheme 1.
The carbon, hydrogen, and nitrogen analyses were obtained
using an Elementar Vario ELIII elemental analyzer and H-NMR
1
spectrum was measured on a Varian 400 NMR (400 MHz) instru-
ment (both from Agilent Technologies Co. Ltd., Beijing, China) in
CDCl3 solution with tetramethylsilane (TMS) as internal standard.
The europium ion was determined by ethylenediaminetetraacetic
acid (EDTA) titration using xylenol orange as an indicator. IR
spectra in the 4000–400 cm-1 region were measured using KBr
pellets on a PerkinElmer spectrometer (PerkinEylmer Chengdu,
Chengdu, China). UV spectra were detected on a LabTech
UV-2100 (Columbia MO, USA) spectrophotometer using ethyl
alcohol to dissolve the samples. Fluorescence spectra were
obtained on a Hitachi F-4500 spectrophotometer (Hitachi Hi-Tech,
Shanghai, China) at room temperature.
Materials
Europium nitrate was prepared according to the literature (12).
Benzylamine and aromatic carboxylic acid were of CP grade.
Methyl salicylate and other reagents were of AR grade and
purchased from commercial suppliers.
* Correspondence to: DongCai Guo, School of Chemistry and Chemical
Engineering, Hunan University, Changsha, 410082, China. Tel: +86-0731-
88821449; Fax: +86-0731-88821449. E-mail: dcguo2001@163.com
School of Chemistry and Chemical Engineering, Hunan University,
Changsha, 410082, China
Luminescence 2012
Copyright © 2012 John Wiley & Sons, Ltd.

D. Guo et al.
OH
OH
a
H
+
H2N
N
COOCH3
O
A
c
O
C
R
O
NH
b
O
R COOH
O
R
Cl
B1-6
L1-6
(a) 100°C, reflux, 12 h; (b) SOCl , N , 60°C, reflux, 5~6 h; (c) CH Cl , N , reflux, 8~9 h
2
2
2
2
2
H3C
Cl
H3CO
CH2
Cl
R2
R3
R1
R4
R5
R6
O
C
O
C
O
C
Cl
H3C
Cl
Cl
Cl
B1
B2
B3
O
C
O
C
O
CH2C
H3CO
Cl
Cl
Cl
Cl
B6
B4
B5
Cl
H3C
NH
O
O
NH
O
NH
O
O
O
O
O
O
L3
L2
L1
H3CO
O
NH
NH
O
NH
O
Cl
O
O
O
O
O
O
L4
L5
L6
Scheme 1. The synthesis route for 2-(benzylcarbamoyl)phenyl derivatives.
Synthesis
The mixture was heated to reflux until benzoic acid was com-
pletely dissolved. Next, the mixture was refluxed for another
5 h and the SOCl2 residue was completely distilled under a
vacuum resulting in benzoyl chloride (B1). Methods used for
compounds B2-6 were similar to that for compound B1.
Synthesis of N-Benzylsalicylamide (A). Methyl salicylate (4.08 g,
30 mmol) and benzylamine (3.21 g, 30 mmol) were added into
a 100-mL three-necked flask. The mixture was heated to reflux
for 12 h, cooled and diluted with 20 mL cold ethyl acetate and a
large white solid precipitate was obtained. This compound was
filtered, washed three times with ethyl acetate and dried under a
vacuum for 24 h. The resulting product was a white solid
with the following features: yield, 80%; mp 129-32ꢀC; 1H-NMR
(CDCl3, 400 MHz); d, 4.56 (d, 2H, CH2), 6.50 (s, 1H, NH), 6.75
(t, 1H, ArH), 6.93 (d, 1H, ArH), 7.18-7.32 (m, 7H, ArH), 12.22
(s, 1H, OH); MS (EI) m/z (%), 227 (M, 50), 228 (M + 1, 11); And IR,
1642 (C = O), 3357, 1546, 699 (N-H), 3357 (O-H).
Synthesis of amide ligands (L1-6). 2-(benzylcarbamoyl)phenyl benzoate
(L1). The obtained benzoyl chloride was dissolved in 20 mL dry
dichloromethane in a 100 mL single-necked flask. Next, a
dichloromethane solution of N-Benzylsalicylamide (4.86 g, 20 mmol)
and triethylamine (5 mL) were added to the flask. The mixture
was stirred for 8 h at room temperature and then became faint
yellow in colour. After adding 30 mL distilled water to the
flask, the mixture was neutralized to pH 7-8 with dilute NaHCO3,
extracted with dichloromethane, washed three times with
distilled water and evaporated to produce a crude product.
Synthesis of acyl chloride (B1-6). Benzoic acid (3.66 g, 20mmol)
and SOCl2 (15 mL) were added into a 100-mL single-necked flask.
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Synthesis and luminescence properties of 2-(benzylcarbamoyl)phenyl derivatives
2-(benzylcarbamoyl)phenyl-2-phenylacetate (L6). This product was
This product was purified over a silica-gel column with the eluent of
ethyl acetate/petroleum ether (1:4, v/v). The resulting solution was
collected, evaporated and then dried under a vacuum, resulting in
a white solid product with the following characteristics: Yield, 45%;
Mp, 106-109ꢀC; 1H-NMR (CDCl3, 400 MHz ), d, 4.50
(d, 2H, ArCH2N), 6.60 (s, 1H, NH), 7.11–7.64 (m, 11H, ArH), 7.90
(d, 1H, ArH) and 8.05 (d, 2H, ArH); MS (EI) m/z (%), 331 (M, 5); IR
(KBr): 1740, 1630 (C = O), 1202 (C-O-C), 3283, 1570, and 707 (N-H).
Analysis data calculated for C21H17NO3 were: C, 76.12; H, 5.17; N,
4.23. Found: C, 75.22; H, 5.20; N, 4.25. Synthesis methods were similar
to those for compound L1.
prepared as above producing a red solid with the following
1
properties: Yield, 60%; Mp, 70-72ꢀC; H-NMR (CDCl3, 400 MHz);
d, 3.69 (s, 2H, CH2), 4.27 (d, 2H, CH2), 6.46 (s, 1H, NH), 7.05-7.84
(m, 14H, ArH); IR (KBr): 1748, 1640 (C = O), 1199 (C-O-C), 3311,
1601, 700 (N-H). Data for C21H16ClNO3 were: C, 76.50; H, 5.54;
N, 4.06. Found: C, 75.59; H, 5.49; N, 3.39.
Preparation of the title complexes
Europium nitrate (0.2 mmol) was dissolved in 5 mL ethyl acetate
in a 100-mL single-necked flask and 0.2 mmol ligand L dissolved
in 15 mL ethyl acetate was added to the flask. The mixture was
stirred for 6 h at room temperature and then 5 mL diethyl ether
was added one drop at a time. A precipitated solid complex was
formed, separated from the solution by suction filtration and
washed several times with ethyl acetate. The complex was then
dried for 48 h under a vacuum at room temperature.
2-(benzylcarbamoyl)phenyl-4-methylbenzoate (L2). This crude product
was purified over a silica-gel column with the eluent of
ethyl acetate/petroleum ether (1:6, v/v), forming a white solid with
the following characteristics: Yield, 40%; Mp, 87-90ꢀC; 1H-NMR
(CDCl3, 400 MHz); d, 2.46 (s, 3H, ArCH3), 4.49 (d, 2H, ArCH2N), 6.65
(s, 1H, NH) and 7.11-7.92 (m, 13H, ArH); MS (ESI) m/z (%), 346.2
(M + 1, 5), 691.4 (2M + 1, 20) and 693.1 (2M + 3, 23); IR (KBr):
1741, 1630 (C = O), 1198 (C-O-C), 3282, 1531 and 692 (N-H). Analyt-
ical data calculated for C22H19NO3 were: C, 76.50; H, 5.54 and
N, 4.06. Found: C, 75.55; H, 5.47and N, 4.03.
Results and discussion
Properties of the complexes
2-(benzylcarbamoyl)phenyl-4-chlorobenzoate (L3). This product was
purified over a silica-gel column with an eluent of ethyl
acetate/petroleum ether (1:6, v/v), forming a white solid with
the following properties: Yield, 65%; Mp, 108-111ꢀC; 1H-NMR
(CDCl3, 400 MHz); d, 4.49 (d, 2H, ArCH2N), 6.88 (s, 1H, NH),
7.13-7.94 (m, 13H, ArH); MS (EI) m/z (%), 365 (M, 5) and 367 (M
+ 2, 2); IR (KBr): 1741, 1646 (C = O), 1206 (C-O-C), 3272, 1554
and 691 (N-H). Data for C21H16ClNO3 were: C, 69.95; H, 4.41;
N, 3.83. Found: C, 69.85; H, 4.47; N, 3.79.
Analytical data for the complexes are listed in Table 1. Results of
elemental analysis indicated that the composition of the six novel
europium complexes conformed to (EuL1-6(NO3)2ꢁ2H2O)NO3ꢁnH2O
(n = 1, 3). L1-6 ligands were easily dissolved in DMSO, DMF, THF,
chloroform and dichloromethane as well as acetone, methanol,
ethanol, diethyl ether and ethyl acetate; however, they hardly
dissolved in cyclohexane. All europium complexes were soluble
in DMSO, DMF, THF, chloroform, acetone, methanol and ethanol,
but only slightly soluble in ethyl acetate and diethyl ether. The
molar conductance data of the complexes in acetone indicated
that all complexes acted as electrolytes (13).
2-(benzylcarbamoyl)phenyl-4-methoxybenzoate (L4). This product was
purified over a silica-gel column with an eluent of ethyl acetate/
petroleum ether (1:5, v/v), forming a white solid with the follow-
ing properties: Yield, 35%; Mp, 87-89ꢀC; 1H-NMR (CDCl3, 400
MHz); d, 3.90 (s, 3H, OCH3), 4.49 (d, 2H, CH2), 6.68 (s, 1H, NH),
6.90-7.49 (m, 10H, ArH), 7.91-7.93 (m, 1H, ArH), 7.95 (m, 2H,
ArH); IR (KBr): 1741, 1653 (C = O), 1206 (C-O-C), 3273, 1608, 691
(N-H). Data for C22H19NO4 were: C, 73.12; H, 5.30; N, 3.88. Found:
C, 72.29; H, 5.27; N, 3.73.
UV spectral analysis
UV data of the ligands and their complexes are listed in Table 2.
Since UV spectra of all complexes were similar, only the UV spectra
of (EuL4(NO3)2ꢁ2H2O)NO3ꢁH2O and (EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O as
well as their corresponding ligands were selected, as shown in
Figs 1 and 2, respectively. Two absorption peaks of the free ligand
L4 (Fig. 1) appeared at 206 nm and 260 nm, which were assigned
to the л–л* and n–л* transitions of L4. The UV spectrum of
(EuL4(NO3)2ꢁ2H2O)NO3ꢁH2O was similar to that of L4 free ligand;
the only difference being that the first strong absorption wave-
length shifted to 212 nm. This was due to the introduction of euro-
pium ion that enlarged the ligand’s congjugated system, which
2-(benzylcarbamoyl)phenyl-3-chlorobenzoate (L5). This product was
prepared as above and produced a white solid with the following
characteristics: Yield, 70%; Mp, 113-115ꢀC; 1H-NMR (CDCl3, 400
MHz); d, 4.29 (d, 2H, CH2), 6.38 (s, 1H, NH), 7.06-7.82 (m, 13H,
ArH); IR (KBr): 1741, 1630 (C = O), 1199 (C-O-C), 3296, 1578, 700
(N-H). Data for C21H16ClNO3 were: C, 68.95; H, 4.41; N, 3.83. Found:
C, 68.88; H, 4.54; N, 3.85.
Table 1. Elemental analytical and molar conductance data of the complexes
Complexes
Found (calculated)(%)
Λm
C
H
N
Eu
(S cm2 mol-1)
(EuL1(NO3)2ꢁ2H2O)NO3ꢁH2O
(EuL2(NO3)2ꢁ2H2O)NO3ꢁH2O
(EuL3(NO3)2ꢁ2H2O)NO3ꢁ3H2O
(EuL4(NO3)2ꢁ2H2O)NO3ꢁH2O
(EuL5(NO3)2ꢁ2H2O)NO3ꢁH2O
(EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O
35.67 (34.87)
34.54 (35.83)
31.99 (31.77)
34.56 (35.07)
34.76 (33.28)
34.99 (35.83)
3.17 (3.20)
3.33 (3.42)
2.97 (3.30)
3.56 (3.34)
2.67 (2.93)
3.56 (3.42)
7.89 (7.75)
7.52 (7.60)
7.04 (7.06)
7.69 (7.44)
7.19 (7.39)
7.77 (7.60)
20.99 (21.01)
19.85 (20.61)
19.87 (19.14)
20.36 (20.17)
20.45 (20.05)
21.09 (20.61)
110
112
105
130
138
115
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D. Guo et al.
only the IR spectra of (EuL2(NO3)2ꢁ2H2O)NO3ꢁH2O and
(EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O as well as their corresponding
ligands were selected (Figs. 3 and 4, respectively). IR spectra of
the free ligands showed bands at 1740–1748 cmꢂ1and 1630–
1653 cmꢂ1, which were assigned to the stretch vibration of the
carbonyl group (υ(C = O)), and υ(C-O-C) appeared at 1198–1206
cmꢂ1. In the IR spectra of the complexes (EuL1-5(NO3)2ꢁ2H2O)
NO3ꢁnH2O, (n = 1, 3), the absorption band for n(C = O) in the high
frequency region remained unchanged but shifted about
8 cmꢂ1 in the low frequency region. As a result, these data
indicated that only the oxygen atom of amide carbonyl group
was coordinated to the europium ion. The characteristic absorp-
tion bands for n(C = O) of ligand L6 appeared at 1748 cmꢂ1 and
1640 cmꢂ1, which shifted ꢃ 7–8 cmꢂ1 towards lower wave
numbers after formation of the complexes. This indicated that
the oxygen atoms of both the amide and carbonyl groups in
ligand L6 were coordinated to the europium ion. The band for
υ(C-O-C) remained unchanged. These results clearly showed that
the oxygen atom of υ(C-O-C) did not take part in coordination
with the europium ion.
The characteristic frequencies of the coordinating nitrate
groups (C2v) appeared at ꢃ 1481 (υ1), 1324 (υ4), 1031 (υ2) and
815 cmꢂ1 (υ3) (15). In addition, the difference between the two
strongest absorption bands of the nitrate groups (|υ1 ꢂ υ4|) was
157 cmꢂ1, indicating that the coordinated nitrate groups in
the complexes were bidentate (16). A characteristic absorption
band assigned to the free nitrate groups was observed at ꢃ 1381
cmꢂ1 in the spectra of the complexes (17). This conformed to
results of the conductivity experiment. Additionally, broad
bands at 3340 cmꢂ1 indicated that H2O was existent in the
complexes, confirming the elemental analysis. The complexes
showed medium intensity bands in the regions of 584–599
cmꢂ1, which were assigned to Eu-O modes.
Table 2. UV data of complexes and corresponding ligands
Complexes max (nm) ligands lmax (nm)
l
(EuL1(NO3)2ꢁ2H2O)NO3ꢁH2O 209, 232
(EuL2(NO3)2ꢁ2H2O)NO3ꢁH2O 214, 242
(EuL3(NO3)2ꢁ2H2O)NO3ꢁH2O 212, 241
(EuL4(NO3)2ꢁ2H2O)NO3ꢁH2O 212, 261
L1
L2
L3
L4
L5
L6
206, 231
208, 240
208, 240
206, 260
206, 235
210, 241
(EuL5(NO3)2ꢁ2H2O)NO3ꢁH2O
(EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O
208
215
2.5
2.0
a
1.5
b
1.0
0.5
0.0
200 210 220 230 240 250 260 270 280 290
190
wavelength/nm
Figure 1. UV spectra of a): (EuL4(NO3)2ꢁ2H2O)NO3ꢁH2O and b): L4.
2.5
2.0
a
Luminescence studies
1.5
The luminescence characteristics of the complexes in solid state
were measured at room temperature under a drive voltage of
700 V, and excitation and emission slit widths were 5.0 nm.
The fluorescence spectral data of (EuL1-5(NO3)2ꢁ2H2O)NO3ꢁnH2O
(n = 1, 3) are listed in Table 4 and the excitation and emission
spectra of (EuL4(NO3)2ꢁ2H2O)NO3ꢁH2O are shown in Figs. 5 and
6, respectively. It can be observed in Table 4 and Figs. 5 and 6
that the excitation spectra of (EuL1-5(NO3)2ꢁ2H2O)NO3ꢁnH2O
(n = 1, 3) were similar, as measured under 614 nm emission
wavelength, and their maximum excitation peaks showed at
395 or 356 nm. Emission spectra of (EuL1-5(NO3)2ꢁ2H2O)NO3ꢁnH2O
(n = 1, 3) were also similar and showed characteristic red
luminescence of europium ion; the strongest emission peak
appeared at 615 nm.
The energy transfer efficiency from ligand to centre ion is one
of the key factors that influences the characteristic luminescence
properties of rare earth ions. It is shown in Table 4 that all com-
plexes presented the characteristic luminescence of europium
ion. This indicated that all the ligands were comparatively good
organic chelators for the absorbtion and transfer of energy to
the europium ion. The relative luminescence intensity of rare
earth complexes is related to the efficiency of the intramolecular
energy transfer between the triple levels of the ligand and the
emitting level of the rare earth ion, which depends on the
energy gap between the two levels. It can be seen in Table 4 that
luminescence intensity of EuL4(NO3)2ꢁ2H2O)NO3ꢁH2O was much
1.0
b
0.5
0.0
190 200 210 220 230 240 250 260 270
wavelength/nm
Figure 2. UV spectra of a): (EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O and b): L6.
indicated that it was coordinated to the europium ion (14). Two ab-
sorption peaks of the free ligand L6 (Fig. 2) appeared at 210 nm and
241 nm, which were assigned to the л–л* and n–л* transitions of L6.
While there was only one absorption peak at 215 nm in the UV spec-
trum of (EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O, this indicated that L6 had coor-
dinated to the europium ion. Data in table 2 and the UV spectra
showed that the other ligands had coordinated to europium ion.
IR spectral analysis
IR spectral data of the ligands and their complexes are listed in
Table 3. Since the IR spectra of all the complexes were similar,
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Synthesis and luminescence properties of 2-(benzylcarbamoyl)phenyl derivatives
Table 3. IR spectral data of the ligands and their complexes (cm-1)
Complex
υ(NO3-)
υ(Eu-O)
υ(C = O)
υ(Ar-O-C)
n1
n4
n2
n3
|n1-n4|
n0
L1
1740, 1630
1741, 1638
1741, 1630
1741, 1639
1741, 1646
1741, 1638
1741, 1653
1738, 1637
1741, 1630
1741, 1639
1748, 1640
1741, 1632
1202
1202
1198
1198
1206
1207
1206
1206
1199
1199
1199
1198
(EuL1(NO3)2ꢁ2H2O)NO3ꢁH2O
1478
1481
1481
1481
1489
1478
1319
1308
1324
1324
1332
1323
1038
1038
1031
1039
1031
1031
815
815
815
815
815
815
159
173
157
157
157
155
1376
1377
1381
1384
1381
1385
599
599
584
599
592
584
L2
(EuL2(NO3)2ꢁ2H2O)NO3ꢁH2O
L3
(EuL3(NO3)2ꢁ2H2O)NO3ꢁH2O
L4
(EuL4(NO3)2ꢁ2H2O)NO3ꢁH2O
L5
(EuL5(NO3)2ꢁ2H2O)NO3ꢁH2O
L6
(EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O
Luminescence intensity of (EuL3(NO3)2ꢁ2H2O)NO3ꢁ3H2O was much
stronger than that of (EuL2(NO3)2ꢁ2H2O)NO3ꢁH2O. The reason was
that the p ! p conjugation effect between the lone pair electrons
of the Cl atom and the p-electron of the phenyl ring were
stronger than the s ! p hyperconjugation effect between the
s-electron of methylic C-H bond and the p-electron of phenyl
ring. L5 had an acceptable electron substituent (ꢂCl) that caused
the electron density of the phenyl ring to decrease. At the same
time, the introduction of the accepting electron group easily
resulted in fluorescence quenching. Therefore, the luminescence
intensity of EuL5(NO3)2ꢁ2H2O)NO3ꢁH2O was weak. Additionally,
a
b
5
7
5
the relative intensity of D0 ! F2 was stronger than that of D0
7F1 in the spectra of complexes, showing that the europium ion
was not in a centro-symmetric coordination site (18). However,
(EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O showed green luminescence that was
emitted by L6; its fluorescence spectral data are listed in Table 5.
The excitation and emission spectra of (EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O
are shown in Figs. 7–10.
4000 3500 3000 2500 2000 1500 1000 500
wavenumber/cm-1
Figure 3. IR spectra of a): (EuL2(NO3)2ꢁ2H2O)NO3ꢁH2O and b): L2.
As can be seen in Fig. 7, the excitation spectra of the L6 and its
complex were measured under the 614 nm emission wavelength
in solid state and the ligand and its complex exhibited broad
excitation bands (lmax = 460 nm). Fig. 8 shows the excitation
spectra of L6 and its complex were measured under 500 nm
emission wavelength. Maximum L6 excitation peaks and its com-
plex were located at 422 and 308 nm, respectively. Emission
spectra of the free ligand L6 and its complex (EuL6(NO3)2ꢁ2H2O)
NO3ꢁH2O can be seen excited at 308 nm in Fig. 9; maximum
emission peaks were located at 461 and 460 nm, respectively.
Luminescence intensity of the complex was much stronger than
that of free ligand L6. Emission spectra of free ligand L6 and its
complex (EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O were excited at 422 nm
(Fig. 10) and the maximum emission peaks were located at 495
and 491 nm, respectively. The luminescence intensity of the free
ligand L6 was much stronger than that of the complex.
a
b
4000 3500 3000 2500 2000 1500 1000 500
wavenumber/cm-1
Figure 4. IR spectra of a): (EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O and b): L6.
Analysis of infrared spectra showed that the oxygen atom of
the amide carbonyl group in (EuL1-5(NO3)2ꢁ2H2O)NO3ꢁnH2O
(n = 1, 3) was coordinated to the europium ion. However, the
oxygen atoms of both the amide and ester carbonyl groups
in (EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O were also coordinated to the
europium ion. The reason for this was that the oxygen atom of
the ester carbonyl group in the ligands L1-5 was adjacent to
the benzene ring, which enlarged the ligand’s л-conjugated
stronger than that of the other four complexes. It appeared that
the triplet levels of the ligand L4 was in an appropriate level to
centre the europium ion and caused an energy transition from
ligand to europium ion more easily. This is because the ligand
L4 has an activating group (ꢂOCH3) that donates electrons to
the aromatic ring and enlarges the ligand’ л-conjugated system.
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Copyright © 2012 John Wiley & Sons, Ltd.
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D. Guo et al.
Table 4. Fluorescence spectral data of the complexes
Complex
lex/
5D0-7F1
5D0-7F2
nm
lem/nm
I/a.u.
l
em/nm
I/a.u.
(EuL1(NO3)2ꢁ2H2O)NO3ꢁH2O
(EuL2(NO3)2ꢁ2H2O)NO3ꢁH2O
(EuL3(NO3)2ꢁ2H2O)NO3ꢁH2O
(EuL4(NO3)2ꢁ2H2O)NO3ꢁH2O
(EuL5(NO3)2ꢁ2H2O)NO3ꢁH2O
395
395
395
356
395
590.4
589.8
589.8
590.4
589.8
468.3
758.3
1176
1390
626
615.0
615.0
615.0
615.0
615.0
1446
1794
3489
4368
847.5
1800
1600
1400
1200
1000
800
600
400
200
0
5000
4000
3000
2000
1000
0
b
a
400 420 440 460 480 500 520 540 560
330
340
350
360
370
380
390
wavelength/nm
wavelength/nm
Figure 7. Excitation spectra of a): (EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O and b): L6, emission
Figure 5. Excitation spectrum of (EuL4(NO3)2ꢁ2H2O)NO3ꢁH2O; emission wavelength
wavelength = 614 nm.
= 614 nm.
10000
9000
5000
4000
3000
2000
1000
0
8000
a
b
7000
6000
5000
4000
3000
2000
1000
280 300 320 340 360 380 400 420 440 460
580
590
600
610
620
630
wavelength/nm
wavelength/nm
Figure 8. Excitation spectra of a): (EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O and b): L6, emission
Figure 6. Emission spectrum of (EuL4(NO3)2ꢁ2H2O)NO3ꢁH2O, excitation wavelength
wavelength = 500 nm.
= 395 nm.
system and caused the electron density of the ester carbonyl
group atom to decrease. Nevertheless, methylene was found
between the carbonyl oxygen atom and the benzene ring in
L6, which decreased the conjugation property and resulted in
an electron density increase of the carbonyl oxygen atom. As a
result, the oxygen atom of the ester carbonyl group was easy
to coordinate with the europium ion. As shown in Figs. 9 and
10, the conjugation effect between carbonyl oxygen atom and
benzene ring caused the triplet levels of L6 to not correspond
very well to the emitting level of europium ion, resulting in
Table 5. Fluorescence spectral data of L6 and (EuL6(NO3)2ꢁ2H2O)
NO3ꢁH2O
Complex
lex/nm
lem/nm
I/a.u.
L6
308
308
422
422
461.4
460.0
495.2
491.0
6902
10000
8707
(EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O
L6
(EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O
5591
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Luminescence 2012

Synthesis and luminescence properties of 2-(benzylcarbamoyl)phenyl derivatives
10000
Acknowledgements
a
The authors are grateful for the financial support of the National
Natural Science Foundation of China (No.J0830415) and the Nat-
ural Science Foundation of Hunan Province (No.11JJ5005). We
also thank Dr. William Hickey, U.S. professor of HRM for the En-
glish editing of this paper.
8000
6000
4000
2000
0
b
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Conclusions
Six novel 2-(benzylcarbamoyl)phenyl derivatives were synthesized
that formed stable solid complexes with the europium ion. The
complex (EuL1-5(NO3)2ꢁ2H2O)NO3ꢁnH2O (n= 1, 3) showed the char-
acteristic red luminescence of europium ion. However, the complex
(EuL6(NO3)2ꢁ2H2O)NO3ꢁH2O showed green luminescence emitted
by L6. The conjugation effect of the L6 caused its triplet levels to
not match very well the emitting level of europium ion, resulting
in an inhibition of intramolecular energy transfer. Luminescence
intensity of (EuL4(NO3)2ꢁ2H2O)NO3ꢁH2O was much stronger than
that of the other four complexes of (EuL1-5(NO3)2ꢁ2H2O)NO3ꢁnH2O
(n= 1, 3). These results are useful for designing ligands that possess
stronger conjugated systems and higher intramolecular energy
transfer efficiency. These complexes are promising candidates for
application in sensory materials and luminescent probes.
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Copyright © 2012 John Wiley & Sons, Ltd.
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