Novel pyrazolone derivatives and corresponding europium(III) complexes: Synthesis and properties research

Article abstract of DOI:10.1016/j.dyepig.2018.05.020

A series of pyrazolone derivatives ligands L^1?7 were successfully synthesized and validated by ¹H NMR and MS, corresponding europium complexes [EuL^1?7(NO₃)₂]NO₃·EtOAc were synthesized. Physico-chemistry properties of title complexes were determined by Elemental analysis, Molar conductance, UV absorption spectra, IR spectra and Thermogravimetric analysis. The title complexes exhibit characteristic red fluorescence of Eu³⁺. The effect of various substituent groups in ligands on the of title Eu³⁺ complexes is ordered: Cl > -Br > -OCH₃ > -F > -CH₃ > -H > -NO₂, and [EuL⁶(NO₃)₂]NO₃·EtOAc containing Cl possesses the strongest fluorescence intensity, so does fluorescence quantum yield. The electrochemical properties indicate that energy gap Eg and LUMO energy level are huge affected by substituent groups, and variation trends of LUMO energy level affected by diverse substituent groups are also different. The prepared title europium complexes have potential application prospects in the fields of photoelectric functional materials and life sciences.

Full text of DOI:10.1016/j.dyepig.2018.05.020

DyesandPigments158(2018)28–35
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Novel pyrazolone derivatives and corresponding europium(III) complexes:
Synthesis and properties research
Dewei Lia,b, Suhao Xionga,c, Tiantong Guod, Dehua Shue, Haihua Xiaoa, Guizhi Lia,
Dongcai Guoa,c,∗
a
School of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, China
Jiangsu Lopal Tech. Co., Ltd., Nanjing 210038, China
Hunan Provincial Key Laboratory for Cost-effective Utilization of Fossil Fuel Aimed at Reducing Carbon-dioxide Emissions, Changsha 410082, China
School of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, China
b
c
d
e
China Geo Engineering Corporation, Beijing 100093, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
A series of pyrazolone derivatives ligands L1−7 were successfully synthesized and validated by 1H NMR and MS,
corresponding europium complexes [EuL1−7(NO3)2]NO3·EtOAc were synthesized. Physico-chemistry properties
of title complexes were determined by Elemental analysis, Molar conductance, UV absorption spectra, IR spectra
and Thermogravimetric analysis. The title complexes exhibit characteristic red fluorescence of Eu3+. The effect
of various substituent groups in ligands on the of title Eu3+ complexes is ordered: Cl > -Br > -OCH3 > -F > -
CH3 > -H > -NO2, and [EuL6(NO3)2]NO3·EtOAc containing Cl possesses the strongest fluorescence intensity, so
does fluorescence quantum yield. The electrochemical properties indicate that energy gap Eg and LUMO energy
level are huge affected by substituent groups, and variation trends of LUMO energy level affected by diverse
substituent groups are also different. The prepared title europium complexes have potential application pro-
spects in the fields of photoelectric functional materials and life sciences.
Pyrazolone derivatives
Eu (III) complexes
Synthesis
Fluorescence
Electrochemical property
1. Introduction
light absorption efficiency of organic ligands and energy transfer effi-
ciency between ligands and rare earth ions [4,18]. Therefore, design
In recent years, due to unique structure and properties (larger
Stokes shift and higher luminescence quantum efficiency), application
of rare earth elements in luminescent materials has received wide-
spread attention [1–6]. Rare earth complexes can emit characteristic
fluorescence via rare earth ions combining with appropriate organic
ligands [7–10]. Especially, fluorescent materials based on rare earth
organic complexes present the advantages of high fluorescence in-
tensity, pure color, low excitation energy and high fluorescence effi-
ciency. Rare earth organic luminescent materials, which combine the
advantages of inorganic luminescent materials and organic luminescent
materials, can be used in the fields of life [6,11–13], industry [14–17]
and other fields with excellent fluorescence performance. However,
there are still some problems that need to be overcome, like poor
thermal stability, lower luminescence intensity and inferior electron
transport efficiency. Therefore, design and synthesis of novel rare earth
complexes with excellent luminescence properties have always been the
direction of research.
and synthesis of appropriate ligand is the key. In our early work, many
rare earth organic ligands complexes are investigated [7,19]. Due to the
presence of coordination active sites (such as carbonyl on pyrazole ring)
[20], pyrazolone derivatives own outstanding coordination ability.
However, corresponding rare earth complexes with excellent perfor-
mance have been rarely reported.
In this work, synthesis and properties of novel pyrazolone deriva-
tives ligands and corresponding rare earth complexes are studied. 1-
phenyl-3-methyl-5-pyrazolone and para-substituted phenols were used
as raw material, a series of novel pyrazolone derivatives ligands were
synthesized by reaction of intermediate 1-phenyl-3-methyl-4-chlor-
oacetyl-5-pyrazolone and phenoxyacetic acid derivatives, and char-
acterized by 1H NMR and MS. The synthetic route was shown in Scheme
1. Europium was taken as the center ion, and corresponding europium
(Ⅲ) complexes were prepared. Their physico-chemistry properties were
explored by molar conductance, elemental analysis, UV spectra, IR
spectra and thermogravimetric analysis. Fluorescence and electro-
chemical properties were also investigated.
Luminescence intensity of rare earth complexes strongly depends on
∗
Corresponding author. School of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, China.
E-mail address: dcguo2001@hnu.edu.cn (D. Guo).
https://doi.org/10.1016/j.dyepig.2018.05.020
Received 16 January 2018; Received in revised form 8 April 2018; Accepted 11 May 2018
0143-7208/©2018ElsevierLtd.Allrightsreserved.

D. Li et al.
DyesandPigments158(2018)28–35
Scheme 1. Synthesis route of 1-phenyl-3-methyl-5-pyrazolone derivatives.
2. Experimental
NaOH was dissolved in mixed solvent of 15 mL deionized water and
5 mL ethanol at room temperature with constant stirring, 45 mmol
phenol was subsequent slowly added. After stirring for another 20 min,
sodium chloroacetate solution was added. Subsequently, the mixture
was refluxed at 102 °C for 5 h. After the mixture was cooled to room
temperature, pH was adjusted to 1–2 with 2.0 mol·L−1 HCl, amounts of
white precipitations were gained. The precipitations were filtered and
washed 3 times with dilute hydrochloric acid, dried at 60 °C. White
crude product was dispersed in 100 mL heated deionized water, pH was
adjusted to 8.0 using saturated potassium carbonate solution, then
mixture solution was filtered, and filtrate was collected. White pre-
cipitated was obtained by adjusting pH of filtrate to 1–2 with
2.0 mol·L−1 HCl. After cooled down to room temperature naturally, the
mixture was filtered, washed with dilute hydrochloric acid, dried
overnight in vacuum, then target product (b1) was obtained. The syn-
thetic procedures of phenoxyacetic acid derivative (b2−7) were similar
to that of phenoxyacetic acid (b1).
2.1. Materials and methods
Eu2O3 (purity 99.99%), 1-phenyl-3-methyl-5-pyrazolone (chemical
pure) and other reagents (analytical pure) were commercially available.
1H NMR was measured by using an INOVA-400 high resolution
nuclear magnetic resonance spectrometer with TMS as internal stan-
dard, and CDCl3 or DMSO‑d6 as solvent. Mass spectra were recorded by
the MAT95XP Mass Spectrometer. Elemental analysis was determined
by Flash EA 1112 Elemental Analyzer. Melting points were obtained on
XT-4 binocular microscopic melting point instrument. UV absorption
spectra were recorded by LabTech UV-2100 UV–visible spectro-
photometer. IR spectra (4000 cm−1-400 cm−1) were carried out on
Shimadzu IRAffinity-1 infrared spectrometer. TG-DTA curves were
measured by a DTG-60 thermogravimetric analyzer with a heating rate
of 20 °C·min−1 under static air atmosphere. Fluorescence spectra was
measured by Hitachi F-2700 fluorescence spectrometer, both excitation
and emission light slits were 5.0 nm. Cyclic voltammetry curve was
tested by using three-electrodes (platinum electrode, a glassy carbon
electrode and a saturated calomel electrode) system, with sodium ni-
trate (0.1 mol·L−1) as the supporting electrolyte solution, DMSO as
solvent, ferrocene as external standard, sensitivity was 0.1 mA·V −1 and
Phenoxyacetic acid (b1), white powder, yield 75%. 1H NMR
(400 MHz, CDCl3) δ/ppm: 8.83 (dd, J = 5.0, 1.5 Hz, 2H), 8.03 (dd,
J = 7.5, 1.5 Hz, 2H), 7.39 (dd, J = 7.5, 5.1 Hz, 2H). MS (EI) m/z (%):
153 (M+1, 8), 152 (M, 86), 108 (8), 107 (100), 94 (26), 79 (24), 77
(87), 65 (14).
P-methyl phenoxyacetic acid (b2), white powder, yield 74%. 1H
NMR (CDCl3) δ/ppm: 7.11 (d, J = 8.4 Hz, 2H, ArH), 6.83 (d,
J = 8.4 Hz, 2H, ArH), 4.66 (s, 2H, CH2), 2.31 (s, 3H, CH3); MS (EI) m/z
(%): 167 (M+1, 10), 166 (M, 100), 121 (53), 107 (53), 91 (60), 77
(38), 65 (19).
scanning speed was 0.1 V·s−1
.
2.2. Synthesis method
P-methoxy phenoxyacetic acid (b3), white powder, yield 75%. 1H
NMR (CDCl3) δ/ppm: 6.90–6.84 (m, 4H, ArH), 4.64 (s, 2H, CH2), 3.78
(s, 3H, OCH3); MS (EI) m/z (%): 183 (M+1, 6), 182 (M, 56), 123 (100),
109 (16), 95 (23), 77 (11).
2.2.1. Synthesis of intermediates
Synthesis of 1-phenyl-3-methyl-4-chloroacetyl-5-pyrazolone
(a), 30 mmol 1-phenyl-3-methyl-5-pyrazolone was dissolved in 50 mL
1,4-dioxane at 60 °C with constant stirring, and then 90 mmol Ca(OH)2
was added. After 3 min, stop heating, and 3 mL chloroacetyl chloride
was immediate dropwise added. After another 5 min, the mixture was
refluxed at 90 °C for 1 h. When mixture was cooled to room tempera-
ture, 80 mL 2.0 mol·L−1 HCl was added with slow stirred. Subsequently,
the mixture is allowed to stand for another 12 h, pale yellow pre-
cipitation was emerged. The precipitation was filtered and washed with
dilute HCl and dried at 60 °C, crude product was formed, then re-
crystallized twice with the ethanol-water mixed solution to yield pale
yellow needle crystals. Yield 60%. 1H NMR (CDCl3) δ/ppm: 7.79 (d, 2H,
ArH), 7.47 (t, 2H, ArH), 7.33 (t, 1H, ArH), 4.45 (s, 2H, CH2), 2.52 (s,
3H,CH3); MS (EI) m/z (%): 252 (M+2, 13), 250 (M, 38), 216 (9), 214
(16), 201 (100), 186(5), 173 (4), 143 (4), 133 (3), 104(3), 92 (5), 91
(8), 77 (12), 51 (4).
P-Nitro phenoxyacetic acid (b4), white powder, yield 72%. 1H
NMR (CDCl3) δ/ppm: 8.24 (d, J = 9.2 Hz, 2H, ArH), 7.00 (d,
J = 9.2 Hz, 2H, ArH), 4.79 (s, 2H, CH2); MS (EI) m/z (%): 198 (M+1,
9), 197 (M, 100), 182 (15), 167 (20), 152 (83), 139 (11), 123 (33), 109
(46), 92 (31), 76 (20).
P-fluoro phenoxyacetic acid (b5), white powder, yield 72%. 1H
NMR (CDCl3) δ/ppm: 7.01 (d, J = 8.0 Hz, 2H, ArH), 6.88 (d,
J = 10.6 Hz, 2H, ArH), 4.67 (s, 2H, CH2); MS (EI) m/z (%): 171 (M+1,
8), 170 (M, 100), 125 (72), 112 (35), 95 (69), 75 (22).
P-chloro phenoxyacetic acid (b6), white powder, yield 77%. 1H
NMR (CDCl3) δ/ppm: 7.28 (d, J = 8.4 Hz, 2H, ArH), 6.87 (d,
J = 8.8 Hz, 2H, ArH), 4.68 (s, 2H, CH2); MS (EI) m/z (%): 188 (M+2,
32), 186 (M, 100), 141 (64), 128 (44), 111 (42), 99 (20), 75 (23).
P-bromo phenoxyacetic acid (b7), white powder, yield 76%. 1H
NMR (CDCl3) δ/ppm: 7.42 (d, 2H, ArH), 6.82 (d, J = 8.6 Hz, 2H, ArH),
4.67 (s, 2H, CH2); MS (EI) m/z (%): 232 (M+1, 100), 230 (M − 1, 96),
187 (45), 185 (47), 174 (29), 172 (28), 157 (34), 155 (30), 143 (16), 75
Synthesis of phenoxyacetic acid derivative (b1−7), 55 mmol
monochloroacetic acid was dissolved in 15 mL deionized water under
the condition of ice water bath, then 30% NaOH solution was used to
adjust pH 8–9, sodium chloroacetate solution was obtained. 45 mmol
29

D. Li et al.
DyesandPigments158(2018)28–35
(13).
CH2), 4.95 (s, 2H, CH2), 2.48 (s, 3H, CH3). MS (EI) m/z (%): 412 (M+1,
6), 411 (M, 26), 353 (5), 244 (6), 232 (19), 214 (21), 201 (100), 197
(20), 174 (16), 152 (22), 109 (14), 92 (17), 91 (30), 77 (43), 65 (15).
Anal. Calcd. for C20H17N3O7: C, 58.39; H, 4.17; N, 10.21. Found: C,
62.34; H, 4.97; N,12.55.
2-(1-phenyl-3-methyl-5-pyrazolone-4-yl)-2-oxoethyl-4-fluoroyl-
phenoxyacetate (L5) Reddish-brown powder, yield 68%; m.p.
76–77 °C; 1H NMR (400 MHz, CDCl3)δ/ppm: 7.75 (d, J = 7.9 Hz, 2H,
ArH), 7.46 (t, J = 7.9 Hz, 2H, ArH), 7.32 (t, J = 7.4 Hz, 1H, ArH), 7.00
(d, J = 8.1 Hz, 2H, ArH), 6.95 (d, J = 4.3 Hz, 2H, ArH), 5.20 (s, 2H,
CH2), 4.81 (s, 2H, CH2), 2.47 (s, 3H, CH3). MS (EI) m/z (%):386 (M+2,
4), 385 (M+1, 22), 384 (M, 94), 358 (3), 245 (31), 244 (29), 231 (23),
216 (13), 201 (100), 187 (26), 170 (11), 125 (52), 97 (14), 95 (34), 91
(16), 77 (29), 67 (8). Anal. Calcd. for C20H17N2O5F: C, 62.50; H, 4.46;
N, 7.29. Found: C, 61.08; H, 4.87; N, 7.08.
2-(1-phenyl-3-methyl-5-pyrazolone-4-yl)-2-oxoethyl-4-chloro-
phenylacetate (L6) Reddish-brown powder, yield 68%; m.p. 78–80 °C;
1H NMR (400 MHz, CDCl3)δ/ppm: 7.75 (d, J = 8.0 Hz, 2H, ArH), 7.46
(t, J = 7.9 Hz, 2H, ArH), 7.36–7.27 (m, 2H, ArH), 6.92 (d, J = 9.0 Hz,
2H, ArH), 5.20 (s, 2H, CH2), 4.82 (s, 2H, CH2), 2.47 (s, 3H, CH3). MS
(EI) m/z (%): 402 (M+2, 26), 400 (M, 75), 358 (3), 245 (36), 244 (34),
231 (28), 216 (12), 201 (100), 186 (32), 174 (8), 143 (13), 141 (35),
113 (13), 111 (22), 91 (14), 77 (26), 65 (7). Anal. Calcd. for
2.2.2. Synthesis of 1-phenyl-3-methyl-5-pyrazolone derivatives (L1−7
)
5 mmol phenoxyacetic acid and 8 mmol anhydrous K2CO3 were
dissolved in 20 mL DMF, refluxed at 80 °C for 1 h. Then 5 mmol 1-
phenyl-3-methyl-4-chloroacetyl-5-pyrazolone dissolved in 20 mL DMF
and a little KI were added. The mixture was refluxed at 80 °C for an-
other 10 h. After cooled to room temperature naturally, a certain
amount of distilled water was blended under constant stirring.
Subsequently, dilute HCl was added, and pale yellow precipitations
were emerged, then filtered and washed with distilled water, dried at
60 °C, the crude product was obtained. Finally, crude product was re-
crystallized from absolute ethanol and dried in vacuum at 60 °C, target
compound L1 was collected. The synthetic procedures of 1-phenyl-3-
methyl-5-pyrazolone derivative (L2−7) were similar to that of Ll.
2-(1-phenyl-3-methyl-5-pyrazolone-4-yl)-2-oxoethyl
phenox-
yacetate (L1) Reddish-brown powder, yield 70%; m.p. 74–75 °C; 1H
NMR (400 MHz, CDCl3) δ/ppm: 7.77 (d, J = 7.7 Hz, 2H, ArH), 7.47 (t,
J = 7.9 Hz, 2H, ArH), 7.37–7.30 (m, 3H, ArH), 7.01 (dd, J = 14.9,
7.1 Hz, 3H, ArH), 5.21 (s, 2H, CH2), 4.86 (s, 2H, CH2), 2.48 (s, 3H,
CH3). MS (EI) m/z (%):368 (M+2, 3), 367 (M+1, 24), 366 (M, 100),
245 (37), 244 (50), 231 (19), 216 (6), 202 (12), 201 (94), 186(24), 152
(12), 107 (48), 92 (4), 79 (7), 77 (18). Anal. Calcd. for C20H16N2O5:
C,65.7; H, 4.95; N, 7.65. Found: C, 66.34; H, 5.37; N, 7.87.
C
20H19N2O5Cl: C, 59.93; H, 4.28; N, 6.99. Found: C, 61.63; H, 5.28; N,
7.17.
2-(1-phenyl-3-methyl-5-pyrazolone-4-yl)-2-oxoethyl-4-bromo
2-(1-phenyl-3-methyl-5-pyrazolone-4-yl)-2-oxoethyl-4-methyl-
phenoxyacetate (L2) Dark red powder, yield 66%; m.p. 82–84 °C; 1H
NMR (400 MHz, CDCl3) δ/ppm: 7.75 (d, J = 7.7 Hz, 2H, ArH), 7.45 (t,
J = 7.3 Hz, 2H, ArH), 7.31 (d, J = 7.1 Hz, 1H, ArH), 7.11 (d,
J = 7.8 Hz, 2H, ArH), 6.88 (d, J = 7.2 Hz, 2H, ArH), 5.19 (s, 2H, CH2),
4.81 (s, 2H, CH2), 2.46 (s, 3H, CH3), 2.29 (d, J = 6.0 Hz,3H, CH3). MS
(EI) m/z (%):382 (M+2, 4), 381 (M+1, 24), 380 (M, 91), 359 (4), 358
(15), 341 (4), 274 (9), 246 (7), 245 (57), 244 (51), 231 (15), 216 (30),
201 (100), 79 (7), 187 (25), 174 (8), 166 (17), 122 (6), 121 (59), 93
(15), 91 (54), 77 (28), 65 (12). Anal. Calcd. for C20H20N2O5: C, 66.31;
H, 5.30; N, 7.76. Found: C, 68.23; H, 5.61; N, 7.95.
phenylacetate (L7) Yellow powder, yield 67%; m.p. 84–86 °C; 1H NMR
(400 MHz, CDCl3) δ/ppm: 7.77 (d, J = 7.9 Hz, 2H, ArH), 7.50–7.40 (m,
4H, ArH), 7.35–7.31 (m, 1H, ArH), 6.88 (d, J = 7.3 Hz, 2H, ArH), 5.20
(s, 2H, CH2), 4.83 (s, 2H, CH2), 2.48 (s, 3H, CH3).MS (EI) m/z (%): 446
(M+1, 35), 444 (M − 1, 36), 358 (2), 245 (27), 244 (26), 232 (27), 201
(100), 187 (42), 185 (33), 174 (23), 157 (22), 155 (17), 143 (8), 133
(6), 105 (9), 92 (12), 91 (23), 77 (39), 65 (12). Anal. Calcd. for
C20H19N2O5Br: C, 53.95; H, 3.85; N, 6.29. Found: C, 52.60; H, 4.53; N,
7.12.
Since the two-dimensional (2D) and three-dimensional (3D) struc-
2-(1-phenyl-3-methyl-5-pyrazolone-4-yl)-2-oxoethyl-4-
ture of the ligand L1−7 are similar, only the structure of compound L1
methoxy-phenoxyacetate (L3) Reddish-brown powder, yield 69%;
m.p. 84–86 °C; 1H NMR (400 MHz, CDCl3) δ/ppm: 7.77 (d, J = 7.6 Hz,
2H, ArH), 7.46 (t, J = 7.3 Hz, 2H), 7.35–7.30 (m, 1H, ArH), 6.94 (d,
J = 9.0 Hz, 2H, ArH), 6.85 (d, J = 7.9 Hz, 2H, ArH), 5.20 (s, 2H, CH2),
4.80 (s, 2H, CH2), 3.77 (s, 3H, CH3), 2.48 (s, 3H, CH3). MS (EI) m/z
(%):398 (M+2, 4), 397 (M+1, 24), 396 (M, 100), 358 (5), 273 (7), 245
(38), 244 (29), 231 (7), 216 (16), 201 (63), 187 (15), 182 (13), 174 (8),
137 (39), 123 (26), 109 (14), 91 (14), 77 (27), 65 (5). Anal. Calcd. for
was selected and shown in Fig. 1.
2.2.3. Preparation of title complexes
Eu2O3 and a certain amount of deionized water were mixed at 60 °C
under constant stirring, and then concentrated nitric acid was added.
When Eu2O3 was completely dissolved, mixture solution was evapo-
rated at 85 °C to remove remaining nitric acid till transparent solution
was formed. Subsequently, ethyl acetate was added with stirring, then
the Eu(NO3)3 in ethyl acetate (EtOAc) solution was obtained. 0.2 mmol
pyrazolone derivative was dissolved in 20 mL of ethyl acetate at 60 °C,
1 mL above-prepared Eu(NO3)3 ethyl acetate solution was added, pH
was adjusted to 6–7 using 1 mol·L−1 sodium ethoxide solution. After
refluxed for 5 h and cooled to room temperature, mixture was blend
into petroleum ether, the precipitations were formed, then filtered,
C
21H20N2O6: C, 63.63; H, 5.09; N, 7.07. Found: C, 65.83; H, 5.76; N,
7.81.
2-(1-phenyl-3-methyl-5-pyrazolone-4-yl)-2-oxoethyl-4-nitro-
phenoxyacetate (L4) Reddish-brown powder, yield 66%; m.p.
88–90 °C; 1H NMR (400 MHz, CDCl3) δ/ppm: 8.25 (d, J = 9.2 Hz, 2H,
ArH), 7.75 (d, J = 7.9 Hz, 2H, ArH), 7.46 (t, J = 7.9 Hz, 2H, ArH), 7.33
(t, J = 6.4 Hz, 1H, ArH), 7.08 (d, J = 9.2 Hz, 2H, ArH), 5.23 (s, 2H,
Fig. 1. 2D(a) and 3D(b) structure of ligand L1.
30

D. Li et al.
DyesandPigments158(2018)28–35
Table 1
Table 2
Elemental analysis and molar conductance data of title europium complexes.
Characteristic absorption wavelength and ε of ligand and corresponding Eu3+
complexes.
Complexes
Measured Value (Theoretical Value)/%
Λm
Compounds
λ (nm)
ε(1.0 × 104 L·mol−1·cm−1
)
C
H
N
Eu
(S·cm2·mol−1
)
L1
271
273
269
271
268
271
271,309
276,313
271
274
271
272
270
0.96
1.15
1.00
1.26
1.35
1.43
1.02,0.74
1.26,0.78
1.24
1.38
1.40
1.52
1.49
[EuL1(NO3)2]
NO3·EtOAc
36.11
(36.23)
37.41
(37.17)
36.63
(36.45)
34.59
(34.37)
35.70
(35.42)
34.99
(34.82)
33.27
(33.03)
3.42 (3.27)
3.66 (3.47)
3.74 (3.40)
3.24 (2.98)
3.33 (3.08)
3.22 (3.02)
3.05 (2.87)
9.01
(8.81)
8.87
(8.67)
8.40
(8.51)
9.73
(10.02)
8.36
(8.61)
8.19
(8.46)
7.85
(8.03)
18.98
(19.23)
18.79
(18.95)
18.22
(18.58)
18.07
(18.25)
18.45
(18.81)
18.09
(18.49)
17.23
(17.53)
73
78
80
69
79
86
82
[EuL1(NO3)2]NO3·EtOAc
L2
[EuL2(NO3)2]
NO3·EtOAc
[EuL2(NO3)2]NO3·EtOAc
L3
[EuL3(NO3)2]
NO3·EtOAc
[EuL3(NO3)2]NO3·EtOAc
L4
[EuL4(NO3)2]
NO3·EtOAc
[EuL4(NO3)2]NO3·EtOAc
L5
[EuL5(NO3)2]
NO3·EtOAc
[EuL5(NO3)2]NO3·EtOAc
L6
[EuL6(NO3)2]
NO3·EtOAc
[EuL6(NO3)2]NO3·EtOAc
L7
[EuL7(NO3)2]
NO3·EtOAc
[EuL7(NO3)2]NO3·EtOAc
274
1.55
washed with ethyl acetate, and dried at 60 °C, finally title europium
complex was formed.
3. Results and discussion
3.1. Composition and physical property of title europium complexes
Pyrazolone derivatives ligand (L1−7
) are easily dissolved in
chloroform, DMF and DMSO, partially in ethanol, methanol, acetone,
ethyl acetate and ether, hardly in cyclohexane and petroleum ether. The
title europium complexes are easily dissolved in DMF and DMSO, par-
tially in chloroform and acetone, hardly in ethanol, methanol, toluene,
cyclohexane and anhydrous ether. Elemental analysis of title europium
complexes were carried out, molar conductivity (dissolved in DMF with
10−3 mol·L−1) was also determined, and the data are listed in Table 1.
From Table 1, it can be seen that the measured value of elemental
contents are coincide well with theoretical values, the mole ratio of
ligand (L1−7) and europium ion is 1:1, so general formula of europium
complexes is [EuL1−7(NO3)2]NO3·EtOAc. Meanwhile, the molar con-
ductivity of the title europium complexes were in the range of
65–90 S cm2·mol−1, indicated that title europium complexes are 1:1
electrolytes. It may be explained that two nitrates are coordinated with
center europium ion in title europium complex, and a free nitrate ion is
existed.
Fig. 2. UV absorption spectra of [EuL4 (NO3)2]NO3⋅EtOAc (a) and L4 (b).
oxygen atom in C=O group of ligand may be shifted, and introduced
Eu3+ increase electron delocalization of the conjugated system, de-
crease corresponding electron transition energy, and improve the en-
ergy absorption and transition of complex, a red shift phenomenon of
π→π* absorption peak can be observed in Eu3+ complex. The molar
3.2. UV absorption spectra analysis
absorption coeffcient
ε
of all ligands and complexes are
(0.9–1.6) × 104. Compared with ligand L1−7, molar absorption coeff-
cient of [EuL1−7(NO3)2]NO3·EtOAc is changed. These results indicated
that ligand L1−7 was coordinated to Eu3+ successfully. Meanwhile, title
Eu3+ complexes own good UV light absorption ability, and it is better
for well fluorescence properties.
UV absorption spectra of ligand compound L1−7 and corresponding
Eu3+ complexes (dissolved in DMSO with 5.0 × 10−5 mol·L−1) were
determined, the characteristic absorption wavelength and molar ab-
sorption coeffcient (ε) are listed in Table 2.
From Table 2, max absorption peaks of ligands L1−7 are located
between 268 and 271 nm, which belong to π→π* transition of ligand
L1−7. Max absorption peaks of corresponding Eu3+ complexes all ex-
hibit red shift, only degrees of red shift are different. Specially, a new
absorption peak of L4 is emerged at 309 nm, which belongs to n→π*
transition of C=N conjugation of ligand L4, and corresponding complex
[EuL4(NO3)2]NO3·EtOAc also presents a absorption peak at 313 nm
with 4 nm red shift.
3.3. Infrared spectra analysis
IR spectra data of ligand L1−7 and corresponding complexes
[EuL1−7(NO3)2]NO3·EtOAc are shown in Table 3. Because IR spectra of
the title complexes are similar, only IR spectra of L6 and corresponding
Eu3+ complex [EuL2(NO3)2]NO3·EtOAc were selected and shown in
Fig. 3.
Because UV absorption spectra of the title complexes are similar,
only UV absorption spectra of L4 and corresponding Eu3+ complex
were selected, and shown in Fig. 2. UV characteristic absorption peaks
of ligand are exhibited in UV absorption spectra of corresponding Eu3+
complex, suggesting that π→π* transition and n→π* transition energy
in ligand are not influenced by the introduced Eu3+, and f-f transition
of Eu3+ is symmetry Laporte-forbidden owing to the nature of lantha-
nide[21]. Due to coordination of Eu3+, the lone pair electrons of
From Table 3 and Fig. 3, it can be seen that L6 exhibits three ab-
sorption peaks of benzene ring at 3043 cm−1
,
1454 cm−1 and
757 cm−1. The absorption peaks at 1713 cm−1 and 1666 cm−1 are as-
signed to ν(C=O) of acyl group and ester group, respectively. The
ν(C=N) of L6 is located at 1593 cm−1, characteristic absorption peak of
ether bond ν(Ar-O-C) appeared at 1248 cm−1 and the ν(C-O-C) at
1173 cm−1. The analysis results confirm the structure of ligand L6.
31

D. Li et al.
DyesandPigments158(2018)28–35
Table 3
IR data of ligand and corresponding complexes (cm−1).
−
compounds
v/O-H
v/C=O
v/C=N
v/Ar-O-C
v/C-O-C
v/NO3
L1
–
1711,1665
1695,1622
1714,1669
1699,1622
1719,1669
1693,1631
1718,1665
1702,1623
1713,1668
1689,1622
1713,1666
1700,1625
1713,1669
1700,1623
1595
1593
1594
1594
1594
1593
1593
1594
1595
1595
1593
1594
1594
1594
1250
1250
1250
1254
1241
1242
1236
1238
1252
1251
1248
1245
1234
1233
1172
1176
1173
1173
1184
1180
1175
1175
1172
1173
1173
1173
1276
1275
[EuL1(NO3)2]NO3·EtOAc
3418
–
3419
–
3419
–
3419
–
3422
–
3416
–
1495,1360,1029,835,1385
1496,1360,1029,835,1385
1496,1361,1029,835,1385
1497,1363,1027,834,1385
1504,1357,1029,835,1385
1493,1358,1028,836,1385
1496,1340,1029,834,1385
L2
[EuL2(NO3)2]NO3·EtOAc
L3
[EuL3(NO3)2]NO3·EtOAc
L4
[EuL4(NO3)2]NO3·EtOAc
L5
[EuL5(NO3)2]NO3·EtOAc
L6
[EuL6(NO3)2]NO3·EtOAc
L7
[EuL7(NO3)2]NO3·EtOAc
3413
200 cm−1 (135 cm−1), indicated that nitrate groups are coordinated to
europium ions as bidentate ligands. The Eu3+ complexes own char-
acteristic absorption peaks of nitrate groups with a strong absorption
peak at 1385 cm−1, implied that complexes own free nitrate groups.
The ν(C=N), ν(Ar-O-C) and ν(C-O-C) in the pyrazolone ring is not
changed significantly, suggested that C=N, Ar-O-C and C-O-C were not
combined with Eu3+. The results confirm that ligand L6 was co-
ordinated to Eu3+ successfully, which is consistent with the results of
above analysis.
3.4. Thermal analysis
Thermal analysis is used to investigate thermal stability and de-
composition process of title complexes, corresponding data are listed in
Table 4. Because thermal behaviors of the title complexes are similar,
only TG-DTA curve (Fig. 4) of [EuL3(NO3)2]NO3·EtOAc is selected for
explanation.
From Table 4 and Fig. 4, [EuL3(NO3)2]NO3·EtOAc presents 10.50%
weight loss in the range of 60–180 °C with a small endothermic peak at
73 °C, which may be due to the loss of the ethyl acetate in complex, and
this value is consistent with corresponding theoretical calculated
weight loss of 10.70%. A major weight loss of 46.27% in the range of
210–420 °C with three exothermic peaks at 246 °C, 297 °Cand 380 °C, is
assigned to the decomposition of ligand L3 (theoretical calculated
content of 48.71%). Then a moderate weight loss of 7.41% among
420–520 °C with an exothermic peak at 448 °C, is attributed to de-
composition of free nitrate ion (theoretical calculated content of
7.53%). Between 550 °C and 680 °C, 12.22% weight was lost with a
exothermic peak at 630 °C, because of the decomposition of two co-
ordination nitrates (theoretical calculated content of 15.07%). Beyond
680 °C, TG curve is basically horizontal, indicated that [EuL3(NO3)2]
NO3·EtOAc has been decomposed completely with 22.34% residual of
Eu2O3 (theoretical value of 21.49%). The TG-DTA analysis results in-
dicate that the title Eu3+ complexes own good thermal stability, and
further validate the composition of title Eu3+ complexes, which are
consistent with the above analysis results.
Fig. 3. IR spectra of [EuL6(NO3)2]NO3·EtOAc(a) and L6(b).
When ligand L6 is combined with Eu3+, complex [EuL2(NO3)2]
NO3·EtOAc exhibits a broad absorption peak at 3416 cm−1, assigned to
the ν(O-H) stretching vibration of enol-type hydroxyl group on the
pyrazolone ring, it is indicated that the structure of pyrazolone ring
may be affected. In addition, the ν(C=O) of acyl group and ester group
in ligand L6 are red shifted to 1700 cm−1 and 1625 cm−1, respectively,
with 13 cm−1 and 41 cm−1 shift. It may be explained that when oxygen
atom of C=O group coordinated to the Eu3+ ions, the electron on the
C=O bonds moved toward europium ions and bond force constant was
changed, so the vibration absorption peak of carbonyl group presents
an obvious shift. It is also confirmed that the two oxygen atoms in C=O
of the acyl group and ester group both are coordinated with Eu3+
.
Besides, the antisymmetric stretching vibration (νas) and symmetrical
stretching vibration (νs) of NO3 are located at 1493 cm−1 and
−
1358 cm−1, the difference of vibration frequency |νas-νs| is less than
Table 4
Thermal analysis data of title Eu3+ complexes.
Complexes
Endothermic peak
°C
Exothermic peak
°C
Residual weight (theoretical value)
°C
[EuL1(NO3)2]NO3·EtOAc
[EuL2(NO3)2]NO3·EtOAc
[EuL3(NO3)2]NO3·EtOAc
[EuL4(NO3)2]NO3·EtOAc
[EuL5(NO3)2]NO3·EtOAc
[EuL6(NO3)2]NO3·EtOAc
[EuL7(NO3)2]NO3·EtOAc
65
75
73
76
75
84
80
246, 290, 378, 438
259, 302, 385, 445
246, 297,380, 448
239, 293, 386, 444
240, 287, 375, 435
252, 366, 422, 620
254, 395, 448, 646
23.23 (22.25)
24.32 (21.92)
22.37 (21.49)
22.73 (21.11)
23.36 (21.76)
23.46 (21.39)
22.26 (20.29)
32

D. Li et al.
DyesandPigments158(2018)28–35
Table 5
Fluorescence spectra data of the title complexes.
Complexes
λex (nm) I (a.u.) 5D0→7F1
5D0→7F2
λem (nm) I (a.u.) λem (nm) I (a.u.)
[EuL1(NO3)2]
NO3·EtOAc
356
356
356
357
355
357
356
180
256
624
67
596
594
595
595
394
595
595
158
174
484
70
620
619
620
620
619
620
620
638
[EuL2(NO3)2]
NO3·EtOAc
788
[EuL3(NO3)2]
NO3·EtOAc
1690
258
[EuL4(NO3)2]
NO3·EtOAc
[EuL5(NO3)2]
NO3·EtOAc
344
717
678
228
514
548
894
[EuL6(NO3)2]
NO3·EtOAc
1876
1732
[EuL7(NO3)2]
NO3·EtOAc
Fig. 4. TG-DTA curve of [EuL3(NO3)2]NO3⋅EtOAc.
3.5. Possible structure of title europium complexes
According to above discussion, the title Eu3+ complexes own si-
milar structure, their two-dimensional and three-dimensional structure
are simulated and shown in Fig. 5.
3.6. Fluorescence properties
Fluorescence spectra of title europium complexes are measured,
corresponding data are listed in Table 5. Because fluorescence spectra
of the title complexes are similar, only spectra of [EuL6(NO3)2]
NO3·EtOAc was selected for illustration, shown in Fig. 6.
The fluorescence emission spectra of the title complexes
[EuL1−7(NO3)2]NO3·EtOAc present the characteristic red fluorescence
of central ion Eu3+. Emission peaks at ∼595 nm and ∼620 nm, are
assigned to 5D0→7F1 transition (magnetic dipole transition) and
5D0→7F2 transition (electric dipole transition), respectively. Emission
peak at 5D0→7F2 transition is sharp, corresponding peak width at half
height is less than 10 nm, indicated that the title europium complexes
own good monochromaticity [22]. Besides, the intensity at ∼620 nm is
strong, it may be because that the free ligand triplet energy level and
Eu3+ resonance emission energy level are highly matched, accordingly,
superior energy transfer efficiency is achieved between ligands and rare
earth ions. Optimal excitation wavelength of [EuL6(NO3)2]NO3·EtOAc
is 357 nm. The fluorescence intensity ratio η(5D0→7F2/5D0→7F1) is
3.65, indicated that Eu3+ is not located on the symmetric center of
complexes [23]. Compared with [EuL1(NO3)2]NO3·EtOAc, fluorescence
intensity of europium complex [EuL2,3(NO3)2]NO3·EtOAc, which con-
tain electron-donating substituent (-CH3 or -OCH3), is significantly
enhanced, this is because the electron cloud density of π bond system in
ligand can be increased by introduction of electron donating groups,
meanwhile, coordination capacity toward europium ion is also en-
hanced. On the other hand, the triplet energy level of L2,3 is better
Fig. 6. Excitation spectra (a) and emission spectra (b) of [EuL6(NO3)2]
NO3·EtOAc.
match to resonance emission energy level of Eu3+ with superior energy
transfer efficiency. Therefore, complex [EuL2,3(NO3)2]NO3·EtOAc own
stronger fluorescence intensity compared to [EuL1(NO3)2]NO3·EtOAc.
Further, fluorescence intensity of [EuL3(NO3)2]NO3·EtOAc is stronger
than [EuL2(NO3)2]NO3·EtOAc, it may be attributed to that -OCH3 owns
more powerful electron donating ability. [EuL4(NO3)2]NO3·EtOAc,
which contains electron-withdrawing groups (-NO2), presents the
smallest fluorescence intensity (258). It may be indicated that -NO2 can
reduce the electron cloud density of π bond system in ligand L4, weaken
corresponding coordination ability, enlarge the variable between triplet
energy level of L4 and resonance emission energy level of Eu3+
However, fluorescence intensity of [EuL5−7(NO3)2]NO3·EtOAc, which
.
Fig. 5. Simulated schematic structure of [EuL1−7(NO3)2]NO3·EtOAc.
33

D. Li et al.
DyesandPigments158(2018)28–35
contains halogen groups, is stronger than [EuL1(NO3)2]NO3·EtOAc.
Halogen atoms own both conjugation effect and induced effect, and the
conjugation effect may plays a dominate role, which enhance π bond of
ligand L5−7 and molecular planarity, so coordination capacity of L5−7
is also improved. In addition, introduction of halogen accelerates en-
maximum UV absorption peak [25–27]. The electrochemical data of
complexes [EuL1−7(NO3)2]NO3·EtOAc are listed in Table 7.
From Table 7, Eox of complexes [EuL1−7(NO3)2]NO3·EtOAc are be-
tween 0.683 V and 0.696 V. Due to the effect of electron-donating
groups (like -CH3 and -OCH3) in L2,3, electron cloud density of L2,3 are
enhanced. When L2,3 are coordinated to europium ions, corresponding
oxidation potential Eox is increased, HOMO energy level is decreased,
however, the LUMO energy level is increased. When electron-with-
drawing substituent is introduced in L4, the Eox of [EuL4(NO3)2]
NO3·EtOAc is lower than [EuL2,3(NO3)2]NO3·EtOAc, but bigger than
[EuL1(NO3)2]NO3·EtOAc. HOMO energy level and LUMO energy level
of [EuL4(NO3)2]NO3·EtOAc are both decreased compared to
[EuL1(NO3)2]NO3·EtOAc. It may be owing to the effect of electron-
withdrawing substituent (-NO2), electron cloud density on benzene ring
are weakened, and corresponding complex [EuL4(NO3)2]NO3·EtOAc is
hard to lose electrons, as a result, HOMO energy level and LUMO en-
ergy level are decreased. Eox of [EuL6(NO3)2]NO3·EtOAc is the smallest
among [EuL5,6,7(NO3)2]NO3·EtOAc, which contain halogen group.
As is well known, fluorescence property of title complexes strongly
depends on light absorption efficiency and energy transfer efficiency
between ligands (L1−7) and center ions (Eu3+). According to the above-
obtained results, the UV light absorption efficiencies of [EuL2,4,5(NO3)2]
NO3·EtOAc are similar, however, the fluorescence property are greatly
different due to the various substituent groups in ligands L2,4,5. The
complex [EuL6(NO3)2]NO3·EtOAc owns excellent UV light absorption
efficiencies among the title complexes, corresponding fluorescence
property is finest, which validate that both light absorption efficiency
and energy transfer efficiency are significant for fluorescence property
of the title complexes, and it also can be deduced that the energy level
of ligand L6 best match with Eu3+. Besides, it also can be seen that
HUMO energy levels of the title europium complexes present negligible
difference, corresponding energy gap Eg and LUMO energy level are
significantly affected by substituent groups. From electrochemical re-
sults it can be concluded that electron-donating group can increase
LUMO energy level, electron-withdrawing groups can reduce the LUMO
energy level.
ergy level matching between ligand and center ion Eu3+
. So
[EuL5−7(NO3)2]NO3·EtOAc exhibit stronger fluorescence intensity.
[EuL6(NO3)2]NO3·EtOAc (which contains Cl atoms) exhibits the stron-
gest fluorescence intensity. Due to heavy atom effect of halogen,
fluorescence quenching may be caused, therefore, fluorescence in-
tensity of [EuL7(NO3)2]NO3·EtOAc is slightly weaken. It can be con-
cluded that ligand L6 achieve more efficient energy transfer, and cor-
responding complex [EuL6(NO3)2]NO3·EtOAc owns finest fluorescence
property.
3.7. Fluorescence quantum yield
Fluorescence quantum yield is measured according to the proposed
measure [24] and calculated by the following equation.
n2x
F
F
std
Astd
Ax
x
Φfx
=
⋅
⋅
⋅Φfstd
n2std
where Φfx represents fluorescence quantum yields, nstd (1.337) and nx
(1.480) are refractive index of the solution for sample and standard,
solvent is DMSO, F is fluorescence integral area and A is UV absorbance,
A
std/Ax is 1, Фfstd (0.55) is fluorescence quantum yield of the standard
solution. The fluorescence quantum yields of the title complexes are
listed in Table 6.
From Table 6, fluorescence quantum yield of title complexes is or-
dered
as
follows:
[Eu(NO3)2L6]NO3·EtOAc > [Eu(NO3)2L7]
NO3·EtOAc > [Eu(NO3)2L3]NO3·EtOAc > [Eu(NO3)2L5]
NO3·EtOAc > [Eu(NO3)2L2]NO3·EtOAc > [Eu(NO3)2L1]
NO3·EtOAc > [Eu(NO3)2L4]NO3·EtOAc. This order is consistent with
the order of fluorescence intensity. So it may be concluded that the
complexes, which contain electron-donating substituent (like -CH3 or
-OCH3) or halogen groups (like Cl), are benefit for the fluorescence
property of complexes. The negative effect may be brought by in-
troducing electron-withdrawing groups (like -NO2) to ligand. Owing to
the heavy atom effect of halogen groups, appropriate halogen should be
adopted. In addition, the triplet energy level of ligand should well
match to the resonance emission energy level of rare ions with superior
energy transfer efficiency. In as-prepared complexes, [Eu(NO3)2L6]
NO3·EtOAc own the highest fluorescence quantum yield, namely the
finest fluorescence property.
4. Conclusions
A series of novel pyrazolone derivatives were synthesized and
characterized by 1H NMR and MS. The corresponding europium (Ⅲ)
complexes were also prepared and characterized by elemental analysis,
molar conductance, UV absorption spectra, IR spectra and thermo-
gravimetric analysis. The general formula of europium complexes is
[EuL1−7(NO3)2]NO3·EtOAc.
3.8. Electrochemical properties
All the europium complexes exhibit characteristic red fluorescence
of central ion Eu3+ with good thermal stability. The effect of various
substituent groups in ligands on the of title complexes is ordered using
fluorescence property as standard: Cl > -Br > -OCH3 > -F > -
CH3 > -H > -NO2, so [EuL6(NO3)2]NO3·EtOAc possesses the strongest
fluorescence intensity and fluorescence quantum yield Φfx due to ex-
cellent UV light absorption efficiency and energy transfer efficiency.
Besides, electron-donating substituent groups can increase the LUMO
energy level of title complexes, however, electron-withdrawing sub-
stituent groups reduce the LUMO energy level. Due to the double-edged
effect of halogen groups, appropriate halogen should be adopted, in our
work, [EuL6(NO3)2]NO3·EtOAc owns the best performance.
The title europium complexes have widely application prospects in
the fields of photoelectric functional materials and life sciences. As the
superb coordination ability in pyrazolone derivatives, synthesis of
various rare earth organic luminescent materials other than Eu can be
achieved, and different colors of fluorescent material with excellent
properties can be investigated. Wide material opportunities can also be
provided for studying appropriate substituent group to exhibit optimal
luminescent behaviors.
Electrochemical properties of title complexes are investigated by
means of a cyclic voltammetric technique in DMSO solution at elec-
trochemical workstation. The HOMO energy level can be calculated
according to equation EHOMO = - (4.74 eV + Eox), Eox represents the
starting value of oxidation potential peak, ferrocene is used as external
standard. LUMO energy level can be obtained by ELUMO = EHOMO + Eg,
Eg is energy gap and calculated via Eg = 1240/λonset (eV), λonset is
Table 6
Fluorescence quantum yield of title europium complex.
Complexes
λex (nm)
I (a.u.)
Фfx
[EuL1(NO3)2]NO3·EtOAc
[EuL2(NO3)2]NO3·EtOAc
[EuL3(NO3)2]NO3·EtOAc
[EuL4(NO3)2]NO3·EtOAc
[EuL5(NO3)2]NO3·EtOAc
[EuL6(NO3)2]NO3·EtOAc
[EuL7(NO3)2]NO3·EtOAc
343
346
342
339
345
347
348
272
328
416
116
336
448
364
0.096
0.136
0.184
0.064
0.144
0.208
0.160
34

D. Li et al.
DyesandPigments158(2018)28–35
Table 7
Electrochemical data of the title complexes.
Complexes
λonset (nm)
Eox (V)
Eg (eV)
EHOMO (eV)
ELUMO (eV)
[EuL1(NO3)2]NO3·EtOAc
[EuL2(NO3)2]NO3·EtOAc
[EuL3(NO3)2]NO3·EtOAc
[EuL4(NO3)2]NO3·EtOAc
[EuL5(NO3)2]NO3·EtOAc
[EuL6(NO3)2]NO3·EtOAc
[EuL7(NO3)2]NO3·EtOAc
273
271
271
276
274
272
274
0.685
0.696
0.696
0.693
0.687
0.683
0.685
4.542
4.576
4.576
4.493
4.526
4.559
4.526
−5.425
−5.436
−5.436
−5.435
−5.427
−5.423
−5.425
−0.883
−0.860
−0.860
−0.942
−0.901
−0.864
−0.899
Acknowledgments
[11] Nishioka T, Yuan J, Yamamoto Y, Sumitomo K, Wang Z, Hashino K, et al. New
luminescent europium(III) chelates for DNA labeling. Inorg Chem
2006;45(10):4088–96. http://dx.doi.org/10.1021/ic051276g.
The authors are grateful for the financial support of the National
Natural Science Foundation of China (No.J1103312; No.J1210040;
No.21341010), the Natural Science Foundation of Hunan Province
(No.11JJ5005), Hunan Provincial Science and Technology Department
(No.2016SK2064), Changsha Science and Technology Bureau
(No.kq1701029; No.kq1701164), the Innovative Research Team in
University (No.IRT1238), and China Outstanding Engineer Training
Plan for Students of Chemical Engineering & Technology in Hunan
University (MOE-No.2011-40). We also thank Dr. William Hickey, the
U.S. professor of HRM, for the English editing on this paper.
[12] Schäferling M, Wolfbeis OS. Europium tetracycline as a luminescent probe for nu-
cleoside phosphates and its application to the determination of kinase activity.
Chem Eur J 2007;13(15):4342–9. http://dx.doi.org/10.1002/chem.200601509.
[13] Fang L, Chen S, Fang T, Fang J, Lu C, Xu Z. Shape-memory polymer composites
selectively triggered by near-infrared light of two certain wavelengths and their
applications at macro-/microscale. Compos Sci Technol 2017;138:106–16. http://
dx.doi.org/10.1016/j.compscitech.2016.11.018.
[14] Jinnai K, Kabe R, Adachi C. A near-infrared organic light-emitting diode based on
an Yb(iii) complex synthesized by vacuum co-deposition. Chem Commun
2017;53(39):5457–60. http://dx.doi.org/10.1039/C7CC01580A.
[15] Wei N, Zuo R-X, Zhang Y-Y, Han Z-B, Gu X-J. Robust high-connected rare-earth
MOFs as efficient heterogeneous catalysts for CO2 conversion. Chem Commun
2017;53(22):3224–7. http://dx.doi.org/10.1039/C7CC00363C.
[16] Zhao B, Zhang H, Miao Y, Wang Z, Gao L, Wang H, et al. Low turn-on voltage and
low roll-off rare earth europium complex-based organic light-emitting diodes with
exciplex as the host. J Mater Chem C 2017;5(46):12182–8. http://dx.doi.org/10.
1039/C7TC03694A.
[17] Jou J-H, Lin Y-X, Peng S-H, Li C-J, Yang Y-M, Chin C-L, et al. Highly efficient yellow
organic light emitting diode with a novel wet- and dry-process feasible iridium
complex emitter. Adv Funct Mater 2014;24(4):555–62. http://dx.doi.org/10.1002/
adfm.201302013.
[18] Latva M, Takalo H, Mukkala V-M, Matachescu C, Rodríguez-Ubis J-C, Kankare J.
Correlation between the lowest triplet state energy level of the ligand and lantha-
nide(III) luminescence quantum yield. J Lumin 1997;75(2):149–69. http://dx.doi.
org/10.1016/S0022-2313(97)00113-0.
[19] Shan W, Liu F, Liu J, Chen Y, Yang Z, Guo D. Synthesis and luminescence properties
of salicylaldehyde isonicotinoyl hydrazone derivatives and their europium com-
plexes. J Inorg Biochem 2015;150(4):100–7. http://dx.doi.org/10.1016/j.
jinorgbio.2015.04.007.
[20] Dai M, Xiao H, Ye C, Shu D, Shi L, Guo D. Synthesis and luminescence properties of
terbium complexes based on 4-acyl pyrazolone derivatives. J Lumin
2017;188:223–9. http://dx.doi.org/10.1016/j.jlumin.2017.04.018.
[21] Bünzli J-CG, Piguet C. Taking advantage of luminescent lanthanide ions. Chem Soc
Rev 2005;34(12):1048. http://dx.doi.org/10.1039/b406082m.
[22] Xu H, Sun Q, An Z, Wei Y, Liu X. Electroluminescence from europium(III) com-
plexes. Coord Chem Rev 2015;293-294:228–49. http://dx.doi.org/10.1016/j.ccr.
2015.02.018.
[23] Barbara PF, Rentzepis PM, Brus LE. Photochemical kinetics of salicylidenaniline. J
Am Chem Soc 1980;102(8):2786–91. http://dx.doi.org/10.1021/ja00528a045.
[24] Ci Y, Ji X. Determination of relative fluorescence quantum yields using a simplified
method. Chin J Anal Chem 1986;14:616–8.
[25] Ding B-D, Zhang J-M, Zhu W-Q, Zhen X-Y, Wu Y-Z, Jiang X-Y, et al. Fast and
convenient determination of HOMO energy level of organic eletroluminescent
material using electrochemistry method. Chem. Res. Appl 2002;14(6):712–4.
[26] Wang D, Wang X, He Q, Zhou M, Rui W, Tao X, et al. Enhanced two-photon ab-
sorption of novel four-branched chromophore via vibronic coupling. Tetrahedron
Lett 2008;49(41):5871–6. http://dx.doi.org/10.1016/j.tetlet.2008.07.116.
[27] Bard A-J, Memming R, Miller B. Terminology in semiconductor electrochemistry
and photoelectrochemical energy conversion. IUPAC 1991;63:569–96.
References
[1] Liang S, Shang M, Lian H, Li K, Zhang Y, Lin J. An efficient rare-earth free deep red
emitting phosphor for improving the color rendering of white light-emitting diodes.
J Mater Chem C 2017;5(11):2927–35. http://dx.doi.org/10.1039/C6TC05499D.
[2] Zhong Y, Ma Z, Zhu S, Yue J, Zhang M, Antaris AL, et al. Boosting the down-shifting
luminescence of rare-earth nanocrystals for biological imaging beyond 1500 nm.
Nat Commun 2017;8(1):1–7. http://dx.doi.org/10.1038/s41467-017-00917-6.
[3] Mahata P, Mondal SK, Singha DK, Majee P. Luminescent rare-earth-based MOFs as
optical sensors. Dalton Trans 2017;46(2):301–28. http://dx.doi.org/10.1039/
C6DT03419E.
[4] Einkauf JD, Clark JM, Paulive A, Tanner GP, De Lill DT. A general model of sen-
sitized luminescence in lanthanide-based coordination polymers and metal-organic
framework materials. Inorg Chem 2017;56(10):5544–52. http://dx.doi.org/10.
1021/acs.inorgchem.6b02838.
[5] Zhu H, Chen X, Jin LM, Wang QJ, Wang F, Yu SF. Amplified spontaneous emission
and lasing from lanthanide-doped up-conversion nanocrystals. ACS Nano
2013;7(12):11420–6. http://dx.doi.org/10.1021/nn405387t.
[6] Liu Y, Ai K, Liu J, Yuan Q, He Y, Lu L. A high-performance ytterbium-based na-
noparticulate contrast agent for in vivo X-ray computed tomography imaging.
Angew Chem Int Ed 2012;51(6):1437–42. http://dx.doi.org/10.1002/anie.
201106686.
[7] Zhang W, He W, Guo X, Chen Y, Wu L, Guo D. Synthesis and luminescence prop-
erties of 1,3,4-oxadiazole acetamide derivatives and their rare earth complexes. J
Alloy Comp 2015;620(3):383–9. http://dx.doi.org/10.1016/j.jallcom.2014.09.153.
[8] Li P, Yang D, Li H. Luminescence ethylenediamine sensor based on terbium com-
plexes entrapment. Dyes Pigments 2016;132:306–9. http://dx.doi.org/10.1016/j.
dyepig.2016.05.013.
[9] Ghosh S, Abbas Z, Dasari S, Patra AK. Luminescent Eu3+ and Tb3+ complexes of 4-
aminophenyl terpyridine (ptpy): photophysical aspects, DNA and serum protein
binding properties. J Lumin 2017;187:46–52. http://dx.doi.org/10.1016/j.jlumin.
2017.02.063.
[10] Busschaert N, Caltagirone C, Van Rossom W, Gale PA. Applications of supramole-
cular anion recognition. Chem Rev 2015;115(15):8038–155. http://dx.doi.org/10.
1021/acs.chemrev.5b00099.
35