Synthesis and luminescence properties of pyrazolone derivatives and their terbium complexes

Article abstract of DOI:10.1002/bio.2804

Seven novel pyrazolone derivatives were synthesized and characterized by ¹H NMR and ¹³C NMR spectra, mass spectra, infrared spectra and elemental analysis. Their terbium complexes were prepared and characterized by elemental analysis, EDTA titrimetric analysis, UV/vis spectra, infrared spectra and molar conductivity, as well as thermal analysis. The fluorescence properties and fluorescence quantum yields of the complexes were investigated at room temperature. The results indicated that pyrazolone derivatives had good energy-transfer efficiency for the terbium ion. All the terbium complexes emitted green fluorescence characteristic of terbium ions, possessed strong fluorescence intensity, and showed relatively high fluorescence quantum yields. Cyclic voltammograms of the terbium complexes were studied and the highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) energy levels of these complexes were estimated.

Full text of DOI:10.1002/bio.2804

Research article
Received: 20 June 2014,
Revised: 10 August 2014,
Accepted: 24 September 2014
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/bio.2804
Synthesis and luminescence properties of
pyrazolone derivatives and their terbium
complexes
Haihua Xiao,a,b Xi Jiang,a Dong Li,a Limin Wu,a Wu Zhanga and
Dongcai Guoa*
1
ABSTRACT: Seven novel pyrazolone derivatives were synthesized and characterized by H NMR and 13C NMR spectra, mass
spectra, infrared spectra and elemental analysis. Their terbium complexes were prepared and characterized by elemental
analysis, EDTA titrimetric analysis, UV/vis spectra, infrared spectra and molar conductivity, as well as thermal analysis. The
fluorescence properties and fluorescence quantum yields of the complexes were investigated at room temperature. The
results indicated that pyrazolone derivatives had good energy-transfer efficiency for the terbium ion. All the terbium
complexes emitted green fluorescence characteristic of terbium ions, possessed strong fluorescence intensity, and showed
relatively high fluorescence quantum yields. Cyclic voltammograms of the terbium complexes were studied and the highest
occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) energy levels of these complexes were
estimated. Copyright © 2014 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: pyrazolone; synthesis; terbium complex; fluorescence quantum yield; cyclic voltammetry
Introduction
Experimental
Rare earth complexes have attracted considerable attention due
to their special physical and chemical properties. To date, rare
earth complexes have been widely used in medicinal chemistry
(1), material chemistry (2) and biochemistry (3). In recent years,
the design and synthesis of rare earth functional coordination
compounds have been hot topics in coordination chemistry
(4,5). Some complexes bearing rare earth ions show very intense
luminescence, which is characterized by a very narrow half-peak
width, a long decay time and fine monochromic light (6).
The luminescence intensity of rare earth complexes is dependent
on the absorption efficiency of ligands in the ultraviolet region and
the efficiency of energy transfer from the ligand to the rare earth ion
(7). Therefore, it is very important to design and synthesize novel
chelating ligands possessing high absorption efficiency. Pyrazolone
and its derivatives are important heterocyclic compounds contain-
ing N and O atoms, and they have been widely applied in pharma-
ceutical and biological reagents, metallurgy, dyes and luminescent
materials (8–10). Meanwhile, pyrazolone derivatives is a kind of ex-
cellent chelator, and they can form corresponding rare earth
complexes which possess good stability, fine luminescent mono-
chromaticity and strong fluorescence intensity (11,12).
Materials and methods
All the starting materials and reagents were purchased from
commercial suppliers. Terbium nitrate was prepared according
to the literature (13). Melting points were determined using
TECH XT-4 melting point apparatus and uncorrected. Infrared
spectra (4000–400 cmꢀ1) were recorded with KBr discs on a
PerkinElmer Spectrum One spectrometer. 1H NMR and 13C
NMR spectra were registered on a Bruker 400 MHz spectrometer
using CDCl3 or DMSO-d6 as solvent and tetramethylsilane (TMS)
as an internal standard, chemical shifts were reported as δ values
in units of ppm. Mass spectra were recorded on LC-MS-Agilent
1100 series. Elemental analyses were performed on Vario EL(III)
elemental analyzer. The terbium ion was determined by EDTA ti-
tration using xylenol orange as an indicator. UV/vis spectra were
detected on a LabTech UV-2100 spectrophotometer using
dimethylsulfoxide (DMSO) as the solvent. Fluorescence spectra
were obtained on a Hitachi F-2700 spectrophotometer at room
temperature, the width of the excitation and emission slits was
2.5 nm and the voltage of the photomultiplier tube (PMT) was
700 V. Molar conductivities were measured on a DDS-12A digital
Based on the above considerations, seven novel pyrazolone
derivatives were synthesized via the condensation reaction
between 1-phenyl-3-methyl-4-acetyl-5-pyrazolone and p-substituted
2-phenoxyacetohydrazide, and characterized. Their terbium com-
plexes were also prepared and characterized. The fluorescence spec-
tral properties, fluorescence quantum yields and electrochemical
properties of the terbium complexes were investigated at room tem-
* Correspondence to: D. Guo, School of Chemistry and Chemical Engineer-
ing, Hunan University, Changsha 410082, China. Tel: +86-0731-88821449;
Fax: +86-0731-88821449. E-mail: dcguo2001@163.com
a
School of Chemistry and Chemical Engineering, Hunan University, Chang-
sha 410082, China
perature. The synthesis route for the pyrazolone derivatives (L1–7
)
b
is shown in Scheme 1.
Hunan Xiangjiang Kansai Paint Co. Ltd, Changsha 410000, China
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H. Xiao et al.
Synthesis of phenoxyacetic acid derivatives (1′a–g). The synthe-
sis procedures for compounds 1′a–g are similar, so only the
synthesis of phenoxyacetic acid 1′a is described for illustration.
In a 50-mL beaker, chloroacetic acid (0.04 mol, 3.78 g) was
dissolved in 12 mL of distilled water, then 10 mL of sodium
hydroxide solution (25%) was added dropwise to form sodium
chloroacetate solution. Meanwhile, sodium hydroxide (0.04 mol,
1.60 g), 12mL of distilled water and 5 mL of absolute ethanol were
added to a 100-mL three-neck flask with stirring, then phenol
(0.04 mol, 3.76 g) was added and the mixture was stirred for
20min. The above-prepared sodium chloroacetate solution was
added to the three-neck flask using a constant pressure drop
funnel. The reaction mixture was heated to reflux for 5 h, then
cooled to room temperature, and acidified using dilute hydro-
chloric acid to form white solid. The white solid was filtered and
then recrystallized from absolute ethanol to obtain white crystals,
which were dried under vacuum for 24 h to obtain phenoxyacetic
acid 1′a.
Scheme 1. Synthesis route for pyrazolone derivatives.
Phenoxyacetic acid (1′a). A white crystal. Yield 74%. 1H NMR (CDCl3)
δ/ppm: 7.32 (dd, J = 8.5, 7.6Hz, 2H, ArH), 7.04 (t, J = 7.4 Hz, 1H, ArH),
6.94 (d, J = 8.6Hz, 2H, ArH), 4.69 (s, 2H, CH2); MS (ESI) m/z (%): 304
(2M, 12), 303 (2M – 1, 100), 151 (M – 1, 28).
p-Methylphenoxyacetic acid (1′b). A white crystal. Yield 71%. 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), 2.30 (s, 3H, CH3); MS (EI) m/z (%): 167 (M + 1, 10), 166
(M, 100), 121 (62), 107 (50), 91 (64), 77 (26), 65 (17).
direct reading conductivity meter using N,N′-dimethylformamide
(DMF) as the solvent. Thermal gravimetric (TG) and differential
thermal analyses (DTA) were performed in static air atmosphere
on a Shimadzu DTG-60 thermogravimetric analyzer at a heating
rate of 20°C/min from 40 to 800°C. The electrochemical proper-
ties of the terbium complexes were investigated by cyclic volt-
ammetry on a CHI 660d electrochemical workstation; sodium
acetate solution (0.1 mol/L) was used as supporting electrolyte
and the terbium complexes were dissolved in DMSO solution
(1.0 × 10ꢀ3 mol/L); the test sweep rate was 100 mV/s and the
sensitivity was 1 mA.
1
p-Methoxyphenoxyacetic acid (1′c). A white crystal. Yield 72%. H
NMR (CDCl3) δ/ppm: 6.84-6.90 (m, 4H, ArH), 4.64 (s, 2H, CH2),
3.78 (s, 3H, OCH3); MS (EI) m/z (%): 183 (M + 1, 6), 182 (M, 64),
123 (100), 109 (18), 95 (26), 77 (10).
1
p-Nitrophenoxyacetic acid (1′d). A white solid. Yield 69%. H NMR
General procedure for the synthesis of the intermediates
(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, 10), 197
(M, 100), 181 (4), 167 (16), 152 (85), 139 (10), 122 (22), 109 (38),
92 (28), 76 (18).
p-Fluorophenoxyacetic acid (1′e). A white crystal. Yield 71%. 1H NMR
(CDCl3) δ/ppm: 7.01 (d, J= 8.0 Hz, 2H, ArH), 6.88 (d, J=8.0Hz, 2H,
ArH), 4.66 (s, 2H, CH2); MS (EI) m/z (%): 171 (M + 1, 10), 170 (M, 100),
125 (78), 112 (42), 95 (68), 75 (17).
p-Chlorophenoxyacetic acid (1′f). A white crystal. Yield 78%. 1H NMR
(CDCl3) δ/ppm: 7.28 (d, J= 8.4 Hz, 2H, ArH), 6.86 (d, J=8.4Hz, 2H,
ArH), 4.67 (s, 2H, CH2); MS (EI) m/z (%): 188 (M + 2, 33), 186 (M, 100),
141 (78), 128 (56), 111 (58), 99 (32), 75 (34).
Synthesis of 1-phenyl-3-methyl-5-pyrazolone (1). Phenyl hydra-
zine (0.02 mol, 2.16 g) and ethyl acetoacetate (0.02 mol, 2.60 g)
were dissolved in absolute alcohol (30 mL) in a 100-mL three-neck
flask, and the reaction mixture was refluxed for 6 h with stirring.
After completion of the reaction, the excess solvent was distilled,
and the resultant residue was poured into ice water to obtain yel-
low needle-shaped crystals. These crystals were filtered, and then
recrystallized from absolute ethanol to give compound 1 (14).
1
Yield 76%. H NMR (CDCl3) δ/ppm: 7.86 (d, J = 7.8Hz, 2H, ArH),
7.39 (t, J = 8.0 Hz, 2H, ArH), 7.18 (t, J = 7.4Hz, 1H, ArH), 3.43 (s, 2H,
CH2), 2.20 (s, 3H, CH3).
Synthesis of 1-phenyl-3-methyl-4-acetyl-5-pyrazolone (2). 1-Phenyl-
3-methyl-4-acetyl-5-pyrazolone (2) was prepared from 1-phenyl-3-
methyl-5- pyrazolone 1 and acetyl chloride using a modified Jensen
procedure (15). In a 100-mL three-neck flask, compound 1 (0.02 mol,
3.48 g) was dissolved in 20 mL dioxane with stirring, then 3.0 g of
calcium hydroxide was added with strong stirring and 2.0 mL acetyl
chloride was added dropwise within 2 min. The reaction mixture be-
came a thick paste and the temperature increased during the first
few minutes. The mixture was heated to reflux for 1h at 90°C, and
then the calcium complexes were decomposed by pouring the mix-
ture into dilute hydrochloric acid (50 mL, 2 mol/L) which caused the
yellowish crystals to separate. The crystals were filtered and recrys-
1
p-Bromophenoxyacetic acid (1′g). A white solid. Yield 75%. H NMR
(CDCl3) δ/ppm: 7.41 (d, J= 9.0 Hz, 2H, ArH), 6.82 (d, J=9.0Hz, 2H,
ArH), 4.66 (s, 2H, CH2); MS (EI) m/z (%): 232 (M + 1, 98), 230 (M –1,
100), 187 (47), 185 (48), 174 (34), 172 (36), 157 (40), 155 (38), 143
(17), 76 (20).
Synthesis of ethyl phenoxyacetate derivatives (2′a–g). In a 100-mL
three-neck flask, p-substituted phenoxyacetic acid (0.02 mol) was
dissolved in absolute ethanol (40 mL) with stirring, then the acetyl
chloride (1.0 mL) was added dropwise. The reaction mixture was
refluxed for 20 h at 80°C, and an excess of ethanol was distilled off
using a rotary evaporator to obtain the ethyl phenoxyacetate deriv-
atives 2′a–g. Compounds 2′a–g were used in the next reaction di-
rectly without purification.
1
tallized from ethanol–water to form white crystals. Yield 72%. H
NMR (CDCl3) δ/ppm: 7.83 (d, J= 8.6 Hz, 2H, ArH), 7.45 (t, J= 7.8Hz,
2H, ArH), 7.27-7.32 (m, 1H, ArH), 2.48 (s, 3H, CH3), 2.47 (s, 3H, CH3);
MS (EI) m/z (%): 218 (M + 2, 2), 217 (M + 1, 15), 216(M, 100), 201
(90), 173 (8), 135 (4), 130 (6), 106 (4), 105 (6), 92 (10), 91 (14), 77 (20).
Synthesis of 2-phenoxyacetohydrazide derivatives (3′a–g). The
synthesis procedures of compounds 3′a–g are similar, so only
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Luminescence 2014

Luminescence properties of terbium complexes
the synthesis of 2-phenoxyacetohydrazide 3′a is given for illus-
tration. Ethyl phenoxyacetate (0.01 mol, 1.80 g), 5 mL of hydra-
zine hydrate (80%) and 30 mL of absolute ethanol were added
to a 100-mL three-neck flask with stirring; the reaction mixture
was then refluxed for 6 h at 85°C. After cooling to room temper-
ature, white needle-shaped crystals were obtained, filtered and
washed thoroughly with ethanol, and then dried under vacuum
to give compound 3′a.
washed with absolute ethanol, then dried under vacuum to give
compound L1.
(E)-N′-(1-(3-methyl-5-oxo-1-phenyl-4,5-dihydro-1H-pyrazol-4-yl)ethyli-
dene)-2-phenoxyacetohydrazide (L1). A pale yellow needle-shaped
crystal. Yield 71%. m.p. 160–162°C. 1H NMR (CDCl3) δ/ppm: 12.36
(s, 1H, OH of enol-isomer), 8.84 (s, 1H, NH), 7.99 (d, J = 8.0Hz, 2H,
ArH), 7.37 (q, J = 8.1Hz, 4H, ArH), 7.16 (t, J = 7.4Hz, 1H, ArH), 7.11
(t, J = 7.4Hz, 1H, ArH), 6.99 (d, J = 8.0 Hz, 2H, ArH), 4.69 (s, 2H,
CH2), 2.39 (s, 3H, CH3), 2.27 (s, 3H, CH3); 13C NMR (CDCl3)
δ/ppm: 167.67 (C=O), 166.60 (C5 of pyrazolone ring), 165.25
(C3 of pyrazolone ring), 156.84 (C1 of phenoxyl), 147.50 (C=N),
138.66 (C1 of 1-substituted aromatic ring), 129.90, 128.79,
124.70, 122.49, 119.22, 114.58 (aromatic ring carbons), 99.92
(CH2), 66.79 (C4 of pyrazolone ring), 17.16 (CH3), 14.25 (CH3); IR
(KBr) ν/cmꢀ1: 3426, 3211, 2981, 1711, 1617, 1589, 1487, 1374,
1214, 756; MS (EI) m/z (%): 366 (M + 2, 4), 365 (M + 1, 36), 364
(M, 100), 257 (46), 243 (18), 215 (26), 199 (59), 185 (12), 123
(17), 107 (14), 91 (10), 77 (46), 67 (11); Anal. calcd for
C20H20N4O3: C, 65.92; H, 5.53; N, 15.38. Found: C, 65.78; H, 5.47;
N, 15.44.
2-Phenoxyacetohydrazide (3′a). A white needle-shaped crystal. Yield
88%. 1H NMR (CDCl3) δ/ppm: 7.80 (s, 1H, NH), 7.35 (t, J=7.9Hz, 2H,
ArH), 7.06 (t, J= 7.4 Hz, 1H, ArH), 6.93 (d, J= 8.5 Hz, 2H, ArH), 4.61
(s, 2H, CH2), 3.93 (s, 2H, NH2); MS (EI) m/z (%): 167 (M + 1, 4), 166
(M, 34), 135 (2), 134 (8), 108 (4), 107 (23), 94 (100), 77 (62), 65 (6).
p-Methyl-2-phenoxyacetohydrazide (3′b). A white needle-shaped
1
crystal. Yield 85%. H NMR (CDCl3) δ/ppm: 7.75 (s, 1H, NH), 7.12
(d, J = 8.4 Hz, 2H, ArH), 6.80 (d, J = 8.4 Hz, 2H, ArH), 4.55 (s, 2H,
CH2), 3.92 (s, 2H, NH2), 2.30 (s, 3H, CH3); MS (EI) m/z (%): 181
(M + 1, 2), 180 (M, 14), 122 (2), 121 (12), 108 (100), 107 (17), 91
(54), 77 (10), 65 (14).
p-Methoxy-2-phenoxyacetohydrazide (3′c). A white needle-shaped
crystal. Yield 86%. 1H NMR (CDCl3) δ/ppm: 7.72 (s, 1H, NH),
6.82–6.90 (m, 4H, ArH), 4.53 (s, 2H, CH2), 3.91 (s, 2H, NH2), 3.77
(s, 3H, OCH3); MS (EI) m/z (%): 197 (M + 1, 4), 196 (M, 30), 138
(1), 137 (9), 124 (100), 109 (28), 107 (16), 92 (10), 77 (16), 64 (6).
(E)-N′-(1-(3-methyl-5-oxo-1-phenyl-4,5-dihydro-1H-pyrazol-4-yl)ethyli-
dene)-2-(p-tolyloxy)acetohydrazide (L2). A yellow needle-shaped
crystal. Yield 72%. m.p. 181–182°C. 1H NMR (CDCl3) δ/ppm:
12.35 (s, 1H, OH of enol-isomer), 8.59 (s, 1H, NH), 7.96 (d,
J = 7.6 Hz, 2H, ArH), 7.36 (t, J = 8.0 Hz, 2H, ArH), 7.13–7.16 (m,
3H, ArH), 6.85 (d, J = 8.6 Hz, 2H, ArH), 4.66 (s, 2H, CH2), 2.39 (s,
3H, CH3), 2.33 (s, 3H, CH3), 2.30 (s, 3H, CH3); 13C NMR (CDCl3)
δ/ppm: 167.78 (C=O), 166.53 (C5 of pyrazolone ring), 165.24
(C3 of pyrazolone ring), 154.79 (C1 of phenoxyl), 147.45 (C=N),
138.67 (C1 of 1-substituted aromatic ring), 131.91, 130.31,
128.79, 124.66, 119.18, 114.42 (aromatic ring carbons), 99.95
(CH2), 67.02 (C4 of pyrazolone ring), 20.53 (CH3), 17.17 (CH3),
14.27 (CH3); IR (KBr) ν/cmꢀ1: 3415, 3214, 2979, 1712, 1618,
1586, 1482, 1374, 1212, 752; MS (EI) m/z (%): 380 (M+ 2, 4), 379
(M+ 1, 26), 378 (M, 100), 257 (20), 243 (10), 199 (6), 126 (4), 72
(18), 59 (26); Anal. calcd for C21H22N4O3: C, 66.65; H, 5.86; N,
14.81. Found: C, 66.78; H, 5.77; N, 14.64.
p-Nitro-2-phenoxyacetohydrazide (3′d). A pale yellow crystal. Yield
82%. 1H NMR (CDCl3) δ/ppm: 8.25 (d, J= 8.0 Hz, 2H, ArH), 7.62 (s, 1H,
NH), 7.01 (d, J= 8.0 Hz, 2H, ArH), 4.67 (s, 2H, CH2), 3.95 (s, 2H, NH2);
MS (EI) m/z (%): 212 (M + 1, 4), 211 (M, 22), 153 (4), 152 (24), 123
(11), 122 (22), 106 (8), 92 (12), 76 (14), 73 (100), 65 (5).
p-Fluoro-2-phenoxyacetohydrazide (3′e).
A white needle-shaped
1
crystal. Yield 87%. H NMR (CDCl3) δ/ppm: 7.70 (s, 1H, NH), 7.02
(d, J = 8.0 Hz, 2H, ArH), 6.89 (d, J = 8.0 Hz, 2H, ArH), 4.54 (s, 2H,
CH2), 3.93 (s, 2H, NH2); MS (EI) m/z (%): 185 (M + 1, 2), 184 (20),
169 (2), 126 (4), 125 (24), 112 (100), 97(28), 95 (76), 83 (22), 75
(24), 73 (28).
p-Chloro-2-phenoxyacetohydrazide (3′f).
A white needle-shaped
(E)-N′-(1-(3-methyl-5-oxo-1-phenyl-4,5-dihydro-1H-pyrazol-4-yl)ethyli-
dene)-2-(p-tolyloxy)acetohydrazide (L3). A yellow crystal. Yield 70%.
m.p. 135–137°C. H NMR (CDCl3) δ/ppm: 12.38 (s, 1H, OH of enol-
1
crystal. Yield 90%. H NMR (CDCl3) δ/ppm: 7.72 (s, 1H, NH), 7.30
(d, J = 9.0 Hz, 2H, ArH), 6.87 (d, J = 9.0 Hz, 2H, ArH), 4.57 (s, 2H,
CH2), 3.95 (s, 2H, NH2); MS (EI) m/z (%): 202 (M + 2, 7), 200 (M,
20), 143 (6), 141 (17), 130 (33), 128 (100), 111 (34), 99 (4), 77
(7), 65 (4).
1
isomer), 8.67 (s, 1H, NH), 7.97 (d, J= 8.0 Hz, 2H, ArH), 7.36 (d,
J= 7.7 Hz, 2H, ArH), 7.14 (t, J= 7.4 Hz, 1H, ArH), 6.85–6.89 (m, 4H,
ArH), 4.63 (s, 2H, CH2), 3.79 (S, 3H, OCH3), 2.38 (s, 3H, CH3), 2.28 (s,
3H, CH3); 13C NMR (CDCl3) δ/ppm: 168.05 (C=O), 166.71 (C5 of
pyrazolone ring), 165.26 (C3 of pyrazolone ring), 154.89 (C1 of
phenoxyl), 151.01 (C4 of phenoxyl), 147.55 (C=N), 138.69 (C1 of 1-
substituted aromatic ring), 128.80, 124.66, 119.15, 115.62, 114.85 (ar-
omatic ring carbons), 99.75 (CH2), 67.54 (C4 of pyrazolone ring),
55.68 (OCH3), 17.14 (CH3), 14.26 (CH3); IR (KBr) ν/cmꢀ1: 3422, 3216,
2984, 1709, 1615, 1582, 1486, 1372, 1208, 749; MS (EI) m/z (%):
396 (M + 2, 4), 395 (M + 1, 26), 394 (M, 100), 257 (20), 243 (39), 215
(20), 199 (24), 123 (21), 109 (8), 77 (12); Anal. calcd for C21H22N4O4:
C, 63.95; H, 5.62; N, 14.20. Found: C, 63.78; H, 5.74; N, 14.04.
p-Bromo-2-phenoxyacetohydrazide (3′g). A white needle-shaped
1
crystal. Yield 87%. H NMR (CDCl3) δ/ppm: 7.69 (s, 1H, NH), 7.42
(d, J = 9.0 Hz, 2H, ArH), 6.80 (d, J = 9.0 Hz, 2H, ArH), 4.55 (s, 2H,
CH2), 3.93 (s, 2H, NH2); MS (EI) m/z (%): 246 (M + 1, 16), 244
(M – 1, 16),187 (16), 185 (18), 174 (97), 172 (100), 157 (49), 155
(46), 145 (8), 143 (8), 106 (7), 93 (11), 77 (18), 65 (24).
General procedure for the synthesis of the pyrazolone derivatives
(L1–7). The synthesis procedures for pyrazolone derivatives L1–7
are similar, so only the synthesis procedure of compound L1 is
shown for illustration. Compound 2 (4mmol, 0.864 g) was dis-
solved in 20 mL of absolute ethanol in a 100-mL three-neck flask.
Meanwhile, 2-phenoxyacetohydrazide (4mmol, 0.664 g) was dis-
solved in hot absolute ethanol (20 mL) in a 50 mL beaker, then
added to the above solution; 1 mL of glacial acetic acid was added
to the flask as a catalyst. The reaction mixture was heated to reflux
for 4 h at 105°C, then cooled to room temperature to form pale
yellow needle-shaped crystals. The crystals were filtered and
(E)-N′-(1-(3-methyl-5-oxo-1-phenyl-4,5-dihydro-1H-pyrazol-4-yl)ethyli-
dene)-2-(4-nitrophenoxy)acetohydrazide (L4). A pale yellow crystal.
1
Yield 68%. m.p. 241–242°C. H NMR (DMSO-d6) δ/ppm: 12.27 (s,
1H, OH of enol-isomer), 11.09 (S, 1H, NH), 8.26 (d, J = 9.2Hz, 2H,
ArH), 7.97 (d, J = 8.1 Hz, 2H, ArH), 7.39 (t, J = 7.9 Hz, 2H, ArH),
7.24 (d, J = 9.2 Hz, 2H, ArH), 7.13 (t, J = 7.4 Hz, 1H, ArH), 4.96 (s,
2H, CH2), 2.35 (s, 3H, CH3), 2.35 (s, 3H, CH3); 13C NMR (DMSO-
Luminescence 2014
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H. Xiao et al.
d6) δ/ppm: 167.01 (C=O), 166.69 (C5 of pyrazolone ring), 165.30
(C3 of pyrazolone ring), 163.21 (C1 of phenoxyl), 147.92 (C=N),
141.95 (C4 of phenoxyl), 139.45 (C1 of 1-substituted aromatic
ring), 129.16, 126.28, 124.31, 118.46, 115.87 (aromatic ring car-
bons), 98.45 (CH2), 66.79 (C4 of pyrazolone ring), 17.30 (CH3),
14.88 (CH3); IR (KBr) ν/cmꢀ1: 3438, 3308, 2984, 1718, 1625,
1589, 1486, 1377, 1219, 746; MS (EI) m/z (%): 411 (M + 2, 5),
410 (M + 1, 26), 409 (M, 100), 258 (10), 257 (59), 243 (12), 215
(24), 199 (55), 174 (9), 123 (16), 109 (12), 91 (12), 77 (20), 65
(6); Anal. calcd for C20H19N5O5: C, 58.68; H, 4.68; N, 17.11.
Found: C, 58.49; H, 4.79; N, 17.04.
(12), 77 (18), 67 (5); Anal. calcd for C20H19ClN4O3: C, 60.23; H,
4.80; N, 14.05. Found: C, 60.51; H, 4.67; N, 14.21.
(E)-2-(4-bromophenoxy)-N’-(1-(3-methyl-5-oxo-1-phenyl-4,5-dihydro-1H-
pyrazol-4-yl)ethylidene)acetohydrazide (L7). A pale yellow solid.
Yield 74%. m.p. 206–208°C. 1H NMR (CDCl3) δ/ppm: 12.33 (s,
1H, OH of enol-isomer), 8.71 (S, 1H, NH), 7.95 (d, J = 7.8 Hz, 2H,
ArH), 7.45 (d, J = 9.0 Hz, 2H, ArH), 7.35 (t, J = 7.6 Hz, 2H, ArH),
7.14 (t, J = 7.4 Hz, 1H, ArH), 6.84 (d, J = 9.0 Hz, 2H, ArH), 4.63 (s,
2H, CH2), 2.37 (s, 3H, CH3), 2.27 (s, 3H, CH3); 13C NMR (CDCl3)
δ/ppm: 167.44 (C=O), 166.64 (C5 of pyrazolone ring), 165.19
(C3 of pyrazolone ring), 155.95 (C1 of phenoxyl), 147.56 (C=N),
138.57 (C1 of 1-substituted aromatic ring), 132.64, 128.83,
124.87, 119.27, 116.38, 114.75 (aromatic ring carbons), 99.79
(CH2), 66.93 (C4 of pyrazolone ring), 17.15 (CH3), 14.30 (CH3); IR
(KBr) ν/cmꢀ1: 3407, 3218, 2985, 1708, 1613, 1587 1486, 1379,
1207, 754; MS (EI) m/z (%): 444 (M + 1, 86), 442 (M – 1, 86), 364
(6), 258 (10), 257 (68), 243 (45), 215 (59), 199 (100), 174 (30),
123 (28), 77 (54), 65 (22); Anal. Calcd for C20H19BrN4O3: C,
54.19; H, 4.32; N, 12.64. Found: C, 54.43; H, 4.57; N, 12.37.
(E)-2-(4-fluorophenoxy)-N′-(1-(3-methyl-5-oxo-1-phenyl-4,5-dihydro-1H-
pyrazol-4-yl)ethylidene)acetohydrazide (L5).
A
yellow needle-
shaped crystal. Yield 72%. m.p. 174–176°C. 1H NMR (CDCl3)
δ/ppm: 12.23 (s, 1H, OH of enol-isomer), 9.00 (S, 1H, NH),
7.95 (d, J = 7.6 Hz, 2H, ArH), 7.33 (t, J = 8.0 Hz, 2H, ArH), 7.13
(t, J = 7.4 Hz, 1H, ArH), 7.02 (dd, J = 11.4, 5.7 Hz, 2H, ArH),
6.87-6.91 (m, 2H, ArH), 4.59 (s, 2H, CH2), 2.34 (s, 3H, CH3),
2.21 (s, 3H, CH3); 13C NMR (CDCl3) δ/ppm: 167.72 (C=O),
166.79 (C5 of pyrazolone ring), 165.24 (C3 of pyrazolone
ring), 156.83 (C1 of phenoxyl), 152.98 (C4 of phenoxyl),
147.59 (C=N), 138.60 (C1 of 1-substituted aromatic ring),
128.81, 124.81, 119.21, 116.10 (aromatic ring carbons),
99.70 (CH2), 67.35 (C4 of pyrazolone ring), 17.10 (CH3), 14.26
(CH3); IR (KBr) ν/cmꢀ1: 3412, 3215, 2984, 1709, 1613, 1586,
1484, 1375, 1208, 753; MS (EI) m/z (%): 384 (M + 2, 3), 383
(M + 1, 18), 382 (M, 76), 258 (10), 257 (64), 243 (42), 215 (45),
199 (100), 185 (18), 174 (14), 125 (31), 123 (43), 95 (62), 77
(78), 67 (30); Anal. Calcd for C20H19FN4O3: C, 62.82; H, 5.01;
N, 14.65. Found: C, 62.56; H, 5.27; N, 14.51.
General procedure for the synthesis of the terbium com-
plexes. Because the synthesis procedures of the terbium
complexes are very similar, only the synthesis procedure of
the complex TbL1(NO3)3·2H2O is selected for illustration. The
compound L1 (0.5mmol, 0.182 g) was dissolved in 20 mL abso-
lute ethanol in a 100 mL three-neck flask. The pH of the
mixture was adjusted to 6–7 with an aqueous solution of
NaOH (1mol/L), and then 5 mL terbium nitrate ethanol solution
(0.1 mol/L) was added. The mixture was stirred for 4 h at 60°C
to form white precipitated solids, which were filtered and
washed several times with ethanol, and then dried under
vacuum for 24 h to get the complex TbL1(NO3)3·2H2O.
(E)-2-(4-chlorophenoxy)-N′-(1-(3-methyl-5-oxo-1-phenyl-4,5-dihydro-1H-
pyrazol-4-yl)ethylidene)acetohydrazide (L6). A pale yellow needle-
shaped crystal. Yield 74%. m.p. 179–180°C. 1H NMR (CDCl3)
δ/ppm: 12.34 (s, 1H, OH of enol-isomer), 8.80 (S, 1H, NH), 7.97
(d, J = 7.8 Hz, 2H, ArH), 7.35 (dd, J = 18.0, 8.3 Hz, 4H, ArH), 7.16
(t, J = 7.4 Hz, 1H, ArH), 6.91 (d, J = 8.9 Hz, 2H, ArH), 4.65 (s, 2H,
CH2), 2.39 (s, 3H, CH3), 2.28 (s, 3H, CH3); 13C NMR (CDCl3)
δ/ppm: 167.41 (C=O), 166.62 (C5 of pyrazolone ring), 165.20
(C3 of pyrazolone ring), 155.42 (C1 of phenoxyl), 147.54 (C=N),
138.57 (C1 of 1-substituted aromatic ring), 129.72, 128.82,
127.45, 124.86, 119.26, 115.90 (aromatic ring carbons), 99.83
(CH2), 67.02 (C4 of pyrazolone ring), 17.14 (CH3), 14.29 (CH3); IR
(KBr) ν/cmꢀ1: 3409, 3218, 2984, 1706, 1611, 1594, 1486, 1376,
1204, 748; MS (EI) m/z (%): 400 (M + 2, 35), 398 (M, 100), 258
(8), 257 (50), 243 (22), 215 (26), 199 (56), 185 (10), 174 (8), 123
Results and discussions
Composition and properties of the terbium complexes
The results of elemental analysis of the terbium complexes are
expressed in Table 1, which are in accordance with the theoret-
ical values calculated, and indicated that the composition of the
seven novel terbium complexes conformed to TbL1–7(NO3)
3·2H2O. Ligands L1–7 were soluble in DMF, DMSO, THF, chloro-
form and acetone as well as dichloromethane, methanol, etha-
nol and ethyl acetate, except that ligand L4 was only soluble in
DMF and DMSO; but they hardly dissolve in cyclohexane, petro-
leum ether and water. All the terbium complexes were soluble
in DMF and DMSO, but only slightly soluble in THF, chloroform
and acetone. The molar conductivity data of the complexes
Table 1. Elemental analytical and molar conductivity data of the terbium complexes
Complex
Found (calcd) (%)
Λm (S/m2/mol)
C
H
N
Tb
TbL1(NO3)3·2H2O
TbL2(NO3)3·2H2O
TbL3(NO3)3·2H2O
TbL4(NO3)3·2H2O
TbL5(NO3)3·2H2O
TbL6(NO3)3·2H2O
TbL7(NO3)3·2H2O
32.01 (32.23)
33.12 (33.21)
32.37 (32.53)
30.24 (30.39)
31.31 (31.47)
30.67 (30.80)
29.01 (29.14)
3.14 (3.25)
3.31 (3.45)
3.26 (3.38)
2.74 (2.93)
2.87 (3.04)
2.75 (2.97)
2.75 (2.81)
13.06 (13.15)
12.77 (12.91)
12.57 (12.64)
14.04 (14.18)
12.61 (12.84)
12.39 (12.57)
11.69 (11.90)
21.54 (21.32)
21.12 (20.93)
20.74 (20.50)
20.43 (20.11)
21.05 (20.82)
20.57 (20.38)
19.62 (19.28)
11
12
10
7
15
18
17
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Luminescence properties of terbium complexes
in DMF (10ꢀ3 mol/L) indicated that all complexes acted as
nonelectrolytes (16).
was chelated with the Tb(III) ion in an enol form. The absorption
bands of C=O and C=N groups in the hydrazide were shifted to
the lower wavenumber, which demonstrated that ligand L6 was
coordinated to the Tb(III) ion by the oxygen atom and nitrogen
atom of the hydrazide group. The wavenumber of cyclic C=N
did not change in the complex, which indicated that ligand L6
was not coordinated to the Tb(III) ion via cyclic C=N. In addition,
the characteristic frequencies of the coordinating nitrate groups
appeared at around 1478 (v1), 1329 (v4), 1026 (v2) and 819 cmꢀ1
(v3) (20). The difference between the two strongest absorption
bands of the nitrate groups (|v1 – v4|) was ~149 cmꢀ1, which indi-
cated that the coordinated nitrate groups in the complex were
bidentate (21). Furthermore, there were two weak bands at
457 and 419 cmꢀ1, which could be assigned to v(Tb-O) and v
(Tb-N), respectively.
UV/vis spectral studies
The UV/vis spectra data of the ligands L1–7 and their terbium com-
plexes were determined in the DMSO solution (10ꢀ4 mol/L) as well
as the molar absorptivities (ε) (17) are listed in Table 2. Because the
UV/vis spectra of all the complexes TbL1–7(NO3)3·2H2O are
similar, only the UV/vis spectra of TbL6(NO3)3·2H2O and its corre-
sponding ligand L6 are selected for illustration, as shown in Fig. 1.
There were two absorption peaks for ligand L6, one appeared at
around 277 nm and another 335nm, which were assigned to the
π–π* and n–π* transitions, respectively, however, these two ab-
sorption peaks of complex TbL6(NO3)3·2H2O appeared at 282
and 338 nm, respectively. This was due to the introduction of
terbium ion that enlarged the conjugation system of ligand L6.
The above results indicated that ligand L6 was coordinated to
the terbium ion (18).
Fluorescence spectral studies
The fluorescence spectra of the terbium complexes were mea-
sured with 2.5 nm slit widths for excitation and emission in the
solid state at room temperature, and the fluorescence spectral
data of the complexes are given in Table 4.
IR spectral studies
The characteristic infrared absorption bands of the pyrazolone
derivatives L1–7 and their corresponding terbium complexes
are listed in Table 3. Because the IR spectra of all the complexes
are similar, only the IR spectra of TbL6(NO3)3·2H2O and its
corresponding ligand L6 are selected for illustration, as shown
in Fig. 2.
1.2
1.0
b
For ligand L6, the medium intensity band at 3409 cmꢀ1 can be
attributed to the v(O–H) of the pyrazolone ring, this was in
agreement with the fact that there was a weak broad peak at
12.34 ppm in the 1H NMR spectrum. These results indicated that
ligand L6 existed in the form of an enol-isomer. The weak band
at 3218 cmꢀ1 corresponds to the v(N–H) stretching vibration
(19), the strong bands at 1706 and 1611 cmꢀ1 were allocated
to the v(C=O) and v(C=N) group of the hydrazide, respectively,
and the band at 1594 cmꢀ1 was assigned to v(C=N) of the
pyrazolone ring.
0.8
0.6
0.4
0.2
0.0
a
For the infrared spectrum of complex TbL6(NO3)3·2H2O, a new
band appeared at ~3374 cmꢀ1, which was due to the presence
of crystal water molecules. Meanwhile, the enol-isomer v(OH)
of the pyrazolone ring disappeared, implying that ligand L6
250
300
350
400
450
wavelength/nm
Figure 1. UV/vis spectra of complex TbL6(NO3)3·2H2O (a) and ligand L6 (b).
Table 2. UV/vis data of the complexes and ligands L1–7 in DMSO solution (10ꢀ4 mol/L)
Compound
λ1 (nm)
ε1 (1.0 × 104 L/mol/cm)
λ2 (nm)
ε2 (1.0 × 104 L/mol/cm)
L1
276
279
277
280
284
288
280
282
277
282
277
282
278
281
1.03
1.15
1.03
1.14
1.01
1.16
1.01
1.12
1.06
1.20
1.09
1.22
1.07
1.19
332
336
333
337
334
337
330
337
335
338
335
338
330
336
0.71
0.77
0.73
0.79
0.67
0.70
0.60
0.67
0.70
0.74
0.84
0.89
0.69
0.81
TbL1(NO3)3·2H2O
L2
TbL2(NO3)3·2H2O
L3
TbL3(NO3)3·2H2O
L4
TbL4(NO3)3·2H2O
L5
TbL5(NO3)3·2H2O
L6
TbL6(NO3)3·2H2O
L7
TbL7(NO3)3·2H2O
Luminescence 2014
Copyright © 2014 John Wiley & Sons, Ltd.
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H. Xiao et al.
v(Tb–N)
Table 3. IR spectral data of the ligands L1–7 and their terbium complexes (cmꢀ1
)
Compound
v(O–H)
v(N–H)
Hydrazide
v(Ar–O–C)
v(NO3ꢀ
)
v(Tb–O)
v(C=O)
v(C=N)
v1
v4
v2
v3
L1
3426
3373
3415
3372
3422
3377
3438
3375
3412
3368
3409
3374
3407
3373
3211
3210
3214
3214
3216
3216
3308
3309
3215
3216
3218
3217
3218
3218
1711
1668
1712
1665
1709
1665
1718
1675
1709
1662
1706
1657
1708
1661
1617
1598
1618
1599
1615
1601
1625
1607
1613
1601
1611
1597
1613
1598
1214
1214
1212
1211
1208
1208
1219
1219
1208
1207
1204
1204
1207
1206
TbL1(NO3)3·2H2O
1481
1480
1480
1482
1479
1478
1480
1325
1324
1329
1321
1326
1329
1328
1024
1026
1022
1018
1025
1026
1027
822
822
821
824
819
819
820
465
463
460
469
460
457
458
429
427
426
432
424
419
422
L2
TbL2(NO3)3·2H2O
L3
TbL3(NO3)3·2H2O
L4
TbL4(NO3)3·2H2O
L5
TbL5(NO3)3·2H2O
L6
TbL6(NO3)3·2H2O
L7
TbL7(NO3)3·2H2O
4000
3000
2000
1000
0
a
b
300
320
340
360
380
400
420
440
4000
3500
3000
2500
2000
1500
1000
500
wavelength/nm
wavenumber/cm-1
Figure 3. Excitation spectrum of complex TbL6(NO3)3·2H2O.
Figure 2. IR spectra of complex TbL6(NO3)3·2H2O (a) and ligand L6 (b).
It can be observed from the excitation spectrum that the max-
imum excitation wavelength was at 379 nm. The emission spec-
trum of the complex TbL6(NO3)3·2H2O displayed four main peaks
at approximately 491 nm (5D4→7F6), 545 nm (5D4→7F5), 586 nm
(5D4→7F4) and 625 nm (5D4→7F3), which was typical for terbium
derivative, and we can see that the strongest emission peak at
Because the fluorescence spectra of the complexes are very
similar, only the fluorescence spectrum of the complex
TbL6(NO3)3·2H2O is selected for illustration. The excitation and
emission spectra of TbL6(NO3)3·2H2O are shown in Figs. 3 and
4, respectively.
Table 4. Fluorescence spectral data of the complexes TbL1ꢀ7(NO3)3·2H2O
Complex
λex (nm)
5D4→7F6
5D4→7F5
5D4→7F4
5D4→7F3
λem (nm)
I (a.u.)
λem (nm)
I (a.u.)
λem (nm)
I (a.u.)
λem (nm)
I (a.u.)
TbL1(NO3)3·2H2O
TbL2(NO3)3·2H2O
TbL3(NO3)3·2H2O
TbL4(NO3)3·2H2O
TbL5(NO3)3·2H2O
TbL6(NO3)3·2H2O
TbL7(NO3)3·2H2O
377
376
389
381
383
380
378
491
491
491
491
491
491
491
1376
1949
2436
614
2842
3611
3242
546
545
546
545
546
545
545
3456
4831
5780
1551
7445
9091
8334
586
586
584
585
585
586
586
278
296
383
102
441
543
507
624
626
626
625
625
625
626
139
91
138
33
144
167
154
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Luminescence properties of terbium complexes
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
the σ–π hyperconjugation effect between the σ-electron of the
methylic C–H bond and the π-electron of the phenyl ring. Other-
wise, the fluorescence intensity of complex TbL4(NO3)3·2H2O
was worse than that of TbL1(NO3)3·2H2O, because ligand L4
had an electrophilic group (ꢀNO2) that caused the electron den-
sity of the phenyl ring to decrease; however, the introduction of
the accepting electron group easily resulted in fluorescence
quenching. The above results indicated that the fluorescence in-
tensity of the terbium complex substituted by the donative elec-
tron group of the corresponding ligand was increased, whereas
the fluorescence intensity of the terbium complex substituted
by the electrophilic group of the corresponding ligand was de-
creased. Moreover, with regard to the fluorescence intensities
of TbL5–7(NO3)3·2H2O substituted by the halogen atom of the
-1000
460 480 500 520 540 560 580 600 620 640
corresponding ligand L5–7
, the fluorescence intensity of
wavelength/nm
TbL6(NO3)3·2H2O was better than that of TbL5(NO3)3·2H2O. This
was because the p–π conjugation effect between the lone pair
electrons of the chlorine atom and the π-electron of the phenyl
ring was stronger than the p–π conjugation effect between the
lone pair electrons of the fluorine atom and the π-electron of
the phenyl ring, and the triplet state energy of ligand L6
matched most closely with the excited state energy of the Tb
(III) ion. However, the fluorescence intensity of complex
TbL7(NO3)3·2H2O was worse than that of TbL6(NO3)3·2H2O, which
was due to the heavy atom effect of the bromine atom in ligand
L7 (27,28).
Figure 4. Emission spectrum of complex TbL6(NO3)3·2H2O.
545 nm was responsible for the green fluorescence of the Tb(III)
complex (22). Meanwhile, the width of the half peaks was ap-
proximately several nanometers, which indicated that the com-
plex TbL6(NO3)3·2H2O had high color purity, and ligand L6 was
a comparatively good organic chelator (23,24).
The energy-transfer efficiency from the ligand to the center
ion is one of the key factors that influence the characteristic fluo-
rescence properties of the rare earth ions. From Table 4, it can be
observed that all the complexes emit fluorescence charac-
teristic of the Tb(III) ion, which indicates that ligands L1–7 are
all comparatively good organic chelators and have an excellent
‘antenna’ effect (25). The relative fluorescence intensity of rare
earth complexes is related to the efficiency of the intramolecular
energy transfer between the triple level of the ligand and the
emitting level of the Tb(III) ion, which depends on the energy
gap between the two levels. The energy difference between
the triplet state energy level of the ligand and the lowest excited
state of Tb(III) can not be too large or too small. If the energy dif-
ference is too large, the energy-transfer efficiency will decrease
due to diminution of the overlap between the energy donor (li-
gands) and acceptor (rare earth ions). By contrast, if the energy
difference is too small, the energy can back-transfer from the
rare earth ions to the triplet state energy of the ligands (26).
It can be seen in Table 4 that the fluorescence intensity of
TbL6(NO3)3·2H2O was stronger than that of the other six com-
plexes, which indicated that the triplet level of ligand L6 was in
an appropriate level to center the Tb(III) ion and the energy tran-
sition from ligand L6 to the Tb(III) ion was easier than with the
other ligands (18). The reason for this was that the p–π conjuga-
tion effect between the lone pair electrons of the Cl atom and
the π-electron of the phenyl ring was stronger than the inductive
effect of the Cl atom in the phenyl ring, therefore the electron
density of ligand L6 was increased and the energy transition
from ligand L6 to the Tb(III) ion was more efficient. Meanwhile,
the fluorescence intensities of complexes TbL2,3(NO3)3·2H2O
were stronger than that of TbL1(NO3)3·2H2O, because ligand L2
and ligand L3 had an donative electron group (ꢀCH3 and -
OCH3, respectively) which enlarged the π-conjugated systems
of ligand L2 and ligand L3. In addition, it can be seen that the
fluorescence intensity of complex TbL3(NO3)3·2H2O was better
than that of TbL2(NO3)3·2H2O, which may be because the p–π
conjugation effect between the lone pair electrons of the O
atom and the π-electron of the phenyl ring was stronger than
Fluorescence quantum yield studies
The fluorescence quantum yield of the unknown terbium
complexes (Фfx) can be calculated according to the following
formula (29,30):
n2x Fx Astd
Φfx
¼
ꢁ
ꢁ
ꢁΦfstd
n2std Fstd Ax
The quinine sulfate (1.0 μg/mL) of a sulfuric acid solution
(0.1 mol/L) was used as a standard reference. Where Фfstd was
the fluorescence quantum yield of the standard and Фfstd = 0.55.
The fluorescence spectral data of complexes TbL1–7(NO3)3·2H2O
were measured at room temperature in DMSO solution with ex-
citation and emission slit widths of 5.0 nm. The fluorescence
quantum yields of complexes TbL1–7(NO3)3·2H2O are listed in
Table 5.
As shown in Table 5, the fluorescence quantum yields of com-
plexes TbL2(NO3)3·2H2O and TbL3(NO3)3·2H2O were both greater
than that of TbL1(NO3)3·2H2O because ligands L2 and L3 had an
Table 5. The fluorescence quantum yields of the complexes
TbL1ꢀ7(NO3)3·2H2O
Complex
λex (nm)
I (a.u.)
Фfx
TbL1(NO3)3·2H2O
TbL2(NO3)3·2H2O
TbL3(NO3)3·2H2O
TbL4(NO3)3·2H2O
TbL5(NO3)3·2H2O
TbL6(NO3)3·2H2O
TbL7(NO3)3·2H2O
313
311
315
308
315
316
314
823
896
1015
524
1104
1357
1232
0.372
0.393
0.405
0.276
0.414
0.482
0.457
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H. Xiao et al.
Table 6. The HOMO and LUMO energy levels of the complexes TbL1ꢀ7(NO3)3·2H2O
Complex
λonset (nm)
EOX (V)
EHOMO (eV)
Eg (eV)
ELUMO (eV)
TbL1(NO3)3·2H2O
TbL2(NO3)3·2H2O
TbL3(NO3)3·2H2O
TbL4(NO3)3·2H2O
TbL5(NO3)3·2H2O
TbL6(NO3)3·2H2O
TbL7(NO3)3·2H2O
257
256
257
257
258
258
257
0.677
0.658
0.651
0.692
0.696
0.688
0.691
ꢀ5.417
ꢀ5.398
ꢀ5.391
ꢀ5.432
ꢀ5.436
ꢀ5.428
ꢀ5.431
4.825
4.844
4.825
4.825
4.806
4.806
4.825
ꢀ0.592
ꢀ0.554
ꢀ0.566
ꢀ0.607
ꢀ0.630
ꢀ0.622
ꢀ0.606
The HOMO and LUMO energy levels of title terbium com-
plexes were obtained according to the equations EHOMO = ꢀ
(4.74 + eEOX), where EOX is the starting value of the oxidation po-
tential peak (32), and ELUMO = EHOMO + Eg. The energy gap (Eg)
was calculated as Eg = 1240/λonset (eV) (33), and λonset was the
value of the largest UV/vis absorption peak.
8
4
Table 6 shows that the HOMO energy levels of the com-
plexes TbL2,3(NO3)3·2H2O were both higher than that of com-
plex TbL1(NO3)3·2H2O, however, the HOMO energy level of
complex TbL4(NO3)3·2H2O was less than that of complex
TbL1(NO3)3·2H2O. This may be because in terbium complexes
with different substituted groups in the relevant ligands, the in-
troduction of a donative electron group in the ligand can in-
crease the HOMO energy levels of the corresponding
complexes, whereas the introduction of an electrophilic group
in the ligand can decrease the HOMO energy level of the corre-
sponding complexes. Moreover, it can be seen that the HOMO
energy levels of complexes TbL5–7(NO3)3·2H2O were both less
than that of complex TbL1(NO3)3·2H2O, this was because of
the p–π conjugation effect and the inductive effect of the hal-
ogen atom in ligands L5–7. Meanwhile, the value of Eg for com-
plexes TbL1–7(NO3)3·2H2O was between 4.806 and 4.844 eV.
Also, we can see that the change rule about the LUMO energy
levels was in keeping with the that for the HOMO energy levels
of complexes TbL1–7(NO3)3·2H2O.
0
-4
-8
-2.4
-1.6
-0.8
0.0
0.8
1.6
Potential/V
Figure 5. Cyclic voltammogram of complex TbL6(NO3)3·2H2O.
donating electron group (ꢀCH3 and -OCH3, respectively) that en-
larged the π-conjugated system of ligands L2,3. However, the
fluorescence quantum yield of complex TbL4(NO3)3·2H2O was
lower than that of TbL1(NO3)3·2H2O because ligand L4 had an
electrophilic group (ꢀNO2) that caused the electron density on
the phenyl ring to decrease and easily resulted in fluorescence
quenching. Meanwhile, the fluorescence quantum yield of
complex TbL6(NO3)3·2H2O was the greatest among complexes
TbL5–7(NO3)3·2H2O. This was because the p–π conjugation effect
of ligand L6 was stronger than that of L5, and also because of the
heavy atom effect of the bromine atom in ligand L7. Meanwhile,
the triplet state energy level of ligand L6 best matched the
excited state energy level of the Tb(III) ion, so the fluorescence
quantum yield of complex TbL6(NO3)3·2H2O reached 0.482. From
the above discussions, we concluded that all the complexes
TbL1–7(NO3)3·2H2O possessed relatively good fluorescence quan-
tum yields.
Conclusions
The pyrazolone derivatives L1–7 existed in the form of an enol-
isomer in the solid state, and their corresponding terbium com-
plexes were also prepared and characterized. All the terbium
complexes had relatively high thermal stability. The fluorescence
intensity of the complex TbL6(NO3)3·2H2O was the strongest
among all terbium complexes. Moreover, the fluorescence quan-
tum yield of complex TbL6(NO3)3·2H2O reached 0.482. In sum-
mary, complex TbL6(NO3)3·2H2O could be used as promising
candidate luminescent materials.
Electrochemical properties studies
The electrochemical properties of the terbium complexes were
studied using cyclic voltammetry (CV) in SMSO solution (31).
The highest occupied molecular orbital (HOMO) and lowest
unoccupied molecular orbital (LUMO) energy levels of the com-
plexes were estimated and the corresponding data are listed in
Table 6. Because the CVs of all the complexes TbL1–7(NO3)
3·2H2O are similar, only the CV of TbL6(NO3)3·2H2O is selected
for illustration, as shown in Fig. 5.
Acknowledgements
The authors are grateful for the financial support of the National
Natural Science Foundation of China (No.J1103312, No.J1210040
and No.21341010), and the Innovative Research Team in Univer-
sity (No.IRT1238) as well as the Science and Technology Project
of Hunan provincial Science and Technology Department
(No.2012GK3156). We also thank Dr William Hickey, the U.S. pro-
fessor of HRM, for the English editing on this paper.
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Luminescence properties of terbium complexes
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