Synthesis, spectroscopic properties and theoretical studies of bis-Schiff bases derived from polyamine and pyrazolones

Article abstract of DOI:10.1016/j.saa.2012.06.005

A series of novel bis-Schiff base were synthesized from 1-aryl-3-methyl-4-benzoyl-5-pyrazolones and diethylenetriamine (or triethylenetetramine) as the starting materials. All of these bis-Schiff bases were characterized by means of NMR, IR, and MS. The UV-vis absorption spectra and fluorescent spectra of these bis-Schiff bases were also measured. Moreover, the B3LYP/6-31G(d) method was used to optimize the ground state geometry of the bis-Schiff bases; and the UV-vis spectroscopic properties of the products were computed and compared with corresponding experimental data based on cc-pVDZ basis set of TD-B3LYP method. It has been found that all of these bis-Schiff bases show a remarkable absorption peak in a wavelength range of 270-340 nm; and their maximum emission peaks are around 348 nm.

Full text of DOI:10.1016/j.saa.2012.06.005

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 167–175
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, spectroscopic properties and theoretical studies of bis-Schiff bases
derived from polyamine and pyrazolones
b
c
a
a
a
a
Tiegang Ren a, , Shuyun Liu , Guihui Li , Jinglai Zhang , Jia Guo , Weijie Li , Lirong Yang
⇑
a Fine Chemistry and Engineering Research Institute, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, People’s Republic of China
b Chemical Engineering and Technology Major, Hunan City University, Yiyang 413000, People’s Republic of China
c Key Laboratory of Ministry of Education for Special Functional Materials, Henan University, Kaifeng 475004, People’s Republic of China
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
A series of novel bis-Schiff bases containing pyrazole group were synthesized using polyamine and
1-aryl-3-methyl-4-benzoyl-5-pyrazolones as the starting materials. The ultraviolet absorption and fluo-
rescence spectra of these compounds have been studied systematically. Moreover, the B3LYP/6-31G(d)
method was used to optimize the ground state geometry of the bis-Schiff bases; and the spectroscopic
properties of the products were computed based on cc-pVDZ basis set of TD-B3LYP method.
"
"
"
A series of novel Schiff bases
containing pyrazole group were
synthesized and characterized.
The UV–vis spectra and fluorescent
spectra of various as-synthesized
products were measured.
The B3LYP/6-31G(d) method was
used for the optimization of the
ground state geometry of the Schiff
bases.
"
The spectroscopic properties of the
Schiff bases were computed based
on cc-pVDZ basis set of TD-B3LYP
method.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 April 2012
Received in revised form 10 May 2012
Accepted 6 June 2012
Available online 13 June 2012
A series of novel bis-Schiff base were synthesized from 1-aryl-3-methyl-4-benzoyl-5-pyrazolones and
diethylenetriamine (or triethylenetetramine) as the starting materials. All of these bis-Schiff bases were
characterized by means of NMR, IR, and MS. The UV–vis absorption spectra and fluorescent spectra of
these bis-Schiff bases were also measured. Moreover, the B3LYP/6-31G(d) method was used to optimize
the ground state geometry of the bis-Schiff bases; and the UV–vis spectroscopic properties of the prod-
ucts were computed and compared with corresponding experimental data based on cc-pVDZ basis set of
TD-B3LYP method. It has been found that all of these bis-Schiff bases show a remarkable absorption peak
in a wavelength range of 270–340 nm; and their maximum emission peaks are around 348 nm.
Ó 2012 Elsevier B.V. All rights reserved.
Keywords:
Pyrazolone
Schiff base
Polyamine
Synthesis
Spectroscopic properties
Theoretical studies
Introduction
Schiff bases as important ligands in coordination chemistry can
be applied in many fields [1–3]. Particularly, the Schiff base
derivatives of 1-aryl-3-methyl-4-benzoyl-5-pyrazolone (AMBP)
⇑
Corresponding author. Tel./fax: +86 378 2866141.
E-mail address: rtg@henu.edu.cn (T. Ren).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.06.005

168
T. Ren et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 167–175
15'
17'
14'
and their metal complexes are of extraordinary significance, since
14
15
they possess high biological and pharmaceutical activities [4–7].
Similarly, polyamine derivatives (such as diethylenetriamine or
triethylenetetramine [8]) as a kind of important pharmaceutical
and chemical intermediates are important in enzyme catalysis,
biological medicine, supramolecular self-assembly and synthesis
of macrocyclic complexes, since they are closely related to cell
growing development, amine nucleic acid metabolism, protein
biological synthesis and sugar, lipid, and hormone metabolism
[9,10]. Therefore, the Schiff base derived from polyamine and
1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) is of special
interest, because it possesses unique structure and chemical prop-
erties. This is the reason why extensive researches have been
focused on the synthesis and crystal structure of several Schiff
bases and their metal complexes derived from diethylenetriamine
and PMBP [11–16].
In our previous work, we synthesized a series of porphyrin com-
pounds and benzimidazole compounds which contain pyrazole
group, and it is found that the introduction of pyrazole group leads
to stronger fluorescence emission, adding to their application as
emitting materials in organic light-emitting diode (OLED), time-
resolved fluoroimmunoassay and DNA probe [17,18]. Unfortu-
nately, little is currently available about the fluorescent properties
of acylpyrazolone-based Schiff bases containing different substitu-
ents in the phenyl group and the correlation between their molec-
ular structure and emission properties, which greatly hinders their
applications in biological and environmental sciences. Thus in the
present research we adopt a simple procedure to synthesize bis-
Schiff base compounds derived from polyamine with AMBP and
investigate the correlation between their molecular structures
and fluorescent properties. The equilibrium geometries and vibra-
tional frequencies of these Schiff bases in their ground state (S0) are
16'
13'
16
13
H
N
17
N'(3)
N(3)
19'
12
19
12'
18'
CH3
10'
18
C
N
N
H
C
H3C
10
N(4)
H
11'
11
9'
8'
7'
8
9
N
N'(2)
N
O
O
7
N
6'
N(2)
N'(1)
N
N(1)
6
1'
2'
5'
5
1
4'
2
4
3'
R
R
3
R= H (1a) ; p-CH3 (2a) ; p-Cl (3a) ; p-Br (4a) ; p-NO2 (5a)
15'
17'
14'
14
15
16'
13'
16
13
H
N
12'
6'
H
N
N'(4)
CH3
10'
N(3)
17
C'
18
19'
12
20'
19
20
N'(3)
N(4)
N
H
18'
C
11
H3C
10
9'
N
N
8'
7'
11
H
8
'
9
N(2)
O
N
N
N'(1)
O
7
N(2)
N
N(1)
1'
2'
5'
6
5
1
4'
3'
2
4
R
R
3
R= H (1b) ; p-CH3 (2b) ; p-Cl (3b) ; p-Br (4b) ; p-NO2 (5b) ; m-Cl (6b)
Fig. 1. The molecular structures of the Schiff base.
Table 1
B3LYP-optimized primary geometric parameters of the ground-state (S0) for 1a–5a: bond lengths (in Å), bond angles and dihedral angles (in °).
Atom numbers
Geometric parameters of S0
1a
2a
3a
4a
5a
C(6)–N(1)
C(3)–R (R = CH3, Cl, Br, NO2)
N(1)–N(2)
C(8)–C(11)
C(11)–N(3)
1.417
1.417
1.510
1.378
1.471
1.285
1.452
1.473
1.479
1.454
1.286
1.485
1.370
1.511
1.421
120.8
125.8
121.9
108.3
111.0
114.0
110.6
119.6
126.8
128.8
121.6
24.0
1.414
1.756
1.378
1.471
1.286
1.453
1.474
1.480
1.453
1.285
1.486
1.371
1.763
1.419
120.8
125.7
121.5
108.3
111.0
114.0
110.2
120.3
127.0
129.0
121.8
17.6
1.417
1.915
1.370
1.487
1.286
1.454
1.481
1.472
1.457
1.303
1.447
1.390
1.913
1.419
121.3
128.8
126.7
119.5
110.7
113.4
111.5
108.8
121.8
121.1
121.6
22.7
1.401
1.451
1.377
1.494
1.281
1.451
1.478
1.478
1.452
1.288
1.474
1.373
1.466
1.415
120.4
126.2
129.2
124.7
113.2
111.7
112.8
106.8
123.8
128.0
118.1
24.3
1.379
1.469
1.286
1.455
1.473
1.479
1.453
1.286
1.485
1.371
N(3)–C(18)
C(19)–N(4)
C(19)0–N(4)
N(3)0–C(18)0
C(11)0–N(3)0
C(8)0–C(11)0
N(1)0–N(2)0
C(3)0–R0 (R = CH3, Cl, Br, NO2)
C(6)0–N(1)0
1.422
120.5
126.0
120.9
108.2
111.1
113.9
110.4
119.9
126.7
129.0
118.4
21.7
C(1)–C(6)–N(1)
C(7)–C(8)–C(11)
C(11)–N(3)–C(18)
N(3)–C(18)–C(19)
C(18)–C(19)–N(4)
C(19)–N(4)–C(19)0
C(18)0–C(19)0–N(4)
N(3)0–C(18)0–C(19)0
C(11)0–N(3)0–C(18)0
C(7)0–C(8)0–C(11)0
C(1)0–C(6)0–N(1)0
C(5)–C(6)–N(1)–N(2)
C(7)–C(8)–C(11)–C(12)
C(8)–C(11)–C(12)–C(13)
C(11)–N(3)–C(18)–C(19)
C(11)0–N(3)0–C(18)0–C(19)0
C(8)0–C(11)0–C(12)0–C(13)0
C(7)0–C(8)0–C(11)0–C(12)0
C(5)0–C(6)0–N(1)0–N(2)0
ꢀ135.1
ꢀ135.1
ꢀ134.4
ꢀ135.2
ꢀ102.3
35.7
35.2
35.4
35.2
13.6
46.9
47.5
45.6
47.9
32.7
ꢀ159.9
113.7
158.5
141.2
ꢀ152.8
124.2
150.1
143.1
ꢀ154.1
120.7
151.2
145.0
ꢀ172.3
101.7
177.9
179.2
ꢀ136.6
126.0
147.7
152.5

T. Ren et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 167–175
169
Table 2
B3LYP-optimized primary geometric parameters of the ground-state (S0) for 1b–6b: bond lengths (in Å), bond angles and dihedral angles (in °).
Atom numbers
Geometric parameters of S0
1b
2b
3b
4b
5b
6b
C(6)–N(1)
C(3)–R (R = CH3, Cl, Br, NO2)
C(4)–R (R = Cl)
N(1)–N(2)
C(8)–C(11)
1.416
1.416
1.510
1.413
1.756
1.413
1.910
1.410
1.444
1.413
1.757
1.378
1.475
1.285
1.452
1.461
1.461
1.450
1.284
1.488
1.377
1.756
1.378
1.474
1.285
1.452
1.461
1.461
1.450
1.284
1.487
1.377
1.377
1.486
1.284
1.450
1.461
1.461
1.452
1.285
1.474
1.378
1.378
1.475
1.285
1.452
1.461
1.461
1.450
1.284
1.487
1.377
1.378
1.475
1.285
1.452
1.461
1.461
1.450
1.284
1.487
1.377
1.379
1.475
1.284
1.452
1.461
1.461
1.450
1.283
1.488
1.378
C(11)–N(3)
N(3)–C(18)
C(19)–N(4)
C(19)0–N(4)
N(3)0–C(18)0
C(11)0–N(3)0
C(8)0–C(11)0
N(1)0–N(2)0
C(4)0–R0 (R0 = Cl)
C(3)0–R0 (R0 = CH3, Cl, Br, NO2)
C(6)0–N(1)0
1.510
1.416
120.7
127.2
121.8
109.7
110.5
113.4
113.5
110.5
109.2
122.3
125.8
119.5
ꢀ35.4
ꢀ148.5
55.9
1.756
1.414
120.9
125.7
117.5
109.2
110.5
113.5
113.4
110.5
109.7
121.9
127.1
120.8
ꢀ33.4
ꢀ148.0
55.5
1.909
1.414
120.9
125.7
122.4
109.1
110.6
113.5
113.4
110.5
109.7
121.9
127.1
120.8
ꢀ33.3
ꢀ148.0
55.4
1.444
1.411
120.7
125.8
122.5
109.9
110.6
113.2
113.2
110.4
109.7
122.1
127.2
120.6
ꢀ30.7
ꢀ150.0
60.0
1.416
120.6
125.8
122.3
109.2
110.5
113.6
113.4
110.5
109.7
121.8
127.1
120.4
ꢀ34.9
ꢀ148.3
55.8
1.413
120.9
125.7
122.4
109.2
110.5
113.4
113.4
110.5
109.7
121.9
127.0
120.7
ꢀ32.7
C(1)–C(6)–N(1)
C(7)–C(8)–C(11)
C(11)–N(3)–C(18)
N(3)–C(18)–C(19)
C(18)–C(19)–N(4)
C(19)–N(4)–C(20)
C(20)0–N(4)0–C(19)0
C(18)0–C(19)0–N(4)
N(3)0–C(18)0–C(19)0
C(11)0–N(3)0–C(18)0
C(7)0–C(8)0–C(11)0
C(1)0–C(6)0–N(1)0
C(5)–C(6)–N(1)–N(2)
C(7)–C(8)–C(11)–C(12)
C(8)–C(11)–C(12)–C(13)
C(11)–N(3)–C(18)–C(19)
N(4)–C(20)–C(20)0–N(4)0
C(11)0–N(3)0–C(18)0–C(19)0
C(8)0–C(11)0–C(12)0–C(13)0
C(7)0–C(8)0–C(11)0–C(12)0
C(5)0–C(6)0–N(1)0–N(2)0
ꢀ147.9
55.0
138.8
ꢀ179.6
150.9
20.4
138.0
ꢀ179.7
151.1
21.5
138.0
ꢀ179.7
151.1
21.6
138.1
ꢀ179.8
150.5
21.2
138.0
ꢀ179.9
150.5
21.3
122.7
ꢀ179.8
150.3
21.8
ꢀ123.7
ꢀ123.9
ꢀ123.1
ꢀ123.2
ꢀ122.9
ꢀ122.6
144.2
143.2
145.9
146.0
148.8
146.7
.6
.5
.4
.3
.2
.1
determined using the B3LYP method with 6-31G(d) basis set, and
their absorption spectra are theoretically calculated using the
TD-B3LYP method with cc-pVDZ basis set and compared to the
experimental ones.
1a
2a
3a
4a
5a
Experimental
Physical measurement and materials
Infrared (IR) spectra of these products were recorded with a
Nicolet 170 SXFT-IR spectrometer within 400–4000 cmꢀ1 (mixed
with KBr and pressed into pellets). Mass spectra (MS) were deter-
mined with an Agilent 1100LC-MS mass spectrometer. Nuclear
magnetic resonance (1H NMR and 13C NMR) spectra were recorded
with an INOVA-400 spectrometer in CDCl3 or dimethyl sulphoxide
(DMSO) using tetramethyl silane (TMS) as an internal standard.
The fluorescence behavior at room temperature was evaluated
using a Hitachi F-7000 facility (light source: Xe arc lamp). Ultravi-
olet–visible light (UV–vis) absorption spectra were measured with
a Hitachi U-4100 spectrophotometer. The equilibrium geometries
and vibrational frequencies of as-synthesized products in their
ground-state were determined by B3LYP method with the 6-
31G(d) basis set, and their absorption spectra were estimated
using the TD-B3LYP method and cc-pVDZ basis set [19], and all
of the calculations were performed in vacuum. All the reagents
were purchased from commercial sources (AR grade); and solvents
used in this study were purified following the standard procedures.
0.0
250
300
350
400
450
500
Wavelength / (nm)
Fig. 2. UV–Vis Absorption spectra of 1a–5a.
General procedure for the preparation of Schiff base
1-aryl-3-methyl-4-benzoyl-5-pyrazoloneswerepreparedaccord-
ing to published procedure [20]. Known structures of synthesized
products were verified by comparing their data with those reported
in the literature. Briefly, a certain amount of 1-aryl-3-methyl-4-ben-
zoyl-5-pyrazolones (4 mmol) was dissolved in 50 mL ethanol,
followed by dropwise addition of ethanol containing an appropriate

170
T. Ren et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 167–175
.7
.6
for 4 h before rotary evaporating to remove solvent and cooling to
room temperature. As-separated yellow crystalline precipitates were
collected by filtration and recrystallized with ethanol-chloroform
(1:3, V/V).
(4Z,40Z)-4,40-(2,20-azanediylbis(ethane-2,1-diyl)bis(azanediyl))-
bis(phenylmethan-1-yl-1-ylidene)bis(3-methyl-1-phenyl-1H-pyr-
azol-5(4H)-one) (1a). APCI-MS (m/z) calcd (M+): 624.8, found:
.5
1b
2b
3b
4b
5b
6b
.4
624.0; IR (KBr, cmꢀ1): 1627 (
mC@N), 1151 (mC–O), 1537, 1498 (mC@C),
.3
3058 (mN–Hꢁ ꢁ ꢁO); 1H NMR (CDCl3) d: 1.34 (s, 6H, 2CH3), 1.6 (b, 1H,
NH), 2.79 (t, 4H, J = 2.8 Hz, CH2–CH2), 3.2 (dd, 4H, J = 5.6, 5.6 Hz,
CH2–CH2), 7.12 (t, 2H, J = 7.1 Hz, Ar–H), 7.36–7.39 (m, 8H, Ar–H),
7.49 (t, 6H, J = 7.5 Hz, Ar–H), 7.99 (d, 4H, J = 8.0 Hz, Ar–H), 11.30
(s, 2H, NH). 13C NMR (CDCl3) d: 166.07, 165.74, 147.97, 139.23,
131.49, 130.50, 129.11, 128.72, 127.59, 124.24, 119.40, 99.80,
48.50, 44.46, 15.40.
.2
.1
0.0
250
(4Z,40Z)-4,40-(2,20-azanediylbis(ethane-2,1-diyl)bis(azanediyl))
bis(phenylmethan-1-yl-1-ylidene)bis(3-methyl-1-p-tolyl-1H-pyr-
azol-5(4H)-one) (2a). APCI-MS (m/z) calcd (M+): 652.8, found:
300
350
400
450
500
Wavelength / (nm)
Fig. 3. UV–Vis Absorption spectra of 1b–6b.
651.2; IR (KBr, cmꢀ1): 1630 (
mC@N), 1156 (mC–O), 1536, 1479 (mC@C),
3038 (mN–Hꢁ ꢁ ꢁO); 1H NMR (CDCl3) d: 1.37 (s, 6H, 2CH3), 2.34 (s, 6H,
2CH3), 2.79 (t, 4H, J = 2.8 Hz, CH2–CH2), 3.2 (dd, 4H, J = 5.6, 3.6 Hz,
CH2–CH2), 7.17 (d, 4H, J = 8.4 Hz, Ar–H), 7.34 (dd, 4H, J = 3.6, 1.6 Hz,
Ar–H), 7.51 (t, 6H, J = 7.5 Hz, Ar–H), 7.85 (d, 4H, J = 8.4 Hz, Ar–H),
11.31 (s, 2H, NH). 13C NMR (CDCl3) d: 165.96, 165.58, 147.69,
136.82, 133.77, 131.51, 130.40, 129.27, 129.13, 127.59, 119.39,
99.87, 48.65, 44.46, 21.08, 15.54.
Table 3
The calculated absorption wavelengths of 1a–5a at the TD-B3LYP/cc-pVDZ level.
Compounds
States
Transition
Absorption
k
f
1a
2a
3a
4a
X1A
(164a)2(165a)2(166a)0
161a ? 166a
(4Z,40Z)-4,40-(2,20-azanediylbis(ethane-2,1-diyl)bis(azanediyl))
bis(phenylmethan-1-yl-1-ylidene)bis(1-(4-chlorophenyl)-
3-methyl-1H-pyrazol-5(4H)-one) (3a). APCI-MS (m/z) calcd (M+):
121A
261A
X1A
266.34 (276.8)a
247.15
0.2241
0.2936
160a ? 167a
(172a)2(173a)2(174a)0
169a ? 174a
101A
201A
X1A
275.04 (275.4)a
255.93
0.1629
0.2865
693.6, found: 693.2; IR (KBr, cmꢀ1): 1626 (
mC@N), 1159 (mC–O),
173a ? 179a
1536, 1492 (
m
C@C), 3066 (mN–Hꢁ ꢁ ꢁO); 1H NMR (CDCl3) d: 1.29 (s,
(180a)2(181a)2(182a)0
177a ? 182a
101A
221A
X1A
275.50(276.0)a
253.29
0.1665
0.2369
6H, 2CH3), 1.46 (b, 1H, NH), 2.81 (t, 4H, J = 2.8 Hz, CH2–CH2), 3.2
(dd, 4H, J = 5.6, 5.6 Hz, CH2–CH2), 7.31 (d, 4H, J = 8.8 Hz, Ar–H),
7.37–7.40 (m, 4H, Ar–H), 7.48–7.54 (m, 6H, Ar–H), 7.98 (d, 4H,
J = 8.8 Hz, Ar–H), 11.24 (s, 2H, NH). 13C NMR (CDCl3) d: 166.18,
165.68, 148.26, 137.89, 131.39, 130.49, 129.11, 128.98, 128.65,
127.54, 120.21, 99.65, 48.28, 44.38, 15.36.
177a ? 185a
(198a)2(199a)2(200a)0
199a ? 200a
31A
297.84
0.2201
0.1925
0.1607
61A
198a ? 201a
282.36 (278.2)a
251.38
241A
X1A
194a ? 201a
5a
(186a)2(187a)2(188a)0
184a ? 188a
51A
384.65
0.1833
0.2719
(4Z,40Z)-4,40-(2,20-azanediylbis(ethane-2,1-diyl)bis(azanediyl)) bis
(phenylmethan-1-yl-1-ylidene)bis(1-(4-bromophenyl)-3-methyl-
1H-pyrazol-5(4H)-one) (4a). APCI-MS (m/z) calcd (M+): 782.5, found:
111A
187a ? 189a
337.76 (340.0)a
a
Experimental values in DMF solution.
782.1; IR (KBr, cmꢀ1): 1626 (
mC@N), 1158 (mC–O), 1536, 1490 (mC@C),
3063 (mN–Hꢁꢁ ꢁO); 1H NMR (CDCl3) d: 1.29 (s, 6H, 2CH3), 1.71 (b, 1H,
NH), 2.81 (t, 4H, J = 2.8 Hz, CH2–CH2), 3.2 (dd, 4H, J = 5.6, 5.6 Hz,
CH2–CH2), 7.37–7.40 (m, 4H, Ar–H), 7.45–7.53 (m, 10H, Ar–H), 7.93
(d, 4H, J = 8.8 Hz, Ar–H), 11.23 (s, 2H, NH). 13C NMR (CDCl3) d:
165.15, 165.69, 148.28, 138.36, 131.54, 131.35, 130.48, 129.09,
127.51, 120.49, 116.71, 99.64, 48.26, 44.37, 15.35.
Table 4
The calculated absorption wavelengths of 1b–6b at the TD-B3LYP/cc-pVDZ level.
Compounds
States
Transition
Absorption
k
f
1b
2b
X1A
(176a)2(177a)2(178a)0
173a ? 179a
(4Z,40Z)-4,40-(2,20-azanediylbis(ethane-2,1-diyl)bis(azanediyl))
bis(phenylmethan-1-yl-1-ylidene)bis(3-methyl-1-(4-nitrophenyl)
-1H-pyrazol-5(4H)-one) (5a). APCI-MS (m/z) calcd (M+): 714.7,
141A
X1A
268.90 (276.8)a
0.1428
(184a)2(185a)2(186a)0
182a ? 187a
121A
301A
X1A
272.15 (276.0)a
252.39
0.1303
0.3179
found: 714.4; IR (KBr, cmꢀ1): 1636 (
mC@N), 1158 (mC–O), 1539,
182a ? 191a
C@C), 3197 (mN–Hꢁ ꢁ ꢁO); 1H NMR (CDCl3) d: 1.21 (s, 6H,
3b
4b
5b
6b
(192a)2(193a)2(194a)0
189a ? 195a
1496 (
m
211A
311A
X1A
270.40 (284.0)a
255.62
0.2680
0.1769
2CH3), 2.12 (b, 1H, NH), 2.87 (t, 4H, J = 2.9 Hz, CH2–CH2), 3.25 (m,
4H, CH2–CH2), 7.43–7.46 (m, 4H, Ar–H), 7.54–7.57 (m, 6H, Ar–H),
8.19–8.26 (m, 8H, Ar–H), 11.23 (s, 2H, NH). 13C NMR (CDCl3) d:
166.58, 149.83, 144.51, 142.99, 131.29, 130.75, 129.22, 127.54,
124.75, 117.75, 99.46, 53.59, 47.95, 44.44, 15.39.
184a ? 194a
(210a)2(211a)2(212a)0
208a ? 213a
201A
311A
X1A
271.64 (287.0)a
256.19
0.3036
0.2207
204a ? 212a
(198a)2(199a)2(200a)0
195a ? 201a
91A
303.48 (340.6)a
277.05
0.3081
0.1631
(4Z,40Z)-4,40-(1,12-diphenyl-2,5,8,11-tetraazadodecane-1,12-
241A
X1A
191a ? 200a
192a)2(193a)2(194a)0
187a ? 194a
diylidene)bis(3-methyl-1-phenyl-1H-pyrazol-5(4H)-one)
(1b).
APCI-MS (m/z) calcd (M+): 667.8, found: 667.4; IR (KBr, cmꢀ1):
241A
311A
265.61 (281.0)a
254.59
0.2291
0.1345
C@C), 3059 (mN–Hꢁ ꢁ ꢁO); 1H
186a ? 194a
1629 (
m
C@N), 1151 (
mC–O), 1536, 1499 (
m
a
NMR (CDCl3) d: 1.41 (d, 6H, J = 16 Hz, 2CH3), 1.80 (b, 1H, NH),
2.44 (s, 2H, CH2), 2.55 (b, 1H, NH), 2.74–2.84 (m, 6H, 3CH2), 3.21
(s, 4H, CH2–CH2), 7.12 (t, 2H, J = 7.1 Hz, Ar–H), 7.22 (d, 2H,
J = 7.2 Hz, Ar–H), 7.35–7.48 (m, 10H, Ar–H), 7.54 (s, 2H, Ar–H),
8.02 (t, 4H, J = 8.0 Hz, Ar–H), 11.26 (d, 2H, NH). 13C NMR (CDCl3)
Experimental values in DMF solution.
amount of amine (4 mmol of diethylenetriamine (DETA) or triethyl-
enetetramine (TETA)). Resultant mixturewas refluxed ina water bath

T. Ren et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 167–175
171
Fig. 4. Theoretical absorption spectra of 1a–5a.
d: 165.58, 147.97, 139.37, 131.57, 130.20, 129.00, 128.69, 127.33,
124.16, 119.12, 99.56, 53.00, 48.48, 44.06, 41.72, 15.42.
137.02, 133.64, 131.73, 130.23, 129.30, 129.05, 127.42, 119.24,
99.69, 53.10, 48.62, 44.10, 41.79, 21.05, 15.48.
(4Z,40Z)-4,40-(1,12-diphenyl-2,5,8,11-tetraazadodecane-1,12-diy-
lidene)bis(3-methyl-1-p-tolyl-1H-pyrazol-5(4H)-one) (2b). APCI-
MS (m/z) calcd (M+): 695.8, found: 695.5; IR (KBr, cmꢀ1): 1631
(4Z,40Z)-4,40-(1,12-diphenyl-2,5,8,11-tetraazadodecane-1,12-
diylidene)bis(1-(4-chlorophenyl)
-3-methyl-1H-pyrazol-5(4H)-
one) (3b). APCI-MS (m/z) calcd (M+): 736.7, found: 735.3; IR
(mC@N), 1153 (
mC–O), 1535, 1479 (
m
C@C), 3452 (mN–Hꢁ ꢁ ꢁO); 1H NMR
(KBr, cmꢀ1): 1636 (
mC@N), 1152 (mC–O), 1536, 1490 (mC@C), 3065
(CDCl3) d: 1.41 (d, 6H, J = 14.0 Hz, 2CH3), 1.82 (b, 1H, NH), 2.32
(d, 6H, J = 8.0 Hz, 2CH3), 2.42 (s, 2H, CH2), 2.54 (t, 1H, J = 2.5 Hz,
NH), 2.74–2.84 (m, 6H, 3CH2), 3.18 (m, 4H, CH2–CH2), 7.16–7.34
(m, 8H, Ar–H), 7.40–7.54 (m, 6H, Ar–H), 7.88 (t, 4H, J = 8.9 Hz,
Ar–H), 11.26 (d, 2H, NH). 13C NMR (CDCl3) d: 165.57, 147.71,
(
mN–Hꢁ ꢁ ꢁO); 1H NMR (CDCl3) d: 1.39 (d, 6H, J = 16.8 Hz, 2CH3),
2.46–2.58 (m, 8H, 2CH2–CH2), 2.79 (s, 1H, NH), 2.85 (t, 1H,
J = 2.9 Hz, NH), 3.21–3.25 (m, 4H, CH2–CH2), 7.21 (d, 2H,
J = 6.8 Hz, Ar–H), 7.27–7.35 (m, 6H, Ar–H), 7.43–7.56 (m, 6H,
Ar–H), 7.99 (d, 4H, J = 9.2 Hz, Ar–H), 11.21 (d, 2H, NH). 13C NMR

172
T. Ren et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 167–175
Fig. 5. Theoretical absorption spectra of 1b–6b.
(CDCl3) d: 165.81, 165.69, 148.26, 137.97, 131.57, 130.54, 129.21,
128.78, 127.38, 120.16, 99.73, 57.45, 53.08, 48.45, 41.83, 15.51.
(4Z,40Z)-4,40-(1,12-diphenyl-2,5,8,11-tetraazadodecane-1,12-
diylidene)bis(1-(4-bromophenyl) -3-methyl-1H-pyrazol-5(4H)-
one) (4b). APCI-MS (m/z) calcd (M+): 835.6, found: 825.3; IR
Ar–H), 7.95 (d, 4H, J = 8.8 Hz, Ar–H), 11.20 (d, 2H, NH). 13C
NMR (CDCl3) d: 165.78, 165.69, 148.29, 137.94, 131.53, 130.54,
129.22, 128.79, 127.36, 120.14, 99.71, 57.44, 53.07, 48.34,
41.80, 15.54.
(4Z,40Z)-4,40-(1,12-diphenyl-2,5,8,11-tetraazadodecane-1,12-
diylidene)bis(3-methyl-1-(4-nitrophenyl)-1H-pyrazol-5(4H)-one)
(5b). APCI-MS (m/z) calcd (M+): 758.8, found: 757.4; IR (KBr,
(KBr, cmꢀ1): 1636 (
mC@N), 1152 (mC–O), 1536, 1488 (mC@C), 3048
(
mN–Hꢁ ꢁ ꢁO); 1H NMR (CDCl3) d: 1.39 (d, 6H, J = 17.2 Hz, 2CH3),
2.46–2.57 (m, 8H, 2CH2–CH2), 2.79 (s, 1H, NH), 2.85 (t, 1H,
J = 2.9 Hz, NH), 3.20–3.24 (m, 4H, CH2–CH2), 7.20 (d, 2H,
J = 7.2 Hz, Ar–H), 7.32–7.34 (m, 2H, Ar–H), 7.43–7.56 (m, 10H,
cmꢀ1): 1638 (
mC@N), 1153 (mC–O), 1540, 1499 (mC@C), 3068 (mN–
Hꢁ ꢁ ꢁO); 1H NMR (CDCl3) d: 1.40 (s, 6H, 2CH3), 2.11 (b, 1H, NH),
2.55 (m, 1H, NH), 2.83–2.91 (m, 8H, 2CH2–CH2), 3.24–3.28 (m,

T. Ren et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 167–175
173
4H, CH2–CH2), 7.24 (d, 2H, J = 8.0 Hz, Ar–H), 7.34–7.59 (m, 8H,
Ar–H), 8.21–8.30 (m, 8H, Ar–H), 7.95 (d, 4H, J = 8.8 Hz, Ar–H),
11.28 (d, 2H, NH). 13C NMR (CDCl3) d: 165.84, 148.45, 138.54,
131.67, 131.51, 130.44, 129.15, 127.30, 120.47, 116.76, 99.59,
57.43, 53.07, 48.42, 44.03, 15.49.
The primary geometric parameters of 1b–6b are shown in Table
2. In combination with the data listed in Table 2, it can be seen that
their ground-state (S0) geometric parameters, bond lengths, bond
angles, and dihedral angles are very similar.
In addition, vibrational frequency analyses based upon B3LYP/
6-31G(d) calculations reveal that the two series of Schiff base have
stable structures on the potential energy surfaces, showing no
imaginary frequency.
(4Z,40Z)-4,40-(1,12-diphenyl-2,5,8,11-tetraazadodecane-1,12-
diylidene)bis(1-(3-chlorophenyl)-3-methyl-1H-pyrazol-5(4H)-one)
(6b). APCI-MS (m/z) calcd (M+): 736.7, found: 735.3; IR (KBr, cmꢀ1):
1637(
m
C@N), 1151 (
m
C–O), 1540, 1478 (
m
C@C), 3058 (mN–Hꢁ ꢁ ꢁO); 1H
NMR (CDCl3) d: 1.39 (d, 6H, J = 18.8 Hz, 2CH3), 2.47–2.58 (m, 8H,
2CH2–CH2), 2.78 (s, 1H, NH), 2.56 (t, 1H, J = 2.6 Hz, NH), 3.21–3.25
(m, 4H, CH2–CH2), 7.08 (t, 2H, J = 7.1 Hz, Ar–H), 7.23 (d, 2H,
J = 8.0 Hz, Ar–H), 7.30–7.34 (m, 4H, Ar–H), 7.42–7.55 (m, 6H, Ar–
H), 7.97 (t, 2H, J = 7.9 Hz, Ar–H), 8.11 (d, 2H, J = 10.0 Hz, Ar–H),
11.21 (d, 2H, NH). 13C NMR (CDCl3) d: 165.72, 148.47, 140.38,
134.45, 131.50, 130.55, 129.84, 129.27, 127.37, 124.01, 118.88,
116.80, 99.70, 57.43, 53.06, 44.11, 41.80, 15.54.
UV–vis spectra
Figs. 2 and 3 show the UV–vis spectra of the two series of as-
synthesized Schiff bases measured in dimethyl formamide (DMF).
In the exploited wavelength region (200–800 nm), all as-synthe-
sized Schiff bases show a remarkable absorption peak at 270–
340 nm, which is attributed to the
p ?
p⁄ transition and n ? p⁄
transition. In the meantime, substituent R of the phenyl group
has significant influence on the absorption wavelength and absor-
bance. On the one hand, the introduction of auxochrome group
such as F, Cl, Br and NO2 to the phenyl group allows conjugation
Results and discussion
of nonbonding electron with
p electron to form p–p conjugation,
leading to enhanced electronic scope of operation and shift of
absorption peak towards longer wavelength. Among the auxo-
chrome group substituent, NO2 as a stronger electron withdrawing
group and chromophore leads to shift of the absorption peak to-
wards longer wavelength. On the other hand, the introduction of
alkyl group to the conjugated systems allows the electron of C–H
Synthesis
In our previous paper [21], a series of benzimidazoles were ob-
tained from 1-arylpyrazole-4-carbaldehyde and o-phenylenedi-
amine, where mono-Schiff base was obtained as an unstable
intermediate which was eventually transformed to benzimidaz-
oles. However, when we used 1-aryl-3-methyl-4-benzoyl-5-pyraz-
olones to replace 1-arylpyrazole-4-carbaldehyde and react with
phenylenediamine, only mono-Schiff bases were obtained, possi-
bly because the benzene ring connected with the carbonyl group
possesses a stronger steric hindrance effect than the H atom con-
nected with the carbonyl and the two –NH2 radicals in phenylene-
diamine molecules are too short. Thus we selected longer
polyamines such as diethylenetriamine and triethylenetetramine
to condense with 1-aryl-3-methyl-4-benzoyl-5-pyrazolones so as
to yield bis-Schiff bases with salen-like configuration [22,23]. Sim-
ilarly, Fredy et al. [15] and Fabio et al. [16] separately synthesized
some bis-Schiff bases from pyrazolone and some diamines, which,
we suppose, might be related to the large steric hindrance for the
connection of phenyl group with carbonyl. Moreover, we also
found that the substituent R on the phenyl group of pyrazolone
had a significant influence on the yield of Schiff bases target prod-
ucts and relevant intermediates. For example, when pyrazolones
containing phenyl group with electron withdrawing substituents
such as F, Cl, Br and –NO2 were used, target products 1-aryl-3-
methyl-5-pyrazolones were obtained without adjusting pH = 7.0
in a higher yield as compared with the pyrazolones containing
phenyl group with electron donating substituents.
bond of the alkyl group to overlap with the
p electron of the con-
jugated system (the so-called hyperconjugation), but the influence
on the absorption wavelength and absorbance is very small.
Theoretical absorption spectra at the B3LYP level
The absorption wavelengths (k in nm) and oscillator strengths
(f) of the two series of Schiff base which are computed using the
TD-B3LYP method with the cc-pVDZ basis set [19] are listed in Ta-
bles 3 and 4, together with the experimental values. Figs. 4 and 5
illustrate the UV–vis spectra of the Schiff bases measured in
DMF. By comparing with the experimental values in DMF solution,
we can see that theoretical absorption spectra values agree well
with the experimental ones. Each of compounds 1a–5a has a main
absorption peak within 270–340 nm, which is attributed to the
p
?
p⁄ transition. Besides, theoretical calculations give two main
absorption peaks within 240–390 nm attributed to the
p
?
p⁄
transition and n ? p⁄ transition (Table 3); and the theoretical
absorption spectra basically agree well with relevant experimental
results. For example, as shown in Table 3, compound 2a has a
ground state of singlet X1A with an electronic configuration of
(172a)2(173a)2(174a)0 and 101A excited state derived from
169a ? 174a orbitals, while its absorption wavelength 275.04 nm
corresponding to the largest f of 0.1629 is in good agreement with
the experimental value of 275.4 nm. Nevertheless, no absorptions
are experimentally observed in relation to the calculated electron
excitation of 173a ? 179a leading to 201A state at 255.93 nm with
f = 0.2865; and the reasons accounting for this disagreement re-
main unknown. Moreover, compounds 1a–4a (except for 5a) with
similar charge conjugation all have the main calculated absorption
wavelength of 276 nm, which indicates that the substituent R of
their phenyl group has little influence on the absorption wave-
length and absorbance. Similarly, the experimentally measured
absorption wavelengths of compounds 1b–6b also agree well with
the theoretically calculated ones, and the theoretical calculations
give more absorptions than the experimental measurements do
(see Fig. 5 and Table 4). Besides, all b-series compounds (except
for 5b) have the main calculated absorption wavelength of
281 nm, due to their similar charge conjugation (Fig. 5).
Ground-state geometries at the B3LYP level
The molecular structures of the two series of Schiff base are de-
picted in Fig. 1, and the B3LYP-optimized primary geometric
parameters (bond lengths, bond angles, and dihedral angles) of
ground state (S0) are summarized in Tables 1 and 2.
As it can be seen in Fig. 1 and Table 1, the five a-series com-
pounds, except for 4a, have the same matrix of 1a and possess very
similar S0 geometric parameters (bond lengths and bond angles).
Compound 4a has better coplanarity than the other a-series com-
pounds, showing dihedral angles of ꢀ172.3°, 101.7°, 177.9° and
179.2°for C(11)0–N(3)0–C(18)0–C(19)0, C(8)0–C(11)0–C(12)0–C(13)0,
C(7)0–C(8)0–C(11)0–C(12)0, and C(5)0–C(6)0–N(1)0–N(2)0. Similarly,
the ground-state geometric parameters of compounds 1a–5a
(bond lengths and bond angles) are very similar.

174
T. Ren et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 167–175
Table 5
By summarizing the data shown in Figs. 4 and 5 as well as in Ta-
The maximum absorption and maximum emission wavelengths data of compounds
1a–5a.
bles 3 and 4, we can find that the introduction of auxochrome
group like F, Cl, Br and NO2 allows nonbonding electrons to conju-
Compounds
kUV.max (nm)
kFL.max (nm)
gate with
p electrons forming p–p conjugation. As a result, the
electronic scope of operation is enhanced, and the absorption is
shifted towards longer wavelength. Since auxochrome group NO2
has stronger ability to facilitate the above-mentioned p–p conjuga-
tion than F, Cl and Br, as-synthesized Schiff bases with NO2 substi-
tutuent in the phenyl group have a longer UV–vis absorption
wavelength.
1a
2a
3a
4a
5a
276.8
275.4
276.0
278.2
340.0
347.4
348.6
348.2
349.4
348.2
Table 6
Fluorescent spectra
The maximum absorption and maximum emission wavelengths data of compounds
1b–6b.
The fluorescence spectra of these Schiff bases measured at room
temperature in DMF are shown in Figs. 6 and 7; and their maxi-
mum absorption and maximum emission wavelengths data are
listed in Tables 5 and 6. Compounds 1a–5a and 1b–6b excited at
295 nm in DMF solution show the maximum emission peak around
348 nm (Tables 5 and 6). This implies that the substituent R of the
phenyl group has a minor influence on the fluorescence wave-
length but a significant influence on the fluorescence intensity of
these Schiff bases. Namely, electron withdrawing substituents such
as p-Cl and p-F cause a slight red-shift of the fluorescent spectra
Compounds
kUV.max (nm)
kFL.max (nm)
1b
2b
3b
4b
5b
6b
276.8
276.0
284.0
287.0
340.6
281.0
348.2
348.6
348.6
348.6
347.8
349.0
and an increase of the fluorescence intensity, while electron donat-
ing substituent like p-CH3 reduces the fluorescence intensity. Spe-
cifically, the increase of the polyamine chain has a minor influence
on the fluorescence wavelength and intensity of these Schiff bases
(Tables 5 and 6), which may be largely due to the increase of the
conjugated system and the decrease of the molecular planarity.
1800
1600
1400
Conclusions
1a
2a
1200
3a
4a
5a
In summary, two series of novel bis-Schiff base have been suc-
cessfully synthesized using 1-aryl-3-methyl-4-benzoyl-5-pyrazo-
lones and various polyamines as the starting materials. UV–vis
absorption spectra and fluorescent spectra of these Schiff bases
have been measured. The equilibrium geometries and vibrational
frequencies of the two series of bis-Schiff base in their ground state
have been determined by B3LYP method with the 6-31G(d) basis
set, and their absorption spectra have been estimated using the
TD-B3LYP method and cc-pVDZ basis set. It has been found that
all of these bis-Schiff bases show a noticeable absorption peak
1000
800
600
400
200
0
300
350
400
450
500
550
within 270–340 nm and
a maximum emission peak around
Wavelength / (nm)
348 nm. The fluorescent properties of the Schiff bases are closely
related to their molecular structure.
Fig. 6. The emission spectra of 1a–5a.
Acknowledgements
1800
The authors gratefully thank the Science and Technology
Department of Hunan province (Project of Science and Technology
Promotion Plan, Grant No. 2011FJ4169) and the Education Depart-
ment of Hunan Province (Science Research Project, Grant No.
10C0499) for financial support.
1600
1400
1200
1000
800
600
400
200
0
1b
2b
3b
4b
5b
6b
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