The synthesis, characterization and optical properties of novel, substituted, pyrazoly 1,3,4-oxadiazole derivatives

Article abstract of DOI:10.1016/j.dyepig.2009.11.003

A series of novel substituted pyrazoly 1,3,4-oxadiazole derivatives were synthesized by the reaction of substituted pyrazole-5-carbohydrazide with substituted benzoic acid in the presence of phosphorus oxychloride. The compounds were characterised using I

Full text of DOI:10.1016/j.dyepig.2009.11.003

Dyes and Pigments 86 (2010) 25e31
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The synthesis, characterization and optical properties of novel, substituted,
pyrazoly 1,3,4-oxadiazole derivatives
,
b
a
a
a
a
Hong-Shui Lv a, Bao-Xiang Zhao a , Ji-Kun Li , Yong Xia , Song Lian , Wei-Yong Liu , Zhong-Liang Gong
*
a Institute of Organic Chemistry, School of Chemistry and Chemical Engineering, Shandong University, 27# Shanda Nanlu, Jinan 250100, Shandong, PR China
b Department of Materials Science and Chemical Engineering, Taishan University, Taian 271021, Shandong, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 July 2009
Received in revised form
6 November 2009
Accepted 12 November 2009
Available online 24 November 2009
A series of novel substituted pyrazoly 1,3,4-oxadiazole derivatives were synthesized by the reaction of
substituted pyrazole-5-carbohydrazide with substituted benzoic acid in the presence of phosphorus
oxychloride. The compounds were characterised using IR, 1H NMR and HRMS and X-ray diffraction
analysis. The absorption and fluorescence characteristics of the compounds were investigated in
dichloromethane. The compounds displayed similar absorption, ranging from 267 to 281 nm with
a strong absorption band occurring at w275 nm. Correlation of the absorption spectra and fluorescence
characteristics of the pyrazoly 1,3,4-oxadiazole derivatives with substituent effects on the benzene rings,
revealed that a methoxy and a bromine group attached to the benzene ring markedly influenced
maximum emission.
Keywords:
1,3,4-Oxadiazole
Synthesis
Ó 2009 Elsevier Ltd. All rights reserved.
Characterization
X-ray
UV absorption
Fluorescence
1. Introduction
This paper concerns the design, synthesis, structural character-
ization and fluorescence properties of novel compounds with
1,3,4-Oxadiazole derivatives are highly attractive compounds for
the development of materials for organic electroluminescent (EL)
devices since these compounds possess high electron-accepting
properties and display strong fluorescence with high quantum yield
[1], as exemplified by 2,5-diphenyl-1,3,4-oxadiazole and 2,5-di-2-
naphthyl-1,3,4-oxadiazole, for which quantum yields of 0.80 and 0.85
in cyclohexane solution, respectively, were reported [2]. Thus,
compounds involving 1,3,4-oxadiazole rings have been used as elec-
tron-transporting materials and emitters in organic EL devices [3e5].
Recently, 1,3,4-oxadiazole derivatives have aroused considerable
interests in the area of organic light-emitting diodes (OLEDs) [6e9].
Oxadiazole fragments have also been connected to classical
chelating ligands (such as bipyridines) in luminescent complexes,
to obtain multifunctional (emitting and charge transporting)
molecular species [10e17]. Furthermore, substituted 1,3,4-oxadia-
zole derivatives also have been reported to show a broad spectrum
of biological activity including anticancer effects [18,19]. In recent
years, the application of 1,3,4-oxadiazoles consisting of five-
membered heterocyclic have been described [20e24].
potential bioactivity in order to investigate the localization of small
molecules in cells or the interaction of small molecules with proteins.
This work describes the synthesis, characterization and optical
properties of novel, substituted pyrazoly 1,3,4-oxadiazole derivatives.
2. Experimental
2.1. General
Thin-layer chromatography (TLC) was conducted on silica gel 60
F254 plates (Merck KGaA). 1H NMR spectra were recorded on
a Bruker Avance 400 (400 MHz) spectrometer, using CDCl3 as
solvent and tetramethylsilane (TMS) as internal standard. Melting
points were determined on an XD-4 digital micro melting point
apparatus. IR spectra were recorded with an IR spectrophotometer
VERTEX 70 FT-IR (Bruker Optics). HRMS spectra were recorded on
a Q-TOF6510 spectrograph (Agilent). UVeVis spectra were recorded
on a U-4100 (Hitachi). Fluorescent measurements were recorded
on a PerkineElmer LS-55 luminescence spectrophotometer.
2.2. Synthesis
The synthetic approach for the preparation of substituted
pyrazoly 1,3,4-oxadiazole derivatives is shown in Fig. 1. To a stirred
* Corresponding author. Tel.: þ86 531 88366425; fax: þ86 531 88564464.
E-mail address: bxzhao@sdu.edu.cn (B.-X. Zhao).
0143-7208/$ e see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2009.11.003

26
H.-S. Lv et al. / Dyes and Pigments 86 (2010) 25e31
Fig. 1. Synthesis of substituted pyraxzoly 1,3,4-oxadiazole derivatives.
solution of compound 1 (1 mmol) in methanol (5 ml), 80%
hydrazine monohydrate (1.2 ml) was added. The reaction mixture
was maintained under reflux for 1e5 h, until TLC indicated the
end of reaction. After this time, the reaction mixture was cooled
to room temperature and left overnight, the ensuing solid mate-
rial being was collected by filtration. The solid was recrystallized
from ethanol to afford compound 2 in 72e93% yields. A solution
of compound 2 (1 mmol) and substituted benzoic acid (1 mmol)
in freshly distilled POCl3 (caution: Reacts violently with water;
incompatible with many metals, alcohols, amines, phenol, DMSO,
strong bases) (5 ml) was refluxed for 6e12 h. Excess POCl3 was
distilled off and the residue was poured into iced water. The
precipitate was filtered, washed with water, dried and recrystal-
lized from ethanol to give compound 3 in 13e26%.
2.2.4. 2-(1-(4-Tert-butylbenzyl)-3-(4-chlorophenyl)-1H-pyrazol-5-
yl)-5-phenyl-1,3,4-oxadiazole (3d)
Yield 18%, Yellow solid, mp 183e185 ꢀC; IR (KBr)
n :
/cmꢁ1
1614 (C]C), 1549 (C]N), 1448 (NeN), 1289 (CeOeC); 1H NMR
(400 MHz, CDCl3) : 1.26 (s, 9H, CH3), 5.96 (s, 2H, CH2), 7.22
d
(s, 1H, ArH), 7.30e7.44 (m, 6H, ArH), 7.51e7.61 (m, 3H, ArH), 7.83
(d, J ¼ 8.3 Hz, 2H, ArH), 8.10 (dd, J1 ¼ 7.9 Hz, J2 ¼ 1.4 Hz, 2H,
ArH); HRMS calcd for [M þ H]þ C28H26ClN4O: 469.1795; found:
469.1787.
2.2.5. 2-(3-Bromophenyl)-5-(1-(4-tert-butylbenzyl)-3-(4-
chlorophenyl)-1H-pyrazol-5-yl)-1,3,4-oxadiazole (3e)
Yield 18%, white solid, mp 199e201 ꢀC; IR (KBr) /cmꢁ1: 1613
n
(C]C), 1545 (C]N), 1470 (NeN), 1290 (CeOeC); 1H NMR
(400 MHz, CDCl3) : 1.26 (s, 9H, CH3), 5.95 (s, 2H, CH2), 7.23 (s, 1H,
d
2.2.1. 2-(1-Benzyl-3-phenyl-1H-pyrazol-5-yl)-5-phenyl-1,3,4-
ArH), 7.32 (d, J ¼ 8.5 Hz, 2H, ArH), 7.36 (d, J ¼ 8.5 Hz, 2H, ArH),
7.39e7.44 (m, 3H, ArH), 7.70 (d, J ¼ 8.3 Hz, 1H, ArH), 7.83 (d,
J ¼ 8.4 Hz, 2H, ArH), 8.05 (d, J ¼ 8.0 Hz, 1H, ArH), 8.23 (t, J ¼ 1.6 Hz,
1H, ArH); HRMS calcd for [M þ H]þ C28H25BrClN4O: 547.0900;
found: 547.0898.
oxadiazole (3a)
Yield 18%, white solid, mp 164e166 ꢀC; IR (KBr) /cmꢁ1: 1611
n
(C]C), 1547 (C]N), 1469 (NeN), 1256 (CeOeC); 1H NMR
(400 MHz, CDCl3) : 6.00 (s, 2H, CH2), 7.20e7.32 (m, 4H, ArH),
d
7.34e7.46 (m, 5H, ArH), 7.50e7.59 (m, 3H, ArH), 7.89 (d, J ¼ 7.4 Hz,
2H, ArH), 8.10 (d, J ¼ 7.9 Hz, 2H, ArH); HRMS calcd for [M þ H]þ
C24H19N4O: 379.1559; found: 379.1596.
2.2.6. 2-(1-(4-Tert-butylbenzyl)-3-(4-chlorophenyl)-1H-pyrazol-5-
yl)-5-p-tolyl-1,3,4-oxadiazole (3f)
Yield 19%, yellow solid, mp 149e151 ꢀC; IR (KBr) /cmꢁ1
n :
2.2.2. 2-(1-(4-Tert-butylbenzyl)-3-phenyl-1H-pyrazol-5-yl)-5-
1612 (C]C), 1555 (C]N), 1472 (NeN), 1289 (CeOeC); 1H NMR
(400 MHz, CDCl3) : 1.26 (s, 9H, CH3), 2.45 (s, 3H, CH3), 5.96 (s,
phenyl-1,3,4-oxadiazole (3b)
d
Yield 16%, white solid, mp 159e161 ꢀC; IR (KBr)
n
/cmꢁ1: 1615
2H, CH2), 7.20 (s, 1H, ArH), 7.31 (d, J ¼ 8.3 Hz, 2H, ArH), 7.34
(d, J ¼ 8.4 Hz, 2H, ArH), 7.37 (d, J ¼ 8.4 Hz, 2H, ArH), 7.41 (d,
J ¼ 8.5 Hz, 2H, ArH), 7.82 (d, J ¼ 8.5 Hz, 2H, ArH), 7.99 (d,
J ¼ 8.3 Hz, 2H, ArH); HRMS calcd for [M þ H]þ C29H28ClN4O:
483.1952; found: 483.1934.
(C]C), 1548 (C]N), 1473 (NeN), 1307 (CeOeC); 1H NMR
(400 MHz, CDCl3) : 1.26 (s, 9H, CH3), 5.97 (s, 2H, CH2), 7.25 (s, 1H,
d
ArH), 7.28e7.40 (m, 5H, ArH), 7.44 (t, J ¼ 7.5 Hz, 2H, ArH), 7.49e7.61
(m, 3H, ArH), 7.90 (d, J ¼ 7.5 Hz, 2H, ArH), 8.10 (d, J ¼ 6.9 Hz, 2H,
ArH); HRMS calcd for [M þ H]þ C28H27N4O: 435.2185; found:
435.2477.
2.2.7. 2-(3-(4-Chlorophenyl)-1-((6-chloropyridin-3-yl)methyl)-1H-
pyrazol-5-yl)-5-phenyl-1,3,4-oxadiazole (3g)
2.2.3. 2-(1-Benzyl-3-(4-chlorophenyl)-1H-pyrazol-5-yl)-5-phenyl-
Yield 14%, white solid, mp 200e201 ꢀC; IR (KBr) /cmꢁ1: 1617
n
1,3,4-oxadiazole (3c)
(C]C), 1553 (C]N), 1472 (NeN), 1289 (CeOeC); 1H NMR
(300 MHz, CDCl3) : 6.00 (s, 2H, CH2), 7.23 (s, 1H, ArH), 7.27 (d,
Yield 22%, white solid, mp 159e160 ꢀC; IR (KBr)
n
/cmꢁ1: 1611
d
(C]C),1551 (C]N),1473 (NeN),1257 (CeOeC); 1H NMR (400 MHz,
CDCl3) : 6.00 (s, 2H, CH2), 7.23(s, 1H, ArH), 7.24e7.35 (m, 3H, ArH),
J ¼ 8.7 Hz, 1H, ArH), 7.43 (d, J ¼ 8.7 Hz, 2H, ArH), 7.52e7.66 (m,
3H, ArH), 7.80 (d, J ¼ 8.4 Hz, 1H, ArH), 7.81 (d, J ¼ 8.4 Hz, 2H,
ArH), 8.12 (d, J ¼ 8.1 Hz, 2H, ArH), 8.56 (d, J ¼ 2.1 Hz, 1H, ArH);
HRMS calcd for [M þ H]þ C23H16Cl2N5O: 448.0732; found:
448.0733.
d
7.42 (d, J ¼ 7.1 Hz, 4H, ArH), 7.50e7.63 (m, 3H, ArH), 7.83 (d,
J ¼ 8.0 Hz, 2H, ArH), 8.10 (d, J ¼ 7.2 Hz, 2H, ArH); HRMS calcd for
[M þ H]þ C24H18ClN4O: 413.1169; found: 413.1163.

H.-S. Lv et al. / Dyes and Pigments 86 (2010) 25e31
27
2.2.8. 2-(3-Bromophenyl)-5-(3-(4-chlorophenyl)-1-((6-
full-matrix least-squares techniques implemented in the SHELXTL-
97 crystallographic software. The non-hydrogen atoms were
refined anisotropically. The hydrogen atoms bound to carbon were
located by geometrical calculations, with their position and
thermal parameters being fixed during the structure refinement.
The final refinement converged at R1 ¼ 0.0721, wR2 ¼ 0.1954 for 3e
and R1 ¼ 0.0601, wR2 ¼ 0.1261 for 3f.
chloropyridin-3-yl)methyl)-1H-pyrazol-5-yl)-1,3,4-oxadiazole (3h)
Yield 19%, white solid, mp 228e230 ꢀC; IR (KBr) /cmꢁ1: 1617
n
(C]C), 1567 (C]N), 1463 (NeN), 1306 (CeOeC); H NMR (400 MHz,
CDCl3) : H NMR (400 MHz, CDCl3) : 6.00 (s, 2H, CH2), 7.25 (s, 1H,
d
d
ArH), 7.27 (d, J ¼ 8.0 Hz, 1H, ArH), 7.43 (d, J ¼ 8.6 Hz, 2H, ArH), 7.45
(d, J ¼ 8.0 Hz,1H, ArH), 7.73 (d, J ¼ 7.8 Hz,1H, ArH), 7.80 (t, J ¼ 7.8 Hz,
1H, ArH), 7.81 (d, J ¼ 8.6 Hz, 2H, ArH), 8.08 (d, J ¼ 7.8 Hz, 1H, ArH),
8.25 (t, J ¼ 1.6 Hz,1H, ArH), 8.55 (d, J ¼ 2.3 Hz,1H, ArH); HRMS calcd
for [M þ H]þ C23H15BrCl2N5O: 525.9837; found: 525.9847.
3. Results and discussion
3.1. Synthesis
2.2.9. 2-(3-(4-Chlorophenyl)-1-((6-chloropyridin-3-yl)methyl)-1H-
pyrazol-5-yl)-5-p-tolyl-1,3,4-oxadiazole (3i)
The compound 1 reacted with hydrazine hydrate to afford
compound 2 in good yield according to our previous reported
method [25]. The reaction of compound 2 and substituted benzoic
acid in the presence of phosphorus oxychloride gave desired
compound 3. After work-up and the recrystallization from suitable
solvent pure products were obtained although the yields were
lower.
Yield 13%, white solid, mp 199e201 ꢀC; IR (KBr) /cmꢁ1: 1613
n
(C]C), 1552 (C]N), 1470 (NeN), 1290 (CeOeC); 1H NMR
(300 MHz, CDCl3) : 2.46 (s, 3H, CH3), 5.99 (s, 2H, CH2), 7.22 (s, 1H,
d
ArH), 7.27 (d, J ¼ 8.1 Hz, 1H, ArH), 7.36 (d, J ¼ 7.8 Hz, 2H, ArH), 7.42
(d, J ¼ 8.7 Hz, 2H, ArH), 7.79 (d, J ¼ 8.7 Hz, 1H, ArH), 7.80 (d,
J ¼ 8.4 Hz, 2H, ArH), 8.00 (d, J ¼ 8.1 Hz, 2H, ArH), 8.55 (d, J ¼ 2.1 Hz,
1H, ArH); HRMS calcd for [M þ H]þ C24H18Cl2N5O: 462.0888; found:
462.0898.
3.2. Structure characterization
2.2.10. 2-(1-(4-Tert-butylbenzyl)-3-(4-methoxyphenyl)-1H-
The assumed structures of compounds 3ael were proved by IR,
1H NMR and HRMS spectra. For example compound 3f, obtained as
yellow crystal, gave a [M þ H]-ion peak at m/z 483.1934 in the
pyrazol-5-yl)-5-phenyl-1,3,4-oxadiazole (3j)
Yield 26%, white solid, mp 176e178 ꢀC; IR (KBr) /cmꢁ1: 1614
n
(C]C), 1549 (C]N), 1481 (NeN), 1251 (CeOeC); 1H NMR
(400 MHz, CDCl3) : 1.26 (s, 9H, CH3), 3.86 (s, 3H, OCH3), 5.95 (s, 2H,
d
CH2), 6.97 (d, J ¼ 7.9 Hz, 2H, ArH), 7.17 (s,1H, ArH), 7.30 (d, J ¼ 7.3 Hz,
2H, ArH), 7.36 (d, J ¼ 7.3 Hz, 2H, ArH), 7.47e7.62 (m, 3H, ArH), 7.82
(d, J ¼ 7.9 Hz, 2H, ArH), 8.10 (d, J ¼ 6.4 Hz, 2H, ArH); HRMS calcd for
[M þ H]þ C29H29N4O2: 465.2291; found: 465.2286.
Table 1
Summary of crystallographic data and structure refinement details for 3e and 3f.
3e
3f
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
C28H24BrClN4O
547.87
293(2) K
0.71073 Å
Monoclinic
P2(1)/n
C29H27ClN4O
483.00
293(2) K
0.71073 Å
Triclinic
2.2.11. 2-(3-Bromophenyl)-5-(1-(4-tert-butylbenzyl)-3-(4-
methoxyphenyl)-1H-pyrazol-5-yl)-1,3,4-oxadiazole (3k)
Yield 14%, yellow solid, mp 175e177 ꢀC; IR (KBr) /cmꢁ1: 1611
n
(C]C), 1544 (C]N), 1478 (NeN), 1288 (CeOeC); 1H NMR
(400 MHz, CDCl3) : 1.26 (s, 9H, CH3), 3.86 (s, 3H, OCH3), 5.95 (s, 2H,
Pꢁ 1
d
Unit cell dimensions
a ¼ 8.405(3)
a ¼ 10.8995(15) Å,
CH2), 6.98 (d, J ¼ 8.7 Hz, 2H, ArH), 7.19 (s, 1H, ArH), 7.31 (d,
J ¼ 8.5 Hz, 2H, ArH), 7.35 (d, J ¼ 8.5 Hz, 2H, ArH), 7.42 (t, J ¼ 7.9 Hz,
1H, ArH), 7.70 (d, J ¼ 7.9 Hz, 1H, ArH), 7.83 (d, J ¼ 8.7 Hz, 2H, ArH),
8.05 (d, J ¼ 7.9 Hz, 1H, ArH), 8.23 (s, 1H, ArH); HRMS calcd for
[M þ H]þ C29H28BrN4O2: 543.1396; found: 543.1399.
Å,
a
¼ 90ꢀ
a
¼ 74.050(3)ꢀ
b ¼ 15.874(6) Å,
b ¼ 10.9450(14) Å,
b
¼ 96.35(8)ꢀ
b
¼ 85.09(3)ꢀ
c ¼ 19.656(8)
c ¼ 12.2368(16) Å,
Å,
g
¼ 90ꢀ
g
¼ 65.13(2)ꢀ
Volume
Z
2606.4(18) A3
4
1272.7(3) A3
2
1.396 Mg/m3
1.260 Mg/m3
0.18 mmꢁ1
508
2.2.12. 2-(1-(4-Tert-butylbenzyl)-3-(4-methoxyphenyl)-1H-
Calculated density
Absorption coefficient 1.70 mmꢁ1
pyrazol-5-yl)-5-p-tolyl-1,3,4-oxadiazole (3l)
Yield 14%, yellow solid, mp 169e171 ꢀC; IR (KBr) /cmꢁ1: 1613
n
F(000)
Crystal size
1120
0.16 ꢂ 0.15 ꢂ 0.12 mm
0.18 ꢂ 0.15 ꢂ 0.12 mm
(C]C), 1555 (C]N), 1480 (NeN), 1288 (CeOeC); 1H NMR
(400 MHz, CDCl3) : 1.26 (s, 9H, CH3), 2.44 (s, 3H, CH3), 3.86 (s, 3H,
q
range for data
collection
1.65e25.05ꢀ
1.73e25.05ꢀ
d
Limiting indices
ꢁ9ꢃh ꢃ 9, ꢁ18 ꢃ k ꢃ 17, ꢁ12 ꢃ h ꢃ 12, ꢁ9ꢃk ꢃ 13,
OCH3), 5.94 (s, 2H, CH2), 6.97 (d, J ¼ 8.7 Hz, 2H, ArH), 7.15 (s, 1H,
ArH), 7.30 (d, J ¼ 8.4 Hz, 2H, ArH), 7.32 (d, J ¼ 8.6 Hz, 2H, ArH), 7.35
(d, J ¼ 8.4 Hz, 2H, ArH), 7.81 (d, J ¼ 8.7 Hz, 2H, ArH), 7.98 (d,
J ¼ 8.6 Hz, 2H, ArH); HRMS calcd for [M þ H]þ C30H31N4O2:
479.2447; found: 479.2689.
ꢁ18 ꢃ l ꢃ 23
ꢁ12 ꢃ l ꢃ 14
6797/4481
[R(int) ¼ 0.033]
99.5
Reflections collected/ 13 128/4587
unique
[R(int) ¼ 0.079]
Completeness to
99.4%
q
¼ 25.05ꢀ
Absorption correction None
None
Max. and min.
transmission
0.8213 and 0.772
0.9788 and 0.9685
2.3. X-ray crystallography
Refinement method
Full-matrix
Full-matrix least-
squares on F2
4481/147/351
least-squares on F2
4587/570/317
Crystals of compounds 3e and 3f suitable for X-ray diffraction
were obtained by slow evaporation of a solution of the solid in ethyl
acetate at room temperature for 7 days, respectively. The crystals
with approximate dimensions of 0.16 mm ꢂ 0.15 mm ꢂ 0.12 mm for
3e and 0.18 mm ꢂ 0.15 mm ꢂ 0.12 mm for 3f were mounted on
Data/restraints/
parameters
Goodness-of-fit on F2 1.024
1.001
Final R indices
[I > 2 (I)]
R1 ¼ 0.0721,
R1 ¼ 0.0601,
wR2 ¼ 0.1261
R1 ¼ 0.1414,
wR2 ¼ 0.1689
0.197 and
s
wR2 ¼ 0.1954
R1 ¼ 0.1480,
wR2 ¼ 0.2523
0.526 and
a Bruker Smart Apex II CCD equipped with a graphite mono-
R indices (all data)
ꢀ
chromated MoK
a
radiation (
l
¼ 0.71073 A) by using
f and u scan
Largest diff. peak
and hole
modes and the data were collected at 293(2) K. The structures
ꢁ0.573 e. Åꢁ3
ꢁ0.199 e. Åꢁ3
of the two crystals were solved by direct methods and refined by

28
H.-S. Lv et al. / Dyes and Pigments 86 (2010) 25e31
at
d
1.26 (9H, 3 ꢂ CH3), 2.45 (3H, CH3), 5.96 (2H, CH2), and 7.20 (1H,
pyrazole moiety) which were readily assigned to the hydrogen of
tert-butyl, methyl, methylene and pyrazole moiety, respectively.
Moreover, compound 3f showed six doublet peaks at
d 7.31 (2H,
J ¼ 8.3 Hz), 7.34 (2H, J ¼ 8.4 Hz), 7.37 (2H, J ¼ 8.4 Hz), 7.41 (2H,
J ¼ 8.5 Hz), 7.82 (2H, J ¼ 8.5 Hz), 7.99 (2H, J ¼ 8.3 Hz) assigned to the
protons on the three benzene ring, respectively. All other signals
are consistent with the structure of 3f.
3.3. Crystal structure
The spatial structures of compounds 3e and 3f were determined
by using X-ray diffraction analysis. A summary of crystallographic
data collection parameters and refinement parameters for 3e and
3f are compiled in Table 1.
The single crystal structure and atomic numbering chosen for 3e
are shown in Fig. 2. The CeC distances of phenyl ring (C11e16) are
ꢀ
ꢀ
quasi equal and close to 1.38 A except C11eC12 (1.391 A) and
ꢀ
C11eC16 (1.366 A), this may be because the interaction between
the pyrazole ring and the C11 atom through C10 atom. The CeC
distances of C4 phenyl ring are quasi equal except C3eC4 and
C4eC5 and this is because the strong interaction between the
pyrazole ring and the C4 atom makes the C4 atom close to the
pyrazole ring. The CeC distances of C23 phenyl ring vary from
ꢀ
ꢀ
ꢀ
1.351 A to 1.407 A. The bond length C9eC21 (1.449 A) is similar to N,
N-Dimethyl-4-[5-(5-methyl-1-phenyl-1H-pyrazol-4-yl)-1,3,4-oxa-
Fig. 2. The molecular structure of compound 3e, with displacement ellipsoids drawn
ꢀ
diazol-2-yl]aniline(C8eC11 1.443 A) [26]. The dihedral angles
at the 50% probability level and H atoms omitted.
between the pyrazole ring and the C4 phenyl or 1,3,4-oxadiazole
ring are 6.72ꢀ and 8.61ꢀ, respectively. The dihedral angle between
the 1,3,4-oxadiazole ring and the C23 phenyl ring is 5.78ꢀ. All the
dihedral angles above are so small that the four rings in 3e is nearly
in the same plane and this coplanar conformation provides a large
conjugated system which makes transporting of electrons easy. In
contrast, the dihedral angle between pyrazole ring and the C11
HRESIMS, in accord with the molecular formula C29H28ClN4O. The
IR spectra of compound 3f showed the characteristic absorption
bands at 1612 (C]C), 1555 (C]N), 1472 (NeN), 1289 (CeOeC). The
1H NMR spectra (CDCl3) of compound 3f revealed four singlet peaks
Fig. 3. The crystal packing of compound 3e.

H.-S. Lv et al. / Dyes and Pigments 86 (2010) 25e31
29
Fig. 6. The UVevis spectra of the compounds 3ael in dichloromethane (2 ꢂ 10ꢁ5 M).
Fig. 4. The molecular structure of compound 3f, with displacement ellipsoids drawn at
the 50% probability level and H atoms omitted.
3.4. Absorption spectral characteristics of the compounds 3ael
The UVevis spectra of the compounds 3ael measured in
dichloromethane solutions are shown in Fig. 6 and the optical
characteristics are summarized in Table 2. As shown in Fig. 6
compounds 3ael display similar absorptions ranging from 267 to
phenyl ring is 80.71 and it means that C11 phenyl ring does not
participate in conjugation system. The crystal packing of 3e is
illustrated in Fig. 3.
The single crystal structure and atomic numbering chosen for 3f
are shown in Fig. 4 and the packing structure of 3f is illustrated in
Fig. 5. The CeC distances and the dihedral angles in 3f are very
similar to 3e. It would be mentioned that the tert-butyl group
exhibits rotational disorder between two orientations in a 0.61:0.39
ratio in 3f.
281 nm that are attributed to pe
p* transition of conjugate system
and the strong absorption band at about 275 nm (Table 2). It is
noticed that the substituent has definite effects on the absorption
bands although it is small. The maximum absorption of compound
3c with electron-withdrawing groups (Cl) result in a blue shift
(4 nm) contrasting compound 3a. Similarly, comparing compound
Fig. 5. The crystal packing of compound 3f.

30
H.-S. Lv et al. / Dyes and Pigments 86 (2010) 25e31
Table 2
bonded to benzene ring influence maximal emission bands much
more.
The optical characteristics of the compounds 3ael in dichloromethane.
Compound
lmax
lex
3max
(molꢁ1 cmꢁ1
Fmax
(nm)
Stokes shift
(nm)
(nm)
(nm)
)
4. Conclusion
3a
3b
3c
3d
3e
3f
3g
3h
3i
271
271
267
274
274
275
275
274
275
273
275
281
278
276
280
280
280
286
275
277
277
281
280
290
34 665
47 060
34 755
35 685
44 175
26 585
44 020
20 180
38 635
34 560
35 935
39 725
369
366
364
360
375
362
360
372
356
406
422
401
91
90
84
80
95
76
85
95
79
A series of novel substituted pyrazoly 1,3,4-oxadiazole deriva-
tives has been synthesized by the reaction of substituted pyrazole-
5-carbohydrazide with substituted benzoic acid in the presence of
phosphorus oxychloride. The structures of compounds obtained
1
were determined by IR, H NMR and HRMS spectra, typically, the
spatial structures of compounds 3e and 3f were determined by
using X-ray diffraction analysis. Absorption and fluorescence
spectral characteristics of the compounds were investigated in
dichloromethane by UVevis absorption and emission spectra. The
absorption spectra and fluorescence characteristics were correlated
with substituent on benzene rings.
3j
3k
3l
125
147
120
3f and 3l, electron-withdrawing groups (Cl) result in a blue shift
(6 nm) with contrast to an electron-donating group (MeO).
Compounds 3dei have almost same maximum absorption
(274e275 nm) that means substituent R2 and R3 do not influence
the absorption.
5. Supplementary materials
CCDC 752716 and 752717 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, by emailing data_
request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystal-
lographic Data Centre, 12, Union Road, Cambridge CB21EZ, UK;
fax: þ44 1223 336033.
3.5. Fluorescence spectral characteristics
Fig. 7 presents the emission spectra of compounds 3ael in
dichloromethane solution (2 ꢂ 10ꢁ6 M). Their excitation wave-
lengths are shown in Table 2. It can be found that their intensity of
fluorescence and maximal emission bands are dependent on the
groups bonded to benzene rings. Maximal emission bands of
compounds 3ael display ranging from 356 to 422 nm. Maximal
emission bands of 3e, 3h and 3k, in which bromine bonded to
benzene ring, are red-shifted 13, 16 and 21 nm, respectively,
comparing to 3f, 3i and 3l, in which methyl group bonded to
benzene ring. Moreover, maximal emission wavelength of 3k is
red-shifted 47 nm comparing to 3e due to the effect of methoxyl
group in benzene ring; similarly, maximal emission wavelength of
3l is red-shifted 39 nm comparing to 3f. Stocks shift of compounds
3ael are also dependent on the groups bonded to benzene rings in
a similar manner. Taken together, methoxyl group and bromine
Acknowledgement
This study was supported by the National Natural Science
Foundation
of
China
(20972088)
and
973
Program
(2010CB933504).
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