The synthesis, characterization and optical properties of novel 5-(3-aryl-1H-pyrazol-5-yl)-2-(3-butyl-1-chloroimidazo[1,5-a]pyridin-7-yl)-1,3, 4-oxadiazole

Article abstract of DOI:10.1016/j.saa.2013.12.016

A series of novel 5-(3-aryl-1H-pyrazol-5-yl)-2-(3-butyl-1-chloroimidazo[1, 5-a]- pyridin-7-yl)-1,3,4-oxadiazole derivatives has been synthesized from 3-butyl-1-chloroimidazo[1,5-a]pyridine-7-carboxylic acid and ethyl 3-aryl-1H-pyrazole-5-carboxylate. The

Full text of DOI:10.1016/j.saa.2013.12.016

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 336–341
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
The synthesis, characterization and optical properties of novel
5-(3-aryl-1H-pyrazol-5-yl)-2-(3-butyl-1-chloroimidazo[1,5-a]
pyridin-7-yl)-1,3,4-oxadiazole
Yan Qing Ge a,b, Jiong Jia a, Teng Wang a, Hong Wei Sun c, Gui Yun Duan b, Jian Wu Wang a,
⇑
a School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, PR China
b School of Chemical Engineering, Taishan Medical University, Taian, Shandong 271016, PR China
c School of Chemistry, Nankai University, Tianjin 300071, PR China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
ꢀ
Novel 1,3,4-oxadiazole derivatives
were prepared and fully
characterized.
UV–vis absorption and fluorescence
spectroscopy of all compounds were
measured.
The minimized structures, the
molecular orbital (HOMO and LUMO)
energies and the orbital maps of
compound 5a–g were calculated.
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel 5-(3-aryl-1H-pyrazol-5-yl)-2-(3-butyl-1-chloroimidazo[1,5-a]- pyridin-7-yl)-1,3,4-oxa-
diazole derivatives has been synthesized from 3-butyl-1-chloroimidazo[1,5-a]pyridine-7-carboxylic acid
and ethyl 3-aryl-1H-pyrazole-5-carboxylate. The compounds were characterized using IR, 1H NMR, HRMS
and UV–vis absorption. The fluorescence spectral characteristics of the compounds in dichloromethane
were investigated. The results showed that absorption kmax and emission kmax was less correlated with
substituent groups on N-1 position of pyrazole moiety and para position of benzene moiety. The calcu-
lated molecular orbital correlates well with their absorption.
Received 5 December 2012
Received in revised form 25 November 2013
Accepted 5 December 2013
Available online 28 December 2013
Keywords:
Pyrazole
Imidazo[1,5-a]pyridine
1,3,4-Oxadiazole
UV absorption
Fluorescence
Ó 2013 Elsevier B.V. All rights reserved.
Introduction
Pyrazole and Imidazo[1,5-a]pyridine unit are important core
structures in a number of natural products. Many pyrazole deriva-
1,3,4-Oxadiazoles have attracted intense attention for their
potential use in organic electronics because either polymers or
small molecules of this kind have been widely used as electron-
transporting materials or electroluminescence (EL) materials in or-
ganic light emitting diodes (OLEDs) [1–10]. In addition, electron
transporting 1,3,4-oxadiazole moiety has been connected to many
chelating ligands to obtain luminescent complexes with more new
functions [11–14].
tives are known to exhibit a wide range of biological properties such
as anti-hyperglycemic, analgesic, anti-inflammatory, anti-pyretic,
anti-bacterial, antifungal, anti-hypoglycemic, sedative-hypnotic
activity, antitumor and anticoagulant activity [15,16]. Imi-
dazo[1,5-a]pyridines derivatives have also been reported to show
broad spectrum of biological activities including cardiotonic agents,
aromatase inhibitors in estrogen-dependent diseases, thromboxane
A2 synthetase inhibitors, and angiotensin II receptor antagonists
[17,18]. They also have potential applications in organic light-emit-
ting diodes (OLEDs), in organic thin-layer field effect transistors
(FETs), and as precursors of N-heterocyclic carbenes [19,20].
⇑
Corresponding author. Tel.: +86 531 88362708; fax: +86 531 88564464.
E-mail address: jwwang@sdu.edu.cn (J.W. Wang).
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.12.016

Y.Q. Ge et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 336–341
337
The design and synthesis of fluorescent small molecules with
desirable bioactivities is of considerable current interest in biology
research. Thus, in continuation of our efforts in synthesizing various
bioactive molecules [21–25] and fluorescent small molecules [26–
31] and based on a fragmented approach, we proposed that 1,3,4-
oxadiazole linking imidazo[1,5-a]pyridine and pyrazole might have
interesting bioactivities such as anticancer activity. On the other
distilled off and the residue was poured into iced water. The pre-
cipitate was filtered, washed with water, dried and recrystallized
from ethanol to give compound 5 in 33–46%.
2-(1-Benzyl-3-phenyl-1H-pyrazol-5-yl)-5-(3-butyl-1-
chloroimidazo[1,5-a]pyridin-7-yl)-1,3,4-oxadiazole (5a)
Yellow solid (46% yield): mp 174.8–177.5 °C; 1H NMR
(300 MHz, CDCl3): d 8.05 (s, 1H), 7.91 (m, 2H), 7.77 (d, J = 7.2 Hz,
1H), 7.48–7.26 (m, 10H), 6.98 (m, 2H), 6.00 (s, 2H), 2.98 (t,
J = 7.2 Hz, 2H), 1.85 (m, 2H), 1.46 (m, 2H), 0.98 (t, J = 7.2 Hz, 3H);
hand, three aromatic rings construct
p-conjugation system that
has cause for expecting improvement in UV–vis absorption and
fluorescence spectral characteristics. Herein, we would like to re-
port the synthesis, UV–vis absorption and fluorescence spectral
characteristics of novel 5-(3-aryl-1H-pyrazol-5-yl)-2-(3-butyl-1-
chloroimidazo- [1,5-a]pyridin-7-yl)-1,3,4-oxadiazole derivatives.
IR (KBr)
m = 3073, 2954, 2920, 2851, 1633, 1491, 1457, 1366,
1296 cmÀ1; HRMS: m/z calcd for C29H26ClN6O [M+H]+ 509.1857,
found 509.1863.
2-(3-Butyl-1-chloroimidazo[1,5-a]pyridin-7-yl)-5-(1-(4-nitrobenzyl)-
3-phenyl-1H-pyrazol-5-yl)-1,3,4-oxadiazole (5b)
Experimental
Yellow solid (35% yield): mp 220.8–223.2 °C; 1H NMR (300 MHz,
CDCl3): d 8.16 (d, J = 8.7 Hz, 2H), 8.09 (s, 1H), 7.91 (d, J = 7.2 Hz, 2H),
7.79 (d, J = 7.5 Hz, 1H), 7.55 (d, J = 8.4 Hz, 2H), 7.50–7.40 (m, 3H),
7.36 (s, 1H), 7.28 (m, 1H), 6.11 (s, 2H), 2.98 (t, J = 7.2 Hz, 2H), 1.85
General
All reagents were commercially available and used without fur-
ther purification. Melting points were determined on an XD-4 dig-
ital micro melting point apparatus. 1H NMR spectra were recorded
on a Bruker Avance 300 (300 MHz) spectrometer, using CDCl3 as
solvent and tetramethylsilane (TMS) as internal standard. IR spec-
tra were recorded with an IR spectrophotometer VERTEX 70 FT-IR
(Bruker Optics). HRMS spectra were recorded on a Q-TOF6510 spec-
trograph (Agilent). UV–vis spectra were recorded on a U-4100 (Hit-
achi). Fluorescent measurements were recorded on a Perkin-Elmer
LS-55 luminescence spectrophotometer.
(m, 2H), 1.46 (m, 2H), 0.98 (t, J = 7.2 Hz, 3H); IR (KBr)
m = 3091,
2956, 2868, 1632, 1493, 1473, 1360, 1246 cmÀ1; HRMS: m/z calcd
for C29H25ClN7O3 [M+H]+ 554.1707, found 554.1703.
2-(3-Butyl-1-chloroimidazo[1,5-a]pyridin-7-yl)-5-(1-(4-
fluorobenzyl)-3-phenyl-1H-pyrazol-5-yl)-1,3,4-oxadiazole (5c)
Yellow solid (33% yield): mp 178.3–179.0 °C; 1H NMR
(300 MHz, CDCl3): d 8.11 (s, 1H), 7.91 (m, 3H), 7.46–7.36 (m, 7H),
6.99 (m, 2H), 5.97 (s, 2H), 3.01 (t, J = 7.2 Hz, 2H), 1.89 (m, 2H),
1.48 (m, 2H), 0.99 (t, J = 7.2 Hz, 3H); IR (KBr)
m = 3068, 2957,
Synthesis
2868, 1633, 1494, 1473, 1228 cmÀ1; HRMS: m/z calcd for C29H25-
ClFN6O [M+H]+ 527.1762, found 527.1764.
The synthetic approach for the preparation of substituted 1,3,4-
oxadiazole derivatives is shown in Fig. 1 (Supplementary data).
Compounds 2 and 4a–g were synthesized according to the litera-
ture method [32,33]. A solution of compound 4 (1 mmol) and 3-bu-
tyl-1-chloroimidazo[1,5-a]pyridine-7-carboxylic acid (1 mmol) in
freshly distilled POCl3 (caution: Reacts violently with water;
incompatible with many metals, alcohols, amines, phenol, DMSO,
strong bases) (15 ml) was refluxed for 9–12 h. Excess POCl3 was
2-(3-Butyl-1-chloroimidazo[1,5-a]pyridin-7-yl)-5-(1-(4-
chlorobenzyl)-3-phenyl-1H-pyrazol-5-yl)-1,3,4-oxadiazole (5d)
Yellow solid (41% yield): mp 176.2–177.2 °C; 1H NMR
(300 MHz, CDCl3): d 8.06 (s, 1H), 7.91 (m, 3H), 7.80 (s, 1H), 7.48–
7.28 (m, 8H), 5.96 (s, 2H), 3.00 (t, J = 7.2 Hz, 2H), 1.86 (m, 2H),
1.46 (m, 2H), 0.98 (t, J = 7.2 Hz, 3H); IR (KBr)
m = 3065, 2957,
n
n
n
p
p
p
p
p
Fig. 1. The synthetic route of unsymmetrical 1,3,4-oxadiazole derivatives.

338
Y.Q. Ge et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 336–341
2869, 1635, 1521, 1473, 1345, 1247 cmÀ1; HRMS: m/z calcd for C29-
1.0
0.8
0.6
0.4
0.2
0.0
H25Cl2N6O [M+H]+ 543.1467, found 543.1471.
5a
5b
5c
5d
5e
5f
2-(1-Benzyl-3-p-tolyl-1H-pyrazol-5-yl)-5-(3-butyl-1-
chloroimidazo[1,5-a]pyridin-7-yl)-1,3,4-oxadiazole (5e)
Yellow solid (42% yield): mp 182.8–183.3 °C; 1H NMR
(300 MHz, CDCl3): d 8.06 (s, 1H), 7.80 (m, 3H), 7.41–7.28 (m, 9H),
7.36 (s, 1H), 7.28 (m, 1H), 5.99 (s, 2H), 3.00 (t, J = 7.2 Hz, 2H),
2.40 (s, 3H), 1.85 (m, 2H), 1.46 (m, 2H), 0.98 (t, J = 7.2 Hz, 3H); IR
5g
(KBr)
m = 3066, 2954, 2867, 1633, 1482, 1455, 1345, 1300,
1245 cmÀ1; HRMS: m/z calcd for C30H28ClN6O [M+H]+ 523.2013,
found 523.2009.
2-(3-Butyl-1-chloroimidazo[1,5-a]pyridin-7-yl)-5-(1-(4-nitrobenzyl)-
3-p-tolyl-1H-pyrazol-5-yl)-1,3,4-oxadiazole (5f)
Yellow solid (40% yield): mp 222.7–223.8 °C; 1H NMR
(300 MHz, CDCl3): d 8.16 (d, J = 8.7 Hz, 2H), 8.08 (s, 1H), 7.80 (d,
3H), 7.54 (d, J = 8.7 Hz, 2H), 7.31–7.28 (m, 4H), 6.09 (s, 2H), 2.99
(t, J = 7.2 Hz, 2H), 2.41 (s, 3H), 1.85 (m, 2H), 1.46 (m, 2H), 0.98 (t,
200
250
300
350
400
450
500
Wavelength/nm
Fig. 2. UV–vis absorption spectra of compounds 5a–g taken in dichloromethane
(c = 1 Â 10À5 M).
J = 7.2 Hz, 3H); IR (KBr)
m = 3072, 2953, 2867, 1632, 1481, 1319,
1230 cmÀ1; HRMS: m/z calcd for C30H27ClN7O3 [M+H]+ 568.1864,
found 568.1872.
Table 1
2-(3-Butyl-1-chloroimidazo[1,5-a]pyridin-7-yl)-5-(1-(4-
The optical characteristics of compounds 5a–g.
fluorobenzyl)-3-p-tolyl-1H-pyrazol-5-yl)-1,3,4-oxadiazole (5g)
Yellow solid (35% yield): mp 164.9–167.7 °C; 1H NMR
(300 MHz, CDCl3): d 8.07 (s, 1H), 7.79 (m, 3H), 7.43 (m, 2H), 7.28
(m, 4H), 6.98 (m, 2H), 5.95 (s, 2H), 2.98 (t, J = 7.2 Hz, 2H), 2.40 (s,
3H), 1.85 (m, 2H), 1.46 (m, 2H), 0.98 (t, J = 7.2 Hz, 3H); IR (KBr)
Compounds
kmax
E (molÀ1 cmÀ1 L)
5a
5b
5c
5d
5e
5f
400
403
403
402
400
404
400
238
241
239
240
244
244
246
4100
13,300
8700
9400
5000
33,800
69,400
52,100
58,700
40,300
87,400
47,900
m
= 3079, 2959, 2860, 1635, 1526, 1481, 1345, 1246 cmÀ1; HRMS:
m/z calcd for C30H27ClFN6O [M+H]+ 541.1919, found 541.1913.
18,100
4100
5g
Results and discussion
Synthesis and structure characterization
500
450
400
350
300
250
200
150
100
50
Starting ethyl 3-butyl-1-chloroimidazo[1,5-a]pyridine-7-car-
boxylate 1 can be easily synthesized by the reactions of commer-
cially available 2-butyl-4-chloro-1H-imidazole-5-carbaldehyde
and ethyl 4-bromobut-2-enoate in the presence of K2CO3. 3-Aryl-
1H-pyrazole-5-carbohydrazide derivatives 4 were synthesized by
the reaction of ethyl 3-aryl-1H-pyrazole-5-carboxylate derivatives
3 and hydrate hydrazine according to the literature[33]. Subse-
quently, diacylhydrazides 5 were synthesized by the reaction of
acid 2 and 3-aryl-1H-pyrazole-5-carbohydrazide derivatives 5 in
33–46% yields. The structures of products 5a–g were characterized
by spectroscopic methods (1H NMR, 13C NMR, IR and HRMS). For
example, compound 5g, obtained as yellow crystals, gave a
[M + H]Àion peak at m/z 541.1913 in the HRMS, in accord with
the molecular formula C30H27ClFN6O. The IR spectra showed the
characteristic absorption bands at 3079, 2959, 2860 (CAH), 1635
5a
5b
5c
5d
5e
5f
5g
0
-50
400
450
500
550
600
(C@C), 1526 (C@N), 1481 (NAN), and 1246 (CAOAC) cmÀ1
.
Wavelength/nm
The 1H NMR spectra (CDCl3) revealed three distinct singlets at d
2.40 (3H, Ar-CH3), 5.95 (2H, Ph-CH2-) and 8.07 (1H, imidazo[1,5-
a]pyridine moiety). Moreover, it showed peaks at d 2.98 (t,
J = 7.2 Hz, 2H), 1.85 (m, 2H), 1.46 (m, 2H), 0.98 (t, J = 7.2 Hz, 3H) as-
signed to the protons of butyl group. All other signals are consis-
tent with the structure of 5g.
Fig. 3. Fluorescence spectra of the compounds 5a–g in dichloromethane (10À6 M).
no absorption was observed beyond 450 nm. It was observed that
compounds 5a–g have similar absorption characteristics, with
absorption peaks ranging from 400 to 404 nm, which are attrib-
uted to the p–
pÃtransition of conjugate backbone. Comparing with
imidazo[1,5-a]pyridinyl 1,3,4-oxadiazole reported in previous pa-
per[31], compounds 5a–g have red shifted about 20 nm, the reason
being that the pyrazole which are linked to 1,3,4-oxadiazole can
Absorption spectral
UV–is absorption spectra of compounds 5a–g were observed in
dichloromethane solution with the concentration of 1 Â 10À5 M, as
shown in Fig. 2 and Table 1. Several absorption peaks could be ob-
served in the wavelength range from 220 to 450 nm, while almost
extend the
p-conjugation system. Furthermore, the substituents
in N-1 position of pyrazole moiety and para position of benzene
moiety hardly influenced the absorption.

Y.Q. Ge et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 336–341
339
-0.04571
-0.07521
360
340
320
300
280
260
240
220
200
180
160
140
120
100
80
-0.04
-0.06
-0.08
-0.10
-0.12
-0.14
-0.16
-0.18
-0.20
-0.22
-0.24
-0.04884
-0.07779
-0.04661
-0.07590
-0.04786
-0.05014
-0.07869
5a
5b
5c
5d
5e
5f
-0.07704
-0.07951
-0.09877
-0.08212
-0.09566
HOMO-1
HOMO
LUMO
5g
LUMO+1
-0.20430
-0.22372
-0.20201
-0.21576
-0.20357
-0.20357
-0.20273
-0.22181
-0.20500
-0.22516
-0.20521
-0.22421
60
-0.20780
-0.23011
40
20
0
-20
400
450
500
550
600
5a
5b
5c
5d
5e
5f
5g
Wavelength/nm
Fig. 6. Molecular orbital energy levels of compounds 5a–g.
Fig. 4. Fluorescence spectra of the compounds 5a–g in acetonitrile (10À6 M).
Theoretical calculation
To enhance our understanding of the relationship between
molecular structures and the electronic spectra of these new
1,3,4-oxadiazoles derivatives, we carried out structure optimiza-
tion and molecular orbital (MO) calculations on compound 5a–g
based on a simplified model with density functional theory (DFT)
on the level of B3LYP. The minimized structures are shown in
Fig. 5 (Supplementary data) and the calculated molecular orbital
(HOMO and LUMO) energies are shown in Fig. 6.
The minimized structures of compound 5 revealed that imi-
dazo[1,5-a]pyridine ring present a coplanar conformation with
the 1,3,4-oxadiazole ring and the pyrazole ring while the benzene
ring attached to N-1 does not. This indicates that imidazo[1,5-
a]pyridine group conjugated with the 1,3,4-oxadiazole ring and
the pyrazole ring efficiently through the single bond yet the ben-
zene does not. This result is in accordance with the similar absorp-
tions spectra of compound 5 with different substituents on the
benzene ring.
The molecular energy levels of the frontier molecular orbital
shown in Fig. 6 revealed that the introduction of electron-with-
drawing group to benzene ring reduced the energy levels of HOMO
and also reduced the energy levels of LUMO for the compound;
therefore, the energy gap between HOMO and LUMO changed lit-
tle. This corresponds well to the experimentally recorded similar
absorption spectra of compound 5.
Table 2
Data of fluorescence spectra of compounds 5a–g.
Compounds
kem (nm)
Stoke’s shift (nm)
CH2Cl2
CH2Cl2
CH3CN
5a
5b
5c
5d
5e
5f
478
461
482
483
480
467
483
478
477
477
480
479
480
479
78
58
79
81
80
53
83
5g
Fluorescence
Fluorescence spectral characteristics of the compounds 5a–g in
dichloromethane and acetonitrile solution with the concentration
of 10À6 M were investigated. From Figs. 3 and 4 and Table 2 it can
be found that the maximum emission spectra of compounds in
two different solvents are also hardly dependent on the groups in
N-1 position of pyrazole moiety and para position of benzene moi-
ety. The intensity of fluorescence is correlated with substituents on
para position of N-1 benzene moiety. Generally, fluorescence inten-
sity of 5b and 5f with nitro group on para position of N-1 benzene
moiety is weaker than others in two different solvents.
The frontier molecular orbital maps of compound 5 in Fig. 7
(supplementary data) revealed that the contribution of the ben-
Fig. 5. The minimized structures of compounds 5a–g.

340
Y.Q. Ge et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 336–341
Fig. 7. Molecular orbital maps of compounds 5a–g.
zene group to HOMO and LUMO is small. Therefore, the calcu-
lated results explain well the similar absorption maximum of
compound 5 because of the little contribution of the benzene
group to HOMO and LUMO.
HRMS spectra. Studies on the optical properties indicate that the sub-
stituents on benzene ring have no significant impact on the UV–vis
absorption and fluorescence emission. Quantum calculation corre-
lates well with their absorption and fluorescence emission.
Conclusion
Acknowledgement
In summary, a series of novel imidazo[1,5-a]pyridine and pyrazole
linked 1,3,4-oxadiazole derivatives have been synthesized. The struc-
tures of the compounds obtained were determined by IR, 1H NMR and
We thank the Science and Technology Development Project of
Shandong Province (Nos. 2011GGH22112 and 2012GSF11812)

Y.Q. Ge et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 336–341
341
[14] N.J. Xiang, L.M. Leung, S.K. So, J. Wang, Q. Su, M.L. Gong, Mater. Lett. 60 (2006)
2909–2913.
[15] S.L. Shen, J. Zhu, M. Li, B.X. Zhao, J.Y. Miao, Eur. J. Med. Chem. 54 (2012) 287–
294.
and the Natural Science Foundation of Shandong Province (No.
ZR2012BL04) for financial support.
[16] H.S. Lv, X.Q. Kong, Q.Q. Ming, X. Jin, J.Y. Miao, B.X. Zhao, Bioorg. Med. Chem.
Lett. 22 (2012) 844–849.
Appendix A. Supplementary material
[17] D. Davey, P.W. Erhardt, W.C. Lumma Jr, J. Wiggins, M. Sullivan, D. Pang, E.
Cantor, J. Med. Chem. 30 (1987) 1337–1342.
[18] L.J. Browne, C. Gude, H. Rodriguez, R.E. Steele, A. Bhatnager, J. Med. Chem. 34
(1991) 725–736.
Supplementary material associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.saa.
2013.12.016.
[19] M. Nakatsuka, T. Shimamura, JP 2001035664.
[20] L. Salassa, C. Garino, A. Albertino, G. Volpi, C. Nervi, R. Gobrtto, K.I. Hardcastle,
Organometallics 27 (2008) 1427–1435.
[21] Y.Q. Ge, J. Jia, Y. Li, L. Yin, J.W. Wang, Heterocycles 78 (2009) 197–206.
[22] Y.Q. Ge, J. Jia, H. Yang, G.L. Zhao, F.X. Zhan, J.W. Wang, Heterocycles 78 (2009)
725–736.
[23] J. Jia, Y.Q. Ge, X.T. Tao, J.W. Wang, Heterocycles 81 (2010) 185–194.
[24] D.T. Zhang, J. Jia, L.J. Meng, W.R. Xu, L.D. Tang, J.W. Wang, Arch. Pharm. Res. 33
(2010) 831–842.
[25] D.T. Zhang, Z.H. Wang, W.R. Xu, F.G. Sun, L.D. Tang, J.W. Wang, Eur. J. Med.
Chem. 44 (2009) 2202–2210.
[26] Y.Q. Ge, J. Jia, H. Yang, X.T. Tao, J.W. Wang, Dyes Pigm. 88 (2011) 344–349.
[27] H. Yang, J.L. Mu, X. Chen, L. Feng, J. Jia, J.W. Wang, Dyes Pigm. 91 (2011) 446–
453.
[28] H. Yang, Y.Q. Ge, J. Jia, J.W. Wang, J. Lumin. 131 (2011) 749–755.
[29] Y.Q. Ge, B.Q. Hao, G.Y. Duan, J.W. Wang, J. Lumin. 131 (2011) 1070–1076.
[30] X.Q. Cao, X.H. Lin, Y. Zhu, Y.Q. Ge, Spectrochim. Acta A 98 (2012) 76–80.
[31] Y.Q. Ge, T. Wang, G.Y. Duan, L.H. Dong, X.Q. Cao, J.W. Wang, J. Fluoresc. 22
(2012) 1531–1538.
[32] H.S. Lv, B.X. Zhao, J.K. Li, Y. Xia, S. Lian, W.Y. Liu, Z.L. Gong, Dyes Pigm. 86
(2010) 25–31.
[33] Y. Xia, Z.W. Dong, B.X. Zhao, X. Ge, N. Meng, D.S. Shin, J.Y. Miao, Bioorg. Med.
Chem. 15 (2007) 6893–6899.
References
[1] Y. Shirota, H. Kageyama, Chem. Rev. 107 (2007) 953–1010.
[2] A.P. Kulkarni, C.J. Tonzola, A. Babel, S.A. Jenekhe, Chem. Mater. 16 (2004) 4556–
4573.
[3] K. Ono, H. Ito, A. Nakashima, M. Uemoto, M. Tomura, K. Saito, Tetrahedron Lett.
49 (2008) 5816–5819.
[4] Y. Tao, Q. Wang, Y. Shang, C. Yang, L. Ao, J. Qin, D. Ma, Z. Shuai, Chem. Commun.
(2009) 77–79.
[5] Y. Tao, Q. Wang, C. Yang, Q. Wang, Z. Zhang, T. Zou, J. Qin, D. Ma, Angew. Chem.
Int. Ed. 47 (2008) 8104–8107.
[6] L. Chen, C. Yang, J. Qin, J. Gao, H. You, D.J. Ma, Organomet. Chem. 691 (2006)
3519–3530.
[7] Z. Xu, Y. Li, X. Ma, X. Gao, H. Tian, Tetrahedron 64 (2008) 1860–1867.
[8] S.H. Jin, M.Y. Kim, J.Y. Kim, K. Lee, Y.S. Gal, J. Am. Chem. Soc. 126 (2004) 2474–
2480.
[9] M.K. Leung, C.C. Yang, J.H. Lee, H.H. Tsai, C.F. Lin, C.Y. Huang, Y.O. Su, C.F. Chiu,
Org. Lett. 9 (2007) 235–238.
[10] G. Hughes, M.R. Bryce, J. Mater. Chem. 15 (2005) 94–107.
[11] Z. Si, J. Li, B. Li, F. Zhao, S. Liu, W. Li, Inorg. Chem. 46 (2007) 6155–6163.
[12] Y.P. Wong, W.F. Xie, B. Li, W.L. Li, Chin. Chem. Lett. 18 (2007) 1501–1504.
[13] N.J. Lundin, A.G. Blackman, K.C. Gordon, D.L. Officer, Angew. Chem. Int. Ed. 45
(2006) 2582–2584.