Asymmetric 1,3,4-oxadiazole derivatives containing naphthalene and stilbene units: Synthesis, optical and electrochemical properties

Article abstract of DOI:10.1016/j.saa.2013.12.104

Six novel asymmetric 1,3,4-oxadiazole derivatives containing naphthalene and stilbene units have been efficiently synthesized and characterized by FT-IR, ¹H NMR, ¹³C NMR, mass spectrometry and elemental analysis. The UV-vis absorptio

Full text of DOI:10.1016/j.saa.2013.12.104

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 91–96
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Asymmetric 1,3,4-oxadiazole derivatives containing naphthalene
and stilbene units: Synthesis, optical and electrochemical properties
⇑
Huixiong Lu, Daohang He
School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, 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
ꢀ
ꢀ
ꢀ
Asymmetrical 1,3,4-oxadiazole dyes
were efficiently synthesized.
Structure–optical properties
relationships were investigated.
The compounds exhibit bright violet–
blue emission with high fluorescence
quantum yields.
ꢀ
The high HOMO levels (ꢁ5.17 to
ꢁ5.03 eV) are beneficial for hole-
transporting.
a r t i c l e i n f o
a b s t r a c t
Article history:
Six novel asymmetric 1,3,4-oxadiazole derivatives containing naphthalene and stilbene units have been
efficiently synthesized and characterized by FT-IR, 1H NMR, 13C NMR, mass spectrometry and elemental
analysis. The UV–vis absorption maximum wavelength, fluorescence excitation wavelength, fluorescence
emission wavelength and fluorescence quantum yield were measured in dilute tetrahydrofuran solution.
The solvent effect was also studied. The HOMO and LUMO levels of these compounds were calculated by
density functional theory (DFT) (B3LYP, 6-31Gꢂ) method and cyclic voltammetry. They emit bright violet
to blue emission with high fluorescence quantum yields (0.23–0.94) and large Stokes shifts (53–102 nm).
These compounds possess high HOMO levels (ꢁ5.03 to ꢁ5.17 eV) and suitable band gaps, indicating that
they could be benefit for hole injection. The results show that they have a potential for application in
optoelectronic materials.
Received 25 November 2013
Accepted 23 December 2013
Available online 7 January 2014
Keywords:
Stilbene
1,3,4-Oxadiazole
Naphthalene
Synthesis
Optical properties
Electrochemical properties
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
Many symmetrical 1,3,4-oxadiazole derivatives have actually been
synthesized to use as TPA materials, polymers and organic electro-
Organic dyes have been extensively investigated for versatile
applications in coloring textiles, dye laser device, organic light
emitting diodes and electroluminescent displays [1–4]. 1,3,4-Oxa-
diazoles are well known not only for their attraction in medicinal
and pesticide chemistry [5–9], but also for their outstanding
photoelectric properties such as electron-transporting capabilities,
durability stability and high fluorescence quantum yields [10–12].
luminescent (EL) devices [13–15]. However, it is well known that
the large -symmetrical system leads to poor solubility, which
limits their synthesis, characterizations and applications [16].
Therefore, the synthesis of asymmetric 1,3,4-oxadiazole deriva-
tives with high efficiency emitting are still in demand.
p
Naphthalene chromophore is an attractive
p center, not only
because it is planar, but it is also an excellent fluorophore. Though
a great deal of excellent work has been reported on the naphtha-
lene derivatives as organic electroluminescent (EL) materials
[17,18], it is still meaningful to extend the research of such
⇑
Corresponding author. Tel./fax: +86 20 87110234.
E-mail address: cehdh@scut.edu.cn (D. He).
1386-1425/$ - see front matter Ó 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.12.104

92
H. Lu, D. He / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 91–96
materials. The naphthyl
ing groups are found to be effective photosensitive, and exhibit
good electrochemical and optical properties [19,20].
p
systems attached to electron withdraw-
Synthesis
The designed synthetic route for the target compounds are
The
p
-conjugated organic materials have attracted much atten-
depicted in Scheme 1. The synthesis procedure and the analytical
data of the compounds can be seen in Supplementary material.
tion owing to the increasing development of potentially active
components for a wide range of electronic and optoelectronic
devices [21]. Stilbene fluorescent compounds are an important
class of fluorescent compounds with strong UV absorption, distinc-
tive fluorescence emission and large Stokes shifts [22–24], which
have developed as optical brighteners, TPA materials and electrolu-
minescent materials [25–27]. The introduction of stilbene unit into
Results and discussion
The synthesis and characterization
The reaction steps for the synthesis and the structures of the
target molecules are shown in Scheme 1. Intermediate 1 was pre-
pared through the oxidative cyclization of hydrazones derived
from aromatic aldehydes and 4-methylbenzohydrazide by chlora-
mine-T, and then reacted with N-bromosuccinimide under the
catalysis of benzoyl peroxide to get compound 2. Compound 2
and triethyl phosphite were mixed to prepare compound 3 through
esterification. We then used compound 3 to react with various
aldehydes, via Wittig–Horner reaction, to get a series of asymmet-
ric 1,3,4-oxadiazole derivatives. Wittig–Horner reaction is an
important synthetic route for the formation of an olefin functional
group. The reaction procedure is convenient, takes place under
mild conditions, and gives good yields. All new compounds were
confirmed by 1H NMR, 13C NMR, MS, FT-IR and elemental analysis.
The spectroscopic data of products are in accordance with the as-
signed structures. The FT-IR spectra show weak bands or shoulders
located at 3100–3000 cmꢁ1, a strong band at 1606–1608 cmꢁ1 and
at 1530 cmꢁ1 which is assigned to aromatic CAH, C@N and aro-
matic CAC, respectively. IR spectra of 4c–4f exhibit the stretching
band at 2963–2826 cmꢁ1 assigned to aliphatic groups and at
1130 cmꢁ1 corresponding to aromatic CAOAC groups. Further-
more, the appearance of moderate intensity sharp C@C vibration
band at 963 cmꢁ1 indicate the existence of stilbene, which suggests
the molecules are trans-structure [34]. In the 13C NMR spectra,
because of the electron withdrawing ability of the imine group,
two resonance peaks appear at around 165 and 163 ppm which
are assigned to two C atoms of 1,3,4-oxadiazole. In the 1H NMR
spectra of target compounds, the total number of hydrogen atoms
is in good agreement with the proposed structure. The protons of
the naphthyl and phenyl attached to oxadiazole are shifted to high-
er chemical shifts (d = 9.30 and 8.20 ppm) due to the electron-
withdrawing ability of the oxadiazole lead to a decrease of the
electron density. The doublet of CH@CH with 16.0–16.7 Hz cou-
pling constant in the 1H NMR spectra of target compounds indicate
the vinyl is trans-structure, but the multiplet of CH@CH appears in
4b and 4e owing to the doublet of vinyl is overlapped with the
peaks of aromatic-H. In the mass spectra, the presence of charac-
teristic molecular ion peaks [M + 1] confirm the proposed
structures.
the oxadiazole dyes not only builds a p-conjugated bridge, but also
leads to a larger molecular length, which would make the electron-
pair in the highest occupied molecular orbit possess a higher
energy; the electron-pair could be excited easily to transit into a
higher orbit [28].
On the basis of our previous studies on organic fluorescent
materials [15,29,30], herein, we report six novel violet–blue asym-
metric 1,3,4-oxadiazole dyes containing naphthalene chromophore
with stilbene unit. As expected, the new dyes have good photoelec-
tric properties such as strong fluorescence intensity, high HOMO
levels and suitable band gaps. In addition, these compounds
possess high fluorescence quantum yields, large Stokes shift and
good electrochemical properties. The results will increase the
knowledge to design and synthesis novel asymmetric 1,3,4-oxadi-
azole derivatives based on stilbene with excellent photophysical
properties.
Experimental
Materials and instruments
All starting materials and reagents were commercially available
and used without further purification. All solvents were carefully
dried and freshly distilled according to common laboratory
techniques. Melting points were determined using RY-1 melting
point apparatus and were uncorrected. 1H NMR and 13C NMR
spectra were recorded in CDCl3 or DMSO-d6 on a Bruker AVANCE-
400 MHz NMR spectrometer using TMS as internal standard. FT-IR
spectra were measured as KBr pellets on a Bruker TENSOR 27 in the
region of 4000–400 cmꢁ1. Mass spectra were obtained with a Bruker
Esquire HCTplus (APCI). Elemental analyzes were performed on a
Vario EL cube V2.1.0 elemental analyzer. UV–vis absorption spectra
were recorded on a Hitachi UV-3010 spectrophotometer. Fluores-
cence spectra were obtained on a Hitachi F-4500 spectrophotometer
at room temperature. The purity of the compounds was confirmed
by TLC on silica gel ‘G’-coated glass plates. Cyclic voltammetry was
carried on
a CHI830B electrochemical analyzer with three-
electrode cell (Pt working electrode, Pt wire counter electrode
and Ag/AgCl reference electrode) in CH2Cl2 solution in the presence
of tetrabutylammonium hexafluorophosphate (0.1 M) as support-
ing electrolyte.
Optical properties
The optical data of the compounds were summarized in Table 1.
The UV–vis absorption spectra and emission spectra of the com-
pounds are given in Figs. 1 and 2 (1 ꢃ 10ꢁ5 mol Lꢁ1 in tetrahydro-
furan solution). It can be observed that these compounds have
similar absorption spectra owing to their molecular structures.
As is apparent in Fig. 1, all derivatives exhibit intense CT absorp-
tions in the visible region from 345 nm to 357 nm, which is attrib-
uted to an intramolecular charge transfer transition (S0 ? CT). The
compound 4c exhibits the largest maximum absorption peak at
357 indicating the introduction of electron-donating methoxy
group into the phenyl results in bathochromic shift. It is also noted
that the red-shift effect of the methoxy substituent is related to the
numbers of methoxy and the substituent position. When the
Measurements
The fluorescence quantum yields (
ing to the literature method [31,32].
U) were determined accord-
Ux ¼ ðAs ꢃ Fx ꢃ n2x ꢃ UsÞ=ðAx ꢃ Fs ꢃ n2s Þ
Here, A is the absorbance at the excitation wavelength, F is the area
under the fluorescence curve, n is the refraction index. Subscripts s
and x refer to the standard and to the sample of unknown quantum
yield, respectively. Quinine sulfate in 0.5 M sulfuric acid was used
as fluorescence standard (
U = 0.546) [33].

H. Lu, D. He / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 91–96
93
Scheme 1. The synthetic route of new target compounds.
Table 1
UV–vis and fluorescent parameters of target compounds.
a
c
Compound
kmax (nm)a
10ꢁ4emax (L molꢁ1 cmꢁ1
)
kex (nm)a
kem (nm)
Stockes shifts (nm)b
Ux
DMSO
THF
CHCl3
4a
4b
4c
4d
4e
4f
345
352
357
356
349
346
4.61
4.24
4.87
4.88
5.10
5.17
348
358
360
362
351
348
417
450
500
467
423
407
404
434
462
437
408
401
406
430
450
430
408
402
56
76
102
75
57
53
0.82
0.59
0.56
0.23
0.84
0.94
a
b
c
Solution in 10ꢁ5 mol Lꢁ1 THF.
Stokes shifts = kem ꢁ kex
.
The fluorescence quantum yields were measured in THF using Quinine sulfate in 0.5 M sulfuric acid as the standard.
phenyl ring is substituted with an AOCH3 group at m- and p-posi-
tion, the kmax values are shifted to 349(4e) and 356(4d) nm, respec-
tively. This can be explained by the decreasing electron donating
effect of the AOCH3 group attached to the m-position. Compared
with 4a, compound 4b exhibits a red shifted absorption maximized
at 352 nm due to longer conjugation length and larger delocalized
system. Compound 4a and 4f have the similar maximum absorp-
tion peaks, indicating that pyridine ring has a limited effect on
their electronic energy levels.
As can be seen in Table 1 and Fig. 2, all of the compounds
exhibit strong violet to blue emission with the maximum peaks
varying from 401 to 462 nm in THF solution. The blue light-emit-
ting materials play a particularly significant role in the develop-
ment of OLEDs, because they can not only be used as a blue light
source, but also be utilized to generate light of green and red color
by energy cascade to a suitable emissive dopant [35,36]. Moreover,
their emission range can be tuned by changing the nature of the
peripheral substituting groups. It is well known that a strong

94
H. Lu, D. He / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 91–96
electron donor could help to stabilize charge-transfer excited state
and cause red shift. The compound 4b exhibits bright blue emis-
sion with peak at 434 nm, which is bathochromically shifted with
respect to that of 4a because of the larger conjugation of naphthyl.
The fluorescence emission peaks for 4c, 4d and 4e are gradually red
shifted due to the increased electron density by -OCH3. The Stokes
shifts for all the compounds are large, ranging from 53 to 102 nm.
absorption and fluorescent spectra, which is an advantage in lumi-
nous material [37]. These compounds exhibit different emission
behaviors by changing the nature of the polarity of the solvents.
With increasing polarity of the solvent, their fluorescence spectra
show bathochromic shifts. For example (Fig. 3), kmax of 4c is located
at 450 nm in CHCl3 and red-shifted to 500 nm in DMSO, indicating
that it is more polarity in the excited state than in the ground state.
These demonstrate that the polarity of the solvent plays an impor-
tant role on the photophysical properties in such strong donor–
acceptor systems. The fluorescence quantum yields of the
compounds are in the range of 0.23–0.94. Concerning 4a and 4b,
the Ux values decrease with the increase of conjugation ascribed
to torsion occur around the olefin bond because of the steric hin-
drance. It can be found that 4c and 4d were lower than 4a, which
might be attributed to the introduction of methoxy affecting the
planarity of the molecules.
The large Stokes shift means
a small overlap between the
Theoretical calculations
The ground-state geometries and electronic structures of the
target compounds were calculated with Gaussian 09 software,
using density functional theory (DFT) at the (B3LYP)/6-31Gꢂ level
Fig. 1. The absorption spectra of target compounds (1 ꢃ 10ꢁ5 mol Lꢁ1 in THF).
Fig. 2. The emission spectra of target compounds (1 ꢃ 10ꢁ5 mol Lꢁ1 in THF).
Fig. 3. The emission spectra of compound 4c in different solvents (1 ꢃ 10ꢁ5
-
Fig. 4. Optimized geometric structure and frontier molecular orbital profiles of
compounds.
mol Lꢁ1) as sample.

H. Lu, D. He / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 91–96
95
Table 2
Electrochemical properties of target compounds.
Compound
HOMO (eV)a
LUMO (eV)a
Band gap (eV)a
Eox (eV)b
HOMO (eV)c
LUMO (eV)c
Eg (eV)d
4a
4b
4c
4d
4e
4f
ꢁ5.55
ꢁ5.48
ꢁ5.48
ꢁ5.31
ꢁ5.51
ꢁ5.70
ꢁ2.04
ꢁ2.06
ꢁ2.02
ꢁ1.93
ꢁ2.00
ꢁ2.19
3.51
3.42
3.46
3.48
3.51
3.51
0.74
0.70
0.63
0.69
0.69
0.77
ꢁ5.14
ꢁ5.10
ꢁ5.03
ꢁ5.09
ꢁ5.09
ꢁ5.17
ꢁ1.99
ꢁ2.18
ꢁ2.12
ꢁ2.07
ꢁ1.90
ꢁ1.97
3.15
2.92
2.91
3.02
3.19
3.20
a
b
c
DFT/B3LYP calculated values.
Oxidation potential in CH2Cl2 (10ꢁ3 mol Lꢁ1) containing 0.1 mol Lꢁ1 (n-C4H9)4NPF6 with a scan rate of 0.05 V sꢁ1
EHOMO = ꢁ(Eox + 4.4) eV, and |ELUMO| = |EHOMO| ꢁ Eg.
.
d
Energy gap was estimated from the absorption edge.
[38]. The electron-density distribution of the highest occupied
molecular orbit (HOMO) and the lowest unoccupied molecular or-
bit (LUMO) of ground-state optimized structures are shown in
Fig. 4. The calculated energy levels are listed in Table 2. Fig. 4
shows that all compounds have good coplanar configurations ex-
cept for 4b, which implies that these compounds have a large
p-
delocalization. And the dihedral angle in 4b between naphthyl
and vinyl is 149.3°. Generally, the more coplanar or rigid structure
the higher fluorescence efficiency is. It can be observed that the
HOMOs are spread over the entire conjugated molecules ascribe
to
p
orbital, while the LUMOs are mainly localized on the oxadiaz-
ole ring, two adjacent phenyl rings and stilbene ascribe to
p
* orbi-
tal, suggesting that the naphthyl and the donor-substituted groups
contribute to enhance the charge mobility of the target com-
pounds. This illustrates that these molecules possess strong intra-
molecular charge transfer ability between donor unit and acceptor
moiety. Concerned on 4d, we can observe that the introduction of
methoxy group changes the electron density distribution of HOMO.
The calculated HOMO and LUMO energy levels of the compounds
are from ꢁ5.70 to ꢁ5.31 eV and from ꢁ2.19 to ꢁ1.93 eV, respec-
tively. The HOMO energy levels of the target compounds are close
to the most well-known hole-transporting materials such as TPD
(ꢁ5.73 eV) and NBP (ꢁ5.30 eV), indicating that they might be ben-
eficial for the hole-transporting [17,39]. Compared with the com-
monly used cathode barium (ꢁ2.2 eV), the low LUMO energy of
these compounds (ꢁ2.19 to ꢁ1.93 eV) have a small barrier to
accept electrons from the cathode [40]. The theoretical band gaps
are in range of 3.42–3.51 eV closed to the most famously blue-
emitting diode ZnO NWs (3.37 eV), which indicate that the target
compounds may be used as a host material for blue emitters
[41–43].
Fig. 6. UV–vis absorption spectra of 4a, 4b, 4c, 4d, 4e and 4f in CH2Cl2 solution.
Electrochemical properties
The electrochemical properties of compounds 4a–4f were
investigated by cyclic voltammetry in CH2Cl2 with 0.1 M tetrabu-
tylammonium hexafluorophosphate as supporting electrolyte at
scan rate of 50 mV sꢁ1 under nitrogen atmosphere. Fig. 5 shows
that compounds exhibit reversible oxidation process with
onset oxidation potential of 0.63–0.77 V. The HOMO and LUMO
energy levels were deduced from the following equations:
ox
onset
HOMO ¼ ꢁðE
þ 4:4Þ, Eg = 1240/konset (see Fig. 6) and
|LUMO| = |HOMO| ꢁ Eg. As shown in Table 2, HOMO levels of com-
pounds are range from ꢁ5.03 to ꢁ5.17 eV, which are higher than
the most widely used HTM NPB (ꢁ5.40 eV) [44]. The higher HOMO
energy the smaller energy barrier between the interface of ITO and
the target compounds, and resulted in higher hole injection effi-
ciency and lower joule heat [45]. These compounds possess small
bang gaps (2.91–3.20 eV), which are smaller or close to the blue
emitter DPB (3.20 eV) [46]. Their LUMO levels (ꢁ1.90 to
ꢁ2.18 eV) exhibit a small barrier for the electron injection from
the commonly used cathode barium (ꢁ2.2 eV) [45]. Thus, these
compounds might have promising potential for application in
OLEDs.
Conclusion
In conclusion, six novel asymmetric 1,3,4-oxadiazole deriva-
tives containing naphthalene and stilbene units were synthesized
in good yields. The compounds exhibit a bright violet to blue emis-
sion with high fluorescence quantum yield. The absorption behav-
iors and emission properties depend largely on their structures.
The emission behaviors of these compounds show bathochromic
shifts with the increasing solvent polarity. The large Stokes shifts
Fig. 5. Cyclic voltammogram of compound 4b as sample, in 0.1 mol Lꢁ1 Bu4NPF6-
ACHCl3, scan rate 50 mV sꢁ1
.

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H. Lu, D. He / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 124 (2014) 91–96
[14] Y. Qian, Z. Lu, C. Lu, Z. Chen, Y. Cui, Dyes Pigments 75 (2007) 641–646.
[15] Y.C. Zhu, D.H. He, Z.R. Yang, Spectrochim. Acta A 72 (2009) 417–420.
[16] Z. Luo, H. Shi, H. Zhu, G. Song, Y. Liu, Dyes Pigments 92 (2012) 596–602.
[17] F. Wang, X. Qiao, T. Xiong, D. Ma, Org. Electron. 9 (2008) 985–993.
[18] S. Barth, P. Muller, H. Riel, P.F. Seidler, W. Riess, H. Vestweber, H. Bassler, J.
Appl. Phys. 89 (2001) 3711–3719.
[19] M.D. Damaceanu, R.D. Rusu, A. Nicolescu, M. Bruma, J. Polym. Sci. Pol. Chem.
49 (2011) 893–906.
[20] M. Planells, N. Robertson, Eur. J. Org. Chem. 2012 (2012) 4947–4953.
[21] Y. Liu, M. Nishiura, Y. Wang, Z.M. Hou, J. Am. Chem. Soc. 128 (2006) 5592–
5593.
(53–102 nm) and high fluorescence quantum yields (0.23–0.94)
are advantages in luminous material. According to DFT calcula-
tions, these compounds possess coplanar configurations, large
p
conjugation, high HOMO levels (ꢁ5.70 to ꢁ5.31 eV) and wide band
gaps (3.42–3.51 eV), which are beneficial for the hole-transporting
or electron-transporting. Six compounds embody high HOMO lev-
els (ꢁ5.17 to ꢁ5.03 eV) for hole injection in Cyclic voltammetry.
Results show that these compounds have promising potential for
the application in organic electroluminescent materials.
[22] E.M. Breitung, C.F. Shu, R.J. McMahon, J. Am. Chem. Soc. 122 (2000) 1154–
1160.
[23] X.M. Wang, D. Wang, G.Y. Zhou, W. Yu, Y.T. Zhou, Q.F. Fang, M.H. Jiang, J. Mater.
Chem. 11 (2001) 1600–1605.
Acknowledgments
[24] V.W.W. Yam, Y. Yang, J.X. Zhang, B.W.K. Chu, N.Y. Zhu, Organometallics 20
(2001) 4911–4918.
[25] A. Momotake, T. Arai, J. Photochem. Photobiol. C 5 (2004) 1–25.
[26] M. Strukelj, R.H. Jordan, A. Dodabalapur, J. Am. Chem. Soc. 118 (1996) 1213–
1214.
The authors thank the Fundamental Research Funds for the
Central Universities (No. 2012ZM0035) and Guangdong Provincial
Natural Science Foundation of China (No. 04300531) for the finan-
cial assistance.
[27] M. Drobizhev, A. Karotki, A. Rebane, C.W. Spangler, Opt. Lett. 26 (2001) 1081–
1083.
[28] S. Barlow, H.E. Bunting, C. Ringham, J.C. Green, G.U. Bublitz, S.G. Boxer, J.W.
Perry, S.R. Marder, J. Am. Chem. Soc. 121 (1999) 3715–3723.
[29] D.H. He, X.W. Li, C. Yang, J. Yang, Spectrochim. Acta A 95 (2012) 184–187.
[30] X. Li, D. He, Dyes Pigments 93 (2011) 1422–1427.
[31] B. Liu, Q. Zhang, H. Ding, G. Hu, Y. Du, C. Wang, J. Wu, S. Li, H. Zhou, J. Yang, Y.
Tian, Dyes Pigments 95 (2012) 149–160.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2013.12.104.
[32] A. Nas, S. Fandaklı, H. Kantekin, A. Demirbasß, M. Durmußs, Dyes Pigments 95
(2012) 8–17.
References
[33] M.S. Baptista, G.L. Indig, J. Phys. Chem. B 102 (1998) 4678–4688.
[34] T.L. Zhang, H.H. Li, Z.L. Yuan, Chin. J. Org. Chem. 25 (2005) 997–1000.
[35] W. Gao, S. Wang, Y. Xiao, X. Li, Spectrochim. Acta A 98 (2012) 215–221.
[36] J. Huang, J.H. Su, X. Li, M.K. Lam, K.M. Fung, H.H. Fan, K.W. Cheah, C.H. Chen, H.
Tian, J. Mater. Chem. 21 (2011) 2957–2964.
[1] V. Bulovic, A. Shoustikov, M.A. Baldo, E. Bose, V.G. Kozlov, M.E. Thompson, S.R.
Forrest, Chem. Phys. Lett. 287 (1998) 455–460.
[2] M.C.R. Castro, P. Schellenberg, M. Belsley, A.M.C. Fonseca, S.S.M. Fernandes,
M.M.M. Raposo, Dyes Pigments 95 (2012) 392–399.
[3] G.S. He, J.D. Bhawalkar, C.F. Zhao, P.N. Prasad, Appl. Phys. Lett. 67 (1995) 2433–
2435.
[4] V.G. Kozlov, V. Bulovic, P.E. Burrows, S.R. Forrest, Nature 389 (1997) 362–364.
[5] V.D. Bobade, S.V. Patil, N.D. Gaikwad, J. Chem. Res. (2012) 25–28.
[6] J. Bostrom, A. Hogner, A. Llinas, E. Wellner, A.T. Plowright, J. Med. Chem. 55
(2012) 1817–1830.
[7] Z.J. Fan, B. Liu, X.F. Liu, B. Zhong, C.L. Liu, Z.M. Li, Chem. J. Chin. U. 25 (2004)
663–666.
[8] H. Tajik, A. Dadras, J. Pestic. Sci. 36 (2011) 27–32.
[9] W.G. Duan, X.R. Li, Q.J. Mo, J.X. Huang, B. Cen, X.T. Xu, F.H. Lei, Holzforschung
65 (2011) 191–197.
[10] S. Hoshino, K. Ebata, K. Furukawa, J. Appl. Phys. 87 (2000) 1968–1973.
[11] J. Kido, M. Kimura, K. Nagai, Science 267 (1995) 1332–1334.
[12] J.Y. Li, D. Liu, C. Ma, O. Lengyel, C.S. Lee, C.H. Tung, S. Lee, Adv. Mater. 16 (2004)
1538–1541.
[37] G. Yu, X. Xu, Y. Liu, Z. Jiang, S. Yin, Z. Shuai, D. Zhu, X. Duan, P. Lu, Appl. Phys.
Lett. 87 (2005) 222113–222115.
[38] M.J. Frisch, G. Trucks, H. Schlegel, G. Scuseria, M. Robb, J. Cheeseman, G.
Scalmani, V. Barone, B. Mennucci, G. Petersson, Inc., Wallingford, CT, 2009.
[39] M. Malagoli, J. Brédas, Chem. Phys. Lett. 327 (2000) 13–17.
[40] H.Y. Wang, J.J. Shi, C. Wang, X.X. Zhang, Y. Wan, H. Wu, Dyes Pigments 95
(2012) 268–274.
[41] Y. Tao, Q. Wang, C. Yang, Z. Zhang, T. Zou, J. Qin, D. Ma, Angew. Chem. 120
(2008) 8224–8227.
[42] S. Nakamura, Science 281 (1998) 956–961.
[43] X.M. Zhang, M.Y. Lu, Y. Zhang, L.J. Chen, Z.L. Wang, Adv. Mater. 21 (2009)
2767–2770.
[44] X.H. Ouyang, H.P. Zeng, G.Y. Ding, W.L. Jiang, J. Li, Synth. Met. 159 (2009)
2063–2069.
[45] M. Thelakkat, H.W. Schmidt, Adv. Mater. 10 (1998) 219–223.
[46] C.H. Yang, T.F. Guo, I. Sun, J. Lumin. 124 (2007) 93–98.
[13] M.D. Damaceanu, R.D. Rusu, M. Bruma, A.L. Rusanov, Polym. Adv. Technol. 22
(2011) 420–429.