Synthesis, characterization and optoelectronic investigations of bithiophene substituted 1,3,4-oxadiazole derivatives as green fluorescent materials

Article abstract of DOI:10.1039/c5ra14550c

A series of novel unsymmetrical bithiophene substituted oxadiazole derivatives 2(a-e) were designed and synthesised by employing palladium catalysed Suzuki cross coupling reaction. These bipolar molecules consist of bithiophene as an electron donor unit (D) and electron transporting oxadiazole as acceptor unit (A). The structural integrity of all the new compounds was confirmed by ¹H NMR, ¹³C NMR and GC-MS analysis. The photophysical and electrochemical properties have been studied in detail using UV-Vis absorption, fluorescence spectroscopy and CV measurements. All compounds emit intense green fluorescence with good quantum yields. Density functional theory computations have been carried out to understand the structure-property relationship, the computed values are found to be in good agreement with the experimental results. The results demonstrated that the novel bithiophene containing oxadiazole derivatives could play an important role in organic optoelectronics.

Full text of DOI:10.1039/c5ra14550c

View Article Online
View Journal
RSC Advances
This article can be cited before page numbers have been issued, to do this please use: N. Deshapande,
N. S. Belavagi, M. G. Sunagar, S. Gaonkar, G. H. Pujar, M. N. Wari, S. R. Inamdar and I. A. M. Khazi, RSC
Adv., 2015, DOI: 10.1039/C5RA14550C.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. This Accepted Manuscript will be replaced by the edited,
formatted and paginated article as soon as this is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/advances

Page 1 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA14550C
Graphical abstract
Spacer
Electron acceptor
N
O
N
N N
O
S
Suzuki cross coupling
S
R
R
Br
Electron donor
Design and synthesise of novel bithiophene substituted oxadiazoles and exploration of their
optoelectronic properties.

RSC Advances
Page 2 of 25
View Article Online
DOI: 10.1039/C5RA14550C
Synthesis, characterization and optoelectronic investigations of bithiophene
substituted 1,3,4ꢀoxadiazole derivatives as green fluorescent materials
a
a
a
Narahari Deshapande , Ningaraddi S. Belavagi , Manjunath G. Sunagar , Supreet Gaonkar
a
b
b
b
a
,
G. H. Pujar , M. N. Wari , S.R. Inamdar and Imtiyaz Ahmed M. Khazi *
a
b
CPEPA, Department of Chemistry, Karnatak University, Dharwad 580003, Karnataka, India.
CPEPA, Department of Physics, Karnatak University, Dharwad 580003, Karnataka, India.
Abstract
A series of novel unsymmetrical bithiophene substituted oxadiazole derivatives 2(aꢀe)
were designed and synthesised by employing palladium catalysed Suzuki cross coupling
reaction. These bipolar molecules consist of bithiophene as an electron donor unit (D) and
electron transporting oxadiazole as acceptor unit (A). The structural integrity of all the new
1
13
compounds was confirmed by H NMR, C NMR and LCꢀMS analysis. The photo physical
and electrochemical properties have been studied in detail using UVꢀVis absorption,
fluorescence spectroscopy and CV measurements. All compounds emit intense green
fluorescence with better quantum yields. Density Functional Theory computations have been
carried out for the better understanding of structureꢀproperty relationship, the computed
values are found to be in good agreement with the experimental results. The results
demonstrated that the novel bithiophene containing oxadiazole derivatives could play
important role in organic optoelectronics.
Keywords: Oxadiazole, Photoluminescence, Quantum yield, Density Functional Theory
Introduction
Photoluminescence (PL) of organic compounds has been studied extensively to
develop thin, efficient, and stable devices with wide viewing angles and fast response. In
recent years, PL of organic materials with excellent characteristics has been exploited for the
development and commercialization display materials. The optoelectronic properties of
conjugated polycyclic aromatic compounds plays significant role in photonic and electronic
devices such as organic lightꢀemitting diodes (OLEDs) which exhibited a great potential of
revolutionizing display technologies in the field of organic electronics. The most successful
1
and sensible OLEDs are better substitute for liquid crystalꢀbased devices, because of their
comparatively low power consumption, compatibility with large area and flexible substrates,
2
,3
and tuneability by molecular structure modification. A great deal of research work has been

Page 3 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA14550C
focused on the development of visible light emitting OLEDs for display and lighting
4
ꢀ7
applications. Compared to other display technologies, OLEDs show their own unique
advantages like, easy processing, selfꢀluminescence, high brightness, high efficiency, low
drive voltage, wide viewing angle, high contrast and highꢀspeed response. OLEDs are
currently used in longꢀlived and highly efficient colour displays and also hold unique
8, 9
10
applications in biological and chemical sensing, highꢀdensity information storage and
11,12
fullꢀcolour lightꢀemitting displays.
For the purpose of practical use, they still have several unsolved problems such as
operational stability of the devices and colour shift after operation. Some of these problems
could be solved by modification of structural backbone of organic compounds. In designing
OLEDs, a luminescent material is required in which electron and hole are recombined
13ꢀ16
resulting in the emission of light.
By employing donor/acceptor strategy one can improve
17
the device efficiency and operational lifetime along with fluorescence properties. In order to
achieve high fluorescence, small bipolar molecules can be designed by incorporating
electronꢀwithdrawing groups like 1,3,4ꢀoxadiazole, phosphineoxide, triazine and electronꢀ
18ꢀ22
donating groups like carbazole, diphenylamine etc.
The performance of diodes is closely
governed by the number of hole (HT) and electron transporting (ET) moieties. Among all
fluorescent heterocyclic ring systems, the molecules containing 1,3,4ꢀoxadiazole, play a
crucial roles like excellent electronꢀacceptor, high thermal stability, high quantum yields.
2
3,24
They are also used as electronꢀtransporting/holeꢀblocking materials in OLEDs.
Indeed,
oxadiazole units advantageously restrict ꢀꢀconjugation to afford materials with deeply lying
highest occupied molecular orbital’s (HOMOs) such that the triplet energies (ETs) are
25ꢀ27
high.
In the present investigation, we have designed 1,3,4ꢀ oxadiazole derivatives with
focus on the HOMOꢀLUMO gap in donorꢀacceptor (D/A) systems which can be tuned either
by altering the strength of D/A units or by extending π conjugation. The incorporation of
electron deficient 1,3,4ꢀ oxadiazole ring with electron rich bithiophene as a donor results in
28,29
strong intramolecular charge transfer (ICT) chromophores.
designed and synthesized a novel series of unsymmetrical small bipolar organic molecules
(aꢀe) (Fig. 1) with bithiophene substituent as an electron donor, which is connected through
In view of this, we have
2
a phenyl spacer with para linkages. The introduction of the bithiophene moiety extends the
πꢀπ conjugation and oxadiazole enhances the electron transporting capability. We have
studied the optoelectronic properties such as UVꢀVis/fluorescence spectra, quantum yields

RSC Advances
Page 4 of 25
View Article Online
DOI: 10.1039/C5RA14550C
and HOMOꢀLUMO calculations. Additionally, we studied the effect of solvents
Solvatochromic behavior) to support strong intramolecular charge transfer property of these
(
compounds. Further, the electrochemical property of the compounds has been studied by
cyclic voltammetry (CV). The thermal properties of compounds were investigated by
thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The
systematic investigation of photophysical, electrochemical and thermal properties of newly
synthesised compounds were performed with a view to examine their suitability in
developing OLEDs.
N
O
N
O
N
N
S
S
S
S
2
a
2b
S
S
S
S
S
N
O
N
N
N
F
S
O
F
2c
2d
S
F
F
F
N
O
N
2e
Scheme 1: Chemical structures of target compounds 2(aꢀe)
Results and Discussion
Synthesis and Characterization
Designed title compounds 2(aꢀe) are illustrated in scheme 1. A relatively simple and
efficient synthetic protocol was employed for the synthesis of compounds 2(aꢀe) as depicted
in scheme 2. The required precursor 4ꢀbromobenzohydrazide was obtained by the
30,31
esterification of 4ꢀbromobenzoic acid followed by treating with hydrazine hydrate.
key intermediates 1(aꢀe) were synthesized by treatment of 4ꢀbromobenzohydrazide with
various aromatic carboxylic acids in refluxing POCl . Subsequent Pdꢀcatalyzed Suzuki crossꢀ
The
3
coupling reaction between 1(aꢀe) and 5’ꢀHexylꢀ2,2’ꢀbithiopheneꢀ5ꢀboronic acid pinacol ester
afforded the target compounds in 80ꢀ85% yields. At the second position of oxadiazole the
bithiophene group is kept constant and we have varied in the substituents in the fifth position
with different groups such as pꢀtertꢀbutylphenyl, thienyl, biphenyl, pentafluorophenyl and 2ꢀ

Page 5 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA14550C
napthyl to modify their spectral properties. The resulting bipolar molecules were purified by
column chromatography on silica gel followed by recrystallization in ethanol before spectral
characterization. All these compounds 2(aꢀe) are amorphous in nature and can be stored
under ambient conditions for longer time without any detectable decomposition. All these
3
compounds are readily soluble in common organic solvents like EtOH, CHCl , DCM and
1
13
THF etc. Their structural identities and purities were confirmed by H NMR, C NMR, IR
and MS and were found to be in good agreement with the proposed structures.
O
O
O
SOCl2
NH NH .H O
NH2
OH
O
2
2
2
N
H
Ethanol, reflux
Ethanol, reflux
Br
Br
Br
4-bromobenzohydrazide
O
HO
R
Reflux, 12 h
POCl3
N
N
Pd, K CO , dioxane
2
3
N N
S
O
o
80 C, 6 h
2
(a-e)
S
R
O
1(a-e)
R
Br
O
B
S
S
O
Scheme 2: Synthetic route for the target compounds 2(aꢀe)
Photophysical Properties
UVꢀVis Absorption and Photoluminescence (PL) spectra
All the derivatives are soluble in common organic solvents, such as tetrahydrofuran
(THF), dichloromethane, chloroform and ethanol. Fig. 1 shows UVꢀvis absorption spectra of
the synthesized compounds in ethanol (HPLC grade). The maximum absorption wavelengths
(ꢁ
ꢃꢂ ꢅ ꢃꢆ ꢄ) of 2a, 2b, 2c, 2d, and 2e are 387, 386, 386, 391 and 381 nm, respectively. Molecules
2(aꢀe) exhibit two distinct peaks in the absorption spectra, even though there was no
conjugation break at the phenylꢀthiophene bond of the compounds, we observed a strong
absorption bands at shorter wavelengths mainly because of πꢀπ* transition of local electrons
present in the bithiophene moiety of the compound (electronꢀdonor) and less intense
absorption bands at longer wavelengths at 350ꢀ450 nm were assigned to the πꢀπ* transition of
whole segment. In the series 2(aꢀe), the derivative 2e shows least ꢁ ꢃꢂ ꢅ ꢃꢆ ꢄ of 381 nm and 2d
exhibited highest ꢁꢃꢅꢆ of 391 nm (Table. 1).
ꢂꢃꢄ

RSC Advances
Page 6 of 25
View Article Online
DOI: 10.1039/C5RA14550C
2
2
2
2
2
a
b
c
d
e
0
0
0
0
.6
.4
.2
.0
Ref
2
00
300
400
500
Wavelength (nm)
Fig. 1: UVꢀVis absorption spectra of compounds 2(aꢀe) in ethanol at room temperature,
compared with Reference (Coumarin 480).
Photoluminescence (PL) spectra (Fig. 2 (a)) could provide good deal of information
on the electronic structure of the synthesised molecules. A marginal bathochromic shift
observed in emission spectra of 2(aꢀe) might be attributed to different aryl/heteroaryl groups
at the fifth position of oxadiazole unit. Even though there was not much deference with
respect to absorption and fluorescence maxima, we observed significant deference in the
intensity of absorption and emission spectra among these compounds (Fig. 1 and Fig. 2 (a))
due to different aryl/heteroaryle groups at the fifth position of the oxadizole moiety. The
emission maxima of 2a, 2b and 2c in ethanol were 461, 462 and 463 nm respectively, while
2d and 2e were redꢀshifted to 466 nm (Table. 1). In addition, emission spectra of
compounds 2(aꢀe) in solid state film were measured by exciting at 385 nm (Fig. 2(b)) to
examine the emission properties of these new compounds. The emission maxima for all
compounds were summarised in Table. 1.

Page 7 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA14550C
2c 2b 2d 2a
6
a
2a
2b
1.0
b
7.5x10
2
c
2
d
2
Ref
e
6
5.0x10
0.5
2e
6
2.5x10
0.0
0.0
5
00
600
700
400
500
600
Wavelength (nm)
Wavelength (nm)
Fig. 2: (a) Emission spectra of compounds 2(aꢀe) in ethanol at room temperature, compared
with Reference (Coumarin 480).
(b) Emission spectra of coumponds 2(aꢀe) in solid state film when excited at λex=385
nm.
The Stoke shift, indicating the extent of the bathochromic shift of the fluorescence
maximum (ꢁ ꢇꢂ ꢂꢃ ꢈꢄ ) compared to the absorption maxima (ꢁ ꢃꢂ ꢅ ꢃꢆ ꢄ), is in the range of 74ꢀ85 nm.
There was a substantial increment in Stoke shift from 2a to 2e except for 2d. Compound 2a
&
2e, respectively, have shown smaller and larger Stoke shifts among the five compounds
(Table 1).
Quantum Yield (Φ) calculations
The radiative quantum yield is an important quantity in molecular chemistry.
Quantum yields provide important information regarding excited electronic states,
radiationless transitions, and coupling of electronic to vibronic states. Fluorescence quantum
yields (Φ) of 2(aꢀe) were measured in ethanol at room temperature by comparison with a
standard dye Coumarin 480 (2,3,5,6-1H,4H-Tetrahydro-8-methylquinolizino-[9,9a,1-gh]-
35
coumarin) of known quantum yield (Φ) using the equation (1). The compounds 2(aꢀb), 2(cꢀ
d) and 2e were excited at 386 nm, 390 nm and 382 nm respectively.
ꢋ ꢌꢍꢊ ꢎꢏꢐ
ꢉ = ꢉꢊ
ꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐ(ꢑ)
ꢋꢊ ꢌꢍ ꢎꢏ
ꢊ
Where I is the integrated intensity, OD is the optical density and n is the refractive index, the
subscript R refers to the reference fluorophore of known quantum yield. The quantum yields

RSC Advances
Page 8 of 25
View Article Online
DOI: 10.1039/C5RA14550C
of all the compounds are in the range of 0.35 to 0.60 (Table. 1). There is a marginal increase
in quantum yield from 2a to 2b, may be due to thiophene ring at the fifth position of
oxadiazole in 2b. The compound 2d has shown higher quantum yield of 0.60 and 2c has
shown comparatively least quantum yield among five compounds.
Table. 1: Summary of Optical and thermal properties of πꢀconjugated molecules 2(aꢀe)
Emission
Absorption
Stoke
shift ꢁλ
(nm )
Quantum
Yield
ꢃꢅꢆ
o
[d]
Compounds
ꢁ
g m c 5d
T /T /T /T [ C]
ꢂꢃꢄ
ꢇꢂꢈ
ꢇꢂꢈ
ꢁ
(
ꢁ
[
a]
ꢂꢃꢄ
b]
ꢂꢃꢄ
[c]
(nm)
[
nm)
(nm)
519
2
a
387
386
461
74
76
0.41
0.44
8
7.36/141.15/ꢀ/267
87.49/139.38,
4
87
2b
462
1
58.58/ꢀ/228
2
2
2
c
d
e
386
391
381
389
463
466
466
457
475
503
465
ꢀꢀꢀꢀ
77
75
85
68
0.35
0.60
0.45
0.95
8
8
7.74/196.13/ꢀ/268
6.86/155.13/ꢀ/214
ꢀ/248.38/ꢀ/235
Ref
ꢀ/ꢀ/ꢀ/ꢀ/
[
[
a] The absorption spectra were measured in ethanol at 10 µM concentration.
b] The emission spectra were measured in ethanol at 10 µM concentration.
[36]
Ref ꢀ Coumarin 480.
c] The emission spectra were measured in solid state film.
d] Obtained from DSC and TGA measurements; T ꢀglass transition temperature,
ꢀmelting temperature and T ꢀcrystallization temperature.
[
[
g
T
m
c
Optical Band Gap
In organic molecules, the energy levels of the electronic states correspond to the
energy carried by UV or visible radiation. At resonance, the molecules can absorb quantified
energy transported by the electromagnetic radiation, and promote an electron from the lowꢀ
37
energy molecular orbital to higher energy molecular orbital. These transitions can be
measured using a UVꢀVis spectrophotometer. The optical band (ꢒ ꢓꢔ ꢕꢖ) corresponds to the
38
energy of the long wavelength edge of the exciton absorption band. The optical band gap
values (ꢒ ꢓꢔ ꢕꢖ) were approximated from the onset of the low energy side of the absorption
spectra (λonset, solution) to the baseline according to the equation (2) and are presented in
(Table. 2).
ꢙꢚꢛ
ꢘ
ꢑꢏꢜꢝ
ꢗ
=
ꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐ(2)
ꢞꢙꢎꢟꢠꢛ

Page 9 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA14550C
Solvent Effect
The solvatochromic behaviour of compounds 2(aꢀe) have been studied in series of
alcohols (methanolꢀpentanol) and some general solvents like toluene, dimethyle sulfoxide
(DMSO), dimethyleformamide (DMF), chloroform and dichloromethane (DCM) with a view
to understand the intramolecular charge transfer effect (ICT) as summarised in Table. 2 and
Fig. 3 & 4.This Solvatochromic behaviour gives the effect of solvents on absorbance and
fluorescence maxima through blue or red shifts in coumponds 2(aꢀe). The study of solvent
effect based on spectral properties of all compounds in solutions was carried out by using the
39
spectral position in the solvents mentioned here. As the shift in λmax values with solvent
type reflects molecular interactions. The spectral position of a compound in a variety of
solvents reveals interesting results. The absorption bands of solute molecules in different
solvents with varying polarity have shown bathochromic as well as hypsochromic shifts.
These shifts arise depending on the way a solute molecule interacts with solvent. The solute
molecule finds itself in a cavity inside the solvent, resulting in a net stabilization of their
ground state. During strong intramolecular charge transfer, if the dipole moment of solute
increases, the excited state is formed inside the solvent cavity which is surrounded by partly
oriented solvent dipoles. The net stabilization of the excited state as compared to the ground
state with increasing solvent polarity results in bathochromic shift. If there is a decrease in
dipole moment of solute during the intramolecular charge transfer, the excited state is formed
in a strained solvent cavity of oriented dipoles not correctly disposed for its efficient
stabilization. The energy of the ground state lowered more than that of the excited state with
increasing solvent polarity results in a hypsochromic shift.

RSC Advances
Page 10 of 25
View Article Online
DOI: 10.1039/C5RA14550C
1
. Methanol
1. Methanol
2. Ethanol
3. Propanol
2
a
31245
3542
2b
3
5241
1
0
0
.0
.5
.0
1
1.0
0.5
0.0
1.0
0.5
0.0
1.0
0.5
2
3
4
5
. Ethanol
. Propanol
. Butanol
. Pentanol
4
5
. Butanol
. Pentanol
3
1
4
2
5
0.0
1.0
300
400
500
600
300
400
500
600
Wavelength (nm)
Wavelength (nm)
3
5421
1.0
1. Methanol 1.0
. Ethanol
. Propanol
. Butanol
. Pentanol
2543 1
1. Methanol
2. Ethanol
3. Propanol
4. Butanol
5. Pentanol
2c
2d
1.0
2
3
4
5
1
5
3
0
.5
0.5
0
.5
4
0.5
0.0
2
1
2
3
4
5
0.0
0.0
0.0
300
400
500
600
300
400
500
600
700
Wavelength (nm)
Wavelength (nm)
1. Methanol
2e
241
5
2431
1.0
1.0
2
. Ethanol
. Propanol
. Butanol
. Pentanol
3
4
3
5
5
0
.5
0.5
0.0
0.0
300
400
500
600
Wavelength (nm)
Fig. 3: Typical absorption and fluorescence spectra of compounds 2(aꢀe) in series of
alcohols.

Page 11 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA14550C
1. Toluene
2
b
1. Toluene
2. DMSO
3. DMF
4. Chloroform
5. DCM
2
a
154 23
5
412
1542 3
1
0
0
.0
.5
.0
1.0
0.5
1.0
0.5
1.0
0.5
2
3
4
5
. DMSO
. DMF
. Chloroform
. DCM
3
3
4
2
5
1
0.0
1.0
0.0
1.0
0.0
1.0
3
00
400
500
600
300
400
500
600
Wavelength (nm)
Wavelength (nm)
1. Toluene
1
. Toluene
2
d
2
.0
c
521
1435
2
124 35
1
2. DMSO
2. DMSO
3
4
5
. DMF
. Chloroform
. DCM
3
4
5
. DMF
. Chloroform
. DCM
4
3
0
0
1
.5
.0
.0
0.5
0.0
1.0
0.5
0.0
0.5
0.0
2
1345
3
00
400
500
600
300
400
500
600
Wavelength (nm)
Wavelength (nm)
2
e
1. Toluene
. DMSO
. DMF
. Chloroform
. DCM
1
1 45 32
2
3
4
5
5
4
2
3
0
0
.5
.0
0.5
0.0
3
00
400
500
600
Wavelength (nm)
Fig. 4: Typical absorption and fluorescence spectra of compounds 2(aꢀe) in general solvents.

RSC Advances
Page 12 of 25
View Article Online
DOI: 10.1039/C5RA14550C
Table. 2: Summary of solvent effect on molecules 2(aꢀe)
2a
2b
2c
2d
2e
Solvent
λ
a
λ
f
λ
a
λ
f
λ
a
λ
f
λ
a
λ
f
λ
a
λ
f
Methanol
Ethanol
Propanol
Butanol
Pentanol
Toluene
DMSO
381
387
376
383
384
385
388
384
474
461
464
469
468
460
472
472
462
462
380
386
361
382
381
383
388
386
384
384
474
462
449
467
466
459
472
473
462
463
389
386
390
390
389
391
395
391
390
389
483
463
455
461
461
462
478
484
463
463
384
391
367
387
387
388
391
386
391
389
501
466
493
493
489
464
506
467
466
473
386
381
392
386
386
389
390
384
387
388
481
466
470
469
466
448
483
486
461
465
DMF
Chloroform 385
DCM 385
λ
λ
a
f
: Absorption maxima in nm
: Emission maxima in nm
Electrochemical Properties
The electrochemical properties of compounds 2(aꢀe) were explored by cyclic
voltammetry (CV). Further HOMOꢀLUMO energy levels of these molecules were calculated
from cyclic voltammetric measurements. HOMOꢀLUMO band gap is derived from the
difference between HOMO and LUMO energy levels. HOMO energy levels were calculated
40, 41
using Eq. (3).
ꢙꢎꢟꢠꢛ
ꢡꢌꢢꢌ = −ꢣꢗꢙꢤ + ꢜ. ꢜꢜꢥꢐ(ꢠꢦ)ꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐ(ꢧ)
The LUMO energy levels were estimated by using Eq. (4) and were compared with
those of Coumarin 480 (Table. 3). These results revealed the facile reversible redox
behaviour of the synthesized compounds and hence they can be applied as bipolar transport
materials for electroluminescence applications.
ꢭꢮꢯ
ꢨꢩꢢꢌ = ꢪꢡꢌꢢꢌ + ꢫꢬ ꢰꢐ(ꢠꢦ)ꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐꢐ(ꢜ)
The trend observed in the optical band gap values exhibited in the order 2e > 2a > 2b
>
2d > 2c. This reveals that the optical band gap values were significantly fluctuating from
(aꢀe). The biphenyl derivative (2c) has shown the lower optical band gap of 2.71 eV and this
was due to the extended conjugation of biphenyl system at the fifth position of oxadiazole
2

Page 13 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA14550C
unit. The difference in the optical band gap was observed between pentafluorophenyl (2d)
and napthyl derivatives (2e), in which (2d) showed comparatively lesser band gap than
compound (2e). Further, it was observed that the electronꢀwithdrawing pentafluorophenyl
based compound 2d has exhibited deepest HOMO level compared to all other derivatives
(Fig. 5).
2 2
Fig. 5: CV curves of compounds 2(aꢀe) were measured in CH Cl in the presence of
ꢀ1
4 6
nBu NPF at a scan rate of 100 mVs .

RSC Advances
Page 14 of 25
View Article Online
DOI: 10.1039/C5RA14550C
Table. 3: Electrochemical data of compound 2(aꢀe)
ꢙꢎꢟꢠꢛ
ꢗ
(
HOMO
(eV)
LUMO
(eV)
ꢙꢚꢛ
ꢘ
ꢙꢤ
Compound
ꢗ
(eV)
a
b
c
eV)
2
a
0.5
ꢀ5.3
ꢀ5.4
ꢀ5.3
ꢀ5.6
ꢀ5.3
ꢀ5.15
ꢀ2.49
ꢀ2.60
ꢀ2.59
ꢀ2.82
ꢀ2.45
ꢀ2.25
2.81 (441)
2.80 (442)
2.71 (457)
2.78 (446)
2.85 (435)
2.90 (427)
2b
0.6
0.5
0.8
0.5
2c
2d
2e
Ref
0.35
a
Oxidation potential relative to Ag/AgCl electrode.
b
Calculated HOMO from the onset Oxidation potentials of the compounds
ꢔꢱꢆꢇꢖ
HOMO =ꢀ[
ꢒ
+ 4.44] (eV).
ꢔꢄ
c
Estimated LUMO using empirical equations LUMO = (HOMO +ꢒ ꢓꢔ ꢕꢖ) (eV).
Theoretical Calculations
In order to explore the electronic structure and the HOMOꢀLUMO gap of
compounds 2(aꢀe), DFT calculations were performed using G09 software with basis sets
42
(
B3LYP/6ꢀ31G). The ground state optimized molecular structures of all compounds are
shown in Fig. 6. The HOMO, LUMO and energy band gap (E ) values are tabulated in
g
Table. 4. As demonstrated in (Fig. 6), the electron clouds of HOMO energy levels are all
mainly located on the bithiophene region of bipolar molecules and this data strongly counts
for good electron donating property of bithiophene unit. LUMO orbitals are mainly
concentrated on the oxadiazole core. Among the five compounds 2(aꢀe), the electronꢀ
withdrawing pentafluorophenyl based compound 2d has showed deepest HOMO level
compared to others (Fig. 6) which is also supported by CV calculations. The partial charge
separation of molecules 2(aꢀe) discloses their strong intramolecular charge transfer property,
which leads to controllable green colour emission. The computationally calculated HOMO
and LUMO energy values are in the range of ꢀ5.60376 eV to ꢀ5.35089 eV and ꢀ2.22809 eV to
ꢀ1.86753 eV respectively. Optical band gaps obtained from absorption thresholds are in the
range of 2.71to 2.85 eV which is in good agreement with the band gaps 3.15 eV to 3.74 eV
obtained using DFT. The energy level diagram of the frontier orbitals are shown in Fig. 7.
The presence of strong electron deficient oxadiazole unit results in the lowering of LUMO
level, which leads to a significant bathochromic shift in the electronic absorption. The
4
3
dihedral angle of the molecule clears that all compounds are approximately planar in nature
Fig. 8). Among the five derivatives, the biphenyl derivative (2c) showing twisted
(

Page 15 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA14550C
o
conformation at the biphenyl unit of around 36.02 and this might be the reason for drop
ꢇꢂꢈ
down in the ꢁ
and also for the decrease in the Stokes shift of around 8 nm in comparison
ꢂꢃꢄ
with naphthyl derivative (2e).
Compounds 2aꢀe
HOMO
LUMO
ꢀ5.36069
2
a
ꢀ2.11434
2
b
ꢀ5.38327
ꢀ2.22809
2
c
ꢀ2.17176
ꢀ5.37538
2
d
ꢀ5.60376
ꢀ1.86753
2
e
ꢀ5.35089
ꢀ2.16223
Fig. 6: Calculated molecular orbital amplitude plots of HOMO and LUMO levels and
optimized molecular structures of compounds 2(aꢀe).

RSC Advances
Page 16 of 25
View Article Online
DOI: 10.1039/C5RA14550C
Table. 4: DFT calculations for compounds 2(aꢀe)
ꢙꢚꢛ
ꢙꢎꢟꢠꢛ
Compounds ꢗꢙꢤ (eV)
HOMO (eV) LUMO (eV)
∆
E
(eV)
ꢐꢗꢘ (eV)
2
a
0.56
0.58
0.57
0.80
0.55
ꢀ5.36069
ꢀ5.38327
ꢀ5.37538
ꢀ5.60376
ꢀ5.35089
ꢀ2.11434
ꢀ2.22809
ꢀ2.17176
ꢀ1.86753
ꢀ2.16223
3.25
3.15
3.20
3.74
3.19
2.81 (441)
2.80 (442)
2.71 (457)
2.78 (446)
2.85 (435)
2b
2c
2d
2e
a
Band gap obtained using B3LYP/6ꢀ31G, ꢁE = HOMOꢀLUMO (eV).
b
Optical band gap energies were calculated from the equation Eopt = hc/λ = 1240/λ (eV),
where λ is the edge wavelength (in nm) of the UVꢀVis absorption spectrum.
LUMO
LUMO
LUMO
-2
-4
-6
LUMO
LUMO
3
.25eV
3
.15eV
3.20eV
3.74eV
3.19eV
HOMO
HOMO
HOMO
HOMO
HOMO
2
a
2b
2c
2d
2e
Fig. 7: Energy diagram of the frontier orbitals of compounds 2(aꢀe) estimated by DFT
calculations.

Page 17 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA14550C
1
5.380
10
2.770
2
2
a
1
5.320
2
3.780
10
2
b
2
3.960
1
3.460
3
6.020
2
c
1
3.270
2
1.410
2
1.730
2
d

RSC Advances
Page 18 of 25
View Article Online
DOI: 10.1039/C5RA14550C
1
5.900
1.660
2
0
.50
2
e
Fig. 8: The dihedral angles of compounds 2(aꢀe) according to the optimized structures.
Thermal Properties
The ability of a material to form morphologically stable films is an important
requirement for the successful operation of OLEDs. The thermal and morphological
stabilities of compounds 2(aꢀe) were determined by differential scanning calorimetry (DSC)
and thermal gravimetric analysis (TGA). The results are shown in (Fig. 9) and summarised in
o
(
Table. 1). DSC was performed in the temperature range 25ꢀ300 C under nitrogen with a
o
–1
heating rate of 10 C min . The phase transition properties of these compounds were
analyzed by DSC, it reveals that, compounds 2a, 2b, 2c and 2d are semicrystalline, and its
DSC curve shows an endothermic baseline shift related to the glass transition temperature
o
o
o
o
(
T ) at 87.36 C, 87.49 C, 87.74 C and 86.86 C respectively. It is important to notice that
g
g
the glass transition (T ) temperatures of compounds 2(aꢀd) are higher than those of the most
popular oxadiazoleꢀbased electronꢀtransporting materials, such as, 2ꢀ(4ꢀbiphenylyl)ꢀ5ꢀ(4ꢀtertꢀ
o
butylphenyl)ꢀ1,3,4ꢀoxadiazole (PBD,
g
T =60
C), 1,3ꢀbis[(4ꢀtertꢀbutylphenyl)ꢀ1,3,4ꢀ
o
oxadiazolyl]phenylene (OXDꢀ7, T
g
=77 C) and are higher than the nonꢀbipolar hostꢀemitters
o
o
25
that contain oxadiazoles (BOBP, T
g
=45 C; TPOs and PPOs, Tgs up to 121 C) . Followed
g
by the glass transition temperature (T ) compounds 2(aꢀd) shows an endothermic melting
o
peaks at temperature around 139ꢀ196 C. Compound 2e is a crystalline material with only one
o
sharp endothermic melting peak at 248.38 C being detected in the thermogram. Exothermic
peaks were not observed at higher temperature resulting from crystallisation, indicates
compounds with excellent amorphous glass state stability. The TGA results suggested that all
compounds were thermally stable with 5% weight loss temperatures (T ) of Compounds 2(aꢀ
5
d
o
2
e) under N , were ranged in 214ꢀ268 C, demonstrating good thermal stability.

Page 19 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA14550C
(a)
(b)
Fig. 9: (a) DSC and (b) TGA thermograms of the compounds 2(aꢀe) measured at a heating
o
ꢀ1
2
rate of 10 C min under N .
Conclusions
We have successfully designed and synthesized novel series of bithiophene
substituted oxadiazoles by employing a relatively simple synthetic protocol. Structures of
these newly synthesized compounds were established by their analytical and spectral data.
We have studied the optoelectronic properties like UVꢀVis spectra, fluorescence emission
spectra and quantum yield calculations. Additionally HOMOꢀLUMO calculations are

RSC Advances
Page 20 of 25
View Article Online
DOI: 10.1039/C5RA14550C
performed. All compounds fluoresce in the green range with high quantum yields. The
fluorescence quantum yield was found to be appreciable for pentafluorophenyl derivative
(2d) of 0.60 compare to reference (Coumarin 480). We have calculated HOMO, LUMO and
energy band gap values for all the compounds and optical band gaps obtained from
absorption thresholds are in good agreement with the band gaps obtained from DFT
calculations. The results revealed that the bithiopheneꢀsubstituted oxadiazole derivatives
could play an important role in optoelectronic applications.
Experimental Section
Physical Measurements
All chemicals are reagent/analytical grade and used without further purification. 5’ꢀ
Hexylꢀ2, 2’ꢀbithiopheneꢀ5ꢀboronic acid pinacol ester was purchased from SigmaꢀAldrich.
Melting points were determined by open capillary method and are uncorrected. The IR
1
spectra were recorded on Nicolet Impact 410 FT IR spectrophotometer using KBr pellets. H
13
3
and C NMR were recorded on Bruker 400ꢀMHz FT NMR spectrometer in CDCl by using
TMS as internal standard. Chemical shifts are reported in ppm downfield (δ) from TMS.
Mass spectra were recorded using Quadrupole LC/MS system with ESI resource. Elemental
analyses were performed on a Vario III elemental analyzer. The UVꢀis absorption spectra
were recorded using JASCO UVꢀVis NIR Spectrophotometer (Model Vꢀ670).
Photoluminescence spectra were measured using Spectroꢀfluorometer (JY Horiba, Floromaxꢀ
4). Fluorescence quantum yields (Φ) of the compound solutions were estimated by comparing
wavelengthꢀintegrated photoluminesce (PL) intensity of the compound solutions with that of
the reference. The DFT calculations were carried out using Gaussianꢀ09. Cyclic voltammetry
(CV) was carried out in a threeꢀelectrode cell with a Pt counter electrode, an Ag/AgCl
ꢀ1
reference electrode, and a glassy carbon working electrode at a scan rate of 100 mV s with
.1 M nBu NPF as the supporting electrolyte, in anhydrous dichloromethane solution. DSC
0
4
6
and TGA were performed with a TA Instruments DSC Q20 V24.10 Build 122 and TA
Instruments SDT Q600 V20.9 Build 20, respectively, under nitrogen with heating rates of 10
o
–1
C min .
Materials and Synthesis
All solvents were freshly distilled over appropriate drying reagents prior to use. All
starting materials were purchased from Sigma Aldrich and were used without further
purification. The required intermediate 4ꢀbromobenzhydrazide and compounds 1(aꢀe) were

Page 21 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA14550C
[30]
synthesized according to the published procedures.
The catalyst Pd(dppf) Cl and 5’ꢀ
2 2
Hexylꢀ2,2’ꢀbithiopheneꢀ5ꢀboronic acid pinacol ester was purchased from SigmaꢀAldrich.
General procedure for the synthesis of final compounds 2(aꢀe)
To a mixture of 4ꢀbromo phenyl 1,3,4ꢀoxadiazole 1(aꢀe) (0.5 g, 1.39 mmol), 5’ꢀHexylꢀ2,2’ꢀ
2 2
bithiopheneꢀ5ꢀboronic acid pinacol ester (0.25 g, 1.54 mmol), Pd(dppf) Cl (0.051 g, 0.07
mmol), as a catalyst were added to a mixure of 1,4 dioxane (10 mL) and aqueous 2M K CO
2
3
o
(
5 mL). The reaction mixture was heated for 6ꢀ8 h at 85ꢀ90 C under nitrogen. The progress
of the reaction was frequently monitored by TLC, the solution was extracted with CH Cl and
the organic layer was washed with water (25 mL) and brine solution (25 mL), and then dried
over anhydrous Na SO . Organic solvent was removed completely under reduced pressure,
2
2
2
4
the crude residue was purified by flash column chromatography on silica gel using plane
chloroform as an eluting solvent to obtain desired compound in 80ꢀ85% yield.
2
ꢀ(4ꢀtertꢀbutylphenyl)ꢀ5ꢀ(4ꢀ(5ꢀ(5ꢀhexylthiophenꢀ2ꢀyl)thiophenꢀ2ꢀyl)phenyl)ꢀ1,3,4ꢀ
oxadiazole (2a):
Yield: 82%, light green colour. MP = 143ꢀ145 °C. H NMR (500 MHz, CDCl
d, J = 7.6 Hz, 2H), 8.09 (d, J = 7.7 Hz, 2H), 7.74 (d, J = 7.6 Hz, 2H), 7.58 (d, J = 7.8 Hz,
H), 7.31 (d, J = 29.3 Hz, 1H), 7.07 (t, J = 19.5 Hz, 2H), 6.71 (d, J = 15.4 Hz, 1H), δ 2.83 (t,
1
3
) δ: 8.14
(
2
13
J = 7.2 Hz, 2H), 1.71 (d, J = 6.9 Hz, 2H), 1.38 (m, 6H), 0.93 (s, 3H); C NMR (126 MHz,
CDCl ) δ: 164.130, 155.349, 140.702, 137.216, 134.377, 127.455, 126.793, 126.065,
3
125.688, 125.018, 124.001, 123.768, 123.553, 122.460, 35.118, 31.586, 31.575, 31.149,
34 2 2
30.228, 29.787, 22.599, 14.107.; MS m/z calculated for C32H N OS 526.76, found 526
+
(
M ); Anal. Calcd (%) for C H N OS : C 72.96, H 6.51, N 5.32 Found: C 72.90, H 6.07, N
3
2
34
2
2
5.25.
2ꢀ(4ꢀ(5ꢀ(5ꢀhexylthiophenꢀ2ꢀyl)thiophenꢀ2ꢀyl)phenyl)ꢀ5ꢀ(thiophenꢀ2ꢀyl)ꢀ1,3,4ꢀoxadiazole
(2b):
Yield: 85%, green colour. MP = 158ꢀ160 °C. 1H NMR (500 MHz, CDCl
J = 2.6 Hz, 4H), 7.61 (3H), 7.20 (d, J = 2.3 Hz, 1H), 7.10 (d, J = 20.2, 2.0 Hz, 1H), 6.80 (d, J
20.2, 2.0 Hz, 1H), 6.71 (d, J = 20.2, 2.0 Hz 1H), 2.80 (2H), 1.72ꢀ1.34 (m, 8H), 0.92 (s, 3H);
3
) δ: 7.91 (d,
=
1
3
3
C NMR (126 MHz, CDCl ) δ: 164.5, 161.2, 143.3, 138.1, 136.7, 134.2, 133.8, 132.2, 128.5,
128.1, 127.9, 127.6, 126.8, 126.2, 125.9, 125.5, 43.1, 32.1, 31.9, 29.1, 22.8, 14.1; MS m/z
+
calculated for C26
H
24
N
2
OS
2
476.68, found 476 (M ); Anal. Calcd (%) for C26
H
24
N
2
OS
3
: C
65.51, H 5.07, N 5.88 Found: C 65.48, H 5.03, N 5.84.

RSC Advances
Page 22 of 25
View Article Online
DOI: 10.1039/C5RA14550C
2ꢀ(4ꢀ(5ꢀ(5ꢀhexylthiophenꢀ2ꢀyl)thiophenꢀ2ꢀyl)phenyl)ꢀ5ꢀ(biphenyl)ꢀ1,3,4ꢀoxadiazole (2c):
1
Yield: 78%, Light brown colour. MP = 198ꢀ200 °C. H NMR (500 MHz, CDCl
3
) δ:
8.17 (d, J = 7.6 Hz, 2H), 8.11 (d, J = 8.0 Hz, 2H), 7.72ꢀ7.61 (m, 4H), 7.45ꢀ7.33 (m, 4H), 7.31
(d, J = 29.3 Hz, 1H), 7.25 (t, J = 7.4 Hz, 1H), 7.07 (t, J = 19.5 Hz, 2H), 6.71 (d, J = 15.4 Hz,
13
1
H), δ 2.83 (t, J = 7.2 Hz, 2H), 1.71 (d, J = 6.9 Hz, 2H), 1.38 (m, 6H), 0.93 (s, 3H); C NMR
(
126 MHz, CDCl ) δ: 164.5, 143.1, 138.4, 136.7, 136.6, 134.2, 133.6, 129.3, 128.0, 127.9,
3
3o 2 2
127.7, 126.2, 125.1, 43.3, 32.1, 31.9, 29.1, 22.8, 14.1.; MS m/z calculated for C34H N OS
+
5
46.74, found 546 (M ); Anal. Calcd (%) for C34
H
30
N
2
OS
2
: C 74.96, H 5.53, N 5.12. Found:
C 74.89, H 5.47, N 5.15.
2
ꢀ(4ꢀ(5ꢀ(5ꢀhexylthiophenꢀ2ꢀyl)thiophenꢀ2ꢀyl)phenyl)ꢀ5ꢀ(perfluorophenyl)ꢀ1,3,4ꢀ
oxadiazole (2d):
Yield: 75%. Colour: dark green. MP = 160ꢀ163 °C. H NMR (500 MHz, CDCl
1
3
) δ:
8.08 (dd, J = 8.0 Hz, 1H), 7.74 (t, J = 10.8 Hz, 1H), 7.38 – 7.28 (m, 1H), 7.14 – 6.98 (m, 3H),
6.72 (dd, J = 3.1 Hz, 1H), δ 2.82 (dd, J = 8.7 Hz, 2H), 1.71 (dq, J = 7.5 Hz, 2H), 1.45 – 1.32
13
(
m, 7H), 0.92 (s, 3H); C NMR (126 MHz, CDCl
3
) δ: 165.49, 147.57, 140.33, 136.74,
135.35, 134.45, 127.85, 125.77, 124.84, 124.02, 123.55, 123.37.;19F NMR (400 MHz,
21 5 2 2
CDCl3) δ: ꢀ135.33, ꢀ147.23, ꢀ159.49; MS m/z calculated for C28H F N OS 560.60, found
+
5
60 (M ); Anal. Calcd (%) for C28
.69, N 4.96.
21 5 2 2
H F N OS : C 59.99, H 3.78, N 5.00 Found: C 59.91, H
3
2ꢀ(4ꢀ(5ꢀ(5ꢀhexylthiophenꢀ2ꢀyl)thiophenꢀ2ꢀyl)phenyl)ꢀ5ꢀ(naphthalenꢀ2ꢀyl)ꢀ1,3,4ꢀ
oxadiazole (2e):
Yield: 85%, Color: Light brown. MP = 238ꢀ240 °C. H NMR (500 MHz, CDCl
.34 (d, J = 8.5 Hz, 1H), 8.26 (d, J = 7.0 Hz, 1H), 8.14 (d, J = 7.8 Hz, 2H), 8.04 (d, J = 8.0
Hz, 1H), 7.93 (d, J = 8.0 Hz, 1H), 7.72 (t, J = 9.2 Hz, 3H), 7.61 (t, J = 7.4 Hz, 2H), 7.31 (d, J
2.3 Hz, 1H), 7.06 (dd, J = 2.0 Hz, 2H), 6.71 (s, 1H), δ 2.81 (t, J = 7.4 Hz, 2H), 1.70 (dd, J =
1
3
) δ:
9
=
1
3
7
1
1
3
.2 Hz, 2H), 1.38 (m, 6H), 0.94 (s, 3H); C NMR (126 MHz, CDCl ) δ: 164.47, 163.81,
46.07, 140.59, 138.85, 137.30, 134.36, 133.85, 132.57, 130.09, 128.69, 128.33, 128.18,
27.53, 126.71, 126.31, 125.63, 125.05, 124.92, 124.87, 123.97, 123.76, 122.22, 120.45; MS
+
m/z calculated for C32
H
28
N
2
OS
2
520.71, found 520 (M ); Anal. Calcd (%) for C32
H
28
N
2
OS
2
:
C 73.81, H 5.42, N 5.38. Found: C 73.75, H 5.38, N 5.36.
Acknowledgements

Page 23 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA14550C
The authors thank University Grants Commission (UGC), New Delhi, India, for
financial support CPEPA (No. 8ꢀ2/2008(NS/PE) and also to the University Scientific
Instruments Centre, Karnatak University, Dharwad for providing the spectral data.
References
1
S. J. Kim, Y. Zhang, C. Zuniga, S. Barlow, S. R. Marder and B. Kippelen, Org.
Electron., 2011, 12, 492ꢀ496.
2
3
4
5
6
7
Y. Yang, P. Cohn, S. H. Eom, K. A. Abboud, R. K. Castellano and J. Xue, J. Mater.
Chem. C., 2013, 1, 2867ꢀ2874.
Z. Li, H. Meng, Organic Light-Emitting Materials and Devices, CRC, Boca Raton,
FL, 2006.
M. A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S. Sibley, M. E. Thompson and
S. R. Forrest, Nature., 1998, 395, 151ꢀ154.
M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson and S. R. Forrest, Appl.
Phys. Lett., 1999, 75, 4ꢀ6.
S. H. Eom, Y. Zheng, E. Wrzesniewski, J. Lee, N. Chopra and F. So, J. Xue, Appl.
Phys. Lett., 2009, 94, 153303.
C. Liu, Y. Li, Y. Li, C. Yang, H. Wu, J. Qin and Y. Cao, Chem. Mater., 2013, 25,
3
320ꢀ3327.
8
9
1
1
J. Shinar and R. Shinar, J. Phys. D: Appl. Phys., 2008, 41, 133001.
S. Landgraf and J. Biochem, Biophys. Methods., 2004, 61, 125ꢀ134.
H. van Santen and J. H. M. Neijzen, Jpn. J. Appl. Phys., 2003, 42, 1110ꢀ1112.
Y. Fukuda, T. Watanabe, T. Wakimoto, S. Miyaguchi and M. Tsuchida, Synth. Met.,
0
1
2
000, 111, 1ꢀ6.
1
2
A. Haldi, J. B. Kim, B. Domercq, A. P. Kulkarni, S. Barlow, A. P. Gifford, S. A.
Jenekhe, S. R. Marder and B. Kippelen, J. Disp. Technol., 2009, 5, 120ꢀ125.
M. K. Huda and S. K. Dolui, Journal of Luminescence., 2010, 130, 2242ꢀ2246.
V. M. Niemi, P. Knuuttila, J. E. Osterholm and J. Korvola, Polymer. 1992, 33, 1559.
O. Bolton and J. Kim, J. Mater. Chem., 2007, 17, 1981.
13
14
15
16
K. Lee, J. M. Rouillard, T. Pham, E. Gulari and Jinsang Kim, Angew. Chem., Int. Ed.
2
007, 46, 4667.
1
1
7
8
K. Okumoto and Y. Shirota, Chem. Mater., 2003, 15, 699ꢀ707.
S. H. Cheng, S. H. Chou, W. Y. Hung, H. W. You, Y. M. Chen, A. Chaskar, Y. H.
Liu and K. T. Wonga, Org. Electron., 2013, 14, 1086ꢀ1093.
19
(a) M. Guan, Z. Chen, Z. Bian, Z. Liu, Z. Gong, W. Baik, H. Lee and C. Huang, Org.
Electron., 2006, 7, 330; (b) Y. Tao, Q. Wang, C. Yang, C. Zhong, K. Zhang, J. Qin
and D. Ma, Adv. Funct. Mater., 2010, 20, 304; (c) S. Gong, Y. Chen, J. Luo, C. Yang,
C. Zhong, J. Qin and D. Ma, Adv. Funct. Mater. 2011, 21, 1168.
20
21
22
(a) H. H. Chou and C. H. Cheng, Adv. Mater., 2010, 22, 2468; (b) C. Fan, F. Zhao, P.
Gan, S. Yang, T. Liu, C. Zhong, D. Ma, J. Qin and C. Yang, Chem. Eur., J. 2012, 18,
5
510; (c) S. O. Jeon and J. Y. Lee, J. Mater., Chem. 2012, 22, 4233.
(a) H. Inomata, K. Goushi, T. Masuko, T. Konno, T. Imai, H. Sasabe, J. J. Brown, C.
Adachi, Chem. Mater., 2004, 16, 1285; (b) H. F. Chen, S. J. Yang, Z. H. Tsai, W. Y.
Hung, T. C. Wang and K. T.Wong, J. Mater. Chem. 2009, 19, 8112.
(a) Z. Ge, T. Hayakawa, S. Ando, M. Ueda, T. Akiike, H. Miyamoto, T. Kajita, M.
Kakimoto, Adv. Funct. Mater., 2008, 18, 584; (b) C. H. Chen, W. S. Huang, M. Y.

RSC Advances
Page 24 of 25
View Article Online
DOI: 10.1039/C5RA14550C
Lai, W. C. Tsao, J. T. Lin, Y. H. Wu, T. H. Ke, L. Y. Chen and C. C. Wu, Adv. Funct.
Mater., 2009, 19, 2661.
23
24
25
26
J. Ma, Z. Li, Y. Zong, Y. Men and G. Xing, Tetrahedron Letters., 2013, 54, 1348ꢀ
1
351.
Y. Liu, K.Wang, G. Huang, C. Zhu, E. Tok, K. G. Neoh, E. T. Kang, Chem. Mater.,
009, 21, 3391ꢀ3399.
2
(a) P. Venkatakrishnan, P. Natarajan, J. N. Moorthy, Z. Lin, T. J. Chow,
Tetrahedron., 2012, 68, 7502ꢀ7508.
(a) C. Wang, G. Y. Jung, Y. Hua, C. Pearson, M. R. Bryce, M. C. Petty, A. S.
Batsanov, A. E. Goeta and J. A. K. Howard, Chem. Mater., 2001, 13, 1167ꢀ1173; (b)
M. Ichikawa, T. Kawaguchi, K. Kobayashi, T. Miki, K. Furukawa, T. Koyama and Y.
Taniguchi, J. Mater. Chem., 2006, 16, 221; (c) A. P. Kulkarni, C. J. Tonzola, A. Babel
and S. A. Jenekhe, Chem. Mater., 2004, 16, 4556; (d) G. Hughes, M. R. Bryce, J.
Mater. Chem., 2005, 15, 94; (e) Y. Shirota and H. Kageyama, Chem. Rev., 2007, 107,
9
53.
27
28
29
30
31
(a) U. Mitschke and P. Baeuerle, J. Mater. Chem., 2000, 10, 1471; (b) P. Strohriegl
and J. V. Grazulevicius, Adv. Mater., 2002, 14, 1439.
G. J. Zhao, R. K. Chen, M. T. Sun, J. Y. Liu, G. Y. Li, Y. L. Gao, K. L. Han, X. C.
Yang and L. Sun, Chem. Eur. J., 2006, 12, 225.
A. S. Kostyuchenko, V. L. Yurpalov, A. Kurowska, W. Domagala, A. Pron and A. S.
Fisyuk, Beilstein J. Org. Chem., 2014, 10, 1596ꢀ1602.
M. Shailaja, M. Anitha, A. Manjula and B. Vittal Rao. Indian J. Chem., 2010, 49B,
1
088ꢀ1097.
(a) K. T. Kamtekar, C. Wang, S. Bettington, A. S. Batsanov, I. F. Perepichka, M. R.
Bryce, J. H. Ahn, M. Rabinal, M. C. Petty and J. Mater. Chem., 2006, 16, 3823ꢀ3835;
(
2
b) C. Wang, L. O. Pålsson, A. S. Batsanov and M. R. Bryce, J. Am. Chem. Soc.,
006, 128, 3789ꢀ3799; (c) G. Mallesham, S. Balaiah, M. Ananth Reddy, B. Sridhar, P.
Singh, R. Srivastava, K. Bhanuprakash and V.J. Rao, Photochem. Photobiol. Sci.,
014, 13, 342ꢀ357.
2
32
Williams Patent, J. Deryck, Dimmic, W. Matt, JR. Haakenson, P. William, Al
Wideman, Shortt, J. Barry, Tim Cheeseright, Crawford, J. Michael, US2009/48311,
2
009, (A1) English.
3
3
3
4
S. Hou, W. K. Chan, Macromolecules., 2002, 35, 850ꢀ856.
S. Singh, L. K. Sharma, A. Saraswat, I. R. Siddiqui, H. K. Kehri and R. K. Pal Singh,
RSC Advances., 2013, 3, 4237ꢀ4245.
35
M. A. Shivkumar, K. S. Adarsh and S. R. Inamdar, Journal of Luminescence., 2013,
1
43, 680ꢀ686.
36
37
38
G. Jones, W. R. Jackson and C. Choi, J. Phys. Chem., 1985, 89, 294ꢀ300.
D. R. T. Zahn, G. N. Gavrila and M. Gorgoi, Chemical Physics., 2006, 325, 99ꢀ112.
P. I. Djurovich, E. I. Mayo, S. R. Forrest and M. E. Thompson, Org. Electron., 2009,
1
0, 515ꢀ520.
39
40
41
42
S. K. Patil, M. N. Wari, C. Y. Panicker and S. R. Inamdar, Spectrochimica Acta Part
A: Mol and Biomol Spectroscopy., 2014, 123, 117ꢀ126.
N. Prachumrak, S. Pansay, S. Namuangruk, T. Kaewin, S. Jungsuttiwong, T.
Sudyoadsuk and V. Promarak, Eur. J. Org. Chem., 2013, 6619ꢀ6628.
P. Kotchapadist, N. Prachumrak, T. Sunonnam, S. Namuangruk, T. Sudyoadsuk, T.
Keawin, S. Jungsuttiwong and V. Promarak, Eur. J. Org. Chem., 2015, 496ꢀ505.
Gaussian 09, Revision D.01,
M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R.
Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M.
Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L.
Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.

Page 25 of 25
RSC Advances
View Article Online
DOI: 10.1039/C5RA14550C
Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E.
Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N.
Staroverov, T. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C.
Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E.
Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K.
Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S.
Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski,
and D. J. Fox, Gaussian, Inc., Wallingford CT, 2013.
43
J. Huang, Y. Jiang, J. Yang, R. Tang, N. Xie, Q. Li, H.S. Kwok, B.Z. Tang and Z. Li,
J. Mater. Chem. C., 2014, 2, 2028ꢀ2036.