Third-order nonlinear optical properties of 3,4-ethylenedioxythiophene copolymers with chalcogenadiazole acceptors

Article abstract of DOI:10.1039/c4nj01899k

Two 3,4-ethylenedioxythiophene (EDOT) based low band gap donor-acceptor (D-A) conjugated copolymers were designed and synthesized via direct arylation, in which the HOMO-LUMO gaps were fine-tuned by the regular insertion of electron deficient units, 2,1,3-benzothiadiazole (BTZ) and 2,1,3-benzoselenadiazole (BTSe), respectively. Structural characterization was performed by FT-IR, ¹H NMR and XPS. In order to investigate the variation in the energy band structure of the copolymers, quantum-chemical calculation using density functional theory was carried out. The alternating insertion of the chalcogenadiazole unit in the PEDOT (poly(3,4-ethylenedioxythiophene)) lowers the HOMO and LUMO energy levels. As a result, the polymers with a lower band gap compared to that of the homopolymer, PEDOT, were obtained. Optical and electrochemical results confirmed that BTSe is marginally superior to BTZ in EDOT based alternate donor-acceptor copolymers. The present experimental results correlate well with HSE06 level theoretical calculations compared to those with the B3LYP level. Z-scan experiments reveal that the copolymers exhibit a strong nonlinear absorption coefficient and a nonlinear refraction coefficient of the order 10^-10 esu and the third-order nonlinear susceptibility is of the order of 10^-11 esu. These findings indicated that the EDOT-chalcogenadiazole copolymers can be developed into excellent third-order nonlinear optical materials.

Full text of DOI:10.1039/c4nj01899k

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Page 1 of 27
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DOI: 10.1039/C4NJ01899K
Thirdꢀorder nonlinear optical properties of 3,4ꢀethylenedioxythiophene
copolymers with chalcogenadiazole acceptors
Sona Narayanan,a§ Sreejesh Poikavila Raghunathan,aǂ Aby Cheruvathoor Poulose,bδ Sebastian
Mathew,cδ Krishnapillai Sreekumar,dΣ Cheranellore Sudha Kartha,eǂ Rani Josepha*
aDepartment of Polymer Science and Rubber Technology, Cochin University of Science and
Technology, Cochin-682022, Kerala, India
bBio-Nano Electronics Research Centre, Toyo University, Tokyo, Japan
cInternational School of Photonics, Cochin University of Science and Technology, Cochin-682022,
Kerala, India
dDepartment of Applied Chemistry, Cochin University of Science and Technology, Cochin-682022,
Kerala, India
eDepartment of Physics, Cochin University of Science and Technology,Cochin-682022, Kerala, India
*Corresponding author. Eꢀmail.: rani@cusat.ac.in, ranigeorge2011@gmail.com, Tel.: 09446467850
ǂ
δ
§Eꢀmail: sonachalil@gmail.com; Eꢀmail: prsreejesh@gmail.com; Eꢀmail: abypoulose@gmail.com;
δEꢀmail: mathewphys@gmail.com; ΣEꢀmail: ksk@cusat.ac.in; ǂEꢀmail: csk@cusat.ac.in
Abstract
Two 3,4ꢀethylenedioxythiophene (EDOT) based low band gap donorꢀacceptor (DꢀA)
conjugated copolymers were designed and synthesized via direct arylation, in which the
HOMOꢀLUMO gaps were fineꢀtuned by the regular insertion of electron deficient units,
2,1,3ꢀbenzothiadiazole (BTZ) and 2,1,3ꢀbenzoselenadiazole (BTSe), respectively. Structural
1
characterization was performed by FTꢀIR, H NMR and XPS. In order to investigate the
variation in energy band structure of the copolymers, quantumꢀchemical calculation using
density functional theory was carried out. The alternating insertion of chalcogenadiazole unit
in the PEDOT (poly(3,4ꢀethylenedioxythiophene)) lowers the HOMO and LUMO energy
levels. As a result, the polymers with lower band gap compared to that of the homopolymer,
PEDOT was obtained. Optical and electrochemical results confirmed that BTSe is marginally
superior to BTZ in EDOT based alternate donorꢀacceptor copolymers. Present experimental
results correlate with HSE06 level theoretical calculations than those with B3LYP level. Zꢀ
scan experiments reveal that the copolymers exhibit strong nonlinear absorption coefficient
and nonlinear refraction coefficient of the order 10–10 esu and the thirdꢀorder nonlinear
susceptibility is of the order of 10–11 esu. These findings indicated that the EDOTꢀ
chalcogenadiazole copolymers can be developed into excellent thirdꢀorder nonlinear optical
material.
Key words: DonorꢀAcceptor polymer; Direct arylation; Nonlinear optical properties.
1

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Introduction
Conjugated polymers with donorꢀacceptor architecture have been widely investigated in
photovoltaic devices,1 electrochromic devices,2 and in light emitting diodes (LEDs),3 owing to
their better electronꢀhole affinities and intramolecular charge transfer properties. Till date,
one of the best strategies to design narrow band gap polymers is the synthesis of an
alternating polymer containing electron rich (donor) and electron deficient (acceptor) unit in
the polyconjugated back bone, thereby allowing intramolecular charge transfer. Among the
conjugated polymers, EDOT based polymers continue to fascinate many researchers due to
their several advantages such as low ionization potential, high conductivity and good
environmental stability.4 EDOT is a good electron donor as it shows relatively high energy
HOMO level and small steric interaction between the repeating units. By copolymerizing
with different electron acceptors it gives low band gap polymers with good conductivity and
high stability. EDOT based low band gap conjugated polymers with alternate donorꢀacceptor
structures in the main chain have been intensively studied in several reports.5 Besides, there
are several reports on polycondensation of EDOT via direct arylation.6 Here we have focused
on the alternate donorꢀacceptor copolymers bearing EDOT, as their electronic properties can
be tuned efficiently by varying the acceptor moieties and a broadening of absorption
spectrum can be resulted. The interaction between the electron donor (D) and acceptor (A)
moieties in an alternating DꢀA copolymer can lead to the hybridization of the highꢀlying
HOMO energy level of the donor and lowꢀlying energy levels of the acceptor, leading to a
relatively small band gap polymer with novel electronic structure and ambipolar charge
transport properties.7
Recently π conjugated polymers bearing the benzothiadiazole (BTZ) unit have received great
deal of interest because of their potential applications in optoelectronic devices.8 The BTZ
moiety ensures strong electron injection or transporting properties and wide visible light
absorption in copolymers. Within the chalcogenadiazole family of charge transfer materials,
replacement of sulphur atom by selenium raises the dimensionality and conductivity of the
materials, because of strong intermolecular interaction between Se atoms and greater
stabilization effect towards radical cations.9 Based on this idea, we have investigated the
effect of introduction of two chalcogenadiazoles, 2,1,3ꢀbenzothiadiazole and 2,1,3ꢀ
benzoselenadiazole (BTSe) in to the PEDOT back bone, keeping in mind the higher acceptor
strength of the BTSe unit than the BTZ unit. In this report, the electronic properties of EDOT
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based DꢀA π conjugated polymers containing BTZ and BTSe moieties have been
investigated, both theoretically and experimentally. BTZ and BTSe units can serve as
electron accepting units, owing to the presence of two electron withdrawing imine (C=N)
nitrogens. Here we discuss the effect of BTZ and BTSe units as electron accepting moieties
and the influence of replacement of sulphur atom in the BTZ unit with selenium by
comparing the HOMO and LUMO energy levels. In recent years, organic photonic materials
possessing large nonlinear optical (NLO) properties are the subject of current research
interest, owing to their potential applications in a wide variety of optoelectronic and photonic
devices.10 Conjugated structures with donorꢀacceptor groups have been studied by several
researchers.11 However, there have been only a few reports on the thirdꢀorder nonlinear
optical properties of the polymers.12 Nevertheless, the organic NLO materials possess large
third order susceptibility, fast response time and processability.13 This in turn attracted our
interest in investigating nonlinear optical properties of donorꢀacceptor copolymers.
Therefore, thirdꢀorder optical nonlinearity of the EDOTꢀchalcogenadiazole copolymers has
been investigated using Zꢀscan method. This is for the first time a synthesis via direct
arylation is being discussed; followed by electrochemistry, optical, thermal and thirdꢀorder
nonlinear optical properties.
Experimental
Materials
3,4ꢀEthylenedioxythiophene (EDOT, Aldrich, 98%), oꢀphenylene diamine (Merck, 98%),
tetrabutyl ammonium bromide (TBAB, Avra Synthesis Pvt. Ltd., 98% ), sodium acetate
(anhydrous) (Spectrochem Pvt. Ltd.), triethyl amine (Spectrochem Pvt. Ltd.), palladium (II)
acetate (Pd(OAc)2, Aldrich, 99.98%), tetrabutyl ammonium hexafluorophosphate (Bu4NPF6,
Aldrich, >99%), thionyl chloride (SOCl2, Merck, 97%), hydrobromic acid (HBr,
Spectrochem Pvt. Ltd., 47%), bromine (Merck), sodium borohydride (NaBH4, Merck, 98%),
ethanol absolute (Merck), diethyl ether (Spectrochem Pvt. Ltd.), magnesium sulphate
(anhydrous) (MgSO4, Spectrochem Pvt. Ltd.) and selenium dioxide (SeO2, Aldrich, 98% )
were used as received. Acetonitrile HPLC grade (CH3CN, Aldrich), dimethyl acetamide
(anhydrous) (DMAc, Spectrochem Pvt. Ltd.), chloroform (CHCl3, Spectrochem Pvt. Ltd.),
dicholoromethane (CH2Cl2, Spectrochem Pvt. Ltd.), tetrahydrofuran HPLC grade (THF,
Spectrochem Pvt. Ltd.), nꢀhexane (Spectrochem Pvt. Ltd.) and methanol (anhydrous)
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(MeOH, Spectrochem Pvt. Ltd.) were dried and distilled when necessary according to the
standard procedures.
Computation methods
To determine the electronic properties of the EDOTꢀchalcogenadiazole copolymers,
(P(EDOTꢀBTZ) and P(EDOTꢀBTSe)), stepwise procedures involving quantum chemical
calculations, based on density functional theory (DFT) methods were followed.14 Initially, the
ground state geometries of oligomers were optimized by means of DFT at the B3LYP
(Becke, three parameter, LeeꢀYangꢀParr) level of theory.15 The DFT calculations at two
different energy levels were carried out with B3LYP and HSEh1PBE referred to as HSE06
(full HeydꢀScuseriaꢀErnzerh functional)16 (Both the calculations used 6ꢀ31G basis set as
implemented in Gaussian 09 package).17 The periodic boundary condition (PBC) calculation
was used to study the electronic properties of EDOTꢀchalcogenadiazole based copolymers.
The starting unit cell geometries for the PBC calculation were taken from the central portion
of the optimized oligomer and optimized inside a given lattice length on the constraints of
PBC by assuming that the unit cell is repeated identically an infinite number of times along
the translation vector. Band structure in the positive region of the first Brillouin zone
(between k=0 and k=π/a) were plotted. i.e., the lowest 4 unoccupied and highest 4 occupied
bands in the positive region of the first Brillouin zone were plotted.
Chemical procedures
Monomer synthesis
Scheme 1 summarizes the synthesis of key monomers. 2,1,3ꢀBenzothiadiazole (2) was
prepared from oꢀphenylenediamine (1) and SOCl2 in DCM, 4,7ꢀdibromo 2,1,3ꢀ
benzothiadiazole (3) was prepared by bromination of 2,1,3ꢀbenzothiadiazole in 47% HBr. To
obtain 4,7ꢀdibromo 2,1,3ꢀbenzoselenadiazole (5), 4,7ꢀdibromo 2,1,3ꢀbenzothiadiazole was
reduced by NaBH4 in absolute ethanol to give 2,3ꢀdiamino 1,4ꢀdibromobenzene (4). The 2,3ꢀ
diamino 1,4ꢀdibromobenzene was reacted with selenium dioxide to give 4,7ꢀdibromo 2,1,3ꢀ
benzoselenadiazole (5). All the reactions were performed according to standard procedures.18
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Polymer Synthesis (Scheme 2)
Synthesis of P(EDOTꢀBTZ) (7)
To a stirred solution of EDOT (6) (0.024 g, 0.17 mmol) in 10 mL DMAc was added TBAB
(0.055 g, 0.17 mmol) and sodium acetate (0.055 g, 0.68 mmol). The reaction mixture was
stirred at room temperature for 30 min followed by addition of 4,7ꢀdibromo 2,1,3ꢀ
benzothiadiazole (3) (0.05 g, 0.17 mmol) and 10% palladium acetate. The reaction mixture
o
was stirred at 90 C for 48 h. The reaction mixture was cooled to room temperature and
poured in to methanol (20 mL). The precipitate was filtered and washed with methanol. The
polymer was purified by soxhlet extraction using hexane and methanol for 24 h. The residue
was dissolved in minimum amount of CHCl3 and precipitated using methanol and dried under
vacuum. Yield: 58 %, FTꢀIR (νmax/cmꢀ1): 2956s and 2874s (CꢀH), 1080w, 1062s and 905w
1
(CꢀO), 1557br (conj.), 3097br (CꢀH ar), 1691(C=N); H NMR (400 MHz, d8ꢀTHF): δ (ppm):
4.5 (m, 4H), 7.6 (m, 2H).
Synthesis of P(EDOTꢀBTSe) (8)
To a stirred solution of EDOT (6) (0.024 g, 0.17 mmol) in 10 mL DMAc was added TBAB
(0.055 g, 0.17 mmol) and sodium acetate (0.055 g, 0.68 mmol). The reaction mixture was
stirred at room temperature for 30 min followed by addition of 4,7ꢀdibromo 2,1,3ꢀ
benzoselenadiazole (5) (0.06 g, 0.17 mmol) and 10% palladium acetate. The reaction mixture
was stirred at 90 oC for 48 h. The reaction was cooled to room temperature and poured in to
methanol (20 mL). The precipitate was filtered and washed with methanol. The polymer was
purified by soxhlet extraction using hexane and methanol for 24 h. The residue was dissolved
in minimum amount of CHCl3 and precipitated using methanol and dried under vacuum.
Yield: 55 %, FTꢀIR (νmax/cmꢀ1): 2956s and 2874s (CꢀH), 1094w, 1056s and 905w (CꢀO),
1
1588br (conjugation), 1697(C=N); H NMR (400 MHz, d8ꢀTHF): δ (ppm): 4.2 (m, 4H), 8.4
(m, 2H).
Instrumentation
Fourier Transform InfraꢀRed (FTꢀIR) spectra were obtained using Perkin Elmer
1
Spectrum 100, FTꢀIR Spectrometer. H Nuclear magnetic resonance (1H NMR) of polymers
was recorded on JEOL, JNMꢀEX400, FT NMR SYSTEM operating at 400 MHz and
chemical shifts were quoted downfield of TMS. Xꢀray Photoelectron Spectra (XPS) were
recorded using Kratos Analytical XPS equipped with a monochromator. The minimization of
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the chiꢀsquare was the criterion for the best fit performance in XPS peak 41 software. Gel
permeation chromatography (GPC) was carried out with Waters GPC with THF as the eluent.
All the electrochemical experiments were performed in dry acetonitrile with Bu4NPF6 (the
supporting electrolyte) using BAS Epsilon Electrochemical analyser with quiet time of 2 sec
and scan rate of 100 mV/s. Absorption spectra were measured with Thermo Scientific,
Evolution 201, UV–Visible spectrophotometer. Fluorescence spectra were recorded with DT
1000CE, Fluorescence spectrophotometer and were corrected for the spectral response of the
machines. Thermogravimetric measurements (TG & DTG) were performed on a TA
Instrument Q 50 thermogravimetricanalyzer with a continuous nitrogen flow and a heating
rate of 10 °C/min. Differential scanning calorimetry (DSC) was carried out on TA Instrument
Q 100 with a continuous nitrogen flow and a heating rate of 2 °C/min.
NLO Measurements
NLO properties were measured by the single beam Zꢀscan technique with nanosecond laser
performed with a Qꢀswitched Nd:YAG laser system (Spectra Physics LABꢀ1760) continuum
with pulse width of 7ns at 10 Hz repetition rate and 532 nm wavelength. The sample was
moved in the direction of light propagation near the focal spot of the lens with focal length of
200 mm. The radius of the beam waist was calculated to be 42.56 ꢁm. The Rayleigh length,
2
Z0 = πωo /λ, was calculated to be 10.69 mm, which was greater than the thickness of the
sample cuvette (1 mm), an essential requirement for zꢀscan experiments. The z scan system
was calibrated using CS2 as a standard. The transmitted beam energy, reference beam energy
and their ratios were measured simultaneously by an energy ratiometer (REj7620, Laser
Probe Corp.) having two identical pyroelectric detector heads (Rjp 735). The effect of
fluctuations of laser beam was eliminated by dividing the transmitted power by the power
obtained at the reference detector; both being measured using identical photo detectors. The
data were analysed by using the procedure described by Bahae et al.,19 and the nonlinear
coefficients were obtained by fitting the experimental zꢀscan plot with the theoretical plots.
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Results & Discussion
Theoretical calculation of electronic structure of conjugated polymers
To understand the electronic structure of P(EDOTꢀBTZ) and P(EDOTꢀBTSe) copolymers,
theoretical calculations were performed by hybrid density functional theory (DFT) using
B3LYP/6ꢀ31G level and HSE06/6ꢀ31G level. These are computationally cost effective
procedures to calculate the electronic structure with a good approximation and enable
elimination of unsuitable materials before synthesis. Before proceeding to evaluate the
electronic structure of the polymers, the ground state geometries of oligomers were optimized
by means of DFT at the B3LYP level of theory using 6ꢀ31G basis set and the results are
summarized in Fig. 1.
Fig. 1 Energy levels of EDOT, EDOT-BTZ, EDOT-BTSe, BTZ and BTSe.
The relative ordering of occupied and virtual orbitals provides reasonable qualitative
information regarding the excitation properties20 and ability of electron/hole transport. The
HOMO/LUMO energy levels describe electron or hole transporting capacity. As EDOT is
copolymerized with chalcogenadiazole moieties, HOMOs are elevated, and the LUMOs are
lowered, which facilitates electron and hole transport. The electron density isocountours of
HOMO and LUMO of the model compounds in P(EDOTꢀBTZ) and P(EDOTꢀBTSe) by
B3LYP/6ꢀ31G levels are plotted in Fig. 2.
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Fig. 2 Frontier molecular orbital distribution of monomeric units of P(EDOT-BTZ) and
P(EDOT-BTSe) by B3LYP/6-31G method.
Here the LUMO isocountours indicate more planar configuration in the singlet excited state,
leading to the efficient excitation of an electron from the HOMO to the LUMO level. Since
electrical and optical activity of materials relies on the ability of a material to transport
electrical charges through their structures, it could be concluded that EDOTꢀ
chalcogenadiazole copolymers consisting of BTZ and BTSe are good candidates for
application as donorꢀacceptor copolymers. Hence periodic boundary condition (PBC)
calculation, which is computationally economic than the oligomer approach was used to
solve the electronic structure of the copolymers at two levels of theory (B3LYP/6ꢀ31G and
HSE06/6ꢀ31G) and the evolved band structures with HSE06/6ꢀ31G levels are depicted in Fig.
3.
Fig. 3 Band structure of (A) P(EDOT-BTZ) and (B) P(EDOT-BTSe) by HSE06/6-31G
method.
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From the band structures, it is revealed that, by the introduction of chalcogenadiazole unit,
energy of HOMO level of PEDOT is lowered by a factor of 0.92 eV and 0.76 eV, while
LUMO level is lowered by a factor of 1.29 eV and 1.14 eV and we get P(EDOTꢀBTZ) and
P(EDOTꢀBTSe) with a reduced band gap of 1.26 eV and 1.25 eV, respectively. The
intramolecular charge transfer induced a quinoid character in the polymer back bone which
caused reduction in band gap. Here the electronic properties of the copolymers did not vary
systematically with the model compounds due to the change in geometry from model
compound to polymer. It could be seen from the band structure that all the polymers are
direct band gap polymers, because the lowest band gap occurs at k=0. There is no significant
decrease in the band gap on the introduction of BTSe unit instead of BTZ. This may be due to
the slight increase in the dihedral angle between the adjacent EDOT and BTSe than the BTZ
unit. Band structure data (HOMO, LUMO and HOMOꢀLUMO gap), ionization potential (IP)
and electron affinity (EA) of PEDOT and copolymers are compiled in Table 1.
Table 1 Computational data of P(EDOT-BTZ) and P(EDOT-BTSe) with DFT/B3LYP/6-31G
and DFT/HSE06/6-31G methods
Polymer
HOMO
(eV)
IP (eV)
LUMO (eV) EA (eV)
Eg (eV)
PEDOT
ꢀ3.62a
ꢀ4.71b
ꢀ4.54c
ꢀ4.51b
3.62a
4.71b
4.54c
4.51b
4.38c
ꢀ1.99a
ꢀ2.99b
ꢀ3.28c
ꢀ2.85b
ꢀ3.13c
1.99a
2.99b
3.28c
2.85b
3.13c
1.64a
1.72b
1.26c
1.66b
1.25c
P(EDOTꢀBTZ)
P(EDOTꢀBTSe)
ꢀ4.38c
b
c
aReproduced from ref.7, Obtained by the DFT/B3LYP/6ꢀ31G method, Obtained by the
DFT/HSE06/6ꢀ31G method.
The balanced transport of both injected electrons and holes are important as far as device
performance is considered. The enhancement in wellꢀdefined properties such as IP and EA
(negative of HOMO and LUMO energy, respectively) indicates an efficient electron
accepting/transporting ability in the copolymers.
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Polymer Synthesis
Donorꢀacceptor EDOTꢀchalcogenadiazole copolymers were synthesized via a simple, new
and facile route, i.e., direct arylation method.21 Usually EDOTꢀchalcogenadiazole copolymers
were synthesized through electrochemical polymerization.22 However, direct arylation
method confirms the regular alternation of donor and acceptor in the polyconjugated back
bone. The synthesis of key monomers and copolymers are summarized in Schemes 1 & 2.
Scheme1. Synthesis of chalocogenadiazole acceptors.
Scheme 2 Synthesis of P(EDOTꢀBTZ) and P(EDOTꢀBTSe).
The resulting copolymers were collected by precipitation to cold methanol followed by
filtration and the crude polymer was further purified by soxhlet extraction using methanol
and hexane to remove the oligomers. The molecular weights of the polymers were obtained
from gel permeation chromatography in THF referring to polystyrene standards. The isolated
yield and molecular weight of both the polymers are summarized in Table 2. The copolymers
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are readily soluble in common organic solvents such as THF and chlorobenzene (50mg/mL),
hence can be easily processed in to thin films.
Table 2 Results of polymerization of copolymers
Copolymer
Mna (Da)
3237
Mwa (Da)
4549
PDIa
1.82
1.66
Yield (%)
P(EDOTꢀBTZ)
P(EDOTꢀBTSe)
58
55
3580
4928
aDetermined by GPC in THF based on polystyrene standards.
Structural characterization
The copolymers, P(EDOTꢀBTZ) and P(EDOTꢀBTSe) were characterized by FTꢀIR
1
(Supporting information Fig. S1), H NMR and XPS. FTꢀIR spectrum of the P(EDOTꢀBTZ)
showed the characteristic peaks at 1080 and 1062 cmꢀ1, which were assigned to the stretching
vibration of bridged CꢀO in the ethylenedioxy unit and the peak at 905 cmꢀ1 is due to the
ethylenedioxy ring deformation mode, signifies the existence of EDOT moieties in the
copolymer.23 Furthermore, the vibration peaks at 3097 cmꢀ1 (aromatic CꢀH stretching) and
1691 cmꢀ1 (imine C=N stretching) were attributed to the incorporation of BTZ unit in the
polymer, P(EDOTꢀBTZ).24 P(EDOTꢀBTSe) also showed the vibration peaks at 1094 and
1056 cmꢀ1 (stretching vibration of bridged C_O in the ethylenedioxy unit) and the peak at 905
cmꢀ1 (ethylenedioxy ring deformation mode). The broad peak at 1697 cmꢀ1 is a marker for
BTSe moieties in the copolymer, P(EDOTꢀBTSe). The broad bands observed at 1557 and
1588 cmꢀ1 for P(EDOTꢀBTZ) and P(EDOTꢀBTSe), respectively prove the polyconjugation in
the copolymers.25 The results of these FTꢀIR analyses clearly indicated that copolymerization
was successfully achieved.
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Fig. 4 1H NMR spectra of (A) P(EDOT-BTZ) and (B) P(EDOT-BTSe)
1
In order to get more insight into the polymer structure H NMR (Fig. 4) was used for
analysis. The P(EDOTꢀBTZ) revealed resonance peaks at δ 7.6 ppm and 4.5 ppm because of
the aromatic protons of the BTZ units and ꢀOꢀCH2ꢀ protons of EDOT units, respectively.
P(EDOTꢀBTSe) also exhibited broad resonance peak at δ 8.4 ppm and 4.2 ppm
corresponding to aromatic protons of BTSe units and ꢀOꢀCH2ꢀ protons of EDOT units, is in
well agreement with FTꢀIR results.
Fig. 5 XPS survey scans of (a) P(EDOT-BTZ) and (b) P(EDOT-BTSe).
The copolymers were further investigated by XPS measurements. XPS survey scans are
summarized in Fig. 5. The signals related to C1s are observed at 284 eV, which are mainly
due to the aromatic carbon atoms of the polymeric conjugated backbone.26 The N1s signals
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appeared at 397 eV and 398 eV, respectively for P(EDOTꢀBTZ) and P(EDOTꢀBTSe) due to
the nitrogen atoms of the imine units of BTZ and BTSe moieties, which are attributed to the
C=N bonding.27 In addition, the O1s signals are observed at 531 eV, as expected. For both
copolymers, the signal related to the 2p core levels of the S atom is observed at 163 eV,
proved the presence of EDOT units. Whereas, P(EDOTꢀBTSe) showed an additional signal at
56 eV which was attributed to the presence of Se atom. Furthermore, the spectra of
copolymers confirmed the lack of contaminates. Noticeable peaks were absent at 334 and 340
eV indicating complete removal of catalyst (palladium) in the copolymers. Fig. 6 represents
the high resolution coreꢀelectron C1s spectra of P(EDOTꢀBTZ) and P(EDOTꢀBTSe)
copolymers. In the C1s coreꢀelectron spectra of P(EDOTꢀBTZ), the peak centered at 283 eV
is assigned to CꢀC and CꢀH bonds, where carbon is nonꢀbonded to any hetero atoms as
oxygen, nitrogen, sulphur etc. The peak centered at 284 eV is attributed to CꢀS bonds in the
copolymer and the peak centered at 286 eV is due to the combination of CꢀO and CꢀN bonds
present in the copolymer.28 In conclusion, the results obtained from XPS of copolymers are in
good agreement with those corresponding to FTꢀIR and 1H NMR.
Fig. 6 (A) C1s high resolution spectra of P(EDOT-BTZ) and (B) C1s high resolution spectra
P(EDOT-BTSe).
Electrochemical properties
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Electrochemical measurements were performed to determine the HOMO and LUMO energy
levels of P(EDOTꢀBTZ) and P(EDOTꢀBTSe). Cyclic voltammetry (CV), differential pulse
voltammetry (DPV) and square wave voltammetry (SWV) were performed on these
copolymers to analyse the electrochemical behaviour of the polymers in detail.
Table 3 Redox properties of P(EDOTꢀBTZ) and P(EDOTꢀBTSe)
Polymer
Onset of
oxidation
(eV)
HOMO
(eV)
Onset of
reduction
(eV)
LUMO
(eV)
Band Gap
(eV)
P(EDOTꢀBTZ)
P(EDOTꢀBTSe)
0.32a
0.26b
0.25c
0.30a
0.23b
0.26c
ꢀ4.72a
ꢀ4.66b
ꢀ4.65c
ꢀ4.70a
ꢀ4.63b
4.66c
ꢀ0.87a
ꢀ0.80b
ꢀ0.80c
ꢀ0.81a
ꢀ0.80b
ꢀ0.80c
ꢀ3.53a
ꢀ3.6b
ꢀ3.6c
ꢀ3.59a
ꢀ3.6b
3.6c
1.19a
1.06b
1.05c
1.11a
1.03b
1.06c
1.64
P(EDOT)d
ꢀ3.62
ꢀ1.99
P(EDOTꢀBTZꢀEDOT)e
1.19
1.05
P(EDOTꢀBTSeꢀ
EDOT)e
b
c
d
aDetermined by CV, Determined by DPV, Determined by SWV, Reproduced from ref.7,
eReproduced from ref.29.
In order to get a clear comparison, the electrochemical data is summarized in Table 3,
revealing that all the methods showed a good agreement with theoretical calculation. From
the onset of oxidation, the HOMO levels of P(EDOTꢀBTZ) and P(EDOTꢀBTSe) were
calculated to be ꢀ4.66 eV and ꢀ4.63 eV (DPV), respectively based on the equation, HOMO=
ꢀ(4.4+Eoxonset). The SCE energy level of ꢀ4.4 eV below the vacuum level is used. While the
LUMO energy levels (from the onset of reduction potential) of P(EDOTꢀBTZ) and P(EDOTꢀ
BTSe) are calculated to be ꢀ3.6 eV and ꢀ3.6 eV, respectively. In both the polymers, the
HOMO and LUMO energies were lowered on copolymerization, indicating enhanced
electron accepting/transporting properties in conjugated backbone. The results are in good
agreement with DFT/PBC calculation, though some deviation still exists. This is due to, the
fact that the predicted band gaps are for the isolated gasꢀphase chains and also, the solid state
effects such as polarization effects and intermolecular packing forces are neglected.30
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Electrochemical measurements, DPV and SWV yielded close values for both copolymers.
Thus, through copolymerization, electron injection and transportation are expected to be
enhanced.
Optical Properties
A regular alternation of conjugated donor and acceptor moieties increases the double bond
character which leads to broadening of valence and conduction band. The normalized
absorption spectra of pristine polymers in THF solution and as thin films are reported in Fig.
7. The absorption spectra of P(EDOTꢀBTZ) and P(EDOTꢀBTSe) were characterized with
strong and broad absorption peaks at 532 and 537 nm (λ max), respectively with onset at 725
and 768 nm, respectively. This can be assigned to the intramolecular charge transfer (ICT)
transition between the donor unit (EDOT) and acceptor unit (chalcogenadiazole). The
copolymers also display a characteristic peak at lower wavelength due to high energy
transition such as πꢀπ* transition of the conjugated backbone. The thin film absorption of
both copolymers has much broad absorption range than solution absorption spectra. The
optical band gaps (Egopt) derived from the absorption edge of the polymer thin film for
P(EDOTꢀBTZ) and P(EDOTꢀBTSe) are 1.04 and 1.04 eV respectively, differing by 0.67 and
0.57 eV respectively, from the solution optical band gap values. As expected, both P(EDOTꢀ
BTZ) and P(EDOTꢀBTSe) copolymers exhibit low band gap compared to PEDOT (1.6 eV),
reflecting the enhanced acceptor property of the BTZ and BTSe unit, which lowers the
LUMO levels, leading to low band gap.
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Fig. 7 UV-Visible spectra of the copolymers in THF solution (a) P(EDOT-BTZ) (b) P(EDOT-
BTSe) and in thin film (c) P(EDOT-BTZ), (d) P(EDOT-BTSe). The polymer films were spin
coated from CHCl3 solution on to glass substrate.
Compared with solution absorption, the film sample prepared by spin coating showed
pronounced peak broadening and a remarkable red shift of approximately above 470 nm of
the absorption edge. This significant red shift is attributed to the planarization of aryl rings
and the presence of inter chain interactions in the solid state. These Egopt values agree closely
with theoretical results, obtained by HSE06/6ꢀ31G method than the B3LYP/6ꢀ31G method.
Photoluminescence properties
The photoluminescence spectra of the polymers in THF solution are shown in Fig. 8. The
wavelengths corresponding to the absorption maxima of the polymers are used as the
excitation wavelength. P(EDOTꢀBTZ) and P(EDOTꢀBTSe) exhibit fluorescence in THF with
an emission max at 689 and 667 nm, respectively, regardless of excitation. The PL emission
spectrum was red shifted for P(EDOTꢀBTZ) relative to those of P(EDOTꢀBTSe) and this
suggests the high energy transfer of EDOT (donor) unit to BTZ (acceptor) unit.
Fig. 8 PL spectra of the polymers (a) P(EDOT-BTZ) and (b) P(EDOT-BTSe) in THF solution.
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Thermal properties
The thermal characteristics of the polymers were investigated by DSC and TGA. The TGA
curves are shown in Fig. 9. DSC showed no characteristic thermal transition between 40 and
200 °C. This suggests that the polymers were in an amorphous glassy state, probably due to
the rigid backbone in the copolymer, making it suitable for device applications. From the
TGA curves, it was found that the copolymers exhibited step wise degradation and the
decomposition exotherms are broad with multiple peaks. The first exotherm can be assigned
to elimination of imine (C=N) nitrogen which is more susceptible to degradation. TGA
o
curves of P(EDOTꢀBTZ) showed degradation temperature of 160 and 426 C and onset
o
degradation temperature of 103 and 344 C, choosing 5% weight loss as the onset loss point.
o
P(EDOTꢀBTSe) has onset degradation temperature of 203 and 371 C and degradation
o
temperature of 335 and 399 C, which is an indication of excellent thermal stability than
PEDOT. The DTA peaks show exotherms at this temperature which is indicative of
degradation rather than vaporization. Kiebooms et al. have reported that PEDOT films are
stable upto 150°C and complete decomposition occurs above 390 °C.31 The P(EDOTꢀBTSe)
exhibits higher onset and peak degradation temperatures than P(EDOTꢀBTZ) and PEDOT.
This is probably due to intermolecular van der Waals bonding between the Se units, which
result in self rigidification in the polymer chain.
Fig. 9 TG and DTG curves of polymers (a) P(EDOT-BTZ) and (b) P(EDOT-BTSe).
Nonlinear optical properties
The nonlinear optical transmission of DꢀA copolymers was investigated using Zꢀscan
technique, which is known for simplicity and sensitivity. The NLO absorption coefficients
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were evaluated by Zꢀscan technique under an open aperture configuration. Fig. 10 presents
the open aperture (OA) Zꢀscan traces of copolymers in dilute CHCl3 solution (a) and as thin
film (b). The solid curves in Fig. 10 are the theoretical fit to the experimental data.
Fig. 10 Open aperture Z-scan traces of P(EDOT-BTZ) and P(EDOT-BTSe) (A) in solution
and (B) as film.
In solution phase, the openꢀaperture curve shows a normalized valley, indicating the presence
of reverse saturation absorption (RSA) with a positive coefficient. However, the copolymer
films exhibit different optical response. The polymers show saturation absorption (SA) in
film phase. The polymers show complete switch over behaviour from RSA to SA in thin film.
This could be due to ground state band bleaching32 i.e., the excited state absorption and free
carrier absorption results ground state band bleaching. From the figure it could be seen that
the experimental curve is fitted well with two photon absorption (TPA) theory. This infers
that TPA is the basic mechanism involved in the nonlinear absorption process. The nonlinear
absorption coefficient, β is obtained by fitting the experimental scan plot of the OA
measurement to equation 1.
∞
T(z)=
ln(1+ q0 e −t 2)dt
(1)
C
∫
π
q0
−∞
where q0(z,r,t) = βI0(t)Leff and Leff = (1ꢀ
)/α is the effective thickness with linear absorption
coefficient α, and I0 is the irradiance at focus. The imaginary part of the thirdꢀorder
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susceptibility, Im Χ(3)=n0 c2 β/(240π2ω), where n0= 1.45 is the linear refractive index of the
2
polymer solution, c is the velocity of light in vacuum, ω is the angular frequency of radiation
used.
The nonlinear refractive (NLR) property of the copolymers was investigated by closed
aperture (CA) Zꢀscan configuration. The pure NLR Zꢀscan curves after excluding nonlinear
absorption effects can be obtained by dividing the CA Zꢀscan data by the corresponding open
aperture data (Fig. 11). The normalized transmittance T(z) is given by equation (2),
4xꢀΦ0
(x2 +9)(x2 +1)
T(z) =1−
(2)
where Φ0 is onꢀaxis nonlinear phase shift and x is given by z/z0. All the spectra display
peakꢀvalley pattern, indicating a negative NLR index due to selfꢀdefocusing. The nonlinear
refractive index (n2), the real parts of χ (3) (Re χ (3)) and thirdꢀorder nonlinear susceptibility
(
χ (3)) are calculated by the following equations (3), (4) and (5).
cn0
n2 (esu)=
γ
(3)
40π
n0 n2
Re χ (3)
=
(esu)
(4)
(5)
3π
χ (3) Re χ (3) +i Im χ (3)
=
where γ, the molecular cubic hyperpolarizability of polymer can be estimated through the
ꢀn0
I0
ꢀΦ0
k Leff
following equations
γ
=
and ꢀn0 =
where k is wave vector.
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Fig. 11 Closed aperture Z-scan traces of P(EDOT-BTZ) and P(EDOT-BTSe).
The nonlinear absorption coefficient (β, m/W), the nonlinear refraction coefficient (n2, esu),
the thirdꢀorder nonlinear susceptibility ( χ (3), esu) and the molecular cubic hyperpolarizability
(γ, esu) are calculated and listed in Table 4. The β is obtainedto be 0.8 ˟ 10ꢀ10 and 2.08 ˟ 10ꢀ10
m/W for P(EDOTꢀBTZ) and P(EDOTꢀBTSe), respectively. In addition, the χ (3) value is also
found to be increased for P(EDOTꢀBTSe). As given in table, it is found that the P(EDOTꢀ
BTSe) show large optical nonlinearity than P(EDOTꢀBTZ), as expected. This is due to the
higher acceptor strength of BTSe than the BTZ unit. The magnitude of the nonlinear
refractive index is directly related to the polarizability of polymers. In DꢀA compounds,
nonlinearity is mainly due to the charge transfer from donor to acceptor unit i.e., the
nonlinearity due to strong delocalization of π electrons or in other words, due to charge
asymmetry.
Table 4 Calculated values of nonlinear absorption, nonlinear refraction, and nonlinear
susceptibility of copolymers.
Copolymer
Nonlinear
absorption
coefficient
(β, m/W)
Nonlinear
refractive
index (n2, esu)
Imaginary part Real part of Nonlinear
of nonlinear nonlinear susceptibility
susceptibility susceptibility
(3), esu)
(Im (Re
(3), esu) (3), esu)
(
χ
χ
χ
P(EDOTꢀBTZ)
0.8 ˟ 10ꢀ10
ꢀ0.464 ˟ 10ꢀ10
0.02 ˟ 10ꢀ10
ꢀ0.714 ˟ 10ꢀ11
0.74 ˟ 10ꢀ11
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P(EDOTꢀBTSe)
PABAzoa
2.08 ˟ 10ꢀ10
3.33 ˟ 10ꢀ10
1.07 ˟ 10ꢀ10
2.17 ˟ 10ꢀ12
ꢀ1.29 ˟ 10ꢀ10
ꢀ0.81 ˟ 10ꢀ11
0.05 ˟ 10ꢀ10
0.11 ˟ 10ꢀ10
ꢀ1.98 ˟ 10ꢀ11
ꢀ1.84 ˟ 10ꢀ11
2.04 ˟ 10ꢀ11
2.15 ˟ 10ꢀ11
PꢀNPAPAꢀ5b
PANI/SiO2c
PMMAꢀM3d
2.29 ˟ 10ꢀ12
b
c
d
aReproduced from ref.33, Reproduced from ref.34, Reproduced from ref.35, Reproduced
from ref.36.
Optical power limiting
The nonlinear process in which the transmittance of a material decreases as the input light
intensity increases is called optical limiting process. This occurs mostly due to nonlinear
absorption. Optical limiters are devices which are transparent at low input fluences, but
become opaque at high inputs, used for the protection of eyes and sensitive optical devices
from laser induced damage. The optical limiting property of the copolymers was investigated
by OA Zꢀscan technique. Fig. 12 shows the transmitted energy of copolymers as a function of
input fluence.
Fig. 12 Optical limiting curves of P(EDOTꢀBTZ) and P(EDOTꢀBTSe).
At lower fluence, polymers obey Beer’s law very well. When the input energy reaches optical
limiting threshold, the transmitted energy starts to deviate and exhibit a typical optical
limiting effect. Optical limiting threshold is determined to be 0.34 and 0.25 GW/cm2 for
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P(EDOTꢀBTZ) and P(EDOTꢀBTSe), respectively. The lower the optical limiting threshold
the better the optical limiting material. The P(EDOTꢀBTSe) showed good optical limiting
response than P(EDOTꢀBTZ). This is due to the large variation of the dipole moment of the
polymer in the excited electronic state.37
Conclusions
Two promising low band gap donorꢀacceptor 3,4ꢀethylenedioxythiophene based alternate
copolymers have been designed and successfully synthesized via direct arylation reaction
using palladium acetate as catalyst. Electronic properties of the two polymers based on 3,4ꢀ
ethylenedioxythiophene and 2,1,3ꢀchalcogenadiazole were calculated using density
functional theory under periodic boundary condition. Theoretical calculation revealed the
highest occupied molecular orbital and lowest unoccupied molecular orbital levels of the
P(EDOTꢀBTZ) at ꢀ4.54 and ꢀ3.28 eV respectively, and showed a band gap of 1.26 eV. The
highest occupied molecular orbital and lowest unoccupied molecular orbital levels of the
P(EDOTꢀBTSe) were revealed at ꢀ4.38 eV and ꢀ3.13 eV respectively, and hence had a band
gap of 1.25 eV. The polymer exhibited good thermal and chemical stability, as evidenced by
thermogravimetry and cyclic voltammetry. Polymers exhibited broad absorption band and the
band gaps were estimated to be 1.04 eV for both P(EDOTꢀBTZ) and P(EDOTꢀBTSe). The
band gap and energy levels of the polymers were determined using both optical and
electrochemical methods. The results showed good agreement with the theoretical prediction
obtained by HSE06/6ꢀ31G method compared to the B3LYP/6ꢀ31G method. The Zꢀscan
results indicated that the copolymers exhibited negative nonlinear refractive index which was
of the order of 10ꢀ10 esu. The nonlinear absorption coefficient (β, m/W) and thirdꢀorder
nonlinear susceptibility ( χ (3), esu) of polymers are in the order of 10ꢀ10 and 10ꢀ11,
respectively. The polymers exhibited good optical power limiting behaviour at 532 nm.
Hence the polymers investigated seem to be promising candidates for future photonic
applications.
Acknowledgement
The authors gratefully acknowledge financial support from University Grants Commission Research
Fellowships in Sciences for Meritorious Students (UGCꢀRFSMS), Department of Science and
Technology (DST) and Council of Scientific and Industrial Research (CSIR), Government of India.
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References
1 (a) P. Dutta, H. Park, W. ꢀH. Lee, I. N. Kang and S. ꢀH. Lee, Polym. Chem., 2014, 5, 132;
(b) Q. Hou, J. Liu, T. Jia, S. Luo and G. Shi, J. Appl. Polym. Sci., 2013, 130, 3276; (c) W.
Zhuang, M. Bolognesi, M. Seri, P. Henriksson, D. Gedefaw, R. Kroon, M. Jarvid, A.
Lundin, E. Wang, M. Muccini and M. R. Andersson, Macromolecules, 2013, 46, 8488; (d)
E. Zhou, J. Cong, K. Hashimoto and K. Tajima, Macromolecules, 2013, 46, 763; (e) L.
Dou, C. ꢀC. Chen, K. Yoshimura, K. Ohya, W. ꢀH. Chang, J. Gao, Y. Liu, E. Richard and
Y. Yang, Macromolecules, 2013, 46, 3384.
2 (a) P. M. Beaujuge and J. R. Reynolds, Chem. Rev., 2010, 110, 268; (b) P. Shi, C. M. Amb,
A. L. Dyer and J. R. Reynolds, Appl. Mater. Interfaces, 2012, 4, 6512; (c) E. Kaya, A.
Balan, D. Baran and A. Cirpan, Organic Electronics, 2011, 12, 202.
3 (a) N. R. Evans, L. S. Devi, C. S. K. Mak, S. E. Watkins, S. I. Pascu, A. Kohler, R. H.
Friend, C. K. Williams and A. B. Holmes, J. Am. Chem. Soc., 2006, 128, 6647; (b) Q.
Huang, G. A. Evmenenko, P. Dutta, P. Lee, N. R. Armstrong and T. J. Marks, J. Am.
Chem. Soc., 2005, 127, 10227.
4 (a) L. Groenendaal, F. Jonas, D. Freitag, H. Pielartzik and J. R. Reynolds, Adv. Mater.,
2000, 12, 481; (b) L. Groenendaal, G. Zotti, P. ꢀH. Aubert, S. M. Waybright and J. R.
Reynolds, Adv. Mater., 2003, 15, 855.
5 (a) H. Huang and P. G. Pickup, Chem. Mater., 1998, 10, 2212; (b) J. RaultꢀBerthelot and
E. Raoult, Adv. Mat. Opt. Electr., 2000, 10, 267; (c) J. RaultꢀBerthelot, E. Raoult, F. L.
Floch, J. Electroanal. Chem., 2003, 546, 29; (d) S. Akoudad and J. Roncali, Chem.
Commun., 1998, 2081.
6 (a) K. Yamazaki, J. Kuwabara and T. Kanbara, Macromol. Rapid Commun., 2013, 34, 69;
(b) J. Kuwabara, T. Yasuda, S. J. Choi, W. Lu, K. Yamazaki, S. Kagaya, L. Han and T.
Kanbara, Adv. Funct. Mater., 2014, 24, 3226; (c) Y. Nohara, J. Kuwabara, T. Yasuda, L.
Han and T. Kanbara, J. Polym. Sci. A Polym. Chem., 2014, 52, 1401; (d) A. E. Rudenko
and B. C. Thompson, J. Polym. Sci. A Polym. Chem., 2014, DOI: 10.1002/pola.27279; (e)
M. K. Poduval, P. M. Burrezo, Juan Casado, J. T. L. Navarrete, R. P. Ortiz and T. ꢀH.
Kim, Macromolecules, 2013, 46, 9220.
7 C. ꢀL. Pai, C. ꢀL. Liu, W. ꢀC. Chen and S. A. Jenekhec, Polymer, 2006, 47, 699.
23

New Journal of Chemistry
Page 24 of 27
View Article Online
DOI: 10.1039/C4NJ01899K
8 S. Ellinger, K. R. Graham, P. Shi, R. T. Farley, T. T. Steckler, R. N. Brookins, P.
Taranekar, J. Mei, L. A. Padilha, T. R. Ensley, H. Hu, S. Webster, D. J. Hagan, E. W. V.
Stryland, K. S. Schanze and J. R. Reynolds, Chem. Mater., 2011, 23, 3805.
9 (a) D. Cowan and A. Kini, The Chemistry of Organic Selenium and Tellurium Compounds:
Wiley: Chichester, U. K, 1987, Vol. 2; (b) M. R. Bryce, J. Mater. Chem., 1995, 5, 1481.
10 (a) M. Bass, J. M. Enoch, E. W. Van Stryland and W. L. Wolfe, Handbooks of optics IV,
Fiber optics and nonlinear optics: New York, McGrawꢀHill, 2001, 2nded.; (b) Y. Guo , C.
K. Kao, E. H. Li and K. S. Chiang, Nonlinear photonics: Berlin, Springer., 2002.
11 (a) S. Webster, J. Fu, L. A. Padilha, O. V. Przhonska, D. J. Hagan, E. W. Van Stryland, M.
V. Bondar, Y. L. Slominsky and A. D. Kachkovski, Chem. Phys., 2008, 348, 143; (b) M.
Charlot, N. Izard, O. Mongin, D. Riehl and M. BlanchardꢀDesce, Chem. Phys. Lett., 2006,
417, 297; (c) L. A. Padilha, S. Webster, O. V. Przhonska, H. Hu, D. Peceli, J. L. Rosch,
M. V. Bondar, A. O. Gerasov, Y. P. Kovtun, M. P. Shandura, A. D. Kachkovski, D. J.
Hagan and E. W. Van Stryland, J. Mater. Chem., 2009, 19, 7503; (d) Y. Jiang, Y. Wang, J.
Hua, S. Qu, S. Qian and H. Tian, J. Polym. Sci. A Polym. Chem., 2009, 47, 4400; (e) B. Li,
R. Tong, R. Zhu, F. Meng, H. Tian and S. Qian, J. Phys. Chem. B, 2005, 109, 10705.
12 (a) R. Sun, Y. ꢀT. Lu, B. ꢀL. Yan, J. ꢀM. Lu, X. ꢀZ. Wu, Y. ꢀL. Song and J. ꢀF. Ge, Thin
Solid Films, 2014, 551, 153; (b) C. Cabanetos, E. Blart, Y. Pellegrin, V. Montembault, L.
Fontaine, F. Adamietz, V. Rodriguez and F. Odobel, Eur. Polym. J., 2012, 48, 116; (c) J.
Britton, M. Durmus, V. Chauke and T. Nyokong, J. Mol. Struct., 2013, 1054–1055, 209.
13 (a) P. N. Prasad and D. J. Williams, Introduction to nonlinear optical effects in molecules
and polymers: New York, Wiley, 1992; (b) H. N. Nalwa and S. Miyata, Nonlinear optics
of organic molecules and polymers: USA, CRC Press, 1997.
14 R. G. Parr and W. Yang, DensityꢀFunctional Theory of Atoms and Molecules: Oxford
University Press, New York, 1989.
15 (a) A. D. Becke, J. Chem. Phys., 1993, 98, 5648; (b) C. Lee, W. Yang and R. G. Parr,
Phys. Rev. B., 1994, 37, 785; (c) P. J. Stephens, F. J. Devlin, C. F. Chabalowski and M. J.
Frisch, J. Phys. Chem., 1994, 98, 11623.
16 J. Heyd, G. E. Scuseria and M. Ernzerhof, J. Chem. Phys., 2003, 118, 8207.
24

Page 25 of 27
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View Article Online
DOI: 10.1039/C4NJ01899K
17 Gaussian 09, Revision B02, 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.
Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, Jr. J. A. Montgomery, J. E. Peralta,
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R.
Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J.
Tomasi, M. Cossi, N. Rega, N. J. 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, Ö. Farkas, J. B.
Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox, Gaussian, Inc., Wallingford CT, 2009.
18 I. Yamaguchi, B. ꢀJ. Choi, T. ꢀA. Koizumi, K. Kubota and T. Yamamoto,
Macromolecules, 2007, 40, 438.
19 M. SheikꢀBahae, A. A. Said, T. ꢀH. Wei, D. J. Hagan and E. W. VanStryland, IEEE
Journal of Quantum Electronics, 1990, 26, 760.
20 M. A. D. Oliveira, H. A. Duarte, J. ꢀM. Pernaut and W. B. D. Almeida, J. Phys. Chem. A
,
2000, 104, 8256.
21 A. Kumar and A. Kumar, Polym. Chem., 2010, 1, 286.
22 M. Sendur, A. Balan, D. Baran, B. Karabay and L. Toppare, Organic Electronics, 2010,
11, 1877.
23 (a) S. G. Im, K. K. Gleason and E. A. Olivetti, Appl. Phys. Lett. 2007, 90, 152112; (b) C.
Varnstrom, H. Neugebauer, S. Blomquist, H. J. Ahonen, J. Kankare and A. Ivaska,
Electrochim. Acta, 1999, 44, 2739.
24 I. Kaya, M. Yildirim and M. Kamaci, Eur. Polym. J., 2009, 45, 1586.
25 S. G. Im and K. K. Gleason, Macromolecules, 2007, 40, 6552.
26 I. Venditti, I. Fratoddi, C. Palazzesi, P. Prosposito, M. Casalboni, C. Cametti, C.
Battocchio, G. Polzonetti and M. V. Russo, J. Colloid. Interf. Sci., 2010, 348, 424.
25

New Journal of Chemistry
Page 26 of 27
View Article Online
DOI: 10.1039/C4NJ01899K
27 (a) A. S. Sarac, S. A. M. Tofail, M. Serantoni, J. Henry, V. J. Cunnane and J. B.
McMonagle, Appl. Surf. Sci., 2004, 222, 148; (b) M. Yildirim, I. Kaya and A. Aydin,
React. Funct. Polym., 2013, 73, 1167.
28 D. Bhattacharyya and K. K. Gleason, Chem. Mater., 2011, 23, 2600.
29 A. Cihaner and F. Algi, Adv. Funct. Mater., 2008, 18, 3583.
30 (a) P. Puschnig, C. AmbroschꢀDraxl, G. Heimel, E. Zojer, R. Resel, G. Leising, M.
Kriechbaum and W. Graupner, Synthetic Met., 2001, 116, 327; (b) V. J. Eaton and D.
Steele, J. Chem. Soc., Faraday Trans., 1973, 2, 1601.
31 R. Kiebooms, A. Aleshin, K. Hutchison, F. Wudl and A. Heeger, Synthetic Met., 1999,
101, 436.
32 A. Thankappan, S. Thomas and V. P. N. Nampoori, Opt. Laser Technol., 2014, 58, 63.
33 N. Li, J. Lu, X. Xia, Q. Xu and L. Wang, Polymer, 2009, 50, 428.
34 N. Li, Q. Xu, J. Lu, X. Xia and L. Wang, Macromol. Chem. Phys., 2007, 208, 399.
35 Y. D. Zhang, L. Ma, C. B. Yang and P. Yuan, Journal of Physics: Conference Series
,
2009, 188, 012030.
36 F. A. Jerca, V. V. Jerca, F. Kajzar, A. M. Manea, I. Rauc and D. M. Vuluga, Phys.Chem.
Chem. Phys., 2013, 15, 7060.
37 (a) J. L. Oudar and D. S. Chemla, J. Chem. Phys., 1977, 66, 2664; (b) H. H. Jaffe and M.
Orchin, Theory and application of ultraviolet spectroscopy: New York, Wiley, 1962.
26

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Table of Contents
3,4-Ethylenedioxythiophene/chalcogenadiazole copolymers with high optical
limiting threshold have been synthesized via direct arylation