2,1,3-Benzothiadiazole-based fluorophores. Synthesis, electrochemical, thermal and photophysical characterization

Article abstract of DOI:10.1016/j.dyepig.2016.07.011

Three photoactive compounds with π-extended conjugation based on the 2,1,3-benzothiadiazole unit were synthesized and characterized. The compounds exhibited absorption in the violet-blue region with molar absorptivity coefficients and radiative rate constants arising from spin and symmetry allowed ¹ππ* electronic transitions. An emission located in the green region with a large Stokes shift was observed, which was most likely due to a charge-transfer mechanism in the excited state. In spin-coated films a dependence on the fluorescence emission intensity with the size of the alkoxy chain could be observed, where an effective non-radiactive channel seems to be present to deactivate the excited state. The thermal properties were analyzed by differential scanning calorimetry (DSC), and all final compounds exhibited a similar behavior with a crystal-isotropic liquid transition during the heating scan and isotropic liquid-crystal transition during the cooling process. Thermogravimetric analysis indicated a main thermal event with an initial decomposition temperature that was higher than 340?°C. The electrochemical characterization indicate that the compounds exhibited a reversible peak at ?1.48?V and an irreversible oxidation process at 0.94?V versus Ag/Ag⁺. The electrochemical band gap was calculated to be approximately 2.30?eV versus NHE. The spectroelectrochemical measurements demonstrated changes in the absorption spectra due to changes in the electronic structure of the conjugated molecules under oxidative and reductive potentials.

Full text of DOI:10.1016/j.dyepig.2016.07.011

Accepted Manuscript
2,1,3-Benzothiadiazole-based fluorophores. Synthesis, electrochemical, thermal and
photophysical characterization
Tiago Elias Allievi Frizon, Julio César Valdivia Martínez, José Luiz Westrup, Rodrigo
da Costa Duarte, Eduardo Zapp, Kelvin Guessi Domiciano, Fabiano Severo
Rodembusch, Alexandre Gonçalves Dal-Bó
PII:
S0143-7208(16)30317-5
10.1016/j.dyepig.2016.07.011
DYPI 5345
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 31 March 2016
Revised Date: 1 July 2016
Accepted Date: 6 July 2016
Please cite this article as: Frizon TEA, Valdivia Martínez JC, Westrup JL, Duarte RdC, Zapp E,
Domiciano KG, Rodembusch FS, Dal-Bó AG, 2,1,3-Benzothiadiazole-based fluorophores. Synthesis,
electrochemical, thermal and photophysical characterization, Dyes and Pigments (2016), doi: 10.1016/
j.dyepig.2016.07.011.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
2,1,3-Benzothiadiazole-based fluorophores. Synthesis,
electrochemical, thermal and photophysical characterization
Tiago Elias Allievi Frizon,a Julio César Valdivia Martínez,a José Luiz Westrup,a
Rodrigo da Costa Duarte,b Eduardo Zapp,c Kelvin Guessi Domiciano,c Fabiano
Severo Rodembusch,b Alexandre Gonçalves Dal-Bóa,*
aUniversidade do Extremo Sul Catarinense, Av. Universitária, 1105, CP 3167, CEP 88806-000.
Criciúma-SC, Brazil.
bGrupo de Pesquisa em Fotoquímica Orgânica Aplicada. Instituto de Química/UFRGS, Av.
Bento Gonçalves, 9500, CEP 91501-970. Porto Alegre-RS, Brazil.
cUniversidade Federal de Santa Catarina, UFSC - Campus Araranguá. Rodovia Governador
Jorge Lacerda, 3201 - Km 35,4. Jardim das Avenidas. CEP 88906072. Araranguá-SC - Brazil.
ABSTRACT
Three photoactive compounds with π-extended conjugation based on the 2,1,3-
benzothiadiazole unit were synthesized and characterized. The compounds
exhibited absorption in the violet-blue region with molar absorptivity coefficients
1
and radiative rate constants arising from spin and symmetry allowed ππ*
electronic transitions. An emission located in the green region with a large
Stokes shift was observed, which was most likely due to a charge-transfer
mechanism in the excited state. In spin-coated films a dependence on the
fluorescence emission intensity with the size of the alkoxy chain could be
observed, where an effective non-radiactive channel seems to be present to
deactivate the excited state. The thermal properties were analyzed by
1

ACCEPTED MANUSCRIPT
differential scanning calorimetry (DSC), and all final compounds exhibited a
similar behavior with a crystal-isotropic liquid transition during the heating scan
and isotropic liquid-crystal transition during the cooling process.
Thermogravimetric analysis indicated a main thermal event with an initial
decomposition temperature that was higher than 340°C. The electrochemical
characterization indicate that the compounds exhibited a reversible peak at -
1.48V and an irreversible oxidation process at 0.94V versus Ag/Ag+. The
electrochemical band gap was calculated to be approximately 2.30 eV versus
NHE. The spectroelectrochemical measurements demonstrated changes in the
absorption spectra due to changes in the electronic structure of the conjugated
molecules under oxidative and reductive potentials.
Corresponding author: Alexandre Gonçalves Dal-Bó
Tel.: +55 (48) 34312775. E-mail address: adalbo@unesc.net
Keywords: 2,1,3-benzothiadiazole, quadrupolar compounds, photophysics,
fluorescence, solvatochromism.
1. Introduction
In recent decades, interest in new organic fluorophores that are metal
free and typically modeled on the D-π-A-π-D-type systems has increased due to
numerous advantages, such as the diversity of molecular structures, high
extinction coefficients molar, simple synthesis, low cost, environmental issues
and application in dye-sensitized solar cells (DSSCs) [1-3].
2

ACCEPTED MANUSCRIPT
The combination of electron-donating aromatic groups with electron
receptors systems, such as 2,1,3- benzothiadiazole, leads to joint fluorophores
with a conjugated
electron affinity [4]. Therefore, this compound is widely used as a constituent in
-conjugated systems to improve the electron transport ability and
π-adjustable wavelength, efficient fluorescence and high
π
electroluminescence in organic photovoltaic cells (OPVs) [5-12], organic light-
emitting diodes (OLEDs) [5,13-16], organic field-effect transistors (OFETs) [7],
organic thin film transistors (OTFTs), [5,17-21] among others [5,7,22].
As previously reported in the literature a 2,1,3-benzothiadiazole based
compound bearing alkylated tetrazoles terminal groups as electron donors
connected through a π-conjugated D-π-A-π-D-type system was synthesized. [4]
This report aimed to study its photophysical properties, as well as the thermal
ones in order to envisage potential applications as liquid crystals or opto-
electronic materials. Despite the good optical properties, any evidence of liquid
crystalline behaviour was observed. In this way, due to promising optical results
reported, this work presents new fluorophores containing the same 2,1,3-
benzothiadiazole group as the electron-acceptor unit but with flexible alkoxy
chains, which could lead to liquid crystalline properties, as already reported in
similar compounds [23]. The alkyl chains containing a variable number of
carbon atoms was chosen in order to study the influence of the alkyl chain on
the electron displacement toward the benzothiadiazole heterocycle. If present in
these structures, this behavior could favors the electronic conductivity of these
compounds as already confirmed by a smaller band gap observed in similar
compounds [4], which is of great interest for technological applications. In
addition this work also aimed to study liquid crystalline properties, since liquid
3

ACCEPTED MANUSCRIPT
crystals containing triple bonds and long alkoxy chains have been presented
[23-25]. As already discussed in the literature, liquid crystals containing carbon
triple bonds are very interesting materials for reasons such as their large
birefringence [23,26]. Additionally, the thermal, electrochemical and
photophysical properties of the synthesized molecules were investigated.
2 EXPERIMENTAL
2.1 Materials and methods
All of the reagents were used as received. The solvents were dried and
distilled prior to use based on previously reported procedures [27]. The
reactions were monitored by TLC using Silica Gel 60 F254. Detection was
achieved by exposure to iodine vapors or using a sulfuric acid solution with
waterproof charring. The FTIR spectra (400-4000 cm-1) were recorded on a
1
Shimadzu IR Prestige-21 with a resolution of 4 cm-1 using KBr pellets. The H
13
and C NMR spectra were recorded in DMSO-d6, MEOD or CDCl3 at 400 and
100 MHz, respectively. The chemical shifts (δ) are reported in parts per million
(ppm) relative to TMS (0.00 ppm), and the coupling constants J are reported in
hertz (Hz). Spectroscopic grade solvents were used in the photophysical study.
The UV-Vis absorption spectra were acquired on a Shimadzu UV-2450
spectrophotometer, and the steady-state fluorescence spectra were measured
on a Shimadzu spectrofluorometer model RF-5301PC. Films were prepared in
glass substrates using a solution of the fluorophores in CHCl3 (1.0 mg.mL-1)
through spin-coating technique (1500 rpm for 1 min) using a MBRAUN glove
box model MB 200B. Elemental analysis of compounds 9a-c were carried out
using a PerkinElmer 2400 Series II CHNS/O Elemental Analyzer System
4

ACCEPTED MANUSCRIPT
The quantum yield of the fluorescence (ΦFL) was determined using
spectroscopic grade solvents with the dilute optical method. Coumarin 343 in
ethanol (ΦFL = 0.63) was used as the quantum yield standard [28]. The
absorption spectra of the spin-coated films were measured on a Shimadzu
UV2450PC spectrophotometer using an ISR-2200 Integrating Sphere
Attachment. The baseline in the solid state was obtained using BaSO4 (Wako
Pure Chemical Industries, Ltd.). The fluorescence spectra of the films were
obtained with a solid sample holder at an angle designed to limit the reflected
excitation beam from the emission monochromator.
The electrochemical measurements were performed with a Biologic
potentiostat (Model SP-200). The cyclic voltammetry experiments were
performed using ca. 0.1 mg/mL solutions of 9a-c in 0.1 M tetra-n-butyl
ammonium hexafluorophosphate (TBAPF6) in dry CH2Cl2 as the supporting
electrolyte, and the ferrocene/ferricenium (Fc/Fc+) redox couple was employed
as the internal reference. The experiments were performed using a standard
three-electrode cell with a circular glassy carbon electrode, a Pt-wire counter
electrode and Ag/Ag+ (AgNO3 0.01 M in acetonitrile) as the reference electrode.
The measurements were performed in an electrolyte solution previously purged
with purified nitrogen gas. The spectroelectrochemical measurements were
performed on a Shimadzu UV-1800 spectrofluorophotometer. Optically
transparent gold mesh was employed as the working electrode, a platinum wire
was used as the auxiliary electrode, and Ag/Ag+ was employed as the reference
electrode. Tetrabutylammonium hexafluorophosphate (0.1 M in CH2Cl2) was
employed as the electrolyte. The spectra of 9 a-c were obtained by applying a
constant potential with the aid of a coupled potentiostat. The thermal properties
5

ACCEPTED MANUSCRIPT
were investigated using differential scanning calorimetry on DSC-50 and SDT
Q600 TA Instruments using a N2 atmosphere with a flow rate of 100 mL·min-1
and a heating rate of 10°C ·min-1.
2.2. Synthesis
1,2-Bis(dodecyloxy)benzene (2a)[29]
To a solution of catechol 1 (15 g, 135 mmol) in potassium carbonate
(75.5 g, 546.5 mmol) and DMF (150 mL), 1-bromododecane (65.8 mL, 273.9
mmol) was added, and the mixture was stirred at 90°C for 24 h. In addition, 250
mL of water were added, and the organic layer was separated. Then, the
aqueous layer was extracted with 3x50 mL of dichloromethane. The extract was
dried over MgSO4 and concentrated under vacuum to afford a residue that was
recrystallized from ethanol to afford compound 2a. Yield: 85%. Melting point:
1
46-48°C. H NMR (CDCl3, 400 MHz, δ ppm): 6.92 (s, 4H), 4.04-4.00 (t, 4H,
J=6.4 Hz), 1.87-1.82 (m, 4H), 1.50-1.30 (m, 36H), 0.94-0.89(m, 6H). 13C NMR
(CDCl3, 100 MHz, δ ppm): 149.3, 121.0, 114.1, 69.3, 31.9, 29.7, 29.7, 29.4,
26.1, 22.7, 14.1. FTIR (vmax/cm-1): 2920, 2846, 1593, 1508, 1465, 1257, 1222,
1122, 732.
1,2-Bis(decyloxy)benzene (2b)
1,2-Bis(decyloxy)benzene 2b was obtained using the same experimental
procedure as that used to synthesize compound 2a. The extract was dried over
MgSO4 and concentrated under vacuum to yield a residue that was
recrystallized from ethanol to afford compound 2b. Yield: 83%. Melting point:
1
40-42°C. H NMR (CDCl3, 400 MHz, δ ppm): 6.90 (s, 4H), 4.02-3.98 (t, 4H,
6

ACCEPTED MANUSCRIPT
13
J=6.4 Hz), 1.87-1.80 (m, 4H), 1.51-1.29 (br, 28H), 0.92-0.87(m, 6H). C NMR
(CDCl3, 100 MHz, δ ppm): 149.2, 120.9, 114.1, 77.4, 69.3, 31.9, 29.6, 29.4,
26.0, 22.7, 14.1. FTIR (vmax/cm-1): 2918, 2843, 1590, 1510, 1463, 1255, 1225,
1120, 736.
1,2-Bis(octyloxy)benzene (2c)
1,2-Bis(octyloxy)benzene 2c was obtained using the same experimental
procedure as that used to synthesize compound 2a. The extract was dried over
MgSO4 and concentrated under vacuum to yield a residue that was
recrystallized from ethanol to afford compound 2c. Yield: 81%. Melting point:
1
23-25°C. H NMR (CDCl3, 400 MHz, δ ppm): 6.93 (s, 4H), 4.06-4.02 (t, 4H,
13
J=6.4 Hz), 1.92-1.82 (m, 4H), 1.54-1.34 (m, 20H), 0.96-0.91 (m, 6H). C NMR
(CDCl3, 100 MHz, δ ppm): 149.3, 121.0, 114.1, 77.2, 69.3, 31.9, 29.5, 29.4,
26.2, 22.8, 14.2. FTIR (vmax/cm-1): 2916, 2845, 1592, 1512, 1465, 1255, 1226,
1121, 736.
1,2-Bis(dodecyloxy)-4-iodobenzene (3a)[30]
A mixture containing 1,2-bis(dodecyloxy-benzene) 2a (10 g, 24.1 mmol),
iodine (2.83 g, 11.15 mmol) in 300 mL of glacial acetic acid, 100 mL of water
and 8 mL of sulfuric acid was heated to 40°C, and 0 .5 g of iodic acid was
added. The solution was stirred at 40°C for 1 h, an d then, a second fraction of
0.5 g iodic acid was added. After 1 h, a third portion of 0.5 g iodic acid was
added. The solution was allowed to stir for 1.5 h at 40°C. Upon cooling, the
solution was added to 200 mL of water and extracted with diethyl ether (5x25
mL). The combined ether extracts were washed with aqueous Na2CO3 and
7

ACCEPTED MANUSCRIPT
brine followed by drying (MgSO4), and the solvent was removed under reduced
pressure to afford compound 3a, which was used without purification. Yield:
68%.
1,2-Bis(decyloxy)-4-iodobenzene (3b)[30]
A mixture containing 1,2-bis(decyloxy-benzene) 2b (10 g, 27.9 mmol),
iodine (2.83 g, 11.15 mmol) in 300 mL of glacial acetic acid, 100 mL of water
and 8 mL of sulfuric acid was heated to 40°C, and 0 .5 g of iodic acid was
added. The solution was stirred at 40°C for 1 h, an d then, a second fraction of
0.5 g iodic acid was added. After 1 h, a third portion of 0.5 g iodic acid was
added. The solution was allowed to stir for 1.5 h at 40°C. Upon cooling, the
solution was added to 200 mL of water and extracted with diethyl ether (5x25
mL). The combined ether extracts were washed with aqueous Na2CO3 and
brine followed by drying (MgSO4), and the solvent was removed under reduced
pressure to afford compound 3b, which was used without purification. Yield:
72%.
1,2-Bis(octyloxy)-4-iodobenzene (3c)[30]
A mixture containing 1,2-bis(octyloxy-benzene) 2c (10 g, 33.1 mmol),
iodine (3.0 g, 11.7 mmol) in 300 mL of glacial acetic acid, 100 mL of water and
8 mL of sulfuric acid was heated to 40°C, and 0.5 g of iodic acid was added.
The solution was stirred at 40°C for 1 h, and then, a second fraction of 0.5 g
iodic acid was added. After 1 h, a third portion of 0.5 g iodic acid was added.
The solution was allowed to stir for 1.5 h at 40°C. Upon cooling, the solution
was added to 200 mL of water and extracted with diethyl ether (5x25 mL). The
8

ACCEPTED MANUSCRIPT
combined ether extracts were washed with aqueous Na2CO3 and brine followed
by drying (MgSO4), and the solvent was removed under reduced pressure to
afford compound 3c, which was used without purification. Yield: 70%.
4-(3,4-Bis-dodecyloxy-phenyl)-2-methyl-but-3-yn-2-ol (4a)[31]
To a mixture of 1,2-bis(dodecyloxy)-4-iodobenzene 3a (3 g, 5.23 mmol),
Pd(PPh3)2Cl2 (0.18 g, 0.261 mmol) and CuI (0.1 g, 0.525 mmol), Et3N (40 mL)
was added. 2-Methyl-3-butyn-2-ol (0.52 g, 6.41 mmol) was added dropwise,
and the mixture was stirred at reflux for 5 h. The precipitate was filtered and
purified by column chromatography on silica gel using hexane/ethyl acetate
(9:1) as the eluent to afford compound 4a. Yield: 70%. Melting point: 65-67°C.
1H NMR (CDCl3, 400 MHz, δ ppm): 7.00 (dd, 1H, J=1.8 Hz and 8.3 Hz), 6.96 (d,
1H, J=1.8 Hz), 6.78 (d, 1H, J=8.3 Hz), 4.01-3.97 (m, 4H), 1.84-1.81 (m, 4H),
1.63 (s, 6H), 1.49-1.29 (m, 36H), 0.92-0.89 (m, 6H). 13C NMR (CDCl3, 100 MHz
δ ppm): 149.6, 148.6, 124.9, 116.7, 114.8, 113.1, 92.1, 82.3, 69.2, 69.1, 65.7,
31.9, 31.6, 29.4, 26.1, 22.8, 14.2. FTIR (vmax/cm-1): 3275, 2920, 2850, 1597,
1515, 1468, 1415,1246, 1213, 1132, 854, 815, 721.
4-(3,4-Bis-decyloxy-phenyl)-2-methyl-but-3-yn-2-ol (4b)
To a mixture of 1,2-bis(decyloxy)-4-iodobenzene 3b (2.7 g, 5.23 mmol),
Pd(PPh3)2Cl2 (0.18 g, 0.261 mmol) and CuI (0.1 g, 0.525 mmol), Et3N (40 mL)
was added. 2-Methyl-3-butyn-2-ol (0.52 g, 6.41 mmol) was added dropwise,
and the mixture was stirred at reflux for 5 h. The precipitate was filtered and
purified by column chromatography on silica gel using hexane/ethyl acetate
(9:1) as the eluent to afford compound 4b. Yield: 72%. Melting point: 59-61°C.
9

ACCEPTED MANUSCRIPT
1H NMR (CDCl3, 400 MHz, δ ppm): 6.98 (dd, 1H, J=2.0 Hz and 8.0 Hz), 6.95 (d,
1H, J=2.0 Hz), 6.80 (d, 1H, J=8.0 Hz), 4.02-3.97 (m, 4H), 1.85-1.80 (m, 4H),
1.63 (s, 6H), 1.50-1.30 (m, 28H), 0.93-0.88 (m, 6H). 13C NMR (CDCl3, 100 MHz,
δ ppm): 149.6, 148.6, 124.9, 116.7, 114.8, 113.1, 92.0, 82.3, 69.2, 69.1, 65.6,
31.9, 29.3, 29.2, 25.9, 22.7, 14.1. FTIR (vmax/cm-1): 3272, 2922, 2853, 1595,
1513, 1465, 1413,1245, 1215, 1135, 855, 818, 725.
4-(3,4-Bis-octyloxy -phenyl)-2-methyl-but-3-yn-2-ol (4c)
To a mixture of 1,2-bis(octyloxy)-4-iodobenzene 3c (2.41 g, 5.23 mmol),
Pd(PPh3)2Cl2 (0.18 g, 0.261 mmol) and CuI (0.1 g, 0.525 mmol), Et3N (40 mL)
was added. 2-Methyl-3-butyn-2-ol (0.52 g, 6.41 mmol) was added dropwise,
and the mixture was stirred at reflux for 5 h. The precipitate was filtered and
purified by column chromatography on silica gel using hexane/ethyl acetate
(9:1) as the eluent to afford compound 4c. Yield: 68%. Melting point: 49-51°C.
1H NRM (CDCl3, 300 MHz, δ ppm): 6.96 (dd, 1H, J=1.8 Hz and 8.2 Hz), 6.95 (d,
1H, J=1.8 Hz), 6.79 (d, 1H, J=8.2 Hz), 4.02-3.96 (m, 4H), 1.85-1.78 (m, 4H),
1.63 (s, 6H), 1.50-1.31 (m, 20H), 0.93-0.88 (m, 6H). 13C NMR (CDCl3, 75 MHz,
δ ppm): 149.6, 148.6, 124.9, 116.7, 114.8, 113.1, 92.1, 82.3, 69.2, 69.1, 65.6,
31.8, 31.6, 29.4, 29.3, 29.2, 26.1, 22.7, 14.1. FTIR (vmax/cm-1): 3270, 2926,
2845, 1598, 1510, 1460, 1415,1230, 1215, 1135, 855, 818, 725.
1,2-Bis(dodecyloxy)-4-ethynyl-benzene (5a)[4,32]
To a mixture of 4a (2.0 g, 3.78 mmol) and NaOH (0.5 g, 12.5 mmol),
toluene (40 mL) was added. The mixture was heated under reflux for 4 h. The
solution was filtered and purified by column chromatography on silica gel using
10

ACCEPTED MANUSCRIPT
hexane as the eluent to afford compound 5a. Yield: 85%. Melting point: 41-43
1
°C. H NMR (CDCl3, 400 MHz, δ ppm): 7.10-7.07 (dd, 1H, J=2.0 Hz and 8.2
Hz), 7.02 (d, 1H, J=2.0 Hz), 6.83 (d, 1H, J=8,2 Hz), 4.04-3.98 (m, 4H), 3.01 (s,
1H), 1.89-1.79 (m, 4H), 1.51-1.30 (m, 36H), 0.94-0.89 (m, 6H). 13C NMR
(CDCl3, 100 MHz, δ ppm): 150.1, 148.6, 125.5, 117.1, 114.1, 113.1, 84.0, 75.5,
69.2, 31.9, 29.7, 29.5, 26.1, 22.7, 14.2. FTIR (vmax/cm-1): 3298, 2920, 2850,
2102, 1597, 1512, 1465, 1413,1236, 1213, 1132, 846, 806, 721.
1,2-Bis(decyloxy)-4-ethynyl-benzene (5b)
To a mixture of 4b (1.78 g, 3.78 mmol) and NaOH (0.5 g, 12.5 mmol),
toluene (40 mL) was added. The mixture was heated under reflux for 4 h. The
solution was filtered and purified by column chromatography on silica gel using
hexane as the eluent to afford compound 5b. Yield: 83%. Melting point: 34-
1
36°C. H NMR (CDCl3, 400 MHz, δ ppm): 7.10-7.07 (dd, 1H, J=1.8 Hz and 8.5
Hz), 7.02 (d, 1H, J=1.8 Hz), 6.83 (d, 1H, J=8.5 Hz), 4.04-3.98 (m, 4H), 3.01 (s,
1H), 1.88-1.79 (m, 4H), 1.50-1.31 (m, 28H), 0.93-0.89 (m, 6H). 13C NMR
(CDCl3, 100 MHz, δ ppm): 150.1, 148.6, 125.5, 120.9, 117.1, 114.0, 113.1,
83.9, 77.0, 69.2, 31.9, 29.4, 29.2, 26.0, 22.9, 22.7, 14.1. FTIR (vmax/cm-1): 3296,
2931, 2852, 2109, 1590, 1510, 1455, 1418,1239, 1215 1140, 849, 810, 715.
1,2-Bis(octyloxy)-4-ethynyl-benzene (5c)
To a mixture of 4c (1.57 g, 3.78 mmol) and NaOH (0.5 g, 12.5 mmol),
toluene (35 mL) was added. The mixture was heated under reflux for 4 h. The
solution was filtered and purified by column chromatography on silica gel using
hexane as the eluent to afford compound 5c. Yield: 80%. 1H NMR (CDCl3, 300
11

ACCEPTED MANUSCRIPT
MHz, δ ppm): 7.07 (dd, 1H, J=1.8 Hz and 8.5 Hz), 7.00 (d, 1H, J=1.8 Hz), 6.80
(d, 1H, J=8.5 Hz), 4.01-3.95 (m, 4H), 2.98 (s, 1H), 1.86-1.77 (m, 4H), 1.49-1.29
13
(m, 20H), 0.92-0.87 (m, 6H). C NMR (CDCl3, 75 MHz, δ ppm): 150.1, 148.7,
125.5, 117.1, 114.1, 113.1, 83.9, 75.4, 69.2, 31.8, 29.4, 29.3, 26.0, 22.7, 14.1.
FTIR (vmax/cm-1): 3292, 2938, 2856, 2102, 1594, 1519, 1459, 1416,1232, 1213
1146, 845, 819, 712.
Benzo[1,2,5]thiadiazole (7)[4]
Benzo[1,2,5]thiadiazole 7 was synthesized according to a previously
1
reported protocol [4]. Yield: 86%. Melting point: 43-44°C. H NMR (CDCl3, 400
MHz, δ ppm): 7.97 (dd, 2H, J=3.1 Hz and 6.6 Hz); 7.56 (dd, 2H, J=3.1 Hz and
6.6 Hz). 13C NMR (CDCl3, 100 MHz, δ ppm): 154.7; 129.2; 121.5. FTIR
(vmax/cm-1): 3088, 3053, 1613.
4,7-Dibromobenzo[1,2,5]thiadiazole (8)[4]
4,7-Dibromobenzo[1,2,5]thiadiazole 8 was synthesized according to the
procedure previously described in the literature [4]. Yield: 84%. Melting point:
1
13
187-188°C. H NMR (CDCl3, 400 MHz, δ ppm): 7.71 (s, 2H). C NMR (CDCl3,
100 MHz, δ ppm): 152.9, 132.3, 113.8. FTIR (vmax/cm-1): 3078, 3045, 1634.
4,7-Bis-(3,4-bis-dodecyloxy-phenylethynyl)-benzo[1,2,5]thiadiazole
(9a)[4,29,33]
Dry Et3N (50 mL), 4,7-dibromo-2,1,3-benzothiadiazole 8 (0.15 g, 0.51
mmol), CuI (0.004 g, 0.02 mmol), triphenylphosphine (C6H5)3P (0.005 g, 0.02
mmol) and Pd(PPh3)2Cl2 (0.025 g, 0.02 mmol) were placed in a flask and
12

ACCEPTED MANUSCRIPT
degassed with argon. Next, 1,2-bis(dodecyloxy)-4-ethynyl-benzene 5a (0.51 g,
1.1 mmol) was added, and the mixture was maintained at 50°C for 18 h. Then,
the solvent was evaporated to dryness, and the crude product was purified by
column chromatography on silica gel using hexane/dichloromethane (7:3) the
eluent to afford compound 9a. Yield: 75% (yellow crystals). Melting point: 133-
1
135°C. H NMR (CDCl3, 400 MHz, δ ppm): 7.78 (s, 2H), 7.26-7.23 (dd, 2H,
J=2.0 Hz), 7.19 (d, 2H, J=2.0 Hz), 6.90 (d, 2H, J=8.5 Hz), 4.08-4.04 (m, 8H),
1.89-1.84 (m, 8H), 1.51-1.29 (m, 72H), 0.91-0.87 (m, 12H). 13C NMR (CDCl3,
100 MHz, δ ppm): 154.4, 150.4, 148.8, 132.2, 125.7, 117.1, 116.8, 114.5, 113.1,
98.1, 84.1, 77.1, 69.4, 69.1, 31.9, 29.7, 29.4, 26.0, 22.7, 14.1. FTIR (vmax/cm-1):
2922, 2850, 2200, 1597, 1514, 1465, 1419,1230, 1215 1132, 848, 813, 721.
Anal. Calcd. for C70H108N2O4S: C, 78.31; H, 10.14; N, 2.61; S, 2.99%; Anal.
Found: C, 78.19; H, 10.21; N, 2.54; S, 2.89%.
4,7-Bis-(3,4-bis-decyloxy-phenylethynyl)-benzo[1,2,5]thiadiazole (9b)
Dry Et3N (50 mL), 4,7-dibromo-2,1,3-benzothiadiazole 8 (0.15 g, 0.51
mmol), CuI (0.004 g, 0.02 mmol), triphenylphosphine (C6H5)3P (0.005 g, 0.02
mmol) and Pd(PPh3)2Cl2 (0.025 g, 0.02 mmol) were placed in a flask and
degassed with argon. Next, 1,2-bis(decyloxy)-4-ethynyl-benzene 5b (0.46 g, 1.1
mmol) was added, and the mixture was maintained at 50°C for 18 h. Then, the
solvent was evaporated to dryness, and the crude product was purified by
column chromatography on silica gel using hexane/dichloromethane (7:3) the
eluent to afford compound 9b. Yield: 70% (orange crystals). Melting point: 136-
1
138 °C. H NMR (CDCl3, 400 MHz, δ ppm): 7.76 (s, 2H), 7.27-7.25 (dd, 2H,
J=1.8 Hz), 7.18 (d, 2H, J=1.8 Hz), 6.88 (s, 2H), 4.07-4.03 (m, 8H), 1.88-1.82 (m,
13

ACCEPTED MANUSCRIPT
8H), 1.52-1.30 (m, 56H), 0.92-0.89 (m, 12H). 13C NMR (CDCl3, 100 MHz, δ
ppm): 154.4, 150.4, 148.8, 132.2, 125.7, 117.1, 116.8, 114.5, 113.1, 98.1, 84.1,
77.1, 69.3, 69.1, 31.9, 29.7, 29.4, 26.0, 22.7, 14.2. FTIR (vmax/cm-1): 2928,
2855, 2195, 1593, 1518, 1466, 1417,1232, 1217 1135, 845, 815, 723. Anal.
Calcd. for C62H92N2O4S: C, 77.45; H, 9.64; N, 2.91; S, 3.33%; Anal. Found: C,
77.31; H, 9.70; N, 2.85; S, 3.27%.
4,7-Bis-(3,4-bis-octyloxy-phenylethynyl)-benzo[1,2,5]thiadiazole (9c)
Dry Et3N (45 mL), 4,7-dibromo-2,1,3-benzothiadiazole 8 (0.15 g, 0.51
mmol), CuI (0.004 g, 0.02 mmol), ), triphenylphosphine (C6H5)3P (0.005 g, 0.02
mmol) and Pd(PPh3)2Cl2 (0.025 g, 0.02 mmol) were placed in a flask and
degassed with argon. Next, 1,2-bis(decyloxy)-4-ethynyl-benzene 5c (0.39 g, 1.1
mmol) was added, and the mixture was maintained at 50°C for 18 h. Then, the
solvent was evaporated to dryness, and the crude product was purified by
column chromatography on silica gel using hexane/dichloromethane (7:3) the
eluent to afford compound 9c. Yield: 70% (orange crystals). Melting point: 140-
1
142°C. H NMR (CDCl3, 400 MHz, δ ppm): 7.78 (s, 2H), 7.29-7.25 (dd, 2H,
J=2.0 Hz), 7.19 (d, 2H, J=2.0 Hz,), 6.90 (d, 2H, J=8,5 Hz), 4.08-4.04 (m, 8H),
1.91-1.82 (m, 8H), 1.60-1.32 (m, 40H), 0.92-0.89 (m, 12H). 13C NMR (CDCl3,
100 MHz, δ ppm): 154.4, 150.4, 148.8, 132.2, 125.7, 117.1, 116.7, 114.5, 113.0,
98.1, 84.1, 77.0, 69.3, 69.1, 31.9, 29.7, 29.4, 26.1, 22.7, 14.1. FTIR (vmax/cm-1):
2925, 2859, 2191, 1597, 1514, 1469, 1413, 1232, 1211 1138, 846, 813, 728.
Anal. Calcd. for C54H76N2O4S: C, 76.37; H, 9.02; N, 3.30; S, 3.78%; Anal.
Found: C, 76.19 1; H, 9.10; N, 3.21; S, 3.71%.
14

ACCEPTED MANUSCRIPT
3 RESULTS AND DISCUSSION
3.1 Synthesis and spectroscopic characterization
The synthetic route for the preparation of the desired compounds 9a-c is
shown in Scheme 1.
[Insert Scheme 1 here]
The catechol 1 was alkylated to 1,2-bis(alkoxy)benzenes 2a-c as
described in the literature [29]. The iodoarenes 3a-c were obtained in good
yields (68%, 72% and 70%, respectively) from an adapted synthetic
methodology previously described [26]. The respective aryl halides reacted with
commercially available 2-methyl-3-butyn-2-ol via a palladium-catalyzed cross-
coupling (Sonogashira’s coupling) [34-36] followed by protective group
elimination to afford compounds 5a-c [4,32]. In contrast, 2,1,3-benzothiadiazole
7 was obtained by condensation of o-phenylenediamine 1 with thionyl chloride
in a basic medium. In the next stage, the selective bromination reaction of 2,1,3-
benzothiadiazole 7 at positions 4 and 7 was performed, producing compound 8.
The final products 9a-c were obtained in high yields (~70%) via Sonogashira
coupling reaction between the intermediate 8 and the respective 1,2-
bis(alkoxy)-4-ethynyl-benzenes 5a-c to afford the desired compounds 9a-c
[4,29,33].
The reaction was monitored by FTIR spectroscopy (Figures S25-S36,
supplementary data). For the final compound 9b (Figure S35), the
disappearance of the characteristic band corresponding to the axial deformation
of ≡C-H located at 3330 cm-1 was observed. In addition, the presence of an
15

ACCEPTED MANUSCRIPT
intense band was observed at 2200 cm-1 due to the C≡C stretching of the
internal alkyne. The same vibrational behavior was observed for compounds 9a
and 9c (Figures S34 and S36, respectively).
1
The H NMR spectra contained characteristic signals of the desired
products (Figures S1-S12). For instance, to compound 9b (Figure S11), seven
signals were observed, and the four sets of equivalent hydrogens related to the
aromatic system located at 7.76 (s, 2H), 7.27-7.25 (dd, 2H, J=1.8 Hz), 7.18 (d,
2H, J=1.8 Hz) and 6.88 (s, 2H). The signal located at 7.76 ppm (s, 2H)
corresponded to the equivalent hydrogens of the benzothiadiazole central unit.
In the region of the aliphatic hydrogens, three sets of signals were observed as
follows: 4.07-4.03 ppm (m, 8H) corresponding to the methylene group, between
1.88 and 1.30 ppm (m, 56H) and at 0.94-0.89 ppm (m, 12H,) corresponding to
the terminal methyl group.
3.2 Photophysical characterization
The absorption spectra of 2,1,3-benzotiadiazoles 9a are shown in Figure
1. The relevant data from UV-Vis absorption spectroscopy are summarized in
Table 1. It is important to note that the additional compounds 9b-c exhibited
similar photophysical behavior in the same solvents. To better compare the
electronic spectra or the effect of the alkoxy moieties on the electronic spectra
of these compounds, the results for all of the studied compounds in the same
media is shown in Figure 1a. These compounds exhibited similar photophysics
in the same organic solvent (Figures S37-38). Additionally, the electronic
spectra of these compounds allowed for the determination of the pure radiative
16

ACCEPTED MANUSCRIPT
0
lifetimes (τ0) and the radiative rate constants (ke ) using the Strickler-Berg
relationship [37]:
1
≈ 2.88ꢂ10ꢃꢄꢅꢆꢁꢇ ꢈ ꢉꢊꢅꢆ , (1)
ꢀꢁ
where ꢅꢆꢁ is the wavenumber of the maximum of the absorption band and
the integral ꢉꢊꢅꢆ is the area under the absorption curve from a plot of the
ꢋ
molar absorptivity coefficient
ε
(M-1·cm-1) as a function of the wavenumber
ꢅꢆ (cm-1) related to a single electron oscillator. In this relationship, the pure
0
radiative lifetime
be obtained from equation (2) [38]:
ꢌ ≈ 4.3ꢂ10ꢃꢄ ꢈ ꢉꢊꢅꢆ . (2)
τ
0 is defined as 1/ke , and the oscillator strength (fe) can
ꢍ
[Insert Figure 1 here]
The 2,1,3-benzotiadiazoles (9a-c) exhibited absorption maxima in the
violet-blue region at approximately 440 nm (λabs). The observed
absorption maxima is 40 nm redshifted in despite of a previously
published compound with the same
π-extended fluorophoric core, as
expected due to the absence of the alkoxy auxochrome moieties in its
structure [23]. Compounds based on the 2,1,3-benzotiadiazole core with a
similar
π-conjugated structure also presents absorption located in the
violet region [4]. In addition, the intense absorption band located around
300 nm was ascribed to the 2,1,3-benzotiadiazole moiety. The molar
absorptivity coefficient (ε) values for both absorption bands as well as the
17

ACCEPTED MANUSCRIPT
0
calculated radiative rate constants (ke ) for all of the compounds indicate
that the spin and symmetry allowed electronic transitions were related to
1ππ* transitions. A small solvatochromic effect (∆λabs~7 nm) was observed
in the ground state, which was independent of the solvent polarity and
indicated a nearly absent charge-transfer character, as observed in a
similar 2,1,3-benzotiadiazole compound [4]. A nearly constant radiative
lifetime (τ
0~3 ns) was observed for all of the compounds in all of the
studied solvents, which most likely indicates that after radiation
absorption, these 2,1,3-benzotiadiazoles populate the same excited state.
[Insert Table 1 here]
The fluorescence emission spectra of 2,1,3-benzotiadiazole 9a are
shown in Figure 2. Compounds 9b-c exhibited a similar photophysical behavior
in the same solvents (Figures S39-40). In addition, compounds 9a-c were
studied in dichloromethane. A related emission profile was observed in 1,4-
dioxane and toluene (data not shown). The emission curves were obtained by
exciting the compounds at the absorption maxima wavelength. The relevant
data from fluorescence emission spectroscopy are listed in Table 2, where the
solvents are presented in order of increasing dipole moment.
[Insert Figure 2 here]
The 2,1,3-benzotiadiazoles (9a-c) exhibited fluorescence emission in the
green region, where the different alkoxy substituents do not play a fundamental
18

ACCEPTED MANUSCRIPT
role in the excited state of the these fluorophores. However, a solvatochromic
effect was observed in the excited state (∆λem~30 nm). A similar emission
maxima was observed in parent compounds [4,23]. With regards to the
chemical structure of these compounds, the solvatochromism as well as the
large Stokes shift (85-121 nm/3604-4862 cm-1) are most likely related to the
charge-transfer character of the excited state. A larger Stokes shift observed in
these compounds in despite of the similar one (97 nm/4122 cm-1) [23] indicates
that the number of alkoxy chains in the fluorophoric unit plays an important role
on the energy loss in the excited state before the radiactive decay. An increase
in the dipole moment of the solvent results in an emission shift to larger
wavelengths due to the nature of the electronic transition, which allows for
better electron delocalization in the excited state. Therefore, the observed
photophysics can be understood when a relaxed excited state is more polar in
the excited state than in the ground state. Similar values to the fluorescence
quantum yields were obtained for these compounds (~30%), indicating that in
solution, the presence of different alkoxy groups in the fluorophore structure do
not appear to play a significant role in the excited singlet state deactivation
channel. However, the spin-coated films of these compounds exhibited an
interesting photophysical behavior (Figure 3 and Table 3).
[Insert Table 2 here]
Figure 3 shows the diffuse reflectance UV-Vis spectra of the spin-coated
films and the absorption maxima were at 443 nm. Similar to that observed in
solution, the chemical structure of the compounds do not appear to affect the
19

ACCEPTED MANUSCRIPT
photophysics of the 2,1,3-benzotiadiazoles in the spin-coated films in the
ground state. However, the fluorescence emission appears to be quite different
from that observed in solution, presenting a dependence on the emission
intensity with the size of the alkoxy chain. In spin-coated films for the
fluorophore containing the longest chain alkoxy, a non-radioactive channel
seems to be very effective to deactivate the excited state, nearly quenching the
fluorescence emission reflected in a lower fluorescence quantum yield.
[Insert Figure 3 here]
[Insert Table 3 here]
3.3 Electrochemical properties
The cyclic voltammogram curves (Figures 4, S41 and S42) exhibited the
distinct anodic and cathodic behavior. In addition, the oxidation and reduction
peaks were directly correlated to the electron transfer at the HOMO (ionization
potential) and LUMO (electron affinity), respectively. Because Ag/Ag+ was used
as a reference electrode, the potential was normalized to NHE using the Fc/Fc+
couple as an internal standard [39]. The well-defined reduction process, at -
1.498V, -1.515V and -1.485V versus Ag/Ag+, can be attributed to reduction of
the benzothiadiazole ring. In addition, at 0.95V, 0.93V and 0.94V versus Ag/Ag+
a well-defined irreversible oxidation process takes place for compounds 9a-c.
The electrochemical band gaps of these compounds were calculated by
subtracting the HOMO level from the LUMO level. The onset values were
estimated by taking the intersection point between the baseline and the tangent
[40]. The observed oxidation and reduction peaks of the compounds 9a-c
20

ACCEPTED MANUSCRIPT
suggests the possibility of both hole and electron transport, leading to an
potential application as electroluminescent device. This feature is very important
since it would not be necessary to employ different molecules in the electron
and hole-transporting layers of organic light emitting devices [41]. Analysis of
the HOMO-LUMO energy level calculations shows that the band gaps are in
good agreement with the CV data and to the UV-vis onset value. The optical
and electrochemical data obtained from these studies are summarized and
compared in Table 4.
[Insert Figure 4 here]
[Insert Table 4 here]
Spectroelectrochemical measurements were performed to investigate the
changes in the absorption spectra due to changes in the electronic structure of
the conjugated molecules as the applied voltage gradually increased [42]. The
applied potentials were chosen before the peak, on the peak and after the peak
positions observed during the cyclic voltammetry (Figure 5). In the
corresponding spectrum obtained at the open-circuit potential (OCP) (Figures
5c, S43 and S44), two main absorption processes (400-500 nm and 250-350
nm) were observed in the analyzed region. The high-energy band may be due
1
to simple ππ* transitions. The reduction potentials (Figures 5a, S43 and S44)
result in CT bands with lower intensities and in the formation of new weak
transitions at lower energies 560 and 720 nm for 9a-c (Figures S45, S46 and
S47). The oxidative potentials result in lower intensities for two main bands and
21

ACCEPTED MANUSCRIPT
the formation of new band at lower energies for 9a-c (Figures 5b, S43 and
S44).
[Insert Figure 5 here]
3.4 Thermal Properties
The thermal stability of the compounds 9a-c was evaluated by
thermogravimetric analysis (TGA) (Figure 6). To better understand the thermal
events, the DTG curves for all of the compounds were obtained from the TGA
curves. The overall degradation process indicates a mass loss of approximately
75%. A main thermal event was observed for the studied compounds and
correspond to a mass loss of approximately 55% at an initial decomposition
temperature of 340°C with a high maximum degradatio n rate located at
approximately 430°C. A small thermal event was dete cted at approximately
550°C. This stage corresponds to a loss of 20%. Sur prisingly, even at 800°C, a
mass residue of approximately 30% remains in the thermogram. It important to
note that information regarding the thermal analysis of these types of
compounds is lacking. 1,2,3-Benzothiadiazole may lead to a polymeric structure
under heat treatment [43]. For polymers or even copolymers containing the
2,1,3-benzothiadiazole unit, a residue of ca. 30% has been observed at
approximately 600°C or higher [44-46]. Therefore, w e believe that the observed
residue in the thermograms may be related to a polymeric structure.
[Insert Figure 6 here]
22

ACCEPTED MANUSCRIPT
The thermal properties were investigated by differential scanning calorimetry
(DSC). The heating and cooling scans were conducted using a rate of
10°C·min -1. To eliminate the non-intrinsic thermal history, second heating scans
were performed (Figure 7). Compounds 9a-c do not exhibit thermotropic
mesomorphism, as already observed in similar compounds containing the same
fluorescent core but a different functional group [4], which indicate that
structural changes also play a important role on the thermal properties of these
compounds. In addition, the amount of alkoxy groups also tailor these
properties since the same fluorescent core with similar functional group
presenting only one alkoxy chain displayed smectic C and nematic phases [23].
Similar melting transition (Cr-I) temperatures were observed for compound 9a
(131.8°C), compound 9b (135.7°C) and compound 9c (139.7°C). However, the
heat of fusion of compound 9c was significantly higher than those of 9a and 9b,
indicating that the octoxyl group is more beneficial to a higher melting point than
the dodecyl group.
[Insert Figure 7 here]
4. Conclusions
A series of D-π-A-π-D-type compounds were synthesized in good yields
and characterized. Their photophysical behaviors were studied using absorption
spectroscopy in the UV-Vis region and using time-resolved, stationary
fluorescence emission. Compounds 9a-c exhibited absorption maxima at
approximately 442 nm with their molar absorptivity coefficient (ε) values being
1
related to the ππ* transitions. Changes in the solvent polarity did not cause a
23

ACCEPTED MANUSCRIPT
significant solvatochromic effect (~6 nm), indicating a nearly absent charge-
transfer characteristic in the ground state. Compounds 9a-c exhibited emissions
in the green region (532-562 nm), which were dependent on the polarity of the
solvent used, and a large Stokes shift (90-117 nm) was observed, which was
most likely due to charge-transfer mechanism (ICT) in the excited state. The
fluorescence emission in spin-coated films showed to be different from that
observed in solution, where a dependence on the emission intensity with the
size of the alkoxy chain was observed. For the fluorophore containing the
longest chain alkoxy, a non-radioactive channel seems to be very effective to
deactivate the excited state, nearly quenching the fluorescence emission in this
compound. The compounds present initial decomposition temperatures around
340°C. Differential scanning calorimetry analysis i ndicate that compounds 9a-c
do not exhibit thermotropic mesomorphism.
The values of the energy levels of the HOMO and LUMO molecular
orbitals as well as the value of the optical band gap of these compounds agree
with those for similar compounds found in the literature. The electrochemical
band gaps confirmed that the energy level required for the materials is
compatible for building electronic devices.
5. Acknowledgements
The authors would like to thank Conselho Nacional de Desenvolvimento
Científico e Tecnológico (CNPq) (440619/2014-9), Fundação de Amparo à
Pesquisa do Estado do Rio Grande do Sul (FAPERGS) and CELESC P&D
5697-8712/2012 for financial support.
24

ACCEPTED MANUSCRIPT
6. References
[1] Lee DH, Lee MJ, Song HM, Song BJ, Seo KD, Pastore M, Anselmi C,
Fantacci S, Angelis FD, Nazeeruddin MK, Gräetzel M, Kim HK. Organic dyes
incorporating
low-band-gap
chromophores
based
on
π-extended
benzothiadiazole for dye-sensitized solar cells. Dyes Pigm 2011; 91:192-198.
[2] Seo KD, Choi IT, Park YG, Kang S, Lee JY, Kim HK. Novel D-A-π-A
coumarin dyes containing low band-gap chromophores for dye-sensitised solar
cells. Dyes Pigm 2012; 94:469-474.
[3] Thomas KRJ, Singh P, Baheti A, Hsu YC, Ho KC, Lin JT. Electro-optical
properties of new anthracene based organic dyes for dye-sensitized solar cells.
Dyes Pigm 2011; 91:33-43.
[4] Westrup JL, Oenning LW, Paula MMS, Duarte RC, Rodembusch FS, Frizon
TEA, da Silva L, Dal-Bó A G. New photoactive D-π-A- π-D benzothiadiazole
derivative: Synthesis, thermal and photophysical properties. Dyes Pigm 2016;
126:209-217.
[5] Yun D, Yoo H, Heo S, Song H, Moon D, Woo J, Park Y. Synthesis and
photovoltaic characterization of D/A structure compound based on N-substituted
phenothiazine and benzothiadiazole. J Ind Eng Chem 2013;19: 421-426
[6] Fang Q, Liu Y, Lai H, Zhong H, Xu E, Du J, Li Y. New low band gap
molecules based on ethylene-separated benzothiadiazoles: synthesis and band
gap comparison. Tetrahedron Lett 2010;51:4462-4465.
[7] Bai F, He Q, He C, Sun Y, Wu H, Li Y. Amorphous molecular material
containing bisthiophenyl-benzothiadiazole and triphenylamine with bipolar and
low-band gap characteristics for solar cells. Thin Solid Films 2008;516:5935-
5940.
25

ACCEPTED MANUSCRIPT
[8] Lee JY, Kim SH, Song IS, Moon DK. Efficient donor-acceptor type polymer
semiconductors with well-balanced energy levels and enhanced open circuit
voltage properties for use in organic photovoltaics. J Mater Chem
2011;21;16480-16487.
[9] Lee JY, Song KW, Song HJ, Moon DK. Synthesis and photovoltaic property
of donor-acceptor type conjugated polymer containing carbazole and 4,7-
dithiazolylbenzothiadiazole moiety utilized as a promising electron withdrawing
unit. Synth Met 2011;161:2434-2440.
[10] Lee JY, Song KW, Ku JR, Sung TH, Moon DK. Development of DA-type
polymers with phthalimide derivatives as electron withdrawing units and a
promising strategy for the enhancement of photovoltaic properties. Sol Energy
Mater Sol Cells 2011;95:3377-3384.
[11] Li Y, Zou Y. Conjugated Polymer Photovoltaic Materials with Broad
Absorption Band and High Charge Carrier Mobility. Adv Mater 2008;20:2952-
2958.
[12] Li Y, Xue L, Hui L, Li Z, Xu B, Wen S, Tian W. Energy level and molecular
structure engineering of conjugated donor-acceptor copolymers for photovoltaic
applications. Macromolecules 2009;42:4491-4499.
[13] Song IS, Heo SW, Lee JY, Moon DK. Study on the ClO"4 doped PEDOT-
PEG in organic solvent using a hole injection layer for PLEDs. J Ind Eng Chem
2011;17:651-656.
[14] Song HJ, Lee SM, Lee JY, Choi BH, Moon DK. The synthesis and
electroluminescent properties of dithienylquinacridone-based copolymers for
white light-emitting diodes. Synth Met 2011;161:2451-2459.
26

ACCEPTED MANUSCRIPT
[15] Song HJ, Lee JY, Song IS, Moon DK., Haw JR. Synthesis and
electroluminescence properties of fluorene-anthracene based copolymers for
blue and white emitting diodes. J Ind Eng Chem 2011;17:352-357.
[16] Yamada S, Park S, Song S, Heo M, Shim JY, Jin Y, Kim I, Lee H, Lee K,
Yoshinaga K, Kim JY, Suh H. Synthesis and characterization of fluorene-
carbazole and fluorene-phenothiazine copolymers with carbazole and
oxadiazole pendants for organic light emitting diodes. Polymer 2010;51:6174-
6181.
[17] Park MJ, Lee JH, Park JH, Lee SK, Lee JI, Chu HY, Hwang DH, Shim HK.
Synthesis and electroluminescence of new polyfluorene copolymers with
phenothiazine derivative. Their application in white-light-emitting diodes.
Macromolecules 2008;41:3063-3070.
[18] Jung MS, Shin W, Park SJ, You HR, Park JB, Suh HS, Lim YH, Yoon DY,
Kim JH. Synthesis and characterization of thermally cross-linkable hole injection
polymer based on poly(10-alkylphenothiazine) for polymer light-emitting diode.
Synth Met 2009;159:1928-1933.
[19] Zou Y, Wu W, Sang G, Yang Y, Liu Y, Li Y. Polythiophene derivative with
phenothiazine-vinylene conjugated side chain: synthesis and its application in
field-effect transistors. Macromolecules 2007;40:7231-7237.
[20] Mondal R, Becerril HA, Verploegen E, Kim D, Norton JE, Ko S, Miyaki N,
Lee S, Toney MF, Bredas J, McGehee MD, Bao Z. Thiophene-rich fused-
aromatic thienopyrazine acceptor for donor-acceptor low band-gap polymers for
OTFT and polymer solar cell applications. J Mater Chem 2010;20;5823-5834.
27

ACCEPTED MANUSCRIPT
[21] Kim CG, Quinn JR, Facchetti A, Marks TJ. Pentacene transistors fabricated
on photocurable polymer gate dielectrics: tuning surface viscoelasticity and
device response. Adv Mater 2010;22:342-346.
[22] Anant P, Mangold H, Lucas NT, Laquai F, Jacob J. Synthesis and
characterization of donor-acceptor type 4,4'-bis(2,1,3-benzothiadiazole) based
copolymers. Polymer 2011;52:4442-4450.
[23] Vieira AA, Cristiano R, Bortoluzzi AJ, Gallardo H. Luminescent 2,1,3-
benzothiadiazole-based liquid crystalline compounds.
2008;875:364-371.
J
Mol Struct
[24] Vasconcelos UV, Dalmolin E, Merlo AA. Synthesis and thermal behavior of
new N-heterotolan liquid crystals. Org Lett 2005;7:1027-1030.
[25] Paraskos AJ, Swager TM. Effects of desymmetrization on thiophene-based
bent-rod mesogens. Chem Mater 2002;14:4543-4549.
[26] Wu ST, Finkenzeller U, Rieffenrath V. Physical properties of
diphenyldiacetylenic liquid crystals. J Appl Phys 1989;65:4372-4376.
[27] Armarego WLF. In Purification of Laboratory Chemicals, 5th ed.; Armarego
WLF, Chai CLL. Elsevier Academic Press: Cornwall, UK, 2003.
[28] Wurth C, Grabolle M, Pauli J, Spieles M, Resch-Genger U. Nature Protoc
2013;8:1535-1550.
[29] Behramand B, Molin F, Gallardo H. 2,1,3-Benzoxadiazole and 2,1,3-
benzothiadiazole-based fluorescent compounds: Synthesis, characterization
and photophysical/electrochemical properties. Dyes Pigm 2012;95;600-605.
[30] Freudenmann R, Behnisch B, Hanack M., Synthesis of conjugated-bridged
triphenylenes and application in OLEDs. J Mater Chem 2001;11:1618-1624.
28