Differently substituted benzothiadiazoles as charge-transporting emitters for fluorescent organic light-emitting diodes

Article abstract of DOI:10.1016/j.dyepig.2019.03.017

Carbazolyl- and 1,2,3,4-tetrahydrocarbazolyl-substituted benzothiadiazoles were prepared by Pd-catalyzed Buchwald-Hartwig and Heck reactions. Photophysical, electrochemical, thermal, charge-transporting properties, and performance in organic light emitting diodes (OLEDs) of the derivatives with donor-π-acceptor-π-donor and donor-acceptor-donor structures are discussed. Photo- and electroluminescent properties of the studied compounds of carbazole and benzothiadiazole are very sensitive to their molecular structures. Their glass transition temperatures range from 145 to 191 °C. Investigation of photophysical properties revealed importance of intramolecular twisting on excited state deactivation. Emission of dilute solutions of the compounds in nonpolar solvents appears in the orange region with fluorescence quantum yields up to 0.6.4,7-(Di (1,2,3,4-tetrahydro)carbazolyl)-[2,1,3]-benzothiadiazole demonstrates phosphorescence and delayed fluorescence at room temperature. Solid-state ionization potentials of the materials range from 5.64 to 5.82 eV. The layer of 4,7-(di (tert-butyl)carbazolyl)-[2,1,3]-benzothiadiazole shows high hole drift mobility of 1.7 × 10^?3 cm²/V·s at an electric field of 5.3 × 10⁵ V/cm and relatively high electron drift mobility of 5.7 × 10^?5 cm²/V·s at an electric field of 5.8 × 10⁵ V/cm. Red OLEDs based of singlet emission with maximum external quantum efficiency values of 1.3 and 0.13% were achieved using new emitters. Much better electroluminescent performance was observed for the compound having donor-acceptor-donor structure relative to the compound with donor-π-acceptor-π-donor structure.

Full text of DOI:10.1016/j.dyepig.2019.03.017

Accepted Manuscript
Differently substituted benzothiadiazoles as charge-transporting emitters for
fluorescent organic light-emitting diodes
Dalius Gudeika, Arunas Miasojedovas, Oleksandr Bezvikonnyi, Dmytro Volyniuk,
Alytis Gruodis, Saulius Jursenas, Juozas V. Grazulevicius
PII:
S0143-7208(18)32804-3
https://doi.org/10.1016/j.dyepig.2019.03.017
DYPI 7406
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 19 December 2018
Revised Date: 28 February 2019
Accepted Date: 8 March 2019
Please cite this article as: Gudeika D, Miasojedovas A, Bezvikonnyi O, Volyniuk D, Gruodis A, Jursenas
S, Grazulevicius JV, Differently substituted benzothiadiazoles as charge-transporting emitters for
fluorescent organic light-emitting diodes, Dyes and Pigments (2019), doi: https://doi.org/10.1016/
j.dyepig.2019.03.017.
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ACCEPTED MANUSCRIPT
Differently substituted benzothiadiazoles as charge-transporting emitters for
fluorescent organic light-emitting diodes
Graphical abstract
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Differently substituted benzothiadiazoles as charge-transporting emitters for
fluorescent organic light-emitting diodes
Dalius Gudeika1, Arunas Miasojedovas2, Oleksandr Bezvikonnyi1, Dmytro Volyniuk1, Alytis Gruodis3,
Saulius Jursenas2, Juozas V. Grazulevicius1*
1Department of Polymer Chemistry and Technology, Kaunas University of Technology, Radvilenu pl.
19, LT- 50254, Kaunas, Lithuania;
2Institute of Photonics and Nanotechnology, Vilnius University, Sauletekio 3, LT-10257 Vilnius,
Lithuania;
3Institute of Chemical Physics, Vilnius University, Sauletekio 9-III, LT-10222 Vilnius, Lithuania;
Abstract
Carbazolyl- and 1,2,3,4-tetrahydrocarbazolyl-substituted benzothiadiazoles were prepared by Pd-
catalyzed Buchwald-Hartwig and Heck reactions. Photophysical, electrochemical, thermal, charge-
transporting properties, and performance in organic light emitting diodes (OLEDs) of the derivatives
with donor-π-acceptor-π-donor and donor-acceptor-donor structures are discussed. Photo- and
electroluminescent properties of the studied compounds of carbazole and benzothiadiazole are very
o
sensitive to their molecular structures. Their glass transition temperatures range from 145 to 191 C.
Investigation of photophysical properties revealed importance of intramolecular twisting on excited
state deactivation. Emission of dilute solutions of the compounds in nonpolar solvents appears in the
orange region with fluorescence quantum yields up to 0.6. 4,7-(Di(1,2,3,4-tetrahydro)carbazolyl)-
[2,1,3]-benzothiadiazole demonstrates phosphorescence and delayed fluorescence at room temperature.
Solid-state ionization potentials of the materials range from 5.64 to 5.82 eV. The layer of 4,7-(di(tert-
butyl)carbazolyl)-[2,1,3]-benzothiadiazole shows high hole drift mobility of 1.7×10-3 cm2/V·s at an
electric field of 5.3×105 V/cm and relatively high electron drift mobility of 5.7×10-5 cm2/V·s at an
electric field of 5.8×105 V/cm. Red OLEDs based of singlet emission with maximum external quantum
efficiency values of 1.3 and 0.13% were achieved using new emitters. Much better electroluminescent
performance was observed for the compound having donor-acceptor-donor structure relative to the
compound with donor-π-acceptor-π-donor structure.
* Corresponding author. Prof. J. V. Grazulevicius, E-mail: juozas.grazulevicius@ktu.lt.
1

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Keywords:
benzothiadiazole,
carbazole,
donor-acceptor,
delayed
fluorescence,
red
electroluminescence.
1. Introduction
The fast growing interdisciplinary terrain of organic optoelectronics exploits organic molecular
derivatives as semiconductors and active components in devices. Organic materiaks containing donor
(D) and acceptor (A) electrophores are of interest for application in OLEDs [1,2,3], organic thin film
transistors [4,5], organic photovoltaic devices [6,7], electrochromic devices [8]. D-A-D type molecules
have also attracted attention for non-linear optical applications due to their high two- and three-photon
absorption cross sections [9,10]. Optoelectronic properties of organic compounds containing electron-
donating and electron-accepting fragments can be optimized by methodically controling the number of
D and A units in the structures [11]. The strength of A-D interactions is influenced by A moieties and π-
conjugated bridges [12]. Usually strong accepting moieties and short bridges enhance A-D interactions
[13]. The intramolecular charge transfer interactions between D and A moieties can decrease band-gap
energies of compounds [14,15].
2,1,3-Benzothiadiazole (BTD) is a typical electron-withdrawing moiety, amenable to facile ring
modification and introduction of such fragments into molecules may facilitate electron-injection or
charge-transport and enable to tune band gaps [16]. BTD moieties are utilized in the design of π-
conjugated compounds for different applications [17].
Carbazole derivatives are known as classic hole transporters [18]. Carbazolyl moieties have been
used extensively in many materials with high charge carrier mobility. Some of them exhibit bipolar
charge-transporting property [19]. Carbazole derivatives are utilized in different electronic and
optoelectronic devices including OLEDs [20]. There are many reports on benzothiadiazole derivatives
containing donor groups. For example, Lee and co-workers [21] synthesized π-conjugated organic dyes
containing triphenylamino and BTD moieties. Compounds with the double-bond bridged moieties
showed bathochromic shift of UV absorption band relative to that of the compound that has a single
bond between the electroactive moieties. Tao et al [22] and Xu et al [23] reported on BTD derivatives
containing carbazole units which appeared to be promising organic light-emitting materials. Promarak
et al [24,25] demonstrated solution processed efficient green and red electroluminescent devices
containing BTD and carbazole derivatives. Recently, Ni et al [26] reported on red TADF emitters with a
D-A-D structure using BTD and diphenylamine moieties, 9,9-dimethyl-9,10-dihydroacridine or 9H-
carbazole. OLEDs containing the D-A-D-type TADF emitter reached maximum maximum external
quantum efficiencies (EQE) of 8.8% [26]. These reeports prove that D-A-D type TADF materials are
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efficient and practical. Derivatives containing carbazole and benzothiadiazole moieties intended for
photovoltaic applications were also reported [27]. Development of new bipolar derivatives of BTD,
which could be used as charge transporting materials or as emitters is still of great interest. Additional
information on the structure properties relationship of BTD and carbazole derivatives would be also
useful for the design of new efficient organic bipolar semiconductors and emitters.
In this paper, new emitters with D-A-D and D-π-A-π-D structures were designed and investigated
by various techniques. The design and synthesis of three 2,1,3-benzothiadiazole derivatives of electron-
accepting benzothiadiazole and donating 3,6-di-tert-butyl-carbazolyl, 9-ethyl-3-vinyl-carbazolyl and
1,2,3,4-tetrahydrocarbazolyl moieties are described. By changing the donor substituents attached to
benzothiadiazole core, we investigated the optical, thermal, morphological, charge-transporting and
electroluminescence properties of the compounds. The newly designed and easily synthesized
compounds demonstrated phosphorescence and delayed fluorescence at room temperature.
2. Experimental section
2.1. General information
1H NMR, 13C NMR spectra were obtained using a Varrian Unity Inova (300 MHz (1H), 75.4 MHz
(13C)). Infrared (IR), mass (MS) spectra, elemental, thermogravimetric analysis, differential scanning
calorimetry (DSC) measurements were carried out as described earlier [28]. Electrothermal MEL-
TEMP apparatus was used for the estimation of melting points. Absorption spectra photoluminescence
(PL) of dilute solutions, molecular dispersions in polystyrene (PS) and of the films were recorded in the
same way as described previously [29, 30]. Low and room temperature PL spectra and transients of the
solid solutions of the compounds in Zeonex were recorded using closed-cycle helium cryostat and time-
gated intensified CCD camera iStar (Andor) [31]. Cyclic voltammetry (CV) measurements were carried
out as described earlier [32]. Ionization potential measurements of the solid samples were performed by
photoelectron emission method in air [33]. Hole and electron mobilities (µh, µe) were studied by time of
flight technique [34,35]. The synthesized fluorescent emitters were tested in vacuum-deposited OLEDs
which were fabricated using pre-patterned ITO-coated glass substrates [36].
3. Results and discussion
Synthesis of the target compounds is illustrated by Scheme 1. Materials 3 and 4 were obtained by
Buchwald-Hartwig reaction [37] of compound 2 with compounds 1a or 1b. Compound 5 was prepared
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by Heck reaction of compound 2 with 9-ethyl-3-vinyl-9H-carbazole (1c) in the presence of tri-o-
tolylphosphine and palladium(II) acetate. The yields of the target compounds after purification by
column chromatography ranged from 54 to 71%. Chemical structures were confirmed by elemental
1
analysis, IR, H NMR, 13C NMR, mass spectrometries. The obtained derivatives were soluble in
chloroform, nitrobenzene, chlorobenzene, hexane etc. The detailed procedures of synthesis and
characterization data for 1-5 are given in Supporting Information.
Scheme 1. Synthesis of 1-5.
3.1. Thermal properties
The behavior of derivatives 3-5 under heating was studied by DSC and TGA. The data are given
in Table 1.
Table 1. Thermal characteristics of 3-5.
Compound
Tm/oC[1]
Tg/°C[1]
145
Tcr/°C[1]
-
Td-5%/°C[2]
268
193
3
4

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347, 347[3]
191
173
296
-
413
362
4
5
-
[1]
Tm is melting point; Tg is glass transition temperature; Tcr is crystallization temperature (scan rate 10
[2]
°C/min, nitrogen blanket).
Td-5% is 5% mass loss temperatures (scan rate 20 °C/min, nitrogen
atmosphere). [3] the second heating scan.
The DSC measurements showed that the synthesized derivatives can form molecular glasses. For
compounds 3-5, Tg ranged from 145 to 191 oC. For example, DSC curves of derivative 4 are presented
in Fig. 1a.
(b)
100
Tdec-5%
(a)
cooling
80
60
40
20
0
1st heating
3
4
5
2
nd heating
Tg= 191 oC
Tcr= 296 oC
Tm= 347 oC
0
200
400
600
800
-50
0
50
100
150
200
250
300
350
400
Temperature, oC
Temperature, oC
Figure 1. (a) DSC thermograms of derivative 4 (10 °C min-1 under nitrogen blanket); (b) TGA curves
of 3-5 (20 oC/min, nitrogen atmosphere).
Melting of the sample of 4 at 347 °C was observed in the first heating scan. It formed glass in the
cooling scan. In the second heating scan the transition glass-liquid of the amorphous sample was
recorded at 191 °C. The further heating revealed exothermic signal of crystallization at 296 °C and that
of melting at 347 °C. Derivative 5 was obtained as amorphous substance. The glass transition
temperature of derivative 5 was observed at 173 oC in the second heating scan (Fig. S1b). Compound 3
containing 1,2,3,4-tetrahydrocarbazolyl moiety was obtained as crystalline substance. The first DSC
o
heating scan of this compound disclosed endothermic melting transition at 193 C. In the following
heating scan Tg was observed at 145 °C (Fig. S1a). Tg of derivatives 4 and 5 containing 3,6-di-tert-
butylcarbazolyl and 9-ethyl-3-vinylcarbazolyl fragments, respectively, was found to be higher by 46
o
and 28 C than that of compound 3 containing 1,2,3,4-tetrahydrocarbazolyl donor substituent. This
observation can be explained by the weaker interaction of molecules in the sample of 3 due to its lower
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molar mass. TGA curves of derivatives 3-5 are shown in Fig. 1b. The decomposition temperatures (Tdec-
5%) of compounds 3-5 ranged from 268 to 413 °C (Table 1). Compounds 4 and 5 containing 3,6-di-tert-
butylcarbazolyl- and 9-ethyl-3-vinylcarbazolyl-substituted moieties, exhibited higher thermal stability
than compound 3 containing 1,2,3,4-tetrahydrocarbazolyl substituent.
3.2.
Theoretical calculations
Ground-state geometries of the benzothiadiazole derivatives in toluene solvent were optimized at
the B3LYP/6-31G(d,p) level using density functional theory (DFT) and Gaussian 09 software [38]. The
calculation revealed that molecules in a ground state can have several conformers (see Supporting
Information Fig. S1). HOMOs and LUMOs of 3 – 5 are illustrated in Fig. 2 (all conformers are depicted
in Fig. S2).
3
4
5
Figure 2. HOMO, LUMO of benzothiadiazole derivatives 3 – 5.
Electron densities in HOMO are extended almost throughout the whole molecules of 3 – 5, while most
of the electron densities in LUMO concentrate on benzothiadiazole unit. Dihedral angles and oscillator
strengths of the derivatives were calculated using time-dependent DFT approach (see Table S1). The
calculations revealed twisted geometries of derivatives 3 and 4 with dihedral angles between acceptor
and donors varying in the range of 61 – 71°. Compound 5 show almost flat structure. The reduction of
dihedral angle from twisted molecule to the flat (3 > 4 > 5) causes the increase of HOMO – LUMO
overlap and oscillator strength.
3.3.
Optical properties
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Absorption spectra of the dilute solutions of derivatives 3-5 in toluene and of the films are
presented in Fig. 3. Normalized fluorescence spectra of the dilute solutions in toluene, of molecular
dispersions in polystyrene, of the solid samples of the derivatives are depicted in Fig. 4. The
photophysical data are summarized in Table S2.
1.0
3
4
5
films
3x104
2x104
1.0
0.8
0.6
0.4
0.2
0.0
3
4
5
3
4
5
0.8
0.6
0.4
0.2
0.0
350
400
450
500
550
600
1x104
Wavelength, nm
0
300
350
400
450
500
550
200
300
400
500
600
Wavelength (nm)
Wavelength, nm
a)
b)
Figure 3. Absorption spectra of the solutions in toluene (a) and spin-coated films (b) of compounds 3 (solid
line), 4 (dashed line), 5 (dotted line).
Absorption spectra of compounds 3-5 demonstrate two broad well-resolved bands. Absorption
maxima at 300-350 nm can be attributed to benzothiadiazole [39] and carbazole [40] moieties. Broad
and structureless band with peak positions at 434, 476 and 497 nm for 3 - 5 respectively, illustrates
presence of intramolecular charge transfer (ICT). The lowest-energy absorption bands of the solutions
of 4 and 5 are shifted by 42 and 63 nm towards longer wavelengths with 2-fold and 10-fold increase of
oscillator strength in comparison with that of compound 3 due to increased π-conjugation system on
carbazole moiety and increased overlapping between HOMO and LUMO. Similarly to toluene
solutions, solid films of compounds 3-5 were characterized by both high-energy absorption bands (300-
350 nm) caused by π–π* and n–π* transitions of the conjugated benzothiadiazole and carbazole
moieties; and by low-energy absorption bands (452-514 nm) originated from the HOMO–LUMO ICT
transition (Figure 3 b). Slight red-shifts of the ICT absorption bands and different distribution of their
intensities were observed for the films of compounds 3-5 in comparison to those recorded for toluene
solutions. This observation can be attributed to either aggregation or polarity effects in solid state.
7

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η
= 0.10
3
a)
η
> 0.01
η
= 0.03
η
= 0.47
4
η
= 0.25
Toluene
Neat film
PS film
b)
η
= 0.50
η
= 0.36
η
= 0.60
5
η
= 0.03
c)
500
600
700
800
Wavelenght (nm)
Figure 4. Normalized fluorescence spectra of the molecular dispersions in PS (1 wt%, dashed line) of
1 µM solutions in toluene (solid line) and of the solid samples (dotted line) of a) 3, b) 4 and c) 5. η is
fluorescence quantum yield.
Derivative 3 dissolved in toluene exhibited broad and weak PL emission with a peak at 613 nm
(see Fig. 4a). Neat film of 3 exhibited PL emission similar to that of the solution with higher intensity
(η = 0.03) and narrower spectrum. 1,2,3,4-Tetrahydrocarbazolyl-substituted benzothiadiazole embedded
in polystyrene matrix demonstrated spectrum with a peak blue-shifted by 40 nm and increased emission
intensity (η = 0.1). The weak emission of 3 in a solution may be explained by twisted molecular
structure (see Supporting Information Table S1) and oscillations of side groups. The suppression of
8

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these oscillations in polymer matrix or neat film leads to the rise of the emission intensity. Dispersed in
PS, derivative 4 demonstrated 5-fold higher PL QY relative to compound 5 without tert-butyl moieties.
PL quantum yield of 0.47 and 0.25 were estimated for solution and neat film of 4, respectively.
Relatively high PL QY of the solid film can be explained by molecular planarization [41].
Photoluminescence spectrum of the liquid solution of 5 in toluene exhibited similar spectrum to that of
the solid solution in PS film, only the estimated PL QY of the molecular dispersion in PS was lower
(η = 0.36 comparing to η = 0.6 for the solution in toluene). Emission of the neat film of derivative 5 was
broad and red shifted, what indicates excimer formation. Decrease of fluorescence efficiency in the
solid state was observed for many compounds [42]. It is explained by excitation migration-related
quenching. Coplanarity of molecule 5 apparently enhances exciton coupling, which promotes the
nonradiative decay due to excitation migration to intrinsic defects [42,43].
Charge transfer phenomena of compounds 3-5 were studied by recording fluorescence spectra of
the solutions in the solvents of different polarity. Photophysical data of the solutions of 3-5 in different
solvents are presented in Supporting Information Table S2 and Fig. S3. Derivative 3 disolved in
solvents of different polarity demonstrated extremely low emission. The similar compound possessing
carbazole instead of 1,2,3,4-tetrahydracarbazolyl substituents demonstrated very efficient luminescence
in a non-polar solvent [44]. Low emission of 3 can apparently be explained by a non-flat carbazolyl
moiety (Fig. S4). Increasing solvent polarity for the solutions of compounds 4 and 5 resulted in
considerable broadening and bathochromic shifts of the fluorescence bands as well as in considerable
decrease of emission quantum yields from ca. 0.47 and 0.6 (for the solutions in nonpolar solvents) to
0.05 and 0.35 (for the solutions in polar solvent), and decrease of emission life time (τ) from 15.7 and
4.9 ns (for the solutions in nonpolar solvents) to 4.3 and 4.4 ns (in polar solvent) respectively. The
estimated radiative (τR) decay time constants are 4-9 times longer for the twisted molecule (4) in
comparison to the flat one (5). The similar dependence was observed for non-radiative (τNR) decay
times.
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PF @292K
DF @292K
PH @20K
ET = 2.15 eV
ES = 2.44 eV
500
600
700
Wavelength (nm)
Figure 5. Prompt (PF), delayed fluorescence (DF) spectra recorded at ambient temperature and
phosphorescence (PH) spectrum recorded at 20 K of 1% wt solid solution of 3 in Zeonex.
PL transients and the spectra of 3-5 embedded into Zeonex matrix were recorded at ambient
conditions and at 20 K. All the compounds demonstrated single exponential prompt fluorescence decays
(Fig. S5). Derivatives 4 and 5 did not show any luminescence after prompt fluorescence. The absence of
long lived states in a similar compound with the carbazole side groups was observed earlier [45].
Compound 3 demonstrated very weak phosphorescence (ET = 2.15 eV) at 20 K (Fig. 5) and delayed
fluorescence at room temperature.
3.4.
Electrochemical characterization
Electrochemical characterization of derivatives 3-5 and intermediates 1a-1c, 2 was performed by
cyclic voltammetry (CV). The results are summarized in Table 2 and Table S3. The cyclic
voltammogram profiles of 3-5 and intermediates 1a-c, 2 are shown in Fig. 6 and Fig. S6.
10

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1st
2nd
3rd
4th
5th
6th
7th
8th
9.0x10-6
3
(b)
6.0x10-6
3.0x10-6
0.0
2.0x10-5
1.5x10-5
1.0x10-5
5.0x10-6
0.0
6.0x10-6
5.0x10-6
4.0x10-6
3.0x10-6
2.0x10-6
1.0x10-6
0.0
1 scan
2 scan
3 scan
4 scan
5 scan
(a)
1.0x10-5
(c)
5
1st
2nd
-1.0x10-6
-2.0x10-6
-3.0x10-6
5.0x10-6
3rd
4th
5th
6th
7th
8th
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Potential, V
4
0.0
-5.0x10-6
-5.0x10-6
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
Potential, V
Potential, V
Figure 6. CV curves and repetitive anodic sweeps (inset) of argon-purged dichloromethane solution of
compound 4 (a). Repetitive anodic sweeps at a platinum electrode of 0.1 M TBAHP6/dichloromethane
solutions of compounds 3 (b) and 5 (c) recorded at 100 mVs-1 scan rate.
Table 2. Electrochemical characteristics of 3-5.
egl /eV[c]
ox
onset
red
Derivative
IPCV/eV[a]
EACV/eV[b]
E
E
vs Fc/V
E
vs Fc/V
onset
0.57/0.59
0.76/0.92
0.53/0.84
-1.82
5.37
5.56
5.33
2.98
3.04
2.87
2.39
2.52
2.46
3
4
5
-1.74
-1.94
[a,b]
ox
onset
Ionization potential, electron affinity values estimated according to IPCV = (
E
+ 4.8) [eV],
ox
onset
red
(where,
E
is onset oxidation potential vs the Fc/Fc+). EACV = (Eorendset + 4.8) [eV], (where,
E
is
onset
onset reduction potential vs the Fc/Fc+). [c] Eegl = IPCV – EACV.
Cyclic voltammograms of compounds 3-5 showed the similar redox behavior. The single
reduction maximum and two oxidation peaks were observed at the negative and positive potential
ranges, respectively. This result can be interpreted in terms of one electron stepwise reduction of
benzothiadiazole moiety and two electron oxidation of 3,6-di-tert-butyl-carbazolyl, 9-ethyl-3-vinyl-
carbazolyl and 1,2,3,4-tetrahydrocarbazolyl moieties. CV curve of 4 is shown in Fig. 6a. Compound 4
showed electrochemical stability under five cycles of CV scan, the current did not drop down and the
11

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two oxidations waves at 0.76 and 0.92 V remained reversible (Fig. 6 a, inset). Electrochemical stability
of 4 can be explained by the presence of alkyl substituents at C-3 and C-6 reactive positions of
carbazole unit. Fig. 6b,c show the different results of electrochemical measurements of derivatives 3
and 5 in a range of 0 to 1.4 V. Since these derivatives have reactive positions in 1,2,3,4-
tetrahydrocarbazole and carbazole moieties their electrochemical stability was found to be poor. For
compound 3, under eight CV scans the current dropped down and two oxidations waves at 0.57 and
0.59 V remained irreversible. For compound 5, the current dropped down to lower voltage with the
increasing number of scans, but the two oxidations waves at 0.53 and 0.84 V turned to be reversible.
Ionization potentials (IPCV) were found to be 5.37 eV for 3, 5.56 eV for 4 and 5.33 eV for 5. IPCV values
of derivatives 3-5 were found to be significantly lower than that of unsubstituted 4,7-
dibromobenzothiadiazole 2 (Table S3). This result can be explained by the presence of 3,6-di-tert-butyl-
carbazolyl, 9-ethyl-3-vinyl-carbazolyl and 1,2,3,4-tetrahydrocarbazolyl moieties, which are strong
electron donors. The band gap value ( E
egl ) is one of the most intrinsic characteristic for organic
compounds used in electronic devices. Eegl value estimated for 3 was found to be slightly lower than
those of 4 and 5. Eegl values established for the derivatives of 3-5 are comparable of the reported
derivatives of benzothiadiazole and carbazole [46]. These materials showed relatively high electron
affinity values, which ranged from 2.87 to 3.04 eV.
3.5.
Photoelectrical properties
Since compounds were designed for optoelectronic applications, ionization potentials (IPEP) of
their thin solid layers were estimated by electron photoemission spectrometry. Electron photoemission
spectra and ionization potentials of 3-5 are depicted in Fig. 7a. IPEP values of the films of 3-5 ranged
from 5.64 to 5.82 eV. Derivatives 3 and 4 were characterized by similar IPEP values, while 4
demonstrated the lowest IPEP due to the presence of stronger donating di-tert-butyl carbazole units. The
differences observed in the values of IPCV and IPEP (Table 3) can be explained by the differences in
molecular arrangement in thin solid layers and in dilute solutions.
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3 Ip = 5.82 eV
4 Ip = 5.64 eV
5 Ip = 5.7 eV
1
0
4.8
5.1
5.4
5.7
6.0
6.3
hν
(eV)
Figure 7. Electron photoemission spectra and ionization potentials of the solid samples of derivatives 3-
5.
Charge transporting properties of the layers of 3-5 were explored by the time of flight (TOF)
technique. The results are summarized in Table 3. Fig. 8 shows plots of hole and electron drift
mobilities (µh, µe) of the layers of 4, 5 and of the layers of molecular dispersions in bisphenol Z
polycarbonate (PC-Z) versus electric field. In wet-deposition processes of fabrication of TOF samples,
PC-Z was used for getting films with uniform thicknesses. Similar charge-transporting properties were
observed for compounds 4 and 5. Thus, hole mobilities (µh) of 4 and 5 ranged from ca. 1×10-4 cm2/Vs to
3×10-4 cm2/Vs at electric field of 2.4×105-1.6×105 Vcm-1, while electron mobilities (µe) of 4 and 5 were
found to be by more than one magnitude lower in comparison to hole mobilities.
vacuum deposition:
10-2
10-3
10-4
10-5
10-6
10-7
10-8
4: holes
4: electrons
wet-deposition (casting):
Al+4: holes
Al+[4+(PC-Z), 1:1]: holes
Al+5:holes
Al+[5+(PC-Z),1:1]:electrons
0
200
400
600
800
1000 1200 1400
E1/2 (V1/2/cm1/2)
13

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Figure 8. Hole and electron drift mobilities versus electric field for the layers of 4, 5 and of 3-5 doped
in PC-Z.
In addition, charge-transporting properties of 4 were investigated using vacuum-deposited
samples. The obtained hole mobilities for these samples were in good agreement with hole mobilities of
wet-casted layer of 4 (Fig. 8). It was imposible to estimate hole and electron mobilities neither for neat
layer nor for the solid solution of 3 since transit times were not obtained from the corresponding current
transients. Apparently, compound 3 exhibited weak charge-transporting properties due to the presence
of weaker donating units of 1,2,3,4-tetrahydrocarbazole in comparison to those of compound 4 having
stronger donating di-tert-butyl carbazole units. Other explanation of this observation can be strongly
dispersive charge-transport due to which transit times were not observed for compound 3. Therefore,
charge-drift mobility of 3 was not estimated. Indeed, compounds 4 and 5 were also characterized by
strongly dispersive charge-transport. It can be stated taking into account the shapes of hole and electron
current transients (Fig. S7). Nevertheless, bipolar charge-transporting properties of the compounds 4, 5
with rather high charge mobilities show that they have potential for the application as non-doped
functional (light-emitting) layers in OLEDs.
Table 3. Hole, electron mobility data for neat layers of 4, 5 and for molecular dispersions of 3-5 in PC-
Z.
Material, host polymer
µe/cm2V-1s-1
µh/cm2V-1s-1
d, µm
Wet-deposited samples
Al+4
-
2.9×10-3 (at 1.6×106 V/cm)
1.8×10-4 (at 1.4×106 V/cm)
2.1×10-4 (at 2.4×105 V/cm)
-
1.4
3.3
6.0
0.5
Al+[4+(PC-Z), 1:1]
Al+5
-
-
Al+[5+(PC-Z), 1:1]
1.5×10-6 (at 6.7×105 V/cm)
Vacuum-deposited samples
5.7×10-5 (at 5.8×105 V/cm)
1.7×10-3 (at 5.3×105 V/cm)
1.9
4
µe - electron drift mobility value; µh - hole drift mobility value; d - layer thickness (µm).
Electroluminescent properties
Compounds 4 and 5 were selected for the study of their electroluminescent properties. Moderate
PLQYs of non-doped solid films and bipolar charge-transport manifest compounds 4 and 5 as
promising emitters for fluorescent OLEDs. To estimate their applicability in fluorescent OLEDs, the
14

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thermally-deposited devices with the following structures were fabricated: indium tin oxide (ITO)/
molybdenum trioxide (MoO3) (1 nm)/N,N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine
(NPB) (40 nm)/non-doped light-emitting layer
4
or
5
(25 nm)/ diphenyl[4-
(triphenylsilyl)phenyl]phosphine oxide (TSPO1) (5 nm)/ 2,2′,2"-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-
benzimidazole) (TPBi) (40 nm) / fluoride lithium (LiF) (0.5 nm)/ Al (80 nm) (Fig. 9a). To ensure
charge balance in the devices, MoO3 (hole-injecting material) and NPB (hole-transporting material),
while TSPO1 and TPBi served as the electron-transporting materials. They posses appropriate HOMO,
LUMO energies and charge-transporting properties (Fig. 9a). The devices with light-emitting layers of 4
and 5 were named as devices A, B, respectively. To plot equilibrium energy diagram for these devices,
PE
electron affinities (EAPE) of 2.5 and 2.85 eV for 4 and 5 in solid-state were obtained by the formula EA
= IPPE-1.37×Eg where the optical band-gap energies (Eg) of 2.29 and 2.08 eV were estimated from
absorption spectra of the layers and the constant of 1.37 was used as it was proposed in [47] (Fig. 3 and
9a, Table 3).
Stable at different applied voltages EL spectra of devices A, B were observed (Fig. 9b). Devices
A and B exhibited red emission with CIE coordinates of (0.55, 0.43) and (0.55, 0.41) at electrical
excitation, respectively (Figure S5). Compounds 4 or 5 demonstrated EL spectra with the closely
situated main peaks at 598 and 604 nm respectively which were very similar to their PL spectra.
Emission related to other functional layers of OLEDs A and B was not observed. This observation
confirms good design of device structure.
a)
b)
15

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1
10000
1000
100
Device A
Device B
400
300
200
100
0
Divice A
Divice B
0.1
10
100
1000
10000
1
Divice A
Divice B
0.1
10
10
100
1000
10000
2
3
4
5
6
7
8
9
10
11
12
-2
Voltage(V)
Brightness (cd m
)
c)
d)
Figure 9. Equilibrium energy diagram and chemical structures of functional materials
NPB,TSPO1 and TPBi (a), EL spectra taken at different voltages (b) brightness–voltage–current density
curves (c) and external quantum efficiency–brightness–current efficiency curves (d) of devices A and B.
Device A displayed the turn-on voltage of 4.9 V which was lower than 5.5 V observed for
device B, which apparently benefited from the higher charge-drift mobilities, according to brightness–
voltage–current density curves (Fig. 9c). Moreover, both higher current efficiency (CE) of 2.65 cd/A
and EQE of 1.3% were obtained for device A based on compound 4 in comparison to CE of 0.29 cd/A
and EQE of 0.13% recorded for device B based on compound 5. These results are consistent with EQEs
of 1.25-1.5% and 0.15-0.23% theoretically predicted for fluorescent devices A, B, respectively. The
theoretical EQEs were estimated according to the formula ηext=γ×ϕPL×χ×ηout, where γ is the charge-
balance factor, ϕPL represents the photoluminescence quantum yield (ϕPL=0.25 for 4 and ϕPL=0.03 for 5
in solid films), χ is the efficiency of exciton formation (χ=0.25 for singlet emission), and ηout is to the
outcoupling efficiency (ηout is usually around 0.2-0.3) [48]. Much better performance of device A
obtained using compound 4 relative to that of device B based on compound 5 can mainly be explained
by higher PLQY, higher charge-drift mobilities of 4 and effective utilization of the excitation energy
from intercrossed-excited-states [49].
Small efficiency roll-off was observed for devices A, B, which can be interpreted in terms of
bipolar charge-transporting properties of both the compounds (4 and 5). The performances of the non-
doped devices A and B are still low especially comparing them with EQEs of the doped OLEDs based
on phosphorescent emitters or those exhibiting thermally activated delayed fluorescence (TADF) [50,
51]. Benefiting from colour purity and stability, highly efficient devices, representing so-called as 3.5
generation of OLEDs) were developed using light-emitting layers based on a combination of TADF
hosts and simple fluorescent emitters [52]. Exploiting the developed here fluorescent emitters 4 and 5 in
16

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combination with appropriate TADF hosts, further improvement of OLED characteristics can be
predicted.
4. Conclusions
Three derivatives of benzothiadiazole having either donor-acceptor-donor or donor-π-acceptor-π-
donor structures were synthesized. Optical, thermal, electrical, charge-transporting properties of the
materials obtained were studied. The compounds possess glass-forming properties. Their glass
o
transition temperatures were found to be in the range of 145-191 C. Ionization potentials of the solid
samples of the compounds estimated by electron photoemission spectrometry were found to be
comaparable (5.64-5.82 eV). The cyclovoltammetric experiments revealed high electrochemical
stability of tert-butylcarbazolyl-substituted benzothiadiazole. Optical characterization together with
DFT calculations disclosed intramolecular charge transfer in investigated derivatives. Reduction of
molecule twisting increases oscillator strength and photoluminescence quantum yield. Dilute solutions
of the carbazolyl-substituted benzothiadiazoles in nonpolar solvent and solid solutions in polystyrene
showed fluorescence quantum yields up to 0.60. Due to molecule twisting emission of
tetrahydrocarbazolyl-substituted benzothiadiazole derivative was very weak, however this compound
exhibited phosphorescence and delayed
fluorescence. Di-tert-butylcarbazolyl-substituted
benzothiadiazole showed efficient transport of holes and electrons. Compounds of carbazole and
benzothiadiazole demonstrated similar electroluminescence spectra with the close situated main peaks
at 598 and 604 nm and very different maximum external quantum efficiency values of 1.3 and 0.13%
depending on their molecular structures. Much better electroluminescent performance was observed for
the compound having donor-acceptor-donor structure.
Acknowledgement
This research was supported by Research Council of Lithuania (grant agreement No S-MIP-17-96).
17

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List of Figure and Table titles
Figure 1. (a) DSC thermograms of derivative 4 (10 °C min-1 under nitrogen blanket); (b) TGA curves
of 3-5 (20 oC/min, nitrogen atmosphere).
Figure 2. HOMO, LUMO of benzothiadiazole derivatives 3 – 5.
Figure 3. Absorption spectra of the solutions in toluene (a) and spin-coated films (b) of compounds 3
(solid line), 4 (dashed line), 5 (dotted line).
Figure 4. Normalized fluorescence spectra of the molecular dispersions in PS (1 wt%, dashed line) of 1
µM solutions in toluene (solid line) and of the solid samples (dotted line) of a) 3, b) 4 and c) 5. η is
fluorescence quantum yield.
Figure 5. Prompt (PF), delayed fluorescence (DF) spectra recorded at room temperature and
phosphorescence (PH) spectrum recorded at 20 K of 1% wt solid solution of 3 in Zeonex.
Figure 6. CV curves and repetitive anodic sweeps (inset) of argon-purged dichloromethane solution of
compound 4 (a). Repetitive anodic sweeps at a platinum electrode of 0.1 M TBAHP6/dichloromethane
solutions of compounds 3 (b) and 5 (c) recorded at 100 mVs-1 scan rate.
Figure 7. Electron photoemission spectra, ionization potentials of the solid samples of derivatives 3-5.
Figure 8. Hole and electron drift mobilities versus electric field for the layers of 4, 5 and of 3-5 doped
in PC-Z.
Figure 9. Equilibrium energy diagram and chemical structures of functional materials NPB,TSPO1 and
TPBi (a), EL spectra taken at different voltages (b) brightness–voltage–current density curves (c) and
external quantum efficiency–brightness–current efficiency curves (d) of devices A and B.
Table 1. Thermal characteristics of 3-5.
Table 2. Electrochemical characteristics of 3-5.
Table 3. Hole, electron mobility data for neat layers of 4, 5 and for molecular dispersions of 3-5 in PC-
Z.
18

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List of figures
(b)
100
Tdec-5%
(a)
cooling
80
60
40
1st heating
3
4
5
2
nd heating
Tg= 191 oC
Tcr= 296 oC
20
0
Tm= 347 oC
0
200
400
600
800
-50
0
50
100
150
200
250
300
350
400
Temperature, oC
Temperature, oC
Figure 1. (a) DSC thermograms of derivative 4 (10 °C min-1 under nitrogen blanket); (b) TGA curves
of 3-5 (20 oC/min, nitrogen atmosphere).
3
4
5
Figure 2. HOMO, LUMO of benzothiadiazole derivatives 3 – 5.
19

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1.0
0.8
0.6
0.4
0.2
0.0
3
films
3x104
2x104
1.0
3
4
5
3
4
5
4
0.8
5
0.6
0.4
0.2
0.0
350
400
450
500
550
600
1x104
Wavelength, nm
0
300
350
400
450
500
550
200
300
400
500
600
Wavelength (nm)
Wavelength, nm
a)
b)
Figure 3. Absorption spectra of the solutions in toluene (a) and spin-coated films (b) of compounds 3 (solid
line), 4 (dashed line), 5 (dotted line).
20

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= 0.10
η
3
a)
η
> 0.01
η
= 0.03
η
= 0.47
4
η
= 0.25
Toluene
Neat film
PS film
b)
η
= 0.50
η
= 0.36
η
= 0.60
5
η
= 0.03
c)
500
600
700
800
Wavelenght (nm)
Figure 4. Normalized fluorescence spectra of the molecular dispersions in PS (1 wt%, dashed line) of
1 µM solutions in toluene (solid line) and of the solid samples (dotted line) of a) 3, b) 4 and c) 5. η is
fluorescence quantum yield.
21

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PF @292K
DF @292K
PH @20K
ET = 2.15 eV
ES = 2.44 eV
500
600
700
Wavelength (nm)
Figure 5. Prompt (PF), delayed fluorescence (DF) spectra recorded at room temperature and
phosphorescence (PH) spectrum recorded at 20 K of 1% wt solid solution of 3 in Zeonex.
1st
9.0x10-6
6.0x10-6
3.0x10-6
3
(b)
2nd
3rd
4th
5th
6th
7th
8th
2.0x10-5
1.5x10-5
1.0x10-5
5.0x10-6
0.0
6.0x10-6
5.0x10-6
4.0x10-6
3.0x10-6
2.0x10-6
1.0x10-6
0.0
1 scan
2 scan
3 scan
4 scan
5 scan
(a)
0.0
1.0x10-5
(c)
5
1st
2nd
3rd
4th
5th
6th
7th
8th
-1.0x10-6
-2.0x10-6
-3.0x10-6
5.0x10-6
0.0
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
Potential, V
4
-5.0x10-6
-5.0x10-6
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
Potential, V
Potential, V
Figure 6. CV curves and repetitive anodic sweeps (inset) of argon-purged dichloromethane solution of
compound 4 (a). Repetitive anodic sweeps at a platinum electrode of 0.1 M TBAHP6/dichloromethane
solutions of compounds 3 (b) and 5 (c) recorded at 100 mVs-1 scan rate.
22

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3
4
5
Ip = 5.82 eV
Ip = 5.64 eV
Ip = 5.7 eV
1
0
4.8
5.1
5.4
5.7
6.0
6.3
hν
(eV)
Figure 7. Electron photoemission spectra, ionization potentials of the solid samples of derivatives 3-5.
vacuum deposition:
10-2
10-3
10-4
10-5
10-6
10-7
10-8
4: holes
4: electrons
wet-deposition (casting):
Al+4: holes
Al+[4+(PC-Z), 1:1]: holes
Al+5:holes
Al+[5+(PC-Z),1:1]:electrons
0
200
400
600
800
1000 1200 1400
E1/2 (V1/2/cm1/2)
Figure 8. Hole and electron drift mobilities versus electric field for the layers of 4, 5 and of 3-5 doped
in PC-Z.
23

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a)
b)
1
10000
1000
100
Device A
Device B
400
300
200
100
0
Divice A
Divice B
0.1
10
100
1000
10000
1
Divice A
Divice B
0.1
10
10
100
1000
10000
2
3
4
5
6
7
8
9
10
11
12
-2
Voltage(V)
Brightness (cd m
)
c)
d)
Figure 9. Equilibrium energy diagram and chemical structures of functional materials
NPB,TSPO1 and TPBi (a), EL spectra taken at different voltages (b) brightness–voltage–current density
curves (c) and external quantum efficiency–brightness–current efficiency curves (d) of devices A and B.
24

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List of tables
Table 1. Thermal characteristics of 3-5.
Compound
Tm/oC[1]
Tg/°C[1]
145
Tcr/°C[1]
Tdec-5%/°C[2]
268
193
-
296
-
3
4
5
347, 347[3]
191
413
-
173
362
[1]
Tm – melting temperature; Tg – glass transition temperature; Tcr – crystallization temperature (scan
[2]
rate 10 °C/min, nitrogen atmosphere). Tdec-5% – 5% weight loss temperatures (scan rate 20 °C/min,
nitrogen atmosphere). [3] the second heating scan.
Table 2. Electrochemical characteristics of 3-5.
egl /eV[c]
ox
onset
red
Derivative
IPCV/eV[a]
EACV/eV[b]
E
E
vs Fc/V
E
vs Fc/V
onset
0.57/0.59
0.76/0.92
0.53/0.84
-1.82
5.37
5.56
5.33
2.98
3.04
2.87
2.39
2.52
2.46
3
4
5
-1.74
-1.94
[a,b]
ox
onset
Ionization potential and electron affinity values estimated according to IPCV = (
E
+ 4.8) [eV],
ox
onset
red
(where,
E
is onset oxidation potential vs the Fc/Fc+). EACV = (Eorendset + 4.8) [eV], (where,
E
is
onset
onset reduction potential vs the Fc/Fc+). [c] Eegl = IPCV – EACV.
Table 3. Hole, electron mobility data for neat layers of 4, 5 and for molecular dispersions of 3-5 in PC-
Z.
Material, host polymer
µe/cm2V-1s-1
µh/cm2V-1s-1
d, µm
Wet-deposited samples
Al+4
-
2.9×10-3 (at 1.6×106 V/cm)
1.8×10-4 (at 1.4×106 V/cm)
2.1×10-4 (at 2.4×105 V/cm)
-
1.4
3.3
6.0
0.5
Al+[4+(PC-Z), 1:1]
Al+5
-
-
Al+[5+(PC-Z), 1:1]
1.5×10-6 (at 6.7×105 V/cm)
Vacuum-deposited samples
5.7×10-5 (at 5.8×105 V/cm)
1.7×10-3 (at 5.3×105 V/cm)
1.9
4
µe - electron drift mobility value; µh - hole drift mobility value; d - layer thickness (µm).
25

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Differently substituted benzothiadiazoles as charge-transporting emitters for
fluorescent organic light-emitting diodes
Dalius Gudeika1, Arunas Miasojedovas2, Oleksandr Bezvikonnyi1, Dmytro Volyniuk1, Alytis Gruodis3,
Saulius Jursenas2, Juozas V. Grazulevicius1†
1Department of Polymer Chemistry and Technology, Kaunas University of Technology, Radvilenu pl.
19, LT- 50254, Kaunas, Lithuania;
2Institute of Photonics and Nanotechnology, Vilnius University, Sauletekio 3, LT-10257 Vilnius,
Lithuania;
3Institute of Chemical Physics, Vilnius University, Sauletekio 9-III, LT-10222 Vilnius, Lithuania;
SUPPORTING INFORMATION
Content
Experimental section
S32
S34
S35
S35
S36
S37
S38
S39
S39
DSC thermograms of benzothiadiazole compounds 3 and 5
HOMO and LUMO charge distribution of different conformers of 3 – 5
TD-DFT calculated HOMO, LUMO of conformers of 3 – 5
Absorption and fluorescence spectra of compounds 3-5 in different polarity solvents
Photophysical properties of derivatives 3-5
Geometry of 3
Photoluminescence decay profile of 1% wt. of 3-5 embedded in Zeonex matrix
Redox potentials, optical band gap energy, IPCV/EACV values of intermediates 1a-c, 2
Cyclic voltammograms in argon-purged dichloromethane solutions of intermediates 1a-c, 2 S40
TOF current transients of electrons for vacuum-deposited films of derivative 4
S40
† Corresponding author. Prof. J. V. Grazulevicius, E-mail: juozas.grazulevicius@ktu.lt.
26

ACCEPTED MANUSCRIPT
Experimental section
Materials and synthesis
1,2,3,4-Tetrahydrocarbazole (1b), tri-tert-butylphosphine solution (1.0 M in toluene), tri(o-
tolyl)phosphine (P(o-tolyl)3), triethylamine, palladium(II) acetate (Pd(OAc)2), potassium tert-butoxide,
sodium tert-butoxide, methyltriphenylphosphonium bromide were purchased from Sigma Aldrich. 9H-
carbazole was obtained from Reakchim. 9-Ethyl-9H-carbazole-3-carbaldehyde was purchased from
Acros.
2,1,3-Benzothiadiazole (1) [53], 4,7-dibromobenzothiadiazole (2) [54], 3,6-di-tert-butyl-9H-
carbazole (1a) [55], 9-ethyl-3-vinyl-9H-carbazole (1c) [56] were synthesized by the known procedures
as described in the literature.
General procedure for the synthesis of 4,7-bis(1,2,3,4-tetrahydro-9H-carbazol-9-
yl)benzo[c][1,2,5]thiadiazole
(3)
and
4,7-bis(3,6-di-tert-butyl-9H-carbazol-9-
yl)benzo[c][1,2,5]thiadiazole (4).
The mixture of 4,7-dibromobenzothiadiazole (0.50 g, 1.7 mmol) and 3,6-di-tert-butyl-9H-
carbazole (1a) (0.95 g, 3.4 mmol) or 1,2,3,4-tetrahydrocarbazole (1b) (0.59 g, 3.4 mmol), palladium(II)
acetate (0.038 g, 0.17 mmol), tri-tert-butylphosphine solution (1.0 M in toluene) (0.011 g, 0.057 mmol),
potassium tert-butoxide (0.76 g, 6.8 mmol) and 25 ml of dry toluene was heated in the temperature of
◦
90 C for 24 h under nitrogen. The reaction mixture was diluted with tetrahydrofuran. The solvent was
removed and the residue was purified twice by column chromatography (n-hexane/ethylacetate, 7:1) to
obtain the products of 3 (orange crystals, yield: 65%) and 4 (yellow crystals, yield: 71%). Compounds 3
and 4 were recrystallized from the mixture of n-hexane/ethylacetate (7:1).
o
1
3: M.p: 187-188 C. H NMR (300 MHz, CDCl3, 298 K) δ [ppm]: 8.13 (dd, J1 = 1.1 Hz, J2 = 8.8 Hz,
1H), 7.81-7.76 (m, 2H), 7.67-7.59 (m, 3H), 7.21-7.19 (m, 1H), 7.17-7.15 (m, 1H), 7.12. (dd, J1 = 1.1
Hz, J2 = 8.8 Hz, 1H), 7.08-7.02 (m, 1H), 2.95-2.88 (m, 4H), 2.72-2.51 (m, 4H), 2.08-1.82 (m, 12H). 13C
27

ACCEPTED MANUSCRIPT
NMR (75.4 MHz, CDCl3, 298 K) δ [ppm]: 129.6, 127.9, 127.6, 122.0, 121.7, 121.1, 121.5, 120.3,
118.5, 118.4, 110.2, 23.5, 23.3, 21.4. IR (KBr, ν, cm-1): 3046 (C-Har), 2925, 2833 (C-Haliph), 1597,
1506, 1457 (C=Car), 1380, 1300, 1230 (C-N), 738 (CHar). Elemental analysis calculated (%) C30H30N4S:
C 75.28, H 6.32, N 11.70; found: C 75.35, H 6.35, N 11.77. MS (APCI+, 20 V), m/z: 479 ([M+H]+).
o
1
4: M.p: 342-343 C. H NMR (300 MHz, CDCl3, 298 K) δ [ppm]: 8.25 (dd, J1 = 0.5 Hz, J2 = 1.9 Hz,
4H), 8,02 (s, 2H), 7.54 (d, J = 1.9 Hz ,1H), 7.51 (d, J = 1.9 Hz, 2H), 7.49 (dd, J1 = 3.5 Hz, J2 = 6.0 Hz,
1H), 7.31 (d, J = 0.5 Hz, 1H), 7.27 (d, J = 0.5 Hz, 2H), 7.24 (dd, J1 = 3.5 Hz, J2 = 6.0 Hz, 1H), 1.53 (s,
13
36H). C NMR (75.4 MHz, CDCl3, 298 K) δ [ppm]: 143.9, 139.6, 130.8, 128.0, 127.6, 124.4, 124.0,
116.9, 110.2, 135.0, 32.3. IR (KBr, ν, cm-1): 3052 (C-Har), 2965, 2930 (C-Haliph), 1587, 1455 (C=Car),
1367, 1318, 1235 (C-N), 745 (CHar). Elemental analysis calculated (%) C46H50N4S: C 79.96, H 7.29, N
8.11; found: C 80.02, H 7.32, N 8.07. MS (APCI+, 20 V), m/z: 691 ([M+H]+).
4,7-Bis((E)-2-(9-ethyl-9H-carbazol-3-yl)vinyl)benzo[c][1,2,5]thiadiazole (5).
A flask was charged with a mixture of 4,7-dibromobenzothiadiazole (0.50 g, 1.7), 9-ethyl-3-vinyl-9H-
carbazole (1c) (0.75 g, 3.4 mmol), palladium(II) acetate (0.038 g, 0.17 mmol), tri(o-tolyl)phosphine
(0.034 g, 0.11 mmol), DMF (8 mL) and triethylamine (2 mL). The mixture was heated at 85 oC for 24 h
under nitrogen blanket. It was filtered and the filtrate was poured into ethanol. The red precipitate was
filtered, washed with ethanol and dissolved in acetone. The crude product was purified by silica gel
column chromatography (ethylacetate/n-hexane, (1:9) to obtain 5 as red solid with the yield of 54%. 1H
NMR (300 MHz, CDCl3, 298 K) δ [ppm]: 8.42 (d, J = 1.5 Hz, 4H), 8.20 (s, 2H), 7.88 (d, J = 1.5 Hz,
1H), 7.85 (d, J = 1.5 Hz, 2H), 7.79 (d, J = 2.4 Hz, 2H), 7.56-7.45 (m, 5H), 7.33 (d, J = 1.1 Hz, 2H), 7.31
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(d, J = 1.1 Hz, 1H), 7.29 (d, J = 1.3 Hz, 2H), 4.45-4.42 (m, 4H), 1.51 (t, 6H). C NMR (75.4 MHz,
CDCl3, 298 K) δ [ppm]: 140.4, 140.1, 133.7, 129.2, 128.8, 126.2, 125.9, 124.8, 123.4, 123.2, 121.8,
120.6, 119.3, 119.2, 108.7. IR (KBr, ν, cm-1): 3044 (CHar), 2972, 2960, 2870 (CHaliphatic), 1618, 1595,
1532, 1491 (C=Car), 1344, 1232 (C-N), 960 (trans, -CH=CH), 798, 745, 727 (CHar). Elemental analysis
calculated (%) C38H30N4S: C 79.41, H 5.26, N 9.75; found: C 79.36, H 5.25, N 9.77. MS (APCI+, 20 V),
m/z: 575 ([M+H]+).
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