Synthesis and thermal, electrochemical, and photophysical investigation of carbazole/diphenyl benzothiadiazole-based fluorophores

Article abstract of DOI:10.1016/j.dyepig.2020.108668

Herein, we describe the syntheses of symmetric and asymmetric benzothiadiazole (BTD)-based fluorophores via the Sonogashira coupling reaction, using 4,7-dibromobenzothiadiazole as the central core and propargyl carbazole and/or propargyl diphenylamine as the side groups. The synthesized fluorophores exhibited absorption bands in the ultraviolet region, with a maxima between 372 and 380 nm due to the π→π* electronic transitions. Although they presented very low fluorescence quantum yields in solution, they demonstrated typical aggregation-induced emission phenomenon. Their oxidation potentials ranged from 0.91 to 1.18 V vs. NHE and reduction potentials from ?1.20 to 1.26 V vs. NHE. Their HOMO energies ranged from ?5.35 to 5.62 eV electron affinity from ?3.18 to 3.24 eV. Thus, the electrochemical bandgap of the BTD-based fluorophores was in the range of 2.16–2.38 eV. The symmetric BTD derivatives 3 and 5 exhibited good thermal stability, with decomposition temperatures at ~330 °C and 200 °C, respectively. BTD 7 showed lower thermal stability with a decomposition temperature of ~110 °C. BTD 3 and 5 showed glass transition temperature (T_g) values of ~75 °C (first heating) and 60 °C (first and second heating), respectively. BTD 7 did not show any T_g. The density functional theory (DFT) and time-dependent DFT calculations were performed at the CAM-B3LYP/6-31G** level of theory, which corroborated with the charge transfer characteristics of these compounds.

Full text of DOI:10.1016/j.dyepig.2020.108668

Journal Pre-proof
Synthesis and thermal, electrochemical, and photophysical investigation of carbazole/
diphenyl benzothiadiazole-based fluorophores
Priscila Sayoko Silva Wakabayashi, Rodrigo da Costa Duarte, Luís Gustavo Teixeira
Alves Duarte, Fabiano da Silveira Santos, Rodrigo Cercená, Eduardo Zapp, Fabiano
Severo Rodembusch, Alexandre Gonçalves Dal-Bó
PII:
S0143-7208(20)31365-6
DOI:
https://doi.org/10.1016/j.dyepig.2020.108668
DYPI 108668
Reference:
To appear in: Dyes and Pigments
Received Date: 30 April 2020
Revised Date: 23 June 2020
Accepted Date: 24 June 2020
Please cite this article as: Silva Wakabayashi PS, da Costa Duarte R, Teixeira Alves Duarte LG,
da Silveira Santos F, Cercená R, Zapp E, Rodembusch FS, Dal-Bó AG, Synthesis and thermal,
electrochemical, and photophysical investigation of carbazole/diphenyl benzothiadiazole-based
fluorophores, Dyes and Pigments, https://doi.org/10.1016/j.dyepig.2020.108668.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition
of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of
record. This version will undergo additional copyediting, typesetting and review before it is published
in its final form, but we are providing this version to give early visibility of the article. 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.
© 2020 Elsevier Ltd. All rights reserved.

Author contributions
Rodrigo da Costa Duarte: Conceptualization; Formal analysis; Roles/Writing - original
draft.
Rodrigo Cercená: Formal analysis; Roles/Writing - original draft.
Fabiano da Silveira Santos: Conceptualization; Formal analysis; Roles/Writing -
original draft.
Luís Gustavo Teixeira Alves Duarte: Formal analysis; Roles/Writing - original draft.
Eduardo Zapp: Formal analysis; Roles/Writing - original draft.
Daniela Brondani: Formal analysis; Roles/Writing - original draft.
Fabiano Severo Rodembusch: Conceptualization; Methodology; Supervision; Writing -
review & editing.
Alexandre Gonçalves Dal-Bó: Funding acquisition; Project administration; Supervision;
Resources.

Synthesis and thermal, electrochemical, and photophysical investigation of
carbazole/diphenyl benzothiadiazole-based fluorophores
Priscila Sayoko Silva Wakabayashi,a Rodrigo da Costa Duarte,a Luís Gustavo Teixeira
Alves Duarte,b Fabiano da Silveira Santos,a Rodrigo Cercená,a Eduardo Zapp,c Fabiano
Severo Rodembusch,d,* Alexandre Gonçalves Dal-Bóa,*
aUniversidade do Extremo Sul Catarinense (UNESC). Av. Universitária, 1105. CEP
88806-000. Criciúma-SC, Brazil. Tel.: +55 (48) 3431 2775. E-mail address:
adalbo@unesc.net
bChemistry Institute, University of Campinas, Campinas, 13083-970, Brazil
cUniversidade Federal de Santa Catarina (UFSC). Rua João Pessoa, 2750. CEP 89036-
256. Blumenau, SC, Brazil
dGrupo de Pesquisa em Fotoquímica Orgânica Aplicada. Instituto de Química
(UFRGS), Av. Bento Gonçalves, 9500, CEP 91501-970. Porto Alegre-RS, Brazil . E-
mail address: rodembusch@iq.ufrgs.br
Abstract
Herein, we describe the syntheses of symmetric and asymmetric benzothiadiazole
(BTD)-based fluorophores via the Sonogashira coupling reaction, using 4,7-
dibromobenzothiadiazole as the central core and propargyl carbazole and/or propargyl
diphenylamine as the side groups. The synthesized fluorophores exhibited absorption
bands in the ultraviolet region, with a maxima between 372 and 380 nm due to the
π→π* electronic transitions. Although they presented very low fluorescence quantum
yields in solution, they demonstrated typical aggregation-induced emission
phenomenon. Their oxidation potentials ranged from 0.91 to 1.18 V vs. NHE and
reduction potentials from -1.20 to 1.26 V vs. NHE. Their HOMO energies ranged from -
5.35 to 5.62 eV electron affinity from -3.18 to 3.24 eV. Thus, the electrochemical
bandgap of the BTD-based fluorophores was in the range of 2.16-2.38 eV. The
symmetric BTD derivatives 3 and 5 exhibited good thermal stability, with
decomposition temperatures at ~330°C and 200°C, respectively. BTD 7 showed lower
thermal stability with a decomposituion temperature of ~110°C. BTD 3 and 5 showed
glass transition temperature (Tg) values of ~75°C (first heating) and 60°C (first and
second heating), respectively. BTD 7 did not show any Tg. The density functional
1

theory (DFT) and time-dependent DFT calculations were performed at the CAM-
B3LYP/6-31G** level of theory, which corroborated with the charge transfer
characteristics of these compounds.
Keywords: benzothiadiazole, fluorescence, polymorphism, carbazole, Sonogashira
1. Introduction
Optoelectronic materials are attracting increasing interest owing to their use in
light technology [1], such as light-emitting and light-detecting devices [2],
photosensitive cell devices, photovoltaic devices [3,4], and stimulated emission devices
[5], among others [6,7]. This class includes light-emitting diodes (LEDs), organic light-
emitting diodes (OLED), and even light amplification by stimulated emission of
radiation (LASERS) [8,9]. In recent times, the demand for the development of devices
such as OLEDs and equipment that employ less energy in their operation has increased
[10,11], and hence the utilization of alternative energy sources such as organic
photovoltaic films (OPVs) is increasingly desired [12,13,14]. Thus, the development of
new molecules with potential optoelectronic applications is of great technological and
industrial interest [15].
Materials based on 2,1,3-benzothiadiazole (BTD) are highly promising for
optoelectronic aplicartions [16] owing to their large molar extinction coefficient values
and good photostability [17]. Additionally, they form the donor/acceptor/donor (D-π-A-
π-D) architectures [18]. Thus, they exhibit very high structural variabilities because a
large number of side groups that can be added to them, such as alkoxyphenyl [19],
phenyl thiophene [20], and oligo(thienylenevinylene) [21]. Therefore, BTD derivatives
are expected to be of significant use in solar cells. Their role in aligning the energy level
between the hole transport layer in perovskite solar cells have been studied, and it has
been reported that they influence the load transfer processes and consequently the
overall photovoltaic performance [22,23]. Likewise, in organic photovoltaic films, this
nucleus is an important building block for new sensitizing compounds that can
influence the optical and electronic properties and thereby the overall photovoltaic
performance [24,25]. In addition, when dye-sensitized solar cells contain BTD - a
strong electron-accepting group - in the porphyrinic ring, the location of their absorption
maxima changes remarkably (from 400 to 500 nm and from 650 to 730 nm), leading to
improved sunlight harvesting [26], short-circuit current density Jsc, open circuit voltage
2

Voc, and energy conversion efficiency
η [27,28]. Additionally, owing to their excellent
optical and electrochemical properties such as high fluorescence quantum yields, large
Stokes shifts, and intramolecular charge transfer (ICT) during photoexcitation as well as
suitable band intervals, BTD is used in the fabrication of OLEDs [29-32]. At the same
time, owing to their photophysical properties, BTD-based compounds have also been
studied as a fluorescent imaging probes [33], for instance in selective mitochondrial
staining [34], selective detection and quantification of double-stranded DNA (dsDNA)
[35], and determination of DNA concentration [36], and as fluorescent tags to disclose
the cellular dynamics and action mechanism of bioactive compounds [37] and as
cellular probes in bioimaging [38,39].
Herein, we describe the synthesis and photophysical, electrochemical, and
thermal characterization of the BTD core, which exhibits dual fluorescent emission in
the violet-blue and cyan green-yellow regions. In these molecules, the BTD core is
generally flanked by propargyl carbazole and/or propargyl diphenylamine, which can be
highly useful in optoelectronic devices, as side groups.
2. Experimental
2.1 Materials and methods
Propargyl bromide solution, carbazole, diphenylamine, 4,7-dibromobenzo[c]-
1,2,5-thiadiazole (1), bis(triphenylphosphine)palladium(II)dichloride (Pd(PPh3)2Cl2),
triphenylphosphine (PPh3), and copper iodide (CuI) were purchased from Sigma-
Aldrich. Silica Gel 60 F254 was employed for thin-layer chromatography (TLC) and
silica Gel 60 Å (70-230 mesh) was used for column chromatography (CC). The
spectroscopic characterization was performed by nuclear magnetic ressonance (NMR
Bruker Avance III) in CDCl3 for 1H and 13C NMR spectroscopies, at 400 and 100 MHz,
respectively. The chemical shifts (δ) were reported in parts per million (ppm), relative to
that of tetramethylsilane TMS (0.00 ppm). The coupling constants (J) were reported in
Hz. The FTIR spectra were acquired on Shimadzu IR Prestige-21, with a resolution of 4
cm-1, employing KBr pellets (600-4,000 cm-1). High-resolution mass spectra (HRMS)
were recorded on a Micromass Q-Tof spectrometer using electrospray ionization (ESI).
All the compounds were analyzed by thermogravimetric analysis (TGA) and differential
scanning calorimetry (DSC). TGA was conducted on a TG-50 analyzer (Shimadzu) at a
heating rate of 10°C∙min-1 in a nitrogen atmosphere. DSC was performed using DSC
3500 Sirius (Netzsch), at a heating rate of 10°C∙min-1 in a nitrogen atmosphere.
3

Ultraviolet-Visible (UV-Vis) absorption spectra were obtained on a Shimadzu UV-2450
spectrophotometer. Steady-state fluorescence spectra were obtained with a Shimadzu
RF-5301PC spectrofluorometer, with slits of 5.0 nm each, for the excitation and
emission. For the emission spectra, the wavelength of maximum absorption was
employed as the excitation radiation. Fluorescence quantum yield (QY) was determined
at 25°C using Coumarin 153 in ethanol as the QY standard [40]. UV-Vis diffuse
reflectance and absorption spectra in the solid state were measured with a Shimadzu
UV2450PC spectrophotometer using an ISR-2200 Integrating Sphere Attachment at
room temperature and using using BaSO4 (Wako Pure Chemical Industries, Ltd.) as the
baseline. Fluorescence spectra in the solid state were measured using a Shimadzu
RF5301 spectrofluorometer with a solid sample holder. For these experiments the
obtained materials were treated as powder. Cyclic voltammetry (CV) experiments were
performed on a PalmSens3 potentiostat/galvanostat (Palm Instruments BV). The
measurements were performed in a dichloromethane solution containing 0.01 M tetra-n-
butylammonium hexafluorophosphate (TBAPF6) as the supporting electrolyte. Before
each measurement, the solutions were purged with argon to remove dissolved oxygen.
CV was performed in a standard three-electrode electrochemical cell comprising a
glassy carbon, a platinum wire and Ag/Ag+ (0.01 M AgNO3 in acetonitrile) electrodes,
as the working, auxiliary, and reference electrodes, respectively. All the potential
measurements were calibrated (versus NHE) using a ferrocene/ferrocenium redox
couple. The electronic ground and excited state geometries, frontier molecular orbitals
(HOMO/LUMO), and vertical transitions were determined by density functional theory
and its time-dependent counterpart (DFT/TDDFT) methods using CAM-B3LYP and 6-
31G** basis sets in ORCA 4.0 [41,42] and Avogadro 1.2 software [43].
2.2 Synthesis
2.2.1 Synthesis of 9-(prop-2-yn-1-yl)-9H-carbazole (2)
Carbazole (2.0 g, 12 mmol) was added to a solution of KOH (1.34 g, 24 mmol)
and DMF (10 mL) and stirred at 0 °C. Thereafter, propargyl bromide (2.85 g, 24 mmol)
was slowly added, and the reaction mixture was stirred for 24 h at 25°C. After the
reaction had been completed, the crude mixture was adsorbed by silica gel and purified
by column chromatography using 2% ethyl acetate in hexane (v/v) as the eluent.
4

9-(prop-2-yn-1-yl)-9H-carbazole (2), white solid, yield 95%, mp 123-124°C. FTIR
1
(NaCl) cm-1: 3263, 3040, 2928, 2848, 2117, 1454. H NMR (CDCl3, 400 MHz) ppm:
8.15 (2H, d, J = 8.0 Hz), 7.73 (4H, m), 7.32 (2H, m), 5.06 (2H, d, J = 4.0 Hz), 2.29 (1H,
13
t, J = 4.0 Hz). C NMR (CDCl3, 100 MHz) ppm: 139.9, 125.9, 123.3, 120.4, 119.6,
108.9, 77.2, 72.2, and 32.3. HRMS (ESI) found: [M+H]+ 206.0983; molecular formula
C15H12N requires [M+H]+ 206.0970.
2.2.2 Synthesis of N-phenyl-N-(prop-2-yn-1-yl)aniline (4)
Diphenylamine (2.0 g, 12 mmol) was added to a solution of KOH (1.34 g, 24
mmol) in DMF (10 mL) with stirring at 0°C. Thereafter, propargyl bromide (2.85 g, 24
mmol) was slowly added, and the reaction mixture was stirred for 24 h at 25°C. After
the completion of the reaction, the crude mixture was adsorbed by silica gel and purified
by column chromatography using 2% ethyl acetate in hexane (v/v) as the eluent.
N-phenyl-N-(prop-2-yn-1-yl)aniline (4), yellow oil, yield 54%. FTIR (NaCl) cm-1: 3293,
1
3035, 2927, 2855, 2112, 1603. H NMR (CDCl3, 400 MHz) ppm: 7.37 (4H, m), 7.16
(3H, m), 7.08 (3H, m), 4.47 (2H, m), 2.29 (1H, m). 13C NMR (CDCl3, 100 MHz) ppm:
147.4, 129.3, 122.2, 121.3, 119.6, 79.9, 72.3, 42.1. HRMS (ESI) found: [M+H]+
208.1115; molecular formula C15H14N requires [M+H]+ 208.1126.
2.2.3 Synthesis of the BTD intermediate 6
Dichloromethane (20 mL) and triethylamine (5 mL) were added to a round-
bottom flask previously degassed with argon for 15 min. Then, 1 (0.250 g, 0.85 mmol),
Pd(PPh3)2Cl2 (0.03 g, 0.042 mmol), and CuI (3.8 mg, 0.02 mmol) were added with
stirring at 60 °C. Thereafter, 2 (0.087 g, 0.42 mmol) was added to the mixture, and the
reaction was maintained in an argon atmosphere for 5 h at 60°C. Next, the reaction
mixture was treated with 50 mL of a saturated solution of NH4Cl and extracted with
dichloromethane (3 x 50 mL). The organic layers were combined and dried employing
MgSO4 and concentrated in vacuum, and were then purified by column chromatography
using hexane/ethyl acetate (9:1) as the eluent.
4-(3-(9H-carbazol-9-yl)prop-1-yn-1-yl)-7-bromobenzo[c][1,2,5]thiadiazole (6), yellow
1
solid, yield 51%, mp 197-198°C. FTIR (NaCl) cm-1: 3049, 2922, 2845, 1596, 1475. H
5

NMR (CDCl3, 400 MHz) ppm: 8.14 (2H, d, J = 8.0 Hz), 7.73 (1H, d, J = 8.0 Hz), 7.64
(2H, d, J = 8.0 Hz), 7.54 (2H, m), 7.45 (1H, d, J = 8.0 Hz), 7.31 (2H, m), 5.44 (2H, s).
13C NMR (CDCl3, 100 MHz) ppm: 154.1, 152.9, 139.9, 133.6, 131.7, 126.0, 123.3,
120.5, 119.6, 115.5, 115.2, 108.9, 90.8, 79.2, 33.5. HRMS (ESI) found: [M+H]+
418.0001; molecular formula C21H13BrN3S requires [M+H]+ 418.0014.
2.2.4 Synthesis of BTD 3
Dichloromethane (30 mL) and triethylamine (5 mL) were added to a round-
bottom flask previously degassed with argon for 15 min. Then, 1 (0.1 g, 0.34 mmol),
Pd(PPh3)2Cl2 (0.016 g, 0.023 mmol), and CuI (0.002 g, 0.01 mmol) were added with
stirring at 60 °C. Next, 2 (0.139 g, 0.68 mmol) was added to the mixture and the
reaction was maintained in an argon atmosphere for 24 h at 60°C. Thereafter, the
reaction mixture was treated with 50 mL of a saturated solution of NH4Cl and extracted
with dichloromethane (3 x 50 mL). The organic layers were combined and dried
employing MgSO4 and concentrated in vacuum, and were then purified by column
chromatography using hexane/ethyl acetate (1:1) as the eluent.
BTD 3, yellow solid, yield 74%, mp 286-287 °C. FTIR (NaCl) cm-1: 3056, 2915, 2852,
1
1452. H NMR (CDCl3, 400 MHz) ppm: 8.16 (4H, d, J = 8.0 Hz), 7.78 (4H, d, J = 8.0
13
Hz), 7.63 (2H, s), 7.50 (4H, t, J = 8.0 Hz), 7.25 (4H, t, J = 8.0 Hz), 5.69 (4H, s). C
NMR (CDCl3, 100 MHz) ppm: 154.0, 140.1, 133.5, 126.4, 123.0, 120.7, 119.9, 116.2,
110.0, 93.0, 79.5, and 33.4. HRMS (ESI) found: [M+H]+ 543.1644; molecular formula
C36H23N4S requires [M+H]+ 543.1643.
2.2.5 Synthesis of BTD 5
Dichloromethane (30 mL) and triethylamine (5 mL) were added to a round-
bottom flask previously degassed with argon for 15 min. Then, 1 (0.1 g, 0.34 mmol),
Pd(PPh3)2Cl2 (0.016 g, 0.023 mmol), and CuI (0.002 g, 0.01 mmol) were added with
stirring, at 60 °C. Next, 4 (0.140 g, 0.68 mmol) was added to the mixture, and the
reaction was maintained in an argon atmosphere for 24 h at 60°C. Thereafter, the
reaction mixture was treated with 50 mL of a saturated solution of NH4Cl and extracted
with dichloromethane (3 x 50 mL). The organic layers were combined and dried
employing MgSO4 and concentrated in vacuum. They were then purified by column
chromatography using hexane/ethyl acetate (1:1) as the eluent.
6

BTD 5, brown solid, yield 58%, mp 145-146 °C. FTIR (NaCl) cm-1: 3046, 2922, 2848,
1591, 1485. 1H NMR (CDCl3, 400 MHz) ppm: 7.55 (2H, s), 7.34 (8H, m), 7.20 (8H, m),
13
4.80 (4H, s). C NMR (CDCl3, 100 MHz): 154.3, 147.5, 132.6, 129.3, 126.7, 122.3,
121.5, 116.8, 93.9, 80.2, 79.8, and 43.3. HRMS (ESI) found: [M+H]+ 547.1949;
molecular formula C36H27N4S requires [M+H]+ 547.1956.
2.2.6 Synthesis of BTD 7
Dichloromethane (30 mL) and triethylamine (5 mL) were added to a round-
bottom flask previously degassed with argon for 15 min. Thereafter, 6 (0.1 g, 0.23
mmol), Pd(PPh3)2Cl2 (0.016 g, 0.023 mmol), and CuI (0.002 g, 0.00001 mmol) were
added with stirring at 60 °C. Next, 4 (0.047 g, 0.23 mmol) was added to the mixture,
and the reaction was maintained in an argon atmosphere for 24 h, at 60°C. Thereafter,
the reaction mixture was treated with 50 mL of a saturated solution of NH4Cl and
extracted with dichloromethane (3 x 50 mL). The organic layers were combined and
dried employing MgSO4 and concentrated in vacuum. They were then purified by
column chromatography using hexane/ethyl acetate (9:1) as the eluent.
BTD 7, yellow solid, yield 40%, mp 155–156oC. FTIR (NaCl) cm-1: 3039, 2927, 2847,
1586, 1458. 1H NMR (CDCl3, 400 MHz) ppm: 8.14 (4H, d, J = 8.0 Hz), 7.63 (2H, d, J =
8.0 Hz), 7.54 (2H, m), 7.47 (2H, s), 7.33 (6H, m), 7.20 (4H, m), 7.05 (2H, m), 5.45 (2H,
13
s), 4.79 (2H, s). C NMR (CDCl3, 100 MHz) ppm: 154.3, 147.5, 139.9, 133.0, 132.6,
129.3, 126.0, 123.3, 122.3, 121.4, 120.4, 119.6, 117.2, 116.0, 108.9, 94.2, 91.2, 80.1,
79.7, 43.2, and 33.5. HRMS (ESI) found: [M+H]+ 545.1808; molecular formula
C36H25N4S requires [M+H]+ 545.1800.
3. Results and discussion
3.1 Synthesis
Terminal alkynes (2-4) were synthesized as described in the literature [44]. The
syntheses of the carbazole/diphenyl compounds (3, 5, and 7) were synthesized using the
BTD unit by the Sonogashira reaction, involving the coupling of 1 with 2 and 4
(Scheme 1). For the symmetrical compounds (3 and 5), 2 was utilized as the terminal
alkyne instead of 1. The reaction was conducted using CuI and Pd(PPh3)2Cl2 as the
catalysts and dichloromethane/Et3N was utilized as the solvent under reflux to yield
7

~60% of both compounds, after purification. For the synthesis of the asymmetric BTD
(7), 6, previously prepared by the monocoupling of 2 equiv. of 1, was synthesized by
the Sonogashira reaction using 1 equiv. of 2. The intermediate was previously purified
by CC to be utilized in the subsequent step. Thereafter, 7 was obtained by the reaction
of 6 and 4, under the same reaction conditions, with a 30% yield after column
chromatography purification [45, 46].
Scheme 1. Synthesis of carbazole/diphenyl BTD-based compounds 3, 5 and 7.
3.2 Photophysical characterization
UV-Vis absorption and fluorescence emission spectroscopies in a 10-6
M
solution were employed to investigate the photophysical properties of the synthesized
carbazole/diphenyl BTD-based fluorophores. The relevant data from these
investigations are presented in Table 1. Figure 1 shows the UV-Vis spectra of 3, 5, and
8

7, where the absorption maxima located between 372 and 380 nm were observed. The
changes in the solvent polarity afforded a solvatochromic shift of 6 nm, with any clear
dependence on the environment polarity, indicating an almost absent charge transfer in
the ground state.
Figure 1. UV-Vis absorption spectra in solution of carbazole/diphenyl BTDs (a) 3, (b)
5, and (c) 7 in different organic solvents [~10-6 M].
Additionally, the oscillator strengths (fe) and theoretical rate constants of the
emissions (ke0) were obtained by the Strickler-Berg relations (Eq. 1 and 2) [47]. In
addition, ke0 was used to determine the pure radiative lifetime (τ0), defined as 1/ke0 [48].
ꢀ ≈ 4.3ꢂ10ꢃꢄ ꢆꢇꢈ
̅
Eq. (1)
Eq. (2)
ꢅ
ꢁ
ꢉꢁꢊ ≈ 2.88ꢂ10ꢃꢄꢈꢋ
ꢆꢇꢈ̅
ꢅ
̅
ꢊ
Using Eq. (1), the values of fe (0.22-0.75) were determined, which indicated
highly probable electronic transitions. Further, the values of the molar absorptivity
coefficient (~104 M-1∙cm-1) obtained from the Beer–Lambert law and ke0 (~108 s-1)
indicated spin- and symmetry-allowed electronic transitions that could be related to
1π→π* transitions. The value of the comparable constant radiative lifetime (~10-9 s)
also indicated that the observed absorptions populated the same excited state. The
fluorescence emission spectra were acquired from the absorption maxima at the
excitation wavelengths. The emission spectra of different organic solvents are shown in
Figure 2, and the relevant data are summarized in Table 1.
9

Figure 2. Steady-state fluorescence emission spectra in solution of carbazole/diphenyl
BTDs (a) 3, (b) 5, and (c) 7 in different organic solvents [~10-6 M].
Despite the presence of the carbazole moiety in the BTD structures, no evidence
of its emission was observed at the working excitation wavelengths [49]. It was
generally observed that the studied compounds exhibited dual fluorescent emission,
with a blue-shifted band at approximately 419-470 nm. The red-shifted band at
approximately 511-571 nm, with a larger Stokes shift (∆λST between 136 and 194 nm),
indicated charge transfer in the excited state. The polarity of the solvent is vital for the
ratiometric behavior; increasing the solvent polarity tended to favor the blue band
intensity. The structural variation of the compounds did not exert any significant
influence on the ground-state behavior, as evaluated by the parameters indicated in
Table 1. Conversely, the blue-shifted band of the emission spectra increased from
carbazole to the asymmetric derivative, and QY was higher for the symmetrical
carbazole derivative because of its higher rigidity than that of the asymmetric
derivative.
10

Table 1. Photophysical data of the synthesized BTDs, where λabs and λem are the absorption and emission maxima, respectively (nm), ε is the
0
molar extinction coefficient (104 M-1·cm-1), fe is the calculated oscillator strength, ke is the calculated radiative rate constant (108 s-1), τ0 is the
calculated pure radiative lifetime (ns), ∆λST is the Stokes shift (nm/cm-1) and QY is the fluorescence quantum yield (%).
0
Compound
Solvent
1,4-Dioxane
fe
ke
QY
λabs
ε
τ0
λem
∆λST
λem
∆λST
374
376
375
372
378
377
380
380
374
379
376
377
375
374
379
2.39
1.40
1.24
2.01
2.17
2.51
1.76
2.35
2.39
2.63
3.44
3.03
2.72
4.06
3.80
0.42
0.22
0.24
0.38
0.43
0.54
0.38
0.50
0.30
0.57
0.66
0.58
0.55
0.75
0.74
3.02
1.57
1.72
2.77
2.99
3.79
2.60
3.44
2.13
3.99
4.64
4.06
3.92
5.35
5.15
3.31
6.37
5.80
3.61
3.34
2.64
3.85
2.91
4.69
2.51
2.16
2.46
2.55
1.87
1.94
421
427
430
419
462
427
435
435
425
470
427
442
440
450
453
47/2985
51/3177
55/3411
47/3015
84/4810
50/3106
55/3327
55/3327
51/3209
91/5109
51/3177
65/3901
65/3939
76/4516
74/4310
539
538
511
516
-
165/8185
162/8008
136/7097
144/7502
-
6.11
2.81
4.30
1.97
4.86
1.66
1.58
1.48
1.19
2.09
3.29
1.44
2.54
1.38
2.40
Dichloromethane
Methanol
3
Acetonitrile
Dimethylsulfoxide
1,4-Dioxane
571
536
-
194/9012
156/7659
-
Dichloromethane
Methanol
5
7
Acetonitrile
549
-
175/8523
-
Dimethylsulfoxide
1,4-Dioxane
570
560
550
-
194/9052
183/8668
175/8485
-
Dichloromethane
Methanol
Acetonitrile
Dimethylsulfoxide
-
-
11

To expand the photophysical characterization of the obtained BTDs, their
electronic properties were also investigated in the solid state based on their UV-Vis
spectra (DRUV), respective diffuse reflectances, and steady-state fluorescence
emission. Despite the comparable behavior observed in solution for all BTDs, 3
presented quite different photophysics in the ground state from those of 5 and 7 (Figure
3a). For 3, relatively low-intensity absorbance in the visible region (from near-infrared
up to the green region) and intense absorption at ~425 nm were observed. In contrast,
for 5 and 7, a strong absorption in the visible region was observed with a similar
maxima at ~425 nm. In all these cases, the absorption maxima redshifted with respect to
the values obtained in solution, indicating a strong interaction between these
compounds in the solid state. Similarly, 5 and 7 presented a quite similar behavior with
a significant decrease in the diffuse reflectance (DR) percentage in the near-infrared
region (900 nm) to a final DR of ~20% in the blue region (Figure S28). Compound 3
showed exceptional behavior, as despite the same final DR value, a drastic decrease was
observed for the DR at ~500 nm.
Using these ground state results, the excited state photophysics of the BTDs was
also investigated as presented in Figure 3b. All the studied compounds are fluorescent
in the solid state. These compounds presented a highly structured main fluorescence
emission with the maxima located at ~550 nm. It is worth mentioning that any shift on
the emission maxima was observed at different excitation wavelengths (Figure S29).
For all the studied compounds, the excitation spectra maxima was located at ~450 nm,
similar to the DRUV spectra (Figure S30). These results obtained in the solid state
suggest the occurrence of aggregation-induced enhanced emission (AIEE) mechanism,
as already observed for BTD-based fluorophores [17,50,51]. Additionally, despite the
expected nonplanar conformation of these compounds, owing to the methylene group
between the BTD core and the carbazole or diphenylamino substituents, quite different
intensities were observed. Thus, the observed intensities can be directly related to the
mobility of the substituents, where the diphenylamino moiety seems to favor
nonradiative decays to a greater extent than the carbazole moiety.
12

Figure 3. (a) UV-Vis absorption spectra (DRUV) and (b) steady-state fluorescence
emission spectra of BTDs in the solid state under excitation of 450 nm. Slits: 1.5nm/3.0
nm (Exc./Em.)
Photophysical investigation revealed that the studied BTDs were weakly
emissive when molecularly dissolved but became highly emissive in the aggregated
state. Taking advantage of this phenomenon, the AIEE properties of the BTDs were
investigated. Changes in their fluorescence intensity were studied as a function of the
water fraction in a dimethylsulfoxide (DMSO)/water mixtures with DMSO being the
good solvent and water acting as a nonsolvent. Figure 4a presents the fluorescence
emission spectra of 3 in different DMSO/water mixtures at an excitation wavelength of
450 nm. BTD 3 showed very weak emission in pure DMSO. However, when the water
content was ~5%, the intensity began to increase, reaching a plateau at ~20% water
content with a significant enhancement compared to the observed in pure DMSO
solution. BTD 5 and 7 presented similar results (Figures S31-S32). The plot of (I/I0)
against water fraction, where I0 and I are fluorescence intensities in DMSO and
DMSO/water mixtures, respectively, allows a better visualization of this phenomenon
(Figure 4b). For both 3 and 5, the fluorescence intensity increased significantly when
the water content reached the critical point for the aggregation to occur and a maxima
was reached when the water content was ~20%. In contrast, 7 showed weaker
fluorescence intensity than 3 and 5 under the same experimental conditions, probably
owing to the weak fluorescence signal even in its solid state. However, similar BTD
13

compounds presented similar behavior and the AIEE phenomenon can not be
overlooked [17].
Figure 4. (a) Steady-state fluorescence emission spectra of BTD 3 (λexc 450 nm) and (b)
I/I0 ratio, where I0 is the fluorescence intensity in DMSO solution of all studied BTDs in
DMSO/water mixtures with different water fraction % (v/v).
3.3 Theoretical calculations
The structures of the chromophores were optimized by DFT in vacuum using the
functional and basis set CAM-B3LYP/6-31G** (Figure 5). In general, predictions of the
frontier molecular orbitals indicated a charge transfer from the donor units to the
benzothiadiazole unit, as observed with the carbazole/diphenyl benzothiadiazole-based
fluorophores (Figure 6). Additional data from this investigation can be found in the
Supplementary Material. The charge transfer was confirmed from the optimization of
the excited state structure (TD-DFT), using which the dipole moment variations in each
system were determined: ∆µ3 = 25, ∆µ5 = 21 and ∆µ7 = 23. Using the predicted
electronic transitions, the charge transfer was identified as vertical excitations of λabs
=
340 nm (f = 0.44) and 270 nm (f = 0.05), λabs = 343 nm (f = 0.38) and 260 nm (f = 0.15),
and λabs = 348 nm (f = 0.24) and 260 nm (f = 0.17) for 3, 5, and 7, respectively. The
identified charge transfer matched with the experimental values.
14

Figure 5. Optimized geometry at the ground state of carbazole/diphenyl
benzothiadiazole-based fluorophores 3, 5, and 7. DFT and TD-DFT calculations were
performed at the CAM-B3LYP/6-31G** level of theory.
Figure 6. HOMO and LUMO orbitals of carbazole/diphenyl benzothiadiazole-based
fluorophores 3, 5, and 7. DFT and TD-DFT calculations were performed at the CAM-
B3LYP/6-31G** level of theory.
15

3.4 Electrochemical and thermal characterization
The electrochemical properties of a D-π-A-π-D-type conjugated system afford
an in-depth understanding of the effects of different molecular architectures on the
functions of their electronic effects due to each group in the molecule. To evaluate the
influence of the donor-acceptor balance on the redox behavior of these BTDs, CV
investigations were conducted, and the respective ionization potentials (IP) and electron
affinities (EA) were obtained. These results are presented in Figure 7, and the relevant
data are summarized in Table 2.
Figure 7. (a) Cyclic voltammograms of the synthesized BTDs obtained in 0.01 M
Bu4NPF6 in CH2Cl2 at a scan rate of 100 mV∙s-1 and (b) the respective absolute values
of electrochemical IP (HOMO) and EA (LUMO).
The arylamine, carbazole, and diphenylamine units are expected to exert more
noticeable effects on the anodic region because of their electron-donating nature,
thereby modulating the HOMO energy [52]. At more positive potentials, an irreversible
oxidation process was observed originating from the formation of a radical cation
[52,53]. Contrarily, the BTD unit, because of its electron-withdrawing nature, is
expected to exert a noticeable effect on the cathodic region, thus modulating the LUMO
energy [53,54]. At increased negative potentials, a quasi-reversible reduction process
was observed, arising from the reduction of the BTD unit [52,55]. Notably, for the
16

symmetric carbazole derivative 3, the onset reduction potential was less negative and its
onset oxidation potential was less positive, compared to that of their parent compounds.
These compounds began to oxidaze in the potential range of 0.74-1.03 V (vs. Ag/Ag+).
The obtained data can be applied to the following empirical relationship to estimate
their HOMO energy levels [31]:
IP (HOMO) = −(Eox + 4.44) eV,
(3)
where Eox (corrected to NHE) is the onset oxidation potential. Moreover, their onset
reductions occurred from –1.35 to –1.40 V (vs. Ag/Ag+) and were employed to estimate
their corresponding LUMO energy levels, using the following empirical relationship
[55]:
EA (LUMO) = −(Ered + 4.44) eV,
(4)
where Ered (corrected to NHE) is the onset oxidation potential. The electrochemical band
gaps (ꢌꢍꢁꢎꢐꢁꢏ) were calculated using the following relationship:
ꢁꢐꢁ
ꢌ
= IP – EA
(5)
ꢍꢎꢏ
Table 2. Electrochemical properties of the synthesized BTDs and their molecular
orbital energies. Eox is the onset potential of oxidation, Ered, is the onset potential of
reduction, IP (HOMO) is the ionization potential, EA (LUMO) is the electron affinity,
and ꢌꢍꢑꢎꢏꢏꢒ are the electrochemical and optical band gaps, respectively, and λonset is
ꢁꢐꢁ
ꢌ
ꢍꢎꢏ
the absorption onset wavelength.
BTDs
5
Parameters
3
7
Eox (V)a
Ered (V)a
IP (HOMO) (eV)b
1.18
0.91
0.91
–1.20
–5.62
–3.24
–1.25
–5.35
–3.19
–1.26
–5.35
–3.18
EA (LUMO) (eV)c
ꢁꢐꢁ
ꢌ
(eV)d
2.38
2.16
437.2
2.84
2.17
ꢍꢎꢏ
λonset
421.6
425.8
ꢑꢏꢒ
ꢌ
(eV)e
2.94
2.91
ꢍꢎꢏ
b
c
e
aversus NHE, IP = –(Eox+ 4.44) eV, EA= –(Ered + 4.44) eV, ꢌꢍꢁꢎꢐꢁꢏ = IP – EA, optical
ꢑꢏꢒ
ꢍꢎꢏ
bandgap calculated for the low energetic edge of the absorption spectrum (ꢌ
=
1240/λonset).
17

The thermal stabilities of the synthesized BTDs were analyzed by TGA and
DSC (Figures S33-S34). The TGA thermograms showed that the decomposition
temperatures of the studied BTDs were between 73 and 273°C and the initial
decomposition temperatures (Tin) at 5% of weight loss were approximately 330°C (3),
200°C (5), and 110°C (7). From the DTG curves, it could be observed that 3 showed
three main peaks with maximum degradation temperatures (Td) at approximately 290°C,
370°C and 830°C. Compounds 5 and 7 each presented two main peaks with Td values of
approximately 240°C and 350°C and 150°C and 320°C, respectively. The char yield
(%) at 950°C was approximately 40% for 3 and 5 and 30% for 7, showing that
complete degradation had not occurred. Finally, 3 and 5 exhibited good thermal
stabilities up to 200°C, which is useful for their application in photovoltaic devices
[56,57]. The DSC results showed that the synthesized compounds can form amorphous
structures. The glass transition temperature (Tg) for 3 was approximately 70°C in the
first heating cycle, and approximately 60°C for 5 during the first and second heating
cycles. The higher Tg of 3 is probably due to the presence of aromatic rings that make
the BTD structure more rigid. However, for 7, the first and second heating cycles did
not demonstrate any transitions.
4. Conclusions
Syntheses of three new BTD-based extended D-π-A-π-D compounds obtained
via the Sonogashira reaction (in moderate yields) is reported herein. The derivatives
exhibited absorption maxima between 372 and 380 nm, related to the electronic
1
transitions with a π→π* character owing to the near absence of the solvatochromic
effect. The derivatives showed dual fluorescent emission, represented by a blue-shifted
band at approximately 419-470 nm and a red-shifted band at approximately 511-571 nm
with QY < 6%. The increased ∆λST between 7502 and 9052 cm-1 indicated charge
transfer in the excited state. The theoretical calculations were performed at the CAM-
B3LYP/6-31G** level of theory. The obtained results corroborated with the observed
charge transfer characteristics of these compounds. A highly remarkable and structured
fluorescence emission in the solid state was observed, which was related to the AIEE
phenomeno. This observation was in correspondence with the fluorescence emission
spectra observed using different DMSO/water mixtures. Using CV investigations of 5-
7, the electrochemical bandgap (2.16-2.38 eV) was estimated from the redox potentials.
18

The results demonstrated that the modification of the electron-donating unit can
significantly change the values of HOMO, LUMO, and the bandgap of the molecules.
The TGA results indicated that 3 presented greater thermal stability than 5 and 7.
Compounds 3 and 5 formed amorphous structures, as demonstrated by glass transition
temperatures obtained by DSC.
5. Acknowledgments
The authors would like to thank the National Council for Scientific and
Technological Development, CNPq, Coordenação de Aperfeiçoamento de Pessoal de
Nível Superior (CAPES) - Finance Code 001, and CELESC (P&D 05697-1718/2018
and 5697-0717/2017) for the financial support.
Funding: This work was supported by the National Council for Scientific and
Technological Development CNPq, Coordenação de Aperfeiçoamento de Pessoal de
Nível Superior - Brasil (CAPES) - Finance Code 001 and CELESC (P&D 05697-
1718/2018 and 5697-0717/2017) for financial support.
References
[1] Neto BAD, Lapis AAM, Júnior ENS, Dupont J. 2,1,3-Benzothiadiazole and
derivatives: synthesis, properties, reactions, and applications in light technology of
small molecules. Eur J Org Chem 2013;228-255.
[2] Wu J, Lai G, Li Z, Lu Y, Leng T, Shen Y, Wang C. Novel 2,1,3-benzothiadiazole
derivatives used as selective fluorescent and colorimetric sensors for fluoride ion. Dye
Pigm 2016;124:268-276.
[3] Mikroyannidis JA, Stylianakis MM, Suresh P, Balraju P, Sharma GD. Low band gap
vinylene compounds with triphenylamine and benzothiadiazole segments for use in
photovoltaic cells. Org Electron 2009;10:1320-1333.
[4] 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.
[5] Hofle S, Zhang M, Dlugosch J, Kuhn M, Hamburger M, Colsmann A.
Thermocleavable poly(fluorene-benzothiadiazole) to enable solution deposition of
multi-layer organic light emitting diodes. Org Electron 2017;42:355-360.
19

[6] Echeverri M, Ruiz C, Gámez VS, Alonso NM, Gutierrez PE, Serrano JL. Stimuli-
responsive benzothiadiazole derivative as a dopant for rewritable polymer blends. ACS
Appl Mater Interfaces 2020;12:10929-10937.
[7] Kacimi R, Abram T, Bejjit L, New organic materiel based on benzothiadiazole for
photovoltaic application solar cells. Mater Today Proc 2019;13:1188-1196.
[8] Park MJ, Lee JH, Park JH, Lee SK, Lee JI, Chu HY. Synthesis and
electroluminescence of new polyfluorene copolymers with phenothiazine derivative.
Their application in white-light-emitting diodes. Macromolecules 2008;41:3063-3070.
[9] Jiang N, Yang HN, Man JX, Determination of emitting dipole orientation in organic
light emitting diodes. Org Electron 2020;78:105611.
[10] Majumdar D, Chakraborti R, Srivastava A. Indoor air quality in offices and
residences in urban areas of India-Mumbai and Kolkata. Res J Chem Environ
2012;16:74-78.
[11] Azrain MM. Effect of high thermal stress on the organic light emitting diodes
(OLEDs) performances. Synth Met 2019;247:191-201.
[12] Hou J, Park MH, Zhang S, Yao Y, Chen LM, Li JH. Bandgap and molecular
energy level control of conjugated polymer photovoltaic materials based on benzo[1,2-
b:4,5-b’] dithiophene. Macromolecules 2008;41:6012-6018.
[13] 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 Pigm 2019;166:217-225.
[14] Ricciardi L, La Deda M, Ionescu A, Godbert N, Aiello I, Ghedini M, Fusè M,
Rimoldi I, Cesarotti E. Luminescent chiral ionic Ir(III) complexes: Synthesis and
photophysical properties. J Lumin 2016;170:812-819.
[15] Duan C, Furlan A, Van Franeker JJ, Willems REM, Wienk MM, Janssen RAJ.
Wide-bandgap benzodithiophene-benzothiadiazole copolymers for highly efficient
multijunction polymer solar cells. Adv Mater 2015;27:4461-4468.
[16] 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.
[17] Pazini A, Maqueira L, Santos FS, Barreto ARJ, Carvalho RS, Valente FM, Back D,
Aucélio RQ, Cremona M, Rodembusch FS, Limberger J. Designing highly luminescent
20

aryloxy-benzothiadiazole derivatives with aggregation-induced enhanced emission. Dye
Pigm 2020;178:1083771.
[18] Liu Y, Lai H, Zhong H. New low bandgap molecules based on ethylene-separated
benzothiadiazoles: Synthesis and bandgap comparison. Tetrahedron Lett 2010;51:4462-
4465.
[19] Crivillers N, Favaretto L, Zanelli A, Manet I, Treier M, Morandi V. Self assembly
and electrical properties of a novel heptameric thiophenebenzothiadiazole based
architectures. Chem Commun 2012;48:12162-12164.
[20] Li XZ, Anhua Liu AH, Xun SD, Qiao WQ, Wan XH, Wang ZY. Synthesis and
characterization of near-infrared absorbing and fluorescent liquid-crystal chromophores.
Org Lett 2008;10:3785-3787.
[21] Wang JL, Xiao Q, Pei J. Benzothiadiazole-based D-π-A-π-D organic dyes with
tunable band gap: synthesis and photophysical properties. Org Lett 2010;12:4164-4167.
[22] Choi H, Ko HM, Ko J. Stable and efficient star-shaped hole transporting materials
with EDOT moiety as side arm for perovskite solar cells. Dye Pigm 2016;126:179-185.
[23] Zhou X, Kong F, Sun Y, Huang Y, Zhang X, Ghadari R. Dopant-free
benzothiadiazole bridged hole transport materials for highly stable and efficient
perovskite solar cells. Dye Pigm 2020;173:107954.
[24] Castro E, Cabrera EA, Deemer E, Echegoyen L. Low-energy-gap organic based
acceptor-donor-acceptor π-conjugated small molecules for bulk-heterojunction organic
solar cells. Eur J Org Chem 2015:4629-4634.
[25] Du J, Biewer MC, Stefan MC, Benzothiadiazole building units in solution-
processable small molecules for organic photovoltaics. J Mater Chem A 2016;4:15771-
15787.
[26] Kang SH, Jung SY, Kim YW, Eom YK, Kim HK. Exploratory synthesis and
photovoltaic performance comparison of D–π–A structured Zn-porphyrins for dye-
sensitized solar cells. Dye Pigm 2018; 149:341-347.
[27] Jie J, Xu Q, Yang G, Feng Y, Zhang B. Porphyrin sensitizers involving a fluorine-
substituted benzothiadiazole as auxiliary acceptor and thiophene as π bridge for use in dye-
sensitized solar cells (DSSCs). Dye Pigm 2020;174:107984.
[28] Tang Y, Wang Y, Song H, Liu Q, Li X, Cai Y, Xie Y. Solar cells sensitized with porphyrin
dyes with a carbazole donor: The effects of an auxiliary benzothiadiazole acceptor and bulky
substituents on the donor. Dye Pigm 2019;171:107776.
21

[29] Wang Z, Peng Z, Huang K, Lu P, Wang Y. Butterfly-shaped π-extended
benzothiadiazoles as promising emitting materials for White OLEDs. J Mater Chem C
2019;7:6706-6713.
[30] Pazini A, Maqueira L, Avila HC, Valente FM, Aderne RE, Back D, Aucélio RQ,
Cremona M, Limberger J. Phenoxy-benzothiadiazole dyes: Synthesis, photophysical
properties and preliminary application in OLEDs. Tetrahedron Lett 2018;59:2994-2999.
[31] Sam FLM, Razali MA, Jayawardena KDGI, Mills CA, Rozanski LJ, Beliatis MJ,
Silva SRP. Silver grid transparent conducting electrodes for organic light emitting
diodes. Org Electron 2014;153:3492-3500.
[32] Eroglu D, Ergun EGC, Onal AM. Cross-exchange of donor units in donor-
acceptor-donor type conjugated molecules: Effect of symmetrical and unsymmetrical
linkage on the electrochemical and optical properties. Tetrahedron 2020;76:131164.
[33] Neto BAD, Carvalho PHPR, Correa JR. Benzothiadiazole derivatives as
fluorescence imaging probes: beyond classical scaffolds. Acc Chem Res 2015;48:1560-
1569.
[34] Neto BAD, Correa JR, Silva RG. Selective mitochondrial staining with small
fluorescent probes: importance, design, synthesis, challenges and trends for new
markers. RSC Adv 2013;3:5291-5301.
[35] Neto BAD, Lapis AAM, Mancilha FS, Vasconcelos IB, Thum C, Basso LA,
Santos DS, Dupont J. New sensitive fluorophores for selective DNA detection. Org Lett
2007;9:4001-4004.
[36] Chi CY, Mikhailovsky A, Bazan GC. Design of cationic conjugated
polyelectrolytes for DNA concentration determination. J Am Chem Soc
2007;129:11134-11145.
[37] Crivat G, Taraska JW. Imaging proteins inside cells with fluorescent tags. Trends
Biotechnol 2012;30:8-16.
[38] Cruz EHG, Carvalho P, Correa JR, Silva DAC, Diogo EBT, Souza JD, Cavalcanti
BC, Pessoa C, Oliveira HCB, Guido BC, Silva DA, Neto BAD, Silva EN. Design,
synthesis and application of fluorescent 2,1,3-benzothiadiazole-triazole-linked
biologically active lapachone derivatives. New J Chem 2014;38:2569-2580.
[39] Glatz JFC, Luiken JJFP, Bonen A. Membrane fatty acid transporters as regulators
of lipid metabolism: implications for metabolic disease. Physiol Rev 2010;90:367-417.
22

[40] Würth C, Grabolle M, Pauli J, Spieles M, Resch-Genger U. Relative and absolute
determination of fluorescence quantum yields of transparent samples. Nat Protoc
2013;8:1535-1550.
[41] Neese F. The ORCA program system. WIRES Comput Mol Sci 2012;2:73–8.
[42] Neese F. Software update: the ORCA program system, version 4.0. WIRES
Comput Mol Sci 2018;8:e1327.
[43] Hanwell MD, Curtis DE, Lonie DC, Vandermeersch T, Zurek E, Hutchison GR,
Avogadro: an advanced semantic chemical editor, visualization, and analysis platform.
J. Cheminformatics 2012;4:17.
[44] Iqbal S, Khan MA, Javaid K, Sadiq R, Rehman SF, Choudhary MI, Basha FZ. New
carbazole linked 1,2,3-triazoles as highly potent non-sugar α-glucosidase inhibitors.
Bioorg Chem 2017;74:72-81.
[45] Frizon TEA, Duarte RC, Westrup JL, Perez JM, Menosso G, Duarte LGTA,
Germino JC, Faleiros MM, Atvars TDZ, Zapp E, Rodembusch FS, Dal-Bó AG.
Synthesis, electrochemical, thermal and photophysical characterization of quinoxaline-
based π-extended electroluminescent heterocycles. Dyes Pigm 2018;157:218-229.
[46] Westrup JL, Oenning LW, Paula MMS, Duarte RC, Rodembusch FS, Frizon TEA,
da Silva L, Dal-Bó AG. New photoactive D-π-A-π-D benzothiadiazole derivative:
Synthesis, thermal and photophysical properties. Dyes Pigm 2016;126:209-217.
[47] Strickler SJ, Berg RA. Relationship between absorption intensity and fluorescence
lifetime of molecules. J Chem Phys 1962;37:814-822.
[48] Turro NJ, Scaiano JC, Ramamurthy V. Principles of Molecular Photochemistry:
An Introduction, University Science Book, 1st ed., 2008.
[49] Zhang L, Zhou J, Zhang L. Synthesis and fluorescent properties of carbazole-
substituted hydroxyethylcelluloses. Macromol Chem Phys 2012;213:57-63.
[50] Chen S, Chen N, Yan YL, Liu T, Yu Y, Li Y, Liu H, Zhao YS, Li Y. Controlling
growth of molecular crystal aggregates for efficient optical waveguides. Chem Commun
2012;48:9011-9013.
[51] Chen S, Qin Z, Liu T, Wu X, Li Y, Liu H, Song Y, Li Y. Aggregation-induced
emission on benzothiadiazole dyads with large third-order optical nonlinearity. Phys
Chem Chem Phys 2013;15:12660-12666.
[52] Kurowska A, Zassowski P, Kostyuchenko AS, Zheleznova TY, Andryukhova KV,
Fisyuk AS, Pron A, Domagala W. Effect of donor to acceptor ratio on electrochemical
23

and spectroscopic properties of oligoalkylthiophene 1,3,4-oxadiazole derivatives. Phys
Chem Chem Phys 2017;19:30261-30276.
[53] Sylvianti N, Kim YH, Marsya MA, Kim DG, Kim JH. A-π-D-π-A type oligomer
based on carbazole and benzothiadiazole for organic solar cells. Mol Cryst Liq Cryst
2017;655:166-172.
[54] Ledwon P, Zassowski P, Jarosz T, Lapkowski M, Wagner P, Cherpak V, Stakhira
P. A novel donor-acceptor carbazole and benzothiadiazole material for deep red and
infrared emitting applications. J Mater Chem C 2016;4:2219-2227.
[55] DaSilveira NBA, Lopes ASA, Ebeling G, Gonçalves RS, Costa VEU, Quina FH,
Dupont J. Photophysical and electrochemical properties of π-extended molecular 2,1,3-
benzothiadiazoles. Tetrahedron 2005;61:10975-10982.
[56] Arrechea S, Clifford JN, Pellejà L, Aljarilla A, de la Cruz P, Palomares E, Langa F.
Charge recombination losses in thiophene-substituted porphyrin dye-sensitized solar
cells. Dye Pigm 2016;126:147-153.
[57] Vaghasiya JV, Sonigara KK, Beuvier T, Gibaud A, Soni SS. Iodine induced 1-D
lamellar self assembly in organic ionic crystals for solid state dye sensitized solar cells.
Nanoscale 2017;9:15949-15957.
24

Highlights
- Extended D-π-A-π-D symmetric and asymmetric BTDs were synthesized via
the Sonogashira reaction.
- Dual fluorescent emission with a large Stokes shift (144-194 nm) probably
related to a charge transfer mechanism in the excited state.
- Cyclic voltammetry showed that the modification of the electron donor unit
significantly changes the values of HOMO, LUMO and band gap of the
molecules.
- Thermogravimetric results showed relative low thermal stability indicated by
low degradation temperature.
- Some of the compounds exhibited polymorphism like organic glass molecular
materials.
1

Declaration of interests
¢ The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests: