Synthesis and mesomorphic behavior of novel (bisthiophene)benzene carbazole nematic liquid crystals

Article abstract of DOI:10.1080/15421406.2021.1895960

Two structural isomers of highly conjugated (bisthiophene)benzene carbazoles were designed and synthesized to study the effect of the substitution pattern on their liquid crystalline behavior, transition temperatures, energy levels, and band gaps. Unusual

Full text of DOI:10.1080/15421406.2021.1895960

Molecular Crystals and Liquid Crystals
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/gmcl20
Synthesis and mesomorphic behavior of novel
(bisthiophene)benzene carbazole nematic liquid
crystals
Guang Hu, Stuart P. Kitney, Yanfang Liu & Kailong Zhang
To cite this article: Guang Hu, Stuart P. Kitney, Yanfang Liu & Kailong Zhang (2021): Synthesis
and mesomorphic behavior of novel (bisthiophene)benzene carbazole nematic liquid crystals,
Molecular Crystals and Liquid Crystals, DOI: 10.1080/15421406.2021.1895960
To link to this article: https://doi.org/10.1080/15421406.2021.1895960
Published online: 28 Jun 2021.
Submit your article to this journal
Article views: 19
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=gmcl20

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
https://doi.org/10.1080/15421406.2021.1895960
Synthesis and mesomorphic behavior of novel
(
bisthiophene)benzene carbazole nematic liquid crystals
a,b
c
a
a
Guang Hu , Stuart P. Kitney , Yanfang Liu , and Kailong Zhang
a
Key Laboratory for Palygorskite Science and Applied Technology of Jiangsu Province, National & Local
Joint Engineering Research Center for Mineral Salt Deep Utilization, Faculty of Chemical Engineering,
b
Huaiyin Institute of Technology, Huaian, Jiangsu, P. R. China; Department of Chemistry, Faculty of
c
Science and Engineering, University of Hull, Cottingham Road, Kingston Upon Hull, UK; Polar OLED,
University of Hull, Cottingham Road, Kingston Upon Hull, UK
ABSTRACT
KEYWORDS
bisthiophene)benzene car-
bazole; 3D molecular
configuration; nematic
liquid crystalline; Suzuki
aryl-aryl cross-
(
Two structural isomers of highly conjugated (bisthiophene)benzene
carbazoles were designed and synthesized to study the effect of the
substitution pattern on their liquid crystalline behavior, transition
temperatures, energy levels, and band gaps. Unusually, only the iso-
mer A with shorter terminal methyl chains exhibits a liquid crystal-
line phase, while the isomer B with longer octyl chains does not. It is
because longer terminal octyl chains of isomer B strengthen not
only the small angle between symmetrical sides of the aromatic
backbone, but also the angle between the terminal alkyl chains and
the aromatic backbone, thereby leading to a lower length-to-
breadth ratio.
coupling reaction
1. Introduction
Many nematic and smectic molecules for liquid crystal displays (LCDs) are bi-phenyl or
tri-phenyl compounds, e.g., homologues of 5CB [1–3]. However, liquid crystalline
CONTACT Guang Hu
guanghu2019@hyit.edu.cn
Key Laboratory for Palygorskite Science and Applied Technology
of Jiangsu Province, National & Local Joint Engineering Research Center for Mineral Salt Deep Utilization, Faculty of
Chemical Engineering, Huaiyin Institute of Technology, Huaian, Jiangsu, 223003, P. R. China; Department of Chemistry,
Faculty of Science and Engineering, University of Hull, Cottingham Road, Kingston Upon Hull, HU6 7RX, UK.
ß 2021 Taylor & Francis Group, LLC

2
G. HU ET AL.
materials with higher degree of aromatic conjugation have been proposed in recent
years as novel organic semiconductors in plastic electronics [4–16]. Particularly, the
least ordered nematic liquid crystalline materials with intrinsically low viscosity are pre-
ferred to form high-quality thin layers or films with a low concentration of charge traps
in opto-electronic devices [17, 18].
Highly conjugated, fused, aromatic carbazoles have attracted much attention to con-
struct organic semiconductor compounds due to strong luminescence, reversible oxida-
tion processes, good hole-transporting capability, high chemical/environmental stability,
and ease of functionalization [8]. Furthermore, the design of alkyl chains attached to
carbazole moieties in lateral or terminal positions could also improve material solubility,
lessen molecular aggregation, and adjust transition temperatures. The hetero-atoms,
such as N, S, or O, in aromatic backbones to construct organic semiconductors have
also been of great interest in materials chemistry due to the improved opto-electronic
properties [19–23]. Therefore, in this work, novel alkyl-substituted (bisthiophene)ben-
zene carbazole liquid crystals were designed and synthesized to study their meso-
morphic behavior, transition temperatures, and physical properties. The influence of the
length of alkyl chains in the symmetrical terminal positions of carbazoles units on the
exhibition of liquid crystalline mesophases was also investigated and discussed in
this paper.
2. Experimental
2.1. Materials and methods
All commercially available starting materials and reaction intermediates, reagents, and
solvents were obtained from British Aldrich, Strem Chem. Inc., Acros, or Lancaster
1
13
Synthesis and were used as supplied, unless otherwise stated. H and C NMR spectra
were recorded using a Japanese JEOL Lambda 400 spectrometer with an internal stand-
ard of tetramethylsilane (TMS). Infrared (IR) spectra were recorded using an American
PerkinElmer Paragon 1000 Fourier Transform-Infrared (FT-IR) spectrometer. Mass
spectra were performed using American Quadrupole MS PerkinElmer gas chromatog-
raphy/mass spectrometer (GC/MS) or Maldi-MS Bruker 384 spot anchorchip. The melt-
ing point and transition temperatures for each final compound were measured using
polarizing optical microscopy (POM), with a Mettler FP-5 hot-stage and an American
Olympus BH2 polarizing microscope. UV-Visible absorbance spectra were measured
using a American Thermo Scientific Evolution 220 UV-Visible Spectrometer. The ion-
ization potential (IP) of the compounds was measured electrochemically by cyclic vol-
tammetry using a computer-controlled scanning potentiostat (British Solartron 1285),
which functions as wave generator, potentiostat, and current-to-voltage converter. The
Corrware and Corrview software packages were used to control and record the cyclic
voltammetry experiments, respectively. The electron affinity (EA) was estimated by sub-
traction of the optical band edge (Eg), taken as the energy of the onset of absorption of
the compound from the IP. Although this approximation does not include a correction
for the exciton binding energy, the values obtained agree within ± 0.05 eV with those
measured electrochemically in our laboratory for other classes of reactive mesogen [9].

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
3
2.2. Material synthesis
2.2.1. 1,4-Bis-(thien-2-yl)benzene (3)
A mixture of Pd(PPh3)4 (0.60 g, 0.52 mmol), 1,4-dibromobenzene (1) (6.00 g,
2
1
5.43 mmol), 2-thienylboronic acid (2)(10.00 g, 76.29 mmol), K CO3 (14.05 g,
2
3
3
01.72 mmol), H O (50 cm ), and DME (100 cm ) was heated at reflux overnight. The
2
3
cooled reaction mixture was poured into H O (150 cm ) and the crude product isolated
2
by filtration under reduced pressure. The crude product was stirred with methanol for
3
h, and the residual solid isolated by filtration under reduced pressure to affords the
desired product as a pale-yellow solid (5.99 g, 97%).
o
Melting Point/ C: 208 (Lit. 204-206) [24].
1
H NMR (CDCl ) d : 7.63 (4H, d, J ¼ 1.0 Hz), 7.35 (2H, dd, J ¼ 7.2 & 1.0 Hz), 7.31
3
H
(
2H, dd, J ¼ 5.2 & 1.0 Hz), 7.11 (2H, dd, J ¼ 4.0 & 1.6 Hz).
þ
MS m/z (EI): 244, 243, 242 (M , M100).
2
.2.2. 1,4-Bis-(5-Bromothiophen-2-yl)benzene (4)
N-bromosuccinimide (NBS) (0.84 g, 4.72 mmol) was added in a small portion into a
3
solution of 1,4-bis-(thien-2-yl)benzene(3) (0.54 g, 2.28 mmol) in DMF (20 cm ) in the
dark. The resultant mixture was stirred overnight at room temperature. The reaction
3
mixture was diluted with ethanol (50 cm ) and stirred for 1 h. A pale-yellow precipitate
3
was filtered off, washed with ethanol (3 ꢀ 50 cm ), and dried under reduced pressure to
give the desired product (0.81 g, 94%).
o
Melting Point/ C: 255(Lit. 251-252) [24].
1
H NMR (CDCl ) d : 7.51 (4H, d, J ¼ 1.0 Hz), 7.08 (2H, d, J ¼ 4.0 Hz), 7.04 (2H,
3
H
d, J ¼ 4.0 Hz).
þ
MS m/z (EI): 402, 401, 400(M ).
2
.2.3. 1,4-Bis-[5-(7-Methoxy-9-octyl-carbazol-2-yl)thiophen-2-yl]benzene (A)
A
mixture of 1,4-bis-(5-bromothiophen-2-yl)benzene (4) (0.20 g, 0.50 mmol),
Pd(OAc) (0.01 g, 0.045 mmol), K CO (0.42 g, 3.00 mmol), (7-methoxy-9-octyl-carbzole-
2
2
3
3
3
2
-yl)boronic acid (5) (0.53 g, 1.50 mmol), and H O (2 cm ) in DME (20 cm ) was heated
at reflux overnight. Then, the cooled reaction mixture was washed with water (100 cm )
2
3
3
and extracted with DCM (3 ꢀ 100 cm ). The combined organic layers were washed with
3
water (2 ꢀ 100 cm ), dried (MgSO ), filtered, and then concentrated down under
4
reduced pressure. The residue was purified using column chromatography [silica, DCM/
hexane 5:10] to afford the desired product as a yellow solid (0.32 g, 76%).
o
Melting Point/ C: Cr 263 N 266 I.
1
H NMR (CDCl ) d : 7.99 (2H, d, J ¼ 8.0 Hz), 7.96 (2H, d, J ¼ 8.8 Hz), 7.69 (4H, d,
3
H
J ¼ 0.8 Hz), 7.57 (2H, d, J ¼ 0.8 Hz), 7.52 (2H, dd, J ¼ 8.0 & 1.6 Hz), 7.39 (2H, d,

4
G. HU ET AL.
J ¼ 4.0 Hz), 7.38 (2H, d, J ¼ 3.6 Hz), 6.86 (4H, dd, J ¼ 6.8 & 2.0 Hz), 4.30 (4H, t,
J ¼ 7.6 Hz), 3.95 (6H, s), 1.90 (4H, quint, J ¼ 7.2 Hz), 1.26-1.46 (20H, m), 0.88 (6H,
t, J ¼ 6.8 Hz).
1
3
C NMR (CDCl ): 159, 145, 143, 141, 134, 130, 125, 124, 121, 117, 107, 105, 94, 56,
3
4
3, 32, 29, 28, 27, 23, 14.
IR ꢀmax/cm : 2921, 2850, 1600, 1508, 1483, 1458, 1351, 1253, 1166, 1148, 1060,
ꢁ1
1
033, 951, 834, 790, 769.
MS m/z (MALDI): 859, 858, 857 (M , M100).
þ
Combustion analysis: Expected: C, 78.46%; H, 7.05%; N, 3.27%; S, 7.48%; Obtained:
C, 78.44%; H, 7.05%; N, 3.36%; S, 7.67%.
2
.2.4. 1,4-Bis-f5-[9-octyl-7-(octyloxy)-carbazol-2-yl]thiophen-2-ylgbenzene (B)
A mixture of Pd(PPh ) (0.01 g, 0.008 mmol), 1,4-bis-(5-bromothiophen-2-yl)benzene
3
4
(
1
8
4) (0.20 g, 0.50 mmol), [N-octyl-7-(octyloxy)-carbazol-2-yl]boronic acid (6) (0.68 g,
3
3
.5 mmol), K CO (0.42 g, 3.00 mmol), and H O (2 cm ) in DMF (30 cm ) was heated at
2 3 2
ꢂ
3
0 C overnight. The cooled reaction mixture was washed with water (100 cm ) and
3
extracted with DCM (3 ꢀ 100 cm ). The combined organic layers were washed with
3
water (2 ꢀ 100 cm ), dried (MgSO ), filtered, and then concentrated under reduced pres-
4
sure. The residue was purified using column chromatography [silica, DCM/hexane 5:10]
to afford the desired product as a yellow solid (0.38 g, 73%).
o
Melting Point/ C: 248.
1
H NMR (CDCl ) d : 7.98 (2H, d, J ¼ 8.0 Hz), 7.94 (2H, d, J ¼ 8.4 Hz), 7.69 (4H, s),
3
H
7
.56 (2H, s), 7.51 (2H, d, J ¼ 8.0 Hz), 7.39 (4H, dd, J ¼ 6.4 & 2.4 Hz), 6.85 (4H, dd,
J ¼ 7.2 & 2.0 Hz), 4.28 (4H, t, J ¼ 7.2 Hz), 4.10 (4H, t, J ¼ 6.8 Hz), 1.91 (8H, m), 1.26-
1
4
8
.53 (40H, m), 0.90 (6H, t, J ¼ 7.2 Hz), 0.87 (6H, t, J ¼ 7.2 Hz).
13
C NMR (CDCl ): 159, 145, 142, 141, 134, 130, 126, 124, 121, 117, 108, 105, 94, 68,
3
4, 32, 29, 26, 22, 14.
ꢁ
1
IR ꢀmax/cm : 2921, 2850, 1599, 1483, 1460, 1356, 1254, 1166, 1146, 1063, 1029, 949,
34, 823, 791, 769.
MS m/z (MALDI): 1055, 1054, 1053 (M . M100).
þ
Combustion analysis: Expected: C, 79.80%; H, 8.42%; N, 2.66%; S, 6.09%; Obtained:
C, 79.77%; H, 8.47%; N, 2.61%; S, 6.15%.
3. Results and discussion
3.1. Synthetic discussion
The two structural isomers A and B were synthesized as shown in the reaction
Scheme 1. A Suzuki aryl-aryl, cross-coupling reaction was carried out to give 1,4-bis-
(thien-2-yl)benzene(3) in excellent yield (97%). A possible reason for high yield is that

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
5
Scheme 1. The reaction pathway used to synthesize the (bisthiophene)benzene carbazole A and B
work-up of the reaction system is relatively simple, involving just washing away the
impurities with methanol due to the relative insolubility of compound 3. The com-
pound 3 was then brominated by using NBS in DMF in darkness to give 1,4-bis-(5-bro-
mothiophen-2-yl)benzene (4) in excellent yield (94%). The syntheses of the boronic
acids 5 and 6 in Schemes 1 have been reported in our previous papers [8, 9], but used
for synthesizing different final products in this paper. The boronic acid 5 was reacted
with the dibrominated aromatic core 4 in a Suzuki aryl-aryl cross-coupling reaction
using Pd(OAc) as catalyst, K CO aqueous as base and DMF as solvent to give 1,4-bis-
2
2
3
[
5-(7-Methoxy-9-octyl-carbazol-2-yl)thiophen-2-yl]benzene (A) with good yield 76%.
1
,4-bis-f5-[9-octyl-7-(octyloxy)-carbazol-2-yl]thiophen-2-ylgbenzene (B) (73%) was syn-
thesized under a similar Suzuki aryl-aryl cross-coupling reaction condition between
compounds 4 and 6 catalyzed by Pd(PPh ) using aqueous K CO and DMF as solvent.
3
4
2
3
Aryl carbon-carbon (C-C) single bond formation is of vital importance in synthetic
organic chemistry. Generally, this process can be achieved with one arene functionalized
with a halogen atom, e.g., bromine or iodine, reacting with the other arene containing
organometallic moiety, e.g., -B(OH) , -Sn(Bu) , -Mg, which are representative of Suzuki
3
3
Coupling [25, 26], Stille Coupling [27, 28], and Grignard reaction [29, 30], respectively.
Sometimes direct arylation through C-H bond activation and cleavage is favored to

6
G. HU ET AL.
Scheme 2. Failed direct arylation pathway for synthesizing compound A
form aryl C-C bonds, due to a reduction in the number of synthetic steps required to
achieve the same conversion [31, 32]. However, the direct arylation method is not
always effective for aryl C-C bond formation. For instance, the direct arylation reaction,
to create compound A between compounds 7 and 8 using DMF or NMP as solvent,
was unsuccessful as shown in Scheme 2. In theory, thiophene moieties are excellent sub-
strates for direct arylation reactions, due to the typically facile palladation through a
concerted metalation-deprotonation (CMD) pathway, which renders the reaction highly
selective for the 2- or 5-positions of the thiophene moieties [33]. Therefore, compounds
7
and 8 should be ideal as starting materials for direct arylation reactions. In this work,
this reaction failed. According to the CMD mechanism of direct arylation [34, 35], the
reaction steps include the oxidative addition of palladium to the C-Br bond of an aryl
bromide, the exchange of the halogen ligand, deprotonation of the thiophene substrate
with simultaneous formation of a metal-carbon bond, and then, the formation of an
important transition state that determines whether the direct arylation can be achieved
or not, and reductive elimination of the transition state. The energy required to form
the transition state can be divided into two components including the energy of distort-
ing the C-H bond of thiophene moiety and the interaction energy between distorted
fragment and palladium center, according to density functional theory (DFT) calcula-
tions of the CMD mechanism [35, 36]. The bromo-substituted carbazole-derivate 7 is
sterically bulky and may, therefore, require more energy to form a palladium active cen-
ter to react with the distorted C-H bond of thiophene moiety. Furthermore, the bulky
structure of the bromo-substituted carbazole-derivate is more likely to trap the palla-
dium center, preventing the closing of distorted C-H bond. Therefore, as direct aryla-
tion was not possible, compound 7 was first lithiated, quenched with a boronate ester,
and then hydrolyzed to obtain the corresponding carbazole-derivate boronic acid 5.
Compound 3 was brominated in the required positions to obtain the compound 4.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
7
Table 1. The phase transition temperatures, ionization potential (eV), band gap (eV), and electron
affinity (eV) of the (bisthiophene)benzene carbazoles A and B.
o
Compound
R
1
Phase Transition Temperatures ( C)
IP
Eg
EA
a
A
B
a
CH
3
Cr 263-N -266 Iso
Cr 248 Iso
5.46
5.45
2.67
2.67
2.79
2.78
C
8
H
17
N : transient nematic phase, Cr: crystalline, Iso: Isotropic.
Finally, Suzuki aryl-aryl cross-coupling reactions were carried out to obtain compounds
A and B with good yields as shown in the Scheme 1. Compared with specific require-
ments for C-H bond and C-Br bond of direct arylation, Suzuki aryl-aryl coupling reac-
tions are more tolerant of other functional groups present on the reagents and are also
more tolerant of the steric demands of the reactants.
3
.2. Mesomorphic behavior, liquid crystalline transition temperatures, energy
levels, and band gaps of two isomers a and B
2
,5-Disubstituted thiophene and 1,4-disubstituted phenyl rings are often present in
organic semiconductor structures due to their influence on light-emitting characteristics,
good charge transport properties, and chemical/environmental stability by influencing
the molecular orbital energy levels and extending the degree of p-conjugation [24, 37].
Two thiophene/phenylene-based carbazoles were synthesized with different length of
terminal aliphatic chains (R ¼ CH or C H ) attached to the phenyl ring of the aro-
1
3
8
17
o
matic core. The liquid crystalline transition temperatures ( C) of the compound A are
collated in Table 1. The alkoxy substituents in a terminal position (R O) were varied in
1
order to study the effect of the alkoxy chains on the mesomorphic behavior of the two
compounds and their liquid crystalline transition temperatures. Of the (bisthiophene)-
benzene carbazoles (A and B), only compound A, with the shorter alkoxy chains, pos-
a
sesses transient nematic liquid crystalline behavior (Cr 263-N -266 Iso). On increasing
the length of alkoxy chains, the compound B was found to exhibit no observable liquid
crystalline phases.
The insertion of linear and co-axial six-membered 1,4-disubstituted-phenyl ring into
two nonlinear and non-co-axial five-membered 2,5-disubstituted thiophene rings
strengthens the rigid structures of the aromatic main chain. It is a possible reason why
compound A exhibits liquid crystalline mesomorphic behavior. However, the addition
of phenylene at the central position of the aromatic main chain leads to a small angle
between symmetrical sides of the aromatic backbone. Therefore, when the length of
symmetrical terminal alkyl chains was increased, the nonlinear and non-co-axial struc-
ture of the whole molecule caused by the angle was strengthened. It can be well illus-
trated in Figure 1 by the optimized 3D geometry models using Chem3D/MM2 energy-
minimized calculation. It could be further proved that the octyl-bithiophene-carbazole

8
G. HU ET AL.
Figure 1. Optimized 3D geometry models using Chem3D/MM2 energy minimized calculation.
Figure 2. The 3D modeling contrast of a side perspective for compounds A and B.
molecule with only removing the phenylene from compound B shows nematic meso-
phase, which has been reported by our group before [9]. In addition, the two bonds of
an oxygen atom attached to aromatic rings and alkyl chains also have an angle, which
means the longer terminal alkyl chains further weaken the linear structure of aromatic
main chains and thus decrease the length-to-breadth ratio of a whole molecule. The 3D
modeling contrast of a side perspective for compounds A and B is shown in Figure 2 to
clearly reveal the unfavorable angle between the terminal octyl chains of compound B
and the aromatic backbone. Therefore, it can be rationally explained why compound A
is liquid crystalline while compound B is not.
The presence of additional 1,4-disubstituted phenyl rings not only affects the meso-
morphic behavior, but also increases the liquid crystalline transition temperatures. It
can be seen from Table 1, that the melting point of the (bisthiophene)benzene carbazole
A is significantly high due to an extended aromatic molecular core. The characteristic
ꢂ
nematic droplets for compound A was observed on heating the sample into 265 C
using POM, shown in Figure 3a. However, the another characteristic point singularities

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
9
Figure 3. Characteristic nematic droplets and Schlieren texture observed for compound A on heating
o
o
from room temperature to 265 C (a) and on cooling from the isotropic state to 266 C (b).
with four- and two-point brushes of a nematic mesophase were observed appropriately
ꢂ
near the clearing point 266 C only on cooling down from the isotropic state, see
ꢂ
Figure 3b, and disappeared at 263 C.The compound B, containing longer alkyl chains
ꢂ
than compounds A, exhibits lower melting points (Cr 248 C-Iso). The presence of flex-
ible alkyl chains usually serves to lower the intermolecular forces of attraction, e.g., Van
der Waals forces, by increasing the intermolecular distance so that lower melting points
and other liquid crystalline transition temperatures can be realized.
The cyclic voltammetry scanning curves of compounds A and B are shown in
Figure 4. Equation (1) was used to calculate the ionization potential (IP), as follows:
Fe
IP ðeVÞ ¼ E – E
þ 0:425 þ 4:7
(1)
ex
1=2
Fe
where Eex is the onset voltage of the semiconductor compound peak, and E
is the
1/2
average voltage derived from the peaks of oxidation and reduction [(Max þ Min)/2] of
the calibration sample of ferrocene. The constant 0.425 eV is that for the ferrocene
standard and 4.7 eV is for the oxidation level of the silver-silver chloride electrode [38].
Thus, the ionization potential (IP) of compounds A and B is calculated as 5.46 eV and
5.45 eV, respectively.
Figures 5 shows the UV-Vis absorption curves of compounds A and B. Equation (2)
was used to calculate the energy gap (Eg) of the HOMO and LUMO energy levels, as
follows:
Eg ðeVÞ ¼ hc=k ¼ 1240=kðk : nmÞ
(2)
ꢁ
15
where h is the Planck constant (4.135 ꢀ 10 eV s), cis the speed of light
1
7
(
3.0 ꢀ 10 nm/s), hc ¼ 1240 eV nm, and k is the absorption maximum (nm) extracted
from the UV-Vis absorption spectrum of the compound being investigated [38].
Therefore, as shown in Figure 5 for compounds A and B, k ¼ 463.45 nm and k ¼
463.91 nm, the band gaps, Eg, of compounds A and B can be calculated as both 2.67 eV
approximately. The LUMO energy level (EA) was estimated by the subtraction of the
value of the optical band gap (Eg) from the ionization potential (IP), which does not
include any correction for the exciton binding energy.

1
0
G. HU ET AL.
Figure 4. The cyclic voltammetry scanning curves of compounds A and B.
Figure 5. The UV-Vis absorption curves of compounds A and B.
The values for the ionization potentials (IP), energy gaps (Eg), and electron affinity
(EA) of compounds A and B are collated in Table 1, and they do not appear to be sig-
nificantly influenced by the length of alkyl chains. The result is consistent with their
electron density distribution of the HOMO and LUMO states mainly localized on the

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
11
Figure 6. Electron density distribution of compounds A and B in the HOMO and LUMO states calcu-
lated by TD-DFT using Gaussian 09 at the B3PW91/6-31G (d) level.
sequentially aromatic units as predicted by TD-DFT using Gaussian09 at the B3PW91/
6
-31G (d) level, see Figure 6.
Conclusions
Two structural isomers of (bisthiophene)benzene carbazoles A and B with different
length of alkyl chains in symmetrical terminal positions were synthesized using opti-
mized reaction pathways and exhibited different mesomorphic behavior but similar val-
ues of energy levels and band gaps. Only the isomer A with shorter terminal alkyl
ꢂ
a
ꢂ
chains exhibits transient nematic liquid crystalline mesophases (Cr 263 C -N -266 C
Iso). The longer octyl terminal chains of the isomer B in turn result in the strengthen-
ing of both kinds of small angles between symmetrical aromatic backbones and between
terminal alkyl chains and the aromatic backbone. Simulated HOMO and LUMO states
proved similar electron density distribution which mainly localized on the sequentially
aromatic units.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
National & Local Joint Engineering Research Center for Mineral Salt Deep Utilization, Huaiyin
Institute of Technology [Grant Number: SF202010]; Huaiyin Institute of Technology [Grant
Number: Z301B19582]; Science and Technology Foundation of Huai’an City [Grant Number:
HAB202064]; University of Hull; China Scholarship Council.

1
2
G. HU ET AL.
References
[1] G. Gray, K. J. Harrison, and J. A. Nash, Electron. Lett. 9 (6), 130 (1973). doi:10.1049/
el:19730096
[2] M. Hird, K. J. Toyne, and G. W. Gray, Mol. Cryst. Liq. Cryst. 206 (1), 187 (1991). doi:10.
1080/00268949108037730
[
[
3] S. P. Kitney et al., Liq. Cryst. 38 (8), 1027 (2011). doi:10.1080/02678292.2011.593198
4] S. M. Kelly, Flat Panel Displays: Advanced Organic Materials (The Royal Society of
Chemistry, Cambridge, UK, 2000).
[5] M. C. Yang, J. I. Hanna, and H. Iino, J. Mater. Chem. C. 7 (42), 13192 (2019). doi:10.
1039/C9TC03990B
[6] C. M. Keum et al., Sci. Rep. 8 (1), 699 (2018). doi:10.1038/s41598-018-19157-9
[7] M. J. Han et al., ACS Cent Sci. 4 (11), 1495 (2018). doi:10.1021/acscentsci.8b00465
[8] G. Hu et al., Liq.Cryst. 45 (7), 965 (2018). doi:10.1080/02678292.2017.1404156
[9] G. Hu et al., Liq.Cryst. 44 (11), 1632 (2017). doi:10.1080/02678292.2017.1306633
[
[
10] M. Ozaki et al., Liq.Cryst. 45 (13–15), 2376 (2018). doi:10.1080/02678292.2018.1530375
11] Y. F. Wang, H. Iino, and J. I. Hanna, Soft Matter. 13 (37), 6499 (2017). doi:10.1039/
c7sm01303e
[12] S. Paul et al., J. Appl. Phys. 118 (13), 135702 (2015). doi:10.1063/1.4931913
[13] H. Iino and J. I. Hanna, Polym. J. 49 (1), 23 (2017). doi:10.1038/pj.2016.101
[14] H. Monobe et al., Mol.Cryst. Liq.Cryst. 647 (1), 119 (2017). doi:10.1080/15421406.2017.
1289443
[15] E. B. Melo et al., Mol. Cryst. Liq. Cryst. 657 (1), 81 (2017). doi:10.1080/15421406.2017.1403232
[16] K. Ohta et al., Mol. Cryst. Liq. Cryst. 397 (1), 25 (2003). doi:10.1080/714965592
[17] M. O’Neill and S. M. Kelly, Adv. Mater. 23 (5), 566 (2011). doi:10.1002/adma.201002884
[18] R. J. Bushby, M. O’Neill, and S. M. Kelly, Liquid Crystalline Semiconductors: materials,
Properties and Applications (Springer, Dordrecht, Netherlands, 2013).
[
[
[
[
19] O. Ostroverkhova, Chem. Rev. 116 (22), 13279 (2016). doi:10.1021/acs.chemrev.6b00127
20] C. Zhang and X. Zhu, Acc. Chem. Res. 50 (6), 1342 (2017). doi:10.1021/acs.accounts.7b00050
21] A. Hlel et al., Comput. Condens. Matter. 3, 30 (2015). doi:10.1016/j.cocom.2015.02.001
22] G. Turkoglu, M. E. Cinar, and T. Ozturk, in Sulfur Chemistry, Chapter 3, edited by X.
Jiang (Springer Nature Switzerland AG, Basel, Switzerland, 2019), pp. 79–124.
23] H. Sahu et al., Phys. Chem. Chem. Phys. 17 (32), 20647 (2015). doi:10.1039/c5cp02872h
24] A. Pelter, I. Jenkins, and D. E. Jones, Tetrahedron 53 (30), 10357 (1997). doi:10.1016/
S0040-4020(97)00629-7
[
[
[25] J. H. Kirchhoff et al., J. Am. Chem. Soc. 124 (46), 13662 (2002). doi:10.1021/ja0283899
[26] N. R. Lee et al., Org. Lett. 20 (10), 2902 (2018). doi:10.1021/acs.orglett.8b00961
[27] S. P. H. Mee, V. Lee, and J. E. Baldwin, Angew. Chem. Int. Ed. Engl. 43 (9), 1132 (2004).
doi:10.1002/anie.200352979
[28] J. H. Li et al., J. Org. Chem. 70 (7), 2832 (2005). doi:10.1021/jo048066q
[29] H. Zong et al., J. Org. Chem. 77 (10), 4645 (2012). doi:10.1021/jo3004277
[30] T. E. Hurst et al., Org. Lett. 21 (11), 3882 (2019). doi:10.1021/acs.orglett.9b00773
[31] H. Bohra and M. Wang, J. Mater. Chem. A. 5 (23), 11550 (2017). doi:10.1039/C7TA00617A
[32] C. Verrier et al., Beilstein J. Org. Chem. 7, 1584 (2011). doi:10.3762/bjoc.7.187
[33] D. Schipper and K. Fagnou, Chem. Mater. 23 (6), 1594 (2011). doi:10.1021/cm103483q
[34] S. I. Gorelsky, Coord. Chem. Rev. 257 (1), 153 (2013). doi:10.1016/j.ccr.2012.06.016
[35] L. G. Mercier and M. Leclerc, Acc. Chem. Res. 46 (7), 1597 (2013). doi:10.1021/ar3003305
[36] S. I. Gorelsky, D. Lapointe, and K. Fagnou, J. Org. Chem. 77 (1), 658 (2012). doi:10.1021/
jo202342q
[
[
37] M. Mushrush et al., J. Am. Chem. Soc. 125 (31), 9414 (2003). doi:10.1021/ja035143a
38] G. Hu et al., Phase Transit. 93 (8), 759 (2020). doi:10.1080/01411594.2020.1775830