Synthesis and characterization of new nematic liquid crystalline compounds-based thiophene units

Article abstract of DOI:10.1080/15421406.2015.1044198

Four new liquid crystalline thiophene compounds (M1-M4) with a long flexible spacer were prepared. Their structures were characterized by Fourier transform infrared and proton nuclear magnetic resonance. The mesomorphism and thermal stability were investigated with differential scanning calorimetry, polarizing optical microscopy, and thermogravimetric analysis. The photo-physical properties were evaluated using ultraviolet/visible spectroscopy and photoluminescence. M1-M4 all showed thermotropic mesogenic properties with excellent thermal stability, and exhibited nematic threaded texture, droplet texture, and Schlieren texture on heating and cooling cycles. The effect of flexible spacer and terminal groups on mesomorphic and spectroscopic property is discussed. The experimental results demonstrated that the tendency toward melting temperature (Tm) decreased, while isotropic temperature (Ti) increased with increasing the flexible spacer length. In CHCl₃ solution, these thiophene compounds displayed an intense broad absorption band peaking within 230-340 nm and a maximum fluorescent emission wavelength at 426-439 nm.

Full text of DOI:10.1080/15421406.2015.1044198

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Synthesis and characterization of new nematic
liquid crystalline compounds-based thiophene
units
Ying-Gang Jia, Dong Su, Zhi-Hao Guo & Jian-She Hu
To cite this article: Ying-Gang Jia, Dong Su, Zhi-Hao Guo & Jian-She Hu (2016) Synthesis
and characterization of new nematic liquid crystalline compounds-based thiophene units,
Molecular Crystals and Liquid Crystals, 624:1, 91-102
To link to this article: http://dx.doi.org/10.1080/15421406.2015.1044198
Published online: 11 Feb 2016.
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Date: 19 February 2016, At: 03:31

MOL. CRYST. LIQ. CRYST.
, VOL. , NO. , –
http://dx.doi.org/./..
Synthesis and characterization of new nematic liquid crystalline
compounds-based thiophene units
Ying-Gang Jia, Dong Su, Zhi-Hao Guo, and Jian-She Hu
Center for Molecular Science and Engineering, College of Science, Northeastern University, Shenyang, P. R. China
ABSTRACT
KEYWORDS
Liquid crystalline;
photoluminescence;
synthesis; thiophene
Four new liquid crystalline thiophene compounds (M1−M4) with a
long flexible spacer were prepared. Their structures were characterized
by Fourier transform infrared and proton nuclear magnetic resonance.
The mesomorphism and thermal stability were investigated with dif-
ferential scanning calorimetry, polarizing optical microscopy, and ther-
mogravimetric analysis. The photo-physical properties were evaluated
using ultraviolet/visible spectroscopy and photoluminescence. M1−M4
all showed thermotropic mesogenic properties with excellent thermal
stability, and exhibited nematic threaded texture, droplet texture, and
Schlieren texture on heating and cooling cycles. The effect of flexi-
ble spacer and terminal groups on mesomorphic and spectroscopic
property is discussed. The experimental results demonstrated that the
tendency toward melting temperature (Tm) decreased, while isotropic
temperature (Ti) increased with increasing the flexible spacer length. In
CHCl3 solution, these thiophene compounds displayed an intense broad
absorption band peaking within 230–340 nm and a maximum fluores-
cent emission wavelength at 426–439 nm.
1. Introduction
In recent year, the organic conjugated materials have attracted considerable interest due to
their excellent electrical and optoelectric properties [1–7], and many important potential
applications in various areas such as organic thin-film transistors [8], solar cells [9], organic
light-emitting diodes [10], sensor arrays [11], large-area plastic displays [12], and power trans-
mission devices [13]. Today, the thiophene derivatives occupy an important position in the
study of organic conjugated materials. Functionalized thiophene derivatives are being shown
to be the potential candidates for high-end applications. [14–20] As known, liquid crystalline
(LC) materials combine order and mobility, form well self-organized assemblies that exhibit a
variety of physical properties, and have been widely used in many fields. [21, 22] From a sci-
entific and industrial point of view, the LC thiophene derivatives are fascinating because they
combine the electrical properties of thiophene with the optical properties of conventional LC
materials [23–32]. These properties are expected to be controllable through the spontaneous
orientation of mesogenic core to enhance the co-planarity of thiophene units.
CONTACT Jian-She Hu
hujs@mail.neu.edu.cn
eastern University, Shenyang , P. R. China.
Center for Molecular Science and Engineering, College of Science, North-
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
©  Taylor & Francis Group, LLC

92
Y.-G. JIA ET AL.
In the present work, we aimed to design and synthesize novel nematic LC thiophene com-
pounds containing long flexible spacer length between thiophene unit and mesogenic unit.
The phase behavior and mesomorphism of these obtained thiophene compounds were char-
acterized using differential scanning calorimetry (DSC) and polarizing optical microscopy
(POM). The thermal stability was measured with thermogravimetric analysis (TGA). The
optical and photoluminescence properties were investigated by ultraviolet visible (UV/Vis)
spectroscopy and fluorescence spectroscopy.
2. Experimental
2.1. Materials
All chemicals were obtained from the indicated sources. 3-Methylthiophene (Shang-
hai, China), N-bromosuccinimide (Shenyang, China), benzoyl peroxide (Shenyang,
China), hexamethylenetetramine (Tianjing, China), malonic acid (Shenyang, China),
4,4ꢀ-dihydroxybiphenyl (Sigma-Aldrich, Shenyang, China), 1,4-dibromobuiane (Shenyang,
China), 1,6-dibromohexane (Shenyang, China), 4-ethoxybenzoic acid (Beijing, China), and
4-pentylbenzoic acid (Yantai, China) were used as received. All other solvents and reagents
used were purified by standard methods.
2.2. Measurements
Fourier Transform Infrared (FTIR) spectra were measured on a PerkinElmer spectrum One
1
(B) spectrometer (PerkinElmer, Foster City, CA). H Nuclear Magnetic Resonance (NMR)
spectra were obtained using a Bruker ARX 600 (Bruker, Fällanden, Swiss) high-resolution
NMR spectrometer, and chemical shifts were reported in ppm with tetramethylsilane (TMS)
as an internal standard. The thermal properties were determined with a Netzsch DSC 204
(Netzsch, Hanau, Germany) equipped with a cooling system. The thermal stability was
measured with a Netzsch TGA 209C thermogravimetric analyzer. The optical texture was
observed with a Leica DMRX POM (Leica, Wetzlar, Germany) equipped with a Linkam
THMSE-600 (Linkam, London, UK) cool and hot stages. UV/Vis absorption spectra were
recorded with a TU-1901 spectrophotometer (Purkinje, Beijing, China) using a quartz cuvette
with a 1.0-cm path length. The photoluminescence studies were carried out on an F-7000 flu-
orescence spectrophotometer (Hitachi, Japan) equipped with a 0.2-cm quartz cuvette. Both
excitation and emission slits were set at 5.0 nm, with a scan voltage of 700 V and scan speed
of 1200 nm min−1.
2.3. Synthesis of intermediate compounds
The synthetic route of intermediate compounds 1–12 is shown in Scheme 1. 3-
(Bromomethyl)thiophene (1), thiophene-3-carboxaldehyde (2), (E)-3-(3-thiophenyl)acrylic
acid (3), 4-(4-bromobutoxy)biphenyl-4’-ol (7), and 4-(6-bromohexyloxy)biphenyl-4’-ol (8)
were synthesized as described in the literature. [33–36]
... Potassium (E)--(-thiophenyl)acrylate (4)
(E)-3-(3-Thiophenyl)acrylic acid (15.4 g, 0.1 mol) was dissolved in 50 mL of methanol, and
then potassium hydroxide (5.6 g, 0.1 mol) in 10 mL of methanol was added drop-wise to the
above solution under quick stirring. The mixture was reacted at room temperature for 2 h.

MOL. CRYST. LIQ. CRYST.
93
Scheme . Synthetic route of compounds −.
After the evaporation of solvent, the crude product was recrystallized by methanol. Yield:
85%.
−1
=
=
=
IR (KBr, cm ): 1641 (C C); 1562 (C O); 1516–1486 (thiophene ring); 1152 (C S).
... -(-Bromobutoxy)biphenyl-ꢀ-ethoxybenzoate (9)
4-Ethoxybenzoyl chloride 5 was obtained through the reaction of 4-ethoxybenzoic acid
with excess thionyl chloride. Then compound 5 (9.2 g, 0.05 mol), dissolved in 10 mL of dry

94
Y.-G. JIA ET AL.
chloroform, was added drop-wise to a stirred solution of compound 7 (16.0 g, 0.05 mol) in
150 mL of chloroform and 4 mL of dry pyridine. The mixture was reacted for 2 h at room
temperature, refluxed for 24 h, and cooled to ambient temperature. After the evaporation
of solvent, the crude product was precipitated by adding methanol to the residue, and
recrystallized with ethanol/acetone (1:1). Yield: 73%, mp: 153°C.
IR (KBr, cm—1): 2977, 2849 (CH3–, –CH2–); 1726 (C O); 1605–1495 (Ar–); 1257 (C–
O–C); 518 (Br–). H NMR (δ, ppm from TMS in CDCl3): 1.45–1.49 (t, 3H, −CH3); 1.88–
=
1
1.95 [m, 4H, −OCH2(CH2)2CH2Br]; 3.56–3.60 [t, 2H, −OCH2(CH2)2CH2Br]; 4.11–4.17 (m,
2H,−OCH2CH3); 4.27–4.31 [t, 2H, −OCH2(CH2)2CH2Br]; 7.01–8.20 (m, 12H, Ar−H).
... -(-Bromohexyloxy)biphenyl-ꢀ-ethoxybenzoate (10)
The synthesis of 10 is similar to that for 9 as described above. Recrystallization from
ethanol/acetone−(11:1). Yield: 74%, mp: 126°C.
=
IR (KBr, cm ): 2977, 2856 (CH3–, –CH2–); 1727 (C O); 1605–1496 (Ar–); 1258
(C–O–C); 519 (Br–). 1H NMR (δ, ppm from TMS in CDCl3): 1.33–1.90 [m, 11H,
−CH3, and −OCH2(CH2)4CH2Br]; 3.55–3.60 [t, 2H, −OCH2(CH2)4CH2Br]; 4.12–4.18 (m,
2H,−OCH2CH3); 4.20–4.26 [t, 2H, −OCH2(CH2)4CH2Br]; 6.99–8.21 (m, 12H, Ar−H).
... -(-Bromobutoxy)biphenyl-ꢀ-pentylbenzoate (11)
The synthesis of 11 is similar to that for 9 as described above. Recrystallization from
ethanol/aceton−e1(2:1). Yield: 75%, mp: 128°C.
=
IR (KBr, cm ): 2924, 2856 (CH3–, –CH2–); 1732 (C O); 1606–1495 (Ar–); 1268 (C–O–
C); 516 (Br–). 1H NMR (δ, ppm from TMS in CDCl3): 0.90–0.94 (t, 3H, −CH3); 1.32–1.96 [m,
10H, −CH2(CH2)3CH3, and −OCH2(CH2)2CH2Br]; 2.68–2.74 [t, 2H, −CH2(CH2)3CH3];
3.55–3.60 [t, 2H, −OCH2(CH2)2CH2Br]; 4.26–4.33 [t, 2H, −OCH2(CH2)2CH2Br]; 6.96–8.17
(m, 12H, Ar−H).
... -(-Bromohexyloxy)biphenyl-ꢀ-pentylbenzoate (12)
The synthesis of 12 is similar to that for 9 as described above. Recrystallization from
ethanol/aceton−e1(2:1). Yield: 74%, mp: 115°C.
=
IR (KBr, cm ): 2926, 2856 (CH3–, –CH2–); 1732 (C O); 1606–1495 (Ar–); 1270 (C–O–
C); 516 (Br–). 1H NMR (δ, ppm from TMS in CDCl3): 0.90–0.95 (t, 3H, −CH3); 1.32–1.75 [m,
14H, −CH2(CH2)3CH3, and −OCH2(CH2)4CH2Br]; 2.66–2.73 [t, 2H, −CH2(CH2)3CH3];
3.57–3.61 [t, 2H, −OCH2(CH2)4CH2Br]; 4.18–4.23 [t, 2H, −OCH2(CH2)4CH2Br]; 6.97–8.17
(m, 12H, Ar−H).
2.4. Synthesis of thiophene compounds
The synthetic route of M1–M4 is shown in Scheme 2. These thiophene compounds were pre-
pared using the same method. As an example, the experimental details of M1 are described as
follows.
... (E)--(-(-(Thiophen--yl)acryloyloxy)butoxy)biphenyl-ꢀ-ethoxybenzoate (M)
Compounds 4 (1.92 g, 0.01 mol), 9 (4.68 g, 0.01 mol), and tetrabutyl ammonium bromide
(0.2 g) were dissolved in 80 mL of tetrahydrofuran (THF). The mixture was reacted for 48 h
at 60°C. After the evaporation of solvent under reduced pressure, the residue was poured into
cold water, and the precipitate was filtered. The crude product was recrystallized from acetone
and purified by silica gel column chromatography (acetone/hexane = 1/1). Yield: 45%. mp:
121°C.

MOL. CRYST. LIQ. CRYST.
95
Scheme . Synthetic route of thiophene compounds M−M.
−1
=
=
IR (KBr, cm ): 2952, 2854 (CH3–, –CH2–); 1728, 1715 (C O); 1633 (C C); 1605–1497
1
=
(thiophene and aromatic ring); 1257 (C–O–C); 1168 (C S). H NMR (δ, ppm from TMS in
CDCl3): 1.46–1.50 (t, 3H, −CH3); 1.89–1.97 [m, 4H, −CH2(CH2)2CH2−]; 4.08–4.10 (t, 2H,
−COOCH2−); 4.12–4.17 (m, 2H, −OCH2CH3); 4.29–4.32 [t, 2H, −CH2(CH2)2CH2O−];
=
=
6.24–6.29 (d, 1H, −CH CHCOO−); 7.65–7.70 (d, 1H, −CH CHCOO−); 6.97–7.01 (d,
4H, Ar-H); 7.23–7.27 (d, 2H, Ar-H); 7.28–7.49 (m, 3H, thiophene-H); 7.50–7.60 (d, 4H, Ar-
H); 8.16–8.20 (d, 2H, Ar-H).
... (E)--(-(-(Thiophen--yl)acr−y1loyloxy)hexyloxy)biphenyl-ꢀ-ethoxybenzoate (M)
=
Yield: 46%. mp: 94°C. IR (KBr, cm ): 2974, 2856 (CH3–, –CH2–); 1728, 1710 (C O);
=
=
1635 (C C); 1604–1495 (thiophene and aromatic ring); 1258 (C–O–C); 1169 (C S).
1H NMR (δ, ppm from TMS in CDCl3): 1.46–1.51 (t, 3H, −CH3); 1.54–1.59 [m, 8H,
−CH2(CH2)4CH2−]; 4.01–4.06 (t, 2H, −COOCH2−); 4.13–4.18 (m, 2H, −OCH2CH3);
=
4.22–4.27 [t, 2H, −CH2(CH2)4CH2O−]; 6.26–6.32 (d, 1H, −CH CHCOO−); 7.67–7.71 (d,
=
1H, −CH CHCOO−); 6.98–7.01 (d, 4H, Ar-H); 7.23–7.27 (d, 2H, Ar-H); 7.28–7.48 (m, 3H,
thiophene-H); 7.50–7.61 (d, 4H, Ar-H); 8.17–8.19 (d, 2H, Ar-H).
... (E)--(-(-(Thiophen--yl)a−cr1yloyloxy)butoxy)biphenyl-ꢀ-pentylbenzoate (M)
=
Yield: 44%. mp: 123°C. IR (KBr, cm ): 2952, 2855 (CH3–, –CH2–); 1727, 1708 (C O); 1631
1
=
=
(C C); 1606–1497 (thiophene and aromatic ring); 1282 (C–O–C); 1168 (C S). H NMR (δ,
ppm from TMS in CDCl3): 0.90–0.94 (t, 3H, −CH3); 1.33–1.71 [m, 6H, −CH2(CH2)3CH3];
1.91–1.99 [m, 4H, −CH2(CH2)2CH2−]; 2.69–2.74 [t, 2H, −CH2(CH2)3CH3]; 4.06–
4.11 (t, 2H, −COOCH2−); 4.27–4.33 [t, 2H, −CH2(CH2)2CH2O−]; 6.24–6.29 (d, 1H,
=
=
−CH CHCOO−); 7.65–7.71 (d, 1H, −CH CHCOO−); 6.96–7.01 (d, 2H, Ar-H); 7.24–
7.28 (d, 2H, Ar-H); 7.29–7.50 (m, 3H, thiophene-H); 7.31–7.36 (d, 2H, Ar-H); 7.51–7.61 (d,
4H, Ar-H); 8.12–8.16 (d, 2H, Ar-H).
... (E)--(-(-(Thiophen--yl)acryloyloxy)hexyloxy)biphenyl-ꢀ-pentylbenzoate (M)
Yield: 47%. mp: 93°C. IR (KBr, cm−1): 2925, 2855 (CH3–, –CH2–); 1734, 1703
=
=
(C O); 1635 (C C); 1608–1499 (thiophene and aromatic ring); 1283 (C–O–C); 1178

96
Y.-G. JIA ET AL.

Figure . H NMR spectrum of M1.
1
=
(C S). H NMR (δ, ppm from TMS in CDCl3): 0.90–0.95 (t, 3H, −CH3); 1.33–1.38
[m, 4H, −CH2CH2(CH2)2CH3]; 1.55–1.59 [m, 4H, −CH2CH2(CH2)2CH2CH2−]; 1.64–
1.71 [m, 2H, −CH2CH2(CH2)2CH3]; 1.73–1.89 [m, 4H, −CH2CH2(CH2)2CH2CH2−];
2.68–2.74 [t, 2H, −CH2(CH2)3CH3]; 4.01–4.05 (t, 2H, −COOCH2−); 4.20–4.26 [t,
=
2H, −CH2(CH2)4CH2O−]; 6.25–6.31 (d, 1H, −CH CHCOO−); 7.65–7.71 (d, 1H,
=
−CH CHCOO−); 6.96–7.01 (d, 2H, Ar-H); 7.22–7.28 (d, 2H, Ar-H); 7.29–7.51 (m, 3H,
thiophene-H); 7.32–7.37 (d, 2H, Ar-H); 7.52–7.62 (d, 4H, Ar-H); 8.12–8.16 (d, 2H, Ar-H).
3. Results and discussion
3.1. Synthesis and characterization
As shown in Scheme 2, the target thiophene compounds containing different long spacer
were successfully synthesized by the mucleophilic substitution reaction of potassium (E)-3-
(3-thiophenyl)acrylate and the compounds 9, 10, 11, and 12, respectively, in THF at 60°C.
All the intermediates and final products were thoroughly purified and characterized by FTIR
1
and H NMR, and the satisfactory analysis data corresponding to their expected molecu-
lar structures were obtained. A typical example of the 1H NMR spectra of M1 is shown in
Fig. 1. The aromatic and thiophene H resonance peaks appeared in the low magnetic region
(δ = 8.2−7.0), substituted acrylate-based 3-thiophenyl olefinic H resonance peaks also in low
magnetic region (δ = 7.7−6.2), whereas the aliphatic H resonance peaks in the high magnetic
region (δ = 2.0−1.5) except the peaks of the near-neighboring aliphatic H to the −O− or
−COO− shifted to the middle region (4.3−4.0).
3.2. DSC analysis
The thermal behavior of the thiophene compounds M1−M4 was investigated with DSC at a
heating and cooling rate of 10°C min−1 under nitrogen atmosphere. The DSC data, obtained
on second heating and cooling scans, are summarized in Table 1. Representative DSC ther-
mographs of M1 are presented in Fig. 2.

MOL. CRYST. LIQ. CRYST.
97
Table . The phase transition temperatures and mesophase of thiophene compounds.
Mesophase, phase transition temperature (°C), and enthalpy changes (J·g−
)
Thiophene compounds
Heating cycle
Cooling cycle
M
M
M
M
Cr. (.) N. (.)I
Cr. (.) N. (.)I
Cr. (.) N. (.)I
Cr. (.) N. (.)I
I. (.) N. (.)Cr
I. (.) N. (.)Cr
I. (.) N. (.)Cr
I. (.) N. (.)Cr
Note: Cr = crystal; N = nematic phase; I = isotropic.
According to DSC curves on heating cycle, M1−M4 showed two endothermal peaks, indi-
cating a melting transition at low temperature and a nematic to isotropic phase transition at
high temperature. On cooling cycle, two exothermal peaks occurred and these represented
an isotropic to nematic phase transition and a crystallization transition. As seen in Table 1,
the molecular structure of M1−M4 had an obvious influence on their phase transition tem-
peratures. For M1 and M2, because of the same terminal groups and mesogenic core, the flex-
ible spacer length affected the melting temperature (Tm) and the isotropic temperature (Ti).
When the methylene number between thiophene unit and mesogenic core increased from
4 to 6, Tm decreased from 120.5°C for M1 to 94.2°C for M2; however, the corresponding Ti
tended to increase from 171.2°C for M1 to 176.2°C for M2, so the mesophase temperature
range widened from 50.7°C for M1 to 82.0°C for M2. Similar results could also be seen for M3
and M4.
3.3. TGA analysis
The thermal stability of M1−M4 was investigated with TGA at a heating rate of 20°C min−1
under nitrogen atmosphere. Their TGA curves are shown in Fig. 3. The corresponding ther-
mal decomposition data are listed in Table 2. Temperatures at which 5% weight loss (Td) of
M1−M4 occurred were above 365°C, indicating that four thiophene compounds had high
thermal stability because the existence of a biphenyl segment and thiophene unit may cause
intermolecular π–π interaction. In addition, Td decreased with increasing the methylene
number between thiophene unit and mesogenic core.
Figure . DSC curves of M1.

98
Y.-G. JIA ET AL.
Figure . TGA curves of M1−M4.
3.4. POM analysis
In general, LC compounds containing achiral unit show either nematic phase or smectic
phase; this mainly depends on relative strength of molecular transverse attractive force and
terminal attractive force. If the molecular transverse attractive force is predominant, only
smectic phase can be seen. Conversely, these LC materials show nematic phase. However,
when the strength of these two kinds of force is about equal, both smectic and nematic phase
appear. Under POM observation, M1−M4 showed typical nematic texture on heating and
cooling cycles. As an example, the mesomorphism and texture of M1 were observed and
recorded in detail as follows. When M1 was heated to 119.3°C, the sample started to melt and
mesomorphism appeared; heating continued, the thread-like texture of nematic phase was
observed, and the texture disappeared at 176.5°C. On cooling the samples from the isotropic
melt, the droplet texture appeared at 175.2°C, cooling continued, the droplet texture grew up
gradually and transformed to schlieren texture, and crystallized at 88.6°C. The optical texture
of M1 is shown in Figs. 4(a and b).
3.5. UV/Vis analysis
Figure 5 shows the UV/Vis absorption spectra of CHCl3 solutions of the selected compounds
M1–M4. All these compounds exhibited an intense broad absorption band peaking within
230–340 nm. Owing to the same conjugated core of thiophene and phenyl rings, four com-
pounds M1–M4 had the similar absorption bands, and the absorption spectra were nearly
identical in shape, which are attributed to the π–π∗ bands.
3.6. Fluorescence analysis
Four thiophene derivatives had good fluorescence optical properties. Figure 6 shows repre-
sentative 2D fluorescence topographical maps of M1 and M3 in CHCl3 solution at a concen-
tration of 15 mg mL−1 and a scan voltage of 700 V. Due to the same conjugated core, the
corresponding 2D fluorescence topographical maps were nearly identical in shape. As seen in
Fig. 6, M1 exhibited a maximum excitation wavelength at 366 nm and emission wavelength at

MOL. CRYST. LIQ. CRYST.
99
Figure . Optical textures of M1 (×) (a) nematic threaded texture at °C; (b) nematic droplet texture
at °C.
426 nm. However, M3 exhibited a maximum excitation wavelength at 367 nm and emission
wavelength at 436 nm. This indicated that the terminal groups also had effects on photolumi-
nescent properties. Since the electron donating effect of pentyl group was stronger than that
of ethoxy group, fluorescence strength and photoluminescence quantum yields of M3 were
greater than that of M1.
Table . TGA data of thiophene compounds.
Weight loss (%)
Sample
Tda (°C)
°C
°C
M
M
M
M




.
.
.
.
.
.
.
.
Note: aTemperature at which % weight loss occurred.

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Y.-G. JIA ET AL.
Figure . UV/Vis absorption spectra of M1−M4 in CHCl.
Figure . D-fluorescence topographical map of CHCl solution: (a) M1, (b) M3.

MOL. CRYST. LIQ. CRYST.
101
4. Conclusions
In this work, four new mesogenic thiophene derivatives were designed, synthesized, and char-
acterized. They all showed thermotropic nematic phase with high thermal stability. With
increasing the flexible spacer length, the corresponding Tm decreased, while Ti increased, and
the mesophase range widened. In CHCl3 solution, four thiophene compounds had the similar
broad absorption bands within 230–340 nm, and the absorption spectra were nearly identi-
cal in shape. Moreover, they all had good fluorescence properties, and showed a maximum
fluorescent emission wavelength at 426–439 nm. The fluorescence strength and photolumi-
nescence quantum yields of thiophene compounds (M3 and M4) with terminal pentyl groups
were greater than that of thiophene compounds (M1 and M2) with terminal ethoxy groups.
Funding
This work was supported by the Science and Technology Committee of Liaoning Province
[2013020103], Science and Technology Bureau of Shenyang [F14-231-1-05], and Fundamental
Research Funds for the Central Universities [N130205001 and N110705001].
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