Synthesis and mesogenic properties of novel terthiophene derivatives

Article abstract of DOI:10.1080/00397910500446290

To develop novel oligothiophene-based liquid crystals involving hydrogen bonding, new terthiophene derivatives containing a stearylamide group, N,N′-distearyl-5,5″-dicyano-2,2′:5′,2″- terthiophene-4,4″-dicarboxamide (DNC₁₈DCN 3T) and N,N′-distearyl-5,5′-dipropyl-2,2′:5′, 2′-terthiophene-4,4″-dicarboxamide (DNC₁₈ DP3T), were designed and synthesized, and their thermal behavior examined. Although DNC ₁₈DP3T did not exhibit liquid crystallinity, DNC₁₈DCN3T was found to form smectic A phase. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910500446290

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Synthesis and Mesogenic Properties of Novel
Terthiophene Derivatives
Ping Liu a , Miaomiao Liu a & Wenji Deng b
a Research Institute of Materials Science , South China University of
Technology , Guangzhou, China
b Department of Applied Physics , South China University of Technology ,
Guangzhou, China
Published online: 16 Aug 2006.
To cite this article: Ping Liu , Miaomiao Liu & Wenji Deng (2006) Synthesis and Mesogenic Properties of Novel
Terthiophene Derivatives, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 36:6, 685-692, DOI: 10.1080/00397910500446290
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Synthetic Communicationsw, 36: 685–692, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500446290
Synthesis and Mesogenic Properties of Novel
Terthiophene Derivatives
Ping Liu and Miaomiao Liu
Research Institute of Materials Science, South China University
of Technology, Guangzhou, China
Wenji Deng
Department of Applied Physics, South China University of Technology,
Guangzhou, China
Abstract: To develop novel oligothiophene-based liquid crystals involving hydrogen
bonding, new terthiophene derivatives containing a stearylamide group, N,N0-
distearyl-5,500-dicyano-2,20 : 50,200-terthiophene-4,400-dicarboxamide (DNC18DCN 3T)
and N,N0-distearyl-5,50-dipropyl-2,20 : 50,20-terthiophene-4,400-dicarboxamide (DNC18
DP3T), were designed and synthesized, and their thermal behavior examined.
Although DNC18DP3T did not exhibit liquid crystallinity, DNC18DCN3T was found
to form smectic A phase.
Keywords: Liquid crystal, terthiophene derivatives
1. INTRODUCTION
Oligothiophenes with well-defined structures have recently received a great
deal of attention not only as model compounds for electrically conducting
polythiophenes but also as a new class of functional p-electron systems. A
variety of oligothiophenes have been synthesized,[1] and their molecular and
crystal structures, [2,3] self-ordering,[4,5] electrochemical,[6,7] photophysical,[8]
optical,[9,10] and electrical properties[11,12] have been studied. In addition their
Received in Japan August 3, 2005
Address correspondence to Ping Liu, Research Institute of Materials Science, South
China University of Technology, Guangzhou, China. Tel.: þ 86-20-87111686; E-mail:
mcpliu@scut.edu.cn
685

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P. Liu, M. Liu, and W. Deng
potential applications for field-effect transistors, photovoltaic devices,[13] and
organic electroluminescent devices[14] have been investigated.
Oligothiophenes are crystalline in nature because of their planar molecular
structures. Vacuum-evaporated and spin-coated films of oligothiophenes have
been reported to be polycrystalline. Because the properties and functionality
of a material are greatly affected by its morphology, it is of both fundamental
and technological interest to exert control over morphology of oligothiophenes
in the design of novel functional organic materials.
Recently, several reports on the liquid crystalline properties of oligothio-
phene derivatives have appeared.[15–17] It has been reported that terthiophenes
substituted with long alkyl or alkanoyl groups at the terminal a- and a00-
positions, for example, 5-alkyloxycarbonyl-500-alkyl-2,20 : 50,200-terthiophenes
and 5, 500-dialkyl-2,20 : 50,200-terthiophenes, exhibit a smectic liquid crystalline
phase. 5-Substituted and 5000-disubstituted quarterthiophenes have also been
reported to exhibit a smectic and nematic liquid crystalline phase. However,
examples of oligothiophene-based liquid crystals are still scarce.
This article reports on the synthesis of new compounds containing 00a
terthiophene moiety, N,N0-distearyl-5,500-dicyano-2,20 : 50,200-terthiophene-4,4 -
dicarboxamide (DN C18DCN3T) and N,N0-distearyl-5,500-dipropyl-2,20 : 50,200-
terthiophene-4,400-dicarboxamide (DNC18DP3T). The relationship between
molecular structure and liquid crystalline behavior is discussed (Scheme 1).
2. RESULTS AND DISCUSSION
Novel families of terthiophene derivatives containing an stearylamide group at
the b- and b0-position of 2,20 : 50,200-terthiophene, DNC18DCN3T and
DNC18DP3T, were synthesized according to the procedures shown in
1
Scheme 2. All compounds were characterized by IR and H NMR spec-
troscopy, mass spectrometry, and elemental analysis.
Differential scanning calorimetry (DSC) and polarized light microscopy
performed on DNC18DCN3T revealed that the compound, containing two
stearylamide groups at the b- and b0-positions of 3T, formed a smectic A
(SmA) phase. Figure 1 shows the polarizing micrograph of the DNC18DCN3T
SmA phase formed from the isotropic liquid in the cooling process. A
focal-conic fan texture typical of the SmA phase was clearly observed.
Scheme 1.

Novel Terthiophene Derivatives
687
Scheme 2.
The formation of a SmA phase by DNC18DCN3T was also evidenced by
DSC. Figure 2 shows the DSC curves for DNC18DCN3T. When the crystalline
sample of DNC18DCN3T was heated, an endothermic peak was observed at
948C to give a SmA phase. Upon further heating, the onset of the transition
from the SmA phase into the isotropic liquid was observed at 1388C. When
the isotropic liquid was cooled, the onset of the transition into the SmA
phase was observed at around 1398C. The SmA phase crystallized at 998C.
The trace was reproducible.
In our previous study, we found that N,N0-distearyl-5,500-dibromo-
2,20 : 50,200-terthiophene-4,400-dicarboxamide (DNC18DBr3T) forms a smectic
A phase, but 4,400-bis(stearyloxycarbonyl)-5,500-dibromo-2,20 : 50,200-terthio-
phene (DOC18DBr3T) did not exhibit liquid crystallinity. The absence of
liquid crystallinity for DOC18DBr3T and changes in the IR spectra suggest
that intermolecular hydrogen bonding through the stearylamide group is
involved in liquid-crystal-phase formation.[18]
It is noteworthy that DNC18DP3T did not form a liquid crystal phase; it
showed only the phase transition between the crystal and the isotropic
liquid. The reason why DNC18DP3T did not form liquid crystal phase is
thought to be that the propyl group at the a- and a0-positions of 3T can
Figure 1. Photomicrograph of the texture of the SmA phase of DNC18DCN3T
obtained upon cooling the melt (magnification ꢀ 200).

688
P. Liu, M. Liu, and W. Deng
Figure 2. DSC curves for DNC18DCN3T.
make the liquid crystalline phase unstable, and it thus favors direct crystalliza-
tion from the isotropic liquid. However, the cyano group at the a- and a0-
positions of 3T can make the liquid crystalline phase stable.
Table 1 summarizes the transition temperatures of DNC18DCN3T and
DNC18DBr3T together with the enthalpy changes (DH) associated with the
phase transitions.
When the isotropic liquid was cooled, the onset of the transition into the
SmA phase for DNC18DCN3T was higher than the DNC18DBr3T. When the
SmA phase was cooled, the the onset of the transition into the crystalline phase
for DNC18DCN3T was lower than that for the DNC18DBr3T. The temperature
range of liquid crystalline phase for DNC18DBr3T and DNC18DCN3T is 168C
Table 1. Transition temperatures and enthalpy changes of DNC18DBr3T and
DNC18DCN3T
Transition temperature/8C;
Compound
enthalpy change (in parentheses)/kJ mol21
DNC18DBr3T[18]a
DNC18DCN3Ta
K
K
107 (56)
99 (43)
SmA
SmA
123 (3.7)
139 (66)
I
I
Note: K: crystal, SmA: smectic A liquid crystal, I: isotropic liquid.
aTransition temperatures and enthalpy changes were determined by DSC on cooling.

Novel Terthiophene Derivatives
689
and 408C, respectively. These results indicate that the cyano group is better
than the bromo group for making the liquid crystalline phase stable.
3. CONCLUSION
A
novel terthiophene derivatives containing a stearylamide group,
DNC18DCN3T and DNC18DP3T, were designed and synthesized.
DNC18DCN3T was found to form a SmA phase, so constituting new oli-
gothiophene-based liquid crystals. DNC18DP3T did not exhibit liquid
crystallinity.
4. EXPERIMENTAL
4.1 Synthesis
2-Bromothiophene, 2,5-dibromothiophene, [1,3-bis-(diphenyphosphino)
propane] nickel(II) chloride [NiCl2-(dppp)], magnesium, diisopropylamine,
butyllithium (hexane solution), thionyl chloride, triethylamine, and monostear-
ylamines (C18H37NH2) were commercially available and used without further
purification. 2,20 : 50,200-Terthiophene (3T) was prepared by Grignard coupling
reaction of 2,5-dibromothiophene with 2-bromomagnesiumthiophene in ether
at a refluxing temperature. Synthetic procedures are illustrated in Scheme 2.
4.1.1. Synthesis of N,N0-Distearyl-5,500-dicyano-2,20 : 50,200-
terthiophene-4,400-dicarboxamide (DNC18DCN3T)
5,500-Dicyano-2,20 : 50,200-terthiophene (DCN3T) was prepared by the reaction
of 3T (10.0 g, 12.1 mmol) with N-chlorosulfonyl isocyanate (CSI) (99.28 mL,
160.8 mmol) in methylene chloride (100 mL) at room temperature for 4 h, and
then DMF (348 mL) was added. The mixture was stirred again for 15 h and
then hydrolyed with water (100 mL). The product was purified by silica-gel
column chromatography using toluene as eluent, yielding a yellow solid
(5.15 g, 43%).
A hexane solution of butyllithium was added to a THF solution of
diisopropylamine at 2788C under a nitrogen atmosphere to give lithium
diisopropylamine (LDA). DCN3T (3.0 g, 10.05 mmol) was added to a THF
solution (50 mL) of LDA (40.20 mmol) at 2788C and the solution stirred
for 1 h. Excess dry ice was added to the solution, and the resulting
mixture was stirred for 2 h. The solution was allowed to warm to room temp-
erature, and aqueous hydrochloric acid was added. After stirring for 5 h, the
resulting solid was collected and washed with hot acetonitrile to give 5,500-
dicyano-2,20 : 50,200-terthiophene-4,400-dicarboxylic acid (yield 58% based on
DCN3T).

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P. Liu, M. Liu, and W. Deng
A dichloromethane solution (100 mL) of 5,500-dicyano-2,20 : 50,200-terthio-
phene-4,400-dicarboxylic acid (2.0 g, 5.17 mmol), and SOCl2 (1.23 g,
10.34 mmol) was heated at reflux for 8 h. After the solvent was removed
under reduced pressure, the resulting solid was added to a THF solution
(100 mL) of stearylamine (2.79 g, 10.34 mmol) in the presence of triethyl-
amine (2.5 mL) at 08C, and the solution was stirred for 5 h at 08C. The
solvent was removed under reduced pressure to give DNC18DCN3T. The
product was purified by silica-gel column chromatography using chloroform
as the eluent (yield 60% based on 5,500-dicyano-2,20 : 50,200-terthiophene-
4,400-dicarboxylic acid). 1H NMR (400 MHz, THF-d8): d (ppm) ¼ 7.32
(s, 2H, ArH), 7.28 (t, 2H, NH), 7.25 (s, 2H, ArH), 3.33 (dt, 4H, stearyl
a-CH2), 1.58 (tt, 4H, stearl b-CH2), 1.45–1.21 (m, 60H, stearyl CH2), 0.88
(t, 6H, CH3). IR (KBr, cm21): 3303 (nN–H), 2957, 2923, 2857 (nC–H), 1625
(nC55O). MS(EI): m/z 889(Mþ). Elemental analysis: found C, 69.95; H,
9.33; N, 6.22; S, 10.86%; calcd. for C52H80N4S3O2 C, 70.22; H, 9.07; N,
6.30; S, 10.81%.
4.1.2. Synthesis of N,N0-Distearyl-5,500-dipropyl -2,20 : 50,200-
terthiophene-4,400-dicarboxamide (DNC18DP3T)
5,500-Dipropyl-2,20 : 50,200-terthiophene (DP3T) was prepared by a Grignard
coupling reaction of DBr3T with bromomagnesiumpropyl in ether at
refluxing temperature (yield 75%).
DP3T (3.0 g, 9.02 mmol) was added to a THF solution (50 mL) of LDA
(36.08 mmol) at 2788C, and the solution was stirred for 1 h. Excess dry ice
was added to the solution, and the resulting mixture was stirred for 2 h. The
solution was allowed to warm to room temperature, and aqueous hydrochloric
acid was added. After stirring for 5 h, the resulting solid was collected and
washed with hot acetonitrile to give 5,500-dipropyl-2,20 : 50,200-terthiophene-
4,400-dicarboxylic acid (yield 73% based on DP3T).
A dichloromethane solution (100 mL) of 5,500-dipropyl-2,20 : 50,200-terthio-
phene-4,400-dicarboxylic acid (2.0 g, 4.76 mmol) and SOCl2 (1.13 g,
9.52 mmol) was heated at reflux for 8 h. After the solvent was removed
under reduced pressure, the resulting solid was added to a THF solution
(100 mL) of stearylamine (2.56 g, 9.52 mmol) in the presence of triethylamine
(2.5 mL) at 08C, and the solution was stirred for 5 h at 08C. The solvent was
removed under reduced pressure to give DNC18DP3T. The product was
purified by silica-gel column chromatography using chloroform as the
eluent (yield 65% based on 5,500-dipropyl-2,20 : 50,200-terthiophene-4,400-dicar-
boxylic acid). 1H NMR (400 MHz, THF-d8): d (ppm) ¼ 7.41 (t, 2H, NH), 7.36
(s, 2H, ArH), 7.27 (s, 2H, ArH), 3.36 (dt, 4H, stearyl a-CH2), 2.80 (t, 4H,
propyl a-CH2), 1.63 (tt, 4H, stearyl b-CH2), 1.55 (tt, 4H, propyl b-CH2),
1.43–1.21 (m, 60H, stearyl CH2), 0.88 (t, 12H, CH3). IR (KBr, cm21):
3311 (nN–H), 2958, 2913, 2853 (nC–H), 1619 (nC55O). MS(EI): m/z 923

Novel Terthiophene Derivatives
691
(Mþ). Elemental analysis: found C, 72.98; H, 10.45; N, 2.85; S, 10.35%; calc.
for C56H94N2S3O2 C, 72.83; H, 10.26; N, 3.03; S, 10.41%.
4.2. Characterization
Differential scanning calorimetry (DSC) was performed using a SSC/5200
(SEIKO I&E) calorimeter. Polarizing microscopy was carried out with an
OPTI-PHOT X2 (Nikon) microscope, fitted with a TH-600PM hot stage
(Linkam) and crossed polarizers.
ACKNOWLEDGMENTS
This work was supported by the Ministry of Education of the People’s
Republic of China (Research Funds for Chinese Scholars Returning from
Abroad) and the Ministry of Science and Technology of the People’s
Republic of China (National Key Program for Basic Research, 2001-
CCA03500). We also thank the Natural Science Foundation of Guangdong
(04105931) and Guangzhou for financial support.
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