Tolane liquid crystals with piperidine, 3,3,4,4,5,5-hexafluoropiperidine as end group: Synthesis and properties

Article abstract of DOI:10.1016/j.molliq.2015.01.043

A series of new tolane liquid crystals with piperidine and 3,3,4,4,5,5-hexafluoropiperidine as their terminal groups were synthesized via Sonagashira reaction by using Pd(PPh₃)₂Cl₂/CuI as the catalyst. Their structures were modified by varying the terminal N-heterocycles and/or the length of the alkyl/alkoxy chains on the benzene ring. Most of these new compounds exhibit Smectic B or G mesophases, good thermal stabilities and high clearing points. The molecule C₂H₅O6F with 3,3,4,4,5,5-hexafluoropiperidine as the end group has a broader HOMO-LUMO energy gap and higher oxidation potential than piperidine derivative C₂H₅O6H. The result indicates that the oxidation resistance of the tolane liquid crystals was improved by introducing the terminal fluorinated piperidine.

Full text of DOI:10.1016/j.molliq.2015.01.043

Journal of Molecular Liquids 204 (2015) 84–89
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Tolane liquid crystals with piperidine, 3,3,4,4,5,5-hexafluoropiperidine
as end group: Synthesis and properties
a
a
a
a
a
a
Dezhao Zhu , Fengying Hong , Hong Zhang , Zhengce Xia , Hongxiang Wu , Qiwei Jiang ,
a
a,b,
Hui Wang , Zhuo Zeng
College of Chemistry & Environment South China Normal University, Guangzhou 510006, China
⁎
a
b
Key Laboratory of Organofluorine Chemistry Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of new tolane liquid crystals with piperidine and 3,3,4,4,5,5-hexafluoropiperidine as their terminal
Received 7 November 2014
Received in revised form 21 January 2015
Accepted 27 January 2015
Available online 28 January 2015
3 2 2
groups were synthesized via Sonagashira reaction by using Pd(PPh ) Cl /CuI as the catalyst. Their structures
were modified by varying the terminal N-heterocycles and/or the length of the alkyl/alkoxy chains on the ben-
zene ring. Most of these new compounds exhibit Smectic B or G mesophases, good thermal stabilities and high
clearing points. The molecule C
HOMO–LUMO energy gap and higher oxidation potential than piperidine derivative C
2
H
5
O6F with 3,3,4,4,5,5-hexafluoropiperidine as the end group has a broader
O6H. The result indi-
2 5
H
Keywords:
Fluorine
Liquid crystals
Properties
cates that the oxidation resistance of the tolane liquid crystals was improved by introducing the terminal fluori-
nated piperidine.
© 2015 Elsevier B.V. All rights reserved.
Heterocycles
Mesophases
1
. Introduction
temperature range of the nematic phase was reduced. Compound
(
b) with cyano substituent in the terminal has higher viscosity than its
Liquid crystals (LCs) as soft materials have attracted considerable at-
fluorine derivative, and the cyano group usually attracts ions which con-
fers a low resistivity (voltage holding ratio) to the liquid crystal material
due to the high polarity and high polarizability. Based on this fact, the
liquid crystal with cyano substituent can't completely satisfy the re-
quired characteristics for the AM-TFT displays based on active matrix
(TFT) [17].
The shortcoming mentioned above can be overcome by introducing
fluorinated heterocycle as terminal group. We have a continuing inter-
est in fluorinated N, O-heterocycles for new building blocks in high per-
formance liquid crystal materials [18]. The four features of tolane-type
liquid crystals with 3,3,4,4,5,5-hexafluoropiperidine as the end group
that make them attractive candidates for further investigation include
the following: a) the introduction of 3,3,4,4,5,5-hexafluoropiperidine
enhances the length to breadth ration of molecule, which favors the for-
mation of liquid crystal phase; b) replacement of the cyano group with
polyfluoroalkyl group in the terminal location improved the resistivity;
c) the polyfluoroalkyl group with high polarizability can enhance the
overall polarizability anisotropy and hence provide high clearing points;
d) in particular, fluorinated N-heterocycle with a strong electron-
withdrawing group can impart novel characteristics.
tention from both academic and industrial researchers in terms of their
unique chemical and physical properties [1–4]. Especially, the super
twisted nematic liquid crystal (STN-LCD) product was widely used in
optical devices such as vehicles, cell phones and PDAs that carry intel-
lectualization alphanumeric display terminals [5–7]. High optical an-
isotropy (△n) of the tolane liquid crystal composition improves the
efficiency of light modulation and brightness, and it serves to widen
the viewing angle in the STN-LCD screen. The tolane liquid crystal pos-
sesses the terminal fluoro substituents which enhance the dielectric an-
isotropy, and confer a low melting point, low threshold voltage and a
high N–I value [5,8–14].
Polar liquid crystal compounds, particularly fluorinated tolane, have
been investigated as possible candidates in the development of new
STN-LCD materials. Some of these reported liquid crystal molecules
are shown in Scheme 1 [15,16].
These commercially available tolane-type liquid crystals with a
mono, difluoro or cyano group as a substituent have large birefringence
values and dielectric anisotropy. However, compound (a) has no liquid
crystal phase, and when it is added to a liquid crystal composition, the
Therefore, in this work, we report the synthesis and properties of
some new tolane-type liquid crystals with piperidine, 3,3,4,4,5,5-
hexafluoropiperidine as the end group. In an effort to establish the im-
pact of different N-heterocycle groups on the physical and chemical
properties of liquid crystal.
⁎
Corresponding author at: College of Chemistry & Environment South China Normal
University, Guangzhou 510006, China.
E-mail address: zhuoz@scnu.edu.cn (Z. Zeng).
http://dx.doi.org/10.1016/j.molliq.2015.01.043
0167-7322/© 2015 Elsevier B.V. All rights reserved.

D. Zhu et al. / Journal of Molecular Liquids 204 (2015) 84–89
85
2.2. Liquid crystalline properties
The new compounds were investigated for their potential liquid
crystalline properties by a combination of hot stage polarizing optical
microscopy (POM) and differential scanning calorimetry (DSC). Their
transition temperatures, mesophase morphology were modified by
varying the terminal N-heterocycle and/or alkyl substituents on the
benzene ring. The assignment of the mesophases was made based on
their optical texture, which are presented in Fig. 1.
Scheme 1. Structures of some typical fluorinated tolane-based Liquid Crystals.
2
. Results and discussion
The new compounds containing piperidine as the end group dis-
play good liquid crystal properties. The transition temperatures and
mesophase behaviors for the liquid crystals are shown in Table 1.
The structure of the N-heterocycles and the nature of the alkyl sub-
stituent have a strong influence on mesophase behaviors. When the
substituent is C H , CH O or C H O and the N-heterocycle is piperidine,
liquid crystal compounds, C H 6H, CH O6H, C H O6H, display the
2 5 3 2 5
mosaic texture of the SmB mesophase. Changing the length of the sub-
stituent from ethyl to n-pentyl gives rise to a decrease in ordered ar-
2
.1. Synthesis
Piperidine-,3,3,4,4,5,5-hexafluoropiperidine-based tolan liquid crys-
tals (C
5 2 5 2 5 3 5 2 5 2 5
H116F, C H 6F, C H O6F, CH O6F, C H116H, C H 6H, C H O6H,
CH O6H) were synthesized as shown in Scheme 2. Details of the synthe-
sis and characterization of the materials are given in the Supplementary
data.
3
2
5
3
2 5
Three synthetic routes for tolan-type liquid crystals have been de-
scribed previously. These include the Fritsch–Buttenberg–Wiechell rear-
rangement [19], the 1,2-dibromo-1,2-diarylethane dehydrobromination
reaction [20], and the Sonogashira coupling reaction [21]. The
Sonogashira coupling reaction has been extensively used in recent
years. The aryl iodides were reacted with terminal acetylenes under the
Sonogashira coupling reaction condition to give a series of tolane in
high yield.
Two synthetic protocols for preparation N-heterocyclic tolan-type
liquid crystals have been employed in this article. In synthetic routine
one, a) the key intermediate 4-amino-4′-pentyldiphenylacetylene (3)
was synthesized by 4-iodobenzenamine and 4-pentyl phenylacetylene
under the Sonogashira coupling reaction condition in high yield. The
trifluoromethanesulfonic acid alkyl or fluoroalkyldily ester (1) or (2)
has been synthesized in our previous report [18a]. Upon cyclization of
the 4-amino-4′-pentyldiphenylacetylene with (2) in ethanol using
rangement and the C H116H shows a typical nematic phase.
5
The fluorinated N-heterocycle also plays a crucial role in determin-
ing the mesophase behaviors. Comparing with the piperidine com-
pounds which show SmB mesophase, the compounds with 3,3,4,4,5,5-
hexafluoropiperidine, C H 6F, C H 6F, CH O6H and C H O6H, have
5
11
2
5
3
2
5
the mosaic texture of the SmG mesophase. It can be seen that the
polar character of the liquid crystals increases markedly by the intro-
duction of a fluorinated heterocycle in the end, and the strong H…F
inter, or intramolecular hydrogen bond favors the formation of the
side hexatic SmG mesophase. e.g., C H O6H (Cr 154.5 °C SmB
2
5
173.5 °C), C H O6F (Cr 150.9 °C SmG 156.1 °C).
2
5
2.3. Thermal stability
Et
3
N as a base at 90 °C for 24 h, there is no desired product (4), which
Thermal stabilities, which range from 289 °C to 343 °C and de-
pend on the N-heterocycle and the alkyl chain substituent, were de-
termined by thermal gravimetric analysis (TGA). The decomposition
temperatures of the new compounds are shown in Table 1, the cor-
relation thermal stability of the new compounds is shown in Fig. 3.
The decomposition temperatures were higher than the clearing
points for these compounds. In general, the compounds with alkoxyl
group as the substituent are thermally less stable than the com-
was observed by TLC. The strong P–π conjugation effect between the
amino group and diphenylacetylene unit results in the decrease of the
nucleophilicity of the amino group. In synthetic routine two, b) first,
there was cyclization of trifluoromethanesulfonic acid alkyl or
fluoroalkyldily esters with 4-iodobenzenamine in ethanol using Et
as a base at 90 °C for 24 h to give aryl iodides 6H or 6F. The compound
H or 6F further reacted with alkyl substituted phenyl acetylene in the
CH CN by using Pd(PPh Cl /CuI as the catalyst to yield the new
3
N
6
3
3
)
2
2
pounds with alkyl group as the substituent. e.g., C
CH O6H, at T 317 °C and T 289 °C, while C 6H, C
335 °C and T 343 °C.
2
H
H
5
O6H and
11 O6H, at
piperidine- or 3,3,4,4,5,5-hexafluoropiperidine-based tolan liquid crys-
tals, R6H or R6F, in 85–90% yield.
3
d
d
2 5
H
5
T
d
d
Scheme 2. Synthesis of the N-heterocycles tolan-type liquid crystals.

86
D. Zhu et al. / Journal of Molecular Liquids 204 (2015) 84–89
2 5 5 3
Fig. 1. Optical texture (a) for C H O6H the mosaic texture of SmB mesophase at 169.1 °C; (b) for C H116H nematic phase upon cooling to 77.2 °C; and (c) for CH O6F the mosaic texture of
SmG mesophase at 150 °C.
The terminal N-heterocycle also influences the thermal stability, for
example, changing the terminal group from piperidine to 3,3,4,4,5,5-
hexafluoropiperidine, gives rise to a decrease in thermal stability,
2.5. Electrochemical properties
The oxidation reduction potential is a very important physical prop-
erty for liquid crystal materials. When an external electric field is ap-
plied to the liquid crystal material, a liquid crystal molecule forms a
permanent dipole and it can be influenced by an electric field. The elec-
e.g., C
5
H
116H and C
2
H
5
6H T
d 5
at 343 °C and 335 °C, while C H116F,
C H
2
5
6F, at T
d
327 °C and T
d
314 °C, respectively.
trochemical C
voltammetry by using C
solution. The data of cyclic voltammetry of C
tested, curve a represented the result for blank solution and curve b de-
scribed the result for the sample in 0.1 mol/L TBAPF /DMF solution in
Fig. 4. It revealed that oxidation potential of C O6F is 1.205 V, but
O6H is 0.823 V. The results show that the electron-withdrawing
2
H
5
O6H and C
2
H
5
O6F potentials were measured by cyclic
O6H or C O6F in 0.1 mol/L TBAPF /DMF
O6H, C O6F were
2
.4. Theoretical study
H
2 5
H
2 5
6
2
H
5
2 5
H
The geometry optimization and frontier orbital distributions of the
O6H, C O6F structures were performed using density functional
C
2
H
5
H
2 5
6
theory (DFT) Becke's three-parameter hybrid function with the non-
local correlation of Lee–Yang–Parr (B3LYP) method in gas phase [22].
The corresponding frequency analyses were computed at the same
level of theory to characterize them as minima (no imaginary frequen-
cies) with the help of Gaussian03 (Revision D.01) suite of programs
2 5
H
2 5
C H
polyfluoroalkyl substituent at the terminal of piperidine ring improve
the oxidation resistance.
[
23]. All of above calculations used a 6-31+G basis set. The computed
3. Conclusion
structures were visualized using the GaussView program [24].
Based on the theoretical calculations six-membered-ring piperdine
and 3,3,4,4,5,5-hexafluoropiperidine have two different conformations,
chair and boat form, the molecular total energy of chair form is lower
than that of boat form by approximately 14.70 kJ/mol, 18.75 kJ/mol
A series of new tolane liquid crystals with piperidine and 3,3,4,4,5,5-
hexafluoropiperidine as the end group were synthesized. Their melting
points, decomposition temperatures, mesophase behaviors and oxida-
tion potential were measured. The properties of these liquid crystals
can be adjusted by using different heterocycles. When piperidine was
used as the terminal group, they display the mosaic texture of SmB
mesophase. Using longer alkyl n-C H11 as the substituent gives the ap-
5
propriate length to width ratio, which favored the formation and stabil-
ity of the nematic phase. The compounds with the corresponding
for C
2
H
5
O6H and C
2 5
H O6F (1 a.u. = 2625.51 kJ/mol). Each of
the two CF
2
groups in the terminal 3,3,4,4,5,5-hexafluoropiperidine
adopts the staggered conformations; the staggered form is lower
in energy which is propitious to the formation and stability of
mesomorphism (Fig. 2).
As shown in Table 2, the introduction of fluorinated N-heterocycle
can increase the dipole moment significantly. For example, the dipole
3
,3,4,4,5,5-hexafluoropiperidine have the mosaic texture of the SmG
mesophase. Based on theoretical calculations, these new molecules
with strong electron-withdrawing polyfluoroalkyl as the end group
have a broader HOMO–LUMO energy gap and a higher dipole moment
2 5 2 5
moment of C H O6F is 5.6770 while that of C H O6H is only 2.1775.
Furthermore, the functional theory (DFT) calculations established
that the introduction of strong electron-withdrawing 3,3,4,4,5,5-
hexafluoropiperidine increased the HOMO–LUMO energy gap [25].
than the corresponding piperidine compounds. The C
2
H
5
O6F exhibits
/DMF so-
higher oxidation potential than C O6H in 0.1 mol/L TBAPF
H
2 5
6
For instance, the HOMO–LUMO gap of C
2
H
5
O6F is 4.177 eV, but
lution which is measured by cyclic voltammetry. These results make
them as a candidate in the development of new tolane-type liquid crys-
talline materials.
2 5
that of C H O6H is 4.024 (Table 3; Fig. 3).
Table 1
4. Experimental
Thermal behavior of the new compounds.
Transition temperatures/°Ca
Td/°Cb
4.1. General considerations
Compd
C
C
C
5
2
2
H
H
H
116F
Cr 101.1 SmG 107.3
Cr 100.3 SmG 103.4
Cr 150.9 SmG 156.1
Cr 154.3 SmG 163.0
Cr 83.6 N 87.2
Cr 127.4 SmB 133.5
Cr 154.5 SmB 173.5
Cr 149.0 SmB 154.2
Iso
Iso
Iso
Iso
Iso
Iso
Iso
Iso
327
314
308
318
343
335
317
289
All the reagents used were analytical reagents purchased from com-
mercial sources and used as received. H and F were recorded on a
400 MHz nuclear magnetic resonance spectrometer operating at 400
5
6F
1
19
5
O6F
CH
3
O6F
C
C
C
5
2
2
H
H
H
116H
and 376 MHz respectively. Chemical shifts were reported relative to
5
6H
O6H
Si for 1H, and CCl
19
Me F for F. The solvent was either CDCl unless
4
3
3
5
otherwise specified. Thermogravimetric analysis (TGA) measurements
3
CH O6H
−
1
were performed at a heating rate of 10 °C min
with a Netzsch
a
Transition temperature was determined by DSC (peak temperature, first heating scan,
−
1
STA409PC (Germany) instrument. The DSC was recorded at a scan
5
K/min ) and confirmed by POM. Cr = crystalline solid, SmB = smectic B, SmG =
−
1
rate of 2 °C min on a Netzsch DSC200PC apparatus. Optical micro-
graphs were observed with a polarizing optical microscope (POM)
smectic G, Iso = isotropic liquid state.
b
Decomposition temperature.

D. Zhu et al. / Journal of Molecular Liquids 204 (2015) 84–89
87
2 5 2 5
Fig. 2. The optimized geometry of C H O6H, C H O6F.
(
Nikon LINKAM-THMSE600) equipped with a heating plate (HCS601).
and dried over anhydrous sodium sulfate. The solvent was removed
under vacuum to give trifluoromethanesulfonic acid 1,5-penanedily
ester or trifluoromethanesulfonic acid 2,2,3,3,4,4-hexafluoro-1,5-
penanedily ester.
All the electrochemical measurements were performed on a CHI 660E
electrochemical workstation (CH Instruments, Shanghai Chenhua In-
strument Corporation, China, http://chi.instrument.com.cn). The GCE
was used as the working electrode and the SCE and Pt wire were used
as the reference and counter electrodes, respectively.
4.3. Procedure for the preparation of 1-(4-iodophenyl)piperidine (6H)
Trifluoromethanesulfonic acid 1,5-penanediyl ester 1 (1 mmol), 4-
4
1
.2. General procedure for the preparation of trifluoromethanesulfonic acid
,5-penanediyl ester (1) and trifluoromethanesulfonic acid 2,2,3,3,4,4-
3
iodobenzenamine (1 mmol), and Et N (2 mL) in 3 mL ethanol were
hexafluoro-1,5-penanedily ester (2)
placed in a Pyrex glass tube, sealed, heated at 90 °C for 24 h and then
allowed to cool to room temperature. The organic solvent was removed
under reduced pressure and 50 mL of dichloromethane was added to
the residue and then washed with water (3 × 30 mL), brine and dried
(Na SO ). The solvent was removed under vacuum and the crude prod-
2 4
uct was purified by chromatography on silica gel to give the pale yellow
1
,5-Penanediol,
1 mmol), pyridine (3 mmol) and dichloromethane (20 mL) were
stirred at 0 °C. After 30 min, trifluoromethanesulfonic anhydride
2.5 mmol) in 10 mL dichloromethane was slowly added over 1 h.
The mixture was stirred for 12 h, then washed with water (3 × 30 mL),
or
2,2,3,3,4,4-hexafluoro-1,5-penanediol
(
(
liquid, yield 78%.
2 5 2 5
Fig. 3. The frontier orbitals of C H O6H, C H O6F calculated at the B3LYP/6-31+G level. Molecular structures of the model compounds are indicated on the top of the figure. Upper orbitals
indicate LUMOs, and the bottom orbitals indicate HOMOs for the model compounds.

88
D. Zhu et al. / Journal of Molecular Liquids 204 (2015) 84–89
Table 2
2 5 2 5
Geometrical parameters of C H O6H, C H O6F calculated by Gaussian03.
1
Compd
Dihedral angles (°)
Bond angles (°)
Bond lengths (10− nm)
Dipole/Debye
2.1715
C
2
5
H O6H
C6\C1\N20\C11
C1\N20\C11\C13
C5\C4\C27\C28
−40.97
150.28
177.53
C1\N20\C11
C2\N20\C12
C1\N20\C13
C1\N20\C19
C1\N20\C16
120.32
120.16
147.50
178.41
148.16
N20\C12
C12\C16
C16\C19
C19\C13
C13\C11
C11\N20
N20\C12
C12\C16
C16\C19
C19\C13
C13\C11
C11\N20
1.471
1.540
1.538
1.539
1.526
1.477
1.456
1.527
1.537
1.537
1.530
1.458
C
2
5
H O6F
C6\C1\N20\C11
C1\N20\C11\C13
C5\C4\C27\C28
−44.62
−107.91
95.17
C1\N20\C11
C1\N20\C12
C1\N20\C13
C1\N20\C19
C1\N20\C16
121.86
122.40
125.48
140.66
125.91
5.6770
Table 3
Energy levels determined by DFT calculations for HOMO, LUMO and the HOMO–LUMO
product was purified by chromatography on silica gel to give the target
product.
2 5 2 5
gap of compounds C H O6H and C H O6F.
3
,3,4,4,5,5-Hexafluoro-1-(4-((4-pentylphenyl)ethynyl)phenyl)pi-
1
Compd
HOMO (ev)
LUMO (ev)
E
HL (ev)
peridine (C
dd, J = 17.3, 8.5 Hz, 4H), 7.17 (d, J = 8.0 Hz, 2H), 6.93 (d, J = 8.8 Hz,
2H), 3.88–3.70 (m, 4H), 2.63 (t, J = 7.6 Hz, 2H), 1.69–1.60 (m, 2H),
.34 (dt, J = 5.7, 2.3 Hz, 4H), 0.91 (t, J = 6.8 Hz, 3H). 19F NMR
376 MHz, CDCl
5 3
H116F), yield 88%. H NMR (400 MHz, CDCl ) δ (ppm): 7.46
(
C
C
2
2
H
H
5
O6H
O6F
−4.727
−5.326
−0.703
−1.149
4.024
4.177
5
1
(
3
) δ (ppm): −123.62 (s 4 F), −139.28 (s 2F). MS (ESI)
4
.4. Procedure for the preparation of 3,3,4,4,5,5-hexafluoro-1-(4-
m/z 439. Anal.Calcd (%) for [C24
Found: C, 65.83; H, 5.32; N, 3.27.
23 6
H F N]: C, 65.60; H, 5.28; N, 3.19.
iodophenyl)piperidine (6F)
3
,3,4,4,5,5-Hexafluoro-1-(4-((4-ethylphenyl)ethynyl)phenyl)pi-
1
Trifluoromethanesulfonic acid 1,5-penanediyl ester 2 (1 mmol), 4-
2 5 3
peridine (C H 6F), yield 89%. H NMR (400 MHz, CDCl ) δ (ppm): 7.71–
iodobenzenamine (1 mmol), and Et
3
N (2 mL) in 3 mL ethanol were
7.33 (m, 4H), 7.17 (d, J = 7.2 Hz, 2H), 7.00–6.81 (m, 2H), 3.77 (s, 4H),
placed in a Pyrex glass tube, sealed, heated at 90 °C for 24 h and then
allowed to cool to room temperature. The organic solvent was removed
under reduced pressure and 50 mL of dichloromethane was added to
the residue and then washed with water (3 × 30 mL), and dried over an-
hydrous sodium sulfate. The solvent was removed under vacuum and
the crude product was purified by chromatography on silica gel to
give the pale yellow liquid,
2.66 (q, J = 7.1 Hz, 2H), 1.34–1.11 (m, 3H). 19F NMR (376 MHz,
CDCl ) δ (ppm): −123.81 (s 4F), −139.13 (s 2F). MS (ESI) m/z 397.
3
Anal.Calcd (%) for [C21
63.56; H, 4.34; N, 3.32.
17 6
H F N]: C, 63.48; H, 4.31; N, 3.52. Found: C,
3,3,4,4,5,5-Hexafluoro-1-(4-((4-ethoxyphenyl)ethynyl)phenyl)pi-
1
peridine (C
(dd, J = 8.4, 6.5 Hz, 4H), 6.97–6.81 (m, 4H), 4.05 (q, J = 7.0 Hz, 2H), 3.78
t, J = 10.0 Hz, 4H), 1.43 (t, J = 7.0 Hz, 3H). 19F NMR (376 MHz, CDCl
) δ
(ppm): −123.56 (s 4F), −139.34 (s 2F). MS (ESI) m/z 413. Anal.Calcd
(%) for [C21 NO]: C, 61.02; H, 4.15; N, 3.39. Found: C, 60.92; H,
.21; N, 3.38.
3,3,4,4,5,5-Hexafluoro-1-(4-((4-methoxyphenyl)ethynyl)phenyl)
2 5 3
H O6F), yield 87%. H NMR (400 MHz, CDCl ) δ (ppm): 7.44
(
3
4
.5. General procedure for the preparation of the piperidine-, 3,3,4,4,5,5-
hexafluoropiperidine-based tolan liquid crystals (R6H, R6F)
17 6
H F
4
To a stirred solution of 1-(4-iodophenyl)piperidine 6H or 3,3,4,4,5,5-
hexafluoro-1-(4-iodophenyl)piperidine 6F (1 mmol) and phenyl
acetylene (1.15 mmol) in dry acetonitrile (4 mL) under nitrogen
1
piperidine (CH
7.51–7.38 (m, 4H), 6.88 (dd, J = 11.3, 8.8 Hz, 4H), 3.83 (s, 3H), 3.77 (t,
J = 9.0 Hz, 4H). 19F NMR (376 MHz, CDCl
) δ (ppm): −123.56 (s 4 F),
139.30 (s 2F). MS (ESI) m/z 399. Anal.Calcd (%) for [C20 NO]: C,
60.15; H, 3.79; N, 3.51. Found: C, 59.91; H, 3.81; N, 3.45.
1-(4-((4-Pentylphenyl)ethynyl)phenyl)piperidine (C
89%. 1H NMR (400 MHz, CDCl
) δ (ppm): 7.40 (dd, J = 8.2, 5.4 Hz,
4H), 7.13 (d, J = 7.8 Hz, 2H), 6.86 (d, J = 8.4 Hz, 2H), 3.21 (t, J =
3 3
O6F), yield 88%. H NMR (400 MHz, CDCl ) δ (ppm):
3
was added CuI (0.05 mmol), and Et N (3 mmol) followed by Pd(PPh
3
)
3
Cl (0.05 mmol). The reaction mixture was stirred at 85 °C for 4 h and
2
−
15 6
H F
2
then allowed to cool to room temperature; the organic solvent was re-
moved under reduced pressure. 50 mL of dichloromethane was added
to the residue and then washed with water (3 × 30 mL), brine and
5
H116H), yield
3
2 4
dried (Na SO ). The solvent was removed under vacuum and the crude
Fig. 4. Cyclic voltammogram testing results in 0.1 mol/L TBAPF
6 2 5 2 5
/DMF solution for liquid crystals C H O6H (left) and C H O6H (right). (Initial E = −2 V, high E = −2 V, low E = −2 V, scan
rate = 0.02 V s− and temperature = 25 °C).
1

D. Zhu et al. / Journal of Molecular Liquids 204 (2015) 84–89
89
[
2] J.W. Goodby, V. Gortz, S.J. Cowling, G. Mackenzie, P. Martin, D. Plusquellec, T.
Benvegnu, P. Boullanger, D. Lafont, Y. Queneau, et al., Chem. Soc. Rev. 36 (2007)
5
4
.3 Hz, 4H), 2.59 (t, J = 7.8 Hz, 2H), 1.69–1.55 (m, 8H), 1.35–1.27 (m,
H), 0.89 (t, J = 6.7 Hz, 3H). MS (ESI) m/z 331. Anal.Calcd (%) for
1971–2032.
[
C
24
H
29N]: C, 86.96; H, 8.82; N, 4.23. Found: C, 86.89; H, 8.87; N, 4.19.
-(4-((4-Ethylphenyl)ethynyl)phenyl)piperidine (C 6H), yield
3
5%. H NMR (400 MHz, CDCl ) δ (ppm): 7.43 (t, J = 8.0 Hz, 4H), 7.18
[3] D. Demus, J. Goobdy, G.W. Gray, H.W. Spiess, V. Vill (Eds.), Handbook of Liquid Crys-
tals, Wiley-VCH, Weinheim, 1998.
[4] D. Pauluth, K. Tarumi, J. Mater. Chem. 14 (2004) 1219–1227.
1
2 5
H
1
8
(
(
[
5] K. Takatoha, A. Harimaa, Y. Kanamea, K. Shinoharaa, M. Akimotoa, Liq. Cryst. 39
d, J = 8.1 Hz, 2H), 6.90 (d, J = 8.0 Hz, 2H), 3.33–3.15 (m, 4H), 2.67
q, J = 7.6 Hz, 2H), 1.72 (s, 4H), 1.63 (q, J = 5.5 Hz, 2H), 1.26 (t, J =
(2012) 715–720.
[6] D. Pauluth, K. Tarumi, J. Mater. Chem. 14 (2004) 1219–1227.
[
[
7] H.S.J. Kwok, Appl. Phys. 80 (1996) 3687–3693.
8] A.V. Dubtsov, S.V. Pasechnik, D.V. Shmeliova, V.A. Tsvetkov, V.G. Chigrinov, Appl.
Phys. Lett. 94 (2009) 181910/1–181910/3.
7
.6 Hz, 3H). MS (ESI) m/z 289. Anal.Calcd (%) for [C21
H, 8.01; N, 4.84. Found: C, 86.77; H, 8.14; N, 4.82.
-(4-((4-Ethoxyphenyl)ethynyl)phenyl)piperidine (C
H23N]: C, 87.15;
1
2
H
5
O6H),
) δ (ppm): 7.40 (dd, J = 14.7,
.6 Hz, 4H), 6.84 (d, J = 8.7 Hz, 2H), 4.04 (q, J = 7.0 Hz, 4H), 3.20 (d,
J = 6.1 Hz, 4H), 1.58–1.50 (m, 6H), 1.41 (t, J = 7.0 Hz, 3H). MS (ESI)
[9] E. Bartmann, Adv. Mater. 8 (1996) 570–573.
[10] X.B. Chen, Z.W. An, L. Jia, A.A. Gao, Chin. J. Chem. 23 (2005) 970–976.
11] S.T. Wu, C.S. Hsu, Y.N. Chen, S.F. Wang, Appl. Phys. Lett. 61 (1992) 2275–2277.
12] S.H. Simpson, R.M. Richardson, S. Hanna, Chem. Phys. 127 (2007) 104901/
1–104901/14.
1
yield 88%. H NMR (400 MHz, CDCl
3
[
[
8
[
13] Q. Song, S. Gauza, H. Xianyu, S.T. Wu, Y.M. Liao, C.Y. Chang, C.S. Hsu, Liq. Cryst. 37
m/z 305. Anal.Calcd (%) for [C21
Found: C, 82.31; H, 7.54; N, 4.04.
H23N]: C, 82.58; H, 7.59; N, 4.59.
(2010) 139–147.
[
14] C. Sekine, N. Konya, M. Minai, K. Fujisawa, Liq. Cryst. 28 (2001) 1361–1367.
1
-(4-((4-Methoxyphenyl)ethynyl)phenyl)piperidine (CH
3
O6H),
) δ (ppm): 7.47–7.34 (m, 4H),
.85 (dd, J = 9.0, 2.4 Hz, 4H), 3.81 (s, 3H), 3.25–3.17 (m, 4H), 1.79–
.67 (m, 4H), 1.63–1.47 (m, 2H). MS (ESI) m/z 291. Anal.Calcd (%) for
21N]: C, 82.44; H, 7.26; N, 4.81. Found: C, 82.40; H, 7.19; N, 4.67.
[15] S.T. Wu, C.S. Hsu, Y.N. Chen, S.R. Wang, S.H. Lung, Opt. Eng. 32 (1993) 1792–1797.
[16] Kuryama, T.; Ogawa, H.; Takeuchi, K.; Nakada, H.; Fujisawa, N. JpPatent. JP
1
yield 89%. H NMR (400 MHz, CDCl
3
08110515, 1996.
6
1
[
17] (a) P. Kirsch, M. Bremer, Angew. Chem. Int. Ed. 14 (2004) 1219;
(b) V.F. Petrov, Liq. Cryst. 19 (1995) 729;
(
c) P. Kirsch, M. Bremer, M. Heckmeier, K. Tarumi, Angew. Chem. Int. Ed. 38 (1999)
989;
d) K. Tarumi, M. Bremer, T. Geelhaar, Annu. Rev. Mater. Sci. 27 (1997) 423.
[C
20
H
1
(
Acknowledgments
[18] (a) W.W. Cao, P.L. Liu, H.R. Chen, Y.H. Zhu, R.H. Chen, Q.F. Zhou, Z. Zeng, Chin. J.
Chem. 31 (2013) 933–938;
(
b) P.L. Liu, H.R. Chen, S. Daniel, D.Y. Hang, L. Zhao, H. Wang, Z. Zeng, J. Fluor. Chem.
56 (2013) 327–332;
c) H.R. Chen, P.L. Liu, H.J. Li, S. Daniel, Z. Zeng, Tetrahedron 69 (2013) 5129–5135;
The authors gratefully acknowledge the support of National Natural
Science Foundation of China (21272080), Department of Science and
Technology, Guangdong Province (2010A020507001-76, 5300410,
FIPL-05-003) and The Scientific Research Foundation for the Returned
Overseas Chinese Scholars, State Education Ministry.
1
(
(d) H.R. Chen, P.L. Liu, H.J. Li, H. Zhang, S. Daniel, Z. Zeng, Eur. J. Org. Chem. (2013)
517–7527;
(
7
e) H.R. Chen, F.Y. Hong, G. Shao, D.Y. Hang, L. Zhao, Z. Zeng, Chem. Asian. J. (2014).
http://dx.doi.org/10.1002/asia.201402576.
[
19] T. Luu, Y. Morisaki, N. Cunningham, R.R.J. Tykwinski, Org. Chem. 72 (2007)
622–9629.
9
Appendix A. Supplementary data
[
[
20] J. Avraamides, A.J. Parker, Aust. J. Chem. 36 (1983) 1705–1717.
21] (a) M. Feuerstein, H. Doucet, M. Santelli, J. Mol. Catal. A Chem. 256 (2006) 75–84;
(b) J.H. Kim, D.H. Lee, B.H. Jun, Y.S. Lee, Tetrahedron Lett. 48 (2007) 7079–7084.
22] (a) D. Feller, J. Chem. Phys. 93 (1990) 579;
Differential scanning calorimeter (DSC) and thermogravimetric analy-
sis (TGA) figure for C5H116F, C2H56F, C2H5O6F, CH3O6F, C5H116H,
C2H56H, C2H5O6H, and CH3O6H, and Polarized Optical Microscopy
figure for C5H116F, C2H56F, C2H5O6F, CH3O6F, C5H116H, C2H56H,
C2H5O6H, and CH3O6H. Supplementary data to this article can be
found online at http://dx.doi.org/10.1016/j.molliq.2015.01.043.
[
(
(
b) A.D. Becke, J. Chem. Phys. 98 (1993) 5648;
c) C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785;
(d) P. Kirsch, M. Bremer, ChemPhysChem 11 (2010) 357.
23] Gaussian 03, Revision D.01, Gaussian, Inc., Wallingford CT, 2004.
24] R. Dennington, T. Keith, J. Millam, K. Eppinnett, W.L. Hovell, R. Gilliland, GaussView,
Version 3.09, Semichem, Inc. Shawnee Mission, 2003.
[
[
[
25] X. Wang, C.S. Vogel, F.W. Heinemann, P. Wasserscheid, K. Meyer, Cryst. Growth Des.
11 (2011) 1974–1988.
References
[1] J.W. Goodby, I.M. Saez, S.J. Cowling, V. Gortz, M. Draper, A.W. Hall, S. Sia, G. Cosquer,
S.E. Lee, E.P. Raynes, Angew. Chem. Int. Ed. 47 (2008) 2754–2787.