Synthesis, liquid crystal property and gelation ability of semi-fluorinated 4-alkoxyphenyl 4-alkoxybenzoates

Article abstract of DOI:10.1080/15421406.2016.1185570

This paper describes the synthesis and physico-chemical properties for 4-(4-perfluorohexylbutoxy)phenyl 4-alkoxybenzoate (compounds 1-n), and the results are compared with the corresponding hydrocarbon derivatives (compounds 2-n). Compounds 1-n show exclu

Full text of DOI:10.1080/15421406.2016.1185570

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Synthesis, liquid crystal property and gelation
ability of semi-fluorinated 4-alkoxyphenyl 4-
alkoxybenzoates
Banpeng Cao, Sana Hayashida, Yuki Morita & Hiroaki Okamoto
To cite this article: Banpeng Cao, Sana Hayashida, Yuki Morita & Hiroaki Okamoto (2016)
Synthesis, liquid crystal property and gelation ability of semi-fluorinated 4-alkoxyphenyl 4-
alkoxybenzoates, Molecular Crystals and Liquid Crystals, 632:1, 49-56
To link to this article: http://dx.doi.org/10.1080/15421406.2016.1185570
Published online: 17 Aug 2016.
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Date: 19 August 2016, At: 05:20

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –

http://dx.doi.org/./..
Synthesis, liquid crystal property and gelation ability of
semi-fluorinated -alkoxyphenyl -alkoxybenzoates
Banpeng Caoa,b, Sana Hayashida , Yuki Morita , and Hiroaki Okamoto
a
a
a
a
b
Graduate School of Science and Engineering, Yamaguchi University, Japan; Jiangxi Key Laboratory of Organic
Chemistry, Jiangxi Science and Technology Normal University, PR China
ABSTRACT
KEYWORDS
This paper describes the synthesis and physico-chemical properties
for 4-(4-perfluorohexylbutoxy)phenyl 4-alkoxybenzoate (compounds 1-
n), and the results are compared with the corresponding hydrocar-
bon derivatives (compounds 2-n). Compounds 1-n show exclusively a
smectic A (SmA) phase, where the SmA–isotropic phase transition tem-
peratures are 142°C for 1-1 and 147°C for 1-6. The SmA phase is charac-
terized using a polarized microscope and DSC measurements. Interest-
ingly, compound 1-6 forms gels in n-octane, ethanol, and aprotic polar
solvents such as acetonitrile and γ -butyrolactone, while compound 1-1
shows no-gelation ability. The n-octane gel is characterized by scanning
electron microscope (SEM) observation, showing nano-fibers assem-
bled with compound 1-6.
synthesis; smectic A phase;
organic gelators; organogels
Introduction
Self-assemble phenomena are of much attention, especially for their application to nanoma-
terials such as liquid crystal (LC) materials and organic gelators. [1–4] A lot of researches and
applications have been reported on the molecular structure and mechanism of the molecular
aggregation. Many LC materials have been reported up to now, where a rigid core and flex-
ible terminal alkyl chain(s) are indispensable for exhibiting a mesomorphic property. It has
been known that perfluoroalkyl group tends to induce smectic properties, probably due to
fluorophilic and/or fluorophobic interactions [5–10].
Recently, many organic gelators have been reported, however, new organic gelators were
often discovered accidentally, and the researches are devoted to understanding the relation-
ship between the molecular structures and the gelation ability. The aggregation of organic
gelators to fibrous network is driven by weak intermolecular interactions such as hydrogen
bonding, dipole-dipole, van der Waals and π-π interactions [1–2]. In fact, many organic gela-
tors reported are consist of two parts, that is, one is protic functional groups such as hydroxyl,
amino, and carboxyl groups, and the other is aprotic ones, bulk aromatic core and/or long
alkyl chains [11,12].
Several organic gelators having perfluoroalkyl chains were also prepared and it has been
clarified that the perfluoroalkyl chains affect the gelation ability differently from the alkyl
chains [13–15]. In our earlier papers, we have reported that 4-(2-perfluorooctyl)ethoxy and
CONTACT Hiroaki Okamoto
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
oka-moto@po.cc.yamaguchi-u.ac.jp
©

5
0
B. CAO ET AL.
Figure . Chemical structure for compounds 1-n.
4
-(2-perfluorooctyl)ethylthio group affect their mesomorphic properties and gelation ability
[
16,17]. Furthermore, we have also investigated some organic gelators having perfluoroalkyl
chains at the both terminal positions of the molecule [18,19].
This paper describes synthesis and physico-chemical properties of LC materials and
organic gelators, 4-(4-perfluorohexylbutoxy)phenyl 4-alkoxybenzoates (compounds 1-n)
and the corresponding hydrocarbon derivatives (4-decyloxyphenyl 4-alkoxybenzoates, com-
pounds 2-n) shown in Figure 1. The molecular characteristics are to incorporate neither protic
function group nor so long hydrocarbon chain. The chemical structure is simple, and simi-
lar to the conventional LC materials. The experimental results are discussed in terms of the
molecular structure.
Experimental
Materials
Compounds 1-n were synthesized according to scheme 1, where compounds 1-n and syn-
1
thetic intermediates were characterized by means of IR and H NMR spectra and the synthetic
procedures are as follows.
1-(Benzyloxy)-4-(but-3-enyloxy)benzene (3): To
a
suspended solution of 4-
benzyloxyphenol (20 g, 0.1 mol) and NaH (6.0 g, 0.15 mol) and catalytic amount of KI in
THF (50 ml) was added 4-bromobut-1-ene (20.25 g, 0.15 mol), and the mixture was refluxed
for 3 days. The reaction mixture was then cooled to room temperature, and quenched with
H O. The reaction mixture was extracted with ethyl acetate twice. The combined organic
2
layer was washed with brine, dried over anhydrous Na SO , and removed in vacuo. The
2
4
residue was purified by silica gel chromatography, and then recrystallized from ethanol to
give compound 3, as a colorless solid (7.0 g, yield: 27%), mp = 50–52°C.
1
IR and H NMR spectra for compound 3: IR (KBr disc) ν = 3083, 2983, 2945, 2906, 2862,
−1 1
1
6
508, and 1290 cm . H NMR (CDCl ) δ = 2.57 (2H, qd, J = 6.8, 1.2 Hz), 4.00 (2H, td, J =
3
.8, 0.8 Hz), 5.05 (2H, s), 5.15 (1H, d, J = 10.0 Hz), 5.21 (1H, d, J = 17.2 Hz), 5.90–6.00 (1H,
m), 6.88 (2H, d, J = 8.4 Hz), 6.95 (2H, d, J = 8.4 Hz,), and 7.34–7.48 (m, 5H), ppm.
1
-(Benzyloxy)-4-(3-iodo-4-perfluorohexylbutoxy)benzene (4): To a mixture of compound
(7.0 g, 27.5 mmol), sodium hydrogen carbonate (2.3 g, 27.5 mmol), and sodium hydrosulfite
4.8 g, 27.5 mmol) in a mixed solvent of CH CN (30 ml) and H O (20 ml) was added per-
3
(
3
2
fluorohexyl iodide (12.3 g, 27.5 mmol) and the reaction mixture was stirred under shielded
light for overnight. The reaction mixture was diluted with ethyl acetate and washed with

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
51
Scheme . Synthetic scheme for compounds 1-n.
H O twice, dried over anhydrous MgSO , and the solvent was removed in vacuo. The residue
2
4
was recrystallized from ethanol to give compound 4, as a colorless solid (11.2 g, yield: 58%),
mp = 68–72°C. Compound 4 has a mesomorphic property and the details will be published
elsewhere.
1
−1
1
IR and H NMR spectra for compound 4: IR (KBr disc) ν = 1512 and 1242 cm . H NMR
(
(
CDCl ) δ = 2.46–2.60 (2H, m), 3.96 (2H, t, J = 6.7 Hz), 5.01 (2H, s), 5.09–5.18 (2H, m), 5.91
3
1H, m), 6.84 (2H, d, J = 8.4 Hz), 6.90 (2H, d, J = 8.4 Hz), and 7.32–7.42 (5H, m) ppm.
1
-(Benzyloxy)-4-(4-perfluorohexylbutoxy)benzene (5): To a solution of compound 4
(
11.2 g, 16 mmol) in THF (100 ml) was added LiAlH (1.2 g, 32 mmol) portionwise, and
4
the reaction mixture was stirred overnight. The reaction mixture was quenched with aque-
ous ammonium chloride and extracted with ethyl acetate twice. The combined organic layer
was washed with brine, dried over anhydrous MgSO , and the solvent was removed in vacuo.
4
The residue was purified by silica gel chromatography, and then recrystallized from ethanol
to give compound 5, as a colorless solid (3.6 g, yield: 39%), mp = 68–77°C. Compound 5 has
a mesomorphic property and the details will be published elsewhere.
1
−1
1
IR and H NMR spectra for compound 5: IR (KBr disc) ν = 1512 and 1242 cm . H NMR
(
(
CDCl ) δ = 1.79–1.97 (4H, m), 2.09–2.20 (2H, m), 3.94 (2H, t, J = 5.7 Hz), 5.01 (2H, s), 6.82
3
2H, d, J = 8.4 Hz), 6.90 (2H, d, J = 8.4 Hz), and 7.31–7.42 (5H, m) ppm.
4
-(4-Perfluorohexylbutoxy)phenol (6): Under hydrogen atmosphere, a mixture of com-
pound 5 (3.5 g, 6.2 mmol) and Pd-C (0.1 g) in a mixed solvent of ethanol (150 ml) and ethyl
acetate (150 ml) was vigorously stirred. After the reaction completed, the reaction mixture
was filtered and the filtrate was concentrated in vacuo. The residue was recrystallized from
toluene to give compound 6, as a colorless solid. (1.76 g, yield: 66%), mp = 72–74°C.
1
−1
IR and H NMR spectra for compound 6: IR (KBr disc) ν = 3460, 1512 and 1242 cm .
1
H NMR (CDCl ) δ = 1.78–1.88 (4H, m), 2.09–2.27 (2H, m), 3.94 (2H, t, J = 5.8 Hz), 4.77
3
(
1H, s), and 6.79 (4H, s) ppm.
General procedure to prepared compounds 1-n and 2-n: Compounds 1 and 2 were pre-
pared by conventional esterification (DCC method in THF) with compound 6 for compounds
or 4-decyloxyphenol for compounds 2 and the corresponding 4-alkoxybenzoic acid. The
1

5
2
B. CAO ET AL.
products were purified by silica gel chromatography, and then recrystallized from ethanol.
The spectra data are as follows.
1
−1
IR and H NMR spectra for compound 1-1: IR (KBr disc) ν = 1730, 1512, and 1201 cm .
1
H NMR (CDCl ) δ = 1.80–1.92 (4H, m), 2.12–2.23 (2H, m), 3.90 (3H, s), 4.01 (2H, t, J =
3
5
(
.8 Hz), 6.92 (2H, d, J = 8.5 Hz), 6.98 (2H, d J = 9.2 Hz), 7.11 (2H, d, J = 9.2 Hz), and 8.15
2H, d, J = 8.5 Hz) ppm.
1
−1
IR and H NMR spectra for compound 1-6: IR (KBr disc) ν = 1724, 1521, and 1202 cm .
1
H NMR (CDCl ) δ = 1.80–1.92 (4H, m), 2.12–2.23 (2H, m), 4.01 (2H, t, J = 5.8 Hz), 6.92
3
(
8
2H, d, J = 9.2 Hz), 6.98 (2H, d, J = 8.5 Hz), 7.11 (2H, d, J = 9.2 Hz), and 8.14 (2H, d, J =
.5 Hz) ppm.
Method
The transition temperatures and latent heats were determined using a Seiko SSC-5200 DSC,
where indium (99.9%) was used as a calibration standard (mp = 156.6°C, 28.4 J/g). The DSC
−1
thermogram was operated at a heating or cooling rate of 5°C min . The mesophases were
characterized using a Nikon POH polarizing microscope fitted with a Mettler thermo-control
system (FP-900). The homogeneous and homeotropic alignments between glass surfaces were
achieved by treatment of glass plates with polyimide (Tore SP-810) and cetyltrimethyl ammo-
1
nium bromide, respectively. H NMR spectra were measured using a JEOL JNM-LA500 spec-
trometer, where tetramethylsilane was used as an internal standard. IR spectra were recorded
with a Shimadzu Prestige-21 infrared spectrometer. The purity of the materials was checked
by HPLC and DSC thermograms using a ‘DSCPURITY’ program (SII instrument) instead of
elemental analysis. Gelation test were achieved as follows. A weighed compound was mixed
with an organic solvent in a micro tube (11 mmφ), and the mixture was heated until the
solid dissolved. The resulting solution was cooled to room temperature and then the gela-
tion was checked visually. When upon inversion of the glass tube no fluid ran down the walls
of the tube, we judged it “successful gel .” When the gel was formed, we evaluated quantita-
tively the gel forming ability by determining the MGC, which is the minimum concentration
of the compound necessary for gelation at room temperature. Scanning electron microscope
(SEM) images were obtained with a JEOL JSM-6510LA. The samples (i.e. xerogels) completely
removed the organic solvent in vacuo were prepared and then were coated with a platinum
vapor using autofinecoater (JEOL JFC-1600). A sample was observed by means of secondary
electron image (SEI) method operated acceleration voltage of 10 kV.
Results and discussion
Mesomorphic properties for compounds 1-n and 2-n were determined by means of DSC mea-
surements and polarized microscope observations.
The DSC thermogram for compound 1-1 shows endotherms at 96°C and 142°C corre-
sponding to the melting and mesophase–isotropic (I) phase transition phenomena on heat-
ing process. The molten material shows a small exotherm at 138°C due to the phase transition
during a cooling process. The formed texture is shown in Figure 2 (a). The polarized micro-
scope observation exhibited a typical focal conic fan texture on a homogeneus glass surface.
For compound 1-6, a similar focal conic fan texture was also observed on cooling process
as shown in Figure 2 (b). We can assume that the mesophases have an orthogonal alignment of
the molecule, since the mesophases showed a typical homeotropic texture (dark under a cross-
polarized microscope) on a homeotropic alignment glass surface. Therefore, the mesophases

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
53
Figure . Polarized micrographs for (a) compound 1- at °C and (b) compound 1- at °C.
was assigned to be a smectic A (SmA) phase. For compound 2-1, a schlieren texture was
observed on cooling process and the mesophase was assigned to be a nematic (N) phase as
shown in Figure 3.
The transition temperatures and latent heats for 1-n and the corresponding hydrocarbon
derivatives (compounds 2-n) are summarized in Table 1.
The latent heats for the SmA–I transition also support the characterization, where the value
−1
−1
for compound 1-1 was determined to be 5.2 kJ mol and that for 1-6 was 8.3 kJ mol . The
SmA–I transition temperatures for 1-n increase slightly on increasing the carbon number,
while the melting points decrease. The thermal stability of mesophase for compounds 1-n is
higher ca. 70°C than that for compounds 2-n, while melting point is slightly high, indicating
the thermal range of the mesophase for compounds 1-n are wider than that for compounds
2-n. The thermal tendency is frequently seen LC materials having a perfluoroalkyl chain
[
5].

5
4
B. CAO ET AL.
Figure . Polarized micrograph for compound 2- at °C.
Table . Transition temperatures for compounds 1-n and 2-n.
Transition temperatures (°C)
Latent heats (kJ mol 
−
)
Compounds
C
SmC
SmA
N
I
mp
SmC–N SmA–I N–I
1
-
•
•
•
•



—
—
—
(•
•
•
—
—


—
—
•
•
•
•
•
.
.
.
.
—
—
—
.
.
.
—
—
—
—
.
.
1
-
-
2
2


)
-

)
•
C, SmC, SmA, N, and I indicate crystal, smectic C, smectic A, nematic and isotropic phases, respectively. Parentheses indicate a
monotropic transition.
) Transition temperatures are cited from ref. [].
Interestingly, compound 1-6 formed a physical gel (i.e. thermo-reversible gel) in several
organic solvents as shown in Figure 4. Therefore, we carried out the gelation test of com-
pounds 1-n and 2-n in several organic solvents.
Table 2 shows the results of the gelation test for compounds 1-n and 2-n in several organic
solvents. Compound 1-6 formed gels in n-octane, ethanol, acetonitrile, and γ -butyrolactone
(
GBL), where the minimum gel concentrations were 3.5, 2.5, 5.0, and 4.5wt%, respectively.
On the other hand, compound 1-1 was precipitated in n-octane, ethanol, 1-octanol, propylene
carbonate, and GBL at 5wt%.
Figure . Photographs for physical gel (thermo-reversible gel); (a) sol state, (b) gel state.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
55
Table . Minimum gel concentration for compounds 1-n and 2-n.
Compounds (concentration, wt%) a)
Solvents
1-
1-
2-
2-
n-Octane
Toluene
Ethanol
P (.)
S (.)
P (.)
P (.)
S (.)
S (.)
P (.)
P (.)
G (.)
S (.)
G (.)
P (.)
S (.)
G (.)
P (.)
G (.)
P (.)
S (.)
P (.)
P (.)
S (.)
P (.)
P (.)
P (.)
P (.)
S (.)
P (.)
P (.)
S (.)
P (.)
P (.)
P (.)

-Octanol
AcOEt
Acetonitrile
b)
PC
c)
GBL
a)
b)
c)
G, S and P are gel, sol and precipitated states, respectively.
PC: Propylene carbonate
GBL: γ -Butyrolactone
On the other hand, compounds 2-1 and 2-6 were precipitated or soluble in the examined
solvents as shown in Table 2. These results indicate that both of a semi-perfluoroalkyl chain
and a subtle long alkyl chain in the molecular structure are indispensable to form the organic
gels.
Figures 5 shows a photograph of organic gels (GBL, acetonitrile, ethanol, and n-octane
gels) formed by compound 1-6 at room temperature on cooling from an isotropic liquid state,
and the gels are cloudy.
The gelation phenomena are also confirmed by means of scanning electron microscope
SEM) observation, and the result for a xerogel prepared from n-octane gel is shown in
(
Figure 6. It is apparent from the figure that the gel consists of several rod-like fibers aligned
to form the network structures with bundles with diameters of less μm order.
In conclusion, intermolecular interaction around the semi-perfluoroalkyl group acts an
impotant role for displaying the mesomorphic property and gelation ability. The terminal sub-
tle long alkoxy group is also indispensable for the gelation ability. The present results should
provide an important information for mesomorphic and gelation phenomena.
Further examination is now underway, and the results will be published elsewhere.
Figure . Photographs for organic gels formed by compound 1-; (a) γ -butyrolactone gel (.wt%), (b) ace-
tonitrile gel (.wt%), (c) ethanol gel (.wt%), (d) n-octane gel (.wt%).

5
6
B. CAO ET AL.
Figure . SEM image for xerogel prepared from n-octane gel (x,).
Acknowledgments
This work is supported by Electric technology research foundation of Chugoku, Kumagai foundation
for science and technology, and SEI group CSR foundation.
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