Synthesis and physico-chemical properties of 2-alkoxy- 6-[4-(2-perfluorohexyl)ethylthiophenyl]naphthalene

Article abstract of DOI:10.1080/15421406.2017.1289617

This paper describes the synthesis of and mesomorphic property and gelation ability for 2-Alkoxy- 6-[4-(2-perfluorohexyl)ethylthiophenyl]naphthalene (compounds 1-n). Compounds 1-n show exclusively a smectic A (SmA) phase, where the SmA–isotropic phase transition temperatures are 192°C for 1-1 and 171°C for 1-6. The SmA phase is characterized using a polarized microscope and DSC measurements. Interestingly, compounds 1-n form physical gels (thermo-reversible gels) in n-octane, ethanol, and aprotic polar solvents such as acetonitrile and γ-butyrolactone, where the sol-gel transition temperatures are 60°C for 1-1 and 80°C for 1-6. The propylene carbonate gel is characterized by scanning electron microscope (SEM) observation, showing nano-fibers assembled with compound 1-6.

Full text of DOI:10.1080/15421406.2017.1289617

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Synthesis and physico-chemical
properties of 2-alkoxy- 6-[4-(2-
perfluorohexyl)ethylthiophenyl]naphthalene
Tomohiro Yoshida, Asami Ohashi, Yuki Morita & Hiroaki Okamoto
To cite this article: Tomohiro Yoshida, Asami Ohashi, Yuki Morita & Hiroaki
Okamoto (2017) Synthesis and physico-chemical properties of 2-alkoxy- 6-[4-(2-
perfluorohexyl)ethylthiophenyl]naphthalene, Molecular Crystals and Liquid Crystals, 647:1,
299-306, DOI: 10.1080/15421406.2017.1289617
To link to this article: http://dx.doi.org/10.1080/15421406.2017.1289617
Published online: 23 May 2017.
Submit your article to this journal
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=gmcl20
Download by: [The UC San Diego Library]
Date: 24 May 2017, At: 00:33

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
http://dx.doi.org/./..
Synthesis and physico-chemical properties of -alkoxy-
-[-(-perfluorohexyl)ethylthiophenyl]naphthalene
Tomohiro Yoshidaa, Asami Ohashia,b, Yuki Moritaa, and Hiroaki Okamotoa
aGraduate School of Science and Engineering, Yamaguchi University, Japan; bAsahi kasei E-materials
Corporation, Japan
ABSTRACT
KEYWORDS
Synthesis; Smectic A phase;
Organic gelators; Organogels
This paper describes the synthesis of and mesomorphic property and
gelation ability for 2-Alkoxy- 6-[4-(2-perfluorohexyl)ethylthiophenyl]
naphthalene (compounds 1-n). Compounds 1-n show exclusively a
smectic A (SmA) phase, where the SmA–isotropic phase transition
temperatures are 192°C for 1-1 and 171°C for 1-6. The SmA phase is
characterized using a polarized microscope and DSC measurements.
Interestingly, compounds 1-n form physical gels (thermo-reversible
gels) in n-octane, ethanol, and aprotic polar solvents such as acetonitrile
and γ -butyrolactone, where the sol-gel transition temperatures are
60°C for 1-1 and 80°C for 1-6. The propylene carbonate gel is charac-
terized by scanning electron microscope (SEM) observation, showing
nano-fibers assembled with compound 1-6.
Introduction
Soft materials such as liquid crystal (LC) materials and molecular gels have attracted a great
amount of great interest because they have much attention from theoretical and practical
applications [1–4]. A lot of compounds have been investigated to determine the relationship
between molecular structures and physical properties. Many LC materials have been reported
now, where a rigid core and flexible terminal alkyl chain(s) are indispensable to exhibit 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 also reported, and the researches are devoted
to elucidate the relationship between the molecular structures and the gelation ability. The
aggregation of organic gelators to fibrous network is driven by weak intermolecular interac-
tions such as hydrogen bonding, dipole-dipole, van der Waals and π-π interactions [1–2]. In
fact, many organic gelators 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 aro-
matic core and/or long alkyl chains [11–12]. The introduction of perfluoroalkyl chain(s) is
known as a common strategy to enhance the self-assembly such as gelation properties [1].
Several organic gelators having perfluoroalkyl chains were also prepared and it has been
clarified that the perfluoroalkyl chain affects the gelation ability differently from the alkyl
chains [13,14]. In our earlier papers, we have investigated that 4-(2-perfluorohexyl)butoxy
CONTACT Hiroaki Okamoto
oka-moto@po.cc.yamaguchi-u.ac.jp
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

300/[568]
T. YOSHIDA ET AL.
Figure . Chemical structure for compounds 1-n.
group affect their mesomorphic properties and gelation ability [15,16]. Furthermore, we have
also reported some organic gelators having perfluoroalkyl chains at the both terminal posi-
tions of the molecule [17,18].
This paper describes synthesis, mesomorphic and gelation properties of perfluoroalkylated
compounds with a 2-alkoxy-6-substituted naphthalene core (compounds 1-n) as shown in
Figure 1. The molecular structures are to incorporate neither protic function group nor so
long hydrocarbon chain. The geometrical structure is simple, rod-like and very similar to the
conventional LC materials.
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 high-
resolution mass spectra (HRMS) were recorded with a Waters LCT Premier/XETM. The syn-
thetic procedures are as follows.
4-[2-(Perfluorohexyl)ethylsulfanyl]bromobenzene (A): 2-(Perfluorohexyl)ethyl iodide
(30.02 g, 63.33 mmol), 4-bromobenzenethiol (11.96 g, 63.29 mmol), and K2CO3 (13.29 g,
96.16 mmol) were added in acetone (100 mL) in a 300 mL recovery flask, and the resulting
mixture refluxed for 1 day. The reaction mixture was allowed to cool to room temperature.
Then saturated NaCl aqueous solution (100 mL) was added to the mixture, and the result-
ing solution was extracted with EtOAc (100 mL × 3). The organic layers were combined and
dried with MgSO4, and after filtration, the filtrate was concentrated using a rotary evapo-
rator under reduced pressure. The crude product was purified by recrystallization (EtOH)
to give 4-[2-(Perfluorohexyl)ethylsulfanyl]bromobenzene (A) (32.41g, 60.76 mmol) in 96%
1
yield as colorless powder: mp = 43–44°C, IR (KBr disc): ν = 1248–1140 cm−1, H NMR
(500 MHz, CDCl3): δ = 2.33–2.43 (2H, m), 3.09–3.12 (2H, m), 7.23 (2H, d, J = 8.5 Hz), 7.46
(2H, d, J = 8.5 Hz) ppm, HRMS (ESI): m/z calcd for C14H7BrF13S [M – H]− 532.9244; found
532.9285.
2-Methoxy-6-[4-(2-perfluorohexyl)ethylsulfanyl]phenyl]naphthalene (compound 1-1): 4-
[2-(Perfluorohexyl)ethylsulfanyl]bromobenzene (A) (13.38 g, 25.00 mmol), 6-methoxy-2-
naphthylbronic acid (5.00 g, 24.75 mmol), Na2CO3 (5.30 g, 50.00 mmol), Pd(OAc)2 (0.05 g,
0.9 mol%), and tri(o-tolyl)phosphine (0.15 g, 2 mol%) were added in 1,4-dioxane (40 mL)
Scheme . Synthetic scheme for compounds 1-n.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
[569]/301
and water (40 mL) in a 200 mL flask, and the mixture was refluxed for 12 h under N2 atmo-
sphere. The reaction mixture was allowed to cool to room temperature. Then saturated NaCl
aqueous solution (100 mL) was added to the mixture, and the resulting solution was extracted
with CHCl3 (100 mL × 3). The organic phases were combined and dried with MgSO4, and
after filtration, the filtrate was concentrated using a rotary evaporator under reduced pres-
sure. The crude product was purified by silica gel column chromatography (eluent: CHCl3)
and recrystallization (EtOH: toluene = 8: 2) to give compound 1-1 (14.55 g, 23.76 mmol) in
1
95% yield as colorless crystals.: IR (KBr disc): ν = 1236−1188 cm−1, H NMR (500 MHz,
CDCl3): δ = 2.40−2.50 (2H, m), 3.12−3.15 (2H, m), 3.95 (3H, s), 7.17 (1H, d, 2.4 Hz),
7.18 (1H, dd, J = 10.9, 2.4 Hz), 7.47 (2H, d, J = 8.5 Hz), 7.68 (2H, d, J = 8.5 Hz), 7.69
(1H, dd, J = 10.9, 2.4 Hz), 7.79 (1H, d, J = 9.8 Hz), 7.81 (1H, d, J = 9.8 Hz), 7.97 (1H,
d, J = 2.4 Hz) ppm, HRMS (ESI): m/z calcd for C25H16OF13S [M−H]− 611.0714; found
611.0712.
2-Ethoxy-6-[4-(2-perfluorohexyl)ethylsulfanyl]phenyl]naphthalene (compound 1-2): 4-
[2-(Perfluorohexyl)ethylsulfanyl]bromobenzene (compound A) (1.24 g, 2.31 mmol), 6-
ethoxy-2-naphthylbronic acid (0.50 g, 2.31 mmol), Na2CO3 (0.49 g, 4.63 mmol), Pd(OAc)2
(0.01 g, 2 mol%), and tri(o-tolyl)phosphine (0.03 g, 4 mol%) were added in 1,4-dioxane
(40 mL) and water (40 mL) in a 200 mL flask, and the mixture was refluxed for 12 h under
N2 atmosphere. The reaction mixture was allowed to cool to room temperature. Then sat-
urated NaCl aqueous solution (100 mL) was added to the mixture, and the resulting solu-
tion was extracted with CHCl3 (100 mL × 3). The organic phases were combined and dried
with MgSO4, and after filtration, the filtrate was concentrated using a rotary evaporator
under reduced pressure. The crude product was purified by silica gel column chromatog-
raphy (eluent: CHCl3) and recrystallization (EtOH: toluene = 8: 2) to give compound 1-
2 (1.26 g, 2.01 mmol) in 87% yield as colorless powder.: IR (KBr disc): ν = 2980, 2936,
1
1238−1211 cm−1, H NMR (500 MHz, CDCl3): δ = 1.50 (3H, t, J = 7.0 Hz), 2.40−2.50
(2H, m), 3.12−3.15 (2H, m), 4.17 (2H, q, J = 6.7 Hz), 7.17 (1H, d, 2.4 Hz), 7.18 (1H, dd,
J = 10.9, 2.4 Hz), 7.47 (2H, d, J = 8.5 Hz), 7.68 (2H, d, J = 8.5 Hz), 7.69 (1H, dd, J =
10.9, 2.4 Hz), 7.79 (1H, d, J = 9.8 Hz), 7.81 (1H, d, J = 9.8 Hz), 7.97 (1H, d, J = 2.4 Hz)
ppm.
2-Hexyloxy-6-[4-(2-perfluorohexyl)ethylsulfanyl]phenyl]naphthalene (compound 1-6):
4-[2-(Perfluorohexyl)ethylsulfanyl]bromobenzene (compound A) (1.18 g, 2.20 mmol), 6-
hexyloxy-2-naphthylbronic acid (0.90 g, 3.30 mmol), Na2CO3 (0.63 g, 5.94 mmol), Pd(OAc)2
(0.01 g, 2 mol%), and tri(o-tolyl)phosphine (0.03 g, 4 mol%) were added in 1,4-dioxane
(40 mL) and water (40 mL) in a 200 mL flask, and the mixture was refluxed for 12 h under
N2 atmosphere. The reaction mixture was allowed to cool to room temperature. Then sat-
urated NaCl aqueous solution (100 mL) was added to the mixture, and the resulting solu-
tion was extracted with CHCl3 (100 mL × 3). The organic phases were combined and dried
with MgSO4, and after filtration, the filtrate was concentrated using a rotary evaporator under
reduced pressure. The crude product was purified by silica gel column chromatography (elu-
ent: CHCl3) and recrystallization (EtOH: toluene = 8: 2) to give compound 1-6 (0.24 g,
0.132 mmol) in 6% yield as colorless powder: IR (KBr disc): ν = 2932, 2860, 1238−1182 cm−1,
1H NMR (500 MHz, CDCl3): δ = 0.93 (3H, t, J = 6.7 Hz), 1.38 (2H, quin, J = 3.7 Hz), 1.52
(2H, quin, J = 7.3 Hz), 1.86 (2H, quin, J = 7.6 Hz), 2.40−2.50 (2H, m), 3.12−3.15 (2H, m),
4.09 (2H, t, J = 6.7 Hz), 7.17 (1H, d, J = 2.4 Hz), 7.18 (1H, dd, J = 10.9, 2.4 Hz), 7.47 (2H, d, J =
8.5 Hz), 7.68 (2H, d, J = 8.5 Hz), 7.69 (1H, dd, J = 10.9, 2.4 Hz), 7.79 (1H, d, J = 9.8 Hz), 7.81
(1H, d, J = 9.8 Hz), 7.97 (1H, d, J = 2.4 Hz) ppm, HRMS (ESI): m/z calcd for C30H26OF13S
[M − H]− 681.1497; found 681.1497.

302/[570]
T. YOSHIDA ET AL.
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
thermogram was operated at a heating or cooling rate of 5°C min−1. 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-
nium bromide, respectively. 1H 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 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 gelation 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 quantitatively the gel forming ability by determining the MGC, which is the mini-
mum 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 were determined by means of DSC measure-
ments and polarized microscope observations.
The DSC thermogram for compound 1-1 shows endotherms at 144°C, 170°C and 192°C
corresponding to the melting, mesophase-mesophase and mesophase–isotropic (I) phase
transition phenomena on heating process. The molten material shows exotherm at 189°C,
166°C and 110°C due to the phase transition on a cooling process. The formed textures are
shown in Figure 2.
The polarized microscope observation exhibited a typical focal conic fan texture under
a homogeneus alignment glass surface and a homeotropic texture (dark under a cross-
polarized microscope) on a homeotropic alignment glass surface. A broken-fan texture
was observed at 166°C and the homeotropic texture under a homeotropic glass surface on
cooling. We can assume that the both mesophases have an orthogonal alignment of the
molecule. Therefore, the mesophases are assigned to be smectic A (SmA) and B (SmB)
phases.
For compound 1-6, a similar focal conic fan texture was observed on cooling process from
isotropic liquid and the upper mesophase was assigned to be the SmA phase as shown in
Figure 3 (a). Lower mesophase for compound 1-6 also shows a broken fan texture as shown
in Figure 3(b), however, the mesophase has a schlieren texture under a homeotropic glass
surface, suggesting a smectic C (SmC) phase.
The transition temperatures and latent heats for 1-n are summarized in Table 1.
The latent heats of compound 1-1 for the SmB-SmA and SmA–I transitions also support
the characterizations, where the value for former transition was determined to be 9.1 kJ mol−1
and that for the later was 9.7 kJ mol−1. The similar tendency was observed for compound
1-2, where the latent heats for the SmB-SmA and SmA-I transitions, that is, 8.6 kJ mol−1

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
[571]/303
Figure . Polarized micrographs for compound 1- (a) at °C and (b) at °C.
and 11.2 kJ mol−1, respectively. The latent heat for the SmA–I transition of compound 1-6
is determined to be 9.6 kJ mol−1, which is similar to that for compounds 1-1 and 1-2. On
the other hand, the latent heat for the lower smectic phase-SmA transition is determined to
be 0.1 kJ mol−1, which is too small to assign to be the SmB-SmA transition. The small value
of the latent heat for the smectic-SmA transition also supports that the lower smectic phase
assigned to be the SmC phase.
Interestingly, compounds 1-n formed a physical gel (i.e. thermo-reversible gel) in several
organic solvents. Therefore, we carried out the gelation test of compounds 1-1 and 1-6 in
several organic solvents.
Table 2 shows the results of the gelation test for compounds 1-1 and 1-6 in several organic
solvents. Compound 1-1 formed gels in n-octane, toluene, ethanol, 1-octanol, acetonitrile,
γ -butyrolactone (GBL) and proprylene carbonate (PC), where the minimum gel concen-
trations were 0.6, 5.0, 0.5, 0.6, 0.4, 0.2 and 0.4 wt%, respectively, while precipitated in N,N-
dimethylformamide (DMF).
On the other hand, compound 1-6 was soluble in toluene and formed gel in the other sol-
vents at similar concentrations as shown in Table 2. The results suggest that gelation ability

304/[572]
T. YOSHIDA ET AL.
Figure . Polarized micrographs for compound 1- (a) at °C and (b) at °C.
for compounds 1-n is an independent of an alkyl chain length in the terminal position of the
molecule. The sol-gel transition temperatures for the PC gels are plotted against the concen-
tration of compounds 1-1 and 1-6 as shown in Figure 4.
The sol-gel transition temperatures for the PC gels increased with increasing the concen-
tration of compounds 1-1 and 1-6. For compound 1-1, the sol-gel transition temperature is
ca. 60°C in more than 1wt% of the concentration. The sol-gel transition temperatures for
compound 1–6 are higher than those for compound 1-1, where the temperature is ca. 80°C at
Table . Transition temperatures for compounds 1-n.
Transition temperatures (°C)
Latent heats (kJ mol−
)
Compounds
C
SmB
SmC
SmA
I
mp
SmB–SmA
SmC–SmA
SmA–I
r
r
r
r
r
r
r
r
r
r
r
1-
1-
1-





—
—
)



.
.
.
.
.
.
.
(.)
.
.
.
r
—
(
C, SmB, SmC, SmA and I indicate crystal, smectic B, smectic C, and smectic A and isotropic phases, respectively. Parentheses
indicate a monotropic transition.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
[573]/305
Table . Minimum gel concentration for compounds 1- and 1-.
Compounds (concentration, wt%)a)
Solvents
1-
1-
n-Octane
Toluene
Ethanol
-Octanol
Acetonitrile
DMF
G (.)
G (.)
G (.)
G (.)
G (.)
P (.)
G (.)
S (.)
G (.)
G (.)
G (.)
G (.)
PCb)
G (.)
G (.)
G (.)
G (.)
GBLc)
a)G, S and P are gel, sol and precipitated states, respectively. b)PC: Propylene carbonate, c)GBL: γ -Butyrolactone.
Figure . Plots for sol-gel transition temperature of propylene carbonate gel against concentration of com-
pounds 1- (circle) and 1- (triangle).
Figure . SEM image for xerogel prepared from propylene carbonate gel (x,).

306/[574]
T. YOSHIDA ET AL.
3 wt% of compound 1-6. These results indicate that the terminal alkyl chain has an important
influence on the sol-gel transition temperature.
The gelation phenomena are also confirmed using scanning electron microscope (SEM)
observation, and the result for a xerogel prepared from propylene carbonate gel containing
3 wt% compound 1-6 is shown in Figure 5. It is apparent from the figure that the gel consists of
several rod-like fibers and the fibers are aligned to form the network structures with diameters
of less µm order.
In conclusion, intermolecular interaction around the terminal alkyl group acts an impotant
role for displaying the mesomorphic property and gelation ability. The perfluorohexylethyl
group is also indispensable for the gelation ability. The present results will provide an impor-
tant information for mesomorphic and gelation phenomena.
Further examination is now underway, and the results will be published elsewhere.
Funding
This work is partly supported by Industrial Technology Research Grant Program in 2006 from New
Energy and Industrial Technology Development Organization (NEDO) of Japan, TEPCO Memorial
Foundation and The Fujikura Foundation.
References
[1] Terech, P., & Weiss, R. G. (1997). Chem. Rev., 97, 313.
[2] Babu, S. S., Praveen, V. K., & Ajayaghosh, A. (2014). Chem. Rev., 114, 1973.
[3] Morita, Y., Kawabe, K., Zhang, F., Okamoto, H., Takenaka, S., & Kita, H. (2005). Chem. Lett., 34,
1650.
[4] Morita, Y., Ushijima, H., Era, K., Kasatani, K., & Okamoto, H. (2008). Mol. Cryst. Liq. Cryst., 494,
282.
[5] Hird, M. (2007). Chem. Soc. Rev., 36, 2070.
[6] Okamoto, H., Murai, H., & Takenaka, S. (1997). Bull. Chem. Soc. Jpn, 70, 3165.
[7] Okamoto, H., Yamada, N., & Takenaka, S. (1998). J. Fluorine Chem., 91, 125.
[8] Duan, M., Okamoto, H., Petrov, V. F., & Takenaka, S. (1999). Bul. Chem. Soc. Jpn, 72, 1637.
[9] Duan, M., Okamoto, H., Petrov, V. F., & Takenaka, S. (1998). Bull. Chem. Soc. Jpn, 71, 2735.
[10] Yano, M., Taketsugu, T., Hori, K., Okamoto, H., & Takenaka, S. (2004). Chem., Eur. J., 10, 3991.
[11] Ajayaghosh, A., & George, S. J. (2001). J. Am. Chem. Soc., 123, 5148.
[12] Bujanowski, V. J., Katsoulis, D. E., & Ziemelis, M. J. (1994). J. Mater. Chem., 4, 1181.
[13] Sato, H., Yajima, T., & Yamagishi, A. (2011). Chem. Commun., 47, 3736.
[14] Pugh, C., Höpken, J., & Möller, M. (1988). Polym. Prep., 29, 460.
[15] Cao, B., Kaneshige, Y., Matsue, Y., Morita, Y., & Okamoto, H. (2016). New J. Chem., 40, 4884.
[16] Cao, B., Hayashida, S., Morita, Y., & Okamoto, H. (2016). Mol. Cryst. Liq. Cryst., 632, 49.
[17] Yoshida, T., Hirakawa, T., Nakamura, T., Yamada, Y., Tatsuno, H., Hirai, M., Morita, Y., &
Okamoto, H. (2015). Bull. Chem. Soc. Jpn, 88, 1447.
[18] Yoshida, T., Nakamura, T., Morita, Y., & Okamoto, H. (2015). Chem. Lett., 44, 512.