Aromatic fluorination effect on the mesomorphic properties of discotic liquid crystal of alkoxybenzoyloxytriphenylene

Article abstract of DOI:10.1246/cl.2007.584

Two homologues, C6F4 and C10F4 having 2,3,5,6-tetrafluorophenylene moieties were synthesized and investigated on the mesomorphic behavior. It was revealed that these exhibit a hexagonal columnar (Col_h) phase, and this mesomorphism is quite diff

Full text of DOI:10.1246/cl.2007.584

584
Chemistry Letters Vol.36, No.5 (2007)
Aromatic Fluorination Effect on the Mesomorphic Properties
of Discotic Liquid Crystal of Alkoxybenzoyloxytriphenylene
Yasuyuki Sasada,1;2;3 Hirosato Monobe,1 Yasukiyo Ueda,ꢀ3 and Yo Shimizuꢀ1
1Synthetic Nano-Function Materials Group, Nanotechnology Research Institute,
Advanced Industrial Science and Technology (AIST), Kansai Center, 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577
2Research Laboratory I, Goi Research Center, Chisso Petrochemical Corporation, 5-1 Goikaigan, Ichihara, Chiba 290-8551
3Department of Chemical Science and Engineering, Faculty of Engineering, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501
(Received January 10, 2007; CL-070030; E-mail: yo-shimizu@aist.go.jp)
F
F
F
F
F
F
F
F
F
F
Two homologues, C6F4 and C10F4 having 2,3,5,6-tetra-
fluorophenylene moieties were synthesized and investigated on
the mesomorphic behavior. It was revealed that these exhibit a
hexagonal columnar (Colh) phase, and this mesomorphism is
quite different from the corresponding nonfluorinated homo-
logues, C6H4 and C10H4 predominantly showing a discotic
nematic (ND) phase.
1)
2), 3), 4)
5)
O
C6F4 (R: C6H13
)
HO
RO
RO
C10F4 (R: C10H21
)
OH
F
1
F
2
3
Scheme 1. Synthetic routes of the fluorinated homologues: 1)
RBr, K2CO3, TBAB, MEK, reflux; 2) n-BuLi/Hexane, THF,
ꢂ78 ꢁC; 3) CO2, ꢂ78 ꢁC; 4) 3 M HCl aq, rt.; 5) 2,3,6,7,10,11-
hexahydroxytriphenylene, DCC, DMAP, CH2Cl2, rt.
C10F4
The fluorinated compounds have attracted much interest
because of their unique properties in chemistry and physics.1
Especially in research field of LCDs technology, liquid-crystal
materials possessing the fluorinated aromatic rings or linkage
groups have been synthesized and reported their properties such
as dielectric anisotropy, rotational viscosity, etc.,2 because the
fluorination gives large dielectric anisotropy without the depres-
sion of the mesomorphic properties. On the other hand, for
fluorinated discotic liquid crystals, only a few reports have been
seen to show that a thermal stability of hexagonal columnar
(Colh) phase is enhanced by introducing perfluoroalkyl struc-
tures to peripheral chains of the central core part, probably
owing to the fluorophilic and fluorophobic interactions.3
Cry
Col
h
C6F4
Iso
Cry
Cry2
Col
h
40
80 120 160 200 240 280
Temperature /°C
OR
X
X
X
Figure 1. DSC curves of C6F4 and C10F4 (heating rate: 5 ꢁC/
min). C: crystal, Colh: hexagonal columnar phase, Iso: isotropic
liquid.
X
X
X
X
X
X
RO
X
X
OR
X
O
O
O
O
O
by H NMR, 19F NMR, FT-IR, elemental analyses, and TOF–
C6F4 : R = C6H13, X = F
C10F4 : R = C10H21, X = F
1
O
O
O
MS.5
X
X
O
X
X
The DSC curves on heating of C6F4 and C10F4 are shown
in Figure 1. These exhibit an enantiotropic mesophase. For
C6F4, three endothermic peaks were observed at 130, 157 and
301 ꢁC with the phase-transition enthalpies (ꢀH), 1.9, 3.6, and
25.4 kJ/mol, respectively. Similarly C10F4 shows two peaks
at 109 and 302 ꢁC (ꢀH: 5.1 and 26.2 kJ/mol, respectively).
The microscopic texture observation revealed that the former
is melting points and the latter clearing ones. The textures of
these mesophases were of typical for columnar mesophase.
The X-ray diffractions patterns of these mesophases at
180 ꢁC (nonaligned samples) show a small number of reflections
as shown in Figure 2. The reflections observed in the small angle
region show a spacing ratio of 1:1/ 3:1/2, which is an evidence
of a hexagonal arrangement of columns. The lattice constant
˚
ahex is calculated to be 30.4 and 32.1 A for C6F4 and C10F4,
respectively. As the molecular diameters evaluated by full-
C6H4 : R = C6H13, X = H
C10H4 : R = C10H21, X = H
RO
O
X
X
X
O
X
O
X
X
X
OR
X
OR
Here, an interesting result is shown in the aromatic fluorina-
tion effect on the mesomorphic behavior where the tetrafluoro-
substitution of the phenyl rings in the peripheral positions to
the central triphenylene core induces a drastic change of meso-
morphism (nematic to columnar phases) with an enhanced
thermal stability.
pffiffi
Two
homologues,
2,3,6,7,10,11-tetrakis(4-hexyloxy-
2,3,5,6-tetrafluorobenzoyloxy)triphenylene (C6F4) and 2,3,6,7,
10,11-tetrakis(4-decyloxy-2,3,5,6-tetrafluorobenzoyloxy)triphen-
ylene (C10F4) were synthesized (Scheme 1) to study the
mesomorphic behavior, and the corresponding nonfluorinated
(hydrocarbon) homologues (C6H4 and C10H4)4 were com-
pared. The identification of these compounds was carried out
˚
extended models are 38 and 47 A for C6F4 and C10F4, the
observed ahex values show a similar correlation with those of
other triphenylene hexagonal columnar mesogens that the
Copyright Ó 2007 The Chemical Society of Japan

Chemistry Letters Vol.36, No.5 (2007)
585
Table 2. Phase-transition temperature of C6F4, C10F4, C6H4,
and C10H4
Phase-transitions temperature/ꢁC
(ꢀH: kJ/mol)
d100
Compound
4.7A
3.5A
C6F4
C10F4
C1 130 (1.9) C2 157 (3.6) Colh 301 (25.4) Iso
C 109 (5.1) Colh 302 (26.2) Iso
3.9A
d110
d200
C6F4
C6H44
C10H44
C 186 (9.5) Colra 193 ND 274 Iso
a
4.7A
3.5A
4.1A
d100
d200
C 142 (34.9) Colra 191 ND 212 Iso
a
d110
aColr: rectangular columnar phase, ND: discotic nematic
phase.
C10F4
5
10
15
20
25
30
35
θ
/ degree
the mixture to have the higher melting point.7
Figure 2. X-ray diffraction patterns of C6F4 and C10F4 at
180 ꢁC.
These drastic changes in the mesomorphic behavior are
quite new and interesting. It seems that these result is due to
several interactions that the tetrafluorophenylene moieties could
have, for example fluorophilic and fluorophobic, quadrupolar
and dipolar interactions. Further studies are in progress.
Table 1. Observed parameters of X-ray diffractions for C6F4
and C10F4 at 180 ꢁC
˚
ahex/A
˚
dhkl/A
Compound
hlk
References and Notes
C6F4
(180 ꢁC)
30.4
100
110
200
26.8
15.2
13.1
4.7 (broad)
3.9 (broad)
3.5 (broad)
1
Organofluorine Chemistry. Principle and Commercial
Applications, ed. by R. E. Banks, B. E. Amart, J. C. Tatlow,
Plenum, New York, 1994.
2
a) Y. Goto, T. Ogawa, S. Sawada, S. Sugimori, Mol. Cryst.
Liq. Cryst. 1991, 209, 1. b) S. Matsui, T. Kondo, K. Sago,
Mol. Cryst. Liq. Cryst. 2004, 411, 127. c) D. Pauluth, K.
Tarumi, J. Mater. Chem. 2004, 14, 1219.
C10F4
(180 ꢁC)
32.1
100
110
200
27.8
16.2
14.1
4.7 (broad)
4.1 (broad)
3.5 (broad)
3
a) N. Terasawa, H. Monobe, K. Kiyohara, Y. Shimizu,
Chem. Lett. 2003, 32, 214. b) B. Alameddine, O. F.
Aebischer, W. Amrein, B. Donnio, R. Deschenaux, D.
Guillon, C. Savary, D. Scanu, O. Scheidegger, T. A. Jenny,
Chem. Mater. 2005, 17, 4798. c) U. Dahn, C. Erdelen,
H. Ringsdorf, R. Festag, J. H. Wendof, P. A. Heiney, N. C.
Maliszewskyj, Liq. Cryst. 1995, 19, 759.
observed ahex is almost 70–80% of the molecular diameters
evaluated by the molecular model. Furthermore, the halos
˚
having the spacings of 4.7, 4.1–3.9, and 3.5 A were observed
˚
in the wide-angle region. The halo centered at 4.7 A could be as-
signed to the averaged molecular width of a tetrafluorophenylene
moiety, according to the estimated molecular width of the
4
5
N. H. Tinh, H. Gasparoux, C. Destrade, Mol. Cryst. Liq.
Cryst. 1981, 68, 101.
a) C6F4: 1H NMR (CDCl3, TMS, 500.0 MHz) ꢁ 0.96 (t,
J ¼ 6:9 Hz, 18H), 1.38–1.41 (m, 24H), 1.52 (quintet,
J ¼ 7:0 Hz, 12H), 1.84 (quintet, J ¼ 6:7 Hz, 12H), 4.33 (t,
J ¼ 6:5 Hz, 12H), 7.97 (s, 6H); 19F NMR (CDCl3, CFCl3,
470.0 MHz) ꢁ ꢂ138:9 (s, 12F), ꢂ158:8 (s, 12F); MS
m=z ¼ 1981:8 (calcd 1981.7 for C96H84F24O18); FT-IR
(KBr, cmꢂ1) 2959, 2934, 2361, 2861, 2342, 1759, 1650,
1489, 1412, 1389, 1323, 1256, 1210, 1117, 1006, 939, 890,
835, 800; Anal. Calcd for C96H84F24O18: C, 58.19; H,
4.27; F, 23.01%. Found: C, 58.29; H, 4.29; F, 23.11%.
b) C10F4: 1H NMR (CDCl3, TMS, 500.0 MHz) ꢁ 0.91
(t, J ¼ 6:5 Hz, 18H), 1.31–1.40 (m, 72H), 1.51 (quintet,
J ¼ 7:5 Hz, 12H), 1.84 (quintet, J ¼ 7:0 Hz, 12H), 4.34 (t,
J ¼ 6:5 Hz, 12H), 8.07 (s, 6H); 19F NMR (CDCl3, CFCl3,
470.0 MHz), ꢁ ꢂ138:8 (s, 12F), ꢂ158:4 (s, 12F), MS
m=z ¼ 2318:0 (calcd 2318.3 for C120H132F24O18); FT-IR
(KBr, cmꢂ1) 2951, 2926, 2861, 2361, 2342, 1759, 1650,
1489, 1412, 1389, 1323, 1256, 1210, 1117, 1006, 939, 890,
835, 800; Anal. Calcd for C120H132F24O18: C, 62.17; H,
5.74; F, 19.67%. Found: C, 62.22; H, 5.69; F, 19.77%.
A. M. Levelut, J. Phys., Lett. 1979, 81.
˚
molecular model (4.7–5.0 A), and the halos at 4.1–3.9 and
˚
3.5 A could be related to the averaged diameter of molten alkyl
chain6 and ꢀ–ꢀ staking distance of triphenylene, respectively.
The X-ray diffraction parameters are summarized in Table 1.
The phase-transition parameters of C6F4 and C10F4 are
summarized in Table 2, with those of the corresponding non-
fluorinated homologues (C6H4 and C10H4). C6F4 and
C10F4 exhibit only a Colh mesophase, though C6H4 and
C10H4 exhibit discotic nematic (ND) phase accompanied with
Colr phase in the lower-temperature range.
The clearing points of C6F4 and C10F4 show almost the
same value, while those of C6H4 and C10H4 become lower
as the increase of chain length. In addition, the enthalpies of
the clearing points for C6F4 and C10F4 are much larger than
the usual ones of Colh phase shown by other triphenylene meso-
gens (<10 kJ/mol). For the fluorination of aromatic rings in tri-
phenylene derivatives, the interesting behavior was reported that
dodecafluorotriphenylene and triphenylene form a complex in
6
7
V. B. Smith, A. G. Massey, Tetrahedron 1969, 25, 5495.
Published on the web (Advance View) March 29, 2007; doi:10.1246/cl.2007.584