Preparation of troponoid liquid crystals with a flexible oxymethylene linking unit

Article abstract of DOI:10.1039/a704536k

2-Benzyloxytropones, which have a saturated oxymethylene (-CH₂O-) linking unit, show a monotropic smectic A phase while the corresponding alkoxybenzyl alkoxyphenyl ethers have poor mesogenic properties. The tropone carbonyl group acting as a dipolar lateral substituent enhances the smectic thermal stability.

Full text of DOI:10.1039/a704536k

J O U R N A L O F
Preparation of troponoid liquid crystals with a flexible oxymethylene
linking unit
Akira Mori,*a Hisashi Taya,b Hitoshi Takeshitac and Seiji Ujiied
aInstitute of Advanced Material Study, 86, Kyushu University, Kasuga-koen, Kasuga,
Fukuoka 816, Japan
C H E M I S T R Y
bGraduate School of Engineering Sciences, 39, Kyushu University, Kasuga-koen, Kasuga,
Fukuoka 816, Japan
cT ohwa Institute for Oriental Science, T ohwa University, Chikushi-ga-oka, Minami-ku,
Fukuoka 815, Japan
dDepartment of Material Science, Interdisciplinary Faculty of Science and Engineering,
Shimane University, Matue 690, Japan
2-Benzyloxytropones, which have a saturated oxymethylene (MCH OM) linking unit, show a monotropic smectic A phase while
the corresponding alkoxybenzyl alkoxyphenyl ethers have poor mesogenic properties. The tropone carbonyl group acting as a
dipolar lateral substituent enhances the smectic thermal stability.
2
A typical liquid crystal structure generally consists of a rigid
core part and two terminal chains. The core usually has
aromatic rings connected either directly or through a linking
unit. It has been recognized that flexible, saturated linking
units such as MCH OM, MCH CH M and MOCH CH OM
are less favorable for the appearance of a mesophase1 since
these linking units do not preserve the linearity of the mol-
ecules. In this paper, we describe the synthesis and meso-
morphic properties of 2-benzyloxytropone derivatives, which
to be nonmesogenic or mesogenic with low thermal persist-
ence.1 The benzene derivative 4b exhibited no mesophase, but
compound 4a showed a mosaic texture and homeotropic
structure. The X-ray diffraction pattern of 4a at 76 °C showed
˚
two sharp reflections at 36.7 and 2.83 A, which suggested the
2
2
2
2
2
exhibition of a smectic B (S ) phase.
Table 2 summarizes the comparison with transition tempera-
B
tures between 1 and the corresponding benzoyloxy series 5.3,6
Compound 5 with a MCOOM linking unit had a lower
melting point and a higher clearing point than 1. This parallels
the behavior of the benzenoid compounds as shown in
Table 3.7–10 Although the formation of liquid crystals from 1
is less likely than from 5, 1 is more favorable than benzenoids 4.
Table 4 summarizes the transition temperatures of 1 when
the alkyl length of the tropone ring was changed and that of
the benzyloxy group was fixed. The length of the alkyl group
of the tropone ring affected the clearing point more than the
melting point whereas the alkyl chain length on the benzyloxy
group did not affect the clearing point so much. On the other
hand, when the alkyl length of the benzyloxy group was
changed, the melting point changed more than the clearing
point, as shown in Table 1. Further, compounds 1-Cl and
showed the monotropic smectic A (S ) phase when the alkoxy
groups were lengthened.
A
The 1H NMR spectra of 5-alkoxy-2-(4-alkoxybenzyloxy)tro-
pones 1 showed no broadened signals at room temperature,
eliminating the occurrence of [1,9] sigmatropy as observed in
2-acyloxytropone derivatives.3–6 The phase transition tempera-
tures were determined by differential scanning calorimetry
(DSC) and the thermal behavior of the microscopic texture
was observed using a polarizing microscope equipped with a
hot stage. The results are summarized in Table 1.
All mesogenic compounds 1 showed a monotropic S phase.
This contrasts with that of corresponding benzenoid com-
pounds with a flexible, saturated linking unit, which are known
A
J. Mater. Chem., 1998, 8(3), 595–597
595

Table 1 Transition temperatures (T /°C) and, in parentheses, enthalpy changes (DH/kJ mol−1) of 1
m
n
K
S
I
m
n
K
S
I
A
A
a
b
c
d
e
f
g
h
i
4
6
6
6
6
6
8
8
8
8
8
8
12
6
7
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
90 (50.4)
88
Ω
58
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
m
n
o
p
q
r
11
11
11
11
11
11
12
12
12
12
12
12
12
1
6
7
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
68
91
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
85 (45.6)
83 (40.0)
84 (46.8)
86 (47.5)
94
87 (38.8)
88 (47.6)
82 (42.7)
80 (46.3)
81 (50.1)
Ω
Ω
Ω
Ω
64 (8.5)
65 (15.9)
67 (8.8)
70 (9.0)
86 (45.7)
86 (45.7)
71 (51.0)
81 (53.2)
70
91
71
89 (48.5)
83 (35.7)
87 (48.9)
83 (44.7)
Ω
79
8
8
Ω
Ω
Ω
80 (17.2)
62
77 (13.7)
10
12
4
6
7
8
10
12
10
12
1
4
6
7
8
10
12
s
t
Ω
Ω
Ω
Ω
Ω
70
74 (9.2)
74 (9.1)
75 (11.9)
75 (11.9)
u
v
w
x
y
j
k
l
Ω
Ω
Ω
Ω
77
80
81 (12.9)
80 (14.2)
Table 2 Comparison of transition temperatures (T /°C) between 1 and 5
1
5
(m, n)
K
S
I
K
S
S
N
I
A
C
A
(6, 12)
(8, 12)
(11, 12)
(12, 4)
(12, 12)a
Ω
Ω
Ω
Ω
Ω
86
81
81
91
83
Ω
Ω
Ω
70
75
77
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
Ω
(Ω 54)b
58
Ω
66
76
85
70
90
Ω
Ω
Ω
Ω
Ω
67
51
64
64
Ω
Ω
Ω
Ω
(Ω 63)b
Ω
80
aRecrystallization temperature was 55 °C. bThe value in parentheses is the monotropic transition temperature.
Table 3 Comparison of the transition temperatures (T /°C) of ethers and esters
(m, n)
(1, 5)
(5, 6)
(12, 8)
K 93 (N 38) Ia
K 89 Ib
K 67 N 72.5 Id
K 57.5 N 84.5 Id
K 70 (S 57.5) S 86 S 90.5 Ie
K 91 (S 76) Ic
B
C
A
aRef. 7. bRef. 9. cThis work. dRef. 8. eRef. 10.
1-CN with a chlorine atom and a cyano group were not
mesogenic although the corresponding troponoid 5-CN
showed monotropic smectic A phases.6
From the contrasting results of the troponoid and the
benzenoid derivatives, mesophases can presumably be stabil-
ized by the tropone carbonyl group, whose permanent dipole
moment increases the attractive dispersion force between mol-
ecules.11,12 The carbonyl group of tropones plays a crucial role
as a polar lateral substituent in the formation of the mesophase.
Experimental
Elemental analyses were performed at Kyushu University. The
NMR spectra were measured using GSX 270H spectrometers
in CDCl , unless otherwise specified, and the chemical shifts
3
are expressed in d units, with J values in Hz. Mass spectra
were measured with a JEOL 01SG-2 spectrometer. The IR
spectra were taken as KBr disks for crystalline compounds
using a JASCO IR-A 102 spectrometer. The UV spectra were
Table 4 Effect on the transition temperatures (T °C) and, in parentheses, enthalpy changes (DH/kJ mol−1) of 1 when the alkyl chain length (m)
was changed
m
n
K
S
I
m
n
K
S
I
A
A
b
h
n
u
6
6
6
6
6
Ω
Ω
Ω
Ω
88
87 (38.8)
91
71
Ω
Ω
Ω
Ω
e
6
10
10
10
10
Ω
Ω
Ω
Ω
84 (46.8)
80 (46.3)
71 (51.0)
87 (48.9)
Ω
67 (8.8)
75 (11.9)
62
Ω
Ω
Ω
Ω
8
11
12
Ω
70
k
q
x
8
11
12
Ω
Ω
Ω
81 (12.9)
c
i
o
v
6
8
11
12
7
7
7
7
Ω
Ω
Ω
Ω
85 (45.6)
88 (47.6)
86 (45.7)
89 (48.5)
Ω
Ω
Ω
Ω
64 (8.5)
74 (9.2)
79
Ω
Ω
Ω
Ω
f
l
r
y
6
8
11
12
12
12
12
12
Ω
Ω
Ω
Ω
86 (47.5)
81 (50.1)
81 (53.2)
83 (44.7)
Ω
Ω
Ω
Ω
70 (9.0)
Ω
Ω
Ω
Ω
75 (11.9)
77 (13.7)
80 (14.2)
77
d
j
p
w
6
8
11
12
8
8
8
8
Ω
Ω
Ω
Ω
83 (40.0)
82 (42.7)
86 (45.7)
83 (35.7)
Ω
Ω
Ω
Ω
65 (15.9)
74 (9.1)
80 (17.2)
80
Ω
Ω
Ω
Ω
596
J. Mater. Chem., 1998, 8(3), 595–597

measured using Hitachi U-3200 and U-3410 spectrophotomet-
ers. The stationary phase for column chromatography was
Wakogel C-300 and the elution solvents were mixtures of
hexane and ethyl acetate.†
Found: C, 78.88; H, 10.18%.
1s: mp 70 °C; Calc. for C H O : C, 76.02; H, 8.98%. Found:
C, 75.94; H, 8.80%.
27 38
4
1t: mp 91 °C; Calc. for C H O : C, 76.88; H, 9.46%. Found:
C, 76.67; H, 9.45%.
30 44
4
1u: mp 71 °C; Calc. for C H O : C, 77.38; H, 9.74%.
Found: C, 77.23; H, 9.53%.
32 48
4
Preparation of 1
1v: mp 89 °C; Calc. for C H O : C, 77.60; H, 9.87%. Found:
C, 77.54; H, 9.72%.
33 50
4
When the sodium salts of 5-alkoxytropolones 2,2 prepared
with NaH in hexamethylphosphoric triamide (HMPT) at room
temp., were reacted with 4-alkoxybenzyl chloride 3 overnight
at 50 °C, compounds 1 were obtained in 42–65% yields after
1w: mp 83 °C; Calc. for C H O : C, 77.82; H, 9.99%.
Found: C, 78.06; H, 9.87%.
34 52
4
1x: mp 87 °C; Calc. for C H O : C, 78.21; H, 10.21%.
36 56
4
SiO chromatography.
Found: C, 78.39; H, 10.14%.
1y: mp 72 °C; Calc. for C H O : C, 78.57; H, 10.41%.
Found: C, 78.75; H, 10.21%.
2
1a: mp 90 °C; d 0.88 (3H, t, J 6.6), 0.96 (3H, t, J 7.3),
1.26–1.53 (20H, m), 1.69–1.82 (4H, m), 3.84 (2H, t, J 6.6), 3.93
H
38 60
4
(2H, t, J 6.6), 5.13 (2H, s), 6.21 (1H, dd, J 11.0, 2.6), 6.80 (1H,
d, J 11.0), 6.87 (2H, d, J 8.8), 7.05 (1H, dd, J 13.2, 2.6), 7.20
(1H, d, J 13.2), and 7.32 (2H, d, J 8.8). d 13.8, 14.1, 19.2, 22.7,
1-Cl: mp 73 °C; Calc. for C H O Cl: C, 74.17; H, 9.66%.
Found: C, 73.80; H, 9.49%.
38 59
4
1-CN: mp 102 °C; Calc. for C H O N: C, 76.92; H, 8.37;
N, 3.32%. Found: C, 77.12; H, 8.42; N, 3.54%.
C
27 35
3
26.1, 29.3, 29.4 (2C), 29.6 (4C), 31.0, 31.9, 68.1, 68.2, 70.9, 107.9,
114.6 (2C), 118.3, 128.1, 129.0 (2C), 132.9, 138.0, 158.7, 159.0,
159.5, and 179.9. n/cm−1 2925, 2850, 1560, 1510, 1450 and
1250. m/z (%): 468 (M+, 7), 276 (21), 275 (100), and 107 (14).
Calc. for C H O : C, 76.88; H, 9.46%. Found: C, 76.88;
Preparation of 4
30 44
4
H, 9.51%.
1b: mp 88 °C; Calc. for C H O : C, 75.69; H, 8.80%.
Found: C, 75.82; H, 8.75%.
Similarly compounds 4 were prepared from 4-alkoxyphenols
and 4-alkoxybenzyl chlorides. 4a: mp 91 °C; d 0.86–0.90 (6H,
m), 1.26–1.46 (28H, m), 1,70–1.82 (4H, m), 3.89 (2H, t, J 6.6),
26 36
4
H
1c: mp 85 °C; Calc. for C H O : C, 76.02; H, 8.98%. Found:
3.95 (2H, t, J 6.6), 4.92 (2H, s), 6.81 (2H, d, J 9.5), 6.86 (2H,
d, J 9.5), 6.89 (2H, d, J 8.8), and 7.32 (2H, d, J 8.8). d 14.1,
22.7 (2C), 26.1 (2C), 29.3 (2C), 29.4 (2C), 29.6 (4C), 29.7 (2C),
27 38
4
C, 76.30; H, 9.03%.
1d: mp 83 °C; Calc. for C H O : C, 76.32; H, 9.15%.
Found: C, 76.49; H, 9.24%.
C
28 40
4
31.8, 31.9, 68.1, 68.6, 70.6, 114.6 (2C), 115.4 (2C), 115.8 (2C),
129.1, 129.2 (2C), 152.9, 153.5, and 159.0. n/cm−1 2925, 2850,
1510, 1235 and 1020. Calc. for C H O : C, 79.79; H, 10.55%.
1e: mp 84 °C; Calc. for C H O : C, 76.88; H, 9.46%.
Found: C, 77.08; H, 9.44%.
30 44
4
33 52
3
1f: mp 86 °C; Calc. for C H O : C, 77.38; H, 9.74%. Found:
C, 77.34; H, 9.54%.
Found: C, 79.73; H, 10.30%.
4b: mp 97 °C; Calc. for C H O : C, 80.38; H, 10.94%.
Found: C, 80.21; H, 10.76%.
32 48
4
37 60
3
1g: mp 94 °C; Calc. for C H O : C, 75.70; H, 8.80%.
Found: C, 76.00; H, 8.81%.
29 36
4
1h: mp 87 °C; Calc. for C H O : C, 76.32; H, 9.15%.
Found: C, 76.15; H, 9.08%.
28 40
4
References
1i: mp 88 °C; Calc. for C H O : C, 76.60; H, 9.30%. Found:
C, 76.51; H, 9.21%.
29 42
4
1
G. W. Gray, in T he Molecular Physics of L iquid Crystals, ed.
G.R. Luckhurst and G.W. Gray, Academic Press, London, New
York, San Francisco, 1979, ch. 1.
A. Mori, H. Taya and H. Takeshita, Chem. L ett., 1991, 579.
A. Mori, M. Uchida and H. Takeshita, Chem. L ett., 1989, 591.
A. Mori, H. Takeshita, K. Kida and M. Uchida, J. Am. Chem. Soc.,
1990, 112, 8635.
K. Kida, A. Mori and H. Takeshita, Mol. Cryst. L iq. Cryst., 1991,
199, 387.
A. Mori, N. Kato, H. Takeshita, M. Uchida, H. Taya and R.
Nimura, J. Mater. Chem., 1991, 1, 799.
The transition temperature to the N phase was determined by
extrapolation. See N. Carr and G.W. Gray, Mol. Cryst. L iq. Cryst.,
1985, 124, 27.
D. Demus, H.-J. Deutschen, D. Marzotko, H. Kresse and A.
Wiegleben, in Proceedings of International L iquid Crystal
Conference, Bangalore, 1980, p. 97.
1j: mp 82 °C; Calc. for C H O : C, 76.88; H, 9.46%. Found:
C, 77.00; H, 9.40%.
30 44
4
2
3
4
1k: mp 80 °C; Calc. for C H O : C, 77.37; H, 9.74%.
Found: C, 77.22; H, 9.60%.
32 48
4
1l: mp 81 °C; Calc. for C H O : C, 77.82; H, 9.99%. Found:
34 52
4
C, 77.87; H, 10.04%.
1m: mp 68 °C; Calc. for C H O : C, 75.69; H, 8.79%.
Found: C, 76.05; H, 8.75%.
5
6
7
26 36
4
1n: mp 91 °C; Calc. for C H O : C, 77.13; H, 9.61%.
Found: C, 77.28; H, 9.54%.
31 46
4
1o: mp 86 °C; Calc. for C H O : C, 77.38; H, 9.74%.
Found: C, 77.42; H, 9.59%.
32 48
4
8
9
1p: mp 86 °C; Calc. for C H O : C, 77.60; H, 9.87%.
Found: C, 77.67; H, 9.57%.
33 50
4
T. Kitamura, H. Yokokura, A. Mukoh and M. Sato, in Abstracts
of 6th Symposium of L iquid Crsytals, Sendai, 1980, IR08.
1q: mp 71 °C; Calc. for C H O : C, 78.02; H, 10.10%.
35 54
4
Found: C, 77.70; H, 10.11%.
1r: mp 81 °C; Calc. for C H O : C, 78.40; H, 10.31%.
10 D. Demus, H. Demus and H. Zaschke, Flussige Kristalle in
¨
¨
Tabellen Deutscher Verlag fur GrundstoYndustrie, Leipzig, 1976.
37 58
4
11 K. Takatoh, K. Sunohara and M. Sakamoto, Mol. Cryst. L iq.
Cryst., 1988, 164, 167.
12 R. Brettle, D. A. Dunmur, L. D. Farrand, N. J. Hindley and C. M.
Marson, Chem. L ett., 1993, 1663.
† Further data are available as supplementary material (SUP 57321;
12 pp.) deposited with the British Library. Details are available from
the editorial office.
Paper 7/04536K; Received 27th June, 1997
J. Mater. Chem., 1998, 8(3), 595–597
597