Flying-seed-like liquid crystals. Part 4: A novel series of bulky substituents inducing mesomorphism instead of using long alkyl chains

Article abstract of DOI:10.1039/c4ra13474e

We synthesized a novel series of flying-seed-like derivatives (3a-g) based on phthalocyaninato copper(ii) (abbreviated as PcCu) substituted by bulky groups {PhO (a), (o-C₁)PhO (b), (m-C₁)PhO (c), (p-C₁)PhO (d), [m,p-(C₁)₂]PhO (e), [m,m′-(C₁)₂]PhO (f), and [m,p,m′-(C₁)₃]PhO (g)} instead of using long alkyl chains, in order to investigate their mesomorphism. Their phase transition behaviour and the mesophase structures were established using a polarizing optical microscope, a differential scanning calorimeter, a thermogravimetry analyser and a temperature-dependent small angle X-ray diffractometer. It was demonstrated that (PhO)₈PcCu (3a) and [(p-C₁)PhO]₈PcCu (3d) show no mesophase, whereas [(m-C₁)PhO]₈PcCu (3c), {[m,p-(C₁)₂]PhO}₈PcCu (3e), {[m,m′-(C₁)₂]PhO}₈PcCu (3f), and {[m,p,m′-(C₁)₃]PhO}₈PcCu (3g) show various kinds of columnar mesophases of Col_ro(P2₁/a), Col_ro(P2₁/a), Col_ro(C2/m) and Col_tet.o, respectively, while [(o-C₁)PhO]₈PcCu (3b) shows a monotropic Col_ro(P2m) mesophase. Thus, we revealed that mesomorphism could be induced by these novel bulky substituents instead of using long alkyl chains, and that the mesophase structures were greatly affected by the number and position of the methoxy groups. In particular, it is very interesting that the derivatives with methoxy group(s) at the meta position(s), namely, 3c, 3e, 3f and 3g, tend to show enantiotropic mesophase(s), whereas neither the derivative with no methoxy group, 3a, nor the derivative with a methoxy group at the para position, 3d, show a mesophase. This journal is

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Flying-seed-like liquid crystals. Part 4:† a novel
series of bulky substituents inducing
Cite this: RSC Adv., 2015, 5, 13828
mesomorphism instead of using long alkyl chains
a
a
Miho Yoshioka, Kazuchika Ohta and Mikio Yasutakeb
*
We synthesized a novel series of flying-seed-like derivatives (3a–g) based on phthalocyaninato copper(II)
(abbreviated as PcCu) substituted by bulky groups {PhO (a), (o-C1)PhO (b), (m-C1)PhO (c), (p-C1)PhO (d),
[m,p-(C1)2]PhO (e), [m,m0-(C1)2]PhO (f), and [m,p,m0-(C1)3]PhO (g)} instead of using long alkyl chains, in
order to investigate their mesomorphism. Their phase transition behaviour and the mesophase structures
were established using a polarizing optical microscope, a differential scanning calorimeter, a thermogravimetry
analyser and a temperature-dependent small angle X-ray diffractometer. It was demonstrated that
(PhO)8PcCu (3a) and [(p-C1)PhO]8PcCu (3d) show no mesophase, whereas [(m-C1)PhO]8PcCu (3c),
{[m,p-(C1)2]PhO}8PcCu (3e), {[m,m0-(C1)2]PhO}8PcCu (3f), and {[m,p,m0-(C1)3]PhO}8PcCu (3g) show
various kinds of columnar mesophases of Colro(P21/a), Colro(P21/a), Colro(C2/m) and Coltet.o, respectively,
while [(o-C1)PhO]8PcCu (3b) shows a monotropic Colro(P2m) mesophase. Thus, we revealed that
mesomorphism could be induced by these novel bulky substituents instead of using long alkyl chains,
and that the mesophase structures were greatly affected by the number and position of the methoxy
groups. In particular, it is very interesting that the derivatives with methoxy group(s) at the meta
position(s), namely, 3c, 3e, 3f and 3g, tend to show enantiotropic mesophase(s), whereas neither the
derivative with no methoxy group, 3a, nor the derivative with a methoxy group at the para position, 3d,
show a mesophase.
Received 30th October 2014
Accepted 23rd December 2014
DOI: 10.1039/c4ra13474e
www.rsc.org/advances
have consisted of a central rigid core and several peripheral long
alkyl chains. Up to date, about 101 000 kinds of liquid crystals
have been synthesized1 and investigated in various elds,
1 Introduction
Generally, liquid crystalline materials are broadly categorized
into rod-like (calamitic) and disk-like (discotic) molecules from
their molecular shapes. In addition to the major calamitic and
discotic molecules, banana-shaped, T-shaped and the other
shaped molecules are also known as minor constituents of
liquid crystalline materials. Regardless of the shape, each of the
liquid crystals has a at rigid central core and several exible
long alkyl chains in the periphery in almost all the cases.1 When
the liquid crystals are heated, the peripheral long alkyl chains
melt to form so parts at rst, whereas the central cores do not
melt. Generally, this may induce a liquid crystalline phase
(¼mesophase). Hence, researchers have long believed that it is
an essential requirement for a liquid crystalline molecule to
have long alkyl chains in the periphery. Since the discovery of
the rst liquid crystals in 1888, almost all the liquid crystals
especially in liquid crystal displays.2
¨
However, in 1911 Vorlander found unique liquid crystals
that had neither a rigid core nor peripheral long alkyl chains.3
Since then though they have largely been forgotten in the past
100 years and very few research papers have reported on this
type of liquid crystals.4–8 Fig. 1-(1) shows a representative
molecular structure of sodium diphenyl acetate, Ph2CHCOONa
(1). In 2006, we revealed for the rst time, by using temperature-
dependent X-ray diffractometer, that this salt, Ph2CHCOONa
(1), has a hexagonal columnar (Colh) mesophase.8 Its meso-
phase structure is depicted in Fig. 1-(1). As can be seen from this
gure, the bulky substituent can freely rotate around the bond
coloured in red ink to form a so corn-shaped part instead of
long alkyl chains, thus showing a columnar mesophase. In this
mesophase, sodium metals form a one-dimensional nano-wire
and freely rotating diphenyl acetates cover the nano-wire to
form an aromatic nanotube. The mesophase-showing mecha-
nism due to the free rotation of the bulky substituent closely
resembles the ying seeds of the maple tree, so much that we
named such unique liquid crystals as ‘ying-seed-like liquid
crystals’.8
aSmart Material Science and Technology, Interdisciplinary Graduate School of Science
and Technology, Shinshu University, 1-15-1 Tokida, Ueda, 386-8567, Japan. E-mail:
ko52517@shinshu-u.ac.jp; Fax: +81-268-21-5492; Tel: +81-268-21-5492
bComprehensive Analysis Center for Science, Saitama University, 255 Shimo-okubo,
Sakura-ku, Saitama 338-8570, Japan. E-mail: yasutake@apc.saitama-u.ac.jp; Tel:
+81-48-858-3671
† Part 3: ref. 12 in this paper.
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(ii) 4-(Triphenylmethyl)phenoxy (3Ph–PhO–), 4-(1,1-diphe-
nylethyl)phenoxy (2PhO–PhO–), 4-(1-methyl-1-phenyl)phenoxy
(1Ph–PhO–) and 4-(tert-butyl)phenoxy (0Ph–PhO–).11,12
Although a very few other liquid crystals with neither a rigid
central core nor exible peripheral long alkyl chains have been
reported to date,13–17 the mesophase-originating mechanism
has never been claried without our ying-seed-like liquid
crystals.8,12,13 Accordingly, herein, our aim was to nd a novel
series of bulky substituents that could induce mesomorphism,
excluding (i) and (ii), in order to further clarify how the
compounds with no alkyl chains could show mesomorphism.
The previous bulky substituents of (i) and (ii) freely rotate by
360ꢀ. However, we sought to answer the question ‘when bulky
substituents rotate not by 360ꢀ but ip-op in a restricted angle
region, can such bulky substituents induce mesomorphism?’
For example, Fig. 1-(3) illustrates {[m,p,m’-(C1)]3PhO}3PcCu (3g)
substituted by trimethoxyphenoxy groups; can the phthalocya-
nine derivative show mesomorphism? In this compound, two
adjacent phenoxy groups cannot freely rotate but ip-op
within the restricted angles. However, when this phenoxy
group is further substituted by three methoxy groups at
the m,p,m0-positions, the resulting bulkier substituent,
[m,p,m0-(C1)]3PhO, leads to a bigger excluded volume due to the
ip-op. Accordingly, this suggests mesomorphism may be
induced not only by free rotation but also by the ip-opping of
bulky substituents.
In this study, we synthesized the PcCu derivatives 3a–g
substituted by a novel series of bulky substituent groups a–g:
(iii) PhO (a); (o-C1)PhO (b); (m-C1)PhO (c); (p-C1)PhO (d); [m,p-
(C1)2]PhO (e); [m,m0-(C1)2]PhO (f); [m,p,m0-(C1)3]PhO (g),
to investigate their mesomorphism. As a result, we found that
the derivatives with methoxy group(s) at the meta position(s)
tend to show enantiotropic mesophase(s). Herein, we report the
interesting results.
Fig. 1 Molecular and mesophase structures of flying-seed-like liquid
crystals. (1) and (2) Rotating bulky substituents induced mesophases in
the previous compounds.8,11 (3) Aim: can we induce mesophases by
using novel bulky substituents? One of the bulky substituents used in
this work is depicted here.
2 Experimental section
2.1 Synthesis
In 2009, Usol'tseva and co-workers found from polarizing
optical microscopic observations that a phthalocyanine (Pc)
derivative substituted by four triphenylmethyl groups,
(3Ph–PhO)4PcCu (2), as depicted in Fig. 1-(2), shows a meso-
phase.9,10 The substituent of the triphenylmethyl group in this
compound very much resembles the molecular structure of
Ph2CHCOONa (1) in Fig. 1-(1). Therefore, we thought that this
Pc derivative might be one of the ying-seed-like liquid crystals
induced by free rotation of the peripheral bulky substituents. In
2012, we carried out temperature-dependent X-ray diffraction
studies on this Pc derivative 2 and revealed that it also showed a
hexagonal columnar mesophase.11 Furthermore, we recently
reported that the introduction of the bulky substituents to the
other cores also induced mesomorphism.12
The phthalocyanine derivatives, 3a–g, were synthesized
according to Scheme 1. The precursor of the phenol derivative
4c was synthesized from commercially available resorcinol
(Wako) and iodomethane (Wako) using our previously reported
method.18 The precursor of the phenol derivative 4e was
synthesized from commercially available 3,4-dimethoxy-
benzaldehyde (Wako) by using our previously reported
method.19 The other phenol derivatives, 4a, 4b, 4d, 4f and 4g,
were purchased from Tokyo Kasei. These phenol derivatives
(4a–g) were reacted with commercially available 4,5-dichlor-
ophthalonitrile (Tokyo Kasei) to obtain the corresponding
phthalonitrile derivatives (5a–g), which were converted into the
corresponding phthalocyanine derivatives (3a–g).
From these investigations, we successfully established two
series of bulky substituents, (i) and (ii), thereby inducing ying-
seed-like liquid crystals, namely:
(i) Diphenylmethyl (Ph2–CH–), 2-methylethyl ((CH3)2–CH–)
and 3-ethylprophyl ((C2H5)2–CH–).8
The detailed synthetic procedures are described below only
for the representative phthalocyanine derivative, [(m-C1)PhO]8-
PcCu (3c). For the other precursors (5a–b and 5d–g) and for the
phthalocyanine derivatives (3a–b and 3d–g), the physical prop-
erty data are only described.
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Scheme 1 Synthetic route for novel flying-seed-like phthalocyanines, 3a–g. (i) 4,5-Dichlorophthalonitrile, K2CO3 and DMA, (ii) CH3I, K2CO3 and
DMF, (iii) conc. H2SO4, 30% H2O2, CHCl3 and CH3OH, (iv) CuCl2, DBU, 1-octanol for 3a, 3c, 3d and 3e; CuCl2, DBU and 1-hexanol for 3b, 3f and
3g. DMF ¼ N,N0-dimethylformamide, DMA ¼ N,N0-dimethylacetamide and DBU ¼ 1,8-diazabicyclo[5,4,0]-undec-7-ene.
evaporator. The residue was puried by column chromatog-
raphy (silica gel, dichloromethane, Rf ¼ 0.53) to obtain 0.856 g
3-Methoxyphenol (4c). A mixture of resorcinol (2.67 g, 24.3
mmol), K2CO3 (5.30 g, 38.3 mmol) and dry DMF (30 ml) placed
in a 100 ml three-necked ask was stirred at 110 ꢀC under a
nitrogen atmosphere for 20 min. Then, iodomethane (7.86 g,
55.4 mmol) was added to the mixture and it was stirred at 110 ꢀC
under a nitrogen atmosphere for 1 h. Aer cooling to rt, the
reaction mixture was extracted with chloroform and washed
with water. The organic layer was dried over Na2SO4 overnight.
Aer removing the Na2SO4 by ltration, the ltrate was evapo-
rated in vacuum using an evaporator. The residue was puried
by column chromatography (silica gel, chloroform, Rf ¼ 0.18) to
obtain 0.882 g of reddish brown liquid. Yield ¼ 29.4%.
ꢀ
of white solid. Yield ¼ 80.8%. M.p. ¼ 134 C.
1H NMR (CDCl3; TMS) d ¼ 7.35 (t; J ¼ 8.08 Hz; 2H, CN-Ar-H),
7.20 (s; 2H, Ar-O-Ar-H), 6.83 (d; J ¼ 8.84 Hz; 2H, Ar-O-Ar-H),
6.66–6.61 (m; 4H, Ar-O-Ar-H), 3.82 (s; 6H, –OCH3) IR (KBr,
cmꢁ1); 2920 (–CH3), 2837 (–OCH3), 2222 (–CN).
4,5-Diphenoxyphthalonitrile (5a). Yield ¼ 78.9%. M.p. ¼
147.9 ꢀC. 1H-NMR (CDCl3; TMS) d ¼ 7.78 (s; 2H, NC-Ar-H), 7.43 (t; J
¼ 8.00 Hz; 4H, Ar-O-Ar-H), 7.23 (t; J ¼ 8.00 Hz; 2H, Ar-O-Ar-H), 7.10
(d; J ¼ 8.00 Hz; 4H, Ar-O-Ar-H). IR (KBr, cmꢁ1); 2249 (–CN).
4,5-Bis(2-methoxyphenoxy)phthalonitrile (5b). Yield
¼
92.8%. M.p. ¼ 138.2 ꢀC. 1H NMR (CDCl3; TMS) d ¼ 7.22 (dd; J1 ¼
8.08 Hz, J2 ¼ 7.83 Hz; 2H, NC-Ar-H), 7.10 (d, J ¼ 8.09 Hz; 2H, Ar-
O-Ar-H), 6.98 (dd; J1 ¼ 8.84 Hz, J2 ¼ 8.08 Hz; 4H, Ar-O-Ar-H), 6.86
(s; 2H, Ar-O-Ar-H), 3.75 (s; 6H, –OCH3). IR (KBr, cmꢁ1); 2930,
2820 (–CH3), 2210 (–CN).
1H-NMR (CDCl3; TMS) d ¼ 7.13 (t; J ¼ 9.60 Hz; 1H, Ar-H), 6.49
(d; J ¼ 9.9 Hz; 1H, Ar-H), 6.45–6.39 (m; 2H, Ar-H), 5.67 (s; 1H,
–OH), 3,77 (s; 1H, –OCH3). IR (KBr, cmꢁ1); 3363 (–OH), 2968
(–CH3), 2842 (–OCH3).
4,5-Bis(3-methoxyphenoxy)phthalonitrile (5c). In a 100 ml
three-necked ask, a mixture of 3-methoxyphenol (4c) (0.780 g,
6.28 mmol), K2CO3 (6.37 g, 46.1 mmol) and dry DMA (30 ml) was
stirred at 110 ꢀC under a nitrogen atmosphere for 15 min. Then,
4,5-dichlorophtalonitrile (0.566 g, 2.87 mmol) was added to the
mixture and it was stirred at 110 ꢀC under a nitrogen atmo-
sphere for 3 h. Aer cooling to rt, the reaction mixture was
extracted with diethyl ether and washed with water. The organic
layer was dried over Na2SO4 overnight. Aer removing Na2SO4
by ltration, the ltrate was evaporated in vacuum using an
4,5-Bis(4-methoxyphenoxy)phthalonitrile (5d). Yield
¼
93.4%. M.p. ¼ 158.0 ꢀC. 1H NMR (CDCl3; TMS) d ¼ 6.98 (m; 6H,
NC-Ar-H and Ar-O-Ar-H), 6.91 (d, J ¼ 8.84 Hz; 4H, Ar-O-Ar-H),
3.79 (s; 6H, –OCH3). IR (KBr, cmꢁ1); 2912 (–CH3), 2233 (–CN).
4,5-Bis(3,4-dimethoxyphenoxy)phthalonitrile (5e). Yield ¼
1
ꢀ
13.3%. M.p. ¼ 189 C. H NMR (CDCl3; TMS) d ¼ 7.10 (s; 2H,
NC-Ar-H), 6.92 (d; J ¼ 8.84 Hz; 2H, Ar-O-Ar-H), 6.67 (d; J ¼ 9.16
Hz, 4H, Ar-O-Ar-H), 3.93 (s; 6H, –OCH3), 3.88 (s; 6H, –OCH3). IR
(KBr, cmꢁ1); 2930, 2836 (–CH3), 2233 (–CN).
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Table 1 Yields, MALDI-TOF mass spectral data and elemental analysis data of 3a–ga
Element analysis; found (%)
(calculated (%))
Yield Mol. formula
(%) (exact mass)
Observed Mol. formula
Compound
mass
(average mass)
C
H
N
3a: (PhO)8PcCu
48.4 C80H48N8O8Cu(1311.29)
1311.17
C80H48N8O8Cu(1312.87)
—
—
—
3b: [(o-C1)PhO]8PcCu
3c: [(m-C1)PhO]8PcCu
3d: [(p-C1)PhO]8PcCu
3e: {[m,p-(C1)2]PhO}8PcCu
3f: {[m,m0-(C1)2]PhO}8PcCu
65.5 C88H64N8O16Cu(1551.38) 1551.27
66.7 C88H64N8O16Cu(1551.38) 1551.24
35.6 C88H64N8O16Cu(1551.38) 1551.29
39.0 C96H80N8O24Cu(1791.46) 1791.27
53.0 C96H80N8O24Cu(1791.46) 1791.37
C88H64N8O16Cu(1553.04) 68.06 (68.44) 4.49 (4.15) 6.92 (7.22)
C88H64N8O16Cu(1553.04) 67.76 (68.44) 4.14 (4.15) 7.12 (7.22)
C88H64N8O16Cu(1553.04)
C96H80N8O24Cu(1793.29)
C96H80N8O24Cu(1793.29)
—
—
—
—
—
—
—
—
—
3g: {[m,p,m0-(C1)3]PhO}8PcCu 80.5 C104H96N8O32Cu(2031.55) 2031.58
C104H96N8O32Cu(2033.46) 61.59 (61.43) 4.46 (4.76) 5.63 (5.51)
a
—: this compound did not completely burn out, so the observed carbon content was lower by several percent than the calculated values. Therefore,
these elemental analysis data are omitted here.
spectrometer (Nicolet NEXUS 670), an elemental analyzer
(Perkin-Elmer elemental analyzer 2400) and a MALDI-TOF mass
4,5-Bis(3,5-dimethoxyphenoxy)phthalonitrile (5f). Yield ¼
21.2%. M.p. ¼ 263.4 ꢀC. 1H NMR (CDCl3; TMS) d ¼ 7.12 (s; 2H,
spectrometer (AutoexIII-2S). The elemental analysis data and
NC-Ar-H), 6.30 (t, J ¼ 2.78 Hz; 2H, Ar-O-Ar-H), 6.15 (s; 4H, Ar-O-
Ar-H), 3.72 (s; 12H, –OCH3). IR (KBr, cmꢁ1); 2923, 2853 (–CH3),
the MALDI-TOF mass spectral data of the phthalocyanine
derivatives 3a–g are summarized in Table 1. Each of the elec-
tronic absorption spectra of all the phthalocyanine derivatives
was recorded using a HITACHI U-4100 spectrophotometer and
the data are summarized in Table 2. The phase transition
behaviour was observed with a polarizing optical microscope
(Nikon ECLIPSE E600 POL) equipped with a Mettler FP82HT hot
stage and a Mettler FP-90 central processor, and a Shimadzu
DSC-50 differential scanning calorimeter. The decomposition
temperatures were measured by a Rigaku Thermo plus TG 820
thermogravity analyser. The mesophases were identied using a
small angle X-ray diffractometer (Bruker Mac SAXS System)
equipped with a temperature-dependent sample holder to
cramp a Mettler FP82HT hot stage (see Fig. S1 and S2 in ref. 20),
2233 (–CN).
4,5-Bis(3,4,5-trimethoxyphenoxy)phthalonitrile (5g). Yield ¼
76.8%. M.p. ¼ 230.2 ꢀC. 1H NMR (CDCl3; TMS) d ¼ 7.42 (s; 2H,
NC-Ar-H), 6.01–5.92 (m; 4H, Ar-O-Ar-H), 3.71 (s; 18H, –OCH3). IR
(KBr, cmꢁ1); 2943, 2833 (–CH3), 2233 (–CN).
[(m-C1)PhO]8PcCu (3c). In a 50 ml three-necked ask, a
mixture of 4,5-bis(3-methoxy-phenoxy)phthalonitrile (5c) (0.505 g,
1.35 mmol), 1-octatanol (5 ml), CuCl2 (0.103 g, 0.766 mmol) and
DBU (4 drops) was reuxed under a nitrogen atmosphere for 17 h.
Aer cooling to rt, the reaction mixture was poured into methanol
to precipitate the target compound. The methanolic layer was
removed by ltration and then the resulting precipitate was
washed with methanol, ethanol and acetone, respectively. The
residue was puried by column chromatography (silica gel,
chloroform : THF ¼ 9 : 1, Rf ¼ 0.70) and recrystallized from ethyl
acetate to obtain 0.347 g of green solid. Yield ¼ 66.7%.
MALDI-TOF mass data for 3a–g: see Table 1.
ꢀ
ꢀ
which was operated with a measurable range from 3.0 A to 100 A
and a temperature range from rt to 375 C.20
ꢀ
Elemental analysis data for 3b, c, g: see Table 1.
UV-vis spectral data 3b, c, e–g: see Table 2.
3 Results and discussion
3.1 Synthesis
Table 1 lists the yields, and the MALDI TOF mass spectral data
2.2 Measurements
and the elemental analysis data of 3a–g. As can be seen from
The compounds synthesized here were identied with a 1H- this table, each of the mass spectral data of 3a–g is in good
NMR spectrometer (BRUKER Ultrashield 400 MHz), a FT-IR accordance with the calculated exact mass. On the other hand,
Table 2 Electronic absorption spectral data of 3a–ga
lmax (nm) (log 3)
Concentrationb
Compound
(ꢂ 10ꢁ5 mol lꢁ1
)
Soret-band
Q-band
3a: (PhO)8PcCu
—
—
—
—
—
—
—
—
3b: [(o-C1)PhO]8PcCu
3c: [(m-C1)PhO]8PcCu
3d: [(p-C1)PhO]8PcCu
3e: {[m,p-(C1)2]PhO}8PcCu
3f: {[m,m0-(C1)2]PhO}8PcCu
1.03
1.03
—
0.948
1.00
278.2 (4.77) 292.9 (4.75) 341.7 (4.84) ca. 400 (4.43) 613.9 (4.58) 651.4 (4.54) 682.8 (5.33)
284.2 (4.94) 341.7 (5.00) ca. 400 (4.55) 614.6 (4.78) 650.7 (4.79) 681.5 (5.41)
—
—
—
—
—
—
291.2 (4.86) 340.9 (4.88) ca. 420 (4.29) 614.6 (4.60) 652.6 (4.59) 684.3 (5.31)
289.2 (4.55) 342.2 (4.62) ca. 390 (4.27) 614.5 (4.34) 651.1 (4.34) 682.4 (4.92)
3g: {[m,p,m0-(C1)3]PhO}8PcCu 9.84
291.6 (3.85) 340 (3.97)
ca. 400 (4.46) 615.3 (3.71) 652.8 (4.69) 683.5 (5.45)
a
—: this derivative was insoluble in all the solvents. b In chloroform.
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the elemental analysis data of 3b and 3g gave satisfactory values
As can be seen from Table 3, the (PhO)8PcCu (3a) derivative
of C, H and N within ꢃ0.4% deviation, but the observed value of with no methoxy group showed no mesophase, and only a
C for 3c is smaller by 0.68% than the calculated value and those crystalline (K) phase from rt to the decomposition temperature
ꢀ
of H and N are within ꢃ0.4%. Since each of the other derivatives at 541 C.
of 3a, 3d, 3e and 3f was much less ammable than 3c, which
As can be seen from Table 3, the [(o-C1)PhO]8PcCu (3b)
gave a much smaller carbon value by several per cent than the derivative substituted by a methoxy group at an ortho-position
calculated value, these data are omitted in this table. This is in the phenoxy group showed a glassy Colro(P2m) mesophase
characteristic of less ammable phthalocyanine derivatives.21 from rt for the freshly prepared virgin sample. When it was
Table 2 summarizes the electronic absorption spectral data of heated over the glass transition temperature at 87.4 ꢀC, it
3a–g. As can be seen from this table, each of the derivatives of relaxed to transform into crystalline phase K1; on further heat-
3b, 3c and 3e–g gave a Q-band and Soret band characteristic to ing, it transformed into another crystalline phase K2, which
the PcCu complex with a D4h symmetry. Since the derivatives, 3a decomposed without weight loss (1st decomposition (decomp.))
and 3d, were insoluble in any solvents, no data are listed in this just aer melting at 299.4 ꢀC, and then decomposed with some
ꢀ
table. However, it could be conrmed from their MALDI-TOF weight loss (2nd decomp.) at 402 C. The two-step decomposi-
mass spectra in Table 1 that the target derivatives, 3a and 3d, tion has already been seen in other liquid crystals based on
were surely synthesized. Also, it could be judged from both the phthalocyanine derivatives and has been studied in detail.22 In
MALDI-TOF mass spectra and the electronic absorption spectra this paper, in the 1st decomp., the absorption spectra indicates
of 3e and 3f in Tables 1 and 2 that they were surely prepared.
that two neighbouring phenyl groups may form a ring by an
intramolecular ring-closing reaction with losing two hydrogen
atoms, which is, therefore, accompanied by almost no weight
loss. The 2nd decomp. is a normal thermal decomposition
accompanied by a large weight loss.
3.2 Phase transition behaviour
The phase transition behaviours of the phthalocyanine deriva-
tives 3a–g synthesized here are summarized in Table 3. These
phase transitions were established by using a polarizing optical
microscope (POM), a differential scanning calorimeter (DSC), a
thermal gravity analyser (TGA) and a temperature-dependent
small angle X-ray diffractometer. The phase transition behav-
iour of all the phthalocyanine derivatives 3a–g is described in
the following paragraphs.
Fig. 2 shows a DSC thermogram on the rst heating run of
[(o-C1)PhO]8PcCu (3b) together with a free energy versus
temperature (G–T) diagram. As can be seen from this DSC
thermogram, over the glass transition temperature (Tg) at
87.4 C, there is an exothermic peak at 111.8 C, which corre-
sponds to the relaxation from the supercooled Colro(P2m)
mesophase to the crystalline phase K1;23 on further heating,
ꢀ
ꢀ
Table 3 Phase transition temperatures and enthalpy changes of 3a–ga
Compounds
a
Phase nomenclature: K ¼ crystal, Colro ¼ rectangular ordered columnar mesophase, Mx ¼ unidentied mesophase, Coltet,o ¼ tetragonal ordered
columnar mesophase, I.L. ¼ isotropic liquid and dc. ¼ decomposition.
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Fig. 2 DSC thermogram and G–T diagram of [(o-C1)PhO]8PcCu (3b) on the 1st heating run.
there is a relatively broad endothermic peak at 177.3 ꢀC, which which decomposed without weight loss (1st decomp.) just aer
is assigned to the solid–solid (K1–K2) phase transition. On the transition, aꢀnd then decomposed with weight loss (2nd
heating, there is a big sharp endothermic peak at 229.4 ꢀC, decomp.) at 405 C.
which is assigned as the melting point, as under the micro-
The [(p-C1)PhO]8PcCu (3d) derivative substituted by a
scope, we could observe that the crystals melted into an methoxy group at a para-position in the phenoxy group showed
isotropic liquid (I.L.) at this temperature. Such monotropic no mesophase, and only a crystalline phase (K) from rt to the
ꢀ
glassy mesophase transformation behaviour can be rationally decomposition temperature at 363 C.
explained by using the G–T diagram, as illustrated in the right-
The {[m,m0-(C1)2]PhO}8PcCu (3f) derivative substituted by two
hand side of Fig. 2. When the freshly prepared virgin sample methoxy groups at the meta- and meta0-positions in the phenoxy
was pressed between two glass plates, it was rigid. However, it is group showed a crystalline phase K from rt, which then melted
crystallographically mesomorphic from the X-ray structural into a Colro(C2/m) mesophase at 310.5 ꢀC. This gradually
analysis, as it does not have a 3D lattice, but instead a 2D decomposed without weight loss (1st decomp.) over the melting
rectangular lattice with a P2m symmetry. Over Tg, this changes point (mp), and then decomposed with weight loss (2nd
ꢀ
into the supercooled Colro mesophase, in which the more decomp.) at 430 C.
mobile molecules easily rearrange into the more stable crys-
talline phase K1 by relaxation. This gives an exothermic peak. three methoxy groups at the meta-, para- and meta0-positions in
On heating, the K1 phase transforms into another crystalline the phenoxy group showed glassy tetragonal ordered
The {[m,p,m0-(C1)3]PhO}8PcCu (3g) derivative substituted by
a
phase K2 by a solid–solid phase transition at 177.3 ꢀC. The columnar (Coltet.o) mesophase at rt. When it was heated over the
crystalline phase K2 transforms into I.L. at 229.4 ꢀC. These glass transition temperature (Tg) at 67.9 ꢀC, it relaxed into a
phase transformations occur in the order of the arrows indi- crystalline phase K1. On further heating, the K1 phase trans-
cated in this G–T diagram, and furthermore, they can be ratio- formed into another crystalline phase K2 at 157.5 ꢀC. The K2
ꢀ
nally explained from a thermodynamic viewpoint.
phase melted into the Coltet.o mesophase at 262.1 C. Over the
As can be seen from Table 3, the [(m-C1)PhO]8PcCu (3c) mp, it gradually decomposed without weight loss (1st decomp.),
ꢀ
derivative substituted by a methoxy group at a meta-position in and decomposed with weight loss (2nd decomp.) at 346 C.
the phenoxy group also showed a glassy rectangular ordered
In our previous work on the long chain-substituted homo-
columnar mesophase Colro(P21/a) at rt for the freshly prepared logues of (p-CnOPhO)8PcCu, (m-CnOPhO)8PcCu and (o-Cn-
virgin sample. When it was heated over the glass transition OPhO)8PcCu, we reported that the steric hindrance of a
ꢀ
temperature at 69.9 C, it relaxed into the crystalline phase K. peripheral chain depends on its substitution position, and
On heating, this crystalline phase K transformed into the becomes bigger in the order of para position / meta position
Colro1(P21/a) mesophase and then another rectangular ordered / ortho position, and that a greater steric hindrance induces a
columnar mesophase, Colro2(P21/a). On further heating, it weaker interaction among the central Pc cores.24 We compared
transformed into an unidentied mesophase Mx at 360.1 ꢀC, the four present homologous PcCu derivatives 3a–d with each
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other, where the non-substituted derivative 3a and the para-
methoxy-substituted derivative 3d show only a crystalline phase,
the meta-methoxy-substituted derivative 3c only shows enantio-
tropic mesophases, and the ortho-methoxy-substituted derivative
3b only shows an isotropic liquid. The PhO group cannot freely
rotate due to the neighbouring PhO group, so that the Ph plane
twists c. 90ꢀ against that of the Pc core. Hence, the angle between
the methoxy group and the Pc core become smaller in the order of
para position / meta position / ortho position. The methoxy
group at the meta position and ortho position on the Pc core plane
become a steric hindrance to weaken the aggregation (¼stacking)
of the Pc cores. Additionally, the methoxy group at the ortho
position covers the Pc core plane.
Therefore, the meta-methoxy-substituted derivative 3c only
shows enantiotropic mesophases, and the ortho-methoxy-
substituted derivative 3b only shows an isotropic liquid.
Fig.
3 Photomicrographs of (a) Colro1(P21/a) mesophase of
[(m-C1)PhO]8PcCu (3c) at 230 ꢀC, (b) Colro(P21/a) mesophase of
{[m,p-(C1)2]PhO}8PcCu (3e) at 250 ꢀC, (c) Colro(P21/a) mesophase
3.3 Polarizing optical microscopic observations
of {[m,m0-(C1)2]PhO}8PcCu (3f) at 320 ꢀC, and (d) Coltet,o mesophase Fig. 3 shows the photomicrographs of the Pc derivatives, 3c, 3e,
of {[m,p,m0-(C1)3]PhO}8PcCu (3g) at 268 ꢀC.
3f and 3g, exhibiting mesophases. Fig. 3(a)–(d) are the
Fig. 4 XRD patterns of the mesophases: [A] [(o-C1)PhO]8PcCu (3b)at rt; [B] [(m-C1)PhO]8PcCu (3c) at 230 ꢀC, 310 ꢀC and 370 ꢀC; [C] {[m,p-(C1)2]-
PhO}8PcCu (3e) at 200 ꢀC; [D] {[m,m0-(C1)2]PhO}8PcCu (3f) at 330 ꢀC; [E] {[m,p,m0-(C1)3]PhO}8PcCu (3g) at rt.
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Table 4 X-ray data of 3b, 3c, 3e, 3f and 3ga
ꢀ
Spacing (A)
Miller indices
ꢀ
Compound (mesophase)
Mesophase lattice constants (A)
Peak no.
Obs.
Calc.
(h k l)
3b: [(o-C1)PhO]8PcCu
(glassy Colro(P2m) at rt)
a ¼ 20.7 b ¼ 19.2 h ¼ 7.00
Z ¼ 1.1 for r ¼ 1.0
1
2
3
4
5
6
19.3
13.9
10.4
7.00
5.15
3.53
19.2
14.1
10.4
—
5.18
3.52
(010)
(110)
(200)
h
(400)
(440)
3c: [(m-C1)PhO]8PcCu
(Colro1(P21/a) at 230 ꢀC)
a ¼ 29.4 b ¼ 26.5 h ¼ 6.09
Z ¼ 2.0 for r ¼ 1.1
1
2
3
4
5
6
7
8
9
10
11
12
13
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1
20.1
13.2
11.8
9.24
8.46
7.39
6.51
6.09
5.17
4.84
4.54
4.41
4.15
21.1
16.8
13.6
8.61
7.18
6.48
5.73
5.33
5.00
4.57
4.32
3.97
3.72
3.55
3.42
19.5
ca. 3.8
19.7
13.3
12.1
9.19
8.46
7.35
6.47
—
5.22
4.82
4.60
4.41
4.15
21.1
16.8
13.6
8.64
7.14
6.52
5.80
5.36
—
(110)
(020)
(120)
(310)
(130)
(400)
(140)
h
(150)
(610)
(620)
(060)
(710)
(110)
(200)
(020)
(320)
(420)
(510)
(340)
(150)
h
(Colro2(P21/a) at 310 ꢀC)
a ¼ 33.6 b ¼ 27.1 h ¼ 5.00
Z ¼ 2.0 for r ¼ 1.1
4.56
4.32
3.98
3.74
3.55
3.42
—
(450)
(640)
(460)
(560)
(840)
(080)
—
(Mx at 370 ꢀC)
2
—
h
3e: {[m,p-(C1)2]PhO}8PcCu
(Colro(P21/a) at 200 ꢀC)
a ¼ 40.2 b ¼ 33.1 h ¼ 4.21
Z ¼ 1.9 for r ¼ 1.0
1
2
3
4
5
6
7
8
25.5
16.5
12.9
9.38
8.41
6.50
5.50
4.21
25.5
16.5
12.8
9.60
8.51
6.49
5.51
—
(110)
(020)
(220)
(410)
(330)
(530)
(060)
h
3f: {[m,m0-(C1)2]PhO}8PcCu
(Colro(C2/m) at 330 ꢀC)
a ¼ 34.2 b ¼ 28.6 h ¼ 4.80
Z ¼ 1.9 for r ¼ 1.2
1
2
3
4
5
6
7
8
21.8
17.3
14.3
9.18
6.56
5.34
4.80
4.15
21.9
17.1
14.3
9.18
6.59
5.30
—
(110)
(200)
(020)
(130)
(240)
(620)
h
4.16
(460)
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Table 4 (Contd.)
ꢀ
Spacing (A)
Miller indices
ꢀ
Compound (mesophase)
Mesophase lattice constants (A)
Peak no.
Obs.
Calc.
(h k l)
3g: {[m,p,m0-(C1)3]PhO}8PcCu
(glassy Coltet,o at rt)
a ¼ 22.3 h ¼ 3.87
Z ¼ 1.0 for r ¼ 1.0
1
2
3
4
5
22.3
15.9
11.4
7.00
3.87
22.3
15.8
11.2
7.07
—
(100)
(110)
(200)
(310)
h
a
h: stacking distance ¼ (0 0 1), r: assumed density (g cmꢁ3).
photomicrographs of [(m-C1)PhO]8PcCu (3c) at 230 ꢀC, {[m,p-
ꢀ
(C1)2]PhO}8PcCu (3e) at 250 C, {[m,m0-(C1)2]PhO}8PcCu (3f) at
320 ꢀC, and {[m,p,m0-(C1)3]PhO}8PcCu (3g) at 268 ꢀC, respec-
tively. Each of these Pc derivatives decomposes without showing
an isotropic liquid and/or rapidly decomposes just aer melting
into isotropic liquid, so that they do not show a natural texture
which would be obtained by slow cooling from an isotropic
liquid. However, as can be seen from the photomicrographs in
Fig. 3, each of the derivatives was spread out and showed
stickiness together with birefringence when the cover glass
plate was pressed at the temperature denoted below the
photomicrograph. Hence, these states could be identied as
mesophases.
3.4 Temperature-dependent X-ray diffraction measurements
In order to clarify the precise mesophase structure, temperature-
dependent small angle X-ray diffraction measurements were
carried out for the Pc derivatives, 3b, 3c, 3e, 3f and 3g, showing
mesomorphism. These X-ray diffraction (XRD) patterns and their
X-ray data are summarized in Fig. 4 and Table 4, respectively.
As can be seen from the XRD patterns, no broad halo around
2Q ¼ 20ꢀ due to the molten long alkyl chains are observed,
although the halo can be generally observed for conventional
liquid crystals. This is a result of there being no long alkyl chains
in the present liquid crystals with only the shortest methoxy
groups.
[(p-C1)PhO]8PcCu (3b). The [(p-C1)PhO]8PcCu (3b) deriva-
tive substituted by a methoxy group at the para position of
the phenoxy group shows a glassy mesophase at rt. As can be
seen from the XRD pattern in Fig. 4[A] and the X-ray data in
Table 4, this glassy mesophase gave six reection peaks. All
the peaks except for Peak no. 4 could be well assigned to the
reections from a 2D rectangular lattice with a P2m symmetry
ꢀ
ꢀ
and the lattice constants, a ¼ 20.7 A and b ¼ 19.2 A, could be
determined from the Reciprocal Lattice Calculation
Method.25 Peak no. 4 could be assigned to the stacking
ꢀ
distance (h ¼ 7 A) among the central PcCu cores. Although
ꢀ
the stacking distance of 7 A is very long in comparison with
ꢀ
the stacking distances usually observed at 4–5 A for conven-
tional rectangular columnar mesophases, this stacking
distance can be proven as a proper value from the Z value
calculation.25
Fig.
5 Dependence of the mesophase structure on the bulky
substituent for flying-seed-like liquid crystals based on PhO8PcCu.
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The number (Z) of molecules in a lattice can be calculated Hence, this mesophase could be identied as a Colro(P21/a)
from this stacking distance (h ¼ 7 A) and the lattice constant of mesophase. The XRD pattern at 310 ꢀC gave een peaks. In the
ꢀ
ꢀ
ꢀ
the 2D rectangular lattice (a ¼ 20.7 A and b ¼ 19.2 A) listed in same manner as described above, this mesophase could also be
Table 4. Where r, V, N and M are the density of the mesophase, identied as another Colro(P21/a) mesophase with different
ꢀ
ꢀ
the volume of the unit lattice, Avogadro's number and the lattice constants and stacking distance: a ¼ 33.6 A and b ¼ 27.1 A,
ꢀ
molecular weight, respectively, the Z value can be obtained from h ¼ 5 A. Thus, this derivative exhibited two Colro(P21/a) meso-
the following equation:
phases with different sets of lattice constants and stacking
distances. On further heating, it showed an unidentied meso-
phase Mx. As can be seen from the XRD pattern in Fig. 4[B] and
the X-ray data in Table 4, the Mx mesophase gave only two peaks,
so that we could not identify it.
Z ¼ (rVN)/M ¼ {r [ a ꢂ b ꢂ h ]N}/M ¼ [1.0 (g cmꢁ3
)
ꢂ (20.7 ꢂ 10ꢁ8 cm) ꢂ (19.2 ꢂ 10ꢁ8 cm) ꢂ (7.00 ꢂ 10ꢁ8 cm)
ꢂ 6.02 ꢂ 1023 (molꢁ1)]/1553.04 (g molꢁ1) ¼ 1.08 z 1
{[m,p-(C1)2]PhO}8PcCu (3e). In the same manner described
above, the mesophase at 200 ꢀC could be identied as a
Colro(P21/a) mesophase having lattice constants: a ¼ 40.2 A, b ¼
The calculated value Z z 1 is the same as the theoretical
number of molecules in a 2D rectangular lattice with a P2m
ꢀ
ꢀ
ꢀ
33.1 A and h ¼ 4.21 A.
ꢀ
symmetry: Z ¼ 1.0. Therefore, this big stacking distance h ¼ 7 A
{[m,m0-(C1)2]PhO}8PcCu (3f). In the same manner as
described above, the mesophase at 330 ꢀC could be identied as
a Colro(C2/m) mesophase with a different symmetry C2/m with
lattice constants: a ¼ 34.2 A and b ¼ 28.6 A, and h ¼ 4.80 A.
{[m,p,m0-(C1)3]PhO}8PcCu (3g). The mesophase in this
derivative 3g decomposed so rapidly in the mesomorphic
temperature region that the XRD pattern was measured for the
glassy mesophase at rt. As can be seen from Fig. 4[E] and Table
4, this glassy mesophase gave ve reections. All the peaks
except for Peak no. 5 could be assigned to the reections from a
is a rationally proper value.
When this glassy Colro(P2m) mesophase was heated over the
glass transition temperature at 87.4 ꢀC, it relaxed into a crys-
talline phase K1. The XRD pattern of the K1 phase gave a lot of
sharp peaks in all the regions, from low angles to high angles.
This apparently implies that the glassy mesophase is crystal-
ꢀ
ꢀ
ꢀ
ꢀ
lized. On heating to the melting point from 299.4 C, no XRD
pattern of the Colro(P2m) appeared again. Therefore, the
Colro(P2m) mesophase is considered monotropic and appears
only for the freshly prepared virgin sample as a glassy
Colro(P2m) mesophase.
ꢀ
2D tetragonal lattice with the lattice constant, a ¼ 22.3 A. Peak
ꢀ
no. 5 could be assigned to the stacking distance (h ¼ 3.87 A).
[(m-C1)PhO]8PcCu (3c). Fig. 4[B] shows the XRD patterns of
the [(m-C1)PhO]8PcCu (3c) derivatives at 230 ꢀC, 310 ꢀC and
370 ꢀC. As can be seen from the XRD patterns inꢀFig. 4[B] and the
X-ray data in Table 4, the XRD pattern at 230 C gave thirteen
3.5 Mesomorphism depending on the number and position
of the methoxy group
peaks. All the peaks except for Peak no. 8 could be well assigned Fig. 5 illustrates the dependence of the mesophase structure on
to the reections from a 2D rectangular lattice with a P21/a the bulky substituent for the present ying-seed-like liquid
ꢀ
ꢀ
symmetry and the lattice constants, a ¼ 29.4 A and b ¼ 26.5 A. crystals based on (PhO)8PcCu. As can be seen from this gure,
ꢀ
Peak no. 8 could be assigned to the stacking distance (h ¼ 6.09 A). the bulkier the substituent becomes, the higher the symmetry of
Table 5 Appearance of mesomorphism for the flying-seed-like compounds (3a–g) based on (PhO)8PcCua
0
Compound
Substituent
X0
H
Xm
H
Xp
H
Xm
Appearance of mesophase
3a: (PhO)8PcCu
H
3b: [(o-C1)PhO]8PcCu
OCH3
H
H
H
3c: [(m-C1)PhO]8PcCu
3d: [(p-C1)PhO]8PcCu
H
H
H
H
H
H
OCH3
3e: {[m,p-(C1)2]PhO}8PcCu
3f: {[m,m0-(C1)2]PhO}8PcCu
OCH3
H
H
H
H
OCH3
3g: {[m,p,m0-(C1)3]PhO}8PcCu
H
OCH3
OCH3
a
: no mesophase appears; : monotropic mesophase appears; : enantiotropic mesophase appears.
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the mesophase becomes, in the order of (c, e) / f / g. Since ortho position, 3b, shows a monotropic mesophase. The reason
the bulkiness of the substituent of c and e induced by the ip- for this could be due to the excluded volume of the phenoxy
op is the same, it may result in the same symmetry of P21/a for group originated by ip-op and steric hindrance of the
3c and 3e.
Table 5 summarizes the appearance of the mesomorphism
methoxy group(s) for stacking of the Pc cores.
Fig. 6 illustrates three representative molecular structures of
of the present (PhO)8PcCu derivatives 3a–g. As can be seen from (PhO)8PcCu (3a) showing no mesophase, [(o-C1)PhO]8PcCu (3b)
this table, the derivatives with methoxy group(s) at the meta showing a monotropic mesophase, and [(m-C1)PhO]8PcCu (3c)
position(s), 3c, 3e, 3f and 3g, show enantiotropic mesophase(s), showing an enantiotropic mesophase. In this gure are also
whereas neither the derivative with no methoxy group, 3a, nor schematically illustrated the excluded volume from ip-
the derivative with a methoxy group at the para position, 3d, opping the substituent as a corn. As can be seen from this
show a mesophase. The derivative with a methoxy group at the gure, the excluded volume in 3a showing no mesophase is
obviously smaller than the excluded volume in 3c showing a
mesophase. Hence, the excluded volume may be strongly
related with the appearance of mesomorphism: it could be that
the excluded volume originated by the ip-opping of the
substituent is too small to form the part so enough for the
appearance of a mesophase.
Accordingly, when a methoxy group is substituted at the para
position in the phenoxy group, such as in 3d, the excluded
volume is too small to show a mesophase. When a methoxy
group is substituted at an ortho position, such as in 3b, the
excluded volume is the same as that of 3c. However, 3c shows
enantiotropic mesophases, whereas 3b show a monotropic
mesophase. This may be attributed to the steric hindrance of
the ortho-methoxy group that covers the Pc core plane, as
already mentioned in the previous Section 3.2. The steric
hindrance may block the stacking of the central Pc cores and
suppress the formation of the columnar mesophase. This may
decrease the clearing point of the mesophase and relatively
elevate the melting point of the crystalline phase to induce the
monotropic mesophase for 3b.
The driving force of columnar structure formation for disk-
like molecules is intermolecular p–p interactions among the
central cores. It has already reported that peripheral substitu-
ents have an effect on the columnar mesophase structures.26–28
Since the intermolecular interaction among the central cores
of a series of the present PcCu-based liquid crystals is also
affected by the peripheral bulky substituents, b, c, e, f and g,
the various kinds of columnar mesophases, Colro(P2m),
Colro(P21/a), Colro(C2/m) and Coltet.o, may be formed. It is very
interesting that the appearance of mesomorphism and the
mesophase structures are greatly affected by the number and
position of the methoxy groups.
4 Conclusion
We have synthesized a novel series of ying-seed-like derivatives
(3a–g) based on phthalocyaninato copper(II) (abbreviated as
PcCu) substituted by bulky groups {PhO (a), (o-C1)PhO (b),
(m-C1)PhO (c), (p-C1)PhO (d), [m,p-(C1)2]PhO (e), [m,m0-(C1)2]PhO
(f), [m,p,m0-(C1)3]PhO (g)} in order to investigate how they show
mesomorphism depending on the number and position of
methoxy groups. As a result, (PhO)8PcCu (3a) and [(p-C1)PhO]8PcCu
(3d) were seen to show no mesophase, whereas [(m-C1)PhO]8PcCu
(3c), {[m,p-(C1)2]PhO}8PcCu (3e), {[m,m0-(C1)2]PhO}8PcCu (3f),
and {[m,p,m0-(C1)3]PhO}8PcCu (3g) show various kinds of
Fig. 6 Appearance of mesomorphism depending on bulkiness of the
substituents. : no mesophase appears; : monotropic mesophase
appears; : enantiotropic mesophase appears.
columnar mesophases of Colro(P21/a), Colro(P21/a), Colro(C2/m)
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and Coltet.o, respectively; [(o-C1)PhO]8PcCu (3b) shows a mono- 11 Y. Takagi, K. Ohta, S. Shimosugi, T. Fujii and E. Itoh, J.
tropic Colro(P2m) mesophase. Thus, the derivative substituted Mater. Chem., 2012, 22, 14418–14425.
by a methoxy group at a para position (3d) does not show 12 A. Hachisuga, M. Yoshioka, K. Ohta and T. Itaya, J. Mater.
mesomorphism because the excluded volume originated by the Chem., 2013, 1, 5315–5321.
ip-opping substituent is small. On the other hand, the 13 C. Eaborn and N. H. Hartshorne, J. Chem. Soc., 1955, 549–
derivatives substituted by (a) methoxy group(s) at (a) meta 555.
position(s) (3c, e, f and g) show enantiotropic mesomorphism 14 J. D. Buning, J. E. Lydon, C. Eaborn, P. M. Jackson,
because the excluded volume is big enough. The derivative
substituted by a methoxy group at an ortho position (3b) shows
J. W. Goodby and G. W. Gray, J. Chem. Soc., Faraday Trans.
1, 1982, 78, 713–724.
monotropic mesomorphism, as the excluded volume is big 15 S. Basurto, S. Garcia, A. G. Neo, T. Torroba, C. F. Marcos,
enough but the steric hindrance may block the stacking of the
D. Miguel, J. Barbera, M. B. Ros and M. R. de la Fuente,
central Pc cores.
Chem.–Eur. J., 2005, 11, 5362–5376.
In this work, we have revealed that mesomorphism could be 16 M. Shimizu, M. Nata, K. Watanabe, T. Hiyama and S. Ujiie,
induced by these novel bulky substituents instead of using long Mol. Cryst. Liq. Cryst., 2005, 441, 237–241.
alkyl chains, and that the mesophase structures are greatly 17 M. Shimizu, M. Nata, K. Mochida, T. Hiyama, S. Ujiie,
affected by the number and position of the methoxy groups. It is
very interesting that the derivatives with methoxy group(s) at the
M. Yoshio and T. Kato, Angew. Chem., Int. Ed., 2007, 46,
3055–3058.
meta position(s), i.e., 3c, 3e, 3f and 3g, tend to show enantio- 18 H. Sato, K. Igarashi, Y. Yama, M. Ichihara, E. Itoh and
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