Flying-seed-like liquid crystals 2: Unprecedented guidelines to obtain liquid crystalline compounds

Article abstract of DOI:10.1039/c2jm32284f

In order to obtain novel "flying-seed-like" liquid crystals, we have prepared a series of bulky group-substituted phthalocyanine derivatives without any long alkyl chains: tetra[4-(triphenylmethyl)-phenoxy] phthalocyaninato copper(ii) (1a), tetra[4-(1,1-d

Full text of DOI:10.1039/c2jm32284f

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PAPER
Flying-seed-like liquid crystals 2: unprecedented guidelines to obtain liquid
crystalline compounds†
a
a
Yasufumi Takagi, Kazuchika Ohta, Shota Shimosugi,a Tatsuya Fujiia and Eiji Itohb
*
Received 12th April 2012, Accepted 14th May 2012
DOI: 10.1039/c2jm32284f
In order to obtain novel ‘‘flying-seed-like’’ liquid crystals, we have prepared a series of bulky group-
substituted phthalocyanine derivatives without any long alkyl chains: tetra[4-(triphenylmethyl)-
phenoxy]phthalocyaninato copper(II) (1a), tetra[4-(1,1-diphenylethyl)phenoxy]phthalocyaninato
copper(II) (1b), tetra[4-(1-methyl-1-phenylethyl)phenoxy]phthalocyaninato copper(II) (1c), tetra[4-
(tert-butyl)phenoxy]phthalocyaninato copper(II) (1d), and octa[4-(triphenylmethyl)phenoxy]
phthalocyaninato copper(II) (4). We have established by using a polarizing optical microscope,
a differential scanning calorimeter and a temperature-dependent small angle X-ray diffractometer that
the Pc derivatives 1a–d, but not 4, show columnar mesomorphism from r.t. to the extremely high
decomposition temperatures at 450–500 ꢀC. Their mesomorphism originates from thermal fluctuations
due to free rotation of the bulky substituents. Thus, we have systematically demonstrated for the first
time that liquid crystals can be also obtained by a series of novel bulky substituents instead of
conventional long alkyl chains. Hence, we will be able to obtain a wide variety of new liquid crystalline
compounds by using these bulky substituents instead of long alkyl chains. Very interestingly, these are
unprecedented guidelines to obtain liquid crystalline compounds.
chains nor a central flat core, as shown in Fig. 1. However, the
Introduction
mesomorphism of Ph2CHCOONa has been forgotten and not
been investigated for about 100 years.4 It is attributable to the
molecular shape that is totally different from conventional
calamitic and discotic liquid cryꢀstals, and a very high mesophase
temperature region above 251 C. There have been only a few
reports on this type of liquid crystalline metal carboxylates by
Demus et al.,5 Sanesi et al.6,7 and Binnemans et al.8
Since the first liquid crystal was found by Reinitzer in 1888,1
about 101 000 liquid crystals2 have been synthesized and inves-
tigated. Most of the liquid crystals are broadly categorized into
‘‘calamitic liquid crystals’’ of rod-like molecules as the first liquid
crystalline group, and ‘‘discotic liquid crystals’’ of disk-like
molecules as the second liquid crystalline group.3 These liquid
crystalline materials are generally categorized by their molecular
shapes, and each of them commonly has a flat lath-like or disk-
like core in the center and long alkyl chains in the periphery.
When the material is heated, the long alkyl chains only melt to
form soft parts and the central cores persistently do not melt.
This leads to mesomorphism. Accordingly, people have long
believed that mesomorphism is the result of ‘‘both the soft part of
premelting long alkyl chains and the remaining solid part of
central flat cores’’, for all the calamitic and discotic liquid crys-
tals. However, it has been reported that a very few liquid crystals
have neither peripheral long chains nor a central flat core.4–12
€
In 1911 Vorlander found mesomorphism of sodium dipheny-
lacetate (Ph2CHCOONa) which has neither peripheral long alkyl
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
bDepartment of Electrical and Electronic Engineering, Shinshu University,
Fig. 1 Molecular structure and mesophase structure of the first flying-
4-17-1 Wakasato, Nagano 380-8553, Japan
† Part 1: ref. 9 in this paper.
seed-like liquid crystal and a photograph of maple seeds.
14418 | J. Mater. Chem., 2012, 22, 14418–14425
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In 2006 we established by using temperature-dependent X-ray
diffraction studies that Ph2CHCOONa exhibits a hexagonal
columnar (Colh) mesophase.9 Since Ph2CHCOONa resembles
a flying seed as shown in Fig. 1, we named this type of liquid
crystals as ‘‘flying-seed-like liquid crystals’’, which are the third
liquid crystalline group.
Recently, Usol’tseva et al. reported a liquid crystalline phtha-
locyanine (Pc) derivative, (3Ph-PhO)4PcCu (1a in Scheme 1),
which has a central flat core and peripheral bulky triphenyl-
methylphenoxy groups instead of long alkyl chains.13,14 This
mesophase was identified as a Colh mesophase only from micro-
scopic observations. The detailed mesophase structure has never
been established by X-ray diffraction studies. However, the
substituent triphenylmethylphenoxy group in this compound
greatly resembles the diphenylmethyl group in the flying-seed-like
liquid crystal of Ph2CHCOONa. Therefore, we regarded this
phthalocyanine (Pc) derivative as one of the novel flying-seed-like
liquid crystals.
In this work, we have synthesized a series of Pc derivatives
including Usol’tseva’s compound 1a ((3Ph-PhO)4PcCu) and four
novel Pc compounds (1b–d and 4) substituted by a series of bulky
groups, as illustrated in Schemes 1 and 2. As can be seen from
these schemes, the Pc compounds, 1b ((2Ph-PhO)4PcCu), 1c
((1Ph-PhO)4PcCu) and 1d ((0Ph-PhO)4PcCu), are substituted by
four bulky groups of (1,1-diphenylethyl)phenoxy, (1-methyl-1-
phenylethyl)phenoxy and (tert-butyl)phenoxy, respectively; the
Pc compound 4 ((3Ph-PhO)8PcCu) is substituted by eight bulky
Scheme 2 Synthetic route for the Pc derivative 4, (3Ph-PhO)8PcCu.
groups of triphenylmethylphenoxy. We have established their
mesomorphism in detail by using a polarizing optical micro-
scope, a differential scanning calorimeter and a temperature-
dependent small angle X-ray diffractometer. Surprisingly, the Pc
derivatives 1a–d having four bulky groups showed columnar
mesophases from r.t. to the extremely high decomposition
temperatures at 450–500 ꢀC; on the other hand, the Pc derivative
4 having eight bulky groups showed not a mesophase but
a crystalline phase from r.t. to the decomposition temperature at
about 470 ꢀC. Thus, we have systematically demonstrated for the
first time that liquid crystals can be also obtained by a series of
novel bulky substituents instead of conventional long alkyl
chains. Hence, we will be able to obtain a wide variety of new
liquid crystalline compounds by using these bulky substituents
instead of conventional long alkyl chains. Very interestingly,
these are unprecedented guidelines to obtain liquid crystalline
compounds. We wish to report here the interesting meso-
morphism of 1a–d.
Experimental
Synthesis
Scheme 1 shows the synthetic route for the tetra-substituted
phthalocyanine derivatives 1a–d. The starting material of 4-
nitrophthalonitrile was purchased from Tokyo Chemical
Industry (Tokyo Kasei). Dicyano derivatives 3a–d were synthe-
sized from 4-nitrophthalonitrile and the corresponding phenol
derivatives 2a–d by the method of Galanin et al.15 The target
phthalocyanine derivatives 1a–d were synthesized from dicyano
derivatives 3a–d by using our previously reported microwave
heating apparatus.16 The synthetic route for the octa-substituted
phthalocyanine derivative 4 is shown in Scheme 2. The starting
material of 4,5-dichlorophthalonitrile was purchased from
Scheme 1 Synthetic route for the Pc derivatives 1a–d. Abbreviation: (X-
PhO)yPcCu (X ¼ the number of phenyl groups in substituent A, y ¼ the
number of A-PhO groups in the PcCu complex). DBU ¼ 1,8-diazabicyclo
[5,4,0]-undec-7-ene.
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Tokyo Chemical Industry (Tokyo Kasei). Dicyano derivative 5
with water and dried over anhydrous sodium sulfate. Then the
solvent was evaporated under reduced pressure. The crude
product was purified by column chromatography (silica gel,
dichloromethane, Rf ¼ 0.76) to give 0.12 g of the pale yellow
solid. Yield ¼ 97%, m.p. ¼ 187.4 ꢀC. IR (KBr): 3045.12 (Ar-H),
2979.27 (–CH3), 2221.95 (–CN), 1486.59 (C]C), 1239.63 (ether)
was synthesized from 4,5-dichlorophthalonitrile and 4-(triphe-
€
17
nylmethyl)phenol by the method of Wohrle et al. The target
phthalocyanine derivative 4 was also synthesized from dicyano
derivative 5 by using the microwave heating apparatus.16 The
detailed procedures are described as follows.
1
cmꢁ1. H-NMR (DMSO-d6: TMS) d 2.16 (s, 3H, –CH3), 7.07–
4-[40-(Triphenylmethyl)phenoxy]-1,2-dicyanobenzene (3a). Into
a 50 ml three-neck flask, 4-nitrophthalonitrile (0.30 g, 1.7 mmol),
dry N,N-dimethylformamide (6.0 ml), 4-(triphenylmethyl)phenol
(0.70 g, 2.1 mmol) and anhydrous potassium carbonate (0.30 g,
2.3 mmol) were placed and the mixture was stirred at 110 ꢀC
under a nitrogen atmosphere for 2.5 h. After cooling to room
temperature, the reaction mixture was extracted with chloro-
form. The organic layer was washed with water and dried over
anhydrous sodium sulfate. Then the solvent was evaporated
under reduced pressure. The crude product was purified by
column chromatography (silica gel, chloroform, Rf ¼ 0.48) twice
to give 0.71 g of the white solid. Yield ¼ 96%, m.p. ¼ 228.2 ꢀC.
IR (KBr): 3050.90 (Ar-H), 2230.39 (–CN), 1593.60 (C]C),
7.35 (m, 14H, Ar-H), 7.41 (dd, 1H, J1 ¼ 9.1 Hz, J2 ¼ 2.7 Hz, CN-
5-Ar-H), 7.82 (d, 1H, J ¼ 2.5 Hz, CN-3-Ar-H), 8.10 (d, 1H,
J ¼ 8.8 Hz, CN-6-Ar-H).
Tetra[4-(1,1-diphenylethyl)phenoxy]phthalocyaninato
cop-
per(II): (2Ph-PhO)4PcCu (1b). A mixture of 4-[40-(10,10-dipheny-
lethyl)phenoxy]-1,2-dicyanobenzene (0.096 g, 0.24 mmol), CuCl2
(0.032 g, 0.24 mmol), DBU (8 drops) and glycerin (6.0 ml) was
poured into a test tube. The air in the test tube was replaced by
a nitrogen atmosphere for 20 min. It was heated by microwave
irradiation and kept at 200 ꢀC for 20 min. After cooling to room
temperature, water was added to the reaction mixture and
filtered with suction. The residue was washed with methanol and
ethanol. The crude product was purified by column chroma-
tography (silica gel, dichloromethane, Rf ¼ 1.0) and purified
from n-hexane by solid–liquid extraction twice to give 0.018 g of
the dark blue glassy liquid crystal. Yield ¼ 18%.
1
1254.09 (ether) cmꢁ1. H-NMR (DMSO-d6: TMS) d 7.11–7.35
(m, 19H, Ar-H), 7.44 (dd, 1H, J1 ¼ 8.8 Hz, J2 ¼ 2.7 Hz, CN-5-
Ar-H), 7.85 (d, 1H, J ¼ 3.0 Hz, CN-3-Ar-H), 8.11 (d, 1H, J ¼ 8.8
Hz, CN-6-Ar-H).
MALDI-TOF mass data: see Table 1.
Tetra[4-(triphenylmethyl)phenoxy]phthalocyaninato copper(II):
(3Ph-PhO)4PcCu (1a). A mixture of 4-[40-(triphenylmethyl)
phenoxy]-1,2-dicyanobenzene (0.22 g, 0.48 mmol), CuCl2 (0.032
g, 0.24 mmol), 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) (15
drops) and glycerin (8.0 ml) was poured into a test tube. The air
in the test tube was replaced by a nitrogen atmosphere for 10
min. It was heated by microwave irradiation and kept at 200 ꢀC
for 20 min. After cooling to room temperature, water was added
to the reaction mixture and filtered with suction. The residue
was washed with methanol and ethanol. The crude product was
purified by column chromatography (silica gel, dichloro-
methane, Rf ¼ 1.0) and purified from n-hexane by solid–liquid
extraction twice to give 0.030 g of the dark blue glassy liquid
crystal. Yield ¼ 13%.
UV-vis spectral data: see Table 2.
4-[40-(10-Methyl-10-phenylethyl)phenoxy]-1,2-dicyanobenzene
(3c). Into a 100 ml three-neck flask, 4-nitrophthalonitrile (1.0 g,
5.8 mmol), dry N,N-dimethylformamide (30 ml), 4-(1-methyl-1-
phenylethyl)phenol (1.9 g, 8.8 mmol) and anhydrous potassium
carbonate (1.5 g, 11 mmol) were placed and the mixture was
ꢀ
stirred at 110 C under a nitrogen atmosphere for 2.5 h. After
cooling to room temperature, the reaction mixture was extracted
with chloroform. The organic layer was washed with water and
dried over anhydrous sodium sulfate. Then the solvent was
evaporated under reduced pressure. The crude product was
purified by column chromatography (silica gel, dichloromethane,
Rf ¼ 0.63) twice to give 1.9 g of the pale yellow solid. Yield ¼
95%, m.p. ¼ 60.1 ꢀC. IR (KBr): 3050.61 (Ar-H), 2970.06 (–CH3),
2231.87 (–CN), 1486.62 (C]C), 1250.44 (ether) cmꢁ1. 1H-NMR
(DMSO-d6: TMS) d 1.67 (s, 6H, –CH3), 7.07–7.37 (m, 10H, Ar-H
and CN-5-Ar-H), 7.77 (d, 1H, J ¼ 2.3 Hz, CN-3-Ar-H), 8.09 (d,
1H, J ¼ 8.8 Hz, CN-6-Ar-H).
MALDI-TOF mass data: see Table 1.
UV-vis spectral data: see Table 2.
4-[40-(10,10-Diphenylethyl)phenoxy]-1,2-dicyanobenzene
(3b).
Into a 50 ml three-neck flask, 4-nitrophthalonitrile (0.052 g,
0.30 mmol), dry N,N-dimethylformamide (1.0 ml), 4-(1,1-
diphenylethyl)phenol (0.10 g, 0.36 mmol) and anhydrous
potassium carbonate (0.059 g, 0.43 mmol) were placed and the
Tetra[4-(1-methyl-1-phenylethyl)phenoxy]phthalocyaninato cop-
per(II): (1Ph-PhO)4PcCu (1c). A mixture of 4-[40-(10-methyl-10-
phenylethyl)phenoxy]-1,2-dicyanobenzene (0.081 g, 0.24 mmol),
CuCl2 (0.032 g, 0.24 mmol), DBU (8 drops) and glycerin (6.0 ml)
was poured into a test tube. The air in the test tube was replaced
ꢀ
mixture was stirred at 110 C under a nitrogen atmosphere for
2.0 h. After cooling to room temperature, the reaction mixture
was extracted with chloroform. The organic layer was washed
Table 1 MALDI-TOF mass spectral data for the Pc derivatives 1a–d and 4
Derivative
Molecular formula
Molecular weight
Mass observed
1a: (3Ph-PhO)4PcCu
1b: (2Ph-PhO)4PcCu
1c: (1Ph-PhO)4PcCu
1d: (0Ph-PhO)4PcCu
4: (3Ph-PhO)8PcCu
C132H88O4N8Cu
C112H80O4N8Cu
C92H72O4N8Cu
C72H64O4N8Cu
C232H160O8N8Cu
1913.75
1665.46
1417.18
1168.90
3251.42
1915.99
1665.46
1415.47
1167.40
3251.55
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Table 2 UV-vis spectral data in chloroform of the Pc derivatives 1a–d and 4
lmax (nm) (log 3)
Q-band
Concentrationa
Derivative
(ꢂ10ꢁ5 mol lꢁ1
)
Soret-band
Q0–1 band
Q0–0 band
1a: (3Ph-PhO)4PcCu
1b: (2Ph-PhO)4PcCu
1c: (1Ph-PhO)4PcCu
1d: (0Ph-PhO)4PcCu
4: (3Ph-PhO)8PcCu
1.31
1.13
1.26
1.37
1.20
287.0 (4.74)
285.4 (4.86)
284.5 (4.73)
284.5 (4.60)
289.3 (4.83)
339.6 (4.86)
339.0 (4.97)
339.9 (4.82)
340.7 (4.70)
341.6 (4.86)
391.2 (4.41)
394.4 (4.47)
389.8 (4.35)
393.4 (4.26)
398.8 (4.47)
613.7 (4.61)
615.9 (4.75)
614.9 (4.60)
614.9 (4.47)
613.7 (4.61)
681.3 (5.17)
682.1 (5.28)
682.1 (5.15)
682.1 (5.01)
682.3 (5.36)
650.9 (4.57)
a
In chloroform.
by a nitrogen atmosphere for 20 min. It was heated by microwave
irradiation and kept at 200 ꢀC for 10 min. After cooling to room
temperature, water was added to the reaction mixture and filtered
with suction. The residue was washed with methanol and ethanol.
The crude product was purified by column chromatography (silica
gel, dichloromethane, Rf ¼ 1.0) and purified from n-hexane by
solid–liquid extraction twice to give 0.021 g of the dark blue liquid
crystal. Yield ¼ 25%.
MALDI-TOF mass data: see Table 1.
UV-vis spectral data: see Table 2.
Bis{4,5-[40-(triphenylmethyl)phenoxy]}-1,2-dicyanobenzene (5).
Into a 50 ml three-neck flask, 4-triphenylmethylphenol (1.1 g,
3.3 mmol), dry N,N-dimethylformamide (20 ml) and anhydrous
potassium carbonate (3.5 g, 26 mmol) were placed and the
mixture was stirred at 120 ꢀC under a nitrogen atmosphere for 10
min. 4,5-Dichlorophthalonitrile (0.30 g, 1.5 mmol) was added to
the mixture. The reaction mixture was stirred at 120 ꢀC for
a further 2.0 h under a nitrogen atmosphere. After cooling to
room temperature, the reaction mixture was extracted with
diethyl ether. The organic layer was washed with water and dried
over anhydrous sodium sulfate. Then the solvent was evaporated
under reduced pressure. The crude product was purified by
column chromatography (silica gel, chloroform, Rf ¼ 0.75) to
MALDI-TOF mass data: see Table 1.
UV-vis spectral data: see Table 2.
4-[40-(tert-Butyl)phenoxy]-1,2-dicyanobenzene
(3d).
Into
a 100 ml three-neck flask, 4-nitrophthalonitrile (1.5 g, 8.7 mmol),
dry N,N-dimethylformamide (30 ml), 4-(tert-butyl)phenol (1.6 g,
10 mmol) and anhydrous potassium carbonate (1.7 g, 13 mmol)
were placed and the mixture was stirred at 110 ꢀC under
a nitrogen atmosphere for 3.0 h. After cooling to room temper-
ature, the reaction mixture was extracted with chloroform. The
organic layer was washed with water and dried over anhydrous
sodium sulfate. Then the solvent was evaporated under reduced
pressure. The crude product was purified by column chroma-
tography (silica gel, dichloromethane, Rf ¼ 0.60) to give 2.1 g of
ꢀ
give 1.1 g of the white solid. Yield ¼ 96%, m.p. ¼ 311.4 C. IR
(KBr): 3054.91 (Ar-H), 2228.88 (–CN), 1590.57 (C]C), 1228.57
(ether) cmꢁ1. 1H-NMR (DMSO-d6: TMS) d 6.88 (4H, d, J ¼ 8.8
Hz, -O-2,6-Ar-H) 7.08–7.29 (34H, m, -O-3,5-Ar-H and Ar-H),
7.94 (2H, s, CN-Ar-H).
ꢀ
the pale yellow solid. Yield ¼ 87%, m.p. ¼ 115.7 C. IR (KBr):
Octa[4-(triphenylmethyl)phenoxy]phthalocyaninato copper(II):
(3Ph-PhO)8PcCu (4). A mixture of bis{4,5-[40-(triphenylmethyl)
phenoxy]-1,2-dicyanobenzene (0.22 g, 0.28 mmol), CuCl2
(0.018 g, 0.14 mmol), DBU (12 drops) and glycerin (8.0 ml) was
poured into a test tube. The air in the test tube was replaced by
a nitrogen atmosphere for 20 min. It was heated by microwave
irradiation and kept at 200 ꢀC for 30 min. After cooling to room
temperature, water was added to the reaction mixture and filtered
with suction. The residue was washed with methanol and ethanol.
The crude product was purified bycolumn chromatography (silica
gel, dichloromethane, Rf ¼ 1.0) and purified from n-hexane by
solid–liquid extraction twice. Furthermore, the crude product was
purified by column chromatography (silica gel, chloroform,
Rf ¼ 0.95) and purified from n-hexane by solid–liquid extraction
twice to give 0.053 g of the green solid. Yield ¼ 24%.
3078.05 (Ar-H), 2975.32 (–CH3), 2232.93 (–CN), 1503.05
(C]C), 1239.63 (ether) cmꢁ1. 1H-NMR (DMSO-d6: TMS) d 1.31
(s, 9H, –CH3), 7.10–7.15 (m, 2H, 3,5-Ar-H), 7.34 (dd, 1H, J1 ¼
8.6 Hz, J2 ¼ 2.5 Hz, CN-5-Ar-H), 7.49 (m, 2H, 2,6-Ar-H), 7.76
(d, 1H, J ¼ 2.5 Hz, CN-3-Ar-H), 8.08 (d, 1H, J ¼ 8.8 Hz, CN-6-
Ar-H).
Tetra[4-(tert-butyl)phenoxy]phthalocyaninato copper(II): (0Ph-
PhO)4PcCu (1d). A mixture of 4-[40-(tert-butyl)phenoxy]-1,2-
dicyanobenzene (0.066 g, 0.24 mmol), CuCl2 (0.032 g,
0.24 mmol), DBU (8 drops) and glycerin (6.0 ml) was poured into
a test tube. The air in the test tube was replaced by a nitrogen
atmosphere for 20 min. It was heated by microwave irradiation
ꢀ
and kept at 200 C for 20 min. After cooling to room tempera-
ture, the reaction mixture was extracted with chloroform. The
organic layer was washed with water and dried over anhydrous
sodium sulfate. Then the solvent was evaporated under reduced
pressure. The crude product was dispersed in acetone by using an
ultrasonic washing machine (SHARP: UT-105S), and left for
a while. The precipitate was collected by filtration and washed
with acetone to give 0.045 g of the dark blue liquid crystal.
Yield ¼ 6.4%.
MALDI-TOF mass data: see Table 1.
UV-vis spectral data: see Table 2.
Measurements
The precursors of dicyanobenzene derivatives 3a–d and 5 were
identified by 1H-NMR measurement (BRUKER DRX-400) and
FT-IR spectroscopy (Nicolet NEXUS 670). The phthalocyanine
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derivatives 1a–d and 4 were identified by MALDI-TOF mass
spectral measurement (PerSeptive Biosystems Voyager DE-Pro
spectrometer) and UV-vis spectroscopy (HITACHI U-4100
spectrophotometer). MALDI-TOF mass spectral data and elec-
tronic spectral data of the phthalocyanine derivatives 1a–d and 4
are summarized in Tables 1 and 2, respectively.
data listed in Tables 1 and 2 gave satisfactory evidence of
successful syntheses of the target Pc compounds.
Phase transition sequences for the Pc derivatives 1a–d and 4
(3Ph-PhO)4PcCu (1a). As can be seen from Table 3, the freshly
prepared (virgin) sample of (3Ph-PhO)4PcCu (1a) gave the same
glass transition temperature (Tg) at 211 ꢀC as reported by
Usol’tseva et al.,13,14 but the non-virgin sample showed another
Tg at 183–187 ꢀC lower than that of the virgin sample. On further
heating, this derivative decomposed at ca. 500 ꢀC. The reason
why two Tg points were observed may be attributed to the
following effects. The virgin sample was vitrified by evaporation
of the solvent under reduced pressure on purification, whereas
the non-virgin sample was vitrified by cooling the neat material
in the Colh mesophase without solvent. The different cooling
rates and viscosities may induce these two different Tg points.
Although Usol’tseva et al. observed the natural texture made
by cooling from the isotropic liquid (I.L.) state,13,14 we could
observe neither the I.L. state nor the natural texture of (3Ph-
PhO)4PcCu (1a). However, when it was pressed on the cover slip,
it was rigid under the Tg points but sticky over the Tg points
(Fig. 2a). Stickiness with birefringence is a characteristic of the
general columnar liquid crystalline phase. The temperature-
dependent small angle X-ray diffraction pattern of (3Ph-
The phase transition sequences for the phthalocyanine deriv-
atives 1a–d and 4 were revealed by using a polarizing optical
microscope (Nikon ECLIPSE E600 POL) equipped with a heat-
ing plate (Mettler FP82HT hot stage, Mettler FP-90 Central
Processor) and a differential scanning calorimeter (Shimadzu
DSC-50). The decomposition temperatures were measured by
a Rigaku Thermo plus TG 820 thermogravity analyser. The
identification of the mesophases was performed by using a small
angle X-ray diffractometer (Bruker Mac SAXS System: Cu-Ka
radiation) equipped with a heating plate (Mettler FP82HT hot
stage, Mettler FP-90 Central Processor). The measurement
region was 2q ¼ 0.8–26.9ꢀ.
Results and discussion
Syntheses of the Pc derivatives 1a–d and 4
The target Pc derivatives 1a–d and 4 were successfully synthe-
sized by using microwave heating,16 which causes rapid heating
and accelerates the rate of reaction. Microwave heating enabled
us to carry out the syntheses in a clean and energy-saving way.
Although elemental analyses of the Pc derivatives 1a–d and 4
synthesised here were carried out, they were not completely burnt
out so that the observed carbon content showed lower percent-
ages than the calculated values by several percent. This is a well-
known characteristic of less flammable phthalocyanine deriva-
tives.18 Hence, the results of the elemental analyses are not listed
here. However, the MALDI-TOF mass and electronic spectral
ꢀ
PhO)4PcCu at 375 C is shown in Fig. 3a. As can be seen from
this pattern, it gave both sharp and broad peaks characteristic of
the liquid crystalline phase. The sharp peaks 1–4 could be
assigned to the reflections from
a 2D hexagonal lattice
ꢀ
(a ¼ 30.0 A). Broad peaks, #1 (no. 5) and #2 (no. 6), are
attributable to the average distances among the freely rotating
phenoxy groups and triphenylmethyl groups, respectively. As
can be seen from the XRD patterns in Fig. 3a–e, each of the
Table 3 Phase transition sequences for the Pc derivatives 1a–d and 4
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tetra-substituted Pc derivatives 1a–d gave a broad peak #1 in
a region of 2q ¼ 10–15ꢀ, so it may correspond to a common
structure of the phenoxy parts in these derivatives 1a–d. On the
other hand, another broad peak #2 at 2q z 20ꢀ could be
observed only for 1a, so it may correspond to the triphe-
nylmethyl parts. These broad peaks represent thermal fluctua-
tions of the bulky substituents, which can cause the softness
necessary for the liquid crystalline phase. This means that liquid
crystals can be also obtained by thermal fluctuation of a series of
novel bulky substituents instead of conventional long alkyl
chains. Peak 7 in the high angle region could be assigned to
a stacking distance (¼ intracolumnar molecular distance:
ꢀ
h ¼ 3.58 A). In Table 4 these X-ray data are listed.
Thus, it was established from the XRD study that (3Ph-
PhO)4PcCu (1a) shows a Colho mesophase, which is consistent
with the identification from polarizing microscopic observation
by Usol’tseva et al.13,14
(2Ph-PhO)4PcCu (1b). As can be seen from ꢀTable 3, (2Ph-
PhO)4PcCu (1b) showed a Tg point at 126–131 C and decom-
posed at ca. 450 ꢀC. This derivative 1b gave neither I.L. nor the
natural texture, and neither did 1a. When 1b was pressed on the
cover slip over the Tg point, it showed stickiness with birefringence
(Fig. 2b). Therefore, 1b apparently showed mesomorphism. The
temperature-dependent small angle X-ray diffraction pattern of
1b gave both sharp and broad peaks (Fig. 3b) which are charac-
teristic of mesomorphism. The sharp peaks 1–4 could be assigned
Fig. 2 Photomicrographs of the Pc derivatives 1a–d and 4. (a) 1a: (3Ph-
PhO)4PcCu; Colho at 375 ꢀC; (b) 1b: (2Ph-PhO)4PcCu; Colho at 375 ꢀC;
(c) 1c: (1Ph-PhO)4PcCu; Colho1 at r.t.; (d) 1c: (1Ph-PhO)4PcCu; Colho2 at
375 ꢀC; (e) 1d: (0Ph-PhO)8PcCu; Colrho at 375 ꢀC; and (f) 4:(3Ph-
PhO)8PcCu; K at 375 ꢀC.
ꢀ
as the reflections from a 2D hexagonal lattice (a ¼ 29.6 A). The
broad peak #1 (no. 5) may correspond to the average distance
among the freely rotating phenoxy parts. Peak 6 in the high angle
ꢀ
region could be assigned to a stacking distance (h ¼ 3.49 A). From
these X-ray data, the mesophase of (2Ph-PhO)4PcCu (1b) could be
identified as a Colho mesophase.
(1Ph-PhO)4PcCu (1c). As can be seen from Table 3, (1Ph-
PhO)4PcCu (1c) showed no Tg point unlike 1a and 1b, but two
different Colho mesophases: Colho1 from r.t. to 76.5 ꢀC and
Colho2 from 76.5 ꢀC to the decomposition temperature at ca. 480
ꢀC. This derivative 1c also gave neither I.L. nor the natural
texture, and neither did 1a and 1b. When 1c was pressed on the
cover slip at r.t., it showed softness with birefringence and spread
like boiled Japonica rice (Fig. 2c). On further heating, it became
much softer to form a thinner film by pressing (Fig. 2d). There-
fore, 1c showed mesomorphism from r.t. Each of the tempera-
ture-dependent small angle X-ray diffraction patterns of 1c at r.t.
and 375 ꢀC gave both sharp and broad peaks (Fig. 3c and d)
which are characteristic of mesomorphism. The sharp peaks 1–4
in Fig. 3c could be assigned as the reflections of a 2D hexagonal
ꢀ
lattice having a ¼ 26.6 A. The broad peak #1 (no. 5) may
correspond to the average distance among the freely rotating
phenoxy parts. Peak 6 in the high angle region could be assigned
ꢀ
to a stacking distance (h ¼ 3.35 A). In the same manner, the
diffraction peaks in Fig. 3d could be analysed to obtain the lattice
constants, a ¼ 28.1 A and h ¼ 3.46 A for Colho2 at 375 ꢀC. Thus,
the mesophases of (1Ph-PhO)4PcCu (1c) could be identified as
two different Colho mesophases.
ꢀ
ꢀ
Fig. 3 X-Ray diffraction patterns of the Pc derivatives 1a–d and 4. (a)
1a: (3Ph-PhO)4PcCu; Colho at 375 ꢀC; (b) 1b: (2Ph-PhO)4PcCu; Colho at
375 ꢀC; (c) 1c: (1Ph-PhO)4PcCu; Colho1 at r.t.; (d) 1c: (1Ph-PhO)4PcCu;
Colho2 at 375 ꢀC; (e) 1d: (0Ph-PhO)8PcCu; Colrho at 375 ꢀC; and (f) 4:
(3Ph-PhO)8PcCu; K at 375 ꢀC.
(0Ph-PhO)4PcCu (1d). As can be seen from Table 3, (0Ph-
PhO)4PcCu (1d) showed a single mesophase from r.t. to the
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Table 4 X-Ray data for the Pc derivatives 1a–da
ꢀ
Spacing/A
Miller indices
(h k l)
ꢀ
Lattice constants/A
Derivative (mesophase)
Peak no.
Observed
Calculated
1a: (3Ph-PhO)4PcCu (Colho at 375 ꢀC)
a ¼ 30.0, h ¼ 3.58, Z ¼ 1.0 for r ¼ 1.0
1
2
3
4
5
6
7
1
2
3
4
5
6
1
2
3
4
5
6
1
2
3
4
5
6
1
2
3
4
5
6
7
26.0
15.1
13.0
9.79
ca. 6.9
ca. 4.7
3.58
25.7
14.7
12.6
9.60
ca. 6.5
3.49
23.0
12.8
11.1
8.50
26.0
15.0
13.0
9.82
—
(1 0 0)
(1 1 0)
(2 0 0)
(2 1 0)
#1
—
—
#2
(0 0 1)h
(1 0 0)
(1 1 0)
(2 0 0)
(2 1 0)
#1
1b: (2Ph-PhO)4PcCu (Colho at 375 ꢀC)
1c: (1Ph-PhO)4PcCu (Colho1 at r.t.)
1c: (1Ph-PhO)4PcCu (Colho2 at 375 ꢀC)
1d: (0Ph-PhO)4PcCu (Colrho at 375 ꢀC)
a ¼ 29.6, h ¼ 3.49, Z ¼ 1.0 for r ¼ 1.0
a ¼ 26.6, h ¼ 3.35, Z ¼ 1.0 for r ¼ 1.0
a ¼ 28.1, h ¼ 3.46, Z ¼ 1.0 for r ¼ 1.0
25.7
14.8
12.8
9.70
—
—
(0 0 1)h
(1 0 0)
(1 1 0)
(2 0 0)
(2 1 0)
#1
(0 0 1)h
(1 0 0)
(1 1 0)
(2 0 0)
(2 1 0)
#1
23.0
13.3
11.5
8.69
—
ca. 5.7
3.35
24.3
13.8
11.8
—
24.3
13.8
11.8
8.9
3
—
22.2
16.6
12.5
10.9
8.20
—
8.93
ca. 6.2
3.46
22.2
16.1
12.6
10.9
8.23
ca. 5.9
3.44
(0 0 1)h
(2 0 0), (1 1 0)
(2 1 0)
(0 2 0)
(2 2 0)
(1 3 0)
#1
a ¼ 44.4, b ¼ 25.0, h ¼ 3.44, Z ¼ 2.0 for
r ¼ 1.0
—
(0 0 1)h
a
#1: Halo of free-rotating phenoxy parts. #2: Halo of free-rotating triphenylmethyl parts. h: stacking distance. r: assumed density (g cmꢁ3).
decomposition temperature at ca. 500 ꢀC. The derivative 1d also
gave neither I.L. nor the natural texture, and neither did 1a–c.
When 1d was pressed on the cover slip at r.t., it showed softness
with birefringence and spread like boiled Japonica rice. On
further heating, it became much softer to form a thinner film by
pressing (Fig. 2e). Therefore, 1d also showed mesomorphism
from r.t. Temperature-dependent small angle X-ray diffraction
patterns of 1d at 375 ꢀC gave both sharp and broad peaks
(Fig. 3e). The sharp peaks 1–5 in Fig. 3e could be assigned as the
Since the core part in a Colhr mesophase has a rectangular lattice,
ꢀ
it shows a long slipped stacking distance of ca. 4.0–5.0 A, like
conventional rectangular columnar (Colr) mesophases. On the
other hand, the core part in a Colrh mesophase has a 2D
hexagonal lattice; it shows a short face-to-face stacking distance
ꢀ
of ca. 3.3–3.6 A, like conventional hexagonal columnar (Colh)
mesophases. As can be seen from Table 4, the present pseudo-
hexagonal columnar mesophase of 1d shows a short stacking
ꢀ
distance, 3.44 A, so it could be identified as a Colrh mesophase.
ꢀ
ꢀ
reflections of a pseudohexagonal lattice (a ¼ 44.4 A, b ¼ 25.0 A,
pffiffi
Thus, it was revealed that (0Ph-PhO)4PcCu (1d) shows a single
Colrh mesophase in a very wide temperature region from r.t. to
the decomposition temperature at ca. 500 ꢀC. Such a single
mesophase of 1d has a great merit for application to organic
thin film solar cells, because no phase transition may lead to
a stable functionality in solar cells. Hence, the (0Ph-PhO)4PcCu
(1d) derivative may be the best candidate for application to solar
cells.
a ¼ 3b) from the precise calculation using a reciprocal lattice
method.19 Peak #1 (no. 6) may correspond to the average
distance among the freely rotating phenoxy parts. Peak 7 in the
high angle region could be assigned to a stacking distance
ꢀ
(h ¼ 3.44 A).
To date, two kinds of pseudohexagonal columnar mesophases,
Colhr (hexagonal–rectangular columnar mesophase) and Colrh
(rectangular–hexagonal columnar mesophase), have been
reported. The Colhr mesophase was firstly reported by Guillon
et al.20 In this mesophase, the whole molecules are packed in a 2D
hexagonal lattice, whereas the central core parts are packed in
a rectangular lattice. On the other hand, the Colrh mesophase
was reported by our group.21 In this mesophase, the whole
molecules are packed in a rectangular lattice, whereas the central
core parts are packed in a 2D hexagonal lattice. These two
pseudohexagonal mesophases show different stacking distances.
(3Ph-PhO)8PcCu (4). As can be seen from Table 3, (3Ph-
PhO)8PcCu (4) showed a single crystalline phase (K) from r.t. to
ꢀ
the decomposition temperature at ca. 470 C, without melting.
Whenever the derivative 4 was pressed on the cover slip until the
instrumental limit temperature of 375 ꢀC, it was always rigid
(Fig. 2f). The temperature-dependent X-ray diffraction pattern
of 4 at 375 ꢀC gave only sharp peaks (Fig. 3f) which are a char-
acteristic of the crystalline phase.
14424 | J. Mater. Chem., 2012, 22, 14418–14425
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Acknowledgements
This work is partially supported by Grant-in-Aid for Science
Research (grant no. 2236012311) from the Ministry of Educa-
tion, Culture, Sports, Science and Technology, Japan. We are
grateful to Associate Professor Mikio Yasutake, Saitama
University for his kind measurements of TOF-MASS spectra of
our compounds.
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