Phthalocyanine-based discotic liquid crystals switching from a molten alkyl chain type to a flying-seed-like type

Article abstract of DOI:10.1039/c7tc01197k

We have synthesised a series of phthalocyanine-based discotic liquid crystals, (m-C_nOPhO)₈PcCu (n = 1-20: 2a-o), and investigated their mesomorphism by using a polarizing optical microscope (POM), a differential scanning calorimeter (DSC) and a temperature-dependent small angle X-ray diffractometer. We found that each of the derivatives 2a-o shows mesomorphism. However, the mesomorphism of the (m-C_nOPhO)₈PcCu derivatives strongly depends on the alkoxy chain length (n). The mesomorphism of the short chain-substituted derivatives 2a-e for n = 1-5 is a flying-seed-like type induced by flip-flop of the peripheral bulky substituents, whereas the mesomorphism of the long chain-substituted derivatives 2j-o for n = 10-20 is a conventional molten alkyl chain type induced by melting of the long alkyl chains. The moderately long chain derivatives (2f-i) for n = 6-9 in between show both types of mesophases. The detailed temperature-dependent X-ray diffraction measurements were carried out for three representative derivatives, 2b (n = 2 for n = 1-5), 2h (n = 8 for n = 6-9), and 2o (n = 20 for n = 10-20). As a result, we revealed that the Col_ro(P2m) mesophase in 2b (n = 2) gave a halo denoted as Halo_arom. at d ? 5.2 ? due to flip-flop of the bulky aromatic substituents, and that the Col_ho mesophase in 2o (n = 20) gave a halo denoted as Halo_alkyl at d ? 4.6-4.8 ? due to melting of the long alkyl chains. Therefore, we can distinguish the type of mesophase from Halo_arom. and Halo_alkyl. Very interestingly, the (m-C₈OPhO)₈PcCu (2h) derivative having moderately long alkyl chains gave Halo_alkyl at about 4.8 ? in the lower temperature mesophase of Col_ho, but Halo_arom. at about 5.2 ? in the higher temperature mesophase of Col_ro(P2₁/a). This means that melting of the alkyl chains induces the Col_ho phase in the lower temperature region, but that flip-flop of the bulky aromatic substituents induces the Col_ro(P2₁/a) phase in the higher temperature region. This unusual reverse phase transition sequence from a higher symmetry of the Col_h mesophase to a lower symmetry of the Col_r mesophase on a heating stage is attributable to such a unique stepwise melting of these two different types of substituents. To the best of our knowledge, this mesogen (2h) is the first example switching mesomorphism from the molten alkyl chain type to the flying-seed-like type in a discotic liquid crystal.

Full text of DOI:10.1039/c7tc01197k

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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
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ARTICLE TYPE
Phthalocyanine-based Discotic Liquid Crystal Switching from Molten
Alkyl Chain Type to Flying-seed-like Type
a
a
a
b
Hiromu Nakamura, Kouki Sugiyama, Kazuchika Ohta* and Mikio Yasutake
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
We have synthesised a series of the phthalocyanineꢀbased discotic liquid crystals, (mꢀC OPhO) PcCu (n
n
8
=
1ꢀ20: 2a-o), and investigated their mesomorphism by using a polarizing optical microscopy (POM), a
differential scanning calorimeter (DSC) and a temperatureꢀdependent small angle Xꢀray diffractometer.
We found that each of the derivatives 2aꢀo shows mesomorphism. However, the mesomorphism of the
(mꢀC OPhO) PcCu derivatives strongly depends on the alkoxy chain length (n). The mesomorphism of
the short chainꢀsubstituted derivatives 2aꢀe for n = 1~5 is flyingꢀseedꢀlike type induced by flipꢀflop of the
peripheral bulky substituents, whereas the mesomorphism of the long chainꢀsubstituted derivatives 2jꢀo
for n = 10~20 is conventional molten alkyl chain type induced by melting of the long alkyl chains. The
moderately long chain derivatives (2f-i) for n = 6ꢀ9 in between show both types of mesophases. The
detailed temperatureꢀdependent Xꢀray diffraction measurements were carried out for three representative
derivatives, 2b (n = 2 for n = 1ꢀ5), 2h (n = 8 for n = 6ꢀ9), and 2o (n = 20 for n = 10ꢀ20). As a result, we
1
1
2
2
0
5
0
5
n
8
revealed that the Col (P2m) mesophase in 2b (n = 2) gave a halo denoted as Halo
at d
5.2 Å due
to flipꢀflop of the bulky aromatic substituents, and that the Colho mesophase in 2o (n = 20) gave a halo
denoted as Haloalkyl at d 4.6ꢀ4.8 Å due to melting of the long alkyl chains. Therefore, we can
distinguish the type of mesophase from Haloarom. and Haloalkyl. Very interestingly, the
mꢀC OPhO) PcCu (2h) derivative having moderately long alkyl chains gave Halo
ro
arom.
(
at about 4.8 Å
8
8
alkyl
in the lower temperature mesophase of Col , but Haloarom at about 5.2 Å in the higher temperature
ho
mesophase of Col (P2 /a) phase. This means that melting of the alkyl chains induces the Col phase in
ro
1
ho
the lower temperature region, but that flipꢀflop of the bulky aromatic substituents induces the Col (P2 /a)
ro
1
phase in the higher temperature region. This unusual reverse phase transition sequence from a higher
symmetry of Col mesophase to a lower symmetry of Col mesophase on heating stage is attributable to
h
r
such a unique stepwise melting of these two different types of substituents. To our best knowledge, this
mesogen (2h) is the first example switching mesomorphism from molten alkyl chain type to
flyingꢀseedꢀlike type in a discotic liquid crystal.
chains in the periphery. However, it has been reported that a very
45 few liquid crystalline compounds have neither a rigid core in the
centre nor flexible long alkyl chains in the periphery.
3
0
1. INTRODUCTION
3
ꢀ11
Since the first liquid crystalline compounds were discovered by
In 1911, Vorländer reported that sodium diphenylacetate,
potassium dimethylacetate and potassium diethylacetate show
mesomorphism although there is neither a rigid core in the centre
1
Reinitzer in 1888, over 100,000 kinds of liquid crystalline
2
compounds have been synthesised up to date. These liquid
crystalline compounds are generally classified into rodꢀlike
molecules and discotic molecules judging from their molecular
shapes, but both of them commonly have a structure having a
rigid core at the centre and several flexible long alkyl chains in
the periphery. When these liquid crystalline compounds are
heated, the long alkyl chains melt at first to form a soft part,
whereas the central cores remain as a rigid part without melting,
so that mesomorphism can be induced. Therefore, until now, we
have long believed that it is essential for a liquid crystalline
molecule to have a rigid core in the centre and flexible long alkyl
3
50
nor flexible long alkyl chains in the periphery. However, he only
3
5
reported that they show mesophases, but that neither their
mesophase identification nor the mesomorphism induction
mechanism was clarified. In the past 100 years, a very few
4
5, 6
7
8
researchers, Demus, Sanesi,
Binnnemans, and our group,
55
have investigated these liquid crystalline compounds. In 2006, we
clarified the mesomorphism induction mechanism of sodium
diphenylacetate, potassium dimethylacetate and potassium
4
0
diethylacetate
diffractometer.
by
using
temperatureꢀdependent
Xꢀray
8
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[journal], [year], [vol], 00–00
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DOI: 10.1039/C7TC01197K
Sodium diphenylacetate shows a hexagonal columnar (Colh)
phase. On the other hand, potassium dimethylacetate and
potassium diethylacetate show a smectic A (SmA) phase. These
compounds form a soft part by free rotation of the bulky
In the past five years, we have explored several novel
14ꢀ19
flyingꢀseedꢀlike liquid crystals.
Figure 1B shows our
developed flyingꢀseedꢀlike phthalocyanine derivatives substituted
by bulky substituents to induce mesomorphism. As can be seen
5
0
5
substituents, diphenylmethyl, dimethylmethyl and diethylmethyl 50 from this figure, the nonꢀsubstituted phenoxy group, the
groups. Sodium metals form a oneꢀdimensional nanoꢀwire and
diphenylmethyl groups freely rotate around the nanoꢀwire to form
an aromatic nanotube, so that sodium diphenylacetate shows a
pꢀmethoxyphenoxy group and pꢀpentafluorosulfanylphenoxy
17, 18
group cannot induce mesomorphism.
On the other hand, the
compounds having a methoxy group at the ortho position or the
17
Col phase. On the other hand, in potassium dimethylacetate and
meta position show mesomorphism. Interestingly, when a
55 methoxy group is introduced at least at the meta position in the
h
1
potassium diethylacetate,
potassium
metals
form
a
1
7
twoꢀdimensional potassium metal sheet and dimethylmethyl or
diethylmethyl groups freely rotate to form an aliphatic sheet, so
that they show a SmA phase. Such unique mesomorphism
induction mechanism has never been reported so far. Since the
phenoxy group, these compounds tend to show mesomorphism.
When a phenoxy group is replaced by a phenylthio group, the
compounds substituted by a methoxy group at the ortho and meta
1
6
positions in the phenylthio also show mesomorphism. This
1
freely rotating substituents very resemble flying seeds of a maple 60 tendency could be seen also for the pentafluorosulfanyl
1
8
tree, we named such type of liquid crystals as flying-seed-like
liquid crystals.
substituted homologue. Thus, the introduction of the substituent
at the mꢀposition can induce the flyingꢀseedꢀlike mesomorphism.
This means that rotation or flipꢀflop of the mꢀmethoxyphenoxy
groups may originate the large exclusion volume to form a soft
8
17
65
part necessary to induce mesomorphism.
[
A]
[
B]
2
2
3
3
4
4
0
5
0
5
0
5
Fig. 1 Flying-seed-like liquid crystals based on phthalocyanine:
[
A] the first flying-seed-like liquid crystals, 1p~s, based on
12-14
phthalocyanine.
; [B] dependence of liquid crystallinity on the
substitution position for phthalocyanine-based compounds,
16-18
2
.
Fig. 2 Variety of liquid crystalline compounds: [A] conventional
molten alkyl chain type of liquid crystals originated from
melting of the long alkyl chains in the periphery, and [B]
flying-seed-like liquid crystals originated from free rotation of
the bulky substituents in the periphery.
In 2009, Usol’tseva et al., reported a phthalocyanine
derivative (1p in Figure 1A) substituted by four
7
0
pꢀ(triphenylmethyl)phenoxy groups shows a Col phase, although
h
1
2, 13
it has no long alkyl chains in the periphery.
In their reports,
Therefore, mesomorphism can be induced from two
different types, as illustrated in Figure 2: [A] melting of the long
alkyl chains in the periphery to induce conventional molten alkyl
chain type of liquid crystals, and [B] free rotation or flipꢀflop of
the bulky substituents in the periphery to induce novel
flyingꢀseedꢀlike liquid crystals.
the mesophase was identified only by polarizing microscopic
observation (POM), without the Xꢀray diffraction measurement.
In 2012, we therefore synthesised a series of phthalocyanine
7
8
8
5
0
5
1
4
homologues (1pꢀs) shown in Figure 1A, in order to investigate
the detailed phase structures of these compounds by the
temperatureꢀdependent Xꢀray diffraction measurements. As a
result, we established that the homologue 1p shows a Colho phase
as reported by Usol’tseva et al. The phthalocyanine homologues
Hereupon, we focused on the phthalocyanine derivative
(mꢀC OPhO) PcCu (2a in Figure 1) showing columnar
1
8
mesomorphism. In this derivative (2a in Figure 3A), a very short
methoxy group is substituted at the meta position of the phenoxy
group. On the other hand, the homologous phthalocyanine
derivative substituted by a long eicosanyloxy group at the meta
position of the phenoxy group (mꢀC OPhO) PcCu (n = 20: 2o in
1
qꢀr also show the same Colho phase, whereas the homologue 1s
14
only shows a pseudohexagonal ordered columnar (Colrho) phase.
Generally, liquid crystalline phases give a halo observed at ca.4.5
Å due to melting of the long alkyl chains. However, the present
phthalocyanine homologues 1pꢀs gave an alternative halo at 5.7
Å ~ 6.9 Å due to free rotation of the bulky substituents. It was
confirmed from these phthalocyanine homologues (1pꢀs) that
introduction of bulky substituents instead of long alkyl chains
into the periphery of a rigid core can also induce mesomorphism.
n
8
Figure 3B) also show columnar mesomorphism, as previously
20, 21
reported.
The flyingꢀseedꢀlike mesomorphism of the
(
mꢀC OPhO) PcCu (2a) derivative may be induced by flipꢀflop of
1
8
the peripheral bulky substituents, as shown in Figure 3A, whereas
the mesomorphism of the (mꢀC OPhO) PcCu (2o) derivative
20
8
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DOI: 10.1039/C7TC01197K
may be induced by melting of the long alkyl chains like
conventional liquid crystals, as shown in Figure 3B. Hence,
mesomorphism of these two derivatives, 2a and 2o, may be
induced from different driving forces. If we will synthesise a 30 previously reported methods.
Scheme
octakis(mꢀnꢀalkoxyphenoxy)phthalocyaninato
(mꢀC OPhO) PcCu (n=2ꢀ9: 2b-i). The synthesis was adopted our
1
shows
synthetic
route
for
copper(II)
n
8
20, 21
Phenol derivatives (3b-i) were
5
series of the (mꢀC OPhO) PcCu derivatives for n = 1ꢀ20 to
synthesised by Williamson ether synthesis with resorcinol and the
corresponding 1ꢀbromoalkane purchased from Wako Pure
Chemical Industries, Ltd. Phthalonitrile derivatives (4b-i) were
synthesised by aromatic substitution with phenol derivatives
35 (3b-i) and 4,5ꢀdichlorophthalonitrile purchased from Tokyo
Chemical Industry (Tokyo Kasei). The target phthalocyanine
derivatives (2b-i) were synthesised by cyclic tetramerization of
the corresponding dicyano compounds (3b-i).
n
8
investigate their mesomorphism, we will be able to reveal the
boundary of mesomorphism inducing driving forces switching
from flyingꢀseedꢀlike type to molten alkyl chain type in the alkyl
chain length, n = 1~ 20.
The detailed procedures are described below only for a
40
representative compound, (mꢀC OPhO) PcCu (2b).
2 8
3
-Ethoxyphenol (3b)
A mixture of resorcinol (4.00 g, 36.4 mmol), K CO (1.49 g, 10.8
2
3
o
mmol) and dry DMF (12.5 mL) was stirred at 70 C under the
nitrogen atmosphere for 25 min. Then, bromoethane (5.13 g, 47.1
o
45
mmol) was added to the mixture and it was stirred at 95 C under
the nitrogen atmosphere for 3 h 50 min. The reaction mixture was
extracted with chloroform and washed with water. The organic
layer was dried over Na SO for 1h. After removing the Na SO
2
4
2
4
by filtration, the filtrate was evaporated in vacuum using an
50
evaporator. The residue was purified by column chromatography
(
silica gel, chloroform, R = 0.25) to obtain 0.276 g of reddish
f
1
brown liquid. Yield = 55.3 %. H NMR (400 MH ; CDCl ;
z
3
1
0
Me Si): δ (ppm) = 1.39 (3 H, t, J = 7.2 H , ꢀCH ), 4.00 (2 H, q, J
4
z
3
Fig. 3 Molecular formulae of liquid crystals based on
phthalocyanine in our previous works: (A) flying-seed-like type
=
6.9 H , ꢀOCH ꢀ), 5.72 (1 H, s, ArꢀOH), 6.41ꢀ6.44 (2 H, m,
z 2
liquid crystal, 2a, and (B) molten alkyl chain type liquid crystal, 55 ArꢀH), 6.45ꢀ6.48 (1 H, m, ArꢀH) and 7.10 (1 H, t, J = 8.4 H
o.
,
z
2
ArꢀH).
Since other homologues (3c-i) were synthesised in the same
way, only the yields and HꢀNMR data are described below.
1
5
In this study, we have therefore synthesised additional
1
homologues of (mꢀC OPhO) PcCu (n = 2ꢀ9: 2b-i in Scheme 1) to
n
8
3
-Propoxyphenol (3c)
Yield = 34.5 %. Liquid at rt. H NMR (400 MH ; DMSO;
investigate the boundary of the alkyl chain length in a series of
the homologues 2a-o (n = 1~ 20). To our best knowledge, such a
unique research has never been done up to date.
1
60
Z
Me Si): δ (ppm) = 0.96 (3 H, t, J ＝ 7.4 H , ꢀCH ), 1.70 (2 H,
4
Z
3
sext., J ＝7.0 H , ꢀCH ꢀ), 3.84 (2 H, t, J ＝ 6.6H , ꢀOCH ꢀ),
Z
2
Z
2
6
.31ꢀ6.36 (3 H, m, ArꢀH), 7.03 (1 H, t, J ＝ 8.0 H , ArꢀH) and
Z
9
.35 (1 H, s, ArꢀOH).
65
3-Buthoxyphenol (3d)
1
Yield = 35.7 %. Liquid at rt. H NMR (400 MH ; CDCl ; Me Si):
Z
3
4
δ (ppm) = 0.90 (3 H, t, J = 7.4 Hz, ꢀCH ), 1.41 (2 H, sext., J = 7.6
3
Hz, ꢀCH ꢀ), 1.68 (2 H, quin., J = 6.1 Hz, ꢀCH ꢀ), 3.86 (2 H, t, J =
2
2
6
.8 Hz, ꢀOCH ꢀ), 4.99 (1 H, s, ArꢀOH), 6.32ꢀ6.35 (2 H, m, ArꢀH),
2
7
7
8
8
0
5
0
5
6.40ꢀ6.42 (1 H, m, ArꢀH) and 7.04 (1 H, t, J = 8.4 Hz, ArꢀH).
-Pentyloxyphenol (3e)
Yield = 20.5 %. Liquid at rt. H NMR (400 MH ; CDCl ; Me Si):
3
1
z
3
4
δ (ppm) = 0.96 (3 H, t, J = 7.1 H , ꢀCH ), 1.36ꢀ1.49 (4 H, m,
z
3
ꢀ
C H ꢀ), 1.80 (2 H, quin., J = 7.0 H , ꢀCH ꢀ), 3.95 (2 H, t, J = 6.6
2
4
z
2
H , ꢀOCH ꢀ), 5.40 (1 H, s, ArꢀOH), 6.43ꢀ6.46 (2 H, m, ArꢀH),
z
2
6
.50ꢀ6.53 (1 H, m, ArꢀH) and 7.14 (1 H, t, J = 8.6 Hz, ArꢀH).
3
-Heptyloxyphenol (3g)
2
0
1
Yield = 18.5 %. Liquid at rt. H NMR (400 MH ; CDCl ; Me Si):
Scheme 1 Synthetic route for (
m
-C
n
OPhO)
8
PcCu (n = 1-20: 2a-o),
z
3
4
DMF = N,N'-dimethylformamide and DBU =
,8-diazabicyclo[5,4,0]-undec-7-ene. a = Ref. 17, k, l = Ref. 20 and
j, m-o = Ref. 21.
δ (ppm) = 0.93 (3 H, t, J = 7.0 H , ꢀCH ), 1.30ꢀ1.50 (8 H, m,
z 3
1
ꢀC H ꢀ), 1.79 (2 H, quin., J = 7.0 H , ꢀCH ꢀ), 3.94 (2 H, t, J = 6.6
4
8
z
2
H , ꢀOCH ꢀ), 5.34 (1 H, s, ArꢀOH), 6.43ꢀ6.46 (2 H, m, ArꢀH),
z
2
6
.50ꢀ6.53 (1 H, m, ArꢀH) and 7.14 (1 H, t, J = 8.4 Hz, ArꢀH).
2
5
2. EXPERIMENTAL
3
-Octyloxyphenol (3h)
1
Yield = 48.3 %. Liquid at rt. H NMR (400 MH ; CDCl ; Me Si):
2
-1. Synthesis
z
3
4
δ (ppm) = 0.91 (3 H, t, J = 7.0 H , ꢀCH ), 1.31ꢀ1.50 (8 H, m,
z
3
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00
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ꢀ
C H ꢀ), 1.79 (2 H, quin., J = 7.0 H , ꢀCH ꢀ), 3.95 (2 H, t, J = 6.6 60 δ (ppm) = 0.82 (6 H, t, J = 7.0 H , ꢀCH ), 1.21ꢀ1.42 (16 H, m,
5
1
0
z
2
z
3
H , ꢀOCH ꢀ), 5.40 (1 H, s, ArꢀOH), 6.43ꢀ6.46 (2 H, m, ArꢀH),
ꢀC H ꢀ), 1.72 (4 H, quin., J = 7.0 Hz, ꢀCH ꢀ), 3.88 (4 H, t, J = 6.6
5 10 2
z
2
6
.50ꢀ6.53 (1 H, m, ArꢀH) and 7.14 (1 H, t, J = 8.4 Hz, ArꢀH).
H , ꢀOCH ꢀ), 6.53ꢀ6.57 (4 H, m, ArꢀH), 6.73ꢀ6.75 (2 H, m, ArꢀH),
z 2
3
-Nonyloxyphenol (3i)
7.13(2 H, s, ArꢀH) and 7.25 (2 H, t, J = 8.4 Hz, ArꢀH). IR: (KBr,
νmax / cm ) 2233 (ꢀCN).
1
ꢀ
1
5
0
5
0
Yield = 16.3 %. Liquid at rt. H NMR (400 MH ; CDCl ; Me Si):
z
3
4
δ (ppm) = 0.92 (3 H, t, J = 6.8 H , ꢀCH ), 1.27ꢀ1.50 (12 H, m, 65 4,5-Bis(3-nonyloxyphenoxy)phthalonitrile (4i)
z
3
o
1
ꢀ
C H ꢀ), 1.79 (2 H, quin., J = 7.2 H , ꢀCH ꢀ), 3.94 (2 H, t, J = 6.6
Yield = 75.9 %. M.p. = 38.0~38.5 C. H NMR (400 MH ; CDCl ;
z 3
6
12
z
2
H , ꢀOCH ꢀ), 5.07 (1 H, s, ArꢀOH), 6.42ꢀ6.45 (2 H, m, ArꢀH),
Me Si): δ (ppm) = 0.81 (6 H, t, J = 6.8 H , ꢀCH ) 1.20ꢀ1.42 (20
4 z 3
z
2
6
.50ꢀ6.53 (1 H, m, ArꢀH) and 7.14 (1 H, t, J = 8.4 Hz, ArꢀH).
H, m, ꢀC H ꢀ), 1.71 (4 H, quin., J = 7.0 Hz, ꢀC H ꢀ), 3.87 (4 H, t,
6 12 2 4
1
1
2
4,5-Bis(3-ethoxyphenoxy)phthalonitrile (4b)
J = 6.6 H , ꢀOCH ꢀ), 6.53ꢀ6.57 (4 H, m, ArꢀH), 6.72ꢀ6.75 (2 H,
z 2
A mixture of 3ꢀethoxyphenol (3b) (0.624 g, 4.52 mmol), K CO
70 m, ArꢀH), 7.13(2 H, s, ArꢀH) and 7.25 (2 H, t, J = 8.0 Hz, ArꢀH).
IR: (KBr, νmax / cm ) 2237 (ꢀCN).
2
3
o
ꢀ
1
(0.632 g, 4.57 mmol) and dry DMF (30 mL) was stirred at 90 C
under the nitrogen atmosphere for 10 min. Then,
,5ꢀdichlorophtalonitrile (0.394 g, 2.00 mmol) was added to the
mixture and it was stirred at 100 C under the nitrogen atmosphere
(m-C OPhO) PcCu (2b)
A mixture of 4,5ꢀbis(3ꢀethoxyphenoxy)phthalonitrile (4b) (0.201
g, 0.502 mmol), 1ꢀoctatanol (5 mL), CuCl2 (0.022 g、0.162
2
8
4
o
for 1 h 50 min. The reaction mixture was extracted with 75 mmol) and DBU (4 drops) was refluxed under the nitrogen
chloroform and washed with water. The organic layer was dried
over Na SO for 1h. After removing the Na SO by filtration, the
filtrate was evaporated in vacuum using an evaporator. The
atmosphere for 3 h 10 min. Methanol was poured into the
reaction mixture to precipitate the target compound. The
methanolic layer was removed by filtration and then resulting
precipitate was washed with methanol, ethanol and acetone,
2
4
2
4
residue was purified by column chromatography (silica gel,
toluene, R = 0.25) to obtain 0.423 g of light blue solid. Yield = 80 respectively. The residue was purified by hot filtration with
f
o
1
5
1.5 %. M.p. = 125.0~125.4 C. H NMR (400 MH ; CDCl ;
chloroform to obtain 0.137 g of green solid. Yield = 65.3 %.
Yields, elemental analysis data and MALDIꢀTOF mass data: See
Table 1.UVꢀvis spectral data: See Table 2.
z
3
Me Si): δ (ppm) = 1.37 (6 H, t, J = 7.0 H , ꢀCH ), 3.78 (4 H, q, J
=
4
z
3
6.9 H , ꢀOCH ꢀ), 6.53ꢀ6.58 (4 H, m, ArꢀH), 6.79ꢀ6.81 (2 H, m,
z 2
2
5
ArꢀH), 7.04 (2 H, s, ArꢀH) and 7.30 (2 H, t, J = 8.2 H , ArꢀH). IR:
The other homologues (2c-i) could be similarly synthesised.
The yields, elemental analysis data and MALDIꢀTOF mass data
are shown in Table 1 and the UVꢀVis spectrum data are
summarized in Table 2.
z
ꢀ
1
85
(KBr, νmax / cm ) 2241 (ꢀCN).
Since other homologues (4c-i) were synthesised in the same
1
way, only the yields, HꢀNMR data and FTꢀIR data are described
below.
Table 1. TOF-Mass spectral data, elemental analysis data and yields of
3
0
4,5-Bis(3-propooxyphenoxy)phthalonitrile (4c)
Yield = 86.1 %. M.p. = 38.0~38.5 C. H NMR (400 MHZ;
o
1
90 (m-C OPhO) PcCu (n=2-9: 2b-i).
n
8
CDCl ; Me Si): δ (ppm) = 1.07 (6 H, t, J = 7.2 Hz, ꢀCH ), 1.84 (4
3
4
3
H, sext, J = 7.0 Hz, ꢀCH ꢀ), 3.95 (4 H, t, J = 6.6 Hz, ꢀOCH ꢀ),
2
2
6
.63ꢀ6.67 (4 H, m, ArꢀH), 6.83ꢀ6.86 (2 H, m, ArꢀH), 7.22 (1 H, s,
ꢀ
1
3
4
4
5
0
5
ArꢀH) and 7.35 (2 H, t, J = 8.2 Hz, ArꢀH). IR: (KBr, νmax / cm )
2
4
238 (ꢀCN).
,5-Bis(3-buthoxyphenoxy)phthalonitrile (4d)
1
Yield = 19.5 %. Liquid at rt. H NMR (400 MH ; CDCl ; Me Si):
δ (ppm) = 1.00 (6 H, t, J = 7.4 Hz, ꢀCH ), 1.52 (4H, sext., J = 7.6
Hz, ꢀCH ꢀ), 1.80 (4 H, quin., J = 6.0 Hz, ꢀCH ꢀ), 3.98 (4 H, t, J =
6
Z
3
4
3
2
2
.4 Hz, ꢀOCH ꢀ), 6.63ꢀ6.67 (4 H, m, ArꢀH), 6.82ꢀ6.85 (2 H, m,
2
ArꢀH), 7.23 (1 H, s, ArꢀH) and 7.34 (2 H, t, J = 8.2 Hz, ArꢀH).
ꢀ
1
IR: (KBr, νmax / cm ) 2233 (ꢀCN).
,5-Bis(3-pentyloxyphenoxy)phthalonitrile (4e)
4
1
Yield = 73.4 %. Liquid at rt. H NMR (400 MH ; CDCl ; Me Si):
z
3
4
Table 2.
n 8
UV-vis spectral data in chloroform of (m-C OPhO) PcCu
δ (ppm) = 0.86 (6 H, t, J = 7.0 H , ꢀCH ), 1.27ꢀ1.41 (8 H, m,
z
3
(n=3-9: 2c-i).
ꢀ
C H ꢀ), 1.72 (4 H, quin., J = 7.0 Hz, ꢀC H ꢀ), 3.88 (4 H, t, J = 6.6
2
4
2
4
H , ꢀOCH ꢀ), 6.53ꢀ6.57 (4 H, m, ArꢀH), 6.72ꢀ6.75 (2 H, m, ArꢀH),
z
2
7
.13(2 H, s, ArꢀH) and 7.25 (2 H, t, J = 8.0 Hz, ArꢀH). IR: (KBr,
ꢀ
1
5
0
νmax / cm ); 2233 (ꢀCN).
,5-Bis(3-heptyloxyphenoxy)phthalonitrile (4g)
4
1
Yield = 98.7 %. Liquid at rt. H NMR (400 MH ; CDCl ; Me Si):
z
3
4
δ (ppm) = 0.82 (6 H, t, J = 6.8 H , ꢀCH ), 1.19ꢀ1.42 (16 H, m,
z
3
ꢀ
C H ꢀ), 1.72 (4 H, quin., J = 7.0 Hz, ꢀCH ꢀ), 3.88 (4 H, t, J = 6.4
4
8
2
5
5
H , ꢀOCH ꢀ), 6.53ꢀ6.57 (4 H, m, ArꢀH), 6.72ꢀ6.75 (2 H, m, ArꢀH),
z 2
7
.13(2 H, s, ArꢀH) and 7.25 (2H, t, J = 8.4 Hz, ArꢀH). IR: (KBr,
ꢀ
1
νmax / cm ) 2233 (ꢀCN).
,5-Bis(3-octyloxyphenoxy)phthalonitrile (4h)
4
1
Yield = 75.9 %. Liquid at rt. H NMR (400 MH ; CDCl ; Me Si):
95
z
3
4
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Page 5 of 10
Journal of Materials Chemistry C
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DOI: 10.1039/C7TC01197K
17, 20, 21
2
-2. Measurements
been reported.
Therefore, Table 3 lists only the present
4
5
5
6
5
0
5
0
derivatives for n = 2ꢀ9 (2bꢀi) and the representative previous
derivatives for n = 1 (2a) and n = 20 (2o). The phase transition
behaviour of the present derivatives for 2b-i are described below.
Compounds 3b-i and 4b-i synthesised here were identified by
HꢀNMR measurements (BRUKER DRXꢀ400) and FTꢀIR
1
measurements (SHIMADZU FTIRꢀ8400). The phthalocyanine
derivatives (2b-i) synthesised here were confirmed by
MALDIꢀTOF mass spectra and elemental analyses (Table 1).
MALDIꢀ TOF mass spectra were measured using Autoflex
IIIꢀ2S. Elemental analyses were performed using a PerkinꢀElmer
elemental analyser 2400. Electronic absorption spectra were
measured using a Hitachi Uꢀ4100 automatic spectrophotometer
(
mꢀC OPhO) PcCu (2b) having ethoxy groups (n = 2)
2 8
5
0
5
0
shows a crystalline phase (K ) at room temperature (rt) for the
2
freshly prepared virgin sample. When it was heated, it
o
transformed into another crystalline phase (K ) at 84.2 C and then
3
o
into K phase at 181.4 C; on further heating, the K phase melted
into a rectangular columnar [Col (P2m)] mesophase at 274.7 C
and it cleared into isotropic liquid (I.L.) at 354.1 C. When the I.L.
4
4
o
r
1
1
2
o
(Table 2). The phase transition behaviour of 2b-i was clarified by
was cooled, it transformed into the Col (P2m) mesophase and
r
polarizing microscope observation (Nikon Eꢀ600 POL
polarization microscope with hot stage consisting of Mettler
FPꢀ90 Central Processor) and differential scanning calorimetry
(Shimadzu DSCꢀ50). The decomposition temperatures were
then another new crystalline phase (K ), which was observed only
1
for the nonꢀvirgin sample.
It is very interesting that each of
the short chain derivatives (2b-d) for n = 2ꢀ4 shows only the
Col (P2m) mesophase, as can been seen from Table 3. The
r
measured with
a
Rigaku Thermo plus TG 8120
propyloxy derivative (2e) for n = 5 also shows the same
thermogravimeter. The mesophases were identified using a small
angle Xꢀray diffractometer (Bruker Mac SAXS System) equipped
with a hot stage (Mettler FP82HT hot stage, Mettler FPꢀ90
Col (P2m) mesophase and an additional monotropic hexagonal
r
ordered columnar (Col ) mesophase. On the other hand, each of
ho
2
2
the moderately long chain derivatives (2f-i) for n = 6ꢀ9 shows
Central Processor). The measuring range of this small angle
Xꢀray diffractometer is from 110 Å to 3.0 Å, and the temperature
another type of rectangular columnar [Col (P2 /a)] mesophase
ro
1
o
65 together with Colho mesophase(s).
is variable from rt. to 375 C.
It is very noteworthy that the derivative 2h for n = 8 shows
an unusual phase transition sequence. As can be seen from the
DSC thermograms (Fig. S1) and the photomicrographs of 2h at
various temperatures (Fig. S2), when the virgin sample of 2h was
3. RESULTS AND DISCUSSION
3
-1. Synthesis
7
7
8
8
9
9
0
5
0
5
0
5
heated from rt, an unidentifiable X1 phase transformed into
2
5
Table 1 summarizes the yields, elemental analysis and TOFꢀmass
spectral results for the phthalocyanine derivatives 2b-i
synthesised here. The electronic absorption spectra are
summarized in Table 2. Figure 4 shows a spectrum of the
representative derivative 2h. However, UVꢀvis spectrum could
not be measured for 2b due to lack of the soluble solvent.
Nevertheless, 2b could be judged from the elemental analysis and
the TOFꢀmass spectrum (Table 1) that it was surely prepared.
o
another unidentifiable X2 phase at 40.4 C; the X phase
2
o
transformed into Col phase at 83.4 C and then into Col (P2 /a)
ho1
ro
1
o
phase at 118.9 C. On further heating, it cleared into I.L. at
97.2 C. Thus, the derivative 2h showed very unusual phase
o
1
transition sequence from a higher symmetry of Col mesophase to
h
3
0
a lower symmetry of Col mesophase on heating stage. Usually, a
r
lower symmetry of Col mesophase transforms into a higher
r
symmetry mesophase on heating stage. As can be seen also
o
from Figs S1 and S2, when the I.L. heated over 205.0 C was
o
cooled down to 200.0 C, it transformed into another hexagonal
0
0
0
0
0
.8
.6
.4
.2
.0
ordered columnar mesophase of Colho3; when the Colho3 at
o
200.0 C was rapidly cooled down to RT, a mixture of
supercooled Colho3 and partially resulted Colho2. Interestingly, the
lower symmetry of Colro mesophase appeared only for the first
heating of the virgin sample during such usual observations by
DSC and POM. Only when the supercooled Col was held at
ho3
o
1
65.0 C, the Col (bright platelets) phase appeared with Col
r
ho2
(
dark hexagons), as can be seen from Fig S2.
In contrast with the moderately long chain derivatives (2f-i)
for n = 6ꢀ9, each of the longer chain derivatives 2j-o for n =
0ꢀ20 shows only Col mesophase(s), as can be seen from Table
300
400
500
600
700
800
1
h
Fig. 4 UV-vis spectrum of (
m
-C
8
O) PcCu (2h) in chloroform
8
-
6
S1 and Table 3.
Thus, the mesomorphism of the present (mꢀC OPhO) PcCu
3
5
(3.46 × 10 mol/L).
n
8
3
-2. Phase transition
derivatives (2a-o) for n = 1ꢀ20 strongly depends on the alkoxy
chain length (n): each of the short chain derivatives (2b-e) for n =
Table S1 summarizes phase transition behaviours of all the
2
ꢀ5 shows the Col (P2m) mesophase; each of the moderately
ro
phthalocyanine derivatives (mꢀC OPhO) PcCu (n = 1ꢀ20: 2a-o),
n
8
long chain derivatives (2f-i) for n = 6ꢀ9 shows another type of
rectangular columnar [Col (P2 /a)] mesophase together with
Colho mesophase(s); each of the longer chain derivatives 2j-o for
which were established by using a polarizing optical microscopy
(POM), differential scanning calorimeter (DSC) and
temperatureꢀdependent small angle Xꢀray diffractometer.
The phase transition behaviours of the previously
synthesized derivatives for n = 1, 10ꢀ20 (2a, 2j-o) have already
4
0
a
a
ro
1
1
00 n = 10ꢀ20 shows Col mesophase(s).
h
Table S2 summarizes small angle Xꢀray diffraction data of all
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Journal of Materials Chemistry C
Page 6 of 10
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DOI: 10.1039/C7TC01197K
the mesophases in the phthalocyanine derivatives 2a-o. The data
of (mꢀC OPhO) PcCu (n = 1, 10ꢀ20: 2a, 2j-o) reported previously
As can be seen from this table, the phthalocyanine
derivatives
5
n
8
17, 20, 21
are also included for the purpose of comparison.
Table 3. Phase transition temperatures and enthalpy changes of (mꢀC
n
OPhO)
8
PcCu (n = 1, 2ꢀ9 and 20: 2a, 2bꢀi and 2o).
Compound
m-C OPhO) PcCu
o
ꢀ1
T ( C) [ H (kJmol )]
Phase
Phase
relaxation
(
n
8
Glassy Col (P2 /a)
ro
1
Tg=69.9
1
91.3 [13.4] Colro1 255.1 [2.69]
360.1 [10.7] Mx
405
Colro2
n = 1: 2a*1
2nd dc.
I.L.
K
(
P2 /a)
1
(P2 /a)
(1st dc.)
1
229.4
354.1 [19.6]
Colr
K1
(
P2m)
274.7 [100.5]
8
4.2
181.4
n = 2: 2b
n = 3: 2c
K2v
K2v
K3
K3
K4
197.0
1
42.8[41.5]
207.4[17.5]
234.1[29.9]
300.1[17.3]
Colr
P2m)
K4
I.L.
(
113.4 [5.0]
K1
Tg=115.7
Glassy Col (P2m)
r
(v)
166.1[6.4]
K2
K3
147.5[10.6]
174.2 [21.0]
249.5 [11.4]
222.3[12.6]
Colr
P2m)
n = 4: 2d
n = 5: 2e
K1
I.L.
I.L.
(
68.4[6.02]
31.0Ï
1
K1v
K2
Colr(P2m)
169.3
Colho
61.6Ï
172.7Ï
177.6Ï
190.8Ï
1
K3
K4
K5
K6
ca. 130~150
5
0.4[3.83]
129.5[8.85]
201.4Ï
204.8Ï
Colro1
P2 /a)
Colro2
K1v
K2
I.L.
n = 6: 2f
(
(P2 /a)
1
1
ca. 160
182.3
83.6
141.0
203.6
Colho1
Colho2
Colho3
Colho4
5
7.4
101.4[6.55]
197.9
202.2[32.9]
202.8
Colro
P2 /a)
1
X1v
X2
I.L.
I.L.
n = 7: 2g
n = 8: 2h
(
175.8
Colho1
Colho2
Colho3
2
03.4[33.7]
40.4 [8.11]
83.4 [3.41]
118.9 [0.81]
197.2 [34.0]
200.4
Colro
X1v
X2
Colho1
(
P2 /a)
1
170.9
Colho2
Colho3
199.3[34.3]
193.0Ï
74.1[1.64]
n = 9: 2i
Colho1(v)
Colho2
I.L.
141-159
Colro
P2 /a)
1
94.9Ï
1
(
50.1[278]
156.3[20.6]
n = 20: 2o*2
K
I.L.
Colho
Phase nomenclature: K= crystal, Colro = rectangular ordered columnar, Colho = hexagonal ordered columnar mesophase, Colhd=hexagonal disordered
Ï
1
2
columnar mesophase, I.L. = isotropic liquid and v = virgin state. : These peaks were so close to calcurate the enthalpy changes. * : Ref[17], * : Ref[21].
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Journal of Materials Chemistry C
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DOI: 10.1039/C7TC01197K
2
b-i (n = 2ꢀ9) synthesised in this study could be identified as
Colro2(P2 /a) phases, and each of the derivatives 2b-d (n = 2ꢀ4)
1
columnar mesophases from the reflections due to
shows a Col (P2m) phase. Therefore, the derivatives 2a-d (n =
r
twoꢀdimensional lattices. Although each of the Colho4 phase of 35 1ꢀ4) tend to show only the rectangular columnar (Colr)
(
mꢀC OPhO) PcCu
(2f)
and
the
Colho3 phase
of
mesophase(s). On the other hand, the derivative 2e (n = 5) shows
6
8
5
(mꢀC OPhO) PcCu (2g) gave no (110) reflection from the 2D
an enantiotropic Col (P2m) mesophase and a monotropic Col
ho
7
8
r
hexagonal lattice, they could be identified as a Col phase from
Z Value Calculation. When the reflection in the lowest angle is
phase. Interestingly, the derivatives 2f-h (n = 6ꢀ8) tend to show
ho
2
3
enantiotropic Colho phase(s) and Col (P2 /a) phase(s). As can be
ro
1
assigned as (1 0 0) of the twoꢀdimensional hexagonal lattice, the 40 seen from Table 3, the Col (P2 /a) phase(s) in the derivatives
ro
1
Z value becomes 1, which is consistent with the identification as
a Colho mesophase. This identification is also compatible with the
textures mentioned below.
2f-h (n = 6ꢀ8) appeared almost only for the freshly prepared
virgin sample. Once it cleared into IL, the nonꢀvirgin sample gave
only Colho mesophases. This phenomenon can be rationally
explained by using Gibbs free energy vs. temperature (GꢀT)
diagram. For a representative derivative 2h (n = 8), the GꢀT
diagram is illustrated in Figure S3. Although the derivatives 2i (n
1
0
24
45
=
9) also shows the Colho and Col (P2 /a) phase(s), the
ro 1
Col (P2 /a) phase was only observed for relaxation from the
ro
1
Colho phase. On the other hand, each of the derivatives 2j-o (n =
50
10ꢀ20) shows only enantiotropic Colh phase(s), without any
rectangular columnar (Col ) phases. Thus, the phase transition
r
behaviour critically changes, between n = 1and 2, between n = 5
and 6, and between n = 9 and 10, as indicated dotted lines in
2
10
4
3
3
2
2
1
1
00
50
00
50
00
50
00
I.L.
cp of
Colro(P2m) 200
cp of Col (P2 /a)
ro
1
cp of Colho
Colho
+
1
1
1
1
90
80
70
60
Col (P2 /a)
ro
1
Haloarom.
+
Haloaklyl
cp of Colhd
Colro2
P2 /a)
(
1
Colho + Colhd
Haloaklyl
r
Col (P2m)
Haloarom.
5
6
7
8
9
10
11
12
Colro1
P2 /a)
(
1
I.L.
Fig. 5 Photomicrographs of (A) Col
r
m
-C
2
OPhO)
8
PcCu
o
o
(
2b) at 340 C; (B) Col
r
(P2m) of
(P2m) of ( -C OPhO)
(P2m) of ( -C OPhO)
(
m
8
-C
o
1
2
2
3
5
0
5
0
(C) Col
r
m
4
PcCu (2d) at 245 C; (D)
Col
r
m
5
8
PcCu (2e) at 200 C; (E) Colho4 of
o
(
m
-C
6
OPhO)
8
PcCu (2f) at 200 C; (F) Colho3 of (
-C
7
OPhO) PcCu
8
o
o
(
2g) at 200 C; (G) Colho3 of (
m
8
-C OPhO)
Colho + Colhd
Colho
o
Colho2 of
(m
9 8
-C OPhO) PcCu (2i) at 196.5 C.
Haloaklyl
Figure 5 shows the photomicrographs of the Col (P2m)
ro
phases of (mꢀC OPhO) PcCu for n = 2ꢀ5 (2bꢀe) and the Col
ho
n
8
5
0
0
phases of (mꢀC OPhO) PcCu for n = 6ꢀ9 (2f-i). As can be seen
n
8
from these photomicrographs, each of 2bꢀe shows the dendritic
textures characteristic to a Col phase, and each of 2fꢀi shows the
r
dendritic textures characteristic to a Colh phase having a C6
symmetry. Furthermore, they showed no birefringence resulted
0
1
(
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20
(k) (l) (m) (n) (o)
a)(b) (c) (d) (e) (f) (g) (h) (i) (j)
from homeotropic alignment. Thus, these Col (P2m) of 2bꢀe and
ro
Colho phases of 2f-i could be identified from the XRD data and
characteristic textures.
In Figure 6, the phase transition temperatures are plotted
against the carbon number (n) in the alkoxy chain. As can be seen
Number of carbon atoms in the alkoxy chain (n)
55
Fig. 6 Phase transition temperatures versus number of carbon
atoms in the alkoxy chain (n) for ( -C OPhO) PcCu (n = 1~20:
a-o).
m
n
8
2
from this figure, the derivative 2a (n = 1) shows Colro1(P2 /a) and
1
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Figure 6. For n = 1, the derivative decomposes at higher 45 and Haloalkyl (#2) show their abrupt value jumps at the phase
temperatures. Excluding this derivative, all the other derivatives
can be classified into three groups: the short chain derivatives
transition temperatures from crystal (K) to columnar (Col)
mesophase. It is noteworthy that the value of Haloarom. (#1)
(
2b-e) for n = 2ꢀ5; the moderately long chain derivatives (2f-i) for
jumps to 5.2 Å at the KꢀCol phase transition temperature,
o
5
0
5
n = 6ꢀ9; the longer chain derivatives 2j-o for n = 10ꢀ20.
274.7 C, whereas the Halo
(#2) jumps to 4.6 Å at the KꢀCol
alkyl
o
At these group boundaries between n = 5 and 6 and between 50 phase transition temperature, 53.7 C. Furthermore, the spacing
n = 9 and 10, the driving force of mesomorphism may be
changed. We predicted from this figure that the driving force of
mesomorphism might be attributable to rotation or flipꢀflop of
only the bulky aromatic substituents for n = 2ꢀ5, but melting of
only the alkyl chains for n = 10ꢀ20. In between for n = 6ꢀ9, both 55 (#1) and Haloalkyl (#2) from their spacing values.
of rotation of the bulky groups and melting of the longer alkyl
groups may originate their mesomorphism. In order to confirm
this hypothesis, we have carried out further detailed
temperatureꢀdependent Xꢀray diffraction measurements.
value of Haloalkyl (#2) gradually increases from 4.6 Å to 4.8 Å
with elevating the temperature to 140 C. Thus, the spacing values
of Haloarom. (#1) and Haloalkyl (#2) are located at ca. 5.2 Å and
4.6ꢀ4.8 Å, respectively. Therefore, we can distinguish Haloarom.
o
1
1
3
-3. Temperature-dependent X-ray diffraction measurements
For the detailed temperatureꢀdependent Xꢀray diffraction
measurements, we chose three representative derivatives from
each of the three groups: 2b (n = 2) for n = 2ꢀ5, 2h (n = 8) for n =
6ꢀ9, and 2o (n = 20) for n = 10ꢀ20.
50
100
150
200
250
300
40
60
80
100
120
140
5
4
.0
.8
5
5
.2
.1
5
2
2
3
3
0
5
0
5
Figure 7 shows the Xꢀray diffraction patterns of the
4.6
4.4
4.2
o
o
mesophases of 2b (n = 2) at 290 C and 2o (n = 20) at 100 C. As
can be seen from Figure 7(1), 2b (n = 2) shows a halo at 2θ
4
.9
3
0
80
130
180
230
280
40
60
80
100
120
140
o
1
7 (about 5.2 Å) (Halo
: denoted as #1) in the Col (P2m)
arom. r
mesophase, which is due to flipꢀflop of the bulky aromatic
Fig. 8 Thermal dependence of the spacing of halos due to the
flip-flopping aromatic groups (ca. 5.2 Å) of ( -C OPhO) PcCu
(2b) and the molten alkyl groups (ca. 4.6~4.8 Å) of
-C20OPhO) PcCu (2o).
substituents. On the other hand, as can be seen from Figure 7(2),
m
2
8
o
2
o (n = 20) shows a halo at 2θ
18.5 (about 4.6 Å) (Haloalkyl:
6
0
(
m
8
denoted as #2) in the Colho mesophase, which is due to the molten
alkyl chains. The Haloarom. of 2b (n = 2) in Figure 7(1) could not
be observed in the Xꢀray diffraction pattern of 2o (n = 20) in
Figure 7(2), whereas the Haloalkyl of 2o (n = 20) in Figure 7(2)
could not be observed in the Xꢀray diffraction pattern of 2b (n =
Figure 9 shows the Xꢀray diffraction patterns for the
moderately long chain derivative 2h (n = 8) showing an unusual
phase transition sequence from the Colho phase to the Col (P2 /a)
phase on heating stage. This is completely reverse to the normal
phase transition sequence. Usually, a phase transition occurs from
a lower symmetry of Colro mesophase to a higher symmetry of
Colho mesophase. This reverse sequence may be attributed to both
flipꢀflop of the bulky aromatic substituents and melting of the
ro
1
2
2
) in Figure 7(1). That means that the mesomorphism of 2b (n =
) is induced only by the driving force originated from flipꢀflop
65
of the bulky substituents, but that the mesomorphism of 2o (n =
0) is induced only by the driving force originated from the
molten alkyl chains.
2
5
10
15
20
25
30
5
10
15
20
25
30
5
10
15
20
25
30
5
10
15
20
25
30
5
10
15
20
25
30
5
10
15
20
25
30
5
10
15
20
25
30
5
10
15
20
25
30
70
Fig. 9 X-ray diffraction patterns of (
m
-C
8
OPhO) PcCu (2h) at
8
o
o
(1)101 C and (2)158 C.
Fig. 7 Two different types of halos in the X-ray diffraction
o
alkyl chains. As can be seen from the Xꢀray diffraction patterns
of Colho1 phase shown in Figure 9(1), Haloalkyl (#2) only appears.
On the other hand, as can been seen from the Xꢀray diffraction
patterns of Col (P2 /a) phase shown in Figure 9(2), Halo
4
0
patterns of (1) (
m
-C
2
OPhO)
8
PcCu (2b) at 290 C and (2)
o
(m
-C20OPhO)
8
PcCu (2o) at 100 C.
In Figure 8 are plotted the spacing values of Haloarom. (#1)
of 2b (n = 2) and Haloalkyl (#2) of 2o (n = 20) against
temperature. As can be seen from this figure, both Haloarom. (#1)
75
ro
1
arom.
(#1) appears as a large peak covered on the Haloalkyl (#2). Hence,
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Journal of Materials Chemistry C
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DOI: 10.1039/C7TC01197K
in the lower temperature region, the alkyl chain only melts to
show the Colho1 phase, but in the higher temperature region, the
bulky aromatic substituents also flipꢀflop to show the Col (P2 /a)
5.4
ro
1
phase.
5.2
5
0
5
To further confirm this phenomenon, we carried out fine
Xꢀray diffraction measurements by changing the temperature in
small increments. Figure 10 shows the Xꢀray diffraction patterns
of (mꢀC OPhO) PcCu (2h) measured in an angle region from
5.0
8
8
5
to 31 degree at 32 different temperatures. As can be seen from
4
.8
.6
1
this figure, the halo due to the molten alkyl chains (Haloalkyl: #2)
appeared for X phase (blue lines) and Colho1 phases (green lines),
2
whereas the halo due to the flipꢀflopping aromatic groups
4
70
100
130
160
(
Haloarom.: #1) appeared only for Colro phase (red lines).
Apparently, the halo suddenly shifted to lower angle at the phase
1
transition from Colho1 phase to Col phase.
ro
#
2
#
1
45
Fig. 11 Thermal dependence of the spacing of halos due to the
molten alkyl groups (ca. 4.6~4.8 Å) and the flip-flopping
aromatic groups (ca. 5.2 Å) of (
m
-C
8
OPhO) PcCu (2h).
8
the mesomorphism. The mesomorphism of the present
mꢀC OPhO) PcCu derivatives (n = 1ꢀ20: 2a-o) strongly depends
(
n
8
5
5
6
6
7
7
0
5
0
5
0
5
on the alkoxy chain length (n). The mesomorphism of the short
chainꢀsubstituted derivatives 2aꢀe for n = 1~5 is flyingꢀseedꢀlike
type induced by flipꢀflop of the peripheral bulky substituents,
whereas the mesomorphism of the long chainꢀsubstituted
derivatives 2jꢀo for n = 10~20 is conventional molten alkyl chain
type induced by melting of the long alkyl chains. The moderately
long chain derivatives (2f-i) for n = 6ꢀ9 in between show both
types of mesophases. The temperatureꢀdependent small angle
Xꢀray diffraction studies revealed that a halo denoted as Haloarom.
appeared in the short chain derivatives (2b-e) for n = 2ꢀ5 at d
5.2 Å due to flipꢀflop of the bulky aromatic substituents, and that
another halo denoted as Haloalkyl appeared in the longer chain
5
10
15
20
Θ/degree
Fig. 10 Temperature-dependent X-ray diffraction patterns of
25
30
2
(m
-C
8
OPhO)
8
PcCu (2h) in the rage of 2Θ = 5~31. Blue lines: X
2
o
phase at 70, 75, 77, 78, 79, 80 and 81 C. Green lines: Colho1
phase at 87, 88, 90, 100, 105, 110, 113, 114, 115, 116, 117 and 118
C. Red lines: Colro phase at 119, 120, 121, 122, 123, 125, 130,
40, 150, 160, 170, 180 and 190 C. #1: Haloarom. = halo due to the
flip-flopping aromatic groups (ca. 5.2 Å). #2: Haloalkyl = halo due
to the molten alkyl chains (ca. 4.6~4.8 Å).
o
2
0
o
1
In Figure 11, all the spacing values of Haloalkyl (#2) and
Haloarom. (#1) of 2h are plotted against temperature on heating
stage. As can be seen from this figure, the spacing values of #2 at
about 4.8 Å in the lower temperature region suddenly jumps to
the spacing value of #1 at about 5.2 Å in the lower temperature
2
3
3
4
5
0
5
0
derivatives 2j-o for n = 10ꢀ20 at d
4.6ꢀ4.8 Å due to melting of
the long alkyl chains. Therefore, we can distinguish the type of
mesophase from Haloarom. and Haloalkyl. Very interestingly, the
moderately long chain derivative (mꢀC OPhO) PcCu (2h) gave
region, just at the phase transition from the Col mesophase to
the Col (P2 /a) mesophase at 118.9 C. Thus, it could be
8
8
ho1
o
the Haloalkyl in the lower temperature mesophase of Colho at
about 4.8 Å, and the Haloarom in the higher temperature
ro
1
confirmed that the Colho phase in the lower temperature region is
originated by melting of the alkyl chains, and that the Col (P2 /a)
phase in the higher temperature region is originated by flipꢀflop
of the bulky aromatic substituents. Such a stepwise melting of
these substituents may result in this present reverse phase
transition sequence from a higher symmetry of Col mesophase to
a lower symmetry of Col mesophase for the moderately long
chain derivative 2h (n = 8). Furthermore, this mesogen is the first
example switching from long alkyl chain type to flyingꢀseedꢀlike
type in a discotic liquid crystal, so far as we know.
mesophase of Col (P2 /a) phase at about 5.2 Å. This means that
ro
1
ro
1
melting of the alkyl chains induces the Colho1 phase in the lower
temperature region, but that flipꢀflop of the bulky aromatic
substituents induces the Col (P2 /a) phase in the higher
ro
1
temperature region. Furthermore, this unusual reverse phase
h
transition sequence from a higher symmetry of Col mesophase to
h
r
a lower symmetry of Colr mesophase is attributable to the
stepwise melting of the substituents. To our best knowledge, this
mesogen (2h) is the first example switching from molten alkyl
chain type to flyingꢀseedꢀlike type in a discotic liquid crystal.
4
. CONCLUSION
Notes
a
In this study,
a
series of phthalocyanine derivatives
Smart Material Science and Technology, Interdisciplinary Graduate
School of Science and Technology, Shinshu University, 1-15-1 Tokida,
(
mꢀC OPhO) PcCu (n = 1ꢀ20: 2a-o) were prepared to investigate
n
8
80
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Journal of Materials Chemistry C
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DOI: 10.1039/C7TC01197K
Ueda, 386-8567, Japan. E-mail: ko52517@shinshu-u.ac.jp; Fax:
81-268-21-5492; Tel: +81-268-21-5492
+
b
Comprehensive Analysis Centre 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
5
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