Flying-seed-like liquid crystals 3: New guideline for the induction of mesomorphism by using bulky groups instead of long alkyl chains

Article abstract of DOI:10.1039/c3tc30584h

In our previous work, we synthesized a series of phthalocyanine-based flying-seed-like compounds, (nPh-PhO)₄PcCu (n = 3, 2, 1 and 0 in nPh-PhO: a-d), and revealed that each of them shows a columnar liquid crystalline phase (Col_ho or Col_rho) from rt to an extremely high temperature near 500 °C. Thus, we could obtain columnar liquid crystalline phases for discotic compounds by using bulky substituents (a-d) instead of long alkyl chains. In order to further study the utility of these bulky substituents (a-d) on the induction of mesomorphism for other shaped molecules, we have synthesized novel flying-seed-like calamitic phenoxybenzoic acid derivatives, nPh-PhOBA (3a-d), and their Mitsubishi-Mark-shaped terbium complexes, (nPh-PhOBA)₃Tb·mMeOH (4a-d), in this work. Very interestingly, the mesomorphism of the phenoxybenzoic aids derivatives nPh-PhOBA (n = 0-3) was induced to show a mesophase (M_x) only by the bulky substituent d (n = 0), whereas the mesomorphism of their corresponding terbium complexes (nPh-PhOBA)₃Tb(III) (n = 0-3) was induced to show rectangular columnar (Col_r) mesophases by the bulky substituents c and d (n = 1, 0). On the other hand, the mesomorphism of the PcCu complexes (nPh-PhOBA)₄PcCu (n = 0-3) in our previous work was induced by all the bulky substituents a, b, c and d (n = 0-3). Thus, it becomes apparent that both calamitic and columnar mesomorphism can be induced by the substitution of bulky groups instead of long alkyl chains, and that the balance of the core size and the bulkiness of the substituents is very important to obtain mesomorphism in flying-seed-like compounds. We believe that this is a new guideline for the induction of mesomorphism by using bulky groups instead of long alkyl chains.

Full text of DOI:10.1039/c3tc30584h

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Materials Chemistry C
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Flying-seed-like liquid crystals 3: new guideline for the
induction of mesomorphism by using bulky groups
instead of long alkyl chains†‡
Cite this: J. Mater. Chem. C, 2013, 1,
5315
a
a
a
Ayaha Hachisuga, Miho Yoshioka, Kazuchika Ohta and Tomoyuki Itayab
*
In our previous work, we synthesized a series of phthalocyanine-based flying-seed-like compounds,
(nPh-PhO)4PcCu (n ¼ 3, 2, 1 and 0 in nPh-PhO: a–d), and revealed that each of them shows a columnar
liquid crystalline phase (Colho or Colrho) from rt to an extremely high temperature near 500 ꢀC. Thus, we
could obtain columnar liquid crystalline phases for discotic compounds by using bulky substituents (a–d)
instead of long alkyl chains. In order to further study the utility of these bulky substituents (a–d) on the
induction of mesomorphism for other shaped molecules, we have synthesized novel flying-seed-like
calamitic phenoxybenzoic acid derivatives, nPh-PhOBA (3a–d), and their Mitsubishi-Mark-shaped
terbium complexes, (nPh-PhOBA)3Tb$mMeOH (4a–d), in this work. Very interestingly, the
mesomorphism of the phenoxybenzoic aids derivatives nPh-PhOBA (n ¼ 0–3) was induced to show a
mesophase (Mx) only by the bulky substituent d (n ¼ 0), whereas the mesomorphism of their
corresponding terbium complexes (nPh-PhOBA)3Tb(III) (n ¼ 0–3) was induced to show rectangular
columnar (Colr) mesophases by the bulky substituents c and d (n ¼ 1, 0). On the other hand, the
mesomorphism of the PcCu complexes (nPh-PhOBA)4PcCu (n ¼ 0–3) in our previous work was induced
by all the bulky substituents a, b, c and d (n ¼ 0–3). Thus, it becomes apparent that both calamitic and
columnar mesomorphism can be induced by the substitution of bulky groups instead of long alkyl
chains, and that the balance of the core size and the bulkiness of the substituents is very important to
obtain mesomorphism in flying-seed-like compounds. We believe that this is a new guideline for the
induction of mesomorphism by using bulky groups instead of long alkyl chains.
Received 29th March 2013
Accepted 24th June 2013
DOI: 10.1039/c3tc30584h
www.rsc.org/MaterialsC
crystalline compounds are outside of this general criterion and
they have neither a rigid at core, nor long exible chains in
their molecules.1–9
1 Introduction
It is well-known that molecular shapes of most liquid crystals
are rod-like (calamitic) or disk-like (discotic). Furthermore, both
molecular structures commonly have a rigid at core and ex-
ible long chains in the periphery. When such shapes of
compounds are heated, the exible long chains melt at rst and
the rigid at cores do not melt, but still aggregate each other.
This pre-melting of the peripheral long chains initiates the so
part to induce liquid-crystalline phases (mesophases). Hence, it
is generally believed that the appearance of mesomorphism
should require both a rigid at core and long exible chains in a
molecule. However, in about 101 000 of the liquid crystals
known to date, it has been reported that a very few liquid
¨
In 1910, Vorlander reported the that alkali metal carboxyl-
ates, Ph2AcONa, (CH3)2AcOK and (C2H5)2AcOK, shown in Fig. 1
exhibit liquid crystalline phases, although they have neither a
at core nor long chains.1 However, these interesting liquid
crystals have been forgotten for about 100 years. It may be
attributable to very high liquid crystalline temperature regions
and their molecular structures being totally different from
general calamitic and discotic liquid crystals.
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 General Education, Nagano National College of Technology, Nagano,
381-8550, Japan. E-mail: itaya@ge; nagano-nct.ac.jp
† Part 2: ref. 12 in this paper.
‡ Electronic supplementary information (ESI) available. See DOI:
10.1039/c3tc30584h
Fig. 1 Photograph of maple seeds and examples of flying-seed-like liquid crys-
tals: ref. 1–4 and 6.
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In 2006, we revealed, by using a temperature-dependent X-
ray diffraction technique that Ph2AcONa shows a hexagonal
columnar (Colh) mesophase, and (CH3)2AcOK and (C2H5)2AcOK
show a calamitic mesophase of the smectic A (SA) phase.6
Nevertheless, it was surprising to us that they have no long
chains necessary for the formation of so parts in the liquid
crystalline phase. Therefore, we thought that the bulky
substituents of the Ph2-, (CH3)2- and (C2H5)2-groups might form
so parts by free rotation, as in the ying-seeds shown in the
photograph of maple seeds in Fig. 1. Accordingly, we named
this type of liquid crystals as “ying-seed-like liquid crystals”.6
They are totally different from conventional calamitic and dis-
cotic liquid crystalline compounds.
In 2004 and 2009, Usol'tseva and her co-workers reported
that a phthalocyanine (Pc) compound (3Ph-PhO)4PcCu exhibits
a Colh mesophase.10,11 Although it has a rigid at core, it has no
long alkyl chains but the bulky triphenylmethylphenoxy groups
(a in Fig. 2) in the periphery. The present bulky triphenylmethy-l-
phenoxy group (a) closely resembles the Ph2-group in a
previous ying-seed-like liquid crystal Ph2AcONa mentioned
above (Fig. 1). Hence, we considered that this Pc compound
(3Ph-PhO)4PcCu was one of the ying-seed-like liquid crystals,
and that the bulky triphenylmethylphenoxy groups (a) also
formed so parts in the mesophase. To certify this idea, we have
Scheme 1 Synthetic route for novel flying-seed-like calamitic nPh-PhOBA (3a–
d) and Mitsubishi-Mark-shaped (nPh-PhOBA)3Tb$mMeOH (4a–d) liquid crystals.
(i) X–OH, polyphosphoric acid; (ii) 48% HBr aq. sol./HOAc; (iii) (1) K2CO3/DMF/p-
nitrobenzoic acid (2) H+, (iv) (NO3)3Tb$6H2O–MeOH–ethylene glycol–NaOH for
4a, b; (NO3)3Tb$6H2O–MeOH–NaOH for 4c, d.
2 Experimental
2.1 Synthesis
synthesized
four
phthalocyanine-based
ying-seed-like
compounds, (nPh-PhO)4PcCu (n ¼ 3–0), by using a series of Scheme 1 shows the synthetic route for the present ying-seed-
bulky substituents (a–d in Fig. 2). Very interestingly, each of like calamitic nPh-PhOBA (3a–d) compounds and the Mitsubishi-
them shows a columnar liquid crystalline phase (Colho or Mark-shaped (nPh-PhOBA)3Tb$mMeOH (4a–d) complexes. The
Colrho) from rt to an extremely high temperature, near 500 ꢀC.12 starting materials, phenol derivatives 2a, c and d, were purchased
Thus, it was shown that columnar liquid crystalline phases can from Tokyo Chemical Industry, and they were used without
be induced for discotic compounds also by using bulky further purication. Since the phenol derivative 2b was not
substituents (a–d in Fig. 2) instead of long alkyl chains.
commercially available, it was prepared as shown in this scheme.
We wished to further study the utility of these bulky substit- Commercially available anisole was reacted with 1,1-diphenyle-
uents (a–d in Fig. 2) on the induction of mesomorphism for the thanol to obtain 4-[1,1-diphenylethoxy]anisole 1b, and then it was
other shaped molecules, such that in this work we have synthe- demethylated with hydrobromic acid by using the method of
sized novel ying-seed-like calamitic phenoxybenzoic acid Evangelista et al.14 to afford the phenol derivative 2b. The phenol
derivatives, nPh-PhOBA (3a–d in Scheme 1), and their Mitsubish- derivatives 2a–d were reacted with p-nitrobenzoic acid to obtain
Mark-shaped13 terbium complexes, (nPh-PhOBA)3Tb$mMeOH the corresponding 4-[4-(bulky-group-substituted)phenoxy]ben-
(4a–d in Scheme 1), to investigate their mesomorphism.
zoic acids, nPh-PhOBA (3a–d). The phenoxybenzoic acids 3a–d
were metalated with terbium(III) nitrate hexahydrate under
basic conditions to afford the solvated derivatives (nPh-PhO-
BA)3Tb$mMeOH (4a–d).
The detailed procedures are described only for the repre-
sentative derivatives, 2b, 3a, 4a and 4c. Almost the same
procedures for 3b, 3c and 3d are described in the ESI le.‡
4-(1,1-Diphenylethyl)phenol (2b). Into a 200 ml three-necked
ask, anisole (1.1 g, 10 mmol), 1,1-diphenylethanol (2.0 g,
10 mmol) and polyphosphoric acid (20 g, 200 mmol) were
poured. It was heated with stirring at 100 ꢀC for 23 hours. Aer
cooling to rt, the reaction mixture was extracted with diethyl
ether and washed with NaCl saturated aqueous solution. The
organic layer was dried over sodium sulfate and the evaporated
in vacuo. Into a 100 ml three-necked ask, 2.5 g of the residue,
58 ml of glacial acetic acid and 14.5 ml of 48% hydrobromic acid
aqueous solution were poured. It was heated with stirring at
100 ꢀC for 16 hours. Aer cooling to rt, the reaction mixture was
extracted with CHCl3 and washed with NaCl saturated aqueous
Fig. 2 Molecular formula of phthalocyanine-based flying-seed-like liquid crys-
tals, (nPh-PhO)4PcCu, in our previous work: ref. 10–12.
5316 | J. Mater. Chem. C, 2013, 1, 5315–5321
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solution. The organic layer was dried over sodium sulfate and DSC-50 differential scanning calorimeter. For the mesophase
then dried in vacuo. The residue was puried by column chro- identication, we employed a new small angle X-ray diffrac-
matography (120 g of silica gel, CH2Cl2, Rf¼ 0.33) to afford 0.68 tometer (Bruker Mac SAXS System) equipped with a tempera-
g of an ocherous solid, obtained in a 25% yield.
IR (KBr): 3487 (Ar–OH) cmꢁ1
ture-variable sample holder adapted Mettler FP82HT hot stage.
.
Fig. S1 and S2‡ illustrate the setup of the SAXS system and the
1H-NMR (DMSO-d6: TMS) d 2.32 (3H, s, –CH3), 7.02–7.24 setup of the temperature-variable sample holder, respectively.
(14H, m, aromatic –H), 9.44 (1H, s, O–H).
As can be seen from Fig. S1,‡ the generated X-ray is bent by two
4-(4-Tritylphenoxy)benzoic acid (3a). A 100 ml three-necked convergence monochrometers to produce a point X-ray beam
ask with a condenser was dried by a heat gun under a nitrogen (diameter ¼ 1.0 mm). The point beam runs through holes of the
atmosphere. Into this ask, p-nitrobenzoic acid (0.18 g, temperature-variable sample holder. As is illustrated in Fig. S2,‡
1.1 mmol), freshly distilled dry DMF (5 ml), K2CO3 (0.35 g, into the temperature-variable sample holder of the Mettler
2.5 mmol), and 4-triphenylmethylphenol (2a: 0.44 g, 1.3 mmol) FP82HT hot stage, a glass plate (76 mm ꢂ 19 mm ꢂ 1.0 mm)
were poured. It was heated with stirring under a dry nitrogen having a hole (diameter ¼ 1.5 mm) is inserted. The hole can be
atmosphere at 110 ꢀC for 6 hours. Aer cooling to rt, it was charged with a powder sample (ca. 1 mg). The measurable range
˚
˚
neutralised by adding 10% hydrochloric acid dilute aqueous is from 3.0 A to 100 A and the temperature range is from rt to
solution, and then extracted with diethyl ether and washed with 375 ꢀC. This SAXS system enabled us to greatly reduce the
NaCl saturated aqueous solution. The organic layer was dried amount of samples. The measurement time only needed 60–300
over sodium sulfate and dried in vacuo. The residue was seconds, which was efficient to suppress the sample decompo-
recrystallised from ethanol to afford 0.33 g of a white solid in a sition. Temperature-dependent uorescence spectra of 4c, d
67% yield. M.p.: see Table 2.
were recorded using a Horiba Fluorolog FL3-21-NIR-OS spec-
IR (KBr): 3489 ( –OH), 1710 (C]O), 1280 (ether) cmꢁ1
.
trouorometer equipped with a handmade hot plate15 available
1H-NMR (DMSO-d6: TMS) d 6.66 (2H, d, J ¼ 9.1 Hz, aromatic from rt to 400 C with a temperature controller.
ꢀ
–H), 6.93 (2H, d, J ¼ 9.0 Hz, aromatic –H), 7.08–7.32 (19H, m,
aromatic –H), 9.36 (1H, s, COO–H).
3 Results and discussion
3.1 Synthesis
(3Ph-PhOBA)3Tb$2MeOH (4a). Into a 50 ml Erlenmeyer ask,
NaOH (0.048 g, 1.2 mmol), terbium(III) nitrate hexahydrate
(0.14 g, 0.30 mmol), 4-(4-tritylphenoxy) benzoic acid (3a: 0.46 g, As can be seen from Scheme 1, the fourth synthetic step (iv)
1.0 mmol), MeOH (5 ml) and ethylene glycol (0.5 ml) were from the phenoxybenzoic acid derivatives to the terbium
added, and it was stirred at rt for 24 hours. The resulting complexes was successful for 4c and d by using a single reaction
precipitate was collected by ltration and washed with MeOH. solvent, MeOH. On the other hand, it was not successful for 4a
The residue was dried in vacuo to afford 0.31 g of white crystals and b by using the single solvent MeOH. This was attributable
in a 60% yield.
to the low solubilities of 3a and b in pure MeOH, which resulted
(2Ph-PhOBA)3Tb$2MeOH (4b). In the same manner as 4a, it from the large number of phenyl groups in the bulky substitu-
could be prepared to afford 0.30 g of white crystals in a 65% ents. When a mixture solvent of MeOH and ethylene glycol
yield.
(1Ph-PhOBA)3Tb$2MeOH (4c). Into a 50 ml Erlenmeyer ask, fully took place, to afford the terbium complexes 4a, and b.
NaOH (0.048 g, 1.2 mmol), terbium(III) nitrate hexahydrate
As can be seen from the elemental analysis data in Table 1,
(10 : 1 v/v) was adopted for 3a and b, the metallation success-
(0.14 g, 0.30 mmol), 4-[4-(1-methyl-1-phenylethyl) phenoxy] each of the terbium complexes 4a–c contained two MeOH
benzoic acid (3c: 0.33 g, 1.0 mmol) and MeOH (5 ml) were molecules as the crystal solvent in the freshly prepared (virgin)
added, and it was stirred at rt for 24 hours. The resulting sample. On the other hand, the terbium complex 4d contained
precipitate was collected by ltration and washed with MeOH. four MeOH molecules as the crystal solvent. The number of
The residue was dried in vacuo to afford 0.25 g of white crystals MeOH molecules (m in Scheme 1) could be also conrmed from
in a 64% yield.
the thermal gravimetric analysis (TGA) as shown in Fig. 3. As
(0Ph-PhOBA)3Tb$4MeOH (4d). In the same manner as 4c, it can be seen from the DSC thermograms in this gure, each of
could be prepared to afford 0.20 g of white crystals in a 55% the virgin samples (the rst heating runs) of 4c and d gave a
ꢀ
yield.
large endothermic peak with an onset at ca. 50 C, whereas it
disappeared in the second heating runs. As can be seen from
the TGA thermograms in this gure, the virgin samples of 4c
and 4d gave 5.1% and 11.9% of weight losses at ca. 50 ꢀC,
2.2 Measurements
The compounds synthesized here were identied by using FT-IR respectively. The weight losses of 4c and 4d exactly correspond
(Nicolet NEXUS670 FT-IR), 1H-NMR (Bruker DRX-400), to the weights of two and four MeOH molecules, respectively. It
elemental analysis (Perkin-Elmer elemental analyzer 2400), and is consistent with the elemental analysis data in Table 1
thermal gravimetric analysis (Rigaku Thermo plus TG8120). The mentioned above. The terbium complex 4d only contains four
phase transition behaviour of the present compounds (3a–d MeOH molecules. It may be attributed to more space around the
and 4a–d) was observed with a polarizing optical microscope Mitsubishi-Mark-shaped terbium complex 4d (n ¼ 0) in
(Nikon ECLIPSE E600 POL) equipped with a Mettler FP82HT hot comparison with the other bulky phenyl-group-substituted
stage and a Mettler FP-90 Central Processor, and a Shimadzu terbium complexes 4a–c (n ¼ 3–1).
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Table 1 Elemental analysis data of (nPh-PhOBA)3Tb$mMeOH, 4a–d
Elemental analysis: found (calcd)/%
Compound
Molecular formula
C
H
N
4a: (3Ph-PhOBA)3Tb$2MeOH
4b: (2Ph-PhOBA)3Tb$2MeOH
4c: (1Ph-PhOBA)3Tb$2MeOH
4d: (0Ph-PhOBA)3Tb$4MeOH
C98H77O11Tb
C83H71O11Tb
C68H65O9Tb
C55H67O13Tb
73.83 (74.05)
70.94 (71.04)
66.85 (67.10)
62.07 (62.14)
4.85 (4.88)
5.02 (5.10)
5.21 (5.38)
6.43 (6.35)
0.02 (0.00)
0.01 (0.00)
0.10 (0.00)
0.01 (0.00)
we could observe the liquid-crystalline texture at 220 ꢀC as
shown in the photomicrograph in Fig. 4. As can be seen from
this photomicrograph, the crystalline phase K was changing
into a marble texture with uidity characteristics to a nematic
phase.19 However, it rapidly sublimed within one minute so that
the mesophase could not be identied unambiguously. Hence,
Table 2 Phase transition sequences for the flying-seed-like calamitic nPh-
PhOBA (3a–d), and desolventized Mitsubishi-Mark-shaped (nPh-PhOBA)3Tb
(4a–d) liquid crystalsa
TðꢀCÞ DHðkJ molꢁ1
Þ
½
ꢃ
Compound
Phaseb
K
Phase
ƒƒƒƒƒƒƒƒƒƒƒƒƒ!
288½73:0ꢃ
3a
I. L. (Subl.)
Fig. 3 DSC and TGA thermograms of (1Ph-PhOBA)3Tb$2MeOH (4c) and
(0Ph-PhOBA)3Tb$4MeOH (4d).
ƒƒƒƒƒƒ!
176½94:7ꢃ
3b
3c
3d
K
K
K
I. L. (Subl.)
I. L. (Subl.)
I. L. (Subl.)
ƒƒƒƒƒƒ!
3.2 Mesomorphic properties
The phase transition sequences for the ying-seed-like calam-
itic phenoxybenzoic acid derivatives nPh-PhOBA (3a–d) and
their corresponding desolventized Mitsubishi-Mark-shaped
terbium complexes (nPh-PhOBA)3Tb (3a–d) are summarized in
Table 2.
193½94:8ꢃ
ƒƒƒƒƒƒ!
Mesomorphism of 0Ph-PhOBA (3d). It is well known and
established that long alkyl-chain-substituted benzoic acid
derivatives form dimers by hydrogen bonding and show meso-
morphism.16–18 The present phenoxybenzoic acid derivatives
nPh-PhOBA (3a–d) may also form dimers as illustrated in
Scheme 1.
356
ƒƒƒƒ!
4a
K
dc
334
ƒƒƒƒ!
4b
4c
K
K
dc
dc
As can be seen from Table 2, the phenoxybenzoic acid
derivatives 3a–c are not liquid-crystalline but crystalline. On the
other hand, the derivative 3d is only liquid-crystalline. All the
compounds 3 are so sublime at high temperatures especially
aer the clearing point that no samples were in the DSC cell and
gave no DSC peaks on the 1st cooling and the 2nd heating runs
(Table 2). Since the derivative 3d is so sublime at high
temperatures, it was very difficult to observe the liquid-crystal-
line texture by a polarizing microscope (POM). When this
derivative was gradually heated from rt, it completely subli-
mated and disappeared before reaching the mesophase
temperature range. Therefore, the sample was inserted into the
hot stage pre-heated at a certain temperature under the clearing
point (cp) of 246 ꢀC. The set temperature was lowered gradually
from the cp and observed by the POM step by step. Eventually,
286½44:1ꢃ
Colr
P21=a
314
ƒƒƒƒƒ!
ƒƒƒƒƒ!
282½35:5ꢃ
Colr
P2m
308
ƒƒƒƒƒ!
4d
K
dc
ƒƒƒƒƒ!
a
All the phase transition temperatures with enthalpy changes were
determined with DSC for the 1st heating run, except for the asterisk-
marked temperature which was observed only with POM. The
decomposition temperatures were determined with TGA as the onset
b
temperatures. Phase nomenclature: K ¼ crystal, Mx ¼ unidentied
mesophase, Colr ¼ rectangular columnar mesophase, I. L. (Subl.) ¼
isotropic liquid (accompanied by vigorous sublimation) and dc ¼
decomposition.
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not clear at the present time, the sublimation enthalpy might be
included. The compound 3d gave the most vigorous sublima-
tion nature among the compounds 3a–d. Hence, it would give
the biggest enthalpy among them.
As mentioned above, the bulky phenyl-group-substituted
phenoxybenzoic acid derivatives 3a–c are not liquid-crystalline.
It may be attributable to too small a core in comparison with the
bulkier substituents. Thus, these ying-seed-like compounds
suggest that the balance of the core size and the bulkiness of the
substituents is very important to obtain mesomorphism.
Mesomorphism of (nPh-PhOBA)3Tb(III) (n ¼ 1, 0: 4c and d).
As can be seen from Table 2, the Mitsubishi-Mark-shaped
terbium complexes 4a and 4b are not liquid-crystalline but
crystalline until their very high decomposition temperatures.
On the other hand, 4c and 4d exhibit a mesophase at very high
temperatures. It is very interesting that the mesomorphism of
the phenoxybenzoic aids derivatives nPh-PhOBA (n ¼ 0–3) was
induced only by the bulky substituent d (n ¼ 0), but that the
mesomorphism of their corresponding terbium complexes
(nPh-PhOBA)3Tb(III) (n ¼ 0–3) was induced by the bulky
substituents c and d (n ¼ 1, 0). On the other hand, the meso-
morphism of the PcCu complexes (nPh-PhOBA)4PcCu (n ¼ 0–3)
in our previous work was induced by all the bulky substituents
a, b, c and d (n ¼ 0–3).12 Therefore, the balance of the core size
and the bulkiness of the substituents is very important to obtain
mesomorphism for ying-seed-like compounds.
Fig. 4 Photomicrograph of 0Ph-PhOBA (3d) at 220 ꢀC. The crystalline phase K
was changing into an unidentified mesophase (Mx) showing a marble texture.
this mesophase was denoted as an unidentied mesophase
(Mx). Nevertheless, this means that we can also obtain calamitic
liquid crystals substituted by bulky groups instead of long alkyl
chains. The present phenoxybenzoic acid derivative 3d is the
rst example of ying-seed-like calamitic liquid crystal, so far as
we know.
As can be seen from Table 2, the enthalpy of 167 kJ molꢁ1
between 220* and 246 ꢀC of 3d seems to be too large even for the
combined enthalpies of melting (K-Mx) and clearing (Mx-I. L.) in
comparison with general mesogenic compounds. Although it is
Fig. 5 X-ray diffraction patterns of (1Ph-PhOBA)3Tb (4c) and (0Ph-PhOBA)3Tb (4d) at 300 ꢀC.
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Fig. 5 shows the X-ray diffraction patterns of 4c and 4d at 300
ꢀC. The corresponding X-ray data are listed in Table 3. As can be
seen from this table, the Mitsubishi-Mark-shaped terbium
complexes 4c and 4d give rectangular columnar mesophases,
Colr(P21/a) and Colr(P2m), respectively. The small symmetrical
difference between them may originate from the difference in
the bulkiness of the substituted groups of c and d. Interestingly,
(1Ph-PhOBA)3Tb (4c) showed two stacking distances of dimers
˚
and monomers at 10.1 and 5.14 A, respectively. This means that
an equilibrium between dimers and monomers exists in the
columns. The Mitsubishi-Mark-shaped terbium complexes 4c
may form anti-parallel dimers in which one Mitsubishi-Mark
stacks on another Mitsubishi-Mark rotated by 60 degree.
As mentioned above, the present terbium complexes 4c and
4d exhibit a mesophase at very high temperatures, which is
characteristic to ying-seed-like liquid crystals.12
Fig.
6
Temperature-dependent fluorescence spectra of (1Ph-PhO-
BA)3Tb$2MeOH (4c) and (0Ph-PhOBA)3Tb$4MeOH (4d).
3.3 Temperature-dependent uorescence spectra
The temperature-dependent uorescence spectra of the thin
lms of 4c and 4d are shown in Fig. 6. In Fig. 7 are plotted the
logarithm of the intensities at 545 nm versus temperature. As
can be seen from these gures, the intensities decrease with
increasing temperature.20–22 A large deformation of the spec-
ꢀ
trum of 4c at 300 C corresponds to a considerable decompo-
sition of the sample in air for the long measurement time. The
decomposition temperature 314 ꢀC listed in Table 2 was the
measured value with TGA under a nitrogen atmosphere. The
present
temperature-dependent
uorescence
spectral
measurements were carried out in air for long time. Therefore,
the decomposition in air started even at temperatures lower
than the TGA decomposition temperatures, and progressed for
a long time. Additionally, the colour of the sample measured at
ꢀ
300 C changed from white to brown.
Although there have been several reports that the uorescence
intensities change with phase transitions,20–23 the present
terbium complexes did not show discernible drastic changes for
Table 3 X-ray data of (1Ph-PhOBA)3Tb (4c) and (0Ph-PhOBA)3Tb (4d)
˚
Spacing/A
Compound
Mesophase
Miller indices
(h k l)
Observed
Calculated
Fig. 7 Fluorescent intensities at 545 nm versus temperature for (1Ph-PhO-
BA)3Tb$2MeOH (4c) and (0Ph-PhOBA)3Tb$4MeOH (4d).
4c: (1Ph-PhOBA)3Tb
Colr (P21/a) at 300 ꢀC
19.6
17.3
10.1
9.37
8.53
7.87
5.14
19.6
17.3
10.1
9.36
8.64
7.75
5.07
(2 0 0)
(1 1 0)
(0 0 1)a
(1 2 0)
(2 2 0)
(3 2 0)
(0 0 2)b
˚
a ¼ 39.2 A
˚
b ¼ 19.3 A
their desolventizing and phase transitions, as can be seen from
Fig. 7. Therefore, the uorescence spectral changes of the present
terbium complexes only depend on their thermal stability.
˚
c ¼ 10.1 A
Z ¼ 4.0 for r ¼ 1.00c
4d: (0Ph-PhOBA)3Tb
Colr(P2m) at 300 ꢀ
C
16.9
12.5
7.14
6.20
16.9
12.5
6.99
6.23
(1 0 0)
(0 1 0)
(2 1 0)
(0 2 0)
4 Conclusion
˚
a ¼ 16.9 A
˚
We have synthesized novel ying-seed-like calamitic phenoxy-
benzoic acid derivatives, nPh-PhOBA (3a–d), and their Mitsubishi-
Mark-shaped terbium complexes, (nPh-PhOBA)3Tb$mMeOH
(4a–d), and investigated their mesomorphism.
b ¼ 12.5 A
a
b
Stacking distance between dimers. Stacking distance between
monomers. c Assumed value.
5320 | J. Mater. Chem. C, 2013, 1, 5315–5321
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Paper
The phenoxybenzoic acid derivatives 3a–c are not liquid-
Journal of Materials Chemistry C
8 M. Shimizu, M. Nata, K. Watanabe, T. Hiyama and S. Ujiie,
Mol. Cryst. Liq. Cryst., 2005, 441, 237–241.
9 M. Shimizu, M. Nata, K. Mochida, T. Hiyama, S. Ujiie,
M. Yoshio and T. Kato, Angew. Chem., Int. Ed., 2007, 46,
3055–3058.
crystalline but crystalline, whereas the derivative 3d is only
liquid-crystalline. The derivative 3d shows an unidentied
ꢀ
mesophase (Mx) at very high temperatures from 220 C to 246
ꢀC. It is the rst example of a ying-seed-like calamitic liquid
crystal, as far as we know. On the other hand, the terbium 10 N. Usol'tseva, V. Bykova, G. Ananjeva, N. Zharnikova and
complexes 4a and 4b are not liquid-crystalline but crystalline,
whereas 4c and 4d exhibit the rectangular columnar meso-
E. Kudrik, Mol. Cryst. Liq. Cryst., 2004, 411, 1371–
1378.
phases Colr(P21/a) and Colr(P2m), respectively. It is very inter- 11 N. Zharnikova, N. Usol'tseva, E. Kudrik and M. Theakkat,
esting that the PcCu complexes (nPh-PhOBA)4PcCu in our J. Mater. Chem., 2009, 19, 3161–3167.
previous work are liquid crystalline for all the bulky substitu- 12 Y. Takagi, K. Ohta, S. Shimosugi, T. Fujii and E. Itoh,
ents a, b, c and d. J. Mater. Chem., 2012, 22, 14418–14425.
Thus, it becomes apparent that both calamitic and columnar 13 Mitsubish-Mark: see http://www.mitsubishi.com/e/group/
mesomorphism can be induced by bulky group substituents mark.html.
instead of long alkyl chains, and that the balance of the core size 14 R. A. Evangelista, H. E. Wong, E. F. G. Templeton,
and the bulkiness of the substituents in ying-seed-like
compounds is very important to obtain mesomorphism. We
T. Granger, B. Allore and A. Pollak, Anal. Biochem., 1992,
203, 218–226.
believe that this is a new guideline for induction of meso- 15 T. Shibuya, Appendix 1 in Master Thesis, Shinshu University,
morphism by using bulky groups instead of long alkyl chains.
Ueda, 2006.
16 N. K. Lokanath, D. Krishne Gowda, D. Revannasiddaiah,
M. M. M. Abdoh, M. A. Sridhar and J. Shashidhara Prasad,
Mol. Cryst. Liq. Cryst. Sci. Technol., Sect. A, 1998, 317, 153–
164.
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