Discotic liquid crystals of transition metal complexes 42?: The detailed phase structures and phase transition mechanisms of two Cub mesophases shown by discotic liquid crystals based on phthalocyanine metal complexes

Article abstract of DOI:10.1142/S1088424610001908

We found in our previous works that the sandwich-type phthalocyanine-based rare earth metal complexes, bis[2,3,9,10,16,17,23,24-octakis(3,4- dialkoxyphenoxy)phthalocyaninato]lanthanoid(III) ({[(C_nO) ₂PhO]₈Pc}₂M,

Full text of DOI:10.1142/S1088424610001908

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2010; 14: 188–197
DOI: 10.1142/S1088424610001908
Published at http://www.worldscinet.com/jpp/
Discotic liquid crystals of transition metal complexes 42†: the
detailed phase structures and phase transition mechanisms
of two Cub mesophases shown by discotic liquid crystals
based on phthalocyanine metal complexes
Hidetomo Mukai, Miho Yokokawa, Masahiro Ichihara, Kazuaki Hatsusaka and
Kazuchika Ohta*◊
Smart Materials Science and Technology, Interdisciplinary Graduate School of Science and Technology, Shinshu
University, 386-8567 Ueda, Japan
Received 19 March 2009
Accepted 4 May 2009
ABSTRACT: We found in our previous works that the sandwich-type phthalocyanine-based rare
earth metal complexes, bis[2,3,9,10,16,17,23,24-octakis(3,4-dialkoxyphenoxy)phthalocyaninato]
lanthanoid(III) ({[(CnO)2PhO]8Pc}2M, M = Eu and Lu, n = 8–16) (1 and 3), exhibited two thermotropic cubic
mesophases, Cub1 and Cub2, together with columnar mesophases. It is rare that the discotic liquid crystalline
compounds show the cubic mesophase. We revealed that their symmetries of the lower temperature Cub1
–
–
mesophase and the higher temperature Cub2 mesophase were Pn3m and Pm3n, respectively. However,
their detailed phase structures were not revealed in the previous works. In this work, we have synthesized
a series of novel sandwich-type phthalocyanine-based terbium complexes, bis[2,3,9,10,16,17,23,24-
octakis(3,4-dialkoxyphenoxy)phthalocyaninato]terbium(III) ({[(CnO)2PhO]8Pc}2Tb, n = 8–16) (2). Their
mesomorphic properties have been investigated using polarization microscope, DSC and temperature-
dependent X-ray diffraction techniques. As the result, the present Tb complexes (2) also showed two cubic
–
–
mesophases, Cub1 (Pn3m) and Cub2 (Pm3n), together with columnar mesophases, as well as the previous
Eu homologs (1) and Lu homologs (3). We have furthermore investigated by using temperature-dependent
electronic absorption spectroscopy to reveal their detailed phase structures and phase transition mechanism
–
of these two Cub mesophases. We have revealed that the Cub1 (Pn3m) mesophase forms a bicontinuous
–
structure consisting of branched columns like jungle gym, but that the Cub2 (Pm3n) mesophase forms a
discontinuous structure consisting of short columns like drums that resulted from the cutting off of the
branched columns.
KEYWORDS: discotic liquid crystal, sandwich type, lanthanoid phthalocyanine, cubic mesophase.
mesophases, and the detailed symmetries of their Cub
INTRODUCTION
mesophases were not investigated until 2007 [17–20].
For example, in 2001 we synthesized phthalocyanine-
based (Pc-based) copper complexes, 2,3,9,10,16,17,23,-
24-octakis(3,4-dialkoxyphenoxy)phthalocyaninato
copper(II), which exhibited a thermotropic Cub meso-
The symmetries of the thermotropic cubic (Cub) meso-
phases of rod-like molecules, polycatenars and dendrim-
ers have been well researched [2–16]. In comparison,
the discotic compounds rarely exhibit thermotropic Cub
phase [19] and in 2007 we reported on the symmetry
of the Cub mesophase as Pn3m for the first time in dis-
–
š
SPP full member in good standing
cotic compounds [21]. From 2003 to 2009 we synthe-
sized the corresponding sandwich-type Pc-based rare
earth metal complexes, bis[2,3,9,10,16,17,23,24-octakis-
*Correspondence to: Kazuchika Ohta, e-mail: ko52517@
shinshu-u.ac.jp
†Part 41, see Reference 1
Copyright © 2010 World Scientific Publishing Company

DISCOTIC LIQUID CRYSTALS OF TRANSITION METAL COMPLEXES
189
–
(3,4-dialkoxyphenoxy)phthalocyaninato]lanthanoid(III)
whereas the Cub2 (Pm3n) may form a discontinuous
Cub structure consisted of short columns like drums that
resulted from cutting off of the long branched columns. If
({[(CnO)2PhO]8Pc}2M, M = Eu and Lu, n = 8–16) (1 and
3), which exhibited two thermotropic Cub mesophases,
Cub1 and Cub2, together with columnar mesophases,
for the first time in discotic compounds [20, 22, 23]. In
these previous works, we reported that the symmetries
of these lower temperature Cub1 and higher temperature
ourhypothesisiscorrect, thelongcolumnswillcutintothe
–
short columns at the phase transition of Cub1 (Pn3m) →
–
Cub2 (Pm3n), which can be observed for the tempera-
ture-dependent electronic spectra corresponding to the
intermolecular force change.
In this paper, we wish to report the detailed mesophase
structures of Cub1 (Pn3m) and Cub2 (Pm3n) and the phase
–
–
Cub2 mesophases were Pn3m and Pm3n, respectively.
However, the detailed phase structures and phase tran-
sition mechanism have never been established. There-
fore, in this work, we have synthesized a series of novel
Tb homologous complexes, bis[2,3,9,10,16,17,23,24-
octakis(3,4-dialkoxyphenoxy)phthalocyaninato]
terbium(III) ({[(CnO)2PhO]8Pc}2Tb, n = 8–16) (2), to
compare their mesomorphism with those of the previ-
ous Eu complexes (1) and Lu complexes (3). The result
shows that the Tb complexes (2) also exhibit two Cub
–
–
–
–
transition mechanism of Cub1 (Pn3m) → Cub2 (Pm3n).
EXPERIMENTAL
Syntheses
–
–
The synthetic route of {[(CnO)2PhO]8Pc}2M (M =
Eu, Tb, Lu; n = 8–16) is shown in Scheme 1. The pres-
ent complexes (2a–i) were prepared by the previously
reported method for the complexes 1 and 3 [19, 20]. For
the purification of these complexes, a Japan Analytical
Industry LC-918 recycling preparative HPLC equipped
with UV detector (UV-50) was used (developing solvent:
chloroform, column: JAIGEL 3H+4H, pressure: 14–15
kg.cm-2, flow rate: 3.9 mL.min-1). Yields, MALDI-TOF
mass spectral data and elemental analysis data of these
complexes are summarized in Table 1.
mesophases, Cub1 (Pn3m) and Cub2 (Pm3n), together
with columnar mesophases, as well as the Eu complexes
(1) and the Lu complexes (3). Hence, we restudied here
in detail these two Cub mesophase structures and phase
transition mechanism of all complexes 1–3. In general,
Cub mesophases consist of the spherical molecules or the
micelle that rod-like molecules aggregated into a spheri-
cal shape. However, the present complexes (1–3) are not
spherical but discotic. Furthermore, in general, their dis-
cotic molecules tend to one-dimensionally stack to form
columnar structures by their π-π interaction. Hence, it is
unimaginable for the present discotic complexes (1–3)
that they could aggregate into the spherical micelle. The
Measurements
–
–
Cub1 (Pn3m) mesophase and the Cub2 (Pm3n) meso-
The synthesized complexes were identified by
elemental analysis (PerkinElmer elemental analyzer
2400), MALDI-TOF mass spectroscopy (Perceptive
Biosystem Voyager, matrix: dithranol) and electronic
absorption spectroscopy (Hitachi U-4100 spectropho-
tometer). The electronic absorption spectral data are
phase of the present complexes (1–3) may be composed
of not the spherically aggregated micelles but the stacked
–
columns. The Cub1 (Pn3m) mesophase may form a
bicontinuous Cub structure consisted of long branched
columns like jungle gym (climbing frame for children),
H2n+1CnO
H2n+1CnO
H2n+1CnO
HO
HO
(i)
(ii)
(iii)
NC
NC
OR
OR
CHO
CHO
H2n+1CnO
OH
2
3
4
5
previous work
this work
OR
RO
OR
OR
RO
RO
N
N
N
N
M = Eu M = Tb
M = Lu
N
N
N
OCnH2n+1
OCnH2n+1
N
(iv)
n = 8 : a
n = 9 : b
n = 10 : c
n = 11 : d
n = 12 : e
n = 13 : f
n = 14 : g
n = 15 : h
n = 16 : i
O
X
O
X
O
X
O
X
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
OR
OR
N
R =
M
OR
N
OR
RO
RO
N
N
N
N
N
N
OR
OR
RO
RO
1: M = Eu
2: M = Tb
3: M = Lu
Scheme 1. Synthetic route to {[(CnO)2PhO]8Pc}2M (M = Eu, Tb, Lu) (1–3). (i): n-alkylbromide, K2CO3, dry DMF; (ii): H2O2, conc.
H2SO4, CHCl3, CH3OH; (iii): 4,5-dichlorophthalonitrile, dry DMSO, K2CO3; (iv): M(CH3COO)3 · 4H2O (M = Eu, Tb, Lu), DBU
(1,8-diazabicyclo[5.4.0]undec-7-ene), 1-hexanol. O = synthesized, X = not synthesized
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 189–197

190
H. MUKAI ET AL.
Table 1. Yields, MALDI-TOF mass spectral data and elemental analysis data of {[(CnO)2PhO]8Pc}2Tb (2a–2i)
Compound
Yield, %
Mol. formula,
mol. wt
Mass spectra
Elemental analysis; found, % (calcd, %)
C
H
N
n = 8: 2a
n = 9: 2b
n = 10: 2c
n = 11: 2d
n = 12: 2e
n = 13: 2f
n = 14: 2g
n = 15: 2h
n = 16: 2i
44
37
24
38
13
39
27
44
27
C416H608N16O48Tb
(6760.41)
6762.05
7210.18
7658.51
8107.31
8553.78
9005.84
9451.55
9902.76
10348.9
74.02 (73.91)
9.19 (9.06)
3.23 (3.32)
C448H672N16O48Tb
(7209.27)
74.48 (74.64)
75.45 (75.28)
75.80 (75.86)
76.48 (76.37)
76.98 (76.83)
76.94 (77.25)
77.45 (77.50)
78.10 (77.97)
9.20 (9.40)
9.63 (9.69)
3.39 (3.11)
3.33 (2.93)
2.89 (2.76)
2.94 (2.62)
2.47 (2.49)
2.67 (2.37)
2.55 (2.26)
2.37 (2.17)
C480H736N16O48Tb
(7658.13)
C512H800N16O48Tb
(8106.99)
9.94 (9.95)
C544H864N16O48Tb
(8555.85)
10.56 (10.18)
10.36 (10.39)
10.67 (10.58)
10.99 (10.73)
11.61 (10.91)
C576H928N16O48Tb
(9004.71)
C608H992N16O48Tb
(9453.57)
C640H1056N16O48Tb
(9902.43)
C672H1120N16O48Tb
(10351.29)
Table 2. UV-vis spectral data in CHCl3 of {[(CnO)2PhO]8Pc}2Tb (2a–2i)
Compound Concentrationa
λmax, nm (log ε)
(10-6 mol/l)
Soret band
b
Q band
Q
0-1 band
c
Q0-0 band
n = 8: 2a
n = 9: 2b
n = 10: 2c
n = 11: 2d
n = 12: 2e
n = 13: 2f
n = 14: 2g
n = 15: 2h
n = 16: 2i
6.71
6.70
6.70
6.65
6.70
6.64
6.69
6.71
6.71
288.7(5.18) 332.5(5.17) 358.2(5.11) 474.2(4.58) 615.4(4.70) 653.6(4.70) 681.5(5.29)
289.9(5.19) 330.4(5.18) 358.9(5.12) 474.2(4.59) 614.8(4.72) 651.8(4.71) 681.5(5.31)
288.6(5.13) 331.8(5.13) 359.5(5.07) 474.6(4.54) 616.4(4.66) 651.8(4.64) 681.7(5.26)
289.3(5.15) 330.5(5.14) 359.9(5.09) 474.6(4.55) 613.9(4.67) 651.1(4.66) 681.6(5.25)
289.0(5.17) 332.1(5.15) 359.3(5.10) 473.2(4.60) 615.0(4.71) 653.7(4.69) 682.1(5.31)
288.4(5.17) 329.1(5.11) 359.1(5.11) 474.6(4.57) 613.9(4.69) 651.8(4.68) 681.5(5.28)
288.8(5.16) 330.5(5.13) 360.1(5.08) 473.8(4.55) 615.4(4.66) 650.8(4.65) 681.7(5.25)
289.7(5.18) 330.1(5.17) 358.5(5.12) 473.9(4.59) 615.1(4.70) 651.8(4.69) 682.1(5.28)
288.6(5.18) 330.1(5.16) 358.7(5.11) 473.9(4.58) 615.3(4.70) 650.9(4.69) 682.1(5.27)
a In chloroform. b The peak related to the radical electron. c Aggregation band of Q0-0 band.
summarized in Table 2. Temperature-dependent elec-
tronic absorption spectra of the thin films of present
complexes were also measured by the Hitachi U-4100
spectrophotometer equipped with a handmade heat-
ing plate [24] controlled by a thermoregulator. The
thin film was prepared by casting method dropping the
chloroform solution to a P102 glass plate. The phase
transition behavior were observed using a polarization
microscope (Olympus BH2) equipped with a heat-
ing plate (Mettler FP-82 HT hot stage) controlled by
a thermoregulator (Mettler FP-90 Central Processor)
and measured by a differential scanning calorimeter
(Shimadzu DSC-50). Temperature-dependent X-ray
diffraction measurements were performed with Cu-Kǩ
radiation using a Rigaku RAD X-ray diffractometer
equipped with a handmade heating plate controlled
by a thermoregulator [24, 25]. The X-ray data of pres-
ent complexes are summarized in Table S1 (see Sup-
porting Information section). In this paper, two Cub
mesophases of the complexes (1 and 3) were restud-
ied to obtain more detailed X-ray data, especially for
Cub2 mesophases of the Eu complexes (1c–i). The new
X-ray data are summarized in Table S2 (supplementary
material).
Copyright © 2010 World Scientific Publishing Company
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DISCOTIC LIQUID CRYSTALS OF TRANSITION METAL COMPLEXES
191
cleared into I.L. at 248 °C. Keeping at this temperature, the
I.L. very slowly transformed into a dendric texture having
a C4 symmetry characteristic of a Coltet mesophase.
RESULTS AND DISCUSSION
Phase transition behavior
In Table 3, the phase transition behavior and enthalpy
changes of the Tb complexes (2) are summarized. As can
be seen, the Tb complexes (2c–i) exhibited plural meso-
phases (Colh, two Cubs and Coltet). Very interestingly, all
the Tb complexes (2a–i) exhibited unique double-clearing
behavior [1, 23, 26–28], which was observed in the pre-
X-ray diffraction studies on two cubic mesophases
In Fig. 2, the phase transition temperatures of the Eu
complexes (1), the Tb complexes (2) and the Lu com-
plexes (3) were plotted against the number of the car-
bon atoms in the alkoxy chain (n). As can be seen, there
are two Cub mesophases, the lower temperature Cub1
vious Eu homologs (1). For example, when the deriva-
–
–
–
(Pn3m) mesophase and the higher temperature Cub2
tive 2e (n = 12) was heated, the Cub2 (Pm3n) mesophase
(Pm3n) mesophase, in the Eu complexes (A) for n ≥ 10,
perfectly cleared into I.L. at 245 °C. On holding at this
temperature, the I.L. very slowly transformed into a den-
dric texture having a C4 symmetry characteristic of a Coltet
mesophase (Fig. 1A). When it was heated up to 282 °C, it
started clearing into I.L. again. The other derivatives also
showed similar double-clearing behavior. As can be seen
from Table 3, the derivatives 2a (n = 8) and 2b (n = 9)
exhibited a slightly different phase transition behavior.
The derivative 2a exhibited not a Cub mesophase but a
Colr (P2m) mesophase. The Colr (P2m) mesophase cleared
into I.L. at 262 °C. Keeping at this temperature, the I.L.
very slowly relaxed into a Colh mesophase and exhibited
a dendric texture having a C6 symmetry characteristic of
the Tb complexes (B) for n ≥ 10, and the Lu complexes
(C) for 13 ≥ n > 10.
Figure 3 illustrates X-ray diffraction patterns of
–
–
the Cub1 (Pn3m) and Cub2 (Pm3n) mesophases of the
representative Eu complex 1e, Tb complex 2e and Lu
complex 3e. As shown, there is an apparent difference
–
in the XRD patterns of the Cub1 (Pn3m) mesophases
–
and the Cub2 (Pm3n) mesophases. Although both
XRD patterns showed three peaks in the small angle
region, a peak assigned to Miller index (2 2 1) could be
observed in each of the Cub1 mesophases. In Table 4
are listed the extinction rules for Cub mesophases. As
can be seen from this table, the reflection correspond-
ing to Miller index (2 2 1) could be observed only for a
a Colh mesophase (Fig. 1B). The Colr (P2m) mesophase
–
of derivative 2b transformed into Cub (Pm3n), and then
Table 3. Please transition temperatures and enthaply changes of {[CnO)2PhO]8Pc}2Tb (2a–2i)
o
Compound
T / C [∆H (kJ/mol)]
Relaxation
Phase
Phase
{[(C O) PhO] Pc} Tb
n
2
8
2
147 [33.1]
149 [21.8]
142 [30.6]
142 [30.6]
316
303
300
**
I.L.
Col (P2m)
r
Col
h
Col
n = 8: 2a
h
262 [18.6]
I.L.
*
_
187 [10.7]
178 [13.2]
165 [12.5]
**
I.L.
Col (P2m)
r
Cub (Pm3n)
Col
Col
Col
Col
Col
Col
tet
tet
tet
n = 9: 2b
h
h
h
248 [6.4]
I.L.
I.L.
I.L.
*
*
*
_
_
**
I.L.
Cub (Pn3m)
Cub (Pm3n)
n = 10: 2c
n = 11: 2d
252 [12.3]
_
_
276
**
I.L.
Cub (Pn3m)
Cub (Pm3n)
244 [8.2]
_
_
165 [12.5]
169 [18.6]
142 [30.6]
140 [25.8]
282
270
**
I.L.
n = 12: 2e
n = 13: 2f
Cub (Pn3m)
Cub (Pm3n)
Col
Col
tet
h
I.L.
I.L.
245 [18.8]
*
*
_
_
36
**
I.L.
K
Cub (Pn3m)
Cub (Pm3n)
Col
Col
Col
Col
3
tet
tet
h
h
32
K
2
232 [10.6]
29
K
1
_
_
167 [26.5]
274
38 [221.9]
137 [21.9]
**
I.L.
n = 14: 2g
K
Cub (Pn3m)
Cub (Pm3n)
1
I.L.
232 [3.0]
*
_
_
161 [14.3]
165 [12.5]
46 [392.7]
134 [16.7]
133 [2.1]
258
252
K
K
Cub (Pn3m)
Cub (Pm3n)
Col
Col
**
I.L.
Col
Col
n = 15: 2h
n = 16: 2i
2
1
tet
h
41
47 [58.1]
K
I.L.
I.L.
1
222 [2.8]
217 [1.1]
*
*
_
_
**
I.L.
Cub (Pn3m)
Cub (Pm3n)
tet
h
Phase nomenclature; K= crystal, Colb = hexagonal columnar mesophase, Cub = cubic mesophase, Coltet = tetragonal columnar
mesophase and I.L. = isotropic liquid. *: very slow; **: gradual decomposition above ca. 270 ЊC
Copyright © 2010 World Scientific Publishing Company
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192
H. MUKAI ET AL.
it could be concluded that the higher temperature Cub2
–
mesophases have a Pm3n symmetry. The present Cub2
–
mesophases having a Pm3n symmetry are the first
examples in discotic compounds, as far as we know.
Hereupon, we thought about each of the detailed phase
structures of the Cub1 and Cub2 mesophases. From our
–
previous work [21], the Cub1 mesophase having a Pn3m
symmetry forms a bicontinuous Cub structure consisting
of long branched columns like jungle gym (Fig. 4A). In
–
contrast, the Cub2 mesophases have a Pm3n symmetry.
–
In general, a Cub structure having a Pm3n symmetry is
composed of the spherical molecules or the micelle that
rod-like molecules aggregated into the spherical shape
(Fig. 4B). However, discotic molecules generally tend
to one-dimensionally stack to form columnar structures
instead of spheres by π-π interaction. Therefore, it is
impossible that the present discotic complexes (1–3)
form such a spherical structure of the micelle illustrated
–
in Fig. 4B. It is rational that the Cub2 (Pm3n) meso-
phases may have a discontinuous Cub structure, as illus-
trated in Fig. 3C, consisting of not spherical micelles
but short drums. If our hypothesis is correct, the long
branched columns in the Cub1 mesophase may be cut
into the short drums in the Cub2 mesophase. The aggre-
gation structure may change in the phase transition from
Cub1 to Cub2.
Fig. 1. Photomicrographs recorded with uncrossed polarizers;
A: {[(C12O)2PhO]8Pc}2Tb (2e) after holding the temperature at
245 °C for 10 min and B: {[(C8O)2PhO]8Pc}2Tb (2a) after hold-
ing the temperature at 262 °C for 10 min
Spectroscopic studies on two cubic mesophases
The temperature-dependent electronic absorption
spectra of thin films of the Lu homologs (3) were very
useful to revealing the aggregation structure [29]. Hence,
in the present work, the temperature-dependent elec-
tronic absorption spectra of the thin films of the Eu and
Tb homologs (1 and 2) were also measured to reveal the
aggregation structures in the Cub1 and Cub2 mesophases,
and verify our hypothesis mentioned above.
–
Pn3m symmetry. Therefore, it could be concluded that
–
the lower temperature Cub1 mesophases have a Pn3m
symmetry. In contrast, each of the Cub2 mesophase has
a peak assigned to Miller index (2 1 0). This reflection
–
only appears for a Pm3n symmetry (Table 4). Hence,
Fig. 2. Phase transition temperature vs. n forA: {[(CnO)2PhO]8Pc}2Eu (1), B: {[(CnO)2PhO]8Pc}2Tb (2) and C: {[(CnO)2PhO]8Pc}2Lu
(3) z: melting point, c: clearing point, ∆: mesophase-mesophase transition
Copyright © 2010 World Scientific Publishing Company
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DISCOTIC LIQUID CRYSTALS OF TRANSITION METAL COMPLEXES
193
Fig. 3. X-ray diffraction patterns of A: {[(C12O)2PhO]8Pc}2Eu (1e), B: {[(C12O)2PhO]8Pc}2Tb (2e) and C: {[(C12O)2PhO]8Pc}2Lu
(3e) at various temperatures
Figure 5 illustrates the temperature-dependent elec-
tronic absorption spectra in the UV-vis region of the thin
films of the Eu complex (1e), the Tb complex (2e) and the
Lu complex (3e). As can be seen, the peaks at about 650
nm gradually shifted up to 680 nm with heating from rt
to the higher temperature of I.L. This shift is attributed to
the change from the molecular aggregates to the discrete
molecules [29]. In other words, the one-dimensional long
columns in the Colh mesophase at lower temperature are
cut into short columns with elevating temperature; finally,
they may degrade into the discrete molecules in the I.L.
phase.
heating the derivatives 1e–3e show a similar spectral
change. For example, the large peak at about 2200 nm
could be observed at rt for the Colh mesophase of Eu com-
plex (1e). This peak can be assigned to an intermolecu-
lar charge transfer (CT) band originated from the radical
electron transfer between the molecules [29]. In the Colh
mesophase, the molecules one-dimensional stacked to
form the columnar structure. Since the radical electron
may go back and forth between the molecules in the col-
umns, the intermolecular CT band may appear as a large
peak. When derivative 1e was heated up to 135 °C, the
intensity of intermolecular CT band at about 2200 nm
decreased. This may be a result of the thermal fluctuation
of the discotic molecules in the columns up and down,
side to side with heating, which prevented the charges
Figure 6 shows temperature-dependent electronic
absorption spectra in the near IR region of the deriva-
tives 1e, 2e and 3e. As can be seen from this figure, on
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 193–197

194
H. MUKAI ET AL.
Table 4. List of reflections corresponding to the extinction rules
electron transfer between two above and below Pc macro-
cycles in a double-decker molecule.
for the space groups of cubic phases
–
–
–
–
h2 + k2 + l2
(h k l)
Pn3m
Im3n
Ia3d
Judging from these spectroscopic results in both the
UV-vis and near IR regions, the Cub1 mesophase may
have the structure illustrated in Fig. 4A. Since the one-
dimensionally stacked discotic molecules in the column
of the Cub1 mesophase thermally fluctuate considerably,
intermolecular charge transfer becomes diffcult to occur.
Instead, intramolecular (intra-double decker) charge
transfer starts to occur. Therefore, it is thought that the
peak of the intramolecular CT band at about 1800 nm
could appear in the Cub1 mesophase. Since the one-
dimensionally stacked discotic molecules in the Cub2
mesophase thermally fluctuate more vigorously, the peak
intensity of intramolecular CT band at about 1800 nm
increases at a higher rate. In contrast, the peak intensity
of intermolecular CT band at about 2200 nm decreases
at a higher rate. However, this intermolecular CT band
can be still observed, so that the molecules in the Cub2
mesophase still one-dimensionally stack to form the col-
umns. Moreover, the peak intensity of intermolecular
CT band in the Cub2 mesophase is weaker than those
of the Colh and Cub1 mesophases, so that the length of
columns in Cub2 mesophase may be shorter than those
in the Colh and Cub1 mesophases. In I.L at 255 °C, the
intramolecular CT band at about 1800 nm appears as the
largest peak. However, the smallest intermolecular CT
band at about 2200 nm can be still observed in I.L. It
is thought that there are still short columns even in I.L.
As mentioned above, after keeping the I.L between two
glass plates at this temperature for long hours under a
microscope, a Coltet mesophase appeared. Therefore, the
short columns in I.L. may slowly stack again to form the
Coltet mesophase by keeping the I.L. at this temperature
for long hours. It took more than one day to complete the
relaxation between two slide glass plates for the micro-
scopic observation. However, the sample for the temper-
ature-dependent electronic absorption spectra should be
prepared on a glass plate. If the I.L. on the glass plate
were to be exposed for a long duration in the air at such
a high temperature, it might decompose in the air before
complete relaxation into the Coltet mesophase. Hence, we
did not measure the temperature-dependent electronic
absorption spectra of the Coltet mesophase.
Pm3n
(224)
(229)
(230)
(223)
×
×
×
×
×
×
×
×
1
2
3
4
5
6
8
9
100
110
111
200
210
211
220
300
221
{
{
{
{
×
{
×
×
{
{
{
{
×
{
×
{
{
×
{
{
×
{
{
×
×
×
×
{
×
×
×
×
10
11
12
13
14
16
17
18
310
311
222
320
321
400
410
411
330
{
{
{
{
×
{
×
×
{
{
{
{
{
{
{
{
×
{
{
×
{
{
×
{
{
×
×
×
{
{
{
{
×
×
×
19
20
21
22
24
25
331
420
421
332
422
430
500
{
{
{
{
×
{
{
{
{
{
×
{
{
×
×
{
{
×
{
{
×
×
×
×
×
26
431
510
{
{
{
{
{
{
{
×
{ appear, × disappear.
from smoothly transferring between the molecules. When
derivative 1e was heated up to 145–165 °C in the tempera-
ture region of the Cub1 mesophase, a new peak appeared
at about 1800 nm. This peak was assigned to an intra-
molecular CT band [29] corresponding to the radical
Thus, we revealed the precise
aggregation structures in columns in
these Cub1 and Cub2 mesophases from
the temperature-dependent electronic
absorption spectra of the thin films.
The mechanism of phase structure
change by phase transition
From the results of both the X-ray
diffractions and the temperature-
dependentelectronicabsorptionspectra,
we considered the possible transition
mechanism of phase structures. As
Fig. 4. Schematic representation for the structures of bicontinuous cubic mesophase
and discontinuous cubic mesophase
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 194–197

DISCOTIC LIQUID CRYSTALS OF TRANSITION METAL COMPLEXES
195
Fig. 5. Temperature-dependent electronic spectra in the UV-vis region (250–800 nm) of A: {[(C12O)2PhO]8Pc}2Eu (1e),
B: {[(C12O)2PhO]8Pc}2Tb (2e) and C: {[(C12O)2PhO]8Pc}2Lu (3e)
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 195–197

196
H. MUKAI ET AL.
Fig. 6. Temperature-dependent electronic spectra in the near IR region of A: {[(C12O)2PhO]8Pc}2Eu (1e), B: {[(C12O)2PhO]8Pc}2Tb
(2e) and C: {[(C12O)2PhO]8Pc}2Lu (3e)
Fig. 7. The mechanism of phase transition
–
illustratedinFig. 7, theColh mesophaseataroundrtforms
a long, straight and one-dimensional columnar structure.
When the Colh mesophase is heated, the discotic
molecules in the columns thermally fluctuate up and
down, side to side, considerably, to form the branched
mesophase transforms into the Cub2 (Pm3n) mesophase.
On further heating, the thermal fluctuation becomes
more vigorous, and the Cub2 (Pm3n) mesophase clears
–
into I.L. The I.L. phase extremely slowly transforms
into the Coltet mesophase. We thought that this Coltet
mesophase might be formed by the columns of the
stacked drums (Fig. 7). On further heating, the Coltet
mesophase clears into I.L. again. This proposed phase
transition mechanism is consistent with the results of
column and the Colh mesophase transforms into the
–
Cub1 (Pn3m) mesophase. On further heating, the ther-
mal fluctuation becomes bigger, the branched col-
–
umns cut into the short columns, and the Cub1 (Pn3m)
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 196–197

DISCOTIC LIQUID CRYSTALS OF TRANSITION METAL COMPLEXES
197
both the temperature-dependent X-ray diffractions and
absorption spectra.
6. Borisch K, Diele E, Göring P, Kresse H and Tsch-
ierske C. J. Mater. Chem. 1998; 8: 529–543.
7. Donnio B and Bruce D W, J. Mater. Chem. 1998; 8:
1993–1997.
8. Seo J S, Yoo Y S and Choi M G. J. Mater. Chem.
2001; 11: 1332–1338.
9. Tschierske C. J. Mater. Chem. 2001; 11:
2647–2671.
10. Fazio D, Mongin C, Donnio B, Galerne Y, Guil-
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2852–2863.
CONCLUSION
A novel series of sandwich-type Pc-based terbium
complexes, bis[2,3,9,10,16,17,23,24-octakis(3,4-dido-
decyloxyphenoxy)phthalocyaninato]terbium(III)
({[(CnO)2PhO]8Pc}2Tb, n = 8–16) (2), were synthesized
and their mesomorphism were investigated. As the result,
the present Tb complexes (2) exhibited two Cub meso-
phases, Cub1 and Cub2, together with columnar meso-
phases as well as the previous Eu homologs (1) and Lu
homologs (3). By using temperature-dependent X-ray
diffraction technique and temperature-dependent elec-
tronic absorption spectroscopy, we revealed the detailed
11. Kutsumizu S, Yamada M and Yano S. Liq. Cryst.
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12. Kutsumizu S, Ichikawa T, Nojima S and Yano S. J.
Phys. Chem. B 2000; 104: 10196–10205.
13. Kutumizu S, Morita K, Ichikawa T, Yano S,
Nojima S and Yamaguchi T. Liq. Cryst. 2002; 29:
1447–1458.
14. Kutsumizu S, Morita K, Yano S and Nojima S. Liq.
Cryst. 2002; 29: 1459–1468.
15. Impe´ror–Clerc M. Curr. Opin. Colloid Interface
Sci. 2005; 9: 370–376.
16. Ujiie S and Mori A. Mol. Cryst. liq. Cryst. 2005;
437: 25–31.
17. Kohne B, Praefcke K and Billard J. Z. Naturforsch
1986; 41b: 1036–1044.
18. Billard J. Zimmermann H, Poupko P and Luz Z, J.
Phys. France 1989; 50: 539–547.
19. Hatsusaka K, Ohta K, Yamamoto I and Shirai H. J.
Mater. Chem. 2001; 11: 423–433.
20. Hatsusaka K, Kimura M and Ohta K. Bull. Chem.
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21. Ichihara M, Suzuki A, Hatsusaka K and Ohta K.
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22. Mukai H, Hatsusaka K and Ohta K. J. Porphyrins
Phthalocyanines 2007; 11: 846–856.
23. Mukai H,Yokokawa M, Hatsusaka K and Ohta K. J.
Porphyrins Phthalocyanines 2009; 13: 70–76.
24. Hasebe H. Master Thesis Shinshu University, Ueda,
1991; Ch. 5.
symmetries and phase structures of these two Cub meso-
–
phases. We found that the Cub1 mesophase has a Pn3m
symmetry and forms a bicontinuous structure consisting
of branched columns like jungle gym, but that Cub2 meso-
–
phase has a Pm3n symmetry and forms a discontinuous
structure consisting of short columns like drums, a result
of the cutting off of the branched columns. Finally, we
proposed a phase transition mechanism consistent with
the results of both the temperature-dependent X-ray dif-
fractions and absorption spectra.
Acknowledgements
This work was supported by a Grant-in-Aid for
Science Research (19022011) in Priority Area “Super-
Hierarchical Structures” from Ministry of Education,
Culture, Sports, Science and Technology, Japan.
Supporting information
Details of the X-ray data for mesophases
(Tables S1–S2) are given in the supplementary material.
This material is available free of charge via the Internet at
http://www.worldscinet.com/jpp/jpp.shtml.
25. Ema H. Master Thesis Shinshu University, Ueda,
1988; Ch. 7.
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