conclude that smaller K33/K11 stabilizes BPs,19,20 while the other
describes that larger K33/K11 stabilizes BPs.21 The relationship
between the ratio and stability of the BPs is not fully clarified.
Though we did not approach the BP stability from the elastic
constants in this study, we would like to measure the constants of
the mixtures of 1 and 3 as our next project.
Acknowledgements
We are grateful to Mukai Science and Technology Foundation,
the Asahi Glass Foundation for the funds, and we thank Grant-
in-Aid for Scientific Research (B) 19350090.
Fig. 13 The estimated models for the time-averaged anti-parallel het-
erodimer 1$3 (molecules 1 and 3 are indicated in blue and red, respec-
tively. Ar ¼ 4-((R)-1-methylheptyloxy)phenyl, Ar0 ¼ 4-octyloxyphenyl)
generated by p–p interactions and attractive electrostatic interactions.
Both molecules in each dimer have the same chirality in their twisted
ester-conformations.
Notes and references
€
1 H. Stegemeyer, T. Blumel, K. Hiltrop, H. Onusseit and F. Porsch,
Liq. Cryst., 1986, 1, 3; Phase Structures and Transitions in
Thermotropic Liquid Crystals, in Handbook of Liquid Crystal
Research, ed. P. J. Collings and J. S. Patel, Oxford University Press,
New York, 1997, ch. 4, pp. 106–108; Phase Transitions, Barois, in
Physical Properties of Liquid Crystals, ed. D. Demus, J. Goodby, G.
W. Gray, H.-W. Spiess and V. Vill, Wiley-VCH, New York, 1999,
ch. 6, pp. 223–224; S. Hekimoglu and J. Conn, Liq. Cryst. Today,
2003, 12, 1; Defect Structures, in One and Two-Dimensional Fluids—
Properties of Smectic, Lamellar and Columnar Liquid Crystals, ed.
A. Jakli and S. Saupe, Taylor and Francis, New York, 2006, ch. 6,
pp. 199–201; K. Higashiguchi, K. Yasui and H. Kikuchi, J. Am.
Chem. Soc., 2008, 130, 6326.
2 P. R. Gerber, Mol. Cryst. Liq. Cryst., 1985, 116, 197; H. J. Coles and
H. F. Gleeson, Mol. Cryst. Liq. Cryst., 1989, 167, 213;
V. E. Dmitrienko, Liq. Cryst., 1989, 5, 847; H.-S. Kitzerow, Mol.
Cryst. Liq. Cryst., 1991, 202, 51; G. Heppke, B. Jerome,
H.-S. Kitzerow and P. Pieranski, J. Phys., 1991, 50, 2291;
P. Etchegoin, Phys. Rev. E: Stat. Phys., Plasmas, Fluids, Relat.
Interdiscip. Top., 2000, 62, 1435.
range. Because of the difference in their core lengths, the anti-
parallel heterodimer 1$6 (Fig. 11d) cannot have enough inter-
molecular attractive interactions.
By addition of 3 to 1 up to 1 : 3 ¼ 6 : 4, an increment in the
BP-I transition temperature was larger than that in the N*–BP
transition temperature, which resulted in the expansion of
temperature range of the BP. This phenomenon is explained as
follows. The achiral rodlike molecule 3 is sterically less-hindered
than the chiral molecule 1. Accordingly, in the BP of the mixture
of 1 and 3, the molecule 3 interacts equally with each of the
laterally surrounded 1, which stabilizes the superstructure
‘‘double twist cylinder’’ of the BP. In contrast, in chiral nematic
phases molecules are aligned one-directionally in each of planes
and the planes stack in parallel with changing the directors
helically. The laterally omnidirectional interaction of molecule 3
with its adjacent molecules generates the heterodimers 1$3 even
within the same plane, which destabilizes the one-dimensionally
helical superstructure of the chiral nematic phase.
3 Y. Hisakado, H. Kikuchi, T. Nagamura and T. Kajiyama, Adv.
Mater., 2005, 17, 96; M. Sato and A. Yoshizawa, Adv. Mater.,
2007, 19, 4145.
~
4 W. Cao, A. Munoz, P. Palffy-Muhoray and B. Taheri, Nat. Mater.,
2002, 1, 111; S. Yokoyama, S. Mashiko, H. Kikuchi, K. Uchida
and T. Nagamura, Adv. Mater., 2006, 18, 48.
5 H.-S. Kitzerow, ChemPhysChem, 2006, 7, 63.
6 H.-S. Kitzerow, H. Schmid, A. Ranft, G. Heppke, R. A. M. Hikmet
and J. Lub, Liq. Cryst., 1993, 14, 911; H. Kikuchi, M. Yokota,
Y. Hisakado, H. Yang and T. Kajiyama, Nat. Mater., 2002, 1, 64.
7 T. Noma, M. Ojima, H. Asagi, Y. Kawahira, A. Fujii, M. Ozaki and
H. Kikuchi, e-J. Surf. Sci. Nanotechnol., 2008, 6, 17.
8 H. J. Coles and M. N. Pivnenko, Nature, 2005, 436, 997.
9 A. Yoshizawa, Y. Kogawa, K. Kobayashi, Y. Takanishi and
J. Yamamoto, J. Mater. Chem., 2009, 19, 5759.
10 C. V. Yelamaggad, N. L. Bonde, A. S. Achalkumar, D. S. S. Rao,
S. K. Prasad and A. K. Prajapati, Chem. Mater., 2007, 19, 2463.
11 S.-L. Wu and W.-J. Hsieh, Chem. Mater., 2003, 15, 4515.
12 W. He, G. Pan, Z. Yang, D. Zhao, G. Niu, W. Huang, X. Yuan,
J. Guo, H. Cao and H. Yang, Adv. Mater., 2009, 21, 2050.
13 C. V. Yelamaggad, V. P. Tamilenthi, D. Shankar Rao, G. G. Nair and
S. Krishna Prasad, J. Mater. Chem., 2009, 19, 2906.
Conclusions
We realized a BP by using simple rodlike monoester compounds
possessing asymmetric carbons and demonstrated that cubic BPs
of a chiral ester compound could be stabilized by addition of its
achiral homologue ester compound. This study suggested that
increase of the intermolecular attractive forces is important for
stabilization of BPs. We believe that this methodology is also
useful to stabilize BPs of other rodlike liquid crystalline ester
compounds. Further, in the mixing of the chiral molecules and
the several achiral homologues, we also found that existence of
the terminal alkyl chains and matching in the core lengths are
important for stabilization of the BP. The information obtained
in these results should also be important for designing the
molecules exhibiting stable BPs.
14 Examples of cubic BPs recently reported: T. Seshadri and
H.-J. Haupt, Chem. Commun., 1998, 735; J. Buey, P. Espinet,
H.-S. Kitzerow and J. Strauss, Chem. Commun., 1999, 441;
ꢁ
R. Bayon, S. Coco and P. Espinet, Chem. Mater., 2002, 14, 3515;
W.-R. Chen and J.-C. Hwang, Liq. Cryst., 2004, 31, 1539;
J. Rokunohe and A. Yoshizawa, J. Mater. Chem., 2005, 15, 275;
M. L. Parra, P. I. Hidalgo and E. Y. Elgueta, Liq. Cryst., 2008, 35,
823; J.-S. Hu, K.-Q. Wei, B.-Y. Zhang and L.-Q. Yang, Liq. Cryst.,
2008, 35, 925; M. L. Parra, P. I. Hidalgo, E. A. Soto-Bustamante,
ꢁ
J. Barbera, E. Y. Elgueta and V. H. Trujillo-Rojo, Liq. Cryst.,
Recently, it is reported that the stability of BPs is related to
their elastic constants, especially the ratio K33/K11 is known as
one of the important factors (K33, K11: elastic constants for bend
and splay transformations, respectively). However, some reports
2008, 35, 1251; Y. Kogawa and A. Yoshizawa, Liq. Cryst., 2011,
38, 303.
15 H. Grebel, R. M. Hornreich and S. Shtrikman, Phys. Rev. A: At.,
Mol., Opt. Phys., 1983, 28, 1114; M. B. Bowling, P. J. Collings,
8490 | J. Mater. Chem., 2012, 22, 8484–8491
This journal is ª The Royal Society of Chemistry 2012