6810 J. Am. Chem. Soc., Vol. 123, No. 28, 2001
Ko¨lbel et al.
by a drastic decrease of the mesophase stability.9 If however,
the lateral groups are incompatible with the terminal chains,
the layer structures can remain. For example, calamitic me-
sogens, carrying two semifluorinated terminal chains and very
bulky aliphatic lateral groups form stable smectic phases (d).12
Even a mesophase stabilizing effect can be achieved, if the
lateral groups provide additional cohesive intermolecular forces.
This was recently shown for calamitic mesogens with two
terminal alkyl chains and a lateral aromatic electron-acceptor
group9b as well as for molecules with a polar lateral group,
capable of hydrogen bonding, such as the 1,2-diol group (facial
amphiphiles e).13 The size of the polar lateral group of the facial
amphiphiles was further increased by introduction of oligooxy-
ethylene chains, which led to the induction of different types
of rectangular columnar mesophases (Colr).14 The formation of
these columnar phases was explained as the result of the inset
of an additional segregation process occurring between the rigid
aromatic cores and the polar lateral groups, whereby the lateral
groups become organized in separate cylinders, which interrupt
the smectic layers in regular intervals.14
Herein we report novel ternary block molecules of type f (see
Figure 1), in which the positions of the polar diol groups and
the alkyl chains were exchanged with respect to the facial
amphiphiles e.15 In such bolaamphiphiles,16 the strongest
attractive forces (H-bonding) are positioned at both terminal
ends of the rigid calamitic cores. This, and the strong segregation
of the polar 1,2-diol groups from the biphenyl cores into separate
sublayers, lead to a dramatic stabilization of smectic phases.17-19
Hence, the parent compound of this series without a lateral
substituent (compound 1/0; see Figure 2) forms an extremely
stable smectic A phase with monolayer structure (SmA1).20
Therefore, such molecules can provide the unique possibility
to change the mesophase structure from a layer structure to more
complex ones by introduction of long lateral alkyl chains.
Because the lateral alkyl chains represent a third incompatible
unit, incompatible with both, the polar terminal diol groups21
and the rigid biphenyl units,6 these molecules represent ternary
block molecules.22 Furthermore, in such molecules, micro-
segregation and rigidity are combined in such a way that they
compete with each other. This means that segregation of the
Figure 1. Schematic presentation of the molecular structures of
mesophase forming binary (a-c) and ternary block molecules (d-e)
comprising a calamitic middle block: (a) conventional calamitic
mesogen; (b) polycatenar mesogen; (c) calamitic mesogen with lateral
alkyl chain; (d) calamitic mesogen with semifluorinated side chains
and lateral alkyl chain; (e) facial amphiphile; (f) bolaamphiphile with
lateral alkyl chain.
chains are usually combined in such a manner that the two
incompatible molecular parts are located in well-defined separate
molecular regions and they are connected in a strictly linear
way (see Figure 1, a).7 This designing principle leads to the
formation of predominately layer structures (smectic phases)
consisting of segregated sublayers of the parallel aligned rigid
cores and sublayers of conformational disordered alkyl chains.8
If, however, additional alkyl chains are grafted in lateral
positions at the rigid core, the layer arrangement is strongly
disturbed.9 This is not only due to the steric effect which
disfavors the alignment of the calamitic cores but also to the
incompatibility of the lateral alkyl chains with the aromatic cores
and especially to their complete compatibility with the terminal
alkyl chains. Thereby, the influence of lateral chains strongly
depends on their position with respect to the terminal chains. If
they are located at the terminal ends, adjacent to the terminal
chains (polycatenar mesogens b), they enlarge the volume
fraction of the flexible chains, which can give rise to a curvature
of the aromatic-aliphatic interface, leading to columnar and
cubic mesophases.10,11 In contrast, the connection of aliphatic
chains to other lateral positions, more close to the center of the
calamitic cores (c), leads to the complete loss of positional order;
i.e., smectic phases are replaced by nematic phases, accompanied
(12) (a) Arehart, S. V.; Pugh, C. J. Am. Chem. Soc. 1997, 119, 3027.
(b) Small, A. C.; Hunt, D. K.; Pugh, C. Liq. Cryst. 1999, 26, 849. (c) Pugh,
C.; Bae, J.-Y.; Dharia, J.; Ge, J. J.; Cheng, S. Z. D. Macromolecules 1998,
31, 5188.
(13) Hildebrandt, F.; Schro¨ter, J. A.; Tschierske, C.; Festag, R.; Klep-
pinger R.; Wendorff, J. H. Angew. Chem., Int. Ed. Engl. 1995, 107, 1780.
(14) (a) Hildebrandt, F.; Schro¨ter, J. A.; Tschierske, C.; Festag, R.;
Wittenberg M.; Wendorff, J. H. AdV. Mater., 1997, 9, 564. (b) Schro¨ter, J.
A.; Tschierske, C.; Wittenberg M.; Wendorff, J. H. J. Am. Chem. Soc. 1998,
120, 10669. (c) Plehnert, R.; Schro¨ter, J. A.; Tschierske, C. J. Mater. Chem.
1998, 8, 2611.
(15) Preliminary communication: Ko¨lbel, M.; Beyersdorff, T.; Sletvold,
I.; Tschierske, C.; Kain, J.; Diele, S. Angew. Chem., Int. Ed. 1999, 38, 1077.
(16) Fuhrhop, J.-H.; Fritsch, D. J. Am. Chem. Soc. 1986, 19, 130.
(17) (a) Festag, R.; Hessel, V.; Lehmann, P.; Ringsdorf, H.; Wendorff,
J. H. Recl. TraV. Chim. Pays-Bas 1994, 113, 222. (b) Hessel, V.; Ringsdorf,
H. Makromol. Chem. Rapid Commun. 1993, 14, 707. (c) Dahlhoff, W. V.
Z. Naturforsch. 1988, 43b, 1367.
(18) Hentrich, F.; Tschierske, C.; Zaschke, H. Angew. Chem., Int. Ed.
Engl. 1991, 30, 440. (b) Hentrich, F.; Diele, S.; Tschierske, C. Liq. Cryst.
1994, 17, 827.
(19) Columnar mesophases have been found for bolaamphiphiles, in
which the headgroups are connected with each other by flexible alkyl chains.
The self-organization of these compounds is related to those found for
conventional amphiphiles: (a) Gulik, A.; Luzzati, V.; De Rosa, M.;
Gambacorta, A. J. Mol. Biol. 1985, 182, 131. (b) Gutman, H.; Loewenstein,
A.; Luz, Z.; Poupko, R.; Zimmermann, H. Liq. Cryst. 1991, 9, 607. (c)
Auze´ly-Velty, R.; Benvegnu, T.; Plusquellec, D.; Mackenzie, G.; Haley, J.
A.; Goodby, J. W. Angew. Chem., Int. Ed. 1998, 37, 251.
(20) Hentrich, F.; Tschierske, C.; Diele, S.; Sauer, C. J. Mater. Chem.
1994, 4, 1547.
(7) Demus, D. In Handbook of Liquid Crystals; Demus, D., Goodby, J.
W., Gray, G. W., Spiess, H.-W., Vill, V., Eds.; Wiley-VCH: Weinheim,
1998; Vol. 1, p 134.
(8) More recently, linear block molecules, built up by more than two
incompatible segments, have also been investigated. Such molecules can
form bilayer structures or layer arrangements composed of three distinct
sublayers. If the volume fraction of one segment is significantly larger,
then modulated smectic, cubic, and columnar mesophases can be formed:
(a) Pensec, S.; Tournilhac, F.-G.; Bassoul P.; Durliat, C. J. Phys. Chem.
1998, 102, 52. (b) Ibn-Elhaj, M.; Mo¨hwald, H.; Cherkaoui M. Z.; Zniber,
R. Langmuir 1998, 14, 504. (c) Newton, J.; Coles, H.; Hodge, P.;
Hannington J. J. Mater. Chem. 1994, 4, 869. (d) Lindner, N.; Ko¨lbel, M.;
Sauer, C.; Diele, S.; Jokiranta, J.; Tschierske, C. J. Phys. Chem. B 1998,
102, 5261. (e) Lose, D.; Diele; S., Pelzl, G.; Dietzmann, E.; Weissflog, W.
Liq. Cryst. 1998, 24, 707. (f) Guittard, F.; Taffin de Givenchy, E.; Geribaldi,
S.; Cambon, A. J. Fluorine Chem. 1999, 100, 85. (g) Lee, M.; Lee, D.-W.;
Cho J. Am. Chem. Soc. 1998, 120, 13258.
(9) (a) Weissflog, W.; Demus, D. Cryst. Res. Technol. 1983, 18, K21.
(b) Weissflog, W. In Handbook of Liquid Crystals; Demus, D., Goodby, J.
W., Gray, G. W., Spiess, H.-W., Vill, V., Eds.; Wiley-VCH: Weinheim,
1998; Vol. 2B, p 835. (c) Berdaue, P.; Bayle, J.-P.; Fujimori, H.; Miyajima.,
S. New J. Chem. 1998, 1005.
(10) Nguyen, H.-T.; Destrade, C.; Malthete, J. In Handbook of Liquid
Crystals; Demus, D., Goodby, J. W., Gray, G. W., Spiess, H.-W., Vill, V.,
Eds.; Wiley-VCH: Weinheim, 1998; Vol. 2B, p 866.
(11) Recent reviews on cubic mesophases: (a) Diele, S.; Go¨ring, P. In
Handbook of Liquid Crystals; Demus, D., Goodby, J. W., Gray, G. W.,
Spiess, H.-W., Vill, V., Eds.; Wiley-VCH: Weinheim, 1998; Vol. 2B, p
887. (b) Bruce, D. W. Acc. Chem. Res. 2000, 33, 831.