Distinct columnar and lamellar liquid crystalline phases formed by new bolaamphiphiles with linear and branched lateral hydrocarbon chains

Article abstract of DOI:10.1002/chem.200800141

A universal building block for the convergent synthesis of a wide variety of different T-shaped ternary amphiphiles was developed and used for the synthesis of a series of new liquid-crystalline materials composed of a rigid biphenyl core with polar glycerol groups at both ends and linear or branched alkyl chains in a lateral position. In addition, compounds with bulky achiral (2,4,6-trimethylphenoxy, adamantane-1-carboxylate, benzoate) or chiral (menthyl or cholesteryl) substituents attached to the end of the lateral alkyl chain were also investigated. In all cases the lateral chains were connected to the aromatic core by an ether linkage. The effect of the ether linking unit on mesophase stability and mesophase type is discussed with respect to conformational effects. The liquid-crystalline phases were investigated by polarizing microscopy, calorimetry, and X-ray diffraction of surface aligned samples. Upon enlarging the lateral chains a series of different polygonal cylinder phases was observed, which were replaced by lamellar phases and a non-cylinder hexagonal columnar phase by further increasing the size of these substituents. Remarkably, only pentagonal, hexagonal, and giant hexagonal cylinder phases could be observed, whereas mesophases composed of cylinders with a smaller number of sides are missing. No distinct chirality effects were observed for the menthyl- and cholesteryl-substituted compounds. However, the rodlike shape of the polycyclic cholesteryl core leads to a unique phase structure combining an organization of the alicyclic cholesteryl cores perpendicular to the layer planes and the aromatic biphenyl cores parallel to the layer planes.

Full text of DOI:10.1002/chem.200800141

DOI: 10.1002/chem.200800141
Distinct Columnar and Lamellar Liquid Crystalline Phases Formed by New
Bolaamphiphiles with Linear and Branched Lateral Hydrocarbon Chains
Marko Prehm,[a, b] Claudia Enders,[a] Maryam Yahyaee Anzahaee,[a] Benjamin Glettner,[a]
Ute Baumeister,[b] and Carsten Tschierske*[a]
Abstract: A universal building block
for the convergent synthesis of a wide
variety of different T-shaped ternary
amphiphiles was developed and used
for the synthesis of a series of new
liquid-crystalline materials composed
of a rigid biphenyl core with polar glyc-
erol groups at both ends and linear or
branched alkyl chains in a lateral posi-
tion.In addition, compounds with
bulky achiral (2,4,6-trimethylphenoxy,
adamantane-1-carboxylate, benzoate)
or chiral (menthyl or cholesteryl) sub-
stituents attached to the end of the lat-
eral alkyl chain were also investigated.
In all cases the lateral chains were con-
nected to the aromatic core by an
ether linkage.The effect of the ether
linking unit on mesophase stability and
mesophase type is discussed with re-
spect to conformational effects.The
liquid-crystalline phases were investi-
gated by polarizing microscopy, calo-
rimetry, and X-ray diffraction of sur-
face aligned samples.Upon enlarging
the lateral chains a series of different
polygonal cylinder phases was ob-
served, which were replaced by lamel-
lar phases and a non-cylinder hexago-
nal columnar phase by further increas-
ing the size of these substituents.Re-
markably, only pentagonal, hexagonal,
and giant hexagonal cylinder phases
could be observed, whereas mesophas-
es composed of cylinders with a smaller
number of sides are missing.No dis-
tinct chirality effects were observed for
the menthyl- and cholesteryl-substitut-
ed compounds.However, the rodlike
shape of the polycyclic cholesteryl core
leads to a unique phase structure com-
bining an organization of the alicyclic
cholesteryl cores perpendicular to the
layer planes and the aromatic biphenyl
cores parallel to the layer planes.
Keywords: amphiphiles
·
liquid
crystals · mesophases · self-assem-
bly · supramolecular chemistry
Introduction
for the self-organization of amphiphilic molecules.[4] Low-
molecular-weight, dendritic or polymeric amphiphiles (e.g.
block copolymers), composed of only two different molecu-
lar parts, usually change their organization depending on the
volume fractions of the two incompatible parts.Thereby,
with increasing volume fraction of one of the parts, starting
from layer structures (smectic phases) for nearly equal
volume fractions, the mesophase morphology changes at
first to columnar and then to mesophases composed of
spheroidic aggregates (see Figure 1).[5–9] Additionally, bicon-
tinuous cubic phases (CubV) and perforated layer structures
were observed as intermediate phases at the transition from
lamellar to columnar organization.[5,7,8] However, the
The design of new molecules forming novel types of liquid-
crystalline (LC) phases[1] is of contemporary interest for the
fundamental understanding of soft-matter self-organiza-
tion.[2,3] Segregation of incompatible molecular segments
into distinct regions is one of the fundamental driving forces
[a] Dr.M.Prehm, Dipl-.Chem.C.Enders, M.Y.Anzahaee,
Dipl-.Chem.B.Glettner, Prof.Dr.C.Tschierske
Institute of Chemistry, Organic Chemistry
Martin-Luther-University Halle-Wittenberg
Kurt-Mothes-Str.2, 06120 Halle (Germany)
Fax : (+49)345-552-7346
E-mail: carsten.tschierske@chemie.uni-halle.de
[b] Dr.M.Prehm, Dr.U.Baumeister
Institute of Chemistry, Physical Chemistry
Martin-Luther-University Halle-Wittenberg
Mühlpforte, 06108 Halle (Germany)
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author. It contains addi-
tional figures (textures and X-ray diffraction patterns), tables with X-
ray data, experimental procedures, and analytical data.
Figure 1.General phase sequence of conventional amphiphiles with re-
spect to the increasing volume fraction of one of the incompatible parts.
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FULL PAPER
number of possible structures that can be realized with
these binary amphiphiles is limited mainly to these few mor-
phologies.
Mesophase morphologies with higher levels of complexity
can be achieved with polyphilic molecules,[10] combining
more than two incompatible units, as successfully demon-
strated for low-molecular-weight T-shaped ternary amphi-
philes.[11–14] and ABC-triblock copolymers.[5,15–17] A wide vari-
ety of different complex soft-matter superstructures was ob-
tained for the bolaamphiphiles An (Figure 2).[12a] Here, the
In the mesophase code used to describe these cylinder
structures[11] the type of the columnar phase is given first
(Colhex, Colrec), followed by the shape of the cylinder cross
section, given by a number in brackets, indicating the
number of walls forming one cylinder (e.g., 6 means hexa-
gons).The abbreviation “cyl” indicates the polygonal cylin-
der structure and the last numerical indicates the number of
molecules in the circumference of each cylinder.This is im-
portant for the giant cylinder phases in which some cylinder
walls are formed by end-to-end pairs.After the slash the
plane group is given.For exam-
ple, Colrec(6)cyl-8/c2mm describes
a stretched hexagonal cylinder
phase in which each hexagonal
cylinder has eight molecules in
the circumference (8-hexagons)
and the resulting plane group is
c2mm (see Figure 12 in the
Conclusions section).[11]
Also a novel class of lamellar
liquid-crystalline phases was
found for these compounds
with fluorinated lateral chains.
In these lamellar phases the ar-
omatic cores and the lateral
chains are organized in distinct
layers.In contrast to the smec-
tic phases of classical rodlike
Figure 2.Dependence of the liquid-crystalline phases of the previously reported alkyl-substituted bolaamphi-
philic tetraols An, on the length (n) and the volume fraction (fR) of the lateral alkyl chain[12a] (light gray=hy-
drogen-bonding networks of the terminal diol groups; white=microsegregated regions of the lateral chains;
gray=rigid biphenyl units).
LC molecules, in which the rod-
like cores are arranged perpen-
dicular to the layer planes or
slightly tilted with respect to
the layer normal, in these la-
organization of the flexible nonpolar chains is in competi-
tion with the organization provided by the rigid biphenyl
units and the polar hydrogen-bonding networks.As shown
in Figure 2, elongation of the lateral alkyl chain of com-
pounds An gives rise to a transition from smectic A phases
(molecules are aligned, on average, perpendicular to the
layer planes, SmA) to a series of columnar phases composed
of cylinders with a polygonal cross section (rhombuses:
Colrec/c2mm; squares: Colsqu/p4mm; pentagons: Colrec/p2gg,
hexagons: Colhex/p6mm).[12a] In these columnar mesophases
the fluid alkyl chains are organized within columns and the
bolaamphiphilic units form cylinder shells framing these col-
umns.Hence, the space required by the lateral chains with
respect to the length of the bolaamphiphilic moieties deter-
mines the shape of the cylinders; the periodic packing of
these cylinders gives rise to honeycomb-like arrays repre-
senting different types of 2D lattices.[11,12a,14]
By using fluorinated lateral chains it was possible to fur-
ther increase the size of the lateral substituents, which lead
to giant cylinder structures built up by stretched hexagons
with eight (8-hexagons) or even ten molecules (10-hexa-
gons) in the circumference (Colrec/c2mm phases) in which
two or four sides are formed by end-to-end pairs of mole-
cules.[12b–d]
mellar phases the rodlike cores of the bolaamphiphiles are
completely disordered (LamIso phase) or aligned on average
parallel to the layer planes (LamN and LamSm pha-
ses).[12b,c,13,18,19] In the lamellar nematic phase (LamN) the ar-
omatic cores adopt a long-range orientational order in the
layers and between adjacent layers there is an orientational
correlation.Hence in this lamellar phase there is a nematic-
like order in the aromatic sublayers and therefore this phase
is assigned as lamellar nematic phase (LamN).Similarly, in
the lamellar smectic phases (LamSm) the rodlike cores adopt
a smectic-like in-plane order.[18]
In the series of compounds reported previously the lateral
alkyl or perfluoroalkyl chains were attached directly to the
aromatic core; this required lengthy syntheses and introduc-
tion of these substituents in one of the first steps of the syn-
thesis.[12a–c] However, the synthesis of molecules with longer
and more complex lateral chains requires a more convergent
synthetic strategy.
Herein we report a convergent methodology of synthesis
for bolaamphiphiles in which the lateral chains were at-
tached in one of the last synthetic steps (Scheme 1; com-
pounds 1–6).This was achieved with the hydroxyl-function-
alized building block 5 (see Scheme 2), which can be alkylat-
ed with different halides or tosylates to yield a wide variety
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6353

C.Tschierske et al.
Scheme 2.T-shaped ternary amphiphiles under discussion and key build-
ing block (compound 5) used for the synthesis of these compounds; for
the abbreviations of the compounds see the legend of Scheme 1.
core that leads to a unique new phase structure in which the
aromatic cores are organized parallel to the layers as typical
for Lam phases and the cholesteryl moieties form separate
layers; these units are organized with their long axes per-
pendicular to the layers as in usual smectic phases (SmA
phases).
Scheme 1.Synthesis of the compounds: Reagents and conditions: i) X =
I: NaI, NaOCl, NaOH, MeOH, 08C, 1 h;[22] ii) X=Br: Br2/AcOH/
CH2Cl2, 08C, 15 min;[23] iii) BrCH2CH=CH2, K2CO3, CH3CN, 808C, 6 h;
iv) OsO4, N-methylmorpholine-N-oxide, 208C, 48 h;[24,25] v) 2,2-dimethox-
Results and Discussion
ypropane, pyridinium p-toluene sulfonate, 208C, 24 h; vi) [Pd(PPh3)4],
N
NaHCO3, glyme, H2O, reflux, 6 h;[20] vii) H2, Pd/C, EtOAc, 408C, 12 h;
viii) RX, K2CO3, DMF, Bu4NI, 808C, 6 h; ix) 10% HCl, MeOH, reflux,
6 h; abbreviations of the compounds: Linn: compounds with linear alky-
loxy chains, n gives the number of carbon atoms in the lateral chain (n=
6–12, 14, 16, 18, 20, 22); Bra22: R=2-decyldodec-1-yl; for Ada, Tmp,
Ment*, Chol*n and Benzn/m: R=(CH2)nX; Ada: X=adamantane-1-car-
bonyloxy, n=11; Tmp: X=2,4,6-trimethylphenoxy, n=12; Ment*: X=
(1R,2S,5S)-menthyloxy, n=12; Chol*n: X=cholest-5-en-3B-oxy, n=
spacer length (n=6, 11); Benzn/m: X=benzoyloxy, n=spacer length
(n=6, 11) and m gives the number of dodecyloxy chains attached to the
benzoyl group (m=1: 4-dodecyloxy, m=2: 3,4-didocyloxy, m=3: 3,4,5-
tridodecyloxy).
Synthesis: Scheme 1 describes the general synthetic pathway
used for all compounds.Accordingly, acetonide-protected
glycerol-substituted aryl halides 3 (X=Br, I) were coupled
in Miyaura–Suzuki cross-coupling reactions[20] with 4-(2,2-di-
methyl-1,3-dioxolan-4-ylmethoxy)benzene
boronic
acid
(4).[12a] For the synthesis of the benzyloxy-substituted aryl
halides 3, 2-benzyloxyphenol[14d,21] was halogenated in para
position to the phenolic OH group by means of NaI/NaOCl/
NaOH[22] or Br2/AcOH/CH2Cl2.[23] The introduction of the
terminal propane-2,3-diol groups was achieved by allylation
followed by OsO4-catalyzed dihydroxylation[24,25] and these
diol groups were protected as cyclic acetals before the cou-
pling reaction was carried out.The benzyl protecting group
was removed by catalytic hydrogenation to yield the OH
functionalized bolaamphiphilic biphenyl derivative 5, with
of different molecular architectures.As a consequence of
this synthetic strategy, all these compounds contain an addi-
tional ether linkage between aromatic core and lateral
chain.The influence of this additional ether linkage on the
mesomorphic properties was investigated first and then new
series of bolaamphiphiles with extremely large and more
complex lateral groups were synthesized (see Scheme 2).
With these molecules giant cylinder structures, as well as
LamN and LamSm phases, previously reported only for fluori-
nated molecules,[12b,13] were obtained for alkyl-substituted T-
shaped bolaamphiphiles if the size of the lateral chains was
increased sufficiently.Compounds with extremely bulky lat-
eral groups form a new noncylinder mode of organization in
which the bolaamphiphilic cores are organized in columns
that are surrounded by the lateral chains.A cholesteryl
group in the lateral chain can act as a second distinct rigid
acetonide protected diol groups at both ends.Compound
5
was then used for the etherification reaction with appropri-
ate alkyl bromides or tosylates.The n-alkyl bromides were
commercially available, and the synthesis of the w-function-
alized halides and tosylates is described in the Supporting
Information.All acetonides 6 were purified by preparative
centrifugal thin-layer chromatography with a Chromatotron
(Harrison Research).In the final step the acetonide protect-
ing groups were removed by acidolytic cleavage.The ob-
tained amphiphiles were purified by repeated crystallization
from appropriate solvents and characterized by 1H NMR,
13C NMR and elemental analysis.The purity was additional-
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Liquid Crystals
FULL PAPER
ly checked by TLC.The synthesis of compound Lin18 is re-
ported in the Experimental Section as example, for all other
compounds the procedures and analytical data are reported
in the Supporting Information.
nally for n>20 to a LamSm phase, in which the organization
of the rodlike biphenyl cores is parallel to the layer planes.
SmA phases: In the SmA phases of compounds Lin6 and
Lin8 the biphenyl cores should be aligned on average per-
pendicular to the layer planes and separated by layers
formed by the hydrogen-bonding networks of the diol
groups (SmA, Figure 2).[27,28] The laterally attached alkyl
chains are located between the biphenyl cores and disturb
this organization due to their tendency to form separate
compartments in which these flexible chains, which are in-
compatible with the aromatic cores, are localized.This leads
to a reduction of the SmA–Iso phase-transition temperature
by elongation of this chain from Lin6 to Lin8.However, it
seems that the relatively short chains[26] of compounds
Lin6–Lin8 cannot fundamentally change the phase struc-
ture.In the case of compounds Lin9–Lin22 with longer lat-
eral chains, these chains are segregated into well-defined
micro compartments that give rise to the formation of
polygonal cylinder structures.
Mesomorphic properties
Polarized light optical microscopy, differential scanning calo-
rimetry, and X-ray diffraction were used to determine the
mode of self-assembly in the liquid-crystalline phases.
Compounds Linn with linear chains—transition from smec-
tic phases via cylinder phases to lamellar phases: The transi-
tion temperatures and corresponding enthalpy values of the
n-alkyloxy-substituted bolaamphiphiles Linn are collated in
Table 1.All compounds with short chains ( n=6–11)[26] have
monotropic (metastable) liquid-crystalline phases, whereas
those of the higher homologues are enantiotropic (thermo-
dynamically stable).Increasing the length of the lateral
chain gives rise to a transition from layer structures (SmA
phases; n=6–8) to polygonal cylinder phases (n>8) and fi-
Table 1.Mesophases of compounds Linn with nonbranched alkyl chains.[a]
[b]
[c]
[d]
n
T [8C][a]
Lattice parameters [nm]
fOR
ncell
nwall
DH [kJmolꢀ1
]
a
b
d
[e]
Lin6
6
Cr 97 (SmA 84) Iso
33.1 2.9
Cr 100 (SmA 77) Iso
20.9 1.2
Cr 116 (Colrec(5)cyl-5/p2gg 90) Iso
15.63.8
–
0.29
0.35
0.37
0.39
0.42
0.44
0.47
0.50
0.53
0.56
0.58
[e]
Lin8
8
–
Lin9
9
5.78
5.55
5.32
20.0
2.0
1.8
2.1
2.1
2.0
1.9
Lin10
Lin11
Lin12
Lin14
Lin16
Lin18
Lin20
Lin22
10
11
12
14
16
18
Cr 112 (Colrec(5)cyl-5/p2gg 100) Iso
5.65
18.1
29.0
4.6
Cr 115 (Colhex(6)cyl-6/p6mm 113) Iso
29.65.0
Cr 101 Colhex(6)cyl-6/p6mm 121 Iso
25.0
Cr 92 Colhex(6)cyl-6/p6mm 131 Iso
6.10 7.5
Cr 65 Colhex(6)cyl-6/p6mm 132 Iso
37.4 7.3
Cr 78 Colrec(6)cyl-8/c2mm 123 Colhex1(6)cyl-6/p6mm 126 Iso
19.1 0.7 5.1
3.55
6.4
3.60
6.3
6.4
3.64
6.0
3.60
5.6
3.63[f] 3.60[g]
3.70
9.58[g]
9.70
5.3[f] 16.0[g]
15.7
1.8[f] 2.0[g]
2.0
20
.8
22
Cr 77 Colrec(6)cyl-8/c2mm 125 Iso
19.66
Cr 93 Colrec(6)cyl-8/c2mm 117 LamSm 123 Iso
3.86[g]
9.64[g]
3.64[h]
15.5[g]
1.9[g]
7.0
1.0
4.4
[a] Transition temperatures (T [8C]) and corresponding enthalpy values (DH [kJmolꢀ1], lower lines, in italics) were taken from the second DSC heating
scans (10 Kminꢀ1); values in parenthesis indicate monotropic mesophases, in this case the enthalpy values were measured in the first cooling scan and
the transition temperatures were determined by polarizing microscopy.Cr =crystalline phase, Iso=isotropic liquid phase, Colrec(6)cyl-8/c2mm=centered
rectangular columnar phase with c2mm plane group symmetry, representing a hexagonal honeycomb formed by stretched hexagonal cylinders with 8
molecules in the circumference (8-hexagons), LamSm =lamellar smectic phase, the other phases are shown in Figure 2.[b] fOR =volume fraction of the lat-
eral chain, including the ether oxygen (calculated using crystal volume increments).[30] [c] ncell =number of molecules per unit cell, calculated according
to ncell =Vcell/Vmol from the volume of the unit cell (Vcell) defined by the dimensions a”b”0.45 nm for rectangular phases and a2 ”sin
(608)”0.45 nm for
G
hexagonal phases and the molecular volumes (Vmol) using crystal volume increments,[30] considering the reduced packing density in the LC state (for
more details of calculations, see Table S2).[d] nwall =average number of molecules in the cross section of the cylinder walls=ncell divided by the number
of cylinder walls per unit cell.[e] Not determined due to rapid crystallization of the sample.[f] Value for the Col hex(6)cyl-6/p6mm phase.[g] Values for the
Colrec(6)cyl-8/c2mm phase.[h] Value for the Lam phase.
Sm
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C.Tschierske et al.
Pentagonal cylinder phases: The typical textures and X-ray
diffraction patterns of the polygonal cylinder phases, ob-
tained for compounds Lin9–Lin22, are shown in Figures 3
and 4.In all cases the wide-angle scattering is diffuse (Figur-
e 3b,e), which indicates the fluid character of these meso-
phases.[29] The small angle scattering provides information
about the lattice type and the lattice parameters.For com-
pounds Lin9 and Lin10 the diffraction pattern can be in-
dexed to a p2gg lattice with parameters (a=5.7–5.8 nm, b=
5.3–5.5 nm, see Table 1) ranging between 2.3 and 2.7 times
the molecular lengths, measured between the ends of the
two glycerol units in the most stretched conformation (L=
2.1 nm). This is a typical range that is also observed for the
pentagonal cylinder phases (Colrec(5)cyl-5/p2gg) of the related
n-alkyl derivatives An with n=10–12[12a] and bolaamphi-
philes with fluorinated lateral chains.[12b] In these cylinder
phases the aromatic cores are organized in pentagonal cylin-
der frames, the alkyl chains fill the interior of the cylinders,
and the hydrogen-bonding networks running along the
edges fuse these cylinders edge-to-edge and side-by-side,
yielding a pentagonal honeycomb, as shown in Figure 3c.
These pentagonal cylinders form pairs that organize in a
herringbone pattern.Formation of cylinder pairs leads to
units with enhanced symmetry, and for this reason the pen-
tagonal symmetry is lost and replaced by the experimentally
observed rectangular lattice with plane group p2gg (see Fig-
ure 3c).Moreover, as regular pentagons cannot tile a plane,
the individual cylinders do not have a regular pentagonal
cross section, but instead these are non-regular pentagons in
which not all side-length and angles are exactly the same.
This slight deformation of the cylinders is possible in the
fluid LC state and allows a tiling of space by (nonregular)
pentagonal cylinders.The number of molecules per unit cell
(ncell) was calculated by dividing the unit cell volume by the
molecular volume (determined by using crystal volume in-
crements[30] and considering the reduced packing density in
the LC state, as described in the Supporting Information,
see Table S2).The unit cell is defined by the lattice parame-
ters and a height of h=0.45 nm, corresponding to the mean
distance between the aliphatic chains and the aromatic cores
(determined from the position of the maximum of the dif-
fuse wide-angle scattering in the X-ray diffraction pattern).
The number of molecules obtained in this way is between
ncell =18 and 20 (see Table 1 and Table S2).This number is
completely in line with the proposed phase structure com-
posed of four pentagonal cylinders per unit cell (4”5=20).
The thickness of the cylinder walls is on average about two
molecules (nwall =1.8–2.0[31]), which is a very typical value
found for nearly all cylinder phases.[11,12,32] Hence, the rec-
tangular columnar phases of compounds Lin9 and Lin10
represent Colrec(5)cyl-5/p2gg phases composed of pentagonal
cylinders in which each cylinder has five molecules in the
circumference and the resulting plane group is p2gg.[11]
Hexagonal cylinder phases: For the mesophases of com-
pounds Lin11–Lin16 with longer chains the textures and the
X-ray diffraction patterns (Figure 4a,b) indicate hexagonal
columnar phases (ahex =3.5 to 3.6 nm). As typical for all hex-
agonal cylinder phases (Colhex(6)cyl-6/p6mm phases) the lattice
parameter corresponds to 31/2 of the molecular length L (see
Table 1), indicating the size of the cylinder walls corre-
sponds to the length of the bolaamphiphilic cores of the
molecules in the most stretched conformation (L=2.1 nm).
The number of molecules per unit cell is between ncell =5.3
and 6.4, which is also in line with the proposed phase struc-
ture (one hexagonal cylinder per unit cell).[32,33] Increasing
the chain length further leads to other phase structures.
Giant cylinder phases: Compound Lin18 is especially inter-
esting, as it shows a temperature-dependent transition from
the Colhex(6)cyl-6/p6mm phase at high temperature to another
mesophase at lower temperature.At the transition to the
low-temperature phase, the texture changes completely, and
the optically isotropic areas (dark areas in Figure 4a)
become strongly birefringent (see Figure 4e).The diffuse
wide-angle scattering in the diffraction pattern remains (see
Figure S1c,d), but numerous new reflections occur in the
Figure 3.a),d) Textures, b),e) X-ray diffraction patterns of surface aligned
samples, and c),f) models of self-assembled superstructures formed by
compounds Lin9–Lin12.Col rec(5)cyl-5/p2gg phases of a) Lin9 at T=858C,
b) Lin10 at T=988C, and c) model of the phase (the dotted lines indi-
cate the cylinder pairs which adopt a herring bone-like packing on a p2gg
lattice); Colhex(6)cyl-6/p6mm phases d) Lin11 at T=1108C, e) of Lin12 at
T=1098C, and f) model of the phase.
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Liquid Crystals
FULL PAPER
tagons become deformed to stretched hexagons, in which
the two longer sides are built up by end-to-end pairs of mol-
ecules (8-hexagons).The terminal diol groups segregate into
columns of their own, located at the corners of these stretch-
ed hexagons and in the middle of the elongated cylinder
walls.These columns of hydrogen-bonding networks inter-
connect the biphenyl cores, creating a honeycomb-like net-
work in which the interior is filled by the lateral alkyl chains
(Colrec(6)cyl-8/c2mm phase, see Figure 4g).The calculated
number of ncell =16 molecules per unit cell (see Table 1) is
in good agreement with this model (16 molecules are re-
quired by two cylinders with 8 molecules in the perimeter)
and indicates that also in this case each of the cylinder walls
is formed by on average about two molecules in the diame-
ter.This type of giant cylinder phase was previously ob-
served only for few bolaamphiphiles with semiperfluorinat-
ed lateral chains[12b,32] and is reported herein the first time
for a non-fluorinated molecule.[34]
The observed replacement of the regular hexagonal cylin-
ders (6-hexagons) by larger stretched hexagonal cylinders
upon elongation of the lateral chain from Lin16 to Lin20
can easily be understood.Because longer chains cannot fit
into the limited space available within the 6-hexagons, elon-
gation of these chains leads to an expansion of these cylin-
ders to 8-hexagons.However, the fact that for compound
Lin18 the 6-hexagon cylinder phase occurs at higher tem-
perature than the 8-hexagon cylinder phase is surprising.As
the alkyl chains have a larger thermal expansion coefficient
compared to the glycerol units,[35] it could be expected that
with increasing temperature the columns inside the cylinders
should expand most.This should favor the larger 8-hexagon
cylinders at higher temperature.The unexpected phase se-
quence observed for Lin18, in which the larger cylinder
structure occurs at lower temperature, can be explained on
the basis of the temperature dependence of the conforma-
tion of the alkyl chains.At higher temperature the alkyl
chains are quite flexible and the comparatively long C18
alkyl chains can easily fill the hexagonal cylinders by adopt-
ing nonlinear conformations (Figure 4d).By reducing the
temperature the flexibility of these chains is reduced and,
hence, the chains cannot be accommodated in the small cyl-
inders of the p6mm phase.In the stretched hexagonal cylin-
ders of the c2mm phase with eight molecules in the circum-
ference more chains can be organized parallel to each other
and in these cylinders less chain deformation is required
(see Figure 4h).This is thought to be a main effect favoring
the larger cylinders at lower temperature.[36,37]
Figure 4.Mesophases of compound Lin18: a)–d) Colhex(6)cyl-6/p6mm
phase; a) texture at 1258C between crossed polarizers, b) X-ray diffrac-
tion pattern of an aligned sample at 1248C; c) model of the organization
of the molecules in the mesophase; d) CPK model showing six molecules
organized in the circumference of a 6-hexagon cylinder; e)–h) Colrec(6)cyl-8
/
c2mm phase; e) texture at 1158C, f) small-angle region of the X-ray dif-
fraction pattern of an aligned sample at 908C with indexation of one
domain; g) model of the organization of the molecules in the mesophase;
h) CPK model showing eight molecules organized in the circumference
of a 8-hexagon cylinder; color versions of a) and e) are given in Figure
S1a,b in the Supporting Information.
small-angle region (Figure 4f).Graphical analysis indicates
a multidomain structure composed of three distinct domains.
One of them is indexed in Figure 4f.All reflections corre-
spond to hk: h+k=2n (h0: h=2n und 0k: k=2n), which in-
dicates a centered rectangular cell with the plane group
c2mm and lattice parameters a=3.60 nm and b=9.58 nm.
The symmetry, the lattice parameters and the number of
molecules per unit cell are in line with the model shown in
Figure 4g.Accordingly, the structure is formed by cylinders
with eight molecules in the circumference.As regular octa-
gons cannot tile a plane without leaving void space, the oc-
Transition from giant cylinder phases to LamSm phase: Com-
pound Lin20 shows the Colrec(6)cyl-8/c2mm phase (a=3.70 nm
und b=9.70 nm) in the whole temperature range, whereas
for compound Lin22 again two LC phases were detected.
The high-temperature phase forms a spherulitic texture as
shown in Figure 5a.Upon cooling, at T=1178C, a strong
change of the birefringence color can be seen and the tex-
ture becomes broken (Figure 5e).In the X-ray diffraction
pattern of the high-temperature mesophase (see Figure 5b)
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C.Tschierske et al.
characterized by a spherulitic texture that is typical for LC
phases with 2D periodicity.This suggests that beside the
layer periodicity there is an additional periodicity between
the hydrogen-bonding networks in the layers formed by the
bolaamphiphilic cores (see Figure 5d).[13,18,38] However, this
additional periodicity is not evident in the X-ray diffraction
pattern and therefore it is assumed that there is no long-
range positional correlation of the in-plane periodicity be-
tween the hydrogen-bonding networks in adjacent layers.In
this case the reflections, caused by the in-plane periodicity,
should be smeared out to streaks parallel to the meridian
and, due to the relatively small electron density modulation
between aromatic cores and glycerol units,[39] the intensity of
these diffuse scatterings is apparently too small to be detect-
ed.This type of lamellar phases with a long-range orienta-
tional correlation (biphenyl cores are aligned parallel in ad-
jacent layers) but only short-range positional correlation be-
[18]
tween the layers is assigned as LamSm
.
The diffraction pattern completely changes at the transi-
tion to the low-temperature phase (see Figure 5f,g).This
pattern can be indexed to a centered rectangular c2mm lat-
tice with a=3.86 nm und b=9.64 nm, indicating
a
Colrec(6)cyl-8/c2mm giant cylinder phase (see Figure 5h).This
is in line with the fact that reduction of temperature reduces
the space required by the alkyl chains and this allows the or-
ganization of the molecules in a honeycomb cylinder struc-
ture instead of an organization in layers.
Hence, in the series of alkoxy-substituted bolaamphiphiles
there is a transition from SmA phases to pentagonal and
hexagonal cylinder structures, which are replaced by stretch-
ed giant hexagonal cylinders with eight molecules in the cir-
cumference, followed by a lamellar mesophase (LamSm
)
upon further increasing the chain length.This phase se-
quence is the same as observed for compounds with fluori-
nated segments[12b] and this indicates that fluorination is not
required for the design of these mesophases.All these meso-
phases can also be obtained with simple alkyl derivatives if
the chain length is increased sufficiently.
Figure 5.Mesophases of compound Lin22: a)–d) LamSm phase; a) texture
at 1208C between crossed polarizers, b) X-ray diffraction pattern of an
aligned sample at 1198C; c) distribution of the wide-angle scattering
Comparison of lateral alkyl and alkoxy chains: In Figure 6
the new compounds Linn with lateral n-alkoxy groups are
compared with related compounds An reported previously,
which have directly attached n-alkyl chains.[12a] The phase
sequence in both homologous series is very similar, but the
Colrec(4)cyl-4/c2mm phase formed by four-sided cylinders with
a rhombic cross section, which was observed over a rather
broad range of chain length for the alkyl-substituted com-
pounds without an ether linkage[12a,b] (An with n=6–9, see
Figures 2 and 6) is completely suppressed in the series of
compounds Linn.In this series the pentagonal cylinder
phase is the smallest type of polygonal cylinder phases.
Moreover, the distinct phase types are slightly shifted to
shorter alkyl chain length for compounds Linn, indicating
that the additional ether oxygen atom should also contribute
to the overall space filling within the polygonal cylinders
(therefore, the volume fractions of the lateral chains fOR in
Tables 1 and 2 were calculated including these ether oxygen
along c (black line) with maxima at 1808 [Irel =I(1198C)/I(1288C, Iso)] in
A
comparison with the c position of the layer reflections (red line); d)
model showing the organization of the molecules; e)–h) Colrec(6)cyl-8/c2mm
phase; e) texture at 1108C, f) X-ray diffraction pattern of an aligned
sample at 1058C (wide-angle region); g) small angle region with indexa-
tion of one domain; h) model showing the organization of the molecules.
only a layer reflection with its second order, corresponding
to d=3.64 nm, can be seen on the meridian, indicating a
mesophase with layer structure.The diffuse wide-angle scat-
tering around 2q=19.68 (d=0.45 nm) has a ringlike shape
with a maximum on the meridian (see Figure 5b,c).Accord-
ingly, this mesophase is a lamellar phase (Lam) composed of
alternating aromatic and aliphatic layers.In this mesophase
the aromatic cores and also significant parts of the alkyl
chains should be organized predominately parallel to the
layer planes.[18] The optical appearance of this mesophase is
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Liquid Crystals
FULL PAPER
laamphiphiles An.In addition,
in most cases the melting points
of the alkoxy-substituted com-
pounds are higher, so that in
general enantiotropic meso-
phases and broader mesomor-
phic regions were found for the
alkyl-substituted
compounds
An.This mesophase destabiliz-
ing effect of replacing the alkyl
by alkoxy groups in a lateral
position at an aromatic rodlike
core is completely reverse to its
effect in terminal position, for
which replacing alkyl groups by
alkoxy groups always gives rise
to mesophase stabilization if
the rodlike unit is an aromatic
system.[1] The higher flexibility
Figure 6.Comparison of the LC phases of alkyl-substituted ( An)[12a] and related alkoxysubstituted bolaamphi-
philes (Linn) with the same number of C-atoms (n) in the lateral chain; monotropic mesophases in brackets;
for the abbreviations of the mesophases, see Table 1 and Figure 2.
ꢀ
of the Ar CH2 linking unit
ꢀ
compared to the Ar O linking
atoms).[40] The comparison in Figure 6 also shows that the
stabilities of the LC phases (LC-to-Iso transition tempera-
tures) of the n-alkoxy-substituted compounds Linn are
slightly lower than those of related n-alkyl-substituted bo-
unit (different rotational barriers)[41,42] should be mainly re-
sponsible for these effects.In terminal position the more
rigid alkoxy groups favor the parallel alignment of the rod-
like cores, which stabilizes LC phases.However, in lateral
position the reduced flexibility
makes the packing of these
chains more difficult.The re-
Table 2.Mesophases of the bolaamphiphiles with bulky lateral chains.
duced flexibility should also be
responsible for the missing of
small cylinder structures com-
posed of only four walls, as for
example, the rhombic cylinders,
seen for the Colrec(4)cyl-4/c2mm
phase of the alkyl-substituted
compounds An (n=6–9, see
Figures 2 and 6).As the orien-
tation of the lateral chains with
respect to the biphenyl core is
more restricted for the alkoxy-
substituted compounds it is
more difficult for these chains
to fill the space in these small
cylinders efficiently.
Total no of C+O T [8C][a]
Lattice parameters [nm] fOR ncell
nwall
atoms in R
DH [kJmolꢀ1
Cr 108 (Colhex(6)cyl-6/p6mm 93) Iso 3.51
57.5 4.9
Cr 62 Colhex(6)cyl-6/p6mm 74 Iso
12.7 4.0
Cr 75 Colrec(6)cyl-8/c2mm 103 Iso
]
a
b
d
Tmp
22
0.55 4.8
0.56 4.7
0.58 14.8
0.66
1.6
1.6
1.9
Ada
24
23
34
3.53
3.73 9.52
Ment*
Chol*6
16.6
5.5
Cr 152 (Lam0Iso 141) Iso
49.61.1
–
[b]
Chol*11 39
Bra22 22
Cr 120 Lam’ 136 Lam0Iso 140 Iso
5.02[c] 4.46[d] 0.69
21.8
Cr 70 LamSm 105 Iso
20.3 5.7
Cr 103 (M1 65 LamSm 81) Iso
21.1 1.4 2.8
Cr 113 (LamN 102) Iso
76.3 3.1
Cr 104 Colhex 121 Iso
69.7 2.0
Cr 84 LamN 103 Iso
48.9 5.3
3.3
1.7
2.72
4.04
4.70
0.58
Benz6/1 28
Benz6/2 41
Benz6/3 54
Benz11/3 59
0.60
0.69
4.95
0.75 11.6[e]
0.77
Compounds with bulky end
groups: The convergent syn-
5.25
[a] Transition temperatures (T [8C]) and corresponding enthalpy values (DH [kJmolꢀ1], lower lines, in italics) thetic strategy allows not only
were taken from the second DSC heating scans (10 Kminꢀ1); abbreviations: LamIso =lamellar isotropic phase,
composed of disordered sublayers of the bolaamphiphilic cores and the aliphatic lateral chains, LamN =lamel-
lar nematic phase, in which the bolaamphiphilic cores are organized with their long axes parallel to the layer
planes and adopt a long-range orientational order within these layers, the sublayers of the alkyl chains are dis-
the preparation of simple n-al-
kyloxy derivatives, but also the
introduction of branched and
other more complex lateral
chains, as shown in Scheme 3
and in Table 2.Only a mono-
tropic hexagonal columnar
phase was observed for com-
pound Tmp with a 2,4,6-trime-
ordered, Lam’ and Lam’Iso describe special types of Lam phases where biphenyl cores and cholesteryl units are
organized in separate sublayers and the cholesteryl units adopt an organization on average perpendicular to
the layer planes; Colhex =non-cylinder hexagonal columnar phase; for the other abbreviations see Figure 2 and
0
Table 1.[b] Not determined due to rapid crystallization.[c] Value for the Lam
phase.[d] Value for the Lam ’
Iso
phase.[e] In this case the volume of the unit cell was calculated by assuming a height of h=1.8 nm corre-
sponding to the length of Benz11/3 measured between the termini of the diol groups and assuming a most
compact conformation of the glycerol groups.
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6359

C.Tschierske et al.
Figure 7.Compound Ment*: a) texture of the Colrec(6)cyl-8/c2mm phase at
1008C (for a color version see Figure S5 in the Supporting Information);
b) XRD pattern of an aligned sample at 958C.
functional units to the ends of these chains, which can
induce useful properties to these nanostructured systems.[43]
A remarkable feature of the Colhex phases of compounds
Tmp and Ada is the relatively small number of molecules in
the unit cell (ncell =4.7–4.8), which indicates a thickness of
the cylinder walls of only 1.6 molecules on average.[31] In
Figure 8 the dependence of ahex and ncell on the volume frac-
tion of the lateral chain (fOR) is shown graphically for all
compounds with Colhex phases.Although ahex is nearly inde-
pendent of fOR (the deviation of ahex is due to limited accura-
cy of measurements and is about ꢁ0.05 nm, and because
these parameters were determined at different tempera-
tures) there is a clear decrease of ncell, that is, the number of
molecules organized in the cylinder walls decreases by en-
larging the lateral substituent from nwall =2.1 for Lin11 to
Scheme 3.Structures of the bolaamphiphiles with bulky end-groups and
branched lateral chains.
nwall =1.6 for Ada.This indicates that increasing volume of
thylphenoxy group attached to the end of the lateral alkoxy
chain (Figures S2a and S3).The lattice parameter ahex
=
3.51 nm is in the range expected for the hexagonal honey-
comb structure (Colhex(6)cyl-6/p6mm phase).A hexagonal col-
umnar phase was also found for the adamantane derivative
Ada (Figures S2b and S4), whereas the menthol derivative
Ment*, with the largest number of atoms in the lateral
chain, has a
Colrec(6)cyl-8/c2mm phase (a=3.73 nm, b=9.52 nm, see
Figure 7 and Figure S5 in the Supporting Information) com-
posed of stretched hexagonal cylinders containing eight mol-
ecules in the circumference (see Figure 5h).This indicates
that quite bulky units can be attached to the ends of the lat-
eral chains of these compounds to produce structures in
which these units can be accommodated in the interior of
honeycomb cylinder frameworks with different shapes.This
shows that it should in principle also be possible to attach
Figure 8.Dependence of the hexagonal lattice parameter ahex (dashed
line) and the number of molecules in a hexagonal unit cell (ncell, solid
line) on the volume fraction of the lateral chain (fOR), as seen for the
Colhex(6)cyl-6/p6mm phases of compounds Lin11–Lin18, Tmp, and Ada.
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Liquid Crystals
FULL PAPER
the lateral chain leads to an expansion of the lipophilic col-
umns inside the hexagonal honeycombs.As the cross-section
area available for the lateral chains inside the hexagonal cyl-
inders is limited by the length of the bolaamphiphilic cores,
the hexagonal lattice parameter increases only slightly upon
enlarging the lateral chains.Hence, expansion of the lipo-
philic columns has to take place mainly along the column
long axis.Due to this expansion the number of molecules in
the cross section of the cylinder walls is reduced within cer-
tain limits.Therefore, ncell and nwall decrease with increasing
size of the lateral substituent and temperature.This was ob-
served for all polygonal cylinder phases and in all series of
T-shaped bolaamphiphiles.[11,12] As the cylinder walls
become thinner these walls become also less stable and fi-
nally burst by giving way to other phase structures.The
transition to 8-hexagons is often observed for hexagonal cyl-
inder phases.It is also interesting to note that for molecules
with linear alkyl chains (Lin11–Lin18) this transition al-
ready takes place at fOR =0.53, whereas compounds Tmp
and Ada with shorter chains and bulky end groups are a bit
more robust and require fOR >0.56.
Effects of chirality: All the reported bolaamphiphiles con-
tain two stereogenic centers in the glycerol units.Therefore,
these compounds actually represent mixtures of diastereo-
mers in their racemic forms.Herein attention is focused on
molecules with additional stereogenic centers located in the
functional groups attached to the ends of an aliphatic spacer
unit.[44] For the menthyl derivative Ment* the same type of
Colrec(6)cyl-8/c2mm phase composed of giant hexagonal cylin-
ders as previously observed for the linear compounds
Lin18–Lin22 was found.No special effects of the chirality
on the phase structure, as for example, change of the phase
symmetry or any hints on the induction of a helical super-
structure,[45] as common in other LC phases formed by chiral
molecules, could be detected.Also for the compounds
Chol*n, with cholesteryl groups in the lateral chain, no
effect of chirality on the phase structure was observed.It
seems that the hydrogen-bonding networks provide quite
robust structures that cannot easily be modified by the rela-
tively weak chirality effects in the lipophilic lateral chains.
Nevertheless, the mesophases of compounds Chol*n are of
interest from another point of view, as in these compounds
two distinct rodlike units, the aromatic biphenyl core and a
polyalicyclic core are combined in a competitive manner.
Figure 9.Compound Chol*11: a) texture of the Lam0Iso phase at 1388C; b)
XRD pattern of an aligned sample at 1368C; c) texture of the Lam’
phase at 1308C; d) XRD pattern of an aligned sample at 1258C; e)
model showing the proposed organization of the molecules in the Lam’
phase; color versions of a) and c) are shown in Figure S6 in the Support-
ing Information.
dark (see Figure 9a), which represent homeotropically
aligned areas of a uniaxial lamellar phase.X-ray diffraction
confirms a lamellar phase, characterized by layer reflections
of the first- and second-order, corresponding to a layer dis-
tance of d=5.02 nm (Figure 9b). The wide-angle scattering
is diffuse, which confirms the LC nature of this mesophase.
For a surface-aligned sample the wide-angle scattering has a
ring-like shape.Remarkably, weak, but distinct, maxima of
the diffuse scattering corresponding to d=0.54 nm are locat-
ed on the equator.They may be assigned to the mean dis-
tance between the cholesteryl units.In this case, the polycyc-
lic cores of the cholesteryl units should adopt a preferred di-
rection on average perpendicular to the layer planes as in
conventional SmA phases and they are assumed to be segre-
gated from the aliphatic segments (spacers and end chains
at the cholesteryl groups) as well as from the bolaamphiphil-
ic biphenyl cores.Hence, the lateral chains are completely
intercalated, so that the rigid alicyclic cores of the cholester-
yl units are located side by side and the spacer units and C8
end chains of the cholesteryl unit are mixed and form
common aliphatic sublayers, as shown schematically in Fig-
ure 9e for the more ordered low-temperature phase.Howev-
er, in this high-temperature phase the orientational order is
Effects of rodlike units in the lateral chain: The textures of
the mesophases of compounds Chol*6 and Chol*11 with lat-
erally attached cholesteryl units indicate the formation of la-
mellar phases (see Figure 9a).Compound Chol*6 with a rel-
atively short C6 spacer shows only a monotropic uniaxial LC
phase with a fanlike texture as typical for SmA and LamIso
-
phases.[18] Compound Chol*11 with a much longer C11
spacer forms two different enantiotropic LC phases.The
high-temperature mesophase shows a texture which is iden-
tical to that observed for Chol*6, characterized by regions
with fanlike texture and regions that appear completely
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6361

C.Tschierske et al.
not very high.The sublayers of the aliphatics and the bo-
laamphiphiles are nearly completely disordered as indicated
by the ring-like shape of the diffuse scattering with the max-
imum at d=0.46 nm (Figure 9b). This phase is assigned as
bines two completely different types of lamellar organiza-
tions in one structure.There is an analogy to smectic phases
of some combined LC main-chain/side-chain polymers[46]
with cholesteryl pedant groups.An intercalated layer mor-
phology with the pedants oriented perpendicular to the
backbones was also observed for these polymers.[47] Other
combined LC polymers with aromatic pedants form nematic
phases where these pedants align parallel to the polymer
backbone.Exclusively nematic phases, in which the distinct
rodlike cores are mixed, have also been observed for all pre-
viously reported low-molecular-weight T-shaped dimeso-
gens.[48,49] It seems that in low-molecular-weight systems not
only the incompatibility of the two distinct rigid units,[50] but
also the incompatibility of the groups attached to their ends
(diol groups at the biphenyls and alkyl chains at the polyali-
cyclics) contribute to the formation of distinct sublayers
comprising different rodlike units.
Lam0Iso
.
At the transition to the low-temperature phase at 1368C a
significant change of the texture as well as of the X-ray dif-
fraction pattern is seen.In the texture of the lamellar low-
temperature phase the homeotropically aligned regions,
seen in Figure 9a, become birefringent (Figure 9c), indicat-
ing a transition to an optically biaxial mesophase (also after
shearing, the sample remains birefringent and no pseudoiso-
tropic areas can be detected).In the diffraction pattern the
position of the layer reflection changes, that is, the layer dis-
tance is reduced to d=4.46 nm. The distinct maxima of the
diffuse wide-angle scattering on the equator (at d=0.54 nm)
become much stronger and less diffuse (Figure 9d).This in-
dicates that the rigid polycyclic parts of the cholesteryl units
retain an organization perpendicular to the layer planes, but
the order parameter of these units is significantly increased
in comparison to the high-temperature phase.An additional
weaker maximum of the diffuse scattering is positioned on
the meridian at d=0.46 nm, which is a typical feature of
Lam phases.[18] As the low-temperature phase is optically
biaxial and a uniformly tilted organization as well as a meso-
phase with 2D lattice (columnar mesophase) is unlikely,
judging from the diffraction pattern, it is thought that the
phase transition is due to the inset of orientational long-
range order within the sublayers of the bolaamphiphilic
cores.This requires an arrangement of the biphenyl cores
on average parallel to the layer planes as in LamN and
Effects of branching of the lateral chain: The X-ray diffrac-
tion pattern of the mesophase of compound Bra22 with a
branched lateral chain is characterized by a layer reflection,
corresponding to d=2.72 nm in the small angle region (Fig-
ure S7).The wide-angle diffraction is diffuse ( d=0.45 nm)
and forms a ring with a maximum on the meridian, as also
observed for the high-temperature mesophase of the isomer-
ic linear compound Lin22.The mesophase grows with a
characteristic shape and finally forms a mosaic texture
(Figure 10).This texture is often seen for smectic phases
LamSm phases.As Lam and LamN phases cannot clearly be
Sm
distinguished on the basis of X-ray diffraction patterns (in
both cases only the layer reflections can be detected) and
also textural observations do not allow an unambiguous dis-
tinction of these two phase types in this case, this low-tem-
perature mesophase is tentatively assigned as Lam’.The bi-
refringent texture developing in the homeotropically aligned
regions (see Figure 9c) is not a schlieren texture as typical
for LamN phases.Therefore, it is more likely that the low-
temperature phase is related to the noncorrelated LamSm
phases with a periodicity within the layers, but with no long-
range positional correlation between the layers.In any case,
the mesophases of compounds Chol*n are unique, as the
two different rodlike segments, the biphenyl units, and the
rigid cycloaliphatic parts of the cholesteryl moieties are in-
compatible and organize into distinct sublayers (see Fig-
ure 9e).Moreover, the orientation of the two distinct types
of rodlike units is different in the distinct sublayers.Where-
as the biphenyl units are disordered (Lam0Iso phase) or or-
ganized with their long axes parallel to the layer planes
(Lam’ phase), the rigid parts of the cholesteryl units are or-
ganized on average perpendicular to the layers as in conven-
tional SmA-type smectic phases.Hence, the Lam ’ phase is a
triply segregated fluid smectic phase representing a hybrid
structure composed of conventional SmA layers and LamN
or LamSm layers.This is a new LC phase structure that com-
Figure 10.Texture of compound Bra22 as seen for the LamSm-phase
during the growing of the mesophase (crossed polarizers; dark areas are
residues of the isotropic liquid phase) at T=1058C.
with additional in-plane order and also for columnar meso-
phases.As no in-plane periodicity can be detected by means
of X-ray scattering, it is likely that this mesophase is a
LamSm phase with a 1D periodicity in the aromatic sublay-
ers, but only a short- or medium-range positional correlation
between the layers, the same as already discussed for the
high-temperature mesophase of compound Lin22 with a
linear chain (LamSm).However, the giant Col rec(6)cyl-8/c2mm
cylinder phase, seen as a low temperature phase below the
LamSm phase for compound Lin22 with a linear chain, is not
observed in the branched compound Bra22 with the same
size of the lateral substituent.The reason for the loss of this
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Liquid Crystals
FULL PAPER
cylinder structure in the case of Bra22 might be that the
branching is located close to the biphenyl core.This increas-
es the area required by the lateral groups at the aromatic–
aliphatic interfaces and therefore it becomes more difficult
to curve these interfaces as required for the formation of
polygonal cylinders.This indicates that beside the overall
space required by the lateral group also their distinct shape
influences the mesophase morphologies.Comparison of
compounds Lin22, Ment*, and Bra22, all having the same
volume fraction of the lateral groups of fOR =0.58 (see
Table 2) indicates that bulky groups at the end of the chains
do not disturb the formation of cylinder structures and even
stabilize these phases, whereas branching close to the aro-
matic core disfavors cylinder structures and favors the for-
mation of Lam phases.Even bolaamphiphiles with much
shorter branched chains form exclusively Lam-type phases
as will be reported in detail in a subsequent manuscript.[38]
Compounds with benzoate units in the lateral chain: A
widely used building block for induction of LC properties in
a broad variety of different compounds is based on mono-,
di-, and trialkoxy-substituted benzoates.[1,2,5,6,9,51] Herein,
such benzoates were used as bulky end-groups, which were
connected with the biphenyl core by means of hexyloxy or
undecyloxy spacers (compounds Benz6/m and Benz11/3, re-
spectively).Compounds Benz6/1 and Benz6/2 with only one
or two dodecyloxy chains attached to the benzoate unit
show monotropic mesophases whereas compounds Benz6/3
and Benz11/3 with three chains form enantiotropic phases
(Table 2).
Figure 11.Textures of the mesophases of compounds Benz6/m as seen
between crossed polarizers (left) and models of the organization of the
molecules in the mesophases (right): a) LamSm phase of Benz6/1; at
808C; b) LamN phase of Benz6/2 at 1008C; c) noncylinder Colhex phase
of Benz6/3 at 1158C.
The mesophase of Benz6/1 develops with a spherulitic
texture (see Figure 11a) and only one layer reflection corre-
sponding to d=4.04 nm was observed in the X-ray diffrac-
tion pattern (Figure S8).Based on texture and X-ray data it
is assumed that this is a LamSm phase, similar to that ob-
served for the compounds Lin22 and Bra22.The X-ray dif-
fraction pattern of the monotropic mesophase of the dialkyl
benzoate Benz6/2 is very similar to that of Benz6/1, indicat-
ing a lamellar phase with d=4.70 nm (see Figure S9). How-
ever, the texture is quite distinct, characterized by a highly
fluid schlieren-like appearance (see Figure 11b).Such tex-
tures are typically observed for LamN phases.[18] In these
LamN phases the bolaamphiphilic cores have only an orien-
tational long-range order, but without periodicity in the aro-
matic layers (Figure 11b, right).[18]
these columns forming a nonpolar continuum (see Fig-
ure 11c right).This phase structure is very similar to invert-
ed Colhex phases of simple amphiphilic molecules, but it is
likely that the aromatic cores are aligned parallel to the
column long axis.[52] In this case the bolaamphiphilic struc-
ture of the polar groups can induce an additional (orienta-
tional and possibly also positional) order within these col-
umns (similar to the organization in the layers of the LamN/
LamSm phases) as shown in Figure 11c at the right.If such a
structure is assumed, approximately 12 molecules are organ-
ized in a hexagonal unit cell with a height of h=1.8 nm (cor-
responding to the shortest possible length of the bolaamphi-
philic core with a compact conformation of the glycerol
units[53]), which means that about 12 biphenyl cores should
form the cross section of the column cores.[54]
Interestingly, elongation of the spacer unit from C6 to C11
in compound Benz11/3 restores the lamellar mesophase (X-
ray diffraction pattern, see Figure S11), because the in-
creased distance of the benzoate branching point from the
biphenyl core decreases the overall taper angle of the lateral
substituent and this reduces the curvature of the aromatic–
aliphatic interface.The increased spacer length also allows a
better intercalation of the three dodecyloxy chains with the
aliphatic spacer units, which additionally contributes to a re-
duction of curvature.Hence, the lateral chains should be
completely intercalated and strongly folded in this lamellar
Compound Benz6/3 behaves completely different and
shows a hexagonal columnar phase as indicated by the tex-
ture (Figure 11c) and the X-ray diffraction pattern of an
aligned sample (see Figure S10).The lattice parameter
(ahex =4.95 nm) is much larger than that allowed for a hexag-
onal honeycomb structure (expected value:
ahex =3.5–
3.6 nm, according to ahex =31/2 L; L=2.1 nm) and, hence, this
hexagonal columnar phase should be quite distinct from the
honeycomb like cylinder structures of the n-alkyl-substituted
compounds Linn (with n=11–16).In the Col
phase of
hex
Benz6/3 the bolaamphiphilic cores should form the interior
of the columns and the lateral chains are organized around
Chem. Eur. J. 2008, 14, 6352 – 6368
ꢀ 2008 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
www.chemeurj.org
6363

C.Tschierske et al.
phase.The texture of this lamellar phase is very similar to
groups were obtained by attaching bis- and tris-
that observed for compound Benz6/2 (see Figure 11b), indi-
A
cating a LamN phase.In contrast to the monotropic Lam
molecules broad regions of LamN phases and new noncylin-
der hexagonal columnar phases were realized.
The complete phase sequence observed for the series of
new compounds is shown in Figure 12.Though some of the
ternary amphiphiles have very large lipophilic parts, their
mesophase behavior is still influenced by the bolaamphiphil-
N
phase of Benz6/2, this mesophase is enantiotropic.No tran-
sition to a LamSm phase is observed in the whole mesomor-
phic temperature range and this compound has the broadest
LamN range ever achieved.Hence, these benzoates are ideal
candidates for more detailed investigations of the LamN
phases, for exploring their po-
tential for applications and to
access new phase structures.
Conclusion
A universal building block for
the convergent synthesis of a
wide variety of different T-
shaped ternary amphiphiles
with complex structures of the
lateral chains was developed
(compound 5, see Schemes 1
and 2).As a consequence of
Figure 12.Phase sequence of T-shaped bolaamphiphiles, reported herein, as observed by enlarging the size of
the lateral group.
this synthetic strategy, the T-shaped bolaamphiphiles ob-
tained by etherification of 5 contain an additional ether link-
age between aromatic core and lateral chain.The influence
of this additional ether linkage on the mesomorphic proper-
ties was investigated for the n-alkyl-substituted compounds
Linn, and it turned out that fundamentally the same super-
structures as previously reported for related n-alkyl-substi-
tuted compounds without ether oxygen can be found.How-
ever, these ether oxygen atoms reduce the flexibility of the
connection between aromatic core and lateral chain and this
restricts the packing of the lateral chains.Therefore, an in-
crease of the melting points, a reduction of the mesophase
stabilities, and a suppression of polygonal cylinder phases
with relatively small cylinder cross sections is observed as a
result of the introduction of the ether linkage.Also the un-
ic structure of the polar group and these molecules behave
like T-shaped ternary amphiphiles rather than as simple
flexible binary amphiphiles.
Though the mesophase morphology is largely determined
by the volume of the lateral chains with respect to the
length of the rodlike building blocks, changes of other mo-
lecular parameters have a significant impact on molecular
self-assembly.For example, bulky substituents located at the
end of the lateral chain are compatible with the polygonal
cylinder structures, whereas the cylinders are removed by
branching the chains close to the connection with the aro-
matic core.This leads to a dominance of Lam
phases also
Sm
for molecules with smaller volume fractions of the lateral
groups.[38]
Compounds Chol*n with laterally attached cholesteryl
groups show a remarkable new type of lamellar phases, in
which two different types of layers with a distinct orienta-
tion of the rodlike units with respect to the layer planes are
combined in a common mesophase.This shows that the rela-
tively simple mode of self-organization in layers has still
many unexplored possibilities and additional new structures
could be expected by further increasing the molecular com-
plexity by tailoring the shape, topology, and incompatibility
of the building blocks.
usual
transition
from
a
smaller
6-hexagon
ACHTREUNG
structure (Colrec(6)cyl-8/c2mm phase) by reducing the tempera-
ture can be explained by the better packing of less flexible
chains in the giant cylinders.The fact that molecules with
lateral alkoxy chains have reduced mesophase stabilities
compared to alkyl derivatives is opposite to the trends usu-
ally seen for rodlike molecules with terminally attached
chains.
As this synthetic strategy also allows an easy synthesis of
compounds with much larger lateral groups, giant cylinder
structures as well as LamN and LamSm phases, reported pre-
viously only for fluorinated molecules,[12b] became available
also for non-fluorinated T-shaped bolaamphiphiles.
Polygonal cylinder arrays composed of 6-hexagons and
giant 8-hexagons were also obtained for compounds in
which additional bulky groups were attached to the ends of
the lateral chain, which in the future will allow the introduc-
tion of functionality into these cylinders.The largest lateral
In summary, these investigations have shown that T-
shaped ternary amphiphiles are successful materials for the
design of soft-matter systems with complex superstructures
and that this structural information is quite robust, so that it
can even dominate the self-assembly of molecules with quite
large lateral groups.This will be used in future work for the
design of functional soft matter materials based on these ter-
nary amphiphiles.
6364
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ꢀ 2008 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
Chem. Eur. J. 2008, 14, 6352 – 6368

Liquid Crystals
FULL PAPER
tion and evaporation of the solvent, the crude product was crystallized
from hexane/EtOAc (3:1, v/v). Colorless solid; yield: 20.7 g (93%); m.p.
Experimental Section
112–1148C; 1H NMR (400 MHz, [D6]acetone, 258C, TMS): d=7.50 (d, 3J-
Investigations: All compounds with exception of the higher homologues
were hygroscopic materials which take up humidity from air.This influ-
enced the stability of LC phases and higher water concentrations could
also lead to a change of the phase type.[55] This required that all experi-
ments were carried out with dried samples under exclusion of humidity.
This was usually achieved by heating the samples on the glass substrate
(for polarizing microscopy) or in the open DSC pan (for DSC) to 1508C
for about 10 s.These samples were immediately sealed and investigated.
For X-ray experiments with aligned samples this strict exclusion of hu-
midity was not possible, and therefore the results obtained by this
method were cross-checked with diffraction patterns obtained from
powder patterns in sealed capillaries.
3
(H,H)=6.8 Hz, 2H; Ar-H), 7.38 (t, J
ACHTREUNG
G
ACHTREUNG
A
N
ACHTREUNG
8.6 Hz, 1H; Ar-H), 5.16 (s, 2H; OCH2Ph), 4.12–4.08 (m, 1H; CHOH),
4.04–3.96 (m, 2H; CH2OH), 3.74–3.59 ppm (m, 2H; OCH2).
4-(2-Benzyloxy-4-bromophenoxymethyl)-2,2-dimethyl-1,3-dioxolane (3):
A
suspension of 3-(2-benzyloxy-4-bromophenoxy)propane-1,2-diol
(20.7 g, 58.6 mmol) and pyridinium p-toluenesulfonate (0.05 g, 0.2 mmol)
in 2,2-dimethoxypropane (400 mL) was stirred at room temperature for
24 h.Thereafter, the solvent was evaporated and the residue was taken
up in diethyl ether.The solution was washed with sat.aq.NaHCO
,
3
water, and brine.After drying over anhydrous Na 2SO4, the solvent was
removed under reduced pressure and the crude product was purified by
column chromatography (silica gel, chloroform/methanol, 10:0.2, v/v).
Colorless solid; yield: 22.3 g (97%); m.p. 66–688C; 1H NMR (400 MHz,
Transition temperatures were measured by means of a Nikon Optiphot
polarizing microscope with a Mettler FP82HT hot stage and control unit
and confirmed using differential scanning calorimetry (DSC-7, Perkin–
ꢀ1
Elmer).The heating and cooling rates were 10 Kmin
.
3
ACHTREUNG
3
CDCl3, 258C, TMS): d=7.41 (d, J
(H,H)=7.2 Hz, 2H; Ar-H), 7.31 (d, 3J
(d, 4J(H,H)=2.3 Hz, 1H; Ar-H), 7.01 (dd, 3J
2.3 Hz, 1H; Ar-H), 6.80 (d, 3J
(H,H)=8.5 Hz, 1H; Ar-H), 5.05 (s, 2H;
Powder X-ray investigations were carried out with a Guinier film camera
(Huber), samples in glass capillaries (1 1 mm) in a temperature-con-
trolled heating stage, quartz-monochromatized CuKa radiation, 30 to
A
ACHTREUNG
A
N
ACHTREUNG
AHCTREUNG
60 min exposure time, calibration with the powder pattern of Pb(NO3)2.
G
OCH2Ph), 4.46–4.40 (m, 1H; OCH), 4.11–4.05 (m, 2H; OCH2), 3.97–3.90
(m, 2H; OCH2), 1.40 (m, 3H; CH3), 1.37 ppm (s, 3H; CH3).
Aligned samples were obtained on a glass plate.Alignment was achieved
upon slow cooling (rate: 1 Kminꢀ1–0.01 Kminꢀ1) of a small droplet of the
sample and took place at the sample–glass or at the sample–air interface,
with domains fiberlike disordered around an axis perpendicular to the in-
terface.The aligned samples were held on a temperature-controlled heat-
ing stage and the diffraction patterns were recorded with a 2D detector
(HI-STAR, Siemens, X-ray beam parallel to the substrate surface).
3-Benzyloxy-4,4’-bis(2,2-dimethyl-1,3-dioxolane-4-ylmethoxy)biphenyl: A
mixture of
3
(11 g, 28 mmol), 4[12a] (8.46 g, 33.6 mmol), [Pd
(PPh3)4]
A
(1.62 g, 1.4 mmol), glyme (100 mL), and sat. aq. NaHCO3 (75 mL) was
stirred under an argon atmosphere at reflux for 12 h.After cooling to
room temperature, the solvent was removed and the residue was extract-
ed with chloroform (3”50 mL).The combined organic layers were
washed with water and brine.After drying over anhydrous Na 2SO4, the
solvent was removed under reduced pressure, and the residue was taken
up in chloroform and filtered through a plug of silica gel.After evapora-
tion of the solvent the crude product was crystallized from chloroform/
petroleum ether (1:1, v/v). Colorless solid; yield: 8.4 g (58%); m.p. 93–
958C; 1H NMR (400 MHz, CDCl3, 258C, TMS): d=7.45–7.28 (m, 5H;
Synthesis and analytical data: Unless otherwise noted, all starting materi-
als were purchased from commercial sources and were used as obtained.
Preparative thin-layer chromatography was performed with a Chromato-
tron (Harrison-Research) using silica gel 60 PF254 (Merck).Column chro-
matography was performed with silica gel 60 (63–200 mm, Merck).For
Lin18 the synthesis is described as an example; the synthesis of all other
compounds was done in an analogous way.For compounds Linn analyti-
cal data are given in the Supporting Information and for all other inter-
mediates and end-compounds the procedures and analytical data are de-
scribed in the Supporting Information.
Ar-H), 7.11 (d, 4J
4J(H,H)=2.1 Hz, 1H; Ar-H), 5.14 (s, 2H; OCH2Ph), 4.48 (quint, 3J-
(H,H)=6.1 Hz, 2H; OCH), 4.18–4.06 (m, 4H; OCH2), 4.03–3.88 (m, 4H;
A
G
AHCTREUNG
AHCTREUNG
OCH2), 1.46 (s, 3H; CH3), 1.42 (s, 3H; CH3), 1.40 (s, 3H; CH3), 1.38 ppm
(s, 3H; CH3).
1-Allyloxy-2-benzyloxy-4-bromophenol:
A
mixture of compound 2[23]
(38.9 g, 0.14 mol), allyl bromide (18.5 g, 0.15 mol) and K2CO3 (96.3 g,
0.70 mol) in acetonitril (500 mL) was stirred for 6 h under reflux. After
cooling to room temperature, the reaction mixture was poured into an
ice/water mixture (500 mL) and extracted with diethyl ether (3”100 mL).
The combined organic layers were washed with water and brine.After
drying over anhydrous Na2SO4, filtration and evaporation of the solvent,
the crude product was purified by crystallization from methanol.Color-
less solid; yield: 40 g (90%); m.p. 50–528C; 1H NMR (400 MHz, CDCl3,
4,4’-Bis(2,2-dimethyl-1,3-dioxolane-4-ylmethoxy)biphenyl-3-ol (5): 2,2-Di-
methyl-4-[2-benzyloxy-4’-(2,2-dimethyl-1,3-dioxolane-4-yloxymethyl)]bi-
phenyl-1,3-dioxolane (1.5 g, 2.88 mmol) was dissolved in THF (50 mL).
Under an argon atmosphere Pd/C (0.03 g; 10% Pd) was added and the
reaction mixture was flushed with hydrogen.After shaking this mixture
at 408C and 2.8 bar hydrogen pressure for 12 h the catalyst was filtered
off and the solvent was evaporated.The crude product was purified by
crystallization from EtOAc/petroleum ether (1:1, v/v).Colorless solid;
yield: 1.1 g (89%); m.p. 135–1378C; 1H NMR (400 MHz, CDCl3, 258C,
258C, TMS): d=7.42 (d, 3J
7.3 Hz, 2H; Ar-H), 7.30 (d, 3J
(H,H)=2.3 Hz, 1H; Ar-H), 7.00 (dd, 3J
1H; Ar-H), 6.76 (d, 3J
(H,H)=8.6 Hz, 1H; Ar-H), 6.08–5.99 (m, 1H;
CH=CH2), 5.38 (dd, 3J(H,H)=17.3 Hz, 2J
(H,H)=1.6 Hz, 1H; CH=CH2),
(H,H)=1.4 Hz, 1H; CH=CH2), 5.09 (s,
A
N
TMS): d=7.44 (d, 3J
2.2 Hz, 1H; Ar-H), 6.98 (dd, J
H), 6.94 (d, 3J(H,H)=8.8 Hz, 2H; Ar-H), 6.92 (d, 3J
Ar-H), 6.24 (brs, 1H; OH), 4.48 (quint, 3J
(H,H)=5.8 Hz, 2H; OCH),
(H,H)=8.9 Hz, 2H; Ar-H), 7.13 (d, 4J
(H,H)=
(H,H)=2.2 Hz, 1H; Ar-
(H,H)=8.4 Hz, 2H;
AHCTREUNG
3
4
ACHTREUNG
A
N
ACHTREUNG
A
ACHTREUNG
G
ACHTREUNG
A
ACHTREUNG
AHCTREUNG
5.26 (dd, 3J
C
ACHTREUNG
4.18–4.03 (m, 4H; OCH2), 3.97–3.88 (m, 4H; OCH2), 1.49 (s, 3H; CH3),
1.46 (s, 3H; CH3), 1.41 (s, 3H; CH3), 1.40 ppm (s, 3H; CH3).
A
N
OCH2).
4,4’-Bis(2,2-dimethyl-1,3-dioxolane-4-ylmethoxy)-3-octadecyloxybiphenyl
(6): A mixture of 5 (150 mg, 0.35 mmol), 1-bromooctadecan (134 mg,
0.37 mmol), K2CO3 (242 mg, 1.75 mmol), and tetrabutylammonium
iodide (5 mg) in anhydrous DMF (50 mL) was stirred at 808C for 6 h.
After cooling to room temperature, the reaction mixture was poured into
ice–water (50 mL), and the aqueous layer was extracted with diethyl
ether (3”50 mL).The combined organic layers were washed with sat.aq.
LiCl, water, and brine.After drying over anhydrous Na 2SO4, filtration
and evaporation of the solvent, the crude product was purified by prepa-
rative thin-layer chromatography (silica gel, petroleum ether/chloroform,
3-(2-Benzyloxy-4-bromophenoxy)propane-1,2-diol: To a mixture of 1-al-
lyloxy-2-benzyloxy-4-bromophenol (20 g, 62.7 mmol) in acetone (150 mL)
was added N-methylmorpholine-N-oxide (8 g, 68.9 mmol of a 50 wt% aq.
solution) and OsO4 (2 mL of a 0.004m solution in tert-butanol).The mix-
ture was stirred at room temperature for 48 h.After addition of saturated
Na2SO3 solution in water (50 mL), the mixture was stirred for 30 min.
Then, the solution was filtered through silica gel and the solvent was re-
moved under reduced pressure.The residue was taken up in EtOAc
(100 mL) and the aqueous layer was extracted with EtOAc (3”50 mL).
The combined organic layers where washed with 10% aq.H SO4, sat.aq.
NaHCO3, water, and brine.After drying over anhydrous Na 2SO4, filtra-
1:2, v/v).Colorless solid; yield: 160 mg (67%); mp..37–39 8C; 1H NMR
2
3
(200 MHz, CDCl3, 258C, TMS): d=7.44 (d, J
A
Chem. Eur. J. 2008, 14, 6352 – 6368
ꢀ 2008 Wiley-VCH Verlag GmbH & Co.KGaA, Weinheim
www.chemeurj.org
6365

C.Tschierske et al.
7.04–7.00 (m, 2H; Ar-H), 6.94 (d, 3J
(quint, 3J
(H,H)=5.9 Hz, 2H; OCH), 4.20–3.86 (m, 10H; OCH2), 1.81
(quint, 3J
N
Mitchell, W-.D.Cho, S.Uchida, M.Glodde, G.Ungar, X.Zeng, Y.
G
Liu, V.S.K. Balagurusamy, P.A. Heiney,
J. Am. Chem. Soc. 2004,
A
126, 6078–6094.
U
[10] F-.G Tournilhac, LM. .Blinov, J.Simon, SV. .Yablonsky,
Nature
CH3).
1992, 359, 621–623; S.Pensec, F-.G.Tournilhac, P.Bassoul, C.Durli-
at, J. Phys. Chem. B 1998, 102, 52–60.
[11] C.Tschierske, Chem. Soc. Rev. 2007, 36, 1930–1970.
[12] T-shaped bolaamphiphiles: a) M.Kçlbel, T.Beyersdorff, XH. .
Cheng, C.Tschierske, J.Kain, S.Diele, J. Am. Chem. Soc. 2001, 123,
6809–6818; b) X.H.Cheng, M.Prehm, M.K.Das, J.Kain, U.Bau-
3-[4’-(2,3-Dihydroxypropoxy)-3-octadecyloxybiphenyl-4-yloxy]propane-
1,2-diol (Lin18): A mixture of 6 (160 mg, 0.23 mmol) and 10% HCl
(5 mL) in MeOH (20 mL) was heated to reflux for 3 h.The progress of
the reaction was monitored by TLC.The solvent was evaporated and sat.
aq.NaHCO (20 mL) was added to the resulting mixture to obtain a pre-
3
meister, S.Diele, D.Leine, A.Blume, C.Tschierske,
Soc. 2003, 125, 10977–10996; c) X.H. Cheng, M.K. Das, U. Bau-
meister, S.Diele, C.Tschierske, J. Am. Chem. Soc. 2004, 126,
12930–12940; d) M.Prehm, F.Liu, U.Baumeister, X.Zeng, G.
Ungar, C.Tschierske, Angew. Chem. 2007, 119, 8118–8121; Angew.
Chem. Int. Ed. 2007, 46, 7972–7975; e) M.Prehm, G.Gçtz, P.
J. Am. Chem.
cipitate.The precipitate was filtered off and washed with water and pe-
troleum ether.The crude product was purified by repeated crystallization
from methanol.Colorless solid; yield: 120 mg (85%);
1H NMR
(400 MHz, [D5]pyridine, 258C, TMS): d=7.68 (d, 3J
(H,H)=8.8 Hz, 2H;
Ar-H), 7.40 (s, 1H; Ar-H), 7.25 (s, 2H; Ar-H), 7.21–7.19 (m, 2H; Ar-H,
overlapped by pyridine), 4.64–4.44 (m, 6H; OCH, OCH2), 4.30–4.22 (m,
4H; OCH2), 4.12 (t, 3J(H,H)=6.5 Hz, 2H, OCH2CH2), 1.81 (quint, 3J-
N
Bꢁuerle, F.Liu, X.Zeng, G.Ungar, C.Tschierske,
Angew. Chem.
2007, 119, 8002–8005; Angew. Chem. Int. Ed. 2007, 46, 7856–7859.
[13] Correlated Lam phases: M.Prehm, S.Diele, MK. .Das, C.
Tschierske, J. Am. Chem. Soc. 2003, 125, 614–615.
ACHTREUNG
AHCTREUNG
(100 MHz, [D5]pyridine, 258C): d=159.1, 150.2, 149.2, 134.8, 133.9, 128.2
(2C), 119.6, 115.7, 115.5 (2C), 113.5, 72.6, 71.6 (2C), 71.2, 69.7, 64.7, 64.5,
32.3, 30.2 (4C), 30.2 (2C), 30.2, 30.1, 30.1 (2C), 30.1, 29.9, 29.8, 26.6, 23.1,
14.5 ppm; elemental analysis calcd (%) for C36H58O7: C 71.72, H 9.70;
found: C 71.80, H 9.89.
[14] T-shaped facial amphiphiles: a) B.Chen, U.Baumeister, S.Diele,
M.K.Das, X.Zeng, G.Ungar, C.Tschierske
2004, 126, 8608–8609; b) B.Chen, X.Zeng, U.Baumeister, S.Diele,
G.Ungar, C.Tschierske Angew. Chem. 2004, 116, 4721–4725;
J. Am. Chem. Soc.
Angew. Chem. Int. Ed. 2004, 43, 4621–4625; Angew. Chem. Int. Ed.
2004, 43, 4621–4625; c) B.Chen, XB. .Zeng, U.Baumeister, G.
Ungar and C.Tschierske, Science 2005, 307, 96–99; d) B.Chen, U.
Baumeister, G.Pelzl, MK. .Das, XB..Zeng, G.Ungar, C.
Tschierske, J. Am. Chem. Soc. 2005, 127, 16578–16591; e) G.Cook,
U.Baumeister, C.Tschierske, J. Mater. Chem. 2005, 15, 1708–1721;
f) F.Liu, B.Chen, U.Baumeister, X.Zeng, G.Ungar, C.Tschierske,
J. Am. Chem. Soc. 2007, 129, 9578–9579.
Acknowledgements
This work was supported by the government of Sachsen Anhalt through
the Cluster of Excellence “Nanostructured Materials” and as part of the
European Science Foundation EUROCORES Programme SONS, project
SCALES by funds from the DFG and the EC Sixth Framework Pro-
gramme, under contract No.ERAS-CT-2003-989409.
[15] a) H.-A. Klok, S. Lecommandoux, Adv. Mater. 2001, 13, 1217–1229;
b) O.Ikkala, G.ten Brinke, Science 2002, 295, 2407–2409.
[16] a) F.S. Bates, G.H. Fredrickson,
Phys. Today 1999, 32–38; b) V.
Abetz, P.F.W.Simon, Adv. Polym. Sci. 2005, 189, 125–212.
[17] Y.Matsushita, Macromolecules 2007, 40, 771–776.
[1] Handbook of Liquid Crystals, Vol. 1–3 (Eds.: D. Demus, J. W.
Goodby, G.W.Gray, H-.W.Spiess, V.Vill), Wiley-VCH, Weinheim,
1998.
[2] a) C.Tschierske, Annu. Rep. Prog. Chem. Sect. C 2001, 97, 191–268;
b) J.W.Goodby, G.H.Mehl, I.M.Saez, R.P.Tuffin, G.Mackenzie,
[18] Lam phases: a) XH. .Cheng, MK. .Das, S.Diele, C.Tschierske,
Angew. Chem. 2002, 114, 4203–4207; Angew. Chem. Int. Ed. 2002,
41, 4031–4035; b) M.Prehm, X.H.Cheng, S.Diele, M.K.Das, C.
Tschierske, J. Am. Chem. Soc. 2002, 124, 12072–12073; c) N.M.
Patel, M.R. Dodge, M.H. Zhu, R.G. Petschek, C. Rosenblatt, M.
Prehm, C.Tschierske, Phys. Rev. Lett. 2004, 92, 015501; d) N.M.
Patel, IM. .Syed, C.Rosenblatt, M.Prehm, C.Tschierske,
Cryst. 2005, 32, 55–61.
[19] This phase designation was introduced in reference [12c]; in the ear-
lier references[18a,b] LamIso was designated as SmA, LamN as SmAb
and LamSm as LamA (or LamX[12b]).
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Liquid Crystals
FULL PAPER
cal with the organization of the compounds An (n=1–7) in the
Handbook of Thermophysical and Thermochemical Data, CRC,
Boca Raton, 1994; D.R.Lide, Handbook of Chemistry and Physics,
CRC, Boca Raton, 1994.
enantiotropic SmA phases, which were investigated by X-ray scatter-
ing.[12a] However, as no X-ray data were available, it is unclear if the
SmA phases of Lin6 and Lin8 represent conventional SmA phases,
characterized by sharp layer reflections or if they belong to the
strongly distorted SmA+ type phases (as observed for compounds
An with n=3–7, see Figure 2), for which a diffuse scattering is seen
in the small-angle region.This diffuse scattering is attributed to the
mean distance between the disordered microdomains containing the
alkyl chains.The layer reflection is weak or completely absent,
probably due to the low electron density modulation between the
layers of the aromatic cores and the layers of the glycerol units.[12a]
[28] Bolaamphiphiles without lateral chains: F.Hentrich, C.Tschierske,
H.Zaschke, Angew. Chem. 1991, 103, 429–431; Angew. Chem. Int.
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[36] Interestingly, similar arguments were used to understand the tem-
perature dependence of phase transitions in columnar phases
formed by polycatenar molecules.The columnar phases of these
compounds are reversed to the polygonal cylinder structures, as the
rodlike cores are organized in the interior of the columns and the
alkyl chains form a honeycomb-like isotropic continuum.In these
systems the Colhex phases at high temperature were often replaced
by rectangular columnar phases at lower temperature.It was pro-
posed that this phase transition is driven by reduction of chain mo-
bility by reducing temperature, which is not isotropic and prohibits
the formation of aromatic column cores with a circular cross section
and hence, the symmetry is reduced: B.Donnio, B.Heinrich, H.Al-
louchi, J.Kain, S.Diele, D.Guillon, D.W.Bruce,
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[29] The superstructures reported herein represent ordered fluids, which
means that there is a high degree of conformational, rotational, and
translational mobility as indicated by the diffuse character of the
wide-angle scattering seen by X-ray diffraction.Hence, these are
highly dynamic fluid systems in which distinct regions with enhanced
concentration of aromatic cores, regions of the polar hydrogen
bonding groups, and regions of the nonpolar segments coexist in
equilibrium structure with long-range periodicity.
[30] A.Immirzi, B.Perini, Acta Crystallogr. Sect. A 1977, 33, 216–218.
[31] As these cylinder structures represent dynamic (fluid) systems, the
number of molecules in the cross section of the cylinder walls is an
average number that does not necessarily represents an integer
number; the cylinder walls can also be slightly thicker or thinner
than exactly two molecules.
[37] As mentioned in reference [33], with increasing temperature there is
a reduction of the lateral expansion of the alkyl chains, which is
compensated by additional expansion along the column long axis.
This can also contribute to the stabilization of 6-hexagon cylinders
at higher temperature.
[38] M.Prehm, X.Cheng, C.Enders, S.Diele, M.K.Das, U.Baumeister,
F.Liu, X.Zeng, G.Ungar, C.Tschierske, unpublished results.
[39] The small electron density difference between aromatic cores and
glycerol units can also be seen in some electron density maps ob-
tained for the polygonal cylinder phases.[12d]
[40] Though the lateral ether oxygen atom has a low mobility and can be
considered as a part of the rigid core it contributes to the space fill-
ing inside the cylinder frames.
[41] HJ..Deutscher, R.Frach, C.Tschierske, H.Zaschke in
Selected
[32] The structures of all types of cylinder phases reported herein were
confirmed for representative examples of compounds An and their
fluorinated analogues by electron density calculations based on syn-
chrotron data: F.Liu, XB. .Zeng, X.Cheng, C.Tschierske, G.
Ungar, unpublished results.
[33] There is a small reduction of ahex with increasing temperature.For
example, for compound An with n=18 (A18[12a]), the parameter
ahex is 3.65 nm at T=808C and 3.60 nm at T=1308C.The same ten-
dency is found for the Colhex phases of the compounds Linn, but
due to the smaller phase ranges of these compounds the change of
the lattice parameter is much smaller and more difficult to measure
accurately.In the case of classical columnar phases, in which the
flexible alkyl chains form the shell around the column cores also a
reduction of ahex with increasing temperature was observed, but the
temperature dependence is often much stronger.For example, in the
case of star-shaped mesogens, a reduction of ahex by 0.45 nm was ob-
served for a temperature increase by 50 Kelvin (see: M.Lehmann,
Topics in Liquid Crystal Research (Ed.: H. D. Koswig), Akademie
Verlag, Berlin, 1990, pp.1–18; E.Kleinpeter, H.Kçhler, A Lunow,
C.Tschierske, H.Zaschke, Tetrahedron 1988, 44, 1609–1612.
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W.Spiess, S.D.Hudsonk, H.Duank,
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[44] Though these stereogenic centers in the side chain are homogene-
ously chiral, due to the presence of the racemic stereogenic centers
in the glycerol groups, the investigated systems actually represent
mixtures of four distinct diastereomers.
[45] H.-S. Kitzerow, C. Bahr, Chirality in Liquid Crystals, Springer, New
York, 2001.
[46] R.Zentel, M.Brehmer, Acta Polym. 1996, 47, 141–149.
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441–451).This means that increasing chain flexibility causes an ex-
pansion along the column long axis and leads to a shrinkage of the
column diameter.In the case of the polygonal cylinder phases the
polygonal frame not only restricts the expansion of the cylinders, it
also limits the shrinkage of the cylinders and therefore the tempera-
ture dependence of the lattice parameters is in this case relatively
small.
[48] W.-S. Bae, J.-W. Lee, J.-I. Jin, Liq. Cryst. 2001, 28, 59–67; J. An-
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[34] Remarkably, the volume of the lateral chains required for the transi-
tion from a hexagonal honeycomb to a stretched hexagonal honey-
comb is identical for the series of bolaamphiphiles with fluorinated
lateral chains (compounds of type An, see Figure 2, with R=
[50] For shape amphiphiles composed of incompatible disc- and rodlike
units see: R.W.Date, D.W.Bruce,
9012–9013.
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axis was postulated for a polycatenar dithiolium salt: F.Artzner, M.
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[53] Generally, in correlated LamSm phases the in-plane periodicity is
around 1.8 nm for biphenyl derived bolaamphiphiles,[13] correspond-
ing to the shortest possible length of the bolaamphiphilic core with
[35] The cubic expansion coefficients are a=81”10ꢀ5 Kꢀ1 for dodecane
and a=50”10ꢀ5 Kꢀ1 for glycerol: D.R. Lide, H.V. Kehiaian, CRC
Chem. Eur. J. 2008, 14, 6352 – 6368
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www.chemeurj.org
6367

C.Tschierske et al.
most compact glycerol units, whereas in the polygonal cylinder
phases the molecules adopt the most extended conformation with
stretched glycerol units which leads to a length of L=2.1 nm.[11,12a,b]
We assume that also in the Colhex phase of Benz3/6 the glycerol
groups adopt a compact conformation as in the Lam phases.
[54] More detailed studies on this type of Colhex phases in a series of
structurally different bolaamphiphiles confirmed an arrangement of
the rodlike cores parallel to the column long axis: M.Prehm, U.
Baumeister, F.Liu, X.Zeng, G.Ungar, C.Tschierske, unpublished
results.
[55] J.A.Schrçter, C.Tschierske, M.Wittenberg, J.H.Wendorff,
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Tschierske, J. Mater. Chem. 1998, 8, 2611–2626; J.A. Schrçter, C.
Tschierske, M.Wittenberg, J.H.Wendorff, Angew. Chem. 1997, 109,
1160–1163; Angew. Chem. Int. Ed. Engl. 1997, 36, 1119–1121.
Received: January 23, 2008
Published online: June 2, 2008
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Chem. Eur. J. 2008, 14, 6352 – 6368