The 2D-correlated structures of a lyotropic liquid crystalline diol with a phenylpyrimidine core

Article abstract of DOI:10.1039/c2jm32868b

Even though the fluid tilted smectic C (SmC) phase is one of the most common phases in thermotropic liquid crystals, the lyotropic analogue to SmC is practically unknown so far. One of the rare examples, a lyotropic liquid crystalline diol, which was reported in 1991 to show this phase, was re-examined by means of detailed X-ray diffraction and polarised optical microscopy. Although the diol possesses a smectic C promoting phenylpyrimidine core, it was not possible to verify the existence of a SmC-analogue lyotropic phase. Instead, the phase diagram shows the existence of five different lyotropic phases identified as nematic, lamellar L_α and hexagonal as well as two novel complex 2D-correlated lyophases. Results obtained by electron density calculations and X-ray diffraction data strongly suggest that the structure of one of these phases possesses a pseudo-c2mm symmetry and is built up of two different kinds of columns, whereas the other one is a ribbon phase of the oblique plane group p2.

Full text of DOI:10.1039/c2jm32868b

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PAPER
The 2D-correlated structures of a lyotropic liquid crystalline diol with a
phenylpyrimidine core†
Johanna R. Bruckner,a Daniel Krueerke,a Jan H. Porada,b Stefan Jagiella,a Dirk Blunkc
a
*
and Frank Giesselmann
Received 7th May 2012, Accepted 16th July 2012
DOI: 10.1039/c2jm32868b
Even though the fluid tilted smectic C (SmC) phase is one of the most common phases in thermotropic
liquid crystals, the lyotropic analogue to SmC is practically unknown so far. One of the rare examples, a
lyotropic liquid crystalline diol, which was reported in 1991 to show this phase, was re-examined by
means of detailed X-ray diffraction and polarised optical microscopy. Although the diol possesses a
smectic C promoting phenylpyrimidine core, it was not possible to verify the existence of a SmC-
analogue lyotropic phase. Instead, the phase diagram shows the existence of five different lyotropic
phases identified as nematic, lamellar La and hexagonal as well as two novel complex 2D-correlated
lyophases. Results obtained by electron density calculations and X-ray diffraction data strongly suggest
that the structure of one of these phases possesses a pseudo-c2mm symmetry and is built up of two
different kinds of columns, whereas the other one is a ribbon phase of the oblique plane group p2.
been given by Schaffheutle and Finkelmann5 using X-ray
Introduction
diffraction and by Ujiie and Yano6 by means of optical textures.
However, the important questions about the stability of SmC-
analogue structures in lyotropics as well as the presence and
characteristics of chirality effects on these structures are yet
unresolved. Due to the substantial similarities of biological
membranes to lamellar phases,7 these points could for instance
lead to a better understanding of chirality related membrane
processes, e.g. inclusion of chiral proteins or steroids.
In thermotropic liquid crystals the SmC phase, known since the
pioneering work of Arnold and Sackmann in 1959,1 is one of the
most common phases. The SmC as well as the SmA phases are
1D-stacks of 2D-fluid layers in which the molecules are orien-
tationally ordered along a common direction, the so-called
director. The SmC phase is distinguished from the orthogonal
SmA phase by a temperature dependent tilt of the director with
respect to the smectic layer normal. Since the 1980s the chiral
variant, denoted as SmC*, has attracted considerable scientific
interest due to its unique macroscopic chirality effects,2 such as
helicity of the tilt direction and spontaneous electric polarisation
of the smectic layers, which render SmC* to be ferroelectric.3
Even though the SmC and SmC* phases are very common in
thermotropic liquid crystals, they are practically unknown in
lyotropic liquid crystals, which are formed by aggregates of
amphiphilic molecules in the presence of a solvent. Indeed, the
In search of a lyotropic SmC-analogue phase, we started to
investigate the diol 5-[4-(5-n-heptylpyrimidine-2-yl)phenoxy]
pentane-1,2-diol/water system (Fig. 1), which has formerly been
reported to exhibit a nematic, a lamellar La (SmA-analogue) and
a lyotropic SmC-analogue phase, identified by texture investi-
gations using polarised optical microscopy.8 This diol combines
the typical structural properties of a thermotropic calamitic
mesogen and a lyotropic amphiphile with its aromatic core and
diol headgroup, respectively. The phenylpyrimidine is known as
a SmC promoting motif9 and therefore it should be an ideal
candidate for the formation of a fluid lamellar tilted phase. But in
0
well-known lamellar Lb phase is tilted (like SmC); however this
phase is not fluid but rather gel-like.4 So far, undoubted evidence
of the existence of the SmC-analogue lyotropic phase has only
aInstitute of Physical Chemistry, University of Stuttgart, 70569 Stuttgart,
Germany. E-mail: f.giesselmann@ipc.uni-stuttgart.de; Fax: +49 (0)
711/685-62569; Tel: +49 (0)711/685-64460
bDepartment of Chemistry and Biochemistry, University of Colorado,
80309 Boulder, CO, USA
c
€
Institute of Organic Chemistry, University of Cologne, 50939 Koln,
Germany
Fig. 1 Chemical structure of 5-[4-(5-n-heptylpyrimidine-2-yl)phenoxy]
pentane-1,2-diol. For the investigations the racemic mixture (rac-1) as
well as the S-enantiomer (S-1, ee ¼ 66%) were used.
† Electronic supplementary information (ESI) available: X-ray
diffraction data and details on the calculation of the electron density
maps. See DOI: 10.1039/c2jm32868b
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the course of our investigations, doubts grew about the correct
assignment of the SmC-analogue phase. Hence, we rein-
vestigated the phase behaviour of the diol/water system in detail.
Herein we now report the results of these investigations
including several new 2D-correlated structures. Next to a revised
phase diagram, the paper covers extensive X-ray investigations
and calculations of electron density maps for a comprehensive
characterisation of all liquid crystalline phases formed by the
diol/water system.
Results and discussion
Phase sequence and textures
The phase diagram of the diol/water system was revised by
polarised optical microscopy. For this investigation the S-enan-
tiomer (S-1) was used, but several points of the phase diagram
were checked against samples of the racemic mixture (rac-1) and
no difference could be detected within the measurement accu-
racy. The result is shown in Fig. 2a. The pure diol does not form
any thermotropic liquid crystalline phase but the addition of only
about 1 wt% water leads to the appearance of a nematic or chiral
nematic phase, respectively (Fig. 2b). Further addition of water
results in the formation of a lamellar La phase which is stabilised
by increasing water concentration. In the phase diagram the
ꢀ
stabilisation of the La phase settles at a temperature of 107 C
over a wide water concentration range (ꢁ3 to 40 wt%). By
increasing the water concentration above roughly 40 wt%, a
phase transition from the La phase to a hexagonal phase is
observed. The La phase shows typical fan shaped (Fig. 2c) or
homeotropic textures. By cooling, the La phase turns into a
further phase, which was previously identified as SmC-
analogue.8 It is the most stable phase in the phase diagram and
exists over a very broad concentration and temperature range,
ꢀ
down to about 45 C. In areas with planar alignment of the La
phase this mesophase exhibits a platelet texture (Fig. 2d), while a
pseudo-focal conic texture is seen in areas where the La phase
was oriented homeotropically (Fig. 2e). This indicates that this
mesophase cannot be a SmC-analogous phase as a textural
change from a fan texture into a broken fan texture or from a
homeotropic texture into a schlieren texture would be mandatory
for such a phase transition. The appearance of the pseudo-focal
conic texture rather suggests the existence of a 2D-correlated
structure consisting of some kind of columns. As will be pre-
sented later this mesophase belongs to the plane group p2 and
will therefore be called p2 phase in the following.
Fig. 2 (a) Schematic phase diagram of the diol/water system. Textures
under crossed polarisers of (b) the N* phase, (c) the La phase, (d) the p2
phase (formerly planar region in the La phase; assumed to be SmC-
analogue), (e) the p2 phase (formerly homeotropic), (f) the hexagonal
phase and (g) the pseudo-c2mm phase.
(Fig. 3). The birefringence is about Dn ¼ 0.1, which is remarkably
high for a lyotropic liquid crystal and close to the values of
thermotropic liquid crystals. This is also reflected in the colourful
textures (cf. Fig. 2) and is caused by the high diol concentration.
Due to the large polarisability along the aromatic system the
higher refractive index should be parallel to the long molecular
axis independently of the aggregate’s shape. Thus, the nematic
phase may possibly be built up by single molecules or oblate
micelles. The existence of cybotactic groups, as revealed by X-ray
diffraction experiments, suggests oblate micelles to be more
likely. Due to the low concentration of water they are most
probably inverted.
Increasing the water concentration over 40 wt% leads to the
formation of two further so far unreported mesophases of the
diol/water system. At temperatures between 105 ꢀC and 88 ꢀC a
hexagonal phase forms which shows the typical pseudo focal
conic textures (Fig. 2f). At lower temperatures the phase changes
into a structure of pseudo-c2mm symmetry as identified by the
results presented later in this paper. This phase shows fairly
regular and remarkable textures consisting of differently sized
trapezoid planes (Fig. 2g).
Properties of the nematic and the lamellar phases
Depending on water concentration and temperature the layer
spacings in the lamellar La phase range from 3.5 nm to 4.2 nm.
Since the length of the diol is l ¼ 2.36 nm10 a partial double layer
The nematic phase formed by the racemic mixture of the diol
(rac-1/water) exhibits an optical positive and uniaxial behaviour
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centred, thus its structure belongs to the plane group p2. The
calculated lattice parameters a, b and g are plotted in Fig. 4c for
different temperatures and two water concentrations, showing
that a change of the latter has the biggest impact on the value of a
and only minor influence on b and g. It also appears that the unit
cell is quite large and therefore a very sophisticated SAXS setup
is needed to separate the single reflexes. This may explain why the
earlier phase assignment was incorrect, as the WAXS measure-
ment might be mistaken for a SmC-analogue phase.
To determine the structure of the p2 phase the electron density
map (Fig. 5a) was reconstructed using the powder diffraction
data of the small angle reflections (see ESI†).11 In this represen-
tation the high electron density region of the solvated hydrophilic
headgroups is pictured in purple, while the intermediate electron
density of the aromatic cores is visualized in green and the low
density regions of the alkyl chains in orange. The map shows that
the p2 phase consists of ribbons or deformed columns, respec-
tively. These ribbons may either be described as normal with
the alkyl chains aligned towards the center or as inverted with the
diol headgroups including the water molecules arranged in the
middle of the ribbons. Due to the small water to diol ratio
between 1 : 1 and 10 : 1, inverted columns appear to characterise
the structure more properly. The ribbons still reflect the former
layers of the lamellar La phase in the direction of b, but are
staggered in the direction of a. The ribbons are tilted with an
angle of approximately 16ꢀ with respect to b.
Fig. 3 Optical properties of the nematic phase in the rac-1/water system:
(a) measured refractive indices of the isotropic phase niso, the extraordi-
nary refractive indices neo and the ordinary refractive indices no of the
nematic phase as well as the calculated mean refractive indices nꢀ; (b)
picture obtained by conoscopy on a homeotropic oriented sample.
arrangement for the structure of the lamellar La phase is
reasonable.
The structure of the p2 phase
By performing X-ray diffraction experiments on the p2 phase, the
typical diffuse reflections of a liquid crystal are observed in the
wide angle region (Fig. 4a). In the small angle region a complex
two-dimensional diffraction pattern is found which shows an
exceptionally large number of reflections (Fig. 4b). Due to the
good alignment of the sample it is possible to index the reflections
in this pattern as shown in Fig. 4b. An indexation of all reflec-
tions may be obtained when assuming that the diffraction
pattern originates from two oriented domains of a highly ordered
2D-correlated structure. The supposed unit cell is oblique and
The formation of the p2 phase and the observed textural
change may be explained compellingly with the structure based
on the calculated electron density map. By cooling from the
lamellar La phase the solvation sphere of the diol headgroups
decreases and thereby reduces the volume of the hydrophilic
sublayer, which is expressed by gradual layer shrinkage.
Reaching the transition temperature, a negative interface
curvature around the hydrophilic regions is enthalpically fav-
oured, causing the layers to break into the ribbons of the p2
phase. As the ribbons are staggered there are two possible main
directions in which the layers may break. At the phase transition
the p2 phase propagates along both directions as observed in an
aligned sample using polarised optical microscopy (Fig. 6). The
angle between these directions has the same value as the angle g
of the unit cell.
This also explains the observation of domains with two
different orientations emerging from a single domain in the La
phase regarding the X-ray diffraction pattern.
Fig. 4 X-ray diffraction pattern of the p2 phase (a) in the WAXS area
and (b) in the SAXS area with indexation for one domain; (c) lattice
parameters a (circles BC), b (diamonds >A) and g (squares ,-) for
7 wt% (closed symbols) and 31 wt% water (open symbols) respectively.
Fig. 5 The structure of the p2 phase: (a) calculated electron density map
and (b) schematic model in which the sketched columns include the
hydrophilic parts and the aromatic core of the diol.
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Fig. 6 (a) Picture as seen through crossed polarisers at the phase tran-
sition of an aligned sample from the lamellar La phase to the oblique p2
phase. The two domains of the growing p2 phase are emphasised with
arrows and include the angle g. The layers of the lamellar phase are
indicated with a dashed line. (b) Schematic model of the two domain’s
unit cells with the diagonals as the growing direction.
According to the symmetry the p2 phase is indeed of tilted and
polar nature just like the thermotropic SmC* phase. However, it
has a highly ordered structure and the tilt is not referring to single
molecules, but to entire ribbons. Therefore electrical switching
between the two orientations might not be possible.
Fig. 8 (a) Electron density map and (b) schematic model of the hexag-
onal phase; (c) electron density map and (d) schematic model of the
pseudo-c2mm phase.
The hexagonal and the pseudo-c2mm phases
The one dimensional X-ray diffraction patterns of the hexagonal
and the pseudo-c2mm phases are plotted in Fig. 7a and b,
respectively. Due to the increased water concentration it has not
been possible to align the samples.
ꢀ
ꢀ
between 88 C and 100 C and excess water. The reconstructed
electron density map (Fig. 8a) shows that the hexagonal phase is
built up of inverted columns, taking into account the still small
water to diol ratio of about 19 : 1 for a lyotropic liquid crystal.
However, in contrast to the p2 phase, the hexagonal phase holds
two different kinds of columns (Fig. 8b). The column in the
origin of the unit cell contains only little water while the water
concentration in the other two columns is significantly higher.
This is probably caused by the low solubility of the diol in water
whereupon the smaller columns mark the maximum uptake of
solvating water.
The indexation of the hexagonal phase is based upon the plane
group p6mm with a lattice parameter a of 8.2 nm to 7.3 nm
The low temperature phase is indexed on the plane group
c2mm. But as the experiments were performed with the racemic
as well as with the enantiomeric diol rac-1 and S-1, respectively,
the plane group of this phase is at least in the case of S-1 not
allowed to contain any reflection symmetry. Hence, this phase is
only centered apparently and is therefore termed pseudo-c2mm
phase. The reconstructed electron density map (Fig. 8c)
demonstrates the close relation of this phase to the hexagonal
phase. The pseudo-c2mm phase results from the high tempera-
ture phase by elongation of the unit cell in the direction of a and
compression in the direction of b. The lattice parameters a and b
at 64 ꢀC and excess water were found to be 19.5 nm and 5.5 nm,
respectively.
Experimental
General information
Samples for polarised optical microscopy were prepared by
quickly heating the desired diol/water mixture above the melting
point between two glass plates followed by sealing the sample
with the UV curable adhesive NOA73 to avoid a loss of water.
Due to the low solubility of the crystalline diol in water it was not
Fig. 7 Powder diffraction pattern of (a) the hexagonal phase and (b) the
pseudo-c2mm phase.
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possible to determine the exact concentration in the samples.
Therefore the phase diagram in Fig. 2 has to be understood as a
qualitative description. The samples were examined with a
polarised optical microscope (BHS, Olympus) equipped with a
hot stage (LTS 350, Linkam). Optical properties were measured
using reflectometric interference spectroscopy (Alton Instru-
ments Lambda LS 2000)12 or a l-compensator,13 respectively.
Samples for the X-ray diffraction experiments were prepared
in Mark capillaries (Hilgenberg, 0.7 mm diameter) and measured
with a Bruker Nanostar system applying CuKa radiation
potassium iodide were added, the vessel was sealed and micro-
waved for 2 hours at 100 ꢀC. The solution was filtered, the
solvent was removed and the residue was purified chromato-
graphically (SiO2, 3 : 1 c-Hex/EtOAc, Rf ¼ 0.56) yielding 327 mg
(97%) of 4 as a colourless solid. mp (DSC): Cr 44.4 SmC 59.4 N
60.1 I (from c-Hex–EtOAc). dH (300 MHz, CDCl3) 8.56 (2H, s;
4-H and 6-H), 8.36 (2H, d, J 8.9; 20-H and 60-H), 6.97 (2H, d, J
8.9; 30-H and 50-H), 5.86 (1H, ddt, J 16.9, 10.1, 6.6; 400-H), 5.07
(1H, ddt, J 17.1, 1.7, 1.7; cis-500-H), 5.01 (1H, ddt, J 10.2, 1.5, 1.5;
trans-500-H), 4.04 (2H, t, J 6.4; 100-H), 2.58 (2H, t, J 7.6;
CH2CH2(CH2)4CH3), 2.32–2.18 (2H, m; 300-H), 1.96–1.86 (2H,
m; 200-H), 1.64 (2H, p, J 7.4; CH2CH2(CH2)4CH3), 1.40–1.24
ꢁ
(l ¼ 1.5418 A). Alignment of the samples was achieved by slowly
cooling in a magnetic field (ꢁ1 T) using an integrated tempera-
€
ture controller (TCPU H, MRI Physikalische Gerate GmbH).
(8H, m; CH2CH2(CH2)4CH3), 0.94–0.83 (3H, t, J 6.8;
NMR spectra were recorded on a Bruker DPX 300. Infrared
spectra were obtained using a Perkin-Elmer Paragon 1000 FTIR
spectrometer as ATR signals on a ZnSe crystal. Mass spectra
were taken on a Finnigan MAT Incos 50 Galaxy System (low
resolution), a Finnigan MAT 900 S (high resolution, CI) or a
Bruker Daltonics micrOTOF-Q (high resolution, ESI). CHN-
combustion analyses were measured using an Elementar Vario
EL Instrument. The enantiomeric excess was determined by
analytic HPLC (Daicel Chiralcel OJ, hexane/2-propanol 90 : 10
at 1.00 nl minꢂ1).
CH2CH2(CH2)4CH3). dC (75 MHz, CDCl3) 162.67 (s; C2),
161.26 (s; C40), 157.01 (d; C4 and C6), 137.87 (d; C400), 132.15 (s;
C5), 130.50 (s; C10), 129.56 (d; C20 and C60), 115.31 (t; C500),
114.60 (d; C30 and C50), 67.43 (t; C100), 31.85 (t;
CH2CH2(CH2)3CH2CH3), 30.88 (t; CH2CH2(CH2)3CH2CH3),
30.28 (t; CH2CH2(CH2)3CH2CH3), 30.22 (t; C300), 29.12 (t;
CH2CH2(CH2)3CH2CH3), 28.62 (t; C200), 22.72 (t;
CH2CH2(CH2)3CH2CH3), 14.13 (q; CH2CH2(CH2)3CH2CH3).
nmax/cmꢂ1 3077 (w), 3017 (w), 2994 (w), 2951 (m), 2924 (s), 2853
(m), 1640 (w), 1606 (m), 1583 (s), 1540 (m), 1513 (m), 1467 (m),
1429 (s), 1393 (m), 1327 (m), 1299 (m), 1251 (s), 1167 (m), 1106
(m), 1054 (m), 1028 (m), 991 (m), 935 (m), 910 (m), 845 (m), 822
(w), 796 (s), 759 (w), 721 (w), 701 (w), 653 (m); LRMS (EI, 70 eV)
m/z: 69 (20%) [C5H9+], 119 (12) [C7H4NO+], 158 (19)
[C9H6N2O+], 185 (100) [M+-C6H13-C5H9], 199 (12) [M+-C5H11-
C5H9], 253 (7) [M+-C6H13], 270 (24) [M+-C5H9], 338 (33) [M+].
HRMS (EI, 70 eV) m/z calcd. for C22H30N2O: 338.2358. Found:
338.236. Anal. calcd for C22H30N2O: C, 77.82; H, 8.90; N, 8.21.
Found: C, 78.06; H, 8.93; N, 8.28%.
Synthesis of 5-[4-(5-n-heptylpyrimidine-2-yl)phenoxy]pentane-
1,2-diol
(rac)-500-[40-(5-n-Heptylpyrimidine-2-yl)phenoxy]pentane-1,2-diol
(rac-1) was synthesised according to the procedure described in
ref. 14.
The chiral compound S-1 was obtained by a sequence of
etherification of the commercially available 4-(5-heptylpyr-
imidin-2-yl)phenol (3, Synthon Chemicals GmbH) with 5-bro-
mopent-1-ene followed by an asymmetric dihydroxylation as
outlined in Scheme 1.
(S)-500-[40-(5-n-Heptylpyrimidine-2-yl)phenoxy]pentane-1,2-diol
(S-1). 327 mg (0.97 mmol) of 4 were solved in 7 ml tert-butanol
and dropped slowly into a cooled solution of 1.4 g AD-mix-a 15
in 7 ml water. The reaction mixture was stirred for 72 hours at 6
ꢀC and for 48 hours at room temperature. The mixture was
extracted twice with ethyl acetate, the organic phase was dried
over magnesium sulfate and the solvent was evaporated. The
residue was purified chromatographically (SiO2, EtOAc) yielding
334 mg (0.88 mmol, 93%) of S-1 as a colourless solid; ee 66%. dH
(300 MHz, CDCl3) 8.56 (2H, s; 4-H and 6-H), 8.33 (2H, d, J 8.7;
30-H and 50-H), 6.97 (2H, d, J 8.8; 20-H and 60-H), 4.06 (2H, t, J
5.9; 500-H), 3.87–3.74 (1H, m, 200-H), 3.68 (1H, dd, J 10.9, 3.1; 100-
Ha), 3.48 (1H, dd, J 11.0, 7.5; 100-Hb), 2.85–2.00 (2H, bs; OH),
2.59 (2H, t, J 8.2; CH2CH2(CH2)4CH3), 2.05–1.80 (2H, m; 400-H),
1.77–1.50 (4H, m; 300-H and CH2CH2(CH2)4CH3), 1.44–
5-Heptyl-2-[40-(pent-400-en-100-yloxy)phenyl]pyrimidine (4). In a
sealable 10 ml microwave vessel, 270 mg (1.0 mmol) 4-(5-hep-
tylpyrimidin-2-yl)phenol (3) were solved in 6 ml acetone. 164 mg
(0.13 ml, 1.1 mmol) 5-bromopent-1-ene (2), 460 mg (2.0 mmol)
tripotassium phosphate monohydrate and 17 mg (0.1 mmol)
1.19 (8H, m; CH2CH2(CH2)4CH3), 0.87 (3H, t,
J 6.4;
CH2CH2(CH2)4CH3). dC (75 MHz, CDCl3) 162.50 (s; C2),
160.96 (s; C10), 157.09 (d; C4 and C6), 132.35 (s; C5), 130.48
(s; C40), 129.57 (d; C30 and C50), 114.54 (d; C20 and C60),
71.99 (d; C200), 67.99 (t; C500), 66.91 (t; C100), 31.86 (t;
CH2CH2(CH2)3CH2CH3), 30.94 (t; CH2CH2(CH2)3CH2CH3),
30.27 (t; CH2CH2(CH2)3CH2CH3), 29.98 (t; C300), 29.14 (t;
CH2CH2(CH2)3CH2CH3), 25.58 (t; C400), 22.75 (t;
CH2CH2(CH2)3CH2CH3), 14.21 (q, CH2CH2(CH2)3CH2CH3).
nmax/cmꢂ1 3450 (bw), 2951 (m), 2924 (m), 2853 (m), 2779 (w),
1738 (m), 1667 (w), 1656 (w), 1606 (m), 1583 (m), 1541 (m), 1512
Scheme 1 Synthesis of (S)-500-[40-(5-n-heptylpyrimidine-2-yl)phenoxy]
pentane-1,2-diol (S-1). (a) K3PO4$H2O, KI, acetone, microwave, 100 ꢀC,
2 h, 97% and (b) AD-mix a, t-BuOH, H2O, 6 ꢀC, 72 h, r.t., 48 h, 93%.
18202 | J. Mater. Chem., 2012, 22, 18198–18203
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Fig. 9 Liquid crystalline phases of the diol/water system: (a) nematic phase, (b) lamellar phase, (c) p2 phase, (d) hexagonal phase and (e) pseudo-c2mm
phase.
(w), 1430 (s), 1371 (m), 1327 (m), 1298 (m), 1236 (s), 1167 (m),
Acknowledgements
1106 (m), 1030 (m), 982 (w), 937 (w), 845 (m), 816 (w), 796 (s),
Financial support by the Deutsche Forschungsgemeinschaft
€
(DFG Gi 243/4) and the Landesgraduiertenforderung is grate-
722 (w), 701 (w), 653 (m), 611 (s). LRMS (EI, 70 eV) m/z: 158
(19%) [C9H6N2O+], 185 (87) [M+-C5H11O2-C6H13], 270 (100)
[M+-C5H11O2], 341 (19) [M+-CH2O], 372 (18) [M+]. HRMS (pos.
ESI) m/z calcd for [C22H32N2O3 + Na]+: 395.2311. Found:
395.2302. Anal. calcd for C22H32N2O3: C, 70.94; H, 8.66; N, 7.52.
Found: C, 70.96; H, 8.66; N, 7.51%.
fully acknowledged. We thank C. Tschierske, University of
Halle, S. Strobel and U. Dawin, University of Stuttgart, for
fruitful discussions.
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Conclusions
We found that the lyotropic phase of 5-[4-(5-n-heptylpyr-
imidine-2-yl)phenoxy]pentane-1,2-diol, which was previously
assumed to be SmC-analogue, is indeed a rather complex 2D-
correlated structure. Thus, this is another striking example of
the unresolved problem why tilted fluid structures – even
though quite common in thermotropics – are rarely found in
lyotropics.
7 M. E. Starzak, The Physical Chemistry of Membranes, Academic
Press, Inc., 1984; G. H. Brown, J. J. Wolken, Liquid Crystals and
Biological Structures, Academic Press, Inc., 1979.
8 N. Pietschmann, A. Lunow, G. Brezesinski, C. Tschierske, F. Kuschel
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9 Q. Song, D. Nonnenmacher, F. Giesselmann and R. P. Lemieux,
€
Chem. Commun., 2011, 47, 4781; S. M. Kelly and J. Funfschilling,
Ferroelectrics, 1996, 180, 269.
10 Calculated with Chem3D Pro 12.0 by applying a MM2 force field.
11 H. Duan, S. D. Hudson, G. Ungar, M. N. Holerca and V. Percec,
Chem.–Eur. J., 2001, 7, 4134; X. Zeng, R. Kieffer, B. Glettner,
Nevertheless the diol/water system exhibits a very rich and
interesting polymorphism with five different mesophases, the
structures of which are summarised in Fig. 9. All meosphases
are of inverted nature, reflecting the uncommon molecular
composition of the diol, i.e., an aromatic core structure, typical
of thermotropics, linked to a hydrophilic headgroup, typical of
lyotropics. At low water concentrations the nematic phase is
formed of discotic micelles. Increasing the water concentration,
the micelles fuse into the layers of the lamellar phase. These
layers then break into the ribbons of the p2 phase on cooling.
By increasing the water concentration further the ribbons turn
into the circular columns of the hexagonal phase, which are able
to include a bigger amount of water molecules than the rather
flat ribbons. Finally cooling leads to the more ordered pseudo-
c2mm phase by elongating the hexagonal phase in one dimen-
sion. Summing up, the diol/water system shows the typical
phase sequence of a lyotropic liquid crystal, regarding the
nematic, the lamellar and the hexagonal phases. However these
conventional phases are mediated by rather uncommon 2D-
correlated phases, which seem to be a distinctive feature for
mesogens on the borderline of thermotropic and lyotropic liquid
crystals.
€
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15 ‘‘AD-mix-a’’ is a commercially available standard mixture of auxiliary
reagents in asymmetric organic synthesis. See for example Sigma-
Aldrich product number 392758.
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J. Mater. Chem., 2012, 22, 18198–18203 | 18203