Molecular factors responsible for the formation of the axially polar columnar mesophase ColhPA

Article abstract of DOI:10.1002/chem.200601192

The structure of hexacatenar bent-shape molecules has been systematically modified in order to determine the main molecular factors responsible for the appearance of the axially polar columnar mesophase. It was found that the stability of the polar phase

Full text of DOI:10.1002/chem.200601192

FULL PAPER
DOI: 10.1002/chem.200601192
Molecular Factors Responsible for the Formation of the Axially Polar
Columnar Mesophase ColhPA
Joanna Matraszek,[a] Jozef Mieczkowski,[a] Damian Pociecha,*[a] Ewa Gorecka,[a]
Bertrand Donnio,[b] and Daniel Guillon[b]
Abstract: The structure of hexacatenar
bent-shape molecules has been system-
atically modified in order to determine
the main molecular factors responsible
for the appearance of the axially polar
columnar mesophase. It was found that
the stability of the polar phase is very
sensitive to the subtle modifications of
the molecular shape: the phase is
solely preserved if the modification is
made at the terminal parts of the meso-
genic core, whilst any other modifica-
tions destabilize the phase. It can be
concluded that the main factor driving
the transition between the phase made
of flat supramolecular discs and the ax-
ially polar phase made of the cone-like
units is the ability to fulfill close pack-
ing conditions in order to eliminate
voids between neighboring molecular
rigid cores.
Keywords: liquid crystals · self-as-
sembly · supramolecular chemistry ·
X-ray diffraction
Introduction
chemistry” approach in which bent-core molecules interact
through noncovalent intermolecular forces to form cone-like
self-assemblies.[5] This supramolecular approach is the first
successful attempt to obtain polar, electrically switchable
phase, despite several attempts to apply the same principle
to columnar phases made of dendrimers[6] and different
types of nonflat objects (mainly macrocycles).[7–17]
Generally, there are two broad classes of polar fluids. In the
first class there are materials made of chiral rod-like or disc-
like molecules; these materials have been studied for nearly
30 years[1] and the principles of their molecular designing
are rather well understood today. The materials of the
second class, discovered a few years ago,[2] are made from
achiral, bent-core (“banana”) molecules, in which the self-
organization into polar structures appears spontaneously as
a result of broken orientational symmetry. Achiral bent-core
molecules form an unexpectedly rich variety of structures, a
result of the interplay between polarity, nanoscopic chirality
and density modulations.[3,4] The most important research in
the field of “banana” molecules concentrates on studies of
lamellar and broken-layer-type columnar phases that have
been showed to be polar and switchable under electric field.
However, recently it has been demonstrated that the polarly
ordered phases can be also formed by a “supramolecular
The columnar phases of studied bent-core polycatenar
materials[5,17,18] are formed by the self-organization of few
molecules packed into an overall flat discoid assembly (Colh
phase) or into a conical-shape unit (ColhPA phase); in both
cases these elementary building blocks are stacked to form
columns, which are arranged into a hexagonal lattice. The
structure of the Colh phase is non-polar while the ColhPA
phase has antiferroelectric properties with electric polariza-
tion vectors oriented along the column axis. Inconsistency
between hexagonal lattice of columns and antiferroelectrici-
ty of the whole structure is solved by appearance of addi-
tional superstructure: the columns are broken along their
axis into blocks having ferroelectric order and the direction
of polarization alternates between the blocks.[5,17,18] In an ex-
ternal electric field the polarization vectors switch by the
collective re-orientation of the molecules forming supra-
molecular cones, the measured value of spontaneous polari-
zation being typically ꢀ200 nCcmÀ2. The Colh–ColhPA phase
transition can be easily detected by the optical methods
(Figure 1). There is a pronounced decrease of the optical bi-
refringence for the light propagating perpendicularly to the
column axis, as the deformations of flat discs into cones in-
[a]Dr. J. Matraszek, Prof. J. Mieczkowski, Dr. D. Pociecha,
Prof. E. Gorecka
Department of Chemistry, Warsaw University
ul. Pasteura 1, 02-093 Warsaw (Poland)
Fax : (+48)22-822-5996
E-mail: pociu@chem.uw.edu.pl
[b]Dr. B. Donnio, Dr. D. Guillon
IPCMS, Groupe des MatØriaux Organiques
BP 43, 23 rue du Loess, 67037 Strasbourg Cedex (France)
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XRD data, in which all the structure factors were taken pos-
1
=
2
itive, as F=I , reveal much sharper profiles in ColhPA phase
than in Colh phase. This shows that in ColhPA phase concen-
tration of the mass increases near the column axis
(Figure 2).
Figure 1. Light transmission through the circular domain, measured as a
function of temperature for compound 9b in three micron cell, reveals a
decrease of optical birefringence at Colh–ColhPA phase transition. In the
inset the texture of Colh and ColhPA phases.
creases the refractive index along the columnar axis but de-
creases the refractive index perpendicular to the columnar
axis.[18] The phase transition is also accompanied by noticea-
ble softening of the dielectric response in the Colh phase
due to the formation of the polarly ordered lower tempera-
ture phase.[18]
Our current aim was to identify some of the molecular
factors driving the formation of the conical phase as well as
describing the influence of the molecular modifications on
the phase stability. In order to carry out this systematic
study, 28 new polycatenar bent-shaped compounds were
prepared, grouped into three main families (compounds
1–8, 9 and 10), depending on the structural modifications.
Figure 2. Electron density maps obtained in the plane perpendicular to
the column axis in Colh and ColhPA phases for compound 1a. The relative
intensities of XRD signals used for electron density calculations were, in
Colh phase: I10/I11/I20 130:1:2; in ColhPA: I10/I11/I20/I21 130:10:10:2.
In order to recognize and identify the possible factors re-
sponsible for the “conical” phase formation, several modifi-
cations were made at the basic molecular structure level,
though preserving the overall molecular motif of 1. The
outer, inner and central parts of molecule were independ-
ently modified, the modifications included selective chlori-
nation (2–4, 6), methylation (5) and changes of terminal
alkyl chain number (7) or the length of “banana” branches
(8). It was found that the only modification preserving the
“conical” phase is the substitution at the most outer part of
molecular core. If one halogen atom is substituted at each
outer phenyl ring, compounds 2a and 2b, the phase transi-
tion temperatures subtly decrease and the phase sequence
remains unchanged. This substitution only slightly increases
the column diameter of both the Colh and the ColhPA
phases, showing that the basic structure of the column stra-
tum is not affected. Moreover, while the substitution of two
halogen atoms at each of the most outer rings (compound 3)
does not change the columnar structure and phase sequence,
the phase transition temperatures being significantly low-
ered, the substitution of halogen atom at any inner ring of
the molecular branch (compounds 4a–c) destabilizes totally
the conical phase: the apolar columnar hexagonal phase is
observed exclusively over a broad temperature range. The
presence of a methyl group at the central ring at position 4
(compounds 5a and 5b) or halogen atom at position 3 (com-
pound 6) also prevents the conical phase appearance, likely
due to steric hindrances. Decreasing the number of terminal
alkyl chains (compounds 7a and 7b) makes the melting and
clearing temperatures very high, that forbids further system-
atic studies of these tetracatenar materials, but it seems that
the conical phase is also formed in this case. Finally, de-
creasing the banana branch length by one phenyl ring (com-
Results and Discussion
The phase sequences, phase transition temperatures and
thermal effects, as well as the crystallographic unit cell pa-
rameters for the studied compounds are given in Table 1.
The molecules of the basic homologues series, compounds
1a–f, have a pyridine central ring linked by ethylene spacers
to four-ring phenyl-biphenyl-phenyl branches. At the termi-
nal phenyl ring three alkyl chains are attached, to ensure
the tendency for large curvature of the column interface.
Based on the X-ray diffraction (XRD) data and assuming a
density close to 1 gcmÀ3 in the mesophase for these com-
pounds, it was deduced that about 3–4 molecules self-assem-
ble to form the elementary columnar stratum, which corre-
sponds to 18–24 alkyl chains in the outer coat of the
column. The dependence of column diameter, D, on the
number of carbon atoms in terminal alkyl chains, n, ÀdD/dn
ꢀ1 Š suggests that there is roughly constant ratio of interdi-
gitated part of the chains with respect to their overall
length. All homologues, 1a–f, show the Colh–ColhPA phase
transition at which the diameter of the column decreases in
accordance with the proposed model for this phase transi-
tion.[5] Moreover, electron density maps computed from
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Liquid Crystals
FULL PAPER
Table 1. Phase sequence with phase transition temperatures (oC) and thermal effects (in parentheses, JgÀ1) for studied compounds. Also crystallographic unit
cell parameters are given. ColX is unidentified columnar phase.
R
Phase sequence
Unit cell
parameters
X=Y=H, R1 =R2 =R3 =R, Z1 =Z2 =Z3 =H
1a
1b
1c
1d
1e
1 f
OC8H17
Cr 89.6 (11.6) ColX 128.1 (0.1)
ColhPA 147.3 (1.8) Colh 189.5 (1.0) I
Colh:
a=61.4 Š
ColhPA:
a=56.5 Š
Colh:
a=63.0 Š
ColhPA:
a=61.7 Š
OC10H21
OC12H25
OC14H29
OC15H31
OC16H33
Cr 72.1
ACHTER(UNG 3.1) ColX 82.2 (0.1) ColhPA
118.5 (2.0) Colh 196.4 (0.4) I
Cr 65.0 (15.5) ColX 83.8 (6.6) ColhPA Colh:
137.2 (1.5) Colh 197.4 (1.2) I a=63.5 Š
ColhPA:
a=59.7 Š
Cr 34.0 (17.1) ColX 83.7 (6.5) ColhPA Colh:
122.5 (1.1) Colh 187.3 (0.9) I a=64.4 Š
ColhPA:
a=61.3 Š
Cr 62.5 (25.6) ColX 88.6 (7.7) ColhPA Colh:
128.5 (1.8) Colh 187.2 (1.0) I a=66.6 Š
ColhPA:
a=63.3 Š
Cr 58.2 (20.3) ColX 90.2 (8.2) ColhPA Colh:
123.2 (1.5) Colh 174.0 (0.9) I
a=68.5 Š
ColhPA:
a=65.0 Š
X=Y=H, R1 =R2 =R3 =R, Z1 =Z2 =H, Z3 =Cl
2a
2b
OC12H25
Cr <50 ColhPA 135.6 (1.1) Colh 192.4
(1.1) I
Cr 54.6 (0.4) ColX 101.7 (0.05)
ColhPA 123.5 (0.9) Colh 185.8 (1.1) I
OC14H29
Colh:
a=66.1 Š
ColhPA:
a=65.2 Š
X=Y=H, R1 =R2 =R3 =R, Z1 =H, Z2 =Z3 =Cl
3
OC14H29
Cr 80.2 (20.6) ColX 95.5 (0.1) ColhPA Colh:
109.8 (0.5) Colh 139.6 (0.3) I
a=64.9 Š
ColhPA:
a=61.8 Š
X=Y=H, R1 =R2 =R3 =R, Z1 =Z2 =Cl, Z3 =H
4a
4b
4c
OC12H25
Cr 101.4 (17.8) Colh 140.1 (1.0) I
Cr 98.6 (17.3) Colh 138.4 (1.0) I
Cr 89.4 (9.5) Colh 119.1 (1.3) I
Colh:
a=57.7 Š
Colh:
a=66.8 Š
Colh:
OC14H29
OC16H33
a=68.5 Š
X=H, Y=CH3, R1 =R2 =R3 =R, Z1 =Z2 =Z3 =H
5a
5b
OC14H29
OC16H33
Cr 100.1 (6.5) Colh 168.4 (2.2) I
Cr 93.9 (3.4) Colh 161.6 (0.9) I
Colh:
a=66.8 Š
X=Cl, Y=H, R1 =R2 =R3 =R, Z1 =Z2 =Z3 =H
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D. Pociecha et al.
Table 1. (Continued)
R
Phase sequence
Unit cell
parameters
6
OC8H17
Cr 43.2 (9.6) Colh 160.1 (0.5) I
Colh:
a=66.8 Š
X=Y=H, R1 =R2 =R, R3 =H, Z1 =Z2 =Z3 =H
7a
7b
OC12H25
OC14H29
ColhPA–Colh >250 I
ColhPA–Colh >250 I
8a
8b
OC8H17
OC12H25
Cr 97.5 (13.9) [Colh 94.6 (0.6)]I
Cr 85.3 (6.7) Colh 108.8 (0.9) I
Colh:
a=56.7 Š
9a
9b
OC8H17 Z=H Cr 104.0 (48.2) I
OC10H21 Z=H Cr 46.4 (20.0) ColhPA 66.4 (1.2) Colh Colh:
107.4 (2.1) I
a=51.1 Š
ColhPA:
a=49.2 Š
9c
9d
OC12H25 Z=H Cr 39.4 (25.6) ColhPA 62.0 (1.0) Colh
109.1 (1.8) I
OC15H31 Z=H Cr 53.4 (10.9) ColhPA 63.3 (0.8) Colh Colh:
105.1 (0.9) I
a=55.5 Š
ColhPA:
a=55.5 Š
9e
9 f
OC16H33 Z=H Cr 46.4 (20.0) ColhPA 66.4 (1.2) Colh
107.4 (2.1) I
OC14H29 Z=Cl Cr 61.1 (49.0) ColhPA 63.3 (0.5) Colh
103.9 (2.0) I
10a
OC8H17
Cr 148.1 (2.1) Colh 240.7 (4.8) I
Colh:
a=49.9 Š
10b
10c
OC10H21
OC12H25
Cr 139.4 (4.9) Colh 236.9 (1.6) I
Cr 69.9 (27.7) Colh 200.5 (0.3) I
Colh:
a=54.8 Š
pounds 8a and 8b) results in the monotropic appearance of
the apolar hexagonal phase, whilst the conical phase is com-
pletely destabilized.
The liquid crystalline behavior of this first family, com-
pounds 1--8, brings some interesting preliminary conclu-
sions. It seems that the formation of the “conical”, ColhPA
phase is driven mainly by the tendency of molecules to
ensure the optimal close packing conditions. At higher tem-
perature, the molecules self-assemble into supramolecular
discs, leaving some voids between the molecular branches
(these voids are obviously filled by the lower and upper mo-
lecular strata), whereas lowering the temperature results in
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Liquid Crystals
FULL PAPER
the filling up of these voids by bringing the branches togeth-
er, which is achieved by the deformation of the flat discs
into supramolecular cones (Figure 3). This is consistent with
obtained electron density profiles (Figure 2). Apparently,
temperature range, as expected.[19] Apparently covalently
bonded banana shaped molecular fragments have not
enough flexibility to tilt and to form cones.
Synthesis
Synthetic route of banana branches is described in
Scheme 1. Esterification of hydroquinone or 4,4’-dihydroxy-
biphenyl with 3,4,5-trialkoxybenzoyl chloride in standard
conditions gave different arms segments (I). The lateral
chlorine substituents were introduced in phenylene rings by
electrophilic substitution by the action of sulfuryl chloride.
The chlorination reaction was very interesting and surpris-
ing. In this case, reversed regioselectivity was observed and
as a result, the chloro substituent was mainly attached into
the position 2 in phenylene ring of gallic acid moiety. Beside
the major monosubstituted product IIa, two disubstituted
compounds were also obtained: the first one with two chlor-
ine atoms in the phenyl ring of the gallic acid part (Z2 and
Figure 3. Supramolecular assemblies of molecules forming column stra-
tum in the Colh (a) and the ColhPA (b) phases. Note that the voids be-
tween molecules, marked as yellow triangle in a) are considerably smaller
due to tilting of the molecules and forming conical structure in b). The
schematic side views of the columns in Colh and ColhPA phases are also
shown.
any bulky substituent at the
banana branches renders the
tilting, which is necessary for
cone formation, difficult due
to the steric hindrances. On
the contrary, structural modifi-
cations at the outer part of the
molecule, where the packing
of molecular fragments in the
column stratum is more flexi-
ble, provide still favorable con-
ditions for creation of supra-
molecular cones.
Formation of the cones is
only possible if there is some
Scheme 1. Synthesis of the bent-shape molecules side-arms.
flexibility in the molecular ar-
rangement. In order to prove
this statement the compounds 9 and 10 were prepared.
Compounds 9 are also bent-core hexacatenars, having the
banana branches linked with the central phenyl ring by ester
groups. Similarly to compounds 1a–f, the Colh–ColhPA
phases sequence is restored. The clearing and melting tem-
peratures are much lower for materials 9a–e than for com-
pounds of basic series 1a–f, likely due to the smaller size of
the branches. The XRD studies show that for compounds 9
the column diameter decrease at the phase transition from
Colh to ColhPA phase is much less pronounced than in mate-
rials 1 and 2. The number of molecules forming the elemen-
tary columnar stratum in both phases is about 3–4, the same
as in compounds 1 and 2.
If, instead of a supramolecular arrangement into discs or
cones, the overall shape of the columnar unit is imposed by
a single molecule, that is, results from the covalent linking
of three banana units (compounds 10a–c) through an triva-
lent core (trimesic acid), the “conical” phase is not formed
and only a columnar hexagonal phase is observed in a broad
Z3, IIb), and the other one, 3’-chloro-4’-hydroxybiphenyl-4-
[2-chloro-3,4,5-tri(alkoxy)]benzoate, with the chlorine
AHCTREUNG
atoms in Z1 and Z2 positions (IIc). This regioselectivity can
be explained by the formation of the sulfuryl ester inter-
mediate in the first step of the reaction concomittant with
the decreasing activity of hydroxy group; thereby new reac-
tion center becomes active.
Compounds of the first family, namely compounds 1–8
were obtained according to the synthetic route shown in
Scheme 2. The first step of the synthesis was the condensa-
tion of 2,6-lutidine derivatives with methyl 4-formylben-
zoate, followed by the transformation of the resulting diester
III into the acid chloride IV; the final compounds 1–8 were
synthesised by esterification of the bent-core acid chlorides
with the appropriate hydroxy group-conatining side arms (I
and II). Detailed of this procedure was described in a previ-
ous paper.[5]
The chloro substituent (compound 6) was attached to the
central core according to the procedure reported in the liter-
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3381

D. Pociecha et al.
Scheme 2. Synthetic procedures of bent-shape molecules 1–8.
ature,[20] while 4-methylpyridine (for compound 5) is com-
mercially available.
cules VII were connected with benzene-1,3,5-tricarbonyl
chloride to give the mesogenic star-shaped compounds 10.
The synthesis of compounds 9 was based on the esterifica-
tion of the side-arms I (n=2) and IIa with isophthaloyl chlo-
ride (Scheme 3). Scheme 4 outlines the reaction chain lead-
ing to discotic compounds 10. In the first step, the hydroxy
group of dimethyl 5-hydroxyisophthalate was protected and
the ester moieties were then hydrolyzed. The obtained or-
ganic salt was converted into acid chloride and this com-
pound was esterified with the beforehand synthesised
branches (I, n=2) to yield bent-shape compounds VI. After
removal of the protecting benzyl group by catalytic hydroge-
nation, the resulting hydroxy-containing bent-shape mole-
Conclusion
In order to form the axially polar ColhPA phase, a few
banana molecules have to self-organize into units able to fill
the column stratum. If the shape of the molecule does not
allow for an efficient filling of a disc space, then at lowering
temperature the molecules tilt to form cones to assure the
close molecular packing. This is however only possible if the
molecules form supramolecular, flexible aggregates and if
the steric hindrances between
the molecules are weak.
Experimental Section
General methods: Compounds struc-
ture and purity were confirmed by
TLC chromatography, 1H NMR, 13C
NMR spectroscopies and elemental
analysis. NMR spectra were recorded
on the Varian Unity Plus spectrome-
ter operating at 200 or 500 MHz for
1H NMR and at 50 or 125 MHz for
13C NMR. Tetramethylsilane was used
as an internal standard. Chemical
shifts are reported in ppm. TLC anal-
yses were performed on Merck 60
silica gel glass plates and visualized
using iodine vapor and UV light.
Column chromatography was carried
Scheme 3. Synthesis of bent-shape materials 9.
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Liquid Crystals
FULL PAPER
Scheme 4. Synthetic procedures of star-shaped molecules 10.
out at atmospheric pressure using silica gel (100–200 mesh, Merck). Ele-
mental analyses were performed to confirm the expected molecular
structure.
chromatography, on silica gel eluted with toluene. Compounds were
eluted in sequence IIc, IIb and IIa. The last compound was the main
product and it was obtained in 36% yield (3.73 g). Products IIb and IIc
was separated in 5% (0.53 g) and 10% (1.08 g) yield, respectively.
The following synthetic procedures are shown for representative com-
pounds. The other compounds of the same series were obtained analo-
gously under the same reaction conditions and mol ratio of substrates.
1
Analytical data for compound IIa: H NMR (CDCl3, 500 MHz): d = 7.55
(d, 2H, J=9.0 Hz), 7.42 (d, 2H, J=8.5 Hz), 7.37 (s, 1H), 7.26 (d, 2H, J=
8.5 Hz), 6.85 (d, 2H, J=8.5 Hz), 4.09 (t, 2H, J=6.5 Hz), 4.05 (t, 2H, J=
7.0 Hz), 4.03 (t, 2H, J=6.5 Hz), 3.50 (s, 1H), 1.88–1.76 (m, 6H), 1.54–
1.44 (m, 6H), 1.40–1.26 (m, 60H), 0.90–0.86 ppm (m, 9H); 13C NMR
(CDCl3, 125 MHz): d = 164.48, 155.39, 151.53, 150.52, 149.65, 146.81,
138.89, 132.86, 128.34, 127.77, 123.79, 122.06, 121.89, 115.70, 111.01, 74.31,
74.16, 69.19, 31.96, 31.95, 30.30, 30.20, 29.76, 29.72, 29.69, 29.65, 29.63,
29.53, 29.49, 29.41, 29.39, 29.21, 26.09, 26.04, 26.01, 22.71, 14.14 ppm; ele-
mental analysis calcd (%) for C61H97ClO6 (961.87): C 76.17, H 10.16, Cl
3.69; found: C 76.25, H 10.25, Cl 3.55.
1
The H and 13C NMR spectra and elemental analyses were performed for
all compounds but only representative results are quoted.
Representative procedure for synthesis side-arms (I)
4’-Hydroxybiphenyl 4-[3,4,5-tri(tetradecyloxy)]benzoate (I, n=2): 4,4’-
Dihydroxybiphenyl (14.9 g, 0.08 mol) and DMAP (40 mg) were dissolved
in the mixture of tetrahydrofuran (100 mL) and triethylamine (20 mL),
then 3,4,5-tri(tetradecyloxy)-benzoyl chloride (38.84 g, 0.05 mol) was
added slowly. The reaction mixture was heated under reflux for 6 h.
After removal of the solvents under vacuum the product was separated
on column chromatography, on silica gel eluted with toluene. The pure
Analytical data for compound IIb: 1H NMR (CDCl3, 500 MHz): d
=
1
compound was obtained (22.9 g, 52%). H NMR (CDCl3, 200 MHz): d =
7.57 (d, 2H, J=9.0 Hz), 7.44 (d, 2H, J=8.5 Hz), 7.33 (d, 2H, J=8.0 Hz),
6.88 (d, 2H, J=8.5 Hz), 4.08–4.03 (m, 7H), 1.84–1.74 (m, 6H), 1.50–1.46
(m, 6H), 1.40–1.22 (m, 60H), 0.89–0.86 ppm (m, 9H); 13C NMR (CDCl3,
7.56 (d, 2H, J=8.4 Hz), 7.46 (d, 2H, J=8.8 Hz), 7.42 (s, 2H), 7.23 (d,
2H, J=8.4 Hz), 6.88 (d, 2H, J=8.4 Hz), 4.96 (s, 1H), 4.08–4.02 (m, 6H),
1.87–1.73 (m, 6H), 1.57–1.10 (m, 66H), 0.7 ppm (m, 9H); 13C NMR
125 MHz): d
= 163.40, 155.29, 149.43, 149.32, 149.14, 139.30, 133.06,
(CDCl3, 50 MHz): d
= 165.25, 155.18, 152.97, 149.99, 143.50, 138.57,
128.50, 128.45, 127.93, 121.74, 120.97, 115.72, 74.66, 74.61, 30.24, 29.76,
29.75, 29.74, 29.72, 29.70, 29.68, 29.66, 29.51, 29.48, 29.41, 26.03, 25.98,
22.74, 14.16 ppm; elemental analysis calcd (%) for C61H96Cl2O6 (996.32):
C 73.54, H 9.71, Cl 7.12; found: C 73.43, H 9.60, Cl 7.05.
133.12, 128.39, 128.37, 127.76, 127.36, 123.87, 121.98, 121.89, 115.68,
108.57, 73.61, 69.27, 31.95, 31.93, 30.35, 29.77, 29.76, 29.72, 29.70, 29.67,
29.65, 29.58, 29.41, 29.40, 29.38, 29.30, 26.09, 26.07, 22.70, 14.13 ppm; ele-
mental analysis calcd (%) for C61H98O6 (927.44): C 79.00, H 10.65; found:
C 78.91, H 10.75.
Analytical data for compound IIc: 1H NMR (CDCl3, 500 MHz): d
=
7.58–7.54 (m, 3H), 7.39 (dd, 1H, J1 =8.5, J2 =2.5 Hz), 7.36 (s, 1H), 7.29
(d, 2H, J=8.5 Hz), 7.08 (d, 1H, J=8.5 Hz), 5.61 (s, 1H), 4.09 (t, 2H, J=
7.0 Hz), 4.05 (t, 2H, J=6.5 Hz), 4.03 (t, 2H, J=7.0 Hz), 1.87–1.75 (m,
6H), 1.52–1.46 (m, 6H), 1.43–1.22 (m, 60H), 0.90–0.86 ppm (m, 9H);
13C NMR (CDCl3, 125 MHz): d = 164.19, 151.54, 150.88, 150.52, 150.13,
146.79, 137.53, 134.06, 127.79, 127.49, 127.14, 123.81, 122.08, 121.98,
120.32, 116.57, 110.96, 74.28, 74.14, 69.18, 31.95, 31.94, 30.30, 30.20, 29.76,
29.73, 29.69, 29.64, 29.63, 29.53, 29.49, 29.41, 29.39, 29.21, 26.09, 26.04,
26.01, 22.71, 14.14 ppm; elemental analysis calcd (%) for C61H96Cl2O6
(996.32): C 73.54, H 9.71, Cl 7.12; found: C 73.40, H 9.65, Cl 7.30.
Representative procedure for introducing lateral chlorine substituents to
side-arms (II)
4’-Hydroxybiphenyl 4-[2-chloro-3,4,5-tri(tetradecyloxy)]benzoate (IIa),
4’-hydroxybiphenyl 4-[2,6-dichloro-3,4,5-tri(tetradecyloxy)]benzoate (IIb)
and 3’-chloro-4’-hydroxybiphenyl 4-[2-chloro-3,4,5-tri(tetradecyloxy)]ben-
zoate (IIc): Sulfuryl chloride (1.0 mL, 13 mmol) was added to a stirred
solution of 4’-hydroxybiphenyl 4-[3,4,5-tri(tetradecyloxy)]benzoate
(10.0 g, 10.8 mmol) in dichloromethane (250 mL). Stirring was continued
for 12 h. Solvent was evaporated and products were isolated on column
Chem. Eur. J. 2007, 13, 3377 – 3385
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3383

D. Pociecha et al.
Representative procedure for synthesis distyrylopyridine derivatives (III)
1.94–1.71 (m, 12H), 1.57–1.18 (m, 84H), 0.91–0.85 ppm (m, 18H);
13C NMR (CDCl3, 125 MHz): d = 165.27, 164.36, 159.30, 153.19, 150.82,
150.43, 143.26, 138.69, 138.22, 136.04, 131.67, 128.98, 128.63, 128.50,
128.42, 127.89, 124.44, 124.02, 122.37, 122.16, 121.60, 108.79, 32.12, 30.56,
29.94, 29.85, 29.80, 29.61, 29.56, 29.51, 26.29, 22.89, 14.32 ppm; elemental
analysis calcd (%) for C113H156O15 (1754.44): C 77.36, H 8.96; found: C
77.25, H 9.05.
2,6-Di-(4’-carbomethoxystyryl)pyridine (III, X=Y=H): 2,6-Lutidine
(5 g, 0.046 mol) and methyl 4-formylbenzoate (23 g, 0.14 mol) were dis-
solved in acetic anhydride (50 mL) and the reaction mixture was stirred
and refluxed for 40 h. Precipitate was filtered off, washed with methanol
and pure product was dried under vacuum over potassium hydroxide
(4.1 g, 22%). 1H NMR (CDCl3, 200 MHz): d = 8.05 (d, 4H, J=8.4 Hz),
7.74 (d, 2H, J=7.2 Hz), 7.67–7.62 (m, 5H), 7.31 (d, 2H, J=1.4 Hz), 7.25
(d, 2H, J=7.0 Hz), 3.92 ppm (s, 6H); 13C NMR (CDCl3, 50 MHz): d =
166.81, 154.90, 141.15, 137.18, 131.86, 130.45, 130.04, 129.58, 127.00,
121.44, 54.14 ppm; elemental analysis calcd (%) for C25H21NO4 (399.44):
C 75.17, H 5.30, N 3.51; found: C 75.01, H 5.38, N 3.41.
Representative
procedure
for
catalytic
hydrogenation
Compounds VII (R=OC10H21): A reaction mixture containing compound
VI with decyloxy terminal chains (5 g, 2.9 mmol), catalytic amount of Pd/
C and ethanol 99.8% (250 mL) was stirred and heated to 408C for 20 h
under hydrogen atmosphere. CH2Cl2 (100 mL) was added and the solu-
tion was filtered through Celite. The solvent was removed under vacuum
and the residue was recrystallized from methanol (4.3 g, 91%). M.p. 134–
Representative procedure for synthesis of acid chlorides
Dichloride IV (X=Y=H): Sodium hydroxide (4 g, 0.1 mol) was added
to a stirred and refluxed solution of 2,6-di-(4’-carbomethoxystyryl)pyri-
dine (III, X=Y=H) (4 g, 0.01 mol) in ethanol (1 L). The reaction was
continued for 10 h. Precipitate was filtered and dried in vacuum over
phosphorus pentoxide. Obtained sodium salt was suspended in dry tolu-
ene (500 mL) and excess of oxalyl chloride (10 mL) was added. The reac-
tion mixture was refluxed for 18 h and inorganic salt was filtered off
from a hot solution. Filtrate was cooled down and yellow crystals precipi-
tated. The crude product (3.2 g, 72% yield) of dichloride was used for
the following reaction.
1
1358C; H NMR (CDCl3, 200 MHz): d = 8.58 (t, 1H, J=1.4 Hz), 7.88 (d,
2H, J=1.4 Hz), 7.65–7.56 (m, 8H), 7.44 (s, 4H), 7.32–7.24 (m, 8H), 6.70
(s, 1H), 4.13–4.03 (m, 12H), 1.82–1.75 (m, 12H), 1.53–1.22 (m, 84H),
0.91–0.85 ppm (m, 18H); 13C NMR (CDCl3, 125 MHz): d
= 165.24,
164.16, 156.73, 152.97, 150.53, 150.19, 142.87, 138.39, 138.04, 131.40,
128.28, 128.22, 123.89, 122.13, 121.93, 108.57, 73.76, 69.29, 31.92, 30.31,
29.74, 29.68, 29.65, 29.60, 29.41, 29.36, 29.29, 26.09, 22.69, 14.12 ppm; ele-
mental analysis calcd (%) for C106H150O15 (1664.32): C 76.50, H 9.08;
found: C 76.15, H 9.05.
Representative procedure for synthesis star-shaped compounds 10
Representative procedure for synthesis compounds 1–8
Compound 10b: Compound VII with decyloxy terminal chains (1 g,
0.6 mmol) was dissolved in CH2Cl2 (50 mL), DMAP (catalytic amount)
and triethylamine (0.5 mL) was added. After 1 h, benzene-1,3,5-tricar-
bonyl chloride was added dropwise. The reaction mixture was stirred at
room temperature over night. The solvent was evaporated and the crude
compound was purified by column chromatography on silica gel using
Compound 2b: 4’-Hydroxybiphenyl 4-[2-chloro-3,4,5-tri(tetradecyloxy)]-
benzoate (2 g, 2.1 mmol), catalytic amount of DMAP and triethylamine
(3 mL) were dissolved in tetrahydrofuran (70 mL) and heated at reflux
for ca. 30 min. The appropriate dichloride IV (0.42 g, 1.0 mmol) was
added and the reaction was continued for 10 h. The solvents were re-
moved under vacuum and the crude product was purified by column
chromatography using CH2Cl2 as eluent. After that the product was re-
crystallized twice from ethyl acetate. Yield was 60% (1.36 g). 1H NMR
(CDCl3, 500 MHz): d = 8.26 (d, 4H, J=8.0 Hz), 7.87–7.79 (m, 7H), 7.65
(d, 8H, J=8.5 Hz), 7.39–7.30 (m, 14H), 4.09 (t, 4H, J=6.5 Hz), 4.07–4.03
(m, 8H), 1.88–1.75 (m, 12H), 1.50–1.45 (m, 12H), 1.38–1.23 (m, 120H),
1
CH2Cl2 (1.0 g, 32%). H NMR (CDCl3, 200 MHz): d = 9.40 (s, 3H), 9.05
(t, 3H, J=1.4 Hz), 8.46 (d, 6H, J=1.6 Hz), 7.70–7.63 (m, 24H), 7.43 (s,
12H), 7.34–7.25 (m, 24H), 4.09–4.03 (m, 36H), 1.88–1.74 (m, 36H), 1.52–
1.22 (m, 252H), 0.91–0.83 ppm (m, 54H); 13C NMR (CDCl3, 125 MHz):
d = 164.05, 164.00, 152.90, 152.00, 142.87, 135.42, 133.42, 132.09, 130.91,
128.50, 128.22, 127.83, 123.43, 121.95, 108.47, 72.32, 70.29, 32.41, 30.62,
30.39, 29.88, 29.40, 29.36, 29.53, 26.39, 23.01, 14.02 ppm; elemental analy-
sis calcd (%) for C327H450O48 (5149.04): C 76.28, H 8.81; found: C 76.15,
H 8.95.
0.90–0.86 ppm (m, 18H); 13C NMR (CDCl3, 125 MHz): d
= 164.84,
164.17, 151.55, 150.52, 150.46, 150.28, 149.32, 146.77, 138.36, 138.23,
128.40, 128.32, 128.27, 128.25, 123.86, 122.08, 122.05, 121.97, 121.89, 74.59,
74.28, 74.14, 69.18, 31.95, 31.94, 31.93, 30.31, 30.20, 29.75, 29.71, 29.67,
29.64, 29.62, 29.53, 29.49, 29.45, 29.41, 29.39, 29.21, 26.09, 26.04, 26.01,
25.95, 22.79, 14.14 ppm; elemental analysis calcd (%) for C145H207Cl2NO14
(2259.10): C 77.09, H 9.24, Cl 3.14, N 0.62; found: C 77.17, H 9.20, Cl
3.20, N 0.87.
The phase sequence, phase transition temperatures and thermal effects
for the studied materials were determined by optical microscopy (Nikon
Optiphot2-Pol polarizing microscope equipped with Mettler FP82HT
heating stage and photodiode FLCE PIN-20 for quantitative monitoring
the light transmission) and confirmed by differential scanning calorimetry
(Perkin Elmer DSC-7). The structure of the mesophases was confirmed
by X-ray measurements performed with powder samples. CuKa radiation
(1.5401 Š) was used; the patterns were registered with Inel CPS 120
curved counter or with imaging plates when the Guinier geometry was
applied. Samples for dielectric and electrooptic studies were prepared in
3–5 mm thick glass cells with ITO electrodes and planar aligning surfac-
tant layers.
Dimethyl-5-benzyloxyisophthalate
(V):
Benzylbromide
(6.0 mL,
0.05 mol) was slowly added to a stirred suspension of dimethyl 5-hydroxy-
isophthalate (10 g, 0.05 mol), potassium carbonate (7 g, 0.05 mol) and
sodium iodide (9 g, 0.06 mol) in DMF. The reaction mixture was stirred
at 808C for 10 h and then was cooled down to room temperature. After
pouring the solution onto an ice-water mixture, the crude product was
precipitated and purified by recrystallization from ethanol (11 g, 77%).
1H NMR (CDCl3, 200 MHz): d = 8.29 (t, 1H, J=1.5 Hz), 7.84 (d, 2H,
J=1.5 Hz), 7.47–7.34 (m, 5H), 5.14 (s, 2H), 3.94 ppm (s, 6H); 13C NMR
(CDCl3, 125 MHz): d = 167.01, 161.80, 140.99, 130.05, 128.80, 127.39,
123.25, 119.67, 77.77, 50.09 ppm; elemental analysis calcd (%) for
C17H16O5 (300.10): C 67.99, H 5.37; found: C 67.85, H 5.45.
Acknowledgements
Representative procedure for esterification of isophthaloyl or 5-benzylox-
yisophthaloyl dichloride with side-arms
The work was supported by UW grant BW-1681/10/2005 and bilateral
Polish–French research program POLONIUM no 6480/R06/R07.
Compound VI (R=OC10H21): 4’-Hydroxybiphenyl 4-[3,4,5-tridecyloxy)]-
benzoate (7,5 g, 10 mmol), and catalytic amounts of DMAP and triethyl-
ACHTREUNGamine (1 mL) were dissolved in THF (100 mL). To the stirred and re-
ˇ
fluxed solution, 5-benzyloxyisophthaloyl dichloride, obtained according
to the general procedure for the synthesis of acid chlorides, (1.5 g,
5 mmol) was added dropwise and the reaction was continued for 5 h. The
solvent was evaporated and the residue was purified by chromatography
on silica gel eluting with CH2Cl2 (5 g, 59%). M.p.. 61–628C; 1H NMR
(CDCl3, 200 MHz): d = 8.68 (t, 1H, J=1.6 Hz), 8.09 (d, 2H, J=1.7 Hz),
7.69–7.63 (m, 8H), 7.52–7.26 (m, 17H), 5.25 (s, 2H), 4.11–4.03 (m, 12H),
ˇ
ˇ
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Received: August 16, 2006
Published online: January 17, 2007
Chem. Eur. J. 2007, 13, 3377 – 3385
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3385