Ester type banana-shaped liquid crystalline monomers: Synthesis and physical properties

Article abstract of DOI:10.1039/b400246f

New ester-type banana (bent-shaped) monomers, 1,3-phenylene bis[4′-(alken-1-yloxy)-biphenyl-4-carboxylate]s Ia-Vb, with different substituent(s) on the central phenyl ring (H, CH₃, Cl or NO ₂) and alkenyl tails in the side arms (decenyl or undecenyl) were prepared. The analogues IIIa-IVb with 4-chloro- or 4,6-dichloro-substituents exhibited a nematic phase, while Va,Vb with 2-nitro-substituent showed a B ₇ phase at relatively low temperature. All the compounds were stable, no degradation or polymerization was observed under applied electric fields or heat treatments. Electro-hydrodynamic instabilities were observed in the nematic phase of each sample. In the B₇ phase of Vb there was an electro-optical switching in the range 112-114.5 °C with a switching time of about 150 μs at 20 V μm^-1 field. At lower temperatures no electro-optical switching occurred, but a ferroelectric-type spontaneous polarization of 22 nC cm^-2 could be detected. The bend angle was calculated by the semiempirical CAChe/MOPAC/PM5 method.

Full text of DOI:10.1039/b400246f

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A R T I C L E
Ester type banana-shaped liquid crystalline monomers: synthesis
and physical properties{
a
Katalin Fodor-Csorba,* Anik o´ Vajda, Antal J a´ kli, Christian Slugovc,
a
a,b
c
c
Gregor Trimmel, Dietrich Demus, Eszter G a´ cs-Baitz, S a´ ndor Holly and
d
e
e
f
Giancarlo Galli
a
Research Institute for Solid State Physics and Optics of the Hungarian Academy
of Sciences H-1525 Budapest, P.O.Box 49, Hungary. E-mail: fodor@szfki.hu;
Fax: 1 36-1-392-2215
b
Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
Institute for Chemistry and Technology of Organic Materials, Graz University of
Technology, Stremayrgasse 16, A-8010 Graz, Austria
c
d
International Scientific Consulting Office, Halle, Germany
Chemical Research Center Hungarian Academy of Sciences, Institute for Chemistry,
e
H-1525 Budapest, P.O.Box 17, Hungary
Universit a` di Pisa, Dipartimento di Chimica e Chimica Industriale, Via Risorgimento 35,
f
5
6126 Pisa, Italy
Received 9th January 2004, Accepted 27th May 2004
First published as an Advance Article on the web 28th June 2004
New ester-type banana (bent-shaped) monomers, 1,3-phenylene bis[4’-(alken-1-yloxy)-biphenyl-4-carboxylate]s
Ia–Vb, with different substituent(s) on the central phenyl ring (H, CH
arms (decenyl or undecenyl) were prepared. The analogues IIIa–IVb with 4-chloro- or 4,6-dichloro-substituents
exhibited a nematic phase, while Va,Vb with 2-nitro-substituent showed a B phase at relatively low
3 2
, Cl or NO ) and alkenyl tails in the side
7
temperature. All the compounds were stable, no degradation or polymerization was observed under applied
electric fields or heat treatments. Electro-hydrodynamic instabilities were observed in the nematic phase of each
sample. In the B
time of about 150 ms at 20 V mm field. At lower temperatures no electro-optical switching occurred, but a
7
phase of Vb there was an electro-optical switching in the range 112–114.5 uC with a switching
21
2
2
ferroelectric-type spontaneous polarization of 22 nC cm could be detected. The bend angle was calculated by
the semiempirical CAChe/MOPAC/PM5 method.
Among rod-shaped liquid crystals, it is well known that
Introduction
azomethine-type compounds (Schiff’s bases) tend to form
smectic phases. The first smectic mesophases of banana-shaped
molecules with five aromatic rings also had azomethine con-
necting groups. It is found that the mesophase behavior of
azomethine banana molecules is very sensitive to the effects of
It has been known since 1996 that achiral banana-shaped (bent-
core) molecules may form polar smectic layers with ferroelectric
1
or antiferroelectric behavior. Soon after it became also clear
that the layers with tilted director structure may become chiral
and can self-assemble in a macroscopically chiral structure,
when the layer chirality is the same in adjacent layers, or a
racemic structure, when the layer chirality alternates in adjacent
8
substituents at various positions on the aromatic rings. The
situation is more complicated if the azomethine linking groups
are replaced by different groups, like ester, thioester or vinyl-
2
5b,12–14
carboxylate groups,
layers. This wealth of new phenomena of chirality and polarity
has led to a new subfield of liquid crystal research. In the past
several years a great number of banana-shaped compounds have
so that the banana molecule contains
ester-type linking groups only. In fact, a few purely ester-type
1
5
banana liquid crystals have been published up to now.
So far little work has been devoted to polymers based on
3
,4
been synthesized and characterized,
different phases (chronologically assigned as B
and at least seven
1
6–20
–B ) have been
1 7
banana monomers.
Bent-shaped diacrylate monomers
5
–8
identified. More recently, banana-shaped liquid crystals have
also been described that form smectic and/or nematic meso-
phases. Among the B phases, electro-optical switching has
been observed in the smectic B , B and B phases. The most
widely studied B phase is identified as a tilted antiferroelectric
were synthesized but showed mesomorphic properties only
after polymerization in a mixture with an appropriate banana
3
,9
1
7
liquid crystal. In one other work 1,3-diene monomers pre-
sented various mesophases but were not stable and suffered
2
5
7
1
8
2
degradation under heat or electric field treatment. In our
previous work divinyl banana monomers, 1,3-phenylene
bis[(alkenyloxy)benzoyloxy]benzoates, were prepared with
polar smectic (SmCP ) phase with either synclinic (SmC P ) or
s A
A
2
a A 7
anticlinic (SmC P ) structures. The B phase is very unique and
6
,10
2
1
interesting due to its beautiful and extraordinary textures and
some of them are thought to have a double tilted director struc-
thermal and field stability. These compounds exhibited
monotropic B and enantiotropic nematic phases below 100 uC.
2
1
1,12
ture with C
1
symmetry.
The B
1
phase has been designated as
a columnar phase with rectangular lattice. The B and B phases
The aim of this work was to investigate the effect of rigidity
and/or flexibility of the arms of banana shaped monomers with
five aromatic rings where the terminal chains have polymeriz-
able double bonds at both ends of the molecule in a new class of
banana monomers, 1,3-phenylene bis[4’-(alkenyloxy)biphenyl-
carboxylate]s Ia–Vb (Fig. 1). The effect of substitution and
3
4
8
are considered to be crystalline phases.
{ Electronic supplementary information (ESI) available: experimental
details. See http://www.rsc.org/suppdata/jm/b4/b400246f/
T h i s j o u r n a l i s ß T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 2 4 9 9 – 2 5 0 6
2 4 9 9

View Article Online
Synthesis
The starting materials, ethyl 4’-hydroxybiphenyl-4-carboxylate
(
(
3), resorcinol (7), 2-methyl-resorcinol (8), 4-chloro-resorcinol
9), 4,6-dichloro-resorcinol (10), 2-nitro-resorcinol (11), decen-
1-ol (1a), and undecen-1-ol (1b), were purchased from Aldrich
and used without further purification. Preparation and spec-
troscopic data of 4a, 4b, 5a, 5b, 6a, and 6b are collected in ESI.{
2
2
Ethyl 4’-(9-decen-1-yloxy)-1,1’-biphenyl-4-carboxylate (4a) .
Cr 37.0 uC [5.51] Cr 66.2 uC [6.97] SmE 77.7 uC [0.47] SmA
1
2
2
1
8
7.7 uC [0.41] 100.7 uC Iso [2.03 kcal mol ].
Fig. 1 General chemical structure of the monomers studied Ia–Vb.
Ethyl 4’-(10-undecen-1-yloxy)-1,1’-biphenyl-4-carboxylate (4b).
Cr 48.1 0 uC [2.96] Cr 54.2 uC [0.33] SmE 74.5 uC [0.44] SmA
1
2
phase behavior was also studied. In addition, due to the
presence of the double bonds in the terminal chains these
compounds could also serve as precursors of polymers built up
from banana-shaped monomers as was shown in our earlier
2
1
8
5.2 uC [0.42] 98.8 uC Iso [2.02 kcal mol ].
4
’-(9-Decen-1-yloxy)-1,1’-biphenyl-4-carboxylic acid (5a). Cr
2
0
167 uC SmC 251 uC N 252 uC Iso.
paper for acyclic diene metathesis polymerization.
2
3
4
’-(10-Undecen-1-yloxy)-1,1’-biphenyl-4-carboxylic acid (5b) .
Cr 160 uC SmC 245 uC N 246 uC Iso.
Experimental
Physical investigations
4’-(9-Decen-1-yloxy)-1,1’-biphenyl-4-carbonyl chloride (6a).
Mp. 82 uC.
Confirmation of the structures of intermediates and products
2
1
was obtained by infrared spectra (resolution 4 cm ) taken
with a Nicolet Magna 750 FT-IR spectrophotometer on KBr
4’-(10-Undecen-1-yloxy)-1,1’-biphenyl-4-carbonyl chloride (6b).
1
pellets and H NMR spectra recorded on a Varian XL-400
spectrometer, the chemical shifts referenced to the internal
Mp. 80 uC.
1
tetramethylsilane peak. H assignments, when necessary, were
General procedure for the preparation of the monomers Ia–Vb
performed with the aid of homonuclear spin decoupling
experiments. Assigments of the proton signals were made
according to Fig. 2. The purity of the samples was checked by
high performance liquid chromatography (HPLC) with a
Merck-Hitachi chromatograph equipped with a Merck RP18
column (Cat. No 16051).
Transition temperatures were measured with an Amplival
POL-U polarizing microscope equipped with a Boetius hot
stage. These data were controlled by differential scanning
calorimetry using a Perkin-Elmer DSC-7.
The physical properties of the newly synthesized materials
were studied by X-ray diffraction, polarizing microscopy,
electro-optical and polarization current measurements.
High resolution X-ray measurements were carried out in the
Midwest Universities Collaborative Access Team (MUCAT)
Powder Diffraction station of the Advanced Photon Source of
Resorcinol derivatives (10 mmol) and an excess of triethyl
amine (30 mmol) were dissolved in dry 2-butanone (20 ml) and
4’-(alken-1-yloxy)-1,1’-biphenyl-4-carbonyl chloride (22 mmol)
was added dropwise. The reaction mixture was maintained
under stirring at room temperature for 24 hours. Then, water
(
10 ml) was added, the layers were separated, the organic phase
extracted with 3 6 10 ml 5% HCl, 3 6 10 ml water, 3 6 10 ml
% NaHCO , 3 6 10 ml water, dried over magnesium sulfate
5
3
and evaporated to dryness. The reaction was monitored by
TLC on Kieselgel 60 F254 sheets, the spots were highly
fluorescent under 254 and 366 nm. The crude product was
purified by flash chromatography on a Kieselgel 60 (0.063–
0
.02 mm) column with 1,2-dichloroethane elution. Phase
transition temperatures and enthalpies are summarized in
Table 1. The reaction conditions, quantities of the reagents and
yields for the final compounds Ia-Vb are summarized in ESI.{
˚
Argonne National Laboratory (E ~ 9.684 keV, l ~ 1.2803 A,
resolution: 3450 6 3450 and detector is at 378.499 mm from
the sample). In the X-ray measurements 20 mm thick samples
were sandwiched between 0.1 mm thick microscopy cover
slides.
For the polarizing microscopy, electro-optical and polariza-
tion current measurements the materials were placed in ready
made 4 mm and 10 mm thick cells purchased from Displaytech
and EHC, Co., respectively. The liquid crystal cells were
placed in a computer controlled heat stage (STC200F from
INSTEC) and the phase sequences were investigated by
polarizing microscopy (BX60 from Olympus), electric current
measurements and electro-optical studies. For these measure-
ments a Digital Oscilloscope (HP 54600B), Digital Multimeter
1
,3-Phenylene bis[4’-(9-decen-1-yloxy)-1,1’-biphenyl-4-carboxyl-
21
ate] (Ia, 10PBBC). IR nmax(KBr)/cm 3078 (nasLCH
924 (n CH ), 2853 (n CH ), 1730 (nCLO, ester), 1641 (nCLC,
2
, vinyl),
2
as
2
s
2
vinyl), 1603, 1528 and 1497 (nCAr
83 and 692 (cCArH and cCArCAr, m-disubst.). H NMR
CDCl ): d ~ 1.25–2.08 (m, 28H, aliphatics), 4.04 (t, 4 H, J ~
.8 Hz, 2 6 OCH ), 4.93 (m, 2H, J ~ 10.3 Hz, LCH ), 4.98
CAr), 831 (cCArH, p-disubst.),
1
7
(
6
(
4
7
3
2
cis
2
m, 2H, Jtrans ~ 17.1 Hz, LCH
2
), 5.82 (m, 2H, CHL), 6.98 (m,
H, 2 6 H3@ 1 2 6 H5@), 7.60 (m, 4 H, 2 6 H2@ 1 2 6 H6@ ),
.69 (m, 4 H, 2 6 H3’ 1 2 6 H5’), 8.21 (m, 4 H, 2 6 H2’ 1 2 6
H6’); elemental analysis calcd (%) for C H O (779.04): C,
0.17, H, 7.50, found C, 80.11, H, 7.48.
5
2
58
6
8
(
3
HP 34401A) and Arbitrary Waveform Generator (HP
3120A) were used.
1
,3-Phenylene bis[4’-(10-undecen-1-yloxy)-1,1’-biphenyl-4-carboxyl-
21
ate] (Ib, 11PBBC). IR nmax(KBr)/cm 3079 (nas LCH , vinyl),
043 (nCArH), 2923 (nasCH
ester), 1642 (nCLC, vinyl), 1603 (nCArCAr), 831 (cC H,
p-disubst.), 783 and 693 (cCArH, 1,3-disubst.).
NMR(CDCl ): d ~ 1.3–2.06 (m, 32H, 16CH ), 4.03 (t, 4 H,
2
3
2
), 2852 (n
s
CH
2
), 1730 (nCLO,
Ar
1
H
3
2
J ~ 6.8 Hz, 20CH
(
4 H, 2(H3@ and H5@)), 7.19 (dd, 2H, J ~ 8.2 1 2.2 Hz, H4 and
2
), 4.94 (m, 2H, Jcis ~ 10.1 Hz, CHL), 5.00
m, 2H, Jtrans ~ 17.1 Hz, CHL), 5.82 (m, 2H, LCH), 7.00 (m,
Fig. 2 Assignments of proton NMR signals.
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 2 4 9 9 – 2 5 0 6
2
5 0 0

View Article Online
2
1
Table 1 Phase transitions (in uC) and enthalpies [in kcal mol ] of the 1,3-phenylene bis[4-(alken-1-yloxy)-1,1’-biphenyl carboxylates]
2
R
4
R
6
R
Code
n
Cr
1
Cr
2
N
B7
I
Ia
Ib
IIa
IIb
IIIa
IIIb
8
9
8
9
8
9
8
9
8
9
H
H
CH
CH
H
H
H
H
NO
NO
H
H
H
H
Cl
Cl
Cl
Cl
H
H
H
H
H
H
H
H
Cl
Cl
H
H
$ 143.6 [11.46]
$ 131.2 [1.69]
$ 140.5 [13.05]
$ 136.6 [10.57]
$ 84.5 [4.02]
—
—
—
—
—
—
—
—
—
—
—
—
—
$
$
$
$
$
$
$
$
$
$
$ 138.4 [6.94]
—
—
3
3
a
—
$ (77.6 ) [0.19]
$ (81.8) [0.18]
$ 98.8 [0.24]
$ 102.7 [0.22]
—
b
c
$ 75.5 [2.11]
$ 89.5 [5.52]
$ 87.6 [1.37]
$ 78.9 [7.73]
$ 119.2 [10.84]
$ 109.7 [1.23]
IVa
IVb
Va
Vb
a
$ 72.7 [5.85]
$ 71.2 [1.40]
$ 74.9 [3.97]
$ 34.3 [2.95]
2
$ (113) [5.27]
2
—
$ 118.0 [6.37]
21
b
Additional unidentified mesophase at 63.2 uC, DH ~ 6.78 [kcal mol ]. Additional unidentified mesophase at 50.1 uC, DH
~
2
.15 [kcal mol ]. Observed only at first heating.
1
c
7
H6), 7.23 (t, 1H, J ~ 2.2 Hz, H2), 7.49 (t, 1H, J ~ 8.2 Hz, H5),
7
J
cis ~ 10.2 Hz, CHL), 4.98 (m, 2H, Jtrans ~ 17.2 Hz, CHL),
.59 (m, 4 H, 2(H2@ and H6@)), 7.69 (m, 4 H, 2(H3’ and H5’)),
.22 (m, 4 H, 2(H2’ and H6’)); elemental analysis calcd (%) for
5.78 (m, 2H, LCH), 6.96 (m, 4 H, 2(H3@ and H5@)), 7.10 (dd,
1H, J ~ 8.7 1 2.6 Hz, H6), 7.24 (d, 1H, J ~ 2.6 Hz, H2), 7.46
(d, 1H, J ~ 8.7 Hz, H5), 7.53 (m, 4 H, 2(H2@ and H6@)), 7.61
and 7.63 (2 m, 4 H, 2(H3’ and H5’)), 8.12 1 8.20 (2 m, 4 H,
8
C H O (807.09): C, 80.36, H, 7.74; found C, 80.29, H, 7.72.
5
4
62
6
2
-Methyl-1,3-phenylene bis[4’-(9-decen-1-yloxy)-1,1’-biphenyl-
2(H2’ and H6’)); elemental analysis calcd (%) for C54H61ClO
(841.54): C, 77.07, H, 7.31, Cl, 4.21, found C, 76,99 H, 7.29, Cl,
4.19.
6
2
1
4
-carboxylate] (IIa, 10MePBBC). IR nmax(KBr)/cm
CH
3078
(n
asLCH
2
, vinyl), 2924 (nasCH
2
), 2854 (n
s
2
), 1731 (nCLO,
ester), 1641 (nCLC, vinyl), 1603 (nCArCAr), 831 (cC H,
Ar
1
p-disubst.), 767 and 693 (cCArH, 1,2,3-trisubst.). H NMR
4,6-Dichloro-1,3-phenylene bis[4’-(9-decen-1-yloxy)-1,1’-biphenyl-
2
1
(
4
CDCl ): d ~ 1.3–2.08 (m, 28H, 14CH ), 2.16 (s, 3H, 2-CH ),
3
4-carboxylate] (IVa, 10DClPBBC). IR nmax(KBr)/cm
(nas LCH , vinyl), 3040 (nCArH), 2924 (nasCH ), 2853 (n
1745 (nCLO, ester), 1641 (nCLC, vinyl), 1603 (nCArCAr), 829
3077
3
2
.05 (t, 4 H, J ~ 6.8 Hz, 20CH ), 4.90 (m, 2H, Jcis ~ 10.2 Hz,
~ 17.1Hz, CHL), 5.83 (m, 2H, LCH),
2
2
2
s
CH ),
2
CHL), 5.02 (m, 2H, J
trans
1
7
.00 (m, 4 H, 2(H3@ and H5@)), 7.18 (d, 2H, J ~ 8.3 Hz, H4
(cCArH, p-disubst.) H NMR(CDCl
14CH ), 4.02 (t, 4 H, J ~ 6.8 Hz, 20CH ), 4.92 (m, 2H, J ~
cis
3
): d ~ 1.3–2.08 (m, 28H,
and H6), 7.32 (t, 1H, J ~ 8.3 Hz, H5), 7.59 (m, 4 H, 2(H2@ and
H6@)), 7.72 (m, 4 H, 2(H3’ and H5’)), 8.275 (m, 4 H, 2(H2’ and
H6’)); elemental analysis calcd (%) for C H O (793.07): C,
2
2
10.2 Hz, CHL), 5.00 (m, 2H, Jtrans ~ 17.2 Hz, CHL), 5.82 (m,
2H, LCH), 7.00 (m, 4 H, 2(H3@ and H5@)), 7.40 (s,1H, H2), 7.62
(m, 4 H, 2(H2@ and H6@)), 7.63 (s, 1H, H5), 7.71 (m, 4 H, 2(H3’
and H5’)), 8.23 (m, 4 H, 2(H2’ and H6’)); elemental analysis
5
3
60
6
8
0.27, H, 7.63, found C, 80.22, H, 7.60.
2
-Methyl-1,3-phenylene bis[4’-(10-undecen-1-yloxy)-1,1’-biphenyl-
2 6
calcd (%) for C52H56Cl O (847.93): C, 73.66, H, 6.66, Cl, 8.36,
found C, 73.61, H, 6.64, Cl, 8.34.
2
1
4
-carboxylate] (IIb, 11MePBBC). IR nmax(KBr)/cm
asLCH , vinyl), 3037 (nCArH), 2923 (nasCH ), 2852 (n
741 and 1726 (nCLO, ester), 1642 (nCLC, vinyl), 1604
Ar), 833 (cCArH, p-disubst.), 7.83 and 690 (cCArH,
3078
(n
2
2
s
CH ),
2
1
(
1
1
4
1
4,6-Dichloro-1,3-phenylene bis[4’-(10-undecen-1-yloxy)-1,1’-biphenyl-
2
1
nCAr
C
4-carboxylate] (IVb, 11DClPBBC). IR nmax(KBr)/cm
(nasLCH , vinyl), 3041 (nCArH), 2923 (nasCH ), 2853 (n
1745 (nCLO, ester), 1641 (nCLC, vinyl), 1603 (nCAr Ar), 827
): d ~ 1.25–2.10 (m,
), 4.01 (t, 4 H, J ~ 6.8 Hz, 20CH ), 4.93 (m, 2H,
cis ~ 10.2 Hz, CHL), 4.99 (m, 2H, Jtrans ~ 17.3 Hz, CHL),
3076
1
,2,3-trisubst). H NMR (CDCl
6CH ), 2.18 (s, 3H, 2-CH ), 4.03 (t, 4 H, J ~ 6.8 Hz, 20CH
.93 (m, 2H, Jcis ~ 10.2 Hz, CHL), 5.00 (m, 2H, Jtrans
7.1 Hz, CHL), 5.81 (m, 2H, LCH), 6.99 (m, 4 H, 2(H3@ and
H5@)), 7.17 (d, 2H, J ~ 8.3 Hz, H4 and H6), 7.35 (t, 1H, J ~
.3 Hz, H5), 7.58 (m, 4 H, 2(H2@ and H6@)), 7.70 (m, 4 H, 2(H3’
and H5’)), 8.25 (m, 4 H, 2(H2’ and H6’)); elemental analysis
calcd (%) for C55 (821.12): C, 80.45, H, 7.86, found C,
3
): d ~ 1.3–2.08 (m, 32H,
2
2
s
CH ),
2
2
3
2
),
C
1
~
(cCArH, p-disubst.). H NMR (CDCl
32H, 16CH
3
2
2
J
8
5.81 (m, 2H, LCH), 7.00 (m, 4 H, 2(H3@ and H5@)), 7.40 (s, 1H,
H2), 7.59 (m, 4 H, 2(H2@ and H6@), 7.64 (s, 1H, H5), 7.71 (m,
4 H, 2(H3’ and H5’)), 8.22 (m, 4 H, 2(H2’ and H6’)); elemental
analysis calcd (%) for C H Cl O (875.98): C, 74.04, H, 6.90,
64 6
H O
8
0.39, H, 7.81.
5
4
60
2
6
Cl, 8.09, found C, 73.93, H, 6.88, Cl, 8.01.
4
-Chloro-1,3-phenylene bis[4’-(9-decen-1-yloxy)-1,1’-biphenyl-
21
4
-carboxylate] (IIIa, 10ClPBBC). IR nmax(KBr)/cm
3076
CH ),
743 (nCLO, ester), 1641 (nCLC, vinyl), 1604 (nCArCAr), 830
2-Nitro-1,3-phenylene bis[4’-(9-decen-1-yloxy)-1,1’-biphenyl-
4-carboxylate] (Va, 10NO2PBBC). IR nmax(KBr)/cm 3078
2
1
(n
asLCH
2
, vinyl), 3041 (nCArH), 2926 (nasCH
2
), 2854 (n
s
2
1
(
(n LCH , vinyl), 3042 (nC H), 2927 (n CH ), 2853 (n CH ),
as
2
Ar
as
2
s
2
1
cCArH, p-disubst.). H NMR (CDCl
3
): d ~ 1.3–2.08 (m, 28H,
1738 (nCLO, ester), 1641 (nCLC, vinyl), 1602 (nCAr
CAr), 1538
1
1
2
8
4CH ), 4.02 (t, 4 H, J ~ 6.8 Hz, 20CH ), 4.93 (m, 2H, J
2
~
(n NO ), 831 (cC H, p-disubst.), 786 and 692 (cCArH, 1,2,3-
as 2 Ar
2
cis
1
trisubst.). H NMR(CDCl
0.2 Hz, CHL), 4.98 (m, 2H, Jtrans ~ 17.2 Hz, CHL), 5.82 (m,
H, LCH), 6.99 (m, 4 H, 2(H3@ and H5@)), 7.19 (dd, 1H, J ~
.8 1 2.7 Hz, H6), 7.33 (d, 1H, J ~ 2.7 Hz, H2), 7.54 (d, 1H,
3 2
): d ~ 1.33–2.09 (m, 28H, 14CH ),
4.02 (t, 4 H, J ~ 6.7 Hz, 2OCH ), 4.95 (m, 2H, J ~ 10.2 Hz,
2
cis
CHL), 5.00 (m, 2H, Jtrans ~ 17.1 Hz, CHL), 5.81 (m, 2H, LCH),
7.00 (m, 4 H, 2(H3@ and H5@)), 7.42 (d, 2H, J ~ 7.4 Hz, H4 and
H6), 7.58 (m, 4 H, 2(H2@ and H6@)), 7.66 (t, 1H, J ~ 7.4 Hz,
H5), 7.70 (m, 4 H, 2(H3’ and H5’)), 8.18 (m, 4 H, 2(H2’ and
J ~ 8.8 Hz, H5), 7.59 (m, 4 H, 2(H2@ and H6@)), 7.59–7.74 (m,
H, 2(H3’ and H5’)), 8.20–8.26 (m, 4 H, 2(H2’ and H6’));
elemental analysis calcd (%) for C H ClO (813.48): C, 76.78,
4
5
2
57
6
H, 7.06, Cl, 4.36, found C, 76.72, H, 6.99, Cl, 4.32.
H6’)); elemental analysis calcd (%) for C52
H57NO
8
(824.04): C,
7
5.80, H, 6.97, N 1.70, found C, 75.75, H, 6.95, N, 1.68.
4
-Chloro-1,3-phenylene bis[4’-(10-undecen-1-yloxy)-1,1’-biphenyl-
2
1
4
-carboxylate] (IIIb, 11ClPBBC). IR nmax(KBr)/cm
3077
2-Nitro-1,3-phenylene bis[4’-(10-undecen-1-yloxy)-1,1’-biphenyl-
21
(
n LCH , vinyl), 3041 (nC H), 2924 (n CH ), 2853 (n CH ),
4-carboxylate] (Vb, 11NO2PBBC). IR nmax(KBr)/cm
, vinyl), 3042 (nCArH), 2925 (nasCH
3078
CH ),
as
2
Ar
as
2
s
2
1
(
743 (nCLO, ester), 1641 (nCLC, vinyl), 1604 (nCAr
C
Ar), 830
(nasLCH
2
2
), 2853 (n
s
2
1
cC H, p-disubst.). H NMR (CDCl ): d ~ 1.25–2.06 (m,
1738 (nCLO, ester), 1641 (nCLC, vinyl), 1603 (nCArCAr),
Ar
3
3
2H, 16CH
2
), 3.98 (t, 4 H, J ~ 6.8 Hz, 20CH
2
), 4.90 (m, 2H,
1539 (nasNO
2
), 831 (cCArH, p-disubst.), 786 and 692 (cCArH,
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 2 4 9 9 – 2 5 0 6
2 5 0 1

View Article Online
1
,2,3-trisubst.). H NMR(CDCl ): d ~ 1.27–2.07 (m, 32H,
1
1
1
2
7
variation of the chemical structure may be considered, includ-
ing the introduction of different substituents on and inter-
connecting groups between the phenyl rings and the addition of
terminal flexible tails.
3
6CH
0.2 Hz, CHL), 5.00 (m, 2H, J
2
), 4.02 (t, 4 H, J ~ 6.7 Hz, 20CH
2
), 4.96 (m, 2H, Jcis
~
~ 17.1 Hz, CHL), 5.80 (m,
trans
H, LCH), 7.00 (m, 4 H, 2(H3@ and H5@)), 7.42 (d, 2H, J ~
.4 Hz, H4 and H6), 7.58 (m, 4 H, 2(H2@ and H6@)), 7.66 (t, 1H,
We focused our attention on the nature of the substituents
on the central phenyl ring of purely ester-type banana meso-
gens (Fig. 1). One special variation of the chemical structure
was the use of alkenyl chains as terminal groups. The CLC
double bonds of the vinyl groups in fact may be exploited to
incorporate banana mesogens into new structures of polymers.
The monomers Ia–Vb comprised a central 1,3-phenylene ring
J ~ 7.4 Hz, H5), 7.70 (m, 4 H, 2(H3’ and H5’)), 8.14 (m, 4 H,
(H2’ and H6’)), elemental analysis calcd (%) for C H NO
2
5
4
61
8
(
852.08): C, 76.12, H, 7.22, N, 1.64 found C, 76.08, H, 7.19 N,
1.61
Results and discussion
2
from resorcinol carrying substituent(s) of various nature (R ,
4
R , R ~ H, CH
6
Synthesis
3 2
, Cl, NO ) at different sites (2-, 4-,
6
both arm sides was used as the terminal tail.
The phase transition temperatures and sequences of the
monomers greatly depended on their chemical structure
-positions). Either a decenyl or an undecenyl segment at
For the synthesis of the key intermediates, 4’-alkenyloxy-biphenyl-
22,23
-carboxylic acids
4
we carried out a Williamson-type ether
formation on ethyl 4’-hydroxy-biphenyl-4-carboxylate 3 with
the appropriate alkenyl bromide 2a and 2b (n ~ 8 and 9,
respectively) (Scheme 1). Hydrolysis of the esters allowed the
(
Table 1). No mesophase was formed by either the unsub-
stituted Ia, Ib or 2-methyl-substituted IIa, IIb derivatives. Each
of the chloro-substituted analogues IIIa–IVb presented a
nematic phase. The introduction of a large chlorine substituent
at the 4-position widens the bend angle of the unsubstituted
4’-(alken-1-yloxy)-1,1’-biphenyl-4-carboxylic acids 5a and 5b
to be obtained with high purity and yield in a short reaction
time. An alternative procedure based on the direct reaction of
4’-hydroxy-biphenyl-4-carboxylic acid with alkenylbromides in
1
,3-phenylene ring (120u) to y135u, rendering the molecules
the presence of potassium hydroxide in ethanol/water solution
led to low purity compounds in low reaction yields. Reaction
with oxalyl chloride of the carboxylic acids 5a and 5b then led
to the corresponding acid chlorides 6a and 6b which were
finally reacted with the substituted resorcinol of choice 7–11.
The HPLC chemical purity of the monomers Ia–Vb was
less prone to polar packing in layers. This ability is more
depressed in 4,6-dichloro-substituted molecules, in which the
bend angle is further enlarged resulting in an elongated, close to
2
4
rod-like conformation as was previously reported for other
8
azomethine banana compounds. Consistent with this inter-
pretation, IVa and IVb formed an enantiotropic, high-clearing
nematic phase relative to IIIa and IIIb, for which the nematic
phase was monotropic. It is worth mentioning that IIIb was
difficult to crystallize and the nematic mesophase could be
frozen in the glassy state on cooling below the glass transition
¢99.8%.
Phase properties
Most banana liquid crystals contain five phenyl rings, the
overall bent shape deriving from a central 1,3-phenylene
temperature at T
derivatives Va and Vb exhibited a B
~ 74 uC. On the other hand, the 2-nitro-
phase that was
g
3
core. Starting from this general formula, several options for
7
Scheme 1 Synthetic pathway for the preparation of monomers Ia–Vb.
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 2 4 9 9 – 2 5 0 6
2
5 0 2

View Article Online
enantiotropic for the latter sample only. The finding of a B
phase in the present monomers supports previous observations
that the introduction of dipolar groups, like the NO group, at
2
the 2-position of the central phenyl ring favors the occurrence
6
of such phases.
One should note that the compounds without substituents or
having electron-donating groups on their central aromatic ring
did not show any mesophase property. By contrast, banana
nematic or B phases were present when electron-withdrawing
substituents (like chloro or nitro) were connected to the central
phenyl ring. Prevention of the onset of a richer variety of
mesophases was most probably due to the presence of very
rigid arms built up from biphenyl carboxylate structures.
phase was formed at 62 uC with strong turbulence and dark fan
shaped domains. A typical texture in the X phase is shown in
Fig. 3d. Interestingly, the texture shows electro-optical switch-
2
1
ing under fields larger than 15 V mm . Under these conditions
the extinction brushes rotated by about ¡10u with the
frequency of the field. However, no simultaneous polarization
current peak could be detected. We suggest that the X phase
has a highly ordered smectic or columnar structure. Unfortu-
nately X-ray studies of this phase are difficult due to its
metastable nature and its precise structure remains to be fully
characterized.
IVa (10DClPBBC). This material also presented uniform
alignment in the nematic phase. At high frequencies there was
no realignment indicating a negative dielectric anisotropy. At
2
1
Physical properties
high frequencies (above y200 Hz) and above 3.5 V mm
instabilities in the form of regular stripes appeared as shown in
We investigated the optical textures and electro-optical
behavior of the monomers IIIa–Vb and present the results in
separate sections.
IIIa (10ClPBBC). The monotropic nematic phase appeared
on cooling to 72 uC with textures in which the optical axis was
oriented along the rubbing direction. Just before freezing at
Fig. 4a. At low frequencies the stripes were decorated with
‘‘worm’’-like defects as shown in Fig. 4b.
IVb (11DClPBBC). Similar to IVb, in its nematic phase the
director aligned parallel to the rubbing direction quite well (see
Fig. 4c). Under applied electric fields up to 100 V there was no
obvious texture change in the frequency range f w 50–100 Hz.
At low frequencies f v 10–50 Hz (depending on the field and
temperature) a hydrodynamic instability occurred with wide
stripes (y50 mm) perpendicular to the rubbing directions
decorated with narrow (5 mm wide) stripes running about ¡45u
with respect to the main stripes (see Fig. 4d). In the subsequent
wide stripes the direction of the narrow stripes interchanged.
Such textures indicate electro-hydrodynamic instabilities of
ionic origin.
6
0 uC some area became completely dark (Fig. 3a and b).
X-Ray analysis confirmed the nematic structure but could not
reveal the nature of the optically isotropic metastable state.
IIIb (11ClPBBC). The X-ray patterns of IIIb only presented
a diffuse diffraction at wide angles corresponding to a nematic
phase. We note that no diffuse peak was observed in the small
angles indicating the absence of layer fluctuations. Similar to
IIIa, the textures of nematic IIIb also showed a uniform planar
alignment (Fig. 3c) in rubbed polymer coated cells. At fre-
quencies above the hydrodynamic instability region (w100 Hz)
no field-induced realignment was observed thus indicating a
negative dielectric anisotropy. The only difference was that
here the director fluctuation appeared to be even stronger than
in the previous case, and the electro-hydrodynamic instabilities
weaker. On cooling, an additional unidentified metastable X
On cooling from the isotropic phase, both Va (10NO2PBBC)
and Vb (11NO2PBBC) formed filaments (ribbons) and other
exotic chiral objects characteristic of B textures (see Fig. 5a
7
and c). Application of electric fields during the phase transition
made the smectic front undergo a jerky motion with the fre-
quency of the applied field. This is reminiscent of the behavior
Fig. 3 Textures of IIIa and IIIb. Pictures indicate 140 mm 6 110 mm areas. Polarizers are vertical and horizontal. Upper row: 8 mm cell of
0ClPBBC. (a) Uniform texture in the nematic phase at 70 uC. Polarizers make ¡45u angle with the rubbing direction. (b) Texture during
crystallization at 60 uC. The coexistence of crystalline and optically isotropic domains (dark between crossed polarizers) can be seen. Lower row:
mm cell of 11ClPBBC. (c) Uniform texture in the nematic phase at 70 uC. Rubbing direction along the arrow. (d) Texture in the unidentified X
phase at 60 uC.
1
4
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 2 4 9 9 – 2 5 0 6
2 5 0 3

View Article Online
Fig. 4 Textures of IVa and IVb. Polarizers are vertical and horizontal. Upper row: Typical textures of the nematic phase of 10DClPBBC sample
(
8 mm thickness). (a) T ~ 90 uC, U ~ 120 V, f ~ 500 Hz; (b) T ~ 90 uC, U ~ 120 V, f ~ 50 Hz. Stripes are perpendicular to the rubbing direction.
Pictures show 300 mm 6 200 mm area. Lower row: typical textures of 11DClPBBC at 81 uC under U ~ 50 V, 30 Hz. (c) Stripes perpendicular to the
rubbing direction (500 mm 6 350 mm area). (d) Illustration of the oblique stripes with periodicity of about 5 mm (picture shows 200 mm 6 140 mm
area).
2
maximum of the polarization is about 55 nC cm for Va and
2
of some B materials, which were identified as smectics with
7
1
2
22
22 nC cm for Vb. These values are much smaller than those
triclinic symmetry. Both materials showed electro-optical
switching in about 2–5 uC range below the isotropic transitions.
In addition, ferroelectric type polarization peaks appeared
under triangular waveform excitations (see Fig. 6), that dis-
appeared in the isotropic phase and decreased slowly at lower
temperatures (for Vb it could be detected down to 40 uC). The
typically observed for other bent core smectics and should be
related to their relatively small molecular dipoles. For example,
the molecular dipole of Vb is 1.92 debye (see Table 2), which
2
1
with molar masses of about 1000 g mol and mass density
2
of about 1 g cm , would add up to about 300 nC cm for
3
22
Fig. 5 Polarizing microscopic textures of 4 mm films of Va and Vb. Upper row: Va (10NO2PBBC). (a) T ~ 118 uC at the isotropic–B
with l plate inserted (area: 150 mm 6 100 mm). (b) T ~ 113 uC (area: 300 mm 6 200 mm). Lower row: Vb (11NO2PBBC). (c) T ~ 113 uC at the
isotropic–B transition with l plate inserted (area: 150 mm 6 120 mm). (b) T ~ 109 uC (area: 150 mm 6 120 mm).
7
transition
7
2
5 0 4
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 2 4 9 9 – 2 5 0 6

View Article Online
Fig. 7 Small angle X-ray pattern for 11NO2PBBC (Vb) at 114 uC.
˚
There is only one peak detected with periodicity of 37.5 A. Insert show
the scattering profile.
Quantum-chemical calculations
The quantum-chemical calculations were carried out by the semi-
empirical CAChe/MOPAC/PM5 method. The PM5 Hamiltonian
is claimed to have an improvement in accuracy by a factor of 4,
compared to AM1 or PM3 (Cache information about MOPAC
2
002). Table 2 contains the heat of formation of the most stable
conformers, the dipole moments and the bend angles of the
compounds in gas phase, and the distance between the
most distant carbons of the two arms of the mesogens with
undecenyl tails. We expect that no appreciable differences
would be computed for the mesogens with just shorter decenyl
tails. It must be emphasized, however, that the calculated data
collected in Table 2 are valid for isolated molecules like those in
the gas phase. In condensed phases like those of liquid crystals,
due to intermolecular interaction the molecular shape can be
substantially changed. One should note that the evaluated bend
angle was lowest for the 2-nitro-derivative Vb (110u). This value
is close to the tetrahedral angle and may suggest a better
suitability to form a B phase for this type of bent-shaped
structure. The other derivatives investigated possessed much
wider bend angles (w120u). However, the bend angle computed
for IVb showed a large deviation (Table 2) from the empirical
Fig. 6 Time dependence of the electric current in 4 mm cell of
10NO2PBBC (Va) and 11NO2PBBC (Vb) under triangular wave
22
excitation. (a) Va at 113 uC, peak corresponds to P
s
~ 55 nC cm
.
(
b) Vb at T ~ 109 uC. The integral area of the electric current peak
22
0
indicates P ~ 22 nC cm spontaneous polarization.
2
2
perfect order. The maximum of 22 nC cm that appears 5 uC
below the clearing point indicates therefore a polar ordering of
about 0.1. This order probably increases at lower temperatures,
however the threshold for switching increases strongly and is
above the experimentally achievable fields. Here we note that
7
ferroelectric type switching in the B phase has been observed
for other materials, too (for example see ref. 25). The absence
of the electrooptical switching at lower temperatures indicates
a F
racemic tilted ferroelectric (SmC P ) or non-tilted (SmAP)
type structures. The polarization current peak position under a
rectangular waveform excitation indicated a switching time of
1
3
results obtained by C NMR spectroscopy, which gave a value
2
4
2
about 150 ms at 20 V mm field.
1
of about 156u. The bend angles in the mesophase are under
investigation by H NMR spectroscopy of appropriately
2
Small angle X-ray measurements (Fig. 7) on 16 mm thick
˚
films evidenced smectic order with a layer spacing of 37.5 A.
deuterated analogues. On the other hand, the 4,6-dichloro-
derivative presented the greatest dipole moment in this
series (3.20 D). The optimized structures derived by CAChe/
MOPAC/PM5 are illustrated in Fig. 8 for representative
monomers.
Interestingly, however, X-ray measurements on powder
samples indicate modulated layer structures similar to other
1
0
7
switchable B materials. This may be related to the partial
alignment formed spontaneously in the film, as indicated by the
diffraction pattern shown in the insert of Fig. 7 for Vb. Further
studies are under way to clarify the difference measured in thin
film and powder specimens.
Conclusion
The studied 1,3-phenylene bis[4’-(alken-1-yloxy)-1,1’-biphenyl-
4
-carboxylate]s present a complex phase dependence on the
Table 2 CAChe/MOPAC/PM5 calculations on the monomers
chemical structure, with nematic, smectic or B phases being
formed in the different analogues. It is remarkable that the
parent, unsubstituted banana monomers do not present liquid
crystal behavior, not even monotropic in character. Nonethe-
less, the mesophase ranges appear at are relatively low tem-
peratures compared to other nematic bent core materials. Thus,
fine details of the chemical structure can affect significantly the
mesophase behavior in banana molecules. The structural
requirements for this class of liquid crystal materials appear
to be more stringent than for calamitic mesogens, for which
more reliable guidelines are available for the design of materials
Heat of formation/
kcal mol
Bend angle/
degree
2
1
a
L /A
˚
Monomer
m/D
Ib
2171.6
2178.8
2176.9
2182.1
2174.0
133
133
138
122
110
1.82
1.89
1.15
3.20
1.92
50.1
50.8
51.1
47.9
44.8
IIb
IIIb
IVb
Vb
a
Distance between the outermost carbon atoms in the two side
arms.
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 2 4 9 9 – 2 5 0 6
2 5 0 5

View Article Online
Fig. 8 Optimized structures for selected monomers with different substituents on the central phenyl ring by CAChe/MOPAC/PM5.
with desired phases and physical properties. One special feature
of these banana monomers may be associated with the electro-
hydrodynamic instabilities in the nematic phase. They indicate
unconventional behavior with possible involvement of flexo-
electricity, and further investigations are in progress. The B7
structure of the 2-nitro-derivatives also has one of the lowest
temperature ranges in the literature, which should make easier
future studies of the polarization and electro-optical switching
properties in such materials.
6
7
8
9
G. Pelzl, S. Diele, A. J a´ kli, Ch. Lischka, I. Wirth and W. Weissflog,
Liq. Cryst., 1999, 26, 135.
D. Shen, A. Pegenau, S. Diele, I. Wirth and C. Tschierske, J. Am.
Chem., Soc., 2000, 122, 1593.
G. Pelzl, S. Diele and W. Weissflog, Adv. Mater., 1999, 11, 707
and references therein.
(a) J. Matraszek, J. Mieczkowski, J. Szydlowska and E. Gorecka,
Liq. Cryst., 2000, 27, 429; (b) I. Wirth, S. Diele, A. Eremin,
G. Pelzl, S. Grande, L. Kovalenko, N. Pancenko and W. Weissflog,
J. Mater. Chem., 2001, 11, 1642.
D. A. Coleman, J. Fernsler, N. Chattham, M. Nakata,
Y. Takanishi, E. K o¨ rblova, D. R. Link, R.-F. Shao, W. G. Jang,
J. E. Maclennan, O. Mondainn-Monval, C. Boyer, W. Weissflog,
G. Pelzl, L.-C. Chien, J. Zasadzinski, J. Watanabe, D. M. Walba,
H. Takezoe and N. A. Clark, Science, 2003, 301, 1204.
W. Weissflog, C. Lischka, S. Diele, G. Pelzl, I. Wirth, S. Grande,
H. Kresse, H. Schmalfuss, H. Hartung and A. Stettler, Mol. Cryst.
Liq. Cryst., 1999, 333, 203.
2
6
1
0
1
Acknowledgements
We are grateful to the Hungarian Research Funds OTKA
T030401 and OTKA T32667 and the EU Center of Excellence
1
(
KFKI-CMRC) ICAI-CT-2000-70029. Part of this work was
also performed within the European COST, Action D14
WG15, and bilateral agreements between the Hungarian
Academy of Sciences, the Italian CNR and US National
Science Foundation. The Midwest Universities Collaborative
Access Team (MUCAT) sector at the APS, Argonne, IL was
supported by the U.S. Department of Energy, Office of Science,
Office of Basic Energy Sciences, through the Ames Laboratory
under Contract No. W-7405-Eng-82.
1
1
2
3
A. J a´ kli, D. Kr u¨ erke, H. Sawade and G. Heppke, Phys. Rev. Lett.,
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B. K. Sadashiva, H. N. Shreenivasa Murthy and S. Dhara, Liq.
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14 E. M a´ tyus and K. Fodor-Csorba, Liq. Cryst., 2003, 30, 445.
001, 86(25), 5715.
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M. Kaspar, V. Hamplova, V. Novotna, M. Glogarova and
P. Vanek, J. Mater. Chem., 2002, 12, 2221.
C. Tschierske, Curr. Opin. Colloid Interface Sci., 2002, 7, 69.
C.-D. Keum, A. Kanazawa and T. Ikeda, Adv. Mater., 2001, 13,
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5
2
5 0 6
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 2 4 9 9 – 2 5 0 6