Ferro-, ferri- and antiferro-electric behaviour in a bent-shaped mesogen

Article abstract of DOI:10.1039/b000128g

The synthesis of a novel bent-shaped, four-ring thiophene-based chiral liquid crystalline ester derived from 5-(4-n-decyloxyphenyl)thiophene-2- carboxylic acid and (S)-1-methylheptyl 4'-hydroxybiphenyl-4-carboxylate is reported, i.e., (S)-4'-(1-methylheptyloxycarbonyl)biphenyl-4-yl 5-(4-n- decyloxyphenyl)thiophene-2-carboxylate. Optical microscopy, differential scanning calorimetry, miscibility study, and complementary electro-optical and current response studies reveal the existence of the SmA*, SmC* ferroelectric, SmC* ferrielectric, SmC* antiferroelectric and SmI* antiferroelectric phase types. Another mesophase type possibly exists below SmI* antiferroelectric which generates a rapid electro-optic response. Comparison with the analogous three-ring compound, i.e., (S)-4-(1- methylheptyloxycarbonyl)phenyl 5-(4-n-decyloxyphenyl)thiophene-2-carboxylate increases the thermal stability by 95.8 °C and the SmI* antiferroelectric phase is observed in addition.

Full text of DOI:10.1039/b000128g

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J O U R N A L O F
Ferro-, ferri- and antiferro-electric behaviour in a bent-shaped
mesogen
a
Avtar S. Matharu,* Chrissie Grover, Lachezar Komitov and Gunnar Andersson
a
b
b
a
Department of Chemistry and Physics, The Nottingham Trent University, Clifton Lane,
Nottingham, UK NG11 8NS. E-mail: avtar.matharu@ntu.ac.uk
Department of Microelectronics and Nanoscience, Chalmers Institute of Technology, S-412
C H E M I S T R Y
b
96, G oÈ teborg, Sweden
Received 6th January 2000, Accepted 22nd March 2000
Published on the Web 4th May 2000
The synthesis of a novel bent-shaped, four-ring thiophene-based chiral liquid crystalline ester derived from 5-(4-
n-decyloxyphenyl)thiophene-2-carboxylic acid and (S)-1-methylheptyl 4'-hydroxybiphenyl-4-carboxylate is
reported, i.e., (S)-4'-(1-methylheptyloxycarbonyl)biphenyl-4-yl 5-(4-n-decyloxyphenyl)thiophene-2-carboxylate.
Optical microscopy, differential scanning calorimetry, miscibility study, and complementary electro-optical and
current response studies reveal the existence of the SmA*, SmC*ferroelectric, SmC*ferrielectric,
SmC*antiferroelectric and SmI*antiferroelectric phase types. Another mesophase type possibly exists below
SmI*antiferroelectric which generates a rapid electro-optic response. Comparison with the analogous three-ring
compound, i.e., (S)-4-(1-methylheptyloxycarbonyl)phenyl 5-(4-n-decyloxyphenyl)thiophene-2-carboxylate
increases the thermal stability by 95.8 ³C and the SmI*antiferroelectric phase is observed in addition.
i.e., (S)-4-(1-methylheptyloxycarbonyl)phenyl 5-(4-n-decyloxy-
5
phenyl)thiophene-2-carboxylate. The inclusion of an extra 1,4-
Introduction
Following the recent 17th International Liquid Crystal
1
Conference, Strasbourg, France, the area of design, synthesis
disubstituted phenyl ring is expected to increase mesophase
thermal stability either with retention, reduction or increase in
the number of phase types. We envisage that the increase in
thermal stability will induce the occurrence of phase types
which appear below the SmC*antiferroelectric phase, e.g.,
either SmI*antiferroelectric and/or high order crystal phases.
and properties of ferri- and antiferro-electric liquid crystals
attracted considerable attention. Compounds that exhibit these
2
properties were ®rst reported by Chandani et al. in 1989. The
antiferroelectric phase is particularly important because it
participates in tristate switching via a very sharp electric ®eld
3
threshold. In some instances, the electric ®eld threshold may
be absent or minimal in which case the switching process is said
to be thresholdless.
Results and discussion
Synthesis
The majority of compounds that exhibit the ferri- and
antiferro-electric phase types are based on the conventional
calamitic structural geometry, i.e., linear and lath-like, and
readily employ 1,4-disubstituted phenylene rings. However,
there are relatively few examples reported in the literature
The synthetic pathway for the preparation of compound 1 is
summarised in Scheme 1. Chiral phenol, 6, was prepared
according to the method reported by Booth et al.
4-n-Decyloxyphenylboronic acid, 3, was prepared from its
corresponding 4-n-decyloxy-1-bromobenzene, 2, via low tem-
6
4
based on either a bent or non-linear molecular architecture.
Thiophene is a ®ve-membered heterocycle containing sulfur
which readily undergoes electrophilic aromatic substitution at
either the a- or 2-, 5-positions (ortho- to the sulfur atom). Such
a disposition of substituents generates an exocyclic bond angle
of 148³ which gives rise to a bend in the molecule. The central
sulfur atom creates a strong transverse dipole moment, which
may favour polar ordering. The exocyclic bond angle is
intermediate between those for 1,4- (180³) and 1,3-phenylene
perature lithiation (278 ³C) followed by trimethyl borate
quench. Palladium-catalysed cross-coupling of the boronic
7
acid, 3, with commercial 2-bromothiophene afforded the
intermediate 2-(4-n-decyloxyphenyl)thiophene, 4, which was
then lithiated and treated with solid carbon dioxide to afford
8
the desired carboxylic acid, 5. Esteri®cation of compound 5, in
the presence of 1,3-dicyclohexylcarbodiimide (DCC) and 4-
dimethylaminopyridine (DMAP) as catalyst, with (S)-1-
methylheptyl 4'-hydroxybiphenyl-4-carboxylate, 6, furnished
the desired (S)-4'-(1-methylheptyloxycarbonyl)biphenyl-4-yl 5-
(4-n-decyloxyphenyl)thiophene-2-carboxylate, 1.
(
120³) and compounds comprising thiophene are expected to
maintain mesomorphic properties. Hence, thiophene appears
to be a natural choice for the study of bent-shaped molecules
5
and is exempli®ed by Byron et al. in a recent publication.
In this study, we aim to combine the attributes of shape
geometry with chirality by investigating the occurrence of
ferro-, ferri-, and antiferro-electricity in a four-ring thiophene-
based chiral ester. To this effect, we now report the synthesis
and characterisation (optical microscopy: glass slide and
coverslip, and free standing ®lms, miscibility study, differential
scanning calorimetry, and complementary electro-optical and
current response studies) of (S)-4'-(1-methylheptyloxycarbo-
Optical microscopy, differential scanning calorimetry, miscibility
study
Table 1 lists the mesomorphic transition temperatures and
thermodynamic data for compound 1. The optical studies were
performed using
a Nikon OPTIPHOT2-POL polarising
microscope equipped with a Sony Hyper HAD SSC-DC38P
digital video camera interfaced to a computer for direct image
processing and storage, and a Mettler FP52 hot stage and FP5
control unit. Thermodynamic data were recorded using a
Perkin-Elmer DSC7 differential scanning calorimeter. Textural
nyl)biphenyl-4-yl 5-(4-n-decyloxyphenyl)thiophene-2-carb-
oxylate, 1. The liquid crystalline properties will be compared
with the analogous three-ring compound reported previously,
DOI: 10.1039/b000128g
J. Mater. Chem., 2000, 10, 1303±1310
This journal is # The Royal Society of Chemistry 2000
1303

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Fig. 1 Focal-conic fan and homeotropic texture (dark) of the SmA*
phase.
transitional effects associated with the SmC*ferroelectric±
SmC*ferrielectric transition. The SmC*ferrielectric phase was
characterised by the appearance of a highly mobile, turbulent,
milky-white texture in the pseudohomeotropic region together
with disruption of the focal-conic fan texture (Fig. 3a). Shortly
afterwards, the intense shimmering ceased to leave a `home-
otropic area' reminiscent of the SmA* phase but instead
corresponds to the SmC*antiferroelectric phase (Fig. 4a). As
the temperature is decreased, the arcs across the backs of the
fans become more pronounced and the pseudohomeotropic
region becomes mobile and exhibits a silver±grey luminescent
texture. Prior to the onset of the next transition, a highly
mobile, golden-yellow schlieren-mosaic-like texture develops
which then clears to leave a very faint dull schlieren-mosaic-like
texture with pronounced band/arc formation across the fans.
At this stage, due its rather confusing texture, i.e., similarities
both of a smectic liquid crystal phase and a smectic crystal
phase, the identity of this phase type could not be determined
with any assurance. As reported later, a miscibility study using
free-standing ®lms was undertaken to ascertain the true
identity of this phase type. The presence of a mosaic texture
with strong grain boundaries in the free-standing ®lm would be
indicative of a high order smectic crystal phase. However at this
stage this phase was tentatively assigned as SmI* due to the
presence of a schlieren-mosaic-like texture which was dif®cult
to bring in to optical focus (Fig. 5a). Thereafter, a granular
texture began to form slowly across the fans suggesting either
the onset of crystallisation evidenced by a large enthalphy of
Scheme 1 Reagents and conditions: i, 1.6 M BuLi, then B(OMe)
, 2 M Na CO , re¯ux; iii,
, 278 ³C to room temp.; iv, DCC, DMAP,
3
,
2
78 ³C; ii, 2-bromothiophene, Pd(PPh
3
)
4
2
3
1
.6 M BuLi, then CO
2
2 2
CH Cl .
investigation of the phase types was undertaken both by
viewing the sample con®ned between a glass slide and coverslip,
and as a free-standing ®lm.
In the case of the sample contained between a glass slide and
a coverslip, on cooling from the isotropic liquid the SmA*
phase was readily characterised by the appearance of focal-
conic fans interspersed within a predominantly homeotropic
texture (Fig. 1). The appearance of a vivid blue colouration
(
selective re¯ection) in the previously homeotropic regions
coupled with formation of faint arcs across the focal-conic fans
marked the onset of the SmC*ferroelectric phase (Fig. 2a).
However, the real or true onset of the phase transition may
have occurred earlier but could not be detected optically
because it probably has a pitch that is shorter than the
wavelength of visible light. The colour in the pseudohomeo-
tropic region changes dramatically from an initial blue to
green/red and then back to blue as the material is cooled. Such
colour changes at a simplistic level show the temperature
dependence of the pitch but interestingly also reveal that the
material changes from short pitch (blue) to long pitch (red) and
back to short pitch (blue). It must be stressed that the onset of
the blue colouration on cooling may also be due to pre-
2
1
transition (15.2 kJ mol ) as detected by DSC or a high order
smectic crystal phase (Fig. 6a). However, the latter seems more
feasible as an electro-response is detected in this phase (see
later).
Usually a textural study of this type is adequate for
a
21 a
Table 1 Liquid crystal transition temperatures (³C) and enthalpy data (kJ mol
decyloxyphenyl)thiophene-2-carboxylate 1
) for (S)-4'-(1-methylheptyloxycarbonyl)biphenyl-4-yl 5-(4-n-
I±SmA*
SmA*±SmC*ferro
SmC*ferro±SmC*ferri
SmC*ferri±SmC*anti
S
C
*anti±SmI*anti
SmI*anti±`SmX'
c
c
c
c
c
1
93.2
7.6]
183.2
159.6
[Ð]
158.3
[Ð]
106
53.2
[15.2]
b
b
[
[0.69]
[1.38]
a
The ®rst row gives transition temperatures and the second row [in square brackets] gives enthalpies of transition on cooling (DSC scan rate
21
b
c
1
0 ³C min ). The enthalpy of transition was too small to be evaluated. Transition temperature determined from free standing ®lm at a cool-
21
ing rate of 1 ³C min
.
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Fig. 2 Optical textures of the SmC*ferroelectric phase: (a) sandwich cell and (b) free-standing ®lm.
mesophase identi®cation and determination of transition
temperatures. However determination of precise temperatures
for the occurrence of the ferri- and antiferro-electric phase
types is dif®cult because of strong and differing boundary
conditions imposed by the glass substrates of the sandwich cell.
Such forces can either induce or destroy the ferrielectric phase,
and lead to problems of co-existence with either the ferro-
electric and/or antiferroelectric phases. To minimise the
in¯uence of boundary conditions, optical textures and
transition temperatures were further determined using the
free-standing ®lm technique.
The sample was heated to the SmA* phase and stretched
across a 1 mm diameter hole, pre-drilled in a copper plate,
using the edge of a coverslip. On cooling from the SmA* phase
which obviously appears optically extinct between crossed
polarisers, the SmC*ferroelectric phase appeared as a specta-
cular blue±green haze (Fig. 2b). Onset of continuous shimmer-
ing marked the transition to the SmC*ferrielectric phase
electric phase produced a rather peculiar ®ngerprint texture
which soon cleared to leave a schlieren-mosaic-like texture
characteristic of the SmI*antiferroelectric (Fig. 5b) phase. The
®ngerprint texture may be due either to molecular re-ordering
as a consequence of the transition or a possible helix inversion.
This texture is quite different to transition bars or the inversion
9
lines reported by Loubser et al., but similar to the textures
1
0
reported by Gorecka et al. We are currently undertaking
elaborate pitch measurement studies to ascertain further the
origin of this peculiar ®nger-print texture. Thereafter, a
granular texture developed in the free-standing ®lm (Fig. 6b)
which may be onset of slow crystallisation or a high order
smectic crystal phase.
Miscibility study, investigating the optical texture of each
mixture as a free standing ®lm, with (S)-1-methylheptyl 4-(4'-
nonyloxybiphenyl-4-ylcarbonyloxy)benzoate, 7, as the stan-
1
1
dard material
[transitions/³C: iso 142.2, SmA* 118.0,
(
(
Fig. 3b). As the shimmering stopped, a clear ®lm developed
pseudohomeotropic) characteristic of the SmC* antiferro-
electric phase (Fig. 4b). Further cooling of the SmC* antiferro-
Fig. 3 Optical textures of the SmC*ferrielectric phase: (a) sandwich cell and (b) free-standing ®lm.
J. Mater. Chem., 2000, 10, 1303±1310
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Fig. 4 Optical textures of the SmC*antiferroelectric phase: (a) sandwich cell and (b) free-standing ®lm.
SmC*ferroelectric 112.0, SmC*ferrielectric 105.0, SmC*anti-
ferroelectric 58.0, SmI*antiferroelectric] reveals continuous
miscibility of the SmC*ferroelectric, SmC*ferrielectric,
SmC*antiferroelectric and SmI*antiferroelectric phases
across the entire composition range (Fig. 7).
Compound 1 and (S)-4-(1-methylheptyloxycarbonyl)phenyl 5-
(4-n-decyloxyphenyl)thiophene-2-carboxylate were prepared
using high purity (R)-octan-2-ol but from different batches.
Hence we can not guarantee identical optical purity which
invalidates the comparison of ferri- and antiferro-electric
thermal stability.
Comparative study
Electro-optic and current response studies
Comparison of the thermal properties of compound 1 with the
analogous three-ring compound reported previously, i.e., (S)-4-
The apparent tilt angle, spontaneous polarisation, electro-optic
and current response were studied in glass cells consisting of
two parallel glass plates with inner surfaces coated with a
transparent conductive layer of indium tin oxide (ITO). The
distance between the two plates was kept constant by spacers of
2 mm thickness. On the inner surface of the ITO layer, a
polyimide alignment layer was deposited which was then
rubbed unidirectionally in order to achieve the bookshelf
geometry, i.e., smectic layers perpendicular with respect to the
glass substrates. The liquid crystal material was heated in to the
isotropic liquid and allowed to enter the cell via capillary
(
1-methylheptyloxycarbonyl)phenyl
5-(4-n-decyloxyphe-
nyl)thiophene-2-carboxylate [transitions/³C: iso 97.4, SmA*
2.2, SmC*ferroelectric 81.4, SmC*ferrielectric 78.8, SmC*an-
tiferroelectric 48.6 cryst.] reveals that the inclusion of an extra
,4-disubstituted phenyl ring increases mesophase thermal
5
9
1
stability by 95.8 ³C. In addition, an extra phase is observed,
namely the SmI*antiferroelectric. However, it is unwise to
make comparisons of the thermal properties of the SmC*ferri-
and SmC*antiferro-electric phases because it is well known
that both are affected by subtle changes in optical purity.
Fig. 5 Optical textures of the SmI*antiferroelectric phase: (a) sandwich cell and (b) free-standing ®lm (emerging from RHS).
J. Mater. Chem., 2000, 10, 1303±1310
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Fig. 6 Optical textures of the `SmX' phase: (a) sandwich cell and (b) free-standing ®lm.
action. The cell was inserted in a Mettler FP52 hot stage with
temperature control within ¡0.1 ³C. The electro-optic
responses of the samples were studied between cross-polarisers
with sample optic axis oriented at 22.5³ with respect to one of
the polarizers.
angle, a, between the positions of the sample optic axis
corresponding to different ®eld polarity. Angle a was found
simply by rotating the sample between the cross polarisers and
detecting the positions of two consecutive minima in the
intensity of the light transmitted through the sample. The
The apparent tilt angle, happ, was measured as a half of the
S
spontaneous polarisation, P , was measured according to the
1
2
capacitance bridge method. The applied voltage was kept
high enough to ensure complete saturation of the ferroelectric
switching.
The temperature dependence of the apparent tilt angle, happ
,
is shown in Fig. 8, and reveals a rather large maximum
apparent tilt angle of approximately 37³. On cooling, happ
increases continuously in the SmC* phase region whereas, in
the SmC* ferri- and antiferro-electric phases, saturation at
different levels is observed.
As shown in Fig. 9, the temperature dependence of the P at
S
1
1
P
00 ³C reveals
a
maximum value of approximately
60 nC cm . Fig. 10 shows the voltage dependence of the
at 158.5 ³C and reveals the presence of the ferrielectric
2
2
S
phase. Initially at low voltages, the P
S
rises sharply (helix
unwinding) and then reaches
(
the ferrielectric state. Thereafter, the P continues to increase
a
P ~70 nC cm ; threshold voltage, V ~8 V) indicative of
short-lived plateau
2
S C
2
S
(
before reaching a second stable saturation point (®eld-induced
®eld-induced transition of the ferri- to the ferro-electric state)
2
2
.
ferroelectric state) with
P
S
approximately 120 nC cm
Fig. 7 Miscibility diagram for various compositions of (S)-4'-(1-
methylheptyloxycarbonyloxy)biphenyl-4-yl
thiophene-2-carboxylate (1) with the standard (S)-1-methylheptyl 4-
4'-nonyloxybiphenyl-4-ylcarbonyloxy)benzoate (7).
5-(4-n-decyloxyphenyl)-
Fig. 8 Temperature dependence of the apparent tilt angle, happ, at an
.
2
1
(
applied electric ®eld of E~15 V mm
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Fig. 11 Current hysteresis loops for the ferrielectric phase at
E~4 V mm (small loop) and E~15 V mm (large loop) for a 2 mm
thick sample.
2
1
21
Fig. 9 Temperature dependence of the spontaneous polarisation, P
for a 2 mm thick sample.
S
,
results are not obtained, for example, the current peaks are
asymmetric (Fig. 13) and the transmittance between the two
peaks either side of the antiferroelectric state is non-identical.
At present we cannot fully explain these unusual results,
however, they may be due to the in¯uence of strong liquid
crystal±glass substrate boundary forces. Such interactions are
well known to destroy ferri- and antiferro-electric ordering and
promote ferroelectric ordering leading to unusual results. Also,
there may be asymmetry in the surface treatment of both
substrate surfaces, i.e., the cell itself. Non-identical transmit-
tance may be due to the fact that this material possesses an
unusually high molecular tilt angle in the region of 33±38³ in
the ferri- and especially in the anti-ferroelectric state, i.e., much
larger than 22.5³.
Although the magnitude of this ratio is not 1 : 3 as readily
described in the literature, the threshold behaviour of P in the
S
ferrielectric phase was further examined by investigation of
current hysteresis loops at lower and higher voltages with
respect to V (Fig. 11).
C
Unfortunately, the classical single loop with tri-step
character at low voltages was not observed due to the
limitations of the instrument. The measurements have been
made at a frequency of 4 Hz, which is still deemed too high for
the ferrielectric state to be detected as it attempts slowly to
relax back from the ®eld-induced ferroelectric state. If a
suf®ciently low operating frequency could have been generated,
such as 0.1 Hz, then a classical loop with tri-step character
would be observed. Increasing the frequency to 1 kHz merely
caused broadening of the hysteresis loop with no change in the
magnitude of the polarisation.
Fig. 12 reveals the characteristics of the ferrielectric phase.
The current response matches changes in optical response.
However, notably, the current response does not fall to zero
immediately (two very close peaks) which clearly discriminates
from being either the ferro- or antiferro-electric phase.
Thereafter, as the temperature is cooled and the antiferro-
electric phase is established, two well separated peaks are
observed for the current response which correspond to the
antiferroelectric phase, i.e., tristate switching (Fig. 13).
The SmI*antiferroelectric phase is characterised by the
development of more current peaks, in our case there are three,
each of them gives a corresponding optical response (Fig. 14).
This behaviour may be attributed to a complex switching
pattern of the antiferroelectric SmI*antiferroelectric phase.
The corresponding DSC data for the ferrielectric phase was
re-examined to check for the possibility of subphases.
Unfortunately, this was inconclusive because of the narrow
temperature interval of the ferrielectric phase (1.3 ³C) coupled
with the weak second-order nature of the transition. The trace
in this region is very diffuse, probably due to co-existence of
phases, and in some parts indistinguishable from the back-
ground. However, possible occurrence of ferrielectric±ferri-
electric transitions should not be discounted and a conoscopic
1
3,14
or similar electric ®eld study
reveal further information.
on free-standing ®lms may
15
Goodby et al. have reported similar complex switching
behaviour for the SmI phase.
Surprisingly, as shown in Fig. 15, a linear electro-optic
Fig. 12±14 depict the current and optic response behaviour
with respect to triangular-wave applied voltage. Classical
Fig. 12 Electro-optical and current response for a 2 mm thick sample in
the ferrielectric phase when a voltage of UPP~40 V and f~0.1 Hz is
applied to the cell. The traces 1, 2 and 3 are the applied voltage, optic
and current response, respectively.
Fig. 10 Voltage dependence of P
for a 2 mm thick sample.
S
in the ferrielectric phase at 158.5 ³C
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Fig. 15 Electro-optic response in the `SmX' at 28 ³C for a 2 mm thick
sample when a voltage of UPP~200 V and f~106 Hz is applied to the
cell.
Fig. 13 Electro-optical and current response for a 2 mm thick sample in
the antiferroelectric phase at 125 ³C when a voltage of UPP~40 V and
f~0.1 Hz is applied to the cell.
lysed (4 M HCl) over a 1 h period. Subsequently, the crude
product was extracted with diethyl ether, dried (MgSO ) and
4
the solvent removed in vacuo to yield the crude 4-n-
decyloxyphenylboronic acid, 3, (91%) as an off-white solid.
A small amount of the boronic acid was puri®ed by washing
with hot petroleum ether (bp 60±80 ³C) followed by recrys-
tallisation from water to furnish the pure 4-n-decyloxyphenyl-
boronic acid, 3, as a white solid. However, the remainder was
used as crude in the next step of the reaction scheme.
response with a response time of approximately 200 ms
(
crystal phase or high order smectic crystal phase, SmX. Since
switching is detected it most likely corresponds to a high order
smectic crystal phase and at present we cannot explain fully its
origin and it is subject to extensive further investigation.
frequency, 100 Hz) was detected deep in to the so called
d
(
H
(CDCl
2 H, quintet, ArOCH
ArH, J~8 Hz), 7.8 (2 H, d, ArH, J~8 Hz); IR nmax (KBr)
550±3200 (OH str.), 2920, 2850, 1605, 1465, 1411, 1351, 1251,
3
): 0.9 (3 H, t, CH
3
), 1.2±1.5 (14 H, m, (CH
2 7
) ), 1.8
2
CH ), 4.0 (2 H, t, ArOCH
2
2
), 6.8 (2 H, d,
Experimental
3
Structural con®rmation of the structures of the intermediates
1
and products was obtained by H NMR spectroscopy (JEOL
2
1
z
1171, 822 cm ; MS, m/z: 278 (M ), 234 (10%), 94 (100%).
FX60Q 270 MHz spectrometer) with tetramethylsilane as the
internal standard and infrared spectroscopy (Perkin-Elmer FT
2
-(4-n-Decyloxyphenyl)thiophene 4
1
605 spectrophotometer). Mass spectra were determined with a
VG 7070E mass spectrometer. The speci®c optical rotation of
compound 1, dissolved in analytical grade CHCl , was
determined at room temperature using a Perkin-Elmer 241
A solution of crude 4-n-decyloxyphenylboronic acid, 3, (8.8 g,
0
mixture of 2-bromothiophene (5.2 g, 0.032 mol), tetrakis(tri-
phenylphosphine)palladium(0) (0.5 g, 0.0004 mol), aqueous
sodium carbonate (2 M, 30 ml) and 1,2-dimethoxyethane
.032 mol) in ethanol (20 ml) was added to a rapidly stirred
3
2
1
2
21
polarimeter and is given in 10 deg cm g . (R)-Octan-2-ol
(ChiraSelect, ¢99%) was purchased from the Aldrich Chemi-
cal Company and chiral phenol, 6, was prepared according to
(
30 ml). The mixture was heated under re¯ux until all the 2-
bromothiophene had been consumed (monitored by thin layer
chromatography). The reaction mixture was then cooled,
6
the method reported by Booth et al.
extracted with diethyl ether, dried (MgSO
removed in vacuo. The resulting brown solid was puri®ed by
ash chromatography on silica gel, eluting with 9 : 1 petroleum
ether (bp 40±60 ³C)±dichloromethane to afford the desired 2-
4-n-decyloxyphenyl)thiophene, 4, 6.6 g (65%) as a pale yellow
solid, 74 ±77 ³C: d (CDCl ) 0.9 (3 H, t, CH ), 1.2±1.45 (14 H,
m, (CH ), 1.8 (2 H, quintet, ArOCH CH ), 4.0 (2 H, t,
4
) and the solvent
4
-n-Decyloxyphenylboronic acid 3
¯
In an inert atmosphere of nitrogen, commercial 1.6 M n-
butyllithium (32 ml, 0.052 mol) was injected, dropwise, to a
cooled (278 ³C), stirred, solution of 4-n-decyloxy-1-bromo-
benzene, 2, (16 g, 0.051 mol) in dry tetrahydrofuran (100 ml) at
such a rate that the temperature did not exceed 265 ³C. After
stirring for a further 2 h, trimethyl borate (22 ml, 0.194 mol)
was injected and the solution was allowed to stir to room
temperature overnight. The reaction mixture was then hydro-
(
H
3
3
2
)
7
2
2
ArOCH ), 6.9 (2 H, d, ArH, J~8 Hz), 7.05 (1 H, d, ThH,
2
J~4 Hz), 7.19 (1 H, d, ThH, J~4Hz), 7.50 (2 H, d, ArH,
J~8 Hz); IR nmax (KBr) 2954, 2918, 2848, 1606, 1533, 1501,
2
473, 1288, 1180, 1036, 854, 700, 681 cm ; MS, m/z: 316 (M ,
1
z
1
1
00%), 176 (20%).
5
-(4-n-Decyloxyphenyl)thiophene-2-carboxylic acid 5
In an inert atmosphere of nitrogen, commercial 1.6 M n-
butyllithium (12 ml, 0.019 mol) was added dropwise to a
stirred, cooled (278 ³C) solution of 2-(4-n-decyloxyphe-
nyl)thiophene, 4, (5.4 g, 0.017 mol) in dry tetrahydrofuran
(
50 ml) at such a rate that the temperature did not exceed
265 ³C. The resulting mixture was stirred for a further 2 h,
poured on to a large excess of solid carbon dioxide and allowed
to stand overnight. The solution was acidi®ed (4 M HCl),
extracted with diethyl ether, dried (MgSO ) and the solvent
4
removed in vacuo to yield a green solid. The carboxylic acid was
used in the next step without further puri®cation. d (CDCl )
H
3
0
ArOCH CH ), 4.0 (2 H, t, ArOCH ), 4.5 (1 H, s, OH,
3 2 7
.9 (3 H, t, CH ), 1.2±1.45 (14 H, m, (CH ) ), 1.8 (2 H, quintet,
Fig. 14 Electro-optical and current response for a 2 mm thick sample in
the SmI*antiferroelectric phase at 95 ³C when a voltage of UPP~57 V
and f~0.1 Hz is applied to the cell.
2
2
2
disappears on D
2
O shake), 6.9 (2 H, d, ArH, J~8 Hz), 7.2 (1
J. Mater. Chem., 2000, 10, 1303±1310
1309

View Article Online
H, d, ThH, J~4 Hz), 7.60 (2 H, d, ArH, J~8 Hz), 7.82 (1 H, d,
ThH, J~4Hz); IR nmax (KBr) 3500±2950 (OH str.), 1702 (CLO
str.), 1253, 1180, 814 cm ; MS, m/z: 360 (M , 2%), 176
ferroelectric phase. This is currently under further investigation
together with elaborate pitch studies on the ®ngerprint texture
of the SmC*antiferroelectric phase. The results of these studies
will be published in a later communication.
2
1
z
(
100%).
(
S)-4'-(1-Methylheptyloxycarbonyl)biphenyl-4-yl 5-(4-n-
decyloxyphenyl)thiophene-2-carboxylate 1
Acknowledgements
1
,3-Dicyclohexylcarbodiimide (0.50 g, 0.0024 mol) and (S)-1-
ASM would like to thank the Royal Society of Chemistry for
the award of a `JWT Jones Travelling Fellowship' in order to
participate in electro-optical characterisation at Chalmers
University of Technology, Sweden, and the Engineering and
Physical Sciences Research Council (research studentship for
C.G.).
methylheptyl 4'-hydroxybiphenyl-4-carboxylate, 6, (0.36 g,
0
2
(
.0014 mol) were added to 5-(4-n-decyloxyphenyl)thiophene-
-carboxylic acid, 5, (0.0014 mol) in dry dichloromethane
25 ml). 4-Dimethylaminopyridine (1±2 crystals) was added as
catalyst and the reaction mixture was left to stir for 2 h at room
temperature. The resultant white precipitate was removed by
®ltration and the ®ltrate was evaporated to dryness under
reduced pressure. The crude residue was puri®ed by ¯ash
chromatography on silica gel eluting with 1 : 1 petroleum ether
References
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17th International Liquid Crystal Conference, Program and
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(
bp 60±80 ³C)±dichloromethane followed by repeated crystal-
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tyloxycarbonyl)biphenyl-4-yl 5-(4-n-decyloxyphenyl)thio-
phene-2-carboxylate, 1, 0.9 g (64%), as an off-white solid.
The liquid crystalline transition temperatures are listed in
Table 1. Found: C, 75.41, H, 7.82%. C H O S requires C,
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4
2
52
5
3
4
5
6
7
7
(
5.45, H, 7.78%; d
H
(CDCl
12 H, m, alkyl), 4.0 (2 H, t, ArOCH ), 5.1 (1 H, sextet,
3
3
) 0.9 (6 H, t, 26CH ), 1.28±1.36
2
3
C*(H)CH ), 6.93 (2 H, d, ArH, J~8 Hz), 7.26 (1 H, d, ThH,
J~4 Hz), 7.29 (2 H, d, ArH, J~8Hz), 7.59 (2 H, d,
ArH. J~8Hz), 7.92 (1 H, d, ThH, J~4 Hz), 8.13 (2 H, d,
ArH, J~8 Hz); IR nmax (KBr) 2924, 2854, 1722(CLO),
1
8
709(CLO), 1605, 1449, 1271, 1205, 1165, 1112, 1081, 1019,
21 z
31, 807, 761 cm . MS, m/z: 668 (M , 15%), 539 (15%), 343
2
~11.9 (c, 0.0016 g ml in CHCl
1
(
100%), 203 (96%). [a]
D
3
).
8
9
Conclusion
1
0
1
Complementary optical microscopy, differential scanning
calorimetry, miscibility, and electro-optical and current
response studies show clear evidence for the existence of the
SmA*, SmC*ferroelectric, SmC*ferrielectric, SmC*antiferro-
electric and SmI*antiferroelectric phase types in a novel bent-
shaped chiral compound, namely: (S)-4'-(1-methylheptyloxy-
carbonyl)biphenyl-4-yl 5-(4-n-decyloxyphenyl)thiophene-2-
carboxylate (1). Electro-optical switching is also observed in
a so-called crystal phase which appears below the SmI*anti-
1
12 G. Andersson, PhD Thesis, 1992, Chalmers University, G oÈ teborg,
Sweden.
1
1
1
3
4
5
E. Gorecka, A. D. L. Chandani, Y. Ouchi, H. Takezoe and
A. Fukuda, Jpn. J. Appl. Phys. Part 1, 1990, 29(1), 131.
K. Itoh, M. Kabe, K. Miyachi, Y. Takanishi, H. Takezoe and
A. Fukuda, J. Mater. Chem., 1997, 7(3), 407.
J. W. Goodby, J. S. Patel and F. M. Leslie, Ferroelectrics, 1984, 59,
137.
1310
J. Mater. Chem., 2000, 10, 1303±1310