Synthesis and mesomorphic properties of 1,1-difluoroalkyl-substituted biphenylthienyl and terphenyl liquid crystals. A comparative study of mesomorphic behavior relative to alkyl, alkoxy and alkanoyl analogs

Article abstract of DOI:10.1039/b102059p

A variety of biphenylthienyl and terphenyl-based liquid crystalline materials were prepared that incorporate a 1,1-difluoropentyl terminal group. The mesogenic properties of these compounds were compared and contrasted with analogs where the CF₂ moiety was replaced by a -CH₂-, -O- or -CO- group. The 1,1-difluoroalkyl group is unique in its behavior and tends to promote orthogonal smectic phase behavior.

Full text of DOI:10.1039/b102059p

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Synthesis and mesomorphic properties of 1,1-difluoroalkyl-
substituted biphenylthienyl and terphenyl liquid crystals. A
comparative study of mesomorphic behavior relative to alkyl, alkoxy
and alkanoyl analogs{
Andre A. Kiryanov, Paul Sampson and Alexander J. Seed*
Department of Chemistry, Kent State University, Kent, OH 44242-0001, USA.
E-mail: aseed@kent.edu
Received 6th March 2001, Accepted 10th October 2001
First published as an Advance Article on the web 31st October 2001
A variety of biphenylthienyl and terphenyl-based liquid crystalline materials were prepared that incorporate a
1,1-difluoropentyl terminal group. The mesogenic properties of these compounds were compared and contrasted
with analogs where the CF2 moiety was replaced by a -CH2-, -O- or -CO- group. The 1,1-difluoroalkyl group is
unique in its behavior and tends to promote orthogonal smectic phase behavior.
unit. Other linking unit-containing thienyl materials Ib–Id
Introduction
(L~-CH2-, -O-, -CO-) were also synthesized in order to allow
us to better understand the influence of the -CF2- moiety. In
order to assess the impact of incorporating a thiophene ring
into these systems, we also targeted the analogous phenyl-
containing mesogens (II). The corresponding laterally fluori-
nated analogs were also prepared and characterized in order to
elucidate the influence of lateral core fluorination in such
materials. An evaluation of the hydrolytic and thermal stability,
and mesomorphic behavior, of all materials is presented.
Until our preliminary communication16 there had been no
reports of liquid crystals containing a 1,1-difluoroalkylthienyl
moiety. In fact, there was only one article describing the incor-
poration of a 1,1-difluoroalkyl chain into any liquid crystalline
material. Bartmann prepared one -C6H4–CF2CH3 and two
-C6H4–CF2H containing mesogens.17 Subsequent to the com-
pletion of our work, a publication by Goodby et al.18 described
the mesomorphic behavior of a variety of a,a-difluoro and
b,b-difluoroalkylterphenyls. Unfortunately, except for general
schemes, no synthetic details were presented. Even in non-
liquid crystal chemistry there are remarkably few examples of
the synthesis of (1,1-difluoroalkyl)arenes and, even then, com-
pounds of general structure ArCF2(CH2)nCH3 when nw1 are
not known as far as we have been able to ascertain.19–23
Lateral core substituents have been used extensively to alter
the mesomorphic behavior of liquid crystalline compounds.
Lateral core fluorine substitution has proven to be especially
useful in this area due to the relatively small size and high
electronegativity of the fluorine atom.24,25 Introduction of
The materials requirements for ferroelectric liquid crystal
displays are stringent, and fine-tuning of the physical properties
of mesogenic materials combined with careful formulation of
mixtures is required for optimal results. Low viscosity, high
photochemical and thermal stability, high dielectric biaxiality
and a wide range of the smectic C (SC) phase are just a few of
the required characteristics for useful materials.1–4
To further augment the physical properties of mesogens
required for ferroelectric applications we are targeting hetero-
cycle-based materials such as thiophenes, which possess low
viscosities and large lateral dipoles that aid in increasing
dielectric biaxiality. Such a property is extremely important
for use in surface-stabilized liquid crystal displays that are
based on either a C1 or C2 chevron geometry.1,5–7 Liquid
crystals containing thiophene in the rigid core are known to
have lower viscosities than the corresponding phenyl deriva-
tives and possess fast response times in the presence of an
electric field.8,9 Ideally, the thiophene ring should be sub-
stituted in the 2- and 5-positions to give the most linear
architecture and therefore the highest clearing points.10,11
A
number of ferroelectric materials containing this heterocycle
are known, although no sustained efforts have been reported
toward improving the dielectric biaxiality of such units, pos-
sibly due to difficulties in synthesis. This paper represents our
initial progress toward this goal.
In an effort to further enhance the dielectric biaxiality it was
decided to incorporate a polar 1,1-difluoroalkyl unit adjacent
to the thiophene core (Ia). This was expected to substantially
improve the dielectric biaxiality of the resulting mesogens and
support tilted phase behavior according to the Wulf,12
McMillan13 and Goodby14 models. In addition, this group
was expected to have only a small detrimental effect on the
mesophase stability [relative to the pentyl analogs (Ib: L~
CH2)] due to the somewhat larger size of the CF2 group vis-a`-
vis the CH2 group.15
The materials targeted in this initial study are achiral and
were designed to provide some insight into the types and
breadth of mesophase transitions supported by the CF2 linking
{Electronic supplementary information (ESI) available: experimental
details for compounds 4, 9, 10, 12, 15–19, 25–39, 45 and 49. See http://
www.rsc.org/suppdata/jm/b1/b102059p/
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This journal is # The Royal Society of Chemistry 2001
DOI: 10.1039/b102059p

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lateral fluorine substituents in terphenyl compounds ortho to a
ring junction within the molecular core causes an inter-annular
twist and disrupts conjugation. In addition, the effective
molecular breadth is increased and intermolecular packing is
somewhat compromised. The replacement of hydrogen with
fluorine in the mesogenic core generally results in a minimal
depression in the mesophase thermal stability, while often
(although not always) giving rise to a drastic reduction in
melting point. Additionally, higher ordered smectic phases
present in many non-fluorinated materials may be suppressed
or completely eliminated in laterally core fluorinated analogs,
thus aiding in mixture formulation. Laterally core fluorinated
terphenyls provide a particularly effective example of these
effects.26 Given the above factors we felt it prudent to addi-
tionally synthesize the laterally core-fluorinated analogs Ia–Id
(R~F) and IIa–IId (R~F) and to therefore explore the impact
of lateral fluorination in the (1,1-difluoropentyl)thienyl sys-
tems. Comparisons with the analogous phenyl systems and
with the alkyl, alkoxy and alkanoyl analogs of both of the
above cores would provide a broad survey of the impact of
lateral fluorination. In line with trends observed previously
with lateral fluorine substitution, we expected to see a decrease
in melting points and to enhance the possibility of obtaining
disordered tilted mesophases such as the smectic C phase.
Synthesis
Scheme 3
The synthesis of each target mesogen exploited a palladium-
catalyzed Suzuki coupling27,28 of suitably functionalized aryl
bromide and arylboronic acid building blocks (Schemes 1–8).
The key intermediates in the synthesis of the majority of our
mesogenic targets were 1,1-difluoropentyl bromoaromatic
building blocks 3 and 4 (Scheme 1) and biphenylboronic
acids 7, 12, 18 and 19 (Schemes 2–4).
Boronic acid 7 was prepared from the corresponding bromide
6, which was obtained from the commercial 4-bromo-4’-hydr-
oxybiphenyl using Williamson’s ether synthesis (Scheme 2).29
The intermediate aryl bromide 16 required for the synthesis of
boronic acid 18 was obtained using selective30 Suzuki coupling
of 4-tridecylphenylboronic acid (15) with 1-bromo-4-iodoben-
zene (Scheme 4). The bromobenzene derivative 14 required for
the synthesis of 15 was made by PdCl2(dppf)-catalyzed reaction
of tridecylmagnesium bromide with 1,4-dibromobenzene.31
This procedure allowed for a one-step synthesis of the required
aryl bromide 14 as compared with the more traditional two-
step Friedel–Crafts acylation–Wolff–Kishner reduction proce-
dure.32 An analogous strategy was employed in the synthesis of
Scheme 1
Scheme 2
Scheme 4
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Scheme 5
the laterally fluorinated biphenylboronic acids 12 and 19
(Schemes 3 and 4).
The key boronic acids 7, 12, 18 and 19 were then coupled
with a variety of aryl bromides (3, 4 and 20–23) under Suzuki
coupling conditions32 to afford the requisite liquid crystalline
target compounds 24–35 and 37–39 (Scheme 5).
finally brominated in the 5-position with NBS.10,35 2-Bromo-5-
pentanoyl thiophene (21) was obtained by Friedel–Crafts
acylation36 of 2-bromothiophene with valeric anhydride.
The synthesis of these aryl bromide building blocks is
outlined below. The pivotal 1,1-difluoropentyl bromoaromatic
building blocks 3 and 4 were efficiently prepared via fluoro-
desulfurization of the corresponding dithiolanes 1 and 2.33 To
obtain 2-bromo-5-pentylthiophene (20), thiophene was acylated
with valeric anhydride, the resulting ketone was reduced using
the Wolff–Kishner procedure34 and the thiophene ring was
Scheme 6
Scheme 7
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was employed to avoid such decomposition. In contrast, the
pure 1,1-difluoroalkyl mesogens 24–27 and 32–35 can be stored
for a year without noticeable decomposition. Compounds 24
and 32, having the highest clearing points, also show rapid
decomposition while in the isotropic liquid or approaching the
isotropic phase.
Results and discussion
Mesomorphic behavior
The transition temperatures for the mesogenic final products
are given in Table 1.
(i) Melting point trends. Upon examination of the melting
points of the non-laterally fluorinated materials (R~H) some
interesting conclusions may be drawn. The vast majority of
liquid crystal literature pertaining to 2,5-disubstituted thienyl
compounds clearly shows that thiophene-based materials are
almost always lower melting than the corresponding phenyl
analogs.10,11,46–53 The reason often cited for this anomaly is the
deviation from linearity brought about by such a substitution
pattern on thiophene which gives rise to less efficient packing.
In our study the pentyl (28) and butoxy (45) based thiophene
materials are lower melting than the phenyl analogs 36 (13.3 uC
difference in melting point) and 38 (27.8 uC difference in
melting point) respectively. However, the non-laterally fluori-
nated 1,1-difluoropentylthienyl systems are much higher melting
than the corresponding phenyl analogs [compare compounds 24
and 32 (51.4 uC difference in melting points) and compounds
26 and 34 (40.0 uC difference in melting points)] which is unpre-
cedented in the liquid crystal literature. The 2-(1,1-difluoro-
pentyl)thienyl mesogen 24 has a substantially higher melting
point than that of the butoxy and pentyl analogs 45 and 28
(compare 155.9 uC to 92.2 uC and 92.3 uC respectively). The
tridecyl side chain analog 26 also exhibits a high melting point
(141.6 uC) approaching that of the corresponding ketone 30
(150.5 uC).
Scheme 8
1-Bromo-4-pentylbenzene (22) was obtained by Friedel–Crafts
acylation of bromobenzene using valeryl chloride followed by
Wolff–Kishner reduction of the resulting ketone.32 1-Bromo-
4-butoxybenzene (23) was obtained by etherification of
4-bromophenol with 1-bromobutane.37
The synthesis of terphenyl 36 was carried out via coupling of
substituted phenylboronic acid 10 with bromobiphenyl build-
ing block 40 (Scheme 6).
Lateral fluoro substitution has a very structure dependent
and profound effect on melting point, mesomorphic stability
and the types of mesophases exhibited by liquid crystalline
compounds.24,25,54,55 Lateral fluoro substitution generally
causes a decrease in melting points when compared to the
non-fluorinated derivatives and favors disordered and tilted
mesophases, although the overall mesomorphic thermal stabi-
lity is often variable.
By introducing fluorine into our new systems in an inter-
annular position we expected to observe decreases in the
melting and clearing points compared to the non-fluorinated
analogs, and to suppress any higher-ordered smectic phases
that might prove detrimental to mixture formulation for
display use. Both of these expectations were realized in our
compounds and we observed mesogens with broad phase
ranges.
In all cases the introduction of lateral fluoro substitution led
to the anticipated significant reduction in melting point. The
thiophene-based materials showed the most dramatic depres-
sions when a 1,1-difluoropentyl side chain was present at the
2-position of the thiophene ring [compare compounds 24 and
25 (85.0 uC reduction) and compounds 26 and 27 (90.7 uC
reduction)]. A somewhat smaller effect was obtained with
2-pentanoyl, 2-butoxy and 2-pentyl side chains [compare
compounds 30 and 31 (65.5 uC reduction), 45 and 49 (27.4 uC
reduction) and compounds 28 and 29 (13.5 uC reduction)]. The
terphenyl-based compounds showed a similar decrease in
melting points [compare compounds 36 and 37 (44.9 uC
reduction—pentyl chain), 32 and 33 (34.5 uC reduction—1,1-
difluoropentyl chain), 34 and 35 (29.8 uC reduction—1,1-
difluoropentyl chain) and compounds 38 and 39 (15.3 uC
The alkoxythiophene moiety in 45 (Scheme 7) was constructed
by a novel ring closure methodology recently developed in our
laboratory.38–40 Friedel–Crafts acylation of bromobenzene
with succinic anhydride followed by DCC–DMAP-mediated
esterification41 afforded c-keto ester 43, which was then cyclized42
using Lawesson’s reagent to obtain alkoxythiophene 44.
Finally, aryl bromide 44 was coupled with boronic acid 10
under Suzuki conditions to afford the desired alkoxythiophene-
containing mesogen 45 in excellent yield.
It was recognized that acylation of 1-bromo-2-fluorobenzene
might be compromised by side-product formation,43 requiring
us to employ a different approach for the construction of the
laterally fluorinated alkoxythiophene mesogen 49 (Scheme 8).
Thus, alkoxydebromination of 2-bromothiophene (46) using
the method of Keegstra et al.44,45 afforded alkoxythiophene 47
in 14% yield. Subsequent bromination of the highly reactive 47
with NBS or bromine at room temperature or reflux resulted in
the competitive formation of significant amounts of 3,5-
dibrominated product in addition to the desired monobromi-
nated adduct 48; however, this problem was largely overcome
by performing this reaction at low temperatures. Suzuki cross-
coupling of 48 with biphenylboronic acid 12 then afforded the
target laterally fluorinated alkoxythiophene mesogen 49.
The limited stability of liquid crystalline compounds having
the 1,1-difluoropentyl side chain causes some purification pro-
blems, especially in the case of thiophene containing com-
pounds 24, 25, 26 and 27. These compounds decomposed to a
substantial degree to the corresponding ketones while in pro-
longed contact with silica gel or acidic impurities in solvents.
Therefore, flash chromatography using short silica columns
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Table 1 Transition temperatures/uC for the mesogenic final products as determined by polarizing optical microscopy (cooling rate of 5 uC)
Compound
R
No. Cr
SX
SG
SE
SF
SB
SC
SA
N
I
H
F
24 . 155.9
—
—
—
—
—
—
. 160.4
—
—
—
—
—
. 172.4
. 109.9
—
—
.
.
25
.
70.9
H
F
26 . 141.6
—
—
—
—
—
—
—
—
—
—
—
—
. 151.9
. 87.2
—
—
.
.
27
.
50.9
H
F
28
29
.
.
92.3
78.8
—
—
—
—
—
—
—
—
—
—
—
.
. 178.7
—
—
. 115.0
.
.
98.0
H
F
45
49
.
.
92.2
64.8
—
—
. 148.8
—
—
—
—
—
—
—
. 166.3 . 181.4
—
. 126.4
.
.
.
80.1
—
H
F
30 . 150.5
31 85.0
—
—
—
—
—
—
. 180.2
—
—
—
—
—
. 219.6
. 167.6
—
—
.
.
.
H
F
32 . 104.5 . 190.1
—
—
—
—
—
—
. 193.5
. 89.3
—
—
. 197.2
. 133.0
—
—
.
.
33
.
70.0
—
H
F
34 . 101.6
35 71.8
—
—
—
—
—
—
—
—
. 168.2
85.4
—
—
—
. 100.1
—
—
.
.
.
.
H
F
36 . 105.6
37 60.7
—
—
. 186.5
—
—
—
—
—
. 202.6
—
.
. 206.9
95.7 . 131.0 . 139.1
—
.
.
.
.
65.6
H
F
38 . 120.0 . 187.2
39 . 104.7 (97.1)
—
—
. 228.2
—
—
—
—
—
—
. 235.0
—
.
.
.
. 137.6 . 162.4 . 170.7
reduction—butoxy chain)] except that the degree of melting
point depression in the presence of the 1,1-difluoropentyl chain
was much smaller than in the corresponding thiophene
mesogens.
and 39 (DT~64.3 uC)]. Compounds with a ketone functionality
had a somewhat lower value of DT [compare compounds 30
and 31 (DT~52.0 uC)] and alkoxythiophenes 45 and 49 showed
an intermediate value of DT (55 uC).
For materials with a 1,1-difluoropentyl chain, the identity of
the other terminal chain (dodecyloxy or tridecyl) proved
important as the melting points of the tridecyl materials were
lower than for the analogous dodecyloxy derivatives [except for
tridecyl derivative 35 which was observed to melt 1.8 uC higher
than the dodecyloxy analog 33]. Again it is notable that the
thiophene compounds show the largest melting point reduc-
tions when substituting a tridecyl for a dodecyloxy terminal
chain [compare compounds 24 and 26 (14.3 uC reduction) and
compounds 25 and 27 (20.0 uC reduction)].
(iii) Trends in mesomorphic phase range. In the case of the
terphenyl core-containing materials, lateral fluoro substitution
decreases the total mesomorphic phase range in all compounds
[compare compounds 34 and 35 (38.3 uC depression), 32 and 33
(29.7 uC depression), 36 and 37 (22.9 uC depression) and
compounds 38 and 39 (49 uC depression)]. In contrast, an
opposite trend is sometimes observed with thiophene-contain-
ing materials. When the terminal chain on the thiophene ring is
a pentyl or butoxy group, a reduction in total mesomorphic
phase range is still seen upon lateral fluoro substitution
[compare compounds 28 and 29 (50.2 uC depression) and
compounds 45 and 49 (27.6 uC depression) respectively], but
when the terminal chain is 1,1-difluoropentyl or pentanoyl, an
increase in the total mesomorphic phase range is observed
[compare compounds 24 and 25 (22.5 uC increase), 26 and 27
(26.0 uC increase) and compounds 30 and 31 (13.5 uC increase)].
(ii) Clearing point trends. As was expected, significant
lowering of the clearing points was also observed for all
compounds upon lateral core fluorination as a result of
increased molecular breadth and inter-annular twisting caused
by the aromatic fluorine substituent.25,56 Interestingly, the
degree to which the clearing temperature was lowered (DT)
does not seem to depend substantially on the nature of the
linking group (-CF2-, -O- or -CH2- unit) [compare compounds
24 and 25 (DT~62.5 uC); 26 and 27 (DT~64.7 uC), 28 and 29
(DT~63.7 uC), 32 and 33 (DT~64.2 uC), 34 and 35
(DT~68.1 uC), 36 and 37 (DT~67.8 uC) and compounds 38
(iv) Trends in SC and other tilted mesophase stabilities. The
tendency of lateral fluorine substituents to induce the SC phase
and other tilted mesophases and to eliminate/depress higher
order smectic phases was observed to be highly structure
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dependent. None of the materials incorporating the 1,1-
difluoromethylene unit exhibit the SC phase. This may be
attributed to a combination of the size of the difluoromethylene
group or possibly the angle that the chain makes with the core.
A study by one of the authors revealed a similar trend when
oxygen in an alkoxy system was replaced by sulfur.57 In such
systems the oxygen-based materials exhibited a broad SC phase
range with associated SC subphases whereas the analogous
alkylsulfanyl materials had substantially depressed SC phases
with only the ferroelectric SC phase being observed. A sub-
sequent publication by Goodby14 referencing these materials
highlighted the importance of the angle that the terminal chains
make with the core for materials to exhibit tilted phases. It is of
note that the only 1,1-difluoropentyl-based material to exhibit
a truly disordered tilted mesophase (SF) is a thiophene-based
system (24). The only other material in this class to exhibit a
tilted phase is 32 which exhibits a quasi-crystalline SX phase
(probably a crystal J or a crystal G phase).
Experimental
Confirmation of the structures of intermediates and products
1
was obtained by H (300 MHz, General Electric GN-300 FT
NMR spectrometer), 13C (75 MHz) and 19F (470 MHz, Varian
INOVA FT NMR spectrometer with VNMR version 5.3
software) NMR spectroscopy in CDCl3 (tetramethylsilane was
used as internal standard), unless another frequency and/or
solvent are stated. IR spectra were recorded on a Biorad
Excalibur FTS 3000 MX Mid-IR spectrophotometer. The
content of carbon, hydrogen and sulfur in all final products was
determined using a LECO Model CHNS-932 elemental
analyzer (St. Joseph, MI).
The progress of reactions was monitored using either TLC
[aluminium backed silica gel plates (Sigma-Aldrich, 200 mm
˚
layer thickness, 2–25 mm particle size and 60 A pore size)] or
GC [Shimadzu gas chromatograph GC-14A with a Restek2
RTX-5 capillary column (30 m) and Shimadzu class VP
software].
SC phases are also observed in compounds 29 and 37 (pentyl-
substituted thienyl and phenyl systems respectively) and
compounds 45, 49 and 39 (butoxy-substituted thienyl and
phenyl systems). Once again it is noteworthy that the 2-pentyl-
thienyl-based material 29 has a higher SC phase thermal
stability than the analogous phenyl based system 37 (2.3 uC
higher). The thienyl-based system 45 also has a SC phase unlike
the analogous phenyl-based system 38. Introduction of lateral
fluorine in SC-devoid terphenyl and thienyl-containing systems
such as 36, 38 and 28 results in formation of wide SC phase
ranges (20.0–32.9 uC) while eliminating higher ordered (SG and
SX) smectic phases. No SC phase was generated upon lateral
fluoro substitution of compounds having the 1,1-difluoropentyl
terminal chain.
Transition temperatures of the final products were measured
using a Mettler FP82HT hot-stage and FP90 control unit in
conjunction with a Leica Laborlux 12PolS polarizing micro-
scope. All transitions are quoted from microscopic measure-
ments and are given upon cooling at a rate of 5 uC per minute.
The control unit was calibrated with three Merck standards
(benzophenone, benzoic acid and caffeine). Differential scan-
ning calorimetry (DSC) measurements were performed using a
TA Instruments Differential Scanning Calorimeter 2920 at
heating and cooling rates of 5 uC per minute with indium as
internal standard.
The SC phase was clearly identified by observation of the
broken focal conic fan texture accompanied by the pseudo-
homeotropic schlieren texture (see Fig. 1). The SF phase was
identified by both the mosaic texture obtained on cooling from
the homeotropically aligned SA phase and additionally from
the ‘chunky’ focal conic texture (see Fig. 2) obtained on cooling
from the focal conic fan texture of the SA phase.
(v) Trends in SB and other orthogonal mesophase stabili-
ties. The thermal stability of the SB phase is greatly affected by
the introduction of a lateral fluorine substituent. The thienyl-
based compounds tend to exhibit much more disordered
mesophases than the analogous phenyl systems with the
exception of butoxy-based system 45, which has a SG phase.
This increase in disorder for the thienyl-based compounds is
likely to be a consequence of the non-linearity of the thienyl
compounds, which give less efficient packing. With the excep-
tion of butoxy-based systems 38 (SE and SX phases) and 39 (SX
phase), all phenyl-based mesogens exhibit the orthogonal SB
phase. As expected, when lateral fluoro substitution is present
these phases are dramatically depressed and, in the case of 39,
the SE phase is completely eliminated. The decreases in thermal
stabilities range from 82.8 uC (comparing compounds 34 and
35) to 137.0 uC (comparing compounds 36 and 37).
The ‘B’ phase in 32, 33, 34, 35, 36 and 37 is tentatively
assigned as being SB (hexatic). This assignment was based on
the rounded shape of the focal conic domains (see Fig. 3) and
the parabolic defects observed on reheating into the SA phase
(see Fig. 4). Transition bars were additionally observed at the
transition point.
All chemicals were used without additional purification
unless otherwise specified. Anhydrous dichloromethane was
obtained by stirring and distillation from calcium hydride.
Anhydrous ether and THF were obtained by distillation from
benzophenone ketyl. All chromatographic separations were
performed using flash column chromatography on silica gel
[Fisher Davisil1 silica gel (60 A, 55–75 mm particle size, grade
˚
1740)] unless otherwise stated.
The syntheses of compounds 22, 23 and 40 are given in
references 32, 58 and 59 respectively. Typical experimental
procedures are provided below.{
Conclusion
A series of 1,1-difluoropentyl-substituted biphenylthienyl and
terphenyl liquid crystals have been synthesized and their
mesogenic properties compared with analogs where the CF2-
C4H9 side chain was replaced by a pentyl, butoxy or pentanoyl
moiety. The 1,1-difluoropentyl-based systems displayed sig-
nificantly different mesomorphic behavior from the other
systems and were characterized by high melting points and
a tendency toward orthogonal phase behavior (SA and SB
phases). Only in a single case was a disordered tilted phase (SF)
observed in such systems.
A number of the analogous alkoxythienyl and alkylthienyl
mesogens display remarkably high SC mesophase stabilities
for ‘bent’ compounds and warrant further investigation as
potential achiral ferroelectric host materials. Asymmetric
analogs also deserve investigation as potential chiral, non-
racemic ferroelectric dopants.
2-Bromo-5-(1,1-difluoropentyl)thiophene (3)
To a pre-dried 50 mL plastic bottle charged with a magnetic
stirrer was added nitrosonium tetrafluoroborate (0.543 g,
4.64 mmol) under dry argon. Anhydrous dichloromethane
(10 mL) and pyridinium polyhydrogen fluoride (PPHF) (2 mL,
70% HF content) were injected into the bottle and the reaction
mixture was cooled to 0 uC. A solution of dithiolane 1 (0.700 g,
2.17 mmol) in anhydrous dichloromethane (4 mL) was then
added dropwise over a period of 3–5 min. The ice bath was
removed and the reaction mixture was stirred for a further
2 min before being diluted with petroleum ether (80 mL) in
a plastic cylinder. The upper (petroleum ether) layer was
removed and the dark bottom layer was extracted with a
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Fig. 1 SC phase of compound 39 at 127.1 uC clearly showing broken
focal conic domains accompanied by regions of pseudohomeotropic
schlieren texture (1006 magnification).
Fig. 3 SB phase of compound 36 at 202.6 uC showing transition bars
upon cooling from the SA into the SB phase. The rounded focal conic
domains are clearly visible (3206 magnification).
Fig. 2 SF phase of compound 24 at 157.0 uC showing the paramor-
photic ‘chunky’ focal conic texture obtained on cooling from the focal
conic SA texture (2006 magnification).
Fig. 4 SA phase obtained on heating the SB phase of compound 36
(203.5 uC). The parabolic defects inherently associated with a hexatic B
phase are clearly visible (3206 magnification).
4’-Dodecyloxybiphenyl-4-ylboronic acid (7)
petroleum ether–dichloromethane mixture (3 : 1, 40 mL). The
organic layers were combined and passed through a short silica
plug (5 cm). The colorless filtrate was concentrated in vacuo to
afford the title compound 3 as a colorless liquid (0.508 g, 87%).
1H NMR d 0.91 (t, J~6.9 Hz, 3H), 1.33–1.52 (m, 4H), 2.17 (m,
n-Butyllithium (1.6 mL, 10 M in hexanes, 0.016 mol) was
added dropwise at 278 uC to a stirred, cooled (278 uC)
solution of bromobiphenyl 6 (4.17 g, 0.010 mol) in anhydrous
THF (220 mL). The reaction mixture was maintained under
these conditions for a further 2 h (GC revealed complete
lithiation as a small reaction sample quenched with water did
not contain any starting bromide) before previously cooled
(0 uC) neat trimethyl borate (2.32 g, 0.0224 mol) was added
dropwise at 278 uC. The reaction mixture was allowed to warm
to room temperature (overnight) and was stirred for 45 min
with hydrochloric acid (10%, 80 mL). The resulting mixture
was extracted with diethyl ether (3660 mL). The combined
organic phases were washed with water (2650 mL), a further
aliquot of water (50 mL) was added and the organic solvent
was evaporated from this biphasic mixture in vacuo. The white
suspension was filtered and the resulting white solid was
washed with petroleum ether and briefly dried on filter to
afford the title compound 7 (3.82 g, 100%) which was used
directly in the next step. 1H NMR (DMSO-d6) d 0.87 (t,
J~6.9 Hz, 3H), 1.26–1.39 (m, 16H), 1.46 (m, 2H), 1.76
(quintet, J~6.6 Hz, 2H), 3.99 (t, J~6.6 Hz, 2H), 6.96 (d,
J~8.7 Hz, 2H), 7.50–7.57 (m, 4H), 7.45 (d, J~8.7 Hz, 2H),
8.09 (s, 2H).
2H), 6.95 (dt, J~3.6 Hz,
JH-F~1.5 Hz, 1H), 6.99 (dt,
J~3.6 Hz, JH-F~0.9 Hz, 1H); 13C NMR d 13.6, 22.2, 24.5,
38.3 (t, JC-F~26.4 Hz), 114.1, 120.5 (t, JC-F~238.4 Hz), 126.1
(t, JC-F~5.7 Hz), 129.5, 140.8 (t, JC-F~32.0 Hz); 19F NMR d
285.1(t, JF-H~16.2 Hz).
4-Bromo-4’-dodecyloxybiphenyl (6)
A mixture of 1-bromododecane (18.68 g, 0.075 mol), 4-bromo-
4’-hydroxybiphenyl (15.0 g, 0.0602 mol) and potassium carbo-
nate (31.0 g, 0.224 mol) in butan-2-one (120 mL) was heated
under reflux for 24 h (GC revealed a complete reaction). After
allowing to cool to room temperature, the potassium salts were
filtered off. The solvent was removed in vacuo and the crude
product was recrystallized from petroleum ether (bp 35–60 uC)
to afford the title compound 6 as white crystals which were
dried in vacuo (P2O5, 24 h) (22.2 g, 89%; purity (GC)w99%);
1H NMR d 0.88 (t, J~6.8 Hz, 3H), 1.27–1.40 (m, 16H), 1.46
(m, 2H), 1.79 (quintet, J~6.6 Hz, 2H), 3.97 (t, J~6.6 Hz, 2H),
6.94 (d, J~8.7 Hz, 2H), 7.39 (d, J~8.4 Hz, 2H), 7.45 (d,
J~8.7 Hz, 2H), 7.51 (d, J~8.4 Hz, 2H,); 13C NMR d 14.0,
22.6, 25.9, 29.2, 29.3, 29.5, 31.8, 68.0, 114.8, 120.6, 127.8, 128.1,
131.6, 132.1, 139.7, 158.9.
4-Bromo-4’-dodecyloxy-2-fluorobiphenyl (11)
To a stirred biphasic mixture of 4-bromo-2-fluoro-1-iodobenzene
(3.61 g, 12.0 mmol), tetrakis(triphenylphosphine)palladium(0)
3074
J. Mater. Chem., 2001, 11, 3068–3077

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(0.700 g, 0.606 mmol) in benzene (20 mL) and aqueous sodium
carbonate (20 mL, 2 M, 40 mmol) under dry argon, was added
phenylboronic acid 10 (4.59 g, 15.0 mmol) followed by ethanol
(15 mL). The reaction mixture was heated under reflux for
72 h. The cooled mixture was diluted with water (50 mL) and
extracted with dichloromethane (3645 mL). The combined
organic extracts were washed with water (50 mL) and brine
(100 mL) before being dried (Na2SO4). The drying agent was
filtered off and the filtrate was concentrated in vacuo. The
resulting yellow solid was suspended in hexanes (250 mL) and
was passed through a short silica plug (hexanes–dichloro-
methane 20 : 1). Concentration in vacuo followed by column
chromatography on silica gel (hexanes) afforded the title
mixture was stirred at rt for a further 2 h (TLC and GC
analyses confirmed a complete reaction) and was then poured
into water (300 mL). The organic layer was separated and the
aqueous layer was extracted with ether (2650 mL). The
combined organic extracts were washed with sodium carbonate
(2 M, 26200 mL) before being dried (MgSO4). The drying
agent was filtered off and the solvent was removed in vacuo to
give a black liquid which was distilled to give the title
compound 21 as a colorless liquid (bp 128–133 uC/0.5 mmHg)
(62.4 g, 82%). 1H NMR d 0.94 (t, J~7.2 Hz, 3H), 1.39 (sextet,
J~7.5 Hz, 2H), 1.70 (quintet, J~7.5 Hz, 2H), 2.82 (t,
J~7.2 Hz, 2H), 7.09 (d, J~3.9 Hz, 1H), 7.44 (d, J~3.9 Hz,
1H); 13C NMR d 13.8, 22.6, 26.6, 38.3, 122.2, 130.5, 132.8,
145.9, 192.3.
1
compound 11 as a white solid (4.75 g, 91% yield). H NMR d
0.91 (3H, t, J~6.7 Hz), 1.20–1.40 (m, 16H), 1.47 (quintet,
J~7.2 Hz, 2H), 1.85 (quintet, J~6.7 Hz, 2H), 4.01 (t, J~
6.5 Hz, 2H), 6.98 (d, J~8.9 Hz, 2H), 7.29–7.35 (m, 3H), 7.448
(d, J~8.8 Hz, 1H), 7.454 (d, J~8.9 Hz, 1H); 13C NMR d 14.3,
22.9, 26.2, 29.4, 29.6 (2), 29.8, 32.1, 68.1 (d, JC-F~15.3 Hz),
114.8, 119.8 (d, JC-F~26.3 Hz), 120.7 (d, JC-F~9.1 Hz), 127.0,
127.8 (d, JC-F~3.4 Hz), 129.6, 130.1 (d, JC-F~2.9 Hz), 131.6
(d, JC-F~4.1 Hz), 159.3, 159.6 (d, JC-F~251.7 Hz); 19F NMR d
2115.7 (dd, JH-F~10, 7 Hz).
2-(4’-Dodecyloxybiphenyl-4-yl)-5-(1,1-difluoropentyl)thiophene
(24)
Palladium(II) chloride (0.1 M solution in water, 0.2 mL,
0.02 mmol) was added in one portion to a stirred mixture of
biphenylboronic acid 7 (0.500 g, 1.30 mmol), bromothiophene
3 (0.210 g, 0.78 mmol) and sodium carbonate (2.0 M, 1.68 mL,
3.36 mmol) in acetone (10 mL) under dry argon. The reaction
mixture was heated under reflux for 40 h and the cooled
reaction mixture was diluted with hydrochloric acid (10%,
10 mL) and extracted with dichloromethane (3620 mL). The
combined organic extracts were washed with water (100 mL)
and dried (Na2SO4). The drying agent was filtered off and the
extract was filtered through a column of silica gel (petroleum
ether–dichloromethane, 3 : 1) before the solvent was removed
in vacuo. The crude product was crystallized from ethyl acetate
followed by petroleum ether (bp 35–60 uC) to afford the title
compound 24 as a white solid, which was dried in vacuo (P2O5,
paraffin wax, 24 h) (0.280 g, 72%). Transitions (uC) Cryst 155.9
SF 160.4 SA 172.4 Iso Liq; 1H NMR d 0.88 (t, J~6.9 Hz, 3H),
0.93 (t, J~7.2 Hz, 3H), 1.27–1.56 (m, 22H), 1.81 (quintet,
J~6.6 Hz, 2H), 2.25 (m, 2H), 4.00 (t, J~6.6 Hz, 2H), 6.98 (d,
J~9.0 Hz, 2H), 7.17 (dt, J~3.9 Hz, JH-F~1.5 Hz, 1H), 7.22
(dt, J~3.6 Hz, JH-F~1.2 Hz, 1H), 7.54 (d, J~8.7 Hz, 2H),
7.57 (d, J~9.0 Hz, 2H), 7.63 (d, J~8.7 Hz, 2H); 13C NMR d
13.7, 14.0, 22.2, 22.6, 24.6, 26.0, 29.2, 29.3 (2), 29.5, 31.8, 38.6
(t, JC-F~26.5 Hz), 68.0, 114.8, 121.2 (t, JC-F~237.5 Hz), 122.3,
126.2, 126.7 (t, JC-F~4.8 Hz), 127.0, 127.8, 131.8, 132.4, 138.2
(t, JC-F~31.2 Hz), 140.5, 145.6, 158.9; 19F NMR d 285.1(t,
1-Bromo-4-tridecylbenzene (14)
To a stirred, cooled (0 uC) solution of [1,1’-bis(diphenyl-
phosphino)ferrocene]dichloropalladium(II) (0.320 g, 0.437 mmol)
and 1,4-dibromobenzene (52.0 g, 0.220 mol) in anhydrous
THF (100 mL) under argon, a solution of Grignard reagent
[prepared from magnesium (6.40 g, 0.263 mol) and 1-bromo-
tridecane (63.7 g, 62.0 mL, 0.242 mol) in anhydrous ether
(150 mL)] was added dropwise over a period of 30 min under
dry argon. The reaction mixture was allowed to warm to room
temperature and was stirred until completion of the reaction
(monitored by GC). Methanol (2.5 mL) was added and the
reaction mixture was diluted with hexanes (500 mL). The
mixture was filtered through a short silica plug and the solvent
was evaporated in vacuo. The residue was distilled to afford
the title compound 14 as a low melting white solid (bp 170–
172 uC/1.2 mmHg) (46.5 g, 62%). 1H NMR d 0.88 (t, J~6.6 Hz,
3H), 1.27–1.46 (m, 20H), 1.57 (quintet, J~7.2 Hz, 2H), 2.53 (t,
J~7.8 Hz, 2H), 7.02 (d, J~8.1 Hz, 2H), 7.36 (d, J~8.1 Hz,
2H); 13C NMR d 14.0, 22.6, 29.1, 29.3, 29.4, 29.5, 29.6, 31.2,
31.9, 35.3, 119.1, 130.0, 131.1, 141.7.
JF-H~16.2 Hz). Anal. calcd for C33H44F2OS: C, 75.24; H, 8.42;
S, 6.09; Found: C, 75.54; H, 8.62; S, 5.97%.
2-Bromo-5-pentylthiophene (20)
4-(4-Bromophenyl)-4-oxobutyric acid (42)
2-Pentylthiophene60 (13.8 g, 89.6 mmol) and N-bromosucci-
nimide (16.0 g, 90.0 mmol) in chloroform (20 mL) and acetic
acid (20 mL) were gently heated under reflux for 45 min. The
resulting black reaction mixture was diluted with water (30 mL)
and extracted with dichloromethane (2640 mL). The com-
bined organic extracts were washed with water (2640 mL),
aqueous potassium hydroxide (5%, 30 mL) and dried (MgSO4).
The drying agent was filtered off and the residue was passed
through a short silica plug (6 cm). Concentration in vacuo gave
a yellow liquid (19.7 g, 94%) which was distilled under reduced
pressure to afford the title compound 20 as a colorless liquid
Anhydrous aluminium(III) chloride (27.0 g, 0.203 mol) was
added in one portion to a mechanically stirred, cooled (0 uC)
mixture of succinic anhydride (10.0 g, 0.100 mol) and bromo-
benzene (102 g, 0.650 mol). After 5 h at 0 uC, the reaction
mixture was allowed to warm up to room temperature and was
stirred for an additional 94 h. The reaction mixture was then
poured into hydrochloric acid (450 mL, 10%), stirred for 1 h
and the product was filtered, washed with water (1.0 L) and
dried. The crude product was crystallized from toluene
(250 mL) and dried under vacuum (P2O5, paraffin wax,
1.1 mmHg, 17 h) to afford the title compound 42 as a white
1
(bp 130–131 uC/1.5 mmHg) (13.8 g, 66%). H NMR d 0.92 (t,
1
J~6.9 Hz, 3H), 1.30–1.40 (m, 4H), 1.65 (quintet, J~7.4 Hz,
2H), 2.75 (t, J~7.6 Hz, 2H), 6.54 (d, J~3.7 Hz, 1H), 6.85 (d,
J~3.6 Hz, 1H); 13C NMR d 14.2, 22.6, 30.5, 31.3, 108.7, 124.5,
129.5, 147.8.
solid (21.0 g, 82%, mp 146–149.5 uC). H NMR (DMSO-d6) d
2.57 (t, J~6.2 Hz, 2H), 3.23 (t, J~6.9 Hz, 2H), 7.73 (d,
J~8.7 Hz, 2H), 7.90 (d, J~8.7 Hz, 2H), 12.18 (br s, 1H); 13C
NMR (DMSO-d6) d 27.8, 33.1, 127.3, 129.9, 131.8, 135.4,
173.8, 197.7.
2-Bromo-5-pentanoylthiophene (21)
Butyl 3-(4-bromobenzoyl)propanoate (43)
Iron(III) chloride (9.95 g, 0.0613 mol) was added in one portion
to a stirred mixture of 2-bromothiophene (50.0 g, 0.307 mol)
and valeric anhydride (65.7 g, 0.353 mol) under dry nitrogen at
rt (a temperature rise to 100 uC was noted). The reaction
To a solution of c-keto acid 42 (10.3 g, 40.1 mmol) in anhy-
drous dichloromethane (600 mL) under dry argon at room
temperature were added 4-(N,N-dimethylamino)pyridine
J. Mater. Chem., 2001, 11, 3068–3077
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(1.84 g, 15.1 mmol), butan-1-ol (2.82 g, 38.1 mmol) and N,N’-
dicyclohexylcarbodiimide (8.84 g, 42.9 mmol). The reaction
mixture was stirred for 20 h and the resulting white precipitate
was filtered off. The filtrate was washed with potassium
hydroxide (5%, 26200 mL), water (200 mL), acetic acid (5%,
200 mL), water (200 mL), brine (200 mL) and dried (Na2SO4).
The drying agent was filtered off and the solvent was removed
in vacuo. The crude semisolid was purified by column chro-
matography on silica gel (hexanes–ethyl acetate 9 : 1) to afford
the title compound 43 as a white solid (11.3 g, 90%, mp 30–
31 uC). 1H NMR d 0.89 (t, J~7.3 Hz, 3H), 1.34 (sextet,
J~7.4 Hz, 2H), 1.58 (quintet, J~7.1 Hz, 2H), 2.73 (t, J~
6.6 Hz, 2H), 3.24 (t, J~6.6 Hz, 2H), 4.07 (t, J~6.7 Hz, 2H),
7.57 (d, J~8.6 Hz, 2H), 7.81 (d, J~9.0 Hz, 2H); 13C NMR d
13.8, 19.2, 28.3, 30.8, 33.5, 64.8, 128.5, 129.7, 132.1, 135.5,
172.9, 197.3.
afford the title compound 48 as a clear liquid (0.270 g, 45%)
and 2,4-dibromo-5-butoxythiophene (0.075 g, 9%): 48: 1H
NMR d 0.96 (t, J~7.3 Hz, 3H), 1.46 (sextet, J~7.4 Hz, 2H),
1.74 (quintet, J~7.0 Hz, 2H), 3.99 (t, J~6.5 Hz, 2H), 5.97 (d,
J~4.0 Hz, 1H), 6.68 (d, J~4.0 Hz, 1H); 13C NMR d 13.8, 19.1,
31.2, 74.1, 97.9, 105.5, 127.3, 165.5; 2,4-dibromo-5-butoxy-
thiophene: 1H NMR d 0.97 (t, J~7.4 Hz, 3H), 1.49 (sextet,
J~7.4 Hz, 2H), 1.77 (quintet, J~7.1 Hz, 2H), 4.06 (t,
J~6.5 Hz, 2H), 6.73 (s, 1H); 13C NMR d 13.8, 19.1, 31.4,
76.4, 92.1, 99.2, 129.6, 158.0.
Acknowledgements
The authors would like to express their sincere thanks to Kent
State University for financial support. In addition we would
like to thank Dr Mahinda Gangoda for assistance in obtaining
some of the NMR spectra and to Dr Robert J. Twieg for use of
his DSC instrument.
2-(4-Bromophenyl)-5-butoxythiophene (44)
Lawesson’s reagent (9.95 g, 24.6 mmol) was added in one
portion to a stirred solution of c-keto ester 43 (6.42 g,
20.5 mmol) in dry toluene (100 ml) under dry argon. The
reaction mixture was heated under reflux for 16 h (GLC
analysis revealed a complete reaction) before the reaction
mixture was cooled to room temperature and the solvent was
removed in vacuo. The crude product was purified thrice by
column chromatography on silica gel [petroleum fraction (bp
40–60 uC)] and was dried in vacuo (CaCl2, P2O5, 48 h) to afford
the title compound 44 as a pale yellow solid (3.30 g, 56%, mp
74–75 uC, purity (GC)w99%). 1H NMR (CDCl3) d 0.95 (3H, t,
J~7.3 Hz), 1.50 (2H, sextet, J~7.3 Hz), 1.80 (2H, quintet,
J~7.3 Hz), 4.20 (2H, t, J~7.3 Hz), 6.15 (1H, d, J~4.0 Hz),
6.95 (1H, d, J~4.0 Hz), 7.35 (2H, d, J~8.7 Hz), 7.50 (2H, d,
J~8.7 Hz); IR (KBr) nmax 3080, 2868, 2265, 1892, 1585, 1551,
1500, 1465, 1390, 1271, 1202, 1112, 1070, 1031, 999, 979, 941,
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purity (GC)w99%). H NMR d 0.97 (t, J~7.4 Hz, 3H), 1.48
(sextet, J~7.4 Hz, 2H), 1.76 (quintet, J~7.0 Hz, 2H), 4.03
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