Synthesis, mesomorphic behaviour and optical anisotropy of some novel materials for nematic mixtures of high birefringence

Article abstract of DOI:10.1039/b400630e

Structural moieties including core units (such as phenyl, naphthyl and thiophenyl), linking groups (such as ethynyl), terminal substituents (such as cyano, isothiocyanato and fluoro), and lateral fluoro substituents have been incorporated into novel mater

Full text of DOI:10.1039/b400630e

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A R T I C L E
Synthesis, mesomorphic behaviour and optical anisotropy of
some novel materials for nematic mixtures of high birefringence{
Michael Hird,a Kenneth J. Toyne,a John W. Goodby,a George W. Gray,a
Victoria Minter,b Rachel P. Tuffinb and Damien G. McDonnellc
aThe Department of Chemistry, University of Hull, Hull, UK HU6 7RX
bQinetiQ Limited, St Andrews Road, Malvern, UK WR14 3PS
cDefence Diversification Agency, Ively Road, Farnborough, UK GU14 0LX
Received 14th January 2004, Accepted 23rd March 2004
First published as an Advance Article on the web 28th April 2004
Structural moieties including core units (such as phenyl, naphthyl and thiophenyl), linking groups (such as
ethynyl), terminal substituents (such as cyano, isothiocyanato and fluoro), and lateral fluoro substituents have
been incorporated into novel materials designed to confer a high birefringence on nematic mixtures. The
materials have all been prepared through convergent syntheses involving palladium-catalysed cross-coupling
reactions of arylboronic acids. The materials were examined for their mesomorphic behaviour as neat materials
and as mixtures; some materials were found to have extremely high nematic phase stability, and others were
non-mesogenic. The materials were evaluated in nematic host mixtures for their optical anisotropy, and they
were all found to show promisingly high values.
conjugated, compact terminal group such as a cyano (–CN) or
Introduction
an isothiocyanato (–NCS) is more appropriate. The isothio-
cyanato group has been shown to be particularly effective in
generating a high optical anisotropy due to the extended
p-system spread over three atoms.3,8,14
The work reported here is part of a long, on-going programme
on the synthesis and evaluation of nematic liquid crystals of
high optical anisotropy.1–8 Nematic liquid crystal mixtures are
of considerable commercial importance in display device
applications; such mixtures contain many components in an
attempt to optimise a range of properties, such as mesomorphic
behaviour, viscosity, elastic constants, dielectric anisotropy
and optical anisotropy.9 Components that confer a high optical
anisotropy are particularly useful for supertwisted nematic
displays, which enables the use of thinner cells and hence lower
threshold voltages and enhanced transmission of light, and
in polymer dispersed liquid crystal (PDLC) applications to
provide a greater contrast between the two switched states.
Additionally, nematic mixtures of very high optical anisotropy
are essential for fast, third-order, non-linear switching using
the optical Kerr effect;10,11 this particular application has been
the basis behind a long term programme of synthesis and
evaluation of materials of high optical anisotropy reported here
and in several previous publications.1–8 More recently, nematic
liquid crystals of high optical anisotropy have been recognised
as having great technological importance in telecommunica-
tions devices, particularly those operating at 1550 nm.12,13
In order to achieve a high optical anisotropy in a mesogenic
material, structural units must be introduced into the molecules
such that the E-ray is retarded and the O-ray is allowed to
travel freely. The polarisable p-electrons of aromatic systems in
conjugation are very effective in retarding the progress of the
E-ray through the system, particularly where that conjugation
is compact as in a naphthalene core unit, for example.
Conjugated linking groups such as ethenyl and ethynyl further
retard the progress of the E-ray and hence increase the
birefringence. Terminal groups in liquid crystalline materials
are often long flexible alkyl or alkoxy chains which serve to
facilitate a low melting point; however, such units do nothing
to retard the E-ray and so for high optical anisotropy one
Accordingly, many of the structural architectures in the
work reported here include terphenyl and naphthalene core
units, with ethynyl linkages and cyano and isothiocyanato
terminal units. Unfortunately, it has been found that those
structural units that generate a high birefringence also generate
a high melting point. Hence, other materials have been targeted
that have only a biphenyl core unit without an ethynyl linkage;
of course these compounds will not generate especially high
birefringence, but should have lower melting points and be
useful components in mixtures. Lateral fluoro substituents
have been included in some of the materials reported here in an
attempt to generate low melting points, despite the fact that
such substitution causes additional inter-annular twisting of
the aromatic rings and hence reduces the longitudinal
polarisability resulting in a lower optical anisotropy. Thus
the work reported here represents a broadening of the range
of materials available for use in nematic mixtures of high
birefringence, and an attempt to further rationalise, and
increase the understanding of, the structural units that best
generate the appropriate compromise of properties.
Discussion of synthetic methods
As mentioned above, a large variety of materials for applica-
tions in nematic mixtures of high birefringence form the basis
of this publication. However, in all cases the synthesis of the
final materials was greatly facilitated by the use of palladium-
catalysed cross-coupling reactions,15–21 indeed in the synthesis
of some materials their use is virtually essential. Schemes 1–6
show the synthesis of several isothiocyanato-substituted mate-
rials, Schemes 7–10 show the synthesis of several cyano-
substituted materials, and Scheme 11 shows the synthesis of a
few fluoro-substituted materials.
Despite the development of palladium-catalysed cross-
coupling reactions to high levels, their exceptional versatility
and their extremely wide tolerance to a whole range of
{ Electronic supplementary information (ESI) available: experimental
procedures for all compounds not already given in this paper. See
http://www.rsc.org/suppdata/jm/b4/b400630e/
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 , 1 7 3 1 – 1 7 4 3
1 7 3 1

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Scheme 1
Scheme 2
Scheme 3
Scheme 4
1 7 3 2
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 7 3 1 – 1 7 4 3

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Scheme 5
Scheme 6
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 7 3 1 – 1 7 4 3
1 7 3 3

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Scheme 7
Scheme 8
Scheme 9
functional groups, those couplings involving isothiocyanato
substituents fail.3 The use of thiophosgene and chloroform in
aqueous calcium carbonate on an aromatic amine is a very
useful and efficient method of introducing the isothiocyanato
group,3,22 and this method was used to good effect in this
research (Schemes 1–6). Note that extra care was taken in the
handling of the aryl amines because of their suspected car-
cinogenic nature. Suzuki cross-coupling reactions15,18,20,21
involving arylboronic acids (e.g. compound 1) and aryl halides
(e.g. compound 3) are invaluable in generating multiaryl
compounds (e.g. compound 4), and this methodology was used
to generate nitro-substituted materials (Schemes 1, 3, 5 and 6).
The appropriate nitro group (e.g. in compound 4) was then
reduced to the amine function (e.g. in compound 6) which was
then converted into the isothiocyanato group (e.g. in com-
pound 8) as described above. Attempts to shorten the syn-
thesis by coupling arylboronic acids (e.g. compound 1) to a
4-halogenoaniline (e.g. compound 11) instead of 1-bromo-4-
nitrobenzene (3) were met with substantial deamination,23
hence the longer route via the nitro compound was much more
1 7 3 4
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 7 3 1 – 1 7 4 3

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Scheme 10
Scheme 11
efficient. The corresponding alkynylzinc chloride coupl-
ings1,2,16,20 involving terminal alkynes (e.g. compound 10)
and 4-iodoaniline (11), as shown in Schemes 2 and 4, caused no
problems in generating the amino-substituted intermediates
(e.g. compound 12), which were converted into the desired
terminal isothiocyanato-substituted materials (e.g. compound
13) using the method described above.
The triflate coupling was used again in Scheme 9 since
compound 55 is readily available and is easily converted into
the appropriate triflate derivative as for compound 45. A
simple palladium-catalysed cross-coupling reaction with boro-
nic acid 32 generated the substituted terphenyl 57. Scheme 10
shows the efficient use of palladium-catalysed cross-coupling
reactions involving difluorophenylboronic acid 31 and thio-
phenylboronic acid 41 with 4-bromobenzonitrile (58) to give
two-ring products 59 and 60 respectively. Hydrogenation of the
alkyne unit in compound 60 generated the saturated alkyl
analogue 61.
Scheme 5, in particular, shows the lengthy syntheses required
to generate highly-substituted aromatic intermediates of the
desired substitution pattern, essential when lateral substituents
are required. The introduction of the alkyl chain (e.g. for
compound 37) involved the coupling of an alkynylzinc reagent
with the appropriate aryl iodide (e.g. compound 24) and
subsequent hydrogenation of the triple bond (e.g. compound
26) to generate the required alkyl chain (e.g. compound 33). An
identical strategy for the introduction of the alkyl chain was
used for the thiophene materials (Scheme 6).
The greater availability of phenols when compared with aryl
bromides make the triflate leaving group very important in
palladium-catalysed cross-coupling reactions.1,2,17,20 Triflate
45, used in previous work, was easily prepared from the
appropriate phenol, and serves as an excellent leaving group
material in palladium-catalysed cross-coupling reactions to
generate substituted phenyl naphthalenes 47–50 and 52
(Scheme 7) and naphthylthiophene 53 (Scheme 8). Compound
53 was hydrogenated to generate the saturated alkyl analogue
(compound 54).
The synthesis of the terminal fluoro- and trifluoromethyl-
phenylnaphthalenes are shown in Scheme 11. Again the
efficiency and versatility of palladium-catalysed cross-coupling
reactions is demonstrated through the coupling of the various
fluoro-substituted bromobenzenes (62–64, 68 and 69) with the
naphthylboronic acid (1) to generate final products 65–67, 70
and 71 respectively.
Discussion of results
The melting points, mesophase morphology, transition tem-
peratures and optical anisotropy values for the reported novel
compounds and some known materials for comparison are
shown in Tables 1–6.
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 7 3 1 – 1 7 4 3
1 7 3 5

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Table 1 Transition temperatures (uC) and optical anisotropies of
phenylnaphthalenes with terminal cyano and isothiocyanato groups
Table 3 Transition temperatures (uC) and optical anisotropies of
terphenyls and biphenyls with terminal cyano and isothiocyanato
groups, and some lateral substituents
Compounds
Physical properties
Compound
Physical properties
Transition
temperatures
No.
Structure
Dn
Transition
temperatures
No. Structure
Dn
8
C 123.5 B 125.0
N 177.0 I
0.44
17
C 94.0 E 248.0 SA
257.5 N 262.0 I
—
8026
57
C 130.0 N 239.0 I
C 58.5 N 113.0 I
0.28
9
728
732
742
758
C 55.0 E 93.0 SA
104.0 N 140.5 I
0.43
0.44
0.33
0.30
0.36
0.25
C 98.1 N 125.7 I
C 125.0 N 159.0 I
C 84.0 N 126.5 I
C 92.0 N 107.0 I
813
8227
37
C 53.5 E 74.5
[N 43] I
0.41
0.25
0.38
C 24.5 N 35.5 I
C 44.5 [N 13] I
38
59
C 51.5 [N 224]
0.38
0.22
Melting points, transition temperatures and mesophase
morphology
C 54.5 [N 211] I
Simple isothiocyanatobiphenyls tend to have rather high
melting points and exhibit ordered smectic phases (e.g. E
and B), whereas the corresponding cyanobiphenyls tend to be
nematogens and hence are more suitable for commercial
applications. However, such a lack of a nematic phase does
not prevent use as an additive that confers a high optical
anisotropy to nematic mixtures. Additionally, alternative
structural units can be employed that do enable the nematic
Table 4 Transition temperatures (uC) and optical anisotropies of
phenylthiophenes and naphthylthiophenes with terminal cyano and
isothiocyanato groups
Table 2 Transition temperatures (uC) and optical anisotropies of
phenyl-naphthylethynes and diphenylethynes with terminal cyano and
isothiocyanato groups
Compound
Physical properties
Transition
temperatures
No. Structure
Dn
Compound
Physical properties
44
C 72.5 [N 26] I
0.44
Transition
temperatures
No. Structure
Dn
13
C 123.0 (SA 117.0) 0.63
N 190.5 I
61
53
C 39.5 (N 16.0) I 0.37
C 104.0 (N 87.0) I 0.48
768
772
788
C 91.5 N 136.7 I 0.54
C 111.5 N 186.0 I 0.42
C 87.0 N 131.8 I 0.46
54
C 72.5 N 92.0 I
0.40
832
842
C 113.0 N 193.0 I 0.41
20
C 91.5 (B 85.5)
[N 85] I
0.44
0.50
797
C 84.8 B 85.4
[N 65] I
C 68.0 N 130.0 I
0.30
1 7 3 6
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Table 5 Transition temperatures (uC) and optical anisotropies of
phenylnaphthalenes with terminal cyano groups in the naphthalene
ring and with lateral substituents
naphthyl unit reduces the smectic phase stability by much more
than the nematic phase stability to generate materials (e.g.
compounds 8 and 9, Table 1) with broad nematic ranges. The
use of the butylsulfanyl terminal chain (compound 72)
completely eliminates all smectic phases, and leaves a nematic
phase of lower phase stability than for the butoxy analogue
(compound 8), and more surprisingly, the pentyl analogue
(compound 9). However, the disadvantage of a large sulfur unit
so close to the core would be expected to far outweigh any
advantages of polarisability, and in fact such a trend in liquid
crystal phase stability has been reported previously8 in the
corresponding three, terminal cyano-substituted materials
(compounds 73–75, Table 1). A respective comparison of the
nematogenic terminal cyano-substituted compounds (73–75)2,8
shows them to have significantly lower nematic phase stability
than the terminal isothiocyanato-substituted compounds (8, 9
and 72), again supported by previous results.
Compound
Physical properties
Transition
temperatures
No.
Structure
Dn
47
C 71.5 N 95.5 I
C 94.5 [N 44] I
0.30
48
0.30
49
50
52
852
C 84.0 (N 79.5) I
C 78.0 [N 27] I
C 64.5 N 129.5 I
C 98.5 N 167.5 I
0.33
0.25
0.33
0.33
The introduction of a linear ethynyl linking group (com-
pound 13, Table 2) serves to reduce the order of the smectic
phase and the phase stability, so in comparison with compound
8, a crystal B phase has been replaced by a smectic A phase at
lower phase stability. However, the nematic phase stability for
compound 13 is much higher due to the enhanced molecular
length and conjugation. The butylsulfanyl analogue (com-
pound 76)8 shows a much lower melting point and no smectic
phases, but does have a reduced nematic phase stability in
comparison with the butoxy analogue (compound 13); a similar
trend to that seen for the phenylnaphthalenes discussed above.
The terminal cyano analogues (compounds 77 and 78)2,8 are
both nematogens, and as was seen for the terminal isothio-
cyanato compounds (13 and 76) the sulfur unit in the terminal
chain causes a significant reduction in melting point and a large
reduction in nematic phase stability. Overall, the cyano-
substituted materials (77 and 78) both have lower melting
points and lower nematic phase stability than the analogous
terminal isothiocyanato compounds (13 and 76); again a
similar trend to that seen for the phenylnaphthalenes discussed
above. Compound 20 is a simple diphenylethyne core with a
terminal isothiocyanato group, and despite the hydrocarbon
terminal chain shows a very high melting point for a two-ring
compound. Compound 20 shows a monotropic crystal B phase,
but no nematic phase; however, an extrapolated value of 85 uC
was recorded for the nematic phase stability. In comparison,
the butylsulfanyl analogue (compound 79)7 melts at a slightly
lower temperature, and surprisingly in view of the previous
comparison between compounds 9 and 72, the crystal B phase
stability is identical; however, the extrapolated nematic phase
stability of 65 uC is lower, as expected.
phase to be generated by terminal isothiocyanato-substituted
materials. For example, some cyclohexylphenylisothiocyanates
reported by Dabrowski and co-workers are nematogens with
low melting points; however, these are of low optical
anisotropy.24,25 The use of a longer core unit (e.g. compound
17 as seen in Table 3) markedly enhances the liquid crystal
phase stability, and allows the generation of a nematic phase,
albeit over a short temperature range. The use of a broadened
Table 6 Transition temperatures (uC) and optical anisotropies of
phenylnaphthalenes with fluoro substituents
Compound
Physical properties
The very high length to breadth ratio and strong longitudinal
polarisability of terphenyl 17 brings extremely high liquid
crystal phase stability (Table 3). The phase morphology is in
keeping with the phenylnaphthalene analogue (compound 9),
although in terms of transition temperatures the more linear
terphenyl (compound 17) supports the smectic phase more than
the nematic phase which leaves a rather short nematic tem-
perature range. The terphenyl core structure shows up the vast
difference that the isothiocyanato group makes to mesophase
morphology in comparison to the well-known cyanoterphenyl
system (compound 80)26 which is nematogenic over a very wide
temperature range to very high phase stability. A lateral methyl
group was introduced into the cyanoterphenyl structure
(compound 57) with the strong expectation of a large reduction
in melting point, and of course a massive reduction in nematic
phase stability. As can be seen from Table 3, the nematic phase
stability has been reduced by 126 uC and the melting point
reduced by just 71.5 uC to leave a much narrower nematic
temperature range in comparison with the parent system (com-
pound 80). Moving on to the smaller biphenyl systems shown
in Table 3, it is apparent that despite three-ring systems being
Transition
temperatures
No. Structure
Dn
65
C 128.5 [N 112] I
C 81.5 [N 42] I
0.27
66
67
0.27
0.25
0.31
C 72.0 (N 63.0) I
C 177.5 [N 95] I
70
71
C 73.5 SA 105.5 [N 55] I 0.29
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 7 3 1 – 1 7 4 3
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capable of generating massively high liquid crystal phase
stability, the two-ring systems have low liquid crystal phase
stability, although of course the pentylcyanobiphenyl (com-
pound 82)27 shows a useful room-temperature nematic phase.
The terminal isothiocyanato biphenyl compound (81)3 has a
higher nematic phase stability (43 uC) than the analogous
cyanobiphenyl (compound 82), although this value is an
extrapolated value. The lateral fluoro substituent in isothio-
cyanato compound 37 has generated the desired result of a
much lower melting point than the parent system (compound
81). Hence compound 37 should be a most useful component of
nematic mixtures, despite a much lower virtual nematic phase
stability in comparison to compound 81. The use of two lateral
fluoro substituents fixed across the long molecular axis
(compounds 38 and 59) proved to be unsuccessful in generating
further reductions in the melting point. The location of the
additional polar fluoro substituent in the outer-edge position
has enhanced the melting point, yet the additional molecular
breadth has considerably reduced the nematic phase stability.
Table 4 shows a series of thiophene materials, and despite the
bent molecular structure of the 2,5-disubstituted thiophene
core, the liquid crystal phase stability of the four materials is
reasonably high. Unfortunately, the two-ring terminal iso-
thiocyanato material (compound 44) has a high melting point,
and even though the nematic phase stability was measured by
extrapolation, it is surprisingly high (26 uC). Despite a lower
nematic phase stability for the terminal cyano-substituted
analogue (compound 61), the melting point is reasonably low
(39.5 uC) and this allows a monotropic nematic phase to be
exhibited at 16 uC. The 2,6-disubstituted naphthyl compound
(54) has an enantiotropic nematic phase over a temperature
range of 20 uC to a phase stability of 92 uC. In comparison with
the linear phenylnaphthalene compound (84),2 the bend from
the thiophene unit (compound 54) has reduced the nematic
phase stability by 38 uC, compared with a reduction of just
19.5 uC seen for the smaller systems (compare compound 61
and compound 82). It would seem that the bend is exaggerated
in the larger systems causing a greater depression in clearing
temperature. The use of an ethynyl terminal chain (compounds
53 and 83) usually has the effect of increasing the nematic phase
stability, and this is seen for linear systems in the comparison of
compound 83 with compound 84 (a significant 63 uC increase in
clearing point caused by the ethynyl chain).2 However, in the
case of the bent molecular core in compounds 53 and 54, the
clearing temperature is actually lower for the ethynyl com-
pound (53) by a few uC compared with the alkyl compound
(54). In this latter comparison the rigidity of the tolane
exaggerates the molecular bend and hence reduces the nematic
phase stability by much more than the increased polarisability
is able to cause an increase.
extrapolation) than where the two fluoro substituents are
fixed on the same side of the molecule (compound 49). The
lateral methyl group is much larger than the lateral fluoro
substituent and hence the nematic phase stability (measured by
extrapolation) is much lower for compound 50 than for either
compound 47 or compound 84, and the melting point is also
higher than for both the comparison compounds.
The efficiency of a terminal fluoro substituent to generate
liquid crystal phases is known to be relatively poor; however,
the terminal fluoro substituent is useful in giving a low resis-
tivity in comparison with the terminal cyano group. Phenyl-
naphthalenes with a terminal fluoro substituent were prepared
as materials of high birefringence yet, high resistivity. The
melting point of the parent system (compound 2) is very high,
and hence no liquid crystal phase is seen; however, the
extrapolated nematic phase stability is very high (112 uC). A
lateral fluoro substituent was introduced (compounds 66 and
67) to reduce the melting point with great success; however, the
nematic phase stability was, of course, also reduced. The largest
reduction in nematic phase stability came from the compound
with the outer-edge lateral fluoro substituent (66), which is
surprising because the inter-annular twisting caused by the
inner core fluoro substituent of compound 67 would normally
reduce the nematic phase stability most significantly. Perhaps
the only explanation why compound 67 has a higher nematic
phase stability than compound 66 is that the lateral fluoro
substituent is more shielded by the broad naphthalene core in
compound 67.
Optical anisotropy
Many examples of our previous work show that the optical
anisotropy is significantly increased when a terminal alkyl
chain is replaced by an alkoxy chain, and further increases can
occur when an alkylsulfanyl chain is used. However, the
comparison of compounds 8, 9 and 72 (Table 1) shows
remarkably similar optical anisotropy values (0.43 to 0.44).
It is most likely that this similarity is because the phenyl-
naphthalene core in conjunction with a terminal isothiocyanato
confers such a high optical anisotropy that the influence of the
terminal chain is minimal, and also there is the influence of the
higher order parameter of those compounds with a smectic
tendency to account for. The optical anisotropy values shown
by the terminal cyano-substituted analogues (compounds 73–
75) represent a more expected trend. It is noticeable that the
terminal isothiocyanato moiety certainly confers a vastly
higher optical anisotropy to compounds than the terminal
cyano group (compare compound 9 with compound 74), a
trend consistent with our previous work.3,7,8
Much of our previous work has shown that the introduction
of an ethynyl linking group significantly enhances optical
anisotropy;1,2,7 however, the massive value measured for
compound 13 is much higher than expected in comparison
with compound 8 (Table 2). In fact, compound 13 has a much
higher optical anisotropy than the alkylsulfanyl analogue
(compound 76), which is rather unusual. However, the higher
order parameter generated by compound 13 because of the
smectic tendency (not a feature of the alkylsulfanyl compound)
is most likely responsible for the remarkably high optical
anisotropy value. The comparison of the terminal cyano-
substituted materials (compounds 77 and 78) is more usual
since there is no smectic tendency of either material. Just as for
the directly-linked materials shown in Table 1, the ethynyl-
linked materials show a much higher optical anisotropy when
substituted with a terminal isothiocyanato group than with a
terminal cyano unit. The ethynyl linking group does not
enhance the optical anisotropy too significantly for the simple
two-ring material with a terminal isothiocyanato group and a
simple alkyl chain. The value of 0.44 for compound 20 is not
significantly higher than for compound 81. Compound 79
Phenylnaphthalenes with a terminal cyano substituent have
already been targeted by us as important materials of high
optical anisotropy. In an attempt to reduce melting points,
lateral substituents (e.g. fluoro and methyl) have been
introduced into the phenyl ring. As can be seen from the
transition temperatures shown in Table 5, the results are
somewhat mixed. The introduction of the lateral fluoro
substituent in the terminal alkyl material (compound 47) has
actually caused a slight increase in melting point (compare with
compound 84), accompanied by a significant reduction in
nematic phase stability. On the other hand, the lateral fluoro
substituent introduced into the terminal alkoxy material
(compound 52) has caused a useful reduction of 34 uC in
melting point; however, the reduction in nematic phase stability
is also quite significant (compare with compound 85).2 The
use of two fluoro substituents generates quite a high melting
point in compounds 48 and 49, and as expected the compound
with the two fluoro substituents fixed either side of the core (48)
has a much lower nematic phase stability (measured by
1 7 3 8
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(alkylsulfanyl terminal chain) has a much higher optical
anisotropy value than for compound 20 (alkyl terminal
chain) and this comparison can be seen as fair because both
compounds have a similar smectic tendency.
However, the phenylnaphthalene core unit does aid high
birefringence, and hence the birefringence of compound 65
(0.27) is not too much lower than that of the cyano-substituted
analogue 73 (0.33). The birefringence of 0.27 is maintained
when a lateral fluoro substituent at the outer edge of the core is
employed (compound 66), but where the lateral fluoro
substituent is in the inner core position (compound 67) then
the increased inter-annular twisting causes a slight reduction in
birefringence (0.25). The terminal trifluoromethyl group is
known to enhance the smectic A character of materials, which
will increase the order parameter and hence a higher than
expected birefringence will result. Compound 70 exemplifies
this reasoning with a birefringence of 0.31, which is remarkably
similar to the terminal cyano-substituted analogue (73), despite
the lack of p-electrons in the terminal group. The usual slight
reduction in birefringence is seen when an inner core lateral
fluoro substituent is introduced (compound 71); however, the
value is still maintained higher than expected due to the smectic
A character as discussed above.
The values of optical anisotropy of the novel materials and
the referenced known materials reported here are wholly com-
parable as they have been measured in an identical manner.
Unfortunately, a lack of published optical anisotropy values
from other groups, and the fact that such values would be
inconsistent with those of the materials reported here, prevents
further meaningful comparison. However, a recent publication
does provide optical anisotropy values of some isothiocyanato
materials, but as mixtures and not as individual compounds.14
A terphenyl would be expected to have a high optical
anisotropy because of the three aromatic rings in conjugation;
however, the rather symmetrical, rigid structure makes
solubility rather difficult in the host material, and so mean-
ingful measurement was impossible. The known cyano
terphenyl (compound 80) has a surprisingly low optical
anisotropy (0.28), particularly since the biphenyl analogue
(compound 82) produces a value of 0.25, and as already
reported, the terminal isothiocyanato biphenyl (compound 81)
has a significantly higher optical anisotropy (0.41). The
introduction of a lateral methyl group (compound 57) further
reduces optical anisotropy, but not significantly so (0.25). The
effect of lateral fluoro substituents on optical anisotropy in
biphenyl units (compounds 37, 38 and 59) was investigated,
and, surprisingly, the value is not significantly lower than for
the parent systems (81 and 82).
Thiophene liquid crystals have been shown in our previous
work to confer a particularly high optical anisotropy.5 The
effect of a thiophene in a phenylisothiocyanate (compound 44)
on optical anisotropy is not so significant, but an increase is
recorded compared with biphenyl 81, probably another
example of the isothiocyanato moiety being so dominant
that other structural changes have minimal effect on optical
anisotropy. In the case of the cyanophenylthiophene material
(compound 61) the optical anisotropy is significantly higher
when compared with the cyanobiphenyl analogue (compound
82). The significant effect of the thiophene unit on optical
anisotropy is further exemplified in the naphthalene systems,
and the already high optical anisotropy value (0.41) for the
ethynylphenylnaphthalene (compound 83) is increased to 0.48
in the thiophene analogue (compound 53). Such an increase is
not massive, but the ethynyl unit is rather dominating the
optical anisotropy. In the case of the alkylphenylnaphthalene
(compound 84) the rather moderate optical anisotropy value of
0.30 is markedly increased by the introduction of a thiophene
moiety in compound 54 to 0.40, a rather similar trend to that
discussed above for the cyanophenyl unit (compounds 82
and 61).
Lateral fluoro substituents in the phenylnaphthalene systems
(Table 5) have very little effect on the optical anisotropy
(compare compounds 47 and 48 with the parent system 84, and
compound 52 with parent system 85), rather similar in trend to
the influence of lateral fluoro substituents in biphenyl systems
discussed above. Surprisingly, the difluorophenylnaphthalene
with the two fluoro substituents fixed on the same side of the
molecule (compound 49) has a higher optical anisotropy (0.33)
than the parent system or other fluoro-substituted analogues
(compounds 84, 47 and 48), which all generate values of 0.30.
Outer-edge fluoro substituents are known to promote smectic
character, and so perhaps the high optical anisotropy value of
compound 49 is due to the enhanced order parameter caused by
the smectic character. The lateral methyl group is, as expected,
more destructive of optical anisotropy than the lateral fluoro
substituent, and such a reduction to 0.25 is consistent with
results discussed above.
In contrast with terminal cyano groups, terminal fluoro
substituents are useful at generating a positive dielectric
anisotropy when a high resistivity is required. Accordingly, it
would be useful to have a range of such materials that were also
of high birefringence, hence compounds 65–67 with terminal
fluoro substituents and compounds 70 and 71 with terminal
trifluoromethyl groups (see Table 6). The terminal cyano group
is well-recognised for generating high birefringence due to the
high concentration of p-electrons; in contrast the terminal
fluoro substituent would be expected to be rather poor.
Summary
A rather diverse, but structurally comparable, range of
materials has been prepared with 2,6-naphthyl and 1,4-
phenyl core units, single bond and ethynyl linking groups
with alkyl, alkoxy, alkynyl, cyano, isothiocyanato, fluoro and
trifluoromethyl terminal moieties, and lateral fluoro and
methyl substituents. All such units chosen and their specific
combinations give rise to a wealth of structure–property
relationship information in respect of melting points, transition
temperatures, mesophase morphology and optical anisotropy.
The 2,6-naphthyl core unit is an excellent core unit for
conferring acceptable mesomorphic properties and a reason-
ably high optical anisotropy. The isothiocyanato terminal
group is particularly useful for conferring a high optical
anisotropy. The ethynyl linking group enhances optical
anisotropy enormously, particularly where it links two
aromatic core units rather than linking an alkyl chain to the
aromatic core. Extremely high optical anisotropy (0.63) is seen
for compound 13 with an alkoxy-naphthyl-phenyl-ethynyl-
isothiocyanato construction.
Experimental
Confirmation of the structures of intermediates and products
was obtained by 1H and 13C NMR spectroscopy (JEOL JNM-
GX270 spectrometer), infrared spectroscopy (Perkin-Elmer
457 grating spectrophotometer) and mass spectrometry
(Finnigan-MAT 1020 GC/MS spectrometer). Elemental ana-
lysis (Fisons EA1108 CHN) data were obtained for each final
compound prepared (8, 9, 13, 17, 20, 37, 38, 44, 47–50, 52–54,
57, 59, 61, 65–67, 70, 71).
The progress of reactions was frequently monitored using a
Chrompack 9001 capillary gas chromatograph fitted with a
CP-SIL 5 CB 10 m 6 0.25 mm, 0.12 mm column (Cat.
No. 7700).
Transition temperatures were measured using a Mettler FP5
hot-stage and control unit in conjunction with an Olympus
BH2 polarising microscope and these were confirmed using
differential scanning calorimetry (Perkin-Elmer DSC-7 and
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 7 3 1 – 1 7 4 3
1 7 3 9

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IBM data station). Where final compounds did not exhibit a
nematic phase, virtual TN–I values were determined from four
binary mixtures (5–30% m/m) in E7 (a nematic host mixture
with a TN–I value of 60 uC). The TN–I values obtained for the
mixtures were extrapolated to 100% of the compound being
examined using a linear regression computer program to give
the line of best fit, and are accurate to ¡5 uC, assuming ideal
mixing behaviour.
The purities of intermediates were checked by GLC analysis
(see above) and the purity of each final compound (8, 9, 13, 17,
20, 37, 38, 44, 47–50, 52–54, 57, 59, 61, 65–67, 70, 71) was
checked by HPLC analysis (Merck-Hitachi with Merck RP 18
column, Cat. No. 16 051) and were found to be w99.5% pure in
each case.
The optical anisotropies of the compounds were measured
using an Abbe´ refractometer (model 60/HR) at 589 nm (D1
sodium line) connected to a Haake thermostatically controlled
heating/cooling unit containing silicon fluid which was kindly
supplied by our collaborators at DERA (Malvern), now
QinetiQ. Three mixtures of each compound were formulated
(5–25% m/m, depending on solubility) in I eutectic (a nematic
host mixture with a TN–I value of 104 uC). The refractive
indices (ne and no) of each mixture were measured between 5
and 65 uC at 10 uC intervals, and for each measurement a
period of 20 min was allowed for the temperature of the prisms
to stabilise. The optical anisotropy (Dn) values (ne 2 no) were
plotted against temperature and gave a straight line, which in
all cases passed through the individual values. The value for
the optical anisotropy at a reduced temperature of 0.7815 of the
TN–I value of each mixture was extrapolated to 100% of the
compound. The reduced temperature value was used to give
consistency to the results by taking into account the variation
of the optical anisotropy with the TN–I value, and hence
allowing a fair comparison of the effect of various structural
units on optical anisotropy between different compounds. The
reduced temperature value corresponds to a temperature of
21.6 uC for the I eutectic host mixture which has a TN–I value of
104 uC, and has been used by us in our extensive previous
work,7,8 and by our collaborators at DERA (Malvern), now
QinetiQ, for many years. However, in some cases the reduced
temperature at which the measurements are quoted are rather
low, and optical anisotropy values are always higher at lower
temperatures.
product was purified by column chromatography (silica gel/
hexane–dichloromethane, 2:1) to give a pale yellow solid which
was recrystallised from ethanol to give colourless crystals.
1
Yield 3.13 g (89%); transitions (uC): C 106.0 N 119.5 I; H
NMR (CDCl3): d 1.00 (3H, t), 1.55 (2H, sext), 1.85 (2H, quint),
4.10 (2H, t), 7.16 (1H, d), 7.21 (1H, dd), 7.70 (1H, dd), 7.81
(1H, d), 7.83 (1H, d), 7.84 (2H, d), 8.01 (1H, d), 8.32 (2H, d); IR
(KBr) nmax (cm21): 2960, 2940, 2860, 1630, 1595, 1520, 1395,
1345, 1205, 850, 755; MS m/z 321 (M1), 265, 219, 289.
2-(4-Aminophenyl)-6-butoxynaphthalene (6)
A stirred mixture of compound 4 (2.82 g, 8.79 mmol) and 5%
palladium on carbon (1.50 g) in THF (135 ml) and ethanol
(10 ml) was hydrogenated for 24 h (GLC and TLC analyses
revealed a complete reaction), and the mixture was filtered and
poured into water. The product was extracted into diethyl ether
(62) and the combined ethereal extracts were washed with
water and dried (MgSO4). The solvent was removed in vacuo to
yield an off-white solid which was used without further
purification.
1
Yield 2.21 g (86%); mp 141–142 uC; H NMR (CDCl3): d
1.00 (3H, t), 1.55 (2H, sext), 1.85 (2H, quint), 3.70 (2H, s), 4.05
(2H, t), 6.79 (2H, d), 7.14 (2H, d), 7.52 (2H, d), 7.65 (1H, d),
7.75 (2H, d), 7.88 (1H, d); IR (KBr) nmax (cm21): 3560, 3390,
2960, 2940, 2860, 1620, 1605, 1520, 1505, 1390, 1275, 1250,
1205, 1175, 1125, 890, 860, 840, 820; MS m/z 291 (M1), 235.
2-Butoxy-6-(4-isothiocyanatophenyl)naphthalene (8)
A solution of compound 6 (2.05 g, 7.04 mmol) in chloroform
(50 ml) was added to a stirred, cooled (0 uC) mixture of water
(10 ml), calcium carbonate (1.10 g, 0.011 mol), chloroform
(5 ml) and thiophosgene (1.00 g, 8.70 mmol). The stirred
mixture was heated at 35 uC for 1.5 h and then poured into
water. The aqueous layer was washed with dichloromethane
and the combined organic extracts were washed with 1%
aqueous hydrochloric acid and dried (MgSO4). The solvent was
removed in vacuo and the residue was purified by column
chromatography (silica gel/dichloromethane) to give a colour-
less solid which was recrystallised from ethanol–ethyl acetate
(1:1) to yield colourless crystals.
Compounds 1,2 2,2 10,2 14,28 18,2 30,29 45,2 46 18 and 51 29
were prepared according to a previous publications. Tetrakis-
(triphenylphosphine)palladium(0) was prepared according to
the literature procedure.30 Compounds 3, 11, 21, 23, 39, 55, 58,
62–64, 68 and 69 are all commercially-available. The nematic
host mixtures (E7 and I-eutectic) were kindly supplied by our
collaborators at Merck Chemicals Limited.
Experimental procedures for all compounds except those
referenced above are given as ESI.{ Experimental procedures
for all final products (8, 9, 13, 17, 20, 37, 38, 44, 47–50, 52–54,
57, 59, 61, 65–67, 70, 71) are also provided below, as are those
of compounds 4 and 6 for essential reference.
Yield 2.05 g (87%); transitions (uC): C 123.5 B 125.0 N 177.0
I; H NMR (CDCl3): d 1.00 (3H, t), 1.55 (2H, sext), 1.85 (2H,
1
quint), 4.10 (2H, t), 7.14 (1H, d), 7.18 (1H, dd), 7.32 (2H, d),
7.63 (1H, dd), 7.68 (2H, d), 7.77 (1H, d), 7.79 (1H, d), 7.93 (1H,
d); IR (KBr) nmax (cm21): 2960, 2940, 2860, 2050, 1625, 1605,
1605, 1500, 1395, 1280, 1255, 1210, 1175, 860, 840, 805; MS m/z
333 (M1), 277. Calc. for C21H19NOS: C, 75.64; H, 5.74; N,
4.20. Found: C, 75.57; H, 5.70; N, 4.20%.
2-(4-Isothiocyanatophenyl)-6-pentylnaphthalene (9)
Note that extra care was taken in the handling of the aryl
amines because of their suspected carcinogenic nature.
Quantities: compound 7 (0.66 g, 2.28 mmol), thiophosgene
(0.35 g, 3.04 mmol), calcium carbonate (0.38 g, 3.80 mmol).
The experimental procedure was as described for the prepara-
tion of compound 8. The crude product was purified by column
chromatography (silica gel/dichloromethane) to give a colour-
less solid which was recrystallised from ethanol to yield
colourless crystals.
2-Butoxy-6-(4-nitrophenyl)naphthalene (4)
A solution of compound 1 (3.22 g, 0.013 mol) in DME (30 ml)
was added dropwise to a stirred, refluxing mixture of com-
pound 3 (2.20 g, 0.011 mol), tetrakis(triphenylphosphine)-
palladium(0) (0.40 g, 0.35 mmol), sodium carbonate (5 g) in
DME (20 ml) and water (50 ml) under nitrogen. The mixture
was heated under reflux for 16 h (GLC and TLC analyses
revealed a complete reaction) and poured into water. The
product was extracted into diethyl ether (62) and the com-
bined ethereal extracts were washed with brine, and dried
(MgSO4). The solvent was removed in vacuo and the crude
Yield 0.36 g (48%); transitions (uC): C 55.0 E 93.0 SA 104.0 N
140.5 I; H NMR (CDCl3): d 0.90 (3H, t), 1.35 (4H, m), 1.70
1
(2H, quint), 2.80 (2H, t), 7.32 (2H, d), 7.37 (1H, dd), 7.62 (1H,
d), 7.65 (1H, dd), 7.69 (2H, d), 7.81 (1H, d), 7.85 (1H, d), 7.97
(1H, d); IR (KBr) nmax (cm21): 2960, 2940, 2860, 2100, 1500,
890, 840, 820; MS m/z 331 (M1), 274. Calc. for C22H21NS: C,
79.72; H, 6.39; N, 4.23. Found: C, 79.70; H, 6.36; N, 4.21%.
1 7 4 0
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 7 3 1 – 1 7 4 3

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1-(6-Butoxynaphth-2-yl)-2-(4-isothiocyanatophenyl)ethyne (13)
The experimental procedure was as described for the prepara-
tion of compound 8. The crude product was purified by column
chromatography (silica gel/dichloromethane) to give a colour-
less solid which was recrystallised from ethanol to yield
colourless crystals.
Quantities: compound 12 (1.89 g, 6.00 mmol), thiophosgene
(0.89 g, 7.74 mmol), calcium carbonate (0.95 g, 9.50 mmol).
The experimental procedure was as described for the prepara-
tion of compound 8. The crude product was purified by column
chromatography (silica gel/dichloromethane) to give an off-
white solid which was recrystallised from ethanol to yield
colourless crystals.
Yield 1.68 g (78%); transitions (uC): C 123.0 (SA 117.0) N
190.5 I; 1H NMR (CDCl3): d 1.00 (3H, t), 1.50 (2H, sext), 1.80
(2H, quint), 4.10 (2H, t), 7.10 (1H, d), 7.16 (1H, dd), 7.20 (2H,
d), 7.51 (1H, dd), 7.53 (2H, d), 7.67 (1H, d), 7.71 (1H, d), 7.96
(1H, d); IR (KBr) nmax (cm21): 2960, 2940, 2860, 2120, 2060,
1620, 1600, 1590, 1510, 1390, 1260, 1215, 1175, 1135, 980, 940,
860, 840, 820; MS m/z 357 (M1), 301. Calc. for C23H19NOS: C,
77.28; H, 5.36; N, 3.92. Found: C, 77.22; H, 5.36; N, 3.87%.
1
Yield 0.80 g (47%); transitions (uC): C 51.5 [N 224] I; H
NMR (CDCl3): d 0.90 (3H, t), 1.35 (4H, m), 1.65 (2H, quint),
2.65 (2H, t), 6.98 (1H, dd), 7.06 (1H, dd), 7.29 (2H, d), 7.51
(2H, dd); IR (KBr) nmax (cm21): 2960, 2940, 2860, 2120, 1490,
1400, 1170, 935, 890, 840, 810; MS m/z 317 (M1), 260. Calc. for
C18H17F2NS: C, 68.11; H, 5.40; N, 4.41. Found: C, 68.04; H,
5.38; N, 4.35%.
2-(4-Isothiocyanatophenyl)-5-pentylthiophene (44)
Quantities: compound 43 (1.98 g, 8.08 mmol), thiophosgene
(1.16 g, 0.010 mol), calcium carbonate (1.26 g, 0.0126 mol). The
experimental procedure was as described for the preparation of
compound 8. The crude product was purified by column
chromatography (silica gel/dichloromethane) to give an off-
white solid which was recrystallised from ethanol to yield
colourless crystals.
Yield 1.63 g (70%); transitions (uC): C 72.5 [N 26] I; 1H
NMR (CDCl3): d 0.90 (3H, t), 1.40 (4H, m), 1.70 (2H, quint),
2.80 (2H, t), 6.75 (1H, d), 7.15 (1H, d), 7.19 (2H, d), 7.55 (2H,
d); IR (KBr) nmax (cm21): 2960, 2940, 2860, 2040, 1505, 945,
835, 800; MS m/z 287 (M1), 230. Calc. for C16H17NS2: C,
66.85; H, 5.96; N, 4.87. Found: C, 66.83; H, 5.95; N, 4.85%.
4-Isothiocyanato-4@-pentylterphenyl (17)
Quantities: compound 16 (2.72 g, 8.63 mmol), thiophosgene
(1.23 g, 0.011 mol), calcium carbonate (1.35 g, 0.014 mol). The
experimental procedure was as described for the preparation of
compound 8. The crude product was purified by column
chromatography (silica gel/dichloromethane) to give a colour-
less solid which was recrystallised from ethanol–ethyl acetate
(1:2) to yield colourless crystals.
Yield 2.52 g (82%); transitions (uC): C 94.0 E 248.0 SA 257.5
N 262.0 I; 1H NMR (CDCl3): d 0.90 (3H, t), 1.35 (4H, m), 1.65
(2H, quint), 2.65 (2H, t), 7.27 (2H, d), 7.31 (2H, d), 7.55 (2H,
d), 7.61 (4H, 2 6 d), 7.68 (2H, d); IR (KBr) nmax (cm21): 2960,
2940, 2860, 2020, 1490, 1400, 1005, 940, 810; MS m/z 357 (M1),
300. Calc. for C24H23NS: C, 80.63; H, 6.48; N, 3.92. Found: C,
80.59; H, 6.48; N, 3.90%.
2-Cyano-6-(2-fluoro-4-pentylphenyl)naphthalene (47)
Quantities: compound 45 (1.26 g, 4.19 mmol), compound 30
(1.06 g, 5.05 mmol). The experimental procedure was as
described for the preparation of compound 4, except that
lithium chloride (0.55 g, 0.013 mol) was added with the
reagents. The crude product was purified by column chroma-
tography (silica gel/hexane–dichloromethane, 2:1) to give a
colourless solid which was recrystallised from ethanol to yield
colourless crystals.
Yield 1.08 g (81%); transitions (uC): C 71.5 N 95.5 I; 1H
NMR (CDCl3): d 0.90 (3H, t), 1.35 (4H, m), 1.65 (2H, quint),
2.65 (2H, t), 7.04 (1H, ddd), 7.09 (1H, dd), 7.45 (1H, dd), 7.62
(1H, dd), 7.81 (1H, ddd), 7.94 (2H, d), 8.04 (1H, d), 8.24 (1H,
d); IR (KBr) nmax (cm21): 2960, 2940, 2860, 2240, 1630, 1430,
1275, 1125, 895, 820; MS m/z 317 (M1), 273, 260. Calc. for
C22H20FN: C, 83.25; H, 6.35; N, 4.41. Found: C, 83.25; H,
6.30; N, 4.40%.
1-(4-Isothiocyanatophenyl)-2-(4-pentylphenyl)ethyne (20)
Quantities: compound 19 (2.38 g, 9.05 mmol), thiophosgene
(1.31 g, 0.011 mol), calcium carbonate (1.45 g, 0.015 mol). The
experimental procedure was as described for the preparation of
compound 8. The crude product was purified by column
chromatography (silica gel/dichloromethane) to give an off-
white solid which was recrystallised from ethanol to yield
colourless crystals.
Yield 2.23 g (81%); transitions (uC): C 91.5 (B 85.5) [N 65] I;
1H NMR (CDCl3): d 0.95 (3H, t), 1.35 (4H, m), 1.65 (2H,
quint), 2.65 (2H, t), 7.18 (2H, d), 7.22 (2H, d), 7.45 (2H, d), 7.51
(2H, d); IR (KBr) nmax (cm21): 2960, 2940, 2860, 2180, 2110,
1510, 1030, 840; MS m/z 305 (M1), 247. Calc. for C20H19NS: C,
78.65; H, 6.27; N, 4.59. Found: C, 78.60; H, 6.25; N, 4.55%.
2-Cyano-6-(2,5-difluoro-4-pentylphenyl)naphthalene (48)
Quantities: compound 45 (1.35 g, 4.49 mmol), compound 31
(1.18 g, 5.18 mmol). The experimental procedure was as
described for the preparation of compound 4, except that
lithium chloride (0.60 g, 0.014 mol) was added with the
reagents. The crude product was purified by column chroma-
tography (silica gel/hexane–dichloromethane, 2:1) to give a
colourless solid which was recrystallised from ethanol to give
colourless crystals.
Yield 1.20 g (80%); transitions (uC): C 94.5 [N 44] I; 1H
NMR (CDCl3): d 0.90 (3H, t), 1.35 (4H, m), 1.65 (2H, quint),
2.65 (2H, t), 7.04 (1H, dd), 7.20 (1H, dd), 7.62 (1H, dd), 7.78
(1H, ddd), 7.96 (2H, d), 8.04 (1H, d), 8.25 (1H, d); IR (KBr)
nmax (cm21): 2960, 2940, 2240, 1510, 1500, 1480, 1420, 1170,
910, 885, 825; MS m/z 335 (M1), 278. Calc. for C22H19F2N: C,
78.78; H, 5.71; N, 4.18. Found: C, 78.75; H, 5.70; N, 4.13%.
2-Fluoro-4’-isothiocyanato-4-pentylbiphenyl (37)
Quantities: compound 35 (2.11 g, 8.21 mmol), thiophosgene
(1.17 g, 0.010 mol), calcium carbonate (1.28 g, 0.013 mol). The
experimental procedure was as described for the preparation of
compound 8. The crude product was purified by column
chromatography (silica gel/dichloromethane) to give an off-
white solid which was recrystallised from ethanol to yield
colourless crystals.
Yield 1.36 g (55%); transitions (uC): C 44.5 [N 13] I; 1H
NMR (CDCl3): d 0.90 (3H, t), 1.35 (4H, m), 1.65 (2H, quint),
2.65 (2H, t), 6.97 (1H, ddd), 7.03 (1H, dd), 7.28 (3H, m), 7.52
(2H, dd); IR (KBr) nmax (cm21): 2960, 2940, 2860, 2120, 1490,
1410, 1130, 1110, 1010, 935, 880, 850, 810, 740, 580; MS m/z
299 (M1), 242. Calc. for C18H18FNS: C, 72.21; H, 6.06; N,
4.68. Found: C, 72.18; H, 6.02; N, 4.64%.
2-Cyano-6-(2,3-difluoro-4-pentylphenyl)naphthalene (49)
2,5-Difluoro-4’-isothiocyanato-4-pentylbiphenyl (38)
Quantities: compound 45 (1.80 g, 5.98 mmol), compound 46
(1.75 g, 7.68 mmol). The experimental procedure was as
described for the preparation of compound 4, except that
Quantities: compound 36 (1.47 g, 5.35 mmol), thiophosgene
(0.78 g, 6.78 mmol), calcium carbonate (0.87 g, 8.70 mmol).
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 7 3 1 – 1 7 4 3
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lithium chloride (0.80 g, 0.019 mol) was added with the
reagents. The crude product was purified by column chroma-
tography (silica gel/hexane–dichloromethane, 2:1) to give a
colourless solid which was recrystallised from ethanol to give
colourless crystals.
2-(6-Cyanonaphth-2-yl)-5-pentylthiophene (54)
Quantities: compound 53 (0.70 g, 2.32 mmol), 10% palladium
on carbon (0.30 g). The experimental procedure was as
described for the preparation of compound 6, except that the
hydrogenation time was 6 h. The crude product was purified by
column chromatography (silica gel/hexane–dichloromethane,
2:1) to give a colourless solid which was recrystallised from
ethanol to yield colourless crystals.
Yield 0.50 g (71%); transitions (uC): C 72.5 N 92.0 I; 1H
NMR (CDCl3): d 0.90 (3H, t), 1.37 (4H, m), 1.70 (2H, quint),
2.83 (2H, t), 6.80 (1H, d), 7.30 (1H, d), 7.56 (1H, dd), 7.80 (1H,
dd), 7.82 (1H, d), 7.84 (1H, d), 7.97 (1H, d), 8.15 (1H, d); IR
(KBr) nmax (cm21): 2990, 2960, 2880, 2220, 1620, 1600, 1495,
1445, 1165, 890, 800; MS m/z 305 (M1), 248. C20H19NS: C,
78.65; H, 6.27; N, 4.59. Found: C, 78.65; H, 6.26; N,4.57%.
1
Yield 1.37 g (68%); transitions (uC): C 84.0 (N 79.5) I; H
NMR (CDCl3): d 0.90 (3H, t), 1.40 (4H, m), 1.70 (2H, quint),
2.70 (2H, t), 7.06 (1H, ddd), 7.22 (1H, ddd), 7.97 (2H, m), 8.05
(1H, d), 8.26 (1H, d); IR (KBr) nmax (cm21): 2960, 2940, 2240,
1460, 1275, 1090, 900, 875, 825, 805; MS m/z 335 (M1), 278.
Calc. for C22H19F2N: C, 78.78; H, 5.71; N, 4.18. Found: C,
78.73; H, 5.68; N, 4.16.
2-Cyano-6-(2-methyl-4-pentylphenyl)naphthalene (50)
Quantities: compound 45 (1.80 g, 5.98 mmol), compound 32
(1.48 g, 7.18 mmol). The experimental procedure was as
described for the preparation of compound 4, except that
lithium chloride (0.80 g, 0.019 mol) was added with the
reagents. The crude product was purified by column chroma-
tography (silica gel/hexane–dichloromethane, 2:1) to give a
colourless solid which was recrystallised from ethanol to yield
colourless crystals.
Yield 1.53 g (82%); transitions (uC): C 78.0 [N 27] I; 1H
NMR (CDCl3): d 0.90 (3H, t), 1.35 (4H, m), 1.65 (2H, quint),
2.65 (2H, t), 7.11 (1H, dd), 7.13 (1H, d), 7.22 (1H, d), 7.60 (1H,
dd), 7.64 (1H, dd), 7.81 (1H, d), 7.92 (2H, 2 6 d), 8.26 (1H, d);
IR (KBr) nmax (cm21): 2960, 2940, 2860, 2230, 1630, 1475, 915,
900, 825, 480; MS m/z 313 (M1), 256, 140. Calc. for C23H23N:
C, 88.13; H, 7.40; N, 4.47. Found: C, 88.10; H, 7.36; N, 4.45%.
2-Methyl-4-pentyl-4@-cyano-1,1’:4’,1@-terphenyl (57)
Quantities: compound 56 (1.93 g, 5.90 mmol), compound 32
(1.46 g, 7.09 mmol). The experimental procedure was as
described for the preparation of compound 4, except that
lithium chloride (0.75 g, 0.018 mol) was added with the
reagents. The crude product was purified by column chroma-
tography (silica gel/hexane–dichloromethane, 2:1) to give a
colourless solid which was recrystallised from ethanol to yield
colourless crystals.
1
Yield 1.10 g (55%); transitions (uC): C 58.5 N 113.0 I; H
NMR (CDCl3): d 0.90 (3H, t), 1.37 (4H, m), 1.68 (2H, quint),
2.31 (3H, s), 2.63 (2H, t), 7.10 (1H, dd), 7.13 (1H, d), 7.19 (1H,
d), 7.45 (2H, d), 7.64 (2H, d), 7.75 (4H, 2 6 d); IR (KBr) nmax
(cm21): 2990, 2960, 2880, 2225, 1605, 1490, 1110, 1010, 825;
MS m/z 339 (M1), 282.
2-(4-Butoxy-2-fluorophenyl)-6-cyanonaphthalene (52)
4’-Cyano-2,5-difluoro-4-pentylbiphenyl (59)
Quantities: compound 45 (2.30 g, 7.4 mmol), compound 51
(1.95 g, 9.20 mmol). The experimental procedure was as
described for the preparation of compound 4, except that
lithium chloride (1.00 g, 0.024 mol) was added with the
reagents. The crude product was purified by column chroma-
tography (silica gel/hexane–dichloromethane, 1:1) to give a
colourless solid which was recrystallised from ethanol to yield
colourless crystals.
Quantities: compound 58 (0.96 g, 5.27 mmol), compound 31
(1.38 g, 6.05 mmol). The experimental procedure was as
described for the preparation of compound 4. The crude
product was purified by column chromatography (silica gel/
hexane–dichloromethane, 2:1) to give a colourless solid which
was recrystallised from ethanol to yield colourless crystals.
1
Yield 0.95 g (63%); transitions (uC): C 54.5 [N 211] I; H
1
NMR (CDCl3): d 0.90 (3H, t), 1.35 (4H, m), 1.65 (2H, quint),
2.65 (2H, t), 7.01 (1H, dd), 7.09 (1H, dd), 7.63 (2H, dd), 7.73
(2H, d); IR (KBr) nmax (cm21): 2960, 2940, 2860, 2240, 1615,
1495, 1400, 1175, 900, 840, 820, 750, 560; MS m/z 285 (M1),
228.
Yield 1.90 g (78%); transitions (uC): C 64.5 N 129.5 I; H
NMR (CDCl3): d 1.00 (3H, t), 1.50 (2H, quint), 1.85 (2H,
quint), 4.00 (2H, t), 6.76 (1H, ddd), 6.82 (1H, dd), 7.45 (1H,dd),
7.61 (1H, dd), 7.78 (1H, ddd), 7.93 (2H, d), 8.00 (1H, d), 8.24
(1H, d); IR (KCl) nmax (cm21): 2960, 2940, 2860, 2240, 1630,
1520, 1495, 1475, 1315, 1290, 1165, 1130, 1040, 900, 840; MS
m/z 319 (M1), 262. Calc. for C21H18FNO: C, 78.98; H, 5.68; N,
4.39. Found: C, 78.96; H, 5.68; N, 4.35%.
2-(4-Cyanophenyl)-5-pentylthiophene (61)
Quantities: compound 58 (1.45 g, 7.97 mmol), compound 41
(1.85 g, 9.54 mmol). The experimental procedure was as des-
cribed for the preparation of compound 4. The crude product
was purified by column chromatography (silica gel/hexane–
dichloromethane, 2:1) and hydrogenated in THF (80 ml) and
ethanol (20 ml) in the presence of 5% palladium-on-charcoal
(0.30 g) catalyst at room temperature and atmospheric
pressure. The catalyst was filtered off and the solvent was
removed in vacuo and the residue was purified by column
chromatography (silica gel/hexane–dichloromethane, 2:1) to
give a colourless oil which was distilled [Kugelrohr, 150 uC
(maximum) at 0.5 mmHg] to yield a colourless solid which was
recrystallised from ethanol to yield colourless crystals.
2-(6-Cyanonaphth-2-yl)-5-pent-1-ynylthiophene (53)
Quantities: compound 45 (2.00 g, 6.64 mmol), compound 41
(1.55 g, 7.99 mmol). The experimental procedure was as
described for the preparation of compound 4, except that
lithium chloride (0.85 g, 0.020 mol) was added with the
reagents. The crude product was purified by column chroma-
tography (silica gel/hexane–dichloromethane, 2:1) to give a
pale yellow solid which was recrystallised from ethanol to yield
very pale yellow crystals.
1
Yield 1.55 g (78%); transitions (uC): C 104.0 (N 87.0) I; H
1
NMR (CDCl3): d 1.00 (3H, t), 1.60 (2H, sext), 2.45 (2H, t), 7.11
(1H, d), 7.31 (1H, d), 7.58 (1H, dd), 7.77 (1H, dd), 7.85 (1H, d),
7.88 (1H, d), 7.96 (1H, d), 8.14 (1H, d); IR (KB) nmax (cm21):
2990, 2960, 2880, 2220, 1620, 1600, 1495, 1445, 1165, 890, 800;
MS m/z 301 (M1), 286, 272. C20H15NS: C, 79.70; H, 5.02; N,
4.65. Found: C, 79.66; H, 4.98; N, 4.62%.
Yield 1.45 g (71%); transitions (uC): C 39.5 (N 16.0) I; H
NMR (CDCl3): d 0.90 (3H, t), 1.35 (4H, m), 1.65 (2H, quint),
2.80 (2H, t), 6.79 (1H, d), 7.24 (1H, d), 7.61 (4H, 2 6 d); IR
(KBr) nmax (cm21): 2960, 2940, 2860, 2240, 1605, 1510, 1470,
1410, 1270, 1215, 1180, 1125, 950, 840, 805, 740, 555, 520; MS
m/z 255 (M1), 198.
1 7 4 2
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 7 3 1 – 1 7 4 3

View Article Online
2-Butoxy-6-(4-fluorophenyl)naphthalene (65)
2-Butoxy-6-[2-fluoro-4-(trifluoromethyl)phenyl]naphthalene (71)
Quantities: compound 62 (1.35 g, 7.71 mmol), compound 1
(2.45 g, 0.01 mol). The experimental procedure was as
described for the preparation of compound 4. The crude
product was purified by column chromatography (silica gel/
hexane–dichloromethane, 3:1) to give a colourless solid which
was recrystallised from ethanol–ethyl acetate (2:1) to yield
colourless crystals.
Quantities: compound 69 (1.48 g, 6.09 mmol), compound 1
(1.93 g, 7.91 mmol). The experimental procedure was as
described for the preparation of compound 4. The crude
product was purified by column chromatography (silica gel/
hexane–dichloromethane, 6:1) to give a colourless solid which
was recrystallised from ethanol to yield colourless crystals.
Yield 1.51 g (68%); transitions (uC): C 73.5 SA 105.5 [N 55] I;
1H NMR (CDCl3): d 1.00 (3H, t), 1.55 (2H, sext), 1.85 (2H,
quint), 4.10 (2H, t), 7.16 (1H, d), 7.20 (1H, dd), 7.45 (1H, dd),
7.51 (1H, dd), 7.61 (1H, ddd), 7.66 (1H, dd), 7.79 (1H, d), 7.81
(1H, d), 7.97 (1H, d); IR (KCl) nmax (cm21): 2960, 2940, 2860,
1620, 1605, 1430, 1340, 1240, 1195, 1160, 1130, 1120, 1070, 940,
885, 865, 835; MS m/z 362 (M1), 306. Calc. for C21H18F4O: C,
69.41; H, 5.27. Found: C, 69.40; H, 5.25%.
1
Yield 1.80 g (79%); transitions (uC): C 128.5 [N 112] I; H
NMR (CDCl3): d 1.00 (3H, t), 1.55 (2H, sext), 1.85 (2H, quint),
4.10 (2H, t), 7.11–7.20 (4H, m), 7.61–7.67 (3H, m), 7.77 (2H,
m), 7.90 (1H, d); IR (KCl) nmax (cm21): 2960, 2940, 2860, 1630,
1610, 1520, 1505, 1470, 1390, 1250, 1205, 1175, 840, 810; MS
m/z 294 (M1), 238. Calc. for C20H19FO: C, 81.60; H, 6.51.
Found: C, 81.56; H, 6.48%.
References
2-Butoxy-6-(3,4-difluorophenyl)naphthalene (66)
1
2
M. Hird, K. J. Toyne and G. W. Gray, Liq. Cryst., 1993, 14, 741.
M. Hird, K. J. Toyne, G. W. Gray, S. E. Day and
D. G. McDonnell, Liq. Cryst., 1993, 15, 123.
M. Hird, A. J. Seed, K. J. Toyne, J. W. Goodby, G. W. Gray and
D. G. McDonnell, J. Mater. Chem., 1993, 3, 851.
A. J. Seed, K. J. Toyne and J. W. Goodby, J. Mater. Chem., 1995,
5, 2201.
A. J. Seed, K. J. Toyne and J. W. Goodby, J. Mater. Chem., 1995,
5, 653.
A. J. Seed, K. J. Toyne, J. W. Goodby and D. G. McDonnell,
J. Mater. Chem., 1995, 5, 1.
G. J. Cross, A. J. Seed, K. J. Toyne, J. W. Goodby, M. Hird and
M. C. Artal, J. Mater. Chem., 2000, 10, 1555.
A. J. Seed, K. J. Toyne, J. W. Goodby and M. Hird, J. Mater.
Chem., 2000, 10, 2069.
S. M. Kelly, Flat Panel Displays: Advanced Organic Materials,
Royal Society of Chemistry, Cambridge, UK, 2000.
Quantities: compound 63 (1.30 g, 6.74 mmol), compound 1
(2.14 g, 8.77 mmol). The experimental procedure was as
described for the preparation of compound 4. The crude
product was purified by column chromatography (silica gel/
hexane–dichloromethane, 6:1) to give a colourless solid which
was recrystallised from ethanol to yield colourless crystals.
Yield 1.46 g (69%); transitions (uC): C 81.5 [N 42] I; 1H
NMR (CDCl3): d 1.00 (3H, t), 1.55 (2H, sext), 1.85 (2H, quint),
4.10 (2H, t), 7.13–7.23 (3H, m), 7.40 (1H, m), 7.49 (1H, m), 7.60
(1H, dd), 7.78 (2H, 2 6 d), 7.89 (1H, d); IR (KCl) nmax (cm21):
2960, 2940, 2860, 1630, 1600, 1530, 1500, 1390, 1310 1275,
1215, 1175, 1215, 1175, 1120, 875, 860, 830, 805, 780; MS m/z
312 (M1), 256. Calc. for C20H18F2O: C, 76.90; H, 5.81. Found:
C, 76.88; H, 5.78%.
3
4
5
6
7
8
9
10 L. Domash, P. Levin, J. Ahn, J. Kumar and S. Tripathy, in Lower-
dimensional Systems and Molecular Electronics, R. M. Metzger,
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11 P. N. Pasad, in Lower-dimensional Systems and Molecular
Electronics, R. M. Metzger, P. Day and G. C. Papavassiliou,
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12 A. d’Alessandro and R. Asquini, Mol. Cryst. Liq. Cryst., 2003,
398, 207.
13 L. Petti, P. Mormile, G. Righini, L. Sirleto and G. Abbate, Mol.
Cryst. Liq. Cryst., 2001, 360, 131.
14 A. Spadlo, R. Dabrowski, M. Filipowicz, Z. Stolarz, S. Gauza,
C. Fan and S. T. Wu, Liq. Cryst., 2003, 30, 191.
15 N. Miyaura, T. Yanagi and A. Suzuki, Synth. Commun., 1981, 11,
513.
2-Butoxy-6-(2,4-difluorophenyl)naphthalene (67)
Quantities: compound 64 (1.37 g, 7.10 mmol), compound 1
(2.27 g, 9.30 mmol). The experimental procedure was as
described for the preparation of compound 4. The crude
product was purified by column chromatography (silica gel/
hexane–dichloromethane, 3:1) to give a colourless solid which
was recrystallised from ethanol to yield colourless crystals.
1
Yield 1.40 g (63%); transitions (uC): C 72.0 (N 63.0) I; H
NMR (CDCl3): d 1.00 (3H, t), 1.55 (2H, sext), 1.85 (2H, quint),
4.10 (2H, t), 6.90–7.00 (2H, m), 7.15 (1H, d), 7.18 (1H,dd), 7.49
(1H, m), 7.57 (1H, ddd), 7.77 (2H, 2 6 d), 7.87 (1H, d); IR
(KCl) nmax (cm21): 2960, 2940, 2860, 1620, 1610, 1595, 1510,
1500, 1390, 1260, 1205, 1175, 1145, 1100, 1070, 900, 855, 805;
MS m/z 312 (M1), 256. Calc. for C20H18F2O: C, 76.90; H, 5.81.
Found: C, 76.90; H, 5.80%.
16 A. O. King, E. Negishi, F. J. Villani and A. Silveira, J. Org. Chem.,
1978, 43, 358.
17 A. M. Echavarren and J. K. Stille, J. Am. Chem. Soc., 1987, 109,
5478.
18 G. W. Gray, M. Hird, D. Lacey and K. J. Toyne, J. Chem. Soc.,
Perkin Trans. 2, 1989, 2041.
19 E. Negishi, A. O. King and N. Okukado, J. Org. Chem., 1977, 42,
1821.
20 M. Hird, G. W. Gray and K. J. Toyne, Mol. Cryst. Liq. Cryst.,
1991, 206, 187.
2-Butoxy-6-[4-(trifluoromethyl)phenyl]naphthalene (70)
Quantities: compound 68 (1.46 g, 6.49 mmol), compound 1
(2.10 g, 8.60 mmol). The experimental procedure was as
described for the preparation of compound 4. The crude
product was purified by column chromatography (silica gel/
hexane–dichloromethane, 5:1) to give a colourless solid which
was recrystallised from ethanol–ethyl acetate (2:1) to yield
colourless crystals.
Yield 1.72 g (77%); transitions (uC): C 177.5 [N 95] I; 1H
NMR (CDCl3): d 1.00 (3H, t), 1.55 (2H, sext), 1.85 (2H, quint),
4.10 (2H, t), 7.16 (1H, d), 7.19 (1H, dd), 7.67 (1H, dd), 7.71
(2H, d), 7.79 (2H, d), 7.81 (2H, d), 7.97 (1H, d); IR (KCl) nmax
(cm21): 2960, 2940, 2860, 1620, 1605, 1395, 1335, 1280, 1255,
1210 1130, 1115, 1075, 1015, 845, 820, 805; MS m/z 344 (M1),
288, 259. Calc. for C21H19F3O: C, 73.24; H, 5.56. Found: C,
73.20; H, 5.53%.
21 N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95, 2457.
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30 D. R. Coulson, Inorg. Synth., 1972, 13, 121.
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 1 7 3 1 – 1 7 4 3
1 7 4 3