The synthesis and mesomorphism of di-, tetra- and hexa-catenar liquid crystals based on 2,2′-bipyridine

Article abstract of DOI:10.1039/a706400d

2,2′-Bipyridines are known to coordinate to a wide variety of metal centres. In this paper, liquid-crystalline two-chained (dicatenar), four-chained (tetracatenar) and six-chained (hexacatenar) bipyridines are synthesised and their mesomorphism is described. For the tetracatenar bipyridines, a full homologous series, from tetramethoxy to tetratetradecyloxy, was synthesised, and the phase diagram showed a classic progression from nematic and smectic C phases at short chain length, through a cubic phase to a columnar phase.

Full text of DOI:10.1039/a706400d

J O U R N A L O F
The synthesis and mesomorphism of di-, tetra- and hexa-catenar
liquid crystals based on 2,2∞-bipyridine
Kathryn E. Rowe and Duncan W. Bruce*
Department of Chemistry, University of Exeter, Stocker Road, Exeter, UK EX4 4QD
C H E M I S T R Y
2,2∞-Bipyridines are known to coordinate to a wide variety of metal centres. In this paper, liquid-crystalline two-chained
(dicatenar), four-chained (tetracatenar) and six-chained (hexacatenar) bipyridines are synthesised and their mesomorphism is
described. For the tetracatenar bipyridines, a full homologous series, from tetramethoxy to tetratetradecyloxy, was synthesised,
and the phase diagram showed a classic progression from nematic and smectic C phases at short chain length, through a cubic
phase to a columnar phase.
2,2∞-Bipyridines are some of the most versatile ligands used in
the construction of metal coordination complexes,1 having
been used to make dendrimers,2 helical structures,3 photoactive
systems,4 and a wide range of other supramolecular structures.5
Their attractiveness comes form their synthetic versatility and
from their ability to coordinate to a very wide variety of
metal centres.
synthesise several more examples and in particular, we exam-
ined tetracatenar (four-chain) and hexacatenar (six-chain)
derivatives. The syntheses and liquid crystal properties of these
new bipyridines are now described.
Synthesis of the bipyridines
In recent publications, we have reported that by suitable
choice of anisotropic ligand, it is possible to form rod-like
liquid crystals based on metals with octahedral stereochemis-
try.6 The approach is based on the assumption that such a
high coordination number metal centre perturbs the anisotropy
of the ligand to which it binds and leads to complexes with
low aspect ratios. Consequently, it is necessary to use rather
highly anisotropic ligands to screen out the perturbing effects
of the metal complex. We have demonstrated that this is
possible with imines orthometallated to MnI 7 and ReI,8 and
with diazabutadienes coordinated to ReI.9 It is, however, of
interest to note that low aspect ratios appear not to be so
much of a disadvantage in the design of columnar mesogens,
as evidenced by the synthesis by Swager10 of mesomorphic
complexes based on octahedral metal centres bound to poly-
substituted b-diketones.
Subsequently, we used the same approach in an effort to
incorporate bipyridines as ligands in metal-based liquid crys-
tals.11 Thus, we reported the synthesis and mesomorphism of
diesters of 2,2∞-bipyridine-5,5∞-dicarboxylic acid,12 simul-
taneously with reports of mesomorphic bipyridines based on
unsymmetrically substituted 5,5∞-disubstituted bipyridines.13
However, when complexed to a whole range of metal centres,
the liquid crystallinity of the bipyridines was lost.14 Curious
to understand the absence of mesomorphism in these systems,
we reasoned that by comparison with our own work and with
that of Deschenaux with 1,3-disubstituted ferrocenes,15 it
seemed necessary to have, in addition to the core of the
molecules, an additional four phenyl rings in order to realise
mesomorphic metal complexes. Thus, when complexed, the
2,2∞-bipyridine unit represented part of the core and, according
to our idea, four extra rings were required. It was therefore
necessary to synthesise a six-ring bipyridine to fulfil this design
criterion, and subsequent complexation to ReI eventually led
to a liquid crystalline complex.16
Four different types of bipyridine were synthesised, shown in
Scheme 1, and their synthesis is now described. Reaction of
methyl 4-hydroxybenzoate, or ethyl 3,4-dihydroxy- or 3,4,5-
trihydroxybenzoate with bromoalkane under basic conditions
led to the related mono-, di- or tri-alkoxybenzoic acid, after
alkaline hydrolysis and an acidic workup. For the mono- and
di-alkylations, butanone was used as the solvent, while penta-
none was preferred for the trialkylation reaction. These acids
were then esterified with hydroquinone which was monopro-
tected with either tetrahydropyran (THP) or with a benzyl
group. Benzyl protection was initially used and was sub-
sequently readily removed by hydrogenolysis. However, hydro-
genolysis of the di- and tri-alkoxy esters was painfully slow,
which led us to change to THP-protection, where the deprotec-
tion using oxalic acid in methanol at reflux gave essentially
quantitative yields. However, we subsequently found that
addition of a small amount of triethylamine during the hydro-
genolysis of the benzyl-protected system led to complete depro-
tection within minutes for any of the systems we studied,
indicating a clearly preferential route, especially as mono THP-
protected hydroquinone is obtained in four steps from hydro-
quinone. After deprotection, the resulting phenol was then
esterified with 2,2∞-bipyridine-5,5∞-dicarbonyl dichloride. This
was the lowest-yielding step of the whole procedure and despite
our best efforts which included evaluation of other possible
esterification methods, we could not obtain more than about
30% yield for this reaction. However, we would recommend
making the diacid chloride just before it is required as under
these circumstances, yields were consistently higher.
For the sake of later clarity, the bipyridines (Scheme 1) will
be abbreviated as follows. The two-chain (or dicatenar) bipyri-
dines, will be labelled Dn, where n denotes the number of
carbon atoms in the alkoxy chains. Similarly, the four-chain
(tetracatenar) and six-chain (hexacatenar) bipyridines will be
abbreviated as Tn and Hn, respectively.
Having shown that two-chained, six-ring derivatives of 2,2∞-
bipyridine could lead to mesomorphic complexes of ReI, we
were keen to pursue the synthesis of further examples as
bipyridines have enormous potential for coordination to a
very wide range of metal centres. Therefore, we proceeded to
The two-chained bipyridines were found to be highly insol-
uble making purification difficult, and while an analytically
pure sample was obtained for the octyloxy derivative, D8, the
other derivatives gave carbon values which were low by
approximately 1%, despite numerous recrystallisations; com-
pound R8 behaved in a similar fashion. Further purification
involved attempts to convert the dicatenar ligands to the
* E-mail: d.bruce@exeter.ac.uk
J. Mater. Chem., 1998, 8(2), 331–341
331

(OH)
OH
(OCnH2n+1
)
(i)
RO2C
OCnH2n+1
HO2C
(ii)
(OH)
R = CH3
(OCnH2n+1
)
Monohydroxy
1 Monoalkoxy
2 Dialkoxy
3 Trialkoxy
Di- or tri-hydroxy R = C2H5
(iii)
(OCnH2n+1
)
(OCnH2n+1)
O
O
O
OCnH2n+1
OCnH2n+1
(OCnH2n+1
(iv)
BzO
HO
O
(OCnH2n+1
)
)
4 Monoalkoxy
5 Dialkoxy
6 Trialkoxy
9 Monoalkoxy
10 Dialkoxy
11 Trialkoxy
(v)
(CnH2n+1O)
CnH2n+1
(CnH2n+1O)
O
O
O
O
O
N
O
O
(OCnH2n+1
OCnH2n+1
(OCnH2n+1
)
N
O
O
Dn Dicatenar
Tn Tetracatenar
Hn Hexacatenar
)
Scheme 1 Synthesis of the polycatenar bipyridines. Reagents and conditions: (i) C H
(iv) H , Pd/C; (v) 2,2∞-bipyridine-5,5∞-dicarbonyl dichloride, toluene, Et N.
Br, KHCO ; (ii) KOH/EtOH; (iii) BzOH, DCC, DMAP;
n
2n+1
3
2
3
corresponding hydrochloride salt, in order to achieve higher
solubility thus aiding purification. Unfortunately this was also
accompanied by decomposition, and so was unsuitable.
Compound T1 was also very insoluble and we could not
obtain good analytical data. However, we are not unduly
disturbed by this as neither of the first two homologues was
mesomorphic.
lower phase (M ) being unidentified. However due to decompo-
sition occurring at these elevated temperatures it was not
1
possible to obtain a clear texture of the lower mesophase on
cooling making identification impossible. Furthermore, this
meant that only data from the first DSC cycle could be used.
The butoxy bipyridine, D4, showed only a nematic phase,
while the longer chain length derivatives, D8, D12 and D14,
showed a smectic C phase before giving way to the nematic
Synthesis of bipyridine, R8
phase at higher temperatures. The temperature of the S –N
transition was found to vary with heating rate, which is
C
One example of a bipyridine with one of the ester groups
reversed was synthesised to examine the effect on mesomorph-
ism. The route is shown in Scheme 2. Thus, benzyl 4-hydroxy-
benzoate was first protected with 3,4-dihydro-2H-pyran under
acid-catalysed conditions at room temperature in ethyl acetate,
before the benzyl group was cleaved, in quantitative yield, with
hydrogen over a palladium-on-charcoal catalyst. This car-
boxylic acid 11 was reacted with 4-octyloxyphenol, using a
standard DCC–DMAP esterification, and the THP group was
subsequently cleaved under acidic conditions, at reflux in
methanol. The resulting phenol 13 was reacted with 2,2∞-
bipyridine-5,5-dicarbonyl dichloride at reflux in toluene con-
taining a few drops of triethylamine, to give the reversed ester,
R8. In common with the dicatenar bipyridines above, this
compound was found to be highly insoluble, again making
purification difficult.
attributed to decomposition occurring in the upper reaches of
the S phase and rapidly accelerating in the nematic phase.
C
Despite this, the S phase range was found to increase with
increasing chain length, as is expected with calamitic materials.
C
On both the heating and cooling cycles of the DSC, D12
showed another mesophase (M ) between the crystal and S
2
C
phase. By microscopy, with careful cooling, this transition was
observed, but persisted for only a degree or so before crystallis-
ation occurred. Due to decomposition occurring in the nematic
phase, it was not possible to obtain a good optical texture for
the S phase, and therefore for the M phase, too. However,
C
2
the relative magnitude of both the entropy and enthalpy
changes (obtained on cooling) leads to a tentative assignment
as a crystal smectic phase.
As this additional phase first appeared in the dodecyloxy
derivative it was hoped that its phase range would increase
with increasing alkoxy chain length. Hence, the tetradecyloxy
derivative, D14, was subsequently synthesised as a direct
attempt to elucidate the nature of this mesophase.
Unfortunately, the range of the phase was found to be equally
short and once more, a good optical texture could not be
obtained, leaving the mesophase unidentified.
Mesomorphism of the dicatenar bipyridines, Dn
Five dicatenar 2,2∞-bipyridine ligands were synthesised with
n=1, 4, 8, 12 and 14; the thermal data for these compounds
are collected in Table 1. The methoxy derivative was found to
exhibit two mesophases, the upper one being nematic, but the
332
J. Mater. Chem., 1998, 8(2), 331–341

O
O
O
O
O
(ii)
(i)
HO
O
OBz
O
OH
OBz
10
11
(iii)
O
O
O
O
O
(iv)
HO
O
OC8H17
OC8H17
13
12
(v)
C8H17
O
O
O
O
O
N
O
O
O
N
O
OC8H17
R8
Scheme 2 The synthesis of the ‘reversed ester’ ligand. Reagents and conditions: (i) 3,4-dihydro-2H-pyran, HCl(g); (ii) H , Pd/C; (iii) 4-
octyloxyphenol, DCC, DMAP; (iv) oxalic acid, MeOH; (v) 2,2∞-bipyridine-5,5∞-dicarbonyl dichloride, toluene, Et N.
2
3
Table 1 Thermal data for the dicatenar bipyridines
conventional discoid molecules. Conventional disc shaped
molecules stack on top of each other to form a column, these
n
Transitiona
T °/C
DH/kJ mol−1
DS/J K−1 mol−1
columns being packed in a two-dimensional array. However,
in the polycatenar systems, between two and four molecules
come together to form what is, in effect, a disc-like repeat unit
representing a slice through the columns, which are then
themselves packed in a two-dimensional array.
1
CrM
237
264
—b
—b
—
—b
—b
—
1
M N
1
Ndecomp. >264
4
8
CrN
Ndecomp.
269
350
45.8
—
84
—
Probably the most interesting of the polycatenar systems
are the tetracatenar compounds which can display lamellar,
cubic and columnar mesophases. Generally, lamellar meso-
phases are observed at short chain lengths while columnar
mesophases are observed at longer chain lengths. At intermedi-
ate chain lengths, this competition can result in the formation
of a frustrated phase, namely the cubic phase. This polymor-
phism arises due to the fact that in the mesophase, segregation
of the aromatic and aliphatic parts of the molecule occurs, and
as such these molecules can be regarded as amphiphilic in
nature. Indeed, their observed polymorphism is similar to that
of lyotropic systems in the sense that two-dimensional oblique
or rectangular columnar phases, or three-dimensional cubic
phases can be inserted in between lamellar and hexagonal
columnar phases. Also, like lyotropic systems, this segregation
of molecular parts results in curvature at the aromatic–ali-
phatic interface. This helps to explain the correlation between
mesophase type and the length of the aliphatic chain, for as
the chain length is increased so the curvature is increased,
resulting in the columnar mesophases being stabilised at the
expense of the lamellar mesophases.
Because of the potential for such rich mesomorphism in
these systems, we undertook the synthesis of a complete
homologous series from n=1–14. We believe that this is the
first time that such an homologous series has been investigated
for tetracatenar mesogens, and the results are presented as a
phase diagram in Fig. 1, while the thermal data are collected
in Table 2.
This series of compounds exhibits a phase behaviour that
is very typical for tetracatenar species, namely nematic
and lamellar phases at short chain lengths, columnar at long
chain lengths, with the changeover being accompanied by the
observation of a cubic phase at intermediate chain lengths.
Until the pentyloxy derivative, T5, only nematic phases
were observed at elevated temperatures, with decomposition
CrS
231
328c
52.3
—b
—
104
—b
—
C
S N
C
Ndecomp. >328
12
14
CrM
M S
210
212
341c
2.1d
35.5d
—b
4d
75d
—b
—
2
C
2
S N
C
Ndecomp. >341
—
CrM
M S
209
211
355c
368c
0.5d
49.0
4.2
1d
102
7
2
C
2
S N
C
NI
—b
—b
aM and M are unidentified mesophases (see text).
1
2
bNot seen by DSC.
cThese temperatures are sensitive to the thermal history of the sample
due to decomposition occuring in the S phase.
C
dThe thermodynamic data for these transitions are taken from the
cooling cycles on the DSC.
Mesomorphism of the tetracatenar bipyridines, Tn
Polycatenar liquid crystals17,18 are those which contain, typi-
cally, three or more chains and a rather extended core. They
are classified both by the number of terminal chains they
possess (tri-, tetra-, penta- and hexa-catenar) and also by the
way these are distributed on the terminal benzene rings.
The hexa- and penta-catenar compounds are found to
exhibit columnar phases, while the tricatenar compounds show
lamellar and cubic mesophases. The columnar phases result
from a strong curvature at the aromatic–aliphatic interface in
a way similar to that observed in lyotropic liquid crystals. The
structure of the columnar mesophase formed from polycatenar
species has been shown by dilatometry studies and X-ray
measurements to be slightly different from those formed by
J. Mater. Chem., 1998, 8(2), 331–341
333

occurring in the upper regions of these phases, beginning above
300 °C and accelerating rapidly above 350 °C. Thus, for the
methoxy (T1) and ethoxy (T2) derivatives, no clearing point
was observed. While the propoxy (T3) and butoxy (T4)
derivatives did clear to the isotropic, this temperature was not
found to be reproducible on subsequent runs as it was
accompanied by extensive decomposition. Nevertheless, the
clearing point decreased quite markedly as the chain length
increased. In initial microscopy studies, it appeared that T2–T4
melted over a large temperature range. DSC data showed that
there was a crystal–crystal transition immediately prior to
melting into the nematic mesophase. Further microscopy
allowed the melting temperature to be ascertained; however
by DSC the first transition was almost complete before the
compounds melted into the nematic phase; hence, the thermo-
dynamic data associated with these melting points are only
approximate.
350
300
250
200
150
I
N
T
Cub
Sc
Colh
12
Cr
0
2
4
6
8
10
14
carbon chain length
Fig. 1 Phase diagram for the tetracatenar bipyridines (Cr=crystal;
N=Nematic, S =smectic C; Cub=cubic and Col =columnar hexag-
onal); D, Cr–N; 1, Cr–S ; 2, Cr–Col ; $, S –N; #, S –Cub; *,
An additional phase, namely S was introduced at the
pentyloxy chain length and was readily characterised by its
C,
C
h
C
h
C
C
optical texture. Thus, the aliphatic chain was now of sufficient
length to stabilise lamellar mesophases. The derivatives T6–T8
represent the change over from lamellar to hexagonal columnar
mesophases, and as is often typical in tetracatenar systems this
is achieved via the cubic phase. Thus, the cubic phase (charac-
terised by its optical anisotropy, by the slow formation of such
a texture via the characteristic appearance of square edges
growing across the preceding texture, its high viscosity and
the accompanying appearance of misshapen air bubbles) first
Cub–N; +, Cub–Col ; %, N–I; &, Cub–I; x, Col –I
h
h
Table 2 Thermal data for the tetracatenar bipyridines
n
Transition
T /°C
DH/kJ mol−1
62.6
—
DS/J K−1 mol−1
1
2
3
4
5
CrN
Ndecomp. >300
259
117
—
CrNa
Ndecomp. >300
262
52.4
99
—c
—c
appears in the hexyloxy derivative, between the S and N
phases, giving one of very few well-authenticated examples of
C
CrNa
NIb
263
345
55.7
—c
104
—
a cubic phase below a nematic.19 In the heptyloxy derivative,
a monotropic columnar hexagonal phase was observed and
by the octyloxy derivative we had a compound that exhibited
enantiotropic lamellar, cubic and hexagonal columnar phases.
We believe that this is also unique in tetracatenar systems.
From T9 onwards, only columnar mesomorphism was
observed, with both the melting and clearing temperatures
remaining remarkably constant, irrespective of chain length.
The optical textures of these hexagonal columnar phases was
highly characteristic, exhibiting beautiful focal conic monodo-
mains and areas of homeotropic orientation. These columnar
mesophases have been identified as disordered hexagonal
columnar mesophases by X-ray diffraction studies which will
be published in due course as part of a much larger structural
study of the phase diagram.20 Thus, spacings in the ratio 1,
CrNa
NIb
242
325
55.6
—c
109
—c
CrS
C
221
229
294
61.8
3.2
1.0
126
6
2
S N
C
NI
6
CrS
196
220
239
(203)
(224)
(229)
272
55.8
1.7
4.0
—c
—c
—c
0.5
120
14
8
—c
—c
—c
1.0
C
S Cub
C
CubN
(CubS )
C
(S Cub)
C
(NS )
C
NI
7
CrS
184
197
(228)
(234.5)
239
59.2
2.9
(3.6)
—c
130
6
(7.0)
—c
7
C
S Cub
C
(ColCub)
˚
√3, √4 were seen and, for example, T12 gave d =43.8 A.
(ICol)
CubI
001
This phase diagram is absolutely ‘text-book’ for the behav-
3.8
iour of tetracatenar mesogens and is, to our knowledge, the
first time that a full homologous series of tetracatenar mesog-
ens, from methoxy upwards, has been synthesised. Thus, the
nematic and smectic C phases observed at short chain lengths
pass through an ‘intermediate’ cubic phase before giving way
to a columnar phase. By contrast, in a related piece of work
where we complexed two dicatenar alkoxystilbazoles in a trans
8
9
CrS
173
188
229
237
56.0
2.4
—
126
5
—
8
C
S Cub
C
CubCol
hd
Col I
4.0
hd
CrCol
171
238
35.6
3.9
4
8
hd
Col I
hd
10
11
12
13
14
CrCol
166
237
45.2
4.3
103
9
hd
fashion across a PtCl centre, the mesomorphism changed
suddenly from smectic C to columnar on passing from the
Col I
2
hd
CrCol
165
236
48.2
5.31
110
11
dodecyloxy derivative (S only) to the tridecyloxy derivatice
(columnar only), without any sign of a cubic phase and without
hd
C
Col I
hd
CrCol
161
234
48.6
5.8
112
11
any of the homologues showing both lamellar and columnar
phases.21 The sensitivity of polycatenar mesogens to their core
structure has been commented on previously.22
hd
Col I
hd
CrCol
161
229
47.7
6.6
110
12
hd
Col I
Close examination of the phase diagram reveals some interes-
ting possibilities. For example, there is a direct nematic–cubic
transition which ought to allow for the production of a cubic
monodomain from an aligned nematic, leading to unequivocal
assignment of the symmetry of the cubic phase, as reported
previously by us for mesomorphic complexes of silver().23
Furthermore, we have in T8, a compound with the enanti-
otropic phase sequence Col = Cub = S , previously found
hd
CrCol
161
230
48.9
6.5
113
13
hd
Col I
hd
aThe DSC data are only approximate due to an incomplete crystal–
crystal transition immediately prior to melting.
bThese temperatures are sensitive to the thermal history of the sample
due to decomposition occurring in the upper regions of the
nematic phase.
h
C
cNot seen by DSC.
only monotropically and not before in symmetric, tetracatenar
334
J. Mater. Chem., 1998, 8(2), 331–341

systems.20 We have recently carried out a detailed investigation
of polycatenar complexes of silver()24 using X-ray scattering,
freeze–fracture electron microscopy,25 and dilatometry, in
which we confirmed an epitaxial relationship between the
columnar and cubic phase, and have proposed a model for the
columnar-to-cubic transition.26 We now have the possibility of
extending this approach to look at the epitaxy of the columnar-
to-cubic-to-smectic C transitions in the same material, which
we hope will give further information on transitions to cubic
phases. These studies are already underway and will be
reported in due course.
Thus, while on cooling from the nematic phase the cubic phase
is thermodynamically preferred, the nematic can supercool due
to these slow kinetics, allowing the appearance of the S phase.
As this phase is thermodynamically unstable with respect to
the cubic, then the latter eventually appears, once more giving
C
way to the (now thermodynamically stable) S phase on
further cooling.
C
A similar situation exists with T7, where the heating and
cooling phase sequences are as shown below:
ColCubI Heating
The mesomorphism of the hexyloxy and heptyloxy deriva-
tives were found to be particularly interesting and are now
discussed in some detail. Thus, on heating, T6 showed the
following phase sequence:
IColCubCol Cooling
Very similar arguments can be invoked here, with a thermo-
dynamically unstable columnar phase appearing on cooling
the isotropic due to the slow kinetics of cubic phase formation.
CrS CubNI
C
However, on cooling the nematic phase gives way to a S
Mesomorphism of the hexacatenar 2,2∞-bipyridines
C
phase rather than a cubic phase. A cubic phase then grows
into the S phase and persists until the S phase reappears
once more. Thus, the phase sequence on cooling is:
As the mesomorphism displayed with the hexacatenar 2,2∞-
bipyridine systems was found to be predominantly columnar,
only four ligands were synthesised with n=1, 4, 8 and 12.
Thermal data are collected in Table 3.
C
C
INS CubS Cr
C
C
The mesomorphism observed in these compounds is typical
of hexacatenar systems, namely columnar mesophases, with
the exception of the methoxy derivative which exhibits a rather
different phase sequence. Thus, the butoxy derivative was
found to show a columnar phase. The cooling cycle of the
DSC only gave the isotropic–columnar transition, but the
crystal–columnar transition was reproducibly obtained on
subsequent heating cycles, following a cold crystallisation
exotherm. The octyloxy and dodecyloxy derivatives exhibited
similar mesomorphism. In both derivatives, the first heating
cycle on the DSC gave two transitions prior to clearing into
the isotropic. On cooling, neither sample crystallised, and
consequently on subsequent heating cycles, the melting trans-
ition was no longer observed, but the other transitions were
reproducibly obtained. By microscopy, these samples were also
observed not to crystallise, with the texture that first appeared
from the isotropic remaining until solidification. As a result,
the mesophase–mesophase transition (reproducible obtained
by DSC), was not initially observed by microscopy. On careful
reexamination of the dodecyloxy derivative by microscopy, it
was possible on the first heat to see a subtle textural change
in the highly birefringent sample, from a smooth to a finely
grained, less focused surface. However, the textures observed
by the first heat were not sufficient for characterisation. The
natural texture of the upper phase observed on cooling was
characteristic of a columnar phase, and the small change in
enthalpy required in the mesophase–mesophase transition
combined with the lack of any observed textural change on
cooling, suggests that the lower phase is also columnar. X-Ray
We were initially perplexed by this behaviour, but following
discussions with Dr Antoine Skoulios of the IPCMS in
Strasbourg, we feel we can offer an explanation. The behaviour
is best explained by considering a schematic free energy
diagram for the system as shown in Fig. 2.
Thus, on increasing the temperature and minimising G,
transitions would be expected (and are observed) from
S CubNI. On cooling, the reverse would clearly be
expected, but the behaviour is modified due to the very slow
kinetics generally found for the formation of cubic phases.
C
Table 3 Thermal data for the hexacatenar bipyridines
n
Transition
T /°C
203
211
217
292
DH/kJ mol−1
—a
—a
—a
—a
DS/J K−1 mol−1
1
CrCub
—a
—a
—a
—a
CubS
A
S N
A
NI
4
8
CrCol
ColI
143
176
26.7
3.5
64
8
CrColb
ColCol∞
ColI
85
157
165
45.2
0.2
6.4
126
1
15
12
CrColb
ColCol∞
Col∞I
54
142
151
38.6
0.3
5.7
114
1
14
Fig. 2 Schematic representation to show the thermodynamic relation-
ship between the mesophases in compounds T6 (a) and T7 (b)
aNot seen by DSC. bThis transition is only observed on the first heat.
J. Mater. Chem., 1998, 8(2), 331–341 335

studies are now in progress in order to ascertain the exact
nature of these mesophases (and the other analogues in this
series).
opposing each other, therefore they are now serving to stabilise
lamellar interactions.
The methoxy derivative was remarkable in showing the
phase sequence:
Conclusions
CrCubS NI
A
While transitions from both S to cubic and nematic to cubic
A number of di-, tetra- and hexa-catenar six-ring 2,2∞-bipyri-
dines have been synthesised. These were found to be novel
liquid-crystalline materials that exhibited a rich polymorphism.
Thus, the dicatenar compounds were found to exhibit
nematic and S phases, with the S phase being stabilised at
the expense of the nematic phase with increasing chain length.
This was the only lamellar phase observed, leading to the
observation reported previously15 that the 2,2∞-bipyridine core
A
are known, we are not aware of the INS Cub phase
sequence having been observed before. All of the phases were
A
readily assigned on the basis of optical microscopy, although
bizarrely, no thermal changes could be observed by DSC. We
have come across this problem before in other studies and
have usually found that by changing the experimental method
slightly, it was possible to obtain reproducible data. However,
in this case it was to no avail.
C
C
seems to strongly promote S phase formation in these types
of compounds. This observation was also borne out when the
direction of the terminal ester functionality was reversed, as
C
only a S phase was observed.
The tetracatenar system, in particular displayed the most
Mesomorphism of ligand, R8
C
Thermal data for R8 and D8 are collected in Table 4. It is well
known that the direction of an ester functionality can have a
profound effect on the observed mesomorphism.27 The six-ring
2,2∞-bipyridines described so far have their ester groups
arranged so that their dipoles oppose one another (see Fig. 3),
leading to net lateral dipoles which can be regarded as being
mutually repulsive and therefore, promoting nematic phases,
as observed. However, if the outer ester groups are reversed,
then the dipoles would be arranged as a kind of ‘outboard’
dipole which should promote smectic phases. Similar effects
are seen on the introduction of fluoro substituents into meso-
morphic systems.28
interesting mesomorphism as these compounds were found to
exhibit nematic and lamellar phases at short chain lengths,
and hexagonal columnar phases at long chain lengths, with a
cubic phase appearing at intermediate chain lengths at the
transferral point between the lamellar and columnar
mesophases.
Finally, the mesomorphism of hexacatenar species syn-
thesised was found to be essentially columnar, with the excep-
tion of the methoxy derivative which behaved as a calamitic
mesogen.
Reversal of the terminal ester group was found to promote
S
phase formation by destabilising both the crystal and the
Experimental
C
nematic phase. Nematic phase formation was suppressed to
the extent that it was no longer observed and the melting
point was lowered by some 34 °C. This is unsurprising as the
dipole moments of the ester functionalities are now no longer
Elemental analysis were determined by the University of
Sheffield Microanalysis Service. Mass spectra were recorded
using the Fast Atom Bombardment technique (FAB), at the
University of Sheffield. Infrared spectra were measured using
a Nicolet MAGNA 550 FTIR infrared spectrometer; UV–VIS
spectroscopy was carried out using a ATI Unicam UV4
machine. NMR spectra were recorded on either a Bruker
ACF-300 or a Bruker DRX-400 spectrometer, where the
chemical shifts are reported relative to the internal standard
of the deuterated solvent used. J values are in Hz. Analysis by
DSC was carried out on a Perkin-Elmer DSC7 instrument
using heating and cooling rates of either 5 or 10 K min−1.
Analysis by hot stage microscopy was carried out using a Zeiss
Labpol, or Olympus BH40 microscope equipped with a Link-
Am HFS91 hot stage, TMS92 controller and LNP2 colling
unit. Silica gel particle size was 40–63 mm.
Table 4 Thermal data for D8 and the ‘reversed’ ester, R8
Comp. Transition
T /°C
DH/kJ mol−1
37.3
—
DS/J K−1 mol−1
80
—
R8
D8
CrS
197
C
S decomp. >280
C
CrS
231
328
52.3
—
—
104
—
—
C
S Na
C
Ndecomp.a >328
aThese temperatures are sensitive to the thermal history of the sample
due to decomposition occurring in the S phase.
C
O
CnH2n+1
O
3
4
O
O
O
N
O
O
5
9
10
2
11
15
14
8
7
N
O
6
16
13
12
OCnH2n+1
D8
O
C8H17
O
O
3
4
O
N
O
9
10
11
12
5
O
O
14 15
8
7
O
N
O
16
13
6
O
OC8H17
R8
Fig. 3 Diagram to show the relative dispositions of dipoles in the dicatenar compounds and the related ‘reversed ester’
J. Mater. Chem., 1998, 8(2), 331–341
336

Synthesis of the 3,4-dialkoxybenzoic acids
2
3
7
8
4
5
All derivatives were prepared similarly and one example is
given. All other derivatives were obtained in yields ranging
from 80–95%.
1
12
13
6
9
O
O
I0
O
15 16
OCH2CH2(CH2)5CH3
22
11
14
7b
8b
14b
4c
OCH2CH2(CH2)5CH3
3
2
6
1
4-(4-Octyloxybenzoyloxy)-1-benzyloxybenzene 4c. 4-Octyloxy-
benzoic acid (5 g, 0.02 mol), 4-benzyloxyphenol (4 g 0.02 mol),
and dicyclohexylcarbodiimide (4.1 g, 0.02 mol), were dissolved
in dichloromethane. To this N,N-dimethylaminopyridine
(0.25 g 0.002 mol) was added and the reaction was stirred at
room temp. for 24 h. The colourless precipitate was removed
by filtration and the solvent was evaporated. Crystallisation
from ethanol (2×) gave the product as a colourless solid.
Yield: 6.8 g (80%); d (CDCl ): 8.05 (2H, AA∞XX∞, H12, J
HO2C
OCH2CH2(CH2)5CH3
4
7a 8a
14a
5
2h
3,4-Bis(octyloxy)benzoic acid 2h. Ethyl-3,4-dihydroxy-
benzoate (5 g, 0.027 mol), potassium carbonate (15.15 g,
0.1 mol) and 1-bromooctane (10.6 g, 0.055 mol) were placed in
butanone (150 cm3), and the reaction heated at reflux for 84 h.
Water (100 cm3) was added and the aqueous phase extracted
against dichloromethane (3×100 cm3). The organic extracts
H
3
AA∞XX∞
9), 7.35 (5H, m, H1–3), 7.05 (2H, AA∞XX∞, H8, J
9), 7.05
AA∞XX∞
(2H, AA∞XX∞, H13, J
9), 5.00 (2H, s, H5), 3.95 (2H, t, H15, 3J 6.5), 1.75 (2H, qt,
H16), 1.40 (2H, m, H17), 1.25 (8H, m, H18–21), 0.80 (3H, t, H22);
9), 6.87 (2H, AA∞XX∞, H7, J
AA∞XX∞
AA∞XX∞
were combined, dried over MgSO , filtered and evaporated to
give a brown solid. A solution of potassium hydroxide (3.07 g,
4
HH
0.055 mol) in ethanol (95%, 100 cm3) was added and the
reaction heated at reflux for 2.5 h. Water (100 cm3) was added
and the solution acidified with HCl (conc., 10 cm3). The
resulting colourless precipitate was collected and crystallised
twice from ethanol to give 3,4-bis(octyloxy)benzoic acid as a
colourless solid. Yield: 9.12 g (88%); d (CDCl ): 7.72 (1H, dd,
d
(CDCl ): 165.3(C10), 163.5(C14), 156.4(C6), 144.8(C9),
C
3
136.9(C4), 132.3(C12), 128.6, 128.0, 127.5(C1–3), 122.6(C8),
121.6(C11), 115.5(C7), 114.3(C13), 70.5(C5), 68.3(C15), 31.8,
29.4, 29.3, 29.1, 26.0, 22.7(C16–21), 14.1(C22).
H
3
Synthesis of the 4-(3,4-dialkoxybenzoyloxy)-1-benzyloxybenzenes
H6, 3J 8.5, 4J 2), 7.60 (1H, d, H2, 4J 2), 6.89 (1H, d, H5,
HH
HH
HH
3J 8.5), 4.07 and 4.05 (4H, t, H7a and b), 1.85 (4H, qt, H8),
All derivatives were prepared similarly and one example is
given. All other derivatives were obtained in yields ranging
from 58% to quantitative.
HH
1.30 (20H, m, H8–13), 0.90 (6H, t, H14)
Synthesis of the 3,4,5-trialkoxybenzoic acids
2
3
All derivatives were prepared similarly and one example is
given. All other derivatives were obtained in yields ranging
from 55–70%.
17b 18b
OCH2CH2(CH2)5CH3
24b
7
8
4
5
1
6
12
9
O
O
10
13
11
OCH2CH2(CH2)5CH3
14
5b 6b
12b
17a 18a
24a
O
16 15
OCH2CH2(CH2)5CH3
2
5h
3
5a 6a
12a
1
HO2C
OCH2CH2(CH2)5CH3
4
4-[3,4-Bis(octyloxy)benzoyloxy]-1-benzyloxybenzene 5h.
This was prepared from 3,4-bis(octyloxy)benzoic acid using
the procedure given for 4c. This gave the product as a
colourless solid. Yield: 3 g (80%); d (CDCl ): 7.82 (1H, dd,
OCH2CH2(CH2)5CH3
3c
H
3
3,4,5-Tris(octyloxy)benzoic acid 3c. Methyl 3,4,5-trihydroxy-
benzoate (5 g, 0.027 mol), potassium carbonate (22.5 g,
0.16 mol) and 1-bromooctane (15.65 g, 0.082 mol), were placed
in pentan-3-one (150 cm3), and the reaction heated at reflux
for 84 h. Water (100 cm3) was added and the aqueous phase
extracted against dichloromethane (3×150 cm3). The organic
H16, 3J 8.5, 4J 2), 7.68 (1H, d, H12, 4J 2), 7.40 (5H, m,
HH HH HH
H1–3), 7.13 (2H, AA∞XX∞, H8, J 9), 7.01 (2H, AA∞XX∞,
AA∞XX∞
H7, J
9), 6.93 (1H, d, H15, 3J 8.5), 5.09 (2H, s, H5),
AA∞XX∞
HH
4.09 and 4.08 (4H, t, H17a and b), 1.87 and 1.86 (4H, qt, H18a
and b), 1.51 (4H, m, H19), 1.35 (16H, m, H20–23), 0.91 (6H, t,
H24); d (CDCl ): 165.4(C10), 156.4(C6), 153.8(C14), 148.7(C13),
C
3
extracts were combined dried over MgSO , filtered and evapor-
144.8(C9), 136.9(C4), 128.6, 128.0, 127.5(C1–3), 124.3(C8),
122.6(16C), 121.8(C11), 115.5(C7), 114.7(C12), 112.1(C15),
70.5(C5), 69.4&69.1(C17a and b), 31.8, 29.4, 29.3, 29.2, 29.1, 26.0,
22.7(C18–23), 14.1(C24).
4
ated to give a brown oil. A solution of potassium hydroxide
(3.04 g, 0.054 mol) in 95% ethanol (150 cm3) was added and
the reaction heated at reflux for 2.5 h. Water (100 cm3) was
added and the solution acidified with conc. hydrochloric acid
(20 cm3). The resulting colourless precipitate was collected and
crystallised (2×) from ethanol to give 3,4,5-tris(octyloxy)ben-
zoic acid as a colourless solid. Yield 11 g (54%); d (CDCl ):
7.30 (2H, s, H2), 4.00 and 4.03 (6H, t, H5a and b), 1.84 (6H, qt,
H6), 1.50 (6H, m, H7), 1.30 (24H, m, H8–11), 0.85 (9H, t, H12);
(CDCl ): 172.0(CO H), 152.8(C3), 143.1(C4), 123.7(C1),
108.5(C2), 73.6(C5a), 6.2(C5b), 31.9, 31.8, 30.3, 29.5, 29.4, 29.3,
26.1, 22.7 (C6–11), 14.1(C12).
Synthesis of the 4-(3,4,5-trialkoxybenzoyloxy)-
1-benzyloxybenzenes
H
3
All derivatives were prepared similarly and one example is
given. All other derivatives were obtained in yields ranging
from 65–89%.
d
C
3
2
2
3
15b 16b
OCH2CH2(CH2)5CH3
22b
7
8
4
5
1
6
12
9
O
O
10
13
Synthesis of the 4-(4-alkoxybenzoyloxy)-1-benzyloxybenzenes
11
OCH2CH2(CH2)5CH3
14
15a 16a
22a
All derivatives were prepared similarly and one example is
given. All other derivatives were obtained in yields ranging
from 70–83%.
O
OCH2CH2(CH2)5CH3
6c
J. Mater. Chem., 1998, 8(2), 331–341
337

4-[3,4,5-Tris(octyloxy)benzoyloxy]-1-benzyloxybenzene 6c.
This was prepared from 3,4,5-tris(octyloxy)benzoic acid using
the procedure described for 4c. The crude product was purified
by crystallisation from ethanol (250 cm3), to give the pure
product as a colourless solid. Yield: 0.88 g (65%); d (CDCl ):
116.2(C2), 114.6(C7), 112.0(C10), 69.4 and 69.1(C12a and b), 31.8,
29.4, 29.3, 29.2, 29.0, 26.0, 22.7(C13–18), 14.1(C19).
Synthesis of the 4-(3,4,5-trialkoxybenzoyloxy)phenols
H
3
All derivatives were prepared similarly and one example is
given. All other derivatives were obtained in yields ranging
from 80–95%.
7.40 (5H, m, H1–3), 7.38 (2H, s, H12), 7.10 (2H, AA∞XX∞, H8,
J
9), 7.00 (2H, AA∞XX∞, H7, J
9), 5.06 (2H, s, H5),
AA∞XX∞
AA∞XX∞
4.05 (6H, m, H15), 1.82 and 1.80 (6H, qt, H16a and b), 1.50 (6H,
m, H17), 1.30 (24H, m, H18–21), 0.85 (9H, t, H22).
10b
21b
2
3
OCH2(CH2)6CH3
8
1
4
7
Synthesis of the 4-(4-alkoxybenzoyloxy)phenols
HO
O
10a
9
21a
6
OCH2(CH2)6CH3
5
All derivatives were prepared similarly and one example is
given. All other derivatives were obtained in yields ranging
from 76% to quantitative.
O
OCH2(CH2)6CH3
11c
2
3
1
7
8
4
4-[3,4,5-Tris(octyloxy)benzoyloxy]phenol 11c. Compound
6c (3.9 g, 5.7 mmol) was dissolved in freshly distilled THF
(150 cm3) and triethylamine (1 cm3) and 10% wet Degassu
Pd/C catalyst (0.05 g) was added. The reaction flask was
evacuated and placed under hydrogen (three times), before
being stirred at room temp. under an atmosphere of hydrogen.
After the calculated amount of hydrogen had been taken up
the catalyst was removed by filtration through Celite and the
solvent was evaporated. The crude product was purified by
flash chromatography on silica gel using THF as the eluent.
Yield: 3.37 g (quantitative); d (CDCl ) 7.38 (2H, s, H7), 7.03
HO
O
O
21
OCH2CH2(CH2)5CH3
10 11
5
6
9
9c
4-(4-Octyloxybenzoyloxy)phenol 9c. 4-(4-Octyloxybenzoy-
loxy)-1-benzyloxybenzene (6.6 g, 0.015 mol) was dissolved in
freshly distilled THF (150 cm3) and triethylamine (1 cm3), and
10% wet Degassu Pd/C catalyst (0.05 g) was added. The
reaction flask was evacuated and placed under hydrogen
(repeated three times), before being stirred at room temp.
under an atmosphere of hydrogen. After 223 cm3 of hydrogen
had been taken up the catalyst was removed by filtration
through Celite and the solvent was evaporated, to give a
colourless solid as the product. Yield: 4.7 g (90%); d (CDCl ):
H
3
(2H, AA∞XX∞, H3, J
9), 6.83 (2H, AA∞XX∞, H2, J
9),
AA∞XX∞
AA∞XX∞
5.18 (1H, s, OH), 4.02 (6H, t, H10), 1.80 and 1.75 (6H, qt,
H11a and b), 1.45 (6H, m, H12), 1.30 (24H, m, H13–16), 0.85 (9H,
t, H17); d (CDCl ): 166.2(C5), 153.8(C1), 152.9(C8), 144.1(C4),
H
3
C
3
8.12 (2H, AA∞XX∞, H7, J
9), 7.02 (2H, AA∞XX∞, H3,
9), 6.80 (2H, AA∞XX∞,
142.8(C9), 123.9(C6), 122.5(C3), 116.2(C2), 108.5(C7),
73.7(C10a), 69.3(C10b), 31.9, 31.8, 31.6, 30.3, 29.5, 29.4, 29.3,
26.9, 26.1, 22.7 (C11–16), 14.1(C17).
∞
∞
AA XX
J
9), 6.95 (2H, AA∞XX∞, H8, J
∞
∞
AA∞XX∞
AA XX
H2, J
9), 5.38 (1H, s, OH), 4.02 (2H, t, H10, 3J 6.5),
1.80 (2H, qt, H11), 1.45 (2H, m, H12), 1.30 (8H, m, H13–16),
0.85 (3H, t, H17); d (CDCl ): 166.2(C5), 163.7(C9), 153.7(C1),
144.2(C4), 132.4(C7) 122.5(C3), 121.4(C6), 116.3(C2), 114.3(C8),
68.4(C10), 31.8, 29.3, 29.2, 29.1, 26.0, 22.7(C11–16), 14.1(C17).
∞
∞
AA XX
HH
Synthesis of the bis[4-(4-alkoxybenzoyloxy)phenyl] 2,2∞-
bipyridine-5,5∞-dicarboxylates
C
3
All derivatives were prepared similarly and one example is
given. Yields and elemental analyses are collected in Table 5.
No 13C NMR data could be obtained for any of these materials
due to poor product solubility.
Synthesis of the 4-(3,4-dialkoxybenzoyloxy)phenols
All derivatives were prepared similarly and one example is
given. All other derivatives were obtained in yields ranging
from 80–95%.
Table 5 Yields and analytical data
12b 13b
23b
2
3
OCH2CH2(CH2)5CH3
1
(Calc. %)
C
Found %
H
7
4
HO
O
5
8
n
Yield (%)
N
6
OCH2CH2(CH2)5CH3
9
12a 13a
23a
D1
D4
D8
D12
D14
T1
T2
T3
T4
T5
20
15
18
12
12
20
15
8
(69.0)
67.6
69.5
72.4
73.2
74.3
64.4
67.4
68.9
69.6
71.0
71.8
72.3
73.3
73.4
74.0
74.6
75.0
75.2
75.7
64.4
69.4
72.4
73.2
71.6
(4.1)
4.0
5.2
6.3
7.2
7.5
4.2
5.0
5.6
6.1
6.7
7.1
7.2
7.9
7.9
8.2
8.5
8.7
9.0
9.0
4.5
6.9
6.3
8.9
6.1
(4.0) 4.2
(3.6) 3.5
(3.1) 3.0
(2.8) 2.8
(2.6) 2.7
(3.7) 3.6
(3.5) 3.3
(3.2) 3.2
(3.0) 3.0
(2.9) 2.8
(2.7) 2.6
(2.5) 2.5
(2.4) 2.5
(2.3) 2.3
(2.2) 2.2
(2.1) 2.1
(2.0) 2.0
(2.0) 2.0
(1.9) 1.8
(3.4) 3.5
(2.6) 2.6
(3.1) 3.0
(2.0) 2.0
(3.1) 3.4
O
11 10
(70.8)
(72.6)
(74.1)
(74.7)
(66.7)
(68.0)
(69.1)
(70.1)
(71.0)
(71.8)
(72.5)
(73.1)
(73.7)
(74.3)
(74.9)
(75.2)
(75.2)
(76.0)
(64.7)
(69.6)
(72.6)
(73.5)
(72.6)
(5.2)
(6.3)
(7.2)
(7.6)
(4.3)
(5.0)
(5.6)
(6.1)
(6.6)
(6.9)
(7.4)
7.7
(8.0)
(8.3)
(8.6)
(8.8)
(9.2)
(9.2)
(4.4)
(6.8)
(6.3)
(8.6)
(6.3)
10h
4-[3,4-Bis(octyloxy)benzoyloxy]phenol 10h. Compound 5h
(6.6 g, 0.0118 mol) was dissolved in freshly distilled THF
(150 cm3) and triethylamine (1 cm3) and 10% wet Degassu
Pd/C catalyst (0.05 g) was added. The reaction flask was
evacuated and placed under hydrogen (three times), before
being stirred at room temp. under an atmosphere of hydrogen.
After the calculated amount of hydrogen had been taken up
the catalyst was removed by filtration through Celite and the
solvent was evaporated. The crude product was purified by
crystallisation from ethanol, to give a colourless solid as the
product. Yield: 5.25 g (95%); d (CDCl ): 7.74 (1H, dd, H11,
18
8
T6
T7
T8
T9
22
22
25
19
10
32
5
T10
T11
T12
T13
T14
H1
H4
H8
H12
R8
5
H
3
3J 8.5, 4J
2), 7.57 (1H, d, H7, 4J
9), 6.85 (1H, d, H10, 3J 8.5), 6.75 (2H AA∞XX∞,
9), 5.15 (1H, s, OH), 4.01 and 4.00 (4H, t, H12),
2), 6.95 (2H, AA∞XX∞,
18
20
12
18
12
24
HH
HH
HH
HH
H3, J
∞
AA XX∞
H2, J
∞
AA XX∞
1.80 (4H, qt, H13), 1.40 (4H, m, H14), 1.25 (16H, m, H15–18),
0.83 (6H, t, H19); d (CDCl ): 166.1(C5), 153.9(C1), 153.7(C9),
C
3
148.6(C8), 144.2(C4), 124.5(C3), 122.5(C11), 121.5(C6),
338 J. Mater. Chem., 1998, 8(2), 331–341

O
O
CnH2n+1
O
3
4
O
O
N
O
O
5
9
10
2
11
15
8
14
7
N
O
6
16
13
12
OCnH2n+1
D8
O
CnH2n+1
O
O
O
CnH2n+1
O
3
4
O
O
N
O
O
5
9 10
2
11
15
8
14
18
7
N
O
6
16
13
12
OCnH2n+1
O
17
OCnH2n+1
T8
Bis[4-(4-octyloxybenzoyloxy)phenyl]
2,2∞-bipyridine-5,5∞-
hot through Celite. The colourless solution was evaporated
and the solid recrystallised (×2) from 1,4-dioxane, giving the
product as a cream solid. Yield: 0.62 g (17%); d (CDCl ): 9.43
dicarboxylate D8. The apparatus was flame dried prior to
use. 2,2∞-Bipyridine-5,5∞-dicarboxylic acid dichloride (2.4 g,
3.6 mmol), and 4-(4-octyloxybenzoyloxy)phenol (1.74 g 7.1
mmol) were placed in freshly distilled toluene (50 cm3).
Triethylamine (1 cm3) was added and the reaction heated at
reflux, under nitrogen overnight. The solvent was evaporated
and dichloromethane added. This was extracted against 10%
ammonia solution. The aqueous phase was then extracted with
dichloromethane (2×100 cm3), the organic extracts combined
and the solvent evaporated to give a crude dark brown solid.
The solid was placed in ethyl acetate, heated to reflux, allowed
to cool to room temp. and the solid collected by centrifugation
(×2). The solid was then heated to reflux in 1,4-dioxane and
collected (×2), giving the product as a cream solid. d (CDCl )
H
3
(2H, dd, H6, 4J 2, 5J 1), 8.65 (2H, dd, H3, 3J 8.5, 5J
HH HH HH
1), 8.55 (2H, dd, H4, 3J 8.5, 4J 2), 7.78 (2H, dd, H18, 3J
HH HH
HH
HH
8.5, 4J
HH
AA∞XX∞, H9 and 10, J
2), 7.60 (2H, d, H14, 4J 2), 7.29 and 7.22 (8H,
HH
9), 6.88 (2H, d, H17, 3J 8.5), 4.03
∞
∞
AA XX
HH
and 4.02 (8H, t, H19a and b), 1.60 (8H, m, H20), 1.43 (8H, m,
H21), 1.30 (32H, m, H22–25), 0.95 (12H, t, H26); d (CDCl ):
C
3
164.9(C12), 163.7(C7), 158.7(C2), 153.9(C16), 151.2(C6), 148.9
and 148.6, 147.8(C8,11 and 15), 138.8(C4), 125.8(C5), 124.4(C3),
122.9 and 122.5(C9 and 10), 121.6(C18), 121.2(C13), 114.5(C14),
111.9(C17), 69.3 and 69.1(C19a and b), 31.8, 29.4, 29.3, 29.1, 29.0,
26.0, 22.7 (C20–25), 14.1(C26).
H
3
9.40 (2H, dd, H6, 4J 2.5, 5J 1), 8.64 (2H, dd, H3, 3J 8.5,
The synthesis of the bis[4-(3,4,5-trialkyloxybenzoyloxy)-
phenyl] 2,2∞-bipyridine-5,5∞-dicarboxylates
HH HH HH
5J 1), 8.54 (2H, dd, H4, 3J 8.5, 4J 2.5), 8.06 (4H, AA∞XX∞,
HH
HH
HH
H14, J
9), 7.22 (8H, AA∞XX∞, H9 and 10), 6.90 (4H, AA∞XX∞,
9); The alkyl region was unresolvable.
∞
∞
AA XX
All derivatives were prepared similarly and one example is
given. Yields and elemental analyses are collected in Table 5.
H15, J
∞
∞
AA XX
Synthesis of the bis[4-(3,4-dialkoxybenzoyloxy)phenyl] 2,2∞-
bipyridine-5,5∞-dicarboxylates
Bis{4-[3,4,5-tris(octyloxy)benzoyloxy]phenyl} 2,2∞-bipyri-
dine-5,5∞-dicarboxylate H8. The apparatus was flame dried
prior to use. 2,2∞-Bipyridine-5,5∞-dicarboxylic acid dichloride
(0.25 g, 0.9 mmol), and 4-[3,4,5-tris(octyloxy)benzoyloxy]-
phenol (10.6 g 1.8 mmol) were placed in freshly distilled toluene
(50 cm3). Triethylamine (1 cm3) was added and the reaction
heated at reflux, under nitrogen overnight. The solvent was
evaporated and dichloromethane added. This was extracted
against 10% ammonia solution. The aqueous phase was then
extracted with dichloromethane (2×100 cm3), the organic
extracts combined and the solvent evaporated to give a crude
dark brown solid. The solid was placed in ethyl acetate, heated
to reflux, allowed to cool to room temp. and the solid collected
by centrifugation (×2), before being crystallised from 1,4-
dioxane. The crude product was placed in chloroform, heated
to reflux and filtered hot through Celite. The colourless solution
was evaporated and the solid recrystallised (×2) from 1,4-
dioxane, giving the product as a cream solid. Yield: 0.23 g
(19%); d (CDCl ): 9.50 (2H, dd, H6, 4J 2, 5J 1), 8.73
All derivatives were prepared similarly and one example is
given. Yields and elemental analyses are collected in Table 5.
Bis{4-[3,4-bis(octyloxy)benzoyloxy]phenyl} 2,2∞-bipyridine-
5,5∞-dicarboxylate T8. The apparatus was flame dried prior to
use. 2,2∞-Bipyridine-5,5∞-dicarboxylic acid dichloride (0.9 g,
3.2 mmol), and 4-[3,4-bis(octyloxy)benzoyloxy]phenol (3 g,
6.4 mmol) were placed in freshly distilled toluene (50 cm3).
Triethylamine (1 cm3) was added and the reaction heated at
reflux, under nitrogen overnight. The solvent was evaporated
and dichloromethane added. This was extracted against 10%
ammonia solution. The aqueous phase was then extracted with
dichloromethane (2×100 cm3), the organic extracts combined
and the solvent evaporated to give a crude dark brown solid.
The solid was placed in ethyl acetate, heated to reflux, allowed
to cool to room temp. and the solid collected by centrifugation
(×2), before being crystallised from 1,4-dioxane. The crude
product was placed in chloroform, heated to reflux and filtered
H
3
HH
HH
HH
(2H, dd, H3, 3J 8.5, 5J 1), 8.63 (2H, dd, H4, 3J 8.5, 4J
HH
HH
HH
CnH2n+1
O
O
O
CnH2n+1
O
3
4
O
O
N
O
O
5
9
10
2
OCnH2n+1
16
CnH2n+1
O
11
8
15
7
14
13
N
O
6
12
OCnH2n+1
O
H8
OCnH2n+1
J. Mater. Chem., 1998, 8(2), 331–341
339

2), 7.42 (4H, s, H14), 7.35 and 7.30 (8H, AA∞XX∞, H9 and 10,
2
3
J
9), 4.08 and 4.06 (12H, t, H17a and b), 1.86 and 1.80
AA∞XX∞
1
4
(12H, m, H18a and b), 1.49 (12H, m, H19), 1.30 (48H, m, H20–23),
0.90 (18H, t, H24); d (CDCl ): 164.9(C12), 163.6(C7), 158.8(C2),
7
8
O
O
O
12 13
6
9
5
C
3
O
15 16
22
153.0(C15), 151.1(C6), 148.8 and 148.0(C8 and 11), 143.3(C16),
138.7(C4), 125.9(C5), 123.6(C13), 122.9 and 122.5(C9 and 10),
121.7(C3), 108.7(C14), 73.6(C17a), 69.3(C17b), 31.9, 31.8, 30.4,
29.5, 29.4, 29.3, 26.1, 22.7 (C18–23), 14.1(C24).
11
14
10
OCH2CH2(CH2)5CH3
12
4-Octyloxyphenyl 4∞-(tetrahydropyran-2-yloxy)benzoate 12.
Compound 11 (2.5 g, 0.012 mol), 4-octyloxyphenol (2.5 g
0.012 mol), and dicyclohexylcarbodiimide (DCC) (2.32 g
0.012 mol) were dissolved in dichloromethane (80 cm3). 4-
(N,N-Dimethylamino)pyridine (0.14 g 1.2 mmol) was then
added and the reaction stirred at room temp. overnight. The
colourless precipitate was removed by filtration and the solvent
evaporated. Crystallisation from ethanol (×2) gave the product
Synthesis of the reversed ester, R8
2
3
1
4
7
8
O
O
O
6
9
5
O
10
11
12
13
14
as a colourless solid. Yield: 4 g (84%); mp 81 °C (sublimes); d
H
(CDCl ): 8.13 (2H, AA∞XX∞, H8, J
9), 7.10 (2H, AA∞XX∞,
∞
∞
3
AA XX
10
15
H7, J
9), 7.15 (2H, AA∞XX∞, H13, J
9), 6.90 (2H,
∞
∞
∞
∞
AA XX
AA XX
AA∞XX∞, H12, J
H15, 3J 6.5), 3.88 (1H, m, H1eq), 3.62 (1H, m, H1ax), 2.05,
9), 5.55 (1H, t, H5, 3J 3), 3.95 (2H, t,
∞
∞
AA XX
HH
HH
Benzyl 4-(tetrahydropyran-2-yloxy)benzoate 10. 3,4-
Dihydro-2H-pyran (20 cm3, 0.22 mol) and ethyl acetate satu-
rated with HCl(g) (3.5 cm3) was added to a solution of benzyl
4-hydroxybenzoate (10 g, 0.044 mol) in ethyl acetate (100 cm3).
The reaction was stirred at room temp. for 12 h before the
solvent was removed. Flash chromatography on neutral alum-
ina using dichloromethane as the eluent gave the product as
a colourless oil which solidified on standing. Yield: 12 g (88%);
mp 68–71 °C (decomp.); d (CDCl ): 8.03 (2H, AA∞XX∞, H8,
1.90 and 1.70 (6H, m, H2,3 and 4), 1.78 (2H, m, H16), 1.45 (2H,
m, H17), 1.30 (8H, m, H18–21), 0.90 (3H, t, H22); d (CDCl ):
C
3
165.3(C10), 161.4(C6), 156.8(C14), 144.4(C11), 132.1(C8),
122.7(C9), 122.4(C12), 116.1(C7), 115.1(C13), 96.1(C5),
68.5(C15), 62.0(C1), 30.1(C4), 25.1(C2), 18.5(C3), 31.8, 29.4,
29.3, 29.2, 26.1, 22.7(C16–21), 14.1(C22).
2
3
O
O
7
8
1
4
H
3
HO
10 11
17
J
9), 7.40 (5H, m, H13–17), 7.06 (2H, AA∞XX∞, 7H, J
6
9
5
AA∞XX∞
AA∞XX∞
OCH2CH2(CH2)5CH3
9), 5.50 (1H, t, H5, 3J 3), 3.88 (1H, m, H1eq), 3.62 (1H, m,
H1ax), 2.01, 1.90 and 1.70 (6H, m, H2,3 and 4); d (CDCl ):
HH
13
C
3
166.2(C10), 161.0(C6), 136.4(C12), 131.6(C8), 128.6, 128.12 and
128.07(C13–15), 123.3(C9), 115.9(C7), 96.1(C5), 66.4(C11),
62.0(C1), 30.1(C4), 25.1(C2), 18.5(C3).
4-Octyloxyphenyl 4-hydroxybenzoate 13. Compound 12 (4 g,
9.4 mmol) and oxalic acid (50 mg) were placed in methanol–
water (100 cm3; 951), and the reaction was heated at reflux
for 72 h. The reaction was cooled to room temp. and the
resulting colourless needles collected and washed with ethanol–
water (151), to give the pure product. The mother liquor was
evaporated and the resulting colourless solid crystallised from
ethanol–water to give more product as colourless needles.
Yield: 2.95 g (95%); mp 159 °C; d (CDCl ): 8.10 (2H, AA∞XX∞,
2
3
1
4
7
8
O
O
6
9
5
O
10
OH
11
H
3
H3, J
9), 7.10 (2H, AA∞XX∞, H7, J
9), 6.89 and 6.93
AA∞XX∞
AA∞XX∞
(4H, AA∞XX∞, H2 and 8, J
9), 5.80 (1H, s, OH), 3.95 ( 2H,
t, H10, 3J 6.5), 1.78 (2H, qt, H11), 1.45 (2H, m, H12), 1.30
(8H, m, H13–16), 0.90 (3H, t, H17); d (CDCl ): 165.5(C5),
162.3(C1), 156.7(C9), 144.5(C6), 132.3(C3), 122.5(C7),
120.6(C4), 115.5, 115.0(C2 and 8), 68.4(C10), 31.8, 29.3, 29.2,
26.0, 22.6(C11–16), 14.1(C17).
4-(Tetrahydropyran-2-yloxy)benzoic acid 11. To a solution
of compound 10 (11.5 g, 0.037 mol) in freshly distilled THF,
wet Degassu Pd/C catalyst was added (10%, 50 mg). The
reaction was placed under vacuum and hydrogen (×3) before
being left to stir under an atmosphere of hydrogen at room
temp. After hydrogen (900 cm3) had been used the reaction
was filtered through Celite and the solvent evaporated. The
crude product was crystallised from ethanol to give a colourless
solid as the product. Yield: 6 g (73%); mp 159 °C (decomp.);
AA∞XX∞
HH
C
3
Bis[(4-octyloxybenzoyloxy)phenyl] 2,2∞-bipyridine-5,5-
dicarboxylate R8. This was prepared from compound 13 using
the procedures for esterification with 2,2∞-bipyridine-5,5∞-dicar-
boxylic acid dichloride described above. This gave the product
d
(CDCl ): 8.05 (2H, AA∞XX∞, H8, J
9), 7.10 (2H,
H
3
AA∞XX∞
AA∞XX∞, 7H, J
9), 5.55 (1H, t, H5, 3J 3), 3.88 (1H,
AA∞XX∞
HH
dt, H1eq), 3.62 (1H, m, H1ax), 2.01, 1.90 and 1.70 (6H, m,
H2,3 and 4); d (CDCl ): 172.0(C10), 161.6(C6), 132.2(C8),
122.4(C9), 116.0(C7), 96.1(C5), 66.4(C11), 62.1(C1), 30.1(C4),
25.1(C2), 18.5(C3).
as a cream solid. Analytical data are found in Table 5. d
(CDCl ): 9.51 (2H, dd, H6, 4J 2, 5J 1), 8.75 (2H, dd, H3,
H
C
3
3
HH
HH
HH
3J 8.5, 5J 1), 8.64 (2H, dd, H4, 3J 8.5, 4J 2), 8.33 (4H,
HH
HH
HH
AA∞XX∞, H10, J
9), 7.44 (4H, AA∞XX∞, H9, J
9),
AA∞XX∞
AA∞XX∞
C8H17
O
O
O
3
4
O
O
N
O
O
9
10
11
12
5
O
14 15
8
7
N
16
13
6
O
OC8H17
R8
340
J. Mater. Chem., 1998, 8(2), 331–341

12 D. W. Bruce and K. E. Rowe, L iq. Cryst., 1995, 18, 161.
13 L. Douce, R. Ziessel, R. Seghrouchni, E. Campillos, A. Skoulios
and R. Deschenaux, L iq. Cryst., 1995, 18, 157.
14 K. E. Rowe and D. W. Bruce, L iq. Cryst., 1996, 20, 183.
15 See e.g. R. Deschenaux and J. W. Goodby, in Ferrocenes, ed
A. Togni and T. Hayashi, VCH, Weinheim, 1995, ch. 9.
16 K. E. Rowe and D. W. Bruce, J. Chem. Soc., Dalton T rans., 1996,
3913.
7.14 (4H, AA∞XX∞, H14, J
9), 6.95 (4H, AA∞XX∞, H15,
AA∞XX∞
J
9), 3.98 (4H, t, H17, 3J 6.5), 1.85 (4H, qt, H18), 1.50
AA∞XX∞
HH
(4H, m, H19), 1.27 (16H, m, H20–23), 0.90 (12H, t, H24); MS
m/z: [M+] 892.39; no 13C NMR data could be obtained due
to the product’s insolubility.
Support from the EPSRC and the University of Exeter is
gratefully acknowledged.
17 J. Matheˆte, H.-T. Nguyen and C. Destrade, L iq. Cryst., 1993, 13,
171.
18 H.-T. Nguyen, C. Destrade and J. Maltheˆte, Adv. Mater., 1997,
9, 375.
19 D. W. Bruce and S. A. Hudson, J. Mater. Chem., 1994, 4, 479;
W. Weissflog, G. Pelzl, I. Letko and S. Diele, Mol. Cryst., L iq.
Cryst., 1995, 260, 157.
20 B. Heinrich and D. Guillon, unpublished results.
21 B. Donnio and D. W. Bruce, J. Chem. Soc., Dalton T rans., 1997,
2745.
22 W. Weissflog, I. Letko, S. Diele and G. Pelzl, Adv. Mater., 1996,
8, 76.
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3
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5
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7
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9
D. W. Bruce and X.-H. Liu, L iq. K., 1995, 18, 165.
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28 M. A. Osman, Mol Cryst, L iq. Cryst., 1985, 128, 45; G. Nestor,
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11 See also: K. Hanabusa, J.-I. Higashi, T. Koyama, H. Shira, N. Hojo
and A. Kurose, Makromol. Chem., 1989 190, 1; T. Kuboki,
K. Araki, M. Yamada and S. Shiraishi, Bull. Chem. Soc. Jpn., 1994,
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L. Douce, R. Ziessel, R. Seghrouchni and A. Skoulios, L iq. Cryst.,
1996, 21, 143.
Paper 7/06400D; Received 2nd September, 1997
J. Mater. Chem., 1998, 8(2), 331–341
341