Non-symmetric liquid crystal dimer containing a carbohydrate-based moiety

Article abstract of DOI:10.1016/j.carres.2012.07.018

The synthesis and characterisation of a novel non-symmetric liquid crystal dimer, 1-[3-O-(d-glucopyranos-3-yl)]-8-[(4-methoxyazobenzene-4′-oxy)] octane is reported. This exhibits glassy behaviour and a highly interdigitated smectic A phase in which the aromatic and alkyl structural fragments overlap. Variable temperature infrared spectroscopy reveals that the strength and extent of hydrogen bonding within the system does not show a marked change at either the glass transition or at the smectic A-isotropic transition. This observation indicates that the smectic A-isotropic transition is driven by changes in the van der Waals interactions between the molecules while hydrogen bonded aggregates persist into the isotropic phase.

Full text of DOI:10.1016/j.carres.2012.07.018

Carbohydrate Research 360 (2012) 78–83
Contents lists available at SciVerse ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Non-symmetric liquid crystal dimer containing a carbohydrate-based moiety
Andrew G. Cook a, James L. Wardell a, Nicholas J. Brooks b, John M. Seddon b, Alfonso Martínez-Felipe c,
Corrie T. Imrie a,
⇑
a Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Meston Walk, Aberdeen AB24 3UE, UK
b Department of Chemistry, Imperial College of Science, Technology and Medicine, Exhibition Road, London SW7 2AY, UK
c Instituto de Tecnología de los Materiales (ITM), Universitat Politècnica de València (UPV) Camino de Vera S/N, 46022 Valencia, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 May 2012
Received in revised form 20 July 2012
Accepted 26 July 2012
Available online 3 August 2012
The synthesis and characterisation of a novel non-symmetric liquid crystal dimer, 1-[3-O-(D-glucopyr-
anos-3-yl)]-8-[(4-methoxyazobenzene-40-oxy)]octane is reported. This exhibits glassy behaviour and a
highly interdigitated smectic A phase in which the aromatic and alkyl structural fragments overlap. Var-
iable temperature infrared spectroscopy reveals that the strength and extent of hydrogen bonding within
the system does not show a marked change at either the glass transition or at the smectic A-isotropic
transition. This observation indicates that the smectic A-isotropic transition is driven by changes in
the van der Waals interactions between the molecules while hydrogen bonded aggregates persist into
the isotropic phase.
Keywords:
Liquid crystal dimer
Sugar
Smectic A phase
Variable temperature FTIR
Hydrogen bonding
Glassy behaviour
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
of the material. For a great many years it was widely believed that
low molar mass liquid crystals actually required molecules
There is now a wide range of low molar mass molecular archi-
tectures based on rod-like structures known to support liquid crys-
tallinity1 and of these, carbohydrate-based liquid crystals have
attracted particular research attention.2,3 This interest has arisen
primarily for two reasons: firstly, the building blocks for these
materials are numerous and inexpensive, and secondly, mesogenic
monosaccharides and polysaccharides play an important role in
many biological processes.4,5 A carbohydrate-based mesogen typi-
cally consists of a hydrophilic (polar) head group attached to which
are one or more lipophilic (nonpolar) chains. These amphiphilic
molecules have a strong tendency to microphase separate into
two distinct microdomains, one composed of the polar sugar moi-
eties and the other, the nonpolar alkyl chains, typically yielding
interdigitated smectic A behaviour.4
Carbohydrate-based liquid crystals are immiscible with conven-
tional thermotropic low molar mass liquid crystals which contain
molecules comprising a single semi-rigid core, normally consisting
of phenyl rings connected by short unsaturated linkages, attached
to which are one or two flexible alkyl chains.6,7 In essence, in these
so-called conventional systems, the anisotropic interactions be-
tween the semi-rigid cores give rise to liquid crystallinity while
the role of the alkyl chains is largely to reduce the melting point
containing a semi-rigid core although this is no longer the case.1
Indeed, liquid crystal dimers which consist of molecules comprised
of two mesogenic groups connected via a flexible spacer, normally
an alkyl chain, represent an inversion of the conventional
architecture and have been the focus of considerable research
attention.8–10
Of particular interest are non-symmetric liquid crystal dimers
in which the molecules contain two different liquid crystal groups
connected by a flexible spacer.9 In the overwhelming majority of
non-symmetric dimers, the two mesogenic groups are chosen with
the expectation that they will exhibit a specific favourable interac-
tion and this design approach led to the discovery of the interca-
lated smectic phases.11–14 However, this molecular architecture
has also been exploited to combine immiscible liquid crystal
groups; for example, rod-like and disc-like moieties have been
connected through flexible spacers.15–17
Molecular architectures which combine the structural elements
of cyclic carbohydrates and conventional rod-like low molar mass
mesogens linked by flexible spacers are rare; examples include,
liquid crystal trimers consisting of two glucopyranoside groups
and a central diphenylbutadiene or azobenzene unit linked by
two flexible spacers,18,19 a non-symmetric dimer containing a
sugar and steroid unit,20 and star-shaped compounds with a carbo-
hydrate-based core and peripheral conventional mesogenic side
chains.21–26
⇑
Corresponding author. Tel.: +44 1224 272567; fax: +44 1224 273105.
E-mail address: c.t.imrie@abdn.ac.uk (C.T. Imrie).
0008-6215/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.carres.2012.07.018

A. G. Cook et al. / Carbohydrate Research 360 (2012) 78–83
79
Recently, Yoshizawa described the properties of a non-symmet-
ric dimer in which a phenylpyrimidine and -glucamine were con-
1,2:5,6-di-O-isopropylidene-
scribed in detail elsewhere.
a-D
-glucofuranose, 4,30 have been de-
D
nected by an alkyl spacer and this showed cytostatic activity
against A549 human lung carcinoma cell lines.27 To our knowledge,
however, there have been no reports of a non-symmetric dimer in
which a conventional mesogenic core and a cyclic monosaccharide
are connected via a flexible spacer, and thus, we prepared 1-[3-O-
2.1. Synthesis of 1-[3-O-(1,2:5,6-di-O-isopropylidene-a-D-
glucofuranos-3-yl)]-8-[(4-methoxyazobenzene-40-oxy)]octane,
5
(D
-glucopyranos-3-yl)]-8-[(4-methoxyazobenzene-40-oxy)]octane,
Compound 5 was prepared using the method described by Bes-
sodes et al.31 Thus, freshly powdered potassium hydroxide (1 g,
17.9 mmol) and 18-crown-6 (0.11 g, 0.4 mmol), were added to a
1, and have characterised its liquid crystalline properties.
solution of 1,2:5,6-di-O-isopropylidene-a-D-glucofuranose, 4,
(2.36 g, 9 mmol) and 1-bromo-8-(4-methoxyazobenzene-40-oxy)-
octane, 3, (4.19 g, 10 mmol) in THF (20 ml). The mixture was stir-
red at room temperature overnight, diluted with CH2Cl2, and
washed several times with water. The organic phase was evapo-
rated under reduced pressure and the alkylated product was puri-
fied by column chromatography (elute 7:3 hexane/ethyl acetate).
Yield 45%. 1H NMR (CDCl3) d (ppm): 1.17–1.60 (m, 22H, (12H,
CH3 isopropylidiene groups), (10H, spacer CH2)), 1.80 (m, 2H,
OCH2CH2), 3.53 (m, 2H, OCH2), 3.9 (s, 3H, OCH3), 3.91–4.17 (m,
6H, (2H, OCH2), (4H on sugar)), 4.30 (qt, 1H, on sugar), 4.50 (d,
1H, CH), 5.85 (d, 1H, H1), 6.95, 7.84 (m, 8H, aromatic).
2. Experimental
Compound 1 was prepared using the synthetic route shown in
Scheme 1. The syntheses of 4-methoxy-40-hydroxyazobenzene,
2,28 1-bromo-8-(4-methoxyazobenzene-40-oxy)octane, 3,29 and
Scheme 1. Synthesis of 1-[3-O-(D
-glucopyranos-3-yl)]-8-[(4-methoxyazobenzene-40-oxy)]octane, 1.

80
A. G. Cook et al. / Carbohydrate Research 360 (2012) 78–83
2.2. Synthesis of 1-[3-O-(D-glucopyranos-3-yl)]-8-[(4-
methoxyazobenzene-40-oxy)]octane, 1
1-[3-O-(1,2:5,6-Di-O-isopropylidene-
a
-
D
-glucofuranos-3-yl)]-
8-[(4-methoxyazobenzene-40-oxy)]octane, 5, (1 g) was refluxed for
8 h in 5% sulphuric acid solution (10 ml). The hydrolysate was
washed with chloroform and water in a separating funnel. The
insoluble material was removed by filtration and recrystallised
from ethanol. The 1H NMR spectrum of this yellow solid obtained
in DMSO-d6 confirmed it to be the deprotected sugar, 1.
Yield 60%. Elemental analysis: anal. calcd for C27H38N2O8: C,
62.51; H, 7.39; N, 5.40. Found: C, 62.22; H, 7.17; N, 5.36. 1H NMR
(DMSO-d6) d (ppm): 1.29 (m, 6H, CH2CH2), 1.40 (m, 2H, CH2CH2),
1.48 (m, 2H, CH2CH2), 1.72 (m, 2H, ArOCH2CH2), 3.13 (m, H3),
3.22 (t, 2H, J = 5.9 Hz, OCH2), 3.40 (m, 2 H6), 3.66 (m, H2, H4, H5)
3.84 (s, 3H, OCH3), 4.02 (t, 2H, J = 6.5 Hz, ArOCH2), 6.60 (br s, 1H,
Figure 1. The DSC traces obtained for 1: (a) first heating, (b) cooling and (c) second
heating. The traces have been arbitrarily displaced along the y-axis for the sake of
clarity.
H1), 7.10 (m, 4H, aromatic), 7.82 (m, 4H, aromatic).). IR (KBr)
m
cmꢀ1: 3442 (O–H stretching), 1600, 1582 and 1500 cmꢀ1 (aromatic
C–C stretching), 1250 (C–O–C stretching).
2.3. Characterisation
The structures of 1 and all intermediates were verified by 1H
NMR spectroscopy using Varian Unity Inova 400 MHz and Bruker
AC-F 250 MHz spectrometers, and by FTIR spectroscopy using an
ATI Mattson spectrometer. Elemental analysis of 1 was performed
by Butterworth Laboratories Ltd. The transitional properties of 1
were determined by differential scanning calorimetry (DSC) in a
nitrogen atmosphere using a Mettler-Toledo DSC821e differential
scanning calorimeter cooled by liquid nitrogen and calibrated
using indium and zinc as standards. The time–temperature pro-
gramme used for the DSC analyses was (i) an initial heat from
ꢀ20 to 180 °C at 10 °C/min; (ii) held for 3 min at 180 °C; (iii) cooled
from 180 to ꢀ20 °C at 10 °C/min; (iv) held for 3 min at ꢀ20 °C and
(v) reheated from ꢀ20 to 180 °C at 10 °C/min. The thermodynamic
data quoted are averaged values from measurements of two ali-
quots of 1 and extracted from the reheating traces. Phase identifi-
cation was performed by polarised light microscopy using an
Olympus BH-2 optical microscope equipped with a Linkam TMHS
600 heating stage and a TMS 92 control unit. The molecular
arrangement within the liquid crystal phase was probed using X-
ray diffraction using a Huber X-ray camera, the calibration of
which was checked using silver behenate (d = 58.3 Å) and found
to be correct within 0.1 Å. The X-ray experiments were performed
on two different samples and the results found to be identical. The
FT-IR spectrum of 1 as a function of temperature was obtained
using a Nicolet Nexus FT-IR bench attached to a Continuum FT-IR
microscope equipped with a Linkam FT-IR 600 heating stage and
a TMS 93 control unit. The sample was sandwiched between a
gold-coated microscope slide and a 3 mm KBr disc. A thin film of
the sample was obtained by first heating it into the isotropic phase.
The spectra were recorded on subsequent reheating in a trans-
reflectance mode that is the IR beam passed through the sample
was reflected by the gold surface back through the sample and
then detected.
Figure 2. The focal conic fan texture seen for the smectic A phase exhibited by 1 at
156 °C.
(Fig. 1c). We note that on repeated cycling the transition tempera-
tures decrease and the associated peaks increase in breadth. This is
indicative of sample decomposition.
On cooling from the isotropic phase, bâtonnets developed
which coalesce to give a focal conic fan texture (Fig. 2) in co-exis-
tence with regions of homeotropic alignment when viewed
through the polarised light microscope. The presence of focal conic
fans implies a layered structure, while the homeotropic alignment
indicates an orthogonal arrangement of the director with respect
to the layer planes. Thus, the phase is assigned as a smectic A
phase. The texture remains unchanged on cooling to room temper-
ature and thus the lower temperature second order transition is as-
signed as a glass transition. The smectic A-isotropic assignment is
supported by the value measured for the entropy change associ-
ated with the smectic A-isotropic transition, expressed as the
dimensionless quantity
DS/R, of 3.23 which is comparable to that
seen for the smectic A-isotropic transition shown by other sym-
3. Results and discussion
metric and non-symmetric liquid crystal dimers.32,33
The X-ray diffraction powder pattern of the smectic A phase of 1
is shown in Figure 3 and confirmed this assignment. Thus, in the
low angle region of the X-ray diffraction pattern of the smectic A
phase, two sharp peaks of similar intensities were observed in
the spacing ratio 1:2 at a spacing, d, of 31.7 Å, while in the wide an-
gle region, a diffuse peak was seen centred at ca. 4.3 Å characteris-
tic of a liquid-like arrangement of the molecules within the layers.
In the low angle region of the X-ray pattern of the smectic A glass,
Figure 1 shows the traces obtained for the heat–cool–heat DSC
cycle of 1. In the first heating, a rather broad endotherm is seen at
about 67.5 °C followed by a second endotherm at 167 °C (Fig. 1a).
On cooling, an exotherm with onset temperature of 165 °C is ob-
served followed by a second order transition with a mid-point at
86 °C (Fig. 1b). On subsequent reheating, a second order transition
with a mid-point at 88 °C is followed by an endotherm at 165 °C

A. G. Cook et al. / Carbohydrate Research 360 (2012) 78–83
81
Figure 3. X-ray patterns of (a) the smectic A phase at 100 °C, and (b) the smectic A glass at 25 °C.
Figure 4. A sketch of the molecular organisation within the interdigitated smectic A phase shown by 1.
two slightly diffuse peaks of similar intensities, in the spacing ratio
1:2 at a spacing of 31.8 Å are seen while in the wide angle region a
diffuse peak is observed centred at ca. 4.3 Å On heating the sample
from 50 °C to 150 °C at 10 °C/h, the X-ray diffraction pattern is
essentially unchanged with only a sharpening of the low angle
peaks into Bragg peaks at ca. 95 °C which corresponds to the glass
transition detected using DSC. The low angle spacing decreases by
ca. 0.5 Å over this temperature range while the diffuse wide-angle
peak appears unchanged over the whole temperature range. The
estimated molecular length, L, is 27.5 Å such that the ratio of the
smectic periodicity to molecular length, d/L, is 1.15, suggesting that
the smectic phase must have an interdigitated structure in which
the alkyl chains and aromatic cores overlap considerably. Figure 4
shows a sketch of the molecular organisation within the smectic A
phase consistent with this d/L value and this is similar to the struc-
ture of the smectic A phase proposed for steroidal glycolipids.34 We
shall discuss the structure of the smectic A phase in more detail
later.
trum of the non-symmetric dimer 1 in the glass, smectic A and iso-
tropic phases. The band associated with O–H stretching is often
used as a test for, and a measure of, the extent and strength of
hydrogen bonding within a system. Thus, a free O–H group gives
rise to a strong and sharp band in the 3650–3590 cmꢀ1 region
while involvement in hydrogen bonding shifts this to lower fre-
quency and it generally becomes much broader. In the glass, the
O–H stretching band is centred at 3456 cmꢀ1. On heating the sam-
ple into the smectic A phase, the band shifts to 3472 cmꢀ1 and on
further heating can be seen at 3526 cmꢀ1 in the isotropic phase.
These shifts point to a reduction in the strength of hydrogen bond-
ing on increasing temperature.
The temperature dependence of the O–H stretching peak is
more easily visualised in Figure 6 which shows this region of the
spectrum as a function of temperature on heating while Figure 7
shows the dependence of the peak position on temperature.
Figure 7 shows that the position of the O–H stretching peak ap-
pears to vary linearly with temperature but with kinks coinciding
approximately with the glass and smectic A-isotropic transition
temperatures. In the glass phase, the gradient of the line of best
fit is 0.32 cmꢀ1/K, in the SmA phase 0.49 cmꢀ1/K, and in the isotro-
pic phase 1.46 cmꢀ1/K. Wolkers et al.36,37 termed these gradients
The liquid crystal behaviour of carbohydrate-based materials is
most commonly attributed to hydrogen bonding between the car-
bohydrate moieties35 and this can be conveniently investigated
using FT-IR spectroscopy. Thus, Figure 5 shows the infrared spec-

82
A. G. Cook et al. / Carbohydrate Research 360 (2012) 78–83
Figure 7. The dependence of the O–H stretching peak position in the infrared
spectra of 1 on temperature.
Figure 5. Infrared spectra for 1 measured in the glass (82 °C), smectic A (122 °C)
and isotropic phases (182 °C). The spectra have been shifted arbitrarily along the y-
axis for the sake of clarity.
rification. The absence of a step change in the position of the O–H
stretching peak at Tg was interpreted by Ottenhof et al.39 as indi-
cating that a threshold of hydrogen bond strength and density is
reached which results in the decrease in molecular mobility yield-
ing vitrification.
By contrast a much larger change is observed in WTC around
the smectic A-isotropic transition (Fig. 7). Surprisingly, however,
no step change is observed in the position of the O–H stretching
peak at the clearing point even thought the structure of the mate-
rial changes significantly. In comparison, cold crystallisation in
conventional sugars is accompanied by a step change in the posi-
tion of the O–H peak, the magnitude of which appears to be linked
to the size of the crystallisation enthalpy.39 This indicates that the
strength and density of the hydrogen bonding in the smectic A
phase exhibited by 1 does not change significantly at the smectic
A-isotropic transition. A similar observation has been reported
for a conventional carbohydrate-based liquid crystal.40
2
)
%
(
ce
an
180
160
b
r
It is also apparent in Figure 5 that the bands at ca. 1600 cmꢀ1
and 1500 cmꢀ1 associated with vibrations of the aromatic ring in-
crease in intensity on increasing temperature. This may be ac-
counted for in terms of a change in alignment of the sample on
increasing temperature. Specifically, the incident IR beam is polar-
ised on reflection at the gold surface41 and so vibrations parallel to
the surface will not be detected. On cooling, the non-symmetric di-
mer tends to adopt homeotropic alignment and hence, the inten-
sity of the bands associated with the in-plane vibrations of the
aromatic rings will decrease.
so
140
b
A
0
120
100
80
60
2800
3200
3600
Figure 6. The dependence of the 3600–2800 cmꢀ1 region of the infrared spectra of
1 on temperature. The spectra have been recorded on heating from the glass phase.
If we now consider thetransitional properties of thetwosymmet-
ric dimers, then 1,8-bis[(4-methoxyazobenzene-40-oxy)]octane, 6,
wavenumber–temperature coefficients (WTC) and measured them
for a range of amorphous sugars above and below the glass transi-
tion. To our knowledge, the values reported here are the first to be
given for a sugar-based liquid crystal. In the glass phase Wolkers
reported WTC values in the range of 0.1–0.45 cmꢀ1/K, and in the li-
quid phase 0.48–0.60 cmꢀ1/K.36 A small change in WTC at the glass
transition implies only small changes in the hydrogen bonding net-
work and correlated with a small
change in WTC at the glass transition was associated with large
values of Cp at Tg. In terms of Angell’s concept of strength and fra-
DCp at Tg. Conversely, a large
melts into the nematic phase at 199 °C, undergoes a nematic-isotro-
pic transition at 217 °C with an associated entropy change,
D
SNI/R,
D
of 1.76.42 The symmetric bolaamphiphile, 1,8-bis[3-O-(
anos-3-yl)]octane, 7,
D-glucopyr-
gility, a larger change in WTC at the glass transition corresponds to
an increase in fragility and a loss of strength in the system.38
For the non-symmetric dimer 1, the change in WTC at Tg is ca.
0.17 cmꢀ1/Kꢀ1, which is smaller than any of the values reported
by Wolkers et al.37 for amorphous sugar glasses. The value of
D
Cp for the glass transition of 1 is 0.37 J gꢀ1 Kꢀ1 and is similar to
that seen for the strongest of the amorphous glasses.37 This indi-
cates that the structure of the smectic A phase changes little on vit-

A. G. Cook et al. / Carbohydrate Research 360 (2012) 78–83
83
References
does not exhibit liquid crystalline behaviour and melts directly into
the isotropic phase between 143 and 145 °C.43 Thus, the nematic
behaviour of the conventional calamitic symmetric dimer has been
extinguished while the tendency of the sugar-based symmetric di-
mer to crystallise has been inhibited in the non-symmetric dimer.
The injection of smectic behaviour is presumably a consequence
of the incompatibility of the two mesogenic units in 1. This cannot
give rise to a monolayer smectic A phase, however, as there exists a
mismatch in the cross-sectional areas of the three structural com-
ponents, that is, the azobenzene-based mesogenic group, the sugar
and the alkyl spacer. Thus, to fill space effectively the azobenzene-
based unit must overlap with the alkyl spacer and this is consistent
with the smectic periodicity measured using X-ray diffraction. The
smectic arrangement, therefore, consists of a highly interdigitated
arrangement with the sugar groups on the outside of the layer and
the alkyl spacer and the azobenzene-based mesogenic overlapping
in the centre of the layer (see Fig. 4). This overlap between the aro-
matic and alkyl groups is unfavourable and in conventional dimers
drives the formation of smectic phases.32 Presumably the hydrogen
bonding between the sugar groups overcomes these unfavourable
interactions and lamellar-like behaviour results from the matching
of the cross-sectional areas of the sugar region and the alkyl-aro-
matic region.
1. Goodby, J. W.; Saez, I. M.; Cowling, S. J.; Gasowska, J. S.; MacDonald, R. A.; Sia,
S.; Watson, P.; Toyne, K. J.; Hird, M.; Lewis, R. A.; Lee, S. E.; Vaschenko, V. Liq.
Cryst. 2009, 36, 567–605.
2. Brooks, N. J.; Hamid, H. A. A.; Hashim, R.; Heidelberg, T.; Seddon, J. M.; Conn, C.
E.; Husseini, S. M. M.; Zahid, N. I.; Hussen, R. S. D. Liq. Cryst. 2011, 38, 1725–
1734.
3. Hashim, R.; Sugimura, A.; Minamikawa, H.; Heidelberg, T. Liq. Cryst. 2012, 39,
1–17.
4. Goodby, J. W.; Gortz, V.; Cowling, S. J.; Mackenzie, G.; Martin, P.; Plusquellec,
D.; Benvegnu, T.; Boullanger, P.; Lafont, D.; Queneau, Y.; Chambert, S.;
Fitremann, J. Chem. Soc. Rev. 2007, 36, 1971–2032.
5. Jewell, S. A. Liq. Cryst. 2011, 38, 1699–1714.
6. Goodby, J. W. Liq. Cryst. 2011, 38, 1363–1387.
7. Hird, M. Liq. Cryst. 2011, 38, 1467–1493.
8. Imrie, C. T.; Henderson, P. A. Curr. Opin. Colloid Interface Sci. 2002, 7, 298–311.
9. Imrie, C. T.; Henderson, P. A. Chem. Soc. Rev. 2007, 36, 2096–2124.
10. Imrie, C. T.; Henderson, P. A.; Yeap, G. Y. Liq. Cryst. 2009, 36, 755–777.
11. Hogan, J. L.; Imrie, C. T.; Luckhurst, G. R. Liq. Cryst. 1988, 3, 645–650.
12. Attard, G. S.; Date, R. W.; Imrie, C. T.; Luckhurst, G. R.; Roskilly, S. J.; Seddon, J.
M.; Taylor, L. Liq. Cryst. 1994, 16, 529–581.
13. Imrie, C. T. Liq. Cryst. 2006, 33, 1449–1454.
14. Yeap, G. Y.; Hng, T. C.; Yeap, S. Y.; Gorecka, E.; Ito, M. M.; Ueno, K.; Okamoto,
M.; Mahmood, W. A. K.; Imrie, C. T. Liq. Cryst. 2009, 36, 1431–1441.
15. Fletcher, I. D.; Luckhurst, G. R. Liq. Cryst. 1995, 18, 175–183.
16. Date, R. W.; Bruce, D. W. J. Am. Chem. Soc. 2003, 125, 9012–9013.
17. Imrie, C. T.; Lu, Z.; Picken, S. J.; Yildirim, Z. Chem. Commun. 2007, 1245–1247.
18. Abraham, S.; Paul, S.; Narayan, G.; Prasad, S. K.; Rao, D. S. S.; Jayaraman, N.; Das,
S. Adv. Funct. Mater. 2005, 15, 1579–1584.
19. Das, S.; Gophinathan, N.; Abraham, S.; Jayaraman, N.; Singh, M. K.; Prasad, S. K.;
Rao, D. S. S. Adv. Funct. Mater. 2008, 18, 1632–1640.
20. Rachedi, F. A.; Chambert, S.; Ferkous, F.; Queneau, Y.; Cowling, S. J.; Goodby, J.
W. Chem. Commun. 2009, 6355–6357.
4. Conclusions
21. Zhang, B. Y.; Xiao, W. Q.; Cong, Y. H.; Zhang, Y. H. Liq. Cryst. 2007, 34, 1129–
1136.
22. Xiao, W. Q.; Zhang, B. Y.; Cong, Y. H. Chem. Lett. 2007, 36, 938–939.
23. Akiyama, H.; Tanaka, A.; Hiramatsu, H.; Nagasawa, J.; Tamaoki, N. J. Mater.
Chem. 2009, 19, 5956–5963.
24. Tian, M.; Zhang, B.-Y.; Cong, Y.-H.; He, X.-Z.; Chu, H.-S.; Zhang, X.-Y. Liq. Cryst.
2010, 37, 1373–1379.
25. Belaissaoui, A.; Cowling, S. J.; Saez, I. M.; Goodby, J. W. Soft Matter 2010, 6,
1958–1963.
26. Belaissaoui, A.; Saez, I. M.; Cowling, S. J.; Zeng, X.; Goodby, J. W. Chem. Eur. J.
2012, 18, 2366–2373.
27. Yoshizawa, A.; Takahashi, Y.; Terasawa, R.; Chiba, S.; Takahashi, K.; Hazawa,
M.; Kashiwakura, I. Chem. Lett. 2009, 38, 310–311.
28. Stewart, D.; Imrie, C. T. Polymer 1996, 37, 3419–3425.
29. Imrie, C. T.; Karasz, F. E.; Attard, G. S. Macromolecules 1992, 25, 1278–1283.
30. Glen, W. L.; Myers, G. S.; Grant, G. A. J. Chem. Soc. 1951, 2568–2572.
31. Bessodes, M.; Shamsazar, J.; Antonakis, K. Synthesis 1988, 7, 560–562.
32. Date, R. W.; Imrie, C. T.; Luckhurst, G. R.; Seddon, J. M. Liq. Cryst. 1992, 12, 203–
238.
33. Attard, G. S.; Garnet, S.; Hickman, C. G.; Imrie, C. T.; Taylor, L. Liq. Cryst. 1990, 7,
495–508.
34. Chambert, S.; Doutheau, A.; Queneau, Y.; Cowling, S. J.; Goodby, J. W.;
Mackenzie, G. J. Carbohydr. Chem. 2007, 26, 27–39.
35. Goodby, J. W.; Watson, M. J.; Mackenzie, G.; Kelly, S. M.; Bachir, S.; Bault, P.;
Gode, P.; Goethals, G.; Martin, P.; Ronco, G.; Villa, P. Liq. Cryst. 1998, 25, 139–
147.
36. Wolkers, W. F.; Oldenhof, H.; Alberda, M.; Hoekstra, F. A. Biochim. Biophys. Acta
1998, 1379, 83–96.
37. Wolkers, W. F.; Oliver, A. E.; Tablin, F.; Crowe, J. H. Carbohydr. Res. 2004, 339,
1077–1085.
38. Angell, C. A.; Imrie, C. T.; Ingram, M. D. Polym. Int. 1998, 47, 9–15.
39. Ottenhof, M. A.; MacNaughtan, W.; Farhat, I. A. Carbohydr. Res. 2003, 338,
2195–2202.
40. Cook, A. G.; Wardell, J. L.; Imrie, C. T. Chem. Phys. Lipids 2011, 164, 118–124.
41. Coats, A. M.; Hukins, D. W. L.; Imrie, C. T.; Aspden, R. M. J. Microsc. 2003, 211,
63–66.
42. Henderson, P. A.; Cook, A. G.; Imrie, C. T. Liq. Cryst. 2004, 31, 1427–1434.
43. Gouéth, P.; Ramiz, A.; Ronco, G.; Mackenzie, G.; Villa, P. Carbohydr. Res. 1995,
266, 171–189.
The liquid crystalline behaviour of the non-symmetric dimer, 1-
[3-O-(D
-glucopyranos-3-yl)]-8-[(4-methoxyazobenzene-40-oxy)]-
octane, in which a conventional rod-like azobenzene-based meso-
genic unit is attached via a flexible alkyl spacer to a cyclic
monosaccharide has been reported. The dimer exhibits a highly
interdigitated smectic A phase in which the aromatic and alkyl
units overlap. There is no step change in the strength and extent
of hydrogen bonding at the smectic A-isotropic transition implying
that hydrogen bonding, although important in stabilising the layer
arrangement, does not in fact drive the formation of the phase. In-
stead it is presumably the change in the van der Waals interactions
between the molecules at the clearing temperature which destroys
the smectic arrangement while hydrogen bonded aggregates re-
main intact. It is surprising, however, that the entropy change asso-
ciated with the smectic A-isotropic transition is comparable to that
observed for conventional liquid crystal dimers. By comparison, for
other carbohydrate-based liquid crystals40 and ionic liquid crys-
tals44 for which aggregates are thought to persist into the isotropic
phase, the entropy change at the clearing point is very small. The
physical significance of this observation is not clear. The molecular
arrangement within the smectic A layers shown by 1 is stabilised
by the matching of the cross-sectional areas of the sugar region
and the alkyl-aromatic region. If, however, such packing is pre-
vented we anticipate that interfacial curvature will give rise to a
range of novel phase behaviour and this now warrants further
study.
Acknowledgments
J.M.S. is pleased to acknowledge support from the EPSRC Plat-
form Grant EP/G00465X and A.M.F from the Grisolia Program from
Generalitat Valenciana.
44. De Roche, J.; Gordon, C. M.; Imrie, C. T.; Ingram, M. D.; Kennedy, A. R.; Lo Celso,
F.; Triolo, A. Chem. Mater. 2003, 15, 3089–3097.