A new family of bent-core C2-symmetric liquid crystals

Article abstract of DOI:10.1139/V10-056

A series of C₂-symmetric compounds with different core sizes and varying lengths and numbers of alkoxy side chains were prepared, and the factors influencing their liquid crystalline mesophase behaviour were investigated. The compounds studied were based on benzophenone, dibenzylidene-acetone, and 1,9-diphenyl-nona-1,3,6,8-tetraen-5-one cores with either 1 or 2 linear alkoxy side chains. The side chains were varied in length from C6H13 to C12H25. The liquid crystalline mesophase behaviour of the compounds was investigated using differential scanning calorimetry, polarizing optical microscopy, and small-angle X-ray scattering (SAXS). It was found that a number of the molecules were able to self-assemble into smectic and nematic liquid crystalline phases.

Full text of DOI:10.1139/V10-056

639
A new family of bent-core C2-symmetric liquid
crystals
Kyle A. Hope-Ross, Paul A. Heiney, and John F. Kadla
Abstract: A series of C2-symmetric compounds with different core sizes and varying lengths and numbers of alkoxy side
chains were prepared, and the factors influencing their liquid crystalline mesophase behaviour were investigated. The com-
pounds studied were based on benzophenone, dibenzylidene-acetone, and 1,9-diphenyl-nona-1,3,6,8-tetraen-5-one cores
with either 1 or 2 linear alkoxy side chains. The side chains were varied in length from C6H13 to C12H25. The liquid crys-
talline mesophase behaviour of the compounds was investigated using differential scanning calorimetry, polarizing optical
microscopy, and small-angle X-ray scattering (SAXS). It was found that a number of the molecules were able to self-as-
semble into smectic and nematic liquid crystalline phases.
Key words: mesophase, C2 symmetric, SAXS, benzophenone, dibenzylidene-acetone and 1,9-diphenyl-nona-1,3,6,8-tetraen-
5-one.
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Resume : On a realise la synthese d’une serie de composes de symetrie C2 comportant des coeurs de tailles differentes et
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des quantites diverses de chaınes laterales alcoxyles de longueurs variables et on a etudie les facteurs qui influencent leur
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comportement comme mesophase de cristal liquide. Les composes etudies ont des coeurs a base de benzophenone, de di-
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benzylideneacetone et de 1,9-diphenyl-1,3,6,8-tetraen-5-one et des chaınes laterales alcoxyles lineaires en positions 1 ou 2.
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Les longueurs de chaınes laterales varient de C6H13 a C12H25. On a etudie leur comportement comme mesophase de cristal
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liquide en faisant appel a la calorimetrie a balayage differentiel, a la microscopie optique polarisante et par la diffusion
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des rayons-X a angle faible (DXAF). On a trouve qu’un certain nombre de molecules peuvent s’autoassembler en phases
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de cristal liquide smectique et nematique.
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Mots-cles : mesophase, symetrie C2, diffusion des rayons X a angle faible (DXAF), benzophenone, dibenzylideneacetone,
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1,9-diphenyl-1,3,6,8-tetraen-5-one.
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[Traduit par la Redaction]
new family of bent-core C2-symmetric molecules, and discuss
various factors that affect their ability to self-assemble into
liquid crystalline mesophases. The compounds prepared were
based on a benzophenone (1), dibenzylidene acetone (2), and
1,9-diphenyl-nona-1,3,6,8-tetraen-5-one (3) core (Fig. 1) with
either one or two linear alkoxy side chains varying in length
from C6H13 to C12H25.
Introduction
Liquid crystals are a growing field of research with appli-
cations in a wide variety of devices, including photovoltaic
solar cells,1 light-emitting diodes,2 and displays.3
Traditionally, molecules displaying liquid crystalline mes-
ophases display a structure that consists of a flat, rigid (usu-
ally aromatic) core with multiple, usually aliphatic, flexible
side chains.4 Liquid crystalline molecules can consist of
disc-like,5 linear6 or bent-shaped7 core structures. In addi-
tion, owing to their inherent ability to self-assemble, based
largely on p-stacking interactions, any factor that influences
the electronic structure of the core will affect the ability of
the molecules to form liquid crystalline mesophases.8 It has
been shown that alkyl side-chain length,9,10 electronics,11
and core size12 all have an impact on molecular self-assem-
bly. To fully exploit the potential applications of liquid crys-
talline materials, we must fully understand the variables that
have an effect on mesophase formation.
Experimental section
All chemicals were purchased from Sigma-Aldrich (Oak-
ville, ON) and used without further purification unless other-
wise noted.
General procedure for the synthesis of 4,4’-
bis(alkyloxy)benzophenones (1a–1d)
4,4’-Bis(hexyloxy)benzophenone (1a)
To a solution of 4,4’-dihydroxybenzophenone (0.50 g,
2.33 mmol) and potassium carbonate (1.29 g, 9.34 mmol) in ace-
Herein, we report the synthesis and characterization of a
Received 1 October 2009. Accepted 30 March 2010. Published on the NRC Research Press Web site at canjchem.nrc.ca on 15 June
2010.
K.A. Hope-Ross and J.F. Kadla.1 Advanced Biomaterials Chemistry Laboratory, Department of Wood Science, The University of
British Columbia, Vancouver, BC V6T 1Z4, Canada.
P.A. Heiney. Department of Physics and Astronomy and Laboratory for Research on the Structure of Matter, University of Pennsylvania,
Philadelphia, PA 19104, USA.
1Corresponding author (e-mail: john.kadla@ubc.ca).
Can. J. Chem. 88: 639–645 (2010)
doi:10.1139/V10-056
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Can. J. Chem. Vol. 88, 2010
Fig. 1. Core structures studied: 1, 2, and 3.
31.58, 31.56, 29.2, 29.1, 25.69, 25.66, 22.6 (4C), 14.0 (4C).
Anal. calcd. for C37H58O5: C, 76.25; H, 10.03. Found: C,
76.06; H, 10.09.
General procedure for the synthesis of 1,5-bis(4-alkoxy-
phenyl)-penta-1,4-dien-3-ones (2a–2d)
1,5-Bis(4-hexyloxy-phenyl)-penta-1,4-dien-3-one (2a)
A solution of sodium hydroxide (0.39 g, 9.75 mmol) in
water (5 mL) and ethanol (5 mL) was cooled to 0 8C for
30 min. To this solution was added acetone (0.11g,
1.95 mmol) and 4-hexyloxy-benzaldehyde (11a, 0.80 g,
3.90 mmol). The resulting solution was allowed to stir at
room temperature. After 3 days, the reaction mixture was
poured into 2.0 mol/L HCl (200 mL), and the organic phase
was separated. The aqueous phase was extracted with di-
chloromethane (2 ꢀ 150 mL) and washed with water
(250 mL). The combined organic phases were dried over
MgSO4, filtered, and the solvent was removed in vacuo. Re-
crystallization from EtOH afforded 2a as yellow crystals
(0.49 g, 58%), mp 97–100 8C. IR (thin film, cm–1): 2934,
tone (25 mL) was added 1-bromohexane (1.54 g, 9.34 mmol)
dropwise. The resulting mixture was heated and allowed to
reflux. After 48 h, the reaction mixture was poured into
water (200 mL) and extracted with CH2Cl2 (3 ꢀ 75 mL).
The combined organic layers were washed with water
(300 mL), dried over MgSO4, filtered, and the solvent was
removed in vacuo. Recrystallization from acetone afforded
1a (0.86 g, 97%) as white crystals, mp 102–105 8C. IR
(thin film, cm–1): 2955, 2938, 2863, 1636, 1604, 1256,
853, 764. 1H NMR (300 MHz, CDCl3) d: 7.79 (d, J =
8.66 Hz, 4H), 6.96 (d, J = 8.66 Hz, 4H), 4.05 (t, J =
6.58 Hz, 4H), 1.84 (quin., J = 6.58 Hz, 4H), 1.56–1.31
(m, 12H), 0.94 (t, J = 6.58 Hz, 6H). 13C NMR (300 MHz,
CDCl3) d: 194.5, 162.4, 132.2, 130.6, 113.9, 68.2, 31.6,
29.1, 25.7, 22.6, 14.0. Anal. calcd. for C25H34O3: C,
78.49; H, 8.96. Found: C, 78.58; H, 8.73.
1
2869, 1651, 1599, 1574, 1512, 1177, 1030, 983. H NMR
(300 MHz, CDCl3) d: 7.72 (d, J = 15.78 Hz, 2H), 7.58 (d, J =
8.66 Hz, 4H), 6.97 (d, J = 15.78 Hz, 2H), 6.94 (d, J = 8.66 Hz,
4H), 4.02 (t, J = 6.58 Hz, 4H), 1.82 (quin., J = 6.58 Hz, 4H),
1.54–1.29 (m, 12H), 0.93 (t, J = 6.58 Hz, 6H). 13C NMR
(300 MHz, CDCl3) d: 188.9, 161.2, 142.7, 130.1, 127.4,
123.4, 114.9; 68.2, 31.6, 29.1, 25.7, 22.6, 14.0. Anal. calcd.
for C29H38O3: C, 80.14; H, 8.81. Found: C, 80.03; H, 8.64.
General procedure for the synthesis of 1,5-bis(3,4-
bis(alkoxy-phenyl))-penta-1,4-dien-3-ones (2e–2h)
General procedure for the synthesis of 3,3’,4,4’-
tetrakis(alkoxy)benzophenones (1e–1h)
1,5-Bis(3,4-bis(hexyloxy-phenyl))-penta-1,4-dien-3-one (2e)
To a solution of 4-(3,4-bis(hexyloxy-phenyl))-but-3-en-2-
one (12e, 0.50 g, 1.44 mmol) and 3,4-bis(hexyloxy)benzal-
dehyde (11e, 0.44 g, 1.44 mmol) in methanol (20 mL) was
added sodium methoxide (25 wt% solution in MeOH,
0.94 mL, 4.33 mmol) dropwise. The resulting solution was
heated to reflux. After 48 h, the reaction mixture was poured
into 2.0 mol/L HCl (200 mL), and the organic phase was
separated. The aqueous phase was extracted with CH2Cl2
(3 ꢀ 75 mL). The combined organics were washed with
H2O (2 ꢀ 200 mL), dried over MgSO4, filtered, and the sol-
vent was removed in vacuo. Recrystallization from acetone
afforded 2e (0.52 g, 57%) as a yellow powder, mp 62–
65 8C. IR (thin film, cm–1): 2955, 2931, 2860, 1648, 1618,
1595, 1511, 1468, 1432, 1258, 1234, 1172, 1137, 1095,
1017. 1H NMR (300 MHz, CDCl3) d: 7.69 (d, J =
15.78 Hz, 2H), 7.21–7.15 (m, 4H), 6.95 (d, J = 15.78 Hz,
2H), 6.90 (d, J = 8.33 Hz, 2H), 4.07 (t, J = 6.58 Hz, 4H),
4.06 (t, J = 6.58 Hz, 4H), 1.87 (quin., J = 6.58 Hz, 4H),
1.86 (quin., J = 6.58 Hz, 4H), 1.56–1.26 (m, 24H), 0.94 (t,
J = 6.58 Hz, 6H), 0.93 (t, J = 6.58 Hz, 6H). 13C NMR
(300 MHz, CDCl3) d: 188.8, 151.6, 149.2, 143.1, 127.8,
123.5, 123.1, 113.0, 112.6, 69.4, 69.1, 31.59, 31.56, 29.2,
29.1, 25.71, 25.67, 22.62, 22.59, 14.03, 14.01. Anal. calcd.
for C41H62O5: C, 77.56; H, 9.84. Found: C, 77.57; H, 9.75.
3,3’,4,4’-Tetrakis(hexyloxy)benzophenone (1e)
To a solution of 3,4-bis(hexyloxy)benzoic acid (9e, 0.34
g, 1.06 mmol) and diethylamine (0.50 mL) in CH2Cl2 was
added SOCl2 (5 mL) dropwise. The resulting solution was
heated to reflux for 1.5 h. Excess SOCl2, diethylamine, and
CH2Cl2 were removed in vacuo, and the resultant acid chlor-
ide was added as a solution in CH2Cl2 (15 mL) to a mixture
of AlCl3 (0.14 g, 1.06 mmol) and 1,2-bis(hexyloxy)benzene
(5e, 0.29 g, 1.06 mmol) in CH2Cl2 (15 mL) at 0 8C under N2
atmosphere. The reaction mixture was stirred for 1 h,
warmed to RT, and stirred overnight. The green solution
was quenched with H2O (10 mL), poured into 2.0 mol/L
HCl (200 mL), and the organic phase was separated. The
aqueous layer was extracted with CH2Cl2 (3 ꢀ 75 mL), and
the combined organic phases were washed with H2O
(200 mL) and brine (200 mL), dried over MgSO4, filtered,
and the solvent was removed in vacuo. Recrystallization
from acetone afforded 1e (0.37 g, 60%) as a white powder,
mp 44–48 8C. IR (thin film, cm–1): 2931, 2860, 1649, 1595,
1
1513, 1428, 1266, 1135, 1017, 760. H NMR (300 MHz,
CDCl3) d: 7.42 (d, J = 1.86 Hz, 2H), 7.37 (dd, J1
=
8.33 Hz, J2 = 1.86 Hz, 2H), 6.90 (d, J = 8.33 Hz, 2H), 4.09
(t, J = 6.58 Hz, 4H), 4.06 (t, J = 6.58 Hz, 4H), 1.93–1.79
(m, 8H), 1.58–1.30 (m, 24H), 0.93 (t, J = 6.58 Hz, 6H),
0.92 (t, J = 6.58 Hz, 6H). 13C NMR (300 MHz, CDCl3) d:
194.6, 152.8, 148.7, 130.7, 124.7, 114.7, 111.5, 69.3, 69.1,
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Hope-Ross et al.
641
General procedure for the synthesis of 1,9-bis(4-alkoxy-
phenyl)-nona-1,3,6,8-tetraen-5-ones (3a–3d)
HCS402 Hot Stage and STC200 Temperature Controller.
All samples that exhibited multiple endothermic transitions
on heating or multiple exothermic transitions on cooling by
DSC analysis were characterized by POM. In a typical ex-
periment, 5–10 mg of sample was heated to the clearing
point, which was estimated by DSC, and cooled slowly to
observe the liquid crystalline textures. POM images were
captured with a Lumenera Infinity1 Digital Camera and
were recorded and analyzed using InfinityCapture software.
1,9-Bis(4-hexyloxy-phenyl)-nona-1,3,6,8-tetraen-5-one (3a)
To a solution of 6-(4-hexyloxy-phenyl)-hexa-3,5-dien-2-
one (18a, 0.20 g, 0.73 mmol) and 4-hexyloxy-cinnam-
aldehyde (17a, 0.17 g, 0.73 mmol) in THF (15 mL) was
added NaOMe (25 wt% in MeOH, 0.48 mL, 2.20 mmol)
dropwise. The resulting dark orange solution was allowed to
stir at RT. After 30 min, the reaction mixture was poured
into 2.0 mol/L HCl (100 mL), and the organic phase was
separated. The aqueous phase was extracted with CH2Cl2
(3 ꢀ 75 mL), and the combined organics were washed with
H2O (2 ꢀ 200 mL), dried over MgSO4, filtered, and the sol-
vent was removed in vacuo. Recrystallization from acetone
afforded 3a as a green/yellow solid (0.22 g, 62%), mp 147–
151 8C. IR (thin film, cm–1): 2926, 2851, 1655, 1592, 1509,
Results and discussion
Synthesis
The synthesis of the mono-alkoxy-substituted benzophe-
nones 1a–1d simply involved appending the alkoxy chains
onto commercially available 4,4’-dihydroxy-benzophenone
using the Williamson ether synthesis15 (eq. [1]).
1
1464, 1359, 1257, 1174, 1071, 1005, 854, 821. H NMR
(300 MHz, CDCl3) d: 7.48 (dd, J1 = 15.13 Hz, J2
=
½1ꢁ
10.41 Hz, 2H), 7.44 (d, J = 8.66 Hz, 4H), 6.95 (d, J =
15.46 Hz, 2H), 6.90 (d, J = 8.66 Hz, 4H), 6.84 (dd, J1 =
15.46 Hz, J2 = 10.41 Hz, 2H), 6.53 (d, J = 15.13 Hz, 2H),
4.0 (t, J = 6.58 Hz, 4H), 1.81 (quin., J = 6.58 Hz, 4H),
1.55–1.30 (m, 12H), 0.91 (t, J = 6.58 Hz, 6H). 13C NMR
(300 MHz, CDCl3) d: 189.0, 160.2, 143.3, 141.2, 128.8,
128.7, 128.1, 124.8, 114.9, 68.2, 31.6, 29.2, 25.7, 22.6,
14.0. Anal. calcd. for C33H42O3: C, 81.44; H, 8.70. Found:
C, 80.56; H, 8.68.
The synthesis of the bis(alkoxy)benzophenones (1e–1h) in-
volved a Friedel–Crafts acylation16 between 3,4-bis(alkoxy)-
benzoic acids (9e–9h) and 3,4-bis(alkoxy)benzenes (5e–5h)
(Scheme 1). The 3,4-bis(alkoxy)benzenes (5e–5h) were
achieved via a Williamson ether synthesis between catechol
(5) and the appropriate n-alkyl bromides (94%–100%). The
substituted benzoic acids were achieved in three steps from
3,4-dihydroxybenzoic acid (7). First, 6 was protected as its
methyl ester 7 by Fischer esterification,17 then Williamson
conditions were used to append the alkoxy chains to achieve
esters 8e–8h18 in yields ranging from 96% (C6) to 100% (C8).
Finally, saponification of 8e–8h19 afforded the benzoic acid
coupling precursors 9e–9h in yields from 88% (C10) to 99%
(C8). Benzoic acids 9e–9h were first converted to their respec-
tive acid chlorides using thionyl chloride and diethylamine.
Characterization
Small-angle X-ray scattering (SAXS) measurements em-
ployed a Bruker-Nonius FR591 rotating-anode generator
with a copper anode operated at 3.4 kW. The beam was col-
limated and focused with Osmic confocal optics and pin-
holes, and the scattered radiation was detected using a
Bruker Hi-Star wire (area) detector.13 Samples were sealed
in 1 mm diameter glass capillaries. Measurements were
made at fixed sample–detector distances of 54 and 11 cm;
the presence or absence of crystalline (three-dimensional or-
der) was established from the 11 cm data sets, while the fi-
nal refinement of the liquid crystal unit cell parameters was
made using the data from the 54 cm configuration. In situ
temperature-dependent measurements employed a Linkam
heating cell. Primary data analysis was performed using Da-
tasqueeze.14
Scheme 1. Synthesis of 3,4-bis(alkoxy)benzophenones (1e–1h).
Differential scanning calorimetry (DSC) measurements
were performed on a TA Instruments Q1000 DSC. All ex-
periments were run with 1–3 mg of sample in aluminum
hermetic pans at heating rates of 10 8C/min and cooling
rates of 5 8C/min unless otherwise noted. The samples were
initially analyzed at temperatures between –90 8C and
250 8C with subsequent runs performed only in the temper-
ature range displaying phase transitions.
1H and 13C NMR spectra were recorded using a 300 MHz
Bruker Avance Ultrashield NMR Spectrometer (300.13 and
75.03 MHz, respectively) at concentrations of approximately
10 mg/mL and referenced to CDCl3 (7.28 ppm) or acetone-d6
1
(2.05 ppm). The number of scans used was 16 for H NMR
and 3072 for 13C NMR.
Polarizing optical microscopy (POM) was performed on
an Olympus BX41 Microscope equipped with an Instec
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Can. J. Chem. Vol. 88, 2010
Table 1. Phase behaviour of 1a–1h.
Scheme 2. Synthesis of mono-alkoxy dibenzylidene-acetones 2a–2d.
Scheme 3. Synthesis of bis(alkoxy)dibenzylidene-acetones (2e–2h).
The acid chlorides were then added to a solution containing
5e–5h and AlCl3. The benzophenones 1e–1h were achieved
in five steps with overall yields from 40% (C12) to 52% (C8).
The synthesis of the mono-alkoxy-substituted dibenzyl-
idene acetones 2a–2d involved a bidirectional aldol condensa-
tion between 1 equiv. of acetone and 2 equiv. of 4-alkoxy-
benzaldehydes (11a–11d), which were achieved again using
a Williamson ether synthesis between 4-hydroxybenzaldehyde
(10) and the appropriate n-alkyl bromides20 (Scheme 2).
The attempted procedure of a bidirectional aldol conden-
sation to achieve the di-alkoxy-substituted dibenzylidene
acetones 2e–2h in a method analogous to that of 2a–2d
proved difficult, with the reaction yielding an inseparable
mixture of the mono- and bis-aldol condensation products.
Instead, two stepwise aldol condensations were employed,
the first reaction between 1 equiv. of acetone and 1 equiv.
of 3,4-alkoxybenzaldehydes (11e–11h), and the second reac-
tion between the resulting 4-(4-alkoxy-phenyl)but-3-en-2-
ones (12e–12h) and a second equiv. of benzaldehydes 11e–
11h (Scheme 3).
chains were appended by the Williamson ether synthesis to
afford 15a–15d in yields from 90% to 98%. Attempted
DIBAL reduction to the aldehydes 17a–17d21 led to a 1:1
mixture of completely reduced alcohol 16a–16d and un-
reacted ester 15a–15d. Instead, a strategy of complete reduc-
tion to the alcohol and subsequent reoxidation to the
aldehyde was employed. The attempted reduction using
LAH22 resulted in reduction of esters 15a–15d as well as
hydrogenation of the olefin; a known result that seems to be
limited to cinnamic acid derivatives.23 A reduction using an
excess of DIBAL afforded the cinnamyl alcohols 16a–16d
in yields ranging from 93% to 96%. Oxidation using the
Corey–Suggs reagent PCC24 led to both the desired a,b-
unsaturated aldehydes 17a–17d (minor) as well as the oxida-
tive olefin cleavage byproduct23 benzaldehyde (major). In-
stead, an oxidation using DDQ in dioxane25 gave 17a–17d
in excellent yields (97% to 100%). Stepwise aldol condensa-
tions; the first between 1 equiv. of aldehydes 17a–17d and
acetone, and the second between the resulting 6-(4-alkoxy-
phenyl)-hexa-3,5-dien-2-ones (18a–18d) and a second equiv.
of 17a–17d, gave the desired 1,9-diphenyl-nona-1,3,6,8-
tetraen-5-ones (3a–3d) in yields of 49% to 67% over two
steps.
The synthesis of mono-alkoxy 1,9-diphenyl-nona-1,3,6,8-
tetraen-5-ones (3a–3d) was performed in a method analogous
to that of 2e–2h, employing stepwise aldol condensations
between acetone and 4-alkoxy cinnamaldehydes. The latter
were obtained, after various functional group interconver-
sions, from commercially available p-coumaric acid
(Scheme 4). The synthesis proceeded in six linear steps
with overall yields of 42% (C10) to 56% (C12).
Characterization
It was found that neither the mono-alkoxybenzophenone
derivatives 1a–1d nor the bis(alkoxy)benzophenones (1e–
1h) were mesogenic. Of the bis(alkoxy)benzophenones, 1e
was seen in SAXS measurements to undergo a crystal-to-
First, p-coumaric acid (13) was converted to its methyl
ester 14 by Fischer esterification in 97% yield. The alkoxy
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Hope-Ross et al.
643
Scheme 4. Synthesis of mono-alkoxy 1,9-diphenyl-1,3,6,8-tetra-en-5-ones (3a–3d).
Table 2. Phase behaviour of 2a–2h.
Table 3. Phase behaviour of 3a–3d.
with a nematic phase with a typical dimension of the cybo-
tatic group of 2.1 nm and a correlation that increases upon
cooling from 1.2 nm near the clearing point to 3.0 nm at
room temperature. Compound 2f shows similar behaviour,
with a cybotatic dimension of 2.4 nm and a correlation
length of 2.0 nm, and similarly 2g has a nematic cybotatic
dimension of 2.6 nm and a correlation length of ~2 nm.
It was found that all four 1,9-diphenyl-nona-1,3,6,8-tetra-
en-5-one derivatives self-assembled into nematic liquid crys-
talline phases. Figure 3 displays POM images of 3b and 3d
in the nematic phase taken at a magnification of 10ꢀ, and
the phase behaviour of 3a–3d is outlined in Table 3.
SAXS on 3a and 3b were consistent with nematic phases
at high temperature, but low signal levels precluded accurate
measurement of cybotatic dimensions or correlation length.
However, SAXS measurements on 3c and 3d showed sharp
diffraction peaks with lamellar d spacings of 3.3 nm (3c)
and 3.5 nm (3d), clearly indicating a smectic phase and in-
consistent with the nematic texture observed in POM
(Fig. 3). The reasons for this discrepancy are unclear, but
are likely related to differences either in thermal history or
anchoring effects by the glass slides and glass capillaries
used in the two measurements.
crystal transition at ~50 8C and to melt at ~100 8C. The
phase behaviour of 1a–1h is outlined in Table 1.
It was found the mono-alkoxy dibenzylidene acetone de-
rivatives 2a–2d were non-mesogenic. By contrast, the C6,
C8, and C10 bis(alkoxy)dibenzylidene acetones 2e, 2f, and
2g were found to self-assemble into nematic mesophases.
Figure 2 displays POM images of 2e and 2f taken at a mag-
nification of 10ꢀ, and the phase behaviour of 2a–2h is out-
lined in Table 2.
SAXS measurements confirm the assignments of 2e, 2f,
and 2g to nematic mesophases above room temperature. A
diffuse maximum in the scattering from 2e is consistent
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Can. J. Chem. Vol. 88, 2010
Fig. 2. Polarized optical micrographs of (a) 2e at 55 8C and (b) 2f at 62 8C (10ꢀ magnification).
Fig. 3. Polarized optical micrographs of (a) 3b at 136 8C and (b) 3d at 122 8C (10ꢀ magnification).
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Conclusions
In summary, we have synthesized a new series of C2-
symmetric compounds, which display liquid crystalline mes-
ophase behaviour. It was determined that the size of the
rigid core, the length of the alkoxy side chain, and the num-
ber of alkoxy side chains have an impact on the ability of
the molecules to self-assemble into liquid crystalline meso-
phases. Increasing the core size as well as increasing the
number of side chains helped induce mesophase formation.
In addition, increasing the length of the alkoxy side chain
expanded the temperature range of the mesophase for the
1,9-diphenyl-nona-1,3,6,8-tetraen-5-ones.
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Supplementary data
Supplementary data for this article (detailed experimental
procedures as well as spectral and analytical data, including
1H and 13C NMR spectra, DSC thermograms, and POM mi-
crographs) are available on the journal Web site (canjchem.
nrc.ca).
Acknowledgement
(11) Wang, C.-S.; Wang, I.-W.; Cheng, K.-L.; Lai, C. K. Tetrahe-
dron 2006, 62 (40), 9383. doi:10.1016/j.tet.2006.07.058.
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(2), 130. doi:10.1002/1521-4095(200101)13:2<130::AID-
ADMA130>3.0.CO;2-L.
The authors thank the Natural Science and Engineering
Research Council of Canada (NSERC) for financial support
(RGPAS 364426). We thank Dr. Mark MacLachlan for help-
ful discussions. We also thank Emilie Voisin and Dr. Vance
Williams for assistance with mesophase characterization.
Structural work at the University of Pennsylvania was sup-
ported by the MRSEC program of the National Science
Foundation (Grant No. DMR05–20020)
(13) See www.lrsm.upenn.edu/lrsm/facMAXS.html for additional
details.
(14) See www.datasqueezesoftware.com for more details.
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