Chirality-induced liquid crystalline properties of seven-ring trimeric mesogens incorporating dual chiral centers

Article abstract of DOI:10.1080/15421400902841353

Two series of novel trimers with benzylidene-1,4-phenylenediamine core units attached by two (S)-2-methylbutyl 4-(4′-phenyl)benzoate moieties via methylene groups at terminal ends have been synthesized and characterized. In each series, the title compounds differ from each other in term of spacers ?OC_nH₂nO- wherein n ranges from 5 to 12. The difference of the second series from their analogues in the first series is due to the presence of two OCH₃ groups residing at the meta position in the benzylidene-1,4-phenylenediamine mesogenic core. The trimers without lateral OCH₃ groups exhibit the SmC* and SmA phases in addition to the N* phase suggesting the possession of high molecular shape anisotropy. The higher-order tilted smectic phases and the blue phase are also observed for the members with odd n numbers in the first series. In the second series, however, the smectogenic characteristics are absent. Whilst the even-parity trimers are nematogenic, the trimers with odd spacers are not mesogenic. The trimers without lateral OCH₃ groups in the first series also exhibit higher mesophase thermal stability in comparison with their analogues in the second series. Taylor & Francis Group, LLC.

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Chirality-Induced Liquid
Crystalline Properties of
Seven-Ring Trimeric Mesogens
Incorporating Dual Chiral
Centers
Guan-Yeow Yeap a , Tiang-Chuan Hng a , Wan Ahmad
Kamil Mahmood a , Ewa Gorecka b , Daisuke Takeuchi
c & Kohtaro Osakada c
a Liquid Crystal Research Laboratory, School of
Chemical Sciences , Universiti Sains Malaysia ,
Penang, Malaysia
b Department of Chemistry , Warsaw University ,
Warsaw, Poland
c Chemical Resources Laboratory , Tokyo Institute of
Technology , Midori-ku, Yokohama, Japan
Published online: 03 Aug 2009.
To cite this article: Guan-Yeow Yeap , Tiang-Chuan Hng , Wan Ahmad Kamil
Mahmood , Ewa Gorecka , Daisuke Takeuchi & Kohtaro Osakada (2009) Chirality-
Induced Liquid Crystalline Properties of Seven-Ring Trimeric Mesogens Incorporating
Dual Chiral Centers, Molecular Crystals and Liquid Crystals, 506:1, 109-133, DOI:
10.1080/15421400902841353
To link to this article: http://dx.doi.org/10.1080/15421400902841353
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Mol. Cryst. Liq. Cryst., Vol. 506, pp. 109–133, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400902841353
Chirality-Induced Liquid Crystalline Properties
of Seven-Ring Trimeric Mesogens Incorporating
Dual Chiral Centers
Guan-Yeow Yeap1, Tiang-Chuan Hng1, Wan Ahmad
Kamil Mahmood1, Ewa Gorecka2,
Daisuke Takeuchi3, and Kohtaro Osakada3
1Liquid Crystal Research Laboratory, School of Chemical Sciences,
Universiti Sains Malaysia, Penang, Malaysia
2Department of Chemistry, Warsaw University, Warsaw, Poland
3Chemical Resources Laboratory, Tokyo Institute of Technology,
Midori-ku, Yokohama, Japan
Two series of novel trimers with benzylidene-1,4-phenylenediamine core units
attachedby two (S)-2-methylbutyl 4-(40-phenyl)benzoatemoieties viamethylene groups
at terminal ends have been synthesized and characterized. In each series, the title
compounds differ from each other in term of spacers -OCnH2nO- wherein n ranges from
5 to 12. The difference of the second series from their analogues in the first series is
due to the presence of two OCH3 groups residing at the meta position in the
benzylidene-1,4-phenylenediamine mesogenic core. The trimers without lateral
OCH3 groupsexhibit the SmCꢀ and SmA phases inadditiontothe Nꢀ phase suggesting
the possession of high molecular shape anisotropy. The higher-order tilted smectic
phases and the blue phase are also observed for the members with odd n numbers in
the first series. In the second series, however, the smectogenic characteristics are
absent. Whilst the even-parity trimers are nematogenic, the trimers with odd spacers
are not mesogenic. The trimers without lateral OCH3 groups in the first series also
exhibit higher mesophase thermal stability in comparison with their analogues in
the second series.
1. INTRODUCTION
In contrast with conventional polymers, semiflexible main chain liquid
crystal polymers are composed of alternating rigid mesogenic fragments
and flexible groups such as the alkyl chains [1]. Liquid crystal dimers
Address correspondence to Guan-Yeow Yeap, Liquid Crystal Research Laboratory,
School of Chemical Sciences, Universiti Sains Malaysia, 11800 Minden, Penang,
Malaysia. E-mail: gyyeap_liqcryst_usm@yahoo.com
109

110
G.-Y. Yeap et al.
are often used as model compounds reflecting these polymers as their
transitional properties in many ways possess similarities to those of
the polymeric system [2]. One of these properties is the significant
odd–even effect exhibited by the clearing temperatures of the dimers.
However, the liquid crystalline behavior of these dimers is different in
comparison with the conventional liquid crystals which contain only
one mesogenic fragment and two flexible terminal groups.
The unique characteristics of liquid crystal dimers have then
prompted many researchers to study the liquid crystal oligomers
[3–5]. One of the liquid crystal oligomers is called trimer which con-
sists of three mesogenic fragments connected by two methylene
spacers [2]. Previous investigations showed that the physical proper-
ties of the trimers were different from those of the dimers and mono-
mers wherein the magnitude of the alternation exhibited by TNI upon
changing the number of carbon atoms in the spacers linking the
mesogenic cores of the 4,40-bis[x-(4-cyanobiphenyl-40-yloxy)alkoxy]
biphenyls was slightly greater than that exhibited by the dimers [6].
As far as liquid crystals are concerned, chirality and chirality-
induced properties are amongst the key features towards the develop-
ment of high-tech materials for display and thermochromic devices,
electro-optics, and many other applications. In addition to the wide
application of chiral liquid crystal materials, researchers are also
interested in chirally induced phenomena as appearance of twist-grain
boundary (TGB) phases, polar smectic phases, and various blue phases
[7–11]. However, until today only a few chiral trimeric liquid crystals
have been reported [12,13].
In this report we present a comprehensive study on two series of novel
symmetric trimers with two chiral centers. The sixteen title compounds
are synthesized in which the benzylidene-1,4-phenylenediamine serves
as the rigid core joining up (S)-2-methylbutyl-4-(40-phenyl)benzoate
moiety via respective methylene group. In our present study, the
spacers with odd and even-parity ranging from C5H10 to C12H24 are
introduced into the trimeric system. Among these trimers, the thermal
stability between the members with and without the two lateral meth-
oxy (OCH3) groups in the central core as well as the influence of these
OCH3 groups on the chiral mesomorphic properties will be documented.
2. EXPERIMENTAL
2.1. Synthesis
The liquid crystal trimers were synthesized according to the synthetic
routes as given in scheme 1. Compound 1 is a product derived from the

Chirality-Induced Liquid Crystalline
111
SCHEME 1 The synthetic routes toward formation of liquid cyrstal trimers
5a–5h and 6a–6h.
Fischer acid-catalyzed esterification in the presence of concentrated
sulphuric acid. Compounds 2a and 2b were synthesized via condensa-
tion reaction from p-phenylenediamine with p-hydroxybenzaldehyde
and vanillin, respectively [14]. In order to obtain compounds 3a–3h
and 4a–4h, the intermediary 2a and 2b were alkylated with a series
of a,x-dibromoalkanes via Williamson synthesis in the presence of
potassium carbonate anhydrous. The title compounds 5a–5h (first
series) and 6a–6h (second series) are the products obtained from the
alkylation between compound 1 and 3a–3h and 4a–4h, respectively,
in which the potassium carbonate anhydrous and potassium iodide
were used as catalysts. These compounds with respective lateral
substituents (H or OCH3) and spacers (C5H10 to C12H24) are tabulated
in Table 1.
2.1.1. Synthesis of Compound 1
4-(4-Hydroxyphenyl)benzoic acid (1.50 g, 7.0 mmole) was added to
25 mL (S)-2-methyl-1-butanol in a round-bottom flask and refluxed
at 90ꢀC for 24 h. A few drops of concentrated H2SO4 were added drop-
wise to the mixture. The resulting solution was left to evaporate off at
room temperature and the crude product was then recrystallized
thrice from hexane and chloroform mixture to yield the white inter-
mediate. Yield 70%. Elemental analysis (%): found, C 76.04, H 7.11;

112
G.-Y. Yeap et al.
TABLE 1 List of Intermediary and Title Compounds
with Respective Lateral Substituents, X and Spacers,
CnH2n in the First and Second Series
Compound
Lateral substituent, X
Spacer (-CnH2n-)
3a
3b
3c
3d
3e
3f
3g
3h
4a
4b
4c
4d
4e
4f
4g
4h
5a
5b
5c
5d
5e
5f
5g
5h
6a
6b
6c
6d
6e
6f
H
H
H
H
H
H
H
H
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
H
H
H
H
H
C5H10
C6H12
C7H14
C8H16
C9H18
C10H20
C11H22
C12H24
C5H10
C6H12
C7H14
C8H16
C9H18
C10H20
C11H22
C12H24
C5H10
C6H12
C7H14
C8H16
C9H18
C10H20
C11H22
C12H24
C5H10
C6H12
C7H14
C8H16
C9H18
C10H20
C11H22
C12H24
H
H
H
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
6g
6h
calculated (C18H20O3), C 76.03, H 7.09. IR (KBr) n=cmꢁ1, 3409 (OH),
2967–2878 (C-H alkyl), 1683 (C¼O ester).1H-NMR (CDCl3) d=ppm,
0.97 (t, 3H, CH3), 1.06 (d, 3H, CH3), 1.34 (m, 1H, CH2), 1.57 (m, 1H,
CH2), 1.91 (m, 1H, CH), 4.16–4.28 (2dd, 2H, OCH2), 6.98 (d, 2H, Ar),
7.54 (d, 2H, Ar), 7.65 (d, 2H, Ar), 8.10 (d, 2H, Ar).
2.1.2. Synthesis of Compound 2a
In a round-bottom flask, 4-hydroxybenzaldehyde (2.55 g, 20.9 mmole)
was dissolved in 70 mL absolute ethanol and heated to 40ꢀC. A hot
ethanolic solution of p-phenylenediamine (1.03 g, 9.5 mmole) was then

Chirality-Induced Liquid Crystalline
113
added dropwise, and the mixture was refluxed at 60ꢁC for 24 h. The
resulting solution was then left to evaporate at room temperature.
The precipitate was finally purified with ethanol twice to give the pure
yellow intermediary compound 2a. Yield 85%. Elemental analysis (%):
found, C 75.96, H 5.11, N 8.86; calculated (C20H16N2O2), C 75.93, H
5.10, N 8.86. IR (KBr) n=cmꢂ1, 3274 (OH), 1618–1590 (C¼N).
2.1.3. Synthesis of Compound 2b
Yield 80%. Elemental analysis (%): found, C 70.22, H 5.38, N 7.45;
calculated (C22H20N2O4), C 70.20, H 5.36, N 7.44. IR (KBr) n=cmꢂ1
3385 (OH), 1621–1599 (C¼N), 1285 (Ar-O-CH3).
,
2.1.4. Synthesis of Compound 3a
In a round-bottom flask, compound 2a (0.32 g, 1.0 mmole) was
dissolved in minimal N,N-dimethylformamide solution prior to the
addition of potassium carbonate anhydrous (0.69 g, 5.0 mmole). A solu-
tion of 1,5-dibromopentane (2.30 g, 10.0 mmole) in 50 mL acetone was
then added dropwise to the mixture and subsequently refluxed for
18 h. The resulting mixture was left to evaporate at room temperature
prior to the addition of water. The precipitate was then filtered off,
dried and recrystallized from hexane and chloroform mixture to yield
the pure yellow powder. Yield 60%. Elemental analysis (%): found, C
58.67, H 5.60, N 4.57; calculated (C30H34Br2N2O2), C 58.65, H 5.58,
N 4.56. IR (KBr) n=cmꢂ1, 2949–2864 (C-H alkyl), 1617–1596 (C¼N),
1247 (O-CH2). 1H-NMR (CDCl3) d=ppm, 1.66–2.02 (m, 12H, CH2),
3.48 (t, 4H, CH2Br), 4.07 (t, 4H, OCH2), 7.01 (d, 4H, Ar), 7.27 (s, 4H,
Ar), 7.86 (d, 4H, Ar), 8.46 (s, 2H, CH¼N).
Compounds 3b–3h and 4a–4h were synthesized via similar method
as described for compound 3a. The analytical data for these com-
pounds are shown in Sections 2.1.5–2.1.19.
2.1.5. Synthesis of Compound 3b
Yield 71%. Elemental analysis (%): found, C 59.84, H 5.99, N 4.35;
calculated (C32H38Br2N2O2), C 59.82, H 5.96, N 4.36. IR (KBr)
1
n=cmꢂ1, 2936–2857 (C-H alkyl), 1606 (C¼N), 1249 (O-CH2). H-NMR
(CDCl3) d=ppm, 1.55–1.96 (m, 16H, CH2), 3.45 (t, 4H, CH2Br), 4.08
(t, 4H, OCH2), 7.01 (d, 4H, Ar), 7.28 (s, 4H, Ar), 7.88 (d, 4H, Ar),
8.46 (s, 2H, CH¼N).
2.1.6. Synthesis of Compound 3c
Yield 58%. Elemental analysis (%): found, C 60.93, H 6.32, N 4.17;
calculated (C34H42Br2N2O2), C 60.90, H 6.31, N 4.18. IR (KBr) n=cmꢂ1
,

114
G.-Y. Yeap et al.
2938–2852 (C-H alkyl), 1616–1597 (C¼N), 1251 (O-CH2). 1H-NMR
(CDCl3) d=ppm, 1.41–1.94 (m, 20H, CH2), 3.45 (t, 4H, CH2Br), 4.05 (t,
4H, OCH2), 7.01 (d, 4H, Ar), 7.28 (s, 4H, Ar), 7.86 (d, 4H, Ar), 8.46 (s,
2H, CH¼N).
2.1.7. Synthesis of Compound 3d
Yield 75%. Elemental analysis (%): found, C 61.92, H 6.66, N 3.99;
calculated (C36H46Br2N2O2), C 61.90, H 6.64, N 4.01. IR (KBr) n=cmꢂ
1, 2936–2856 (C-H alkyl), 1605 (C¼N), 1250 (O-CH2). 1H-NMR (CDCl3)
d=ppm, 1.39–1.91 (m, 24H, CH2), 3.44 (t, 4H, CH2Br), 4.05 (t, 4H,
OCH2), 7.01 (d, 4H, Ar), 7.28 (s, 4H, Ar), 7.86 (d, 4H, Ar), 8.46 (s, 2H,
CH¼N).
2.1.8. Synthesis of Compound 3e
Yield 57%. Elemental analysis (%): found, C 62.82, H 6.97, N 3.85;
calculated (C38H50Br2N2O2), C 62.81, H 6.94, N 3.86. IR (KBr)
1
n=cmꢂ1, 2918–2850 (C-H alkyl), 1603 (C¼N), 1248 (O-CH2). H-NMR
(CDCl3) d=ppm, 1.37–1.92 (m, 28H, CH2), 3.44 (t, 4H, CH2Br), 4.05
(t, 4H, OCH2), 7.01 (d, 4H, Ar), 7.28 (s, 4H, Ar), 7.85 (d, 4H, Ar),
8.46 (s, 2H, CH¼N).
2.1.9. Synthesis of Compound 3f
Yield 68%. Elemental analysis (%): found, C 63.67, H 7.23, N 3.72;
calculated (C40H54Br2N2O2), C 63.66, H 7.21, N 3.71. IR (KBr)
1
n=cmꢂ1, 2936–2850 (C-H alkyl), 1606 (C¼N), 1248 (O-CH2). H-NMR
(CDCl3) d=ppm, 1.37–1.93 (m, 32H, CH2), 3.42 (t, 4H, CH2Br), 4.07
(t, 4H, OCH2), 7.01 (d, 4H, Ar), 7.28 (s, 4H, Ar), 7.88 (d, 4H, Ar),
8.46 (s, 2H, CH¼N).
2.1.10. Synthesis of Compound 3g
Yield 52%. Elemental analysis (%): found, C 64.47, H 7.49, N 3.60;
calculated (C42H58Br2N2O2), C 64.45, H 7.47, N 3.58. IR (KBr)
1
n=cmꢂ1, 2919–2850 (C-H alkyl), 1602 (C¼N), 1250 (O-CH2). H-NMR
(CDCl3) d=ppm, 1.33–1.91 (m, 36H, CH2), 3.44 (t, 4H, CH2Br), 4.05
(t, 4H, OCH2), 7.01 (d, 4H, Ar), 7.28 (s, 4H, Ar), 7.86 (d, 4H, Ar),
8.46 (s, 2H, CH¼N).
2.1.11. Synthesis of Compound 3h
The synthetic route is similar to that described for 3a. But, upon
completion of reflux, the excess 1,12-dibromododecane was first
removed with acetone and the desired precipitate was subsequently
recrystallized from hexane and chloroform mixture. Yield 60%.

Chirality-Induced Liquid Crystalline
115
Elemental analysis (%): found, C 65.21, H 7.72, N 3.46; calculated
(C44H62Br2N2O2), C 65.18, H 7.71, N 3.46. IR (KBr) n=cmꢂ1
,
1
2935–2849 (C-H alkyl), 1606 (C¼N), 1252 (O-CH2). H-NMR (CDCl3)
d=ppm, 1.31–1.92 (m, 40H, CH2), 3.43 (t, 4H, CH2Br), 4.06 (t, 4H,
OCH2), 7.01 (d, 4H, Ar), 7.28 (s, 4H, Ar), 7.87 (d, 4H, Ar), 8.45 (s,
2H, CH¼N).
2.1.12. Synthesis of Compound 4a
Yield 44%. Elemental analysis (%): found, C 57.00, H 5.69, N 4.17;
calculated (C32H38Br2N2O4), C 56.99, H 5.68, N 4.15. IR (KBr)
n=cmꢂ1, 2938–2866 (C-H alkyl), 1618–1595 (C¼N), 1268 (O-CH2).
1H-NMR (CDCl3) d=ppm, 1.64–1.99 (m, 12H, CH2), 3.48 (t, 4H,
CH2Br), 4.00 (s, 6H, OCH3), 4.12 (t, 4H, OCH2), 6.96 (d, 2H, Ar),
7.28 (s, 4H, Ar), 7.31 (dd, 2H, Ar), 7.64 (s, 2H, Ar), 8.44 (s, 2H, CH¼N).
2.1.13. Synthesis of Compound 4b
Yield 65%. Elemental analysis (%): found, C 58.15, H 6.05, N 4.00;
calculated (C34H42Br2N2O4), C 58.13, H 6.03, N 3.99. IR (KBr)
n=cmꢂ1, 2935–2860 (C-H alkyl), 1619–1595 (C¼N), 1270 (O-CH2).
1H-NMR (CDCl3) d=ppm, 1.55–1.94 (m, 16H, CH2), 3.44 (t, 4H,
CH2Br), 4.00 (s, 6H, OCH3), 4.12 (t, 4H, OCH2), 6.97 (d, 2H, Ar),
7.28 (s, 4H, Ar), 7.33 (dd, 2H, Ar), 7.65 (s, 2H, Ar), 8.44 (s, 2H, CH¼N).
2.1.14. Synthesis of Compound 4c
Yield 62%. Elemental analysis (%): found, C 59.22, H 6.36, N 3.83;
calculated (C36H46Br2N2O4), C 59.19, H 6.35, N 3.83. IR (KBr)
n=cmꢂ1, 2936–2857 (C-H alkyl), 1618–1595 (C¼N), 1268 (O-CH2).
1H-NMR (CDCl3) d=ppm, 1.41–1.94 (m, 20H, CH2), 3.44 (t, 4H,
CH2Br), 4.00 (s, 6H, OCH3), 4.11 (t, 4H, OCH2), 6.96 (d, 2H, Ar),
7.28 (s, 4H, Ar), 7.33 (dd, 2H, Ar), 7.65 (s, 2H, Ar), 8.44 (s, 2H, CH¼N).
2.1.15. Synthesis of Compound 4d
Yield 70%. Elemental analysis (%): found, C 60.17, H 6.66, N 3.71;
calculated (C38H50Br2N2O4), C 60.16, H 6.64, N 3.69. IR (KBr)
n=cmꢂ1, 2937–2856 (C-H alkyl), 1617–1595 (C¼N), 1269 (O-CH2).
1H-NMR (CDCl3) d=ppm, 1.38–1.93 (m, 24H, CH2), 3.44 (t, 4H,
CH2Br), 4.00 (s, 6H, OCH3), 4.11 (t, 4H, OCH2), 6.96 (d, 2H, Ar),
7.28 (s, 4H, Ar), 7.33 (dd, 2H, Ar), 7.64 (s, 2H, Ar), 8.44 (s, 2H, CH¼N).
2.1.16. Synthesis of Compound 4e
Yield 70%. Elemental analysis (%): found, C 61.08, H 6.94, N 3.55;
calculated (C40H54Br2N2O4), C 61.07, H 6.92, N 3.56. IR (KBr)
n=cmꢂ1, 2936–2854 (C-H alkyl), 1618–1596 (C¼N), 1268 (O-CH2).

116
G.-Y. Yeap et al.
1H-NMR (CDCl3) d=ppm, 1.36–1.92 (m, 28H, CH2), 3.43 (t, 4H,
CH2Br), 4.00 (s, 6H, OCH3), 4.10 (t, 4H, OCH2), 6.96 (d, 2H, Ar),
7.28 (s, 4H, Ar), 7.31 (dd, 2H, Ar), 7.64 (s, 2H, Ar), 8.44 (s, 2H, CH¼N).
2.1.17. Synthesis of Compound 4f
Yield 71%. Elemental analysis (%): found, C 61.94, H 7.19, N 3.43;
calculated (C42H58Br2N2O4), C 61.92, H 7.18, N 3.44. IR (KBr)
n=cmꢂ1, 2922–2854 (C-H alkyl), 1624–1597 (C¼N), 1266 (O-CH2).
1H-NMR (CDCl3) d=ppm, 1.34–1.93 (m, 32H, CH2), 3.43 (t, 4H,
CH2Br), 4.00 (s, 6H, OCH3), 4.11 (t, 4H, OCH2), 6.97 (d, 2H, Ar),
7.28 (s, 4H, Ar), 7.34 (dd, 2H, Ar), 7.64 (s, 2H, Ar), 8.44 (s, 2H, CH¼N).
2.1.18. Synthesis of Compound 4g
Yield 73%. Elemental analysis (%): found, C 62.72, H 7.45, N 3.33;
calculated (C44H62Br2N2O4), C 62.71, H 7.42, N 3.32. IR (KBr)
n=cmꢂ1, 2925–2853 (C-H alkyl), 1619–1596 (C¼N), 1269 (O-CH2).
1H-NMR (CDCl3) d=ppm, 1.30–1.92 (m, 36H, CH2), 3.41 (t, 4H,
CH2Br), 4.01 (s, 6H, OCH3), 4.11 (t, 4H, OCH2), 6.97 (d, 2H, Ar),
7.28 (s, 4H, Ar), 7.33 (dd, 2H, Ar), 7.63 (s, 2H, Ar), 8.43 (s, 2H, CH¼N).
2.1.19. Synthesis of Compound 4h
Upon completion of reflux, the excess 1,12-dibromododecane was
first removed with acetone and the desired precipitate was sub-
sequently recrystallized from hexane and chloroform mixture. Yield
58%. Elemental analysis (%): found, C 63.45, H 7.67, N 3.23; calculated
(C46H66Br2N2O4), C 63.44, H 7.64, N 3.22. IR (KBr) n=cmꢂ1, 2928–2854
(C-H alkyl), 1623–1597 (C¼N), 1267 (O-CH2). 1H-NMR (CDCl3) d=ppm,
1.31–1.93 (m, 40H, CH2), 3.43 (t, 4H, CH2Br), 4.00 (s, 6H, OCH3),
4.11 (t, 4H, OCH2), 6.96 (d, 2H, Ar), 7.28 (s, 4H, Ar), 7.32 (dd, 2H,
Ar), 7.64 (s, 2H, Ar), 8.44 (s, 2H, CH¼N).
2.1.20. Synthesis of Compound 5a
In a round-bottom flask, a mixture of compound 1 (0.28 g, 1.0
mmole), potassium carbonate anhydrous (0.28 g, 2.0 mmole) and cata-
lytic amount of potassium iodide was heated with stirring in 50 mL
acetone. Compound 3a (0.25 g, 0.4 mmole) was dissolved in minimal
N,N-dimethylformamide and subsequently added dropwise to the
mixture. The overall mixture was heated under reflux for 18 h. The
acetone was removed via evaporation at room temperature, and both
potassium carbonate anhydrous and potassium iodide were removed
with the addition of water. The excess compound 1 was removed using
absolute ethanol and the desired product was finally recrystallized
from ethyl acetate. Yield 50%. Elemental analysis (%): found, C

Chirality-Induced Liquid Crystalline
117
77.64, H 7.12, N 2.75; calculated (C66H72N2O8), C 77.62, H 7.11, N
2.74. IR (KBr) n=cmꢂ1, 2949–2867 (C-H alkyl), 1711 (C¼O ester),
1606 (C¼N), 1251 (O-CH2). 1H-NMR (CDCl3) d=ppm, 0.99 (t, 6H,
CH3), 1.06 (d, 6H, CH3), 1.34 (m, 2H, CH2), 1.57–1.94 (m, 16H, CH
and CH2), 4.07–4.24 (2t and 2dd, 12H, OCH2), 7.03 (2d, 8H, Ar),
7.28 (s, 4H, Ar), 7.58 (d, 4H, Ar), 7.66 (d, 4H, Ar), 7.86 (d, 4H, Ar),
8.10 (d, 4H, Ar), 8.46 (s, 2H, CH¼N).
Compounds 5b–5h and 6a–6h were synthesized via similar steps as
mentioned for compound 5a. The analytical data for these compounds
are listed in Sections 2.1.21–2.1.35.
2.1.21. Synthesis of Compound 5b
Yield 52%. Elemental analysis (%): found, C 77.85, H 7.31, N 2.68;
calculated (C68H76N2O8), C 77.83, H 7.30, N 2.67. IR (KBr) n=cmꢂ1
,
2940–2875 (C-H alkyl), 1715 (C¼O ester), 1604 (C¼N), 1249 (O-CH2).
1H-NMR (CDCl3) d=ppm, 1.01 (t, 6H, CH3), 1.07 (d, 6H, CH3), 1.34 (m,
2H, CH2), 1.57–1.91 (m, 20H, CH and CH2), 4.06–4.26 (2t and 2dd,
12H, OCH2), 7.02 (2d, 8H, Ar), 7.26 (s, 4H, Ar), 7.56 (d, 4H, Ar), 7.65
(d, 4H, Ar), 7.86 (d, 4H, Ar), 8.09 (d, 4H, Ar), 8.46 (s, 2H, CH¼N).
2.1.22. Synthesis of Compound 5c
Yield 56%. Elemental analysis (%): found, C 78.04, H 7.50, N 2.62;
calculated (C70H80N2O8), C 78.04, H 7.48, N 2.60. IR (KBr) n=cmꢂ1
,
2940–2868 (C-H alkyl), 1715 (C¼O ester), 1604 (C¼N), 1249 (O-CH2).
1H-NMR (CDCl3) d=ppm, 0.99 (t, 6H, CH3), 1.06 (d, 6H, CH3), 1.34
(m, 2H, CH2), 1.54–1.91 (m, 24H, CH and CH2), 4.03–4.22 (2t
and 2dd, 12H, OCH2), 7.02 (2d, 8H, Ar), 7.27 (s, 4H, Ar), 7.57 (d, 4H,
Ar), 7.65 (d, 4H, Ar), 7.86 (d, 4H, Ar), 8.09 (d, 4H, Ar), 8.46 (s, 2H,
CH¼N).
2.1.23. Synthesis of Compound 5d
Yield 59%. Elemental analysis (%): found, C 78.24, H 7.69, N 2.55;
calculated (C72H84N2O8), C 78.23, H 7.66, N 2.53. IR (KBr) n=cmꢂ1
,
2935–2856 (C-H alkyl), 1716 (C¼O ester), 1605 (C¼N), 1249
(O-CH2). 1H-NMR (CDCl3) d=ppm, 1.01 (t, 6H, CH3), 1.07 (d, 6H,
CH3), 1.34 (m, 2H, CH2), 1.57–1.92 (m, 28H, CH and CH2),
4.04–4.29 (2t and 2dd, 12H, OCH2), 7.02 (2d, 8H, Ar), 7.25 (s, 4H,
Ar), 7.56 (d, 4H, Ar), 7.64 (d, 4H, Ar), 7.85 (d, 4H, Ar), 8.09 (d, 4H,
Ar), 8.45 (s, 2H, CH¼N).
2.1.24. Synthesis of Compound 5e
Yield 52%. Elemental analysis (%): found, C 78.42, H 7.85, N 2.49;
calculated (C74H88N2O8), C 78.41, H 7.83, N 2.47. IR (KBr) n=cmꢂ1
,

118
G.-Y. Yeap et al.
2937–2851 (C-H alkyl), 1706 (C¼O ester), 1605 (C¼N), 1249 (O-CH2).
1H-NMR (CDCl3) d=ppm, 0.99 (t, 6H, CH3), 1.06 (d, 6H, CH3), 1.34
(m, 2H, CH2), 1.41–1.92 (m, 32H, CH and CH2), 4.02–4.24 (2t and
2dd, 12H, OCH2), 7.00 (2d, 8H, Ar), 7.27 (s, 4H, Ar), 7.57 (d, 4H,
Ar), 7.63 (d, 4H, Ar), 7.85 (d, 4H, Ar), 8.10 (d, 4H, Ar), 8.45 (s, 2H,
CH¼N).
2.1.25. Synthesis of Compound 5f
Yield 50%. Elemental analysis (%): found, C 78.60, H 8.00, N 2.42; cal-
culated (C76H92N2O8), C 78.58, H 7.98, N 2.41. IR (KBr) n=cmꢂ1
,
2936–2852 (C-H alkyl), 1715 (C¼O ester), 1604 (C¼N), 1250 (O-CH2).
1H-NMR (CDCl3) d=ppm, 1.00 (t, 6H, CH3), 1.07 (d, 6H, CH3), 1.34 (m,
2H, CH2), 1.40–1.94 (m, 36H, CH and CH2), 4.03–4.29 (2t and 2dd,
12H, OCH2), 7.02 (2d, 8H, Ar), 7.28 (s, 4H, Ar), 7.56 (d, 4H, Ar), 7.64
(d, 4H, Ar), 7.85 (d, 4H, Ar), 8.08 (d, 4H, Ar), 8.45 (s, 2H, CH¼N).
2.1.26. Synthesis of Compound 5g
Yield 58%. Elemental analysis (%): found, C 78.78, H 8.15, N 2.35;
calculated (C78H96N2O8), C 78.75, H 8.13, N 2.35. IR (KBr) n=cmꢂ1
,
2937–2850 (C-H alkyl), 1708 (C¼O ester), 1605 (C¼N), 1248
(O-CH2). 1H-NMR (CDCl3) d=ppm, 0.99 (t, 6H, CH3), 1.06 (d, 6H,
CH3), 1.34–1.91 (m, 42H, CH and CH2), 4.03–4.26 (2t and 2dd, 12H,
OCH2), 7.01 (2d, 8H, Ar), 7.27 (s, 4H, Ar), 7.57 (d, 4H, Ar), 7.65
(d, 4H, Ar), 7.85 (d, 4H, Ar), 8.10 (d, 4H, Ar), 8.45 (s, 2H, CH¼N).
2.1.27. Synthesis of Compound 5h
Yield 70%. Elemental analysis (%): found, C 78.94, H 8.30, N
2.29; calculated (C80H100N2O8), C 78.91, H 8.28, N 2.30. IR (KBr)
n=cmꢂ1, 2935–2850 (C-H alkyl), 1716 (C¼O ester), 1605 (C¼N), 1250
(O-CH2). 1H-NMR (CDCl3) d=ppm, 1.01 (t, 6H, CH3), 1.07 (d, 6H,
CH3), 1.34–1.91 (m, 46H, CH and CH2), 4.03–4.28 (2t and 2dd, 12H,
OCH2), 7.02 (2d, 8H, Ar), 7.25 (s, 4H, Ar), 7.56 (d, 4H, Ar), 7.64
(d, 4H, Ar), 7.85 (d, 4H, Ar), 8.08 (d, 4H, Ar), 8.45 (s, 2H, CH¼N).
2.1.28. Synthesis of Compound 6a
Yield 60%. Elemental analysis (%): found, C 75.54, H 7.10, N 2.61;
calculated (C68H76N2O10), C 75.53, H 7.08, N 2.59. IR (KBr) n=cmꢂ1
,
2951–2871 (C-H alkyl), 1711 (C¼O ester), 1618–1603 (C¼N), 1268
(O-CH2). 1H-NMR (CDCl3) d=ppm, 0.99 (t, 6H, CH3), 1.06 (d, 6H,
CH3), 1.34 (m, 2H, CH2), 1.57–2.01 (m, 16H, CH and CH2), 4.00
(s, 6H, OCH3), 4.06–4.24 (2t and 2dd, 12H, OCH2), 6.97 (d, 2H, Ar),
7.02 (d, 4H, Ar), 7.28 (s, 4H, Ar), 7.31 (dd, 2H, Ar), 7.58 (d, 4H, Ar),
7.63 (s and d, 6H, Ar), 8.09 (d, 4H, Ar), 8.44 (s, 2H, CH¼N).

Chirality-Induced Liquid Crystalline
119
2.1.29. Synthesis of Compound 6b
Yield 49%. Elemental analysis (%): found, C 75.79, H 7.29, N 2.51;
calculated (C70H80N2O10), C 75.78, H 7.27, N 2.52. IR (KBr) n=cmꢂ1
,
2932–2854 (C-H alkyl), 1713 (C¼O ester), 1620–1602 (C¼N), 1268
(O-CH2). 1H-NMR (CDCl3) d=ppm, 0.99 (t, 6H, CH3), 1.06 (d, 6H,
CH3), 1.34 (m, 2H, CH2), 1.57–1.94 (m, 20H, CH and CH2), 4.00
(s, 6H, OCH3), 4.04–4.26 (2t and 2dd, 12H, OCH2), 6.97 (d, 2H, Ar),
7.02 (d, 4H, Ar), 7.28 (s, 4H, Ar), 7.31 (dd, 2H, Ar), 7.57 (d, 4H, Ar),
7.63 (2d, 6H, Ar), 8.09 (d, 4H, Ar), 8.44 (s, 2H, CH¼N).
2.1.30. Synthesis of Compound 6c
Yield 64%. Elemental analysis (%): found, C 76.04, H 7.45, N 2.45;
calculated (C72H84N2O10), C 76.03, H 7.44, N 2.46. IR (KBr) n=cmꢂ1
,
2935–2857 (C-H alkyl), 1712 (C¼O ester), 1618–1602 (C¼N), 1269
(O-CH2). 1H-NMR (CDCl3) d=ppm, 0.99 (t, 6H, CH3), 1.06 (d, 6H,
CH3), 1.34 (m, 2H, CH2), 1.53–1.94 (m, 24H, CH and CH2), 4.00 (s,
6H, OCH3), 4.02–4.24 (2t and 2dd, 12H, OCH2), 6.97 (d, 2H, Ar),
7.02 (d, 4H, Ar), 7.28 (s, 4H, Ar), 7.31 (dd, 2H, Ar), 7.57 (d, 4H, Ar),
7.64 (2d, 6H, Ar), 8.09 (d, 4H, Ar), 8.44 (s, 2H, CH¼N).
2.1.31. Synthesis of Compound 6d
Yield 56%. Elemental analysis (%): found, C 76.28, H 7.63, N 2.40;
calculated (C74H88N2O10), C 76.26, H 7.61, N 2.40. IR (KBr) n=cmꢂ1
,
2932–2854 (C-H alkyl), 1712 (C¼O ester), 1620–1603 (C¼N), 1269
(O-CH2). 1H-NMR (CDCl3) d=ppm, 0.99 (t, 6H, CH3), 1.06 (d, 6H,
CH3), 1.34 (m, 2H, CH2), 1.52–1.92 (m, 28H, CH and CH2), 4.00 (s,
6H, OCH3), 4.03–4.26 (2t and 2dd, 12H, OCH2), 6.97 (d, 2H, Ar),
7.02 (d, 4H, Ar), 7.28 (s, 4H, Ar), 7.31 (dd, 2H, Ar), 7.57 (d, 4H, Ar),
7.63 (2d, 6H, Ar), 8.09 (d, 4H, Ar), 8.44 (s, 2H, CH¼N).
2.1.32. Synthesis of Compound 6e
Yield 68%. Elemental analysis (%): found, C 76.50, H 7.80, N 2.36; cal-
culated (C76H92N2O10), C 76.48, H 7.77, N 2.35. IR (KBr) n=cmꢂ1
,
2931–2853 (C-H alkyl), 1711 (C¼O ester), 1616–1603 (C¼N), 1270
(O-CH2). 1H-NMR (CDCl3) d=ppm, 0.99 (t, 6H, CH3), 1.06 (d, 6H, CH3),
1.34 (m, 2H, CH2), 1.41–1.94 (m, 32H, CH and CH2), 4.00 (s, 6H,
OCH3), 4.01–4.24 (2t and 2dd, 12H, OCH2), 6.96 (d, 2H, Ar), 7.02
(d, 4H, Ar), 7.28 (s, 4H, Ar), 7.32 (dd, 2H, Ar), 7.57 (d, 4H, Ar), 7.63
(s and d, 6H, Ar), 8.09 (d, 4H, Ar), 8.44 (s, 2H, CH¼N).
2.1.33. Synthesis of Compound 6f
Yield 58%. Elemental analysis (%): found, C 76.71, H 7.93, N 2.30;
calculated (C78H96N2O10), C 76.69, H 7.92, N 2.29. IR (KBr) n=cmꢂ1
,

120
G.-Y. Yeap et al.
2930–2852 (C-H alkyl), 1715 (C¼O ester), 1620–1602 (C¼N), 1272
(O-CH2). 1H-NMR (CDCl3) d=ppm, 0.99 (t, 6H, CH3), 1.06 (d, 6H,
CH3), 1.34–1.93 (m, 38H, CH and CH2), 4.00 (s, 6H, OCH3),
4.03–4.26 (2t and 2dd, 12H, OCH2), 6.96 (d, 2H, Ar), 7.02 (d, 4H,
Ar), 7.28 (s, 4H, Ar), 7.30 (dd, 2H, Ar), 7.57 (d, 4H, Ar), 7.63 (2d, 6H,
Ar), 8.09 (d, 4H, Ar), 8.43 (s, 2H, CH¼N).
2.1.34. Synthesis of Compound 6g
Yield 69%. Elemental analysis (%): found, C 76.90, H 8.09, N 2.24;
calculated (C80H100N2O10), C 76.89, H 8.07, N 2.24. IR (KBr) n=cmꢀ1
,
2924–2852 (C-H alkyl), 1714 (C¼O ester), 1616–1602 (C¼N), 1268
(O-CH2). 1H-NMR (CDCl3) d=ppm, 0.99 (t, 6H, CH3), 1.06 (d, 6H,
CH3), 1.34–1.93 (m, 42H, CH and CH2), 4.00 (s, 6H, OCH3), 4.03–4.24
(2t and 2dd, 12H, OCH2), 6.96 (d, 2H, Ar), 7.02 (d, 4H, Ar), 7.28 (s, 4H,
Ar), 7.31 (dd, 2H, Ar), 7.57 (d, 4H, Ar), 7.64 (2d, 6H, Ar), 8.09 (d, 4H, Ar),
8.44 (s, 2H, CH¼N).
2.1.35. Synthesis of Compound 6h
Yield 51%. Elemental analysis (%): found, C 77.10, H 8.21, N 2.20;
calculated (C82H104N2O10), C 77.08, H 8.20, N 2.19. IR (KBr) n=cmꢀ1
,
2919–2851 (C-H alkyl), 1716 (C¼O ester), 1621–1603 (C¼N), 1272
(O-CH2). 1H-NMR (CDCl3) d=ppm, 0.99 (t, 6H, CH3), 1.06 (d, 6H,
CH3), 1.34–1.92 (m, 46H, CH and CH2), 4.00 (s, 6H, OCH3),
4.03–4.27 (2t and 2dd, 12H, OCH2), 6.95 (d, 2H, Ar), 7.00 (d, 4H, Ar),
7.28 (s, 4H, Ar), 7.31 (dd, 2H, Ar), 7.57 (d, 4H, Ar), 7.63 (s and d, 6H,
Ar), 8.09 (d, 4H, Ar), 8.43 (s, 2H, CH¼N).
2.2. Characterization
All intermediates and title compounds were characterized using several
spectroscopic techniques. The samples were analyzed in the form of KBr
pellets and the spectra were recorded in the range of 4000–400 cmꢀ1
using a Perkin Elmer 2000 FT-IR spectrophotometer. The 1H-NMR
spectra were obtained using a Bruker 400 MHz UltrashieldTM FT-NMR
spectrometer. The samples were prepared in CDCl3 solutions with
TMS as internal standard. For compounds with partial solubility in
CDCl3 at room temperature, spectrometer internal heater was used to
maintain the temperature at 50ꢁC throughout the analyses. Carbon,
Hydrogen, and Nitrogen (CHN) microanalyses were performed using
a Perkin Elmer 2400 LS Series CHNS=O analyzer. The liquid crystal-
line textures were observed using a Carl Zeiss Axioskop 40 polarizing
microscope equipped with a Linkam LTS350 hotstage and TMS94
temperature controller. The heats of fusion and phase transition

Chirality-Induced Liquid Crystalline
121
temperatures of the compounds were subsequently determined with a
Seiko DSC6200R differential scanning calorimeter at the heating and
cooling rate of ꢂ5ꢁC minꢀ1. The X-ray diffraction studies were per-
formed with a Bruker D8 diffractometer (CuKa line) equipped with a
¨
Gobel mirror, Vantec linear detector and vertical goniometer. Sample
temperature was controlled by Anton Paar heating stage and the h–h
scans were performed every 0.5ꢁC. Prior to the measurements, the sam-
ples were heated to the isotropic phase and cooled slowly into the smec-
tic phase to obtain the homeotropic alignment. All measurements were
performed on one surface free sample. For the conformational study of
the trimers, the MM2 calculations were performed using the CS
Chem3D Pro software produced by CambridgeSoft Corporation. Com-
pounds 5a, 5c, 5e, 5f, and 5g were selected for the calculations in line
with the powder X-ray diffraction analyses on similar compounds.
3. RESULTS AND DISCUSSION
3.1. Thermal Properties of Compounds 5a–5h
The homologous compounds 5a–5h exhibit enantiotropic mesophases.
The phase transition temperatures, phase sequences, and respective
transitional enthalpies are given in Table 2a. The dependence of the
transition temperatures on the number of methylene units, n, in the
flexible alkyl spacers for compounds 5a–5h upon heating is shown in
Fig. 1. The DSC trace for compound 5a is shown in Fig. 2. All compounds
exhibit the predominant enantiotropic Nꢃ phase. In addition to this,
compounds 5a–5h are also smectogenic. It is apparent that all transition
temperatures are strongly influenced by the length and the parity of the
spacers. A strong odd–even effect for all types of phase transition tem-
peratures is observed in this series. For the melting points, pronounced
attenuation is not observed on increasing n even though the alternation
is strong. For SmA-Nꢃ transition, the trimers with odd n methylene
spacers exhibit significantly lower transition temperatures in compari-
son with the even homologues with n ꢀ 1. In similar manner, strong
alternation is also observed for the isotropization temperatures on
increasing n. For the trimers with odd n, the isotropization tempera-
tures are derived from the unresolved Nꢃ-BP and BP-I transitions in
the DSC thermograms. Overall, the smectogenic properties are not
enhanced on increasing n. For both odd and even members, the stability
of the SmCꢃ phase decreases on increasing n and results in monotropic
SmCꢃ phase for compounds 5f and 5g. For compound 5h, the SmCꢃ
phase is not present. For the SmA phase, the widest temperature range
(38.3ꢁC) is recorded for compound 5b (n ¼ 6) whilst the smallest

122
G.-Y. Yeap et al.
TABLE 2a. Phase Transition Temperatures (ꢁC) and Associated Enthalpies
(kJ molꢂ1) of Compounds 5a–5h (. ¼ Enantiotropic Phase, ꢁ ¼ Monotropic
Phase; only the Highest Melting Point of Crystal is Reported; Cr ¼ Crystal,
SmX ¼ Unidentified Smectic, SmCꢀ ¼ Chiral Smectic C, SmA ¼ Smectic A,
Nꢀ ¼ Chiral Nematic, BP ¼ Blue Phase, I ¼ Isotropic)
Compound
Cr
SmX
SmCꢀ
SmA
Nꢀ
BP
I
5a
. 161.7
(18.2)
. 192.3
(86.9)
. 148.3
(73.2)
. 174.5
(69.5)
. 146.7
(56.2)
. 174.7
(81.0)
. 138.1
(56.7)
. 169.7
(76.6)
ꢁ [141.1]a
. 190.0a
. 221.7
(0.5)
. 226.9b
(0.3)b
. 226.9b
.
(0.3)b
5b
5c
5d
5e
5f
. 225.0a
. 263.3a
. 266.0
(18.5)
.
.
.
.
.
.
.
ꢁ [140.9]
. 164.6
(0.1)
. 190.5a
. 200.0
(1.5)
. 216.9a
. 212.0b
(2.0)b
. 212.0b
(5.7)
(2.0)b
. 222.2a
ꢁ [140.6]
. 155.4
(0.2)
ꢁ [174.0]a
. 185.6
(1.2)
. 204.7a
. 200.8b
(2.9)b
. 211.6
(4.9)
. 187.6b
(3.4)b
. 200.8b
(8.6)
(2.9)b
5g
5h
ꢁ [134.0]d
ꢁ [137.8]d
. 170.5
(0.4)
. 173.9a
. 187.6b
(10.0)
(3.4)b
. 194.7
(5.1)
aDenotes transition temperatures determined via polarizing microscopy, undetected
via DSC.
bDenotes transition temperatures and enthalpies derived from unresolved peaks.
cDenotes SmX ¼ SmFꢀ for compound 5c.
dDenotes SmA-SmCꢀ-SmX transition temperatures upon cooling which are not well
resolved.
[] Denotes transition temperatures information of monotropic SmX, SmFꢀ or SmCꢀ, phase.
temperature range (4.2ꢁC) is observed for the trimer with n ¼ 12 spacers
(5h). However, the decreasing tendency in smectogenic properties with
increasing n does not conform to common observation in homologous ser-
ies of liquid crystals and semiflexible main chain liquid crystal polymers
despite few reported exceptions [15]. One of the examples is a series of
trimers with three biphenyl cores and spacers with n ¼ 3–12 [2]. Con-
trary to the smectic phases, the overall Nꢀ temperature range increases
from 5.2ꢁC (5a) to 20.8ꢁC (5h) on increasing n with the even members
exhibiting more pronounced increase than its analogues with odd n.
3.2. Optical Properties and Smectic Phase
Characterization of Compounds 5A–5H
Upon cooling the SmA phase, the SmCꢀ texture appears as broken fans
coexisting with homeotropic domains. The texture is regarded as

Chirality-Induced Liquid Crystalline
123
FIGURE 1 The dependence of the transition temperatures on the number of
methylene units, n in the spacers for compounds 5a–5 h. The blue phase range
is not depicted in this figure as it is very narrow.
pseudo-homeotropic as it is viewed along helical axis, i.e., along optic
axis [16]. More distinctive dechiralization lines across the fans of the
SmCꢀ phase are observed on cooling compared to the heating run
FIGUREꢂ21 DSC trace of compound 5a with heating and cooling rate of
ꢃ5ꢁC min
.

124
G.-Y. Yeap et al.
[17,18]. The SmA phase is assigned based on the coexistence of
the fan-shaped texture and homeotropic regions [19,20]. The SmA
phase is also identified by the absence of the dechiralization lines
across the fans and more apparent extinct homeotropic regions. The
homeotropic domains reflect the uniaxiality of the SmA phase [20].
A photomicrograph of the SmA fan-shaped texture is shown in Fig. 3.
In order to investigate the molecular organization in the smectic
phases, powder X-ray diffraction is conducted for aligned sample of
compounds 5a, 5c, 5e, 5f, and 5g. For these five trimers, the plots
demonstrating the layer spacing dependence upon descending tem-
perature are given in Figs. 4a–e, respectively. The transition tempera-
tures determined by the diffractometer is a few degrees different from
the temperatures obtained via DSC. The shift in the temperatures can
be due to the slight decomposition experienced by the samples which
were held for several hours at high temperature before the measure-
ments are completed.
From the powder X-ray diffraction results, for compounds 5a, 5c,
5e, and 5g exhibiting the SmA and SmCꢀ phases, it can be observed
that the transition between the orthogonal and tilted phases is of sec-
ond order as indicated by the continuous decrease of layer thickness in
the SmCꢀ phase. It is, therefore, reasonable to assume that the
SmA-SmCꢀ transition for other members in this series is also second
order as well. The average value of SmA layer spacing is in agreement
with the MM2 approximate length of the trimer in all-trans conforma-
tion (i.e., for 5c, the molecular length determined in simulation is
FIGURE 3 The SmA fan-shaped texture for compound 5d at 198.2ꢁC on
heating.

Chirality-Induced Liquid Crystalline
125
FIGURE 4 The dependence of molecular layer spacing in the smectic phases
on temperature for (a) compound 5a, (b) compound 5c, (c) compound 5e,
(d) compound 5f, and (e) compound 5g.

126
G.-Y. Yeap et al.
˚
˚
67.5 A, and the layer thickness is 65.9 A), and therefore, the phase can
be undoubtedly assigned as the SmA1 (monolayer SmA) phase.
At higher temperature, the slight reduction in SmA layer spacing is
attributed to the tendency of the molecules from consecutive layers
to intercalate and the less stretched conformation adopted by mole-
cules preceding the Nꢀ phase. This phenomenon is not uncommon as
molecules gain higher degree of fluidity and flexibility on elevating
temperature. In other words, the conformational order is lower at
higher temperature, and this is reflected by the decrease of layer
spacing as reported in cyanobiphenyl-based dimer [4]. For the studied
homologous series, the temperature influence on layer thickness is
stronger upon increasing length of the alkyl spacers between the
mesogenic cores. The SmA layer periodicity for compound 5g
decreases in the most apparent fashion in comparison to other odd tri-
mers 5a, 5c, and 5e in this series, indicating that the trimers with
C11H22 spacers possess greater flexibility and fluidity to intercalate
more effectively than the shorter odd counterparts. It is, therefore,
suggested that long odd spacers can also be the driving force in forma-
tion of intercalated smectic phases which are usually observed for the
nonsymmetric oligomers [4,19]. Upon transition to the SmCꢀ phase,
the layer periodicity decreases steadily indicating the increase in
molecular tilt (to 22ꢁ for 5c and 18ꢁ for 5e) in the SmCꢀ phase. As
the sample is supercooled, in some homologues, the additional SmX
phase is detected below the SmCꢀ phase. Despite the increase in layer
spacing in this mesophase, the periodicity remains less than the mole-
cular length, reflecting that the molecules are tilted. From the powder
X-ray diffraction analyses, the monotropic hexatic phase seems to be
either the SmIꢀ or SmFꢀ phase. The SmIꢀ and SmFꢀ phases are often
difficult to be distinguished from one another due to the similarities in
molecular orderings between the two mesophases. However, the ambi-
guity in assigning the mesophase to either SmIꢀ or SmFꢀ can be
resolved based on the textures. For compound 5c, the hexatic phase
is represented by the formation of mosaic platelets containing
schlieren-like brushes (Fig. 5) upon cooling the SmCꢀ phase. Contrary
to SmIꢀ phase which usually exhibit typical schlieren texture, the
SmFꢀ phase exhibits the mosaic-schlieren texture as reported
for terephthalylidene-bis-4-n-decylaniline [16]. Thus, with the
information from powder X-ray diffraction and polarizing microscopy,
the monotropic hexatic phase of compound 5c is assigned as the
SmFꢀ phase. For compound 5e, the identification of the addi-
tional smectic phase based on the texture and powder X-ray
diffraction studies is more difficult as compared to compound 5c
(Figs. 6a–c and 7).

Chirality-Induced Liquid Crystalline
127
FIGURE 5 The photomicrograph of SmF mosaic-schlieren texture of
compound 5c upon cooling the SmCꢀ phase.
3.3. The Blue Phase of Compounds 5a, 5c, 5e, and 5g
In addition to the SmCꢀ, SmA, and Nꢀ phases, the odd trimers also
exhibit the blue phase preceding the isotropic phase. With heating
rate of 0.1ꢁC minꢂ1, the blue phase appears slowly as the oily streaks
of Nꢀ phase diminish. The blue phase is identified as BPI on the basis
of its platelet texture which appears blue, red, and green in colour as
shown in Fig. 8 [21]. The presence of blue phase for the trimers reflects
the strong chirality of the compounds [22]. The platelet texture is more
FIGURE 6 Evolution from (a) the SmA homeotropically extinct texture at
164.4ꢁC to (b) pseudo-homeotropic texture of SmCꢀ phase at 152.0ꢁC to
(c) the coexistence of homeotropic and platelet=fan-like texture of SmX phase
at 136.0ꢁC.

128
G.-Y. Yeap et al.
FIGURE 7 The mosaic texture of the monotropic SmX phase of compound 5e.
apparent on cooling the isotropic phase as compared to the heating
cycle. In comparison to the trimers with even spacers, the tendency
for the odd members to exhibit the blue phase, whilst the even mem-
bers do not, is consistent with those reported for (R)-2,20-bis{6-[4-(2-
(2-fluoro-4-butyloxyphenyl)pyrimidine-5-yl)phenyloxy]alkyloxy}-1,10-
binaphthyls and also the CBOnO.(S)2MB dimers [7,23]. The results
obtained by Blatch et al. [7], however, showed that there is no
FIGURE 8 The blue phase platelet texture of compound 5e upon cooling the
isotropic phase.

Chirality-Induced Liquid Crystalline
129
apparent difference in the helical twisting power between the odd and
even chiral dimers apart from a slight increase with the length of the
spacer, and therefore, cannot be used to justify the presence of blue
phase for the odd members.
3.4. Thermal and Optical Properties of Compounds 6a–6h
The phase transition temperatures and respective transitional enthal-
pies of compounds 6a–6h are given in Table 2b. With the presence of
two meta OCH3 groups, pronounced differences in mesomorphic prop-
erties are observed for 6a–6h in comparison to 5a–5h. For 6a–6h, the
even members are nematogenic enantiotropically whilst the odd
members are not mesogenic. The exclusive nematogenic behavior for
even-parity trimers indicates the presence of predominant terminal
intermolecular attractions rather than lateral intermolecular attrac-
tions [24]. For these compounds, a decreasing trend of Nꢀ phase tem-
perature range is also observed with lengthening of the spacers which
can be due to higher degree of flexing along the long molecular axis
[24]. In other words, as the spacer length is increased, the molecules
lack rigidity resulting in reduced mesomorphic properties. Although
we are certain that the nematogenic characteristic for the odd trimers
is absent, we are keen to investigate the possibility of these trimers
exhibiting a high-order smectic phase. Hence, powder X-ray diffrac-
tion is carried out for a representative compound 6g and the results
obtained confirm the absence of smectogenic properties. The non-
mesogenicity of the odd trimers can be explained by considering two
TABLE 2b. Phase Transition Temperatures (ꢁC) and
Associated Enthalpies (kJ molꢂ1) of Compounds 6a–6h
(. ¼ Enantiotropic Phase, ꢁ ¼ Monotropic Phase, Only
the Highest Melting Point of Crystal is Reported.
Cr ¼ Crystal, Nꢀ ¼ Chiral Nematic, I ¼ Isotropic)
Compound
Cr
Nꢀ
I
6a
6b
6c
6d
6e
6f
. 88.8 (0.5)
.
.
.
.
.
.
.
.
. 136.7 (50.7)
. 112.7 (7.5)
. 136.0 (60.6)
. 110.3 (10.4)
. 134.4 (57.7)
. 118.0 (15.4)
. 134.9 (75.3)
. 166.1a
. 158.7 (3.0)
. 144.9 (7.6)
. 139.3a
6g
6h
aDenotes transition temperature determined via polarizing
microscopy, undetected via DSC.

130
G.-Y. Yeap et al.
factors. Firstly, the increased molecular breadth due to meta OCH3
groups hinders close intermolecular packing. Secondly, the odd-parity
spacers reduce the molecular shape anisotropy with the decrease in
molecular linearity. If only the first factor taken into account, only
the smectogenic properties are diminished for compounds 6a–6h
owing to the lateral hindrance induced by meta OCH3 groups. How-
ever, the combined effect of the two factors results in the absence of
mesomorphic properties for compounds 6a, 6c, 6e, and 6g.
Our microscopic observation on compound 6b reveals the oily
streaks texture of the Nꢀ phase. Figure 9 shows the oily streaks
texture in the Nꢀ matrix which possess high degree of fluidity prior
to transformation into the isotropic phase [21,25]. Compound 6d, on
the other hand, exhibits the Nꢀ phase with iridescent colours of
violet=blue with oily streaks present in the brightly coloured domains
[26]. As shown in Fig. 10, a huge concentration of the oily streaks
defects emerges gradually at the Cr-Nꢀ transition and forms a dense
network throughout the microscopic sample [27]. However, the possi-
bility of compound 6d exhibiting BPI and BPII is ruled out as the
texture does not possess the characteristics of the blue phase platelets
such as the sharp edges which reflect the cubic structure of the phase
[21]. At the same time, it does not contain the attributes of the
amorphous texture of BPIII [28].
For the even trimers, the depression of the clearing temperatures
(Tc) is largely due to the increase in molecular breadth at positions
FIGURE 9 Photomicrograph of oily streaks of the Nꢀ phase during the heat-
ing cycle prior to Nꢀ-I transition (compound 6b).

Chirality-Induced Liquid Crystalline
131
FIGURE 10 Photomicrograph of Nꢀ phase exhibiting violet=blue iridescent
colors in formation of oily streaks texture (compound 6d).
where OCH3 groups are introduced. The broadening of the liquid
crystal molecules reduces the shape anisotropy and thus depresses
the stability of the nematics [29]. It is interesting to note that the Tc
for compound 5b is 99.9ꢁC higher than that of compound 6b with
similar spacer length. The Tc for compound 5h is 194.7ꢁC but upon
introducing the meta OCH3 groups, the Tc is reduced by 55.4ꢁC for
compound 6h in the second series.
4. CONCLUSIONS
Every homologue in the first series of benzylidene-1,4-phenylenedia-
mine-based liquid crystal trimers exhibited the chiral mesophases.
These trimers were both smectogenic and nematogenic. The powder
X-ray diffraction analyses revealed that the odd trimers also exhibited
the higher-order tilted smectic phases besides the monolayer SmA and
SmCꢀ phases which was predominant in this series. For compound 5c,
the monotropic SmFꢀ phase was identified on the basis of its mosaic-
schlieren texture in support of the powder X-ray diffraction results.
The odd members also exhibited the blue phase in short temperature
range between the Nꢀ and isotropic phase.
In the second series, compounds 6a–6h with the presence of two
meta OCH3 groups were not smectogenic. Whilst the even trimers
exhibited the Nꢀ phase, the odd trimers were not mesogenic. The pre-
sence of lateral OCH3 groups at the benzylidene-1,4-phenylenedia-
mine mesogenic core suppressed the clearing temperature by nearly

132
G.-Y. Yeap et al.
100ꢁC for compound 6b in comparison to compound 5b with similar
spacer. For compounds 6a–6h, the increase in molecular breadth
reduced the molecular shape anisotropy and hindered lateral intermo-
lecular interaction which is essential to induce the smectic layered
arrangement. The shape anisotropy was further reduced for com-
pounds 6a, 6c, 6e, and 6g with the presence of odd spacers resulting
in the absence of mesomorphic properties.
ACKNOWLEDGMENTS
The main author (G.-Y. Yeap) acknowledges the Malaysian Higher
Education Ministry and the Ministry of Science, Technology and Inno-
vation (MOSTI) for the financial support in terms of research grants
(Fundamental Research Grant Scheme, Account No. 203=PKIMIA=
671025 and eScience, Account No. 305=PKIMIA=613315). The authors
are also grateful to Professor Corrie T. Imrie from the University of
Aberdeen, Scotland for his helpful comments and discussion regarding
this work.
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