Self-assembled 1,2-bis[4-(4-(10-decyloxy)phenylazo)]benzoylhydrazine dimer and its hydrogen-bonded complexes

Article abstract of DOI:10.1080/10610278.2013.792341

We report the synthesis and investigation of a new self-assembled benzoylhydrazine-based compound, namely 1,2-bis[4-(4-(10-decyloxy)phenylazo)] benzoylhydrazine and their hydrogen-bonded complexes with different carboxylic acid derivatives, of which some exhibit liquid crystalline properties and some are non-mesogens. The conversion of the non-liquid crystalline target compound that is free from carboxylic acid to liquid crystalline complexes containing various carboxylic acids can probably be rationalised through the breaking of intermolecular hydrogen bonding within the supramolecular assembly by carboxylic acid dopants. The enhancement of liquid crystalline properties of benzoylhydrazine compounds with respect to various carboxylic dopants is documented. Other salient features can be exemplified by the formation of discotic columnar phase as shown by the azo-linkage containing 4-(4′-(10-decyloxy)phenylazo)benzoic acid-doped complex.

Full text of DOI:10.1080/10610278.2013.792341

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Self-assembled 1,2-bis[4-(4-(10-
decyloxy)phenylazo)]benzoylhydrazine dimer and its
hydrogen-bonded complexes
Guan-Yeow Yeap a , Subramanian Balamurugan a , Samikannu Rakesh b , Chun-Chieh Han c
Hong-Cheu Lin c
&
a Liquid Crystal Research Laboratory, School of Chemical Sciences, Universiti Sains
Malaysia , 11800 , Minden , Penang , Malaysia
b Department of Chemistry , Anna University , Chennai , Tamil Nadu , 600 025 , India
c Department of Materials Science and Engineering , National Chiao Tung University ,
Hsinchu , 300 , Taiwan , Republic of China
Published online: 22 May 2013.
To cite this article: Guan-Yeow Yeap , Subramanian Balamurugan , Samikannu Rakesh , Chun-Chieh Han & Hong-Cheu Lin
(2013) Self-assembled 1,2-bis[4-(4-(10-decyloxy)phenylazo)]benzoylhydrazine dimer and its hydrogen-bonded complexes,
Supramolecular Chemistry, 25:7, 424-431, DOI: 10.1080/10610278.2013.792341
To link to this article: http://dx.doi.org/10.1080/10610278.2013.792341
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Supramolecular Chemistry, 2013
Vol. 25, No. 7, 424–431, http://dx.doi.org/10.1080/10610278.2013.792341
Self-assembled 1,2-bis[4-(4-(10-decyloxy)phenylazo)]benzoylhydrazine dimer and its hydrogen-
bonded complexes
Guan-Yeow Yeapa*, Subramanian Balamurugana, Samikannu Rakeshb, Chun-Chieh Hanc and Hong-Cheu Linc
aLiquid Crystal Research Laboratory, School of Chemical Sciences, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia;
bDepartment of Chemistry, Anna University, Chennai, Tamil Nadu 600 025, India; cDepartment of Materials Science and Engineering,
National Chiao Tung University, Hsinchu 300, Taiwan, Republic of China
(Received 13 January 2013; final version received 21 March 2013)
We report the synthesis and investigation of a new self-assembled benzoylhydrazine-based compound, namely 1,2-bis[4-(4-(10-
decyloxy)phenylazo)]benzoylhydrazine and their hydrogen-bonded complexes with different carboxylic acid derivatives, of
which some exhibit liquid crystalline properties and some are non-mesogens. The conversion of the non-liquid crystalline target
compound that is free from carboxylic acid to liquid crystalline complexes containing various carboxylic acids can probably be
rationalised through the breaking of intermolecular hydrogen bonding within the supramolecular assembly by carboxylic acid
dopants. The enhancement of liquid crystalline properties of benzoylhydrazine compounds with respect to various carboxylic
dopants is documented. Other salient features can be exemplified by the formation of discotic columnar phase as shown by the
azo-linkage containing 4-(40-(10-decyloxy)phenylazo)benzoic acid-doped complex.
Keywords: liquid crystalline; hydrogen bonding; supramolecular assembly; discotic columnar phase
1. Introduction
Since the target compound inherently possesses donor (ZNH)
and acceptor (ZCvO) between the two mesogenic units, it
induces the polymeric self-assembly through intermolecular
hydrogen bonding. However, the use of carboxylic acid (non-
liquid crystalline and liquid crystalline) to break down the
polymeric self-assemblies as a way to convert the non-liquid
crystalline benzoylhydrazines to mesogenic complexes will
also be reported in the present report.
The supramolecular assembly plays an important role in the
design and engineering of architectures of chemical
molecules (1, 2). Although the conventional chemical
structures involve the covalent bond, supramolecular
chemistry places emphasis on the weaker non-covalent
interactions between molecules. These forces include
hydrogen bonding (H-bonding), van der Waals force, dative
bonds associated with coordination compounds, hydro-
phobic force and electrostatic effect. Among these, the H-
bonding can alter the liquid crystalline properties through
rigidity and molecular order (3). The importance of H-
bonding towards the formation and/or stabilisation of liquid
crystalline phases has actually received growing attention in
recent years (4–6). The same phenomenon can also be
observed in the typical liquid crystal dimers of aromatic
carboxylic acids (7) and their analogue possessing
supramolecular assembly (8); polymeric assembly of plural
molecules (9); assembly of molecules in the side-chain
polymers (10) and formation of bent shape, hockey-stick
shape, discshape andstarshape molecules(11–13). Someof
the related reports described the presence of intermolecular
H-bonding at the end of the mesogen as a prerequisite to
command a specific molecular shape (14, 15). However, the
intermolecular H-bonding introduced at the middle of the
mesogen seemed to enhance the molecular order.
2. Experimental
2.1. Materials and methods
The chemicals were obtained from Sigma-Aldrich Chemi-
cals (St. Louis, Missouri, USA) and Merck (Darmstadt,
Germany). All the solvents were purified and dried by
standard methods, and the crude samples were purified by
column chromatographic technique using silica gel (230–
400 mesh) as a stationary phase. Thin-layer chromatography
was performed on aluminium sheets pre-coated with silica
gel(Merch, Kieselgel60,F254). Theinfrared(IR)spectrafor
all compounds were recorded in the range 4000–400 cm21
using a PerkinElmer 2000 FT-IR spectrophotometer
(Waltham, Massachusetts, USA) with the samples
embedded in KBr discs. The 1H NMR and 13C NMR spectra
were obtained using a Bruker 500 MHz Ultra-Shield
spectrometer (Karlsruhe, Germany). CDCl3 and DMSO-d6
were used as solvents and trimethylsilane as the internal
standard. Carbon, Hydrogen and Nitrogen microanalyses
were carried out on a PerkinElmer 2400 LS Series CHNS/O
In this paper, we report the synthesis of difunctional
(donor and acceptor) benzoylhydrazine-containing com-
pounds with alkyl chain (C10H21–) at both ends of terminals.
*Corresponding author. Email: gyyeap@usm.my
q 2013 Taylor & Francis

Supramolecular Chemistry
425
Analyzer (Waltham, Massachusetts, USA). The liquid
crystalline textures were observed under a Carl Zeiss
Axioskop40polarisingmicroscope(Oberkochen, Germany)
equipped with a Linkam TMS94 temperature controller
(Guildford, Surrey, UK) and a LTS350 hot stage (Guildford,
Surrey, UK). The transition temperatures and enthalpy
changes were measured by a differential scanning
calorimeter TA Q200 (Delaware, New Castle, USA) at a
rate of 58C min21 for both heating and cooling cycles.
H2N
CN
HCl/NaNO2
NaOH/ phenol
N
N
1
CN
HO
C10H21Br/ acetone/K2CO3/KI
N
CN
C10H21O
N
2.2. Synthesis
2
The synthetic methods used to obtain all intermediates 1–
3, compound 4 (Scheme 1) and hydrogen-bonded
complexes (Scheme 2) are described.
NaOH/ethanol
OH
N
O
C10H21O
N
3
2.2.1. Synthesis of 4-(40-hydroxyphenylazo)benzonitrile
(1)
SOCl2 / benzene
NH2–NH2/ THF
4-Cyanoaniline (0.07 mol) was dissolved in a mixture of
hydrochloric acid (16 ml) and water (16 ml), and the
reaction mixture was cooled in ice bath with constant
stirring at 0–58C. A solution of sodium nitrite (0.07 mol)
in 20 mL of water was added dropwise to the reaction
mixture. Phenol (0.07 mol) was dissolved in 10% sodium
hydroxide solution (45 ml) in a round-bottomed flask, and
the solution was cooled to 58C. The reaction mixture was
N
OC10H21
O
N
HN
NH
N
N
O
C10H21O
4
Scheme 1. Synthetic pathway towards the formation of
compound 4.
Non-LCs
LCs
COOH
HOOC
OC10H21
a
4/a
f
4/f
OC10H21
F
COOH
OC10H21
HOOC
N
b
F
N
g
h
4/b
4/c
4/g
4/h
F
O
O
OC10H21
COOH
COOH
Cl
HOOC
c
HN
O
O
N
NH
HC
N
OC10H21
H3CO
O2N
HOOC
HOOC
d
i
4/i
4/d
N
N
COOH
OC10H21
N
j
e
4/e
4/j
OC10H21
LCs
LCs
4
Non-LCs
Scheme 2. Synthetic pathway for the formation of complexes 4a–4j.

426
G.-Y. Yeap et al.
vigorously stirred and cold diazonium salt solution was
added dropwise, and then the mixture was kept in an ice
bath for 30 min. Upon completion of the reaction, the
mixture was poured into water (500 ml) and acidified with
aqueous hydrochloric acid to get an orange colour product.
The crude product was filtered through a Buchner funnel
(Shanghai Gongtao Ceramics Co., Ltd., Shanghai, China)
with gentle suction and washed well with water. The
resulting product was an orange-red colour solid and dried
in vacuum oven at 608C for 24 h (yield: 66%).
Elemental analysis. Calcd for C13H9N3O: C, 69.95; H,
4.06; N, 18.82, found: C, 69.90; H, 4.00; N, 18.75. FT-IR
(KBr pellet) ymax (cm21): 3319 (ZOH), 2235(ZCN),
1582 (ZCvCZ), 1421 (ZNvNZ). 1H NMR (CDCl3,), d
(ppm): 7.92 (d, 2H, J ¼ 8.4 Hz, ArH), 7.73 (d, 2H,
J ¼ 8.8 Hz ArH), 7.19 (d, 2H, J ¼ 8.8 Hz, ArH), 6.98 (d,
2H, J ¼ 8.2 Hz, ArH). 13C NMR (CDCl3) d (ppm): 159.5,
154.7, 146.9, 133.1, 125.6, 123.1, 118.1, 116.0, 113.2.
(100 ml) was refluxed for 4 h. The reaction mixture was
poured into water (500 ml) and acidified with aqueous
hydrochloric acid. The crude product was filtered off and
washed with water and recrystallised from ethanol (yield:
95%).
Elemental analysis. Calcd for C22H28N2O3: C, 71.71;
H, 7.66; N, 7.90, found: C, 71.51; H, 7.29; N, 7.81. FT-IR
(KBr pellet) ymax (cm21): 3409 (ZOH), 3015 (ZCH3),
2919, 2854 (ZCH2Z), 1706 (acid-CvO), 1475
(ZCvCZ) aromatic, 1421 (ZNvNZ), 1252, 1178
1
(ZOCH2Z). H NMR (CDCl3,), d (ppm): 8.09 (d, 2H,
J ¼ 8.5 Hz, ArH), 7.82 (d, 4H, J ¼ 9.9 Hz, ArH), 7.01 (d,
2H, J ¼ 8.4 Hz, ArH), 4.12 (t, 2H, J ¼ 7.2 Hz, ZOCH2),
1.71–1.79 (q, 2H, ZCH2), 1.43–1.48 (q, 2H, ZCH2),
1.31–1.33 (m, 4H, ZCH2), 0.91 (t, 3H, J ¼ 7.6 Hz,
ZCH3). 13C NMR (CDCl3) d (ppm): 168.4. 162.6, 154.4,
146.2, 136.1, 132.7, 123.4, 121.9, 116.8, 115.6, 113.4,
68.2, 32.1, 29.2, 28.6, 25.6, 22.5, 13.4.
2.2.2. Synthesis of 4-(40-(10-decyloxy)
phenylazo)benzonitrile (2a)
2.2.4. Synthesis of 1,2 bis4-(4-(10-
decyloxy)phenylazo)benzoylhydrazine (4)
The compound 4-(40-(10-decyloxy)phenylazo)benzonitrile
was synthesised by suspension of 4-(40-hydroxyphenyla-
zo)benzonitrile (0.01 mol), anhydrous K2CO3 (0.02 mol)
and a pinch of potassium iodide (KI) in dry dimethylfor-
mamide (DMF) (80 ml). 1-Bromodecane (0.01 mol) was
added dropwise to the reaction mixture and refluxed at
908C for 24 h. Upon completion of the reaction, the
mixture was filtered and washed with excess of DMF. The
filtrate was poured into ice water, extracted using diethyl
ether and dried with anhydrous sodium sulphate. The
solvent was evaporated under reduced pressure and
purified by column chromatography over silica gel using
chloroform as an eluent. Thus, an orange-coloured solid
was obtained with 75% yield.
4-(40-(10-Decyloxy)phenylazo)benzoic acid (3.8 g,
0.01 mol) was dissolved in benzene (50 ml) in the presence
of one drop of dimethylformamide before thionyl chloride
(1 ml; 0.015 mol) was added dropwise to the reaction
mixture. The mixture was refluxed for 2 h with constant
stirring. The benzene and excess thionyl chloride were
removed under vacuum whereupon 4-(40-(10-decyloxy)-
phenylazo)benzoylchloride was formed. It was dissolved
in 100 ml dry tetrahydrofuran (THF) and added to the
solution of hydrazine hydride (0.25 ml, 0.005 mol) in THF.
Dry triethylamine (1.7 ml, 0.012 mol) was added and the
reaction was carried out for 12 h. The precipitated
triethylamine hydrochloride was removed by filtration
and the precipitate was washed with THF. The filtrate was
evaporated under reduced pressure and purified by column
chromatography over silica gel using a mixture –of
ethylacetate–hexane (1:5) as an eluent that afforded the
red-coloured solid (yield 87%).
Elemental analysis. Calcd for C22H27N3O: C, 75.61;
H, 7.79; N, 12.02, found: C, 75.58; H, 7.81; N, 12.11. FT-
IR (KBr pellet) ymax (cm21): 3011 (ZCH3), 2921, 2848
(ZCH2Z), 2233 (ZCN), 1648, 1475 (ZCvCZ) aromatic,
1421 (ZNvNZ), 1252, 1111 (ZOCH2Z). 1H NMR
(CDCl3,), d (ppm): 8.42 (d, 2H, J ¼ 8.5 Hz, ArH), 7.88 (d,
4H, J ¼ 9.9 Hz, ArH), 7.21 (d, 2H, J ¼ 8.6 Hz, ArH),
4.56 (t, 2H, J ¼ 7.2 Hz, ZOCH2), 1.72 (q, 2H, ZCH2),
1.81 (q, 2H, ZCH2), 1.64 (m, 2H, ZCH2), 1.56 (m, 2H,
ZCH2), 1.41 (m, 2H, ZCH2), 1.37 (m, 2H, ZCH2), 0.95 (t,
3H, J ¼ 7.6 Hz, ZCH3). 13C NMR (CDCl3) d (ppm):
161.7, 155.1, 146.1, 133.6, 122.2, 117.1, 114.0, 113.1,
67.8, 32.1, 29.1, 28.3, 25.1, 19.4, 14.0.
Elemental analysis. Calcd for C46H60N6O4: C, 72.60;
H, 7.95; N, 11.04, found: C, 72.58; H, 7.92; N, 11.53. FT-
IR (KBr pellet) ymax (cm21): 3439 (ZNH), 2915,
2849(ZCH2Z), 1600 (ZCvO), 1497(ZCvCZ) aro-
matic, 1415 (ZNvNZ), 1197 (ZOCH2Z). 1H NMR
(CDCl3,), d (ppm): 10.52 (s, 1H, ZNH), 10.34 (s, 1H,
ZNH), 7.94–7.98 (m, 8H, J ¼ 9.8 Hz, ArH), 7.79 (d, 4H,
J ¼ 8.5 Hz, ArH), 7.02 (d, 4H, J ¼ 8.0 Hz, ArH), 4.05 (t,
4H, J ¼ 6.8 Hz, ZOCH2), 1.81–1.84 (q, J ¼ 7.6 Hz, 4H,
ZCH2), 1.28–1.38 (m, 28H, ZCH2), 0.88 (t, 6H,
J ¼ 7.6 Hz, ZCH3). 13C NMR (CDCl3,), d (ppm):
162.8, 154.8, 146.7, 133.4, 128.0, 125.4, 125.2, 123.0,
122.8, 118.6, 114.8, 113.9, 113.1, 68.5, 31.8, 29.5, 29.3,
29.1, 26.0, 22.6, 14.0.
2.2.3. Synthesis of 4-(40-(10-decyloxy)phenylazo)
benzoic acid (3a)
A mixture of 4-(40-(7-decyloxy)phenylazo)benzonitrile
(0.05 mol), potassium hydroxide (0.1 mol) and ethanol

Supramolecular Chemistry
2.3. Preparation of hydrogen-bonded complexes
427
All hydrogen-bonded complexes were prepared by dissol-
ution method. The compound 4 reacted with carboxylic acid
in a molar ratio of 1:2 in the presence of distilled pyridine.
The solution was stirred for 3 h at room temperature and the
pyridine was allowed to slow evaporation, and the resulting
solid was dried in vacuum for 24h.
3. Results and discussion
Benzoylhydrazine-based azobenzene compound 4 was
first synthesised and was subsequently used to form two
series of hydrogen-bonded complexes. The first series
consist of non-liquid crystalline compound 4 complexed
with non-liquid crystalline carboxylic acid derivatives
such as benzoic acid (a), 2,6-difluorobenzoic acid (b), 4-
chloro-2-fluorobenzoic acid (c), 4-methoxyphenylacetic
acid (d) and 4-nitrobenzoic acid (e). However, the second
series consists of a non-liquid crystalline compound 4
complexed with liquid crystalline carboxylic acid
derivatives such as 4-decyloxybenzoic acid (f), 40-
(decyloxy)biphenyl-4-carboxylic acid (g), 4-(4-(decylox-
y)benzoyloxy)benzoic acid (h), 4-(4-(decyloxy)benzyli-
Figure 1. FT-IR spectra of (i) benzoic acid; (ii) compound 4 and
(iii) hydrogen-bonded complexes 4a.
compound 4 is presumed to be due to the spinning of the
rod around the long axis suppressed by the lateral
intermolecular H-bonding, which has destabilised the
liquid crystal phase but stabilised the crystalline state. In
addition, the intermolecular interaction between the layers
increases the rigidity. The carboxylic acid derivatives are
then introduced as a dopant to compound 4, which reduces
the molecular rigidity via the intermolecular reorganis-
ation (Figure 3) (16). A noteworthy feature of this study is
that both compound 4 and carboxylic acids (a–e) are non-
mesogenic, but the resulting complexes exhibit meso-
morphic properties. The complex 4a shows SmA and N
phases on heating and cooling cycles (Figure 4(a),(b)). On
cooling from the isotropic phase, the N phase formed at
102.48C and further cooling gave the SmA at 86.58C. Both
deneamino)benzoic
acid
(i)
decyloxy)phenylazo)benzoic acid (j).
and
4-(40-(10-
The FT-IR spectra of compound 4 and its complexes
4a–4j were recorded and analysed. Figure 1 shows the
comparison of the FT-IR spectra of benzoic acid, compound
4 and its complex 4a. The benzoic acid prefers to form an
acid dimer that exhibits a broad OZH absorption band at
2200–3400 cm21 and the CvO stretching band at
1686 cm21. However, the FT-IR spectrum for the hydro-
gen-bonded complex 4a showed the disappearance of the
broad band at 2200–3400 cm21, suggesting the absence of
dimerisation of carboxylic acid (OZH· · ·OvC) in the
complexes. This observation indicates the formation of
intermolecular H-bonding between the compound 4 and
benzoic acid. The absorption bands of CvO group in the
respective compound 4 and benzoic acid can be observed
at 1600 and 1686 cm21. The CvO absorption frequency
for compound 4a is found to be identical with that
observed in benzoic acid. This can probably be attributed
to the presence of identical hydrogen bonding within the
respective benzoic acid and compound 4a. Figure 2
illustrates the intramolecular H-bonding of these mol-
ecules which resemble the dimerisation of carboxylic acid
(14). On the other hand, the absorption band ascribed to
NZH stretching vibration is shifted from 3445 to
3439 cm21, suggesting the formation of the hydrogen
bond between NZH and OvC groups.
OC
H
10 21
(b)
N
N
H
O
H
N
O
N
N
O
H
O
H
O
N
(a)
O
O
H
O
O
O
H
The phase sequence, transition temperatures and the
associated enthalpies of the compound 4 and its complexes
are summarised in Table 1. The compound 4 has a sharp
melting point at 104.78C. The absence of mesophase in
OC
H
10 21
Figure 2. Intermolecular hydrogen bonds in (a) benzoic acid
and (b) complex 4a.

428
Table 1. Phase transition temperatures (8C) and enthalpies [J g21] for series 1.
Phase transition behaviour
Cooling
G.-Y. Yeap et al.
Complex
Heating
4
Cr 104.7 [91.7] I
Cr 89.4 [99.2] SmA 98.2 [15.3] N 103.0 [14.8] I
Cr 98.6 Nc 108.5 [93.0] I
I 83.6 [86.2] Cr
4a
4b
4c
4d
4e
I 102.4a N 86.5 [20.5]b SmA 67.2 [74.1] Cr
I 106.5a N 91.6 [2.0] SmA 82.8 [84.2] Cr
I 88.9a N 76.0 [72.3] Cr
Cr 93.6 Nc 95.5 [83.7] I
Cr 79.4 [88.7] N 96.3 [42.1] I
Cr 101.9 Nc 104.6 [97.4] I
I 80.3 [38.7] N 62.4 [83.6] Cr
I 100.9 [4.2] N 96.6a SmA 79.6 [86.3] Cr
Notes: Phase transition temperatures were determined by DSC thermogram. Cr, crystal; N, nematic; SmA, smectic A; I, isotropic phase.
a Phase transition was observed by POM and weak transition was detected by DSC in which the enthalpy change was not observed.
b Two transitions such as I–N and N–SmA enthalpies are combined.
c Phase transition was merely observed by POM wherein the mesophase range is very short that could not be detected by DSC.
the transitions I–N and N–SmA are very close to each
other and hence the values of enthalpy changes are
combined as 20.5 J g21 (Figure 5). Complex 4b exhibits N
phase on heating, whereas on cooling it shows N and SmA
phases. On heating, however, the N phase was observed by
Polarized optical microscopy (POM) on very slow heating
rate (28C min21). It possesses very short temperature range
associated with N phase, and hence the phase transition
could not be detected by Differential scanning calorimetry
(DSC). Complexes 4c and 4d display N phase on heating
and cooling cycles. The low N-phase stability for complex
4c is found to be similar to the phenomenon that occurred
in complex 4b. This has again hindered us from using DSC
to detect the phase transition N–I. This phenomenon can
also be inferred from complex 4e which exhibits short N-
phase stability on heating whereas on cooling it exhibits
schlieren N and focal-conic fan texture of SmA (Figure
4(c),(d)). The I–N transition was observed at 100.98C with
very low enthalpy of 4.2 J g21. Although the phase
transition from N to SmA is observed at 96.68C, the
enthalpy value could not be detected by DSC. On further
cooling, it crystallised at 79.68C.
O
H
R
O
N
HO
R
O
H
H
O
N
N
O
N
N
O
N
H
O
H
O
H
H
O
N
N
O
O
H
O
H
O
R
H
Non–LCs
LCs
Figure 3. A diagrammatic representation for the segregation of non-liquid crystalline molecules into mesomorphic complexes by
carboxylic acid dopant.

Supramolecular Chemistry
429
Figure 4. Photomicrographs showing (a) N phase at 98.48C in complex 4a, (b) SmA phase at 82.08C in complex 4a, (c) N phase at
99.08C in complex 4e and (d) SmA phase at 84.58C in complex 4e.
Table 2. Phase transition temperatures (8C) and enthalpies [J g21] for series 2.
Phase transition behaviour
Complex
Heating
Cooling
4f
Cr 82.6 [77.1] SmA 121.6 [26.9] I
I 118.2 [23.6] SmA 79.8 [67.5] I
4 g
4 h
4i
Cr 79.2 [80.8] SmA 101.9c N 115.8 [14.6] I
Cr 62.5 [76.9] SmA 142.1 [25.5] N 177.6 [16.7] I
Cr 98.9 [106.1] N 210.0 [35.6] I
I 112.5 [10.3] N 99.9 [2.1] SmA 77.0 [63.1] Cr
I 174.3 [15.6] N 140.7 [23.1] SmA 60.5 [70.8] Cr
I 201.1 [27.9] N 90.7 [96.1] I
4j
Cr 78.4 [20.1] Cr1 116.2 [48.6] Col 141.3 [28.5] I
I 138.4 [20.1] Col 113.6 [42.6] Cr175.0 [16.8] Cr
Notes: Phase transition temperatures were determined by DSC thermogram. Cr, Cr1, crystal; N, nematic; SmA, smectic A; Col, columnar; I, isotropic
phase.
The polarising optical microscopy and DSC thermo-
gram are employed to study the thermal behaviour of the
complexes 4f–4j. Table 2 gives the transitional
temperature and the associated enthalpies of series 2
complexes. These complexes are obtained from the
reactions of non-liquid crystalline compound 4 with liquid
crystalline carboxylic acid derivatives f–j. Moreover, the
terminal chain length of the carboxylic acid was
maintained as alkyl chain (C10H21). All the complexes
exhibit enantiotropic mesomorphism. The complex 4f
shows focal conic SmA phase (Figure 6(a)). On cooling
from the isotropic phase, SmA phase is developed at
118.28C and crystallised at 79.88C. The compounds 4 g
and 4 h exhibit dimesomorphism of N and SmA. The
complex 4 g exhibits schlieren N phase at 112.58C on
cooling from isotropic phase, followed by the focal-conic
Figure 5. DSC thermogram of complex 4a.
SmA that can be observed at 99.98C (Figure 6(b)) prior to

430
G.-Y. Yeap et al.
Figure 6. Photomicrographs showing (a) SmA phase at 98.48C in complex 4f, (b) SmA phase at 82.08C in complex 4g, (c) N phase at
99.08C in complex 4h and (d) N phase at 84.58C in complex 4i.
crystallisation at 77.08C. Complex 4 h exhibits N phase at
174.38C (Figure 6(c)). On further cooling, SmA phase
observed at 140.78C and it possesses large smectic phase
temperature range (DTSmA ¼ 80.28C). As for complex 4i,
it possesses very high N-phase stability (DTN ¼ 110.48C)
on cooling (Figure 6(d)).
proposed columnar phase, the X-ray diffraction (XRD)
study was carried out on complex 4j. The XRD pattern (1D
and 2D) was shown in Figure 8(a),(b) (at 1408C upon
cooling). The molecular arrangement of the rectangular
columnar phase in complex 4j is depicted in Figure 8(c) of
which the d1 ¼ 4.36 nm (2u ¼ 1.88) and d2 ¼ 3.41 nm
(2u ¼ 2.218) are the long and short axes of Colr phase,
respectively, and l ¼ 0.5 nm (2u ¼ 15.48) is the lateral
molecular distance (11, 18). The present complex 4j that
possesses four azo linkages favours the disc-shaped
arrangement as that reported for nicotinic acid derivatives
(19). This observation has strongly implied that the
One of the remarkable features can be ascribed to the
presence of discotic columnar phase as shown by complex
4j (Figure 7(a),(b)). On cooling from the isotropic phase,
complex 4j shows dendritic growth aggregation of a
discotic columnar phase (bright) from the isotropic melt
(dark) at 138.48C (17). To establish the nature of the
Figure 7. Photomicrographs showing columnar phase in complex 4j at (a) 99.08C and (b) 82.58C.

Supramolecular Chemistry
431
Figure 8. (a) One-dimensional XRD pattern of complex 4j upon cooling, (b) 2D XRD patterns of complex 4j upon cooling (at 1308C)
and (c) a schematic diagram of the molecular arrangement in the rectangular column phase.
(b) Hoogenboom, R.; Fournier, D.; Schubert, U.S. Chem.
Commun. 2008, 155–162.
(3) Niori, T.; Sekine, T.; Watanabe, J.; Furukawa, T.; Takezoe,
H. J. Mater. Chem. 1996, 6, 1231–1233.
presence of azo linkage plays a key role in the formation of
columnar phase.
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1161; (b) Nakade, H.; Jordan, B.J.; Srivastava, S.; Xu, H.;
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(10) Gayathri, K.; Balamurugan, S.; Kannan, P. J. Chem. Sci.
2011, 123, 255–263.
(11) Chen, W.H.; Chuang, W.T.; Jeng, U.S.; Sheu, H.S.; Lin,
H.C. J. Am. Chem. Soc. 2011, 133, 15674–15685.
(12) (a) Ruben, M.; Payer, D.; Landa, A.; Comisso, A.;
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4. Conclusion
Intermolecular H-bonded non-liquid crystalline compound
1,2-bis[4-(4-(10-decyloxy)phenylazo)]benzoylhydrazine
(4) and its complexes were synthesised. The thermal and
optical behaviours were analysed by DSC and POM. It has
been claimed that the restricted motion of the molecular
spinning suppressed the liquid crystalline properties of
compound 4. The intermolecular hydrogen-bonded sites
within compound 4 are found to be deteriorated through
the addition of carboxylic acid. It is noteworthy that, in the
first series, the non-liquid crystalline compound 4
complexed with non-liquid crystalline carboxylic acid
derivatives a–e leading to liquid crystalline complexes.
Similarly, in second series, the non-liquid crystalline
compound 4 and liquid crystalline carboxylic acid
derivatives f–j enabled the formation of liquid crystalline
complexes. Generally, the ultimate complexes exhibited N
and SmA phases except complex 4j that showed
predominantly columnar phase.
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46, 4691–4703.
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Int. Ed. 2006, 45, 38–68; (b) Sagara, Y.; Kato, T. Supramol.
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(18) Wang, L.Y.; Chiang, I.H.; Yang, P.-J.; Li, W.S.; Chao, I.T.;
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(19) Saravanan, C.; Ambili, V.; Kannan, P. React. Funct. Polym.
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Acknowledgements
The main author (G.-Y. Yeap) would like to thank Malaysian
Ministry of Higher Education (MOHE) for the Fundamental
Research Grant Scheme (FRGS) No. 203/PKIMIA/6711265.
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