Columnar liquid-crystalline phase from a series of symmetrical bent diphenylamine derivatives: Synthesis and characterization

Article abstract of DOI:10.1080/15421400903568146

A series of symmetrical bent-shaped materials with six alkoxy chains at the terminal position has been designed and synthesized. All except one exhibit columnar mesophase behavior. The mesomorphic properties of the compounds have been studied with the help of polaralizing optical microscopy (POM) and differential scanning colorimetry (DSC) experiments.

Full text of DOI:10.1080/15421400903568146

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Columnar Liquid-Crystalline Phase
from a Series of Symmetrical Bent
Diphenylamine Derivatives: Synthesis
and Characterization
K. C. Majumdar a , Inul Ansary a & B. Roy a
a Department of Chemistry , University of Kalyani , Kalyani, West
Bengal, India
Published online: 18 Mar 2010.
To cite this article: K. C. Majumdar , Inul Ansary & B. Roy (2010) Columnar Liquid-Crystalline Phase
from a Series of Symmetrical Bent Diphenylamine Derivatives: Synthesis and Characterization,
Molecular Crystals and Liquid Crystals, 518:1, 160-167, DOI: 10.1080/15421400903568146
To link to this article: http://dx.doi.org/10.1080/15421400903568146
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Mol. Cryst. Liq. Cryst., Vol. 518: pp. 160–167, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400903568146
Columnar Liquid-Crystalline Phase from a Series
of Symmetrical Bent Diphenylamine Derivatives:
Synthesis and Characterization
K. C. MAJUMDAR, INUL ANSARY, AND B. ROY
Department of Chemistry, University of Kalyani, Kalyani,
West Bengal, India
A series of symmetrical bent-shaped materials with six alkoxy chains at the terminal
position has been designed and synthesized. All except one exhibit columnar
mesophase behavior. The mesomorphic properties of the compounds have been
studied with the help of polaralizing optical microscopy (POM) and differential
scanning colorimetry (DSC) experiments.
Keywords Bent shape; columnar phase; diphenylamine; Schiff’s base
Introduction
Liquid crystals (LCs) formed by bent-shaped molecules represent an expanding topic
in liquid crystal research [1,2]. These materials form new smectic and two-
dimensional phases that are unlike those obtained from normal calamitic molecules
[3]. Mesophases formed by discotic liquid crystals are now well recognized as suitable
for many device applications [4,5]. Most of the discogens reported to date consist of
a flat, or nearly flat, rigid core surrounded by a number of aliphatic side chains
having binary, trigonal, tetragonal, or hexagonal symmetries [6–9].
General mesomorphic properties are a result of interplay between many
competing and=or cooperative molecular interactions, though it can be argued that
to a great extent the type of mesophase, lamellar, or columnar phases are pre-
dominantly formed by molecules having disc-like [10] or bow-like shapes [11]. In
particular, columnar phases, characterized by indefinitely long molecular columns
aggregating into two-dimensional (2D) lattices with different symmetries, are of
great of significance. This is because they allow the possibility of combining several
physical properties with the orientational control of the molecular order, self-healing
of structural defects, and ease of processability when compared to the inorganic
semiconductors or zone-refined single crystals currently used in electronic applica-
tions. The commonly observed columnar mesophases are hexagonal columnar
Address correspondence to K. C. Majumdar, Department of Chemistry, University of
Kalyani, Kalyani, West Bengal 741235, India. Tel.: þ91-33-2582-7521; Fax: þ91-33-2582-
8282; E-mail: kcm_ku@yahoo.co.in
160

Columnar Liquid-Crystalline Phase
161
(Colh), rectangular columnar (Colr), lamellar columnar (ColL), or nematic columnar
(ColN) [12]. A transition between these phases, for example, Colh ! Colr or Colh !
ColN, was occasionally observed, and these phase transitions were all related to the
temperature dependency or=and side chain length dependency of compounds. Wang
et al. [13] first synthesized a series of mesogenic derivatives based on triphenyl amine.
They observed that mesophases were side-chain dependent. Compounds with one,
two, and three side chains formed a lamellar columnar phase and compounds with
four and six side chains exhibited a hexagonal columnar phase. In our earlier
communication [14] on liquid-crystalline material based on a triphenylamine
(TPA) core we reported that tri-substitution on TPA core with a Schiff’s base linkage
resulted in columnar mesophase behavior. Recently we have also reported [15] a
homologous series of Schiff’s bases consisting of N-methyl diphenylamine moiety
at the central core with two alkoxy side-chains exhibiting temperature dependent
SmAd ! SmA2 transition. Here we report the synthesis and characterization of
bent-shaped materials based on an N-methyl diphenylamine core having six alkoxy
chains. We have also attempted to investigate the effect of number of alkoxy chains
on the mesophase behavior.
Experimental Details
Reagents and Technique
All chemicals were procured from either Sigma Aldrich Chemicals Pvt. Ltd. or
Spectrochem Pvt. Ltd. Mumbai, India. Silica gel (60–120 mesh) was used for
chromatographic separation. Silica gel G (E-Merck, India) was used for thin layer
chromotography (TLC). Petroleum ether refers to the fraction boiling between
60ꢀC and 80ꢀC. Infrared (IR) spectra were recorded on a Perkin-Elmer (India)
1
Pvt. Ltd. L 120-000A spectrometer (nmax in cmꢁ1) on KBr disks. H NMR and
13C NMR spectra were recorded with a Bruker India Scientific Pvt. Ltd. DPX-400
and Bruker DPX-300 spectrometer, respectively, using CDCl3 as a solvent and
TMS as an internal standard (d ¼ 0.00 ppm). The liquid-crystalline properties for
compounds 10a-e were established using a Nikon polarizing microscope (Nikon
Corporation, Japan) LV100POL attached with Instec hot and cold stage HCS302,
with STC200 temperature controller configured for HCS302 and the phase transi-
tions were confirmed by differential scanning calorimetry (Perkin-Elmer Diamond
DSC Pyris1 system). CHN was recorded on a 2400 series II CHN analyzer Perkin
Elmer (India) Pvt. Ltd.
Synthesis
4-40-Diformyl-N-methyldiphenylamine 3 was prepared starting from diphenylamine
1 by subsequent methylation with methyliodide, followed by Vilsmeier-Haack
reaction. 3,4,5–Trialkoxy benzoicacids (7a-e) were prepared by the reaction of ester
derivative of gallic acid 5 with long-chain alkyl bromides in the presence of
anhydrous potassium carbonate and catalytic amount of sodium iodide in refluxing
acetone for 7–9 days, followed by hydrolysis of the esters 6a-e with potassium
hydroxide in ethanol and subsequent acidification with concentrated hydrochloric
acid. The acid derivatives 7a-e were then converted into their nitro derivatives
8a-e by reacting the acid chlorides with p-nitrophenol in dichloromethane (DCM)
in the presence of triethylamine as a base and 4-dimethylamino pyridine (DMAP)

162
K. C. Majumdar et al.
Scheme 1. (i) CH3I, and anhydrous K2CO3, dry acctone, reflux, 24 h. (ii) POCI3, DMF, 90ꢀC,
4 h (iii) EtOH, conc. H2SO4, reflux, 6 h. (iv) RBr, anhydrous K2CO3, NaI, dry accetone, reflux,
5–7 days. (v) KOH, rectified spirit, reflux, 6 h, HCl. (vi) SOCl2, reflux, 3 h. (vii) p-Nitrophenol,
DMAP, NEt3 dry CH2Cl2, r.t., overnight. (viii) H2-Pd=C, EtOAc, r.t., overnight. (ix) Dry
EtoH, AcOH, reflux, 3–6 h.
as a catalyst. The nitro derivatives 8a-e on hydrogenation give the corresponding
amine derivatives 9a-e. The condensation between aldehyde 3 and amines 9a-e give
corresponding Schiff’s base derivatives 10a-e (Scheme 1).
Substrate 3 and 9a-e were Prepared According to the Published Procedure [14,15].
General Procedure for the Preparation of Compounds 10a-e by Schiff’s base
Formation. Compound 3 (0.209 m.mol) was dissolved in dry hot ethanol (3 mL)
and a catalytic amount of glacial acetic acid was added. To this solution amine
derivatives 9a-e (0.418 m.mol) dissolved in dry hot ethanol (5 mL) were added
drop-wise. After 4–6 h a yellowish-brown gummy material separated out, which
was filtered in hot condition and washed thrice with hot ethanol (3 ꢂ 5 mL) to
give a solid compound 10a-e as a pure one.
Compound 10a. Yield 90% (pale yellow solid); IR nmax 2905, 1720, 1585,
1
1494 cmꢁ1; H NMR (300 MHz, CDCl3): dH 0.86–1.86 (m, 114H), 3.47 (s, 3H),
4.05 (t, 12H, J ¼ 4.5 Hz), 7.17–7.29 (m, 12H), 7.42 (s, 4H), 7.85 (d, 4H, J ¼ 8.7 Hz),
8.43 (s, 2H); 13C NMR (100 MHz, CDCl3): dC 14.14, 22.71, 26.10, 29.38, 29.60,
29.76, 30.37, 31.95, 40.13, 69.27, 73.59, 108.55, 120.41, 121.84, 122.38, 123.91,
130.28, 142.99, 148.94, 150.66, 152.98, 159.63, 165.19. Anal. Calcd. for
C101H151N3O10: C, 77.40; H, 9.71; N, 2.68. Found: C, 77.60; H, 10.01; N, 2.78%.

Columnar Liquid-Crystalline Phase
163
Compound 10b. Yield 85% (pale yellow solid); IR nmax 2910, 1720, 1580,
1
1488 cmꢁ1; H NMR (400 MHz, CDCl3): dH 0.85–2.15 (m, 138H), 3.43 (s, 3H),
4.02 (t, 12H, J ¼ 5.28 Hz), 7.16–7.30 (m, 12H), 7.40 (s, 4H), 7.83 (d, 4H, J ¼ 8.56 Hz),
8.41 (s, 2H); 13C NMR (100 MHz, CDCl3): dC 14.13, 22.71, 26.10, 29.38, 29.41,
29.60, 29.66, 29.76, 30.36, 31.95, 40.13, 69.27, 73.59, 108.55, 120.41, 121.84,
122.38, 123.91, 130.27, 142.99, 148.93, 150.66, 152.97, 159.65, 165.19. Anal. Calcd.
for C113H175N3O10: C, 78.20; H, 10.16; N, 2.42. Found: C, 78.43; H, 10.41; N, 2.73%.
Compound 10c. Yield 80% (pale yellow solid); IR nmax: 2911, 1722, 1578,
1
1490 cmꢁ1; H NMR (400 MHz, CDCl3): dH 0.85–1.84 (m, 162H), 3.43 (s, 3H),
4.02 (t, 12H, J ¼ 5.12 Hz), 7.16–7.30 (m, 12H), 7.40 (s, 4H), 7.83 (d, 4H, J ¼ 8.6 Hz),
8.41 (s, 2H); 13C NMR (100 MHz, CDCl3): dC 14.14, 22.71, 26.10, 29.32, 29.40, 29.60,
29.66, 29.69, 29.73, 29.76, 30.37, 31.95, 40.13, 69.27, 73.59, 108.55, 120.41, 121.83,
122.37, 123.90, 130.26, 142.99, 148.93, 150.65, 152.97, 159.65, 165.20. Anal. Calcd.
for C125H199N3O10: C, 78.85; H, 10.54; N, 2.21. Found: C, 79.07; H, 11.01; N, 2.23%.
Compound 10d. Yield 95% (pale yellow solid); IR nmax: 2900, 1720, 1581,
1
1495 cmꢁ1; H NMR (400 MHz, CDCl3): dH 0.85–1.84 (m, 186H), 3.46 (s, 3H),
4.02 (t, 12H, J ¼ 5.28 Hz), 7.16–7.27 (m, 12H), 7.40 (s, 4H), 7.83 (d, 4H, J ¼ 8.44 Hz),
8.41 (s, 2H); 13C NMR (75 MHz, CDCl3): dC 14.06, 22.67, 26.09, 29.35, 29.39, 29.70,
30.36, 31.92, 40.07, 69.34, 73.58, 108.73, 120.40, 121.78, 122.32, 123.95, 129.94,
130.20, 143.18, 148.96, 149.98, 150.68, 152.99, 159.53, 165.12. Anal. Calcd. for
C
137H223N3O10: C, 79.40; H, 10.85; N, 2.03. Found: C, 78.92; H, 11.10; N, 2.49%.
Compound 10e. Yield 92% (pale yellow solid); IR nmax: 2910, 1718, 1575,
1
1490 cmꢁ1; H NMR (400 MHz, CDCl3): dH 0.85–1.84 (m, 210H), 3.46 (s, 3H),
4.02 (t, 12H, J ¼ 5.0 Hz), 7.16–7.30 (m, 12H), 7.40 (s, 4H), 7.83 (d, 4H, J ¼ 8.44 Hz),
8.41 (s, 2H). 13C NMR (100 MHz, CDCl3): dC 14.14, 22.71, 25.95, 26.10, 29.32,
29.38, 29.42, 29.60, 29.66, 29.72, 29.76, 30.37, 31.95, 40.14, 69.26, 73.59, 108.54,
120.41, 121.84, 122.39, 123.90, 130.29, 142.99, 148.94, 150.65, 152.97, 159.63,
165.19. Anal. Calcd. for C149H247N3O10: C, 79.87; H, 11.11; N, 1.88. Found: C,
79.56; H, 11.21; N, 2.11%.
Results and Discussion
Mesogenic Properties
The liquid-crystalline phase transitions have been characterized by differential
scanning calorimetry (DSC) and the characterization of textures was confirmed by
viewing the birefringence of the samples between crossed polarizers in a polarizing
microscope. The clearing transition peak in DSC (from liquid crystal to isotropic
liquid phase) was somewhat broad in all samples. The phase transition temperatures
and associated enthalpy recorded from DSC studies are summarized in Table 1.
Phase types were assigned by comparison of the microscopic textures observed in
polarized light with those published for reference compounds and established trends
in thermodynamic stability [16–18]. Compound 10a did not show mesomorphic
property due to the shorter chain length at the terminal position but all the other
compounds 10b-e exhibited enantiotropic hexagonal columnar phase with decreasing
clearing temperatures as terminal chain length increased. A typical pseudo-focal
conics or fan-shaped texture was observed on both heating and cooling cycle of
the compound 10b when placed in a thin cell with a cell gap of d ¼ 5 ꢃ 0.2 mm under

164
K. C. Majumdar et al.
Table 1. Transition temperatures and associated enthalpy calculated from DSC
Thermogram
43:50m
74:97
Colh ꢁ!
ð14:73Þ
55:73
I ꢁ!
ð1:01Þ
39:50
Colh ꢁ!
ð0:21Þ
10b
10c
10d
10e
iCr ꢁ!
Cr
Cr
Cr
Cr
(0.60)j
(0.85)
(0.60)
(0.30)
n
ð0:48Þ
44:72
Cr ꢁ!
ð40:89Þ
68:40
Colh ꢁ!
ð8:73Þ
50:62
I ꢁ!
ð0:58Þ
40:47
Colh ꢁ!
ð0:29Þ
51:11
Cr ꢁ!
ð87:13Þ
66:82
Colh ꢁ!
ð2:04Þ
62:58
Colh ꢁ!
ð30:65Þ
65:80
I ꢁ!
ð1:92Þ
58:85
I ꢁ!
ð1:92Þ
41:23
Colh ꢁ!
ð77:76Þ
53:56
Colh ꢁ!
ð117:97Þ
59:43
Cr ꢁ!
ð67:41Þ
Scan rate for all the samples is 5 degrees per minute.
ꢀ
m ¼ corresponds to temperature in C.
n ¼ change in enthalpy KJmolꢁ1
.
i ¼ Cr, crystal; Colh, hexagonal columnar; I, isotropic.
j ¼ width at half height (in centimeter) on heating cycle.
Figure 1. Polarizing micrograph of all compounds (a) and (b) were taken in indium tin oxide
(ITO) coated cell with cell gap of d ¼ 5 ꢃ 0.2 mm. (c) to (f) taken in glass plate sandwiched by a
coverslip.

Columnar Liquid-Crystalline Phase
165
homogeneous planar boundary conditions (Figs. 1a and b). This type of texture is
characteristic or signature of hexagonal columnar (Colh) phases [19–21]. On the DSC
analysis, all compounds exhibited two enantiotropic transitions, crystal-to-columnar
(Cr ! Colh) and columnar-to-isotropic (Colh ! I). Other compounds 10b,c showed
the same type of characteristic texture and shape of textures is somewhat dumbbell
like in appearance (Figs. 1c–e), but compound 10d having 16 carbon terminal
trialkoxy chain showed the focal conic texture as well as dumbbell like texture,
and compound 10e showed the spherulitic texture (Fig. 1f), which is also a charac-
teristic texture of columnar mesophase [22].
Computational Details
All computational calculations have been performed by the Chem3D version 10 [23]
with Gaussian 03 Interface [24]. The geometry was optimized by the semi-empirical
AM1 method to obtain the value of dipole moment and dipolar orientation of the
molecules. The value of dipole moment was calculated for six terminal trialkoxy
chains with C6 units. The calculated dipole moment of the molecule was found to
be 2.0656 D (X ¼ 1.277204, Y ¼ ꢁ0.377771, Z ¼ 1.579031). If we suppose the Z-axis,
as the molecular axis and the maxima of dipole is along the positive Z-axis, then the
location of the dipole is along the central part of the molecule (Fig. 2). We assume
that there must be axial dipole moment in the molecule as the dipolar orientation is
along the molecular axis. The appearance of columnar phase in this bent shaped
molecule may be due to the absence of transverse dipolar moment that can stabilize
the B phases by orienting the molecules in near-neighbor antiparallel fashion. In the
case of axial dipole the near neighbor correlation cannot be established, which
disfavors the formation of banana phases.
Figure 2. The optimized structure of compound 10 having six alkoxy chains with C6 unit at
the terminals. The arrow indicates the direction of net dipole moment.

166
K. C. Majumdar et al.
Summary and Conclusions
In our earlier communications [14,15] we have confirmed that triphenylamine
(TPA)- and diphenylamine (DPA)-based molecules exhibit columnar, SmAd, and
SmA2 phases. N-Methyldiphenylamine shows a partial bilayer SmAd to bilayer
SmA2 transition as temperature is lowered when the terminal chain is monoalkoxy.
Here we report the substitution by a trialkoxy chain at the terminal of both the arms
of the bent-shaped molecule. The mesophase observed was identified as hexagonal
columnar phase except for compound 10a. The molecules (10b-e) are bent in shape
but the presence of trialkoxy terminal chains makes the difference in mesophase
behavior because it is assumed that the chains are spread all over to form a disc-
like shape.
Acknowledgments
We thank the DST (New Delhi) for financial assistance. I. A. is thankful to the
U.G.C. (New Delhi) for his fellowship.
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