Synthesis and liquid crystal property of new fluoro coumarin carboxylates

Article abstract of DOI:10.1080/15421406.2012.704824

New liquid crystalline 4-alkoxyphenyl-coumarin-3-carboxylates 6a-e, 7a-g, 8a-e, and 9a-e were prepared by reacting various coumarin-3-carboxylic acids 5a-d with 4-(alkoxy) phenols 4a-g in the presence of 1(3-dimethylaminopropyl-3- ethylcarbodiimide/dimethyl amino pyridine (EDCI/DMAP) as a coupling agent. The structures of the new coumarin derivatives were confirmed by spectral analysis and the liquid crystalline property was established by polarizing optical microscope and by differential scanning calorimetric techniques. The diethyl amine and morpholine were taken as electron-donating and -CF₃ as electron-withdrawing groups at the seventh position of the coumarin-3-carboxylic acids to check the mesomorphic property in all new 4-alkoxyphenyl-coumarin-3- carboxylates. Among them, only 4-alkoxyphenyl-7-triflouromethyl-coumarin-3- carboxylates 7a-g exhibited liquid crystalline SmA phase.

Full text of DOI:10.1080/15421406.2012.704824

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Synthesis and Liquid Crystal Property of
New Fluoro Coumarin Carboxylates
a
a
Kittappa M. Mahadevan , Hosanagara N. Harishkumar , Jagadeesh
a
b
N. Masagalli & Hosapalya T. Srinivasa
a
Department of Post Graduate Studies and Research in
Chemistry, School of Chemical Sciences , Kuvempu University ,
Shankaraghatta , Karnataka , India
b
Raman Research Institute , Bangalore , Karnataka , India
Published online: 22 Jan 2013.
To cite this article: Kittappa M. Mahadevan , Hosanagara N. Harishkumar , Jagadeesh N.
Masagalli & Hosapalya T. Srinivasa (2013) Synthesis and Liquid Crystal Property of New
Fluoro Coumarin Carboxylates, Molecular Crystals and Liquid Crystals, 570:1, 20-35, DOI:
10.1080/15421406.2012.704824
To link to this article: http://dx.doi.org/10.1080/15421406.2012.704824
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Mol. Cryst. Liq. Cryst., Vol. 570: pp. 20–35, 2013
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.704824
Synthesis and Liquid Crystal Property of New
Fluoro Coumarin Carboxylates
1,∗
KITTAPPA M. MAHADEVAN, HOSANAGARA N.
1
1
HARISHKUMAR, JAGADEESH N. MASAGALLI,
AND HOSAPALYA T. SRINIVASA2
1Department of Post Graduate Studies and Research in Chemistry, School of
Chemical Sciences, Kuvempu University, Shankaraghatta, Karnataka, India
2
Raman Research Institute, Bangalore, Karnataka, India
New liquid crystalline 4-alkoxyphenyl-coumarin-3-carboxylates 6a–e, 7a–g, 8a–e,
and 9a–e were prepared by reacting various coumarin-3-carboxylic acids 5a–d
with 4-(alkoxy) phenols 4a–g in the presence of 1(3-dimethylaminopropyl-3-
ethylcarbodiimide/dimethyl amino pyridine (EDCI/DMAP) as a coupling agent. The
structures of the new coumarin derivatives were confirmed by spectral analysis and
the liquid crystalline property was established by polarizing optical microscope and
by differential scanning calorimetric techniques. The diethyl amine and morpholine
3
were taken as electron-donating and –CF as electron-withdrawing groups at the sev-
enth position of the coumarin-3-carboxylic acids to check the mesomorphic property in
all new 4-alkoxyphenyl-coumarin-3-carboxylates. Among them, only 4-alkoxyphenyl-7-
triflouromethyl-coumarin-3-carboxylates 7a–g exhibited liquid crystalline SmA phase.
Keywords 4-Alkoxyphenyl-coumarin-3-carboxylate; fluorinated coumarins; focal
conic texture; liquid crystal; mesophase
Introduction
Coumarin derivatives exhibit unique photochemical and photophysical properties, hence
they become useful in various applications like brightening agents [1] and organic light-
emitting diodes (LED) [2], etc. 7-(dimethylamino)-4-methyl coumarin dye doped in meso-
porous organosilica (PMO) has been reported as a light-harvesting antenna [3]. Liquid
crystalline polymers linked with coumarin moieties have been reported as a new kind of
photoalignment layer for liquid crystals in which the photodimerization of the coumarin
unit occurs by exposure to UV light, and hence the direction of orientation of the liquid
crystals could be adjusted by the polarization direction of the irradiated light [4,5].
Recently, Yanqing Tian et al. [6] have reported the cyclic tetramethyltetrasiloxanes
containing coumarin moieties for liquid crystalline property in which the thermal properties
of the cyclic tetramethyltetrasiloxanes depend on the nature of the length of the tail ester
group at the third position in coumarin moiety. Further, the addition of coumarin units into
∗
Address correspondence to Kittappa M. Mahadevan, Department of Post Graduate Studies
and Research in Chemistry, School of Chemical Sciences, Kuvempu University, Shankaraghatta
577 451, Karnataka, India. Tel.: 0091-9164621170; Fax: 0091 8282 256255. E-mail: mahadevan@
kuvempu.ac.in
20

Fluoro Coumarin Carboxylates
21
the polymer/oligomer backbones and nanostructured block copolymers were reported to
control the liquid crystal properties of the polymers [4] in which the length and position
of tail groups and spacers on the coumarin units affect the liquid crystalline properties.
Recently, Haruko Takechi et al. [7] have also studied the mesomorphic and crystalline
properties of 7-(diethyl amino)-3-phenylcoumarin-3-alkylcarboxylates. Similarly, several
coumarin derivatives have also been reported to exhibit liquid crystal properties and hence
possess many related applications [8–10].
Hence, based on our experience in the synthesis of coumarins and other heterocy-
cles [11–33] in this paper, we focused on the synthesis, characterization, and evaluation
of liquid crystal property of suitably designed 4-alkoxyphenyl-7-substituted coumarin-3-
carboxylates 6a–e, 7a–g, 8a–e, and 9a–e as a new class of compounds.
Experimental
All the chemicals used were of analytical grade. Melting points were recorded in an open
capillary and are uncorrected. Purity of the compounds were checked by TLC on silica
gel and purified by column chromatography on silica gel (230–400) mesh and as well
as by the crystallization method. The structures of newly synthesized compounds were
determined by using infrared (IR) spectroscopy (Shimadzu FTIR-8400 spectrophotometer),
1
13
H NMR, C NMR, DEPT-135 (Bruker 400 spectrometer), LC-MS, and elemental analysis
(Carlo-Erba1106 analyzer). The transition temperature and the associated enthalpy value
for all compounds were determined by using differential scanning calorimetry (DSC)
Perkin-Elmer, Model Pyris 1). The textures of mesophase were observed by using a
polarizing optical microscope (POM) (Olympus BX50) equipped with a heating stage
Mettler FP82HT) and a central processor (Mettler FP90).
(
(
A Typical Procedure for the Synthesis of 2-Oxo-2H-chromene-3-carboxylic acid-4-
octyloxy-phenylester (6a)
A mixture of coumarin-3-carboxylic acid 5a (1 g, 5.25 mmol), 1(3-dimethylaminopropyl-
3-ethylcarbodiimide. hydrochloride) (EDCI) (1.1 g, 5.78 mmol), and mole equivalent of
DMAP (dimethyl amino pyridine, 0.70 g, 5.78 mmol) were taken in dichloromethane. To
this reaction mixture, the 4-alkoxy phenol 4a (1.28 g, 5.78 mmol) was added, stirred at
room temperature for 5 h, and the progress of the reaction was monitored by TLC (ethyl
acetate: pet ether 1:1). After the completion of the reaction, the reaction mass was diluted
with water and extracted with DCM (25 mL × 2). The organic layer was washed with
saturated brine solution and dried over anhydrous sodium sulfate. The crude product (6a)
thus obtained was purified by column chromatography by using ethyl acetate: petroleum
ether (2:8) as eluent followed by recrystallization by ethanol. The 600 mg of yield was
obtained as white solid.
The synthesis of intermediate 1-(benzyloxy)-4-alkoxybenzenes 3a–g and 4-(alkoxy)
phenols 4a–g were reported in literature [36–38] and used here as key intermediates for the
synthesis of the new 4-alkoxyphenyl-coumarin-3-carboxylates 6a–e, 7a–g, 8a–e, and 9a–e
compounds to study their liquid crystal properties.
Spectroscopic Details 2-Oxo-2H-chromene-3-carboxylic acid-4-octyloxy-
phenylester (6a)
◦
◦
1
Yield: 94%; mp: 114 C–118 C; H NMR (400 MHz, DMSO-d6): δ = 9.06 (s, 1H),
.0 (dd, J = 1.20 Hz, 1.6 Hz, 1H), 7.78–7.825 (m, 1H), 7.44–7.50 (m, 2H), 7.16–7.20
8

22
K. M. Mahadevan et al.
(
(
m, 2H), 6.99–7.02 (m, 2H), 3.99 (t, J = 6.4 Hz, 2H), 1.69–1.75 (m, 2H), 1.40–1.45
13
m, 2H), 1.29–1.33 (m, 8H), 0.86–0.88 (m, 3H) ppm; C NMR (100 MHz, DMSO-d6):
1
1
1
61.84, 157.02, 156.36, 155.25, 150.65, 144.00, 135.46, 131.04, 125.46, 123.04, 118.32,
17.13, 116.73, 115.53, 68.31, 31.71, 29.21, 29.14, 26.00, 22.55, 14.43 ppm; IR(KBr): v =
−1
−1
726(aromatic C=O) cm , 1759(ester C=O) cm ; GCMS = 394.1; elemental analysis
calcd for C24H26O5 = C, 73.08, H, 6.64% Found: C, 73.66, H, 6.66%.
2-Oxo-2H-chromene-3-carboxylic acid-4-decyloxy-phenylester (6b)
◦
◦
1
Yield: 96%; mp: 98 C–101 C; H NMR(400 MHz, DMSO-d6): δ = 9.05 (s, 1H), 7.99 (d,
J = 7.60 Hz, 1H), 7.77–7.81 (m, 1H), 7.44–7.50 (m, 2H), 7.18 (d, J = 8.8 Hz, 2H), 7.0
(
d, J = 9.20 Hz, 2H), 3.98 (t, J = 6.40 Hz, 2H), 1.69–1.71 (m, 2H), 1.39–1.44 (m, 2H),
13
1
1
1
1
.27–1.35 (m, 12H), 0.87 (t, J = 6.40 Hz, 3H) ppm; C NMR (100 MHz, DMSO-d6):
61.97, 157.17, 155.44, 149.68, 143.79, 134.76, 129.71, 124.96, 122.24, 117.87, 117.72,
16.93, 115.11, 68.46, 31.90, 29.58, 29.40, 29.32, 26.05, 22.68, 14.11 ppm; IR(KBr): v =
−1
−1
728(aromatic C=O) cm , 1755(ester C=O) cm ; GCMS = 422.2; elemental analysis
calcd for C26H30O5 = C, 73.91, H, 7.16% Found: C, 73.92, H, 7.18%.
2-Oxo-2H-chromene-3-carboxylic acid-4-dodecyloxy-phenylester (6c)
◦
◦
1
Yield: 95%; mp: 89 C–92 C; H NMR(400 MHz, CDCl3): δ = 8.71 (s, 1H), 7.64–7.71
m, 2H), 7.34–7.41 (m, 2H), 7.12–7.15 (m, 2H), 6.91–6.93 (m, 2H), 3.96 (t, J = 6.4 Hz,
H), 1.74–1.80 (m, 2H), 1.47–1.43 (m, 2H), 1.27–1.35 (m, 16H), 0.88 (t, J = 6.8 Hz, 3H)
(
2
13
ppm; C NMR (100 MHz, DMSO-d6): 161.97, 157.17, 156.44, 155.45, 149.69, 143.79,
1
2
1
7
34.77, 129.71, 124.97, 122.24, 117.87, 117.71, 116.93, 115.11, 68.46, 31.92, 29.64, 29.60,
−1
9.40, 29.35, 29.38, 26.05, 22.69, 14.12 ppm; IR(KBr): v = 1728(aromatic C=O) cm ,
−1
758(ester C=O) cm ; GCMS = 450.3; elemental analysis calcd for C28H34O5 = C,
4.64, H, 7.61% Found: C, 74.65, H, 7.61%.
2-Oxo-2H-chromene-3-carboxylic acid-4-tetracyloxy-phenylester (6d)
◦
◦
1
Yield: 98%; mp: 95 C–97 C; H NMR(400 MHz, DMSO-d6): δ = 9.05 (s, 1H), 8.0 (d,
J = 8.0 Hz, 1H), 7.78–7.82 (m, 1H), 7.44–7.50 (m, 2H), 7.18 (d, J = 8.8 Hz, 2H), 7.01 (d,
J = 8.80 Hz, 2H), 3.99 (t, J = 6.40 Hz, 2H), 1.69–1.74 (m, 2H), 1.41–1.43 (m, 2H), 1.29
1
3
(
1
1
m, 18H), 0.87 (t, J = 6.0 Hz, 3H) ppm; C NMR (100 MHz, DMSO-d6): 161.98, 157.16,
56.45, 155.48, 149.70, 143.81, 134.77, 129.71, 124.97, 122.26, 117.88, 117.72, 116.94,
15.11, 68.46, 31.95, 29.64, 29.62, 29.40, 29.35, 30.38, 26.06, 22.69, 14.14 ppm; IR(KBr):
v = 1727(aromatic C=O) cm , 1759(ester C=O) cm ; GCMS = 478; elemental analysis
calcd for C30H38O5 = C, 75.28, H, 8.00% Found: C, 75.29, H, 8.01%.
−1
−1
2-Oxo-2H-chromene-3-carboxylic acid-4-octadecyloxy-phenylester (6e)
◦
◦
1
Yield: 93%; mp: 95 C–99 C; H NMR(400 MHz, CDCl3): δ = 8.71 (s, 1H), 7.64–7.71
(
m, 2H), 7.35–7.42 (m, 2H), 7.12–7.15 (m, 2H), 6.91–6.94 (m, 2H), 3.96 (t, J = 8.0 Hz,
2
H), 1.74–1.81 (m, 2H), 1.42–1.47 (m, 2H), 1.26 (m, 28H), 0.88 (t, J = 8.0 Hz, 3H) ppm;
C NMR (100 MHz, DMSO-d6): 161.96, 157.17, 156.44, 155.45, 149.68, 143.79, 134.77,
29.71, 124.96, 122.24, 117.71, 116.93, 115.10, 68.46, 31.93, 29.70, 29.61, 29.41, 29.37,
13
1
2
−1
9.28, 26.05, 22.69, 14.12 ppm; IR(KBr): v = 1726(aromatic C=O) cm , 1759(ester

Fluoro Coumarin Carboxylates
23
−1
C=O) cm ; GCMS = 534.3; elemental analysis calcd for C34H46O5 = C, 76.37, H, 8.67%
Found: C, 76.39, H, 8.68%.
2-Oxo-7-trifluoromethyl-2H-chromene-3-carboxylic acid-4-butoxy-pheynylester (7a)
◦
◦
1
Yield: 94%; mp: 190 C–191 C; H NMR (300 MHz, CDCl3): δ = 8.69 (s, 1H), 7.80 (d,
J = 8.0 Hz, 1H), 7.6 (s, 1H), 7.61 (d, 8.0 Hz, 1H), 7.12–7.16 (m, 2H), 6.91–6.95 (m, 2H),
3
.97 (t, J = 6.4 Hz, 2H), 1.74–1.81 (m, 2H), 1.46–1.54 (m, 2H), 1.00 (t, J = 7.2 Hz, 3H)
13
ppm; C NMR (100 MHz, DMSO-d6): 161.42, 157.30, 155.33, 154.92, 147.95, 143.63,
1
36.39, 136.03, 135.69, 135.39, 130.39, 124.22, 122.12, 121.47, 120.22, 120.11, 115.15,
−1
1
14.36, 31.30, 19.23, 13.83 ppm; IR(KBr): v = 1728(aromatic C=O) cm , 1757(ester
−1
C O) cm ; LCMS m/z = 406.36; elemental analysis calcd for C21H17F3O5 = C, 62.07,
H, 4.2% Found: C, 61.90, H, 4.1%.
2-Oxo-7-trifluoromethyl-2H-chromene-3-carboxylic acid-4-hexyloxy-pheynylester (7b)
◦
◦
1
Yield: 92%; mp: 166 C–170 C; H NMR (400 MHz, CDCl3): δ = 8.70 (s, 1H), 7.80 (d,
J = 8.0 Hz, 1H), 7.64 (s, 1H), 7.61 (d, J = 1.2 Hz, 1H),7.12–7.15 (m, 1H), 6.91–6.94
(
m, 2H), 3.89 (t, J = 6.80 Hz, 2H), 1.75–1.80 (m, 2H), 1.44–1.47 (m, 2H), 1.26–1.32 (m,
6
1
1
H), 0.87–0.91 (m, 3H) ppm; 13C NMR (100 MHz, DMSO-d6): 161.44, 157.20, 155.40,
55.09, 148.01, 143.59, 135.49, 136.03, 136.69, 135.44, 131.39, 125.22, 123.12, 121.37,
20.22, 120.10, 115.13, 114.68, 32.34, 19.03, 13.93 ppm; IR(KBr): v = 1726(aromatic
−1
−1
C=O) cm , 1755(ester C=O) cm ; LCMS m/z = 435(M+1); elemental analysis calcd
for C23H21F3O5 = C, 63.59, H, 4.87% Found: C, 63.52, H, 4.89%.
2-Oxo-7-trifluoromethyl-2H-chromemene-3-carboxylic acid-4-decyloxy-
phenylester (7c)
◦
◦
1
Yield: 96%; mp: 144 C–146 C; H NMR (400 MHz, CDCl3): δ = 8.69 (s, 1H), 7.80 (d,
J = 8.0 Hz, 1H), 7.64 (s, 1H), 7.61 (d, J = 8.0, 1H),7.13–7.15 (m, 1H), 6.91–6.94 (m,
1
H), 6.81(s, 2H), 3.87–3.97 (m, 2H), 1.71–1.80 (m, 2H), 1.39–1.47 (m, 2H), 1.26–1.31
13
(m, 12H), 0.87–0.91 (t, J = 6.4, 3H) ppm; C NMR (100 MHz, DMSO-d6): 161.43,
157.34, 155.36, 154.99, 147.95, 143.65, 130.42, 122.14, 121.48, 120.24, 120.12, 115.18,
1
14.44, 68.49, 31.82, 29.36, 32.25, 26.44, 22.76, 14.10 ppm; IR(KBr): v = 1725(aromatic
−1
−1
C=O) cm , 1756(ester C=O) cm ; LCMS m/z = 491(M+1); elemental analysis calcd
for C27H29F3O5 = C, 66.11, H, 5.96% Found: C, 66.10, H, 5.76%.
2-Oxo-7-trifluoromethyl-2H-chromene-3-carboxylic acid-4-dodecyloxy-
phenylester (7d)
◦
◦
1
Yield: 95%; mp: 134 C–138 C; H NMR (400 MHz, CDCl3): δ = 8.69 (s, 1H), 7.79 (d,
J = 8.40 Hz, 1H), 7.64 (s, 1H), 7.60 (d, J = 1.20 Hz, 1H), 7.11–7.14 (m, 2H), 6.91–6.94
(
m, 2H), 3.95 (t, J = 6.40 Hz, 2H), 1.75–1.82 (m, 2H), 1.42–1.48 (m, 2H), 1.27–1.37 (m,
13
1
1
1
2
6H), 0.88 (t, J = 6.8 Hz, 3H) ppm; C NMR (100 MHz, DMSO-d6): 161.41, 157.30,
55.35, 154.91, 147.98, 136.35, 136.02, 135.68, 135.35, 130.43, 124.22, 122.12, 121.47,
20.23, 120.08, 115.15, 114.38, 114.35, 68.47, 31.92, 29.64, 29.60, 29.40, 29.35, 29.26,
−1
6.04, 22.69, 14.11 ppm; IR(KBr): v = 1726(aromatic C O) cm , 1759(ester C O)
−1
cm ; elemental analysis calcd for C29H33F3O5 = C, 67.17, H, 6.41% Found: C, 67.18, H,
.43%.
6

24
K. M. Mahadevan et al.
2-Oxo-7-trifluoromethyl-2H-chromene-3-carboxylic acid-4-tetradecyloxy-
phenylester (7e)
Yield: 93%; mp: 128 C–130 C; H NMR (400 MHz, CDCl3): δ = 8.70 (s, 1H), 7.64–7.71
m, 1H), 7.34–7.41 (m, 1H), 7.13 (m, 2H), 6.90–6.93 (m, 1H), 6.81 (s, 2H), 3.89 (t,
J = 6.40 Hz, 2H), 1.72–1.78 (m, 2H), 1.41–1.45 (m, 2H), 1.26–1.31 (m, 20H), 0.88 (t,
◦
◦
1
(
13
J = 6.8 Hz, 3H) ppm; C NMR (100 MHz, DMSO-d6): 161.41, 157.17, 156.43, 155.45,
1
1
53.22, 149.68, 143,79, 134.76, 129.70, 124.96, 122.24, 117.87, 117.72, 116.94, 115.41,
15.11, 68.70, 68.46, 31.93, 29.67, 29.60, 29.42, 29.36, 26.07, 22.69, 14.12 ppm; IR(KBr):
−1
−1
v = 1727(aromatic C=O) cm , 1758(ester C O) cm ; LCMS m/z = 547; elemental
analysis calcd for C31H37F3O5 = C, 68.12, H, 6.82% Found: C, 68.15, H, 6.84%.
2-Oxo-7-trifluoromethyl-2H-chromene-3-carboxylic acid-4-hexadecyloxy-phenylester
(
7f)
◦
◦
1
Yield: 98%; mp: 124 C–127 C; H NMR (400 MHz, CDCl3): δ = 8.69 (s, 1H), 7.80 (d, J =
8
.0 Hz, 1H), 7.64 (s, 1H), 7.61 (d, J = 1.20 Hz, 1H), 7.13–7.15 (m, 2H), 6.91–6.93 (m, 2H),
.95 (t, J = 8.0 Hz, 2H), 1.75–1.80 (m, 2H), 1.42–1.49 (m, 2H), 1.26–1.34 (m, 24H), 0.88
3
(
13
t, J = 6.4 Hz, 3H) ppm; C NMR (100 MHz, DMSO-d6): 161.41, 157.30, 155.32, 154.91,
1
1
1
47.94, 143.62, 136.37, 136.03, 135.69, 135.34, 130.38, 124.21, 122.10, 121.46, 120.21,
20.11, 115.15, 114.39, 114.362, 68.47, 31.92, 26.03, 22.68, 14.10 ppm; IR(KBr): v =
−1
−1
726(aromatic C=O) cm , 1753(ester C=O) cm ; LCMS m/z = 575(M+1); elemental
analysis calcd for C33H41F3O5 = C 68.97, H, 7.19% Found: C, 68.58, H, 8.33%.
2-Oxo-7-trifluoromethyl-2H-chromene-3carboxylic acid-4-octadecyloxy-
phenylester (7g)
◦
◦
1
Yield: 94%; mp: 122 C–125 C; H NMR (400 MHz, CDCl3): δ = 8.69 (s, 1H), 7.80 (d,
J = 8.0 Hz, 1H), 7.65 (s, 1H), 7.60 (d, J = 1.20 Hz, 1H), 7.14 (d, J = 2.40, 2H), 6.92
(
d, J = 2.40, 2H), 3.95 (t, J = 6.80 Hz, 2H), 1.75–1.80 (m, 2H), 1.44–1.48 (m, 2H),
13
1
1
1
2
.26–1.34 (m, 28H), 0.88 (t, J = 6.4 Hz, 3H) ppm; C NMR (100 MHz, DMSO-d6):
61.42, 157.30, 155.33, 154.92, 147.96, 143.63, 136.03, 135.70, 130.40, 124.22, 122.12,
21.47, 120.22, 120.11, 115.15, 114.40, 68.48, 31.93, 29.70, 29.61, 29.40, 29.37, 29.26,
−1
6.04, 22.69, 14.11 ppm; IR(KBr): v = 1725(aromatic C=O) cm , 1753(ester C=O)
−1
cm ; LCMS m/z = 603(M+1); elemental analysis calcd for C35H45F3O5 = C, 69.75, H,
7
.53% Found: C, 69.77, H, 7.51%.
7-Morpholin-4yl-2-oxo-2H-chromene-3-carboxylic acid-4-octyloxy-phenyl ester (8a)
◦
◦
1
Yield: 97%; mp: 147 C–148 C; H NMR (400 MHz, CDCl3): δ = 8.61 (s, 1H), 7.46 (d,
J = 9.20 Hz, 1H), 7.10 (d, J = 2.4 Hz, 2H), 6.89–6.92 (m, 2H), 6.82 (dd, J = 2.40, 8.80 Hz,
1
H), 6.68 (d, J = 2.40 Hz, 1H), 3.94 (t, J = 6.8 Hz, 2H), 3.85 (t, J = 4.8 Hz, 4H), 3.40 (t, J =
4
.8 Hz, 4H), 1.71–1.81 (m, 2H), 1.41–1.47 (m, 2H), 1.23–1.34 (m, 8H), 0.88–0.90 (m, 3H)
13
ppm; C NMR (100 MHz, DMSO-d6): 162.70, 158.20, 157.52, 156.95, 155.66, 149.92,
1
9
44.03, 131.02, 128.71, 122.41, 116.04, 115.58, 115.04, 114.67, 111.28, 110.79, 109.65,
9.45, 68.44, 66.30, 47.03, 31.82, 29.36, 29.28, 29.24, 26.05, 22.65, 14.09 ppm; IR(KBr):
−1
−1
v = 1728(aromatic C O) cm , 1755(ester C O) cm ; GCMS = 480; elemental analysis
calcd for C28H33NO6 = C, 70.13, H, 6.94, N, 2.92% Found: C, 70.15, H, 6.96, N, 2.93%.

Fluoro Coumarin Carboxylates
25
7-Morpholin-4yl-2-oxo-2H-chromene-3-carboxylic acid-4-decyloxy-phenylester (8b)
◦
◦
1
Yield: 83%; mp: 150 C–152 C; H NMR (400 MHz, CDCl3): δ = 8.63 (s, 1H), 7.48 (d,
J = 8.80 Hz, 1H), 7.27 (s, 2H), 7.11–7.13 (m, 2H), 6.91 (t, J = 2.16 Hz, 1H), 6.69 (d, J
=
2 Hz, 1H), 3.88 (t, J = 9.72 Hz, 4H), 3.42 (t, J = 9.80 Hz, 4H), 1.79–1.82 (m, 3H),
13
1
.75–1.77 (m, 3H), 1.44–1.46 (m, 12H), 0.89 (t, J = 4.0 Hz, 3H) ppm; C NMR (100 MHz,
DMSO-d6): 149.91, 158.22, 131.02, 122.41, 115.42, 115.04, 111.27, 109.67, 115.04, 99.48,
6
8.70, 68.44, 66.31, 47.03, 31.92, 26.05, 22.69, 14.11 ppm; IR(KBr): v = 1728(aromatic
−1
−1
C=O) cm , 1759(ester C O) cm ; elemental analysis calcd for C30H37NO6 = C, 70.98,
H, 7.35, N, 2.76% Found: C, 70.99, H, 7.36%, N, 2.78%.
7-Morpholin-4yl-2-oxo-2H-chromene-3-carboxylic acid-4-dodecyloxy-phenylester (8c)
◦
◦
1
Yield: 87%; mp: 161 C–163 C; H NMR (400 MHz, CDCl3): δ = 8.62 (s, 1H), 7.48 (d,
J = 9.20 Hz, 1H), 7.13 (d, J = 4.00 Hz, 2H), 6.92 (d, J = 4.40 Hz, 2H), 6.83 (d, J = 4.80 Hz,
2
3
1
3
H), 3.88 (t, J = 5.20 Hz, 4H), 3.42 (t, J = 4.80 Hz, 4H), 1.75–1.80 (m, 3H), 1.46–1.50 (m,
13
H), 1.42–1.46 (m, 16H), 0.89 (t, J = 1.20 Hz, 3H) ppm; C NMR (100 MHz, DMSO-d6):
58.19, 156.94, 149.86, 131.00, 122.40, 115.02, 111.24, 109.66, 99.47, 68.44, 66.31, 47.04,
1.93, 29.70, 29.41, 29.36, 26.05, 22.69, 14.12 ppm; IR(KBr): v = 1726(aromatic C=O)
−1
−1
cm , 1758(ester C O) cm ; GCMS = 535; elemental analysis calcd for C32H41NO6 =
C, 71.75, H, 7.71, N, 2.61% Found: C, 71.79, H, 7.72, N, 2.62%.
7-Morpholin-4yl-2-oxo-2H-chromene-3-carboxylic acid-4-tetradecyloxy-
phenylester (8d)
◦
◦
1
Yield: 89%; mp: 142 C–145 C; H NMR (400 MHz, CDCl3): δ = 8.63 (s, 1H), 7.48 (d,
J = 8.8 Hz, 1H), 7.12 (d, J = 2.4Hz, 2H), 6.92 (d, J = 2.4 Hz, 1H), 6.9 (s, 1H), 6.83
(
3
d, J = 4.0 Hz, 2H), 3.90 (t, J = 6.8 Hz, 4H), 3.40 (t, J = 6.4 Hz, 4H), 1.75–1.79 (m,
13
H), 1.46–1.50 (m, 23H), 0.90 (t, J = 1.20 Hz, 3H) ppm; C NMR (100 MHz, DMSO-
d6): 162.71, 156.86, 149.91, 144.03, 131.02, 128.74, 122.44, 116.04, 115.58, 115.04, 0.69,
1
11.30, 110.80, 109.65, 46.69, 44.67, 32.47, 47.04, 31.87, 29.38, 29.28, 29.36, 26.05, 22.69,
−1
−1
1
4.11 ppm; IR(KBr): v = 1726(aromatic C=O) cm , 1758(ester C O) cm ; elemental
analysis calcd for C34H45NO6 = C, 72.44, H, 8.05, N, 2.48% Found: C, 72.45, H, 8.06, N,
2.49%.
7-Morpholin-4yl-2-oxo-2H-chromene-3-carboxylic acid-4-octadecyloxy-
phenylester (8e)
◦
◦
1
Yield: 95%; mp: 150 C–154 C; H NMR (400 MHz, CDCl3): δ = 8.61 (s, 1H), 7.47 (d,
J = 8.8 Hz, 1H), 7.11 (dd, J = 2.40, 6.80 Hz, 2H), 6.90 (dd, J = 2.00, 6.80 Hz, 2H), 6.84
(
4
d, J = 2.4 Hz, 1H), 6.69 (d, J = 2.4 Hz, 1H), 3.95 (t, J = 6.4 Hz, 4H), 3.42 (t, J = 4.8 Hz,
H), 1.74–1.80 (m, 2H), 1.42–1.47 (m, 2H), 1.26–1.32 (m, 30H), 0.88 (t, J = 6.4 Hz, 3H)
13
ppm; C NMR (100 MHz, DMSO-d6): 158.21, 156.95, 149.89, 131.0, 122.41, 115.03,
1
11.26, 109.67, 99.48, 68.44, 66.31, 47.04, 31.93, 26.05, 22.69, 14.12 ppm; IR(KBr): v =
−1
−1
1
728(aromatic C=O) cm , 1753(ester C O) cm ; LCMS m/z = 620(M+1); elemental
analysis calcd for C38H53NO6 = C, 73.63, H, 8.62, N, 2.26% Found: C, 73.65, H, 8.64, N,
.27%.
2

26
K. M. Mahadevan et al.
7-Diethylamino-4yl-2-oxo-2H-chromene-3-carboxylic acid-4-octyloxy-phenylester (9a)
◦
◦
1
Yield: 97%; mp: 108 C–112 C; H NMR (400 MHz, CDCl3): δ = 8.58 (s, 1H), 7.39 (d, J =
.20 Hz, 1H), 7.11 (dd, J = 2.40, 6.80 Hz, 2H), 6.90 (dd, J = 2.00, 6.80 Hz, 2H), 6.63 (dd,
J = 2.40, 9.00 Hz, 1H), 6.50 (d, J = 2.40 Hz, 1H), 3.95 (t, J = 6.80 Hz, 2H), 3.44–3.46 (m,
H), 1.76–1.81 (m, 2H), 1.43–1.47 (m, 2H), 1.32–1.34 (m, 14H), 0.90 (t, J = 3.20 Hz, 3H)
9
4
13
ppm; C NMR (100 MHz, DMSO-d6): 163.14, 158.79, 158.05, 156.83, 153.24, 150.09,
1
2
1
=
44.20, 131.32, 122.52, 114.99, 109.68, 107.95, 107.81, 96.80, 68.42, 45.17, 31.82, 29.37,
−1
9.30, 29.24, 26.05, 22.66, 14.10, 12.45 ppm; IR(KBr): v = 1728(aromatic C=O) cm ,
−1
757(ester C O) cm ; LCMS m/z = 466(M+1); elemental analysis calcd for C28H35NO5
C, 72.23, H, 7.58, N, 3.01% Found: C, 72.24, H, 7.59, N, 3.03%.
7-Diethylamino-4yl-2-oxo-2H-chromene-3-carboxylic acid-4-decylo-phenylester (9b)
◦
◦
1
Yield: 90%; mp: 106 C–110 C; H NMR (400 MHz, CDCl3): δ = 8.59 (s, 1H), 7.42 (d,
J = 8.8 Hz, 1H), 7.11 (d, J = 8.8 Hz, 2H), 6.91 (t, J = 8.4 Hz, 2H), 6.71–6.68 (m, 1H),
6
.55 (d, J = 1.6 Hz, 1H), 3.95 (t, J = 6.8 Hz, 2H), 3.50–3.44 (m, 4H), 1.81–1.74 (m,
13
2H), 1.47–1.42 (m, 2H), 1.32–1.24 (m, 18H), 0.878 (t, J = 6.4 Hz, 3H) ppm; C NMR
(100 MHz, DMSO-d6): 162.11, 158.77, 158.07, 156.84, 153.23, 150.08, 144.20, 131.31,
1
2
1
7
22.51, 114.97, 109.62, 107.90, 107.79, 96.77, 68.41, 45.16, 31.92, 29.70, 29.61, 29.41,
−1
9.35, 29.30, 26.05, 22.67, 14.13, 12.44 ppm; IR(KBr): v = 1726(aromatic C=O) cm ,
−1
759(ester C O) cm ; GCMS = 493.5; elemental analysis calcd for C30H39NO5 = C,
2.99, H, 7.96, N, 2.84% Found: C, 73.01, H, 7.95, N, 2.83%.
7-Diethylamino-4yl-2-oxo-2H-chromene-3-carboxylic acid-4-dodecyloxy-
phenylester (9c)
◦
◦
1
Yield: 94%; mp: 99 C–101 C; H NMR (400 MHz, CDCl3): δ = 8.69 (s, 1H), 7.79 (d,
J = 8.4 Hz, 1H), 7.64 (s, 1H), 7.60 (d, J = 8.0 Hz, 1H),7.16–7.12 (m, 2H), 6.94–6.90 (m,
2
1
1
1
1
H), 3.96 (t, J = 6.4 Hz, 2H), 3.50–3.44(m, 4H), 1.75–1.82 (m, 2H), 1.42–1.47 (m, 2H),
13
.32–1.28 (m, 22H), 0.88 (t, J = 6.8 Hz, 3H) ppm; C NMR (100 MHz, DMSO-d6): 161.42,
57.31, 155.43, 154.92, 147.92, 143.62, 130.41, 122.13, 121.48, 120.24, 120.11, 115.17,
14.41, 68.49, 31.91, 29.58, 29.40, 29.31, 29.27, 26.05, 22.68, 14.11 ppm; IR(KBr): v =
−1
−1
726(aromatic C=O) cm , 1753(ester C O) cm ; GCMS = 521.2; elemental analysis
calcd for C32H43NO5 = C, 73.67, H, 8.31, N, 2.68% Found: C, 73.61, H, 8.29, N, 2.66%.
7-Diethylamino-4yl-2-oxo-2H-chromene-3-carboxylic acid-4-tetradecyloxy-
phenylester (9d)
◦
◦
1
Yield: 97%; mp: 92 C–95 C; H NMR (400 MHz, CDCl3): δ = 8.69 (s, 1H), 7.40 (d,
J = 9.20 Hz, 1H), 7.13 (d, J = 2.0 Hz, 2H), 6.91 (d, J = 2.0 Hz, 2H), 6.64 (dd, J = 2.80,
9
2
1
.00 Hz, 1H), 6.50 (m, 1H), 3.95 (t, J = 6.40 Hz, 2H), 3.41–3.50 (m, 4H), 1.77–1.79 (m,
H), 1.43–1.48 (m, 2H), 1.20–1.23 (m, 26H), 0.89 (t, J = 6.8 Hz, 3H) ppm; IR(KBr): v =
−1
−1
725(aromatic C=O) cm , 1755(ester C O) cm ; LCMS m/z = 550(M+1); elemental
analysis calcd for C34H47NO5 = C, 74.28, H, 8.62, N, 2.55% Found: C, 73.10, H, 8.61, N,
.33%.
2

Fluoro Coumarin Carboxylates
27
7-Diethylamino-4yl-2oxo-2H-chromene-3-carboxylic acid-4-octadecyloxy-
phenylester (9e)
Yield: 93%; mp: 120 C–126 C; H NMR (400 MHz, CDCl3): δ = 8.58 (s, 1H), 7.39 (d, J
8.80 Hz, 1H), 7.09–7.12 (m, 2H), 6.88–6.91 (m, 2H), 6.62 (dd, J = 2.40, 9.20 Hz, 1H),
◦
◦
1
=
6
.49 (d, J = 2.0 Hz, 1H), 3.94 (t, J = 6.40 Hz, 2H), 3.46 (q, J = 6.80 Hz, 4H), 1.74–1.79
13
(m, 2H), 1.43–1.47 (m, 2H), 1.23–1.26 (m, 34H), 0.88 (t, J = 7.20 Hz, 3H) ppm; C NMR
(100 MHz, DMSO-d6): 163.12, 158.78, 158.06, 156.83, 153.24, 150.09, 144.20, 131.33,
1
2
1
=
22.51, 114.98, 109.69, 107.91, 107.80, 96.78, 68.42, 45.17, 31.93, 29.70, 29.61, 29.42,
−1
9.36, 29.31, 26.06, 22.69, 14.12, 12.45 ppm; IR(KBr): v = 1728(aromatic C=O) cm ,
−1
753(ester C O) cm ; LCMS m/z = 606(M+1); elemental analysis calcd for C38H55NO5
C, 75.33, H, 9.15, N, 2.31% Found: C, 74.98, H, 9.16, N, 2.30%.
Results and Discussion
In this paper, we prepared a series of four different liquid crystalline 4-alkoxyphenyl-
coumarin-3-carboxylates 6a–e, 7a–g, 8a–e, and 9a–e by suitably modified synthetic path-
way as shown in Scheme 1. In Scheme 1, initially the benzylation of hydroquinone was
carried out by using benzyl chloride in the presence of dry potassium carbonate in methyl
ethyl ketone as solvent to get the desired 4-(benzyloxy)phenol 2. Further, the various
1-(benzyloxy)-4-alkoxybenzenes 3a–g were prepared by reacting compound 2 with dif-
ferent bromoalkylhalides [34] in the presence of dry potassium carbonate in acetone.
Further, the deprotection of benzyl group by hydrogenolysis [35] of compound 3 using
Pd/C in 1,4-dioxane produced 4-(alkoxy) phenols 4a–g. Finally, the required various 4-
alkoxyphenyl-coumarin-3-carboxylates 6a–e, 7a–g, 8a–e, and 9a–e were synthesized by
reacting compounds 4a–g with various coumarin-3-carboxylic acids 5a–d in the presence
EDCI/DMAP as a coupling agent (Table 1).
Scheme 1. Synthesis of 4-alkoxyphenyl-coumarin-3-carboxylates.

28
K. M. Mahadevan et al.
Table 1. Physical data of 4-alkoxyphenyl-coumarin-3-carboxylates 6a–e, 7a–g, 8a–e, and
a–e
9
Yields (%)a
94
MP C
◦
Entry
Products
6a
114–118
6
b
96
95
98
93
94
98–101
6c
6d
6e
7a
89–92
95–97
95–99
190–191
7b
7c
7d
7e
92
96
95
93
166–170
144–146
134–138
128–130
(Continued on next page)

Fluoro Coumarin Carboxylates
29
Table 1. Physical data of 4-alkoxyphenyl-coumarin-3-carboxylates 6a–e, 7a–g, 8a–e, and
9a–e (Continued)
Yields (%)a
98
MP C
◦
Entry
Products
7f
124–127
7g
94
97
122–125
8a
8b
8c
8d
8e
9a
147–148
150–152
161–163
142–145
150–154
108–112
83
87
89
95
97
(Continued on next page)

30
K. M. Mahadevan et al.
Table 1. Physical data of 4-alkoxyphenyl-coumarin-3-carboxylates 6a–e, 7a–g, 8a–e, and
9
a–e (Continued)
Yields (%)a
90
MP C
◦
Entry
Products
9b
106–110
9
c
94
97
93
99–101
9
d
e
92–95
9
120–126
aIsolated yield.
Since the present work was mainly focused on investigation of liquid crystal proper-
ties of new 4-alkoxyphenyl-coumarin-3-carboxylate derivatives, the four different types of
-alkoxyphenyl-coumarin-3-carboxylates 6a–e, 7a–g, 8a–e, and 9a–e were synthesized in
4
which the morpholine, N,N-diethyl amine, and triflouromethane were present as electron-
donating and electron-withdrawing groups on the seventh position of the coumarin moiety,
while third position carries various long-chain 4-alkoxyphenyl groups. Interestingly, in a se-
ries, only the trifluoromethane group present at the seventh position on the 4-alkoxyphenyl-
coumarin-3-carboxylates exhibited liquid crystal property as depicted in Fig. 1. All the
1
13
new compounds were characterized by the IR, H NMR, C NMR, LC-MS, and elemental
analysis.
Liquid Crystal Property
The new series of 4-alkoxyphenyl-coumarin-3-carboxylates 6a–e, 7a–g, 8a–e, and 9a–e
were studied for liquid crystal property. The liquid crystal property was confirmed by the
polarizing optical microscope. The highest electronegativity and smaller size of the fluorine
atom led to high polar and less steric effect [8]. Hence, the presence of trifluoromethane
group in compounds 7a–g provides higher values of positive dielectric anisotropy, which

Fluoro Coumarin Carboxylates
31
Figure 1. A typical focal conic texture from the isotropic phase for some selected 4-alkoxyphenyl-
◦
◦
7
-triflouromethyl-coumarin-3-carboxylates 7a at 206.1 C and 7b at 202.9 C.
could be the reason for the liquid crystalline property of 4-alkoxyphenyl-7-triflouromethyl-
coumarin-3-carboxylates 7a–g. From the results, we depicted that (Table 2) the fluorine
atoms in –CF3 effectively balance the polar effect in favor of steric factor, while sub-
stituent such as morpholine and N,N-diethyl amine present at the seventh position ex-
hibited poor polarization power that may affect the formation of liquid crystal property
in 4-alkoxyphenyl-7-CF3-coumarin-3-carboxylates. Thus, the 4-alkoxyphenyl-coumarin-
3-carboxylate containing—CF3 substituent at the seventh position was found to form liquid
crystals at various transition temperatures depending on the length of the 4-alkoxyphenyl
chain (C4 to C18) on the third position of coumarin ring as shown in Fig. 3. It was ob-
served that the liquid crystal property was reduced when chain length was increased in
which the packing layer had been disturbed significantly and hence only 4-alkoxyphenyl-
7-triflouromethyl-coumarin-3-carboxylates 7a–g exhibited liquid crystalline property.
Further, the thermal study revealed that the 4-alkoxyphenyl-7-triflouromethyl-
coumarin-3-carboxylates 7a–g showed wide thermal range of mesophase with increasing
Figure 2. DSC thermograms of some selected compounds 7a and 7b.

32

Fluoro Coumarin Carboxylates
33
Figure 3. Transition temperatures/number of carbon atoms of compounds 7a–g.
alkyl chain length as shown in Fig. 2. The smaller the chain length, the range of mesophase
was less.
In the 4-alkoxyphenyl-7-triflouromethyl-coumarin-3-carboxylates 7a–g, where n = 4
◦ ◦
7a), the crystal was melt at 190 C to form Smectic A phase, which stands up to 207 C and
(
then it changes to isotropic form. The same was reversed on cooling, in which the compound
◦
◦
7
a showed mesophase from 206 C and then it attained crystalline phase at 160 C to give a
◦
long range of transition temperatures about 53 C. The typical texture is as shown in Fig. 2.
◦
When n = 18 (7g), the crystal melts at 132 C and then attains mesophase which stands up to
◦
1
7
85 C to produce an isotropic phase. The same was observed while cooling the compound
◦
◦
g in which it showed mesophase from 184 C, and then it crystallized at 120 C to produce
long transition temperature about 65 C when compared to shorter alkoxyphenyl chain
◦
(Fig. 2). A similar thermal stability was observed for compounds containing alkoxyphenyl
chain from n = 4 to 18, respectively. The wide-range thermal stability and their enthalpy
data for selected compounds are given in Table 2.
The graphs were plotted by using phase transition temperature versus carbon number
of alkoxyphenyl groups as shown in Fig. 3.
Conclusion
A convenient approach to obtain series of 4-alkoxyphenyl-coumarin-3-carboxylates 6a–e,
7a–g, 8a–e, and 9a–e has been developed. The PMO studies strongly evidenced that all
the trifluoromethane-substituted 4-alkoxyphenyl coumarin-3-carboxylates 7a–g exhibited
SmA phases.
Acknowledgments
The authors are thankful to Mrs. K. N. Vasuda, Raman Research Institute, Bangalore for
providing DSC spectral data and Indian Institute of Science, Bangalore for spectral analysis.

34
K. M. Mahadevan et al.
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