Synthesis and mesomorphic properties of coumarin derivatives with chalcone and imine linkages

Article abstract of DOI:10.1016/j.molliq.2019.111920

We report here design and synthesis of two new mesogenic homologous series of coumarin derivatives consisting of chalcone and imine central linkages along with terminal n-alkoxy chain. All the compounds were synthesized and characterized by combination of elemental analysis and standard spectroscopic methods. All compounds were screened under polarising optical microscope (POM) for liquid crystalline properties, thermogram of all compounds were studied using differential scanning calorimetry (DSC) to get phase transition temperatures, enthalpy and entropy. X-ray single crystal study of n-octyloxy coumarin derivative 16 g was resolved with imine central linkage, which showed linear rod like geometry.

Full text of DOI:10.1016/j.molliq.2019.111920

Journal Pre-proof
Synthesis and mesomorphic properties of coumarin derivatives with chalcone and
imine linkages
Sunil Dutt Durgapal, Rina Soni, Shubhangi S. Soman, A.K. Prajapati
PII:
S0167-7322(19)34509-X
DOI:
https://doi.org/10.1016/j.molliq.2019.111920
MOLLIQ 111920
Reference:
To appear in: Journal of Molecular Liquids
Received Date: 10 August 2019
Revised Date: 1 October 2019
Accepted Date: 12 October 2019
Please cite this article as: S.D. Durgapal, R. Soni, S.S. Soman, A.K. Prajapati, Synthesis and
mesomorphic properties of coumarin derivatives with chalcone and imine linkages, Journal of Molecular
Liquids (2019), doi: https://doi.org/10.1016/j.molliq.2019.111920.
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Synthesis and Mesomorphic properties of coumarin derivatives with
chalcone and imine linkages
*
Sunil Dutt Durgapal, Rina Soni, Shubhangi S Soman , A. K. Prajapati
Department of Chemistry, Faculty of Science, The M. S. University of Baroda, Vadodara - 390 002, India.
*Corresponding author’s e-mail: shubhangiss@rediffmail.com
Ph. No.: +91-265-2795552
Coumarin with chalcone and imine linked n-alkoxy derivatives were synthesized for their
mesomorphic study.

Synthesis and mesomorphic properties of coumarin derivatives with
chalcone and imine linkages
*
Sunil Dutt Durgapal, Rina Soni, Shubhangi S Soman , Ashish K. Prajapati
Department of Chemistry, Faculty of Science, The M. S. University of Baroda, Vadodara - 390 002, India.
*Corresponding author’s e-mail: shubhangiss@rediffmail.com
Ph. No.: +91-265-2795552
Abstract
We report here design and synthesis of two new mesogenic homologous series of coumarin
derivatives consisting of chalcone and imine central linkages along with terminal n-alkoxy
chain. All the compounds were synthesized and characterized by combination of elemental
analysis and standard spectroscopic methods. All compounds were screened under polarizing
optical microscope (POM) for liquid crystalline properties, thermogram of all compounds
were studied using differential scanning calorimetry (DSC) to get phase transition
temperatures, enthalpy and entropy. X-ray single crystal study of n-octyloxy coumarin
derivative 16g was resolved with imine central linkage, which showed linear rod like
geometry.
Keywords: Coumarin, Chalcone, Imine, Thermotropic liquid crystals, Single crystal study
1
. Introduction
1
Liquid crystalline material contains properties of both liquid and crystal. Due to their dual
2
properties, earlier application of these materials was as liquid crystal displays. Recently,
applications of liquid crystalline material are extended to liquid crystal thermometers, optical
3
-5
storage, chemical and biological sensors. As a result of wide range of applications of liquid
crystalline materials, there is increase in need to develop new liquid crystalline materials
6
specially of thermotropic class. Design of rod like thermotropic liquid crystal material
mainly consists of phenyl rings in rigid core while alkyl chains in flexible terminal core. To
develop thermotropic liquid crystalline compounds containing heterocyclic ring is one of the
7
-9
interesting area of research. As heteroatoms present in ring not only affect type of
mesophase exhibited by molecules and its transition temperature, but also affect the other
properties of molecules including dipole moment, polarizablility, dielectric constant,
1
0
photoluminescence. Heterocyclic liquid crystalline materials have shown applications in
both photonic and electronic displays devices. Recently there are reports on such materials
1
1-12
comprising of organic compounds as well as organic-inorganic hybrids.
Chalcone linkage
has been used in liquid crystalline compounds due to its geometrical shape, thermal stability,
1

1
3-20
charge transfer property by π-bond conjugation and high photosensitivity.
Imine group is
also well explored in liquid crystalline compounds due to its stepped structure, molecular
2
1-23
linearity, ability to self-organize and property of incorporating mesophases in molecules.
Major disadvantage of imine is their inherent chemical, thermal and photo-physical
2
4
instability, which reduces its potential applications in electro-optic displays.
Coumarins are one of the largest classes of naturally occurring compounds. Coumarins
derivatives with liquid crystalline and gel properties can be seen as new type of photo cross-
2
5-26
linkable materials for their practical applications.
material chemistry as optical materials, fluorescent whiteners, fluorescent tags, laser dyes,
Coumarin derivatives have been used in
2
7-32
non-linear optical chromophores.
Position of substituents and type of substituents on
coumarin ring play very important role to overall optical properties of coumarin derivatives.
Polymeric and non-polymeric coumarin derivatives have been reported for their liquid
3
3-35
crystalline properties.
Coumarin derivatives with alkyne-, ester- and azo- linkages have
been reported and explored for their mesogenic properties (Figure 1).
Figure 1: Coumarin derivatives with liquid crystalline properties
Trivedi et al. and Dave et al. have reported coumarin ester derivatives as liquid crystalline
3
6-37
compounds.
Merlo et al. have reported alkyne linked coumarin derivative 2 with their
38
applications in solar cell. Srinivasa et al. have synthesized ethyl 7-hydroxycoumarin-3-
carboxylate derivatives 3-4 with ester linkage, which showed excellent liquid crystal
2

3
9-40
behaviour majorly smectic A (SmA) and nematic phase.
Hagar et al. have reported 7-
hydroxy-4-methyl-coumarin derivatives 5-6 with ester and azoester for mesophase study
4
1
(Figure 1).
Hereby we report synthesis of coumarin derivatives and the effect of chalcone and imine
linkages on the mesomorphic properties for thermotropic liquid crystals. The mesomorphic
properties were studied by Differential Scanning Calorimetry (DSC) and Polarising Optical
Microscope (POM). The mesomorphic behaviour of the homologous compounds with two
different linkages is rationalized based on the varying lengths of the alkyl chain.
2
. Experimental
2
.1 Material and methods
Reagent grade chemicals and solvents were purchased from commercial supplier and used
after purification. Thin-layer chromatography (TLC) was performed on silica gel F254 plates
(Merck). Acme’s silica gel (60-120 mesh) was used for column chromatographic purification.
All reactions were carried out in nitrogen atmosphere. Melting points are uncorrected and
were measured in open capillary tubes, using a Rolex melting point apparatus. IR spectra
1
were recorded as potassium bromide (KBr) pellets on Perkin Elmer RX 1 spectrometer. H-
1
3
NMR and C-NMR spectral data were recorded on Advance Bruker 400 spectrometer (400
MHz) with Deuterated chloroform (CDCl ) or Deuterated dimethyl sulfoxide (DMSO-d ) as
3
6
solvent and tetramethyl silane (TMS) as internal standard. J values are in Hz. Mass spectra
were determined by ESI-MS, using a Shimadzu LCMS 2020 apparatus. Elemental analyses
were recorded on Thermosinnigan Flash 11-12 series EA. Thermograms were recorded on
DSC (DSC-822, Mettler Toledo having Stare software). Photographs were obtained by
Polarizing optical microscope Leica DM200P attached with camera Leica DFC295 and
separate heating unit with controller Linkpad by Linkam. UV-Vis spectra were recorded on
PerkinElmer UV/Vis Spectrometer Lambda 35 with WinLab software.
2
.2 Synthesis
Synthesis of 3-acetyl-7-hydroxy coumarin (8)
To a solution of 2,4-dihydroxy benzaldehyde (15.0 g, 0.108 mol, 1.0 eq) in ethanol (50 mL)
was added ethyl acetoacetate (13.62 mL, 0.108 mol, 1.0 eq) followed by catalytic amount of
piperidine (0.1 mL). The resulting mixture was refluxed for 18 h. The completion of reaction
was checked by thin-layer chromatography (TLC). After completion of reaction, reaction
mixture was allowed to cool down to room temperature and concentrated on a rotavapor. The
viscous liquid obtained was poured into ice cold water to give solid. The solid obtained was
3

filtered, washed with water, dried and recrystallized from ethanol to give compound 8 as
4
2
green crystals. Yield: 95%; M.P. 236-238 ºC (Lit M.P. 238 ºC)
E)-7-hydroxy-3-(3-(4-hydroxyphenyl)acryloyl)-2H-chromen-2-one (10)
(
To a solution of compound 8 (1.02 g, 5.0 mmol) in ethanol (50 mL) was added 4-hydroxy
benzaldehyde (0.61 g, 5.0 mmol) and stirred for 10-15 min. To this mixture, catalytic amount
of pyrrolidine and acetic acid were added and resulting mixture was refluxed at 78-80 °C for
3
6 h. The completion of reaction was checked by TLC. After completion of reaction, the
reaction mixture was allowed to cool to room temperature (rt), concentrated on rotavapor and
poured into ice cold water to give brown solid. The crude product was filtered, washed with
water, and dried. The crude compound was purified by column chromatography using
petroleum ether:ethyl acetate (7:3) to give pure compound 10 as bright orange solid. Yield:
1
4
8%; M.P: >260 ºC; H-NMR (400 MHz, DMSO-d ): δ 6.7 (d, 1H), 6.82-6.86 (m, 3H), 7.58
6
(d, J=8.4 Hz, 2H), 7.62 (d, J=15.6 Hz, 1H), 7.62 (d, J=15.6 Hz, 1H), 7.77 (d, J=8.4 Hz, 1H),
1
3
8
.61 (s, 1H), 10.16 (s, 1H); C-NMR (100 MHz, DMSO-d ): δ ppm 102.28, 111.55, 114.60,
6
116.44, 120.81, 121.68, 126.13, 131.21, 132.79, 144.18, 148.37, 157.47, 159.56, 160.69,
1
64.35, 186.58.
Synthesis of Alkoxy Coumarin Chalcone derivatives 11a-j.
To compound 10 (1.00 mmol) in N,N-dimethyl formamide (DMF) (20 mL) was added anhy.
K CO (4.0 mmol) and stirred for 10-15 min at rt. To this alkyl halide (2.0 mmol) was added
2
3
and resulting solution was heated at 70-72 °C for 18-20 h. The completion of reaction was
monitored with TLC. After completion of reaction, mixture was cooled to room temperature
and poured into ice cold water to give solid. The solid was filtered, washed with water and
air dried. The crude compound was purified by column chromatography using pet.ether:ethyl
acetate (9:1 to 8:2) to give compounds 11a-k.
Characterization data of all even members alkyl chain derivatives.
(E)-7-Ethoxy-3-{3-[4-(ethoxy)phenyl]acryloyl}-2H-chromen-2-one (11a)
Yellow solid, Yield: 95 %; M.P: 166-168 ºC; IR (KBr): 3092, 3047, 2982, 2933, 2872, 1729,
-1 1
1
656, 1599, 1507, 1425, 1354, 1292, 1254, 1167, 1113, 1040, 918, 826, 794 cm ; H-NMR
(
400 MHz, CDCl ): δ 1.45 (t, J=7.0 Hz, 3H), 1.50 (t, J=7.2 Hz, 3H), 4.07-4.10 (q, J=7.0 Hz
3
2
H), 4.15 (q, J=7.2 Hz, 2H), 6.85 (d, J=2.4 Hz, 1H), 6.90-6.95 (m, 3H), 7.57 (d, J=8.8 Hz
H), 7.65 (d, J= 8.8 Hz, 2H), 7.86 (d, J=16.0 Hz, 1H), 7.93 (d, J=15.6 Hz, 1H), 8.60 (s, 1H);
1
1
3
C-NMR (100 MHz, CDCl ): δ ppm 14.52, 14.75, 63.65, 64.56, 100.68, 112.31, 114.16,
3
114.81, 121.42, 121.73, 127.61, 130.77, 131.25, 144.62, 148.40, 157.63, 159.96, 161.24,
4

1
64.48, 186.33; Anal. Calc. for C H O ; C, 70.51; H, 5.53; found: C, 70.68; H, 5.42 %;
22 20 5
+
ESI-MS: 365.10 [M+H] .
E)-7-Butoxy-3-{3-[4-(butoxy)phenyl]acryloyl}-2H-chromen-2-one (11b)
Yellow solid, Yield: 92 %; M.P: 132-134 ºC; IR (KBr): 3082, 3045, 2953, 2870, 1723, 1653,
(
-1 1
1
595, 1567, 1505, 1467, 1426, 1376, 1251, 1165, 1059, 991, 957, 823 cm ; H-NMR (400
MHz, CDCl ): δ 1.02-1.03 (m, 6H), 1.47-1.58 (m, 4H), 1.76-1.87 (m, 4H), 4.02 (t, J=6.6 Hz,
3
2
H), 4.08 (t, J=6.6 Hz, 2H), 6.85 (s, 1H), 6.89-6.94 (m, 3H), 7.56 (d, J=8.4 Hz, 1H), 7.64 (d,
13
J=8.4 Hz, 2H), 7.85 (d, J=15.6 Hz, 1H), 7.93 (d, J=15.6 Hz, 1H), 8.60 (s, 1H); C-NMR
100 MHz, CDCl ): δ ppm 13.81, 13.87, 19.16, 19.22, 30.90, 31.20, 67.85, 68.69, 100.68,
(
3
112.27, 114.19, 114.83, 121.36, 121.69, 127.54, 130.75, 131.23, 144.64, 148.41, 157.64,
1
59.98, 161.46, 164.69, 186.34; Anal. Calc. for C H O ; C, 74.26; H, 6.71; found: C, 74.28;
2
6
28
5
+
H, 6.55 %; ESI-MS: 421.15 [M+H] .
E)-7-(Hexyloxy)-3-{3-[4-(hexyloxy)phenyl]acryloyl}-2H-chromen-2-one (11d)
Yellow solid, Yield: 96 %; M.P: 138-140 ºC; IR (KBr): 3096, 2923, 2854, 1717, 1655, 1596,
(
-1 1
1
543, 1507, 1466, 1426, 1372, 1296, 1254, 1163, 1066, 1016, 985, 826, 720 cm ; H-NMR
(
400 MHz, CDCl ): δ 0.91-0.95 (m, 6H), 1.34-1.39 (m, 8H), 1.45-1.52 (m, 4H), 1.78-1.88 (m,
3
4
H), 4.02 (t, J=6.6 Hz, 2H), 4.07 (t, J=6.6 Hz, 2H), 6.85 (d, J=2.4 Hz, 1H), 6.90-6.94 (m,
H), 7.57 (d, J=8.8 Hz, 1H), 7.64 (d, J=8.8 Hz, 2H), 7.85 (d, J=15.6 Hz, 1H), 7.93 (d, J=16.0
3
1
3
Hz, 1H), 8.60 (s, 1H); C-NMR (100 MHz, CDCl ): δ ppm 14.06, 14.07, 22.59, 22.62,
3
2
1
1
4
5.62, 25.70, 28.86, 29.13, 31.51, 31.58, 68.17, 69.01, 100.68, 112.27, 114.20, 114.83,
21.35, 121.68, 127.54, 130.76, 131.23, 144.64, 148.41, 157.63, 159.98, 161.46, 164.69,
86.34; Anal. Calc. for C H O ; C, 75.60; H, 7.61; found: C, 75.68; H, 7.60; %; ESI-MS:
30
36
5
+
77.35 [M+H] .
(E)-7-(Octyloxy)-3-{3-[4-(octyloxy)phenyl]acryloyl}-2H-chromen-2-one (11f)
Yellow solid, Yield: 95 %; M.P: 116-118 ºC; IR (KBr): 3097, 2930, 2863, 1718, 1654, 1596,
-1 1
1
543, 1507, 1466, 1424, 1373, 1292, 1251, 1163, 1123, 1062, 985, 827 cm ; H-NMR (400
MHz, CDCl ): δ 0.90-0.92 (m, 6H), 1.31-1.36 (br s, 16H), 1.44-1.52 (m, 4H), 1.78-1.88 (m,
3
4
H), 4.01 (t, J=6.6 Hz, 2H), 4.07 (t, J=6.6 Hz, 2H), 6.85 (d, J=2.0 Hz, 1H), 6.90-6.94 (m,
H), 7.56 (d, J=8.8 Hz, 1H), 7.64 (d, J= 8.8 Hz, 2H), 7.85 (d, J=15.6 Hz, 1H), 7.93 (d, J=15.6
3
1
3
Hz, 1H), 8.60 (s, 1H); C-NMR (100 MHz, CDCl ): δ ppm 14.13, 22.67, 25.94, 26.02,
3
2
8.89, 29.16, 29.21, 29.25, 29.29, 29.35, 31.79, 31.82, 68.18, 69.01, 100.69, 112.27, 114.18,
14.84, 121.37, 121.70, 127.55, 130.74, 131.21, 144.62, 148.38, 157.64, 159.96, 161.46,
64.69, 186.32; Anal. Calc. for C H O ; C, 76.66; H, 8.33; found: C, 76.52; H, 8.48 %;
1
1
3
4
44
5
+
ESI-MS: 533.07 [M+H] .
5

(E)-7-(Decyloxy)-3-{3-[4-(decyloxy)phenyl]acryloyl}-2H-chromen-2-one (11g)
Yellow solid, Yield: 89 %; M.P: 118-120 ºC; IR (KBr): 3082, 2921, 2850, 1733, 1653, 1597,
-1 1
1
507, 1468, 1420, 1338, 1299, 1258, 1165, 1068, 1051, 852, 825, 719 cm ; H-NMR (400
MHz, CDCl ): δ 0.90 (t, J=6.8 Hz, 6H), 1.29-1.34 (br s, 24H), 1.44-1.51 (m, 4H), 1.78-1.88
3
(m, 4H), 4.01 (t, J=6.6 Hz, 2H), 4.07 (t, J=6.6 Hz, 2H), 6.85 (d, J=2.4Hz, 1H), 6.90-6.94 (m,
3
H), 7.56 (d, J=8.8 Hz, 1H), 7.64 (d, J=8.4 Hz, 2H), 7.86 (d, J=15.6 Hz, 1H), 7.93 (d, J=15.6
1
3
Hz, 1H), 8.60 (s, 1H); C-NMR (100 MHz, CDCl ): δ ppm 14.15, 22.70, 25.93, 26.01,
3
2
1
1
5
8.89, 29.16, 29.32, 29.39, 29.55, 29.57, 31.90, 68.18, 69.01, 100.69, 112.27, 114.19, 114.84,
21.38, 121.70, 127.55, 130.75, 131.21, 144.63, 148.38, 157.64, 159.97, 161.46, 164.69,
86.33; Anal. Calc. for C H O ; C, 77.51; H, 8.90; found: C, 77.65; H, 9.02 %; ESI-MS:
38
52
5
+
89.36 [M+H] .
(E)-7-(Dodecyloxy)-3-{3-[4-(dodecyloxy)phenyl]acryloyl}-2H-chromen-2-one (11h)
Yellow solid, Yield: 92 %; M.P: 124-126 ºC; IR (KBr): 2953, 2921, 2850, 1733, 1654, 1596,
1
7
1
508, 1468, 1421, 1339, 1299, 1260, 1166, 1144, 1068, 1023, 987, 953, 852, 851, 825, 804,
-1 1
44, 721 cm ; H-NMR (400 MHz, CDCl ): δ 0.90 (t, J=6.8 Hz, 6H), 1.28-1.36 (br s, 32H),
3
.44-1.49 (m, 4H), 1.78-1.88 (m, 4H), 4.01 (t, J=6.6 Hz, 2H), 4.06 (t, J=6.4 Hz, 2H), 6.84 (d,
J=2.0 Hz, 1H), 6.89-6.94 (m, 3H), 7.56 (d, J=8.8 Hz, 1H), 7.64 (d, J= 8.8 Hz, 2H), 7.85 (d,
1
3
J=15.6 Hz, 1H), 7.93 (d, J=15.6 Hz, 1H), 8.60 (s, 1H); C-NMR (100 MHz, CDCl ): δ ppm
3
1
2
1
7
4.16, 22.72, 25.93, 26.02, 28.90, 29.17, 29.33, 29.37, 29.40, 29.55, 29.59, 29.61, 29.65,
9.67, 31.94, 68.18, 69.01, 100.69, 112.27, 114.18, 114.83, 121.36, 121.69, 127.54, 130.75,
31.21, 144.62, 148.38, 157.64, 159.96, 161.46, 164.69, 186.31; Anal. Calc. for C H O ; C,
4
2
60
5
8.22; H, 9.38; found: C, 78.40; H, 9.42 %
(E)-7-(Tetradecyloxy)-3-{3-[4-(tetradecyloxy)phenyl]acryloyl}-2H-chromen-2-one (11i)
Yellow solid, Yield: 85 %; M.P: 122-124 ºC; IR (KBr): 3070, 3046, 2918, 2850, 1720, 1658,
-1
1
613, 1568, 1510, 1469, 1425, 1373, 1294, 1254, 1197, 1170, 1071, 979, 828, 774, 723 cm ;
1
H-NMR (400 MHz, CDCl ): δ 0.89 (t, J=6.4 Hz, 6H), 1.28-1.33 (br s, 40H), 1.43-1.48 (m,
3
4
H), 1.77-1.88 (m, 4H), 4.0 (t, J=6.6 Hz, 2H), 4.06 (t, J=6.4 Hz, 2H), 6.84 (d, J=2.0Hz, 1H),
6
.89-6.94 (m, 3H), 7.56 (d, J=8.8Hz, 1H), 7.64 (d, J=8.8 Hz, 2H), 7.85 (d, J=15.6 Hz, 1H),
13
7
.93 (d, J=15.6 Hz, 1H), 8.60 (s, 1H); C-NMR (100 MHz, CDCl ): δ ppm 14.16, 22.72,
3
2
5.94, 26.02, 28.90, 29.17, 29.34, 29.39, 29.55, 29.60, 29.62, 29.68, 29.71, 31.94, 68.18,
9.01, 100.68, 112.26, 114.18, 114.83, 121.34, 121.68, 127.54, 130.74, 131.21, 144.63,
48.38, 157.63, 159.96, 161.46, 164.69, 186.29; Anal. Calc. for C H O ; C, 78.81; H, 9.78;
6
1
4
6
68
5
found: C, 78.74; H, 9.92 %
6

(E)-7-(Hexadecyloxy)-3-{3-[4-(hexadecyloxy)phenyl]acryloyl}-2H-chromen-2-one (11j)
Yellow solid, Yield: 90 %; M.P: 120-122 ºC; IR (KBr): 3070, 3047, 2917, 2850, 1720, 1658,
-1 1
1
614, 1568, 1510, 1469, 1425, 1374, 1253, 1198, 1167, 1022, 980, 831, 774, 722 cm ; H-
NMR (400 MHz, CDCl ): δ 0.89 (t, J=6.8 Hz, 6H), 1.27 (br s, 48H), 1.47-1.49 (m, 4H), 1.78-
3
1
.88 (m, 4H), 4.01 (t, J=6.6 Hz, 2H), 4.06 (t, J=6.4 Hz, 2H), 6.85 (d, J=2.0 Hz, 1H), 6.90-
.94 (m, 3H), 7.56 (d, J=8.4 Hz, 1H), 7.64 (d, J=8.4 Hz, 2H), 7.85 (d, J=15.6 Hz, 1H), 7.93
6
13
(
d, J=15.6 Hz, 1H), 8.60 (s, 1H); C-NMR (100 MHz, CDCl ): δ ppm 14.17, 22.72, 25.94,
3
2
6.02, 28.90, 29.17, 29.34, 29.39, 29.56, 29.60, 29.62, 29.69, 29.72, 31.95, 68.18, 69.01,
00.68, 112.27, 114.19, 114.83, 121.36, 121.68, 127.54, 130.75, 131.22, 144.64, 148.40,
57.64, 159.97, 161.46, 164.69, 186.33; Anal. Calc. for C H O ; C, 79.32; H, 10.12; found:
1
1
5
0
76
5
C, 79.51; H, 10.05 %
(E)-7-(Octadecyloxy)-3-{3-[4-(octadecyloxy)phenyl]acryloyl}-2H-chromen-2-one (11k)
Yellow solid, Yield: 94 %; M.P: 118-120 ºC; IR (KBr): 2918, 2849, 1716, 1655, 1601, 1568,
-1
1
1
508, 1467, 1425, 1253, 1172, 1069, 1026, 977, 828, 801, 776, 720 cm ; H-NMR (400
MHz, CDCl ): δ 0.89 (t, J=6.6 Hz, 6H), 1.27 (br s, 56H), 1.47-1.48 (m, 4H), 1.77-1.86 (m,
3
4
H), 4.01 (t, J=6.6 Hz, 2H), 4.06 (t, J=6.4 Hz, 2H), 6.84 (s, 1H), 6.89-6.94 (m, 3H), 7.56 (d,
J=8.8 Hz, 1H), 7.64 (d, J=8.4 Hz, 2H), 7.85 (d, J=15.6 Hz, 1H), 7.93 (d, J=15.6 Hz, 1H),
1
3
8
2
.60 (s, 1H); C-NMR (100 MHz, CDCl ): δ ppm 14.16, 22.72, 25.94, 26.02, 28.90, 29.17,
3
9.34, 29.39, 29.56, 29.60, 29.62, 29.69, 29.72, 31.95, 68.18, 69.01, 100.68, 112.27, 114.19,
114.83, 121.36, 121.69, 127.54, 130.75, 131.21, 144.63, 148.39, 157.64, 159.96, 161.46,
1
64.69, 186.31; Anal. Calc. for C H O ; C, 79.75; H, 10.41; found: C, 79.81; H, 10.43 %
5
4
84
5
Synthesis of 3-acetamido-7-hydroxy coumarin (12)
To a stirring solution of 2,4-dihydroxybenzaldehyde 7 (20.0 g, 144.92 mmol, 1.0 eq) in acetic
anhydride (68.36 mL, 724.6 mmol, 5.0 eq) N-acetylglycine (16.9 g, 144.92 mmol, 1.0 eq) and
sodium acetate (47.55 g, 579.68 mmol, 4.0 eq) were added and the resulting mixture was
heated at 100-110 °C for 7 hours or till the completion of reaction as monitored by TLC. On
completion of reaction it was cooled to room temperature, water (20 mL) was added and the
resulting solid was filtered, dried and then recrystallized from absolute ethanol to give 3-
acetamido-7-hydroxy coumarin 12 as crystalline solid. % Yield: 48 %; M.P.: 242-244 ºC
4
3
(
Lit . M. P. 244-246 ºC)
Synthesis of 3-amino-7-hydroxycoumarin (13)
To a solution of above obtained 3-acetamido-7-hydroxy-coumarin 12 (20.0 g) in ethanol (150
mL), conc HCl (30 mL) was added and the resulting solution was refluxed for an hour. On
completion of reaction it was cooled to room temperature, concentrated to a small volume
7

and then neutralized with sodium bicarbonate solution to yield crude compound. The
resulting solid was filtered, dried and then recrystallized from absolute ethanol to give pure
4
3
crystalline 3-amino-7-hydroxy-coumarin 13. % Yield: 66 %; M.P. 248-250 ºC (Lit M.P.
50 ºC).
2
Synthesis of 3-amino 7-alkoxy Coumarin derivatives (14)
To a solution of 3-amino 7-hydroxycoumarin (1.0 eq) in dimethyl formamide (DMF) (20 mL)
was added anhy. K CO (2.5 eq) and stirred at room temperature for 10-15 min. To this
2
3
mixture, alkyl bromide (1.0 mmol) was added and resulting solution was stirred at room
temperature (rt) for 22-24 h. The completion of reaction was checked by TLC. After
completion of reaction, the reaction mixture was poured into ice-cold water to give solid. The
solid was filtered, washed with water, dried and recrystallized from ethanol to give
compound 13 as off white solid. These compounds 14a-l were directly used for next step.
Synthesis of 4-alkyloxybenzaldehyde derivatives (15)
Compounds 15a-l were prepared using same method as described for compounds 14a-l. The
crude compounds were obtained as colourless oil. All the compounds were purified by
column chromatography and used for next step.
General procedure for Synthesis of (E)-7-alkoxy-3-((4-alkoxybenzylidene)amino)-2H-
chromen-2-one (16a-l)
To a solution of 3-amino 7-alkoxy coumarin 14a-l (1.0 eq) and 4-alkoxy benzaldehyde 15a-l
(1.0 eq) in ethanol (10 mL) was refluxed for 18-20 h in presence of catalytic amount of acetic
acid (0.1-0.2 mL). The reaction mixture was allowed to cool down to room temperature and
concentrated to half volume. The solid separated out on standing was filtered, washed with
cold ethanol, cold petrolium ether and dried to give compound 16a-l.
Characterization data of all even members alkyl chain derivatives.
(E)-7-Butoxy-3-{[4-(butoxy)benzylidene]amino}-2H-chromen-2-one (16c)
Yellow solid, Yield: 61%, M.P:142-144 ºC; IR (KBr): 3080, 2956, 2872, 1421, 1614, 1569,
-
1
1
1
1
2
9
6
1
3
504, 1473, 1285, 1240, 1166, 1654, 961, 769 cm ; H-NMR (400MHz, CDCl ) δ ppm :
3
.00-1.03 (m, 6H), 1.48-1.58 (m, 4H), 1.78-1.86 (m, 4H), 4.02-4.06 (m, 4H), 6.84-6.89 (m,
H), 6.98 (d, J=8.8 Hz, 2H), 7.41 (d, J=8.4 Hz, 1H), 7.55 (s, 1H), 7.87 (d, J=8.8 Hz, 2H),
1
3
.10 (s, 1H), C-NMR (100MHz, CDCl ) δ ppm: 13.8, 13.9, 19.2, 19.2, 31.0, 31.2, 67.9,
3
8.3, 100.9, 113.3, 114.6, 128.5, 129.0, 130.8, 132.4, 132.8, 153.7, 159.0, 161.6, 162.3,
62.4; Anal. Calc. for C H NO ; C, 73.26; H, 6.92; N, 3.56; found: C, 73.41; H, 6.80; N,
2
4
27
4
.62 %
8

(E)-7-(Hexyloxy)-3-{[4-(hexyloxy)benzylidene]amino}-2H-chromen-2-one (16e)
Yellow solid, Yield: 66%, M.P: 140-142 ºC; IR (KBr): 2923, 2854, 1720, 1622, 1251, 1171,
-1 1
1
153, 1133, 843, 769 cm ; H-NMR (400 MHz, CDCl ) δ ppm: 0.91-0.95 (m, 6H), 1.38-1.39
3
(m, 8H), 1.45-1.52 (m, 4H), 1.79-1.86 (m, 4H), 4.00-4.05 (m, 4H), 6.84-6.88 (m, 2H), 6.97
(d, J=8.8 Hz, 2H), 7.41 (d, J=8.8 Hz, 1H), 7.55 (s, 1H), 7.87 (d, J=8.8 Hz, 2H), 9.09 (s, 1H),
1
3
C-NMR (CDCl , 100 MHz) δ ppm 14.1, 22.6, 25.6, 25.7, 29.0, 29.1, 31.5, 31.6, 68.2, 68.6,
3
1
00.8, 113.3, 114.6, 128.5, 129.0, 130.8, 132.4, 132.8, 153.7, 159.0, 161.6, 162.2, 162.4;
Anal. Calc. for C H NO ; C, 74.80; H, 7.85; N, 3.12; found: C, 74.66; H, 7.80; N, 3.01 %
2
8
35
4
(E)-7-(Octyloxy)-3-{[4-(octyloxy)benzylidene]amino}-2H-chromen-2-one (16g)
Yellow solid, Yield: 63%, M.P: 140-142 ºC; IR (KBr): 2922, 2854, 1720, 1623, 1250, 1152,
-
1 1
1
1
132, 842, 766 cm ; H -NMR (400 MHz, CDCl ) δ ppm : 0.89-0.93 (m, 6H), 1.26-1.40 (m,
3
6H), 1.45-1.52 (m, 4H), 1.79-1.86 (m, 4H), 4.01-4.06 (m, 4H), 6.85-6.88 (m, 2H), 6.97 (d,
1
3
J=8.8 Hz, 2H), 7.41 (d, J=8.4 Hz, 1H), 7.55 (s, 1H), 7.87 (d, J=8.8 Hz, 2H), 9.10 (s, 1H). C-
NMR (100 MHz,CDCl ) δ ppm : 14.1, 22.6, 25.9, 26.0, 29.0, 29.1, 29.2, 29.2, 29.3, 29.3,
3
3
1.7, 31.8, 68.2, 68.6, 100.9, 113.3, 113.4, 114.7, 128.5, 129.1, 130.8, 132.5, 132.8, 153.7,
58.6, 158.9, 161.6, 162.3, 162.4; Anal. Calc. for C H NO ; C, 76.00; H, 8.57; N, 2.77;
1
32
43
4
found: C, 75.84; H, 8.80; N, 2.52 %
(E)-7-(Decyloxy)-3-{[4-(decyloxy)benzylidene]amino}-2H-chromen-2-one (16h)
Yellow solid, Yield: 55%, M.P: 134-136 ºC; IR (KBr): 2921, 2852, 1720, 1624, 1606, 1567,
-1 1
1
507, 1332, 1135, 843, 769 cm ; H-NMR (400 MHz, CDCl ) δ ppm: 0.89 (t, 6H), 1.34-1.36
3
(m, 24H), 1.44-1.50 (m, 4H), 1.79-1.86 (m, 4H), 4.00-4.05 (m, 4H), 6.84-6.88 (m, 2H), 6.97
(d, J=8.8 Hz, 2H), 7.41 (d, J=8.4 Hz, 1H), 7.55(s, 1H), 7.87 (d, J=8.8 Hz, 2H), 9.10 (s, 1H);
1
3
C-NMR (100 MHz, CDCl ) δ ppm: 14.2, 22.7, 26.0, 26.0, 29.0, 29.2, 29.3, 29.4, 29.4, 29.6,
3
3
1
1.9, 68.2, 68.6, 100.9, 113.4, 114.6, 114.7, 128.5, 129.0, 130.9, 132.5, 132.8, 153.7, 159.0,
61.6, 162.4, 162.4; Anal. Calc. for C H NO ; C, 76.97; H, 9.15; N, 2.49; found: C, 76.96;
3
6
51
4
+
H, 9.11; N, 2.50 %, ESI-MS: 563.2 [M+H] .
E)-7-(Dodecyloxy)-3-{[4-(dodecyloxy)benzylidene]amino}-2H-chromen-2-one (16i)
Yellow solid, Yield: 62%, M.P: 138-140 ºC; IR (KBr): 2920, 2851, 1721, 1623, 1607, 1570,
(
-1 1
1
507, 1470, 1425, 1399, 1381, 1293, 1253, 1171, 1153, 1053, 1023, 977, 843, 769 cm ; H-
NMR (400MHz, CDCl ) δ ppm : 0.90 (t, J=6.4 Hz, 6H), 1.28-1.50 (br s, 32H), 1.64 (s, 4H),
3
1
.81-1.85 (m, 4H), 4.01-4.05 (m, 4H), 6.84-6.89 (m, 2H), 6.97 (d, J=8.8 Hz, 2H), 7.41 (d,
J=8.4 Hz, 1H), 7.56 (s, 1H), 7.87 (d, J=8.8 Hz, 2H), 9.10 (s, 1H); Anal. Calc. for C H NO ;
4
0
59
4
C, 77.75; H, 9.62; N, 2.27; found: C, 77.52; H, 9.62; N, 2.23 %
9

(E)-7-(Tetradecyloxy)-3-{[4-(tetradecyloxy)benzylidene]amino}-2H-chromen-2-one (16j)
Yellow solid, Yield: 59%, M.P: 132-134 ºC; IR (KBr): 2919, 2850, 1720, 1622, 1570, 1470,
-
1 1
1
4
4
7
1
426, 1380, 1292, 1252, 1152, 1135, 1058, 1010, 910, 843, 802, 768 cm ; H-NMR (CDCl
3,
00MHz) δ ppm : 0.90 (t, J=6.4Hz, 6H), 1.28 (br s, 40H), 1.45-1.48 (m, 4H), 1.79-1.85 (m,
H), 4.01-4.05 (m, 4H), 6.81-6.89 (m, 2H), 6.97 (d, J=8.8 Hz, 2H), 7.41 (d, J=8.4 Hz, 1H),
.56 (s, 1H), 7.87 (d, J=8.8 Hz, 2H), 9.10 (s, 1H); Anal. Calc. for C H NO ; C, 78.41; H,
4
4
67
4
0.02; N, 2.08; found: C, 78.25; H, 10.14; N, 2.12 %
E)-7-(Hexadecyloxy)-3-{[4-(hexadecyloxy)benzylidene]amino}-2H-chromen-2-one (16k)
Yellow solid, Yield: 67%, M.P: 130-132 ºC; IR (KBr): 2919, 2851, 1721, 1623, 1570, 1509,
(
-1
1
1
470, 1293, 1254, 1171, 1153, 1058, 1021, 910, 843, 802, 769 cm ; H-NMR (400MHz,
CDCl ) δ ppm : 0.90 (t, J=6.4Hz, 6H), 1.28 (br s, 48H), 1.45-1.49 (m, 4H), 1.79-1.85 (m,
3
4
7
1
H), 4.01-4.05 (m, 4H), 6.85-6.88 (m, 2H), 6.97 (d, J=8.8 Hz, 2H), 7.41 (d, J=8.4 Hz, 1H),
.55 (s, 1H), 7.87 (d, J=8.4 Hz, 2H), 9.10 (s, 1H); Anal. Calc. for C H NO ; C, 78.96; H,
4
8
75
4
0.35; N, 1.92; found: C, 78.98; H, 10.54; N, 1.87 %
(E)-7-(Octadecyloxy)-3-{[4-(octadecyloxy)benzylidene]amino}-2H-chromen-2-one (16l)
Yellow solid, Yield: 55%, M.P: 126-128 ºC; IR (KBr): 2919, 2850, 1721, 1624, 1570, 1508,
-1
1
1
470, 1293, 1254, 1171, 1152, 1136, 1058, 910, 843, 803, 769 cm ; H-NMR (400MHz,
CDCl ) δ ppm : 0.90 (t, J=6.4 Hz, 6H), 1.28 (br s, 56H), 1.49 (br s, 4H), 1.83 (br s, 4H), 4.03
3
(s, 4H), 6.85-6.88 (m, 2H), 6.98 (d, J=8.4 Hz, 2H), 7.41 (d, J=8.4 Hz, 1H), 7.56 (s, 1H), 7.87
(
d, J=8.8 Hz, 2H), 9.10 (s, 1H); Anal. Calc. for C H NO ; C, 79.44; H, 10.64; N, 1.78;
52
83
4
found: C, 79.28; H, 10.72, N; 1.69 %.
3
3
3
2
. Results and Discussion
.1 Chemistry
-Acetyl-7-hydroxy-2H-chromen-2-one 8 was prepared by Knoevenangel condensation of
,4-dihydroxy benzaldehyde 7 with ethyl acetoacetate using catalytic amount of piperidine in
ethanol. Compound 8 on reaction with 4-hydroxy benzaldehyde 9 by refluxing for 36 h in
presence of catalytic amount of pyrrolidine and acetic acid in ethanol gave (E)-7-hydroxy-3-
[
3-(4-hydroxyphenyl)acryloyl]-2H-chromen-2-one 10. Compound 10 was alkylated with
different n-alkyl bromides using anhydrous K CO in N,N-dimethyl formamide (DMF) at 70–
2
3
7
2 ºC to give bis-alkyloxy derivatives 11a-k of Series-I (Scheme 1).
1
0

Scheme 1: Synthesis of chalcone containing coumarin derivatives
The structures of compounds 11a-k were confirmed by different analytical techniques such as
1
13
H-NMR, C-NMR, IR, ESI-MS and CHN analysis. In general, compounds 11a-k exhibited
-1
three peaks in the range 3095-2840 cm for the alkyl chain in IR spectra, while carbonyl
-1
stretching frequency of lactone was observed at 1730-1718 cm , carbonyl group of chalcone
-1
1
was observed at 1660-1650 cm . In the H-NMR spectra of compounds 11a-k, terminal
methyl groups of both alkyl chain were observed as triplet in the upfield region of δ 0.88-1.00
while methylene protons were observed as multiplet at δ 1.33-1.88. Methylene protons
attached with oxygen were observed as triplets in the region of 3.99- 4.08 ppm. All aromatic
protons of coumarin and phenyl rings were observed between δ ~6.84-7.65. Chalcone protons
were observed as a doublet at 7.83-7.95 ppm with trans coupling (J) value of 16.0Hz and
th
proton of 4 position of coumarin were observed as singlet around δ 8.60 ppm.
1
3
In the C-NMR spectra of 11a-k, peaks for methyl and other alkyl carbons were in range of
δ 14-31 ppm, two methylene carbons adjacent to oxygen were observed at δ 68 and 69 ppm.
All aromatic carbons were appeared in range of δ 100-161 ppm, coumarin lactone carbonyl
carbon at 164 ppm and carbonyl carbon of chalcone at 184 ppm. The ESI-MS of all the
compounds were recorded giving molecular ion peak corresponding to molecular weight of
compounds.
In another series, chalcone linkage was replaced by imine linakge. Alkylation of 3-amino-7-
hydroxy-2H-chromen-2-one and 4-hydroxybenzaldehyde were done separately using
different n-alkyl bromides and anhydrous K CO in dry DMF at room temperature. Resulting
2
3
1
1

alkylated compounds were reacted in ethanol using catalytic amount of acetic acid to give
Schiff bases 16a-l Series-II (Scheme 2).
Scheme 2 Synthesis of imine containing coumarin derivatives
The structures of all the compounds 16a-l were confirmed by using different analytical
1
13
techniques such as H-NMR, C-NMR, IR, ESI-MS and CHN analysis. In IR spectra of
-1
compounds 16a-l exhibited band at 2922-2854 cm for the C-H stretching of alkyl chain,
-1
-1
band at 1720 cm for carbonyl stretching of lactone ring, 1623 cm for carbonyl stretching of
1
chalcone moiety. In the H-NMR spectra of compounds 16a-l, two terminal methyl groups of
alkyl chain were observed as triplet in the upfield region of δ ~ 0.88-0.93. Methylene protons
at δ 1.20-1.88 were observed as multiplet, methylene groups adjacent to oxygen were
overlapped and appeared as multiplet in region of 4.02- 4.05 ppm, All aromatic protons were
observed in region of δ 6.84-7.88 ppm, while imine proton was appeared as singlet around δ
9
.10 ppm.
1
3
In the C-NMR spectra of 16a-l, two methyl carbons and methylene carbons were observed
around δ 14-31 ppm, methylene carbon adjacent to oxygen were observed at 68-69 ppm. All
aromatic carbons were observed in range of 100-161 ppm lactone carbonyl carbon observed
+
at 162 ppm. All compounds 16a-l were analysed by ESI-MS to give [M+H] peak
corresponding to their molecular weight
.
1
2

3
3
.2 Mesomorphic properties
.2.1 Differential scanning calorimetry study (DSC)
The phase transition temperatures, enthalpy-entropy changes and mesophase textures of the
pure compounds 11a-k and 16a-l are summarised in Table 1 and 2. Clear-cut transition
temperatures and textures could be obtained from DSC curves and POM observations for all
of the compounds, and they were in good agreement with each other for the multiple
heating/cooling cycles. Thermograms were calculated by DSC (DSC-822, Mettler Toledo
having Stare software). Phase transitions of all the compounds were measured in both heating
and cooling cycle at rate of 10 ºC/min. Chalcone derivatives of coumarin compounds 11a,
1
1b and 11c showed one endotherm for crystalline to isotropic liquid phase (Cr-Iso) on
heating and one exotherm from isotropic liquid phase to crystallization (Iso-Cr) on cooling
without any mesogenic property.
TABLE-1
:
DSC phase transition temperature, enthalpy and entropy of alkoxy coumarin
a
chalcone linked compounds 11a-11k
Heating
Cooling
-1
-1
-1 -1
-1 -1
Temp ºC (∆H KJmol , ∆S Jmol K )
Temp ºC (∆H KJmol , ∆S Jmol K )
Compd
n
SmA
N
Iso
N
SmA
Cr
1
69.56
88.35
(2.39, 6.62)
90.43
(2.28, 6.29)
64.33
(14.16, 41.97)
46.03
(1.89, 5.92)
79.00
(1.37, 3.89)
83.09
(4.06, 11.41)
73.62
(4.70, 13.58)
73.60
(3.02, 8.71)
73.55
1
1a
1b
2
4
(
3.64, 8.22)
32.45
6.19, 15.28)
26.66
1
1
(
(
1
1
1c
1d
1e
1f
5
8.32, 20.81)
138.01
(0.45, 1.10)
104.00
(0.84, 2.27)
115.48
(0.40, 1.03)
118.66
(0.86, 2.20)
124.91
(1.92, 4.82)
121.83
(1.51, 3.83)
119.99
(1.42, 3.61)
118.66
1
16.88
135.06
(1.17, 2.87)
102.00
(2.94, 7.84)
111.56
1
6
(
5.28, 13.54)
6.33
9
1
7
(
3.61, 9.57)
108.91
(5.75, 15.09)
8
6.94
1.54, 4.28)
3.71
5.02, 14.07)
4.29
1.31, 3.77)
3.78
3.91, 10.96)
3.22
7.95, 21.73)
6.38
4.24, 11.48)
105.21
(0.07, 0.18)
117.87
(1.18, 3.01)
121.14
(1.86, 4.71)
118.89
(1.39, 3.55)
117.39
1
8
(
(0.25, 0.66)
8
1
1g
1h
10
12
14
16
18
(
7
1
(
8
1
1i
1j
1k
(
(
(
(3.05, 8.80)
80.11
(6.24, 17.67)
83.20
9
1
(1.68, 4.30)
116.73
(0.79, 2.03)
9
1
(0.49, 1.24)
(4.66, 13.08)
a
SmA = Smectic A phase, N = Nematic phase, Iso = Isotropic phase, Cr = Crystalline solid
1
3

Compounds 11d and 11e exhibited two endotherms from crystalline solid to nematic phase
Cr-N) and nemtic phase to isotropic liquid phase (N-Iso) on heating. Similarly on cooling
(
two exotherms are observed corresponding to isotropic liquid phase to nematic phase (Iso-N)
and nematic phase to crystalline solid state (N-Cr). Compound 11f showed three endotherms
for heating cycle and three exotherms on cooling cycle, while heating first transition was
observed from crystalline solid to smectic A phase (Cr-SmA), second transition was observed
for smectic A phase to nematic phase (SmA-N) and third transition was observed for nematic
mesophase to isotropic liquid phase (N-Iso). In cooling cycle, compound 11f showed three
exotherms for Isotropic liquid phase to nematic phase (Iso-N), nematic to smectic A phase
(N-SmA) and smectic A phase to crystalline solid (SmA-Cr) (Figure 2, Table 1). Compounds
1
1g-11k showed only two transitions in both heating and cooling cycles corresponding to
smectic A mesophase in between crystal and isotropic phases.
Figure-2: DSC plot of octyloxy coumarin chalcone derivative 11f in both heating and
cooling cycle along with transition temperatures
DSC thermograms for alkoxy coumarin derivatives 16a-l with imine linkage were evaluated,
which was used for calculations of enthalpy and entropy values for all the synthesized
compounds. Compound 16a exhibited one endotherm from Cr-Iso in heating cycle with no
mesogenic property. Compounds 16b-16f showed two endotherms in heating cycle from Cr-
N and N-Iso. In cooling cycle, compounds 16b, 16d and 16f exhibited two exotherms for Iso-
N and N-Cr transitions, whereas compound 16c and 16e exhibited three exotherms from Iso-
N, nematic phase to crystal-1 and crystal-1 to crystalline solid (Figure 3a, Table 2).
1
4

TABLE-2
:
DSC phase transition temperature, enthalpy and entropy of all alkoxy coumarin
a
imine linkage compounds 16a-l
Heating
Cooling
-1
-1
-1 -1
-1 -1
Temp ºC (∆H KJmol , ∆S Jmol K )
Temp ºC (∆H KJmol , ∆S Jmol K )
Compd
n
SmA
N
Iso
N
SmA
Cr
1
29.83
91.91
(2.96, 8.13)
82.5
(
4.57, 11.34)
133.00
1
05.00
128.00
1
6b
3
4
5
6
(
(
9.55, 25.26)
(0.31, 0.76)
(0.14, 0.35)
(5.55, 15.61)
5
6.77
1
13.10
143.35
(0.14, 0.33)
140.07
(0.17, 0.41)
(8.92, 27.05),
40.03
1
6c
4.93, 12.76)
(
2.20, 7.03)
55.00
7
7.00
129.00
128.00
1
6d
(
5.85, 16.71 )
(1.65, 4.10) (0.23, 0.701)
(7.14, 17.80)
0.04
8
8
2.95
139.99
(0.57, 1.38)
136.75
(0.59, 1.44)
(0.26, 0.74)
60.18
1
6e
(
10.33, 29.09)
(
1.65, 4.95)
68.50
8
4.00
112.00
(1.89, 4.90)
139.96
(0.76, 1.84)
136.67
(0.85, 2.07)
136.63
(2.52, 6.18)
132.38
(0.88, 2.17)
131.35
(2.21, 5.47)
126.69
107.00
(0.40, 1.05)
136.76
1
6f
6g
6h
7
(
4.72, 13.22)
126.66
(0.23, 0.58)
(8.13, 23.84)
70.42
(9.15, 26.64)
70.24
9
9.86
3.55, 9.54)
3.12
10.03, 27.40)
9.71
13.63, 36.64)
6.48
1.08, 2.94)
05.85
11.30, 29.89)
09.89
9.67, 25.31)
123.40
(0.20, 0.50)
124.05
1
8
(
(0.39, 0.95)
9
1
10
12
14
16
18
(
(
(0.47, 1.18) (10.60, 30.90)
9
134.11
(1.99, 4.89)
126.06
80.22
(9.94, 28.15)
64.54
1
6i
9
1
6j
(
(1.29, 3.23)
128.72
(1.87, 5.54)
92.19
1
1
6k
6l
(
(1.52, 3.79) (10.93, 29.94)
123.39 96.99
(0.76, 2.06) (15.12, 40.97)
1
1
(
(1.20, 3.01)
a
SmA = Smectic A phase, N = Nematic phase, Iso = Isotropic phase, Cr = Crystalline solid
Compound 16g showed three endotherms on heating first for Cr-SmA, second for SmA –N
and third corresponding to N-Iso, while three exotherms during cooling are observed
corresponding to Iso-N, N-SmA and SmA-Cr transitions (Figure 3b, Table 2). Compounds
1
6h-l showed two endotherms for Cr-SmA and SmA-Iso transitions on heating and two
exotherms for Iso-SmA and SmA-Cr transitions on cooling. Only SmA phase was observed
in both heating and cooling cycle for compounds 16h-l (Table 2).
1
5

Figure 3: DSC plots of imine derivatives (a) compound 16c with butyloxy showing cryst-1 to
cryst modification in cooling cycle and (b) compound 16g octyloxy at different temperature.
3
.2.2 Polarising optical microscopy (POM) study
The mesogenic properties of all the compounds 11a-k and 16a-l were observed by using
Leica DM2500P attached with camera Leica DFC295 along with the separate heating plate
on microscope. Thin film of the samples was prepared by sandwiching a small amount of
each compound between slide and coverslip.
Lower members of n-alkoxy coumarin chalcone derivatives with ethyl (11a), butyl (11b) and
pentyl (11c) chain did not show any mesomorphic properties. Compounds 11d and 11e
having n-hexyl and n-heptyl chain showed nematic phase, 11f with n-octyl chain length
showed two phases viz Nematic phase (Figure 4a) and smectic A (Figure 4b) respectively on
cooling. All the higher members 11g-11k showed only smectic A phase similar to compound
1
1f as shown in Figure 4b.
Coumarin imine linkage derivatives 16a-l showed different textures under polarising optical
microscope. Compound 16a did not show any mesogenic phase, while compounds 16b to 16f
showed marble texture, characteristic of nematic phase during heating and colloing cycles.
Compound 16g showed both smectic A and nematic phases on heating cycle. During cooling
cycle for compound 16g, isotropic phase was first transformed into tiny spherical droplets
(Figure 4c) later coalesced into the Schlieren texture characteristic of nematic phase (Figures
4
d-e), which on further cooling exhibited focal conic texture characteristic of smectic A
phase (Figure 4f) before crystallization. Compounds 16h-16l exhibited only focal conic
texture characteristic of smectic A phase on both heating and cooling cycle.
1
6

(a)
(b)
(c)
(d)
(e)
(f)
Figure 4: POM images of compound 11f and 16g. Optical photomicrographs were taken
during the cooling cycle of compound 11f showed transition from isotropic liquid to Nematic
Schlieren texture (a) at 111.56 ºC, further on cooling nematic to focal conic Smectic-A phase
(
b) was observed at 105.21 ºC. On cooling compound 16g from isotropic liquid, nematic
droplets (c) appeared at 136.76 ºC and coalesced to form the typical schlieren texture (d) at
36.00 ºC, On further cooling gives marble texture (e) of nematic phase at 134.28 ºC and
finally transition from nematic to focal conic smectic A (f) at 123.40 ºC was observed.
1
3
.3 Structure-mesomorphic property relationship
The graph of phase-transition temperatures against the number of carbons in chalcone and
imine derivatives of the n-alkoxy chain enabled to identify the effects of the terminal chain
on the mesomorphic properties. The relationship was established from two different plots
1
7

(Figure 5). Based on Figures 5a-b, the transition curves Cr-SmA/N/Iso, SmA/N-Iso, SmA-
Iso, are obtained.
The Cr-SmA/N/Iso transition curve exhibited sharp falling tendency up to n-dodecyloxy
derivative 11h and covers large area which may be responsible for the enantiotropy nature of
the series. From compounds 11h to 11k ascending trend was observed this may be due to the
excessive Van der Waals attractive forces between the long alkyl chains, the melting
4
4
temperatures increased from the carbon chain length 12 to 18 members. The lower members
with short chain 11a, 11b and 11c did not show any mesogenic properties.
Figure-5: Mesomorphic behaviour as a function of the number of carbon atoms (n) in the
terminal alkoxy chain (a) Series-I with chalcone central linkage in heating cycle (b) Series-II
with imine central linkage in heating cycle.
The isotropic liquid of lower members does not supercool sufficiently for monotropic
nematic mesophase to be obtained. Lower members are in fact not mesomorphic, the high
melting points of these lower members of series may be partially responsible for the lack of
mesophase formation. Mesophases are most commonly observed when a suitable compound
is heated to a temperature above that at which the crystal lattice is stable. All the compounds
of the present series comprised of a molecules which are long, narrow, and linear containing
dipolar groups, which should give strong intermolecular attractions. It seems that these
intermolecular attractions are too strong, selective weakening of the cohesive forces may not
occur until high temperatures are reached, and when the melting process does begin, the
thermal vibrations may be too great to allow an ordered arrangement of the molecules to
persist. Middle members 11d, 11e and 11f showed falling tendency and pronounce odd-even
effect for the N-Iso transition temperatures. Smectic A phase commences from compound 11f
1
8

and persist up to the last homologue synthesized in the series. SmA-Iso transition temperature
curve showed descending trend from compound 11h to 11k (Figure-5a).
Similarly, the phase diagram for coumarin derivatives with imine central linkage was also
plotted against the transition temperatures versus the number of carbon atoms present in the
n-alkoxy terminal chain (Figure 5b). Compound 16a with ethoxy chain did not exhibit any
mesogenic property. Mesophase was observed from compound 16b till the last member long
chain synthized in this series. Only Nematic mesophase was observed for compound 16b
with n-propyloxy to compound 16g with n-octyloxy. The N-Iso, transition temperatures
exhibited falling tendency with marked odd-even effect (Figure 5b). The SmA mesophase
commences from n-octyloxy derivative 16g as an enantiotropy and persist up to the last
member synthesized in this series. SmA-Iso transition temperatures exhibited smooth falling
tendency from compound 16g to compound 16l.
All the compounds of series-I exhibited lower mesophase range and thermal stability as
compared to compounds of series-II. Both the series have common coumarin ring as a core
rd
th
moiety substituted at 3 and 7 positions and differ at the central linkage only. Series-I has
chalcone central linkage whereas series II has imine central linkage. It seems that chalcone
central linkage increases the breadth of the molecule of series I little as compared to
molecules of series II, which may be responsible for the lower mesophase range and thermal
4
5
stability (Mesophase-Isotropic transition) of compounds of series-I.
3
.4 X-ray diffraction study
Compound 16g with imine linkage and octyloxy substituent was further studied by X-ray
single crystal diffraction (CCDC No. 1943900). The structure is shown in Figure 6 and data
is given in Table 3.
Figure 6: Single crystal of compound 16g with coumarin imine n-octyl derivative
1
9

Table 3: Crystal data and structure refinement for compound 16g
3
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
a/Å
C H NO
4
505.67
293
triclinic
P-1
10.6388(19)
11.6468(17)
ρcalcg/cm
ꢀ/mm
F(000)
1.139
0.074
548.0
0.4 × 0.13 × 0.1
MoKα (λ = 0.71073)
6.26 to 58
3
2
43
-
1
3
Crystal size/mm
Radiation
2Θ range for data collection/°
b/Å
Index ranges
-13 ≤ h ≤ 14, -15 ≤ k ≤ 15, -
1
7 ≤ l ≤ 17
c/Å
α/°
12.6960(18)
74.709(13)
Reflections collected
Independent reflections
32012
7150 [Rint = 0.1022, Rsigma =
0
.1175]
β/°
γ/°
Volume/Å
76.399(14)
88.388(14)
1473.9(4)
2
Data/restraints/parameters
Goodness-of-fit on F
Final R indexes [I>=2σ (I)]
Final R indexes [all data]
7150/0/336
0.986
R = 0.0793, wR = 0.1567
1 2
2
3
Z
R = 0.2599, wR = 0.2329
1 2
The crystal packing of molecules in the unit cell were arranged in a linear fashion one on
other. Three π⋯π stackings were observed by one molecule as shown in figure 7a, first was
between phenyl rings of two different molecules at a distance of 3.381 Å, second was
observed at distance of 3.328 Å between carbonyl carbon of lactone of two different
molecules and third was observed between phenyl rings of coumarin moiety of two different
molecules.
Figure 7a: X-ray single crystal analysis showing strong π-π stacking between two layers in
compound 16g.
Short contacts were observed with value of 2.64 Å between oxygen of alkoxy and C-H of
benzene ring (O⋯C-H) on head to head manner as shown in Figure 7b. The results of X-ray
single crystal undoubtedly indicated that the molecule is linear and each molecule is stacked
on other by intermolecular interactions. Single crystal data for compound 11h was also
obtained and provided in supporting information.
2
0

Figure 7b: Short contacts between oxygen of alkoxy and hydrogen of benzene ring in
compound 16g.
Ball and stick model of n-dodecyloxy coumarin chalcone derivative 11h and n-octyloxy
coumarin imine derivative 16g were shown in figure 8. From ball and stick model obtained
from X-ray single crystal was used for calculation of length/breadth ratio, which showed that
L/B ratio for compound with chalcone linkage was lower than L/B ratio for compound with
imine linkage.
Figure 8: Ball and stick model of chalcone and imine derivative along with the molecular
length and breadth. X-ray single crystal spectroscopic technique, Mercury 3.10 software was
used to obtain Dimensions of n-octyloxy derivatives for chalcone (a) L/B ratio 8.343 and
imine (b) with L/B ratio 9.550
3
.5 UV-Vis Study
-5
Compounds 11f and 16g were analysed for UV-Vis absorption spectra in chloroform (1×10
M) at room temperature (Figure 9). Compound 11f with chalcone linkage showed broad
absorption bands at 269 and 391 nm. Shoulder peak at 383 nm was observed in π-π*
2
1

transition peak due to shifting of electron density from donor alkoxy moiety to the aromatic
core. Compound 16g with imine linkage showed two intense absorption bands at 286 and 341
nm. Effect of octyloxy group on absorption spectra can be seen due to push-pull effect
between alkoxy group and aromatic ring (Figure 9). The absorbance maximum attributed to
the π-π* transition were chosen as excitation wavelength for fluorescence measurements.
Compounds 11f and 16g were excited at 391 and 341 nm respectively and emission spectra
were recorded in chloroform. Both compounds showed very low emission in chloroform this
is probably due to non radiative decay of the compounds.
Figure 9: UV-Vis absorbance spectra for compounds 11f and 16g in chloroform
4
. Conclusion
We have designed and synthesized two new homologous series of n-alkoxy coumarin
derivatives with chalcone and imine linkages. The effect of chalcone and imine linkages on
mesophase appearance and stability were studied using DSC and POM. All the compounds
from both the series upto n-heptyl chain length showed only nematic phase. POM study of
compound 11f with chalcone linkage and 16g with imine linkage with n-octyl chain, showed
two phases. Focal conic phase is indicative of smectic A phase and nematic phase with
different textures, which was further confirmed by DSC study. All the higher members from
both the series with alkyl chain length n-decyl and above showed only focal conic smectic A
phase. The mesophase range and thermal stability of coumarin derivatives with chalcone
linkage was lower as compared to the coumarin derivatives with imine linkage.
2
2

Acknowledgements
One of the authors (RS) is thankful to Department of Science & Technology, Government of
India for financial support vide reference no. SR/WOS-A/CS-1028/2014 under Women
Scientist Scheme. Authors are also thankful to The Head, Department of Chemistry, Faculty
of Science, The M. S. University of Baroda for providing laboratory facilities, DST-FIST for
providing NMR, POM and DSC facilities, DST-PURSE for providing X-ray single crystal
facility, Zydus Research Centre, Ahmedabad, for the ESI-MS analyses.
Conflict of Interest
The authors declare that there is no conflict of interest regarding the publication of this paper.
Supplementary Information
1
13
Supporting information contains H-NMR, C-NMR, ESI-MS and IR spectra. This material
can be found via the “Supplementary Content” section of this article’s webpage.
5
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2
6

Highlights
ꢀ
ꢀ
ꢀ
ꢀ
Synthesis of n-alkoxy coumarin derivatives with chalcone and imine linkages
Study of liquid crystalline properties by DSC and POM
Effect of central linkages chalcone and imine on mesophase stability
Effect of chain length on mesophases for both chalcone and imine linkages

Synthesis and mesomorphic properties of coumarin derivatives with chalcone
and imine linkages
*
Sunil Dutt Durgapal, Rina Soni, Shubhangi S Soman , Ashish K. Prajapati
Department of Chemistry, Faculty of Science, The M. S. University of Baroda, Vadodara - 390 002, India.
*Corresponding author’s e-mail: shubhangiss@rediffmail.com
Ph. No.: +91-265-2795552
Conflict of Interest
The authors declare that there is no conflict of interest regarding the publication of this paper.