Alkoxy/halostyryl benzoic acids: Synthesis, crystal structure, and study of mesomorphic and photophysical properties

Article abstract of DOI:10.1080/15421406.2017.1328215

Alkoxy/halostyrylbenzoic acids were synthesized and evaluated for their mesomorphic and photophysical properties. The trans geometry of the molecules was established by the presence of large coupling constants in ¹H-NMR spectra and confirmed fu

Full text of DOI:10.1080/15421406.2017.1328215

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Alkoxy/halostyryl benzoic acids: Synthesis,
crystal structure, and study of mesomorphic and
photophysical properties
Khushi Muhammad, M. Khawar Rauf, M. Nawaz Tahir & Shahid Hameed
To cite this article: Khushi Muhammad, M. Khawar Rauf, M. Nawaz Tahir & Shahid Hameed
(2017) Alkoxy/halostyryl benzoic acids: Synthesis, crystal structure, and study of mesomorphic
and photophysical properties, Molecular Crystals and Liquid Crystals, 650:1, 32-45, DOI:
10.1080/15421406.2017.1328215
To link to this article: http://dx.doi.org/10.1080/15421406.2017.1328215
Published online: 23 Aug 2017.
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Date: 23 August 2017, At: 22:38

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
https://doi.org/./..
Alkoxy/halostyryl benzoic acids: Synthesis, crystal structure,
and study of mesomorphic and photophysical properties
Khushi Muhammada, M. Khawar Raufa, M. Nawaz Tahirb, and Shahid Hameeda
aDepartment of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan; bDepartment of Physics, University of
Sargodha, Sargodha, Pakistan
ABSTRACT
KEYWORDS
Edge-to-face orientation;
fluorescent core;
high-temperature nematics;
Stoke’s shift; styryl acids
Alkoxy/halostyrylbenzoic acids were synthesized and evaluated for
their mesomorphic and photophysical properties. The trans geometry
of the molecules was established by the presence of large coupling
constants in 1H-NMR spectra and confirmed further by X-ray diffraction
(XRD) analysis of two of the compounds. The straight-chain acids were
found fairly stable showing first sign of decomposition above 290°C. The
enantiotropic mesophases could only be studied in acids with seven or
more methylene groups in the alkoxy chain. Textures of nematic and
smectic phases were exhibited by these acids under polarizing optical
microscope. Photophysical behavior of the compounds in solution was
also investigated.
1. Introduction
Carboxylic acids have been used for the synthesis of liquid crystal materials either by for-
mation of their esters or supramolecules through non-covalent interactions. Mesophase
generation through the formation of hydrogen-bonded complexes has gained much impor-
tance in recent years. Mesophases with reasonable temperature ranges have been reported
for such compounds. Alkylbenzoates of 4-pyridylbenzoic acid [1] and hydroxyhexyl esters
of aroyloxybenzoic acids [2] have been reported to show smectic phases. Alkoxybiphenyl-
carboxylic acid esters prepared by Wu and Hsu [3] exhibit SmA∗, SmC∗, and SmX phases.
A non-mesogenic acid, when H-bonded with a non-mesogenic acceptor, may result in the
induction of liquid crystallinity in the complex formed. The complexes formed from bipyridyl
and 4-alkylbenzoic acids exhibit smectic phases while both the components are non-liquid
crystalline [4]. Similarly, alkoxy/halobenzoic acids [5] and aryloxyalkyloxybenzoic acids [6]
form smectic C and nematic complexes, respectively, by hydrogen bonding with pyridyl moi-
ety of the acceptors. The H-bonded complexes of 4-n-alkoxyphenylazo benzoic acids have
been reported to show SmC and nematic phases [7]. Mesophases have been induced through
the formation of homo- or hetero-dimeric structures of low molecular mass carboxylic
acids [7–9]. The 4-(cyanobiphenylhexyloxy)benzoic acid dimer exhibited a monotropic
twist-bend nematic (NTB) in addition to the normal nematic phase [10]. Aromatic carboxylic
acids have also gained much importance in the realization of both supermolecular [11, 12]
CONTACT ShahidHameed
shameed@qau.edu.pk; shahidhameed@daad-alumni.de
i-Azam University, Islamabad , Pakistan.
DepartmentofChemistry, Quaid-
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
©  Taylor & Francis Group, LLC

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
33
and supramolecular side-chain liquid crystal polymers [13, 14]. Metal complexes of aromatic
acids are among the typical metallomesogens [15, 16]. Mesogenic chiral dopants have also
been prepared through esterification of chiral acids [17]. Halogen bonding has also been
shown to induce [6] and extend [18] mesophase temperature ranges. 2-Styrylbenzoic acids
have been synthesized as intermediates for 2-azachrysenes [19]. Stilbene carboxylic acids
have also been investigated as scaffolds for calcium sensors [20]. Cooksey et. al. have isolated
two stilbene-2-carboxylic acid phytoalexins from the leaves of pigeon pea [21]. Stilbene-4-
carboxylic acids have also been reported to induce differentiation of human promyelocytic
leukemia cell line HL-60 to mature granulocytes [22].
In continuation of our work on liquid crystal materials for commercial applications,
alkoxy/halostyryl benzoic acids were prepared as intermediates for side-chain liquid crystal
polymers. The alkoxy chain was varied from one to twelve carbon atoms to establish the effect
of chain length on thermal, mesomorphic, and photophysical properties. Some branched
chain and halogen-substituted derivatives were also synthesized for comparison purposes.
2. Experimental
2.1. Materials
1-Bromopropane, 1-iodobutane, 1-bromo-2-methylpropane, 2-bromobutane, 1-bromopent-
ane, 1-iodo-3-methylbutane, 1-bromoheptane, 1-hexanol, 1-dodecanol, butanone, and ben-
zoyl peroxide were purchased from Merck. Triphenylphosphine, N-bromosuccinimide, and
4-hydroxybenzaldehyde were supplied by International Laboratory USA whereas iodoethane,
anisaldehyde, and p-toluic acid were the products of Fluka. Dichloromethane was supplied
by Lab-Scan. Pyridine, carbon tetrachloride, 1-octanol, and 1-decanol were bought from
ˇ
Riedel-de-Haen. p-Toluenesulphonyl chloride, 1-bromoundecane, 3-chlorobenzaldehyde,
4-chlorobenzaldehyde, 3-fluorobenzaldehyde, and 4-fluorobenzaldehyde were the products
of Aldrich. Commercial methanol and toluene were distilled before use.
2.2. Characterization
Melting points were determined using Gallenkamp melting point apparatus and are uncor-
rected. Thermo Scientific Nicolet 6700 FT-IR spectrophotometer was used to record infrared
1
spectra. The H and 13C NMR spectra were acquired on a Bruker Avance 300 MHz NMR
spectrometer. Thermal behavior was studied using a Mettler Toledo TGA 851e and DSC
823e. Polarizing optical microscope (Olympus BH-2) equipped with a Linkam hot-stage
(Linksys 32) was used for textural studies. The UV-visible spectra were recorded on Dynam-
ica HALO DB-20 series spectrophotometer and fluorescence measurements were made on
Perkin Elmer LS 55 Luminescence Spectrometer.
2.3. Synthesis
Methyl alkoxy/halostyrylbenzoates (2a–r) were prepared by condensation of (4-
(methoxycarbonyl)benzyl)triphenylphosphonium bromide with alkoxy/halobenzaldehydes.
The hydrolysis of methyl alkoxy/halostyrylbenzoates (2a–r) afforded the target molecules as
outlined in Scheme 1.

34
K. MUHAMMAD ET AL.
Scheme . Synthesis of alkoxy/halostyrylbenzoic acids (3a–r). Reaction conditions: (i) NaOH/CHCl, r.t.;
(ii) NaOH/THF/HO, reflux.
... General method for preparation of methyl -((E)--alkoxy/halostyryl)benzoates
(2a–r)
To an ice-cooled solution of equimolar amounts (0.006 moles) of the Wittig salt (1) and
substituted aldehyde in 30 mL dichloromethane, was slowly added five times its amount
(0.03 moles) of NaOH dissolved in water (50% solution). The reaction mixture was stirred
until the reaction was complete (2–3 hr). The contents of the reaction flask were poured into
separating funnel and washed twice with 30 mL distilled water. The organic layer was removed
and the solvent evaporated under vacuum. The product was purified by crystallization from
ethanol. The characterization data for alkoxystyrylbenzoates (2a-n) are available in literature
[23] while those of halostyrylbenzoates are given as under.
2.3.1.1. Methyl 4-((E)-3-chlorostyryl)benzoate (2o). Yield: 72%; m.p.: 103–105°C; Rf =
−1
=
0.62 (n-hexane: ethyl acetate; 7:3); IR (neat): ῡ (cm ) 3016, 2963, 1720 (C O str.), 1601,
=
1561 (C C arom. str.), 1429, 1283, 1179, 1105 (C-Cl str.), 1008, 959, 871, 791, 763, 699.
1H-NMR (CDCl3): δ(ppm) 3.95 (s, 3H, -COOCH3), 7.15 (s, 2H, H-x and H-y), 7.26–7.35 (m,
2H, H-4ꢀꢀ, H-5ꢀꢀ), 7.41 (dt, 1H, J = 7.2 and 1.8 Hz, H-6ꢀꢀ), 7.54 (t, 1H, J = 1.8 Hz, H-2ꢀꢀ), 7.57
(d, 2H, J = 8.7 Hz, H-3ꢀ, 5ꢀ), 8.05 (d, 2H, J = 8.4 Hz, H-2ꢀ, 6ꢀ). 13C-NMR (CDCl3): δ(ppm)
52.17 (-CH3), 125.04 (C-6ꢀꢀ), 126.49 (C-3ꢀ, 5ꢀ), 126.55 (C-2ꢀꢀ), 128.11 (C-y), 128.96 (C-x),
129.29 (C-1ꢀꢀ), 129.69 (C-4ꢀꢀ), 130.00 (C-5ꢀꢀ), 130.09 (C-2ꢀ, 6ꢀ), 134.76 (C-3ꢀꢀ), 138.62 (C-1ꢀꢀ),
+ˑ
=
141.23 (C-4 ), 166.81 (C O). EI-MS: m/z (relative abundance) 272 (M , 80%), 241 (53%),
213 (18%), 178 (100%), 111 (6%), 76 (15%), 75 (9%), 51 (5%).
2.3.1.2. Methyl 4-((E)-4-chlorostyryl)benzoate (2p). Yield: 70%; m.p.: 148–150°C; Rf =
0.61 (n-hexane: ethyl acetate; 7:3); IR (neat): ῡ (cm−1) 1721, 1486, 1435, 1285, 1105, 967, 848,
815, 766, 708. 1H-NMR (CDCl3): δ(ppm) 3.94 (s, 3H, -COOCH3), 7.10 (d, 1H, J = 16.5 Hz,
H-x), 7.18 (d, 1H, J = 16.5 Hz, H-y), 7.36 (d, 2H, J = 8.4 Hz, H-3ꢀꢀ,5ꢀꢀ), 7.47 (d, 2H, J =
8.4 Hz, H-2ꢀꢀ,6ꢀꢀ), 7.56 (d, 2H, J = 8.1 Hz, H-3ꢀ,5ꢀ), 8.04 (d, 2H, J = 8.1 Hz, H-2ꢀ,6ꢀ). 13C-NMR
(CDCl3): δ(ppm) 52.17 (-CH3), 126.38 (C-3ꢀ, 5ꢀ), 127.94 (C-2ꢀꢀ, 6ꢀꢀ), 128.14 (C-y), 128.99 (C-
3ꢀꢀ, 5ꢀꢀ), 129.11 (C-1ꢀ), 129.85 (C-x), 130.08 (C-2ꢀ, 6ꢀ), 133.86 (C-+1˙ꢀꢀ), 135.24 (C-4ꢀꢀ), 141.43
ꢀ
+.
=
(C-4 ), 166.85 (C O). EI-MS: m/z (relative abundance) 274 (M , 12%), 272 (M , 37%),

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
35
243 (7%), 241 (30%), 213 (10%), 179 (16%), 178 (100%), 177 (29%), 176 (39%), 152 (18%),
151 (25%), 89 (16%), 88 (42%), 76 (20%), 75 (22%), 63 (13%), 59 (17%), 51 (21%).
2.3.1.3. Methyl 4-((E)-3-fluorostyryl)benzoate (2q). Yield: 71%; m.p.: 104–106°C; Rf =
0.60 (n-hexane: ethyl acetate; 7:3); IR (neat): ῡ (cm−1) 3065, 3002, 2952, 2848, 1715, 1609,
1581, 1565, 1509, 1484, 1448, 1437, 1413, 1280, 1265, 1196, 1185, 1144, 1112, 1014, 958, 866,
1
833, 790. H-NMR (CDCl3): δ(ppm) 3.95 (s, 3H, -COOCH3), 7.01 (tdd, 1H, J = 8.7, 2.4,
1.8 Hz, H-4ꢀꢀ), 7.13 (d, 1H, J = 16.2 Hz, H-x), 7.20 (d, 1H, J = 16.2 Hz, H-y), 7.23–7.39 (m,
3H, H-2ꢀꢀ,5ꢀꢀ,6ꢀꢀ), 7.58 (d, 2H, J = 8.7 Hz, H-3ꢀ,5ꢀ), 8.06 (d, 2H, J = 8.4 Hz, H-2ꢀ,6ꢀ). 13C-NMR
(CDCl3): δ(ppm) 52.15 (CH3), 113.04 (d, 2JC,F = 21.75 Hz, C-2ꢀꢀ), 115.04 (d, 2JC,F = 21.75 Hz,
C-4ꢀꢀ), 122.78 (d, 4JC,F = 2.25 Hz, C-6ꢀꢀ), 126.48 (C-3ꢀ, 5ꢀ), 128.88 (C-y), 129.28 (C-1ꢀ), 129.96
4
3
3
(d, JC,F = 2.25 Hz, C-x), 130.08 (C-2ꢀ, 6ꢀ), 130.24 (d, JC,F = 9.0 Hz, C-5ꢀꢀ), 139.1 (d, JC,F
= 7.5 Hz, C-1ꢀꢀ), 141.27 (C-4ꢀ), 163.18 (d, 1JC,F = 244.5 Hz, C-3ꢀꢀ), 166.82 (C = O). EI-MS:
m/z (relative abundance) 256 (M+˙, 100%), 225 (71%), 197 (62%), 196 (71%), 177 (23%), 170
(10%), 112 (10%), 98 (23%), 85 (9%), 75 (7%).
2.3.1.4. Methyl 4-((E)-4-fluorostyryl)benzoate (2r). Yield: 72%; m.p.: 128–130°C; Rf =
0.58 (n-hexane: ethyl acetate; 7:3) IR (neat): ῡ (cm−1) 1722, 1597, 1510, 1437, 1285, 1246,
1
1181, 1107, 964, 848, 818, 764. H-NMR (CDCl3): δ(ppm) 3.94 (s, 3H, -COOCH3), 7.03–
7.12 (m, 3H, H-x, 3ꢀꢀ, 5ꢀꢀ), 7.20 (d, 1H, J = 16.2 Hz, H-y), 7.50–7.58 (m, 4H, H-3ꢀ, 5ꢀ, 2ꢀꢀ, 6ꢀꢀ),
8.04 (d, 2H, J = 8.1 Hz, H-2ꢀ, 6ꢀ). 13C-NMR (CDCl3): δ(ppm) 52.14 (-CH3), 115.80 (d, 2JC,F
= 21.75 Hz, C-3ꢀꢀ, 5ꢀꢀ), 126.26 (C-3ꢀ, 5ꢀ), 127.34 (d, 5JC,F = 2.25 Hz, C-x), 128.34 (d, 3JC,F
=
8.25 Hz, C-2ꢀꢀ, 6ꢀꢀ), 128.94 (C-1ꢀ), 129.98 (C-y), 130.07 (C-2ꢀ, 6ꢀ), 132.94 (d, 4JC,F = 3.75 Hz,
ꢀꢀ
C-1ꢀꢀ), 141.65 (C-4ꢀ), 162.69 (d, 1JC,F = 244.5 Hz, C-4 ), 166.88 (C O). EI-MS: m/z (relative
=
abundance) 256 (M+˙, 100%), 225 (66%), 197 (38%), 196 (61%), 177 (15%), 176 (12%), 170
(9%), 112 (9%), 98 (19%), 85 (8%), 75 (5%), 51 (4%).
... General method for the preparation of -((E)--alkoxy/halostyryl)benzoic acids
(3a–r)
Methyl 4-alkoxy/halostyrylbenzoate (0.014 mol) and NaOH (0.014 mol, 0.56 g) were dis-
solved in a mixture of THF (40 mL) and water (10 mL) and the mixture refluxed for 4 hr.
The contents were diluted to 500 mL by the addition of distilled water and acidified with 6N
HCl solution. The precipitated solid was filtered and purified by crystallization from ethanol
and THF mixture. The spectroscopic data for compounds 3c, 3d, 3g, 3i, 3k, 3l, 3m, 3n and
those with halogen substitution (3o–r) have already been published [24] while for the rest of
the compounds are presented here.
2.3.2.1. 4-((E)-4-Methoxystyryl)benzoic acid (3a). Yield: 97%; m.p.: 259–260°C; Rf = 0.26
−1
=
(n-hexane: ethyl acetate; 7:3); IR (neat): ῡ, (cm ): 3024–2290 (O-H str.), 1674 (C O str.),
=
1595, 1505 (C C arom. str.), 1422, 1286 (C˗O acid str.), 1250, 1174, 1111, 1025, 959, 846,
824, 767, 719, 692. 1H-NMR (DMSO): δ(ppm) 3.78 (s, 1H, -OCH3), 6.97 (d, 2H, J = 8.7 Hz,
H-3ʺ, 5ʺ), 7.17 (d, 1H, J = 16.5 Hz, H-x), 7.36 (d,1H, J = 16.5 Hz, H-y), 7.59 (d, 2H, J = 8.7 Hz,
H-2ʺ, 6ʺ), 7.67 (d, 2H, J = 8.4 Hz, H-3ꢀ, 5ꢀ), 7.92 (d, 2H, J = 8.4 Hz, H-2ꢀ, 6ꢀ), 12.89 (s, 1H,
-COOH). 13C-NMR (DMSO): δ(ppm) 55.64 (C-1), 114.71 (C-3ʺ, 5ʺ), 125.49 (C-x), 126.56
(C-3ꢀ, 5ꢀ), 128.69 (C-2ʺ, 6ʺ), 129.44 (C-1ʺ), 129.71 (C-1ꢀ), 130.22 (C-2ꢀ, 6ꢀ), 131.12 (C-y),
142.29 (C-4ꢀ), 159.86 (C-4ʺ), 167.59 (-COOH).

36
K. MUHAMMAD ET AL.
2.3.2.2. 4-((E)-4-Ethoxystyryl)benzoic acid (3b). Yield: 96%; m.p.: 277–280°C; Rf = 0.27
(n-hexane: ethyl acetate; 7:3); IR (neat): ῡ (cm−1): 3150–2750 (O-H str.), 1683 (C=O str.),
1597, 1508, 1474 (C=C arom. str.), 1426, 1287 (C-O carboxyl), 1248, 1179, 1111, 1043, 961,
848, 810, 768, 694. 1H-NMR (DMSO): δ(ppm) 1.33 (t, 3H, J = 6.6 Hz, H-2), 4.04 (q, 2H, J =
6.6 Hz, H-1), 6.94 (d, 2H, J = 7.8 Hz, H-3ꢀꢀ, 5ꢀꢀ), 7.16 (d, 1H, J = 16.5 Hz, H-x), 7.35 (d, 1H,
J = 16.5 Hz, H-y), 7.57 (d, 2H, J = 8.1 Hz, H-2ꢀꢀ, 6ꢀꢀ), 7.66 (d, 2H, J = 7.8 Hz, H-3ꢀ, 5ꢀ), 7.92
(d, 2H, J = 8.1 Hz, H-2ꢀ, 6ꢀ), 12.87 (s, 1H, -COOH). 13C-NMR (DMSO): δ(ppm) 15.12 (C-2),
63.39 (C-1), 114.78 (C-3ʺ, 5ʺ), 125.24 (C-x), 126.23 (C-3ꢀ, 5ꢀ), 128.37 (C-2ʺ, 6ʺ), 129.46 (C-1ʺ),
129.79 (C-1ꢀ), 130.00 (C-2ꢀ, 6ꢀ), 130.93 (C-y), 142.38 (C-4ꢀ), 159.36 (C-4ʺ), 167.61 (-COOH).
2.3.2.3. 4-((E)-4-Isobutyloxystyryl)benzoic acid (3e). Yield: 97%; m.p.: 272–276°C; Rf =
0.28 (n-hexane: ethyl acetate; 7:3); IR (neat): ῡ (cm−1): 3025–2475 (O-H str.), 1679 (C=O
str.), 1596, 1505, 1464 (C=C arom. str.), 1423, 1287 (C-O acid str.), 1269, 1242, 1175, 1128,
1
1113, 1028, 966, 878, 844, 811, 767, 719, 694. H-NMR (DMSO): δ(ppm) 0.98 (d, 6H, J =
6.6 Hz, H-3), 1.95–2.06 (m, 1H, H-2), 3.76 (d, 2H, J = 6.6 Hz, H-1), 6.96 (d, 2H, J = 8.7 Hz,
H-3ʺ, 5ʺ), 7.16 (d, 1H, J = 16.2 Hz, H-x), 7.35 (d, 1H, J = 16.2 Hz, H-y), 7.57 (d, 2H, J =
8.7 Hz, H-2ʺ, 6ʺ), 7.67 (d, 2H, J = 8.1 Hz, H-3ꢀ, 5ꢀ), 7.92 (d, 2H, J = 8.1 Hz, H-2ꢀ, 6ꢀ), 12.88 (s,
1H, -COOH). 13C-NMR (DMSO): δ(ppm) 19.51 (C-3), 28.17 (C-2), 74.21 (C-1), 115.20 (C-
3ʺ, 5ʺ), 125.39 (C-x), 126.55 (C-3ꢀ, 5ꢀ), 128.69 (C-2ʺ, 6ʺ), 129.39 (C-1ʺ), 129.57 (C-1ꢀ), 130.22
(C-2ꢀ, 6ꢀ), 131.14 (C-y), 142.32 (C-4ꢀ), 159.41 (C-4ʺ), 167.59 (-COOH).
2.3.2.4. 4-((E)-4-sec-Butyloxystyryl)benzoic acid (3f). Yield: 96%; m.p.: 235–243°C; Rf =
0.30 (n-hexane: ethyl acetate; 7:3); IR (neat): ῡ (cm−1): 2970–2258 (O-H str.), 1673 (C=O
str.), 1594, 1505, 1467 (C=C arom. str.), 1425, 1377, 1293 (C-O acid str.), 1246, 1184, 1097,
1026, 968, 952, 930, 879, 842, 823, 806, 768, 719, 693. 1H-NMR (DMSO): δ(ppm) 0.92 (t, 3H,
J = 7.5 Hz, H-3), 1.23 (d, 3H, J = 6.0 Hz, H-2a), 1.53–1.71 (m, 2H, H-2), 4.42 (sextet, 1H,
J = 5.7 Hz, H-1), 6.94 (d, 2H, J = 8.7 Hz, H-3ʺ, 5ʺ), 7.15 (d, 1H, J = 16.5 Hz, H-x), 7.35
(d, 1H, J = 16.5 Hz, H-y), 7.56 (d, 2H, J = 8.7 Hz, H-2ʺ, 6ʺ), 7.67 (d, 2H, J = 8.4 Hz, H-3ꢀ, 5ꢀ),
7.92 (d, 2H, J = 8.4 Hz, H-2ꢀ, 6ꢀ), 12.88 (s, 1H, -COOH). 13C-NMR (DMSO): δ(ppm) 10.00
(C-3), 19.49 (C-2a), 29.00 (C-2), 74.56 (C-1), 116.23 (C-3ʺ, 5ʺ), 125.33 (C-x), 126.55 (C-3ꢀ, 5ꢀ),
128.74 (C-2ʺ, 6ʺ), 129.38 (C-1ʺ), 129.41 (C-1ꢀ), 130.22 (C-2ꢀ, 6ꢀ), 131.16 (C-y), 142.34 (C-4ꢀ),
158.43 (C-4ʺ), 167.59 (-COOH).
2.3.2.5. 4-((E)-4-(Isopentyloxy)styryl)benzoic acid (3h). Yield: 94%; m.p.: 248–261°C; Rf
= 0.29 (n-hexane: ethyl acetate; 7:3); IR (neat): ῡ (cm−1): 3200–2450 (O-H str.), 1682 (C=O
str.), 1599, 1564, 1507, and 1468 (C=C arom. str.), 1425, 1316, 1292 (C-O acid str.), 1248,
1177, 1111, 1060, 1020, 959, 881, 848, 829, 768, 661. 1H-NMR (DMSO): δ(ppm) 0.93 (d, 6H,
J = 6.6 Hz, H-4), 1.61 (q, 2H, J = 6.6 Hz, H-2), 1.71–1.84 (m, 1H, H-3), 4.0 (t, 2H, J = 6.6 Hz,
H-1), 6.96 (d, 2H, J = 8.4 Hz, H-3ʺ, 5ʺ), 7.16 (d, 1H, J = 16.5 Hz, H-x), 7.35 (d, 1H, J =
16.2 Hz, H-y), 7.56 (d, 2H, J = 8.4 Hz, H-2ʺ, 6ʺ), 7.67 (d, 2H, J = 8.4 Hz, H-3ꢀ, 5ꢀ), 7.92 (d, 2H,
J = 8.1 Hz, H-2ꢀ, 6ꢀ), 12.88 (s, 1H, -COOH). 13C-NMR (DMSO): δ(ppm) 22.89 (C-4), 25.03
(C-3), 37.87 (C-2), 66.40 (C-1), 115.18 (C-3ʺ, 5ʺ), 125.38 (C-x), 126.55 (C-3ꢀ, 5ꢀ), 128.68 (C-2ʺ,
6ʺ), 129.40 (C-1ʺ), 129.56 (C-1ꢀ), 130.22 (C-2ꢀ, 6ꢀ), 131.15 (C-y), 142.32 (C-4ꢀ), 159.31 (C-4ʺ),
167.59 (-COOH).
2.3.2.6. 4-((E)-4-Heptyloxystyryl)benzoic acid (3j). Yield: 96%; m.p.: 210–262°C; Rf = 0.20
(n-hexane: ethyl acetate; 7:3); IR (neat): ῡ (cm−1): 3200–2450 (O-H str.), 1680 (C=O str.),

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
37
Table . Thermogravimetric data of representative styryl acids.
b
Compound
Ta (°C)
T (°C)
Extent of decomp.(%)
3a
3b
3c
3g
3h
3i
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
3j
3k
3l
3m
3n
aTemperature at which decomposition starts.
bTemperature of maximum decomposition.
1597, 1563, 1504, and 1469 (C=C arom. str.), 1426, 1314, 1290 (C-O acid str.), 1245, 1176,
1112, 1063, 1024, 957, 883, 842, 828, 769, 663. 1H-NMR (DMSO): δ(ppm) 0.83 (t, 3H, J =
6.9 Hz, H-7), 1.31–1.39 (m, 8H, H-3-6), 1.69 (quin. 2H, J = 6.6 Hz, H-2), 3.96 (t, 2H, J =
6.6 Hz, H-1), 6.93 (d, 2H, J = 8.7 Hz, H-3ʺ, 5ʺ), 7.15 (d, 1H, J = 16.5 Hz, H-x), 7.34 (d,
1H, J = 16.2 Hz, H-y), 7.55 (d, 2H, J = 9.0 Hz, H-2ʺ, 6ʺ), 7.66 (d, 2H, J = 8.4 Hz, H-3ꢀ, 5ꢀ),
7.92 (d, 2H, J = 8.4 Hz, H-2ꢀ, 6ꢀ), 12.87 (s, 1H, -COOH). 13C-NMR (DMSO): δ(ppm) 14.40
(C-7), 22.53 (C-6), 25.95 (C-3), 28.93, 29.15 (C-2,4), 31.71 (C-5), 67.95 (C-1), 115.15 (C-3ʺ,
5ʺ), 125.38 (C-x), 126.53 (C-3ꢀ, 5ꢀ), 128.67 (C-2ʺ, 6ʺ), 129.43 (C-1ʺ), 129.55 (C-1ꢀ), 130.21
ꢀ
ꢀ
ꢀ
–
(C-2 , 6 ), 131.14 (C-y), 142.30 (C-4 ), 159.32 (C-4ʺ), 167.59 ( COOH).
3. Results and discussion
3.1. Thermal stability
In order to find temperature up to which a compound can be safely heated without any decom-
position, the acids were subjected to thermogravimetric analysis. The data are given in Table 1.
All the compounds show two-step degradations as exemplified in Fig. 1. Major loss in weight
(80–90%) occurred in the first step while second step involves 8–18% weight loss.
Figure . TGA thermograms of representative compounds.

38
K. MUHAMMAD ET AL.
Figure . DSC thermograms of compound 3f (red trace in A), 3g (black trace in A), and 3n (B).
3.2. Liquid crystalline properties
Liquid crystalline properties of the synthesized acids were determined by differential scanning
calorimetry (DSC) and polarizing optical microscopy (POM). Compounds (3a–c) were found
non-mesomorphic because their melting point ranges are as of normal organic compounds
and show only melting transitions in DSC. The next three members of the series (3d–f) having
four-carbon alkoxy chain, show melting and decomposition peaks in DSC thermograms (red
trace in Fig. 2(A) for compound 3f). In the next three acids (3g–i), there is a lower temperature
peak representing some change in crystal structure, a second large peak for melting transition,
and a third small peak indicating decomposition (black trace in Fig. 2(A) for compound 2g).
It was observed that these compounds decompose in the nematic phase before the onset of
isotropic clear liquid phase. Multiple peaks are present in DSC graphs for the higher homologs
as depicted in Fig. 2(B) for compound 3n. The last (right) peak in this graph represents melt-
ing transition as is evident from its large enthalpy value of 16.29 kJ mol−1 in comparison to
1.29–4.55 kJ mol−1 for other peaks in DSC of compound 3n. The pre-melting peaks represent
transitions among smectic phases (see images C to F in Fig. 3).
The liquid crystal phase exhibited by these compounds was recognized as nematic from
the characteristic schlieren texture under POM as shown in Fig. 3(A). The disclination lines
connecting a point from one surface to the other (thread-like defects) could clearly be seen in
Fig. 3(B), which usually appear in thick samples. In lower homologs (C4 to C6), the nematic
phase is monotropic as the compound undergoes decomposition before the clearing point.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
39
Figure . Polarized light microscopic images: (A) Schlieren texture of compound 3e at °C, (B–F) textures
shown by compound 3n in cooling cycle at .°C (B), .°C (C), .°C (D), .°C, (E) and °C (F).
In higher homologs, the nematic phase formed after melting the compound, lasts for a few
degrees, and is followed by isotropization. This is why a single broad peak is observed instead
of two separate peaks for melting and isotropization in DSC thermograms. The textures exhib-
ited under POM by compound 3n on cooling from isotropic liquid are shown in Figs. 3(B)–
(F)). Image B corresponds to edge-dislocations at the nematic to smectic C transition, C and
D exhibit schlieren texture of the smectic C phase while E is that of a highly ordered smec-
tic phase. This smectic phase finally changes into the crystal phase (texture F) as cooling is
continued.
3.3. Single crystal X-ray crystallography
For the structure and stereochemistry elucidation of the synthesized compounds, single crys-
tals of the products were grown by dissolving the compounds in a mixture of ethanol and

40
K. MUHAMMAD ET AL.
tetrahydrofuran (70:30). Crystals of 3b and 3f were grown by slow evaporation of the sol-
vent at room temperature. The colorless crystals were mounted in random orientation on a
glass fiber on a Stoe IPDS-II two circle diffractometer [25] equipped with graphite monochro-
˚
mated MoKα radiation (λ = 0.71073 A). The structure was solved by direct methods using
SHELXS97 and refined with full-matrix least-squares on F2 with SHELXL-97 [26]. All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were located in a difference
map but refined using a riding model. For molecular graphics, XP from the SHELXTL suite
[27] was used.
CCDC 1486916-1486917 contains the supplementary crystallographic data for this article.
These data can be obtained free of charge from the Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/datarequest/cif.
... Crystals and molecular structures of 3b and 3f
Table 2 summarizes the crystal data and refinement details for compounds 3b and 3f.
Although there exist some discrete differences for the two compounds, there are general sim-
ilarities both in terms of the core trans-stilbene moieties of the individual molecules and
the intermolecular interactions between neighboring molecules in the crystals of 3b and 3f.
The individual molecules show some deviation from planarity with the phenyls twisted at
dihedral angles of 8–11°. The molecular structures of 3b and 3f are shown in Figs. 4 and 5.
Compound 3b crystallized with two independent conformers in the asymmetric unit while
3f had one molecule in the asymmetric unit. The two molecules in 3b have a pseudo-glide
symmetry relationship, that is, the two molecules are packed in an edge-to-face orientation
having a herringbone pattern or a T-shape, or, with an angle of 57.96° between the planes
passing through the identical selections (Fig. 6). Some selected bond lengths and bond angles
Table . Crystal data and structure refinement for 3b and 3f.
b
f
Formula
FW
CHO
.
CHO
.
Crystal system
Triclinic
P-
.()
.()
orthorhombic
Pbca
.()
.()
.()
Space group
˚
a (A)
˚
b (A)
˚
c (A)
.()
α, β, γ (°)
.()
.()
.
.
.()
.(), 
()
., .
.
.
.(), 
()
., .
.

˚
V (A ), Z
T (K)
DC Mg m−, μ (mm−
F()
)
Crystal size (mm)
θ range (°)
. × . × .
. × . × .
. to 
. to 
Index ranges
− ࣘ h ࣘ 
− ࣘ k ࣘ 
− ࣘ l ࣘ 
,
− ࣘ h ࣘ 
− ࣘ k ࣘ 
− ࣘ l ࣘ 
,
Reflections collected
Indept. Reflect. [R(int)]
Completeness to θ
Max. & min. transmission
Data/restraints/parameters
Goodness-of-fit on F
 [Rint = .]
 [Rint = .]
.
.
. & −.
//
.
. & −.
//
.
R [I > σ(I)], wR [all data]
R = ., wR = .,
R = ., wR = .
./−.
R = ., wR = .
R = ., wR = .
./−.
−
˚
Largest peak and hole (eA
)

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
41
Figure . Molecular structure of 3b showing atom numbering scheme.
Figure . Molecular structure of 3f showing atom numbering scheme.
have been delineated in Table 3. In the crystal packing, both the molecules possess inter-
molecular O(2)-H(1)···O(1)i, O(1)-H(1)···O(2)i and O(5)-H(5)···O(4)ii {Symmetry codes:
(i)5/2−X,1−Y,1/2+Z (3b), (i) 2−X,1−Y, −Z, (ii) 3−X, −Y, −Z (3f)} H-bonds (Table 4) that
link the molecules into centrosymmetric dimers (Figs. 7 and 8).
˚
Table . Selected bond lengths (A) and angles (°) for 3b and 3f.
3b
O-C
O-C
O-C
CA-CA
O-CA
O-C
.()
.()
.()
.()
.()
.()
O-C-CA
O-C-CA
CA-O-C
O-C-O
CA-CA-CA
CA-CA-CA
.()
.()
.()
.()
.()
.()
3f
O-C
.()
.()
.()
.()
.()
.()
O-C-O
O-C-C
O-C-C
C-O-C
C-C-C
C-C-C
.()
.()
.()
.()
.()
.()
O-C
O-C
O-C
C-C
C-C
Table . The intermolecular and intramolecular hydrogen bonds for compounds 3b and 3f.
D—H···A
D—H
H···A
D···A
D—H···A
3b
3f
O()-H()···O()i
O()-H()···O()i
O()-H()···O()ii
.
.
.
.
.
.
.()
.()
.()
.
.
.
Symmetry codes: (i) / − X,  − Y, / + Z (3a), (i)  − X,  − Y, − Z, (ii)  − X, − Y, − Z (3b).

42
K. MUHAMMAD ET AL.
Figure . Edge-to-face orientation having a herringbone pattern or a T-shape view of 3b in space fill model.
Figure . Centrosymmetric dimers of 3b, hydrogen bonds are shown as dashed lines.
Figure . Centrosymmetric dimer of 3f, hydrogen bonds are shown as dashed lines.
3.4. Photophysical properties
Solutions of the compounds prepared in tetrahydrofuran were used for UV-visible absorp-
tion measurements. The data are presented in Table 5 and the UV-visible spectra for some
synthesized compounds are depicted in Fig. 9. All the alkoxy-substituted acids (3a–n) show
single maxima in 333–337 nm wavelength range. The spectra of compounds with halogen
group (3o–r) exhibit a central maxima at 319–324 nm, with shoulder on each side as shown
in Fig. 9(B). The lone pair on alkoxy oxygen or halogens is in conjugation with benzene rings
Table . UV-visible absorption data of reported compounds.
Compound
Absorption (λmax
)
Fluorescence (λmax
)
Stoke’s shift
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
43
Figure . UV-visible absorption spectra of alkoxystyrylbenzoic acids (A) and halostyrylbenzoic acids (B).
and the carboxyl group. This extended conjugation in the rigid core lowers the energy differ-
ence between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular
orbital (LUMO) resulting in strong absorptions with molar absorptivity (ε) values ranging
from 2.98 × 104 to 3.58 × 104 M−1 cm−1. The high ε-values indicate that the absorptions are
due to π–π∗ electronic transitions.
The fluorescence spectra of compounds were recorded using the same solutions as used for
UV-visible absorption measurements and are shown in Fig. 10. The excitation radiations hav-
ing wavelength of 333 nm and 322 nm were used for alkoxy- and halogen-substituted acids,
respectively. The λmax of blue fluorescent light has the range of 408.5–416.5 nm in the former
and 380.5–386.5 nm in the later acids. The increase in wavelength of the emitted light (Stoke’s

44
K. MUHAMMAD ET AL.
Figure . Fluorescence spectra of alkoxystyrylbenzoic acids (A) and halostyrylbenzoic acids (B).
shift) ranges from 72.5 to 81.5 nm in alkoxyacids while 61.5 to 63.5 nm in haloacids. The
smaller Stoke’s shift in halogen derivatives may be attributed to lesser tendency of delocaliza-
tion of lone electron pair in halogen atoms.
4. Conclusion
Alkoxystyrylbenzoic acids having 1–12 carbon atoms were prepared and studied through
thermogravimetric analysis, differential scanning calorimetry, polarizing optical microscopy,
and X-ray diffraction. The straight chain acids are thermally stable up to 291–298°C. Nematic
phase is shown by all the acids with alkoxy chain longer than C4 while higher homologs
(C7–C12) also exhibit smectic C and a higher order smectic phase. X-ray diffraction stud-
ies show that propoxystyrylbenzoic acid crystallizes with two independent conformations in
the asymmetric unit with an edge-to-face orientation having a herringbone pattern while sec-
butoxystyrylbenzoic acid has one molecule in the asymmetric unit. The UV-visible spectra of
alkoxy acids exhibit an absorption maximum in the wavelength range of 333–337 nm whereas
the λmax range is 319–324 nm in case of halogen-substituted acids. All the acids show blue
fluorescence.
References
[1] Adomeniene, O., Adomenas, P., Gleiznys, A., Poloudina, L., & Gotoh, Y. (2001). Mol. Cryst. Liq.
Cryst., 365, 75.
[2] Muhammad, K., Hameed, S., Tan, J., & Liu, R. (2011). Liq. Cryst., 38, 333.
[3] Wu, S.-L., & Hsu, H.-N. (2007). Liq. Cryst., 34, 1159.
[4] Miranda, M. D., et al. (2014). Liq. Cryst., 41, 1743.
[5] Naoum, M. M., Fahmi, A. A., Muhammady, S. Z., & Abaza, A. H. (2010). Liq. Cryst., 37, 475.
[6] Cho, C. M., Wang, X., Li, J. J., He, C., & Xu, J. (2013). Liq. Cryst., 40, 185.
[7] Zhou, X., Narayanan, T., & Li, Q. (2007). Liq. Cryst., 34, 1243.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
45
[8] Roohnikan, M., Ebrahimi, M., Ghaffarian, S. R., & Tamaoki, N. (2013). Liq. Cryst., 40, 314.
[9] Rambabu, M., Pisipati, V. J. K. M., Kumar, J. V. S., & Prasad, K. R. S. (2013). Liq. Cryst. Today,
22, 4.
[10] Mandle, R. J. (2016). Soft Matter, 12, 7883.
[11] Ujiie, S., et al. (2014). In: Handbook of Liquid Crystals, Goodby, J., Collings, P. J., Kato, T.,
Tschierske, C., Gleeson, H., & Raynes, P. (Eds.), Wiley-VCH Weinheim, 7: III 11, 1–34.
[12] Mandle, R. J., & Goodby, J. W. (2016). Chemphyschem., 17, 967.
[13] Lehn, J.-M. (2002). Polym. Int., 51, 825.
[14] Kato, T. (1996). Korea Polym. J., 4, 125.
[15] Hudson, S. A., & Maltlis, P. M. (1993). Chem. Rev., 93, 861.
[16] Bardaji, M. (2014). Inorganics, 2, 433.
[17] Tojo, K., Hirose, T., & Aoki, Y. (2008). Liq. Cryst., 35, 681.
[18] McAllister, L. J., et al. (2013). Chem. Commun., 49, 3946.
[19] Pampin, C., Estevez, J. C., Castedo, L., & Estevez, R. J. (2002). Tetrahed. Lett., 43, 4551.
[20] Behanna, H. A., & Stupp, S. I. (2005). Chem. Commun., 38, 4845.
[21] Cooksey, C. J., Dahiya, J. S., Garratt, P. J., & Strange, R. N. (1982). Phytochemistry, 21, 2935.
[22] Kagechika, H., et al. (1989). J. Med. Chem., 32, 1098.
[23] Muhammad, K., Nazir, S., Hameed, S., & Bechtold, I. H. (2016). Liq. Cryst., 43, 863.
[24] Muhammad, K., Hameed, S., Siddiqi, H. M., Eccher, J., & Bechtold, I. H. (2016). Liq. Cryst., 44,
628. Available at https://doi.org/10.1080/02678292.2016.1226974.
[25] Bruker (2007). APEX2 (Version 2.1-4), SAINT (version 7.34A), SADABS (version 2007/4), Bruk-
erAXS Inc.: Madison, Wisconsin, USA.
[26] Sheldrick, G. M. (1997). SHELXS97 and SHELXL97, University of Göttingen: Germany.
[27] Macrae, C. F., et al. (2006). J. Appl. Cryst., 39, 453.