Synthesis mesomorphic and theoretical studies of some new unsymmetrical dimeric ethers of 6-amino-1,3-dimethyluracil and biphenyl cores

Article abstract of DOI:10.1016/j.molstruc.2016.03.052

New sets of unsymmetric calamitic molecules with uracil unit at one end and biphenyl core at another end were synthesized. Liquid crystal property of these molecules was investigated by POM and DSC techniques. All compounds exhibit LC property depending o

Full text of DOI:10.1016/j.molstruc.2016.03.052

Accepted Manuscript
Synthesis mesomorphic and theoretical studies of some new unsymmetrical dimeric
ethers of 6-amino-1,3-dimethyluracil and biphenyl cores
AbdulKarim-Talaq Mohammad, H.T. Srinivasa, Hameed Madlool Mohammed, S.
Hariprasad, Guan-Yeow Yeap
PII:
S0022-2860(16)30247-2
10.1016/j.molstruc.2016.03.052
MOLSTR 22363
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 21 November 2015
Revised Date: 12 March 2016
Accepted Date: 15 March 2016
Please cite this article as: A.-T. Mohammad, H.T. Srinivasa, H.M. Mohammed, S. Hariprasad, G.-Y.
Yeap, Synthesis mesomorphic and theoretical studies of some new unsymmetrical dimeric ethers of
6-amino-1,3-dimethyluracil and biphenyl cores, Journal of Molecular Structure (2016), doi: 10.1016/
j.molstruc.2016.03.052.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Synthesis mesomorphic and theoretical studies of some new
unsymmetrical dimeric ethers of 6-amino-1,3-dimethyluracil and
biphenyl cores
AbdulKarim-Talaq Mohammad1, Srinivasa, H. T2, Hameed Madlool Mohammed3,
Hariprasad, S4, Guan-Yeow Yeap5
1Chemistry Department, College of Science, University of Anbar, Ramadi, Iraq
2Raman Research Institute, Soft Condensed Matter Group, Sadashivanagara,
Bengaluru-560080, Karnataka, India
3Chemistry Department, College of Science for Women, University of Baghdad,
Baghdad, Iraq
4Department of Chemistry, Central College Campus, Bangalore University,
Bengaluru-560001, Karnataka, India
5Liquid Crystal Research Laboratory, School of Chemical Sciences, Universiti Sains
Malaysia, Minden 11800, Penang, Malaysia
Abstract
New sets of unsymmetric calamitic molecules with uracil unit at one end and
biphenyl core at another end were synthesized. Liquid crystal property of these
molecules was investigated by POM and DSC techniques. All compounds exhibit LC
property depending on the spacer and terminal alkoxy chain of the molecules. First set
shows smectic phase in lower members and nematic phase appeared in higher
members. The second set favour nematic liquid crystalline phase with respect to
spacer alkyl chain length. Molecules are escaped from the planarity as a result
disturbing the layer stacking leads to nematic phase in higher analogues. Theoretical
studies have been performed for all the compounds and are found to be in agreement
with the results of the current studies.
Keyword: liquid crystals, dimers, mesophases, heterocycles, uracil, theoretical
studies
_________
*Author for correspondence: *AbdulKarim-Talaq Mohammad, Tel; +9647902529959
E-mail address: drmohamadtalaq@gmail.com.
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1. Introduction
It has been well documented that the liquid crystalline behaviour of an organic
compound is dependent on its molecular architecture in which a slight change in its
molecular geometry gives rise to a considerable change in its mesomorphic properties
[1-6]. Liquid crystalline materials possess many applications in scientific and
technological areas, in particular as display devices, organic light emitting diodes
(OLEDs), anisotropic networks, photoconductors and semiconductor materials [7-9].
Dimer is one, in the classification of liquid crystals in which two rigid mesogenic
units are joined by a flexible spacer [9]. The phase transition behaviour of dimer
depends on the chain length especially the parity of the connecting spacer [11, 12].
Recently, research based on dimers has received considerable attention owing to the
fact that the dimers could behave as model compounds for the understanding of the
technologically important semi-flexible main chain liquid crystal polymers and as
model compounds for side group liquid crystal polymers [13-15]. On the other hand,
studies on mesogenic structures containing heterocyclic rings have increased
remarkably, owing to their abilities to exhibit mesogenic behavior either similar to or
superior to the linear phenyl analogs [16-21]. Further, the presence of heteroatoms (O,
S and N) has lead to significant changes in the corresponding liquid crystalline phases
and/or in the physical properties of the observed phases because the heteroatoms are
more polarizable than carbon. Therefore, a large dipole may eventually be introduced
into a liquid crystal structure in comparison with the analogous phenyl-based
mesogens [22-24]. With respect to the nucleic acid bases, the cholesteric mesophase
has been observed only in adenine and thymine with cholesterol moiety [25, 26].
Due to our interest, we are continuing our investigations on preparation and
characterization of heterocycle-based thermotropic liquid crystals. Moreover,
recently, we have reported mesogenic compounds possessing a biphenyl ester moiety
with a 6-amino-1,3-dimethyluracil unit [27]. Here, we wish to access two more
homologous series of compounds synthesis, characterization and evaluation for their
liquid crystals properties belong to unsymmetric dimer series of 5-(4-(5-(4'-
(alkyloxy)biphenyl-4-yloxy)alkyloxy)benzylideneamino)-1,3-dimethylpyrimidine-
2,4(1H,3H)-dione containing 6-amino-1,3-dimethyluracil at one end and with
alkoxyphenyl terminal at the other end possessing chains of varying central methylene
spacer lengths (n = 6 and 8).
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The physical properties of the title compounds were studied by Fourier-
Transform Infra-Red (FT-IR) Spectroscopy and high resolution nuclear magnetic
resonance (NMR) techniques. The phase transition temperatures and enthalpy values
of the title compounds were measured by differential scanning calorimetry (DSC) and
the textures of the mesophases were studied using polarizing optical microscope
(POM).
2. Results and discussion
2.1 Synthesis and characterization
The synthetic route for the target compounds 4a-4n is shown in Scheme 1.
Spectroscopic methods such as FT-IR and NMR (1H and 13C) were employed to
elucidate the structures of compounds 4a-n. Molecular structure characterizations
were in good agreement with software predictions. Compounds 4a-g having
methylene spacer length n = 6 and terminal alkyl chain varies from n = 6-18, whereas
compounds 4h-n has methylene spacer length n = 8 with varying terminal alkyl chain
from n = 6-18.
Insert Scheme 1 is about here
FT-IR spectra of compounds 4a-n exhibit absorption bands that can be
assigned to the stretching of aliphatic C-H within the frequency range 2995-2868
cm-1. The C=O stretch frequency appears between the range of 1777-1760 cm-1. The
band which appears at the frequency 1628-1618 cm-1 is attributed to the stretching of
C=N. The ether group of spacer chain and terminal chain gave rise to strong
absorptions at 1255-1250 cm-1. The FT-IR spectroscopic study was further supported
1
13
by the application of H NMR and C NMR in an effort to elucidate the molecular
structures. The NMR spectra obtained indicate that all members of the homologous
1
series exhibit similar trend in H-1H splitting and chemical shifts. The NMR
resonances with respect to the diagnostic peaks are discussed based on the
representative compound 4a (with -C6H12- methylene spacer and -C6H13 terminal
1
chain). H NMR assignment of compound 4a has been carried out with aid of two
dimensional 1H-1H COSY experiment. A singlet at 6.83 ppm is attributed to the vinyl
proton of the hetero uracil ring. The presence of the azomethine protons (-CH=N-)
appears as singlet at 8.84 ppm. The absorption of 12 aromatic protons from two
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different distinguishable positions at the aromatic rings gave rise to a multiplet
between 6.87-8.60 ppm. Another three triplets were detected at 4.17 ppm, 4.05 ppm
and 3.91 ppm were assigned to the ethoxy protons adjacent to the methylene protons
in spacer chain and terminal alkoxy chain respectively. Two singlets at 3.42 ppm and
3.12 ppm were assigned to methyl groups attached to nitrogen atom in 6-amino-1,3-
dimethyluracil ring. A triplet was observed at the high-field of 0.81 ppm, which can
be assigned to the methyl protons of the terminal hexyl group in compound 4a.
insert Table 1 is about here
2.2 Phase transitions and mesomorphic behaviours
Phase transition temperatures and optical textures were analysed by
differential scanning calorimetry (DSC) and polarizing optical microscopy (POM).
The transition temperatures (ºC) and respective enthalpies (kJ mol-1) obtained from
the DSC thermograms are given in Table 1. All the synthesized molecules 4a-n
tended to exhibit enantiotropic liquid crystal properties. The solid samples were
sandwiched between untreated glass plate and a cover slip and subjected to heating
followed by cooling scans at the rate of 5 °C/min for textural observations through
POM. In the first set of compounds 4a-g, SmA phase was observed in compounds 4a-
d, whereas compounds 4e-g shows nematic phase. The representative DSC scans of
4c as shown in Fig 1. For example compound 4c show transitions at 143.30 °C
(22.08) and 160.31 °C (1.23) on heating scan which corresponds to Cr-to-SmA-to-Iso
phase sequence. In the cooling scan reverse transitions were abserved at 141 °C (-
23.22) and 154 °C (-1.78) which corresponds to Iso-to SmA-to-Cr state. Compound
4c displayed sandy texture having small focal conics as depicted in Fig 2 (a) and focal
conic texture for 4d as shown in Fig 2 (b). Compounds 4e-g shows enantiotropic
nematic phase. The difference in the mesophase behavior of 4a-d and 4e-g molecules
can be explained by the number of aliphatic chains present at the periphery and at
spacer position of the molecules. In this regard, a smaller aliphatic chain seems to be a
co-ordinating in terms of achieving a good packing and may leads to SmA
mesophase. In case of 4e-g the peripheral, spacer alkyl chains and bulky of 6-amino-
1,3-dimethyluracil moiety may not allow molecules to pack each other as a result
nematic phase is existed.
Insert Figure 1 is about here
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Notably, in the second set of compounds 4h-n, only 4h shows SmA phase,
whereas other members showing enantiotropic nematic phase. The representative
DSC scans of compound 4i shown in Fig 1. On heating the sample 4i melts to a
nematic mesophase with Schlieren texture at 138.89 °C and then it went to isotropic
liquid state at 161.23 °C. In a similar way, in cooling scan nematic mesophase re-
appeared at 155.90 °C and then crystallised at 133.12 °C. The textures observed on
heating scan from crystal can be observed in Figure 2 (c) for 4l and (d) for 4n. The
SmA phase is observed in 4h compound and nematic phase was observed in the
compounds of 4i-n, this could be the result of a lower degree of planarity from the
terminal bulky 6-amino-1,3-dimethyluracil group. This lack of planarity prevents
molecular packing and end up with less ordered nematic mesophase in higher
members.
Insert Figure 2 is about here
However, both the set of compounds 4a-g (spacer n = 6) and 4h-n (spacer n = 8)
shows completely irrelevant results with respect to spacer, for this kind of unexpected
results we reason that, it is known that the pronounced odd even effect is relevant to a
spacer in dimers and this trend is not followed by present case, because only two
spacers (n = 6 and 8) were studied and also both are even members. Usually in
dimers, lower members favour the nematic phase and higher members favour the
smectic phase with add-even effects [34]. The present results are fully contraries than
expected. The effects of the spacer length on the transition temperatures and phase
behaviour observed in this series are not in accord with those observed for
conventional low molar mass mesogens or dimers. The same effect is observed in
present series of compounds with increasing carbon atoms in both the terminal and
spacer alkyl chain. The results are found here are unusual when compare to the
normal behaviour of the dimers [35].
Further, all the compounds which are showing nematic to isotropic transitions
are associated with higher enthalpy values than the associated enthalpies of SmA to
Isotropic transitions. This factor is completely depend on the orientation order of the
molecules, means high orientation order is existed between the molecules in the
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nematic phase, as a result molecules requires high enthalpy to transform another
phase, same fact has been observed in this case. Moreover, this is presumably due to
the rather bulky shape of the 6-amino-1,3-dimethyluracil group and this increased
molecular biaxiality has been used to account for relatively high clearing entropies.
Thus, the orientational order is enhanced and a higher enthalpy values for nematic to
isotropic transitions would be expected [36,37]
A plot of transition temperature as a function of alkyl chain length at
periphery as well as in the spacer for the sets of 4a-g and 4h-n is shown in Fig 3 (a)
and (b). The clearing temperature for both sets of compounds shows a tendency of
ascending curve along with increasing in the number of carbons at periphery and
spacer chain throughout the set of compounds. The first set 4a-h compounds have
little lower transition temperature than the second set 4h-n of compounds. A
comparison of mesomorphic behaviour of these unsymmetrical sets of compounds
reveals that crystal-to-mesophase average range is about 16 °C for the set 4a-g,
whereas in 4h-n set of compounds average crystal-to-mesophase range was increased
to 19 °C. The study proves that the increase of spacer and terminal chain length
favour stabilization of the mesophases.
Insert Figure 3 is about here
2.3 Theoretical studies
Theoretical studies have been carried out by Hyper Chem program to get a
better understanding of the relationship between the structure and type of phases.
Theoretical models of compounds 4a, 4g, 4h and 4h are depicted in Figure 4 in which
the length of spacer alkoxy chain varied from n = 6 and 8, respectively. Theoretically
calculated data and experimental results are in agreement to the title compounds.
Insert Figure 4 is about here
As shown in Figure 4, 1,3-dimethyluracil ring and biphenyl ring which is
adjacent to the spacer appeared at different positions which depended on the number
of carbons at the alkoxy spacer [31-33]. The models indicated that 1,3-dimethyluracil
and biphenyl core groups take different opposite terminal ends according to number
of carbons at spacer change from n = 6 and 8. Non-planar geometry of 1,3-
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dimethyluracil and biphenyl rings was observed in compound 4a and this geometry
tends to exhibit Smectic A. However, a more planar geometry of 1,3-dimethyluracil
and biphenyl was found in compounds 4f molecular conformation favoured
arrangement of a nematic phase. Likewise, same phenomena have been observed in
compounds type 4h-n when a carbon spacer n = 8, compounds 4h (Figure 4) show
also non-planar geometry of 1,3-dimethyluracil and biphenyl rings, while compounds
4n shown more planarity comparison with compound 4h. Also we can revels from
figure 4 the terminal alkyl chain play well to effected the planarity of 1,3-
dimethyluracil and biphenyl rings
Finally, the study reveals that the variation of terminal alkyl chain and spacer
chain length plays an important role in the type of phase occurred in both set of
compounds.
3. Conclusions
In this article, the synthesis, mesomorphic and theoretical models of some novel
dimeric liquid crystalline compounds have been studied.
All title compounds
exhibited liquid crystal properties. Smectic A was observed with short spacer groups,
while nematic phase appears with longer spacer groups. Theoretical models presented
for few compounds are in good agreement with our results.
Acknowledgement
AK-T M extends heartfelt thanks to Professor John West and the Liquid Crystal
Institute at the Kent State University, for performing theoretical studies and
hospitality. The authors would also like to thank the University of Anbar and
Universiti Sains Malaysia for supporting this project.
4. Experimental
4.1. Materials
Bromoalkanes, α,ω-dibromoalkanes, 4-hydroxybenzaldehyde, 6-amino-1,3-
dimethyluracil, 4,4'-dihydroxybiphenyl were obtained from Aldrich. The fine
chemicals and required solvents were used directly from the bottles without further
purification. Thin-layer chromatography (TLC) was performed on pre-coated silica-
gel on aluminium plates.
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4. 2 Measurement
The FT-IR spectra of the intermediates and title compounds were analyzed in
the form of KBr pellets and the spectra were recorded in the range of 4000-400 cm-1
using a Perkin Elmer 2000 FT-IR spectrophotometer. The elemental microanalyses
(CHN) were performed using a Perkin Elmer 2400 LS Series CHNS/O analyzer. The
13
1H and C NMR spectra were recorded in dimethylsulphoxide (DMSO-d6) at 298 K
on a Bruker 400 MHz Ultrashied™ FT-NMR spectrometer equipped with a 5 mm
BBI inverse gradient probe. Chemical shift values (δ) were referenced to internal
standard tetramethylsilane (TMS). The concentration of solute molecules was 40 mg
in 1.0 ml DMSO. Standard Bruker pulse programs [28] were used throughout the
entire experiment. Texture observation was carried out using Carl Zeiss Axioskop 40
optical microscope equipped with Linkam LTS350 hot stage and TMS94 temperature
controller. The transition temperatures and associated enthalpy values were
determined using a differential scanning calorimeter (Elmer Pyris 1 DSC) operated at
a scanning rate of ± 5 °C min-1 on heating and cooling, respectively.
Theoretical models were obtained using Hyper Chem 8.0.8 (Hypercube Inc.)
in the Liquid Crystal Institute of Kent State University, USA. Data set of the
compounds was entered as two-dimensional sketches into Hyper Chem program.
4.3 Synthesis
The synthetic routes of the intermediates 1a-b, 2a-g, 3a-n and title
compounds 4a-n are shown in Scheme 1. The Williamson’s etherification method
used for the preparation of compounds 1a-b, 2a-g and 3a-n. Compounds 1a-b were
synthesised via reaction between equimolar amounts of 1,6-dibromohexane or 1,8-
dibromooctane with 4-hydroxybenzaldehyde in DMF in present of K2CO3 at 145 °C
for 4 hr [29, 30]. Compounds 2a-g were synthesised by the reaction between 4,4'-
dihydroxybiphenyl with a series of alkylbromides ranging from 6 to 18 carbons. The
final compounds 3a-n was obtained by the reaction between 1a-b and 2a-g.
4.3.1 General synthetic procedure for 4a-n
4.3.2. 5-[-{6-(4'-Alkyloxy)biphenyl-4-yloxy)alkyloxy)benzylideneamino}-1,3-dimethyl-
pyrimidine]2,4(1H,3H)-dione (4a-4n)
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The target compounds were synthesised according to method described by
Majumdar et al [27, 30]. A mixture of compound 6-amino-1,3-dimethyluracil (128
mg, 0.827 mmol) and 4-(6-(4'-(hexyloxy)biphenyl-4-yloxy)hexyloxy)benzaldehyde
3a (500 mg, 0.827 mmol) was refluxed in absolute ethanol in the presence of a
catalytic amount of glacial acetic acid for 2 h. The Schiff base 4a was obtained as a
precipitate from the hot reaction mixture. Further, to get pure compound it was
repeatedly washed with hot ethanol and dried in vacuum.
1
The analytical data of FT-IR, H and 13C NMR for title compounds are
summarized as follows:
5-(6-(4'-(Hexyloxy)biphenyl]-4-yloxy)hexyloxy)benzylidene)-1,3-
dimethylpyrimidine-2,4(1H,3H)-dione (4a). Yield 73 %; Anal: found for C37H45N3O5
(%): C, 72.83; H, 7.24; N, 6.99. Calc. C, 72.64; H, 7.41; N, 6.87. IR: υmax(KBr, cm-1):
2995, 2883, 1770 1620, 1580, 1251. 1HNMR δ (ppm, DMSO): 8.84 (s, 1H. -CH=N-),
6.87-8.60 (m, 12H, Ar-H), 6.83 (s, 1H), 4.17 (t, 2H, J = 6.89 Hz, -OCH2-), 4.05 (t,
2H, J = 6.67 Hz), 3.91 (t, 2H, J = 6.14 Hz), 3.42 (s, 3H), 3.12 (s, 3H), 1.89-1.71 (m,
16H), 0.81 (t, 3H, -CH3). 13C NMR δ : 176.04, 169.70, 162.00 (C=O), 161.20 (C=N),
160.94, 158.23 (Ar-C-O), 115.12-141.04 (Ar-C), 62.67 (C-O-C), 21.20 (CH2), 15.11
(CH3) ppm.
5-(6-(4'-(Octyloxy)biphenyl]-4-yloxy)hexyloxy)benzylidene)amino)-1,3-
dimethylpyrimidine-2,4(1H,3H)-dione (4b). Yield 78 %; Anal: found for C39H49N3O5
(%): C, 73.08; H, 7.60; N, 6.43. Calc. C, 73.21; H, 7.72; N, 6.57. IR: υmax(KBr, cm-1):
2989, 2871, 1766 1618, 1573, 1250. 1HNMR δ (ppm, DMSO): 8.76 (s, 1H, -CH=N-),
6.86-8.58 (m, 12H, Ar-H), 6.80 (s, 1H), 4.14 (t, 2H, J = 6.88 Hz, -OCH2-), 4.01 (t,
2H, J = 6.20 Hz), 3.90 (t, 2H, J = 6.38 Hz), 3.41 (s, 3H), 3.11 (s, 3H), 1.87-1.74 (m,
13
20H), 0.85 (t, 3H, -CH3). C NMR δ : 175.30, 168.11, 162.89 (C=O), 161.59 (C=N),
161.08, 159.44 (Ar-C-O), 114.77-140.39 (Ar-C), 62.07 (C-O-C), 21.20 (CH2), 14.56
(CH3) ppm.
5-(6-(4'-(Decyloxy)-biphenyl]-4-yloxy)hexyloxy)benzylidene)-1,3-
dimethylpyrimidine-2,4(1H,3H)-dione (4c). Yield 69 %; Anal: found for C41H53N3O5
(%): C, 73.89; H, 8.11; N, 6.14. Calc. C, 73.73; H, 8.00; N, 6.29. IR: υmax(KBr, cm-1):
2992, 2880, 1772 1628, 1587, 1255. 1HNMR δ (ppm, DMSO): 8.82 (s, 1H, -CH=N-),
6.92-8.63 (m, 12H, Ar-H), 6.87 (s, 1H), 4.17 (t, 2H, J = 6.39 Hz), 4.07 (t, 2H, J =
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6.67 Hz, -OCH2-), 3.93 (t, 2H, J = 6.09 Hz), 3.49 (s, 3H), 3.15 (s, 3H), 1.87-1.73 (m,
24H), 0.88 (t, 3H, -CH3). 13C NMR δ : 174.95, 168.78, 162.50 (C=O), 161.06 (C=N),
161.86, 160.17 (Ar-C-O), 114.90-140.07 (Ar-C), 62.30 (C-O-C), 22.30 (CH2), 14.60
(CH3) ppm.
5-(6-(4'-(Dodecyloxy)-biphenyl]-4-yloxy)hexyloxy)benzylidene)-1,3-
dimethylpyrimidine-2,4(1H,3H)-dione (4d). Yield 75 %; Anal: found for C43H57N3O5
(%): C, 74.40; H, 8.49; N, 6.27. Calc. C, 74.21; H, 8.26; N, 6.04. IR: υmax(KBr, cm-1):
2990, 2884, 1775 1622, 1583, 1253. 1HNMR δ (ppm, DMSO): 8.80 (s, 1H, -CH=N-),
6.95-8.65 (m, 12H, Ar-H), 6.88 (s, 1H), 4.18 (t, 2H, J = 6.28 Hz), 4.05 (t, 2H, J =
6.89 Hz, -OCH2-), 3.96 (t, 2H, J = 6.19 Hz), 3.45 (s, 3H), 3.18 (s, 3H), 1.86-1.76 (m,
28H), 0.89 (t, 3H, -CH3). 13C NMR δ : 175.11, 167.20, 162.93 (C=O), 160.75 (C=N),
159.23, 158.30 (Ar-C-O), 114.06-140.69 (Ar-C), 61.07 (C-O-C), 21.44 (CH2), 15.05
(CH3) ppm.
5-(6-(4'-(Tetradecyloxy)-biphenyl]-4-yloxy)hexyloxy)benzylidene)-1,3-
dimethylpyrimidine-2,4(1H,3H)-dione (4e). Yield 81 %; Anal: found for C45H61N3O5
(%): C, 74.80; H, 8.31; N, 5.64. Calc. C, 74.65; H, 8.49; N, 5.80. IR: υmax(KBr, cm-1):
2992, 2882, 1777 1625, 1589, 1251. 1HNMR δ (ppm, DMSO): 8.65 (s, 1H, -CH=N-),
6.95-8.51 (m, 12H, Ar-H), 6.86 (s, 1H), 4.19 (t, 2H, J = 6.70 Hz), 4.08 (t, 2H, J =
6.47 Hz, -OCH2-), 3.94 (t, 2H, J = 6.49 Hz), 3.49 (s, 3H), 3.14 (s, 3H), 1.87-1.70 (m,
32H), 0.92 (t, 3H, -CH3). 13C NMR δ : 174.88, 167.84, 164.02 (C=O), 162.20 (C=N),
159.22, 158.90 (Ar-C-O), 114.00-140.27 (Ar-C), 62.04 (C-O-C), 22.15 (CH2), 15.38
(CH3) ppm.
5-(6-(4'-(Hexadecyloxy)-biphenyl]-4-yloxy)hexyloxy)benzylidene)-1,3-
dimethylpyrimidine-2,4(1H,3H)-dione (4f). Yield 76 %; Anal: found for C47H65N3O5
(%): C, 75.20; H, 8.55; N, 5.71. Calc. C, 75.06; H, 8.71; N, 5.59. IR: υmax(KBr, cm-1):
2986, 2872, 1774 1628, 1584, 1255. 1HNMR δ (ppm, DMSO): 8.72 (s, 1H, -CH=N-),
6.85-8.40 (m, 12H, Ar-H), 6.80 (s, 1H), 4.12 (t, 2H, J = 6.09 Hz, -OCH2-), 4.01 (t,
2H, J = 6.60 Hz), 3.92 (t, 2H, J = 6.70 Hz), 3.47 (s, 3H), 3.12 (s, 3H), 1.88-1.76 (m,
36H), 0.81 (t, 3H, -CH3). 13C NMR δ : 176.02, 168.00, 164.96 (C=O), 161.83 (C=N),
160.80, 159.30 (Ar-C-O), 115.20-140.98 (Ar-C), 61.60 (C-O-C), 22.83 (CH2), 14.36
(CH3) ppm.
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5-(6-(4'-(Octadecyloxy)-biphenyl]-4-yloxy)hexyloxy)benzylidene)-1,3-
dimethylpyrimidine-2,4(1H,3H)-dione (4g). Yield 70 %; Anal: found for C49H69N3O5
(%): C, 75.60; H, 8.76; N, 5.50. Calc. C, 75.44; H, 8.92; N, 5.39. IR: υmax(KBr, cm-1):
2983, 2868, 1770 1625, 1580, 1254. 1HNMR δ (ppm, DMSO): 8.76 (s, 1H, -CH=N-),
6.93-8.46 (m, 12H, Ar-H), 6.83 (s, 1H), 4.18 (t, 2H, J = 6.84 Hz), 4.06 (t, 2H, J =
6.75 Hz), 3.95 (t, 2H, J = 6.19 Hz, -OCH2-), 3.48 (s, 3H), 3.11 (s, 3H), 1.89-1.77 (m,
40H), 0.80 (t, 3H, -CH3). 13C NMR δ : 175.69, 166.49, 164.03 (C=O), 160.10 (C=N),
160.21,159.11 (Ar-C-O), 115.00-140.31 (Ar-C), 62.09 (C-O-C), 22.30 (CH2), 14.07
(CH3) ppm.
5-(8-(4'-(Hexyloxy)-[biphenyl]-4-yloxy)octyloxy)benzylidene)-1,3-
dimethylpyrimidine-2,4(1H,3H)-dione (4h). Yield 66 %; Anal: found for C39H49N3O5
(%): C, 73.45; H, 7.80; N, 6.39. Calc. C, 73.21; H, 7.72; N, 6.57. IR: υmax(KBr, cm-1):
2980, 2871, 1769 1622, 1583, 1250. 1HNMR δ (ppm, DMSO): 8.74 (s, 1H, -CH=N-),
6.90-8.51 (m, 12H, Ar-H), 6.85 (s, 1H), 4.19 (t, 2H, J = 6.93 Hz), 4.08 (t, 2H, J =
6.41 Hz, -OCH2-), 3.93 (t, 2H, J = 6.63 Hz), 3.44 (s, 3H), 3.18 (s, 3H), 1.87-1.71 (m,
20H), 0.85 (t, 3H, -CH3). 13C NMR δ : 174.09, 165.20, 163.20 (C=O), 162.60 (C=N),
161.57, 160.29 (Ar-C-O), 114.69-141.14 (Ar-C), 62.39 (C-O-C), 21.30 (CH2), 15.21
(CH3) ppm.
5-(8-(4'-(Octyloxy)-[biphenyl]-4-yloxy)octyloxy)benzylidene)-1,3-
dimethylpyrimidine-2,4(1H,3H)-dione (4i). Yield 67 %; Anal: found for C41H53N3O5
(%): C, 73.88; H, 8.25; N, 6.40. Calc. C, 73.73; H, 8.00; N, 6.29. IR: υmax(KBr, cm-1):
2993, 2882, 1772 1620, 1584, 1253. 1HNMR δ (ppm, DMSO): 8.72 (s, 1H, -CH=N-),
6.86-8.58 (m, 12H, Ar-H), 6.80 (s, 1H), 4.15 (t, 2H, J = 6.76 Hz, -OCH2-), 4.02 (t,
2H, J = 6.90 Hz), 3.98 (t, 2H, J = 6.12 Hz), 3.48 (s, 3H), 3.20 (s, 3H), 1.89-1.73 (m,
24H), 0.87 (t, 3H, -CH3). 13C NMR δ : 175.50, 164.58, 162.99 (C=O), 162.00 (C=N),
160.46, 159.33 (Ar-C-O), 114.19-140.29 (Ar-C), 62.00 (C-O-C), 22.58 (CH2), 15.44
(CH3) ppm.
5-(8-(4'-(Decyloxy)-[biphenyl]-4-yloxy)octyloxy)benzylidene)-1,3-
dimethylpyrimidine-2,4(1H,3H)-dione (4j). Yield 73 %; Anal: found for C43H57N3O5
(%): C, 74.30; H, 8.08; N, 6.20. Calc. C, 74.21; H, 8.26; N, 6.04. IR: υmax(KBr, cm-1):
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2988, 2869, 1774 1625, 1580, 1251. 1HNMR δ (ppm, DMSO): 8.68 (s, 1H, -CH=N-),
6.92-8.53 (m, 12H, Ar-H), 6.86 (s, 1H), 4.18 (t, 2H, J = 6.00 Hz, -OCH2-), 4.06 (t,
2H, J = 6.20 Hz), 3.94 (t, 2H, J = 6.44 Hz), 3.40 (s, 3H), 3.29 (s, 3H), 1.88-1.70 (m,
28H), 0.79 (t, 3H, -CH3). 13C NMR δ : 176.10, 166.90, 164.20 (C=O), 163.50 (C=N),
162.50, 160.90 (Ar-C-O), 114.88-140.00 (Ar-C), 62.61 (C-O-C), 21.95 (CH2), 15.83
(CH3) ppm.
5-(8-(4'-(Dodecyloxy)-[bipheny]-4-yloxy)octyloxy)benzylidene)-1,3-
dimethylpyrimidine-2,4(1H,3H)-dione (4k). Yield 70 %; Anal: found for C45H61N3O5
(%): C, 74.51; H, 8.60; N, 5.66. Calc. C, 74.65; H, 8.49; N, 5.80. IR: υmax(KBr, cm-1):
2990, 2874, 1760 1618, 1589, 1254. 1HNMR δ (ppm, DMSO): 8.63 (s, 1H, -CH=N-),
6.93-8.50 (m, 12H, Ar-H), 6.84 (s, 1H), 4.12 (t, 2H, J = 6.77 Hz, -OCH2-), 4.00 (t,
2H, J = 6.30 Hz), 3.89 (t, 2H, J = 6.62 Hz), 3.45 (s, 3H), 3.22 (s, 3H), 1.89-1.71 (m,
32H), 0.89 (t, 3H, -CH3). 13C NMR δ : 176.30, 166.09, 164.20 (C=O), 163.40 (C=N),
162.33, 161.18 (Ar-C-O), 114.21-140.48 (Ar-C), 61.20 (C-O-C), 22.07 (CH2), 14.40
(CH3) ppm.
5-(8-(4'-(Tetradecyloxy)-[biphenyl]-4-yloxy)octyloxy)benzylidene)-1,3-
dimethylpyrimidine-2,4(1H,3H)-dione (4l). Yield 65 %; Anal: found for C47H65N3O5
(%): C, 75.30; H, 8.92; N, 5.73. Calc. C, 75.06; H, 8.71; N, 5.59. IR: υmax(KBr, cm-1):
2987, 2870, 1769 1623, 1580, 1251. 1HNMR δ (ppm, DMSO): 8.68 (s, 1H, -CH=N-),
6.90-8.62 (m, 12H, Ar-H), 6.88 (s, 1H), 4.13 (t, 2H, J = 6.50 Hz, -OCH2-), 4.02 (t,
2H, J = 6.47 Hz), 3.83 (t, 2H, J = 6.20 Hz), 3.48 (s, 3H), 3.27 (s, 3H), 1.87-1.72 (m,
36H), 0.84 (t, 3H, -CH3). 13C NMR δ : 174.10, 165.78, 163.20 (C=O), 160.94 (C=N),
161.23, 159.03 (Ar-C-O), 114.88-140.05 (Ar-C), 61.77 (C-O-C), 22.30 (CH2), 14.57
(CH3) ppm.
5-(8-(4'-(Hexadecyloxy)-[biphenyl]-4-yloxy)octyloxy)benzylidene)-1,3-
dimethylpyrimidine-2,4(1H,3H)-dione (4m). Yield 69 %; Anal: found for C49H69N3O5
(%): C, 75.52; H, 8.82; N, 5.48. Calc. C, 75.44; H, 8.92; N, 5.39. IR: υmax(KBr, cm-1):
2980, 2872, 1768 1625, 1582, 1250. 1HNMR δ (ppm, DMSO): 8.70 (s, 1H, -CH=N-),
6.98-8.50 (m, 12H, Ar-H), 6.86 (s, 1H), 4.18 (t, 2H, J = 6.10 Hz, -OCH2-), 4.06 (t,
2H, J = 6.42 Hz), 3.92 (t, 2H, J = 6.79 Hz), 3.42 (s, 3H), 3.21 (s, 3H), 1.88-1.70 (m,
40H), 0.88 (t, 3H, -CH3). 13C NMR δ : 174.30, 165.60, 163.11 (C=O), 160.00 (C=N),
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160.19, 159.67 (Ar-C-O), 114.07-140.29 (Ar-C), 61.30 (C-O-C), 22.80 (CH2), 14.69
(CH3) ppm.
5-(8-(4'-(Octadecyloxy)-[biphenyl]-4-yloxy)octyloxy)benzylidene)-1,3-
dimethylpyrimidine-2,4(1H,3H)-dione (4n). Yield 77 %; Anal: found for C51H73N3O5
(%): C, 75.64; H, 9.28; N, 5.08. Calc. C, 75.80; H, 9.10; N, 5.20. IR: υmax(KBr, cm-1):
2985, 2873, 1770 1622, 1580, 1254. 1HNMR δ (ppm, DMSO): 8.73 (s, 1H, -CH=N-),
6.93-8.56 (m, 12H, Ar-H), 6.88 (s, 1H), 4.19 (t, 2H, J = 6.99 Hz, -OCH2-), 4.04 (t,
2H, J = 6.79 Hz), 3.96 (t, 2H, J = 6.11 Hz), 3.48 (s, 3H), 3.24 (s, 3H), 1.89-1.72 (m,
44H), 0.90 (t, 3H, -CH3). 13C NMR δ : 175.00, 165.88, 162.09 (C=O), 160.60 (C=N),
160.71, 159.14 (Ar-C-O), 114.49-140.67 (Ar-C), 62.09 (C-O-C), 21.20 (CH2), 14.27
(CH3) ppm.
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Table 1. The heating/cooling phase transition temperatures (oC) and the associated
enthalpies (kJ mol-1) for target compounds 4a-n.
Compound
4a
n
6
R
C6H13
Heating /Cooling scans
Cr 112.2 (22.84) SmA130.1 (4.20) Iso
Cr 98.5 (-19.32) SmA 118.7 (-2.11) Iso
Cr 119.6 (25.10) SmA 136.3 (3.80) Iso
Cr 111.4 (-21.45) SmA 126.2 (-6.78) Iso
Cr 143.3 (22.08) SmA 160.3 (1.23) Iso
Cr 141 (-23.22) SmA 154 (-1.78) Iso
Cr 159.2 (27.08) SmA 176.5 (2.44) Iso
Cr 154.4 (-18.56) SmA 170.9 (3.30) Iso
Cr 171.1 (15.60) N 190.5 (4.67) Iso
Cr 167.8 (-21.45) N 183 (-5.44) Iso
Cr 185.1 (29.18) N 202.3 (5.98) Iso
Cr 178.8 (-27.06) N 195.8 (-6.04) Iso
Cr 197.7 (21.55) N 211.8 (7.89) Iso
Cr 189.9 (-18.90) N 204.7 (-8.78) Iso
Cr 116.2 (25.76) SmA 130.2 (8.35) Iso
Cr 104.7 (-23.54) SmA 121.1 (-3.45) Iso
Cr 138.9 (24.90) N 161.2 (2.09) Iso
Cr 133.1 (-17.67) N 155.9 (-1.30) Iso
Cr 148.2 (19.00) N 173.1 (2.98) Iso
Cr 142.1 (-26.40) N 167.5 (-2.49) Iso
Cr 173 (25.06) N 190.1 (3.50) Iso
Cr 166.9 (-19.17) N 182 (-3.88) Iso
Cr 188.2 (19.34) N 206.2 (5.66) Iso
Cr 181.2 (-25.00) N 198.4 (-4.79) Iso
Cr 194.1 (17.70) N 215.6 (7.82) Iso
Cr 187.2 (-20.60) N 208.6 (-6.49) Iso
Cr 210 (18.33) N 232.1 (9.08) Iso
Cr 205.8 (-18.0) N 226 (-7.20) Iso
4b
4c
4d
4e
4f
6
6
6
6
6
6
8
8
8
8
8
8
8
C8H17
C10H21
C12H25
C14H29
C16H33
C18H37
C6H13
4g
4h
4i
C8H17
4j
C10H21
C12H25
C14H29
C16H33
C18H37
4k
4l
4m
4n
Cr = Crystal; SmA = Smectic A phase; N = Nematic phase; Iso = Isotropic phase
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Fig 1. DSC scans of 4c and 4i on heating and cooling cycles.
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Fig 2. (a) (colour online) Optical photomicrographs of compound 4c exhibiting SmA
mesophase upon heating at 150 °C (b) 4d upon heating displaying SmA at 165 °C (c)
4l displaying nemaic phase upon heating at 194 °C (d) 4n exhibiting nematic texture
upon heating at 228 °C.
(a)
mesophase-Cr
Iso-mesophase
210
180
150
120
90
Iso
Cr
4a/6
4b/8
4c/10
4d/12
4e/14
4f/16
4g/18
Name/No. of carbon atoms in the alkyl chain
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240
210
180
150
120
90
(b)
mesophase-Cr
Iso-mesophase
Iso
Cr
4h/6
4i/8
4j/10
4k/12
4l/14
4m/16
4n/18
Name/No. of carbonatoms inthe alkyl chain
Fig 3. (colour online) Plot of cooling scan transition temperature as a function of the
number of carbon atoms in the terminal chain for the sets (a) 4a-g and (b) 4h-n.
HyperChem of 4a
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HyperChem of 4f
4

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HyperChem of 4h
5

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HyperChem of 4n
Fig 4. (colour online) Theoretical molecular models of compound 4a, 4f, 4h, and 4n
using HyperChem program
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OH
OH
R-Br
HO
Br(CH2)nBr
OH
OHC
RO
OHC
O(CH2)n-Br
R = Hexyl, Octyl, Decyl, Dodecyl,
Tetradecyl, Hexadecyl, Octadecyl
n = 6 and 8
1a-b
2a-g
O
CH3
N
CHO
O(CH2)nO
3a-n
RO
H2N
O
N
O
CH3
CH3
O
N
H
C
O(CH2)nO
RO
N
N
CH3
4a-n
Scheme 1. Synthetic route for 4a-n
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Highlights
● New sets of unsymmetric calamitic molecules with uracil and biphenyl core were
synthesized.
● Liquid crystal properties are investigated by DSC and POM techniques.
● Theoretical studies was also studied.
● Smectic phase in lower members and nematic phase appeared in higher members