Molecular structure-thermal behaviour relationship of dimers consisting of different terminal substituents and sulphur-sulphur linking group

Article abstract of DOI:10.1016/j.molstruc.2014.03.071

A new series of dimers 6-(4-oxybenzylidine-4′-substituted-aniline)hexyldisulphides containing various terminal substituents (CH₃, C₂H₅, Cl and Br) have been synthesized. The correlation between the molecular structure and

Full text of DOI:10.1016/j.molstruc.2014.03.071

Accepted Manuscript
Molecular structure-thermal behaviour relationship of dimers consisting of dif-
ferent terminal substituents and sulphur-sulphur linking group
Guan-Yeow Yeap, Faridah Osman, Wan Ahmad Kamil Mahmood, Daisuke
Takeuchi
PII:
S0022-2860(14)00339-1
DOI:
http://dx.doi.org/10.1016/j.molstruc.2014.03.071
MOLSTR 20505
Reference:
Journal of Molecular Structure
To appear in:
Received Date:
Revised Date:
Accepted Date:
15 October 2013
31 March 2014
31 March 2014
Please cite this article as: G-Y. Yeap, F. Osman, W.A.K. Mahmood, D. Takeuchi, Molecular structure-thermal
behaviour relationship of dimers consisting of different terminal substituents and sulphur-sulphur linking group,
Journal of Molecular Structure (2014), doi: http://dx.doi.org/10.1016/j.molstruc.2014.03.071
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Molecular structure-thermal behaviour relationship of
dimers consisting of different terminal substituents and
sulphur-sulphur linking group
Guan-Yeow Yeapa*, Faridah Osmana, Wan Ahmad Kamil Mahmooda and Daisuke Takeuchib
aLiquid Crystal Research Laboratory, School of Chemical Sciences, Universiti Sains
Malaysia, 11800 Minden, Penang, Malaysia
bChemical Resources Laboratory (Mailbox R1-03), Tokyo Institute of Technology 4259
Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan
Abstract
A
new series of dimers 6-(4-oxybenzylidine-4’-substituted-aniline)hexyldisulphides
containing various terminal substituents (CH3, C2H5, Cl and Br) have been synthesized. The
correlation between the molecular structure and the properties of all the ultimate compounds
has been made on the basis of their thermal behaviour. The dimers with CH3 and C2H5
substituents exhibit predominantly the monotropic N phase of which the C2H5-containing
derivative possesses more stable nematogenic temperature range in comparison to its methyl-
containing analogue. As for the member with Cl substituent, it exhibits enantiotropic N and
monotropic smectic A phase. However, the dimer in which the Cl was substituted by Br
exhibits purely enantiotropic smectic A phase. Upon cooling all of the final compounds show
the transition from isotropic to mesophase prior to the change from mesophase to crystal
except the member with Br substituent which displays mosaic B phase even at room
temperature. An extensive study to further substantiate the relationship between the stability
of the phase and associated transition temperatures due to different terminal substituent is
also studied. This study reveals that the terminal Br increases the clearing temperature and
polarizability which enhances the formation and stability of SmA and mosaic B phases.
Keywords: Structural studies, thermal behaviour, dimers, terminal substituents, sulphur-
sulphur linkage
____________ꢀ
*Corresponding author: G.Y.Yeap (Email: gyyeap@usm.my and fax: 60-4-6574854 )

Introduction
Liquid crystal dimers have been the focus of many researchers as their properties are
quite different from conventional liquid crystals [1] and they could also act as the model
compounds for main chain polymeric liquid crystals [2]. There are two types of liquid crystal
dimers: Symmetric and non-symmetric dimers. Symmetric dimers consist of two identical
mesogenic units connected by a single spacer while non-symmetric dimers consist of two
different mesogenic units linked by a single spacer.
It has also been revealed that for typical dimers in which the two individual
mesogenic groups attached to each other via a flexible polymethylene spacer unit, the
stability of mesophase can be varied through the change in the linking group and substituent.
For instance, the aromatic imine-based dimers are well known for their abilities to exhibit
mesomorphic behaviour resulted from their high-shape anisotropy and the presence of
terminal halogen which helped to increase the molecular polarizability [3-5]. Furthermore,
previous researchers had also reported that the linking group such as disulphide (S-S) reduced
the transitional properties of the dimers [6, 7].
In this report, we present a comprehensive study on a series of symmetric dimer with
sulphur-sulphur linkage in the hexamethylene spacer. In these dimers the substituents CH3,
C2H5, Cl and Br are attached to the aniline fragments at both terminal ends. Hence, the effect
of different terminal substituents on the thermal behaviour of the aniline fragments and their
relationship with its molecular structure will be presented. The synthetic routes for the
preparation of intermediates and title compounds with atomic numbering scheme are
summarized in Scheme 1.
2.0
Experimental details
2.1
Materials
4-hydroxybenzaldehyde, 4-substituted-aniline, 1,6-dibromohexane, potassium
thioacetate and potassium metabisulphide were purchased from Acros Organics (Belgium).
Sodium hydroxide and concentrated hydrochloric acid were purchased from Fischer
Scientific (United Kingdom) whilst sodium iodide was purchased from R&M Chemicals
(United Kingdom). All solvents and reagents were used without further purification.
2.2
Characterization
2.2.1 Physical measurements

Melting points were determined by Gallenkamp melting point apparatus. The CHN
microanalyses were performed on a Perkin Elmer 2400 LS Series CHN/O analyzer.
2.2.2 FTIR measurement
Fourier transform infrared (FT-IR) data were recorded by a Perkin Elmer 2000-FTIR
spectrophotometer in which the samples were mixed with KBr. The frequency range used for
recording the IR spectra was set at 4000-400 cm-1.
2.2.3 NMR measurement
1
The H and 13C-NMR spectra were recorded on Bruker Avance 500 Ultrashield
1
spectrometer. The 1D NMR data were supported by the aids of 2D H-1H correlation
1
1
spectroscopy (COSY), H-13C heteronuclear multiple quantum correlation (HMQC) and H-
13C heteronuclear multiple bond correlation (HMBC) by using deuterated chloroform
(CDCl3) as solvent and tetramethylsilane (TMS) as internal standard.
2.2.4 Phase transition temperatures and enthalpy values
The phase transition temperature and enthalpy change were obtained by Seiko
DSC6200R differential scanning calorimeter at the heating and cooling rates of 2 °C miní1.
2.2.5 Texture observation
Texture observation was carried out in which the sample sandwiched between glass
slide and cover glass. The thermal condition for the respective sample was varied from room
temperature to clearing temperature at the rates of 2 °C miní1. The sample in the cell was
then observed under the Carl Zeiss Axioskop 40 polarizing microscope equipped with a
Linkam LTS350 hot stage and TMS94 temperature controller.
2.3
Synthesis
The formation of all the compounds 1-5 within the same series follows the same
method. The experimental procedure related to the representative compounds 1c, 2c, 3c, 4c
and 5c will be described as follows:
2.3.1 Synthesis of 4-hydroxybenzylidine-4'-chloroaniline, 1c (X = Cl).
4-chloroaniline (2.1g, 16.4 mmol) was dissolved in 15 mL of absolute methanol. A
methanolic solution of 4-hydroxybenzaldehyde (15 mL, 2.0 g, 16.4 mmol) was added
dropwise and the mixture was stirred at room temperature for ½ hour. The yellow precipitate

thus formed was filtered and washed with 10 mL methanol to afford the desired compound
1c.
2.3.2 Synthesis of 4-bromohexyloxybenzylidine-4’-chloroaniline, 2c.
A mixture containing compound 1c (2.0 g, 8.63 mmol) and anhydrous potassium
carbonate (6.0 g, 43.16 mmol) was heated in 50 mL acetone. The excess of 1,6-
dibromohexane (8.42 g, 34.52 mmol) was added dropwise to the mixture. The resulting
mixture was refluxed for 12 hours. The mixture was subsequently cooled to room
temperature and 40 mL of water was added to the mixture. The precipitate thus obtained was
filtered out and washed by 10 mL n-hexane.
2.3.3 Synthesis of 6-(4-oxybenzylidine-4’-chloroaniline)hexylthioacetate, 3c.
The compound 2c (1.53 g, 3.88 mmol) was reacted with potassium thioacetate (0.89
g, 7.76 mmol) in acetone (40 mL) under reflux for 18 hours. The mixture was cooled under
reduced pressure. The residue was washed by water (20 mL) and filtered. The crude product
was then recrystallized from ethanol (20 mL) in order to obtain the compound 3c.
2.3.4 Synthesis of 6-(4-oxybenzylidine-4’-chloroaniline)hexylthiol, 4c.
The thioacetate compound 3c (1.18 g, 3.03 mmol) was dissolved in acetone (15 mL)
and treated with 3M aqueous NaOH (10 mL, 3.64 g, 30 mmol) for 12 hours at room
temperature. The solution was neutralized with concentrated HCl to pH 7 before it was
filtered, dried and purified by column chromatography with chloroform:petroleum ether (8:2)
as eluent in order to obtain compound 4c.
2.3.5 Syntheses of 6-(4-oxybenzylidine-4’-chloroaniline)hexyldisulphide, 5c.
A solution containing compounds 4c in dichloromethane (15 mL) was stirred and
added with a catalytic amount of sodium iodide (0.12 g, 8.01 mmol) and 10 mL of 30%
hydrogen peroxide. The solution initially changed to purple and it was left with stirring for 3
hours. A solution of metabisulphide (5 ml, 0.30 g, 1.35 mmol,) was added to the solution
until the purple colour disappeared. The precipitate in solution was filtered and purified using
column chromatography with chloroform:petroleum ether (8:2) as eluent to afford 5c.

3.
Results and Discussion
The analytical data for intermediates 1a-1d, 2a-2d, 3a-3d, 4a-4d and final compounds
5a-5d are tabulated in Table 1. The CHN microanalyses suggest that the experimental values
are in agreement with the respective empirical formula.
3.1
Spectroscopic technique
From the FT-IR spectra (Table 2), a strong intensity at 2856-2937 cm-1 can be
assigned to the C-H stretching of the hexyl moiety. A weak absorption at 1620 cm-1 can be
attributed to the imine (C=N) group. A fairly strong absorption band observed at 1607 cm-1
can be ascribed to the aromatic C=C stretching and a medium absorption frequency at 1252
cm-1 is assigned to the C-O stretching of ether.
1H-NMR spectral data for compounds 5a-5d are summarized in Table 3. The 2D
1
NMR was also employed in order to further elucidate the molecular structures of 5a-5d. H-
1H COSY data for compounds 5a-5d are listed in Table 1 (ESIЪ). For discussion, the
compound 5d was chosen as a representative.
The 1H-NMR data for compound 5d show several overlapping multiplets at į = 1.45-
1.85 ppm and these can be attributed to the methylene proton. The two triplets are observed at
į = 2.70 and 4.08 ppm which can be assigned to the presence of methylene protons H19 and
H14, respectively. Eight aromatic protons for compound 5d resonate at į = 6.95-7.82 ppm in
the form of four doublets which can be assigned to the H2 and H6, H3 and H5, H9 and H13
and H10 and H12. A singlet peak assignable to azomethine proton H7 is observed at į = 8.33
ppm.
1
The correlation of the H-1H COSY experiment of compound 5d is employed to
resolve the complexity in the assignment of the eight aromatic protons. From Fig. 1 (ESIЪ),
H2 and H6 at į = 7.48 correlate with H3 and H5 at į = 7.06 ppm. A similar phenomenon can
also be observed on H9 and H13 from the aromatic ring at į = 7.81 ppm which correlates
with respective H10 and H12 at į = 6.96 ppm. The correlation inferred from COSY spectra
has also shown that the ether group of proton H14 is correlated with the respective proton
H15. In the same way, a correlation can also be found on H19 which correlates with H18.
13
Table 4 summarizes the C-NMR spectroscopic data of compounds 5a-5d. It can be
seen from Table 4 that C1 is observed at į = 118.91-141.75 ppm owing to the presence of
different terminal group connected to C1. The aromatic carbons of all final compounds give
rise to four strong peaks in the region of į = 114.66-130.61 ppm. The azomethine carbon C7

resonates at į = 158.98-160.02 ppm. The resonances recorded at į = 149.79-151.30 ppm,
128.83-129.90 ppm and 161.66-162.05 ppm can be attributed to the quaternary carbons C4,
C8 and C11, respectively. The C14 observed at į = 67.98-68.04 ppm can be ascribed to the
methylene carbon bonded to the oxygen atom. The other methylene carbons (C15-C18 in
flexible spacer) resonate at į = 25.69-29.98 ppm. While the resonance observed at į = 38.97-
38.98 can be attributed to C19 which is connected to sulphur atom. It can be noted that each
of 5a and 5b possesses an additional peak. The peak at į = 20.96 ppm can be ascribed to the
carbon of the terminal substituent (methyl group) while the peaks observed at į = 28.40 and
15.64 ppm can be attributed to the presence of terminal ethyl group.
1
The H-13C HMQC spectra of compounds 5a-5d provide the information on the
interaction between the protons and the carbon atoms which are bonded directly to each other
(Table 2, ESIЪ). The discussion on these correlations will be based on the spectrum for
representative compound 5d. It can be observed from Fig. 2 (ESIЪ) that the two peaks at į =
25.69 and 28.20 ppm correlated with H16 and H17 can be assigned to the C16 and C17,
respectively. An overlapping peak observed clearly at į = 29.04-29.08 ppm can be assigned
to H15 and H18 and these peaks correlated with C15 and C18. A peak at į = 38.98 ppm is
assigned to C19 due to its correlation with H19. The aromatic protons for H2 (magnetically
equivalent to H6), H3 (magnetically equivalent to H5), H9 (magnetically equivalent to H13)
and H10 (magnetically equivalent to H12) are correlated with C2 (magnetically equivalent to
C6), C3 (magnetically equivalent to C5), C9 (magnetically equivalent to C13) and C10
(magnetically equivalent to C12), respectively. Moreover, a peak at į = 160.07 ppm can be
attributed to the azomethine carbon C7 owing to its correlation with H7.
The aromatic quaternary carbons for all compounds 5a-5d were confirmed via the
correlation between carbon and its neighbouring proton by HMBC experiment. From Fig. 3
(ESIЪ) the quaternary carbon C1 is assigned based on its correlation with H2 (magnetically
2
3
equivalent to H6) and H3 (magnetically equivalent with H5) with J and J. A similar
phenomenon for the quaternary carbon C4 can be assigned based on its correlation with H2
3
(magnetically equivalent to H6) and H7 with J. The C8 can also be assigned based on its
correlation with H7, H9 (magnetically equivalent to H13) and H10 (magnetically equivalent
2
3
to H12) with J and J. Finally, C11 is found to established connectivity with H9
(magnetically equivalent to H13), H10 (magnetically equivalent to H12) and H14 with 2J and
3J. In addition to the quaternary carbons, CH, CH2 and CH3 carbons are also employed to
establish the assignment with the aids of DEPT-90, DEPT-135 and DEPT-45 experiments.

3.2
Thermal behaviour and texture observation
The phase transition and the associated enthalpy values of the 5a-5d obtained from
the DSC thermogram are listed in Table 5. All of these compounds 5a-5d exhibit liquid
crystalline properties.
The texture observation reveals that compounds 5a and 5b are monotropic N phase.
On cooling the N phase associated with compounds 5a and 5b can be substantiated by the
formation of droplets at the point of the transition through the dim flash and high mobility of
the phase [8]. On further cooling the nematic droplets transform to nematic Schlieren phase
with two- and four-brushes defects (Fig. 1(a)). However, compound 5c exhibits enantiotropic
N and monotropic fan-shaped texture of SmA phase (Fig. 1(b) and 1(c)) while compound 5d
exhibits enantiotropic fan-shaped texture of SmA and mosaic B phases (Fig. 1(d) and 1(e)).
The transformation from mosaic B to SmA phase can be supported by the appearance of
transition bars [9].
The DSC thermogram related to compounds 5a-5d agreed with the results obtained
from POM. Thus, a representative thermogram for compound 5c (Fig. 2) will be described in
this section. From the DSC of compound 5c, on heating cycle there are two endothermic
peaks representing Cr-N and N-I transitions at 109.2 °C and 121.1 °C, respectively. The
associated enthalpies for these transitions are ǻH= 64.55 kJmol-1 and 2.36 kJmol-1. While on
cooling, there are four exotherms representing the phase sequence I-N, N-SmA, SmA-Cr and
Cr1-Cr2 transitions at 119.4 °C (2.39 kJmol-1), 104.2 °C (1.44 kJmol-1), 89.2 °C (4.69 kJmol-1)
and 62.0 °C (9.51 kJmol-1), respectively.
3.3
Evaluation on mesomorphic behaviour from different chemical constitution
The changes of mesomorphic properties resulted from the attachment of two identical
mesogenic groups with different terminal substituent such as CH3, C2H5, Cl and Br wherein
the alkyl spacer (n = 6) remains unaltered and the introduction of disulphide linkage (S S)
between the spacer has been studied extensively.
It can be deduced from Table 5 that the melting and clearing temperatures are affected
by the presence of sulphur-sulphur linkage and different terminal substituents. The present
series exhibit lower melting and clearing temperatures as compared to the previous reported
dimers [5-8]. This can be rationalized by the introduction of disulphide-bridge which helps to
increase the flexibility of the spacer because the S-S rotation is more facile than C-C rotation.
In addition the S-S bond is assumed to be practically unhindered compared to the CH2-CH2
bond. Consequently, this linkage helps to reduce the melting and clearing temperature of the

molecule. Moreover, among the present dimers with halogen in the aniline fragment, the
clearing temperature for compound 5c is lower than 5d. This can probably be caused by Cl
atom which possesses higher electronegativity in comparison to Br. As a result, it leads to
perturbation and reduction of the degree of molecular order. Hence, only little heat is required
for turning from solid to liquid [10]. For alkyl substituent, the clearing temperature for
compound 5a is higher than compound 5b and this observation is similar with earlier reported
dimeric compound [3] in which compound 5a with CH3 group has higher thermal stability
than C2H5 group leading to the higher clearing temperature. The order of correlation between
clearing temperature and various terminal substituents for the present dimers can be
summarized below:
Br > Cl > CH3 > C2H5
The entire phenomena revealed that the existence of SmA phase upon heating and
cooling as exhibited by compound 5d is more effective in comparison to 5c. This can be
attributed to the presence of Br atom which is considered larger than Cl. In addition, the Br
atom possesses high polarizability value (82.10 0.5 x 10-24 cm3) (Table 6) than the Cl atom
(79.76 0.5 x 10-24 cm3) as the valence electrons located at Br atom are far apart from the
nucleus [11]. Consequently, the overall intermolecular attraction also increases with the
appearance of a polarizable Br atom. This is an important characteristic in the formation of
higher order mesophases such as the SmA phase [12]. On the other hand, by comparing the
terminal alkyl chain, the compound with ethyl substituent is more polarizable than compound
incorporated with methyl group. From Table 6, it revealed that the polarizability value of
ethyl group (83.27 0.5 x 10-24 cm3) is higher than that for methyl group (79.62 0.5 x 10-24
cm3). Hence, the thermal stability of nematic phase for compound 5b is higher than
compound 5a by ǻN= 11.1 °C.
Besides, a comparison between 5b and 5d shows that compound 5b has higher
polarizability than its analogue 5d. This observation implies that the presence of ethyl
substituent in 5b has not favoured the formation of SmA phase. This can be rationalized
using what have been proposed by Date et al. wherein the formation of smectic phase in the
symmetric Schiff base dimer is dependent on the length of terminal alkyl chain which must
be greater than half the spacer length [13].
4.
Conclusion

A new series of symmetric disulphide dimers in which two mesogenic imine groups
connected by different terminal substituents has been isolated and characterized. Sulphur-
sulphur linkage in these dimers helps to increase the flexibility of the molecule which led to
low melting and clearing temperatures. Dimers with terminal aliphatic chain exhibit
monotropic
N
phase. On the other hand, derivatives 6-(4-oxybenzylidine-4’-
chloroaniline)hexyldisulphide exhibits enantiotropic N and monotropic SmA phases while 6-
(4-oxybenzylidine-4’-bromoaniline)hexyldisulphide shows enantiotropic SmA and mosaic B
phases. The mesomorphic properties exhibited by the present series reveal that the analogue
compound with Br substituent tends to exhibit higher stability of the smectic phase as
compared with the other members in this series due to the higher polarizability of the
molecule.
Acknowledgements
The main author would like to thank Ministry of Higher for funding the project
through Fundamental Research Grant Scheme (Account No. 203/PKIMIA/6711265).
References
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Transt. 84 (2011) 29-37.
[4] G.Y. Yeap, E.A. Al-Taifi, C.H. Ong, W.A.K. Mahmood, D. Takeuchi, M.M. Ito, Phase
Transt. 85(2012) 483-496.
[5] J.I. Jin, J.H. Park, Mol. Cryst. Liq. Cryst. 110 (1984) 293-308.
[6] S.K. Pal, V.A. Raghunathan, S. Kumar, Liq. Cryst. 34(2007) 135-141.
[7] H.C. Lee, Z. Lu, P.A. Henderson, M.F. Archard, W.A.K. Mahmood, G.Y. Yeap, C.T.
Imrie, Liq. Cryst. iFirst (2011) 1-10.
[8] P. A. Henderson, O.Niemeyer and C. T. Imrie, Liq. Cryst. 28 (2001) 1427-1434.
[9] P. E. Cladis and J. W. Goodby, Mol. Cryst. Liq. Cryst. 72 (1982) 307-312.
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(2006) 205-211.

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Publishing Ltd, 1990.
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238.

HIGHLIGHTS
• A new series of disulphide dimers containing various terminal substituents of CH3,
C2H5, Cl and Br.
• Correlation between the molecular structure and thermal behaviour is documented
along with the relationship between the stability of the phase and associated transition
temperatures due to different terminal substituent
• Disulphide dimers with terminal aliphatic chain exhibit monotropic N phase.
• Whilst the dimers with Cl substituent exhibit enantiotropic N and monotropic SmA
phases, their analogues containing Br substituent exhibit enantiotropic SmA and
mosaic B phases.
• The derivative with terminal Br exhibits higher stability of SmA as it possesses higher
polarizability.

&IGUREꢀS
(b)
(a)
(c)
(d)
(e)
Figure 1. Photomicrographs (a) and (b) show the Schlieren textures for compound 5a-5c, (c)
SmA texture for compound 5c, (d) and (e) display the SmA and mosaic B texture for
compound 5d.

Figure 2. DSC traces of compound 5c upon heating and cooling.

3CHEME
OHC
OH
X
NH2
CH3OH
R.T
X
N
CH
OH
1a-1d
Br(CH2)6Br
K2CO3
CH3COCH3
Reflux
X
N
CH
O
Br
6
2a-2d
CH3COCH3
Reflux
KSAc
O
X
N
CH
O
S
CH3
6
3a-3d
1) NaOH / H2O
2)Conc. HCl
R.T.
X
N
CH
4a-4d
O
SH
6
H2O2 , 30%
NaI
DCM
R.T.
9
10
2
6
3
18
16
14
S
O
CH
N
X
4
8
1
X
N
CH
O
S
15
17
19
7
5
13
12
5a-5d
Compound
X
CH3
C2H5
Cl
5a
5b
5c
5d
Br
Scheme 1. Synthetic pathway towards the formation of compounds 5a-5d.

4ABLEꢀS
Table 1
Physical and analytical data of compounds 1a-1d, 2a-2d, 3a-3d, 4a-4d and 5a-5d
Compounds
Formula
MW
M+ (relative
intensity)
%
Yield
80
%Ca
%Ha
%Na
1a
1b
1c
1d
2a
2b
2c
2d
3a
3b
3c
3d
4a
4b
4c
4d
5a
5b
5c
5d
C14H13NO
211.26
225.29
231.68
276.13
374.31
388.34
394.73
439.18
369.52
383.55
389.94
434.39
327.48
341.51
347.90
392.35
652.95
681.00
79.59
(79.59)
79.97
6.21
(6.20)
6.71
6.63
(6.63)
6.22
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
C15H15NO
85
82
87
75
78
72
76
64
60
59
61
53
50
48
55
32
37
35
30
(79.97)
67.40
(6.71)
4.35
(6.22)
6.05
C13H10ClNO
C13H10BrNO
C20H24BrNO
C21H26BrNO
C19H21BrClNO
C19H21Br2NO
C22H27NO2S
C23H26NO2S
C21H24ClNO2S
C21H24BrNO2S
C20H25NOS
(67.39)
56.55
(4.35)
3.65
(6.05)
5.09
(56.55)
64.17
(3.65)
6.46
(5.07)
3.74
(64.17)
64.95
(6.46)
6.75
(3.74)
3.61
(64.95)
57.81
(6.75)
5. 36
(5. 36)
4.83
(3.61)
3.55
(57.81)
51.96
(3.55)
3.19
(51.96)
71.54
(4.82)
7.36
(3.19)
3.80
(71.51)
72.02
(7.36)
7.65
(3.79)
3.65
(72.02)
64.68
(7.62)
6.20
(3.65)
3.59
(64.68)
58.06
(6.20)
5.57
(3.59)
3.35
(58.06)
73.37
(5.57)
7.69
(3.32)
4.30
(73.35)
73.90
(7.69)
7.97
(4.28)
4.15
C21H27NOS
(73.86)
65.63
(7.97)
6.37
(4.10)
4.06
C19H22ClNOS
C19H22BrNOS
C40H48N2O2S2
C42H45N2O2S2
(65.59)
58.16
(6.37)
5.68
(4.03)
3.60
-
(58.16)
73.18
(5.65)
7.33
(3.57)
4.18
653.32(>1)
(73.58)
73.48
(7.41)
7.95
(4.29)
4.06
681.35(>1)
693.21(>1)
783.11(1)
(73.86)
65.65
(7.97)
6.12
(4.10)
3.91
C38H42Cl2N2O2S2 693.79
C38H42Br2N2O2S2 782.69
(65.78)
58.31
(6.10)
5.33
(4.04)
3.51
(58.31)
(5.41)
(3.58)
aCalculated values in parentheses.

Table 2
Absorption frequencies of FT-IR (Ȟ/cm-1) and relative intensities of 5a-5d
Compounds
Ȟ(C-H) aliphatic Ȟ(C=N)
Ȟ(C=C)
aromatic
1607(s)
1608(s)
1604(s)
1607(s)
Ȟ(C-O)
ether
1251(m)
1255(m)
1250(m)
1252(m)
imine
5a
5b
5c
5d
2937, 2856(s)
2962, 2874(s)
2939, 2854(s)
2937, 2856(s)
1623(w)
1621(w)
1623(w)
1620(w)
s, strong; m, medium; w, weak.
Table 3
1H-NMR chemical shifts (į/ppm) of X-6-SS-6-X
Proton
H2&H6
H3&H5
H7
5a (X= CH3)
5b (X= C2H5)
5c (X=Cl)
5d (X= Br)
7.48 (d, J=8.5Hz)
7.06 (d, J=8.5Hz)
8.33 (s)
7.81 (d, J=8.5Hz)
6.96 (d, J=8.5Hz)
4.01 (d, J=6.5Hz)
1.79-1.85 (m)
1.45-1.55 (m)
1.70-1.75 (m)
2.70 (t, J= 7.0Hz)
-
7.21 (d, J= 8.0Hz) 7.23 (d, J= 8.0Hz)
7.14 (d, J= 8.5Hz) 7.16 (d, J= 8.0Hz)
7.36 (d, J= 8.5Hz)
7.15 (d, J=9.0Hz)
8.36 (s)
8.40 (s)
8.41 (s)
H9&H13
H10&H12
H14
7.84 (d, J= 8.5Hz) 7.85 (d, J= 9.0Hz)
7.84 (d, J= 8.5Hz)
6.98 (d, J= 8.5Hz) 6.98 (d, J= 9.0 Hz) 6.99 (d, J= 8.5Hz)
4.04 (t, J= 6.5Hz)
1.82-1.87 (m)
1.51-1.57 (m)
1.73-1.79 (m)
2.73 (t, J= 7.0Hz)
2.39 (s)
4.04 (t, J= 6.5Hz)
1.82-1.87 (m)
1.50-1.55 (m)
1.73-1.79 (m)
2.72 (t, J= 7.5Hz)
-
4.05 (t, J= 6.5Hz)
1.83-1.88 (m)
1.52-1.57 (m)
1.73-1.77 (m)
2.73 (t, J= 7.0Hz)
-
H15
H16, H17
H18
H19
Ar-CH3
Ar-CH2CH3
Ar-CH2CH3
1.28 (t, J= 7.5Hz)
2.68 (m)
-
-
-

Table 4
13C-NMR chemical shifts (į/ppm) of 5a-5d
Carbon
5a (X=CH3) 5b (X=C2H5) 5c (X=Cl) 5d (X=Br)
C1
135.31
130.38
120.77
149.79
158.98
129.27
129.71
114.66
161.66
67.98
29.09
25.69
28.21
29.06
38.98
20.96
-
141.75
130.39
120.66
149.99
159.01
128.83
129.29
114.66
161.66
67.99
29.09
25.70
28.21
29.06
38.98
-
131.00
130.61
122.18
150.86
160.00
128.87
129.18
114.74
161.99
68.03
29.08
25.69
28.20
29.04
38.97
-
118.91
132.14
122.59
151.30
160.02
129.90
131.14
114.75
162.05
68.04
29.98
25.69
28.20
29.04
38.98
-
C2&C6
C3&C5
C4
C7
C8
C9&C13
C10&C12
C11
C14
C15
C16
C17
C18
C19
Ar-CH3
Ar-CH2CH3
Ar-CH2CH3
15.64
28.40
-
-
-
-
-
Table 5
Phase transition temperatures and enthalpy changes for 5a-5d
Compound
Phase transition temperature,°C heating cooling (associated
enthalpy change, kJmol-1)
5a
5b
5c
5d
Cr 120.5 (74.8) I
I 108.7 (2.9) N 91.4 (43.4) Cr
Cr 99.7 (52.6) I
I 100.9 (2.6) N 72.5 (2.8) Cr 64.1 (31.7) Cr1
Cr 109.2 (64.6) N 121.1 (2.4) I
I 119.4 (2.4) N 104.2 (1.4) SmA 89.2 (4.7) Cr 62.0 (9.5) Cr1
Cr 119.4 (64.0) Mosaic B 121.0a (-) SmA 129.5 (8.2) I
I 127.2 (8.0) SmA 111.3 (5.7) Mosaic B*
Cr, crystal; SmA, smectic A; N, nematic; I, isotropic.
aMeasured by polarized light microscopy
*The formation of Mosaic B was observed until room temperature.
Table 6
Calculated polarizability values for compounds 5a-5d
Compound
Polarizabilitya (Į 0.5 x 10-24 cm3)
5a
5b
5c
5d
79.62
83.27
79.76
82.10
aValues calculated by using ACD/Chemsketch Version 11.