Anisotropic and magnetic properties in non-metal and non-radical organic aggregates of tri-substituted phenyl derivatives

Article abstract of DOI:10.1039/c9nj02730k

A new series of tri-substituted phenyl derivatives containing an aromatic imine unit and biphenyl ester possessing various numbers of carbon atoms at the terminal alkoxy chain, OC_nH_2n+1 (n = 7-12), along with a lateral o-ethoxy substituent have been successfully prepared and characterised by CHN microanalysis along with spectroscopic techniques (FTIR, ¹H- and ¹³C-NMR). The texture observation under polarized light revealed that all the soft condensed materials exhibited an enantiotropic nematic (N) phase. The current studies have shown that the mesomorphic behaviour is greatly influenced by the length of the alkoxy chains wherein the thermal stability of a tri-substituted phenyl derivative will decrease if the terminal alkoxy chain is increased from n = 7 to 12. For the first time, these materials which do not possess any magnetic species in their structure, demonstrate magnetic interaction through naked eye observation as well as quantitative measurement using a SQUID magnetometer.

Full text of DOI:10.1039/c9nj02730k

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Anisotropic and magnetic properties in non-metal
and non-radical organic aggregates of
tri-substituted phenyl derivatives†
Cite this: New J. Chem., 2020,
44, 210
a
a
b
Nur Amanina Juniasari Tun Nur Iskandar, Yeap Guan-Yeow, * Nobuyuki Maeta,
Masato M. Ito,
b
c
d
d
Yoshiyuki Nakamura, Katarzyna Gas
and Maciej Sawicki
A new series of tri-substituted phenyl derivatives containing an aromatic imine unit and biphenyl ester
possessing various numbers of carbon atoms at the terminal alkoxy chain, OC 2n+1 (n = 7–12), along
with a lateral o-ethoxy substituent have been successfully prepared and characterised by CHN
n
H
1
13
microanalysis along with spectroscopic techniques (FTIR, H- and C-NMR). The texture observation
under polarized light revealed that all the soft condensed materials exhibited an enantiotropic nematic
(N) phase. The current studies have shown that the mesomorphic behaviour is greatly influenced by the
length of the alkoxy chains wherein the thermal stability of a tri-substituted phenyl derivative will
decrease if the terminal alkoxy chain is increased from n = 7 to 12. For the first time, these materials
which do not possess any magnetic species in their structure, demonstrate magnetic interaction
through naked eye observation as well as quantitative measurement using a SQUID magnetometer.
Received 26th May 2019,
Accepted 20th November 2019
DOI: 10.1039/c9nj02730k
rsc.li/njc
shortest terminal chain (n = 10) displayed the absence of meso-
morphic property, while the remaining homologues (n = 12–16)
1
. Introduction
A wide range of materials in the state of matter that cannot be exhibit an enantiotropic SmA phase. They also revealed that
classified merely as crystalline solids or simple liquids are both the phase transition temperatures and the mesophase
1
generally known as soft condensed materials. There are various temperature range were also influenced by the length of the
7
forms of soft condensed materials including the fourth unique terminal chains. Besides, the appearance of enantiotropic
2
state of matter which is liquid crystals. It has been well mesophases, namely N and Sm phases has been observed in
8
established that the vital requirement for a compound to exhibit the higher membered chains.
liquid crystalline behaviour depends on the structure of the
Since more than a decade ago, the physical properties and
compound. The materials usually consist of rod-like rigid units, mesomorphic behaviour of these compounds have been asso-
terminal and lateral substituents that are packed in a parallel ciated with the influence brought about by the presence of the
3
,4
5
9,10
manner and large molecular length-to-breadth ratio. One of substituent at the strategic position in the central core.
these works had focussed on the influence of different terminal general, the lateral substituent reduces both the clearing and
In
1
1
alkoxy chains on the Schiff base esters in which the lengthening melting temperature by broadening the core of the mesogen.
of the terminal alkoxy chains lengths resulted in a significant For instance, the fluoro lateral substituents are frequently
6
effect on the mesomorphic behaviour. Recently, a study on the employed in liquid crystal (LC) systems to suppress the
effect of various alkyloxy chains on the heterocyclic derivative presence of the smectogenic phase in forming an N phase that
1
2
having an ester-chalcone central linkage has shown that the exhibits low melting temperature. A review on the influence
of two homologous series with chloro and methyl lateral groups
a
Liquid Crystal Research Laboratory, School of Chemical Sciences, Universiti Sains
showed that the chloro lateral group displayed N and Sm
phases while the methyl group only exhibited an N phase.
Malaysia, 11800 Minden, Penang, Malaysia. E-mail: gyyeap@usm.my;
1
3
Fax: +(60)-4-6574854
b
c
Comparison studies of both lateral substituents with structurally
related homologous series revealed that the increase in the
breadth of mesogens with the lateral group in the ortho position
led to a decline in the mesophase thermal stability as compared
to the unsubstituted analogue. They also stated that the position
of both lateral substituents influenced the thermal stability and
Faculty of Science & Engineering, Soka University, 1-236 Tangi-cho, Hachioji,
Tokyo 192-8577, Japan
Nanospace Catalysis Unit, Institute of Innovative Research, Tokyo Institute of
Technology, 4259-S1 Nagatsuta-cho, Midori-ku, Yokohama-shi, Kanagawa,
2
26-8503, Japan
d
Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46 PL-02668,
Warsaw, Poland
13,14
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/c9nj02730k mesomorphic behaviour.
It has been reported that the melting
2
10 | New J. Chem., 2020, 44, 210--217
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ꢀ1
1
13
point of LC monomers comprising a reactive group in the lateral the frequency range 400–4000 cm . The H and C-NMR spectra
position decreased as the length of the lateral substituent for the intermediates and target compounds were obtained from
15
increased with the molecular long axis. Herein, we are prompted the Bruker-Avance 500 MHz spectrometer equipped with ultra-
to study a new series of tri-substituted phenyls in which a biphenyl shield magnets. Deuterated chloroform (CDCl ) and dimethyl
3
ester with various numbers of carbon atoms at the terminal alkoxy sulfoxide (DMSO) were used as the solvents and TMS as the
chains and an aromatic imine fragment are connected to a central internal standard. Thin-layer chromatography (TLC) was per-
phenyl core along the long axis while an ethoxy group is attached formed with a TLC plate coated with silica and the spots on it
to this phenyl centre at the ortho position. Besides, we also attempt were visualised by short wave UV light irradiation. The transition
to explore the presence of magnetism in these materials which are temperatures and associated enthalpy values were measured using
categorized as non-metal or non-radical substances.
Seiko DSC120 model 5500 differential scanning calorimeters
available in the Faculty of Engineering, Soka University, Japan
with a heating and cooling rate of ꢁ2 1C. The liquid crystal textures
of the target compounds were observed under a Carl Zeiss
Axioskop 40 polarising microscope equipped with a Linkam
LTS350 hot stage and TMS94 temperature controller at the Liquid
Crystal Research Laboratory, School of Chemical Sciences, USM.
The attraction of all the title compounds at room temperature was
investigated first by direct observation under a permanent magnet.
The magnetic phenomenon of a selected compound from this
series at variable temperature was further investigated using the
superconducting quantum interference device (SQUID) magneto-
meter MPMS XL5 of Quantum Design at the Institute of Physics,
Polish Academy of Sciences, Warsaw, Poland.
2. Experimental
2.1 Chemicals and reagents
4
-(4-Hydroxyphenyl)benzoic acid, 3-ethoxy-4-hydroxybenzaldehyde
0
and N,N -dicyclohexylcarbodiimide (DCC) were purchased from
TCI (Tokyo Chemical Industry), Japan. 1-Bromoheptane, 1-bromo-
octane, 1-bromononane, 1-bromodecane, 1-bromoundecane
and 1-bromododecane were obtained from Merck, UK. Potassium
hydroxide, glacial acetic acid, 4-(dimethylamino)pyridine (DMAP),
ethanol, dichloromethane, p-anisidine and diethyl ether were
purchased from Sigma Aldrich, USA.
2
.2 Physical measurement
The carbon, hydrogen and nitrogen (CHN) microanalyses for all
the target compounds were carried out using a PerkinElmer The synthesis of 2-ethoxy-4-(((4-methoxyphenyl)imino)methyl)-
2
.3 Synthesis
0
0
2400 LS Series CHNS/O analyzer. The FT-IR spectra were phenyl-4 -(alkyloxy)-1,1 -biphenyl-4-carboxylate, 3a–3f, was carried
0
recorded using a PerkinElmer 2000 FT-IR spectrophotometer in out following Scheme 1. 4 -Alkoxy-4-biphenylcarboxylic acid, 1a–1f,
Scheme 1 Synthetic route towards the preparation of target compounds 3a–3f.
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was prepared by the etherification reaction between 4 -hydroxy-4-
Paper
0
3c: yield 73%. Elemental analysis (%): found, C 76.96, H
5
biphenylcarboxylic acid and 1-bromoalkane in the presence of 7.33, N 2.51; calculated (C38H43NO ), C 76.87, H 7.30, N 2.36.
ꢀ
1
potassium hydroxide in ethanol. The compound thus obtained FTIR n/cm , 2926–2856 (C–H alkyl), 1605 (CQN), 1729 (CQO
1
was reacted subsequently with 3-ethoxy-4-hydroxybenzaldehyde ester). H NMR (DMSO) d/ppm, 0.85–0.88 (t, 3H, CH ), 1.40–
3
under Steglich esterification conditions using 4-dimethylamino- 1.45 (m, 3H, CH ), 1.23–1.77 (m, 14H, CH ), 3.79 (s, 3H, OCH ),
3
2
3
0
pyridine (DMAP) and N,N -dicyclohexylcarbodiimide (DCC) to 4.02–4.05 (t, 2H, OCH
2
), 4.13–4.17 (q, 2H, OCH
2
), 7.00 (d, 2H,
form benzaldehyde derivatives, 2a–2f. A condensation reaction Ar), 7.07 (d, 2H, Ar), 7.32 (d, 2H, Ar), 7.39 (d, 1H, Ar), 7.55
between the appropriate p-anisidine and compounds 2a–2f in (d, 1H, Ar), 7.72 (t, 3H, Ar), 7.87 (d, 2H, Ar), 8.17 (d, 2H, Ar), 8.66
ethanol led to the formation of title compounds 3a–3f. Detailed (s, 1H, CHQN).
discussion on the target compounds 3a–3f can be based on a
representative compound 3c as these compounds possess identical
2.4 Magnetic measurements
characteristics.
Magnetic studies are performed using the commercial super-
conducting quantum interference device (SQUID) magneto-
meter MPMS XL5 of Quantum Design. To facilitate SQUID
measurements of powdered samples of expected weak signal,
without introducing strong signals of gelatine capsules or other
unreliable carriers, the powdered samples were stabilized by
mixing them with a strongly diluted GE-varnish. Subsequently,
0
2
.3.1 Synthesis of 4 -alkoxy-4-biphenylcarboxylic acid, 1a–1f.
0
4
-Hydroxy-4-biphenylcarboxylic acid and potassium hydroxide
(KOH) were dissolved in ethanol/water (9/1) in a round bottom
flask and the solution was stirred for 20 min. 1-Bromononane
was then added dropwise and the mixture was refluxed over-
night. Upon completion of the reaction, one equimolar of KOH
was added and the mixture was refluxed for another 4 hours.
The resulting mixture was left to evaporate at room temperature
and the mixture was poured into distilled water and acidified
with glacial acetic acid (pH = 2–3). The precipitate thus obtained
was filtered off and washed twice with distilled water and
diethyl ether. The crude product was recrystallized from glacial
acetic acid.
3
these mixtures were transferred into 5 ꢂ 4 ꢂ 0.15 mm pieces of
previously well magnetically characterized silicon (Si), to provide
a solid support and to ease the sample handling at the same
time. Then, such an open sandwich was attached to the center of
a long silicon strip and the whole arrangement was lowered into
the SQUID sample chamber. The preparation procedure for
representative compound 3f is exemplified in the ESI.† All the
measurements, data reduction and final magnetic moment
determination were performed by strictly following the already
described procedures adequate for high sensitivity studies of
1c: yield 93%. Elemental analysis (%): found, C 78.10, H
ꢀ
1
8.35; calculated (C H O ), C 77.61, H 8.29. IR (KBr) n/cm ,
22 28 3
1
2929–2857 (C–H alkyl), 1684 (CQO ester), 3006 (O–H). H-NMR
16
(DMSO) d/ppm, 0.84–0.87 (t, 3H, CH ), 1.26–1.75 (m, 14H, CH ),
3
2
samples of minute magnetic signals.
4.00–4.02 (t, 2H, OCH
2
), 7.02 (d, 2H, Ar), 7.66 (d, 2H, Ar),
7
.73 (d, 2H, Ar), 7.97 (d, 2H, Ar).
0
0
2
.3.2 Synthesis of 2-ethoxy-4-formylphenyl-4 -(alkyloxy)-[1,1 - 3. Results and discussion
biphenyl]-4-carboxylate, 2a–2f. A mixture of 3-ethoxy-4-hydroxy-
benzaldehyde, intermediary compound 1c and 0.32 equivalent of
DMAP was dissolved in an appropriate amount of DCM. To this
mixture, N,N -dicyclohexylcarbodiimide (DCC) in a minimum
amount of DCM was added dropwise and the mixture was stirred
3
.1 Chemical composition
The chemical composition of title compounds 3a–3f can be
inferred from the CHN microanalytical data (Table 1). It is
apparent that all the compounds 3a–3f exhibit high purity because
the composition of C, H and N as derived from experimental data
is in good agreement with the calculated values.
0
0
overnight at room temperature. The white solid of N,N -dicyclo-
hexylurea was removed by filtration and the filtrate obtained was
evaporated at room temperature to remove the remaining sol-
vent. The desired product was recrystallized twice from ethanol to
yield a white precipitate.
3
.2 FT-IR spectroscopy studies
The FT-IR data for 3a–3f show that the stretching frequency for
–H of elongated terminal groups attached to the biphenyl
C
sp
3
2c: yield 67%. Elemental analysis (%): found, C 76.75, H
ꢀ
1 17
ꢀ
1
rings appeared at 2926–2856 cm
at 2870 cm is due to the presence of an ethoxy group at the
phenyl ring. The C–O stretching for the ether group displayed a
signal at 1251 cm while the stretching vibration of CQO for
the ester group showed a strong absorption band at 1729 cm
An absorption band with a strong intensity at 1605 cm can be
ascribed to CQN of the imine group. The FT-IR spectrum of
representative compound 3c is illustrated in Fig. 1 for clarity.
.
A weak absorption band
7.51; calculated (C H O ), C 76.20, H 7.43. FTIR n/cm , 2924–
31 36 5
ꢀ
1
1
2
856 (C–H alkyl), 1730 (CQO aldehyde). H NMR (CDCl3)
), 1.46–1.48 (t, 3H, CH ), 1.28–1.84
), 4.00–4.03 (t, 2H, OCH ), 4.14–4.17 (m, 2H, OCH ),
.99 (d, 2H, Ar), 7.35 (d, 1H, Ar), 7.52 (d, 2H, Ar), 7.60 (d, 2H, Ar),
.69 (d, 2H, Ar), 8.22 (d, 2H, Ar), 9.97 (s, 1H, CHO).
.3.3 Synthesis of 2-ethoxy-4-(((4-methoxyphenyl)imino)-
d/ppm, 0.87–0.89 (t, 3H, CH
m, 14H, CH
3
3
ꢀ
1
(
6
7
2
2
2
ꢀ1
.
ꢀ
1
2
0
0
methyl)phenyl-4 -(alkyloxy)-[1,1 -biphenyl]-4-carboxylate, 3a–3f.
An ethanolic solution of 4-methoxyaniline was added dropwise
to a stirring hot ethanolic solution of compound 2c in a round
1
13
3.3 H and C-NMR spectroscopy studies
bottom flask. The mixture was refluxed overnight at 70 1C. The Since the NMR spectra for 3a–3f show identical splitting
white precipitate thus formed was filtered off and recrystallized patterns, the assignment of these compounds can be described
1
13
twice from ethanol.
using the spectra of representative compound 3c. H and C-NMR
2
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Table 1 Molecular formulas, molecular weight (MW), percentage yields (%) and CHN microanalytical values for title compounds 3a–3f
a
a
a
Compounds
Molecular formulas
MW
% Yield
% C
% H
% N
3a
3b
3c
3d
3e
3f
C
36
C
37
C
38
C
39
C
40
C
41
H39NO
H41NO
H43NO
H45NO
H47NO
H49NO
5
5
5
5
5
5
565.71
579.74
593.76
607.79
621.82
635.85
65
58
73
81
58
56
76.85 (76.43)
76.84 (76.66)
76.96 (76.87)
77.09 (77.07)
77.67 (77.26)
77.55 (77.45)
6.99 (6.95)
7.15 (7.13)
7.33 (7.30)
7.48 (7.46)
7.66 (7.62)
7.80 (7.77)
2.68 (2.48)
2.54 (2.42)
2.51 (2.36)
2.40 (2.30)
2.47 (2.25)
2.29 (2.20)
Fig. 1 FT-IR spectrum of representative compound 3c.
2
spectra of compound 3c and its molecular structure with complete region due to the effect of the p bond of sp hybridization and
atomic numbering are shown in Fig. 2 and 3.
the electron-withdrawing group of the nitrogen atom.
The methylene proton from the nonyloxy chains (H2–H8)
From Fig. 3, the peak at d = 159.95 ppm can be ascribed to
gave rise to several sets of multiplets at d = 1.23–1.34 ppm and the carbon C29 which was attached to the nitrogen atom in the
d = 1.71–1.77 ppm. The signals assignable to the methyl proton CQN group whereas several peaks observed at d = 115.63,
at the terminal ethoxy chains (H38) overlapped leading to a 129.10, 127.97, 130.14, 123.89, 122.26, 112.98, 123.00 and
multiplet at d = 1.40–1.45 ppm. The appearance of an intense 115.08 ppm were attributed to the aromatic carbons of C11&C12,
singlet at d = 3.79 ppm was attributed to the proton H36 from C13&C14, C17&C18, C19&C20, C24, C26, C27, C31&C32 and
the methoxy group. A triplet at d = 4.02–4.05 ppm can be C33&C34, respectively. The signals that emerged at d = 14.20,
ascribed to the oxymethylene protons at the terminal nonyloxy 56.03 and 14.96 ppm suggest that these peaks can be ascribed to
chains (H9) whilst a quartet observed at d = 4.13–4.17 ppm was the carbons C1, C36 and C38, respectively. Meanwhile, the
assigned to the oxymethylene protons of ethoxy chains at the methylene carbons C2–C8 were found to appear in the upfield
ortho position (H37). The aromatic protons H19&H20 appeared region of d = 21.97–32.17 ppm. The resonances due to carbon
as a doublet at d = 8.17 ppm. These protons appeared at a more from the oxymethylene group, C9 and C37, were observed at
downfield region than the other biphenyl aromatic protons d = 64.16 and 67.87 ppm, respectively.
owing to the diamagnetic anisotropic effect of the ester group.
Six doublet signals resonated at d = 7.00, 7.07, 7.32, 7.39, 7.55
3.4 Mesomorphic behaviour
and 7.87 ppm can be ascribed to H33&H34, H11&H12, The mesophase behaviour of all target compounds 3a–3f was
H31&H32, H24, H26 and H17&H18, respectively. The signal observed under a polarizing optical microscope (POM) on
attributed to H13&H14 seemed to appear as a triplet instead of heating and cooling cycles. The POM observation revealed that
a doublet and this could probably be due to the overlapping all the title compounds 3a–3f display an enantiotropic nematic
with the signal of H27.
(N) phase. The nematic phase associated with these compounds
The proton from the imine group (H29) appeared at d = 8.66 ppm has been substantiated by the texture observation wherein the
as a singlet. This proton was observed at the most downfield development of N droplets coalesced into the schlieren texture
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1
Fig. 2 H-NMR spectrum of representative compound 3c.
13
Fig. 3
C-NMR spectrum of representative compound 3c.
with two-brush and four-brush defects is presented for repre- 238.4 1C upon cooling. On further cooling, only crystallization is
sentative compound 3d in Fig. 4. Upon heating, the compound observed.
3
1
d shows a crystal to crystal (Cr –Cr ) phase transition at
The phase sequence for all target compounds 3a–3f was
18.4 1C. The continuous heating has led to the transformation further confirmed by the DSC experiment. The transition tem-
phase into a schlieren texture of the N phase at peratures and associated enthalpy values of these compounds are
40.0 1C. Subsequently, isotropization occurred at 244.8 1C. The tabulated in Table 2. Fig. 5 illustrates a DSC thermogram of
1
2
of the Cr
2
2
formation of N droplets which coalesced into the schlieren representative compound 3e. Upon heating, two endothermic
texture with two-brush and four-brush defects is observed at peaks representing Cr–N and N–I transitions were observed at
2
14 | New J. Chem., 2020, 44, 210--217
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ꢀ1
ꢀ1
values of DH = ꢀ1.4 kJ mol and ꢀ37.8 kJ mol assignable to
the I–N and N–Cr transitions. The peak ascribed to the transition
of Cr –Cr upon both heating and cooling is found to be weak
1
2
and therefore unnoticed under the DSC thermogram. However,
the Cr –Cr transition is observable under the POM.
1
2
Fig. 6 shows a plot of transition temperatures versus the
number of carbon atoms in the alkoxy chain, n, for the title
compounds 3a–3f. As shown in Fig. 6, the melting point (Cr –N)
2
apparently decreased from 249.3 1C (3a) to 231.0 1C (3f) on
lengthening the terminal alkoxy chains. This observation is due
to compound 3a which has comparatively high rigidity and
relatively low length-to-breadth ratio among these compounds
3b–3f which favours a rigid rod conformation. This conformation
promotes the binding forces between the molecules that are
18
positioned in an orderly manner in the crystal lattice. Likewise,
Fig. 4 Photomicrograph showing nematic droplets coalesce into the it also can be implied from Fig. 6 that the clearing temperature
schlieren texture with two-brush and four-brush defects of compound decreased as the terminal chains increased. This descending
3
d at 238.4 1C upon cooling.
trend could be due to the dilution of the interaction between
the mesogenic cores resulting from the flexibility owing to the
1
9,20
longer terminal chains.
Compound 3a has the highest
Table 2 Phase transition temperatures (1C) and associated enthalpy
values (kJ mol , in parentheses) of compounds 3a–3f
ꢀ1
clearing temperature at 266.1 1C wherein the enthalpy value
ꢀ1
DH is 1.9 kJ mol while compound 3f has the lowest clearing
Compound
n
Cr
1
Cr
2
N
I
ꢀ1
temperature at 234.1 1C with DH = 2.7 kJ mol . A noticeable
a
3a
3b
3c
3d
3e
3f
7
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
125.3a
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
249.3 (54.3)
248.6 (ꢀ24.1)
244.9 (51.2)
241.8 (ꢀ22.1)
240.7 (47.9)
238.1 (ꢀ23.2)
233.5 (45.6)
230.3 (ꢀ23.7)
232.9 (50.6)
229.8 (ꢀ37.8)
231.0 (41.7)
227.7 (ꢀ38.6)
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
266.1 (1.9)
264.3 (ꢀ1.6)
260.9 (1.8)
258.0 (ꢀ1.3)
253.9 (2.2)
250.8 (ꢀ1.7)
242.0 (2.1)
237.6 (ꢀ1.5)
239.8 (2.0)
237.6 (ꢀ1.4)
234.1 (2.7)
233.9 (ꢀ1.9)
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
ꢃ
feature among all the target compounds is that compound 3a is
thermally more stable than the other title compounds 3b–3f.
This indicates that the tri-substituted phenyl derivatives with a
shorter terminal alkoxy chain were thermally more stable and
the trend follows the order of n = 7 4 8 4 9 4 10 4 11 4 12.
Besides, the length of the terminal chains influenced the
thermal stabilities of the mesomorphic behaviour in which the
long terminal alkoxy chains led to a reduction in the N thermal
124.1
124.4a
a
8
123.9
124.1a
a
9
121.7
a
10
11
12
118.4a
111.9
a
123.3a
116.8
121.4a
a
2
1
stability. Significant decreases in the temperature range of N
phase from 16.8 1C (3a) to 3.1 1C (3f) can be observed for all the
target compounds by lengthening the terminal alkoxy chains.
This phenomenon is due to the lengthy carbon chain being
attracted and intertwined, facilitating the lamellar molecular
packing of this compounds leading to a low N phase tempera-
116.8
Cr
1
2
= crystal 1; Cr = crystal 2; N = nematic phase; I = isotropic.
2
2–24
ture range.
Fig. 5 DSC thermogram of compound 3e upon heating and cooling cycles.
ꢀ
1
2
32.9 1C and 239.8 1C with enthalpy (DH) values of 50.6 kJ mol
ꢀ
1
and 2.0 kJ mol , respectively. Upon cooling, two exothermic
peaks emerged at 237.6 1C and 229.8 1C with respective enthalpy atoms in the alkoxy chain for title compounds 3a–3f.
Fig. 6 A plot of transition temperature versus the number of carbon
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To quantify the strength of the magnetic response, we
measured the room temperature magnetization M of the sample
3f using SQUID magnetometry in magnetic fields H up to
10 kOe. The main result obtained from these studies is that
the sample 3f is predominantly diamagnetic (M is linear in H
with a negative slope) and that its diamagnetic susceptibility,
ꢀ
7
ꢀ1
w
dia = ꢀ6.3 ꢂ 10 emu g , is approximately 5 times stronger
than that of Si, as presented in Fig. 7(a).
The additional magnetic contribution to M can only be revealed
by numerical subtraction of the diamagnetic signal, which we
approximate as Mdia(H) = wdiaH. The resulting signal DM(H) =
M(H) ꢀ Mdia(H) is presented in Fig. 7(b), which clearly exhibits a
ferromagnetic-like character. Generally, the behavior presented
in Fig. 7(b) can be classified as superparamagnetic-like, which
is indicative of the presence of swiftly magnetizing large spins
(macrospins) originating from some magnetically coupled
volumes of a currently unspecified configuration. It is assumed
that a mutual coupling (probably by magnetic dipolar inter-
action) among these magnetic configurations is responsible for
the observed shape of DM(H). It is noted that the reported
signal is rather weak, nevertheless, the magnetism is clearly
observed in the specimen, despite the fact that magnetic
species like transition metals, rare-earth elements or organic
radical elements are absent in these target compounds.
Fig. 7 (a) A comparision of the room temperature magnetic response of
the sample 3f with the response of the Si support on which the sample was 4. Conclusions
deposited. The observed diamagnetic signal in the 3f sample is approximalely
5
times stronger than that of Si. (b) The nonlinear, superparamagnetic-like, part New tri-substituted phenyl derivatives with different alkoxy
DM(H) present in panel (a) magnetization of sample 3f.
chains on the terminal of the biphenyl ester and an aromatic
imine system containing an o-ethoxy substituent were success-
fully prepared and characterised. All the title compounds 3a–3f
exhibit the enantiotropic N phase. The flexible terminal alkoxy
chains have a strong influence on the thermal stabilities and
exhibit a mesomorphic behaviour in which the long terminal
alkoxy chains led to a reduction in the thermal stability. Surpris-
ingly, we have uncovered for the first time the magnetic beha-
viour of non-magnetic species of compounds 3a–3f. Through
observation by the naked eye, an unusual short-range magnetic
interaction in which the title compounds 3a–3f were attracted to
the magnet in the solid state was observed. In addition, these
compounds were also attracted to the magnet in the presence of a
water surface at room temperature. The studies have also shown
that longer terminal alkoxy chains seem to give rise to a greater
magnetic behaviour. Most importantly, the magnetic response
has been observed in these compounds without having any
magnetic species deliberately introduced into their structures.
3
.5 Magnetic properties
In addition, the study of these liquid crystalline materials has
also been explored to show some unique features of magnetic
behaviour. As far as the magnetism is concerned, it has always
been associated with the presence of metal or rare-earth
2
5,26
elements and organic radical compounds.
time, the magnetism arises from these purely organic materials
a–3f without having magnetic species capable of exhibiting
For the first
3
magnetic behaviour. The magnetic character of the present
material can be observed straightforwardly, without resorting
to any advanced techniques. As indicated in the ESI,† a solid
sample of the representative compound 3f, which is a purely
organic substance, is attracted to the weak permanent magnet.
The sample remains attached to the magnet unless an external
force is applied to detach it. The magnetic response is even
better documented by another experiment in which a sample of
the same compound is placed on the surface of water, when it
flows without any restriction (ESI†). This magnetic attraction is Conflicts of interest
observed at room temperature for the solid sample of a few
millimeters across and the same magnet is positioned in close
There are no conflicts to declare.
proximity to the sample. Comparing the lowest homolog 3a and
highest member 3f, compound 3f exhibits stronger magnetic
behaviour than compound 3a. Therefore, the elongation of the
Acknowledgements
length of the terminal alkoxy chains from n = 7 to n = 12 has The main author (G.-Y. Yeap) would like to thank Universiti
contributed to the greater magnetic response.
Sains Malaysia for providing the research facilities and partial
2
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NJC
financial support through Research University RU Grant No.
Different Lateral Groups, Mol. Cryst. Liq. Cryst., 2012, 562(1),
76–84.
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1
4 J. S. Dave, C. B. Upasani and P. D. Patel, Effect Of Lateral
Substitution On Mesogenic Properties Of Fluoro Aniline
Derivatives, Mol. Cryst. Liq. Cryst., 2010, 533(1), 73–81.
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