Room temperature helical fluids in single-component systems

Article abstract of DOI:10.1016/j.molliq.2018.11.081

Technologically significant chiral nematic (N*) phase is a helicoidal superstructure, that is generally formed by the spontaneous self-assembly of entire chiral mesogens (mostly calamitics) or by the LC mixtures where a chiral dopant is being added to the

Full text of DOI:10.1016/j.molliq.2018.11.081

Accepted Manuscript
Room temperature helical fluids in a single-component system
G. Shanker, A. Bindushree, K. Chaithra, P. Pratap, Ravindra
Kumar Gupta, A.S. Achalkumar, C.V. Yelamaggad
PII:
S0167-7322(18)32723-5
DOI:
Reference:
https://doi.org/10.1016/j.molliq.2018.11.081
MOLLIQ 9991
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
25 May 2018
9 October 2018
17 November 2018
Please cite this article as: G. Shanker, A. Bindushree, K. Chaithra, P. Pratap, Ravindra
Kumar Gupta, A.S. Achalkumar, C.V. Yelamaggad , Room temperature helical fluids in a
single-component system. Molliq (2018), https://doi.org/10.1016/j.molliq.2018.11.081
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ACCEPTED MANUSCRIPT
Room Temperature Helical Fluids in a Single-Component System
G. Shanker*a, A. Bindushreea, K. Chaithraa, P. Pratapa, Ravindra Kumar Guptab, A. S.
Achalkumarband C. V. Yelamaggad*c
aDepartment of Studies in Chemistry,
Jnana Bharathi Campus, Sneha Bhavan,
Bangalore University, Bangalore 560056, India
bDepartment of Chemistry
Indian Institute of Technology Guwahati
Guwahati-781039, Assam.
cCentre for Nano and Soft matter Sciences (CeNS),
P. B. No. 1329, Prof. U. R. Rao Road,
Jalahalli, Bangalore 560013.
*Corresponding Authors. E-mail:maanshanker@gmail.com; yelamaggad@cens.res.in
Abstract: Technically significant chiral nematic (N*) phase is a helicoidal superstructure, that
is generally formed by the spontaneous self-assembly of entire chiral mesogens (mostly
calamitics) or by the LC mixtures where a chiral dopant is being added to the host nematic (N)
phase. However, the stabilization of the N* phase at room temperature solely by chiral
mesogens is highly challenging where the molecular designing is rather crucial, and thus
scarcely reported. Working in this direction, we have rationally designed, synthesized and
characterized new chiral materials namely, non-symmetric dimers derived from cholesterol.
Notably, as expected, some of these dimers exhibit room temperature N* phase over a wide
thermal range. The exclusive occurrence of N* phase has been evidenced unequivocally with
the help of optical polarizing microscope (POM) and differential scanning calorimeter (DSC).
The chiroptical property of the phase has been studied by recording circular dichroism (CD)
spectra as a function of temperature where the intense bisignate bands (change of sign within
the band) were observed. Notably, one of the dimers forms stable gel in an aprotic solvent
such as hexadecane. Thus, our study reveals a new molecular architecture to stabilize the
technologically important N* phase at ambient temperature.
Key words: Chiral neamtic phase, dimers, pitch, selective reflection & circular dichroism.
I. Introduction
Among a large variety of thermotropic liquid crystal (LC) phases reported hitherto, the chiral
nematic (N*) phase, commonly referred to as cholesteric phase, has attracted wide attention
owing to its defect free helicoidal superstructure and technologically important optical
properties1-17 but also ubiquitous in living systems.18 Moreover, it provides opportunities to
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tune its properties under the influence of external stimuli, such as light, temperature, pressure,
electric field and dopants.11-22 For instance, the N* phase composed of photo-active organic
segments/additives, when exposed to light, displays many technologically significant
properties which has opened-up a multitude of potential applications.11-13,21,22 Given the fact
that the N* phase forms a self-assembled one dimensional (1D) photonic structure, where the
periodic modulation of the refractive index along the helical axis occurs, featuring an optical
band gap, it serves as an active media in optical sensors.23,24 This periodic helicoidal
superstructure phase is formed either by the spontaneous self-assembly of chiral mesogens 25-
29 or by the preparation of LC mixtures (doped LCs) where the helical order stems from the
interaction of a chiral guest molecule (the dopant) with an achiral host nematic (N) phase.
This exceptional LC phase, being a chiral variant of the N mesophase, can be considered as a
stack of layers of mesogens with an orientational order, rotating each layer with an invariable
angle with respect to its adjoining layer. Thermodynamically, the N* phase is analogous to
that of an achiral nematic phase that has only long-range orientational order where the long
axes of the constituent mesogens, such as rod-like LC molecules (calamitics), point on the
average in the same direction, which is defined by a unit vector called the director (n). Each
layer of the helicoidal structure of the N* phase may be regarded as a nematic structure in one
plane; in other words, the N phase can be simply visualized as the N* phase having infinite
pitch. This chiral phase is characterized by helical pitch (P) and handedness. The helical pitch
is defined by a 360° (2π) molecular rotation; i.e. it is the distance over which the director
completes 360° rotation. Handedness refers to helix sense (helical twist) which can be either
left or right depending upon which of the two optical isomers (enantiomers) forms the N*
phase; in fact, it describes the direction in which the molecular orientation rotates along the
helical axis. One of the most outstanding optical properties of N* phase, in its planar
orientation, is inherent exhibition of temperature-dependent selective reflection of light
according to the Bragg law. When homogeneously oriented N* phase, where the helices stand
perpendicular to the substrate, is irradiated with a white light and colors variation with the
change in the temperature observed. The reflected light will have a characteristic wavelength
determined by the pitch of the structure, which in turn depends upon the chemical structure of
mesogens stabilizing the N* phase, and by the viewing angle.
Within this reflection bandwidth, right circularly polarized (CP) light is reflected by a
right-handed helix, while left CP light is transmitted. Beyond the reflection bandwidth, both
left-handed and right-handed CP lights are transmitted. Most importantly, as said above, if the
pitch length of the helix is of the order of wavelength of visible light then colors are reflected
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selectively and this phenomenon is the cause for the unique optical properties of this phase.
Since the pitch is temperature-dependent, the colour-shifts (colour change) are observed as a
function of temperature. This distinctive property of changing reflected colour, when
illuminated by white light, with change in temperature has been well-utilized in thermal
sensors and thermography. 1-17 However, in device fabrication involving the N* phase as an
active organic media, it should possess certain features/qualities. One of the most essential
needs is that the N* phase should necessarily occur at room temperature (RT) with a very
broad thermal span, say from sub-ambient (−10 to -30 °C) to high temperature (+60 to +80
°C). As is known, this basic material’s characteristic requirement has been effectively full-
filled by developing chiral organic systems in the form of either single component chiral
calamitics25-29 or suitably formulated LC mixture (so called doped LCs) obtained by
dissolving a chiral guest, dopant(not necessarily liquid crystalline), in a nematic host.30-35The
latter approach is very popular and applied widely. However, the usage of optically pure
single component mesogens to stabilize the N* phase, for device application, is advantageous
not only because it takes care of technical concerns, such as uniformity (no phase separation),
enhanced stability and fast response to external fields, but also enables pitch variation while
keeping other physical parameters constant.1-17 Thus, constant efforts have been made
directing towards the design and synthesis of single component chiral mesogens capable of
displaying room temperature N* phase occurring over a wide thermal range.25-29 However, the
creation of such single component chiral mesogens appear to be rather difficult for a number
of reasons, which primarily include limitations in molecular architecture.
It is quite remarkable, on the other hand, to note that the N* phase is invariably seen in
mesogens derived from a natural sterol namely, cholesterol. 36-44 This is especially noteworthy
in the case of non-symmetric dimers that are formed by covalently linking the pro-mesogenic
cholesterol to one of the termini of another(non-cholesterol) mesogenic core via a flexible
spacer of varying length and parity.43-58 Such dimers customarily stabilize the N* phase apart
from a range of highly frustrated and re-entrant phases, and unprecedented phase sequences.
43,44Notably, however, the cholesterol-based dimers displaying the N* phase with the above
said physical parameters required for applied science have been barely reported.59,60Therefore,
we became interested to design and synthesize new cholesterol-based dimers exhibiting room
temperature N* phase occurring over a wide thermal range. In the past, we have well
demonstrated that the incorporation of 2,3,4-trialkoxybenzene moiety helps not only in
stabilizing the LC phase at ambient temperature but also widens the thermal range of the LC
phase.59,61 Accordingly, we inserted such a moiety in cholesterol-based dimeric molecular
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architecture to accomplish the objectives. In this paper, we report the synthesis and
characterization
of
cholesteryl
ω-((4((2,3,4-trisalkoxy)benzylidene)amino)-
phenoxy)alkanoates. In ordered to gain insight into the effect of structural variations on
thermal properties, the length and parity of the flexible spacer and the terminal n-alkoxy
chain, attached to the 2,3,4-trialoxybenzene unit, have been varied. In particular, the spacers
namely, 4-oxybutanoyloxy (C4; even-parity spacer), 5-oxypentanoyloxy (C5; odd-parity
spacer), 6-oxyhexanoyloxy(C6; even-parity spacer) and 8-oxyoctanoyloxy (C8; even-parity
spacer) have been used; the n-alkoxy tails viz.,n-octyloxy, n-decyloxy and n-dodecyloxyhave
been employed. A general molecular structure of these new dimers realized has been depicted
in Scheme-I and for convenience they have been referred to as DS series meaning Dimeric
Schiff base.
II. Results and discussion
II.1. Synthesis and characterization:
The proposed non-symmetric dimers (DS-series of mesogens) along with their
intermediates were synthesized as shown in Scheme I. Cholesteryl ω-bromoalkanoates (2a-d)
were prepared as per literature published procedure56,62 that involves treating cholesterol (1)
with freshly distilled 4-bromobutanoyl / 5-bromopentanoyl/ 6-bromohexanoyl / 8-
bromooctanoyl chlorides in the presence of pyridine. Primary amines, cholesteryl ω-(4-
aminophenoxy)alkanoates (4a-d), were synthesized in quantitative yields by catalytic
hydrogenation (10% Pd-C, H2, 1 atm, balloon) of cholesteryl ω-(4-nitrophenoxy)alkanoates
(3a-d), which in turn, were realized by O-alkylation of 4-nitrophenol with alkanoates 2a-d in
the presence of a mild base (K2CO3). 2,3,4-Tris(n-alkoxy)benzaldehydes (6a-c) were prepared
by O-alkylation of 2,3,4-trihydroxybenzaldehyde (5) with 1-bromooctane / 1-bromodecane /
1-bromododecane in the presence of a mild base (anhydrous K2CO3), in butanone.Finally,
benzaldehydes 6a-c were condensed with primary amines 4a-c in the presence of a catalytic
amount of acetic acid (AcOH) to obtain the target DS-series of dimers in good yields (68-80
%). In the supporting information (SI), the details of the synthetic protocols along with the
characterization data of the target mesogens and intermediates are given.
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Scheme-I: Synthesis of dimeric Schiff bases (DS-series)
(i)
( )
n
O
HO
Br
O
1
2a : n= 3; 2b : n= 4
2c : n= 5; 2d : n= 7
(ii)
CHO
OH
( )
n
O
HO
O2N
O
OH
5
O
3a : n= 3; 3b : n= 4
3c : n= 5; 3d : n= 7
(iv)
(iii)
CHO
OR
( )
n
O
RO
H2N
O
OR
O
4a : n= 3; 4b : n= 4
4c : n= 5; 4d : n= 7
6a : R = C8H17; 6b : R = C10H21
6c : R = C12H25
(v)
( )
O
N
O
n
RO
O
H
RO
OR
DS-3, 8 : n=3; R = C8H17
DS-3, 10 : n=3; R = C10H21
DS-3, 12 : n=3; R = C12H25
DS-4, 8 : n=4; R = C8H17
DS-4, 10 : n=4; R = C10H21
DS-4, 12 : n=4; R = C12H25
DS-5, 8 : n=5; R = C8H17
DS-5, 10 : n=5; R = C10H21 DS-7, 10 : n=7; R = C10H21
DS-5, 12 : n=5; R = C12H25 DS-7, 12 : n=7; R = C12H25
DS-7, 8 : n=7; R = C8H17
Reagents and conditions:
(i) n-Bromoalkonyl chloride, pyridine, 0-5 oC to rt (80-84 %). (ii) 4-Nitrophenol, K2CO3, butanone, 85 oC, 12 h
(74-80 %). (iii) 10% Pd-C (10 wt %) , H2 (1 atm, balloon), THF, rt, 10 h (95-98 %). (iv) 1-Bromooctane /
1-bromodecane / 1-bromododecane, anhydrous K2CO3, Butanone, 85 oC, 12 h (87-90 %). (v) Anhydrous EtOH,
AcOH (catalytic) reflux 1 h (68-80 %)
The molecular structures of the mesogens have been authenticated with the help of
1
13
spectroscopic techniques such as FTIR, H NMR, C NMR (see SI, Figs. S1-S3) and FAB+
Mass and elemental analyses. In view of the fact that the majority of the intermediates are
reported in the literature, their molecular structures have been ascertained with aid of
spectroscopic (see SI for details).
II.2. Evaluation of liquid crystalline and thermal properties
The mesomorphic and thermal properties of the non-symmetric dimers synthesized were
investigated using polarized optical microscopy (POM) and differential scanning calorimetry
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(DSC). DSC traces of the heating and cooling cycles were recorded at scanning rate of 10 ° C
min−1and the results obtained were standardized to indium. While enthalpies of phase
transitions were determined using DSC traces, POM was especially employed for the phase
identifications by textural observation and also to confirm the phase transition temperatures.
The existence of LC phase was determined by examining the birefringence and mobility of
the samples under POM. The phase-transition temperatures and enthalpy changes derived
from above mentioned complementary techniques are shown in Table 1 and graphically
represented in Fig.1.The entropy change at the phase transition temperatures is expressed as
ΔS/R, in which ΔS is calculated from ΔS=ΔH/T; where ΔH is calculated in kJ mol-1, T is the
corresponding phase transition temperature in Kelvin and R=8.314 J K-1 mol-1 gas constant.
Table 1.Transitional properties of cholesteryl ω-((4((2,3,4-tris-alkoxy)benzylidene)amino)phenoxy)alkanoates
(DS-sereis).Phase transition temperatures (°C)a and associated enthalpies ΔH (k Jmol-1)b, and entropy ΔS (JK-
1mol-1), Cr: Crystal; N*: Chiral nematic phase; Iso: Isotropic phase.
Dimers
Phase
T / aC
∆H /
∆S /
∆S/ R
transition
k J mol-1
0.6
J K-1 mol-1
2
cN* — Iso
54
54
69
67
60
83
82
57
0.2
0.2
2.1
2
DS-3,8
Iso — N*c
cN* — Iso
Iso — N*c
Cr — N*
N* — Iso
Iso — N*
N* — Cr
Liquid
0.4
4.8
4.5
99
6.4
6.3
91.5
1.4
17.6
16.6
401.6
24.1
23.8
375.0
DS-3,10
DS-3,12
48.3
2.9
2.9
45.1
DS-4,8
Liquid
DS-4,10
DS-4,12
Cr — Iso
Iso — Cr
cN* — Iso
Iso — N*c
cN* — Iso
Iso — N*c
Cr — N*
N* — Iso
Iso — N*
N* — Cr
Liquid
62
40
80
80
75
74
53
76
75
53
96.1
95.9
8
7.9
8
7.7
155
10.5
10
391.8
422
47.1
50.8
3.2
26.9
26.5
29.5
28.4
659
41.4
39.5
642
DS-5,8
3.2
3.5
3.4
DS-5,10
DS-5,12
79.3
5
4.8
151
77.2
DS-7,8
Liquid
DS-7,10
DS-7,12
Cr — Iso
Iso — Cr
48
44
127
128
561.9
574.4
67.6
69.1
aPhase transition temperatures were determined by both POM and DSC studies: peak temperatures in the DSC
b
traces obtained during the first heating-cooling cycles at 10 °C/min. Transition enthalpies were obtained from
the DSC traces. c The sign of crystallization was not seen in both DSC traces and in POM observation.
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Figure 1. Bar graph showing the thermal behavior of dimers (first heating)
It can be generally seen from Table 1 that the dimers having an even-numbered spacer behave
thermally different from those with an odd-numbered spacer in a fashion reminiscent of other
reports.43-58 This behaviour is often interpreted in terms of the dependence of the overall
molecular (rod or bent) shape on the parity of the spacer considered in the all-trans
conformation. As shown in Fig. 2a, the dimer DS-3,8, containing even-membered (4-
oxybutanoyloxy) spacer attain an overall rod-like shape and by contrast, the corresponding
dimer DS-4,8 with an odd-membered (5-oxypentanoyloxy) spacer have a bent-shape (Fig.
2b). The even-parity spacers, with the exception of 8-oxyoctanoyloxy spacer, favour the
formation of N* phase. In the context of the objectives of the present investigation, the
mesomorphic behaviour of dimers DS-3,8, DS-3,10, DS-5,8 and DS-5,10, comprising even-
parity spacers, is really noteworthy. They stabilize the N* phase at RT occurring over a wide
thermal range – an important feature in the context of applied science. The dimers having odd-
parity (5-oxypentanoyloxy; C5) spacer such as DS-4,8, DS-4,10 and DS-4,12, on the other
hand, do not favour the mesomorphism. Explicitly, the dimers DS-4,8 and DS-4,10 are liquids
while the compound DS-4,12 is crystalline that was evidenced based on the observation that
upon heating DS-4,12 transforms directly into the isotropic melt and the LC phases are not
seen even while cooling. As discussed earlier, this observation can be attributed to the bent-
shape imposed by the spacer of these dimers, which leads to an overall reduction in the shape-
anisotropy. Likewise, the dimers DS-7,8, DS-7,10 and DS-7,12 do not stabilize mesophases
7

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implying that the longer spacer length impedes the mesomorphism. Among the liquid
cystalline dimers, the increase in the length of terminal tails leads to a reduction in the
mesophase width, which can be noted in the case of DS-3,12 and DS-5,12. Thus, the
mesomorphic behaviour of these dimers largely depends on the parity of the spacer than on
the length of terminal chain.
(b)
(a)
Figure 2. Energy minimized space-filling models of dimers DS-3,8 (a) and DS-4,8 (b). Seemingly, the
mesogenic (aromatic and cholesterol) cores incompoundDS-4,8 (b) are inclined to each other imposing
a bent-shape to the dimer.
The energy minimized structure of DS-3,8 and DS-4,8 are shown in figure 2a and 2b. The
quantum mechanical calculation of molecular properties were performed using DFT by
employing the combination of Becke3-lee-Yang-Parr (B3LYP) hybrid functional and 6-
31G(d,p) basic set using Gaussian09 package 63,64, to obtain the information related to
molecular confirmation (refer to ESI for standard orientation of dimers DS-3,8 and DS-4,8)
The presence of N* phase at RT in dimers DS-3,8, DS-3,10, DS-5,8 and DS-5,10, was
evidenced unambiguously by naked-eye examination and microscopic observation (see Figs. 3
and 4a-d), are describe as follows. The first obvious hint to this revelation came from the fact
that these dimers, after purification, were isolated as fluid mass conveying iridescent colour to
surface of the container (Fig. 3). In fact, the samples held between a slide and a cover slip
could be readily spread by mechanical shearing. As expected, the spread over samples showed
birefringent texture under microscope clearly implying the existence of LC phase at RT. On
o
cooling at a rate of 5 C /min from their isotropic phase of dimers held between a glass slide
and a cover slip and viewed under a polarizing optical microscope, a transition to the
cholesteric phase occurs with a hazy focal conic / fan-shaped textural growth emanating from
the dark background of isotropic phase.
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Figure 3. Sample vials comprising dimers DS-3,8, DS-3,10, DS-5,8 and DS-5,10 displaying the chiral
nematic (N*) phase at room temperature.
25 µm
(a)
(b)
(d)
25 µm
Top
Glass
Substrate
(c)
(d)
Bottom
Glass
Substrate
30
25
20
15
10
65C
540
510
480
450
420
(f)
25C
(e)
40C
45C
35C
55C
450
550
600
500 / nm
25
30
35
40
45
50
55
T / C
Figure 4. (a) A microphotograph of optical texture seen for the N* phase occuring just below the isotropic liquid
of dimer DS-5,8. (b) Grandjean plane texture of the N* phase obtained after dusturbing the hazy focal-conic
texture (a). (c) Schematic representation of vertically aligned helicesof the N* phase held between substrates
treated for planar oerientation. (d) The colour varition seen in the planar texture as a function of temperature for
the N* phase of dimer DS-5,8. (e) Selective reflection (transmission) spectra recorded as a function of
9

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temperature while heating the N* phase of dimer DS-5,8; notice that the wavelength of light shifts due to change
in the colour (pitch) of the phase. (f) Temperature dependence of light wavelength λmin in the N* phase of DS-
5,8.
Fig. 4a shows such a textural pattern where a random ordering of the helix exists. When the
cover slip was pressed gently (subjected to a mechanical stress), the fan-like texture
transforms instantaneously in to oily streaks characteristic of the Grandjean plane texture (Fig.
4b) where supramolecular helical structure orients predominantly such that the helix axis
remains perpendicular to the substrates. The vertically aligned helices of the phase are shown
in Fig. 4c. As expected, a uniform colour seen under the microscope, at a given temperature,
does not change or disappear with a rotation of the sample between crossed polarisers as the
optic axis remains parallel to the light propagation direction.
However, as shown in Fig.4d, the film (texture) changes its colour as a function of
temperature which a significant feature required for developing thermal sensors. To
substantiate this observation, temperature-dependent selective reflection measurements in the
N* phase formed by the sample DS-5,8 (held between quartz plates) were carried out using a
UV-VIS spectrophotometer in the wavelength range of 200-800 nm. Fig. 4e shows the
transmission spectrum obtained at different temperatures. As can be seen, these spectra are
characterized by a Bragg reflection band centred at min, which is related to the pitch P. With
the increase in the temperature, the desire for the molecules to move apart from each other
cannot be achieved by expansion, thus they twist to higher angles. This leads to an increased
twist, resulting in a shorter pitch, consequently the selective reflection of the bluish color
(Fig.4e, f) prevails Figure 4f shows the thermal dependence of min in the entire range of the
cholesteric phase indicating a strong variation in the pitch as the temperature is varied.
In Table 1, the entropy (ΔS/R) values obtained for the phase transitions such Cr-N* /
N*-Cr or N*-Iso / Iso-N* are given. As can be seen, in the case of dimers DS-3,12 and DS-
5,12 the change in the entropy is higher for Cr-N* / N*-Cr transition than for N*-Iso / Iso-N*
transition, as the former involves a greater change in order to less ordered structure (Table 1).
In dimers DS-3,8, DS-3,10, DS-5,8, DS-5,10, that show N*—Iso / Iso — N* transitions, the
entropy values enhance with the increase in molecular length result from the increase in the
length of the terminal chain / the spacer length. This behavior could be attributed to higher
order in the N* phase due to increase in the overall molecular length. For example, the ΔS/R
values for the N*—Iso transition for dimers DS-3,8 and DS-3,10 are 0.2 and 2.1 respectively.
Similarly, the increase in the entropy was seen with increase in spacer length; for example,
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consider the N*-Iso transition of dimers DS-3,10 and DS-5,10. Thus, the entropy values
indicate that the order of the N* phase enhances with the increase in the terminal chain length
/ spacer..48,49 The DSC traces recorded for the heating-cooling cycles at a rate of 10 °C min−1
of samples, DS-3,8, DS-3,10, DS-5,8 and DS-5,10, corroborated the optical observations. As
representative cases, the DSC profiles obtained for the dimers DS-5,8 and DS-5,10 during two
successive heating-cooling cycles are shown in Fig. 5a and 5b respectively; it is immediately
apparent that the DSC traces of two consecutive heating-cooling cycles remain identical
meaning that mesogens are stable to heat. As can be seen, in the heating profiles a signature
(an endothermic peak) due to a transition from N* to isotropic liquid could be seen; the
cooling cycle traces possess only one exothermic peak corresponding to a reverse transition.
In fact, the thermodynamic stability is the key for occurrence of the N* phase at room
temperature, traces of crystallization happens due to the super-cooling phenomenon in
supercooled LC phases. Unaltered DSC thermograms obtained for the RT N* dimer DS-3,10
even after a expose to open atmosphere for more than 3 months time, thus once again
confirms their stability without any trace of recrystallization (Fig S4). Corroborating the
textural pattern mentioned earlier in conjunction with the data derived from DSC
thermograms support the fact that the N* phase occurs at RT with wide thermal range in
dimers DS-3,8, DS-3,10, DS-5,8 and DS-5,10.
`
II
N*
Iso
I
N*
Iso
II
I
I
I
I
II
II
Heating
Cooling
Heating
Cooling
(b)
80
(a)
30
40
50
60
T / C
70

30
40
50
60
70
80
90
T / C
Figure 5. DSC traces obtained for the two successive heating-cooling cycles at a rate of 10 °C / min.
for the dimers DS-5,8 (a) and DS-5,10 (b). Notice that the thermograms of the two heating-cooling
cycles are identical signifying the chemical/thermal stability.
XRD study of a representative dimer DS-3,8 was carried at room temperature and
typical pattern obtained for liquid crystalline phase with a diffused peak in the wide angle
maxima at d=0.49nm, corresponding to the mean lateral distance between the molecules
indicating fluidity. The low angle peak shows no strong reflection and a broad diffused nature
11

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could be attributed to averaged reflections arising from different segments the molecules as
shown in Figure S5. The very weak diffused peak in the low angle with d-value of 1.9 nm
may be due to low electron-density interactions and the longitudinal distance is only about
one-half of the total molecular length in the most extended conformation, Lmax = 4.3 nm. The
absence of sufficient flexibility and also electrostatic interaction between the aromatics and
the sterodial core appear to be conscientious for the absence of any order phase and complete
mixing of aromatics in the N* phase65. Thus, the optical textures corroborated with XRD
studies unambiguously confirm the presence of N* phase at room temperature.
II.3. Electronic absorption and circular dichroism studies
Given the fact that dimers possess chromophores and molecular chirality, their fluid N* phase
and isotropic liquid states were probed for the electronic absorption and chiroptical properties.
UV-Vis spectroscopy was used to measure the wavelength and intensity of ordinary light
absorption by the chromophores of constituent dimers. On the other hand, circular dichroism
(CD) spectroscopic technique was employed to study chiroptical behaviour of the N* phase.
For these spectroscopic studies, locally fabricated thin-films of the sample cells were used and
thus, experiments carried are purely qualitative. In fact, usage of such cells was essential
given the fact that when the samples were inserted in pre-fabricated standard (commercial)
cells and measured, intense CD bands were obtained that were beyond the quantifiable range
of the instrument. A tiny quantity of the dimers (DS-3,8 / DS-3,10/ DS-5,8 / DS-5,10) placed
between two clean, untreated quartz slides was heated to isotropic phase and firmly pressed
repeatedly so as to obtain thin-films where uniform distribution of samples throughout the cell
is ensured. UV-Vis spectra were recorded in the isotropic state and then in the N* phase after
cooling the samples. As expected, these dimers, irrespective of the temperatures at which
measurement was carried out (whether in the bulk liquid state or N* phase), showed identical
UV-Vis spectra with three absorption maxima (λmax = 340, 293, and 241) (see Fig 6a, Fig. S6
& Table 2).
12

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1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
85 C
75 C
65 C
60 C
55 C
50 C
45 C
150
100
50
(b)
(a)
0
45 C
50 C
55 C
60 C
65 C
70 C
-50
-100
-150
-200
75 C
Iso
200
300
400
500
600
700
800
200
300
400
500
600
 / nm
/ nm
Figure 6. UV-Vis (a) and CD spectra (b) recorded in the isotropic liquid state and the N* phase (as a
function of temperature) exhibited by dimer DS-5,8.
Table 2: Temperature dependant UV–visible and CD data obtained for the N* phase of dimer
Dimer
DS-3,8
T / °C
UV-vis
λmax/nm
CD
λmax/nm
391.5,343,318
CD signal/mdeg
50
45
40
35
30
28
26
25
75
65
60
55
50
45
65
60
55
50
45
35
70
65
60
55
50
45
35
291,339
180.48,-120.57,-113.57
146.0,-110.961,-88.67
91.86,-116.67,-88.65
68.22,-30.91,-29.29
64.83,-139.25,-77.049
53.31,-59.64,-40.24
49.94,-41.09,-28.61
38.05,-101.652,-65.68
154.47,-181.75,
153.80,-181.66
146.19,-180.47
134.38,-167.22
119.85,-138.51
92.48,-105.56
88.09,-177.76
87.48,-175.98
73.31,-171.73
67.57,-116.52
56.45,-107.90
14.03,-10.36
166.83,-194.16
157.77,-79.78
129.19,-53.38
290,339
290,339
289,338
291,338
291,339
-
394.5,358,315
398,360,317
400,362,313
402.5,365.5,314
395.5,359,315
403,362,316.5
397,357.5,316
399,350,
-
292,341
293,341
294,339
293,339
294,339
294,340
294,339
290,338
290,338
291,337
290,337
290,338
295,340
294,339
295,339
295,340
295,339
295,340
296,340
DS-5,8
399,349.5
397,349
395.5,346.5
397.5,349
396.5,345.5
419.5,351
410.5,350.5
440.5,355
403.5,350
406,354
392,340.5
400,352
398,351.5
395,346.5
394,344
DS-3,10
DS-5,10
110.79,-44.73
85.47,-34.91
38.38,-18.43
22.64,-9.54
392.5,340.5
389,334
389,326.5
13

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As is known, the N* phase, being the defect free helical super structure exhibits circular
dichroism (CD) phenomenon.66 As discussed earlier, this occurs when white (unpolarized)
light beam (with equal amount of left and right handed circularly polarized components) at a
given wavelength is directed at the N* phase where the incident light splits into two
components, left and right circularly polarized (CP) light. In fact, depending on the helical
sense of the phase, dictated by the constituent major enantiomer of a chiral material forming
the N* phase, the CP light of a particular handedness is completely reflected while its
counterpart is transmitted. Precisely, when white light propagates through a left-handed (LH)
helix, the left-handed CP component with wavelength of the helix pitch is selectively reflected
whereas the right-handed (RH) component is wholly transmitted. Hence, chiroptical study
using CD spectroscopy would not only formally confirm the helicoidal structure (wherein
intermolecular interactions between electronic transitions occur) but also indicate the screw
sense of the chiral nematic structure.
Thus, the chiroptical behaviour of the N* phase formed by dimers DS-3,8, DS-3,10,
DS-5,8 and DS-5,10, was studied with the aid of CD spectroscopy. For this spectroscopic
study, thin-films of the sample cells fabricated for the above mentioned UV-Vis study were
used. The CD spectra recorded in the isotropic state of the samples, unlike in the N* phase,
did not show any significant signature implying that chromophores are not influenced by the
molecular chirality, but they are affected by the macroscopic chirality of the fluid phase. The
samples from their isotropic liquid state were then cooled gradually in to the N* phase and the
CD spectra were obtained as a function of temperature. Notably, CD spectra recorded in the
entire thermal width of the N* phase of the samples exhibited a clear bisignate CD curve; the
intensity of curve increases with decrease in temperature suggesting the higher mobility of the
flexible units of mesogens at higher temperature of the mesophase. The genuineness of a
bisignate CD peak shown in the N* phase was validated by recording the spectra at four and
six different orientations achieved by in-plane rotation of the sample cells by 90o and 60o
respectively. The CD spectra obtained were found to be virtually identical ruling out the
possible linear dichroism (LD) effects due to macroscopic orientation. Moreover, no
bands/signatures of any kind stemming from LD activity were found when measured directly
using inbuilt program of the CD instrument. These observations clearly indicate that a
bisignate band seen for the mesophase is genuine and not originating from the possible LD
artefact.
14

ACCEPTED MANUSCRIPT
As a representative case, the CD spectra obtained in the N* phase of dimer DS-5,8 has
been depicted in Fig. 6b; as can be seen, the spectrum recorded at a given temperature shows a
bisignate CD pattern, (i.e., CD with split Cotton effect) with a positive peak at ~ 400 nm and
negative peak at ~ 348 nm with a cross over at ~ 375 nm. Besides, low intensity positive and
negative exciton could be observed at ~ 275 nm and ~ 214 nm respectively before crossing the
UV region. Such a pattern symbolizes the through-space coupling of at least two
chromophores in the chiral macroscopic structure. In other words the CD signals account for a
helical disposition of at least two chromophores in the mesophase, and is consistent with the
helical stacking of mesogens in the LC phase. As mentioned earlier, the intensity of the CD
bands increase with decrease in temperature; very low intense peak observed at 75 °C clearly
indicate higher degree of disorderedness (ΔS/R ≈ 3.2; Table 1) of the structure which
completely disintegrate in the isotropic phase. The occurrence of such temperature-dependent
CD curve intensity variation implies that the chiroptical properties of these dimers could be
modulated by light and it has potential to be used as a dopant in achiral LC hosts. The
emergence of a bisignate peak from positive region to negative-side perhaps suggests a right-
handed twist of the cholesteric helix.
II.4.Gelation property
Low molar mass organogels have great significance in the field of biological and
material science.67 Cholesterol derivatives are one such example, wherein they have tendency
to form stable gel with various solvents that are of high interest as novel molecular
recognition systems, sensing and external stimuli responsive systems, light harvesting
systems, templates for the realization of nanofibrous materials etc. Several “Gemini” shaped
gelators containing azobenzene and cholesterol moieties are reported, which show odd-even
effect on gelation.68,69 Similarly the effect of spacer parity on gelation was observed for
trimers containing two cholesterol moieties and a central azobenzene unit connected through
spacers. They found better gelation for the trimers with ethylene spacers.67
Considering the dimeric structure with a cholesterol unit, we thought that this
molecular design will be conducive for gelation.42 Thus qualitative gelation studies were
performed on some selected dimers in solvents like ethanol, m-xylene, decane and
hexadecane. Keeping the terminal chain of the dimer constant with n-dodecyloxy chain, we
studied the effect of spacer and the inferences on their gelation ability are tabulated in Table 2.
15

ACCEPTED MANUSCRIPT
Except DS-3,12 none of the other dimers exhibit gelation. DS-3,12 forms gel in hexadecane as
confirmed by the inversion of glass vial (Fig.7) at different weight percent, but was found to
be soluble in m-xylene and decane. The critical gelation concentration (CGC) for the
compound DS-3,12 was found to be 4g/100 mL in hexadecane. This was carried out by
heating 40 mg of the sample in 1 mL hexadecane in a screw-capped vial until it dissolves
(Fig.7a). When the clear solution was allowed to reach ambient temperature, it yielded a gel
which was negative to the inversion test (Fig.7b). The xero-gel of the dimer DS-3,12was
probed with scanning probe microscopy but we were not successful to obtain an image, which
may be due to its instability. Although ethanol favours the gel formation in most of the
cholesterol based dimers,42,67 this dimer series exhibited precipitation in ethanol including DS-
3,12. We could not notice any spacer effect in gelation, instead we postulate that the dimer
with shorter spacer may have good gelation capability, which is in line with the earlier
report.70 Thus we can conclude that the organogels self-assembly is much more sensitive to
the structural modulation and demands a fine balance between molecular structure, overall
shape and its interaction with the solvents. The presences of large excess of solvent molecules
diminish the effect of the overall molecular shape (directed by the spacer parity) on the
organogel self-assembly. However with a shorter spacer, as in the case of DS-3,12 the
stiffness of the molecule is increased which enhances the solvent-solute interactions,
stabilizing the organogelation. Nevertheless, this study provides a guideline for the molecular
design towards the better organogelators based on cholesterol dimers. Preliminary rheological
properties of the gel (DS-3,12) was studied and the results are furnished in the supporting
information (Fig S7).
Figure 7. Solution of DS-3,12in hexadecane (a) and the inverted vial showing the gelation (b).
IV. Conclusions
16

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In summary, several room temperature cholesteric LCs capable of selectively reflecting light
in the visible region upon varying the temperature have been realized; this finding is notable
given the fact that such mesogens are rarely reported in the literature. Generally speaking, the
synthesis and characterization of twelve new, non-symmetrical dimeric mesogens (Schiff
bases) formed by covalently linking cholesterol with 2,3,4-trialkoxybenzene moiety through a
flexible spacer of varying length and parity (odd/even) have been reported. To study the
structure-property correlations, the length of the terminal n-alkoxy chain, attached to the
2,3,4-trialoxybenzene core, has also been varied. In general, the dimers having an even-
numbered spacer show a different thermal property when compared to the compounds with
odd-numbered spacer. The dimers having even-parity spacers, with an exception, stabilize of
N* phase; notably some these stabilize the N* phase at room temperature existing over a wide
thermal range. The dimers having odd-parity or longer even-parity spacers do not favour the
mesomorphism. The thermal behaviour of these dimers largely depends not only on the parity
of the spacer but also on the length of terminal chain. Most importantly, the transition
temperatures of these dimers, although Schiff bases, are reproducible even after long periods
of time provided the samples are not exposed to moisture and acid vapours. One of the dimers
with the shortest spacer formed a weak gel in hexadecane solvent and no effect of spacer
parity was noticed. Overall, the present study suggest that the dimeric molecular design of
combining a rod-shaped mesogen with a 2,3,4-substituted aromatic core serves an entirely
new strategy to realize technologically significant cholesteric phase occurring over wide
thermal range including room temperature.
V. Experimental
V.1. General Information
Requisite chemicals / reagents of analytical grade, procured either from overseas
agencies such as Sigma Aldrich, Lancaster and TCI companies, or local approved vendors,
were used as received. Analytical Reagent (AR) grade organic solvents used for reactions
were dried using appropriate drying agents. Industrial grade dichloromethane (DCM) and
hexanes used for column chromatography were distilled twice prior to use. Active aluminium
oxide (configured as neutral) was used as the stationary phases in column chromatography.
Purity of the compounds (other than the target Schiff bases) and progress of the reaction were
examined with the help of thin layer chromatography (TLC).TLC plates made of aluminium
17

ACCEPTED MANUSCRIPT
sheets pre-coated with silica gel (Merck, Kieselgel 60, F254) were used. UV-light and iodine
vapours were used for visualization. The absorption spectra of the thin-films of the samples
sandwiched between two quartz plates were recorded on a Perkin-Elmer’s Lambda 20 UV-Vis
spectrometer. The FT infrared (FTIR) spectra were recorded in transmission mode (in the
range of 300–4000 cm-1) using a Perkin-Elmer Spectrum 1000 FTIR instrument and the
spectral positions are given in wave number (cm-1) unit.1H and 13C NMR spectra were
recorded in CDCl3 solvent at RT using Bruker AMX-400 NMR machine. The chemical shifts
are reported in ‘ppm’ on scale downfield from TMS regarded as an internal standard and the
1
coupling constants (J) are given in Hz. The pattern (splitting or multiplicity) of the H NMR
signals are presented as: s = singlet, d = doublet, dd = doublet of doublet, brd = broad singlet,
t = triplet etc. Microanalytical data was obtained from a PerkinElmer's 2400 Series II
CHNS/O instrument. Mass spectra were determined on JEOL JMS-600H spectrometer in
FAB+ mode using 3-nitrobenzyl alcohol as a liquid matrix. The quantum mechanical
calculation of molecular properties were performed using DFT by employing the combination
of Becke3-lee-Yang-Parr (B3LYP) hybrid functional and 6-31G(d,p) basic set using
Gaussian09 package, 63,64 to obtain the information related to molecular confirmation.
The dimers, before subjecting to the thermal characterization, were dissolved in
CH2Cl2 and micro-filtered to remove the fine particles, cotton threads, filter paper fibers, etc.
The mesophase characterization and determination of transition temperatures of the chiral
dimers were achieved with the help of an Olympus BX50 (BX50F4 model) optical polarizing
transmitted light microscope attached to a digital camera and a Mettler FP82HT hot stage
programmed by an FP90 Central Processor. In order to determine the enthalpies of phase
transitions, Differential scanning calorimeter (DSC), Perkin-Elmer Diamond DSC with the PC
system operating on Pyris software, was employed. The DSC instrument prior to sample
measurement was calibrated using pure indium as a standard. DSC traces recorded at a
scanning rate of 10 °C/min were considered to determine the transition temperatures and
associated enthalpies shown in Table 1.
V.2. Synthesis and characterization
The synthetic procedures and characterization data of all the intermediates namely,
cholesteryl ω-bromoalkanoates (2a-d), cholesteryl ω-(4-nitrophenoxy)alkanoates (3a-d),
cholesteryl ω-(4-aminophenoxy)alkanoates (4a-d) and 2,3,4-tris(n-alkoxy)benzaldehydes (6a-
c) have been given in SI.
18

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General procedure for the synthesis of cholesteryl ω -((4((2,3,4-tris-alkoxy)benzyli-
dene)am-ino)phenoxy)alkanoates (DS-series).
A mixture of cholesteryl ω-(4-aminophenoxy)alkanoates(4a-d) (1.86 mmol, 1 equiv.),
2,3,4-trialkoxybenzaldehyde (6a-c)(1.86 mmol, 1 equiv.) and catalytic amount of glacial
acetic acid (2 drops) in anhydrous ethanol was refluxed for 1 h. The solid / gummy mass
obtained upon cooling was collected by filtration, washed with hot ethanol and further
purified by repeated reprecipitation for solid dimers using CH2Cl2:EtOH (1:9) and ethanol
1
wash for gummy mass dimers. Representative H and 13C NMR spectra of the dimers are
shown in Figures S.1 to S.3
DS-3,8: Cholesteryl 4 -((4((2,3,4-tris-octyloxy)benzylidene)amino)phenoxy)butanoate
A gummy mass; yield: 83 %; IR (KBr Pellet): max in cm-1: 2933, 2855, 1732, 1504, 1289,
1090; 1H NMR (400 MHz, CDCl3): δ 8.76 (s, 1H, N=CH), 7.84 (d, J = 8 Hz, 1H, Ar), 7.19 (d,
J = 8 Hz, 2H, Ar), 6.91 (d, J = 12 Hz, 2H, Ar), 6.74 (d, J = 8 Hz, 1H, Ar) 5.38 (brs, 1H, 1 ×
olefinic), 4.67 - 4.61 (m, 1H, 1 × CHOCO), 4.12 - 3.97 (m, 8H, 4 × OCH2), 2.52 (t, 2H, J = 8
Hz, 1 × CH2CO), 2.33 - 2.31(m, 4H, 2 × allylic CH2), 2.13 - 0.68 (m, 88H, 6 × CH, 29 × CH2,
13
8 × CH3); C NMR (100 MHz, CDCl3): 167.50, 166.96, 165.90, 164.27, 163.34, 162.40,
161.07, 159.58, 151.95, 149.13, 143.75, 74.89,73.92, 73.72, 68.82, 67.67, 56.73. 56.18, 50.07,
42.35, 39.55, 31.93, 31.90, 30.37, 30.31, 30.31, 29.74, 29.70, 29.68, 29.65, 29.61, 29.53,
29.44, 29.41, 29.37, 28.04, 26.22, 26.19, 26.12, 22.83, 22.71, 22.58, 14.12, 11.88; MS
(FAB+): m/z calcd for C68H111NO6 (M+2): 1037.83, Found: 1037.56; Anal. calcd for
C68H109NO6: C, 78.79; H, 10.60, N, 1.35. Found: C, 78.89; H, 10.67, N, 1.39.
DS-4,8: Cholesteryl 5-((4((2,3,4-tris-octyloxy)benzylidene)amino)phenoxy)pentanoate
Yellow liquid; yield: 62 %; IR (KBr Pellet): max in cm-1: 2930, 2855, 1735, 1504, 1293,
1
1091; H NMR (400 MHz, CDCl3): δ 8.76 (s, 1H, N=CH), 7.84 (d, J = 12 Hz, 1H, Ar), 7.19
(d, J = 8 Hz, 2H, Ar), 6.91 (d, J = 8 Hz, 2H, Ar), 6.74 (d, J = 8 Hz, 1H, Ar), 5.38 (brs, 1H, 1 ×
olefinic), 4.64 - 4.61 (m, 1H, 1 × CHOCO), 4.12 - 3.97 (m, 8H, 4 × OCH2), 2.37 - 2.31 (m,
4H, 2 × allylic CH2), 2.02 - 0.68 (m, 90H, 6 × CH, 30 × CH2, 8 × CH3) 13C NMR (100 MHz,
CDCl3): 172.50, 154.61, 122.70, 122.24, 114.97, 108.66, 74.93, 73.86, 73.78, 68.84, 67.95,
19

ACCEPTED MANUSCRIPT
56.77, 56.20, 50.09, 31.97, 31.93, 31.89, 29.41, 29.35, 22.75, 22.64, 19.40, 18.79,
14.17,11.94; Anal. calcd for C69H111NO6: C, 78.88; H, 10.65, N, 1.33. Found: C, 78.96; H,
10.44, N, 1.56.
DS-5,8: Cholesteryl 6-((4((2,3,4-trisoctyloxy)benzylidene)amino)phenoxy)hexanoate
A gummy mass; yield: 81 %; IR (KBr Pellet):max in cm-1: 2930, 2857, 1734, 1586, 1504,
1
1291, 1090, 1026.; H NMR (400 MHz, CDCl3): δ 8.76 (s, 1H N=CH), 7.84 (d, J = 12 Hz,
1H, Ar), 7.19 (d, J = 8 Hz, 2H, Ar), 6.90 (d, J = 8 Hz, 2H, Ar), 6.74 (d, J = 8 Hz, 1H, Ar) 5.38
(brs, 1H, 1 × olefinic), 4.63 - 4.59 (m, 1H, 1 × CHOCO), 4.11 - 3.96 (m, 8H, 4 × OCH2), 2.34
- 2.30 (m, 4H, 2 × allylic CH2), 2.02 - 0.68 (m, 92H, 6 × CH, 31 × CH2, 8 × CH3); 13C NMR
(100 MHz, CDCl3 ): 173.03, 157.40, 156.13, 154.08, 145.76, 141.34, 139.71, 123.28, 122.64,
122.16, 122.10, 114.93, 108.64, 74.89, 73.83, 73.71, 68.82, 67.93, 56.73, 56.18, 50.08, 42.35,
39.56, 37.04, 36.64, 35.58, 34.62, 31.96, 29.73, 29.66, 29.41, 28.04, 24.86, 22.84, 22.73,
22.59, 21.07, 19.35, 18.75, 14.14, 11.89; MS (FAB+): m/z calcd for C70H115NO6 (M+2):
1065.86, Found: 1065.64; Anal. calcd for C70H113NO6: C, 78.97; H, 10.70, N, 1.32. Found: C,
78.76; H, 10.92, N, 1.56.
DS-7,8: Cholesteryl 8 -((4((2,3,4-tris-octyloxy)benzylidene)amino)phenoxy)octanoate
Yellow liquid; yield: 65 %; IR (KBr Pellet): max in cm-1: 2930, 2855, 1733, 1504, 1291,
1
1090; H NMR (400 MHz, CDCl3): δ 8.76 (s, 1H N=CH), 7.84 (d, J = 12 Hz, 1H, Ar), 7.19
(d, J = 8 Hz, 2H, Ar), 6.91 (d, J = 8 Hz, 2H, Ar), 6.74 (d, J = 8 Hz, 1H, Ar) 5.38 (brs, 1H, 1 ×
olefinic), 4.63 - 4.60 (m, 1H, 1 × CHOCO), 4.12 - 3.97 (m, 8H, 4 × OCH2), 2.39 - 2.28 (m,
4H, 2 × allylic CH2), 2.02 - 0.68 (m, 96H, 6 × CH, 33 × CH2, 8 × CH3) 13C NMR (100 MHz,
CDCl3): 172.86, 156.11, 154.53, 154.46, 145.73, 141.25, 139.64, 122.06, 114.87, 108.55,
74.85, 73.88, 73.68, 68.74, 67.60, 56.66, 56.10, 49.99, 39.71, 39.50, 36.16, 35.78, 31.89,
29.61, 29.57, 29.34, 22.68, 14.11, 11.83; Anal. calcd for C72H117NO6: C, 79.14; H, 10.79, N,
1.28. Found: C, 79.38; H, 10.65, N, 1.37.
DS-3,10: Cholesteryl 4-((4((2,3,4-tris-decyloxy)benzylidene)amino)phenoxy)butanoate
A gummy mass; yield: 84 %; IR (KBr Pellet): max in cm-1: 2924, 2853, 1732, 1504, 1292,
1
1091; H NMR (400 MHz, CDCl3): δ 8.76 (s, 1H N=CH), 7.84 (d, J = 12 Hz, 1H, Ar), 7.19
20

ACCEPTED MANUSCRIPT
(d, J = 8 Hz, 2H, Ar), 6.91 (d, J = 12 Hz, 2H, Ar), 6.74 (d, J = 8 Hz, 1H, Ar) 5.38 (brs, 1H, 1
× olefinic), 4.65 - 4.61 (m, 1H, 1 × CHOCO), 4.11 - 3.97 (m, 8H, 4 × OCH2), 2.5(t, J= 8 Hz,
2H, COCH2), 2.33 - 2.31 (m, 4H, 2 × allylic CH2), 2.13 - 0.68 (m, 100H, 6 × CH, 35 × CH2, 8
× CH3); 13C NMR (100 MHz, CDCl3): 172.70, 157.24, 156.21, 154.69, 154.15, 145.93,
123.25, 122.73, 122.22, 114.99, 108.14, 74.95, 74.13, 73.77, 68.82, 67.09, 50.09, 39.60,
32.01, 30.37, 29.68, 29.45, 29.26, 22.91, 22.77, 22.66, 14.21, 11.94; MS (FAB+): m/z calcd
for C74H123NO6 (M+2): 1121.92, Found: 1121.67; Anal. calcd for C74H121NO6: C, 79.30; H,
10.88, N, 1.25. Found: C, 79.05; H, 11.08; N, 1.37.
DS-4,10: Cholesteryl 5-((4((2,3,4-trisdecyloxy)benzylidene)amino)phenoxy)pentanoate
Yellow liquid; yield: 63 %; IR (KBr Pellet): max in cm-1:2926, 2854, 1735, 1616, 1504, 1291,
1
1091; H NMR (400 MHz, CDCl3): δ 8.76 (s, 1H, N=CH), 7.84 (d, J = 12 Hz, 1H, Ar), 7.19
(d, J = 8 Hz, 2H, Ar), 6.91 (d, J = 8 Hz, 2H, Ar), 6.74 (d, J = 8 Hz, 1H, Ar) 5.38 (brs, 1H, 1 ×
olefinic), 4.66 - 4.60 (m, 1H, 1 × CHOCO), 4.11 - 3.97 (m, 8H, 4 × OCH2), 2.39 - 2.30 (m,
13
4H, 2 × allylic CH2), 2.02 - 0.68 (m, 102H, 6 × CH, 36 × CH2, 8 × CH3); C NMR (100
MHz, CDCl3 ): 172.87, 157.30, 156.15, 154.54, 154.09, 145.83, 141.35, 139.70, 123.74,
123.28, 122.66, 122.17, 122.11, 114.95, 108.65, 75.37, 74.89, 73.92, 73.72, 68.82, 67.67,
56.73, 56.18, 31.93, 31.90, 29.74, 29.70, 29.68, 29.65, 29.61, 29.53, 29.44, 29.41, 29.37,
29.22, 26.19, 26.12, 22.83, 22.71, 22.58, 14.12; Anal. calcd for C76H125NO6: C, 79.38; H,
10.93, N, 1.23. Found: C, 79.66; H, 11.05; N, 1.33.
DS-5,10: Cholesteryl 6 -((4((2,3,4-tris-decyloxy)benzylidene)amino)phenoxy)hexanoate
A gummy mass; yield: 82 %; IR (KBr Pellet): max in cm-1: 2925, 2853, 1733,
1504,1294,1091; 1H NMR (400 MHz, CDCl3): δ 8.76 (s, 1H, N=CH), 7.84 (d, J = 12 Hz, 1H,
Ar), 7.19 (d, J = 8 Hz, 2H, Ar), 6.90 (d, J = 8 Hz, 2H, Ar), 6.74 (d, J = 8 Hz, 1H, Ar) 5.38
(brs, 1H, 1 × olefinic), 4.61 (m, 1H, 1 × CHOCO), 4.11 - 3.95 (m, 8H, 4 × OCH2), 2.34 - 2.30
(m, 4H, 2 × allylic CH2), 2.02 - 0.68 (m, 104H, 6 × CH, 37 × CH2, 8 × CH3); 13C NMR (100
MHz, CDCl3 ): 173.07, 157.41, 156.15, 154.53, 154.09, 145.76, 141.34, 139.72, 123.28,
122.64, 122.17, 122.11, 119.94, 108.65, 74.89, 73.84, 73.72, 68.82, 67.93, 56.73, 56.18,
39.55, 31.96, 31.94, 29.74, 29.71, 29.68, 29.65, 29.61, 29.53, 29.44, 29.41, 29.37, 29.23,
26.19, 22.83, 22.58, 14.13; MS (FAB+): m/z calcd for C76H127NO6 (M+2): 1149.95, Found:
21

ACCEPTED MANUSCRIPT
1149.69; Anal. calcd for C76H125NO6: C, 79.46; H, 10.97, N, 1.22. Found: C, 79.41; H, 10.87,
N, 1.39.
DS-7,10: Cholesteryl 8 -((4((2,3,4-tris-decyloxy)benzylidene)amino)phenoxy)octanoate
Yellow liquid; yield: 61 %; IR (KBr Pellet): max in cm-1: 2926, 2853, 1734, 1504, 1291,
1
1091; H NMR (400 MHz, CDCl3): δ 8.76 (s, 1H N=CH), 7.84 (d, J = 12 Hz, 1H, Ar), 7.19
(d, J = 8 Hz, 2H, Ar), 6.91 (d, J = 8 Hz, 2H, Ar), 6.74 (d, J = 8 Hz, 1H, Ar) 5.38 (brs, 1H, 1 ×
olefinic), 4.64 - 4.60 (m, 1H, 1 × CHOCO), 4.11 - 3.97 (m, 8H, 4 × OCH2), 2.39 - 2.38 (m,
13
4H, 2 × allylic CH2), 2.02 - 0.62 (m, 108H, 6 × CH, 39 × CH2, 8 × CH3); C NMR (100
MHz, CDCl3): 172.96, 157.34, 154.14, 145.82, 141.63, 139.73, 122.72, 122.24, 122.16,
114.97, 108.66, 74.95, 73.78, 68.84, 67.70, 56.77, 56.20, 50.09, 31.99, 29.77, 29.74, 29.66,
29.47, 29.43, 22.77, 14.21, 11.94; Anal. calcd for C78H129NO6: C, 79.60; H, 10.05, N, 1.19.
Found: C, 79.37; H, 10.33, N, 1.36.
DS-3,12:Cholesteryl 4-((4((2,3,4-trisdodecyloxy)benzylidene)amino)phenoxy)butanoate
Crystalline solid; yield: 86 %; IR (KBr Pellet): max in cm-1:2907, 2869, 1728, 1507, 1292,
1
1063; H NMR (400 MHz, CDCl3): δ 8.76 (s, 1H, N=CH), 7.84 (d, J = 12 Hz, 1H, Ar), 7.19
(d, J = 8 Hz, 2H, Ar), 6.91 (d, J = 8 Hz, 2H, Ar), 6.74 (d, J = 8 Hz, 1H, Ar) 5.38 (brs, 1H, 1 ×
olefinic), 4.65 - 4.63 (m, 1H, 1 × CHOCO), 4.11 - 3.97 (m, 8H, 4 × OCH2), 2.52 (t, J = 6Hz,
2H, COCH2), 2.33 - 2.31 (m, 4H, 2 × allylic CH2), 2.15 - 0.68 (m, 112H, 6 × CH, 41 × CH2, 8
× CH3); 13C NMR (100 MHz, CDCl3 ): 172.62, 157.19, 156.16, 154.61, 154.09, 145.94,
141.347, 139.68, 123.25, 122.67, 122.16, 114.97, 108.64, 74.88, 73.71, 68.81, 67.08, 56.72,
56.17, 50.06, 39.54, 36.62, 31.94, 29.71, 29.68, 29.64, 29.60, 29.52, 29.43, 29.38, 29.32,
28.03, 26.18, 26.11, 22.82, 22.71,22.57, 14.12; MS (FAB+): m/z calcd for C80H134NO6
(M+1): 1205.01, Found: 1205.708; Anal. calcd for C80H133NO6: C, 79.74; H, 11.13, N, 1.16.
Found: C, 79.91; H, 11.40, N, 1.31.
DS-4,12: Cholesteryl 5-((4((2,3,4-trisdodecyloxy)benzylidene)amino)phenoxy)pentanoate
Crystalline solid; yield: 84 %; IR (KBr Pellet): max in cm-1: 2924, 2850, 1731, 1504, 1247,
1
1086; H NMR (400 MHz, CDCl3): δ 8.76 (s, 1H N=CH), 7.84 (d, J = 12 Hz, 1H, Ar), 7.19
(d, J = 8 Hz, 2H, Ar), 6.91 (d, J = 8 Hz, 2H, Ar), 6.74 (d, J = 8 Hz, 1H, Ar) 5.38 (brs, 1H, 1 ×
22

ACCEPTED MANUSCRIPT
olefinic), 4.64 - 4.59 (m, 1H, 1 × CHOCO), 4.12 - 3.97 (m, 8H, 4 × OCH2), 2.39 - 2.30 (m,
4H, 2 × allylic CH2), 2.02 - 0.68 (m, 114H, 6 × CH, 42 × CH2, 8 × CH3); 13C NMR (100 MHz,
CDCl3 ): 172.86, 157.30, 156.15, 154.53, 154.10, 145.83, 141.35, 139.70, 123.28, 122.66,
122.17, 122.12, 114.95, 108.65, 74.89, 73.92, 73.72, 68.82, 67.67, 56.73, 56.19 50.08, 39.55,
31.96, 31.90, 29.72, 29.69, 29.66, 29.62, 29.53, 29.44, 29.42, 29.40, 28.04, 26.22, 26.20,
26.13, 22.84, 22.72, 22.58, 18.75, 14.13; MS (FAB+): m/z calcd for C81H136NO6 (M+1):
1219.03, Found: 1219.72; Anal. calcd for C81H135NO6: C, 79.81; H, 11.16, N, 1.15. Found: C,
79.66; H, 11.38, N, 1.29.
DS-5,12: Cholesteryl 6 -((4((2,3,4-tris-dodecyloxy)benzylidene)amino)phenoxy)hexanoate
Crystalline solid; yield: 84 %; IR (KBr Pellet): max in cm-1: 2924, 2856, 1740, 1506, 1244,
1
1088; H NMR (400 MHz, CDCl3): δ 8.76 (s, 1H N=CH), 7.84 (d, J = 12 Hz, 1H, Ar), 7.19
(d, J = 8 Hz, 2H, Ar), 6.90 (d, J = 8 Hz, 2H, Ar), 6.74 (d, J = 8 Hz, 1H, Ar), 5.38 (brs, 1H, 1 ×
olefinic), 4.64 - 4.58 (m, 1H, 1 × CHOCO), 4.11 - 3.95 (m, 8H, 4 × OCH2), 2.34 - 2.30 (m,
4H, 2 × allylic CH2), 2.02 - 0.68 (m, 116H, 6 × CH, 43 × CH2, 8 × CH3); 13C NMR (100 MHz,
CDCl3 ): 173.03, 157.39, 156.12, 154.47, 154.08, 145.76, 141.33, 139.71, 123.28, 122.63,
122.16, 122.10, 114.93, 108.64, 74.88, 73.83, 73.71, 68.81, 67.92, 56.73, 56.18, 50.07, 42.35,
36.63, 31.95, 30.37, 29.73, 29.69, 29.66, 29.61, 29.53, 29.44, 29.40, 28.04, 26.19, 26.13,
22.83, 22.72, 22.58, 14.13; MS (FAB+): m/z calcd for C82H138NO6 (M+1): 1233.04, Found:
1233.48; Anal. calcd for C82H137NO6: C, 79.88; H, 11.20, N, 1.14. Found: C, 79.67; H, 10.93,
N, 1.27.
DS-7,12: Cholesteryl 8 -((4((2,3,4-tris-dodecyloxy)benzylidene)amino)phenoxy)octanoate
Crystalline solid; yield: 83 %; IR (KBr Pellet): max in cm-1: 2919, 2850, 1732, 1504, 1247,
1173, 1085; 1H NMR (400 MHz, CDCl3): δ 8.76 (s, 1H N=CH), 7.84 (d, J = 12 Hz, 1H, Ar),
7.19 (d, J = 8 Hz, 2H, Ar), 6.91 (d, J = 8 Hz, 2H, Ar), 6.74 (d, J = 8 Hz, 1H, Ar) 5.38 (brs,
1H, 1 × olefinic), 4.64 - 4.59 (m, 1H, 1 × CHOCO), 4.11 - 3.97 (m, 8H, 4 × OCH2), 2.39 -
2.28 (m, 4H, 2 × allylic CH2), 2.03 - 0.68 (m, 120H, 6 × CH, 45 × CH2, 8 × CH3); 13C NMR
(100 MHz, CDCl3 ): 172.86, 157.28, 156.14, 154.55, 154.08, 145.79, 141.32, 139.68, 123.24,
122.64, 122.16, 114.94, 108.63, 74.88, 73.92, 73.71, 68.60, 67.66, 58.47, 56.72, 56.17, 50.06,
42.34, 39.54, 36.62, 31.94, 29.71, 29.67, 29.71,29.67, 29.64, 29.60, 29.52, 29.43, 29.38,
28.03, 26.18, 22.82, 22.71, 22.57, 18.73, 14.12, 11.87; MS (FAB+): m/z calcd for C84H142NO6
23

ACCEPTED MANUSCRIPT
(M+1): 1261.08, Found: 1261.758; Anal. calcd for C84H141NO6: C, 80.01, H, 11.20, N, 1.11.
Found: C, 79.85; H, 11.30, N, 1.33.
Acknowledgement: GS sincerely thank Science and Engineering Research Board (SERB)
for the financial support through ECR project No. ECR/2016/001224, dated 03/01/2017
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Graphical abstract
Self-assembly of rod-shaped molecules into room temperature chiral nematic structure
29