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doi.org/10.1002/chem.201905707& Phase Transitions

Chiral Bent-Shaped Molecules Exhibiting Unusually Wide Range ofBlue Liquid-Crystalline Phases and Multistimuli-Responsive
Behavior
Vidhika Punjani, [a] Golam Mohiuddin,[a] Supreet Kaur,[a] Angshuman Roy Choudhury,[a]Sathyanarayana Paladugu,[b] Surajit Dhara,[b] Sharmistha Ghosh,[c] and Santanu Kumar Pal*[a]Introduction
Chirality is ubiquitous in nature and is accountable for the development of living and nonliving matter. Concurrently, it isimmensely important for the pharmaceutical industry and forthe propagation of contemporary technological advancement. [1, 2] The presence of the chiral center in a molecule canresult in complex configurations. For example, if chirality is incorporated into a liquid-crystal (LC) system, it can produce
complex phase structures, such as BPs (BPIII, BPII, BPI), twist
grain boundary (TGB), smectic blue phase (SmBP), and chiralnematic (N*). The N* phase or a cholesteric liquid crystal (CLC)[a] V. Punjani, Dr. G. Mohiuddin, S. Kaur, Dr. A. R. Choudhury, Dr. S. K. Pal
Department of Chemical Sciences
Indian Institute of Science Education and Research (IISER) Mohali
Sector 81, Knowledge City, Manauli, 140306 (India)
E-mail : skpal@iisermohali.ac.in[b] Dr. S. Paladugu, Dr. S. Dhara
School of Physics, University of Hyderabad, Hyderabad, 500046 (India)[c] Dr. S. Ghosh
Department of Physics, University of Calcutta
92 Acharyya Prafulla Chandra Road, Kolkata, 700009 (India)
Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under :https ://doi.org/10.1002/chem.201905707.
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bent molecular architecture, with a bent angle of 1488, andrevealed the presence of two different molecular conformations in an asymmetric unit of compound 1-4. A DFT study
corroborated that the Cl moiety at the central core of themolecule led to an increase in the dipole moment along thetransverse direction, which, in turn, facilitated the unusual
stabilization of frustrated structures. Crystal polymorphism
has been evidenced in three homologues (1-10, 1-12, and 114) of the series. On the application of mechanical pressure
through grinding, compound 1-10 transformed from abright yellow crystalline solid to a dark orange–green amorphous solid, which reversed upon dropwise addition of dichloromethane, indicating reversible mechanochromism inthis class of compounds. In addition, excellent thermochromic behavior has been observed for compound 1-10 with acontrolled temperature–color combination.

is a twisted helicoidal state[2] of the nematic phase. These chirality-induced phases find various applications in imaging devices, information displays, reflectors/polarizers, tunable bandpass filters, and temperature or pressure sensors. [3–5] Comparedwith chiral liquids, LC materials, due to their ordered nature,along with liquidity, can amplify the molecular chirality by
manyfold. [6, 7] BP is a frustrated phase, consisting of doubletwist cylinders, that occurs just below the isotropic liquid overa narrow temperature range. [8–10] BPs are extremely important
for the development of next-generation optoelectronic devices
that do not require alignment layers (i.e., polyimide coating),
which simplifies the LC display manufacturing process. They
can also be used to develop devices such as light filters, lasers,
fast light modulators, and tunable photonic crystals. [11–13] The
TGB phase, which is the LC analogue of the Abrikosov vortex
state in “type II superconductors”, [14] is a rich, complex, andfrustrated phase structure. It usually appears in the temperature range between the N* and Sm phases (SmA/A* or
SmC*). [14–21]
In the contemporary era of LC research, bent-core liquid
crystals (BCLCs) are the frontrunner, due to their extremely
rich, diverse, and unparalleled phase structures.[22] The presence of the small kink at the molecular core of the BCLC helps
to develop additional order (unlike rodlike or disklike LCs) that5859

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Abstract: Recently, an unprecedented observation of polarorder, thermochromic behavior, and exotic mesophases in
new chiral, bent-shaped systems with a CH 3 moiety placedat the transverse position of the central core was reported.
Herein, a homologous series of compounds with even-numbered carbon chains from n = 4 to 18 were synthesized, inwhich Cl was substituted for CH3 at the kink position anda drastic modification in the phase structure of the bentshaped molecule was observed. An unusual stabilization of
the cubic blue phase (BP) over a wide range of 16.4 8C has
been witnessed. Two homologues in this series (1-12 and 114) exhibit an interesting phase sequence consisting of BPI/
II, chiral nematic, twist grain boundary, smectic A, and smectic X (SmX) phases. The higher homologues (1-16 and 1-18)
stabilize the SmX phase enantiotropically over the entire
temperature range. Crystal structure analysis confirmed theChemistry—A European Journal

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arm of the BCLC (Figure 1), promotes rigidness in the molecular architecture, which eventually leads to the realization of different frustrated phases. The methyl group (CH3), with the + I
effect and its bulky size (relative to H), widened the bent angle
and supported the stabilization of different phase structures.
Unlike the methyl group (CH 3), herein, we have purposely
placed an electronegative chloro moiety (3-amino-2-chlorobenzoic acid as the central core [50, 51]) at the transverse position of
the central core to realize its electronegative effect upon thestabilization of frustrated phases (Figure 1 b). On one side of
the core, there is a cholesterol moiety attached through anester linkage, whereas, on the other side, there is a 4-n-alkoxy2-hydroxybenzaldehyde moiety attached through an imine
linkage. The homologous series with even chains, from n= 4 to18, was synthesized. An increase in the alkyl chain length leads
to the thermodynamic stabilization of the liquid-crystalline material enantiotropically, as the series makes a transition from
nonliquid crystalline (1-4, 1-6) to monotropic LC (1-8, 1-10, 112, and 1-14) and enantiotropic LC (1-16, 1-18). Compound 110 exhibited a stable BP over a wide range of 16.4 8C. In addition, we observe a variety of phases, such as BPI/II, N*, TGBA,
SmA, and an unknown tilted phase, SmX, for two homologues(1-12 and 1-14), similar to that previously reported.[47] Compounds 1-16 and 1-18 stabilize the SmX phase enantiotropically. The phase sequence of all compounds is summarized in Figure S83 in the Supporting Information during cooling. The
presence of the Cl moiety in the central core, which is evident from the single-crystal structure and density functional
theory (DFT) analysis, has allowed more insights regarding stabilization of the frustrated structures in these molecular systems. Three of the compounds (1-10, 1-12, and 1-14) wereshown to exhibit crystal polymorphism. An excellent thermochromic property has been observed for 1-10 with a controlledtemperature–color combination. Application of a grinding
force on 1-10 converted the yellow color of the sample to adark orange–green color that can be reversed back to yellow
color after the dropwise addition of a solvent (dichloromethane).

Results and Discussion
Synthesis and characterization
Details of the synthetic approach are summarized in
Scheme S1 in the Supporting Information, and the corresponding molecular characterizations are elaborated in Figures S1–
S32 in the Supporting Information.
Single-crystal X-ray diffraction (SCXRD) studies

Figure 1. Chiral bent-core molecules with a) a CH3 moiety at the kink position (previously reported in ref. [47]) and b) a Cl moiety at the kink positionof the central unit (the molecule described herein).
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Interestingly, we were able to successfully grow crystals suitable for SCXRD experiments (see the Supporting Information for
details) of one of the representative examples, compound 1-4,
to demonstrate the bent angle of the compound, which is an
important parameter in the field of BCLCs and investigate theelusive characteristics of molecular packing (Figure 2 a–f).[52–57]
Compound 1-4 was found to crystallize in the monoclinic

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can be polar, biaxial nematic, octupolar, and/or chiral, despite
being formed from achiral molecules.[22–31] BCLCs, due to their
negative bend-splay elastic constant ratio, if doped with an external chiral agent, can stabilize the frustrated BPs in the mixture, [32] but single-component BCLCs exhibiting BPs and TGB
phases are limited. [33–38] A combination of the additional orderof bent-core molecules with molecular chirality provided by
the stereocenters present in the chiral moiety can lead to thestabilization of the frustrated phases.
There has been increasing interest in recent years in materials that have the ability to change their color, either reversiblyor permanently, in response to applied external stimuli.[39–42]
Materials that exhibit a change in the photoluminescence
properties upon application of mechanical pressure, grinding,shearing, or crushing are known as mechanochromi c luminescent materials or piezochromic luminescent materials. Thesemechanochromic materials have potential applications inmemory storage, sensors, security inks, pressure sensing, andoptical-recording systems. [39–42] The change in emission properties after grinding can be reversed by either solvent or thermal
annealing. The reversibility of the neat compound is because
there is no involvement of bond breakage, but there is a transformation of stacking modes involving weak interactions.
BCLCs containing a salicylideneaniline moiety and cholesterol
unit can be potentially used as mechanochromic materials. The
salicylideneaniline moiety exhibits excited-state intramolecular
proton transfer (ESIPT) due to the formation of intramolecularhydrogen bonding between OH and CH=N and switches
between the ESIPT ON/OFF state due to mechanical grinding.
The cholesterol unit has the tendency to change color and circular dichroism with a change in the helical pitch and handedness.[43–45] Therefore, the salicylideneaniline and cholesterol
units play an important role in the mechanochromic behaviorof this class of compounds. [43–46] In our previous report, [47] weshowed that 3-amino-2-methylbenzoic acid (as the central
core,[47–49, 52, 53,55] Figure 1 a) based smart bent-core materials exhibited frustrated structures that stabilized BPs for about 2.0 8C
and the TGB phase for about 31.0 8C. The direct attachment of
the cholesterol moiety to the central core, functioning as anChemistry—A European Journal

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system with the P21 space group, with two independent molecules of different conformations (conformations A (C1A toC45A) and B (C1B to C45B)) in the asymmetric unit (Z= 4, Z’ =2). Structural analysis revealed the major dissimilarities in thesetwo conformations at the terminal OC 4H9 chain and in thealkyl chain of the cholesterol moiety (Figure 2 b,c). C1A-C2AC3A-C4A in conformer A (aC2A-C3A-C4A-O1A = 175.14(7)8)
adopted an anti conformation with respec t to the C3AC4A
bond, (Figure 2 b), whereas C1B-C2B-C3B-C4B in conformer B(aC2B-C3B-C4B-O1B = 62.43(11)8) adopted a staggered conformation with respect to the C3BC4B bond (Figure 2 c). Anothersignificant difference in the conformations was observed in thealkyl chain of the cholesterol moiety (aC35A-C38A-C40AC41A = 172.27(6)8 and aC40A-C41A-C42A-C43A = 171.71(8)8 in
conformer A(Figure 2 b);
aC35B-C38B-C40B-C41B =179.16(7)8 and aC40B-C41B-C42B-C43B = 175.14(8)8 in conformer B (Figure 2 c)).
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Most importantly, the molecule attained a bent-shaped geometry with a bent angle (the angle between the centroids ofthe rings C5A-C6A-C7A-C8A-C9A-C10A, C12A-C13A-C14AC15A-C16A-C17A, and C19A-C20A-C21A-C22A-C23A-C24A ofconformer A and C5B-C6B-C7B-C8B-C9B-C10B, C12B-C13BC14B-C15B-C16B-C17B, and C19B-C20B-C21B-C22B-C23B-C24B
of conformer B) of 148.858 for conformer A (Figure 2 b) and148.358 for conformer B (Figure 2 c). Details of the structural
analysis are summarized in Figures S33–S39 and Tables S1–S4
in the Supporting Information. Other than these major differences, the two molecules had differences in other bond angles
and torsion angles of  28. These differences were manifested
by Z’ = 2 with a large unit cell (V = 4046.7(4) 3 ; Table S5 in the
Supporting Information). The structure of the cholesterolbased BC compound under investigation is shown in Figure 2 a, for which the bent architecture was proved by meansof SCXRD analysis.

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Figure 2. a) Structure of the lowest homologue. Molecular crystal structure of b) conformers A (1-4) and c) B (1-4) with dihedral angles varying at the terminal
alkyl chain and cholesterol moiety. d) Conformer A (1-4) with CCl···p interactions and e) conformer B (1-4) with CCl···p interactions . f) The 3D structural arrangement of 1-4.

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A DFT study was performed on compound 1-4 (as a representative case) and an analogous compound with a methyl
core reported earlier.[47] It was found that the dipole moment
along the y directio n (Figure S40 and Tables S6 and S7 in the
Supporting Information) was much larger (my = 2.55 D) in compound 1-4 than that in the previously reported molecule (my =1.272 D), although the dipole moments along the other two directions (x and z) remained similar in both compounds. Thisobservation implies that the introduction of the Cl moiety inthe kink direction of the molecule (Figure 2 a) electronically affects nucleation of the usual mesophases (e.g., nematic or Sm)
and stabilizes the frustrated BPs.
Thermal behavior: Polarized optical microscopy (POM) anddifferential scanning calorimetry (DSC) studies
The phase transition temperature of BPs was not observed bymeans of DSC, but rather a POM study in reflectance mode
was employed to determine the BP range of the compounds.
On a normal glass slide with a coverslip (without any coating),
compound 1-10 (as a representative case) melted at a temperature of 145.4 8C, which, upon cooling (rate 0.5 8C min 1),formed a striking platelet-like texture (Figure 3 c) of cubic BP,
appearing at a temperature of 129.0 8C and retained up to125.2 8C. A further decrease in temperature from 125.2 8C led
to the nucleation of the helical N cyb * phase, which crystallized
at 105.6 8C. A surprising result was observed if compound 1-10
was used to fill a 4.8 mm polyimide–ITO-coated homogeneous/planar cell, which was investigated by means of POM. This
sample exhibited the appearance of a platelet-like texture of
cubic BPs at 124.9 8C, which remained stable up to 108.5 8C(cooling rate 0.5 8C min1 ; Figure 3 a,b and Figure S47 in the
Supporting Information). Hence, the BP range was extended
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from 3.8 (Figure S45 in the Supporting Information; on anormal glass slide with a coverslip) to 16.4 8C (elaborated in
Figure S47 in the Supporting Information), if inserted in aplanar cell, which was also substantially stable (Figure S46 in
the Supporting Information). Available literature suggests that
this is a rare report of single-component BCLCs forming a
cubic BP structure stabilized by a range of 16.4 8C. Upon further cooling the sample, the Ncyb* phase appeared and crystallized at 100.6 8C. The above results were attained at a coolingrate of 0.5 8C min1 . However, if the rate of cooling was
3 8C min 1 , crystallization was suppressed and attained at atemperature of 90.4 8C (Figure S48 in the Supporting Information). This observation of elongation of the BP range and suppression of crystallization was also reported earlier.[58]For compound 1-14, on a normal glass slide with a coverslip(without any coating), upon cooling, a transient BP (Figure S55
in the Supporting Information) was observed followed by theappearance of a focal conic-type texture of N* at 128.4 8C,
which, upon further cooling, changed to a fingerprint-like [59]texture typical of the TGBA phase at 126.0 8C. The fingerprint
texture further transformed into a characteristic filamentous [59]texture of TGBA and started to become homeotropic at
121.4 8C (Figure S56 in the Supporting Information). Crystallization of 1-14 was observed at 78 8C. However, compound 1-14
(inserted in a 3.2 mm polyimide–ITO-coated planar cell) duringcooling, exhibited the appearance of BP, N*, and TGBA phases(Figure S58 in the Supporting Information). Upon further cooling, focal conic-like textures characteristic of SmA start toappear below the TGBA phase. Below the SmA phase, an unidentified tilted phase, SmX, forms at a temperature of
117.6 8C. The change of SmA to SmX is characterize d by thedevelopment of stripes on focal conics (Figure S59 in the Supporting Information). Similarly, compound 1-14, if inserted in a

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Figure 3. POM micrographs of BPI (a) and BPII (b) phases of compound 1-10 at 121.5 and 11 8.0 8C, respectively, in a 4.8 mm polyimide–indium tin oxide (ITO)coated planar cell ; c) cubic BP of compound 1-10 at 126.8 8C on a normal glass coverslip ; d) filamentous texture of the TGBA phase of compound 1-14 at
125.8 8C in a 3.3 mm polyimide–ITO-coated homeotropic cell ; SmA (e) and SmX (f) phases of compound 1-12 at 11 3.8 and 105.2 8C, respectively, in a 4.8 mm
polyimide–ITO-coated planar cell.

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Table 1. Phase transition temperatures (peak temperature, 8 C) and enthalpies of transition (DH [kJ mol 1] in parentheses) determined by meansof DSC (scan rate of 10 8C min1 , second heating and cooling cycles) andPOM.

Compound Phase transitions[a]
1-4
1-6
1-8
1-10
1-12

1-14

1-16
1-18

heating: Cr 176.1 (20.2) Iso
cooling: Iso 120.8 (6.4) Cr
heating: Cr 152.0 (20.5) Iso
cooling: Iso 134.2 (20.1) Cr
heating : Cr 150.3 (29.9) Iso
cooling: Iso 124.9 BPI/II[b] 115.2 Cr[b]heating: Cr1 110.0 (3.3) Cr 2 145.4 (21.2) Iso
cooling : Iso 124.9 BPI/II[b] 108.5 Ncyb *[b] 100.6 Cr 1[b]heating: Cr1 132.8 (29.0) Iso
cooling: Iso 131.5 BPI/II 128.9 (0.96) N* 125.0 TGBA 123.7
SmA[b] 111.0 SmX[b] 95 Cr2 46.5 (2.5) Cr1
heating: Cr1a 61.7 (8.0) Cr 2b 70.4 (24.3) Cr 3c 136.7 (46.8) Iso
cooling : Iso 128.7 BPII/II 128.4 (3.6) N* 126.0 TGBA 121.4
SmA[b] 117.6 SmX [b] 78.0 Cr 4[c]heating: Cr 116.9 (13.6) SmX 133.5 (4.8) Iso
cooling: Iso 131.3 (4.8) SmX 94.4 (4.8) Cr
heating: Cr 113.7 (10.5) SmX 132.8 (4.1) Iso
cooling: Iso 131.6 (4.2) SmX 97.6 (10.6) Cr[a] Cr = crystal ; Iso = isotropic ; N cyb* = chiral nematic phase composed of
Sm clusters ; TGBA = twist grain boundary phase ; Smectic A = SmA;
Smectic X = SmX. [b] Phase transitions observed by means of POM in an
ITO-coated planar cell (antiparallel rubbing). [c] Phase transitions observed by means of SAXS/WAXS. (1-14: Cr1a = amorphous, Cr2b = transition
crystalline state, Cr3c = crystal polymorph.)

Dielectric measurements

Small- and wide-angle X-ray (SAXS/WAXS) studies
SAXS/WAXS analyses were carried out on LC samples in a
0.7 mm capillary to gain more insights into the LC phase behavior. The X-ray diffractogram of compound 1 -10 at 115 8C
showed two diffused peaks: one in the small-angle region,
with a d value of 39.49 , and the other in the wide-angle
region, with a d value of 5.78  (Figure 4 a). This observation ofdiffuse peaks in both small- and wide-angle regions confirmed
the presence of a disordered mesophase. In the XRD scan of 110 upon cooling, the intensity of the small-angle peak was
greater than that of the wide-angle peak,[60, 61] indicating thepresence of clusters in the chiral nematic phase (N cyb *; Figure 4 a and Figure S71 b in the Supporting Information). The inChem. Eur. J. 2020, 26, 5859 – 5871

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tensity of the small-angle peak became sharper with a gradualdecrease in temperature, which also substantiated the earlier
observation of cluster formation (as d/L  0.89–0.96) in theNcyb* phase (Figure S71 a in the Supporting Information). The
correlation length (x) and d spacing for 1-10 increased with decreasing temperature over the entire nematic range, inferring
the cybotactic nature of the chiral nematic phase (Ncyb*; Figure 4 c). The value of d spacing increased from 31.89 to
39.49 , whereas the correlation length increased from 55.30
to 446.35  as the sample was cooled from the melte d liquid(Table S8 in the Supporting Information).
For compound 1-14, a transient chiral nematic (N*) phase
was observed. The XRD profile of 1-14 at 128 8C was composedof two diffused peaks: one in the small-angle region, with a dvalue of 38.89 , and the other in the wide-angle region, witha d value of 5.73 , which confirmed the nematic phase (Figure 4 b). A gradual decrease in temperature led to the formation of a sharper and more intense small-angle peak, showing
nucleation of N*, TGBA, SmA, and SmX phases from the isotropic melt, whereas the wide-angle peak remained diffuse, as
observed earlier (Figure S75 a in the Supporting Information).
Upon cooling to 80 8C, the XRD results for compound 1-14
consisted of a sharp small-angle peak with a d value of 35.54 
and a wide-angle halo with a d value of 5.61  (Figure 4 b). The
d = f(T) plot analysis showed that, at first, the d value increased
from 34.49 to 42.83  up to 125 8C and further decreased from42.83 to 35.54  until the compound crystallized at 78 8C. This
proved the exhibition of TGBA, SmA, and SmX phases (Figure 4 d an d Table S10 and Figure S80 in the Supporting Information), in which d/L  0.95 for TGBA, d/L  0.94 for SmA, andd/L decreased with temperature from 0.92 to 0.79 for SmX.
The plot of x = f(T) displayed a drastic increase in the correlation length as the sample made a transition from N* to TGBA
from 58.34 to 956.71 , which further increased after 956.71 
to 1520.89  (Figure 4 d, Table S10 in the Supporting Information). XRD analyses of 1-12, 1-14, 1-16, and 1-18 are discussed
in detail in Figures S73, S75 b, S76–S79, S81, and S82 and Tables S9 and S11 in the Supporting Information.

We performed dielectric relaxation studies on compound 1-18
as a representative example of the SmX phase. Compound 118 was used to fill a planar cell made of two ITO-coated glass
plates with a separation of 8 mm. Both real and imaginary partsof the dielectric constants were measured in the frequency
range of 1 kHz to 1 MHz at various temperatures. Compound
1-18 exhibited dielectric relaxation throughout the entire SmX
phase and frequency dispersions of real and imaginary parts ofdielectric constants at 120, 117, and 112 8C are presented in
Figure 5 a–c. It should be noted from Figure 5 that 1-18 exhibited two relaxations: one at a low frequency, which was temperature dependent, and the other at high frequency ( 1 MHz), which was temperature independent. The low-frequency dielectric relaxation was due to the molecular dipoles
and the high-frequency relaxation due to the finite resistanceof the ITO layers. The relaxations were fitted with a complex di-5863

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3.3 mm polyimide–ITO-coated homeotropic cell, confirmed theformation of the TGBA phase through a characteristic fingerprint and filamentous texture (Figure 3 d and Figure S57 in the
Supporting Information). Compound 1-12 exhibits a similarphase sequence of BPI/II, N*, TGBA, SmA, and SmX (Figures S49–S54 in the Supporting Information). POM micrographsof 1-12 for SmA and SmX are shown in Figure 3 e and f, respectively. Compounds 1-16 and 1-18 showed enantiotropic
mesomorphism and exhibited the SmX phase in the heating
and cooling cycles. Details of the POM study of compounds 18, 1-14, and 1-18 are discussed in detail in Figures S43, S44,
and S60–S68 in the Supporting Information. The observed
mesophases, transition temperatures, and associated enthalpies, as observed by means of DSC, are summarized in Table 1(Figures S69 and S70 in the Supporting Information).

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Figure 5. Frequency dispersions of real (triangles) and imaginary (circles) parts of dielectric constants at a) 120, b) 117, and c) 112 8C of 1-18. d) Cole–Cole plotof 1-18.
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Figure 4. Intensity versus 2 q plot showing a) the N cyb* phase of compound 1-10 in the small-angle region ; inset showing the wide-angle peaks, b) the N* andSmX phases of compound 1-14 in the small-angle region ; inset showing the wide-angle peaks. Plot of d spacing and correlation length (small-angle peak)versus temperature for compounds 1-10 (c) and 1-14 (d).

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electric constant (e* = e’ie’’) as a function of frequency toobtain the dipole relaxation frequency. The complex dielectric
constant is given by Equation (1): [62]e * ¼ e0  ie00 ¼

e0  e1e 1  e1þ
þ e1
ð1 þ iwtÞ1a ð1 þ iwt1Þ 1a1

ð1ÞFigure 6. Variation of relaxation time (semilogarithmic scale) as a function of
1/T in the SmX phase of compound 1-18. The continuous line is a theoretical
fit to the Arrhenius equation.

Electro-optical (EO) performance
A typical voltage versus transmission (V–T) curve in the BP ofcompound 1-10 is shown in Figure 7 a. The in-plane switching(IPS)-type cell (Instec USA), with comb-type interdigitated electrodes fabricated on the bottom substrate, was used for the
EO study. The width of the electrodes and the distance between them were both 15 mm. The cell gap was 9 mm. The
substrates had homogeneous alignment and rubbin g wasdone parallel to the electrode, although no surface treatment
was necessary for the BP. Transmission gradually increased
with applied voltage; however, only 65 % transmission was observed at a maximum applied voltage (  100 V). Upon decreasing the voltage, V–T almost overlapped with that of the increased voltage and only a slight hysteresis was observed.
However, this hysteresis-free behavior was obtained up to 2 8C
below the isotropic to BP transition temperature (TIso-BP).
Beyond this temperature range, the electric-field-induced transition from BP to N* was observed. As the strength of the electric field increased, the medium became anisotropic along theelectric-field direction and the change in birefringence obeyed
the Kerr effect in the low-field region. The output light intensity (Iout ) is given by I out = I insin2(f/2), in which I in is the input intensity and f is the optical retardation. The induced birefringence, Dninduced , can be obtained from f= 2pdDn induced /l, in
which d is the cell gap and l is the wavelength of the incident
light. Because the ratio of induced birefringence to the wavelength of the incident light in the low-field region is proportional to the square of the electric field and the proportionality

Figure 7. a) Voltage versus transmission curve for 1 -10 at TT Iso-BP= 2 8C. b) Plot of Dn induced/l as a function of E2 .
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in which e 0 is the static dielectric permittivity, e1 is the highfrequency limit of the dielectric constant, a and a 1 are theCole–Cole distribution parameters, and t and t1 are the relaxation times of low and high relaxation modes. The fits of complex dielectric constant are shown in Figure 5 with continuouslines. The values of a and a1 were found to be very small (<0.02), which suggested that the relaxation was of Debye type,
and this was further supported by Cole–Cole plots (Figure 5 d).
The temperature-dependent relaxation time, as a function of
1/T, is shown in Figure 6. Below the isotropic transition, the relaxation time (t) decreases slowly at the beginning (region I)
and then decreases rapidly in the middle of the SmX phase (region II). As the temperature approaches the crystalline phase,the relaxation time again decreases very slowly with a different
slope (region III). This trend is opposite to that of typical Arrhenius behavior. However, such anomalous behavio r was observed in several liquid-crystalline systems and often attributed
to supramolecular LC formation. [63–65] As far as the uncommon
temperature dependence of the dielectric relaxation times isconcerned, this is probably due to an additional polar ester
linking group, which causes a larger dipole moment, and theirrepulsive interaction accounts for an increase in relaxation
time with increasing temperature.[66]To obtain a quantitative estimation, three different regionsof the curve are fitted to the Arrhenius equation, t = t 0exp(U/RT), in which U is the activation energy (shown in Figure 6 witha continuous line). It gives negative activation energies: valuesof 88, 292, and 20 kJ mol 1 in regions I, II, and III, respectively.
These results suggest that the relaxation mechanisms in the
SmX phase are very complex.
The higher values of activation energy could be due to theenhanced elasticity and soft-glassy behavior of the SmX
phase.[67] The dielectric study of compound 1-10 is elaborated
in Figure S84 in the Supporting Information.

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constant is the Kerr constant (K) of the medium, Dn induced/l =KE2 (E = electric field). Figur e 7 b shows the plot for Dninduced /lversus the square of the electric field (E2) at TTIso-BP = 2 8C.
Within the voltage range that our experimental setup could
supply, the induced birefringence was almost proportional toE 2. Thus, the Kerr law was valid in this voltage range and theslope represented the Kerr constant. The magnitude of K for
sample 1-10 was K= 5.87  10 10 mV2.
Crystal polymorphism

Mechanochromism
Materials containing the cholesterol and salicylideneaniline
moieties can be potentially used as mechanochromic materials.
The study presented herein exploits the chiral bent-shapedmaterials for mechanochromic properties. All compounds ofthe homologous series were weakly fluorescent in solution(Figure S32 in the Supporting Information for the representative compound 1-14) and exhibited strong photoluminescencein the solid state. Upon applying mechanical energy throughgrinding, the visible color of compound 1-10 (as a representative case) changed from bright yellow to dark orange–green,
as depicted in Figure 9 a. Compound 1-10 also became amorphous and sticky upon grinding. The color change obtained
upon grinding was reversible after the dropwise addition of dichloromethane to the well-ground sample (Figure 9 a). Mechanochromic photoluminescent properties were confirmed bymeans of solid-state UV (in reflectance mode with KBr; Figure 9 b) for representative compound 1-10. The p–p* band in
the neat state absorbed at a wavelength of l = 375 nm. However, upon mechanical grinding, the p–p* band shifted to a
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Thermochromism
Thermochromism is the ability of the material to change color
as the temperature is varied. The pitch of the CLCs is in theorder of the wavelength of light (l = 400–700 nm). Therefore,
CLCs can undergo Bragg scattering and a change in temperature leads to a change in layer spacing. Hence, the color variation observed is due to a change in pitch (l = nP, in which n is
the average refractive index of the LC material and P is thepitch length of the helical structure).[2] In this context, theeffect of the phase transition of CLC materials cannot be ignored and combine with the effect of pitch length variation of thematerial to result in the observed thermochromism. CLCs arewidely considered as thermochromic materials that find various applications, such as in a liquid-crystalline thermometer,
thermography in medicine, and various branches of engineering. In general, thermotropic CLCs are viewed against a black
background because the selective reflection caused by CLCs
can be effectively seen upon it. In the present study, compound 1-10, exhibiting the Ncyb * phase, showed thermochromic behavior upon cooling the sample. [47,68]
The sample melted at a temperature of 145.4 8C and ayellow liquid was formed (Figure 10 a). Upon cooling and subsequently holding sample 1-10 at 125.0 8 C, the melted yellow
sample started to convert into green at one of the corners(Figure 10 b) because it converted to the N* phase from theyellow liquid. Subsequent cooling to 120 8C resulted in a green
color that spread over a larger area (Figure 10 c). At 115 8C, thegreen color covered the entire sample (Figure 10 d,e). Furthermore, at 110 8C, the greenish color of the sample started tochange to yellow. At 105 8C, most of the sample turned yellow
with a few greenish lines along the edge (Figure 10 f). This
conversion of green to yellow at 105 8C could be rationalized
due to crystallization of the sample. Upon further cooling to
100 and 90 8C, the yellow color spread all over the sample due
to complete crystallization of the sample and it persisted
down to room temperature (Figure 10 g,h). The schematic illustration in Figure 10 i demonstrates the increase in pitch lengthwith a decrease in temperature.

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Of the materials studied herein, compounds 1-10, 1-12, and 114 exhibited crystal polymorphism during the heating cycle.
Compound 1-10 underwent a transition from crystal 1 (Cr1 ) to
crystal 2 (Cr2 ) upon heating at a temperature of around110.0 8C. The optical micrographs of the change in Cr1 to Cr2state are presented in Figure 8 h–j. The SAXS/WAXS measurements of compound 1-10 at two different temperatures confirmed the presence of crystal polymorphism in the heating
cycle. The intensity versus 2 q plot revealed the difference inpeak position and peak nature recorded at two different temperatures, 100 and 120 8C, for Cr1 and Cr2, respectively (Figure 8 a). The 2D diffractograms also substantiated the formation of two different crystal polymorphs. Interestingly, we havealso observed morphological changes in compound 1-10 uponannealing at a temperature of 117 8 C, as verified by FESEM(field emission scanning electron microscopy) (Figure 8 f,g).
The color of the compound changed from bright yellow atroom temperature (pristine compound) to whitish-yellow after
heating to 117 8C (Figure 8 b,d). The color change was also observed in the two samples under UV light (Figure 8 c,e). This
whitish-yellow color of the compound remained stable for several hours. Details of crystal polymorphism of 1-12 and 1-14
are summarized in Figures S41, S42, S70, S72, and S74 in the
Supporting Information.

lower wavelength of 357 nm. The emission spectrum for 1-10
displayed a red shift as l em shifted from l = 533 to 542 nm
upon grinding the sample and the band returned to its original position after the addition of DCM (Figure 9 d). Powder Xray diffraction (PXRD) analysis showed that the material obtained after grinding was different from the neat sample because the crystallinity of the compound after grinding was reduced. The peaks in the ground sample were less sharp thanthose in the neat sample (Figure 9 c). FESEM studies further
confirmed the formation of a different sample after grinding.
FESEM images obtained before grinding were different fromthe SEM images after grinding. The FESEM image of the neat
sample had long fibers/rod-like structures (Figure 9 f). However,upon mechanical grinding, it formed a sponge-like structurewith a different stacking mode (Figure 9 g). The schematic representation in Figure 9 e elaborates the breaking of intermolecular interactions without breaking any covalent bonds.

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Figure 8. a) X-ray plot of two different crystal polymorphs of 1-10 at 100 8C (Cr 1, black) and 120 8C (Cr2, red) along with their 2D images. b) Compound 1-10 inits pristine state in normal daylight. c) Compound 1-10 under UV light in its pristine state. d) Compound 1-10 upon thermal annealing at 117 8C in normal day
light. e) Thermally annealed compound 1-10 at 117 8C under UV light, (f,g) FESEM images of pristine compound 1-10 and after annealing at 117 8C respectively; POM micrographs of compound 1-10 showing (h) crystal 1 (Cr 1) at 107.7 8C (i) coexistence of Cr1 and Cr2 at 116.8 8C (a broad peak in the transition from Cr1
to Cr2 and a slight change in the temperature observed by DSC and POM, respectively), (j) Cr2 at 121.8 8C.

Conclusion
We have successfully engineered a chiral BCLC, in which an
electronegative chloro moiety was introduced at the transverse
position of the central benzene ring. Previously, we had placeda methyl group at the same kink position of the molecular architecture and observed exotic BPIII, BPII/I, N cyb*, TGBA, SmAP A,
SmA, and SmX phases (Figure 1 a). [47] Herein, the compounds
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with a chloro core (Figure 1 b) showe d a cubic BP over a wide
range of 16.4 8C; this is one of the few reports on a single-component BCLC compound. In addition, two homologues (1-12
and 1-14) exhibited an exotic phase sequence consisting of
BPI/II, N*, TGBA, SmA, and SmX; these are similar to thosephases reported previously. [47] Comparative DFT studies of thetwo types of molecules (one with a chloro core, compound 1-4(Figure 1 b), and another with a methyl core (Figure 1 a)) sug-

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Figure 9. a) Images of compound 1-10 showing the change in color upon mechanical shearing and the reversibility of color change after the addition of dichloromethane (DCM); inset showing the images under UV light (l = 365 nm). b) Absorption spectr a of 1-10 in the solid state : the black line indicates the
spectrum before grinding; the blue line indicates the spectrum after grinding. c) Intensity versus 2 q plot of 1-10 showing the change in the XRD pattern
before and after mechanical grinding. d) Emission spectra of 1-10 in the solid state: the black line indicates the spectrum before grinding; the blue line indicates the spectrum after grinding ; the pink line indicates the spectrum after the addition of DCM, l ex= 375 nm. e) Schematic illustration of the molecular arrangement before and after grinding, showing the change in weak molecular interactions. FESEM images of 1-10 before (f) and after (g) grinding.

gested an increased dipole moment along the transverse direction (due to the I effect of the Cl group), which immensely
helped to stabilize the long-range cubic BP. Basically, theChem. Eur. J. 2020, 26, 5859 – 5871

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chloro substituent makes the central core electron deficient
relative to that of the methyl core. SCXRD analysis confirmed
the bent architecture of the molecule and revealed fundamen-

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formed on the samples by using CuKa (l= 1.54 ) radiation from a
GeniX3D microsource, with a Pilatus 200 K detector in the
Xeuss 2.0 SAXS/WAXS system. Single-crystal XRD data were collected by using a Rigaku XtaLABmini X-ray diffractometer equippedwith a mercury charge-coupled device (CCD) detector. Graphite
monochromated Mo Ka radiation (l = 0.71073 ) at room temperature with w scans was used, and the space group determination
was performed by using Olex2.

General procedure for synthesis of 1-n

Figure 10. Photographs displaying the thermochromic behavior of 1-10
during cooling from an isotropi c liquid (a), the transition to the mesophase(b,c), the mesophase (d,e), the transition to a crystal (f; the yellow color surrounded by the green line), and the crystal (g,h). i) A schematic illustrationof the change in pitch and visible color of CLC with decreasing temperature.

tal structural insights, regarding the presence of two different
types of conformers in an asymmetric unit, and their different
weak intra- and intermolecular interactions, such as CH···p and
CCl···p interactions. These weak interactions are of immense
importance to unravel many fundamental aspects of structural
biology and chemistry. The compounds exhibited multistimuliresponsive properties of polymorphism, mechanochromism,
and thermochromism. The thermochromic behavior was excellent, showing a color change as a function of temperature, andthe color at every temperature interval was extremely stable(in terms of several minutes).

Scheme 1. Schematic route for the preparation of the desired bent-shaped
LCs. DCC = N,N’-dicyclohexylcarbodiimide, DMAP = 4-dimethylaminopyridine.

Compound 1-4

Experimental Section
GeneralDetails of the characterization techniques have been publishedelsewhere. [47, 60] Briefly, the instrumental details are as follows. Structural characterization of the compound was performed through a
combination of 1 H and 13C NMR spectroscopy (Bruker Biospin Switzerland Avance III 400 MHz). NMR spectra were recorded as solutions in deuterated chloroform, with tetramethylsilane (TMS) as aninternal standard. Attenuated total reflectance (ATR; FTIR BrukerALPHA Bruker-1227-3513), UV/Vis/near-IR spectrophotometry (Labindia UV/Vis spectrophotometer 3000 +), spectrofluorophotometry (Shimadzu, RF-6000), and mass spectrometry (Waters synaptg2s) were also used. FESEM was performed by using a JEOL JSM7600F instrument. Mesomorphic studies were performed throughPOM, DSC, and SAXS/WAXS measurements. POM textural observations of the mesophase were performed with a Nikon Eclipse
LV100POL polarizing microscope equipped with a Linkam heatingstage (LTS 420). DSC measurements were performed on a PerkinElmer DSC 8000 instrument coupled to a controlled liquid nitrogen accessory (CLN 2) at a scan rate of 108C min 1. All images were
captured by using a Q-imaging camera. XRD studies were perChem. Eur. J. 2020, 26, 5859 – 5871

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Yield: 85 %; 1H NMR (400 MHz, CDCl 3): d = 13.49 (s, 1 H; OH), 8.49
(s, 1 H ; CH=N), 7.56 (dt, J = 7.4, 1.6 Hz, 1 H; ArH), 7.36–7.27 (m,3 H; ArH), 6.51–6.48 (m, 2 H; ArH), 5.44 (d, J = 5.0 Hz, 1 H; CH=C in cholesteryl), 4.95–4.87 (m, 1 H; CHO in cholesteryl), 4.01
(t, J = 8 Hz, 2 H ; OCH2), 2.52–2.44 (m, 2 H; CH 2 in cholesteryl),
2.06–0.85 (m, 45 H; extensive coupling in cholesteryl), 0.68 ppm (s,3 H; CH 3 in cholesteryl); 13 C NMR (100 MHz, CDCl3): d= 11.9, 13.9,
18.7, 19.2, 19.4, 21.1, 22.6, 22.9, 23.9, 24.3, 27.8, 28.1, 28.3, 31.1,
31.9, 32.0, 35.8, 36.2, 36.7, 37.0, 38.1, 39.5, 39.7, 42.3, 50.0, 56.1,
56.7, 68.0, 75.8, 101.6, 108.0, 112.8, 121.6, 123.0, 127.2, 127.7, 127.8,
133.1, 133.9, 139.5, 147.0, 162.9, 164.0, 164.2, 165.6 ppm; ATR:
2867–2930 (intramolecular H-bond of OH···N), 1734 (C=O stretching of ester), 1612 cm1 (CH=N stretching of imine); UV/Vis: l =278, 334 nm; HRMS (ESI-MS): m/z calcd for C45 H62ClNO 4 [M++H] + :
716.4445; found: 716.4409.

Compound 1-6
Yield: 82 %; 1H NMR (400 MHz, CDCl 3): d = 13.48 (s, 1 H; OH), 8.50
(s, 1 H; CH=N), 7.57 (dd, J = 7.4 Hz, 1.8 Hz, 1 H ; ArH), 7.37–7.28(m, 3 H; ArH), 6.52–6.49 (m, 2 H; ArH), 5.44 (d, J = 5.1 Hz, 1 H; 
CH=C in cholesteryl), 4.95–4.87 (m, 1 H; CHO in cholesteryl),
4.01 (t, J= 4, 8 Hz, 2 H ; OCH 2), 2.51–2.44 (m, 2 H; CH2 in cho-5869

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Scheme 1 provides the route for preparing the desired bentshaped LCs. The final compounds were prepared by heating a solution of c-n (4-n-alkyloxy-2-hydroxybenzaldehyde, 1 equiv) withcompound g (1 equiv) at reflux in ethanol with a few drops of glacial acetic acid as a catalyst for 3 h. The precipitated product was
purified by repeated recrystallization from absolute ethanol. The
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lesteryl), 2.03–0.86 (m, 49 H; extensive coupling in cholesteryl),
0.69 ppm (s, 3 H ; CH 3 in cholesteryl); 13C NMR (100 MHz, CDCl3):
d = 11.9, 14.1, 18.7, 19.4, 21.1, 22.60, 22.62, 22.9, 23.9, 24.3, 25.7,
27.8, 28.0, 28.3, 29.0, 31.6, 31.9, 32.0, 35.8, 36.2, 36.7, 37.0, 38.0,
39.5, 39.7, 42.3, 50.0, 56.1, 56.7, 68.3, 75.7, 101.6, 108.0, 112.8,
121.6, 123.0, 127.2, 127.7, 127.8, 133.1, 133.9, 139.5, 147.0, 162.8,
164.0, 164.2, 165.6 ppm; ATR: 2850–2950 (intramolecular H-bondof OH···N), 1725 (C=O stretching of ester), 1619 cm1 (CH=Nstretching of imine); UV/Vis: l = 278, 334 nm ; HRMS (ESI-MS): m/z
calcd for C47 H 66ClNO 4 [M++H] + : 744.4758; found: 744.4728.

Compound 1-8

Compound 1-10
Yield: 84 %; 1 H NMR (400 MHz, CDCl3): d = 13.48 (s, 1 H; OH), 8.50
(s, 1 H; CH=N), 7.57 (dd, J = 7.5 Hz, 1.8 Hz, 1 H ; ArH), 7.37–7.28(m, 3 H; ArH), 6.52–6.49 (m, 2 H; ArH), 5.44 (d, J = 5.1 Hz, 1 H; 
CH=C in cholesteryl), 4.95–4.87 (m, 1 H; CHO in cholesteryl),
4.01 (t, J= 4, 8 Hz, 2 H ; OCH 2), 2.51–2.49 (2 H; m, CH 2 in cholesteryl), 2.03–0.86 (57 H; extensive coupling in cholesteryl),
0.69 ppm (s, 3 H ; CH 3 in cholesteryl); 13C NMR (100 MHz, CDCl3):
d = 11.9, 14.2, 18.7, 19.4, 21.1, 22.6, 22.7, 22.9, 23.9, 24.3, 26.0, 27.8,
28.0, 28.3, 29.1, 29.35, 29.39, 29.6, 31.87, 31.92, 31.95, 35.8, 36.2,
36.7, 37.0, 38.0, 39.5, 39.7, 42.3, 50.0, 56.1, 56.7, 68.4, 75.7, 101.6,
108.0, 112.8, 121.5, 123.0, 127.2, 127.7, 127.8, 133.1, 133.9, 139.5,
147.0, 162.8, 164.0, 164.2, 165.6 ppm; ATR: 2824–2943 (intramolecular H-bond of OH···N), 1711 (C=O stretching of ester), 1605 cm1
(CH=N stretching of imine); UV/Vis: l= 278, 334 nm ; HRMS (ESIMS): m/z calcd for C 51H74ClNO 4 [M++H] + : 800.5384; found: 800.5345.

Compound 1-12
Yield: 85 %; 1 H NMR (400 MHz, CDCl3): d = 13.47 (s, 1 H; OH), 8.50
(s, 1 H; CH=N), 7.57 (dd, J = 7.5, 1.8 Hz, 1 H; ArH), 7.36–7.27 (m,3 H; ArH), 6.52–6.49 m, 2 H ; ArH), 5.44 (d, J = 5.0 Hz, 1 H ; CH=C in cholesteryl), 4.93–4.87 (m, 1 H ; CHO in cholesteryl), 4.01
(t, J = 4, 8 Hz, 2 H; OCH 2), 2.51–2.49 (m, 2 H; CH 2 in cholesteryl), 2.03–0.86 (m, 61 H; extensive coupling in cholesteryl), 0.69 ppm(s, 3 H; CH3 in cholesteryl); 13 C NMR (100 MHz, CDCl3 ): d = 11.9,
14.2, 18.7, 19.4, 21.1, 22.6, 22.7, 22.9, 23.9, 24.3, 26.0, 27.8, 28.0,
28.3, 29.1, 29.4, 29.59, 29.62, 29.66, 29.69, 31.9, 32.0, 35.8, 36.2,
36.7, 37.0, 38.1, 39.5, 39.7, 42.3, 50.0, 56.1, 56.7, 68.4, 75.8, 101.6,
108.0, 112.8, 121.6, 123.0, 127.2, 127.7, 127.8, 133.2, 133.9, 139.5,
147.0, 162.9, 164.0, 164.2, 165.6 ppm; ATR: 2849–2940 (intramolecular H-bond of OH···N), 1715 (C=O stretching of ester), 1605 cm1
(CH=N stretching of imine); UV/Vis: l= 278, 334 nm ; HRMS (ESIMS): m/z calcd for C 53H78 ClNO4 [M++H] + : 828.5697; found: 828.5660.
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Yield: 81 %; 1H NMR (400 MHz, CDCl 3): d = 13.49 (s, 1 H; OH), 8.49
(s, 1 H; CH=N), 7.56 (dd, J = 7.4 Hz, 1.8 Hz, 1 H ; ArH), 7.36–7.27(m, 3 H; ArH), 6.51–6.48 (m, 2 H; ArH), 5.44 (d, J = 4.7 Hz, 1 H; 
CH=C in cholesteryl), 4.95–4.87 (m, 1 H; CHO in cholesteryl),
4.00 (t, J= 8 Hz, 2 H; OCH2 ), 2.52–2.44 (m, 2 H; CH2 in cholesteryl), 2.06–0.86 (m, 65 H; extensive coupling in cholesteryl),
0.69 ppm (s, 3 H ; CH 3 in cholesteryl); 13C NMR (100 MHz, CDCl 3):
d = 11.9, 14.2, 18.7, 19.4, 21.1, 22.6, 22.7, 22.9, 23.9, 24.3, 26.0, 27.8,
28.0, 28.3, 29.1, 29.4, 29.58, 29.62, 29.65, 29.69, 29.71, 29.73, 31.9,
32.0, 35.8, 36.2, 36.7, 37.0, 38.0, 39.5, 39.7, 42.3, 50.0, 56.1, 56.7,
68.4, 75.7, 101.6, 108.0, 112.8, 121.5, 123.0, 127.2, 127.7, 127.8,
133.1, 133.9, 139.5, 147.0, 162.8, 164.0, 164.2, 165.6 ppm; ATR:
2847–2945 (intramolecular H-bond of OH···N), 1715 (C=O stretching of ester), 1605 cm1 (CH=N stretching of imine); UV/Vis: l =278, 334 nm; HRMS (ESI-MS): m/z calcd for C55 H82ClNO 4 [M++H] + :
856.6010; found: 856.5967.

Compound 1-16
Yield: 87 %; 1H NMR (400 MHz, CDCl 3): d = 13.48 (s, 1 H; OH), 8.49
(s, 1 H ; CH=N), 7.56 (dt, J = 7.3, 1.4 Hz, 1 H; ArH), 7.36–7.27 (m,3 H; ArH), 6.51–6.48 (m, 2 H; ArH), 5.44 (d, J = 5.0 Hz, 1 H; CH=C in cholesteryl), 4.95–4.87 (m, 1 H; CHO in cholesteryl), 4.00
(t, J = 8 Hz, 2 H ; OCH2), 2.52–2.47 (m, 2 H; CH 2 in cholesteryl),
2.06–0.86 (m, 69 H; extensive coupling in cholesteryl), 0.69 ppm (s,3 H; CH 3 in cholesteryl); 13 C NMR (100 MHz, CDCl3): d= 11.9, 14.2,
18.7, 19.4, 21.1, 22.6, 22.7, 22.9, 23.9, 24.3, 26.0, 27.8, 28.1, 28.3,
29.1, 29.4, 29.6, 29.63, 29.69, 29.71, 29.73, 31.9, 32.0, 35.8, 36.2,
36.7, 37.0, 38.1, 39.5, 39.7, 42.3, 50.0, 56.1, 56.7, 68.4, 75.8, 101.6,
108.0, 112.8, 121.6, 123.0, 127.2, 127.7, 127.8, 133.2, 133.9, 139.5,
147.0, 162.9, 164.0, 164.2, 165.6 ppm; ATR: 2850–2920 (intramolecular H-bond of OH···N), 1717 (C=O stretching band of ester),
1615 cm1 (CH=N stretching of imine); UV/Vis: l = 278, 334 nm;
HRMS (ESI-MS): m/z calcd for C57H 86ClNO 4 [M++H] + : 884.6323;
found: 884.6349.

Compound 1-18
Yield : 85 %; 1H NMR (400 MHz, CDCl 3): d = 13.47 (s, 1 H; OH), 8.50
(s, 1 H; CH=N), 7.57 (d, J= 7.2 Hz, 1 H; ArH), 7.37–7.27 (m, 3 H ;ArH), 6.52–6.49 (m, 2 H; ArH), 5.44 (d, J= 3.4 Hz, 1 H; CH=C incholesteryl), 4.94–4.87 (m, 1 H ; CHO in cholesteryl), 4.00 (t, J =8, 4 Hz, 2 H ; OCH2 ), 2.51–2.49 (m, 2 H ; CH2 in cholesteryl),
2.03–0.86 (m, 73 H; extensive coupling in cholesteryl), 0.69 ppm (s,3 H; CH 3 in cholesteryl); 13 C NMR (100 MHz, CDCl3): d= 11.9, 14.2,
18.7, 19.4, 21.1, 22.6, 22.7, 22.9, 23.9, 24.3, 26.0, 27.8, 28.1, 28.3,
29.1, 29.4, 29.59, 29.63, 29.69, 29.73, 31.9, 32.0, 35.8, 36.2, 36.7,
37.0, 38.1, 39.5, 39.7, 42.3, 50.0, 56.1, 56.7, 68.4, 75.8, 101.6, 108.0,
112.8, 121.6, 123.0, 127.2, 127.7, 127.8, 133.2, 133.9, 139.5, 147.0,
162.9, 164.0, 164.2, 165.6 ppm; ATR: 2849–2915 (intramolecular Hbond of OH···N), 1714 (C=O stretching of ester), 1607 cm 1 (CH=Nstretching of imine); UV/Vis: l = 278, 334 nm ; HRMS (ESI-MS): m/z
calcd for C59 H90ClNO 4 [M++H] + : 912.6636; found: 912.6690.

Acknowledgements
IISER Mohali is acknowledged for the SAXS’WAXS, NMR, FESEM
and departmental single-crystal diffractometer. V.P. and S.K. acknowledge IISER Mohali for PhD fellowships. G.M. acknowledges DST-SERB, India, for a National Post-Doctoral Fellowship(NPDF/2016/000560) and Prof. N. V. S. Rao. S.K.P. acknowledges

5870

 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Printed by [University of Hyderabad - 014.139.069.133 - /doi/epdf/10.1002/chem.201905707] at [02/07/2020].

Yield: 83 %; 1 H NMR (400 MHz, CDCl3): d = 13.48 (s, 1 H; OH), 8.50
(s, 1 H ; CH=N), 7.57 (dt, J= 7.4, 1.6 Hz, 1 H; ArH), 7.37–7.27 (m,3 H; ArH), 6.52–6.49 (m, 2 H; ArH), 5.44 (d, J = 4.7 Hz, 1 H; CH=C in cholesteryl), 4.94–4.88 (m, 1 H; CHO in cholesteryl), 4.00
(t, J = 8, 4 Hz, 2 H; OCH 2), 2.50–2.44 (m, 2 H; CH 2 in cholesteryl), 2.04–0.87 (m, 53 H; extensive coupling in cholesteryl), 0.68 ppm(s, 3 H; CH3 in cholesteryl); 13 C NMR (100 MHz, CDCl3 ): d = 11.9,
14.1, 18.7, 19.4, 21.1, 22.6, 22.7, 22.9, 23.9, 24.3, 26.0, 27.8, 28.1,
28.3, 29.1, 29.3, 29.3, 31.8, 31.9, 32.0, 35.8, 36.2, 36.7, 37.0, 38.1,
39.5, 39.7, 42.3, 50.0, 56.1, 56.7, 68.4, 75.8, 101.6, 108.0, 112.8,
121.6, 123.0, 127.2, 127.7, 127.8, 133.2, 133.9, 139.5, 147.0, 162.9,
164.0, 164.2, 165.6 ppm; ATR: 2837–2950 (intramolecular H-bondof OH···N), 1736 (C=O stretching of ester), 1611 cm1 (CH=Nstretching of imine); UV/Vis: l = 278, 334 nm ; HRMS (ESI-MS): m/z
calcd for C49 H 70ClNO 4 [M++H] + : 772.5071; found: 772.5041.

Compound 1-14

Chemistry—A European Journal

Full Paper
doi.org/10.1002/chem.201905707

CSIR Project File No. 02(0311)/17/EMR-II and SERB Project FileNo. (CRG/2019/000901/OC).

Conflict of interest
The authors declare no conflict of interest.
Keywords: liquid crystals · mechanochromism
transitions · single crystals · thermochromism

·

phase

Chem. Eur. J. 2020, 26, 5859 – 5871

www.chemeurj.org

Manuscript received : December 18, 2019
Revised manuscript received: February 2, 2020
Accepted manuscript online : February 21, 2020
Version of record online : April 21, 2020

5871

 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Printed by [University of Hyderabad - 014.139.069.133 - /doi/epdf/10.1002/chem.201905707] at [02/07/2020].

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