DOI: 10.1002/chem.201701578

Full Paper& Liquid Crystals

Room-Temperature Oligomeric Discotic Nematic Liquid Crystals
over a Wide Temperature Range: Structure–Property
Relationships
Monika Gupta,[a] Santosh Prasad Gupta,[a] Subhransu Sekhar Mohapatra,[b] Surajit Dhara,[b]and Santanu Kumar Pal*[a]Abstract: The design and synthesis of three room-temperature discotic nematic (ND) liquid crystals (LCs) is presented.
The LC consists of an azobenzene core attached to which
are four pentaalkynylbenzene (PA) units through flexible
alkyl spacers. The presence of a short azo linking group provides more disorder in the system, thereby reducing theIntroduction
Discotic liquid crystals (LCs) formed by disc-shaped molecules
generally self-organize into an ordered supramolecular architecture, giving rise to the formation of columnar mesophases
owing to strong p–p interactions between the poly-aromaticcores.[1] In contrast, discoids showing the nematic (ND) phase
where the discs have only long-range orientational order are
rare, but are of particular importance in many display devices.
In fact, they have obtained specific interest since their commercialization as compensation foils to enlarge the viewing
angle of LC displays based on negative birefringent films
formed by polymerized nematic discogens.[2] Unfortunately,
among the limited number of discotic nematogens reported
so far, most are often accompanied by high clearing temperatures and a narrow temperature range of the ND phase.[3] However, the ND phase at room-temperature and over a wide temperature range is vital for their usability in devices.
A literature survey reveals that hexa- and pentaalkynylbenzene (PA) derivatives have been the most investigated systems
among various discotic nematic LCs.[3] In those cases, the stacking of discs in columns is inhibited by the rotational freedom
provided by the alkynyl linkers. Subsequently, few other derivatives based on triphenylene (TP), truxene, thiotruxene, naph[a] M. Gupta, Dr. S. P. Gupta, 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] S. S. Mohapatra, Prof. S. Dhara
School of Physics, University of Hyderabad, Hyderabad 500046 (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.201701578.
Chem. Eur. J. 2017, 23, 10626 – 10631

packing efficiency among the PA units and resulting into theformation of a room-temperature ND phase over a wide temperature range. Dielectric constant and birefringence studies
were performed to gain further insights into the physicalproperties of the mesophase.

thalene, etc. have also been reported to show the ND phase.[4]Star-shaped 1,3,5-trisalkynylbenzene and discotic twins containing two TP units linked through diacetylene spacers or
thiophene units were also found to display the ND mesophase.[5] Recently, hydrogen bonding has also been employed
for the preparation of ND LCs. For example, Lee et al. have reported discotic nematogens through hydrogen bonding between phenol and pyridine moieties as well as between phloroglucinol and alkoxystillbazole moieties.[6] However, in all of
the above cases, the ND phase appears at higher temperatures,
which limits their widespread use in applications.
On the other hand, to date, only a very few approaches
have been reported to obtain room-temperature ND mesophases. The first example of a room-temperature ND mesogen
was reported by Kumar and co-workers, by using a PA derivative with branched alkyl spacers.[7] Later on, the discotic TP
core possessing poly(ethylene oxide) side chains was also
found to possess a room-temperature ND phase.[8] Lee and coworkers developed a new strategy to obtain a ND phase by replacing one side-arm of the discotic multi-alkynylbenzene witha trisalkoxy side-arm.[9] Further, they showed a room-temperature ND phase over a wide temperature range by introducing
an attraction-enhancing protrusion onto the multi-alkynylbenzene system.[10] Recently, we have reported a new approach forthe design of a room-temperature ND LC dimer consisting ofa TP and a PA unit linked through flexible alkyl spacers. The
formation of the room-temperature ND phase is likely due tofolding of the dimer, which prevents p–p stacking among thecomposite disc units.[11] In this communication, we have developed another new strategy to obtain a room-temperature ND
phase over a wide temperature range by connecting four PA
units to an azobenzene core through flexible alkyl spacers. We
hypothesized that the presence of a short rigid azo group inthese oligomers can lead to a system in which PA units will be10626

T 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
randomly oriented with respect to each other. Consequently,
these oligomeric units could be disordered enough to prevent
efficient packing of the molecules and thus, may lead to therealization of a room-temperature ND phase.

Table 1. Thermal behavior of the synthesized compounds 6.[a,b]Results and Discussion
Target compounds 6 a–d were synthesized by the route outlined in Scheme 1. The synthesis of compounds 2, 3, and 5 has
been discussed previously.[12] Compounds 6 were prepared byreacting the pentayne 3 and azobenzene tetracarboxylic acid 5in presence of potassium hydroxide and tetrabutylammonium
bromide under reflux conditions (see the Experimental Section). All the compounds were characterized by 1H NMR,13C NMR, IR, UV/vis, and elemental analysis (Supporting Information, Figures S1–S10).

Scheme 1. Synthesis of the target compounds 6. Reagents and conditions:(i) K2CO3, KI, Br-(CH2)n-Br, butanone, 80 8C, 18 h, 88 %; (ii) Pd(PPh3)2Cl2, 4-pentylphenylacetylene, PPh3, CuI, Et3N, 100 8C, 15 h, 85 %; (iii) NaOH, dextrose,
80 8C, HCl, 70 %; (iv) KOH, H2O, tetraoctylammonium bromide (TOAB), reflux,
5 h, 50 %.

The thermal behavior of the compounds 6 a–d (precise transition temperatures in 8C and respective enthalpy changes in
kJ mol@1) was examined by differential scanning calorimetry(DSC, Table 1) whereas the mesophase behavior was investigated by polarizing optical microscopy (POM) and X-ray scatteringstudies. Among the synthesized compounds, 6 a–c displayedbright birefringent textures at room temperature (with shearaChem. Eur. J. 2017, 23, 10626 – 10631

www.chemeurj.org

Compd.

Heating scan

Cooling scan

6a
6b
6c
6d

ND 45.44 (0.42) I
ND 57.50 (0.52) I
ND 60.44 (1.02) I–

I 42.08 (0.32) ND
I 51.16 (0.37) ND
I 55.68 (0.78) ND
I 51.6 G[a] Phase transition temperatures (peak) in 8C and transition enthalpies in
kJ mol@1 (in parentheses). [b] Phase assignments: ND = discotic nematic,
G = glassy, I = isotropic.

bility) and were transformed to isotropic liquids at various temperatures on heating (see below). On cooling from the isotropic phase, a nice schlieren texture (typical of a nematic phase)
was obtained for all of these oligomers (Figure 1 a, Figure S11
in the Supporting Information). Interestingly, compound 6 d
was in the isotropic state at room-temperature as it displayeda dark appearance in POM observations (Figure S11 in the Supporting Information). However, on cooling below room temperature, a peak was observed at @51.6 8C (Figure S12 a in the
Supporting Information), which is probably due to formationof a glassy state.

Figure 1. (a) Optical photomicrograph of compound 6 a at 30 8C (on cooling,crossed polarizers). (b) X-ray diffraction patterns of compound 6 a, 6 b, and6 c in their mesophase. (c) Schematic of the structure of compound 6, modeled as four pentakis(phenylethynyl)benzene discs connected with flexible
chains to azobenzene core. (d) Local arrangement of the model unit in thenematic phase.

The DSC thermogram of compound 6 a exhibited a peak at
45.44 8C (DH = 0.42 kJ mol@1) corresponding to a mesophase toisotropic transition (Figure S12 b in the Supporting Information). On cooling, it displayed a transition from isotropic tomesophase at 42.08 8C (DH = 0.32 kJ mol@1). Similarly, the isotropization temperatures for compounds 6 b and 6 c were10627

T 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
found to be 57.50 8C (DH = 0.52 kJ mol@1) and 60.44 8C (DH =1.02 kJ mol@1), respectively. Upon further cooling, a mesophaseappeared at 51.16 8C for 6 b (DH = 0.37 kJ mol@1) and 55.68 8C(DH = 0.78 kJ mol@1) for 6 c. No sign of crystallization was observed until @50 8C for all the compounds.
The quantitative study of the nematic phases of these compounds was detailed by small angle X-ray scattering (SAXS)/
wide angle X-ray scattering (WAXS) investigations (Figure 1 b,
Figures S13 and S14 in the Supporting Information). Diffraction
patterns of compounds 6 a–6 c (recorded at 25 8C) are very similar to the monomeric PA derivatives.[3] However, in comparison
to most of the PA derivatives, the ND mesophase is observed
even at room temperature for compounds 6 a–6 c. The diffraction pattern corresponding to mesophase of 6 a showed one
relatively strong reflection in the small angle region and one
broad peak in the wide angle regime. The calculated d-spacingof 21.40 a for the signal in the small angle region corresponds
to intra and intermolecular correlation of the PA units and approximates the diameter of the single PA disc ( & 19 a). The
spacing of the wide angle peak is calculated to be 4.74 a,which mainly originates from the liquid-like correlation of themolten chains. The diffraction pattern corresponding to thenematic phases of compounds 6 b and 6 c are identical to 6 aand were analyzed in a similar way (Figure 1 b). The d-spacing
corresponding to first peak is found to deviate in a decreasingmanner from 6 a to 6 c (Table 2). According to POM observations, compound 6 d exists as an isotropic liquid.

equivalent to Scherrer’s equation. Here, k is the shape factor,a typical value of which is 0.89, l is the wavelength of the incident X-ray, q is the scattering vector (q = 4pSinq/l), q is the
maximum of the reflection, and Dq is the broadening in q at
half of the maximum intensity. The Dq is obtained by Lorentzian fitting of the peaks obtained in the diffraction pattern(Figures S15–S16 in the Supporting Information). For compound 6 a, the correlation lengths for the reflections at 21.40 aand 4.74 a are calculated to be 32.66 a and 8.64 a, respectively. For effective comparison, the correlation length was divided
by the d-spacing values, which results in a measure for the
spatial order in terms of the molecular length scale. The respective correlation lengths for compounds 6 were found to
decrease with increasing chain length of the alkyl spacer. The
decrease in correlation length is significant for the reflection
corresponding to the small angle region (Table 2). Variation ofcorrelation length (x; corresponding to reflection at small
angles) with respect to number of methylene groups of alkyl
spacers (m) for compounds 6 a–d is shown in the Figure 2,

Table 2. X-ray reflections and corresponding correlation lengths obtained
after fitting the peak profiles with Lorentzian profiles in the nematic
phase of compounds 6 a–c and in the isotropic phase of compound 6 d.
Compd.

Properties

Small-angle peakWide-angle peak

6ad-spacing [a]correlation length (x [a])x/dd-spacing [a]correlation length (x [a])x/dd-spacing [a]correlation length (x [a])x/dd-spacing [a]correlation length (x [a])x/d21.40 : 0.20
32.66 : 2.52
1.53 : 0.13
20.86 : 0.25
27.04 : 2.52
1.30 : 0.14
19.24 : 0.30
24.17 : 2.52
1.26 : 0.15
19.04 : 0.30
21.76 : 2.86
1.14 : 0.17

4.74 : 0.30
8.64 : 1.75
1.82 : 0.48
4.79 : 0.35
8.41 :1.75
1.76 : 0.49
4.80 : 0.35
8.35 : 1.75
1.74 : 0.49
4.81 : 0.35
8.23 : 1.75
1.71 : 0.49

6b

6c

6d

Figure 2. Variation of correlation lengths corresponding to reflections at
small angles for compounds 6 a–d with respect to the varying number ofmethylene groups of the alkyl spacer (m). The half-filled blue diamonds
show the correlation length (x) data with error bars. The red line shows thefit to the data, which follows an exponential decay (x = a + x0 exp(@m/mc)).
The characteristic number of methylene groups of the alkyl spacer (mc) is
4.11 : 0.89, which describes that the correlation length decreases moderately with m.

To get further insights into this atypical behavior of 6 d, we
have recorded its diffraction pattern in the isotropic state. The
diffraction pattern showed two peaks; one in the small angle
and another in the wide angle regime, similar to other compounds exhibiting mesophases (Figure S14 in the Supporting
Information). However, the calculated d-spacing for the small
angle peak is found to be 19.04 a, which is about 2 a less thanin compound 6 a and is almost comparable to compound 6 c.
The spacing of the wide angle peak is calculated to be 4.80 a,which is nearly the same as observed in other compounds.
The correlation length, that is, the degree of order within
the mesophase, was calculated by using x = [k 2p]/[(Dq)];
Chem. Eur. J. 2017, 23, 10626 – 10631

www.chemeurj.org

which follows an exponential decay (x = a + x0 exp(@m/mc)).
The characteristic number of methylene groups of the alkyl
spacer (mc) is 4.11 : 0.89, which describes that the correlation
length decreases moderately with m. The decrease in correlation length can be explained as follows. As compounds 6 arediscotic mesogenic quadric based on pentakis(phenylethynyl)benzene linked through flexible alkyl spacers, they could bemodeled as four PA discs linked with flexible chains to an azobenzene core (Figure 1 c). In the case of PA, the phenyl rings
are generally not in-plane because of the rotational freedom
provided by the ethynyl linkers, which prevents columnar
stacking. In addition, orientational freedom of the PA group in-

10628

T 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
creases on increasing the spacer length, which is reflected in
the decreasing value of the corresponding correlation lengths.
However, the decrease in correlation length for compound 6 dis large enough to avoid mesophase formation at room temperature and, thus, it is found to exhibit an isotropic phase.
The physical properties (e.g., elastic constants, birefringence,dielectric anisotropy) of the nematic mesogens strongly affects
the electro-optical characteristics of LC displays and thus are
the main factors to be considered. Therefore, to further explore
the behavior of the ND phase of compounds 6 a–c, we measured some physical properties such as birefringence and dielectric constant as a function of voltage and temperature. The
details of the cell preparation are given in the Supporting Information. We have used a phase modulation technique tomeasure the birefringence and an impedance analyzer formeasuring the dielectric constant simultaneously.[13–15] Compounds 6 a–6 c could not be aligned homogeneously and thus
it was impossible to conduct direct measurements of birefringence. However, the samples showed good homeotropic alignment on AL-1254 polyimide coated cells. Hence, we first measured the birefringence at a fixed temperature as a function ofvoltage. To study the temperature dependence of the birefringence, we applied higher voltage than the Fr8edericksz threshold voltage to get voltage-induced homogeneous alignment.
The dielectric constant of the samples was also measured asa function of voltage at a fixed frequency (2 kHz) by using animpedance analyzer.[16]The insets of Figure 3 a–c show the variation of voltage-dependent birefringence. The birefringence is zero at zero voltage as expected owing to the homeotropic state. It increases
beyond a particular voltage and finally leads to saturation. The
Fr8edericksz threshold voltage (Vth) at a relative voltage isslightly higher in compound 6 c than 6 a and 6 b. For example,
Vth for compounds 6 a and 6 b is about 2.5 V whereas it isabout 5 V for 6 c. For measuring the temperature-dependent
birefringence, a voltage of 20 V was applied for all the samples.
At a relative temperature, the birefringence of compound 6 a
is slightly lower than 6 b and 6 c. For example, at T@TNI =@12 8C, Dn for 6 a is 0.055 whereas in case of 6 b and 6 c, it isabout 0.08. This is expected because the polarizability anisotro-

py and hence the birefringence increases with increasing
length of the flexible alkyl spacer.
The temperature- and voltage-dependent variation of dielectric constants of compounds 6 b and 6 c are shown in Figure 4(owing to the very high ionic conductivity of 6 a and difficultyin alignment of the sample, its measurement was not carriedout). The insets show that beyond the Fr8edericksz threshold

Figure 4. Temperature-dependent dielectric (e) of compound (a) 6 b at
a fixed voltage of 15 V and frequency of 2 kHz, inset: voltage-dependent dielectric (e) at a fixed temperature, T@TNI = @5 8C; and (b) 6 c at a fixed voltageof 15 V and frequency of 2 kHz, inset: voltage-dependent dielectric (e) at
a fixed temperature, T@TNI = @6 8C.

voltage, the dielectric constant increases and tends to saturate.
The approximate dielectric anisotropy (De), that is, the difference between the dielectric constant measured at zero voltage
and at 20 V is much smaller in 6 b than 6 c. For example, for
6 b, De & 0.07 whereas for 6 c, De & 0.2. The temperature-dependent dielectric constant was studied at 20 V simultaneously. Although absolute values of the dielectric constants of compounds 6 b and 6 c are slightly different, their temperature-dependent behavior is similar.
Further, the bend elastic constant (K33) of the samples canalso beestimatedpﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
ﬃ from the Fr8edericksz threshold voltage,
Vth = p K 33 =e0 De of the voltage dependent dielectric data. For
example, the Fr8edericksz threshold voltages for 6 b and 6 c
are 3.7 V and 4.9 V, respectively. The corresponding bend elastic constants at those temperatures are calculated to be 0.1 pn
and 0.42 pn, respectively. There are a few reports that describe
the detailed physical properties of room-temperature discotic

Figure 3. Temperature-dependent birefringence (Dn) of (a) 6 a at a fixed voltage of 20 V and frequency of 4 kHz, inset: voltage-dependent birefringence (Dn)at a fixed temperature, T@TNI = @4.89 8C; (b) 6 b at a fixed voltage of 15 V and frequency of 2 kHz, inset: voltage-dependent birefringence (Dn) at a fixed temperature, T@TNI = @5 8C; and (c) 6 c at a fixed voltage of 15 V and frequency of 2 kHz, inset: voltage-dependent birefringence (Dn) at a fixed temperature,
T@TNI = @6 8C.
Chem. Eur. J. 2017, 23, 10626 – 10631

www.chemeurj.org

10629

T 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
nematic compounds.[14] We observed that the birefringenceand dielectric anisotropies of the synthesized compounds are
significantly lower in comparison to those reported in the literature. The low birefringence of these compounds could be advantageous for employing them as compensating films in LC
devices where the difference in the value of birefringence between the device material and the compensating film has tobe lower.
Overall, we observed that a combination of four PA units
linked with the azo group sufficiently perturbed the system toyield a room-temperature ND phase. In the assembly of PA
units of monomeric derivatives, efficient packing of the discs isforbidden as a result of free rotation of phenyl rings provided
by the ethynyl linkers. However, in most of the cases, the packing is not disordered enough to exhibit the nematic phase atroom temperature. Previously, room-temperature ND mesophases have been obtained by perturbing the symmetry of the
PA unit leading to more disordered systems.[9–10] Here, we
reveal that grouping of PA units by connecting them witha short azobenzene linking unit by flexible spacers could show
a room-temperature ND phase. In general, several other factors,
such as molecular topology, micro-segregation, etc. might also
be involved in the mesophase formation, however, conformational flexibility plays the main role here. This is also evident
from the X-ray studies that show a decrease in correlation
length with increasing number of alkyl spacers. In fact, wefound that compound 6 d with the longest alkyl spacer displays isotropic behavior at room temperature. This observation
can be explained on the basis that PA discs within each oligomer are randomly oriented and so the oligomer is too. Hence,the doubly disordered effect owing to random orientation of(i) individual PA units of each oligomer and thus (ii) oligomers
composed of PA discs, reduces the packing efficiency enoughto result in a room-temperature ND phase. However, in compound 6 d, the disorder was high enough to avoid the emergence of a ND phase.

Conclusion
We have synthesized three new oligomeric LCs showing ND
phases at room temperature. The ND mesophase has beencharacterized by POM, DSC, and XRD studies and was further
explored by voltage- and temperature-dependent dielectricand birefringence studies. These compounds are promisingmaterials for display device applications and also point theway towards development of new anisotropic soft materials.

Experimental Section
For the synthesis of the final compounds 6, compound 5 (1 equivalent) was dissolved in aqueous KOH (1.1 equivalent) solution. To
that solution, compound 3 (6 equivalents) was added followed by
the addition of tetraoctylammonium bromide in catalytic amounts.
The reaction mixture was heated at reflux under vigorous stirringfor 5 h and was then cooled to room temperature. The compound
was extracted with chloroform. The organic layer was washed withbrine and dried over anhydrous sodium sulfate. The chloroform
Chem. Eur. J. 2017, 23, 10626 – 10631

www.chemeurj.org

was removed by rotary evaporation and the resulting residue waspurified by column chromatography over silica gel by using
hexane and ethyl acetate as the eluent. Full characterization details
and 2D diffraction patterns are provided in the Supporting Information.

Acknowledgments
We are grateful to the NMR, HRMS, and SAXS/WAXS facility at
IISER Mohali. S.K.P. and S.D. are grateful for financial support
from INSA (bearing sanction No. SP/YSP/124/2015/433) and
DST, FIST-II, respectively. M.G. acknowledges the receipt ofa graduate fellowship from IISER Mohali. S.K.P. is grateful forthe the financial support from CSIR bearing Sanction No.
02(0311)/17/EMR-II for the project entitled “Synthesis and Characterization of Nanographenes based on hexabenzocoronene
Discotics for Photovoltaics Applications”.

Conflict of interest
The authors declare no conflict of interest.
Keywords: azobenzene · birefringence · dielectric · discotic
nematic · pentaalkynylbenzene[1] a) S. Kumar, Chem. Soc. Rev. 2006, 35, 83 – 109; b) T. Wçhrle, I. Wurzbach,J. Kirres, A. Kostidou, N. Kapernaum, J. Litterscheidt, J. C. Haenle, P. Staffeld, A. Baro, F. Giesselmann, S. Laschat, Chem. Rev. 2016, 116, 1139 –
1241; c) S. Kumar, Chemistry Of Discotic Liquid Crystals: From Monomers
to Polymers, CRS Press, Taylor & Francis Group, Boca Raton, 2011.
[2] a) M. Lu, K. H. Yang, Jpn. J. Appl. Phys. 2000, 39, L412 – L415; b) H. Mori,Y. Itoh, Y. Nishuira, T. Nakamura, Y. Shinagawa, Jpn. J. Appl. Phys. 1997,
36, 143 – 147.
[3] H. K. Bisoyi, S. Kumar, Chem. Soc. Rev. 2010, 39, 264 – 285.
[4] a) T. J. Phillips, J. C. Jones, D. G. McDonnell, Liq. Cryst. 1993, 15, 203 –
215; b) P. Hindmarsh, M. J. Watson, M. Hird, J. W. Goodby, J. Mater.
Chem. 1995, 5, 2111 – 2123; c) K. Praefcke, B. Kohne, D. Singer, Angew.
Chem. Int. Ed. Engl. 1990, 29, 177 – 179; Angew. Chem. 1990, 102, 200 –
202; d) C. Destrade, H. Gasparoux, A. Babeau, N. H. Tinh, Mol. Cryst. Liq.
Cryst. 1981, 67, 37 – 47; e) W. K. Lee, B. A. Wintner, E. Fontes, P. A.
Heiney, M. Ohba, J. N. Haseltine, A. B. Smith, Liq. Cryst. 1989, 4, 87 – 102;f) L. Mamloc, J. Malthete, N. H. Tinh, C. Destrade, A. M. Levelut, J. Phys.
Lett. 1982, 43, 641 – 647; g) K. Praefcke, B. Kohne, K. Gutbier, N. Johnen,
D. Singer, Liq. Cryst. 1989, 5, 233 – 249; h) C. T. Imrie, Z. Lu, S. J. Picken,
Z. Yildirim, Chem. Commun. 2007, 1245 – 1247.
[5] a) B. G. Kim, S. Kim, S. Y. Park, Tetrahedron Lett. 2001, 42, 2697 – 2699;b) S. Kumar, S. K. Varshney, Org. Lett. 2002, 4, 157 – 159; c) S. Kumar, S. K.
Varshney, Liq. Cryst. 2001, 28, 161 – 163; d) L. Zhang, D. L. Hughes, A. N.
Cammidge, J. Org. Chem. 2012, 77, 4288 – 4297; e) L. Zhang, H. Gopee,
D. L. Hughes, A. N. Cammidge, Chem. Commun. 2010, 46, 4255 – 4257.
[6] a) J. H. Lee, I. Jang, S. H. Hwang, S. J. Lee, S. H. Yoo, J. Y. Jho, Liq. Cryst.
2012, 39, 973 – 981; b) J. H. Lee, M.-J. Han, S. H. Hwang, I. Jang, S. J. Lee,S. H. Yoo, J. Y. Jho, S.-Y. Park, Tetrahedron Lett. 2005, 46, 7143 – 7146.
[7] a) S. Kumar, S. K. Varshney, Angew. Chem. Int. Ed. 2000, 39, 3140 – 3142;
Angew. Chem. 2000, 112, 3270 – 3272; b) S. Kumar, S. K. Varshney, D.
Chauhan, Mol. Cryst. Liq. Cryst. 2003, 396, 241 – 250; c) S. K. Varshney, V.
Prasad, H. Takezoe, Liq. Cryst. 2011, 38, 53 – 60.
[8] S. Kohmoto, E. Mori, K. Kishikawa, J. Am. Chem. Soc. 2007, 129, 13364 –
13365.
[9] S. C. Chien, H. H. Chen, H. C. Chen, Y. L. Yang, H. F. Hsu, T. L. Shih, J. J.
Lee, Adv. Funct. Mater. 2007, 17, 1896 – 1902.
[10] H.-H. Chen, H.-A. Lin, S.-C. Chien, T.-H. Wang, H.-F. Hsu, T.-L. Shih, C. Wu,
J. Mater. Chem. 2012, 22, 12718 – 12722.

10630

T 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper[11] M. Gupta, S. P. Gupta, M. V. Rasna, D. Adhikari, S. Dhara, S. K. Pal, Chem.
Commun. 2017, 53, 3014 – 3017.
[12] a) M. Gupta, N. Agarwal, A. Arora, S. Kumar, B. Kumar, G. Sheet, S. K. Pal,
RSC Adv. 2014, 4, 41371 – 41377; b) M. Gupta, S. K. Pal, Liq. Cryst. 2015,
42, 1250 – 1256; c) M. Gupta, I. Bala, S. K. Pal, Tetrahedron Lett. 2014, 55,
5836 – 5840; d) M. Gupta, S. K. Pal, Langmuir 2016, 32, 1120 – 1126.
[13] P. Sathyanarayana, M. C. Varia, A. K. Prajapati, B. Kundu, V. S. S. Sastry, S.
Dhara, Phys. Rev. E 2010, 82, 05070.
[14] D. VenkataSai, G. Mirri, P. Kouwer, R. Sahoo, I. Musevic, S. Dhara, Soft
Matter 2016, 12, 2960 – 2964, and references therein.

Chem. Eur. J. 2017, 23, 10626 – 10631

www.chemeurj.org[15] P. Sathyanarayana, M. Mathews, Q. Li, V. S. S. Sastry, H. Takezoe, S.
Dhara, Phys. Rev. E 2010, 81, 010702.
[16] P. Sathyanarayana, V. S. R. Jampani, M. Skarabot, I. Musevic, K. V. Le, H.
Takezoe, S. Dhara, Phys. Rev. E 2012, 85, 011702.

Manuscript received: April 8, 2017
Accepted manuscript online: May 16, 2017
Version of record online: July 19, 201710631

T 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim