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Supramolecular self-assembly of thiol
functionalized pentaalkynylbenzene-decorated
gold nanoparticles exhibiting a room temperature
discotic nematic liquid crystal phase†
Monika Gupta, a Subhransu Sekhar Mohapatra,b Surajit Dharab andSantanu Kumar Pal *a
Thiol terminated pentaalkynylbenzene (PA) units were synthesized for coating on gold nanoparticles(GNPs) in order to obtain materials with a combination of the properties of GNPs and discotic

Received 28th November 2017,
Accepted 31st January 2018

nematogens. The PA unit with the longest terminal alkyl spacer was found to exhibit a discotic nematic

DOI: 10.1039/c7tc05444k

eﬀect of GNPs on the orientational order parameter and the dielectric properties of the ND mesophasersc.li/materials-c

have been investigated from various physical measurements. To the best of our knowledge, this is thefirst example of a room-temperature discotic nematic liquid crystal made of gold nanoparticles.

(ND) mesophase at room temperature which was preserved even after coating them on GNPs. The

Introduction
While a limited number of discotic liquid crystals (DLCs) showing
a nematic phase (ND) have been reported in the literature, they areof great importance in many display device applications.1 They
have received particular interest since their commercialization as
optical compensation films for enlarging the viewing angle ofcommonly used LC displays.2 Unfortunately, most of the discotics
possess ND mesophases at high temperature and over a small
temperature range.3 However, for application in devices, a ND
phase at room temperature is immensely essential.4
Furthermore, grafting LCs on a metal cluster such as gold
nano-particles (GNPs) oﬀers a combination of the properties of
LCs with the size-dependent characteristics of GNPs. The inherent
property of LCs to form mesophases due to their shape andpolarizability anisotropy also influences the self-assembly of
GNPs, whereas the GNPs aﬀect the electro-optic and alignment
properties of LCs in devices leading to collective advantages forboth the components.5 However, achieving an LC phase in GNPs
is quite a challenging task. Generally, to obtain a mesophasein such a system, the size of the GNPs should be suﬃciently
small so as to minimize the surface-anchoring eﬀect of the LCs
and thus they can behave the same as in the bulk phase.6
aDepartment of Chemical Sciences, Indian Institute of Science Education andResearch (IISER) Mohali, Sector-81, Knowledge City, Manauli-140306, India.
E-mail: skpal@iisermohali.ac.in, santanupal.20@gmail.combSchool of Physics, University of Hyderabad, Hyderabad-500046, India† Electronic supplementary information (ESI) available: Detailed synthetic
procedure, characterization details, POM, DSC and SAXS/WAXS studies. See
DOI: 10.1039/c7tc05444k

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Furthermore, crowding of LC molecules at the surface of GNPs
should also be avoided as that can lead to reduced mobilityof the mesogens with a total loss of LC behaviour. For thispurpose, a dendritic kind of molecules can be employed which
will direct the LC molecules to position themselves at a distancefrom each other.7 Because of the design challenges imposed,
most of the GNPs coated with LC molecules have been found to
be non-LC.8 Several reports are available in the literature wherethese non-LC GNPs were dispersed in the LC materials.9 These
LC-GNP composites have shown enhanced processability, plasmaemitting properties as well as interesting applications in
opto-electronics, catalysis, electrically controlled light-scattering
properties etc.10 These nano-composites have also shown adrastic enhancement in the dielectric behaviour resulting intheir remarkably enhanced switching speeds as compared tothe pure LCs.11
Investigation of a low-ordered nematic phase (where onlyorientational order is present) provides a promising approach if
we take into account the design challenges imposed for a GNP-LC
system. Moreover, for practical applications, a key challenge isto obtain GNPs in which the LC phase can be made stable atroom temperature and over a wide temperature range. Till now,
only three reports are available in the literature as reported
by Mehl and co-workers which has described the synthesis of
nematic LC GNPs.6,12 Among them, one of the LC gold nanoparticle
systems exhibited a nematic mesophase at room temperature.12b
All these reports are based on laterally connected mesogens(calamitic) to the GNPs. This lateral connection not only provided a control over the size of GNPs but also prevented thecrowding of mesogens at the gold surface leading to the

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upon cooling from the isotropic phase. The ND phase has been
well characterized by polarized optical microscopy (POM) and
X-ray scattering studies (SAXS/WAXS). Furthermore, we havecoated these thiol terminated derivatives on GNPs and foundthat coating with the longest alkyl spacer retained the ND phaseat room temperature. To study the eﬀect of GNPs, we have also
carried out temperature- and voltage-dependent dielectric andbirefringence studies and compared it with pure thiol.

Results and discussion

Scheme 1 Design of the gold nanoparticles decorated with pentaalkynylbenzene units synthesized in this study.

formation of a room-temperature mesophase. Surprisingly,
till today, there are no reports on a ND mesophase made ofgold nanoparticles. In this paper, we have investigated the first
LC GNP system that exhibits a room temperature ND phase overa wide temperature range.
Here, we have synthesized GNPs decorated with thiol terminated pentaalkynylbenzene (PA) units (Scheme 1). The PA
derivatives are known to form a ND mesophase due to rotational
freedom provided by the ethynyl linkers which avoids column
formation.3 It has been observed in the earlier reports that
GNPs coated with triphenylene, cyanobiphenyl etc. were foundto be non-LC.13 In our approach, we have chosen the conformationally flexible PA units for coating GNPs whose size wasregulated to be in the range of 2–3 nm. The PA units when
attached to these smaller sized GNPs can induce a ND LC phase by
avoiding crowding on the surface of GNPs due to their dendritic
structure. We hypothesized that when PA units are attached tosmaller GNPs, the resulting system could be disordered enough toprevent efficient packing of the PA-GNPs and thus, may lead to therealization of a room temperature ND phase. Furthermore, since
PA units are optically negative birefringent (Dn = ne no, where
ne and no are the extraordinary and ordinary refractive indices,
respectively), these LC GNPs are not only capable of showing
improved opto-electronic properties but can also serve as compensation foils in the LC display devices.
We first synthesized a series of thiol terminated PA derivatives. Interestingly, we found that one of the derivatives with thelongest alkyl spacer displayed a ND phase even at room temperature while the others stabilized a ND phase at room temperature

2304 | J. Mater. Chem. C, 2018, 6, 2303--2310

Thiol terminated PA derivatives 5 were prepared using thesynthetic route outlined in Scheme 2. Synthesis of compounds 2,
3 and 4 was carried out following earlier reported procedures.14
For the synthesis of the final compound 5, compound 4 wasdissolved in a 1 : 1 mixture of dichloromethane and methanol.
To that mixture, potassium carbonate was added and it wasstirred for around 5 hours at room temperature to obtain the
crude product which was further purified via column chromatography to yield the pure compound 5 (see the ESI† for details).
All the synthesized compounds 5a–d were characterized using
1
H NMR, 13C NMR, IR, UV-vis and mass spectrometry (ESI,†
Fig. S1–S19).
The thermal behaviour of compounds 5 (precise transition
temperatures and respective enthalpy changes) was examinedusing diﬀerential scanning calorimetry (DSC) and the mesophasebehaviour was further explored via POM and SAXS/WAXS.
Compound 5a was solid at room temperature and displayeda crystal to ND mesophase transition at 58.2 1C followed byisotropization at 110 1C (Table 1). On cooling, the mesophaseappeared at 104 1C and remained stable up to 10.2 1C. Similarly,
compounds 5b and 5c melted at around 59.8 1C and 66 1C to form
the ND mesophase (Fig. 1a), which clears at 68.9 1C and 83.8 1C,
respectively. On cooling, the mesophase appeared at 41 1C andScheme 2 Synthesis of the target compounds 5. Reagents and conditions: (i) K2CO3, KI, Br-(CH2)n-Br, butanone, 80 1C, 18 h, 88%; (ii) KSCOCH3,
DMF, RT, 8 h, 80%; (iii) Pd(PPh3)2Cl2, 4-pentylphenylacetylene, PPh3, CuI,
Et3N, 100 1C, 15 h, 85%; (iv) K2CO3, MeOH: CH2Cl2 (1 : 1), 5 h, 50%.

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Table 1

Paper

Thermal behaviour of the synthesized compounds 5ab

CompoundHeating scan

Cooling scan

5a
5b
5c
5d

Cr 58.2 (0.51) ND 110 I
Cr 59.8 (4.34) ND 68.9 (0.18) I
Cr 66 (4.0) ND 83.8 (0.58) I
ND 50 (0.49) I

I 104 ND 10.2 (4.72) Cr
I 41 ND 29.7 (1.38) Cr
I 47 ND 15.7 (1.70) Cr
I 43 ND 27.2 (3.70) Cr

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aPhase transition temperatures (peak) in 1C and transition enthalpies
in kJ mol 1 (in parentheses). b Phase assignments: Cr = Crystalline,
ND = discotic nematic, I = isotropic. Some of the transitions were notobserved in the DSC scan, however, they were confirmed from POM
studies.

47 1C which transformed to the crystalline state at 29.7 1C and15.7 1C for 5b and 5c, respectively. Interestingly, compound
5d existed in the LC state even at room temperature andbecame isotropic at 50 1C on heating the sample.
On cooling back from the isotropic state, a Schlieren texture(typical of ND phase) appeared at 43 1C which further crystallized
at 27.2 1C (Fig. 1b and ESI,† Fig. S20, S21). The compounds ofseries 4 also exhibited mesomorphic behaviour. Additionally,
two of the compounds 4c and 4d displayed ND phase even atroom temperature on cooling from the isotropic phase (ESI,†
Table S1 and Fig. S22, S23).
The quantitative study of the nematic phases of all thecompounds of series 5 was investigated via SAXS/WAXS studies(Fig. 1c). All the compounds of series 5 in their mesophasedisplayed one narrow reflection in the small angle region andone broad peak in the wide angle regime, respectively. Thispattern confirms the presence of a ND phase. The compoundsof series 4 also displayed similar diﬀractograms to those ofseries 5 in their mesophase (ESI,† Fig. S24 and Table S2). For
compound 5a, the calculated d-spacing of around 19.95 Å forthe signal in the small angle region corresponds to the separation between the PA units and thus approximates the diameterof a single PA disc (B19 Å). The spacing of the wide angle peakis 4.93 Å which originates from the liquid-like correlation of themolten chains. The diﬀraction patterns corresponding to thenematic phases of compounds 5b, 5c and 5d are very identical
to 5a and analysed in a similar way.
The correlation length, i.e., the degree of order within themesophase, was calculated from the Scherrer’s equation.15 For
compound 5a, the correlation lengths for the reflections at
19.95 Å and 4.93 Å are calculated to be 39.18 Å and 9.22 Å,
respectively. In order to measure spatial order in terms of themolecular length scale, the correlation length was divided
by the d-spacing values (Table 2). The respective correlation
lengths for compounds 5 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). This can be
due to the fact that compounds 5 are discotic mesogens based on
pentakis(phenylethynyl)benzene composed of flexible alkyl chains
and a terminal thiol group (Fig. 1d). In the case of PA, the phenyl
rings are generally not in plane because of rotational freedom
provided by ethynyl linkers which prevents columnar stacking.
Furthermore, orientational freedom of the PA group increases on
increasing the terminal alkyl chain length which is also reflected in
the decreasing value of the corresponding correlation lengths.
Our next goal was to synthesize and characterize GNPs coatedwith PA units. The preparation of GNPs was carried out by closely

Fig. 1 Optical photomicrograph of compound (a) 5c at 36.6 1C and (b) 5d at 41.8 1C representing the ND phase (on cooling from isotropic, crossed
polarizers). (c) X-ray diﬀraction pattern of compounds 5a–d in the nematic phase. (d) The schematic representation of the arrangement of PA units in themesophase.

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Table 2 X-ray reflections and corresponding correlation lengths in the
discotic nematic phases of compound 5a–d

CompoundProperties

Small angle
peakWide angle
peak

5a

d-Spacing (Å)
Correlation length (x) (Å)
x/d

19.95
39.18
1.96

4.93
9.22
1.87

5b

d-Spacing (Å)
Correlation length (x) (Å)
x/d

19.96
36.60
1.83

4.89
10.58
2.16

5c

d-Spacing (Å)
Correlation length (x) (Å)
x/d

19.9
34.97
1.75

4.87
9.78
2.00

5d

d-Spacing (Å)
Correlation length (x) (Å)
x/d

19.99
30.81
1.54

4.85
9.17
1.89

following an earlier reported method (see the Experimental
section for details).16 All the synthesized GNPs were characterised using 1H NMR, UV-vis and TEM analysis. Their thermotropic behaviour was analysed via POM, DSC and further
characterized using SAXS/WAXS techniques. The 1H NMR spectraof the synthesized nanoparticles displayed broadened peaks ascompared to those obtained for thiols and thus indicates that
thiols are attached to the surface of gold nanoparticles and are
not present in their free form (ESI,† Fig. S25). Furthermore,a characteristic peak at 517 nm in the UV-vis spectra arises due
to surface plasmon resonance and represents the formation of
spherical GNPs (ESI,† Fig. S26).17
We have found that GNPs with shorter chain lengths i.e.
5a–c GNPs were sticky solids at room temperature and displayed

an increase in birefringence with some phase separation occurringon heating. On cooling, they did not display any birefringence tillroom temperature and existed as isotropic liquids during thesecond heating/cooling cycles. A possible reason for this behaviour
could be because of the non-uniform coverage of the capping
agent on the gold cluster due to steric hindrance arising from theshorter chain length of the terminal alkyl chain. Interestingly, incontrast to the above observations, 5d-GNPs were very stable anddisplayed an enantiotropic mesophase which existed even at room
temperature. Therefore, we have discussed 5d-GNPs in detail in
the next section.
The 5d-GNPs were displaying birefringence with shearabilityof textures at room temperature which confirms the presence ofa LC phase which on heating converted to isotropic liquid at
60 1C (Fig. 2a). On further cooling, a Schlieren texture typical of anematic mesophase was observed at 57 1C which remained stable
up to 12.95 1C (Fig. 2b and ESI,† Fig. S27). It can be thus inferredthat the room temperature ND phase of 5d was retained even after
coating 5d on the GNPs. However, the mesophase range wasshifted to a higher temperature as compared to pure thiol 5d.
The size of the 5d-GNPs was found to be in the range of
2.5–3.1 nm from TEM observations (Fig. 2c). Dynamic lightscattering measurements also indicated the formation of GNPs
with a size of B2.76 nm with a polydispersity index of 0.35. The
number of mesogens attached to a single GNP was found to bearound 263 from TGA analysis (ESI,† Fig. S28). The mean
formula for 5d-GNPs is found to be Au574(PA)263. The nematic
mesophase exhibited by 5d-GNPs was further characterised via
SAXS/WAXS studies (Fig. 2d and e).
The XRD pattern exhibited two peaks: one sharp peak at
a small-angle and another diﬀuse peak in the wide-angle

Fig. 2 The POM textures of 5d-GNPs (a) on heating at 45 1C and (b) on cooling from the isotropic at 40 1C (crossed polarizers, magnification: 200).
(c) TEM image of 5d-GNPs obtained by dispersing the dilute solution of 5d-GNPs in toluene on a carbon coated copper grid. (d) The wide-angle
X-ray scattering (WAXS), (e) small-angle X-ray scattering (SAXS) pattern of 5d-GNPs in the ND phase at room-temperature and (f) their schematic
representation in the ND mesophase.

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region (Fig. 2d). In our case, the nematic gold nanoparticles are
possibly intercalated and the observed d-spacing (42.68 Å) in
the small angle, likely corresponds to the average side by side
separation between centres of two GNPs covered with PA units.
The peak in the wide angle regime observed at 4.86 Å corresponds to liquid like correlation of the molten alkyl chains.
Fig. 2e shows the 5d-GNP modelled as a gold cluster surrounded
by PA units and the arrangement of the model units in thenematic mesophase. The correlation lengths for the reflectionsat 42.68 Å and 4.86 Å are calculated to be 135.16 Å and 14.72 Å,
respectively. For measuring the spatial order in terms of themolecular length scale, the correlation length was divided by
the d-spacing values which were around 3.16 Å and 3.02 Å forthe peak at a small- and wide-angle, respectively, and is about
double of the values as observed for compound 5d. A reason forthe stabilization of the mesophase in the case of the 5d-GNPs
could be due to a longer terminal alkyl spacer length of thiol 5dwhich avoids crowding of the mesogens on the gold surface andthus ensures a uniform coating of mesogens on the GNPs which
may not be feasible in the case of shorter spacer length of thiols
5a–c. We have excluded the layering or other packing from thePOM as well as XRD studies. In POM, we can easily observe theSchlieren texture which is typical of a nematic mesophase.
Furthermore, in the XRD studies we did not observe any higher
order peak which excludes the possibility of any positional orderamong the mesogens.
It should be noted that TEM studies only indicate the size ofgold core which we found to be in the range of 2.5–3.1 nm. The
TEM studies were carried out by drop casting a very dilute
5d-GNP solution in toluene onto a carbon supported copper
grid (200 Mesh Cu). However, the distance between two gold
nanoparticles was found to be about B3.3 nm which is lessPaper

than the ligand diameter indicating partial intercalation of
PA units. A DLS study was also performed in a dilute 5d-GNP
solution in toluene. The obtained particle sizes (B2.76 nm) wasin very close agreement with the TEM results. The XRD was
carried out in Lindeman capillary in the nematic phase itself.
It gives an average length of the GNPs covered with the PA
mesogens, which is expected to be higher than the size of only
the gold core.
To investigate the physical properties and bring out the eﬀectof the GNPs, we have conducted birefringence and dielectricmeasurements. The details of the experimental techniques havebeen reported previously.18 We used polyimide (AL-1254) coatedcells with antiparallel rubbing. Such cells provide planar alignment of the calamitic nematic LCs. In the case of ND LCs, it
provides homeotropic alignment of the director (i.e. the plane ofdiscs is parallel to the substrates). Fig. 3a shows the voltage
dependent eﬀective dielectric constant (eeﬀ) for compounds 5dand 5d-GNPs. eeﬀ is slightly larger for the 5d-GNPs as comparedto 5d. It shows a small increase beyond a particular voltage andgets saturated at a much higher voltage. At the low voltage, thedirector is perpendicular to the substrate and at the higher
voltage (above the Fréedericksz threshold voltage, Vth) it turns
parallel.
The increase of eeﬀ with voltage in both the samples indicatesthat they have a negative dielectric anisotropy and their values
are very small (De E 0.1). Fig. 3b shows the variation of eeﬀ(i.e., eII) in the nematic phase measured at a fixed voltage of
18 V. It shows that eII is almost constant in the nematic phaseand it is higher by about 10% in the 5d-GNPs than in 5d. Fig. 3cshows the variation of birefringence (Dn) with applied voltage.
We observed that beyond the Fréedericksz threshold voltage(Vth D 2 V), Dn increases and saturates beyond 15 V. This means

Fig. 3 (a) Voltage-dependent dielectric constant of compound 5d at a fixed temperature T
TNI = 3.59 1C and 5d-GNPs at a fixed temperature
T TNI = 4.0 1C. (b) Temperature-dependent dielectric constant of compound 5d and 5d-GNPs at a fixed voltage of 18 V and a frequency of 2 kHz.
(c) Voltage-dependent birefringence (Dn) of 5d at a fixed temperature of T TNI = 3.78 1C and of 5d-GNPs at a fixed temperature of T TNI = 6.20 1C.
(d) Temperature-dependent birefringence (Dn) of 5d and 5d-GNPs at a fixed voltage of 20 V and frequency of 2 kHz.

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Fig. 4 (a) Variance of conductivity of 5d and 5d-GNPs at a fixed temperature ( 2.50 1C). (b) Temperature variation of conductivity of 5d and 5d-GNPs at
a fixed voltage of 18 V and a frequency of 2 kHz.

that the director of the ND mesogens is completely re-orientatedto the planar state. Fig. 3d shows the temperature dependent
variation of the birefringence measured at a fixed voltage of
18 V. It is observed that Dn in the compound 5d-GNPs is significantly
shorter than in compound 5d. For example, at T TNI = 9 1C, Dn in
5d-GNPs is about 40% smaller than that of 5d.
Since Dn is proportional to the orientational order parameter S, we conclude that the inclusion of gold nanoparticles
has reduced the order parameter significantly and this is consistent with our proposed model presented in Fig. 2f where the
GNPs are surrounded by PA units.
We further measured the eﬀective electrical conductivity (seﬀ)of the sample as a function of voltage and temperature. The
frequency of measurements is 2 kHz and only ionic conductivity
is expected to contribute in the measurements. Fig. 4a showsthat 5d-GNPs has a larger conductivity than that of 5d. With
increasing voltage, seﬀ slightly decreases below the Fréedericksz
threshold voltage, Vth = 2 V, followed by an increase at a higher
voltage. The decrease of seﬀ below Vth could be due to the reduction of the bulk charge density due to selective ion absorptions
at the electrodes. Since the conductivity along the director is
expected to be larger than in the perpendicular direction, theincrease in seﬀ at a higher voltage in both the compounds cannot
be due to reorientation of the director. This could be attributed
to an increase in the mobility of the charges at a higher voltage.
Fig. 4b shows the temperature dependent variation of sII for
both the compounds measured at a frequency of 2 kHz. sII in
5d-GNPs is about 30% larger than that of 5d. Therefore, it canbe inferred that incorporation of GNPs has reduced the orientational order parameter and enhanced the electrical conductivity
significantly. The enhancement in the dielectric and conductivity in 5d-GNPs are expected due to the Maxwell–Wagner
effects.19

Conclusions
In summary, this report describes for the first time the synthesis of GNPs decorated with thiol functionalized PA units which
exhibits a ND phase at room temperature. These ND GNPs haveshown an enhanced dielectric response and increased conductivity

2308 | J. Mater. Chem. C, 2018, 6, 2303--2310

values as compared to the thiols. Therefore, these GNPs exhibitinga ND mesophase at room temperature are very interestingmaterials for display applications and also points the way
towards the development of new anisotropic soft materials fortheir usability in devices.

Experimental section
Preparation of thiol-coated gold nanoparticles
For the preparation of thiol-coated GNPs, a solution of tetraoctylammonium bromide (0.124 mmol) in toluene (5 ml) was
prepared and added to an aqueous solution of HAuCl43H2O(0.028 mmol). The resulting solution was stirred for 20 minutes
to ensure a complete transfer of gold chloride from the aqueous
to organic layer. The organic layer was separated and washedwith distilled water. A solution of thiol (0.038 mmol) in toluene(2 ml) was added to the above solution and the resulting mixture
was stirred for 30 minutes. An aqueous solution of NaBH4(0.28 mmol) was added dropwise to the above solution and the
mixture was stirred for a further period of 6 h. The toluene layer
was washed with distilled water, diluted with methanol (250 ml)
and kept in a refrigerator overnight. The precipitate obtained
was purified by re-suspending in toluene and was then centrifuged after the addition of methanol (10 ml). This purification
step was repeated several times to ensure the complete removalof any non-covalently bound organic material. Full characterization details, TGA, DSC, POM textures are provided in theESI.†
Characterization
Structural characterization of the compound was carried out
through a combination of infrared spectroscopy (Perkin Elmer
Spectrum AX3), 1H NMR and 13C NMR (Bruker Biospin Switzerland
Avance-iii 400 MHz and 100 MHz spectrometers respectively),
UV-vis-NIR spectrophotometer (Agilent Technologies UV-vis-NIR
Spectrophotometer) and mass spectrometry (Waters synapt G2s).
NMR spectra were recorded using deuterated chloroform (CDCl3)
as the solvent and tetramethylsilane (TMS) as an internal standard.
DSC measurements were performed using a Perkin Elmer DSC
8000 coupled to a Controlled Liquid Nitrogen Accessory (CLN 2)
with a scan rate of 5 1C min 1. Textural observations of theThis journal is © The Royal Society of Chemistry 2018

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mesophase were performed using a Nikon Eclipse LV100POL
polarising microscope provided with a Linkam heating stage(LTS 420). All images were captured using a Q-imaging camera.
X-ray diﬀraction (XRD) was carried out on powder samples
using Cu Ka (l = 1.54 Å) radiation from a source (GeniX 3D,
Xenocs) operating at 50 kV and 0.6 mA. The diﬀraction patterns
were collected on a two module Pilatus detector.

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Materials
Chemicals and solvents were all of AR quality and were usedwithout further purification. Pentabromophenol, 1-ethynyl-4-pentylbenzene, copper iodide, bis(triphenylphosphine) palladium(II)dichloride, triphenylphosphine, triethylamine, dibromohexane,
dibromooctane, dibromodecane, dibromododecane, potassium
carbonate, potassium iodide, potassium thioacetate, methanol,
butanone, dimethylformamide and dichloromethane were allpurchased from Sigma-Aldrich (Bangalore, India). Column
chromatographic separations were performed on silica gel(60–120, 100–200 & 230–400 mesh). Thin layer chromatography(TLC) was performed on aluminium sheets pre-coated withsilica gel (Merck, Kieselgel 60, F254).

Conflicts of interest
There are no conflicts to declare.

Acknowledgements
We are grateful to the NMR, HRMS and SAXS/WAXS facility
at IISER Mohali. Dr SK Pal and Dr S Dhara are grateful for
financial support from INSA (bearing sanction No. SP/YSP/124/
2015/433) and DST, FIST-II (University of Hyderabad), respectively.
SKP acknowledges CSIR Project File No. 02(0311)/17/EMR-II.
M. Gupta acknowledges the receipt of a graduate fellowshipfrom IISER Mohali.

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