A new class of supramolecular liquid crystals derived from azo calix[4]arene functionalized 1,3,4-thiadiazole derivatives

Article abstract of DOI:10.1039/C8NJ04997A

A new class of bowl-shaped supramolecular liquid crystals (LCs) is described derived from calix[4]arene substituted with 1,3,4-thiadiazole derivatives, inbuilt with Schiff base and ester on the lower rim and with an azo group on the upper rim with an alkyl side chain (-OC₃H₇,-OC₈H₁₇). In the present investigation, we have synthesized six new supramolecular-based derivatives having three linking units with a substituted 1,3,4-thiadiazole ring and a variable trisubstituted side alkoxy chain on the lower rim of calix[4]arene. These supramolecular compounds were investigated by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and high temperature X-ray diffraction studies (XRD). All synthesized compounds exhibited good blue fluorescence in solution under long wavelength UV light. The present compounds are promising for stabilizing the hexagonal columnar phase over a broad thermal range. The bowl-shaped calixarene-based LCs pack into columns with enhanced intermolecular interactions. The liquid crystalline properties are influenced by the structures of the spacers on the calix[4]arene skeleton and enhance the phase transition temperatures.

Full text of DOI:10.1039/C8NJ04997A

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“A New Class of Supramolecular LCs derived from Azo Calix[4]arene
Functionalized 1,3,4-thiadiazole derivatives”
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Vinay S.Sharmaa*, Akshara P.Shahb, Anuj S.Sharmac
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a*: Department of Chemistry, Faculty of Basic and Applied Science, Madhav University, Sirohi,
Rajasthan.
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b: Department of Chemistry, Mumbai University, Santacruz, Mumbai.
c: Department of Chemistry, School of Science, Gujarat University, Ahmedabad, Gujarat.
Corresponding author: vinaysharma3836@gmail.com
Abstract
A new class of bowl-shaped supramolecular LCs derived from calix[4]arene substituted with
1,3,4-thiadiazoles derivatives inbuilt with schiff base and ester on lower rim while azo group on
upper rim with presence of alkyl side chain (-OC3H7, -OC8H17). In the present investigation, we
have synthesized total six newly supramolecular based derivatives having three linking unit with
substituted 1,3,4-thidiazole ring and variable trisubstituted side alkoxy chain on the lower rim of
calix[4]arene. These supramolecular compounds were investigated by polarizing optical
microscope (POM), differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA)
and high temperature X-ray diffraction studies (XRD). All synthesised compounds exhibited good
blue fluorescences in solution under long wavelength UV light. The present compounds are
promising to stabilize the hexagonal columnar phase over a broad thermal range. The bowl
shaped calixarene based LCs packs into columns with enhanced intermolecular interactions. The
liquid crystalline properties were influenced by the structures of the spacers on calix[4]arene
skeleton to enhance the phase transition temperatures.
Key words: Calixarene, 1,3,4-thiadiazole, liquid crystals, azo, schiff-base.
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1. Introduction
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Calixarenes and their based derivatives are the most attractive compounds for the third
generation supramolecular chemistry after crown ether and cyclodextrin1. Calixarenes,
possessing tunable 3D-shaped hydrophobic cavities belong to the important building blocks in
supramolecular chemistry after crown ether and cyclodextrin2. The bowlic LCs may possess
some special physical properties, such as genuine ferroelectricity and second-harmonic
generation3.The calixarenes broaden functionalized at the upper and lower rim affords them with
suitable binding sites for guest encapsulation and molecular assembly4. Importantly, the four
hydroxyl groups present in calix[4]arene interact by hydrogen bonding and also stabilize the
cone conformation5. In recent years, the calixarene core was also successfully used as a rigid
core to prepare liquid crystalline compounds6.
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In the recent reports, there has been a renewed interest in the incorporation of
heterocycles in the molecular design of mesogens due to the wide variety of structures and hence
the resultant properties. Hetero atoms like nitrogen, oxygen and sulfur provide a reduced
molecular symmetry, strong lateral and/or longitudinal dipoles and a donor-acceptor interaction
within the molecule, which in turn affects the LC self-assembly and electronic behavior of the
mesogens7. Additionally, the mesogens with heterocyclic moieties in their molecular structures
provide emission color tunability and also enable a polarized emission. This is the most
important property which finds application in the area of OLEDs8. In this regard, many LCs
bearing a heterocyclic moiety in their molecular structures are well reported in literature. There
are relatively more reports on 1,3,4-Oxadiazole based LCs as compared to their sulfur analogues
1,3,4-thiadiazole based LCs. Unfortunately, oxadiazole based mesogens shows some drawbacks
such as high melting point and also clearing temperatures, narrow mesophase range and poor
solubility which render their applications in certain region. Reports on their sulfur analogues, i.e.
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1,3,4-thiadiazole based mesogens are well reported limited in literature9-15. It is anticipated that,
the substitution of oxygen atom by sulfur atom which increases the dipole moments, packing of
molecules, viscosity, melting and clearing temperatures. There are various types of LCs like
Calamitic LCs, banana shaped LCs, hydrogen bonded LCs and polymeric LCs based on 1,3,4-
thiadiazole are well reported in literature 16-20. However, very few compounds based on
supramolecular bowl-shaped calix[4]arene are reported for only their biological and sensing
application till the present date 21-22. Thus, we wish to report azo functionalized bowl-shaped
supramolecular LCs based on trisubstituted 1,3,4-thiadiazole derivatives and calix[4]arene
connected with two linking unit. As part of our effort to combine trisubstituted 1,3,4-thiadiazole
derivatives on the lower rim of azo functionalized calix[4]arene for searching new
supramolecular room temperature LCs with high temperature range. Azo functionalized
materials are well known for their effectiveness in optoelectronic devices, food additives,
indicators, dyes, photochemical molecular switches and therapeutic agents. The photochromic
behavior of azo compounds improves the activity of enzymes and polypeptides in biological
systems23.
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Liquid crystalline materials based on calix[4]arene rigid core was first reported in
199024. Calixarene based liquid crystalline compounds which are the significant part of
macrocycles based liquid crystals were investigated in some literature25-26. For instance, the
calixarene liquid crystals with substitution of long aliphatic side chains were prepared and
displayed interesting liquid crystalline behaviours27. Yonetake et al. synthesized two liquid
crystal based on tert-butyl calix[8]arene to displayed smectic and nematic mesophase 28. Yang et
al. reported mesomorphic property in calix[4]arene cholesterol derivatives. They studied the
mesophase appeared with the presence of columnar type molecular arrangement of calixarene
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with cholesterol derivatives29. In another reports, Yang et al. synthesized and studied the liquid
crystalline behavior of calixarene-linked triphenylene derivatives30. Later, his group reported the
mesomorphic properties of gallic-calixarene derivatives with stable cone conformation31.
Previouslly, Yang et al. reported calix[4]resorcinarene cholesterol based columnar liquid crystals
having schiff-base linking group32. Marcos and his coworkers synthesized and studied the
mesomorphic property of calixarene schiff base derivatives which have binding recognition and
selectivity towards Zn+2 ion33. Recently, our group reported the two liquid crystalline series of
calix[4]arene based on schiff-base and ester linking group and also studied their biological
behaviour34.
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A comprehensive literature reports reveals that the azo functionalized 1,3,4-thiadiazole
supramolecular bowl-shaped LCs based on calix[4]arene are never be reported till the date. In
this present investigation, we have designed new bowl-shaped supramolecular LCs in which
calix[4]arene was chosen as rigid core which is functionalized by azo group on upper and schiff
base-ester on lower rim with presence of tri-alkyl substituted 1,3,4-thiadiazole derivatives. The
present bowl-shaped supramolecular LCs based on 1,3,4-thiadiazole calix[4]arene showed good
photophysical properties, which may establish as promising materials for applications in
photomechanics, instant displays, reversible holographic storage, and digital storage due to their
high resolution and sensitivity.
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2. Result and Discussion
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2.1 Synthesis and characterization
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The synthetic approach for the preparation of calix[4]arene and thiadiazole derivatives are
presented in Scheme-1. Calix[4]arene (1) is prepared by the deterbutylation reaction of p-tert-
butyl calix[4]arene27. The diazo derivatives of calix[4]arene (2) were prepared by the reported
method in literature35. 3,4,5-trialkoxy benzohydrazide (4) was synthesized from the reaction of a
compound (3) with hydrazine hydrate in the presence of n-butanol36. 3,4,5-trimethoxy-(4'-nitro
benzoyl) benzohydrazide (5) is prepared from compound (4) with 4-nitro benzoyl chloride in the
presence of pyridine. This intermediate (5) upon heating in the presence of phosphorous
pentasulfide (P2S5) provided the thiadiazole derivative (6)36. Compounds (6) were reduced by
using catalytic hydrogenation to yield the corresponding amine derivatives (7), which on further
heated with 4-formylbenzoic acid in the presence of a few drops of acetic acid in ethanol to form
compound (8) respectively37. Scheme-2 shows the synthetic routes of the final target calixarene
derivatives. The final target compounds (9a-9f) were prepared by the reaction of a compound
(8a-8c) and compound (2a-2b) in DCM with the presence of DCC and a catalytic amount of
DMAP respectively38. The resultant crude residue was purified by using column chromatography
on silica gel eluting with methanol: dichloromethane as eluent (1:4). From the 1H NMR, the cone
confirmation of final targets compounds was confirmed by the presence of –CH2- peaks at 3.26
ppm and 4.12 ppm respectively. The 1H NMR, 13C NMR, MALDI-TOF and IR results also well
supported to the corresponding structures of derivatives and final target compounds are shown in
ESI (supporting information).
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Scheme 1: (i) HCl-NaNO2, 4-alkoxy amino benzene, 0-5˚C; (ii) NH2NH2.H2O, n-butanol, reflux,
24 hr; (iii) 4-nitrobenzoyl chloride, pyridine, 60˚C, 10 hr; (iv) P2S5, THF, 60˚C, 18 hr; (v) 10%
Pd-C, H2 (balloon, 1 atm), THF, rt, 10-12 hr; (vi) 4-hydroxy benzaldehyde, few drops of glacial
acetic acid, EtOH, 2 hr.
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Scheme 2: (i) DCC/DMAP, DCM, 24 hr, RT.
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2.2 DSC investigation
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The mesomorphic behavior of compounds 9a-9f were preliminarily studied by using
differential scanning calorimetry (DSC) analysis. The transition temperatures and the associated
enthalpy changes obtained from the DSC scans of second heating-cooling cycles are mentioned
in Table-1 and Figure-1 respectively. Figure-2 summarizes the thermal behavior of these
synthesized samples in the heating cycle. All the synthesized compounds (9a to 9f) display two
thermal peaks on heating and cooling cycles. Comp.9a with shortest alkyl chain (-OC4H9) on
upper rim, exhibited enantiotropic columnar mesophase spanning a higher thermal range of 41.2
degrees in heating cycle after passing through crystal to phase transition to isotropic at 144.1 ˚C
to 185.3 ˚C with an enthalpy change of 24.2 kJ/mol respectively as evidenced by DSC
thermograms which was further confirmed by using POM study. Similarly, Compound 9f with
higher alkyl chain (-OC8H17) on upper rim showed two endothermic peaks at 114.4 ˚C and 138.8
˚C on heating cycle which is corresponding to Cr-Colh and Colh-I phase transition. Also, these
two thermal peaks appeared at 134.3˚C and 108.8 ˚C on cooling process which indicated the
reversible phase transition process of I-Colh, Colh-Cr phase upon second heating and cooling
condition. Compound 9b with butyloxy chain group on upper rim and trisubstituted hexyloxy
chain on lower rim traced two endothermic peaks at 141.3 ˚C and 177.3 ˚C on heating cycles;
these exothermic peaks were observed at 173.8 ˚C and 139.6 ˚C on cooling cycle. It could
observe that, compound 9a with the butyloxy chain group on upper rim and trisubstituted on
lower rim showed broad temperature range of mesophase as compare to other compounds which
contain a higher alkyl chain group on the upper and lower rim. The thermal range of mesophase
in compounds 9a, 9b, 9c, 9d, 9e and 9f is founds as 41.2 ˚C, 36.0 ˚C, 30.7 ˚C, 25.6 ˚C, 21.4 ˚C
and 24.4˚C respectively. The result obtained from DSC study is further confirmed by POM and
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XRD analysis, respectively. The DSC thermograms of compounds 9e and 9f are shown in Figure
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S1 (ESI).
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Table 1: Phase transition temperatures (˚C) and corresponding enthalpies (kJ/mol) of
synthesised compounds
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Compound
Phase sequence
Heating
Cooling
9a
9b
9c
9d
9e
9f
Cr 144.1 (31.7) Colh185.3 (24.2) I
Cr 141.3 (30.3) Colh 177.3 (28.1) I
Cr 136.5 (28.6) Colh 167.2 (16.5) I
Cr 132.6 (24.8) Colh 158.2 (12.9) I
Cr 124.8 (31.9) Colh 146.2 (9.5) I
Cr 114.4 (23.9) Colh 138.8 (8.2) I
I 181.4 (29.4) Colh 142.9 (40.9) Cr
I 173.8 (31.2) Colh 139.6 (37.8) Cr
I 163.6 (25.9) Colh 131.2 (32.2) Cr
I 154.5 (19.6) Colh 127.7 (29.5) Cr
I 141.4 (14.5) Colh 119.5 (34.7) Cr
I 134.3 (12.3) Colh 108.8 (28.3) Cr
a Peak temperatures in the DSC thermograms obtained during the first heating and first cooling
cycles at 10˚C/min; Colh = columnar hexagonal phase.
Figure 1: The DSC traces of compounds 9a (a), 9b (b), 9c (c), 9d (d) on second heating
and cooling (scan rate 10˚C/min).
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Figure 2: Thermal behaviour of comp.9a-9f (based on heating scans from DSC).
2.3 POM investigation
The phase transition temperatures of newly synthesized compounds were further carried
out by using of polarizing optical microscope (POM) by observing the textures when the sample
was sandwiched between a clear glass slide and a cover slip. The all synthesized bowl-shaped
supramolecular azo calix[4]arene derivatives display a texture pattern of columnar phase. It can
be noted that, the observed defect texture images pattern of hexagonal columnar phase, which is
commonly observed for Colh phase. The observed texture pattern of compounds 9a, 9b, 9c and
9f are shown in Figure-3. Compound 9a and 9c showed similar texture pattern of hexagonal
columnar phase at 142.6 ˚C and 133.8 ˚C on heating condition (Fig.2a, 2d), but having different
isotropic temperature range. Similarly, compounds 9f and 9e showed same texture pattern of
hexagonal columnar mesophase at 112.9 ˚C and 121.2 ˚C with different temperature range of
mesophase on heating condition (Fig.3b, 3c). On cooling condition, same textural pattern of Colh
mesophase was observed before forming the solid crystal. Thus, an enantiotropic mesomorphic
behaviour over a broad thermal range of mesophase was seen for the present synthesized bowl-
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shaped supramolecules based on calixarene core. The texture pattern of compound 9b and 9d at
139.1 ˚C and 129.8˚C are shown in Figure S2 (ESI). This proposal was further confirmed by
XRD analysis.
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Figure 3: POM texture image of compound 9a at 142.6 ˚C (a) compound 9f at 112.9 ˚C (b)
compound 9e at 121.2 ˚C (c) and compound 9c at 133.8 ˚C (d) on heating condition from solid
crystalline state as seen under cross polarizers.
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2.4 XRD analysis
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To confirm the mesophase observed through a polarising microscope (POM) and
differential scanning calorimetry (DSC), XRD studies have been performed to confirm the liquid
crystalline phase. The liquid crystalline behavior of supramolecular azo based calixarene LCs
(9a-9f) were further confirmed by using X-ray scattering studies of unoriented samples filled in
Lindemann capillaries. All the samples have been studied for their LC phase at their transition
temperature. The sample was filled by melting as isotropic state and cooled down to their LC
state and scanned for X-ray studies. The X-ray patterns of LC phases of all the supramolecular
calix[4]arene derivatives showed three reflections at small angle region and to two diffuse
scattering peaks in the wide angle region as shown in Figure-4 (a-d) and Figure S3 (a,b)
respectively. Compound 9a at 2.71˚, 4.81˚ and 5.53˚, compound 9b at 2.76˚, 4.82˚ and 5.57˚,
compound 9c at 2.51˚, 4.86˚ and 5.68˚, compound 9d at 2.02˚, 3.51˚ and 4.06˚, compound 9e at
2.06˚, 3.58˚ and 4.09˚, compound 9f at 2.04˚, 3.51˚ and 4.08˚ in the small angle region and the
single small reflection appeared at 19.08˚, 19.07˚, 18.73˚, 19.01˚, 19.78˚ and 19.83˚ for
compounds 9a, 9b, 9c, 9d, 9e and 9f in the wide angle region. In addition, one more reflection
peak was appeared at 21.18˚, 21.20˚, 21.18˚, 21.29˚, 21.63˚ and 21.29˚ for compounds 9a, 9b, 9c,
9d, 9e and 9f in the wide angle region. The d-spacing value for compound 9a is 32.57 Å, 18.36
Å, 16.49 Å in small angle region. Similarly, 31.98 Å, 18.32 Å and 15.86 Å for compound 9b,
35.16 Å, 18.17 Å and 16.98 Å for compound 9c, 43.70 Å, 25.15 Å and 21.75 Å for compound
9d, 42.84 Å, 24.66 Å and 21.59 Å for compound 9e, 43.27 Å, 25.15 Å and 21.75 Å for
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compound 9f. The ratio of these present reflections agreed with 1:
:1 , signifying the
1/√3 /√4
d[100], d[110] and d[200] plane of hexagonal lattice. The presence of small diffuse peak at wide
angle region at 21.18˚, 21.20˚, 21.18˚, 21.29˚, 21.63˚ and 21.29˚ with d-spacing 4.54 ~ 4.82 Å for
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compounds 9a to 9f due to the presence of core-core interactions of calixarene to form ordered
hexagonal phase in addition of self-assembly organizations. The literature survey indicated that
the similar XRD traces were reported for supramolecular calix[4]arene liquid crystals with
different substituted derivatives on lower rim30. The estimated molecular length of present
synthesised compounds is nearer to the observed molecular length. It can be noted that the
presence of broad halos at 2Ɵ = 18.63~19.83˚ indicating the ordering of the peripheral alkyl
chain group at lower and upper rim of calix[4]arene core. The proposed mechanism (Figure 5) of
present synthesized compounds indicated the arrangement of the bowlic shape calixarene column
with substitution on lower and upper rim by schiff-base ester and azo group with presence of
variable aliphatic alkyl chain on lower terminal end while propyloxy and octyloxy chain on the
upper terminal end of calix[4]arene core unit. Based on all the data of DSC, POM and XRD, it is
confirmed that all the synthesised azo schiff base-ester 1,3,4-thiadiazole calix[4]arene derivatives
display hexagonal columnar liquid crystalline mesophase respectively.
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Figure 4: XRD profiles depicting the intensity against the 2Ɵ obtained for the Colh phase of
compound 9d at 131.0 ˚C (a); Colh phase of compound 9a at 143.0 ˚C (b); Colh phase of
compound 9e at 124.0 ˚C (c); Colh phase of compound 9b at 141.0 ˚C (d) on cooling from
isotropic temperature; the insert shows the image pattern obtained.
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Figure 5: Schematic representations of the columnar hexagonal molecular arrangements
(comp.9a).
2.5 Thermal stability
Thermal stability of compounds 9a-9f were studied by thermogravimetric analysis
(TGA) shown in Figure 6(a, b). All the synthesized 1,3,4-thiadiazole based supramolecular
calixarene derivatives were stable at least up to
and complete degradation occurs at
≈ 300˚C
around 450˚C. As there is no loss seen up to 150 °C that means no water or other solvent
entrapped in mesophase formation. All the synthesized compounds show good thermal stability.
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Figure 6: TGA curves of the compounds 9a-9c (a); compounds 9d-9f (b) carried out at a rate of
10 ˚C/min.
2.6 Photophysical behaviors
The photophysical properties of these supramolecular calix[4]arene compounds 9a, 9b,
9c, 9d, 9e and 9f were studied in solution. Figure-7 represents the absorption and emission
spectra of compound 9a in various organic solvents respectively. One can see that the
absorbance and the emission intensities of compound 9a are higher in organic solvents as
compared to polar solvents. The absorbance and emission intensities of compound 9a in THF is
higher as compare to other organic solvents because of its moderately nature to dissolve wide
range of nonpolar and polar chemical compounds39. Micromolar THF solutions of all
supramolecular compounds 9a-9f were used to measure the absorption and fluorescence spectra
mention in Figure-8. The corresponding spectral data were depticated in Table-1. The azo
linkage containing compounds was irradiated with UV light, the band corresponding to Π-Π* and
n-Π* transitions which is decreases with increasing irradiation time40. The low intense short
wavelength absorption maxima appeared at nearly 279 to 283 nm, this is due to the presence of
Π-Π* transition in phenyl rings respectively. However, the high intense longer wavelength
absorption maxima observed at 348 to 354 nm, this is attributed to the presence of a Π-Π*
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transition involving the π-electronic system throughout the whole mesogenic portion, with a
considerable charge transfer character40. Compound 9a irradiated at 364 nm, E-Z isomerization
taking place which is decrease in the absorption band from 346 nm is ascribed to Π-Π* transition
of the trans (E) isomer observed in azo group respectively. The further very weak absorption
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band found in the visible region around at 452 nm which is represents to n-Π* transition of cis
(Z) isomer in the azo group was gradually increased by reaching photo stationary state at 80 sec.
After that, no change observed in the absorption spectrum which is further confirms the photo-
saturation of E-Z (trans-cis) isomerization. From figure-7 and figure-9(a,b), its clear that all the
other derivatives showed n-Π* transition at nearly 451 nm which confirmed the presence of E-Z
(trans-cis) isomerization process in present synthesized derivatives. The highly delocalized
electronic systems and Π-Π* transitions with the presence of heteroaromatic part inbuilt with the
lower rim of calixarene derivatives with high molar absorption coefficient (ε = 23.6-27.4 × 106 L
mol-1cm-1) recognized to the maximum absorption in the present synthesised azo based
supramolecular compounds. The absorption and fluorescence of the higher alkyl substituted
compounds (9d-9f) were higher than lower alkyl substituted compounds (9a-9c), this is due to
the variation of the side alkyl chain group which suggesting that the long alkyl substitution with
electron donating oxygen and the conjugation of aromatic rings with electron accepting imide
group inbuilt with azo group increases the intramolecular charge transfer efficiency which
fluctuated the fluorescence and absorbance intensity. As can be seen in the Figure-8b, all the
compounds showed light sky bluish fluorescence in THF solution respectively. This is promising
as the blue light emitting materials are not only limited blue also their energy levels are high.
They provide an efficient approach in fine-tuning the emission wavelength on combining with
another dopant emitter in the construction of white OLEDs36. The emission spectra of all the
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compounds showed the one stable emission maxima bands at center around 436-440 nm which
attributed to the electronic transition from lowest unoccupied molecular orbital (LUMO) to the
highest occupied molecular orbital (HOMO) respectively. Supramolecular calix[4]arene azo-
schiff-base ester derivatives exhibited a bathochromic shift in the absorption and emission
maxima. Relative quantum yields were measured in solution as reported earlier36. The quantum
yields of present synthesised compounds are in the range of 0.44-0.56 respectively.
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Table 1: Photophysical properties of the supramolecular mesogens recorded in the THF (5μM)
solution.
Compounds Absorption λabs/nm
(ε/106 L.mol-1 cm-1)
Emission
λem/nm
Stoke shift
nm
Quantum yielda
9a
9b
9c
9d
9e
9f
283, 348 (23.6)
281, 352 (24.2)
280, 351 (24.8)
279, 351 (25.8)
279, 352 (26.2)
279, 354 (27.4)
437
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436
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a: Relative quantum yield calculated with respect to quinine sulphite solution in 0.1 M
H2SO4 with a quantum yield of 0.54.
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Figure 7: Absorption and fluorescence spectra of compound 9a in 5μM different solvents.
Figure 8: Absorption and fluorescence spectra of compounds 9a-9f in 5μM THF solution.
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Figure 9: Absorbance spectra of compound 9a (a); compound 9d (b).
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3. Conclusions
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9
In summary, we have designed and synthesized newly supramolecular azo based 1,3,4-
thiadiazole calix[4] arene derivatives inbuilt with mono substituted and tri-substituted variable
peripheral alkoxy side chain on the lower and the upper rim with schiff-base and ester unit are a
promising class of bowlic shaped columnar liquid crystals with a good thermal stability of
mesophase. These synthesized derivatives are fully characterized and investigated for their
thermal and photophysical behaviour. The thermal behaviour was studied with the help of TGA,
DSC, POM and XRD studies. The self-assemble of building blocks in the design to form an
ordered hexagonal columnar phase with good thermal range of mesophase. The studies on
photophysical properties revealed that these supramolecular derivatives exhibited good
fluorescence properties. These all synthesised calix[4]arene derivatives show blue light emission
in the solution. The length of the side spacer alkyl chain had no effect on the absorption and
emission properties but it fluctuated the intensity of absorption and emission. The present
research suggested that not only the bowl-shaped liquid crystal of calix[4]arene derivatives could
be prepared by substitution on lower and upper rim, but also its enhanced by substitution of
various 1,3,4-thiadiazole derivatives to achieved the stable columnar hexagonal phase, which
allowed a approach to design and synthesis of newly fluorescent supramolecular liquid
crystalline derivatives of calix[4]arene and also it will be of great attention to the scientific
community working in the area of supramolecular columnar liquid crystal.
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Acknowledgments
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VS acknowledge thanks to Department of Chemistry, Faculty of Basic and Applied Science,
Madhav University for providing lab facility. AP is thankful to the University Grants
Commission, New Delhi, India for providing financial support under the MANF (Maulana Azad
National Fellowship). Authors are also thankful to NFDD Centre for providing analytical and
spectral services. Authors thanks to Sunil Patel (Department of Chemistry, Gujarat University)
for helping fruitful discussion in high temperature XRD analysis.
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Graphical Abstract
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