Facile synthesis, X-ray diffraction studies, photophysical properties and DFT-D based conformational analysis of octa and dodecacyanomethoxycalix[4]resorcinarenes

Article abstract of DOI:10.1016/j.molstruc.2020.128215

This paper reports the synthesis of two new supramolecules, Phenyl(octacyanomethoxy)calix[4]resorcinarene (3a) and 4-Cyanomethoxyphenyl(octacyanomethoxy)calix[4]resorcinarene (3b) by alkylating the hydroxyl groups present in Phenylcalix[4]resorcinarene an

Full text of DOI:10.1016/j.molstruc.2020.128215

Journal Pre-proof
Facile synthesis, X-ray diffraction studies, photophysical properties and DFT-D based
conformational analysis of octa and dodecacyanomethoxy-calix [4]resorcinarenes
A.M. Shebitha, S.S. Sreejith, P.B. Sherly Mole, Nithya Mohan, G. Avudaiappan, K.
Hiba, K.S. Priya, K. Sreekumar
PII:
S0022-2860(20)30540-8
DOI:
https://doi.org/10.1016/j.molstruc.2020.128215
MOLSTR 128215
Reference:
To appear in: Journal of Molecular Structure
Received Date: 24 December 2019
Revised Date: 25 March 2020
Accepted Date: 7 April 2020
Please cite this article as: A.M. Shebitha, S.S. Sreejith, P.B. Sherly Mole, N. Mohan, G. Avudaiappan, K.
Hiba, K.S. Priya, K. Sreekumar, Facile synthesis, X-ray diffraction studies, photophysical properties and
DFT-D based conformational analysis of octa and dodecacyanomethoxy-calix [4]resorcinarenes, Journal
of Molecular Structure (2020), doi: https://doi.org/10.1016/j.molstruc.2020.128215.
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Facile Synthesis, X-ray Diffraction Studies, Photophysical Properties and
DFT-D Based Conformational Analysis of Octa and Dodecacyanomethoxy-
calix[4]resorcinarenes
a
b
a,
c
a
A. M. Shebitha , S. S. Sreejith , P. B Sherly mole , Nithya Mohan , G.
a
a
a
a,

Avudaiappan , K. Hiba , K. S. Priya , K. Sreekumar
a
Department of Applied Chemistry, Cochin University of Science and Technology, Kochi 682022, Kerala, India
Department of Chemical Science, Indian Institute of Science Education and Research, Kolkata
Department of Applied Science, Model Engineering College, Thrikkakara, Cochin- 682021, Kerala, India
b
c
*
Corresponding author
Email: K. Sreekumar – kskpolymer.cusat@gmail.com
Credit Author Statement
A. M. Shebitha – Conceptualization, Investigation, Writing - Original Draft
S. S. Sreejith - Formal analysis
P. B Sherly mole - Resources
Nithya Mohan- Resources, Formal analysis
G. Avudaiappan - Resources
K. Hiba - Formal analysis
K. S. Priya - Resources
K. Sreekumar - Corresponding author

Facile Synthesis, X-ray Diffraction Studies, Photophysical Properties and
DFT-D Based Conformational Analysis of Octa and Dodecacyanomethoxy-
calix[4]resorcinarenes
a
b
a,
c
a
A. M. Shebitha , S. S. Sreejith , P. B Sherly mole , Nithya Mohan , G.
a
a
a
a,

Avudaiappan , K. Hiba , K. S. Priya , K. Sreekumar
a
Department of Applied Chemistry, Cochin University of Science and Technology, Kochi 682022, Kerala, India
Department of Chemical Science, Indian Institute of Science Education and Research, Kolkata
Department of Applied Science, Model Engineering College, Thrikkakara, Cochin- 682021, Kerala, India
b
c
*
Corresponding author
Email: K. Sreekumar – kskpolymer.cusat@gmail.com
Graphical Abstract

Facile Synthesis, X-ray Diffraction Studies, Photophysical Properties and
DFT-D Based Conformational Analysis of Octa and Dodecacyanomethoxy-
calix[4]resorcinarenes
a
b
a,
c
a
A. M. Shebitha , S. S. Sreejith , P. B Sherly mole , Nithya Mohan , G.
a
a
a
a, �
Avudaiappan , K. Hiba , K. S. Priya , K. Sreekumar
a
Department of Applied Chemistry, Cochin University of Science and Technology, Kochi 682022, Kerala, India
Department of Chemical Science, Indian Institute of Science Education and Research, Kolkata
Department of Applied Science, Model Engineering College, Thrikkakara, Cochin- 682021, Kerala, India
b
c
*
Corresponding author
Email: K. Sreekumar – kskpolymer.cusat@gmail.com
Abstract
This paper reports the synthesis of two new supramolecules,
Phenyl(octacyanomethoxy)calix[4]resorcinarene (3a) and 4-Cyanomethoxyphenyl-
octacyanomethoxy)calix[4]resorcinarene (3b) by alkylating the hydroxyl groups present in
(
Phenylcalix[4]resorcinarene and 4-Hydroxyphenylcalix[4]resorcinarene respectively. Full O-
alkylation was done at room temperature by simple stirring. The X-ray diffraction studies,
were done to get the crystal-packing arrangements of alkylated resorcinarene derivatives.
Absorption and emission spectra of the compounds were recorded in different organic
solvents and both exhibited negative solvatochromism with the polarity of solvents.
Molecular geometry optimization, vibrational wave numbers and frontier molecular orbitals
were calculated by dispersion corrected DFT-D method using hybrid density functional
�
B97X-D and the split-valence double-zeta basis set 6-31G(d). DFT-D studies revealed that
the synthesized supramolecules existed in two different conformers, chair (C ) and Boat
2
h
(
C ). Boat (C ) conformer had more stability than the chair (C ) conformer. HOMO-
2V 2v 2h
LUMO energies were calculated to explain the kinetic stability of the compounds, found that
Phenyl(octacyanomethoxy)calix[4]resorcinarene has more kinetic stability.
Keywords: Calix[4]resorcinarene; O-alkylation; X-ray diffraction studies; Solvatochromism;
DFT-D studies; HOMO-LUMO energy.

1
. Introduction
Resorcinarenes are multifunctional molecules with prodigious potential [1,2]. The special
interest for these types of macromolecules comes from the varied and easy manipulation of
the frame-work. Chemical modifications change the shape of the concave cavity and open the
possibility of making receptor molecules, which are platforms for molecular recognition
phenomena [3–5]. The three dimensional orientation adopted through modification enhances
the formation of self-assembled molecular capsules [6]. Configuration of the substituents
promotes functions such as solubility, catalytic activity and sensing [7–10].
Resorcinarenes are readily accessible platforms for designing new supramolecular
architecture via surface functionalization [1]. Alkylated resorcinarenes represent an active
area of research because of their supramolecular properties. Discrete techniques are available
in the literature for complete and selective O-alkylation of hydroxyl groups present in the
frame-work. However, most of the reported methods are time consuming, reported low yield
because of the difficulties in exhaustive functionalization of all the hydroxyl groups and
required refluxing condition for product formation [11–14]. Resorcinarene macrocycles can
undergo conformational interconversion and the chemical modifications may influence the
stability of conformers [15–17]. For unfunctionalized and lower rim functionalized
resorcinarenes, usually, the crown isomer is thermodynamically more stable, the case is
different for O-alkylated resorcinarenes [18,19].
In the present work, full O-alkylation was done at room temperature by simply
stirring the precursor with alkylating reagent chloroacetonitrile in dry DMF using mild base
catalyst K CO and the co-solvent PEG-400, which has high solubilization potential. Mild
2
3
reaction conditions and simple work up procedure with good yield (70-75 %) are the
highlights of the new protocol. In addition, photophysical properties of synthesised
architectures were studied and solvatochromic behaviour was explained. Currently, only a
few literature reports are available on the solvatochromic behaviour of calix[4]arenes [20–
2
2]. Furthermore, single-crystal X-ray diffraction studies were used to explain the crystal-
packing arrangements of these resorcinarene derivatives. Since the conventional KS-DFT
Kohn–Sham density functional theory) techniques fail to describe the long-range van der
(
Waals (dispersion) interactions present in the supramolecules, the DFT-D (density functional
theory with empirical dispersion corrections) calculations were used to predict the preferred
conformational arrangement, energy, thermodynamic properties and stability of the system,

which may be greatly affected by alkylation [23–25]. They have structural similarity with the
previously reported macrocycles having nitrile groups in the periphery. Thus they can act as
macrocyclic ligands for selective extraction of ions and molecules.
2
2
. Experimental Section
.1 Materials and physical measurements
Resorcinol, Benzaldehyde, 4-Hydroxybenzaldehyde and Chloroacetonitrile were purchased
from Spectrochem Pvt. Ltd, and used as received. Other chemicals used were of reagent
grade.
Mass spectra of the synthesized compounds were taken on WATERS 3100 Mass Detector
using Electro - Spray Ionization technique. The IR spectra of the compounds were recorded
-1 1
on JASCO FT-IR-4100 spectrometer using KBr pellets in the range of 4000–400 cm . H
1
3
and C NMR spectra of the compounds were recorded on Bruker AMX Advanced III 400
MHz FT – NMR spectrophotometer in DMSO using TMS as internal standard (STIC, SAIF,
CUSAT). The electronic spectra of the compounds were recorded on Thermo Scientific
Evolution 201 UV–Visible spectrophotometer. Emission spectra were taken at the excitation
wave length 480 nm, using Horiba Fluorolog-3 Spectrofluorimeter.
2
.2 X-ray crystallography
Single-crystal analysis of the compound 3a was performed from STIC, SAIF, CUSAT on a
Bruker SMART APEX diffractometer, equipped with a graphite crystal incident-beam
monochromator, and a fine focus sealed tube with Mo Kα (λ = 0.71073 Å) as the X-ray
source. Data collection was performed at 293(2) K and data acquisition and integration were
done using Bruker SMART and Bruker SAINT software [26] with absorption corrections
carried out using SADABS based on Laue symmetry using equivalent reflections [27]. The
structure was solved by direct methods and refined by full-matrix least-square calculations
with the SHELXL-2016 software [28] in the WINGX software package [29]. The structural
images were generated using DIAMOND version 3.2 k [30] and ORTEP-3 for windows [29]
softwares.
In the compound 3b, the distance between carbon atom and nitrogen atom in the nitrile group
were restrained to possess same values using SADI instruction. SIMU instruction was given

to the disordered nitrile group and adjacent carbon atoms in the compound and also to
disordered components of the lattice methanol (C39, C39′, O7, O7′) and DMF (C40, C41,
N7, C42, O8) molecules to restrain anisotropic displacement parameters. The oxygen–carbon
distances in the lattice solvent molecules were restrained using DFIX instruction with a
distance restraint of
O–C = 1.20 ± 0.02 Å for DMF and 1.36 ± 0.02 Å for methanol.
Similarly, DFIX instruction was used to restrain the nitrogen–carbon distances (1.42± 0.02
Å) for DMF and some reflections were omitted.
2
.3. Computational Procedure
Theoretical studies of the newly synthesised supramolecules were carried out using
Dispersion-corrected Density Functional Theory (DFT-D) method [23–25,31]. The long-
range corrected (LC) hybrid density functional � B97X-D and the split-valence double-zeta
basis set 6-31G(d) were employed for geometry optimization [25,32,33]. The nature of
optimized molecular geometries on the potential energy surface was characterized by
frequency calculation. Vibrational frequencies computed at � B97X-D/6-31G(d) level have
no imaginary frequency which confirmed a minimum on the potential energy surface. All
these calculations were executed using the computational package, Gaussian 09 [34] and
analysed using ChemCraft.
2
2
.4. Synthesis
.4.1. Procedure used for the synthesis of Calix[4]resorcinarenes
To a 50 ml round bottom flask, resorcinol (5 mmol), ethanol (4 mL) and p-TsOH (5 mol% of
resorcinol) were added. The mixture was stirred until homogeneous and to this, the
corresponding aldehyde (5mmol) was added. Stirring was continued and after 1h, the solid
product formed was washed with cold methanol – water mixture (1:1v/v). The product
1
13
obtained was characterized by Mass spectroscopy, FT-IR, H NMR and C NMR. The
results were in good agreement with the reported data.
Compound 2a: Phenylcalix[4]resorcinarene (RES) - Pale yellow powder; Yield: 85%;
1
MP: > 350 � ; m/z: 791.26 [M]‾; H-NMR (400 MHz, DMSO-d ) δ ppm: 8.49 – 8.59 (m, 8H,
6
ArOH), 6.63- 6.88 (m, 12H, ArH), 6.61 – 6.62 (m, 8H, ArH), 6.35 – 6.36 (m, 4H, ArCH),
1
3
6
.13 – 6.14 (m, 4H, ArH), 5.54 & 5.57 (s, 4H, ArCHAr); C-NMR (100 MHz, DMSO-d )
6
δ ppm: 42.09, 101.61, 120.61, 121.00, 124.37, 126.91, 127.12, 127.23, 128.52, 128.86,
44.16, 145.63, 152.48, 152.68: IR (KBr) ῡ: 3470 (br), 3028 (w), 2928 (w), 1618 (vs), 1427
1
-1
(
s), 1194(s), 701 (s) cm .

Compound 2b: 4-Hydroxyphenylcalix[4]resorcinarene (RESOH) – Pink powder; Yield:
1
9
0%; MP: > 250 � ; m/z: 891.25 [M+K]‾; H-NMR (400 MHz, DMSO-d ) δ ppm: 8.71 (s,
6
4
H, ArOH), 8.51(s, 4H, ArOH), 8.40 (d, 4H, ArOH), 6.34 – 6.64 (m, 16H, ArCH), 6.31 (d,
H, ArH), 6.29(s, 2H, ArH), 6.09 (d, 2H, ArH), 5.92 (s, 2H, ArCH), 5.43 and 5.53 (s, 2H,
2
1
3
ArCHAr);
C-NMR (100 MHz, DMSO-d ) δ ppm: 41.18, 101.56, 101.72,
6
1
1
02.01, 113.82, 120.78, 121.84, 128.47, 129.48, 129.74, 131.53, 134.39, 135.91, 152.22,
52.26, 152.54, 154.18, 154.35; IR (KBr) ῡ: 3369 (br), 3028 (w), 2908 (w), 1618 (vs), 1517
-1
(s), 1241 (s), 1075(s), 826(s),550 (s) cm
2
.4.2. Procedure used for the synthesis of Octa and Dodecacyanomethoxycalix[4]
resorcinarenes
Compound 2a/2b (0.6 mmol), chloroacetonitrile (15 mmol), potassium carbonate (8 mmol),
and 5mL of polyethylene glycol 400 were mixed in dry DMF. The mixture was stirred at
room temperature for 4 – 5h. The filtrate was added to 0.01N aqueous HCl (500 mL)
solution; precipitate obtained was washed with distilled water up to neutral pH. The
purification was done by flash column chromatography on silica gel using ethyl acetate:
methanol (9:1v/v) solvent. The product obtained was characterized by Mass spectroscopy,
1
13
FT-IR, H NMR and C NMR.
Compound 3a: Phenyl(octacyanomethoxy)calix[4]resorcinarene (RESCN) - Straw coloured
1
powder; Yield 72-75%; m/z: 1139.31 [M+K]‾; H-NMR (400 MHz, DMSO-d ) δ ppm: 6.9 -
6
7
.05 (br, 16H, ArH), 6.55 - 6.62 (m, 8H, ArH), 6.36 (m, 2H, ArH), 6.05, 5.64 - 5.66 (m, 2H,
1
3
ArH), 5.50 - 5.61(m, 4H, ArCH), 4.88 – 5.11(br, 16H, -OCH -CN); C-NMR (100 MHz,
2
DMSO-d ) δ ppm: 54.11, 54.42, 60.15, 69.74, 72.25, 116.14, 125.47, 127.90, 128.42, 152.85;
6
IR (KBr) ῡ: 3415 (m), 3027 (m), 2925 (s), 2260 (sh), 1606 (vs), 1500 (vs), 1291 (vs), 1102
-
1
(
s), 1038 (s), 896 (w), 701 (s) cm .
Compound 3b: 4-Cyanomethoxyphenyl(octacyanomethoxy)calix[4]resorcinarene
RESOHCN) Straw coloured powder; Yield 75-80%; m/z: 1359.29 [M+K]‾ ; H-NMR (400
MHz, DMSO-d ) δ ppm: 7.04 (s, 8H, ArH), 6.96 (s, 8H, ArH), 6.69 - 6.71 (m, 2H, ArH), 6.15
1
1
(
-
6
–
6.53 (m, 4H, ArH), 5.14 (s, 2H, ArH), 5.61-5.62 (m, 4H, ArCH), 4.92 – 5.16 (m, 24H,
1
3
-
OCH -CN); C-NMR (100 MHz, DMSO-d ) δ ppm: 41.52, 53.31, 54.46, 69.73, 99.9,
2
6
1
1
2
00.01, 100.05, 114.23, 116.17, 116.41, 116.52, 125.54, 126.05, 126.48, 129.01, 134.64,
35.45, 152.48, 152.73, 152.90, 154.55, 154,66; IR (KBr) ῡ: 3433(m), 3055 (sh), 2977 (m),
-1
300(sh), 1600 (s), 1508 (vs), 1286 (s), 1042 (vs), 821 (m), 677 (w) m .

3
3
. Results and Discussion
.1. Synthesis
The precursors used for the synthesis of cyanomethoxy derivatives were
calix[4]resorcinarenes with eight and twelve hydroxyl groups, such as
phenylcalix[4]resorcinarene (2a) and
In 200l, Robert et al. have reported p-TsOH catalysed solvent less synthesis of resorcinarenes
35]. Here, precursor synthesis was carried out using 5 mol% of the catalyst, para-
4-hydroxyphenylcalix[4]resorcinarene (2b).
[
Toluenesulphonic acid (p-TsOH) in ethanol by simply stirring at room temperature for 1h as
shown in Scheme 1. Practical difficulty in mixing and grinding the reactants in mortar and
pestle by using toxic p-TsOH and the product loss due to difficulties in transferring small
quantities of glassy products, can be overcome by using small quantity of the solvent. The
workup procedure was reduced to simple filtration.
The calix[4] resorcinarenes synthesised using aryl aldehyde were obtained as mixtures
of stereomers and their ratio changed with the nature of the aldehyde and the reaction
time [16,36]. The use of p-TsOH as catalyst in ethanol, and the use of substituted aldehyde
1
favoured the chair isomer as the major product [37]. On examining the HNMR spectra of
RES (2a) and RESOH (2b), it was concluded that, the products were isomeric mixtures of C4v
(
crown) and C (chair), with C (chair) as the dominant stereomer. The integration ratio of
2h 2h
1
H-NMR signals at 5.43 ppm and 5.53 ppm for ArCHAr protons in RESOH was 0.51:1.0 and
it was 0.45:0.95 for RES, which indicated that the conformers, C /C were in the ratio 1:2.
4
v
2h
To attain full O-Alkylation, the compound 2a/2b was stirred with the alkylating
reagent chloroacetonitrile in the presence of K CO in dry DMF at room temperature which
2
3
resulted in straw coloured products 3a and 3b in good yield. The reaction used for the
1
synthesis is shown in Scheme 2. The products were characterized by Mass spectroscopy, H
1
3
and C NMR spectroscopy, FT-IR and single crystal structural analysis. Due to the presence
1
of too many protons in different chemical environments, the signals of H –NMR spectrum
overlapped heavily. For 3a, the broad peak at 4.88 – 5.11 ppm was from sixteen protons of
eight methylene groups and peak at 5.50 - 5.61 ppm was of four bridging methine protons. It
was difficult to predict the actual structure of the synthesised macrocycles from these broad
1
peaks of the H –NMR spectra.

O
HO
OH
HO
OH
+
P-TsoH
Ethanol, RT
4
R1
R
1
1
1
a : R = H
b : R = OH;
2
2a : R
2b : R = p-OHC H
6 4
1 6 5
= C H
1
Scheme 1: Synthesis of Compound 2a and 2b
HO
OH
OCH CN
NCCH O
2
2
ClCH CN, K CO
3
2
2
PEG-400, RT, 4h
4
4
R1
a : R = C H
6 5
R2
2
3
2
2
1
3
a : R = C H
2 6 5
b : R = p-OHC H
1
6
4
3b : R = p-(CNCH O)C H
2 2 6 4
Scheme 2: Synthesis of Compound 3a and 3b
3
.2. Crystal structure
Single crystal X – ray analysis gives direct structural insight by considering the intra and inter
molecular interactions present in the compounds, which are responsible for the various
properties of the compounds. Crystals of 3b suitable for single crystal analysis were grown
from a saturated solution of 3b in DMF-Methanol (95:5 v/v) by slow evaporation technique at
room temperature. Crystals of 3a, developed in this manner were microcrystalline powders,
not suitable for X-ray analysis.
ꢀ
The compound 3b crystallized in a triclinic P1 space group (Figure-1). The asymmetric unit
contained one half of the compound along with a lattice DMF molecule and methanol solvent
molecule. The resorcinarene core was in a chair conformation and had a C symmetry. In the
2
h
structure, there was a C rotational axis of symmetry passing across the cavity of the
2
molecule. The shortest centroid-centroid distance between the opposite rings in the
resorcinarene core was about 5.69 Å and the longest being 7.89 Å with angles between them
being 178.81° and 174.24° respectively (Figure 1).
The compound contained three types of intramolecular non-classical hydrogen bonding
interactions, with O and N as acceptor atoms. In the “non-classical” hydrogen bonds
(
NCHBs), less electronegative C–H bonds act as hydrogen bond donors [38–40]. Compound
b has three types of NCHBs with in the molecule, (C(2)–H(2)···N(4) 2.62Å, C(7)–
H(7)···O(6) 2.26Å, C(20)–H(20)···O(4) 2.35 Å) (Figure-2, Table 1). The interaction energy
3
-1
of NCHBs (−0.5 to −3.7 kcal mol ) are much less than the classical hydrogen bonds, in

which polar X-H bonds (X=O, N, F) act as hydrogen bond donors [41,42]. However the
stability of the system was greatly enhanced by the presence of this relatively weak hydrogen
bonds.
Each individual molecule was connected to each other via intermolecular hydrogen bonding
interactions leading to the formation of 1D supramolecular chains along crystallographic ‘a’
axis (Figure-3, C35–H35C···N4). Each of these supramolecular chains was hydrogen bonded
with the lattice solvent molecules on either side (C37–H37B···O8, C40–H40A···N5, C42–
H42···N5)
Figure 1 - Left: ORTEP diagram of the compound 3b along with solvent drawn with 30% ellipsoid
showing the atom labelling. (Disordered components and hydrogen atoms are omitted for clarity); Right:
Distance between opposite aromatic rings in the resorcinarene skeleton adopting a chair conformation;
for clarity, substituent groups in the methine bridges are displayed as R.
T
able 1: Hydrogen bonding interactions present in the compound 3b
D–H···A
Intra)
D–H (Å)
H···A (Å)
D···A (Å)
<D–H···A (°)
(
X-ray
Theory
1.08
X-ray
Theory
2.51
X-ray
3.24
2.72
2.71
Theory X-ray Theory
a
a
C2–H2···N4
C7–H7···O6
0.93
0.98
0.98
2.62
2.26
2.35
3.33
2.73
2.75
124
107
101
131
101
91
1.09
2.46
a
C20–H20···O4
Inter)
1.09
2.50
(
b
c
c
C35–H35C···N4
C37–H37B···O8
0.97
2.62
2.40
2.60
3.42
140
165
126
0.97
0.96
3.34
3.26
C40–H40A···N5

d
C42–H42···N5
0.93
2.24
2.67
107
Equivalent position codes: a = -x, 1-y, 1-z; b = 1+x, y, z; c = -x, 1-y, -z; d = -1+x, y, z.
Figure 2 - Right: Crystal structure showing intramolecular H-bonding interactions of compound 3b;
Left: Optimized structure using ꞷ B97X-D/6-31G(d)level of theory, showing intramolecular H-bonding
interactions of compound 3b.
The presence of both intra and inter molecular nonclassical hydrogen bonding interactions
strengthened the solid-state structure of the compound (Figure-1). The crystallographic data
and structure refinement parameters are reported in Table S1 (Supplementary details). Other
noncovalent interactions present in the solid-state structure of the compound were mainly of
two types as obtained from the single crystal XRD data. These fall under C–H···π and C–
N···π interactions respectively as in Figure-4 and Table S2 (Supplementary details).

Figure 3: Parallel 1D supramolecular chains propagating along crystallographic ‘a’ axis
Figure 4: C–H···π and C–N···π interactions present in the packing diagram.
3
.3. Photophysical properties
The newly synthesized supramolecular architectures, RESCN and RESOHCN were found to
exhibit greenish fluorescence under UV light in the solution state. The photophysical charac-
teristics of RESOHCN and RESCN have been studied in different organic solvents. The
choice of solvents were based on the good solubility of the compounds 3a and 3b,
polarity/dielectric constant of the solvent. The absorption and emission spectra, pictured in
-4
the Figure-S12 and S13 (supplementary details) were recorded at a concentration of 2 x 10
M. The observed hypsochromic shift was not regular with the increase in polarity of solvent,
tabulated in Table-2. However, it could be concluded that, both the newly synthesised
supramolecules exhibited negative solvatochromism due to more stabilization of the
molecular ground state in the polar solvents. Thus, the molecular electronic transitions
presented in the newly synthesised macrocyclic ring systems are n-π* transitions [43]. The
ꢄ
linear variation of the Stokes shift with normalized Reichardt polarity scale (ꢁꢂ ꢅ argue
ꢃ
general type of solute - solvent
interaction [44,45]. However, for both RESCN

and RESOHCN, the solvatochromic plots exhibited slight variation from linearity. It is
illustrated in the Figure-5. This irregular solvatochromic behaviour might be as a result of
cavitand structure of the compounds with intra and intermolecular hydrogen bonds, which
could encapsulate the solvent molecules in their cavity. The non-covalent and non-
conventional interactions between the synthesised supramolecules and the solvent molecules
were also found to have an impact on solvatochromism.
Table-2: Spectroscopic data of compounds 3a and 3b in diꞷ erent organic solvents
-1
-1
-1
ꢄ
ꢃ
a
Solvent
λa (nm)
ν (cm )
λf (nm)
ν (cm )
Stock shift (cm )
ꢂ
a
f
RESCN
RESOHCN
RESCN
RESOHCN
RESCN
RESOHCN
RESCN
RESOHCN
RESCN
RESOHCN
Acetic acid 448
Acetonitrile 446
448
443
449
447
442
22321 22321
22422 22573
22026 22272
22222 22371
22624 22624
540
548
555
554
553
541
544
550
546
550
18519 18484
18248 18382
18018 18182
18051 18315
18083 18182
3802
4174
4008
4207
4541
3837
4191
4090
4056
4442
0.648
0.472
0.444
0.404
0.207
DMSO
DMF
THF
454
450
442
-1
-1
ꢈ
Stock shift: ν (cm )- ν (cm ); ꢆ : Empirical solvent polarity parameter; a-Reference [46–49]
a
f
ꢇ

-1
-1
ꢈ
Figure 5 - Solvatochromic linear plots, ν (cm )-ν (cm ) vs. ꢆ ꢁ(ꢉ, ꢊꢅ (Reichardt); Left – RESCN;
a
f
ꢇ
Right – RESOHCN
3
.4. Theoretical studies
Geometries of all the possible stereomers of cyanomethoxy derivatives were
optimised using dispersion corrected DFT-D method. Dispersion correction is an add-on term
for the treatment of non-covalent interactions. Since dispersion correction contributes to the
force acting on the atoms, geometry optimization with dispersion correction will lead to
better results than without. The commonly used hybrid functional B3LYP[50,51], can not
describe long range electron correlations that are responsible for the dispersion forces. The
hybrid GGA (Generalized gradient approximation) functional, � B97X-D which is able to
describe both short-range and long-range interactions was used. The conformational analysis,
vibrational wave numbers and frontier molecular orbitals were computed using � B97X-D/6-
3
1G(d) level of theory.
O-alkylated resorcinarenes are conformationally flexible and in solid state, they can
adopt crown, boat and chair geometries [13,52]. Thus in geometry optimization, the probable

geometries optimized were crown, chair and boat conformers. In the hydroxyl group
substituted resorcinarene, the cyclic pattern of H-bonds did not exist which resulted in a
conformational change from crown (C ) to boat (C ) [19,53,54]. A similar conclusion was
4
v
2v
made from geometry optimization, for the input crown (C ) geometry, the optimized output
4
v
obtained was boat (C ). Thus the newly synthesised supramolecules, RESCN and
2
V
RESOHCN may exist as a mixture two streomers, boat (C ) and chair (C ). Since H-
2
v
2h
bonding and the steric effects play a crucial role in molecular geometry, the possibility of the
synthesised supramolecules to exist as crown conformer is negligible.
The optimized molecular geometries of synthesised supramolecules are presented in
Figure-4. Theoretically obtained intramolecular nonclassical hydrogen bonding interactions
of compound 3b, visualized using ChemCraft are depicted in Figure-2 and the values are
tabulated in Table-1. The distance between the opposite aromatic rings in the resorcinarene
skeleton (Compound 3b) were marked and angles between them are shown in Figure S14,
Table S3 (supplementary details). Correlating the experimental and theoretical studies, the
results obtained for bond lengths, centroid-centroid distance between the aromatic rings of
the frame- work and the intramolecular H…A distances, in angstrom were in good
agreement. But, certain observable variations were there in the bonding and dihedral angles.
The discrepancy between the experimental and calculated values can be associated to the
state of the matter under study. The theoretical calculations were performed for molecules in
isolated, gaseous state. But in the experimental results the supramolecule under study, was in
the solid state. And the differences reinforced the fact that, the molecular geometry in the
crystalline state is influenced by the collective interactions of different non-covalent
interactions present in the molecule.
-1
Generally, cyanides show a unique intense peak in the region 2280 – 2200 cm .
However, in both theoretical and experimental IR spectra (supplementary details) of the
newly synthesised supramolecules, it was observed that, the intensity of CN stretching
frequency was considerably decreased, this might be the result of electronegative oxygen
atom adjacent to the same carbon as the nitrile group. The shift of νC≡N, can also be attributed
to the H-bonding interactions present in the compound [55]. In the FT-IR spectra, the barely
-1
-1
noticeable peak at 2300 cm and 2260 cm are -C≡N stretching vibrations of RESOHCN and
-1
RESCN respectively. Calculated -C≡N stretching frequencies are at the range of 2400 cm .
The data listed in the Table S4 (supplementary details) showed that the calculated and
experimental vibrational frequencies were in good correlation. Thus it was observed that the

selected density functional and basis set (� B97X-D/6-31G(d)) were suitable for the studied
entities.
a
b
c
d
Figure 6: Optimized geometries of cyanomethoxyresorcinarenes at ꞷ B97X-D/6-31G(d) level of theory;
a – chair (C ) conformer of 3a; b – Boat (C ) conformer of 3a; c – chair (C ) conformer of 3b; d – Boat
2
h
2v
2h
(
C ) conformer of 3b.
2v
3
.5. Stability and HOMO-LUMO Energies
The zero point energy, electronic energy, dipole moment and the thermochemical values at
98.15 K in Hartree, obtained using � B97X-D/6-31G(d) level of theory are presented in the
Table S (supplementary details). The relative stability of the system can be predicted by
2
5
looking in to the electronic energy and thermal enthalpies of the system. For both the
synthesised supramolecular architectures, the boat (C ) conformer was found to be relatively
2
v
more stable than the chair (C ) conformer. The boat conformer remained in solution without
2
h
crystalizing. In the boat conformer all the substituents present at the lower rims of
resorcinarene skeleton were located at the bottom of the boat, this may facilitate more
interaction with solvent molecules. Stability differences between the chair (C ) and boat
2
h
(
C ) conformers were calculated as 7.53 Kcal/mol and 8.79 Kcal/mol for RESCN and
2v
RESOHCN respectively.

Table-3: Theoretically calculated HOMO-LUMO Energies and HOMO-LUMO Gap (∆EHL) in eV
HOMO (eV)
LUMO (eV) HOMO–LUMO
Gap (eV)
Compounds
RESCN (3a)
Conformers
Chair
Boat
Chair
Boat
-7.75
-8.09
-7.96
-8.23
1.29
0.83
0.94
0.40
9.04
8.92
8.90
8.69
RESOHCN (3b)
Figure 7: Schematic diagram for HOMO-LUMO energy levels determined using ꞷ B97X-D/6-31G(d) level
of theory; a: Compound 3b; b: Compound 3b
The thermodynamic and kinetic stability, signifies the synthetic accessibility and the potential
isolability of a molecule [56]. Thermodynamic stability is the relative stability of the
molecule, while the kinetic stability was the stability of the molecule with respect to further

chemical reactions. HOMO-LUMO energy difference has been used to examine the kinetic
stability and chemical reactivity of molecules [57–60]. The HOMO-LUMO energy levels
determined using � B97X-D/6-31G(d) level of theory has been delineated in the Figure-7 and
their values in eV are tabulated in Table-3. By looking in to the HOMO - LUMO energy
differences, it was concluded that, for both the synthesized structures, the chair (C )
2
h
conformer was kinetically more stable than the boat (C ) conformer. Correlating the kinetic
2
V
stability of 3a and 3b, it was observed that the cyanomethoxy derivative 3a was kinetically
more stable and in terms of chemical reactivity, 3b was the most likely candidate.
4
. Conclusions
Two new resorcinarenes with supramolecular architecture, phenyl(octacyanometoxy)calix[4]
resorcinarene and 4-Cyanomethoxyphenyl(octacyanomethoxy)calix[4]resorcinarene were
prepared by full O-alkylation at room temperature. The results of DFT-D calculations
revealed that, the synthesised cayanomethoxy resorcinarene derivatives existed in two
different conformers, chair (C ) and boat (C ), in which boat (C ) conformer had more
2
h
2V
2v
stability. The synthesised compounds were found to be thermodynamically and kinetically
stable. Absorption and emission spectra of the compounds were recorded in different organic
solvents and the negative solvatochromic behaviour with the polarity of solvent indicated the
presence of n-π* electronic transitions. The synthesised supramolecules were interesting
architectures, for further functionalization. The macrocyclic ligands exhibited fluorescence
property in solution under UV light. This was exploited to test the selective binding property
of the synthesised macrocyclic ligands with metal ions and molecules through
spectrofluorimetry. These studies are in progress.
.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest
Acknowledgement

The authors acknowledge Dr. K Babu Varghese, SAIF IIT, Madras and Mr. Mohammed Sadik N. K., Research
Scholar, Applied Chemistry, CUSAT for their timely help. The authors are thankful to STIC, SAIF, CUSAT for
various analysis.
Supplementary data
The three dimensional coordinates of conformers obtained by DFT calculations are given in the supplementary
details. Crystallographic data, CCDC No: 1909210
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Facile Synthesis, X-ray Diffraction Studies, Photophysical Properties and
DFT-D Based Conformational Analysis of Octa and Dodecacyanomethoxy-
calix[4]resorcinarenes
a
b
a,
c
a
A. M. Shebitha , S. S. Sreejith , P. B Sherly mole , Nithya Mohan , G.
a
a
a
a,

Avudaiappan , K. Hiba , K. S. Priya , K. Sreekumar
a
Department of Applied Chemistry, Cochin University of Science and Technology, Kochi 682022, Kerala, India
Department of Chemical Science, Indian Institute of Science Education and Research, Kolkata
Department of Applied Science, Model Engineering College, Thrikkakara, Cochin- 682021, Kerala, India
b
c
*
Corresponding author
Email: K. Sreekumar – kskpolymer.cusat@gmail.com
Highlights
•
Synthesis of two new supramolecules, Phenyl(octacyanomethoxy)calix[4] resorcin-
arene and 4-Cyanomethoxyphenyl(octacyanomethoxy)calix[4] resorcinarene by full
O-alkylation at room temperature.
•
•
•
The X-ray diffraction studies, were done to get the crystal-packing arrangements of
alkylated resorcinarene derivatives.
Absorption and emission spectra of the compounds were recorded in different organic
solvents and both exhibited negative solvatochromism with the polarity of solvents.
Molecular geometry optimization, vibrational wave numbers and frontier molecular
orbitals were calculated by dispersion corrected DFT-D method using hybrid density
functional
B97X-D and the split-valence double-zeta basis set 6-31G(d).
•
HOMO-LUMO energies were calculated to explain the kinetic stability of the
compounds

Declaration of interests
☒
The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐
The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests:
The authors declare that they have no known competing financial interests or personal relationships that
could have appeared to influence the work reported in this paper.