Head-to-Tail interlocking aromatic rings of a hydrazine functionalized Schiff base for the development of Nano-aggregates with blue emission: Structural and spectroscopic characteristics

Article abstract of DOI:10.1016/j.molliq.2021.117193

We report the synthesis, physicochemical and morphological characterisation, supramolecular interactions and aggregation-induced blue emission of a newly developed Schiff base, 1,2-bis(phenyl(pyridin-2-yl)methylene)hydrazine (P18). The compound was synthesised through a condensation reaction between hydrazine and 2-benzoylpyridine under reflux in ethanol. The photophysical behaviour of the Schiff base was studied in both monomeric and aggregated forms. Interestingly, the molecular aggregate showed a significant blue shift with ~ 20 fold higher fluorescence intensity with lifetime, 0.99 ns in the aqueous phase than that of monomeric form, attributed to the development of J-type aggregation. The crystal structure, C–H···π and π…π interactions, were enumerated to decipher the nature of aggregation. The Schiff base consisting of four aromatic rings (two pyridine and two phenyl rings) displayed a short C–H···π and a long distant π···π interactions causing a head-to-tail type interlocking of aromatic rings. Energy framework analysis confirmed the predominance of dispersive forces (-192.4 kJ/mol) to the cluster of molecules, thus playing a significant role in the restriction of intramolecular motion of the aromatic rings of P18. A restrain on the rotational probability of = N–N = and Ar–C– bonds leads to an enhancement of an intense fluorescence property of nano-aggregate with blue light emission in solid state. The propagation of the rectangular-shaped monomeric probe in the nano-aggregate with an average hydrodynamic size of 270(±3) nm was established with field emission scanning electron microscopy, dynamic scattering light, and electron dispersive X-ray spectral analysis.

Full text of DOI:10.1016/j.molliq.2021.117193

Journal of Molecular Liquids ±40 (2021) 11719±
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Head-to-Tail interlocking aromatic rings of a hydrazine functionalized
Schiff base for the development of Nano-aggregates with blue emission:
Structural and spectroscopic characteristics
a
b
b
a,
⇑
Prafullya Kumar Mudi , Ajit Das , Nagendranath Mahata , Bhaskar Biswas
a
Department of Chemistry, University of North Bengal, Darjeeling 734013, India
Department of Chemistry, Sidho-Kanho-Birsha University, Purulia 723104, India
b
a r t i c l e i n f o
a b s t r a c t
Article history:
We report the synthesis, physicochemical and morphological characterisation, supramolecular interac-
tions and aggregation-induced blue emission of a newly developed Schiff base, 1,2-bis(phenyl(pyridin-
Received 2 May 2021
Revised 2 August 2021
Accepted 4 August 2021
Available online 12 August 2021
2-yl)methylene)hydrazine (P18). The compound was synthesised through a condensation reaction
between hydrazine and 2-benzoylpyridine under reflux in ethanol. The photophysical behaviour of the
Schiff base was studied in both monomeric and aggregated forms. Interestingly, the molecular aggregate
showed a significant blue shift with ~ 20 fold higher fluorescence intensity with lifetime, 0.99 ns in the
aqueous phase than that of monomeric form, attributed to the development of J-type aggregation. The
Keywords:
Energy frameworks
Molecular aggregation
Schiff base
Supramolecular interactions
Synthesis
crystal structure, C–HÁÁÁ
The Schiff base consisting of four aromatic rings (two pyridine and two phenyl rings) displayed a short C–
HÁÁÁ and a long distant ÁÁÁ interactions causing a head-to-tail type interlocking of aromatic rings.
p and p. . .p interactions, were enumerated to decipher the nature of aggregation.
p
p p
Energy framework analysis confirmed the predominance of dispersive forces (-192.4 kJ/mol) to the clus-
ter of molecules, thus playing a significant role in the restriction of intramolecular motion of the aromatic
rings of P18. A restrain on the rotational probability of = N–N = and Ar–C– bonds leads to an enhancement
of an intense fluorescence property of nano-aggregate with blue light emission in solid state. The prop-
agation of the rectangular-shaped monomeric probe in the nano-aggregate with an average hydrody-
namic size of 270(±±) nm was established with field emission scanning electron microscopy, dynamic
scattering light, and electron dispersive X-ray spectral analysis.
X-ray structure
Ó 2021 Elsevier B.V. All rights reserved.
1
. Introduction
The advancement of functional luminophores in light-emitting
molecular aggregate [1–±]. The advent of newly developed proper-
ties endowed by molecular aggregates introduces new characteris-
tics and functionalities in the molecular aggregate compared to
single molecules [±,4,7].
and light-harvesting processes shows a great promise in bringing
novel characteristics and properties to the materials [1,2]. The evo-
lution of light-dependent molecular devices and technologies has
triggered a paramount interest to material scientists for the indis-
pensable contribution of molecular devices in scientific and soci-
etal advancement [±]. In this context, molecular aggregation
beyond the microscopic level is a highly fascinating phenomenon
that attributes novel properties to functional materials and the
design of high-tech photo-electronic devices [4–6]. Nowadays,
the aggregation-induced emission (AIE) phenomenon provides an
exciting avenue in scientific research to unveil the properties of
AIE deals with a class of molecules having dim or low emission
properties in dilute solution. However, the compounds display a
pronounced effect on enhancing emission properties in molecular
aggregates [8]. A systematic study by Tang et al. on different AIE
systems summarises that the restriction of active intramolecular
motion in the molecular aggregate limits the excited-state non-
radiative decay. In contrast, dynamic intramolecular motion
increases the non-radiative decay and quenches the molecular
emission [9]. Further, the motion-responsive molecular aggregates
exhibit strong emission properties in solid state, enabling unique
applications in different dimensions, including chemical sensors,
fluorescent imaging, photonic drugs, bio-probes, optoelectronics
and others [4–7,10].
⇑
Corresponding author at: Dept. of Chemistry, University of North Bengal,
Darjeeling 7±401±, India.
E-mail address: bhaskarbiswas@nbu.ac.in (B. Biswas).
https://doi.org/10.1016/j.molliq.2021.11719±
0
167-7±22/Ó 2021 Elsevier B.V. All rights reserved.

P. Kumar Mudi, A. Das, N. Mahata et al.
Journal of Molecular Liquids 340 (2021) 117193
Typically, azines contain aromatic units bridged through rotat-
able N–N bonds and are the highly stable condensation products of
carbonyl compounds and hydrazine [14,15]. Azine compounds
show an excellent promise for their straightforward synthetic
approach, high yield and easy isolation of the products, cost-
effective, high stability to apply for suitable technological applica-
tions and devices [11–1±]. In general, H-type aggregation induces a
non-radiative deactivation process, while the J-type aggregation
imparts a relatively high fluorescence efficiency [16–18].
2.4. Crystal structure determination, refinement and Hirshfeld surface
analysis
The Schiff base’s single crystal X-ray diffraction data were col-
lected on a Rigaku XtaLABmini diffractometer equipped with Mer-
cury ±75R (2 Â 2 bin mode) CCD detector. The data were collected
with graphite monochromated Mo-Ka radiation (k = 0.7107± Å) at
100 K using
x scans. The data were reduced using CrysAlisPro
1.171.±9.±5c [±±], and the space group determination was done
using Olex2. The structure is resolved by the dual space method
using SHELXT-2015 and refined by full-matrix least-squares proce-
dures using the SHELXL-2015 [±4,±5] software package through
the OLEX2 suite [±6]. The Crystal Explorer17.5 [±7] programme
was used to generate Hirshfeld surfaces and 2D fingerprint plots
of the Schiff base. The details of the analysis are reported else-
where [±8,±9].
Intermolecular non-covalent interactions involving aromatic
systems are considered emerging inductors to develop a vast array
of long-range crystalline architectures through crystal engineering
[
19–22]. Different weak forces such as hydrogen bonding,
p
ÁÁÁ
p and
C–HÁÁÁ short contacts in crystalline materials are imperative to
p
design new materials with novel properties [2±,24]. Therefore,
the proper understanding of weak forces allows envisioning the
role of supramolecular assemblies in developing novel functional
properties [25,26]. It is evident that weak intermolecular forces
have a pronounced effect on AIE property and, eventually, may
bring a substantial change in the size and phase of crystalline
materials [27,28]. Herein, we report the design and synthesis of
an azine type Schiff base and explore its aggregation behaviour
with a suite of spectroscopic and crystallographic studies. The
dominant dispersive forces significantly stabilise the cluster of
molecules and mingle the aromatic rings through the head to tail
type interlocking. This phenomenon imposes a strict restriction
on the intramolecular rotation and vibration of aromatic rings in
the Schiff base with the development of blue emission.
2.5. Preparation and characterisation of the molecular aggregate
A stock solution of 1.020 mM P18 was prepared in a DMSO
medium. 20 mL of the DMSO solution of P18 was injected into
mL of Milli-Q-water and kept undisturbed for 10 mins at room
2
temperature. The molecular aggregate of P18 was developed fol-
lowing the drop-casting method and recorded the Field Emission
Scanning Electron Microscope (FESEM) images on a clean alu-
minium foil. FESEM images and the electron dispersive X-ray
(
EDX) plot were recorded with a JSM-6700F FESEM, JEOL, Japan
instrument, which confirmed the nature of molecular aggregate
in the solid state. The dynamic light scattering (DLS) study of the
aggregation study in an aqueous medium was carried out at 25
2
. Experimental
.1. Chemicals, solvents and starting materials
99% pure 2-benzoylpyridine (Aldrich, USA) and > 98% pure
0
C on a Malvern Instrument with Zetasizer Nano ZS90 instrument.
The hydrodynamic size of the P18 was measured by adding 100 lL
of P18 solution to 1.5 mL of water and recorded in triplicate to find
an average number size distribution.
2
>
hydrazine monohydrate (TCI, Japan) were procured from the
respective commercial sources. All the chemicals and solvents
were of spectroscopic grade and used as received.
3
. Results and Discussion
3.1. Synthesis of the Schiff base
2.2. Preparation of Schiff base
The Schiff base was synthesised through the condensation reac-
The Schiff base was prepared following a reported synthetic
tion between hydrazine and 2-benzoyl pyridine in ethanol and
under refluxing conditions for 8 h (Scheme 1). The method of
recrystallisation was employed to develop the single crystals in
methanol. The schematic synthetic route is shown below.
procedure with a little modifications [29–±2]. The Schiff base
was synthesised by refluxing 2-benzoylpyridine (0.±660 g, 2 mmol)
with hydrazine monohydrate (0.050 g, 1 mmol) in ±0 mL ethanol
for 10 h. The reaction solution was filtered and dried. The com-
2
pound was stored in vaccuo over CaCl . Yield: 0.±60 g (~86.50%).
3
.2. Spectroscopic characterisation of P18
Anal. Calc. for C24
H
18
N
4
(P18): C, 79.54; H, 5.01; N, 15.46; Found:
À1
C, 79.58; H, 5.05; N, 15.50. IR (KBr, cm ; Fig. S1): 1624, 1582
Different spectroscopic and analytical methods were used to
1
(m
C=N); H NMR (d ppm, 400 Mz, DMSO d
6
; Fig. S2) d = 8.702–6.6
determine the molecular structure and its structural characteris-
tics. The FT-IR spectrum of the Schiff base showed characteristic
stretching vibrations (Fig. S1) at 1624 and 1582 cm which were
assignable to the azomethine group of the Schiff base. Other peaks
at 1460 and 1±49 cm for P18 attributed to –C = C– groups in the
1
±
1
7 (Ar–H, 18H), C NMR (400 MHz, Fig. S±): 158.±4–121.11;
MALDI TOF MS (m/z, Fig. S4): ±62.48 (Expt.); UV–Vis (kmax, nm;
Fig. S5): 26± (0.4±±), 285 (0.±8±);
À1
À1
2.3. Physical Measurements
Schiff base. These appearances of the characteristic peaks resemble
very well with the previously reported values [40,41].
The infrared spectrum of the compound was recorded with an
6
The NMR spectral analysis of P18 was carried out in DMSO d .
1
1±
FTIR-8400S SHIMADZU spectrophotometer in the range 400–
Figs. S2 and S± displayed the H and C NMR spectra of P18,
respectively. The appearance of the protons signals in the range
8.70 to 6.61 ppm corresponded to the aromatic-H of phenyl and
pyridine rings for P18 (Fig. S2). The characteristic C-signals of
P18 were observed from 159.64 to 121.11 ppm in the 1±C NMR
spectra (Fig. S±) which confirmed the presence of azomethine-C
and aromatic-C atoms. The dense-splitting patterns of the signals
were attributed to the presence of Ar-H and Ar-C in P18 and por-
À1
1
1±
±
600 cm . The H and C NMR spectra of P18 were obtained on
a Bruker Advance 400 MHz spectrometer at 25 °C. The MALDI
TOF mass spectrum of the Schiff base was recorded using a Q-
tof-micro quadruple mass spectrometer. All the ground-state
absorption spectra were recorded on a JASCO V-7±0 UV–Vis spec-
trophotometer, and the fluorescence spectra were measured on a
Hitachi F-7000 spectrofluorometer. Elemental analyses were car-
ried out on a Perkin Elmer 2400 CHN microanalyser.
trayed
a pure signature for the existence of non-covalent
2

P. Kumar Mudi, A. Das, N. Mahata et al.
Journal of Molecular Liquids 340 (2021) 117193
Scheme 1. Preparation method of the Schiff base.
interactions as previously evident from the report of Zhao et al.
42]. The MALDI TOF mass spectrum was also recorded for P18 at
the increase of the concentration of monomeric P18 in the solution
phase.
[
room temperature, which confirmed the presence of molecular
ion peak at m/z ±62.48±7 (Fig. S4). The absence of any other peaks
in the mass spectrum ensures the absence of the impurities in the
solution.
The electronic spectra of P18 were recorded in aqueous and
DMSO media in the 200–900 nm range. The electronic spectrum
of P18 in DMSO showed blue-shifted electronic bands than those
in the aqueous medium. P18 exhibited characteristic absorption
bands at 26± and 285 nm (Fig. S5), attributing the intra-ligand
p–p*/n–p* electronic transitions of the P18 probe. The reported
electronic bands for P18 were in well-agreement with the reported
values [4±].
The steady-state fluorescence spectrum of P18 in an aqueous
medium was also recorded and shown in Fig. S6. The emission
maximum for P18 was observed at ±00 nm with low intensity.
The nature of the fluorescence spectrum suggests its mild fluores-
cence properties in the aqueous medium at room temperature.
3.4. Spectroscopic studies on the P18 aggregate
The insight of the molecular aggregation and the nano-
aggregates’ photophysical properties were investigated in detail.
Fig. S5 showed the comparison of the spectral bands of P18 and
its aggregated form, respectively. It is well observed from Fig. S5
that the absorption spectral profile of P18 aggregates (272 and
±06 nm) is red-shifted compared to the monomeric form of P18
(26± and 285 nm) in the aqueous phase. Literature on molecular
aggregation suggests that a red-shift of the electronic band for a
species commonly happens for the J type of aggregation [17,18].
In this case, an average red-shift of ~ 10–20 nm was noticed for
the absorption bands of the P18 aggregates compared to its mono-
meric form, and this phenomenon is a pure indication for the
development of J aggregates in the aqueous phase.
To consolidate the origin of the red-shift in the aggregated form
of P18 and find out the solvent role, the polarity of the solvent was
varied. The absorbance of P18 was measured in another polar sys-
tem (methanol:water), where the polarity of the solvent mixture
was kept close to that of water:DMSO solvent mixture. The absorp-
tion maxima of P18 in the methanol:water mixture found at
261 nm that was lower than the wavelength maximum (272 nm)
of P18 aggregates. The larger red-shift of the electronic band for
P18 nano-aggregates confirms that the solvent polarity didn’t
induce this red-shift of the electronic band; perhaps the structural
aggregation remains the driving force for the P18 aggregation. The
molecular exciton theory may explain the shifts in the electronic
band of the aggregated forms [44]. By the principle of molecular
exciton theory, a molecule is treated as a point dipole, and the exci-
tonic energy state of the molecular aggregate may be split into two
tiers based on the nature of dipoles [45]. The resultant electronic
transition may proceed through lower or higher energy transitions
leading to J and H type of molecular aggregation. The different
kinds of dipole–dipole interactions within two monomers in the
aggregated form are principally accountable for splitting energy
levels in the molecular aggregates [45].
The molecular exciton theory further suggests that face-to-face
interactions of the transition dipoles for H-aggregates make a shift
of absorption maximum towards the blue region while a head-to-
tail type of orientations for J-aggregates makes a shift in absorption
maximum to the red region. Crystal structure analysis and detailed
study on self-assembly of P18 provide an essential source of light
on this aspect. The excited states of these aggregates are also inves-
tigated with the measurement of steady-state and time-resolved
fluorescence studies. Fig. S6 displays the comparison of the
3
.3. Microscopic analysis of the aggregate of Schiff base
The FESEM images of the aggregated form of P18 (Fig. 1a) were
recorded to study the aggregation properties of the monomeric
form of P18 in the solution phase. The individual particles of the
probe in the aggregated form were distinctly observed in a rectan-
gular shape. FESEM images exhibit a large number of aggregated
islands of the monomeric P18 particles in the solid state. Interest-
ingly, the P18 particles in each of the aggregated islands get
agglomerated with each other in a solid state. Close inspection
on the nature of agglomeration suggests that most of the individual
particles participated in fusion with others using different edges of
the rectangular-shaped particle. It is better to say that a head-to-
tail type of interlocking of individual particles was observed
through the linking of rectangular particles’ edges in the aggre-
gated form. The average size of the individual particles was deter-
mined as ~ 250(±±) nm from the FESEM images. Furthermore, EDX
spectral characterisation with elemental mapping is used to deter-
mine the elemental distribution in the formation of aggregate. EDX
spectrum (Fig. 1b) shows a %elemental distribution of C and N to
the aggregated form. Elemental mapping for P18 (Fig. 1c) further
consolidates the observation noticed in EDX plot of the nano-
aggregates. Moreover, the size of the aggregated form of P18 was
determined with dynamic light scattering (DLS) measurements
(Fig. 2). The DLS plot of P18 in the aqueous phase indicates that
the average particle size of the aggregated form is 270(±±) nm.
The effect of the solution concentration on the aggregation beha-
viour of P18 was also examined. The particle size increased with
±

P. Kumar Mudi, A. Das, N. Mahata et al.
Journal of Molecular Liquids 340 (2021) 117193
Fig. 1. a) FESEM images for the aggregate form of P18; b) Elemental mapping of the molecular aggregate of P18; c) EDX plot showing the distributed % of C and N in the
aggregated form.
its monomeric form. The fluorescence intensity of the P18 nano-
aggregate enhanced by ~ 20 fold in intensity with the emission
of blue light. Therefore, upon aggregation, the mildly fluorescent
monomeric P18 turns out to be highly fluorescent with blue light
Fig. 2. Dynamic light scattering measurement of P18 in the aggregated form in
aqueous médium.
fluorescence spectra of P18 in its monomeric with the aggregated
forms under identical parameter set up.
It is evident from Fig. S5 that upon excitation on 272 nm, the
emission maxima for the P18 nano-aggregate was red-shifted than
Fig. 3. Time-dependent photoluminescence decay profile for P18 in aggregated
form.
4

P. Kumar Mudi, A. Das, N. Mahata et al.
Journal of Molecular Liquids 340 (2021) 117193
emission. The measurement of an average lifetime in the aqueous
phase, estimated as t = 0.99 ns (Fig. ±) further confirmed the highly
emissive characteristics of the nano-aggregate. The excited states
of the nano-aggregate get stabilised upon interlocking of the aro-
matic rings for P18 in the aqueous medium and exhibit intense
blue light emission.
Table 1
Structural refinement parameter of the Schiff base.
Parameters
P18
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
24 18 4
C H N
±62.42
100
Monoclinic
C2/c
3.5. Description of crystal structure and self-assembly
21.6921(9)
5.5760(2)
15.2461(5)
1840.79(12)
4
1.±08
0.079
760
2.7–±2.8
0.0±0
±208
10,872
0.0668, 0.2199
0.58, À0.50
b (Å)
c (Å)
Volume (ű)
Z
The single crystals of P18 were successfully grown in solution to
reveal the nature of weak intermolecular forces in the develop-
ment of nano-aggregate. The crystal structure analysis revealed
that the molecule crystallised in a monoclinic crystal system. The
ball and stick model of the asymmetric unit and molecular struc-
ture of the Schiff base is shown in Fig. 4a and Fig. 4b. The structural
refinement parameter is summarised in Table 1. The bond dis-
tances and bond angles of the compound are presented in
Table S1. The Schiff base crystallised in a nearly planar anti-
stereomer as revealed by the bond angles’ measurement (Fig. 4d,
Table S1). The C6-N2 and N2–N2a bonds correspond to a pure dou-
ble and single bond character, as evident from their bond distance
values, 1.295(±0.0017) Å and 1.±888 (±0.0015) Å, respectively
q
l
(gcm–±)
(mm–1)
F (000)
h ranges (°)
R(int)
Number of unique reflections
Total number of reflections
Final R indices
Largest peak and hole (e Aꢀ- ±)
phenyl centroids exhibited short-ranged C–HÁÁÁ
p
interactions in
the crystalline phase (Table S2) [46,47].
(
Tables S1).
The packing diagram of the Schiff base showed edge to face type
orientations of the asymmetric units along the b axis (Fig. S7).
3.6. Hirshfeld surface and energy framework analysis
There is no considerable intermolecular H-bonding in the self-
assembled structure. However, long distant
p
. . .
p
and short-
The Hirshfeld surface analysis was further carried out to under-
stand the role of intermolecular interactions, as illustrated in Fig-
ure S8. The surface volume and surface area of P18 were
calculated as 451.84 Å and 411.11 Å , with asphericity and glob-
ularity indices evaluated as 0.094 and 0.69±, respectively. The
intermolecular interactions of P18 are also manifested in terms
ranged C–H. . . interactions play a significant role in forming
p
self-assembled crystalline architecture. Interaction mapping over
the molecule further suggests the high propensity of the hydropho-
bic interaction (Fig. 4C). In the structure of P18, four aromatic rings
±
2
(
two pyridine and two phenyl rings) are connected to imine-Cs
through N–N single bonds in this molecule. Close inspection on
the supramolecular framework (Fig. 5) suggests that the pyridine
of two dimensional fingerprint plots between d
The highly influential C–HÁÁÁ interaction contributes nearly
±1.5% of total Hirshfeld surface coverage having a nearly sharp
e i
and d (Fig. S9).
p
centroids stacked through a weaker
pÁÁÁp interactions, while the
Fig. 4. Displacement ellipsoid representation of the molecule: (a) Asymmetric unit of the Schiff base; (b) Ball and stick model of the compound; (c) Interaction propensity of
the molecule; (d) Planarity of the asymmetric unit.
5

P. Kumar Mudi, A. Das, N. Mahata et al.
Journal of Molecular Liquids 340 (2021) 117193
Fig. 5. Development of long-range crystalline architecture of P18 mediated by C–HÁÁÁ
p and pÁÁÁp interactions.
tooth in fingerprint plots which indicates the strength of interac-
tion. The interaction has only about ±% of Hirshfeld surface
ÁÁÁ
The energy framework analysis is computed on Crystal Explorer
21.2 software (Turner et al., 2017, Mackenzie et al., 2017) with
HF/±-21G basis sets using TONTO software for the cluster environ-
ment of ±.8 Å surrounding a particular molecule of interest. The
p
p
coverage, and the bright blue spot on fingerprint plot represents
the strength of the interaction. The absence of any sharp tooth
from fingerprint plots indicates the lack of any strong hydrogen
bonding interactions in the molecule, i.e. less contribution from
the Coulumb energy parameter in total energy expression. One
centroid of an electron-deficient pyridyl moiety attracts two
C À H protons of electron-dense benzene ring forming C–H(dono
total interaction energy is articulated as
E
tot
=
ele
k -
´
´
´
´
disp + krep rep, where the k values belong to
Eele + kpolEpol + kdisp
E
E
´
the scale factors for benchmarked energy models. Eele represents
´
the electrostatic energy, Epol represents the polarisation energy,
´ ´
Edisp represents the dispersion energy, and Erep represents the
r)ÁÁÁ
p
(acceptor) interaction where electron density of electron-
repulsive energy (Table S4). To identify the type of interaction
energies developed due to supramolecular interactions, we set
the tube dimension factor ±00 where a greater tube radius is
directly proportional with stronger and more prominent interac-
tion. From Fig. 6 it is clearly evident that the contribution of disper-
sive forces in total interaction energy is maximum over coulomb
energy. These short-ranged dispersive forces account for isoener-
deficient pyridyl moiety is increased to some extent over the other
electron-deficient pyridyl ring (oriented in head-to-tail fashion)
which bears a single C–H(donor)ÁÁÁ
p(acceptor) interaction. The C–
and interactions are the only interactions involved in
HÁÁÁ
p
pÁÁÁp
developing long-range supramolecular crystal architecture. The
percentage share of individual elements with other elements for
crystalline architecture is presented in Table S±.
getic and isotropic C–HÁÁÁ
p
and
pÁÁÁp interactions, thus playing a
6

P. Kumar Mudi, A. Das, N. Mahata et al.
Journal of Molecular Liquids 340 (2021) 117193
Fig. 6. (a) Energy framework diagram, (b) total energy plot, (c) coulomb energy contribution plot, and (d) dispersive energy contribution plot mapped for P18 along b-axis.
significant role in aggregation behaviour of P18. The predominance
of dispersive forces is justified by the greater inner dimension of
green cylinders than red cylinders between the same molecules.
The total dispersive energy involved in the cluster of molecules is
estimated to be À192.4 kJ/mol.
It is a well-established fact that the charge transfer of
anti-bonding orbital of C–H bond principally account for the origin
of C–HÁÁÁ interactions [58,59]. Nishio et al., surveyed the C–HÁÁÁ
interactions for 6-membered -electronic systems varying the
positions of hydrogen atoms on a -plane [57] (Scheme 2), where
pln, Dlin and Datm define the HÁÁÁ (plane), HÁÁÁ(C line) and HÁÁÁC
distances, respectively. The dihedral angles between the -plane
and HC angle (X = C,O, etc.) are represented
as
HÁÁÁ
h < 60°, |
for region 2; Datm < Dmax, h < 60°,50°</ < 90° for region ± (/ = HC
p-e to the
p
p
p
p
D
p
1
C
2
1
p
1
C
2
plane as \HXC
1
3.7. Structural perspectives and underlying mechanism for AIE
x
p
and h, respectively. This model was applied by considering
distances shorter than a cut-off Dmax value and Dpln < Dmax,
property of the Schiff base
x
|<90° for region 1; Dlin < Dmax, h < 60°, 90°<|
x
|<1±0°
I).
To decipher the role of weak forces for the assembled polarised
or non-polarised aromatic molecules in supramolecular organic
frameworks, we explored the propensity of dispersive energy for
1
This method is advantageous to validate the C–HÁÁÁAr contacts,
and it is revealed that higher acidic-H will give rise to shorter mean
intermolecular C–HÁÁÁ
p
and
p p interactions in the clusterisation
ÁÁÁ
values of HÁÁÁ
smaller values. They obtained the mean H. . .
aromatic- C–HÁÁÁ aromatic interaction as 2.76 ± 0.10 Å for a
2,282 number of CHÁÁÁAr contacts [57]. Previously, Alvarez
reported an interesting work for intermolecular contacts showing
p
distances and the Dpln, and Datm will also produce
of P18. Interesting, Martinez et al. [48] attributed a valuable insight
for the driving force in the association of polarised/non-polarised
aromatic molecules through different proposals based on experi-
mental observations and theoretical calculations such as the
p
distance for
p
±
polar/
interactions [50,51], propensity of heteroaromatic
and a large contact surface of -electrons [5±]. The synthetic Schiff
p
model [49], alternating e-rich and e-deficient aromatic-
p
p-systems [52]
p
base contains flat and robust type phenyl and pyridine rings with a
relatively large contact surface that might enable the dispersion
force-induced stabilisation of the molecular aggregate as proposed
by Martinez et al. [52]. However, flexible conformation with
twisted orientations of aromatic rings facilitates the steric hin-
drance among the neighbouring aromatic rings, leading to a long
distant face-to-face aromatic interaction [54]. It is scientifically
evident that considerable intermolecular C–H. . .p interactions, also
known as edge-to-face [55], T-shaped [56], can stabilise the crystal
packing through restricted rotational orientations of the aromatic
rings and make a pronounced effect on the molecular properties.
Nishio and co-workers envisioned a significant effort to obtain
valuable insights into the nature of C–HÁÁÁ
p interactions [21,57].
Scheme 2. C–HÁÁÁ
nearest and second nearest sp -C to H,
h is \HXC ; b) Region: Reg1, H is above on
out of the aromatic ring but may interact with
p
surveying model; a) O is the centre of the plane, C
1
and C
and \HC
-aromatic, Reg2 and Reg± indicates H is
-electrons.
2
They reported that orientations of aromatic rings causing C–HÁÁÁ
p
2
x
is the dihedral angle, \C
p
1
OC
2
1 2
C ,
interactions have a significant contribution in molecular packing
and self-assembly.
1
p
7

P. Kumar Mudi, A. Das, N. Mahata et al.
Journal of Molecular Liquids 340 (2021) 117193
distance distribution maps between an element and a probe ele-
ment, X, mostly oxygen [60]. The author summarised that most
elements reserve a different distance in the distribution and pro-
vide a clear depiction between bonded and non-bonded atom pairs
hydrogen bonding in crystalline phase. Hirshfeld surface analysis
suggests that highly influential C–HÁÁÁ
p interaction contributed
nearly ±1.5% while long-distant interactions have only about
pÁÁÁp
±% of total Hirshfeld surface coverage. The total dispersive energy
[
60]. We also attempted to validate and examine the propensity of
interactions for P18 and tetraphenylethene (TPE) following
involved in the cluster of molecules is manifested in terms of C–
C–HÁÁÁ
p
HÁÁÁ interactions and estimated to be À192.4 kJ/mol to the stabil-
p
the method of Nishio et al. The measurement of Dpln, Dlin, h and
x
isation of aggregate. The nano-cluster of the probe in the aggre-
gated form displayed the development of intensively emissive
blue light. The beautiful rectangular-shaped particles of an average
hydrodynamic size of 270(±±) nm propagate through the head-to-
was well corroborated between P18 and TPE (Table S5).
Furthermore, the underlying principle of the AIE properties for
this Schiff base was unveiled by comparing the structural charac-
teristics of a widely studied tetraphenylethene (TPE) which exhib-
ited a pronounced AIE phenomenon with the synthetic P18. TPE is
a nearly planar non-emissive molecule (Fig. S10) in solution
because the excited-state energy of TPE dissipates through the
free-rotations of the four phenyl rings attached to ethylene-C
tail type interlocking of aromatic rings mediated with short C–HÁÁÁ
p
and long interactions enables a restriction to the intramolec-
pÁÁÁp
ular motion of the probe leading to nano-clusters in the solid state.
Therefore, exploitation of spectroscopic, photophysical and crystal
engineering perspectives on this molecular aggregation phe-
nomenon will undoubtedly throw some new structural insights
to understand the role of intermolecular interactions (specially
[
2,61,62]. However, intermolecular interactions restrict the
intramolecular movement of the phenyl rings in the aggregated
state and enable them to emit bright light [2,61,62]. It is well
established that TPE locked the phenyl rings in aggregated form
based on restriction of intramolecular rotation (RIR) and vibrations
C–HÁÁÁ
p associations) for the formation of molecular aggregates.
We deeply believe that suitable adaptation of the azine chro-
mophore of this molecule may envision new supramolecular
organic frameworks (SOF) with intriguing AIE properties and may
act as a probe of great promise for designing optoelectronic devices
and green energy harvesting phenomenon.
(
RIV), leading to an intriguing turn-on of fluorescence properties in
molecular aggregates [61,62]. The X-ray crystal structure of TPE
was previously reported by Hoekstra et al. [6±], and we down-
loaded the deposited CIF from Cambridge Structural Database
(
CCDC 1275289) to compare structural features and C–HÁÁÁ
bution in the construction of supramolecular frameworks. Fig. S10
a,b,c,d) displayed a combination of crystal structure, structure
p contri-
CRediT authorship contribution statement
(
Prafullya Kumar Mudi: Conceptualization, Formal analysis,
Methodology, Investigation. Ajit Das: Formal analysis, Methodol-
ogy, Investigation. Nagendranath Mahata: Formal analysis, Visu-
alization. Bhaskar Biswas: Conceptualization, Writing – review &
editing, Supervision.
with selected bond distances and angles and interaction mapping
of TPE which displayed close structural characteristics of P18. Fur-
ther, TPE showed two different short-ranged C–HÁÁÁ
p
interactions
(
(
2.76 Å & 2.91 Å) while P18 showed one short C–HÁÁÁ
p interactions
p interactions (Fig. S11).
2.94 Å) with one distant (±.18 Å) C–HÁÁÁ
Both the compounds exist in nearly planar structures and exhib-
ited a similar propensity for hydrophobic interactions (Fig. S10-b,
c,d).
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
We also considered a previously reported azine compound, sal-
icylaldehyde azine (SAA), comparing AIE properties with P18. Typ-
ically, SAA adopts complete planarity due to its strong
intramolecular hydrogen bonding interaction; however, the com-
plete planarity of P18 molecule cannot be achieved without any
intramolecular H-bonding. SAA exhibits excited-state intramolecu-
lar proton transfer (ESIPT) and AIE characteristics [64,65]. AIE and
ESIPT processes are entirely different, although both are mutually
compatible to turn on the fluorescence property of the molecules.
The AIE property stems from RIR and RIM characteristics leading to
emission enhancement, while ESIPT facilitated by excited-state
proton transfer and consequent causing of significant Stokes shift
with bright emission. In contrast to SAA, the synthetic P18 mole-
Acknowledgement
The authors gratefully acknowledge the hona’ble Editor and the
learned reviewers for providing useful comments and guidance to
improve this work. BB sincerely thanks Science and Engineering
Research Board (SERB), India, for financial support under the
EMPOWERMENT & EQUITY OPPORTUNITIES FOR EXCELLENCE IN
SCIENCE (EEQ/2020/000079).
Appendix A. Supplementary material
cule displayed predominance short C–HÁÁÁ
p interactions. Therefore,
based on a spectroscopic, photophysical and detailed study on self-
assembly, energy framework analysis, it is recommended that
interlocking of head-to-tail type of aromatic rings through domi-
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.molliq.2021.11719±.
nant C–HÁÁÁ
p short contacts lead to the nano-dimension aggrega-
tion with intense blue light emission.
References
[
1] C. Zhu, R.T.K. Kwok, J.W.Y. Lam, B.Z. Tang, Aggregation-Induced Emission: A
Trailblazing Journey to the Field of Biomedicine, ACS Appl 1768 Bio Mater. 1
(
2018), https://doi.org/10.1021/acsabm.8b00600.
4
. Conclusions
[
2] Y. Chen, J.W.Y. Lam, R.T.K. Kwok, B. Liu, B.Z. Tang, Aggregation-induced
emission: fundamental understanding and future developments, Mater. Horiz.
6 (±) (2019) 428–4±±, https://doi.org/10.10±9/C8MH01±±1D.
Herein, we studied the aggregation characteristics of a newly
designed azine type Schiff base with a suite of spectroscopic, pho-
tophysical, and crystallographic methods. The nearly planar struc-
ture of the probe was established with single crystal X-ray
diffraction analysis and different spectroscopic methods. Interest-
ing, supramolecular frameworks of the compound adopted long
[±] Z. Zhao, H. Zhang, J.W.Y. Lam, B.Z. Tang, Aggregation-Induced Emission: New
Vistas at the Aggregate Level, Angew. Chem. Int. Ed. 59 (25) (2020) 9888–9907,
https://doi.org/10.1002/anie.v59.2510.1002/anie.201916729.
[
4] Y. Huang, J. Xing, Q. Gong, L.C. Chen, G. Liu, C. Yao, Z. Wang, H.L. Zhang, Z. Chen,
Q. Zhang, Reducing aggregation caused quenching effect through co-assembly
of PAH, chromophores and molecular barriers, Nat. Commun. 10 (2019) 169,
https://doi.org/10.10±8/s41467-018-08092-y.
distant
p
. . .
p
interactions and short C–HÁÁÁ
p interactions
[
5] D. Liu, K. Sun, G. Zhao, J. Wei, J. Duan, M. Xia, W. Jiang, Y. Sun, Spatial
separation of a TADF sensitizer and fluorescent emitter with a core-dendron
(
>2.92 Å) beyond vdW limit without considerable intermolecular
8

P. Kumar Mudi, A. Das, N. Mahata et al.
Journal of Molecular Liquids 340 (2021) 117193
system to block the energy loss in deep blue organic light-emitting diodes, J.
[28] Xinhua Huang, Young-Il Jeong, Byeong Kyu Moon, Lidong Zhang, Dae Hwan
Kang, Il Kim, Self-Assembly of Morphology-Tunable Architectures from
Tetraarylmethane Derivatives for Targeted Drug Delivery, Langmuir 29 (10)
(201±) ±22±–±2±±, https://doi.org/10.1021/la±05069e.
[29] Subrata Das, Amrita Sahu, Mayank Joshi, Suvendu Paul, Madhusudan Shit,
Angshuman Roy Choudhury, Bhaskar Biswas, Ligand-Centered Radical Activity
by a Zinc-Schiff-Base Complex towards Catechol Oxidation ChemistrySelect. ±
(±8) (2018) 10774–10781, https://doi.org/10.1002/slct.201801084.
[±0] Prafullya Kumar Mudi, Nilaj Bandopadhyay, Mayank Joshi, Madhusudan Shit,
Suvendu Paul, Angshuman Roy Choudhury, Bhaskar Biswas, Schiff base
triggering synthesis of copper(II) complex and its catalytic fate towards
mimics of phenoxazinone synthase activity, Inorg. Chim. Acta. 505 (2020)
119468, https://doi.org/10.1016/j.ica.2020.119468.
[±1] Suvojit Roy, Provakar Paul, Monaj Karar, Mayank Joshi, Suvendu Paul,
Angshuman Roy Choudhury, Bhaskar Biswas, Cascade detection of fluoride
and bisulphate ions by newly developed hydrazine functionalised Schiff
bases, J. Mol. Liq. ±26 (2021) 11529±, https://doi.org/10.1016/
j.molliq.2021.11529±.
[±2] Shreya Mahato, Nishith Meheta, Muddukrishnaiah Kotakonda, Mayank Joshi,
Prasanta Ghosh, Madhusudan Shit, Angshuman Roy Choudhury, Bhaskar
Biswas, Ligand directed synthesis of a unprecedented tetragonalbipyramidal
copper (II) complex and its antibacterial activity and catalytic role in oxidative
dimerisation of 2-aminophenol, Appl. Organomet. Chem. ±4 (11) (2020),
https://doi.org/10.1002/aoc.v±4.1110.1002/aoc.59±5.
Mater. Chem.
C9TC0±±±4C.
7
(±5) (2019) 11005–1101±, https://doi.org/10.10±9/
[
6] O.D. Parashchuk, A.A. Mannanov, V.G. Konstantinov, D.I. Dominskiy, N.M.
Surin, O.V. Borshchev, S.A. Ponomarenko, M.S. Pshenichnikov, D.Y. Paraschuk,
Molecular Self-doping controls Luminescence of pure organic single crystals,
Adv. Funct. Mater. 28 (21) (2018) 1800116, https://doi.org/10.1002/adfm.
v28.2110.1002/adfm.201800116.
[
7] S. Kagatikar, D. Sunil, Aggregation-induced emission of azines: An up-to-date
review,
J
Mol. Liq. 292 (2019) 111±71, https://doi.org/10.1016/
j.molliq.2019.111±71.
[
8] J. Luo, Z. Xie, J.W.Y. Lam, L. Cheng, H. Chen, C. Qiu, H.S. Kwok, X. Zhan, Y. Liu, D.
Zhu, B.Z. Tang, Aggregation-induced emission of 1-methyl-1,2,±,4,5-
pentaphenylsilole, Chem. Commun. (2001) 1740–1741, https://doi.org/
1
0.10±9/B105159H.
[
9] J. Chen, C.C.W. Law, J.W.Y. Lam, Y. Dong, S.M.F. Lo, I.D. Williams, D. Zhu, B.Z.
Tang, Synthesis, Light Emission, Nanoaggregation, and Restricted
Intramolecular Rotation of 1,1-Substituted 2,±,4,5-Tetraphenylsiloles, Chem.
Mater. 15 (7) (200±) 15±5–1546, https://doi.org/10.1021/cm021715z.
10] Z. Zhao, X. Zheng, L. Du, Y. Xiong, W. He, X. Gao, C. Li, Y. Liu, B. Xu, J. Zhang, F.
Song, Y. Yu, X. Zhao, Y. Cai, X. He, R.T.K. Kwok, J.W.Y. Lam, X. Huang, D. Lee
Phillips, H. Wang, B.Z. Tang, Nat. Commun. 10 (2019) 2952, https://doi.org/
[
[
1
0.10±8/s41467-019-10818-5.
11] G. Yu, S. Yin, Y. Liu, J. Chen, X. Xu, X. Sun, D. Ma, X. Zhan, Q. Peng, Z. Shuai, B.
Tang, D. Zhu, W. Fang, Y.i. Luo, Structures, Electronic States,
Photoluminescence, and Carrier Transport Properties of 1,1-Disubstituted
[±±] CrysAlisPro 1.171.±9.±5c, (2017) Rigaku Oxford Diffraction, Rigaku
Corporation: Tokyo, Japan.
2
,±,4,5-Tetraphenylsiloles, J. Am. Chem. Soc. 127 (17) (2005) 6±±5–6±46,
[±4] G.M. Sheldrick, SHELXT- Integrated space-group and crystal-structure
determination Acta. Cryst, Acta Cryst A71 (2015) ±–8.
https://doi.org/10.1021/ja044628b10.1021/ja044628b.
s00110.1021/ja044628b.s00210.1021/ja044628b.s00±.
[±5] George M. Sheldrick, Crystal structurere finement with SHELXL, Acta Cryst.
C71 (1) (2015) ±–8.
[±6] Oleg V. Dolomanov, Luc J. Bourhis, Richard J. Gildea, Judith A.K. Howard, Horst
Puschmann, OLEX2: a complete structure solution, refinement and analysis
program, J. Appl. Cryst. 42 (2) (2009) ±±9–±41, https://doi.org/10.1107/
S0021889808042726.
[
12] Z. Li, Y. Dong, B. Mi, Y. Tang, M. Häussler, H. Tong, Y. Dong, J.W.Y. Lam, Y. Ren,
H.H.Y. Sung, K.S. Wong, P. Gao, I.D. Williams, H.S. Kwok, B.Z. Tang, Structural
Control of the Photoluminescence of Silole Regioisomers and Their Utility as
Sensitive Regiodiscriminating Chemosensors and Efficient Electroluminescent
Materials, J. Phys. Chem. B 109 (20) (2005) 10061–10066, https://doi.org/
1
0.1021/jp050±46210.1021/jp050±462.s001.
[±7] M.J. Turner, J.J. McKinnon, S.K. Wolff, D.J. Grimwood, P.R. Spackman, D.
Jayatilaka, M.A. Spackman, Crystal Explorer, (2017), http://hirshfeldsurface.
net17.
[
1±] C.-W. Chang, C.J. Bhongale, C.-S. Lee, W.-K. Huang, C.-S. Hsu, E.-G. Diau,
Relaxation Dynamics and Structural Characterization of Organic Nanobelts
with Aggregation-Induced Emission, J. Phys. Chem. C 116 (28) (2012) 15146–
[±8] Mark A. Spackman, Dylan Jayatilaka, Hirshfeld Surface Analysis. Cryst. Eng.
Comm. 11 (1) (2009) 19–±2, https://doi.org/10.10±9/B818±±0A.
[±9] M.A. Spackman, J.J. McKinnon, Crys.t Eng. Comm. 4 (2002) ±78.
[40] S. Pal, B. Chowdhury, M. Patra, M. Maji, B. Biswas, Ligand centered radical
pathway in catechol oxidase activity with a trinuclear zinc-based model:
Synthesis, structural characterization and luminescence properties,
Spectrochim, Acta Part A: Mol. Biomol. Spectros. 144 (2015) 148–154,
https://doi.org/10.1016/j.saa.2015.02.046.
1
5154, https://doi.org/10.1021/jp±04117n.
[
[
[
[
14] H.-H. Fang, J. Yang, R. Ding, J. Feng, Q.-D. Chen, H.-B. Sun, Top down fabrication
of organic nanocrystals by femtosecond laser induced transfer method, J. Am.
Chem. Soc. 14 (14) (2012) 4596, https://doi.org/10.10±9/c2ce06579g.
15] S.A. Jenekhe, J.A. Osaheni, Excimers and Exciplexes of Conjugated Polymers,
Science
1
265
(517±)
(1994)
765–768,
https://doi.org/
0.1126/science:265.517±.765.
16] R.H. Friend, R.W. Gymer, A.B. Holmes, J.H. Burroughes, R.N. Marks, C. Taliani, D.
D.C. Bradley, M. Lo, W.R. Salaneck, D.A.D. Santos, J.L. Bre, Nature ±97 (1999)
[41] D. Dey, G. Kaur, M. Patra, A.R. Choudhury, N. Kole, B. Biswas, A perfectly linear
trinuclear zinc–Schiff base complex: Synthesis, luminescence property and
photocatalytic activity of zinc oxide nanoparticle, Inorg. Chim. Acta. 421
(2014) ±±5–±41, https://doi.org/10.1016/j.ica.2014.06.014.
[42] Jiang Zhao, Zhao Feng, Daokun Zhong, Xiaolong Yang, Yong Wu, Guijiang Zhou,
Zhaoxin Wu, Cyclometalated Platinum Complexes with Aggregation-Induced
Phosphorescence Emission Behavior and Highly Efficient Electroluminescent
Ability, Chem. Mater. ±0 (±) (2018) 929–946, https://doi.org/10.1021/acs.
chemmater.7b0470810.1021/acs.chemmater.7b04708.s00110.1021/acs.
chemmater.7b04708.s002.
[4±] Chanchal Kumar Pal, Shreya Mahato, Mayank Joshi, Suvendu Paul, Angshuman
Roy Choudhury, Bhaskar Biswas, Transesterification Activity by a Zinc(II)-
Schiff Base Complex with Theoretical Interpretation, Inorg. Chim. Acta. 506
(2020) 119541, https://doi.org/10.1016/j.ica.2020.119541.
[44] R. Wang, C. Hao, P. Li, N.G. Wei, J. Chen, J. Qiu, Clusters, J. Comput. Chem. ±1
(2010) 2157–216±.
1
2±–128.
17] D. Oelkrug, A. Tompert, H.-J. Egelhaaf, M. Hanack, E. Steinhuber, M. Hohloch, H.
Meier, U. Stalmach, Towards highly luminescent phenylene vinylene films,
Synth. Met. 8± (±) (1996) 2±1–2±7, https://doi.org/10.1016/S0±79-6779(96)
0
4484-0.
[
[
[
18] B.-K. An, J. Gierschner, S.Y. Park,
p-Conjugated cyanostilbene derivatives: a
unique self-assembly motif for molecular nanostructures with enhanced
emission and transport, Acc. Chem. Res. 45 (4) (2012) 544–554, https://doi.
org/10.1021/ar2001952.
19] R. Taylor, O. Kennard, Crystallographic evidence for the existence of CH.
cntdot.cntdot.cntdot.O, CH.cntdot.cntdot.cntdot.N and CH.cntdot.cntdot.
cntdot.Cl hydrogen bonds, J. Am. Chem. Soc. 104 (19) (1982) 506±–5070,
https://doi.org/10.1021/ja00±8±a012.
20] G.R. Desiraju, Hydrogen Bridges in Crystal Engineering: Interactions without
Borders Acc, Chem. Res. ±5 (2002) 565–57±, https://doi.org/10.1021/
ar010054t.
[45] (a) M. Kasha, H.R. Rawls, M.A. El-Bayoumi, The exciton model in molecular
spectroscopy, Pure Appl. Chem. 11 (1965) ±71–±92, https://doi.org/
10.1±51/pac1965110±0±71. (b) A. Datta, S.K. Pati, Dipole orientation effects
on nonlinear optical properties of organic molecular aggregates J. Chem. Phys.
118 (200±) 8420, https://doi.org/10.106±/1.1565±20
[
[
21] M. Nishio, CH/
p hydrogen bonds in crystals, Cryst. Eng. Comm. 6 (2004) 1±0–
58, B±1±104A.
1
22] S. Mukherjee, S. Roy, S. Mukherjee, B. Biswas, Oxidative dimerisation of 2-
aminophenol by a copper(II) complex: Synthesis, non-covalent interactions
and bio-mimics of phenoxazinone synthase activity, J. Mol. Struct. 1217 (2020)
[46] P.K. Mudi, S. Pradhan, A. Sahu, D. Saha, B. Biswas, Synthesis, X-Ray Structure
and Evaluation of Bactericidal Activity of an O-Vanillin Functionalized Schiff
1
28±48, https://doi.org/10.1016/j.molstruc.2020.128±48.
Base, J. Appl. Microbiol. Theory & Technology 2 (2021) 18–28, https://
[
2±] G.R. Desiraju, Crystal engineering: solid state supramolecular synthesis, Curr
Opin Solid State Mater Sci. 2 (4) (1997) 451–454, https://doi.org/10.1016/
S1±59-0286(97)80088-5.
ojs.wiserpub.com/ index.php/ AMTT/article/view/719.
[47] M. Karar, P. Paul, B. Biswas, T. Majumdar, A. Mallick, Excitation wavelength as
logic operator, J. Chem. Phys. 152 (2020), https://doi.org/10.106±/1.5142045
075102.
[48] C.R. Martinez, B.L. Iversion, Rethinking the term ‘‘pi-stacking”, Chem. Sci. ±
(2012) 2191–2201, https://doi.org/10.10±9/C2SC20045G.
[49] C.A. Hunter, Aromatic Interactions in Proteins, DNA and Synthetic Receptors
Philos, Trans. R. Soc. London, Ser. A ±45 (199±) 77–85.
[50] S. Nepogodiev, J. Stoddart, Cyclodextrin-Based Catenanes and Rotaxanes,
Chem. Rev. 98 (1998) 1959–1976, https://doi.org/10.1021/cr970049w.
[51] J.J. Reczek, K.R. Villazor, V. Lynch, T.M. Swager, B.L. Iverson, Tunable Columnar
[
24] B. Chowdhury, M. Karar, S. Paul, M. Joshi, A.R. Choudhury, B. Biswas, Salen
Type Ligand as a Selective and Sensitive Nickel(II) ion Chemosensor: A
Combined Investigation with Experimental and Theoretical Modelling, Sens.
Actuators, B 276 (2018) 560–566, https://doi.org/10.1016/j.snb.2018.08.141.
25] S. Alvarez, A cartography of the van der Waals territories, Dalton Trans. 42 (24)
[
[
(
201±) 8617, https://doi.org/10.10±9/c±dt50599e.
26] D. Dey, A. Basu Roy, C.-Y. Shen, H.-L. Tsai, A. Ranjani, L. Gayathri, S.
Chandraleka, D. Dhanasekaran, M.A. Akbarsha, N. Kole, B. Biswas, Synthesis
and bio-catalytic activity of isostructural cobalt(III)-phenanthroline
complexes, J. Chem. Sci 127 (2015) 649–661, https://doi.org/10.1007/
s120±9-015-0817-y.
Mesophases Utilizing C
2
Symmetric Aromatic DonorÀAcceptor Complexes, J.
Am. Chem. Soc. 128 (2006) 7995–8002, https://doi.org/10.1021/ja061649s.
[52] I.E. Craven, M.R. Hesling, D.R. Laver, P.B. Lukins, G.L.D. Ritchie, J. Vrbancich,
Polarizability anisotropy, magnetic anisotropy, and quadrupole moment of
cyclohexane, J. Phys. Chem. 9± (1989) 627–6±1, https://doi.org/10.1021/
j100±±9a026.
[
27] B. Olenyuk, J.A. Whiteford, A. Fechtenkotter, P.J. Stang, Self-assembly of
nanoscale cuboctahedra by coordination chemistry, Nature ±98 (1999) 796–
7
99.
9

P. Kumar Mudi, A. Das, N. Mahata et al.
Journal of Molecular Liquids 340 (2021) 117193
[
5±] J.C. Ma, D.A. Dougherty, The CationÀ
p
Interaction, Chem. Rev. 97 (1997) 1±0±–
[59] M.-F. Fan, Z. Lin, J.E. McGrady, D.M.P. Mingos, J. Chem. Soc. Perkin Trans. 2
(1996) 56±.
1
±24, https://doi.org/10.1021/cr960±744.
[
54] J. Chen, C.C.W. Law, J.W.Y. Lam, Y. Dong, S.M.F. Lo, I.D. Williams, D. Zhu, B.Z.
Tang, Synthesis, light emission, nanoaggregation, and restricted
intramolecular rotation of 1,1-substituted 2,±,4,5-tetraphenylsiloles, Chem.
Mater. 15 (200±) 15±5–1546, https://doi.org/10.1021/cm021715z.
[60] S. Alvarez, Dalton Trans. 42 (201±) 8617–86±6.
[61] N.L.C. Leung, N. Xie, W. Yuan, Y. Liu, Q. Wu, Q. Peng, Q. Miao, J.W.Y. Lam, B.Z.
Tang, Chem. Eur. J. 20 (2014) 1–6.
[62] J. Shi, N. Chang, C. Li, J. Mei, C. Deng, X. Luo, Z. Liu, Z. Bo, Y.Q. Dong, T.B. Zhong,
Locking the phenyl rings of tetraphenylethene step by step: understanding the
mechanism of aggregation-induced emission, Chem. Commun. 48 (2012)
10675–10677, https://doi.org/10.10±9/C2CC±5641D.
[6±] A. Hoekstra, A. Vos, Acta Crystallographica, Section B:Struct. Crystallogr. Cryst.
Chem. ±1 (1975) 1716.
[64] J.E. Kwon, S.Y. Park, Advanced organic optoelectronic materials: harnessing
excited-state intramolecular proton transfer (ESIPT) process, Adv. Mater. 2±
(2011) ±615–±642, https://doi.org/10.1002/adma.201102046.
[65] Z. Xie, B. Yang, G. Cheng, L. Liu, F. He, F. Shen, Y. Ma, Cross Dipole Stacking in
the Crystal of Distyrylbenzene Derivative: The Approach toward High Solid
StateLuminescence Efficiency, Chem. Mater. 17 (2005) 1287–1289, https://doi.
org/10.1021/ja054661d.
[
55] A.V. Muehldorf, D. van Engen, J.C. Warner, A.D. Hamilton, Aromatic-aromatic
interactions in molecular recognition: a family of artificial receptors for
thymine that shows both face-to-face and edge-to-face orientations, J. Am.
Chem. Soc. 110 (1988) 6561–6562, https://doi.org/10.1021/ja00227a045.
56] J. Pawliszyn, M.M. Szczesniak, S. Scheiner, Interactions between aromatic
systems: dimers of benzene and s-tetrazine, J. Phys. Chem. 88 (1984) 1726–
[
[
[
1
7±0, https://doi.org/10.1021/j15065±a01±.
57] Y. Umezawa, S. Tsuboyama, K. Honda, M. Nisho, Bull, CH/
p
Interaction in the
Crystal Structure of Organic Compounds: A Database Study, Bull. Chem. Soc.
Jpn. 71 (1998) 1207–121±, https://doi.org/10.1246/bcsj.71.1207.
58] T. Takagi, A. Tanaka, S. Matsuo, H. Maezaki, M. Tani, H. Fujiwara, Y. Sasaki,
Computational studies on CH/
p interactions, J. Chem. Soc. Perkin Trans. 2
(
1987) 1015, https://doi.org/10.10±9/P29870001015.
10