Crystallographic Elucidation of Stimuli-Controlled Molecular Rotation for a Reversible Sol-Gel Transformation

Article abstract of DOI:10.1021/acs.joc.9b02944

To get an idea about the most probable microporous supramolecular environment in the gel state, gelator molecule 1 has been crystallized from its gelling solvent (dimethylformamide). Crystal structure analysis of 1 shows a strong ?···πstacking interaction between the electron-deficient pentafluorophenyl ring and electron-rich naphthyl ring. The gelling solvent situated in the "molecular pocket" stitches the gelators through weak H-bonding interactions to facilitate the formation of an organogel. Scanning electron microscopy analysis exhibits a ribbonlike fibrous morphology that resembles the supramolecular arrangement of 1 in its crystalline state, as evidenced by powder X-ray diffraction. In the presence of external stimuli (tetrabutylammonium fluoride), the organogel of 1 disassembles into sol. This sol-gel transformation phenomenon has been explained on the basis of X-ray single-crystal analysis. Single crystals obtained from the sol state show that naphthylic-OH of 1 gets deprotonated, resulting in C-C bond rotation that plays a major role in the sol-gel transformation. Gelator 1 exhibits weak green fluorescence in the gel state, whereas it shows highly intense yellow fluorescence in the sol state. Furthermore, a reversible sol-gel transformation associated with changes in the spectroscopic properties has been observed in the presence of acids and fluoride ions, respectively.

Full text of DOI:10.1021/acs.joc.9b02944

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Article
A Crystallographic Elucidation of Stimuli Controlled
Molecular Rotation for Reversible Sol-Gel Transformation
Mehebub Ali Khan, Soumen Ghosh, Sachinath Bera, Anamika Hoque,
Ismail Sk, Shagufi Naz Ansari, Shaikh M. Mobin, and Md. Akhtarul Alam
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b02944 • Publication Date (Web): 20 Feb 2020
Downloaded from pubs.acs.org on February 23, 2020
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A Crystallographic Elucidation of Stimuli Controlled
Molecular Rotation for Reversible Sol-Gel Transformation
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Mehebub Ali Khan, Soumen Ghosh, * Sachinath Bera, Anamika Hoque, Ismail Sk,
§
§
†
Shagufi Naz Ansari, Shaikh M. Mobin, * Md. Akhtarul Alam *
†Department of Chemistry, Aliah University, Action Area IIA/27, New Town, Kolkata-700160, India
*
*
E-mail: soumen0003@gmail.com
E-mail: alam_iitg@yahoo.com
‡Department of Chemistry, Jadavpur University, 188, Raja S.C. Mallick Rd, Kolkata – 700032, India
§
Discipline of Chemistry, IIT Indore, Indore-453552, India
* E-mail: xray@iiti.ac.in
TOC
Supporting Information Placeholder
ABSTRACT: To get an idea about the most probable microporous supramolecular environment in the gel state, the
gelator molecule has been crystallized from it’s gelling
solvent (DMF). Crystal structure analysis of 1 shows a strong
… stacking interaction between the electron deficient penta-
1

fluorophenyl ring and electron rich naphthyl ring. The gelling
solvent situated in the ‘molecular pocket’, stitch the gelators
through weak H-bonding interactions to facilitate the formation
of organogel. SEM analysis exhibits ribbon-like fibrous
morphology which resemblances the supramolecular arrangement of
1 in its crystalline state as evidence by PXRD. In presence of
external stimuli (TBAF), the organogel of 1 disassemble into
sol. This sol-gel transformation phenomenon has been explained on the basis of x-ray single crystal analysis.
Single Crystal obtained from sol state shows that naphthylic –OH of 1 gets deprotonated, resulting in C-C bond
rotation which plays a major role in sol-gel transformation. Gelator 1 exhibits a weak green emission in the
gel state whereas it shows highly intense yellow emission in the sol state. Furthermore a reversible sol-gel
transformation associated with the changes in the spectroscopic properties has been observed in presence of
acid and fluoride ion respectively.
INTRODUCTION
in the fields of sensors, drug delivery, biomedicine
and pharmaceutical Among various
chemistry.1-7
external stimuli (such as light, pH, cations, anions
etc), anions are of particular interest because of
Stimuli
assisted
modification
of
the
physical/chemical properties of low molecular weight
geletors (LMWG) have attracted great interests to the
scientific community due to their wide applications
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their importance in chemical, biological and
environmental processes.8-13
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To realize the physical as well as chemical
properties of gel, it is important to understand the
supramolecular interactions present in the gel state.
In this context, powder X-ray diffraction is one of
the widely accepted method.14-15 However, during the
recording of X-ray powder diffraction (XRPD) data of
gel the solvent molecule gets evaporated which may
spoils the quality of data because of scattering
Scheme 1. Schematic representation for reversible sol-
gel transformation through C–C single bond rotation of
the gelator (1).
1
6
contribution. Therefore, in most of the cases XRPD
measurement is conducted with the xerogel to predict
the probable supramolecuar interactions present in
the gel. On the other hand, single crystal structure
of the gelator molecule in solid state can also
provide valuable information about the supramolecular
interactions present in gel phase. In this
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RESULTS AND DISCUSSION
Amido-Schiff base (1) and two control compounds (2
and 3) have been synthesized (Figure 1 and Scheme S1)
and characterized by 1H, 13C NMR, IR spectroscopy and
HRMS (ESI-TOF) (Figure S1-S9).
connection,
available showing the single crystal structure of the
gelator molecules, containing supramolecular
a
handful of literature reports are
interactions among themselves and also with the
16
gelling solvents. However, most of them did not try
to make analogy of the gel state morphology with the
single crystal structural analysis.17-19
Figure 1. Structure of amido-Schiff base 1 and
control compounds 2 and 3.
Sol-gel transition phenomenon has been emerged as
a
promising research area for designing smart
materials having various potential applications.2-4 So
far, direct evidences of structural changes as well
as modification in supramolecular interactions of the
molecules during sol-gel transition are rare.
Among the above Schiff bases, only 1 has been
obtained as single crystal from DMF-ether medium. The
single crystal X-ray crystallographic studies reveal
that 1 crystallizes as monoclinic system with space
group P21/c (Table S1). The crystal structure of 1
shows that the 1-hydroxy-naphthalene moiety and the
Recently, Watanabe et al.
and Giuseppone et al.
independently reported controlled sol-gel transitions
of supramoleculer polymer.9,20 However, they also did
not provide any the direct evidence for structural
changes of the molecule during sol-gel transition.
2
,3,4,5,6-penta fluorobenzene moiety are almost in
the same plane having dihedral angle of 0.52(Figure
2a, Figures S10-S11). The amide C=O is hydrogen
bonded with –OH (hydroxyl group of naphthalene
Herein, we have reported an amido-Schiff base
(E)-3-hydroxy-N'-((perfluorophenyl)methylene)-2-
rich
(
naphthohydrazide) containing an electron
moiety) through
a
six member ring (O1….H1O2,
distance: 2.581Å), as a result the naphthalene moiety
and rest of the molecular unit make an angle of
fluorophore unit and an electron deficient aromatic
moiety as low molecular weight gelator (1). Gelator 1
is weakly green fluorescent in gel state, however,
upon addition of external stimuli (tetrbutylammonium
1
44.86 to create
a
“molecular pocket” which
accommodates the gelling solvent (DMF) as guest
molecule (Figure 3). The DMF molecule is attached
through H–bonding between –C=O of DMF and amide –NH
of 1(C21–O3….H3–N3, distance: 2.883Å) and also by
several weak C–H...O interactions (Figure 2b, Table
S2).
fluoride, TBAF) it turns into
a
highly yellow
fluorescent sol. The change in the fluorescence
property as well as sol-gel transition of 1 has been
elaborately explained by spectroscopic and X-ray
crystallographic study of
solvent and in presence of external stimuli TBAF.
Furthermore, reversible sol-gel transformation
1
containing gelling
a
associated with the reversal of its physical
+
properties has been observed in presence of H and
TBAF respectively (Scheme 1).
To the best of our knowledge, structural changes
of a gelator molecule during sol-gel transition have
not been supported by X-ray single crystal analysis
till now. In this connection the present work is the
first report which explains the sol-gel transition
through C-C bond rotation on the basis of X-ray
single crystal analysis.
Figure 2. (a) Single crystal structure of the
geletor molecule 1, (b) … interactions
between the gelator molecules and H-bonding
interactions between getalor molecules and DMF
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FT-IR spectra of 1 in solid state show sharp bands
at 1646, 3256 and a broad band 3129 cm– belonging to
C=O, O–H and N–H groups respectively. While in the
gel of 1 all the aforesaid three peaks are merged
with the solvent peak. Therefore FT-IR spectral
analysis is unable to explain the structural changes
as well as supramolecular interactions of 1 in the
gel state (Figure S19).
1
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Figure 3. Molecular pocket in 1 (left) and DMF
molecule attach with the molecular pocket in 1
The lattice diagram of 1 shows that one molecular
unit is top to another molecular unit in a reverse
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fashion to form a dimer through strong π…π stacking
(3.546 Å) interactions between the electron deficient
penta-fluorobenzene ring and electron rich
naphthalene ring (Figure 2b and Figure S12). Besides,
DMF molecule also takes part to stabilize the dimer
of 1 by C–H…O type interactions between the formyl
Figure 5.
SEM images of the gel of 1 and
(
C21–H21) and methyl (C19–H19) protons of DMF
molecular arrangement (a) before addition of
TBAF (b) after consecutive addition of TBAF and
molecule and the amide C=O of 1 (C21–H21...O1, 2.836
Å; C19–H19...O1, 2.409 Å). Furthermore, there is a C–
H...F (C6–H6...F4, 2.621 Å) type hydrogen bonding
The molecular aggregation feature of the gel has
21
been investigated by Scanning Electron Microscope.
The SEM image of the gel of 1 exhibits ribbon like
morphology (Figure 5). The ribbon-like morphology of
the gel might be attributed to the supramolecular
interactions
fluorophenyl
between
unit,
the
which
naphthyl
help to
unit
form
and
1D
supramolecular structure (Figure 4). This 1D network
has further been connected through CH…F hydrogen
bonding between the methyl C–H of DMF with the
fluorine atom of the penta-fluorophenyl ring (C19–
H19A...F2, 2.668 Å) to form 3D supramolecular
structure, where the solvent molecule are inside the
interactions (such as C-H…O, C-H…F and π…π
stacking interactions) within the gelator 1 as well
as with the gelling solvents (Figure 4 and Figure
S13).
molecular
cavity
(Figures
S13-
S14).
In order to check the supramolecular interactions
present in the gel, we have performed the powder X-
ray diffraction (PXRD) studies of gel, xerogel (gel
at room temperature dry state) and bulk (pre-gel dry
state). PXRD analysis revealed that the peak patterns
of the gel and xerogel are almost similar to the
simulated PXRD patterned of the single crystal
structure of 1(Figure S20). Based on these results,
it is logical to assume that the gelling solvent
molecules might be included in the crystal lattice of
the gel in it’s native state as well as in the
xerogel. The presence of the gelling solvent (DMF) in
the xerogel can be explained in terms of less
volatility of DMF at room temperature. As a result,
the trapped DMF molecules in molecular pocket remain
unperturbed in the xerogel. Therefore it can be
predicted that similar type of supramolecular
arrangement is present in gel, xerogel and single
crystal of 1.
Figure 4.
1D supramolecular arrangement of 1
through C–H...F interations.
The gelation ability of all the three compounds
1, 2 and 3) has been examined by dissolving them 5%
(
by weight in a variety of solvents and mixture of
solvents (Table S3). Among the three compounds, only
compound 1 is able to form semi-transparent gel in
2
DMF/H O (v/v, 2:1) mixture after slow cooling from
the hot solutions (Figure S21). The structural
dissimilarities of 2 and 3 from 1 may be responsible
for this. The molecular simulation of 2 exhibits that
alike 1 it does not possess any molecular pocket
The gel of 1 obtained from DMF/water mixture is
highly stable at room temperature and it is thermally
reversible as confirmed by heating and cooling of the
(
Figure S15). Due to the lack of molecular pocket it
cannot accommodate the DMF molecule. On the other
hand the naphthyl ring and the pentafluorophenyl ring
are not in same plane, which may affect … staking
interaction (Figure S16). The optimized structure of
sol-gel
phase.
The
sol-gel
phase
transition
temperature (Tg) has been measured with the help of
drop ball method which is found to be higher than
0
22-23
60 C (Figure S22).
(prepared by using
Rheological study of the gel
wt% DMF/water (v/v, 2:1)
3
also shows that naphthyl ring and the phenyl ring
5
are not in same plane (Figures S17- S18). The lack of
overall planarity in the molecule and the absence of
fluorine atoms in the phenyl ring make the …
stacking interactions very weak. Furthermore, the C–
H...F type hydrogen bonding interactions will also
become invalid.
mixture) has been performed to examine the
viscoelastic properties of the gel (Figure S23).2
The storage or elastic modulus G’ and loss or viscous
modulus G” of the gel have been measured as
function of strain at constant frequency of 1.0 Hz at
4
a
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ºC. It is observed that with increasing the
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applied stress both G’ and G’’ values were departed
from linearity and collapse when the applied value is
about 1.80% of strain. The frequency sweep experiment
of the gel has been performed at a fixed strain of
0
.1%, where the G’ and G’’ values are frequency
invariant over the entire range of study (Figure S
3). This study clearly indicates the viscoelastic
2
nature of the gel.
Figure 6.
(a) Emission study of gel upon
The gel obtained from
1
(DMF/water mixture)
addition of TBAF (ex at 400 nm) (b) Decay
profile of 1 in DMF, Gel state and sol state
exhibits reversible sol-gel transition in presence of
TBAF and H+ ions. Addition of solid TBAF (2 equiv.)
into the gel, a gradual decomposition of gelatinous
state has been observed followed by a color change
from colorless to brown (Figure S24). On the other
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In an attempt to get information about the excited
transition,
has been
state
fluorescence lifetime of the compound
phenomenon
during
sol-gel
4
hand, addition of HClO (0.5 equiv.) to the sol, the
1
solution re-gelated again showing white color (Figure
S24). UV-Vis and emission experiments have been
performed to illustrate the sol-gel transition
phenomenon in presence of TBAF. Gelator 1 exhibits
broad absorption bands at 400 nm (Figure S25). Upon
addition of TBAF, the absorption band intensity at
recorded in it’s gelling solvent, in gel state as
well as in sol state. The decay profiles of 1 in the
above mentioned three environments are found to be
distinctly different from each other. Compound
a
1
exhibits tri-exponential decay pattern in DMF
having average lifetime (av) 0.4ns, where as in gel
state it shows substantial increase in average
lifetime (av =3.3ns). The increase in average
lifetime can be attributed to the increase in
viscosity of the medium in the gel state which
4
4
00 nm decrease with the appearance of a new band at
+
60 nm. When H has been added to the sol, it shows
exactly same type of absorption spectra observed in
case of gel (Figure S25). Under similar experimental
condition no considerable change in the absorption
spectra of the gel has been found with the addition
reduces
the
radiation
less
transitions.26
Additionally, the molecules get aggregated in the
highly viscous gel state. This aggregated state
having higher lifetime also contributes to the
average lifetime of the gel.27 However, after
addition of TBAF, sol shows bi-exponential decay
having lower average lifetime (av =2.5ns) compared to
the gel state (Figure 6b and Table S4).
2 4 3
of other anions such as AcO¯, H PO ¯, Cl¯, NO ¯ and
CN¯ (Figure S26).
The emission profile of the gel exhibits a weak
broad emission band at 500 nm upon excitation at 400
nm (Figure 6a, green line). After addition of TBAF,
initially the emission band at 500 nm decreases, then
a new red shifted emission band appears at 530 nm.
The intensity of the band at 530 nm increases
gradually with concomitant addition of TBAF (Figure
6a, orange line). Consequently the gel has been
The reversibility of sol-gel transition has also
been investigated using excited state lifetime
measurement by consecutive addition of TBAF and H+
ions (Figure S29 and Table S5). The above experiments
indicate that the sol-gel transition of compound 1 is
reversible in nature. However, the lifetime profile
as well as the average lifetime of gel is slightly
different than that of the regenerated gel because it
converted to sol completely accompanied by a visual
change in fluorescence from green to yellow. When H+
has been added to the sol, it regains it’s initial
green fluorescence which has also been reflected by
the emission spectra (Figure S27). In contrast, all
other above mentioned anions hardly shows any
modification of the emission property of the gel
may be a mixture of 1 and protonated form of 1
(Figure S30).
(
been investigated by SEM analysis of the resultant
Figure S28). The reversibility phenomenon has also
+
material after consecutive addition of TBAF and H
ions. The SEM image describes that it possesses
similar type morphology observed in the gel state,
confirming the regeneration of gel after addition of
H+ to the sol (Figure 5b). 25
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1H NMR titration experiment in DMSO-d
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conducted to investigate the interactions between 1
and fluoride ion. As shown in Figure S30 upon
addition of 0.0–2.0 equiv of tetrabutyl ammonium
fluoride ion, the phenolic OH proton signal
completely disappears and the NH proton signal
becomes broadened with
a
observations clearly indicate the F ion interacts
downfield shift. These
–
with both the amide NH and phenol OH groups resulting
the deprotonation of the phenolic OH.28
To explain the reversible changes in the
photophysical properties as well as physical state of
1
1
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1
during sol-gel transition, single crystal of 1 has
been grown from it’s sol state using ether diffusion
technique. The crystal structure obtained from the
above experiment shows that one tetrabutyl ammonium
group is present with the deprotonated form of 1 (1’,
Figure 7a). The molecular structure describes that
after deprotonation the naphthyl ring rotates in such
a way so that the deprotonated phenolic oxygen (O1)
and the amide hydrogen (N1–H1) come closer to each
other to form a strong hydrogen bond via six member
ring (O1. . .H1–N1, distance 2.420 Å, Figures S32-
33). As a result, the molecule suffers a significant
twisting having dihedral angle 24.10 between the
naphthalene moiety and pentafluoro phenyl ring. It is
worth mentioning that no solvent molecule is attached
with the deprotonated form 1’, probably due to lack
of molecular pocket unlike 1 (Figure S34). Here, the
amide N-H is engaged in H-bonding interaction with
the deprotonated phenolic oxygen (O1). As a result
the solvent molecule (DMF) can’t find any H-bonding
site in the molecule.
Figure 8.
Different types of C-H…O
interactions in 1’ and tetrabutylammonium ion
deprotonated phenolic oxygen comes into H–bonding
distance with the amide –NH hydrogen, which makes the
molecule more rigid to show strong emission by
reducing non-radiative channels (such as rotational
and vibrational motions within the molecule). In
recent past, few groups proposed the origin of
fluorescence of this type of deprotonated molecules
using
mechanism.
inter-molecular
2
proton
However, we have shown that origin of
transfer
(ESPT)
9-31
the emission in the anionic form (1’) is not from
any proton transferred (PT) state, it is the local
emission of the anion (1’). At first, we have
recorded the excitation spectra of 1’ in its sol
state which exhibits excitation maxima at 460 nm
which resembles the absorption maxima of the anion
(1’) in the sol state (Figure S 38 and S39). This
observation indicates that there is no existence of
any new excited state species (such as proton
transferred form). Furthermore, we have recorded the
emission of the sol at ex =460 nm which is actually the
absorption maxima of anion (1’) in the sol state and
found that the emission occurs at same wavelength
having greater intensity than the previous case
Crystal lattice of deprotonated form of 1 (1’)
shows that an intermolecular offset π…π staking
(
3.525 Å) interaction is present between naphthyl
ring with penfluoro phenyl ring to form a zig-zag
type network (Figure 7b and Figure S35). Furthermore,
the tetrabutyl ammonium group uses its four arms to
interact with the surrounding three molecular units
via different types of weak H-bonding interaction
(Figure S40). From the above two experiments it can
be predicted that the emission at 530 nm is the local
emission of the anion (1’) in sol state.
(
such as C–H…O and C–H…F) (Figure 8). Moreover, the
On the other hand crystal structure analysis may
penta fluorophenyl ring used its four fluorine atom
to hold three tetrabutyl ammonium ion (F1-H0ID, F2-
H02D, F3-H01L and F5-H02E distance: 2.495, 2.597,
also provide
transition phenomenon. The crystal structure of
a
possible explanation of sol-gel
1
obtained from DMF/ether mixture shows the molecules
2
(
.455, 2.295 Å, respectively) to make a 3D network
Figures S36-S37).
are attached with each other via strong π…π
interactions and different type of H–bonding
interactions among themselves as well as with the
solvents, whereas the crystal structure of the
deprotonated form 1’ exhibits that the molecule
becomes non-planer which affects π…π stacking
interactions among them. Again, the solvent (DMF) has
been displaced from the crystal lattice of it. As a
result the supramolecular interactions which are
present in 1 become very much weaker or negligible in
As, we have considered that the gel of the
compound 1 has been formed because of several types
Figure 7. (a) Single crystal structure of 1’
with TBAF, (b) … interactions between
naphthyl ring and penfluoro phenyl ring.
1’.
of supramolecular interactions (like π…π, C–H…O
and C–H…F) which becomes weak or negligible in 1’
as seen in case of the crystal structure analysis.
From the above crystal structure analysis, it has
been found that compound 1 suffers C–C single bond
rotation upon addition of TBAF. As a result, the
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Page 6 of 9
Consequently, the gel has been transferred to sol
upon addition of TBAF (Scheme 1).
times larger than those of the attached non-hydrogen
atom. Successful convergence was indicated by the
maximum shift / error of 0.001 for the last cycle of
the least squares refinement. Absorption corrections
were carried out using the SADABS program. All
calculations were carried out using SHELXS 97, PLATON
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
CONCLUSIONS
In summary, we have synthesized amido-schiff base
1) and two control compounds (2 and 3) having same
(
basic framework. Depending on the structure, only 1
9, ORTEP-32 and WinGX system Ver-1.64.32 Powder X-ray
9
diffraction (PXRD) patterns were recorded on an XPERT
can form gel in DMF-water mixture. Crystal structure
supramolecular
Philips diffractometer for Cu K radiation (
analysis of
1
describes that the
-1
=
studies were carried out by using Malvern Kinexus
1.5406 Å), with a scan speed of 2 min . Rheology
arrangement of the gelator 1 along with the gelling
solvent (DMF) exhibit ribbon like structure which is
almost similar to it’s gel state morphology. This gel
undergoes reversible sol-gel transition in presence
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
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1
2
3
4
5
6
7
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1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Pro+ rheometer. Scanning Electron Microscopy (SEM)
measurement was carried out with JEOL JSM-6700F
field-emission microscope. Gaussian 03 software was
used to optimize the geometry of compounds 2 and 3.33
Time Correlated Single Photon Counting (TCSPC)
spectrophotometer (Horiba Jobin Yovin) has been used
to acquire fluorescence lifetime using a employing a
nanosecond diode laser (IBH, nanoLED-07) operating at
+
of external stimuli (TBAF and H ) accompanied by
changes in its fluorescence from green to yellow and
vice versa. The gel to sol transition phenomenon has
been
explained
on
the
basis
of
modification via C-C bond rotation of 1 as evidence
structural
by X-ray single crystallography.

ex =375 nm as the light source to trigger the
fluorescence of gel, addition of TBAF to gel and
1
EXPERIMENTAL SECTION
Materials
in DMF at different emission maxima (em =500 nm
for gel, em =560 nm after addition of TBAF and (em
=420 nm for 1 in DMF)
and TBX-04 as the detector.
All reagents and spectroscopic grade solvents were
used as received from commercial sources without
further purification. All anions in the form of
tetrabutylammonium salts were purchased from Sigma-
The emission signals from the samples have been
collected with an emission polarizer kept at the
magic angle (~54.7). The decays have been evaluated
using Data Station v-2.5 decay analysis software. The
Aldrich
Chemical
Company.
Solvents
used
for
parameters which are considered here for goodness of
2
spectroscopic studies were of spectroscopic grade.
Oil bath was generally used for heating the reaction.
fit are

values, Durbin–Watson parameter and
visually good residual plot. Average lifetimes (avg)
of fluorescence for multiexponential decay have been
calculated from the decay times (s) and pre-
exponential factors (a) using the following equation:
Methods
Hitachi UV–vis (Model U-3501) spectrophotometer and
Perkin Elmer LS-55 spectrofluorometer, were used to
record the absorption spectra and emission spectra

avg
=
performed
a
i
i. Theoretical calculations have been
using Gaussian 09W suite program.
−
1
respectively. IR spectra (KBr pellet, 4000–400 cm )
were recorded on a Parkin Elmer model 883 infrared
spectrophotometer. Elemental analyses were done using
Theoretical calculations have been performed using
Gaussian 09 software with B3LYP-hybrid functional and
6
-31++G(d,p) basis set .
a
Perkin-Elmer
series
II
2400
instrument.
Electrospray ionization mass spectrometry (ESI-MS
positive) ion mass spectra were acquired using a Xevo
G2-S Q-ToF (Waters) mass spectrometer, equipped with
a Z-spray interface, over a mass range of 100−1200
Da, in a continuum mode. Aqueous sodium formate was used
for Q-oa-ToF calibration. L-Leucine was used as the
external mass calibrant lock with mass [M+H]+
Synthesis:
(perfluorophenyl)methylene)-2-naphthohydrazide (1)
The amido-Schiff base 1 was prepared by drop wise
addition of methanolic solution of 2,3,4,5,6-penta
fluoro benzaldehyde (0.40 g, 2.0 mmol) into
methanolic solution of 3-Hydroxy-naphthalene-2-
Synthesis
of
(E)-3-hydroxy-N'-
(
a
carboxylic acid hydrazide (0.38 g, 1.9 mmol). The
reaction mixture was reflux with stirring for 2 hr. A
pale yellow precipitation of Compound 1 was appeared.
It was filtered and washed with methanol and dried in
desiccators Yield: 0.58 g, 75%. 1H NMR (500 MHz,
13
1
5
56.2771 Da. 1H NMR and
C{ H} NMR spectra were
recorded on a Bruker, Avance 500 spectrometer, where
chemical shifts ( in ppm) were determined with
respect to tetramethylsilane (TMS) as internal
standards. The single crystals were mounted on
a
DMSO-d
s,), 8.40 (1H, s,), 7.92 (1H, d, J= 7.5 Hz), 7.78
6
)  12.20 (1H, s,), 11.06 (1H, s,), 8.58 (1H,
Bruker-AXS SMART APEX II diffractometer equipped with
a graphite monochromator and Mo K ( = 0.71073 Å)
radiation. The crystal was placed at 60 mm from the
CCD and 360 frames were measured with a counting time
of 5 s. The structure was solved using Patterson
method by using the SHELXS 97. Subsequent difference
(
7
1H, d, J= 7.5 Hz), 7.52 (1H, t, J= 7.5 Hz), 7.39-
)  164.0,
.33 (2H, m). 13C{ H} NMR (125 MHz, DMSO-d
1
6
155.5, 148.8, 134.8, 132.5, 131.3, 130.5, 129.4,
128.6, 128.5, 128.2, 127.6, 127.4, 124.9. IR (KBr)
3
1
1
261, 3123, 3060, 1642, 1624, 1594, 1541, 1511, 1493,
446, 1428, 1392, 1363, 1309, 1262, 1208, 1178, 1077,
Fourier
revealed the positions of the remaining non-hydrogen
atoms. Non-hydrogen atoms were refined with
synthesis
and
least-square
refinement
–1
006, 970, 881, 727, 667, 620, 477 cm . Anal. Calcd
).(C NO) : C, 55.63; H, 3.56; N,
.27. Found: C, 55.78; H, 3.61; N, 9.32. HRMS (ESI-
TOF) m/z calcd for C18
[M+H]+ 381.058, found
81.055.
for 1 (C18
9
H
9
F
5
N
2
O
2
3 7
H
independent anisotropic displacement parameters.
Hydrogen atoms were placed in idealized positions and
their displacement parameters were fixed to be 1.2
9 5 2 2
H F N O
3
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The Journal of Organic Chemistry
Preparation of single crystal of 1: Amido-Schiff base
MAA like to thank DST, Govt. of West Bengal, India
(Project No. 376(Sanc.)/ST/ P/S&T/9G-16/2013) for
financial support.
1
2
3
4
5
6
7
8
9
1 (20 mg, 0.05 mmol) was dissolved in 3 ml of DMF.
Then the DMF solution of 1 was transferred to 6 small
tubes (crystallization tubes, volume 3 ml) and was
placed in a large tube (10 ml) containing diethyl
ether solvent and this tube then sealed and kept at
room temperature. After 5 to 6 days rod shape light
yellow colour crystals was obtained. Yield: 12 mg,
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
6
0 %.
MAA thanks Prof. K. Ghosh, University of Kalyani,
Kalyani, for rheological study, and Mrs. Aratrika
Chakraborty for SEM analysis.
Sample preparation for PXRD: Amido-Schiff base 1 (40
mg, 0.1 mmol) was suspended in 5 ml of DMF and 2.5 ml
of water in a 25 ml beaker and then the beaker was
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
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3
3
3
3
3
3
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4
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5
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5
5
5
5
5
5
5
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0
1
2
3
4
5
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7
8
9
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2
3
4
5
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3
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heated until
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obtained. When the beaker was left open in the air at
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