Synthesis and characterization of bis[N′-(4-carboxybenzylidene)]- pyridine-2,6-dicarbohydrazide: Colorimetric and fluorometric modulation in presence of F- ions

Article abstract of DOI:10.1016/j.saa.2013.07.045

(Graph Presented) A novel organic compound bis[N′-(4- carboxybenzylidene)]-pyridine-2,6-dicarbohydrazide (L) was synthesized and characterized using spectroscopic and X-ray diffraction techniques. Tetrabutyl ammonium halides [(Bu)₄N⁺X^-] X = F, Cl, Br and I were allowed to react separately with a solution of L in DMSO (1 × 10^-5 M). The solution of L turned to shining yellow colour in the presence of F^- ion only. The binding properties have been studied using absorption, emission and ¹H NMR titrations. Theoretical studies on compound L and compound L + X^- (X = F, Cl and Br) in DMSO medium were carried out using density functional theory (DFT) at the B3LYP/6-31G(d,p)/6-31G+(d,p) level. The theoretical calculations agreed to the experimental results.

Full text of DOI:10.1016/j.saa.2013.07.045

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 286–294
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
0
Synthesis and characterization of bis[N -(4-carboxybenzylidene)]-
pyridine-2,6-dicarbohydrazide: Colorimetric and fluorometric
ꢀ
modulation in presence of F ions
⇑
Priti Sinha, Ashish Kumar Srivastava, Lallan Mishra
Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221 005, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
0
0
F
ion recognition with a novel organic compound bis[N -(4-carboxybenzylidene)]-pyridine-2,6-dicarbo-
ꢁ
ꢁ
ꢁ
Bis[N -(4-carboxybenzylidene)]-
pyridine-2,6-dicarbohydrazide has
been prepared and characterized.
Colorimetric and fluorometric
1
hydrazide (L) is monitored using UV–vis, fluorescence and H NMR spectroscopic titrations and DFT/TD-
DFT calculations which supported the experimental results.
ꢀ
modulations in presence of F has
been studied.
DFT calculation carried out in DMSO
medium supported the experimental
results.
a r t i c l e i n f o
a b s t r a c t
0
Article history:
Received 20 May 2013
Received in revised form 8 July 2013
Accepted 21 July 2013
Available online 30 July 2013
A novel organic compound bis[N -(4-carboxybenzylidene)]-pyridine-2,6-dicarbohydrazide (L) was syn-
thesized and characterized using spectroscopic and X-ray diffraction techniques.
Tetrabutyl ammonium halides [(Bu)
+ ꢀ
4
N X ] X = F, Cl, Br and I were allowed to react separately with a
ꢀ5
solution of L in DMSO (1 ꢂ 10 M). The solution of L turned to shining yellow colour in the presence
ꢀ
1
of F ion only. The binding properties have been studied using absorption, emission and H NMR titra-
ꢀ
tions. Theoretical studies on compound L and compound L + X (X = F, Cl and Br) in DMSO medium were
carried out using density functional theory (DFT) at the B3LYP/6–31G(d,p)/6–31G+(d,p) level. The theo-
retical calculations agreed to the experimental results.
Keywords:
Bis-carbohydrazide
Colorimetry
Ó 2013 Published by Elsevier B.V.
Fluorometry
NMR titrations
DFT calculations
Introduction
ment of highly sensitive anion sensors [1–7]. Anion-compound
interactions, mainly through hydrogen bonding or electrostatic
Design and synthesis of chemical sensors for the recognition of
anions is demanding area of current research. The importance of
anions in nature as fertilizers, industrial raw materials and
corresponding environmental concerns necessitated the develop-
interaction are different than that of metal–ligand coordination
in cation-compound interactions. The design of anion compounds
differs substantially from that of cation compounds [8–17]. Most
of the anion compounds bear amide or urea derivatives and pyrrole
groups as binding sites and form NAHꢃ ꢃ ꢃ anion bonds or the
positively charged ammonium groups (or guanidinium groups)
+
⇑
Corresponding author. Tel.: +91 542 6702449; fax: +91 542 2368174.
E-mail address: lmishrabhu@yahoo.co.in (L. Mishra).
that involve N AHꢃ ꢃ ꢃXꢀ type hydrogen bonds [18–23]. One of the
1
386-1425/$ - see front matter Ó 2013 Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.saa.2013.07.045

P. Sinha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 286–294
287
frequently used strategies to design anion sensors involves the
constructions of compounds showing luminescent and colorimet-
ric responses [24–26]. Such systems are generally composed of an-
ion binding sites and the chromogenic groups. When anions
interact with the sensor via electrostatic, hydrogen bonding, coor-
dination to a metal centre, hydrophobic interaction, or a combina-
tion of any two or more of these interactions, the sensor can output
binding information either by its altered fluorescence, absorption
spectra or both [27–29]. Colour changes as signalling event de-
tected by the naked eye are widely used owing to the low cost of
equipment required. Among various anions, fluoride ion has at-
tracted the interest of chemists due to its applications in many
industrial products. It has been used in dental care and in the hu-
man diet. A large intake of fluoride ions can lead to osteoporosis,
fluorosis and other diseases [30,31]. Keeping these precedence in
view, a simple bis-hydrazide containing amido and imino groups
at 2,6-positions of a pyridyl ring has been synthesized and charac-
titration experiments were performed by maintaining the concen-
ꢀ5
tration of L constant at 10 M while varying the concentration of
ꢀ
6
the fluoride anion within (1–10) ꢂ 10 M and the fluorescence
was measured after each addition until fluorescence intensity
was found maximum.
1
H NMR titrations and ESI–MS studies
1H NMR titrations were carried out in DMSO – d
as internal standard) using JEOL AL-300 MHz spectrometer. Con-
solution (TMS
6
ꢀ
3
ꢀ
centration of host (L) as 10 M was titrated against guest (F ) con-
ꢀ2
centration 10 M. Chemical shift was measured in d ppm. ESI–MS
was recorded on micromass LCT (Waters) mass spectrometer.
Computational method
ꢀ
terized. It selectively detected F anion by naked-eye as well as by
changes in the optical signals in DMSO solution.
Geometry optimization was performed using Gaussian 09 suite
of programs [36]. A hybrid version of DFT and Hartree–Fock (HF)
methods was used, namely, B3LYP density functional theory method
in which the exchange energy from Becke’s exchange function was
combined with exact energy from Hartree–Fock theory [37,38].
LanL2DZ was used for I while for the C, H, N, F, O and
Experimental
Materials and methods
ꢅꢅ
ꢅꢅ
Br atoms, 6-31G basis set was used for compound L. 6-31G+ ba-
ꢀ
sis set used for compound L + X (X = F, Cl, and Br). The calculations
for compound L + I tried but it did not satisfy energy convergence
Tetra-n-butylammonium (TBA) halides were purchased from
Sigma–Aldrich Chem Co. All solvents were purchased from
E. Merck and freshly distilled prior to their use. The compound L
was prepared and characterized using reported procedure [32].
ꢀ
criteria. In addition, we also performed time dependent density
function theory (TD-DFT) [39,40].
X-ray structural studies
Synthesis and characterization
Single crystal X-ray diffraction data of L was collected in the
temperature range of 100(2)–293(2) K on a Oxford diffraction
XCALIBUR-EOS diffractometer using graphite monochromatized
MoKa radiation (k = 0.71073 Å). Intensities of these reflections
were measured periodically to monitor crystal decay. The crystal
structure was solved by direct methods and refined by full matrix
least squares (SHELX-97) [33]. Drawings were carried out using
MERCURY [34].
Preparation of compound L
L was synthesized in three steps starting from 2,6-pyridine
dicarboxylic acid (1 mmol, 0.167 g). Its methyl ester was prepared
by stirring it in excess methanol in the presence of catalytic
amount of concentrated thionyl chloride (SOCl ) at room tempera-
ture for one day. The ester (1 mmol, 0.171 g) thus isolated was then
reacted with aqueous hydrazine hydrate (2.1 mmol, 0.12 mL) in
methanol under reflux for 3 h which resulted solid 2,6-pyridine
dicarboxylic acid, 2,6-dihydrazide. It (1 mmol, 0.195 g) was finally
reacted with 4-formyl-benzoic acid (2 mmol, 0.300 g) in methanol
at room temperature. Reaction was monitored using TLC. The prod-
2
Absorption titrations
UV–vis absorption spectra were recorded on ‘‘Jasco V-630’’
spectrophotometer at 25 °C. The absorption titrations of L with
fluoride salt was performed by monitoring the changes in the
uct thus obtained was filtered and then purified by repeated
1
recrystallization from hot ethanol. Yield: 85%, H NMR (DMSO-d
6
,
300 MHz): d (ppm) 13.20 (b, 2H, ACOOH), 12.44 (s, 2H, ANH),
ꢀ5
absorption spectrum of L (10 M) in DMSO. The concentration of
8.81 (s, 2H, CH@N), 8.37 (m, 2H, CHpy), 8.33 (m, 1H, CHpy), 8.04
ꢀ5
13
L was kept constant a 10 M while the concentrations of fluoride
(d, 4H, ArH), 7.92 (d, 4H, ArH). C NMR (dmso-d
6
, 300 MHz): d
, ArH), 127.41 (C , ArH),
, ACH@N), 159.70 (C , AC(O)NH),
9
, Py), 125.79 (C10, Py). IR (KBr pellet, cm ):
ꢀ6
salt was varied within (1–10) ꢂ 10 M. The absorption of guest
molecule is eliminated initially by keeping their equal quantities
separately in host L and reference solution. From the absorption
(ppm) 166.98 (C
132.12 (C , ArH), 140.11 (C
148.89–148.15 (C , C
1
, ACOOH), 138.18 (C
2
4
5
6
7
ꢀ1
8
data, the intrinsic association constant K
a
was determined from a
3463 (˜CONH), 1671 (ACOOH), 1609 (AC@N).
plot of [guest]/(
e
a
ꢀ
e
f
) vs [guest] using [35] Eq. (1).
Crystal data: C27H35N5O11S2, M = 669.74, Monoclinic,
a = 26.7068(15),
b = 110.310(6),
b = 10.1394(4),
= 90, space group C 2/c, Z = 4, V/Å = 3173.2(3),
c = 12.4951(6),
a = 90,
½
guestꢄ=ð
e
a
ꢀ
e
f
Þ ¼ ½guestꢄ=ð
e
b
ꢀ
e
f
Þ þ ½k
a
ð
e
b
ꢀ
e
f
Þꢄꢀ
1
ð1Þ
3
c
Reflections collected/unique = 6463/3552 [R(int) = 0.0196], Final R
indices [I > 2sigma(I)] = R1 = 0.0360, wR2 = 0.0871.
where [guest] is the concentration of fluoride salt. The apparent
absorption coefficients , and correspond to Aobsd/[L], the
extinction coefficient of the free L and extinction coefficient of L
e
a
,
e
f
e
b
in fully bound form respectively. K
to the intercept.
a
is given by the ratio of slope
Preparation of adduct of L with tetrabutylammonium fluoride
Crystalline solid of L (1 mmol, 0.459 g) was added to a solution
of tetrabutylammonium fluoride in DMSO (1 mmol) and stirred for
5 h, filtered to get pale yellow solid. This compound was washed
with methanol followed by diethyl ether. Yield: 60%, 19F NMR
(DMSO-d , 300 MHz): d (ppm) – 47.45 ppm, IR (KBr pellet, cm ):
6
3418 (˜CONH), 1681 (ACOOH), 1654 (AC@N). ESI–MS: calcd. m/z
720.46, found 721.53.
Fluorescence titrations
ꢀ1
Fluorescence spectra were measured using a Perkin–Elmer LS-
5 luminescence spectrometer. Host (L) displayed fluorescence at
4
kemiss556 nm at excitation wavelength kex315 nm. Fluorescence

2
88
P. Sinha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 286–294
Scheme 1.
Fig. 1. Molecular structure of L.
Results and discussion
crystal lattice, one molecule of DMSO and two molecules of water
are present. One of water molecule is present in its cleft (S3). The
oxygen atom (O5) involved in H-bonding with ANH(3) proton of
compound L (N(2)AH(3)ꢃ ꢃ ꢃO(5) with distance 2.147 Å) and oxygen
atom (O4) of DMSO is also involved in H-bonding with hydrogen
atom (H9) of carboxylic group of compound L (S(1)@O(4)ꢃ ꢃ ꢃH(9)
distance 1.753 Å). Water of crystallization acts as a bridge between
two molecules of compound L. Here H(11) of water molecule
formed H-bonding with O(3) of carboxylic group of compound L
(C(12)AO(3)ꢃ ꢃ ꢃH(11) distance 2.147 Å) and H(12) formed H-bond-
ing with O(1) of compound L (C(4)AO(1)ꢃ ꢃ ꢃH(12) distance 1.932 Å)
(S3). The packing diagram of compound L showed helical type of
network along crystallographic c axis (S4). In this structure, DMSO
molecules were embedded between two chains of compound
molecules.
As shown in Scheme 1, compound L was synthesized using two-
steps simple-controlled reactions from diester to dihydrazide, then
to final compound L in good yields. Elemental analysis and spectro-
1
13
scopic characterizations ( H NMR, C NMR, IR, UV-vis and fluores-
cence) supported the formation of the bis-hydrazide, L. It showed
characteristic infrared band of amido and imino groups at 3463
ꢀ1
and 1609 cm respectively. The structure of compound L was sup-
1
13
ported by its H and C NMR spectra (S1, S2). The most deshielded
protons of COOH group of compound L appeared as broad peak at d
1
3.20 ppm where as protons of amido and imino groups appeared
as singlet at d 12.44 ppm and 8.81 ppm respectively. Pyridyl pro-
tons were observed as multiplet at d 8.38–8.26 ppm where as phe-
nyl protons appeared at d 8.04 (J = 8.1 Hz) and 7.92 (J = 9 Hz)
respectively. The UV–vis spectrum of compound L showed a peak
at kmax 315 nm where as an emission band from L was displayed
at kemiss 556 nm at excitation wavelength of kexcitation 315 nm.
Naked eye detection and ESI–MS studies
Changes in colour were studied in a first step in DMSO by addi-
ꢀ3
tion of
5
equiv. (5 ꢂ 10 M) of the corresponding anion
Crystal structure of compound L
The proposed molecular structure of L was further supported by
its single crystal X-ray diffraction study. Crystal structure analysis
of compound L exhibited a special configuration with two amide –
carboxy phenyl arms disposed at 2 and 6 positions of pyridyl group
with space group C2/c (Fig. 1). The two parts of the molecule are
symmetrically related with the nitrogen atom N(1) of the pyridine
ring lying on the twofold axis to form a helical species. In the
ꢀ3
Fig. 2. Colour changes of L (2 ꢂ 10 M, DMSO) with the addition of tetrabutylam-
-
-
-
ꢀ
monium salts (from left to right: free L, 5 equiv. F , Cl , Br and I in DMSO).

P. Sinha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 286–294
289
Fig. 3. ESI–MS spectrum of complex (M + H)+ in acetonitrile/dmso (9:1 v/v) solution.
ꢀ
ꢀ
ꢀ
ꢀ
(
F , Cl , Br and I ) separately as tetrabutylammonium salts to
Absorption spectral response for anions
ꢀ3
solutions of compound L (1 ꢂ 10 M) in DMSO. The most selective
colour change occurred in the presence of fluoride anion from
white to yellow colour (Fig. 2). An image of visual colour changes
with increasing concentration of fluoride ions is given as S5. In
interference experiment, we can say that in presence of excess of
other halides like Cl , Br and I did not show any visual changes
in compound–fluoride complex colouration with the persistence of
pale yellow colour (S6).
ꢀ5
UV–vis spectra of the solution of L (1.0 ꢂ 10 M) recorded
ꢀ
upon the incremental addition of F is shown in Fig. 4. Upon addi-
ꢀ
tion of F , the intensity of the absorption peak of L observed at k
315 nm was found to be decreasing and peak position also shifted
at k 319 nm. However, the absorbance of its peak observed at k
275 nm was increasing. The resulting titrations showed isosbestic
point at k 285 nm. Observation of isosbestic point showed that a
stable complex of definite stoichiometry between L and anion
was formed. Interestingly, addition of other halide ions like
ꢀ
ꢀ
ꢀ
ESI–MS as depicted in Fig. 3, supported the formation of
+
ꢀ
ꢀ
[
LꢃTBA F ] and [LꢃF ] complexes showing corresponding peaks at
ꢀ
ꢀ
ꢀ
m/z 720 and 479 respectively.
Cl , Br and I did not bring out any observable change in the
Fig. 4. Absorption spectra of L = (10 M, DMSO) in absence (a) and in the presence of increasing amounts of F = (1–10) ꢂ 10ꢀ6 M (in DMSO) at room temperature. Inset: (a)
ꢀ
5
ꢀ
ꢀ
change of absorbance at 574 nm and (b) absorbance changes upon increasing F concentrations.

2
90
P. Sinha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 286–294
Fig. 5. Emission spectra of L = (10 M, DMSO) in absence (a) and in the presence of increasing amounts of F = (1–10) ꢂ 10ꢀ6 M (in DMSO) at room temperature. Inset:
ꢀ
5
ꢀ
ꢀ
emission intensity changes upon increasing F concentrations.
ꢀ
absorption spectrum of L (S7) at this wavelength. The selective
binding with of F as compared to Cl , Br and I may be attributed
to its higher basicity [41].
Colour changes occur most probably due to formation of hydro-
gen bonds between the amido groups and fluoride ions. The forma-
tion of these hydrogen bonds affects the electronic properties of
the chromophore resulting in a colour change with a subsequent
new charge-transfer interaction between the fluoride-bound ami-
do group and the electron deficient 4-carboxyphenyl group [42].
It was supported by the appearance of a new peak at k 574 nm
Fig. 2. This clearly showed that except F , no colorimetric response
was observed on addition of any other anions in DMSO solution of
L in comparable concentration. In interference experiment, kmax of
ligand (L) appeared at 315 nm but after addition of fluoride salt it
shifted to 319 nm. However, addition of excess salt like chloride,
bromide and iodide in same solution show little perturbation
(ꢆ1 nm) in UV–vis spectra (S9).
ꢀ
ꢀ
ꢀ
ꢀ
Flourescence response from anions
ꢀ5
upon addition of fluoride solution. The value of association con-
Fluorescence from compound L (1.0 ꢂ 10 M) in the absence
and presence of fluoride anions, in DMSO medium was recorded
keeping tetrabutylammonium (TBA) cation constant in each case.
A weak emission band at kmax 351 nm was displayed from free
compound L, which was attributed to the intrinsic emission from
phenyl group and a strong luminescent band observed at kmax
556 nm was attributed to the excimer emission [43] resulting from
the intramolecular excimer formation by
two phenyl rings (Fig. 5). Owing to the involvement of
non-bonding electron of NH group in H-bonding with F anion,
5
stant (K
a
) of fluoride binding was found as 1 ꢂ 10 . This was fur-
ther supported by Job’s plot (S8) and ESI–MS analysis. Electronic
spectra for L remained unchanged even in the presence of excess
20 mol equivalents) of other halide salts like Cl , Br and I . For
ꢀ
ꢀ
ꢀ
(
these anions, the absence of any change in absorption spectral pat-
tern suggested either no interaction with L or the interaction of
corresponding anions with L is too weak to perturb the energies
of the frontier orbitals of the compound molecule. The observed
changes in solution (DMSO) of L upon addition of 5.0 M equivalents
of tetrabutyl ammonium salts of respective anions are shown in
ꢅ
p
–p
stacking between
ꢀ
ꢅ
ꢅ
n ?
p transition which normally masks the p ? p transition
ꢀ
5
ꢀ
ꢀ
ꢀ
ꢀ
Fig. 6. The emission spectra of L (2 ꢂ 10 M, DMSO) in absence or presence of a 5 mol ratio of F and 20 mol ratio of anions Cl , Br and I anions (in DMSO) at room
temperature.

P. Sinha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 286–294
291
Fig. 7. 1H NMR spectra of L(1 mM) in DMSO-d
in the presence of increasing amounts of F at 25 °C.
ꢀ
6
(
responsible for the emission behaviour), its fluorescence intensity
the binding stoichiometry of 1:1 with a binding constant of
ꢀ
ꢀ
ꢀ
5
ꢀ1
is enhanced [44]. Upon addition of Cl , Br and I anions as their
TBA salts in a 20-fold excess, no change in their emission was ob-
served. However, a strong fluorescence enhancement was ob-
1 ꢂ 10 M
.
1
H NMR titration
ꢀ
served in the presence of a small amount of F anion as shown
in Fig. 6. Moreover, the fluorescence ‘‘switch on’’ rather than
1
ꢀ3
H NMR titration of L at its fixed concentration (10 M) with
‘
‘switch off’’ upon recognition is preferred in order to notice a
greater signal output and could be of interest in sensing processes.
The binding constant K is determined from the changes in fluores-
cence intensity resulting from the titration of dilute solutions
ꢀ2
guest (fluoride anions) of concentration (10 M) was performed.
Initially, ANH peak appeared at
2.59 ppm on addition of 0.50 equivalent of fluoride ions in a solu-
tion of L. Further addition of 0.25 equivalent of fluoride ions shifted
the NHA peak at d 12.75 ppm (Fig. 7). Finally, at 1.0 equivalent of
fluoride ions, NHA peak appeared at d 13.02 ppm. The deshielding
of NH protons supported their involvement in H-bonding with
fluoride ions. Upon addition of 10.0 equivalent of fluoride ions in
d 12.44 ppm shifted to d
s
1
ꢀ5
ꢀ
(
10 M) of L against F anion solutions. The linear fit of the fluo-
rescence intensity data at a particular wavelength for 1:1 complex-
ation was obtained [45] by applying the following equation:
ꢇ
F
ꢇ
F
I =ðI
F
ꢀ I Þ ¼ ½a=ðb ꢀ aÞꢄ½1=K
s
½Mꢄ þ 1ꢄ
ð2Þ
ꢀ
the solution of L, formation of HF2 was considered since a peak ap-
peared at d 15.80 ppm was found in consistence with the earlier re-
port for HF2 anion [46]. As a consequence of deshielding of NH
ꢇ
where IF andI
F
are the fluorescence intensities of the free L and
ꢀ
L-anion complex, respectively; [M] is the concentration of the anion
added for the complexation. The K
s
is obtained as intercept/slope
protons, imino protons (CH@N) were also deshielded from d
8.81 ppm to d 8.82 ppm. Thus, NMR titrations demonstrated 1:1
binding ratio between compound L and F ions as no further
ꢇ
ꢇ
ꢀ1
ratio from the plot of I /(I
F
ꢀ I ) against [M] . The results of the
F
F
ꢀ
systematic analysis of fluorescence titrations (Fig. 6) also supported
ꢀ
Fig. 8. Optimized structures (top view) of compound L and compound L + X (X = F, Cl and Br).

2
92
P. Sinha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 286–294
ꢀ
Fig. 9. Optimized structures (side view) of compound L and compound L + X (X = F, Cl and Br).
changes in either NH or CH@N protons could be observed even up-
acceptable donor–acceptor distances [48]. Side view of optimized
geometry shows fluorine atom fits in plane of compound L whereas
chlorine and bromine are out of plane as depicted in Fig. 9. The en-
ꢀ
to 3.0 equivalent ration of F ions as compared to L. This observa-
ꢀ
tion supported that binding site of F ion is most likely with NH
groups and its charge is counter balanced by TBA ion as evidenced
by its peak observed at d 0.89–1.54 ppm. However, addition of
other TBA halides separately even in 20-fold excess to a solution
of L brought no significant change in peak position of either NH
or CH@N protons.
FT-IR analysis
ꢀ
The electronic rearrangement of compound L + F is demon-
strated also by IR spectra (S10 and S11). In particular, stretching
band of ˜CONH and ACH@N groups observed at 3463 and
ꢀ
ꢀ
1
1
1
1
609 cm
654 cm
respectively in compound L, shifted to 3418 and
in the spectrum of compound L + F . This indicated
ꢀ
weakening of NAH bond and strengthening of ACH@N bond and
supported co-operativity of amide and imine groups in H-bonding.
[
47].
DFT calculations
Fig. 10. Energy level diagram of HOMO and LUMO orbitals of compound L and
compound L + F complex.
DFT calculations were performed to optimize the structures as
shown in Fig. 8. The energy of optimized structure of compound
L and its adduct with F , Cl and Br ions were found as
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
43860.9811 eV,
ꢀ46584.6394 eV,
ꢀ56389.2885 eV
and
Table 2
ꢀ
ꢀ113846.0214 respectively. The relevant frontier molecular orbi-
Summary of electronic transition of compound L and compound L + F complex.
ꢀ
tals of the compound L and of its adduct with X (X = F, Cl and
Br) ion are depicted in (S12 and S13). The HOMO distribution of
compound L is concentrated only on both arms of L where as LUMO
distribution is concentrated on whole molecule including pyridine
Electronic
Transition
TDDFT//B3LYP/6-31G (d,p)/6–-31 + G (d,p)
fb
Compositionc
CId
Excitation
energy
a
ꢀ
Compound
L
S
0
0
? S
? S
1
4
3.6162 eV
342.86 nm
3.7633ev/
0.6362 H-1 ? L + 1
H ? L
1.2778 H-1 ? L + 1
H ? L + 1
0.35287
0.60309
0.36767
0.59270
ring. Some useful optimized parameters of compound L and L + X
(
X = F, Cl and Br) are given in Table 1. The optimized structure of
S
ꢀ
L + F shows that hydrogen bonding interactions exist within the
329 (nm)
Compound
L + F
S
0
0
? S
? S
1
2
3.3743 eV
367(nm)
3.4756 eV/ 0.6576 H-1 ? L + 1
356 nm
0.5354 H-1 ? L + 1
H ? L
0.23503
0.66095
0.69848
ꢀ
S
Table 1
–
Some useful optimized parameters of compound L and L + X (X = F, Cl, Br).
S0 ? S4
3.5611 eV/ 0.8765 H ? L + 1
0.69524
3
48 nm
ꢀ
ꢀ
ꢀ
Compound
L
HAX (Å)
N2AH3 (Å)
N2AX
HAX AH (°)
a
Only selected excited states were considered. The numbers in parentheses are
the excitation energy in wavelength.
1.01
1.05
1.02
1.02
ꢀ
L + F
L + Cl
1.63
2.40
2.49
2.66
3.37
3.47
100
75
71
b
ꢀ
Oscillator strength (only the f > 0.2 was considered).
H stands for HOMO and L stands for LUMO.
The CI coefficients are in absolute values.
c
ꢀ
L + Br
d

P. Sinha et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 286–294
293
Table 3
Appendix A. Supplementary material
ꢀ
Mulliken charges on compound L and L + F .
ꢀ
Compound L
Compound L + F
Atom
CCDC reference numbers 760554 contains the supplimentary
crystallographic data for L. This data can be obtained free of charge
at www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cam-
bridge Crystallographic Data Centre, 12, Union Road, Cambridge
CB2 1EZ, UK; fax: +44 1223/336 033; E-mail: deposit@ccdc.cam.a-
c.uk). The experimental details (Absorption, fluorescence, NMR,
ESI-MS, X-ray and computational studies) of ligand can be found
in online version.
Atom
Charges
Charges
N1
C3
C4
O1
N2
H3
N3
C5
ꢀ0.635
0.254
0.605
ꢀ0.542
ꢀ0.406
ꢀ0.305
ꢀ0.265
0.113
N1
C3
C4
O1
N2
H3
N3
C5
ꢀ0.032
ꢀ0.014
0.346
ꢀ0.652
ꢀ0.646
0.452
0.229
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2013.07.045.
ꢀ0.147
H4
C6
0.119
0.091
H4
C6
0.168
0.244
C12
O3
O2
H9
0.561
C12
O3
O2
H9
0.910
0.500
0.553
0.412
ꢀ0.512
ꢀ0.501
0.347
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