Spectrophotometric and spectroscopic studies of charge transfer complex of 1-Naphthylamine as an electron donor with picric acid as an electron acceptor in different polar solvents

Article abstract of DOI:10.1016/j.molstruc.2010.05.032

The charge transfer complex of 1-Naphthylamine as a donor with π-acceptor picric acid has been studied spectrophotometrically in different solvents at room temperature. The results indicate that the formation of charge transfer complex is high in less polar solvent. The stoichiometry of the complex was found to be 1:1 by straight line method. The data are analysed in terms of formation constant (K_CT), molar extinction coefficient (ε_CT), standard free energy (ΔG^o), oscillator strength (f), transition dipole moment (μ_EN), resonance energy (R_N) and ionization potential (I_D). It is concluded that the formation constant (K_CT) of the complex is found to be depends upon the nature of both electron acceptor and donor and also on the polarity of solvents. Further the charge transfer molecular complex between picric acid and 1-Naphthylamine is stabilized by hydrogen bonding.

Full text of DOI:10.1016/j.molstruc.2010.05.032

Journal of Molecular Structure 977 (2010) 197–202
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Spectrophotometric and spectroscopic studies of charge transfer complex
of 1-Naphthylamine as an electron donor with picric acid as an electron acceptor
in different polar solvents
Neeti Singh, Afaq Ahmad *
Department of Chemistry, Faculty of Science, Aligarh Muslim University, Aligarh 202 002, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The charge transfer complex of 1-Naphthylamine as a donor with p-acceptor picric acid has been studied
spectrophotometrically in different solvents at room temperature. The results indicate that the formation
of charge transfer complex is high in less polar solvent. The stoichiometry of the complex was found to be
Received 13 February 2010
Received in revised form 22 May 2010
Accepted 24 May 2010
1
:1 by straight line method. The data are analysed in terms of formation constant (KCT), molar extinction
Available online 31 May 2010
o
coefficient (
e
CT), standard free energy (
D
G ), oscillator strength (f), transition dipole moment (
lEN), reso-
nance energy (R
N
) and ionization potential (I
D
). It is concluded that the formation constant (KCT) of the com-
Keywords:
Charge transfer complex
Visible region
plex is found to be depends upon the nature of both electron acceptor and donor and also on the polarity of
solvents. Further the charge transfer molecular complex between picric acid and 1-Naphthylamine is
stabilized by hydrogen bonding.
Formation constant
FTIR spectroscopy
Ó 2010 Elsevier B.V. All rights reserved.
1
H NMR spectrum
1
. Introduction
Charge transfer complexation is important phenomenon in bio-
carbons such as anthracene [13], some aniline derivatives [14] and
also with aromatic amines [15–17]. Mulliken suggested that the
formation of molecular complexes from two aromatic molecules
can arises due to an electron transfer from a –molecular orbital
of a Lewis base to vacant -molecular orbital of a Lewis acid, with
chemical and bioelectrochemical energy transfer process [1].
Charge transfer phenomenon was introduced first by Mulliken.
The term charge transfer gives a certain type of complex resulting
from interactions of donor and acceptor with the formation of
weak bands [2,3] and discussed widely by Foster [4]. Molecular
interactions between electron donors and acceptors are generally
associated with the formation of intensely colored charge transfer
p
p
resonance between this dative structure and the no-band structure
stabilizing the complex [2].
This study deals with the interaction of PiOH (picric acid) with
NPA (1-Naphthylamine) in solvents of different polarity at room
temperature by using visible spectra data of CT complex (
p–p) of
complexes (CTC
S
) in which absorb radiation in the visible region
1-Naphthylamine (donor) with -acceptor, picric acid in different
p
[
5]. Molecular complexation and structural recognition are impor-
solvents viz. acetone, ethanol, and methanol. The effect of solvents
on the formation of CT complex was also studied with the aim to
determine kCT reaction stoichiometry, formation constant. The
nature and structure of the reaction product both in solution and
solid phase has been studied to interpret the nature of interactions
tant processes in biological systems, for example, drug action,
enzyme catalysis and ion transfers through lipophilic membranes
all involve complexation [6]. Charge transfer complexes are cur-
rently of great importance since these materials can be utilized
as organic semiconductors [7], photo catalysts [8] and dendrimers
1
using H NMR, FTIR spectra and electronic absorption.
[
9]. They are also important in studying redox processes [10], sec-
ond order non-liner optical activity [11] and micro emulsion [12].
This paper describes the studies on the formation of CT complex
formed between picric acid (acceptor) and 1-Naphthylamine (do-
nor). Picric acid forms molecular complexes with aromatic hydro-
2. Experimental
2.1. Materials and methods
1
-Naphthylamine (CDH), picric acid (Aldrich) of the highest
purity were used without further purification. Ethanol (Merck ana-
lytical grade), acetone (Merck), methanol (Merck) were used as
supplied ascertaining their purities.
*
Corresponding author. Tel.: +91 941198305.
E-mail addresses: neetisingh72@gmail.com (N. Singh), afaqahmad212@gmail.-
com (A. Ahmad).
0
022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.05.032

1
98
N. Singh, A. Ahmad / Journal of Molecular Structure 977 (2010) 197–202
2
.2. Preparation of standard solutions
the maximum absorbance 445 nm for acetone and methanol and
50 nm for ethanol were recorded The concentration of the donor
in the reaction mixture was kept greater than acceptor, [D
] ꢀ [A
[19,20] and changed over a wide range from a concentration 0.1–
0.3 M. The concentration of -acceptor (picric acid) was kept fixed
[19] at 0.01 M in each solvent. These molar ratios (10:1–30:1) of
donor:acceptor was used to draw a straight line diagram for deter-
mination of the formation constants of CT complex.
4
Solutions of 1-Naphthylamine (donor) of different concentra-
o
o
]
tions, 0.1 M, 0.15 M, 0.2 M, 0.25 M, and 0.3 M were prepared sepa-
rately in different volumetric flasks in different solvents (acetone,
ethanol, and methanol).
p
0
.01 M standard solution of picric acid (acceptor) was prepared
by dissolving in above solvents respectively.
The electronic absorption spectra of the donor 1-Naphthyl-
amine, acceptor picric acid and the resulting complex in acetone,
ethanol and methanol respectively were recorded in the visible
range 400–600 nm using a spectrophotometer (ELICO SL 177 scan-
ning mini spectrophotometer) with a quartz cell of 1 cm path
length.
The electronic absorption spectra of 0.01 M PiOH, and 0.1 M
NPA in different solvents were recorded and the longest wave-
length peak was considered as CT peak [21]. The addition of the do-
nor changed the absorption intensity to higher values. These
measurements were based on the CT absorption bands exhibited
by the spectra of the systems mentioned as above and are given
in Figs. 2–4. In all systems studied the absorption spectra are of
similar nature except for the position of absorption maxima (kCT
of the complex. The CT complex absorption spectra were analyzed
by fitting to the Gaussian function,
)
2
.3. Synthesis of CT complex
The solid CT complex of picric acid and 1-Naphthylamine was
prepared by mixing equal weight of saturated solution of the donor
in chloroform with saturated solution of acceptor. The mixture was
stirred at room temperature for half an hour producing the CT
complex (solid). The complex was filtered off, washed with chloro-
form several time and then dried under vacuum.
pffiffi
2
2
y ¼ y þ ½A=w
ð
p
=2ÞÞꢁ exp½ꢂ2ðx ꢂ x Þ =w ꢁ
c
0
where x and y denote the wavelength and absorbance, respectively.
The results of the Gaussian analysis for all the systems under study
are shown in Table 1. The wavelengths at these new absorption
FTIR spectrum of picric acid, 1-Naphthylamine, and the reaction
product obtained from solid state reaction between acceptor and
donor was recorded with the help of FTIR spectrometer INTER-
SPEC-2020 (spectra lab, UK) measured in KBr pellets.
2
1
1
1
1
1
.0
.8
.6
.4
.2
.0
1
The nuclear magnetic resonance, H NMR spectrum of CT com-
plex is measured in DMSO using Bruker Advance II 400 NMR
spectrometer.
Absorption maxima 445
3
. Results and discussion
3.1. Observation of CT bands
0.8
0
0
0
.6
.4
.2
A 3 ml volume of donor and acceptor were scanned separately
by spectrophotometric titration [18] at room temperature at their
wavelength of maximum absorption, 380 nm for picric acid,
4
20 nm for 1-Naphthylamine in acetone and 320 nm for blank sol-
0.0
4
00
450
500
550
600
vent (acetone) (Fig. 1). The reaction mixture of donor (10 ml) and
acceptor (10 ml) in different solvents viz, acetone, ethanol and
methanol formed a dark yellow colored charge transfer complex.
The complex for each of the reaction mixture was kept overnight
at room temperature to form a stable complex, before analysis at
Wave length (nm)
ꢂ2
Fig. 2. Absorption spectra of picric acid (1 ꢃ 10 M) in acetone with addition of 1-
Naphthylamine concentrations ranging from 0.1 M to 0.3 M are shown with
increasing concentrations bottom to top.
D
1
1
0
0
.5
.0
.5
.0
C
B
2.0
Absorption maxima 450 nm
A
1
1
0
0
.5
.0
.5
.0
400
450
500
550
600
3
00
350
400
450
500
550
600
Wave length (nm)
Wave length (nm)
ꢂ2
Fig. 3. Absorption spectra of picric acid (1 ꢃ 10 M) in ethanol with addition of 1-
Naphthylamine concentrations ranging from 0.1 M to 0.3 M are shown with
increasing concentrations bottom to top.
Fig. 1. Absorption spectra of: (A) blank solvent (acetone) (B) picric acid 0.01 M (C)
-Naphthylamine 0.1 M (D) CTC of NPA 0.1 M and PiOH 0.01 M acetone.
1

N. Singh, A. Ahmad / Journal of Molecular Structure 977 (2010) 197–202
199
where
maximum of the CT absorption,
and R is the resonance energy of the complex in the ground state,
which, obviously is a contributing factor to the stability constant of
the complex (a ground state property). The values of R for the com-
N
plex under study are given in Table 2.
e
CT is the molar extinction coefficient of the complex at the
m
CT is the frequency of the CT peak
2
1
1
0
0
.0
.5
.0
.5
.0
N
Absorption maxima 445 nm
o
3
.5. Determination of standard free energy changes (
*
(ECT) of the p–p interaction between donor and acceptor
DG ) and energy
o
The standard free energy changes of complexation (DG ) were
calculated from the association constants by using the equation
derived by Martin et al. [24]
o
D
G ¼ ꢂ2:303RT log KCT
ð6Þ
o
ꢂ1
4
00
450
500
550
600
where
D
G is the free energy change of the complex (kJ mol ), R is
ꢂ1
Wave length (nm)
the gas constant (8.314 J mol K), T is the temperature in Kelvin
degrees (273+ °C) and KCT is the association constant of the complex
ꢂ2
Fig. 4. Absorption spectra of picric acid (1 ꢃ 10 M) in methanol with addition of
ꢂ1
(
l mol ) in different solvents at room temperature.
1
-Naphthylamine concentrations ranging from 0.1 M to 0.3 M are shown with
*
The energy (ECT) of p–p interaction between donor (NPA), and
increasing concentrations bottom to top.
acceptor, (PiOH), is calculated by using the equation derived by
Briegleb [25]
CT ¼ 1
243:667
ð7Þ
maxima (kCT = x
summarized in Table 2.
c
) and the corresponding transition energies (hm) are
E
k
CT
where kCT is the wavelength of the CT band.
3.2. Determination of ionization potentials of the donor
The calculated values of ECT are given in Table 5.
The ionization potentials of the donor (I ) in the charge transfer
complex are calculated by using empirical equation derived by Alo-
isi and Pignataro [22]
D
3
.6. Spectrophotometric study of formation constants of the charge
transfer complex of PiOH/NPA in different polar solvents
ðeVÞ ¼ 5:76 þ 1:53 ꢃ 10ꢂ4
Stoichiometries and the formation constants of the charge
transfer complex of 1-Naphthylamine with picric acid have been
determined in different polar solvents viz-acetone, ethanol and
methanol at room temperature using Benesi–Hildebrand equation
I
D
m
CT
ð1Þ
ꢂ1
where
mCT is the wave number in cm of the complex determined
in different solvents, viz, acetone, ethanol and methanol.
[
26,27]. The spectrophotometric data was employed to calculate
3
.3. Determination of oscillator strength (f) and transition dipole
the values of formation constants, KCT of the complex. The changes
in the absorbance upon addition of NPA to a solution of PiOH of
fixed concentration follow the Benesi–Hildebrand [26,27] equation
in the form.
moment (
EN
l )
From the CT absorption spectra, one can extract oscillator
strength. The oscillator strength f is estimated by using the
formula
½
Aꢁ =A ¼ ð1=KCT
e
CTÞ ꢃ 1=½Dꢁ þ 1=
e
CT
ð8Þ
o
o
Z
o o
where [D] and [A] are the concentrations of the 1-Naphthylamine
donor, and picric acid acceptor, respectively, A is the absorbance of
the donor–acceptor mixture at kCT against the solvents as reference,
f ¼ 4:32 ꢃ 10ꢂ9
e
d
m
ð2Þ
CT
R
where
CT
e dm is the area under the curve of the extinction coeffi-
cient of the absorption band in question vs. frequency. To a first
K
CT is the formation constant and
e
CT is the molar extinction coeffi-
[19,20]
cient, Eq. (8) [26,27] is valid under the condition [D]
for 1:1 donor–acceptor complex. The concentration of the donor
(NPA) was changed over a wide range from 0.1 M to 0.3 M while
o
ꢀ [A]
o
approximation
f ¼ 4:32 ꢃ 10ꢂ9
e
CT
D
m
1=2
ð3Þ
concentration of p-acceptor PiOH was kept fixed at 0.01 M in each
where
e
CT is the maximum extinction coefficient of the band and
reaction mixture. These produced solutions with donor:acceptor
D
m
1/2 is the half-width, i.e., the width of the band at half of the max-
molar ratio vary from 10:1 to 30:1.
imum extinction. The observed oscillator strengths of the CT bands
are summarized in Table 2.
The Benesi–Hildebrand [26,27] method is an approximation
that has been used many times and giving decent results. But the
extinction coefficient is really a different one between the complex
and free species that absorbs at the same wavelength. The intensity
in the visible region of the absorption bands, measured against the
solvent as reference, increases with increasing polarity and addi-
tion of NPA. The typical absorbance data for charge transfer com-
plex of NPA with PiOH in different polar solvents at room
temperature is reported in Tables 1 and 3. In all the systems, good
linear plots according to Eq. (7) [26,27] are obtained, shown in
Fig. 5. Formation constants for the complex in different polar sol-
vents at room temperature determined from the Benesi–Hilde-
brand plots are summarized in Table 3. The correlation
The extinction coefficient is related to the transition dipole by
1
=2
lEN ¼ 0:0952 ½
e
CT
D
m
1=2
=
D
m
ꢁ
ð4Þ
for the
R
P
where at
D
m
ꢄ
m
e
CT and
l
EN is defined as ꢂe wex ir
i
w d
s
g
complex of PiOH with NPA are given in Table 2.
N
3.4. Determination of resonance energy (R )
Briegleb and Czekalla [23] theoretically derived the relation to
obtain the resonance energy given as below:
e
CT ¼ 7:7 ꢃ 10ꢂ4=½h
m
CT=½R
N
ꢁ ꢂ 3:5ꢁ
ð5Þ
o
coefficients of all such plots were more than 0.95. Plots of [A] /A

2
00
N. Singh, A. Ahmad / Journal of Molecular Structure 977 (2010) 197–202
Table 1
Gaussion curve analysis for the CTC in spectrum of PiOH with NPA in different polar solvents.
Systems
Solvents
A
W
X
c
Y
0
PiOH + NPA
PiOH + NPA
PiOH + NPA
Acetone
Ethanol
Methanol
123.25 ± 9.10
154.94 ± 10.63
132.50 ± 8.17
53.05 ± 3.91
64.88 ± 4.075
56.27 ± 3.37
429.97 ± 1.52
435.89 ± 1.61
431.66 ± 1.33
0.0382 ± 0.0460
ꢂ0.0135 ± 0.0479
ꢂ0.00168 ± 0.0399
Table 2
CTC absorption maxima (kCT), transition energies (h
m
CT) of PiOH complex, experimentally determined ionization potential (I
D
) of the donor, oscillator strength (f), transition dipole
strengths (
l
EN) and resonance energy (R ) of complex.
N
5
Systems
Solvents
k
CT (nm)
h
m
CT (eV)
I
D
(eV)
f ꢃ 10
l
EN (Debye)
N
R (eV)
PiOH + NPA
PiOH + NPA
PiOH + NPA
Acetone
Ethanol
Methanol
429.97
435.89
431.66
2.89
2.85
2.88
9.30
9.26
9.29
2.22
2.77
2.45
0.936
0.946
0.955
0.0072
0.0072
0.0074
Table 3
Data for spectrophotometric determination of stoichiometry, absorption maxima (kCT) and association constant (KCT), molar absorptivities (
e
CT), of CTC of PiOH and NPA in
acetone, ethanol and methanol at 298 K.
ꢂ1
ꢂ1
ꢂ1
Systems
Solvents
Acetone
Temperature (K)
298
Donor concentration in M
0.1
[A]
o
M
Absorbance at kCT (nm)
k
CT (nm)
K
CT (l mol
)
e
CT (1 mol cm
)
PiOH + NPA
1.832
1.863
1.875
1.898
1.913
0
0
0
0
.15
.2
.25
.3
0.01
0.01
445
450
445
157
117
107
194
198
202
PiOH + NPA
PiOH + NPA
Ethanol
298
298
0.1
1.835
1.857
1.896
1.913
1.945
0
0
0
0
.15
.2
.25
.3
Methanol
0.1
0.01
1.843
1.894
1.915
1.945
1.960
0
0
0
0
.15
.2
.25
.3
3
.7. Effect of solvents on the formation of CT complex
5
5
5
5
5
5
4
.5
The experimental results of the CT interaction between PiOH
with NPA in different polar solvents show the values of association
constants as KCT 157(l mol ) in acetone, 117(1 mol ) in ethanol,
and 107(1 mol ) in methanol and the values of molar extinction
coefficient eCT 194(1 mol cm ) in acetone, 198(1 mol cm ) in
ethanol, and 202(1 mol cm ) in methanol. The spectroscopic
properties were markedly affected by the variation in solvent
polarity. The KCT values increases significantly from methanol to
acetone with decreasing solvents polarity. Moreover, the increase
in KCT values with decreasing solvents polarity, may also be due
to the fact that, CT complex is stabilized in less polar solvent
.4
.3
.2
.1
.0
.9
ꢂ1
ꢂ1
ꢂ1
ꢂ1
ꢂ1
ꢂ1
ꢂ1
acetone
ethanol
methanol
ꢂ1
ꢂ1
+
ꢂ
[
28]. Dissociation of the complex into D AA radicals have been
found to occur in the ground state [29]. It means the CTC should
be strong in less polar solvent than polar solvent. The red shift oc-
curred in CTC complex caused by polarity change on going from
acetone to methanol.
3
4
5
6
7
8
9
10
11
1
/[D]0
o o
Fig. 5. Relation between [A] /A and 1/[D] of PiOH + NPA in acetone, ethanol,
methanol.
However the data given in Table 3 shows that PiOH interacts
more strongly with NPA in acetone among the other two solvents.
The experimentally determined values of oscillator strength (f) is
ꢂ5
ꢂ5
ꢂ5
2
.22 ꢃ 10 in acetone, 2.77 ꢃ 10 in ethanol, and 2.45 ꢃ 10
against 1/[D]
in Fig. 5 for 1:1 charge transfer complex, i.e., the straight lines are
obtained with the slopes 1/KCT CT. These results suggest the forma-
tion of the 1:1 CT complex. From slope 1/KCT CT and intercept,
CT, KCT and CT of the complex were calculated.
o
were found to be linear in all the systems are shown
in methanol, the values of transition dipole moment (lEN) is
0
(
0
.936 (Debyes) in acetone, 0.946 (Debyes) in ethanol, and 0.955
Debyes) in methanol, and values of resonance energy R (eV) is
.0072 in acetone, 0.0072 in ethanol, and 0.0074 methanol, (given
e
N
e
1
/e
e

N. Singh, A. Ahmad / Journal of Molecular Structure 977 (2010) 197–202
Table 6
201
in Table 2) indicate that the complex should be stable in less polar
ꢂ1
Characteristic infrared frequencies (cm ) and tentative assignments for PiOH, NPA
and their complex.
solvent (acetone). The very low values of f indicate the neutral
character of CT complex in their ground state.
The parameters thus obtained are presented in Table 4. These
values show that the complexation is thermodynamically favored.
The free energy change of the complexation also reveals that the CT
PiOH
NPA
Complex
Assignments
3104s, br 3409br
–
3209br
3083br
m
m
m
(OAH), PA
(NAH), NPA mas (CAH), CH + CH
3 3
(CAH), aromatic
3338br
+
m ( NH)
complex formation between donor (NPA) and acceptor (PiOH) is of
o
–
2
–
3206br
3043br
exothermic nature. The values of
D
G for complexation in acetone,
870w
–
o
ethanol, and methanol are given in Table 4. The values of
DG tend
2845br
2591br
Hydrogen bonding b/w AOHAHANH
to be more negative as the association constants for CT complex in-
creases. This is because of the fact that as the bond between the
components becomes stronger so that the components are sub-
1
1
1
–
633vs
606ms
531br
–
1623vs
1572vs
1510vs
1450S
1406br
1373sh
–
1287vs
1170w
1083br
1608ms
1569ms
1530ms
1493vs
1417ms
1334br
–
1267br
1165ms
1083ms
m
m
as(NO
2
), PA
(C@C), aromatic
jected to more physical strain or loss of freedom, resulting is the
d def(NAH), +NH
CAH deformation
2
ring breathing bands
o
more negative values of
D
G .
The ionization potentials I
by using the experimentally determined kCT of the CT complex
from Eq. (1) [22]. The calculated values of I in acetone, ethanol,
methanol are shown in Table 5. The approximate constancy of I
D
(eV) of the donor can be calculated
1435ms
–
m
m
m
s 2
(CAC), m NO , PA
as(CAN)
(CAO)
1343vs
1277vs
1150ms
D
D
values, indicate that the ionization potential show a negligibly
1089ms
m
s
(CAN)
1012sharp
small effect on KCT values.
9
8
16ms
30w
951sharp
854sharp
936sharp d(CAH) in plane bending
915sharp drock, +NH CH rock skeletal vibrations
2
2
3.8. Comparative study of FTIR spectra of CT complex and reactants
783sharp
7
63vs
768vs
697ms
539sh
468br
–
CAH out of plane bending
7
6
5
27ms
63w
44w
666vs
574ms
457ms
–
FTIR spectrum of the free acceptor and donor as well as the
formed CT complex is given in Fig. 6 and their bands assignments
reported in Table 6.
d(ONO), PiOH
CNC deformation
521w
4
19sharp 417sharp
412ms
S, strong, w, weak; m, medium, sh, shoulder, v, very; vs, very strong, br, broad;
stretching; , symmetrical stretching; as, asymmetrical stretching.
m,
Table 4
m
s
m
Association constant (KCT), correlation coefficients (r) and standard free energy
changes (
o
D
G ) of PiOH/NPA complex obtained from Benesi–Hildebrand plots.
ꢂ1
o
ꢂ1
Systems
Solvents
K
CT (l mol
)
ꢂ
D
G
(298 K) (kJ mol
)
r
ꢂ1
The FTIR spectrum of picric acid shows a peak at 3104 cm due
PiOH + NPA
PiOH + NPA
PiOH + NPA
Acetone
Ethanol
Methanol
157
117
107
12.495
11.754
11.525
0.971
0.947
0.991
to
m
OH vibrations whereas the FTIR spectrum of 1-Naphthylamine
ꢂ1
show a number of peaks at 3409–3043 cm due to
m
NH2 vibra-
tions. As a result of complexation vibrational frequencies of OH,
NH
2
bands are broadened and shifted to lower wave number
ꢂ1
(
3209–2591 cm ) [30]. In the FTIR spectrum of complex the
ꢂ1
ꢂ1
Table 5
The CTC transition energies (ECT), CTC Absorption maxima (kCT), and ionization
Potential (I ) of donor of in different polar solvents.
broadened peaks occurred at 2845 cm
and 2591 cm
region
are due to hydrogen bonding in the complex. These results show
that the AOH group of picric acid is hydrogen bonded with the
hydrogen atom of amino group of 1-Naphthylamine. Thus, one
can say that a charge transfer molecular complex between picric
acid and 1-Naphthylamine is stabilized by hydrogen bonding.
D
Systems
Solvents
E
CT (eV)
k
CT (nm)
D
I (eV)
PiOH + NPA
PiOH + NPA
PiOH + NPA
Acetone
Ethanol
Methanol
2.794
2.763
2.794
445
450
445
9.19
9.15
9.19
1
3
.9. H NMR spectrum of CT complex
The 1H NMR spectrum of CT complex is shown in Fig. 7. The
spectrum of CT complex was compared with the reactants and
the chemical shifts (d) of the different types of protons of the do-
nor, acceptor and CT complex.
The singlet peak at d = 8.593 ppm has been assigned to the two
protons of the same kind in picric acid moiety in the complex. The
signal is split into triplet by two neighborhood proton one
8
C
.571 ppm [31]. The triplet peaks at d = 8.032 ppm is due to the
, C and C carbon atom of 1-Naphthyl amine and the doublet
, C carbon atom
1
2
3
peak 7.793 ppm is assigned to the proton on C
4
5
of 1-Naphthyl amine moiety in the complex. The same were ob-
served in free 1-Naphthylamine. The multiple peak at 7.669 ppm
are assigned to the proton on C , C , C , C and C10 carbon atom
6 7 8 9
of 1-Naphthyl amine and these peaks are also observed in free 1-
Naphthylamine molecule. The peak observed at 3.513 ppm in com-
+
ꢂ
plex is due to the formation of hydrogen bonding (N AHAO ) be-
tween picric acid and 1-Naphthylamine because in free picric acid
the peak at d = 11.94 ppm is due to the AOH proton of picric acid
[31] which are absent in spectrum on CT complex. These shifts
Fig. 6. FTIR spectrum of (A) complex of NPA and PA, (B) acceptor PA and (C) donor
NPA.

2
02
N. Singh, A. Ahmad / Journal of Molecular Structure 977 (2010) 197–202
the Benesi–Hildebrand method. The spectroscopic and thermody-
namic parameters of the complex were found to be solvent depen-
dent. The values of oscillator strengths, (f) transition dipole
moments, (
l
EN) resonance energies, (R
N
) and standard free ener-
o
gies, (DG ) have been estimated for the PiOH/NPA systems in dif-
ferent polar solvents. The results show that the investigated
complex is stable, exothermic and spontaneous. From the trends
in the CT absorption bands, the ionization potentials of the donor
1
molecules have been estimated. The FTIR and H NMR spectrum
shows that the charge transfer molecular complex formed between
NPA and PA stabilized by hydrogen bonding which is formed be-
tween AOH group of picric acid and AH atom of amino group of
1
-Naphthylamine.
Acknowledgements
Authors thanks Prof. K.S. Siddique, Chairman of Chemistry
Department, Aligarh Muslim University, Aligarh, India, for provid-
ing the research facilities. Financial assistance by the UGC, New
Delhi, is also gratefully acknowledged. The authors also thank the
learned referee for making valuable comments.
References
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[
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(
[
[
[
[
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4
. Conclusions
[
25] G. Briegleb, Z. Angew. Chem. 76 (1964) 326.
The UV–Vis spectrophotometric method for the study of CTC of
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[
[
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(
methanol. In all the systems the stoichiometry is unaltered by
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[
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