Synthesis, spectrophotometric, structural and thermal studies of the charge transfer complex of p-phenylenediamine, as an electron donor with π acceptor 3,5-dinitrobenzoic acid

Article abstract of DOI:10.1016/j.saa.2010.03.005

The interaction between p-phenylenediamine (PPD) as a donor with the π acceptor 3,5-dinitrobenzoic acid (DNB) has been investigated spectrophotometrically in methanol at room temperature. CT complex formed as a result of transfer of lone pair of electrons and exhibits well resolved charge transfer bands in the regions where neither donor nor acceptor have any absorption. The stoichiometry of the charge transfer complex (CTC) was found to be 1:1. The solid state CTC has also been synthesized, and has been characterized by elemental analysis, FTIR spectra, ¹H NMR spectroscopy and electronic absorption. The thermal stability of CT complex was studies using TGA and DTA analyses techniques. On the basis of the studies, the structure of CT complex is [(PPD)(DNB)], and a general mechanism for its formation is proposed. The formation constant and other physical parameters of the CT complex were determined by the Benesi-Hildebrand equation.

Full text of DOI:10.1016/j.saa.2010.03.005

Spectrochimica Acta Part A 76 (2010) 315–321
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, spectrophotometric, structural and thermal studies of the charge
transfer complex of p-phenylenediamine, as an electron donor with ␲ acceptor
3,5-dinitrobenzoic acid
Ishaat M. Khan, Afaq Ahmad∗
Department of Chemistry, Faculty of Science, Aligarh Muslim University, Aligarh 202002, Uttar Pradesh, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The interaction between p-phenylenediamine (PPD) as a donor with the ␲ acceptor 3,5-dinitrobenzoic
acid (DNB) has been investigated spectrophotometrically in methanol at room temperature. CT complex
formed as a result of transfer of lone pair of electrons and exhibits well resolved charge transfer bands
in the regions where neither donor nor acceptor have any absorption. The stoichiometry of the charge
transfer complex (CTC) was found to be 1:1. The solid state CTC has also been synthesized, and has been
characterized by elemental analysis, FTIR spectra, 1H NMR spectroscopy and electronic absorption. The
thermal stability of CT complex was studies using TGA and DTA analyses techniques. On the basis of
the studies, the structure of CT complex is [(PPD)(DNB)], and a general mechanism for its formation is
proposed. The formation constant and other physical parameters of the CT complex were determined by
the Benesi–Hildebrand equation.
Received 12 November 2009
Received in revised form 4 March 2010
Accepted 11 March 2010
Keywords:
P-phenylenediamine
3,5-Dinitrobenzoic acid
Charge transfer
Formation constant
Thermograms
1H NMR
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
␲–␲* molecular complexes of 3,5-dinitrobenzoic acid (DNB)
with O-tolidine and p-toluidine [23], and ␲ → ␲* molecular
Interest in electron donor–acceptor (EDA) or charge trans-
fer complexes studies is due to their wide applications such as
organic semiconductors [1], photocatalysts [2] and dendrimers
[3], in studying redox processes [4], second order nonlinear opti-
cal activity [5], micro-emulsion and in surface chemistry [6], in
solar energy storage [7] as well as in many biological fields [8].
EDA interactions are also important in the field of drug-receptor
binding mechanism. The CT complexes can act as intermediates
in a wide variety of reactions involving nucleophiles and electron
deficient molecules [9–11]. The charge transfer reactions of cer-
tain ␲-acceptor have been successfully utilized in pharmaceutical
analysis [12–16]. The wide application of CT complexes, therefore,
prompted extensive studies on them [17–19].
The electron donor–acceptor interactions had been widely stud-
ied spectrophotometrically in the determination of drugs based
on the CT complexes formation with some electron acceptors
such as 2,6-dichloroquinone-4-chloroimide (DCQ, Gibbs reagent),
7,7ꢀ,8,8ꢀ-tetracyanoquinodimethane (TCNQ), p-chloranil (CL) and
chloranilic acid (CLA) [12,14]. The review of literature in the last
decade have been mainly concentrated on the CT complexes spec-
tral studies [20–22].
complexes of O-phenylenediamine with tetracyanoethylene [24]
were investigated spectrophotometrically. The charge transfer
interactions of p-phenylenediamine with xylidine, p-chloranil
and chloranil have been reported [25–27]. The interaction of
3,5-dintrobenzoic acid with 3,5-dinitrobenzote quinclidine and
5,10,15,20-tetra(p-tolyl)porphyrin were also reported due to their
interesting properties [28–30].
In continuation of our studies of charge transfer interaction
[31–33], this paper presents the results obtained from electronic
and vibrational absorptions on the chemical product formed in the
reaction of p-phenylenediamine (PPD) as an electron donor and the
3,5-dinitrobenzoic acid as the ␲ acceptor. On the basis of the stud-
ies, the reaction stoichiometry, formation constant and structure
of the reaction product in both solution and solid and the nature of
interaction have been reported with the help of 1H NMR, FTIR spec-
tra, elemental analysis, electronic absorption as well as thermal
analyses (TGA and DTA).
2. Experimental
2.1. Materials
P-phenylenediamine (Merck, AR grade), 3,5-dinitrobenzoic acid
(Aldrich Chemicals Co.), chloroform (Merck) and methanol (spec-
troscopic grade) were used throughout the investigation.
∗
Corresponding author. Tel.: +91 9412174753.
E-mail addresses: ishaat.chem@gmail.com (I.M. Khan),
drafaqahmad7@gmail.com (A. Ahmad).
1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.03.005

316
I.M. Khan, A. Ahmad / Spectrochimica Acta Part A 76 (2010) 315–321
Table 1
The electronic absorption spectral data for charge transfer complex of PPD with DNB in methanol at room temperature.
Concentration of
acceptor
Concentration of
donor (M)
Absorbance at
ꢀCT 238 nm
Formation
constant (KCT) l
mol−1
Molar extinction
coefficient (εCT) l
cm−1 mol−1
(×10−4 M)
1.00
1.18
1.50
2.00
2.50
3.00
1 × 10−5
0.986
1.111
1.264
1.663
1.913
2.307
2.04 × 103
5.882 × 105
1 × 10−5
1 × 10−5
1 × 10−5
1 × 10−5
1 × 10−5
2.2. Preparation of standard solutions
thermal analyses (TGA and DTA) were carried out under nitrogen
atmosphere with a heating rate of 20 ◦C/min for TGA and DTA by
Shimadzu model DTG-60H Thermal Analyzers.
A standard solution of p-phenylenediamine (donor) at a con-
centration of 1 × 10−2 M was prepared in 50 ml of methanol and
diluting with the same solvents and a standard solution of DNB
1 × 10−2 M (acceptor) was prepared in 50 ml of methanol.
PPD (donor) and DNB (acceptor) were scanned separately
through a spectrophotometric titration [34] at room temperature
at wavelength of their maximum absorption. On mixing the solu-
tion of acceptor and donor, a charge transfer complex was formed.
The wavelength of maximum absorption of the resulting solution
was determined. The complex of the 1:1 reaction mixture standing
overnight at room temperature forming stable complex, was also
analyzed.
2.3. Synthesis of the solid CT complex
The solid CT complex [(PPD)(DNB)] was prepared by mixing the
saturated solution of p-phenylenediamine (0.108 gm, 1 mmol) in
CHCl3 (15 ml) and a saturated solution of 3,5-dinitrobenzoic acid
(0.636 gm, 3 mmol) in CHCl3 (50 ml). A light green color was formed
that produced to yellow precipitate. The precipitate was filtered off,
washed several times with small amounts (5 ml) of CHCl3 and dried
under vacuum over CaCl2. Reactants are soluble in chloroform but
the product (yellow) does not dissolve in chloroform. The complex
thus obtained was characterized by elemental analysis (theoreti-
cal values are shown in brackets): [(PPD)(DNB)], (C13H12N4O6) CT
complex (M/w: 320.26 g): C, 48.75% (48.81%); H, 2.52% (2.58%); N,
17.49% (17.58%).
3. Results and discussion
3.1. Observation of CT electronic spectra
The electronic absorption spectra of 1 × 10−4 M solution
of p-phenylenediamine (PPD) as donor 1 × 10−4 M solution of
3,5-dinitrobenzoic acid (DNB) as an acceptor, and their 1:1
(donor:acceptor) CT complex (e.g., to obtain the electronic absorp-
tion spectra of CT complex of PPD and DNB, solution of 1 × 10−4 M
PPD and 1 × 10−4 M DNB in methanol were mixed) in methanol
were recorded against methanol as reference are shown in Fig. 1.
Once the donor and acceptor solutions were mixed, change in color
was observed showing new absorption band in regions where nei-
ther donor nor acceptor has any absorption peaks. This is a clear
indication of the formation of CT complex of PPD and DNB and this
CT absorption band appeared at 238 nm for (PPD)–(DNB) mixture
(CTC). The absorbances of the CT complex increases on addition of
increased concentration of acceptor to the fixed amount of donor
are reported in Table 1. These measurements were based on the
CT absorption bands exhibited by the spectra of the systems men-
tioned as above and given in Fig. 1.
The stoichiometry of the CT complex was determined by apply-
ing straight line method based on Benesi–Hildebrand [35] equation.
It was also used to calculate the formation constant of the com-
plex using the absorbance of the CT complex. Benesi–Hildebrand
equation depends on the experimental conditions that either donor
concentration or acceptor concentration should be larger than the
other [36]. The formation constant was evaluated at max wave-
length of the absorbance of formed CT complex using the following
equation given below:
2.4. Spectral measurements and determination of formation
constant
The electronic absorption spectra of the donor (p-
phenylenediamine), acceptor (3,5-dinitrobenzoic acid) and
the resulting CT complex in methanol, were recorded in the region
of 700–200 nm by a Intra 10 UV–Visible spectrophotometer with a
1 cm quartz cell paths length are shown in Fig. 1. The FTIR spectra
of the reactants and the resulting CT complex were recorded using
KBr disc on the spectroscopic 2020 FTIR spectrometer. 1H NMR
spectra of the CT complex, donor and acceptor were recorded
in DMSO using Bruker Advance II 400 NMR Spectrometer. The
[D]0
A
1
1
1
εCT
[A]0
A
1
1
1
εCT
=
.
+
or
=
.
+
KCT εCT [A]0
KCT εCT [D]0
where [A]0 and [D]0 are the initial concentration of the acceptor
and donor respectively, A is the absorbance of the donor–acceptor
mixture (CTC) at ꢀCT against the methanol as reference, and εCT
the extinction coefficient of CT complex. The Benesi–Hildebrand
method [35] is an approximation that has been used many times
and gives decent result. The concentration of the ␲ acceptor in
each of the reaction mixture was kept greater than the donor and
changed over a wide range of concentration from 1 × 10−4 M to
3 × 10−4 M while concentration of the donor (PPD) was fixed at
Fig. 1. Electronic absorption spectra of (A) PPD, donor (1 × 10−4 M); (B) DNB,
acceptor (1 × 10−4 M) and (C) donor–acceptor CT complex, in methanol at room
temperature.

I.M. Khan, A. Ahmad / Spectrochimica Acta Part A 76 (2010) 315–321
317
Fig. 2. Benesi–Hildebrand plots of charge transfer complex of PPD with DNB [D]0/A
vs. 1/[A]0 in methanol at room temperature.
1 × 10−5 M in each of the reaction mixture. These produced solu-
tions with acceptor:donor molar ratios varying from 10:1 to 30:1,
these concentrations were used to obtain straight line diagram for
determination of formation constant (KCT) and molar extinction
coefficient (εCT) of CT complex (reported in Table 1).
The equation is valid under the condition [A]0 ꢁ [D]0 or
[D]0 ꢁ [A]0 [35,37] for 1:1 donor–acceptor CT complexes. By plot-
ting the values [D]0/A vs. 1/[A]0 straight line was obtained is shown
in Fig. 2 which indicates a 1:1 CT complex much in the same way
as 1:1 CT complex of p-phenylenediamine and p-chloranil [26].
This observed reaction stoichiometry is in good agreement with the
results of elemental analysis and 1H NMR for the solid CT complex
of PPD and DNB. Accordingly, the formed CT complex is formulated
as [(PPD)(DNB)].
Fig. 3. FTIR of (A) 3,5-dinitrobenzoic acid; (B) p-phenylenediamine; (C) charge
transfer complex of PPD and DNB.
itate to liberate the protons of COOH and in position 4H to make
intermolecular hydrogen bonds with lone pair of electrons on the
nitrogen atoms for the two amine groups of p-phenylenediamine.
It can be said that the donation process has been carried out by
–NH2 group in the case of DNB. It is also observed that the inter-
action between p-phenylenediamine with 3,5-dinitrobenzoic acid
does not have any role of –COOH group to the above mentioned
change in the CT complex. This justifies the complexation between
–NH2 and –COOH group in 3,5-dinitrobenzoic acid via intermolecu-
lar hydrogen bonding followed by migration of proton transfer from
acceptor to donor and assigned to N+–H–O− similar to the interac-
tion between p-toluidine and 3,5-dinitrobenzoic acid [23]. The N–H
stretching vibration is observed at 3413 cm−1 in spectrum of the
CT complex whereas in free PPD this is observed at 3372 cm−1. The
band at 3105 cm−1 is due to the aromatic C–H stretching vibration.
This shift has been attributed to the involvement of –NH2 group
in formation of CT complex. The COOH band has disappeared in
the spectrum of CT complex whereas in free DNB this is observed
at 1702 cm−1. This has also been attributed to the transfer of pro-
ton from acceptor to donor to form hydrogen bonding between
them. The –NH2 deformation mode is observed by absorption at
1621 cm−1. This band overlaps with the aromatic C C stretch-
ing vibrations. The bands at 1550 cm−1 and 1344 cm−1 confirm
the asymmetric and symmetric stretching vibrations of the –NO2
group respectively. Normally the asymmetric and the symmetric
stretching vibration of –NO2 group is sensitive to the polar influ-
ences and electronic states of the nucleus. Therefore, at appears
The existence of new CT band in CT complex indicates that the
transfer of lone pair of electrons from donor to acceptor occurred
due to the hydrogen bonding in the CT complex. The energy of these
interactions (ECT) is calculated using the following relation [38]:
1243.667
ECT
=
nm
ꢀCT
where ꢀCT is the wavelength of the CT band of the complexes. The
value of ECT was found to be 5.225 eV.
3.2. Comparative study of FTIR spectra of p-phenylenediamine,
3,5-dinitrobenzoic acid and their CT complex
The FTIR absorption spectra of the p-phenylenediamine, 3,5-
dinitrobenzoic acid and their CT complex are shown in Fig. 3 while
their band assignments are given in Table 2. It is observed that
the formation of the CT complex during the reaction of PPD with
DNB is strongly evidenced by the presence of the main character-
istic FTIR bands of the donor (PPD) and acceptor (DNB) (except
band of COOH) in the spectrum of the product (CTC). However,
most of frequencies of the donor decreases while most of fre-
quencies of acceptor increases with changes in their intensities in
the FTIR spectrum of CT complex. This shift has been attributed
to the charge transfer from donor to acceptor upon complexa-
tion. This happens because of the expected changes in molecular
symmetry and electronic structure of the reactants upon complex-
ation. Therefore, CT complexation between p-phenylenediamine
and 3,5-dintrobenzoic acid is strongly supported by FTIR spectra.
There was an increase in intensity of the peaks that distinguish
the –NH2 group (the donation sites for the PPD) and also there
were shifting for the peaks. The withdrawing groups on DNB facil-
that the frequency decreases of the ␯as(NO2) vibration (1550 cm−1
)
in the spectrum of the CT complex compared with the free DNB
(1595 cm−1) is due to the increased electron density on the DNB
moiety because of the charge transfer interaction in the CT complex.
The elemental analysis of the synthesized [(PPD)(DNB)] CT com-
plex matches exactly the calculated percentages corresponding to
(PPD:DNB) of the stoichiometric ratio 1:1.
3.3. 1H NMR spectra
1H NMR spectra of the donor (PPD), acceptor (DNB) and their
CT complex are measured in DMSO and the proton of the DMSO
in the spectrum CT complex appears at ı 2.56 ppm. The spectrum

318
I.M. Khan, A. Ahmad / Spectrochimica Acta Part A 76 (2010) 315–321
Table 2
Infrared frequenciesa (cm−1) and tentative assignmentsb for p-phenylenediamine (PPD), 3,5-dinitrobenzoic acid (DNB) and their CT complex [(PPD)(DNB)].
PPD
DNB
[(PPD)(DNB)]
3413 s
Assignmentsb
3372 m
3300 m
3462 w
␯(OH) of COOH; DNB ␯(NH); free PPD and CT complex
3295 mw
3187 s
Hydrogen bonding
3203 mw
3092 mw
2957 vw
2884 vw
2821 vw
3105 m
2920 m br
2638 m br
␯(C–H); C C–H and combination aromatic
1858 m
1627 s
1609 w
1514 vs
1967 vw
1848 w
1702 vs
2150 w br
1800 sh
Overtone of ␦CH; (out-of-plane) and combination aromatic + ␯(C–H); PPD + ␯(C O) + ␯(C N)
1452 m
1629 s
1595 ms
1540 vs
1473 vs
1621 s
1550 w
1534 m
1514 s
1452 s
␦(NH2), ␦(NH), ␦(CH), (C C) aromatic, ␯ (NO2); PPD, DBN and CT complex
as
1341 m
1308 vs
1414 vs
1423 w
␯ (NO2); DNB + ␯(C–O); COOH, PPD and CT complex
s
1348 vs
1285 vs
1344 vs
1277 s
1257 vs
1129 vs
1062 s
1039 m
1008 vw
1181 vs
1096 ms
1077 vs
1007 vw
1212 w
1170 w br
1125 w
1077 s
1000 vw
␯s(C–O); C–NH2 + in-plane bending of aromatic CH
934 m
881 vs
718 s br
952 ms
921 vs
806 s
918 s
899 ms
836 vs
OH and CH out-of-plane def. (aromatic ring + ␯(C–N); C–NH2 + ␯(C–N); C–NH2
669 sh
776 ms
723 vs
699 vs
795 s
730 sh
718 vs
518 vs
425 vs
640 s
670 w
Aromatic ring character of ortho substitution + NH2 def. + ␦b (CNO); NO2
620 ms
530 vs
452 ms
643 w
551 w
567 w
507 vs
476 s
460 m
a
br, broad; m, medium; s, strong; sh, shoulder; w, weak; ␯, stretching, ␦, bending.
Stretching and bending.
b
of CT complex was compared with the reactants and the chemical
shifts (ı) of the different types of protons of the donor, acceptor and
CT complex are listed in Table 3. We have embodied the 1H NMR
spectrum of the complex, donor and acceptor in Fig. 4 while their
peaks assignments and structure of donor acceptor and proposed
CT complexation are given in Scheme 1.
Further study on the CT complex of ␲-acceptor 3,5-
dinitrobenzoic acid with p-phenylenediamine is discussed
(Scheme 1) to their molecular structure and the different types
of interaction involved. It is found that these are changes in the
Table 3
1H NMR spectral data of PPD, DNB and their CT complex.
Compound
PPD
Chemical shift, ı (ppm)
Assignment
4.24
6.32
(s, 4H, two −NH2 group)
(s, 4H, Ar–H)
DNB
2.42
8.77
9.01
(s, 1H, Ar–COOH)
(s, 2H, Ar–H)
(s, 1H, Ar–H)
[(PPD)(DNB)]
5.8
6.69
9.01
(br s, 6H, 2 × +NH3 group)
(s, 4H, Ar–H of PPD)
(m, 2H, Ar–H of DNB)
Scheme 1. Mechanism of the reaction between PPD and DNB.

I.M. Khan, A. Ahmad / Spectrochimica Acta Part A 76 (2010) 315–321
319
Fig. 4. 1H NMR spectra of (A) p-phenylenediamine; (B) 3,5-dinitrobenzoic acid; (C) charge transfer complex of PPD and DNB.
Table 4
Weight loss, enthalpy (ꢁH), and degradation temperature (T), 3,5-dinitrobenzoic acid, p-phenylenediamine and CT complex of PPD and DNB.
Step
3,5-Dinitrobenzoic acid
p-Phenylenediamine
Weight loss (%)
CT complex of PPD & DNB
Weight loss (%)
ꢁH (J/gm)
T (◦C)
ꢁH (J/gm)
T (◦C)
Weight loss (%)
ꢁH (J/gm)
T (◦C)
I
II
98.937
–
−42.374
266.25
–
94.686
–
−46.065
201.13
–
48.80
51.27
−282.64
−4.89
174.935
499.24
–
–

320
I.M. Khan, A. Ahmad / Spectrochimica Acta Part A 76 (2010) 315–321
the two amino groups in the donor and the H-4 for DNB. The H-4
has more acidic character which facilitates to make intermolecular
hydrogen bond with one of amino group because H-4 is located
in the ortho position relative to two nitro groups (withdrawing),
making it easy to liberate. The other amino group is attached
with proton of the carboxylic group (intermolecular hydrogen
bond). The spectrum of the CT complex has shifted to –NH2 group
site of donation from ı 4.240 ppm (s, 4H, two –NH2 group) to ı
5.80–6.35 ppm (br s, 6H, 2 × NH3 group of p-phenylenediamine)
and ı 6.32 ppm (s, 4H, Ar–H) of PPD and ı 8.77 ppm (s, 2H, Ar–H)
of DNB have shifted to ı 6.69 ppm (s, 4H, Ar–H) and ı 9.091 ppm
(m, 2H, Ar–H), respectively. This shift has been attributed to the
involvement of the two amino groups during the formation of the
CT complex. This fact is supported by the electronic absorption
spectra and elemental analysis. FTIR analyses suggesting, the
absence of the carboxylic group character and the disappearance
of the value of ␯(C O) of the –COOH group around 1702 cm−1
,
suggests the dissociation of –COOH group.
3.4. Comparative study of thermograms for 3,5-dinitrobenzoic
acid, p-phenylenediamine and their CT complex
Thermal analyses was carried out for 3,5-dinitrobenzoic acid,
p-phenylenediamine and their CT complex. A heating rate of
20 ◦C/min within the temperature range of 25–1000 ◦C was main-
tained.
The thermal analyses results of PPA, DNB and their CT complex
has been presented in the combined GTG and DTA thermograms,
obtained in nitrogen atmosphere. It can be seen that both acceptor
and donor decompose in one step [39] as shown in Fig. 5A and B,
respectively. The weight loss of acceptor is 98.937% which is rather
higher than that of donor [40]. This can readily be expected due to
the higher value of degradation enthalpy for donor (−46.055 J g−1
)
compared with acceptor. It can also be observed that the accep-
tor degrades at higher temperature than that of the donor. It is
important to notice that the step wise degradation of both donor
and acceptor is also clearly depicted in TGA–DTA thermograms of
CT complex. Table 4 shows the weight loss, degradation enthalpy
and onset temperatures of degradation. It is obvious that the first
weight loss in Fig. 5C is due to the loss of donor molecule, which is
in good agreement with previous studies on similar structures [25],
while the second step (51.27%) is consistent with the loss of major
part of acceptor. The very small endothermic change associated
with the loss of acceptor is very much less (−4.84 J g−1) compared
with donor in the form of CT complex. The argument is that the loss
of carbon residue is, however, an exothermic change which causes
the reduction in the enthalpy value of the second step.
4. Conclusions
Fig. 5. TGA–DTA curves for (A) 3,5-dinitrobenzoic acid; (B) p-phenylenediamine;
(C) charge transfer complex of PPD and DNB.
Charge transfer interaction between the donor, p-
phenylenediamine and
␲ acceptor, 3,5-dinitrobenzoic acid
was extensively studied in methanol at room temperature. It is
observed that the reaction stoichiometry is 1:1 between donor
and acceptor, and the resulting CT complex was shown to have
the formula: [(PPD)(DNB)]. The interaction between the donor
and acceptor was found due to be due to transfer of lone pair of
electrons of nitrogen atoms of donor. The results showed that
the two –NH2 groups of p-phenylenediamine were involved in
the complexation with acceptor rather than the nitrogen of the
aromatic ring formed solid CT complex is more thermal stable
as compare to donor and acceptor. Transition energy, formation
constant, molar extinction coefficient and transition energy of the
CT complex have been estimated.
chemical shift values of the CT complex rather than the free
PPD and DNB similar to the 1H NMR spectra of CT complexes of
3,5-dinitrobenzoic acid with O-tolidine and p-toluidine [23]. The
1:1 molar ratio of (PPD:DNB) has been interpreted by 1H NMR
spectrum (Fig. 4, Scheme 1). All the observed peaks in the spectrum
of the individual reactants are also observed in the spectrum of
the CT complex suggesting its formation. The proton signals of the
donor PPD are usually down field shifted to higher ppm values
indicating transfer of n electrons from the donor to the acceptor.
The 1H NMR spectrum of the CT complex of p-phenylenediamine
as a donor with ␲-electron acceptor (DNB) occurs through one of

I.M. Khan, A. Ahmad / Spectrochimica Acta Part A 76 (2010) 315–321
321
Acknowledgements
[14] F.L. Zhao, B.Z. Xu, Z.Q. Zhang, S.Y. Tong, J. Pharm. Biomed. Anal. 21 (1999) 355.
[15] A.S. Amin, A.M. El-Beshbeshy, Microchim. Acta 137 (2001) 63.
[16] A.A. Mostafa, L.I. Bebawy, H.H. Refaat, J. Pharm. Biomed. Anal. 27 (2002) 889.
[17] Y.M. Issa, Spectrochim. Acta Part A 40 (1984) 1375.
[18] E.H. Mossalamy, K.Y. El-Baradic, Monatshfte for Chemic 128 (1997) 255.
[19] A.A. Boraei, Spectrochim. Acta Part A 58 (2002) 1895.
Special thanks to Chairman, Department of Chemistry, AMU for
providing research facilities at Physical Chemistry Lab and to UGC,
New Delhi for financial assistance under contingency and scholar-
ship to one of us (I.M. Khan).
[20] C.S.P. Sastry, B.S. Sastry, J. Venkateswara Roa, R. Ramakirshna, Talanta 40 (4)
(1993) 571.
[21] C.S.P. Sastry, K.R. Rao, D.S. Prasada, Microchim. Acta 126 (1–2) (1997) 167.
[22] G.G. Mohamed, S.M. Khalil, M.A. Zayed, M.A. El-Shall, J. Pharm. Biomed. Anal.
28 (2002) 1127.
References
[23] M.S. Refat, S.A. Sadeek, H.M. Khater, Spectrochim. Acta Part A 64 (2006) 778.
[24] A.S. Aljabar, E. Nour, Spectrochim. Acta Part A 70 (2008) 997.
[25] X. Li, M. Hung, R. Cheu, Y. Jin, Y. Yang, J. Appl. Poly. Sci. 81 (2001) 3107.
[26] M. Paliwal, M.L. Kalrab, S.C. Ameta, J. Indian Chem. Soc. 85 (2008) 1038.
[27] K.K. Kalninsh, G.M. Makhov, Russian J. Appl. Chem. 82 (2009) 563.
[28] S. Chantrapromma, H. Fun, A. Usman, J. Mol. Struct. 789 (2006) 30.
[29] S. Chantrapromma, A. Usman, H.K. Fun, B.L. Poh, C. Karalai, J. Mol. Struct. 688
(2004) 59.
[30] M.E. El-Zaria, A.R. Genady, Appl. Organomet. Chem. 21 (2007) 983.
[31] I.M. Khan, A. Ahmad, Spectrochim. Acta Part A 73 (2009) 966.
[32] I.M. Khan, N. Singh, A. Ahmad, Can. J. Anal. Sci. Spectrosc. 54 (2009) 31.
[33] I.M. Khan, A. Ahmad, Mol. Cryst. Liq. Cryst. 515 (2009) 154.
[34] S. Bhattacharya, S. Banerjee, C. Subrata, S. Chattopadhyay, M. Banerjee, Chem.
Phys. Lett. 393 (2004) 510.
[1] A. Eychmuller, A.L. Rogach, Pure Appl. Chem. 72 (2000) 179.
[2] R. Dabestani, K.J. Reska, M.E. Sigman, J. Photochem. Photobiol. A 117 (1998)
223.
[3] R. Jakubiak, Z. Bao, L. Rothberg, Synth. Met. 114 (2000) 61.
[4] K. Brueggermann, R.S. Czemuszewicz, J.K. Kochi, J. Phys. Chem. 96 (1992) 4405.
[5] M. Krishnamurthy, K. Surendrababu, U. Muralikrishna, Indian J. Chem. A 27
(1988) 669.
[6] S.M. Andrade, S.M.B. Costa, R. Pansu, J. Colloid Interf. Sci. 226 (2000) 260.
[7] K. Takahasi, K. Horino, T. Komura, K. Murata, Bull. Chem. Soc. Jpn. 66 (1993)
733.
[8] A.M. Slifkin, Charge Transfer Interaction of Biomolecules, Academic Press, New
York, 1971.
[9] A. Korolkovas, Essentials of Medicinal Chem, Second ed., Wiley, New York, 1998,
Chapter 3.
[35] H.A. Benesi, J.H. Hildebrand, J. Am. Chem. Soc. 71 (1949) 2703.
[36] H. Duymus, M. Arslan, M. Kucukislamoglu, M. Zangin, Spectrochim. Acta Part A
65 (2006) 1120.
[37] M. Hasani, R. Alireza, Spectrochim. Acta Part A 65 (2006) 1093.
[38] G. Briegleb, Z. Angew, Chemistry 72 (1960) 401.
[10] H.S. Bazzi, A. Mostafa, S.Y. AlQaradawi, E. Nour, J. Mol. Struct. 842 (2007) 1.
[11] A.S. Gaballa, C. Wagner, S.M. Teleb, E. Nour, M.A.F. Elmosallamy, G.N. Kalud-
erovic, H. Schmidt, D. Stembom, J. Mol. Struct. 876 (2008) 301.
[12] A.S. Amin, G.O. El-Sayed, Y.M. Issa, Analyst 120 (1995) 1189.
[13] H.H. Abdine, F.A. El-Yazbi, S.M. Blath, R.A. Shaalan, Spectrosc. Lett. 31 (1998)
355.
[39] M.S. Refat, H.M.A. Killa, Ivo Grabeher, Spectrochim. Acta Part A 68 (2007) 123.
[40] G. Li, W. Mo, H. Lin, H. Xiong, Appl. Catal. A: Gen. 333 (2007) 172.