Spectroscopic and structural characterization of the charge-transfer interaction of N,N′-bis-alkyl derivatives of 1,4,6,8-naphthalenediimide with chloranilic and picric acids

Article abstract of DOI:10.1016/j.saa.2007.10.007

Charge-transfer (CT) complexes formed from the reactions of two N,N′-bis-alkyl derivatives of 1,4,6,8-naphthalenediimide such as N,N′-bis[2-hydroxyethyl)]-1,4,6,8-naphthalenediimide (BHENDI) and N,N′-bis-[2-N,N-dimethylaminoethyl)]-1,4,6,8-naphthalenediimide (BDMAENDI) with chloranilic acid (CLA) and piciric acid (PA) as π-acceptors, have been studied spectrophotometrically in methanol and chloroform, respectively at 25 °C. The photometric titration curves for the reactions indicated that the data obtained refer to 1:1 charge-transfer complexes of [(BHENDI)(CLA)], [(BDMAENDI)(CLA)], [(BHENDI)(PA)] and [(BDMAENDI)(PA)] were formed. Benesi-Hildebrand and its modification methods were applied to the determination of association constant (K), molar extinction coefficient (ε). The solid CT complexes have been synthesized and characterization by different spectral methods.

Full text of DOI:10.1016/j.saa.2007.10.007

Available online at www.sciencedirect.com
Spectrochimica Acta Part A 70 (2008) 907–915
Spectroscopic and structural characterization of the
ꢀ
charge-transfer interaction of N,N -bis-alkyl
derivatives of 1,4,6,8-naphthalenediimide with
chloranilic and picric acids
a,∗
b
Moamen S. Refat , Hamdy A. Ahmed ,
c
a
Ivo Grabchev , Lamia A. El-Zayat
a
Department of Chemistry, Faculty of Education, Port Said, Suez-Canal University, Egypt
b
Department of Chemistry, Faculty of Science, Zagazig University, Zagazig, Egypt
c
Institute of Polymers, Bulgarian Academy of Science, 103A Acad. G. Bonchev, 1113 Sofia, Bulgaria
Received 19 July 2007; received in revised form 14 September 2007; accepted 4 October 2007
Abstract
ꢀ
ꢀ
Charge-transfer (CT) complexes formed from the reactions of two N,N -bis-alkyl derivatives of 1,4,6,8-naphthalenediimide such as N,N -bis[2-
ꢀ
hydroxyethyl)]-1,4,6,8-naphthalenediimide (BHENDI) and N,N -bis-[2-N,N-dimethylaminoethyl)]-1,4,6,8-naphthalenediimide (BDMAENDI)
with chloranilic acid (CLA) and piciric acid (PA) as π-acceptors, have been studied spectrophotometrically in methanol and chloroform, respec-
◦
tively at 25 C. The photometric titration curves for the reactions indicated that the data obtained refer to 1:1 charge-transfer complexes of
[
(BHENDI)(CLA)], [(BDMAENDI)(CLA)], [(BHENDI)(PA)] and [(BDMAENDI)(PA)] were formed. Benesi–Hildebrand and its modification
methods were applied to the determination of association constant (K), molar extinction coefficient (ε). The solid CT complexes have been
synthesized and characterization by different spectral methods.
©
2007 Elsevier B.V. All rights reserved.
Keywords: 1,4,6,8-naphthalenediimide; CT complexes; Chloranilic acid; Piciric acid
1
. Introduction
have been performed [13]. In the recent few years N,N-bis-
substituted-1,4,6,8-naphthalenediimides have been investigated
intensively because of their promising applications. They can
be used in solar energy collectors [14], electronic and molecu-
lar devises [15,16], DNA sensors [17] or antibacterial agents
[18,19] and photoactive materials [20,21]. The quenching
effect on the fluorescence intensity of N,N-bis-substituted-
1,4,6,8-naphthalendiimides have been investigated [22,23]. A
systematic quantitative study of the solubility of various naph-
thalendiimides in organic solvents with different polarity has
been investigated by means of UV–vis spectroscopy [24]. In
Charge-transfer complexes (CT-complexes) are being
regarded as important materials due to their ample applications
1–4]. Such complexes are known to take part in many chemi-
[
cal reactions like addition, substitution and condensation [5,6].
These complexes have been studied in organic conductors and
photoconductors [7,8]. Electron donor–acceptor (EDA) inter-
action is also important in the field of drug-receptor binding
mechanism [9], in solar energy storage [10] and in surface chem-
istry [2] as well as in many biological fields [11]. On the other
hand, the EDA reactions of certain π-acceptors have success-
fully utilized in pharmaceutical analysis [12]. For these wide
applications extensive studies on CT-complexes of π-acceptors
ꢀ
this article, the CT complexes of two N,N -bis-alkyl derivatives
of 1,4,6,8-naphthalenediimide (BHENDI) and (BDMAENDI)
with chloranilic acid (CLA) and picric acid (PA) as π-acceptors
have been studied. Association constants (K), molar extinction
coefficient (ε), oscillator strength (f) are evaluated. The solid
complexes were synthesized and discussed by using elemental
∗
Corresponding author. Tel.: +20127649416.
1
E-mail address: msrefat@yahoo.com (M.S. Refat).
analysis (CHN), infrared, electronic absorption, H NMR and
1
386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.10.007

9
08
M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 907–915
the empirical formula of the complex is C24H N2O10Cl2
16
with molecular weight 563 g/mol. The other CT complex,
(BDMAENDI)(CLA)], was prepared as the same of previous
method but a red colored complex was formed with empirical
formula as C28H N4O8Cl2 with molecular weight 617 g/mol.
[
26
ꢀ
Scheme 1. Synthesis of N,N -bis-alkyl derivatives of 1,4,6,8-naphthalen-
ediimide. (Where R = CH2CH2OH for (BHENDI) and CH2CH2N(CH3)2 for
2
.3.2. [(BHENDI)(PA)] and [(BDMAENDI)(PA)]
complexes
The solid CT complex of (BHENDI) with picric acid was
(
BDMAENDI)).
prepared by mixing 1.0 mmol of the donor in 15 ml chloroform
with (0.229 mg, 1.0 mmol) of PA acceptor in the same solvent.
The mixture was stirred at room temperature for ∼20 min, where
the solid precipitation after the reduction of volume of the sol-
vent to the half. A yellow complex was filtered off, washed
several times with diethyl ether, and then dried over CaCl2.
mass spectra, thermo gravimetric analysis as well as molar ratio
determination of the molecular complexes.
2
. Experimental
2
.1.1. Materials and solutions
The empirical formula of the complex is C24H17N O13 with
5
molecularweight583.11 g/mol. ThesecondyellowCTcomplex,
ꢀ
The synthesis of N,N -bis-alkyl derivatives of 1,4,6,8-
[(BDMAENDI)(PA)], was prepared as the previous method with
naphthalenediimide was discussed [25] (Scheme 1). The
chloranilic acid (CLA) and picric acid (PA) were purchased
from Aldrich. Stock solutions of (BHENDI), (BDMAENDI)
and acceptors were freshly prepared and the spectroscopic grade
of chloroform (Merck Co.) and methanol (BDH) were used as
received.
the empirical formula of the complex is C28H27N7O11 with
molecular weigh 637.21 g/mol.
2.4. Infrared spectra
IR measurements (KBr discs) of the solid donors, acceptor
and CT complexes were carried out on a Bruker FT-IR spec-
trophotometer (400–4000 cm ).
2
2
.2. Instrumentation and physical measurements
−1
.2.1. Electronic spectra
The Electronic spectra of the donors (BHENDI),
.5. 1H NMR spectra
2
(
BDMAENDI), π-acceptors and the resulted CT complexes in
methanol and chloroform were recorded in the region of (200–
00 nm) by using a Jenway 6405 Spectrophotometer with
quartz cells, 1.0 cm path in length.
1
H NMR spectra were obtained on a Varian Gemini 200 MHz
1
spectrometer. H NMR data are expressed in parts per million
ppm), referenced internally to the residual proton impurity in
dmso (dimethylsulfoxide, d ) solvent and the reported of chem-
8
(
6
ical shift (m = multiplet and s = singlet; br = broad).
2
.2.2. Photometric titration
Photometric titration were preformed at 25 C for the reac-
◦
2.6. Mass spectra
tions of (BHENDI), (BDMAENDI) with chloranilic acid (CLA)
and picric acid (PA) in methanol and chloroform, respectively,
as follow: the concentration of the donor in the reaction mixtures
The compositions of the [(BHENDI)(CLA)] and
(BDMAENDI) (PA)] were confirmed from mass spectra
at 70 eV by using AEI MS 30 mass spectrometer.
[
−
4
was kept fixed at 1.0 × 10 M, while the concentration of π-
−
4
acceptors were changed over a wide range from 0.25 × 10 to
−4
4
.00 × 10 M. These produced solutions with donor: acceptor
2
.7. Thermal analysis
molar ratios varying from 1:0.25 to 1:4.00.
The thermal analysis (TGA&DTG) was carried under nitro-
2
2
.3. Synthesis of the CT complexes
gen atmosphere with a heating rate of 10 C/min using a
Shimadzu TGA-50H thermal analyzers.
.3.1. [(BHENDI)(CLA)] and [(BDMAENDI)(CLA)]
complexes
The solid CT complex of (BHENDI) with chloranilic
3. Results and discussion
acid was prepared by mixing (0.354 mg, 1.0 mmol) of the
donor in CH3OH (10 ml), a solution of chloranilic acid was
added (0.209 mg, 1 mmol) in the same solvent (10 ml) with
continuously stirring for about 2 h at room temperature. A violet
color developed and the solution was allowed to evaporate
slowly at room temperature. A dark gray complex was formed,
filtered, washed several times with little amounts of methanol,
and dried under vacuum over anhydrous calcium chloride;
3.1. Elemental analysis and conductivity measurements
The elemental analysis and physical measurements data
of the CT complexes formed [(BHENDI)(CLA)], [(BDMAE-
NDI)(CLA)], [(BHENDI)(PA)] and [(BDMAENDI)(PA)] are
agreement with the suggested CT complexes. The N,N -bis-
alkyl derivatives of 1,4,6,8-naphthalenediimide charge transfer
complexes are stable in air, soluble in DMSO and DMF.
ꢀ

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 907–915
909
Fig. 1. Electronic absorption spectra of: (A) BHENDI-CLA reaction in MeOH. (B): BDMAENDI-CLA reaction in MeOH. (C) BHENDI-PA reaction in CHCl3.
−
4
−4
(
D) BDMAENDI-PA reaction in CHCl3. (a) donor (1 × 10 M), (b) acceptor (1 × 10 M), (c) donor-acceptor CT-complex (measured immediately) and (d)
donor–acceptor CT-complex (measured after 24 h).
The electrical conductivity of the complexes in DMSO
bands appeared at 380 nm for BHENDI/CLA system, 525 nm
for BDMAENDI/CLA system, 420 nm for BHENDI/PA system,
and 414 nm BDMAENDI/PA systems. The color of solutions in
all systems of charge transfer interactions were changed imme-
diately, when firstly mixing (freshly prepared), this ensures that
new absorption bands (CT bands) were appeared. Furthermore,
the all systems were also measured spectrophotometrically after
24 h to take an idea about the stability of the systems in solution
manner (Fig. 1).
− −1
1
2
(
25–30 ꢀ cm mol ) indicates that all the complexes have
slightly electrolytes than the reactants. The level of purity in the
complexes was checked by TLC on silica gel-coated plates.
3
.2. Electronic spectra
The aromatic compounds (donors) represent a very impor-
tant class of donating compounds because of the ability of these
compounds to play the role as a π and/or n electron donors in
the charge-transfer interactions. The electronic absorption spec-
Photometric titration measurements were performed to deter-
mine the mode of interaction in CHCl3/MeOH between the
−
4
ꢀ
tra of 1.0 × 10 M solutions of each of two donors BHENDI
N,N -bis-alkyl-1,4,6,8-naphthalenediimide derivative donors
and BDMAENDI with acceptors chloranilic acid (CLA) and
and each acceptors. The photometric titrations were dealing
with the new absorption bands of the formed CT complexes.
Worthy mentioned that, the donor/acceptor molar ratio was
found to be the same 1:1. These stoichiometries results were
supported by elemental analysis for the sold CT complexes.
Accordingly, the formed CT complexes are formulated as
[(BHENDI)(CLA)], [(BDMAENDI)(CLA)], [(BHENDI)(PA)]
−
4
piciric acid (PA) 1.0 × 10 M solutions of each acceptor along
with those of the formed CT complexes in MeOH (in case of
CLA complexes) and in CHCl3 (in case of PA complexes) are
shown in Fig. 1. New detected bands in the UV/vis. spectra of
the CT complexes were exhibited, since both donor and accep-
tor alone did not absorb in this region. These CT absorption

9
10
M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 907–915
Table 1
Spectroscopic data of CT-complexes
K (l mol 1)
−
ε (l mol cm
−1
−1
)
E (eV)
f
μ
CT complexes
λ (nm)
4
4
2
2
2
2
[
[
[
[
(BHENDI)(CLA)]
(BDMAENDI)(CLA)]
(BHENDI)(PA)]
380
525
420
414
12.67 × 10
6.36 × 10
5.08 × 10
2.40 × 10
10.75 × 10
3.27
2.36
2.96
3.00
1.86 × 10
0.06 × 10
0.16 × 10
0.09 × 10
123
25
37
4
6
4
4
1.06 × 10
4
2.41 × 10
4
(BDMAENDI)(PA)]
1.15 × 10
28
Table 2
Infrared frequenciesa (cm ) and band assignments for (A): BHENDI, (B): BDMAENDI, (C): [(BHENDI)(CLA)], (D): [(BDMAENDI)(CLA)], (E):
(BHENDI)(PA)], and (F): [(BDMAENDI)(PA)] compounds
−1
[
A
B
C
D
E
F
Assignmentsb
3
424 br
3521 vs
3569 mw
3521 ms
3442 ms
3238 mw
3446 s, br
3522 vs
ν(O–H); BHENDI, CLA, PA and H2O of KBr
3
3
393 s, br
250 sh
3
080 ms
3067 mw
2993 ms,sh
3068 w
3080 vw
3068 w
νas(C–H); CH2 + CH3
ν(C–H); aromatic
2974 w
2949 w
2855 w
2821 ms
2770 ms
2956 mw
2892 w
2777 w
2960 w
2895 w
2975 vw
2901 vw
2855 vw
2821 vw
2768 vw
2956 w
2892 w
ν(C C); CH aromatic
νs(C–H); CH2 + CH3
–
–
2700 w
2740 vw
2700 vw
2725 vw
2650 vw
2550 vw
2730 vw
2700 vw
2660 vw
2500 vw
Hydrogen bonding
2650 w
2630 vw
2500 vw
1
1
702 s
658 vs
1695 s
1646 vs
1702 s
1668 s
1696 w
1647 vs
1705 vs
1668 vs
1694 vs
1646 vs
ν(C O); donors + CLA
1630 ms
1
1
1
1
581 ms
514 vw
456 s
1578 s
1582 ms
1521 vs
1487 ms
1371 ms
1581 mw
1612 ms
1560 s
1491 mw
1456 ms
1578 ms
ν(C C); aromatic
νas(NO2); PA
δ(CH); CH def.
δ(CH); aromatic
1455 s
1367 s
1456 ms
1362 s
1456 s
1367 s
375 w
1
1
432 vw
364 sh
1
1
1
1
350 s
287 ms
244 s
1329 vs
1245 vs
1178 vs
1341 ms
1249 ms
1210 vw
1164 ms
1332 sh
1250 vs
1177 ms
1338 vs
1269 s
1245 s
1160 vs
1330 s
1245 vs
1178 vs
νas(CN)
ν(C–O); C–OH
νs(NO2); PA
163 ms
1
1
111 m
043 ms
1052 vs
1009 w
1114 w
1036 w
1050 vs
1110 ms
1076 w
1052 vs
1009 w
νs(CN)
1041 ms
9
9
8
8
8
86 vw
57 vw
95 w
52 w
08 vw
960 vw
886 mw
856 w
994 w
919 vw
888 w
831 ms
986 ms
886 ms
848 s
999 vw
911 m
886 ms
δ(CH); in-plan bend
7
7
71 s
14 w
768 s
722 w
763 ms
719 vw
768 s
717 vw
613 w
771 s
746 w
711 s
768 s
722 w
δ(CH); CH-rock
ν(C–Cl); CLA
671 vw
602 mw
571 mw
445 vw
410 ms
590 w
573 ms
509 vw
466 vw
418 w
569 s
502 vw
431 w
598
548 vw
590 w
501 w
410 w
δ(CH); out-of-plan
502 m
463 vw
410 ms
a
br, broad; m, medium; s, strong; sh, shoulder; w, weak; ν, stretching; δ, bending.

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 907–915
911
and [(BDMAENDI)(PA)]. The ratio (1:1) of (donor:acceptor)
the Eq. (6).
could be associated with the steric hindrance effect of the donor
which is expected to occur in case of chloranilic and picric acid
acceptors. The CT bands in the case of the four studied com-
plexes occur at different wavelength values, this dependently on
the nature of the donor molecule. There is only new one CT
transition band (bathochromic (red) shift) in case of CT com-
plexes as: a singlet absorption at 380 nm for [(BHENDI)(CLA)],
weak broad band at 525 nm for [(BDMAENDI)(CLA)], shoul-
derabsorptionat420 nmfor[(BHENDI)(PA)], andat414 nmthe
weak broad band was exhibited for [(BDMAENDI)(PA)] com-
plexes, respectively. The appearance of only one new absorption
band in all these complexes is agreement with the reaction stoi-
chiometry of 1:1.
Ip = a + b(hνmax)
(6)
*
*
Where hνmax is the π–π and/or n–π transition energy in elec-
tron volts eV; a and b are 5.11 and 0.701 [32] 4.39 and 0.857 [33]
or 5.156 and 0.778 [34], respectively. This means that the ion-
ization potential values of BHENDI and BDMAENDI which
calculated by this method are 7.29 and 6.99 eV, respectively.
The calculated values of W (Eq. (4)) using the defined accep-
tor (CLA) are 2.92 and 3.53 eV for BHENDI and BDMAENDI,
respectively, where the electron affinity (EA) of chloranilic acid
is 1.10 eV [31].
Generally, these complexes show high values of both the for-
mation constant (K) and the extinction coefficients (ε). These
high values of K confirm the expected high stabilities of the
formed CT-complexes as a result of the expected high donation
of the donors. The equilibrium constants are strongly dependent
on the nature of the used acceptor including the type of electron
withdrawing substitute to it like nitro and halo groups.
The 1:1 modified Benesi–Hildebrand Eq. (1) [26] was used to
−
1
calculate the values of the equilibrium constant, K (l mol ), and
−
1
−1
the extinction coefficient, ε (l mol cm ), for the BHENDI,
and BDMAENDI charge transfer complexes.
o
o
o
o
C C l
1
Kε
(C + C )
A
D
A
D
=
+
(1)
A
ε
3.3. Infrared spectra
o
A
o
D
Where C and C are the initial concentrations of the acceptors
and donors, respectively, while A is the absorbance at the definite
The infrared spectra of the BHENDI and BDMAENDI,
along with the [(BHENDI)(CLA)], [(BDMAENDI)(CLA)],
(BHENDI)(PA)] and [(BDMAENDI)(PA)] charge transfer
o
o
o
o
CT bands. Plotting the values of C C l/A against (C + C )
A
D
A
D
values of (Eq. (1)), straight lines are obtained with a slope of 1/ε
and intercept of 1/Kε.
[
complexes are assigned and given in Table 2. The present
of the essential infrared bands of the donors (BHENDI and
BDMAENDI) and acceptors CLA and PA in the resulted
CT-complexes spectra strongly support the formation of CT-
complexation. It is clearly obviously that finding small shifts in
both wavenumber values and the intensities of bands in compar-
ison between free donors and the CT-complexes were formed.
This fact is due to the structure configurations upon the com-
plexation. For example;
The values of (ε) and (K) for the CT complexes are calculated
according to the slope and intercept of the linear relationship
o
o
o
o
of (C + C ) against (C C )/A. The oscillator strength (f),
A
D
A
D
which is dimensionless quantity, used to express the transition
probability of the CT-band [27] and the transition dipole moment
(
(
μ) of the CT complexes [28]. Table 1, have calculated data (ε),
K), (μ), and (f) through the following equations [29]:
f = 4.32 × 10−9(εmaxꢁν1/2)
(2)
(3)
ꢀ
ꢁ
1/2
(
i) Concerning the CT-complexes of BHENDI, the ν(O–H)
εmaxꢁν1/2
νmax
μ = 0.0958
vibration of the donor is observed as a broad band at
−
1
−1
3
424 cm in the spectrum of free donor, at 3235 cm
−
1
Where ꢁν1/2 is the half bandwidth of absorbance, εmax and
νmax the extinction coefficient and wavenumber at maximum
absorption peak of the CT complex, respectively. The dissocia-
tion energy (W), can be calculated from the corresponding CT
energy ECT, ionization potential of the donor (Ip) and electron
affinity of the acceptor (EA) using the relationship as follow
(strong broad) for CLA, at 3416 cm (broad) for PA and at
−
1
−1
3569 cm as medium weak and 3393 cm as strong broad
−1
bands for [(BHENDI)(CLA)] complex and at 3446 cm
as strong broad band for [(BHENDI)(PA)] complex, these
shifts in both wavenumbers and intensities make ensure that
one of OH groups of the BHENDI donor was involved in
the complexation.
[
30]:
(
ii) The change in both intensities and wavenumbers con-
cerning asymmetric and symmetric stretching vibrations
νs(C–H) + νas(C–H) for CH2 + CH3 groups in the case of
the CT complexes rather than donors were represented in
Table 2. These changes in the intensity and the value of
wavenumber of ν(C–H) can be interpreted accordingly the
location of CH2 + CH3 groups beside the OH and N(CH3)2
ECT = Ip − EA − W
(4)
*
The energy of the π–π interaction (ECT) is calculated using the
following equation [31]:
1
243.667
ECT =
(5)
λCTnm
Where λCT is the wavelength of the CT band of the complexes.
(
the place of complexation) for BHENDI and BDMAENDI,
respectively.
The ECT values calculated from Eq. (5) are listed in Table 1. The (iii) The ir spectra of the four new CT complexes are charac-
−
terized by a group of bands within the 2740–2500 cm
1
ionization potential value of the donors is calculated by using

9
12
M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 907–915
range which are not present in the spectra of the free donors.
Table 3
1
HNMR spectral data of BHENDI, BDMAENDI, [(BDMAENDI)(CLA)]
(BHENDI)(PA)] compounds
These bands are assigned to the intermolecular hydrogen
bonding [35] between OH group (lone pair of electron on
oxygen atom) of donor BHENDI or N(CH3)2 group (lone
pair of electron on nitrogen atom) of donor BDMAENDI
with phenolic OH group in case of CLA and PA. Electron-
withdrawing groups (NO2 and chloro groups) attached with
benzene ring increase the acidic of phenolic groups in
case of the acceptors CLA and PA, accordingly, this fact
that phenolic group play role of the acceptors. The pro-
posed mechanism of the interaction between acid and base,
meaning that acidic proton of the acceptor has a tendency
to transfer to the donor (base). This fact can be applied
herein in our study between CLA and PA with BHENDI
and BDMAENDI as donors. Such assumption is strongly
supported by the existence of a new bands of weak inten-
sity (hydrogen bonding) in the spectra of each complexes
prepared.
[
Compound
Chemical shift, Assignment
δ (ppm)
BDMAENDI
8.72
4.34
(s, 4H); naphthalene ring
(t, 4H, 2 × NCH2)
(t, 4H, 2 × CH2N)
(12H, NCH3)
2.68
.35
2
[
(BDMAENDI)(CLA)] 11.42
(s, br, H; OH of CLA)
8
4
3
2
.49
.51
.39
.88
(s, 4H); naphthalene ring
(s, br, H); NH-hydrogen bonding
(t, 4H, 2 × NCH2)
(t, 4H, 2 × CH2N)
(12H, NCH3)
+
2.52
BHENDI
8.46
4.85
4.10
(s, 4H); naphthalene ring
(t, 2H, OH)
(t, 2 × HOCH2)
3.63
(q, 4H, 2 × CH2N)
(
iv) The main stretching vibrations of ν(C O) and ν(C C) of
the two donors not affected upon complexation, this clearly
obviously that the lone pair of electron on the nitrogen atoms
in the napthalimide ring not participated in the complexation
process between donor and acceptor.
[(BHENDI)(PA)]
8.62 + 8.58
(s, 4H + 2H); naphthalene ring + PA
(t, 2H, OH) + hydrogen bonding
(t, 2 × HOCH2)
4.28
4.14
3.70
(q, 4H, 2 × CH2N)
(
v) Respecting, the two complexes of BDMAENDI donor,
found that, the priority of donation within the lone pair of
electron on nitrogen atom in the N(CH3)2 group rather than
nitrogen atom of napthalimide ring come from the presence
of two methyl group (donating group) which increasing the
donation behavior. This result was supported by the change
in the intensities of ν(C–H) of methyl group and ν(C–N)
stretching vibrations (Table 2).
ported the charge migration from the acceptor acid towards
the nitrogen atom of the donor.
(
ii) In the case of [(BHENDI)(PA)] complex, the signal which
distinguish for the proton of OH of PA acceptor is disap-
peared, this fact is strongly supported the formation of CT
complex, this due to the participation of hydrogen proton of
acceptor in the complexation process. The OH signal of the
donor in case of the CT-complex was upfield shifted toward
decreasing in the ppm value at 4.28 ppm rather than the
value of the free donor at 4.85 ppm. This result was proved
that the OH group of the donor was involved in the complex-
ation. On the other side, the ppm values of (t, 2 × OHCH2)
at 4.10 ppm, (q, 4H, 2 × CH2N) at 3.63 ppm and (s, 4H,
naphthalene ring) at 8.46 ppm have not show pronounced
shift upon complexation, this means that the complexation
occur through OH group of the donor and the nitrogen atom
of naphthalene ring not participated in the formation of the
.4. 1H NMR spectra
3
1
The H NMR spectra of the [(BDMAENDI)(CLA)] and
[
(BHENDI)(PA)] compounds were measured in DMSO solvent
using tetramethylsilane (TMS) as internal standard. The chem-
ical shifts (δ) of the different types of protons of the BHENDI,
BDMAENDI, [(BDMAENDI)(CLA)] and [(BHENDI)(PA)]
are listed in Table 3. The main signals of the two CT-complexes
were compared with the reactants. Interestingly, the nuclear
magnetic resonance spectra are well agreement with the infrared
spectra and their assignments concerning the place of CT com-
plexation as follows:
[(BHENDI)(PA)] complex. These data is agreed quite well
with the CHN analysis and the infrared spectra.
3.5. Mass spectra
(
i) Respecting to the [(BDMAENDI)(CLA)] complex and
1
comparison with the H NMR of BDMAENDI free donor
Electron impact mass spectra of the [(BHENDI)(CLA)] and
[
25], the presence of weak broad signal at 11.42 ppm indi-
[(BDMAENDI)(PA)] CT complexes confirms and occurrence
supports of the formation of CT complexes by showing the both
peaksofdonorsandtheacceptors(CLAandPA)at354and209 u
cate that only one of the OH phenolic group of CLA was
participated in chelating as hydrogen bonding, and the sec-
ond group is still free. It is clearly obvious that formed a
fortheC18H14N2O (BHENDI)andC H2Cl2O4 (CLA), respec-
6
6
+
new signal peak at 4.51 ppm which assigned to NH proton
tively, and at 408 and 229 u for C22H24N4O4 (BDMAENDI)
due to the protonation of the donor. All the observed proton
peaks in the spectra of the starting reactants are also exist in
the formed CT-complexes spectra with small shifted (down-
field)toincreasingppmvalues. Thesechangesintheδ(ppm)
values of the donor and resulted complex are strongly sup-
and C H3N3O7 (PA), respectively, and other peaks like 124,
6
153, 181, 249, 281, 293, 311 and 323 u may correspond to var-
ious fragments in the case of [(BHENDI)(CLA)] complex. The
intensity of these peaks gives an idea of the stability of these
fragments.

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 907–915
913
Scheme 2. The mode of interactions of [(BHENDI)(CLA)], [(BDMAENDI)(CLA)], [(BHENDI)(PA)] and [(BDMAENDI)(PA)] CT-complexes.
Single crystals of the complexes could not be isolated from
any organic solutions, thus, no definite structures could be
described. However, theanalyticalandspectroscopicdataenable
us to predict possible structures as shown in Scheme 2.
decomposition reaction are given in Table 4, together with
evolved moiety and the theoretical percentage mass losses.
Thermal techniques, such as thermogravimetric analysis
(TGA and DTG), has been successfully employed for the study
of the energetic of interactions of charge transfer complexes
[36–39]. The weight loss profiles are analyzed the amount or per-
3
.6. Thermal analysis
cent of weight loss at any given temperature, and the temperature
ranges of the degradation process were determined.
The thermogravimetric analysis (TG) were carried out using
The overall loss of mass from the TG curves is 84.51%
for [(BHENDI)(CLA)] and 75.00% for [(BDMAENDI)(CLA)]
complexes, respectively. Both of these complexes have
two essential maxima peaks mass loss. The first sharp
endothermic peak concerning the resulted CT-complexes exhib-
a Schimadzu TGA-50H thermal analyzer, in temperature range
of 25–800 C, at heating rate 10 C min . The analyses were
carried out over samples varying from 50 to 90 mg.
◦
◦
−1
The [(BHENDI)(CLA)] and [(BDMAENDI)(CLA)] com-
plexeswerestudiedbythermogravimetricanalysisfromambient
◦
◦
◦
ited at 430 C for [(BHENDI)(CLA)] and at 290 C for
(BDMAENDI)(CLA)] complex may be due to loss of
chloranilic acid (C H2O4Cl2) molecule and the second decom-
temperature to 800 C in nitrogen atmosphere. The TG curves
[
were redrawn as percent mass loss vs. temperature (TG) curves.
The temperature ranges and percentage mass losses of the
6
Table 4
Thermal data of the (A): [(BHENDI)(CLA)] and (B) [(BDMAENDI)(CLA)] complexes
◦
Compound
Steps
Temperature range ( C)
DTGmax
TG Weight loss (%)
Assignments
Calc.
Found
A
B
1st
25–450
450–800
430
625
37.11
47.98
36.57
47.94
15.49
33.15
41.85
25.00
C6H2O4Cl2 (CLA molecule)
C11H14N2O6 (organic moiety)
7C residue
C6H2O4Cl2 (CLA molecule)
C9H24N4O4 (organic moiety)
13C residue
2nd
14.91
1st
nd
25–350
350–800
290
550
33.86
40.87
2
25.27

9
14
M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 907–915
Table 5
Kinetic thermodynamic data of [(BHENDI)(CLA)] and [(BDMAENDI)(CLA)] CT complexes
◦
Complexes
T/ C
DTG/Max
ꢁE
ꢁH
ꢁS
ꢁG
r
[
[
(BHENDI)(CLA)]
(BDMAENDI)(CLA)]
25–450
25–350
430
290
156
136
−4523
−3854
−95
−86
29821
12356
0.9785
0.9845
ꢀ
position step refer to the pyrolysis of the N,N -bis-alkyl
derivatives of 1,4,6,8-naphthalenediimide rest.
The two endothermic decomposition stages correspond to
decomposition of the chloranilic acid (acceptor) then fol-
lowed by donor. The TG curve of the complex shows a
weight loss (Found 75.00%, Calcd. 74.73% corresponding
to the loss of one molecule of CLA and C H N O organic
9 24 4 4
rest.
(
i) [(BHENDI)(CLA)] complex
◦
The BHENDI complex melts at above >300 C with
simultaneous decomposition. The main degradation peak
was observed at 430 C in the TG profile and interpreted
◦
3
.7. Kinetic study
to the loss of chloranilic moiety (C H2O4Cl2). From the
6
TG curve, it appears that the second decomposition step at
ꢀ
In order to study the influence of the N,N -bis-alkyl deriva-
◦
ꢀ
DTGmax ∼625 C discussed to the loss of N,N -bis-alkyl of
tives of 1,4,6,8-naphthalenediimide with fixed CLA as acceptor
on the stability of the resulted CT complexes, there investigated
kinetically were carried out using the Coats–Redfern method
Eq. (7) [40]. The results are listed in Table 5, and shown in
Fig. 2. The calculating of thermodynamic data applied on the
first decomposition peak in each three CT complexes.
1
,4,6,8-naphthalenediimide (C11H14N2O ). The decompo-
6
sition occurs with a mass loss of 47.94% and its calculated
value is 47.98%.
(
ii) [(BDMAENDI)(CLA)] complex
Thermal analysis curves of the [(BDMAENDI)(CLA)]
complex show that decomposition takes place in two stages
◦
◦
ꢂ−
ꢃ
ꢀ
ꢁ
in temperature range 25–800 C (DTGmax: 290 and 550 C).
ln(1 − α)
ZR
ϕE
E
ln
= ln
−
(7)
2
T
RT
where α, and ϕ are the fraction of the sample decomposed at time
t and the linear heating rate, respectively. R is the gas constant
−
1
and E is the activation energy in kJ mol
.
2
A plot of ln[−ln(1 − α)/T ] against 1/T was found to be linear
Fig. 8, from the slope of which E, was calculated and Z (Arrhe-
nius constant) can be deduced from the intercept. The enthalpy
of activation, ꢁH, and the free enthalpy of activation, ꢁG, can
be calculated (Table 5) via the equations;
ꢁH = E − RTm; ꢁG = ꢁH − TmꢁS
Accordingly, the kinetic data in Table 5, all of the CT
complexes have −ve entropy, which indicates that activated
complexes have more ordered systems than reactants. On the
looking of Table 5, found that the [(BHENDI)(CLA)] complex
has a higher activation energy and association constant than
[(BDMAENDI)(CLA)] complex, this fact is strongly supported
with the thermal stabilities which mentioned in thermogravimet-
ric section.
4. Conclusion
ꢀ
Charge-transfer interactions between the two N,N -
bis-alkyl derivatives of 1,4,6,8-naphthalenediimide such
ꢀ
as
(
N,N -bis[2-hydroxyethyl)]-1,4,6,8-naphthalenediimide
ꢀ
BHENDI) and N,N -bis-[2-N,N-dimethylaminoethyl)]-1,4,6,8-
naphthalenediimide (BDMAENDI) donors with chloranilic and
piciric acids as π-acceptors were studied spectrophotometrically
in chloroform and methanol. The results show that the stoi-
chiometry is the same 1:1 ratio and the formed CT-complexes
were shown to have the molecular formula [(donor)(acceptor)].
The spectral data indicate that the intermolecular hydrogen
Fig. 2. The kinetic thermodynamic diagrams of (A) [(BHENDI)(CLA)] and (B)
(BDMAENDI)(CLA)] CT complexes using Coats and Redfern (CR) equation.
[

M.S. Refat et al. / Spectrochimica Acta Part A 70 (2008) 907–915
915
bond formed between the donors and acceptors via lone pair
of electrons on oxygen and nitrogen atoms of the terminal
OH and N(CH3)2 groups of the BHENDI and BDMAENDI
donors, respectively, with phenolic OH group in the case of
both acceptors. The CT complexes were confirmed on the
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Acknowledgements
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Canal University Egypt.
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