Charge transfer complex formation between p-chloranil and 1,n-di(9-anthryl)alkanes

Article abstract of DOI:10.1016/j.saa.2005.07.073

Dimer model compounds of polyvinylanthracenes (1,n-di(9-anthryl)alkanes, when n = 1-5) were synthesized to model the effects of distance and orientation between anthracene groups in polymeric systems. Charge transfer (CT) complexes of anthracene, 9-methylanthracene and 1,n-di(9-anthryl)alkanes with p-chloranil (p-CHL) have been investigated spectrophotometrically in dichloromethane. The colored products are measured spectrophotometrically at different wavelength depending on the electronic transition between donors and acceptor. The formation constants of the CT complexes were determined by the Benesi-Hildebrand equation. The thermodynamic parameters were calculated by Van't Hoff equation. Stochiometries of the complexes formed between donors and acceptor were defined by the Job's method of the continuous variation and found in 1:1 complexation with donor and acceptor at the maximum absorption bands.

Full text of DOI:10.1016/j.saa.2005.07.073

Spectrochimica Acta Part A 64 (2006) 711–716
Charge transfer complex formation between
p-chloranil and 1,n-di(9-anthryl)alkanes
Mustafa Arslana,∗, John Masnovib
a
Sakarya University, Faculty of Arts and Sciences, Department of Chemistry, Sakarya, Turkey
b
Cleveland State University, Department of Chemistry, 44115 Cleveland, Ohio, USA
Received 27 June 2005; accepted 26 July 2005
Abstract
Dimer model compounds of polyvinylanthracenes (1,n-di(9-anthryl)alkanes, when n = 1–5) were synthesized to model the effects of distance
and orientation between anthracene groups in polymeric systems. Charge transfer (CT) complexes of anthracene, 9-methylanthracene and 1,n-
di(9-anthryl)alkanes with p-chloranil (p-CHL) have been investigated spectrophotometrically in dichloromethane. The colored products are
measured spectrophotometrically at different wavelength depending on the electronic transition between donors and acceptor. The formation
constants of the CT complexes were determined by the Benesi–Hildebrand equation. The thermodynamic parameters were calculated by Van’t
Hoff equation. Stochiometries of the complexes formed between donors and acceptor were defined by the Job’s method of the continuous
variation and found in 1:1 complexation with donor and acceptor at the maximum absorption bands.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Charge transfer complexes; 1,n-Di(9-anthryl)alkanes; p-Chloranil; Spectrophotometrically determination
1. Introduction
donors (D) are mixed with electron acceptors (A) [6,7]. Col-
ors accompany complex formation in solution, as a result of
electronic interchanges between components [8].
Photoconductive polymers are used commercially in elec-
trophotography and as storage media for light-weight batter-
ies and photovoltaic cells for solar energy conversion [1,2].
Photoconductive polymers absorb radiation in the UV region.
In order to generate hole carriers and bring absorption into
the visible region, dopants are added. Photoconductive poly-
mers can be doped with electron acceptors to form electron
donor–acceptor (EDA) complexes [3]. Charge transport in
doped polymer systems is visualized as a donor–acceptor
process. Charge transfer (CT) processes to generate posi-
tively charged dopant molecules, which are radical cations
in the polymer [4]. Optical absorption of radiation in the CT
(visible region) by the EDA complexes gives photocarrier
generation [5].
EDA type complexes have important conductive proper-
ties in many types of chemical reactions. EDA complexes are
commonly found as intermediates in a variety of reactions
involving electron rich species or donors, such as nucle-
ophiles and bases, and electron deficient acceptors [6,8].
Aromatic donors readily form EDA complexes with various
typesof␲acceptors, suchaschloranilandtetracyanoethylene
(TCNE) [9]. EDA complexes promote reactivity by bring-
ing the reactants together and encouraging the correct orbital
overlap required for electronic reorganization [10].
EDA complexes have great attention for non-linear opti-
cal materials and electrical conductivities [11–15]. And also
EDA interactions play an important role in the field of drug-
receptor binding mechanism [16].
In this work, dimer model compounds of polyvinylan-
thracenes (1,n-di(9-anthryl)alkanes, when n = 1–5) were syn-
thesized to model the effects of distance and orientation
between anthracene groups in polymeric systems. Formation
constants, stochiometries, thermodynamic parameters of the
The formation of EDA complexes is readily apparent from
the observation of new optical absorptions when electron
∗
Corresponding author. Tel.: +90 264 276 0237x109;
fax: +90 264 346 03 71.
E-mail address: marslan@sakarya.edu.tr (M. Arslan).
1386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2005.07.073

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M. Arslan, J. Masnovi / Spectrochimica Acta Part A 64 (2006) 711–716
complexes between dimer compounds and p-chloranil were
determined.
chromatography on alumina with hexane/dichloromethane
eluting fractionally.
2.3. Stoichiometric relationship
2. Experimental
The stoichiometries of the 1,n-di(9-anthryl)alkanes with
chloranil were investigated. The method of continuous vari-
ations as given by Job’s plot [18] is used to establish
the stoichiometries of the complexes. Equimolar samples
of anthracene, 9-methylanthracene, di(9-anthryl)alkanes and
chloranil were prepared separately in methylene chloride.
The concentrations of the sample were dependent on the sol-
ubility of the individual compounds in CH2Cl2. Aliquots of
solutions were varied alternately from 0.2 to 0.8 ml for donor
and chloranil solutions to hold the total volume at 1 ml in
the cuvette by using a 1 ml syringe. Average optical densities
were calculated from three runs on the same sample and aver-
age values at 812–820 nm were subtracted from the average
values at the maxima.
2.1. Apparatus
A Hewlett-Packard HP8452A diode array spectropho-
tometer was used for UV–vis spectra using dichloromethane
as the solvent. Proton (1H) and 13C NMR spectra were
obtained with a Bruker AC300F spectrometer using CDCl3
solvent (Cambridge Isotopes).
2.2. Materials
Anthracene (M1) (Merck), 9-methylanthracene (M2)
(Merck), p-chloranil (Merck), were used as bought.
Dichloromethane used as solvent was spectroscopic grade.
1,n-Di(9-anthryl)alkanes were synthesized as below.
2.4. Equilibrium constants
2.2.1. Di(9-anthryl)methane (1)
The Benesi–Hildebrand equation [19] was used to cal-
culate equilibrium constants for the formation of EDA com-
plexesoftheanthracene, 9-methylanthraceneandtheseriesof
1,n-di(9-anthryl)alkanes. In these experiments, the electron
acceptor (chloranil) was used at high concentration (initially,
∼0.02 M) and the donor anthracenes were kept at a constant
concentration which was always at least 20 times smaller
than the concentration of chloranil. Chloranil background
was measured before each spectrum was taken.
In the method for calculation of the equilibrium constants
of EDA complexes using the Benesi–Hildebrand equation,
10 ml stock solutions of dianthryl in dichloromethane were
prepared and 1 ml of the solution was placed in a 1 cm UV–vis
cuvette. Chloranil was added to the 1 ml cuvette sample at
∼21 mM concentration. The concentration of chloranil was
decreased during the experiment by adding 0.1 ml divisions
of the stock donor solution to the cuvette, which was used
for measurement. The UV–vis spectrum was measured after
each addition of 0.1 ml of solution. About 15 dilutions were
run with each anthracene. The reverse concentration method,
which involves keeping the chloranil concentration constant
and adding a solution of anthracene compound to the sample
cuvette, was not possible due to the low solubilities of the
dianthrylalkanes (when n = 1 and 2).
9-Anthrylmagnesium bromide was prepared by react-
ing 0.0166 moles of magnesium with 0.0062 moles of 9-
bromoanthracene in 30 ml of anhydrous ethyl ether for 24 h at
room temperature with a small amount of iodine to initiate the
reaction. Then, 0.0062 moles of 9-(chloromethyl)anthracene
in 40 ml of anhydrous benzene were added to the cream
colored grignard reagent and refluxed for 15 h. The reac-
tion mixture was then cooled and extracted with 0.1 M HCl
(50 ml). The yellow precipitate was filtered through a Buch-
ner funnel and the final di(9-anthryl)methane product was
isolated by recrystallization from toluene and then chloro-
form.
2.2.2. 1,2-Di(9-anthryl)ethane (2)
1,2-Di(9-anthryl)ethane was synthesized by reductive
dimerization of 9-anthraldehyde with LAH refluxing 3 h in
THF. The product was purified by recrystallization from
toluene and chloroform.
2.2.3. 1,3-Di(9-anthryl)propane (3)
Trans-1,3-di(9-anthryl)propenone was prepared accord-
ing to the literature procedure [17]. The compound was
reduced by sodium borohydride in tetrahydrofuran to 1,3-
di(9-anthryl)propan-1-ol and 1,3-di(9-anthryl)propan-1-one.
In the last step, these two compounds were reduced to the
1,3-di(9-anthryl)propane with LAH/AlCl3 in ethyl ether.
2.5. Thermodynamic constants
Van’t Hoff and Beer–Lambert equations were used to cal-
culate thermodynamic parameters for the EDA complexes of
anthracene compounds with chloranil.
2.2.4. 1,4-Di(9-anthryl)butane (4) and
1,5-di(9-anthryl)pentane (5)
1,4-Di(9-anthryl)butane and 1,5-di(9-anthryl)pentane
were prepared via the formation of di-grignard reagents
from 1,n-dibromoalkanes (n = 4 and 5) followed by reaction
with anthrone. The compounds were purified by column
Measurements were run at 0, 7, 14, 21, 28 and 35 ◦C
(except for di(9-anthryl)methane due to precipitation at
14 ◦C). Samples of the anthracene series of compounds with
chloranil were prepared in volumetric flasks and placed into

M. Arslan, J. Masnovi / Spectrochimica Acta Part A 64 (2006) 711–716
713
a 1 cm UV–vis cuvette. Measurements at 0 ◦C were run
in a glove bag under nitrogen atmosphere in order to pre-
vent condensation on the cuvette. Chloranil was used as
a background. Samples were measured three times at the
same temperature. From the averaged data was subtracted
the absorbance due to anthracene compounds in the sol-
vent (CH2Cl2) measured separately. The concentrations were
corrected for the volume changes at the different temper-
ature. The constants were calculated by plotting ln(ABS/
∈) − 2 ln(Ao − ABS/∈)(Do − ABS/∈) versus 1/T (K).
Scheme 1. Charge transfer transitions for HOMOs of the donor compounds
and LUMOs of the acceptor compounds.
3. Results and discussions
excitation of an electron on the donor to an empty orbital
on the acceptor. This is shown schematically in Scheme 1 in
which hvCT depicts the energy of the CT transitions. The low-
est energy CT transition will involve promotion of an electron
residing in the highest occupied molecular orbital (HOMO)
of the donor to the acceptor as shown for hvCT. Charge trans-
fer transitions involving electrons in lower energy orbitals
also are possible and would result in higher energy CT tran-
The absorption spectra of solutions containing anthracene
series compounds and p-chloranil together exhibit new
absorptions at longer wavelength than either the donors
(λ < 400 nm) or the acceptor (λ < 450 nm) alone. EDA com-
plexes between chloranil and anthracene has highest tran-
sition energy (lower λ = 632 nm) of the other anthracene
compounds, di(9-anthryl)methane is second (λ = 670 nm)
and 1,2-di(9-anthryl) ethane is third (λ = 674 nm). Transi-
tion energies of other dianthracene compounds are lowest
(λ = 680 nm).
The new and broad absorptions indicates that the
formation of electron donor–acceptor (EDA) complexes.
Anthracene series compounds are relatively electron rich and
p-chloranil are relatively electron poor compounds. When a
solution containing both an electron rich and electron poor
compound, they tend to associate with one another interac-
tion known as EDA complexes. The interactions of all studied
donor compounds with p-chloranil in dichloromethane gave
different color from the original mention charge transfer com-
plex formation.
sitions as shown hvC1 T
Theinteractionbetweenthedonorandacceptorgave␲–␲
.
*
transitions by the formation of radical ion pairs as shown in
Scheme 2.
The stoichiometries of the EDA complexes of the series of
anthracene compounds with chloranil was determined by the
methods of continuous variations and shown to be 1:1 and
shown in Fig. 1. EDA complexes of dimer compounds with
chloranil showed formation constants approximately double
these of anthracene and 9-methylanthracene, which corre-
lates with the number of anthracene groups present.
The Benesi–Hildebrand equation was used for the deter-
mination of formation constants (K) and extinction coef-
ficient, (ε), for the complexetion between anthracene and
chloranil. The association constants were evaluated at wave-
length formed complex for each donor and acceptor using the
The new and low energy absorptions observed in solutions
containing both donor and an acceptor have been described
by Mulliken [20] as charge transfer transitions involving the
Scheme 2. The molecular structure of compound and charge transfer transition between donor and acceptor.

714
M. Arslan, J. Masnovi / Spectrochimica Acta Part A 64 (2006) 711–716
Fig. 1. The plot of Job’s method for methylanthracene (MEA) and 1,4-di(9-
anthryl)butane (DAB) with p-CHL.
Fig. 2. Benesi–Hildebrand plot of [donor]/absorbance vs. 1/[chloranil] at
the maximum wavelength (nm) for EDA complex of anthracene series com-
pounds and chloranil (ANH: M1, MEA: M2, DAM: 1, DAE: 2, DAR: 3,
DAP: 5).
equation given below.
[Do]
1
1
[Ao]
1
1
values of di(9-anthryl)alkanes are around 3.3 which is about
double of the mono anthracene compounds. Anthracene com-
pounds with chloranil forms more EDA complexes than EDA
complexes of anthracene compounds with TNM according to
the KBH values of the complexes because anthracene com-
pounds form stronger complexes with chloranil than TNM
[21].
The small values of the intercept which are close to zero
in these graphs causes large uncertainty in the values of the
extinction coefficients so that ε of the EDA complexes could
not be determined exactly. Therefore, the average value of
the intercepts found for all graphs was used to approximate
ε, which was assumed to be independent of the anthracene
used.
The ꢀS values in di(9-anthryl)alkanes show that the two
anthracene groups behave independently and do not interfere
one another in complexation for n > 2. The space between two
anthracene ring allows complex formation of one anthracene
group which is not affected by the presence of the other
anthracene ring, except for di(9-anthryl)methane.
The thermodynamic constants of the electron donor–
acceptor complexes of anthracene compounds with chloranil
were determined by Van’t Hoff equation. Enthalpies (ꢀH)
and entropies (ꢀS) of complex formation were determined
using the Van’t Hoff and Beer–Lambert equations for the
=
+
or
=
+
ABS
Kε[Ao]
ε
ABS
Kε[Do]
ε
where [Ao] is the concentration of the acceptor; [Do] the con-
centration of the donor; ABS the absorbance of the complex;
∈
the molar absorptivity of the complex formed and KCT
CT
is the association constant of the complex. On plotting of the
values [Do]/ABS versus 1/[Ao], straight lines were obtained
in Fig. 2 from which molar absorptivity, correlation coeffi-
cient and association constant given in Table 1. The slopes
and Kε values were calculated from the Benesi–Hildebrand
plots which used a high concentration of acceptor and low
concentration of donor.
The slopes of the Benesi–Hildebrand plots for the
dianthryl compounds were around 0.24 × 10−3 to give a
Kε value of 4170 M−1 cm−1 l. The slopes of the Benesi–
Hildebrand plots for the monoanthracene compounds were
around 0.472 × 10−3 to have a Kε value 2120 M−1 cm−1 l.
The calculated Kε for chloranil complexes of dianthryl
compounds were, thus, about double the values for
monoanthracene compounds. The values for anthracene and
9-methylanthracene were expected to be half of the dianthryl
compounds, which have twice number of anthracene groups
in each molecule.
KBH values of the complexes of anthracene and 9-
methylanthracene with chloranil are about 1.70 and KBH
Table 1
Least-squarescalculatedslopesandKεandλmax valuesofanthracene–chloranilcomplexesatλmax forBenesi–Hildebrandplots(εassumedtobe1240 M−1 cm−1
)
Compounds–chloranil
Slope × 10−3 (1/Kε)
Kε
r2
KBH
λmax (nm)
Anthracene
0.475 0.013
0.468 0.0091
0.2565 0.0091
0.227 0.0104
0.2349 0.0073
0.2492 0.0078
0.253 0.016
2100 60
2140 40
3900 130
4400 190
4260 130
4010 120
3950 230
0.993
0.996
0.990
0.979
0.990
0.990
0.960
1.70 (5)a
1.72 (4)
3.14 (11)
3.55 (16)
3.43 (10)
3.24 (10)
3.19 (19)
632
680
670
674
678
678
680
Methylanthracene
DAMethane
1,2-DAEthane
1,3-DAPropane
1,4-DAButane
1,5-DAPentane
a
Determined to be 1.0 at 25 ◦C, with [anthracene]/[chloranil] ≥ 30 [23].

M. Arslan, J. Masnovi / Spectrochimica Acta Part A 64 (2006) 711–716
715
Table 2
Van’t Hoff experiments-calculated slopes and intercepts of the anthracene series compounds–chloranil complexes
Compound–chloranil
Slope
Intercept
r2
ꢀH (kcal mol−1
)
ꢀS (eu)
K(calc.) 21 ◦C
Anthracene
Methylanthracene
DAMethane
1,3-DAPropane
1,4-DAButane
1,5-DAPentane
a
1206.7 26
1352.8 97
1422.3 39
1288 16.7
1298.8 33
1325.6 38
−4.216 .010
−4.31 .040
−4.379 .014
−3.662 .006
−3.741 .012
−3.752 .017
0.998
0.960
0.997
0.999
0.997
0.993
−2.40 (6)a
−2.69 (19)
−2.83 (8)
−2.56 (3)
−2.58 (7)
−2.63 (8)
−8.4 (1)a
−8.6 (1)
−8.7 (1)
−7.3 (1)
−7.4 (1)
−7.5 (1)
0.89 .24
1.34 .62
1.58 .32
2.05 .23
1.97 .34
2.13 .42
ꢀH = −2.7 0.3 kcal/mol and ꢀS = −8.7 0.8 eu [23].
series of anthracenes with chloranil.
transfer complexes of carbazole, ethylcarbazole and 1,n-
dicarbazolylalkanes with some acceptors [22]. There is an
agreement between the trends in K(calc.) and KBH values for
the EDA complexes of anthracene with chloranil except for
di(9-anthryl)methane, for which KBH is relatively high.
The thermodynamic constants, ꢀH, ꢀS of mono
anthracene compounds and di(9-anthryl)methane are more
negative than dianthracene compounds. There is a good
agreement with the literature values for the ꢀH, ꢀS val-
ues of anthracene compound which are −2.7 0.3 kcal/mol
and −8.7 0.8 cal/◦ mol [23], compared to ꢀS = −8.4 and
ꢀH = −2.40 kcal/mol reported in here.
ln(ABS)
−ꢀH
ꢀS
R
=
+
ε
RT
ꢀ
ꢁ ꢀ
ꢁ
ABS
ABS
+ ln Do −
Ao −
ε
ε
While the intercept is giving ꢀH values, ꢀS values can be
obtained from the slope of the plot shown in Fig. 3.
Entropies of formation were lowest for monoanthracene
complexes, along with diarylmethanes and (where deter-
mined) diarylethanes. The ꢀS and ꢀH values of the com-
plexes are given in Table 2. The obtained results reveal that
the CT complex formation process is exothermic and spon-
taneous.
The thermodynamic constants, ꢀH, ꢀS and equilibrium
constants can be calculated from the slopes and the intercept
of the EDA complexes of chloranil with anthracene com-
poundsaregiveninTable2. Theslopeandtheinterceptvalues
were calculated from the experiments, which were used 1:1
ratio of the concentration of acceptor to the concentration of
donor groups.
As a result, these dimeric compounds were prepared
to model the behavior of polymeric systems related to
polyvinylanthracenes. In pendant types of polymeric sys-
tems (for instance, polyvinylanthracenes, polyvinylcarbazole
[24], polypyrole [25]), photoconductivity depends on the
spacing of the pendant units in the polymer backbone. Con-
duction in polymers involves removal of one electron from
one of the pendent groups, followed by hopping of the
remaining positive hole from group to group through the
polymer. The effects of distance and orientation between
anthracenegroupswasinvestigatedbysynthesizingthese1,n-
di(9-anthryl)alkanes (when n = 1–5). From the X-ray crystal
structure [21], the 1,3-di(9-anthryl)propane is most similar
to the poly(9-vinylanthracene) due to comparable separation
of the anthracene groups.
K(calc.) (at 21 ◦C) values of the complexes of monoan-
thracene compounds with chloranil are about 1.1 and val-
ues of K(calc.) at for dianthracene compounds (n = 3–5) are
around 2 which is about double of the mono anthracene com-
pounds. The value for di(9-anthryl)methane is 1.58 which
is intermediate. Similiar results were obtained for charge
Acknowledgements
SupportfromtheCSUCollegeofGraduateStudiesandthe
Turkish Ministry of Education is gratefully acknowledged.
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