Vol. 1 (4), 2014, 112‒122

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Journal of Chemistry and Materials Research
Vol. 1 (4), 2014, 112122
JCMR
Journal of Chemistry and
Materials Research
ORICPublications
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Original Research
New Materials Based on Acridine: Correlation Structure – Properties
and Optoelectronic Applications
Hayat Sadki 1
, Samir Chtita 2
, Mohammed Naciri Bennani 1
, Tahar Lakhlifi 2
, Mohammed Bouachrine 3,
*
1
LME, Faculty of Science, University Moulay Ismail, Meknes, Morocco
2
L.C.S.N. Faculty of Science, University Moulay Ismail, Meknes, Morocco
3
MEM, High School of Technology (ESTM), University Moulay Ismail, Meknes, Morocco
Received 11 October 2014; accepted 18 October 2014
Abstract
This paper is mainly about the theoretical investigations of the structural, optoelectronic and photovoltaic properties of sixteen conjugated
compounds based on acridine. The quantum chemical calculations based on density functional theory (DFT) at B3LYP method with 6‒31G (d)
basis set for all atoms is used as a measure to investigate the theoretical ground-state geometry and electronic structure of the pre-mentioned
materials. Furthermore, Gaussian 09 program package was used as a program to get the calculations done; the results were strengthened
through the use of Gauss View 5.0. This paper also discussed the effect of different other substituent groups branched to the acridine ring on
the geometries and electronic properties of these materials in order to investigate and then understand the relationship between molecular
structure and optoelectronic properties. As a method of calculation, the TD‒B3LYP/6‒31G (d) method was used to calculation the absorption
properties (λmax, Ea, OS) of such compounds. The S1/S0 electronic excitation is said to be the highest Occupied Molecular Orbital (HOMO) to
lowest Unoccupied Molecular Orbital (LUMO) transition and it is different in terms of oscillator strength. Studying the organic solar cells can’t
be effective except if it is accompanied with a deep understanding of the theoretical knowledge of the HOMO and LUMO energy levels of the
components, for this reason the researcher has calculated and discussed the HOMO, LUMO and Gap energy Voc (open circuit voltage) of the
studied compounds. Therefore, these materials were suggested as a good candidate for organic dye-sensitized solar cells.
Keywords: π-conjugated molecules, acridine, organic solar cells, low band-gap, electronic properties, Voc (open circuit voltage).
1. Introduction
Conjugated organic oligomers and polymers were given
much consideration in areas that have to do with chemistry and
physics, and they are repeatedly studied due to their remark-
able optical and electronic properties [1,2]. Thanks to H.
Shirakawa, A.J. Heeger and A.G. Mac Diarmid’s research in
this field, for which they won the Nobel Prize in 2000, the
importance and the potentiality of this class were recently ack-
nowledged by the world scientific community [3]. The high
specific capacitance of this type of the polymers in their
* Corresponding author. Tel.: +212660736921.
E-mail address: bouachrine@gmail.com (M. Bouachrine).
All rights reserved. No part of contents of this paper may be reproduced or
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neutral and oxidized states has stimulated suggestions for a
variety of applications such as organic light emitting diodes
(OLEDs) [4,5], field‒effect transistors [6‒8] (OTFTs), photov-
oltaic cells [9‒11], portable electronic [12], and lasers [13,14].
With a booming in research effort to develop cost-effective
renewable energy devices, dye sensitized solar cells (DSSC),
also known as Grätzel cells [15] have been the focus of
thousand of papers just in 2010 [16].
Short‒chain compounds synthesis based on conjugated
molecules has been the focus of many researchers in the field
just because they are not amorphous and can be synthesized as
well defined structures [17‒22]. On the other hand, the
invention of the ultra fast and ultra efficient photo lead to the
electron transfer between π-conjugated systems and fullerene
derivatives. Considerable interest for hetero-junction solar
cells based on interpenetrating networks of conjugated systems
and C60 derivatives has been generated [23,24]. Roquet et al.
distinguished between the nature of acceptor groups in the
molecule and the photovoltaic performance [25,26].

H. Sadki et al. / Journal of Chemistry and Materials Research 1 (2014) 112–122 113
Fig. 1. Chemical structure of studied compounds A (1‒4), B (1‒4), C (1‒4) and D (1‒4)
Table 1 Energy values of ELUMO (eV), EHOMO (eV), and Egap (eV) of the studied molecules obtained by B3LYP/6-31G (d) level.
Rings Studied molecules EHOMO (eV) ELUMO (eV) Egap(ELUMO ‒ EHOMO) (eV)
A
A1 -5.074 -1.276 3.798
A2 -5.284 -1.773 3.511
A3 -5.755 -2.286 3.469
A4 -4.815 -1.657 3.158
B
B1 -5.040 -1.390 3.649
B2 -5.223 -1.704 3.519
B3 -5.692 -2.149 3.543
B4 -4.772 -1.612 3.160
C
C1 -5.439 -1.192 4.247
C2 -5.611 -1.520 4.091
C3 -5.858 -2.443 3.415
C4 -5.138 -1.412 3.726
D
D1 -5.439 -1.411 4.028
D2 -5.412 -1.524 3.888
D3 -5.723 -2.573 3.150
D4 -5.201 -1.417 3.784
In the previous two decades, low band gap polymers which
are designed to better match solar output have been studied
and acridine was distinguished from anthracene, though they
are very close in structure, in terms of the nitrogen atom. Acri-
dine said to possess the nitrogen atom in its central ring. It was
widely used along with its derivatives as dyes for photovoltaic
cells organic electroluminescent diodes and fluorescent prob-
es. Therefore, acridine containing polymers combining the opt-
ical properties of acridine and the valuable properties of polyi-
mides seem to be perspective materials for optoelectronic app-
lications [27].
To benefit from their adaptive properties to photovoltaic
cells, we should understand the ultimate relations between
structure and properties of these materials. Recent experim-
ental work on these new materials together with the theoretical
efforts constitute an important source of valuable information
which complements the experimental studies, thereby to the
understanding of the molecular electronic structure as well as
the nature of absorption and photoluminescence [28‒32].
In what follows, theoretical study by using DFT method on
sixteen conjugated compound based on acridine shown in
Fig.1 is reported. Different electron side groups were introdu-
ced to investigate their effects on the electronic structure. A
systematic theoretical study of such compound has not been
reported as we know. Thus, our aim is first, to explore their
electronic and absorption properties on the basis of the DFT
quantum chemical calculations. Second, we are interested to
elucidate the parameters that influence the photovoltaic
efficiency toward better understanding of the structure–
property relationships. We think that the presented study of
structural, electronic and optical properties for these compoun-
ds could help to design more efficient functional photovoltaic
organic materials.

114 H. Sadki et al. / Journal of Chemistry and Materials Research 1 (2014) 112–122
The quantum chemical investigation has been performed to
the optical and electronic properties of a series of compounds
based on acridine. Different electron side groups were introdu-
ced to investigate their effects on the electronic structure. The
theoretical knowledge of the HOMO and LUMO energy levels
of the components is a basis in studying organic solar cells, so,
the HOMO, LUMO and Gap energy of the studied compounds
have been calculated and reported.
In this paper, sixteen compounds based on acridine A
(1‒4), B (1‒4), C (1‒4) and D (1‒4) (shown Fig. 1), are
designed. The geometries, electronic properties, absorption
and emission spectra of these studied compounds are studied
by using density functional theory (DFT) and time‒dependent
density functional theory (TD/DFT) with the goal to find
potential sensitizers for use in organic solar cells.
2. Materials and Methods
All computations of the studied compounds in this work
were carried out with the Gaussian 09 program package [33]
on an Intel Pentium IV 3.3 GHz PC running Linux supported
by Gauss View 5.0 [34]. These methods are widely used beca-
use theycan leadtosimilar precision to other methods and beca-
usetheyarealsoless demandingand timesavingfrom the compu-
tational point of view. Using the B3LYP functional [Becke’s
three‒parameter functional (B3) and includes a mixture of HF
with DFT exchange terms associated with the gradient corre-
cted correlation functional of Lee, Yang and Parr (LYP)] exch-
ange correlation functional [35,36]. The 6‒31G (d) basis set
was chosenas acompromise between the quality of the theoreti-
cal approach and thehighcomputationalcostassociated with the
high numberofdimensions to the problem for all atoms [37,38].
A1 A2 A3 A4
B1 B2 B3 B4
C1 C2 C3 C4
D1 D2 D3 D4
Fig. 2. Optimized geometries obtained by B3LYP/6-31G (d) of the studied molecules

Gauss View software program (version 3.07) and the
graphical molecular orbital were used to generate the 3D
structures of the molecules. The HOMO, LUMO and gap’s
energies were also deduced from the stable structure of the
neutral and doped forms, where the Egap is evaluated as the
difference between LUMO and HOMO energies. In this paper,
the transition energies were calculated at the ground-state and
excite‒state geometries using TD‒DFT calculations on the
fully optimized geometries. And the results obtained gave us
the absorption and emission maxima, their corresponding
transition energies, and the factor oscillation.
Finally, the nature and the energy of vertical electron
transitions (the main singlet–singlet electron transitions with
highest oscillator strengths) of molecular orbital wave functi-
ons were presented. Then, the theoretical simulated absorption
spectrum was calculated using the S. Wizard program [39].
The electronic absorption in vacuum was carried out using
CIS/TD DFT (B3LYP/6‒31G (d)) method on the basis of the
optimized ground and excited structures, respectively [40].
3. Results and discussion
3.1.Geometry optimization
Fig. 1 presents the sketch map of studied structures while
Fig. 2 depicts the optimized geometries obtained by
B3LYP/6‒31G (d) of the studied molecules. The findings of
the optimized structures show that they have similar
conformations (quasi planar conformation). And it is found
also that the modification of several groups attached to the
acridine does not change the geometric parameters.
3.2.Optoelectronic properties
The optoelectonic properties depend essentially on the
appropriate HOMO and LUMO energy levels and the electron
and hole mobilities. Everyone knows that (Egap) between the
highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO) is an essential
parameter that determines the molecular admittance since it is
a measure of the electron density hardness. The band gap is
estimated as the difference between the HOMO and the
LUMO level energies (Eg = ∆EHOMO–ELUMO) on the ground
singlet state. The results of the experiment showed that the
HOMO and LUMO energies were obtained from an empirical
formula based on the onset of the oxidation and reduction
peaks measured by cyclic voltametry [41,42]. However,
theoretically speaking the HOMO and LUMO energies can be
calculated by DFT method of calculation. It is remarkable that
the solid‒state packing effects are not calculated in DFT
calculations, this fact affects the HOMO and LUMO energy
levels in a thin film compared to an isolated molecule as
considered in the calculations. Though these calculated energy
levels lack some accuracy still we can use them to get
information by comparing similar oligomers or polymers [43].
The theoretical electronic properties parameters (EHOMO,
ELUMO and Gap) are listed in Table 1. This table also clearly
shows the effect of the different other substituent groups
branched to the acridine ring on the HOMO and LUMO
energies. This implies that different side substituent structures
play key role in electronic properties and the effect of slight
structural variations. In addition the calculated band gap (Egap)
of the studied compounds increases in the following order:
D3 < A4 < B4 < C3 < A3 < A2 < B2 < B3 < B1 C4 < D4<
A1 < D2 < D1 < C2 < C1
3.3.Frontier molecular orbitals
The frontier molecular orbital (MO) contribution is of a
high importance in determining the charge‒separated states of
the studied molecules because the relative ordering of
occupied and virtual orbital provides a reasonable qualitative
indication of excitation properties and provides also the ability
of electron hole transport. The iso‒density plots of the model
compounds are shown in Fig. 2. In general, and as plotted in
this figure (LUMO, HOMO), the HOMOs of these oligomers
in the neutral form possess a π‒bonding character within
subunit and a π‒antibonding character between the consecutive
subunits. On the other hand, the LUMO of all studied
compounds generally possess a π‒antibonding character within
subunit and a π‒bonding character between the subunits. This
implies that the singlet excited state involving mainly the
promotion of an electron from the HOMO to the LUMO
should be more planar. The HOMO is delocalized along the
four radical R through the π‒conjugated bridges group. The
LUMO is delocalized in the aciridine ring. The examination of
the HOMO and LUMO of the three organic dyes indicates that
HOMO→LUMO excitation moves the electron distribution
from the R radical to the acridine group.
3.4.Photovoltaic properties
To evaluate the possibilities of electron transfer from the
excited studied molecules to the conductive band of the
acceptor PCBM the HOMO and LUMO levels were
compared. Generally, the most efficient material solar cells are
based on the bulk hetero‒junction structure of the blend of
π‒conjugated molecule or polymer donors and fullerene
derivative acceptors. Here, we studied the photovoltaic
properties of the compounds A(1‒4), B(1‒4), C(1‒4) and
D(1‒4) as donor blended with [6.6]‒phenyl‒C61‒butyric acid
methyl ester (PCBM), which are the most broadly used as an
acceptor in solar cell devices. The HOMO and the LUMO
energy levels of the donor and acceptor components are very
important factors to determine whether effective charge
transfer will happen between donor and acceptor. As shown in-

Table 2 Energy values of ELUMO (eV), EHOMO (eV), Egap (eV), α and the open circuit voltage Voc (eV) of the studied molecules obtained
by B3LYP/6-31G (d) level.
PCBM C60 (A) PCBM C60 PCBM C70 PCBM C76
Compounds EHOMO (ev) ELUMO (ev) Egap (ev) Voc (ev) ev Voc (ev) ev Voc (ev) ev Voc (ev) ev
A1 -5.074 -1.276 3.798 1.074 2.424 1.304 2.194 1.234 2.264 0.984 2.514
A2 -5.284 -1.773 3.511 1.284 1.927 1.514 1.697 1.444 1.767 1.194 2.017
A3 -5.755 -2.286 3.469 1.755 1.414 1.985 1.184 1.915 1.254 1.665 1.504
A4 -4.815 -1.657 3.158 0.815 2.043 1.045 1.813 0.975 1.883 0.725 2.133
B1 -5.040 -1.390 3.649 1.040 2.310 1.270 2.080 1.200 2.150 0.950 2.400
B2 -5.223 -1.704 3.519 1.223 1.996 1.453 1.766 1.383 1.836 1.133 2.086
B3 -5.692 -2.149 3.543 1.692 1.551 1.922 1.321 1.852 1.391 1.602 1.641
B4 -4.772 -1.612 3.160 0.772 2.088 1.002 1.858 0.932 1.928 0.682 2.178
C1 -5.439 -1.192 4.247 1.439 2.508 1.669 2.278 1.599 2.348 1.349 2.598
C2 -5.611 -1.520 4.091 1.611 2.180 1.841 1.950 1.771 2.020 1.521 2.270
C3 -5.858 -2.443 3.415 1.858 1.257 2.088 1.027 2.018 1.097 1.768 1.347
C4 -5.138 -1.412 3.726 1.138 2.288 1.368 2.058 1.298 2.128 1.048 2.378
D1 -5.439 -1.411 4.028 1.439 2.289 1.669 2.059 1.599 2.129 1.349 2.379
D2 -5.412 -1.524 3.888 1.412 2.176 1.642 1.946 1.572 2.016 1.322 2.266
D3 -5.723 -2.573 3.150 1.723 1.127 1.953 0.897 1.883 0.967 1.633 1.217
D4 -5.201 -1.417 3.784 1.201 2.283 1.431 2.053 1.361 2.123 1.111 2.373
PCBM C60
(A)
-6.1 -3.700
PCBM C60 - -3.470
PCBM C70 - -3.540
PCBM C76 - -3.790
-6
-5
-4
-3
-2
-1
PCBM C60
HOMO
LUMO
A1
A2
A3
A4
B1
B2
B3
B4
C1
C2
C3
C4
D1
D2
D3
D4
PCBM C60
EnergyLevel(eV)
EgA3
=3.469
EgC4
=3.726
EgC3
=3.415
EgC2
=4.091
EgC1
=4.247
EgB4
=3160
EgB3
=3.543
EgB2
=3.519
EgB1
=3.649
EgA4
=3.158
EgA1
=3.798
EgA2
=3.511
EgD1
=4.028
EgD2
=3.888
EgD3
=3.150
EgD4
=3.784
Fig. 3. Sketch of B3LYP/6-31G (d) calculated energies of the HOMO, LUMO level of studied molecules.
Table 2, the change of the electron-donor shows a great effect
on the HOMO and LUMO levels. Fig. 3 shows detailed data of
absolute energy of the frontier orbitals for the studied
compounds and PCBM derivatives. It is deduced that the
nature of donor or acceptor pushes up/down the HOMO/
LUMO energies in agreement with their electron character.
Table 2 lists the calculated frontier orbital energies and
energy Egap between highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO)
and the Egap energy of the studied molecules, also the open
circuit voltage Voc (eV) and The difference between both the
energy levels LUMO of the donor and acceptor α [44].

Table 3 The contour plots of HOMO and LUMO orbitals of all studied compounds obtained by B3LYP/6- 31G (d).
Compounds Contour Plots
HOMO LUMO
A1
A2
A3
A4
B1
B2
B3
B4

C1
C2
C3
C4
D1
D2
D3
D4

On the other hand and from the above analysis, we know
that the LUMO energy levels of the studied compounds are
much higher than that of the ITO conduction band edge (‒4.7
eV). Thus, the studied molecules A(1‒4), B(1‒4), C(1‒4) and
D(1‒4) have a strong ability to inject electrons into ITO
electrodes. The experiment phenomenon is quite consistent
with previous literature [45], this latter reported that the
increase of the HOMO levels may suggest a negative effect on
organic solar cell performance due to the broader gap between
the HOMO level of the organic molecules and the HOMO
level of several acceptor PCBM. (C60, C70, C76) (Fig. 4).
It is known that the architecture of photoactive layer is one
of the principle factors of efficiencies of solar cells. The most
efficient technique to generate free charge carriers is bulk
hetero-junction where the π‒conjugated compounds donors are
blended with fullerene derivatives us acceptor [46]. In our
study, PCBM and derivatives (C60, C70, C76) were included
for comparison purposes.
As shown in Table 3, both HOMO and LUMO levels of
the studied molecules agree well with the requirement for an
efficient photosentizer. It should be noted that the LUMO
levels of all studied compounds are higher than that of PCBM
derivatives which varies in literature from ‒4.0 to ‒3.47 eV
(C60 (‒3.47 eV) ;C70 (‒3.54 eV); C76 (‒3.79 eV) [47].
The most effcient cell design, leading to the highest power
conversion effciencies, is the bulk‒heterojunction (BHJ) solar
cell [48,49]. The active layer of BHJ solar cells consists of an
interpenetrating network of two types of organic materials, an
electron donor and an electron acceptor, and is formed through
the control of the phase separation between the donor and
acceptor parts in the bulk. Accordingly, the large donor
acceptor area can favour charge separation and, hence,
increases the conversion effciency of the cell [50].
On the other hand and knowing that in organic solar cells,
the open circuit voltage is found to be linearly dependent on
the HOMO level of the donor and the LUMO level of the
acceptor [51,52]. The power conversion efficiency (PCE) was
calculated according to the following equation (1):
PCE = 1/Pin (FF. Voc. Jsc) (1)
where Pin is the incident power density, Jsc is the short‒circuit
current, Voc is the open-circuit voltage, and FF denotes the fill
factor.
To evaluate the possibilities of electron transfer from the
studied molecules to the conductive band of the proposed
acceptors, the HOMO and LUMO levels are compared.
Knowing that in organic solar cells, the open circuit voltage is
found to be linearly dependent on the HOMO level of the
donor and the LUMO level of the acceptor. The maximum
open circuit voltage (Voc) of the Bulk Hetero Junction solar
cell is related to the difference between the highest occupied
molecular orbital (HOMO) of the electron donor (A(1‒4),
B(1‒4), C(1‒4) and D(1‒4)) and the LUMO of the electron
acceptor (PCBM derivatives), taking into account the energy
lost during the photo‒charge generation [53‒55]. The
theoretical values of open‒circuit voltage Voc have been
calculated from the following expression (2):
Voc =│EHOMO (Donnor)│–│ELUMO (Acceptor)│‒ 0.3 (2)
The theoretical values of the open circuit voltage Voc of the
studied compounds calculated according to the equation (2)
range from (0.772 to 1.858 eV) for PCBM C60(A); (1.045 to
2.088 eV) for PCBM C60; (0.932 to 2.018 eV) for PCBM C70
and (0.682 to 1.768 eV) for PCBM C76 (Table 4).
Table 4 Main transition states, their assignments, the corresponding wavelength and oscillator strength for all compounds have been obtained
by using TD-DFT//B3LYP/6-31G (d) levels
Compounds Transition Wavelength (λ, nm) Ea (eV) O.S MO/character
A1 S0→S1 287.50 117,34 0.1493 HOMO→LUMO+1 (40%)
A2 S0→S1 408.97 82,49 0.3206 HOMO→LUMO (91%)
A3 S0→S1 404.58 83,38 0.5959 HOMO→LUMO (83%)
A4 S0→S1 450.13 74,947 0.2925 HOMO→LUMO (93%)
B1 S0→S1 271.69 124,17 0.2062 HOMO→LUMO+2 (50%)
B2 S0→S1 313.26 107,69 0.8078 HOMO→LUMO+1 (72%)
B3 S0→S1 386.73 87,23 0.2688 HOMO→LUMO (82%)
B4 S0→S1 333.43 101,18 0.7123 HOMO→LUMO+1 (84%)
C1 S0→S1 299.89 112,49 0.1039 HOMO-1→LUMO (75%)
C2 S0→S1 329.41 102,413 0.5828 HOMO-1→LUMO (78%)
C3 S0→S1 360.48 93,59 0.7212 HOMO-1→LUMO (98%)
C4 S0→S1 367.88 91,70 0.4184 HOMO→LUMO (94%)
D1 S0→S1 241.17 139,88 0.6290 HOMO-3→LUMO (61%)
D2 S0→S1 363.67 92,76 0.1742 HOMO→LUMO (84%)
D3 S0→S1 357.49 94,37 0.1404 HOMO→LUMO+1 (79%)
D4 S0→S1 373.18 90,40 0.1785 HOMO→LUMO (96%)

These values are sufficient for a possible efficient electron
injection. Therefore, all the studied molecules can be used as
organic solar cell sensitizers because the electron injection
process from the excited molecule to the conduction band of
the acceptor (PCBM derivatives) and the subsequent
regeneration is possible. We noted that the best values of Voc
are indicated for the studied compounds blended with C60 or
C70 and higher value are given for compound C3 (2.088 eV)
and (2.018 eV) blended with C60 and C70 respectively.
3.5.Absorption properties
The absorption properties of a new material matches with
the solar spectrum is an important factor for the application as
a photovoltaic material, and a good photovoltaic material
should have broad and strong visible absorption characteri-
stics. The TD‒DFT method has been used on the basis of the
optimized geometry to obtain the energy of the singlet–singlet
electronic transitions and absorption properties (λmax) of
A(1‒4), B(1‒4), C(1‒4) and D(1‒4). The corresponding
simulated UV‒Vis absorption spectra of all studies
compounds, presented as oscillator strength against
wavelength are shown in Fig. 5. As illustrated in Table 4, we
can find the values of calculated absorption λmax (nm) and
oscillator strength (O.S) along with main excitation
configuration of all studied compounds.
The calculated wave length λabs of the studied compounds
decreases in the following order:
A4 > A2 > A3 > B3 > D4 > C4 > D2 > C3 > D3 > B4 >
C2 > B2 > C1 > A1 > B1 > D1
This bathochromic effect from D1 (λmax = 241.17 nm) to
A4 (λmax =450.13nm) is obviously due to a higher mean
conjugation length and to inter-chain electronic coupling [56]
and to the effect of the different other substituent groups
branched to the Acridine ring. Those interesting points are
seen both in the studying the electronic and absorption
properties.
In addition, we note that the broader absorption peak
means that there is a distribution of energy level corresponding
to the π→π* transition. This interesting point is seen both by
analyzing electronic and absorption results. Excitation to the
S1 state corresponds exclusively to the promotion of an
electron from the HOMO to the LUMO. As in the case of the
oscillator strength, the absorption wavelengths arising from
S0→S1 electronic transition increase progressively with the
increasing of conjugation lengths. It is reasonable, since
HOMO→LUMO transition is predominant in S0→S1
electronic transition; the results are a decrease of the LUMO
and an increase of the HOMO energy.
C60 C70 C76
Fig. 4. Structure of the investigated fullerenes
100 200 300 400 500 600
Wavelength (nm)
Absorbance(a.u)
A1
A2
A3
A4
B1
B2
B3
B4
100 200 300 400 500
Wavelength (nm)
Absorbance(a.u)
C1
C2
C3
C4
D1
D2
D3
D4
Fig. 5. Simulated UV-visible optical absorption spectra of title compounds with the calculated data at the TD-DFT/B3LYP/6-31G (d) level.

4. Conclusions
In this study, we have used the Density Functional Theory
DFT method and 6‒31G (d) basis set at density functional
B3LYP level to investigate theoretical analysis on the
geometries and electronic properties of sixteen compounds
based on the acridine ring which displays the effect of
substituted groups on the structural and optoelectronic
properties of these materials and leads to the possibility to
suggest these materials for organic solar cells application and
in order to guide the synthesis of novel materials with specific
electronic properties. The concluding remarks are:
 The results of the optimized structures for all studied
compounds so that they have similar conformations (quasi
planar conformation). We found that the modification of
several groups does not change the geometric parameters.
 The calculated frontier orbital energies HOMO level,
LUMO level, and band gap of the studied compounds
were well controlled by the different other substituent
groups branched to the acridine ring. The calculated band
gap Egap of the studied molecules was in the range 3.150‒
4.247 eV.
 The energy Egap of molecule D3 (3.150eV) is much
smaller than that of the other compounds.
 The best values of Voc are indicated for the studied
compounds blended with C60 or C70 and higher value are
given for compound C3 (2.088 eV) and (2.018 eV)
blended with C60 and C70 respectively.
 The UV‒Vis absorption properties have been obtained by
using TD/DFT calculations. The obtained absorption
maximums are in the range 241.17 to 450.13 nm.
These obtained values are sufficient for a possible efficient
electron injection. Therefore, all the studied molecules can be
used as sensitizers because the electron injection process from
the excited molecule to the conduction band of the acceptor
and the subsequent regeneration is possible in organic
sensitized solar cell.
Finally, the procedures of theoretical calculations can be
employed to predict the electronic properties on the other
compounds, and further to design novel materials for organic
solar cells.
Acknowledgement(s):
This work has been supported by the project Volubilis AI
n°: MA/11/248 and by CNRST/CNRS cooperation (Project
Chimie 10/09). We are grateful to the “Association Marocaine
des Chimistes Théoriciens” (AMCT) for its pertinent help
concerning the programs.
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