Synthesis and spectral characterization of D-A based cyano-stilbene derivatives for organic solar cell applications

Article abstract of DOI:10.14233/ajchem.2019.22187

Ten donor-acceptor based (D-A) cyano-stilbene derivatives were synthesized and their structure was confirmed by ¹H NMR, GC-MS, FT-IR. The absorption was calculated by UV-visible spectrometer. From the UV-Vis study, stilbenes are having broad an

Full text of DOI:10.14233/ajchem.2019.22187

Asian Journal of Chemistry; Vol. 31, No. 10 (2019), 2337-2340
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2019.22187
Synthesis and Spectral Characterization of D-A Based
Cyano-Stilbene Derivatives for Organic Solar Cell Applications
1,*,
2
R. GANESAMOORTHY
and P. SAKTHIVEL
1Department of Chemistry, School of Basic Sciences, Vels Institute of Science, Technology & Advanced Studies (VISTAS), Chennai-600117, India
2Department of Nanoscience and Technology, Bharathiar University, Coimbatore-641046, India
*Corresponding author: E-mail: chemgmoorthy@gmail.com
Received: 7 May 2019;
Accepted: 13 June 2019;
Published online: 30 August 2019;
AJC-19547
Ten donor-acceptor based (D-A) cyano-stilbene derivatives were synthesized and their structure was confirmed by 1H NMR, GC-MS, FT-
IR. The absorption was calculated by UV-visible spectrometer. From the UV-Vis study, stilbenes are having broad and strong absorption
in the UV-visible region. The strong and broad absorption in the UV-visible region is the desired property for the high power conversion
efficiency organic photovoltaic cells.
Keywords: Cyano-stilbene, Organic photovoltaic, Power conversion efficiency.
reactive but if any hydroxyl or some other functional group
present in the stilbene it is highly reactive. Stilbenoids (hydroxy-
lated derivatives of stilbene) are produced by plants are used
as an important antibiotic material in their life time. The stilbene
derivatives have also medical and biological activities, such
as antimicrobial, antifungal, insecticidal and anti-inflammatory
[5,6].
Stilbenes can be synthesized by many methods in that most
important methods are given as follows,Aldol-type condensation,
Wittig-Horner reaction, Perkin reaction, Negishi-Stille reactions
and Heck reaction. In the above mentioned methods, Aldol-
type condensation between an aromatic aldehyde with active
methylarene compound is most common because of economically
benign, simple and easy way of preparation in short span of
time [7-11]. TheAldol condensation type of stilbene synthesis
involves the formation of carbanion and addition to the carbonyl
group. The strong or weak base like NaOH, pyridine or piperidine
initiates the reaction by deprotonation of active methylarene.
The carbanion then adds to carbon atoms of the carbonyl group
of the aldehyde [12-15].
INTRODUCTION
The stilbene name was derived from the Greek word 'stilbos'.
Stilbene derivatives can be easily prepared by some conven-
tional and eco-friendly methods. They are thermally and
chemically stable and possess absorption and fluorescence
properties [1]. The stilbene are mainly present in two isomeric
forms namely trans-stilbene (E) and cis-stilbene (Z). In the
above two forms, trans-form is more stable than cis-form
because of steric factor and high energy in the later isomer.
The two isomers are in equilibrium at room temperature but
at high temperature or exposed to light the trans-form is
predominant because of the stability and energy difference.
The energy of cis-form higher than the trans-form. They are
insoluble in water but soluble in most of the common organic
solvents [1,2].
Stilbenes are widely used in the manufacture of industrial
dyes, dye lasers, optical brighteners, phosphor materials, scinti-
llator and other materials. Donor-acceptor (D-π-A) dyestuff
and colorants represent a vast majority of organic chromogens.
Some of these compounds are also used as sources of dye
laser radiation [3,4]. They are playing an increasingly prominent
role in the area of photophysical, photochemical, biophysical
and biomedical investigations. Unsubstituted stilbenes are less
Broad and strong absorption band in visible and near infrared
region to match the solar spectrum for increasing short circuit
current (Jsc) [16-19]. A broad class of dyestuff and colorants
are based on electron donor-acceptor (D-π-A) chromogens
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2338 Ganesamoorthy et al.
Asian J. Chem.
were synthesized by Asiri [20]. Due to the broad absorption in
UV-visible region stilbenes can be used as an efficient dye for
organic photovoltaic. This observation leads us to synthesis
stilbene dyes for the applications in organic photovoltaic.
stilbene was washed with water and ethanol for several times
to eliminate NaOH and unreacted present in the reaction mixture.
The product was further purified by recrystallization in ethanol.
The product formation was further confirmed by GC-MS, UV-
1
visible, FT-IR and H NMR. The consolidated data for the
EXPERIMENTAL
synthesized cyano-stilbenes are summarized in Table-1.
(E)-2-(5-Bromothiophen-2-yl)-3-(4-hydroxyphenyl)
acrylonitrile (S-1): m.f.: C13H8NOSBr, calculated mass: 305,
observed mass: 306. FT-IR (KBr, νmax, cm-1): 3303 (O-H), 2945
(arom. C-H), 2270 (C-N), 1487, 1429 (arom. C=C), 615 (C-
Br). 1H NMR (400 MHz, CDCl3): (δ 7.26 ppm, s) 7.7 (2H, d),
7.3 (1H, d), 7.3 (1H, d), 7.2 (1H, s), 7.0 (1H, q), 6.9 (2H, d).
(E)-3-(4-Bromophenyl)-2-(5-bromothiophen-2-
yl)acrylonitrile (S-2): m.f.: C13H7NSBr2, calculated mass: 367,
observed mass: 367. FT-IR (KBr, νmax, cm-1): 3034 (arom. C-
H), 2223 (C-N), 1587, 1581, 1487 (arom. C=C), 810 (C-Br).
1H NMR (400 MHz, CDCl3): (δ 7.26 ppm, s), 7.7 (2H, s), 7.5
(2H, d), 7.1 (2H, t), 7.0 (1H, d).
(E)-2-(5-Bromothiophen-2-yl)-3-(furan-2-yl)acrylonitrile
(S-3): m.f.: C11H6NOSBr, calculated mass: 278, observed mass:
279. FT-IR (KBr, νmax, cm-1): 2945 (arom. C-H), 2227 (arom.
C-N), 1487, 1429 (arom. C=C), 695 (C-Br). 1H NMR (400 MHz,
CDCl3): (δ 7.26 ppm, s), 7.6 (1H, d), 7.1 (2H, d), 7.0 (2H, t), 6.5
(1H, q).
Thiophene-2-carboxaldehyde, 4-hydroxybenzaldehyde,
4-bromobenzaldehyde, 5-bromothiophenecarboxaldehyde,
ethanol, vanillin, furfural, 5-bromothiopheneacetonitrile,
4-hydroxyphenylacetonitrile, potassium tert-butoxide, 4-fluoro-
phenylacetonitrile and 4-nitrophenylacetonitrile were purchased
from Sd-Fine Chem. Ltd., India. All the solvents were distilled
prior to usage.
Synthesis of cyano-stilbene: Aryl acetonitrile (20 mmol)
was dissolved in 20 mL of ethanol and taken in a three neck
flask. To this, 10 mmol of alcoholic potassium tert-butoxide
was added and stirred for 0.5 h. An alcoholic solution of
aromatic aldehyde (20 mmol) was added dropwise into the
above solution. Within a few minutes formation of coloured
product was started. The reaction mixture was again stirred
for 3 h at room temperature. Progress was monitored by TLC.
The reaction mixture was then poured into crushed ice and
neutralized with sufficient amount of water. The precipitated
product was filtered by using a Buchner funnel. The filtered
TABLE-1
CONSOLIDATED DATA FOR CYANO-STILBENES
Ar
Ar'
E-stilbenes
Yield (%)
m.p. (°C)
170
Colour
Brown
Stilbenes
S-1
S
HO
Br
Br
S
HO
CHO
Br
95
CN
CN
Br
NC
CN
S
S
Golden
yellow
Br
87
83
220
90
S-2
S-3
OHC
S
Br
CN
O
Br
CHO
Br
Br
Greenish
yellow
O
CN
S
CN
S
S
CHO
Br
Light
Yellow
Br
S
90
97
55
58
63
110
190
190
217
140
S-4
S-5
S-6
S-7
S-8
CN
CN
S
Br
Br
CN
HO
Light
Yellow
Br
HO
O2N
O2N
HO
OHC
HO
CN
CN
CHO
HO
Reddish
brown
Br
H3CO
NC
H3CO
CN
HO
HO
CHO
Dark yellow
Yellow
NO2
CN
O
O
CN
CN
CN
HO
CHO
O
CN
F
CHO
Brownish
yellow
O
90
88
84
86
S-9
F
F
CN
F
Br
OHC
Light yellow
S-10
Br

Vol. 31, No. 10 (2019)
Synthesis and Spectral Characterization of D-A Based Cyano-Stilbene Derivatives 2339
(E)-2,3-bis(5-Bromothiophen-2-yl)acrylonitrile (S-4):
m.f.: C11H5NS2Br2, calculated mass: 372, observed mass: 373,
FT-IR (KBr, νmax, cm-1): 3305 (arom. C-H), 2231 (arom. C-N),
1583, 1610, 1514 (arom. C=C), 821 (C-Br). 1H NMR (400 MHz,
CDCl3): (δ 7.26 ppm, s), 7.27 (2H, d), 7.1 (2H, t), 7.0 (1H, d).
(E)-3-(4-Bromophenyl)-2-(4-hydroxyphenyl)acrylonitrile
(S-5): m.f.: C15H10NOBr, calculated mass: 298, observed mass:
299. FT-IR (KBr, νmax, cm-1): 3379, 3338 (O-H), 3230 (arom.
acetonitrile based stilbenes such as S-9 and S-10 showed
absorption between 250-380 nm. Whereas, thiophene based
stilbenes such as S-3, S-4 and vanillin based stilbenes such as
S-6 showed maximum absorption between 250-450 nm (Fig.
1). The enhancement in absorption was attributed to the
presence of electron rich or electron donating groups. Stilbenes
like S-1, S-2, S-5, S-7 and S-8 showed medium absorption
between 300-400 nm (Fig. 1). From the electronic spectra,
the presence of electron rich thiophene is confirmed and furan
units will enhance the absorption whereas the introduction of
electron withdrawing groups such as fluoro, nitro groups will
results hypsochromic shift in the absorption spectra.
1
C-H), 2227 (C-N), 1610, 1583 (C=C), 821 (C-Br). H NMR
(400 MHz, CDCl3): (δ 7.26 ppm, s), 7.7 (2H, d), 7.5 (4H, t), 7.3
(1H, s), 6.9 (2H, d), 5.3 (1H, s).
(E)-3-(4-Hydroxy-3-methoxyphenyl)-2-(4-nitrophenyl)-
acrylonitrile (S-6): m.f.: C16H12N2O4, calculated mass: 296,
observed mass: 297. FT-IR (KBr, νmax, cm-1): 3130 (O-H), 3094
(arom. C-H) 2227 (arom. C-N), 1610 (C-O-C), 1570 (C=O),
1215 (N-O). 1H NMR (400 MHz, CDCl3): (δ 7.26 ppm, s), 8.3
(2H, q), 7.84 (2H, q), 7.80 (1H, s), 7.6 (1H, s), 7.3 (1H, q), 7.0
(1H, d), 6.0 (1H, s), 4.0 (2H, s).
(E)-2-(4-Hydroxyphenyl)-3-(4-nitrophenyl)acrylo-
nitrile (S-7): m.f. C15H10N2O3, calculated mass: 266, observed
mass: 267. FT-IR (KBr, νmax, cm-1): 3404 (O-H), 2214 (C-N),
1585, (arom. C=C), 1512 (N=O). 1H NMR (400 MHz, CDCl3):
(δ 7.26 ppm, s), 8.3 (2H, d), 7.9 (2H, d), 7.8 (2H, d), 7.6 (1H,
s), 6.9 (2H, d).
(E)-3-(Furan-2-yl)-2-(4-hydroxyphenyl)acrylonitrile
(S-8): m.f.: C16H12N2O4, calculated mass: 296, observed mass:
297. FT-IR (KBr, νmax, cm-1): 3269 (arom. C-H), 2227 (C-N),
1614, 1591 (C=O), 1514 (C-Br). 1H NMR (400 MHz, CDCl3):
(δ 7.26 ppm, s), 7.8 (1H, d), 7.6 (1H, s), 7.5 (2H, d), 7.0 (1H,
d), 6.7 (3H, m), 5.3 (1H, s).
1.0
S-1
S-2
S-3
S-4
S-5
0.8
S-6
S-7
S-8
0.6
S-9
S-10
0.4
0.2
0
300
400
500
600
Wavelength (nm)
Fig. 1. UV-vis spectra of the synthesized stilbenes
(E)-2-(4-Fluorophenyl)-3-(furan-2-yl)acrylonitrile (S-
9): m.f: C13H8NOF, calculated mass: 213, observed mass: 214.
FT-IR (KBr, νmax, cm-1): 3156 (arom. C-H), 2337 (C-N), 748,
588 (C-F). 1H NMR (400 MHz, CDCl3): (δ 7.26 ppm, s): 7.8
(2H, d), 7.6 (H, s), 7.3 (2H, d), 7.1 (2H, d), 6.9 (1H, d), 6.4
(1H, s).
(E)-3-(4-Bromophenyl)-2-(4-fluorophenyl)acrylonitrile
(S-10): m.f: C15H9NBrF, calculated mass: 300, observed mass:
302. FT-IR (KBr, νmax, cm-1): 3026 (arom. C-H), 2216 (C-N),
1834, (arom. C=C), 1512, ( C-N), 1246, (C-Br), 1078 (C-F).
1H NMR (400 MHz, CDCl3): (δ 7.26 ppm, s), 7.9 (2H, d), 7.8
(1H, s), 7.6 (2H, d), 7.5 (2H, d), 7.01 (2H, d), 6.4 (1H, s).
CONFLICT OF INTEREST
The authors declare that there is no conflict of interests
regarding the publication of this article.
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Cyano-stilbenes are most widely used in organic solar
cells to construct a D-A acceptor system with broad absorption
in the UV-vis region. In this paper, we reported synthesis and
characterization of some of cyano-stilbene derivatives.The UV-
visible absorption studies revealed that broad and stronger
absorption of cyano-stilbenes. The strong and broad absorption
is the desired property for the high power conversion efficient
organic photovoltaic.
The UV-vis spectra of stilbenes exhibited the presence n-
π* and π-π* electronic transitions. Band around 260-300 nm
corresponds to π-π* transition in C=C (aromatic). The appea-
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electronic transition of -C=N group. In addition, the peak around
400-450 nm belongs to n-π* of C=N group. 4-Fluorophenyl-
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