Characterization and Thermal Study of Schiff-Base Monomers and Its Transition Metal Polychelates and Their Photovoltaic Performance on Dye Sensitized Solar Cells

Article abstract of DOI:10.1134/S0022476618010092

Azo dye monomer 4,4′-(4,4′-biphenylylenebisazo)-disalicylaldehyde-4n-butylphenyl aniline (H₂A) is synthesised by the reaction of 4,4′-bis[(salicylaldehyde-5)-azo]biphenyl (Azo) and n-butylaniline in the 1:2 molar ratio and its metal polychelate

Full text of DOI:10.1134/S0022476618010092

Journal of Structural Chemistry. Vol. 59, No. 1, pp. 53-63, 2018.
Original Russian Text © 2018 S. M. Al-Barody.
CHARACTERIZATION AND THERMAL STUDY
OF SCHIFF-BASE MONOMERS AND ITS TRANSITION
METAL POLYCHELATES AND THEIR PHOTOVOLTAIC
PERFORMANCE ON DYE SENSITIZED SOLAR CELLS
S. M. Al-Barody
Azo dye monomer 4,4′-(4,4′-biphenylylenebisazo)-disalicylaldehyde-4n-butylphenyl aniline (H2A) is
synthesised by the reaction of 4,4′-bis[(salicylaldehyde-5)-azo]biphenyl (Azo) and n-butylaniline in the 1:2
molar ratio and its metal polychelates are also synthesized with Co(II), Ni(II), Cu(II), and Zn(II) metal ions.
1
13
The synthesized compounds are characterized by H, C NMR, Fourier transform infrared (FT-IR)
spectroscopy, electronic spectra (UV-Vis), elemental analysis (C, H, N, O), gas chromatography-mass (GC-
mass) spectrometry, magnetic susceptibility and molar conductivity techniques. Thermal properties of the
title compounds are studied using the thermogravimetric analysis (TGA). The metal molar ratio in all of the
polychelates is found to be consistent with 1:1 (metal/ligand) stoichiometry. The influence of organic dyes
H2A and the [CuA(H2O)2]n polychelate are investigated as photosensitizers on the photovoltaic parameters
by current–voltage (I–V) measurements on TiO2 photoelectrode dye sensitized solar cells (DSSCs). The
[CuA(H2O)2]n metal polychelate demonstrates the best performance as compared to the cell sensitized with
H2A.
DOI: 10.1134/S0022476618010092
Keywords: synthesis, bis-azo dye, polychelates, coordinate polymer, poly Schiff-base, dye sensitized solar
cell (DSSC).
INTRODUCTION
The unique properties of polychelates in many specific applications [1-3] such as conductivity, catalysis, coating
material, magnetism, and thermal filling give them the benefit of using over organic polymers [4, 5]. Polychelates can be
synthesized by coordinating the organic back-bone with a proper metal salt in an appropriate solvent [6-8]. During the last
years many studies have been performed on coordination polymers with functional groups, such as P, S, O, and N, mainly
due to their biological and physicochemical properties [9, 10]. Between different types of solar cells, dye sensitized solar
cells (DSSCs) [11] are cheapest to successfully work in low light and are less wasting energy to heat [12]. They can be
formed by a photo-sensitized anode and an electrolyte with a semiconductor between the two [13]. The role of the
semiconductor TiO2 electrode is crucial [14], and the cell overall energy conversion efficiency strongly depends on the
surface and electronic properties of the electrode [15]. Many papers on coordination ligands and thermal studies have been
Department of Chemistry, College of Science, University of Al-Mustansiriyah, Baghdad, Iraq;
sadeemaaa@yahoo.com. The text was submitted by the authors in English. Zhurnal Strukturnoi Khimii, Vol. 59, No. 1,
pp. 59-69, January-February, 2018. Original article submitted January 9, 2016; revised March 6, 2016.
0022-4766/18/5901-0053 © 2018 by Pleiades Publishing, Ltd.
53

published in our laboratory [16-18], and as a continuation of our ongoing research work we report herein the synthesis and
characterization of an azo dye derived from benzidine and its metal polychelates with Co(II), Ni(II), Cu(II), and Zn(II) ions.
1
13
These compounds are characterized by various spectral techniques such as infrared, H NMR and C NMR spectroscopy.
The thermal stability of these compounds was also determined using the thermogravimetric analysis (TGA). The UV-Vis,
magnetic moment, and conductivity measurements support the proposed geometry around the metal ions. The effect on the
DSSC photovoltaic performance has also been studied.
MATERIALS AND METHODS
All chemicals were analytical grade and used without any purification. Melting points were determined using
an Electro thermal IA9100 digital apparatus. Elemental analyses (C, H, N, O) were carried out on LECO Corporation
TruSpec® Micro Series (USA). The metal percentage in H2A–metal polychelates was determined by complexometric
–1
titration with EDTA after decomposition with fuming HNO3. The FT-IR spectra were recorded in the range 4000-200 cm
by a universal attenuated total reflection (UATR) technique on a Perkin Elmer 100 series FT-IR spectrometer using a CsI
disc. NMR spectra were recorded on JEOL ECA400 FT NMR and JEOL ECX500 FTNMR spectrometer systems. Dimethyl
1
sulfoxide (DMSO) was used as a solvent. Tetramethylsilane (TMS) was used as the internal standard for H (500 MHz) and
13
C (500 MHz) spectra. Chemical shifts were reported in ppm and coupling constants were given in Hz. Electronic spectra
–3
were recorded in a DMSO solution with a concentration 1×10 M for the free ligand and its metal polychelates on a UV-
160A Shimadzu UV-visible recording spectrophotometer in the range 200-800 nm. Magnetic susceptibility measurements
–1
were carried out employing Magway MSB MK at room temperature. The molar conductivity of the metal polychelates were
measured in N,N-dimethylformamide (DMF) as a solvent in 0.001 M solutions using a CON 510 bench conductivity meter,
with a 2-ring stainless steel conductivity electrode (cell constant, K = 1.0) built in the temperature sensor. Mass spectra were
recorded by electron impact mass spectrometry (EIMS) using a Direct Injection Probe on a Shimadzu GCMS – QP5050A
spectrometer (Shimadzu Europe, Duisburg, Germany). HRESIMS spectra were recorded on a Shimadzu UFLC-IT-TOF mass
spectrometer. Thermal stability (weight changes) of the samples was analyzed by Mettler Toledo TGA851 and STA 6000
(Perkin Elmer, Schwerzenbach, Switzerland) at the temperature up to 1000°C. The current–voltage characterizations were
measured using a Keithey 2400 electrometer.
EXPERIMENTAL
Preparation of 4,4′-bis[(salicylaldehyde-5)-azo]biphenyl (Azo). 4,4′-Bis[(salicylaldehyde-5)-azo]biphenyl was
prepared using the method reported in [19]. To 33.5 mmol (6.61 g) benzidine dissolved in 6 M (15 ml) HCl, 34 mmol
(2.39 g) NaNO2 dissolved in 15 ml of cold water were added dropwise in an ice bath under constant mechanical stirring.
33.5 mmol (4.08 g) salicylaldehyde dissolved in 10% (15 ml) NaOH was gradually added. The reaction mixture temperature
was kept at (0-5)°C, and then dilute acetic acid was added. A brown precipitate was obtained, filtered, washed with water,
and recrystallized from ethanol (Scheme 1). Yield: 95%, mp = 190°C. Anal. Calcd. for C26H18N4O4 (450): C 69.33, H 4.00,
N 12.50, O 14.20%. Found: C, 69.30, H 3.50, N 12.20, O 15.00%.
Synthesis of 4,4′-(4,4′-biphenylylene bisazo)-disalicylaldehyde-4n-butylphenyl aniline (H A). 1 mmol (0.45 g)
2
4,4′-(4,4′biphenylylenebisazo)-disalicylaldehyde (Azo) in 20 ml of ethanol, 2 mmol (0.14 g) n-butylaniline in 20 ml of
ethanol and few drops of glacial acetic acid as a catalyst were mixed and refluxed for 3 h, then left aside at room temperature
for overnight. Brownish orange precipitate formed was filtered and recrystallized from ethanol. Yield: 95%; mp = 350°C.
Anal. calcd. for C46H44N6O2 (712) (%): C 77.53, H 6.18, N 11.80, O 4.49. Found (%): C 77.50, H 5.30, N 11.83, O 5.32.
Synthesis of polychelates. All polychelates were prepared by adding 1 mmol metal salt MCl2⋅XH2O (where
M = Co, Ni, Cu, and Zn) dissolved in 25 ml of ethanol to 1 mmol (0.71 g) H2A in 25 ml of ethanol and allowed to reflux for
3 h. The precipitate was filtered and washed well with ethanol, followed by hot water. The products were dried at 45°C.
54

Scheme 1. Synthesis of the H2A ligand and its metal polychelates.
Photoelectrode preparation. The procedure for fabricating a TiO2-coated working electrode of DSSCs (Fig. 1) is as
follows. Mix 6 g of titanium dioxide powder with 9 ml of an acetic acid solution (pH 3-4 in deionized water). Put the titanium
dioxide powder into the mortar and add 1 ml portions of the acid solution with the pipette while grinding with a pestle. Store
the titanium dioxide suspension in a small plastic capped bottle and allow it to equilibrate for at least 15 min for the best
results. The resulting paste was spread on the top of the substrate consisting of glass covered with a transparent conductive
oxide (TCO) material, usually indium tin oxide (ITO). Allow the slide to heat for ten min on an alcohol burner, and then cool
the slide to room temperature on the wire screen. After air drying, the film electrode was fired for 30 min at 200°C. The
resulting film thickness was about 20 μm [20]. The dye sensitized electrodes were prepared by immersing the films in the
H2A dye and its polychelate dyes.
Assembling DSSCs. The dye sensitized electrode was assembled in a typical sandwich-type cell; namely, the
identical carbon ITO counter electrode was placed over the dye sensitized electrode, and then the electrolyte solution,
containing 0.5 M KI, and 0.05 M I2, was sandwiched between the photo anode and the counter electrode by firm press and the
2
2
cell edges were sealed. The cell area was 2 cm (1×2 cm ). Direct sun light was used to illuminate DSSCs. A digital source
meter (Keithley 2400) was used to measure the open-circuit photovoltage and the short-circuit photocurrent of DSSCs. In
addition, the power conversion efficiency η of DSSCs is given by [21]
I V FF
sc oc
η =
.
(1)
P
in
In equation (1), Voc, Isc, and Pin represent the open-circuit photo voltage, the short-circuit photocurrent per unit area, and the
2
incident light power (1000 mW/cm ), respectively. The fill factor FF is determined by [21]
V I
max max
FF =
.
(2)
55
V I
oc sc

Fig. 1. Schematic DSSC with a TiO2-coated electrode.
In equation (2), Vmax and Imax represent the voltage and the current per unit area at the maximum output power point,
respectively.
RESULTS AND DISCUSSION
The reaction of the symmetric bidentate H2A ligand with MCl2⋅XH2O (where M = Co, Ni, Cu and Zn) resulted in the
formation of colored polychelates that are stable in air, insoluble in water and common solvents but soluble in DMF and
DMSO. The melting points of the metal polychelates were higher than 350°C, revealing that the polychelates are much more
–3
stable than the ligand [22]. The molar conductivity (Λm) of 10 M solutions of the metal polychelates in DMF falls in the
–1
range 2-32 Ω mol cm . These low values suggest that the polychelates have a non-electrolytic nature [23]. Elemental
–1
2
analyses and some physical properties of the H2A ligand and its reported metal polychelates are listed in Table 1.
–1
FT-IR spectra. The FT-IR spectra were recorded in the range 4000-200 cm by the universal attenuated total
reflection (UATR) technique using a CsI disc. The FT-IR spectrum of the H2A ligand has a strong and broad band centered at
–1
3225-3128 cm , which is assigned to ν(OH), The low frequency of this band is probably due to a considerable degree of
TABLE 1. Analytical Data and General Behavior of H2A–Metal Polychelates
Calculated (found), %
Compound
Yield, %
m.p., °C
C
H
N
O
M
C46H46N6O4Co
C46H46N6O4Ni
C46H46N6O4Cu
C46H46N6O4Zn
90
85
88
90
>350
>350
>350
>350
68.48 (68.45) 5.83 (5.80) 10.42 (10.45) 7.94 (8.20)
68.48 (68.49) 5.83 (5.84) 10.42 (10.46) 7.94 (7.90)
68.06 (68.00) 5.79 (5.85) 10.35 (10.30) 7.89 (7.99)
67.98 (67.88) 5.78 (5.88) 10.34 (10.30) 7.88 (7.92)
7.32 (7.10)
7.27 (7.32)
7.89 (7.92)
8.03 (97.99)
56

–1
–1
H-bonding to ortho (OH⋯N = C) [19]. There are also bands at 1174 cm and 1136 cm , which may be assigned to the in-
–1 –1
plane OH bending vibration [24]. The ligand shows strong and sharp bands at 1635 cm and 1595 cm , which may be due to
–1 –1
ν(C = N) and ν(N = N) [17]. The sharp bands at 1440 cm and 1380 cm are representatives of the phenolic (C–O)
–1 –1
vibration. The bands appeared at 3041 cm and 1531-1519 cm for aromatic ν(C–H, C=C) respectively and two bands at
–1
2957-2868 cm for aliphatic ν(C–H) [18]. A comparison of the FT-IR spectra of the polychelates with that of the free H2A
–1
ligand revealed that all polychelates showed a broad band at 3292 cm assignable to ν(OH) of coordinated water [25].
–1
Moreover, in the spectra of these metal polychelates, a narrow intense band was seen at 824-780 cm , which is specific for
a coordinated water molecule. Also the participation of the OH group is apparent from a shift in the position of the δ(OH)
–1
in-plane bending at 1174 cm and 1138 cm . The band at 1635 cm , characteristic of ν(C = N) in the free ligand, was
–1
–1
–1
shifted to a lower frequency range 1617-1614 cm after coordination [25]. This feature could be explained by the withdrawal
of electrons from the nitrogen atom to the metal ion due to coordination, indicating the involvement of the azomethine
–1
nitrogen atom in coordination and the formation of metal–ligand bonds. The band at 1440-1380 cm in the FT-IR spectrum
of the ligand is ascribed to the phenolic (C–O) stretching vibration. This band was shifted to a higher frequency and found in
–1
the range 1475-1389 cm in the FT-IR spectra of the polychelates, showing the involvement of the phenolic oxygen atom in
–1
–1
coordination [25]. The non-ligand bands at 496-429 cm and 580-512 cm were observed due to M–O and M–N, which
gave conclusive evidence regarding the bonding of azomethine nitrogen and phenolic oxygen atoms of the Schiff base to the
metal ion [19].The characteristic FT-IR data on the ligand and their polychelates are listed in Table 2.
1
13
H, C NMR spectra. The NMR spectra were recorded using DMSO as a solvent and TMS was used as the internal
standard. Chemical shifts were reported in ppm and coupling constants were given in Hz. Singlet peaks observed at δ ppm
10.02 and 8.79 are assigned to phenolic hydroxyl (OH) protons and azomethine (CH=N) protons, respectively. This
downfield shift of the phenolic hydroxyl protons can be explained by the intramolecular hydrogen bonding with the
1
1
unsaturated azomethine nitrogen atom [16]. The full H NMR data and their assignments of the H2A ligand are H NMR
(500 MHz, DMSO) δ, ppm: 10.02 (s, 2H, H7), 8.79 (s, 2H, H6), 8.15 (d, 2H, H5), 7.94 (d, 4H, H8–H8′), 7.86 (d, 2H, H3), 7.79
(dd, 4H, H2–H2′), 7.30 (dd, 4H, H1–H1′), 7.04 (d, 2H, H4), 7.02 (d, 4H, H9–H9′), 2.70 (t, 4H, H10), 1.64 (quintet, 4H, H11), 1.39
1
(sextet, 4H, H12), 0.94 (t, 6H, H13) (Figs. 2, 3). Only the H NMR spectrum of the Zn(II) polychelate was recorded due to the
paramagnetic properties of the other transition metal ions. The absence of the phenolic-OH signal (10.02 ppm in H2A) and
a significant shift (8.79-8.44 ppm) in the peak position of –N=CH in the spectrum of [ZnA(H2O)2]n, which implies the
bonding through the phenolic hydroxyl (OH) proton and the azomethine (CH=N) proton of the ligand to the metal ion [26].
1
1
The full H NMR data and their assignments of the [ZnA(H2O)2]n polychelate are as follows. H NMR (500 MHz, DMSO)
δ, ppm: 8.44 (s, 2H, H6), 8.12 (d, 2H, H5), 7.84 (d, 4H, H8–H8′), 7.76 (d, 2H, H3), 7.25 (dd, 4H, H2–H2′), 7.23 (dd, 4H,
H1–H1′), 7.21 (d, 2H, H4), 7.00 (d, 4H, H9–H9′), 2.62 (t, 4H, H10), 1.58 (quintet, 4H, H11), 1.02 (sextet, 4H, H12), 0.87 (t, 6H,
13
H13) (Fig. 4). Similar shifts observed in the C NMR spectra were of a considerable magnitude in the case of carbon atoms
directly attached to the bonding atoms (phenolate-O and azomethine-N) while those observed for the carbon atoms close to
the bonding atoms were of a smaller magnitude.
UV-Vis spectra and magnetic susceptibility. The electronic spectra of the H2A ligand and its metal polychelates
were recorded in DMSO. The electronic spectral bands and their magnetic properties are summarized in Table 3. Within the
–1
TABLE 2. Important IR Frequencies (cm ) of H2A and Its Metal Polychelates
Compound
ν(OH)
ν(C=N)
ν(C–O)phenolic
δ(OH)in plane bending
ν(M–O)
ν(M–N)
H2A (C46H44N6O2)
[CoA(H2O)2]n
[NiA(H2O)2]n
[CuA(H2O)2]n
[ZnA(H2O)2]n
3225, 3128
3287
1635
1617
1614
1914
1914
1440, 1380
1475, 1389
1475, 1384
1473, 1388
1473, 1388
1174, 1136
1154, 1110
1155, 1109
1193, 1161
1155, 1108
–
–
496–435
495–429
497–430
498–430
588–512
583–514
580–517
583–513
3200, 3188
3288
3280
57

1
Fig. 2. H NMR spectrum of the H2A ligand.
–1 –1
UV-Vis spectrum of the ligand, two high-intensity absorption bands were displayed at 20,242 cm and 24,330 cm , which
1
were assigned to intraligand π→π*, n→π* transitions [26]. For the high spin Co(II) polychelate, the ground state term S with
4
4
4
4
4
4
4
a low-lying P excited term exhibits three transitions: T1g → T2g (F), T1g → A2g (F), and T1g → T1g (P). The UV-Vis
–1
spectrum shows three bands at 9,890 cm , 14,771 cm , and 20,540 cm respectively. Considering an octahedral structure,
–1
–1
this was further confirmed by its magnetic susceptibility value (4.2 BM) [27]. In the Ni(II) polychelate three spin-allowed
3 3
transitions are expected because of the splitting of the free ion ground F term and the presence of the P term and the three
3
3
3
3
3
bands are: A2g → T2g (F), A2g → T1g (F), and A2g → T1g (P). The electronic spectrum shows three absorption bands at
3
–1
10,896 cm , 18,181 cm , and 24,768 cm respectively. The Ni(II) polychelate gave a magnetic moment value of 3.0 BM
–1
–1
6 2
because of the presence of two unpaired electrons, which may suggest a high-spin regular octahedral geometry (t2g eg ) and
3
2
sp d hybridization [28]. The electronic spectrum data on the Cu(II) polychelate shows bands at 13,430 cm and
–1
–1
11,560 cm . These bands are assigned to B1g → A2g and B1g → B2g, E transitions respectively, in favor of the octahedral
2
2
2
2
2
g
structure. The magnetic susceptibility value of the Cu(II) polychelate being comparable to its mononuclear metal complex
58

1
Fig. 3. H NMR spectrum of the H2A ligand (aromatic range).
(1.83 BM) is indicative of non-interacting metal centers and suggests the octahedral geometry [29]. The spectrum of the
–1
Zn(II) polychelate exhibited a band at 19,610 cm assigned to charge transfer from the metal to the ligand and vice versa.
10
The Zn(II) polychelate is diamagnetic, as expected for the d configuration [26].
1
Fig. 4. H NMR spectrum of the [ZnA(H2O)2]n polychelate.
59

TABLE 3. Electronic Transition Bands, Magnetic Moments, and Conductivity Data of H2A and Its Reported Metal
Polychelate
–1
–1 2
Λm, Ω ⋅cm ⋅mol
–1
Compound
H2A
UV-Vis, cm
Assignments
µeff, BM
⋯
⋯
20,242
24,330
9,890
π–π*
n–π*
4
4
4
T1g → T2g (F)
⋯
[CoA(H2O)2]n
4.2
4
14,771
20,540
T1g → A2g (F)
4
4
T1g → T2g (P)
3
3
3
A2g → T2g (F)
[NiA(H2O)2]n
10,896
18,181
24,768
3.0
10
3
A2g → T1g (F)
3
3
A2g → T1g (p)
2
2
B1g → A2g
[CuA(H2O)2]n
[ZnA(H2O)2]n
13,430
11,560
1.83
Dia.
23
2
2
2
B1g → B2g, E
g
19,610
Charge transfer
31.5
Mass spectra. Mass spectra were recorded using a Direct Injection Probe. The mass spectral features of the H2A
ligand, as illustrated in Fig. 5, was described by a molecular ion peak at m/z = 712, which matched with the molecular weight
of the C46H44N6O2 ligand. The main fragment peaks were m/z [fragment, intensity, %]: 713 [M+1, 8], 712 [M, 10], 665
+
+
+
[M–C H , 15], 393 [M–2(C4H9C6H6N=CH ), 15], 208 [C12H8N , 15], 196 [C6H6N = CC6H6OH , 50], 186 [C6H6OH , 40],
+
+
4
9
4
+
+
153 [C12H9, 25], 133 [M–C H , 25], 114 [2(C4H9) , 100], 93 [C6H6OH , 30].
+
10 13
Thermogravimetric analyses. Thermal decomposition of the H2A ligand and its metal polychelates was studied by
the thermogravimetric method. The thermogravimetric curves of the ligand and its metal polychelates are depicted in Fig. 6.
The thermal analytical data are listed in Table 4. All the compounds were highly heat-resistant and did not decompose easily.
In the present study, no sharp weight loss was observed in the TGA curves of metal polychelates, which shows their
polymeric nature [30]. In the case of metal polychelates, the curve showed a 4.4-4.5% weight loss corresponding to two water
molecules up to 195°C. The presence of water molecules in these polychelates was also supported by the FT-IR studies. For
the ligand, a steady and regular weight loss was observed and at 200°C the weight loss was about 16%. The temperature of
the maximum decomposition rate for the ligand was 688°C and almost the entire ligand was lost by 800°C, whereas only 87-
89% of the polychelates were lost. This result revealed that all the polychelates showed a higher thermal stability than the
polymeric ligand due to the insertion of metal ions into the polymeric chain as a result of chelation. Another factor that may
be responsible for the enhanced thermal stability of the polychelates is an increase in the molecular weight due to the joining
of two different polymer chains.
Current-voltage measurement of DSSCs. The materials with imine units are investigated as hole transporting
compounds. In order to investigate the usefulness of new synthesized imines as hole-transport materials, a preliminary study
of current–voltage characteristics was performed [31, 32]. Fig. 7 shows curves I–V of DSSCs with H2A and [CuA(H2O)2]n
Fig. 5. Mass spectrum of H2A.
60

Fig. 6. TGA of H2A and its metal polychelates.
Fig. 7. DSSC photocurrent-voltage characteristics.
dyes under illumination. It was found that the cell sensitized with [CuA(H2O)2]n polychelates dye showed the largest area of
the current-density curve, indicating that this cell generated the highest output power.
Meanwhile, the cell utilizing the H2A dye showed the smallest area of the current-density curve, generating the
lowest power. However, it was noticeable that the areas of curves I–V of the cells were not much different, leading to small
distinctions in the photovoltaic parameters presented in Table 5. From the table, it can be seen that DSSCs with [CuA(H2O)2]n
polychelate dyes performed with the highest Isc, Voc, and η. Meanwhile, the device sensitized with the H2A dye demonstrated
the lowest Isc, Voc, and η. This leads to more electrons being injected from polychelate dye molecules to the conduction band
of TiO2 upon light illumination, resulting in an enhancement of the cell photovoltaic parameters such as Isc and η.
TABLE 4. Thermal Properties of the H2A Ligand and Its Metal Polychelates
Temperature,
Residue
Weight
loss, %
Compound
Assignments of mass loss, %
°C
at 900°C
H2A
197-100
685-688
16.01
84.12
4.46
Loss of two (C4H9) molecules
Decomposition of (C38H26N6O2)
0.0
[CoA(H2O)2]n 195-198
220-550
Loss of two coordinated water molecules
64.06 Decomposition of the non-coordinated part of the ligand (C29H26N5O)+(C4H9)
Decomposition of the polymer and formation of CoO
Loss of two coordinated water molecules
64.08 Decomposition of the non-coordinated part of the ligand ((C29H26N5O)+(C4H9)
Decomposition of the polymer and formation of NiO
Loss of two coordinated water molecules
63.74 Decomposition of the non-coordinated part of the ligand (C29H26N5O)+(C4H9)
Decomposition of the polymer and formation of CuO
Loss of two coordinated water molecules
895-900
9.29
9.30
9.86
10.07
–2
[NiA(H2O)2]n 196-198
230-650
4.59
897-900
[CuA(H2O)2]n 198-110
230-580
4.47
898-900
[ZnA(H2O)2]n 196-100
220-583
10.07
63.66 Decomposition of the non-coordinated part of the ligand (C29H26N5O)+(C4H9)
Decomposition of the polymer and formation of ZnO
896-900
TABLE 5. Photovoltaic Parameters of H2A and [CuA(H2O)2]n DSSCs
–2
–2
Compound
ISC, mA/cm
VOC, mV
Im, mA/cm
Vm, mV
FF
η×10 , %
H2A
[CuA(H2O)2]n
7.9
9.5
340
400
7
8
230
260
0.59
0.54
1.58
2.05
Abbreviations: Isc: Short circuit current; Voc: Open circuit voltage; Im: Maximum current; Vm: Maximum voltage; FF:
Fill factor; η: overall energy conversion yield.
61

CONCLUSIONS
A novel azo dye monomer 4,4′-(4,4′-biphenylylenebisazo)-disalicylaldehyde-4n-butylphenylaniline (H2A) was
synthesised by the reaction of 4,4′-bis[(salicylaldehyde-5)-azo]biphenyl (Azo) and n-butylaniline in the 1:2 molar ratio. The
coordination to Co(II), Ni(II), Cu(II), and Zn(II) yields new metal polychelates. The collected results are consistent with the
stoichiometry [MA(H2O)2]n, where the octahedral coordination around the metal(II) ions was accomplished by the bidentate
ligand through phenolic oxygen and azomethine nitrogen atoms with two coordinated water molecules. It has been observed
that the attachment of metal ions in the polymeric backbone enhances the thermal activity, as well as demonstrates the best
photovoltaic performance compared with a cell sensitized with the [CuA(H2O)2]n dye which showed the highest short–circuit
–2
density ISC of 9.5 mA/cm and a conversion efficiency of 2.05%.
The author would like to thank the Ministry of Science and Technology, Iraq for providing the current–voltage
measurement of DSSC and Dr. Haslina Ahmad, Faculty of Science, University Putra Malaysia for providing C, H, N, O
measurements.
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