Synthesis and characterization of nitrobenzoylthiourea derivatives as potential conductive biodegradable thin films

Article abstract of DOI:10.1080/10426507.2013.844137

The application of thiourea derivatives as conjugated molecular wire candidates in the field of material sciences has attracted great attention recently. To date, conjugated thiourea systems as molecular wires are surprisingly unexplored although the well-known rigid π-systems promise a wide range of electronic properties. Due to this matter, five novel thiourea derivatives A-ArC(O)NHC(S)NHAr-D with polar head and tail groups, namely NO2 (acceptor A) and alkoxy with varying chain lengths (donor D = OC _nH2_n+1, n = 6, 7, 8, 9,10), were successfully synthesized and characterized. All compounds were characterized by IR, UV-vis, ¹H and ¹³C NMR spectroscopy, and CHNS elemental microanalysis. The investigation of their potential as dopant systems in polymer conducting films has been accomplished by incorporating of chitosan via the solution casting technique. The conductivity values were obtained using impedance spectroscopy. They show that the ionic conductivities of the N-(4-alkoxyphenyl)-N'-(4- nitrobenzoyl)thioureas increase with increasing chain length of the alkoxy chain. The compounds exhibit great potential for the exploration of future applications as doping systems in conductive materials. Copyright

Full text of DOI:10.1080/10426507.2013.844137

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Phosphorus, Sulfur, and Silicon and the
Related Elements
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Synthesis and Characterization of
Nitrobenzoylthiourea Derivatives as
Potential Conductive Biodegradable Thin
Films
Wan M. Khairulac, Khalisah Asilah Moktharac, M. I. N. Isab, A. S.
Samsudinb, Hasyiya Karimah Adliac, Saidatul Radhiah Ghazaliac
Adibah Izzati Daudac
&
a Department of Chemical Sciences, Faculty of Science and
Technology, Universiti Malaysia Terengganu, 21030 Kuala
Terengganu, Malaysia
b Department of Physical Sciences, Faculty of Science and
Technology, Universiti Malaysia Terengganu, 21030 Kuala
Terengganu, Malaysia
c Institute of Marine Biotechnology, Universiti Malaysia Terengganu,
21030 Kuala Terengganu, Malaysia
Accepted author version posted online: 25 Sep 2013.Published
online: 14 May 2014.
To cite this article: Wan M. Khairul, Khalisah Asilah Mokthar, M. I. N. Isa, A. S. Samsudin, Hasyiya
Karimah Adli, Saidatul Radhiah Ghazali & Adibah Izzati Daud (2014) Synthesis and Characterization
of Nitrobenzoylthiourea Derivatives as Potential Conductive Biodegradable Thin Films, Phosphorus,
Sulfur, and Silicon and the Related Elements, 189:5, 640-651, DOI: 10.1080/10426507.2013.844137
To link to this article: http://dx.doi.org/10.1080/10426507.2013.844137
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Phosphorus, Sulfur, and Silicon, 189:640–651, 2014
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2013.844137
SYNTHESIS AND CHARACTERIZATION OF
NITROBENZOYLTHIOUREA DERIVATIVES AS POTENTIAL
CONDUCTIVE BIODEGRADABLE THIN FILMS
Wan M. Khairul,1,3 Khalisah Asilah Mokthar,1,3 M. I. N. Isa,2
A. S. Samsudin,2 Hasyiya Karimah Adli,1,3 Saidatul Radhiah
Ghazali,1,3 and Adibah Izzati Daud1,3
1Department of Chemical Sciences, Faculty of Science and Technology, Universiti
Malaysia Terengganu, 21030 Kuala Terengganu, Malaysia
2Department of Physical Sciences, Faculty of Science and Technology, Universiti
Malaysia Terengganu, 21030 Kuala Terengganu, Malaysia
3Institute of Marine Biotechnology, Universiti Malaysia Terengganu, 21030 Kuala
Terengganu, Malaysia
GRAPHICAL ABSTRACT
Abstract The application of thiourea derivatives as conjugated molecular wire candidates
in the field of material sciences has attracted great attention recently. To date, conjugated
thiourea systems as molecular wires are surprisingly unexplored although the well-known
rigid π-systems promise a wide range of electronic properties. Due to this matter, five novel
thiourea derivatives A-ArC(O)NHC(S)NHAr-D with polar head and tail groups, namely NO2
(acceptor A) and alkoxy with varying chain lengths (donor D = OCnH2n+1, n = 6, 7, 8, 9,
10), were successfully synthesized and characterized. All compounds were characterized by IR,
UV-vis, 1H and 13C NMR spectroscopy, and CHNS elemental microanalysis. The investigation
of their potential as dopant systems in polymer conducting films has been accomplished by
incorporating of chitosan via the solution casting technique.
Received 25 April 2013; accepted 10 September 2013.
The authors would like to thank Department of Chemical Sciences, Institute of Marine Biotechnology (IMB),
and Department of Physical Sciences, Faculty of Science and Technology, Universiti Malaysia Terengganu for
the technical and research support.
Address correspondence to Associate Prof. Dr. Wan Mohd Khairul Wan Mohamed Zin, Department of Chem-
ical Sciences, Faculty of Science and Technology, Universiti Malaysia Terengganu, 21030 Kuala Terengganu,
Malaysia. E-mail: wmkhairul@umt.edu.my
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gpss.
640

CONDUCTIVE THIN FILM FEATURING THIOUREA DERIVATIVES
641
The conductivity values were obtained using impedance spectroscopy. They show that the ionic
conductivities of the N-(4-alkoxyphenyl)-N’-(4-nitrobenzoyl)thioureas increase with increasing
chain length of the alkoxy chain. The compounds exhibit great potential for the exploration of
future applications as doping systems in conductive materials.
Keywords Thiourea; molecular wire; conductive thin film
INTRODUCTION
In recent years, a widespread interest in convenient use of smaller, lighter, quicker,
and more efficient electronic devices is observed. The focus for current research on molecu-
lar electronics is due to the process of miniaturization in the field of information processing
technology according to the Moore’s Law.1 However, it is challenging to find suitable and
applicable molecular materials for their utilization in molecular electronic devices. Re-
cently, organic polymer thin films have attracted a great deal of attention from researchers
in the field of molecular electronic devices.2,3 A large variety of techniques have been
developed for thin film deposition such as spray pyrolysis technique,4,5 chemical vapor de-
position (CVD)6 spin coating,7 solution casting technique8 and inkjet printing or stamping.9
Among different techniques for organic thin film deposition, solution casting technique has
been chosen in this study due to its advantages such as applicability of low-temperature pro-
cesses, requirement of only small sample amounts and uniform film thickness obtained.10
Moreover, this general and convenient method can be applied to form highly uniform thin
films on all kinds of substrates.11
It is known that for the past few decades, thiourea derivatives with their reso-
nance structures have been widely studied as versatile ligands in various applications.
This is due to their unique properties which enable to coordinate with numerous tran-
sition metal ions as monodentate or bidentate ligands.12 They are classical additives for
the electro deposition of copper and other metals,13 corrosion inhibitors,14,15 vulcaniza-
tion accelerators,16 and pharmaceuticals products.17 Meanwhile, the thiourea system has
turned out to be a great candidate to construct D-A molecular wire compounds, which
can act as excellent transporters.18,19 The electron transportation through these compounds
which is widely known to have π-conjugated system has become the fundamental im-
portance as molecular wire.20 They can act as the simplest electronic component for
the conduction of current. These compounds should display ideal characteristics such
as wide concentration range, fast response time and good selectivity coefficient for many
cations.
To date, to the best of our knowledge, the idea and work on manipulating conjugated
thiourea derivatives as molecular wire candidate has never been carried out and reported
beyond our research team. Therefore, this present work involves the materials syntheses,
characterization, data analysis as well as the development of thin films by solution casting
technique. In addition, their behavior and characteristics including their electrical proper-
ties via formation of thin film by solution casting techniques were also carried out. As it
is processed in a final application, a thin film should be best measured for the material
properties including the electrical properties.21 The so-called molecular wire were synthe-
sized and studied by several chemical analyses such as IR, 1H and 13C NMR, UV-Visible
spectroscopy, and CHNS elemental analysis as well as impedance measurements for their
conductivity analysis.

642
W. M. KHAIRUL ET AL.
RESULTS AND DISCUSSION
Spectroscopic Studies
1
The H NMR spectra for this series of compounds show methyl resonances in the
range of δH 0.91–0.93 ppm while protons for alkyl group were observed in the range δH
1.32–1.81 ppm. For OCH2, the signals were detected in the range δH 3.97–3.99 ppm as
triplets as reported previously for similar systems.22 The aromatic protons were observed
in the range δH 6.95–8.41 ppm and show a pseudo-doublet for the AB system of the arene
protons which is due to the para-substitution of the aromatic rings in these compounds.23
Furthermore, two singlet resonances due to two NH groups in these compounds were ob-
served at δH 9.18–9.36 ppm and δH 12.21–12.24 ppm. The 1H NMR data for all compounds
synthesized in this series are shown in Table 1.
The 13C NMR spectra for the series of these derivatives show methyl group res-
onances at δC 14.1 ppm and carbon resonances for alkyl groups in each compounds
at δC 22.6–31.9 ppm. Chemical shifts for CH2O in this series were observed at δC
68.3 ppm and resonances for both aromatic ring carbons were observed in the range
δC 114.7–128.8 ppm. One resonance each was observed in the range δC 164.9–165.0 ppm
and δC 177.9–178.1 ppm which corresponds to the C O and C S carbons respectively.
The C O and C S resonances were slightly de-shielded to higher chemical shifts which
may be due to intramolecular hydrogen bonding of the compounds and the electronegativ-
ity of oxygen and sulfur.22,23. Table 2 shows the 13C NMR data for all compounds in this
series.
The infrared spectra of these derivatives show six absorption bands of interest namely
ν(NH), ν(CH), ν(C O), ν(N O), ν(C–O) and ν(C S). Table 3 shows the absorption data
for these derivatives.
For this series of compounds, it can be clearly seen that the absorption bands of
NO2 appear in the range of 1533 to 1515 cm−1 and 1350 to 1342 cm−1 due to resonance
effects. The absorption bands for a nitro group should be shifted to lower frequencies at
1550–1490 cm−1 and 1355–1315 cm−1 due to conjugation with an aromatic ring.24 In this
series of compounds, the nitro group is located in the para-position of the aromatic ring and
the vibration frequencies are in the corresponding range. The absorption bands of C S in
these compounds were observed at 713 to 709 cm−1, which confirmed the formation of the
thioureas.25–27 The electronic absorption spectra of 1–5 were recorded in dichloromethane
and show two principal bands which were expected to arise from the C O and C S
moieties. Table 4 shows the principal UV-vis absorption data of 1–5.
Functional carbonyl (C O) and thiocarbonyl (C S) groups exhibit two principal UV
transitions, the allowed π–π∗ transition (190 nm) and the forbidden n–π∗ (280 nm) tran-
sition.25 However, under usual experimental conditions only the forbidden n–π∗ transition
is commonly observed. Due to the extended π-electron conjugation, the absorption peak
is red-shifted (bathochromic shift). Therefore, the absorption bands for C O and C S
chromophores in thiourea derivatives appear in the range of 232.0 to 233.6 nm and 256.2 to
260.0 nm, respectively, since the carbonyl and thione groups in thiourea derivatives are part
of the conjugated system.28 Furthermore, the electron withdrawing NO2 group also exhibits
a pronounced bathochromic shift of the n–π∗ transition and π–π∗ transition. It shows a
broad band at of 256 to 260 nm, due to the conjugation effect. The broad absorption bands
observed in the region between 250 to 350 nm is due to π-conjugation of the compounds
with the phenyl ring (π–π∗ transition), probably arising from orbital overlapping between
C S and NO2.

CONDUCTIVE THIN FILM FEATURING THIOUREA DERIVATIVES
643
Table 1 1H NMR data for all synthesized compounds
Compound
Moieties
Chemical shift δH (ppm)
1
(t, JHH = 7 Hz, 3H, CH3)
(m, 6H, 3 × CH2)
0.93
1.35–1.50
1.81
(m, 2H, CH2)
(t, JHH = 6 Hz, 2H, CH2)
3.99
6.96
7.54
(pseudo-d, JHH = 9 Hz, 2H, C6H4) (pseudo-d, JHH = 9 Hz,
2H, C6H4)
(pseudo-d, JHH = 9 Hz, 2H, C6H4)
(pseudo-d, JHH = 9 Hz, 2H, C6H4)
(2 × s, 1H, NH)
8.11
8.39
9.29, 12.23
0.92
1.36–1.48
1.76
2
3
4
5
(t, JHH = 7 Hz, 3H, CH3)
(m, 8H, 4 × CH2)
(m, 2H, CH2)
(t, JHH = 6 Hz, 2H, CH2)
(pseudo-d, JHH = 9 Hz, 2H, C6H4) (pseudo-d, JHH = 9 Hz,
2H, C6H4)
3.97
6.97
7.55
8.11
(pseudo-d, JHH = 9 Hz, 2H, C6H4)
(pseudo-d, JHH = 9 Hz, 2H, C6H4)
(2 × s, 1H, NH)
8.39
9.25, 12.22
0.92
1.32–1.37
1.73
(t, JHH = 7 Hz, 3H, CH3)
(m, 10H, 5 × CH2)
(m, 2H, CH2)
(t, JHH = 6 Hz, 2H, CH2)
(pseudo-d, JHH = 9 Hz, 2H, C6H4) (pseudo-d, JHH = 9 Hz,
2H, C6H4)
3.99
6.96
7.56
8.11
(pseudo-d, JHH = 9 Hz, 2H, C6H4)
(pseudo-d, JHH = 9 Hz, 2H, C6H4)
(2 × s, 1H, NH)
8.40
9.22, 12.22
0.91
1.38–1.51
1.76
(t, JHH = 7 Hz, 3H, CH3)
(m, 12H, 6 × CH2)
(m, 2H, CH2)
(t, JHH = 6 Hz, 2H, CH2)
(pseudo-d, JHH = 9 Hz, 2H, C6H4) (pseudo-d, JHH = 9 Hz,
2H, C6H4)
3.97
6.95
7.55
8.13
(pseudo-d, JHH = 9 Hz, 2H, C6H4)
(pseudo-d, JHH = 9 Hz, 2H, C6H4)
(2 × s, 1H, NH)
8.40
9.36, 12.24
0.91
1.35–1.50
1.79
(t, JHH = 7 Hz, 3H, CH3)
(m, 14H, 7 × CH2)
(m, 2H, CH2)
(t, JHH = 6 Hz, 2H, CH2)
(pseudo-d, JHH = 9 Hz, 2H, C6H4) (pseudo-d, JHH = 9 Hz,
2H, C6H4)
3.98
6.95
7.56
(pseudo-d, JHH = 9 Hz, 2H, C6H4)
(pseudo-d, JHH = 9 Hz, 2H, C6H4)
(2 × s, 1H, NH)
8.12
8.41
9.18, 12.21
CHNS Elemental Analysis
CHNS elemental analysis was used to determine the percentage of carbon (C), hydro-
gen (H), nitrogen (N), and sulfur (S). Elemental analysis can be used to determine the purity
of the compounds of interest by comparison between experimental and theoretical percent-
age of the elements.29 Table 5 shows CHNS analytical data of the thiourea derivatives.

644
W. M. KHAIRUL ET AL.
Table 2 The data of 13C NMR spectra for compounds 1–5
Compound
Moiety
Chemical Shift, δC (ppm)
1
(s, CH3)
(4 × s, 4 × CH2)
(s, CH2O)
14.1
22.6, 25.7, 29.2, 31.6
68.3
(8 × s, C6H4)
114.7, 115.0, 122.3, 124.0, 124.3, 125.8, 128.3,
(s, C O)
128.9
(s, C S)
165.0
177.9
2
3
4
5
(s, CH3)
(5 × s, 5 × CH2)
(s, CH2O)
14.1
22.6, 26.0, 29.1, 29.2, 31.8
68.3
(8 × s, C6H4)
114.7, 122.3, 124.0, 124.3, 125.7, 128.2, 128.9,
(s, C O)
129.7
165.0
177.9
14.1
(s, C S)
(s, CH3)
(6 × s, 6 × CH2)
(s, CH2O)
22.7, 26.0, 29.2, 29.3, 29.4, 31.8
68.3
(8 × s, C6H4)
114.7, 115.0, 122.3, 124.0, 124.3, 125.7, 128.2,
(s, C O)
128.9
164.9
178.0
14.1
(s, C S)
(s, CH3)
(7 × s, 7 × CH2)
(s, CH2O)
22.7, 26.0, 29.2, 29.3, 29.4, 29.6, 31.9
68.3
(8 × s, C6H4)
114.7, 115.0, 122.3, 124.0, 124.3, 125.8, 128.2,
(s, C O)
128.9
165.0
178.1
14.1
(s, C S)
(s, CH3)
(8 × s, 8 × CH2)
(s, CH2-O)
22.7, 26.0, 29.2, 29.3, 29.3, 29.4, 29.6, 31.9
68.3
(8 × s, C6H4)
114.7, 115.0, 122.3, 124.0, 124.4, 125.7, 128.2,
(s, C O)
128.8
164.9
177.9
(s, C S)
Table 3 IR Absorption data of the nitrobenzoylthioureas 1–5
ν(NH) cm−1 ν(CH) cm−1 ν(C O) cm−1 ν(NO2) cm−1 ν(C–O) cm−1 ν(C S) cm−1
Compound
1 Intensity
2 Intensity
3 Intensity
4 Intensity
5 Intensity
3306 (m)
3238 (m)
3326 (s)
3350 (m)
3341 (s)
2857 (m)
2855 (s)
2854 (s)
2853 (s)
2853 (s)
1651 (m) 1524 (m) 1348 (m) 1112 (m)
1677 (s) 1515 (m) 1351 (m) 1111 (m)
711 (m)
710 (m)
713 (m)
709 (m)
709 (m)
1675 (m) 1518 (s) 1344 (m)
1661 (m) 1528 (s) 1342 (m)
1110 (m)
1113 (m)
1674 (m) 1533 (m) 1343 (m) 1111 (m)

CONDUCTIVE THIN FILM FEATURING THIOUREA DERIVATIVES
645
Table 4 The principal UV-vis absorption data of nitrobenzoylthioureas
Compound
Concentration/M
C
O λ/nm (ε/M−1cm−1
)
C )
S λ/nm (ε/M−1cm−1
1
2
3
4
5
2.3633 × 10−5
2.2208 × 10−5
2.8310 × 10−5
2.7144 × 10−5
2.9090 × 10−5
232.0 (38307)
232.0 (39941)
233.6 (33324)
233.6 (34593)
232.2 (33957)
258.0 (22566)
258.0 (23532)
257.0 (22501)
260.0 (23755)
256.2 (22417)
All synthesized thioureas show good results of C, H, N, and S in elemental analysis
with only slight deviations from the theoretical percentages.
Electrical Conductivity Study
The impedance spectra (or Cole–Cole plot) at ambient temperature obtained on
conductive thin film based on chitosan doped with different thioureas is shown in Figure 1.
The conductivity values of the samples were calculated by use of equation (1). From the
plots of negative imaginary impedance, Zi versus real impedance, Zr with the horizontal and
vertical axes having the same scale, the bulk resistance, Rb for all samples can be obtained.
When ever Rb was difficult to obtain from the complex impedance data, the impedance data
were converted into admittance data and plotted according to the admittance formalism
from which 1/Rb may be easier to obtain.30 Table 6 shows the data (Rb and thickness, t) for
all thin film samples.
The ionic conductivity at room temperature (r.t.) for all samples is illustrated in
Figure 2. It depends on several factors, such as ionic dopant concentration, cationic or
anionic type charge carriers, the charge carriers’ mobility and the temperature. From the
plot, it can be found that the conductivity of K0 (chitosan-acetate) sample is at 6.80 ×
Table 5 Analytical data (%)∗ of 1–5
Compound
C
H
N
S
1
2
3
4
5
60.32 (59.88)
60.84 (60.75)
61.66 (61.52)
62.76 (62.28)
63.11 (63.05)
5.87 (5.79)
6.39 (6.07)
6.38 (6.34)
6.70 (6.59)
6.92 (6.83)
10.42 (10.48)
10.08 (10.12)
9.89 (9.78)
9.51 (9.47)
9.42 (9.19)
8.12 (7.99)
7.88 (7.72)
7.68 (7.47)
7.47 (7.23)
7.04 (7.01)
∗Theoretical values in brackets.
Table 6 The values (Rb and thickness, t) obtained for thin films
Sample
Rb
t (cm)
K0
K1
K2
K3
K4
K5
2.13 × 106
2.25 × 106
1.50 × 106
8.33 × 105
7.50 × 105
6.88 × 105
0.006
0.007
0.012
0.008
0.009
0.010

646
W. M. KHAIRUL ET AL.
Figure 1 The Rbvalue obtained from the Cole–Cole Plot and the Cole–Cole Plot of all of the samples obtained
using EIS.
10−10 S cm−1 and its show a similar range for pure chitosan film which has been reported.31
Therefore, it was used as polymer host in this work to observe any changes of conductivity
by addition of several types of thiourea compound. It can be seen, with the addition of
nitrobenzoylthiourea, the ionic conductivity of thin films was found to be increased and the
highest conductivity was observed for sample K5 with the value 3.50 × 10−9 S cm−1. The
highest value of conductivity for sample K5 due to the increased of length of the alkoxy
(donor) group as shown from the previous study for compound 5, thus the conductivity
increases. Moreover, the molecular weight of the sample also gives the significant result to
the conductivity as an increase of the molecular weight enhances the conductivity. This is
supported by previous literature reports which claimed that as the amount of doping material
(wt.%) increases, the conductivity of sample also increases.32 Apparently, the conductivites
of samples in this study increase as the length of alkoxy group in a sample increases with
its molecular weight.
The results show that nitrobenzoylthioureas are very promising potential candidates
to be used as molecular wires due to their π-conjugation system and charge carriers of the
compound.33
CONCLUSIONS
Linear conjugated organic compounds A-ArC ONHC SNHAr-D [N-
alkoxyphenyl-Nꢁ-(4-nitrobenzoyl)thioureas] have been successfully designed, prepared,

CONDUCTIVE THIN FILM FEATURING THIOUREA DERIVATIVES
647
Figure 2 The ionic conductivity of thin films at room temperature (r.t.).
and characterized prior to form conductive thin film. All compounds were spectroscopically
1
and analytically characterized by H and 13C NMR, FT-IR, UV-vis spectroscopy. The
conductivity behavior of the compounds was revealed by using Electrical Impedance
Spectroscopy (EIS). Data from EIS show an increase as the molecular weight of the
samples increase as well as the length of the alkoxy group. This demonstrates that these
compounds are promising candidates and exhibit great potentials to be explored and used
as molecular wires in numerous microelectronics applications in the future.
EXPERIMENTAL
Materials and General Methodology
All reactions were carried out under an ambient atmosphere and no special precau-
1
tions were taken to exclude air or moisture during work-up. H (400.11 MHz) and 13C
(100.61 MHz) NMR spectra were recorded by use of a Bruker Avance III 400 Spectrometer
with CDCl3 as solvent and internal standard at r.t. in the range between δH 0–15 ppm
and δC 0–200 ppm, respectively. IR spectra in the spectral range of 4000–400 cm−1 were
recorded on KBr pellets using a FT-IR Perkin Elmer 100 spectrophotometer. UV-vis spectra
were recorded with a Shimadzu UV-vis 1601 spectrometer by use of a 1 cm3 cuvette in
CH2Cl2 as solvent. Finally, the sample that form in thin films state were then characterized
via EIS using a HIOKI 3532-Z LCR in the range 50 Hz–1 MHz in order to calculate the
conductivity.
General Synthesis
The synthesis of the nitrobenzoylthiourea involved a reaction between 4-nitrobenzoyl
chloride and ammonium thiocyanate with 4-alkoxyaniline at reflux for ca. 4 h. The reac-
tion was carried out in acetone to give a yellow solution with a white precipitate of the
inorganic salt as byproducts. After completion, the reaction mixture was cooled to r.t.

648
W. M. KHAIRUL ET AL.
and filtered. The yellow filtrate was cooled with three ice cubes and filtered to obtain the
N-(4-alkoxyphenyl)-Nꢁ-(4-nitrobenzoyl)thioureas as yellow solids with moderate yields
(34–54%). For 4-alkoxyanilines, they have been reported in previous occasions34,35 and
characterization results have been referred. Scheme 1shows the synthetic approach applied
in this study.
Scheme 1
N-[4-(Hexyloxy)phenyl]-N’-(4-nitrobenzoyl)thiourea (1)
A suspension of 4-nitrobenzoyl chloride (1.81 g, 9.7 mmol) in 50 mL acetone was
added to ammonium thiocyanate (0.74 g, 9.7 mmol) in 50 mL of acetone to give a pale
yellow solution and a white precipitate. The solution was stirred at r.t. for ca. 4 h before
4-(hexyloxy)aniline (1.87 g, 9.7 mmol) was added. After stirring for another ca. 4 h, the
color of the solution turned from pale yellow to bright yellow. After adjudged completion
by TLC (hexane/DCM = 4:6), the reaction mixture was cooled to r.t. and filtered. The
yellow filtrate was cooled with three ice cubes and filtered to obtain yellow precipitate.
The yellow precipitate was then recrystallized from MeOH to afford the title compound 1
(2.08 g, 54%).
N-[4-(Heptyloxy)phenyl]-N’-(4-nitrobenzoyl)thiourea (2)
Compound 2 (3.05 g, 34%) was prepared from 4-nitrobenzoyl chloride (4.01 g,
2.16 mmol), ammonium thiocyanate (1.65 g, 2.16 mmol), and 4-(heptyloxy)aniline (4.47 g,
2.16 mmol) as described above.
N-[4-(Octyloxy)phenyl]-N’-(4-nitrobenzoyl)thiourea (3)
Compound 3 (4.50 g, 49%) was prepared from 4-nitrobenzoyl chloride (4.01 g,
2.16 mmol), ammonium thiocyanate (1.64 g, 2.16 mmol), and 4-(octyloxy)aniline (4.79 g,
2.16 mmol) as described above.

CONDUCTIVE THIN FILM FEATURING THIOUREA DERIVATIVES
649
N-[4-(Nonyloxy)phenyl]-N’-(4-nitrobenzoyl)thiourea (4)
Compound 4 (5.14 g, 54%) was prepared from 4-nitrobenzoyl chloride (4.07 g,
2.16 mmol), ammonium thiocyanate (1.64 g, 2.16 mmol), and 4-(nonyloxy)aniline (5.08 g,
2.16 mmol) described above.
N-[4-(Decyloxy)phenyl]-N’-(4-nitrobenzoyl)thiourea (5)
Compound 5 (3.52 g, 36%) was prepared from 4-nitrobenzoyl chloride (4.08 g,
2.16 mmol), ammonium thiocyanate (1.65 g, 2.16 mmol), and 4-(decyloxy)aniline (5.39 g,
2.16 mmol) as described above.
Thin Film Preparation
The thin films were prepared by the solution casting technique. 2 g Chitosan (Eastern
Global) which was used as the polymer host was dissolved in 100 mL of 1% acetic acid
solution. Then, different (nitrobenzoyl)thioureas in 0.4 wt.% o were added separately into
the chitosan solution. The mixture was continuously stirred until the complete dissolution
of the (nitrobenzoyl)thiourea. The mixture was then poured into different Petri dishes and
left dried at ambient temperature for film formation. The films were kept in desiccators
for further drying before characterized to ensure no water present. Table 7 shows the
composition and designation of the thin film.
Electrical Conductivity Measurement
In order to investigate the ionic conductivity of the chitosan-(4-nitrobenzoyl)thiourea
based thin films, the impedance spectroscopy was performed. The biodegradable films
were cut into small discs of 2 cm diameter and sandwiched between two stainless steel
electrolytes under spring pressure (as shown in Figure 2). The samples were characterized
via EIS using HIOKI 3532–50 LCR Hi-Tester interfaced to a computer in a frequency
range between 50 Hz and 1 MHz. The conductivity σ of the film can be calculated from
the equation:
t
σ =
(1)
RbA
Table 7 Composition of the thin films
Weight of dopant (sample)
Volume of 1% acetic acid (ml) (g)
Designation
Chitosan (g)
K0
K1
K2
K3
K4
K5
2
2
2
2
2
2
100
100
100
100
100
100
—
0.4 wt.% of 1
0.4 wt.% of 2
0.4 wt.% of 3
0.4 wt.% of 4
0.4 wt.% of 5

650
W. M. KHAIRUL ET AL.
Here, A (cm2) is the electrode–electrolyte contact area of the film and t its thickness. Rb
is the bulk resistance obtained from the complex impedance plot (Cole–Cole plot) at the
intersection of the plot and the real impedance axis.
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