ORIGINAL PAPER
Synthesis, Crystal Structure and Electrical Studies of Naphthoyl-Thiourea as Potential Organic Light Emitting Diode
Siti Maryam Jasman1 • Wan M. Khairul1 • Tei Tagg1 • K. KuBulat1 •
Rafizah Rahamathullah1,4 • Suhana Arshad2 • Ibrahim Abdul Razak2 •
Mohamed Ibrahim Mohamed Tahir3
Received: 25 March 2015 / Accepted: 11 June 2015 / Published online: 18 June 2015
� Springer Science+Business Media New York 2015
Abstract A new type of naphthoyl-thiourea derivative
namely N-(5-methylpyridine)-N0-(1-naphthoyl) thiourea
(NT) was successfully synthesized prior to form conduc-
tive layer in organic light emitting diode (OLED). The
structure of compound was determined via single crystal
X-ray crystallography analysis and spectroscopically
characterized by infrared spectroscopy, 1H and 13C nuclear
magnetic resonance, UV–Vis, UV-fluorescence, cyclic
voltammetry analysis as well evaluated theoretically via
Gaussian 09 software employing DFT approach with set of
basis function B3LYP/6-31G (d,p). In turn, the compound
was deposited onto ITO substrate through electrochemical
deposition method prior the electrical conductivity and
performance as OLED was investigated via Four Point
Probe and Two Point Probe. From the crystal structure, NT
crystallizes as triclinic crystal system in P-1 space group,
unit cell parameters a = 7.4916(5) A, b = 9.4050(7) A,
c = 12.0584(9) A, a = 69.685 (7)�, b = 82.130 (6)� and
c = 71.917 (7)�. The conductivity analysis of NT per-
formed better and exhibited semiconductor material;
0.231 Scm-1 under dark condition which indicates this
single molecular system can act as potential OLEDs.
Graphical Abstract This contribution reports on the
design, preparation, and characterization of new type of
naphthoyl-thiourea derivative namely N-(5-methylpyr-
idine)-N0-(1-naphthoyl) thiourea (NT) prior acting as
potential Organic Light Emitting Diode (OLED).
Keywords Thiourea � Crystal structure � Organic light
emitting diode (OLED)
Introduction
Nowadays, organic light emitting diode (OLED) is one of
rapidly developing technology and becomes as an exciting
approach for efficient, high contrast, power saving and low-
cost devices to grab the challenge of the rising demand for
green and clear light supply [1, 2]. Within these concerns,
significant progress has been made to develop an active
material featuring conjugated polymer and small molecule
organic semiconductors [3–5]. This is due to the fact that
these compounds offer unique properties which consist
conjugated molecular unit and excellent electronic
behaviours.
& Wan M. Khairul
1 School of Fundamental Science, Universiti Malaysia
Terengganu, 21030 Kuala Terengganu, Malaysia
2 School of Physics, Universiti Sains Malaysia,
11800 USM Penang, Malaysia
3 Department of Chemistry, Faculty of Science, Universiti
Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
4 Faculty of Engineering Technology, Universiti Malaysia
Perlis, 02600 Arau, Perlis, Malaysia
123
J Chem Crystallogr (2015) 45:338–349
DOI 10.1007/s10870-015-0599-6
Recently, significant contributions of organic conjugated
molecular wires in wide range of the molecular electronic
applications have been extensively studied and proven to
show great performances [6, 7]. The organic molecular wire
has the unique characteristics of electronic delocalisation in
its extended p-orbital system, through which electrons can
move along the molecules [8, 9]. By making use of these
characteristics in the molecules, the design and the prepa-
ration of molecules should have been extensively studied
and modified with the goal of making them potentially
useful in numerous approaches such as in OLEDs.
In this context, thiourea derivatives are widely known to
be versatile ligand due to their ability of electronic trans-
portation that arises from rigid p-conjugated systems on
resonance structures which have been studied in numerous
applications [10–12], including in molecular electronics
[13, 14]. The uniqueness of thiourea derivatives are due to
their lone pair of N, S and O atoms which involve in the
resonance that leads to electronic delocalization throughout
the molecular backbone of conjugated molecular system
which lead to the effective electrical conductivity proper-
ties [15–17].
Moving towards this interest, lots of previous studies
reported on the exploration of 1-acyl-thiourea family
especially 1-(2-naphthoyl) substituted thiourea to deter-
mine their various properties such as synthesis and char-
acterization, crystal structure, thermal behavior and its
usage in various applications [18–20]. Due to this matter
with highly interest in developing single molecule OLEDs,
we are presenting naphthoyl-thiourea derivative as organic
material candidate to be applied as conductive layer in
OLED as shown in Fig. 1. This study also involved a
contribution of molecular modeling by Gaussian 09 in
order to predict conductivities as well crystal structure and
examination of its potential to act as single layer OLED.
Experimental Section
Materials
All reagents, including materials and solvents were com-
mercially purchased from various standard suppliers and
used as received without further purification. All reactions
were carried out under an ambient atmosphere and no pre-
caution was taken to exclude air or moisture during work up.
In this present work, chemicals used namely 1- naphthoyl
chloride, ammonium thiocyanate and 2-amino-5-methyl-
pyridine were purchased from Sigma-Aldrich, Merck and R
& M Chemical. Whilst, solvents used in this study namely
acetone, methanol, dichloromethane, chloroform, diethyl
ether, acetonitrile and dimethylsulphoxide were supplied by
Merck, Fisher scientific and R & M chemicals.
Characterization and Instrumentation
The infrared (IR) spectrum was recorded on Perkin Elmer
100 Fourier Transform Infrared Spectroscopy by using
potassium bromide (KBr) pellets in the spectral range of
4000–400 cm-1. Meanwhile, 1H and 13C NMR spectra were
recorded using Bruker Avance III 400 Spectrometer in
CDCl3 as solvent and internal standard at room temperature
in the range between dH 0–15 and dC 0–200 ppm, respec-
tively. For UV–Vis analysis, the compound was recorded by
Shimadzu UV–Vis in 1 cm3 cuvette. The emissions of the
compound was characterised by using Shimadzu UV-Fluo-
rescence in 1 cm3 cuvette. The crystallographic structure for
X-ray analysis was performed on Oxford Diffraction Gemini
diffractometers using Cu Ka radiation. Thermogravimetric
analysis was performed using Perkin–Elmer TGA analyzer
from 30 to 700 �C at a heating rate of 10 �C/min under
nitrogen atmosphere. Afterwards, cyclic voltammetry (CV)
analysis was carried out via Electrochemical Impedance
Spectroscopy (EIS) PGSTAT302. Finally, the targeted
molecule was optimized using Gaussian 09 quantum
mechanical software package at the theoretical level of DFT
(B3LYP)/6-31G (d,p) to calculate energy band gap and
predict the conductivity value.
Synthesis of Naphthoyl-Thiourea (NT)
The experimental details regarding to the synthesis of NT
was adapted from the methods carried out by Douglas-Dains
[21] involving reactants of 1-naphthoyl chloride (1.5 mL,
1 mol) with equimolar amount of ammonium thiocyanate
(0.76 g, 1 mol) in ca. 50 mL acetone in 100 mL two-necked
round-bottom flask. The reaction mixture was put at reflux
with continuous stirring for ca. 5 h. Then, a solution of
2-amino-5-methylpyridine (1.07 g, 1 mol) in ca. 50 mL
acetone was added to the reaction mixture and was put at
reflux with continuous stirring for ca. 7 h. The progress of
the reaction was monitored by TLC (hexane:CH2Cl2; 3:2).
Once the reaction has completed, the reaction mixture was
cooled to room temperature and filtered into a beaker con-
taining some ice cubes. The resulting light yellow crystalline
solid obtained was recrystallized from acetone to afford the
title compound (98 % yield). The synthetic route of NT is
NNH
HN
S
O
Fig. 1 The molecular structure
of N-(5-methylpyridine)-N0-(1-naphthoyl) thiourea
(NT)
J Chem Crystallogr (2015) 45:338–349 339
123
presented in Scheme 1. C18H15N3OS requires: C, 67.27; H,
4.70; N, 13.07; S, 9.98. Found: C, 68.83; H, 4.80; N, 13.24;
S, 9.33 %. 1H NMR (CDCl3, 400.11 MHz): d 2.38 (s, 3H,
CH3); 7.48–7.57 (m, 3JHH = 9 Hz, 5H, C10H7 ? C5H3);
7.82 (d, 3JHH = 7 Hz, 1H 9 C5H3); 7.92 (d, 1H x C5H3);
8.05 (d, 3JHH = 8 Hz, 1H x C10H7); 8.69(d, 3JHH = 8 Hz,
1H 9 CH); 8.29, 9.19 (2 9 s, 1H, NH).13C NMR (CDCl3,
100.61 MHz): d 18.03 (CH3); 124.49, 124.59, 126.57,
126.85, 127.20, 128.42, 128.94, 129.87, 130.03, 133.69
(C10H7), 133.90, 135.03, 143.42, 143.88, 146.59 (C5H3);
148.27 (C = S); 148.87 (C = O).
X-ray Data Collection and Structure Refinement
Single crystal of NT was found to be suitable for X-ray
analysis and the analysis was performed on Oxford
Diffraction Gemini diffractometer using Cu Ka radiation.
The crystal structure was determined by single crystal X-ray
diffraction from data collected at low temperature using the
oxford cryosystem open-flow nitrogen cryostat [22]. Data
collection, cell refinement and data reduction was performed
under the CrysAlisPro software [23]. Absorption correction
was applied to the final crystal data by using the CrysAlisPro
software [23]. The crystal structure was solved by direct
method using the program SHELXTL [24] and was refined
by full-matrix least squares technique on F2 using aniso-
tropic displacement parameters using SHELXTL [24]. All
geometrical calculations were carried out using the program
PLATON [25]. The molecular graphics were drawn using
SHELXTL [24] and Mercury program [26]. The non-hy-
drogen atoms were refined anisotropically. The hydrogen
atoms which bounded to the nitrogen atom were found from
the difference fourier maps and refined with a bond restraint
N–H = 0.85 (2) A [refined distance: N1–H1N1 = 0.847(9)
A and N2–H1N2 = 0.852(9) A]. All the other hydrogen
atoms were positioned geometrically (C–H = 0.93 or
0.96 A) and refined using riding model Uiso(H) = 1.2 or 1.5
Ueq(C). A rotating group model was applied to the methyl
group. A summary of crystal data and relevant refinement
parameters of the title compound is given in Table 1.
Preparation of NT on ITO Substrate
The preparation of NT on ITO substrate has been deposited
by applying electrochemical deposition (ECD) method in
the following conditions: 0.05 V, 0.05 V/S, potential
range: 0.85 V until 1.5 V in 50 mL acetonitrile, 0.5 M
sulphuric acid (as supporting electrolyte) with sample
concentration of 1 9 10-3 M.
Electrical Conductivity of Thin Films
Four Point Probe was used to determine the conductivity of
the thin film. The sheet resistivity in produced film was
measured by using Four Point Probing System consists of
the Jandel Universal Probe combined with a Jandel RM3
Test Unit and calculated using Eq. 1.
Sheet resistivity (Rs) calculation for wafer and film
RS ¼ 4:532 � V=I ð1Þ
Four probes were aligned and lowered onto the sample. The
two outer probes supplied a voltage difference that drove a
current through the film while the two inner probes picked up a
voltage difference. Where, RS is the sheet resistance (resis-
tivity), 4.532 is the correction factor,V is the voltage measured
and I is the current applied from the test unit. Then, electrical
conductivity can be determined which it is the reciprocal
(inverse) of the electrical resistivity, r as shown in Eq. 2.
Cl
O
+ NH4SCN NCS
OAcetone
Reflux
1-Naphthoyl chloride
Ammonium thiocyanate
Naphthoyl thiocyanate
Acetone
Reflux2-amino-5-methylpyridine
N-(5-methylpyridine)-N'-(1-naphthoyl) thiourea (NT)
N
+
NNH
HN
S
O H2N
Scheme 1 Synthetic approach
for the synthesis of NT
340 J Chem Crystallogr (2015) 45:338–349
123
Electrical conductivity calculation
r ¼ 1=Rs ð2Þ
where r is electrical conductivity and RS is sheet resistance
(resistivity).
Current–Voltage Diode Characterization
The performance of organic diode was measured by using
Keithley 4200 SCS Semiconductor Characterization
System and Probe Station. In this study, ITO substrate act
as hole collecting layer (anode) while NT act as hole and
electron carriers. The coated ITO substrates were masked
with low work function metal which is aluminium which
acts as cathode. The IV characteristic curve shows the
relationship between the currents and voltages gradient
associated with the different current terminal (anode and
cathode) of the diode. The obtained curve displays the
forward current, reverse current, knee voltage and break-
down voltage of the diode. The fabricated diodes with NT
are illustrated in Fig. 2.
Results and Discussion
Spectroscopic Studies
The infrared spectrum of NT revealed all the expected
bands of interest namely m(N–H), m(C = O), m(C–N), m(C–
O) and m(C = S). Two N–H stretching modes can be
identified at 3369 and 3114 cm-1 due to the existence of
C = O���H–N intramolecular hydrogen bonding [27–30].
The C–H stretching vibration for methyl v(C–H) can be
seen at 2922 cm-1. The strong absorption band at
1673 cm-1 was ascribed to the stretching of carbonyl
group. The decrease in the wavenumber compared to the
typical carbonyl absorption (1710 cm-1) was due to the
conjugated resonance with the phenyl ring and formation
of molecular hydrogen bonding with N–H [31, 32]. The
v(C–N) band can be observed at around 1289 cm-1 due to
resonance affect of the double bond character between the
ring and the attached nitrogen atoms [33]. Additionally, the
existence of C = S stretching band can be assigned at low
frequency of 790 cm-1 due to less double bond character
and lower nucleophilic character of sulfur atom that were
in close agreement with previously reported series of
thiourea derivatives [34–36].1H NMR spectrum of NT showed methyl resonance at
dH 2.38 ppm. Whilst, the overlapping distinctive unre-
solved signal of the aromatic protons can be observed at
around dH 7.48–8.69 ppm. These resonances characteristic
are strongly influenced by the o and p-substituents posi-
tions of methyl groups at the pyridine rings [37]. The
resonance for NH(1)C = O and NH(2)C = S can be
observed at around dH 8.29 ppm and dH 9.19 ppm
Fig. 2 Diode arrangements for I–V characteristic measurement
Table 1 Crystal data and structure refinement for naphthoyl-thiourea
(NT)
Compound NT
CCDC deposition numbers 1048526
Molecular formula C18H15N3OS
Molecular weight 321.39
Crystal system Triclinic
Space group P-1
a (A) 7.4916 (5)
b (A) 9.4050 (7)
c (A) 12.0584 (9)
a (�) 69.685 (7)
b (�) 82.130 (6)
c (�) 71.917 (7)
V (A3) 757.01 (9)
Z 2
l (mm-1) 1.96
Crystal size (mm) 0.28 9 0.19 9 0.12
Dcalc (Mg m-3) 1.410
Crystal dimensions (mm) 0.38 9 0.36 9 0.12
l/mm-1 2.84
Radiation, k (A) 1.54180
F(000) 336
Tmin/Tmax 0.610/0.799
Reflections measured 2910
Ranges/indices (h, k, l) h = -8 ? 9
k = -10 ? 11
l = -0 ? 14
h limit (�) 3.9–71.5
Unique reflections 2910
Observed reflections (I[ 2r(I)) 2677
Parameters/restraints 217/2
R1a, wR2 [I C 2r(I)]b 0.038, 0.104
Goodness of fit (GOF) on F2c 1.05
Largest diff. peak and hole, e/A-3 0.32 and -0.27
For NT, w = 1/[r2(Fo2) ? (0.0604P)2 ? 0.3749P], where P = (Fo
2 ?
2Fc2)/3
a R1 = R||Fo| - |Fc||/R|Fo|b Rw = {wR(|Fo| - |Fc|)
2/Rw|Fo|2}}1/2
c GOF = {Rw(|Fo| - |Fc|)2/(n–p)}1/2, where n is the number of
reflections and p the total number of parameters refined
J Chem Crystallogr (2015) 45:338–349 341
123
respectively. The resonance for NH(1)C = O slightly
deshielded to higher chemical shifts compared to
NH(2)C = S was due to oxygen atom presence which is
known to be more electronegative than sulphur. These
signals are different in term of chemical shift which is due
to the intramolecular hydrogen bonded N–H bonds in the
trans and cis conformations, respectively [31, 38]. The 13C
NMR of NT showed methyl resonance can be clearly
observed at dC 18.03 ppm. Whilst, resonances for aromatic
rings can be found in the range of dC 116.13–144.03 ppm
and the carbon for C = O and C = S can be identified
at dC 148.27 ppm and 148.87 ppm respectively. The for-
mation of intra-molecular hydrogen bonding of the com-
pound and the increasing electronegativity of oxygen and
sulphur caused the deshielding effect to higher chemical
shifts [39, 40].
Optical Properties
The electronic absorption spectrum of NT revealed two
principal bands which were expected to arise from C = O,
C = S and phenyl moieties at around kmax 243 nm and
275 nm. The absorption band of C = O chromophore can
be identified in the range of kmax 240 nm to 243 nm due to
the effect of p-conjugation of carbonyl with the phenyl
group, thus the transition of p ? p* shifted to the longer
wavelength. Strong absorption band centered at around
kmax 275 nm can be attributed to p ? p* and n ? p*
transitions of C = S and naphthoyl in thiourea moiety. The
broad absorption band observed in the region was due to p-
conjugation of this compound with the phenyl rings (p - p*
transition) and orbitals overlapping between C = O and
C = S.
Whilst, the energy band gap (Eg) values was calculated
from the absorption edge (koff-set) of the compound in the
range of kmax 200–600 nm region by using (Eg = hc/k)
equation. From the UV–Vis, the predicted HOMO–LUMO
energy band gap for NT was 4.07 eV. In comparison, the
theoretical value was calculated using Gaussian 09 at the
theoretical level of DFT/B3LYP 6-31G (d,p) and the result
was in agreement with experimental which the energy band
gap, Eg was around 4.05 eV.
Meanwhile, the absorption and fluorescence spectrum
of NT was carried out in methanol (1 9 10-6 M). The
fluorescence emission spectrum exhibited almost mirror-
image of the corresponding absorption spectra and the
remarkable mirror image relationship observed between
the spectra should be noted with a small Stokes shift
(90 nm) [41]. The absorption spectrum of NT has intense,
short wavelength band at 294 nm and the emission
spectra showed one maxima wavelength at 370 nm
respectively.
Crystal Structure Determination of NT
The single crystal of NT was obtained from slow evapo-
ration process in acetone at room temperature. NT crys-
tallizes as triclinic crystal system in P-1 space group, unit
cell parameters a = 7.4916(5) A, b = 9.4050(7) A,
c = 12.0584(9) A, a = 69.685 (7)�, b = 82.130 (6)� and
c = 71.917 (7)�. Table 2 shows the selected bond lengths
and angles of NT in comparison with the corresponding
values observed for related thiourea derivatives [42–44].
All geometrical parameters of NT are within the normal
ranges [45] and comparable with the corresponding values
tabulated in Table 2.
The molecular structure of NT is shown in Fig. 3a with
displacement ellipsoids plotted at 50 % probability level.
The compound adopts trans–cis configuration with respect
to the position of naphthalene (C1–C10) and picoline (N3/
C13–C18) moieties relative to the S1 atom across their
C12–N1 and C12–N2 bonds. The molecule is stabilized by
intramolecular N2–H1N2���O1 [46] and C14–H14A���S1
hydrogen bonds (Table 3), forming two six-membered
rings with the graph-set notation S(6) [47]. The non-
bonding distances of N2���O1 and C14���S1 are 2.6487 (18)
and 3.2571 (18) A, respectively in agreement with
intramolecular hydrogen bond observed in other related
structures [42, 48], where the reported values are in the
range of 2.590–3.210 A. Formation of these S(6) ring
motifs is important for molecular conformations because it
prevents free rotation within the central carbonyl thiourea
moiety and locks its atoms in a nearly planar arrangement
[48]. Additionally, the planar structure of the central –
C(O)NHC(S)NH– moiety with opposite orientation
between the C = O and C = S bonds (S-form) is reported
to be the most stable conformation in comparison to the
non-planar synclinal conformer (U-form) [49].
The O1–C11 bond distance of 1.226(2) A indicates
double bond character in agreement with literature data
(Table 2). The observed C–N [N1–C11 = 1.379(2), N1–
C12 = 1.407(2) and N2–C12 = 1.340(2) A] and C–S [S1–
C12 = 1.6610(16) A] bond lengths of NT are all shorter
than the average single C–N (1.48 A) and C–S (1.82 A)
bond lengths, indicating partial double bond character.
Thus, it can be deduced that this thiourea makes up a multi-
electron conjugated p-bond [50] and also the existence of
resonance interactions extended over the whole planar –
C(O)NHC(S)NH– moiety [51, 52].
The essentially planar –C(O)NHC(S)NH– moiety with
maximum deviation of 0.0904(5) A at S1 atom forms
dihedral angles of 54.74(6) and 16.20(8)� with the terminal
naphthalene [C1–C10; maximum deviation of 0.036(2) A
at atom C9] and pyridine [N3/C13–C17; maximum devi-
ation of 0.007(2) A at atom C15 and C16] rings, respec-
tively. The naphthalene ring and the methyl substituted
342 J Chem Crystallogr (2015) 45:338–349
123
Table 2 Selected geometrical parameters (bond lengths and angles) of NT
Parameters NT Aydin et al. [42] Aydin et al. [43] Arslan et al. [44]
Bond lengths (A)
S1–C12 1.6610 (16) 1.6521 (14) 1.672 (4)
1.658 (4)
1.6696 (17)
O1–C11 1.226 (2) 1.2241 (18) 1.224 (5)
1.228 (5)
1.224 (2)
N1–C11 1.379 (2) 1.3748 (18) 1.374 (5)
1.363 (5)
1.377 (2)
N1–C12 1.407 (2) 1.3931 (17) 1.384 (5)
1.394 (5)
1.3974 (19)
N2–C12 1.340 (2) 1.3450 (17) 1.317 (5)
1.324 (5)
1.327 (2)
N2–C13 1.414 (2) 1.4114 (17) 1.454 (5)
1.449 (5)
1.4408 (19)
C10–C11 1.494 (2) 1.4826 (19) 1.483 (6)
1.482 (6)
1.488 (2)
Bond angles (�)C11–N1–C12 129.13 (14) 129.20 (12) 129.6 (4)
130.3 (4)
128.11 (13)
C12–N2–C13 131.14 (14) 129.66 (12) 124.2 (4)
123.5 (4)
123.59 (13)
C9–C10–C11 119.36 (14) 122.71 (12) 125.6 (4)
117.7 (4)
121.68 (14)
C1–C10–C11 119.79 (14) 117.77 (13) 117.7 (4)
124.1 (4)
118.24 (14)
O1–C11–N1 122.57 (15) 121.61 (13) 121.9 (4)
121.1 (4)
122.77 (14)
O1–C11–C10 122.30 (14) 121.95 (13) 122.5 (4)
121.6 (4)
121.33 (14)
N1–C11–C10 115.12 (13) 116.44 (12) 115.6 (4)
117.3 (4)
115.88 (13)
N2–C12–N1 114.11 (14) 114.01 (12) 117.8 (4)
116.9 (4)
116.72 (14)
N2–C12–S1 128.65 (13) 127.60 (10) 123.9 (4)
125.2 (4)
124.47 (12)
N1–C12–S1 117.20 (12) 118.38 (10) 118.3 (3)
117.9 (3)
118.81 (11)
C14–C13–N2 125.48 (14) 123.97 (13) 114.9 (4)
112.4 (4)
118.36 (14)
Torsion angles (�)C12–N1–C11–O1 2.8 (3) 3.8 (3) 0.2 (7)
-6.3 (7)
-4.8 (3)
C12–N1–C11–C10 -177.62 (15) -176.61 (14) 179.9 (4)
-6.3 (7)
173.38 (14)
C9–C10–C11–O1 129.48 (17) -156.35 (17) 164.6 (5)
17.4 (6)
140.14 (17)
C1–C10–C11–O1 -46.5 (2) 20.8 (2) -13.6 (7)
-165.0 (5)
-32.9 (2)
J Chem Crystallogr (2015) 45:338–349 343
123
pyridine ring makes dihedral angle of 39.14(7)� to each
other. Additionally, the naphthalene ring is twisted at C10–
C11 bond with C1–C10–C11–O1 torsion angle value of
46.5 (2)� as shown in Fig. 3b.
In the crystal packing, the molecules are connected into
infinite one-dimensional chain along the a-axis via inter-
molecular C8–H8A���O1 and C9–H9A���N3 hydrogen
bonds [symmetry code: x - 1, y, z; Table 3]. As shown in
Fig. 4a, both C–H���O and C–H���N hydrogen bonds lead to
formation of R22(11) ring motifs [47]. This chain is inter-
connected with the adjacent chain by C18–H18A���Cg1
(symmetry code: -x?2, -y?2, -z?1; Table 3) interac-
tions, where Cg1 is the centroid of the C1–C6 ring. This
type of interaction extend along [100] to form a
supramolecular column (Fig. 4b). Furthermore, the crystal
structure is stabilized by p���p interactions (symmetry code:
1-x,1-y,1-z; Fig. 4c), involving the centroid of Cg2 ring
(C1/C6–C10) [53, 54]. The interplanar and centroid to
centroid distances of Cg2���Cg2 interaction are 3.7096(7)
and 3.8332(11) A, respectively, with a slip angle (the angle
between the centroid vector and the normal to the slip
plane) of 14.59�. The p���p interactions further link the
supramolecular columns into a two dimensional sheet
parallel to ab-plane (Fig. 4c). Figure 4d shows the full
molecular structure arrangement of NT where the C–H���O,
C–H���N, C–H���p and p���p interactions connect the
molecules into a supramolecular two-dimensional sheet
architecture.
Fig. 3 a The molecular structure of N-(5-methylpyridine)-N0-(1-
naphthoyl) thiourea (NT) showing the atomic numbering scheme.
Displacement ellipsoids are drawn at the 50 % probability level.
Dashed lines represent the intramolecular hydrogen bond. b Projection
of the twisted naphthalene ring
Table 3 Hydrogen bonding geometry of NT
Bond Bond length (A) Angle (�)
D–H���A D–H H���A D���A D–H���A
N2–H1N2���O1 0.85 (1) 1.93 (1) 2.6487 (18) 142 (2)
C14–H14A���S1 0.93 2.66 3.2571 (18) 123
C8–H8A���O1i 0.93 2.50 3.407 (2) 166
C9–H9A���N3i 0.93 2.61 3.523 (2) 168
C18–H18A���Cg1ii 0.96 2.79 3.740 (2) 170
Symmetry codes: ix - 1, y, z; ii-x?2, -y?2, -z?1
Cg1 is the centroid of the C1–C6 ring
Table 2 continued
Parameters NT Aydin et al. [42] Aydin et al. [43] Arslan et al. [44]
C9–C10–C11–N1 -50.1 (2) 24.0 (2) -15.1 (7)
-163.6 (4)
-38.0 (2)
C1–C10–C11–N1 133.87 (15) -158.86 (14) 166.7 (5)
14.1 (6)
148.88 (15)
C13–N2–C12–N1 178.69 (15) -177.42 (14) 175.5 (4)
-177.5 (4)
176.77 (14)
C13–N2–C12–S1 1.2 (3) 1.7 (2) -3.5 (6)
2.2 (6)
-3.9 (2)
C11–N1–C12–N2 -8.0 (2) 6.0 (2) 3.0 (7)
-177.5 (4)
-4.2 (2)
C11–N1–C12–S1 169.83 (13) -173.22 (13) -178.0 (4)
2.2 (6)
176.37 (13)
C12–N2–C13–C14 21.4 (3) -28.7 (3) 85.4 (5)
106.5 (5)
-103.42 (19)
344 J Chem Crystallogr (2015) 45:338–349
123
Fig. 4 Hydrogen bonding interactions in NT a intermolecular C–
H���O and C–H���N hydrogen bonds observed in the crystal packing,
b formation of column via C–H���p interactions, c p ���p interactions
stabilized the crystal structure d the crystal packing of NT connected
into a two-dimensional network. Dashed lines show the intermolec-
ular hydrogen bonds. H atoms not involved in hydrogen bonding are
omitted for clarity
J Chem Crystallogr (2015) 45:338–349 345
123
Thermogravimetric Analysis (TGA)
Thermal stability of the material is important to be inves-
tigated for fabrication of any thin films application. Ther-
mal properties of NT was evaluated via TGA at heating
rate of 10 �C/min under nitrogen atmosphere with tem-
perature range of 30–700 �C as shown in Fig. 5. Based on
the thermogram data, there was no mass loss occurred
below 100 �C and it showed that there was no presence of
water or any solvent in the sample. From the thermogram,
the degradation process showed that NT has the highest
onset which started to degrade at around 200 �C (Tonset)
and ended at 320 �C (Toffset) in a single step. During the
decomposition of this stage, a minor shoulder between 240
to 260 �C was also present in the thermogram and the total
mass loss was about 92 %. Therefore, it can be summa-
rized that NT was thermally stable according on its onset
and it gave good indication that they can be potentially
good coating material for the fabrication of thin film at
high temperature.
Cyclic Voltammetry
The electrochemical behaviour of NT as a focalpoint
compound in this study was investigated further by using
CV analysis in order to determine the redox reaction and
potential range of different electrochemical processes. The
oxidation peak for NT occurred at DEpa = 1.30 V while
the reduction peak occurred at DEpc = 1.15 V as depicted
in Fig. 6. The concentration decreased rapidly at the
electrode surface as the anodic current decreased which
resulted the current to peak. There was a report claimed
that the first oxidation of thiourea is defined at *0.7 V
which represents to the formation of formamidine disul-
phide [55]. In this study, NT strongly oxides to NT2? at
*1.15 V and the current started to decay as NT became
more depleted and NT2? surrounded the electrode. As the
anodic current continues, the electrode is sufficiently strong
to reductant to reduce NT2? which has accumulated
adjacent to the electrode surface. Thus, the cathodic current
rapidly increased and the surface concentration of NT2?
was diminished causing the current to peak (*1.3 V) and
the current started to decay as solution surrounding the
electrode was depleted of NT2?. Thus, it can be concluded
that the redox potential of NT appeared in the positive
region with its electro-oxidation stage with a separation
about 1 V.
Theoretical Evaluation: Prediction of Electrical
Conductivity
Theoretically, to predict the relation between the sub-
stituent of NT with the conductivity, Mulliken charge
values was measured where Ln v2 for the first and the
second benzene rings of NT was evaluated at the theoret-
ical level of B3LYP/6-31G (d,p). In this study the natural
logarithm of v2 were employed as a measure of the degree
of delocalization among the benzene rings of the targeted
molecule. As a standard, the value of the total Ln v2 for the
benzene ring evaluated at the same theoretical level is -31.
When there is a substituent existed in the ring, these values
should increase to a certain number which represent how
far the electron delocalization deviates from the aro-
maticity of the benzene ring.
In this study, the calculated total value of -R Ln (v2)
was -70.087, in which the first ring (naphtyl) contributed
the highest values of -47.405 and the second ring (pyr-
idine) contributed as -22.682. Based on theoretical find-
ings, it can be summarized that the conductivity depended
on the delocalization of the aromatic portions of NT
derivative. Thus, we believed the performance of the
electrical conductivity showed positive results under dark
condition was caused by the conjugation and delocalization
of the first benzene ring and the movement of electron from
the para-position along the molecular framework.
Performance of Diode and Emitting Light
with Different Voltage from ITO Substrate
The IV characteristic curve of NT was investigated to
determine their performances as diode which the optimum
values of voltage applied into the circuit for diode in this
study was in the range of -9.0E-6 to -3.0E-6 V. The
shape of the curve determined the transport charge carrier
through the depletion layer or depletion region that exists at
the P–N junction which referred to the semiconductor
properties. P–N junction formed when the electrons diffuse
from N-doped region (positively charge donor) into
P-doped region (negatively charge acceptor) which that theFig. 5 The thermogram of NT
346 J Chem Crystallogr (2015) 45:338–349
123
electrons recombined. Additionally, the knee voltage of
NT was around 0.7 V where the values lower than the knee
voltages of Schottky diode (0.2–0.3 V) and pn junction
diode (0.55–0.60 V) [56]. Thus, it can be summarized that
NT exhibited a semiconductor properties and it can be used
in rectification application such as OLED as the electric
current can pass through the P–N junction. Afterwards,
ITO substrates were tested with direct current and different
voltage in the range of 15–30 V in order to investigate
diode performance in various conditions, as depicted in
Fig. 7. The output of light was emitted from ITO substrates
and increased by the increasing amount of current voltage.
Therefore, this proposed material gave good indication for
conductive layer in fabrication of thin film to be applied as
OLED.
Conclusion
The performance of single molecule compound of naph-
thoyl-thiourea derivative namely N-(5-methylpyridine)-N0-(1-naphthoyl) thiourea (NT) has been successfully syn-
thesized with good yields prior to form conductive layer in
OLED. Conformational and structural properties were
characterized via several spectroscopic technique and sin-
gle crystal X-ray diffraction analysis. The X-ray structure
3.80E-05
4.30E-05
4.80E-05
5.30E-05
1.1 1.121.141.161.18 1.2
Curr
ent,
I (A)
Potential, E (V)
scan 1
scan 2
scan 3
scan 4
scan 5
Epa(A)
9.00E-05
1.40E-04
1.90E-04
1.2 1.25 1.3 1.35 1.4
Curr
ent,
I (A)
Potential, E (V)
scan 1scan 2scan 3
Epc(B)Fig. 6 Cyclic voltammogram
of NT in (1 9 10-3 M
acetonitrile ? 0.5 M sulphuric
acid), 298 K at 0.05 V, 0.05
Vs-1
15V 20V 25V 30V
Fig. 7 The emission of light of NT with different voltages
J Chem Crystallogr (2015) 45:338–349 347
123
shows the usual value for bond lengths and bond angles
and adopts trans–cis configuration. The molecular confor-
mation of NT stabilized by strong intramolecular N–
H���O = C hydrogen bond occurs between the carbonyl
and thioamide groups which forming a planar six-mem-
bered ring with respect to the hydrogen bonding. In the
crystal packing, supramolecular arrangement of NT formed
two-dimensional sheet parallel to the ab-plane via C–
H���O, C–H���N, C–H���p and p���p interactions. From the
evaluation of conductivity study, NT/ITO thin film can
conduct electricity better under dark condition and the
emission of light from ITOs can be observed. In conclu-
sion, this type of system featuring naphthoyl-thiourea
exhibits wide potential to be applied as conductive layer in
OLED.
Supplementary Materials
This data CCDC: 1048526 can be obtained free of charge
at www.ccdc.cam.ac.uk.conts/retrieving.html/ or from the
Cambridge Crystallographic Data Centre (CCDC), 12
Union Road, Cambridge CB2 IEZ, UK; fax: ?44(0)
1223-336033; e-mail: [email protected].
Acknowledgments The authors would like to acknowledge MOE
for Fundamental Research Grant Schemes (FRGS), Grant No. 59253
and MyBrain15 Fund for postgraduate student’s fellowship and the
School of Fundamental Science, Universiti Malaysia Terengganu for
instrumentations and characterisations facilities.
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