Aerobic synthetic approach and characterisation of some acetylide-thiourea derivatives for the detection of carbon monoxide (CO) gas

Article abstract of DOI:10.1016/j.molstruc.2015.03.065

Novel acetylide-thiourea systems (PAT, EBT, and ETT), that possess both withdrawing and donating system properties were successfully synthesised with good yield (64-72%) and were characterised via several spectroscopic and analytical techniques. In turn,

Full text of DOI:10.1016/j.molstruc.2015.03.065

Accepted Manuscript
Aerobic Synthetic Approach and Characterisation of Some Acetylide-thiourea
Derivatives for the Detection of Carbon Monoxide (CO) Gas
Adibah Izzati Daud, Wan M. Khairul, Hafiza Mohamed Zuki, K. Kubulat
PII:
S0022-2860(15)00300-2
DOI:
http://dx.doi.org/10.1016/j.molstruc.2015.03.065
MOLSTR 21449
Reference:
To appear in:
Journal of Molecular Structure
Received Date:
Revised Date:
Accepted Date:
5 November 2014
3 March 2015
30 March 2015
Please cite this article as: A.I. Daud, W.M. Khairul, H.M. Zuki, K. Kubulat, Aerobic Synthetic Approach and
Characterisation of Some Acetylide-thiourea Derivatives for the Detection of Carbon Monoxide (CO) Gas, Journal
of Molecular Structure (2015), doi: http://dx.doi.org/10.1016/j.molstruc.2015.03.065
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Aerobic Synthetic Approach and Characterisation of Some Acetylide-thiourea
Derivatives for the Detection of Carbon Monoxide (CO) Gas
1
1,*
2
1
Adibah Izzati Daud , Wan M. Khairul , Hafiza Mohamed Zuki , & K.Kubulat
1
School of Fundamental Science, Universiti Malaysia Terengganu, 21030 Kuala Terengganu,
Terengganu, Malaysia.
2
School of Marine Science and Environment, Universiti Malaysia Terengganu, 21030 Kuala
Terengganu, Terengganu, Malaysia.
Running Tittle: Single Molecule for the Detection of Carbon Monoxide Gas
Keywords: Acetylide, Thiourea, Chemosensor, Gaussian
Corresponding author full name email address:
*
Assoc. Prof. Dr Wan Mohd Khairul Wan Mohamed Zin
Email: wmkhairul@umt.edu.my
1

ABSTRACT
Novel acetylide-thiourea systems (PAT, EBT, and ETT), that possess both withdrawing and
donating system properties were successfully synthesised with good yield (64-72%) and were
characterised via several spectroscopic and analytical techniques. In turn, all synthesised
derivatives were deposited onto glass substrates by dip-coating, and then their responses
towards CO exposure were evaluated via UV-visible spectroscopy to identify their thin-film
sensitivity towards CO. Theoretical studies using Gaussian 09 analysis were used to
determine the relationship between the experimental and theoretical analyses of the
molecules. The data revealed that acetylide-thiourea derivatives exhibit great potential for the
detection of CO.
Graphical Abstract:
1
. Introduction
Gas sensors play a crucial role in detecting, monitoring, and controlling the presence of
harmful gases in the atmosphere at very low concentrations. Environmental gas monitoring is
currently recognised as an important area, in which intense research has been focusing on the
development of suitable gas-sensitive materials for the continuous monitoring for the presence
of harmful gases beyond the levels specified by Occupational Safety and Health regulations.
Among many different gases present in the atmosphere, carbon monoxide (CO) is classified
as a harmful gas that is dangerous for human health, even at very low concentration, due to
the ability of CO to interact with oxygen transport in our respiratory system [1-3]. Thus, it is
necessary to detect the presence of CO with highly sensitive materials at a very low
concentration for early prevention. These materials must be simple, small, low in cost to

produce, and easy to fabricate into thin films. Conventionally, CO has been detected mostly
by conductive polymer-based materials [4-6], metal-oxide derivatives [7-9], and carbon nano-
tubes based materials [10-12], which used large instrumentation that requires high
temperature and inert environment. Alternatively, single molecules can be employed as an
active layer for sensing the mechanisms for selected gases. The advantages of using single
molecules are that they can act at room temperature in the ambient atmosphere, and they are
easy to synthesise, fabricate, tune, and modify, thus, it is suitable for the analyte to be detected
[13].
Due to the high level of interest in developing single molecules as CO gas sensors, we are
introducing several novel systems of acetylide-thiourea derivatives, N-(4-
phenylethynylaniline)-N’-(1-naphthoyl)thiourea
(PAT),
(EBT),
N-(4[4-
N-([4-
aminophenyl]ethynlbenzonitrile)-N’-(1-naphthoyl)thiourea
and
aminophenyl]ethynl toluene)-N’-(1-naphthanoyl)thiourea (ETT), in the form of thin-films
entrapped in a PVC matrix, as new materials for the detection of CO gas. For EBT, the
synthesis and the ability of the compound to detect CO have been reported by our group in
previous occasion [14]. In this contribution, the comparisons in respect of performance
between the other members of the system have been discussed in thorough. To date, there is
an obvious loop of reports on the detection of CO based on chemical sensors using acetylide-
thiourea derivatives. These acetylide-thiourea derivatives consist of both electron
withdrawing and donating systems, that comprise the presence of a number of functional
moieties such as conjugated double and triple bonds and a reactive carbonyl (C=O) group,
which are believed to contribute an ideal interaction with CO. In this study, all of the
synthesised materials were immobilised onto solid supports for application in optical sensing.
The substrates were typically entrapped physically by absorption or chemically bonded to the
solid support [15,16]. Poly(vinyl chloride) (PVC) was used for the preparation of membrane
thin films due to its relatively low cost and ability to be plasticised [17].
For several decades, due to their capacity for electron transport that arises because they have
rigid π-conjugated systems, thiourea, acetylide and their resonance structures have been
widely studied individually in numerous applications [18,19], especially in molecular
electronics [20,21]. Investigation on these practical gas sensors can be performed by direct
spectroscopic measurements of the changes in the optical properties of materials in thin films
exposed to the selected analyte (CO gas). In addition, this study also involves a combination
3

of molecular modelling by Gaussian 09 software for density functional theory (DFT)
calculations in terms of the stabilisation energy (kJ/mol) between the synthesised compounds
and CO with the synthesise, characterisation, and investigation of their potential to act as
single-molecule CO gas sensors, analysed by examining the differences in the spectral
features of UV-visible spectrophotometer before and after exposure to CO. The newly
developed optical sensors proposed, had shown significant absorbance signal changes upon
exposure to CO gas with concentrations of 10, 20, and 30 ppm. Based on this study, a material
that was highly sensitive to a low CO concentration and provided a rapid method for the
detection of CO gas was developed with both experimental and theoretical results that were
satisfactory. Figure 1 depicts all molecular structures of interest synthesised in this study.
Figure 1: The molecular structure of acetylide-thiourea derivatives (PAT, EBT, and ETT)
2.0 Results and discussion
2.1. Spectroscopic and characterisation studies
The infrared (IR) spectra of the synthesised materials (PAT, EBT, ETT) showed six
absorption bands of interest, namely, ν(N-H), ν(C-H), ν(C=O), ν(C-N), ν(C≡C), and ν(C-O),
-
1
ranging from weak to strong intensities. The band in the range of 3169-3220 cm represented
the asymmetric and symmetric stretching vibrations of ν(N-H) in the secondary thioamide
-
1
moiety. The assignments of NH above 3000 cm had been examined due to the existence of
intramolecular hydrogen bonding [22-24]. The stretching frequencies observed in the range of
-
1
1
405-1441 cm corresponded to ν(C-N) and were assigned by comparison with the spectra of
-1
other thiourea derivatives at 1400-1000 cm [25]. Moreover, the ν(C≡C) stretching vibration
-1
in these compounds (PAT and ETT) occurred at 2214-2218 cm as a medium-intensity peak.
However, for EBT, there was an overlapping band with strong intensity observed between the
4

-
1
C≡C and C≡N moieties at 2214 cm . In fact, the strong absorption band for ν(C=O) in PAT,
-
1
EBT, and ETT was distinguished at 1667-1672 cm because of the resonance effect with the
fused-aromatic and phenyl rings, as well as the existence of intramolecular hydrogen bonding
with N-H. This result agrees with those of previously reported studies [26,27]. The most
crucial changes were observed for the presence of the C=S stretching frequency at 741-760
-
1
cm . The frequencies for ν(C=S) were found at low frequency due to the decreased double-
bond character and the lower nucleophilic character of the sulphur atom in the C=S moiety of
the synthesised materials [28,29].
The electronic-transition spectra of PAT, EBT and ETT were recorded in an acetonitrile
-5
solution obtained in a 1 cm path length quartz cell with concentration of 1 x 10 M, and they
exhibited two principal bands that are believed to arise from the C=O, C=S, and phenyl
-
1
-1
moieties. The primary bands observed at λmax 217-301 nm (ε=44760-74080 M cm ) were
*
assigned to the π→π transition of the aromatic moiety, which shifted strongly to lower
wavelength with molar absorptivity, influenced by the inductive interaction between the fused
aromatic (naphthoyl) and carbonyl group [30,31]. The existence of overlapping C=O and C=S
bands can be observed at λmax within the range of 305.00-321.50 nm. For EBT, the presence
of the electron-withdrawing group C≡N also induced a pronounced bathochromic shift of the
n→π* and π→π* transitions with a broad band at λmax 343 nm as an effect of the conjugation.
The broad absorption band observed in the region at λmax 305-321.50 nm was due to the π-
conjugation of the synthesised materials with phenyl rings (π→π* and n→π*) and the orbital
overlap between the C=O and C=S moieties.
1
For the H NMR spectra, the unresolved resonance of the fused-aromatic protons can be
clearly observed as multiplet resonances between δ
proton signals of the fused-aromatic system. Additionally, the aromatic protons of the benzoyl
moiety can be clearly seen in the range δ 7.21-8.43 ppm as a pseudo-doublet system that was
influenced by the para-substituted benzoyl moiety. For ETT, there was a methyl (-CH
resonance at a chemical shift of δ 2.41 ppm on the aryl ring that was assigned as singlet
H
7.38-7.87, ppm due to the overlapping
H
3
)
H
resonance due to the effect from the neighbouring proton. There were two singlet resonances
for amide (N-H) protons that can be observed in two different environments within the range
H H
of δ 9.09-9.15 ppm and δ 12.77-12.83 ppm, respectively, due to the presence of two
consecutive amide (N-H) groups resulted from the intramolecular hydrogen bonding of N-H
in the trans- and cis-conformation [32,33]. Indeed, the amide resonance of N-H (C=S) was
5

observed at a higher chemical shift than the amide proton of N-H (C=O) due to the
deshielding effect and intramolecular hydrogen bonding [34,35].
13
The C NMR spectra for all of the synthesised derivatives showed resonances of acetylide
carbons, C≡C, which were located at δ 88.2-88.8 ppm and 90.4-93.2 ppm. For EBT, the
resonance of the carbon in the cyano C≡N moiety was located in the downfield region at δ
C
C
1
38.2 ppm due to the nitrogen atom attached to the cyano carbon. Additionally, the aromatic
carbon resonances can be observed at δ
C
111.5- 138.5 ppm and are attributed to the phenyl
169.2 ppm and
77.7-177.8 ppm corresponded to the C=O and C=S carbons. Both the C=O and C=S
rings of the synthesised materials. Two resonances that were observed at δ
C
1
resonances were slightly deshielded to a higher chemical shift due to the intramolecular
hydrogen bonding formed in the compound and the electronegativity contributed by the
oxygen and sulphur atoms [36,37].
2.2 Thermal-stability analysis for the synthesised materials
The thermal stability of the material is the crucial factor to be investigated for fabrication for
gas sensor applications. The thermal properties of the synthesised compounds were
investigated by thermogravimetric analysis (TGA) at the heating rate of 283K/min under
nitrogen atmosphere (Figure 2). The observed thermogram had revealed that no weight loss
occurred below 373K, which showed that there were no trace of water molecules or solvents
present in the synthesised compounds. It was observed that the onset temperature at which
PAT, EBT, and ETT started to degrade was 473K-520K, with maximum degradation.
Indeed, the range of decomposition of EBT is larger, with EBT starting to degrade at 520K
(
onset) with a large range of decomposition to 821K (offset) because EBT had a higher
molecular weight than PAT and ETT and also because of the abundance of C≡N with highly
conjugated bonds in the compound. Therefore, the synthesised thiourea derivatives exhibited
stability at high temperature and should provide great potential for various fabrication
methods at high temperature.
6

Figure 2: The thermogram of the synthesised compounds
.3 Studies on the sensing of CO via UV-Vis spectroscopy
2
The PAT, EBT, and ETT sensors were investigated for three different carbon monoxide
CO) concentrations, which were 10, 20, and 30 ppm (each gas sample was purchased
(
commercially from Gas Sensor Sdn. Bhd., Kuala Lumpur, Malaysia). The absorption spectra
of the optical carbon monoxide gas sensor in the presence of increasing concentrations of CO
with thin films were investigated in advance to determine the sensitivity of the film substrate
for the detection of CO. Results from all of the absorption spectra revealed that significant
changes occurred in the electronic transitions of the synthesised compounds (PAT, EBT, and
ETT), which were studied as thin films, before and after exposure to various concentrations
of CO (10, 20, and 30 ppm). From the spectra, it can be seen that absorption of PAT, EBT,
and ETT with CO gas produced similar trends in the absorption spectra. There were two
shifted bands that resulted from the electronic-transition changes of the HUMO and LUMO
after the synthesised compounds had interacted with CO. However, obvious and most changes
st
of absorbance can be observed within 1 band of wavelength range at λmax = 256-258 nm.
Therefore, λmax=256 nm (PAT), λmax=258 nm (EBT) and λmax= 257 nm (ETT) were
monitored to evaluate the response of the sensor to CO gas concentrations. The results
revealed that, upon exposure to an increased CO concentration, the maximal absorbance of
the film substrate decreased to a lower absorbance, showing that an interaction of the
acetylide-thiourea film substrate with CO occurred.
7

The results obtained for the sensing properties show that the sensor response (sensitivity) of
PAT and EBT featuring the electron-withdrawing substituents of the hydrogen (-H) and
cyano (CN) moieties decreased with increased CO concentration. PAT exhibits the highest
sensitivity, compared to EBT and ETT, to 10 ppm of CO with a 35.82% response, followed
by 25.87% (20 ppm), and 13.93% (30 ppm), respectively. In contrast, EBT exhibited a
3
1.02% response to 10 ppm of CO, followed by 25.00% (20 ppm), and 21.30% (30 ppm). In
fact, PAT and EBT feature electron-withdrawing substituents with a lack of electron density
to facilitate interaction with the π-molecular orbital of CO [38,39], thus, due to the presence
of a high CO concentration, a saturation effect occurred. This finding appears to be consistent
with those reported by Tavoli and coworkers [40].
In contrast, ETT featuring electron-donating substituted exhibits a higher sensitivity to a high
CO concentration with 55.26% for 30 ppm of CO, 25.44% for 20 ppm of CO and only
1
8.71% for 10 ppm of CO. The gas response of ETT increased linearly with no sign of
saturation. This is because ETT with an electron-donating substituent has sufficient electron
density to facilitate interaction with the π-molecular orbital of CO in the presence of a high
CO concentration. Theoretically, CO is a well-known, strong pi-accepting molecule that is
able to accept electron donation from ETT molecules to form an ETT-CO complex at a high
CO concentration. Figure 3 illustrates the sensor response (sensitivity) bar chart of the film
substrates (PAT, EBT, and ETT) to CO after exposure to various concentrations of CO (from
1
0 to 30 ppm).
Figure 3: The bar chart of materials sensitivity towards 10, 20, and 30 ppm CO

2
.4 Theoretical evaluation: Insight from density functional theory (DFT) calculations
The targeted acetylide-thiourea molecules, also known as free-sensor molecules, and the
possible sensor-analyte complex with the CO molecule were optimised to the minimal
potential energy using the Gaussian 09 quantum mechanical software package at the
theoretical level of DFT (B3LYP)/6-31G (d,p). From the computational modelling studies, it
was discovered that the various substituents of thiourea affect the stabilisation energy and the
interaction distance of the sensor-analyte complexes.
Theoretically, to predict the possible interaction between PAT, EBT, and ETT with CO, the
Mulliken charge values were measured. The Mulliken charges on the selected atoms of PAT,
EBT, and ETT, as well as the possible interaction distances, are listed in Table 1. The
analysis shows that all of the charges on the oxygen atom of the (C=O amide) were two times
higher than those of the sulphur atom of (C=S) in the thiourea moiety. The values of the
Mulliken charges of oxygen in the (C=O amide) were observed to be in the range of -0.533 to
-0.537, compared to only approximately -0.247 to -0.256 for a sulphur atom. Due to the
highly negative values of the charges on the oxygen atoms, we believe that the interactions
that were formed between the acetylide-thiourea derivatives of PAT, EBT, and ETT with CO
are able to interact at the oxygen atom of the (C=O amide). The presence of various
substituents on the thiourea derivatives also affected the stabilisation energy of the
interactions. The total electronic energies of the compounds and their stabilisation energies,
along with the values for the individual thiourea and CO molecules are listed in Table 2.
Table 1: Mulliken effective charges on selected oxygen and sulfur of PAT, EBT, and ETT
and the interaction distance between CO and C=O
Compound
Mulliken charges
Calculated distance between
CO and C=O, (Ǻ)
O (C=O)
S (C=S)
-0.255
-0.247
-0.256
PAT
EBT
ETT
-0.533
-0.536
-0.537
3.14
3.14
3.14
Note: Mulliken charge of C (C=O) = +0.174
9

The results show that, of the three complexes, PAT was the most sensitive material to CO,
with the value -6.56 kJ/mol, followed by ETT (-6.54 kJ/mol) and EBT (-6.30 kJ/mol). All of
the complexes were stabilised by van der Waals bonds (non-bonding interaction), which were
caused by the quantum mechanical fluctuating in the electron density of the interacting atoms.
The binding that occurred was realised by the electrostatic interaction between the delocalised
conducting electrons and the positive ions localised within the compounds. The expected
results obtained were in accordance with PAT>ETT>EBT at an equimolar concentration of
the free-sensor molecule and CO. In summary, from these theoretical evaluations, the
interaction of PAT, EBT, and ETT with CO is possible with significant interaction distance
and stabilisation energy of the complexes (PAT/ EBT /ETT + CO).
Table 2: SCF energy of sensor-analyte complexes, CO, and acetylide-thiourea (PAT, EBT,
and ETT) during their interaction and stabilisation with CO
Compound SCF energy, SCF energy, a.u. SCF energy, a.u.
Stabilization
a.u. (complex)
-1697.8665
-1790.1083
-1737.1874
(CO)
(acetylide-
thiourea)
-1584.5545
energy, (kJ/mol)
PAT
EBT
ETT
-113.3095
-113.3095
-113.3095
-6.56 [1]
-6.30 [3]
-6.54 [2]
-1676.7964
-1623.8754
3
. Conclusion
These new acetylide-thiourea materials (PAT, EBT, and ETT) that were highly sensitive for
the determination of carbon monoxide (CO) had been successfully synthesised and
characterised prior to forming active film substrates entrapped in a PVC matrix for the
detection of CO gas. The response of the film substrates to CO at room temperature was
observed using the difference in the spectral features prior to and upon interaction with CO.
The PAT and EBT film substrates exhibited good sensitivity to low CO concentrations of 10
and 20 ppm and possessed low sensitivity to a high CO concentration of 30 ppm. Although
ETT exhibited good sensitivity to a high CO concentration of 30 ppm, it gave low responses
with lower CO concentrations of 10 and 20 ppm. The differences in the sensor performances
of these newly synthesised derivatives were influenced by the materials’ molecular system
behaviour. In fact, the theoretical analysis proved that PAT, EBT, and ETT exhibited ideal
interaction energies (-6.30 kJ/mol to -6.56 kJ/mol) for sensing CO. In conclusion, a novel
10

approach involving a single-molecular acetylide-thiourea system (PAT, EBT, and ETT)
exhibited promising ability and potential for carbon monoxide sensing.
4
. Experimental
4
.1 Reagents
All reagents, including solvents, chemicals and materials, were commercially purchased from
various standard suppliers and used as received without further purification. Most of the
chemicals used, namely, ammonium thiocyanate, 1-naphthoyl chloride, 4-ethynylbenzonitrile,
palladium chloride (PdCl
borate, triphenyl phosphate, and sodium sulphate, were purchased from Merck, Sigma-
Aldrich, Acrós Organics, and R & M Chemical. The catalyst, Pd(PPh Cl was prepared by
2
), triphenylphosphine, polyvinyl chloride, sodium tetraphenyl
3
)
2
2
literature method [41]. All solvents used in this study, such as acetone, chloroform,
dichloromethane, diethyl ether, ethyl acetate, hexane, methanol, acetonitrile, and
triethylamine, were purchased from Merck, Sigma-Aldrich, and R&M Chemical. For the gas-
sensing studies, carbon monoxide (CO) gas with concentrations of 10, 20, and 30 ppm was
purchased from Gas Sensor Sdn. Bhd., UKM-MTDC Technology Centre, Bangi, Selangor,
Malaysia.
4.2 Characterisation
CHNS microanalysis was performed using a FLASHEA 1112 CHNS analyser for
determination of the percentage of CHNS elements present in the synthesised compounds. IR
spectra were recorded using a Perkin Elmer 100 FTIR spectrophotometer within the spectral
-
1
range 4000 to 450 cm . Additionally, the UV-Vis spectra of the synthesised compounds were
recorded using a Shidmazu 1601 series UV-Vis spectrophotometer in 1 cm path length quartz
-
5
cell with acetonitrile as solvent and sample concentration of 1 x 10 M. Thermogravimetric
analysis was performed using a Perkin-Elmer TGA analyser from 273-1073K at a heating rate
of 283K/min in the presence of a constant nitrogen flow. NMR spectra were recorded on
1
13
Bruker Avance III 400 ( H 400.11 MHz, C 100.61 MHz) using deuterated chloroform
CDCl ) at room temperature acting as the solvent and an internal standard within the ranges
C
0-15 ppm for H NMR and δ 0-200 ppm for C NMR. Finally, the ab initio quantum
(
3
1
13
δ
H
mechanical software package of Gaussian 09 was used to calculate the stabilisation energy
and the intermolecular distance of the interaction between the synthesised compounds and
carbon monoxide at a minimum potential at the theoretical level of DFT B3LYP/6-31G (d,p).
11

4
4
.3 Sonogashira cross-coupling reaction: Preparation of the precursors (PHE, AEB, AET)
.3.1 Synthesis of 4-phenylethynylaniline (PHE)
The experimental details with regard to the synthesise of the precursors (PHE, AEB, and
AET) had already been reported in the previous literature [42,43,14]. However, several
modifications in the synthetic work-up were made, improved and discussed in this report. The
3 2 2
synthesis of PHE proceeded via Pd(PPh ) Cl /CuI (5 mmol%)-catalysed coupling of 4-
iodoaniline (1 g, 4.56 mmol) with two molar equivalents of phenylacetylene (1 g, 9.13 mmol).
The reaction was refluxed using water as the solvent and triethylamine as a base under
ambient atmosphere for ca. 24 hours, forming two layers of solution. The organic phase was
collected, dried over sodium sulphate, and evaporated to dryness. The crude product obtained
was then purified via column chromatography, eluted with a mixture of hexane and
dichloromethane (7:3). Evaporation of the solvents afforded the product PHE as a brown
1
solid (70% yield). H NMR (400.11 MHz, CDCl
3
): δ 3.83 (s br, 2H, NH
); 7.52 (pseudo-d, JHH= 9Hz, 2H, C ); 7.29-7.39 (m, 5H, C
NMR (100.61 MHz, CDCl ): δ 87.3, 90.1 (2 x s, 2 x C� C); 112.6, 114.7, 123.9, 127.6,
28.2, 131.3, 132.9, 146.6 (8 x s, Ar); Elemental analysis for C15 : [Found (Calcd.): C =
2
); 6.67 (pseudo-d,
13
JHH=9 Hz, 2H, C
6
H
4
6
H
4
6 5
H ); C
3
1
8
10 2
H N
6.51 (87.01); H = 5.53 (5.74); N = 7.24 (7.25).
4.3.2 Synthesis of 4[(4-aminophenyl)ethynylbenzonitrile](AEB)
The yellow solid of the compound AEB (0.7 g, 70%) was prepared from 4-iodoaniline (1 g,
.56 mmol), 4-ethynylbenzonitrile (1.16 g, 9.13 mmol), and the palladium catalyst
4
Pd(PPh
3
)
2
Cl
2
, using copper iodide (5 mmol%) as a co-catalyst in the same manner as for
): δ 3.94 (s br, 2H, NH ); 6.67 (pseudo-d, JHH=9 Hz, 2H,
); 7.58 (pseudo-d, JHH=8 Hz, 2H, C ); 7.61
); C NMR (100.61 MHz, CDCl ): δ 86.1, 95.1 (2 x s, 2 x
C� C); 147.4 (s, C� N); 110.6, 111.3, 114.7, 118.7, 129.0, 131.7, 131.9, 133.3 (8 x s, Ar);
1
PHE. H NMR (400.11 MHz, CDCl
3
2
C
6
H
4
); 7.38 (pseudo-d, JHH= 8Hz, 2H, C
6
H
4
6 4
H
13
(pseudo-d, JHH=9 Hz, 2H, C
6
H
4
3
12

10 2
Elemental analysis for C15H N : [Found (Calcd.): C = 82.22 (82.55); H = 4.54 (4.62); N =
12.55 (12.84).
4.3.3 Synthesis of 4[(4-aminophenyl)ethynyltoulene](AET)
The pale-brown solid of the compound AET (0.85 g, 89%) was prepared from 4-iodoaniline
1 g, 4.56 mmol), 4-ethynyltoluene (1.06 g, 9.13 mmol), and the palladium catalyst
Pd(PPh Cl , using copper iodide (5 mmol%) as a co-catalyst in the same manner as for
PHE. H NMR (400.11 MHz, CDCl ): δ 2.39 (s, 3H, CH ); 3.83 (s br, 2H, NH ); 6.66
pseudo-d, JHH=8 Hz, 2H, C ); 7.17 (pseudo-d, JHH= 8Hz, 2H, C ); 7.35 (pseudo-d,
HH=9 Hz, 2H, C ); 7.36 (pseudo-d, JHH=9 Hz, 2H, C ); C NMR (100.61 MHz, CDCl ):
δ 87.4, 89.3 (2 x s, 2 x C� C); 21.4 (s, CH ); 112.8, 114.7, 120.8, 129.0, 131.2, 132.9, 137.7,
46.5 (8 x s, Ar); Elemental analysis for C15 : [Found (Calcd.): C = 86.19 (86.92); H =
.13 (6.32); N = 6.73 (6.76).
(
3
)
2
2
1
3
3
2
(
6
H
4
6 4
H
1
3
J
6
H
4
6
H
4
3
3
1
6
10 2
H N
4
.4 Synthesis of N-(4-phenylethynylaniline)-N’-(1-naphthoyl)thiourea (PAT)
The general synthetic pathway to produce PAT is as shown in Scheme 1. The intermediate 1-
naphthoyl thiocyanate was produced by the reaction between 1-naphthoyl chloride and an
equimolar amount of ammonium thiocyanate in acetone. The reaction progress was monitored
2 2
by TLC (hexane:CH Cl :3:2). Treatment of the latter with an equimolar amount of PHE in
acetone produced N-(4-phenylethynylaniline)-N’-(1-naphthoyl)thiourea (PAT) as the targeted
product. The product was then recrystallised from acetonitrile, yielding the yellow crystalline
1
solid of PAT (70% yield) in a needle-like shape. H NMR (400.11 MHz, CDCl
3
): δ 7.38-7.39
); 8.09
); 8.43 (pseudo-d,
); 9.10, 12.78 (2 x s, 1H, NH); C NMR (100.61 MHz, CDCl ): δ 88.8,
0.0 (2 x s, 2 x C≡C); 121.6, 123.1, 123.4, 124.5, 126.4, 127.1, 128.3, 130.6, 131.6, 132.2,
33.3, 133.8, 137.4 (18 x s, Ar); 169.2 (s, C=O); 177.8 (s, C=S); Elemental analysis for
(
(
m, 3H, C
pseudo-d, JHH=8 Hz, 2H, C
HH=8 Hz, 1H, C
6
H
5
); 7.56-7.77 (m, 7H, naphthoyl); 7.88 (pseudo-d, JHH=7 Hz, 2H, C
6 4
H
6
H
4
); 8.11 (pseudo-d, JHH=8 Hz, 1H, C
6 4
H
1
3
J
6
H
4
3
9
1
13

27 17 3
C H N S: [Found (Calcd.): C = 77.13 (76.82); H = 4.30 (4.46); N = 7.17 (6.89); S = 8.13
(7.89).
4
.5 Synthesis of N-(4[4-aminophenyl]ethynylbenzonitrile)-N’-(1-naphthoyl)thiourea (EBT)
Yielding pale-yellow single crystals (64% yield) in a rectangular-like shape, EBT was
prepared from 1-naphthoyl chloride (2 g, 10.49 mmol), ammonium thiocyanate (0.79 g, 10.49
mmol), and 4[(4-aminophenyl)ethynylbenzonitrile] (2.29 g,10.49 mmol) in same manner as
1
reported by Daud et al., 2014 [14]. H NMR (400.11 MHz, CDCl
3
): δ 7.56-7.71 (m, 7H,
); 7.91 (pseudo-d, JHH=8 Hz, 2H, C ); 7.96
); 8.43 (pseudo-d, JHH=8 Hz, 2H, C ); 9.15, 12.83 (2 x s,
H, NH); C NMR (100.61 MHz, CDCl ): δ 88.3, 93.2 (2 x s, 2 x C≡C); 138.2 (s, C≡N);
11.5, 118.5, 120.4, 123.5, 124.5, 124.5, 126.4, 126.4, 127.1, 128.0, 128.3, 128.8, 129.8,
30.5, 132.4 (18 x s, Ar); 169.2 (s, C=O); 177.8 (s, C=S); Elemental analysis for C27 S:
naphthoyl); 7.86 (pseudo-d, JHH=7 Hz, 2H, C
6
H
4
6 4
H
(
pseudo-d, JHH=7 Hz, 2H, C
6
H
4
6 4
H
1
3
1
1
1
3
17 3
H N
[Found (Calcd.): C = 75.74 (75.15); H = 3.76 (3.97); N = 9.97 (9.74); S = 7.23 (7.62).
4
.6 Synthesis of N-([4-aminophenyl]ethynyltoluene)-N’-(1-naphthoyl)thiourea (ETT)
Yielding pale-yellow single crystals (72% yield) in a needle-like shape, ETT was prepared
from 1-naphthanoyl chloride (2 g, 10.49 mmol), ammonium thiocyanate (0.79 g, 10.49
mmol), and 4(4-aminophenyl)ethynyltoluene, (2.17 g, 10.49 mmol) in the same manner as for
1
PAT. H NMR (400.11 MHz, CDCl
3
): δ 2.41 (s, 3H, CH
); 7.63-7.87 (m, 7H, naphthoyl); 7.98 (pseudo-d,
); 8.11 (pseudo-d, JHH=8 Hz, 1H, C ); 8.43 (pseudo-d, JHH=8 Hz, 2H,
); 9.09, 12.77 (2 x s, 1H, NH); C NMR (100.61 MHz, CDCl ): δ 21.5 (s, CH ); 88.2,
3
); 7.21 (pseudo-d, JHH= 8 Hz, 2H,
C
6
H
4
); 7.56 (pseudo-d, JHH=7 Hz, 2H, C
6 4
H
J
HH=8 Hz, 1H, C
6
H
4
6 4
H
1
3
C
6
H
4
3
3
90.2 (2 x s, 2 x C≡C); 120.0, 121.8, 123.4, 124.5, 124.6, 126.4, 127.1, 128.2, 128.8, 129.1,
1
29.8, 130.6, 131.5, 132.1, 133.2, 133.8, 137.2, 138.5 (18 x s, Ar); 169.2 (s, C=O); 177.7 (s,
14

C=S); Elemental analysis for C27
N = 6.86 (6.66); S = 7.25 (7.62).
17 3
H N S: [Found (Calcd.): C = 77.00 (77.12); H = 4.67 (4.79);
Scheme 1: General overview of synthetic work-up
4
.7 Preparation of the polymer-film substrate
The film precursor solution was prepared by dissolving a mixture of 120 mg of
polyvinylchloride (PVC), 240 mg of the plasticiser tributyl phosphate (TBP), 1.5 mg of
sodium tetraphenyl borate and 1.6 mg of acetylide-thiourea (PAT, EBT, ETT) in 4 ml of
dried tetrahydrofuran (THF) in a glass vial. The solution was stirred for ca. six hours to
achieve complete homogeneity. The prepared precursor solution contained a ratio of 33%
PVC: 66% plasticisers by weight (1:2), which is in accordance with the literature [44,14]. The
solution was then spread onto a glass substrate by dip-coating. The films obtained were stored
in a desiccator to avoid undesirable reaction with any gases/pollutants in the ambient air. The
absorption spectra of the thin film before and after exposure to CO were recorded in closed,
designated quartz cells. All the experiments were performed at room temperature under
aerobic environment.

Acknowledgements
The authors would like to acknowledge the Ministry of Education (MOE) for the research
grant ERGS 55102, MyBrain15 for the postgraduate student’s scholarship, and the School of
Fundamental Science, Universiti Malaysia Terengganu for the facilities and research aid.
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17

Highlights:
1
2
3
4
5
. Novel derivatives of acetylide-thiourea have been synthesised and characterised.
. They are used as a single molecular sensor towards three concentration of CO gas.
. Thin films formations were deposited via dip-coating technique.
. These derivatives exhibit ideal interaction towards CO gas.
. Synthesised molecules exhibit van der Waals (non-bonding) interaction with CO.
18