Fluorescent properties of some polythiophenes synthesized from 2-(thiophen-3-yl)acetohydrazide and acetophenone

Cite this paper: Vietnam J. Chem., 2020, 58(5), 688-696 Article 
DOI: 10.1002/vjch.202000101 
688 Wiley Online Library © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH 
Fluorescent properties of some polythiophenes synthesized from 
2-(thiophen-3-yl)acetohydrazide and acetophenone 
 Nguyen Ngoc Linh1, Ha Manh Hung2, Doan Thi Yen Oanh3, Bui Thi Thuy Linh4, Nguyen Tien Cong5, 
Nguyen Thuy Chinh
6,7
, Thai Hoang
6,7
, Vu Quoc Trung
8* 
1
Faculty of Training Bachelor of Practice, Thanh Do University, Kim Chung, Hoai Duc, Hanoi 10000, Viet Nam 
2
Faculty of General Education, Hanoi University of Mining and Geology, 
Duc Thang ward, Bac Tu Liem district, Hanoi 10000, Viet Nam 
3
Publishing House for Science and Technology, Vietnam Academy of Science and Technology, 
18 Hoang Quoc Viet, Cau Giay district, Hanoi 10000, Viet Nam 
4
Faculty of Pharmacy, Nguyen Tat Thanh University, 
ward 13, district 4, Ho Chi Minh City 70000, Viet Nam 
5
Faculty of Chemistry, Ho Chi Minh City University of Education, 280 An Duong Vuong, ward 4, district 5, 
Ho Chi Minh City 70000, Viet Nam 
6
Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 
18 Hoang Quoc Viet, Cau Giay district, Hanoi 10000, Viet Nam 
7
Institute for Tropical Technology, Vietnam Academy of Science and Technology, 
18 Hoang Quoc Viet, Cau Giay district, Hanoi 10000, Viet Nam 
8
Faculty of Chemistry, Hanoi National University of Education, 
136 Xuan Thuy, Cau Giay district, Hanoi 10000, Viet Nam 
Received June 18, 2020; Accepted July 28, 2020 
Abstract 
In this study, new polythiophenes containing hydrazone groups from derivatives of acetophenone were synthesized by 
chemical oxidative coupling polymerization. Ultraviolet-visible spectroscopy (UV-Vis) combined with infrared (IR) 
analyses proved the supposed structure of novel polythiophenes and proved conformance of the expected synthetic 
method. Morphology and surface properties of the synthesized polymers were investigated by field-emission scanning 
electron microscopy (FE-SEM). Thermal gravimetry analysis (TGA) has been reported that there was still the presence 
of small FeCl3 catalyst in polymers and polymers had a stable thermal stability under air atmosphere. The polymers 
displayed fluorescence emissions at about 590 nm attributed to the π-conjugated polythiophene. Polymers without 
doping have a good electrical conductivity (around 4.03×10
–7
 S/cm at 1 MHz). 
Keywords. Polythiophenes, chemical polymerization, conducting polymer, fluorescent properties. 
1. INTRODUCTION 
The synthesis, characterization and physicochemical 
of polymers have been commonly researched thanks 
to the ability in complex applications of ionic, 
electronic conductivity and optoelectronic 
characteristics.
[1,2]
 Polythiophene derivatives are of 
special importance among polymers owing to an 
exclusive association of high environmental 
sustainability, structural flexibility of structure, 
electrochemical, optical and magnetic 
electrochemical properties.
[3]
 A lot of works have 
been done on polythiophenes containing long alkyl- 
or alkoxy- sidegroups as functional substances, for 
example, organic field-effect transistors (OFETs),
[4,5]
organic lightemitting diodes (OLEDs),
[6,7]
 organic 
photovoltaic (OPV) cells,
[8,9]
 and nother 
optoelectronic mechanisms.
[10,11]
 Polythiophene 
derivatives all exhibit significant optical features, for 
instance, thermochromism,
[12]
 photochromism
[13]
 and 
biochromism.
[14]
 A further application area of 
polythiophenes is the finding of small bioanalyses, 
DNA, proteins, metal ions, using water-soluble 
sensing sensors.
[15-19]
Vietnam Journal of Chemistry Vu Quoc Trung et al. 
© 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 689 
 At first, polythiophene was not studied 
commonly because of its medium electrical 
conductivity, as well as its low solubility in water-
miscible solvents. However, these disadvantages can 
be improved by attaching alkoxy or alkyl groups 
thiophene ring to the 3-position, for 
example, poly(3- and 3,4-alkylthiophene)s, poly(3- 
and 3,4-alkoxythiophene)s,...
[20-21]
 In addition, the 
length of alkyl side chains also can effect on 
structure, electrochemical and optical characteristics 
of polythiophens.
[22-26]
 As a result, it is very 
interesting to prepare polymers from thiophene 
monomers having long side groups.
[27]
Herein, we present the synthesis and fluorescent 
properties of a new progression of polythiophenes 
from 2-(thiophen-3-yl)acetohydrazide and 
acetophenone. The morphology, thermal stability, 
optical and conductivity features of the obtained 
polythiophenes were studied not only on various 
techniques, but also their capable characteristics and 
their various functions. 
2. MATERIALS AND METHODS 
2.1. Synthesis 
2.1.1. Synthesis of monomers from 2-(thiophen-3-
yl)acetohydrazide and acetophenone 3a-e 
The synthesis of methyl 2-(thiophen-3-yl)acetate 1, 
and 2-(thiophen-3-yl)acetohydrazide 2, were 
reported in our previous study.
[27] 
- Synthesis of monomers from 2-(thiophen-3-
yl)acetohydrazide and acetophenone 3a-e 
The amounts of 2 (3 mmol) and an appropriate 
aromatic acetophenone (4.5 mmol) with acid acetic 
(1.8 mL) were refluxed in ethanol (30 mL) for 6 h. 
The obtained mixture was kept at room temperature. 
The precipitates were filtered and recrystallized 
from ethanol to get monomers 3a-e (yield 60 % to 
75 %) in the shape of crystals with color from white 
to milky-white; m.p. 163 
o
C to 200 
o
C. 
The morphology, molecular formula, molecular 
mass, melting point and IR spectroscopy data of five 
monomers have been presented in our thesis.
[44]
Especially, crystal and molecular structures of two 
monomers 3b, 3c were summarized using X-ray 
diffraction (XRD) ... nce and normalized 
photoluminescence intensity of four polymers were 
shown in figure 5. Two polymers 4c, 4e had the 
strongest photoluminescence intensity; polymer 4a 
had average photoluminescence intensity and 
polymer 4d was not luminescent. These polymers 
displayed maximum fluorescence emission at about 
540 and 590 nm under 415-nm excitation. It is 
evident that R-substituents in the benzyl moiety have 
almost no influence on the photoluminescence of the 
polymers. This difference may be due to the length 
of the π-conjugated polymer. 
Table 7: Emission properties of polymers 4a, 4c-e 
Polymer λemission, nm Intensity, a.u 
4a 542; 587 10280; 1516 
4c 547; 580 23827; 23600 
4d - - 
4e 590 24404 
Vietnam Journal of Chemistry Fluorescent properties of some polythiophenes 
© 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 694 
Figure 5: Photoluminescence spectra (a) and normalized photoluminescence intensity 
(b) of polymers 4a, 4c-e 
3.3.4. Electrical conductivity of polymers 4a-e 
Electrical conductivity of polymers in the pressed 
pellets with diameter of 0.5 cm was measured 
following the increase of frequency from 0Hz to 1 
MHz at 30 
o
C. The electrical conductivity was 
increased with the increase in frequency. Polymer 4a 
displayed an average conductivity value of 4.03×10
-7
S/cm at 1 MHz. As can be seen, electron-donating or 
-withdrawing groups in acetophenone derivatives 
had an irregular effect on the conductivity of 
polymers. This is probably due to the position of 
these groups too far away from the conjugated main 
chain. 
0.0 200.0k 400.0k 600.0k 800.0k 1.0M
0
1x10
-7
2x10
-7
3x10
-7
4x10
-7
4e
4c
4a
C
o
n
d
u
c
ti
v
it
y
 (
S
/c
m
)
Frequency (Hz)
Figure 6: Electrical conductivity of polymers 
 4a, 4c and 4e 
In comparison with polythiophenes synthesized 
from derivatives of benzaldehyde in our previous 
study, the conductivity of polymers synthesized 
from derivatives of acetophenone (4a, 4c and 4e) 
was not significantly different.
[36] 
However, 
compared with undoped polythiophene with the 
conductivity between 10
-7
 and 10
-6
 S/cm;
[37] 
and 
undoped p-type semiconductor poly(3-
hexylthiophene) with moderately low conductivity 
(∼10-8 S/cm) in the Hz frequency range of 
concentration on the majority of electronic 
functions,
[38] 
the conductivity of synthesized 
polythiophene had about 10 times higher. It could 
be noticed that polythiophenes synthesized from 
acetophenone derivatives (especially 4a) have a 
moderately good electrical conductivity. 
4. CONCLUSION 
In this work, a novel series of polythiophenes 
containing hydrazone groups from 2-(thiophen-3-
yl)acetohydrazide and acetophenone was 
polymerized by oxidative coupling using anhydrous 
FeCl3 in dry CHCl3 to obtain irregioregular 
polythiophenes in general. However, properties of 
these polymers were improved by the long alkyl side 
chain attached to polymer. Ultraviolet-visible (UV-
Vis) spectroscopy combined with infrared (IR) 
analyses proved the success of the polymerization 
reaction. Thermal gravimetry analysis indicated that 
polymers had medium thermal stability in the 
atmosphere at about 420-520 
o
C. The maximum 
fluorescence emission of these polymers was at 
about 540 and 590 nm; and polymers in the undoped 
state had a high-quality electrical conductivity, 
which can be applied for fluorescent dyes or 
transport materials. 
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Corresponding author: Vu Quoc Trung 
Faculty of Chemistry 
Hanoi National University of Education 
136, Xuan Thuy, Cau Giay, Hanoi 10000, Viet Nam 
E-mail: trungvq@hnue.edu.vn.