Enhanced electrochromic performances of Polythieno[3,2-b]thiophene with multicolor conversion via embedding EDOT segment

Article abstract of DOI:10.1016/j.polymer.2018.11.018

A heterocyclic oligomer, thieno[3,2-b]thiophene (TT) end-capped famous 3,4-ethylenedioxythiophene (EDOT) unit and their electrosynthesized polymer P(TT-EDOT-TT) have been facilely achieved. To in-depth understand the effects of structural modification on physico-chemical properties and electrochromic performances of monomers and/or polymers, the absorption spectroscopy, electrochemistry, micromorphology, and spectroelectrochemistry were systematically studied. In contrast to TT and EDOT, TT-EDOT-TT possessed extended π-conjugation and narrowed band gap in molecular level. Through carefully comparison with PTT, it has been found that the electrochromic performances of P(TT-EDOT-TT) film exhibited much higher optical contrast (69%, while 3% for PTT in the near-infrared region) and superior coloring efficiency (255.3 cm² C^?1, while 36.8 cm² C^?1 for PTT), and switching times (within 1 s, while more than 9 s for PTT). Notably, P(TT-EDOT-TT) film can achieve the mutual conversion between RGB primary colors (red–green–blue) under variable voltages, which hold quite promising for display applications.

Full text of DOI:10.1016/j.polymer.2018.11.018

Polymer159(2018)150–156
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Enhanced electrochromic performances of Polythieno[3,2-b]thiophene with
multicolor conversion via embedding EDOT segment
Yu Xuea, Zexu Xuea, Wenwen Zhangb, Wenna Zhanga, Shuai Chena,∗, Kaiwen Linc,
Jingkun Xub,d,∗∗
a School of Pharmacy, Jiangxi Science & Technology Normal University, Nanchang, 330013, Jiangxi, China
b Jiangxi Engineering Laboratory of Waterborne Coatings, School of Chemistry & Chemical Engineering, Jiangxi Science & Technology Normal University, Nanchang,
330013, Jiangxi, China
c Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou,
510640, China
d School of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao, 266042, Shandong, China
H I G H L I G H T S
Facilely preparation method.
•
Excellent electrochromic performances.
•
Multicolor conversion between RGB color space.
•
A R T I C L E I N F O
A B S T R A C T
Keywords:
A heterocyclic oligomer, thieno[3,2-b]thiophene (TT) end-capped famous 3,4-ethylenedioxythiophene (EDOT)
unit and their electrosynthesized polymer P(TT-EDOT-TT) have been facilely achieved. To in-depth understand
the effects of structural modification on physico-chemical properties and electrochromic performances of
monomers and/or polymers, the absorption spectroscopy, electrochemistry, micromorphology, and spectro-
electrochemistry were systematically studied. In contrast to TT and EDOT, TT-EDOT-TT possessed extended π-
conjugation and narrowed band gap in molecular level. Through carefully comparison with PTT, it has been
found that the electrochromic performances of P(TT-EDOT-TT) film exhibited much higher optical contrast
(69%, while 3% for PTT in the near-infrared region) and superior coloring efficiency (255.3 cm2 C−1, while
36.8 cm2 C−1 for PTT), and switching times (within 1 s, while more than 9 s for PTT). Notably, P(TT-EDOT-TT)
film can achieve the mutual conversion between RGB primary colors (red–green–blue) under variable voltages,
which hold quite promising for display applications.
Conjugated polymers
Polythieno[3,2-b]thiophene
Electrochromism
1. Introduction
thiophenes, stereroregular thieno[3,2-b]thiophene (TT) has extended
rigid planar π-electronic structure and also promotes a more deloca-
The development of novel environmentally benign and energy
conservation functional materials are imminent to retard the
rapid exhausted of fossil energy sources [1–3]. Organic π-electron
conjugated thiophene-based polymers attract much attention for fab-
ricating modern flexible and smart optoelectronic devices, e.g. elec-
trochromic displays, in terms of their superiority in stability, mechan-
ical flexibility, photoelectric performances [4–6]. In contrast to
lized HOMO distribution, which enables effective charge transport of
both negative and positive charges along polymer backbone [7–12].
However, in view of its relatively large optical band gap and limitation
to utilize the near-IR photons, the application of its polymer (PTT) is
seriously hindered in electrochromic area [8]. One of the effective ap-
proaches among others to enlarge their photoelectric performances is
structural modification via changing the composition of the polymer,
∗ Corresponding author.
∗∗ Corresponding author. Jiangxi Engineering Laboratory of Waterborne Coatings, School of Chemistry & Chemical Engineering, Jiangxi Science & Technology
Normal University, Nanchang, 330013, Jiangxi, China.
E-mail addresses: chenshuai@ms.xjb.ac.cn (S. Chen), xujingkun@tsinghua.org.cn (J. Xu).
https://doi.org/10.1016/j.polymer.2018.11.018
Received 21 September 2018; Received in revised form 31 October 2018; Accepted 7 November 2018
Availableonline13November2018
0032-3861/©2018ElsevierLtd.Allrightsreserved.

Y. Xue et al.
Polymer159(2018)150–156
which is the key method to control the property of the material as well
as their device performance [6,13–15]. Cirpan et al. presented the
multicolored electrochromic polymers via introducing TT as donor
units in the benzotriazole (BTz) based donor-acceptor-donor (DAD)
type polymers [16]. Meng et al. reported a neutral green electrochromic
material with excellent electrochromic performance benefiting from
modified TT unit as an unconventional donor [17]. Therefore, to full
utilize the structural advantage of PTT to explore high-performances
electrochromic materials, in this work, we embedded famous EDOT
segments into PTT backbones at the molecular level. PEDOT, the re-
presentative of conductive polymer materials, have been confirmed its
superiority in electrochromic area not only their excellent electronic
properties, remarkable stability, and favorable electrochromic beha-
vior, but EDOT itself could be employed as the building block for
for stirring 97 h. The crude product was added to the mixture solution
of LiOH (1 mol L−1 50 mL) and THF (150 mL) (1/3 v/v) and added
0.1 M HCl (15 mL) solution after reflux for 6 h to get the solid powder.
The solid powder was added to quinolone (4 mL) solution with Cu
powder (0.1 g) stirring at 260 °C for 1 h. The crude product was purified
by column chromatography (petroleum ether (PE)) and dried in vacuo
to give pure TT as white solid. (1.9 g 28%). 1H NMR (400 MHz, CDCl3)
δ 7.37 (d, J = 4.9 Hz, 2H), 7.26–7.24 (m, 2H). Anal. Calcd for C6H4S2:
C, 51.34, H, 2.85 and S, 44.21. Found: C, 51.36, H, 2.56 and S, 44.23.
2,5-Bis(thieno[3,2-b]thiophen-2-yl)-2-3,4-ethylenedioxythiophene
(TT-EDOT-TT). n-BuLi (5.4 mL, 1.6 M) was added in 25 mL THF solu-
tion with TT (1.0 g, 7.0 mmol) at −78 °C and reacted 1 h. SnBu3Cl
(1.8 mL, 10.8 mmol) was added in mixed solution at −40 °C and slowly
warmed to 0 °C gives crude product tributyl(thieno[3,2-b]thiophen-2-
yl)stannane, which was used directly in the next further step without
purification. Crude product was added in toluene solution containing
Br-EDOT-Br (1.33 g, 4.3 mmol) and Pd(PPh3)2Cl2 (0.50 g, 0.70 mmol).
After reacted at 100 °C for 24 h, it was separated by chromatography on
silica gel (CH2Cl2: PE, 1:5) to afford 1.29 g TT-EDOT-TT as yellow solid
(0.83 g 44.9%). 1H NMR (400 MHz, CDCl3) δ 7.44 (s, 2H), 7.33 (d,
J = 5.2 Hz, 2H), 7.23 (s, 2H), 4.44 (s, 4H). Anal. Calcd for C18H10O2S5:
C, 51.62, H, 2.40%, O, 38.22 and S, 7.66. Found: C, 52.27, H, 2.41, O,
36.63 and S, 7.42.
multifunctional semiconducting materials [18–21]. Accordingly,
a
novel conductive polymer has been grown via electropolymerization of
TT end-capped EDOT oligomer (TT-EDOT-TT) in acetonitrile-Bu4NPF6
electrolytes. Difference from structure, physico-chemical properties,
energy gap, micromorphology, and photoelectrochemical behaviors
have been investigated, in addition to a systematic exploration of its
electrochromic performances. (see Tables 1 and 2)
2. Experimental section
2.1. Materials
2.3. Electrochemical measurements
3-Bromothiophene (99%; Energy Chemical), lithium diisopropyla-
mide (LDA, 98%; Sigma Aldrich), N-formylpiperidine (99%; Energy
Chemical), ethyl 2-sulfanylacetate (99%; Energy Chemical), quinolone
(98%; Energy Chemical), EDOT (98%; Sigma Aldrich), n-butyllithium
(n-BuLi, 1.6 M; Energy Chemical), tributylstannyl chloride (SnBu3Cl,
98%; J&K Chemical), N-bromosuccinimide (NBS, 98%; Energy
Chemical) and transdichlorobis(triphenyl-phosphine)palladium(II) (Pd
(PPh3)2Cl2, 98%; 15% Pd, Sigma-Aldrich) were stored at 4 °C and used
without further purication. Tetrabutylammonium hexafluorophosphate
(Bu4NPF6, 99%; Shanghai Vita Chemical) was dried under vacuum at
60 °C for 24 h before use. Dichloromethane (CH2Cl2, 99.9%; J&K
Chemical), and acetonitrile (ACN, 99.9%; J&K Chemical) were all used
directly without further purification. Tetrahydrofuran (THF) was dis-
tilled over sodium (Na) under N2 before used. Other reagents were all
analytical grade and used directively.
All electrochemical measurements were performed using a Versa
Stat 3 electrochemical workstation under computer control. The elec-
trochemical properties of the oligomers and polymers were evaluated in
a three-electrode cell consisting of a working electrode (Pt), a reference
electrode (Ag) and an auxiliary electrode (Pt). Both electrodes wires for
Pt and Ag/AgCl of 1 mm diameter. All electrochemical experiments
were carried out in 5 mL ACN−Bu4NPF6 (0.10 mol L−1) electrolyte
solution with 0.6 mM monomer. We determined the polymerization
behavior of the monomers by cyclic voltammetry and obtained the
superior quality polymer film by optimization of electrical conditions.
2.4. Preparation and characterization of polymers
Polymers were fabricated by electrochemical polymerization of
monomers to deposit onto the surface of the Pt wires (working elec-
trodes) or ITO (3.0 cm × 2.0 cm) glass electrodes. After washed with a
large number of ACN solvent before a series of characterization were
performed. The electrochemical behaviors and redox stability of the
polymer-modified working electrodes were studied by cyclic voltam-
metry in blank ACN−Bu4NPF6 system. The resulting polymers were
employed for FT-IR characterization with samples in KBr pellets. The
surface morphologies of polymer films deposited onto the surface of
ITO glasses were investigated by field emission scanning electron mi-
croscope (FESEM).
2.2. Syntheses
Thieno[3,2-b]thiophene (TT). Its synthesis was referenced the four-
step method according to previous reports by us and Fuller et al.
[22,23]. Lithium diisopropylamide (LDA) (27.4 mL 218.9 mmol) was
added in the 100 mL of dry THF solution with 3-bromothiophene (7.9 g,
48.5 mmol) and N-formylpiperidine (6.1 mL 54.8 mmol) was added
after stirred 30 min at 0 °C. After simple purification, the crude product
was add to the N,N-dimethylformamide (100 mL) solution containing
ethyl 2-sulfanylacetate (4.12g 34.3 mmol) and K2CO3 (8.6 g 62.2 mmol)
Table 1
Spectroscopic and electronic properties of oligomers and polymers.
λmax (nm)a
λonset(nm)
Hexp/HDFT (eV)b
Lexp/LDFT(eV)
Eg
(eV)c
Eg DFT(eV)d
opt
Sample
TT
262, 271, 281
485
288
676
450
645
−6.10/−5.85
−5.06/−
−1.79/−0.73
−3.20/−
4.31
1.83
2.74
1.92
5.12
–
PTT
TT-EDOT-TT
P(TT-EDOT-TT)
270, 315, 397
480
−5.45/−4.79
−5.16/−
−2.71/−1.76
−3.24/−
3.04
–
a
b
c
d
Measured in CH2Cl2.
Hexp and Lexp are the HOMO and LUMO levels calculated using formula Hexp = −(Eonset + 4.8) (eV) and Lexp = (Hexp + Egopt) (eV).
Estimated values from the UV-vis absorption edge of the thin films (Egopt = 1240/λonset eV).
Calculated using formula Eg DFT = LDFT− HDFT (HDFT and LDFT are the HOMO and LUMO levels calculated at B3LYP/6-31G level of theory based on gas-phase
geometry).
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Y. Xue et al.
Polymer159(2018)150–156
Table 2
Electrochromic parameter comparison of PTT and P(TT-EDOT-TT).
Sample
Wavelength (nm)
Tred (%)
Tox (%)
ΔT (%)
Response time (s)
Ox
CE (cm2 C−1
)
Red
PTT
485
65.8
64.3
46.9
49.6
85.9
78.8
67.8
61.3
76.4
72.0
16.5
18.7
2.0
9.83
9.19
2.63
3.57
0.58
0.60
9.78
9.32
1.87
2.33
0.98
1.00
23.7
36.8
81.7
92.3
255.3
275.6
1050
480
3.0
P(TT-EDOT-TT)
29.5
22.4
69.4
60.1
(500 s)a
1050
(500s)
a
After 500 s of cycling. Notes: the calculation formula of the data see experimental details.
2.5. Spectroelectrochemical and electrochromic studies
Spectroelectrochemical and electrochromic properties were tested
in rectangular quartz cuvette (path length 1 cm) via combination the
UV-vis spectrometer (SPECORD 200 PLUS) and electrochemical work-
station (Versa Stat 3). The polymer films were deposited onto the pre-
treated ITO surface (3 cm × 0.8 cm) through electrochemical poly-
merization and washed with the corresponding solvent (ACN). The
electrochromic properties of the polymers were in-depth studied
through the kinetics study, including optical contrast (ΔOD), coloring
efficiency (CE), switching time, etc, and the calculation method ac-
cording to the following formula [6]:
ΔOD = log(Tox / Tred
)
(1)
(2)
CE = ΔOD / Qd
Notes: Tox and Tred are transmittance of oxidized and reduced
polymer films, respectively. Qd is the total amount of charge injected
and extracted from the polymer surface per unit of time.
Fig. 1. Absorption spectra of TT and TT-EDOT-TT in CH2Cl2.
3. Results and discussion
it is evident that the optical band gap of TT-EDOT-TT was significantly
lower than the TT due its extended conjugate structure.
3.1. Synthesis
The synthesis of TT was referenced the simplest four-step method
according to previous reports and TT-EDOT-TT was through Stille
coupling reaction with an appreciable yield (44.9%) as shown in
Scheme 1. The pure products were characterized by 1H NMR and ele-
mental analysis (EL III).
3.3. Electrochemical polymerization
The initial oxidation potential was determined by the method of
anodic polarization as appeared in Fig. 2. Finding that the initial oxi-
dation potential of TT-EDOT-TT (0.66 V) was much lower than TT
(1.30 V) due to its long conjugated structure. It is recognized that
polymerization at low potential tends to grow the high quality polymers
because of the primary molecular structure not be destroyed and could
also effectively prevent the occurrence of side reactions [25].
3.2. Optical property
Advanced Electronic materials
The electronic transitive behavior of TT and TT-EDOT-TT were
studied by UV-visible absorption spectrum to determine the interrela-
tions between the structure and properties as shown in Fig. 1. The
absorption band of TT was concentrated between 230 and 300 nm can
be assigned to intramolecular π–π* transitions. The low-energy ab-
sorption band of TT-EDOT-TT was concentrated between 330 and
450 nm can be assigned to π–π* transitions from EDOT core [24].
Furthermore, the optical band gap of two monomers can be calculated
as 4.30 eV (TT) and 2.76 eV (TT-EDOT-TT) by the absorption onsets and
Cyclic voltammograms were used to investigate the dynamic elec-
trochemical behavior of monomers as shown in Fig. 3. The successive
increase of the peak current density indicated that the electroactive
polymers has been obtained, meanwhile, visual inspection during
electropolymerization demonstrated that the formation of deep colored
substance on the surface of working electrode [26]. There was a pair of
obvious redox (anode and cathode) peaks and almost similar peak in-
tensities for PTT, indicated that it has good doping and dedoping cap-
abilities under switching voltage. While for TT-EDOT-TT fail to achieve
Scheme 1. Synthesis route of TT and TT-EDOT-TT.
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Y. Xue et al.
Polymer159(2018)150–156
Both polymer films exhibit moderate redox stability. The electroactive
substances of PTT began to degrade sharply after 500 cycles, never-
theless, the electroactive substances of P(TT-EDOT-TT) began to de-
grade sharply after the 100 cycles. The electroactive substances of the
two polymers only remained 32.4% and 22.6% after 2000 cycles, re-
spectively. The reduction of electroactive substances may because of
the poor adhesion of the electroactive materials to the working elec-
trode [29].
3.5. Morphology
Surface morphologies can be served as the favorable evidence to
explain the optoelectronic and electrochemical feature of the polymers.
The micromorphology of the films coated onto ITO glasses in difference
doping levels (−0.2 V, 0 V, 1.0 V) were in-depth studied by SEM as
shown in Fig. 6. The bumpy and rough surface of PTT could because of
the higher polymerization voltage. However, the smooth and flat
morphology was presented for the films of P(TT-EDOT-TT) and such
morphology was a foundation to achieve the superior electrochromic
behavior [30]. We believe that the reason for obtaining such a smooth
and morphology film was the low oxidation voltage driven by the
embeddedness of EDOT group.
Fig. 2. Anodic polarization curves of 0.6 mM TT and TT-EDOT-TT in
ACN−Bu4NPF6 (0.1 M) under potential scan rate of 50 mV s−1
.
ordered polymerization by observing CV spectra, there was slightly
inconsistence due to the inadequate polymerization at the initial stage.
And two pairs of redox peaks were found indicated the polymerization
of TT-EDOT-TT was not strictly controlled at the α-position due to the
exposed site of TT at β-position.
3.6. Spectroelectrochemistry
The spectroelectrochemistry of PTT and P(TT-EDOT-TT) films were
investigated via combination the electrochemical workstation and UV-
Vis spectrophotometer to capture the change of the colors of the
polymer films under different voltages and explore its electronic tran-
sitive behavior. The dominant wavelength of both polymer films were
located in the visible region (almost centered at 480 nm), however, the
simple electronic transition modes of PTT lead to a slightly change in
optical absorption between −0.2 and 1.2 V. In contrast with PTT, the
polaronic absorption of P(TT-EDOT-TT) was emerged in the visible
region (745 nm), which could brought the color contribution of red for
polymer [16]. Strong absorption occurred in the near infrared region
indicated the formation of charge carriers such as bipolarons during the
electronic transition. The colors changes and corresponding colors
contribution (L*, a*, b*) of polymers were presented in Fig. 7C and D.
The color contribution from the films of PTT and P(TT-EDOT-TT) be
defined by CIELAB color coordinates [6], and the color difference
reached 8.46 (PTT), 21.97 (P(TT-EDOT-TT)), respectively. As a result,
the inclusion of EDOT promote the delocalization of the π-electrons
along the backbone of the polymers, which enables effective charge
transport both negative and positive charges.
3.4. Electrochemistry of polymers
3.4.1. Cyclic voltammetry of polymers
Cyclic voltammetry of polymers were tested in monomers–free
ACN–Bu4NPF6 system as shown in Fig. 4 to determine the redox activity
and the relationships between scan rate and peak current density of the
polymers. A distinct anodic wave of the CV of PTT fail to found but a
broad and distinct cathode wave was generated due to (1) a broad
distribution of the polymers chain undergoes slow movement during
doping and dedoping (2) static coupling defects occurred during poly-
merization, etc. [27,28]. P(TT-EDOT-TT) present obvious redox peaks
during doped and dedoped states, meanwhile, there was an obvious
difference between the anodic and cathodic peak potentials due to slow
heterogeneous electron transfer and local rearrangement of polymer
chains, etc.. The good linear dependence of the current on the scan rates
was observed (Fig. 6C and D), indicating this process was controlled by
slow diffusion.
3.4.2. Stability
The long-term stability was studied in free-monomer ACN–Bu4NPF6
at the same cycles times (2000) under scan rate of 200 mV s−1 (Fig. 5).
E
=
( L*)2 + ( a*)2 + ( b*)2
(3)
Fig. 3. Cyclic voltammograms (CVs) of 0.6 mM TT and TT-EDOT-TT in ACN−Bu4NPF6 (0.1 M) under potential scan rate of 50 mV s−1
.
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Y. Xue et al.
Polymer159(2018)150–156
Fig. 4. Cyclic voltammograms (CVs) of PTT
(A) and P(TT-EDOT-TT) (B) in monomer-
free of ACN–Bu4NPF6 (0.1 mol L−1) at po-
tential scan rates form 25 mV s−1 to
300 mV s−1 and the linearity relationships
of anodic (jp,a
) and cathodic (jp,c) peak
current densities vs. scan rates between the
neutral and oxidized states of PTT (C) and P
(TT-EDOT-TT) (D).
Fig. 5. Cyclic voltammograms (CVs) of PTT and P(TT-EDOT-TT) cycled 2000 times at the potential. scan rate of 200 mV s−1 in 0.1 M ACN–Bu4NPF6 solution.
Fig. 6. SEM images of PTT (A) (B) (C) and P(TT-EDOT-TT) (E) (F) (G) polymerized electrochemically on the ITO-coated glasses. Magnification: 5000×.
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Polymer159(2018)150–156
Fig. 7. Spectroelectrochemistry of PTT (A)
and P(TT-EDOT-TT) (B) films on ITO-coated
glasses in ACN–Bu4NPF6 (0.1 M) solution at
applied potentials from 0 V to + 1.2 V.
Color changes and colorimetric measure-
ments of PTT (C) and P(TT-EDOT-TT) (D)
films at different potentials. (For inter-
pretation of the references to color in this
figure legend, the reader is referred to the
Web version of this article.)
Figure 8. Time-transmittance profiles of PTT (left) and P(TT-EDOT-TT) (right) recorded at the switching time of 10 s under indicated wavelengths on ITO-coated
glasses in ACN−Bu4NPF6 (0.1 M) solution.
3.7. Kinetic studies
performance electrochromic materials. The ratio of the optical ab-
sorption change of material to charge inject and extraction per unit area
was called the coloring efficiency. PTT exhibits very low coloring effi-
ciency due to its poor optical contrast, however, the coloring efficiency
has significantly improved and reached 275.6 cm2 C−1 when the in-
clusion of EDOT into the polymer molecular chain.
Internal electrochromic behavior of polymer films can be reflected
through the kinetics study. The photoelectric properties of materials
were studied via constantly regulate the color states of the polymer
films using square wave potential method. Obviously, the optical
transmittance has not much changed in the doped and dedoped states
may due to single electronic transitive behavior of PTT. However, the
optical contrast (Fig. 8) was significantly improved from less than 3% to
more than 60% when EDOT unit was embedded into PTT molecular
backbones. Therefore, strong absorption occurs in the near-infrared
regions, which lead to new polaron and bipolaron energy levels. Re-
sponse times could be used to evaluate switching rate of polymer films
from the colored state to faded state (or from the faded state to colored
state) under dynamic voltages. Obviously, the switching time of P(TT-
EDOT-TT) was significantly better than PTT both at oxidation and re-
duction states and the switching time for P(TT-EDOT-TT) was main-
tained within 1 s, which fully meeting the requirements of high
4. Conclusions
In this work, a heterocyclic monomer, TT end-capped famous 3,4-
ethylenedioxythiophene (EDOT) unit and their electrosynthesized
polymer P(TT-EDOT-TT) have been facilely achieved. The structural
modification plays a significant effect on the physico-chemical prop-
erties and electrochromic performances of monomers/polymers. In
contrast to TT, TT-EDOT-TT showed extended conjugation and nar-
rowed bandgap at the molecular level. The incorporation of EDOT in
the PTT backbone at molecular level improved its poor electrochromic
performances greatly from contrast ratios, coloring efficiencies,
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Polymer159(2018)150–156
switching voltage to response times. Moreover, P(TT-EDOT-TT) can
present RGB primary color conversion, which could meet future ap-
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are believed as promising functional units to exploit high-performance
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Acknowledgements
We are grateful to the National Natural Science Foundation of China
(No. 51603095 and 51863009), Innovation Driven “5511” Project of
Jiangxi Province (No. 20165BCB18016), Natural Science Foundation of
Jiangxi Province (20181ACB20010), Key Project of Jiangxi Educational
Committee (No. GJJ170657), Scientific Fund of Jiangxi Science &
Technology Normal University (No. 2016QNBJRC003), Jiangxi
Educational Committee for a Postgraduate Innovation Program Grant
(No. YC2018-S404, and YC2018-X29) for their financial support of this
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Appendix A. Supplementary data
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