Self-assembled flexible metallo-supramolecular film based on Fe(II) ion and triphenylamine-subsituted alkyl terpyridine towards electrochromic application

Article abstract of DOI:10.1016/j.dyepig.2021.109623

A new metallo-supramolecular film was prepared by a liquid–liquid interface self-assembly method based on the metal ion Fe(II) in water solution and a star-shaped ligand of triphenylamine-substituted alkyl terpyridine in organic solvents. The film obtaine

Full text of DOI:10.1016/j.dyepig.2021.109623

Dyes and Pigments 194 (2021) 109623
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Self-assembled flexible metallo-supramolecular film based on Fe(II) ion and
triphenylamine-subsituted alkyl terpyridine towards
electrochromic application
,
,**
Yu Kuaia, Tao Yanga, Feiya Yuana, Yujie Donga *, Qingbao Songa, Cheng Zhanga
,
,c,***
Wai-Yeung Wongb
a College of Chemical Engineering, Zhejiang University of Technology, Chaowang Road, Hangzhou, 310014, PR China
b Department of Applied Biology & Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, PR China
c Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen, 518057, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
A new metallo-supramolecular film was prepared by a liquid–liquid interface self-assembly method based on the
metal ion Fe(II) in water solution and a star-shaped ligand of triphenylamine-substituted alkyl terpyridine in
organic solvents. The film obtained exhibited excellent flexibility due to the presence of flexible alkyl arms, and
could tightly adhere to the surface of ITO glass with very smooth surface morphology via SEM characterization.
Spectroelectrochemical experiments demonstrated that the film displayed the electrochromism with purplish
color in the neutralized state at 0 V vs Ag/AgCl turning to yellow-green color in the oxidized state at 1.2 V vs Ag/
AgCl. This work further indicates that the liquid–liquid interfaciad self-assembly method is a promising strategy
to prepare the metallo-supramolecular film towards electrochromic applications.
Self-assembly
Metallo-supramolecular film
Electrochromism
Terpyridine
Triphenylamine
1. Introduction
solution, has emerged as a new method to prepare the electrochromic
film materials, in which metal ions and ligands meet at the interface
In the past decades, the electrochromic (EC) materials have been
investigated extensively because of their potential application in
reflecting mirrors, electronic skin, flat-panel display, smart windows
and so on [1–9]. For EC applications, the materials are usually prepared
as a uniform thin film on ITO electrode, generally by electrochemical
polymerization, spray/spin-coating or evaporation/sputtering methods
[10–17]. However, electropolymerization has high requirements for
monomers as well as spray/spin-coating. The monomers for electro-
polymerization and solution-processing need electroactive sites and
good solubility, respectively. Sputtering methods only adapt to the
inorganic materials, while the evaporation method is difficult to be
widely used in commercial electrochromic field because of its high cost
of instruments and it is also limited to the small organic matter or some
inorganic materials [18–25]. Therefore, exploration of new film forming
methods for electrochromic materials is of great significance.
between aqueous phase and organic phase to form a thin film via the
coordination interaction. The terpyridine derivatives have been widely
adopted as the ligand, and Fe (II), Co(II) and Ni(II) ions are usually the
metal ions [26–29]. The strong coordination interaction force makes the
final thin film at the interface to be a highly stable one, and suitable
combination of metal ions and ligand will enable the film obtained with
desired optical and electrical properties [30–35]. Some reported
metallo-supramolecular films seem to be fragile and not easy to be
transferred and processed, possibly due to the strong rigidity of the
ligand structure [36–39].
A
simple idea is that
a
flexible
metallo-supramolecular films might be obtained through the adjustment
of the rigidity of the ligand structure via the liquid/liquid interfacial
self-assembly method.
In this work, a new star-shaped molecular structure (TBT) with tri-
phenylamine as the central core and tripyridine as the three arms was
designed and synthesized, but the central core and arms are linked with
butamethylene fragment to break the conjugation between
Recently, the liquid/liquid interfacial self-assembly between metal
ions dissolved in aqueous solution and ligand dissolved in organic
* Corresponding author.
** Corresponding author.
*** Corresponding author. Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen, 518057, PR China.
E-mail addresses: dongyujie@zjut.edu.cn (Y. Dong), czhang@zjut.edu.cn (C. Zhang), wai-yeung.wong@polyu.edu.hk (W.-Y. Wong).
https://doi.org/10.1016/j.dyepig.2021.109623
Received 1 June 2021; Received in revised form 25 June 2021; Accepted 1 July 2021
Available online 3 July 2021
0143-7208/© 2021 Elsevier Ltd. All rights reserved.

Y. Kuai et al.
Dyes and Pigments 194 (2021) 109623
triphenylamine and tripyridine structures, which is expected to increase
the flexibility of the metallo-supramolecular films by introducing flex-
ible alkyl chains. The corresponding metallo-supramolecular film (TBT-
Fe) was successfully fabricated on the ITO surface directly. The film
obtained exhibited excellent flexibility, and displayed very smooth
surface morphology. After applying different voltages, the TBT-Fe films
finally exhibited obvious electrochromism.
column chromatography on a silica gel with dichloromethane/hexane
(1:2, v/v) to yield a white solid (0.46 g, 50%). 1H NMR (500 MHz,
CDCl3) δ 7.53 (d, J = 8.7 Hz, 6H), 7.49 (d, J = 8.8 Hz, 6H), 7.22 (d, J =
8.6 Hz, 6H), 6.97 (d, J = 8.8 Hz, 6H), 4.07 (t, J = 6.3 Hz, 6H), 3.53 (t, J
= 6.4 Hz, 6H), 2.15–2.09 (m, 6H), 2.02–1.97 (m, 6H). ESI HRMS (mass
m/z): 924.1227 [M+ + H] (calculated: 924.1257).
Synthesis of ([2, 2’: 6′, 2′′-terpyridin]-4′-yl)phenol (4)
2. Experimental
P-Methoxybenzaldehyde (0.14 g, 1 mmol), potassium hydroxide
(0.14 g, 2.5 mmol) and 2-acetylpyridine (0.3 g, 2.5 mmol) were stirred
in ethanol (30 ml), followed by the addition of ammonium hydroxide
(30 ml). After stirring for 24 h at room temperature, the greyish-green
solid was precipitated. The precipitate was filtered and washed using
tetrahydrofuran and then the crude product was purified by recrystal-
lization with ethanol to yield an orange solid (0.27 g, 80%). 1H NMR
(500 MHz, CDCl3) δ 8.75 (d, J = 4.3 Hz, 2H), 8.73 (s, 2H), 8.69 (d, J =
7.9 Hz, 2H), 7.91–7.87 (m, 4H), 7.37 (dd, J = 6.5, 4.8 Hz, 2H), 7.05 (d, J
= 8.8 Hz, 2H), 3.91 (s, 3H). ESI HRMS (mass m/z): 340.1435 [M+ + H]
(calculated: 340.1444).
2.1. Materials and instruments
Reagents and solvents used in the synthesis and characterization
were purchased from J&K, Aladdin, Energy Chemical, Admas and
Bidepharm, and used without further purification if not specified. The
spectroelectrochemistry tests (optical contrast, switching time) were
investigated by Shimadzu UV-1800 spectrophotometer (Shimadzu,
Japan) integrated with the CHI660E electrochemical workstation in a
three-compartment system containing 0.1 M Bu4NClO4 in acetonitrile
solution. The morphology of films was tested using a Hitachi S-4800
scanning electron microscope (Hitachi, Japan). The structure investi-
gation of the synthesized compounds were recorded by AVANCE III HD
NMR (Bruker, Switzerland) and autoflex maX MALDI-TOF(TOF)
(Bruker, Switzerland).
Synthesis of tris(4’-(4-bromobutoxy)-[1, 1′-biphenyl]-4-yl)amine (5)
Compound 4 (0.34 g, 1 mmol) and pyridine hydrochloride (2.3 g, 20
mmol) were added into a 10 ml reaction tube. The reaction mixture was
heated up to 180 ◦C and stirred under N2 for 24 h. After cooling to room
temperature, the reaction mixture was poured into deionized water (10
ml) and filtered. The residue was washed using deionized water and
dried to yield a brown solid (0.1 g, 30%). 1H NMR (500 MHz, DMSO‑d6)
δ 8.91–8.84 (m, 4H), 8.79 (s, 2H), 8.32–8.25 (m, 2H), 7.91 (d, J = 8.6
Hz, 2H), 7.78–7.69 (m, 2H), 7.00 (d, J = 8.7 Hz, 2H). ESI HRMS (mass
m/z): 326.1294 [M+ + H] (calculated: 326.1288).
2.2. Synthesis of ligand
Synthesis of tris(4′-methoxy-[1, 1′-biphenyl]-4-yl)amine (1)
Tri (4-bromophenylamine) (0.48 g, 1 mmol) and p-methoxypheny
lboric acid (0.53 g, 3.5 mmol) were stirred in ethylene glycol diethyl
ether (30 ml), followed by the addition of tetrakis (triphenylphosphine)
palladium (0.12 g, 0.1 mmol). The reaction mixture was quickly heated
to reflux and stirred in N2 for 24 h. After cooling to room temperature,
the reaction mixture was poured into 100 ml deionized water and
extracted with dichloromethane. The organic phase was dried by mag-
nesium sulfate and evaporated. The crude product was purified by col-
umn chromatography on a silica gel with dichloromethane/hexane (1:3,
v/v) to yield a white solid (0.5 g, 90%). 1H NMR (500 MHz, CDCl3) δ
7.54 (d, J = 8.8 Hz, 6H), 7.49 (d, J = 8.7 Hz, 6H), 7.23 (d, J = 8.7 Hz,
6H), 6.99 (d, J = 8.8 Hz, 6H), 3.87 (s, 9H). ESI HRMS (mass m/z): found:
564.2518 [M+ + H] (calculated: 564.2533).
Synthesis of tris(4’-(4-(4-([2,2’:6′,2′′-terpyridin]-4′-yl)phenoxy)butoxy)-
[1,1′- biphenyl]-4-yl)amine (TBT)
Compound 3 (0.92 g, 1 mmol) and compound 5 (1.3 g, 4 mmol) were
stirred in N-dimethylformamide (30 ml) under N2, followed by the
addition of potassium carbonate (0.62 g, 4.5 mmol). The reaction
mixture was heated up to 80 ◦C and stirred under N2 for 24 h. After
cooling to room temperature, the reaction mixture was poured into
deionized water (100 ml) and filtered. The residue was washed using
ethyl alcohol and dried to yield a brown solid (0.58 g, 35%). 1H NMR
(500 MHz, CDCl3) δ 8.84–8.77 (m, 12H), 8.75 (d, J = 8.0 Hz, 6H),
8.01–7.91 (m, 12H), 7.54 (d, J = 8.7 Hz, 6H), 7.49 (d, J = 8.6 Hz, 6H),
7.46–7.40 (m, 6H), 7.22 (d, J = 8.6 Hz, 6H), 7.06 (d, J = 8.6 Hz, 6H),
7.00 (d, J = 8.7 Hz, 6H), 4.20–4.10 (m, 12H), 2.12–2.02 (m, 12H).
MALDI-TOF MS (mass m/z): 1659.8082 [M] (calculated: 1659.8073).
13C NMR (600 MHz, CDCl3) δ 160.04, 158.20, 156.03, 155.47, 149.87,
148.80, 146.30, 137.17, 135.14, 130.47, 128.58, 127.71, 127.40,
124.37, 123.87, 121.57, 118.51, 114.87, 67.59, 26.06. Melting point:
110 ± 5 ◦C.
Synthesis of 4′, 4′′′, 4′′′’’-nitrilotris(([1, 1′-biphenyl]-4-ol)) (2)
Compound 1 (0.56 g, 1 mmol) was stirred in dichloromethane (30
ml), followed by the addition of a boron tribromide solution of
dichloromethane (1 mol/L, 3 ml, 3 mmol) dropwise. After the reaction
mixture was stirred at room temperature for 12 h, the reaction mixture
was poured into deionized water (100 ml) and extracted with
dichloromethane. The organic phase was dried by magnesium sulfate
and evaporated. The crude product was purified by column chroma-
tography on a silica gel with dichloromethane to yield a white solid
(0.42 g, 80%). 1H NMR (500 MHz, DMSO‑d6) δ 9.49 (s, 3H), 7.54 (d, J =
8.7 Hz, 6H), 7.47 (d, J = 8.6 Hz, 6H), 7.10 (d, J = 8.6 Hz, 6H), 6.83 (d, J
= 8.8 Hz, 6H). ESI HRMS (mass m/z): 522.2053 [M+ + H] (calculated:
522.2064).
2.2.1. Preparation of the films TBT-Fe
The 50 ml of aqueous solution of Fe(BF4)2⋅6H2O (50 mM) was added
into a watch glass and then ITO glass was also put into the solution. A
0.10 mM solution of TBT was prepared by dissolving TBT (1.7 mg,
0.001 mmol) in 10 ml dichloromethane solution. The solution of TBT
(0.5 ml) was injected onto the glass surface with a syringe. The film
emerged at the interface between aqueous solution and dichloro-
methane solution along with the dichloromethane solvents volatilized,
and attached onto the ITO glass eventually. The ITO with the film
attached would be immersed into deionized water, ethyl alcohol and
dichloromethane in sequence to remove Fe(BF4)2 and TBT.
Synthesis of 4’-(4-methoxyphenyl)-2, 2’: 6′, 2′′-terpyridine (3)
1, 4-Dibromobutane (1.3 g, 6 mmol) and potassium carbonate (0.48
g, 3.5 mmol) were stirred in acetone (30 ml), followed by the addition of
compound 2 (0.52 g, 1 mmol). The reaction mixture was heated up to
reflux and stirred under N2 for 24 h. After cooling to room temperature,
the reaction mixture was poured into 100 ml deionized water and
extracted with dichloromethane. The organic phase was dried by mag-
nesium sulfate and evaporated. The crude product was purified by
3. Results and discussion
The synthesis route of the star-shaped molecule TBT is shown in
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Y. Kuai et al.
Dyes and Pigments 194 (2021) 109623
Scheme 1. The synthesis route of ligand molecule TBT.
Fig. 1. A) The prepared TBT-Fe film adhering on the ITO glass. B) The photo of flexible film finally generated in water via liquid-liquid interfacial self-assembly
method. C) The scheme of preparation process of liquid-liquid interfacial self-assembly method and the molecular structure of the metallo-supramolecular film.
Scheme 1 and the experimental detail for the synthesis has been
described in the experimental part. NMR and mass spectral character-
ization prove the successful acquisition of the molecular structure of
TBT. The corresponding metallo-supramolecular film of TBT-Fe was
then prepared by the liquid-liquid interfacial self-assembly method at
the interface between the aqueous phase of Fe(BF4)2 in water and the
organic phase of TBT in dichloromethane. Due to the very good solu-
bility of TBT, the insoluble film of TBT-Fe could not be formed at the
interface initially. The preparation method was improved by injecting
the dichloromethane solution (0.5 ml) of TBT (0.1 mmol/L) to the ITO
glass surface which had been put in the aqueous solution of Fe(BF4)2 (50
mmol/L) as shown in Fig. 1c. The TBT-Fe film would appear at the
interface between aqueous and organic phases gradually, and eventually
adhere on the surface of ITO along with the dichloromethane solvent
totally volatilized after several days. By this method, TBT-Fe films were
obtained directly on the surface of ITO glass without the additional
transference process (Fig. 1a).
It was surprising that the final TBT-Fe films exhibited highly flexible
Fig. 2. The SEM image of body (a) and edge (b) of the TBT-Fe film on ITO glass.
3

Y. Kuai et al.
Dyes and Pigments 194 (2021) 109623
Table 1
The EDS data of the TBT-Fe films.
element
C
N
O
F
Si
Fe
In
Sn
Atomic percent
63.54%
1.19%
11.74%
5.61%
7.81%
0.20%
8.16%
1.12%
Fig. 4. The cycle voltammogram curve of the TBT-Fe films with the applied
potential between 0 and 1.2 V at a scanning rate of 0.1 V sꢀ 1 with a three-
compartment system containing 0.1 M Bu4NClO4 in acetonitrile solution as
the electrolyte.
Fig. 3. The UV–Vis absorption spectra of TBT-Fe film and TBT ligand
in solution.
property, which could be dragged and pulled by tweezers on the surface
of aqueous solution without easily down as shown in Fig. 1b. Consid-
ering the flexible alkyl chain in the ligand structure of TBT and in
comparison to the reported relatively fragile metallo-supramolecular
film with a rigid ligand structure [40], the flexibility of TBT-Fe was
supposed to be mainly ascribed to the introduction of alkyl chains. This
indicated that it is possible to obtain the corresponding property we
desired for metallo-supramolecular films by modifying the ligand
structure.
The surface morphology of the TBT-Fe films adhering to the ITO
glass was further evaluated by scanning electron microscopy (SEM). It
was found that the TBT-Fe film showed a smooth surface morphology as
shown in Fig. 2a. Some small round pits were observed at the surface of
film, and it was thought to be caused by the bubbles owing to the
volatilization of dichloromethane solvent in the film forming process. As
shown in Fig. 2b, the multi-layer film structure was observed at the edge
of TBT-Fe films, which might indicate the layer growth model of
metallo-supramolecular film, corresponding with the growth of film as
the volatilization of dichloromethane solvents gradually. Energy
dispersive spectroscopy (EDS) was also used to evaluate the composition
of TBT-Fe films and the results were listed in Table 1. It was found that
the atomic percentages of N and Fe were measured to be 1.19% and
0.20% respectively. The calculated ratio of N/Fe was nearly 6/1, very
close to the ideal ratio of 6.6/1 in the metal complex structure of TBT-Fe
films. These results indicated the successful fabrication of TBT-Fe films
through the liquid-liquid interfacial self-assembly of Fe (II) metal ions
and TBT ligand molecules. IR spectrum showed the peak at about 1584
Fig. 5. UV–vis absorption spectra of the TBT-Fe films with the applied po-
tential from 0 V to 1.2 V vs Ag/AgCl in a solution of acetonitrile containing 0.1
M Bu4NClO4. Insets are the photos of TBT-Fe films with the applied potentials at
0 V vs Ag/AgCl and 1.2 V vs Ag/AgCl.
with an obvious redshift of about 220 nm in comparison to that of TBT
ligand, which should be attributed to the metal-to-ligand charge transfer
transition of the Fe (II)-terpyridine group and well consistent with those
data of the reported Fe (II)-terpyridyl coordination compounds. Thus the
UV spectra indicated the successful fabrication of TBT-Fe films through
the liquid-liquid interfacial self-assembly of Fe (II) metal ions and TBT
ligand molecule.
cmꢀ 1 which belongs to the C C stretching vibration of TBT which
–
–
shifted to 1602 cmꢀ 1 in TBT-Fe, indicating that terpyridyl ligand is
coordinated to the metal ion. In addition, the peak at around 1090 cmꢀ 1
should be attributed to BFꢀ4 [30].
The cycle voltammogram curve of TBT-Fe films was carried out in a
three-compartment system containing the ITO glass with TBT-Fe films
as the working electrode, Ag/AgCl as the reference electrode, platinum
wire as the counter electrode, and 0.1 M Bu4NClO4 in acetonitrile so-
lution as the electrolyte. As shown in Fig. 4, there were two pairs of
redox peaks at about 0.9/0.75 V and 1.2/1.0 V, respectively, which
The UV–Vis absorption spectra of TBT-Fe films were also charac-
terized as shown in Fig. 3. A stinging absorption peak at about 570 nm
and a wide absorption peak at about 350 nm were observed. TBT ligand
exhibited an obvious absorption peak at about 350 nm in the UV–Vis
absorption spectra. It was obvious that the absorption peak at 570 nm in
the UV–Vis absorption spectra of TBT-Fe films was newly generated
4

Y. Kuai et al.
Dyes and Pigments 194 (2021) 109623
Fig. 6. A) Optical contrast, response time of b) coloring and c) discoloring of the TBT-Fe films by applying the repeated step-potential with 0 V and 1.2 V vs Ag/AgCl
at 570 nm.
should be attributed to the redox behavior of central triphenylamine and
Fe (II)-terpyridyl groups respectively. In comparison to the similar Fe
(II)-terpyridyl derivant which had reported [40,41], the redox potential
of Fe (II)-terpyridyl groups of TBT-Fe film was semblable, while that of
triphenylamine group was lower obviously, which might be ascribed to
the breaking in the linkage of the electron-withdrawing Fe (II)-terpyr-
idyl groups to the triphenylamine group owing to the alkyl chain.
The electrochromic properties of TBT-Fe films were determined by
spectroelectrochemical experiments. As shown in Fig. 5, the TBT-Fe
films displayed a purple color in the neutral state at 0 V, with the
maximum absorption peak located at about 570 nm. When the applied
voltage of TBT-Fe films was increased from 0 V vs Ag/AgCl to 1.0 V vs
Ag/AgCl, a new and wider absorption peak appeared in the range of
700–1100 nm in the absorption spectra, which was consistent with the
absorption peak of oxidized triphenylamine groups according to the
reported literature. It further proved that the redox peaks at 0.9/0.75 V
vs Ag/AgCl in the cyclic voltammetry curve was attributed to that of the
triphenylamine group in the TBT-Fe films. The film color did not change
much at 1.0 V vs Ag/AgCl due to the change of absorption almost located
at the range of invisible spectral range. When the applied voltage was
further increased from 1.0 to 1.2 V vs Ag/AgCl, the absorption peak of
TBT-Fe films at 570 nm is reduced obviously and almost disappears
finally, accompanied with the film color changed from original purple
color in the neutral state to yellow-green color in the oxidized state.
Such a transformation of absorption spectra was very similar to that of
the reported coordinated terpyridine-Fe (II) groups [30], which proved
that the redox peak at 1.2 V/1.0 V vs Ag/AgCl in the cyclic voltammetry
curve was supposed to be attributed to the redox behavior of the coor-
Fig. 7. (A) The structure of the solid-state device. (b) UV–vis spectrum of the
dinated terpyridine-Fe (II) group in the TBT-Fe films. Therefore, it is
solid-state device with the applied potential from 0 V to 3.0 V. Insets are the
obvious that the redox activity of the TBT-Fe films was composed of two
photos of the solid-state device at 0 V and 3.0 V.
redox processes, including the terpyridine-Fe (II) group and the central
triphenylamine group, both of which promote the electrochromic pro-
A solid-state electrochromic device using TBT-Fe films as the elec-
cess of the TBT-Fe films to turn from purple to yellow-green color.
trochromic layer was fabricated with a double layer device structure as
The optical contrast and response time of TBT-Fe films were also
shown in Fig. 7a. Solid-state electrolyte was prepared from poly (methyl
measured under the repeated step voltages between 0 V vs Ag/AgCl and
methacrylate) (PMMA) and lithium perchlorate, and it was sandwiched
1.2 V vs Ag/AgCl with the residence time set as 10 s and 15 s, respec-
between a ITO glass adhering with TBT-Fe films and another blank ITO
tively. As shown in Fig. 6a, the optical contrast of the TBT-Fe films at
glass and further sealed to form the solid-state electrochromic device.
570 nm is estimated to be about 20%. The switching time, which is
The electrochromic device displayed an original purple color at 0 V
calculated as the time required to achieve 95% of the full switch of the
which is in the neutral state, and the maximum absorption peak exists at
transmittance, was estimated to be about 14.3 s for coloring and 7.3 s for
about 570 nm (Fig. 7b), which is the same as that of TBT-Fe film. When
discoloring as shown in Fig. 6b and c, respectively. Compared with the
the applied voltage was increased to 3 V, a new and wider absorption
response time of about 1 s of the previously reported TPA-TPY-Fe films,
peak appeared at 700–1100 nm, and at the same time, the original ab-
the response time is obviously larger in the case of TBT-Fe films. This is
sorption peak at 570 nm decreased in intensity, accompanying with the
ascribed to the introduction of alkyl chain which could break the
device color changed from purple to yellow-green (Fig. 7b inset). The
conjugation of ligand structure and thus decrease the charge trans-
changes in colors and UV–vis spectra in electrochromic device were the
porting ability of TBT-Fe films. In addition, the coloration efficiency
same as those of TBT-Fe films measured in the electrochemical cell
(CE) was also calculated with the equation CE = ΔOD/Qd, and ΔOD =
system.
log (Tc/Tb), where Tc is the transmittance of oxidation, Tb is the trans-
mittance of the neutral state, Qd is the injected electronic charge in unit
4. Conclusion
area. The CE of TBT-Fe is 172.82 cm2/C, which is close to most of other
electrochromic materials reported [17,42].
A flexible metallo-supramolecular film, a terpyridine-Fe (II) complex
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Dyes and Pigments 194 (2021) 109623
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–liquid interfacial self-assembly method. The resulting metal-
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flexible property of the final metallo-supramolecular electrochromic
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Yu Kuai: Synthesis, characterization, graphing, Formal analysis,
Writing – review & editing. Tao Yang: Participate in synthesis. Feiya
Yuan: Data curation. Yujie Dong: Supervision, Writing – review &
editing, Funding acquisition. Qingbao Song: Formal analysis. Cheng
Zhang: Funding acquisition. Wai-Yeung Wong: Funding acquisition.
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Thanks are given to the financial supports from National Natural
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52073242) and Zhejiang Provincial Natural Science Foundation of
China (LY19E030006, LQ19E030016). W.-Y. W. would also like to thank
the Hong Kong Research Grants Council (PolyU 153058/19 P), Hong
Kong Polytechnic University (1-ZE1C) and The Endowed Professorship
in Energy from Ms. Clarea Au (847 S) for the financial support.
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