Electrochromic/electrofluorochromic poly(urea-urethane) bearing oligoaniline and tetraphenylethylene groups: Synthesis, characterization, and H2O2 visualized determination

Article abstract of DOI:10.1016/j.dyepig.2021.109594

The elegant electroswitchable color/emission properties of electrochromic/electrofluorochromic dual-functional materials motivates the exploration of their new applications. In this work, a new poly (urea-urethane) was synthesized via nucleophilic copolym

Full text of DOI:10.1016/j.dyepig.2021.109594

Dyes and Pigments 194 (2021) 109594
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Electrochromic/electrofluorochromic poly(urea-urethane) bearing
oligoaniline and tetraphenylethylene groups: Synthesis, characterization,
and H2O2 visualized determination
,
*
Yingchao Zhanga, Yunfei Xiea, Mingjuan Zhoua, Erik B. Berdab, Danming Chaoa
a College of Chemistry, Jilin University, Changchun, 130012, PR China
b Department of Chemistry and Materials Science Program, University of New Hampshire, Durham, NH, 03824, United States
A R T I C L E I N F O
A B S T R A C T
Keywords:
The elegant electroswitchable color/emission properties of electrochromic/electrofluorochromic dual-functional
materials motivates the exploration of their new applications. In this work, a new poly (urea-urethane) was
synthesized via nucleophilic copolymerization of electroactive oligoaniline derivative, solid-emissive tetraphe-
nylethylene groups, and alkyl isocyanate. The resultant poly (urea-urethane) exhibited good electroactivity and
desirable aggregation-induced emission properties. High-performance electrochromic/electrofluorochromic
behavior had been disclosed with a high optical contrast ratio of ΔT = 50.4%, a moderate fluorescence on/off
ratio of 10.5, and high coloration efficiency of 503 cm2/C at 768 nm. A reflective/emissive dual-mode display
device had also been manufactured based on the resultant poly (urea-urethane) and charge-balancing V2O5,
exhibiting a reversible color change and tunable fluorescence conversion upon the electric stimulus. Further-
more, this polymer showed an interesting color/fluorescence response to H2O2, due to the linkage mechanism
between its redox states and optical properties. The spray-coated poly (urea-urethane) test strips were employed
in visualized dual-determination of H2O2 with gradual color change from gray to dark green, along with an
obvious fluorescence change from light blue to dark, which displays easy operation and rapid detection.
AIE
Oligoaniline
Electroactive
Electrochromic
Electrofluorochromic
1. Introduction
durability [11–13]. To eliminate the aggregation-caused quenching ef-
fect, some high solid fluorescence-efficiency tetraphenylethylene (TPE)
Electrochromic/electrofluorochromic (EC/EFC) dual-functional
materials have attracted great attention and interest from researchers
because of their elegant electroswitchable color/emission feature [1–3].
Thereinto, the polymeric materials exhibit the tremendous advantage of
flexible molecular design and engineering, tunable photoelectric prop-
erties, as well as facile large-scale processability [4–6]. Hence, a series of
EC/EFC dual-functional polymers have been prepared through multi-
farious synthetic strategies. For example, several novel functional
monomers integrated propeller structural triphenylamine and
high-efficiency fluorophore have been designed to prepare EC/EFC
dual-functional polymers, yielding a rational color/emission switching
behavior under electric stimuli [7–10]. The oligoanilines have also been
utilized as electroactive units to construct EC/EFC polymeric systems,
due to their low redox potentials and reversible electroactivity. The
resultant polymers exhibit improved electroswitchable color/emission
behavior with low energy consumption and well electrochemical
derivatives have been involved in the dual-functional polymeric archi-
tecture [14–20]. As is expected, high-performance EC/EFC properties
with approving fluorescence on/off ratio are revealed from these
resultant TPE-based materials. Moreover, a few fluorescent quantum
dots (CdS dots, carbon dots) were adopted to manufacture polymer
composites, which show high fluorescence contrast, fast response time,
and new functions such as light-induced coloration, electro-
chemiluminescence, and photocurrent responsiveness [21–23].
By means of multifarious synthetic tactics, the improvement of EC/
EFC performance has received a relatively matured development.
However, the application exploit of these EC/EFC polymers is still an
infant. Only a few practicality explorations have been revealed, such as
anti-counterfeiting inks [24], reflective/emissive dual-mode displays
[25], energy storage level color/fluorescence dual-indicating super-
capacitor [26], smart sensors for cyanide anions and cancer cell surface
glycoprotein [27,28]. Nevertheless, more effort should be devoted to the
* Corresponding author.
E-mail address: chaodanming@jlu.edu.cn (D. Chao).
https://doi.org/10.1016/j.dyepig.2021.109594
Received 1 June 2021; Received in revised form 21 June 2021; Accepted 24 June 2021
Available online 25 June 2021
0143-7208/© 2021 Elsevier Ltd. All rights reserved.

Y. Zhang et al.
Dyes and Pigments 194 (2021) 109594
further application expansion and deep practical exploration of EC/EFC
dual-functional polymers.
7.3 Hz, 1H), 6.64–6.58 (m, 4H), 6.34 (d, J = 8.4 Hz, 2H), 5.03 (s, 4H).
13C NMR (101 MHz, DMSO‑d6): δ 162.08, 157.18, 145.93, 145.93,
145.70, 145.65, 141.00, 138.92, 137.74, 136.41, 135.06, 131.41,
129.90, 121.51, 120.84, 120.65, 119.85, 119.34, 118.44, 118.09,
117.80, 115.87, 114.94, 114.79, 109.06. HRMS (ESI): m/z: calcd for [M
ꢀ H]+ C43H36N6O3: 683.2765, found: 683.2769. Tm (m.p. by DSC):
156 ◦C.
In this paper, a novel poly (urea-urethane) (PUU) bearing electro-
active oligoaniline and AIE-active TPE groups via nucleophilic copoly-
merization reaction. The EC and EFC performance of the resultant PUU
was disclosed through the electrochemical workstation coupled with a
UV–vis spectrometer and/or fluorescence spectrometer. In addition, an
improvised test strip featuring EC/EFC was manufactured to achieve
sensitive monitoring of H2O2. The visualized color/fluorescence dual-
determination of H2O2 was accomplished as a result of the redox reac-
tion (between oligoaniline and H2O2) and the energy transfer (between
oligoaniline and TPE).
2.2.3. Synthesis of PUU
DEDO (219 mg, 0.6 mmol), TA-NH2 (618 mg, 1.2 mmol), HMDI
(301 mg, 1.8 mmol), and 6 mL of DMF were added in a dry round-
bottom flask under N2 atmosphere. The random copolymerization was
carried out at 60 ◦C for 36 h, followed by precipitation successively from
ethanol and DCM solution, yielding 1.02 g of PUU for light gray powder
with 90% yield. 1H NMR (400 MHz, DMSO‑d6): δ 9.40, 9.35 (–CONH–),
8.47, 8.34 (–NHCONH–), 7.78, 7.71 (–NH– in the TA-NH2), 7.51–6.41
(mH, Ar–H), 6.13, 5.75 (–NHCONH–), 4.02–3.62 (mH, –CH2-),
3.10–2.89 (mH, –CH2-), 2.76–2.65 (mH, –CH2-). FTIR (KBr, cmꢀ 1): 3426
2. Experimental section
2.1. Materials
Benzophenone, bis(4-hydroxyphenyl)methanone, titanium tetra-
chloride (TiCl4), zinc powder (Zn), hexamethylene diisocyanate (HMDI)
were purchased from Aladdin. Hydrogen peroxide (H2O2, 30% mass
fraction) were obtained from Sinopharm Chemical Reagent Co., Ltd.
–
–
–
(
νN-H), 2927 (νC-H of aryl groups), 1651 (
ν
O), 1514, and 1442 (ν
–
C
C
of benzenoid rings), 1098 (νC-N). Gel permeation chromatography (GPCC)
date: Mw: 130800, polydispersity index: 2.10.
•
Potassium carbonate (K2CO3), hydrazine monohydrate (N2H4 H2O),
polymethyl methacrylate (PMMA), propylene carbonate (PC), N,N′-
dimethylformamide (DMF), lithium perchlorate (LiClO4), dichloro-
methane (DCM) and tetrahydrofuran (THF) were purchased from En-
ergy Chemical. Other reagents and solvents were employed directly as
received from commercial sources. The indium tin oxide glass (ITO, 10
Ω/cm2) was obtained from Zhuhai Kaivo Optoelectronic Technology
Co., Ltd.
2.3. Fabrication of PUU/ITO electrode
The ITO substrates were cut into a square shape with a dimension of
3 × 3 cm2 or 1 × 5 cm2 for the electrochemical measurements (sheet
resistance = 10 Ω/cm2), which were ultrasonically cleaned with
toluene, acetone, alcohol, and ultrapure water for 30 min, respectively.
After dried with N2 flow, the ITO substrates were performed to hydro-
philization using Plasma Cleaner under O2 flow. Finally, the PUU/ITO
electrodes were manufactured through the drop-coating method using
2.2. Synthetic procedure
100 μ
L 3 mg/mL PUU DMF solution and following dried at 50 ◦C under
vacuum. The size of the PUU capacity was set at 1 cm2 (area) × 400 nm
2.2.1. Synthesis of 4,4’-(2,2-diphenylethene-1,1-diyl)diphenol (DEDO)
DEDO was synthesized by a common McMurry approach [29]. A
mixture of benzophenone (4.00 g, 21.97 mmol), bis(4-hydroxyphenyl)
methanone (4.70 g, 21.97 mmol), Zn power (5.70 g, 88 mmol), and
150 mL anhydrous THF was mixed into a two-necked flask, and cooled
down to ꢀ 78 ◦C. Then drop-by-drop addition of 9.7 mL TiCl4 (87.8
mmol) into the above mixture was performed under nitrogen atmo-
sphere. The solution was kept at ꢀ 78 ◦C under constant stirring for 30
min and further warmed to room temperature (RT) for another 8 h. It
(thickness) measured by a profilometer.
2.4. Manufacture of PUU test strips
A typical procedure to fabricate test strips based on PUU is stated as
follows. The qualitative filter paper was cut with a dimension of 1 × 5
cm2. Then the top of the filter paper strip (1 × 1 cm2 area) was spray-
coated with PUU through a high-pressure spray gun using 5 mg/mL
PUU DMF solution. The spraying time was fixed at 5 s. The resultant test
strips would be dried with an N2 flow and then sealed storage for the
following testing analyses of H2O2.
◦
was continued to reflux at 70 C for an additional 15 h. After cooling
down, the reaction was quenched by the addition of a saturated K2CO3
solution. The mixtures were then extracted with DCM to remove any
soluble hydrocarbons, followed by washing with 0.1 M HCl solution and
drying with Na2SO4. After the solvent was removed by rotary evapora-
tion, the raw product was purified by column chromatography (SiO2,
DCM/petroleum ether, V/V = 1:3–1:5) to render DEDO as pale yellow
solid (6.80 g, 85% yield). FTIR (KBr, cmꢀ 1): 1607, 1594, 1505, 1441
2.5. The H2O2 visualized determination with PUU test strips
The as-fabricated PUU test strips were immersed into the H2O2 so-
lution (pH = 1, adjusted by HCl solution) for 30 s and dried under the air
atmosphere for another 30 s. The change of color and fluorescence was
collected by the spectrum instruments as well as a digital camera.
(-C C- stretch in the aromatic region), 3311 (-OH stretch). 1H NMR
–
–
(400 MHz, DMSO‑d6): δ 9.30 (s, 2H, –OH), 7.14–7.05 (m, 6H), 6.95–6.90
(m, 4H), 6.73 (d, J = 8.6 Hz, 4H), 6.48 (d, J = 8.6 Hz, 4H). 13C NMR
(101 MHz, DMSO‑d6): δ 156.34, 144.65, 141.07, 138.11, 134.56,
132.51, 131.24, 128.23, 126.44, 115.03. HRMS(ESI): m/z: calcd for
[M+H]+ C26H21O2: 365.1536, found: 365.1531. ΦF = 28.25%. Tm (m.p.
by DSC): 195 ◦C.
2.6. Instrumentation
1H NMR and 13C NMR spectra of the synthetic molecules were
received on a Bruker Avance NEO 400 system (400 MHz) using
deuterated dimethyl sulfoxide (DMSO‑d6). All the chemical shifts were
presented in ppm using tetramethylsilane as the internal standard.
BRUKER VECTOR 22 Spectrometer was used to gather the Fourier-
2.2.2. Synthesis of 2,6-bis(4-aminophenoxy)-N-(4-(phenylamino)phenyl)
benzamide (TA-NH2)
TA-NH2 was synthesized by a series of oxidative coupling reaction,
amidation reaction, and nucleophilic substitution according to the
established method [30]. All the characterization data are presented as
follow. FTIR (KBr, cmꢀ 1): 3385 (-NH2 stretch), 1661 (amide group). 1H
NMR (400 MHz, DMSO‑d6): δ 10.28 (s, 1H), 7.78 (s, 1H), 7.73 (s, 1H),
7.65 (s, 1H), 7.58 (d, J = 8.9 Hz, 2H), 7.16 (dd, J = 10.4, 5.0 Hz, 3H),
6.98 (ddd, J = 16.5, 7.8, 4.8 Hz, 13H), 6.89–6.84 (m, 4H), 6.70 (t, J =
transform infrared spectra (FTIR) in the range of 4000–400 cmꢀ 1
.
High-resolution mass spectra (HRMS) signs were collected on the Bruker
Agilent1290-micrOTOF Q II. The thermal stability of PUU was measured
by thermogravimetric analysis (TGA) on PerkinElmer PYRIS 1 TGA in
the temperature range of 100–800 ◦C with a rate of 10 ◦C/min under N2
flow. Differential scanning calorimetric (DSC) analysis was carried out
on DSC821e at a scanning rate of 10 ◦C/min using 50 mL/min nitrogen
2

Y. Zhang et al.
Dyes and Pigments 194 (2021) 109594
flow for the melting point test. The transmittance and/or absorption
spectrum of PUU were monitored using UV–vis spectra on a UV-3101 PC
spectrometer (SHIMADZU). Photoluminescence (PL) spectra were
collected on an F97Pro fluorospectro photometer (Shanghai Lengguang
Co. Ltd., Shanghai, China). Fluorescence quantum yields (ΦF, tested by
using a calibrated integrating sphere) were determined using an Edin-
burgh FLS920fluorescence spectrophotometer. The data of CIE L*a*b*
were obtained from a high-quality portable colorimeter (Shenzhen 3
nhCo., Ltd., Shenzhen, China). The cyclic voltammetry (CV) and elec-
trochemical impendence spectroscopy (EIS) for PUU was collected on a
CHI 660E Electrochemical Workstation (CH Instruments, USA) using a
three-electrode electrochemical cell, which was constituted with an Ag/
AgCl reference electrode, a platinum counter electrode, and a PUU/ITO
working electrode.
aliphatic linkage has also been involved in the polymeric structure.
The 1H NMR and 13C NMR spectra of the as-synthesized monomers
(DEDO and TA-NH2) are presented in Fig. 1. The chemical shift at 9.3
ppm is assigned to the hydroxy groups of DEDO. The aromatic signals of
DEDO can be found from 6.47 ppm to 7.14 ppm. The characteristic
signals of amino groups of TA-NH2 appear at 10.28, 7.78, 7.73, 7.65,
and 4.13 ppm, and terminal amino groups at 5.03 ppm. In the 13C NMR
spectra, all the chemical shifts and splits of carbon groups could verify
their molecular structure well, respectively. Moreover, the FTIR spectra
were also utilized to characterize the molecular structure of the mono-
mers. Fig. 2a shows the characteristic vibration of –OH stretch at 3311
cmꢀ 1, and the skeleton vibration of the aromatic ring at 1607, 1594,
1505, and 1441 cmꢀ 1 for the DEDO monomer. In the FT-IR curve of TA-
NH2, the peak at 3385 cmꢀ 1 and 1661 cmꢀ 1 can be assigned to the
stretching vibration of –NH2 and amide groups. In addition, these
structures of DEDO and TA-NH2 were further accurately confirmed by
high-resolution mass spectrometry (HRMS) data.
3. Results and discussion
3.1. Synthesis and structure characterization
The polymeric structure of the as-prepared PUU was carefully
investigated through FT-IR spectrum, 1H NMR spectrum, and GPC
measurement. The FTIR spectrum in Fig. 2a shows the characteristic
absorption around 3426 cmꢀ 1, corresponding to the N–H stretching
vibration, and around 2927 cmꢀ 1 due to the C–H stretching vibrations of
aryl groups. The vibration around 1651 cmꢀ 1 is attributed to the
As shown in Scheme 1, the AIE-active DEDO was synthesized
through McMurry coupling reaction catalyzed by Zn–TiCl4, which was
used as a general tactic to prepare AIE compounds. Scheme 1 also dis-
plays the synthesis of novel poly (urea-urethane) via nucleophilic
copolymerization of DEDO, TA-NH2, and HMDI. In this smart electro-
optical polymeric architecture, the TPE-derived DEDO unit is held
accountable for the membrane-state emission, and tetraaniline is uti-
lized as an electro-control unit attributed to its low redox potentials and
excellent reversibility. To suppress the charge transfer effect, an
–
–
stretching vibration of carbonyl groups. The stretching vibration of C
C
groups in the benzene rings is observed at 1514 and 1442 cmꢀ 1. The
characteristic stretching vibration of C–N appears at 1098 cmꢀ 1. Fig. 2b
illustrates the 1H NMR spectrum of the as-prepared PUU. The peaks of
9.40, 9.35 ppm according to the –CONH–, the peaks of 8.47, 8.34, 6.13,
Scheme 1. Synthetic procedure for AIE-active DEDO and PUU.
3

Y. Zhang et al.
Dyes and Pigments 194 (2021) 109594
Fig. 1. (a) 1H NMR spectra and (b) 13C NMR spectra of DEDO; (c) 1H NMR spectra and (d) 13C NMR spectra of TA-NH2.
Fig. 2. (a) FTIR spectra of DEDO, TA-NH2, and PUU. (b) 1H NMR spectra of PUU. (c) TGA curve of the PUU under N2 atmosphere.
5.75 ppm were matched to –NHCONH– in carbamide, the signs of 7.78,
7.71 ppm were assigned to –NH– in the TA unit. Furthermore, the PUU
displays a general number-average molecular weight of 130800 with an
acceptable polydispersity index of 2.10.
The obtained PUU exhibits good solubility in polar solvents of DMF,
DMSO, NMP, and DMAc, due to its large pendant groups and flexible
aliphatic segments. Furthermore, the thermostability of PUU was eval-
uated by TGA. The resulting curve in Fig. 2c reveals that there is no
weight loss before 225 ◦C. The 5% degradation is observed at the tem-
The excellent solubility is beneficial to the processibility of the
polymeric materials towards large-scale production in the application.
◦
perature of 289 C, associated with the gradual decomposition of the
Fig. 3. (a) UV–vis absorption and PL spectra of PUU DMF solution and PUU film. (b) FL spectra of PUU in DMF-water mixture solution with diverse solvent ratio
(inset: the images of fluorescence variation in different proportion solutions).
4

Y. Zhang et al.
Dyes and Pigments 194 (2021) 109594
polymeric main chain. The overall thermal stability of PUU is quite
satisfactory in the actual application scenario in the future.
integrated four-electron molecular transition of tetraaniline segments
[33]. This simplified redox process of PUU material should be attributed
to its low content of electroactive tetraaniline segments and fast scan-
ning speed. Moreover, the CV curves remain stable after 200 cycles,
benefiting from the high stability of PUU and good anchoring strength
with the ITO substrate during the electrochemical measurements. Then
the electrochemical activity of PUU was evaluated at different scanning
speeds from 10 to 100 mV/s (Fig. 4b). The peak currents increased
concomitantly with the elevated scanning rates, and a quasi-linear
relationship between the peak current and the square root of the
sweep rate further proves that a slow diffusion-controlled process
dominates the electrochemical behavior. ESI measurements were
applied to the PUU/ITO electrode for the conductivity test. The Nyquist
curve was fitted by the Randles type equivalent circuit model to assess
the electrical conductivity as shown in Fig. 4c. Charge transfer resistance
(Rct) estimated from the semicircle diameter in Nyquist plots was about
78 Ω and 110 Ω corresponding to the applied voltages of 1.0 V and 0 V,
respectively, indicating that the voltage-driven PUU/ITO electrode fa-
cilitates counterion diffusion in the electrolyte.
3.2. Photophysical properties
Photophysical properties of PUU solution and PUU film were studied
by UV–vis absorption and PL spectra as shown in Fig. 3a. The PUU ab-
sorbs the UV light with intense absorption maxima at λabs = 295 nm and
332 nm for its solution and film states, respectively, which were
assigned to the π → π* transition of the aromatic zone in AIEgens and TA-
NH2. The obvious 37 nm red-shifted for the PUU film should be
attributed to tight packing in the solid aggregation state. Moreover,
π-π
the PUU film is a highly fluorescent material showing intense emission
in the blue region at λPL = 436 nm, whereas almost no fluorescence
emission is observed in its solution state. The absolute fluorescence
quantum yield of PUU film was measured to be 22.5%. It is obvious that
this semblable AIE performance of PUU should be ascribed to the DODE
groups. Hence the AIE behavior of PUU was further investigated by
mixing H2O as a poor solvent into the soluble DMF solution. The diverse
blue light emission of the resulting PUU DMF-H2O mixed solution with
various proportions was observed with naked eyes. As increasing water
content, the PUU aggregated to varying extent in the mixed system. A
concentration-dependent blue light emission behavior was observed for
PUU with the excitation light of 365 nm in Fig. 3b. The maximum
fluorescent around λPL = 436 nm was enhanced with higher H2O con-
tent. The respective photographs of enhanced blue emission were
recorded as the inset in Fig. 3b. The distinct AIE phenomenon could be
explained by the restriction of the intramolecular rotations mechanism
proposed by professor Tang [31]. The flexible intramolecular rotations
of TPE-analog units in the solution state dissipate the excited-state en-
ergy via the non-radiatively decay channel, while the restriction of free
rotations in the aggregate state efficiently refrains the dissipation path,
leading to the illustrious fluorescence emission. The intrinsic strong
fluorescence of AIE polymer would ensure high fluorescence on/off ratio
in the EFC process of PUU film.
3.4. Electrochromic performance
The spectroelectrochemical process was carried out to investigate
the optical modulation and color switch upon the driven voltage. The
PUU/ITO electrode was used as a working electrode in the spec-
troelectrochemical cell. Reversible and reliable color-skip was studied
by sequential transmittance variation with incremental potential from 0
V to 1.0 V with a retention time of 100 s. There is an overall dropping of
transmittance in the visible light band from 380 to 800 nm as shown in
Fig. 5a, along with an apparent improvement in the UV- region from
300 nm to 380 nm. To elucidate valence electron transitions, the cor-
responding absorbance variation was also obtained by the classic
Lamber-Beer law as follows:
A = lg I0/It = -lg T =
ε
bc
.(1)
where A represents absorbance, I0 represents the intensity of incident
light, It represents the intensity of transmitted light, T is the trans-
3.3. Electrochemical properties
mittance, ε is the molar absorption coefficient, b is the optical path and c
The reversibility and stability test of the PUU/ITO electrode was
evaluated by cyclic voltammetry firstly, which was carried out in a
three-electrode cell with PUU/ITO working electrode, Ag/AgCl refer-
ence electrode, and platinum wire counter electrode, respectively. The
polyaniline and its derivatives usually display two pairs of redox peaks
during the CV cycle, which indicates a typical two-step continuous two-
electron redox transition from leucoemeraldine base (LEB) to emer-
aldine base (EB), and from the EB to pernigraniline base (PNB) [32].
However, the resultant PUU exhibited only one pair of redox peaks at
0.51/0.25 V as shown in Fig. 4a. It would be speculated as an incorpo-
rated redox process containing LEB/EB and EB/PNB, indicating an
is the concentration. The resultant absorbance variation was plotted in
Fig. 5b. The absorption peak around 350 nm should be ascribed to π-π*
transition in the benzoid rings. While the absorption in the range of
400–800 nm could be assigned to the transitions between polaron and
π/π*. During this process, the PUU/ITO electrode switched from neutral
light yellow (0 V, L* = 26.38, a* = -0.33, b* = 0.49), to semi-oxidized
blue (0.6 V, L* = 19.07, a* = 2011, b* = -0.36), and finally to full
oxidized dark blue (1.0 V, L* = 18.02, a* = 3.10, b* = 0.04), respec-
tively (Fig. 5c). The rapid transformation of two oxidation doped states
in oligoaniline segments under an applied electric field facilitates the
heterochromatic changes well.
Fig. 4. (a) CV curves of the PUU/ITO electrode through the driving voltage from 0 V to 1.0 V, with the scanning speed of 100 mV/s (b) CV curves of the PUU/ITO
electrode with the gradient increasing scanning rate, the inset shows a linear correlation on the peak current of the redox with the square root of the scan rate. (c) EIS
of the PUU film with different voltages of 0 V and 1.0 V.
5

Y. Zhang et al.
Dyes and Pigments 194 (2021) 109594
Fig. 5. (a) Transmittance spectra and (b) absorbance spectra of PUU film under the applied potentials from 0 to 1 V in 0.1 M HCl solution. (c) Inset shows the color
photographs of PUU/ITO electrode at different potentials. (d) The cycling stability of transmittance changes of PUU/ITO electrode in spectrochronoamperometry
measurements. (e) The representative transmittance switching at 489 nm and 768 nm of PUU/ITO electrode under a step-voltage of 0 and 1.0 V. (f) Optical density vs
charge density curves of PUU/ITO electrode.
The optical contrast and switching behavior of PUU/ITO were
studied in the spectroelectrochemical cell by the chronoamperometry
technology, repeatedly switching between the applied potentials of 0 V
and 1.0 V with the retention time of 15 s, monitoring the optical
response at specified wavelengths (Fig. 5d). The optical contrast is
calculated from a relatively larger spectral change at 489 nm around
34% (ΔT1: changing from 75.8% to 41.8%) and at 768 nm around
50.4% (ΔT2: changing from 82.5% to 32.1%) between its bleaching and
coloring states. The responsiveness for the coloring/bleaching switching
was calculated to be 9.6 s/9.8 s and 8.2 s/7.8 s, respectively, as shown in
Fig. 5d, which was determined from the response time of 90% trans-
mittance fluctuation at 489 nm and 768 nm. The periodic contrast
response is shrunk markedly compared to that in prolonged voltage field
under square wave voltammetry, mainly attributed to its hasty residence
time in which the electron transfer or doping cannot reach saturation.
Subsequently, the cycling performance of spectrum fluctuation for PUU
film was presented in Fig. 5e. Applying the alternative potentials of 0 V
and 1.0 V with the residence time of 15 s, the PUU/ITO electrode ex-
hibits acceptable cycling performance after 200 cycles. It still retains
80.3% and 84.7% optical contrast at the respective wavelengths, indi-
cating the well electrochemical reversibility and stability of PUU film.
The strong hydrogen bond interaction between urethano/urea groups
and hydroxyl groups on ITO substrate, coupled with agile and reversible
redox nature in oligoaniline segments would enhance the charge
transfer rate in the interface effectively, which is favorable for the
improvement of electrochromic performance.
obtained from the slope of the quasi-linear curve was about 322 and 503
cm2/C at 489 nm and 768 nm, indicating a higher electron utilization
efficiency for the electroactive PUU compared to numerous classic EC
polymeric materials [9–13,22,23,34–36].
3.5. Electrofluorochromic performance
Considering the light-emitting performance of classical AIEgens in
aggregation state as well as the fluorescence quenching effect of
oxidized oligoaniline segment, we would study the EFC properties of
PUU integrated above two functions in the molecular design. It is ex-
pected extremely that the higher brightness AIEgens and electroactive
oligoaniline segments could also assemble a subtle EFC system. Above
all, the EFC performance of PUU was investigated by monitoring the
fluorescence fluctuation through these continuously driven voltages.
The PUU film gives bright blue emission, centered at 438 nm derived
from the localized emission of TPE unites in the neutral state as shown in
Fig. 6a, with a moderate fluorescence quantum yield of 22.5%. As the
applied voltage increases from 0.0 to 1.0 V with a retention time of 100
s, the emission of PUU film decreases gradually, almost resulting in 97%
fluorescence quenching (at 1.0 V) compared with its original emission
state at 0.0 V. The energy transfer between the quinone structures of the
oxidized oligoaniline segments and the excited state of the AIE-active
groups would be accountable for the effective fluorescence quenching
essence. The PL intensity could restore to its initial state when the
applied potential was changed to 0 V. The fluorescence switching
contrast ratio was calculated at about 41.7, which is better than previous
reports [11–13,22,23,26]. The large fluorescence on/off contrast of PUU
film could be ascribed to the effective solid-state emission of AIEgens
and high-efficiency electro-modulation of oligoaniline segments, as well
as restrained charge transfer effect through a nonconjugated aliphatic
chain structure. Furthermore, spectrochronoamperometry was carried
out to investigate the detail of EFC behavior for PUU. The
fluorescence-emission changes centered at 438 nm were detected
through alternative square-wave voltages of 0 and 1.0 V, with a reten-
tion time of 15 s. The on/off response speed was calculated around
9.1/9.2 s marked at 90% conversion of fluorescence intensity, shown in
magnified EFC switching curves in Fig. 6b. The fluorescence switching
In addition, coloration efficiency (CE) is a key parameter, defining
the charge utilization during the optical contrast change and thus
expressing the charge efficiency of EC materials widely. CE can be
determined according to the following eq (2):
CE = ΔOD/ΔQ = log(Tb/Tc)/ΔQ
.2
where ΔQ represents the transmissive charge density of the active region
of PUU/ITO, which can be calculated by corresponding I-t integral curve
from chronoamperometry experiment. Tb and Tc are the transmittance
values of bleached and colored states at a specified wavelength for a
square signal voltage. The curves of ΔOD vs charge density at 489 nm
and 768 nm were presented in Fig. 5f. The CE value of the polymer PUU
6

Y. Zhang et al.
Dyes and Pigments 194 (2021) 109594
Fig. 6. (a) Fluorescence emission of PUU film under diverse potentials from 0.0 to 1.0 V. (b) Magnified EFC switching cycles and switching times of PUU/ITO
electrode. (c) Fluorescent switching stability of PUU film monitored at 438 nm under alternative potentials of 0 and 1.0 V. (d) The optical images of EC/EFC dual-
mode device under daylight and UV light.
contrast ratio at the alternative voltages of 0 and 1.0 V declines to 10.5,
ascribed to its short residence time in spectrochronoamperometry
measurements. After 200 cycles, the PL switching process maintains an
87% modulation range of the original state, which demonstrates the
quite good switching durability of EFC performance in Fig. 6c.
Compared with other EC/EFC polymers bearing tetraphenylethylene
groups (Table 1), the resultant PUU demonstrates advanced electro-
optic behavior with lower onset oxidation potential, high coloration
efficiency, moderate EC contrast, and good electrochemical durability,
which greatly promote the application of the intelligent materials in the
optoelectronics filed.
electrolyte include PMMA, PC, and lithium perchlorate with a mass ratio
of 5:10:1. An electrophoretic deposited V2O5/ITO electrode was
employed as a counter electrode for charge balance during the electro-
chemical process. The as-assembled device reveals moderate CE of 265
cm2 Cꢀ 1 at 768 nm, an acceptable switching time of 10 s, a large optical
contrast of 90% in the visible region (489 nm and 768 nm), and a
fluorescence contrast ratio of 9.5. The optical image of reflective and
emissive mode was displayed in Fig. 6d. Thanks to the outstanding dual-
mode electro-optical feature, the prepared PUU material reveals great
application potential in smart chemosensors, intelligent displays, and
encrypted information devices.
Given the higher fluorescence on/off contrast ratio, good switching
durability, and low switching potentials of its EFC performance, as well
as good EC properties, a simple EC/EFC dual-mode device was fabri-
cated by PUU film as shown in Fig. 6d. The components of the gel
3.6. H2O2 visualized determination
H2O2 is an important signaling molecule in many diseases and is an
Table 1
The electro-optic properties of the PUU and reported polymers in the literatures.
Polymer
Ox potential
Cycli-cality
EC
EFC
Ref.
E
onset (V)
Contrast (%)
Tb/Tc (s)
CE (cm2Cꢀ 1
)
on/off
on/off
time (s)
contrast
PA-TPEa
0.62
0.31
1.0
100
100
10
–
6.7/1.2
2.04/1.45
1.5/4.0
–
2.6/0.8
1.8/1.1
8.2/7.8
127
–
64.7/4.9
8.46/0.9
–
417
–
[37]
PI5ab
87.9
36
–
[20]
ProDOT-TPEc
TPA–CN–TPEd
TPEOTPA-PAe
PA7f
–
64
[14]
1.6
300
200
300
200
–
385
7.1
42.1
82
[15]
0.6
39
3.1/1.1
0.4/2.9
9.1/9.2
[38]
0.35
0.2
–
[19]
PUU
50.4
503
41.7
This work
a
An electro-optic polyamide containing diphenylamine-tetraphenylethylene moiety.
A polyamides containing tetraphenylethylene unit and triphenylamine.
b
c
d
e
f
An alternating polymer bearing tetraphenylethylene and 3,3-bis((2-ethylhexyloxy)methyl)-3,4-dihydro-2H-thieno [3,4-b], [1,4]-dioxepine.
An aromatic polyamide with tetraphenylethene and triphenylamine moieties.
An electro-optic polymer with tetraphenylethylene and triphenylamine units.
A polymer containing tetraphenylethylene and tetraphenyl-p-phenylenediamine units.
7

Y. Zhang et al.
Dyes and Pigments 194 (2021) 109594
enzyme-catalyzed outcome [39]. Many enzymatic reactions, such as
xanthine and xanthine oxidase, will produce H2O2 in metabolism. Up to
now, many effective methods for determining H2O2 have been devel-
oped, among them, the colorimetric and fluorescent methods are more
practical owing to their fast responsiveness and simple operation
[40–43]. Whereas, the general method focuses on detection with the aid
of spectroscopic instruments in the solution state, so that the practicality
of visualization is ignored, and the results are susceptible to unexpected
factors of concentration of background, the polarity of the solvent, etc.
Herein, the fluorescence and colorimetric dual-mode visualization
method in form of membrane assay of H2O2 in our design may effec-
tively improve the test repeatability, remove the interference from the
background, which makes the detections more accurate and portable. To
elaborately investigate the dual-signal sensing of H2O2, the as-fabricated
PUU-based test strips were studied by means of spectro-analysis firstly.
The gradient increase of H2O2 content can cause a regular response of
both the UV–vis absorption spectra and the PL emission spectra as
shown in Fig. 7a and b. With the increase of H2O2 concentration from 0
mM to 20 mM, PUU was oxidized correspondingly along with the
stepped incremental of the absorption at 405 nm, 489 nm, 768 nm, and
gradually attenuate at 325 nm (Fig. 7a). Meanwhile, the appearance of
the PUU test strips altered from light gray to dark blue (Fig. 7d). The
color for different PUU test strips after the treatment of different H2O2
concentrations was quantified using the CIELAB colorspace, whose
values were collected and shown in Table 2. The extensive color index
changes further prove the reliability of color indication rigorously for
H2O2 test strips. Besides, the fluorescence intensity decreased gradually
with the increase of H2O2 concentration (Fig. 7b), ascribed to the fast
charge transfer effect between oxidized oligoaniline segments and lu-
minous AIEgens. The PL intensity for the PUU test strip and the H2O2
concentration showed a quasi-linear relationship ranging from 0 to 1
mM H2O2, which indicates that the portable test strips possessed
excellent fluorescent indicator credentials for the quantitative detection
of H2O2 (Fig. 7c). The appearance photos of the PUU test strips were
captured with the camera instantly, changed continuously from light
gray to light blue and dark blue at the maximum concentration of 20
mM H2O2. The blue fluorescence of these PUU test strips was weakening
evidently under radiation by UV lamp, which intuitively demonstrated
the application prospect of the test strips for H2O2 dual-mode detection
(Fig. 7d).
4. Conclusions
We have synthesized a novel electroswitchable color/emission dual-
functional electrochromic/electrofluorochromic poly (urea-urethane)
bearing AIE-active tetraphenylethylene unit and electroactive oligoa-
niline derivative. The approving AIE effect, high fluorescence contrast of
41.7, and good electrochemical durability in the EFC process, as well as
the desirable electrochromic performance with outstanding CE of 503
cm2/C, moderate switching speed, and a large optical contrast of 50.4%,
demonstrate that PUU was an excellent bifunctional EC/EFC material.
The assembled dual-functional device based on PUU and V2O5 also
demonstrated a subtle color/emission switching function. Moreover, the
PUU test strips exhibit outstanding color/fluorescence dual-mode
determination of H2O2 by the appearance changing from light gray to
dark blue gradient, along with fluorescence changing from light blue to
faint. Easy operation, low cost, and reliably visual distinguish could
impart this novel polymer to bright application prospects in H2O2 fast
determination. The dual-sign color/fluorescence test strips would
endow novel insights in the convenient and sensitive biological analysis
fields.
Fig. 7. (a) UV–vis absorption spectra and (b) PL emission spectra changes of the PUU test strips with different H2O2 concentrations. (c) The curve of H2O2 con-
centration vs fluorescence intensity of the PUU test strips. (d) The optical image change of the PUU test strips after treating with different concentrations of H2O2
(0–20 mM) under daylight and UV radiation.
8

Y. Zhang et al.
Dyes and Pigments 194 (2021) 109594
Table 2
Colorimetry of these PUU test strips via the oxidation of H2O2 with different concentrations in CIELAB space.
0
μM
200
μ
M
400
μ
M
600
μ
M
800
μ
M
1 mM
2 mM
5 mM
10 mM
20 mM
L*
a*
b*
26.01
ꢀ 0.69
ꢀ 0.23
18.99
3.76
13.82
7.19
1.58
17.56
3.92
0.18
16.64
3.79
0.53
18.06
2.47
0.07
17.84
2.78
0.18
18.64
2.16
15.67
5.69
0.83
13.15
5.82
2.63
ꢀ 0.05
ꢀ 0.13
[16] Lin HT, Huang CL, Liou GS. Design, synthesis, and electrofluorochromism of new
triphenylamine derivatives with AIE-active pendent groups. ACS Appl Mater
Interfaces 2019;11(12):11684–90.
CRediT author statement
Yingchao Zhang: Investigation, Methodology, Writing – original
draft. Yunfei Xie: Investigation, Methodology, Formal analysis. Min-
gjuan Zhou: Investigation, Formal analysis. Erik B. Berda: Writing –
review & editing, Formal analysis. Danming Chao: Conceptualization,
Writing – review & editing, Supervision, Project administration.
[17] Lu Q, Yang C, Qiao X, Zhang X, Cai W, Chen Y, Wang W. Multifunctional AIE-active
polymers containing TPA-TPE moiety for electrochromic, electrofluorochromic and
photodetector. Dyes Pigments 2019;166:340–9.
[18] Sun N, Su K, Zhou Z, Wang D, Fery A, Lissel F, Chen C. “Colorless-to-Black”
electrochromic and AIE-Active polyamides: an effective strategy for the highest-
contrast electrofluorochromism. Macromolecules 2020;53(22):10117–27.
[19] Sun N, Su K, Zhou Z, Tian X, Jianhua Z, Chao D, Wang D, Lissel F, Zhao X, Chen C.
High-performance emission/color dual-switchable polymer-bearing pendant
tetraphenylethylene (TPE) and triphenylamine (TPA) moieties. Macromolecules
2019;52(14):5131–9.
Declaration of competing interest
[20] Yu T, Han Y, Yao H, Chen Z, Guan S. Polymeric optoelectronic materials with low-
voltage colorless-to-black electrochromic and AIE-activity electrofluorochromic
dual-switching properties. Dyes Pigments 2020;181. 108499.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[21] Liu J, Luo G, Mi S, Zheng J, Xu C. Trifunctional CdSe quantum dots-polymer
composite film with electrochromic, electrofluorescent and light-induced
coloration effects. Sol Energy Mater Sol Cell 2018;177:82–8.
Acknowledgments
[22] Zhou Y, Berda EB, Ma Q, Liu X, Wang C, Chao D. Flexible and robust electro-
optically responsive films based on novel silica/oligoaniline/carbon dots
composite. ChemElectroChem 2019;6(20):5293–300.
We graciously acknowledge the National Natural Science Founda-
tion of China for funding (grant No. 21774046), Jilin Provincial Science
and Technology Department, China (Grant Nos. 20200801057 GH and
20190201075JC), and the Science and Technology Research Project of
the Education Department of Jilin Province (JJKH20211048KJ).
[23] Zhou Y, Ma Q, Berda EB, Liu X, Wang C, Chao D. Fabrication and
electrochemically-modulated optical properties of viologen and carbon dots hybrid
glass composite films. Dyes Pigments 2020;174. 108048.
[24] Qiu S, Gao Z, Yan F, Yuan H, Wang J, Tian W. 1, 8-Dioxapyrene-based
electrofluorochromic supramolecular hyperbranched polymers. Chem Commun
2020;56(3):383–6.
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[25] Pietsch M, Rodlmeier T, Schlisske S, Zimmermann J, Romero-Nieto C, Hernandez-
Sosa G. Inkjet-printed polymer-based electrochromic and electrofluorochromic
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