Synergistic effect between electroactive tetraphenyl-: P -phenylenediamine and AIE-active tetraphenylethylene for highly integrated electrochromic/electrofluorochromic performances

Article abstract of DOI:10.1039/c9tc02001b

Switchable fluorescent materials have gained great attention due to their promising applications in sensors, memory devices and displays. However, further progress is hindered by the low fluorescence contrast, modest response speed and inferior long-term cycling stability. Based on a rational design strategy by combining a highly conjugated tetraphenyl-p-phenylenediamine (TPPA) unit and an aggregation induced emission (AIE)-active tetraphenylethylene (TPE) unit, we synthesized a novel diamine "N,N′-bis(4-aminophenyl)-N,N′-di(4-(1,2,2-triphenylethenyl)phenyl)-1,4-phenylenediamine" to construct an electro- and AIE-active polymer. In addition to the high efficiency solid-state fluorescence and the extremely stable redox properties, the resulting polymer TPE-TPPA-PA realized highly integrated emission/color dual-switchable properties, including multistage color-changing, high fluorescence on/off contrast up to 252, impressively rapid response rate (1.3/0.5 s for EC and 0.7/2.1 s for EFC processes) and excellent cycling stability over 10000 s. The demonstrated synergistic effect between stable electroactive TPPA and AIE-active TPE may provide a new pathway for further molecular design to realize high-performance emission/color dual-switchable materials.

Full text of DOI:10.1039/c9tc02001b

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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
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DOI: 10.1039/C9TC02001B
Journal Name
ARTICLE
Synergistic effect between electroactive tetraphenyl-p-
phenylenediamine and AIE-active tetraphenylethylene for highly
integrated electrochromic/electrofluorochromic performances
Received 00th January 20xx,
Accepted 00th January 20xx
a,b
a
b
a
a
b
DOI: 10.1039/x0xx00000x
Ningwei Sun,‡ Kaixin Su,‡ Ziwei Zhou, Xuzhou Tian, Daming Wang, Nicole Vilbrandt, Andreas
b
*b
*a
*a
Fery , Franziska Lissel, Xiaogang Zhao and Chunhai Chen
www.rsc.org/
Switchable fluorescent materials have gained great attention due to their promising applications in sensors, memory
devices and displays. However, further progress is hindered by the low fluorescence contrast, modest response speed and
inferior long-term cycling stability. Based on a rational design strategy by combining a highly conjugated tetraphenyl-p-
phenylenediamine (TPPA) unit and an aggregation induced emission (AIE)-active tetraphenylethylene (TPE) unit, we
synthesized a novel diamine “N,N’-bis(4-aminophenyl)-N,N’-di(4-(1,2,2-triphenylethenyl)phenyl)-1,4-phenylenediamine”
to construct an electro- and AIE-active polymer. In addition to the high efficiency solid-state fluorescence and the
extremely stable redox properties, the resulting polymer TPE-TPPA-PA realized highly integrated emission/color dual-
switchable properties, including multistage color-changing, high fluorescence on/off contrast up to 252, impressively rapid
response rate (1.3/0.5 s for EC and 0.7/2.1 s for EFC processes) and excellent cycling stability over 10000 s. The
demonstrated synergistic effect between stable electroactive TPPA and AIE-active TPE may provide a new pathway for
further molecular design to realize high-performance emission/color dual-switchable materials.
contrast up to 242 with a rapid response time of 0.4 s/38 s.
However, the high oxidation potential (1.25 V) caused by the
introduction of the electron-withdrawing cyano group could
Introduction
Unlike most mammals, humans are primarily guided by our visual
sense, driving research into innovative stimuli-responsive optical
1
6
decreased the electrochemical and EFC stability. Despite great
efforts devoted to the design of novel EFC polymers, to the best of
our knowledge, few of them could simultaneously comprise all the
features needed for high-performance EFC materials, namely high
fluorescence on/off contrast, fast response speed and excellent
long-term cycling durability. Therefore, a further molecular-design
guided optimization to enable the preparation of more
sophisticated electroactive/fluorescent polymers is in great demand
to realize highly integrated EFC performances.
1
-5
materials. Among these, electrofluorochromic (EFC) materials,
allowing controllable fluorescence modulation by electric
stimulus, possess vast prospects for applications in sensors,
a
6
-8
information encryption and displays. In general, EFC materials can
be classified into three categories: electroactive/fluorescent
composites, molecular fluorophores and intrinsically switchable
fluorescent polymers.9 Compared with the other two types,
intrinsically switchable fluorescent polymers are deemed as more
promising candidates owing to their facile structural tunability, fast
response speed and competitive processability. To date, only a few
EFC polymers have been exploited. E. Kim et al. described the
electrochemical fluorescence switching of photo-patternable
polyoxadiazole, which exhibited a reversible fluorescence switching
over 1000 cycles but only with a low fluorescence on/off contrast of
-14
Among the key EFC parameters, especially the high on/off contrast
is essential. However, most EFC materials reveal low contrast ratios
due to a weak fluorescence in the solid state, resulting from the
1
7,18
aggregation-caused quenching of conventional luminophores.
To circumvent this drawback, the introduction of aggregation-
induced emission (AIE)-active luminophores is a facile and effective
method to obtain materials exhibiting a higher fluorescence when
utilized as solid films. Tetraphenylethene (TPE) with four peripheral
phenyl rings is a prototypical AIE-active luminogen and has been
1
5
2
.5. Poly(4-cyanotriphenylamine) reported by Liou et al. made a
breakthrough for EFC polymers as it showed high fluorescence
1
9-24
intensively investigated by Tang and coworkers.
In dilute
a. Key Laboratory of High Performance Plastics (Jilin University), Ministry of
Education, National & Local Joint Engineering Laboratory for Synthesis
Technology of High Performance Polymer, College of Chemistry, Jilin University,
Changchun 130012, PR China
Leibniz Institut für Polymerforschung Dresden e.V , Hohe Str. 6, D-01069, Dresden,
Germany
solution, the isolated TPE molecules emit no fluorescence. Upon
aggregation formed in the solid state, TPE derivatives are found to
possess efficient light emission attributed to the mechanism of
restricted intramolecular rotation (RIR). Although TPE is redox
active, its high oxidation potentials and poor reversibility severely
b.
†
Electronic
DOI: 10.1039/x0xx00000x
N. Sun and K. Su contributed equally to this work.
Supplementary
Information
(ESI)
available.
See
2
5
restrict its applications in EFC devices. Consequently, exploring a
‡
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novel molecular-design strategy by combination of TPE and Fig. 1 Design concept of a high-performance EC/VEieFwCArpticolelyOmnliener
electroactive moieties with low trigger potentials is of great containing TPPA and TPE moieties.
significance. Triphenylamine (TPA) with its star-shape structure is
DOI: 10.1039/C9TC02001B
well known for the photoactive and electroactive properties, which
has been widely applied in light emitters, dye-sensitized solar cells,
Experimental
Materials
resistive memory and electrochromic (EC) devices.26-37 Recently,
electroactive fluorophores with TPA and TPE moieties have been
Benzophenone (TCI), 4-bromobenzophenone (TCI), p-
phenylenediamine (TCI), 4-fluoronitrobenzene (Acros),
trimethylamine (Aladdin), TiCl
potassium carbonate (K CO
reported for EFC applications, effectively increasing the
3
8-40
fluorescence on/off contrast.
However, switching stability and
4
(Aladdin), zinc (Zn, TCI),
3
, Aladdin), copper powder
response time, two important parameters for EFC materials, were
not well realized due to the short conjugation and moderate
2
stability of mono-TPA. Notably, TPA derivatives with extended (Aladdin), 10% palladium on charcoal (Pd/C, TCI), hydrazine
conjugation, such as tetraphenyl-p-phenylenediamine (TPPA), monohydrate (TCI) and triphenyl phosphite (TPP, TCI) were
usually possess improved HOMO levels and thus lowered oxidation used
as
received.
Commercially
available
1,4-
potential. TPPA-based polymers revealed much enhanced cyclohexanedicarboxylic acid (CHDA, TCI) was dried under
electrochemistry and electrochromic switching stability even up to vacuum at 100 °C prior to use. N-methyl-2-pyrrolidone (NMP),
1
0000 continuous cycles.41-44 Furthermore, the highly twisty
dimethyl sulfoxide (DMSO), o-dichlorobenzene and pyridine
Aladdin) were dried using 4 Å molecular sieves prior to use.
structures of TPE and TPPA can efficiently prevent the close packing
of the polymer chains to thus accelerate the electrolyte ion
(
Tetrabutylammonium perchlorate (TBAP, Aladdin) was
recrystallized twice from ethanol under nitrogen atmosphere
and dried under vacuum prior to use. All the other reagents
and solvents were used as received from commercial sources.
Monomer synthesis
4
5
transport. And the highly conjugated TPPA can also enhance the
intra-molecular charge mobility ability, potentially shortening the
response time as well. Therefore, the design and construction of an
electroactive fluorophore by combining TPPA and TPE moieties and
incorporating it into polymer backbone is expected to
synergistically improve the EC as well as EFC performances of the
1
-bromo-4-(1,2,2-triphenylethenyl)benzene (TPE-Br, 1)
resulting polymers, surely promoting their commercial optical TPE-Br was synthesized through the McMurry reaction.46 Zn
applications in the near future.
To show the promise of this design concept, in this study we
carefully devised and synthesized a novel electroactive/AIE-active
powder (15.0 g, 231.3 mmol) was added to anhydrous THF
650 mL) in a three-necked round bottom flask under argon
atmosphere. The resulting suspension was cooled to -5 °C, and
TiCl (12.7 mL, 115.6 mmol) was slowly added with a syringe.
Then the above mixture was heated to reflux temperature for
h. Subsequently, the mixture was cooled to -5 °C again,
charged with pyridine (7.5 mL), and stirred for another 0.5 h.
Then a solution of benzophenone (7.5 g, 41.1 mmol) and 4-
bromobenzophenone (8.6 g, 33.1 mmol) in 50 mL of THF was
added into the mixture slowly, and the reaction proceeded for
another 12 h at the reflux temperature. After the end of
reaction (as monitored by TLC), the reaction was quenched by
(
diamine,
N,N’-bis(4-aminophenyl)-N,N’-di(4-(1,2,2-
4
triphenylethenyl)phenyl)-1,4-phenylenediamine, as well as the
derived semi-aromatic polymer (aliphatic structure leads to a
reduced charge transfer effect, which will greatly increase the
3
1
7
fluorescence ). By composing the electroactive luminophores to
contain TPPA and TPE units, the resulting EC/EFC polymer is
expected to highly integrate comprehensive performances including
AIE effect, outstanding electrochemistry stability, high contrast
ratio, fast responsive speed, superior cycling life and facile solution-
processability. The careful design concept of the electroactive/AIE-
active polymer is illustrated in Fig. 1, and its properties including
solubility, thermal stability, electrochemistry, fluorescence, EC and
EFC switching were studied in detail.
2 3
adding 10% K CO aqueous solution and extracted with
dichloromethane. The organic layer was collected and purified
by chromatography using ethyl acetate/petroleum ether
mixture (1:4) to get the desired product (7.6 g, yield 55%). 1H
NMR (300 MHz, DMSO-d
.22 – 7.09 (m, 9H), 6.98 (m, 6H), 6.90 (d, J = 8.4 Hz, 2H).
N,N’-di(4-nitrophenyl)-1,4-phenylenediamine (TPPA-2NO
TPPA-2NO was synthesized according to a reported method
6
, δ, ppm): 7.34 (d, J = 8.4 Hz, 2H),
7
2
, 2)
2
with some modifications.47 In a 500 mL three-neck round-
bottom flask, a mixture of p-phenylenediamine (10.8 g, 100
mmol), 4-fluoronitrobenzene (32.4 g, 230 mmol),
triethylamine (23.4 g, 230 mmol) and anhydrous DMSO (150
mL) was heated at 95 °C for 120 h. After cooling to room
temperature, the mixture was poured into ice water, affording
a mass of red powder. Then the crude product was purified by
recrystallization for three times (DMSO/ethanol = 1:2) to give
1
1
1.2 g of red crystals (32 % of yield). H NMR (300 MHz, DMSO-
2
| J. Name., 2012, 00, 1-3
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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
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ARTICLE
d
7
6
, δ, ppm): 9.31 (s, 2H), 8.09 (d, J = 9.3 Hz, 4H), 7.27 (s, 4H), 9.80 (s, 2H, amide), 7.54 (d, J = 8.9 Hz, 4H, H
.03 (d, J = 9.3 Hz, 4H). 18H, H +H +H +H ), 7.07 – 6.90 (m, 16H,
), 6.82 (d, J = 8.7 Hz, 4H, H ), 6.67 (d, J = 8.7 Hz, 4H, H
Measurements
a
), 7.25 – 7.08 (m,
View Article Online
D
H
O
+
I:
H
1
0
+
.
H
10
3
)
9
,
/
6
C
.
9
8
T
5
C0(s
2
,
0
4H,
0
1B
k
j
h
g
i
f
b
N,N’-Bis(4-nitrophenyl)-N,N’-di(4-(1,2,2-
triphenylethenyl)phenyl)-1,4-phenylenediamine (TPPA-TPE-
H
c
e
d
).
2
2
NO , 3)
Nuclear magnetic resonance (NMR) spectra were collected on
TPPA-TPE-2NO
2
was synthesized through the Ullman coupling a BRUKER-300 spectrometer using deuterated DMSO as a
reaction. In a 250 mL round-bottom flask, a mixture of 2.1 g solvent. Fourier transform infrared (FTIR) spectra were
(
(
0
6.0 mmol) of TPPA-2NO
24.0 mmol) of copper powder, 6.6 g (48.0 mmol) of K
.9 g (3.3 mmol) of 18-crown-6 ether was dispersed in 25 mL (GPC) analysis was carried out on a PL-GPV 220 instrument
2
, 5.1 g (12.3 mmol) of TPE-Br, 1.6 g recorded through a Bruker Vector 22 spectrometer in the
-1
2 3
CO and range of 400-4000 cm . Gel permeation chromatographic
of o-dichlorobenzene, and stirred under nitrogen atmosphere with DMF as an eluent at a flow rate of 1.0 mL/min, and was
at 160 °C for 24 h. Then the inorganic salts and copper powder calibrated with polystyrene standards. Differential scanning
were filtered from the hot reaction mixture. The filtrate was calorimetric (DSC) analysis was performed on TA Q100 at a
poured into ethanol to precipitate a red crude product, which scanning rate of 10 °C/min in a nitrogen flow of 50 mL/min.
was purified by silica gel column chromatography (petroleum Thermo gravimetric analysis (TGA) in the temperature range of
ether/ethyl acetate: 3/1) to yield 3.1 g of the desired TPPA- 100-800 °C was obtained on the TA 2050, with a heating rate
-
1
-1
TPE-2NO
2
1
in 52 %. FTIR (KBr): 1310 cm , 1580 cm (-NO
2
of 10 °C/min under nitrogen atmosphere. Electrochemical
stretch). H NMR (300 MHz, DMSO-d
6
, δ, ppm): 8.09 (d, J = 9.2 measurements were performed by a CHI 660e electrochemical
Hz, 4H), 7.25 – 7.12 (m, 5H), 7.09 – 6.96 (m, 5H), 6.83 (d, J = 9.3 workstation. Cyclic voltammetry (CV) tests were conducted in
Hz, 4H).
a common liquid cell with polymer film coated on an ITO glass
as the working electrode, a platinum wire as an auxiliary
electrode, an Ag/AgCl, KCl (sat.) as a reference electrode and
N,N’-Bis(4-aminophenyl)-N,N’-di(4-(1,2,2-
triphenylethenyl)phenyl)-1,4-phenylenediamine (TPPA-TPE-
2
NH
In a 250 mL round-bottom flask equipped with a stirring bar,
.5 g (2.5 mmol) of TPPA-TPE-2NO and 0.15 g of 10% Pd/C
2
, 4)
3
0.1 M TBAP in dried CH CN as the supporting electrolyte,
respectively. UV-vis-NIR spectra were recorded by a Shimadzu
UV 3101-PC spectrophotometer. Photoluminescence (PL)
spectra were determinate with an Edinburgh FLS920
fluorescence spectrophotometer. The spectroelectrochemical
cell was composed of a 1 cm cuvette with a three-electrode
system similar to the CV tests.
2
2
were dispersed in 40 mL of dioxane. After heating the
suspension solution to reflux, 6.3 g of hydrazine monohydrate
was dropwise added to the above mixture. After stirred at the
reflux temperature for another 8 h, Pd/C was removed by
immediate filtration, and the filtrate was cooled under a Results and discussion
nitrogen flow to precipitate yellow powder. The powder was
collected by filtration and dried under vacuum at 90 °C,
Synthesis and characterization of the diamine and polyamide
A novel electroactive/AIE-active diamine with TPPA and TPE
was synthesized by a multi-step procedure as depicted in
Scheme 1a. TPE-Br 1 was synthesized by McMurry reaction
between 4-bromobenzophenone and benzophenone. TPPA-
yielding 1.7 g of the desired PDA-TPE-2NH
2
in 71 %. FTIR (KBr):
stretch). H NMR (300 MHz, DMSO-
, δ, ppm): 7.15 (t, J = 7.5 Hz, 4H, H ), 7.13 – 7.04 (m, 14H,
+H +H ), 6.98 (t, J = 8.8 Hz, 8H, H ), 6.93 (d, J = 7.5 Hz, 4H, H ),
.78 (s, 4H, H ), 6.75 (d, J = 8.1 Hz, 4H, H ), 6.71 (d, J = 8.2 Hz,
H, H ), 6.58 – 6.49 (m, 8H, H +H ), 5.04 (s, 4H, -NH
). 13C NMR
, δ, ppm): 147.18, 146.66, 144.10, 143.99,
43.80, 142.32, 140.98, 139.85, 135.32, 135.01, 131.85, 131.18,
-1
-1
1
3
375 cm , 3458 cm (-NH
2
d
6
k
H
j
h
g
i
f
2
NO
of p-phenylenediamine and 4-fluoronitrobenzene under
trimethylamine assistance. Then, TPPA-TPE-2NO 3 was
successfully synthesized by Ullman reaction of TPE-Br and
TPPA-2NO . Subsequent reduction of TPPA-TPE-2NO by
means of Pd/C and hydrazine gave the target diamine TPPA-
TPE-2NH 4. The chemical structures of these four monomers
were identified by FTIR and NMR analysis. The FTIR spectra of
TPPA-TPE-2NH shows the characteristic stretching absorption
2
2 was obtained from a nucleophilic substitution reaction
6
4
c
e
b
d
a
2
2
(75 MHz, DMSO-d
6
1
1
2
2
28.33, 128.20, 126.88, 126.77, 126.73, 124.38, 119.05, 115.36.
Polymer synthesis (TPPA-TPE-PA, 5)
2
The novel polyamide TPPA-TPE-PA was synthesized from the
as-prepared diamine TPPA-TPE-2NH and dicarboxylic acid
2
2
-1
-1
CHDA) through a direct polycondensation (Scheme 1b).48
pairs of amino groups at 3375 cm and 3458 cm (Fig. S1). The
1H NMR together with its COSY spectra and 13C NMR spectrum
2
, 0.172 g (1 mmol) of CHDA,
(
0
0
.951 g (1 mmol) of TPPA-TPE-2NH
.2 g of CaCl , 1 mL of TPP, 0.5 mL of Py and 2 mL of NMP were
2
of TPPA-TPE-2NH are illustrated in Fig. S2 and Fig. S3, from
2
which it is observed that all the resonances signals are well
assigned to the protons of the molecular structure, indicating
the successful synthesis of the target diamine. After
synthesizing the pure TPPA-TPE-2NH , the subtly designed
2
luminophor with TPPA and TPE units could be readily
incorporated into the polyamide backbones by a conventional
heated with stirring at 110 °C for 4 h. After cooling to room
temperature, the resulting polymer solution was slowly
poured into vigorously stirred ethanol to produce a fiber-like
precipitate, which was collected by filtration, purified by
Soxhlet extraction with water and ethanol, and then dried
1
under vacuum at 80 °C. H NMR (300 MHz, DMSO-d
6
, δ, ppm):
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polymerization (Scheme 1b). The structure of the resulting state gradually decreased. Meanwhile, two new bViaewndArsticaletO4nl2in1e
polyamide TPPA-TPE-PA 5 were also confirmed by FTIR and nm in the visible region and 1154 nmDOinI: 1
r- fr
t
0
h
.1
e
03
n
9
e
/C
a
9
T
i
C
n
0
2
a
0
r
01B
e
d
NMR techniques. As shown in Fig. S4, the FTIR spectrum region appeared, corresponding to the formation of the
revealed characteristic amide stretching absorption bands at monocation radical of TPPA-TPE-PA. The near-infrared
-1
-1
1
3
310 cm (N-H) and 1662 cm (C=O). The H NMR spectrum of absorption was ascribed to an inter-valence charge transfer
TPPA-TPE-PA was illustrated in Fig. S5, showing proton signals effect.42 With the applied potentials increased from 0.70 V to
corresponding well to the hydrogen atoms in a polyamide 1.10 V, the monocation radical of TPPA-TPE-PA was further
repeat unit. Thus, all the above results demonstrate that the oxidized to the dication radical, accompanied by a decrease of
novel polyamide with electroactive TPPA and AIE-active TPE the absorption bands at 421 nm and 1154 nm and the
units was successfully synthesized.
emergence of a new absorption band at 858 nm. The series of
To further reveal the inherent physical properties of TPPA-TPE- absorption spectra changes are well consistent with the
PA, its molecular weight, inherent viscosity, solubility behavior distinguished color changes of the TPPA-TPE-PA film. The
and thermal properties were systematically studied. The polymer film switched its apparent color from near colorless in
number-average molecular weights and polydispersity of the neutral state to green-yellow in the first oxidation state
TPPA-TPE-PA were tested to be 41200 and 1.36, respectively. and then to light blue in the second oxidation state. Moreover,
The inherent viscosity was measured to be 1.09, further kinetic studies were performed to estimate the EC switching
indicating the high molecular, which is beneficial for the stability and response time. The EC film of TPPA-TPE-PA in the
thermal and mechanical properties. The solubility was first redox state exhibited stable switching properties over 500
evaluated at 10% w/v concentration in various organic cycles (Fig. S7). The excellent stability compared with the PA
solvents. As listed in Table S1, TPPA-TPE-PA exhibited excellent containing diphenylamine-TPE unit could be attributed to the
solubility, demonstrating that the polyamide film could be low oxidation potential and increased resonance stability of
facilely fabricated by competitive solution casting, a major the highly conjugated TPPA unit.36 As for the second redox
advantage for practical application. Additionally, the thermal state, the absorbance decreased gradually after continuous
properties of TPPA-TPE-PA were investigated by TGA and DSC 300 cycles, which could be attributed to the side reactions
(Fig. S6). TPPA-TPE-PA revealed high thermal stability with 10 % caused by the applied high voltage. It is worth noting that
weight loss happened at 467 °C and the glass transition TPPA-TPE-PA displays a very fast response rate, showing the
temperature was found up to 244 °C.
Electrochemical and electrochromic properties
coloration/blenching time 1.3/0.5 s at 421 nm, 1.5/0.8 s at
1154 nm and 1.2/0.6 s at 858 nm. The intrinsic switching time
is much shorter than most of the EC polymers (even hybrid
materials), and is the shortest value to our knowledge for the
TPA-based EC polymers.30,43 The fast response benefits from
the incorporation of the highly twisted TPPA and TPE units,
leading to a loose polymer chain packing and an efficiently
accelerated ion-diffusion in the polymer film (Fig. S7). Besides,
in comparison with mono-TPA unit, the highly conjugated
TPPA can enhance the intra-molecular charge mobility ability
to help shortening the response time as well.
The electrochemical analyses of TPPA-TPE-PA by cyclic
voltammetry (CV) were conducted in a three electrode system
with a TPPA-TPE-PA thin film coated on an ITO substrate as the
working electrode, an Ag/AgCl as a reference electrode, a
3
platinum wire as a counter electrode and 0.1 M TBAP/CH CN
as the supporting electrolyte. The CV curves revealed two
quasi-reversible redox couples at 0.74/0.39 V and 1.12/0.75 V,
respectively. After 100 continuous cyclic scans, the TPPA-TPE-
PA thin film maintained a good CV reversibility with only a
small decrease of peak current (Fig. 2a). Remarkably, the first
redox process from 0.00 V to 0.70 V exhibited a much more
stable electrochemical behavior due to the low oxidation
potentials (Eonset = 0.40 V) and the highly conjugated TPPA
structure (Fig. 2b). The superior CV reversibility in continuous
5
00 cyclic scans demonstrates that the first oxidation stage
possesses a more valuable application potential, which could
be utilized as a promising electro-switching modulator.
During the CV scanning process, the TPPA-TPE-PA thin film
revealed obvious two-stage color changes. Thus
spectroelectrochemical experiments were employed to further
evaluate the optical properties of the EC film. For this
investigation, the polymer film was monitored in situ by a UV-
vis spectrophotometer under the potential control of an
electrochemistry workstation. As shown in Fig. 2c, upon
oxidation (steadily increasing potentials from 0.00 V to 0.70 V), Scheme 1 Synthetic route of the diamine TPPA-TP E-2NH
2
(a)
the intensity of the absorption band at 342 nm in the neutral and the polyamide TPPA-TPE-PA (b).
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Fluorescence and EFC properties
similar maximum absorption peaks (316 and 318VniewmA)rtiicnleNOnMlinPe
solution and drop-cast film states (Fig. S8) ri
fluorescence spectra showed a huge difference between
solution and solid state. TPPA-TPE-PA in NMP solution
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The interesting photophysical properties of the polymer were
further investigated regarding the fluorescence and EFC
properties. The absorption spectra of TPPA-TPE-PA exhibited
Fig. 2 (a) CV diagram of TPPA-TPE-PA from 0.00 V to 1.20 V. (b) CV diagram from 0.00 V to 0.80 V for the first redox process. (c)
Absorbance spectra of TPPA-TPE-PA thin film electrode in 0.1 M TBAP/CH CN at different applied potentials from 0.00 V to 1.10
3
V. (d) CIE chromaticity at different potentials (0.00 V Yxy: 97.56, 0.3053, 0.3139; 0.80 V Yxy: 44.77, 0.3131, 0.3172). (e) Twist
structure of TPPA-TPE. (f) EC switching time of TPPA-TPE-PA thin film electrode between 0.00 V and 0.07 V.
revealed rather weak emission intensity, whereas the the pure NMP solution. Gradually increasing the water fraction
fluorescence of TPPA-TPE-PA in the solid state was greatly from 0% to 90% in the NMP-water mixtures enhanced the
enhanced, demonstrating a pronounced AIE characteristic. To fluorescence emission accordingly, which can be visually
further investigate the AIE effect, we tested the fluorescence observed in the inset images of Fig. 3a. The active
of TPPA-TPE-PA in NMP-water mixtures containing different intramolecular motion of TPPA and TPE in NMP consumes the
water fractions. TPPA-TPE-PA express a weak fluorescence in exciton energy through nonradiative relaxation channel, while
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Journal Name
the aggregation of TPPA-TPE-PA in NMP-water mixtures bright green-yellow light, which can be quenched VtoiewdAarrtikclewOhnleinne
activates the RIR process, resulting in the significant applying the positive potentials from 0.0
fluorescence enhancement.19
testing process, the fluorescence intensity at 532 nm
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Furthermore, when the TPPA-TPE moiety was oxidized to its dramatically decreased and the fluorescence on/off contrast
cation radical, the combined effect of absorption band shift, between neutral fluorescent state and oxidized non-
structural planarization and electron effect changing electron fluorescent state reached up to 252 (Fig. 3d). With the
donating to electron withdrawing could effectively quench the applications of the reverse potential, the fluorescence
strong fluorescence of TPPA-TPE-PA. Therefore, the switchable recovered, indicating a reversible fluorescence modulation.
fluorescence properties in response to electrochemical redox The systematical investigation of fluorescence switching
were further investigated by recording the fluorescence behavior is discussed below.
spectra of TPPA-TPE-PA at different applied potentials. As EFC switching performances
depicted in Fig. 3c, the AIE-active TPPA-TPE-PA film emits
The response of the fluorescence switching was examined by
Fig. 3 (a) PL spectra of TPPA-TPE-PA in NMP-water mixtures with different water contents (inset: fluorescence images in NMP-
water mixtures). (b) Increase of PL intensity with the increasing water fraction of NMP-water mixtures. (c) PL spectra changes of
TPPA-TPE-PA film at different applied potentials from 0.00 V to 0.80 V. (d) Decrease of PL intensity with the applied potentials
increased from 0.00 V to 0.80 V.
monitoring the fluorescence emission changes when applying applying 0.80 V potential led to a slower response speed and
stepping potentials. To realize the optimized fluorescence lower on/off contrast compared with 0.70 V. This
switching, the influence of the applied potentials was phenomenon may be ascribed to the decrease of the
investigated by changing the oxidation potentials from 0.30 V absorption band in the range of 420-500 nm and more ions
to 0.80 V. As shown in Fig. 4a, with the oxidation potentials getting trapped in the polymer film. Therefore, repetitive
increased (at a duration time of 10 s), the fluorescence applying voltage pulses between 0.00 V and 0.70 V was
intensity is quenched to a lower value together with a faster selected as the optimal condition to switch the fluorescence
quenching speed, resulting from the larger potential on/off states. Additionally, the fluorescence switching
difference. During the fluorescence recovering process, behavior at different duration time was also studied. When
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progressively increasing the duration time from 10 s to 360 s, measured at the duration time of 20 s. As shown iVniewFiAgr.tic4lecO, ntlhinee
the fluorescence on/off contrast increased on account of the EFC switching of TPPA-TPE-PA exhibited li
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h
more completed redox reaction in the longer duration time. only slight delay in continuous 10000 s (500 cycles). In view of
Notably, compared with previously reported EFC the solution switching condition used here, it is feasible to
materials,7,15,16 which usually showed a decrease of the expect that the even improved switching stability could be
fluorescence contrast upon shortening of the duration time, attained on optimization of the EFC devices (packaging the
TPPA-TPE-PA largely maintained its high fluorescence on/off device, introduction of counter layer for charge balance and so
contrast with the duration time shortened. This feature is on). The excellent switching stability in comparison with
benefiting from the faster response kinetics, and could enable mono-TPA-based materials could also attributed to the
a high fluorescence contrast under a short duration time. To excellent electrochemical stability of TPPA structure. The EFC
circumvent the inherent contradiction between switching time switching time calculated at 90% of full modulation was 0.7 s
and fluorescence contrast, the long-term stability was finally and
2.1
s
for
fluorescence
Fig. 4 (a) Fluorescence switching response of TPPA-TPE-PA at different double potential steps from 0.00 V to 0.30 V, 0.40 V, 0.50
V, 0.60 V, 0.70 V and 0.80 V. (b) Fluorescence switching response under applied potentials between 0 V and 0.7 V with different
step cycle time from 360 s to 10 s. (c) Long-term fluorescence switching at the step cycle time of 20 s for continuous 10000 s. (d)
Response time of the fluorescence switching at the step cycle time of 20 s: 0.7 s and 2.1 s for fluorescence off and on processes
estimated at 90% of the full modulation.
quenching and lighting processes, respectively. The excellent the fluorescence on/off contrast was found up to 82 at the
fluorescence on/off response speed can be attributed to the duration time of 20 s. Even if only partial fluorescence was
synergistic effect of the introduction of highly twisted TPE and recovered, the value is still much higher than those reported in
the conjugated TPPA units, facilitating the transport of the previous studies.14,16,17 Thus, a EFC polymer with highly
electrolyte ions and enhancing intra-molecular charge integrated performances comprising superb cycling stability,
mobility. In comparison to the EC process, the relatively longer fast response speed, high fluorescence on/off contrast and
response time of EFC switching may be ascribed to the more facile solution-processability was effectively realized, paving a
sensitive characteristic of fluorescence. Furthermore, thanks way for the smart applications in the future.
to the AIE-activity and fast response kinetics of TPPA-TPE-PA,
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1
4 J.-T. Wu, H.-T. Lin and G.-S. Liou, ACS AVipewplA.rticMle Oantelinre.
Conclusion
Interfaces, 2019, 11, 14902.
5 S. Seo, Y. Kim, J. You, B. D. Sarwade, P. P. Wadgaonkar, S. K.
Menon and A. S. More, Macromol. Rapid Commun., 2011, 32,
DOI: 10.1039/C9TC02001B
In summary, a molecular-design concept synergistically
introducing TPE and TPPA was used to prepare a novel
electroactive and AIE-active polymer. In addition to the
excellent thermal and solubility properties, the resulting
polyamide TPPA-TPE-PA also exhibited high solid-state
fluorescence and outstanding electrochemistry stability. EC
process of TPPA-TPE-PA showed two-stage color changes
1
6
1
1
37.
6 J.-H. Wu and G.-S. Liou, Adv Funct. Mater., 2014, 24, 6422.
7 N. Sun, S. Meng, D. Chao, Z. Zhou, Y. Du, D. Wang, X. Zhao,
H. Zhou and C. Chen, Polym. Chem., 2016, 7, 6055.
8 C.-P. Kuo, C.-N. Chuang, C.-L. Chang, M.-k. Leung, H.-Y. Lian
and K. C.-W. Wu, J. Mater. Chem. C, 2013, 1, 2121.
9 J. Mei, N. L. C. Leung, R. T. K. Kwok, J. W. Y. Lam and B. Z.
Tang, Chem. Rev., 2015, 115, 11718.
0 J. Mei, Y. Hong, J. W. Y. Lam, A. Qin, Y. Tang and B. Z. Tang,
Adv. Mater., 2014, 26, 5429.
1 X. Fang, Y. Zhang, K. Chang, Z. Liu, X. Su, H. Chen, S. X.-A.
Zhang, Y. Liu and C. Wu, Chem. Mater., 2016, 28, 6628.
2 S. Abraham, S. Mangalath, D. Sasikumar and J. Joseph,
Chem. Mater., 2017, 29, 9877.
3 Y. Bao, E. Guégain, V. Nicolas and J. Nicolas, Chem.
Commun., 2017, 53, 4489.
1
(colorless to green to blue), while EFC process stably revealed
a switching between bright fluorescence and quenching dark.
Remarkably, TPPA-TPE-PA achieved highly integrated EC and
EFC performances comprising fast intrinsic response speed,
high optical contrast up to 252 and splendid long-term stability
in continuous 10000 s by the synergistic effect of TPE and TPPA
moieties, which opens up a new pathway for designing high-
performance switchable optical materials and enables
widespread applications in multifunctional optoelectronic
devices and sensors.
1
2
2
2
2
2
2
4 X. Liu and G. Liang, Chem. Commun., 2017, 53, 1037.
5 R. Rathore, S. V. Lindeman, A. S. Kumar and J. K. Kochi, J.
Conflicts of interest
There are no conflicts to declare.
Am. Chem. Soc., 1998, 120, 6931.
2
2
6 Y. Shirota, J. Mater. Chem., 2005, 15, 75.
7 G. Zhang, H. Bala, Y. Cheng, D. Shi, X. Lv, Q. Yu and P. Wang,
Acknowledgements
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Journal of Materials Chemistry C
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DOI: 10.1039/C9TC02001B
Table of Contents
Based on the design concept by combining highly conjugated p-phenylenediamine
and AIE-active tetraphenylethylene, a novel electroactive/fluorescent polymer was
successfully synthesized. The resulting polymer exhibited highly integrated
electrochromic /electrofluorochromic performances including high solid-state
fluorescence, highly stable electrochemistry over 500 cycles, high fluorescence
on/off contrast of 252, long-term switching stability over 10000 s and fast EC/EFC
response speed.