Synthesis and optical properties of redox-active triphenylamine-based derivatives with methoxy protecting groups

Article abstract of DOI:10.1039/c8tc05196h

A series of novel redox-active triphenylamine-based materials, 4,4′-bis(4,4′-dimethoxydiphenylaminyl)-4′′-methoxytriphenylamine (BDATPA) and four related derivatives, including tris(4-methoxyphenyl)amine (TPA), N,N,N′,N′-tetrakis(4-methoxyphenyl)-1,4-phenylenediamine (TPPA), N,N,N′,N′-tetrakis(4-methoxyphenyl)-1,1′-biphenyl-4,4′-diamine (TPB) and tris(4-(4,4′-dimethoxyphenylaminyl)phenyl)amine (TPAPA), were readily prepared and their electrochemical, photoluminescence (PL) and electrochromic (EC) behaviors were investigated. Interestingly, only TPB exhibited high PL intensities in both solution and solid state, while the others revealed a much lower PL intensity in solution. All of these electroactive materials showed excellent electrochemical reversibility by cyclic voltammetry scanning with multi-color changes at the related oxidation states. Furthermore, UV-Vis and spectroelectrochemical measurements were also applied to evaluate and calculate the molar extinction coefficients in order to facilitate these materials as a color palette.

Full text of DOI:10.1039/c8tc05196h

Journal of
Materials Chemistry C
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PAPER
Synthesis and optical properties of redox-active
triphenylamine-based derivatives with methoxy
protecting groups†
Cite this: J. Mater. Chem. C, 2018,
, 13345
6
a
a
ab
Jung-Tsu Wu, ‡ Ting-Lin Hsiang‡ and Guey-Sheng Liou ‡*
0
0
A series of novel redox-active triphenylamine-based materials, 4,4 -bis(4,4 -dimethoxydiphenylaminyl)-
00
4
-methoxytriphenylamine (BDATPA) and four related derivatives, including tris(4-methoxyphenyl)amine
0
0
0
0
(
TPA), N,N,N ,N -tetrakis(4-methoxyphenyl)-1,4-phenylenediamine (TPPA), N,N,N ,N -tetrakis(4-methoxy-
0
0
0
phenyl)-1,1 -biphenyl-4,4 -diamine (TPB) and tris(4-(4,4 -dimethoxyphenylaminyl)phenyl)amine (TPAPA),
were readily prepared and their electrochemical, photoluminescence (PL) and electrochromic (EC)
behaviors were investigated. Interestingly, only TPB exhibited high PL intensities in both solution and
solid state, while the others revealed a much lower PL intensity in solution. All of these electroactive
materials showed excellent electrochemical reversibility by cyclic voltammetry scanning with multi-color
changes at the related oxidation states. Furthermore, UV-Vis and spectroelectrochemical measurements
were also applied to evaluate and calculate the molar extinction coefficients in order to facilitate these
materials as a color palette.
Received 15th October 2018,
Accepted 17th November 2018
DOI: 10.1039/c8tc05196h
rsc.li/materials-c
polyimides and epoxides) reported by our group reveal excellent
electrochromic (EC) performance with interesting multi-color
Introduction
To date, various energy-saving products have emerged with behavior. Furthermore, some of these triarylamine-based poly-
the growing awareness of the importance of protecting the mers could be applied to polymeric memory devices, while also
environment. For instance, smart windows and energy storage displaying high photoluminescence (PL) capabilities in both
1
,2
20–26
devices are both based on the electrochromic effect, a pheno- film and fiber states.
menon of color changing that occurs when an electroactive Recently, highly transparent to truly black electrochromic
material gains or loses one or more electrons during an devices (ECDs) based on TPA-containing polyamide films
3
electrochemical redox procedure. Meanwhile, numerous lumi- were prepared as excellent shutters for next generation trans-
2
7
nescent materials have been studied due to their outstanding parent displays. However, some insufficient but crucial issues
performance and tremendous potential in many applications were raised when more advanced performances were requested
4
such as organic light emitting diodes (OLEDs), fluorescent such as the response time of the obtained polymeric ECDs.
5
6
biosensors, solar cells, and so on.
To overcome this impasse, a novel panchromatic mono-
Triphenylamine (TPA)-based materials have been widely meric type ECD shutter based on a structurally similar TPA-
used for optoelectronic applications because of their advan- containing derivatives was successfully fabricated by our group
tages such as excellent electron-donating nature, easy oxidiz- recently, which could effectively enhance the EC response
7
ability, light-emitting and hole-transporting capabilities. Over capability, thus greatly reducing the switching and bleaching
2
8
the past twenty years, they have been developed into diverse times.
8
–10
material systems, including electropolymerized poly-TPAs,
In this study, we attempt to extend our effort to the design
Especially, and synthesis of a series of novel TPA-based materials, a new
(polyamides, compound of 4,4 -bis(4,4 -dimethoxydiphenylaminyl)-4 -methoxy-
1
1–13
14,15
conjugated polymers,
and metal complexes.
1
6–19
0
0
00
various types of high-performance polymers
triphenylamine (BDATPA) and other derivatives (TPA, TPPA, TPB
a
Institute of Polymer Science and Engineering, National Taiwan University, 10607,
Taipei, Taiwan. E-mail: gsliou@ntu.edu.tw
and TPAPA) with related structures. The optical properties such
as the UV-Vis absorption, PL, electrochemical stability, and EC
behavior of these TPA-based materials were investigated and
compared systematically. We expect that all of these materials
can be applied not only for ECDs but also in electrofluorochromic
devices (EFCDs) in the near future.
b
Advanced Research Center for Green Materials Science and Technology,
National Taiwan University, 10607, Taipei, Taiwan
†
Electronic supplementary information (ESI) available: Experimental section,
data analysis, supporting figures and tables. See DOI: 10.1039/c8tc05196h
These authors equally contributed to this work.
‡
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Experimental
Materials
into the container and then the solution was refluxed for
3
hours. After cooling to room temperature, the mixture was
diluted with dichloromethane and filtered by celite. The filtrate
was purified by flash column chromatography (dichloromethane/
hexane = 0.5) and poured into methanol to obtain 6.77 g of pale
Tri-tert-butylphosphine, propylene carbonate (PC), toluene,
N-methyl-2-pyrrolidone (NMP) and g-butyrolactone (GBL) were
used as received. Cesium fluoride, sodium tert-butoxide, sodium
tetrafluoroborate and tetra-n-butylammonium bromide were
stored in the auto dry box. Tetra-n-butylammonium tetrafluoro-
ꢀ1
green powder (79%, yield), mp: 242–247 1C. FT-IR (KBr, cm ):
1
n = 2928, 2831, 1497, 1240, 1036, 824; H NMR (400 MHz,
DMSO-d
6
, d): 6.95 (d, J = 8.8 Hz, 12 H, H
b
), 6.89–6.84 (m, 18 H,
).
4
borate (TBABF ) was acquired by the following process: excess
Hc+d), 6.75 (d, J = 8.9 Hz, 6 H, H
e
), 3.71 (s, 18 H, H
a
saturated sodium tetrafluoroborate aqueous solution was added
into a saturated tetra-n-butylammonium bromide aqueous
solution, and the white precipitate was then filtered and
recrystallized by methanol and water. TPA, TPPA, TPB, BDATPA
and their intermediates were synthesized according to pre-
Measurement
Melting point was mainly detected by OptiMelt-Automated
ꢀ
1
Melting Point System at a scan rate of 5 1C min and DSC at
ꢀ
1
1
2
8–30
a scan rate of 5 1C min , unless otherwise stated. H NMR and
viously reported procedures.
The precursors, tris(4-nitro-
1
3
C NMR spectra were recorded on Bruker DPX-400 NMR
400 MHz) and Bruker AVIII-500 MHz FT-NMR (125 MHz),
0
00
phenyl)amine (TPA-3NO ) and 4,4 ,4 -triaminotriphenylamine
2
(
(
TPA-3NH ), of TPAPA can be referred to in previous litera-
2
3
1,32
respectively. The definition of the splitting pattern is as follows:
s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet. Fourier
transform infrared (FT-IR) spectra were obtained from PerkinElmer
Spectrum 100 Model FT-IR spectrometer. Ultraviolet-visible
ture,
and the details can be found in the ESI.† The rest of
the reagents were received from a commercial source and used
without further purification.
0
0
00
4
,4 -Bis(4,4 -dimethoxydiphenylaminyl)-4 -methoxytriphenyl-
(UV-Vis) spectra were carried out on Agilent 8453 UV-visible
amine (BDATPA). Tris(dibenzylideneacetone)dipalladium(0)
Spectroscopy System. Elemental analysis (EA) was run in an
elementar vario EL cube (for NCSH & O). Mass spectrometry
(Pd
2
3
(dba) , 55 mg, 0.060 mmol) and tri-tert-butylphosphine
(
P(tBu)
3
, 0.028 mL, 0.120 mmol) were added into a 50 mL
(MS) was carried out by THERMO Q Exactive Plus. Electro-
round-bottom flask containing 20 mL anhydrous toluene in
the glove box preferentially. After stirring at room temperature
under nitrogen atmosphere for 10 minutes to undergo ligand
exchange, 4-bromoanisole (1.51 mL, 12.0 mmol) and TPA-2NH2
chemistry was conducted with CH Instrument 611B Electro-
chemical Analyzer or CH Instrument 612C Electrochemical
Analyzer. Cyclic voltammetry was performed at a scan rate of
ꢀ1
5
0 mV s . The parameters of the differential pulse voltam-
(
0.76 g, 2.5 mmol) were added to the flask sequentially and
stirred for another 10 minutes. Sodium tert-butoxide (NaOtBu,
.45 g, 15 mmol) was added and then the solution was refluxed
ꢀ
1
metry are listed below: scan rate of 2 mV s , pulse amplitude of
0 mV, pulse width of 25 ms and pulse period of 0.2 s. The scan
range for the spectroelectrochemical measurement is from
00 to 1100 nm. A three-electrode system combined with an
5
1
for 3 hours. After cooling to room temperature, the mixture was
diluted with dichloromethane and filtered by celite. The filtrate
was purified by flash column chromatography (dichloromethane/
hexane: 0.5) and poured into methanol to obtain 1.67 g of pale
pink powder (92% yield), mp: 245–247 1C (measured by DSC with
3
optically transparent thin layer electrochemical (OTTLE) cell
was used for the electrochromic investigation. An ITO coated
glass or an 80 mesh platinum gauze served as the working
electrode, platinum wire as an auxiliary electrode, and Ag/AgCl,
ꢀ
1
ꢀ1
the scan rate of 5 1C min ). FT-IR (KBr, cm ): n = 2833, 1499,
1
0.3 M KCl as a reference electrode.
1
239, 1036, 825; H NMR (400 MHz, C
6 6
D , d): 7.18 (d, J = 9.0 Hz,
2
H, H ), 7.12 (d, J = 9.0 Hz, 12 H, Hb+d), 7.06 (d, J = 9.0 Hz, 4 H,
g
H
e
3
), 6.72 (d, J = 9.0 Hz, 10 H, Hc+f), 3.30, 3.29 (s + s, 15 H, Ha+h);
Results and discussion
Synthesis and basic characterization of the TPA-based
1
13
2
9
C NMR (125 MHz, C
6
D
6
, d): 156.2 (C ), 156.0 (C ), 143.8 (C ),
6
10
5
4
11
142.9 (C ), 142.1 (C ), 141.8 (C ), 126.6 (C ), 126.1 (C ), 124.4
8
7
3+12
14+1
materials
(C ), 123.6 (C ), 115.1 (C
), 55.0 (C
); Anal. calcd for
47 43 3 5
C H N O : C 77.34, H 5.94, N 5.76; found: C 77.08, H 5.96, TPA, TPPA, and TPB were synthesized following the previous
+
N 5.70; ESI-MS: calcd. For (C H N O ) : m/z 729.32; found: literatures using the Ullmann reaction for TPA and Buchwald–
4
7
43 3 5
2
7–29
m/z 729.32.
Hartwig amination for the others.
The preparation routes
0
Tris(4-(4,4 -dimethoxyphenylaminyl)phenyl)amine (TPAPA). for BDATPA and TPAPA were modified from TPPA by obtaining
Tris(dibenzylideneacetone)dipalladium(0) (Pd (dba) , 0.280 g, the diamine or triamine intermediates first and then reacting
2
3
0.306 mmol) and tri-tert-butylphosphine (P(tBu)
3
, 0.160 mL, with 4-bromoanisole (Scheme 1). The structure of the novel
0.612 mmol) were added into a 150 mL three-necked round-bottom BDATPA compound was confirmed by IR (Fig. S1, ESI†) and NMR
flask containing 60 mL anhydrous toluene in the glove box prefer- spectroscopies as shown in Fig. 1 and 2. In Fig. S1 (ESI†), the
ꢀ
1
entially. After stirring at room temperature under nitrogen atmo- characteristic absorption peaks of –NH stretching (3000–3500 cm
)
ꢀ1
sphere for 10 minutes to undergo ligand exchange, 4-bromoanisole and –NH bending (B1600 cm ) disappeared when the diamine
7.7 mL, 61.1 mmol) and TPA-3NH (2.69 g, 9.25 mmol) were added groups were completely reacted. The H, H–H COSY, C and C–H
2
1
13
(
to the flask sequentially and stirred for another 10 minutes. HMQC NMR spectra of BDATPA are depicted in Fig. 1 and 2,
Sodium tert-butoxide (NaOtBu, 7.34 g, 76.4 mmol) was added respectively. The peak assignment for the protons and carbons
1
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Scheme 1 Synthesis routes of BDATPA and TPAPA.
13
Fig. 2 (a) C and (b) C–H HSQC NMR spectra of BDATPA in C
D .
6 6
Table 1 Optical properties of TPA-based materials
TPA
TPPA
TPB
BDATPA
TPAPA
abs
l
max [nm] (solution)
299
397
6.7
311
424
5.1
351
448
34.5
313
435
5.0
341
442
4.8
em
a
l
max [nm] (solution)
b
F
PL [%] (solution)
abs
l
max [nm](powder)
303
420
324
441
4.5
362
456
32.4
330
445
356
447
em
a
l
max [nm] (powder)
c
F
PL [%] (powder)
a
em
abs
b
Both of lmax of solution and solid state were excited at lmax
.
The
quantum yield was measured using quinine sulfate (dissolved in 1 N
SO with a concentration of 10 mM, assuming a photoluminescence
H
2
4
c
quantum efficiency of 0.546) as a standard at 25 1C. PL quantum
1
Fig. 1 (a) H and (b) H–H COSY NMR spectra of BDATPA in C
6
D
6
.
yields of molecules determined using a calibrated integrating sphere.
agreed well with the expected structure of the target compound. aromatic rings and the nitrogen atoms. The PL spectra for
1
The H NMR spectra of the other intermediates are also the compounds in DMSO solution displayed emitting bands
depicted in Fig. S2 and S3 (ESI†). The NMR spectrum for TPAPA with maximum peaks at around 397–448 nm within the violet-
is also added to Fig. S4 (ESI†).
to-blue region as shown in Fig. 3. In addition, these materials in
the solid state exhibited absorption peaks between 303–362 nm
and PL emission peaks between 420–460 nm as summarized
Optical and electrochemical properties
The UV-Vis absorption and PL spectra of the materials were in Fig. 4. Interestingly, according to the PL spectra in Fig. 3
measured both in a dilute dimethyl sulfoxide (DMSO) solution and 4, TPB revealed a unique PL behavior when compared
(10 mM) and in the solid state, and the results are summarized with the PL intensity results of the other materials, displaying
in Table 1. These TPA-based derivatives demonstrated strong cyan emission with a maximum peak at 448 nm and a PL
UV-Vis absorption bands with peaks at around 299–351 nm quantum yield of 34.5% in DMSO solution, the most intense
in the DMSO solution, which were assigned to the p–p* transi- peak was at 460 nm with a PL quantum yield of 32.4% in the
tion resulting from the resonance structures between the solid state.
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five kinds of anodic EC materials. TPA shown in Fig. 5a exhibited
only one oxidation peak at 0.75 V, TPPA revealed two oxidation
stages with peaks at 0.55 and 1.00 V in Fig. 5b, respectively, and TPB
also displayed two oxidation stages, with peaks at 0.71 and 0.86 V as
shown in Fig. 5c. BDATPA depicted in Fig. 5d displayed three
oxidation redox peaks at 0.46, 0.74 and 1.32 V, respectively. Further-
more, TPAPA had only two clear oxidation peaks at 0.49 and 0.71 V
in Fig. 5e, while Fig. S5 (ESI†) confirms that there should be four
oxidation stages at 0.42, 0.69, 1.09 and 1.21 V, using differential
pulse voltammetry (DPV) measurement. The introduction of para-
methoxy groups into the TPA units can effectively prevent the
intermolecular coupling reaction for the formation of dimers during
Fig. 3 (a) Absorption spectra and (b) PL spectra of TPA, TPPA, TPB, BDATPA
and TPAPA in DMSO solution (solution concentration: 10 mM).
20
the oxidation procedure, as reported in our previous literatures.
CV measurements could also be used to evidence the excellent
electrochemical stability of the series of TPA-based derivatives
between their neutral and first oxidation states for 1000 cycles,
respectively, and the results shown in the insets of Fig. 5 clearly
confirm the excellent redox stability of all the materials in this study.
Fig. 4 (a) Absorption spectra and (b) PL spectra of TPA, TPPA, TPB, BDATPA
and TPAPA in the solid state.
Spectroelectrochemistry
Spectroelectrochemical measurements were employed for
validating the optical behavior of the series of EC materials.
Preliminary investigation of the electrochromism of five com-
pounds was carried out by an OTTLE coupled with UV-Vis spectro-
scopy and the scanning conditions were replicated for the CV
measurements. The results are summarized in Fig. 6 and their
The electrochemical behavior of the as-prepared five redox-active
TPA-based materials was investigated by cyclic voltammetry (CV)
conducted with an optically transparent thin-layer electrochemical
(
OTTLE) cell containing solvent (propylene carbonate (PC),
g-butyrolactone (GBL), or N-methyl-2-pyrrolidone (NMP)) with
mM EC materials and 0.1 M tetra-n-butylammonium tetrafluoro-
borate (TBABF ) as the supporting electrolyte under nitrogen atmo-
1
4
sphere. These materials exhibited one to four oxidation stages
corresponding to the quantity of redox nitrogen centers in their
molecular structures. Fig. 5 summarizes the CV diagrams of these
Fig. 5 Cyclic voltammetric diagrams of (a) TPA, (b) TPPA, (c) TPB,
ꢀ
1
(
d) BDATPA, and (e) TPAPA at the scan rate of 10 mV s . Inset: Electro-
Fig. 6 Spectroelectrochemical measurements and EC behaviors of
(a) TPA, (b) TPPA, (c) TPB, (d) BDATPA, and (e) TPAPA at applied potentials
ꢀ1
chemical stability measurements at the scan rate of 50 mV s for the
corresponding materials; 10 M TPA, TPPA and TPB were dissolved in
ꢀ3
ꢀ3
of the related oxidation stages. 10 M of TPA, TPPA and TPB were dis-
ꢀ
3
ꢀ3
0
.1 M TBABF
4
/PC; 10 M BDATPA was dissolved in 0.1 M TBABF
4
/GBL;
solved in 0.1 M TBABF
4
/PC; 10 M of BDATPA was dissolved in 0.1 M
ꢀ
3
ꢀ3
1
0
M TPAPA was dissolved in 0.1 M TBABF /NMP.
4
TBABF
4
/GBL; 10 M of TPAPA was dissolved in 0.1 M TBABF
4
/NMP.
1
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the intensity of the characteristic absorption of BDATPA with a
peak at 313 nm decreased during the first oxidation process,
while three new absorption peaks at 426, 540, 775 nm, and one
broad absorption band in the near-IR region were observed.
In the second stage of the oxidation process, the intensity of the
peak at 426 nm weakened while the characteristic peak at 540 nm
strengthened with a slight red shift, and the IV-CT band with a
peak at 1030 nm was greatly enhanced. For the TPAPA com-
pound, the spectral differences at varied potentials that relate to
the distinctive oxidation stages are presented in Fig. 6e. The
characteristic peaks at 436 and 1071 nm are generated during the
first oxidation process. Then, the peak at 436 nm decreased with
a slight red-shift, while the intensity of the IV-CT band increased
significantly, accompanied by a slight blue-shift in the second
oxidation stage. Moreover, the absorption peaks at 450 and
553 nm revealed no significant difference for the preceding third
and fourth oxidation states, while the intensity of the IV-CT band
subsequently decreased accompanied by a red-shift.
Furthermore, the color changes for these TPA-based EC
different oxidation states. 10 M of TPA, TPPA and TPB were dissolved in materials at different oxidation stages were identified and evalu-
Fig. 7 Chemical structures, the corresponding electrochromism, and
L*a*b* values of (a) TPA, (b) TPPA, (c) TPB, (d) BDATPA, and (e) TPAPA at
ꢀ3
ꢀ3
0
.1 M TBABF
4
/PC, respectively; 10 M of BDATPA was dissolved in 0.1 M
ated by CIELAB data and are summarized in Fig. 7. For TPA, the
color changed from colorless (L*: 98.11, a*: 0.00, b*: 0.00) to cyan
ꢀ3
TBABF /GBL; 10 M of TPAPA was dissolved in 0.1 M TBABF /NMP.
4
4
(L*: 83.42, a*: ꢀ29.26, b*: ꢀ19.69); the colors that could be
corresponding color changes are depicted in Fig. 7. First, the produced for TPPA ranged from colorless (L*: 97.57, a*: ꢀ0.01,
spectroelectrochemical measurement for TPA is shown in b*: 0.02) to light green (L*: 80.54, a*: 2.09, b*: 9.97) and then
Fig. 6a and the characteristic peaks appear at 369 and 724 nm intense cyan (L*: 55.99, a*: ꢀ17.72, b*: ꢀ27.83). TPB could also
corresponding to the first oxidation state, which also agrees with bring out multi-color changes from colorless (L*: 97.62, a*:
3
3
the previous study. The optical changes of TPPA at different ꢀ0.15, b*: 0.34) to light orange (L*: 72.73, a*: 13.77, b*: 43.58),
oxidation states shown in Fig. 6b reveal that the characteristic and then atrovirens (L*: 45.02, a*: 0.22, b*: 37.24). For the novel
absorption peak of the neutral TPPA at 310 nm diminished BDATPA, it could give rise to polyelectrochromism from color-
gradually with the formation of the radical cation of TPPA during less (L*: 97.92, a*: ꢀ0.16, b*: 0.38) to yellow green (L*: 76.06, a*:
the first oxidation stage (0.0–0.7 V), while three new peaks at 414, ꢀ8.56, b*: 45.63), purple (L*: 49.07, a*: 8.75, b*: ꢀ10.04), and
560 and 983 nm appeared simultaneously. The absorption peak then grey-green (L*: 59.44, a*: 16.30, b*: 17.81). In the case of
in the near-IR region can be ascribed to intervalence charge TPAPA, the color changed from colorless (L*: 96.76, a*: ꢀ0.55, b*:
transfer (IV-CT) excitation associated with the electron transfer 1.32) to yellow (L*: 85.70, a*: ꢀ11.38, b*: 78.98), while the rest of
between active neutral nitrogen and cation radial nitrogen atoms the oxidation states exhibited no significant color change.
within the p-phenylenediamine moiety of TPPA, which is also
consistent with the phenomenon classified by Robin and Day.
Furthermore, in order to predict the color-merging effects of
these EC materials, accurate characterization of the extinction
3
4
When higher voltages (0.8–1.0 V) were applied to achieve the coefficients, so called absorption coefficient, would be crucial and
ꢀ
1
ꢀ1
second oxidation state, the peaks belonging to the first oxidation inevitable. Thus, the molar extinction coefficients (e, M cm
)
state decreased and two new peaks at 609 and 772 nm appeared, of these TPA-based derivatives at the first oxidation state was
generating a blue color. Then, the characteristic absorption peak also evaluated in this study following the Beer–Lambert law
at 333 nm for the neutral form of TPB could be observed, which (A = ebc), and the results are summarized in Fig. 8. As described
verifies the redshift caused by the more conjugated biphenyl in Fig. 8a, the absorbance was obtained from spectroelectro-
ꢀ3
moiety relative to the TPPA unit. Afterwards, three new peaks chemical measurements with a concentration of 10 M and
ꢀ
1
appeared during the first oxidation process, two in the visible light path length of 10 cm. According to Fig. 8b, the extinction
light region (476 and 693 nm) and one in the near-IR region as coefficient of these redox-active materials in the neutral form
shown in Fig. 6c. The IV-CT excitation of TPB observed at longer revealed some regularity. When the structure changed from TPA
wavelengths of 1100 nm implies that the electronic coupling to TPPA, the absorption band in the UV region became broader,
interaction between the active neutral nitrogen and the radical and the peak also enhanced with a red shift from 298 to 310 nm.
nitrogen cations, within the benzidine moiety of TPB, is weaker Comparing the three structurally related TPA-based materials,
than the one of TPPA mentioned above. Then, a new intense TPPA, BDATPA and TPAPA with different number of multi-
absorption band with a peak at 864 nm appeared, and the arylamine moieties, the peak wavelengths for their maximum
characteristic peaks for the first oxidation state at 476 and absorption displayed no significant difference (310–314 nm)
6
93 nm also increased during the second oxidation process. but exhibited greatly enhanced absorbance (1.8–3.2), molar
5
ꢀ1
ꢀ1
Fig. 6d represents the optical absorption change of BDATPA; extinction coefficients (1.8–3.2 ꢁ 10 M cm ), and enlarged
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Acknowledgements
This study was financially supported by the ‘‘Advanced Research
Center for Green Materials Science and Technology’’ from The
Featured Area Research Center Program within the framework of
the Higher Education Sprout Project by the Ministry of Education
(107L9006) and the Ministry of Science and Technology in Taiwan
(MOST 107-3017-F-002-001 and 104-2113-M-002-002-MY3).
Fig. 8 (a) Schematic measurement of extinction coefficient, (b) extinction
coefficients for these materials at their neutral states and (c) extinction
ꢀ3
coefficients for these materials at their first oxidation states. 10 M of TPA,
ꢀ
3
Notes and references
TPPA and TPB were dissolved in 0.1 M TBABF
4
/PC; 10 M of BDATPA was
ꢀ3
dissolved in 0.1 M TBABF
TBABF /NMP.
4
/GBL; 10 M of TPAPA was dissolved in 0.1 M
1
A. Azens and C. Granqvist, J. Solid State Electrochem., 2003,
, 64.
4
7
2
3
4
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full width at half maximum (FWHM) corresponding to the
number of arylamines within the structure of these materials.
Furthermore, TPB gave rise to moderately higher absorbance
and molar extinction coefficient values with significant red
shift and enlarged FWHM when compared with those of TPPA,
owing to the higher conjugation length of benzidine moiety.
Meanwhile, the values for the molar extinction coefficient were
also in good agreement with the number of arylamine units.
Subsequently, the electro-optical behavior for each EC materials
at their first oxidation states was investigated. The values for the
absorbance, molar extinction coefficient, and the wavelength of
the peak of maximum absorption for these EC materials in
visible region demonstrated a similar trend as the ones at the
neutral states, and the results are depicted in Fig. 8c. TPPA,
BDATPA and TPAPA displayed their main absorption bands with
the peaks ranging from 415 to 440 nm, while the main absorp-
tion peak wavelength for TPB appeared at around 480 nm, which
could also be verified in Fig. 6.
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Conclusions
A series of redox-active TPA-based EC materials, a novel BDATPA
and other four structurally related derivatives were successfully
prepared via the Ullmann reaction and Buchwald–Hartwig
amination. Incorporation of the electron-donating methoxy
groups into the TPA-based materials at the para position of
the phenyl ring can effectively prevent coupling reactions in
their oxidized states, thus the electrochemical stability of the
obtained materials was greatly enhanced. In addition, TPB
demonstrates an interesting and unique optical behavior both
in solution and in solid state with high light-emission and PL
quantum yields. By merging and coordinating the molar extinc-
tion coefficient data of these obtained redox-active TPA-based
materials, the colors of different EC derivatives can be easily
tuned and predicted. Thus, the application potential of fabri-
cated ECDs can be greatly enhanced according to the resulting
outcomes of our present study.
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Conflicts of interest
4 H. J. Yen, J. H. Wu, W. C. Wang and G. S. Liou, Adv. Opt.
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There are no conflicts to declare.
1
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