Electrochromic properties of novel chalcones containing triphenylamine moiety

Article abstract of DOI:10.1016/j.dyepig.2014.02.018

A series of novel electrochromic chalcones containing triphenylamine units were synthesized by Aldol reaction and characterized by NMR, IR and MS. Their optical, electrochemical properties were investigated using UV-vis, photoluminescence spectra and cyclic voltammetry. The molecular orbital energy levels and excitation energies were calculated by quantum chemical calculation. It was found that the fluorescence intensity is decreasing with formation of charge-transfer state. The existence of electron donating group on triphenylamine unites caused a significant bathochromic shift of the UV absorption maximum and increased E_HOMO and E_LUMO. The electrochromic property of the synthesized compounds was studied by spectroelectrochemical experiments. The results showed that the chalcones containing triphenylamine moiety presented good electrochromic stability, with a color change from yellow to blue as applied potentials ranging from 0.0 to 2.8 V. The coloring and bleaching time was in the range of 2.9-4.2 s and 1.7-3.3 s, respectively.

Full text of DOI:10.1016/j.dyepig.2014.02.018

Dyes and Pigments 106 (2014) 154e160
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Electrochromic properties of novel chalcones containing
triphenylamine moiety
,
,
b
,
c
,
a
,
,b
Huiyi Jin a b, Xianggao Li a , Tingfeng Tan
, Shirong Wang b, Yin Xiao a
,
*
**
Jianhua Tian a
,
b
a School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People’s Republic of China
b Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300072, People’s Republic of China
c School of Science, Tianjin Chengjian University, Tianjin 300384, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel electrochromic chalcones containing triphenylamine units were synthesized by Aldol
reaction and characterized by NMR, IR and MS. Their optical, electrochemical properties were investi-
gated using UVevis, photoluminescence spectra and cyclic voltammetry. The molecular orbital energy
levels and excitation energies were calculated by quantum chemical calculation. It was found that the
fluorescence intensity is decreasing with formation of charge-transfer state. The existence of electron
donating group on triphenylamine unites caused a significant bathochromic shift of the UV absorption
maximum and increased EHOMO and ELUMO. The electrochromic property of the synthesized compounds
was studied by spectroelectrochemical experiments. The results showed that the chalcones containing
triphenylamine moiety presented good electrochromic stability, with a color change from yellow to blue
as applied potentials ranging from 0.0 to 2.8 V. The coloring and bleaching time was in the range of 2.9
e4.2 s and 1.7e3.3 s, respectively.
Received 28 November 2013
Received in revised form
27 January 2014
Accepted 17 February 2014
Available online 3 March 2014
Keywords:
Quantum chemical calculation
Triphenylamine
Chalcone
Electrochemistry
Electrochromism
Spectroelectrochemical
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
two para-positions of TPA, where TPA could be modified by some
function groups. Three new fluorophores containing TPA moiety
In recent years, electrochromic materials have attracted a lot of
attention because of their potential applications such as tunable
windows [1], variable reflectance mirrors [2], and electrochromic
displays [3]. Compared to widely used inorganic electrochromic
materials [4e6], organic electrochromic materials, such as viol-
ogens [7] and conducting polymers [8], have aroused more and
more interests due to their large-scale processability, fast response
time, high coloration efficiency and easy color adjustment [9e11].
Triphenylamine (TPA) derivatives have been extensively inves-
tigated as hole-transport material [12e14] and photovoltaic ma-
terials [15e17] due to their well-known electron-rich property. In
addition, TPA derivatives can also easily be oxidized to form
cationic radicals accompanying with a noticeable change of color-
ation [18e21]. Liou and co-workers reported that TPA-containing
polyimides show excellent electrochromic/electroactive stability
[22e25]. However, acylamino groups of polyimides would occupy
were reported by Kim et al. [26]. But hydrogen atom at p-position of
the TPA benzene ring lost during electrochromism, which resulted
in the polymerization of TPA and low electrochromic stability.
In this paper, a series of novel chalcones with TPA moiety were
designed and synthesized. Optical, electrochemical and electro-
chromic properties of these compounds were studied in detail. The
detailed electronic transitions of neutral and radical absorptions
were investigated by quantum chemical calculations. Furthermore,
electrochromic devices based on TPA-chalcones were fabricated to
study the electrochromic property of the synthesized compounds.
2. Experimental section
2.1. Materials and methods
All the chemical reagents and solvents, unless otherwise stated,
were used as received from commercial sources without further
purification. N,N-dimethylformamide (DMF) and phosphorus oxy-
chloride (POCl3) were redistilled before use. Dichloromethane
(CH2Cl2) was used after drying by calcium chloride. NMR spectra
(1H at 400 MHz, 13C at 100 MHz) were obtained in CDCl3 using an
* Corresponding author. School of Chemical Engineering and Technology, Tianjin
University, Tianjin 300072, People’s Republic of China. Tel./fax: þ86 22 27404208.
** Corresponding author.
E-mail addresses: lixianggao@hotmail.com (X. Li), tantingfeng@126.com (T. Tan).
http://dx.doi.org/10.1016/j.dyepig.2014.02.018
0143-7208/Ó 2014 Elsevier Ltd. All rights reserved.

H. Jin et al. / Dyes and Pigments 106 (2014) 154e160
155
AVANCE III spectrometer with tetramethylsilane (TMS) as internal
(m, 3H), 2.72 (s, 3H), 2.46 (s, 3H); 13C NMR (100 MHz, CDCl3)
d:
standard. Mass spectra were recorded on an LCQ Deca XP MAX
mass spectrometer. Infrared and UVevis spectra were recorded on
a Thermo Nicolet 380 spectrometer and a PE LAMBDA35 spec-
trometer, respectively. Cyclic voltammetry (CV) experiment was
performed on a CHI660E electrochemistry workstation. Fluores-
cence spectra were measured using F-7000 spectrometer.
(ppm) 186.7, 150.2, 147.0, 146.3, 144.3, 143.5, 137.2, 135.2, 134.1,
130.2, 129.5, 129.4, 127.6, 126.1, 125.9, 125.1, 123.8, 122.4, 121.2, 21.0,
15.8, 15.0; FT-IR (cmꢁ1, KBr): 821, 976, 1171, 1221, 1265, 1295, 1319,
1483, 1504, 1580, 1648.
2.2.4. 3-(4-(N,N-Di(4-methylphenyl)amino)phenyl)-1-(2,5-
dimethylthiophen-3-yl)prop-2-en-1-one (1c)
2.2. Synthesis
Yellow powder, yield 3.56 g (81%), m.p. 121.0e122.0 ꢀC; MS
(APCI): m/z calcd for C29H27NOS: 438.19 [MþH]þ; found: 438.34; 1H
The synthesis route of compounds 1ae1f is given in Scheme 1.
Firstly, 2-Methylthiophene (2) was formylated by Vilsmeier reagent
at room temperature to afford 5-methylthiophene-2-carbaldehyde
(3). Then, 2,5-dimethylthiophene (4) was obtained through the
NMR (400 MHz, CDCl3)
d
: (ppm) 7.67 (d, J ¼ 15.6 Hz, 1H), 7.44 (d,
J ¼ 8.6 Hz, 2H), 7.17e6.94 (m, 13H), 2.72 (s, 3H), 2.46 (s, 3H), 2.36 (s,
6H); 13C NMR (100 MHz, CDCl3)
d: (ppm) 186.8, 150.4, 146.2, 144.3,
143.6,137.2,135.2,133.9,130.1,129.5,127.2,126.1,125.6,122.1, 120.5,
20.9, 15.8, 15.0; FT-IR (cmꢁ1, KBr): 818, 978, 1134, 1174, 1220, 1265,
1294, 1321, 1503, 1582, 1650.
KishnereWolffeHuang
reduction
reaction.
3-Acetyl-2,5-
dimethylthiophene (5) was prepared by FriedeleCrafts reaction in
good yield. TPA derivatives 7ae7f were synthesized via corre-
sponding TPA 6ae6f and Vilsmeier reagent [27].
2.2.5. 1-(2,5-Dimethylthiophen-3-yl)-3-(4-(N-phenyl-N-(4-
methoxyphenyl)amino)phenyl)prop-2-en-1-one (1d)
2.2.1. General procedure
Yellow powder, yield 3.66 g (83%), m.p. 146.0e147.0 ꢀC; MS
(APCI): m/z calcd for C28H25NO2S: 440.19 [MþH]þ; found: 440.22;
To a mixture of 3-acetyl-2,5-dimethylthiophene (5) (1.54 g,
10 mmol), corresponding aldehyde (10 mmol) and ethanol
(140 mL) was added aqueous solution of sodium hydroxide (13 M)
(20 mL). The mixture was stirred at room temperature until cor-
responding aldehyde was consumed completely (monitored by
thin-layer chromatography). The crude product was collected by
filtration, followed by washing with water and recrystallization
from ethanol to afford the products 1ae1f.
1H NMR (400 MHz, CDCl3)
d
: (ppm) 7.67 (d, J ¼ 15.6 Hz, 1H), 7.45 (d,
J ¼ 8.6 Hz, 2H), 7.34e7.28 (m, 2H), 7.18e7.05 (m, 7H), 6.98 (d,
J ¼ 8.6 Hz, 2H), 6.90 (d, J ¼ 8.9 Hz, 2H), 3.84 (s, 3H), 2.72 (s, 3H), 2.45
(s, 3H); 13C NMR (100 MHz, CDCl3)
d: (ppm) 186.7,156.9,150.3,147.0,
146.3,143.6,139.7,137.2,135.2,129.6,129.4,128.0,127.3,126.1,124.7,
123.6,122.1,120.4,115.0, 55.5,15.8,15.0; FT-IR (cmꢁ1, KBr): 824, 999,
1135, 1186, 1224, 1244, 1289, 1326, 1437, 1505, 1567, 1644.
2.2.2. 1-(2,5-Dimethylthiophen-3-yl)-3-(4-(N,N-diphenylamino)
phenyl)prop-2-en-1-one (1a)
2.2.6. 1-(2,5-Dimethylthiophen-3-yl)-3-(4-(N-(4-methylphenyl)-N-
(4-methoxyphenyl)amino)phenyl)prop-2-en-1-one (1e)
Yellow powder, yield 3.63 g (92%), m.p. 143.0e144.5 ꢀC; MS
(APCI): m/z calcd for C27H23NOS: 410.16 [MþH]þ; found: 410.35; 1H
Yellow powder, yield 2.92 g (64%), m.p. 151.5e152.0 ꢀC; MS
(APCI): m/z calcd for C29H27NO2S: 454.18 [MþH]þ; found: 454.30;
NMR (400 MHz, CDCl3)
d
: (ppm) 7.67 (d, J ¼ 15.6 Hz, 1H), 7.48 (d,
1H NMR (400 MHz, CDCl3)
d
: (ppm) 7.67 (d, J ¼ 15.5 Hz, 1H), 7.43
J ¼ 8.5 Hz, 2H), 7.32 (t, J ¼ 7.7 Hz, 4H), 7.22e7.09 (m, 7H), 7.08e6.99
(d, J ¼ 8.6 Hz, 2H), 7.14e7.11 (m, 8H), 6.94 (d, J ¼ 8.6 Hz, 2H), 6.89
(d, J ¼ 8.9 Hz, 2H), 3.83 (s, 3H), 2.72 (s, 3H), 2.45 (s, 3H), 2.36 (s,
(m, 3H), 2.72 (s, 3H), 2.46 (s, 3H); 13C NMR (100 MHz, CDCl3)
d:
(ppm) 186.6, 150.0, 146.9, 146.4, 143.4, 137.1, 135.2, 129.5, 129.5,
128.1, 126.0, 125.4, 124.0, 122.6, 121.8, 15.8, 15.0; FT-IR (cmꢁ1, KBr):
700, 759, 1136, 1171.75, 1222, 1279, 1325, 1488, 1504, 1583, 1650.
3H); 13C NMR (100 MHz, CDCl3)
d: (ppm) 186.7, 156.8, 150.6, 146.2,
144.4, 143.7, 139.8, 137.2, 135.1, 133.7, 130.1, 129.6, 127.7, 126.7,
126.1, 125.3, 121.8, 119.7, 114.9, 55.5, 20.9, 15.8, 15.0; FT-IR (cmꢁ1
,
KBr): 823, 999, 1136, 1185, 1224, 1244, 1289, 1326, 1435, 1505,
1572, 1646.
2.2.3. 1-(2,5-Dimethylthiophen-3-yl)-3-(4-(N-phenyl-N-(4-
methylphenyl)amino)phenyl)prop-2-en-1-one (1b)
Yellow powder, yield 3.58 g (85%), m.p. 153.5e154.5 ꢀC; MS
(APCI): m/z calcd for C28H25NOS: 424.17 [MþH]þ; found: 424.54; 1H
2.2.7. 3-(4-(N,N-Di(4-methoxyphenyl)amino)phenyl)-1-(2,5-
dimethylthiophen-3-yl)prop-2-en-1-one (1f)
NMR (400 MHz, CDCl3)
d
: (ppm) 7.67 (d, J ¼ 15.6 Hz, 1H), 7.48 (d,
Yellow powder, yield 4.13 g (88%), m.p. 166.0e168.0 ꢀC; MS
(APCI): m/z calcd for C29H27NO3S: 470.18 [MþH]þ; found: 470.40;
J ¼ 8.5 Hz, 2H), 7.32 (t, J ¼ 7.7 Hz, 4H), 7.22e7.09 (m, 7H), 7.08e6.99
Scheme 1. Synthesis routes of compounds 1ae1f.

156
H. Jin et al. / Dyes and Pigments 106 (2014) 154e160
at room temperature. The empty cell, which was dipped in the
above mixture, was evacuated in a vacuum chamber and filled with
Argon through the opening of vacuum chamber. Finally, the
opening was sealed up by epoxy resin.
3. Results and discussion
3.1. Quantum chemical calculation
To gain an insight into the structureeproperty relationship of
compounds 1ae1f, density functional theory (DFT) calculations
were performed on these compounds via the Gaussian 03 program
at the B3LYP/6-31G* level [28]. Pictorial representations of the
frontier molecular orbitals of 1ae1f are shown in Fig. 2. As shown
in Fig. 2, the HOMO of TPA-chalcones was mainly located on TPA
moiety and extended to the keto-vinyl bridge, while the LUMO was
mainly located on the keto-vinyl bridge and adjacent phenyl group.
The results suggested that chalcones containing TPA units is a
Fig. 1. Structure of electrochromic device.
strong electron donor-(p-spacer)eacceptor (D-p-A) system linked
by a keto-vinyl bridge [29], which is beneficial to increasing their
polarity.
Time-dependent density functional theory (TD-DFT) calculation
was performed to obtain excitation energies of neutral forms
(B3LYP/6-31G*) and cation radical (UB3LYP/6-31G*). Excitation
energies, oscillator strength coefficients and dominant transitions
of 1ae1f are listed in Table 1. The calculated maximum absorption
of 1ae1f as neutral form are in the range of 404.41e418.71 nm. The
existence of electron donating group on TPA unites caused a sig-
nificant bathochromic shift. The calculated absorption of corre-
sponding cation radical shifted to the near-infrared region range
(795.01e834.38 nm).
Fig. 2. Energy levels obtained from DFT calculations on 1ae1f at the B3LYP/6-31G*
level.
3.2. Photophysical properties
1H NMR (400 MHz, CDCl3)
J ¼ 8.6 Hz, 2H), 7.13e7.06 (m, 6H), 6.88 (d, J ¼ 8.8 Hz, 6H), 3.83 (s,
6H), 2.71 (s, 3H), 2.45 (s, 3H); 13C NMR (100 MHz, CDCl3)
: (ppm)
186.8,156.7,150.9,146.1,143.8,139.8,137.3,135.1,129.6,127.4,126.3,
126.1, 121.6, 118.7, 114.9, 55.5, 15.8, 15.0; FT-IR (cmꢁ1, KBr): 826, 999,
1032, 1136, 1185, 1244, 1289, 1329, 1435, 1504, 1573, 1646.
d
: (ppm) 7.66 (d, J ¼ 15.6 Hz, 1H), 7.42 (d,
The UVevis absorption and fluorescence emission spectra of
compounds 1ae1f in dichloromethane solution were presented in
Fig. 3 and the corresponding data are summarized in Table 2. All
TPA-chalcones showed similar spectra with strong absorption
d
maximum (lmax) at 413e422 nm corresponding to the pep* tran-
sition resulting from the TPA-keto-vinyl moieties, which is in
agreement with the TD-DFT calculation. For compounds 1ae1c, the
introduction of methyl groups led to a bathochromic shift of the
maximal absorption, which could be explained by the fact that the
electron donating effects of methyl substituents could enhance the
intramolecular charge transfer (ICT) between TPA donating unit
and carbanyl group acceptor moiety. The red shift of 1d compared
to 1b could be ascribed to stronger electron donating property of
methoxyl group. The 1ae1f showed fluorescence emission peaks
around 540e575 nm in the green region. The Emission maxima of
1ae1c decreased in the order of 1a > 1b > 1c and little emission
was found for 1de1f. Because the DeA character of these com-
pounds is increasing with donor strength, thus led to the formation
of non-emissive charge-transfer state and reduced fluorescence
2.3. Electrochromic devices fabrication
The electrochromic devices were fabricated as following pro-
cedure and structure is illustrated in Fig. 1. ITO-coated glass slides
were washed subsequently with water, acetone, isopropanol, and
then dried with nitrogen stream. ITO/glass cells were prepared by
joining two slides through a PMMA spacer (2 mm thickness) placed
along the whole perimeter but with an opening (1 mm wide) in one
corner. The cell was compressed and heated at 120 ꢀC for a few
minutes, and then the two slides were pasted with epoxy resin
along the edges. Chalcone (0.01 mmol) and Bu4PF6 (0.1 mmol) were
dissolved in propylene carbonate (1 mL) with ultrasonic treatment
Table 1
Excitation energies (
D
E), oscillator strength (f) and dominant transitions of 1ae1f obtained from TD-DFT calculations (H: HOMO; L: LUMO).
Neutral form Cation radical
E (eV, nm) E (eV, nm)
Compound
D
f
Dominant transitions (%)
D
f
Dominant transitions (%)
1a
1b
1c
1d
1e
1f
3.0658, 404.41
3.0369, 408.26
3.0047, 412.63
3.0027, 412.90
2.9801, 416.05
2.9611, 418.71
0.7335
0.7417
0.7470
0.7309
0.7459
0.7524
H / L (65.83)
H / L (65.89)
H / L (65.96)
H / L (66.03)
H / L (66.04)
H / L (66.10)
1.5595, 795.01
1.5572, 796.19
1.5639, 792.77
1.4658, 845.85
1.4889, 832.70
1.4859, 834.38
0.2698
0.2876
0.2985
0.2974
0.3024
0.3243
H-3 / L
H-3 / L
H-3 / L
H-3 / L
H-3 / L
H-3 / L
b
b
b
b
b
b
(91.39)
(91.55)
(91.70)
(90.91)
(91.19)
(91.32)

H. Jin et al. / Dyes and Pigments 106 (2014) 154e160
157
rate of 100 mV sꢁ1 at room temperature. Platinum wire and glassy
carbon were used as working and counter electrode, respectively,
and a double junction electrode of Ag/Agþ in acetonitrile as the
reference electrode. All solutions have been deaerated with N2 gas
prior to the experiments. As shown in Fig. 4, for 1a and 1b, there
were two oxidation peaks attributed to the oxidation of TPA and
tetraphenylbenzidine (TPB) and no reduction peak was found as the
p-position hydrogen atom on the benzene ring of TPA could be lost
easily during electropolymerization [19]. In the case of 1ce1f, a pair
of redox peaks was observed, which is attributed to the reversible
redox reaction of TPA derivatives, since no hydrogen atom was lost
and electropolymerization could not happen. The onset oxidation
potentials (Eonset) value of ferrocene/ferrocenium (Fc/Fcþ) is known
to be 4.80 eV below the vacuum level and used as a calibration
reference. The energy of HOMO and LUMO levels of 1ae1f were
listed in Table 2. The EHOMO values are in the range of ꢁ5.73 to
ꢁ5.13 eV, and ELUMO values in the range of ꢁ2.58 to ꢁ2.71 eV. The
EHOMO and ELUMO values of 1ae1f increased with increased donor
strength at p-position on the benzene ring of TPA.
3.4. Spectroelectrochemical and electrochromic properties
Spectroelectrochemical experiments were performed to probe
the optical properties of the electrochromic devices. The color of
devices for 1ae1f switched to blue when the external electrical
potential is increased to 2.8 V. By applying DC voltage to the elec-
trochromic devices, color of 1ae1f would change from yellow to
blue, which is ascribed to the oxidation of the compounds from
natural molecules to radical cation. The cation could recover at
0.0 V after 8 h. Reflection spectra and CIE coordinates of electro-
chromic devices were tested and depicted in Fig. 5. Reflection
spectra and the color change of 1ae1f in the process of electro-
chromism are shown in Fig. 6. Ignoring the transmission of light
due to the light-tight sample stage, according to KubelkaeMunk
theory [30] the luminous flux of incident light can be evaluated by
Eq. (1).
F
ð
l
Þ ¼ FR
ð
l
Þ þ FA
ð
l
Þ
(1)
Fig. 3. UVevis absorption (a) and fluorescence (b) spectra of 1ae1f in dichloro-
methane solution (c ¼ 10ꢁ5 mol Lꢁ1).
where FR
(l
) and FA
(
l
) are the luminous flux of reflected and
absorbed light, respectively. The reflectance R( ) and absorbance
l
intensity. This could be confirmed by dipole moments of the
compounds, which are 5.0, 5.0, 5.6, 6.0, 6.6, and 7.7 D in DFT cal-
culations, respectively.
A( ) could be expressed by FR )/ ) and FA(l)/F(l), respectively.
l
(l
F(l
Therefore, the relation between reflectance and absorbance is
described by Eq. (2).
3.3. Electrochemical properties
The CV measurements were carried out on
a CHI660E
electrochemistry workstation with three-electrode cell in
a
dichloromethane in the presence of tetrabutylammonium hexa-
fluorophosphate (Bu4PF6) as supporting electrolyte with a scanning
Table 2
Optical and electrochemical properties of 1ae1f.
Compound
lmax
lonset
Egopt
lem
Eonset
EHOMO
ELUMO
(nm)
(nm)
(eV)a
(nm)
(V)b
(eV)c
(eV)d
1a
1b
1c
1d
1e
1f
413
415
421
417
422
421
466
471
478
481
486
486
2.66
2.63
2.59
2.58
2.55
2.55
540
553
565
567
575
571
0.68
0.62
0.56
0.52
0.49
0.44
ꢁ5.37
ꢁ5.31
ꢁ5.25
ꢁ5.21
ꢁ5.18
ꢁ5.13
ꢁ2.71
ꢁ2.68
ꢁ2.66
ꢁ2.63
ꢁ2.63
ꢁ2.58
Optical energy gap: Egopt (eV) ¼ 1024/lonset
.
a
b
c
The oxidation onset potentials.
The HOMO energy levels were calculated from Eonset and were referenced to
ferrocene (4.80 eV): EHOMO (eV) ¼ ꢁ(Eonset ꢁ EFc/Fcþ þ 4.80) (eV).
Fig. 4. CV curves of 1ae1f in dichloromethane (1.0 ꢂ 10ꢁ3 mol Lꢁ1) with a platinum
ELUMOðeVÞ ¼ EHOMO þ Egopt
.
wire working electrode at a scan rate of 100 mV sꢁ1
.
d

158
H. Jin et al. / Dyes and Pigments 106 (2014) 154e160
calculation, absorption of the radical cation corresponds to the
excitation of HOMO-3 to LUMO with the largest transitional pro-
portion. The exciting energy of the radical cation is much lower
than one of the neutral form as HOMO-3 and LUMO are all
distributed throughout TPA-keto-vinyl moieties and no ICT is found
when exciting, hence the reflectance minima of the radical cation is
shifted to the long wavelength compared to neutral molecule. The
reflectance minima of 1b and 1c show blue-shifted compared to 1a,
because methyl group could decrease the conjugation of the radical
cation due to hyperconjugation between the methyl group and
benzene ring. For 1de1f, methoxyl group could conjugate with the
TPA radical cation and extend the whole conjugated system, which
led to red-shifted reflectance minima (1e and 1f vs. 1c, 1d vs. 1b).
Since response of eyes would be weakening while the light band
comes near 780 nm, it is clear that 1c is the most excellent elec-
trochromic materials in the six compounds. The corresponding CIE
coordinates are shown in Fig. 7. The CIE coordinates of 1ae1f shift
from yellow region to blue region under DC voltage. After removing
DC voltage, they could recover to initial points through white re-
gion slowly.
To investigate the switching time and electrochromic changes
stability of these compounds, potential step switching experiments
were conducted between 0.0 and 2.8 V. The reflectance at 738, 734,
696, 733, 738, and 752 nm for 1ae1f, respectively, were monitored
to investigate the switching time of the devices. Reflectance
switching curves of 1ae1f were shown in Fig. 8. At the second cycle,
reflectance of 1ae1f dropped by 5, 39, 1, 2, 3, and 1%, respectively,
which indicates good electrochromic stability of 1ce1f. The
switching time was calculated at 90% of the full switch because it is
difficult to perceive any further color change with naked eye
beyond this point. As depicted in Fig. 8, 1ae1f required 3.9, 4.2, 3.7,
3.1, 2.9, and 3.5 s at 2.8 V for coloring, and spent 3.3, 1.7, 2.7, 2.8, 2.7,
and 2.8 s for bleaching, which demonstrated that the synthesized
compounds presented fast switchability.
Fig. 5. Principle of measuring reflection spectra.
1 ¼ Rð
l
Þ þ Að
l
Þ
(2)
Accordingly, the reflectance could be expected to decrease with
increasing of the absorbance, that is, reflectance minima corre-
sponds to absorption maxima. As shown in Fig. 6, the spectrum of
1a exhibited reflectance minima at 443 nm as neutral form. With
applied voltage (2.8 V), reflectance at 443 nm increase gradually
and a new reflectance minima at 738 nm appeared, which is caused
by the consumption of the natural molecules and the produce of
the radical cation. After removing DC voltage, reflectance minima at
443 nm decreased and at 738 nm increased because that the radical
cation obtained electrons from anode to recover to neutral form.
Similar to compound 1a, compounds 1be1f also showed similar
spectra alteration when applying DC voltage. Without DC voltage,
reflectance minima of 1be1f are at 442, 449, 454, 457, and 457,
respectively. When applying 2.8 V voltage, reflectance minima are
found at 734, 696, 733, 738, and 752 nm for 1be1f, respectively,
which are greater than the values obtained from TD-DFT calcula-
tions because of solvent effect. In molecular simulations
Fig. 6. Reflection spectra of 1ae1f (a) as neutral form, (b) when applying 2.8 V voltage, (c) after removing DC voltage and (d) the color change. (For interpretation of the references
to color in this figure legend, the reader is referred to the web version of this article.)

H. Jin et al. / Dyes and Pigments 106 (2014) 154e160
159
could be achieved in the electrochromic devices. When applying
2.8 V voltage, color of 1ae1f would change from yellow to blue and
the minimum reflectance minima were found at 738, 734, 696, 733,
738, and 752 nm, respectively. Chronoamperometric and reflec-
tance measurements showed that 1ae1f required 3.9, 4.2, 3.7, 3.1,
2.9, and 3.5 s at 2.8 V for coloring, and spent 3.3, 1.7, 2.7, 2.8, 2.7, and
2.8 s for bleaching, respectively. By this token, chalcones containing
TPA groups is a novel approach for tuning the coloration changed.
Acknowledgments
This work was financially supported by the National Natural
Science Foundation of China (Grant no. 21102098) and the Key
Technology R&D Program of Tianjin (Grant no. 11ZCKFGX01700).
References
[1] Shirota Y, Kageyama H. Charge carrier transporting molecular materials and
their applications in devices. Chem Rev 2007;107:953e1010.
[2] Adachi C, Nagai K, Tamoto N. Molecular design of hole transport materials for
obtaining high durability in organic electroluminescent diodes. Appl Phys Lett
1995;66:2679e81.
[3] Ersman PA, Kawahara J, Berggren M. Printed passive matrix addressed elec-
trochromic displays. Org Electron 2013;14:3371e8.
[4] Karuppasamy A. Electrochromism in surface modified crystalline WO3 thin
films grown by reactive DC magnetron sputtering. Appl Surf Sci 2013;282:77e
83.
[5] Liu JW, Zheng J, Wang JL, Xu J, Li HH, Yu SH. Ultrathin W18O49 nanowire as-
semblies for electrochromic devices. Nano Lett 2013;13:3589e93.
[6] Sorar I, Pehlivan E, Niklasson GA, Granqvist CG. Electrochromism of DC
magnetron sputtered TiO2 thin films: role of deposition parameters. Sol En-
ergy Mater Sol Cells 2013;115:172e80.
[7] Wang G, Fu XK, Huang J, Wu CL, Wu L, Du QL. Synthesis of a new star-shaped
4,40-bipyridine derivative and its multicolor solid electrochromic devices. Org
Electron 2011;12:1216e22.
Fig. 7. Plot of the CIE 1931 xy chromaticity diagram of 1a (square), 1b (circle), 1c
(triangle), 1d (inverted triangle), 1e (five-pointed star) and 1f (X mark) as neutral form
(yellow), when applying 2.8 V voltage (blue) and after removing DC voltage (LT gray).
(For interpretation of the references to color in this figure legend, the reader is referred
to the web version of this article.)
4. Conclusions
In the present work, six novel electrochromic compounds con-
taining TPA and chalcone units have successfully been synthesized
and characterized. Their photophysical, electrochemical and elec-
trochromic properties were studied and discussed in terms of
correlation with their chemical structures. Compounds 1ae1f
exhibited strong UVevis absorption at 413e422 nm. Fluorescence
intensity decreased with the increasing donor strength on TPA
unites and there was almost no emission when methoxyl group
was introduced. CV results revealed that the EHOMO values are in the
range of ꢁ5.73 to ꢁ5.13 eV, and ELUMO values in the range of ꢁ2.58
to ꢁ2.71 eV. The EHOMO and ELUMO values of 1ae1f increased with
increasing the electron donating ability of the substituents on p-
position on the benzene ring of TPA. Spectroelectrochemical mea-
surements demonstrated that electrochromism of TPA-chalcones
[8] Luo J, Ma YG, Pei J, Song YL. Recent progress on organic and polymeric elec-
trochromic materials. Curr Phys Chem 2011;1:216e31.
[9] Cao Y, Tao YJ, Cheng HF, Zhang ZY. Tricolor electrochromism of PEDOT film
electrodeposited in mixed solution of boron trifluoride diethyl etherate and
tetrahydrofuran: hypsochromic effect. J Appl Polym Sci 2013;129:3764e71.
[10] Karakus M, Nurioglu AG, Akpinar HZ, Toppare L, Cirpan A. Synthesis and
electrochromic properties of trans-stilbene bearing copolymers obtained with
different repeat unit and chain length. Electrochim Acta 2013;100:110e7.
[11] Hu B, Lv XJ, Sun JW, Bian GF, Ouyang M, Fu ZY, et al. Effects on the electro-
chemical and electrochromic properties of 3,6 linked polycarbazole derivative
by the introduction of different acceptor groups and copolymerization. Org
Electron 2013;14:1521e30.
[12] Kochapradist P, Prachumrak N, Tarsang R, Keawin T, Jungsuttiwong S,
Sudyoadsuk T, et al. Multi-triphenylamine-substituted carbazoles: synthesis,
characterization, properties, and applications as hole-transporting materials.
Tetrahedron Lett 2013;54:3683e7.
[13] Planells M, Abate A, Hollman DJ, Stranks SD, Bharti V, Gaur J, et al. Diacetylene
bridged triphenylamines as hole transport materials for solid state dye
sensitized solar cells. J Mater Chem A 2013;48:6949e60.
[14] Lin MW, Chen RT, Yeh CH, Wen TC, Guo TF. Bright, efficient, deep blue-
emissive polymer light-emitting diodes of suitable hole-transport layer and
cathode design. Org Electron 2012;13:3067e73.
[15] Shirota Y. Photo- and electroactive amorphous molecular materi-
alsdmolecular design, syntheses, reactions, properties, and applications.
J Mater Chem 2005;15:75e93.
[16] Roquet S, Cravino A, Leriche P, Alévêque O, Frère P, Roncali J. Triphenylamine-
thienylenevinylene hybrid systems with internal charge transfer as donor
materials for heterojunction solar cells. J Am Chem Soc 2006;128:3459e66.
[17] Deng D, Yang Y, Zhang J, He C, Zhang MJ, Zhang ZG, et al. Triphenylamine-
containing linear D-A-D molecules with benzothiadiazole as acceptor unit for
bulk-heterojunction organic solar cells. Org Electron 2011;12:614e22.
[18] Beaupré S, Dumas J, Leclerc M. Toward the development of new textile/plastic
electrochromic cells using triphenylamine-based copolymers. Chem Mater
2006;18:4011e8.
[19] Ramírez CL, Parise AR. Solvent resistant electrochromic polymer based on
methylene-bridged arylamines. Org Electron 2009;10:747e52.
[20] Ouyang M, Wang GH, Zhang C. A novel electrochromic polymer containing
triphenylamine derivative and pyrrole. Electrochim Acta 2011;56:4645e9.
[21] Chen FK, Fu XY, Zhang J, Wan XH. Near-infrared and multicolored electro-
chromism of solution processable triphenylamine-anthraquinone imide
hybrid systems. Electrochim Acta 2013;99:211e8.
[22] Cheng SH, Hsiao SH, Su TH, Liou GS. Novel aromatic poly(amine-imide)s
bearing a pendent triphenylamine group: synthesis, thermal, photophysical,
electrochemical, and electrochromic characteristics. Macromolecules
2005;38:307e16.
Fig. 8. Reflectance switching curves of 1ae1f.

160
H. Jin et al. / Dyes and Pigments 106 (2014) 154e160
[23] Yen HJ, Lin HY, Liou GS. Novel starburst triarylamine-containing electroactive
aramids with highly stable electrochromism in near-infrared and visible light
regions. Chem Mater 2011;23:1874e82.
[24] Yen HJ, Liou GS. Solution-processable triarylamine-based electroactive high
performance polymers for anodically electrochromic applications. Polym
Chem 2012;3:255e64.
[25] Huang LT, Yen HJ, Wu JH, Liou GS. Preparation and characterization of near-
infrared and multi-colored electrochromic aramids based on aniline-de-
rivatives. Org Electron 2012;13:840e9.
[26] Kima SH, Ryu JH, Choi HJ, Kim HS. Electrochromic properties of new fluo-
rophores containing triphenylamine moiety. Dyes Pigments 2005;64:279e81.
[27] Nandurkar NS, Bhanushali MJ, Bhor MD, Bhanage BM. N-Arylation of aliphatic,
aromatic and heteroaromatic amines catalyzed by copper bis(2,2,6,6-
tetramethyl-3,5-heptanedionate). Tetrahedron Lett 2007;48:6573e6.
[28] Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA, Cheeseman JR.
Gaussian 03. Revision E. 01. Wallingford, CT: Gaussian, Inc.; 2004.
[29] Danko M, Andics A, Kosa C, Hrdlovic P, Vegh D. Spectral properties of chalcone
containing triphenylamino structural unit in solution and in polymer
matrices. Dyes Pigments 2012;92:1257e65.
[30] Yen WM, Shionoya S, Yamamoto H. Phosphor handbook. Boca Roton: CRC;
2007.