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Physical Chemistry Chemical Physics
Page 2 of 7
DOI: 10.1039/C8CP00338F
ARTICLE
Journal Name
shaped monomers TPAT, TPABT and PHT as reference (Fig. 1)
These four star-shaped monomers can generate the cross-
linked polymer structure via electrochemical
.
in a 100mL two necked round bottom flask. Pd(PPh3)4 (94.0mg,
0.08mmol) was added to the stirred suspension, which was
then heated rapidly to 130oC and maintained under reflux
conditions for 4 hours under a nitrogen atmosphere25. After
cooling to room temperature, deionized water (50mL) was
added to precipitate the main part of the product and then the
mixture was washed by water and extracted with
dichloromethane consecutively. The product was then dried
with MgSO4 and purified on a silica gel column (petroleum
ether-CH2Cl2 5:1 as eluent) to obtain the final product as a
white powder (0.38g, yield 91%).MALDI-TOF-MS (M) (m /
z):325.7 [M + H]+.1H NMR (500 MHz, CDCl3) δ 7.76 (s, 3H), 7.43
(dd, J = 3.6, 1.2 Hz, 3H), 7.36 (dd, J = 5.1, 1.1 Hz, 3H), 7.15 (dd, J
= 5.0, 3.6 Hz, 3H).
polymerization22,23 and may possess some microporous
structures in the polymer film (Fig. 1). The different central
cores of triphenylamine/phenyl and peripheral arms of
thiophene/bithiophene may help us to deeply understand the
relationship between the structure and electrochromic
property in the case of the star-shaped molecular system.
PHBT was synthesized successfully and further prepared into
the pPHBT polymer film via electrochemical polymerization.
Under the positive voltage, pPHBT exhibited the excellent
electrochromic properties with the surprising multi-color
changing between orange-yellow, green and blue three colors
and the fast color switching speed. After deeply studying the
electronic structure and cyclic voltammetry curves of four
polymers pPHT, pPHBT, pTPAT, and pTPABT, we found that the
electrochromism of pTPABT may consist of two parts deriving
from the oxidative states of triphenylamine and quadruple
thiophene groups respectively. These results offer us a new
insight into the electrochromism mechanics of conjugated
polymers, and further demonstrate that the oxidative
potential or ionization energy of polymer was one of the key
factors determining the electrochromism24. The detailed
experimental data and results will be shown as follows.
1,3,5-tri(5-bromothiophen-2-yl)benzene(M1)
To a 100mL round bottom flask which was wrapped around
with tinfoil, added PHT (0.49g, 1.5mmol) which was dissolved
in 20mL DMF, then NBS (0.85g, 4.8mmol) which was dissolved
in 10mL DMF was added drop wise for two times separately
every half hour. The mixture was stirred in the dark overnight.
The product was extracted with CH2Cl2, then the organic layer
was washed with brine and dried with MgSO4, and purified on
a silica gel column (petroleum ether-CH2Cl2 8:1 as eluent) to
obtain the product M1 as a light yellow powder (0.66g, yield
1
80%). H NMR (500 MHz, CDCl3) δ 7.55 (s, 3H), 7.15 (d, J = 3.8
Hz, 3H), 7.09 (d, J = 3.8 Hz, 3H).
1,3,5-tri(2,2’-bithiophen-5-yl)benzene(PHBT)
Results and discussion
Experimental
The synthesis process of PHBT is the same with PHT only
used 1,3,5-tri(5-bromothiophen-2-yl)benzene M1 (0.56g,
1.0mmol) to replace 1,3,5-tribromobenzene and PHBT was
obtained as a yellow powder (0.18g, yield 32%). MALDI-TOF-
MS (M) (m / z):571.8 [M + H]+.1H NMR (500 MHz, CDCl3) δ 7.72
(s, 3H), 7.36 (d, J = 3.8 Hz, 3H), 7.26 (dd, J = 2.4, 1.2 Hz, 6H),
7.21 (d, J = 3.8 Hz, 3H), 7.10 – 7.05 (m, 3H).
The terminal compounds PHBT was synthesized according to
the synthesis route in Fig. 2, and characterized by NMR and
Mass spectra. All the reagents or chemicals were commercial
products without further purification. 1H (500MHz) NMR
spectra of the synthesized compounds were recorded on
Bruker AVANCE III instrument (Bruker, Switzerland). Mass
spectra (MALDI-TOF-MS) analysis was recorded using an
AXIMA-CFRTM plus instrument.
Electrochemical polymerization
The pPHBT polymer film was fabricated on ITO substrates
via electrochemical polymerization through the coupling
reaction of the peripheral bithiophene groups, by applying a
continuous scanning voltage at a potential scan rate of 100
mV/s in
a
conventional three-electrode cell with 0.1M
perchlorate (TBAP)
tetrabutylammonium
dichloromethane/acetonitrile (7/3,v/v) mixture solvent as the
electrolyte solution. The pTPABT polymer film was prepared in
the totally same conditions as that of pPHBT except from the
TPABT monomer, while the pTPAT and pPHT were prepared by
the previously reported method25. Their cyclic voltammetry
curves of electrochemical polymerization were shown in Figure
S1 in the supporting information part. All the electrochemical
polymerization of monomers and the electrochemical
properties of polymer films were performed on CHI660E
electrochemical analyzer (Chenhua, China).
Fig. 2 The molecular structures and synthesis routes of star-shaped monomer PHBT
.
1,3,5-Tri(thiophen-2-yl)benzene(PHT)
Fig. 3 showed the cyclic voltammetry curves (0-1.4V, 10
cycles) during the electrochemical polymerization process of
PHBT (1.5mM). The current intensity in their cyclic
voltammetry curves rose up gradually as the scanned cycle
Thiophene-2-boronicacid (1.02g, 8.0mmol) was mixed with
1,3,5-tribromobenzene (0.41g, 1.3mmol) and K2CO3
(1.21g,8.8mmol) in ethoxyethanol/deionized water (9:1, 15mL)
2 | J. Name., 2012, 00, 1-3
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