Synthesis, characterization and properties of novel star-shaped π-conjugated oligomers with triphenylamine core

Article abstract of DOI:10.1002/cjoc.201201197

Four new star-shaped π-conjugated oligomers (TPA-CZ3, TPA-TPA3, TPA-PTZ3 and TPA-BT3) with triphenylamine as a core and different electron-donating ability groups, carbazole, triphenylamine, phenothiazine and bithiophene, as peripheral units have been designed and synthesized via the Heck reaction. These oligomers show good solubility in common organic solvents. Their photophysical, electrochemical, electronic structure and charge transfer properties between these star-shaped π-conjugated oligomers and N,N′-bis(1-ethylpropyl)-3, 4:9,10-perylene bis(tetracarboxyl diimide) (EP-PDI) have been investigated by UV-vis absorption spectra, photoluminescence (PL) spectra, cyclic voltammetry (CV) measurement, theoretical calculations and fluorescence quenching. The results show that the absorptions and fluorescences of TPA-CZ3, TPA-TPA3 and TPA-PTZ3 are red shifted with the electron-donating ability of the peripheral unit increasing from carbazole to triphenylamine and phenothiazine. In addition, although the bithiophene group has a weaker electron-donating ability than carbazole, triphenylamine and phenothiazine, the absorption and fluorescence of TPA-BT3 have a red shift than those of TPA-CZ3, TPA-TPA3 and TPA-PTZ3 because TPA-BT3 has a longer conjugation length than TPA-CZ3, TPA-TPA3 and TPA-PTZ3. The triphenylamine core and the peripheral units can constitute a large conjugated structure. The fluorescence quenching properties indicate that efficient charge transfer can happen between the star-shaped oligomers and EP-PDI. The core of these new star-shaped oligomers is electron-donating group, triphenylamine. The peripheral units are four hole-transporting chromophores with different electron-donating ability. The photophysical properties of these oligomers can be tuned through changing the electron-donating ability and conjugation length of the peripheral units.

Full text of DOI:10.1002/cjoc.201201197

FULL PAPER
DOI: 10.1002/cjoc.201201197
Synthesis, Characterization and Properties of Novel
Star-Shaped π-Conjugated Oligomers with Triphenylamine
Core
Leijing Liu,a Qing Guo,a Jiyang Li,b Bin Yao,c and Wenjing Tian*,a
a State Key Laboratory of Supramolecular Structure and Materials, Jilin University, Changchun, Jilin 130012,
China
b State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University,
Changchun, Jilin 130012, China
c Key Laboratory of Physics and Technology for Advanced Batteries, Ministry of Education, Jilin University,
Changchun, Jilin 130012, China
Four new star-shaped π-conjugated oligomers (TPA-CZ3, TPA-TPA3, TPA-PTZ3 and TPA-BT3) with
triphenylamine as a core and different electron-donating ability groups, carbazole, triphenylamine, phenothiazine
and bithiophene, as peripheral units have been designed and synthesized via the Heck reaction. These oligomers
show good solubility in common organic solvents. Their photophysical, electrochemical, electronic structure and
charge transfer properties between these star-shaped π-conjugated oligomers and N,N'-bis(1-ethylpropyl)-3,4:9,10-
perylene bis(tetracarboxyl diimide) (EP-PDI) have been investigated by UV-vis absorption spectra, photolumines-
cence (PL) spectra, cyclic voltammetry (CV) measurement, theoretical calculations and fluorescence quenching.
The results show that the absorptions and fluorescences of TPA-CZ3, TPA-TPA3 and TPA-PTZ3 are red shifted
with the electron-donating ability of the peripheral unit increasing from carbazole to triphenylamine and phenothi-
azine. In addition, although the bithiophene group has a weaker electron-donating ability than carbazole,
triphenylamine and phenothiazine, the absorption and fluorescence of TPA-BT3 have a red shift than those of
TPA-CZ3, TPA-TPA3 and TPA-PTZ3 because TPA-BT3 has a longer conjugation length than TPA-CZ3,
TPA-TPA3 and TPA-PTZ3. The triphenylamine core and the peripheral units can constitute a large conjugated
structure. The fluorescence quenching properties indicate that efficient charge transfer can happen between the
star-shaped oligomers and EP-PDI.
Keywords triphenylamine, star-shaped oligomer, synthesis design, electron-donor ability, conjugation length
Introduction
that makes the TPA containing molecules exhibit an
amorphous structure and good solubility. Moreover, the
TPA cored compounds have high hole mobility and are
widely used as hole-transporting materials in organic
light-emitting diodes (OLEDs),[2] sensitizers in dye-
sensitized solar cells (DSSCs)[3] and photovoltaic cells.[4]
It has been found that the electronic energy levels and
optical properties of these type molecules can be con-
trolled by modifying the peripheral units.
Some star-shaped D-π-A structured molecules con-
taining TPA as the core and donor unit have been de-
signed and synthesized for the applications as solution-
processable organic photovoltaic donor materials. In
these molecules, the peripheral units are composed of
acceptor units[5] or a combination of acceptor units and
π bridges[6,7] or a combination of acceptor units and do-
nor units.[8] However, a systematic investigation on the
Organic molecules with a large conjugated plane are
a type of classic functional materials. The chromophores
can be connected each other by single, double or triple
bonds to form a large conjugated structure. Especially,
the chromophores connected by trans double bonds are
in the same plane and can lead to a large conjugated
system. Organic molecules with a larger conjugated
system usually have a narrow band gap and can absorb
the sunlight in the long wavelength, which increases the
probability of these materials to be utilized in solar
cell.[1]
Star-shaped triphenylamine (TPA) based π-conju-
gated systematic compounds are one of the most exten-
sively studied classes of organic compounds. The TPA
unit possesses a three-dimensional propeller structure
*
E-mail: wjtian@jlu.edu.cn; Tel.: 0086-0431-85166368; Fax: 0086-0431-85193421
Received December 6, 2012; accepted January 24, 2013; published online March 1, 2013.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201201197 or from the author.
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Chin. J. Chem. 2013, 31, 456—464

Synthesis, Characterization and Properties of Novel Star-Shaped π-Conjugated Oligomers
synthesis and properties of star-shaped molecules con-
taining TPA as a core and different electron-donating
ability groups as peripheral units are still scarce.[9,10] On
the other hand, the absorption of the star-shaped mole-
cules in which the TPA core and the peripheral units are
connected by double bonds has a red shift than that of
the star-shaped molecules in which the TPA core and the
peripheral units are connected by single or triple
bonds.[7,11]
Carbazole, triphenylamine, phenothiazine and
bithiophene are four excellent hole-transporting chro-
mophores. Their derivatives are often used as the
hole-transporting materials for organic light-emitting
diodes (OLEDs)[12,13] and organic solar cells (OSCs)[7,14]
due to the good hole-transporting property, high charge
mobility and high thermal stability.[10,15] Nevertheless,
the electron-donating ability of these four hole-trans-
porting chromophores are different, i.e. bithiophene＜
carbazole＜triphenylamine＜phenothiazine. We think
that combination of the triphenylamine core with hole-
transporting chromophores of different electron-donat-
ing ability to form a series of star-shaped molecules
should bring about some new electrical and photo-
physical properties and applications.
In this present work, we designed and synthesized
four new star-shaped π-conjugated oligomers with tri-
phenylamine as a core and carbazole, triphenylamine,
phenothiazine and bithiophene, as peripheral units,
which are connected by trans double bonds. These oli-
gomers show good solubility in common organic sol-
vents. The optical, electrochemical, electronic structure
and fluorescence quenching properties were investi-
gated. The results indicate that the absorption and fluo-
rescence of the molecules are influenced by the elec-
tron-donating ability and conjugation length of the pe-
ripheral units. The triphenylamine core and the periph-
eral units can constitute a large conjugated structure.
The fluorescence quenching properties indicate that ef-
ficient charge transfer can happen between the star-
shaped oligomers and N,N'-bis(1-ethylpropyl)-3,4:9,10-
perylene bis(tetracarboxyl diimide) (EP-PDI).
tilled under the protection of nitrogen. THF and toluene
were refluxed for 24 h with sodium, and when appear-
ing blue after added dibenzophenone, distilled under the
protection of nitrogen.
Instrument
1H NMR spectra were measured using a Bruker
AVANCE-500 NMR spectrometer spectrometer and a
Varian Mercury-300 NMR. The elemental analysis was
carried out with an American PERKIN ELMER 2400LS
II CHNS-Ovelemental analyzer. The infrared spectros-
copy spectra were recorded via the KBr pellet method
by using a Bruker IFS266V FTIR spectrophotometer.
The mass spectra were recorded on a Kratos MALDI-
TOF mass system, and the spectrum was recorded in the
linear mode with anthracene-1,8,9-triol as the matrices.
UV-visible absorption spectra were measured using a
Shimadzu UV-3100 spectrophotometer. The photolumi-
nescence spectra of spin-cast films and solutions were
measured with an RF-5301PC fluorophotometer. Elec-
trochemical measurements were performed with a Bio-
analytical Systems BAS 100 B/W electrochemical
workstation.
N-Ethylcarbazole (1) In a 100-mL round bottom
flask under nitrogen, sodium hydroxide (0.18 g) was
added to 60 mL of DMSO. After the solution was vig-
orously stirred for 30 min, carbazole (5.01 g, 30 mmol)
was added. After 1 h, ethyl bromide (3.24 g, 30 mmol)
was dropped into the reaction mixture slowly. The mix-
ture was heated to reflux temperature with stirring for
12 h. The reaction mixture was condensed to remove
DMSO, and then was poured into a large amount of
water (150 mL) and extracted using CH2Cl2 (70 mL×3).
The organic phase was dried over anhydrous magne-
sium sulfate, and then the solvent was removed using a
rotary evaporator. The crude product was purified by
column chromatography using petroleum ether as the
eluent to give 4.68 g of white solid with a yield of 80%.
N-Ethylcarbazole-3-carboxaldehyde (2)
In a
100-mL round bottom flask, a solution of phosphorus
oxychloride (3.2 mL) in DMF (10 mL) was dropped
slowly into the solution of N-ethylcarbazole (7.8 g, 40
mmol) in DMF (60 mL). The mixture was heated for 4 h
at 80 ℃. After cooling to room temperature, the mix-
ture was poured into water (150 mL), and the solution
was filtered to give crude product as yellow solids. The
crude product was purified by column chromatography
using a cosolvent (dichloromethane/petroleum ether,
1∶3, V/V) as the eluent to give 4.7 g of shallow yellow
solid with a yield of 53%.
Experimental
Materials
2-Bromothiophene, Ni(dppp)Cl2 and methyltriphe-
nylphosphonium bromide were purchased from Acros.
Triphenylamine, carbazole and phenothiazine were ob-
tained from Beijing Chemical Reagent Company.
DMSO and POCl3 were purchased from Beijing
Chemical Plant. Palladium acetate, potassium phosphate,
potassium iodide and potassium iodate were obtained
from Shanghai Chemical Reagent Company. All the
other chemicals and solvents were purchased from Tian-
jin Chemical Reagent Company. DMF was dried over
anhydrous MgSO4 for 24 h, and then obtained by vac-
uum distillation. CH2Cl2, CHCl3 and acetonitrile were
refluxed for 24 h with anhydrous CaCl2, and then dis-
N-Ethyl-3-vinylcarbazole (3)[16]
In a 100-mL
round bottom flask, methyltriphenylphosphonium bro-
mide (4.29 g, 12 mmol) and N-ethylcarbazole-3-alde-
hyde (2.23 g, 10 mmol) were dissolved in 20 mL of
freshly distilled THF, and then the flask was put in an
ice-water bath and a solution of potassium tert-butoxide
(1.68 g, 15 mmol) in THF was dropped slowly into this
mixture. After the solution mixture reacted for 5 h, THF
Chin. J. Chem. 2013, 31, 456—464
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457

Liu et al.
FULL PAPER
solvent was removed using a rotary evaporator. The
crude product was purified by column chromatography
using petroleum ether as the eluent to give 1.53 g of
Bithiophene (9) In a 100 mL three-neck flask
Grignard reagent [prepared from magnesium turnings
(0.16 g, 7 mmol) and 2-bromothiophene (1.17 g, 7
mmol) in THF (40 mL) under reflux] was added drop-
wise to a solution of 2-bromothiophene (0.78 g, 4.0
mmol), Ni(dppp)Cl2 (11 mg, 0.5 mol%) in THF (10 mL)
under stirring at room temperature. After the mixture
was refluxed for 8 h, the reaction was quenched with
HCl (2 mol/L), and extracted with CH2Cl2 (20 mL×3).
The organic phase was dried, and the solvent was re-
moved using a rotary evaporator. The crude product was
purified by column chromatography using petroleum
ether as the eluent to give 0.47 g of colorless crystal
with a yield of 71%. m.p. 32－33 ℃. 1H NMR (CDCl3,
500 MHz, TMS) δ: 7.02 (dd, J＝4.8, 3.6 Hz, 2H), 7.20
(m, 4H). Anal. calcd for C8H6S2: C 57.79, H 3.64; found
C 57.49, H 3.54.
1
white solid with a yield of 69%. m.p. 66－67 ℃. H
NMR (500 MHz CDCl3) δ: 1.45 (m, 3H), 4.35 (m, 2H),
5.19 (d, J＝11.5 Hz, 1H), 5.77 (d, J＝17.5 Hz, 1H),
6.90 (m, 1H), 7.24 (m, 1H), 7.35 (d, J＝8.5 Hz, 1H),
7.40 (d, J＝8.5 Hz, 1H), 7.46 (t, J＝8.5 Hz, 1H), 7.57 (d,
J＝8.5 Hz, 1H), 8.09－8.10 (m, 2H).
p-Diphenylaminobenzaldehyde (4) In a 100-mL
round bottom flask, a solution of phosphorus oxychlo-
ride (3.2 mL) in DMF (10 mL) was dropped slowly into
the solution of triphenylamine (9.28 g, 40 mmol) in
DMF (60 mL). The mixture was reacted for 2 h at 45
℃, cooled to room temperature, poured into some water,
and then the solution was filtered to give crude product
as yellow solid. The crude product was purified by
column chromatography using a cosolvent (dichloro-
methane/petroleum ether, 1∶2, V/V) as the eluent to
give 7.5 g of shallow yellow solid with a yield of 69%.
m.p. 148－150 ℃. 1H NMR (500 MHz, CDCl3) δ: 7.01
(d, J＝8.5 Hz, 2H, Ar), 7.17 (m, 6H, Ar), 7.34 (m, 4H,
Ar), 7.67 (d, J＝9.5 Hz, 2H, Ar), 9.85 (s, 1H, CHO).
Vinyltriphenylamine (5) In a 100-mL round bot-
tom flask, methyltriphenylphosphonium bromide (8.57
g, 24 mmol) and p-diphenylaminobenzadehyde (5.46 g,
20 mmol) were dissolved in 20 mL of freshly distilled
THF, and then the flask was put in an ice-water bath and
a solution of potassium tert-butoxide (3.36 g, 30 mmol)
in THF was dropped slowly into this mixture. After the
solution mixture was reacted for 10 h, it was poured into
ice water to end the reaction. The aqueous solution was
extracted with dichloromethane (20 mL×3), and the
organic phase was dried over anhydrous magnesium
sulfate and the solvent was removed using a rotary
evaporator. The crude product was purified by column
chromatography using a cosolvent (dichloromethane/
petroleum ether, 1∶1, V/V) as the eluent to give 3.74 g
of white solid with a yield of 69%. 1H NMR (500 MHz
CDCl3) δ: 5.06 (d, J＝10.8 Hz, 1H), 5.53 (d, J＝17.5
Hz, 1H), 6.54 (dd, J＝10.8, 17.5 Hz, 1H), 6.92－7.03
(m, 10H), 7.15－7.22 (m, 4H).
5-(2-Thienyl)thiophene-2-carboxaldehyde
(10)
In a 250 mL ampoule, bithiophene (2.087 g, 12.5 mol)
was dissolved in 20 mL of THF. The solution was
cooled to −80 ℃ and to which solution (1.6 mmol/mL,
8.63 mL, 13.8 mmol) of N-butyllithium in N-hexane
was dropped. After the mixture solution was stirred for
20 min at −80 ℃, 0.97 mL (12.5 mmol) of DMF was
added and the ampoule was heated to room temperature.
After 1 h, the reaction solution was poured into
ice-water (50 mL), extracted with CH2Cl2 (35 mL×3).
The organic phase was dried over anhydrous magne-
sium sulfate and the solvent was removed using a rotary
evaporator. The crude product was purified by column
chromatography using a cosolvent (petroleum ether/
dichloromethane, 10∶1, V/V) as the eluent to give 2.09
1
g of colorless solid with a yield of 86%. H NMR
(CDCl3, 500 MHz, TMS) δ: 7.08 (t, J＝9.0 Hz, 1H),
7.25 (d, J＝4.0 Hz, 1H), 7.36 (s, 1H), 7.37 (s, 1H), 7.67
(d, J＝4.0 Hz, 1H), 9.86 (s, 1H). Anal. calcd for
C9H6OS2: C 55.64, H 3.11; found C 55.59, H 3.14.
2-(2-Thienyl)-5-vinylthiophene (11) Compound
11 was synthesized in the similar method to synthesize
compound 3, and N-ethylcarbazole-3-aldehyde was
substituted with 5-(2-thienyl)thiophene-2-carboxalde-
hyde. The product was colorless liquid with a yield of
1
N-(2-Ethyl)-phenothiazine (6)[17] Compound 6
was synthesized in the similar method to synthesize
compound 1, and carbazole was substituted with phe-
nothiazine. The product was white solid with a yield of
85%.
57%. H NMR (CDCl3, 500MHz, TMS) δ: 5.13 (d, J＝
11.0 Hz, 1H), 5.53 (d, J＝17.0 Hz, 1H), 6.75－6.78 (dd,
J＝11.0, 17.5 Hz, 1H), 6.84 (d, J＝3.5 Hz, 1H), 6.96 (t,
J＝8.5 Hz, 1H), 7.00 (d, J＝3.5 Hz, 1H), 7.14 (d, J＝
3.5 Hz, 1H), 7.18 (d, J＝5.0 Hz 1H). Anal. calcd for
C10H8S2: C 62.46, H 4.19; found C 62.50, H 4.14.
9-(2-Ethyl)-phenothiazine-3-carbaldehyde
(7)
Tris-(4-iodophenyl)amine (12) 30 mL of glacial
acetic acid was added to a mixture of triphenylamine
(2.45 g, 10 mmol) and potassium iodide (3.4 g, 100
mmol). The reaction mixture was refluxed under argon
until a clear, yellow solution was obtained. KIO3 (2.4 g,
11 mmol) was added in small portions, and the mixture
was refluxed to colorless. Thereafter 20 mL of NaSO3
solution (5 w%) was added to precipitate the white
crude product. The residue was filtered off and chroma-
tographed on silica gel column (ethyl acetate/petro-
Compound 7 was synthesized in the similar method to
synthesize compound 2, and N-ethylcarbazole was sub-
stituted with N-(2-ethyl)-phenothiazine. The product
was shallow yellow solid with a yield of 56%.
3-Ethyl-9-(2-ethyl)-phenothiazine (8) Compound
8 was synthesized in the similar method to synthesize
compound 3, and N-ethylcarbazole-3-aldehyde was
substituted with 3-aldehyde-9-(2-ethyl)-phenothiazine.
The product was shallow yellow solid with a yield of
63%.
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Chin. J. Chem. 2013, 31, 456—464

Synthesis, Characterization and Properties of Novel Star-Shaped π-Conjugated Oligomers
leumether＝1∶15, V/V) to produce 4.95 g ivory-white
solid of tris-(4-iodophenyl)amine with a yield of 79%.
1H NMR (CDCl3, 500 MHz, TMS) δ: 6.80 (d, J＝8.5
Hz, 6H), 7.53 (d, J＝9.0 Hz, 6H). Anal. calcd for
C18H12I3N: C 34.70, H 1.94, N 2.25; found C 34.69, H
1.94, N 2.23.
oxychloride and DMF acted as the acylating agent.
Bithiophene aldehyde (10) was synthesized by using
n-butyllithium and DMF as the acylating agent, and the
key to success lies in the control of the anhydrous and
anaerobic conditions. The vinylation synthesis reaction
adopted Wittig reaction. In these processes, it was im-
portant to seriously control the reaction temperature and
dropping rate of the reactants.
General procedure for synthesis of the star-shaped
oligomers
The star-shaped oligomers, TPA-CZ3, TPA-TPA3,
TPA-PTZ3 and TPA-BT3, were synthesized by palla-
dium-catalyzed Heck reaction and the trans double
bond of the molecules were characterized by infrared
spectroscopy. The typical absorption peak for trans
double bond is located at 980－965 cm−1, and the four
molecules have obvious absorption at around 960 cm−1,
which indicates the double bonds in the molecules adopt
a trans structure. Furthermore, the structures of the oli-
gomers were also confirmed by NMR and mass spec-
trometry. The four star-shaped oligomers are soluble in
common organic solvents, such as CH2Cl2, THF and
DMF.
Tris-(4-iodophenyl)amine (4 mmol), vinyl deriva-
tives (16 mmol), K3PO4 (18 mmol) and palladium ace-
tate (0.24 mmol) were added to a round-bottom flask,
and then 2 mL DMAC was added. The mixture was re-
acted for 24 h at 110 ℃ under the protection of N2,
then cooled to room temperature. Thereafter some water
was added to precipitate the solid. The residue was fil-
tered off and chromatographed on silica gel column
(petroleumether/dichloromethane＝1∶3, V/V) to pro-
duce the compound.
TPA-CZ3 Shallow yellow solid with a yield of
44%, m.p. 118 ℃. 1H NMR (CDCl3, 500 MHz, TMS) δ:
1.45 (m, 9H), 4.37 (m, 6H), 7.17 (m, 9H), 7.26 (m, 6H),
7.40 (t, J＝16.0 Hz, 6H), 7.48 (t, J＝16.5 Hz, 9H), 7.68
(d, J＝8.5 Hz, 3H), 8.13 (d, J＝7.5 Hz, 3H), 8.23 (d,
3H). MALDI/TOF MS calcd for C66H54N4 902.4, found
903.3. Anal. calcd for C66H54N4: C 87.77, H 6.03, N
6.20; found C 87.68, H 6.12, N 6.21.
Optical properties
Figure 1 shows the normalized UV-vis absorption
and photoluminescence (PL) spectra of the four star-
shaped oligomers in dilute CH2Cl2 solution (10−6 mol/L).
The relevant spectroscopic data of these oligomers in
CH2Cl2 solution are summarized in Table 1. For the
UV-Vis absorption spectra, all the four oligomers dis-
play multiple absorption bands. The ca. 300 nm rela-
tively weak absorption band can be assigned to the π-π*
transition of the oligomers, while the ca. 400 nm strong
absorption band arises from the intramolecular charge
transfer (ICT) transition between the triphenylamine
core and the peripheral groups. For TPA-CZ3, TPA-
TPA3 and TPA-PTZ3, their absorption and PL spectra
are red shifted with the electron-donating ability of the
peripheral units increasing from carbazole to triphenyl-
amine and phenothiazine. Specially, for the oligomer
TPA-BT3, although the bithiophene group has a weaker
electron-donating ability than the other three groups, the
absorption and PL spectra of TPA-BT3 have a red shift
than those of the other three star-shaped oligomers,
TPA-CZ3, TPA-TPA3 and TPA-PTZ3. We think the
reason for this phenomenon is that TPA-BT3 has a
longer conjugation length than TPA-CZ3, TPA-TPA3
and TPA-PTZ3 because the conjugated unit for the lat-
ter three star-shaped oligomers is stilbene, but for TPA-
BT3 the conjugated unit is styrene-thiophene. On the
other hand, the absorption of TPA-BT3 has a red shift
compared with that of the star-shaped molecule in
which the TPA core and the peripheral units are con-
nected by single bonds.[13]
TPA-TPA3 Yellow solid with a yield of 47%, m.p.
1
173 ℃. H NMR (CDCl3, 500 MHz, TMS) δ: 6.97 (s,
6H), 7.04 (m, 12H), 7.08－7.12 (m, 18H), 7.26 (m,
12H), 7.38 (m, 12H). MALDI/TOF MS calcd for
C78H60N4 1052.5, found 1053.3. Anal. calcd for
C78H60N4: C 88.94, H 5.74, N 5.32; found C 88.99, H
5.78, N 5.23.
TPA-PTZ3 Yellow solid with a yield of 38%, m.p.
1
123 ℃. H NMR (CDCl3, 500 MHz, TMS) δ: 1.43 (m,
9H), 3.93 (m, 6H), 6.968－6.929 (m, 15H), 7.091 (m,
6H), 7.15 (m, 6H), 7.28 (m, 6H), 7.37 (d, J＝8.5 Hz,
6H). MALDI/TOF MS calcd for C66H54N4S3 998.4,
found 999.2. Anal. calcd for C66H54N4S3: C 79.32, H
5.45, N 5.61; found C 79.39, H 5.44, N 5.55.
TPA-BT3 Orange solid with a yield of 39%, m.p.
1
110 ℃. H NMR (CDCl3, 500 MHz, TMS) δ: 6.86 (d,
J＝16.0 Hz, 3H), 6.94 (d, J＝3.5 Hz, 3H), 7.02－7.04
(m, 3H), 7.07－7.11 (m, 12H), 7.18 (d, J＝3.0 Hz, 3H),
7.22 (d, J＝5.0 Hz, 3H), 7.37 (m, 6H). MALDI/TOF
MS calcd for C48H33NS6 815.1, found 815.6. Anal. calcd
for C48H33NS6: C 70.64, H 4.08, N 1.72; found C 70.65,
H 4.99, N 1.73.
Results and Discussion
Synthesis and characterization
The general synthetic routes toward the intermedi-
ates and oligomers are shown in Scheme 1 and Scheme
2. The intermediates carbazole aldehyde (2), triphenyl-
amine aldehyde (4) and phenothiazine aldehyde (7)
were synthesized by Vilsmeier reaction, and phosphorus
Figure 2 shows the normalized UV-vis absorption
and PL spectra of the four star-shaped oligomers in thin
solid films. The relevant spectroscopic data are summa-
rized in Table 1. The absorption and fluorescence be-
havior of the molecules in the solid films is similar to
Chin. J. Chem. 2013, 31, 456—464
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Liu et al.
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Scheme 1 Synthetic route to the intermediates
C2H5
C2H5
N
C2H5
N
H
N
N
C2H5Br
DMF
t-BuOK
CH3PPh3Br
DMSO, NaOH
POCl3
CHO
3
1
2
DMF
Ph3PCH3Br
t-BuOK,THF
N
N
N
POCl3
CHO
4
5
H
N
N
N
N
Ph3PCH3Br
DMF
POCl3
C2H5Br
DMSO, NaOH
t-BuOK,THF
S
S
CHO
S
S
8
6
7
CHO
S
S
Mg
Ph3PCH3Br
S
BuLi
DMF
Br
THF
t-BuOK,THF
S
S
S
S
9
11
10
I
KI,KIO3
N
N
CH3COOH
I
I
12
Scheme 2 Synthetic route to the star-shaped oligomers
D-Ar
I
D-Ar-CH=CH2
(3, 5, 8, or 12)
N
N
DMAC,PdAC,K3PO4
I
I
Ar-D
12
D-Ar
S
S
N
D-Ar =
N
S
N
C2H5
TPA-CZ3
TPA-BT3
TPA-PTZ3
TPA-TPA3
those in solution, except for several nanometers of red
shift due to the aggregation effect. The phenomenon
that the UV-vis absorption and PL spectra in solid films
have a red shift compared with those in solution indi-
cates that these star-shaped oligomers tend to arrange in
a direction parallel to the substrate, and this arrange-
ment can enhance the solar absorption in the longer
wavelength and the charge carrier transport in the direc-
tion perpendicular to the substrate.[18] These properties
make these star-shaped oligomers have the potential
application in solar cells.
Electrochemical properties
The electrochemical characteristics of TPA-CZ3,
TPA-TPA3, TPA-PTZ3 and TPA-BT3 were investi-
gated by cyclic voltammetry (CV) in anhydrous ace-
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Chin. J. Chem. 2013, 31, 456—464

Synthesis, Characterization and Properties of Novel Star-Shaped π-Conjugated Oligomers
Figure 1 Normalized absorption (a) and photoluminescence (PL) (excited at 365 nm) (b) spectra of the star-shaped oligomers in dilute
dichloromethane solution (1×10−6 mol/L).
Figure 2 Normalized absorption (a) and PL (excited at 365 nm) (b) spectra of the star-shaped oligomers in thin solid film.
Table 1 Optical properties of the four star-shaped oligomers
Compound
λmaxabs,sol/nm, εmax/(mol−1•L•cm−1)
λmaxem,sol/nm
λmaxabs,film/nm
λmaxem,film/nm
TPA-CZ3
TPA-TPA3
TPA-PTZ3
TPA-BT3
399, 94680
409, 98330
417, 93940
434, 131600
463
469
499
513
402
413
426
442
485
496
516
519
onset
tonitrile, using a platinum button as working electrode, a
platinum wire as counter electrode, an Ag/AgNO3 as
reference electrode, and tetrabutylammonium perchlo-
rate (0.1 mol/L) as supporting electrolyte. Ferrocene
was used as the internal standard and showed a peak at
＋0.13 V versus Ag/Ag＋. During the anodic scan, all
the four star-shaped oligomers exhibit quasireversible
ELUMO
(
−
4.67) eV
＋
＝
Ered
E
g
ELUMO EHOMO
−
＝
The electrochemical parameters are summarized in
Table 2. The electron-donating ability of the four pe-
ripheral units is as follows: bithiophene＜carbazole＜
triphenylamine＜phenothiazine, so the onset oxidation
potentials of TPA-CZ3, TPA-TPA3 and TPA-BT3
arise from the triphenylamine group and are nearly
identical. However, as for TPA-PTZ3, the onset oxida-
tion potential is attributed to the phenothiazine group.
Because the electron-donating ability of phenothiazine
group is strong than that of triphenylamine group, the
onset oxidation potential of TPA-PTZ3 is smaller than
those of the other three star-shaped oligomers.
oxidation waves (see Figure 3). From the onset oxida-
onset
tion potential ( E
) and the onset reduction potential
ox
onset
( E
) of the molecules, the HOMO and LUMO en-
red
ergy levels as well as the electrochemical energy band
gap (Eg,El) can be calculated according to the following
equations:
onset
EHOMO
(
−
4.67) eV
＋
＝
Eox
Chin. J. Chem. 2013, 31, 456—464
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461

Liu et al.
FULL PAPER
Figure 3 Cyclic voltammetry curves of the star-shaped oligomers film on platinum electrode in 0.1 mol/L acetonitrile solution of
tetrabutylammonium perchlorate at a scan rate of 100 mV/s.
Table 2 Electrochemical properties of the four star-shaped oli-
gomers
onset
ox
onset
/ HOMO/ LOMO/ Eg,EL/ Eg,Opt /
red
b
E
/ E
Compound
V
V
eV
eV
eV
－
－
－
eV
TPA-CZ3
0.38
－
－
－
−5.05 −2.35 a
−4.97 −2.31 a
−4.86 −2.29 a
2.70
2.66
2.57
TPA-TPA3 0.30
TPA-PTZ3 0.19
TPA-BT3
0.33 −2.15 −5.00
−2.58 2.48 2.42
a LUMO energy levels obtained by HOMO＋Eg,Opt. b Eg,Opt values
were calculated from the absorption band edge of the molecule
films, Eg,Opt＝1240/λedge
.
Theoretical calculation
The ground-state geometry and electron-state-den-
sity distribution of the HOMO and LUMO energy levels
of TPA-BT3, TPA-CZ3, TPA-PTZ3 and TPA-TPA3
have been fully optimized using density functional the-
ory (DFT) based on the B3LYP method with a 6-31G*
basis in Gaussian 03 program package. The HOMO and
LUMO pictograms and corresponding energy levels for
the four star-shaped oligomers are presented in Figure 4.
The calculation results demonstrate that the three phe-
nyls of the triphenylamine core and adjacent aromatic
rings of the peripheral units constitute a large conju-
gated planar structure, respectively. The HOMO energy
levels of the four star-shaped oligomers distribute
Figure 4 HOMO and LUMO pictograms and corresponding
energy levels of TPA-CZ3, TPA-TPA3, TPA-PTZ3 and
TPA-BT3 obtained at B3LYP/6-31G* level.
mainly on the centered triphenylamine core with some
extending to the adjacent aromatic rings of the periph-
eral units. As for the LUMO energy levels, they are two
quasidegenerate virtual orbitals for each oligomer.
Moreover, they distribute mainly on the part of the pe-
ripheral units close to the triphenylamine core with
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Chin. J. Chem. 2013, 31, 456—464

Synthesis, Characterization and Properties of Novel Star-Shaped π-Conjugated Oligomers
some extending to the triphenylamine core. Distin-
guishingly, TPA-BT3 shows better delocalization of
electron density, which should arise from the longer
conjugation length than the other oligomers. In general,
the theoretical HOMO energy levels of these oligomers
are consistent with those obtained from electrochemical
measurement, and the theoretical band gaps agree with
their optical band gaps. The LUMO energy levels ex-
hibit some bias. The differences between the theoretical
and electrochemical and optical values are a well-
known consequence of performing calculations that lack
medium-related factors.
blend ratio between the star-shaped oligomers and
EP-PDI ranges from 10∶1 to 10∶50. It can be seen
that the PL of the star-shaped oligomers are gradually
quenched with the concentration of EP-PDI increasing,
and when the mole blend ratio is 10∶50, most of the
PL of the star-shaped oligomers are quenched. The ob-
servation obviously indicates that efficient charge
transfer can happen between the star-shaped oligomers
and EP-PDI.
Fluorescence quenching properties
Based on the optical and electrochemical properties
of the four star-shaped oligomers, an energy level dia-
gram of the star-shaped oligomers and EP-PDI is pre-
sented in Figure 5. It can be seen that all the four mole-
cules have an energy level matching relationship of
electron donor-acceptor with EP-PDI, which indicates
that the excimer can dissociate efficiently at the inter-
face of the donor and acceptor. PL quenching in donor-
acceptor composites is a useful indication for the effi-
cient charge transfer between the two components.[19]
Figure 6 shows the PL spectra of four star-shaped oli-
gomers∶EP-PDI composite solutions with different
concentrations of EP-PDI. The concentration of the
star-shaped oligomers are 5×10−2 mol/L, and the mole
Figure 5 Energy diagram of the star-shaped oligomers and
EP-PDI.
Conclusions
Four novel star-shaped π-conjugated oligomers con-
sisting of triphenylamine as a core and different elec-
tron-donating ability groups, carbazole, triphenylamine,
phenothiazine and bithiophene, as peripheral units have
Figure 6 PL spectra of the four star-shaped oligomers∶EP-PDI composite solutions with different concentrations of EP-PDI (the con-
centration of oligomers is constant: 5×10−2 mol/L, and the blend ratio is molar ratio).
Chin. J. Chem. 2013, 31, 456—464
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www.cjc.wiley-vch.de
463

Liu et al.
FULL PAPER
[6] (a) Roquet, S.; Cravino, A.; Leriche, P.; Alévêque, O.; Frère, P.;
Roncali, J. J. Am. Chem. Soc. 2006, 128, 3459; (b) Cremer, J.;
Bäuerle, P. J. Mater. Chem. 2006, 16, 874; (c) Cravino, A.; Roquet,
S.; Leriche, P.; Alévêque, O.; Frère, P.; Roncali, J. Chem. Commun.
2006, 1416.
been synthesized via the Heck reaction. These oli-
gomers exhibit good solubility in common organic sol-
vents. Their photophysical, electrochemical and PL
quenching properties were investigated. The results
show that the absorption and fluorescence of these star-
shaped π-conjugated oligomers can be tuned through
changing the electron-donating ability and conjugation
length of the peripheral units. The triphenylamine core
and the peripheral units can constitute a large conju-
gated structure. The fluorescence quenching properties
confirm that efficient charge transfer can happen be-
tween the star-shaped oligomers and EP-PDI.
[7] Zhang, J.; Deng, D.; He, C.; He, Y.; Zhang, M.; Zhang, Z.; Zhang,
Z.; Li, Y. Chem. Mater. 2011, 23, 817.
[8] (a) Shang, H.; Fan, H.; Liu, Y.; Hu, W.; Li, Y.; Zhan, X. Adv. Mater.
2011, 23, 1554; (b) Zhang, J.; Yang, Y.; He, C.; He, Y.; Zhao, G.; Li,
Y. Macromolecules 2009, 42, 7619; (c) He, C.; He, Q.; Yi, Y.; Wu,
G.; Bai, F.; Shuai, Z.; Li, Y. J. Mater. Chem. 2008, 18, 4085.
[9] Metri, N.; Sallenave, X.; Beouch, L.; Plesse, C.; Goubard, F.; Chev-
rot, C. Tetrahedron Lett. 2010, 51, 6673.
[10] Metri, N.; Sallenave, X.; Plesse, C.; Beouch, L.; Aubert, P.-H.;
Goubard, F.; Chevrot, C.; Sini, G. J. Phys. Chem. C 2012, 116,
3765.
Acknowledgement
[11] Jana, D.; Ghorai, B. K. Tetrahedron Lett. 2012, 53, 1798.
[12] (a) Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.;
Mackay, K.; Friend, R. H.; Burn, P. L.; Holmes, A. B. Nature 1990,
347, 539; (b) Ostroverkhova, O.; Moerner, W. E. Chem. Rev. 2004,
104, 3267; (c) Yang, J. X.; Tao, X. T.; Yuan, C. X.; Yan, Y. X.;
Wang, L.; Liu, Z.; Ren, Y.; Jiang, M. H. J. Am. Chem. Soc. 2005,
127, 3278.
[13] Cremer, J.; Briehn, C. A. Chem. Mater. 2007, 19, 4155.
[14] (a) Wang, Y. N.; Zhou, Y. H.; Xu, Y.; Sun, X. B.; Wu, W. C.; Tian,
W. J.; Liu, Y. Q. Chin. Phys. B 2008, 17, 1674; (b) Li, Y. W.; Xue,
L. L.; Li, H.; Li, Z. F.; Xu, B.; Wen, S. P.; Tian, W. J.
Macromolecules 2009, 42, 4491.
This work was supported by National Natural Sci-
ence Foundation of China (No. 21004027), the Research
Fund of State Key Laboratory of Inorganic Synthesis
and Preparative Chemistry, Jilin University (Grant No.
2011-25), and the Research Fund of Key Laboratory of
Physics and Technology for Advanced Batteries, Minis-
try of Education (Grant No. 201206).
References
[1] Hou, J. H.; Tan, Z.; Yan, Y.; He, Y. J.; Yang, C. H.; Li, Y. F. J. Am.
Chem. Soc. 2006, 128, 4911.
[2] (a) Yang, Y.; Zhou, Y.; He, Q.; Yang, C.; Bai, F.; Li, Y. J. J. Phys.
Chem. B 2009, 113, 7745; (b) Jiang, Z.; Ye, T.; Yang, C.; Yang, D.;
Zhu, M.; Zhong, C.; Qin, J.; Ma, D. Chem. Mater. 2011, 23, 771; (c)
Shirota, Y. J. Mater. Chem. 2005, 15, 75.
[15] Yuan, J. B.; Zhang, Z. G.; Leung, L. M.; Zhang, K. L. Chin. Chem.
Lett. 2008, 19, 647.
[16] Limbug, W. W.; Williams, D. J. Macromolecules 1973, 6, 787.
[17] Hwang, D. H.; Kim, S. K.; Park, M. J.; Lee, J. H.; Koo, B. W.; Kang,
I. N.; Kim, S. H.; Zyung, T. Chem. Mater. 2004, 16, 1298.
[18] (a) An, B. K.; Kwon, S. K.; Jun, S. D.; Park, S. Y. J. Am. Chem. Soc.
2002, 124, 14410; (b) Videlot, C.; Kassmi, E. A.; Fichou, D. Sol.
Energy Mat. Sol. C 2000, 63, 69; (c) De Bettignies, R.; Nicolas, Y.;
Blanchard, P.; Levillain, E.; Nunzi, J. M.; Roncali, J. Adv. Mater.
2003, 15, 1939.
[19] (a) Neuteboom, E. E.; Meskers, S. C. J.; Van Hal, P. A.; Van Duren,
J. K. J.; Meijer, E. W.; Janssen, R. A. J.; Dupin, H.; Pourtois, G.;
Cornil, J.; Lazzaroni, R.; Bredas, J.-L.; Beljonne, D. J. Am. Chem.
Soc. 2003, 125, 8625; (b) Sariciftci, N. S.; Smilowitz, L.; Heeger, A.
J.; Wudl, F. Science 1992, 258, 1474.
[3] Wang, J. L.; He, Z.; Wu, H.; Cui, H.; Li, Y.; Gong, Q.; Cao, Y.; Pei,
J. Chem. Asian J. 2010, 5, 1455.
[4] (a) Metri, N.; Sallenave, X.; Plesse, C.; Beouch, L.; Aubert, P.;
Goubard, F.; Chevrot, C.; Sini, G. J. Phys. Chem. C 2012, 116, 3765;
(b) Yang, Y.; Zhang, Z.; Zhou, Y.; Zhao, G.; He, C.; Li, Y.;
Andersson, M.; Inganäs, O.; Zhang, F. J. Phys. Chem. C 2010, 114,
3701; (c) Zhao, G.; Wu, G.; He, C.; Bai, F.; Xi, H.; Zhang, H.; Li, Y.
J. Phys. Chem. C 2009, 113, 2636.
[5] Wu, G.; Zhao, G.; He, C.; Zhang, J.; He, Q.; Chen, X.; Li, Y. Sol.
Energy. Mater. Sol. C 2009, 93, 108.
(Zhao, X.)
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