Jacketed polymers with dendritic carbazole side groups and their applications in blue light-emitting diodes

Article abstract of DOI:10.1021/ma101814m

Styrene-based monomers with the first- and second-generation dendronized carbazoles were synthesized by a convergent strategy. Conventional free radical polymerizations were carried out to synthesize the dendronized jacketed polymers using these two monomers. The apparent molecular weights of the two polymers determined by gel permeation chromatography were 57 000 and 34 000 g/mol, respectively. The polymers had excellent thermal stability with their 5% weight loss temperatures all above 360 °C. Their photophysical properties in solutions and films were investigated. Different solvents had negligible effects on their UV-vis or photoluminescent (PL) spectra. A 10 nm blue shift of the emission peak was observed in the PL spectra of films compared with those of solutions. After the films were annealed, the emission peaks became narrower. X-ray diffraction techniques were utilized to examine the phase structures of the dendronized jacketed polymers. The first-generation polymer formed a hexatic columnar nematic phase, while the second-generation one exhibited a columnar nematic phase. This stiff main-chain conformation and the dendritic side-group structure could reduce the intramolecular interactions and aggregations of the carbazole side groups and prevent the formation of excimers, which would be beneficial to the optoelectronic properties. The two polymers showed similar electrochemical properties. Their HOMO levels were about -5.3 eV, which was quite close to that of PEDOT:PSS. Electroluminescent (EL) devices were fabricated in two configurations. A new emission peak was found in the EL spectra compared with the PL spectra. All the devices emitted blue lights and possessed low driving voltages. An introduction of an electron-transporting layer could greatly improve the device properties. The best device could reach a luminescence of 2195 cd/m², a current efficiency of 0.240 cd/A, and an external quantum efficiency of 0.353%.

Full text of DOI:10.1021/ma101814m

8468 Macromolecules 2010, 43, 8468–8478
DOI: 10.1021/ma101814m
Jacketed Polymers with Dendritic Carbazole Side Groups and Their
Applications in Blue Light-Emitting Diodes
Hao Jin, Yiding Xu, Zhihao Shen,* Dechun Zou,* Dan Wang, Wei Zhang, Xinghe Fan,* and
Qifeng Zhou*
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of
Ministry of Education, College of Chemistry and Molecular Engineering, Peking University,
Beijing 100871, China
Received August 9, 2010; Revised Manuscript Received September 14, 2010
ABSTRACT: Styrene-based monomers with the first- and second-generation dendronized carbazoles were
synthesized by a convergent strategy. Conventional free radical polymerizations were carried out to
synthesize the dendronized jacketed polymers using these two monomers. The apparent molecular weights
of the two polymers determined by gel permeation chromatography were 57 000 and 34 000 g/mol,
respectively. The polymers had excellent thermal stability with their 5% weight loss temperatures all above
360 °C. Their photophysical properties in solutions and films were investigated. Different solvents had
negligible effects on their UV-vis or photoluminescent (PL) spectra. A 10 nm blue shift of the emission peak
was observed in the PL spectra of films compared with those of solutions. After the films were annealed, the
emission peaks became narrower. X-ray diffraction techniques were utilized to examine the phase structures
of the dendronized jacketed polymers. The first-generation polymer formed a hexatic columnar nematic
phase, while the second-generation one exhibited a columnar nematic phase. This stiff main-chain
conformation and the dendritic side-group structure could reduce the intramolecular interactions and
aggregations of the carbazole side groups and prevent the formation of excimers, which would be beneficial
to the optoelectronic properties. The two polymers showed similar electrochemical properties. Their HOMO
levels were about -5.3 eV, which was quite close to that of PEDOT:PSS. Electroluminescent (EL) devices
were fabricated in two configurations. A new emission peak was found in the EL spectra compared with the
PL spectra. All the devices emitted blue lights and possessed low driving voltages. An introduction of an
electron-transporting layer could greatly improve the device properties. The best device could reach a
luminescence of 2195 cd/m2, a current efficiency of 0.240 cd/A, and an external quantum efficiency of 0.353%.
Introduction
much easier for carrier injection and transport,9,10 and the stiff
main chain is also of benefit to inhibit the aggregation of light-
Organic light-emitting diodes (OLEDs) have attracted con-
siderable attention for their applications in flat panel displays and
lighting during the past decade because of their high electro-
optical conversion efficiency, wide viewing angle, low driving
voltage, and low cost.1-4 Vacuum deposition techniques were
applied to prepare the thin films to reduce the bias voltage of the
devices and give a relatively high efficiency. The first polymer-
based OLED (PLED) was fabricated in 1990,5 and then numer-
ous electroluminescent (EL) polymers with different chemical
compositions and architectures were synthesized.6-8 Compared
with OLEDs from small molecules, PLEDs are able to fulfill
different functions in one layer by incorporating charge-trans-
porting groups and light-emitting groups in a single polymer
chain, and thus the device structure will be much simpler. PLEDs
are also considered as the most promising technology to realize
flexible and large-area displays by wet-chemistry fabrication
processes such as spin-coating or inkjet-printing.
emitting groups and prevent fluorescence quenching and forma-
tion of excimers. However, their molecular weights (MWs) are
difficult to control during polymerization, and the MW distribu-
tions are usually broad. In addition, conjugated polymers also
suffer from the poor solubility in organic solvents. Compared
with main-chain-type polymers, side-chain-type polymers can be
synthesized through free radical polymerization and usually
possess a vinyl main chain.11,12 Different polymers can be readily
synthesized by changing the covalently bonded functional side
groups to adjust the light-emitting wavelength and device prop-
erties.13 Recently, controlled/living polymerization techniques,
such as nitroxide-mediated polymerizations (NMP)14,15 and
reversible addition-fragmentation transfer (RAFT) polymeriza-
tions,16 are more and more frequently utilized to synthesize these
polymers, with their structure parameters exactly controlled. And
electroluminescent polymers with complex architectures can be
obtained. Mixed-type electroluminescent copolymers have also
been reported.17 The copolymer chains are composed of two
blocks, one being a side-chain type and the other a main-chain
type. Such copolymers provide an excellent model to investigate
the relationship between the phase structure and optoelectronic
properties of the electroluminescent polymers.
Electroluminescent polymer materials can be divided into
three groups, namely, main-chain type, side-chain type, and
mixed type. Main-chain-type polymers possess a stiff conjugated
main chain and are usually synthesized by condensation poly-
merizations. The conjugated main-chain structures make them
Mesogen-jacketed liquid crystalline polymers (MJLCPs) refer
to a class of side-chain liquid crystalline polymers (SCLCPs) in
which the side-chain mesogens are side-on attached with a very
*To whom correspondence should be addressed. E-mail: (X.F.)
fanxh@pku.edu.cn; (Z.S.) zshen@pku.edu.cn; (D.Z.) dczou@pku.
edu.cn; (Q.Z) qfzhou@pku.edu.cn.
pubs.acs.org/Macromolecules
Published on Web 09/30/2010
r 2010 American Chemical Society

Article
Macromolecules, Vol. 43, No. 20, 2010 8469
Experimental Details
Materials. 2,20-Azobis(isobutyronitrile) (AIBN) was recrys-
tallized from ethanol. Chlorobenzene was washed with sulfuric
acid and then distilled under reduced pressure. All the other
reagents were used as received.
Characterization. 1H NMR spectra were recorded on a Mer-
cury plus 300 MHz or Bruker 400 MHz using deuterated chloro-
form (CDCl3) or deuterated dimethyl sulfoxide (DMSO-d) as
solvents at room temperature. The chemical shifts were reported
in ppm with tetramethylsilane (TMS) as the internal standard.
Mass spectra were recorded on a Bruker Apex IV FTMS or
Autoflex III MALDI-TOF spectrometer. Elemental analyses
were carried out on an Elementar Vario EL (Germany). Gel
permeation chromatographic (GPC) measurements were car-
ried out at 35 °C on a Waters 2410 instrument equipped with
Figure 1. Cylindrical structure of the dendronized jacketed polymer.
short spacer or without any spacer at all.18,19 The main chain was
forced to take an extended chain conformation because of the
steric hindrance exerted by the highly populated bulky, rigid side
groups. Although MJLCPs, as SCLCPs, can beeasilysynthesized
by conventional and controlled/living free radical polymeriza-
tions, they behave like main-chain liquid crystalline polymers in
that the whole polymer chain serves as a supramolecular meso-
gen. In the past two decades, systematic research on the struc-
ture-property relationships for MJLCPs with different side
groups has been done.20,21 Recently, the functionalization of this
system has been researched. It has been proven that introducing
bulky, rigid side groups to form electroluminescent jacketed
polymers was helpful in inhibiting the aggregation of functional
groups, and some jacketed polymers can be used for electropho-
sphorescent systems as host materials.22-26
˚
three Waters μ-Styragel columns (103, 104, and 105 A) in series,
using tetrahydrofuran (THF) as the eluent at a flow rate of
1.0 mL/min. All of the GPC data were calibrated with linear
polystyrene standards.
Thermogravimetric analysis (TGA) was performed with a
Q600 SDT instrument at a heating rate of 20 °C/min in a nitrogen
atmosphere. Differential scanning calorimetry (DSC, PerkinElmer
Pyris I with a mechanical refrigerator) was utilized to study the
glass transitions of the polymers. A typical DSC sample size was
about 2 mg. The samples were encapsulated in hermetically sealed
aluminum pans, and the pan weights were kept constant. The
temperatures and heat flow scales at different cooling and heating
rates were calibrated using standard materials such as indium
and benzoic acid. The glass transition temperatures (Tg’s) were
obtained from the second heating curves.
Dendronized polymers27,28 are special polymer brushes with a
dendronized side group in each repeating unit. When the gen-
eration of the dendrons is high enough, the steric hindrance
produced by the huge side groups will force the main chain to
exhibit a stiff conformation similar to MJLCPs.29-33 Usually,
there are three strategies to construct a dendronized polymer,
namely, “graft through”, “graft from”, and “graft onto”.34-36
Among these three methods, the “graft through” strategy is also
called the macromonomer strategy, which means the polymeri-
zation of a macromonomer with a dendrimer structure.33 This
method can control the structure more precisely, and each
repeating unit can be introduced with dendrons having the same
structures and generations, avoiding uneven, uncontrolled gen-
erations or distributions of dendrons on the main chain in the
other two strategies. However, the huge steric hindrance usually
leads to a low conversion of the macromonomers, and the
removal of the unreacted monomers is tedious. Several reports
on main-chain-type dendronized electroluminescent polymers
have demonstrated the importance of the dendritic structure
for suppressing aggregations and fluorescence quenching.37,38
However, little work has been done on vinyl dendronized
electroluminescent polymers.
Carbazoles and their derivatives have been used widely as hole-
transporting materials and emitting materials.39,40 In this con-
tribution, dendritic carbazole side groups were introduced by the
“graft through” method into MJLCPs for the first time. The
phase structures and optoelectronic properties of the resulting
polymers were investigated. Compared with traditional side-
chain polymers, these polymers were expected to have the
advantage of distributing carbazoles on the surface of the rod-
like polymer chain, and thus the electroluminescent functions of
carbazoles could be utilized sufficiently. In addition, the rigid
rod-like polymer chain might inhibit the aggregation of the
carbazoles and provide a continuous channel for transporting
holes. From the viewpoint of molecular engineering, the length
(L) of the stiff, cylindrical chain could be controlled by the degree
of polymerization, and the diameter (D) could be adjusted by the
number of generations of carbazole side groups (Figure 1).
Therefore, the optoelectronic properties of the polymers could
be tailored.
Absorption spectra were measured with a Jasco V-550 spec-
trophotometer, and photoluminescent (PL) spectra were ob-
tained using a Hitachi F-4500 fluorescence spectrophotometer.
The electrochemical properties were measured using a voltam-
metric analyzer (CHI630C from Shanghai Chenhua Instrument
Company, China) at a scanning rate of 100 mV/s at room
temperature. A three-electrode system was used. A polymer-
coated carbon electrode was used as the working electrode,
Ag/AgCl electrode as reference electrode, and platinum wire
electrode as auxiliary electrode, supported with 0.1 M (n-Bu)4-
NClO4 in acetonitrile. A solution of ferrocene (FOC) (1 ꢀ 10-3
M in acetonitrile) was tested by the same method to obtain the
half-wave potential (U1/2,FOC) of FOC/FOCþ. The energy levels
of polymers were calculated using the FOC value of -4.8 eV
with respect to vacuum level, which was defined as zero. There-
fore, the HOMO levels of the polymers could be calculated by
the equation EHOMO=-e[Uonset(ox)þ(4.8 V-U1/2,FOC)] and the
LUMO levels could be estimated by the equation ELUMO
-e[Uonset(red) þ (4.8 V - U1/2,FOC)].
=
The phase structures of the samples at different temperatures
were studied by one-dimensional (1D) and two-dimensional
(2D) wide-angle X-ray diffraction (WAXD) experiments. 1D
WAXD experiments were performed on a Philips X’Pert Pro
diffractometer with a 3-kW ceramic tube as the X-ray source
(Cu KR) and an X’celerator detector. Silicon powder and silver
behenate were used to calibrate the reflection peak positions at
2θ> 15° and 2θ < 10°, respectively. A hot stage (Paar Physica
YCU 100) was utilized to study the phase structure evolutions
with varing temperature. The heating and cooling rates in all
WAXD experiments were 10 °C/min. 2D WAXD experiments
were performed on a Bruker D8Discover diffractometer with
GADDS as a 2D detector. Silicon powder and silver behenate
were used as standards again. The 2D diffraction patterns were
recorded in a transmission mode at room temperature. The
oriented samples were prepared by mechanically shearing the
films at 120 °C. The sheared film was positioned so that the
mechanical shearing direction was either perpendicular or par-
allel to the point-focused X-ray beam. For both the 1D and 2D
diffractions, the background scattering was recorded and sub-
tracted from the sample patterns.

8470 Macromolecules, Vol. 43, No. 20, 2010
Jin et al.
Device Fabrication and Characterization. The patterned in-
dium tin oxide (ITO) substrate was cleaned by detergents,
deionized water, acetone, and ethanol, in sequence, and then
treated with UV-ozone for about 25 min. Poly(3,4-ethylene-
dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was
spin-coated on the precleaned ITO substrate and dried in air
at 120 °C for 2 h. Then the polymer was spin-coated from a
chlorobenzene solution (10 mg/mL) through a 0.45-μm Teflon
filter. The thickness of the spin-coated film was controlled by the
spinning speed. The coated ITO substrate was transferred into a
deposition chamber with a base pressure of 6 ꢀ 10-4 Pa. 1,3,5-
Tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBI), 8-hydro-
xyquinoline aluminum (AlQ), and metal layers were deposited
on top of the polymer layer. The emitting area was 2 ꢀ 2 mm2.
The EL spectra were measured with a spectrofluorometer FP-
6200 (JASCO). A source-measure unit R6145 (Advantest),
multimeter 2000 (Keithley), and luminance meter LS-110
(Minolta) were used for I-V-L measurements. Relative lumi-
nance was directly detected by using a multifunctional optical
meter 1835-C (Newport). All the fabrication and characteriza-
tion of the devices were performed in air and at room tempera-
ture without protective encapsulation.
8.08-8.12 (m, 2H, Ar-H). Anal. Calcd for C15H15ON: C,
79.97; H, 6.71; N, 6.22. Found: C, 80.00; H, 6.76; N, 6.24.
Synthesis of Bis[3-(9H-carbazol-9-yl)propyl]-5-(benzyloxy)-
isophthalate (3). 5-(Benzyloxy)isophthalic acid (3.8 g, 14.0
mmol), 3-(9H-carbazol-9-yl)-propan-1-ol (7.2 g, 32 0.0 mmol),
N,N0-dicyclohexylcarbodiimide (DCC, 7.2 g, 35.0 mmol), and
4-(dimethylamino)pyridine (DMAP, 0.5 g, 4.2 mmol) were
added into 200 mL of CH2Cl2. The mixture was stirred overnight
at room temperature and filtered. The filtrate was concentrated
by a rotary evaporator, and the residue was washed with acetone
first and then purified through a silica gel column (CH2Cl2:
petroleum ether = 3:2) to afford the pure product as a white
solid (6.1 g, 8.9 mmol) in 64% yield. 1H NMR (300 MHz,
CDCl3, δ, ppm): 2.35-2.41 (m, 4H, CH2CH2CH2), 4.32-4.38
(t, 4H, CH2N), 4.47-4.53 (t, 4H, COOCH2), 5.16 (s, 2H,
OCH2), 7.16-7.26 (m, 4H, Ar-H), 7.35-7.50 (m, 13H, Ar-H),
7.80 (s, 2H, Ar-H), 8.05-8.09 (d, 4H, Ar-H), 8.31-8.32 (t, 1H,
Ar-H). Anal. Calcd for C45H38O5N2: C, 78.70; H, 5.58; N, 4.08.
Found: C, 78.76; H, 5.80; N, 4.13.
Synthesis of Bis[3-(9H-carbazol-9-yl)propyl]-5-(3-hydroxy-
propoxy)isophthalate (4). Bis[3-(9H-carbazol-9-yl)propyl]-5-
(benzyloxy)isophthalate (17.0 g, 24.8 mmol) was dissolved in
THF (250 mL), and Pa/C catalyst (3.0 g) was added. The
mixture was stirred under a hydrogen atmosphere at room
temperature for 8 h. Then the mixture was filtered through
Celite, and the filtrate was concentrated to obtain a white solid,
which was dissolved in acetone (250 mL), followed by the
addition of 3-bromopropan-1-ol (6.9 g, 49.5 mmol), anhydrous
potassium carbonate (6.8 g 49.5 mmol), and potassium iodide
(1.2 g, 7.2 mmol). The mixture was refluxed for 8 h, and the hot
solution was filtered. The filtrate was concentrated by a rotary
evaporator, and the residue was washed with ethanol to give
the crude product. The pure product was obtained through a
silica gel column (ethyl acetate:petroleum ether = 1:1) as a
white powder (15.6 g, 23.8 mmol) in 95% yield. 1H NMR (300
MHz, CDCl3, δ, ppm): 2.06-2.15 (m, 2H, HOCH2CH2),
2.29-2.42 (m, 4H, COOCH2CH2), 3.89-3.93 (t, 2H, HOCH2),
4.19.-4.23 (t, 2H, OCH2), 4.33-4.37 (t, 4H, CH2N), 4.48-4.52 (t,
4H, COOCH2), 7.18-7.25 (m, 4H, Ar-H), 7.39-7.43 (m, 8H,
Ar-H), 7.73-7.74 (d, 2H, Ar-H), 8.06-8.09 (d, 4H, Ar-H),
8.31-8.32 (t, 1H, Ar-H). Anal. Calcd for C41H38O6N2: C, 75.21;
H, 5.85; N, 4.28. Found: C, 75.21; H, 5.91; N, 4.26.
Synthesis of Monomer 1. Bis[3-(9H-carbazol-9-yl)propyl]-
5-(3-hydroxypropoxy)isophthalate (5.4 g, 8.3 mmol), 2-vinyl-
terephthalic acid (0.8 g, 4.1 mmol), DCC (1.9 g, 9.1 mmol), and
DMAP (0.1 g, 0.9 mmol) were added into 100 mL of CH2Cl2
simultaneously. The mixture was stirred overnight at room
temperature and filtered. The filtrate was concentrated by a
rotary evaporator, and the residue was purified through a silica
gel column using CH2Cl2 as the eluent. The target monomer 1
was obtained as a white solid (3.7 g, 2.5 mmol) in 61% yield. 1H
NMR (400 MHz, CDCl3, δ, ppm): 2.29-2.40 (m, 12H,
CH2CH2CH2), 4.18-4.22 (m, 4H, OCH2), 4.32-4.35 (t, 8H,
CH2N), 4.47-4.50 (t, 8H, COOCH2), 4.54-4.59 (q, 4H,
COOCH2), 5.34-5.37 (d, 1H, dCH2), 5.67-5.71 (d, 1H,
dCH2), 7.17-7.25 (m, 8H, Ar-H), 7.33-7.43 (m, 17H, Ar-H,
CHd), 7.72 (s, 4H, Ar-H), 7.86-7.93 (m, 2H, Ar-H),
8.05-8.07 (d, 8H, Ar-H), 8.19 (s, 1H, Ar-H), 8.30 (s, 2H,
Ar-H). MS (HR-ESI): m/z 1482.60299 [M þ NH4]þ. Anal.
Calcd for C92H80O14N4: C, 75.39; H, 5.50; N, 3.82. Found: C,
75.11; H, 5.68; N, 4.00.
Synthesis. Syntheses of the monomers and polymers were
carried out following the routes outlined in Scheme 1.
Synthesis of 5-(Benzyloxy)isophthalic Acid (1). After dissol-
ving 5-hydroxyisophthalic acid (5.0 g, 27.5 mmol) in methanol
(25 mL), concentrated sulfuric acid (3.2 mL) was added drop-
wise. The reaction mixture was refluxed for 5 h. After the
mixture was cooled, methanol was removed by a rotary eva-
porator to give a white powder, which was dissolved in ethyl
acetate (100 mL) and washed with water (100 mL ꢀ 3), a
saturated sodium bicarbonate solution (100 mL ꢀ 3), and water
(100 mL). Then the organic layer was dried with anhydrous
magnesium sulfate for 30 min, and the solvent was evaporated.
The residue was dissolved in acetone (100 mL), with the addition
of bromomethylbenzene (5.6 g, 33.0 mmol) and anhydrous
potassium carbonate (7.0 g, 50.0 mmol). The mixture was
refluxed for 2 h, and the hot solution was filtered. The filtrate
was concentrated by a rotary evaporator to give a white powder,
which was dissolved in THF (50 mL), and a sodium hydroxide
solution (5 M, 25 mL) was added. Then the reaction temperature
was increased to 60 °C. After 8 h, the mixture was poured into
800 mL of water and acidified with hydrochloride acid to give a
white precipitate. Filtered, washed with water, and dried in a
vacuum oven, the target product was obtained as a white
1
powder (5.6 g, 20.6 mmol) in 75% yield. H NMR (300 MHz,
DMSO-d, δ, ppm): 5.25 (s, 2H, -OCH2), 7.33-7.57 (m, 5H,
Ar-H), 7.76 (s, 2H, Ar-H), 8.11 (s, 1H, Ar-H), 13.35 (s, 2H,
-COOH). Anal. Calcd for C15H15ON: C, 66.17; H 4.44. Found:
C, 66.36; H, 4.53.
Synthesis of 3-(9H-Carbazol-9-yl)propan-1-ol (2). To a mag-
netically stirred solution of 3-bromopropan-1-ol (10.0 g, 71.8
mmol) in N,N0-dimethylformamide (DMF, 30 mL) was added
3,4-dihydro-2H-pyran (12.1 g, 143.5 mmol) dropwise, and then
the solution was stirred at room temperature. After 1 h, carba-
zole (6.0 g, 35.9 mmol) and sodium hydroxide (2.9 g, 71.8 mmol)
were added to the solution, and the temperature was increased
to 90 °C. The mixture was stirred for 5 h. After the hot solution
was filtered, the filtrate cake was washed by DMF three times,
The filtrate was added with methanol (30 mL) and 4-methyl-
benzenesulfonic acid (3.4 g, 17.9 mmol), and the reaction
mixture was stirred overnight at 50 °C and then concentrated
at 65 °C under reduced pressure. The crude product was
dissolved in ethanol and precipitated in a large amount of water.
After the precipitate was filtered and dried, the pure product was
obtained by silica gel column chromatography (CH2Cl2:petro-
leum ether = 3:1) as a white solid (5.1 g, 22.6 mmol) in 63%
yield. 1H NMR (300 MHz, CDCl3, δ, ppm): 2.06-2.18 (m, 2H,
HOCH2CH2), 3.59-3.65 (t, 2H, HOCH2), 4.44.-4.51 (t, 2H,
CH2N), 7.19-7.29 (m, 2H, Ar-H), 7.46-7.48 (m, 4H, Ar-H),
Synthesis of BnCbzG2 (5). 5-(Benzyloxy)isophthalic acid
(1.1 g, 4.0 mmol), bis[3-(9H-carbazol-9-yl)-propyl]-5-(3-hydroxy-
propoxy)isophthalate (5.3 g, 8.1 mmol), DCC (1.9 g, 9.2 mmol),
and DMAP (0.1 g, 0.8 mmol) were added into CH2Cl2 (100 mL).
The mixture was stirred at room temperature for 9 h and filtered.
The filtrate was concentrated by a rotary evaporator, and the
residue was purified through a silica gel column (CH2Cl2:ethyl
acetate =100:1) to give the pure product as a white solid
1
(3.9 g, 2.5 mmol) in 62% yield. H NMR (400 MHz, CDCl3,

Article
Macromolecules, Vol. 43, No. 20, 2010 8471
Scheme 1. Syntheses of the First- and Second-Generation Monomers and Polymers
δ, ppm): 2.29-2.38 (m, 12H, CH2CH2CH2), 4.16-4.19 (t, 4H,
OCH2), 4.30-4.33 (t, 8H, CH2N), 4.45-4.48 (t, 8H, COOCH2),
4.53-4.57 (t, 4H, COOCH2), 5.03 (s, 2H, OCH2), 7.16-7.20 (m,
8H, Ar-H), 7.33-7.42 (m, 21H, Ar-H), 7.69-7.70 (d, 4H,
Ar-H), 7.77-7.78 (d, 2H, Ar-H), 8.04-8.06 (d, 8H, Ar-H),
8.28-8.29 (m, 3H, Ar-H). MS (LR-ESI): m/z 1546.6 [M þ H]þ.
Anal. Calcd for C97H84O15N4: C, 75.37; H, 5.48; N, 3.62. Found:
C, 75.50; H, 5.74; N, 3.63.
Synthesis of HC3CbzG2 (6). To a solution of BnCbzG2 (11.0
g, 7.1 mmol) in THF (250 mL) was added Pa/C catalyst (2.5 g).
The mixture was stirred under a hydrogen atmosphere at room
temperature for 10 h and then filtered through Celite. The
filtrate was concentrated to obtain a white solid, which was
dissolved in acetone (250 mL), followed by the addition of
3-bromopropan-1-ol (2.8 g, 19.8 mmol), anhydrous potassium
carbonate (2.7 g 19.8 mmol), and potassium iodide (0.3 g,

8472 Macromolecules, Vol. 43, No. 20, 2010
Jin et al.
1.6 mmol). The mixture was refluxed for 7 h, and the hot
solution was filtered. The filtrate was concentrated by a rotary
evaporator, and the residue was washed with ethanol to give the
crude product. The pure product was obtained through a silica
gel column (ethyl acetate:petroleum ether =2:1) as a white
Table 1. Molecular Weights and Thermal Properties of the Polymers
polymer yield (%) Mn (g/mol)a Mw/Mn
Td (°C)b Tg (°C)c
a
PCbzG1
PCbzG2
75
40
57 000
34 000
1.89
1.55
364
382
87
86
a Determined by GPC in THF using polystyrene standards. b 5%
weight loss temperature evaluated by TGA under a nitrogen atmosphere
at a heating rate of 20 °C/min. c Evaluated by DSC during the second
heating cycle at a rate of 20 °C/min.
1
powder (10.2 g, 6.7 mmol) in 94% yield. H NMR (400 MHz,
CDCl3, δ, ppm): 1.94-2.00 (m, 2H, HOCH2CH2), 2.29-2.39
(m, 12H, CH2CH2CH2), 3.76-3.79 (t, 2H, HOCH2), 4.07-4.10
(t, 2H, OCH2), 4.17-4.20 (t, 4H, OCH2), 4.31-4.34 (t, 8H,
CH2N), 4.45-4.49 (t, 8H), 4.54-4.57 (t, 4H, COOCH2),
7.11-7.21 (m, 8H, COOCH2), 7.37-7.42 (m, 16H, Ar-H),
7.69-7.70 (d, 6H, Ar-H), 8.04-8.06 (d, 8H, Ar-H),
8.26-8.29 (m, 3H, Ar-H). MS (LR-ESI): m/z 1513.6 [M þ
H]þ. Anal. Calcd for C93H84O16N4: C, 73.79; H, 5.59; N, 3.70.
Found: C, 73.55; H, 5.75; N, 3.65.
Synthesis of Monomer 2. HC3CbzG2 (5.5 g, 3.6 mmol),
2-vinylterephthalic acid (0.3 g, 1.8 mmol), DCC (0.9 g, 4.6 mmol),
and DMAP (0.1 g, 0.9 mmol) were added into CH2Cl2 (150 mL)
simultaneously. The mixture was stirred overnight at room tem-
perature and filtered. The filtrate was concentrated by a rotary
evaporator, and the residue was purified through a silica gel
column (CH2Cl2:ethyl acetate = 30:1) to give the pure product
as a white solid (2.8 g, 0.9 mmol) in 49% yield. 1H NMR
(400 MHz, CDCl3, δ, ppm): 2.28-2.37 (m, 28H, CH2CH2CH2),
4.08-4.18 (m, 12H, OCH2), 4.30-4.33 (t, 16H, CH2N),
4.44-4.47 (t, 20H, COOCH2), 4.53-4.56 (t, 8H, COOCH2),
5.33-5.35 (d, 1H, dCH2), 5.65-5.69 (d, 1H, dCH2), 7.14-7.21
(m, 16H, Ar-H), 7.30-7.41 (m, 33H, Ar-H, dCH), 7.68-7.70
(m, 12H, Ar-H), 7.82-7.89 (m, 2H, Ar-H), 8.03-8.05 (d, 16H,
Ar-H), 8.15 (s, 1H, Ar-H), 8.26-8.28 (m, 6H, Ar-H). MS
(MALDI-TOF): m/z 3204.5 [M þ Na]þ. Anal. Calcd for
C196H172O34N8: C, 73.95; H, 5.45; N, 3.52. Found: C, 71.30; H,
5.40; N, 3.36.
Polymerization of Monomer 1. Monomer 1 (100 mg), chloro-
benzene (864 mg), and 37 μL of chlorobenzene solution con-
taining 0.22 mg of AIBN were transferred into a precleaned
glass tube. After three freeze-pump-thaw cycles, the tube was
sealed off under vacuum. Polymerization was performed at
60 °C for 20 h, and the mixture was quenched in liquid nitrogen.
Then the tube was opened, and the solution was diluted with
5 mL of THF. The target polymer was precipitated in 200 mL of
acetone. To ensure that the unreacted monomers was elimi-
nated, the precipitation process was repeated three times. By
filtration, the target polymer PCbzG1 was obtained as a white
solid in 75% yield.
Polymerization of Monomer 2. Monomer 2 (300 mg), chloro-
benzene (1.14 g), and 52 μL of chlorobenzene solution contain-
ing 0.31 mg of AIBN were transferred into a precleaned glass
tube. Polymerization was carried out similarly compared to that
for synthesizing PCbzG1. The target polymer PCbzG2 was
obtained as a white solid in 40% yield.
utilized to prevent side reactions of the double bond in the
long synthetic routes. To ensure high yields of the mono-
mers, highly efficient reactions, such as Williamson ether-
ification, DCC esterification, and catalytic hydrogenation
reactions, were chosen. The monomer structures were con-
1
firmed by H NMR spectra, mass spectra, and elemental
analysis.
PCbzG1 and PCbzG2 were synthesized under the same
conditions by conventional free radical polymerization in
solution using chlorobenzene as the solvent. The number-
average molecular weight (Mn), the molecular weight dis-
tribution, and the thermal properties of the polymers are
summarized in Table 1. Although the two polymerizations
were carried out under the same conditions, with the same
ratio (50:1) of monomer concentration to initiator concen-
tration, monomer weight concentration (10%), solvent,
temperature, and reaction time, they showed different poly-
merization results. The second-generation monomer had a
larger molecular weight than the first-generation one. How-
ever, PCbzG2 had a lower Mn and a lower monomer con-
version compared with PCbzG1, which was probably due to
a lower concentration of the double bond and a larger steric
hindrance of monomer 2. To reduce the steric hindrance
in the polymerization and improve the reactivity of the
monomers, a short spacer had been introduced between the
core and the dendritic shells in both monomers. However,
monomer 2 still had a much stronger steric hindrance effect
than monomer 1. Excellent solubility was of great importance
for dendronized polymers, especially for OLED applica-
tions. Therefore, we constructed the monomers with ester
connections, which was also beneficial to the film-forming
ability in a wet-processing technology. The polymers ob-
tained could be readily dissolved in common organic sol-
vents, such as THF, chlorobenzene, CH2Cl2, CHCl3, ethyl
acetate, DMF, etc. In addition, the dendronized monomer 1
and monomer 2 could be readily dissolved in acetone and thus
could be removed easily after the polymerization.
The glass transition temperatures of the polymers were
approximately 85 °C. Both polymers exhibited 5% weight
loss temperatures above 360 °C, and the temperature of
PCbzG2 was about 20 °C higher than that of PCbzG1. No
weight loss was found at low temperatures. The excellent
thermal properties indicated that these kind of dendronized
polymers were suitable for device fabrication.
Photophysical Properties. The photophysical properties of
the two polymers were investigated in different solvents and
films. The absorption and emission data are summarized in
Table 2. The UV-vis absorption spectra of the polymers are
shown in Figure 2. All the spectra showed similar absorption
bands with peaks at about 262 and 295 nm, which were due to
the π-π* transition of the carbazole moiety.42 The minor
difference in the absorbing wavelength suggested that dif-
ferent solvents or different states had little influence on the
ground-state electronic transitions.
Results and Discussion
Synthesis and Characterization of Monomers and Poly-
mers. As mentioned before, the “graft through” strategy
can control the chemical structure of dendronized polymers
more precisely. We chose to synthesize the dendritic macro-
monomers first and then perform the polymerizations as
illustrated in Scheme 1. In this way, a dendronized polymer
with the same dendritic side groups in each repeating unit
could be obtained. There are usually two ways to synthesize a
dendritic molecule.41 One is the divergent method. A core is
synthesized first in this method, and then the dendritic shells
grow from the core sequentially to form different generations
of molecules. The other way is the convergent method, which
begins with the synthesis of different generations of dendritic
shells, followed by a reaction with the core. In the present
work, the core had a styrene structure for the polymerization
in the final step. Therefore, the convergent method was
The PL spectra were obtained after excitation at 280 nm.
The spectra of the two polymers in THF and CHCl3
all showed a single emission at approximately 440 nm

Article
Macromolecules, Vol. 43, No. 20, 2010 8473
Table 2. UV-Vis and PL Spectra Data in Solutions and Films
in THFa
in CHCl3
in films
a
polymer
UV (nm)
PL (nm)b
UV (nm)
PL (nm)b
UV (nm)c
PL (nm)b,c
PL (nm)b,d
PCbzG1
PCbzG2
261, 295
262, 295
439
437
263, 295
263, 295
440
441
262, 297
262, 297
429
431
430
415
a 0.1 mg/mL. b Excitation wavelength was 280 nm. c Films were cast from THF solutions and dried at room temperature. d Films were cast from THF
solutions, dried at room temperature, and then annealed at 120 °C for 2 h.
Figure 3. Normalized PL spectra in solutions (a) and films (b).
Figure 2. Normalized UV-vis absorption spectra in solutions (a) and
films (b).
transition would not lead to the aggregation of the dendritic
functional groups.
(Figure 3a). No obvious differences were found between the
spectra of the two polymers in different solvents, which also
supported the conclusions that different solvents played a
minor role in the photophysical behavior and that similar
excitation structures and radiative transition processes ex-
isted in the two polymers. Interestingly, we found that the PL
emission in films (Figure 3b) showed different characteristics
compared with that in solutions. The films were prepared
from the corresponding polymer solutions (10 mg/mL) by
spin-coating on a quartz plate and then dried at room
temperature. The maximum emission peaks in the spectra
of the two polymer films were both ∼430 nm, which blue-
shifted 10 nm compared with those of the polymer solutions.
Since no additional conjugated structures were available in
the polymers, the blue shift of the PL spectra could be due to
the rearrangements of the polymer chains in films. After the
polymer films were annealed at 120 °C for 2 h, the emission
spectra became even narrower, and no excimer emissions
were found at longer wavelengths, which further indicated
the transition of the polymer conformation and that this
Phase Structures of the Dendronized Polymers. In order to
investigate the underlying reason for the changes in the PL
spectra in films and study the phase behaviors of the two new
jacketed polymers, 1D and 2D WAXD experiments were
carried out to determine their phase structures. About 30 mg
of sample was dissolved into 2 mL of THF, and then the
solution was cast onto a cleaned copper substrate. The
solvent was evaporated at room temperature, and finally
the film was annealed at 120 °C for 48 h before testing. Figure
4 shows the 1D WAXD patterns of the first- and second-
generation dendronized polymers during the first heating
and the subsequent cooling processes. For PCbzG1, a sharp
diffraction peak with a 2θ value of 3.04° was observed at
40 °C, indicating the existence of an ordered packing. With
increasing temperature, the intensity of the peak increased.
And the intensity decreased during cooling. Because of
the limited number of diffractions, it was difficult to deter-
mine the exact phase structure from the 1D WAXD results
alone. The phase structure could be a columnar nematic

8474 Macromolecules, Vol. 43, No. 20, 2010
Jin et al.
low-angle peak for PCbzG1, probably due to the lower MW
of PCbzG2 as the phase behavior of MJLCPs are MW-
dependent.21 However, the LC phase of PCbzG2 was less
ordered than that of PCbzG1, based on the much less intense
low-angle diffraction peak in parts c and d of Figure 4. In
addition to the regular amorphous halo at ∼20°, a second
amorphous halo at ∼12° was always present in Figure 4a-d,
and it was also found in the diffraction patterns of the
monomers. Therefore, it might result from the short-range
arrangement of the dendritic carbazole side groups.
2D WAXD was also utilized to determine the phase
structures of the two polymers. The samples were annealed
at 170 °C and then sheared at the same temperature. Figure 5
shows the diffraction patterns with the X-ray incident beam
perpendicular and parallel to the shear direction. As shown
in Figure 5, the two polymers showed different diffraction
patterns. For PCbzG1, when the X-ray incident beam was
parallel to the shear direction (Figure 5a), six diffraction arcs
were observed in the low-angle region. The azimuthal scan of
the low-angle diffraction arcs exhibited six maxima which
were separated by 60° from the adjacent ones (Figure 5c),
indicating a 6-fold symmetry. On the other hand, the pattern
obtained with the X-ray incident beam perpendicular (along
Y direction) to the shear direction showed a pair of low-angle
arcs on the meridian along with a diffuse high-angle halo
concentrated on the equator (Figure 5b). These two patterns
confirmed the existence of a columnar phase, actually a
hexatic columnar nematic phase (ΦHN, Figure 6a), instead
of a smectic phase. From the low-angle d-spacing of 2.90 nm,
which was consistent with the 1D WAXD results, the diam-
eter of the polymer columns was calculated to be 3.35 nm.
This value was close to the simulated molecular length
(2.81 nm) of monomer 1, and the difference could be
attributed to the loose packing of the nematic phase. In
addition, the weak diffraction at a 2θ of ∼8°, which corre-
sponded to the weak diffraction with a 2θ of 7.9° in the 1D
WAXD patterns, appeared to be ring-like or arc-like in
Figure 5a. Therefore, it might be attributed to the lateral
packing of the polymer, possibly to the lateral periodic
arrangement of aromatic units of the side groups. This weak
diffraction was not observed in Figure 5b, probably due to
the smaller Y dimension compared with the X dimension of
the film. For PCbzG2, when the X-ray incident beam was
parallel to the shear direction, only a close-to-ring pattern
was observed in the low-angle region (Figure 5d). When the
X-ray incident beam was along Y (Figure 5e) and Z
(Figure 5f) directions (both perpendicular to the shear
direction), the patterns were similar. A pair of low-angle
diffraction arcs with a d-spacing of 4.07 nm appeared on the
median in addition to a diffuse high-angle halo concentrated
on the equator (Figure 5e,f). The low-angle ring pattern in
Figure 5d and the resemblance of the patterns in Figures 5e
and 5f confirmed the existence of a columnar phase instead
of a smectic phase. Although it was still difficult to determine
the exact phase structure due to limited diffractions, the
phase of PCbzG2 could be a columnar nematic phase, ΦN
(Figure 6b). The columnar diameter of PCbzG2 was 4.07 nm,
also quite close to the simulated molecular length (3.88 nm)
of monomer 2. The different phase structures of the two
polymers might originate from the different degrees of
polymerization. PCbzG1 had a higher MW than PCbzG2
(Table 1). However, the columnar diameter of PCbzG1 was
smaller than that of PCbzG2. Therefore, the aspect ratio
(L/D) of PCbzG1 was larger than that of PCbzG2 (Figure 6)
so that PCbzG1 was prone to form a more ordered structure.
For side-chain-type electroluminescent polymers, the
main chain tend to take a coil-like conformation. Most of
Figure 4. 1DWAXDpatterns ofPCbzG1(a and b) and PCbzG2(c and
d) during their first heating and the subsequent cooling processes.
(ΦN) phase with a d-spacing of 2.90 nm, although it was
difficult to confirm by polarized light microscopy due to the
rigid nature of the sample. A weaker diffraction peak at
∼7.90° with a d-spacing of 1.12 nm was also found during the
two processes. It was also difficult to judge the origin of this
peak from the 1D patterns. For PCbzG2, only one diffrac-
tion peak could be found in the low-angle region, and
the diffraction angel was 2.17° with a d-spacing of 4.07 nm.
The intensity of this peak was much weaker than that of the

Article
Macromolecules, Vol. 43, No. 20, 2010 8475
Figure 5. 2D WAXD patterns of PCbzG1 (a and b) and PCbzG2 (d, e, and f) with the X-ray incident beam parallel (a and d) and perpendicular (b, e,
and f) to the shear direction; azimuthal scan of (a) for 2θ = 2-3° (c); schematic drawing of the shearing geometry with X-axis the shear direction (g).
the functional side groups are wrapped into the coil and can
easily interact with one another. For the dendronized jacketed
polymers in this work, when the supramolecular columns
formed, the jacketed main chain extended into a rod-like

8476 Macromolecules, Vol. 43, No. 20, 2010
Jin et al.
Table 3. Electrochemical Properties of the Dendronized Polymers
polymer λedge (nm)a Eg (eV)b Uonset(ox) (V)c EHOMO (eV) ELUMO (eV)
PCbzG1
PCbzG2
358
357
3.46
3.47
0.91
0.90
-5.26
-5.25
-1.80
-1.78
a The onset value of absorption spectrum in the long-wavelength
range. b Estimated from the formula Eg=1240/λedge
.
c Measured by cyclic
voltammetry.
Figure 6. Schematic illustrations of the hexatic columnar nematic
phase of PCbzG1 (a) and the columnar nematic phase of PCbzG2 (b).
Figure 8. Energy level diagram of the materials used in this study.
easier to lose electrons. Changing the generation of the
polymer only resulted in a different diameter of the cylin-
drical structure, and it had little effect on the electron
receiving or losing properties. Therefore, both the polymers
had high HOMO levels that were quite close to that of
PEDOT:PSS (Figure 8), which suggested that they were very
suitable for transporting of holes.
Electroluminescent Properties. The electroluminescent de-
vices were fabricated in two configurations (device a, ITO/
PEDOT:PSS/sample/TPBI(15 nm)/LiF(1 nm)/Al(100 nm);
device b, ITO/PEDOT:PSS/sample/TPBI(15 nm)/AlQ(30
nm)/LiF(1 nm)/Al(100 nm)). In order to investigate the
light-emitting properties of the target polymers with den-
dronized carbazole units, a hole-blocking layer was intro-
duced into the devices to inhibit the formation of excitons
near the electrode. TPBI has a lower HOMO level and thus
possesses excellent hole-blocking properties. Therefore, it
was chosen in this study. For device b, when the TPBI layer
was removed, excitons formed in the AlQ layer, and we
obtained the green emission from AlQ rather than the blue
emission from the polymers. The electroluminescent spectra
of devices a were collected at 6 V, and the two polymers
exhibited similar EL behavior with the main emission peaks
at around 435 and 488 nm (Figure 9). With increasing
number of generation of dendrons, little difference was
observed between the two EL spectra. Compared with PL
spectra, the main emission peak only red-shifted 5-8 nm,
which indicated that similar excited-state structures formed
in both optic and electronic exciting processes. A new shoulder
emission appeared at a longer wavelength, probably due to
the formation of a new molecular exciting state under the
electric field.
Figure 7. Cyclic voltammograms of the dendronized polymer films
coated on the carbon electrode.
conformation, and all the functional groups were distributed
on the surface of the column. This stiff main-chain structure
and the dendritic side-group structure could reduce the
intramolecular interactions and aggregations of the func-
tional groups and prevent the formation of excimers, which
would be beneficial to the photophysical properties.
Electrochemical Properties. In order to investigate the
electrochemical properties of the dendronized polymers,
cyclic voltammetry (CV) was utilized. The results are illus-
trated in Figure 7. As carbazoles and their derivatives are
usually electron-rich systems, it was difficult to obtain the
reduction information from the CV test, and we could only
find the oxidation peaks in the CV curves. The HOMO levels
of the dendronized polymers were estimated from the onset
oxidation potentials by the equation EHOMO=-e[Uonset(ox)
þ
(4.8 V - U1/2,FOC)]. Since the reduction peaks could not
be obtained, we used the optical band gap (Eg) to estimate the
LUMO levels by the equation ELUMO=EHOMO þ Eg, where
Eg was calculated from the onset absorbing wavelength in the
UV-vis spectra in films. The detailed data are summarized
in Table 3.
The properties of the devices are summarized in Table 4.
The luminous efficiency (ηL) vs voltage curves and external
quantum efficiency (ηext) vs voltage curves are shown in
Figure 10. All the devices could be turned on at a low
voltage of no more than 6.1 V. These voltages were even
lower than those of devices made from our previously
reported jacketed polymers.22,24,26 This was probably due
to the good hole-transporting properties of the carbazole
As shown in Figure 7 and Table 3, the two polymers
exhibited similar electrochemical properties. This could be
attributed to the jacketed structures of the polymers. The
carbazole units were all attached on the surface of the
cylindrical polymer chains, which made the carbazoles much

Article
Macromolecules, Vol. 43, No. 20, 2010 8477
units, especially when the carbazoles were grafted onto
the surfaces of the cylindrical polymer chains, which
might result in the formation of a continuous carrier-
transporting channel. In addition, the better matching of
the HOMO levels also contributed to the lower turn-
on voltages.
Conclusions
In summary, jacketed polymers with the first- and second-
generation carbazole dendrons were synthesized by a “graft
through” strategy. The second-generation polymer had a lower
apparent molecular weight and a lower yield than those of the
first-generation polymer. The glass transition temperatures and
the 5% weight loss temperatures of the two polymers were about
85 and 360 °C, respectively. Their photophysical properties were
similar in different solvents. The PL spectra in films blue-shifted
10 nm compared with those in solutions. After the films were
annealed, the emission peaks in PL spectra became narrower,
which was probably due to the transition of the chain conforma-
tion. X-ray diffraction experiments revealed that the first-
generation polymer formed a hexatic columnar nematic phase
and the second-generation polymer formed a columnar nematic
phase. Electrochemical studies showed that the HOMO levels of
the two polymers were quite high and close to that of PEDOT:
PSS, which suggested that they possessed excellent hole-trans-
porting properties. All the EL devices possessed low turn-on
Although a hole-blocking layer had been introduced into
the devices to confine the holes in the emitting layer, the
current efficiencies of devices a were quite low, which
indicated the existence of a current leakage and a low
electro-optic conversion efficiency. In order to reduce the
current leakage, a better balance between the electron trans-
port and hole transport was important. Therefore, in devices
b, an electron-transporting layer (AlQ) was incorporated,
resulting in greatly improved devices properties. Device b
with PCbzG1 had the best comprehensive properties. The
maximum luminescence was 2195 cd/m2, and the maximum
external quantum efficiency was 0.353%, with both values 4
times higher than those of device a. The maximum current
efficiency and the power efficiency were 0.240 cd/A and 0.110
lm/W, respectively, both of which were 2 times higher than
those of device a. These data were better than those obtained
with the jacketed polymers we reported previously.22,26 The
turn-on voltages of devices b were a little higher than those of
devices a, which was due to the incorporation of an addi-
tional AlQ layer. These results could be explained from the
energy level diagram in Figure 8. In device a, electrons were
injected from the Al cathode directly to the TPBI layer, in
which process an energy barrier of 1.5 eV needed to be
overcome. When an AlQ layer was introduced into the
device, the energy barrier went down to 0.9 eV, which
greatly increased the injection and transport of electrons
and thus greatly improved the balance of the carrier trans-
port. The better EL properties of PCbzG1 than PCbzG2
in both device configurations were probably due to the
introduction of more nonfunctional components into
monomer 2.
Figure 10. Luminous efficiency-voltage (a) and external quantum
efficiency-voltage (b) curves for the devices with different polymers.
Figure 9. Electroluminescent spectra of devices a.
Table 4. Electroluminescent Properties of the Dendronized Polymers
device
polymer
Vonset (V)a
Lmax (cd/m2)b
η
Imax (cd/A)c
η
Lmax (lm/W)d
η
extmax (%)e
CIE coordinatef
(0.18, 0.16)
λ (nm)g
a
a
b
b
PCbzG1
PCbzG2
PCbzG1
PCbzG2
4.6
5.1
6.1
5.3
555
327
2195
1796
0.110
0.107
0.240
0.236
0.056
0.051
0.110
0.106
0.087
0.078
0.353
0.158
428, 483
(0.18, 0.20)
(0.19, 0.22)
434, 487
439, 488
a Turn-on voltage at 1 cd/m2. b Maximum luminance. c Maximum current efficiency. d Maximum luminescence efficiency. e Maximum external
quantum efficiency. f 1931 CIE coordinate. g Emission wavelength at 6 V.

8478 Macromolecules, Vol. 43, No. 20, 2010
Jin et al.
voltages compared with those having some other side-chain-type
EL polymers. After the optimization of the device structure,
device b with PCbzG1 obtained the best performance. The
maximum luminescence, current efficiency, and external quan-
tum efficiency were 2195 cd/m2, 0.240 cd/A, and 0.353%,
respectively. The comprehensive properties were better than
those of the devices with the jacketed polymers we reported
previously because the novel dendronized jacketed structure
could reduce the intramolecular interactions of functional
groups, make full use of the large surfaces of the supramolecular
columns, and provide a continuous channel for transporting of
holes. With increasing number of generation of the dendrons, the
EL properties became worse due to the decrease in the content of
functional units. Currently we are investigating the controlled/
living polymerization of the two dendronized monomers and the
applications of these new jacketed polymers as host materials for
electrophosphorescent devices.
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