Zinc tetraphenylporphyrin-fluorene branched copolymers: Synthesis and light-emitting properties

Article abstract of DOI:10.1021/ma9023119

Three novel branched zinc tetraphenylporphyrin (ZnTPP)-fluorene copolymers P12, P100, and P1000, with different ZnTPP content, were designed and synthesized by a "A₂ + A_2′ + B ₄" approach based on a facile one-pot Suzuki polycondensation reaction. The molar ratio of ZnTPP to fluorene units in the copolymers is 5.50% for P12, 0.91 % for P100, and 0.08% for P1000. The copolymers are thermally stable, readily soluble in common organic solvents, and show ZnTPP content-dependent absorption and emission properties. The band gap of the copolymers decreased with increasing content of ZnTPP from P1000 to P12, and the emission color of the copolymers changed from purplish pink to red. The OLED device using P12 as emitter showed pure red emission (CIE coordinates of x = 0.64, y = 0.30) with a maximum luminance of 740 cd/m², which is among the highest values for pure red light-emission OLEDs based on porphyrin-containing copolymers. It is noteworthy that these devices all show reasonably stable efficiency over a broad current range, which is a satisfactory performance meeting the need for active-matrix-driven devices.

Full text of DOI:10.1021/ma9023119

Macromolecules 2010, 43, 709–715 709
DOI: 10.1021/ma9023119
Zinc Tetraphenylporphyrin-Fluorene Branched Copolymers:
Synthesis and Light-Emitting Properties
Xiaochen Wang,† Haiqiao Wang,† Yi Yang,‡ Youjun He,‡ Lei Zhang,† Yongfang Li,*,‡ and
Xiaoyu Li*,†
†College of Materials Science and Engineering, Beijing University of Chemical Technology, Key Laboratory of
Advanced Process and Preparation Technique of Nanomaterials, Ministry of Education, Beijing 100029, China
and ‡Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids, Institute of
Chemistry, Chinese Academy of Sciences, Beijing 100190, China
Received October 16, 2009; Revised Manuscript Received December 15, 2009
ABSTRACT: Three novel branched zinc tetraphenylporphyrin (ZnTPP)-fluorene copolymers P12, P100,
0
and P1000, with different ZnTPP content, were designed and synthesized by a “A2 þ A2 þ B4” approach
based on a facile one-pot Suzuki polycondensation reaction. The molar ratio of ZnTPP to fluorene units in
the copolymers is 5.50% for P12, 0.91% for P100, and 0.08% for P1000. The copolymers are thermally stable,
readily soluble in common organic solvents, and show ZnTPP content-dependent absorption and emission
properties. The band gap of the copolymers decreased with increasing content of ZnTPP from P1000 to P12,
and the emission color of the copolymers changed from purplish pink to red. The OLED device using P12 as
emitter showed pure red emission (CIE coordinates of x = 0.64, y = 0.30) with a maximum luminance of
740 cd/m2, which is among the highest values for pure red light-emission OLEDs based on porphyrin-
containing copolymers. It is noteworthy that these devices all show reasonably stable efficiency over a broad
current range, which is a satisfactory performance meeting the need for active-matrix-driven devices.
Introduction
based on Suzuki coupling method. For getting better red emis-
sion, we used ZnTPP instead of free base TPP. The high
Organic light-emitting diodes (OLEDs) and organic/polymeric
light-emitting materials have attracted tremendous interest due to
their potential application in large area flat-panel displays.1,2 To
achieve full-color displays, three primary colors are required.
Short wavelength light-emitting blue fluorescent materials are
commonly used as either emitter or host, while green and red
fluorescent materials can be used as the emitter or the dopant in
the fabrication of OLEDs. Some organic dyes were used as the
red emission doping materials.3 Porphyrin is one kind of the red-
emission organic dyes, which exhibits reasonable fluorescence
efficiency and good thermal stability. Examples of porphyrins
used as red emitting materials include tetraphenylporphyrin
(TPP) and porphyrin-platinum(II).4 However, in the OLED
devices based on guest-host doped emitter system, the optimum
dopant concentration is usually very low and the effective doping
range is very narrow, which are due to the doped red dyes being
prone to aggregate in solid film at higher doping concentration,
and thus leads to self-quenching of their fluorescence and results
in lower efficiency for the devices.5 In addition, the doped red
dyes tend to crystallize, which is also not propitious to high per-
formance light-emitting devices. While at lower doping concen-
tration, the energy transfer from the host materials to the guest
(red dyes) is often incomplete, which brings the devices to a poor
color purity.6,7 To overcome above-mentioned problems, some
polymers based on porphyrin derivative were investigated.8,9 But
the brightness of devices made from these polymers were gene-
rally very low (<200 cd/m2) or even not mentioned at all.
photoluminescence quantum efficiency oligofluorenes were cho-
sen to harvest energy and transfer it to porphyrins. Using this
kind of “A2 þ A20 þ B4” copolymerization method, we can easily
adjust the content of porphyrin in a broader composition range
and do not influence the molecular weight of the materials
significantly at the same time, and thus the emitting color of
the copolymers can be changed in a large color range from pink to
pure red. Furthermore, compared with linear polymers, the
branched polymers could have larger harvest energy section
and larger steric hindering effect because of its ball-shaped
structure. Larger harvest energy section could lead to more
effective energy transfer, and larger steric hindering is favorable
of stable glass formation and less prone to self-aggregation in the
solid state.10 The OLED devices results show that the emission
color of the three copolymers changed from purplish pink of
P1000 to red of P12 with the increase of ZnTPP content in the
copolymers, which indicates that energy transfer extent from
fluorene units to ZnTPP units in these three copolymers were
very different. The maximal brightness of the OLEDs reached
740 cd/m2 for P12 with pure red emission, 1040 cd/m2 for P100
and 2320 cd/m2 for P1000. To the best of our knowledge, the
device employing P12 as emitter demonstrated one of the highest
brightness in the pure red emission OLEDs based on the
porphyrin derivatives as reported up to now.
Experimental Section
Here, we report one kind of zinc tetraphenylporphyrin
(ZnTPP)-fluorene branched copolymers, as shown in Scheme 1,
Materials. All reagents and solvents were commercial grade
and used without further purification. 2-Bromo-9,9-dioctyl-
fluorene (5),11 9,9-dioctylfluorene-2-boronic acid (6),12 2,7-
dibromo-9,9-dioctylfluorene (3), and 9,9-dioctylfluorene-2,
7-bis(trimethylene boronate) (4)13 were synthesized by the
0
which were synthesized by a novel “A2 þ A2 þ B4” approach
*Corresponding authors. E-mail: liyf@iccas.ac.cn (Y.L.); lixy@
mail.buct.edu.cn (X.L.).
r 2009 American Chemical Society
Published on Web 12/28/2009
pubs.acs.org/Macromolecules

710 Macromolecules, Vol. 43, No. 2, 2010
Scheme 1. Molecular Structures of the Copolymers
Wang et al.
methods as reported in the corresponding literatures. All reac-
tions were performed under nitrogen atmospheres.
stirred and refluxed for 5 h. After evaporation of the solvent, the
residue was purified by silica gel column chromatography
(CH2Cl2/petroleum ether) to afford a purple solid (1.59 g, 85%).
1H NMR (600 MHz, CDCl3): δ (ppm) 8.94 (s, 2H), 8.06 (d, 2H),
7.90 (d, 2H).
Synthesis of the Polymers. The synthesis of the polymers was
carried out using palladium-catalyzed Suzuki coupling between
monomer 5,10,15,20-tetra(4-bromophenyl)porphyrin zinc (2),
2,7-dibromo-9,9-dioctylfluorene (3), and 9,9-dioctylfluorene-
2,7-bis(trimethylene boronate) (4), as shown in Scheme 3. All
starting materials, reagents, and solvents were carefully puri-
fied, and all procedures were performed under an air-free
environment.
Under the protection of nitrogen, monomers 2, 3, and 4 were
dissolved in a mixture consisting of toluene, THF, and Na2CO3
(2 M). The solution was flushed with nitrogen for 10 min, and
Pd(PPh3)4 (1-2 mol %) was added. After another flushing
with nitrogen for 20 min, the reactant was heated to reflux for
12-48 h. The terminal 2-bromo-9,9-dioctylfluorene (5) and 9,9-
dioctylfluorene-2-boronic acid (6) were added as end-cappers,
with5 added first and 6 added12 h later. After stirring for another
12 h, the reaction solution was cooled to room temperature. The
reaction mixture was added dropwise to 200 mL of ethanol,
filtered through a Soxhlet thimble, and then subjected to Soxhlet
extraction with ethanol, hexane, and chloroform. The polymer
was recovered as a solid from the chloroform fraction after rotary
evaporation. The solid was dried under vacuum. The yields of the
polymerization reactions were 37-68%.
Measurements and Characterization. The gel permeation
chromatography (GPC) measurements were performed on a
Waters 515-2410 with polystyrenes as reference standard and
tetrahydrofuran (THF) as an eluent. The NMR spectra were
recorded on a Bruker AV 600 spectrometer in CDCl3 at room
temperature. Elemental analyses were performed on a Flash EA
1112 analyzer or Elementar vario EL III. Thermal gravimetric
analysis (TGA, Netzsch TG209C) and the differential scanning
calorimetry (DSC, TA-Q100) measurements were carried out
under a nitrogen atmosphere at a heating rate of 10 °C/min.
UV-vis absorption spectra were recorded on a Shimadzu
spectrometer model UV-3150. Emission spectra were measured
at room temperature with a Varian CARY Elipse fluorescence
spectrophotometer. Fluorescence quantum yields (ΦF) of the
samples in toluene were determined by using ZnTPP (0.033
in toluene) and 1,6-diphenyl-1,3,5-hexatriene (DPH) (0.80 in
cyclohexane) as standards. The electrochemical cyclic voltam-
metry was conducted on a Zahner IM6e electrochemical work-
station with a Pt plate, Pt wire, and Ag/Agþ electrode as the
working electrode, counter electrode, and reference electrode,
respectively, in a 0.1 mol/L tetrabutylammonium hexafluoro-
phosphate (Bu4NPF6)-acetonitrile solution. Polymer thin films
were formed by drop-casting 1.0 mm3 of polymer solutions in
THF (analytical reagent, 1 mg/mL) on the working electrode
and were then dried in air.
Synthesis of the Monomers. 5,10,15,20-Tetra(4-bromophe-
nyl)porphyrin (1). A solution of 4-bromobenzaldehyde (9.25 g,
50 mmol) in 6 mL of DMSO was added into 120 mL of propionic
acid, and then the mixture was stirred and heated to reflux.
A mixture of 3.5 mL of pyrrole (50 mmol) and 10 mL of acetic
anhydride was added dropwise to the above reaction mixture.
The reaction mixture was stirred for 2 h and then cooled to room
temperature. The precipitate was collected after filtration and
washed with propionic acid. The solid was purified by recrys-
tallization in ethanol to obtain the title compound 1 (2.29 g,
19.7%). 1H NMR (600 MHz, CDCl3): δ (ppm) 8.83 (s, 2H), 8.06
(d, 2H), 7.90 (d, 2H), -2.89 (s, 0.5H).
P12. 1H NMR (600 MHz, CDCl3): δ (ppm) 9.05-9.25 (broad,
3H), 8.60-8.85 (broad, 21H), 8.38 (broad, 15H), 7.90-8.10
(broad, 33H), 7.83 (broad, 100H), 7.66 (broad, 215H), 2.12
(broad, 201H), 1.54 (broad, 241H), 1.00-1.35 (broad, 1369H),
0.60-1.00 (broad, 612H). GPC: Mn = 25.7K, Mw = 58.6K,
PDI = 2.28. Elemental Anal. Found: C: 85.19, H: 9.58, N: 0.84.
P100. 1H NMR (600 MHz, CDCl3): δ (ppm) 9.10-9.20
(broad, 1H), 8.60-8.85 (broad, 2H), 8.38 (broad, 2H),
7.95-8.20 (broad, 8H), 7.83 (broad, 100H), 7.67 (broad,
217H), 2.12 (broad, 201H), 1.00-1.35 (broad, 1211H), 0.60-
1.00 (broad, 570H). GPC: Mn = 19.3K, Mw = 41.4K, PDI =
2.14. Elemental Anal. Found: C: 88.14, H: 10.46, N: 0.13.
5,10,15,20-Tetra(4-bromophenyl)porphyrin Zinc (2). Zn(OAc)2
2H2O (2.19 g, 10 mmol) was added into a solution of compound 1
(1.75 g, 1.88 mmol) in DMF (150 mL). The reaction mixture was
3
1
P1000. H NMR (600 MHz, CDCl3): δ (ppm) 7.83 (broad,
100H), 7.67 (broad, 214H), 2.11 (broad, 201H), 1.00-1.35

Article
Macromolecules, Vol. 43, No. 2, 2010 711
Scheme 2. Synthetic Route of 5,10,15,20-Tetra(4-bromophenyl)porphyrin Zinc
Scheme 3. Synthetic Routes of the Copolymers
(broad, 1213H), 0.60-1.00 (broad, 565H). GPC: Mn = 27.0K,
Mw = 50.9K, PDI = 1.89. Elemental Anal. Found: C: 88.01, H:
10.49, N: 0.04.
Fabrication and Characterization of the OLED Devices. The
device configuration of the OLEDs is ITO/PEDOT:PSS-
(30 nm)/PVK-poly-TPD(50 nm)/copolymers(100 nm)/Ca-
(10 nm)/Al(100 nm). The ITO-coated glass substrate was
cleaned with detergent, then ultrasonicated in acetone and
isopropyl alcohol, and subsequently dried in an oven. Then
PEDOT:PSS (P-4083, Bayer AG) was spin-casted (2000 rpm)
with a thickness of ∼30 nm from aqueous solution. The
substrate was dried at 150 °C for 30 min in air and then moved
into a glovebox for spin-casting the active layers. The binary-
host PVK/poly-TPD were dissolved in chlorobenzene and
spin-cast on top of the PEDOT:PSS as the HTL (host-trans-
porting layer). The HTL was annealed at 110 °C for 45 min.
Then, the solution of the copolymers in toluene was spin-cast
on the top of the HTL as the EML (electroluminescent layer).
Similarly, the EML was also treated by thermal annealing at
100 °C for 30 min. At last, a layer of Ca capped with Al was
thermally deposited through a shade mask at a pressure of ca. 5
ꢀ 10-5 Pa. The thickness of the active layer was determined by
an Ambios Tech. XP-2 profilometer. The current-voltage
(I-V) and luminance-voltage (L-V) characteristics were
conducted on a computer-controlled Keithley 236 source-
measure unit and a Keithley 2000 multimeter coupled with a
Si photomultiplier tube.
polymers can be readily processed to form smooth and
pinhole-free films upon spin-coating. Feed ratio, number-
average molecular weight (Mn), weight-average molecular
weight (Mw), and polydispersity index (PDI) of the polymers
are shown in Table 1.
Thermal Analysis. The thermal properties of the polymers
were determined by thermogravimetric analysis (TGA) and
differential scanning calorimetry (DSC) under nitrogen.
P12, P100, and P1000 have good thermal stability with onset
decomposition temperatures with 5% weight loss at 436, 430,
and 429 °C, respectively, as shown in Figure 1a. Figure 1b
shows DSC traces of the three polymers. Glass transitions
were observed at 80-90 °C for the three polymers. P100 and
P1000 have melting points at 141-145 °C. Although P12 has
no melting point, it has another glass transition point at
160 °C. It is obvious that the Tg of the copolymers was
increased after introducing the porphyrin unit, which is
possibly due to reduced segmental motions as well as long
oligofluorenes chain in the polymers.
Optical Properties. Figure 2 shows the optical properties
of the polymers in chloroform solutions and in films on
quartz plates. In chloroform solutions, all three polymers
exhibited a broad absorption from 300 to 415 nm, which is
corresponding to the absorption of the oligofluorene seg-
ments. The intensive Soret band at 428 nm and weak
Q-bands in the absorption of three polymers are due to the
porphyrin segments. Compared with their absorption in the
solutions, the Soret bands in the absorption of the polymer
films were red-shifted by about 6 nm, and there were only
slight broadening peaks, which is due to the aggregation of
the porphyrin rings.
Results and Discussion
Synthesis of Monomers and Polymers. The synthetic
routes of the monomers and corresponding polymers are
outlined in Schemes 2 and 3, respectively. 5,10,15,20-Tetra-
(4-bromophenyl)porphyrin (1) was synthesized in about
20% yield by acid-catalyzed condensation of pyrrole with
4-bromobenzaldehyde, followed by oxidation with DMSO
at refluxing temperature in one pot, similar to Adler’s
method.14 Then porphyrin 1 was treated with zinc acetate,
and zinc porphyrin 2 was readily obtained in high yield.
Copolymers were prepared by Suzuki coupling reaction15
1
and confirmed by H NMR spectroscopy and elemental
analysis. Based on the elemental analysis, the compositions
of three copolymers are in well agreement with the expected
results (as shown in Table 1), indicating that the synthetic
approach enables the design and adjustment of the por-
phyrin content in copolymer expediently according to our
demand.
All these polymers have good solubility in common or-
ganic solvents such as chloroform, THF, and toluene. All the
The normalized photoluminescent (PL) spectra of the
polymers in chloroform solutions and films are shown in

712 Macromolecules, Vol. 43, No. 2, 2010
Table 1. Polymerization Results and Characterization of the Copolymersa
Wang et al.
elemental analysis:b found (wt %)
H
ZnTPP content (mol %)
feed ratio (2:3:4)
Mw
PDI
C
N
calculatedc
foundd
P12
P100
P1000
1:5:7
1:49:51
1:499:501
58.6K
41.4K
50.9K
2.28
2.14
1.89
85.19
88.14
88.01
9.58
10.46
10.49
0.84
0.13
0.04
8.33
1.00
0.10
5.50
0.91
0.28
a Number-average molecular weight (Mn), weight-average molecular weight (Mw), and polydispersity index (PDI) determined by means of GPC.
b Elemental analyses were performed on a Flash EA 1112 analyzer for P12 and Elementar vario EL III for P100 and P1000. c ZnTPP content of the
copolymers was calculated from the feed ratio. d Actual molar fraction of the ZnTPP unit in the copolymers was determined by elemental analysis (EA).
Table 2. Photophysical Properties of the Copolymers
a
λAbs (nm) (in solution)
λPL (nm) (in soloution)
λAbs(nm) (in film)
λPL (nm) (in film)
ΦPL
P12
P100
P1000
384, 429
388, 427
390
416, 450, 602, 652
420, 444
423, 444
378, 434
380, 436
382, 436
617, 668
440, 467, 610, 662
441, 467, 614, 666
0.04
0.68
0.96
a Fluorescence quantum yields (ΦF) of the copolymers, using ZnTPP as standards for P12 and 1,6-diphenyl-1,3,5-hexatriene (DPH) for P100 and
P1000.
Figure 1. (a) TGA plots of the polymers with a heating rate of 10 °C/min under an inert atmosphere. (b) DSC thermogram of the polymers.
Figure 2. Normalized absorption and PL spectra ofthe polymers: (a) UV-vis absorption ofpolymers in chloroform. (b) Photoluminescence spectra of
polymers solutions in chloroform (excited at 360 nm). (c) UV-vis absorption of polymers films on quartz plates. (d) Photoluminescence spectra of
polymer films on quartz plates (excited at 360 nm).

Article
Macromolecules, Vol. 43, No. 2, 2010 713
energy levels of the polymers are higher than that of
polyfluorenes (PFs) (-5.8 eV),19 which implies a lower
barrier for the hole injection in the devices based on the
ZnTPP-fluorene copolymers than that in the TPP/PFs-
doped systems. ZnTPP molecules have a HOMO-LUMO
energy separation smaller than that of PFs, so they could
act as efficient charge traps. It has been shown that PFs-
based OLEDs are injection limited,20 and the current flow-
ing through such devices is dominated by holes.21 The
introduction of hole traps would lead to a reduction in
the hole current and an enhanced electron injection. The
band gaps of the polymers decreased with the increasing of
fluorene content. From the HOMO and LUMO energy
levels, the band gaps of the copolymers were estimated to
be 2.08, 2.19, and 2.28 eV for P12, P100, and P1000,
respectively.
Figure 3. Cyclic voltammograms of the polymer films on Pt electrode
in 0.1 mol/L Bu4NPF6, CH3CN solution with a scan rate of 100 mV/s.
Electroluminescent Properties. OLEDs with the config-
uration of ITO/PEDOT:PSS/PVKþpoly-TPD(1:1)/poly-
mer/Ca/Al were fabricated to investigate the electrolumine-
scent (EL) properties of the copolymers. The binary
hole-transporting layer of PVKþpoly-TPD(1:1) was used
to take the advantages of poly-TPD (which can resist the
solvent dissolving during the spin-coating of the EML) and
PVK (with a higher LUMO level as an electron-blocking
material).22 Figure 4a shows the EL spectra of the poly-
mers, which are very different from the corresponding
PL spectra. In EL spectra, the polymers exhibited emis-
sions in a single peak instead of double ones in PL spectra
in either blue or red regions. The complete disappearance
of the blue emission from the oligofluorene segments in-
dicated that an efficient energy transfer from oligofluo-
rene segments to porphyrin moieties occurred in P12.
P100 and P1000 exhibited emissions in both blue and red
regions. More interestingly, P12 shows a pure red EL
peak at 630 nm with a narrow full width at half-maximum
(fwhm) of 28 nm. In comparison with the PL spectrum
of P12 film (see Figure 2d), the shoulder peak at 668 nm
in the PL did not appear in its EL spectrum, which could
be due to different mechanism of the PL and EL. The
PL mainly resulted from the energy transfer from oligo-
fluorenes to the porphyrin units, while the EL may result
from the charge trapping of the charge injection in the
OLEDs.
Figure 4b,c shows the characteristics of luminance and
current density versus bias of the OLEDs based on the
polymers, and the related EL data are summarized in
Table 4. The turn-on voltage (at 1 cd/m2) of TPP-doped
devices increased with the concentration of TPP.7 But, in this
copolymer system, the turn-on voltages of the EL devices are
in the range of 7.9-8.2 V, which keeps constant and is much
lower than that (ca. 20 V) of the TPP/PFs blend device.7 The
maximal luminance and current efficiency are 740-2320 cd/m2
and 0.06-0.45 cd/A, respectively. The emission changed
gradually with increasing ZnTPP content in the copolymers,
from purplish pink to red (Figure 5).
Table 3. Electrochemical Potentials and Band Gaps of the Polymers
HOMO (eV)
LUMO (eV)
Eegc (eV)
Eogpt (eV)a
P12
P100
P1000
-5.66
-5.69
-5.73
-3.58
-3.50
-3.45
2.08
2.19
2.28
2.00
2.38
2.78
a Optical band gap was obtained from the empirical formula Eogpt
=
1240/λedge, in which λedge is the onset wavelength of its absorption peak
in the longer wavelength direction.
Figure 2b,d. In solutions, P12 exhibited emissions both in
blue and red regions, but P100 and P1000 only exhibited
emissions in blue regions. The blue emission is due to the
incomplete energy transfer from oligofluorene segments to
the porphyrin segment. In films, P12 displayed an intensive
red emission peak at around 617 nm with a shoulder at
670 nm, while the emissions from the oligofluorene seg-
ments almost disappeared. P100 and P1000 revealed both
emission from fluorene segments (400-525 nm) and from
the TPP moieties (600-700 nm). The pure red emission of
P12 indicates that the energy transfer in P12 is more
efficient than in P100 and P1000. The more efficient energy
transfer in films than that in solutions is probably due to
the smaller torsion angle between porphyrin and fluorene,3
the shorter chromophore distances, and efficient inter-
molecular exciton mobility in films.7 The fluorescence
quantum yields (ΦF) of the polymers in dilute chloroform
solutions with ZnTPP (ΦF = 0.033) and 1,6-diphenyl-
1,3,5-hexatriene (DPH) (ΦF = 0.80) as the reference stan-
dard were 0.04, 0.68, and 0.96 for P12, P100, and P1000,
respectively.
Electrochemical Properties. Cyclic voltammetry has been
employed and considered as an effective tool in investigating
electrochemical properties of conjugated oligomers and
polymers.16 From the onset oxidation and reduction poten-
tials in the cyclic voltammogram, the highest occupied
molecular orbital (HOMO) and lowest unoccupied mole-
cular orbital (LUMO) energy levels can be readily estimated,
which correspond to ionization potential (IP) and electron
affinity (EA), respectively.17
Specifically, the EL spectrum of P12 peaked at about
630 nm, and the fwhm of the EL peak is very narrow (only
28 nm). The OLEDs using P12 as emitting material showed
pure red emission (CIE coordinates of x = 0.64, y = 0.30)
with a luminance of 740 cd/m2 at a driving voltage of 17.4 V.
The brightness of this device is much higher than most of
the OLEDs based on porphyrins.3,8,9,23 It is noteworthy
that these devices all show reasonably stable efficiency over
a broad current range,3a,24 as shown in Figure 4d, which
is a satisfactory performance meeting the need for active-
matrix-driven devices.
Cyclic voltammograms of the polymer films are shown in
Figure 3. The HOMO and LUMO energy levels of the
polymers are calculated from the onset oxidation potentials
and the onset reduction potentials and by assuming the
energy level of ferrocene/ferrocenium (Fc/Fcþ) to be -4.8
eV below the vacuum level.18 The formal potential of Fc/Fcþ
was measured to be 0.09 V against Ag/Agþ. The results were
also listed in Table 3.
The LUMO energy levels of the polymers were estimated
to be -3.58, -3.50, and -3.45 eV, respectively. The HOMO

714 Macromolecules, Vol. 43, No. 2, 2010
Wang et al.
Figure 4. (a) EL spectra, (b) luminance-voltage curves, (c) current density-voltage curves, and (d) efficiency-voltage curves of the OLED devices.
Table 4. EL Properties of the OLEDs
device
Vona (V)
Lmaxb (cd/m2)
EL peak wavelength (λem, nm)
current efficiency (cd/A)c
CIE coordinates (x, y)
P12
P100
P1000
7.9
8.2
8.0
740
1040
2320
630
432, 445, 612, 660
431, 630
0.06
0.23
0.45
(0.64, 0.30)
(0.54, 0.27)
(0.41, 0.23)
a Turn-on voltage at 1 cd/m2. b Luminance at maximum bias voltage. c Maximum current efficiency.
Conclusion
Three copolymers of fluorene and ZnTPP have been suc-
cessfully synthesized by the palladium-catalyzed one-pot
Suzuki coupling reaction. They demonstrated moderate glass
transition temperatures (>80 °C) and good thermal stability
(Td > 420 °C). The EL devices based on the copolymers
displayed much lower turn-on voltages and higher luminance
than those of the devices based on TPP/PFs. The maximal
luminance and current efficiency are 740, 1040, and 2320 cd/m2
and 0.06, 0.23, and 0.45 cd/A for P12, P100, and P1000,
respectively. The EL emission color was gradually changed
with the ZnTPP contents in the copolymers, from purplish
pink at low content of ZnTPP in P1000 to pure red at high
content of ZnTPP in P12. One of the brightest red OLEDs
based on porphyrins was achieved using P12 as emitting
material, which showed pure red emission (CIE coordinates
of x = 0.64, y = 0.30) with a narrow fwhm (28 nm) of the EL
peak and a luminance of 740 cd/m2 at a driving voltage of 17.4
V. The results reveal that this kind of porphyrin-fluorene
branched copolymers would be promising red light-emitting
materials. More importantly, this work has developed a novel
molecular design toward improving color purity and lumi-
nance of the red-light-emitting materials.
Acknowledgment. This work was supported by the Pro-
gram of Introducing Talents of Discipline to Universities,
China (Grant No. B08003) and NSFC (Nos. 50633050 and
20721061).
Figure 5. CIE chromaticity coordinates of the OLEDs based on P12,
P100, and P1000.

Article
Macromolecules, Vol. 43, No. 2, 2010 715
References and Notes
(10) Liu, X. M.; He, C. B.; Hao, X. T.; Tan, L. W.; Li, Y. Q.; Ong, K. S.
Macromolecules 2004, 37, 5965.
(1) (a) Burroughes, J. H.; Bradley, D. D. C.; Brown, A. B.; Marks, R.
N.; Mackay, K.; Friend, R. H.; Bum, P. L.; Holmes, A. B. Nature
(London) 1990, 347, 539. (b) Gross, M.; Muller, D. C.; Nothofer, H. G.;
Scherf, U.; Neher, D.; Brauchle, C.; Meerholz, K. Nature (London)
2000, 405, 661. (c) Muller, D. C.; Falcou, A.; Reckefuss, N.; Rojahn,
M.; Wlederhirm, V.; Rudati, P.; Frohne, H.; Nuyken, O.; Becker, H.;
Meerhotz, K. Nature (London) 2003, 421, 829. (d) Hou, Q.; Zhang, Y.;
Li, F. Y.; Peng, J. B.; Cao, Y. Organometallics 2005, 24, 4509.
(2) Li, B. S.; Li, J.; Fu, Y. Q.; Bo, Z. S. J. Am. Chem. Soc. 2004, 126, 3430.
(3) (a) Chen, C. T. Chem. Mater. 2004, 16, 4389. (b) Tang, C. W.;
VanSiyke, S. A.; Chen, C H. Appl. Phys. Lett. 1989, 65, 3610.
(c) Picciolo, L. C.; Murata, H.; Kafafi, Z. H. Appl. Phys. Lett. 2001,
78, 2378.
(4) (a) Baldo, M. A.; O’Brien, D. F.; You, Y.; Shoustikov, A.; Sibley,
S.; Thompson, M. E.; Forrest, S. R. Nature (London) 1998, 395,
151. (b) Kwong, R. C.; Sibley, S.; Dubovoy, T.; Baldo, M.; Forrest,
S. R.; Thompson, M. E. Chem. Mater. 1999, 11, 3709. (c) Guo, T. F.;
Chang, S. C.; Yang, Y.; Kwong, R. C.; Thompson, W. E. Org.
Electrochem. 2000, 1, 15.
(11) (a) Kannan, R.; He, G. S.; Lin, T. C.; Prasad, P. N. Chem. Mater.
2004, 16, 185. (b) Ding, J. F.; Day, M.; Robertson, G.; Roovers, J.
Macromolecules 2002, 35, 3474.
(12) Kanibolotsky, A. L.; Berridge, R.; Skabara, P. J.; Perepichka, I. F.;
Bradley, D. D. C.; Koeberg, M. J. Am. Chem. Soc. 2004, 126,
13695.
(13) Xin, Y.; Wen, G. A.; Zeng, W. J.; Zhao, L.; Zhu, X. R.; Fan, Q. L.;
Feng, J. C.; Wang, L. H.; Wei, W.; Peng, B.; Cao, Y.; Huang, W.
Macromolecules 2005, 38, 6755.
(14) Adler, A. D.; Longo, F. R.; Finarelli, J. D.; Goldmacher, J.;
Assour, J.; Korsakoff, L. J. Org. Chem. 1967, 32, 476.
(15) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
(16) (a) Morgado, J.; Cacialli, F.; Friend, R. H.; Iqbal, R.; Yahioglu,
G.; Milgrom, L. R.; Moratti, S. C.; Holmes, A. B. Chem. Phys.
Lett. 2000, 325, 552. (b) Tang, C. W.; VanSlyke, S. A.; Chen, C. H.
J. Appl. Phys. 1989, 65, 3610. (c) Hsieh, B. Y.; Chen, Y. Macro-
molecules 2007, 40, 8913.
(17) (a) Li, Y. F.; Cao, Y.; Gao, J.; Wang, D. L.; Yu, G.; Heeger, A. J.
Synth. Met. 1999, 99, 243. (b) Sun, Q. J.; Wang, H. Q.; Yang, C. H.; Li,
Y. F. J. Mater. Chem. 2003, 13, 800.
(18) Prommerehne, J.; Vestweber, H.; Guss, W.; Mahrt, R. F.; Bassler,
H.; Porsch, M.; Daub, J. Adv. Mater. 1995, 7, 551.
(5) Tang, C. W.; Van Slyke, S. A.; Chen, C. H. J. Appl. Phys. 1989, 65,
3610.
(6) (a) Bulovic, V.; Shoustikov, A.; Baldo, M. A.; Bose, E.; Kozlov,
V. G.; Thompson, M. E.; Forrest, S. R. Chem. Phys. Lett. 1998,
287, 455. (b) Hamada, Y.; Kanno, H.; Tsujioka, T.; Takahashi, H.;
Usuki, T. Appl. Phys. Lett. 1999, 75, 1682. (c) Tao, X. T.; Miyata, S.;
Sasabe, H.; Zhang, G. J.; Wada, T.; Jiang, M. H. Appl. Phys. Lett. 2001,
78, 279. (d) Picciolo, L. C.; Murata, H.; Kafafi, Z. H. Appl. Phys. Lett.
2001, 78, 2378.
(19) (a) Yang, J.; Jiang, C. Y.; Zhang, Y.; Yang, R.; Yang, W.; Hou, Q.;
Cao, Y. Macromolecules 2004, 37, 1211. (b) Xia, C. J.; Advincula,
R. C. Macromolecules 2001, 34, 5854.
(20) Janietz, S.; Bradley, D. D. C.; Grell, M.; Giebeler, C.; Inbasekaran,
M.; Woo, E. P. Appl. Phys. Lett. 1998, 73, 2453.
(21) Redecker, M.; Bradley, D. D. C.; Inbasekaran, M. E.; Woo, P.
Appl. Phys. Lett. 1998, 73, 1565.
(7) Virgili, T.; Lidzey, D. G.; Bradley, D. D. C. Adv. Mater. 2000,
12, 58.
(22) (a) Sun, Q. J.; Fan, B. H.; Tan, Z. A.; Yang, C. H.; Li, Y. F.; Yang,
Y. Appl. Phys. Lett. 2006, 88, No. 163510. (b) Sun, Q. J.; Hou, J. H.;
Yang, C. H.; Li, Y. F.; Yang, Y. Appl. Phys. Lett. 2006, 89, No. 153510.
(c) Zhou, Y.; Sun, Q. J.; Tan, Z. A.; Zhong, H. Z.; Yang, C. H.; Li, Y. F.
J. Phys. Chem. C 2007, 111, 6862. (d) Zhou, Y.; He, Q. G.; Yang, Y.;
Zhong, H. Z.; He, C.; Yang, C. H.; Liu, W.; Bai, F. L.; Li, Y. F. Adv.
Funct. Mater. 2008, 18, 3299.
(23) (a) Montes, V. A.; Perez-Bolivar, C.; Agarwal, N.; Shinar, J.;
Anzenbacher, P., Jr. J. Am. Chem. Soc. 2006, 128, 12436. (b) Zhang,
X. H.; Xie, Z. Y.; Wu, F. P.; Zhou, L. L.; Wong, O. Y.; Lee, C. S.;
Kwong, H. L.; Lee, S. T.; Wu, S. K. Chem. Phys. Lett. 2003, 382,
561.
(8) (a) Iabal, R.; Yahioglu, G.; Milgrom, L.; Moratti, S. C.; Holmes,
A. B.; Cacialli, F.; Morgado, J.; Friend, R. H. Synth. Met. 1999,
102, 1024. (b) Iqbal, R.; Moratti, S. C.; Holmes, A. B.; Yahioglu, G.;
Milgrom, L. R.; Cacialli, F.; Morgado, J.; Friend, R. H. J. Mater. Sci.:
Mater. Electron. 2000, 11, 97. (c) Morgado, J.; Cacialli, F.; Friend,
R. H.; Iqbal, R.; Yahioglu, G.; Milgrom, L. R.; Moratti, S. C.; Holmes,
A. B. Chem. Phys. Lett. 2000, 325, 552. (d) Morgado, J.; Cacialli, F.;
Iqbal, R.; Moratti, S. C.; Holmes, A. B.; Yahioglu, G.; Milgromd, L. R.;
Friend, R. H. J. Mater. Chem. 2001, 11, 278. (e) Lo, S. C.; Burn, P. L.
Synth. Met. 1999, 102, 1089. (f) Fei, Z. P.; Li, B. S.; Bo, Z. S.; Lu, R.
Org. Lett. 2004, 6, 4703.
(24) Yang, Y.; Zhou, Y.; He, Q. G.; He, C.; Yang, C. H.; Bai, F. L.; Li,
Y. F. J. Phys. Chem. B 2009, 113, 7745.
(9) Li, B. S.; Xu, X. J.; Sun, M. H.; Fu, Y. Q.; Yu, G.; Liu, Y. Q.; Bo,
Z. S. Macromolecules 2006, 39, 456.