Charge-transporting polymers based on phenylbenzoimidazole moieties

Article abstract of DOI:10.1002/adfm.200901590

A series of novel styrene functionalized monomers with phenylbenzo[d] imidazole units and the corresponding homopolymers are prepared. These side-chain polymers show high glass-transition temperatures that even exceed the corresponding value for the commo

Full text of DOI:10.1002/adfm.200901590

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Charge-Transporting Polymers based on
Phenylbenzoimidazole Moieties
By Marc Debeaux, Manuel W. Thesen, Daniel Schneidenbach, Henning Hopf,
¨
Silvia Janietz, Hartmut Kruger, Armin Wedel, Wolfgang Kowalsky, and
Hans-Hermann Johannes*
are mounting when multistacked devices
are aspired by wet-chemical protocols.
However, solution-based processes are still
favourable compared to OLEDs fabricated
by vacuum techniques in terms of produc-
tion costs and for special applications (e.g.,
large-area flat-panel displays).[3]
OLED materials must fullfil a large
variety of demands. These demands con-
cern the electronic behavior, the availability,
the process and long-term stabilities, and
foremost the efficiency. The stability of the
amorphous state of these materials is also
essentialforthelifetimeofadevice, because
crystallization processes can damage an
OLED irreparably.[4] Therefore, in small-
molecule-based OLEDs molecular glasses
are often applied.[5] They show low affinity
A series of novel styrene functionalized monomers with
phenylbenzo[d]imidazole units and the corresponding homopolymers are
prepared. These side-chain polymers show high glass-transition
temperatures that even exceed the corresponding value for the common
electron-transporting material 1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-
yl)benzene (TPBI). Similar electronic behavior between the polymers and TPBI
is shown. The polymers are used as matrices for phosphorescent dopants.
The fabricated devices exhibit current efficiencies up to 38.5 cd Aꢀ1 at
100 cd mꢀ2 and maximum luminances of 7400 cd mꢀ2 at 10 V with a
minimum turn-on voltage as low as 2.70 V in single-layer devices with an ITO/
PEDOT:PSS anode (ITO ¼ indium tin oxide, PEDOT:PSS ¼ poly(3,4-
ethylenedioxythiophene) doped with poly(styrenesulfonate)) and a CsF/Ca/
Ag cathode.
to crystallization, which is indicated by their high glass-transition
temperatures (Tg). On the other hand, polymers have advantages
because high glass-transition temperatures can be achieved
relatively easily and degradation procecces caused by phase
separation are negligible.[6]
1,3,5-Tris(1-phenylbenzo[d]imidazol-2-yl)benzene (TPBI; Fig. 1)
is a widely used electron-transporting and hole-blocking material
in small-molecule-based OLEDs.[7,8] Whereas the electrochemical
behavior of this material with its HOMO energy level between
ꢀ6.2 eV and ꢀ6.7 eV and a LUMO energy level of ꢀ2.7 eV
to ꢀ2.9 eV is due to the phenylbenzo[d]imidazole units, the
1. Introduction
Since the pioneering contributions by Tang et al. and Burroughes
et al. organic light-emitting diodes (OLEDs) have attracted
considerable interests in a broad range of different sciences, such
as physics, electrical engineering, and chemistry.[1,2] In general,
two different manufacturing processes for OLEDs compete with
each other. The most common used vacuum techniques can
process ‘‘small molecules’’ to form multiple-stacked devices. The
disadvantages of these polymeric light-emitting diodes (PLEDs)
[*] Dr. H.-H. Johannes, M. Debeaux, D. Schneidenbach,
Prof. W. Kowalsky
¨
Labor fur Elektrooptik am Institut fur Hochfrequenztechnik
Technische Universitat Braunschweig
¨
N
N
¨
Bienroder Weg 94, 38106 Braunschweig (Germany)
E-mail: h2.johannes@ihf.tu-bs.de
N
N
¨
M. W. Thesen, Dr. S. Janietz, Dr. H. Kruger, Dr. A. Wedel
Fraunhofer-Institut f¨ur Angewandte Polymerforschung
Wissenschaftspark Golm
Geiselbergstr. 69, 14476 Potsdam (Germany)
E-mail: hartmut.krueger@iap.fraunhofer.de
N
N
Prof. H. Hopf
¨
Institut fur Organische Chemie
Technische Universitat Brauschweig
¨
Hagenring 30, 38106 Braunschweig (Germany)
E-mail: h.hopf@tu-bs.de
Figure 1. Star-shaped electron transporting material 1,3,5-tris(1-phenyl-
1H-benzo[d]imidazol-2-yl)benzene (TPBI).
DOI: 10.1002/adfm.200901590
Adv. Funct. Mater. 2010, 20, 399–408
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‘‘star-shaped’’ geometry causes the high glass-transition tempera-
ture (Tg ¼ 120 8C) of this molecular glass and its practicability in
OLEDs.[9,10] As only a few side-chain polymers with electron-
transporting groups have been described so far we attempt to
generate polymeric analogues to TPBI with even higher glass-
transition temperatures than the parent compound.[11]
Furthermore, styrene-substituted functional materials can be
incorporated in the ambipolar polymer approach developed by
Suzuki et al., resulting in highly efficient devices.[6]
Cl
O
i)
NH
O
+
NH
N
H
Br
NH2
Br
2
3
4
Dendritic ambipolar materials based on a combination of
phenylbenzo[d]imidazole and triarylamine units have reported to
ii)
be proper matrices for efficient phosphorescent devices.[12]
A
corresponding polymeric material could also be attractive for
optoelectronic purposes.
In this paper, we describe the syntheses of novel styrene-
functionalized transporting materials with phenylbenzo[d]imid-
azole moieties and their polymerization into homopolymers.
These polymers are characterized and discussed in terms of
temperature stability, electronic behavior, and their application as
transporting and matrix materials in PLED devices.
iii)
N
N
N
Br
Ph
N
9
1
2. Results and Discussion
vi)
v)
iv)
2.1. Syntheses and Characterization
All polymerizable phenylbenzo[d]imidazole derivatives were
synthesized starting with the bromide 1 as a cyclization product
of the amide 2 which is itself a condensation product of diamine 3
and acid chloride 4 (Scheme 1).[12a] For the synthesis of the small
phenylbenzo[d]imidazole derivative 5 the bromide 1 was lithiated
with n-butyllithium and the resulting intermediate quenched with
dimethyl formamide to obtain the formylated compound 6. In the
next step the aldehyde was converted by Wittig reaction to yield the
monomer 5 with an overall yield of 55% (Scheme 1). 5 was also
obtained through Stille coupling using 1 as the starting material
and vinyltributyltin as the coupling partner (Scheme 1). It was
found that the product can be isolated in good yields (73%) but
impurities from alkyltin compounds can be avoided by the first
mentioned protocol.
N
N
N
CHO
N
5
6
Scheme 1. Syntheses of the monomer 5 and the biphenyl derivative 9.
Reagents and conditions: i) DMA, 1 h, r.t., 95% 2. ii) AcOH, 16 h, reflux, 98%
1. iii) PhB(OH)2, Pd(PPh3)4, Na2CO3, DME/H2O 4:1, 3 h, reflux, 74% 9.
iv) 1. n-BuLi, THF, 2 h, ꢀ80 8C; 2. DMF, 2 h, r.t. ! reflux, 75% 6. v)
MePPh3Br, KOtBu, THF, 18 h, 0 8C !r.t., 79% 5. vi) vinyltributyltin,
PdCl2(PPh3)2, DMF, 1 d, 60 8C, 73% 5.
For the synthesis of the monomer 7 it was found that the direct
Suzuki coupling of 1 and 7 resulted in mixtures of product,
de-halogenated starting material and starting material that were
hardly separable by normal phase column chromatography.
Therefore, the bromide was converted into the aldehyde 8 under
Suzuki conditions in 95% yield and following the subsequent
Wittig reaction took place in 72% yield (Scheme 2). As a
consequence of this route, the side products were better separable
due to quite different polarities of product and starting materials
after coupling. The biphenyl-derivative 9, which was synthesized
for comparison reasons, was obtained from the Suzuki reaction of
1 and phenylboronic acid (74% yield; Scheme 1).
To synthesizethetwo branchedstructures 10 and 11 theboronic
acid 12 was used. The discovery of this acid was published recently
during the progress of this work.[12a] In comparsion to reactions
carried out with the corresponding trimethyltin compound, the
Suzuki reaction conditions gave better yields. As starting materials
dibromobenzaldehyde 13 and the diiodo compound 14 were
used.[13] Suzuki coupling and further Wittig reaction of 15 and 16
yielded the dendritically structured monomers 10 and 11 in
moderate yields (Scheme 2).
The structure assignments of all synthesized compounds rest
on 1H and 13C NMR spectroscopy, IR spectroscopy, UV–vis
spectroscopy, mass spectrometry, and elemental analysis, and are
described in the Experimental Section.
2.2. Polymers
The monomers were polymerized in a free-radical polymerization
process to yield the polymers P1–P4 (Fig. 2). The results of GPC
and DSC measurements on these materials are given in Table 1.
The glass-transition temperature of P1 is 183 8C, and the polymers
prepared from the larger monomeric structures exhibit even
higher values. P2 has a glass-transition temperature of 209 8C, P3
shows a value of 226 8C, and P4 223 8C. The increase in the
glass-transition temperatures in the direction P1! P3/P4 is most
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CHO
Br
ii)
i)
N
N
=
1
7
8
CHO
B(OH)2
CHO
iii)
iv)
+
Br
Br
13
12
15
10
CHO
CHO
v)
vi)
N
N
N
I
I
14
16
11
Scheme 2. Syntheses of the monomers 7, 10 and 11. Reagents and conditions: i) 4-Formylphenylboronic acid, Pd(PPh3)4, Na2CO3, DME/H2O 4:1, 18 h,
reflux, 95% 8. ii) MePPh3Br, KOtBu, THF, 17 h, 0 8C !r.t., 72% 7. iii) Pd(PPh3)4, Na2CO3, DME/H2O 6:1, 16 h, reflux, 51% 15. iv) MePPh3Br, KOtBu, THF, 2
d, 0 8C !r.t., 69% 10. v) 12, Pd(PPh3)4, Na2CO3, DME/H2O 3:1, 16 h, reflux, 57% 16. vi) MePPh3Br, KOtBu, THF, 16 h, reflux, 77% 11.
likely due to higher required spaces of the substituents, which leads
to a higher rigidity of the polymer backbone.[14] The molecular
weights Mn are in the range of 15 700 g molꢀ1 for P4 to
51 100 g molꢀ1 for P3. The polydispersities, 1.83 for P1 and 2.24
for P4, areintherangeexpectedfora free-radicalpolymerization.[15]
P2 (2.70) and P3 (3.19) show higher polydispersities. Combined
with the higher molecular weight and the obtained yields the
high polydispersity of P3 is most likely due to the Trommsdorff
effect.[15] Furthermore, a bimodal distribution of P3 was observed.
The polymers exhibit good solubilities in tetrahydrofuran
and chlorinated solvents such as o-dichlorobenze, and form stable
films.
Figure 3 represents an atomic force microscopy(AFM) image of
thepolymerP1whichhadbeenspin-coatedontoalayerofpoly(3,4-
ethylenedioxythiophene) doped with poly(styrenesulfonate)
(PEDOT:PSS). After the same thermal treatment that was applied
for the device preparation, the surface is very homogeneous with a
surface-roughness root mean square (rms) of 0.67 nm. The
homogeneity of spin-coated films for the other polymers are of the
same quality.
2.3. Electrochemical and Photophysical Properties
In order to investigate the oxidation and reduction potentials, we
performed differential pulse voltammetry (DPV) on the mono-
mers 5, 7, 10, and 11, which was compared to TPBI, 9, and 1,2-
diphenyl-1H-benzo[d]imidazole (17).[16,17] It was found that the
reduction potentials are accessible in dimethyl formamide
solution whereas the oxidation potentials were measured in
dichloromethane. The results of these measurements are
summarized in Table 2, displayed in Figure 4, and are given
relative to the ferrocene/ferrocenium reference. Additionally,
Table 2 summarises the optical bandgaps, which were determined
as the onsets from absorption spectra.
The redox potential of TPBI was found to be ꢀ2.49 V. This value
is more comparable to the biphenyl derivative 9 (ꢀ2.52 V) than to
that of the phenyl derivative 17 (ꢀ2.75 V). Otherwise, the oxidation
potential of TPBI (1.17 V) correlates better with the potential of the
phenyl derivative 17 (1.13 V) than with that of the biphenyl
derivative 9 (1.03 V). In comparison, the reported monomers 5, 7,
and 10 exhibit very similar reduction potentials in the range of
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n
n
N
N
N
N
P1
P2
n
Figure 3. AFM image (1 mm ꢁ 1 mm) of the spin-coated polymer P1
(100 nm) atop a PEDOT:PSS layer (80 nm).
N
N
N
N
ꢀ2.52 V for 11 to ꢀ2.44 V for 7. Thus, we assume good electron-
transporting properties for the corresponding polymers, compar-
able to TPBI. The oxidation potentials for 5, 7, and 10 range from
0.93 V (7) to 1.00 V (5). The ambipolar monomer 11 exhibits a low
oxidation potential of 0.38 V, which is apparently contributed to by
the oxidation of the triarylamine moiety, whereas the redution
potential remains notably unaffected (ꢀ2.52 V).
P3
n
Forallreportedcompoundstheopticalbandgapsareinexcellent
correlation with the electrochemical bandgaps, as determined by
DPV measurements. Additionally, the emission spectra were
recordedassummarizedinTable2. Theenergiesofthemaximum-
emission wavelengths at an excitation of 300 nm measured in
trichloromethane solutions exhibit the same trends as the
bandgaps determined from electrochemical and optical measure-
ments and corroborate these results.
N
N
N
N
N
P4
Figure 2. Polymers P1–P4.
Table 2. Electrochemical and optical properties of the monomers com-
pared to TPBI, 9, and 17.
Ered [V] [a]
Eox [V] [a]
DEel [V] [a]
DEopt [eV] [b]
Eem [eV] [c]
Table 1. Properties of the polymers P1–P4.
5
ꢀ2.50
ꢀ2.44
ꢀ2.47
ꢀ2.52
ꢀ2.49
ꢀ2.52
ꢀ2.75
1.00
0.93
0.99
0.38
1.17
1.03
1.13
3.50
3.37
3.46
2.90
3.66
3.55
3.88
3.52
3.37
3.48
2.97
3.66
3.54
3.77
3.37
3.23
3.32
2.78
3.42
3.35
3.50
7
Polymer
Mn
Mw
PDI
Tg
[ 8C] [b] [eV] [c]
DEopt
Eem
10
11
TPBI
9
[103 g molꢀ1] [a] [103 g molꢀ1] [a]
[eV] [d]
P1
P2
P3
P4
21.6
26.3
51.1
15.7
39.5
71.1
1.83
2.70
3.19
2.24
183
209
226
223
3.70/3.53 3.38/3.26
3.49/3.27 3.12/3.03
3.46/3.25 3.00/2.99
2.93/2.75 2.73/2.68
17
163.0
53.1
[a] Measured by DPV relative to the Fc/Fcþ couple (Fc is ferrocene).
Reduction potential Ered measured in DMF, oxidation potential Eox in
dichloromethane. DEel ¼ Eox ꢀ Ered. [b] Determined as the on-sets from
absorption spectra in 10ꢀ5 M trichloromethane solutions. [c] Energies of
maximum emission wavelength measured in trichloromethane solutions
with an excitation wavelength lex ¼ 300 nm.
[a] Determined from GPC. [b] Determined from DSC measurements.
[c] Determined as the on-sets from absorption spectra in 10ꢀ5 M (referred
to one monomer unit) trichloromethane solutions and from thin films.
[d] Energies of maximum emission wavelength measured in trichlorometh-
ane solutions and from thin films (excitation wavelength lex ¼ 300 nm).
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the long-wave absorption band of P4 peaking at 368 nm (see
Supporting Information) can be ascribed to a charge transfer p–pꢂ
transition.[12] The LUMO energy of P4 can be obtained when
the optical bandgap (2.75 eV, from film) is taken into account,
leading to values of ꢀ2.65 eV (calculated from photoemission
spectroscopy) and ꢀ2.52 eV (calculated from cyclic voltammetry
measurement).
Surprisingly, the oxidation potential of TPBI measured by DPV
resultsinaHOMO energyofaboutꢀ6.00 eVand—byconsidering
an optical band gap of 3.66 eV—in a LUMO energy level of
ꢀ2.31 eV, a value that was also determined by DPV. The energy
levels for the frontier orbitals of TPBI reported in literature could
not be reproduced, whereas other OLED materials measured
under similar conditions gave very good correlations to values
reported recently by Djurovich et al.[9,16]
Figure 4. Energy levels of the first reductions and oxidations measured by
differential pulse voltammetry.
2.4. Electrophosphorescent Polymer LEDs
The applicability of the polymers as matrices for phosphorescent
polymer LEDs was examined in single-layer devices with TEG as
the phosphorescent green-emitting dopant (8 wt% doping con-
centration) and N,N,N0,N0-tetrakis(4-methylphenyl)benzidine
(TTB) as a hole-transporting material. The concentration of TTB
for the devices with P1–P3 was set to 30 wt%. In the case of the
ambipolar polymer P4 no TTB was used, to demonstrate both the
electron- and hole-transporting properties of the polymer.
PLED devices (Fig. 5) were fabricated on glass substrates with a
pre-patterned indium tin oxide (ITO) electrode. First, a hole-
injection layer of PEDOT:PSS was spin-coated on these substrates.
Then the emissive layer was spin-coated from a solution of the
polymers, the emitter, and TTB (for P1–P3). The films were dried
The absorption and emission spectra of the polymers were
measured as chloroform solutions and in thin films (see
Supporting Information). In comparsion, the absorption spectra
in the solid state are redshifted to the solution spectra (Table 1),
which can be ascribed as an indicator for electronic interactions
between the benzo[d]imidazole moieties in the solid state. The
electrochemistry of the polymers was investigated by cyclic
voltammetry studies with thin films on a glassy-carbon working
electrode. The polymers P1–P3 exhibited irreversible reduction
and oxidation waves (see Supporting Information) that were
accompanied by decomposition of the electrolyte solution and
therefore could not be interpreted clearly. The optical bandgaps
from solution spectra (Table 1) of the polymers P1 (3.70 eV) and P2
(3.49 eV) exhibited larger values than from the according
monomers 5 (3.52 eV) and 7 (3.37 eV). This is obviously due to
an decrease in the conjugation length after the polymerization
process. The values of the reference compounds 17 (3.77 eV) and 9
(3.54 eV) are, however, close to the band gaps determined for P1
and P2, respectively. Therefore, we assume that the oxidation and
reduction potentials of P1 and P2 are in the range of these
reference compounds. When the branched monomer 10 (3.48 eV)
is polymerized yielding P3 (3.46 eV) the optical bandgap remains
almost constant. This fact is attributed to the meta connection of
the vinyl group with respect to the benzo[d]imidazole units. Thus,
it can be assumed that the electrochemical behavior of P3 is
comparabletothatof10. InthecaseofP4theoxidationdetermined
by cylic voltammetry is reversible with a half-wave potential
of 1.04 V against a Ag/AgCl reference, which corresponds to a
HOMO energy of ꢀ5.40 eV.[18] Additionally, the HOMO energies
of the polymers were investigated by photoemission spectroscopy.
Because HOMO values lower than ꢀ6.0 eV cannot be measured
with this equipment, a HOMO energy was only accessible in the
case of polymer P4, and was determined to be ꢀ5.27 eV. This value
is in good agreement with the oxidation potential measured by
cyclic voltammetry. The absorption spectrum of P4 is significantly
redshifted compared to P1–P3. In all, the electrochemical
and optical measurements on P4 indicate a strong involvement
of the triarylamine moiety on the HOMO energy. Therefore,
CsF/Ca
Polymer:(TTB):TEG
PEDOT:PSS
ITO
O
O
m
N
N
S
n
SO3
PEDOT:PSS
TTB
Figure 5. PLED stack with a single transporting and emitting layer and the
molecular structures of the compounds used.
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Table 3. Device performance and EL characteristics of the OLED devices.
Polymer
Thickness [nm]
Uturn-on [V] [a]
Current efficiency [cd Aꢀ1
]
Luminance [cd mꢀ2] @ 10 V
fwhm [nm] [b]
lmax [nm] [b]
CIEx,y [b]
@ 100 cd mꢀ2
@1000 cd mꢀ2
P1
P2
P3
P4
90
110
91
3.22
2.97
2.70
3.74
38.5
23.9
19.9
2.2
35.9
24.4
21.8
–
6740
6640
7440
530
75
81
81
96
520
524
522
553
0.31, 0.63
0.33, 0.62
0.33, 0.62
0.42, 0.55
124
[a] Voltage at a minimum luminance of 10 cd mꢀ2. [b] At a voltage of 10 V.
and a cathode bilayer of CsF and calcium was formed by vacuum
deposition and was covered with a silver protective layer. The
thickness of the active layer was optimized for best efficiencies
(Table 3). Only the most efficient devices for each polymer are
reported in this paper.
Figure 6 depicts the electroluminescence (EL) spectra of the
devices with polymer P1 and P4 and corresponding Commission
´
Internationale de l’Eclairage 1931 (CIE) coordinates of (0.31, 0.63)
and (0.42, 0.55), respectively. As no emission deriving from the
matrices is observed, an efficient energy transfer to the
phosphorescent dopant can be assumed. The EL spectra of
thedevicesP1–P3arealmostthesamewithsimilarnarrow-banded
green emissions with full width at half maxima (fwhm) of 75–
81 nm and emission maxima between 520 and 524 nm (Table 3).
For the device with P4 a broadened emission (fwhm ¼ 96 nm) is
observed. The shoulderintheemission spectrumofP1–P3located
at about 550 nm is exceptionally strong in the case of P4. This leads
to an emission maximum shift to 553 nm in this device and
elucidates the broadening of the emission spectrum. The proper
reason for this fact is unknown presently but we propose that it
originates from exciplex formation that is overlapping the
vibrational satellite. The devices exihibt relatively low turn-on
voltages (minimum luminance at 10 cd mꢀ2) ranging from 2.70 V
forP3to3.74 VforP4(Table3)whichindicatesgoodcharge-carrier
injection into the devices.
device, with current efficiencies up to 38.5 cd Aꢀ1 at 100 cd mꢀ2
,
andthedevicewithambipolarpolymerP4showsaverylowcurrent
efficiency (2.2 cd Aꢀ1 at 100 cd mꢀ2). Polymers P2 and P3 also
result in efficient devices with current efficiencies of 23.9 and
19.9 cd Aꢀ1 (bothat100 cd mꢀ2).Alldevicesexhibitalowefficiency
roll-off for higher luminances, indicating that the device is quite
independentoftheappliedbiasanddemonstratingastablecharge-
carrier balance with negligible triplet–triplet annihilation.
We assume that the low efficiencies for the devices with the
ambipolar polymer are due to a poorly balanced ratio of electron- to
hole-transporting moieties. As Ge et al. have reported a ratio of 3:1
for these units in dendritic structures, a ratio of 2:1 in P4 could be
toolow.[12a,12b] Additionally,itcanbeassumedthattheundisturbed
conjugation between the phenylbenzo[d]imidazole units and the
triarylamine moiety is the main reason for the low efficiencies.[12]
The syntheses of derivatives of P4 with electronically decoupled
charge carrier units are in progress.
3. Conclusions
The polymerizable monomers 5, 7, 10, and 11 were synthesized
using different protocols whereby the highest purities and best
yields were archieved by Wittig reaction of the corresponding
aldehydes with methyltriphenylphosphonium bromide. The
substances were fully characterized by NMR, mass spectrometry,
IR and UV–vis spectroscopy, and elemental analysis to investigate
In Figure 7 the current efficiency versus luminance character-
istics are displayed. The polymer P1 results in the most efficient
520
515
510
530
540
550
560
505
500
570
580
590
600
620
495
490
700
485
480
470
380
Figure 6. Electroluminescence spectrum of the device with polymers P1
and P4 and CIE color representation (inset).
Figure 7. Current efficiency as a function of luminance.
404
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128.9 (s), 128.8 (d), 127.4 (d), 124.0 (s), 123.6 (d), 123.2 (d), 119.9 (d),
110.5 ppm (d); IR (ATR): n ¼ 3050 (w), 1593 (m), 1498 (m), 1467 (m), 1447
(s), 1404 (s), 1375 (m), 1323 (m), 1264 (m), 1195 (w), 1180 (w), 1106 (m),
1068 (m), 1009 (m), 974 (m), 930 (w), 828 (s), 764 (m), 740 (vs), 721 (m),
698 (s), 637 (w), 613 (m), 574 cmꢀ1 (m); UV/Vis (CHCl3): lmax (e) ¼ 299
(21500), 242 (18600), 231 nm (16200); UV/Vis (CH3CN): lmax (e) ¼ 297
(21200), 234 (20000), 204 (59800), 193 nm (46700); EIMS (m/z (%)): 350/
348 (23/28) [Mþ], 349/347 (100/82) [Mþ ꢀ H], 268 (31) [Mþ ꢀ HBr], 267
(33). Anal. calcd for C19H13BrN2: C 65.35, H 3.75, N 8.02; found: C 65.40, H
3.65, N 7.79.
Synthesis of 2-(Biphenyl-4-yl)-1-phenyl-1H-benzo[d]imidazole (9): A mix-
ture of 1 (2.00 g, 5.73 mmol), phenylboronic acid (838 mg, 6.87 mmol),
Pd(PPh3)4 (199 mg, 172 mmol), 2 M aqueous sodium carbonate solution
(8 mL), and 1,2-dimethoxyethane (32 mL) was stirred under reflux for 3 h.
The mixture was allowed to cool to room temperature and saturated (sat.)
ammonium chloride solution (50 mL) was added. After 1 h a solid
precipitated, which was filtered off and washed with methanol to obtain 9
(1.46 g, 74%) as colorless flakes: m.p. 200–201 8C; 1H NMR (400 MHz,
CDCl3, d): 7.90 (ddd, J ¼ 8.1, 0.9, 0.9 Hz, 1 H; ArH), 7.65 (AA0BB0,
N ¼ 8.6 Hz, 2 H; ArH), 7.59–7.56 (m, 2 H; ArH), 7.55ꢀ7.45 (m, 5 H; ArH),
7.44–7.38 (m, 2 H; ArH), 7.37–7.30 (m, 4 H; ArH), 7.29–7.22 ppm (m, 2 H;
ArH); 13C NMR (101 MHz, CDCl3, d): 152.1 (s), 143.1 (s), 142.0 (s), 140.1
(s), 137.3 (s), 137.1 (s), 129.9 (d), 129.8 (d), 128.8 (d), 128.8 (s), 128.6 (d),
127.7 (d), 127.5 (d), 127.0 (d), 126.9 (d), 123.3 (d), 123.0 (d), 119.8 (d),
110.4 ppm (d); IR (ATR): n ¼ 3054 (w), 3013 (w), 1594 (m), 1494 (m), 1474
(m), 1444 (m), 1409 (m), 1376 (m), 1323 (m), 1310 (m), 1262 (m), 1202
(w), 1162 (w), 1108 (w), 1073 (w), 1002 (m), 841 (m), 765 (s), 744 (vs), 729
(s), 700 (s), 685 (s), 654 (m), 611 (m), 549 cmꢀ1 (m); UV/Vis (CHCl3): lmax
(e) ¼ 309 (31700), 263 nm (16600); UV/Vis (CH3CN): lmax (e) ¼ 306
(28500), 262 (15800), 204 (58700), 193 nm (53000); EIMS (m/z (%)): 346
(73) [Mþ], 345 (100) [Mþ ꢀ H]. Anal. calcd for C25H18N2: C 86.68, H 5.24, N
8.09; found: C 86.27, H 5.23, N 8.06.
Synthesis of 4-(1-Phenyl-1H-benzo[d]imidazol-2-yl)benzaldehyde (6): To a
mixture of 1 (7.00 g, 20.0 mmol) in dry THF (80 mL) a 1.6 M n-butyllithium
solution in n-hexane (15 mL, 24.1 mmol) was added dropwise while
keeping the reaction temperature at ꢀ80 8C. After the addition the solution
was stirred for 2 h at this temperature and then quenched with dry N,N-
dimethylformamide (10 mL). The reaction mixture was allowed to warm to
room temperature for 1 h before stirring under reflux for another 1 h. After
cooling to room temperature an aqueous solution of sat. ammonium
chloride (100 mL) was added and the mixture was extracted with
trichloromethane (3 ꢁ 100 mL). The combined organic phases were
washed with water (3 ꢁ 100 mL), dried over magnesium sulfate and
concentrated. The residual oil was purified by silica gel column
chromathography (diethyl ether) to obtain 6 as a colorless solid (4.50 g,
75%): m.p. 154–156 8C; 1H NMR (400 MHz, CDCl3, d): 10.00 (s, 1 H;
CHO), 7.93–7.90 (m, 1 H; ArH), 7.81 (AA0BB0, N ¼ 8.5 Hz, 2 H; ArH), 7.75
(AA’BB’, N ¼ 8.5 Hz, 2 H; ArH), 7.56–7.50 (m, 3 H; ArH), 7.39–7.25 ppm
(m, 5 H; ArH); 13C NMR (101 MHz, CDCl3, d): 191.6 (d; CHO), 150.7 (s),
143.0 (s), 137.4 (s), 136.6 (s), 136.4 (s), 135.6 (s), 130.1 (d), 129.9 (d),
129.5 (d), 129.0 (d), 127.3 (d), 124.1 (d), 123.4 (d), 120.2 (d), 110.6 ppm
(d); IR (ATR): n ¼ 3068 (w), 3026 (w), 2835 (w), 2740 (w), 1694 (s), 1609
(m), 1596 (m), 1572 (w), 1499 (m), 1480 (m), 1448 (m), 1419 (w), 1379
(m), 1325 (w), 1300 (m), 1280 (w), 1259 (w), 1208 (m), 1167 (m), 1108 (w),
1003 (w), 975 (w), 835 (s), 761 (s), 747 (vs), 697 (s), 682 (m), 614 (m),
578 cmꢀ1 (w); UV/Vis (CHCl3): lmax (e) ¼ 323 (4230), 280 (14800, sh),
237 nm (9100); UV/Vis (CH3CN): lmax (e) ¼ 319 (37800), 205 (68000),
193 nm (57300); EIMS (m/z (%)): 298 (81) [Mþ], 297 (100) [Mþ ꢀ H], 269
(20) [Mþ ꢀ CHO]. Anal. calcd for C20H14N2O: C 80.52, H 4.73, N 9.39;
found: C 80.51, H 4.67, N 9.39.
their structure and purity. The polymers P1–P4 were prepared
using a free-radical polymerization process resulting in high-
molecular-weight polymers with high glass-transition tempera-
tures that form homogeneous films. Devices with a single active
layer and a green-phosphorescent dopant exhibit high current
efficiencies up to 38.5 cd Aꢀ1 at 100 cd mꢀ2 with a low efficiency
roll-off for higher luminances. These results promise a good
applicability of phenylbenzo[d]imidazole-based polymers in
PLEDs to achieve highly efficient devices. This comprises not
only single-layer devices but also multi-stacked PLEDs, which are
accessible by use of crosslinkable polymer films or the incorpora-
tion of orthogonal solvents for spin-casting.[19]
4. Experimental
General Methods: All reagents, unless otherwise specified, were
obtained from Aldrich, Acros, and Fluka and used as received.
Pd(PPh3)4 was puchased from ABCR. All solvents were purified before
use. All reactions were performed under nitrogen atmosphere. Dry solvents
stored over molecular sieve were purchased from Fluka.
NMR experiments were collected on a Bruker DPX-400 spectrometer
and reported in parts per million (ppm). 1H chemical shifts were recorded
relative to tetramethylsilane (TMS) as an internal standard and 13C
measurements were referred to the corresponding NMR solvent signal. All
J and N values are rounded to the nearest 0.1 Hz. UV–Vis spectra were
recorded on a Varian Cary 100 Bio instrument as solutions in spectro-
scopic-grade solvents. PL spectra were measured using a Kontron SF-25
spectrometer in degassed solvents. Infrared spectra were recorded on a
Bruker Tensor 27 spectrometer with a Diamond ATR sampling element.
Mass spectra were recorded on a Thermofinnigan MAT95. Melting points
were measured on a Stuart Melting Point SMP3 apparatus and are
uncorrected. Elemental analyses were performed on a Vario EL Elemental
Analysis Instrument (Elementar Co.).
Synthesis of 4-Bromo-N-(2-(phenylamino)phenyl)benzamide (2): To a
solution of 4-bromobenzoyl chloride (4) (23.8 g, 109 mmol) in N,N-
dimethylacetamide (150 mL) N-phenyl-o-phenylenediamine (3) (20.0 g,
109 mmol) was added slowly and the mixture stirred for 1 h at room
temperature. After addition of water (1.1 L) the precipitated solid was
filtered off and washed with water and methanol. The solid was dried under
reduced pressure and recrystallized from a N,N-dimethylformamide/water
7:1 mixture and washed with water to obtain light brownish crystals (37.8 g,
95%): m.p. 179 ꢀ 180 8C; 1H NMR (400 MHz, DMSO-d6, d): 9.77 (s, 1 H;
NHCO), 7.85 (AA0BB0, N ¼ 8.6 Hz, 2 H; ArH), 7.70 (AA0BB0, N ¼ 8.6 Hz, 2
H; ArH), 7.56 (dd, J ¼ 7.8, 1.4 Hz, 1 H; ArH), 7.47 (s, 1 H; NH), 7.30 (dd,
J ¼ 8.1, 1.3 Hz, 1 H; ArH), 7.22ꢀ7.13 (m, 3 H; ArH), 7.00 (ddd, J ¼ 7.8, 7.6,
1.4 Hz, 1 H; ArH), 6.93 (dd, J ¼ 8.6, 1.1 Hz, 2 H; ArH), 6.79 ppm (dd,
J ¼ 7.5, 1.1 Hz, 1 H; ArH); 13C NMR (101 MHz, DMSO–d6, d): 164.6 (s, C-
2), 143.9 (s), 137.0 (s), 133.6 (s), 131.2 (d), 129.7 (d), 128.9 (d), 128.8 (s),
126.3 (d), 126.0 (d), 125.1 (s), 121.4 (d), 119.8 (d), 119.5 (d), 116.6 ppm
(d); IR (ATR): n ¼ 3378 (w), 3269 (w), 3058 (w), 1641 (m), 1588 (m), 1525
(m), 1509 (m), 1479 (m), 1450 (m), 1423 (m), 1308 (s), 1260 (w), 1177 (w),
1108 (w), 1069 (w), 1009 (m), 914 (w), 883 (w), 837 (m), 744 (vs), 711 (m),
696 (s), 680 (m), 594 (w), 573 cmꢀ1 (w); UV/Vis (CHCl3): lmax (e) ¼ 285
(14800, sh), 243 (21200), 230 nm (26900); UV/Vis (CH3CN): lmax (e) ¼ 263
(17400, sh), 239 (23300), 199 (57500), 193 nm (51400); EIMS (m/z (%)):
368/366 (23/28) [Mþ], 350/348 (52/68) [Mþ ꢀ H2O], 349/347 (100/61),
268 (43), 267 (29), 185 (23), 183 (33), 182 (36). Anal. calcd for
C19H15BrN2O: C 62.14, H 4.12, N 7.63; found: C 62.18, H 4.12, N 7.63.
Synthesis of 2-(4-Bromophenyl)-1-phenyl-1H-benzo[d]imidazole (1): 2
(10.1 g, 27.5 mmol) was stirred for 16 h in acetic acid (30 mL) under
reflux. The solvent was evaporated to obtain a colorless solid (9.36 g,
98%): m.p. 165–166 8C; 1H NMR (400 MHz, CDCl3, d): 7.90–7.86 (m, 1 H;
ArH); 7.55–7.46 (m, 3 H; ArH), 7.46–7.41 (m, 4 H; ArH), 7.36–7.32 (m, 1
H; ArH), 7.32–7.21 ppm (m, 4 H; ArH); 13C NMR (101 MHz, CDCl3, d):
151.2 (s), 142.9 (s), 137.2 (s), 136.7 (s), 131.5 (d), 130.8 (d), 130.0 (d),
Synthesis of 1-Phenyl-2-(4-vinylphenyl)-1H-benzo[d]imidazole (5): To a
suspension of methyltriphenylphosphonium bromide (7.04 g, 19.7 mmol)
and potassium tert-butylate (2.32 g, 20.7 mmol) in dry THF (50 mL) a
solution of 6 (2.94 g, 9.86 mmol) in anhydrous THF (50 mL) was added at
0 8C over 30 min, and the mixture was allowed to warm to room
temperature. After 18 h an aqueous solution of sat. ammonium chloride
(100 mL) and trichloromethane (100 mL) were added and the layers were
separated. The aqueous layer was extracted with trichloromethane
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(2 ꢁ 100 mL). The combined organic layers were dried over magnesium
sulfate and filtered before the solvent was removed. The residue was
purified by silica gel column chromatography (dichloromethane/ethyl
acetate 20:1) yielding 5 as a colorless powder (2.30 g, 79%): m.p. 170–
171 8C; 1H NMR (400 MHz, CDCl3, d): 7.89 (d, J ¼ 8.1 Hz, 1 H; ArH), 7.56–
7.45 (m, 5 H; ArH), 7.36–7.31 (m, 5 H; ArH), 7.29–7.22 (m, 2 H; ArH), 6.68
(dd, J ¼ 17.5, 10.9 Hz, 1 H; CHCH2), 5.77 (d, J ¼ 17.5 Hz, 1 H; CHCH2),
5.29 ppm (d, J ¼ 10.9 Hz, 1 H; CHCH2); 13C NMR (101 MHz, CDCl3, d):
152.0 (s), 138.5 (s), 142.9 (s), 137.2 (s), 137.0 (s), 136.1 (d; CHCH2), 129.9
(d), 129.6 (d), 129.1 (s), 128.6 (d), 127.4 (d), 126.1 (d), 123.4 (d), 123.1 (d),
119.8 (d), 115.2 (t; CHCH2), 110.4 ppm (d); IR (ATR): n ¼ 3049 (w), 3004
(w), 1594 (m), 1561 (w), 1497 (m), 1475 (m), 1448 (s), 1408 (m), 1379 (s),
1323 (m), 1262 (m), 1188 (w), 1149 (w), 1107 (w), 1012 (w), 988 (m), 930
(w), 905 (s), 841 (vs), 761 (s), 740 (s), 699 (s), 647 (m), 601 cmꢀ1 (m); UV/
Vis (CHCl3): lmax (e) ¼ 314 (28300), 263 (11400), 239 nm (11300); UV/Vis
(CH3CN): lmax (e) ¼ 306 (27300), 260 (15900), 203 (52000), 192 nm
(49600); EIMS (m/z (%)): 371 (100) [Mþ], 370 (100) [Mþ ꢀ H]. Anal. calcd
for C21H16N2: C 85.11, H 5.44, N 9.45; found: C 85.28, H 5.55, N 9.31.
Synthesis of 4(-(1-Phenyl-1H-benzo[d]imidazol-2-yl)biphenyl-4-
carbaldehyde (8): A mixture of bromide 1 (10.00 g, 28.6 mmol), 4-
formylphenylboronic acid (Apollo Scientific) (5.16 g, 34.4 mmol),
Pd(PPh3)4 (900 mg, 858 mmol), 2 M aqueous sodium carbonate solution
(40 mL), and 1,2-dimethoxyethane (160 mL) was stirred under reflux for
18 h. The mixture was allowed to cool to room temperature and sat.
ammonium chloride solution (100 mL) and trichloromethane (100 mL)
were added. The organic layer was separated and the aqueous layer was
extracted with trichloromethane (2 ꢁ 100 mL). The combined organic
layers were dried over magnesium sulfate, filtered and the solvent was
removed. The residue was purified by silica gel column chromatography
(dichloromethane/diethyl ether 1:1 as eluent) to yield a slightly yellow solid
(10.16 g, 95%): m.p. 154–157 8C; 1H NMR (400 MHz, CDCl3, d): 10.04 (s, 1
H; CHO), 7.95–7.89 (m, 3 H; ArH), 7.73 (AA0BB0, N ¼ 8.3 Hz, 2 H; ArH),
7.69 (AA0BB0, N ¼ 8.7 Hz, 2 H; ArH), 7.58 (AA0BB0, N ¼ 8.7 Hz, 2 H, ArH),
7.55–7.49 (m, 3 H; ArH), 7.38–7.33 (m, 3 H; ArH), 7.31–7.23 ppm (m, 2 H;
ArH); 13C NMR (101 MHz, CDCl3, d):191.7 (d; CHO), 151.6 (s), 146.0 (s),
143.1 (s), 140.4 (s), 137.4 (s), 137.0 (s), 135.5 (s), 130.2 (d), 130.1 (s),
130.0 (d), 130.0 (d), 128.7 (d), 127.6 (d), 127.5 (d), 127.2 (d), 123.6 (d),
123.1 (d), 119.9 (d), 110.5 ppm (d); IR (ATR): n ¼ 3054 (w), 3036 (w), 2821
(w), 2728 (w), 1695 (s), 1603 (m), 1494 (m), 1477 (m), 1451 (m), 1426 (w),
1403 (w), 1380 (m), 1326 (w), 1309 (m), 1262 (m), 1218 (m), 1191 (m),
1172 (m), 1116 (w), 1002 (w), 974 (w), 844 (m), 819 (vs), 767 (s), 745 (s),
717 (m), 698 (s), 666 (w), 632 (w), 613 (m), 581 (w), 548 cmꢀ1 (w); UV/Vis
(CHCl3): lmax (e) ¼ 323 (42300), 280 (14800, sh), 237 nm (9100); UV/Vis
(CH3CN): lmax (e) ¼ 319 (37800), 205 (68000), 193 nm (57300); EIMS (m/
z (%)): 374 (57) [Mþ], 373 (67) [Mþ ꢀ H], 346 (98) [Mþ ꢀ CO], 345 (100)
[Mþ ꢀ CHO], 343 (26). Anal. calcd for C26H18N2O: C 83.40, H 4.85, N 7.48;
found: C 83.85, H 4.89, N 7.20.
(m), 1494 (m), 1474 (m), 1448 (w), 1400 (m), 1375 (m), 1320 (m), 1261
(w), 1196 (w), 1145 (w), 1110 (w), 1073 (w), 991 (m), 913 (m), 825 (vs),
763 (m), 744 (s), 701 (s), 638 (m), 619 (m), 602 (m), 543 cm–1 (w); UV/Vis
(CHCl3): lmax (e) ¼ 321 (47000), 240 nm (13100); UV/Vis (CH3CN): lmax
(e) ¼ 315 (44100), 207 (67500), 193 nm (55000); EIMS (m/z (%)): 371
(100) [Mþ], 370 (100) [Mþ ꢀ H]. Anal. calcd for C27H20N2: C 87.07, H 5.41,
N 7.52; found: C 86.95, H 5.48, N 7.33.
Synthesis of 3,5-Bis(4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)-
benzaldehyde(15): 3,5-Dibromobenzaldehyde (842 mg, 3.19 mmol), boron-
ic acid 12 (2.20 g, 7.02 mmol), Pd(PPh3)4 (74 mg, 64 mmol), 2 M aqueous
sodium carbonate solution (16 mL) and 1,2-dimethoxyethane (100 mL)
were stirred under reflux for 16 h. An aqueous solution of sat. ammonium
chloride (150 mL) was added and the mixture was extracted with
trichloromethane (3 ꢁ 100 mL). The combined organic layers were dried
over magnesium sulfate and concentrated by rotary evaporation. The
residue was purified by silica gel column chromatography (dichloro-
methane/ethyl acetate 10:1 ! 3:1) and hot extraction (EtOH) yielding 15 as
a colorless powder (1.04 g, 51%): m.p. 257–260 8C; 1H NMR (400 MHz,
CDCl3, d): 10.11 (s, 1 H; CHO), 8.05–8.01 (m, 3 H; ArH), 7.91 (d,
J ¼ 8.0 Hz, 2 H; ArH), 7.70 (d, J ¼ 8.5 Hz, 4 H; ArH), 7.60 (d, J ¼ 8.5 Hz, 4
H; ArH), 7.57–7.47 (m, 6 H; ArH), 7.38–7.33 (m, 6 H; ArH), 7.30–7.23 ppm
(m, 4 H; ArH); 13C NMR (101 MHz, CDCl3, d): 191.8 (d; CHO), 151.7 (s),
143.1 (s), 141.8 (s), 140.3 (s), 137.6 (s), 137.4 (s), 137.1 (s), 131.3 (d),
130.04 (d), 129.99 (d), 129.9 (s), 128.7 (d), 127.5 (d), 127.3 (d), 127.0 (d),
123.5 (d), 123.1 (d), 119.9 (d), 110.5 ppm (d); IR (ATR): n ¼ 3051 (w), 2812
(w), 2734 (w), 1705 (m), 1596 (m), 1501 (m), 1486 (m), 1446 (m), 1383
(m), 1326 (w), 1306 (w), 1260 (w), 1172 (m), 1015 (w), 796 (w), 907 (w),
840 (s), 761 (s), 741 (s), 697 (vs), 669 (m), 641 (m), 615 (m), 571 (m),
548 cmꢀ1 (m); UV/Vis (CHCl3): lmax (e) ¼ 313 (59000), 250 nm (39700);
UV/Vis (CH3CN): lmax (e) ¼ 311 (59800), 238 (42600), 203 (111500),
193 nm (97900); EIMS (m/z (%)): 642 (100) [Mþ], 641 (57), 320 (44). Anal.
calcd for C45H30N4O: C 84.09, H 4.70, N 8.72; found: C 83.86, H 4.63, N
8.34.
Synthesis of 3,5-Bis(4-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)-
vinylbenzene (10): To
a suspension of methyltriphenylphosphonium
bromide (558 mg, 1.56 mmol) and potassium tert-butylate (184 mg,
1.64 mmol) in dry THF (10 mL) a solution of 15 (250 mg, 389 mmol) in
dry THF (5 mL) was added at 0 8C and the mixture was allowed to warm to
room temperature. After 2 d an aqueous solution of sat. ammonium
chloride (20 mL) and trichloromethane (20 mL) was added and the layers
were separated. The aqueous layer was extracted with trichloromethane
(2 ꢁ 20 mL). The combined organic layers were dried over magnesium
sulfate and filtered before the solvent was removed in vacuo. The residue
was purified by silica gel column chromatography (hexane/ethyl acetate
1:1). By concentration of the product fractions
a colorless solid
precipitated, which was filtered and washed with hexane yielding 10 as
colorless microcrystalline solid (173 mg, 69%): m.p. 152–156 8C; 1H NMR
(400 MHz, CDCl3, d): 7.91 (br. d, J ¼ 8.1 Hz, 2 H; ArH), 7.69–7.64 (m, 5 H;
ArH), 7.60–7.46 (m, 12 H; ArH), 7.38–7.32 (m, 6 H, ArH), 7.30–7.22 (m, 4
H; ArH), 6.80 (dd, J ¼ 17.6, 10.9 Hz, 1 H; CHCH2), 5.85 (d, J ¼ 17.5 Hz, 1
H; CHCH2), 5.33 ppm (d, J ¼ 10.9 Hz, 1 H; CHCH2); 13C NMR (101 MHz,
CDCl3, d): 152.0 (s), 143.1 (s), 141.7 (s), 141.1 (s), 138.7 (s), 137.4 (s),
137.1 (s), 136.5 (d; CHCH2), 129.9 (d), 129.8 (d), 129.2 (s), 128.6 (d), 127.5
(d), 127.0 (d), 125.4 (d), 124.4 (d), 123.4 (d), 123.0 (d), 119.9 (d), 114.9 (t;
CHCH2), 110.4 ppm (d); IR (ATR): n ¼ 3038 (w), 2982 (w), 1726 (m), 1594
(m), 1496 (m), 1482 (m), 1449 (m), 1377 (m), 1323 (m), 1261 (m), 1193
(w), 1113 (w), 1047 (w), 982 (w), 908 (w), 840 (s), 745 (vs), 698 (s), 614
(m), 539 (w); UV/Vis (CHCl3): lmax (e) ¼ 314 (57700), 244 nm (36500);
UV/Vis (CH3CN): lmax (e) ¼ 312 (54500), 239 (34500), 204 (89000),
193 nm (79900); EIMS (m/z (%)): 640 (78) [Mþ], 639 (46) [Mþ ꢀ H], 319
(44); HRMS (EI, m/z): [Mþ ꢀ H] calcd for C46H31N4 639.254872; found:
639.25354.
Synthesis of 1-Phenyl-2-(4(-vinylbiphenyl-4-yl)-1H-benzo[d]imidazole
(7): To
a mixture of methyltriphenylphosphonium bromide (5.73 g,
16.0 mmol) and potassium tert-butylate (1.89 g, 16.8 mmol) in dry THF
(40 mL) was added dropwise 8 (3.00 g, 8.02 mmol) in dry THF (20 mL) at
0 8C. After 1 h the mixture was allowed to stir at room temperature for 16 h.
An aqueous solution of sat. ammonium chloride (50 mL) and dichloro-
methane (50 mL) was added and the layers were separated. The aqueous
layer was extracted with dichloromethane (2 ꢁ 50 mL). The combined
organic layers were dried over magnesium sulfate and filtered before the
solvent was removed. The residue was purified by silica-gel column
chromatography (hexane/diethyl ether 1:1) and washed with cold ethanol
yielding 7 as a colorless powder (2.15 g, 72%): m.p. 187–188 8C; 1H NMR
(400 MHz, CDCl3, d): 7.91 (ddd, J ¼ 8.1, 1.0, 1.0 Hz, 1 H; ArH), 7.65
(AA0BB0, N ¼ 8.7 Hz, 2 H; ArH), 7.58–7.49 (m, 7 H; ArH), 7.47 (AA0BB0,
N ¼ 8.2 Hz, 2 H; ArH), 7.39–7.33 (m, 3 H; ArH), 7.31–7.23 (m, 2 H; ArH),
6.74 (dd, J ¼ 17.6, 10.9 Hz, 1 H; CHCH2), 5.79 (dd, J ¼ 17.6, 0.8 Hz, 1 H;
CHCH2), 5.28 ppm (dd, J ¼ 10.9, 0.8 Hz, 1 H; CHCH2); 13C NMR
(101 MHz, CDCl3, d): 152.0 (s), 142.7 (br. s), 141.6 (s), 139.4 (s), 137.3 (s),
137.1 (s), 137.0 (s), 136.3 (d; CHCH2), 130.0 (d), 129.8 (d), 128.7 (d), 128.6
(s), 127.5 (d), 127.1 (d), 126.7 (d), 126.7 (d), 123.4 (d), 123.1 (d), 119.7 (d),
114.2 (t; CHCH2), 110.5 ppm (d); IR (ATR): n ¼ 3054 (w), 2977 (w), 1959
Synthesis of 4-(Bis(4’-(1-phenyl-1H-benzo[d]imidazol-2-yl)biphenyl-4-
yl)amino)benzaldehyde (16): A mixture of 4-(bis(4-iodophenyl)amino)ben-
zaldehyde (14) (5.00 g, 9.52 mmol), boronic acid 12 (8.98 g, 28.6 mmol),
Pd(PPh3)4 (220 mg, 190 mmol), 2 M aqueous sodium carbonate solution
(60 mL) and 1,2-dimethoxyethane (200 mL) was stirred under reflux for
16 h. An aqueous solution of sat. ammonium chloride (200 mL) was added
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and the mixture was extracted with trichloromethane (3 ꢁ 200 mL). The
combined organic layers were dried over magnesium sulfate and
concentrated by rotary evaporation. The residue was purified by silica
gel column chromatography (n-hexane/ethyl acetate 1:1 ! 1:2), further
washing with hot ethanol (50 mL) for 16 h and subsequent hot extraction
with dichloromethane/n-hexane 1:1 (50 mL). After cooling to room
temperature the precipitated solid was filtered yielding 16 as a yellow
solid (4.41 g, 57%): m.p. 293 8C (decomp.); 1H NMR (400 MHz, CDCl3, d):
9.85 (s, 1 H CHO), 7.90 (d, J ¼ 8.0 Hz, 2 H; ArH), 7.72 (AA0XX0, N ¼ 8.8 Hz,
2 H; ArH), 7.66 (AA0BB0, N ¼ 8.6 Hz, 4 H; ArH), 7.59–7.47 (m, 14 H; ArH),
7.39–7.32 (m, 6 H, ArH), 7.31–7.20 (m, 8 H, ArH), 7.13 ppm (AA0XX0,
N ¼ 8.7 Hz, 2 H; ArH); 13C NMR (101 MHz, CDCl3, d): 190.3 (d; CHO),
152.8 (s), 152.0 (s), 145.8 (s), 143.1 (s), 140.9 (s), 137.4 (s), 137.1 (s),
136.6 (s), 131.3 (d), 129.92 (d), 129.94 (d), 128.9 (s), 128.6 (d), 128.3 (d),
127.5 (d), 126.5 (d), 126.2 (d), 123.4 (d), 123.1 (d), 120.5 (d), 119.9 (d),
110.4 ppm (d) [20]; UV/Vis (CHCl3): lmax (e) ¼ 362 (62700), 305 (37800),
240 (40600), 232 nm (34800); IR (ATR): n ¼ 3065 (w), 3033 (w), 2827 (w),
2806 (w), 2737 (w), 1690 (m), 1591 (s), 1497 (s), 1472 (m), 1449 (m), 1379
(m), 1323 (s), 1279 (s), 1217 (m), 1165 (m), 1111 (w), 1002 (m), 925 (w),
822 (vs), 762 (m), 740 (s), 724 (m), 697 (s), 637 (w), 613 (m), 558 cmꢀ1
(m); EIMS (m/z (%)): 809 (100) [Mþ], 808 (31) [Mþ ꢀ H], 404 (30); HRMS
(EI, m/z): [Mþ] calcd for C57H39N5O 809.31549; found: 809.31838. Anal.
calcd for C57H39N5O: C 84.52, H 4.85, N 8.65; found: C 83.84, H 4.72, N
8.26.
10 K minꢀ1 scanning rate. Photoelectron spectroscopy were recorded using
a Riken Keiki AC-2. The investigated polymers were measured as powders.
Polymer Synthesis: The polymers described were synthesized in a free
radical process. The monomer concentration of each reaction was set to
100 g Lꢀ1 in freshly distilled THF and 2 mol% N,N-azobisisobutyronitrile
(AIBN) was choosen as the initiator. All reactions were carried out in a
glove-box system at 50 8C for 72 h. The resulting solutions were allowed to
cool to room temperature and demonomerized by repeated precipitation
into mixtures of MeOH/Et2O 2:1.
The polymers were dissolved in THFand filtered through a syringe PTFE
0.2-mm filter. The solutions were concentrated and precipitated into
MeOH/Et2O 2:1. The residues were filtered by the use of PTFE-filters pore
size 0.45 mm and dried for 30 h at 80 8C in vacuo.
Synthesis of P1: from 5; 1H NMR (500 MHz, CDCl3, d): 7.85–7.45 (b, 1 H;
ArH), 7.40–6.55 (b, 10 H; ArH), 6.50–5.90 (b, 2 H; ArH), 1.70–0.70 ppm (b,
3 H; alkyl chain). Anal. calcd for (C21H16N2)n: C 85.11, H 5.44, N 9.45;
found: C 84.36, H 5.46, N 9.61.
Synthesis of P2: from 7; 1H NMR (500 MHz, CDCl3, d): 7.90–7.70 (b, 1 H;
ArH), 7.55–6.80 (b, 14 H; ArH), 6.75–6.15 (b, 2 H; ArH), 2.10–0.80 ppm (b,
3 H; alkyl chain). Anal. calcd for (C27H20N2)n: C 87.07, H 5.41, N 7.52;
found: C 86.15, H 5.36, N 7.68.
Synthesis of P3: from 10; 1H NMR (500 MHz, CDCl3, d): 7.85–7.50 (b, 2
H; ArH), 7.50–5.90 (b, 27 H; ArH), 2.40–0.60 ppm (b, 3 H; alkyl chain).
Anal. calcd for (C46H32N4)n: C 86.22, H 5.03, N 8.74; found: C 85.46, H
4.98, N 8.76.
Synthesis of 4-(Bis(4’-(1-phenyl-1H-benzo[d]imidazol-2-yl)biphenyl-4-
yl)amino)vinylbenzene (11): 16 (500 mg, 617 mmol) was dissolved in dry
THF (20 mL) by heating under reflux. A suspension of methyltriphenylphos-
phonium bromide (440 mg, 1.23 mmol) and potassium tert-butylate
(146 mg, 1.30 mmol) in dry THF (20 mL) was added and the mixture
was stirred 16 h under reflux. After cooling to room temperature an
aqueous solution of sat. ammonium chloride (50 mL) and trichloro-
methane (50 mL) was added and the layers were separated. The aqueous
layer was extracted with trichloromethane (3 ꢁ 50 mL). The combined
organic layers were dried over magnesium sulfate and filtered before the
solvent was removed. The residue was purified by silica gel column
chromatography (n-hexane/ethyl acetate 1:1) to yield 11 as a yellow powder
(386 mg, 77%): m.p. 258–260 8C; 1H NMR (400 MHz, CDCl3, d): 7.90 (br.
d, J ¼ 8.1 Hz, 2 H; ArH), 7.63 (AA0BB0, N ¼ 8.6 Hz, 4 H; ArH), 7.55–7.45
(m, 14 H, ArH), 7.37–7.22 (m, 12 H; ArH), 7.15 (AA0XX0, N ¼ 8.7 Hz, 4 H;
ArH), 7.08 (AA0XX0, N ¼ 8.6 Hz, 2 H; ArH), 6.67 (dd, J ¼ 17.6, 10.9 Hz, 1 H;
CHCH2), 5.66 (d, J ¼ 17.6 Hz, 1 H; CHCH2), 5.18 ppm (d, J ¼ 10.9 Hz, 1 H;
CHCH2); 13C NMR (101 MHz, CDCl3, d): 152.1 (s), 147.1 (s), 146.8 (s),
143.1 (s), 141.3 (s), 137.4 (s), 137.1 (s), 136.1 (d; CHCH2), 134.4 (s), 132.8
(s), 129.9 (d), 129.8 (d), 128.6 (d), 128.4 (s), 127.8 (d), 127.5 (d), 127.2 (d),
126.3 (d), 124.4 (d), 124.3 (d), 123.3 (d), 123.0 (d), 119.8 (d), 112.7 (t;
CHCH2), 110.4 ppm (d); IR (ATR): n ¼ 3062 (w), 3032 (w), 1595 (s), 1500
(s), 1473 (s), 1449 (s), 1377 (m), 1322 (s), 1278 (s), 1192 (w), 1180 (w),
1113 (w), 992 (w), 898 (w), 821 (s), 761 (m), 741 (vs), 695 (s), 635 (w), 612
(m), 577 (w), 549 cmꢀ1 (w); UV/Vis (CHCl3): lmax (e) ¼ 368 (66700), 302
(39500), 241 (41100), 232 nm (31400); EIMS (m/z (%)): 807 (100) [Mþ],
806 (32) [Mþ ꢀ H], 402 (37); HRMS (EI, m/z): [Mþ ꢀ H] calcd for C58H40N5
806.328371; found: 806.32804.
Synthesis of P4: from 11; 1H NMR (500 MHz, CDCl3, d): 7.95–7.55 (b, 2
H; ArH), 7.55–6.00 (b, 36 H; ArH), 2.20–0.75 ppm (b, 3 H; alkyl chain).
Anal. calcd for (C58H41N5)n: C 86.22, H 5.11, N 8.67; found: C 85.30, H
5.12, N 8.69.
Polymer Film for AFM Measurements: Glass substrates were cleaned for
5 min in an ultrasonic cleaner and dried. A layer of PEDOT:PSS (Baytron
CH8000, H. C. Starck) was spin-coated to a thickness of 80 nm and dried at
130 8C for 15 min. Then, a film of P1 was deposited by spin-coating of a 3%
solution of P1 in o-dichlorobenzene to a thickness of 100 nm. This layer was
tempered at 110 8C for 15 min. AFM-measurements were performed using
an Nanosurf easy scan 2.
Device Fabrication: The transparent indium tin oxide (ITO) covered
glass slides were received from OPTREX Europe GmbH, feature a sheet
resistance of 20 V sqꢀ1 and were chemically wet cleaned in an ultrasonic
bath before used. The hole-injecting layer was PEDOT:PSS (Baytron
CH8000, H.C. Starck) and dried at temperatures above 130 8C for 5 min to
remove the residual solvent, followed by a spin-coating process of the
emitting polymer solution from 1,2-dichlorobenzene to receive polymer
layers of different thicknesses after another annealing step for 10 min at
110 8C. The polymers were dissolved for 24 h at room temperature in 1,2-
dichlorobenzene using a shaker and filtered through PTFE syringe filters
with pore sizes of 0.1 mm before use. The cathodes (CsF 4 nm; Ca 30 nm;
Ag 50 nm) were assembled by thermal evaporation process at pressures
below 10ꢀ5 Pa. Four devices of each polymer were build to guarantee
uniformity. The complete sample preparation and measurements have
been investigated in a clean room under inert atmosphere.
Device Characterization: The current–voltage and the luminance–
voltage characteristics of the devices were measured simultaneously with
a computer controlled Keithley 236 Source-Measure-Unit in combination
with an Optometer Model GO352 equipped with a calibrated sensor head
for the luminance measurements. The electroluminescence spectra were
recorded with a diode-array Spectrometer EPP 2000 from Stella Net Inc.
Electrochemical Measurements: The redox and oxidation potentials of
the non-polymeric materials were measured from differential pulse
voltammetry (DPV) using a Metrohm mAutolab III potentiostat equipped
with a 1-mm platinum working electrode, a platinum-wire counter
electrode, and a saturated Ag/AgCl reference electrode. The electrolyte
Bu4NPF6 was dissolved in dry DMF and dry CH2Cl2, respectively, to
generate a 0.1 M stock solution. Analyte concentrations were set to 1 mM.
DPV measurements were recorded with a step potential of 10 mV and a
modulation amplitutde of 100 mV. Under these conditions the oxidation
potentials of ferrocene were determined to be 0.60 V (DMF) and 0.47 V
(CH2Cl2) against the reference electrode. Voltammograms of the polymer
Polymer Analysis: High-resolution (500 MHz) 1H NMR spectra in CDCl3
were recorded using a UNITY INOVA 500 spectrometer from Varian.
Elemental analyses were obtained using a Thermo Scientific FlashEA 1112
CHNS/O Automatic Elemental Analyser. Gel-permeation chromatography
(GPC) at 25 8C in THF was used to determine the molecular weight. For this
purpose a combination of a Waters HPLC-Pump 515, Autosampler 717
plus, Dual l Absorbance Detector 2487 and a Refrative Index Detector
2414 was used.
A pre-column and three columns from Waters
(7.8 mm ꢁ 300 mm; Styragel HR3, HR4, HR5) filled with a copolymer of
styrene and divinylbenzene 5 mm and PS-Standards from Polymer
Laboratories (Varian) were used. The polymer solution (2 mg mLꢀ1 in
THF) stirred for 24 h at room temperature and filtered through a syringe
PTFE (polytetrafluoroethylene) filter 1 mm. 2 ꢁ 100 mL of each polymer-
solution were injected. Molecular weights were calculated with the
Empower software from Waters. Thermal analysis was performed with
differential scanning calorimetry (DSC) using a Netzsch DSC 204 with
Adv. Funct. Mater. 2010, 20, 399–408
ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
407

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films were obtained using an EG&G Parc model 273 potentiostat,
controlled by an IBM P70 computer. A three-electrode configuration was
applied, contained in an undivided cell consisting of a glassy carbon
electrode (area 0.5 cm2) where the polymer film was deposited, a platinum
mesh as the counter electrode, and an Ag/AgCl (3 M NaCl and sat. AgCl)
reference electrode. 0.1 M Bu4NBF4 in acetonitrile was used as electrolyte
and prior each measurement the electochemical cell was deoxygenated
with nitrogen. Furthermore, the electrochemical cell was calibrated by the
use of a ferrocene standard and the ferrocene half-wave potential was
estimated to 435 mV for this assembly. 1 wt-% solutions of polymers in
trichloromethane were prepared and 5 mL were deposited on the glassy
carbon electrode. The prepared electrodes were kept under vacuum and
dried at 60 8C for 2 h.
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Acknowledgements
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We thank the Deutsches Zentrum fur Luft und Raumfahrt e.V. (DLR) and
the Bundesministerium fur Bildung und Forschung (BMBF) (01 BD 0687
¨
and 01 BD 0685) for financial support. The phosphorescent dopant was
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Received: August 24, 2009
Published online: January 4, 2010
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408
ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2010, 20, 399–408