Synthesis, properties and applications of biphenyl functionalized 9,9-bis(4-diphenylaminophenyl)fluorenes as bifunctional materials for organic electroluminescent devices

Article abstract of DOI:10.1002/ejoc.201200641

Four new bifunctional materials, namely BPTF, CBPTF, CMBPTF and BPVTF, having 9,9-bis(4-diphenylaminophenyl)fluorene as a molecular platform and biphenyl derivatives as end-capping substituents were synthesized and characterized. Their optimized structure

Full text of DOI:10.1002/ejoc.201200641

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FULL PAPER
DOI: 10.1002/ejoc.201200641
Synthesis, Properties and Applications of Biphenyl Functionalized 9,9-Bis(4-
diphenylaminophenyl)fluorenes as Bifunctional Materials for Organic
Electroluminescent Devices
A-monrat Thangthong,[a] Narid Prachumrak,[a] Supawadee Namuangruk,[b]
Siriporn Jungsuttiwong,[a] Tinnagon Keawin,[a] Taweesak Sudyoadsuk,[a] and
Vinich Promarak*[a]
Keywords: Hyperconjugation / UV/Vis spectroscopy / Biaryls / Semiconductors / Photochromism / Light-emitting diodes
Four new bifunctional materials, namely BPTF, CBPTF,
CMBPTF and BPVTF, having 9,9-bis(4-diphenylamino-
phenyl)fluorene as a molecular platform and biphenyl deriv-
atives as end-capping substituents were synthesized and
characterized. Their optimized structures revealed that both
triphenylamine moieties at the C-9 position of the fluorene
ring generated a bulky molecular structure. These molecules
showed strong blue emission in both solution and in the solid
state, and were thermally stable amorphous materials with
glass transition temperatures up to 207 °C. The abilities of
these materials to act as blue-light-emitting materials for
blue OLEDs and hole-transporting materials for green
OLEDs in terms of device performance and thermal proper-
ties were superior to commonly used N,NЈ-diphenyl-N,NЈ-
bis(1-naphthyl)-(1,1Ј-biphenyl)-4,4Ј-diamine (NPB). Ef-
ficient, and bright nondoped deep-blue and Alq3-based
green OLEDs with maximum luminance efficiencies and CIE
coordinates of 2.48 cdA–1 and x = 0.15 and y = 0.07, and
4.40 cdA–1 and x = 0.28 and y = 0.52 were achieved, respec-
tively, with BPTF having two biphenyl substituents as active
layers. Both devices showed low turn-on voltages of 3.1 and
2.8 V, respectively. Notably, the color purities of these deep-
blue and green devices were close to the National Television
Standards Committee blue (CIE coordinates of x = 0.14 and
y = 0.08) and green (CIE coordinates of x = 0.26 and y = 0.65)
standards.
(EL) properties of the blue materials need to be improved,
particularly in terms of EL efficiencies and color purity. The
materials that emit a deep-blue color with excellent Com-
mission International De L’Eclairage (CIE) coordinates of
x = 0.14 and y = 0.08 for the National Television Standards
Committee (NTSC) standard blue need to have excited en-
ergies near 3.1 eV.[4] Such deep-blue emitters have high ion-
ization potentials and low electron affinities. Although
many blue light-emitting materials based on pyrene,[5] an-
thracene,[6] fluorenes,[7] aromatic hydrocarbon,[8] and tri-
arylamine[9] derivatives have been reported, the EL effi-
ciencies of these deep-blue OLEDs (CIE coordinates of x
= 0.15 and y = 0.10) are rather poor compared to those of
sky-blue OLEDs (CIE coordinates of x = 0.15 and
yϾ0.15). Therefore, the search for new efficient deep-blue
fluorescent materials with high performance remains a
major challenge.
Among the blue emitters, inclusion of moieties such as
fluorenes, spirofluorenes, oligomeric fluorenes, polyfluor-
enes (PFs), and their derivatives have been intensively inves-
tigated and these are regarded as the most promising candi-
dates for blue OLEDs.[10] However, the application of these
materials as potential candidates for deep-blue OLEDs is
still problematic because of deficiencies including low color
purity due to unwanted emission at longer wavelengths
from the aggregates, excimers, and fluorenone defects,[11]
Introduction
Organic light-emitting diodes (OLEDs) have attracted a
great deal of attention due to their potential applications in
full-color or large-area flat panel displays, backlight, and
general illumination.[1] In the past decades, we have seen
great progress in the development of electroluminescent ma-
terials with high luminescent efficiency, good thermal/op-
tical stability, excellent charge-carrier injection and trans-
port, and designed film morphology, as well as in the fabri-
cation of high-performance devices.[2] For full-color display
applications, blue, green, and red materials and devices with
high emission efficiency and high color purity are required.
The performance of deep-blue OELDs are usually inferior
to those of green and red OLEDs due to poor carrier injec-
tion into the emitters,[3] and hence the electroluminescent
[a] Center for Organic Electronic and Alternative Energy,
Department of Chemistry and Center of Excellence for
Innovation in Chemistry, Faculty of Science, Ubon Ratchathani
University,
Warinchumrap, Ubon Ratchathani 34190, Thailand
Fax: +66-45-288379
E-mail: pvinich@ubu.ac.th
Homepage: http://chem.sci.ubu.ac.th/adom/
[b] National Nanotechnology Center (NANOTEC),
130 Thailand Science Park, Klong Luang, Pathumthani 12120,
Thailand
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201200641.
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Scheme 1. Synthesis of the target molecules. Reagents and conditions: (a) CrO3, acetic anhydride, room temp., 92%; (b) triphenylamine,
CH3SO3H, 190 °C, 61%; (c) [Pd(PPh3)4], 2 m Na2CO3, THF, heat; (d) carbazole, Cu, K2CO3, 18-crown-6, o-dichlorobenzene, heat;
(e) 1. nBuLi, THF, –78 °C; 2. 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, –78 °C to room temp. and 3. acidic work up; (f) 5-
bromo-2-iodotoluene, [Pd(PPh3)4], K2CO3, THF/H2O, heat.
and inefficient hole-injection that requires the use of hole- ration of a biphenyl moiety into this platform should assure
transporting layers to obtain a balance in charge carriers, intense deep-blue emission.[21] The use of fluorene and bi-
leading to a complex device structure.[12,3] The hole-injec- phenyl groups has a number of advantages, including the
tion ability of these fluorene derivatives has been success- capability of the material to emit in the blue part of the
fully improved by many approaches such as blending with visible spectrum, and to increase chemical and photochemi-
hole-transporting triarylamines,[13] end-capping the poly- cal stability.[22] The high steric hindrance in the molecule
mer chain with triarylamines,[14] copolymerization with tri- also leads to good solubility and, thus, thermally stable
arylamine-containing monomers,[15] and substitutions at amorphous thin films could be deposited by inexpensive
the C-9 position of the fluorene block with triarylamines.[16] solution processes. This would result in the generation of
The latter approach was proven to be more effective, and new bifunctional materials with combined blue emitting
involved a less complex synthesis. For example, 9,9-bis(4- and hole-transporting properties. In this work, we present
diphenylaminophenyl)fluorene [9,9-bis(triphenylmine)fluor- the synthesis and characterization of such materials, namely
ene] has been successfully used as a building block for the BPTF, CBPTF, CMBPTF, and BPVTF. An investigation of
synthesis of many blue emitting PFs and derivatives with their physical and photophysical properties, and their appli-
improved hole-injection and suppressed aggregation.[17] cations as active layers in OLEDs is also reported.
Hence, using this fluorene building block to construct new
molecular materials might be a simple approach to the de-
velopment of efficient deep-blue emitters.[18] Therefore, we
herein implemented all required aspects in the designed mo-
lecules (Scheme 1). The use of 9,9-bis(4-diphenylamino-
phenyl)fluorene as a molecular framework offers an ideal
Results and Discussion
Synthesis and Quantum Calculations
The designed molecules were synthesized as outlined in
bulky molecule with high thermal stability and an improved Scheme 1. We began with air oxidation of 2,7-dibromo-
hole injection and transport ability from the pendent tri- fluorene (1) with KOH/air in dimethyl sulfoxide (DMSO)
phenylamine (TPA) units.[19] The presence of such bulky to give 2,7-dibromofluorenone (2) as a yellow solid in low
groups at the C-9 position of the framework would also yield (31%). An improved yield of fluorenone 2 was ac-
suppress the aggregation phenomena and reduce excimer complished by oxidation of 1 with CrO3 as an oxidizing
formation, resulting in a stable blue emission.[20,16] Incorpo- reagent in acetic anhydride, which produced 2 in good yield
2
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Bifunctional Materials for Organic Electroluminescent Devices
(92%). The 9,9-bis(4-diphenylaminophenyl)fluorene (3) in- phenyl plane. The HOMO–LUMO energy gaps (Eg cal.)
termediate was then synthesized by a tandem protocol that obtained from quantum chemical calculations were found
involved treatment of 2 with an excess of triphenylamine, to be in the range of 3.06–3.49 eV. These values were
catalyzed by CH3SO3H at 190 °C, and the product 3 was slightly higher than those estimated from the optical ab-
obtained as a white solid in 61% yield. Coupling of 3 with sorption edge (Eg) (Table 1). There are factors that could be
commercially available 4-biphenylboronic acid and 4-bi- responsible for the discrepancy because the orbital energy
phenylvinyleneboronic acid under Suzuki cross-coupling difference between HOMO and LUMO is still an approxi-
conditions catalyzed by [Pd(PPh3)4] in the presence of mation of the transition energy because the transition en-
Na2CO3 as base in tetrahydrofuran (THF) afforded BPTF ergy also contains significant contributions from some two-
and BPVTF in good yields as white and yellow solids, electron integrals. The real situation is that an accurate de-
respectively; coupling of 3 with 4-carbazol-9-ylbiphenyl- scription of the lowest singlet excited state requires a linear
dioxaborolanes 4 and 5 (see below) under the same condi- combination of a number of excited configurations.
tions gave CBPTF and CMBPTF as white solids in good
yields of 75 and 82%, respectively. The borolanes 4 and 5
were prepared in two steps. Ullmann coupling of commer-
cially available 4,4Ј-dibromobiphenyl (6) with carbazole cat-
alyzed by Cu/18-crown-6 in the presence of K2CO3 as base
in o-dichlorobenzene followed by lithiation of the resultant
compound 7 with nBuLi in THF, trapping the anion
formed with 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxa-
borolane and acidic workup, gave 4 as a white solid in
85% yield. Suzuki cross-coupling of 2-[4-(carbazol-9-yl)-
benzene]-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (9) with
5-bromo-2-iodotoluene followed by treatment of the result-
ant compound 10 with nBuLi/2-isopropoxy-4,4,5,5-tetra-
methyl-1,3,2-dioxaborolane afforded borolane 5 as a white
solid in 71% yield. The chemical structures and purities of
these materials were established unambiguously through the Figure 1. The HOMO and LUMO orbitals of BPTF.
use of NMR spectroscopy, mass spectrometry, and elemen-
tal analysis. Importantly, all the compounds showed good
solubility in organic solvents, which opened the door to
solution processing techniques.
Photophysical and Physical Properties
To understand the electronic properties and the geome-
The optical properties of BPTF, CBPTF, CMBPTF and
tries of the synthesized molecules, quantum chemical calcu- BPVTF were investigated in dilute CH2Cl2 solution and as
lations were performed by using the TDDFT/B3LYP/6-31G a thin film obtained by thermal evaporation on a quartz
(d,p) method;[23] the results are shown in Figure 1 and in substrate (Figure 2, Table 1). Their absorption spectra in
the Supporting Information. The optimized structures of solution showed two absorption bands: one at approxi-
these compounds revealed that both TPA moieties at the C- mately 300 nm assigned to the π-π* local electron transition
9 position of the fluorene ring generated high steric hin- of the pendant TPA moieties, and a second, strong absorp-
drance, resulting in a bulky molecular structure and thereby tion band at longer wavelengths (327–395 nm) correspond-
preventing a close π-π stacking interaction of the molecule. ing to the π-π* electron transition of the fluorene–biphenyl
In the highest occupied molecular orbitals (HOMO) of conjugated backbone. The latter absorption band of
BPTF, CBPTF, CMBPTF, and BPVTF, π-electrons are lo- CBPTF was red-shifted compared to that of BPTF due to
calized on the TPA pendant groups, whereas in their lowest the π-electrons in the ground sate being able to delocalize
unoccupied molecular orbitals (LUMO), the excited elec- over the fluorene–biphenyl backbone and carbazole
trons are delocalized over the quinoid-like fluorene-bi- through the lone electron pair of the nitrogen atom of the
Table 1. Physical and photophysical properties of the synthesized molecules.
[b]
Thin film [nm][a]
ΦF
Tg/Tc/Tm/T5d [°C][c] E1/2 vs. SCE [V][d]
E1O, E2O, E3O
Eg [eV][e]
Eg cal. [eV][f] HOMO/LUMO [eV][g]
λabs
λem
Epc
BPTF
CBPTF
CMBPTF 327
BPVTF 395
327
346
426
438
408, 426
446, 467
0.35
0.24
0.20
0.49
166/ – / – /456
207/324/359/487
192/270/320/343
164/246/320/330
0.98, 1.51
0.98, 1.23
0.98, 1.30
0.96, 1.22, 1.37
0.73
3.31
3.47
3.39
3.49
3.06
–5.32/–2.01
–5.32/–2.13
–5.33/–2.07
–5.29/–2.91
0.74, 0.83 3.19
0.74, 0.81 3.26
–
2.88
[a] Measured as a thin film obtained by thermal evaporation. [b] Measured in CH2Cl2 solution. [c] Obtained from DSC and TGA measure-
ments. [d] Obtained from CV at a scan rate of 50 mV/s. [e] Estimated from the optical absorption edge, Eg = 1240/λonset. [f] Obtained
from quantum calculations using TDDFT/B3LYP/6-31G (d,p). [g] Calculated by HOMO = –(4.44 + Eonset), and LUMO = HOMO – Eg,
where Eonset is the onset potential of the oxidation.
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carbazole. The absorption band of CMBPTF was nearly therefore investigated by thermogravimetric analysis (TGA)
identical to that of BPTF and blue shifted with respect to and differential scanning calorimetry (DSC) (Table 1, and
CBPTF. This is due to the methyl substituent on the bi- the Supporting Information). These results suggested that
phenyl moiety of CMBPTF restricting free rotation of the all compounds were thermally stable materials with 5%
biphenyl moiety, limiting the interaction between the fluo- weight loss temperatures (T5d) well over 330 °C. DSC ther-
rene–biphenyl and carbazole moieties. However, BPVTF mograms of all compounds displayed baseline shift due to
possesses a more extended π-conjugation backbone due to glass transition temperatures (Tg) ranging from 166 to
the presence of the vinylene bond between the fluorene and 207 °C. These results indicated that the materials were
biphenyl units, as observed in the DFT calculation, and its stable amorphous materials with high Tg values that were
absorption spectrum was further red-shifted. In the solid higher than those of commonly used HTMs such as N,NЈ-
state, similar absorption features with a slight redshift com- diphenyl-N,NЈ-bis(1-naphthyl)-(1,1Ј-biphenyl)-4,4Ј-diamine
pared to their corresponding solution spectra were ob- (NPB) (Tg = 100 °C) and N,NЈ-bis(3-methylphenyl)-N,NЈ-
served. These materials exhibited strong emission intensity bis(phenyl)benzidine (TPD) (Tg = 63 °C), and other tri-
and deep-blue emission in both solution and the solid state. phenylamine derivatives.[24] The results proved that the use
Their fluorescence quantum yields (ΦF) measured in of 9,9-bis(4-diphenylaminophenyl)fluorene as a molecular
CH2Cl2 solution using quinine sulfate solution in 0.01 m platform could improve the amorphous stability of the ma-
H2SO4 (ΦF = 0.54) ranged from 0.20 to 0.49. The solution terials, which, in turn, could increase the service time in
photoluminescence (PL) spectra of BPTF, CBPTF and device operation and enhance the morphological stability
CMBPTF showed a featureless emission peak in the blue of the thin film.[25] Moreover, the abilities of these materials
region (448–454 nm), whereas the spectrum of BPVTF ex- to form molecular glass and dissolve in organic solvents
hibited two emission peaks at 459 and 482 nm. The thin- offers the possibility of preparing good thin films by both
film PL emission spectra of these materials appeared at the thermal evaporation and solution casting techniques, which
same region as their solution PL spectra, indicating that are highly desirable for fabrication of OLED devices.
less ordered solid state packing occurred in this case due to
their bulky molecular structures.
Electrochemical behaviors of all compounds were investi-
gated by cyclic voltammetry (CV) (Figure 3, Table 1). In all
cases, the first quasi-reversible oxidation wave appeared at
nearly the same position (0.96–0.98 V) and was assigned
to the removal of electrons from the TPAs and carbazoles,
resulting in the formation of the corresponding radical cat-
ions, whereas the rest oxidation waves indicated the removal
of electrons from the fluorene–biphenyl backbone. CV
curves of BPTF, CBPTF and CMBPTF showed additional
peaks at lower potential on the cathodic scan (Epc) at 0.73
and 0.83 V, which corresponded to electrochemical cou-
pling reactions of the TPA radical cation (TPA·+) and
carbazole radical cation (CAZ·+), respectively. Repeated CV
scans of these compounds also revealed an increasing
change in their CV curves, demonstrating a series of electro-
chemical reactions leading to electro-polymerization of
those radical cation species on the glassy carbon electrode
surface. The multiple CV scans of BPVTF revealed a small
change in CV curves, indicating a weak oxidative coupling
of the pendent TPAs; thus, among the synthesized materi-
als, BPVTF is a more electrochemically stable molecule.
Usually, this type of electrochemical coupling reaction is
detected in most TPA and carbazole derivatives with unsub-
stituted p-position of the phenyl ring and unsubstituted 3,6-
positions, such as in case of 2,7-bis[2-(4-diphenylamino-
phenyl)-1,3,4-oxadiazol-5-yl]-9,9-bis-n-hexylfluorene.[26]
A
Figure 2. UV/Vis absorption (Ϫ) and PL spectra (----) measured
(a) in CH2Cl2 solution and (b) as a thin film obtained by thermal
deposition on quartz substrate.
proposed oxidation and electrochemical coupling reaction
of these materials is outlined in Figure 4. During the first
oxidation, electrons are removed from nitrogen atom of
For OLED applications, thermal stability of organic ma- both TPA and carbazole moieties to give radical cation
terials is crucial for device stability and lifetime. Thermal (TPA·+ and CAZ·+) form A, which undergoes electron delo-
instability or low glass transition temperature (Tg) of the calization to generate resonance forms B, C and D. These
amorphous organic layer may result in degradation of or- radical cations are highly reactive species and readily un-
ganic devices due to morphological changes. The thermal dergo dimerization coupling to form a stable neutral mole-
properties of BPTF, CBPTF, CMBPTF and BPVTF were cule. Resonance forms A, B and D, having the radical sited
4
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Bifunctional Materials for Organic Electroluminescent Devices
Figure 3. (a) CV curves of the synthesized materials, and multiple CV scans of (b) BPTF, (c) CBPTF, and (d) BPVTF measured in
CH2Cl2/nBu4NPF6 at a scan rate of 50 mV/s.
Figure 4. A proposed oxidation and electrochemical reaction of triphenylamine and carbazole moieties.
either on the nitrogen atom (A) or on ortho-C atoms (B and CMBPTF, and BPVTF were calculated from the oxidation
D), are less likely to undergo dimerization coupling reac- onset potentials (Eonset) and energy gaps (Eg) and the re-
tions due to high steric hindrance, thus this electrochemical sults are summarized in Table 1. The HOMO levels of these
reaction is more likely to take place through resonance form materials ranged from 5.29 to 5.33 eV, matching well with
C.
the work functions of the gold (Au) or indium tin oxide
However, the TPA units of BPVTF are unlikely to un- (ITO) electrodes and, hence, favoring the injection and
dergo such electrochemical reactions due to steric hin- transport of holes.
drance from the adjacent 4-biphenylvinylene moiety, which
keep them away from each other and prevents coupling.
Furthermore, this type of electrochemical reaction will be-
Electroluminescence Properties
come inactive in nondiffusion systems or in the solid state.
Moreover, under these CV experiment conditions, no dis-
Owing to their intense blue fluorescence and their
tinct reduction process was observed in any of the cases. HOMO levels (5.3 eV) lying between those of PEDOT:PSS
The HOMO and LUMO energy levels of BPTF, CBPTF, (5.00 eV) and Alq3 (5.80 eV), the new synthesized materials
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BPTF, CBPTF, CMBPTF, and BPVTF could be used as whereas device IV emitted a sky-blue light with peak cen-
bifunctional materials, namely blue light-emitting and hole- tered at 467 nm (Figure 5a). The electroluminescence (EL)
transporting materials. This encouraged us to investigate spectra of all diodes matched with their corresponding PL
the use of these compounds as emissive layers (EML) for spectra. No emission shoulder at longer wavelength owing
blue OLED and hole-transporting layer (HTL) for Alq3- to excimer and exciplex species formed at the interface of
based green OLED. The blue light-emitting diodes with the EML and HBL materials, which often occurs in the devices
device structure of indium tin oxide (ITO)/PEDOT:PSS/ fabricated from EML with planar molecular structure, was
EML(50 nm)/BCP(40 nm)/LiF(0.5 nm):Al(150 nm)
and detected in the EL spectra of devices I–III. The EL spec-
green light-emitting diodes with the device structure of trum of device IV, having BPVTF as EML, displayed an
ITO/PEDOT:PSS/HTL(40 nm)/Alq3(50 nm)/LiF(0.5 nm): emission shoulder corresponding to excimer and exciplex
Al(150 nm) were fabricated. Tris(8-hydroxyquinoline) alu- emissions.[29] The former might arise from the ladder-type
minum [Alq3; acting as the green light-emitting (EML) and aggregate of the planar 2,7-bis[4-(biphenyl-4-yl)vinylene]-
electron-transporting layers (ETL)], the conductive poly- fluorene moiety, whereas the latter is often observed at the
mer, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulf- interface of organic/organic layers in an OLED and can be
onate) [PEDOT:PSS; acting as the hole injection layer], and tuned by adjusting the thickness of those layers.[30] In de-
2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline [BCP; act- vices I–III, the formation of these species could be pre-
ing as the hole blocking layer (HBL)], were integrated to- vented by the nonplanar nature of the biphenyl–fluorene
gether to enable the creation of high-performance devices. backbones as well as the bulky nature of the 9,9-bis(4-di-
From our study and other reports,[27] it was found that the phenylaminophenyl)fluorene implemented as the molecular
incorporation of PEDOT:PSS in the device as a hole injec- platform. Additionally, stable emission was obtained from
tion layer not only increased the maximum luminance from all devices; the EL spectra did not change significantly over
6127 cdm–2 (η of 1.29 cdA–1) in device XI to 26067 cdm–2 the entire driven voltages (see the Supporting Information).
(η of 4.40 cdA–1) in device VI, but also significantly de- The current density-voltage-luminance (I-V-L) characteris-
creased the turn-on voltage from 5.8 V to 2.8 V (Table 2). tics of the devices are shown in parts b–d of Figure 5, and
Moreover, their EL spectra were almost identical. It has their electrical parameters are summarized in Table 2. The
been pointed out that the lower operating voltage of PE- light turn-on voltage at 1 cdm–2 for all devices was in the
DOT:PSS-based devices can be attributed to the rough and range of 3.1–3.5 V and the operating voltage at 100 cdm–2
porous surface of the spin-coated PEDOT:PSS polymer was in the range of 4.9–5.7 V, indicating good performance
layer, which increases the contact area to enhance hole in- was achieved for all the devices. The device characteristics
jection and lowers the barrier at the organic–organic inter- in terms of maximum brightness, turn-on voltage, and
face by relocating the barrier to the more conductive PE- maximum luminous efficiency clearly verified that the blue-
DOT:PSS layer.[28] To enable high-performance devices, emitting abilities of these newly synthesized materials were
therefore, PEDOT:PSS was integrated into all devices as a greater than NPB-based blue device (device V). The results
hole injection layer. To compare blue light-emitting and also revealed that BPTF, bearing two biphenyl moieties at-
hole-transporting abilities of the synthesized materials, tached to the 2,7-positions of the 9,9-bis(4-diphenylami-
NPB, a commonly used commercial HTM, was employed nophenyl)fluorene framework, had the best EML proper-
as reference EML and HTL materials and the reference de- ties among these four materials in terms of both device per-
vices (V and X) of the same structure were fabricated.
formance and purity of emission color. Device I showed a
As nondoped blue emitters, under applied voltage, de- high maximum brightness of 7277 cdm–2 at 10.2 V, a maxi-
vices I–III emitted bright deep-blue light with maximum mum luminous efficiency of 2.48 cdA–1, a maximum exter-
peaks centered at 420, 419, and 428 nm, respectively, nal quantum efficiency of 0.35%, and a low turn-on voltage
Table 2. Device characteristics of OLEDs.
[a]
[b]
[c]
[d]
Device Structure
Von
V100
λmax
Lmax
I[e]
η[f]
EQE[g]
CIE[h]
I
II
ITO/PEDOT:PSS/BPTF/BCP/LiF:Al
ITO/PEDOT:PSS/CBPTF/BCP/LiF:Al
3.1
3.3
4.9
4.9
5.3
5.7
5.5
4.9
4.5
5.3
5.5
4.1
6.5
5.4
420
419
428
467
436
516
516
517
516
516
516
518
7277
2603
2230
2248
343
26067
24000
23802
21675
30044
6127
564
476
467
411
2.48
1.06
0.91
0.72
0.73
4.40
4.31
4.13
3.85
4.45
1.29
0.91
0.35
0.35
0.30
0.12
0.24
0.22
0.21
0.20
0.19
0.22
0.10
0.05
0.15, 0.07
0.16, 0.10
0.16, 0.04
0.17, 0.23
0.15, 0.07
0.28, 0.52
0.28, 0.52
0.29, 0.53
0.28, 0.52
0.30, 0.54
0.28, 0.52
0.30, 0.54
III
IV
V
VI
VII
VIII
IX
X
ITO/PEDOT:PSS/CMBPTF/BCP/LiF:Al 3.5
ITO/PEDOT:PSS/BPVTF/BCP//LiF:Al
ITO/PEDOT:PSS/NPB/BCP/LiF:Al
ITO/PEDOT:PSS/BPTF/Alq3/LiF:Al
ITO/PEDOT:PSS/CBPTF/Alq3/LiF:Al
3.4
3.4
2.8
2.8
241
1075
1197
917
ITO/PEDOT:PSS/CMBPTF/Alq3/LiF:Al 3.1
ITO/PEDOT:PSS/BPVTF/Alq3/LiF:Al
ITO/PEDOT:PSS/NPB/Alq3/LiF:Al
ITO/BPTF/Alq3/LiF:Al
3.3
3.1
5.8
4.2
919
1362
1114
693
XI
XII
ITO/PEDOT:PSS/Alq3/LiF:Al
4961
[a] Turn-on voltage [V] at 1 cdm–2. [b] Voltage [V] at luminance of 100 cdm–2. [c] Emission maximum [nm]. [d] Maximum luminance
[cdm–2]. [e] Current density at maximum luminance [mAcm–2]. [f] Luminance efficiency [cdA–1]. [g] External quantum efficiency [%].
[h] CIE coordinates (x, y).
6
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Bifunctional Materials for Organic Electroluminescent Devices
Figure 5. (a) PL (Ϫ) and EL (----) spectra; (b) V–L characteristics; (c) I–V characteristics; (d) variation of luminance efficiency with
current density of the fabricated blue OLED devices using the synthesized materials as EML.
of 3.1 V, which is considered to be one of the lowest turn-
As HTLs, devices VI–IX exhibited light turn-on voltages
on voltages for deep-blue OLED. This device also emitted at 1 cd m–2 in the range of 2.8–3.3 V and the operating volt-
intense deep-blue color (420 nm) with CIE coordinates of x ages at 100 cdm–2 in the range of 4.9–5.5 V, indicating good
= 0.15 and y = 0.07, which is close to the National Televi- performance is achieved for all the devices (Figure 6,
sion System Committee (NTSC) deep-blue (CIE coordi- Table 2). By comparison with the reference device XII, it
nates of x = 0.14 and y = 0.08) standard.[4] A lower device was found that the incorporation of BPTF, CBPTF,
performance was observed from devices II (CBPTF as CMBPTF, and BPVTF in the devices as HTL not only in-
EML) and III (CMBPTF as EML), displaying a maximum creased the maximum luminance from 4961 cdm–2 (η of
luminous efficiency of 1.06 and 0.93 cdA–1, respectively. 0.91 cdA–1) to 21675–26067 cdm–2 (η of 3.85–4.40 cdA–1)
The trend in device luminous efficiencies of devices I–III in devices VI–IX, but also significantly decreased the turn-
matched very well with the observed decrease in PL quan- on voltage from 4.2 V to 2.8–3.3 V. Furthermore, their EL
tum efficiencies of the EML on going from BPTF to spectra were nearly identical. Moreover, the device charac-
CBPTF to CMBPTF (Table 1). It has been demonstrated teristics in terms of luminous efficiency clearly demon-
that the efficiency of an OLED depends both on the bal- strated that the hole-transporting abilities of these materials
ance of electrons and holes, and on the ΦF of the emitter.[31] were comparable to those of the NPB-based device (device
Analysis of the band energy diagrams of these diodes also X). Device VI, having compound BPTF as HTL, exhibited
revealed that the HOMO levels of BPTF, CBPTF, the best performance with a high maximum brightness of
CMBPTF, and BPVTF (5.29–5.33 eV) sat perfectly between 26067 cdm–2 for green OLED at 10.4 V, a low turn-on volt-
those of the hole injection layer (PEDOT:PSS, 5.00 eV) and age of 2.8 V, a maximum luminous efficiency of 4.40 cdA–1,
HBL (BCP, 6.50 eV), resulting the an efficient charge re- and a maximum external quantum efficiency of 0.22%. A
combination in the emitting layer and better device per- comparable device performance was observed from devices
formance (see the Supporting Information). Fluorescence VII (CBPTF as HTL) and VIII (CMBPTF as HTL)
quantum yield (ΦF) of BPVTF, however, was higher than (Table 2). Under the applied voltage, all devices (VI–VIII)
BPTF, and was also significantly higher than those of exhibited a bright-green emission with peaks centered at
CBPTF and CMBPTF. In contrast, the emission efficiency 516 nm, and CIE coordinates of x = 0.28 and y = 0.52
of device V, having BPVTF as EML, was relatively low (Figure 6, a). The electroluminescence (EL) spectra of these
among these four EMLs. The reason for the poor perform- diodes were identical, and matched with the PL spectrum
ance of device IV might come from the presence of excimer of Alq3, the EL of the reference devices (X–XII), and also
and exciplex emission at the longer wavelength side in the of other reported EL spectra of Alq3-based devices.[34] No
EL spectrum.[32] Excimer formation has also been found on emission at the longer wavelength owing to exciplex species
polyfluorenes (PFs).[33]
formed at the interface of HTL and ETL materials, which
Eur. J. Org. Chem. 0000, 0–0
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FULL PAPER
Figure 6. (a) EL spectra; (b) V–L characteristics; (c) I–V characteristics; (d) variation of luminance efficiency with current density of the
fabricated green OLED devices using the synthesized materials as HTL.
often occurs in the devices fabricated from HTL with stability of these materials. Strong deep-blue emission in
planar molecular structure, was detected.[35] In our case, the solution was also obtained. All of the compounds were
formation of exciplex species could be prevented by the thermally stable amorphous materials, with the lowest glass
bulky nature of the 9,9-bis(4-diphenylaminophenyl)fluor- transition temperature being 166 °C. Their abilities to act
ene. From these results, and in view of the fact that a bar- as both blue light-emitting materials for blue OLEDs and
rier for electron-migration at the Alq3/HTL interface (ca. as hole-transporting materials for green OLEDs in terms of
0.9 eV) is higher than those for hole-migration at the HTL/ device performance and thermal properties were greater
Alq3 interface (ca. 0.5 eV), under the present device config- than commonly used NPB. Importantly, BPTF, bearing two
uration of ITO/PEDOT:PSS/HTL(50 nm)/Alq3(50 nm)/ biphenyl moieties attached to the 2,7-positions of the 9,9-
LiF(0.5 nm):Al(200 nm), BPTF, CBPTF, CMBPTF and bis(4-diphenylaminophenyl)fluorene, showed promising po-
BPVTF would act only as HTL, and Alq3 would act prefer- tential as both a deep-blue light-emitting and hole-trans-
ably as an electron blocker more than as a hole blocker and porting material for use in OELD devices. Nondoped deep-
charge recombination thus confined to Alq3 layer. More blue OLEDs with a maximum luminance efficiency of
importantly, a stable emission was obtained from all diodes 2.48 cdA–1, and green OLEDs with maximum luminance
(VI–VIII), with the EL spectra and CIE coordinates re- efficiency of 4.40 cdA–1, were achieved with low turn-on
maining unchanged over the entire applied voltages (see the voltages of 3.1 and 2.8 V, respectively. Notably, the color
Supporting Information). Although many blue-emitting purities of these deep-blue (CIE coordinate of x = 0.15 and
and hole-transporting materials have been reported, in y = 0.07) and green (CIE coordinate of x = 0.28 and y =
terms of the amorphous morphology, high Tg, and device 0.52) devices were close to the NTSC blue and green stan-
efficiency, BPTF is among the best bifunctional materials dards. High EL efficiencies and good color qualities make
available.
these materials very promising for display applications. The
use of this type of molecular platform might be an effective
way to prepare high Tg amorphous materials for long-life-
time device applications, especially for high-temperature ap-
plications in OLEDs or other organic optoelectronic de-
vices.
Conclusions
We have successfully designed and synthesized four new
bifunctional materials, namely BPTF, CBPTF, CMBPTF,
and BPVTF, as nondoped deep-blue light-emitting and
hole-transporting materials for OLEDs. By the use of 9,9-
bis(4-diphenylaminophenyl)fluorene as a molecular plat-
form, we were able to maintain high blue emissive ability of
Experimental Section
General: All reagents were purchased from Aldrich, Acros, or
the fluorene in the solid state, and improve the amorphous Fluka and used without further purification. All solvents were sup-
8
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Bifunctional Materials for Organic Electroluminescent Devices
plied by Thai companies and used without further distillation.
THF was heated to reflux with sodium and benzophenone, and
freshly distilled prior to use. Dichloromethane for cyclic voltamme-
try (CV) measurements was washed with conc. H2SO4 and distilled
twice from calcium hydride. 1H and 13C NMR spectra were re-
corded with a Bruker AVANCE 300 MHz spectrometer. Infrared
(IR) spectra were measured with a Perkin–Elmer FTIR spec-
troscopy Spectrum RXI spectrometer. Ultraviolet-visible (UV/Vis)
spectra were recorded with a Perkin–Elmer UV Lambda 25 spec-
trometer and photoluminescence spectra, and the fluorescence
quantum yields (ΦF) were recorded with a Perkin–Elmer LS 50B
Luminescence Spectrometer as dilute CH2Cl2 solution and thin
film obtained by thermal evaporation. Quinine sulfate solution in
0.01 m H2SO4 (ΦF = 0.54) was used as a reference standard.[36]
Differential scanning calorimetric (DSC) analysis and thermogravi-
were subsequently deposited through a shadow mask on the top of
the EML/HTL film without braking vacuum to form active diode
areas of 4 mm2. Measurement of the device efficiency was per-
formed according to M. E. Thomson’s protocol and external quan-
tum efficiencies of the device were calculated by using the pre-
viously reported procedure.[37] Current density–voltage–lumines-
cence (I–V–L) characteristics were measured simultaneously by the
use of a Keithley 2400 source meter and a Newport 1835C power
meter equipped with a Newport 818-UV/CM calibrated silicon
photodiode. The EL spectra were acquired with an Ocean Optics
USB4000 multichannel spectrometer. All the measurements were
performed under ambient atmosphere at room temperature.
9,9-Bis(4-diphenylaminophenyl)-2,7-dibromofluorene (3): A mixture
of 2 (2.57 g, 6.79 mmol), triphenylamine (16.67 g, 67.99 mmol), and
CH3SO3H (0.45 mL) was heated at 190 °C for 6 h. The cooled mix-
ture was poured into water and the greenish precipitate was filtered,
washed with water, and dried to afford the crude product. Purifica-
tion by column chromatography (silica gel; CH2Cl2/hexane) fol-
lowed by recrystallized (methanol/CH2Cl2) afforded a light white
metric analysis (TGA) were performed with
a METTLER
DSC823e thermal analyzer and a Rigaku TG-DTA 8120 thermal
analyzer, respectively, with a heating rate of 10 °C/min under a ni-
trogen atmosphere. Cyclic voltammetry (CV) measurements were
carried out with an Autolab potentiostat PGSTAT 12 with a three-
electrode system (platinum counter electrode, glassy carbon work-
ing electrode, and Ag/Ag+ reference electrode) at scan rate of
50 mV/s in the presence of tetrabutyl ammonium hexafluorophos-
phate (nBu4NPF6) as a supporting electrolyte in CH2Cl2 under an
argon atmosphere. Melting points were measured with an Electro-
thermal IA 9100 series digital melting point instrument and are
uncorrected. High-resolution mass spectrometry (HRMS) analysis
was performed with a Bruker micrOTOF (Q-ToF II) mass spec-
trometer. Elemental analysis was performed with a PerkinElmer
2400 Series II CHNS/O Elemental Analyzer at Chulalongkorn Uni-
versity.
1
solid (3.72 g, 61%). H NMR (300 MHz, CDCl3): δ = 6.99 (d, J =
9.0 Hz, 4 H), 7.00 (t, J = 9.0 Hz, 8 H), 7.09 (d, J = 9.0 Hz, 8 H),
7.26 (t, J = 9.0 Hz, 8 H), 7.55 (t, J = 9.0 Hz, 4 H), 7.58 (d, J =
9.0 Hz, 2 H) ppm; 13C NMR (75 MHz, CDCl3): δ = 64.65, 121.55,
121.76, 122.77, 123.06, 124.5, 124.68, 128.69, 129.27, 129.38,
130.82, 137.66, 137.98, 146.74, 147.52, 153.47 ppm; HRMS: calcd.
for C49H34Br2N2 808.1089; found 809.1169 [M + H]+.
2,7-Bis[4-(biphenyl-4-yl)]-9,9-bis(4-diphenylaminophenyl)fluorene
(BPTF): A mixture of 3 (0.70 g, 0.86 mmol), 4-biphenylboronic
acid (0.43 g, 2.16 mmol), [Pd(PPh3)4] (99 mg, 0.086 mmol), and an
aqueous Na2CO3 solution (2 m, 10 mL) in THF (15 mL) was de-
gassed with N2 for 5 min. The mixture was heated at reflux under
an N2 atmosphere for 20 h. After the mixture was cooled to room
temperature, water (50 mL) was added and the mixture was ex-
tracted with CH2Cl2 (2ϫ 50 mL). The combined organic phase was
washed with water, brine solution, dried with anhydrous Na2SO4,
filtered, and the solvents were removed to dryness. Purification by
column chromatography (silica gel; CH2Cl2/hexane) followed by
recrystallization (methanol/CH2Cl2) afforded a white solid (0.74 g,
Quantum Chemical Calculations: The ground state geometries of all
molecules were fully optimized by using density functional theory
(DFT) at the B3LYP/6-31G (d,p) level, as implemented in Gaussian
03.[23] TDDFT/B3LYP calculations of the lowest excitation
energies were performed at the optimized geometries of the ground
states.
Fabrication and Characterization of OLEDs: OLED devices using
the synthesized materials as EML with configuration of ITO/PE-
DOT:PSS/EML(50 nm)/BCP(40 nm)/LiF(0.5 nm):Al(150 nm), and
double-layer green OLED devices using the synthesized materials
as HTL with configuration of ITO/PEDOT:PSS/HTL(40 nm)/
Alq3(50 nm)/LiF(0.5 nm):Al(150 nm) were fabricated and charac-
terized as follows. The patterned indium tin oxide (ITO) glass sub-
strate with a sheet resistance 14 Ω/square (purchased from Kintec
company) was thoroughly cleaned by successive ultrasonic treat-
ment in detergent, deionized water, 2-propanol, and acetone, and
then dried at 60 °C in a vacuum oven. A 50 nm thick PEDOT:PSS
hole injection layer was spin-coated on top of the ITO from a 0.75
wt.-% dispersion in water at a spin speed of 3000 rpm for 20 s and
dried at 200 °C for 15 min under vacuum. Thin films of each or-
ganic EML or HTL were deposited on top of the PEDOT:PSS
layer by evaporation from resistively heated alumina crucibles at an
evaporation rate of 0.5–1.0 nm s–1 in vacuo evaporator deposition
(ES280, ANS Technology) under a base pressure of ca. 10–5 mbar.
The film thickness was monitored and recorded with a quartz oscil-
lator thickness meter (TM-350, MAXTEK). A 40 nm thick hole-
blocking layer of BCP or a 50 nm thick green-emitting layer of
Alq3 was then deposited on the organic EML or HTL, respectively,
without breaking the vacuum chamber. The chamber was vented
with dry air to load the cathode materials and pumped back; a
0.5 nm thick layer of LiF and a 150 nm thick layer of aluminum
90%); m.p. Ͼ250 °C. FTIR (KBr): ν = 3415, 3030, 1600, 1480,
˜
1
1300, 813, 751 cm–1. H NMR (300 MHz, CDCl3): δ = 6.94–7.01
(m, 8 H), 7.08 (d, J = 7.80 Hz, 8 H), 7.19–7.25 (m, 12 H), 7.35–
7.40 (m, 2 H), 7.48 (t, J = 7.80 Hz, 4 H), 7.64–7.73 (m, 16 H), 7.80
(d, J = 7.80 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 64.76,
120.58, 122.83, 123.07, 124.51, 124.88, 126.64, 127.08, 127.40,
127.55, 127.59, 128.87, 128.98, 139.08, 139.44, 140.19, 140.30,
140.70, 146.35, 147.67, 152.65 ppm. HRMS: calcd. for C73H52N2
956.4130; found 955.1625 [M+]; C73H52N2 (957.23): calcd. C 91.60,
H 5.48, N 2.93; found C 91.69, H 5.47, N 2.80.
2,7-Bis[4-(biphenyl-4-yl)vinylene]-9,9-bis(4-diphenylaminophenyl)-
fluorene (BPVTF): Synthesized from 3 (0.5 g, 0.62 mmol) and
trans-2-(4-biphenyl)vinyleneboronic acid (0.29 g, 1.30 mmol) in a
similar manner to BPTF, and obtained as a yellow solid (0.40 g,
71%); m.p. Ͼ250 °C. FTIR (KBr): ν = 3410, 3026, 1590, 1470,
˜
1325, 1275, 827, 760 cm–1. 1H NMR (300 MHz, CDCl3): δ = 6.96–
7.03 (m, 9 H), 7.10 (d, J = 8.10 Hz, 9 H), 7.15–7.26 (m, 15 H),
7.34–7.39 (m, 2 H), 7.47 (t, J = 7.80 Hz, 4 H), 7.58–7.67 (m, 15
H), 7.76 (d, J = 7.80 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3):
δ = 64.10, 120.40, 122.84, 123.00, 124.52, 125.94, 126.90, 127.34,
127.86, 128.80, 128.97, 129.11, 129.19, 136.43, 136.93, 139.27,
139.49, 140.26, 140.65, 146.33, 147.67, 152.58 ppm. HRMS: calcd.
for C77H56N2 1008.4443; found 1009.6281 [M+]; C77H56N2
Eur. J. Org. Chem. 0000, 0–0
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FULL PAPER
(1009.30): calcd. C 91.63, H 5.59, N 2.78; found C 91.33, H 5.47,
N 2.90.
4-[4Ј-(Carbazol-9-yl)-2-methylbiphenyl]-4,4,5,5-tetramethyl-1,3,2-di-
oxaborolane (5): Synthesized from 10 (2.80 g, 6.79 mmol) in a sim-
ilar manner to 4, and obtained as a white solid (2.21 g, 71%). FTIR
4-Bromo-4Ј-(carbazol-9-yl)biphenyl (7): A mixture of carbazole
(3.35 g, 20.03 mmol), 6 (25.00 g, 80.13 mmol), K2CO3 (5.53 g,
40.06 mmol), Cu powder (1.27 g, 20.03 mmol), and 18-crown-6
(0.79 g, 3.04 mmol) in o-dichlorobenzene (90 mL) was stirred and
heated at reflux under an N2 atmosphere for 44 h. The solvent was
completely removed under vacuum to give a brown residue that
was then dissolved in CH2Cl2 (100 mL) and water (100 mL). The
organic phase was separated and washed with water, brine solution,
dried with anhydrous Na2SO4, filtered, and the solvents were re-
moved to dryness. Purification by column chromatography (silica
get; CH2Cl2/hexane) gave a white solid (5.10 g, 64%). FTIR (KBr):
1
(KBr): ν = 3414, 1611, 1521, 1425, 1359, 1316, 1099, 852 cm–1. H
˜
NMR (300 MHz, CDCl3): δ = 1.43 (s, 12 H), 2.42 (s, 3 H), 7.29–
7.47 (m, 4 H), 7.50–7.64 (m, 7 H), 7.77 (d, J = 7.5 Hz, 1 H), 7.81 (s,
1 H), 8.17 (d, J = 7.5 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ
= 20.35, 24.90, 83.88, 109.87, 119.97, 120.32, 123.43, 125.95,
126.65, 129.33, 130.53, 132.39, 134.71, 136.52, 136.98, 140.88,
140.97, 143.00 ppm. HRMS: calcd. for C31H30BNO2 459.2370;
found 459.5677 [M+].
2,7-Bis[4-(carbazol-9-yl)-4-biphenyl-4-yl]-9,9-bis(4-diphenylamino-
phenyl)fluorene (CBPTF): Synthesized from 3 (0.50 g, 0.62 mmol)
and 4 (0.64 g, 1.35 mmol) in a similar manner to BPTF, and ob-
tained as a white solid (0.60 g, 75%); m.p.Ͼ 250 °C. FTIR (KBr):
ν = 3413, 1604, 1526, 1450, 1335, 1231, 1077, 1002 cm–1. 1H NMR
˜
(300 MHz, CDCl3): δ = 7.31 (t, J = 7.50 Hz, 2 H), 7.41–7.49 (m, 4
H), 7.56 (d, J = 8.70 Hz, 2 H), 7.62–7.67 (m, 4 H), 7.79 (d, J =
8.40 Hz, 2 H), 8.17 (d, J = 7.50 Hz, 2 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 109.79, 120.08, 120.37, 121.98, 123.49, 126.01, 127.46,
127.51, 128.08, 128.34, 128.53, 128.72, 132.03, 132.10, 137.29,
139.04, 139.20, 139.31, 140.80 ppm. HRMS: calcd. for C24H16BrN
397.0466; found 397.5682 [M+].
ν = 3412, 3027, 1617, 1491, 1275, 812, 748 cm–1 1H NMR
.
˜
(300 MHz, CDCl3): δ = 6.98–7.03 (m, 8 H), 7.11 (d, J = 7.80 Hz,
8 H), 7.22–7.28 (m, 10 H), 7.34 (t, J = 7.20 Hz, 4 H), 7.48–7.54
(m, 8 H), 7.72–7.82 (m, 16 H), 7.87–7.93 (m, 8 H), 8.19 (d, J =
7.80 Hz, 4 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 62.80, 109.87,
120.02, 120.35, 120.64, 122.88, 123.05, 123.46, 124.54, 124.88,
125.99, 126.68, 127.41, 127.52, 127.75, 128.38, 128.98, 129.21,
4-Bromo-4Ј-(carbazol-9-yl)-2-methylbiphenyl (10): A mixture of 9
(3.65 g, 9.88 mmol), 5-bromo-2-iodotoluene (3.50 g, 11.86 mmol), 137.00, 139.19, 139.39, 139.72, 140.09, 140.64, 140.86, 147.66,
and K2CO3 (8.19 g, 59.30 mmol) in a mixture of THF (60 mL) and 152.74 ppm. HRMS: calcd. for C97H66N4 1287.5321; found
water (20 mL) was stirred and degassed with N2 for 5 min and then
[Pd(PPh3)4] (0.57 g, 0.49 mmol) was added. The reaction mixture
was heated to reflux under an N2 atmosphere for 18 h. After the
mixture was cooled to room temperature, water (100 mL) was
added and the mixture was extracted with CH2Cl2 (2ϫ 70 mL).
The combined organic phase was washed with water, brine solu-
tion, dried with anhydrous Na2SO4, filtered, and the solvents were
removed to dryness. The crude residue was purified by column
chromatography (silica gel; CH2Cl2/hexane) to give a white solid
1287.2800 [M+]; C97H66N4 (1287.62): calcd. C 90.48, H 5.17, N
4.35; found C 90.62, H 5.00, N 4.35.
2,7-Bis[4-(carbazol-9-yl)-2-methylbiphenyl-4-yl]-9,9-bis(4-diphenyl-
aminophenyl)fluorene (CMBPTF): Synthesized from
3 (0.5 g,
0.62 mmol) and 5 (0.62 g, 1.35 mmol) in a similar manner to BPTF,
and obtained as a white solid (0.67 g, 82%); m.p. 216 °C. FTIR
1
(KBr): ν = 3410, 3032, 1590, 1500, 1464, 1275, 814, 748 cm–1. H
˜
NMR (300 MHz, CDCl3): δ = 2.51 (s, 4 H), 6.98–7.03 (m, 8 H),
7.11 (d, J = 7.80 Hz, 8 H), 7.23 (d, J = 8.10 Hz, 10 H), 7.34 (t, J
= 7.20 Hz, 4 H), 7.47 (t, J = 7.80 Hz, 8 H), 7.53–7.68 (m, 16 H),
7.71–7.76 (m, 4 H), 7.91 (d, J = 7.80 Hz, 2 H), 8.19 (d, J = 7.80 Hz,
4 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 20.87, 60.05, 109.87,
120.02, 120.35, 120.64, 122.88, 123.05, 123.46, 124.54, 124.88,
125.99, 126.68, 127.41, 127.52, 127.75, 128.38, 128.98, 129.21,
137.00, 139.19, 139.39, 139.72, 140.09, 140.64, 140.86, 147.66,
152.74 ppm. HRMS: calcd. for C99H70N4 1315.5634; found
1315.8442 [M+]; C99H70N4 (1315.67): calcd. C 90.38, H 5.36, N
4.26; found C 89.95, H 5.09, N 4.67.
(3.15 g, 77%). FTIR (KBr): ν = 3412, 1605, 1528, 1490, 1453, 1336,
˜
1
1232, 1077, 1003 cm–1. H NMR (300 MHz, CDCl3): δ = 2.40 (s,
3 H), 7.23–7.36 (m, 1 H), 7.44–7.56 (m, 10 H), 7.66 (d, J = 9.00 Hz,
2 H), 8.20 (d, J = 9.00 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3):
δ = 20.35, 109.79, 120.08, 120.37, 121.98, 123.49, 126.01, 127.46,
127.51, 128.08, 128.34, 128.53, 128.72, 132.03, 132.10, 137.29,
139.04, 139.20, 139.31, 142.81 ppm. HRMS: calcd. for C25H18BrN
411.0623; found 411.3369 [M+].
2-[4-(Carbazol-9-yl)-biphenyl]-4,4,5,5-tetramethyl-1,3,2-dioxa-
borolane (4): A solution of 7 (3.00 g, 7.53 mmol) in THF (150 mL)
was degassed with N2 and cooled to –78 °C in a dry-ice/acetone
bath. nBuLi (1.6 m in hexane, 9.41 mL, 15.06 mmol) was added by
using a syringe and the mixture was stirred at room temperature
for 20 min. The mixture was cooled to –78 °C in an dry-ice/acetone
bath and 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
(1.68 g, 9.03 mmol) was added. The reaction mixture was warmed
to room temperature and stirred overnight. Water (50 mL) was
added and the mixture was extracted with CH2Cl2 (3ϫ 50 mL).
The combined organic phased was washed with water, brine solu-
tion, dried with anhydrous Na2SO4, filtered, and the solvents were
removed to dryness. Recrystallization (CH2Cl2/hexane) gave a
Supporting Information (see footnote on the first page of this arti-
cle): Synthesis of 2, quantum calculation results, DSC-TGA and
CV curves, energy diagrams, and EL spectra of the fabricated
1
OLEDs, and H NMR and 13C NMR spectra.
Acknowledgments
This work was financially supported by the Thailand Research
Fund (RMU5080052). We acknowledge the scholarship support
from the Center of Excellence for Innovation in Chemistry
(PERCH-CIC), Ubon Ratchathani University, and the Strategic
Scholarships for Frontier Research Network for Research Groups
(CHE-RES-RG50) from the Office of the Higher Education Com-
mission, Thailand.
white solid (2.85 g, 85%). FTIR (KBr): ν = 3415, 1610, 1529, 1452,
˜
1360, 1255, 1142, 1091, 1007 cm–1. 1H NMR (300 MHz, CDCl3):
δ = 2.42 (s, 12 H), 7.31 (t, J = 7.5 Hz, 2 H), 7.41–7.50 (m, 4 H),
7.66 (d, J = 7.8 Hz, 2 H), 7.72 (d, J = 7.5 Hz, 2 H), 7.86 (d, J =
7.8 Hz, 2 H), 7.97 (d, J = 7.5 Hz, 2 H), 8.17 (d, J = 7.5 Hz, 2
H) ppm. 13C NMR (75 MHz, CDCl3): δ = 24.92, 83.93, 109.85,
120.00, 120.33, 123.46, 125.98, 126.43, 127.34, 128.61, 135.44,
137.17, 140.09, 140.85, 142.88 ppm. HRMS: calcd. for
C30H28BNO2 445.2213; found 446.0125 [M + H+].
[1] a) B. W. D’Andrade, S. R. Forrest, Adv. Mater. 2004, 16, 1585–
1595; b) A. C. Grimsdale, K. L. Chan, R. E. Martin, P. G. Jok-
isz, A. B. Holmes, Chem. Rev. 2009, 109, 897–1091; c) S.-C. Lo,
P. L. Burn, Chem. Rev. 2007, 107, 1097–1116.
10
www.eurjoc.org
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Bifunctional Materials for Organic Electroluminescent Devices
[2]
[17]
[18]
[19]
M. Surin, E. Hennebicq, C. Ego, D. Marsitzky, A. C.
Grimsdale, K. Müllen, J.-L. Brédas, R. Lazzaroni, P. Leclère,
Chem. Mater. 2004, 16, 994–1001.
S. B. Jiao, Y. Liao, X. J. Xu, L. P. Wang, G. Yu, L. M. Wang,
Z. M. Su, S. H. Ye, Y. Q. Liu, Adv. Funct. Mater. 2008, 18,
2335–2347.
a) H.-G. Li, G. Wu, M.-M. Shi, H.-Z. Chen, M. Wang, Synth.
Met. 2010, 160, 1648–1653; b) Z. H. Li, M. S. Wong, H. Fukut-
ani, Y. Tao, Org. Lett. 2006, 8, 4271–4274; c) A. Thangthong,
N. Prachumrak, R. Tarsang, T. Keawin, S. Jungsuttiwong, T.
Sudyoadsuk, V. Promarak, J. Mater. Chem. 2012, 22, 6869–
6877.
a) K.-T. Wong, Z.-J. Wang, Y.-Y. Chien, C.-L. Wang, Org. Lett.
2001, 3, 2285–2288; b) M. E. El-Khouly, Y. Chen, X. Zhuang,
S. Fukuzumi, J. Am. Chem. Soc. 2009, 131, 6370–6371.
N. Matsumoto, T. Miyazaki, M. Nishiyama, C. Adachi, J.
Phys. Chem. C 2009, 113, 6261–6266.
a) C.-H. Wu, C.-H. Chien, F.-M. Hsu, P.-I. Shih, C.-F. Shu, J.
Mater. Chem. 2009, 19, 1464–1470; b) Z. Zhao, C. Deng, S.
Chen, J. W. Y. Lam, W. Qin, P. Lu, Z. Wang, H. S. Kwok, Y.
Ma, H. Qiu, B. Z. Tang, Chem. Commun. 2011, 47, 8847–8849;
c) Y.-M. Shen, G. Grampp, N. Leesakul, H.-W. Hu, J.-H. Xu,
Eur. J. Org. Chem. 2007, 3718–3726; d) S.-H. Liao, J.-R. Shiu,
S.-W. Liu, S.-J. Yeh, Y.-H. Chen, C.-T. Chen, T. J. Chow, C.-I.
Wu, J. Am. Chem. Soc. 2009, 131, 763–777.
A. W. Grice, D. D. C. Bradley, M. T. Bernius, M. Inbasekaran,
W. W. Wu , E . P. Wo o, Appl. Phys. Lett. 1998, 73, 629–631.
a) W. B. Im, H. K. Hwang, J. G. Lee, K. Han, Y. Kim, Appl.
Phys. Lett. 2001, 79, 1387–1389.
[3]
[4]
[5]
[20]
a) T. Kumchoo, V. Promarak, T. Sudyoadsuk, M. Sukwattanas-
initt, P. Rashatasakhon, Chem. Asian J. 2010, 5, 2162–2167; b)
J.-F. Gu, G.-H. Xie, L. Zhang, S.-F. Chen, Z.-Q. Lin, Z.-S.
Zhang, J.-F. Zhao, L.-H. Xie, C. Tang, Y. Zhao, S.-Y. Liu, W.
Huang, J. Phys. Chem. Lett. 2010, 1, 2849–2853; c) J. Hu, M.
Era, M. R. J. Elsegood, T. Yamato, Eur. J. Org. Chem. 2010,
72–79; d) G. Venkataramana, S. Sankararaman, Eur. J. Org.
Chem. 2005, 4162–4166.
a) A. Thangthong, D. Meunmart, N. Prachumrak, S. Jungsutti-
wong, T. Keawin, T. Sudyoadsuk, V. Promarak, Chem. Com-
mun. 2011, 47, 7122–7124; b) J. W. Park, P. Kang, H. Park,
H. Y. Oh, J. H. Yang, Y. H. Kim, S. K. Kwon, Dyes Pigm. 2010,
85, 93–98; c) H. Huang, Q. Fu, S. Zhuang, Y. Liu, L. Wang, J.
Chen, D. Ma, C. Yang, J. Phys. Chem. C 2011, 115, 4872–4878.
a) K. Okumoto, Y. Shirota, Chem. Mater. 2003, 15, 699–707;
b) J. Y. Shen, C. Y. Lee, T. H. Huang, J. T. Lin, Y. T. Tao, C. H.
Chien, C. Tsai, J. Mater. Chem. 2005, 15, 2455–2463; c) K. H.
Lee, S. O. Kim, S. Kang, J. Y. Lee, K. S. Yook, J. Y. Lee, S. S.
Yoon, Eur. J. Org. Chem. 2012, 2748–2755.
a) T. Qin, W. Wiedemair, S. Nau, R. Trattnig, S. Sax, S. Wink-
ler, A. Vollmer, N. Koch, M. Baumgarten, E. J. W. List, K.
Müllen, J. Am. Chem. Soc. 2011, 133, 1301–1303; b) F. Liu, L.-
H. Xie, C. Tang, J. Liang, Q.-Q. Chen, B. Peng, W. Wei, Y.
Cao, W. Huang, Org. Lett. 2009, 11, 3850–3853.
a) D. Gebeyehu, K. Walzer, G. He, M. Pfeiffer, K. Leo, J.
Brandt, A. Gerhard, P. Stößel, H. Vestweber, Synth. Met. 2005,
148, 205–211; b) Q. D. Liu, J. Lu, J. Ding, M. Day, Y. Tao, P.
Barrios, J. Stupak, K. Chan, J. Li, Y. Chi, Adv. Funct. Mater.
2007, 17, 1028–1036.
a) S.-I. Kawano, C. Yang, M. Ribas, S. Baluschev, M.
Baumgarten, K. Müllen, Macromolecules 2008, 41, 7933–7937;
b) Z. Q. Gao, Z. H. Li, P. F. Xia, M. S. Wong, K. W. Cheah,
C. H. Chen, Adv. Funct. Mater. 2007, 17, 3194–3199; c) K. H.
Lee, S. O. Kim, K. S. Yook, S. O. Jeon, J. Y. Lee, S. S. Yoon,
Synth. Met. 2011, 161, 2024–2030; d) F. Liu, C. Tang, Q. Q.
Chen, F. F. Shi, H. B. Wu, L. H. Xie, B. Peng, W. Wei, Y. Cao,
W. Huang, J. Phys. Chem. C 2009, 113, 4641–4647; e) S. Tao,
Y. Zhou, C.-S. Lee, X. Zhang, S.-T. Lee, Chem. Mater. 2010,
22, 2138–2141.
[21]
[22]
a) Z. Peng, S. Tao, X. Zhang, J. Tang, C. S. Lee, S.-T. Lee, J.
Phys. Chem. C 2008, 112, 2165–2169; b) M. R. Craig, M. M.
de Kok, J. W. Hofstraat, A. P. H. J. Schenning, E. W. Meijer, J.
Mater. Chem. 2003, 13, 2861–2862.
[6]
[23]
M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Mont-
gomery Jr., R. E. Stratmann, J. C. Burant, S. Dapprich, J. M.
Millam, A. D. Daniels, K. N. Kudin, M. C. Strain, O. Farkas,
J. Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C.
Pomelli, C. Adamo, S. Clifford, J. Ochterski, G. A. Petersson,
P. Y. Ayala, Q. Cui, K. Morokuma, P. Salvador, J. J. Dannen-
berg, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B.
Foresman, J. Cioslowski, J. V. Ortiz, A. G. Baboul, B. B. Ste-
fanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gom-
perts, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y.
Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B.
Johnson, W. Chen, M. W. Wong, J. L. Andres, C. Gonzalez, M.
Head-Gordon, E. S. Replogle, J. A. Pople, Gaussian 98, revision
A.7 Gaussian, Inc., Pittsburgh, PA, 1998.
a) V. Promarak, M. Ichikawa, T. Sudyoadsuk, S. Saengsuwan,
T. Keawin, Opt. Mater. 2007, 30, 364–369; b) D. Seka, E. Grab-
ieca, H. Janeczeka, B. Jarzabeka, B. Kaczmarczyka, M. Dom-
anskia, A. Iwan, Opt. Mater. 2010, 32, 1514–1525.
R. Fink, Y. Heischkel, M. Thelakkat, H. Schmidt, Chem. Ma-
ter. 1998, 10, 3620–3625.
K. T. Kamtekar, C. Wang, S. Bettington, A. S. Batsanov, I. F.
Perepichka, M. R. Bryce, J. H. Ahn, M. Rabinal, M. C. Petty,
J. Mater. Chem. 2006, 16, 3823–3835.
S. Kirchmeyer, K. Reuter, J. Mater. Chem. 2005, 15, 2077–
2088.
W. Kim, G. Kushto, G. Kim, Z. Kafafi, Polym. Sci. B: Polym.
Phys. 2003, 41, 2522–2528.
a) K. L. Chan, M. Sims, S. I. Pascu, M. Ariu, A. B. Holmes,
D. D. C. Bradley, Adv. Funct. Mater. 2009, 19, 2147–2154; b)
R. Abbel, M. Wolffs, R. A. A. Bovee, J. L. J. van Dongen, X.
Lou, O. Henze, W. J. Feast, E. W. Meijer, A. P. H. J. Schenning,
Adv. Mater. 2009, 21, 597–602.
[7]
[8]
[24]
[9]
[25]
[26]
[10]
[27]
[28]
[29]
[11]
a) U. Scherf, D. Neher (Eds.), Advances in Polymer Science
2008, 212 XII, 322 p. 234; b) R. Grisorio, G. Allegretta, P.
Mastrorilli, G. P. Suranna, Macromolecules 2011, 44, 7977–
7986.
M. Gross, D. C. Müller, H.-G. Nothofer, U. Scherf, D. Neher,
C. Bräuchle, K. Meerholz, Nature 2000, 405, 661–665.
D. Sainova, T. Miteva, H. G. Nothofer, U. Scherf, I. Glowacki,
J. Ulanski, H. Fujikawa, D. Neher, Appl. Phys. Lett. 2000, 76,
1810–1812.
T. Miteva, A. Meisel, W. Knoll, H. G. Nothofer, U. Scherf,
D. C. Müller, K. Meerholz, A. Yasuda, D. Neher, Adv. Mater.
2001, 13, 565–570.
a) C.-S. Wu, Y. Chen, J. Mater. Chem. 2010, 20, 7700–7709; b)
J.-I. Lee, H. Y. Chu, H. Lee, J. Oh, L.-M. Do, T. Zyung, J. Lee,
H.-K. Shim, ETRI J. 2005, 27, 181–187.
[30]
a) K. Itano, H. Ogawa, Y. Shirota, Appl. Phys. Lett. 1998, 72,
636–638; b) J. Feng, F. Li, W. B. Gao, S. Y. Liu, Y. Liu, Y.
Wang, Appl. Phys. Lett. 2001, 78, 3947–3949.
[12]
[13]
[31]
[32]
U. Mitschke, P. Bäuerle, J. Mater. Chem. 2000, 10, 1471–1507.
a) S.-A. Chen, T.-H. Jen, H.-H. Lu, J. Chin. Chem. Soc. 2010,
57, 439–458; b) K. H. Lee, S. M. Kim, J. Y. Kim, Y. K. Kim,
S. S. Yoon, Bull. Korean Chem. Soc. 2010, 31, 2884–2888; c)
K. T. Kamtekar, A. P. Monkman, M. R. Bryce, Adv. Mater.
2010, 22, 572–582.
a) V. N. Bliznyuk, S. A. Carter, J. C. Scott, G. Klarner, R. D.
Miller, D. C. Miller, Macromolecules 1999, 32, 361–369; b)
L. M. Herz, R. T. Phillips, Phys. Rev. B 2000, 61, 13691–13697;
c) I. Prieto, J. Teetsov, M. A. Fox, D. A. V. Bout, A. J. Bard, J.
Phys. Chem. A 2001, 105, 520–523; d) G. Zeng, W. L. Yu, S. J.
Chua, W. Huang, Macromolecules 2002, 35, 6907–6914.
[14]
[15]
[16]
[33]
C. Ego, A. C. Grimsdale, F. Uckert, G. Yu, G. Srdanov, K.
Müllen, Adv. Mater. 2002, 14, 809–811.
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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V. Promarak et al.
FULL PAPER
[34] a) A. Thaengthong, S. Saengsuwan, S. Jungsuttiwong, T. Kea-
win, T. Sudyoadsuk, V. Promarak, Tetrahedron Lett. 2011, 52,
4749–4752; b) Y. K. Kim, S.-H. Hwang, Synth. Met. 2006, 156,
1028–1035.
[36]
T. Kartens, K. Kobs, J. Phys. Chem. 1980, 84, 1871–1872.
[37] S. R. Forrest, D. D. C. Bradley, M. E. Thomson, Adv. Mater.
2003, 15, 1043–1048.
Received: May 14, 2012
[35] D. Y. Kim, H. N. Cho, C. Y. Kim, Prog. Polym. Sci. 2000, 25,
Published Online: ᭿
1089–1139.
12
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Job/Unit: O20641
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Date: 02-08-12 11:49:24
Pages: 13
Bifunctional Materials for Organic Electroluminescent Devices
Bifunctional Materials
Newly designed biphenyl functionalized
9,9-bis(4-diphenylaminophenyl)fluorenes
show promising potential as deep-blue
emitters and hole-transporters for OLEDs.
Efficient nondoped deep-blue and Alq3-
based green OLEDs with maximum lumin-
ance efficiencies of 2.48 and 4.40 cd/A are
achieved, respectively
A.-m. Thangthong, N. Prachumrak,
S. Namuangruk, S. Jungsuttiwong,
T. Keawin, T. Sudyoadsuk,
V. Promarak* .................................. 1–13
Synthesis, Properties and Applications of
Biphenyl Functionalized 9,9-Bis(4-di-
phenylaminophenyl)fluorenes as Bifunc-
tional Materials for Organic Electrolumi-
nescent Devices
Keywords: Hyperconjugation
/ UV/Vis
spectroscopy / Biaryls / Semiconductors /
Photochromism / Light-emitting diodes
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
13