Highly efficient dual-core derivatives with EQEs as high as 8.38% at high brightness for OLED blue emitters

Article abstract of DOI:10.1039/c9tc04603h

Three blue fluorescent materials were newly synthesized by attaching triphenylamine side groups at their ortho, meta, and para positions to a dual core moiety of anthracene and pyrene, two chromophores with good luminous efficiency; these three materials were 2-(6-(10-(2-(diphenylamino)phenyl)anthracen-9-yl)pyren-1-yl)-N,N-diphenylaniline (o-TPA-AP-TPA), 3-(6-(10-(3-(diphenylamino)phenyl)anthracen-9-yl)pyren-1-yl)-N,N-diphenylaniline (m-TPA-AP-TPA), and 4-(6-(10-(4-(diphenylamino)phenyl)anthracen-9-yl)pyren-1-yl)-N,N-diphenylaniline (p-TPA-AP-TPA), respectively. The optical, thermal, and electroluminescence (EL) properties of the synthesized materials were measured. All three materials were found to be real blue emitters in the solution state and display high PLQY values. A device doped with p-TPA-AP-TPA displayed a very high efficiency of 9.14 cd A^-1 and an EQE of 8.38% at a high luminance of 5000 cd m^-2.

Full text of DOI:10.1039/c9tc04603h

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Materials Chemistry C
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Highly efficient dual-core derivatives with EQEs as
high as 8.38% at high brightness for OLED blue
emitters†
Cite this: J. Mater. Chem. C, 2019,
7, 14709
b
Seokwoo Kang,a Hyocheol Jung,a Hayoon Lee,a Sunwoo Park,a Joonghan Kim
a
and Jongwook Park
*
Three blue fluorescent materials were newly synthesized by attaching triphenylamine side groups at their
ortho, meta, and para positions to a dual core moiety of anthracene and pyrene, two chromophores with
good luminous efficiency; these three materials were 2-(6-(10-(2-(diphenylamino)phenyl)anthracen-9-yl)-
pyren-1-yl)-N,N-diphenylaniline (o-TPA-AP-TPA), 3-(6-(10-(3-(diphenylamino)phenyl)anthracen-9-yl)pyren-
1-yl)-N,N-diphenylaniline (m-TPA-AP-TPA), and 4-(6-(10-(4-(diphenylamino)phenyl)anthracen-9-yl)pyren-1-
yl)-N,N-diphenylaniline (p-TPA-AP-TPA), respectively. The optical, thermal, and electroluminescence (EL)
properties of the synthesized materials were measured. All three materials were found to be real blue
emitters in the solution state and display high PLQY values. A device doped with p-TPA-AP-TPA displayed
Received 20th August 2019,
Accepted 22nd October 2019
DOI: 10.1039/c9tc04603h
a very high efficiency of 9.14 cd AÀ1 and an EQE of 8.38% at a high luminance of 5000 cd mÀ2
.
rsc.li/materials-c
although they do display excellent efficiency levels.10–18 Extensive
research was conducted on TADF materials from the time TADF
Introduction
Organic light-emitting diodes (OLEDs) have received much theory was established by Adachi until recently. However, these
attention in industry and academia since their development materials have not yet been commercialized due to their short
was first reported in 1987 by Tang and Vanslyke. OLEDs have device lifetimes and roll-off phenomenon similar to that of blue
been successfully applied to televisions, mobile phones, and phosphorescent materials, as well as due to the low purity of
lighting devices because of their self-luminance, fast response, their emitted color resulting from their large full width at half
flexibility, and full-color emission ability.1–7 Full-color OLED maximum (FWHM).19–24
displays require red, green, and blue emitters with pure color
For industrial application of OLED displays, there is a need
emission, high efficiency, thermal stability, and long device to develop a stable blue-light-emitting dopant that is highly
lifetime. Unlike the cases of red and green light emitters, hole efficient at high brightness without roll-off. In our previous
and electron injections are difficult to achieve in blue light work, we studied the use of dual-core and fused-core-type emitters
emitters due to their wide intrinsic band gaps, and the proper- combining two chromophores as emitting materials.25–29 In the
ties of blue light emitters are inferior to those of emitters of current work, we designed a new blue-light-emitting material
light of other colors.8,9 Materials displaying blue phosphores- including a dopant to enhance the color purity of the light emitted
cence and those displaying thermally activated delayed fluores- and to realize stable efficiency without roll-off at high brightness.
cence (TADF) have been continuously studied as alternatives to We used the following strategy to design the new emitter. (1) We
blue fluorescent materials. However, it has been difficult to used a dual core combining anthracene and pyrene, which are
develop host and dopant materials having a triplet energy chromophores with high luminous efficiency levels. In a previous
corresponding to blue phosphorescence color. And blue phos- study, we observed that using this dual core rather than a single
phorescent and TADF materials are also limited by the roll-off core outstanding EL efficiency and long lifetime were obtained,
phenomenon and short device lifetimes at high luminance and these advantages were attributed to both anthracene and
pyrene contributing to the absorption and emission processes.25,27
(2) We used a triphenylamine (TPA) group as a side group
because it contains a nitrogen atom capable of improving the
charge transfer. Also, the use of bulky TPA as a side group
yielded a twisted molecular structure, preventing intermolecular
a Department of Chemical Engineering, Kyunghee University, Gyeonggi-do, 17104,
Korea. E-mail: jongpark@khu.ac.kr
b Department of Chemistry, The Catholic University, Gyeonggi-do, 14662, Korea.
E-mail: joonghankim@catholic.ac.kr
interactions. (3) We attached the TPA substituent at its ortho,
meta, and para positions to the dual core to provide a series of
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c9tc04603h
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isomers with varying conjugation lengths and bulkiness levels, and 461 nm, respectively, all in the blue region. In the film
and in this way developed a means of controlling the emission of state, o-TPA-AP-TPA, m-TPA-AP-TPA, and p-TPA-AP-TPA exhibited
light in the blue region.30
UVmax values of 408, 404, and 405 nm and PLmax values of 463,
457, and 473 nm, respectively, in the blue region. Of the synthe-
sized materials, m-TPA-AP-TPA displayed the most blue-shifted
emission in both solution and film states. This result was
attributed to linkage through the meta position producing the
weakest electron-donating effect of the side group. For the three
compounds, the full width at half maximum (FWHM) values of
the PL peaks ranged from 55 to 66 nm, and differed by only about
1 nm between the solution and film states. Generally, chromo-
phore compounds in the film state pack extensively with each
other, which generates a variety of PL transitions and leads to a
greater FWHM compared to that in the solution state. However,
all three compounds studied here had highly twisted chemical
structures in their core and side positions, preventing strong
intermolecular packing of chromophores in the film state. Thus,
all three compounds exhibited similar absorptions and emissions
in the film and solution states.
Gaussian density functional theory (DFT) calculations were
carried out to predict the most likely conformations and in
particular dihedral angles adopted by the three compounds
(Fig. S2, ESI†). The dihedral angles of the a, b, and g directions
between the dual core and triphenylamine were in the range of
54.7–101.81, indicating a highly twisted molecular structure.
The absolute PLQY values were measured for 1 wt% of each
emitter dispersed in poly(methyl methacrylate) (PMMA) films,
and the results are shown in Table 1. Of the three compounds,
p-TPA-AP-TPA had the highest PLQY of 85%, which was expected
to achieve a high EL performance.
Results and discussion
Molecular design, synthesis, and optical properties
In previous studies, we reported the characteristics of OLED
materials having an anthracene–pyrene dual core. We have also
compared the characteristics of anthracene and pyrene each
as single-core emitters with the characteristics of a dual-core
emitter including anthracene and pyrene.26 In the present
study, the TPA side group was attached to the dual core
structure (Fig. 1), since this side group can hinder intermole-
cular packing and donate electrons to the core to increase the
EL efficiency. In addition, we varied the linkage position of the
TPA group to investigate its effects on the optical, thermal, and
electrical properties of the resulting emitters.
The structures of the synthesized compounds were confirmed
using nuclear magnetic resonance (NMR) spectroscopy, elemental
analysis (EA), and mass analysis. The three compounds, denoted
as o-TPA-AP-TPA, m-TPA-AP-TPA, and p-TPA-AP-TPA, were each
synthesized by a Suzuki aryl–aryl coupling reaction, as shown
in Fig. S1 (ESI†). The synthetic method is described in the
Experimental section.
The UV-visible (UV-vis) absorption spectra and photolumi-
nescence (PL) spectra of the synthesized compounds are shown
in Fig. 2. Table 1 summarizes their optical, thermal, and electrical
properties. In the solution state, o-TPA-AP-TPA, m-TPA-AP-TPA,
and p-TPA-AP-TPA showed UVmax values of 405, 400, and 400 nm,
respectively; their spectra were similar in shape and showed the
typical vibronic absorption of anthracene. The PLmax values of
o-TPA-AP-TPA, m-TPA-AP-TPA, and p-TPA-AP-TPA were 457, 445,
To understand the PL efficiency differences between the
three structures, their time-resolved PL spectra were recorded
and are shown in Fig. S3 (ESI†). The related constants were
calculated and are summarized in Table S1 (ESI†). The radiative
and non-radiative rate constants (krad and knr) of the synthesized
compounds were calculated based on the results of fluorescence
lifetime measurements. The fluorescence lifetimes of o-TPA-AP-TPA,
m-TPA-AP-TPA, and p-TPA-AP-TPA were 6.78, 1.89, and 0.78 ns,
respectively. p-TPA-AP-TPA showed faster decay than o-TPA-AP-TPA
and m-TPA-AP-TPA. o-TPA-AP-TPA showed a krad of 0.66 Â 108 sÀ1
Fig. 1 Chemical structures of the synthesized light-emitting materials.
Fig. 2 UV-visible absorption spectra and PL spectra of the synthesized materials (a) in toluene solution (1.0 Â 10À5 M) and (b) thin film state.
14710 | J. Mater. Chem. C, 2019, 7, 14709--14716
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Table 1 Optical, thermal, and electrical properties of the synthesized compounds
Solutiona
Filmb
Thermal properties
PLmax FWHMc
(nm) (nm)
PLmax FWHMc
(nm) (nm)
HOMOe LUMO Band
Compound
UVmax (nm)
UVmax (nm)
Tg (1C) Tm (1C) Td (1C) Ffd (eV)
(eV)
gap (eV)
o-TPA-AP-TPA 353, 383, 405 457
m-TPA-AP-TPA 359, 379, 400 445
61
54
65
364, 387, 408 463
61
55
66
161
152
194
—
—
—
443
469
513
45 5.78
74 5.77
85 5.66
2.91
2.87
2.93
2.87
2.90
2.73
383, 404
385, 405
457
473
p-TPA-AP-TPA 381, 400
461
a
b
c
d
Toluene solution (1.0 Â 10À5 M). Film thickness: 50 nm on a glass substrate. Full width at half maximum. Absolute PLQY of 1 wt%
e
dispersed film in PMMA. Ultraviolet photoelectron spectroscopy (Riken-Keiki, AC-2).
and a knr of 8.14 Â 107 sÀ1, and m-TPA-AP-TPA showed a krad of electrons were mainly distributed around the anthracene, and the
3.91 Â 108 sÀ1 and a knr of 13.8 Â 108 sÀ1. However, p-TPA-AP-TPA TPA connected to the anthracene. The electron distribution of
showed the highest krad of 10.9 Â 108 sÀ1 and knr of 19.3 Â 107 sÀ1
.
LUMO+2 was concentrated in the pyrene.
Thus, the values of krad/knr for o-TPA-AP-TPA, m-TPA-AP-TPA, and
The theoretical band gap (DEH–L) values were calculated
p-TPA-AP-TPA were 0.81, 2.83, and 5.64, respectively. As a result, the by DFT calculations and the results shown in Fig. 3 exhibit
trend of the krad/knr values of the three compounds was the same as the following trend: m-TPA-AP-TPA (3.38 eV) 4 o-TPA-AP-TPA
that of their fluorescence quantum efficiency values. As shown in (3.36 eV) 4 p-TPA-AP-TPA (3.29 eV). The experimentally measured
Table S1 (ESI†), the order of PLQY is p-TPA-AP-TPA, m-TPA-AP-TPA, band gaps were 2.87, 2.90, and 2.73 eV, hence showing the same
and o-TPA-AP-TPA and the order of krad/knr is also the same as that trend as that shown by the calculated values.
of PLQY. With respect to the tF value, o-TPA-AP-TPA has the largest
among the three materials.
The absorption maximum wavelengths, oscillator strength
(f) values, and degrees of contribution to this strength by
This may be due to the distorted chemical structure of ortho various electronic transitions were calculated by performing
linkage and the related excited state disorder. Thus, the krad time-dependent (TD) DFT calculations using the TD-B3LYP/
value of o-TPA-AP-TPA which is a reciprocal term is the smallest 6-311G(d) method. Table S2 (ESI†) summarizes the results.
value, and krad/knr is also the smallest value.
o-TPA-AP-TPA showed an oscillator strength of 0.136 at a wave-
length of 419 nm, with 88% of this oscillator strength value
represented by the HOMO - LUMO+1 transition. At 406 nm, it
Thermal properties
Table 1 summarizes the thermal properties of the synthesized had an oscillator strength of 0.223, and the main transition was
compounds determined using thermal gravimetric analysis HOMOÀ2 - LUMO. m-TPA-AP-TPA had oscillator strength values
(TGA) and differential scanning calorimetry (DSC). The newly of 0.370 and 0.503 at 399 and 358 nm, respectively, but the main
synthesized materials showed high thermal stability levels, with transition process (93%) was HOMOÀ2 - LUMO. p-TPA-AP-TPA
Tg values greater than 151 1C and Td values greater than 443 1C had oscillator strengths of 0.204, 0.526, and 0.117 at 424, 414,
(see also Fig. S4, ESI†). In particular, p-TPA-AP-TPA exhibited a and 396 nm, respectively. At 424 nm, the main transition was
higher thermal stability than the other two materials, attributed to HOMOÀ1 - LUMO. At 414 nm, the main transition was
the greater structural stability resulting from the para linkage. HOMO - LUMO+1. The transition at 396 nm was composed
Molecules with higher Tg and Td values generally display greater primarily (86%) of HOMOÀ2 - LUMO. Therefore, in the dual
resistance to changes in morphology during heating, such as core concept, the distributions of HOMOÀ2, HOMOÀ1, and
those encountered during operation of an OLED device.31
LUMO+1 are important in addition to the electron density
distributions of the HOMO and LUMO; both anthracene and
pyrene play important roles in the overall efficiency.25,27
Theoretical calculations
DFT calculations were performed to determine whether the
electron transition properties of the dual core changed when
Electroluminescence properties
TPA groups were introduced as the side groups using ortho, EL performances of OLED devices using each of the synthesized
meta, and para linkages (Fig. 3). The highest occupied mole- compounds were determined. Each device was fabricated with the
cular orbitals (HOMOs) of o-TPA-AP-TPA and p-TPA-AP-TPA configuration ITO/2-TNATA (60 nm)/NPB (15 nm)/a,b-ADN: synthe-
were each calculated to have a relatively strong electron density sized material 4% (30 nm)/TPBi (30 nm)/LiF (1 nm)/Al (200 nm).
around the pyrene and TPA, a result attributed to an extension 2-TNATA and NPB were used as the hole injection layer and the
of conjugation provided by the introduction of the TPA side hole transport layer, respectively. a,b-ADN was used as the host
group and to the electron-donating effect of TPA. On the other material, and each synthesized material was used as a dopant
hand, for m-TPA-AP-TPA, conjugation was limited due to the material in the host-dopant emitters. TPBi was used as an electron-
meta connection, so the HOMO electron density was weak transporting and hole-blocking layer. EL performance of the OLED
near the pyrene. Regarding the lowest unoccupied molecular devices is shown in Fig. 4, 5 and Table 2. Fig. 4a shows plots of
orbitals (LUMOs), in all three materials, the electron density current density and luminance versus voltage; the graphs show
was greatest near the anthracene, consistent with general results typical diode characteristics. Fig. 4b–d show current efficiency,
for anthracene derivatives.25 In HOMOÀ1 and HOMOÀ2, the external quantum efficiency versus luminance, and band diagram.
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Fig. 3 Pictorial representations of the frontier orbitals and a plot of the HOMOÀ2, HOMOÀ1, HOMO, LUMO, and LUMO+1 energy levels for o-TPA-AP-TPA,
m-TPA-AP-TPA, and p-TPA-AP-TPA (calculated using the B3LYP/6-31G(d) method).
As summarized in Table 2, the ELmax value was found to be The current efficiencies (cd AÀ1) of o-TPA-AP-TPA, m-TPA-AP-
almost equal to the PLmax value of the solution state, so that the TPA, and p-TPA-AP-TPA were each measured at 100, 1000, and
light emitted from the driven device was primarily PL emission. 5000 cd mÀ2, respectively. The corresponding current efficiencies
The turn-on voltages of o-TPA-AP-TPA, m-TPA-AP-TPA, and of o-TPA-AP-TPA, m-TPA-AP-TPA, and p-TPA-AP-TPA were, respÀec1-
p-TPA-AP-TPA were 3.5, 4.0, and 3.1 V, respectively. The rela- tively, 3.87/4.52/3.64, 2.99/3.58/—, and 6.93/8.80/9.14 cd A
;
.
tively high turn-on voltage of m-TPA-AP-TPA was due to its m-TPA-AP-TPA did not achieve a luminance of 5000 cd mÀ2
relatively limited conjugation length, which was caused, as o-TPA-AP-TPA and m-TPA-AP-TPA showed efficiency roll-off as
noted above, due to the side group being linked at its meta the luminance was increased, whereas p-TPA-AP-TPA achieved a
position. This high turn-on voltage would make injections high efficiency of 9.14 cd AÀ1 without roll-off. The external
more difficult for this compound than for the other two. quantum efficiencies (EQEs) of o-TPA-AP-TPA, m-TPA- AP-TPA,
14712 | J. Mater. Chem. C, 2019, 7, 14709--14716
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Fig. 4 EL characteristics of devices using the synthesized materials as dopants: (a) I–V–L curves, (b) current efficiency versus luminance, (c) external
quantum efficiency versus luminance, and (d) band diagram of the materials in an OLED device.
Fig. 5 (a) EL spectra of devices and (b) CIE x, y values of the synthesized compounds.
and p-TPA-AP-TPA were 4.07/4.75/4.03%, 4.34/5.11/—%, and other two materials. First, the high EQE of p-TPA-AP-TPA arose
6.51/8.09/8.38%, respectively.
from its high PLQY, due to its superior ratio of rate of radiative
Similar to the case of current efficiency, the p-TPA-AP-TPA decay to rate of non-radiative decay (Fig. S3 and Table S1, ESI†).
material showed a high EQE of 8.38% at a high luminance of Second, in the dual core case, the secondary core chromophore
5000 cd mÀ2 without roll-off. We derived an explanation for why pyrene was indicated, as mentioned in our previous report,
the p-TPA-AP-TPA material exhibited more than two times the to play an important role, in addition to the role played by
efficiency and EQE at a luminance of 5000 cd mÀ2 than did the the main chromophore anthracene. For p-TPA-AP-TPA, both
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Table 2 Electroluminescence efficiency levels of the synthesized compounds: ITO/2-TNATA (60 nm)/NPB (15 nm)/a,b-ADN: synthesized material 4%
(30 nm)/TPBi (30 nm)/LiF (1 nm)/Al (200 nm)
CEc (cd AÀ1
100/1000/5000
)
EQEd (%)
100/1000/5000
Lmax (cd mÀ2
)
CIEe (x, y)
ELmax (nm)
a
b
Compounds
Von (V)
o-TPA-AP-TPA
m-TPA-AP-TPA
p-TPA-AP-TPA
3.5
4.0
3.1
5874
2318
7055
3.87/4.52/3.64
2.99/3.58/—
6.93/8.80/9.14
4.07/4.75/4.03
4.34/5.11/—
6.51/8.09/8.38
0.15, 0.12
0.15, 0.09
0.14, 0.15
455
447
461
a
b
c
d
Turn-on voltage at a luminance of 1 cd mÀ2
.
Maximum luminance. Current efficiency levels at 100, 1000, 5000 cd mÀ2
.
External quantum
efficiency levels at 100, 1000, 5000 cd mÀ2
.
Commission International de l’Eclairage.
e
anthracene and pyrene were found to participate in transitions, dichloromethane and water. The organic layer was dried with
with pyrene especially yielding a relatively high oscillator anhydrous MgSO4 and filtered. The solvent was evaporated. The
strength of 0.526 in the transition of ‘HOMO to LUMO+1’. This crude product was purified by column chromatography on silica
result can be explained in terms of its high PLQY and high gel using 1 : 10 dichloromethane/hexane (yield: 51%). 1H NMR
EQE.25 Third, in our previous study, we demonstrated an (300 MHz, DMSO): d (ppm) 7.76–7.73 (d, 1H), 7.49–7.44 (t, 1H),
increased EL efficiency based on the regenerated excitons in 7.31–7.23 (m, 6H), 6.99–6.94 (t, 2H), 6.88–6.85 (d, 4H).
the dual core material system. In order to understand the
Synthesis of N,N-diphenyl-2-(4,4,5,5-tetramethyl-1,3,2-dioxa-
high EQE value and the order of EL efficiency, a transient EL borolan-2-yl)aniline (5). 2-Bromo-N,N-diphenylaniline 3.0 g
experiment was performed and the results are shown in Fig. S5 (9.25 mmol) was added to 150 mL of anhydrous THF in a
(ESI†). The regenerated singlet exciton was provided by triplet– 3-neck round bottom flask under an N2 atmosphere. At À78 1C,
triplet annihilation (TTA), and the p-TPA-AP-TPA device showed 2.5 M n-BuLi 5.55 mL (13.88 mmol) was slowly added to the
the highest EL intensity and the longest decay time among mixture and stirred for 30 min. 2-Isoproxy-4,4,5,5-tetramethyl-
three devices. The decay time of o-TPA-AP-TPA, m-TPA-AP-TPA, 1,3,2-dioxaborane 2.83 mL (13.8 mmol) was added to the
and p-TPA-AP-TPA was 5.43, 3.58, and 9.75 ms, respectively. mixture and stirred overnight to react. After the reaction was
The order of decay time also matched with the EL efficiency complete, the reaction mixture was extracted with dichloro-
order. These features might have also caused the increased EL methane and DI water. The organic layer was dried with
efficiency found in the current experiment.26,32 In particular, anhydrous MgSO4 and filtered. The solvent was evaporated.
for the p-TPA-AP-TPA, excellent results were obtained with no The crude product was re-precipitated using THF and methanol
roll-off at high current densities, unlike the results for the other (yield: 74%). 1H NMR (300 MHz, THF): d (ppm) 7.63–7.60
two materials. These results can be explained by injected (d, 1H), 7.49–7.43 (t, 1H), 7.21–7.16 (m, 5H), 7.00–6.97 (d, 1H),
charge moving without congestion for the compound having 6.90–6.85 (t, 6H), 0.96 (s, 12H).
the core and the side group linearly connected through the para
Synthesis of N,N-diphenyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxa-
position. In addition, the high Tg (194 1C) and Td (513 1C) values borolan-2-yl)aniline (6). 3-Bromo-N,N-diphenylaniline 0.6 g
also provided a stable device operating with neither any mole- (1.85 mmol) was added to 120 mL of anhydrous THF in a
cular deformation nor roll-off under the high luminance.
3-neck round bottom flask under an N2 atmosphere. At À78 1C,
In the CIE (x, y) system, lower y coordinate values indicate 1.48 mL of 2.0 M n-butyllithium (2.03 mmol) was slowly added
the presence of more blue light (Fig. 5). In mobile phones and to the mixture and stirred for 10 min. 2-Isoproxy-4,4,5,5-
televisions, the y coordinate must be 0.15 or less. The CIE (x, y) tetramethyl-1,3,2-dioxaborane 0.56 mL (2.74 mmol) was added
values of the synthesized materials indicated emission of light to the mixture and stirred overnight to react. After the reaction
in the blue region (CIE y value: r0.15). Therefore, all three was complete, the reaction mixture was extracted with dichloro-
synthesized materials showed good y coordinate values.
methane and DI water. The organic layer was dried with
anhydrous MgSO4 and filtered. The solvent was evaporated.
The crude product was re-precipitated using THF and methanol
(yield: 38%). 1H NMR (300 MHz, THF): d (ppm) 7.50 (s, 1H),
7.44–7.40 (d, 1H), 7.23–7.19 (m, 5H), 7.14–7.10 (d, 1H), 7.01–
7.00 (d, 4H), 6.99–6.91 (t, 2H), 1.27 (s, 12H).
Experimental
Synthetic methods
The synthesis methods for compounds 1–3 in Scheme S1 (ESI†)
Synthesis of (4-(diphenylamino)phenyl)boronic acid (7).
4-Bromo-N,N-diphenylaniline 5.0 g (15.4 mmol) was added to
are reported in a previous study.25
Synthesis of 2-bromo-N,N-diphenylaniline (4). Diphenylamine 200 mL of anhydrous THF in a 3-neck round bottom flask
10.0 g (59.0 mmol), 1-bromo-2-iodobenzene 14.8 mL (118.0 mmol), under an N2 atmosphere. At À78 1C, 11.56 mL of 2.0 M
Pd(oac)2 0.66 g (2.95 mmol), tri-tert-butylphosphine 5.9 mL n-butyllithium (23.1 mmol) was added slowly to the mixture
(24.3 mmol), and sodium tert-butoxide 6.81 g (70.8 mmol) were and stirred for 10 min. Triethyl borate 3.93 mL (23.1 mmol) was
added to 300 mL of anhydrous toluene solution in a 3-neck round then added to the mixture and stirred overnight to react. After
bottom flask under an N2 atmosphere. The mixture was reacted the reaction was complete, the reaction mixture was extracted
by heating at 110 1C for 1 day under an N2 atmosphere. After with ethyl acetate and DI water. The organic layer was dried
the reaction was complete, the mixture was extracted with with anhydrous MgSO4 and filtered. The solvent was evaporated.
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Paper
The crude product was re-precipitated using THF and hexane (yield: 0.5 g (0.93 mmol), (4-(diphenylamino)phenyl)boronic acid 0.59 g
61%). 1H NMR (300 MHz, CDCl3): d (ppm) 8.02–8.00 (d, 1H), 7.32– (2.05 mmol), Pd(oac)2 0.05 g (0.07 mmol), and tricyclohexyl-
7.29 (m, 2H), 7.16–7.13 (m, 2H), 7.06–7.03 (m, 2H), 1.53 (s, 2H).
phosphine 0.04 g (0.15 mmol) were added to 100 mL of
Synthesis of 2-(6-(10-(2-(diphenylamino)phenyl)anthracen-9- anhydrous toluene under N2 and stirred. Tetraethylammonium
yl)pyren-1-yl)-N,N-diphenylaniline o-TPA-AP-TPA. Compound 3 hydroxide (20 wt%) 4.4 mL (4.4 mmol) was added to the mixture
0.467 g (0.87 mmol), N,N-diphenyl-3-(4,4,5,5-tetramethyl-1,3,2- and stirred under reflux at 110 1C to react for 24 h. The product
dioxaborolan-2-yl)aniline 0.71 g (1.91 mmol), Pd(oac)2 0.02 g was extracted from the reaction mixture with dichloromethane
(0.069 mmol), and tricyclohexylphosphine 0.048 g (0.174 mmol) and water. The organic layer was dried with anhydrous MgSO4
were added to 60 mL of anhydrous toluene under N2 and stirred. and filtered. The solvent was evaporated. The crude product was
Tetraethylammonium hydroxide (20 wt%) 4.1 mL (4.1 mmol) was purified by column chromatography on silica gel using 1 : 3 chloro-
added to the mixture and stirred under reflux at 110 1C to react for form/hexane (yield: 73.6%). 1H NMR (300 MHz, THF): d (ppm)
24 h. The product was extracted from the reaction mixture with 8.45–8.44 (d, 1H), 8.43–8.40 (d, 1H), 8.27–8.25 (d, 1H), 8.22–8.20
dichloromethane and water. The organic layer was dried with (d, 1H), 8.08–8.07 (d, 1H), 8.05–8.02 (d, 1H), 7.94–7.91 (d, 2H), 7.87–
anhydrous MgSO4 and filtered. The solvent was evaporated. The 7.84 (d, 1H), 7.59–7.55 (m, 2H), 7.49–7.46 (m, 1H), 7.43–7.30
crude product was purified by column chromatography on silica (m, 22H), 7.23–7.20 (m, 6H), 7.11–7.08 (m, 4H). 13C-NMR
gel using 1 : 3 dichloromethane/hexane (yield: 75.1%). 1H NMR (75 MHz, CDCl3): d = 114.70, 114.65, 114.10, 114.03, 104.68,
(300 MHz, DMSO): d (ppm) 8.48–8.37 (q, 1H), 8.15–8.10 (q, 1H), 104.40, 102.18, 101.90, 101.11, 99.43, 99.09, 99.06, 98.29, 98.11,
8.05–7.98 (q, 1H), 7.95–7.92 (d, 1H), 7.87–7.82 (t, 1H), 7.79–7.71 97.85, 97.80, 97.15, 97.05, 96.48, 96.28, 96.24, 95.63, 94.76, 94.67,
(q, 3H), 7.68–7.57 (m, 3H), 7.54–7.46 (t, 5H), 7.33–7.25 (q, 2H), 94.29, 94.09, 94.06, 92.57, 92.14, 92.05, 91.92, 91.78, 91.60, 91.48,
7.18–7.06 (m, 4H), 6.98–6.91 (m, 7H), 6.87–6.82 (t, 2H), 6.74–6.55 91.39, 90.18, 89.97, 89.93. HRMS (FAB-MS, m/z): calcd for C66H44N2,
(m, 11H), 6.43–6.40 (d, 2H). 13C-NMR (75 MHz, CDCl3): d = 114.91, 864.35; found: 865.3554 [M]+. Anal. calcd for C66H44N2: C 91.63,
114.38, 113.93, 113.64, 105.52, 102.35, 102.10, 101.61, 101.32, 101.30, H 5.13, N 3.24%; found: C 91.452, H 5.223, N 3.244%.
100.95, 100.88, 100.49, 100.43, 97.63, 97.44, 96.93, 96.34, 96.24,
96.06, 95.79, 95.62, 95.58, 95.53, 95.48, 95.23, 95.21, 94.99, 94.62,
94.24, 94.00, 93.93, 93.88, 93.79, 93.66, 93.37, 92.55, 92.46, 91.68,
Conclusions
91.58, 91.55, 91.51, 91.17, 90.99, 90.93, 90.87, 90.84, 90.64, 90.30,
o-TPA-AP-TPA, m-TPA-AP-TPA, and p-TPA-AP-TPA were success-
fully synthesized by linking the electron-donating side group
triphenylamine through, respectively, its ortho, meta, and para
positions to the anthracene–pyrene dual core. o-TPA-AP-TPA,
m-TPA-AP-TPA, and p-TPA-AP-TPA materials emitted blue light
with maximum wavelengths of 457, 445, and 461 nm, respec-
tively, in the solution state. The three compounds showed high
thermal stability, with Tg greater than 152 1C and Td greater
90.19, 89.25, 88.63, 88.45, 88.20, 88.17. HRMS (FAB-MS, m/z): calcd
for C66H44N2, 864.35; found: 865.3580 [M]+. Anal. calcd for C66H44N2:
C 91.63, H 5.13, N 3.24%; found: C 91.429, H 5.195, N 3.233%.
Synthesis of 3-(6-(10-(3-(diphenylamino)phenyl)anthracen-9-
yl)pyren-1-yl)-N,N-diphenylaniline m-TPA-AP-TPA. Compound 3
0.25 g (0.46 mmol), N,N-diphenyl-2-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)aniline 0.38 g (1.02 mmol), Pd(oac)2 0.02 g
(0.046 mmol), and tricyclohexylphosphine 0.02 g (0.074 mmol)
were added to 40 mL of anhydrous toluene under N2 and stirred.
than 443 1C. Of the three materials, p-TPA-AP-TPA displayed the
highest absolute quantum efficiency of 85%. When the synthe-
Tetraethylammonium hydroxide (20 wt%) 2.2 mL (2.2 mmol) was
added to the mixture and stirred under reflux at 110 1C to react for
sized materials were applied as dopants, p-TPA-AP-TPA achieved a
high efficiency of 9.14 cd AÀ1 and EQE of 8.38%, even at a high
24 h. The product was extracted from the reaction mixture with
luminance of 5000 cd mÀ2. This result was attributed to the
dichloromethane and water. The organic layer was dried with
p-TPA-AP-TPA material displaying a higher PLQY and radiative-to-
anhydrous MgSO4 and filtered. The solvent was evaporated. The
nonradiative decay ratio than the other two isomers. In addition,
crude product was purified by column chromatography on silica
the linking of the nitrogen-containing bulky triphenylamine side
group through its para position to the core effectively balanced
charge and prevented intermolecular packing. The p-TPA-AP-TPA
gel using 1 : 3 chloroform/hexane (yield: 60.4%). 1H NMR
(300 MHz, THF): d (ppm) 8.43–8.38 (t, 1H), 8.30–8.27 (d, 1H),
8.25–8.15 (q, 2H), 8.06–8.03 (d, 1H), 8.00–7.95 (q, 1H), 7.93–7.88
materials were found to have high oscillator strengths and affect
(d, 2H), 7.86–7.77 (q, 1H), 7.58–7.44 (m, 2H), 7.40–7.14 (m, 29H),
the electronic transitions of both anthracene and pyrene moieties.
7.05–6.97 (t, 4H). 13C-NMR (75 MHz, CDCl3): d = 114.89, 114.77,
114.64, 114.60, 109.01, 106.83, 104.53, 104.49, 104.07, 104.01,
102.19, 102.16, 97.96, 97.93, 97.65, 97.27, 96.56, 96.32, 96.06, Conflicts of interest
96.04, 95.96, 95.93, 95.43, 94.49, 94.41, 94.20, 93.87, 93.79,
There are no conflicts to declare.
93.73, 93.60, 92.82, 92.56, 92.42, 92.29, 91.98, 91.83, 91.53,
91.47, 91.33, 91.28, 91.22, 91.20, 91.17, 89.72, 89.67, 89.64,
89.54, 89.23. HRMS (FAB-MS, m/z): calcd for C66H44N2, 864.35;
Acknowledgements
found: 865.3575 [M]+. Anal. calcd for C66H44N2: C 91.63, H 5.13,
N 3.24%; found: C 91.336, H 5.167, N 3.376%.
This research was supported by the National R&D Program through
Synthesis of 4-(6-(10-(4-(diphenylamino)phenyl)anthracen-9- the National Research Foundation of Korea (NRF), funded by the
yl)pyren-1-yl)-N,N-diphenylaniline p-TPA-AP-TPA. Compound 3 Ministry of Science & ICT (No. 2017M3A7B4041699). This research
This journal is ©The Royal Society of Chemistry 2019
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Journal of Materials Chemistry C
14 S. Choi, M. Godumala, J. H. Lee, G. H. Kim, J. S. Moon,
J. Y. Kim, D. Yoon, J. H. Yang, J. Kim and M. J. Cho, J. Mater.
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was supported by the Basic Science Research Program through
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14716 | J. Mater. Chem. C, 2019, 7, 14709--14716
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