Extremely deep-blue fluorescent emitters with CIEy?≤?0.04 for non-doped organic light-emitting diodes based on an indenophenanthrene core

Article abstract of DOI:10.1016/j.dyepig.2017.05.014

The fluorescent molecules 7,7-dimethyl-N,N-diphenyl-7H-indeno[1,2-a] phenanthren-9-amine (DIP) and 4-(7,7-dimethyl-7H-indeno[1,2-a]phenanthren-9-yl)-N,N-diphenylaniline (TIP), with indenophenanthrene cores and attached arylamine structures, were synthesiz

Full text of DOI:10.1016/j.dyepig.2017.05.014

Dyes and Pigments 144 (2017) 9e16
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Extremely deep-blue fluorescent emitters with CIEy ꢀ 0.04 for
non-doped organic light-emitting diodes based on an
indenophenanthrene core
*
Seongjin Jeong, Jong-In Hong
Department of Chemistry, College of Natural Sciences, Seoul National University, Seoul, 08826, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 31 March 2017
Received in revised form
The fluorescent molecules 7,7-dimethyl-N,N-diphenyl-7H-indeno[1,2-a] phenanthren-9-amine (DIP) and
4-(7,7-dimethyl-7H-indeno[1,2-a]phenanthren-9-yl)-N,N-diphenylaniline (TIP), with indenophenan-
threne cores and attached arylamine structures, were synthesized for use as extremely deep blue
fluorescent emitting materials. A non-doped device using DIP as an emitting material exhibited a
maximum external quantum efficiency of 3.27% and had Commission Internationale de l’Eclairage (CIE)
color coordinates of (0.158, 0.040).
24 April 2017
Accepted 5 May 2017
Available online 6 May 2017
©
2017 Elsevier Ltd. All rights reserved.
Keywords:
Deep-blue emitter
Non-doped system
Fluorescent organic light-emitting diodes
Indenophenanthrene
Charge balance
1
. Introduction
l’Eclairage (CIE) chromaticity coordinates and low quantum effi-
ciencies; this occurs because the emitters tend to be closely packed
and aggregated in the emitting layer [5e7]. To overcome these
problems, bulky side groups or spiro moieties were introduced to
reduce packing between the molecules and limit the emission
quenching, and this should enhance the purity and stability of the
blue emissions, along with the photoluminescence (PL) quantum
efficiency [4,8,9]. However, the introduction of bulky side groups or
spiro moieties in flat blue emitters sometimes results in an unex-
pected bathochromic shift of the emitters in the solid state [10,11].
Therefore, an alternative way of developing deep blue emitters is
required.
Deep-blue fluorescence OLEDs based on spirocyclic aromatic
hydrocarbon derivatives and purine derivatives exhibit CIE co-
ordinates of (0.16, 0.08) with a maximum current efficiency of
1.1 cd/A and CIE coordinates of (0.15, 0.06) with an external
quantum efficiency (EQE) of 3.1%, respectively [12,13]. In addition,
deep-blue emitters based on twisted asymmetric anthracene de-
rivatives with triphenyltriazine- or triphenylamine-substituted
xylene units have been reported to exhibit EQEs of 4.62 and
6.6% with CIE coordinates of (0.154, 0.049) and (0.145, 0.068),
respectively [3,14]. Nevertheless, there have been few reports
concerning color-pure, deep-blue fluorescent materials with CIE y-
values around 0.04 and EQEs greater than 3% in non-doped de-
vices [15].
Full-color displays and white lighting require three primary
color emissions (red, green, and blue (RGB)) of relatively equal
stability, efficiency, and color purity [1]. In particular, extremely
deep-blue-emitting materials play an important role in the devel-
opment of efficient organic light-emitting diodes (OLEDs) because
the deep blue emission is more energy efficient than a normal blue
color when strong microcavity structures are chosen to enhance
color purity [2].
Current deep-blue emitters are based on chromophores con-
sisting of flat aromatic compounds such as anthracene, fluorene,
and pyrene, which show high electroluminescence efficiencies. The
9
-alkylated fluorene moiety is expected to be a good electrolumi-
nescent backbone for blue-emitting materials because of its
excellent fluorescence properties and excellent morphological,
thermal, and electrochemical stabilities [3,4]. However, in most
planar aromatic compounds utilized for emitting materials, exci-
mers or exciplexes are usually formed by intramolecular or inter-
molecular interactions between the emitters, resulting in
bathochromic shifts of the Commission Internationale de
*
Corresponding author.
E-mail address: jihong@snu.ac.kr (J.-I. Hong).
http://dx.doi.org/10.1016/j.dyepig.2017.05.014
143-7208/© 2017 Elsevier Ltd. All rights reserved.
0

10
S. Jeong, J.-I. Hong / Dyes and Pigments 144 (2017) 9e16
In this study, we designed and synthesized two extremely deep-
2.2.3. Phenanthren-1-ylboronic acid (4)
blue emitting materials based on an indenophenanthrene core for
non-doped blue OLEDs with excellent color purity: 7,7-dimethyl-
N,N-diphenyl-7H-indeno[1,2-a]phenanthren-9-amine (DIP) and 4-
1-Bromophenanthrene (3) (3.0 g, 11.667 mmol) was dissolved in
dry THF (100 mL) under an atmosphere of nitrogen. This solution
was cooled to ꢃ78 C, followed by the dropwise addition of n-
ꢁ
(
7,7-dimethyl-7H-indeno[1,2-a]phenanthren-9-yl)-N,N-diphenyla-
butyllithium (2.5 M in hexane, 11.667 mL, 29.168 mmol). This
mixture was stirred for 1 h and then treated with trimethylborate
(6.539 mL, 58.336 mmol). After stirring at RT for 15 h, the reaction
mixture was added to an aqueous solution of HCl (1 N) and stirred
for 2 h. The aqueous phase was separated and extracted with
dichloromethane (3 ꢂ 50 mL). The combined organic extracts were
dried using sodium sulfate, concentrated in vacuo, and purified by
niline (TIP). Because phenanthrene is less conjugated than
anthracene [16], we designed an indenophenanthrene core by hy-
bridizing a phenanthrene moiety with fluorene to induce a deep
blue emission [17]. The non-doped OLED device using DIP as an
emitting material had a maximum EQE of 3.27% with CIE color
coordinates of (0.158, 0.040), and is therefore better than the device
fabricated using the TIP emitter in terms of the EQE and CIE color
coordinates because of the better charge balance.
column chromatography (SiO
2
, dichloromethane:methanol ¼ 9:1)
to afford phenanthren-1-ylboronic acid (1.8 g, 8.105 mmol, 69.5%)
1
as a white solid. H NMR (300 MHz, acetone-d ): (ppm) 8.88 (dd,
6
d
2
. Materials and general methods
J ¼ 8.4, 5.4 Hz, 2H), 8.51 (d, J ¼ 9.0 Hz, 1H), 7.97 (d, J ¼ 7.2 Hz, 2H),
13
7
.82 (d, J ¼ 9.0 Hz, 1H), 7.71e7.60 (m, 3H). C NMR (75 MHz,
2.1. Materials
acetone-d ): (ppm) 135.0, 132.8, 131.8, 130.6, 128.3, 127.7, 126.5,
6
d
1
26.4, 126.3, 125.7, 124.0, 122.7. HR-Mass (EIþ): calcd for C14
H11BO
2
All solvents and materials were used as received from com-
222.0852, found 222.0848.
mercial suppliers without further purification. Synthetic routes to
DIP and TIP are outlined in Fig. 2. The two final products (DIP and
TIP) were purified by temperature gradient vacuum sublimation.
2.2.4. Methyl 5-bromo-2-(phenanthren-1-yl)benzoate (5)
A
mixture of methyl 5-bromo-2-iodobenzoate (3.849 g,
11.259 mmol), phenanthren-1-ylboronic acid (4) (3 g,
2
2
.2. Synthetic procedure
13.510 mmol), 2 M aqueous potassium carbonate (30 mL), and
tetrakis(triphenylphosphine)palladium (0.651 g, 0.563 mmol) in
THF (100 mL) and methanol (30 mL) was heated at reflux in a ni-
trogen atmosphere for 24 h. After the reaction mixture had been
concentrated in vacuo, the resulting mixture was extracted with
dichloromethane. The organic layer was washed with water and
brine and dried using anhydrous sodium sulfate. The filtrate was
concentrated in vacuo to give a crude mixture that was purified by
.2.1. 1-((Z)-2-(2-Bromophenyl)-1-ethenyl)-2-iodobenzene (2)
ꢁ
To a cooled (0 C) suspension of (2-bromobenzyl)triphenyl-
phosphonium bromide (1) (33.000 g, 64.425 mmol) in tetrahy-
drofuran (THF, 350 mL), potassium tert-butoxide (8.434 g,
7
iodobenzaldehyde (12.457 g, 53.688 mmol) in THF (100 mL) was
added over 1 h. The reaction was left to warm to room temperature
5.163 mmol) in THF (50 mL) was added. After 30 min, 2-
column chromatography (SiO
afford methyl 5-bromo-2-(phenanthren-1-yl)benzoate (3.5 g,
2
, dichloromethane:hexane ¼ 1:4) to
(
RT) and was stirred for 24 h. Then, water (100 mL) was added. The
aqueous phase was separated and extracted with diethyl ether
3 ꢂ 300 mL). The combined organic extracts were dried (MgSO ),
concentrated in vacuo, and purified by column chromatography
SiO , hexane) to yield an inseparable 9:1 mixture of (Z)- and (E)-
isomers (18.7 g, 48.566 mmol, 90.5%) as a pale-yellow oil. H NMR
of (Z)-isomer (300 MHz, CDCl ):
(ppm) 7.87 (dd, J ¼ 7.9,1.1 Hz,1H),
.57 (dd, J ¼ 7.3, 1.8 Hz, 1H), 7.11e6.93 (m, 5H), 6.89 (td, J ¼ 7.7,
1
8.945 mmol, 79%) as a white solid. H NMR (300 MHz, CDCl
(ppm) 8.80 (d, J ¼ 12.6 Hz, 2H), 8.22 (s, 1H), 7.88 (d, J ¼ 7.8 Hz, 1H),
7.77 (dd, J ¼ 5.1, 1.8 Hz, 1H), 7.73e7.60 (m, 4H), 7.40 (dd, J ¼ 7.8,
3
):
(
4
d
13
(
2
1.5 Hz, 2H), 7.32 (d, J ¼ 8.1 Hz, 1H), 3.41 (s, 3H). C NMR (75 MHz,
CDCl ): (ppm) 166.4, 140.7, 139.0, 134.6, 133.5, 133.1, 131.7, 130.3,
130.2, 130.0, 128.5, 127.2, 126.8, 126.7, 125.7, 123.9, 122.9, 122.4,
1
3
d
3
d
7
121.5, 52.1. HR-Mass (EIþ): calcd for C22
2
H15BrO 390.0255, found
13
1
.9 Hz,1H), 6.76 (d, J ¼ 11.8 Hz,1H), 6.68 (d, J ¼ 11.8 Hz,1H). C NMR
392.0257.
of (Z)-isomer (75 MHz, CDCl ): (ppm) 140.9, 139.2, 137.0, 135.4,
3
d
132.8, 131.1, 130.8, 130.6, 129.0, 128.9, 128.0, 127.1, 124.3, 100.0.
2.2.5. 2-(5-Bromo-2-(phenanthren-1-yl)phenyl)propan-2-ol (6)
HRMS (FABþ): [M þ H: C14
H10BrI] 383.9011, found 383.9018.
To a solution of methyl 5-bromo-2-(phenanthren-1-yl)benzoate
5) dissolved in dry THF (120 mL) under a nitrogen atmosphere, a
(
2
.2.2. 1-Bromophenanthrene (3)
A solution of stilbene 2 (9:1 mixture of (Z)- and (E)-isomers,
5.1 g, 39.217 mmol), tributyltin hydride (13.697 g, 47.060 mmol),
solution of methylmagnesium bromide solution in diethyl ether
(1.4 M, 14.85 mL, 21.162 mmol) was slowly added. The mixture was
heated at reflux for 4 h. After the reaction mixture had been
concentrated in vacuo, the resulting mixture was extracted with
dichloromethane. The organic layer was washed with water and
brine and dried using anhydrous sodium sulfate. The filtrate was
concentrated in vacuo to give a crude mixture that was purified by
1
and azobisisobutyronitrile (AIBN) (1.288 g, 7.843 mmol) in toluene
ꢁ
(
200 mL) was heated at 90 C for 16 h in nitrogen atmosphere and
then cooled to RT. Additional tributyltin hydride (2.283 g,
7.843 mmol) and AIBN (0.258 g, 1.569 mmol) were added, and the
ꢁ
reaction was heated for a further 8 h at 90 C. After cooling to RT
column chromatography (SiO
afford the 2-(5-bromo-2-(phenanthren-1-yl)phenyl)propan-2-ol
(2.7 g, 6.900 mmol, 75%) as a white solid. H NMR (300 MHz,
2
, ethyl acetate:hexane ¼ 1:20) to
and concentration in vacuo, the resulting mixture was extracted
with excess dichloromethane. The organic layer was washed suc-
cessively with water and brine and dried using anhydrous sodium
sulfate, which was filtered through celite and potassium fluoride.
The product mixture was purified by column chromatography (10%
1
CDCl
3
):
d
(ppm) 8.77 (d, J ¼ 5.1 Hz, 2H), 8.03 (d, J ¼ 1.8 Hz, 1H), 7.89
(d, J ¼ 4.5 Hz, 1H), 7.88e7.62 (m, 4H), 7.52e7.47 (m, 2H), 7.33 (d,
13
J ¼ 9.3 Hz, 2H), 7.03 (d, J ¼ 8.1 Hz, 1H), 1.39 (s, 3H), 1.22 (s, 3H).
C
KF/SiO
3
2
,
hexane) to afford 1-bromophenanthrene (8.4 g,
NMR (75 MHz, CDCl ): (ppm) 149.5, 140.4, 1367, 134.2, 131.7, 131.0,
3
d
1
2.668 mmol, 83.3%) as a white solid. H NMR (300 MHz, CDCl
3
):
130.5, 130.2, 129.6, 129.4, 128.6, 128.0, 127.2, 126.9, 125.4, 125.0,
d
(ppm) 8.68 (d, J ¼ 8.2 Hz, 2H), 8.23 (d, J ¼ 9.2 Hz, 1H), 7.95e6.89
122.9, 122.5, 122.1, 73.7, 32.3, 31.7. found 392.0, HR-Mass (EIþ):
(
m, 2H), 7.86 (d, J ¼ 9.2 Hz, 1H), 7.73e7.62 (m, 2H), 7.50 (dd, J ¼ 8.2,
.9 Hz, 1H). 13C NMR (75 MHz, CDCl
): (ppm) 132.2, 132.1, 130.9,
30.8,130.1,128.9,128.7,127.4,127.3,127.0,125.5,123.9,123.1,122.5.
HR-Mass (EIþ): calcd for C14 Br 255.9888, found 255.9886.
calcd for C23H19BrO 390.0619, found 390.0622.
7
1
3
d
2.2.6. 9-Bromo-7,7-dimethyl-7H-indeno[1,2-a]phenanthrene (7)
H
9
Concentrated sulfuric acid (4.5 mL) was added to a stirred

S. Jeong, J.-I. Hong / Dyes and Pigments 144 (2017) 9e16
11
solution of 2-(5-bromo-2-(phenanthren-1-yl)phenyl)propan-2-ol
2.3. General methods
ꢁ
6) (2.7 g, 6.918 mmol) in acetic acid (139 mL) at 100 C, After
(
ꢁ
1H and 13C NMR spectra were recorded using an Agilent
stirring for 3 h at 100 C, the mixture was poured into water and
extracted with dichloromethane. The organic layer was washed
with water and brine and dried using anhydrous sodium sulfate.
The filtrate was concentrated in vacuo to give a crude mixture that
1
400 MHz Varian spectrometer in CDCl
in CDCl were referenced to CHCl
shifts in CDCl were reported relative to CHCl
3
. H NMR chemical shifts
13
3
3
(7.27 ppm). C NMR chemical
(77.23 ppm).
3
3
was purified by column chromatography (SiO
2
, hexane) to afford 9-
(1.8 g,
.830 mmol, 70.0%) as a white solid. H NMR (300 MHz, CDCl ):
(ppm) 8.76 (t, J ¼ 5.4 Hz, 2H), 8.63 (d, J ¼ 9.3 Hz, 1H), 8.24 (d,
UVevisible spectra were recorded on a Beckman DU650 spec-
trophotometer. Fluorescence spectra were recorded on a Jasco
FP-6500 spectrophotometer. Fluorescent quantum yields in the
solid films were recorded on an Otsuka electronics QE-2000
spectrophotometer. Mass spectra were obtained using matrix-
assisted laser desorptioneionization time-of-flight mass spec-
trometry (MALDI-TOF-MS) from Bruker. High-resolution masses
were measured by either fast atom bombardment (FAB) or
electron ionization (EI) using a JEOL HP 5890. Analytical thin-
layer chromatography was performed using Kieselgel 60F-254
plates from Merck. Column chromatography was carried out on
Merck silica gel 60 (70e230 mesh). Decomposition temperatures
bromo-7,7-dimethyl-7H-indeno[1,2-a]phenanthrene
1
4
3
d
J ¼ 8.4 Hz, 1H), 7.74 (d, J ¼ 8.7 Hz, 1H), 7.97e7.91 (m, 2H), 7.71e7.59
13
(
1
1
m, 4H), 1.59 (s, 6H). C NMR (75 MHz, CDCl
30.2, 128.6, 127.9, 126.9, 126.7, 126.5, 126.2, 124.7, 123.0, 122.3,
20.9, 120.7, 46.6, 26.9. HR-Mass (EIþ): calcd for C23 17Br 372.0514,
found 372.0514.
3
): d (ppm) 157.0, 152.7,
H
2
9
.2.7. 7,7-Dimethyl-N,N-diphenyl-7H-indeno[1,2-a]phenanthren-
-amine (DIP)
To a mixture of 9-bromo-7,7-dimethyl-7H-indeno[1,2-a]phen-
d g
(T ) and glass transition temperatures (T ) were obtained by
anthrene (7) (2.65 g, 7.099 mmol), diphenylamine (1.561 g,
.229 mmol), and palladium acetate (0.111 g, 0.497 mmol) in dry
toluene (80 mL) under an N atmosphere, a solution of tri-tert-
butylphosphine (0.287 g, 1.420 mmol) and potassium tert-butoxide
3.187 g, 28.389 mmol) in toluene (20 mL) was added. The mixture
was heated to reflux under nitrogen. After 12 h, the reaction
mixture was concentrated in vacuo, and the resulting mixture was
extracted with dichloromethane. The organic layer was washed
successively with water and brine and dried using anhydrous so-
dium sulfate. The filtrate was concentrated in vacuo to give a crude
thermogravimetric analysis (TGA, Q-5000-IR) and differential
9
scanning calorimetry (DSC, DSC-Q-1000), respectively. The TGA
ꢁ
2
and DSC analyses were performed at a heating rate of 10
C
ꢃ1
min under a nitrogen atmosphere. The T
g
was determined from
(
the third heating scan. The electrochemical properties of DIP and
TIP were studied using cyclic voltammetry (CV) in CH Cl solu-
tions (1.00 mM) with 0.1 M tetra-n-butylammonium hexa-
fluorophosphate (TBAPF ) as the supporting electrolyte. A glassy
2
2
6
carbon electrode was employed as the working electrode and
referenced to a Ag reference electrode. All potential values were
þ
mixture, which was purified by column chromatography (SiO
2
,
calibrated against the ferrocene/ferrocenium (Fc/Fc ) redox
hexane) to afford 7,7-dimethyl-N,N-diphenyl-7H-indeno[1,2-a]
phenanthren-9-amine (2.15 g, 4.658 mmol, 66%) as a bright yellow
couple. The onset potential was determined from the intersection
of two tangents drawn at the rising and background current of
the cyclic voltammogram.
1
solid. H NMR (400 MHz, CDCl
8
1
3
):
d
(ppm) 8.66 (d, J ¼ 8.4 Hz, 1H),
.61 (d, J ¼ 8.4 Hz, 1H), 8.56 (d, J ¼ 9.2 Hz, 1H), 8.14 (d, J ¼ 8.0 Hz,
H), 7.84 (d, J ¼ 8.0 Hz, 1H), 7.79 (d, J ¼ 9.6 Hz, 1H), 7.64 (d,
2.4. Theoretical calculations
J ¼ 8.0 Hz, 1H), 7.59 (t, J ¼ 7.2 Hz, 1H), 7.52 (t, J ¼ 7.2 Hz, 1H),
7
6
.26e7.18 (m, 6H), 7.12e7.05 (m, 4H), 6.98 (t, J ¼ 7.2 Hz, 2H), 1.43 (s,
The optimized geometries and frontier molecular orbital en-
1
3
H). C NMR (100 MHz, CDCl
3
): d (ppm) 157.0, 152.7, 130.2, 128.6,
ergy levels for DIP and TIP were obtained using density func-
tional theory (DFT) calculations with Gaussian 09. The
geometries were optimized using the Becke 3-parameter Lee-
eYangeParr (B3LYP) functional with the 6-311G-level atomic
basis set.
127.9,126.9,126.7, 126.5,126.2,124.7, 123.0,122.3,120.9,120.7, 46.6,
2
6.9. HR-Mass (EIþ): calcd for C35H27N 461.2143, found 461.2147.
2.2.8. 4-(7,7-Dimethyl-7H-indeno[1,2-a]phenanthren-9-yl)-N,N-
diphenylaniline (TIP)
A mixture of 9-bromo-7,7-dimethyl-7H-indeno[1,2-a]phenan-
threne (7) (1.5 g, 4.018 mmol), 4-(diphenylamino)-phenylboronic
acid (1.4 g, 4.822 mmol), tetrakis(triphenylphosphine)palladium
2.5. Device fabrication & characterization
0 0 0 0
N,N -Di(1-naphthyl)-N,N -diphenyl-(1,1 -biphenyl)-4,4 -
(
0.232 g, 0.201 mmol), and aqueous sodium carbonate (2 M, 20 mL)
0
00
in THF (100 mL) and methanol (20 mL) was heated to reflux in a
nitrogen atmosphere for 24 h. After the reaction mixture had been
concentrated in vacuo and the resulting mixture extracted with
dichloromethane, the organic layer was washed with water and
brine and dried using anhydrous sodium sulfate. The filtrate was
concentrated in vacuo to give a crude mixture, which was purified
diamine (NPB), 4,4 ,4 -tris(N-carbazolyl)triphenylamine (TCTA),
and 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI) were
purchased from commercial sources and used without purifica-
tion. The fabrication of OLEDs was conducted by the high-
ꢃ6
vacuum (2 ꢂ 10
Torr) thermal evaporation of the organic
materials onto indium tin oxide (ITO)-coated glass (sheet resis-
tance: 15 /square; Applied Film Corp.). Glass substrates with
patterned ITO electrodes were washed with isopropyl alcohol
and then cleaned by O plasma treatment. The OLED devices
by column chromatography (SiO
to afford 4-(7,7-dimethyl-7H-indeno[1,2-a]phenanthren-9-yl)-N,N-
2
, dichloromethane:hexane ¼ 1:9)
U
1
diphenylaniline (1.4 g, 2.604 mmol, 64.8%) as a yellow solid.
NMR (400 MHz, CDCl ):
(ppm) 8.73 (d, J ¼ 8.4 Hz, 3H), 8.40 (d,
J ¼ 7.6 Hz, 1H), 7.94e7.87 (m, 3H), 7.76 (d, J ¼ 8.4 Hz, 1H), 7.73 (s,
H), 7.69e7.65 (m, 2H), 7.62e7.56 (m, 4H), 7.29 (t, J ¼ 8.0 Hz, 4H),
H
2
3
d
were fabricated with a configuration of ITO/NPB/TCTA/DIP or TIP/
TPBI/LIF/Al. NPB and TCTA (hole transporting layers), TPBI
(electron transporting layer), LiF (electron injection layer), and Al
electrodes were deposited sequentially on the substrate.
The emission properties were determined using a PR-650 Spec-
1
13
7
.16 (t, J ¼ 8.8 Hz, 4H), 7.02 (t, J ¼ 7.6 Hz, 3H) 1.52 (s, 6H). C NMR
100 MHz, CDCl ): (ppm) 155.5, 152.7, 147.6, 147.2, 139.0, 138.9,
34.3, 133.3, 131.3, 130.0, 129.3, 128.5, 127.8, 127.6, 126.8, 126.3,
25.7, 124.4, 124.4, 124.0, 123.9, 123.6, 122.9, 122.7, 122.3, 121.0,
20.8, 46.5, 27.1. HR-Mass (FABþ): calcd for C41 31N 537.2457,
found 537.2457.
(
3
d
1
1
1
traScan SpectraColorimeter as
rentevoltage characteristics
a
source meter. The cur-
were measured using
a
H
programmable electrometer equipped with current and voltage
sources (Keithley 2400).

12
S. Jeong, J.-I. Hong / Dyes and Pigments 144 (2017) 9e16
3
. Results and discussion
moieties along with the fluorene moiety of indenophenanthrene,
while the lowest unoccupied molecular orbitals (LUMOs) of
DIP and TIP are dispersed over the indenophenanthrene core
3.1. Theoretical calculation
[
18]. The DFT-calculated HOMO and LUMO energies are similar,
Optimized geometries and frontier molecular orbital energy
at 5.23 and 1.60 eV for DIP and 5.21 and 1.58 eV for TIP,
respectively [19].
levels for DIP and TIP were obtained from DFT calculations at the
B3LYP/6-311G level using Gaussian ’09. As shown in Fig. 1, the
indenophenanthrene moiety is slightly distorted from the
perfect planarity because of the syn-pentane-like interactions
between the hydrogen at the C5 position and the hydrogen at the
C14 position of DIP and the C13 position of TIP. The calculated
results show that the dihedral angle connecting the C5-C4-C9-
3.2. Synthesis
The synthetic routes to DIP and TIP are illustrated in Fig. 2. The
synthesis of 9-bromo-7,7-dimethyl-7H-indeno[1,2-a]phenan-
threne (7) was started from 1-bromophenanthrene (3) [20]. Methyl
5-bromo-2-(phenanthren-1-yl)benzoate (5) was obtained using a
Suzuki cross-coupling reaction between phenanthren-1-ylboronic
acid (4) and methyl 5-bromo-2-iodobenzoate. Next, Grignard
methylation followed by Friedel-Craft cyclization under acidic
conditions afforded compound 7. DIP and TIP consist of two main
components: either diphenylamine or triphenylamine as the hole-
transporting moiety and indenophenanthrene as the emissive
moiety; these two components were connected by the Buchwald
ꢁ
C14 of DIP is twisted about 1.7 , and the dihedral angle con-
ꢁ
necting the C5-C4-C8-C14 of TIP is 2.4 , respectively. In TIP, the
dihedral angle between additional phenyl ring and inden-
ꢁ
ophenanthrene moiety is 37.1 . The introduction of the twisted
structure of the diphenylamine and triphenylamine moieties
inhibited the aggregation of DIP and TIP in the non-doped film.
The highest occupied molecule orbitals (HOMOs) of DIP and
TIP are localized on the diphenylamine and triphenylamine
Fig. 1. Optimized structures and calculated highest occupied molecular orbital and lowest occupied molecular orbital density maps obtained from DFT calculations of DIP and TIP,
performed at the B3LYP/6-311G level of theory.

S. Jeong, J.-I. Hong / Dyes and Pigments 144 (2017) 9e16
13
Fig. 2. Synthetic routes to DIP and TIP.
cross-coupling and the Suzuki cross-coupling reactions, respec-
3.4. Photophysical properties
1
13
tively [21]. DIP and TIP were characterized by H NMR, C NMR,
and low- and high-resolution mass spectrometry. These two blue
emitting materials were purified further by train sublimation under
Fig. 4 shows the normalized UVevis absorbance and PL spectra
of DIP and TIP (Table 1). All absorption bands between 330 and
400 nm for DIP and TIP originate from the intramolecular charge-
transfer transitions from the arylamine to indenophenanthrene
moiety. The absorption band shape of the brominated inden-
ophenanthrene (7), an intermediate synthetic compound, is similar
ꢃ4
reduced pressure (<10 Torr).
3.3. Thermal properties
compared to those of DIP and TIP (Fig. S1). In toluene, the PL l
max
peaks of DIP and TIP were observed around 420 nm. Compared to
the solution state, the emission maxima of DIP and TIP in the solid
state show a slight bathochromic shift of about 10 nm, indicating
that the aggregation effect is rarely observed in the solid states of
DIP and TIP. Despite the extra phenyl unit introduced in TIP, the PL
The thermal properties of DIP and TIP were investigated using
DSC and TGA (Fig. 3). DIP and TIP exhibit high thermal stability with
a decomposition temperature (T
of 326.9 and 354.4 C, respectively, and a T
d
, corresponding to 5% weight loss)
ꢁ
ꢁ
g
of 90.3 and 112.8 C,
respectively. TIP is more thermally stable than DIP because of the
additional phenyl linker moiety [22].
Fig. 4. UVevis absorption and PL spectra of DIP (black squares) and TIP (red circles).
(Dashed lines and open symbols: UVevis absorption in toluene (10
m
M); solid lines and
open symbols: PL spectra in toluene (10
mM); and solid lines and filled symbols: PL
Fig. 3. DSC and TGA graphs of DIP and TIP.
spectra in the film state.).

14
S. Jeong, J.-I. Hong / Dyes and Pigments 144 (2017) 9e16
Table 1
Thermal and photophysical properties of DIP and TIP.
ꢁ
a
a
b
c
HOMO /LUMOe (eV)
d
T
d
/T
g
( C)
l
abs (nm)
l
PL (nm)
l
PL (nm)
F
fl
g
E (eV)
a
b
b
DIP
TIP
326.9/90.3
354.4/112.8
364, 382
358, 370
415
413, 429
426
428
0.77 , 0.44
3.1
3.1
5.3, 2.2
5.4, 2.3
a
0.90 , 0.52
a
1
0
m
M in toluene.
Neat film.
Onset absorption wavelength in toluene.
b
c
d
e
þ
CV oxidation potential in dichloromethane (Fc/Fc as reference: 4.7 eV).
Deduced from HOMO and E
g
.
emission spectra in solution and solid states of DIP and TIP are very
similar [19]. These results demonstrate that the additional phenyl
ring of TIP does not contribute to the extension of the conjugation
length because of the distorted dihedral angle (37.1 ) between the
additional phenyl ring and the indenophenanthrene moiety.
3.5. Electroluminescence properties
OLED devices were fabricated using DIP or TIP as a non-doped
deep-blue fluorescent emitter in the emitting layer (EML). The
device configuration was ITO/NPB (40 nm)/TCTA (20 nm)/EML (DIP
or TIP, 30 nm)/TPBI (15 nm)/LiF (1 nm)/Al (100 nm). Fig. 5(a) shows
the current densityevoltage characteristics of the OLED devices
containing DIP and TIP used as the EML, and the performances of
the OLEDs are summarized in Table 2 and Fig. S3. Both of the de-
ꢁ
The fluorescence quantum yields (
measured to be 0.77 and 0.90, respectively, using 9,10-di(naphth-2-
yl)anthracene (ADN,
¼ 0.57) as a reference at room temperature
Table 1) [23]. And the fluorescence quantum yields ( ) of solid
DIP and DIP are 0.44 and 0.52, respectively (Table 1).
fl
F ) of DIP and TIP were
F
fl
(
F
fl
2
vices had low turn-on voltages (at a luminance of 1 cd/m ) at 3.2 V,
The absorption onsets of the UVevis spectra of DIP and TIP
were both found to be 400 nm, which corresponds to an optical
bandgap of 3.1 eV. From the optical bandgap and the HOMO en-
ergy levels of 5.3 and 5.4 eV for DIP and TIP, respectively, esti-
mated from the CV measurements, the LUMO energy levels were
calculated to be 2.2 and 2.3 eV for DIP and TIP, respectively
possibly originating from the small injection barriers in the devices.
The current density of the TIP-based device was higher than that of
the DIP-based device at the same voltage, whereas the luminance
values of the DIP-based devices was higher than that of the TIP-
based device at the same current density, as shown in Fig. 5(b).
The current density mainly depends on the differences in the en-
ergy levels of the thin organic layers in OLEDs [24]. These results
(Fig. S2, Table 1).
Fig. 5. Device performance of the deep-blue OLEDs containing DIP and TIP. (a) The current density-voltage characteristics (inset: energy level diagram of the devices), (b) lumi-
nanceevoltage characteristics, (c) quantum efficiencyecurrent density characteristics, and (d) electroluminescence spectra (inset: device structure and thickness of each layer).

S. Jeong, J.-I. Hong / Dyes and Pigments 144 (2017) 9e16
15
Table 2
The performance of the non-doped deep blue devices containing DIP and TIP as the emitting layers.
a
EQEb (%)
LEmaxc
(cd A
PEmaxd
(lm W
b
CIEb
(x, y)
FWHMb
(nm)
EML
V
on
EQEmax (%)
ELmax (nm)
ꢃ1
ꢃ1
)
(
V)
)
DIP
TIP
3.2
3.2
3.27
1.77
3.25
1.70
1.11
1.00
0.89
0.83
424
428
(0.158, 0.040)
(0.158, 0.069)
44
52
a
2
Turn-on voltage at 1 cd/m .
At 10 mA/cm .
Luminance efficiency (LE).
Power efficiency (PE).
b
c
2
d
indicate that the electroluminescent (EL) performance of the DIP-
based device is more efficient than that of the TIP-based device.
The quantum efficiencyecurrent density of two devices is plotted
in Fig. 5(c). The DIP-based device shows a better maximum EQE of
density is lower in comparison with electron density at the same
voltage, whereas, in the case of the DIP-based device, the hole and
electron densities are well matched at the same voltage. This
phenomenon can be explained by the differences in the HOMO and
LUMO energy levels between DIP and TIP. Because of the higher
HOMO energy level of 5.3 eV of DIP and 5.4 eV of TIP than that
(5.7 eV) of TCTA, neither have a hole injection barrier from the hole
transport layer (HTL) to the EML. In contrast, the LUMO energy
levels of DIP and TIP are 2.1 and 2.2 eV, respectively, indicating that
electron injection from the electron transport layer (ETL) to the
EML of TIP is easier than to that of DIP. Despite the small difference
in the energy levels of both deep-blue emitters, there is a
discrepancy in the current densities at the same voltage (Fig. 5(a)).
Thus, the DIP-based device is more efficient than the TIP-based
device because of the relatively better hole and electron charge
balance. Although more excitons were generated from the TIP-
based device than the DIP-based device, the excess electron injec-
tion caused exciton-polaron quenching, arising from the hole and
electron imbalance. Therefore, the DIP-based device exhibited
higher efficiency than the TIP-based device [19,26]. These results
agree with the energy level diagrams of devices using DIP and TIP as
EMLs (Fig. 5(a) inset).
3
.27% compared to that (1.77%) of the TIP-based device. Fig. 5(d)
shows the normalized EL spectra of the DIP and TIP-based devices
with maximum peak wavelengths at 424 and 428 nm, respectively,
which originates from the singlet exciton of each emitter without
any other emission from the adjacent layers. The CIE coordinates of
the DIP and TIP-based devices are (0.158, 0.040) and (0.158, 0.069),
respectively. The much smaller y-coordinate value of the DIP-based
device results from its narrower EL spectrum (the full width at half
maximum (FWHM) of 44 nm) compared to the TIP-based device
(
the FWHM of 52 nm) [25].
For the investigation of the carrier balance of the DIP and TIP-
based devices, hole-only and electron-only devices were also
fabricated. The configuration of the hole-only devices was ITO/NPB
(
40 nm)/TCTA (20 nm)/DIP or TIP (30 nm)/NPB (5 nm)/Al (100 nm),
and the electron-only devices had an ITO/TPBI (5 nm)/DIP or TIP
(
(
30 nm)/TPBI (15 nm)/LiF (1 nm)/Al (100 nm) structure. NPB
LUMO: 2.3 eV) on the cathode side of the hole-only devices and
TPBI (HOMO: 6.3 eV) on the anode side of the electron-only devices
were utilized to block electron injection from Al (4.3 eV, corre-
sponding to a large energy barrier of 2.0 eV) and hole injection from
ITO (4.8 eV, corresponding to a large energy barrier of 1.5 eV),
respectively. Fig. 6 shows the current densityꢃvoltage curves of
hole-only and electron-only devices of DIP and TIP, respectively.
Both the hole and electron carrier densities of the TIP-based device
are higher than carrier density of the DIP-based device at the same
voltage. However, in the case of the TIP-based device, the hole
4. Conclusion
Novel luminescent molecules with indenophenanthrene cores
attached to either triphenylamine or diphenylamine moieties were
designed and synthesized for use as extremely deep blue fluores-
cent emitting materials. Because the DIP-based OLED device has a
well-matched hole and electron density at the same voltage, the
DIP-based device exhibited a higher efficiency than the TIP-based
device. A non-doped device using DIP as the emitting material
exhibited a maximum EQE of 3.27% with CIE color coordinates of
(0.158, 0.040). The introduction of the indenophenanthrene moiety
reported in this study suggests a new strategy for the molecular
design of highly efficient non-doped deep blue OLED materials.
Acknowledgements
This work was supported by the NRF grant (2015R1A2A-
1A15055347) funded by the MSIP. We thank the Samsung Display
Co., Ltd. for financial support.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2017.05.014.
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