Friedel-Crafts arylmethylation: A simple approach to synthesize bipolar host materials for efficient electroluminescence

Article abstract of DOI:10.1016/j.orgel.2016.08.018

In order to simplify the synthesis of bipolar host materials of OLEDs, a facile synthetic approach was developed and a series of sulfone-contained bipolar host materials were synthesized via mild one-step Friedel-Crafts arylmethylation. Due to π-conjugate-interrupted connection between donor moiety and sulfone moiety, those materials keep high triplet energy and separate the HOMO and LUMO levels. Furthermore, the introduction of sulfone group can significantly lower LUMO level. Based on newly synthesized sulfone-based bipolar host materials, efficient solution-processed sky-blue phosphorescent OLEDs were fabricated with high current efficiency of 16.5?cd/A. Our results demonstrate Friedel-Crafts arylmethylation is powerful synthetic strategy to construct bipolar host materials.

Full text of DOI:10.1016/j.orgel.2016.08.018

Organic Electronics 38 (2016) 370e378
Contents lists available at ScienceDirect
Organic Electronics
journal homepage: www.elsevier.com/locate/orgel
Friedel-Crafts arylmethylation: A simple approach to synthesize
bipolar host materials for efficient electroluminescence
,
,
, **
Chang-Jin Ou a b, Jin-Yi Lin a b, Jie Mao b, Shuang-Quan Chu b, Yu Zhao b, Ling-Hai Xie b
,
Hong-Tao Cao b, Xin-Wen Zhang b ***, Ying Wei b, Wei Huang a
,
, b, *
a Key Laboratory of Flexible Electronics (KLOFE), Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced
Materials (SICAM), Nanjing Tech University, Nanjing 211816, China
b Institute of Optoelectronic Materials (IOM), Key Laboratory for Organic Electronics & Information Displays (KLOEID), Institute of Advanced Materials
(IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing University of Posts & Telecommunications, Nanjing 210046,
China
a r t i c l e i n f o
a b s t r a c t s
Article history:
In order to simplify the synthesis of bipolar host materials of OLEDs, a facile synthetic approach was
developed and a series of sulfone-contained bipolar host materials were synthesized via mild one-step
Received 20 June 2016
Received in revised form
15 August 2016
Friedel-Crafts arylmethylation. Due to
p-conjugate-interrupted connection between donor moiety and
sulfone moiety, those materials keep high triplet energy and separate the HOMO and LUMO levels.
Furthermore, the introduction of sulfone group can significantly lower LUMO level. Based on newly
synthesized sulfone-based bipolar host materials, efficient solution-processed sky-blue phosphorescent
OLEDs were fabricated with high current efficiency of 16.5 cd/A. Our results demonstrate Friedel-Crafts
arylmethylation is powerful synthetic strategy to construct bipolar host materials.
© 2016 Published by Elsevier B.V.
Accepted 18 August 2016
Keywords:
Bipolar host materials
Sulfone
Friedel-Crafts arylmethylation
Solution process
1. Introduction
transport of carriers, which determines the quantum efficiency of
devices [5e10].
The study enthusiasm on phosphorescence and thermally-
activated delayed fluorescence (TADF)-based OLEDs is soaring
since both can simultaneously harvest singlet and triplet excitons,
which enables a 100% internal quantum efficiency [1e3]. While,
due to long lifetime of triplet excitons, triplet-triplet annihilation
and triplet-polaron annihilation become serious problems at high
exciton density in both PhOLEDs and TADF OLEDs [4]. In order to
solve the problems, the emitters should be dispersed into a host
material with higher triplet energy level at low doped concentra-
tion to confine triplet excitons on emitters. Numerous studies
demonstrate that bipolar host materials, incorporating electron-
donating (D) and electron-accepting (A) components into mole-
cule structures, can facilitate and balance the injection and
Phosphine oxide (PO) group is widely used to construct bipolar
host materials, which have exhibited excellent device performance,
while PO-based materials are synthesized via multiple steps
[11e15]. Novel synthetic approaches should be developed to
simplify synthesis and meet the need of commercialization of
OLEDs. Lee and Kim groups respectively reported 4,5-
diazofluorenone and thioxanthe-9-one-S,S-dioxide condensed
with carbazole derivatives under acid catalysis and afforded bipolar
host materials [16,17]. Huang group reported highly efficient blue
PhOLEDs with maximum current efficiency of 42.1 cd/A based on
carbazole-pyridine hybridized bipolar host materials, which were
synthesized via one-step CeN coupling approach [18]. Generally, D
components of bipolar host material, such as carbazole, triphe-
nylamine, dibenzothiophene, are typically synthetic precursors for
Friedel-Crafts (FC) reaction [19e21]. In addition, the D and A syn-
thons are available individually, and can be freely combined via
rational molecular design to construct a desired bipolar host ma-
terial. So one-step FC arylmethylation may be an intriguing reaction
to construct efficient bipolar host materials. Quan et al. reported
* Corresponding author. Key Laboratory of Flexible Electronics (KLOFE), Institute
of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for
Advanced Materials (SICAM), Nanjing Tech University, Nanjing 211816, China.
** Corresponding author.
*** Corresponding author.
4,5-diazofluorene-9-ol
(A
synthon)
facile
attached
to
E-mail address: iamwhuang@njupt.edu.cn (W. Huang).
http://dx.doi.org/10.1016/j.orgel.2016.08.018
1566-1199/© 2016 Published by Elsevier B.V.

C.-J. Ou et al. / Organic Electronics 38 (2016) 370e378
371
triphenylamine (D synthon) via sulfuric acid-catalyzed FC arylme-
thylation, and they found the number of A component in host
material affects device current efficiency dramatically [22]. Our
group has utilized FC arylmethylation to construct several kinds of
bipolar materials [23e25]. Huang et al. developed bulky 9-
pyridinylfluorenyl moiety functionalized bipolar host materials
via FC arylmethylation [24]. However, due to lack of A synthons of
FC arylmethylation and harsh reaction condition, researchers have
paid less attention to this synthetic strategy.
Nowadays, sulfone has become attractive building block in bi-
polar host materials and TADF emitters due to outstanding
electron-accepting and transporting ability [17,26e34]. Kim [14],
Poriel [28] and Su [29] groups respectively reported sp3-C con-
nected thioxanthene 10,10-dioxide with carbazole or triphenyl-
amine bipolar host materials, showing separated HOMO and LOMO
energy levels, and high current efficiency of over 20 cd/A in Firpic-
based sky-blue PhOLEDs. However, there is still a lacks of a general
and convenient approach to construct sulfone-based bipolar host
materials. Herein, two sulfone-contained A synthons, 9-hydroxy-9-
phenylthioxanthene 10,10-dioxide and 9-hydroxy-9-(4-(octyloxy)
phenyl)thioxanthene 10,10-dioxide, were synthesized via directed
ortho-metalation of diphenyl sulfone. Those A synthons can effec-
tively link to D synthons, and construct bipolar host materials un-
der mild BF3$Et2O-mediated FC arylmethylation. Finally, efficient
solution-processed sky-blue PhOLEDs were fabricated with high
current efficiency of 16.5 cd/A based on synthesized bipolar host
materials.
was added into reaction after 3 h. Removing cool bath and stirring
at room temperature about 24 h, then saturated NH4Cl solution
was added to quench and hydrolyze, and extracted with dichloro-
methane. The combined organic abstract was dried over anhydrous
MgSO4 and filtered. The solution was evaporated under vacuum
condition and the crude product was purified by silica gel column
chromatography to afford white solid (9.4 g) with 88.0% yield. 1H
NMR (400 MHz, CDCl3)
d
8.11 (d, J ¼ 7.6 Hz, 2H), 7.94 (d, J ¼ 8.0 Hz,
2H), 7.64 (dd, J ¼ 7.6, 1.6 Hz, 2H), 7.56 (dd, J ¼ 7.6, 1.2 Hz, 2H),
7.28e7.24 (m, 5H), 3.23 (s, 1H); 13C NMR (100 MHz, CDCl3)
d
143.93, 143.63, 136.06, 132.92, 128.86, 128.44, 128.18, 127.89,
126.80, 123.69, 74.09. IR (KBr):
y
¼ 3452 (OeH), 3057 (Aryl CeH),
1593 (Aryl C]C), 1581 (Aryl C]C), 1494 (Aryl C]C), 1469 (Aryl C]
C), 1448 (Aryl C]C), 1437 (Aryl C]C), 1377 (OeH), 1280 (eSO2e),
1213, 1157 (eSO2e), 1142 (CeO), 1026, 906, 870, 760, 746, 594 cmꢁ1
.
9-hydroxy-9-(4-(octyloxy)phenyl)thioxanthene 10,10-dioxide
(OPhSOH). The synthetic procedure is similar to PhSOH, and
afford light yellow solid product (8.5 g) with 72.1% yield. 1H NMR
(400 MHz, CDCl3)
d
8.11 (dd, J ¼ 7.6, 1.2 Hz, 2H), 8.00 (d, J ¼ 8.0 Hz,
2H), 7.65 (td, J ¼ 7.6, 1.2 Hz, 2H), 7.56 (t, J ¼ 7.6 Hz, 2H), 7.10 (d,
J ¼ 9.2 Hz, 2H), 6.74 (d, J ¼ 9.2 Hz, 2H), 3.86 (t, J ¼ 6.8 Hz, 2H), 3.17 (s,
1H), 1.75e1.68 (m, 2H), 1.42e1.35 (m, 2H), 1.30e1.24 (m, 8H), 0.87
(t, J ¼ 6.8 Hz, 3H). 13C NMR (100 MHz, CDCl3)
d 158.85, 144.03,
135.99, 135.92, 132.83, 128.69, 128.19, 127.54, 123.75, 114.19, 73.95,
67.96, 31.79, 29.30, 29.20, 29.17, 26.00, 22.63, 14.08. IR (KBr):
y
¼ 3506 (OH), 3066 (Aryl CH), 2922 (CH2, CH3), 2854 (CH2, CH3),
1608 (Aryl C]C), 1579 (Aryl C]C), 1506 (Aryl C]C), 1465 (Aryl C]
C), 1441 (Aryl C]C), 1392 (CH3), 1288 (eSO2e), 1248 (Ar-O-R), 1153
2. Experimental section
(eSO2e), 1136 (CeO), 1043, 1024, 910, 825, 763, 756, 626, 592 cmꢁ1
.
Synthesis of 1b. 9-phenylcarbazole (0.97 g, 4 mmol) and OPh-
SOH (0.45 g, 1 mmol) were dissolved in anhydrous dichloro-
methane solution (50 mL). Then, the BF3$Et2O (0.14 g, 1 mmol) was
added slowly into the reaction mixture. Large amount of water was
added to quench reaction after 8 h, and extracted with dichloro-
methane. The combined organic abstract was dried over anhydrous
MgSO4 and filtered. The solution was evaporated under vacuum
condition and the crude product was purified by silica gel column
chromatography to afford light yellow solid (0.61 g) with 91.0%
2.1. Materials and instruments
All of chemicals were purchased from J&K Scientific Co. Ltd., and
were used without further purification unless otherwise state.
Anhydrous THF was distilled from Na/benzophenone.
1H NMR and 13C NMR spectra were measured on a Varian
Mercury Plus 400 spectrometer with tetramethylsilane as the in-
ternal standard. Absorption and photoluminescence spectra were
measured in dichloromethane solution using a SHIMADZU UV-
3600 spectrophotometer and a SHIMADZU RF-5301PC spectro-
photometer, respectively. Low-temperature phosphorescence were
measured in 2-methylTHF at 77 K using a HITACHI F4600 spec-
trophotometer. Thermogravimetric analysis (TGA) was undertaken
with a Shimadzu thermogravimetry and differential thermal anal-
ysis DTG-60H at a heating rate of 10 ꢀC/min under N2. Differential
scanning calorimetry (DSC) measurements were performed under
a nitrogen atmosphere at both heating and cooling rates of 10 ꢀC/
min, using Shimadzu DSC-60A. Elemental analyses were recorded
at the Vario EL III (Elemeraor Co. Ltd, Germany). FT-IR spectra were
recorded at Shimadzu IRPrestige-21. The single crystal data
collection was performed at 100 or 298 K on a Bruker 2000 CCD
yield. 1H NMR (400 MHz, CDCl3)
d
8.22 (dd, J ¼ 7.6, 1.2 Hz, 2H), 7.89
(d, J ¼ 7.6 Hz, 1H), 7.59e7.55 (m, 5H), 7.55e7.51 (m, 2H), 7.50e7.44
(m, 3H), 7.41e7.35 (m, 2H), 7.28 (d, J ¼ 8.8 Hz, 2H), 7.24e7.19 (m,
1H), 7.13 (d, J ¼ 8.0 Hz, 2H), 6.84 (dd, J ¼ 8.8, 1.8 Hz, 1H), 6.81e6.74
(m, 4H), 3.93 (t, J ¼ 6.4 Hz, 2H), 1.83e1.71 (m, 2H), 1.47e1.40 (m,
2H), 1.33e1.26 (m, 8H), 0.88 (t, J ¼ 6.8 Hz, 3H). 13C NMR (100 MHz,
CDCl3) d 158.08, 146.37, 141.29, 139.75, 137.51, 137.32, 136.88, 136.18,
132.01, 131.68, 131.23, 129.87, 128.60, 127.82, 127.54, 126.96, 126.16,
124.02, 123.19, 122.77, 122.39, 120.36, 120.04, 113.92, 109.93, 109.35,
67.97, 58.64, 31.82, 29.37, 29.31, 29.24, 26.09, 22.65, 14.10. MALDI-
TOF MS: calculated for C45H41NO3S 675.88; found: 675.14 (Mþ).
Elemental analysis calculated for C45H41NO3S: C, 79.97%; H, 6.11%;
N, 2.07%; O, 7.10%; S, 4.74%. Found: C, 80.10%; H, 6.19%; N, 2.25%. IR
area detector using graphite-monochromated Mo K
a
radiation
(KBr):
y
¼ 3061 (aryl CH), 2926 (CH2, CH3), 2854 (CH2, CH3), 1597
(l
¼ 0.71073 Å). All structures were solved by direct methods using
(Aryl C]C), 1502 (Aryl C]C), 1456 (Aryl C]C), 1440 (Aryl C]C),
1361, 1307 (eSO2e), 1249 (Ar-O-R), 1234 (Ar-N-Ar), 1165 (eSO2e),
1145, 1056, 827, 758, 731, 698, 584, 572 cmꢁ1. Molar extinction
coefficient (ε, m2/mol): 2150 (300 nm), 550 (346 nm). Melting
point: 233 ꢀC.
SHELXS-2014 and refined against F2 using SHELXL-2014. Hydrogen
atoms were fixed geometrically and refined isotropically. CCDC No.
of PhSOH, OPhSOH, 1c, 1d and 1e are 1,473,561, 1,473,563, 1,479,132,
1,473,566 and 1,479,421, respectively.
Synthesis of 2b. 9-phenylcarbazole (0.24 g, 1 mmol) and OPh-
SOH (0.95 g, 2.1 mmol) were dissolved in anhydrous dichloro-
methane solution (100 mL). Then, the BF3$Et2O (0.42 g, 3 mmol)
was added slowly into the reaction mixture. Large amount of water
was added to quench reaction after 8 h, and extracted with
dichloromethane. The combined organic abstract was dried over
anhydrous MgSO4 and filtered. The solution was evaporated under
vacuum condition and the crude product was purified by silica gel
2.2. Synthesis
9-hydroxy-9-phenylthioxanthene
10,10-dioxide
(PhSOH).
Diphenyl sulfone (7.2 g, 33 mmol) was dissolved in anhydrous THF
solution (200 mL) and stirred at dry ice-alcohol bath, and then
2.5 M n-BuLi/n-hexane solution (27.7 mL, 69.3 mmol) was added
slowly. Methyl 40-bromobiphenyl-2-carboxylate (4.08 g, 30 mmol)

372
C.-J. Ou et al. / Organic Electronics 38 (2016) 370e378
column chromatography to afford white solid 2b (0.72 g) with
64.9% yield.1H NMR (400 MHz, CDCl3)
7.54e7.50 (m, 8H), 7.44 (m, 5H), 7.24 (d, J ¼ 9.0 Hz, 2H), 7.16 (d,
J ¼ 2.0 Hz, 2H), 7.07 (d, J ¼ 8.0 Hz, 1H), 6.79 (dd, J ¼ 8.8, 2.0 Hz, 2H),
6.76e6.72 (m, 4H), 6.70e6.66 (m, 4H), 3.93 (t, J ¼ 6.8 Hz, 4H),
1.83e1.73 (m, 4H), 1.50e1.40 (m, 4H), 1.34e1.24 (m, 16H), 0.87 (t,
C), 1361, 1294 (eSO2e), 1229 (Ar-N-Ar), 1168 (eSO2e), 1147, 1130,
1059, 804, 790, 760, 700, 570 cmꢁ1. Molar extinction coefficient (ε,
m2/mol): 4782 (304 nm), 507 (356 nm). Melting point: 355 ꢀC.
Synthesis of 2c. The synthetic procedure is similar to 2b, and
afford white solid product (0.95 g) with 77% yield. 1H NMR
d
8.19 (dd, J ¼ 7.6,1.2 Hz, 4H),
(400 MHz, CDCl3)
d
8.25 (dd, J ¼ 7.6, 1.2 Hz, 4H), 8.07 (d, J ¼ 1.2 Hz,
J ¼ 6.8 Hz, 6H). 13C NMR (100 MHz, CDCl3)
d
158.13, 146.10, 140.08,
2H), 7.65 (dd, J ¼ 8.4, 1.2 Hz, 2H), 7.63e7.60 (m, 10H), 7.56 (t,
J ¼ 7.6 Hz, 4H), 7.51e7.45 (m, 8H), 7.32 (d, J ¼ 8.8 Hz, 2H), 7.30e7.27
(m, 6H), 7.15 (d, J ¼ 8.0 Hz, 4H), 6.92e6.89 (m, 4H), 6.86 (dd, J ¼ 8.4,
137.33, 137.24, 136.60, 136.49, 132.03, 131.63, 131.45, 129.82, 128.29,
127.82, 127.55, 126.72, 124.01, 122.84, 122.06, 113.76, 109.46, 68.00,
58.50, 31.81, 29.38, 29.35, 29.24, 26.13, 22.65, 14.10. MALDI-TOF MS:
2.0 Hz, 2H). 13C NMR (101 MHz, CDCl3)
d 146.15, 144.44, 140.47,
calculated for
C
72H69NO6S2 1108.45; found: 1107.25 (Mþ).
140.26, 137.48, 137.44, 136.59, 134.53, 132.16, 131.75, 130.21, 129.94,
128.76, 128.16, 127.95, 127.62, 127.32, 126.90, 126.24, 124.10, 123.67,
123.01, 122.57, 119.05, 110.15, 109.47, 59.29. MALDI-TOF MS: calcu-
lated for C74H48N2O4S2 1093.31; found: 1092.05 (Mþ). Elemental
analysis calculated for C74H48N2O4S2: C, 81.29%; H, 4.43%; N, 2.56%;
O, 5.85%; S, 5.87%. Found: C, 81.13%; H, 4.29%; N, 2.41%. IR (KBr):
Elemental analysis calculated for C72H69NO6S2: C, 78.02%; H, 6.27%;
N, 1.26%; O, 8.66%; S, 5.79%. Found: C, 78.31%; H, 6.15%; N, 1.50%. IR
(KBr):
y
¼ 3063 (aryl CH), 2926 (CH2, CH3), 2853 (CH2, CH3), 1606
(Aryl C]C), 1506 (Aryl C]C), 1467 (Aryl C]C), 1440 (Aryl C]C),
1307 (eSO2e), 1249 (Ar-O-R), 1169 (eSO2e), 1056, 827, 759, 700,
594, 582 cmꢁ1. Molar extinction coefficient (ε, m2/mol): 3288
(305 nm), 700 (353 nm). Melting point: 298 ꢀC.
y
¼ 3061 (aryl CH), 1595 (Aryl C]C), 1500 (Aryl C]C), 1470 (Aryl
C]C), 1440(Aryl C]C), 1359, 1307 (eSO2e), 1232 (Ar-N-Ar), 1170
(eSO2e), 1147, 1130, 1057, 808, 758, 698, 594, 572 cmꢁ1. Molar
extinction coefficient (ε, m2/mol): 4938 (310 nm), 513 (359 nm).
Melting point: 340 ꢀC.
Synthesis of 1a. The synthetic procedure is similar to 1b, and
afford light yellow solid product (0.32 g) with 79.5% yield. 1H NMR
(400 MHz, CDCl3)
1H), 7.59e7.54 (m, 7H), 7.48 (t, J ¼ 8.0, 1.2 Hz, 3H), 7.39 (d, J ¼ 7.6 Hz,
2H), 7.30e7.28 (m, 4H), 7.21 (td, J ¼ 7.2, 1.6 Hz, 2H), 7.12 (d,
J ¼ 8.0 Hz, 2H), 6.88 (dd, J ¼ 7.2, 1.6 Hz, 2H), 6.84 (dd, J ¼ 8.8, 2.0 Hz,
1H). MALDI-TOF MS: calculated for C37H25NO2S 547.66; found:
547.05 (Mþ). Elemental analysis calculated for C37H25NO2S: C,
81.14%; H, 4.60%; N, 2.56%; O, 5.84%; S, 5.85%. Found: C, 81.04%; H,
d
8.23 (dd, J ¼ 7.6, 1.2 Hz, 2H), 7.87 (d, J ¼ 8.0 Hz,
Synthesis of 1d. The synthetic procedure is similar to 2a, and
afford light yellow solid product (0.78 g) with 85% yield. 1H NMR
(400 MHz, CDCl3)
d
8.37 (s, 1H), 8.27e8.16 (m, 4H), 7.74 (dd, J ¼ 8.4,
1.6 Hz, 1H), 7.69 (m, 2H), 7.65e7.58 (m, 8H), 7.55 (td, J ¼ 7.6, 1.2 Hz,
2H), 7.52e7.46 (m, 8H), 7.35e7.28 (m, 2H), 7.17 (d, J ¼ 7.6 Hz, 2H),
6.86 (dd, J ¼ 8.7, 1.6 Hz, 1H), 6.79 (s, 4H), 3.92 (t, J ¼ 6.4 Hz, 2H),
1.81e1.71 (m, 2H), 1.47e1.37 (m, 2H), 1.32e1.23 (m, 8H), 0.87 (t,
4.81%; N, 2.33%. IR (KBr):
y
¼ 3057 (aryl CH), 1597 (Aryl C]C), 1502
(Aryl C]C), 1471 (Aryl C]C), 1448 (Aryl C]C), 1358, 1328, 1288
(eSO2e), 1230 (Ar-N-Ar), 1165 (eSO2e), 1057, 813, 761, 748, 732,
702, 650, 594.571 cmꢁ1. Molar extinction coefficient (ε, m2/mol):
2125 (299 nm), 513 (346 nm). Melting point: over 185 ꢀC.
Synthesis of 2a. The synthetic procedure is similar to 2b, and
afford white solid product (0.88 g) with 74.3% yield. 1H NMR
J ¼ 6.8 Hz, 3H). 13C NMR (100 MHz, CDCl3)
d 158.09, 146.43, 141.36,
140.45, 140.24, 140.05, 137.76, 137.58, 137.32, 136.97, 136.18, 134.69,
134.23, 132.04, 131.74, 131.29, 129.91, 128.70, 127.85, 127.55, 127.47,
127.08, 126.92, 126.19, 126.07, 125.90, 124.04, 123.91, 123.79, 123.50,
123.07, 122.48, 120.45, 119.97, 119.03, 118.97, 113.94, 110.17, 109.96,
109.88, 109.40, 67.97, 58.69, 31.79, 29.35, 29.29, 29.21, 26.07, 22.64,
14.09. MALDI-TOF MS: calculated for C63H52N2O3S 917.16; found:
916.31 (Mþ). Elemental analysis calculated for C63H52N2O3S: C,
82.50%; H, 5.71%; N, 3.05%; O, 5.23%; S, 3.50%. Found: C, 82.31; H,
(400 MHz, CDCl3)
d
8.21 (dd, J ¼ 7.6, 1.2 Hz, 4H), 7.55e7.52 (m, 8H),
7.45 (td, J ¼ 8.0, 1.2 Hz, 5H), 7.29e7.27 (m, 4H), 7.25e7.22 (m, 4H),
7.12 (d, J ¼ 1.6, Hz, 2H), 7.06 (d, J ¼ 7.6 Hz, 4H), 6.83e6.81 (m, 6H).
13C NMR (100 MHz, CDCl3)
d145.82, 145.82, 144.63, 144.63, 140.11,
5.70; N, 3.28%. IR (KBr):
y
¼ 3061 (aryl CH), 2924 (CH3, CH2), 2854
137.37, 137.28, 136.41, 132.13, 131.65, 130.25, 129.88, 128.59, 128.04,
127.94, 127.66, 127.22, 126.75, 124.07, 122.73, 122.24, 109.66, 59.12.
MALDI-TOF MS: calculated for C56H37NO4S2 852.03; found: 851.06
(Mþ). Elemental analysis calculated for C56H37NO4S2: C, 78.94%; H,
4.38%; N, 1.64%; O, 7.51%; S, 7.53%. Found: C, 79.12%; H, 4.45%; N,
(CH3, CH2), 1597 (Aryl C]C), 1500 (Aryl C]C), 1470 (Aryl C]C),
1446 (Aryl C]C), 1361, 1305 (eSO2e), 1249 (Ar-O-R), 1230 (Ar-N-
Ar), 1168 (eSO2e), 1057, 804, 760, 698, 582 cmꢁ1. Molar extinction
coefficient (ε, m2/mol): 6663 (305 nm), 700 (355 nm). Melting
point: over 320 ꢀC.
2.01%. IR (KBr):
y
¼ 3061 (aryl CH), 1597 (Aryl C]C), 1500 (Aryl C]
Synthesis of 2d. The synthetic procedure is similar to 2b, and
afford white solid product (0.88 g) with 70.4% yield. 1H NMR
C), 1487 (Aryl C]C), 1440 (Aryl C]C), 1365, 1307 (eSO2e), 1237
(Ar-N-Ar), 1167 (eSO2e), 1147, 1128, 1056, 810, 758, 738, 698, 594,
571 cmꢁ1. Molar extinction coefficient (ε, m2/mol): 2750 (305 nm),
650 (350). Melting point: 320 ꢀC.
Synthesis of 1c. The synthetic procedure is similar to 2a, and
afford light yellow solid product (0.92 g) with 93% yield. 1H NMR
(400 MHz, CDCl3)
d
8.23 (dd, J ¼ 7.6, 1.2 Hz, 4H), 8.07 (d, J ¼ 1.2 Hz,
2H), 7.67e7.63 (m, 4H), 7.61e7.57 (m, 8H), 7.54 (td, J ¼ 7.6, 1.2 Hz,
4H), 7.50e7.44 (m, 8H), 7.30 (d, J ¼ 8.8 Hz, 2H), 7.14 (d, J ¼ 7.6 Hz,
4H), 6.85 (dd, J ¼ 8.8, 2.0 Hz, 2H), 6.80e6.74 (m, 8H), 3.92 (t,
J ¼ 6.8 Hz, 4H), 1.79e1.70 (m, 4H), 1.41 (m, 4H), 1.33e1.22 (m, 16H),
(400 MHz, CDCl3)
d
8.37 (d, J ¼ 1.2 Hz, 1H), 8.25 (dd, J ¼ 7.6, 1.2 Hz,
0.87 (t, J ¼ 6.8 Hz, 6H). 13C NMR (100 MHz, CDCl3)
d 158.07, 146.42,
2H), 8.21 (d, J ¼ 8.0 Hz, 1H), 8.15 (d, J ¼ 1.2 Hz, 1H), 7.75 (dd, J ¼ 8.4,
1.2 Hz, 1H), 7.69e7.60 (m, 10H), 7.57 (d, J ¼ 8.0 Hz, 2H), 7.54e7.43
(m, 9H), 7.33 (d, J ¼ 8.4 Hz, 1H), 7.31e7.28 (m, 4H), 7.17 (d, J ¼ 7.6 Hz,
1H), 6.92 (d, J ¼ 7.6 Hz, 1H), 6.91 (d, J ¼ 7.6 Hz, 1H), 6.86 (dd, J ¼ 8.8,
140.44, 140.22, 137.53, 137.31, 136.92, 136.20, 134.56, 132.04, 131.73,
131.29, 129.90, 128.70, 127.83, 127.57, 126.90, 126.28, 124.03, 123.69,
123.00, 122.45, 119.13, 113.94, 110.10, 109.38, 67.95, 58.68, 31.80,
29.36, 29.31, 29.22, 26.07, 22.64, 14.09. MALDI-TOF MS: calculated
for C90H80N2O6S2 1349.74; found: 1349.31 (Mþ). Elemental analysis
calculated for C90H80N2O6S2: C, 80.09%; H, 5.97%; N, 2.08%; O, 7.11%;
2.0 Hz, 1H). 13C NMR (100 MHz, CDCl3)
d 146.17, 144.44, 141.37,
140.47, 140.28, 140.06, 137.75, 137.56, 137.46, 136.64, 134.72, 134.22,
132.17, 131.76, 130.21, 129.93, 128.76, 128.18, 127.97, 127.59, 127.49,
127.34, 127.08, 126.92, 126.24, 126.10, 125.86, 124.10, 123.92, 123.76,
123.50, 123.11, 122.59, 120.43, 120.00, 119.00, 118.98, 110.22, 109.97,
109.92, 109.47, 59.31. MALDI-TOF MS: calculated for C55H36N2O2S
788.95; found: 788.04 (Mþ). Elemental analysis calculated for
S, 4.75%. Found: C, 79.82%; H, 6.17%; N, 2.15%. IR (KBr):
y
¼ 3063
(aryl CH), 2926 (CH3, CH2), 2853 (CH3, CH2), 1597 (Aryl C]C), 1502
(Aryl C]C), 1470 (Aryl C]C), 1439 (Aryl C]C), 1361, 1307 (eSO2e),
1248 (Ar-O-R), 1134 (Ar-N-Ar), 1168 (eSO2e), 1147, 1128, 1057, 873,
806, 758, 698, 572 cmꢁ1. Molar extinction coefficient (ε, m2/mol):
7175 (310 nm), 700 (359 nm). Melting point: 329 ꢀC.
C
55H36N2O2S: C, 83.73%; H, 4.60%; N, 3.55%; O, 4.06%; S, 4.06%.
Found: C, 83.53%; H, 4.65%; N, 3.29%. IR (KBr):
¼ 3061 (aryl CH),
1597 (Aryl C]C), 1500 (Aryl C]C), 1471 (Aryl C]C), 1444 (Aryl C]
y
Synthesis of 1e. The synthetic procedure is similar to 2a, and
afford white solid product (0.56 g) with 87% yield. 1H NMR

C.-J. Ou et al. / Organic Electronics 38 (2016) 370e378
373
(400 MHz, CDCl3)
d
8.23 (dd, J ¼ 7.6, 1.2 Hz, 2H), 8.15 (d, J ¼ 7.6 Hz,
alcohols, 9-hydroxy-9-phenylthioxanthene-10,10-dioxide (PhSOH)
and 9-hydroxy-9-(4-(octyloxy)phenyl)thioxanthene-10,10-dioxide
(OPhSOH), are shown in Scheme 1. Due to directed ortho-metal-
ation of sulfone group, dilithation of diphenyl sulfone was per-
formed well under treating diphenyl sulfone with 2.1 equivalent n-
butyllithium [35]. Then, using methyl benzoate or 4-
octoxylbenzoate to trap the dilithation, and affording PhSOH and
OPhSOH with high yield of 88% and 72.1%, respectively. In order to
study the reactivity of PhSOH and OPhSOH, we chose 9-
phenylcarbazole (PhCz) as a D synthon and used our previous re-
action condition of FC arylmethylation [19,36]. Fortunately, the
reaction ran very well under mild BF3$Et2O catalyst, which is quite
different from strong protonic acid-catalyzed 9-aryl-4,5-
diazofluoren-9-ol and 9-pyridine-2-ylfluoren-9-ol [12,24]. Due to
electron-accepting effect, carbazole group is deactivated by sulfone
group, mono- or di-substitution of phenylcarbazole (PhCz) can be
easily controlled by adjusting the loading ratio of D and A, and
afford 1a, 2a, 1b, and 2b with high yield of 79.5%, 74.3%, 91% and
64.9%, respectively. Since bicarbazole derivatives, 9,90-diphenyl-
3,30-bicarbazole (DPhBCz) and 1,3-biscarbazol-9-ylbenzene (mCP),
are typical and frequently used unipolar host materials, they can be
functionalized easily by PhSOH and OPhSOH, and afford corre-
sponding mono-, di- or tri-substituted derivatives. In addition, di-
substituted mCP has two isomers, 2e and 2e0, and the ratio 2e to
2e0 is about 5:1 (evaluating from 1H NMR, Fig. S31). The chemical
structures of the compounds were confirmed by FT-IR spectra, 1H
and 13C NMR spectra, and MALDI-TOF mass spectra. Sulfone-
substituted derivatives show high thermal decomposition tem-
perature (Td), the values are all higher than 390 ꢀC (Table 1,
Figs. S35eS39). In addition, the glass transition temperatures (Tg) of
1c, 2c, 2d and 1e, are 202, 250, 172 and 178 ꢀC, respectively, and the
other derivatives do not show obvious Tg, indicating sulfone-
substituted derivatives have outstanding thermal and morpho-
logic stability.
2H), 7.88 (d, J ¼ 7.6 Hz, 1H), 7.85e7.81 (m, 2H), 7.72e7.67 (m, 2H),
7.56e7.53 (m, 4H), 7.50 (d, J ¼ 8.0 Hz, 2H), 7.47 (td, J ¼ 7.6, 1.6 Hz,
2H), 7.45e7.41 (m, 4H), 7.32e7.22 (m, 6H), 7.11 (d, J ¼ 8.0 Hz, 2H),
6.89e6.86 (m, 3H). 13C NMR (101 MHz, CDCl3)
d 146.05, 144.44,
141.03, 140.69, 139.49, 139.43, 139.20, 137.49, 137.02, 132.14, 131.79,
131.31, 130.23, 128.89, 128.22, 128.02, 127.38, 126.51, 126.22, 126.09,
125.74, 125.23, 124.14, 123.62, 123.47, 123.15, 122.61, 120.56, 120.52,
120.39, 109.93, 109.67, 109.40, 59.29. MALDI-TOF MS: calculated for
C
49H32N2O2S 712.86; found: 712.10 (Mþ). Elemental analysis
calculated for C49H32N2O2S: C, 82.56%; H, 4.52%; N, 3.93%; O, 4.49%;
S, 4.50%. Found: C, 82.23%; H, 4.34%; N, 3.79%. IR (KBr):
y
¼ 3061
(aryl CH), 1560 (Aryl C]C), 1497 (Aryl C]C), 1448 (Aryl C]C), 1334,
1303 (eSO2e), 1230 (Ar-N-Ar), 1166 (eSO2e), 1147, 1057, 790, 750,
700, 650, 594, 570 cmꢁ1. Molar extinction coefficient (ε, m2/mol):
4538 (293 nm), 1012 (341 nm). Melting point: 307 ꢀC.
Synthesis of 2e, 2e0 and 3e. The synthetic procedure is similar to
2b, and afford white solid product 2e and 2e0 (0.74 g) and white
solid 3e (0.17 g). The isomers of 2e and 2e0 cannot be purified via
column chromatography, and the ratio of 2e to 2e0 is about 5:1
evaluating from 1H NMR spectra. 1H NMR spectra data of 3e: 1H
NMR (400 MHz, CDCl3)
d
8.23e7.19 (m, 6H), 7.86 (d, J ¼ 7.6 Hz, 1H),
7.78 (s, 1H), 7.76 (t, J ¼ 8.0 Hz, 1H), 7.66e7.63 (m, 2H), 7.59e7.51 (m,
7H), 7.48e7.34 (m, 11H), 7.31e7.20 (m, 10H), 7.12e7.09 (m, 4H), 7.03
(d, J ¼ 8.0 Hz, 4H), 6.87 (dd, J ¼ 7.6, 1.2 Hz, 2H), 6.83 (dd, J ¼ 8.8,
1.6 Hz, 3H), 6.79 (d, J ¼ 7.6 Hz, 4H). MALDI-TOF MS: calculated for
C
87H56N2O6S3 1321.58; found: 1321.15 (Mþ). Elemental analysis
calculated for C87H56N2O6S3: C, 79.07%; H, 4.27%; N, 2.12%; O, 7.26;
S, 7.28%. Found: C, 79.25%; H, 4.11%; N, 2.42%. IR (KBr):
y
¼ 3061
(aryl CH), 1599 (Aryl C]C), 1492 (Aryl C]C), 1456 (Aryl C]C), 1440
(Aryl C]C), 1307 (eSO2e), 1236 (Ar-N-Ar), 1166 (eSO2e), 1147,
1126, 1057, 806, 756, 732, 700, 594, 572 cmꢁ1. Molar extinction
coefficient (ε, m2/mol): 4062 (299 nm), 825 (345 nm).
2.3. Device fabrication and testing
3.2. Crystal structures
Solution-processed OLEDs were fabricated with the configura-
tion of indium tin oxide (ITO)/poly(ethylenedioxythiophene)-pol-
y(styrenesulfonic acid) (PEDOT:PSS, 20 nm)/emissive layer
Single crystals of PhSOH, OPhSOH, and 1be1e were obtained at
ambient temperature by slowly evaporating chloroform/n-hexane
solution. 1e belongs to monoclinic system with P21/c group, and
the others belong to triclinic system with P-1 group (Fig. 1 and
Table S1 and S2). Since sulfone group is a good hydrogen acceptor,
strong hydrogen bonds form in PhSOH and OPhSOH with the dis-
tance of OeH/O]S of 1.994 and 2.053 Å, respectively (Figs. S40
and S41). Thioxanthene-10,10-dioxide moiety adopts a butterfly-
shaped structure and bend along the S-C9 axis. The dihedral an-
gles between the two benzene rings of Thioxanthene-10,10-dioxide
moiety are 21.83ꢀ, 29.99ꢀ, 36.91ꢀ, 24.18ꢀ, 39.46ꢀ, and 30.33ꢀ in
PhSOH, OPhSOH, 1b, 1c, 1d and 1e, respectively. In addition, 1e
shows two crystallographically independent conformations and
adopts alternative arrangement and layered packing pattern in
crystal (Figs. S42 and S43). As seen in 1be1e, due to sterically
hindered sulfone group, and sp3-hybridized C connection of D and
A moieties, the sulfone functionalized derivatives adopt twisted
and non-planar 3D structures, which can effectively suppress
intermolecular interactions and form stable amorphous films.
(~40
nm)/1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene
(TmPyPB,
60 nm)/LiF (0.8 nm)/Al (100 nm). PEDOT:PSS layer with a thickness
of 20 nm was spin-coated directly onto pre-cleaned ITO glass at a
spin speed of 3000 rpm for 60 s, and dried at 120 ꢀC for 20 min
under vacuum condition. The Firpic and dye were dissolved in
chlorobenzene with a concentration of 2 and 15 mg/mL, respec-
tively, and then different weight ratio of Firpic/dye were prepared.
Then the emissive layer was spin-coated onto top of PEDOT:PSS
layer from Firpic/dye chlorobenzene solution and annealed at
100 ꢀC for 20 min to remove residual solvents. TmPyPB, LiF and Al
cathode were successively vacuum-deposited under the pressure
lower than 5 ꢂ 10ꢁ4 pa in order of device configuration, respec-
tively. The thickness of organic films was measured using a spec-
troscopic ellipsometry (a-SE, J.A.Wollam Co. Inc.). The current
density-voltage-luminance characteristics were measured by a
Keithley 2602 source meter with a calibrated silicon photodiode.
The electroluminescence spectra of devices were analyzed with a
spectrometer PR655. All device characterizations were carried out
under ambient laboratory air at room temperature. The emission
area of the devices is 12 mm2.
3.3. Photophysical properties
In order to investigate the effect of the functionalization of
sulfone groups on photophysical properties, absorption, emission
and low temperature phosphorescence were measured, and their
spectra are shown in Fig. 2 and key data are listed in Table 1.
Comparison with parent compounds, the absorption and emission
of sulfone functionalization show bathochromic shift within 10 nm,
3. Results and discussion
3.1. Synthesis and thermal behaviours
The synthetic routes of the key sulfone-contained tertiary

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C.-J. Ou et al. / Organic Electronics 38 (2016) 370e378
Scheme 1. Synthesis of sulfone-contained tertiary alcohols, PhSOH and OPhSOH, and sulfone-substituted carbazole, bicarbazole and mCP derivatives. Donor includes 9-
phenylcarbazole, 9,90-diphenyl-3,30-bicarbazole and 1,3-biscarbazol-9-ylbenzene. It exists two isomers in di-sulfone-substitution of mCP (2e and 2e0), and the ratio 2e to 2e0 is
about 5:1.
Table 1
Physical properties of PhCz, DPhBCz, and mCP, and their sulfone-substituted derivatives.
HOMOd (eV)
LUMOe (eV)
Eg (eV)
ET (eV)
a
c
f
g
Entry
Tg/Tm/Td (ꢀC)
labsb (nm)
lemb (nm)
lph (nm)
PhCz
1a
2a
1b
2b
DPhBCz
1c
2c
1d
2d
NM
293,327,340
299,333,346
305,336,350
300,334,346
305,336,353
304,353
304,356
310,359
305,355
310,359
350,364
358,371
363,375
357,371
365
407,429
412,433
413,438
412,438
414,437
346,361
354,369
356,370
360,373
411,440
419,448
420,448
419,447
420,448
449,479
454,480
456,484
454,483
456,483
412,440
418,446
418,447
419,448
ꢁ5.63
ꢁ5.68
ꢁ5.70
ꢁ5.70
ꢁ5.69
ꢁ5.34
ꢁ5.35
ꢁ5.38
ꢁ5.37
ꢁ5.39
ꢁ5.72
ꢁ5.73
ꢁ5.74
ꢁ5.76
ꢁ2.07
ꢁ2.20
ꢁ2.28
ꢁ2.22
ꢁ2.26
ꢁ1.94
ꢁ2.00
ꢁ2.06
ꢁ2.01
ꢁ2.05
ꢁ2.14
ꢁ2.22
ꢁ2.24
ꢁ2.29
3.56
3.48
3.42
3.48
3.43
3.40
3.35
3.32
3.36
3.34
3.58
3.51
3.50
3.47
3.02
2.96
2.95
2.96
2.95
2.76
2.73
2.72
2.73
2.72
3.01
2.97
2.97
2.96
no/no/410
no/no/402
no/233/397
no/298/393
NM
202/353/496
250/no/433
no/no/404
172/329/425
NM
mCP
1e
2e(2e')
3e
293,326,340
293,327,341
298,331,344
299,333,345
178/307/504
NM
NM
a
Tg: glass transition temperature; Tm: melting point temperature; Td: decomposition temperature; NM: not measurement.
Measured in dichloromethane solution.
Measured in 2-MeTHF at 77 K.
Determined from on-set oxidation potential in dichloromethane, and from equation, HOMO ¼ ꢁ(Eon ꢁ E4)ꢁ4.80 eV, where E4 is on-set oxidation potential in
b
c
d
dichloromethane, the value is 0.40 V vs Ag/AgCl.
e
Evaluated from on-set reduction potential in tetrahydrofuran, and from equation, LUMO ¼ ꢁ(Eon ꢁ E4)ꢁ4.80 eV.
f
Calculated from the equation Eg ¼ LUMO-HOMO.
g
Calculated from phosphorescence spectrum.

C.-J. Ou et al. / Organic Electronics 38 (2016) 370e378
375
Fig. 1. ORTEP drawing (50% ellipsoid probability) of PhSOH, OPhSOH, and 1be1e.
and the number of substitution also affects the red shift of ab-
sorption and emission spectra. While in phosphorescence, there is
about 8 nm red-shift after sulfone functionalization, and spectra
change a little with the change of the number of sulfone sub-
stitutions. All above results clearly indicate that the conjugation-
interrupted link of D and A moieties has a weak electron coupling
interaction, which makes sulfone-substituted derivatives keep high
triplet energy (ET). The ET levels are about 2.96, 2.72 and 2.92 eV in
the sulfone-functionalized PhCz, DPhBCz and mCP derivatives,
respectively, and the drop of ET is very small (less than 0.1 eV). The
ET is high enough for typical sky-blue phosphorescent emitter, bis
[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III)
(Firpic, ET: 2.68 eV), so the sulfone-substituted derivatives can be
used as host materials for Firpic-based sky-blue PhOLEDs.
levels separately locate on sulfone and carbazole moieties.
Furthermore, sulfone functionalization significantly lower LUMO
levels, while HOMO levels keep constant, which is consistent with
the results evaluated from cyclic voltammetry. So using sulfone
group to functionalize can effectively construct bipolar host mate-
rials for PhOLEDs or TADF OLEDs.
In addition, sulfone-substituted derivatives exhibit different
electrochemical stability. PhCz exhibits irreversible oxidation pro-
cess, and a new reduction peak around 0.90 V, indicating electro-
coupling reaction takes place, and bicarbazole derivatives may form
in this process (Fig. S45. Similarly, mono-substituted derivatives (1a
and 1b) show the same behaviors as PhCz; while, di-substituted
derivatives (2a and 2b) show reversible oxidation process, and
exhibit well electrochemical stability under multiple CV scans
(Figs. S46eS48), that means di-substitution of 3,6-position of
carbazole can improve electrochemical stability of carbazole.
DPhBCz and its sulfone-substitution derivatives display two well
reversible oxidation peaks, implying that bicarbazole derivatives
possess excellent electrochemical stability (Figs. S49eS53). mCP
and its derivatives also show electrocoupling behaviors and irre-
versible oxidation process (Figs. S54eS57), indicating electro-
chemical stability of mCP derivatives is not very well.
3.4. Electrochemical properties
Electrochemical behaviors of sulfone-functionalized carbazole
derivatives were probed by cyclic voltammetry. As shown in Fig. 3,
S44 and Table 1, the sulfone-substituted derivatives and its parent
compounds have similar on-set oxidation potentials, while the
introduction of sulfone group can apparently lower the on-set
reduction potentials, and the number of substitution has little in-
fluence on the on-set reduction potential. The electrochemical data
indicate that the introduction electron-accepting sulfone groups
have a little influence on the HOMO levels, while significantly lower
the LUMO energy levels. Taking mCP and 1e for example, the LUMO
level decreases from ꢁ1.84 eV of mCP to ꢁ2.12 eV of 1e. The fall of
LUMO levels is beneficial to the injection of electron from electron-
transporting layer. Theoretical calculation indicates that the intro-
duction of sulfone group can effectively modulate the distribution
of HOMO and LUMO energy levels (Fig. 4). The HOMO and LUMO
3.5. Electroluminescent devices
To evaluate the applications of sulfone-functionalized carbazole
derivatives as bipolar host materials, 1d and 1e were chosen as host
materials to test feasibility, and fabricated solution-processed sky-
blue phosphorescent devices using Firpic as a dopant. The device
performances are shown in Fig. 5, S59 and the key parameters are
summarized in Table 2. Fig. 5 shows current density-voltage-
luminance curves, and current efficiency and power efficiency

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C.-J. Ou et al. / Organic Electronics 38 (2016) 370e378
Fig. 2. Absorption, emission and phosphorescence spectra of sulfone-functionalized PhCz, DPhBCz and mCP derivatives. (Left column) Absorption and fluorescence were taken from
dichloromethane solution at 10ꢁ5 mol/L at room temperature. (Right column) Phosphorescence was recorded in 2-MeTHF at 77 K.
Fig. 3. Cyclic voltammograms of sulfone-functionalized DPhBCz and mCP derivatives in dichloromethane (oxidation) and tetrahydrofuran (reduction) solution with 0.1 M TBAPF6 as
the supporting electrolyte at the scanning of 0.1 V/s at room temperature.

C.-J. Ou et al. / Organic Electronics 38 (2016) 370e378
377
Fig. 4. The distribution of HOMO and LUMO energy levels, and its corresponding values of DPhBCz, 1c, mCP and 1e under B3LYP/6-31G(d) level.
Fig. 5. Solution-processed Firpic-based electroluminescent performance using 1d and 1e as host materials. Current density-voltage-luminance curves, and current efficiency and
power efficiency versus luminance curves based on 1d (top) and 1e (bottom).
Table 2
modest electroluminescent performance with a maximum CE of
10.5 cd/A. Hole-only and electron-only devices of 2d and 1e also
were fabricated to compare hole and electron densities within
emitting layers. As shown in Fig. S63, there are large difference in
current densities in 2d-based hole-only and electron-only devices,
while 1e shows small difference in hole and electron densities and
balance carrier transporting property. That's the main reason why
1e-based device has better performance than 2d-based device. The
above results indicates that sulfone-based bipolar host materials
constructed via Friedel-Crafts reaction can effectively tune carrier-
transporting characteristics of materials and improve device
performance.
Summary of device performances of this work and literature.
Host
Von (V) CEmax (cd/A) PEmax (lm/W) EQEmax (%) Ref.
mCP
1d
1e
SPA-TXO2
p-DCz-SO2 2.6
m-DCz-SO2 2.8
8.2
5.6
5
11.5
10.5
16.5
30
3.6
4.7
9.2
19.8
32.3
33.7
12.4
8.2
2.4
3.8
7.2
11.4
15.6
13.4
11.5
4.8
This work
This work
This work
25
26
26
14
23
2.9
31.5
30
EBCz-ThX
3
3.7
3.9
23
14.8
All the reported devices were fabricated via vacuum deposition using Firpic and
sulfone derivatives as dopant and host materials, respectively.
4. Conclusions
versus luminance curves. The turn-on voltages (Von) of 1d and 1e-
based OLEDs are at the region of 5e6 V, and Von of 1e-based device
is slightly lower than that of 1d. The device based on 1e exhibited a
low current density, a maximum luminance of 3678 cd/m2, and a
maximum current efficiency (CE) of 16.5 cd/A at doping concen-
tration of 8%. While the unmodified unipolar mCP-based device
shows modest device performance with a maximum CE of 11.5 cd/A
(Fig. S59). The device based on 1d shows high current density
(more 2 times than 1e-based devices under same applied bias), and
In summary, we have synthesized two sulfone-contained ter-
tiary alcohols, and those A synthons can be used to construct bi-
polar host materials under mild one-step FC arylmethylation
reaction. Using sulfone acceptors to functionalize can effectively
modulate the distribution of HOMO and LUMO energy levels, and
lower LUMO level, while keep high ET. Efficient solution-processed
sky-blue Firpic-based PhOLEDs were fabricated using sulfone-
functionalized mCP as a bipolar host, and exhibited a maximum

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C.-J. Ou et al. / Organic Electronics 38 (2016) 370e378
19179e19188.
CE of 16.5 cd/A. Those results demonstrate that FC arylmethylation
is a powerful synthetic strategy to construct bipolar host materials.
[16] C.-J. Zheng, J. Ye, M.-F. Lo, M.-K. Fung, X.-M. Ou, X.-H. Zhang, C.-S. Lee, New
ambipolar hosts based on carbazole and 4, 5-diazafluorene units for highly
efficient blue phosphorescent OLEDs with low efficiency roll-off, Chem. Mater.
24 (2012) 643e650.
[17] Y.P. Jeon, K.S. Kim, K.K. Lee, I.K. Moon, D.C. Choo, J.Y. Lee, T.W. Kim, Blue
phosphorescent organic light-emitting devices based on carbazole/
thioxanthene-S,S-dioxide with a high glass transition temperature, J. Mater.
Chem. C 3 (2015) 6192e6199.
[18] C. Tang, R. Bi, Y. Tao, F. Wang, X. Cao, S. Wang, T. Jiang, C. Zhong, H. Zhang,
W. Huang, A versatile efficient one-step approach for carbazoleepyridine
hybrid molecules: highly efficient host materials for blue phosphorescent
OLEDs, Chem. Commun. 51 (2015) 1650e1653.
Acknowledgements
The project was supported by the National Natural Science
Funds for Excellent Young Scholar (21322402), National Natural
Science Foundation of China (U1301243, 61136003), Doctoral Fund
of Ministry of Education of China (20133223110007), Excellent
Science and Technology Innovation Team of Jiangsu Higher Edu-
cation Institutions (2013), Synergetic Innovation Center for Organic
Electronics and Information Displays.
[19] L.-H. Xie, X.-Y. Hou, Y.-R. Hua, C. Tang, F. Liu, Q.-L. Fan, W. Huang, Facile
synthesis of complicated 9,9-Diarylfluorenes based on BF3$Et2O-mediated
FriedelꢁCrafts reaction, Org. Lett. 8 (2006) 3701e3704.
[20] P.-I. Shih, C.-L. Chiang, A.K. Dixit, C.-K. Chen, M.-C. Yuan, R.-Y. Lee, C.-T. Chen,
E.W.-G. Diau, C.-F. Shu, Novel carbazole/fluorene hybrids: host materials for
blue phosphorescent OLEDs, Org. Lett. 8 (2006) 2799e2802.
Appendix A. Supplementary data
[21] K.-T. Wong, Y.-M. Chen, Y.-T. Lin, H.-C. Su, C.-C. Wu, Nonconjugated hybrid of
carbazole and Fluorene: a novel host material for highly efficient green and
red phosphorescent OLEDs, Org. Lett. 7 (2005) 5361e5364.
[22] Z. Fan, H. Zhao, N. Li, Y. Quan, Q. Chen, S. Ye, S. Li, Y. Wang, Q. Fan, W. Huang,
Tuning charge balance in solution-processable bipolar triphenylamine-
diazafluorene host materials for phosphorescent devices, ACS Appl. Mater.
Interfaces 7 (2015) 9445e9452.
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.orgel.2016.08.018.
References
[23] Y. Qian, Y. Ni, S. Yue, W. Li, Z. Zhang, L. Xie, M. Sun, Y. Zhao, W. Huang, Spiro
[1] S. Hirata, Y. Sakai, K. Masui, H. Tanaka, S.Y. Lee, H. Nomura, N. Nakamura,
M. Yasumatsu, H. Nakanotani, Q. Zhang, Highly efficient blue electrolumi-
nescence based on thermally activated delayed fluorescence, Nat. Mater. 14
(2015) 330e336.
fluorene-9,90-xanthene -based universal hosts for understanding structure-
property relationships in RGB and white PhOLEDs, RSC Adv.
5 (2015)
29828e29836.
[24] X.-H. Zhao, Z.-S. Zhang, Y. Qian, M.-D. Yi, L.-H. Xie, G.-H. Xie, H. Xu, C.-M. Han,
Y. Zhao, A bulky pyridinylfluorene-functionalizing approach to synthesize
diarylfluorene-based bipolar host materials for efficient red, green, blue and
white electrophosphorescent devices, J. Mater. Chem. C 1 (2013) 3482e3490.
[25] Y. Qian, G. Xie, S. Chen, Y. Ni, X. Zhou, L. Xie, J. Liang, Y. Zhao, M. Yi, Y. Zhao,
W. Wei, W. Huang, A new spiro[fluorene-9,90-xanthene]-based host material
possessing no conventional hole- and electron-transporting units for efficient
and low voltage blue PHOLED via simple two-step synthesis, Org. Electron 13
(2012) 2741e2746.
[2] C.W. Lee, J.Y. Lee, External quantum efficiency in blue phosphorescent organic
light-emitting diodes using pyrido [2, 3-b] indole derivatives as host mate-
rials, Adv. Mater. 25 (2013) 5450e5454.
[3] H. Uoyama, K. Goushi, K. Shizu, H. Nomura, C. Adachi, Highly efficient organic
light-emitting diodes from delayed fluorescence, Nature 492 (2012) 234e238.
[4] C. Han, L. Zhu, J. Li, F. Zhao, Z. Zhang, H. Xu, Z. Deng, D. Ma, P. Yan, Highly
efficient multifluorenyl host materials with unsymmetrical molecular con-
figurations and localized triplet states for green and red phosphorescent de-
vices, Adv. Mater. 26 (2014) 7070e7077.
[26] M. Romain, C. Quinton, D. Tondelier, B. Geffroy, O. Jeannin, J. Rault-Berthelot,
C. Poriel, Thioxanthene and dioxothioxanthene dihydroindeno [2, 1-b] fluo-
renes: synthesis, properties and applications in green and sky blue phos-
phorescent OLEDs, J. Mater. Chem. C 4 (2016) 1692e1703.
[27] M. Romain, D. Tondelier, O. Jeannin, B. Geffroy, J. Rault-Berthelot, C. Poriel,
Properties modulation of organic semi-conductors based on a donor-spiro-
acceptor (D-spiro-A) molecular design: new host materials for efficient sky-
blue PhOLEDs, J. Mater. Chem. C 3 (2015) 9701e9714.
[28] M. Romain, D. Tondelier, B. Geffroy, A. Shirinskaya, O. Jeannin, J. Rault-Ber-
thelot, C. Poriel, Spiro-configured phenyl acridine thioxanthene dioxide as a
host for efficient PhOLEDs, Chem. Commun. 51 (2015) 1313e1315.
[29] K. Liu, X.-L. Li, M. Liu, D. Chen, X. Cai, Y.-C. Wu, C.-C. Lo, A. Lien, Y. Cao, S.-J. Su,
9, 9-Diphenyl-thioxanthene derivatives as host materials for highly efficient
blue phosphorescent organic light-emitting diodes, J. Mater. Chem. C 3 (2015)
9999e10006.
[30] Y. Li, Z. Wang, X. Li, G. Xie, D. Chen, Y.-F. Wang, C.-C. Lo, A. Lien, J. Peng, Y. Cao,
Highly efficient spiro [fluorene-9, 90-thioxanthene] core derived blue emitters
and fluorescent/phosphorescent hybrid white organic light-emitting diodes,
Chem. Mater. 27 (2015) 1100e1105.
[5] S. Gong, Q. Fu, W. Zeng, C. Zhong, C. Yang, D. Ma, J. Qin, Solution-processed
double-silicon-bridged oxadiazole/arylamine hosts for high-efficiency blue
electrophosphorescence, Chem. Mater. 24 (2012) 3120e3127.
[6] S.O. Jeon, S.E. Jang, H.S. Son, J.Y. Lee, External quantum efficiency above 20% in
deep blue phosphorescent organic light-emitting diodes, Adv. Mater. 23
(2011) 1436e1441.
[7] A. Chaskar, H.F. Chen, K.T. Wong, Bipolar host materials: a chemical approach
for highly efficient electrophosphorescent devices, Adv. Mater. 23 (2011)
3876e3895.
[8] J.C. Xiao, B. Yang, J.I. Wong, Y. Liu, F.X. Wei, K.J. Tan, X. Teng, Y.C. Wu, L. Huang,
C. Kloc, F. Boey, J. Ma, H. Zhang, H.Y. Yang, Q.C. Zhang, Synthesis, character-
ization, self-assembly and physical properties of 11-methylbenzo[d]pyreno[4,
5-b]furan, Org. Lett. 13 (2011) 3004e3007.
[9] H.H. Chou, C.H. Cheng, A highly efficient universal bipolar host for blue, green,
and red phosphorescent OLEDs, Adv. Mater. 22 (2010) 2468e2471.
[10] Q.C. Zhang, Y. Divayana, J.C. Xiao, Z.J. Wang, E.R.T. Tiekink, H.M. Doung,
H. Zhang, F. Boey, X.W. Sun, F. Wudl, Synthesis, characterization, and bipolar
transporting behavior of a new twisted polycyclic aromatic hydrocarbon:
10,40-diphenyl-naphtho-(20.30:1.2)-pyrene-60-nitro-70-methyl
carboxylate,
[31] Z. Chen, X.-K. Liu, C.-J. Zheng, J. Ye, X.-Y. Li, F. Li, X.-M. Ou, X.-H. Zhang, A high-
efficiency hybrid white organic light-emitting diode enabled by a new blue
fluorophor, J. Mater. Chem. C 3 (2015) 4283e4289.
[32] S.O. Jeon, T. Earmme, S.A. Jenekhe, New sulfone-based electron-transport
materials with high triplet energy for highly efficient blue phosphorescent
organic light-emitting diodes, J. Mater. Chem. C 2 (2014) 10129e10137.
[33] C.-Y. Chan, Y.-C. Wong, M.-Y. Chan, S.-H. Cheung, S.-K. So, V.W.-W. Yam, Hole-
transporting spirothioxanthene derivatives as donor materials for efficient
small-molecule-based organic photovoltaic devices, Chem. Mater. 26 (2014)
6585e6594.
Chem. Eur. J. 16 (2010) 7422e7426.
[11] S. Thiery, D. Tondelier, B. Geffroy, E. Jacques, M. Robin, R. Metivier, O. Jeannin,
J. Rault-Berthelot, C. Poriel, Spirobifluorene-2,7-dicarbazole-40-phosphine
oxide as host for high-performance single-layer green phosphorescent OLED
devices, Org. Lett. 17 (2015) 4682e4685.
[12] S. Gong, Y.-L. Chang, K. Wu, R. White, Z.-H. Lu, D. Song, C. Yang, High-power-
efficiency blue electrophosphorescence enabled by the synergistic combina-
tion of phosphine-oxide-based host and electron-transporting materials,
Chem. Mater. 26 (2014) 1463e1470.
[13] X. Yang, H. Huang, B. Pan, M.P. Aldred, S. Zhuang, L. Wang, J. Chen, D. Ma,
Modified 4, 40, 4 00-Tri (N-carbazolyl) triphenylamine as a versatile bipolar host
for highly efficient blue, orange, and white organic light-emitting diodes,
J. Phys. Chem. C 116 (2012) 15041e15047.
[14] H. Liu, G. Cheng, D. Hu, F. Shen, Y. Lv, G. Sun, B. Yang, P. Lu, Y. Ma, A highly
efficient, blue-phosphorescent device based on a wide-bandgap host/FIrpic:
rational design of the carbazole and phosphine oxide moieties on tetraphe-
nylsilane, Adv. Funct. Mater. 22 (2012) 2830e2836.
[34] J. Ye, Z. Chen, M.-K. Fung, C. Zheng, X. Ou, X. Zhang, Y. Yuan, C.-S. Lee,
Carbazole/Sulfone hybrid D-p-A-structured bipolar fluorophores for high-
efficiency blue-violet electroluminescence, Chem. Mater. 25 (2013)
2630e2637.
[35] A. Chopra, D.C. Dorton, C.A. Ogle, Directed ortho dilithiation of diaryl com-
pounds: facile synthesis of tricyclic compounds based on heterocycles fused
to two benzene rings, Main. Group Met. Chem. 20 (1997) 783e786.
[36] L.-H. Xie, X.-Y. Hou, C. Tang, Y.-R. Hua, R.-J. Wang, R.-F. Chen, Q.-L. Fan, L.-
H. Wang, W. Wei, B. Peng, W. Huang, Novel H-Shaped persistent architecture
based on a Dispiro building block system, Org. Lett. 8 (2006) 1363e1366.
[15] C. Han, Z. Zhang, H. Xu, S. Yue, J. Li, P. Yan, Z. Deng, Y. Zhao, P. Yan, S. Liu,
Short-axis substitution approach selectively optimizes electrical properties of
dibenzothiophene-based phosphine oxide hosts, J. Am. Chem. Soc. 134 (2012)