H.-M. Guan et al.
Dyes and Pigments 177 (2020) 108273
phenanthro [9,10-d]imidazol-1-yl)phenyl)adamantane (AD-BPI) with
two phenanthroimidazole moieties bridged by an adamantane unit is
purposefully designed and synthesized to address above issues. Non-
doped blue OLEDs adopting AD-BPI as active layer achieves the peak
external quantum efficiency (EQE), power efficiency and current effi-
ciency of 5.8%, 3.9 lm wÀ 1 and 4.4 cd AÀ 1 with the CIE coordinates of
(0.15, 0.07). With the adamantane-bridged phenanthroimidazole
molecule as universal host material, highly efficient red (19.1%, 14.5 lm
WÀ 1, 20.8 cd AÀ 1), yellow (16.7%, 35.6 lm WÀ 1, 50.3 cd AÀ 1) and green
(23.3%, 57.7 lm WÀ 1, 82.5 cd AÀ 1) phosphorescent OLEDs are realized
with negligible efficiency roll-off.
1H NMR (500 MHz, CDCl3) δ 7.17 (d, J ¼ 7.6 Hz, 4H), 6.65 (d, J ¼ 7.7
Hz, 4H), 2.24 (s, 2H), 1.87 (s, 8H), 1.73 (s, 4H).
2.2.3. Synthesis of AD-BPI
9, 10-phenanthrene quinone (10 mmol, 3.08 g), 4,4’-((1s,3s,5r,7r)-
adamantane-1,3- diyl)dianiline (5 mmol, 1.62 g), ammonium acetate
(40 mmol, 3.08 g), benzaldehyde (10 mmol, 1.0 mL) were added into the
flask in turn and then glacial acetic acid (100 mL) was charged. The
system then reacted for 10 h under heating reflux with N2 atmosphere.
After that, the solution was poured into 500 mL sodium chloride solu-
tion. The crude solid products were received by extraction and filtration.
White powder was obtained through column chromatography (silica gel:
300–400 mesh; petroleum ether: ethyl acetate ¼ 20: 1, V/V). Yield: 53%.
HRMS (APCI, MþHþ), Exact mass: 872.3879; Obtained mass: 873.4805.
1H NMR (500 MHz, CDCl3) δ 8.93 (d, J ¼ 7.9 Hz, 2H), 8.79 (d, J ¼ 8.3
Hz, 2H), 8.73 (d, J ¼ 8.3 Hz, 2H), 7.77 (t, J ¼ 7.4 Hz, 3H), 7.65 (d, J ¼
17.8, 14.4, 7.3 Hz, 10H), 7.55–7.47 (m, 6H), 7.38–7.25 (m, 10H), 7.22
(d, J ¼ 8.4 Hz, 2H), 2.49 (s, 2H), 2.28 (s, 2H), 2.14 (d, J ¼ 3.0 Hz, 7H).
13C NMR (126 MHz, CDCl3) δ 151.69, 150.32, 135.63, 128.85, 128.69,
128.44, 128.16, 127.65, 127.54, 126.68, 126.02, 125.59, 125.02,
124.24, 123.48, 122.45, 122.24, 120.26, 76.63, 76.38, 76.13, 48.06,
41.64, 37.05, 35.03, 28.86. Elemental Analysis: Anal. Cacld. for
2. Experimental section
2.1. General information
Raw materials and reagents involved in this experiment including 1-
adamantanol, 9,10-phenanthroquinone, acetanilide and benzaldehyde
are commercially available. All the reactions are operated in standard
glass reactor under inert gas (nitrogen or argon). The silica gel (300–400
mesh) is used for column chromatography. HRMS (high-resolution mass
spectrometry) is undertaken on an Agilent 6530B Q-TOF LCMS. NMR
spectra with TMS (tetramethylsilane) as the internal standard are ob-
tained via Bruker AC 500 spectrometer. Elemental analyses are acquired
by Vario Micro cube analyzer. DSC (differential scanning calorimetry) is
recorded in American TA company DSC-Q20 with the heating rate of 10
�C minÀ 1 from 50 to 400 �C under nitrogen. The Tm (melting point) and
Tg (glass transition temperature) are obtained from the first and the
second heating scan, respectively. TGA (thermogravimetric analysis) is
carried out on American TA company TG-DTA Q600 thermal analyzer at
a heating rate of 10 �C minÀ 1 from 50 to 800 �C in the atmosphere of
nitrogen. The PL (photoluminescence) and UV–Vis absorption spectra
are received on LS 55 and Lambda 900 spectrophotometer both from
PerkinElmer company, respectively. CV (cyclic voltammetry), which
was calibrated by Fc/Fcþ redox couple as the internal reference in
dichloromethane containing Bu4NPF6 (tetrabutylammonium hexa-
fluorophosphate, 0.1 M), is carried out on an AUTOLAB PGSTAT 302 N
workstation with a scan rate of 50 mV sÀ 1 under the atmosphere of ni-
trogen. DFT (density functional theory) calculations are implemented
through Gaussian 09 employing the B3LYP functional together with 6-
31G (d, p) basis set.
C
64H48N4: C, 88.04%; H, 5.54%; N, 6.42%. Found: C, 88.77%; H, 5.26%;
N, 6.16%.
2.3. Devices fabrication and characterization
Devices were made on pre-patterned ITO-coated glass substrates (15
Ω cmÀ 2). Prior to device, the substrates were rinsed with soap and ul-
trapure H2O, and sonicated for 15 min. Afterwards, two subsequent
rinses and 12-min sonication baths in acetone and isopropanol were
performed sequentially. All organic layers as well as the Al cathode were
deposited in a vacuum thermal evaporator at not less than 6 � 10À 4 Pa.
The luminance and EL spectra of OLEDs were obtained on PR650
spectrometer. The single-carrier devices and voltage-current properties
of the OLEDs were received by Keithley 2400 source meter. All mea-
surements of devices without encapsulations at ambiet temperature
were performed in the dark.
3. Results and discussion
3.1. Synthesis and characterization
2.2. Synthesis
AD-BPI’s chemical structure and its complete synthesis routes are
shown in Scheme 1. The key intermediate 4,4’-((1s,3s,5r,7r)-ada-
mantane-1,3-diyl)dianiline was obtained via two-step reaction including
Friedel-Crafts alkyl reaction and hydrolysis reaction, respectively, with
the total yield of 35%. The classic Debus-Radziszewski reaction was then
adopted to smoothly prepare the target compound AD-BPI in one pot
with high isolated yield of 53%. All the intermediates and target com-
pound were characterized by elemental analysis, HRMS and NMR
spectrometry.
2.2.1. Synthesis of N,N’-(((1s,3s,5r,7r)-adamantane-1,3-diyl)bis(4,1-
phenylene)) diacetamide
A two-necked flask was charged with 1-adamantanol (2.5 mmol,
0.375 g), acetanilide (5 mmol, 0.78 g) and 98% sulfuric acid (7.5 mL) at
room temperature (25 �C), and then reacted for 5 h under magnetic
stirring. Subsequently, white crude solid was obtained once H2O was
poured into the mixture. The pure white solid was got via column
chromatography (silica gel, 300–400 mesh). Yield: 56%. HRMS (APCI,
MþHþ): Exact mass: 402.2307; Obtained mass: 403.2380. 1H NMR (500
MHz, DMSO‑d6) δ 9.85 (d, J ¼ 4.5 Hz, 2H), 7.49 (d, J ¼ 6.7 Hz, 4H), 7.31
(d, J ¼ 6.7 Hz, 4H), 2.23 (s, 1H), 2.01 (s, 7H), 1.87 (d, J ¼ 18.8 Hz, 10H),
1.72(s,2H).
3.2. Thermal property
The morphological stability and thermal property of AD-BPI were
determined by DSC and TGA at a heating rate of 10 �C minÀ 1 under
streaming N2, respectively. TGA and DSC plots of AD-BPI were presented
in Fig. 1. As showed in Fig. 1, AD-BPI exhibited the high decomposition
temperature (Td, 5% decomposition temperature) of 509 �C, and simi-
larly a relatively high melting point Tm of 358 �C (Fig. S1) and Tg of 188
�C were observed via DSC analysis (Inset of Fig. 1), which could guar-
antee the subsequent vacuum evaporation smoothly. In addition, the Tg
2.2.2. Synthesis of 4,4’-((1s,3s,5r,7r)-adamantane-1,3-diyl)dianiline
N,N’-(((1s,3s,5r,7r)-adamantane-1,3-diyl)bis(4,1-phenylene)) diac-
etamide (0.75 mmol, 0.30 g) in ethanol (4 mL) and H2O (1 mL) including
sodium hydroxide (12 mmol, 0.48 g) was put into the flask in turn. The
mixture was refluxed with constant stirring for 6 h. Following that, the
solution was cooled to ambient temperature, and then saturated brine
was added to obtain the yellowish-colored raw solid. Further recrys-
tallization with ethanol enabled to the white solid product. Yield: 63%.
HRMS (APCI, MþHþ), Exact mass: 318.2096; Obtained mass: 319.2222.
and Tm of AD-BPI roughly followed the Boyer-Kauzmann rule (Tg/Tm
�
0.7) on the Kelvins temperature [35]. The slightly high value of Tg/Tm
(0.73) based AD-BPI indicated strong intermolecular interaction in the
2