H.-M. Guan et al.
Dyes and Pigments xxx (xxxx) xxx
Fig. 1. Chemical structures of FL-PI and FL-BPI.
yellow (EQE: 14.5%) and green (EQE: 18.2%) electrophosphorescent
devices were prepared in 2014 [14]; efficient green phosphorescent
OLEDs (EQE: 26.6%, PE: 92.7 lm Wꢀ 1) were also elaborated with a
coworker reported efficient blue emitters with phenan-
with Edinburgh FLS1000 Series of Fluorescence Spectrometers.
2.2. Synthesis of compounds
2.2.1. Synthesis of 9-phenyl-9H-fluoren-9-ol
troimidazole-π-indolizine system for application in OLEDs, which
Magnesium 0.264 g (11 mmol) was placed into the flask with dried
THF (10 mL) accompanied by trace iodine as initiator, and then bro-
mobenzene 1.57 g (10 mmol) dissolving in THF solution was dripped
into the flask. After dropping, the reaction solution was refluxed
continuously for 2 h. Subsequently, 9H-fluoren-9-one 1.802 g (10 mmol)
dissolving in THF solution was added into flask, and further stirred for
12 h. Hydrolysis, extraction, drying and column chromatography were
performed successively to obtain the target product of 2.1 g. Yellow-
white solid. Yield: 80%. FTIR (Neat, cmꢀ 1): 3054, 1696, 1658, 1440,
1290.1H NMR (CDCl3, 500 MHz) δ 7.65 (d, J = 7.3 Hz, 4H), 7.53–7.48
(m, 5H), 7.47 (d, J = 7.5 Hz, 2H), 7.29 (d, J = 7.3 Hz, 3H). HRMS (APCI):
Found: [M ꢀ H]- 257.0975; Molecular formula C19H14O requires [M ꢀ
H]- 257.0972.
showed the maximum EQE of over 6% at ultrahigh brightness and
deep-blue emission with the CIE of (0.151, 0.076) [18]. High perfor-
mance of the OLEDs was mainly attributed to the novel-designed blue
fluorophore with hybridized local and charge-transfer features. How-
ever, it is still rare and challenging to develop high-emissive phenan-
throimidazole-based blue fluorophore which acts simultaneously as host
of low-energy phosphorescent or TADF material (thermally activated
delayed fluorescence) in OLEDs [19–25]. Liu et al. reported the phe-
nanthroimidazole derivatives PPI-PPITPA and PPI-PPIPCz with small
singlet-triplet splitting features and dual carrier-transporting charac-
teristics, which were applied as emitters and hosts to realize highly
efficient non-doped deep-blue devices and RYG (red/yellow/green)
phosphorescent OLEDs [24]. Tong and Lee demonstrated an ideal blue
phenanthroimidazole-based host emitter coupled with new electron
acceptor [1,2,4] triazolo[1,5-a]pyridine (TP-PPI) for high-efficiency
single-emissive-layer (TP-PPI + PO-01) hybrid white OLEDs [25]. As a
matter of fact, efficient deep-blue host emitters especially
near-ultraviolet emitters are still greatly limited up to now [26–29].
In this study, two multifunctional phenanthroimidazole materials
integrated into 9,9-diphenyl-fluorene through non-conjunction N1 po-
sition of imidazole part (FL-PI and FL-BPI, showed in Fig. 1) were
designed and synthesized as near-ultraviolet emitter and host for
application in OLEDs. Here, 9,9-diphenyl-fluorene plays a bridge be-
tween two phenanthroimidazoles and fluorene unit has high PLQY/ET,
good carrier transporting ability and film-forming property [21,30]. The
2.3. Synthesis of 4-(9-phenyl-9H-fluoren-9-yl)aniline
Under nitrogen protection, 0.2583 g (1 mmol) 9-phenyl-9H-fluoren-
9-ol dissolving in chloroform solution was dipped into the flask with
methanesulfonic acid 0.065 mL (1 mmol), acetaniline 0.1352 g (1 mmol)
and chloroform solution, and then the reaction solution was refluxed for
3 h. Crude products were obtained by extraction and drying. Subse-
quently, 0.53 mL water and 0.53 mL HCl were drip into it and then
continued to react for 12 h at 140 ◦C. Finally, the intermediate was
neutralized by sodium hydroxide to acquire the target product of 0.26 g.
Light white solid. Yield: 77%. FTIR (Neat, cmꢀ 1): 3441, 3060, 2350,
1450, 1250.1H NMR (CD2Cl2, 500 MHz) δ 7.57 (d, J = 7.5 Hz, 2H),
7.50–7.44 (m, 2H), 7.20 (t, J = 7.4 Hz, 2H), 7.07 (d, J = 11.8 Hz, 6H),
6.99–6.92 (m, 2H), 6.77 (dd, J = 14.9, 7.2 Hz, 3H), 5.24 (s, 2H). HRMS
(APCI): Found: [M+H]+ 334.1591; Molecular formula C25H19N requires
[M+H]+ 334.1590.
purpose
of
the
material
design
is
to
guarantee
deep-blue/near-ultraviolet emission, mild PLQY, high ET and efficient
carrier injection and transport. As it turned out, the FL-BPI-based
non-doped OLEDs illustrated the outstanding performances (5.4%, 3.8
cd Aꢀ 1 and 2.8 lm Wꢀ 1) with the CIE1931 coordinates of (0.15, 0.05).
Furthermore, highly efficient green phosphorescent OLEDs utilizing
FL-PI (16.3%, 28.8 cd Aꢀ 1) and FL-BPI (21.1%, 75.3 cd Aꢀ 1) as hosts
were expounded, respectively.
2.4. 4,4’-(9H-fluorene-9,9-diyl)dianiline
Under nitrogen protection, 0.1802 g (1 mmol) 9H-fluoren-9-one,
0.06 mL (1 mmol) methanesulfonic acid and 0.2703 g (2 mmol) aceta-
niline were placed into the flask and reacted for 24 h at 160 ◦C.
Following, HCl aqueous solution was added and continued to react for
12 h. The intermediate was neutralized with saturated NaOH to get the
target product of 0.17 g. Grey-green solid. Yield: 50%. FTIR (Neat,
cmꢀ 1): 3323, 3024, 2362, 1611, 1506, 1437, 1250.1H NMR (DMSO‑d6,
500 MHz) δ 7.85 (d, J = 7.5 Hz, 2H), 7.36–7.30 (m, 4H), 7.26 (t, J = 7.4
Hz, 2H), 6.82–6.71 (m, 4H), 6.48–6.32 (m, 4H), 4.94 (s, 4H). HRMS
(APCI): Found: [M+H]+ 349.1707; Molecular formula C25H20N2
2. Experimental section
2.1. General information
The raw materials and reagents involved in this work can be pur-
chased conveniently via the Reagent Company. Testing, characteriza-
tion and theoretical calculation of FL-PI and FL-BPI are consistent with
our recent publication [10]. In addition, the decay lifetime is obtained
2