Inorganic Chemistry
00 nm) is estimated to be 3.4%. Because the turn-on voltage
Article
7
reflux for 24 h and cooled to room temperature. The precipitate was
collected by filtration and washed with ethanol, acetone, and hexane
in sequence and then dried in a vacuum thoroughly. The dimers
of the device is showing more than 4 V, it is expected that one
may achieve higher performance upon further optimization of
the device structure. Nevertheless, the device results in this
study show that the synthesized emitters work well as deep-red
emitters in PHOLEDs with a performance that is already high
enough for many practical applications. The EL properties of 1
complexes as shown in Scheme S2. The photophysical
properties of the proposed emitters, as well as the device
performance of the OLEDs made with them, provide strong
evidence for their importance in the development of deep red
and NIR PHOLEDs using rigid-system-based iridium emitters.
1
2
[
Ir(L /L ) (μ-Cl)] were obtained in high purity (∼70%) and used
2
2
1 2
without further purification. A suspension of [Ir(L /L ) (μ-Cl)] (1
2
2
equiv), ancillary ligand PyPzCF3 (2.4 equiv) and Na CO (20.0
2
3
equiv) in 2-methoxy ethanol (15 mL) was stirred at reflux for 12 h
and cooled to room temperature. The reaction mixture was poured
into water and extracted with dichloromethane. The organic layer was
separated and dried using anhydrous Na SO , and the solvent was
removed under a vacuum. The crude product was collected and
purified by column chromatography (SiO , ethyl acetate/n-hexane =
2
4
2
1
:3) to give the desired products.
Preparation of Ir(III) Complex 1. Iridium dimers was obtained as
a dark powder from the reaction of iridium trichloride hydrate (200
mg, 0.67 mmol) and ligand L (450 mg, 1.66 mmol) in 2-
ethoxyethanol (9 mL) and water (3 mL). The complex 1 was
obtained as a brown solid from the reaction of [Ir(L ) (μ-Cl)] (530
1
CONCLUSIONS
Rigid naphthalene benzimidazole-based bidentate ligands
with/without substituents) were utilized to make two deep
■
(
1
2
2
CF3
mg, 0.35 mmol), ancillary ligand PyPz (178 mg, 0.83 mmol) and
Na CO (740 mg, 6.92 mmol) in 2-methoxy ethanol (15 mL). Yield:
red iridium emitters 1 and 2. These emitters were prepared by
a simple two-step method with the aid of pyridine pyrazole
based ancillary ligand. Complexes 1 and 2 show a strong
emission in the range of 630−700 nm with a relatively high
quantum yield (Φ = 0.29 (1), and 0.27 (2)) in PMMA film.
The introduction of donor units (diphenylamine) on the
organic frameworks was shown to result in remarkable red-
shifted emission, which extends up to 800 nm. The PL decay
lifetime decay values of 1 and 2 suggest that the emission arises
2
3
1
5
8
8
7
1
1% (340 mg, 0.36 mmol). H NMR (DMSO-d , 400 MHz, ppm): δ
6
.54 (m, 2H), 8.44 (d, J = 8.12 Hz, 1H), 8.39 (d, J = 8.08 Hz, 1H),
.34−8.30 (m, 2H), 8.21 (d, J = 7.88 Hz, 1H), 8.08−8.03 (m, 2H),
.79−7.74 (m, 2H), 7.68 (d, J = 8.44 Hz, 1H), 7.60 (d, J = 8.52 Hz,
H), 7.55−7.49 (m, 2H), 7.41 (s, 1H), 7.33−7.25 (m, 3H), 7.07 (d, J
19
=
8.32 Hz, 1H), 7.03 (d, J = 8.48 Hz, 1H), 6.03−6.00 (m, 2H).
F
NMR (376 MHz, DMSO-d ): δ −58.140 (s, 3H, Pz-CF ). Anal. Calc.
6
3
for (C H F IrN O ): C, 57.32; H, 2.46; N, 10.4. Found: C, 57.14;
4
5
23
3
7
2
+
H, 2.64; N, 10.37. MS(ESI): m/z 944.8, [M ].
Preparation of Ir(III) Complex 2. Iridium dimers were obtained
as a dark powder from the reaction of iridium trichloride hydrate (200
mg, 0.67 mmol) and ligand L (728 mg, 1.66 mmol) in 2-
ethoxyethanol (9 mL) and water (3 mL). The complex 2 was
obtained as a brown solid from the reaction of [Ir(L ) (μ-Cl)] (772
from the lowest-lying triplet excited state (T ). From the DFT
1
and TD-DFT calculation, it is revealed that T excited state of
1
2
3
1
has a mixed metal-to-ligand charge transfer ( MLCT) and
3
ligand-centered ( LC) characters, whereas 2 shows a dominant
2
3
2
2
LC character. For OLED applications, emitter 1 achieves a
CF3
mg, 0.35 mmol), ancillary ligand PyPz (188 mg, 0.83 mmol) and
Na CO (770 mg, 7.2 mmol) in 2-methoxyethanol (15 mL). Yield:
relatively high performance with electroluminescence peaks
positioned at 644 and 700 nm, respectively, with maximum
EQE of 10.9% in total and 3.4% in the NIR region. Similarly,
the emitter 2 also shows a maximum EQE of 6.9% with an
emission at 657 and 722 nm. Overall, these results give solid
support for the notion that developing rigid bidentate ligand-
based iridium emitters with a short radiative lifetime can be an
effective approach for deep-red and near-infrared OLEDs.
2
3
1
30% (250 mg, 0.19 mmol). H NMR (DMSO-d , 400 MHz, ppm):
8.44 (dd, J = 8.2, 0.64 Hz, 2H), 8.37 (d, J = 8.16 Hz, 1H), 8.30 (d, J =
8.12 Hz, 1H), 8.17 (d, J = 8.04 Hz, 1H), 8.07 (dt, J = 7.8, 1.44 Hz,
6
1
H), 7.90 (d, J = 5.44 Hz, 1H), 7.48−7.17 (m, 18H), 7.07−6.96 (m,
1
2H), 6.84 (d, J = 8.64 Hz, 1H), 6.80 (d, J = 8.72 Hz, 1H), 5.97−5.90
1
9
(
m, 2H). F NMR (376 MHz, DMSO-d , ppm): δ −57.996 (s, 3H,
6
Pz-CF ). Anal. Calc. for (C H F IrN O ): C, 64.88; H, 3.24; N,
3
69 41
3
9
6
+
9.87. Found: C, 65.00; H, 3.35; N, 9.71. MS(ESI): m/z 1278.9, [M ].
Photophysical Measurements. UV/vis absorption and photo-
luminescence (PL) spectra were recorded on a Varian Cary 100 and
FS5 spectrophotometer, respectively. Solution PL spectra were
EXPERIMENTAL SECTION
■
Methods. All reactions were carried out under nitrogen
atmosphere using standard Schlenk and glovebox techniques.
Anhydrous-grade solvents (Aldrich and TCI) were dried over
activated molecular sieves (5 Å). Spectrophotometric-grade solvents
and commercial reagents were used as received without further
obtained in both aerated as well as nitrogen purged CH Cl solution
2 2
(0.5 μM solution). PL spectra and absolute photoluminescence
quantum yields (PLQYs, ΦPL) of film samples were obtained with
poly(methylmethacrylate) (PMMA) matrices doped with compounds
(5 wt %, prepared with THF solutions) on quartz plates. Absolute
PLQYs of solutions and films were measured on an absolute PL
quantum yield spectrophotometer (Quantaurus-QY C11347-11,
Hamamatsu Photonics) equipped with a 3.3-in. integrating sphere.
Transient PL (Tr-PL) decays were measured on a FS5 spectropho-
tometer (Edinburgh Instruments) using a time-correlated single-
photon counting (TCSPC) method with an EPL-375 ps pulsed diode
laser as a light source.
1
19
measured on a Bruker Avance 400 spectrometer. ESI-mass
spectrometry was performed on a BRUKER micrOTOF-Q II at
KAIST. Elemental analysis was carried out on a Heraeus CHN-O
rapid elementary analyzer. Thermogravimetric analysis (TGA) was
performed using a NETZSCH TGA 209F3 instrument under an N
2
−
1
atmosphere at a heating rate of 20 °C min . Single-crystal data were
collected on a Bruker Axs kappa apex3 CCD diffractometer, with
graphite-monochromated Mo Kα (λ = 0.71073 Å) radiation at 223 K.
The data were integrated using SAINT PLUS, and absorption
correction was done using a multiscan absorption correction method
Computational Details. To study the structural and photo-
physical properties of the target Ir(III) emitters, density functional
theory (DFT) and time-dependent density functional theory (TD-
DFT) were carried out. The ground states (S ) of complexes 1 and 2
0
60,61
(
SADABS). The structure was solved by direct method (SHELXS-97)
were optimized using the B3LYP hybrid functional
and 6-31G(d)
62
and refined using the SHELXL-2018/3 program. All non-hydrogen
[6-31G*] basis set for all atoms, excluding the iridium atom wherein
58,59
63
atoms were refined anisotropically.
General Procedure for the Preparation of Ir(III) Complexes.
LANL2DZ effective core potential (ECP) was treated. Then,
electronic vertical excitation was calculated by employing the same
hybrid functional/basis set at the level of TD-DFT. An optimized T1
1
2
Iridium trichloride hydrate (1 equiv) and ligand L /L (2.5 equiv)
were taken in Schlenk flask, and a mixture of 2-ethoxyethanol and
water (3:1) was added. The reaction mixture was allowed to stir at
geometry referenced from S geometry are obtained spin-unrestricted
0
DFT level without any symmetry, and their first 20 triplet excited
G
Inorg. Chem. XXXX, XXX, XXX−XXX