Saturated red iridium(iii) complexes containing a unique four-membered Ir-S-C-N backbone: Mild synthesis and application in OLEDs

Article abstract of DOI:10.1039/c9tc05806k

A series of new iridium(iii) cyclometalated complexes (4tfmpiq)₂Ir(tiptha), (4tfmpiq)₂Ir(phdiptha), (4tfmpiq)₂Ir(fphdiptha) and (4tfmpiq)₂Ir(ipdptha) (4tfmpiq = 4-(4-(trifluoromethyl)phenyl)isoquinoline, tiptha

Full text of DOI:10.1039/c9tc05806k

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Materials Chemistry C
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Saturated red iridium(III) complexes containing a
unique four-membered Ir–S–C–N backbone: mild
synthesis and application in OLEDs†
Cite this:DOI: 10.1039/c9tc05806k
ab
c
d
c
Guangzhao Lu, aJdingwen Yao,
Zhanxiang Chen, Dongge Ma* and
Chuluo Yang
*
A
series of new iridium(III) cyclometalated complexes (4tfmpiq)
4tfmpiq) Ir(fphdiptha) and (4tfmpiq) Ir(ipdptha) (4tfmpiq = 4-(4-(trifluoromethyl)phenyl)isoquinoline,
tiptha = 1,1,3-triisopropylthiourea, phdiptha = 1,1-diisopropyl-3-phenylthiourea, fphdiptha = 3-(4-fluoro-
phenyl)-1,1-diisopropylthiourea, ipdptha 3-isopropyl-1,1-diphenylthiourea) containing unique
2 2
Ir(tiptha), (4tfmpiq) Ir(phdiptha),
(
2
2
=
a
four-membered ring Ir–S–C–N backbone were facilely synthesized under mild conditions. By introducing
different substituents such as isopropyl, phenyl, 4-fluorophenyl, diisopropylamine and diphenylamine on
the thiourea ancillary ligands, not only the S–C–N ligands can be extensively derived, but also the emission
Received 23rd October 2019,
Accepted 11th December 2019
P
colors (lpeak = 627–636 nm) and photoluminescence quantum efficiencies (F = 38.0–42.0%) can be
regulated. Employing these complexes as emitters, the organic light emitting diodes (OLEDs) exhibited good
performances with a maximum external quantum efficiency (EQEmax) of 13.1% for saturated red emission
with CIE coordinates of (0.68, 0.32). These results demonstrate the great potential of the S–C–N ancillary
ligands for developing new Ir(III) complexes towards OLED applications.
DOI: 10.1039/c9tc05806k
rsc.li/materials-c
2
increase the cost. It is important, but difficult, to find suitable
ligands which can synthesize phosphorescent complexes at
1
. Introduction
Among different types of emitters for organic light-emitting relatively low temperature efficiently to reduce the production
3
devices (OLEDs), phosphorescent iridium(III) complexes are cost significantly.
excellent candidates due to their high efficiency and colorful
emissions. And the green and red phosphorescent iridium(III) Ir(C N) (L X), ancillary ligands (L X) usually contain C, N,
complexes have been used in commercial OLEDs. In order to and O atoms, such as acetylacetone (acac, L X = O O),
speed up the process of OLED industrialization, cost reduction 2-pyridinecarboxylic acid (pic, L X = N O), 2,2 -bipyridine
Among the Ir(III) complexes with the structure of
1
4
4
4
2
4
4
4
4
0
4
4
3
seems to be extremely important. But for the production of (bipy, L X = N N), etc. However, the coordination with sulfur
most Ir(III) complexes, the last reaction process is always to and nitrogen atoms simultaneously in the ancillary ligands for
4
reflux the [(C^N)
2 2
Ir(m-Cl)] chloride-bridged dimer with cyclo- the Ir(III) complexes used in OLEDs is rarely reported.
metalated or ancillary ligands at high temperature (exceeding
In the previously reported Ir(III) complexes, ancillary ligands
10 1C) for a long time (over 12 h), which would inevitably and central iridium atoms mainly formed five-membered or
1
six-membered ring structures, whereas four-membered ring
structures are rarely studied because of the special electronic
structures of the starting materials which should have two
consecutive double bonds (Scheme 1(a)). But the Ir(III) com-
plexes containing four-membered ring structures make the angle
formed by the two coordinated atoms of the ancillary ligand
and the iridium atom much reduced, suggesting that the four-
membered metallocycles would possess greater coordination
a
Shenzhen Key Laboratory of Polymer Science and Technology, College of Materials
Science and Engineering, Shenzhen University, Shenzhen 518060, China.
E-mail: clyang@szu.edu.cn
b
c
Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education
and Guangdong Province, College of Optoelectronic Engineering,
Shenzhen University, Shenzhen 518060, China
State Key Laboratory of Luminescent Materials and Devices, Institute of Polymer
Optoelectronic Materials and Devices, South China University of Technology,
Guangzhou 510640, P. R. China. E-mail: msdgma@scut.edu.cn
Hubei Key Lab on Organic and Polymeric Optoelectronic Materials,
Department of Chemistry, Wuhan University, Wuhan, 430072, China
Electronic supplementary information (ESI) available. CCDC 1950975, 1950977
4
strain energy. Although some groups investigated the Ir(III)
d
complexes containing four-membered ring structures, only
amidinate and dithiocarbamate ancillary ligands were reported.
For example, Liu et al. mainly studied the phosphorescent Ir(III)
complexes containing a four-membered amidinate-ligated ring
†
and 1950978. For ESI and crystallographic data in CIF or other electronic format
see DOI: 10.1039/c9tc05806k
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Scheme 1 (a) Schematic structures of six-, five- and four-membered backbones. (b) Chemical structures of the new iridium complexes using thiourea
derivatives as ancillary ligands.
and good device performances were achieved with the maximum color and photoluminescence quantum efficiency of the com-
5
10
external quantum efficiency of up to 24.0%. Zheng et al. reported plexes can be effectively adjusted within a certain range.
four-membered Ir(III) complexes containing dithiocarbamate In addition, due to the nitrogen heterocycle in the 4-(4-(trifluoro-
6
as the ancillary ligand. For example, the complexes of methyl)phenyl)isoquinoline main ligand, these complexes would
(
4tfmpq)
2 2
Ir(Czdtc) with red emission and (TNT) Ir(dipdtc) with have bipolar properties, which are also beneficial for their device
11
bluish green emission achieved the maximum current efficiency performances.
ꢀ1
ꢀ1
6
of 40.6 cd A and 86.5 cd A , respectively. However, the four-
membered ring structures of Ir(III) complexes with both sulfur and
nitrogen atoms in the ancillary ligands are rarely studied in
OLEDs, and there is no new progress in the research on the
Ir(III) complexes containing the four-membered ring based on the
2
. Results and discussion
7
Synthesis and characterization
Ir–S–C–N backbone. Moreover, these ancillary ligand derivatives The chemical structures of the iridium complexes are outlined
have strong selectivity to the cyclometalated ligand for efficient in Scheme 1. The cyclometalating ligand, 4-(4-(trifluoromethyl)-
8
Ir(III) complexes. The Ir(III) complexes containing four-membered phenyl)isoquinoline, was synthesized by a Suzuki reaction.
ring structures make the distance between the ligand and the The ancillary ligands of thiourea derivatives were obtained in a
iridium atom shorter, and the ligand has a great effect on nucleophilic reaction of isothionitrile ester and electron-donating
the metal center, resulting in some promising properties of the compounds such as diisopropylamine or diphenylamine. The
9
complexes.
final complexes, (4tfmpiq) Ir(tiptha), (4tfmpiq) Ir(phdiptha),
2 2
In this work, four novel Ir(III) complexes, named (4tfmpi- (4tfmpiq) Ir(fphdiptha) and (4tfmpiq) Ir(ipdptha), were syn-
2
2
q)
and (4tfmpiq)
electron-deficient
4tfmpiq) moiety as the main ligand and the single mono- were synthesized by the reaction of a [(C^N)
anionic thiourea derivatives (tiptha = 1,1,3-triisopropylthiourea, bridged dimer with thiourea derivatives at room temperature
phdiptha 1,1-diisopropyl-3-phenylthiourea, fphdiptha in 40 min with high yields of above 70%. Because most Ir(III)
-(4-fluorophenyl)-1,1-diisopropylthiourea, ipdptha = 3-isopropyl- complexes were prepared at high temperature for a long time, the
,1-diphenylthiourea) as ancillary ligands. All the complexes have sulfur and nitrogen atom-containing ligands developed in this
2
Ir(tiptha), (4tfmpiq)
Ir(ipdptha), were synthesized by using the hydrates were reacted with an excess of ligand 4tfmpiq (2.5 equiv.)
4-(4-(trifluoromethyl)phenyl)isoquinoline to afford dichloride bridged dimers. Second, four Ir(III) complexes
Ir(m-Cl)] chloride-
2 2
Ir(phdiptha), (4tfmpiq) Ir(fphdiptha) thesized in a two-step procedure. First, iridium chloride tri-
2
(
2
2
=
=
3
1
a unique four-membered Ir–S–C–N backbone built by the iridium study can reduce the cost of materials for promoting OLED
center and the ancillary ligand. The complexes containing industrialization significantly. The rapid reaction mechanism
thiourea as an ancillary ligand have some exceeding advantages. has been proved by previous reports, in which both the calculated
Firstly, the coordination capability of sulfur and nitrogen atoms Gibbs free energy changes, DG, and the experimental process all
with iridium atoms is strong, resulting in the completion of the indicate that the reactions using ligands with strong coordination
reaction in several minutes with high yield, and also conducive atoms such as S and N are exothermic and thermodynamically
6
to molecular stability which is helpful to boost the sublimation favorable processes. The crude products (4tfmpiq) Ir(tiptha),
2
yield of Ir(III) complexes. By changing the substituents in the (4tfmpiq) Ir(phdiptha), (4tfmpiq) Ir(fphdiptha) and (4tfmpiq) -
2
2
2
thiourea, not only the diversity of the S–C–N ligands can be Ir(ipdptha) were purified by silica chromatography and further
ꢀ
7
greatly enriched but also the energy gaps and the rigidity of the refined by sublimation at 10 Torr, and then were identified by
1
complexes can be effectively tuned, so that the luminescent
H NMR, HR-MS and elemental analyses.
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Table 1 Thermal, electrochemical and photophysical data of (4tfmpiq)
2
Ir(tiptha), (4tfmpiq)
2
Ir(phdiptha), (4tfmpiq)
2 2
Ir(fphdiptha) and (4tfmpiq) -
2 2
Ir(ipdptha) in CH Cl solution
a
b
b
d
P
e
Compound
T
d
(1C) Absorption l (nm) Emission lmax (nm)
t
298K (ms)
F
(%) HOMO/LUMO (eV) Energy gap (eV)
b
c
c
c
c
(
(
(
(
4tfmpiq)
4tfmpiq)
4tfmpiq)
4tfmpiq)
2
2
2
2
Ir(tiptha)
Ir(phdiptha)
Ir(fphdiptha) 319
Ir(ipdptha) 344
283
276
231/368/437/472
233/267/423/482
231/268/417/476
233/284/424/468
636 /635
0.83
0.91
0.79
0.93
41
38
39
42
ꢀ5.25/ꢀ3.30
ꢀ5.14/ꢀ3.18
ꢀ5.17/ꢀ3.20
ꢀ5.32/ꢀ3.33
1.95
1.96
1.97
1.99
b
632 /631
b
630 /630
b
627 /626
a
b
c
d
Decomposition temperature. Measured in degassed CH
2
Cl
2
.
Measured in 8 wt% doped TCTA films. F: emission quantum yields were
e
calculated in degassed CH
Cl
2 2
solution. HOMO (eV) = ꢀ(Eox ꢀ E1/2,Fc) ꢀ 4.8, LUMO (eV) = HOMO + Ebandgap
.
The thermal stability of these complexes was investigated by irregular. The coordinated S and N atoms of ancillary ligands
thermogravimetric analysis (TGA) under a nitrogen atmo- reside in the equatorial plane trans to the metalated C (4tfmpiq)
sphere. As observed from Fig. S1 (ESI†), (4tfmpiq)
2
4tfmpiq) Ir(phdiptha), (4tfmpiq) Ir(fphdiptha) and (4tfmpiq) -
2
Ir(tiptha), atoms. From the above analysis, this compact and tensile
(
2
2
bonding mode is well understood, and the relatively short
Ir(ipdptha) phosphors exhibited high thermal decomposition distances between the Ir atom and the S–C–N ligand is also
temperatures (T , corresponding to 5% weight loss) of 283 1C, crucial for improving the MLCT (metal–ligand charge transfer)
d
4
,9
2
76 1C, 319 1C and 344 1C, respectively (Table 1), indicating the of the resulting phosphorescent complexes,
thus leading
high morphological stability of the amorphous phase in the to the increased radiative transfer and the enhanced photo-
deposited films.
luminescence (PL) quantum efficiency.
X-ray crystallography analysis
Electrochemical properties and theoretical calculations
The molecular structures of the four complexes are further To investigate their electrochemical properties and calculate
confirmed by single crystal structures. Molecular structures by the energy levels of the highest occupied molecular orbital
the ORTEP drawing of the Ir(III) complexes (4tfmpiq)
2
Ir(tiptha), (HOMO) and the lowest unoccupied molecular orbital (LUMO),
(
4tfmpiq) Ir(phdiptha) and (4tfmpiq) Ir(ipdptha) are shown in the electrochemical behaviors of four Ir(III) complexes were
2
2
Fig. 1, and the crystallographic data and the selected bond measured by cyclic voltammetry in CH Cl solution at room
2
2
lengths/angles are summarized in Tables S1 and S2 (ESI†), temperature, relative to an internal ferrocenium/ferrocene
+
respectively. Three complexes have distorted octahedral coor- reference (Fc /Fc) (Fig. S2, ESI†). According to equation EHOMO
=
dination geometry around the iridium center by three chelating ꢀ(Eox ꢀ EFc/Fc
+
+ 4.8) eV, the HOMO energy levels (EHOMO) of four
ligands with cis-C–C and trans-N–N dispositions. The four- complexes were obtained. Based on the EHOMO and optical band
membered Ir–S–C–N backbones could lead to significantly gap calculated by equation DEbandgap= 1240/labs-onset, the lowest
more acute S–Ir–N bite angles (65.51, 66.091 and 66.021) than unoccupied molecular orbital (LUMO) energy levels were
seen for the larger five-membered or six-membered hetero- also obtained. From Table 1 it can be observed that their
1
2
cycles based on such as pic, acac derivatives. The Ir–C HOMO and LUMO levels are in the ranges of ꢀ5.14–5.32 eV
bond lengths are 1.994–2.010 Å and the Ir–N bond lengths and ꢀ3.18–3.33 eV, respectively.
are 2.034–2.052 Å, which are slightly shorter than the Ir–S
To gain more insight into the electronic structures of these
bonds (2.455–2.473 Å). These values of Ir–C and Ir–N are similar iridium complexes, quantum chemical calculations based on
to those reported in other mononuclear complexes with a density functional theory (DFT) calculations were performed.
4
13
(
C N)
2
Ir fragment. The much longer bond lengths of Ir–S1 The spatial distributions of the HOMO and LUMO energy levels
(2.455–2.473 Å) than that of Ir–N3 (2.188–2.196 Å) in the of these iridium complexes are shown in Fig. 2 and the details
complexes indicate that the formed quaternion ring plane is of the theoretical calculations are included in the ESI.†
Fig. 1 ORTEP diagram of (4tfmpiq)
2
Ir(tiptha) (CCDC no. 1950978), (4tfmpiq)
2
Ir(phdiptha) (CCDC no. 1950975) and (4tfmpiq)
2
Ir(ipdptha) (CCDC no.
1
950977)† with the atom-numbering schemes. Hydrogen atoms are omitted for clarity. Ellipsoids are drawn at a 50% probability level.
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2 2 2
Fig. 2 The isodensity surface plots and HOMO/LUMO orbital levels of (4tfmpiq) Ir(tiptha), (4tfmpiq) Ir(phdiptha), (4tfmpiq) Ir(fphdiptha) and
(
2
4tfmpiq) Ir(ipdptha) complexes.
As shown in Fig. 2, the HOMOs of four Ir(III) complexes were assigned to spin-allowed singlet metal-to-ligand charge transfer
1
predominately distributed over the d-orbitals of the iridium ( MLCT); while the weak absorption bands above 380 nm were
3
14
atom (31.2–39.53%) together with the thiourea derivatives ascribed to the spin-forbidden MLCT transitions. With the
35.55–47.94%) with a small portion over 4tfmpiq (20.86– altering of the substituents on the nitrogen atom of isothio-
5.37%). A larger scale distribution of electron clouds on the cyanic acid from isopropyl and phenyl to 4-fluorophenyl, the
(
2
iridium atom indicates an efficient MLCT of the phosphores- maximum emission peak of the complexes stayed almost
cent complexes, crucial to the high PL quantum efficiency, unchanged with 636 nm for (4tfmpiq) Ir(tiptha), 632 nm for
2
which may be caused by the relatively short distances between (4tfmpiq) Ir(phdiptha) and 630 nm for (4tfmpiq) Ir(fphdiptha),
2
2
4
,9
the iridium atom and S–C–N ligand. However, the LUMO respectively. A slight blue-shift was observed for (4tfmpiq)
orbitals were largely localized at the p* orbitals of the main (ipdptha) with the emission peak at 627 nm in comparison with
ligand (92.67–94.31%) and to a small extent on the Ir d orbitals (4tfmpiq) Ir(tiptha), which was attributed to the introduction
3.14–4.88%) and ancillary ligand (2.45–2.55%).
2
Ir-
2
(
of the less electron-donating substituent diphenylamine in the
thiourea derivatives. The emission peaks of the four complexes
measured in 8 wt% doped TCTA films are 635 nm, 631 nm,
Photophysical properties
630 nm and 626 nm, respectively, which are very close to those
The UV-vis absorption and photoluminescence (PL) spectra
measured in CH Cl solution (Fig. S3, ESI†). The slight changes
of the four complexes were recorded in CH
Cl
2 2
solution (Fig. 3).
2
2
in the emission wavelength of the four complexes coincide with
the little difference of the energy gaps by both the electro-
chemical analysis and the theoretical calculation. The PL
The intense absorption bands below 340 nm can be assigned to
the spin-allowed p–p* transitions from the conjugated ligands;
and the absorption bands between 340 nm and 380 nm were
2 2 2
Fig. 3 The UV-vis absorption (a) and emission (b) spectra of complexes (4tfmpiq) Ir(tiptha), (4tfmpiq) Ir(phdiptha), (4tfmpiq) Ir(fphdiptha) and
Ir(ipdptha) in degassed dichloromethane (5 ꢁ 10ꢀ M) at room temperature.
5
(
4tfmpiq)
2
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quantum yields of four Ir(III) complexes were measured as 41%, expected to be broadened. Besides, the HOMO energy level of
8%, 39% and 42%, respectively, in degassed CH Cl . And the TmPyPB is 0.6 eV lower than that of 2,6DCzPPy and the LUMO
lifetimes are in the range of microseconds for the four complexes energy level of TAPC is 0.6 eV higher than that of TCTA, which
0.83 ms for (4tfmpiq) Ir(tiptha), 0.91 ms for (4tfmpiq) - will result in the well confinement of excitons (hole–electron
3
2
2
(
2
2
Ir(phdiptha), 0.79 ms for (4tfmpiq) Ir(fphdiptha) and 0.93 ms pairs) within emissive layers and the triplet exciton quenching
2
for (4tfmpiq)
2
Ir(ipdptha), respectively) (Fig. S4, ESI†).
avoided effectively. Furthermore, holes and electrons can be
injected into the HOMO and LUMO levels of host materials or
trapped by the dopants directly owing to the obvious difference of
OLED performances
To illustrate the electroluminescence properties of these complexes, the HOMO/LUMO levels between the Ir(III) complexes and the host
typical OLEDs using these complexes as dopants were fabricated. materials. In contrast to the single-layer-emitting layer devices, the
Firstly, the device configuration consists of double emissive holes and electrons in the double-emissive-layer ones could be
layers with ITO/HAT-CN (6 nm)/TAPC (55 nm)/TCTA:Ir(III) com- distributed in a more balanced way and the exciton recombination
plexes (8 wt%, 8 nm)/2,6DCzPPy:Ir(III) complexes (8 wt%, 8 nm)/ zone is expected to be broadened, which can improve the utiliza-
TmPyPB (55 nm)/LiF (1 nm)/Al (100 nm). The devices with tion ratio of the hole–electron pairs, and thus improve EL perfor-
(
4tfmpiq)
and (4tfmpiq)
respectively. As shown in Scheme 2, materials HAT-CN doping concentration. The EL spectra, current density ( J)–voltage
2
Ir(tiptha), (4tfmpiq)
2 2
Ir(phdiptha), (4tfmpiq) Ir(fphdiptha) mances and efficiency roll-off. All the devices were optimized and
2
Ir(ipdptha) as emitters are denoted as D1–D4, display the best electroluminescence (EL) performances at 8 wt%
0
0
(dipyrazino[2,3-f:2 ,3 -h]quinoxaline-2,3,6,7,10,11-
c
(V)–luminance (L), current efficiency (Z ) versus luminance, and
hexacarbonitrile) and LiF served as hole- and electron-injecting EQE as a function of luminance characteristics of the devices are
interface modified materials, respectively. Materials TCTA displayed in Fig. 4. All the parameters are summarized in Table 2.
0
00
(
4,4 ,4 -tris(carbazol-9-yl)triphenylamine) and 2,6DCzPPy (2,6-
bis(3-(carbazol-9-yl)phenyl)pyridine) were chosen as host materials. 620 nm, respectively, of the devices are very close to those
TAPC (di-[4-(N,N-ditolylamino)phenyl]cyclohexane) and TmPyPB measured in CH Cl solution and doped films, respectively
1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene) act as hole-transport and (Fig. 4(a)), indicating that the EL emission of the devices originates
The EL emission peaks at 624 nm, 627 nm, 625 nm and
2
2
(
electron-transport materials, respectively. The stepwise changed from the triplet emission of the phosphors. Due to the same main
HOMO energy levels of TAPC (ꢀ5.5 eV), TCTA (ꢀ5.7 eV) ligand, similar molecular structures of the ancillary ligands and
and 2,6DCzPPy (ꢀ6.1 eV) are beneficial for the hole injection the approximate photoluminescence quantum efficiency, these
and transport. Similarly, it is also beneficial for the injection and materials exhibited the similar device performances.
transport of electrons owing to the gradually changed LUMO
Device D1 employing (4tfmpiq) Ir(tiptha) as an emitter
2
energy levels of TmPyPB (ꢀ2.7 eV), 2,6DCzPPy (ꢀ2.6 eV) and TCTA shows EL performances with a turn-on voltage of 3.8 V, a
ꢀ
2
(
ꢀ2.4 eV). Thus, holes and electrons will be distributed in more maximum luminance (Lmax) of above 4200 cd m , a peak
ꢀ1
balanced emissive layers and the exciton recombination zone is current efficiency (Zc,max) of 9.4 cd A and a maximum external
Scheme 2 Energy level diagram of HOMO and LUMO levels of materials investigated and their chemical molecular structures.
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Fig. 4 Characteristics of double emitting-layer devices: (a) EL spectra, (b) J–V–L, (c) Z
Table 2 The key EL data of devices D1–D4
c
–L and (d) EQE–L curves.
a
ꢀ2
ꢀ1
ꢀ1
b
ꢀ1
b
c
Device
V
turn-on (V)
L
max (cd m
)
Zc,max (cd A
)
Zext,max (%)
Zp,max (lm W
)
Z
c
(cd A
)
Z
ext (%)
CIE (x, y)
D1
D2
D3
D4
3.6
3.8
3.6
3.8
4222
6334
6982
3534
9.4
7.4
10.5
10.0
12.0
10.2
13.1
11.6
8.2
5.3
8.4
8.2
7.1
6.5
8.6
7.8
8.7
8.7
10.5
9.0
(0.66, 0.31)
(0.68, 0.32)
(0.67, 0.32)
(0.66, 0.32)
a
ꢀ2
b
ꢀ2
c
Turn on voltage at 1 cd m
.
Recorded at 1000 cd m
.
Measured at a driving voltage of 5 V.
quantum efficiency (EQEmax) of 12.0%, respectively. Relatively, the under mild conditions. Through changing the substituents on the
4tfmpiq) Ir(phdiptha)-based device D2 displays EL performances nitrogen and carbon atoms in isothiocyanic acid, respectively, the
with a Lmax, Zc,max and EQEmax of 6334 cd m , 7.4 cd A and diversity of the S–C–N ligands is greatly enriched, resulting in
0.2%, respectively. the slight variation of the emission wavelengths and PLQYs.
Device D4 based on (4tfmpiq) Ir(ipdptha) with the diphenyl- A device fabricated with a double-emitting-layer using complex
(
2
ꢀ
2
ꢀ1
1
2
amine substituent at a doping concentration of 8 wt% displayed (4tfmpiq) Ir(fphdiptha) as the dopant displays good performance
2
ꢀ
2
higher characteristics with a Lmax of 3534 cd m , a Zc,max of with an EQEmax of 13.1% for saturated red emission with the
0.0 cd A and an EQEmax of 11.6% with CIE coordinates of (0.66, satisfied CIE coordinates of (0.67, 0.32). Even at a brightness of
.32), which are quite close to the standard red demanded by the 1000 cd m , the EQE can still be obtained as 10.5%. This study
ꢀ
1
1
0
ꢀ
2
National Television System Committee (NTSC). Device D3 based provides a route to design various S–C–N ligands for mild synthesis
on (4tfmpiq) Ir(fphdiptha) showed the best EL performances with of high-performance Ir(III) complexes with a four-membered ring
a high brightness of 6982 cd m and the Zc,max and EQEmax are up structure.
2
ꢀ2
ꢀ1
to 10.5 cd A and 13.1%, respectively. The CIE coordinates of
0.67, 0.32) also fall in the red region. Furthermore, the device
efficiency roll-off is slow. As for device D3, the Z
(
and EQE can still Conflicts of interest
c
ꢀ
1
be obtained as 8.6 cd A and 10.5%, respectively, when the
There are no conflicts to declare.
ꢀ
2
luminance reaches 1000 cd m
.
3. Conclusions
Acknowledgements
In conclusion, four cyclometalated Ir(III) complexes containing a The authors gratefully acknowledge the financial support from
unique four-membered ring Ir–S–C–N backbone were prepared the Shenzhen Peacock Plan (KQTD20170330110107046), the
J. Mater. Chem. C
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Journal of Materials Chemistry C
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National Natural Science Foundation of China (No. 91833304
and 91433201), the Science and Technology Innovation
Commission of Shenzhen (JCYJ20180507182244027), and the
China Postdoctoral Science Foundation funded project (Grant
No. 2019M653034).
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This journal is © The Royal Society of Chemistry 2019
J. Mater. Chem. C