Four-membered red iridium(iii) complexes with Ir-S-C-S structures for efficient organic light-emitting diodes

Article abstract of DOI:10.1039/d0tc01312a

Three sulfur atom containing ligands (diphenylcarbamodithioate (dpdtc), di-p-tolylcarbamodithioate (medtc) and bis(4-(trifluoromethyl)phenyl)carbamodithioate (cf3dtc)) were prepared for three red iridium(iii) complexes. All(tfmpqz)₂Ir(dpdtc),(tfmpqz)₂Ir(medtc)and(tfmpqz)₂Ir(cf3dtc)complexes were synthesized rapidly at room temperature in 5 min with high yields owing to strong coordination ability between sulfur and iridium atoms, in which 4-(4-(trifluoromethyl)phenyl)quinazoline (tfmpqz) was used as the main ligand. Three Ir(iii) complexes show distinct PL emissions in the range of 617-629 nm with a high phosphorescence quantum yields of up to 83%, respectively. With these complexes as dopants, the organic light-emitting devices (OLEDs) with the double-emissive-layer structure ofITO/HATCN(hexaazatriphenylenehexacabonitrile, 5 nm)/TAPC(bis(4-(N,N-ditolyl-amino)phenyl)cyclohexane, 30 nm)/Ir(iii) complexes:TCTA(4,4′,4′′-tris(carbazol-9-yl)-triphenylamine) (12 wt%, 10 nm)/Ir(iii) complexes:26DCzppy(2,6-bis-(3-(carbazol-9-yl)phenyl)pyridine) (12 wt%, 10 nm)/TmPyPB(1,3,5-tri((3-pyridyl)-phen-3-yl)benzene, 30 nm)/LiF (1 nm)/Al (100 nm) achieved good performances. In particular, the device employing the(tfmpqz)₂Ir(cf3dtc)complex exhibits champion performances with a maximum luminance of 30?740 cd m^?2and a maximum external quantum efficiency of 26.10%, respectively.

Full text of DOI:10.1039/d0tc01312a

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Four-membered red iridium(III) complexes with Ir-S-C-S
structures for efficient organic light-emitting diodes
Ning Su a,b, Fang-Ling Li a, You-Xuan Zheng a*
Received 00th January 20xx,
Accepted 00th January 20xx
Three sulfur atom contained ligands (diphenylcarbamodithioate (dpdtc), di-p-tolylcarbamodithioate (medtc) and
bis(4-(trifluoromethyl)phenyl)carbamodithioate (cf3dtc)) were prepared for three red iridium(III) complexes.
All (tfmpqz)2Ir(dpdtc), (tfmpqz)2Ir(medtc) and (tfmpqz)2Ir(cf3dtc) complexes were synthesized rapidly at room
temperature in 5 min with high yields owing to strong coordination ability between sulfur and iridium atoms, in
which 4-(4-(trifluoromethyl)phenyl)quinazoline (tfmpqz) was used as main ligand. Three Ir(III) complexes
show distinct PL emissions at the range of 617 - 629 nm with high phosphorescence quantum yields up to of
83%, respectively. With these complexes as dopants, the organic light-emitting devices (OLEDs) with the
double-emissive-layer structure of ITO/ HATCN (hexaazatriphenylenehexacabonitrile, 5 nm)/ TAPC ((bis(4-
(N,N-ditolylamino)phenyl)cyclohexane, 30 nm)/ Ir(III) complexes: TCTA (4,4',4''-tris(carbazol-9-yl)-
triphenylamine) (12 wt%, 10 nm)/ Ir(III) complexes: 26DCzppy (2,6-bis-(3-(carbazol-9-yl)phenyl)pyridine) (12
wt%, 10 nm)/ TmPyPB (1,3,5-tri((3-pyridyl)-phen-3-yl)benzene, 30 nm)/ LiF (1 nm)/ Al (100 nm) achieved
good performances. In particular, the device employing (tfmpqz)2Ir(cf3dtc) complex exhibits the champion
performances with a maximum luminance of 30 740 cd m-2 and a maximum external quantum efficiency of
26.10%, respectively.
DOI: 10.1039/x0xx00000x
diisopropyl-guanidinate (dipig) were applied as ancillary ligands,
Introduction
respectively, and a maximum external quantum efficiency (EQEmax
)
of 16.7% was obtained with CIE coordinates of (0.69, 0.31). 8
Organic light-emitting device (OLED) emerges as one of the
promising candidate in flat-panel displays and solid-state lightings.1
Among organic materials, the phosphorescent emitters have been
extensively studied in past decades owing to their high
photoluminescence quantum yields (PLQYs) by harvesting capability
of singlet and triplet excitons.2 Especially, the cyclometalated
iridium(III) complexes have attracted much attention because of their
high PLQYs as well as various luminescence colours.3 Many design
strategies have been applied for efficient cyclometalated Ir(III)
complexes to tune their emissions cover the whole region.4
For red Ir(III) complexes, 1-phenylisoquinoline (piq) with large π-
conjugation degree and acetylacetone (acac)/ pyridinic acid (pic) or
their derivatives were usually employed as main and ancillary ligands,
respectively.5 Therefore, most Ir(III) complexes often have five or six
membered ring structures, while four membered ring ones were rarely
studied.6 Moreover, four membered ring Ir(III) complex would has
strong metal to ligand charge transfer (MLCT) effect, which is
attributed to short distance of metal center to the ligand, leading to
promising photophysical and electroluminescent properties.7 Hence,
it is necessary to design novel four-membered ring red Ir(III)
complexes for highly efficient OLEDs. For example, Liu et.al
reported four red Ir(III) complexes (bt)2Ir(dipba), (bt)2Ir(dipig),
(fpiq)2Ir(dipba) and (f2piq)2Ir(dipba) with four membered ring
structures, in which 2-benzothiozolato-phenyl (bt) and fluorophenyl-
isoquinoline derivatives (fpiq and f2piq) were used as main ligands,
and N,N’-diisopropylbenzamidinate (dipba), N,N’-diisopropyl-
Most reported Ir(III) complexes usually contain N^N, N^O and O^O
coordination patterns, while S^S based ligands were rarely reported.9
For example, Yang et al. firstly reported Ir(III) complexes
(ppy)2Ir(Et2dtc),
(ppy)2Ir(Et2dtp),
(bfoxd)2Ir(Et2dtc)
and
(bfoxd)2Ir(Et2dtp) with four-membered Ir-S-C-S structure, in which
2-phenylpyridine (ppy) and 1,3,4-oxadiazole derivatives (bfoxd) were
utilized as cyclometalated ligands, while N,N’-diethyl
dithiocarbamate (Et2dtc) and O,O’-diethyldithiophosphate (Et2dtp)
were employed as ancillary ligands, respectively, and the device based
on (bfoxd)2Ir(Et2dtc) complex showed a maximum current efficiency
(c,mac) of 9.88 cd A-1.9a, 9b Mei et al. also reported the Ir(dpp)2(dta)
complex with diethyldithiocarbamate as ancillary ligand, and its
device obtained the EQEmax of 9.28%.9c However, most Ir(III)
complexes were synthesized by mixing the chlorine bridging products
with the ancillary ligands/main ligands under high temperature for a
long reaction time, which greatly increase time and power cost.10 It is
vital to design new ancillary ligands to form Ir(III) complexes at room
temperature (RT) to further reduce synthesis time and accelerate
OLEDs development.
As we known, sulfur (S) atom with large atomic radius is
coordinated easily with heavy metal atom, such as mercury. Therefore,
it is prospective to apply S atom into ancillary ligands to form Ir(III)
complexes rapidly and efficiently at RT to simplify the synthesis
process of Ir(III) complexes. Recently, our group developed a series
of S-contained four-membered red Ir(III) complexes with Ir-S-C-S
and Ir-S-P-S structures.11 It is found that these Ir(III) complexes can
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DOI: 10.1039/D0TC01312A
be synthesized rapidly and efficiently at RT with both good synthesis resonance (NMR), high resolution mass spectrometer (HRMS) and X-
and sublimation yields, which are useful to reduce the material cost.
To further explore this type complexes, in this work, three S atom
ray crystallography.
Fig. 1 depicts the single crystal structures of three complexes, their
contained ligands (diphenylcarbamodithioate (dpdtc), di-p- crystal information and selected bond lengths/ angles are collected in
tolylcarbamodithioate (medtc) and bis(4-(trifluoromethyl)phenyl) Table S1 and Table S2, respectively. Stereotactic Ir(III) complexes are
carbamodithioate (cf3dtc)) were applied for three four-membered red composed of two C^N main ligands and one S^S ancillary ligand. The
Ir(III) complexes (tfmpqz)2Ir(dpdtc), (tfmpqz)2Ir(medtc) and S-Ir-S bite angles range from 71.14º to 71.60º because of different
(tfmpqz)2Ir(cf3dtc), in which 4-(4-(trifluoromethyl)phenyl)- substitution
groups
in
ancillary
ligands.
Moreover,
quinazoline (tfmpqz) was used as the main ligand. Three Ir(III) (tfmpqz)2Ir(medtc) complex shows completely mirror symmetric
complexes were obtained rapidly at RT for 5 min with high yields. single crystal structure as revealed in Fig. 1. In addition, Ir-S bonds
Trifluoromethyl (-CF3) group of tfmpqz ligand would efficiently lengths (2.412 (3) - 2.4801 (1) Å) are much longer than Ir-C bond
restrain the molecular packing and triplet-triplet annihilation (TTA) lengths (1.955 (8) - 2.016 (5) Å) and Ir-N bonds lengths (2.004 (7) -
effect, and the nitrogen heterocycle would improve the electron 2.057 (4) Å), which are well agreement with our previous reported
mobility of the Ir(III) complex.11b With these Ir(III) complexes as four-membered Ir(III) complexes.11
dopants, their devices achieve good performances with the maximum
luminance (Lmax) of 30 740 cd m-2 and the maximum external quantum
efficiency (EQEmax) of 26.10%, respectively.
CF3
CF3
CF3
Cl
Cl
a
Ir
Ir
N
N
N
N
N
2
N
Fig. 1 ORTEP diagrams of (tfmpqz)2Ir(dpdtc) complex (CCDC No. 1891565),
(tfmpqz)2Ir(medtc) complex (CCDC No. 1885951) and (tfmpqz)2Ir(cf3dtc)
complex (CCDC No. 1885886) with the atom-numbering schemes. Hydrogen
atoms are omitted for clarity. Ellipsoids are drawn at the 50% probability level.
2
tfmpqz
R
R
CF3
R
S
c
b
S
NH
In order to assess the thermal stabilities of three Ir(III) complexes,
thermogravimetric analysis (TGA) measurements were carried out
(Fig. S1). Three complexes (tfmpqz)2Ir(dpdtc), (tfmpqz)2Ir(medtc)
and (tfmpqz)2Ir(cf3dtc) exhibit gradually decreasing decomposed
temperatures (Td: corresponding to 5% weight loss) of 373, 369 and
349 oC, respectively, which are related to their molecular weights and
spatial sizes (Table 1).12 In general, all complexes have good thermal
stabilities, indicating the OLEDs fabricated would have long
operation lifetime.
N
Ir
N
S- Li+
S
N
N
2
R
R
R
R = H, (tfmpqz)2Ir(dpdtc)
R = CH3, (tfmpqz)2Ir(medtc)
R = CF3, (tfmpqz)2Ir(cf3dtc)
R = H, dpdtc
R = CH3, medtc
R = CF3, cf3dtc
(a) IrCl , EtOCH CH OH/H O, 115 °C, 12 h; (b) -BuLi, CS , 0 °C, 12 h;
n
3
2
2
2
2
(c) EtOCH2CH2OH, rt, 5 min
Scheme 1 Synthetic route of ancillary ligands and Ir(III) complexes.
Photophysical property
Fig. 2 shows the UV-visible absorption spectra of (tfmpqz)2Ir(dpdtc),
(tfmpqz)2Ir(medtc) and (tfmpqz)2Ir(cf3dtc) complexes in degassed
dichloromethane (DCM) solution (10-5 M) at RT. Three Ir(III)
complexes exhibit homologous absorption peaks from 230 to 600 nm.
The strong absorption peaks observed at 230 - 380 nm are accounted
for the ligand-centered (LC) transitions, while the less intense ones
above 400 nm are due to metal to ligand charge transfer (MLCT)
transitions.
Three complexes exhibit distinct photoluminescence (PL) emission
peaks at 627, 629 and 617 nm, respectively, which are attributed to
their diverse ancillary ligands. It is worth noting that
(tfmpqz)2Ir(cf3dtc) complex displays a 10 nm blue-shifted emission
peak compared to (tfmpqz)2Ir(dpdtc) complex, suggesting the
introduction of -CF3 group in ancillary ligand takes effect on material
emission. While (tfmpqz)2Ir(medtc) complex has a 2 nm red-shifted
Results and discussion
Synthesis and Characterization of Ir(III) complexes
As shown in Scheme 1, three
S atom contained ligands
diphenylcarbamodithioate (dpdtc), di-p-tolylcarbamodithioate (medtc)
and bis(4-(trifluoromethyl)phenyl)carbamodithioate (cf3dtc) were
successfully synthesized by the reaction of corresponding
diphenylamine derivatives with n-BuLi and CS2, respectively. Three
Ir(III) complexes (tfmpqz)2Ir(dpdtc), (tfmpqz)2Ir(medtc) and
(tfmpqz)2Ir(cf3dtc) were prepared with high yields above 80% by
mixing μ-chloro-bridged dimer [(tfmpqz)2Ir(μ-Cl)]2 with the ancillary
ligand salts (dpdtc, medtc or cf3dtc) in 2-ethoxyethanol at RT for 5
min, respectively. High purity complexes were achieved by flash
silica gel column and vacuum sublimation successively. The
molecular structures were characterized by nuclear magnetic
2 | J. Name., 2012, 00, 1-3
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emission peak with -CH3 group modification of the ancillary ligand. properties with ferrocene as the internal reference. The redox curves
Moreover, their 77 K phosphorescent spectra were also measured and were shown in Fig. S3, and their EHOMO values were estimated as -
showed in Fig. S2. It is obvious that their emission bands become 5.54, -5.55 and -5.62 eV for (tfmpqz)2Ir(dpdtc), (tfmpqz)2Ir(medtc)
narrower and the shoulder bands around 700 nm are also appeared, and (tfmpqz)2Ir(cf3dtc), respectively (Table 1), using an empirical
which would due to the molecular aggregation at 77 K. Furthermore, formula of EHOMO = - (Eox + 4.8) eV.13 Furthermore, their ELUMO values
the triplet energies (ET) of three Ir(III) complexes were calculated as were calculated as -3.56, -3.57 and -3.61 eV for (tfmpqz)2Ir(dpdtc),
2.09, 2.05 and 2.12 eV, respectively (Table 1).
(tfmpqz)2Ir(medtc) and (tfmpqz)2Ir(cf3dtc), respectively, which were
In addition, three Ir(III) complexes show high photoluminescence determined by their EHOMO values and optical band gap from their UV-
quantum yields (ΦPL) of 60%, 68% and 83%, respectively. Especially, visible absorption spectra. It is noted that these complexes have
(tfmpqz)2Ir(cf3dtc) complex obtains the highest ΦPL value due to the similar EHOMO and ELUMO values due to their similar structures.
-CF3 group in ancillary ligand. Moreover, the phosphorescent lifetime
Furthermore, density functional theory (DFT) calculations were
(τp) values of three complexes are 1.55, 1.63 and 1.69 μs, respectively, simultaneously performed to investigate the orbital distributions of
explaining their emissions originate from the triplet excited states of these Ir(III) complexes (Fig. 3). As can be seen clearly in Table S3,
the complexes.11a In general, three complexes exhibit distinct the LUMOs of Ir(III) complexes are largely localized on π* orbitals
photophysical properties owing to their different ancillary ligands.
of the main ligand tfmpqz with the proportion of 91.33% - 94.29%,
and little distributions on the Ir atom and ancillary ligands. Moreover,
the HOMOs are mainly distributed on π* orbitals of the C-chelated
block (40.77% - 43.55%) and d- orbitals of Ir center (47.66% -
48.78%), while little distribution on π* orbitals of ancillary ligands
(8.79% - 10.69%), which are consistent with their similar EHOMO and
ELUMO values calculated by CV measurements.
1.0
(tfmpqz)2Ir(dpdtc)
(tfmpqz)2Ir(medtc)
0.8
0.6
0.4
0.2
0.0
(tfmpqz)2Ir(cf3dtc)
300
400
500
600
700
800
Wavelength (nm)
Fig. 2 Normalized absorption and emission spectra of the Ir(III) complexes in
dilute DCM (10-5 M) at RT.
Table 1 Photophysical data of the Ir(III) complexes.
b
c
Td
PLa
ΦPL
τp
ET
EHOMO
ELUMO
Fig. 3 Theoretical HOMO/LUMO energy levels of the Ir(III) complexes.
Complex
(oC)
(nm)
(%)
(μs)
(eV)d
(eV)e
(eV)f
(tfmpqz)2Ir(dpdtc)
(tfmpqz)2Ir(medtc)
(tfmpqz)2Ir(cf3dtc)
373
369
349
627
629
617
60
68
83
1.55
1.63
1.69
2.09
2.05
2.12
-5.54
-5.55
-5.62
-3.56
-3.57
-3.61
Electroluminescent property
In order to explore the electroluminescence (EL) performances of
three Ir(III) complexes, the double emissive-layer OLEDs with the
structure of ITO/ HATCN (hexaazatriphenylenehexacabonitrile, 5
nm) / TAPC ((bis(4-(N,N-ditolylamino)phenyl)cyclohexane, 30 nm)/
Ir(III) complexes: TCTA (4,4',4''-tris(carbazol-9-yl)-triphenylamine)
(12 wt%, 10 nm)/ Ir(III) complexes: 26DCzppy (2,6-bis-(3-(carbazol-
9-yl)phenyl)pyridine) (12 wt%, 10 nm)/ TmPyPB (1,3,5-tri((3-
pyridyl)-phen-3-yl)benzene, 30 nm)/ LiF (1 nm)/ Al (100 nm) were
fabricated and named G1, G2 and G3 (Scheme 2), respectively.
HATCN and LiF were served as hole-and electron-injecting layers,
respectively. TAPC and TmPyPB acted as hole- and electron-
a Measured in DCM (10-5 M) at RT; b Measured in DCM (10-5 M) in N2 atmosphere with a
reference of fac-Ir(ppy)3 (ΦPL = 40%); c Measured in DCM (10-5 M) in N2 atmosphere; d ET
(triplet energy): Estimated from the highest energy peaks of the 77 K phosphorescence
e
spectra. Calculated from empirical equation: EHOMO = - (Eox + 4.8) eV; f Calculated from
ELUMO = Egopt + EHOMO.
Electrochemical property and DFT calculation
In order to calculate the highest occupied molecular orbital (HOMO)
and the lowest unoccupied molecular orbital (LUMO) energy levels
(EHOMO/ELUMO) of Ir(III) complexes, cyclic voltammetry (CV)
measurements were used to investigate their electrochemical
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NC
N
CN
N
the devices due to its prominent bipolar properties. TCTA (ET = 2.82
eV) and 26DCzPPy (ET = 2.71 eV) have high triplet energy levels as
shown in Scheme 2.14 Therefore, it is beneficial for the carrier balance
in emitting layer (EML). The EL spectra, luminance (L) versus
voltage (V), current efficiency (ηc) versus luminance, and power
efficiency (ηp) versus luminance characteristics of G1, G2 and G3
devices are depicted in Fig. 4, and the key EL data are presented in
Table 2.
N
N
N
N
NC
CN
N
N
NC
CN
HATCN
CF3
TAPC
-1.8 eV
-2.4 eV
R
-2.6 eV
-2.7 eV
-3.56 ~
N
S
- 3.61 eV
Ir
N
S
N
N
-4.3 eV
LiF/Al
N
2
N
N
R
-5.1 eV
ITO
R = H, (tfmpqz)2Ir(dpdtc), ET = 2.09 eV
R = CH3,(tfmpqz)2Ir(medtc), ET = 2.05 eV
R = CF3,(tfmpqz)2Ir(cf3dtc), ET = 2.12 eV
-5.5 eV
-5.54 ~
TCTA, ET = 2.82 eV
-5.5 eV
- 5.62 eV
-5.7 eV
-6.1 eV
N
All devices show distinct red EL emissions at 620, 616 and 606 nm,
respectively, which are quite similar to the PL emissions in DCM
solutions of Ir(III) complexes, indicating the EL emissions originate
from their triplet excited states. It is worth noting that there is no
obvious emission peak from TCTA and 26DCzppy host materials in
all devices, suggesting the quite efficient energy transfer from TCTA
and 26DCzppy to the dopants in emissive layers upon electrical
excitation. Furthermore, their CIE coordinates locate at (0.65, 0.33),
(0.64, 0.33) and (0.61, 0.36), respectively (Table 2).
-6.7 eV
N
N
N
N
26DCzPPy, ET = 2.71 eV
-9.5 eV
N
TmPyPB
Scheme 2. The OLEDs device structures, their molecular structures used in
this work.
transport media, respectively. TCTA was utilized as host material due
to its compatible energy level and excellent hole transport properties.
Simultaneously, another host material 26DCzppy was also added into
105
G1
G2
G3
(b)
(a)
G1
G2
G3
104
103
102
101
100
3
4
5
6
7
8
9
10
11
400
100
500
600
800
Wavelength (nm) 700
Voltage (V)
100
10
1
(c)
G1
G2
G3
10
1
G1
G2
G3
(d)
0.1
0.01
0.1
0.01
0
1000
2000
3000
4000
5000
0
1000
2000
3000
4000
5000
Luminance (cd m-2)
Luminance (cd m-2)
Fig. 4 Device characteristics of G1-G3: (a) EL spectra; (b) L-V curves; (c) ηc-L curves and (d) ηp-L curves.
Moreover, three devices achieved increasing device performances EQEmax of 16.80%, respectively. By further modification of the
with the emitters changing from (tfmpqz)2Ir(dpdtc) to dopants (tfmpqz)2Ir(dpdtc) complex with methyl and trifluoromethyl
(tfmpqz)2Ir(medtc), (tfmpqz)2Ir(cf3dtc) complexes. For example, groups, respectively, device G2 with (tfmpqz)2Ir(medtc) complex as
device G1 doping with (tfmpqz)2Ir(dpdtc) complex achieves the dopant and device G3 employing (tfmpqz)2Ir(cf3dtc) complex as
performances with the Lmax of 20 681 cd m-2, the ηc,max of 22.49 cd emitter exhibited better properties than device G1, respectively. For
A-1, the maximum power efficiency (ηp,max) of 16.42 lm W-1 and the example, device G2 showed the EL performances with a Lmax of 26
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939 cd m-2, a ηc,max of 26.61 cd A-1, a ηp,max of 19.89 lm W-1 and an using petroleum ether (PE)/ DCM (V/V=1:3) as eluent to obtain red
EQEmax of 18.30%. Device G3 achieved the best performances with a solid. The target Ir(III) complexes were further purified by vacuum
Lmax of 30 740 cd m-2, a ηc,max of 46.86 cd A-1, a ηp,max of 37.73 lm W-1 sublimation to give red crystals.
1
and an EQEmax of 26.10%, which is due to the large steric hindrance
of trifluoromethyl group in (tfmpqz)2Ir(cf3dtc) complex.
(tfmpqz)2Ir(dpdtc) (yield: 80%). H NMR (400 MHz, CDCl3) δ
10.39 (d, J = 1.1 Hz, 2H), 8.82 (d, J = 8.6 Hz, 2H), 8.43 - 8.32 (m,
Furthermore, it is found that device performances are related with 4H), 8.09 - 7.99 (m, 2H), 7.91 - 7.82 (m, 2H), 7.43 (d, J = 7.7 Hz, 4H),
phosphorescence quantum yields of the dopants, such as device G3 7.36 (t, J = 7.7 Hz, 4H), 7.29 (dd, J = 5.8, 3.7 Hz, 2H), 7.16 (d, J =
showed the best EL performances with (tfmpqz)2Ir(cf3dtc) complex 8.4 Hz, 2H), 6.73 (s, 2H). 19F NMR (377 MHz, CDCl3) δ -63.19 (s).
as emitter, which has the highest phosphorescence quantum yields of HRMS (m/z): calcd for C43H26F6IrN5S2 [M+H]+ 984.1241, found
83% among three complexes. While device G1 and device G2 984.1236.
1
achieved lowest and medium OLEDs properties, which are matched
(tfmpqz)2Ir(medtc) (yield: 83%). H NMR (400 MHz, CDCl3) δ
well with their dopants’ phosphorescence quantum yields of 60% and 10.38 (s, 2H), 8.82 (d, J = 8.5 Hz, 2H), 8.41 - 8.32 (m, 4H), 8.08 -
68%, respectively. 8.00 (m, 2H), 7.90 - 7.81 (m, 2H), 7.29 (d, J = 8.3 Hz, 4H), 7.15 (dd,
In general, three devices obtained good device performances, which J = 8.3, 3.3 Hz, 6H), 6.74 (s, 2H), 2.27 (s, 6H). 19F NMR (377 MHz,
are attributed to the following reasons. Firstly, three S-atom contained CDCl3) δ -63.30 (s). HRMS (m/z): calcd for C45H30F6IrN5S2 [M+H]+
ancillary ligands were successfully introduced into Ir(III) complexes 1012.1554, found 1012.1461.
1
forming four-membered ring structures, which helps suppress
(tfmpqz)2Ir(cf3dtc) (yield: 86%). H NMR (400 MHz, CDCl3) δ
molecular packing and reduces TTA and triplet-polaron annihilation 10.28 (s, 2H), 8.84 (d, J = 8.6 Hz, 2H), 8.41 (d, J = 8.4 Hz, 2H), 8.34
(TPA) effect. Secondly, nitrogen heterocyclic structures of tfmpqz (d, J = 8.4 Hz, 2H), 8.06 (t, J = 7.2 Hz, 2H), 7.89 (t, J = 7.2 Hz, 2H),
main ligand are beneficial for promoting electronic mobility ability of 7.63 (d, J = 8.5 Hz, 4H), 7.55 (d, J = 8.4 Hz, 4H), 7.19 (d, J = 7.1 Hz,
the emitters and realizing the balanced injection and transportation of 2H), 6.71 (s, 2H). 19F NMR (377 MHz, CDCl3) δ -62.80 (s), -63.32
carriers.15 Finally, two host materials TCTA and 26DCzppy were used (s). HRMS (m/z): calcd for C45H24F12IrN5S2 [M+H]+ 1120.0989,
to construct double emissive-layer devices to further boost the found 1120.0960.
injection of hole/electron and transportation of exciton from host to
Conclusions
guest, leading to good device performances.
In summary, three sulfur atom contained red Ir(III) complexes
(tfmpqz)2Ir(dpdtc), (tfmpqz)2Ir(medtc) and (tfmpqz)2Ir(cf3dtc) were
obtained rapidly and efficiently at room temperature in 5 min with
high yields (> 80%). They show distinct PL emissions at 617 - 629
nm with high phosphorescence quantum yields of up to 83% due to
the variation of the ancillary ligands. Employing the complexes as
emitters, all devices achieved good performances with the maximum
luminance of 30 740 cd m-2, the maximum current efficiency of 46.86
cd A-1 and the maximum external quantum efficiency of 26.10%. This
research is beneficial to reduce the material production cost and speed
up the process of OLEDs industrialization.
Table 2. Key EL data of devices G1-G3.
Device
Von
Lmax
ηc,max
ηp,max
EQEmax
(%)e
CIE
(V)a (cd m-2)b (cd A-1)c (lm W-1)d
(x,y)
G1
G2
G3
4.1
3.5
3.7
20 681
26 939
30 740
22.49
26.61
46.86
16.42
19.89
37.73
16.80
18.30
26.10
(0.65,0.33)
(0.64,0.33)
(0.61,0.36)
a Turn-on voltage, the driving voltage at 1 cd m-2; b Maximum luminance; c Current
d
e
efficiency; Power efficiency; External quantum efficiency calculated within
visible spectrum region.
Acknowledgments
Experiments
This work was supported by the National Natural Science Foundation
of China (21975119, 51773088) and China Postdoctoral Science
Foundation (2019M663036).
General synthesis of the ancillary ligands and Ir(III) complexes
n-BuLi (3.70 mL, 5.92 mmol) was slowly added into diphenylamine
or di-p-tolylamine or bis(4-(trifluoromethyl)phenyl)amine (2.96
mmol) in dry tetrahydrofuran (THF) (6 mL) at 0 ºC. After stirred for
30 min, CS2 (449 mg, 5.92 mmol) was added, and the system was
warmed to room temperature for 12 h. Then, ethyl ether was mixed
into the system to form the white ancillary ligand salt precipitates
(dpdtc, medtc, cf3dtc), respectively, and they were utilized directly in
the next step without further purification. Then, the ancillary ligand
salts (dpdtc, medtc, cf3dtc) (2.28 mmol) stirred with chloro-bridged
dimer [(tfmpqz)2Ir(μ-Cl)]2 (0.76 mmol, 0.33 eq) in 2-ethoxyethanol
(15 mL) at RT for 5 min, respectively. After removing the solution,
the crude products were purified through a flash silica gel column
Conflicts of interest
There are no conflicts to declare.
Notes and references
aState Key Laboratory of Coordination Chemistry, Jiangsu Key
Laboratory of Advanced Organic Materials, School of Chemistry and
Chemical Engineering, Nanjing University, Nanjing 210093, P. R.
China. E-mail: yxzheng@nju.edu.cn
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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bCollege of Physics and Optoelectronic Engineering, Shenzhen
University, Shenzhen 518060, China.
Y. Gu, J. Qin, X. Ning, S. Gong, G. Xie and C. Yang, J. Mater.
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E-mail: suning@szu.edu.cn
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Journal of Materials Chemistry C
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DOI: 10.1039/D0TC01312A
Three sulfur atom contained red Ir(III) complexes were synthesized rapidly at room temperature
in 5 min with high yields and their OLEDs show an EQEmax up to of 26.10%.