Asymmetric Heteroleptic Ir(III) Phosphorescent Complexes with Aromatic Selenide and Selenophene Groups: Synthesis and Photophysical, Electrochemical, and Electrophosphorescent Behaviors

Article

pubs.acs.org/IC

Cite This: Inorg. Chem. XXXX, XXX, XXX −XXX

Asymmetric Heteroleptic Ir(III) Phosphorescent Complexes with

Aromatic Selenide and Selenophene Groups: Synthesis and

Photophysical, Electrochemical, and Electrophosphorescent

Behaviors

Zhao Feng,^†Dezhi Wang,^‡Xiaolong Yang,^†Deyuan Jin,^†Daokun Zhong,^†Boao Liu,^†

Guijiang Zhou,*^,†Miaofeng Ma,*^,‡and Zhaoxin Wu*^,§

^†MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Institute of Chemistry for New Energy

Materials, Department of Chemistry, School of Science, Xi’an Jiaotong University, Xi’an 710049, People’s Republic of China

^‡Department of Applied Chemistry, College of Chemistry & Pharmacy, Northwest A&F University, Yangling 712100, People’s

Republic of China

^§Key Laboratory of Photonics Technology for Information School of Electronic and Information Engineering, Xi’an Jiaotong

University, Xi’an 710049, People’s Republic of China

S

* Supporting Information

ABSTRACT: With the aim of evaluating the potential of selenium-containing groups

in developing electroluminescent (EL) materials, a series of asymmetric heteroleptic

Ir(III) phosphorescent complexes (Ir-Se0F, Ir-Se1F, Ir-Se2F, and Ir-Se3F) have

been synthesized by using 2-selenophenylpyridine and one ppy-type (ppy = 2-

phenylpyridine) ligand with a ﬂuorinated selenide group. To the best of our

knowledge, these complexes represent unprecedented examples of asymmetric

heteroleptic Ir(III) phosphorescent emitters bearing selenium-containing groups.

Natural transition orbital (NTO) analysis based on optimized geometries of the ﬁrst

triplet state (T₁) have shown that the phosphorescent emissions of these Ir(III)

3

complexes dominantly show π−π* features of the 2-selenophenylpyridine ligand

with slight metal to ligand charge transfer (MLCT) contribution. In comparison with

their symmetric parent complex Ir-Se with two 2-selenophenylpyridine ligands, these

asymmetric heteroleptic Ir(III) phosphorescent complexes can show much higher

phosphorescent quantum yields (Φ_P) of ca. 0.90. Both the hole- and electron-trapping ability of these Ir(III) phosphorescent

complexes can be enhanced by selenophene and ﬂuorinated selenide groups to improve their EL eﬃciencies. The EL abilities of

these asymmetric heteroleptic Ir(III) phosphorescent emitters fall in the order Ir-Se3F > Ir-Se2F > Ir-Se1F > Ir-Se0F. The

highest EL eﬃciencies have been achieved by Ir-Se3F in the solution-processed OLEDs with external quantum eﬃciency (η_ext),

current eﬃciency (η_L), and power eﬃciency (η_P) of 19.9%, 65.6 cd A⁻¹, and 57.3 lm W⁻¹, respectively. These encouraging EL

results clearly indicate the great potential of selenium-containing groups in developing high-performance Ir(III) phosphorescent

emitters.

luminescence (EL) eﬃciencies of the concerned OLEDs.^7,9In

addition, the phenyl sulﬁde groups can be converted into

INTRODUCTION

■

Owing to their distinctive electronic features, elements in

phenyl sulfone moieties by proper oxidizing agents to endow

group VIA have been widely employed to construct groups to

the Ir(III) and Pt(II) phosphorescent emitters with enhanced

functionalize phosphorescent Ir(III) and Pt(II) complexes

electron injection/electron transport (EI/ET) performance to

with 2-phenylpyridine (ppy)-type ligands, since they can

furnish charge carrier injection/transport features to the

concerned emissive complexes which can show great potential

induce improved EL eﬃciencies as well.^1,3,8Beyond this,

aromatic systems with oxygen or sulfur have been employed to

synthesize the ppy-type ligands for the Ir(III) and Pt(II)

for making highly eﬃcient organic light-emitting diodes

phosphorescent emitters as well.^3,10−17To date, several kinds

of aromatic units, such as thiophene,^16,18benzothio-

phene,^13,14,17benzofuran,^11,14dibenzothiophene,^3,19dibenzo-

furan,^3,20thiazole,^21,22benzothiazole,^3,23,24etc., have been

(OLEDs).¹⁻⁸Typically, these functional groups have been

synthesized with oxygen or sulfur atoms embedded into or

attached to the aromatic rings.^5,7,9Through an attaching

strategy, both phenyl ether and phenyl sulﬁde groups have

been introduced to the ppy-type Ir(III) and Pt(II)

phosphorescent complexes to enhance their hole injection/

hole transport (HI/HT) ability and hence improve electro-

Received: June 13, 2018

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DOI: 10.1021/acs.inorgchem.8b01639

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

were measured on an Edinburgh Instruments, Ltd. (FLSP920),

ﬂuorescence spectrophotometer. Phosphorescent quantum yields

(Φ_P) against fac-[Ir(ppy)₃] (Φ_P= 0.97) standard were measured in

CH₂Cl₂solution at 293 K.³³The diﬀerential scanning calorimetry

(DSC) and thermal gravimetric analysis (TGA) data were acquired

on a NETZSCH DSC 200 PC unit and a NETZSCH STA 409C

instrument, respectively. Cyclic voltammetry (CV) was conducted

with a Princeton Applied Research Model 273A potentiostat at a 100

mV s⁻¹scan rate. All of the CV experiments were conducted with a

three-electrode compartment cell possessing a Pt-sheet counter

electrode, a glassy-carbon working electrode, and an Ag/AgCl

reference electrode. The supporting electrolyte was a 0.1 M

acetonitrile solution of [nBu₄N]BF₄with ferrocene as internal

reference. The data of elemental analysis were obtained on a Flash

EA 1112 elemental analyzer. Fast atom bombardment (FAB) mass

spectra were recorded on a Finnigan MAT SSQ710 system. High-

resolution mass spectrometry (HRMS) data were obtained on a

Waters I-class Vion IMS QTof microspectrometer. FT-IR spectra

were acquired on a Bruker Vertex 70 spectrometer.

introduced to the ppy-type ligands to optimize the EL

properties of the Ir(III) and Pt(II) phosphorescent emitters

as well. Similarly, as the oxidized counterpart of dibenzothio-

phene, diphenylene sulfone can enhance the EI/ET ability of

the ppy-type Ir(III) phosphorescent emitters to bring about

attractive EL eﬃciencies.^3,25

In the same group of elements as oxygen and sulfur,

selenium can also aﬀord exciting properties with great potential

for various applications. In addition to medical activity from

the selenides,²⁶conjugated compounds containing seleno-

phene unit have served as key organic semiconductors in

advanced optoelectronic devices, such as organic thin ﬁlm

transistors (OTFTs)^27,28and solar cells,^28,29exhibiting great

potency. Inspired by the success of the phosphorescent

emitters with oxygen- and sulfur-containing units in the ﬁeld

of OLEDs, the design and synthesis of phosphorescent

analogues bearing selenium-containing groups should deﬁ-

nitely represent a feasible strategy to bring about high EL

eﬃciencies in OLEDs. To the best of our knowledge, this

aspect has been rarely explored in EL research and only the

selenophene unit has been employed to prepare one symmetric

fac-[Ir(4-phenyl-2-(selenophen-2-yl)quinoline)₃] phosphores-

cent complex with a phosphorescent quantum yield (Φ_P) of

0.07 to investigate its EL ability.²Considering the critical role

played by the Φ_Pin enhancing EL performances, improving

the Φ_Pof selenium-containing Ir(III) phosphorescent emitters

should represent an important way to fully explore their

potential in the ﬁeld of OLEDs. Recently, it has been shown

that the ppy-type Ir(III) phosphorescent emitters with an

asymmetric structure can show obvious advantages over the

traditional counterparts adopting a symmetric conﬁguration,

since the two diﬀerent major organic ligands constructing the

asymmetric structure can provide great space to optimize the

optoelectronic features of the concerned phosphorescent

emitters.³⁰⁻³²Taking the advantages of both selenium-

containing groups and asymmetric conﬁgurations should

represent another feasible way to develop new phosphorescent

emitters with high EL eﬃciencies. Bearing all this in mind, we

have obtained a series of new asymmetric ppy-type Ir(III)

phosphorescent emitters with both selenophene and aryl

selenide units to show the potential of selenium-containing

groups for constructing functional materials in the EL ﬁeld.

Owing to the unique electronic properties of the selenium-

containing groups, all of the investigated ppy-type Ir(III)

phosphorescent emitters show impressive EL performances.

This research should represent not only a new pathway for

developing new phosphorescent emitters with high EL ability

but also more comprehensive information about the crucial

role played by group VIA elements in the design of high-

performance optoelectronic materials.

General Procedure for the Synthesis of Asymmetrical

Diaryl Selenones. Under ambient conditions, in a round-bottomed

ﬂask charged with 1,2-bis(4-bromophenyl)diselenide (1.0 equiv) were

placed the corresponding arylboronic acid (1.5 equiv), CuO

nanoparticles (0.03 equiv), and anhydrous DMSO. The reaction

mixture was stirred at 100 °C for 24 h. After the reaction mixture was

cooled to room temperature, it was poured into a saturated aqueous

solution of NaCl and then extracted with petroleum ether three times.

The organic phase was dried with anhydrous Na₂SO₄. Then, the

solvent was removed under reduced pressure and the residue was

redissolved in CHCl₃. To the reaction mixture was added m-

chloroperbenzoic acid (mCPBA) (5.0 equiv) in small portions at

room temperature. After overnight reaction, the reaction mixture was

subjected to ﬁltration. The residue was washed with petroleum ether/

CH₂Cl₂(2/1, v/v) twice. The ﬁltrates were combined, and the

solvent was removed under reduced pressure. The residue was

puriﬁed through chromatography on silica gel using CH₂Cl₂as eluent

to gain a pure product.

Br-SeO-0F. Yield: 67.5%. ¹H NMR (400 MHz, CDCl₃, δ): 7.98 (d,

J = 7.6 Hz, 2H), 7.86 (d, J = 8.8 Hz, 2H), 7.75 (d, J = 8.4 Hz, 2H),

7.69 (t, J = 6.6 Hz, 1H), 7.62 (t, J = 7.4 Hz, 2H). ¹³C NMR (100

MHz, CDCl₃, δ): 142.32, 141.38, 134.28, 133.45, 130.37, 129.45,

128.41, 126.86. FAB-MS (m/z): 344, 346 [M]⁺. Anal. Calcd for

C₁₂H₉BrO₂Se: C, 41.89; H, 2.64. Found: C, 41.78; H, 2.55.

Br-SeO-1F. Yield: 64.3%. ¹H NMR (400 MHz, CDCl₃, δ): 8.00 (tt,

J = 7.0, 2.0 Hz, 2H), 7.85 (d, J = 8.4 Hz, 2H), 7.76 (dt, J = 6.8, 1.6 Hz,

2H), 7.31 (t, J = 8.6 Hz, 2H). ¹³C NMR (100 MHz, CDCl₃, δ):

166.11 (d, J = 256.2 Hz), 141.37, 137.82 (d, J = 3.4 Hz), 133.61,

129.76, 129.68 (d, J = 3.7 Hz), 128.36, 117.85 (d, J = 22.8 Hz) . ¹⁹F

NMR (376 MHz, CDCl₃, δ): −101.58. FAB-MS (m/z): 362, 364

[M]⁺. Anal. Calcd for C₁₂H₈BrFO₂Se: C, 39.81; H, 2.23. Found: C,

39.75; H, 2.11.

Br-SeO-2F. Yield: 57.9%. ¹H NMR (400 MHz, CDCl₃, δ): 7.87 (d,

J = 8.8 Hz, 2H), 7.79 (d, J = 8.8 Hz, 2H), 7.52−7.55 (m, 2H), 7.13

(tt, J = 8.4, 2.2 Hz, 1H). ¹³C NMR (100 MHz, CDCl₃, δ): 163.27

(dd, J = 257.9, 11.0 Hz), 144.80 (t, J = 7.9 Hz), 140.57, 133.79,

130.20, 128.36, 110.79 (dd, J = 20.1, 8.5 Hz), 110.16 (t, J = 24.8 Hz).

¹⁹F NMR (376 MHz, CDCl₃, δ): −102.53. FAB-MS (m/z): 380, 382

EXPERIMENTAL SECTION

[M]⁺. Anal. Calcd for C₁₂H₇BrF₂O₂Se: C, 37.92; H, 1.86. Found: C,

37.82; H, 1.74.

■

General Information. Commercially available chemicals were

used directly for synthesis with no further puriﬁcation. All solvents for

the reactions were dried and distilled in the proper way. The reactions

were monitored with thin-layer chromatography (TLC) materials

purchased from Merck & Co., Inc.; silica gel used for ﬂash column

chromatography and preparative TLC plates were purchased from

Br-SeO-3F. Yield: 55.1%. ¹H NMR (400 MHz, CDCl₃, δ): 7.85 (d,

J = 8.8 Hz, 2H), 7.80 (d, J = 8.4 Hz, 2H), 7.69 (t, J = 5.4 Hz, 2H). ¹³C

NMR (100 MHz, CDCl₃, δ): 151.97 (ddd, J = 260.1, 10.8, 2.8 Hz),

143.89 (dt, J = 262.0, 14.4 Hz), 140.58, 137.48 (dd, J = 10.9, 5.4 Hz),

133.90, 130.39, 128.31, 112.46 (dd, J = 16.8, 7.6 Hz). ¹⁹F NMR (376

MHz, CDCl₃, δ): −126.49 (d, J = 22.6 Hz, 2F), −148.08 (t, J = 18.8

Hz, 1F). FAB-MS (m/z): 398, 400 [M]⁺. Anal. Calcd for

C₁₂H₆BrF₃O₂Se: C, 36.21; H, 1.52. Found: C, 37.05; H, 1.36.

General Procedure for the Synthesis of L-SeO-0F−L-SeO-

3F. Under a nitrogen atmosphere, to a solution of Br-SeO-0F/Br-

SeO-1F/Br-SeO-2F/Br-SeO-3F (1.1 equiv) and 2-(tributylstannyl)-

Shenghai Qingdao (300−400 mesh). H, ¹⁹F, and ¹³C NMR spectra

1

were measured on a Bruker Avance 400 MHz spectrometer in CDCl₃.

Chemical shifts were referenced to the solvent residual peak at δ 7.26

ppm for ¹H and 77.0 ppm for ¹³C NMR spectra, respectively. UV−vis

absorption spectra were recorded on a PerkinElmer Lambda 950

spectrophotometer. Emission spectra and lifetimes of these complexes

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pyridine (1.0 equiv) in toluene was added Pd(PPh₃)₄(0.05 equiv) as

catalyst. The reaction mixture was reacted at 110 °C for 20 h. After

the mixture was cooled to room temperature, the solvent was

removed under vacuum. The residue was puriﬁed by column

chromatography on silica gel using CH₂Cl₂/ethyl acetate (15/1, v/

v) as eluent.

Hz), 156.65, 149.72, 138.28, 136.79, 135.91 (d, J = 7.9 Hz), 133.08,

132.21, 127.72, 124.87 (d, J = 3.4 Hz), 122.25, 120.31, 116.64 (d, J =

21.3 Hz). ¹⁹F NMR (376 MHz, CDCl₃, δ): −113.69. FAB-MS (m/z):

329 [M]⁺. Anal. Calcd for C₁₇H₁₂FNSe: C, 62.21; H, 3.69; N, 4.27.

Found: C, 62.08; H, 3.59; N. 4.17.

L-Se2F. Yield: 88.3%. ¹H NMR (400 MHz, CDCl₃, δ): 8.71 (d, J =

4.4 Hz, 1H), 7.98 (dd, J = 6.8, 1.6 Hz, 2H), 7.78 (td, J = 7.4, 1.6 Hz,

1H), 7.74 (d, J = 8.0 Hz, 1H), 7.67 (dt, J = 8.4, 1.8 Hz, 2H), 7.25−

7.28 (m, 1H), 6.88 (dd, J = 7.2, 2.4 Hz, 2H), 6.66 (tt, J = 8.8, 2.2 Hz,

1H). ¹³C NMR (100 MHz, CDCl₃, δ): 163.06 (dd, J = 250.4, 12.4

Hz), 156.38, 149.82, 139.81, 136.90, 135.48 (t, J = 8.7 Hz), 135.18,

129.35, 128.17, 122.57, 120.58, 113.79 (dd, J = 19.3, 6.9 Hz), 102.38

(t, J = 25.4 Hz). ¹⁹F NMR (376 MHz, CDCl₃, δ): −109.18. FAB-MS

(m/z): 347 [M]⁺. Anal. Calcd for C₁₇H₁₁F₂NSe: C, 58.97; H, 3.20; N,

4.05. Found: C, 58.89; H, 3.11; N. 3.96.

L-SeO-0F. Yield: 85.2%. ¹H NMR (400 MHz, CDCl₃, δ): 8.73 (dd,

J = 4.8, 0.8 Hz, 1H), 8.24 (dt, J = 8.4, 1.8 Hz, 2H), 8.10 (d, J = 8.8 Hz,

2H), 8.02 (dt, J = 6.8, 1.6 Hz, 2H), 7.82 (td, J = 7.6, 2.0 Hz, 1H), 7.77

(d, J = 8.0 Hz, 1H), 7.68 (tt, J = 7.4, 2.0 Hz, 1H), 7.62 (t, J = 7.4 Hz,

2H), 7.33 (ddd, J = 7.0, 4.8, 1.4 Hz, 1H). ¹³C NMR (100 MHz,

CDCl₃, δ): 154.93, 150.14, 144.97, 142.69, 142.44, 137.17, 134.12,

130.30, 128.61, 127.45, 126.96, 123.56, 121.16. FAB-MS (m/z): 343

[M]⁺. Anal. Calcd for C₁₇H₁₃NO₂Se: C, 59.66; H, 3.83; N, 4.09.

Found: C, 59.56; H, 3.72; N. 3.92.

L-SeO-1F. Yield: 82.3%. ¹H NMR (400 MHz, CDCl₃, δ): 8.73 (dd,

J = 3.0, 0.4 Hz, 1H), 8.24 (d, J = 8.8 Hz, 2H), 8.08 (dd, J = 6.8, 1.6

Hz, 2H), 8.04 (tt, J = 7.0, 2.0 Hz, 2H), 7.82 (td, J = 7.7, 2.0 Hz, 1H),

7.77 (d, J = 8.0 Hz, 1H), 7.28−7.35 (m, 3H). ¹³C NMR (100 MHz,

CDCl₃, δ): 165.96 (d, J = 255.8 Hz), 154.78, 150.13, 145.09, 142.32,

138.11 (d, J = 2.8 Hz), 137.15, 129.69 (d, J = 9.5 Hz), 128.66, 127.31,

123.58, 121.13, 117.68 (d, J = 22.7 Hz). ¹⁹F NMR (376 MHz, CDCl₃,

δ): −102.07. FAB-MS (m/z): 361 [M]⁺. Anal. Calcd for

C₁₇H₁₂FNO₂Se: C, 56.68; H, 3.36; N, 3.89. Found: C, 59.57; H,

3.24; N. 3.79.

L-Se3F. Yield: 86.1%. ¹H NMR (400 MHz, CDCl₃, δ): 8.70 (d, J =

4.8 Hz, 1H), 7.97 (dd, J = 6.6, 1.8 Hz, 2H), 7.78 (td, J = 7.6, 1.6 Hz,

1H), 7.73 (d, J = 7.6 Hz, 1H), 7.62 (dt, J = 8.8, 2.0 Hz, 2H), 7.25−

7.28 (m, 1H), 7.03 (t, J = 7.0 Hz, 2H). ¹³C NMR (100 MHz, CDCl₃,

δ): 156.33, 151.35 (ddd, J = 252.4, 10.3, 3.7 Hz), 149.84, 138.98 (dt, J

= 250.5, 15.3 Hz), 139.76, 136.90, 134.56, 129.93, 128.20, 126.68

(dd, J = 12.2, 6.8 Hz), 122.58, 120.55, 115.88 (dd, J = 16.2, 6.0 Hz).

¹⁹F NMR (376 MHz, CDCl₃, δ): −133.27 (d, J = 22.6 Hz, 2F),

−161.51 (t, J = 18.8 Hz, 1F). FAB-MS (m/z): 365 [M]⁺. Anal. Calcd

for C₁₇H₁₀F₃NSe: C, 56.06; H, 2.77; N, 3.85. Found: C, 55.95; H,

2.68; N. 3.79.

L-SeO-2F. Yield: 84.7%. ¹H NMR (400 MHz, CDCl₃, δ): 8.73 (d, J

= 4.4 Hz, 1H), 8.27 (d, J = 8.8 Hz, 2H), 8.09 (d, J = 8.4 Hz, 2H), 7.83

(tt, J = 7.6, 1.6 Hz, 1H), 7.79 (d, J = 8.0 Hz, 1H), 7.56−7.58 (m, 2H),

7.35 (ddd, J = 7.2, 4.8, 1.6 Hz, 1H), 7.11 (tt, J = 8.4, 2.4 Hz, 1H). ¹³C

NMR (100 MHz, CDCl₃, δ): 163.26 (dd, J = 257.7, 11.0 Hz), 154.58,

150.18, 145.53, 145.20 (t, J = 7.8 Hz), 141.56, 137.20, 128.86, 127.39,

123.70, 121.17, 110.79 (dd, J = 20.1, 8.5 Hz), 109.94 (t, J = 24.8 Hz).

¹⁹F NMR (376 MHz, CDCl₃, δ): −102.87. FAB-MS (m/z): 379

[M]⁺. Anal. Calcd for C₁₇H₁₁F₂NO₂Se: C, 53.98; H, 2.93; N, 3.70.

Found: C, 53.87; H, 2.85; N. 3.59.

2-(Selenophen-2-yl)pyridine (L-Se). Under a nitrogen atmos-

phere, to a solution of 2-bromoselenophene (2.00 g, 9.5 mmol) and 2-

(tributylstannyl)pyridine (3.50 g, 9.5 mmol) in toluene was added

Pd(PPh₃)₄(0.55 g, 0.47 mmol) as catalyst. The reaction was allowed

to proceed at 110 °C for 20 h. After the reaction mixture was cooled

to room temperature, the solvent was removed under reduced

pressure. The residue was chromatographed with a silica gel column

using CH₂Cl₂/petroleum ether (1/3, v/v) as eluent. The product was

1

obtained as a colorless solid (1.65 g, 83.8%). H NMR (400 MHz,

L-SeO-3F. Yield: 83.6%. ¹H NMR (400 MHz, CDCl₃, δ): 8.74 (d, J

= 4.4 Hz, 1H), 8.28 (dd, J = 6.8, 1.6 Hz, 2H), 8.08 (dd, J = 7.2, 1.6

Hz, 2H), 7.83 (td, J = 7.6, 1.6 Hz, 1H), 7.79 (d, J = 7.6 Hz, 1H), 7.72

(t, J = 5.6 Hz, 2H), 7.35 (ddd, J = 7.0, 5.0, 1.2 Hz, 1H). ¹³C NMR

(150 MHz, CDCl₃, δ): 154.49, 151.81 (ddd, J = 259.8, 10.9, 2.4 Hz),

150.20, 145.65, 143.75 (dt, J = 261.1, 14.63 Hz), 141.57, 137.89 (dd,

J = 10.5, 5.3 Hz), 137.20, 128.92, 127.32, 123.74, 121.15, 112.46 (dd,

J = 18.2, 5.9 Hz). ¹⁹F NMR (376 MHz, CDCl₃, δ): −126.87 (d, J =

22.6 Hz, 2F), −148.62 (t, J = 18.8 Hz, 1F). FAB-MS (m/z): 397

[M]⁺. Anal. Calcd for C₁₇H₁₀F₃NO₂Se: C, 51.53; H, 2.54; N, 3.54.

Found: C, 51.43; H, 2.45; N. 3.39.

General Procedure for the Synthesis of L-Se0F−L-Se3F.

Under a nitrogen atmosphere, to a mixture of L-SeO-0F/L-SeO-1F/

L-SeO-2F/L-SeO-3F (1.0 equiv) and Pd/C (0.01 equiv, 10 wt % Pd

content) in ethanol was added hydrazine hydrate (3.0 equiv). The

reaction mixture was allowed to react at 60 °C for 6 h. After it was

cooled to room temperature, the mixture was ﬁltered and the residue

was washed with CH₂Cl₂. Then, the solvent was removed under

reduced pressure and the resultant residue was puriﬁed by column

chromatography on silica gel using CH₂Cl₂/petroleum ether (1/1, v/

v) as eluent.

CDCl₃, δ): 8.53 (d, J = 4.8 Hz, 1H), 8.05 (dd, J = 5.6, 0.8 Hz, 1H),

7.74 (dd, J = 4.0, 0.8 Hz, 1H), 7.66 (dd, J = 4.8, 1.2 Hz, 2H), 7.37 (t, J

= 4.8 Hz, 1H), 7.14 (dd, J = 8.8, 4.8 Hz, 1H). ¹³C NMR (100 MHz,

CDCl₃, δ): 154.02, 151.75, 149.64, 136.53, 132.84, 130.72, 126.07,

121.92, 117.79. FAB-MS (m/z): 209 [M]⁺. Anal. Calcd for C₉H₇NSe:

C, 51.94; H, 3.39; N, 6.73. Found: C, 51.87; H, 3.28; N. 6.65.

General Procedure for the Synthesis of Ir-Se0F−Ir-Se3F.

Under a nitrogen atmosphere, to a mixture of THF and H₂O (3/1, v/

v) were added L-Se (1.0 equiv) and IrCl₃·nH₂O (0.9 equiv, 60 wt % Ir

content). The reaction mixture was stirred at 80 °C for 2 h. After the

mixture was cooled to room temperature, L-Se0F/L-Se1F/L-Se2F/

L-Se3F (1.0 equiv) was added under a nitrogen ﬂow, and then the

resulting mixture was stirred at 110 °C for another 8 h. After it was

cooled to room temperature, the reaction mixture was extracted with

CH₂Cl₂three times. The organic phases were combined and dried

with anhydrous Na₂SO₄. After most of the solvent was removed, the

colored Ir(III) μ-chloro-bridged dimer was precipitated with

petroleum ether; the precipitate was obtained through centrifugation

and dried under vacuum. Subsequently, thallium(I) acetylacetonate

[Tl(acac)] (2.2 equiv) was added to a anhydrous CH₂Cl₂solution of

the colored Ir(III) μ-chloro-bridged dimer (1.0 equiv). The reaction

mixture was allowed to react at room temperature overnight.

Centrifugation was conducted to remove the inorganic salt, and the

solvent was removed under vacuum from the organic phase. The

residue was puriﬁed with preparative thin-layer chromatography

(TLC) made of silica gel using proper eluent. Caution: thallium(I)

acetylacetonate (Tl(acac)) is extremely toxic and must be dealt with

carefully.

L-Se0F. Yield: 89.7%. ¹H NMR (400 MHz, CDCl₃, δ): 8.68 (dd, J

= 4.0, 0.8 Hz, 1H), 7.89 (dd, J = 6.4, 1.6 Hz, 2H), 7.75 (td, J = 7.6, 1.6

Hz, 1H), 7.70 (dd, J = 6.8, 1.2 Hz, 1H), 7.55 (dt, J = 8.4, 2.0 Hz, 2H),

7.49−7.52 (m, 2H), 7.29 (t, J = 3.0 Hz, 3H), 7.23 (ddd, J = 7.2, 4.8,

1.2 Hz, 1H). ¹³C NMR (100 MHz, CDCl₃, δ): 156.74, 149.73,

138.38, 136.78, 133.22, 132.97, 132.59, 130.78, 129.39, 127.70,

127.51, 122.23, 120.34. FAB-MS (m/z): 311 [M]⁺. Anal. Calcd for

C₁₇H₁₃NSe: C, 65.81; H, 4.22; N, 4.51. Found: C, 65.74; H, 4.09; N.

4.36.

Ir-Se0F. Yield: 26.2%. ¹H NMR (400 MHz, CDCl₃, δ): 8.48 (d, J =

5.6 Hz, 1H), 8.18 (d, J = 6.0 Hz, 1H), 7.79−7.76 (m, 2H), 7.69 (td, J

= 7.8, 1.2 Hz, 1H), 7.48 (t, J = 7.8 Hz, 1H), 7.36 (d, J = 8.0 Hz, 1H),

7.34−7.30 (m, 3H), 7.21−7.16 (m, 3H), 7.11 (t, J = 6.0 Hz, 1H),

6.84 (dd, J = 8.0, 1.6 Hz, 1H), 6.81 (dd, J = 6.6, 1.2 Hz, 1H), 6.28 (d,

J = 1.6 Hz, 1H), 6.22 (d, J = 5.2 Hz, 1H), 5.21 (s, 1H), 1.79 (s, 3H),

1.78 (s, 3H). ¹³C NMR (100 MHz, CDCl₃, δ): 184.63, 184.46,

L-Se1F. Yield: 85.4%. ¹H NMR (400 MHz, CDCl₃, δ): 8.68 (d, J =

4.8 Hz, 1H), 7.88 (dd, J = 6.6, 1.8 Hz, 2H), 7.74 (td, J = 7.6, 2.0 Hz,

1H), 7.69 (dt, J = 8.0, 0.8 Hz, 1H), 7.54−7.50 (m, 2H), 7.48 (dt, J =

8.8, 2.0 Hz, 2H), 7.23 (ddd, J = 7.2, 4.8, 1.2 Hz, 1H), 7.01 (tt, J = 9.0,

2.4 Hz, 2H). ¹³C NMR (100 MHz, CDCl₃, δ): 162.67 (d, J = 246.3

C

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Scheme 1. Synthetic Scheme for the Organic Ligands

168.41, 166.40, 153.22, 148.32, 147.87, 147.06, 143.61, 137.39,

136.84, 135.97, 135.87, 134.92, 133.50, 133.03, 132.93, 130.64,

129.09, 127.03, 123.90, 123.79, 121.16, 118.32, 118.23, 118.10,

100.43, 28.65, 28.61. HRMS-ESI Calcd for C₃₁H₂₅IrN₂O₂Se₂

809.9876, found 807.9848 [M

C₃₁H₂₅IrN₂O₂Se₂: C, 46.10; H, 3.12; N, 3.47. Found: C, 45.95; H,

3.02; N. 3.39.

825.9769 [M + H]⁺. Anal. Calcd for C₃₁H₂₄FIrN₂O₂Se₂: C, 45.10; H,

2.93; N, 3.39. Found: C, 45.01; H, 2.86; N. 3.28.

Ir-Se2F. Yield: 30.3%. ¹H NMR (400 MHz, CDCl₃, δ): 8.51 (d, J =

5.2 Hz, 1H), 8.20 (d, J = 5.6 Hz, 1H), 7.83−7.79 (m, 2H), 7.73 (td, J

= 7.4, 1.6 Hz, 1H), 7.52 (td, J = 7.4, 1.2 Hz, 1H), 7.43 (d, J = 8.0 Hz,

1H), 7.38 (d, J = 8.0 Hz, 1H), 7.15 (td, J = 6.4, 1.6 Hz, 1H), 6.95 (dd,

J = 8.0, 1.6 Hz, 1H), 6.84 (td, J = 6.6, 1.2 Hz, 1H), 6.77 (dd, J = 7.2,

2.0 Hz, 2H), 6.60 (tt, J = 8.8, 2.0 Hz, 1H), 6.31 (d, J = 1.6 Hz, 1H),

+

H]⁺. Anal. Calcd for

Ir-Se1F. Yield: 25.8%. ¹H NMR (400 MHz, CDCl₃, δ): 8.46 (d, J =

5.6 Hz, 1H), 8.13 (d, J = 5.6 Hz, 1H), 7.78−7.76 (m, 2H), 7.69 (td, J

= 7.6 Hz, 1H), 7.52 (td, J = 8.0, 1.6 Hz, 1H), 7.35 (d, J = 8.0 Hz, 1H),

7.33−7.28 (m, 3H), 7.10 (td, J = 6.6, 1.2 Hz, 1H), 6.87 (t, J = 8.8 Hz,

2H), 6.83−6.78 (m, 2H), 6.22 (d, J = 5.2 Hz, 1H), 6.03 (d, J = 2.0

Hz, 1H), 5.20 (s, 1H), 1.79 (s, 3H), 1.78 (s, 3H). ¹³C NMR (100

MHz, CDCl₃, δ): 184.66, 184.43, 168.37, 166.37, 162.44 (d, J = 245.3

Hz), 153.32, 148.32, 147.84, 147.26, 143.28, 137.30, 136.86, 136.68

(d, J = 7.9 Hz), 135.78, 134.99, 134.44, 134.05, 132.96, 124.29 (d, J =

3.1 Hz), 123.76, 122.50, 121.10, 118.20, 118.17, 117.98, 116.30 (d, J

= 21.4 Hz), 100.44, 28.65, 28.60. ¹⁹F NMR (376 MHz, CDCl₃, δ):

−114.22. HRMS-ESI: calcd for C₃₁H₂₄FIrN₂O₂Se₂827.9781, found

6.22 (d, J = 5.2 Hz, 1H), 5.23 (s, 1H), 1.81 (s, 3H), 1.80 (s, 3H). ¹³

C

NMR (100 MHz, CDCl₃, δ): 184.73, 184.56, 168.15, 166.51, 162.73

(dd, J = 249.9, 12.3 Hz), 153.06, 148.44, 147.88, 147.84, 144.85,

137.51, 137.39, 136.98, 135.91, 135.01 (t, J = 8.9 Hz), 134.75, 133.22,

130.23, 125.12, 124.14, 121.58, 118.50, 118.33, 118.09, 114.69 (dd, J

= 19.0, 6.8 Hz), 102.23 (t, J = 25.2 Hz), 100.48, 28.65, 28.59. ¹⁹F

NMR (376 MHz, CDCl₃, δ): −109.52. HRMS-ESI: calcd for

C₃₁H₂₃F₂IrN₂O₂Se₂845.9687, found 843.9482 [M + H]⁺. Anal.

Calcd for C₃₁H₂₃F₂IrN₂O₂Se₂: C, 44.13; H, 2.75; N, 3.32. Found: C,

44.02; H, 2.68; N. 3.18.

D

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Scheme 2. Synthetic Scheme for the Asymmetric ppy-Type Ir(III) Phosphorescent Emitters with both Selenophene and Aryl

Selenide Units Together with Their Parent Complex Ir-Se

Ir-Se3F. Yield: 31.1%. ¹H NMR (400 MHz, CDCl₃, δ): 8.48 (d, J =

5.2 Hz, 1H), 8.17 (d, J = 5.6 Hz, 1H), 7.81−7.79 (m, 2H), 7.72 (td, J

= 7.4, 1.6 Hz, 1H), 7.55 (td, J = 7.4, 1.2 Hz, 1H), 7.41 (d, J = 8.0 Hz,

1H), 7.37 (d, J = 8.0 Hz, 1H), 7.14 (td, J = 6.6, 1.2 Hz, 1H), 6.94−

6.88 (m, 3H), 6.84 (td, J = 6.6, 1.2 Hz, 1H), 6.21 (d, J = 5.2 Hz, 1H),

6.07 (d, J = 1.6 Hz, 1H), 5.22 (s, 1H), 1.80 (s, 3H), 1.79 (s, 3H). ¹³C

NMR (100 MHz, CDCl₃, δ): 184.74, 184.52, 168.06, 166.48, 153.11,

150.86 (ddd, J = 251.8, 10.0, 3.5 Hz), 148.39, 147.88, 147.81, 144.35,

139.11 (dt, J = 249.7, 15.1 Hz), 137.36, 136.99, 135.82, 135.59,

134.79, 133.27, 131.59, 125.26 (dd, J = 12.1, 6.6 Hz), 123.98, 123.58,

121.49, 118.41, 118.17, 117.89, 117.71 (dd, J = 16.2, 5.6 Hz), 100.51,

28.64, 28.59. ¹⁹F NMR (376 MHz, CDCl₃, δ): −133.53 (d, J = 22.6

Hz, 2F), −161.27 (t, J = 18.8 Hz, 1F). HRMS-ESI: calcd for

C₃₁H₂₂F₃IrN₂O₂Se₂863.9593, found 861.9590 [M + H]⁺. Anal. Calcd

for C₃₁H₂₂F₃IrN₂O₂Se₂: C, 43.21; H, 2.57; N, 3.25. Found: C, 43.08;

H, 2.48; N. 3.16.

132.86, 118.17, 118.00, 100.52, 28.54. HRMS (ESI): calcd for

C₂₃H₁₉IrN₂O₂Se₂707.9406, found 705.9380 [M + H]⁺. Anal. Calcd

for C₂₃H₁₉IrN₂O₂Se₂: C, 39.15; H, 2.71; N, 3.97. Found: C, 39.08; H,

2.76; N, 3.88%.

X-ray Crystallography. Single crystals of Ir-Se2F and Ir-Se3F

that were suitable for X-ray diﬀraction studies were successfully grown

through slow diﬀusion of hexane into their chloroform solutions.

Single-crystal data were collected on a Bruker SMART CCD

diﬀractometer (Mo Kα radiation and λ = 0.71073 Å) in Φ and ω

scan modes at 293 K. The molecular structure was solved by direct

methods followed by diﬀerence Fourier syntheses and then reﬁned by

full-matrix least-squares techniques against F²using the SHELXL-

9720 program.³⁴The positions of hydrogen atoms were calculated

and reﬁned isotropically using a riding model. All other non-hydrogen

atoms were reﬁned isotropically. Absorption corrections were applied

using SADABS.³⁵

Computational Details. DFT calculations were conducted with

the B3LYP method for all of the iridium(III) complexes. The 6-

31G(d,p) basis set was applied for C, H, N, O, F, and Se atoms, while

eﬀective core potentials employed for Ir atoms were a LanL2DZ basis

set.^36,37Excitation behaviors were acquired by TD-DFT calculations

Ir-Se. Yield: 20.3−24.1%. ¹H NMR (400 MHz, CDCl₃, δ): 8.32 (d,

J = 5.6 Hz, 2H), 7.81 (d, J = 5.2 Hz, 2H), 7.58 (td, J = 8.0, 1.2 Hz,

2H), 7.44 (d, J = 8.0 Hz, 2H), 6.92 (td, J = 6.6, 1.2 Hz, 2H), 6.33 (d, J

= 5.2 Hz, 2H), 5.22 (s, 1H), 1.81 (s, 6H). ¹³C NMR (100 MHz,

CDCl₃, δ): 184.51, 167.04, 152.18, 148.16, 137.43, 135.74, 135.31,

E

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on the basis of the optimized ground state geometries. Additionally,

the natural transition orbital (NTO) based on the ﬁrst triplet state

(T₁) geometries optimized by UB3LYP was analyzed for S₀→ T₁

excitation. All of the calculations were performed using the Gaussian

09 program.³⁸

proton bonded with the C atom adjacent to the C atom

bonded with the phenyl unit in the pyridine ring, the multiplet

resonance peaks located in the range of 7.54−7.50 ppm can be

assigned to two aromatic protons attached to the C atoms at

the meta position of the ﬂuorinated C atom in the pendant

phenyl ring, the doublet of triplets resonance peak at 7.48 ppm

should be attributed to two aromatic protons linked to the C

atoms at the ortho position of the C atom bonded with the Se

atom in the phenyl unit of ppy, and the doublet of doublets of

doublets resonance peak at 7.23 ppm should be assigned to the

aromatic proton attached to the C atom at the para osition of

the C atom bonded with the phenyl unit in the pyridine ring of

ppy. The triplet of triplets resonance peak at 7.01 ppm should

be assigned to the two aromatic protons linked to the C atoms

at the ortho position of the ﬂuorinated C atom in the pendant

RESULTS AND DISCUSSION

■

Synthesis and Characterization. Synthetic protocols of

the organic ligands and the asymmetric ppy-type Ir(III)

phosphorescent complexes are shown in Schemes 1 and 2,

respectively. The ligand L-Se can be easily prepared by Stille

cross-coupling between 2-(tributylstannyl)pyridine and 2-

bromoselenophene prepared by the bromination of seleno-

phene with NBS. For synthesis of the ligands with an aryl

selenide unit,the key intermediate diselenide Br-2Se has to be

prepared by the reaction between 4-bromoiodobenzene and

selenium powder according to the reported literature (Scheme

1).³⁹The diaryl selenones Br-SeO-0F−Br-SeO-3F have been

synthesized by two successive steps. First, Br-2Se was coupled

with the corresponding arylboronic acid with nano CuO as

catalyst (Scheme 1).⁴⁰Second, the CuO catalyst was removed

by ﬁltration and the solvent was evaporated. The residue was

dissolved in CHCl₃, and m-chloroperbenzoic acid (mCPBA)

was added at room temperature. After the diaryl selenones

were obtained, they were coupled with 2-(tributylstannyl)-

pyridine, respectively, to give the ligand precursors L-SeO-0F−

L-SeO-3F, which were reduced by hydrazine hydrate into the

target ligands L-Se0F−L-Se3F with an aryl selenide unit

(Scheme 1). In addition, these organic ligands can also be

prepared by the strategy developed by Ranu’s group.⁴¹In order

to enhance the EI/ET ability of the concerned Ir(III)

phosphorescent complexes, a ﬂuorine group has been

introduced to balance the HI/HT ability and bring enhanced

EL performance.

1

phenyl ring. In the H NMR spectrum of L-Se, the doublet

resonance peak at 8.53 ppm can be safely assigned to the

aromatic proton linked to the C atom next to the N atom in

the pyridine ring, the doublet of doublets resonance peak at

8.05 ppm should be attributed to the aromatic proton linked

with the C atom adjacent to the C atom bonded with the

pyridyl unit in the selenophene ring of L-Se, and the doublet of

doublets resonance peak at 7.13 ppm should be ascribed to the

aromatic proton linked to the C atoms at the meta position of

the C atom bonded with the pyridyl unit in the selenophene

ring of L-Se. A full assignment of resonance signals observed

1

for H NMR spectra of other obtained ligands is shown in

Figure S1.

After the organic ligands were obtained, metalation of the

corresponding cyclometalating ligand (L-Se0F/L-Se1F/L-

Se2F/L-Se3F) and cyclometalating ligand L-Se with IrCl₃·

nH₂O yielded the colored cyclometalated Ir(III) μ-chloro-

bridged dimers (Scheme 2). Then, the dimers were converted

into the designed asymmetric Ir(III) phosphorescent com-

plexes by mixing the corresponding μ-chloro-bridged dimer

with Tl(acac) in CH₂Cl₂at room temperature. The synthetic

approach based on the reaction of IrCl₃·nH₂O with equimolar

amount of two diﬀerent cyclometalating ligands should result

in the formation of a statistical mixture of one heteroleptic

[Ir(N^∧C₁)(N^∧C₂)(acac)] complex and two homoleptic [Ir-

(N^∧C)₂(acac)] complexes.^45,46Except for the target asym-

metric heteroleptic complexes with two diﬀerent ppy-type

ligands, two symmetric heteroleptic complexes with the same

ppy-type ligands have been observed as well. The symmetric

heteroleptic complex with aromatic selenophene groups (Ir-

Se) is obtained with reaction yields in the range of 20.3−

24.1%, while another kind of symmetric heteroleptic complex

with aromatic selenide groups appears with reaction yields in

the range of 19.8−23.3%. The overall yields for both the

asymmetric heteroleptic Ir(III) complex and two symmetric

heteroleptic Ir(III) complexes are in the range of 67.5−72.4%.

The emerging statistical mixture of this synthetic approach is

obviously not beneﬁcial to enhance the reaction yields in terms

of the target asymmetric heteroleptic Ir(III) complexes.

Eﬀective synthetic approaches still need to be explored. All

of the asymmetric Ir(III) complexes and their symmetric

heteroleptic parent complex Ir-Se have been characterized by

Clearly, it should be more convenient to obtain the target

ligands L-Se0F−L-Se3F through Stille cross-coupling between

2-(tributylstannyl)pyridine and the corresponding brominated

aryl selenide (Scheme S1 in the Supporting Information)

without both the oxidation of the brominated aryl selenides

and the reduction of the ligand precursors (Scheme 1).

Unfortunately, the protocol in Scheme S1 involves two

drawbacks. First, it was hard to purify the brominated aryl

selenides by column chromatography due to their polarity

being very similar to that of the impurities. Second, the yield of

the Stille coupling between 2-(tributylstannyl)pyridine and the

brominated aryl selenides was very low (<20%). This might be

ascribed to the electron-donating selenium atom in the

brominated aryl selenides passivating the bromine group in

the concerned aryl selenides. In contrast, the bromine groups

in the diaryl selenones are much more active in the mechanism

of the Stille cross-coupling reaction.⁴²⁻⁴⁴

All the obtained ligands have been characterized by ¹H, ¹³C,

1

and ¹⁹F NMR spectra. In the H NMR spectrum of L-Se1F,

the doublet resonance peak at 8.68 ppm can be safely assigned

to the aromatic proton linked to the C atom next to the N

atom in the pyridine ring, the doublet of doublets resonance

peak at 7.88 ppm should be attributed to the two aromatic

protons linked to the C atoms adjacent to the C atom bonded

with a pyridyl unit in the phenyl ring of ppy, the triplet of

doublets resonance peak at 7.74 ppm should be attributed to

the aromatic proton linked to the C atom at the para position

of the N atom in the pyridine ring, the doublet of triplets

resonance peak at 7.69 ppm should be ascribed to the aromatic

1

¹H, ¹³C, and ¹⁹F NMR spectra. In the H NMR spectra for all

the asymmetric complexes, two sets of doublet resonance

peaks located at ca. 8.50 and 8.20 ppm have been observed for

the two aromatic protons linked to the C atoms next to the N

atoms in the two pyridine rings of the two diﬀerent ppy-type

ligands, respectively. The resonance signals at ca. 1.80 ppm

F

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assigned to the two methyl groups in the acetylacetonate

auxiliary ligands of these Ir(III) phosphorescent complexes

split into two singlet peaks as well. However, only one

resonance peak was detected for these aforementioned protons

in the traditional heteroleptic Ir(III) complexes with two

identical cyclometalating ppy-type ligands.³

S4. In the ¹⁹F NMR spectra for Ir-Se1F and Ir-Se2F, only

singlet resonance signals at −114.20 and −109.50 ppm can be

found. In contrast, Ir-Se3F can show two sets of peaks with 2:1

peak area ratio for the doublet peak at −133.50 ppm and the

triplet peak at −161.30 ppm due to the F−F coupling. All of

these ¹⁹F NMR results clearly indicate the expected

substitution pattern of the ﬂuorine groups in these asymmetric

heteroleptic Ir(III) complexes. In the ¹³C NMR spectrum of

Ir-Se1F, the doublet resonance peak at 162.44 ppm induced by

F−C coupling with J_FC= 245.3 Hz can be safely assigned to

the aromatic carbon linked with an −F group and the doublet

resonance peak at 136.68 ppm induced by F−C coupling with

³J_FC= 7.9 Hz can be safely assigned to the aromatic carbon at a

position ortho to the Se atom in the pendant phenyl of L-

Se1F. Meanwhile, the doublet resonance peak at 124.29 ppm

1

In the H NMR spectra for their symmetric heteroleptic

parent complex Ir-Se, only one doublet resonance peak located

at 8.32 ppm has been observed for two aromatic protons linked

to the C atoms next to the N atoms in the two pyridine rings in

the two ligands L-Se. Meanwhile, only one doublet resonance

peak located at 6.33 ppm has been observed for the two

aromatic protons bonded with the C atoms adjacent to the C

atoms coordinating to Ir atoms in the selenophene rings of the

two ligands L-Se. Two singlet resonance peaks at 5.22 and 1.81

ppm can be safely ascribed to the acetylacetonate auxiliary

4

induced by F−C coupling with J_FC= 3.1 Hz can be safely

ascribed to the aromatic carbon attached to an Se atom and the

1

ligands. In the H NMR spectrum for Ir-Se1F, two sets of

doublet resonance peaks located at 8.46 and 8.13 ppm have

been observed for the aromatic protons attached to the C atom

next to the N atoms in L-Se1F and that in L-Se, respectively.

The multiplet resonance peaks located in the range of 7.78−

7.76 ppm can be assigned to the aromatic proton linked to a C

atom adjacent to the Se atom in the ligand L-Se and the

aromatic proton attached to the C atom next to the C atom

bonded with the phenyl unit in the pyridine ring of L-Se1F,

respectively. The triplet of doublets resonance peak at 7.69

ppm should be ascribed to the aromatic proton attached to the

C atom at the para position of the N atom in the pyridine ring

of L-Se1F. The triplet of doublets resonance peak at 7.52 ppm

should be attributed to the aromatic proton linked to the C

atom at the para position of the N atom in the pyridine ring of

L-Se, while the doublet resonance peak at 7.35 ppm should be

ascribed to the aromatic proton linked to the C atom adjacent

to the C atom bonded with the selenophene unit in L-Se. The

multiplet resonance peaks located in the range of 7.33−7.28

ppm can be assigned to the aromatic proton linked to the C

atom at the meta position of the C atom coordinating to the Ir

atom and two aromatic protons bonded with the C atoms at

the meta position of the ﬂuorinated C atom in L-Se1F,

respectively. Induced by the proton on the pyridine ring in L-

Se1F, the triplet of doublets resonance peak at 7.10 ppm

should be assigned to the proton attached to the C atom at the

para position of the C atom bonded with the phenyl unit. The

triplet resonance peak at 6.87 ppm should be assigned to the

two aromatic protons linked to the C atoms at the ortho

position of the ﬂuorinated C atom in L-Se1F. The multiplet

resonance peaks located in the range of 6.83−6.78 ppm can be

assigned to one aromatic proton linked to the C atom at the

para position of the C atom coordinating to the Ir atom in L-

Se1F and one aromatic proton bonded with the C atom at the

para position of the C atom bonded with the selenophene unit

in the pyridine ring of L-Se, respectively. Two sets of doublet

resonance peaks located at 6.22 and 6.03 ppm have been

observed for the aromatic protons linked to the C atom

adjacent to the C atom coordinating to the Ir atom in L-Se and

that in L-Se1F, respectively. The singlet resonance signals at

5.20 ppm can be safely ascribed to the proton linked to the C

atoms adjacent to the two carbonyl groups in the

acetylacetonate after coordinating to the Ir atom, while two

singlet resonance peaks at 1.79 and 1.78 ppm can be assigned

to the two methyl groups in the acetylacetonate auxiliary

doublet resonance peak at 116.30 ppm induced by F−C

2

coupling with J_FC= 21.4 Hz can be safely ascribed to an

aromatic carbon at a position ortho to the ﬂuorinated atom in

L-Se1F. For Ir-Se2F, the doublet of doublets resonance peak

located at 162.73 ppm due to F−C coupling with J_FC= 249.9

Hz has been observed for the two aromatic carbons linked with

an −F group and the triplet resonance peak located at 135.01

3

ppm with J_FC= 8.9 Hz should be attributed to the aromatic

carbon bonded with an Se atom. The doublet of doublets

resonance peak at 114.69 ppm induced by F−C coupling with

²J_FC= 19.0 Hz can be safely assigned to the aromatic carbon at

a position ortho to the Se atom in L-Se2F and the triplet

resonance peak at 102.23 ppm induced by F−C coupling with

²J_FC= 25.2 Hz can be safely ascribed to the aromatic carbon

between the two aromatic carbon atoms bonded with an −F

group. The ¹³C NMR spectrum for Ir-Se3F shows a doublet of

doublets of doublets resonance peak at 150.86 ppm induced by

F−C coupling with J_FC= 251.8 Hz assigned to the two

ﬂuorinated aromatic carbons at a position meta to the Se atom

in L-Se3F, while the doublet of triplets resonance peak at

139.11 ppm induced by F−C coupling with J_FC= 249.7 Hz can

be attributed to a ﬂuorinated aromatic carbon at a position

para to the Se atom in L-Se3F. Meanwhile, the doublet of

doublets resonance peak located at 125.26 ppm due to F−C

3

coupling with J_FC= 12.1 Hz has been observed for the

aromatic carbon linked to an Se atom and the doublet of

doublets resonance peak located at 117.71 ppm due to F−C

2

coupling with J_FC= 16.2 Hz should be attributed to the

aromatic carbon at a position ortho to the Se atom in L-Se3F.

When the results of their ¹⁹F NMR spectra are combined with

those of ¹³C NMR spectra, the structures of these asymmetric

heteroleptic Ir(III) complexes have been properly conﬁrmed.

In addition, L-SeO-0F−L-SeO-3F have also been employed to

synthesize asymmetric heteroleptic Ir(III) complexes with L-

Se with the aim to take advantage of the electronic features of

the aromatic selenone group (−SeO₂Ar). Unexpectedly, the

selenone group (−SeO₂Ar) had been transferred into the

selenide unit (−SeAr) and just Ir-Se0F−Ir-Se3F were

obtained. On the basis of all the results (Scheme S2 and

Table S1), it can be safely concluded that the selenone group

in the synthesis of these asymmetric complexes has been

mainly reduced by the solvent mixture THF/H₂O with IrCl₃·

nH₂O as catalyst. Also as a catalyst, the dimer formed in the

ﬁrst step can contribute to the reduction of the selenone group

in the synthesis of these asymmetric Ir(III) complexes as well.

1

ligand. Full assignment of the H NMR signals for other

asymmetric heteroleptic Ir(III) complexes is shown in Figure

G

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Single-Crystal X-ray Crystallography. The single

crystals of Ir-Se2F and Ir-Se3F with high quality have been

successfully obtained through slow diﬀusion of hexane into

their chloroform solutions. Their structures were determined

by single-crystal X-ray crystallography (Figure 1). Detailed data

ophene⁴⁷units, the C−S−C bond angles in thiophene units

and C−Te−C bond angles in tellurophene units are ca. 90 and

80°, respectively. The bond lengths in the selenophene units

for Ir-Se2F and Ir-Se3F are ca. 1.86 Å, similar to the reported

data,⁴⁷while those in the thiophene and tellurophene units are

1.73 and 2.10 Å, respectively.

Thermal and Photophysical Properties. The thermal

properties of these asymmetric heteroleptic Ir(III) complexes

have been examined with thermogravimetric analysis (TGA)

and diﬀerent scanning calorimetry (DSC) under a nitrogen

ﬂow. The TGA results reveal their thermal stability with

decomposition temperatures (T_d) ranging from ca. 280 to 290

°C (Table S4 and Figure S17), similar to that of their parent

complex Ir-Se. The DSC traces have indicated their glass-

transition temperature (T_g) in the range from ca. 110 to 115

°C (Table S4 and Figure S16).

In their UV−vis spectra (Figure 2a), the high-energy

absorption bands before ca. 370 nm can be safely assigned

to the π−π* transition of the two ppy-type ligands.⁴⁸On the

basis of the results of time-dependent density functional theory

(TD-DFT) calculations, the characters of their S₀→ S₁

transitions corresponding to the major absorption bands can

be represented by their HOMO → LUMO (H → L)

transitions due to their large contribution of over 95%

(Table 3). Hence, on the basis of the H → L transition

features of these asymmetric heteroleptic Ir(III) complexes,

their major absorption bands should exhibit ligand to ligand

charge transfer (LLCT) features from the π orbitals of the ppy-

type ligand with the selenophene unit to the π* orbitals of the

ppy-type ligand with the selenide group, while the Ir-

(ppy)₂(acac)-type complexes typically show intraligand charge

transfer (ILCT) features in their absorption bands from the

phenyl π orbitals to the pyridyl π* orbitals in the ppy-type

ligand.^2,7In addition, obvious metal to ligand charge transfer

(MLCT) features from the Ir(III) center to the π* orbitals of

the ppy-type ligand with a selenide group can be involved in

the weak singlet-state absorption bands between 370 and 450

nm (Figure 2a) of these asymmetric heteroleptic Ir(III)

complexes. The weak triplet-state absorption bands with the

lowest energy after 450 nm should be mainly induced by the

³π−π* transition of the ppy-type ligand L-Se with the

selenophene ring together with some ³MLCT transition

characters from the Ir(III) center to the π* orbitals of the

pyridyl ring in the ligand L-Se (Figure 3 and Table 3). These

asymmetric heteroleptic Ir(III) complexes show almost

identical absorption spectra in the visible-light region (Figure

2a) with sequential introduction of electron-withdrawing

ﬂuorine substituents to the selenide groups, mainly due to

the negligible contribution of the ﬂuorinated phenyl ring to

both HOMO and LUMO orbitals as well as the HOMO →

LUMO (H → L) transition (Figure 3) on the basis of the

results of time-dependent density functional theory (TD-DFT)

calculations.

Figure 1. Perspective views of (a) Ir-Se2F and (b) Ir-Se3F with

thermal ellipsoids are drawn at the 30% probability level. All hydrogen

atoms are omitted for clarity.

of each structure are given in Table 1 as well as Tables S2 and

S3. In their single crystals, the molecules of both Ir-Se2F and

Ir-Se3F pack in the same space group P1 to form a triclinic

̅

crystal system (Table 1). As depicted in Figure 1, two ppy-type

ligands and one acetylacetone anion around the Ir center

furnish a slightly distorted octahedral chelating skeleton with

cis-C,C, cis-O,O, and trans-N,N chelating disposition for Ir-

Se2F and Ir-Se3F. For Ir-Se2F, the N1−Ir1−N2, O1−Ir1−

C24, and O2−Ir1−C7 bond angles are 174.3(3)°, 173.2(3)°,

and 174.9(3)°, while those for Ir-Se3F are 173.3(17)°,

174.06(18)°, and 174.08(18)°, respectively. The Ir−C, Ir−N,

and Ir−O bond lengths are similar to those of our previously

reported asymmetric heteroleptic Ir(III) complexes.³¹⁻³³The

C−Se−C bond angles in the aryl selenide units are 99.2(4)°

for Ir-Se2F and 101.6(2)° for Ir-Se3F, which are less than the

theoretical 109.5° due to the electrostatic repulsion between

the unshared pair electrons on selenium atoms and the

bonding electrons of the Se−C bonds. In their analogous

complexes with aromatic ether and aromatic sulﬁde units, the

C−O−C (ca. 104°) and C−S−C (ca. 120°) bond angles are

larger than that of C−Se−C in the aryl selenide units of these

asymmetric heteroleptic Ir(III) complexes.⁷The C−Se−C

bond angles in the aryl selenophene units are 86.2(4)° for Ir-

Se2F and 85.6(3)° for Ir-Se3F, similar to the reported data.⁴⁷

In their analogous scaﬀolds with thiophene¹⁸and tellur-

The excitation spectra of these heteroleptic Ir(III)

complexes have been measured with a monitoring wavelength

at ca. 580 nm in CH₂Cl₂solution and at ca. 584 nm in doped

CBP ﬁlms at 293 K (Figures S10 and S11 and Table 2). It has

been found that the excitation spectra are quite similar to the

absorption spectra (Figure 2a) at 293 K. All of these

heteroleptic Ir(III) complexes show almost identical spectral

lines in their excitation features and similar maximum

excitation wavelengths located at ca. 338 nm. Increasing the

number of −F substituents on the selenide groups has nearly

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Table 1. Crystal and Data Parameters for Structures Ir-Se2F and Ir-Se3F

Ir-Se2F

Ir-Se3F

1819887

CCDC no.

formula

formula wt

cryst syst

space group

a (Å)

b (Å)

c (Å)

α (deg)

β (deg)

γ (deg)

V (Å³)

1819886

C₃₁H₂₃F₂IrN₂O₂Se₂

843.63

triclinic

C₃₁H₂₂F₃IrN₂O₂Se₂

861.62

triclinic

P1

̅

P1

̅

8.6268(4)

12.1741(7)

14.3748(8)

99.161(5)

101.247(4)

103.133(4)

1408.86(14)

2

8.3973(7)

12.3883(9)

14.2705(11)

100.594(2)

102.471(2)

95.113(2)

1411.91(19)

2

Z

D_calcd(g nm⁻³

)

1.989

2.207

cryst size (mm³)

0.400 × 0.100 × 0.050

804

12.514

0.200 × 0.150 × 0.100

820

7.359

F(000)

μ (mm⁻¹

)

θ range (deg)

4.43−73.27

10041

5504

2.48−27.50

35207

6446

no. of diﬀrn reﬂns

total no. of rﬂns

no. of params

363

372

a

R1, wR2 (I > 2.0σ(I))

R1, wR2 (all data)

0.0440, 0.1112

0.0549, 0.1226

0.765

0.0390, 0.1009

0.0474, 0.1053

1.012

b

GOF on F²

a

b

2

R1 = ∑||F_o| − |F_c||/∑|F_o|. wR2 = {∑[w(F_o− F_c²)²]/∑[w(F_o)²]}^1/2. GOF = [(∑w|F_o| − |F_c|)²/(N_obs− N_param)]^1/2

.

Figure 2. (a) UV−vis absorption spectra and (b) photoluminescence (PL) spectra of the asymmetric heteroleptic Ir(III) complexes in CH₂Cl₂

solution recorded at 293 K.

no eﬀect on their excitation features, which is due to the fact

that the ﬂuorinated phenyl rings make almost no contribution

to the composition of HOMO and LUMO orbitals and NTOs

(Figures 3 and 4) on the basis of the results of the TD-DFT

calculations.

Photoluminescent (PL) spectra of these heteroleptic Ir(III)

complexes have been measured in CH₂Cl₂solution at 293 K.

Under irradiation with 360 nm UV light, all of these

heteroleptic Ir(III) complexes emit an orange-red phosphor-

escent band at ca. 580 nm accompanied by a slightly weaker

band at ca. 631 nm and a shoulder peak at ca. 691 nm (Figure

2b and Table 2), while their symmetric parent complex Ir-Se

shows a bathochromic shift in the emission color with an

orange-red phosphorescent band at 586 nm accompanied by a

slightly weaker band at 633 nm and a shoulder peak at 700 nm.

All of the heteroleptic Ir(III) complexes show a very high Φ_P

value of ca. 0.9, much higher than that of their symmetric

parent complex Ir-Se (Φ_Pca. 0.6), indicating the advantage of

their chemical structures in furnishing high Φ_P. These

observations demonstrate that the design strategy of the

asymmetric heroleptic Ir(III) complexes can ﬁnely tune the

emission wavelength and Φ_P.^30,32They share nearly identical

spectral lines for their phosphorescence signals in both CH₂Cl₂

solution and doped CBP ﬁlms (Figure 2b and Figures S9 and

S12). The PL emission intensity of the emission band around

584 nm in doped CBP ﬁlms is markedly enhanced in

comparison with that in CH₂Cl₂solution, while the PL

emission intensity of the emission band around 631 nm in

doped CBP ﬁlms is signiﬁcantly reduced and the PL emission

intensity of the emission band around 691 nm in doped CBP

ﬁlms almost disappears. These results may be due to variation

of the vibration mode of the excited Ir(III) complexes in the

rigid matrix of CBP ﬁlms. In addition, the Ir(ppy)₂(acac)-type

complexes generally exhibit a featureless emission spectrum

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Table 2. Photophysical of the Asymmetric Heteroleptic Ir(III) Complexes and Their Parent Complex Ir-Se

b

c

d

e

excitation (293 K)

emission (293 K)

Φ_P(%) degassed/ τ_P(μs) degassed/

a

absorption (293 K) λ_abs(nm)

λ_max(nm)

λ_em(nm)

aerated

Ir-Se0F 256 (4.18), 285 (4.15), 319 (4.16), 418 (3.35),

580, 631, 690^sh

580, 631, 691^sh

581, 632, 691^sh

581, 632, 692^sh

586, 633, 700^sh

91.23/3.65

3.99/0.23 (580)

466 (3.33)

338 (580)

337 (580)

337 (581)

339 (581)

338 (586)

Ir-Se1F 254 (4.38), 288 (4.36), 318 (4.40), 418 (3.57),

93.09/3.94

90.14/3.42

93.21/4.16

60.32/2.03

3.81/0.21 (580)

3.86/0.22 (581)

4.16/0.24 (581)

3.93/0.24 (586)

466 (3.54)

Ir-Se2F 258 (4.54), 285 (4.50), 317 (4.50), 416 (3.67),

465 (3.65)

Ir-Se3F 254 (4.48), 290 (4.47), 317 (4.48), 418 (3.64),

466 (3.62)

Ir-Se

256 (4.07), 282 (4.17), 307 (4.22), 371 (3.77),

423(3.56), 479(3.59)

a

b

Measured at a concentration of ca. 10⁻⁵M in CH₂Cl₂, with log ε values given in parentheses. sh: shoulder. Measured at a concentration of ca.

10⁻⁵M in CH₂Cl₂. λ_maxrepresents the excitation wavelength at which the maximum emission intensity of the monitoring wavelength was obtained.

c

d

The monitoring wavelength is shown in parentheses (in nm). Measured at a concentration of ca. 10⁻⁵M in CH₂Cl₂, with λ_ex400 nm. Relative to

e

fac-[Ir(ppy)₃] (Φ_P= 0.97) in CH₂Cl₂solution, with λ_ex360 nm. Measured at a sample concentration of ca. 10⁻⁵M in CH₂Cl₂solution at 293 K.

The monitoring wavelength is provided in parentheses (in nm).

Table 3. TD-DFT Results of These Asymmetric Heteroleptic Ir(III) Complexes on the Basis of Their Optimized S₀

Geometries

contribn of metal d_πorbitals and π

orbitals of ligand to MOs (%)

main conﬁgn of S₀→ S₁excitation, E_cal(eV)/λ_calmain conﬁgn of S₀→ T₁excitation/, E_cal(eV), λ_cal

a

complex MO

(nm)/f

(nm)

Ir

L-Se

82.12

3.56

34.73

0.73

L-Se

80.06

5.51

32.72

6.50

L-Se

81.80

3.22

36.35

6.96

L-Se

81.78

3.07

37.01

6.38

L-Se0F

9.05

acac

2.31

1.60

4.38

1.51

acac

2.28

1.80

4.30

6.99

acac

2.37

1.59

4.56

32.94

acac

2.37

1.56

4.51

32.08

Ir-Se0F L+1

6.52

4.49

48.88

3.88

Ir

6.58

4.66

48.28

14.42

Ir

6.48

4.44

48.06

39.95

Ir

6.48

4.38

47.92

38.45

H → L (96.73), 2.595, 477.7, 0.0239

H → L (95.82), 2.672, 464.0, 0.0319

H → L (96.97), 2.555, 485.2, 0.0213

H → L (97.02), 2.547, 486.7, 0.0198

H → L+1 (77.54), 2.201, 563.32

H → L+1 (73.74), 2.192, 565.7

H → L+1 (77.52), 2.205, 562.3

H → L+1 (77.99), 2.207, 561.8

L

H

H-1

90.35

12.01

93.88

L-Se1F

11.08

88.04

14.70

72.09

L-Se2F

9.35

90.75

11.03

20.15

L-Se3F

9.37

Ir-Se1F

L+1

L

H

H-1

Ir-Se2F

L+1

L

H

H-1

Ir-Se3F

L+1

L

90.99

10.56

23.09

H

H-1

a

H→L denotes the transition from the HOMO to LUMO. E_cal, λ_cal, and f denote the calculated excitation energy, calculated emission wavelength,

and oscillator strength, respectively. The oscillator strength of S₀→ T₁is zero owing to the spin-forbidden character of the singlet−triplet transition

under TD-DFT calculations in the Gaussian program with no consideration of spin−orbital coupling.

3

with a predominant MLCT emission feature, while these

asymmetric complexes display structured phosphorescent

spectra in both CH₂Cl₂solution and doped CBP ﬁlms,

especially for the major emission bands (Figure 2b and Figures

S9 and S12).^3,7In order to interpret the phosphorescent

feature, i.e. T₁state character of these asymmetric heteroleptic

Ir(III) complexes, natural transition orbital (NTO) analysis

has been conducted for their S₀→ T₁excitations on the basis

of the optimized T₁geometries.

features associated with the selenophene unit to facilitate the

electron transition process. Due to the slight contribution of L-

Se0F−L-Se3F to the NTOs of Ir-Se0F−Ir-Se3F, sequential

introduction of electron-withdrawing ﬂuorine substituents to

the selenide groups has nearly no eﬀect on their NTO

distribution (Figure 4). This may account for the nearly

identical emission spectra for these asymmetric heteroleptic

Ir(III) complexes. Thus, we can conclude that ligand-centered

³π−π* dominates the character of the T₁state of all the

asymmetric heteroleptic Ir(III) complexes. On the basis of the

reported photophysical results for phosphorescent com-

plexes,⁴⁹⁻⁵¹the ligand-centered ³π−π* features of the T₁

state typically may display vibronic progressions in the

phosphorescent spectra. As a result, structured line proﬁles

From the distribution patterns of the NTO hole and particle

orbitals for all of these asymmetric heteroleptic Ir(III)

complexes, it can be seen clearly that they all display a

predominant ligand-centered feature, centering on the ligand

L-Se due to its large contribution to the NTOs (Figure 4 and

Table 4). This outcome might be ascribed to the electron-rich

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asymmetric heteroleptic Ir(III) complexes, infrared (IR)

spectroscopic investigations were carried out, and the IR

spectra are almost identical (Figure S19). Vibrations at ca.

1570 and ca. 1510 cm⁻¹can be assigned to CO and CC

stretching modes, respectively. There are many vibrations in

the region between 1250 and 1500 cm⁻¹, including symmetric

and asymmetric vibrations. The two intense vibration bands at

ca. 1469 and 1390 cm⁻¹can be ascribed to the C−C stretching

mode in the aromatic systems of the two diﬀerent ppy-type

ligands. The emission bands in the PL spectra at 77 K (Table

S4 and Figure S9) of these asymmetric heteroleptic Ir(III)

complexes show two vibronic spacings (from ca. 576 to 627

nm and from ca. 627 to 690 nm) around ca. 1410 and 1430

cm⁻¹, respectively. Thus, the vibronic spacings in the emission

bands are similar to vibration frequencies in the aromatic

systems. These outcomes should be able to further account for

3

the ligand-centered π−π* character of the T₁state of all the

Figure 3. Molecular orbital (MO) patterns (isocontour value 0.030)

of the asymmetric heteroleptic Ir(III) complexes on the basis of their

optimized S₀geometries: (a) Ir-Se0F; (b) Ir-Se1F; (c) Ir-Se2F; (d)

Ir-Se3F.

asymmetric heteroleptic Ir(III) complexes. In addition to the

3

dominant π−π* features, the T₁state of all the asymmetric

heteroleptic Ir(III) complexes should possess some MLCT

features by considering the diﬀerence in contributions from the

Ir(III) center to the NTO hole and particle orbitals (Table 4).

This result should account for the structureless spectral line

proﬁle at the long-wavelength region in the phosphorescent

spectra of all the asymmetric heteroleptic Ir(III) complexes

(Figure 2b). Clearly, there is good consistency between

experimental and theoretical results, indicating the validity of

the employed theoretical strategies. From the structured

pattern of the PL spectra of the parent complex Ir-Se (Figure

S8), it can be concluded that the T₁state of Ir-Se also

dominantly shows the ³π−π* feature of the L-Se ligand.

Hence, Ir-Se can exhibit phosphorescent wavelength and

spectral pattern very similar to those of the asymmetric

heteroleptic Ir(III) complexes (Table 2, Figure 2b, and Figure

S8).

Figure 4. Natural transition orbital patterns (isocontour value 0.030)

for S₀→ T₁excitation for these heteroleptic Ir(III) complexes on the

basis of their optimized T₁geometries: (a) Ir-Se0F; (b) Ir-Se1F; (c)

Ir-Se2F; (d) Ir-Se3F.

The emission lifetimes of all these asymmetric heteroleptic

Ir(III) complexes in aerated and degassed CH₂Cl₂solution are

ca. 0.23 and 3.90 μs (Table 2, Figures S13 and S14),

respectively, while their lifetimes in 8 wt % doped CBP ﬁlms

are ca. 3.10 μs (Table S4 and Figure S15). The lifetimes in

degassed CH₂Cl₂solution and in doped CBP ﬁlms are

enhanced by ca. 17- and 14-fold, respectively, in comparison

with those in the aerated CH₂Cl₂solution. This trend also

appears in the changes of the Φ_Pvalues for all these

asymmetric heteroleptic Ir(III) complexes. Hence, the

phosphorescence of all these asymmetric heteroleptic Ir(III)

complexes can be signiﬁcantly quenched by oxygen. However,

after purging with N₂, their Φ_Pvalues can be enhanced by ca.

30-fold (Table 2), indicating their potential as oxygen

sensors.⁵²

Electrochemical Properties. Electrochemical properties

of these asymmetric heteroleptic Ir(III) complexes have been

characterized in acetonitrile solution by cyclic voltammetry

(CV) measurements with ferrocene (Fc) as the internal

standard under a nitrogen atmosphere. In the anodic scan, all

of the complexes can show a reversible oxidation wave with

potential (E_pa) at ca. 0.40 V, while that for the parent complex

Ir-Se is about 0.35 V (Table 5 and Figure S18). This oxidation

potential comes from oxidation of the Ir(III) center, which is

typically observed in the ppy-type Ir(III) complexes.^7,31Owing

to the strong electron-withdrawing associated with the −F

group, the reversible oxidation potential moves slightly to more

positive potential region with an increase in the number of −F

Table 4. NTO Results for the Heteroleptic Ir(III)

Complexes on the Basis of Optimized T₁Geometries

contribn of metal d_πorbitals and π orbitals of

ligand to NTOs (%)

a

complex

NTO

Ir

22.61

7.33

Ir

23.00

7.44

Ir

22.07

7.32

Ir

21.88

7.33

L-Se

72.86

82.66

L-Se

71.93

82.46

L-Se

73.73

83.00

L-Se

73.97

82.98

L-0F

3.12

8.00

L-1F

3.65

8.06

L-2F

2.77

7.59

L-3F

2.74

7.61

acac

1.41

2.01

acac

1.42

2.04

acac

1.43

2.09

acac

1.41

2.08

Ir-Se0F

H

P

Ir-Se1F

Ir-Se2F

Ir-Se3F

H

P

H

P

H

P

a

H and P denote NTO hole and particle orbitals, respectively.

measured in CH₂Cl₂solution at 293 and 77 K as well as in 8 wt

% doped CBP ﬁlms have been obtained for the phosphor-

escent bands of all these asymmetric heteroleptic Ir(III)

complexes (Figure 2b and Figures S9 and S12). The emission

bands around 581, 631, and 691 nm can be assigned to the

transfer of 0−0, 0−1, and 0−2 vibronic states, respectively. In

order to interpret the emission ﬁne structure of these

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Table 5. Redox Properties of the Heteroleptic Ir(III) Complexes and Their Parent Complex Ir-Se

E_g(eV)

c

d

E_g^cv

e

f

complex

E_pa(V)

E_pc(V)

E_g^opt

E_HOMO(eV)

E_LUMO(eV)

a

b

Ir-Se0F

Ir-Se1F

Ir-Se2F

Ir-Se3F

Ir-Se

0.40

0.41

0.43

−2.56, −2.77

2.47

2.42

2.82

2.81

2.79

2.77

−5.20

−5.21

−5.23

−5.15

−2.38

−2.40

−2.42

−2.44

−2.38

a

b

−2.52, −2.77

a

b

−2.48, −2.78

a

b

−2.48, −2.78

a

b

0.35

−2.62, −2.84

a

b

c

Reversible. The value was set as E_1/2. Irreversible or quasi-reversible. The value was derived from the cathodic peak potential. Optical energy gap

d

e

E_g^optcalculated from the absorption onset of the UV−vis absorption spectra. CV energy gap E_g^cv= LUMO − HOMO. HOMO levels are

f

calculated according to the equation HOMO = −(4.8 + E_pa) eV. Data are obtained from the onset potential of the ﬁrst reduction wave of the CV

data.

Figure 5. Device structure of the solution-processed OLEDs together with an energy level diagram and molecular structures of the materials used in

the fabricated OLEDs.

substituents in the asymmetric heteroleptic Ir(III) complexes

through the conjugation eﬀect (Table 5). The electron-rich

character of the two coordinating selenophene units makes the

Ir(III) center in the parent complex Ir-Se more easily oxidized.

Hence, Ir-Se exhibits lower oxidation potential in comparison

to the asymmetric heteroleptic Ir(III) complexes (Table 5). It

seems that introducing a selenophene unit can promote hole

injection: i.e., the hole-trapping ability of the concerned Ir(III)

complexes.

All of the asymmetric heteroleptic Ir(III) complexes also

display similar reduction behavior with two irreversible

reduction waves at ca. −2.50 and −2.80 V, which can be

ascribed to the reduction of the pyridyl units in the organic

ligands (Table 5 and Figure S18). Cleary, the −F substituents

in the organic ligands with a selenide group should make the

pyridyl moieties more inclined to be reduced owing to their

strong electron-withdrawing ability. As a result, more −F

substituents can furnish slightly lower reduction potential to

the pyridyl rings in Ir-Se1F, Ir-Se2F, and Ir-Se3F in

comparison to those in Ir-Se0F and Ir-Se (Table 5). Clearly,

a ﬂuorinated selenide group can improve electron injection:

i.e., the electron-trapping ability of the concerned Ir(III)

complexes. Attached with two electron-rich selenophene units,

the pyridyl rings in Ir-Se should be more reluctant to be

reduced to furnish Ir-Se with the highest reduction potential of

ca. −2.62 V (Table 5).

On the basis of the aforementioned results, the asymmetric

structure of these heteroleptic Ir(III) complexes can provide

the opportunity to tune the electrochemical properties of the

concerned Ir(III) complexes through two diﬀerent ppy-type

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ligands, indicating the advantage associated with the

asymmetric structure for developing new Ir(III) phosphor-

escent emitters.

and 44.5 lm W⁻¹(Table 6 and Figure 8c). Finally, the highest

EL eﬃciencies have been achieved by device D2 based on Ir-

Se3F with η_ext= 19.9%, η_L= 65.6 cd A⁻¹, and η_P= 57.3 lm

W⁻¹, respectively (Table 6 and Figure 8d). In addition to their

attractive EL eﬃciencies, these solution-processed OLEDs can

show high luminance over 10000 cd m⁻²at a driving voltage of

less than 20 V (Table 6 and Figure 7). For the device D2 with

the highest EL eﬃciencies, the eﬃciency rolloﬀ can be

maintained at ca. 12% and 25% at luminances of 100 and

1000 cd m⁻², respectively. Although −F groups on the ligand

of a phosphorescent Ir(III) emitter are generally considered to

be detrimental to device stability, a recent report concerning

the inﬂuence of ﬂuorination on Ir(III) complexes as

phosphorescent emitters in OLEDs suggests that rational

incorporation of ﬂuorine atoms in the ligands in phosphor-

escent Ir(III) complexes not only can have little eﬀect on the

photophysical and thermal properties but also can ﬁne-tune the

performance of the resulting device.⁵⁴All of these results can

clearly indicate the great potential of these novel asymmetric

heteroleptic Ir(III) phosphorescent emitters with both

selenophene and selenide groups. Lee, Jin, et al. prepared a

red-emitting fac-[Ir(4-phenyl-2-(selenophen-2-yl)quinoline)₃]

complex with Φ_P= ca. 0.07; this complex can show good EL

eﬃciencies of 17.60%, 12.78 cd A⁻¹, and 11.46 lm W⁻¹.²Our

previous green-emitting symmetric heteroleptic Ir(III) phos-

phorescent emitters with a diphenyl sulﬁde group could furnish

EL eﬃciencies of 5.97%, 20.77 cd A⁻¹, and 12.02 lm W⁻¹.⁷In

comparison with all these EL results, the great potential of

these asymmetric heteroleptic Ir(III) phosphorescent emitters

with both selenophene and selenide groups can be seen.

Obviously, the EL eﬃciencies noticeably increase with the

introduction of more −F substituents to the selenide group in

the concerned phosphorescent emitter (Table 6). This result

can be explained by both the energy-level layout in the

emission layer of the OLEDs and the electronic features of

these asymmetric heteroleptic Ir(III) phosphorescent emitters

(Table 5, Figure 5, and Figures S18 and S23). Owing to the

hole-injection capacity provided by the selenophene unit, the

HOMO levels (ca. 5.20 eV) of these phosphorescent emitters

are much higher than those of CBP (ca. 5.90 eV, Figure 5).

Therefore, the holes injected into the emission layer of the

OLEDs can be easily trapped by these phosphorescent

emitters. On the other hand, their LUMO levels are very

close to that of the host material CBP (ca. 2.50 eV, Figure 5).

In addition, the CV results have shown that the ﬂuorinated

selenide groups can enhance the electron-injection capacity of

these phosphorescent emitters. All of these results indicate that

these phosphorescent emitters can be electronically excited by

direct charge trapping.⁵⁵⁻⁵⁷In view of their aforementioned

high hole-trapping ability, the EL eﬃciencies of these

asymmetric heteroleptic Ir(III) phosphorescent emitters

should be mainly up to their electron-trapping capacity.

From Ir-Se0F to Ir-Se3F, their LUMO levels decline gradually

(Figure 5), indicating their gradually enhanced electron-

trapping ability. The results of single-carrier devices demon-

strate that the asymmetric heteroleptic Ir(III) complexes can

show improved transporting ability for both holes and

electrons. In addition, with an increase in the number of −F

substituents on the selenide groups, their hole-transporting

ability is reduced, while the electron-transporting ability is

enhanced, indicating more balanced charge-transporting

properties. Hence, Ir-Se3F shows the highest EL eﬃciencies

among these complexes (Figure S23). The EL ability of these

Electroluminescent Properties. According to the liter-

ature, the EL potential for the asymmetric heteroleptic Ir(III)

phosphorescent emitters with selenium-containing groups has

not been explored. In addition, these asymmetric heteroleptic

Ir(III) complexes possess a high Φ_Pvalue of ca. 0.90, which is

crucial for achieving high EL eﬃciencies.⁵³On this basis, the

EL performances of these asymmetric heteroleptic Ir(III)

complexes have been characterized by simple solution-

processed OLEDs with the conﬁguration ITO/PEDOT:PSS

(45 nm)/Ir x wt %:CBP (40 nm)/TPBi (45 nm)/LiF (1 nm)/

Al (100 nm) (Figure 5). The hole injection layer (HIL) of the

devices is constructed by spin-coating the solution of

PEDOT:PSS. The hole-blocking and electron-transporting

functions of the OLEDs are both fulﬁlled by the TPBi layer,

while LiF serves as an electron-injection layer.

When a proper voltage is applied, all OLEDs can emit

orange electrophosphorescence at ca. 584 nm (Figure 6 and

Figure 6. EL spectra for the optimized OLEDs at ca. 10 V.

Figure S21). The EL data of these solution-processed OLEDs

are summarized in Table 6. As depicted in Figure 6 and Figure

S21, the EL spectral line shapes for the OLEDs show a great

resemblance to those of the PL spectra based on these

asymmetric heteroleptic Ir(III) complexes in solution and

doped CBP ﬁlms (Figure 2b and Figure S12), indicating that

electrophosphorescence indeed originates from the triplet

states of these asymmetric heteroleptic Ir(III) complexes.

Current density−voltage−luminance characteristics and EL

eﬃciency−luminance curves for these solution-processed

OLEDs are shown in Figure 7 and 8 and Figures S21 and

S22. The optimal EL eﬃciencies have been achieved with 8 wt

% doping level of these asymmetric heteroleptic Ir(III)

complexes in the emission layer of the OLEDs. All of the

devices show a relatively low turn-on voltage of ca. 4.0 V

(Table 6), which might beneﬁt from the charge carrier

injection/transporting ability associated with selenophene and

ﬂuorinated selenide groups. The optimized device A2 based on

Ir-Se0F can show a maximum external quantum eﬃciency

(η_ext) of 15.2%, a maximum current eﬃciency (η_L) of 49.4 cd

A⁻¹, and a maximum power eﬃciency (η_P) of 37.0 lm W⁻¹,

while the data for device B2 with Ir-Se1F as emitter are 15.8%,

50.9 cd A⁻¹, and 42.5 lm W⁻¹, respectively. (Table 6 and

Figure 8a,b). In addition, device C2 with Ir-Se2F as emitter

can show even higher EL eﬃciencies of 18.2%, 58.4 cd A⁻¹,

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Table 6. EL Performance of the Electrophosphorescent OLEDs

a

d

device

dopant (amt (wt %))

V_turn‑on(V)

luminance L_max(cd m⁻²

)

η_ext(%)

η_L(cd A⁻¹

)

η_P(lm W⁻¹

)

λ_max(nm)

a

A1

Ir-Se0F (6.0)

4.3

10730 (19.1)

13.3 (4.3)

42.6 (4.3)

39.2

33.5

49.4 (4.2)

38.5

28.8

44.8 (4.2)

39.8

32.7

40.1 (4.2)

38.0

34.4

50.9 (3.8)

31.9

20.1

26.6 (3.7)

18.5

12.1

34.5 (4.8)

29.5

24.4

58.4 (4.1)

53.0

46.4

40.9 (4.1)

37.1

32.6

60.0 (3.5)

55.2

48.1

65.6 (3.6)

57.7

48.6

51.9 (3.6)

47.7

30.8 (4.3)

17.7

11.2

37.0 (4.2)

16.6

9.2

33.6 (4.2)

16.6

9.4

30.0 (4.2)

19.8

13.7

42.5 (3.8)

10.8

4.8

22.8 (3.7)

7.8

3.6

22.6 (4.8)

13.3

8.8

44.5 (4.1)

26.2

17.8

31.2 (4.1)

18.6

12.9

54.3 (3.5)

31.3

20.5

57.3 (3.6)

30.6

19.3

45.1 (3.6)

27.1

584 (0.59, 0.40)

584 (0.59, 0.41)

584 (0.59, 0.40)

584 (0.57, 0.41)

584 (0.59, 0.41)

584 (0.58, 0.41)

584 (0.59, 0.41)

b

12.2

10.5

c

A2

A3

B1

B2

B3

C1

C2

C3

D1

D2

D3

Ir-Se0F (8.0)

Ir-Se0F(10.0)

Ir-Se1F (6.0)

Ir-Se1F (8.0)

Ir-Se1F (10.0)

Ir-Se2F (6.0)

Ir-Se2F (8.0)

Ir-Se2F (10.0)

Ir-Se3F (6.0)

Ir-Se3F (8.0)

Ir-Se3F (10.0)

4.2

3.8

3.7

4.8

4.1

3.5

3.6

9119 (18.9)

10708 (18.4)

12053 (16.5)

8437 (20.3)

9950 (18.6)

12940 (14.4)

12628 (16.8)

12887 (16.8)

11817 (16.0)

10981 (16.9)

11410 (15.0)

15.2 (4.2)

11.9

8.9

14.0 (4.2)

12.4

10.2

13.9 (4.2)

13.2

11.9

15.8 (3.8)

9.9

6.2

8.2 (3.7)

5.7

3.7

10.6 (4.8)

9.1

7.5

18.2 (4.1)

16.5

14.4

12.7 (4.1)

11.5

10.1

18.5 (3.5)

17.0

14.8

19.9 (3.2)

17.5

14.7

15.7 (3.6)

14.4

13.1

43.3

19.8

a

b

Maximum values of the devices. Values in parentheses are the voltages at which they were obtained (in V). Values were collected at 100 cd m⁻².

c

d

Values were collected at 1000 cd m⁻². Values were collected at 10 V, and CIE coordinates (x, y) are shown in parentheses.

CONCLUSION

■

In conclusion, a series of asymmetric heteroleptic Ir(III)

phosphorescent complexes have been successfully prepared

through employing ppy-type ligands with selenophene and

selenide groups. All of these novel asymmetric heteroleptic

Ir(III) phosphorescent species can show high Φ_Pvalues of ca.

0.90 to beneﬁt their EL performances. It has also been found

that the nature of their phosphorescent emission is mainly

determined by the ppy-type ligand with a selenophene group,

3

dominantly showing π−π* features. By an increase in the

number of −F substituents on the selenide groups, the EL

eﬃciencies of these asymmetric heteroleptic Ir(III) phosphor-

escent complexes can be obviously improved due to their

enhanced electron-trapping behavior, which can balance their

high hole-trapping ability. As a result, the optimized solution-

processed OLED can show impressive EL eﬃciencies with a

maximum η_extvalue of 19.9%, η_Lvalue of 65.6 cd A⁻¹, and η_P

value of 57.3 lm W⁻¹, representing state of the art EL

performance achieved by selenium-containing phosphorescent

emitters. This research should clearly reveal the great potential

Figure 7. Current density−voltage−luminance (J−V−L) curves for

optimized OLEDs.

asymmetric heteroleptic Ir(III) phosphorescent emitters falls

in the order Ir-Se3F > Ir-Se2F > Ir-Se1F > Ir-Se0F (Table 6).

N

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Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Figure 8. Relationship between EL eﬃciencies and luminance for the optimized devices: (a) device A2; (b) device B2; (c) device C2; (d) device

D2.

selenium-containing groups have in the development of high-

performance ppy-type Ir(III) phosphorescent emitters.

*Z.W.: e-mail, zhaoxinwu@mail.xjtu.edu.cn.

ORCID

Guijiang Zhou: 0000-0002-5863-3551

Zhaoxin Wu: 0000-0003-2979-3051

Notes

ASSOCIATED CONTENT

* Supporting Information

The Supporting Information is available free of charge on the

ACS Publications website at DOI: 10.1021/acs.inorg-

chem.8b01639.

■

S

The authors declare no competing ﬁnancial interest.

ACKNOWLEDGMENTS

■

Synthetic scheme via selenide intermediates, experimen-

tal scheme of the selenone group (−SeO₂Ar) reduction,

structural data from X-ray crystallographic results for Ir-

Se2F and Ir-Se3F, NMR spectra of all the obtained

Ir(III) complexes and ligands, experimental HRMS and

calculated isotopic distribution spectra of all the ﬁnal

Ir(III) complexes, electrochemical, thermal, and photo-

physical properties and IR data for all the ﬁnal Ir(III)

complexes, OLED fabrication and measurements, EL

results for the devices except the optimized ones, and

single-carrier devices with 8 wt % doped CBP ﬁlms using

the asymmetric heteroleptic Ir(III) complexes and

Ir(ppy)₂(acac) as active layer (PDF)

This research was ﬁnancially supported by the National

Natural Science Foundation of China (21572176, 21602170),

Fundamental Research Funds for the Central Universities

(cxtd2015003 and 01091191320074), the China Postdoctoral

Science Foundation (2015M580831 and 20130201110034),

the Natural Science Foundation of Shaanxi Province

(2016JM3035), and the Key Creative Scientiﬁc Research

Team in Yulin City (2015cxy-25). Financial support from the

State Key Laboratory for Mechanical Behavior of Materials is

also acknowledged. We thank Miss Axin Lu at the Instrument

Analysis Center of Xi’an Jiaotong University for her assistance

with the analysis of HRMS data and simulation of spectral

patterns (isotopic distribution) for all the obtained Ir(III)

complexes.

Accession Codes

CCDC 1819886−1819887 contain the supplementary crys-

tallographic data for this paper. These data can be obtained

free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by

emailing data_request@ccdc.cam.ac.uk, or by contacting The

Cambridge Crystallographic Data Centre, 12 Union Road,

Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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Q

DOI: 10.1021/acs.inorgchem.8b01639

Inorg. Chem. XXXX, XXX, XXX−XXX

Article Doi

Asymmetric Heteroleptic Ir(III) Phosphorescent Complexes with Aromatic Selenide and Selenophene Groups: Synthesis and Photophysical, Electrochemical, and Electrophosphorescent Behaviors

DOI: 10.1021/acs.inorgchem.8b01639

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Full text of DOI:10.1021/acs.inorgchem.8b01639

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