Synthesis of cationic iridium(III) complexes with high quantum yield via enhancing the steric hindrance of ligands

Article abstract of DOI:10.1016/j.jorganchem.2011.12.020

A series of cationic Ir(III) complexes 1a-4a functionalized with carbazole-9-yl-n-butyl group (CZB) were designed and synthesized. An investigation of their photophysical properties showed that the attachment of CZB moiety into the complexes resulted in large improvement in the photoluminescence quantum yield (PLQY) of solid film although the emission spectra and excited-state character presented little change compared with those of the parent complexes. Besides, the functionalized complexes also exhibited good thermal stability and film-forming property. In light of our quantum chemical calculations and X-ray data, these advantages of functionalized complexes mainly derived from the CZB moiety which was superior in reducing the intermolecular interaction and inhibiting the quenching process. Furthermore, to verify our results and design cationic Ir(III) complexes with much higher efficiency, four Ir(III) complexes G0-G3 were synthesized, in which different number of CZB moieties (from 0 to 3) were introduced into the complexes, respectively. Noticeably, in case of G3, the obvious high neat film PLQY of 43% was obtained. In comparison with its dispersed film, a large retaining percentage (90%) was realized, indicating that the CZB moiety could suppress the quenching of luminescence effectively.

Full text of DOI:10.1016/j.jorganchem.2011.12.020

Journal of Organometallic Chemistry 702 (2012) 27e35
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis of cationic iridium(III) complexes with high quantum yield via
enhancing the steric hindrance of ligands
,
b,
Guo-Gang Shan a, Hai-Bin Li a, Zhong-Cheng Mu a, Dong-Xia Zhu a, Zhong-Min Su a , Yi Liao
*
**
a Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, No. 5268 Renmin Street, Changchun, Jilin 130024, PR China
b Department of Chemistry, Capital Normal University, Beijing 100000, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of cationic Ir(III) complexes 1ae4a functionalized with carbazole-9-yl-n-butyl group (CZB) were
designed and synthesized. An investigation of their photophysical properties showed that the attach-
ment of CZB moiety into the complexes resulted in large improvement in the photoluminescence
quantum yield (PLQY) of solid film although the emission spectra and excited-state character presented
little change compared with those of the parent complexes. Besides, the functionalized complexes also
exhibited good thermal stability and film-forming property. In light of our quantum chemical calcula-
tions and X-ray data, these advantages of functionalized complexes mainly derived from the CZB moiety
which was superior in reducing the intermolecular interaction and inhibiting the quenching process.
Furthermore, to verify our results and design cationic Ir(III) complexes with much higher efficiency, four
Ir(III) complexes G0eG3 were synthesized, in which different number of CZB moieties (from 0 to 3) were
introduced into the complexes, respectively. Noticeably, in case of G3, the obvious high neat film PLQY of
43% was obtained. In comparison with its dispersed film, a large retaining percentage (90%) was realized,
indicating that the CZB moiety could suppress the quenching of luminescence effectively.
Ó 2011 Elsevier B.V. All rights reserved.
Received 4 November 2011
Received in revised form
11 December 2011
Accepted 13 December 2011
Keywords:
Cationic iridium complex
Steric hindrance
Benzimidazole
Carbazole-9-yl-n-butyl
Photophysical property
DFT
1. Introduction
aqueous media and rich photophysical properties [18e22]. Gener-
ally, LECs possess several advantages over conventional OLEDs,
Phosphorescent transitionemetal complexes (TMCs) have
attracted considerable interest because of their potential applica-
tions in the fields of chemosensors [1e4], biological probes [5e7],
photocatalysts [8,9] and optoelectronic materials, etc. [10e14].
Particularly, more attention has been paid to phosphorescent iri-
dium(III) complexes due to their high emission efficiency, good
photo- and thermal stabilities, relatively long excited-state lifetime
and easy tunability of the emission color [15]. Up to now, the re-
ported Ir(III)-based complexes can be categorized into two classes:
neutral Ir(III) complexes, such as Ir(C^N)3 or Ir(C^N)2(L^X) (where
C^N and L^X represent cyclometalated ligand and a monoanionic
ancillary ligand, respectively) and cationic Ir(III) complexes such as
[Ir(C^N)2(N^N)]þ, featuring neutral diimine ligands [16]. The
former usually is used as triplet emitters in the organic light-
emitting diodes (OLEDs) [10e14,17] while the latter is developed
as a new type of solid-state cells (LECs) because of their ionic
character, good solubility in polar organic solvents or even in
such as the simple device architecture, low turn-on voltage and
independence of the work function. Therefore, they are regarded as
good candidates for potential flat-panel displays and low-cost
solid-state lighting sources. Since the first report of Ir(III)-based
LECs [23], the green, yellow, orange and red emitting ones have
been developed [24e28]. In addition, the white LECs were also
realized by combining a blue-green and a red emitting cationic
Ir(III) complexes in a hosteguest system [19e22].
However, excited-state self-quenching associated with
tripletetriplet annihilation for Ir(III)-based complexes always
happens because of the strong interaction between closely packed
molecules, which remarkably hampers the development of their
applications in highly efficient and stable devices. A variety of
approaches have been taken in order to solve the problem in
neutral complexes, including attaching enhanced steric hindrance
or bulky side groups into the complexes to separate chromophoric
units [29e38]. Recently, Park and his co-workers have prepared
Ir(III) complex containing tetraphenylsilyl-substituted cyclo-
metalated ligands. This complex displays luminescence in the
deep-red region and exhibits high photoluminescence quantum
yield (PLQY) as well as external quantum efficiency (EQE) [29].
Wang et al. [30e32], Lo et al. [35], and Burn et al. [36] also have
* Corresponding author. Fax: þ86 431 85684009.
** Corresponding author.
E-mail addresses: zmsu@nenu.edu.cn (Z.-M. Su), liaoy271@nenu.edu.cn (Y. Liao).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.12.020

28
G.-G. Shan et al. / Journal of Organometallic Chemistry 702 (2012) 27e35
developed a series of Ir(III) dendrimers with a high degree of steric
hindrance for highly efficient OLEDs. Successful example of
enhancing the efficiency of Ir(III) complexes by introducing bulky
side groups into ligands has also reported by Xu and his-cowokers
[39,40]. However, there were few reports about improvement of
quantum efficiency for cationic Ir(III) complexes by increasing the
steric hindrance of complexes [41e46], especially through grafting
the rigid ring end-capped aliphatic chains, such as carbazole-9-yl-
n-butyl group (here, abbreviated as ‘CZB’), on the bis-
cyclometalated ligands and/or ancillary ligands of cationic Ir(III)
complexes.
In this paper, we designed a series of cationic Ir(III) complexes
(1e4a) in which CZB moiety was only covalently attached to the
cyclometalated or ancillary ligands. Additionally, their related
parent complexes (1e4b) were also prepared for comparative
studies (Scheme 1). Here, the carbazole group was chosen as
hindrance unit due to their high stability and hole-transporting
properties [47,48]. The functionalized Ir(III) complexes exhibited
better photophysical, film-forming as well as thermal stability
properties in comparison with their parent complexes. The exper-
imental results were also interpreted with the help of density
functional theory (DFT) and timedependent density functional
theory (TD-DFT) calculations. On the basis of our studies, four new
complexes with different number of CZB moieties (0e3) were
designed and synthesized, which showed much higher photo-
luminescence quantum yields (PLQYs) and better stability. The
results studied in this text would provide useful guidelines for
further designing new high-efficiency cationic Ir(III) complexes
with desired photophysical property.
fluorescent indicator UV254). Elemental analyses (C, H, and N) were
performed on a PerkineElmer 240C elemental analyzer. TG anal-
yses were performed on a PerkineElmer TG-7 analyzer heated from
30 to 900 ꢀC in flowing of nitrogen. Powder X-ray diffraction (XRD)
patterns of the samples were collected on a Rigaku Dmax 2000. 1H
NMR spectra were measured on Bruker Avance 500 MHz with
tetramethylsilane as the internal standard. The molecular weights
of complexes were also tested by using matrix-assisted laser
desorption-ionization time-of-flight (MALDI-TOF) mass spectrom-
etry. UVevis absorption spectra were recorded using a PE UVevis
lambdazo spectrometer. The emission spectra were recorded on
the F-7000 FL spectrophotometer equipped with a xenon lamp at
room temperature. The photoluminescence quantum yields
(PLQYs) in neat film were measured with an integrating sphere. The
excited-state lifetime was measured on a transient spectrofluo-
rimeter (Edinburgh FLS920) with time-correlated single-photo
counting technique.
2.2. Synthesis
The cyclometalated chloride-bridged dimers were synthesized
according to a procedure described in the literature [49] by
refluxing IrCl3$3H2O with the corresponding cyclometalated
ligands in the mixture of 2-ethoxythanol and water. The cationic
Ir(III) complexes were readily achieved from the reaction of cyclo-
metalated chloride-bridged dimers with corresponding ancillary
ligands by a bridge-splitting reaction, respectively. The crude
products were purified by column chromatography on silica gel.
The synthesis of bis-cyclometalated ligands (dfppz, dclppz, mebd,
crbd) and ancillary ligands (DBI, bdme, and bdcr) were presented
in Scheme S1 and S2. The identities of complexes have been char-
acterized spectroscopically, with satisfactory result obtained.
2. Experimental section
2.1. General information and materials
2.2.1. Synthesis of [Ir(dclppz)2Cl]2
The organometallated dimer [Ir(dclppz)2Cl]2 was synthesized
from reaction of IrCl3$3H2O (0.81 g, 2.32 mmol) with 1-(2,4-
dichlorophenyl)-1H-pyrazole (dclppz, 1.0 g, 5.13 mmol) in 2-
ethoxyethanol and water mixture (V:V ¼ 3:1, 40 mL) for 24 h.
After cooling to the room temperature, the product was filtered out
and washed with diethyl ether followed by ethanol, and dried
(yield: 79%). On the basis of a procedure similar to prepare
[Ir(dclppz)2Cl]2, other chloride-bridged dimers, [Ir(dfppz)2Cl]2,
[Ir(mebd)2Cl]2 and [Ir(crbd)2Cl]2 were synthesized.
All reagents and solvents employed were commercially avail-
able and used as received without further purification. The solvents
for synthesis were freshly distilled over appropriate drying
reagents. All experiments were performed under a nitrogen
atmosphere by using standard Schlenk techniques. All reactions
were monitored using precoated TLC plates (0.20 mm with
2.2.2. Synthesis of [Ir(dclppz)2(bdcr)]PF6 (1a)
A solution of ligand bdcr (0.88 g, 2.1 mmol) and the dichloro-
bridged diiridium complex [Ir(dclppz)2Cl]2 (1.3 g, 1.0 mmol) in
dichloromethane (30 mL) and methanol (15 mL) were heated to
reflux for 24 h in the dark. After cooling to room temperature, the
mixture was filtrated, and then an excess of solid KPF6 was added
and stirred for another 0.5 h at room temperature. The solvent was
removed under reduced pressure and the residue was purified by
column chromatography on silica gel with ethyl acetate as the
eluent, to yield the off-white solid (1a). Yield (58%). 1H NMR
(500 MHz, DMSO-d6,
d
[ppm]): 9.26 (d, J ¼ 3.5 Hz, 1H), 9.13 (d,
J ¼ 3.5 Hz, 1H), 8.56 (d, J ¼ 8 Hz, 1H), 8.19e8.23 (m, 1H), 8.14 (d,
J ¼ 7.5 Hz, 2H), 8.09e8.10 (m, 1H), 7.92 (d, J ¼ 8.5 Hz, 1H), 7.70e7.73
(m, 1H) 7.50e7.50 (m, 2H), 7.40e7.43 (m, 4H), 7.39 (d, J ¼ 2 Hz, 1H),
7.31 (d, J ¼ 2 Hz, 2H), 7.16e7.20 (m, 3H), 6.78 (t, J ¼ 2.5 Hz, 1H), 6.69
(t, J ¼ 2.5 Hz, 1H), 6.25 (d, J ¼ 8.5 Hz, 1H), 5.95 (d, J ¼ 2 Hz, 1 H), 5.94
(d, J ¼ 2 Hz, 1H), 4.88e4.97 (m, 2H), 4.32e4.43 (m, 2H), 1.85e2.02
(m, 4H). Anal. Calcd. for IrC46H34N8F6Cl4P: C, 46.91; H, 2.91; N,
9.51. Found: C, 47.09; H, 3.02, N, 9.86. MS (MALDI-TOF): m/z 1031.0
(M ꢁ PF6). The related complexes were prepared using the similar
procedures.
Scheme 1. Chemical structures of cationic complexes 1e4.

G.-G. Shan et al. / Journal of Organometallic Chemistry 702 (2012) 27e35
29
2.2.3. [Ir(dclppz)2(bdme)]PF6 (1b)
(m, 2H), 6.5 (d, J ¼ 1 Hz, 2H), 6.31 (d, J ¼ 7.5 Hz, 2H), 6.15 (d, J ¼ 8 Hz,
2H), 4.35 (s, 6H), 4.21 (s, 6H). Anal. Calcd. for IrC36H32N8F6P: C,
47.31; H, 3.53; N, 12.26. Found: C, 47.53; H, 3.68, N, 12.46. MS
(MALDI-TOF): m/z 767.2 (M ꢁ PF6).
Yield: 65%. 1H NMR (500 MHz, DMSO-d6,
d [ppm]): 9.22 (d,
J ¼ 3 Hz, 1H), 9.16 (d, J ¼ 3 Hz, 1H), 8.7 (d, J ¼ 8 Hz, 1H), 8.27e8.31
(m, 1H), 8.11 (d, J ¼ 5 Hz, 1H), 7.93 (d, J ¼ 8.5 Hz, 1H), 7.69 (t,
J ¼ 6.5 Hz, 1H), 7.47 (t, J ¼ 7.5 Hz, 1H), 7.43 (d, J ¼ 1.5 Hz, 1H), 7.35 (d,
J ¼ 2 Hz,1H), 7.30 (dd, J1 ¼ 2 Hz, J2 ¼ 6 Hz, 2H), 7.17 (t, J ¼ 7.5 Hz,1H),
6.73 (d, J ¼ 3 Hz, 2H), 6.23 (d, J ¼ 8.5 Hz, 1H), 5.97 (d, J ¼ 2 Hz, 2H),
4.41 (s, 3H). Anal. Calcd. for IrC31H21N7F6Cl4P: C, 38.36; H, 2.18; N,
10.10. Found: C, 38.46; H, 2.34, N, 10.27. MS (MALDI-TOF): m/z 823.9
(M ꢁ PF6).
2.2.10. [Ir(mebd)2(bdme)]PF6 (G0)
Yield: 78%. 1H NMR (500 MHz, DMSO-d6,
d [ppm]): 8.77 (d,
J ¼ 8.5 Hz, 1H), 8.33 (t, J ¼ 8 Hz, 1H), 8.15 (d, J ¼ 5.5 Hz, 1H),
8.04e8.08 (m, 2H), 7.94 (d, J ¼ 8.5 Hz,1H), 7.73e7.78 (m, 3H), 7.47 (t,
J ¼ 8 Hz,1H), 7.27 (t, J ¼ 8 Hz,1H), 7.24 (t, J ¼ 8 Hz,1H), 7.03e7.13 (m,
3H), 6.93 (t, J ¼ 8 Hz, 1H), 6.81e6.89 (m, 2H), 6.78 (t, J ¼ 8 Hz, 1H),
6.38 (d, J ¼ 7.5 Hz, 1H), 6.23 (d, J ¼ 7.5 Hz, 2H), 5.77 (d, J ¼ 7.5 Hz,
1H), 5.58 (d, J ¼ 7.5 Hz, 1H), 4.45 (s, 3H), 4.37 (s, 3H), 4.29 (s, 3H).
Anal. Calcd. for IrC41H33N7F6P: C, 51.25; H, 3.46; N, 10.20. Found: C,
51.30; H, 3.56, N, 10.30. MS (MALDI-TOF): m/z 816.2 (M ꢁ PF6).
2.2.4. [Ir(dfppz)2(bdcr)]PF6 (2a)
Yield: 61%.1H NMR (500 MHz, DMSO-d6,
d [ppm]): 8.61 (d,
J ¼ 2.5 Hz, 1H), 8.49e8.50 (m, 2H), 8.15 (t, J ¼ 8 Hz, 1H), 8.10e8.12
(m, 3 H), 7.86 (d, J ¼ 8 Hz, 1H), 7.67 (t, J ¼ 6.5 Hz, 1H), 7.37e7.49 (m,
6H), 7.10e7.22 (m, 6H), 6.70 (t, J ¼ 2.5 Hz, 1H), 6.60 (, J ¼ 2.5 Hz, 1H),
6.32 (d, J ¼ 8 Hz, 1H), 5.63e5.67 (m, 2H), 4.89e4.91 (m, 2H),
2.2.11. [Ir(mebd)2(bdcr)]PF6 (G1)
Yield: 60%. 1H NMR (500 MHz, DMSO-d6,
d [ppm]): 8.66 (d,
4.29e4.38 (m, 2H), 1.99e2.01 (m,
4 H). Anal. Calcd. for
J ¼ 8 Hz, 1H), 8.25 (t, J ¼ 8 Hz, 1H), 8.06e8.14 (m, 4H), 8.00 (d,
J ¼ 8 Hz, 1H), 7.96 (d, J ¼ 8.5 Hz, 1H), 7.77 (d, J ¼ 8.5 Hz, 1H)
7.70e7.73 (m, 1H), 7.40e7.44 (m, 2H), 7.25e7.29 (m, 2H), 7.05e7.17
(m, 9H), 6.80e6.88 (m, 3H), 6.61 (t, J ¼ 8 Hz, 1H), 6.39 (d, J ¼ 7.5 Hz,
1H), 6.26 (d, J ¼ 8.5 Hz, 1H), 6.22 (d, J ¼ 7.5 Hz, 1H), 5.75 (d,
J ¼ 8.5 Hz, 1H), 5.54 (d, J ¼ 8.5 Hz, 1H), 4.96e5.05 (m, 2H), 4.38 (s,
3H), 4.09 (s, 3 H), 3.99e4.02 (m, 1H), 3.77e3.83 (m, 1H), 1.87e1.90
(m, 1H), 1.76e1.79 (m, 1H), 1.60e1.60 (m, 2H). Anal. Calcd. for
IrC56H46N8F6P: C, 57.58; H, 3.97; N, 9.59. Found: C, 57.67; H, 4.12, N,
9.63. MS (MALDI-TOF): m/z 1023.3 (M ꢁ PF6).
IrC46H34N8F10P: C, 49.68; H, 3.08; N, 10.08. Found: C, 49.82; H, 3.25,
N, 10.22. MS (MALDI-TOF): m/z 967.2 (M ꢁ PF6).
2.2.5. [Ir(dfppz)2(bdme)]PF6 (2b)
Yield: 72%. 1H NMR (500 MHz, DMSO-d6,
d [ppm]): 8.76 (d,
J ¼ 8 Hz, 1H), 8.61 (d, J ¼ 3 Hz, 1H), 8.57 (d, J ¼ 3 Hz, 1H), 8.31e8.34
(m, 1 H), 7.96 (d, J ¼ 8.5 Hz, 1H), 8.14 (d, J ¼ 5 Hz, 1H), 7.69e7.71 (m,
1H), 7.46e8.49 (m, 1H), 7.10e7.25 (m, 5H), 6.70e6.72 (m, 2H), 6.32
(d, J ¼ 8 Hz, 1H), 5.67e5.70 (m, 2H), 4.41 (s, 3H). Anal. Calcd. for
IrC31H21N7F10P: C, 41.15; H, 2.34; N, 10.84. Found: C, 41.36; H, 2.54,
N, 10.66. MS (MALDI-TOF): m/z 760.0 (M ꢁ PF6).
2.2.12. [Ir(crbd)2(bdme)]PF6 (G2)
Yield: 50%. 1H NMR (500 MHz, DMSO-d6,
d [ppm]): 8.61 (d,
2.2.6. [Ir(crbd)2(Ph)]PF6 (3a)
J ¼ 8.5 Hz, 1H), 8.06e8.19 (m, 6H), 7.91e7.94 (m, 2H), 7.74 (d,
J ¼ 8.5 Hz, 2H), 7.55e7.61 (m, 2H), 7.37e7.46 (m, 4 H), 7.30 (t,
J ¼ 7.5 Hz, 2H), 6.90e7.23 (m, 14H), 6.70e6.74 (m, 2H), 6.31 (d,
J ¼ 7.5 Hz, 1H), 8.23 (d, J ¼ 8 Hz, 1H), 8.16 (d, J ¼ 8.5 Hz, 1H), 5.77 (d,
J ¼ 8 Hz, 1H), 5.77 (d, J ¼ 8.5 Hz, 1H), 4.84e4.90 (m, 4H), 4.37e4.39
(m, 1H), 4.29e4.30 (m, 1 H), 4.18 (s, 3H), 3.96e3.97 (m, 1H),
3.75e3.76 (m, 1H), 1.69e2.04 (m, 8H). Anal. Calcd. for
IrC71H59N9F6P: C, 62.00; H, 4.32; N, 9.16. Found: C, 62.12; H, 4.39, N,
9.25. MS (MALDI-TOF): m/z 1230.4 (M ꢁ PF6).
Yield: 70%. 1H NMR (500 MHz, DMSO-d6,
d [ppm]): 8.70 (dd,
J1 ¼1.5 Hz, J2 ¼ 7.5 Hz, 2H), 8.31 (dd, J1 ¼1 Hz, J2 ¼ 5 Hz, 2H), 8.20 (s,
2H), 8.12 (d, J ¼ 8 Hz, 4H), 7.92 (d, J ¼ 7.5 Hz, 2H), 7.86e7.89 (m, 2H),
7.66 (d, J ¼ 8 Hz, 2H), 7.29e7.31 (m, 8H), 7.15e7.18 (m, 4H), 7.12 (t,
J ¼ 8 Hz, 2H), 7.03 (t, J ¼ 7.5 Hz, 2H), 6.68e6.72 (m, 4H), 6.29 (d,
J ¼ 7.5 Hz, 2H), 5.24 (d, J ¼ 8.5 Hz, 2H), 4.83e4.87 (m, 4H), 4.31e4.34
(m, 2H), 4.16e4.19 (m, 2H), 2.01e2.03 (m, 4H), 1.81e1.83 (m, 4H).
Anal. Calcd. for IrC70H56N8F6P: C, 62.44; H, 4.19; N, 8.32. Found: C,
62.78; H, 4.29, N, 8.51. MS (MALDI-TOF): m/z 1199.4 (M ꢁ PF6).
2.2.13. [Ir(crbd)2(bdcr)]PF6 (G3)
2.2.7. [Ir(crbd)2(Ph)]PF6 (3b)
Yield: 45%. 1H NMR (500 MHz, CDCl3,
d
[ppm]): 8.38 (d, J ¼ 8 Hz,
Yield: 72%. 1H NMR (500 MHz, DMSO-d6,
d [ppm]): 8.89 (dd,
1H), 8.25 (t, J ¼ 8 Hz, 1H), 8.13 (d, J ¼ 8 Hz, 2H), 8.07 (d, J ¼ 8 Hz, 2H),
7.99e8.02 (m, 3H), 7.60 (d, J ¼ 8 Hz, 1H), 7.54 (d, J ¼ 7.5 Hz, 1H)
7.43e7.46 (m, 2H), 7.26e7.34 (m, 6H), 7.21e7.24 (m, 4H), 7.14e7.16
(m, 2H), 6.87e7.09 (m, 11H), 6.82e6.85 (m, 3H), 6.77 (t, J ¼ 7.5 Hz,
1H), 6.70 (t, J ¼ 7.5 Hz, 1H), 6.66 (d, J ¼ 8 Hz, 1H), 6.56 (t, J ¼ 7.5 Hz,
1H), 6.40 (d, J ¼ 7.5 Hz, 1H), 6.33 (d, J ¼ 7.5 Hz, 1 H), 6.23 (d,
J ¼ 8.5 Hz,1H), 5.81 (d, J ¼ 8 Hz,1H), 5.56 (d, J ¼ 8 Hz,1H), 4.51e4.52
(m, 3H), 4.36e4.42 (m, 3H), 4.16e4.19 (m, 1H), 4.04e4.07 (m, 1H),
3.80e3.87 (m, 2H), 3.67e3.70 (m, 1H), 3.58e3.61 (m, 1H), 2.10e2.12
(m, 4H),1.79e1.89 (m, 8H). Anal. Calcd. for IrC86H72N10F6P: C, 65.26;
H, 4.59; N, 8.85. Found: C, 65.35; H, 4.91, N, 8.53. MS (MALDI-TOF):
m/z 1437.5 (M ꢁ PF6).
J1 ¼ 1 Hz, J2 ¼ 8 Hz, 2H), 8.41 (dd, J1 ¼ 1 Hz, J2 ¼ 5 Hz, 2H), 8.31 (s,
2H), 8.05e8.10 (m, 4H), 7.72 (d, J ¼ 8 Hz, 2H), 7.19 (t, J ¼ 7.5 Hz, 2H),
7.09e7.13 (m, 2H), 6.90 (td, J1 ¼1 Hz, J2 ¼ 7.5 Hz, 2H), 6.71e6.74 (m,
2H), 6.37 (d, J ¼ 7.5 Hz, 2H), 5.26 (d, J ¼ 8 Hz, 2H) 4.34 (s, 6H). Anal.
Calcd. for IrC40H30N6F6P: C, 51.55; H, 3.24; N, 9.02. Found: C, 51.63;
H, 3.38, N, 9.10. MS (MALDI-TOF): m/z 785.2 (M ꢁ PF6).
2.2.8. [Ir(crbd)2(DBI)]PF6 (4a)
Yield: 65%. 1H NMR (500 MHz, DMSO-d6,
d [ppm]): 8.13 (d,
J ¼ 7.5 Hz, 4H), 7.75 (d, J ¼ 8 Hz, 4H), 7.36e7.47 (m, 10H), 7.28 (t,
J ¼ 1 Hz, 2H), 7.17e7.20 (m, 4H), 7.05 (t, J ¼ 1 Hz, 2H), 6.83 (t,
J ¼ 1 Hz, 2H), 6.57 (t, J ¼ 1 Hz, 2H), 6.32 (d, J ¼ 1 Hz, 2H), 6.23 (d,
J ¼ 8 Hz, 2H), 6.09 (d, J ¼ 8 Hz, 2H), 4.82e4.84 (m, 4H), 4.33e4.37
(m, 4H), 4.09 (s, 6H), 1.96e1.99 (m, 4H), 1.86e1.88 (m, 4H). Anal.
Calcd. for IrC66H58N10F6P: C, 59.67; H, 4.40; N, 10.54. Found: C,
59.86; H, 4.61, N, 10.65. MS (MALDI-TOF): m/z 1181.4 (M ꢁ PF6).
2.3. X-ray crystallography study
Data collection of complexes 2ae4b and G0 were performed on
a
Bruker Smart Apex II CCD diffractometer with graphite-
monochromated Mo Ka radiation (
l
¼ 0.71069 Å) at 293 K.
2.2.9. [Ir(mebd)2(DBI)]PF6 (4b)
Absorption corrections were performed by using the multi-scan
technique. The crystal structure was solved by Direct Methods of
SHELXTL-97 [50] and refined by full-matrix least-squares tech-
niques using SHELXTL-97 within WINGX [51]. The hydrogen atoms
Yield: 69%. 1H NMR (500 MHz, DMSO-d6,
d [ppm]): 7.99 (d,
J ¼ 7.5 Hz, 2H), 7.79 (d, J ¼ 8.5 Hz, 2H), 7.52 (d, J ¼ 1.5 Hz, 2H), 7.34 (t,
J ¼ 7.5 Hz, 2H), 7.08 (t, J ¼ 7.5 Hz, 2H), 6.95e6.98 (m, 2H), 6.70e6.73

30
G.-G. Shan et al. / Journal of Organometallic Chemistry 702 (2012) 27e35
of aromatic rings were included in the structure factor calculation
at idealized positions by using a riding model. Anisotropic thermal
parameters were used to refine all non-hydrogen atoms except for
part of nitrogen and carbon atoms. The detailed crystallographic
data and structure refinement parameters are summarized in
Table S1. Further details of the crystal structure determination have
been deposited to the Cambridge Crystallographic Data Centre as
supplementary publication. CCDC 846582 (2a), 846581 (2b),
846583 (3b), 846584 (4b) and 846585 (G0) contain the supple-
mentary crystallographic data for this paper.
2.048 (4) Å, respectively, while the longest bond lengths to iridium
atom is from the nitrogen atom on the phenanthroline ligand with
the distance of 2.142 (4) and 2.151 (5) Å, respectively. The two kinds
of IreN bonds (Ir1eN1/N2 and Ir1eN3/N5) show considerable
differenceethe bond length of former is significantly longer than
that of latter which might be attributed to the strong trans-influ-
ence of the carbon donors [21,44]. In addition, a small bite angles of
C(13)eIr(1)eN(3) [79.3 (2)ꢀ], C(28)eIr(1)eN(5) [79.0 (2)ꢀ] and
N(1)eIr(1)eN(2) [77.13 (17)ꢀ] and bond angles of C(28)eIr(1)eN(1)
[172.43 (19)ꢀ], C(13)eIr(1)eN(2) [175.08 (18)ꢀ] and N(3)eIr(1)e
N(5) [169.96 (18)ꢀ] have been estimated. Except 2a and 2b, other
crystals structures do not give the relative information about steric
hindrance, but they can provide the significant data for the struc-
ture character and theoretical study (vide infra).
2.4. Theoretical calculations
Calculation on the ground and excited electronic state of
complexes were investigated by performing DFT and TD-DFT at
PBE0 level [52,53]. The 6-31G* basis sets were employed for opti-
mizing the C, H, N atoms and the LANL2DZ basis sets for Ir atom. An
effective core potential (ECP) replaces the inner core electrons of
iridium leaving the outer core (5s)2(5p)6 electrons and the (5d)6
valence electrons of Ir (III). All calculations were carried out with
the C.02 revision of the Gaussion 03 program package [54].
3.2. Photophysical properties
The absorption and emission spectra recorded for 1e4 in
degassed CH2Cl2 at room temperature are shown in Fig. 2. As shown
in Fig. 2, all complexes exhibit two major absorption bands in their
absorption spectra. The dominant absorption band in the range of
200e350 nm are assigned to spin-allowed
the ligands. These results are confirmed by the observation of
a spectral profile of the * transitions for the corresponding free
pep* transitions from
3. Results and discussion
pep
3.1. X-ray structure characterization
ligands (Fig. S2). The low-energy absorption from 350 nm extend-
ing to the visible region are ascribed to both spin-allowed, spin-
forbidden metal-to-ligand charge transfer (3MLCT) and ligand-to-
ligand charge transfer (1LLCT) character with reference to that re-
ported for other Ir(III) compounds [19e21,55]. Upon photoexcita-
tion, the complexes exhibit highly intensive luminescence in
CH2Cl2 solvent and neat film (Fig. S3). The significant variations of
emission intensity and excited-state lifetime are observed between
degassed and aerated CH2Cl2 solvent, indicating the emission of
these compounds is the phosphorescence (Table S2). Table 1
summarizes the photophysical properties of the Ir(III) complexes
1e4. Generally, for cationic Ir(III) complexes, three excited states
Crystal structures of 2ae4b were obtained by the slow evapo-
ration of diethyl ether into the CH2Cl2 or CHCl3 solution. Because
the cyclometalated chloride-bridged dimers were prepared at high
temperature (see Experimental section), the dimers with the
common cis-C,C and trans-N,N arrangement of cyclometalated
ligand should be obtained. Thus, the corresponding cationic Ir(III)
complexes, N,N-trans-[Ir(C^N)2(N^N)]þ, with cis-N,N and trans-N,N
cyclometalated ligand geometrical configurations were expected
[19,20]. This is supported by the X-ray crystallography study. As
depicted in Fig. 1 and Fig. S1, the complexes reveal the distorted
octahedral geometry around the Ir atom with two cyclometalated
ligands and one ancillary ligand. The two cyclometalated ligands
both adopt a mutually eclipsed configuration with two nitrogen
atoms residing at trans locations. The overall structural arrange-
ment is similar with several previously reported ones [20,21]. For
example, in 3b, the nitrogen atoms of two cyclometalated ligands
are trans to each other with IreN bond lengths of 2.048 (4) and
contribute to the observation of light emission, namely, LC 3p
ep*,
3MLCT and 3LLCT. The emission spectra from MLCT state are
usually broad and featureless, while the obvious structured emis-
sion band are always attributed to the LC 3p
ep* state. At room
temperature, complexes 1e3 display almost featureless emission
spectra, indicating that the emissive excited states of them take on
much more 3MLCT or 3LLCT characters than 3ILCT. In case of 4,
Fig. 1. ORTEP diagrams of 3b (a) and 4b (b) with thermal ellipsoids shown at the 30% probability level. All hydrogen atoms and counter anions have been omitted for clarity.

G.-G. Shan et al. / Journal of Organometallic Chemistry 702 (2012) 27e35
31
Fig. 2. UVevis absorption and emission spectra of 1e4 in CH2Cl2.
a distinct vibronic structure develops in their emission spectra.
Hence, an origin of lowest lying excited state arising from LC 3
pep*
have been realized. By carefully inspecting the crystal packing of
2a and 2b (Fig. 3), we find that the bulkiness of bdcr ligand plays
an important role in preventing intermolecular interactions, as
indicated by the shortest IreIr distance 8.459 Å in 2a, whereas the
corresponding closest IreIr distance in 2b is 11.235 Å,
respectively.
To better understand the intrinsic photophysical properties,
the PLQYs of 2 and 3 in 20 wt% PMMA dispersed film were also
investigated. The PLQY values in doped film were 80% for 2a, and
87% for 2b, respectively. The PLQY values of 2a and 2b in neat films
remained at 33% and 18% of those in PMMA blend films, implying
that the CZB should provide efficient hindrance against intermo-
lecular interactions in neat film. Much higher retaining percentage
of neat film PLQY value of 3a (ca. 43%) was realized, which
demonstrated that the segregation of emitting iridium core was
an effective strategy for restraining the quenching effect in solid
film.
character could be tentatively assigned for 4. Both in solutions and
film, the emissions of functionalized complexes are very similar to
those of their corresponding parent complexes, suggesting that
incorporation of CZB units into either cyclometalated or ancillary
ligands have little effect on the emission color. The negligible
influence of the CZB groups on the emission spectra indicated that
the electronic natures of the excited state of functionalized
complexes should be very similar to those of their parent
complexes. These emission properties of the complexes have been
rationalized by our quantum chemical calculations (vide infra).
In general, EQE is an important factor for evaluating the
emitting-light devices and efficiency of LECs should be evaluated
from PLQY measurements in thin films [56]. In diluted CH2Cl2
solution, all complexes show much higher quantum yields than
those in neat film. It should be noted that the order of PLQY in
solution differs from that in film. It is well known that the photo-
luminescence of molecules in solution with low concentrations
mainly show characteristics of single molecule because of the long
distance between the two molecules. However, the distance
between two molecules should be decreased in film and solid-state,
which in turn might increase the intermolecular interaction. These
interactions play a very important role in PLQY of the film. As
presented in Table 1, the film PLQYs of 1ae4a are obviously higher
than those of 1be4b. It was believed that replacement of methyl
group with n-butyl group and introduction of the carbazole
moieties into the ligands could bring about more efficiently spatial
hindrance in neat film. As a result, the reduced intermolecular
interactions between two molecules and improved PL efficiency
3.3. DFT and TD-DFT calculations
To further understand the nature of the emissive excited state
involved in the emission process and investigate the effect of CZB
group on the excited state, the quantum chemical calculations were
performed. The excitation energies and molecular orbitals involved
in the excitations of selected complexes are summarized in Table 2
and Fig. 4, respectively. Furthermore, the molecular orbital
composition analysis of cationic Ir(III) complexes was also per-
formed at PBE0/LANL2DZ/6-31g* level using AOMix program
[57,58] to clearly estimate their excited-state characters. The
numerical data are listed in Table 3. The calculated data of others
are included in Table S3eS7. Selected bond distance compared with
single crystal data are listed in Table S3. The close similarity
between the calculated bond lengths and experimental values
ensures the proper descriptions of the nature of the lowest excited
states. As mentioned above, 4 show pronounced vibronic structure
in their emission wavelength at room temperature, which leads to
Table 1
Photophysical properties of the Ir(III) complexes 1e4.
Solventa
Film
b
c
d
lmax
Fsolvent
sr
[
ms]
lmax
Fneat
FPMMA
DFe
1a 514
0.80
0.45
0.53
0.48
0.32
0.51
3.5
2.5
1.8
1.5
0.48
0.37
522
522
512
512
568
567
0.20
0.07
0.26
0.16
0.15
0.08
e
e
a conclusion that 4 will process much more LC 3p
than others as speculated above. Our calculated data can sustain
that. As depicted in Table S4eS6, 4 bearing the large LC 3p
ep*
ep* character
1b 513
2a 512
2b 511
3a 558
3b 558
e
e
0.80
0.87
0.35
0.78
e
0.33
0.18
0.43
0.10
e
character could be clearly understood. In addition to that, the
influence of CZB substitutes on the excited states could also be
interpreted with the help of the quantum calculations. Fig. 4
displays the electronic density contours calculated for the HOMOs
and LUMOs of 2a, together with those obtained for the 2b. Based on
the TD-DFT calculation, the HOMO-4/LUMO and HOMO-
2/LUMO transition were contributed to a large extent by 3MLCT
mixed with 3LLCT for low-lying triplet excited-state of 2a and 2b,
respectively. By analyzing orbital diagrams, the distributions of
HOMO-4 of 2a are similar to that of HOMO-2 of 2b, which residing
4a 484, 516 0.08
0.069 (80%), 501, 524 0.02
0.38 (20%)
4b 486, 518 0.03
0.043 (71%), 501, 525 0.01
0.45 (29%)
e
e
a
The data were measured in degassed CH2Cl2 (1 ꢂ 10ꢁ5 M) solution.
b
The Fsolvent (photoluminescence quantum yields, PLQY) was measured versus
quinine sulfate (
F
¼ 0.545 in 1 M H2SO4).
c
PLQY in neat film.
d
e
PLQY when doped with 20 wt% in PMMA (polymethylmethacrylate) film.
DF
¼
= .
Fneat FPMMA

32
G.-G. Shan et al. / Journal of Organometallic Chemistry 702 (2012) 27e35
Fig. 3. Molecular structures of 2a (a) and 2b (b); the crystal packing of 2a (c) and 2b (d). The solvent molecules, counter anions and hydrogen atoms are omitted for clarity.
on iridium d orbital and
p
orbital of benzimidazole group. It can
analysis (TGA) under a nitrogen atmosphere (Fig. S5). The results
show that, the decomposition temperatures with a 5% weight loss
(Td5) are all higher than 350 ꢀC, indicative of the good thermal
stability. It is known that the alkyl modification can improve the
good solubility, but it may remarkably decrease the thermal
performance at the same time. Interestingly, the decomposition
temperature of 2a and 3a were not significantly changed
compared with those of the parent complexes (2b and 3b),
although the CZB group contained a long alkyl chain. It might be
attributed to the carbazole groups which increased the thermal
stability of the functionalized complexes. Moreover, the film-
forming properties of emitting-materials are crucial for the
performances of devices. The power X-ray diffraction (XRD) of 2
and 3 were investigated in order to find out the phase status of the
spin-coated films. The XRD patterns of them are shown in Fig. S6.
For case 2a and 3a with carbazole end-capped aliphatic chain
group, they show relatively weaker scattering peaks, which are
different to the distinct peaks observed for 2b and 3b, respectively.
The data of XRD suggest that the 2a and 3a can possess good film-
forming property [40,60]. The solid-films of them were obtained
be noted that LUMO orbital for 2 all mainly localizes on the 2-(2-
pyridyl)benzimidazole of ancillary ligands, while CZB moiety does
not dominates their excited-state. Thus, the same nature of lowest
triplet excited states for 2a and 2b can be supported, which nicely
explains that substitutions on ancillary ligands using CZB do not
influence their emission spectra. Accordingly, in the case of 3,
when the CZB was attached into the bis-cyclometalated ligand,
the character of excited state has been not changed as evidenced
by the calculations data. Furthermore, the calculated excited
energies for functionalized complexes are almost same as parent
ones, suggesting the emission wavelength of them should be
identical (Table 2). This was consistent with our experimental
data.
3.4. Thermal and film-forming properties
Except PLQY, other factors such as the thermal stability and
film-forming property can also affect the lifetime and efficiency of
LECs [37,59]. Herein, the thermal property and thin film
morphologies were investigated. Taking 2 and 3 as examples, the
thermal stability of them were evaluated by thermogravimetric
Table 2
Calculated energy levels of the lowest lying transitions of complexes.
Complex
States
T1
E [eV]
f
Assignment
Nature
2a
2.68
0
H-4/L (62%)
H-7/L (14%)
H-10/L (6%)
H-2/L (64%)
H-5/L (14%)
H-7/L (6%)
H-2/L (39%)
H-10/Lþ1 (20%)
H-14/Lþ1 (9%)
H/L (42%)
3MLCT/3LLCT/3ILCT
3MLCT/3LC
3MLCT/3LLCT/3ILCT
3MLCT/3LLCT/3ILCT
3MLCT/3LC
2b
3a
3b
T1
T1
T1
2.69
2.59
2.59
0
0
0
3MLCT3/LLCT/3ILCT
3MLCT/3LLCT
3MLCT/3LLCT
3MLCT/3LLCT
3MLCT/3LLCT
H-6/Lþ1 (19%)
3MLCT/3LLCT
H-8/Lþ1 (9%)
3MLCT/3LLCT
Fig. 4. Selected frontier orbitals of representative complexes 2 and 3.

G.-G. Shan et al. / Journal of Organometallic Chemistry 702 (2012) 27e35
33
Table 3
Molecular orbital composition analysis at PBE0/LANL2DZ/6-31g* level using AOMix
program.
Complex
Orbital
Ir atom
C^N ligand
N^N ligand
CZB moiety
2a
LUMO
2.3
39.8
6.8
14.0
0.3
38.4
7.6
13.2
0.4
0.5
19.7
6.9
30.0
0.4
19.2
7.8
34.0
1.1
96.5
39.6
85.6
55.0
97.3
42.4
84.6
52.8
98.5
96.4
1.5
46.9
52.8
98.5
96.4
1.5
0.7
0.9
0.7
1.0
HOMO-4
HOMO-7
HOMO-10
LUMO
HOMO-2
HOMO-5
HOMO-7
LUMOþ1
LUMO
HOMO-2
HOMO-10
HOMO-14
LUMOþ1
LUMO
2b
3a
0.0
0.0
0.4
0.7
0.1
3.0
0.6
34.1
13.6
21.2
0.4
64.0
38.8
25.9
1.1
3b
3.0
0.6
HOMO
HOMO-6
HOMO-8
34.0
14.3
21.0
64.5
39.7
24.9
46.0
54.1
through spin-coating corresponding Ir(III) complexes from CH3CN
solution. Observation of these thin films with an image restoration
microscope (Fig. S7) reveals that they are homogeneous and no
aggregates or crystals are observed. To further investigate the
morphology of the 2a and 3a with relatively high film PLQYs, the
atomic force microscopy (AFM) measurements were performed,
demonstrating that, in solid film, the surface of them shows
a small root mean square (RMS) roughness of 0.57 and 0.51 nm for
2a and 3a, respectively (Fig. 5), further indicating the excellent
film-forming property.
Scheme 2. Structures of Ir(III) complexes G0eG3.
by our calculated data. As shown in Table S4eS7, the T1 states of
them originate from iridium core and phenyl group of cyclo-
metalated ligands to the ancillary ligands, thereby the exited-
state characters could be assigned to 3MLCT mixed with some
3LLCT characters. It was similar to our experimental results.
Noticeably, the different number of CZB moieties was introduced
into G1eG3 where they have little effect on the T1 states, which
is similar to the finding of complexes 1e4.
3.5. Molecule design
Additionally, by comparing their PLQYs in neat film with that in
20 wt% doped PMMA film, a further increase in number of CZB
group from 0 to 3 leads to enhanced high-efficiency as well as
larger retaining percentages (90% for G3) in neat film (Table S7). The
introduction of much more sterically bulky CZB groups which can
effectively reduce the intermolecular interaction and inhibit the
quenching process is attributed to the improvement of PLQYs in
G1eG3. Moreover, the obtained TG curves reveal that G3 possesses
excellent thermal stability with decomposition temperature above
350 ꢀC among them (Fig. S5). These data are all consistent with
results from complexes 1e4.
In view of the result that attachment of CZB moiety into the
cyclometalated and/or ancillary ligands can result in an
enhanced efficiency compared with the parent complexes, four
much higher efficiency cationic Ir(III) complexes with different
number of CZB units, namely G0eG3 (Scheme 2) have been
designed and prepared. Fig. 6 and Fig. S4 display their emission
spectra in solution and film, respectively, showing almost iden-
tical emission wavelength in both states. The broad structureless
emission spectra indicated that the excited states for them were
mainly attributed to 3MLCT characters, which was rationalized
Fig. 5. AFM images showing 5
m
m ꢂ 5
mm areas of spin-coated (a) 2a and (b) 3a films at room temperature.

34
G.-G. Shan et al. / Journal of Organometallic Chemistry 702 (2012) 27e35
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In summary, a series of the carbazole-9-yl-n-butyl group (CZB)
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have not been changed in comparison with their parent complexes.
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The authors gratefully acknowledge financial support from NSFC
(20971020,
20903020
and
21131001),
973
Program
(2009CB623605), and the Science and Technology Development
Planning of Jilin Province (20100540, 20100182 and 201101008),
and open Project of State Key Laboratory of Supramolecular
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