Synthesis, characterization, luminescence properties, and DFT calculation of a cationic cyclometalated iridium(III) complex with fluorine-containing phenylquinolinyl and 2,2′-bipyridine ligands

Article abstract of DOI:10.1016/j.ica.2012.08.002

A cationic bis-cyclometalated iridium(III) complex, [Ir(hfppq) ₂(bipy)][PF₆]·0.5H₂O (hfppq = 1,1,1,3,3,3-hexafluoro-2(2-phenylquinolin-4-yl)propan-2-ol, bipy = 2,2′-bipyridine, 1), was obtained from the reaction of the μ-chloro-bridged dimeric complex [Ir(hfppq)₂(μ-Cl)]₂ and bipy in the presence of KPF₆. Complex 1 shows a strong emission both in the solid state (ca. 595 nm) and in CH₂Cl₂ solution (ca. 585 nm) at room temperature with the phosphorescence quantum yield of ca. 0.698 and emission lifetime of 0.96 μs. Density functional theory (DFT) calculation was performed on the ground and excited states of complex 1 to provide insight into the structural, electronic, and optical properties of the cationic cyclometalated iridium(III) complex.

Full text of DOI:10.1016/j.ica.2012.08.002

Inorganica Chimica Acta 394 (2013) 184–189
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Inorganica Chimica Acta
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Synthesis, characterization, luminescence properties, and DFT calculation
of a cationic cyclometalated iridium(III) complex with fluorine-containing
phenylquinolinyl and 2,20-bipyridine ligands
Jia-Yan Qiang a,b, Ya-Qing Xu a,b, Bihai Tong b, Xiu-Fang Ma b, Qun Chen a, Wa-Hung Leung c,
Qian-Feng Zhang a,b,
⇑
a Department of Applied Chemistry, School of Petrochemical Engineering, Changzhou University, Jiangsu 213164, PR China
b Institute of Molecular Engineering and Applied Chemistry, Anhui University of Technology, Ma’anshan, Anhui 243002, PR China
c Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A cationic bis-cyclometalated iridium(III) complex, [Ir(hfppq)2(bipy)][PF6]ꢀ0.5H2O (hfppq = 1,1,1,3,3,
3-hexafluoro-2(2-phenylquinolin-4-yl)propan-2-ol, bipy = 2,20-bipyridine, 1), was obtained from the
Received 16 October 2011
Received in revised form 27 July 2012
Accepted 5 August 2012
reaction of the
l-chloro-bridged dimeric complex [Ir(hfppq)2(l-Cl)]2 and bipy in the presence of KPF6.
Complex 1 shows a strong emission both in the solid state (ca. 595 nm) and in CH2Cl2 solution (ca.
585 nm) at room temperature with the phosphorescence quantum yield of ca. 0.698 and emission life-
Available online 23 August 2012
time of 0.96 ls. Density functional theory (DFT) calculation was performed on the ground and excited
states of complex 1 to provide insight into the structural, electronic, and optical properties of the cationic
cyclometalated iridium(III) complex.
Keywords:
Iridium(III) complex
Cyclometalated
Synthesis
Ó 2012 Elsevier B.V. All rights reserved.
Crystal structure
Photoluminescence
DFT calculation
1. Introduction
Notwithstanding, suitable Ir-based materials for the application
as OLEDs still need to be further developed.
Owing to the strong spin–orbit coupling which can harvest
both singlet and triplet excitons for emission, heavy metal–organic
complexes are good candidates for organic light-emitting diodes
(OLEDs) [1]. Particularly, bis- and tris-cyclometalated (C^N)
complexes of iridium(III) based on 2-phenylquinoline and its
derivatives have been widely used as one of the promising electro-
luminescent materials for the OLED technology [2–7]. It is known
that the HOMO of the cyclometalated iridium(III) complexes is
The main requirements for phosphorescent materials are that
phosphorescence should have high color purity and that the phos-
phorescence quantum yields should be high [13]. With this in
mind, we are interested in synthesizing a new sterically hindered
fluorinated ligand 1,1,1,3,3,3-hexafluoro-2(2-phenylquinolin4-yl)
propan-2-ol (hfppq) and its bis-cyclometalated (C^N) iridium(III)
complex [Ir(hfppq)2(bipy)]PF6. The incorporation of fluorine into
the organic molecules may result in profound changes in the phys-
ical and chemical properties of the molecules [14]. There also have
been several effects of the trifluoromethyl group in the cyclometa-
lated iridium(III) complexes. The first one is the strong electron
determined by the 5d orbital of iridium(III) with the
p orbitals of
the polypyridine ligand and the LUMO is related to the p⁄ orbitals
of the diimine ligand [8,9]. For the cationic complexes of bipyri-
dine derivatives, the HOMO primarily resides on the iridium center
and the phenyl groups of C^N ligand, the LUMO is mainly located
on the N^N ligands [3,10]. Thus, by changing the structures of the
ligands, one can modulate the HOMO and LUMO energies of irid-
ium(III) complexes in order to tune the emission colors [11,12].
withdrawing effect on the ligand
p-system, which can lower of
the HOMO and LUMO energies [15–17], and the second is to pro-
vide steric protection around the metal, which is an important
parameter for increasing the intensity of the emission [18,19]. In
addition, the incorporation of fluorine into the molecule can effec-
tively enhance the stability of the compound. Compared with the
similar cationic iridium(III) complexes [7], the present iridium(III)
complex, [Ir(hfppq)2(bipy)]PF6 (bipy = 2,20-bipyridine), having
⇑
Corresponding author at: Department of Applied Chemistry, School of Petro-
chemical Engineering, Changzhou University, Jiangsu 213164, PR China. Tel./fax:
+86 555 2312041.
both a short excited-state lifetime (0.96
ls) and a high phospho-
rescence yield (0.698), should be advantageous to realization of
E-mail address: zhangqf@ahut.edu.cn (Q.-F. Zhang).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.08.002

J.-Y. Qiang et al. / Inorganica Chimica Acta 394 (2013) 184–189
185
highly efficient OLEDs. The structural characterization and photo-
luminescence properties along with theoretical investigations of
[Ir(hfppq)2(bipy)]PF6 are reported in this paper.
eluent. Yield: 52 mg, 37.2%. FT-IR (KBr, cmꢂ1):
(OH) 3054(s), m
([PF6]) 835–860(s). 1H NMR (DMSO-d6, ppm)
m
(H2O) 3448(br),
m
d 9.81 (s, 2H), 8.82 (br, 2H), 8.39 (dd, J = 8.0 Hz, 4H), 8.12 (dd,
J = 7.2 Hz, 6H), 7.69 (d, J = 6.4 Hz, 2H), 7.51 (m, 4H), 7.28 (d,
J = 7.6 Hz, 2H), 7.13 (d, J = 8.0 Hz, 2H), 6.96 (d, J = 7.2 Hz, 2H),
6.57 (d, J = 7.6 Hz, 2H). 31P NMR (DMSO-d6, ppm) d ꢂ144.19
(septet, JP–F = 707 Hz). 19F NMR (DMSO-d6, ppm) d ꢂ69.27 (s),
ꢂ74.16 (d, J = 708 Hz). MS ((+)-ESI): m/z = 1089 (Calc. 1089
for [Ir(hfppq)2(bipy)]+). Anal. Calc. for C46H28N4O2F18PIrꢀ(H2O): C,
44.45; H, 2.35; N, 4.51. Found: C, 44.27; H, 2.32; N, 4.47%.
2. Experimental
2.1. Materials and measurements
All synthetic manipulations were carried out under dry nitrogen
by standard Schlenk techniques. All silica gel column chromatogra-
phy was performed with use of silica gel (200–300 mesh). All re-
agents, unless otherwise specified, were purchased from Aldrich
and were used as received. 1H NMR spectra were recorded on a
Bruker ALX Plus 400 spectrometer operating at 400 MHz with tet-
ramethylsilane (TMS) as the internal standard. Infrared spectra
(KBr) were recorded on a Perkin-Elmer 16 PC FT-IR spectropho-
tometer with use of pressed KBr pellets. Electronic absorption
spectra were measured in CH2Cl2 solution on a Shimadzu UV-
3000 spectrophotometer. Luminescence properties were measured
and recorded using an FLS-920 fluorescence spectrometer. Posi-
tive-ion ESI mass spectra were recorded on a Perkin-Elmer Sciex
API 365 mass spectrometer. Photoluminescence (PL) spectra were
measured with a Shimadzu RF-5301PC fluorescence spectropho-
tometer. Luminescence lifetime was determined on an Edinburgh
FL920 time-correlated pulsed single-photon-counting instrument.
Melting point was recorded on an SGW X-4 electrothermal appara-
tus. Elemental analyses were carried out using a Perkin-Elmer
2400 CHN analyzer.
2.4. Crystal structure determination
Single crystals of complex 1 were grown from the mixed dichlo-
romethane/–hexane (1:2) solution by slow evaporation at room
temperature. The determination of the unit cell and data collection
for 1 was performed on a Bruker SMART Apex CCD diffractometer
with MoKa radiation at 296 K using a x scan mode. The collected
frames were processed with the software SAINT [20]. The data were
corrected for absorption using the program SADABS [21]. The struc-
ture was solved by direct methods and refined by full-matrix
least-squares on F2 using the SHELXTL software package [22,23]. All
non-hydrogen atoms were refined anisotropically. The positions
of all hydrogen atoms were generated geometrically (Csp3
–
H = 0.96, Csp2–H = 0.93 Å) and included in the structure factor cal-
culations with assigned isotropic displacement parameters, but
were not refined. The oxygen atom of water molecule was isotrop-
ically refined without hydrogen atoms. Crystal data, data collection
parameters and details of the structure refinement are given in
Table 1.
2.2. Synthesis of the ligand (Hhfppq)
2.5. Computational details
The ligand Hhfppq was prepared according to procedures de-
scribed in the literature [13]. Under an atmosphere of nitrogen,
Me3SiCF3 (854 mg, 6.00 mmol) was charged to a solution of methyl
2-phenylquinoline-4-carboxylate (737 mg, 2.80 mmol) in anhy-
drous ethylene glycol dimethyl ether (5 mL), and then the mixture
was cooled to 0 °C. A catalytic amount of CsF was added to the mix-
ture, and the temperature was slowly warmed to room tempera-
ture. After stirring overnight, the hydrolysis was carried out over
3 h by addition of 4 N HCl (4 mL). The resulting product was ex-
tracted with ethyl acetate (10 mL ꢁ 3). After the removal of sol-
vent, the residue was purified by chromatography on a silica gel
column using hexane/ethyl acetate (v:v = 6:1) as an eluent. Yield:
470 mg, 63.8%. m.p.: 203–206 °C. 1H NMR (CDCl3, ppm): d 8.92
(s, 1H), 8.28 (dd, J = 8.4 Hz, 1H), 8.15 (dd, J = 6.8 Hz, 3H), 7.79 (dd,
J = 7.6 Hz, 1H), 7.60 (m, 4H). 19F NMR (376 MHz, CDCl3) d ꢂ73.30
(s). MS ((+)-ESI): m/z = 347 (Calc. 347 for [C16H11NOF6]+). Anal. Calc.
for C16H11NOF6: C, 55.34; H, 3.19; N, 4.03. Found: C, 55.23; H, 3.16;
N, 4.01%.
The ground state molecular geometries full optimization of the
complex was carried out with the density functional theory (DFT)
at the Becke3LYP (B3LYP) level [24,25]. Frequency calculations at
the same level of theory have also been performed to identify the
stationary point as minima (zero imaginary frequency). On the ba-
Table 1
Crystallographic data and experimental details for [Ir(hfppq)2(bipy)][PF6]ꢀ0.5H2O (1).
Compound
1
Empirical formula
Formula weight
Crystal system
a (Å)
b (Å)
c (Å)
C
46H29N4O2.5F18PIr
1242.90
Orthorhombic
26.7123(8)
17.8006(5)
19.9131(6)
90
a
(°)
b (°)
90
c
(°)
90
9469.6(5)
Pbcn
V (Å3)
2.3. Synthesis of complex [Ir(hfppq)2(bipy)][PF6]ꢀ0.5H2O (1)
Space group
Z
8
In
a
25 mL rounded-bottomed flask, IrCl3ꢀxH2O (40 mg,
Dcalc (g cmꢂ3
)
1.744
0.113 mmol) and ligand Hhfppq (98 mg, 0.283 mmol) were dis-
solved in a 3:1 v/v mixture of 2-ethoxyethanol and distilled water
(12 mL). The mixture was refluxed overnight under nitrogen atmo-
sphere with exclusion of light, and then cooled to the ambient tem-
perature. Bipy (35 mg, 0.224 mmol) was directly added to the
reaction solution, and the mixture was stirred for 6 h at room tem-
perature. Addition of an excess KPF6 (835 mg, 4.54 mmol) in a
methanol solution (5 mL) to the reaction solution resulted in for-
mation of the orange solid. The resulting solid product was filtered,
and washed with absolute ethanol and dried in vacuum. The or-
ange precipitation was purified by chromatography on a silica gel
column using dichloromethane/ethyl acetate (v/v = 2:1) as an
Temperature (K)
296(2)
7170
2.969
75864
10948
F(000)
l
(Mo-K
a
) (mmꢂ1
)
Total reflections
Independent reflections
No. of parameters
613
Rint
0.0991
0.0638, 0.1251
0.0998, 0.1688
1.040
b
R1a, wR2 (I > 2
r(I))
R1, wR2 (all data)
Goodness-of-fit (GOF)c
P
P
a
b
c
R1 = ||Fo| ꢂ |Fc||/ |Fo|.
P
P
wR2 = [ w(|Fo2| ꢂ |Fc2|)2/ w|Fo2|2]1/2
.
P
GOF = [ w(|Fo| ꢂ |Fc|)2/(Nobs ꢂ Nparam)]1/2
.

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J.-Y. Qiang et al. / Inorganica Chimica Acta 394 (2013) 184–189
sis of the optimized geometries, the natural bond orbital (NBO) is
employed to analyze the molecular orbital compositions (%). The
lowest 10 singlet–singlet and singlet–triplet excitations have been
computed by means of TDDFT. The effective core potentials (ECPs)
of Hay and Wadt with a double f-valence basis set (LANL2DZ) [26]
were used for the iridium atom, the 6-311G⁄ basis set for the atoms
bonded to metal iridium atom directly, the 6-311G [27,28] for the
other atoms. The basis set for r iridium atom is a modified
LANL2DZ plus an f-type polarization function and the two 4p func-
tions of the standard LANL2DZ are replaced by the optimized 4p
functions from Couty and Hall [29,30]. Starting geometries were
taken from X-ray crystal structures. All the calculations were per-
formed with the Gaussian 03 software package [31].
3. Results and discussion
Treatment of IrCl3ꢀxH2O with 2.5 equivalents of Hhfppq in
2-ethoxyethanol/water solution at reflux gave the chloride-
bridged cyclometalated iridium(III) precursor [Ir(hfppq)2(l-Cl)]2
which further reacted with 2,20-bipyridine (bipy) in the presence
of KPF6 to afford the cationic cyclometalated iridium(III) complex
[Ir(hfppq)2(bipy)][PF6]ꢀ0.5H2O (1) (see Scheme 1). Microanalytical
data were consistent with the solid having a 2:1:1 of (hfppq):
(bipy):(PF6) ratio. The characteristic peaks at 3448 and 3054
cmꢂ1 in the IR spectrum of 1 may be attributed to the stretching
vibrations of the water molecule and hydroxyl group, respectively.
The IR spectrum of 1 showed the P–F stretching in the region 835–
860 cmꢂ1. The 19F NMR spectrum of 1 displays one singlet at d
ꢂ69.27 and one doublet at d ꢂ74.16 ppm assignable to the CF3
and PF6 groups, respectively.
Fig. 1. Perspective view of [Ir(hfppq)2(bipy)]+ cation in 1. Thermal ellipsoids are
The structure of 1 has been unambiguously established by X-ray
diffraction. Fig.
1
shows
a
perspective view of the cation
shown at the 35% probability level.
[Ir(hfppq)2(bipy)]+ in 1. The asymmetric unit of the crystal struc-
ture consists of two ion pairs and half of water molecule in the lat-
tice. The geometry around the iridium(III) center is distorted
octahedral with two mutually cis hfppq ligands and the two nitro-
gen atoms of pyridyl groups being trans to the Ir–C bonds. The
average Ir–C (1.998(8) Å) and Ir–N(hfppq) (2.104(6) Å) distances
are normal by the comparison with other related bis-cyclometalat-
ed Ir(III) complexes. The average Ir–N(bipy) bond length (2.164
(8) Å) is slightly longer than the average Ir–N(hfppq) bond length,
which is probably due to trans influence of the aryl groups of
hfppq.
The absorption spectra of complex 1 and the free ligand Hhfppq
in dichloromethane are shown in Fig. 2. Intense absorption band
from 220 to 290 nm are observed in the ultraviolet region of the
spectra, which can be assigned to the spin-allowed
1
(p–
p⁄) transi-
tion of the cyclometalating ligand. The band around 350 nm is
most likely a
p–
p⁄ transition on the ligand which has shifted on
coordination. Indeed, in Fig. 2, the bands at 330 nm for the ligand
and 350 nm for the complex appear very similar. The band around
458 nm will therefore be assigned to spin-allowed metal–ligand
Cl
Ir
Ir
N
Cl
N
OH
OH
CF3
CF3
F3C
O
O
HO
(ii)
CF3
CH3
CF3
F3C
2
(i)
2
(iii)
N
N
N
N
Ir
[PF6]
N
OH
F3C
CF3
2
Scheme 1. Synthetic route to [Ir(hfppq)2(bipy)][PF6]ꢀ0.5H2O (1). Reagents and conditions: (i) CsF/Me3SiCF3/HCl/H2O, THF, r.t.; (ii) IrCl3ꢀ3H2O, ethoxyethanol/H2O (v/v: 3:1),
reflux.; (iii) bipy/K[PF6], CH2Cl2, MeOH, r.t.

J.-Y. Qiang et al. / Inorganica Chimica Acta 394 (2013) 184–189
187
120
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
(a)
Emission in solid
Emission in solution
Excitation in solution
100
80
60
40
20
0
350
400
450
500
550
600
650
700
750
250
300
350
400
450
500
550
600
650
Wavelength (nm)
Wavelength (nm)
(b)
Fig. 2. UV–Vis absorption spectra of the free ligand (black) and complex 1 (red)
measured in CH2Cl2 solution at room temperature. (For interpretation of the
references to color in this figure legend, the reader is referred to the web version of
this article.)
2000
1500
1000
500
0
charge transfer band (1MLCT) [d (Ir)–p⁄ (bipy)]. The 3MLCT bands
p
normally appear as no more than a shoulder on the 1MLCT bands as
appear around 550 nm in this case [11,32,33]. This information
indicates an efficient spin–orbit coupling that is prerequisite for
phosphorescent emission. The emission spectrum of complex 1
in the solid state is quite similar to that in solution except a slight
red shift was found. As shown in Fig. 3a, it exhibits the maximum
at 610 nm in the solid state which is red-shifted by 16 nm relative
to that in solution. The red-shift of the emission spectrum in the
solid state is related to strong intermolecular interactions, indica-
tive of slight excited-state quenching of the cationic cyclometalat-
ed iridium(III) complex in the solid state. Actually, the absorption
spectrum of complex 1 is similar to that of Ir(pq)2(N^N) reported
in the literature [34–36]. Compared with unmodified complexes
Ir(pq)2(N^N), the emission spectrum of complex 1 has a red shift
of ca. 34 nm [34–36]. Therefore, this has a great effect on the
lifetimes and quantum yield of this type of complex when the
spectra of the samples were recorded in the aerated or deareated
conditions.
0
2000
4000
6000
8000
10000
Time (ns)
Fig. 3. (a) Excitation spectrum of complex 1 measured in CH2Cl2 and emission
spectra of 1 in CH2Cl2 solution and in solid state. (b) PL decay of complex 1 in solid
state at room temperature.
We optimized the molecular structure of 1 and compared it with
its X-ray data. The Ir–C and Ir–N bond distances calculated for
complex 1 are listed in Table 2 together with the experimental val-
ues. Compared with X-ray values, theoretical values are overesti-
mated by the B3LYP functional [24]. This overestimation has
already been reported for similar cationic cyclometalated iridium
(III) complexes [41,42]. A schematic representation of the molecu-
lar orbital energies of complex 1 was investigated, while contours
of four HOMOs and LUMOs of complex 1 are illustrated in Fig. 4.
The HOMO (ꢂ7.95 eV) of complex 1 is an Ir(t2g) orbital (45.6%) com-
The quantum efficiency of complex 1 in dichloromethane at
room temperature is about 0.698 by using [Ru(bipy)3]2+
(Uem = 0.042) as the reference [37]. Normally cyclometalated irid-
ium(III) complexes are known to have the highest triplet quantum
yields due to three factors below: (a) The central iridium(III) nor-
mally undergoes the large d-orbital splitting compared to other
metals in the series. (b) The strong ligand field strength of the aro-
matic anion ligand increases the energy between the t2g and eg
orbitals, leading to an enhanced gap between the eg and LUMO
bined in an anti-bonding fashion with the phenyl carbon
p orbitals
of the ligand. (c) Close-lying
p–
p⁄ and MLCT states together with
of the hfppq ligand (41%), while the LUMO (ꢂ5.01 eV) is mostly on
the bipy ligand (94.1%), which implied that the substitution of fluo-
rine induces the lowering of HOMO and LUMO due to the electron-
withdrawing fluorine atoms. To gain insight into the absorption
processes of the investigated complex, we analyzed the 10 lowest
singlet–singlet and singlet–triplet excitations calculated at both
the ground state S0 and lowest excited triplet state T1 optimized
geometries. The orbital energies and compositions of the complex
are compiled in Table 3. The absorption spectrum of the present
complex shows an obvious feature with the low-energy spectral re-
gion being dominated by transition of mostly MLCT character,
the heavy atom effect enhance the spin–orbit coupling [4,38]. Thus,
high quantum efficiency realized for the present complex is note-
worthy and may be ascribed to the combination of one more fac-
tors enumerated above. The PL decay curve of complex 1 is
shown in Fig. 3b and the lifetime of 1 is 0.96 ls. Because long life-
time will give rise to the emission saturation and then decrease the
efficiency, suitable lifetimes of the cyclometalated Ir(III) complexes
(0.1–14 ls) make them ideal candidates for the OLEDs application
[11,39]. Compared with similar complexes reported in the litera-
tures [2–7], complex 1 has a shorter lifetime with a higher phos-
phorescence yield, which may be ascribed to incorporation of
fluorine into molecules [15–19]. The reduced radiationless deacti-
vation processes and decreased radiative lifetime raised by CF3
groups may increase the quantum yield [40].
while at higher energy, transitions of main p–
p⁄ character are also
found. At the ground-state geometry of complex 1, the lowest
DFT excited states of 1 are calculated to be triplet character at
568, 559 and 554 nm, essentially corresponding to HOMO–LUMO,

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J.-Y. Qiang et al. / Inorganica Chimica Acta 394 (2013) 184–189
Table 2
Structural data from X-ray crystal determination and optimized geometries of complexes at B3LYP/genecp level.
Bond length (Å)
Experimental (Å)
Calculated (Å)
Bond angles (Å)
Experimental (°)
Calculated (°)
Ir1–N1
Ir1–N2
Ir1–N3
Ir1–N4
Ir1–C2
Ir1–C20
2.116(6)
2.091(6)
2.177(7)
2.150(8)
2.011(8)
1.985(9)
2.1253
2.1249
2.2230
2.2241
2.0143
2.0140
N1–Ir1–N2
N1–Ir1–C2
N2–Ir1–C2
N2–Ir1–C20
N3–Ir1–C2
N4–Ir1–C2
N4–Ir1–C20
C2–Ir1–C20
171.8(3)
79.1(3)
94.9(3)
79.2(3)
170.0(3)
98.2(3)
170.4(3)
90.8(4)
171.4
79.8
94.1
79.8
170.2
98.2
170.0
90.2
HOMO-3
HOMO-2
HOMO-1
HOMO
LUMO
LUMO+2
LUMO+3
LUMO+1
Fig. 4. Schematic representation of the frontier orbitals of complex 1.
calculated to give rise to quite an intense HOMO–LUMO+2 transi-
tion at 500 nm (f = 0.0214), followed at higher energy by an intense
HOMOꢂ1-LUMO+1 transition at 395 nm (f = 0.0220), with still at
higher energy a HOMOꢂ1–LUMO+2 transition of relevant intensity
(f = 0.0204) calculated at 387 nm. The 500 and 395 nm transitions
are therefore assigned as having MLCT character, in agreement with
experimental values of 459 and 351 nm. The 387 nm transition
Table 3
Frontier molecular orbital energy (eV) and compositions (%) for complex at B3LYP/
genecp level.
Orbital
Energy
Ir
Ph
1.9
9.8
1
0.5
41
42.9
36
61.9
N1N2
N3N4
LUMO+3
LUMO+2
LUMO+1
LUMO
ꢂ4.17
ꢂ4.79
ꢂ4.86
ꢂ5.01
ꢂ7.95
ꢂ8.57
ꢂ8.76
ꢂ8.84
3
3.8
3.8
6.4
84.2
91.8
1.8
9.8
37.1
39
88.7
2.2
3.4
94.1
3.6
3.5
essentially corresponds to a p–
p⁄ excitation within the hfppq and
3.6
HOMO
45.6
16.5
23.1
22.4
bipy ligands therefore belonging to the
p–
p⁄ manifold extending
HOMO–1
HOMO–2
HOMO–3
into the UV region.
1.9
3.5
In summary, we have synthesized and structurally character-
ized a cationic cyclometalated iridium(III) complex, [Ir(hfppq)2
(bipy)][PF6]ꢀ0.5H2O (1), with fluorine-containing phenylquinolinyl
ligands. Complex 1, having both a short excited-state lifetime
and a high phosphorescence yield, should be advantageous to real-
ization of highly efficient OLEDs. DFT calculation was performed on
the ground and excited states of complex 1 to provide insight into
the structural, electronic and optical properties of the cationic
cyclometalated iridium(III) complex. Investigations into and appli-
cations of a series of related cyclometalated iridium(III) complexes
are currently in progress in our laboratory.
12.2
Ir, the central iridium(III) atom; Ph, two phenyl rings of the hfppq ligands.
N1N2, two phenylquinolinyl rings of the hfppq ligands.
N3N4, two pyridyl rings of bipy.
HOMO–LUMO+1 and HOMO–LUMO+2 MLCT transitions, as shown
in Table 4. This feature is related to spin-forbidden singlet–triplet
transitions which become allowed due to the strong spin–orbit cou-
pling of the iridium(III) center. The lowest singlet excited-state is

J.-Y. Qiang et al. / Inorganica Chimica Acta 394 (2013) 184–189
189
Table 4
Calculated lowest singlet–triplet and singlet–singlet transitions (nm, f > 0.02) related to the absorption spectra for complex 1.
nm
Excitation energy (eV)
Assignment
S0–T1
S0–T2
S0–T3
S0–Sn
567.9
559.3
553.5
n = 3
2.18
2.22
2.24
2.48
H ? L+1 (+56%)
H ? L (+35%), H ? L+2 (+28%)
H ? L (+49%), H ? L+2 (33%)
H ? L+2 (+92%)
499.7 (0.0214)
n = 6
394.9 (0.0220)
n = 8
386.7 (0.0204)
n = 10
373.0 (0.0244)
S0–Sn
S0–Sn
S0–Sn
3.14
3.21
3.32
Hꢂ1 ? L+1 (+72%)
Hꢂ1 ? L+2 (+80%)
Hꢂ2 ? L+1 (+47%), Hꢂ3 ? L+1 (22%)
For singlet–triplet transitions, oscillator strengths are zero because of the neglect of spin–orbit coupling in the TDDFT calculations.
H, HOMO; L, LUMO; L+1, LUMO+1, etc.
[20] SMART and SAINT+ for WINDOWS NT (version 6.02a), Bruker Analytical X-ray
Instruments Inc., Madison, Wisconsin, USA, 1998.
Acknowledgements
[21] G.M. Sheldrick, SADABS, University of Göttingen, Göttingen, Germany, 1996.
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This project was supported by the National Natural Science
Foundation of China (50903001 and 20771003) and the Hong Kong
Research Grants Council (Project No. 602310).
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