Highly phosphorescent iridium complexes containing both tridentate bis(benzimidazolyl)-benzene or -pyridine and bidentate phenylpyridine: Synthesis, photophysical properties, and theoretical study of Ir-bis(benzimidazolyl)benzene complex

Article abstract of DOI:10.1021/ic060796o

Novel mixed-ligand Ir(III) complexes, [Ir(L)(N∧C)X]ⁿ⁺ (L = N∧U∧N or N∧N∧N; X = Cl, Br, I, CN, CH₃CN, or -CCPh; n = 0 or 1), were synthesized, where NACAN = bis(N-methylbenzimidazolyl)benzene (Mebib) and bis(N-phenylbenzimidazolyl)benzene (Phbib), N∧N∧N = bis(N-methylbenzimidazolyl)pyridine (Mebip), and N∧C = phenylpyridine (ppy) derivatives. The X-ray crystal structures of [Ir(Phbib)(ppy)Cl] and [Ir(Mebib)(mppy)Cl] [mppy = 5-methyl-2-(2′-pyridyl)phenyl] indicate that the nitrogen atom of the ppy ligand is located trans to the coordinating carbon atom in Me- or Phbib, while the coordinating carbon atom in ppy occupies the trans position of Cl. [Ir(Mebip)(ppy)Cl]⁺ showed a quasireversible Ir(lll/IV) oxidation wave at +1.05 V, while the Ir complexes, [Ir(Mebib)(ppy)Cl], were oxidized at +0.42 V versus Fc/Fc⁺. The introduction of an Ir-C bond in [Ir(Mebib)(ppy)Cl] induces a large potential shift of 0.63 V in a negative direction. Further, the oxidation potential of [Ir(Mebib)(Rppy)X] was altered by the substitution of R, R′, and X groups. Compared to the oxidation potential, the first reduction potential revealed an almost constant value at -2.36 to -2.46 V for [Ir(L)(ppy)Cl] (L = Mebib and Phbib) and -1.52 V for [Ir(Mebip)(ppy)Cl. The UV-vis spectra of [Ir(Mebib)(R-ppy)X] show a clear singlet metal-to-ligand charge-transfer transition around 407-425 nm and a triplet metal-to-ligand charge-transfer transition at 498-523 nm. [Ir(Mebip)(PPy)Cl]⁺ emits at 610 nm with a luminescent quantum yield of Φ = 0.16 at room temperature. The phosphorescence of [Ir(Mebib)(ppy)X] was observed at 526 nm for X = CN and 555 nm for X = Cl with the high luminescent quantum yields, Φ = 0.77-0.86, at room temperature. [Ir(Phbib)(ppy)Cl] shows the emission at 559 nm with a luminescent quantum yield of Φ = 0.95, which is an unprecedentedly high value compared to those of other emissive metal complexes. Compared to the luminescent quantum yields of the Ir(ppy)₂(L) derivatives and [Ir(Mebip)(ppy)Cl]⁺, the neutral Ir complexes, [Ir(L)(R-ppy)X] (L = Me- or Phbib), reveal very high quantum yields and large radiative rate constants (k_r) ranging from 3.4 × 10⁵ to 5.5 × 10⁵ s^-1. The density functional theory calculation suggests that these Ir complexes possess dominantly metal-to-ligand charge-transfer and halide-to-ligand charge-transfer excited states. The mechanism for a high phosphorescence yield in [Ir(bib)(ppy)X] is discussed herein from the perspective of the theoretical consideration of radiative rate constants using perturbation theory and a one-center spin-orbit coupling approximation.

Full text of DOI:10.1021/ic060796o

Inorg. Chem. 2006, 45, 8907−8921
Highly Phosphorescent Iridium Complexes Containing Both Tridentate
Bis(benzimidazolyl)-benzene or -pyridine and Bidentate Phenylpyridine:
Synthesis, Photophysical Properties, and Theoretical Study of
Ir-Bis(benzimidazolyl)benzene Complex
Shinya Obara,† Masumi Itabashi,† Fumio Okuda,§ Satoru Tamaki,† Yoshiaki Tanabe,† Youichi Ishii,†
Koichi Nozaki,*,‡ and Masa-aki Haga*,†
Department of Applied Chemistry, Faculty of Science and Engineering, Chuo UniVersity, 1-13-27,
Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan, Department of Chemistry, Graduate School of
Science, Osaka UniVersity, 1-16, Machikaneyama, Toyonaka, Osaka 560-0043, Japan, and
Central Research Laboratories, Idemitsu Kosan Co., Ltd., 1280 Kami-Izumi, Sodegaura,
Chiba 299-293, Japan
Received May 10, 2006
+
Novel mixed-ligand Ir(III) complexes, [Ir(L)(N
CCPh; n 0 or 1), were synthesized, where N
(N-phenylbenzimidazolyl)benzene (Phbib), N
∧
C)X]n (L
)
)
N
∧
C
∧
N or N
∧
N
∧
N; X ) Cl, Br, I, CN, CH3CN, or
−
)
∧
C
)
∧
N
bis(N-methylbenzimidazolyl)benzene (Mebib) and bis-
∧
N
∧
N
bis(N-methylbenzimidazolyl)pyridine (Mebip), and N
∧
C
)
)
phenylpyridine (ppy) derivatives. The X-ray crystal structures of [Ir(Phbib)(ppy)Cl] and [Ir(Mebib)(mppy)Cl] [mppy
5-methyl-2-(2
carbon atom in Me- or Phbib, while the coordinating carbon atom in ppy occupies the trans position of Cl. [Ir-
(Mebip)(ppy)Cl]+ showed a quasireversible Ir(III/IV) oxidation wave at
1.05 V, while the Ir complexes, [Ir(Mebib)-
(ppy)Cl], were oxidized at C bond in [Ir(Mebib)(ppy)Cl] induces
0.42 V versus Fc/Fc+. The introduction of an Ir
a large potential shift of 0.63 V in a negative direction. Further, the oxidation potential of [Ir(Mebib)(Rppy)X] was
altered by the substitution of R, R , and X groups. Compared to the oxidation potential, the first reduction potential
revealed an almost constant value at 2.36 to 2.46 V for [Ir(L)(ppy)Cl] (L Mebib and Phbib) and 1.52 V for
[Ir(Mebip)(ppy)Cl. The UV vis spectra of [Ir(Mebib)(R-ppy)X] show a clear singlet metal-to-ligand charge-transfer
transition around 407 425 nm and a triplet metal-to-ligand charge-transfer transition at 498 523 nm. [Ir(Mebip)-
(ppy)Cl]+ emits at 610 nm with a luminescent quantum yield of Φ ) 0.16 at room temperature. The phosphorescence
of [Ir(Mebib)(ppy)X] was observed at 526 nm for X CN and 555 nm for X Cl with the high luminescent
quantum yields, Φ ) 0.77 0.86, at room temperature. [Ir(Phbib)(ppy)Cl] shows the emission at 559 nm with a
′
-pyridyl)phenyl] indicate that the nitrogen atom of the ppy ligand is located trans to the coordinating
+
+
−
′
−
−
)
−
−
∼
∼
)
)
∼
luminescent quantum yield of Φ ) 0.95, which is an unprecedentedly high value compared to those of other
emissive metal complexes. Compared to the luminescent quantum yields of the Ir(ppy)2(L) derivatives and [Ir-
(Mebip)(ppy)Cl]+, the neutral Ir complexes, [Ir(L)(R-ppy)X] (L
)
Me- or Phbib), reveal very high quantum yields and
large radiative rate constants (kr) ranging from 3.4
× ×
105 to 5.5 105 s-1. The density functional theory calculation
suggests that these Ir complexes possess dominantly metal-to-ligand charge-transfer and halide-to-ligand charge-
transfer excited states. The mechanism for a high phosphorescence yield in [Ir(bib)(ppy)X] is discussed herein
from the perspective of the theoretical consideration of radiative rate constants using perturbation theory and a
one-center spin−orbit coupling approximation.
Introduction
emitting diodes (OLEDs).1,2 It has recently been demon-
strated that luminescent cyclometalated Ir(III) complexes
such as Ir(ppy)3 and Ir(ppy)2(acac) (ppy ) phenylpyridinate
and acac ) acetylacetonate) may serve as triplet-emitting
dopants for constructing OLEDs.3-13 A significant research
The design of luminescent inorganic compounds continues
to attract great interest in the development of organic light-
* Authors to whom correspondence should be addressesd. Phone: 81
3-3817-1908. Fax: 81 3-3817-1895. E-mail: mhaga@chem.chuo-u.ac.jp
(M.-a.H.) and nozaki@ch.wani.osaka-u.ac.jp (K.N.).
† Chuo University.
(1) Baldo, M. A.; O’Brien, D. F.; Shoustrikov, A.; Sibley, S.; Thompson,
M. E.; Forrest, S. R. Nature 1998, 395, 151.
(2) Baldo, M. A.; Thompson, M. E.; Forrest, S. R. Nature 2000, 403,
750.
‡ Osaka University.
§ Idemitsu Kosan Co., Ltd.
10.1021/ic060796o CCC: $33.50
Published on Web 09/29/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 22, 2006 8907

Obara et al.
Chart 1. Examples of Ir Complexes with Tridentate Ligands
Chart 2. Chemical Structures of Ligands, Their Ir Complexes, and
effort has been made to improve the internal quantum
efficiency of OLEDs by use of Ir(III) cyclometalated
complexes with high luminescence quantum yields. As a
consequence, many bis- and tris-cyclometalated complexes
of Ir(III) with relatively high quantum efficiency (∼0.5) have
been synthesized. Recently, [Ir(ppy)2(X)2]- (X ) CN, NCS,
and NCO) have been reported to exhibit unprecedentedly
high quantum yields (∼1);14 however, these results are
puzzling because of the inability of other groups, including
us, to reproduce the data. On the other hand, only limited
examples of luminescent Ir(III) complexes with tridentate
ligands are known (Chart 1).15-20
Their Numberinga
The octahedral Ir complexes can be classified in categories
by the coordination atoms around the Ir ion, that is, Ir(N)6
type for [Ir(tpy)2]3+, Ir(N)5X for [Ir(tpy)(bpy)Cl]2+, Ir(N)4-
(C)2 for [Ir(bpy)(ppy)2]+, Ir(N)3(C)3 for [Ir(ppy)3], Ir(N)2-
(C)2(O)2 for [Ir(ppy)2(acac)], Ir(N)3(C)2O for [Ir(ppy)2(pic)],
and so forth. The coordination environment around the Ir-
(III) ion strongly affects the Ir 5d orbital energy, and the
excited-state properties of Ir complexes are governed by the
orbital mixing between Ir 5d and ligand π* orbitals. In
particular, the introduction of an Ir-C bond leads to a
stronger ligand field on the Ir ion, which induces the
destabilization of Ir 5d orbitals; as a result, there is larger
a The abbreviation of ligands and the proton-numbering system is also
shown for the assignment of H NMR spectra.
1
state mixing of the metal-to-ligand charge-transfer (MLCT)
excited state with ligand-centered ones. We have recently
synthesized the Ir(N)6- and Ir(N)5(C)-type Ir complexes, [Ir-
(Mebip)2]3+ and [Ir(Mebip)(Mebib)]2+ [Mebip ) bis(N-
methyl-2-benzimidazolyl)pyridine and Mebib ) bis(N-
methyl-2-benzimidazolyl)benzene].21,22 The mixed-ligand
complex, [Ir(Mebip)(Mebib)]2+, showed a higher lumines-
cence quantum yield than the Ir(N)6-type complex, [Ir-
(Mebip)2]3+. Furthermore, the comparison of the emission
quantum yields for [Ir(Mebip)2]3+, [Ir(Mebip)(Mebib)]2+, and
[Ir(Mebip)(bpy)Cl]2+ revealed that the mixed-ligand coor-
dination environments of the Ir ion surrounded by both
tridentate and bidentate ligands lead to higher-emission
quantum yields.
Therefore, the judicious selection of coordination atoms
and an appropriate ligand π-orbital system hold the key to
facilitating the development of highly emissive Ir complexes.
We report herein the synthesis and photophysical properties
of highly luminescent Ir(N)3(C)2(X)-type Ir(III) complexes
containing both tridentate N∧C∧N and bidentate N∧C
ligands, as shown in Chart 2. For comparison, the corre-
sponding Ir(N)4(C)(X)-type complex, [Ir(Mebip)(ppy)X]+,
was also synthesized.
(3) Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.; Lee, H.-
E.; Adachi, C.; Burrows, P. E.; Forrest, S. R.; Thompson, M. E. J.
Am. Chem. Soc. 2001, 123, 4304-4312.
(4) Huang, W. S.; Lin, J. T.; Chien, C. H.; Tao, Y. T.; Sun, A. S.; Wen,
Y. S. Chem. Mater. 2004, 16, 2480.
(5) Jenmifer, B. M.; Rayabarapu, D. K.; Cheng, C. H. AdV. Mater. 2004,
16, 2480.
(6) Chen, T. M.; Laskar, I. R. Chem. Mater. 2004, 16, 111.
(7) Cheng, C. H.; Sun, P. P.; Duan, J. P. AdV. Mater. 2003, 15, 224.
(8) Sun, I. W.; Tai, C. C.; Yang, C. H. J. Mater. Chem. 2004, 14, 947.
(9) Tsuboyama, A.; Iwawaki, H.; Furugori, M.; Mukaide, T.; Kamatani,
J.; Igawa, S.; Moriyama, T.; Miura, S.; Takiguchi, T.; Okada, S.;
Hoshino, M.; Ueno, K. J. Am. Chem. Soc. 2003, 125, 12971-12979.
(10) Tamayo, A. B.; Alleyne, B. D.; Djurovich, P. I.; Lamansky, S.; Tsyba,
I.; Ho, N. N.; Bau, R.; Thompson, M. E. J. Am. Chem. Soc. 2003,
125, 7377-7387.
(11) Grushin, V. V.; Herron, N.; LastName, D. L.; Marshell, W. J.; Petrov,
V. A.; Wang, Y. Chem. Commun. 2001, 1494.
(12) Li, J.; Djurovich, P. I.; Alleyne, B. D.; Yousufuddin, M.; Ho, N. N.;
Thomas, J. C.; Peters, J. C.; Bau, R.; Thompson, M. E. Inorg. Chem.
2005, 44, 1713.
(13) Hwang, F.-M.; Chen, H.-Y.; Chen, P.-S.; Liu, C.-S.; Chi, Y.; Shu,
C.-F.; Wu, F.; Chou, P.-T.; Peng, S.-M.; Lee, G.-H. Inorg. Chem.
2005, 44, 1344.
(14) Nazeeruddin, M. K.; Humphry-Baker, R.; Berner, D.; Rivier, S.;
Zuppiroli, L.; Graetzel, M. J. Am. Chem. Soc. 2003, 125, 8790-8797.
(15) Collin, J. P.; Dixon, I. M.; Sauvage, J. P.; Williams, J. A. G.;
Barigelletti, F.; Flamigni, L. J. Am. Chem. Soc. 1999, 121, 5009.
(16) Lo, K. K. W.; Chung, C. K.; Ng, D. C. M.; Zhu, N. New. J. Chem.
2002, 26, 81.
Experimental Section
Materials. Isophthalic acid (Aldrich), NH4PF6 (Wako), 1-phenyl-
2-(trimethylsilyl)acethylene (Aldrich), Pd(PPh3)4 (Kanto), 2,4-
difluorophenylbronic acid (Aldrich), pyridine dicarboxylic acid
(17) Yoshikawa, N.; Matumura-Inoue, T. Anal. Sci. 2003, 19, 761.
(18) Polson, M.; Fracasso, S.; Bertolasi, V.; Ravaglia, M.; Scandola, F.
Inorg. Chem. 2004, 43, 1950.
(19) Wilkinson, J. A.; Goeta, A. E.; Foster, C. E.; Williams, J. A. G. Inorg.
Chem. 2004, 43, 6513.
(20) Neve, F.; Crispini, A.; Serroni, S.; Loiseau, F.; Campagna, S. Inorg.
Chem. 2001, 40, 1093.
(21) Yutaka, T.; Obara, S.; Ogawa, S.; Nozaki, K.; Ikeda, N.; Ohno, T.;
Ishii, Y.; Sakai, K.; Haga, M.-a. Inorg. Chem. 2005, 44, 4737-4746.
(22) Yutaka, T.; Obara, S.; Haga, M.; Yokoyama, Y.; Sakai, K. Acta
Crystallogr., Sect. E 2005, 61, m1357-m1359.
8908 Inorganic Chemistry, Vol. 45, No. 22, 2006

Highly Phosphorescent Iridium Complexes
(Aldrich), N-methyl-1,2-phenylenediamine (Aldrich), 2-(p-tolyl)-
pyridine (mppy) (Aldrich), and IrCl3‚nH2O (Heraeus) were used
as received. The other synthetic reagents were purchased from
Kanto Kagaku and used as received. For the photophysical
measurements, dichloromethane, acetonitrile, N,N-dimethylforma-
mide (spectroscopic grade), methanol, and ethanol (HPLC grade)
were purchased from Kanto Kagaku and used as received. For the
electrochemical measurements, N,N-dimethylformamide for non-
aquesous titrimetry (Kanto) was used as supplied, and tetra-n-
butylammonium tetrafluoroborate (Nacalai) was purified by
recrystallization from EtOH. Ir(Mebip)Cl3, 2-(4′,6′-difluoro-
phenyl)pyridine (dfppy), Mebib, Mebip,23 and 2,6-bis(1-phenyl-
benzimidazol-2-yl)benzene (Phbib)7 were prepared according to the
literature.
Synthesis. [Ir(Mebib)Cl2]2. IrCl3‚4H2O (0.10 g, 0.27 mmol) and
Mebib (0.183 g, 0.54 mmol) were refluxed in methanol (15 mL)
for 5 h. After cooling to room temperature, the resulting precipitate
was collected and washed with methanol and then ether. This
complex is insoluble in common organic solvents and was therefore
used without purification for further preparation. Yield: 0.13 g
(82%). Anal. Calcd for [C22H17N4IrCl2]2: C, 44.00; H, 2.85; N, 9.33.
Found: C, 43.98; H, 3.00; N, 9.72. MALDI-MS: m/z 1201.91
(1201.09 required for [C44H35N8Ir2Cl4]+).
[Ir(Mebib)(ppy)I]. The synthetic procedure was the same as that
used for [Ir(Mebib)(ppy)Br], substituting NaBr for NaI. Yield: 50%.
Anal. Calcd for C33H25N5IrI: C, 48.89; H, 3.11; N, 8.64. Found:
C, 48.41; H, 3.30; N, 8.85. 1H NMR (CDCl3): δ 4.23 (s, 6H, N-Me),
5.61 (d, 1H, J ) 6.9 Hz, H1′), 6.20 (d, 1H, J ) 8.0 Hz, H1), 6.42
(t, 1H, J ) 8.3 Hz, H2′), 6.54 (t, 1H, J ) 8.0 Hz, H3′), 6.85 (t, 2H,
J ) 8.3 Hz, H2), 7.09 (t, 2H, J ) 7.7 Hz, H3), 7.17 (2H, m, H4),
7.31 (t, 1H, J ) 7.7 Hz, H6), 7.39 (d, 1H, J ) 9.2 Hz, H4′), 7.52
(t, 1H, J ) 7.2 Hz, H7′), 7.94 (d, 2H, J ) 7.4 Hz, H5), 8.03 (m,
2H, H5′,6′), 11.01 (d, 1H, J ) 5.2 Hz, H8′).
[Ir(Mebib)(ppy)(CN)]. [Ir(Mebib)(ppy)Cl] (0.05 g, 0.07 mmol)
and KCN (0.0091 g, 0.14 mmol) were heated by microwave
irradiation (650 W) in ethylene glycol (10 cm3) for 5 min. After
the mixture was cooled to room temperature, the addition of water
resulted in the formation of a yellow precipitate, which was
collected by filtration and washed with water and ether. The
purification was performed by recrystallization from CH2Cl2-
hexane. Yield: 0.03 g (61%). Anal. Calcd for C34H25N6Ir: C, 57.53;
1
H, 3.55; N, 11.84. Found: C, 57.75; H, 3.33; N, 11.45. H NMR
(CDCl3): δ 4.20 (s, 6H, N-Me), 5.79 (d, 1H, J ) 6.3 Hz, H1′),
6.19 (d, 2H, J ) 8.0 Hz, H1), 6.48 (t, 1H, J ) 7.5 Hz, H2′), 6.60
(t, 1H, J ) 6.3 Hz, H3′), 6.86 (t, 2H, J ) 8.0 Hz, H2), 7.09 (d, 2H,
J ) 8.0 Hz, H3), 7.19 (t, 2H, J ) 8.0 Hz, H6), 7.35 (t, 1H, J ) 7.5
Hz, H5′), 7.47 (d, 1H, J ) 8.0 Hz, H7′), 7.91 (d, 2H, J ) 7.5 Hz,
H5), 8.03 (d, 2H, J ) 4.5 Hz, H5′,6′), 10.48 (d, 1H, J ) 5.7 Hz,
H1′). FT-IR (KBr): 2102.6 cm-1 [ν(CN)]. MALDI MS: m/z 710.07
(710.18 required for [C34H25N6Ir]+).
[Ir(Phbib)Cl2]2. This complex was synthesized in a manner
similar to that for [Ir(Mebib)Cl2]2, except that bis(N-phenylbenz-
imidazolyl)benzene (Phbib) was used instead of Mebib. A pale
yellow precipitate was obtained. This complex was used as a starting
compound for the next reaction without further purification.
Yield: 66%.
[Ir(Mebib)(dfppy)Cl]. The mixture of [Ir(Mebib)Cl2]2 (0.1 g,
0.084 mmol) and dfppy (0033 g, 0.17 mmol) in glycerol (10 cm3)
was irradiated with a microwave (650 W, multimode) for 4 min
under a nitrogen atmosphere. After the mixture cooled to room
temperature, water (50 cm3) was added to give the yellow-orange
precipitate. The precipitate was collected by filtration and washed
with hexane and ether. Purification was performed by the diffusion
of ether to a CH2Cl2 solution of the complex. Yield: 0.046 g (32%).
Anal. Calcd for C33H23N5IrClF2: C, 52.48; H, 3.07; N, 9.27.
[Ir(Mebib)(ppy)Cl]. The mixture of [Ir(Mebib)Cl2]2 (0.1 g, 0.084
mmol) and ppy (0.46 g, 1.4 mmol) in glycerol (30 mL) was
irradiated in a microwave (650 W, multimode) for 6 min. After
the mixture cooled to room temperature, water (50 cm3) was added
to give a yellow-orange precipitate. After the precipitate was filtered
and washed with hexane and ether, an orange precipitate was
obtained. Yield: 0.03 g (23%). Anal. Calcd for C33H25N5IrCl: C,
1
1
55.11; H, 3.50; N, 9.74. Found: C, 54.86; H, 3.60; N, 9.85. H
Found: C, 52.12; H, 3.43; N, 9.55. H NMR (CDCl3): δ 4.25 (s,
NMR (CDCl3): δ 4.29 (s, 6H, N-Me), 5.84 (d, 1H, J ) 7.0 Hz,
H1′), 6.26 (d, 2H, J ) 8.0 Hz, H1), 6.47 (t, 1H, J ) 6.9 Hz, H2′),
6.60 (t, 1H, J ) 7.5 Hz, H3′), 6.91 (t, 2H, J ) 7.5 Hz, H2), 7.15 (t,
2H, J ) 7.5 Hz, H3), 7.24 (d, 2H, J ) 8.0 Hz, H4), 7.39 (t, 1H, J
) 8.0 Hz, H6), 7.50 (d, 1H, J ) 8.0 Hz, H4′), 7.64 (t, 1H, J ) 7.0
Hz, H7′), 7.97 (d, 2H, J ) 7.5 Hz, H5), 8.10 (m, 2H, H5′,6′), 10.61
(d, 1H, J ) 5.7 Hz, H8′). ESI MS: m/z 719.405 (719.143 required
for [C33H25N5IrCl]+).
6H, N-Me), 5.27 (d, 1H, J ) 9.5 Hz, H1′), 6.02 (t, 1H, J ) 10.5
Hz, H3′), 6.12 (d, 2H, J ) 8.6 Hz, H1), 6.88 (t, 2H, J ) 7.5 Hz,
H2), 7.12 (t, 2H, J ) 7.5 Hz, H3), 7.21 (d, 2H, J ) 8.0 Hz, H4),
7.34 (t, 1H, J ) 8.0 Hz, H6), 7.58 (t, 1H, J ) 7.5 Hz, H7′), 7.91 (d,
2H, J ) 7.5 Hz, H5), 8.04 (t, 1H, J ) 8.6 Hz, H6′), 8.41 (d, 1H, J
) 8.6 Hz, H5′), 10.57 (d, 1H, J ) 5.7 Hz, H8′). 19F NMR (CDCl3):
δ -110.0, -110.6. ESI MS: m/z 755.411 (755.123 required for
[C33H23N5F2IrCl]+).
[Ir(Mebib)(ppy)Br]. [Ir(Mebib)(ppy)Cl] (0.05 g, 0.07 mmol)
and NaBr (0.0215 g, 0.35 mmol) were heated by microwave
irradiation (650 W) in ethylene glycol (20 cm3) for 6 min. After
the mixture was cooled to room temperature, the addition of water
resulted in the formation of an orange precipitate, which was
collected by filtration and washed with water and ether. The
purification was performed by recrystallization from CH2Cl2-
hexane. Yield: 0.034 g (64%). Anal. Calcd for C33H25N5IrBr: C,
[Ir(Mebib)(mppy)Cl]‚2CH2Cl2. The synthetic procedure was
the same as that used for the [Ir(Mebib)(dfppy)Cl] analogue,
substituting dfppy for mppy. Orange crystals suitable for X-ray
analysis were obtained by the diffusion of ether to a CH2Cl2 solution
of the complex. Yield: 32%. Anal. Calcd for C34H27N5IrCl‚2CH2-
Cl2: C, 47.88; H, 3.46; N, 7.75. Found: C, 47.65; H, 3.20; N,
7.89. 1H NMR (CDCl3): δ 1.85 (s, 3H, Ph-Me), 4.29 (s, 6H, N-Me),
5.62 (s, 1H, H1′), 6.26 (d, 2H, J ) 8.0 Hz, H1), 6.40 (d, 1H, J )
6.3 Hz, H3′), 6.90 (t, 2H, J ) 7.5 Hz, H2), 7.13 (t, 2H, J ) 8.0 Hz,
H3), 7.22 (t, 2H, J ) 8.0 Hz, H4), 7.37 (t, 2H, J ) 7.0 Hz, H6),
7.58 (t, 1H, J ) 7.0 Hz, H7′), 7.96 (d, 2H, J ) 7.5 Hz, H5), 8.04
(m, 2H, H5′,6′), 10.56 (d, 1H, J ) 5.1 Hz, H8′). ESI MS: m/z 733.175
(733.155 required for [C34H27N5IrCl]+).
1
51.90; H, 3.30; N, 9.17. Found: C, 51.86; H, 3.60; N, 9.35. H
NMR (CDCl3): δ 4.29 (s, 6H, N-Me), 5.79 (d, 1H, J ) 7.4 Hz,
H1′), 6.26 (d, 2H, J ) 8.6 Hz, H1), 6.47 (t, 1H, J ) 7.4 Hz, H2′),
6.60 (t, 1H, J ) 7.4 Hz, H3′), 6.91 (t, 2H, J ) 7.7 Hz, H2), 7.15 (t,
2H, J ) 7.4 Hz, H3), 7.23 (m, 2H, H4), 7.38 (t, 1H, J ) 7.7 Hz,
H6), 7.49 (d, 1H, J ) 7.4 Hz, H4′), 7.62 (t, 1H, J ) 6.9 Hz, H7′),
7.98 (d, 2H, J ) 7.4 Hz, H5), 8.11 (m, 2H, H5′,6′), 10.81 (d, 1H, J
) 6.3 Hz, H8′).
[Ir(Mebib)(dfppy)CN]. The complex was synthesized in a
manner similar to that for [Ir(Mebib)(ppy)CN]. Yield: 72%. Anal.
Calcd for C34H23N6IrF2: C, 54.76; H, 3.11; N, 11.27. Found: C,
54.42; H, 3.50; N, 11.52. 1H NMR (CDCl3): δ 4.30 (s, 6H, N-Me),
5.31 (d, 1H, J ) 8.2 Hz, H1′), 6.09 (t, 1H, J ) 10.0 Hz, H3′), 6.18
(23) Addison, A. W.; Burke, P. J. J. Heterocycl. Chem. 1981, 18, 803-
805.
Inorganic Chemistry, Vol. 45, No. 22, 2006 8909

Obara et al.
(d, 1H, J ) 8.0 Hz, H1), 6.95 (t, 2H, J ) 7.5 Hz, H2), 7.19 (t, 2H,
J ) 7.5 Hz, H3), 7.29 (d, 2H, J ) 8.0 Hz, H4), 7.42 (t, 1H, J ) 8.0
Hz, H6), 7.57 (t, 1H, J ) 7.2 Hz, H7′), 7.98 (d, 2H, J ) 7.5 Hz,
H5), 8.12 (t, 1H, J ) 7.5 Hz, H6′), 8.45 (d, 1H, J ) 9.8 Hz, H5′),
10.55 (d, 1H, J ) 4.6 Hz, H8′). FT-IR (KBr): 2105.8 cm-1 [ν-
(CN)]. MALDI MS: m/z 745.95 (746.16 required for [C34H23N6F2-
Ir]+).
[Ir(Mebib)(ppy)(CH3CN)](OTf)‚Et2O. [Ir(Mebib)(ppy)Cl] (0.05
g, 0.07 mmol) and AgOTf (0.036 g, 0.14 mmol) in acetonitrile (20
cm3) were refluxed for 3 h. After the mixture was cooled to room
temperature, the solution was filtered through Celite. The resulting
yellow filtrate was concentrated in vacuo to one-fourth of its original
volume, and the addition of ether afforded the precipitation. The
purification was performed by recrystallization from CH2Cl2-ether.
Yield: 92%. Anal. Calcd for C36H28N6IrF3SO3‚Et2O: C, 50.68; H,
4.04; N, 8.86. Found: C, 50.26; H, 4.41; N, 8.51. 1H NMR
(CDCl3): δ 4.26 (s, 6H, N-Me), 5.64 (d, 1H, J ) 8.0 Hz, H1′),
6.06 (d, 2H, J ) 8.0 Hz, H1), 6.42 (t, 1H, J ) 8.0 Hz, H2′), 6.58
(t, 1H, J ) 8.0 Hz, H3′), 6.93 (t, 2H, J ) 7.5 Hz, H2), 7.20 (t, 2H,
J ) 7.5 Hz, H3), 7.46 (d, 2H, J ) 8.0 Hz, H4), 7.50 (t, 1H, J ) 8.0
Hz, H4′), 7.71 (m, 1H, H7′), 8.11 (d, 2H, J ) 8.0 Hz, H5), 8.22 (d,
2H, J ) 4.5 Hz, H5′,6′), 9.75 (d, 1H, J ) 5.7 Hz, H8′). ESI MS:
m/z 725.132 (725.201 required for [C35H28N6Ir]+).
[Ir(Mebib)(mppy)(CH3CN)](OTf). The complex was synthe-
sized in a manner similar to that for [Ir(Mebib)(ppy)(CH3CN)](OTf),
except that [Ir(Mebib)(mppy)Cl] (0.051 g, 0.07 mmol) was used
as a starting compound. Yield: 88%. Anal. Calcd for C37H30N6-
IrF3SO3: C, 50.05; H, 3.40; N, 9.46. Found: C, 49.63; H, 3.90; N,
1
10.07. H NMR (CDCl3): δ 1.79 (s, 3H, Ph-Me), 4.37 (s, 6H,
N-Me), 5.58 (s, 1H, H1′), 6.16 (d, 2H, J ) 8.6 Hz, H1), 6.49 (t, 2H,
J ) 8.0 Hz, H2′), 7.03 (t, 2H, J ) 7.5 Hz, H2), 7.30 (t, 2H, J ) 7.5
Hz, H3), 7.48 (d, 1H, J ) 7.5 Hz, H4′), 7.56 (d, 2H, J ) 8.0 Hz,
H4), 7.61 (t, 1H, J ) 8.0 Hz, H6), 7.76 (t, 1H, J ) 6.0 Hz, H7′),
8.20 (d, 2H, J ) 8.0 Hz, H5), 8.28 (m, 2H, H5′,6′), 9.79 (d, 1H, J )
4.0 Hz, H8′). ESI MS: m/z 739.124 (739.216 required for [C36H30N6-
Ir]+).
[Ir(Phbib)(ppy)(CH3CN)](OTf). The complex was synthesized
in a manner similar to that for [Ir(Mebib)(ppy)(CH3CN)](OTf),
except [Ir(Phbib)(ppy)Cl] was used as a starting compound.
Yield: 30%. Anal. Calcd for C46H32N6IrF3SO3: C, 55.36; H, 3.23;
1
N, 8.42. Found: C, 55.00; H, 3.40; N, 8.77. H NMR (CD3CN):
[Ir(Mebib)(mppy)(CCPh)]. The mixture of KF (20 mg, 0.339
mmol) and Me3Si-CCPh (20 mg, 0.113 mmol) in methanol (10
cm3) was stirred for 30 min at room temperature under a nitrogen
atmosphere. To the solution was added [Ir(Mebib)(mppy)(CH3CN)]-
(OTf) (0.05 g, 0.056 mmol), and the solution was refluxed for 2 h.
After the solution cooled to room temperature, a yellow precipitate
was formed, which was collected by filtration and washed with
methanol and ether. The complex was recrystallized from CH2-
Cl2-ether. Yield: 54%. Anal. Calcd for C42H32N5Ir: C, 63.14; H,
4.04; N, 8.76. Found: C, 62.96; H, 3.72; N, 9.02. 1H NMR
(CDCl3): δ 1.72 (s, 3H, Ph-Me), 4.31 (s, 6H, N-Me), 5.60 (s, 1H,
H1′), 6.19 (d, 2H, J ) 8.0 Hz, H1), 6.38 (d, 1H, J ) 8.0 Hz, H2′),
6.78 (d, 2H, J ) 6.9 Hz, C-Ph), 6.85 (t, 1H, J ) 7.5 Hz, C-Ph),
6.92 (m, 3H, J ) 8.0 Hz, C-Ph, H2), 7.19 (t, 2H, J ) 7.5 Hz, H3),
7.45 (m, 4H, H6,4,4′), 7.63 (q, 1H, H7′), 8.12 (d, 2H, J ) 4.6 Hz,
δ 5.71 (d, 1H, J ) 7.4 Hz, H1′), 6.24 (d, 2H, J ) 8.0 Hz, H1), 6.55
(t, 1H, J ) 6.9 Hz, H2′), 6.71-6.69 (m, 3H, H2,6), 6.89 (t, 1H, J )
8.0 Hz, H3′), 7.07-7.06 (m, 4H, H2,5), 7.20 (t, 2H, J ) 7.7 Hz,
H3), 7.58 (d, 2H, J ) 7.4 Hz, N-Ph), 7.63 (d, 1H, J ) 7.4 Hz, H4′),
7.76-7.69 (m, 8H, N-Ph), 7.84 (t, 1H, J ) 5.4 Hz, H7′), 8.32 (dt,
2H, J ) 6.9 and 3.4 Hz, H5′,6′), 9.90 (d, 1H, J ) 5.2 Hz, H8′). ESI
MS: m/z 861.06 (861.02 required for [C46H32N6Ir]+).
[Ir(Mebip)(ppy)Cl](PF6)‚2CH3CN. A mixture of [Ir(Mebip)-
Cl3] (0.1 g, 0.16 mmol) and ppy (0.03 g, 0.19 mmol) in glycerol
(30 mL) was irradiated in a microwave (650 W, multimode) for
12 min under a nitrogen atmosphere. After the mixture cooled to
room temperature, a saturated aqueous solution of NH4PF6 (20 cm3)
was added to give an orange-red precipitate. The resulting
precipitate was filtered and washed with hexane, CHCl3, and ether.
Single crystals were grown from a slow evaporation of ether into
a CH3CN solution of the complex. The crystals lost solvated Et2O
in vacuo. Yield: 0.03 g (61%). Anal. Calcd for C36H31ClF6N8IrP:
C, 45.59; H, 3.29; N, 11.82. Found: C, 45.94; H, 3.10; N, 11.65.
1H NMR (DMSO-d6): δ 4.59 (s, 6H, N-Me), 5.90 (d, 2H, J ) 8.6
Hz, H1), 6.08 (d, 1H, J ) 7.5 Hz, H1′), 6.73 (t, 1H, J ) 6.9 Hz,
H2′), 6.82 (t, 1H, J ) 7.5 Hz, H3′), 7.20 (t, 2H, J ) 8.0 Hz, H2),
7.51 (t, 2H, J ) 7.7 Hz, H3), 7.85 (d, 2H, J ) 8.0 Hz, H4′), 7.93
(m, 3H, H4,7′), 8.41 (t, 1H, J ) 8.0 Hz, H6′), 8.50 (t, 1H, J ) 8.3
Hz, H5), 8.57 (d, 1H, J ) 8.0 Hz, H5′), 8.82 (d, 2H, J ) 8.6 Hz,
H6), 10.35 (d, 1H, J ) 4.5 Hz, H8′). ESI MS: m/z 721.52 (721.15
required for [C32H25N6IrCl]+).
H
5′,6′), 8.15 (d, 2H, J ) 8.0 Hz, H5), 10.69 (d, 1H, J ) 5.7 Hz,
H8′). ESI MS: m/z 799.564 (799.229 required for [C42H32N5Ir]+).
[Ir(Phbib)(ppy)Cl]. This complex was synthesized in a manner
similar to that for [Ir(Mebib)(ppy)Cl], except that Phbib was used
instead of Mebib. The crude compound was purified by column
chromatography on silica with CH2Cl2-methanol (25:1 v/v) and
recrystallized from CH2Cl2-benzene-hexane. Red crystals were
obtained. Yield: 24%. Anal. Calcd for C43H31N5IrClO: C, 59.95;
1
H, 3.63; N, 8.10. Found: C, 59.93; H, 3.46; N, 7.60. H NMR
(CDCl3-d): δ 5.92 (d, 1H, J ) 7.4 Hz, H1′), 6.34 (d, 2H, J ) 8.6
Hz, H1), 6.55 (t, 1H, J ) 7.4 Hz, H2′), 6.68 (t, 1H, J ) 7.4 Hz,
H3′), 6.74 (m, 3H, H4,6), 6.95 (dt, 4H, J ) 7.3 and 3.6 Hz, H2,5),
7.07 (t, 2H, J ) 7.4 Hz, H3), 7.53 (t, 2H, J ) 3.1 Hz, N-Ph), 7.58
(d, 1H, J ) 8.0 Hz, H4′), 7.60-7.68 (m, 8H, J ) 3.7 and 1.9 Hz,
N-Ph), 7.70 (t, 1H, J ) 6.3 Hz, H7′), 8.12 (t, 1H, J ) 7.5 Hz, H6′),
8.17 (d, 1H, J ) 8.0 Hz, H5′), 10.71 (d, 1H, J ) 5.7 Hz, H8′).
Physical Measurements. 1H NMR, ESI MS, MALDI-TOF MS,
and UV-vis spectra were recorded with a Mercury 300 (Varian)
or JNM-ECA 500 (JEOL) spectrometer, a Micromass electrospray
LCT, and Shimadzu MALDI-TOF AXIMA-CFR mass spectrom-
eter, and a Hewlett-Packard 8453 UV-vis spectrophotometer,
1
[Ir(Phbib)(ppy)CN]‚2H2O. The complex was obtained by a
metathesis reaction of [Ir(Phbib)(ppy)Cl] with KCN under condi-
tions similar to those for [Ir(Mebib)(ppy)(CN)]. A yellow powder
was obtained. Yield: 21.0%. Anal. Calcd for C44H33N6IrO2: C,
respectively. For the assignment of H NMR spectra, the proton-
numbering system in Chart 1 is used in this paper. Electrochemical
measurements were carried out in a standard one-compartment cell
under N2 gas, equipped with a BAS platinum (φ 1.6 mm) or a BAS
glassy-carbon (φ 3 mm) working electrode, a platinum wire counter
electrode, and a Ag/Ag+ reference electrode with an ALS/CH model
660A electrochemical analyzer. The reference electrode was Ag/
AgNO3 (0.01 M in 0.1 M TBABF4 CH3CN), abbreviated as Ag/
Ag+. The ferrocene/ferrocenium (Fc/Fc+) oxidation process was
used as an internal reference standard, and all potentials are reported
versus Fc/Fc+. The E1/2 values for the Fc/Fc+ couple were +0.04
1
60.74; H, 3.82; N, 9.66. Found: C, 61.03; H, 3.46; N, 9.85. H
NMR (CDCl3-d): δ 5.92 (d, 1H, J ) 7.4 Hz, H1′), 6.35 (d, 2H, J
) 7.4 Hz, H1), 6.63 (t, 1H, J ) 7.2 Hz, H2′), 6.72-6.78 (m, 4H,
H3′,4,6), 6.97 (dt, 4H, J ) 7.4 and 3.7 Hz, H2,5), 7.09 (t, 2H, J ) 8.0
Hz, H3), 7.50 (t, 2H, J ) 6.0 Hz, N-Ph), 7.60 (d, 1H, J ) 8.0 Hz,
H4′), 7.63-7.72 (m, 9H, H7′, N-Ph), 8.16 (m, 2H, H5′,6′), 10.66 (d,
1H, J ) 5.7 Hz, H8′).
8910 Inorganic Chemistry, Vol. 45, No. 22, 2006

Highly Phosphorescent Iridium Complexes
V versus Ag/Ag+, which was found to be 0.33 V more negative
than that versus a saturated calomel electrode. Emission spectra
were recorded using a grating monochromator (Triax 1900, Jobin
Yvon) with a CCD image sensor (S7031, Hamamatsu). The spectral
sensitivity of the spectrofluorometer was corrected using a bromine
lamp (IPD 100V 500WCS, Ushio). A sample solution in a 1 mm
quartz cell was deoxygenated and excited using an LD-excited solid-
state Nd:YAG laser (355 nm, 440 ps, 13 kHz, 6 mW, JDS
Uniphase). The emission quantum yields of the Ir(III) compounds
were determined using 9,10-diphenylanthracene (DPA; Φ ) 0.91)
as a reference.24 Depolarized light was used in all cases to determine
emission quantum yields. The error in the emission quantum yields
is determined primarily by the accuracy of the sensitivity correction
in the spectral range from 450 to 800 nm, which is (5%. The
Huang-Rhys factors of accepting modes were determined by a
one-mode Franck-Condon analysis of emission spectra using eq
1 in ref 26b.25,26
For the determination of emission lifetimes, the deoxygenated
sample solution was photoexcited using a pulsed Nd:YAG laser.
The light from the sample was monochromated using a grating
monochromator (H-20, Jobin Yvon) and converted into current
signals by a photomultiplier tube (R3896, Hamamatsu). The
transient signals for 10 240∼2560 shots were accumulated on a
digitizing oscilloscope (HP 54520 Hewlett-Packard) to get the decay
profile of the emission intensity, which was fit to a single-
exponential function with convolution of the instrumental response
function of the measuring system. The time resolution of the system
was 2 ns.. The measurements at 77 K were performed using a
cylindrical quartz cell (1 mm inner diameter) and a liquid-nitrogen
Dewar.
For the computations with ADF, an uncontracted triple-ú Slater-
type orbital basis set with one polarization function was used
(denoted as tzp). The core orbitals (C and N, 1s; Cl, 1s2p; Ir, 1s4d)
were obtained as solutions of an all-electron calculation on the
isolated atom and kept frozen during the self-consistent field
calculation of the molecule. The zero-order regular approximation36-38
was used for relativistic corrections. Both the local spin density
approximation with the parametrization of Vosko, Wilk, and Nusair
(VWN)39 and the generalized gradient approximated correlation
functional proposed by Perdew and Wang (PW91) were employed.
Drawing of the molecular orbitals was performed using MOLE-
KEL.40,41
X-ray Diffraction Studies for 5‚2CH2Cl2, 9‚C6H14, 11OTf‚
Et2O, 13OTf, and 14PF6‚2CH3CN‚0.5Et2O. Red block crystals
of [Ir(Mebib)(mppy)Cl]‚2CH2Cl2 (5‚2CH2Cl2), yellow block crys-
tals of [Ir(Mebib)(ppy)(CH3CN)]OTf‚Et2O (11OTf‚Et2O), yellow
plate crystals of [Ir(Phbib)(ppy)(CH3CN)]OTf (13OTf), orange
block crystals of [Ir(Phbib)(ppy)Cl]‚C6H14 (9‚C6H14), and orange
blockcrystalsof[Ir(Mebip)(ppy)Cl]PF6‚2CH3CN‚0.5Et2O(14PF6‚2CH3-
CN‚0.5Et2O) were obtained by the slow diffusion of diethyl ether
or n-hexane into the corresponding dichloromethane or acetonitrile
solutions. Diffraction data for 5‚2CH2Cl2, 11OTf‚Et2O, 13OTf, 9‚
C6H14, and 14PF6‚2CH3CN‚0.5Et2O were collected on a Rigaku
Mercury CCD area detector with graphite monochromated Mo KR
radiation (λ ) 0.710 69 Å) at -150 ( 1 °C for the 2θ range of
5-55°. Intensity data were corrected for numerical absorptions
(NUMABS42 for 14PF6‚2CH3CN‚0.5Et2O) or empirical absorptions
(REQAB43 for 5‚2CH2Cl2, 11OTf‚Et2O, 9‚C6H14, and 13OTf) and
for Lorentz and polarization effects. Corrections for secondary
extinction were further applied for 14PF6‚2CH3CN‚0.5Et2O (coef-
ficient, 0.162 05), for 13OTf‚Et2O (coefficient, 30.82), and for 9‚
C6H14 (coefficient, 148.07).44 The structure solution and refinements
were carried out using the CrystalStructure package.45,46 The
positions of the non-hydrogen atoms were determined by heavy-
atom Patterson methods (SHELX-9747 for 14PF6‚2CH3CN‚0.5Et2O
and 5‚2CH2Cl2; PATTY48 for 11OTf‚Et2O) or direct methods
Density functional theory (DFT) calculations were performed
with the Gaussian 98, revision A11.3, suite (G98)27 and with the
Amsterdam Density Functional program package (ADF, version
2002).28-30 The basis functions used in the computations with G98
were Dunning-Hay’s split-valence double-ú for C, H, and N atoms
(D95) and the Hay-Wadt double-ú with a Los Alamos relativistic
effective core potential for heavy atoms (LANL2DZ).31,32 Becke’s
stylethree-parameterhybridfunctionalofB3PW91wasemployed.33-35
(35) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(36) Lenthe, E.; Baerends, E. J.; Snijders, J. G. J. Chem. Phys. 1993, 99,
4957.
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8943.
(38) Lenthe, E. V.; Leeuwen, R. V.; Baerends, E. J.; Snijders; J. G. J.
Quantum. Chem. 1996, 57, 281.
(39) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys. 1980, 58, 1200.
(40) Flukiger, P.; Luthi, H. P.; Portmann, S.; Weber, J. Swiss Center for
Scietific Computing, Manno, Switzerland, 2000-2002.
(41) Portmann, S.; Luthi, H. P. Chimia 2000, 54, 766.
(42) Higashi, T. NUMABS: Numerical Absorption Correction; Rigaku
Corp.: Tokyo, Japan, 1999.
(24) Murov, S. L.; Carmichael, I.; Hug, G. L. Handbook of Photochemistry,
2nd ed.; Marcel Dekker: New York, 1993.
(25) Kober, E. M.; Casper, J. V.; Lumpkin, R. S.; Meyer, T. J. J. Phys.
Chem. 1986, 90, 3722-3734.
(26) Islam, A.; Ikeda, N.; Nozaki, K.; Ohno, T. J. Photochem. Photobiol.,
A 1997, 106, 61-66.
(27) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels,
A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone,
V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.;
Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R.
L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara,
A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B. G.;
Chen, W.; Wong, M. W.; Andres, J. L.; Head-Gordon, M.; Replogle,
E. S.; Pople, J. A. Gaussian 98, version A11.3; Gaussian Inc.:
Pittsburgh, PA, 1998.
(28) Baerends, E. J.; Ellis, D. E.; Ros, P. Chem. Phys. 1993, 2, 42.
(29) Boerrigter, P. M.; Velde, G. t.; Baerends, E. J. Int. J. Quantum Chem.
1988, 33, 87.
(30) Velde, G. t.; Baerends, E. J. J. Comput. Phys. 1992, 99, 84.
(31) Dunning, T. H., Jr.; Hay, P. J. In Modern Theoretical Chemistry;
Schaefer, H. F., III, Ed.; Plenum: New York, 1976; Vol. 3.
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(33) Perdew, J. P. Phys. ReV. B: Condens. Matter Mater. Phys. 1986, 33,
8822.
(43) Jacobson, R. A. REQAB: PriVate Communication to Rigaku Corp.;
Rigaku Corp.: Tokyo, Japan, 1998.
(44) Larson, A. C. In Crystallographic Computing; Proceedings of an
International Summer School Organized by The Commission on
Crystallographic Computing of the International Union of Crystal-
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S. R., Huber, C. P., Eds.; Munksgaard: Copenhagen, Denmark, 1970;
pp 291-295.
(45) CrystalStructure 3.60: Single Crystal Structure Analysis Software;
Rigaku Corp: Tokyo, Japan; MSC: The Woodlands, TX, 2000-2004.
(46) Watkin, D. J.; Prout, C. K.; Carruthers, J. R.; Betteridge, P. W.
CRYSTALS Issue 10; Chemical Crystallography Laboratory: Oxford,
U. K., 1996.
(47) Sheldrick, G. M. SHELX-97: Program for the Refinement of Crystal
Structure; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
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Inorganic Chemistry, Vol. 45, No. 22, 2006 8911

Obara et al.
Table 1. X-ray Crystallographic Data for 5‚2CH2Cl2, 9‚C6H14, 11OTf‚Et2O, 13OTf, and 14PF6‚2MeCN‚0.5Et2O
5‚2CH2Cl2
9‚C6H14
11OTf‚Et2O
13OTf
14PF6‚2MeCN‚0.5Et2O
chemical formula
fw
C36H31Cl5IrN5
903.16
C49H43ClIrN5
929.59
C40H38F3IrN6O4S
948.05
C46H32F3IrN6O3S
998.07
C38H36ClF6IrN8O0.5
985.39
P
cryst color, habit
dimensions of crystal
cryst syst
space group
a, Å
red, block
0.30 × 0.15 × 0.10
monoclinic
P21/c
orange, block
0.90 × 0.80 × 0.80
monoclinic
P21/c
yellow, block
0.50 × 0.40 × 0.20
triclinic
P1
8.94(2)
yellow, plate
0.50 × 0.35 × 0.15
monoclinic
C2/c
orange, block
0.20 × 0.20 × 0.20
monoclinic
P21/c
14.360(6)
10.53(2)
26.59(3)
11.156(2)
b, Å
14.339(6)
20.44(3)
13.21(2)
10.36(1)
16.503(3)
c, Å
17.123(7)
18.15(5)
16.71(3)
29.29(3)
21.440(4)
R, deg
â, deg
γ, deg
V, Å3
78.19(8)
79.99(11)
82.88(9)
1894.9(50)
2
1.661
36.53
0.5335-1.0000
17204
107.460(6)
99.04(6)
99.76(4)
102.924(3)
3363.3(24)
4
1.783
44.13
0.6326-1.0000
12694
3859.1(14)
4
1.600
35.82
0.4692-1.0000
34574
7951.8(14)
8
1.667
34.85
0.5335-1.0000
36271
3847.2(13)
4
1.701
36.62
0.4129-0.5559
28274
Z
F
calcd, g cm-3
µ, cm-1
range of trans. factors
no. rflns measured
no. unique rflns
Rint
6562
0.090
9713
0.078
8112
0.047
11397
0.056
8668
0.068
no. rflns used
no. params refined
R [I > 3 σ(I)]a
2548 [I > 3σ(I)]
5407 [I > 3σ(I)]
6951 [I > 3σ(I)]
7401 [I > 3σ(I)]
3052 [I > 2σ(I)]
430
519
535
573
534
0.055 [I > 3σ(I)]
0.056 [I > 3σ(I)]
1.002
0.062 [I > 3σ(I)]
0.066 [I > 3σ(I)]
1.000
0.040 [I > 3σ(I)]
0.041 [I > 3σ(I)]
1.000
0.048 [I > 3σ(I)]
0.050 [I > 3σ(I)]
1.000
0.031 [I > 2σ(I)]
0.033 [I > 2σ(I)]
1.000
R
w [I > 3 σ(I)]b
GOF [I > 3 σ(I)]c
2
2
2
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑wFo ]1/2, w ) [pF0 + qσ(F0 ) + 0.5]-1 [p ) 0 (11OTf, 12‚C6H14, 14PF6‚2MeCN‚0.5Et2O),
0.0007 (5‚2CH2Cl2), 0.0001 (11OTf‚Et2O); q ) 0.185 (14PF6‚2MeCN‚0.5Et2O), 1.35 (5‚2CH2Cl2), 2.98 (11OTf‚Et2O), 2.075 (9‚C6H14), 2.033 (13OTf)].
c GOF ) [∑w(|Fo| - |Fc|)2/(Nobs - Nparams)]1/2
.
(SHELX-9747 for 9‚C6H14; SIR-9749 for 11OTf) and subsequent
Fourier syntheses (DIRDIF99).50 For 14PF6‚2CH3CN‚0.5Et2O, the
C(10) and C(17) atoms were refined with isotropic parameters,
while the solvating Et2O molecule positioned on the center of
symmetry was modeled over two positions with occupancies of
50%. For 5‚2CH2Cl2, the C(2), C(5), C(10), C(16), and C(18) atoms
were refined with isotropic parameters. For 9‚C6H14, the carbon
atoms of n-hexane were refined with isotropic parameters. All of
the other non-hydrogen atoms were refined on Fo [I > 2σ(I) for
14PF6‚2CH3CN‚0.5Et2O; I > 3σ(I) for the others] by full-matrix
least-squares techniques with anisotropic thermal parameters, while
all of the hydrogen atoms were placed at the calculated positions
(C-H distance of 0.95 Å) with fixed isotropic parameters. The
atomic scattering factors were taken from ref 51. Anomalous
dispersion effects were included in Fc.52 The values of ∆f′ and ∆f′′
were taken from refs 53 and 54. The maximum and minimum
residual peaks on the final difference Fourier maps were 0.63/-
0.63, 0.78/-0.88, 1.14/-1.47, 2.66/-2.43, and 2.27/-1.73 for
14PF6‚2CH3CN‚0.5Et2O, 5‚2CH2Cl2, 11OTf‚Et2O, 9‚C6H14, and
13OTf, respectively. Details of the X-ray diffraction study are
summarized in Table 1, and selected bond lengths, bond angles,
and selected torsion angles between planes are listed in Tables 1S
and 2S in the Supporting Information.
Results and Discussion
Syntheses and Characterizations. The reaction of Mebib
or Phbib with IrCl3‚4H2O in methanol gave an insoluble
yellow precipitate (P), of which MALDI-TOF mass spec-
trometry provides the mass peak corresponding to [Ir2(L)2-
Cl4]+ (L ) Mebib or Phbib). Because the compound was
insoluble in common organic solvents and water, this
compound P was used as a starting material without further
characterization. The corresponding Rh(III) complexes have
been synthesized by the reaction of ligand L with RhCl3‚
3H2O, in which the insoluble product might be formulated
as [Rh2(L)2X4] (L ) Hbib and Mebib; X ) Cl, Br, and I) by
1
FAB-MS and H NMR for [Rh2(Hbib)2Cl4] in DMSO-d6.55
New mixed-ligand Ir(III) complexes with the coordination
environment of [Ir(L)(N∧C)Cl] (L ) N∧N∧N and N∧C∧N)
were prepared by the reaction of compound P with the N∧C
ligand under microwave irradiation conditions in glycerol,
where Mebip, Me- or Phbib, and ppy were used as N∧N∧N,
N∧C∧N, and N∧C, respectively (see Chart 1). As for [Ir-
(L)(N∧C)Cl], two geometrical isomers are possible because
N∧C is coordinated to Ir in an asymmetrical manner; that
is, two isomers are shown in Chart 3 as an example of [Ir-
(Mebib)(ppy)Cl].
(49) Altomare, A.; Burla, M.; Camalli, M.; Cascarano, G.; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A.; Polidori, G.; Spagna, R. J. Appl.
Crystallogr. 1999, 32, 115-119.
(50) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de
Gelder, R.; Israel, R.; Smits, J. M. M. DIRDIF99: The DIRDIF-99
Program System; Technical Report of the Crystallography Laboratory;
University of Nijmegen: Nijmengen, The Netherlands, 1999.
(51) Cromer, D. T.; Waber, J. T. International Tables for X-ray Crystal-
lography; Ibers, J. A., Hamilton, W. C., Eds.; Kynoch Press:
Birmingham, England, 1974; Vol. IV, Table 2.2 A.
(52) Ibers, J. A.; Hamilton, W. C. Acta Crystallogr. 1964, 17, 781.
(53) Creagh, D. C.; McAuley, W. J. International Tables for X-ray
Crystallography; Wilson, A. J. C., Ed.; Kluwer Academic Publish-
ers: Boston, MA, 1992; Vol. C, Table 4.2.6.8.
When the reaction took place in ethylene glycol under
reflux conditions for 15 h, the reaction product gave a
complicated NMR spectrum, which arose from the formation
of a mixture of the two isomers. However, upon microwave
(54) Creagh, D. C.; Hubbell, J. H. International Tables for X-ray Crystal-
lography; Wilson, A. J. C., Ed.; Kluwer Academic Publishers: Boston,
MA, 1992; Vol. C, Table 4.2.4.3.
(55) Gayathri, V.; Leelamani, E. G.; Gowda, N. M. N.; Reddy, G. K. N.
Polyhedron 1999, 18, 2351.
8912 Inorganic Chemistry, Vol. 45, No. 22, 2006

Highly Phosphorescent Iridium Complexes
Figure 1. Time-dependent 1H NMR spectra of [Ir(Mebib)(ppy)Cl] in CD3-
CN-d3. Time after dissolution: (1) 0 h, (2) 17 h, and (3) 62 h. Isolated
sample of [Ir(Mebib)(ppy)MeCN](OTf) in CD3CN-d3 (4).
Chart 3. Two Possible Geometrical Isomers of [Ir(Mebib)(ppy)Cl]
Figure 2. Crystal structures of 5‚2CH2Cl2, 9‚C6H14, 11OTf‚Et2O, 13OTf,
and 14PF6‚2MeCN‚0.5Et2O.
irradiation conditions (6∼12 min irradiation at 650 W) in
glycerol, one geometrical isomer was selectively formed. To
increase the selectivity, the longer microwave irradiation time
and the use of a solvent such as glycerol with a higher boiling
point were required for the preparation of [Ir(Mebip)(N∧C)-
Cl], compared to that of [Ir(Mebib)(N∧C)Cl]. The pure
isomer was obtained by recrystallization from CH2Cl2-
hexane. Characterization was carefully done by elemental
during the course of the reaction. The time profile of the
change in absorbance follows first-order kinetics. In contrast,
[Ir(Phbib)(ppy)Cl] (9) and [Ir(Mebip)(ppy)Cl]+ (14) are less
reactive in CD3CN under the same conditions and the same
time domain as those for 1 and show no Cl- substitution
reaction with CD3CN at room temperature. The sharp
contrast for the reactivity difference between 1 and 14 is
attributable to the electron richness of 1 compared to 14.
[Ir(R3bib)(N∧C)Cl] (R3 ) Me or Ph) reacted with Ag(OTf)
in CH3CN to give the cationic complex [Ir(R3bib)(N∧C)-
(CH3CN)]+ separately. Further, the reaction of [Ir(Mebib)-
(ppy)(CH3CN)]+ (9) with phenylacetylene in the presence
of potassium fluoride provided a neutral complex, [Ir-
(Mebib)(ppy)(CCPh)] (8). All of the Ir(III) complexes were
characterized by 1H NMR, ESI- and MALDI-TOF MS, and
elemental analysis. Single crystals of 5, 9, 11, 13, and 14
suitable for X-ray crystallographic analysis were obtained
by recrystallization from CH2Cl2-hexane or CH3CN-ether,
some of which included the solvent.
Crystal Structures of 5‚2CH2Cl2, 9‚C6H14, 11OTf‚Et2O,
13OTf, and 14PF6‚2MeCN‚0.5Et2O. The X-ray crystal
structures of 5‚2CH2Cl2, 9‚C6H14, 11OTf‚Et2O, 13OTf, and
14PF6‚2MeCN‚0.5Et2O are shown in Figure 2. The selected
bond distances, bond angles, and torsion angles are provided
in Tables 2, 1S, and 2S (1S and 2S as Supporting Informa-
tion). The coordination geometries of Ir(III) centers for all
four complexes were found to be distorted octahedral. The
torsion angles are provided in Table 2S, showing that three
rings formed by bib tridentate coordination are almost
coplanar and that distortion from the planes is relatively small
1
analysis, H NMR, and ESI or MALDI-TOF mass spectra.
The metathesis reaction of [Ir(Mebib)(N∧C)Cl] with an
anionic ligand X (X ) Br, I, and CN-) in ethylene glycol
under microwave irradiation gave the corresponding complex
[Ir(Mebib)(N∧C)(X)] (X ) Br, I, and CN) quantitatively.
A
1H NMR chemical shift of the H8′ proton on the
coordinated ppy of [Ir(Mebib)(ppy)(X)] (X ) Cl, Br, I, and
CN) around δ 10.2∼10.7 ppm is a good indicator of the
anion exchange; that is, the chemical shift reveals the
downfield shift in the order X ) CN > Cl > Br > I, which
is consistent with the increase in the deshielding effect of
the Ir-X bond on neighboring H8′ protons. The Ir complexes
adopt the structure A shown in Chart 3, as confirmed by the
X-ray crystallographic analysis described later.
When [Ir(Mebib)(ppy)Cl] was kept in a CD3CN solution,
a new set of 1H signals gradually appeared (t1/2 ∼ 20 h; see
1
Figure 1). These new H signals are consistent with those
of [Ir(Mebib)(ppy)(CH3CN)](OTf) (11), which was sepa-
rately synthesized and isolated from the substitution reaction
of coordinated Cl with CH3CN in 1. Furthermore, when the
reaction of [Ir(Mebib)(ppy)Cl] (1) in CH3CN was monitored
by the absorption spectra, the isosbestic points were observed
Inorganic Chemistry, Vol. 45, No. 22, 2006 8913

Obara et al.
Table 2. Selected Bond Lengths (Å) for Complexes 5‚2CH2Cl2, 9‚C6H14, 11OTf‚Et2O, 13OTf, and 14PF6‚2MeCN‚0.5Et2O
11 13
5
9
14
Ir(1)-N(1)
Ir(1)-N(2)
Ir(1)-C(1)
Ir(1)-N(3)
Ir(1)-C(2)
Ir(1)-Cl(1)
2.07(1)
2.04(1)
1.92(2)
2.14(2)
2.00(1)
2.487(4)
Ir(1)-N(1)
Ir(1)-N(2)
Ir(1)-C(1)
Ir(1)-N(3)
Ir(1)-C(2)
Ir(1)-Cl(1)
2.058(8)
2.088(9)
1.92(1)
2.15(1)
1.99(1)
2.474(3)
Ir(1)-N(1)
Ir(1)-N(2)
Ir(1)-C(1)
Ir(1)-N(3)
Ir(1)-C(2)
Ir(1)-N(6)
N(6)-C(34)
2.053(4)
2.050(4)
1.945(6)
2.157(4)
2.013(5)
2.113(5)
1.136(7)
1.472(8)
Ir(1)-N(1)
Ir(1)-N(2)
Ir(1)-C(1)
Ir(1)-N(3)
Ir(1)-C(2)
Ir(1)-N(6)
N(6)-C(44)
2.029(5)
2.059(5)
1.965(6)
2.155(5)
2.007(6)
2.122(5)
1.138(8)
1.468(9)
Ir(1)-N(1)
Ir(1)-N(2)
Ir(1)-N(4)
Ir(1)-N(3)
Ir(1)-C(2)
2.037(8)
2.02(1)
1.972(7)
2.059(7)
2.00(1)
Ir(1)-Cl(1)
2.475(3)
C(34)-C(35)
C(44)-C(45)
the range of 1.90∼1.95 Å.59,60 Further, the Ir-Cbib bond
length in [Ir(Mebip)(Mebib)]2+ was found to be 2.018 Å,21
which is similar to the values reported for Ir(ppy)3 deriva-
tives. Therefore, the Ir-Cbib bond lengths appear to be
influenced by not only the steric requirement for the
tridentate accommodation of Mebib but also electronic
effects. In [Ir(Phbib)(ppy)Cl], the N-phenyl groups adopt a
tilted orientation ∼66° to the tridentate Phbib plane (see
Table 2S, Supporting Information). In 14, the Mebip ligand
is coordinated to the Ir atom in a tridentate manner, and the
Ir-C bond in the Ir-ppy moiety occupies the trans position
of the Ir-Cl bond. The Ir-Nppy bond length is 2.059(7) Å.
The Ir-Cl and Ir-Cppy bond lengths were found to be 2.475-
(3) and 2.00(1) Å, respectively, with a trans influence of
the Ir-Cppy bonds being observed.
Electrochemistry. Electrochemical data for all of the new
Ir(III)-Mebib complexes are summarized in Table 3,
together with the UV spectroscopic data. Complex 14 in CH3-
CN shows a quasireversible Ir(III/IV) oxidation wave at
+1.05 V versus Fc+/0 and two reduction waves at -1.52
and -1.91 V versus Fc+/0 as reversible and irreversible
processes, respectively. Similarly, a reversible Ir(III/IV)
oxidation of complex 1 in N,N′-dimethyl formamide (DMF)
occurred at +0.42 V versus Fc+/0, while two quasireversible
and irreversible reduction processes were observed at -2.42
and -2.80 V versus Fc+/0 respectively for Mebib and ppy
reductions. The introduction of an Ir-C bond into Ir(N)3-
(C)2X-type complex 1 induces a large negative shift (∼0.6
V) in the Ir(III/IV) oxidation potential, compared to Ir(N)4-
(C)X-type complex 14. The Ir(III/IV) oxidation potential is
shifted to the negative direction in the order [Ir(Mebib)-
(dfppy)CN] (7) (+0.77 V) > [Ir(Mebib)(ppy)CN] (4) (+0.65
V) > [Ir(Mebib)(dfppy)Cl] (6) (+0.57 V) > [Ir(Mebib)(ppy)-
Cl] (1) (+0.42 V) > [Ir(Mebib)(mppy)Cl] (5) (+0.40 V),
although the first reduction potentials are almost unchanged
for all of these complexes (∼-2.40 V vs Fc+/0). The
substitution of X from Cl to CH3CN on [Ir(Mebib)(ppy)X]n+
induces a large positive shift in the oxidation potential.
UV-vis Absorption Spectra. The UV-vis spectrum of
1 in CH2Cl2 shows the MLCT bands at 425, 472, and 523
nm in addition to the ππ* transition at 244 nm for ppy and
299 and 360 nm for the Mebib ligand (see Figure 3). Upon
the substitution of Cl by CN or ppy by dfppy, a shorter
wavelength shift of the MLCT band was observed (Figure
Chart 4. Tridentate Pincer Ligand Systems
except in 4 and 5. The X-ray structure of 5 reveals that the
Ir-Cbib bond in the tridentate Ir(Mebib) moiety is located
trans to the nitrogen atom in the mppy ligand, while the other
Ir-Cppy bond in the Ir(mppy) moiety is trans to the Ir-Cl
bond, confirming the structure of the isomers as isomer A
in Chart 3. For the structure of 11, the CH3CN ligand
occupied a trans position in relation to the coordinating
carbon atom in ppy, as shown in Figure 2. In four complexes,
5, 9, 11, 13, two Ir-C bonds were located at the cis position.
The cyclometalated Ir-C bonds in the mixed-ligand Ir(bib)-
(ppy) system induce a strong trans influence on the bond
length; that is, the bond lengths of the central Ir-Cbib bond
are 1.92(2) and 1.945(6) Å for 5 and 9, while the Ir-Nppy
bonds, which are located trans to the Ir-Cbib bond, are 2.14-
(2) and 2.157(4) Å, respectively (Table 2). These Ir-Nppy
bond lengths are longer than those of Ir-Cppy [2.00(1) and
2.013(5) Å], which are within the range of typical Ir-C bond
lengths. Furthermore, the Ir-Cl bond length at the position
trans to the Ir-Cppy bond in 5 [2.487(4) Å] is longer than
that seen in [Ir(tpy)(dmbpy)Cl]2+ (tpy ) 2,2′:6′,2′′-terpyri-
dine, dmbpy ) 4,4′-dimethyl-2,2′-bipyridine) (2.357 Å).56
These results indicate that the strong σ donation in the Ir-C
bond results in the elongation of Ir-N and Ir-Cl bonds at
the trans position. A similar trans influence of Ir-C bonds
has been observed in the X-ray crystallographic structures
of fac- and mer-Ir(tppy)3 [tppy ) 2-(p-tolyl)pyridine].10 In
particular, the Ir-Cbib bond lengths are relatively short
compared to those of other Ir-C bonds reported in fac-Ir-
(tppy)3 derivatives (average Ir-C ) 2.018 Å). The two fused
five-membered coordination modes in Ir(N∧C∧N) com-
plexes are relevant to the “pincer”-ligated metal complexes
such as [Ir(P∧C∧P)H2], [Pt(N∧C∧N)Cl], and [Pd(N∧C∧N)l]
(see Chart 4), in which the Ir-C bond distances range from
2.00 to 2.09 Å57,58 and the Pd or Pt-C bond distances are in
(56) Yoshikawa, N.; Sakamoto, J.; Kanehisa, N.; Kai, Y.; Matsumura-Inoue,
T.; Takashima, H.; Tsukahara, K. Acta Crystallogr., Sect. E 2003,
59, m830.
(57) Gottker-Schnetmann, I.; LastName, W. P.; Brookhart, M. Organo-
metallics 2004, 23, 1766.
(59) Gagliado, M.; Rodriguez, G.; Dam, H. H.; Lutz, M.; Spek, A. L.;
Havenith, R. W. A.; Coppo, P.; De Cola, L.; Hartl, F.; van Klink, G.
P. M.; van Koten, G. Inorg. Chem. 2006, 45, 2143.
(58) Zhang, X.; Emge, T. J.; Ghost, R.; Goldman, A. S. J. Am. Chem. Soc.
2005, 127, 8250.
(60) Williams, J. A. G.; Beeby, A.; Davies, E. S.; Weistein, J. A.; Wilson,
C. Inorg. Chem. 2003, 42, 8609-8611.
8914 Inorganic Chemistry, Vol. 45, No. 22, 2006

Highly Phosphorescent Iridium Complexes
Table 3. Absorption Spectral and Electrochemical Data for Ir(Mebib)(R-ppy)X at Room Temperaturea,b
λabs
E1/2ox (∆Ep)c or EPa
E1/2red (∆Ep)c or EPc
complex
nm (ꢀ × 103/M-1 cm-1
)
V vs Fc+/Fc (mV)
0.42 (60)
V vs Fc+/Fc (mV)
[Ir(Mebib)(ppy)Cl] (1)
244 (50.0), 299 (38.7), 360 (7.7), 404 (14.0),
425 (15.6), 472(3.1), 523(0.84)
-2.46 (66),d -2.80e
-2.45 (68),d -2.82e
-2.44 (70),d -2.81e
-2.42 (66),d -2.79e
-2.46 (65),d -2.82e
-2.40 (65),d -2.79e
-2.37 (66),d -2.70e
-2.49 (65),d -2.90e
[Ir(Mebib)(ppy)Br] (2)
[Ir(Mebib)(ppy)I] (3)
244 (40.0), 300 (29.4), 361 (5.44), 403 (11.4),
424 (12.9), 470sh (2.64), 531 (0.50)
250sh (53.5), 267sh (42.4), 299 (38.5), 359 (8.66),
404 (15.1), 423 (15.9), 474sh (3.49),531 (0.88)
242 (54.9), 299 (37.8), 353 (7.9), 392 (15.8),
413 (19.0), 506 (0.35)
236 (50.0), 300 (44.6), 361 (6.5), 405 (13.5),
426 (15.2), 473 (3.0), 526 (0.75)
245 (61.1), 299 (45.6), 355 (8.7), 397 (17.4),
418 (18.7), 455 (3.7), 514 (0.50)
0.46 (60)
0.45 (60)
0.65 (59)
0.40 (70)
0.57 (60)
0.77 (58)
0.61 (65)
[Ir(Mebib)(ppy)CN] (4)
[Ir(Mebib)(mppy)Cl] (5)
[Ir(Mebib)(dfppy)Cl] (6)
[Ir(Mebib)(dfppy)CN] (7)
[Ir(Mebib)(mppy)(CCPh)] (8)
242 (52.4), 298 (35.0), 349 (7.7), 386 (15.2),
407 (17.6), 498 (0.30)
236 (68.3), 272(56.2), 298 (63.7), 360 (6.9),
419 (12.9), 437 (15.9), 482 (3.4), 530 (0.88)
301 (39.3), 406 (15.3), 429 (17.1), 527 (0.52)
298 (43.0), 393 (18.1), 414 (21.5), 510 (0.38)
247 (50.5), 298 (37.2), 380 (17.9), 398 (18.2),
496 (0.36)
245 (65.4), 296 (50.1), 379 (22.2), 396 (23.1),
490 (0.27)
245sh (64.9), 297 (32.8), 381 (17.3), 400 (17.4),
498 (0.61)
[Ir(Phbib)(ppy)Cl] (9)
0.52 (60)
0.78 (60)
0.81 (65)
-2.36 (68),d -2.78e
-2.24 (60),d -2.69e
-2.32,e -2.57,e -2.75e
[Ir(Phbib)(ppy)CN] (10)
[Ir(Mebib)(ppy)(MeCN)]+ (11)b
[Ir(Mebib)(mppy)(MeCN)]+ (12)
[Ir(Phbib)(ppy)(MeCN)]+ (13)
[Ir(Mebip)(ppy)Cl](PF6) (14)
f
f
f
f
242 (38.2), 313 (27.2), 348 (23.9), 510 (0.42),
575 (0.14)
1.05e
-1.52 (68),d -1.91e
a UV-vis spectra were measured in CH2Cl2 and electrochemical data in DMF unless otherwise noted. b Electrochemical measurement was done in CH3CN.
c Peak-to-peak separation. d Quasireversible process. e Irreversible process. f Not measured.
Figure 3. UV spectra of Ir complexes 1 (red) and 4 (black) in CH2Cl2 and 14 (black, dashed line) in CH3CN at room temperature.
3). In contrast, the UV absorption maxima of [Ir(Mebip)-
(ppy)X] are unaltered by the substitution of X ) Cl to Br or
I, which is unexpected. Further, the alternation of methyl to
a phenyl group on the benzimidazole moiety leads to a
slightly longer wavelength shift on the MLCT band, while
the spectral shapes are almost identical. The band around
510∼530 nm can be assigned as a triplet MLCT band,
compared to other reported Ir(ppy) complexes. This MLCT
band for [Ir(Mebib)(R-ppy)X] is shifted to a shorter wave-
length in the order 5 > 1 > 6 > 4 > 7, and at the same
time, the intensity of the band is decreasing in this order
(Table 3).
Emission Spectra. Figure 4 shows the emission spectra
of 1 in Ar-saturated CH2Cl2 at 295 K and CH2Cl2-toluene
(1:1 v/v) at 77 K. The complex exhibits a strong emission
band with a vibrational structure at around 555 nm with a
lifetime of 1.20 µs at room temperature. In a glass matrix at
77 K, the emission spectra of all of the Ir(III)-Mebib and
Ir(III)-Phbib complexes exhibited almost the same vibra-
tional structures with a small sideband at about 1500 cm-1
lower, while for the Ir-Mebip complex 14, a vibrational
sideband appeared approximately 1360 cm-1 lower with a
relatively high intensity. Emission maxima of 1 were tuned
by the substitution of ppy or Cl; that is, the maxima were
shifted to a shorter wavelength in the order 1 ∼ 5 > 6 > 4
> 7 (Figure 5 and Table 4). A strong relationship between
UV spectral data and electrochemical data has been re-
ported.61 In the Ir-Mebib complexes, plots of emission
maxima versus the redox potential are shown in Figure 6.
The Ir(III/IV) oxidation potential shows a good linear
relationship with the emission maxima; in contrast, the
reduction potential appears to remain almost constant upon
changes in the emission maxima. This linear relationship
strongly indicates that the excited state of [Ir(L)(N∧C)X]
complexes has considerable MLCT character.
The emission maxima of the Ir complexes shift to higher
energy (600∼675 cm-1) on going from room temperature
to 77 K. A relatively large rigidochromic shift indicates a
(61) Vlcek, A. A.; Dodsworth, E. S.; Pietro, W. J.; Lever, A. B. P. Inorg.
Chem. 1995, 34, 1906 and references therein.
Inorganic Chemistry, Vol. 45, No. 22, 2006 8915

Obara et al.
Figure 4. Emission spectra of complexes 1 (a) and 9 (b) in Ar-saturated CH2Cl2 at room temperature (red) and in CH2Cl2-toluene (1:1 v/v) (red) at 77
K (blue) and 14 (c) in Ar-saturated CH3CN at room temperature (red) and in DMF-EtOH-MeOH (1:5:5 v/v) at 77 K (blue).
s-1 for [Ir(Mebib)(ppy)CN] to 5.5 × 105 s-1 for [Ir(Mebib)-
(mppy)Cl], while those of the nonradiative rate constant (knr)
are from 0.6 × 105 s-1 for [Ir(Mebib)(dfppy)CN] to 1.6 ×
105 s-1 for [Ir(Mebib)(mppy)Cl]. The kr values are greater
than those reported for [Ir(ppy)3] (2.0 × 105 s-1) and [Ir-
(ppy)2(acac)] (2.1 × 105 s-1). The substitution of the ligand
L from Mebip to Mebib in [Ir(L)(ppy)Cl] leads to a shorter
wavelength shift of emission maxima and an increasing
quantum yield. On the other hand, the emission maxima of
[Ir(Mebib)(ppy)X] are unaltered by the substitution of Xd
Cl to Br or I, which is reflected in the UV absorption spectra.
As for the complexes [Ir(Mebib)(ppy)(CH3CN)]+ and [Ir-
(Mebib)(mppy)(CH3CN)]+, the substitution of Cl with CH3-
Figure 5. Emission spectra of Ir complexes 7 (blue line), 4 (green), 6
(orange), and 1 (red) in CH2Cl2-toluene (1:1 v/v) at 77 K.
CN leads to a drastic decrease in the luminescent quantum
yield (Φ ) 0.24 and 0.22, see Table 4), while a high quantum
yield is maintained for the complex [Ir(Mebib)(mppy)-
(CCPh)] prepared by the replacement of Cl in the complex.
Plots of kr and ln knr values versus emission energy are shown
in Figures 7a and b. Although radiation theory predicts that
the kr value is proportional to the cube of the emission
greater polarity of the excited state. A similar rigidochromic
effect has been previously reported for [Ir(ppy)3] derivatives
and emissive metal complexes.9,62 Surprisingly, all of the
present neutral Ir(III) complexes [Ir(L)(R-ppy)X] (L ) Mebib
and Phbib; R ) H, CH3, and F; X ) Cl and CN) exhibited
a high luminescent quantum yield (Φ ) 0.63∼0.95), with
energy,63 the kr values of these Ir complexes fall as the
[Ir(Phbib)(ppy)Cl] having the highest yield of Φ ) 0.95.
emission energy increases (Figure 7a). However, employing
Several Ir complexes containing bidentate ppy derivatives
Mebip instead of Mebib leads to a decrease in the emission
have been reported to have high quantum yields; for example,
energy, and the kr values decrease considerably. The varia-
tions in the radiative rate with tridentate ligands or X are
relevant to the phosphorescence mechanism of these Ir
complexes, and evaluations of kr values based on DFT
calculations are described later.
[Ir(tppy)3] and [Ir(ppbi)2(acac)] have luminescent quantum
yields of 0.54 and 0.78, respectively.3,10 However, variations
in the substituent of ppy leads to large changes in the
quantum yield. In the present system, the luminescent
quantum yields were high even if the substituent of ppy was
changed. The values of the radiative rate constant (kr) for
the [Ir(Mebib)(R-ppy)X] complexes range from 3.9 × 105
On the basis of the linear relationship of ln knr versus the
emission energy (Figure 7b), the present Ir system closely
(62) Cummings, S. D.; Eisenberg, R. J. Am. Chem. Soc. 1996, 118, 1949-
1960.
(63) Strickler, S. J.; Berg, R. A. J. Chem. Phys. 1962, 37, 814.
8916 Inorganic Chemistry, Vol. 45, No. 22, 2006

Highly Phosphorescent Iridium Complexes
Table 4. Photophysical Properties of [Ir(Mebib)(Rppy)X] in Ar-Saturated CH2Cl2
complex
λ
em/nm
77 Kb
SM, ν/cm-1
77 K
τ/ms
Φa
kr
knr
295 K
555
295 K
77 Kb
105 s-1
105 s-1
[Ir(Mebib)(ppy)Cl](1)
535, 580, 633
0.85, 1490
1.78
(1.61)c
1.73
1.83
2.17
1.40
1.63
2.50
1.46
1.55
2.02
0.96
0.79
2.00
2.22
(2.84)c
2.28
2.28
2.50
2.28
2.26
2.70
2.33
2.17
2.45
2.82
2.86
13.5
0.78
(0.59)c
0.87
0.81
0.84
0.77
0.86
0.85
0.75
0.95
0.89
0.24
0.22
0.16
4.4 ( 0.30
(3.7 ( 0.35)c
5.0 ( 0.26
4.4 ( 0.25
3.9 ( 0.26
5.5 ( 0.36
5.3 ( 0.33
3.4 ( 0.20
5.1 ( 0.30
6.1 ( 0.29
4.4 ( 0.24
2.5 ( 0.52
2.9 ( 0.75
0.80 ( 0.25
1.2 ( 0.30
(2.6 ( 0.35)c
0.8 ( 0.26
1.0 ( 0.25
0.7 ( 0.26
1.6 ( 0.36
0.9 ( 0.33
0.6 ( 0.20
1.7 ( 0.30
0.3 ( 0.29
0.5 ( 0.24
7.9 ( 0.52
9.9 ( 0.75
4.20 ( 0.25
[Ir(Mebib)(ppy)Br](2)
[Ir(Mebib)(ppy)I](3)
[Ir(Mebib)(ppy)CN](4)
553
553
526
556
540
517
563
562
533
513
512
610
532, 579, 632
533, 579, 632
510,552,600
536,582,636
521, 565,616
501, 542, 590
542, 590, 645
541, 588, 645
515, 558, 608
520, 564, 614
519, 562, 614
578
0.78, 1490
0.76, 1480
0.84, 1510
0.77, 1490
0.82, 1480
0.82, 1490
0.74, 1520
0.74, 1490
0.80, 1490
0.83, 1510
0.85, 1500
1.05, 1360
[Ir(Mebib)(mppy)Cl](5)
[Ir(Mebib)(dfppy)Cl] (6)
[Ir(Mebib)(dfppy)CN] (7)
[Ir(Mebib)(mppy)(CCPh)] (8)
[Ir(Phbib)(ppy)Cl] (9)
[Ir(Phbib)(ppy)CN](10)
[Ir(Mebib)(ppy)(MeCN)]+ (11)
[Ir(Mebib)(mppy)(MeCN)]+ (12)
[Ir(Mebip)(ppy)Cl](PF6) (14)
a The emission quantum yields of the Ir(III) compounds were determined using DPA () 0.91)24 as a reference. The error in the yields is (5%. b In
CH2Cl2-toluene (1:1 v/v). c In Ar-saturated CH3CN.
Figure 6. Plots of emission energies vs redox potentials (the number in
the plots corresponds to the complex numbering).
Figure 8. Frontier molecular orbitals of complex 5, which were obtained
by DFT calculation at the B3PW91/LANL2DZ level.
fashion, while the lowest unoccupied molecular orbital
(LUMO) and LUMO+1 originate from Mebib π* and ppy
π* orbitals, respectively.
The energy differences between the HOMOs and occupied
Figure 7. Plots of kr values vs emission energy (a) and plots of ln knr vs
emission energy (b).
orbitals with a larger contribution of Ir 5d are one of the
important factors determining the kr values of phosphores-
cence.65,66 Orbital energy levels for complexes 5, 11, and
14 are depicted in Figure 9 together with their orbital
parentage. The differences in orbital energy between HOMO
and HOMO-1 are 0.20 eV for 5, 0.33 eV for 11, and 0.50
follows the energy gap law,64 except for X ) CH3CN. The
Ir complexes with CH3CN show somewhat shorter lifetimes
at room temperature, while the lifetimes at 77 K are
comparable to those of the other Ir-Mebib complexes,
suggesting the presence of additional decay pathways involv-
3
ing thermally accessible excited states such as via dd.
eV for 14, reflecting orbital interactions with the ligands.
DFT Calculations. To shed light on the characterization
The Ir dxy orbital in these Ir complexes is the most
of the emitting states in the present iridium complexes, DFT
destabilized among the Ir t2g orbitals because of π donation
calculations were carried out for the Ir complexes with
from both a phenyl anion in ppy and imidazole moieties in
available X-ray structures. Frontier molecular orbitals (MOs)
Mebib or Mebip and thus contributes to the HOMO.
of complex 5 obtained at the B3PW91/LAN2DZ level are
HOMO-1 of these Ir complexes is composed of the Ir dyz
shown in Figure 8. For complex 5, both the highest occupied
orbital, which is destabilized by mixing with π orbitals of a
molecular orbital (HOMO) and HOMO-1 are formed from
a combination of Ir 5d and Cl 2p orbitals in an antibonding
(65) Siddique, Z. A.; Yamamoto, Y.; Ohno, T.; Nozaki, K. Inorg. Chem.
2003, 42, 6366.
(64) Kober, E. M.; Caspar, J. V.; Lumpkin, R. S.; Meyer, T. J. J. Phys.
Chem. 1986, 90, 3722.
(66) Siddique, Z. A.; Ohno, T.; Nozaki, K.; Tsubomura, T. Inorg. Chem.
2004, 43, 663.
Inorganic Chemistry, Vol. 45, No. 22, 2006 8917

Obara et al.
The replacement of Cl by CH3CN with weak π-donating
ability does not give remarkable change in kr, as shown in
Table 3.
Mechanism of High Phosphorescence Yield in [Ir-
(Mebib)(ppy)Cl]. The phosphorescence of transition metal
complexes originates from the mixing of emissive singlet
states into the lowest triplet state due to spin-orbit coupling
of the d electrons. The transition dipole moments of the
singlet states are therefore the origin of the radiative
capability of the lowest triplet state. The radiative rate
constant kr of phosphorescence can be calculated from the
transition dipole moment of the perturbed triplet state using
the following expression:
16π3 × 106E3n3
2
kr )
|M|
(1)
3hꢀ0
Figure 9. MO levels calculated at the B3PW91/LANL2DZ level for X-ray
structures of [Ir(Mebib)(mppy)Cl] (5) (a), [Ir(Mebib)(ppy)CH3CN]+ (11)
(b), and [Ir(Mebip)(ppy)Cl]+ (14) (c). The molecule is oriented so that the
z axis is the C2 axis of the tridentate ligand and the y axis is parallel with
the Ir-X bonding.
where E is the emission energy and n, h, and ꢀo are the
refractive index of the medium, Planck’s constant, and the
vacuum permittivity, respectively. According to the first-
order perturbation theory, the transition dipole moment from
the triplet state to the ground state MT is given by
phenyl moiety in Mebib involving 5 and 11 or the pyridyl
moiety in Mebip of 14; however, the Ir dyz orbital of 14 is
less destabilized because of the weaker π-donating ability
of Mebip, and thus, the energy difference between HOMO
and HOMO-1 is much larger than in the Ir-Mebib com-
plexes. As shown in Figure 9, the energy gap in 5 is smaller
than that for 11 because Ir dxy and dyz orbitals are considerably
destabilized by the antibonding interaction with the Cl 2px
and 2pz orbitals, respectively.
ΨT|HSO|ΨSn
M )
MSn
(2)
∑
T
3ET - 1ES
n
n
where Ψs and Es are eigenfunctions and eigenvalues of the
Hamiltonian without spin-orbit coupling (HSO), respectively.
MS is the transition dipole moment from the nth singlet state
n
to the ground state. Thus, the radiative rate constant of the
phosphorescence is dominated by three factors: spin-orbit
coupling matrix element, the energy gap between T1 and Sn,
and Ms.
The LUMO of these Ir-Mebib complexes is the π*
orbitals of Mebib, which is consistent with the observed
invariance of the first reduction potentials in the Ir-Mebib
complexes. Further, the π* orbitals of ppy are located at a
higher energy than those of Mebib. For complex 14, the
LUMO and LUMO+1 are localized on the 2-pyridylbenz-
imidazolyl moiety (pbim) in Mebip, which is probably due
to the deconstructive interaction between the π* orbitals of
two pbim moieties through the phenylene group. Conse-
quently, the promoted electron in MLCT states of Ir-Mebip
complexes is not delocalized over the Mebip ligand but
instead tends to be localized on one of the pbim moieties,
which is probably responsible for the pronounced vibrational
sideband in the emission spectra of complex 14 (Figure 4c).
Time-dependent DFT calculations revealed that the elec-
tronic configuration of the lowest triplet MLCT state involves
primarily the HOMO and LUMO (Tables 3S, 4S, and 5S in
the Supporting Information), and therefore, the emitting state
consists of the combination of Ir dπ to Mebib π* ligand
charge transfer (MLCT) and Cl 3p to Mebib π* (XLCT) in
the Ir complexes with the Cl anion. In particular, the orbital
mixing in an antibonding fashion between Ir dπ and Cl 2p
orbitals plays an important role in controlling the MLCT
characters in these complexes, which can determine the
excited-state properties such as radiative and nonradiative
rate constants and quantum yields. Concerning the complex
having CH3CN as X, the lowest state is characterized by a
mixture of MLCT and ππ* of the ppy and Mebip ligands.
The radiative rate of 3ππ* in Rh(III) compounds has been
proposed to be the result of two entirely different mechan-
isms.67-69 In one mechanism, the increase in the radiative
character induced by heavy metal is ascribed to a direct
3
1
1
spin-orbit coupling between ππ* and dπ* () MLCT)
electronic configurations.67 This hypothesized mechanism,
however, does have drawbacks. Because the spin-orbit
3
1
coupling between ππ* and dπ* involves only the two-
center integrals on the metal center, the magnitudes of the
spin-orbit coupling are usually quite small. Therefore, the
spin-orbit coupling between 3ππ* and 1dπ* does not seem
to be responsible for the large effect of the heavy metal.
Accordingly, Miki et al. have proposed a new mechanism
3
3
in which ππ* is mixed with dπ* by a configurational
3
1
interaction because the mixing between dπ* and dπ* is
induced effectively by one-center spin-orbit coupling.68,69
Thus, the magnitude of the spin-orbit coupling element in
3
eq 2 increases as the contribution of the dπ* electronic
configuration in the lowest triplet state increases. In an
(67) Komada, Y.; Yamauchi, S.; Hirota, N. J. Phys. Chem. 1986, 90, 6425.
(68) Miki, H.; Shimada, M.; Azumi, T.; Brozik, J. A.; Crosby, G. A. J.
Phys. Chem. 1993, 97, 11175.
(69) (a) Azumi, T.; Miki, H. Top. Curr. Chem. 1997, 191, 1. (b) Solomon,
E. I.; Lever, A. B. P. Inorganic Electronic Structure and Spectroscopy;
John Wiley & Sons: New York, 1999; Vol. I, Chapter 1.
8918 Inorganic Chemistry, Vol. 45, No. 22, 2006

Highly Phosphorescent Iridium Complexes
Table 5. Data Used for the Evaluation of Phosphorescence Radiative Rate Constants
Ir(Mebib)(mppy)Cl
[Ir(Mebib)(ppy)CH3CN]+
(11)
[Ir(Mebip)(ppy)Cl+
(5)
(14)
T1
Sn
E/eVa
Cdxy
1.97
0.63
2.62
0.58
1.72
0.56
b
E/eVa
2.49 (S2)
0.58
0.074
3.43 (S3)
0.48
0.227
2.50 (S3)
0.44
0.024
b
Cdyz
f a
∆E (Sn-T1)/ cm-1
SOC (Sn-T1)/cm-1 c
kr/s-1 (n ) 1.42)d
kr,obsd/s-1 (CH2Cl2)
4190
6530
6290
809
617
546
1.0 × 106
1.3 × 106
4.6 × 104
4.4 × 105
2.5 × 105
8.0 × 104
a Obtained from the calculation at the TD-B3PW91/LANL2DZ level. b Coefficient of the natural atomic orbital of Ir 5d in HOMO (T1) or HOMO-1 (Sn)
obtained from NBO analysis. c Absolute value of the spin-orbit coupling matrix element calculated from eq 4. d Value calculated using eq 3.
alternative interpretation using recent MO theory, the elec-
tronic state is often described by a linear combination of
electronic transitions between delocalized MOs constructed
by a combination between metal-centered and ligand-
centered orbitals. Using the MO model, the coupling element
in eq 2 increases with the increase in the contribution of d
orbitals in the MOs ascribed to the lowest triplet state.
Because the DFT calculation for the present Ir complexes
indicates a greater contribution of the Ir 5d orbital in the
HOMO, as shown in Figures 8 and 9, one-center spin-orbit
rescence mechanism is then confirmed by evaluating the kr
value using a crude approximation of the one-center spin-
orbit coupling element. From the definition of oscillator
2
strength in vacuo f ) 8π2mE|M| /3he2 and eq 2, eq 1 can be
transformed as
3
n3ET S|HSO|T
fS
2
kr(T1) ≈
×
(3)
(
)
1.5 ES - ET
ES
where the emission energy E and matrix element are in cm-1.
Among the spin-orbit coupling elements between S2 (dyzfπ*)
and triplet sublevels of T1 (dxyfπ*), that is, T1,x, T1,y, and
T1,z, only the element involving T1,y has a nonzero value.
When the element between spin-orbitals involving ú () dxy)
and ê () dyz) given in eq 9 in ref 69a or eq 67 in ref 69b,
the one-center spin-orbit coupling element can be evaluated
as
3
1
coupling between dπ* and dπ* is considered to be the
predominant mechanism for the intense phosphorescence of
the complexes.
Theoretical consideration of spin-orbit coupling places
1
further restrictions on the electronic configuration of dπ*,
which can be coupled with 3dπ* in the lowest triplet
state.65,66,70 Both 3dπ* and 1dπ* should involve the same π*
orbital because spin-orbit couplings of π electrons are
negligibly small. Furthermore, as any atomic angular mo-
menta in low-symmetry transition metal complexes are
quenched, the spin-orbit coupling of the d electron works
between the dπ* configurations involving different d orbitals.
Consequently, under the assumption of one-center spin-orbit
integrals, the 3dπ* electronic configuration in the lowest state
is effectively coupled with the specific 1dπ* configurations
involving the d orbital with a different orientation and having
a common π* orbital.65,66,70
i
2
S2|HSO|T1,y ) ( CdxydRxy|HSO|Cdyzdyâz
-
i
Cdxydâxy|HSO|CdyzdRyz ) ) úIr-5dCdxyCdyz (4)
2
where úIr-5d is the one-electron spin-orbit coupling constant
of the 5d electron in iridium and Cdxy and Cdxz are the
coefficients of the 5d orbital involved in HOMO and HOMO-
1, respectively. Using theoretical values of ú5d-Ir ) 4430
cm-1 for the Ir(III) ion,70,71 ∆E (S2-T1) ) 4190 cm-1, and
f ) 0.074 obtained by TDDFT and the coefficients of natural
atomic orbitals obtained using an NBO 5.0 program72 of Cdxy
) 0.63, Cdxz ) 0.58, and n ) 1.42 (CH2Cl2), eq 3 gives 1.0
× 106 s-1 as the kr value of complex 5. For complex 11, a
similar analysis indicates that spin-orbit coupling with S3
is the origin of the radiative probability of the T1 state, and
the kr value is calculated as 1.3 × 106 s-1 (Table 5).
The temperature-dependent density functional theory (TD-
DFT) calculation of complex 5 at the B3PW91/LANL2DZ
level indicates that the lowest triplet state (T1) is the HOMO
f LUMO electronic configuration in which the donor 5dxy
orbital interacts with the accepting Mebib π* in a pseudo-δ
bonding fashion. As described above, spin-orbit coupling
of the Ir 5d electron effectively mixes 5dxy f LUMO in T1
with the other MLCTs from different d orbitals to LUMO.
A rather smaller kr value of 4.6 × 104 s-1 is predicted for
the Ir-Mebip complex 14. Thus, it turns out that the
evaluation based on one-center spin-orbit coupling almost
reproduces the magnitude of kr values of the present Ir
Thus, T1 is mixed with 5dyz f LUMO in S2 and 5dxz
f
LUMO in S6 (see Figure 9 and Table 3S). Because the
oscillator strengths (f) of S2 and S6 are 0.074 and 0.009,
respectively, the intense phosphorescence of complex 5
originates from the mixing between S2 and T1 because of
the spin-orbit coupling of Ir 5d electrons. This phospho-
(71) Fraga, S.; Saxena, K. M. S.; Karwowski, J. Handbook of Atomic Data.
Physical Sciences Data; Elsevier: Amsterdam, The Netherlands, 1976;
Vol. 5.
(72) Weinhold, F.; Landis, C. R. Chem. Ed.: Res. Practice Eur. 2001, 2,
(70) Nozaki, K. J. Chin. Chem. Soc. 2006, 53, 101.
91.
Inorganic Chemistry, Vol. 45, No. 22, 2006 8919

Obara et al.
MCT ) φd|µ|φπ* + λa( φπ*|µ|φπ* - φd|µ|φd ) +
λb φπ|µ|φπ* + λc φπ′*|µ|φπ* + λf φd|µφp + λg φd|µ|φp*
(6)
complexes. The relatively large deviation for complex 11
can be ascribed to the oversimplifications of spin-orbit
interactions: a more reliable evaluation would require the
consideration of spin-orbit interactions with many excited
states and geometrical changes of emitting states.70 Neverthe-
less, the present simplified analysis can rationalize the
observed variation of kr values. As shown in Table 4, the
replacement of Cl by CH3CN does not cause a large change
in kr. HOMO-1 in the Cl complex 5 is composed of Ir 5d
and Cl 3p orbitals, while HOMO-1 in the CH3CN complex
11 is produced from Ir 5d and Mebib π orbitals. The larger
contribution of Mebib π orbitals in HOMO-1 in complex
11 gives rise to the stronger oscillator strength of S3
(HOMO-1 f LUMO) from which the T1 state borrows its
intensity. On the other hand, the larger contribution of Mebib
orbitals in HOMO-1 increases the magnitude of the exchange
integral in S3 and thereby increases the energy gap ∆E(S3-
T1), which compensates for the increase in the oscillator
strength of S3. Consequently, the resulting kr value of
phosphorescence is almost the same as that of complex 5.
In the Mebip complex (14), because the LUMO is
localized on the pbim moiety, as described above, it mixes
only weakly with HOMO-1 with Cs symmetry, which is
responsible for the rather small oscillator strength of S3
(HOMO-1 f LUMO). Moreover, the energy gap ∆E(S3-
T1) is larger than that for complex 5 because of a larger
energy difference between HOMO and HOMO-1 (Figure 9).
Both of these effects remarkably reduce the kr value of
phosphorescence in the Mebip complex.
The TDDFT calculation indicates that the transition dipole
moments of S2 in 5 and S3 in 11 are oriented along the x
axis, not along the CT direction, that is, the C2 axis of the
Ir-Mebib subunit. The origin of the transition dipole moment
of MLCT in a mononuclear complex has been studied by
Day and Sanders.73 When a transition metal ion is coordi-
nated to ligands, the d orbitals interact with the π* orbitals
to form the donor and acceptor orbitals ascribed to CT
transitions. Mixing of the other metal-centered or ligand-
centered orbitals will lead to other sources of intensity. The
donor and the acceptor orbitals ascribed to the CT transition
are then given by
where µ denotes a dipole operator. The first term is the
contact CT term, which is usually negligible. The second is
the product of a mixing coefficient and the dipole moment
of the transferred charge, often called the transfer term. The
transfer term should be the origin of the intensity of the
MLCT transitions between the d and π* orbitals with a large
resonance integral, and therefore, the transition dipole
moment is oriented along the CT direction. The intense
MLCT absorption in tris(2,2′-bipyridine) complexes of Fe-
(II), Ru(II), and Os(II) with a D3 point group is ascribed to
the transfer term in e f e transitions.74-76 Recent theoretical
investigation of the phosphorescence in [fac-Ir(ppy)3] and
[Ru(bpy)3]2+ has revealed that the lowest triplet state borrows
1
the transfer term of the dπ* (b1 f b1) transition in the
pseudo-C2V point group.70
The other four terms in eq 6 are the moments borrowed
from interunit transitions. The third term is the moment
borrowed from 1ππ* due to d-orbital delocalization over the
ligands. The fourth term is borrowed from the transition
between π* and π′*. The latter is the unoccupied orbital
mixed into the d orbital through π back-donation. The fifth
and sixth terms are the moments of Laporte-allowed metal-
centered transition d T p. The intensity-borrowing mecha-
nism could possibly contribute to the CT intensity when the
resonance integral between d and π* is very small because
of their unfavorable overlapping. In particular, when the d
and π* orbitals interact in a π-bonding fashion but are
different in symmetry, the d orbital is mixed with π and π′*,
for which the symmetry is different from that of the accepting
π* orbital. In such complexes, the CT band may borrow
intensity from the π f π* transition or from the transition
between unoccupied ligand orbitals π′* T π*. The intensity
of the e f a2 transition in [Ru(bpy)3]2+ with the D3 point
group is considered to borrow from the transition between
unoccupied ligand orbitals e f a2.76
The contributions of parent fragment orbitals in each
frontier MO of Ir(Mebib)(mppy)Cl (5) were calculated using
the ADF program package and are summarized in Table 6.
Because the contributions were calculated at the pure DFT
level, they are somewhat different from those determined
by the hybrid B3PW91 calculations shown in Figure 9 and
Table 5; in particular, the contributions of Cl 3p in HOMO
and HOMO-1 seem to be rather large compared with those
at the hybrid DFT level. The HOMO is characterized
primarily by antibonding between Cl 3px and Ir 5dxy, with a
small contribution of the occupied 31st MO in mppy (ppy-
31) and the 61st MO in Mebib (bib-61) and of the
unoccupied 64th MO in Mebib (bib-64*). The HOMO-1 is
antibonding between Cl 3pz and Ir 5dyz with small contribu-
tions of bib-62, bib-65*, and bib-68*. While the LUMO is
formed from bib-64*, the LUMO+1 is from ppy-33*. The
transition dipole moment of the CT transition GS T S2
cannot be accounted for by the transfer term because the
donor dyz and the acceptor bib-64* orbital are different in
φD ) φd + λaφπ* + λbφπ + λcφπ′*
φA ) φπ* - λaφd + λfφp + λgφp* (5)
where φd and φp are the metal-centered d and p orbitals,
respectively, and π and π′* are ligand-centered occupied or
unoccupied orbitals, respectively, other than π*. λ is the
mixing coefficient. The mixing coefficients increase with
increasing resonance integrals between orbitals. Normaliza-
tion factors are neglected for simplification. Ignoring higher-
order terms, the transition dipole moment (M) of the CT
transition is thus given by
(73) Day, P.; Sanders, N. J. Chem. Soc. A 1967, 1530.
(74) Daul, C.; Schlaepfer, W. J. Chem. Soc., Dalton Trans. 1988, 393.
(75) Kober, E. M.; Meyer, T. J. Inorg. Chem. 1982, 21, 3967.
(76) Ceulemans, A.; Vanquickenborne, L. G. J. Am. Chem. Soc. 1981, 103,
2238.
8920 Inorganic Chemistry, Vol. 45, No. 22, 2006

Highly Phosphorescent Iridium Complexes
Table 6. Fragment Analysis for the Frontier Molecular Orbitals in
Ir(bib)(mppy)Cl at X-ray Structure Using the ADF 2002 Program
Packagea
transition between unoccupied orbitals bib-65* f bib-64*
also produces a large transition dipole moment. The direction
of the dipole moment of both intra-bib transitions is along
the inter-bim direction, which is the x axis, consistent with
the results obtained by TDDFT.
MO
major contribution of fragment orbital (%)
Unoccupied
LUMO+2
LUMO+1
LUMO
bib-65* (59), ppy-34* (24), 5dyz (4.0), bib-68* (2.1)
ppy-33* (80), ppy-34* (9.2), ppy-32 (3.6), 5dxz (2.7)
bib-64* (82), bib-63 (11), 5dxy (2.7)
Consequently, the theoretical consideration based on DFT
calculations revealed that the intense phosphorescence of the
Ir-Mebib complexes is accounted for in terms of the
effective mixing between the 5dxy f LUMO configuration
in the lowest triplet state with 5dyz f LUMO in singlet states
through spin-orbit coupling. In addition, the intensity of the
singlet dπ* transition originates from the very unique
electronic structure of Mebib, which allows for an electronic
interaction between the spatially separated bim moieties.
Occupied
HOMO
3px (48), 5dxy (33), ppy-31 (6.9), bib-61 (5.3),
bib-64* (1.4)
HOMO-1
HOMO-2
3pz (60), 5dyz (23), bib-62 (3.8), bib-68* (1.4),
bib-65* (1.3)
3px (29), bib-61 (19), 5dxz (16), 5dxy (13),
ppy-31 (6.0), bib-60 (4.1), ppy-30 (2.5),
bib-57 (2.3), bib-58 (2.0)
a The * denotes unoccupied orbital.
Conclusion
In the present study, we achieved the selective synthesis
of novel mixed-ligand Ir complexes of the general formula
[Ir(N∧C∧N)(ppy)X] (N∧C∧N ) Me- or Phbib; X ) Cl,
Br, I, -CCPh, or CN), which have high luminescent quantum
yields, Φ ) 0.77∼0.95. The X-ray structures of [Ir(Phbib)-
(ppy)Cl] and [Ir(Mebib)(mppy)Cl] ′reveal that the nitrogen
atom in the ppy ligand is located at a position trans to the
central carbon atom in N∧C∧N (Me- or Phbib), while the
coordinating carbon atom in ppy occupies a trans position
in relation to Cl. Upon a change of substituent on ppy or X,
the Ir(III/IV) oxidation potential exhibits a strong dependence
on the ligand substitution, although the reduction potentials
remain almost constant. These findings suggest that the
excited state involves a large contribution of MLCT char-
acter, which is supported by DFT calculations. Therefore,
the present Ir(bib) complexes provide new insight into the
molecular design of a new type of highly emissive phos-
phorescent Ir complexes. Investigation of Ir(III) complexes
with regard to this concept is now in progress.
Acknowledgment. M.H. gratefully acknowledges finan-
cial support from the Institute of Science and Engineering
at Chuo University, the Ministry of Education, Science,
Sports, and Culture (Monkasho) for a Grant-in-Aid for
Scientific Research (No. 15310076 and 16074215 “Chem-
istry of Coordination Space”). K. N. gratefully acknowledges
Monkasho for a Grant-in-Aid for Scientific Research
(16550056).
Figure 10. Molecular orbitals involved in the interligand transition ascribed
to the intensity of the S2 transition in Ir(Mebib)(mppy)(Cl).
symmetry. The CT transition in S2 is therefore borrowed
intensity from interunit transitions. Because HOMO-1 has
the contribution of both the occupied bib-62 and unoccupied
bib-65*, the CT transition can borrow intensity from both
bib-62 f bib-64* and bib-65* f bib-64* intra-Mebib
transitions. As shown in Figure 10, bib-64* contains the π*
orbitals on two benzimidazoyl (bim) moieties with out-of-
phase combination, while the π orbitals are combined in an
in-phase fashion in bib-62. Therefore, the electronic transition
bib-62 f bib-64* generates a strong electronic oscillator
between two π systems of bim moieties approximately 10
Å apart. Similarly, bib-65* involves an in-phase interaction
between the π* orbitals of bim moieties; therefore, the
Supporting Information Available: CIF files of 5‚2CH2Cl2,
9‚C6H14, 11OTf‚Et2O, 13OTf, and 14PF6‚2MeCN‚0.5Et2O, and
Tables 1S and 2S give their selected bond distances and angles
and the torsion angles between planes. Tables 3S, 4S, and 5S
summarize the excitation energy, oscillator strength (f), and major
electronic configurations for Ir(Mebib)(mppy)Cl (5), Ir(Mebib)-
(ppy)(CH3CN)+ (11), and Ir(Mebip)(ppy)Cl+ (14). This material
is available free of charge via the Internet at http://pubs.acs.org.
IC060796O
Inorganic Chemistry, Vol. 45, No. 22, 2006 8921