Iridium(III) emitters based on 1,4-disubstituted-1 H -1,2,3-triazoles as cyclometalating ligand: Synthesis, characterization, and electroluminescent devices

Article abstract of DOI:10.1021/ic3018419

A series of blue and blue-green emitters based on neutral bis- and tris-cyclometalated Ir(III) complexes with 1-benzyl-4-(2,6-difluorophenyl)-1H-1, 2,3-triazole (dfptrBn) as cyclometalating ligand is reported. The bis-cyclometalated complexes of the type [Ir(dfptrBn)₂(L ^{^}X)] with different ancillary ligands, L^{^}X = picolinate (pic) (2) or 2-(5-(perfluorophenyl)-2H-1,2,4-triazol-3-yl)pyridine (pytrF ₅) (3), are described and their photophysical properties compared with the analogous complexes containing the archetypal 2-(2,4-difluorophenyl) pyridinato (dfppy) as cyclometaled ligand (C^{^}N). Complex 2 exhibits a marked solvatochromic behavior, from 475 nm in toluene to 534 nm in formamide, due to the strong MLCT character of its emissive excited state. Complex 3 displays a true-blue emission, narrower in the visible part than FIrpic. In addition, the homoleptic complex [Ir(dfprBn)₃] (4) and the heteroleptic compounds with mixed arylpyridine/aryltriazole ligands, [Ir(dfptrBn)₂(C^{^}N)] (C^{^}N = 2-phenylpyridinato (ppy) (5) or dfppy (6)), have been synthesized and fully characterized. The facial (fac) complex fac-4 is emissive at 77 K showing a deep-blue emission, but it is not luminescent in solution at room temperature similarly to their phenylpyrazole counterparts. However, the fac isomers, fac-5 and fac-6, are highly emissive in solution and thin films, reaching emission quantum yields of 76%, with emission colors in the blue to blue-green region. The photophysical properties for all complexes have been rationalized by means of quantum-chemical calculations. In addition, we constructed electroluminescent devices, organic light-emitting diodes (OLEDs) by sublimation of fac-6, and by solution processed polymer-based devices (PLEDs) using complexes fac-5 or fac-6 as dopants.

Full text of DOI:10.1021/ic3018419

Article
pubs.acs.org/IC
Iridium(III) Emitters Based on 1,4-Disubstituted‑1H‑1,2,3-triazoles as
Cyclometalating Ligand: Synthesis, Characterization, and
Electroluminescent Devices
Jesus M. Fernandez-Hernandez,*,† Juan I. Beltran,‡ Vincent Lemaur,‡ Maria-Dolores Galvez-Lopez,†
́
́
́
́
́
́
Chen-Han Chien,† Federico Polo,† Enrico Orselli,§ Roland Frohlich,∥ Jerome Cornil,*,‡
́
̂
̈
and Luisa De Cola*,†,⊥
†Physikalisches Institut, Center for Nanotechnology (CeNTech), Westfalische Wilhelms-Universitat Munster,
̈
̈
̈
Heisenbergstrasse 11, 48149 Munster, Germany
̈
‡Service de Chimie des Mater
§Solvay S. A., Rue de Ransbeek 310, 1120 Brussels, Belgium
∥Organisch-Chemisches Institut, Westfalische Wilhelms-Universitat Munster, Corrensstrasse 40, 48149 Munster, Germany
́ ́
iaux Nouveaux, Universite de Mons, Place du Parc 20, 7000 Mons, Belgium
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: A series of blue and blue-green emitters based on
neutral bis- and tris-cyclometalated Ir(III) complexes with
1-benzyl-4-(2,6-difluorophenyl)-1H-1,2,3-triazole (dfptrBn) as
cyclometalating ligand is reported. The bis-cyclometalated com-
plexes of the type [Ir(dfptrBn)2(L∧X)] with different ancillary
ligands, L∧X = picolinate (pic) (2) or 2-(5-(perfluorophenyl)-
2H-1,2,4-triazol-3-yl)pyridine (pytrF5) (3), are described and
their photophysical properties compared with the analogous
complexes containing the archetypal 2-(2,4-difluorophenyl)-
pyridinato (dfppy) as cyclometaled ligand (C∧N). Complex
2 exhibits a marked solvatochromic behavior, from 475 nm
in toluene to 534 nm in formamide, due to the strong MLCT
character of its emissive excited state. Complex 3 displays a
true-blue emission, narrower in the visible part than FIrpic. In addition, the homoleptic complex [Ir(dfprBn)3] (4) and the
heteroleptic compounds with mixed arylpyridine/aryltriazole ligands, [Ir(dfptrBn)2(C∧N)] (C∧N = 2-phenylpyridinato
(ppy) (5) or dfppy (6)), have been synthesized and fully characterized. The facial (fac) complex fac-4 is emissive at 77 K
showing a deep-blue emission, but it is not luminescent in solution at room temperature similarly to their phenylpyrazole
counterparts. However, the fac isomers, fac-5 and fac-6, are highly emissive in solution and thin films, reaching emission
quantum yields of 76%, with emission colors in the blue to blue-green region. The photophysical properties for all complexes
have been rationalized by means of quantum-chemical calculations. In addition, we constructed electroluminescent devices,
organic light-emitting diodes (OLEDs) by sublimation of fac-6, and by solution processed polymer-based devices (PLEDs)
using complexes fac-5 or fac-6 as dopants.
of both the singlet and the triplet excitons produced when
electrons and holes recombine, reaching up to 100% internal
efficiency.1,30,31 In order to develop full-color display and
lighting technologies, a key factor is employment of molecules
that can emit the primary colors (red, green, and blue).
Cyclometalated Ir(III) complexes possess color of the
emission in the visible range (from red to blue) dictated
by careful design of the structure and nature of the ligands
bound to the metal center.11,29,32 Although efficient red- and
green-emitting Ir(III) complexes have been described and
are now in the commercialization phase due to their
INTRODUCTION
■
In recent years, increasing interest has been devoted to phos-
phorescent metal complexes and their application as emitters in
electroluminescent devices, i.e., organic light-emitting diodes
(OLEDs) or light-emitting electrochemical cells (LEECs) for
displays and lighting applications.1−9 Luminescent complexes
are generally based on heavy metals such as ruthenium(II),
osmium(II),10−12 platinum(II),11,13−18 copper(I),19−25 or iridium-
(III). Compounds based on iridium are the most studied
among them1−9,26,27 due to their relatively short excited-state
lifetime, high emission quantum yield, and facile color tuning
through ligand structure control.1,28−30 The triplet character of
the emission, induced by the strong spin−orbit coupling in these
complexes, is of great importance, since it allows for harvesting
Received: August 22, 2012
Published: February 5, 2013
© 2013 American Chemical Society
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Article
excellent stability in devices, finding stable and efficient blue
emitters is still an issue.11,33−36
EXPERIMENTAL SECTION
■
General Information and Materials. Solvents were dried using
standard procedures. All other reagents were used as received from
commercial sources, unless otherwise stated. 1-Benzyl-4-(2,4-difluor-
ophenyl)-1H-1,2,3-triazole (dfptrBn), 2-(5-(perfluorophenyl)-2H-
1,2,4-triazol-3-yl)pyridine (pytrF5), and dimer [Ir2(dfptrBn)4Cl2] (1)
were synthesized as described elsewhere.51,52,55,57 NMR spectra were
recorded on an ARX 300 or AMX 400 from Bruker Analytische
Among the cyclometalating ligands employed to prepare
Ir(III) complexes, the most widely used are those in which a
carbon from a phenyl ring acts as a donor and the adjacent
fragment involved in formation of the metallocycle is an
N-heterocycle ring.11 These ligands are represented by C∧N,
with 2-phenylpyridine (ppyH) as the archetypical example.
These cyclometalating ligands are anionic and form a strong
bond with the metal, yielding a highly stabilized ligand field that
increases the splitting of d−d orbitals compared to complexes
with only neutral diimine ligands.29 Thus, the photophysical
properties of these complexes are often remarkable, leading to
highly luminescent organometallic compounds.36 Furthermore,
the C∧N ligand can be easily substituted with electron-withdrawing
or -donating groups, and these substitutions have an important
effect on their HOMO and LUMO energies and consequently
on the metal complex emission. In order to obtain blue emitters,
several strategies can be followed. Incorporation of electron-
withdrawing groups on the aryl fragment stabilizes the HOMO,
while substituting the pyridine or N-heterocycle with electron-
donating groups raises the LUMO, leading to an overall increase
of the energy of the emission. An alternative strategy to raise the
LUMO of the complex is to change the pyridine moiety by a
smaller N-heterocyclic ring that has higher reduction potentials than
pyridine. Blue shifts of the emission maxima have been obtained
using pyrazoles,36−40 N-heterocyclic carbenes (NHC),34,41−44or
triazoles. For the latter, Samuel et al. showed that 5-aryl-1,3-
disubstituted-[1,2,4]-triazole can be successfully used as cyclo-
metalating ligand to obtain bluer emitters than the arylpyridine
counterparts.45,46 An interesting alternative to the phenyl-1,2,4-
triazole is the use of 1,4-disubstituted-1H-1,2,3-triazole. These
compounds can be easily prepared by “click chemistry”, which
allows for wide functionalization of the aryl or triazole moieties
via the acetylene or organic azide.47,48 Recently, we and others
successfully synthesized 1-substituted-4-aryl-1H-1,2,3-triazoles
and exploited them as cyclometalating ligands in neutral and
cationic Ir(III) complexes.49−53 Although it has been shown that
their emission can be blue shifted compared to their arylpyridine
counterparts,49−51,53 to the best of our knowledge, the number of
neutral efficient blue or sky blue emitters based on these ligands
is rather limited and their use as dopant in electroluminescent
devices is rare.
Herein, we report a new class of blue and blue-green emitters
based on neutral bis- and tris-cyclometalated Ir(III) complexes
with 1-benzyl-4-(2,6-difluorophenyl)-1H-1,2,3-triazole (dfptrBn)
as cyclometalating ligand. The bis-cyclometalated complexes of
the type [Ir(dfptrBn)2(L∧X)] with different ancillary ligands,
L∧X = picolinate (pic) or, pytrF5, are described as well as the
heteroleptic tris-cyclometalated complexes with mixed arylpyr-
idine/aryltriazole ligands, [Ir(dfptrBn)2(C∧N)] (C∧N = ppy or
dfppy). The properties have been investigated and compared
with analogous complexes containing the archetypal dfppy as
cyclometalating ligand (C∧N).54−56 We also present the
synthesis and photophysical characterization of the first example
of a homoleptic tris-cyclometalated complex based on 1,4-di-
substituted-1H-1,2,3-triazole. The photophysical properties for all
complexes have been rationalized by means of quantum-chemical
calculations. In addition, device characteristics of polymer light-
emitting diodes (PLEDs) and OLEDs doped with the tris-
cyclometalated Ir(III) complexes are presented.
1
Messtechnik (Karlsruhe, Germany). H NMR chemical shifts (δ) of
the signals are given in ppm and referenced to residual protons in
the deuterated solvents: CDCl3 (7.26 ppm), dimethyl sulfoxide-d6
(2.50 ppm), or CD3CN (1.94 ppm). 19F NMR chemical shifts are
referenced to CFCl3 (0.00 ppm) as an internal standard. Signal
splittings are abbreviated as follows: s = singlet; d = doublet;
t = triplet; q = quartet; m = multiplet. All coupling constants (J) are given
in Hertz (Hz). Mass spectrometry was performed in the Department
of Chemistry, University of Munster. Electrospray ionization (ESI) mass
̈
spectra were recorded on a Bruker Daltonics (Bremen, Germany)
MicroTof with loop injection. Elemental analysis was recorded at the
University of Milan, Italy.
Preparation. [Ir(dfptrBn)2(pic)] (2). To a solution of 1 (118 mg,
0.0768 mmol) in 2-ethoxyethanol (7 mL), picolinic acid (21 mg, 0.169
mmol) and sodium carbonate (80 mg, 0.754 mmol) were added. The
reaction mixture was placed under inert atmosphere and refluxed for
16 h in the dark. To the cooled reaction mixture 50 mL of EtOAc was
added. The mixture was washed three times with water (3 × 15 mL),
and the organic phase was dried over MgSO4. Crude product was
purified by flash chromatography on silica gel using EtOAc as eluent.
Product can be recrystallized from MeCN/Et2O. Yield: 96 mg, (75%).
1H NMR (DMSO-d6, 300 MHz): δ 8.77 (d, J = 1.4, 1H), 8.73 (d,
J = 1.4, 1H), 8.05 (m, J = 11.5, 7.8, 4.1, 2H), 7.76 (d, J = 4.9, 1H), 7.57
(ddd, J = 7.2, 5.4, 1.9, 1H), 7.47−7.16 (m, 10H), 6.81 (dd, J = 9.9, 2.2,
1H), 6.72 (m, dd, J = 9.9, 2.2, 1H), 5.74 (AB-system, 4H, CH2), 5.57
(dd, J = 9.1, 2.2, 1H), 5.44 (dd, J = 9.0, 2.3, 1H). 19F{1H} NMR (282
MHz, DMSO-d6): δ −110.22 (d, J = 7.3, 1F), −111.04 (d, J = 6.9, 1F),
−111.52 (d, J = 7.3, 1F), −112.52 (d, J = 6.9, 1F). m/z (ESI-MS+):
878.1446 ([M + Na+]+). Anal. Calcd for C36H24F4IrN7O2: C, 50.58; H,
2.83; N, 11.47. Found: C, 50.33; H, 2.77; N, 11.41.
[Ir(dfptrBn)2(pytrF5)] (3). To a solution of 1 (90 mg, 0.058 mmol)
in 8 mL of dichloromethane/ethanol (3:1), pytrF5 (40.2 mg, 0.129
mmol) was added. The reaction mixture was placed under inert
atmosphere and refluxed for 24 h in the dark. After evaporation of the
solvent, the crude product was purified by flash chromatography on a
silica gel column using dichloromethane/MeCN (9:1). Product can be
1
recrystallized from dichloromethane/Et2O. Yield: 70 mg (60%). H
NMR (300 MHz, CDCl3): δ 8.50 (bs, 1H), 7.94 (d, J = 5.3, 1H), 7.88
(t, J = 7.5, 1H), 7.67−7.52 (m, 2H), 7.46−7.32 (m, 6H), 7.27 (m,
2H), 7.21−7.05 (m, 3H), 6.51−6.39 (m, 1H), 6.34 (td, J = 10.1, 2.2,
1H), 5.77 (dd, J = 8.8, 2.2, 1H), 5.66 (dd, J = 9.0, 2.2, 1H), 5.45 (m,
4H). 19F{1H} NMR (282 MHz, CDCl3): δ −109.32 (bs, 1F), −109.83
(bs, 1F), −111.90 (bs, 1F), −112.78 (bs, 1F), −138.66 (m, 2F),
−154.22 to −156.71 (m, 2F), −163.08 (m, 2F). m/z (ESI-MS+):
found 1067.155 ([M + Na+]+). Anal. Calcd for C43H24F9IrN10: C,
49.47;H, 2.32; N, 13.42. Found: C, 49.08; H, 2.31; N, 13.10.
mer-[Ir(dfptrBn)3] (mer-4). A mixture of 1 (172 mg, 0.112 mmol),
dfptrBn (64 mg, 0.235 mmol), and K2CO3 (155 mg, 1.12 mmol) in
2-ethoxyethanol (5 mL) was flushed with nitrogen for 20 min and
refluxed for 18 h protected from light. The mixture was concentrated
to dryness and extracted in dichloromethane/water. After drying the
organic phase with MgSO4, solvent was evaporated and the residue
was purified by flash chromatography with silica gel and dichloromethane
as eluent and protected from light. Yield: 60 mg (30%). 1H NMR (300
MHz, CDCl3): δ 7.57 (d, J = 2.1, 1H), 7.53 (d, J = 1.5, 1H), 7.50 (d,
J = 1.3, 1H), 7.43−7.25 (m, 9H), 7.24−7.09 (m, 6H), 6.43 (dd, J = 8.3,
2.3, 1H), 6.34 (m, 3H), 6.12 (dd, J = 8.0, 2.2, 1H), 5.78 (dd, J = 9.5,
2.2, 1H), 5.56−5.24 (m, 6H). 19F{1H} NMR (282 MHz, CDCl3):
δ −111.38 (d, J = 7.1, 1F), −111.69 (d, J = 6.4, 1F), −112.34 (d,
J = 6.0, 1F), −113.89 (d, J = 7.1, 1F), −114.01 (d, J = 6.4, 1F), −114.45
(d, J = 6.0, 1F). m/z (ESI-MS+): found 1026.210 ([M + Na+]+). Anal.
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Calcd for C45H30F6IrN9 C, 53.89; H, 3.01; N, 12.57. Found: C, 53.60;
H, 3.30; N, 12.60
fac-[Ir(dfptrBn)2(dfppy)] (fac-6). Yield: 35 mg (from 40 mg of mer-6).
1H NMR (300 MHz, CD2Cl2): δ 8.33−8.20 (m, 1H), 7.76 (dd, J = 5.6,
0.8, 1H), 7.73−7.62 (m, 3H), 7.48−7.30 (m, 6H), 7.30−7.11 (m, 4H),
6.95 (ddd, J = 7.1, 5.6, 1.2, 1H), 6.54−6.33 (m, 3H), 6.30 (dd, J = 9.3,
2.5, 1H), 6.15 (dd, J = 9.7, 2.3, 2H), 5.47 (AB system, 4H). 19F{1H}
NMR (282 MHz, CD2Cl2): δ −110.25 (d, J = 9.7, 1F), −111.45 (d,
J = 9.7, 1F), −111.87 (d, J = 7.1, 1F), −112.21 (d, J = 6.9, 1F), −114.05
(d, J = 7.1, 1F), −114.27 (d, J = 6.9, 1F). m/z (ESI-MS+): found 924.18
([M + H+]+), 946.16 ([M + Na+]+). Anal. Calcd for C41H26F6IrN7: C,
53,36; H, 2,84; N, 10,62. Found: C, 52.76; H, 2,75; N, 10,37.
Photoisomerization. A Lot-Oriel 200 W high-pressure mercury
lamp equipped with a 280−400 nm dichroic mirror (to remove IR and
visible light) was used for photoisomerization of mer to fac isomers.
Photophysical Measurements. All absorption and emission
spectra as well as time-resolved measurement were recorded as described
elsewhere using the same equipment.51
X-ray Crystallography. Data set was collected with a Nonius
KappaCCD diffractometer. Programs used: data collection COLLECT
(Nonius B.V., 1998), data reduction Denzo-SMN,58 absorption correction
Denzo,59 structure solution SHELXS-97,60 structure refinement
SHELXL-97,61 graphics XP (BrukerAXS, 2000). Graphics show
thermal ellipsoids with 50% probability; R values are given for the
observed reflections with respect to values for all reflections.
fac-[Ir(dfptrBn)3] (fac-4). The fac complex was obtained by irradia-
tion of an argon-purged MeCN solution of the mer complex (ca.
40 mg/3 mL) for 40 min. The product precipitates in this solvent as
1
colorless crystals. H NMR (300 MHz, CDCl3): δ 7.53 (d, J = 2.0,
3H), 7.40−7.29 (m, 9H), 7.20−7.07 (m, 6H), 6.36 (ddd, J = 10.5, 9.3,
2.3, 3H), 6.22 (dd, J = 9.7, 2.3, 3H), 5.51−5.28 (AB system, 6H).
19F{1H} NMR (282 MHz, CDCl3): δ −111.59 (d, J = 6.9, 3F),
−114.22 (d, J = 6.9, 3F). m/z (ESI-MS+): found 1026.206 ([M +
Na+]+). Anal. Calcd for C45H30F6IrN9 C, 53.89; H, 3.01; N, 12.57.
Found: C, 53.77; H, 3.45; N, 12.66
General Procedures for Synthesis of Complexes mer-5, mer-6,
fac-5, and fac-6. Synthesis of these complexes was adapted from already
published procedures.38 To a solution of dimer 1 in acetone (10 mL),
2 equiv of silver triflate was added and the mixture was stirred 50 °C
overnight. After cooling the reaction mixture, the resulting suspension
was filtered through Celite and the filtrate concentrated to dryness.
Residue was dissolved in methyl ethyl ketone (MEK), and 1.5 equiv of
the appropriate cyclometalating ligand and 2 equiv of triethylamine
were added. The mixture was refluxed for 20 h. After cooling, the reac-
tion mixture was concentrated to give an oily residue that was purified
by flash chromatography on silica gel using hexane/EtOAc (4:1 to 2:1)
as eluent to give the mer isomers.
Electrochemistry. Electrochemical characterization of the metal
complexes herein reported has been performed in N,N-dimethylfor-
mamide/0.1 M tetrabutylammonium hexafluorophosphate (TBAH).
Glassy carbon has been employed as working electrode, platinum wire
as counter electrode, and platinum (or silver) wire as quasi-reference
(QRE) electrode. For electrochemical experiments, a CHI750C
Electrochemical Workstation (CH Instruments, Inc., Austin, TX)
was used. Electrochemical experiments were performed in a glass cell
under an argon atmosphere. To minimize the ohmic drop between the
working and the reference electrodes, the feedback correction was
employed. Electrochemical experiments were performed using a 1.5 mm
diameter glassy carbon, GC (66-EE047 Cypress Systems), electrode.
GC electrodes were stored in ethanol and before experiments polished
with a 0.05 μm diamond suspension (Metadi Supreme Diamond
Suspension, Buehler) and ultrasonically rinsed with ethanol for 5 min.
Electrodes were electrochemically activated in the background solution
by means of several voltammetric cycles at 0.5 V s−1 between the
anodic and the cathodic solvent/electrolyte discharges until the same
quality features recently described were obtained. The reference
electrode was a Ag quasi-reference electrode (Ag-QRE), which was
separated from the catholyte by glass frits. The reference electrode was
calibrated at the end of each experiment against the ferrocene/ferricenium
couple, whose formal potential is 0.464 V against the KCl saturated
calomel electrode (SCE);62 in the following, all potential values will be
reported against SCE. A platinum ring or coil served as the counter
electrode. In Table 4, standard potentials are calculated as the average
value between cathodic and anodic peak potentials, when the processes
are reversible or quasi-reversible, while the values for the HOMO−
LUMO gap are calculated as the difference between the standard
potential for the first oxidation and the first reduction, respectively.
Computational Methods. The ground-state geometry of the
complexes has been optimized at the density functional theory (DFT)
level using the Gaussian 03 package. We start from the X-ray
structures, when available, and relax the geometry until atomic forces
are less than 0.0001 hartree/Bohr. The chosen exchange correlation
(XC) functional is the widely used B3LYP63 in view of its good
compromise between accuracy and computational cost; the basis set
for description of the electrons of nonmetallic atoms is 6-31G**,64
while the LANL2DZ basis set has been used for Ir.65 Characterization
of the nature of the lowest lying singlet and triplet excited states,
involved in absorption and emission, respectively, relies on time-
dependent density functional theory (TD-DFT) calculations per-
formed on the basis of the ground-state geometry using the same
functional and basis set. Figure 5 has been generated using the Jmol
program [Jmol: an open-source Java viewer for chemical structures in
3D; http://www.jmol.org/. VMD: http://www.ks.uiuc.edu/Research/
vmd/; Humphrey, W., Dalke, A. and Schulten, K., J. Molec. Graphics,
The fac complexes were obtained by irradiation of an argon-purged
MeCN solution of the respective mer complex (ca. 40 mg/3 mL) for
40 min. The reaction was followed by TLC and stopped when the mer
isomer complex was consumed. Then the mixture was transferred to a
flask and evaporated to dryness. Residue was suspended in dichloro-
methane and precipitated with MeOH. The resulting solid was filtered
and washed with MeOH.
mer-[Ir(dfptrBn)2(ppy)] (mer-5). Following the general procedure,
dimer 1 (187 mg, 0.121 mmol) and silver triflate (63 mg, 0.243 mmol)
were used. Chromatography has to be carried out protected from light
to avoid isomerization to fac-5. Yield: 100 mg (50%). 1H NMR (300 MHz,
CDCl3): δ 8.05 (dd, J = 5.6, 0.9 Hz, 1H), 7.90 (d, J = 8.2 Hz, 1H),
7.80−7.69 (m, 1H), 7.67−7.58 (m, 1H), 7.48 (dd, J = 5.4, 1.5 Hz,
2H), 7.38−7.29 (m, 6H), 7.21−7.09 (m, 4H), 7.09−6.93 (m, 3H),
6.94−6.80 (m, 1H), 6.42−6.27 (m, 2H), 6.09 (dd, J = 7.9, 2.2 Hz,
1H), 5.85 (dd, J = 9.5, 2.2 Hz, 1H), 5.50−5.18 (m, 4H). 19F{1H}
NMR (282 MHz, CDCl3): δ −111.40 (d, J = 6.4 Hz), −111.96 (d,
J = 7.0 Hz), −113.65 (d, J = 6.4 Hz), −114.27 (d, J = 7.0 Hz). m/z
(ESI-MS+): found 888.1996 ([M + H+]+), 910.1814 ([M + Na+]+).
Anal. Calcd for C41H28F4IrN7: C, 55.52; H, 3.18, N, 11.05. Found: C,
55.20; H, 2.95; N, 10.70.
mer-[Ir(dfptrBn)2(dfppy)] (mer-6). Following the general proce-
dure, dimer 1 (137.5 mg, 0.089 mmol) and silver triflate (46 mg, 0.179
mmol) were used. Chromatography has to be carried out protected
1
from light to avoid isomerization to fac-6. Yield: 114 mg (70%). H
NMR (300 MHz, CDCl3): δ 8.29 (d, J = 10.9, 1H), 8.09 (dd, J = 5.6,
1.0, 1H), 7.64 (t, J = 7.8, 1H), 7.51 (m, 2H), 7.43−7.28 (m, 6H), 7.17
(td, J = 6.7, 3.0, 4H), 6.90−6.84 (m, 1H), 6.49 (dd, J = 7.9, 2.5, 1H),
6.46−6.28 (m, 3H), 6.02 (dd, J = 7.9, 2.2, 1H), 5.76 (dd, J = 9.4, 2.2,
0H), 5.36 (AB system, 4H). 19F{1H} NMR (282 MHz, CDCl3): δ
−110.60 (d, J = 8.9, 1F), −111.01 (d, J = 6.6, 1F), −111.13 (d, J = 8.9,
1F), −111.34 (d, J = 7.1, 1F), −113.37 (d, J = 6.6, 1F), −113.83 (d,
J = 7.1, 1F). m/z (ESI-MS+): found 924.1833 ([M + H+]+), 946.1659
([M + Na+]+). Anal. Calcd for C41H26F6IrN7: C, 53,36; H, 2,84, N,
10,62. Found: C, 53.26; H, 2,85; N, 10,35.
fac-[Ir(dfptrBn)2(ppy)] (fac-5). After photoisomerization the com-
pound was recrystallized in dichloromethane/Et2O. Yield: 30 mg (from
40 mg of mer-5). 1H NMR (300 MHz, CDCl3): δ 7.86 (d, J = 8.2 Hz,
1H), 7.79−7.72 (m,1H), 7.71−7.56 (m, 3H), 7.51 (d, J = 2.0 Hz, 1H),
7.44−7.28 (m, 6H), 7.24−7.16 (m, 2H), 7.16−7.07 (m, 2H), 6.99−
6.80 (m, 4H), 6.43−6.25 (m, 2H), 6.19 (ddd, J = 11.4, 9.8, 2.3 Hz,
2H), 5.41 (m, 4H). 19F NMR (282 MHz, CDCl3): δ −111.37 (d, J =
7.1 Hz), −112.13 (d, J = 6.7 Hz), −114.34 (d, J = 7.1 Hz), −114.53
(d, J = 6.7 Hz). m/z (ESI-MS+): found 888.1996 ([M + H+]+),
910.1814 ([M + Na+]+). Anal. Calcd for C41H28F4IrN7: C, 55.52; H,
3.18, N, 11.05. Found: C, 55.10; H, 3.01; N, 10.73.
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Scheme 1. Schematic Procedure for the Synthesis of the Different Complexes
1996, 14, 33-38.] Note that the unrestricted formalism (UBLYP) has
been systematically used for description of the properties related to the
triplet state, while the restricted formalism has been used for those
related to the singlet ground state. Our approach is motivated by
previous works showing its adequacy to describe the electronic and
optical properties of iridium complexes.51,66,67 Note that these
calculations neglect intersystem crossing processes mixing states of
the singlet and triplet manifold.
For the OLED preparation, di-[4-(N,N-ditolyl-amino)phenyl]-
cyclohexane (TAPC), 1,4-bis(triphenylsilyl)benzene (UGH2), 2,6-
bis(3-(9H-carbazol-9-yl)phenyl)pyridine (26DCzPPy), and 1,3-bis-
(3,5-dipyrid-3-yl-phenyl)benzene (BmPyPB) were purchased from
Luminescence Technology Corp. and purified by sublimation before
use, while Plexcore OC RG-1100 was provided by Plextronics Inc. The
device structure consists of a 120 nm transparent ITO layer as the
bottom electrode supported on a glass substrate. With the
exception of Plexcore, which was spun on top of ITO using a
Suss Microtec Delta6 RC spincoater, all other materials were
vacuum deposited in an evaporation chamber at a pressure of 2.0−
5.0 × 10−7 mbar. The ITO surface was pretreated for 10 min with
UV−ozone cleaner prior to any further processing. The hole-
injection layer was annealed at 180 °C for 20 min. All fabricated
OLEDs were encapsulated together with an oxygen- and moisture-
absorbing desiccant sheet using a glass lid and a UV-curable epoxy
resin inside a nitrogen-filled glovebox. Devices were characterized
optically and electrically with a C9920-12 External Quantum
Efficiency Measurement System from Hamamatsu.
Device Fabrication. The PLEDs were fabricated in the structure
ITO/PEDOT:PSS (35 nm)/emitting layer (60−80 nm)/TPBI (30 nm)/
CsF (15 Å)/Al (80 nm) in which ITO is indium tin oxide, PEDOT:PSS
is poly(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene), and
TPBI is 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene. The ITO glass
substrate was treated for 10 min with UV/O3 (UVO Cleaner 144AX,
Jelight Co.) prior to any further processing. The PEDOT:PSS was spin
coated directly onto ITO substrate using a spincoater P6700 from
Specialty Coating Systems and then dried at 100 °C for 10 min. The
emitting layer, containing a poly(N-vinylcarbazole) (PVK) host polymer
blended with 30 wt % of 1,3-bis(5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-
yl)benzene (OXD-7) and 7 wt % of iridium(III) complex, was spin coated
on top of the PEDOT:PSS layer using chlorobenzene as the solvent;
sample was then dried for 90 min at 50 °C. Prior to film casting, the
polymer solution was filtered through a Teflon filter (0.45 μm). The
TPBI layer was grown through thermal sublimation in a vacuum of
3 × 10−6 mbar using a MBraun evaporation chamber. The cathode was
completed through thermal deposition of CsF (15 Å)/Al (80 nm). The
electroluminescent device was characterized by attaching a computer-
controlled low-noise single-channel direct-current (d.c.) power source that
can act as both voltage source and current source and a voltage meter or
current meter (Keithley 2600, Keithley Instruments). Light from the
diode was coupled to a photodiode and read out by an electrometer/high-
resistance meter (Keithley 6517, Keithley Instruments). The output of the
data was handled by a Labview (National Instruments)-based program.
Calibration of the photodiode was done at a fixed current with a
luminance meter (LS-100 minolta). For every diode with a different
spectral distribution of light, the photocurrent as measured by the
photodiode was correlated to the light output in candelas per square
meter by this calibration. The EL spectrum was obtained using a Spex
FluoroLog-3 spectrofluorometer (Horiba-Jobin-Yvon Inc.).
RESULTS AND DISCUSSION
■
Synthesis and Characterization. Dimer [Ir2(dfptrBn)4Cl2]
(1) was prepared following the procedure recently described in
our group by reaction of IrCl3 with the cyclometalating ligand
dfptrBn in a 3:1 mixture of 2-ethoxyethanol:water at 140 °C for
20 h.51,52 We have shown the utility of 1 as precursor for
preparation of cationic bis-cyclometalated Ir(III) complexes.51
Furthermore, this dimer can also be used as starting material for
synthesis of neutral bis-cyclometalated and tris-cyclometalated
Ir(III) complexes (Scheme 1). By refluxing a suspension of 1 in
a dichloromethane:ethanol mixture (3:1) with picolinic acid (picH)
or 2-(5-(perfluorophenyl)-2H-1,2,4-triazol-3-yl)pyridine (pytrF5)
in the presence of a base, neutral complexes, [Ir(dfptrBn)2(pic)]
(2) and [Ir(dfptrBn)2(pytrF5)] (3), were obtained in high yields
(Scheme 1). On the other hand, the facial (fac) tris-cyclo-
metalated homoleptic complex, fac-[Ir(dfptrBn)3] (fac-4), and
heteroleptic complexes, fac-[Ir(dfptrBn)2(ppy)] (fac-5) and
fac-[Ir(dfptrBn)2(dfppy)] (fac-6), were synthesized modifying
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Figure 1. Crystal structure of 2 (left) and fac-5 (right). Selected parameters of the crystal structures are shown in Tables S1 and S2, Supporting
Information.
a procedure described in the literature (Scheme 1).38 First, the
meridional (mer) isomers, mer-4, mer-5, and mer-6, were
isolated by reaction of 1 and AgOTf in acetone followed by
addition of the corresponding cyclometalating ligand and a base
(Scheme 1). Subsequently, the meridional isomers were trans-
formed to their facial counterparts by irradiation of degassed
MeCN solutions of the corresponding complexes with UV light
probably due to packing effects. We find no indication of π−π
interactions since the shortest distance between the centers of
the benzyl groups is 6.141 Å.
Quantum-Chemical Calculations. Optimized geometrical
parameters calculated for complexes 2 and fac-5 are in good
agreement with X-ray experimental data (Table S3, Supporting
Information); this ensures a proper description of the nature of
the lowest excited states, provided that the complex keeps a
similar geometry in solution. In a second step, we examined the
nature of the frontier electronic levels that will be predomi-
nantly involved in the lowest excited states of all complexes by
analyzing for each electronic level the contribution from the
different fragments (Table 1).
Table 1 shows that the HOMO orbital is mainly localized on
the iridium atom (around 50%) for all complexes, except com-
plex 3 for which the major contribution of the HOMO orbital
(61%) lies on the coordinating ligand (pytrF5), with only 23%
on the iridium atom. Among the six highest occupied molecular
orbitals, all complexes exhibit three molecular orbitals with a
large contribution from the iridium atom (HOMO, HOMO-1,
and HOMO-5 for complexes 2 and 3 and HOMO, HOMO-1,
and HOMO-2 for complexes fac-4, fac-5, and fac-6). For the
three other orbitals, a significant contribution can be observed
from different ligands. While most of the complexes have their
HOMO level in the same energy range (from −5.25 to −5.00 eV),
complex 3 has a much deeper HOMO level (−5.49 eV). All
complexes exhibit the same pattern for localization of the
LUMO orbital; in all cases, the contribution from the
coordinating ligand exceeds 90% (see also Figure 2). None of
the six lowest unoccupied orbitals has a large contribution from
the iridium atom. Note that each ligand has at least one
significant contribution in one of the LUMO levels listed in
Table 1. In contrast to the HOMO level, the energies of the
LUMO level vary much more among the complexes (−0.63,
−1.10, −1.18, −1.29, and −1.45 eV for complexes fac-4, fac-5,
fac-6, 2, and 3, respectively).
1
(Scheme 1). All complexes were characterized using H NMR,
19F NMR, high-resolution mass spectrometry, and elemental
analysis (see Experimental Section).
For complexes 2 and fac-5, single crystals suitable for X-ray
crystallographic analysis were obtained by crystallization in
acetonitrile/Et2O and chloroform/Et2O, respectively (Figure 1).
In both complexes, the central Ir atom is in a distorted
octahedral coordination geometry. For complex 2, two
independent molecules (molecules A and B) are observed in
the unit cell (probably due to packing effects) and the distances
are equal within three standard deviations for both molecules
(Figure S1, Supporting Information). It is interesting to
compare the crystal structure of 2 and the structure of the
analogous complex with dfppy as cyclometalated ligand, the
well-known [Ir(dfppy)2(pic)] (FIrpic) that was described
elsewhere.68 In FIrpic, both Ir−C distances are very similar
(1.994(4) and 1.997(5) Å) and shorter than in 2 (2.032(11)
and 2.068(8) Å for molecule A, 2.028(8) and 2.059(8) Å for
molecule B), while the Ir−Npyridine of cyclometalated dfppy
(2.041(4) and 2.045(4) Å) is slightly longer compared to Ir−
Ntriazole in 2 (2.029(7) and 2.037(8) Å for molecule A, 2.019(7)
and 2.036(7) Å for molecule B). Ir−O distances in 2 are
2.162(7) Å for molecule A and 2.163(5) Å for molecule B and
similar to the distance found in FIrpic (2.152(3) Å). There is
no indication for π−π interactions since the shortest distance
between the centers of the benzyl groups is 5.093 Å.
The crystal structure of complex fac-5 confirms the facial
arrangement of the cyclometalated ligands in the complex. The
three Ir−C distances in fac-5 are similar (Ir−C(12) = 2.021(5)
Å, Ir−C(31) = 2.045(5) Å, and Ir−C(51) = 2.037(4) Å), also
when compared to Ir−C (2.016 Å) found in the homoleptic
complex fac-[Ir(ppy)3].69 On the other hand, Ir−N(21)
(2.153(4) Å) is slightly longer than the other two Ir−N distances in
the complex (Ir−N(1) = 2.123(4) Å and Ir−N(41) = 2.121(4) Å),
Photophysical properties and DFT Calculations. It is
well known that mer isomers have different spectroscopic
properties compared to fac geometries, with lower quantum
yields and poor photostability that make them not suitable for
photonic applications.37,38 In our systems we faced the same
problems with the stability of the mer isomers compared to the
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Table 1. Energy (in eV) and Localization of the Frontier Electronic Levels from HOMO-5 to LUMO+5 in Complexes 2, 3, fac-4,
a
fac-5, and fac-6
complex 2
complex fac-4
Ir dfptrBn1
dfptrBn
FO
eV
dfptrBn2
dfptrBn3
LUMO
−0.63
−0.62
−0.60
−0.44
−0.41
−0.40
2
90
6
6
2
FO
eV
Ir
pic
transN
transO
LUMO+1
LUMO+2
LUMO+3
LUMO+4
LUMO+5
2
2
1
1
1
89
2
3
HOMO-5
HOMO-4
HOMO-3
HOMO-2
HOMO-1
HOMO
−6.27
−6.01
−5.94
−5.86
−5.64
−5.25
−1.29
−0.91
−0.87
−0.76
−0.64
−0.61
54
8
14
15
42
23
16
23
1
24
60
11
10
8
2
93
13
1
21
4
51
42
6
35
56
8
7
41
64
31
9
2
85
46
complex fac-5
48
20
1
dfptrBn
LUMO
3
95
14
4
LUMO+1
LUMO+2
LUMO+3
LUMO+4
LUMO+5
3
14
73
15
30
80
69
19
22
60
12
FO
eV
Ir
ppy
transN
transC
4
HOMO-5
HOMO-4
HOMO-3
HOMO-2
HOMO-1
HOMO
−5.91
5
81
10
2
5
8
3
61
8
−5.74
−5.66
−5.19
−5.14
−5.00
−1.10
−0.80
−0.66
−0.60
−0.55
−0.40
7
24
64
17
22
12
2
59
27
29
12
9
2
7
1
6
48
49
51
4
6
complex 3
17
28
93
4
dfptrBn
LUMO
1
FO
eV
Ir
pytrF5
transN
trans3N
LUMO+1
LUMO+2
LUMO+3
LUMO+4
LUMO+5
2
2
92
11
3
HOMO-5
HOMO-4
HOMO-3
HOMO-2
HOMO-1
HOMO
−6.38
−6.28
−6.18
−5.99
−5.57
−5.49
−1.45
−1.10
−0.95
−0.89
−0.80
−0.60
45
0
31
98
2
12
1
12
0
3
79
4
7
3
90
1
14
9
19
72
15
5
66
14
27
11
2
1
5
94
1
4
1
1
97
35
23
4
22
61
93
7
complex fac-6
dfptrBn
LUMO
1
LUMO+1
LUMO+2
LUMO+3
LUMO+4
LUMO+5
5
8
80
16
34
53
96
FO
eV
Ir
dfppy
transN
transC
4
41
18
29
1
39
45
15
3
HOMO-5
HOMO-4
HOMO-3
HOMO-2
HOMO-1
HOMO
−5.94
−5.82
−5.77
−5.36
−5.33
−5.20
−1.18
−0.87
−0.69
−0.66
−0.61
−0.46
7
59
33
3
12
15
64
8
22
46
25
16
18
16
1
4
6
2
8
1
48
46
51
4
28
7
complex fac-4
28
18
2
FO
eV
Ir
dfptrBn1
dfptrBn2
dfptrBn3
14
92
3
HOMO-5
HOMO-4
HOMO-3
HOMO-2
HOMO-1
HOMO
−5.83
−5.71
−5.71
−5.29
−5.28
−5.13
10
9
33
50
7
31
35
24
24
14
16
26
5
LUMO
LUMO+1
LUMO+2
LUMO+3
LUMO+4
LUMO+5
2
2
93
9
9
60
6
2
26
37
18
1
63
36
3
45
45
49
25
12
17
3
24
78
1
30
18
1
1
97
a
We defined the following fragments: Ir, ligands (pic, pytrF5, ppy, and dfppy), and cyclometalated dfptrBn which are characterized with respect to
the bond in trans of the atom in the coordinating ligand (pic, pytrF5, ppy, and dfppy for complexes 2, 3, fac-5, and fac-6, respectively).
fac analogues (see Table S5 in Supporting Information), and
therefore, we focused only on the photophysical properties of
the fac isomers, while the photophysics for the mer isomers are
reported in the Supporting Information.
[Ir(dfppy)3].37 This is due to an increase in the energy gap
between the metal d orbitals and the π* orbitals of the
cyclometalating ligand, because of the higher energy of π*
orbitals observed for triazole compared to pyridine moi-
eties.49,70 This is also observed for phenylpyrazolyl-based Ir(III)
complexes.37,38 Furthermore, complexes fac-5 and fac-6 have
in general a higher extinction coefficient compared to 2, 3, or
fac-4 due to the presence of arylpyridine ligand. For complexes
3, fac-4, fac-5, and fac-6, the weak absorption band at 420, 392,
467, and 450 nm, respectively, could be assigned to a spin-
forbidden singlet-to-triplet transition. These transitions might
be partially allowed due to the presence of a heavy atom, such
as iridium, with a strong spin−orbit coupling. Indeed, these
values are similar to the one observed for the first band in the
emission spectra at low temperature for these complexes (Table 2).
We further calculated the nature of the lowest singlet excited
states at the TD-DFT level to assist interpretation of the
experimental spectra. Figure S2 and Table S4 (Supporting
Absorption spectra of complexes 2, 3, fac-4, fac-5, and fac-6
were recorded at room temperature in dichloromethane solu-
tions (Figure 3), and absorbance values of the most important
bands are shown in Table 2.
The intense bands (ε > 104 cm−1 M−1) in the region 230−
320 nm are assigned to π−π* transitions localized on the
coordinated ligands, while the bands at lower energy are
typically assigned to spin-allowed and spin-forbidden ligand-
centered (LC) and metal-to-ligand charge transfer (MLCT)
transitions.
In complexes 2 and 3, the absorbance bands at low energy
(>320 nm) are blue shifted compared to the dfppy counter-
parts.54,55 For the homoleptic complex fac-4, the MLCT
transitions are higher in energy than for the dfppy analogue,
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the TD-DFT calculations. Theoretical results for complexes 2
and 3 match well the experimental results. The energies of the
different absorption bands are well reproduced. For complex 2,
the absorption peaks at low energy have mainly MLCT and
ligand-to-ligand charge transfer (LLCT) character. The
calculated absorption peak at 383 nm (ES1, Table S4,
Supporting Information) involves the LUMO orbital which is
localized on the pic ligand; the MLCT thus occurs between the
iridium atom and the pic ligand, while the LLCT occurs
between the transN dfptrBn and transO dfptrBn ligands and
the pic ligand. For all absorption bands listed in Table S4,
Supporting Information, the MLCT always occurs from the
iridium atom to the pic (383 (ES1) and 342 nm (ES3)) or
transO dfptrBn (345 nm (ES2)) ligands, while transfers to the
transN dfptrBn ligand are negligible. At higher energy, the
intensity of the peaks grows as a result of introduction of an
increasing ligand-centered (LC) character. The first LC
contribution arises from the ligand transO dfptrBn (ES55),
then from transN dfptrBn (ES57), and finally from pic (ES82).
For complex 3, surprisingly, the first absorption peak has
mainly LC character, in addition to a MCLT character. That
the MLCT character is not the dominant character for this peak
results from the much lower localization of the HOMO orbital
on the iridium atom (only 23%) compared to complex 2. Since
the HOMO and LUMO levels are mainly localized on the
coordinating ligand (pytrF5), it has a dominant intraligand
charge transfer character. Moreover, the weak intensity of the
absorption band can be easily understood since the HOMO
and LUMO levels lay on different parts of the pytrF5 ligand. At
higher energy, the contribution of the aryltriazole ligand
increases the LLCT character of the absorbance, although the
LC character involving the pytrF5 ligand is still important. For
the facial complexes, the simulations systematically over-
estimate the energy of the lowest two absorption peaks (by
about 0.5 eV, because the solvent effects have been neglected
and/or the uncertainty in the experimental value due to
possible spin-forbidden transitions of low intensity), while good
agreement is obtained at higher energy. However, the relative
shifts between the energy of the various absorption bands of
fac-4, fac-5, and fac-6 are well reproduced. Given that fac-4 is a
homoleptic complex, the number of transitions contributing to
an absorption band is much larger compared to all other
complexes since all ligands are identical in fac-4. In fact, the
lowest simulated absorption band is made of three dominant
excited states involving an electron transition from the HOMO
level to the LUMO, LUMO+1, and LUMO+2 level. All these
transitions can be considered as equivalent since the quasi-
degenerate LUMO, LUMO+1, and LUMO+2 are localized on
the three different ligands (vide supra). Complexes fac-5 and
fac-6 are only differing by the presence of two fluorine atoms
on the ppy ligand in fac-6. Therefore, the energy as well as the
nature of the transitions in the absorption bands are quite
similar. In both cases, the lowest three absorption bands have a
strong MLCT character involving a transition from the iridium
atom to the ppy (dfppy) ligand for fac-5 (fac-6). The fourth
absorption band is characterized in both complexes by MLCT
character from the iridium atom to the three ligands. At higher
energy, a LC contribution is relevant to the excited states. For
the fifth absorption band, the LC character involves the ppy
(ES27,ES28) for fac-5 and dfppy (ES20,ES22) for fac-6, while
for the next absorption band, it is mainly the transC dfptrBn
ligand even though transN dfptrBn has a small contribution.
Note also that in Figure S2, Supporting Information, the
Figure 2. Representation of the optimized molecular geometry of the
complexes and of the localization of the HOMO (left) and LUMO
(right) orbitals. Labels of the different ligands used in Table 1 are also
displayed.
Figure 3. Absorbance spectra in aerated dichloromethane solutions of
complexes 2, 3, fac-4, fac-5, and fac-6.
Information) summarize the experimental absorption features
of the complexes in dichloromethane as well as the excited
states (ES) contributing to the absorption peaks according to
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Table 2. Photophysical Data of Iridium Complexes
c
complex
abs, λ/nm (ε, M−1cm−1
)
em, λ/nm
Φ
d
τ (μs)
kr (105 s−1
)
knr (105 s−1
)
a
e
d
e
2
solution
240(49 000)
268(sh)(20 000)
300 (10 000)
395 (750)
498
458
0.012 (0.009)
0.027 (0.021)
4.4
365.8
b
butyronitrile glass
solution
12.6
d
e
e
e
d
e
3
234 (59 900)
284(25 200)
323(10 000)
420(35)
440, 462
0.05 (0.01)
0.56 (0.16)
0.9
2.9
4.3
16.9
b
butyronitrile glass
425, 454, 480
5.6
a
fac-4
solution
234(64 216)
257(sh)(41 330)
300 (15 093)
323(8240)
371(224)
392(72)
b
b
b
butyronitrile glass
392, 418
480, 510
13.8
a
d
d
e
fac-5
solution
236(61 100)
257(43 700)
274(21 593)
332(9400)
387(2450)
417(1574)
467(136)
0.76 (0.04)
2.6 (0.09)
0.9
neat film
487, 513
480, 510
0.18
0.50
0.32(29%)
0.77(71%)
1.73(17%)
3.06(83%)
4.43
10% PMMA
butyronitrile glass
467, 492, 501, 528
465, 489
a
d
d
e
fac-6
solution
241 (58 625)
270 (34 857)
301(16 338)
325 (9956)
377(1033)
422(368)
0.50 (0.06)
1.15 (0.1)
4.3
450(143)
neat film
467, 490
0.15
0.42
0.27(41%)
0.60(59%)
0.90(15%)
2.29(85%)
3.60
10% PMMA
butyronitrile glass
461, 488
448, 472, 480, 509
a
b
c
d
e
Solution in dichloromethane. At 77K. PL QYs were determined with a calibrated integrating sphere system. Deaerated solution. Aerated
solution.
relative intensities of the absorption bands are well reproduced
for the five complexes.
theoretical results (see below). To gain insight into the CT
character of the excited state, emission spectra of complex 2 in
different solvents at room temperature have been further
studied (Figure S3, Supporting Information). Thus, by
increasing the polarity of the solvent, e.g., toluene, dichloro-
methane, MeCN and formamide the emission maxima shift to
the red, λem = 475, 498, 508, and 534 nm, respectively. This
strong solvatochromic behavior is in agreement with a pronounced
CT character of the excited state, as confirmed by calculations (see
below). The excited-state lifetimes are short, both in the presence
and in the absence of oxygen, τaer = 21 ns and τdeaer = 27 ns,
respectively. Furthermore, the emission quantum yields (QY)
mirror this behavior being around 0.9% and 1.2% in aerated and
deaerated solutions, respectively.
Experimentally, complex 2 presents an unstructured emission
spectrum with a maximum at 498 nm in dichloromethane
solution at room temperature (Figure 4). This emission
maximum is blue shifted (1105 cm−1, 30 nm) compared to
the analogous 1,4-disubstituted-1H-1,2,3-triazole complex, [Ir-
(C∧N)2(pic)] (C∧N = 1-decyl-4-phenyl-1H-[1,2,3]triazolyl),
(λem = 527 nm) described recently in the literature49 due to the
presence of fluorine atoms in our compound. However, the
emission is red shifted compared to the arylpyridine counter-
parts, FIrpic (λem = 468 nm).54,56 Furthermore, the 77 K
spectrum in butyronitrile glass has a maximum at 458 nm and is
blue shifted compared to the emission in solution. Interestingly,
it still shows a broad emission that would correspond to a high
MLCT character of the excited state, which agrees with
Complex 3 has a structured emission spectrum at room
temperature with maxima at 440 and 462 nm, while at 77 K the
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from ppy to dfppy due to the presence of fluorine atoms that
lower the HOMO. Additionally, the presence of aryltriazole as
cyclometalating ligand in fac-5 and fac-6 shifts the emission
maxima to the blue compared to homoleptic complexes fac-
[Ir(ppy)3] (λem = 509 nm) and fac-[Ir(dfppy)3] (λem = 469 nm)
described in the literature.36,37 The photophysical proper-
ties in solution of complexes fac-5 and fac-6 make them
promising candidates as dopants in electroluminescent
devices (see below). Thus, the emission properties in thin films,
both neat films and 10 wt % doped in a poly(methyl
methacrylate) (PMMA) films, were studied. For both
complexes, the emission spectra in neat film are slightly red
shifted compared to solution or 10 wt % doped film spectra
while the latter are almost identical to the spectra in solution
(Table 2 and Figure S4, Supporting Information). The QYs in
neat films (18% for fac-5 and 15% for fac-6) are significantly
lower than the QY in doped films (50% for fac-5 and 42% for
fac-6). Furthermore, the lifetimes in neat film are significantly
shorter than the ones observed in 10 wt % doped films (Table 2).
The higher quenching observed in neat films compared to the
diluted films is due to a higher degree of triplet−triplet
annihilation. It is interesting to compare the emission of
complexes fac-5 and fac-6 with their phenylpyrazolyl counter-
part described in the literature.36−38 Thus, complexes fac-5 and
fac-6 mimic the behavior of the dfppz analogues, fac-
[Ir(dfppz)2(ppy)] (λem = 475 nm, QY = 0.93, τ = 2.6 μs)36
and fac-[Ir(dfppz)2(dfppy)] (λem = 457 nm, QY = 0.60, τ = 1.3 μs).36
The higher QY of fac-5 could be due to higher activation
energy of the nonradiative state compared to fac-6.36
Figure 4. Emission spectra of the investigated complexes in
dichloromethane at RT (top) and butyronitrile glass matrix at 77 K
(bottom).
spectrum is slightly blue shifted and much more structured
(Figure 4). The emission in solution is ca. 20 nm (890 cm−1)
blue shifted compared to the one observed for the dfppy
analogue, [Ir(dfppy)2(pytrF5)], synthesized in our group.55
Furthermore, complex 3 shows a QY of 5% and a short excited-
state lifetime (0.56 μs) in deaerated solutions that yields a high
nonradiative rate constant (knr). The high value for knr could be
related to a distortion from coplanarity between the triazole of
the pytrF5 ligand and the substituted pentafluorophenyl ring
connected to it, as observed in complex [Ir(dfppy)2(pytrF5)],55,71
although the QY (16%) is higher in the latter. In fact, the DFT
results show that the excited state is more localized on the dfppy
ligand for [Ir(dfppy)2(pytrF5)],71 while in 3 it is more localized on
the pytrF5 (see below).
On the other hand, homoleptic fac-4 shows no emission in
solution at RT but a structured deep-blue emission at 77 K in
butyronitrile glass matrix (Figure 4). This behavior is similar to the
one found for the analogous complex with difluorophenylpyrazole
(dfppz) as the cyclometalating ligand, [Ir(dfppz)3].36−38 However,
the lifetime for fac-4 (13.2 μs) is almost one-half that of the
corresponding dfppz (27 μs). Accordingly, we assign the excited
state to a mixed MLCT/LC character. We believe that the reasons
for the lack of luminescence at room temperature of complex fac-4
are the same as for fac-[Ir(dfppz)3], i.e, a thermal activation of a
nonradiative state, formed by decoordination of the N-heterocyclic
ring in the excited state.36,72 A similar explanation was used by
Samuel et al. to justify the lowering in the emission in a series of
phenyl-1,2,4-triazoles Ir(III) complexes.45
Table 3 summarizes the TD-DFT-calculated nature of the
lowest triplet excited state for all complexes. It shows a nice
Table 3. Characterization of the Lowest Triplet Excited State
at the TD-DFT Level in the Absence of Spin−Orbit
Coupling for Complexes 2, 3, fac-4, fac-5, and fac-6
complex
occ
vir
eV/nm
%
2
HOMO
LUMO
3.16/392
50
27
49
40
16
11
41
19
29
17
HOMO-2
HOMO-1
HOMO
LUMO
3
LUMO
2.90/428
3.34/371
2.75/450
2.88/430
LUMO
fac-4
fac-5
fac-6
HOMO
LUMO+10
LUMO+11
LUMO
HOMO-1
HOMO
HOMO-5
HOMO
LUMO
LUMO
HOMO-5
LUMO
Complexes fac-5 and fac-6 present structured emission
spectra in solution at room temperature, while emission spectra
in butyronitrile glass matrix at 77 K show a much more
structured and blue shifted emission (Figure 4). This behavior
supports the MLCT character of the lowest-lying excited state
with a pronounced LC character, similar to what was observed
for the phenylpyrazolyl analogues.38 Both complexes show a
high QY in deaerated solution. The lifetimes of the excited state
of complexes fac-5 and fac-6 in deaerated solutions are 2.6 and
1.15 μs, respectively, while in air-equilibrated solutions they are
shorter and in the range of 0.1 μs. This is in accordance with
the triplet character of the lowest lying excited states, a mixed
3LC/3MLCT. In both cases, lifetime decays were mono-
exponential. Interestingly, emission of fac-6 (λem = 465 nm) is
blue shifted compared to fac-5 (λem = 480 nm) when changing
agreement with the experimental results except for complex 2
for which the calculated emission band is blue shifted by ca.
100 nm while it is only about 30 nm for the other complexes.
Among the facial isomers, the emission band at higher energy
of fac-4 is well reproduced as well as the impact of the
fluorination of ppy on fac-6. A graphical representation of the
character of the triplet state is displayed in Figure 5. For
complexes 3, fac-5, and fac-6, Figure 5 demonstrates that the
triplet state has a strong intraligand charge-transfer character
and a small MLCT character. In contrast, for fac-4, all
fragments of the complex are involved. For complex 2, the
triplet excited state has mainly MLCT and LLCT characters.
The large discrepancy observed in the calculations and
experimental data for 2 might be partly rationalized by the
large observed solvatochromism due to the strong CT character
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(ΔEp) is greater than 80 mV even for slower scan rate. In all the
cases, the ratio between cathodic and anodic peak currents
is ∼1. In good agreement with the DFT calculations, the
oxidation for complex fac-5 is associated with the phenyl of
the ppy and the Ir atom, while for fac-6 it is located on the
difluorophenyl moieties and the iridium atom. Additionally, the
reduction occurs on the pyridine of the ppy ligand for fac-5 and
on the pyridine of the dfppy for fac-6, according to the DFT
calculations. Interestingly, the reduction potential for fac-6 is
100 mV higher (0.080 eV energy difference at the DFT level)
than for fac-5 due to the electron-withdrawing effect of the
fluorine atoms in the dfppy unit, resulting in a higher LUMO
for fac-5. Furthermore, fluorine substituents on dfppy also
affect the oxidation potential of fac-6, which is observed to be
200 mV (0.2 eV also at the DFT level) higher than for fac-5.
Taking into account these results, we can therefore conclude
that the fluorination of the ppy ligand in these complexes
lowers the LUMO in a lesser extent than the HOMO, giving
rise to an increase in the HOMO−LUMO gap in fac-6
compared to fac-5 as observed by the ΔE 70 meV higher for
the former. This effect is similar to the one observed for the
phenylpyrazole analogues.38
Electroluminescent Devices. Due to their high lumines-
cence quantum yields in solution and thin films, complexes fac-
5 and fac-6 were selected as triplet emitter in the fabrication of
polymer light-emitting diodes (PLEDs). Furthermore, emitter
fac-6 was selected for further tests as dopant in small-molecule
OLEDs prepared by vacuum deposition because of its more
saturated blue color.
For the PLEDs, we used a host matrix containing poly(N-
vinylcarbazole) (PVK) and 1,3-bis(5-(4-tert-butylphenyl)-1,3,4-
oxadiazol-2-yl)benzene (OXD-7) for achieving optimal envi-
ronment for these blue phosphorescent complexes. The device
configuration consists of ITO/PEDOT:PSS (35 nm)/
PVK:OXD-7 (30 wt %):Ir complex (7 wt %) (60−80 nm)/
TPBI (30 nm)/CsF (15 Å)/Al (80 nm), in which ITO,
PEDOT:PSS, and TPBI stand for indium tin oxide, poly-
(styrenesulfonate)-doped poly(3,4-ethylenedioxythiophene),
and 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, respec-
tively.
Figure 5. Representation of the character of the triplet state.
Red/blue [yellow/green] isosurface is generated by the Jmol program
[Jmol: an open-source Java viewer for chemical structures in 3D;
http://www.jmol.org/. VMD: http://www.ks.uiuc.edu/Research/
vmd/; Humphrey, W., Dalke, A. and Schulten, K., J. Molec. Graphics,
1996, 14, 33-38.] by combining for each atom the LCAO coefficients
in all occupied [unoccupied] molecular orbitals involved in the
TD-DFT description of the triplet state and their CI contributions.
of the excited state (see above). To complement our descrip-
tion of the T1 state, a spin density analysis has been performed.
Figure S5, Supporting Information, confirms the TD-DFT
analysis. The spin densities are localized in the iridium atom
and one ligand for complexes 3, fac-5, and fac-6 while for 2 and
fac-4, they are more distributed over the whole complex.
Electrochemistry. The cyclic voltammetry (CV) of com-
plexes fac-5 and fac-6 was measured in 0.1 M solution of
TBAH in DMF, and the potentials referenced to SCE (Table 4).
The EL spectrum and representative performance data of
Ir(III) complexes are depicted in Figure 6 and Table 5,
a
Table 4. Electrochemical Data of Iridium Complexes
EHOMO
(eV)
ELUMO
(eV)
ΔEHOMO−LUMO
complex
Eox (V)
Ered (V)
(eV)
bd
e
f
f
g
,
fac-5
fac-6
+1.06
+1.24
−2.27
−2.17
−5.86
−6.04
−2.53
−2.63
3.33
cd
,
e
f
f
g
3.41
a
b
Cyclic voltammetry recorded in DMF/0.1 M TBAH. Quasi-reversible
Figure 6. (a) EL spectra (at around 100 cd/m2) of the studied PLED
devices doped with fac-5 and fac-6 and FIrpic. (b) External quantum
efficiency (ηext) and luminous efficiency (ηc) vs current density for the
fac-6-based diode with device configuration ITO/PEDOT:PSS/
PVK:OXD-7:7 wt % fac-6/TPBI/CsF/Al.
process (ΔEp > 60 mV).73 Reversible process (ΔEp ≈ 60 mV). Eox has
c
d
been evaluated as the mean value between the anodic and cathodic
e
peak potential. Irreversible process: Ered is related to the cathodic peak
f
potential. Energy levels (HOMO and LUMO) are calculated referring
to the energy level of ferrocene/ferricenium couple.74 HOMO−
g
LUMO energy gap, measured by cyclic voltammetry and calculated
upon conversion of mV to eV.74
respectively. The EL spectrum shows a dominant emission
from the Ir(III) complex without any other residual emission
from host and/or adjacent layers, thus revealing effective energy
transfer from the host to Ir dopants. The 1931 Commission
Internationale de L’Eclairage coordinates (CIE) of fac-5 and
In both cases, they show an irreversible reduction at all scan
rates (up to 5 V s−1), while the oxidation is reversible for fac-6
and quasi-reversible for fac-5 since the peak-to-peak separation
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Table 5. Summary of PLED Characteristics Using fac-5,
fac-6, and FIrpic as Dopants
a
b
b
Von
Lmax
ηext,max
[%]
ηc,max
fwhm
[nm]
c
[V]
[cd/m2]
[cd/A]
CIEx,y
fac-6
fac-5
FIrpic
3.4
3.4
3.7
5587
3.9
6.0
3.8
8.0
16.4
8.5
55
78
60
(0.17, 0.34)
(0.22, 0.52)
(0.19, 0.40)
21 285
7792
a
b
Recorded at 1 cd/m2. External quantum efficiency: ηext. Luminous
c
efficiency: ηc. At around 100 cd/m2.
fac-6 calculated from the EL spectrum at around 100 cd/m2 are
(0.22, 0.52) and (0.17, 0.36), respectively. Upon varying the
driving voltage from 5 to 13 V, the EL spectra barely change
(Figure S6, Supporting Information) and the CIE values remain
almost constant. Among these two Ir emitters, the CIE
coordinates of the device incorporating fac-6 indicate purer and
bluer emission than the device doped with FIrpic. The fac-6-
based device exhibits a turn-on voltage at 3.4 V (defined as bias
at a luminance of 1 cd/m2) and a maximum luminance of 5587
cd/m2 (at 12 V). The peak external quantum and luminous
efficiencies, without device optimization, are 3.9% and 8.0 cd/A,
respectively. Though quantum efficiency roll-off, attributed to
triplet−triplet annihilation, is observed at high current density,
the efficiency remains still more than 80% (corresponding to
3.4% and 6.9 cd/A) at a benchmark luminance of 500 cd/m2.
However, it has to be noted that results with PLEDs give
poorer performance as compared to devices made by vacuum
thermal deposition. We therefore built up multilayered device
structure by vacuum sublimation for the bluer emitter, fac-6.
For the OLEDs, four types of devices were made in total
using this emitter. Two devices (devices I and II) were fabri-
cated with the following configuration, differing only in the host
used: ITO/Plexcore (25 nm)/TAPC (30 nm)/Host:fac-6 (11%)
(10 nm)/BmPyPB (40 nm)/Cs2CO3 (1 nm)/Al (100 nm) where
for device I, Host = UGH2 and for device II, Host =26DCzPPy.
Device III configuration consisted of ITO/Plexcore (25 nm)/
TAPC (25 nm)/26DCzPPy (5 nm)/UGH2:fac-6 (11%) (10 nm)/
BmPyPB (40 nm)/Cs2CO3 (1 nm)/Al (100 nm), while the
configuration of device IV can be represented as follows: ITO/
Plexcore (25 nm)/TAPC (30 nm)/26DCzPPy:fac-6 (6%) (10 nm)/
UGH2:fac-6 (11%) (5 nm)/BmPyPB (40 nm)/Cs2CO3
(1 nm)/Al (100 nm). In this stack, the dual-emissive layer
has the aim of improving efficiencies by localizing the recom-
bination zone and exciton formation at the interface between
the two EMLs.
Figure 7. Electroluminescent spectra of devices I−IV.
Figure 8. Current density−voltage −Luminance (I−V−L) plots of
devices I−IV.
Figure 9. External quantum efficiency plots of devices I−IV.
The performances of the devices are summarized in Table 6.
Electroluminescent (EL) spectra plotted in Figure 7 show for
490 nm. CIE coordinates calculated for devices I, II, and IV are
all around (0.15, 0.28), while those of device III are (0.19, 0.34)
due to its slightly red shifted spectra. Figures 8 and 9 show
current−voltage−luminance (I−V−L) plots and external
quantum efficiency (ηext) plots, respectively. The impact of
using a host with a wide energy band gap (UGH2) can be
clearly seen by comparing devices I and II where the turn-on
voltage for device I is 0.6 V higher, likely due to the more
difficult charge injection into the EML. Device II shows the
highest efficiency, reaching maximum external quantum
efficiency, current efficiency, and power efficiency of 6.5%,
13.5 cd/A, and 12.1 lm/W, respectively. Adding an additional
layer of 26DCzPPy between TAPC and the EML, i.e.,
going from device I to device III, raises the efficiencies from
ηext = 4.3% to ηext = 5.9% as well as improve the luminous
efficiency to 10.7 cd/A and the power efficiencies to 7.3 lm/W
(Table 6). The enhancement in performance suggests that hole
Table 6. Performances of Vacuum-Deposited Devices
Containing fac-6
a
b
b
b
Von
ηext,max
[%]
ηc,max [cd/ ηp,max [lm/
c
[V]
A]
W]
CIEx,y
device I
3.7
3.1
4
4.3
6.5
5.9
5.8
8.8
6.9
12.1
7.3
(0.16; 0.28)
(0.19; 0.34)
(0.15; 0.28)
(0.16; 0.29)
device II
device III
device IV
13.5
10.7
11
4.2
7.4
a
b
Recorded at 1 cd/m2. ηext: External quantum efficiency. ηc:
c
Luminous efficiency. ηp: Power efficiency. Recorded at 100 cd/m2.
devices I, III, and IV a main peak at 460 nm with a less intense
shoulder around 488 nm, while for device II the main peak is
slightly red shifted around 465 nm with a shoulder centered at
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injection into the EML as well as device charge balance are
improved. Having a dual-emissive layer (device IV) improves
only slightly the performances, which could indicate that for
UGH2-based devices charge balance was already close to
optimum in device III.
ACKNOWLEDGMENTS
■
J.M.F.-H. and M.D.G.-L. would like to acknowledge Fundacion
Seneca (Agencia Regional de Investigacion, Region de Murcia)
́
́
́
́
and Ministerio de Ciencia e Innovacion, respectively, for a
grant. C.-H.C. thanks the NSC and DAAD Sandwich Program
for financial support. The work in Mons is supported by the
Belgian National Fund for Scientific Research (FNRS). This
research used resources of the Interuniversity Scientific
Computing Facility located at the University of Namur,
Belgium, which is supported by the F.R.S.-FNRS under
convention No. 2.4617.07. J.C. is a senior research associate
of FNRS.
CONCLUSIONS
■
A family of blue- and blue-green-emitting neutral bis- and tris-
cyclometalated Ir(III) complexes based on 1-benzyl-4-(2,6-
difluorophenyl)-1H-1,2,3-triazole (dfptrBn) as cyclometalating
ligand has been reported and their photophysical properties
investigated. The bis-cyclometalated complex 2 exhibits a
marked solvatochromic behavior due to the strong MLCT
character of its emissive excited state. A true blue emitter was
obtained when 2-(5-(perfluorophenyl)-2H-1,2,4-triazol-3-yl)-
pyridine (pytrF5) was used as ancillary ligand. The homoleptic
complex fac-4 is emissive at 77 K, showing a deep-blue emission,
but it is not luminescent in solution at room temperature. The
heteroleptic tris-cyclometalated complexes, with mixed arylpyr-
idine/aryltriazole ligands, fac-5 and fac-6, are highly emissive in
solution and thin films, with emission colors in the blue to blue-
green region. In both cases, the emission is blue shifted
compared to the homoleptic arylpyridine Ir(III) counterparts.
Furthermore, fluorination of the ppy ligand in fac-6 increases
the HOMO−LUMO gap and a blue shift of the emission is
observed compared with fac-5. We rationalized the photo-
physical and electrochemical properties of the complexes under
study by means of DFT calculations. We obtained an overall
good agreement with the experimental data and the expect-
ations for the band assignment. Due to the high emission
quantum yield of complexes fac-5 and fac-6 we employed them
as dopants in electroluminescent devices. Interestingly, for the
polymer-based devices complex fac-6 compared in the same
conditions with FIrpic presents a very similar or even better
performance than the standard blue emitter with a similar CIE.
REFERENCES
■
(1) Yersin, H. Highly Efficient OLEDs with Phosphorescent Materials;
Wiley-VCH: Weinheim, 2008.
(2) Baldo, M. A.; O’Brien, D. F.; You, Y.; Shoustikov, A.; Sibley, S.;
Thompson, M. E.; Forrest, S. R. Nature 1998, 395, 151−154.
(3) He, L.; Qiao, J.; Duan, L.; Dong, G. F.; Zhang, D. Q.; Wang, L.
D.; Qiu, Y. Adv. Funct. Mater. 2009, 19, 2950−2960.
(4) Ulbricht, C.; Beyer, B.; Friebe, C.; Winter, A.; Schubert, U. S.
Adv. Mater. 2009, 21, 4418−4441.
(5) Duan, L. A.; Hou, L. D.; Lee, T. W.; Qiao, J. A.; Zhang, D. Q.;
Dong, G. F.; Wang, L. D.; Qiu, Y. J. Mater. Chem. 2010, 20, 6392−
6407.
(6) Kamtekar, K. T.; Monkman, A. P.; Bryce, M. R. Adv. Mater. 2010,
22, 572−582.
(7) Xiao, L. X.; Chen, Z. J.; Qu, B.; Luo, J. X.; Kong, S.; Gong, Q. H.;
Kido, J. J. Adv. Mater. 2011, 23, 926−952.
(8) Farinola, G. M.; Ragni, R. Chem. Soc. Rev. 2011, 40, 3467−3482.
(9) Zhou, G.; Wong, W.-Y.; Suo, S. J. Photochem. Photobiol. C:
Photochem. Rev. 2011, 11, 133−156.
(10) Chi, Y.; Chou, P. T. Chem. Soc. Rev. 2007, 36, 1421−1431.
(11) Chi, Y.; Chou, P. T. Chem. Soc. Rev. 2010, 39, 638−655.
(12) Lee, T. C.; Hung, J. Y.; Chi, Y.; Cheng, Y. M.; Lee, G. H.; Chou,
P. T.; Chen, C. C.; Chang, C. H.; Wu, C. C. Adv. Funct. Mater. 2009,
19, 2639−2647.
(13) Brooks, J.; Babayan, Y.; Lamansky, S.; Djurovich, P. I.; Tsyba, I.;
Bau, R.; Thompson, M. E. Inorg. Chem. 2002, 41, 3055−3066.
(14) Vezzu, D. A. K.; Deaton, J. C.; Jones, J. S.; Bartolotti, L.; Harris,
C. F.; Marchetti, A. P.; Kondakova, M.; Pike, R. D.; Huo, S. Inorg.
Chem. 2010, 49, 5107−5119.
ASSOCIATED CONTENT
■
S
* Supporting Information
X-ray crystallographic data file (CIF), crystal data, and structure
refinement parameters for complexes 2 and fac-5; DFT-
calculated distances of the representative bonds involving the
iridium atom in the ground-state geometry of complexes 2 and
fac-5; table with comparison of the experimental and simulated
absorption spectra features for complexes 2, 3, fac-4, fac-5, and
fac-6; emission spectra of complex 2 in different solvents;
comparison of emission spectra of complexes fac-5 and fac-6 in
solution, neat film, and 10 wt % PMMA films; EL spectra of
fac-5 and fac-6 at different driving voltages. This material is
available free of charge via the Internet at http://pubs.acs.org.
(15) Zhou, G. J.; Wong, W. Y.; Yang, X. L. Chem.Asian J. 2011, 6,
1706−1727.
(16) Wang, Z. B.; Helander, M. G.; Hudson, Z. M.; Qiu, J.; Wang, S.;
Lu, Z. H. Appl. Phys. Lett. 2011, 98, 213301.
(17) Mydlak, M.; Mauro, M.; Polo, F.; Felicetti, M.; Leonhardt, J.;
Diener, G.; De Cola, L.; Strassert, C. A. Chem. Mater. 2011, 23, 3659−
3667.
(18) Strassert, C. A.; Chien, C. H.; Lopez, M. D. G.; Kourkoulos, D.;
Hertel, D.; Meerholz, K.; De Cola, L. Angew. Chem., Int. Ed. 2011, 50,
946−950.
(19) Zhang, Q. S.; Zhou, Q. G.; Cheng, Y. X.; Wang, L. X.; Ma, D.
G.; Jing, X. B.; Wang, F. S. Adv. Mater. 2004, 16, 432.
(20) Zhang, Q. S.; Zhou, Q. G.; Cheng, Y. X.; Wang, L. X.; Ma, D.
G.; Jing, X. B.; Wang, F. S. Adv. Funct. Mater. 2006, 16, 1203−1208.
(21) Armaroli, N.; Accorsi, G.; Holler, M.; Moudam, O.;
Nierengarten, J. F.; Zhou, Z.; Wegh, R. T.; Welter, R. Adv. Mater.
2006, 18, 1313−1316.
(22) Armaroli, N.; Accorsi, G.; Cardinali, F. o.; Listorti, A.
Photochemistry and Photophysics of Coordination Compounds:
Copper. In Photochemistry and Photophysics of Coordination Compounds
I; Springer Berlin Heidelberg: Berlin, Heidelberg, 2007; Vol. 280, pp
69−115.
(23) Moudam, O.; Kaeser, A.; Delavaux-Nicot, B.; Duhayon, C.;
Holler, M.; Accorsi, G.; Armaroli, N.; Seguy, I.; Navarro, J.; Destruel,
P.; Nierengarten, J.-F. Chem. Commun. 2007, 3077−3079.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: decola@uni-muenster.de, decola@unistra.fr (L.D.C.);
Jerome.Cornil@umons.ac.be (J.C.); jfern_01@uni-muenster.de
(J.M.F.-H.).
Present Address
⊥Institut de Science et d’Ingen
́
ierie Supramolec
́
ulaires (I.S.I.S.),
Universite
́
de Strasbourg, 8 allee Gaspard Monge, 67000
́
Strasbourg, France.
Notes
The authors declare no competing financial interest.
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Inorganic Chemistry
Article
(24) Zhang, L.; Li, B.; Su, Z. J. Phys. Chem. C 2009, 113, 13968−
13973.
(25) Czerwieniec, R.; Yu, J.; Yersin, H. Inorg. Chem. 2011, 50, 8293−
8301.
(26) 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.
(27) Deaton, J. C.; Young, R. H.; Lenhard, J. R.; Rajeswaran, M.;
Huo, S. Q. Inorg. Chem. 2010, 49, 9151−9161.
(51) Fernandez-Hernandez, J. M.; Yang, C.-H.; Beltran, J. I.; Lemaur,
V.; Polo, F.; Frohlich, R.; Cornil, J.; De Cola, L. J. Am. Chem. Soc.
̈
2011, 133, 10543−10558.
(52) Botelho, M. B. S.; Fernandez-Hernandez, J. M.; de Queiroz, T.
B.; Eckert, H.; De Cola, L.; de Camargo, A. S. S. J. Mater. Chem. 2011,
21, 8829−8834.
(53) Ladouceur, S.; Fortin, D.; Zysman-Colman, E. Inorg. Chem.
2011, 50, 11514−11526.
(54) You, Y. M.; Park, S. Y. J. Am. Chem. Soc. 2005, 127, 12438−
12439.
(28) Thompson, M. E.; Djurovich, P. E.; Barlow, S.; Marder, S.
Organometallic Complexes for Optoelectronic Applications. In
Comprehensive Organometallic Chemistry III; Elsevier: Oxford, 2007;
Vol. 12, pp 101−194.
(55) Orselli, E.; Kottas, G. S.; Konradsson, A. E.; Coppo, P.; Frohlich,
R.; Frtshlich, R.; De Cola, L.; van Dijken, A.; Buchel, M.; Borner, H.
Inorg. Chem. 2007, 46, 11082−11093.
(56) Baranoff, E.; Curchod, B. F. E.; Monti, F.; Steimer, F.; Accorsi,
(29) Flamigni, L.; Barbieri, A.; Sabatini, C.; Ventura, B.; Barigelletti,
F. Top. Curr. Chem. 2007, 281, 143−203.
G.; Tavernelli, I.; Rothlisberger, U.; Scopelliti, R.; Gratzel, M.;
̈
Nazeeruddin, M. K. Inorg. Chem. 2012, 51, 799−811.
(57) Wang, Z.-X.; Zhao, Z.-G. J. Heterocycl. Chem. 2007, 44, 89−92.
(58) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307−
326.
(30) Yersin, H.; Rausch, A. F.; Czerwieniec, R.; Hofbeck, T.; Fischer,
T. Coord. Chem. Rev. 2011, 255, 2622−2652.
(31) Adachi, C.; Baldo, M. A.; Thompson, M. E.; Forrest, S. R. J.
Appl. Phys. 2001, 90, 5048−5051.
(59) Otwinowski, Z.; Borek, D.; Majewski, W.; Minor, W. Acta
Crystallogr., Sect. A 2003, 59, 228−234.
(60) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467−473.
(61) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112−122.
(62) Antonello, S.; Musumeci, M.; Wayner, D. D. M.; Maran, F. J.
Am. Chem. Soc. 1997, 119, 9541−9549.
(63) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. Rev. B 1988, 37, 785−
789.
(64) Curtiss, L. A.; Redfern, P. C.; Raghavachari, K.; Pople, J. A. J.
Chem. Phys. 2001, 114, 108−117.
(65) Chiodo, S.; Russo, N.; Sicilia, E. J. Chem. Phys. 2006, 125,
104107.
(32) You, Y.; Park, S. Y. Dalton Trans. 2009, 1267−1282.
(33) Holmes, R. J.; Forrest, S. R.; Sajoto, T.; Tamayo, A.; Djurovich,
P. I.; Thompson, M. E.; Brooks, J.; Tung, Y. J.; D’Andrade, B. W.;
Weaver, M. S.; Kwong, R. C.; Brown, J. J. Appl. Phys. Lett. 2005, 87,
243507.
(34) Sajoto, T.; Djurovich, P. I.; Tamayo, A.; Yousufuddin, M.; Bau,
R.; Thompson, M. E.; Holmes, R. J.; Forrest, S. R. Inorg. Chem. 2005,
44, 7992−8003.
(35) Yang, C.-H.; Cheng, Y.-M.; Chi, Y.; Hsu, C.-J.; Fang, F.-C.;
Wong, K.-T.; Chou, P.-T.; Chang, C.-H.; Tsai, M.-H.; Wu, C.-C.
Angew. Chem., Int. Ed. 2007, 46, 2418−2421.
(36) Sajoto, T.; Djurovich, P. I.; Tamayo, A. B.; Oxgaard, J.;
Goddard, W. A.; Thompson, M. E. J. Am. Chem. Soc. 2009, 131, 9813−
9822.
(37) 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.
(38) Dedeian, K.; Shi, J. M.; Shepherd, N.; Forsythe, E.; Morton, D.
C. Inorg. Chem. 2005, 44, 4445−4447.
(39) Tamayo, A. B.; Garon, S.; Sajoto, T.; Djurovich, P. I.; Tsyba, I.
M.; Bau, R.; Thompson, M. E. Inorg. Chem. 2005, 44, 8723−8732.
(40) Yang, C.-H.; Li, S.-W.; Chi, Y.; Cheng, Y.-M.; Yeh, Y.-S.; Chou,
P.-T.; Lee, G.-H.; Wang, C.-H.; Shu, C.-F. Inorg. Chem. 2005, 44,
7770−7780.
(66) Avilov, I.; Minoofar, P.; Cornil, J.; De Cola, L. J. Am. Chem. Soc.
2007, 129, 8247−8258.
(67) Yang, C. H.; Beltran, J.; Lemaur, V.; Cornil, J.; Hartmann, D.;
Sarfert, W.; Frohlich, R.; Bizzarri, C.; De Cola, L. Inorg. Chem. 2010,
49, 9891−9901.
(68) Xu, M.-L.; Che, G.-B.; Li, X.-Y.; Xiao, Q. Acta Crystallogr., Sect. E
2009, 65, m28.
(69) Berger, R. J. F.; Stammler, H.-G.; Neumann, B.; Mitzel, N. W.
Eur. J. Inorg. Chem. 2010, 11, 1613−1617.
(70) Tamao, K.; Uchida, M.; Izumizawa, T.; Furukawa, K.;
Yamaguchi, S. J. Am. Chem. Soc. 1996, 118, 11974−11975.
(71) Orselli, E.; Albuquerque, R. Q.; Fransen, P. M.; Frohlich, R.;
Janssen, H. M.; De Cola, L. J. Mater. Chem. 2008, 18, 4579−4590.
(72) Treboux, G.; Mizukami, J.; Yabe, M.; Nakamura, S. Chem. Lett.
2007, 36, 1344−1345.
(41) Chien, C.-H.; Fujita, S.; Yamoto, S.; Hara, T.; Yamagata, T.;
Watanabe, M.; Mashima, K. Dalton Trans. 2008, 916−923.
(42) Chang, C.-F.; Cheng, Y.-M.; Chi, Y.; Chiu, Y.-C.; Lin, C.-C.;
Lee, G.-H.; Chou, P.-T.; Chen, C.-C.; Chang, C.-H.; Wu, C.-C. Angew.
Chem., Int. Ed. 2008, 47, 4542−4545.
(73) Bard, A. J.; Faulkner, L. R. Electrochemical Methods,
Fundamentals and Applications, 2nd ed.; Wiley: New York, 2001.
(74) Thelakkat, M.; Schmidt, H.-W. Adv. Mater. 1998, 10, 219−220.
(43) Haneder, S.; Da Como, E.; Feldmann, J.; Lupton, J. M.;
Lennartz, C.; Erk, P.; Fuchs, E.; Molt, O.; Munster, I.; Schildknecht,
̈
C.; Wagenblast, G. Adv. Mater. 2008, 20, 3325−3330.
(44) Sasabe, H.; Takamatsu, J.; Motoyama, T.; Watanabe, S.;
Wagenblast, G.; Langer, N.; Molt, O.; Fuchs, E.; Lennartz, C.; Kido, J.
Adv. Mater. 2010, 22, 5003−5007.
(45) Lo, S.-C.; Shipley, C. P.; Bera, R. N.; Harding, R. E.; Cowley, A.
R.; Burn, P. L.; Samuel, I. D. W. Chem. Mater. 2006, 18, 5119−5129.
(46) Lai, W.-Y.; Levell, J. W.; Jackson, A. C.; Lo, S.-C.; Bernhardt, P.
V.; Samuel, I. D. W.; Burn, P. L. Macromolecules 2010, 43, 6986−6994.
(47) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed.
2001, 40, 2004−2021.
(48) Finn, M. G.; Kolb, H. C.; Fokin, V. V.; Sharpless, K. B. Prog.
Chem. 2008, 20, 1−4.
(49) Beyer, B.; Ulbricht, C.; Escudero, D.; Friebe, C.; Winter, A.;
Gonzalez, L.; Schubert, U. S. Organometallics 2009, 28, 5478−5488.
(50) Felici, M.; Contreras-Carballada, P.; Smits, J. M. M.; Nolte, R. J.
M.; Williams, R. M.; De Cola, L.; Feiters, M. C. Molecules 2010, 15,
2039−2059.
1824
dx.doi.org/10.1021/ic3018419 | Inorg. Chem. 2013, 52, 1812−1824