Unusual dual-emissive heteroleptic iridium complexes incorporating TADF cyclometalating ligands

Article abstract of DOI:10.1039/c9dt04672k

Five new neutral heteroleptic iridium(iii) complexes IrL₂(pic) (2-6) based on the archetypical blue emitter FIrpic have been synthesised. The cyclometallating ligands L are derived from 2-(2,6-F₂-3-pyridyl)-4-mesitylpyridine (7), 2-(

Full text of DOI:10.1039/c9dt04672k

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Unusual dual-emissive heteroleptic iridium
complexes incorporating TADF cyclometalating
Cite this: DOI: 10.1039/c9dt04672k
ligands†
a,c
Helen Benjamin, a Yonghao Zheng, a,b Valery N. Kozhevnikov,
Jamie S. Siddle,a Luke J. O’Driscoll, a Mark A. Fox, a Andrei S. Batsanov,
a
Gareth C. Griffiths,d Fernando B. Dias, d Andrew P. Monkman d and
a
Martin R. Bryce
*
Five new neutral heteroleptic iridium(III) complexes IrL2(pic) (2–6) based on the archetypical blue emitter
FIrpic have been synthesised. The cyclometallating ligands L are derived from 2-(2,6-F2-3-pyridyl)-4-
mesitylpyridine (7), 2-(3-cyano-2,6-F2-phenyl)-4-mesitylpyridine (8), 2-(2,6-F2-phenyl)-4-[2,7-(HexO)2-
9H-carbazol-9-yl]pyridine (9), 2-(2,6-F2-3-pyridyl)-4-[2,7-(HexO)2-9H-carbazol-9-yl]pyridine (10) and
2-(3-cyano-2,6-F2-phenyl)-4-[2,7-(HexO)2-9H-carbazol-9-yl]pyridine (11) for complexes 2, 3, 4, 5 and
6, respectively. The carbazole-functionalised ligands 9–11 show weak thermally activated delayed fluor-
escence (TADF) in solution. Complexes 5 and 6 reveal dual emission in polar solvents. A broad charge
transfer (CT) band appears and increases in intensity relative to the higher energy emission band as
solvent polarity is increased. The dual emission occurs when the energy of the ligand 3CT state is compar-
able to that of the 3MLCT state of the complex, resulting in fast interconversion between the two.
Assignment of the ligand TADF and dual emission properties is supported by hybrid density functional
theory (DFT) and time dependent DFT (TD-DFT) calculations. Phosphorescent organic light emitting
devices (PhOLEDs) have been fabricated using these complexes as sky-blue emitters, and their perform-
ance is compared to devices using FIrpic and the previously reported complex IrL2(pic) 1 (L from the 2-
(2,6-F2-phenyl)-4-mesitylpyridine ligand). For identical device structures, the device containing the car-
bazole complex 4 performs best out of the seven complexes. The dual emission observed in solution for
complexes 5 and 6 is not observed in their devices.
Received 7th December 2019,
Accepted 23rd January 2020
DOI: 10.1039/c9dt04672k
rsc.li/dalton
two distinct excited states of a molecule emit simultaneously.
Dual emission can be facilitated by the strong spin–orbit coup-
Introduction
A vast number of luminescent transition metal complexes ling (SOC) associated with heavy metal atoms, and the
(LTMCs) have been studied because of their fundamentally multiple charge-transfer transitions that occur in LTMCs.
interesting photophysical properties and for their versatile Platinum6,7 and iridium8 complexes with extended
applications, notably in bioimaging, photocatalysis, sensing, π-conjugated ligands show both fluorescence from a peripheral
phosphorescent organic light emitting diodes (PhOLEDs) and organic substituent and phosphorescence associated either
solid-state lighting.1–5 However, there are notably few reports with the metal and ligating unit, or purely from the ligand,
of complexes that exhibit dual emission, a phenomenon where sensitised by the strong SOC effect of the metal. Neutral9 and
cationic10 iridium complexes that emit from different chromo-
phoric ligands have been reported, and the relative intensities
of the emission bands were modulated by the presence of
aDepartment of Chemistry, Durham University, Durham DH1 3LE, UK.
E-mail: m.r.bryce@durham.ac.uk
bSchool of Optoelectronic Science and Engineering, University of Electronic Science
and Technology of China (UESTC), Chengdu 610054, China
cDepartment of Applied Sciences, Northumbria University, Newcastle-Upon-Tyne,
NE1 8ST, UK
dDepartment of Physics, Durham University, Durham DH1 3LE, UK
†Electronic supplementary information (ESI) available. CCDC 1962578 and
1962579. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c9dt04672k
certain metal ions. Cationic cyclometalated Ir complexes with
pendant ligands that show dual emission from ligand-centred
(LC) and interligand charge transfer (ILCT) states have been
synthesised and shown to function as sensors for bio-
molecules.11 An iridium complex containing a dibenzoyl-
methane ancillary ligand has been reported to exhibit different
emission spectra from two distinct polymorphs, related to the
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difference in π-stacking interactions in the solid state.12 and reduce concentration quenching in devices, thus devices
Iridium complexes have also been incorporated into polymer fabricated from 1 are more efficient than those from FIrpic.
chains containing other emissive materials of different
The motivation for the present work was to explore 1 as a
colours.13,14 Some iridium complexes with relatively simple platform for the systematic development of complexes with
structures that display dual emission include a neutral mer- dual emission properties where the expected blue emission is
homoleptic complex studied by Yeh et al., which displayed two accompanied with a second lower energy emission. In a pre-
main emission features in solution, assigned to an ILCT/ vious study by Wu et al., donor (diarylamine or phenoxy) and
MLCT state and a localised ligand to ligand charge transfer acceptor (phenylsulfone) units were attached to cyclometalat-
(LLCT)/MLCT state, whose relative intensities varied with ing ligands within the same complex; however, dual emission
temperature.15 Zysman-Colman et al. investigated a dual emis- was not observed.22 Here, a family of related complexes 2–6,
sive neutral heteroleptic complex that displayed strong solvato- were synthesised by introducing a strong acceptor (difluoropyr-
chromism in solution, with wavelength-dependent excited idyl or difluorobenzonitrile) and/or a donor (carbazole) unit
state lifetimes and oxygen quenching sensitivity.16,17 Kumar into the ligand structure. Dual emission in solutions was
et al. described a family of complexes with 8-sulfonamidoqui- observed only from complexes 5 and 6 where both strong
noline-based ancillary ligands that displayed two emission acceptor and donor units are present. PhOLEDs fabricated
bands, both in solution (DMSO) and the frozen glass state, from these dual emitters along with the sky-blue emitters
originating from different MLCT, LLCT and LC transitions.18 FIrpic and complexes 1–4 are also discussed. To the best of
Climent et al. reported a dual emissive complex containing a our knowledge, the devices fabricated using complexes 5 and 6
Schiff base ligand with a solvatochromic higher energy fluo- are the first PhOLEDs to be reported using dual emissive Ir
rescent band at 400–525 nm and a lower energy phosphores- complexes.
cent band at 525–700 nm which were assigned to 1ILCT and
3MLCT respectively.19
As highlighted above, reports of dual emissive complexes
are sporadic, often limited to a single molecule or related to a
Results and discussion
Synthesis
single functional group, providing little guidance for future
synthetic design. We previously reported that complex 1
(Chart 1), which differs from the ubiquitous blue emitter
iridium(III) bis[4,6-(difluorophenyl)pyridinato-N,C2′]picolinate
(FIrpic)20 only by the presence of the mesityl groups, is an
efficient sky-blue emitter in PhOLEDs with a solution-pro-
cessed emitting layer.21 The mesityl groups increase solubility
The syntheses of the ligands 7–11 for the target complexes 2–6
are shown in Schemes 1 and 2. Ligands 7 and 8 were syn-
thesised via Suzuki couplings between 2-chloro-4-(2,4,6-tri-
methylphenyl)pyridine21 12 and the desired boronate ester (13
or 14) in moderate yields (34–51%). For ligands containing the
dialkoxy substituted carbazole moiety, dimethoxycarbazole23
Chart 1 Complexes 1–6 studied in this work.
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Scheme 1 Synthesis of mesityl-functionalised complexes 2 and 3. Reagents and conditions: (ai) Pd2(dba)3, PCy3, K3PO4, 1,4-dioxane/water, 60 °C;
(aii) Pd(OAc)2, SPhos, K3PO4, 1,4-dioxane/water, 90 °C; (b) IrCl3·3H2O, 2-ethoxyethanol/water, 110 °C followed by picolinic acid, 2-ethoxyethanol,
110 °C.
Scheme 2 Synthesis of carbazole-functionalised complexes 4–6. Reagents and conditions: (a) 4-Iodo-2-chloropyridine, CuI, 1,10-phenanthroline,
K2CO3, DMF (dry), 120 °C; (b) BBr3, CH2Cl2 (dry), 0 °C; (c) 1-bromohexane, K2CO3, DMSO; (di) 2,4-difluorophenylboronic acid, Pd(PPh3)4, K2CO3, 1,4-
dioxane/water, 90 °C; (dii) 13, SPhos, Pd(OAc)2, K3PO4, 1,4-dioxane/water, 60 °C; (diii) 14, SPhos, Pd(OAc)2, K3PO4, 1,4-dioxane/water, 60 °C; (ei)
IrCl3·3H2O, 2-ethoxyethanol/water, 120 °C followed by picolinic acid, Na2CO3, 2-ethoxyethanol, 120 °C; (eii) IrCl3·3H2O, diglyme, 130 °C followed by
picolinic acid, 130 °C; (eiii) IrCl3·3H2O, 2-ethoxyethanol/water, 110 °C followed by picolinic acid, Na2CO3, 2-ethoxyethanol, 110 °C.
15 was first coupled with 2-chloro-4-iodopyridine in an Ullman- MIDA derivatives followed literature procedures with experi-
type reaction to give 16 (96% yield). The methoxy ethers were mental details described in the ESI (Scheme S1†). The MIDA
then deprotected with BBr3 to give the dihydroxycarbazole esters were used due to the instability of the parent boronic
derivative 17 (72%) and hexyl chains were added to improve the acids under the reaction conditions. Longer reaction times, as
solubility of the resulting complexes, via a Williamson ether required for coupling reactions with the less active 2-chloro-
synthesis, to give the key intermediate 18 (79%).
pyridine derivatives, suffer from competing deborylation, par-
The next step was to perform Suzuki coupling reactions ticularly for highly electron-deficient boronic acids.24,25 The
with 2,4-difluorophenylboronic acid or N-methyliminodiacetic Suzuki couplings between boronic esters 13 and 14 and chlor-
acid (MIDA) boronate derivatives 13 or 14. The synthesis of the ide 18 followed the protocol described by Burke et al.,25 and
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the products were isolated in good yields (87% for 10 and 83% Ir-Py-Mes rod is substantially non-linear, bending by 16.5° in 2
for 11).
or 21° in 3, as in other analogous complexes (cf. 39.6° in 1).29
The target heteroleptic picolinate iridium complexes 2–6 The packing of both 2 and 3 shows no π–π stacking and is
were then synthesised (Schemes 1 and 2) via the standard dominated by edge-to-face or arene–solvent interactions. In
method.26,27 Reaction of the ligands (7–11) with IrCl3·3H2O both complexes, the Ir atom has a distorted octahedral coordi-
gave yellow precipitates presumed to be the intermediate nation, with metal–ligand bond lengths similar to the reported
μ-dichloro-bridged dimers. Picolinic acid was added and the crystal structures for FIrpic.30–34
solution heated to 110–130 °C. The desired complexes 2–6
were isolated in 21–55% yields. For 5 and 6, if the reaction
temperature was increased to 130 °C a large number of pro-
ducts was observed, identified by mass spectrometry as the
products of sequential replacements of fluorine substituents
Electrochemical and photophysical
properties
with 2-ethoxyethoxy groups, presumably via an SNAr reaction
Electrochemistry
(Fig. S1†). The instability of the 2,4-difluoro-2′,3-bipyridine
The electrochemical properties of complexes 1–6 and the car-
bazole ligands 9–11 were investigated by cyclic voltammetry
with the data summarised in Table 1 and their cyclic voltam-
mograms shown in Fig. 2. The oxidation potentials of com-
ligand under the standard reaction conditions has been
observed previously, wherein the methoxyethanol solvent
attacks the ligands and the tetra-alkoxylated heteroleptic
complex was isolated as the major product in good yield.28
Single crystal X-ray structures obtained for complexes 2 and
3 are depicted in Fig. 1 with the crystal data summarised in
Table S1.† As expected for complexes synthesised from the
μ-dichloro-bridged dimers, the Ir–N bonds of the two C^N
ligands are trans to each other and ca. 0.08 Å shorter than the
Ir–N(picolinato) bond, which is affected by the trans-influence
of an Ir–C bond. Both Ir–C bonds in 2 are slightly shorter than
in the isoelectronic complex 1 (2.001(2) and 1.988(2) Å,
Table S2†).29 In both 2 and 3, the dihedral angles between
each pyridine ring and its attached mesityl ring are such as to
preclude π-conjugation, viz. 63.4° and 78.0° in 2, 69.1° and
63.4° (or 70.2° for an alternative position of the disordered
mesityl) in 3, cf. 67.0° and 78.7° in 1. Interestingly, the Mes-Py-
Table 1 Electrochemical data and energy levels for complexes 1–6 and
ligands 9–11
Complex
Ea a/V
HOMOb/eV
LUMOc/eV
Optical gapd (eV)
FIrpic
1
2
3
4
5
6
9
0.95
0.94
1.26
1.40
0.66
0.63
0.65
0.64
0.65
0.67
−5.69
−5.68
−6.00
−6.14
−5.40
−5.37
−5.39
−5.38
−5.39
−5.41
−2.96
−3.06
−3.24
−3.46
−2.82
−2.69
−2.77
−1.83
−1.91
−1.98
2.73
2.62
2.76
2.68
2.58
2.68
2.62
3.55
3.48
3.43
10
11
a All values reported vs. FcH/FcH+ = 0.00 V; measured in 0.1 M
nBu4NPF6 in CH2Cl2 at 298 K with scan rate of 100 mV s−1 b E(HOMO)
.
= −4.74 − Ea eV with respect to the FcH/FcH+ couple at 4.80 V. c LUMO
energies estimated from the HOMO level + the optical gap determined
from Fig. 3/Fig. S9.† d Optical gap determined from the onset of
absorption in Fig. 3/Fig. S9.†
Fig. 1 X-ray molecular structures of 2 (left) and 3 (right). Minor disorder
components and solvent of crystallisation are omitted, thermal ellipsoids
are drawn at the 50% probability level.
Fig. 2 Cyclic voltammograms of complexes 1–6 and ligands 9–11.
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plexes 1–3 are assigned to the Ir3+/Ir4+ couple and are similar
to those reported for their mesityl-free analogues.35 The poten-
tials required to oxidise the iridium centre increase in accord-
ance with the increased electron withdrawing properties of the
ligand L (difluorophenyl < difluorocyanophenyl < difluoropyri-
dyl). By contrast, the first oxidation potentials of the com-
plexes 4–6 containing the 2,7-dialkoxycarbazole moiety are
similar (anodic potentials at 0.63–0.66 V). This observation,
and comparison with the voltammograms of ligands 9–11,
suggests that, for these complexes, the first oxidation orig-
inates from the carbazole moiety. The voltammograms of com-
plexes 4–6 and ligands 9–11 also show a change in profile on
increasing the number of cycles (Fig. S3–8†). It is known that
oxidation of carbazole derivatives results in the formation of a
radical cation on the carbazole subunit, and that these radical
cations can dimerise at the 3- (6-) positions.25 The additional
peaks observed in the subsequent scans are assigned to the
oxidation of dimeric/polymeric species formed via carbazole
dimerisations.
Table 2 Photophysical data for selected compounds
b
abs
em
λ
(ε)/nm
λ
/
PLQY/
ΦPL
max
max
Compound (×103 M−1 cm−1 a
)
nm
τP d/μs
c
1
290 (32.7), 323
(17.6), 345 (10.2),
MCH 470, 497
CBZ 472, 498
—
0.44
—
—
1.72
—
385 (7.3), 430 (2.9), CHCl3 467, 496
459 (0.9)
2
3
4
290 (31.5), 317
(22.3), 365 (8.8),
MCH 446, 475
CBZ 447, 474
—
0.37
—
—
0.30
—
—
0.41
—
—
1.76
—
—
1.61
—
—
1.90
—
411 (1.1), 438 (0.4), CHCl3 444, 472
293 (40.8), 306
(34.2), 377 (8.0),
MCH 460, 489
CBZ 459, 486
422 (2.4), 450 (0.8), CHCl3 454, 484
296 (52.4), 315
(46.6), 364 (29.8),
379 (26.2), 400
(16.7), 436 (3.8),
463 (1.8)
MCH 477, 508
CBZ 480, 510
CHCl3 475, 506
5
6
306 (55.9), 313
(53.0), 365 (33.8),
382 (38.7), 445 (0.9)
MCH 460, 484
—
—
CBZ
461, 489, 565 0.30
0.83
(460),
0.79
(550)
—
CHCl3 456, 488, 564
Zeonex 459, 486
MCH 463, 490
—
0.08
—
1.69
—
Absorption and emission
296 (64.5), 308
(62.3), 372 (31.0),
389 (33.8), 454 (1.7)
CBZ
469, 499, 583 0.13
0.52
(470),
0.49
(550)
—
The absorption spectra of complexes 1–6 and ligands 9–11 in
toluene are shown in Fig. 3 and Fig. S9,† respectively, with
data listed in Table 2. The complexes possessing carbazole
units (4–6) show larger extinction coefficients than the other
complexes (1–3). The strong bands between 290–325 nm are
assigned to π–π* transitions on the ligand based on the
absorption spectra of ligands 9–11 (Fig. S9†). The intense
bands at 350–425 nm are assigned to the 1MLCT bands, as
they are not present in the ligand spectrum, while the signifi-
CHCl3 464, 496, 581
MCH 406
CBZ
—
—
9
306 (24.6)
—
469
0.09
0.039,e
[0.02] 0.768e
[0.030]
CHCl3 479
302 (24.1), 314 (sh, MCH 427
23.6) CBZ 504
—
—
—
10
11
—
0.10
0.099,e
[0.01] 0.946e
[0.029]
cantly weaker (0.8–1.8 × 103 dm3 mol−1 cm−1 3MLCT bands
)
can be seen at 425–475 nm based on the calculations of Hay.36
The influence of solvent polarity on the absorption spectra of
complexes 4–6 and corresponding ligands 9–11 was investi-
gated (Fig. S10†), and negligible solvatochromic behaviour was
observed.
CHCl3 521
302 (26.5), 315 (sh, MCH 451
24.1) CBZ 512
—
—
—
—
0.09
0.094,e
[0.02] 0.574e
[0.023]
CHCl3 534
—
—
The emission spectra of the complexes 1–6 in various sol-
vents are shown in Fig. 4. In the non-polar solvent methyl-
a Data obtained in toluene solution at 20 °C, sh = shoulder. b Data
obtained in degassed solvent, with λex = 365 nm for 1–6, λex = 340 nm
for 9–11. MCH = methylcyclohexane, CBZ = chlorobenzene, zeonex = a
cyclic olefin polymer.37 c For 1–6, measured in degassed solvent, rela-
tive to quinine sulfate (ΦPL = 0.546 in 0.5 M H2SO4) at 20 °C; for 9–11,
measured using an integrating sphere, [ ] refers to the PLQY in aerated
solvent; estimated error 5%. d Estimated error 5%, measured in dea-
erated solvent. The number within ( ) refers to the wavelength corres-
ponding to the lifetime. [ ] refers to a lifetime in aerated solvent.
e Lifetimes for prompt and delayed fluorescence respectively.
cyclohexane (MCH), all the complexes display structured emis-
sions in the 450–500 nm region, typical of emission from a
mixed LC/MLCT state. On increasing the solvent polarity (to
chlorobenzene, then chloroform) little change can be seen in
the emission profiles for complexes 1–4. However, complexes 5
and 6 exhibit a broadening of emission, with the appearance
of a featureless band at 510–560 nm that increases in intensity
relative to the higher energy LC/MLCT emission band on
Fig. 3 UV-Vis absorption spectra of the complexes in toluene [10−5 M].
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Fig. 4 Emission spectra of complexes 1–6 in different solvents [10−5 M]. MCH = methylcyclohexane.
increasing solvent polarity. Compared to 5, the effect of complex 5 (Fig. S11†), which shows no significant change in
solvent polarity on the emission of 6 is weaker. spectral features during the decay, suggesting that the emis-
The PLQYs and lifetimes of complexes 1–6 in solution sion bands come from two states where interconversion is fast.
(chlorobenzene) are listed in Table 2. For complexes 5 and 6, In order to better understand the source of the broadened
the lifetimes of the two emission bands were measured, and emission in complexes 5 and 6, more photophysical measure-
the values for the two features are the same within experi- ments were conducted on complex 5. The effect of temperature
mental error. This is highlighted by the decay profile of on the emission spectrum of complex 5 in chlorobenzene
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shifts significantly on increasing solvent polarity, consistent
with a charge transfer (CT) state. Notably, the emission of 9 is
significantly blue-shifted in all solvents compared to the emis-
sion of 10 and 11; this can be attributed to the significantly
weaker acceptor strength of the difluorophenyl group com-
pared to the difluorocyanophenyl or difluoropyridyl groups.
The emission of the ligands was quenched by oxygen
(Fig. S16–18†), and the ratio (ΦDF/ΦPF) between the prompt
emission (PF) and the delayed emission (DF), calculated from
the steady-state emission spectra, ranged from 1.02 (for 9) to
3.07 (for 11). Lifetime measurements (Fig. S19–21†) indicated
the presence of two decays, one on the order of 40–100 ns, and
the other on the order of 500–1000 ns. Based on these obser-
vations, and the donor–acceptor structure of the ligands, the
emissions from 9–11 are attributed to TADF processes.38
Fig. 5 The temperature dependence of the emission profile of 5 in
chlorobenzene [10−5 M].
With the knowledge that ligands 9–11 possess low-lying
emissive states, the emission behaviour of complexes 4–6 can
now be interpreted. In Fig. 7, the energies of the ligand 1CT
states, estimated from the onset of the emission of 9–11, were
(Fig. 5) showed that on decreasing the temperature from room compared to the energies of the LC/MLCT states of the com-
temperature to 230 K the ratio between emission bands plexes, which were determined from the onset of their charac-
changed, with an increase in the intensity of the lower energy teristic emission feature. This comparison clearly highlights
feature relative to the higher energy feature. The possibility of the difference between complex 4, where the ligand has a
the second feature corresponding to emission from an excimer weaker acceptor, and complexes 5 and 6, where the ligands
was dismissed as emission spectra of 5 recorded in both con- have stronger acceptors. In the case of 4, the energy of the
centrated and dilute chlorobenzene solution had comparable emissive state of the ligand was always significantly greater
spectral profiles (Fig. S12†). Additionally, there was no change (>0.3 eV) than that of the MLCT state of the complex irrespec-
in spectral profile on exposure to oxygen (Fig. S13†); the emis- tive of solvent polarity. However, for 5 and 6 while the gap is
sion intensity decreased as expected for a state with triplet wide (>0.3 eV) in MCH it decreased dramatically on increasing
character. These findings are consistent with the lifetime solvent polarity, dropping to only 0.05 eV in chloroform. Based
measurements, which indicated that the emission bands orig- on this observation, we propose that the emissive behaviour of
inate from states that are able to quickly interconvert. The 5 and 6 is due to the formation of a mixed CT-MLCT state,
possibility of the dual emission being due to a degradation which arises when the 1CT state on the ligand lies close in
product of 5 in polar solvents was also ruled out. The emission energy to that of the 3MLCT state of the complex. As TADF was
spectrum of a sample of 5 dissolved in CHCl3 was measured observed for ligands 9–11, the energy of the 3CT state is
and showed the dual emission feature, the solvent was then expected to be similar to that of the 1CT state. The lack of
removed in vacuo and the residue redissolved in MCH. The change in the emission decay profile of 5 in chlorobenzene,
emission spectrum was then measured again and the second and the fact that the profile emission is unchanged on
emission feature was not observed (Fig. S14†).
exposure to oxygen, indicates that a fast equilibrium exists
The emission of 5 was also investigated in the solid state, in between the 3CT and 3MLCT states. Changing solvent, or chan-
the form of spin-coated zeonex (a cyclic olefin polymer)37 films ging the temperature, perturbs this equilibrium and shifts the
3
3
(1–5% w/w), and are summarised in Table 2. The emission emission to favour either the CT or MLCT state. Under con-
profile (Fig. S15†) resembles that of the emission in non-polar ditions where the gap between the 3CT and 3MLCT is large
MCH solution. The emission of the film was also investigated (>0.3 eV), such as for complex 4 in all solvents, and complexes
at low temperatures (to 230 K), but no change in emission 5 and 6 in MCH, there is no state mixing and emission occurs
profile was observed (Fig. S15†). The lack of a broadened emis- purely from the MLCT state. It is noted here that the broad CT
sion in these films compared to chlorobenzene solutions feature in the emission of complexes 5 and 6 is lower in energy
could be due to the low polarity of host material, the lack of than in the spectra of the free ligands; this can be explained
free molecular motions in the solid state, or both.
by coordination to the metal centre shifting the energy of the
As the appearance of the second emission feature was 3CT state.
observed only for complexes 5 and 6 it is clear that the carba-
zole moiety plays a significant role in the emissions. In order
to understand this, the emissions of ligands 9–11 were investi-
DFT calculations
gated (Fig. 6), with lifetime and PLQY data listed in Table 2.
All three ligands exhibit broad, featureless emissions with Electronic structure calculations were carried out on com-
large Stokes shifts. The emission maximum in each ligand plexes 2–6 and ligands 7–11 to explore their frontier orbitals
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Fig. 6 Emission spectra of ligands 9–11 in solvents of differing polarities. MCH = methylcyclohexane, CBZ = chlorobenzene.
and understand the nature of the transitions involved in the
There is also a noticeable difference in the molecular orbi-
emissions. In the case of complexes with carbazole moieties tals between the carbazole complexes 5 and 6, which display
(4–6) four minima were located with approximately equal ener- dual emissions, and the carbazole complex 4, which does not.
gies, differing only by orientation of the carbazole groups In 5 and 6, the orbitals possessing significant Ir contribution
(Fig. S22–24†). The orbital contributions were comparable for are much lower in energy (HOMO−4, HOMO−5, see Tables S5–
all four conformers so only one conformer is discussed here S16†) than those of 4. This lack of metal contribution in the
for convenience.
frontier occupied orbitals could explain the relatively low
The frontier orbitals for representative Ir complexes 2, 4 quantum yields of these complexes compared to the mesityl
and 5 are shown in Fig. 8, with the orbitals for complexes 3 analogues. The complexes that show dual emission also have a
and 6 presented in the ESI (Fig. S25†). The percentage contri- different LUMO makeup to the other complexes. The LUMOs
butions of groups to the MOs are listed in Tables S3–S16.† A of complexes 2–4 all possess large contributions (30–60%)
clear difference can be seen between the complexes that from the picolinate ligand, while its contribution to the
contain carbazole moieties (4–6) and those that do not (2, 3). LUMOs of 5 and 6 is below 25% (see Tables S2–S15†).
For complexes 2 and 3 the HOMO has a considerable contri-
TD-DFT calculations were performed on the S0 optimised
bution from the Ir centre (40–55%), while for complexes 4–6 geometries of 2–6 to give insight into their emission behav-
the HOMO and HOMO−1 are located on the two carbazole iour; the results are summarised in Tables S17–S30.† For com-
fragments, with the Ir contributing to occupied orbitals at plexes 2 and 3 the character of all the lowest energy triplet
lower energies (HOMO−2 and below, see Tables S5–S16†). This transitions is similar and can be described as MLCT/LLCT in
is consistent with the cyclic voltammetry measurements which nature, with electron density transferring from the Ir (with
indicated that the first oxidation takes place at the carbazole 35–50% change in character) and the phenyl groups to the pyr-
units in complexes 4–6.
idine rings and picolinate ligand. The corresponding tran-
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sitions for complex 4 still show a large amount of MLCT char-
acter across all geometries, with changes of 26–40% in the Ir
electron density, despite the fact the HOMO and HOMO−1 are
carbazole based. The carbazole moiety contributes to some of
the transitions, with contributions ranging from 2 to 40%,
with greater contributions to states higher in energy. Electron
density is mostly transferred to the picolinate ligands and the
pyridine moiety.
In the case of complexes 5 and 6, there exist four states
within 0.06 eV in energy that differ quite significantly in their
composition. Two of the four states involve electron density
transfer from one of the carbazole units (95–100%) to the pyri-
dine, difluoropyridyl/difluorocyanophenyl and picolinate moi-
eties, indicating a state of strong CT character. The other two
states can be described as mixed MLCT/LLCT states, with elec-
tron density being transferred predominantly from Ir (13–16%
change) and carbazole (47–62% change) to the pyridine,
difluoropyridyl/difluorocyanophenyl and picolinate moieties.
Compared to complexes 2–4 the metal centre is clearly less
Fig. 7 Energy levels of the free ligand CT state in ligands 9–11,
measured from the onset of the emission, compared to the energy level
of the LC/MLCT state in complexes 4–6, measured from the onset of
the emission. MCH = methylcyclohexane, CBZ = chlorobenzene, CFM =
chloroform.
Fig. 8 Frontier molecular orbitals for 2, 4, and 5. Isocontours set to 0.02 e per bohr3. The % orbital contribution ratio is listed for each orbital in
the order Ir : mesityl/carbazolyl : phenylpyridyl : picolyl.
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Fig. 9 Frontier molecular orbitals for 7, 9, and 10. Isocontours set to 0.02 e per bohr3.
involved in the transitions for 5 and 6. These two different
transition characters correspond to the CT and MLCT emis- Fig. 9, with the orbitals for ligands 8 and 11 visualised in the
The frontier orbitals of ligands 7, 9 and 10 are shown in
3
3
sions observed for 5 and 6.
ESI (Fig. S26†). For ligands 7 and 8, the HOMOs are located
over the mesityl groups, while for ligands 9–11 the HOMOs are
exclusively located on the carbazole moieties. In all ligands,
the LUMOs are spread over the 2-phenylpyridine framework.
The HOMO–LUMO gaps for ligands 9–11 are notably smaller
(3.47–3.84 eV) than those of 7–8 (4.70–4.90 eV), a result of the
introduction of the electron-rich carbazole moiety.
Table 3 ΔES–T for ligands 7–11 from TD-DFT computations
Optimised geometry
‘Perpendicular’ geometry
ES1
(eV)
ET1
(eV)
ΔES–T
ES1
(eV)
ET1
(eV)
ΔES–T
Small singlet–triplet energy gaps (ΔES–T) in donor–acceptor
molecules usually promote TADF so ΔES–T energies for ligands
7–11 were calculated from the vertical excitation energies
determined from TD-DFT and listed in Table 3. At the opti-
mised S0 geometries, ΔES–T is relatively small for ligands 9–11
(<0.30 eV) while the values are much larger for ligands 7–8
Ligand
(eV)
(eV)
7
8
9
10
11
4.290
4.195
3.369
3.162
3.056
3.267
3.179
3.080
3.067
3.022
1.023
1.016
0.289
0.095
0.034
—
—
3.216
3.012
2.914
—
—
3.094
3.008
2.911
—
—
0.122
0.004
0.003
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(1.02 eV), which is consistent with the assignment of TADF ΔES–T drops to ca. 0.12 eV for 9 and <0.005 eV for 10 and 11,
emissions from ligands 9–11. When the dihedral angle thus TADF would increase. This dependence on conformation
between the carbazole donor and the pyridyl acceptor is may be a factor in the differences between solution and solid
restricted to 90° (‘Perpendicular’ geometry in Table 3) the state emissions for complexes 5 and 6.
Table 4 Summary of device data
λELmax
nm
/
Max brightness/
cd m−2
Turn-on
Current efficiency/
Power efficiency/
CIE coordinates/
Complex
voltagea/V
Max EQE/%
cd A−1
lm W−1
(x, y)b
FIrpic
473
477
450–500
468
484
472–491
476
2179
3195
274.4
1383
5013
1657
2988
7.2
7.3
10.3
8.2
6.8
9.3
8.0
2.14
4.26
0.27
2.06
5.69
1.46
2.09
4.63
9.44
0.55
3.57
13.84
3.44
4.73
1.36
2.83
0.13
0.96
4.05
0.91
1.09
(0.17, 0.37)
(0.17, 0.39)
(0.22, 0.33)
(0.16, 0.29)
(0.17, 0.46)
(0.22, 0.38)
(0.19, 0.38)
1
2
3
4
5
6
a Measured at a brightness of 10 cd m−2 b Measured at 12 V.
.
Fig. 10 Device data for complexes 1–6. The device structure is as follows: ITO/PEDOT:PSS (50 nm)/PVK:OXD:Ir complex [100 : 50 : 8] (75 nm)/TPBi
(25 nm)/LiF (1 nm)/Al.
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The lack of solvatochromic effects in the absorption spectra formances compared to the devices based on the related
for 9–11 (Fig. S10†) can be explained as their S0 → S1 CT tran- mesityl complexes 2 and 3, with superior maximum bright-
sitions have low oscillator strengths (Tables S31–33†) due to nesses (Fig. 10c), current efficiencies (Fig. 10e) and turn-on vol-
the almost total lack of overlap between the HOMO and the tages; however, the emission of devices based on carbazole-
LUMO in each case. The solvatochromic low energy bands pre- containing complexes was again less blue than their mesityl
dicted at 3.1–3.4 eV (Table 3) for 9–11 were not observed above analogues (Table 4). The device from the carbazole complex 6
the noise levels in the absorption spectra (Fig. S10†). The showed very similar performance and emission colour to the
TD-DFT results for ligands 9–11 indeed predict that the oscil- FIrpic device.
lator strengths for these transitions are very weak.
Conclusions
Device data
A series of iridium complexes (2–6) were synthesised contain-
To our knowledge, no OLED devices have been reported that ing ligands with donor and acceptor groups of varying
use complexes that display dual emissive properties in solution strengths to establish design rules for dual-emitting com-
as the emissive material. Complexes containing ligands with plexes. Ligands containing the carbazole group (9–11) showed
donor and acceptor groups, both on the same ligand,28 and on weak TADF emissions due to their strong donor–acceptor
different ligands,36 that do not show dual emission properties systems, with small ΔES–T gaps as determined by TD-DFT com-
in solution have been used in OLED devices, and display putations compared to ligands with a mesityl group (7, 8)
favourable performances due to their enhanced charge trans- which have large ΔES–T gaps. Complexes 5 and 6, derived from
port properties. OLEDs using complexes 1–6 as the emitters TADF ligands 10 and 11 respectively, showed dual emissions
were fabricated and compared to a reference device containing in polar solvents with a broad CT band that increases in rela-
FIrpic. The hole transporting layer and emissive layer were de- tive intensity compared to the MLCT emission with increasing
posited by solution processing techniques, and the electron solvent polarity. Photophysical investigations revealed that
3
transporting, electron injection layers and the cathode were dual emission occurs when the energy of the ligand CT state,
then fabricated by vacuum deposition. The device structure is which is highly susceptible to the solvent environment,
3
as follows: ITO/poly(3,4-ethylenedioxythiophene):poly(styrene- approaches the energy of the MLCT state, which experiences
sulfonate) (PEDOT:PSS, 50 nm)/poly(vinylcarbazole) (PVK):1,3- little change on increasing solvent polarity. The nature of
bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD-7):Ir these states was confirmed by DFT calculations. Dual emission
complex [100 : 50 : 8] (75 nm)/2,2′,2″-(1,3,5-benzinetriyl)-tris is observed from both states simultaneously and with the
(1-phenyl-1H-benzimidazole) (TPBi, 25 nm)/LiF (1 nm)/Al. The same lifetime, indicating a fast equilibrium between the 3LC
efficiency and luminance data of the devices are summarised and 3MLCT states. This equilibrium can be perturbed to
in Table 4.
favour one state over the other by changes in temperature and
The electroluminescence (EL) spectra from the devices are solvent polarity. Devices of the iridium complexes were fabri-
shown in Fig. 10a. For complexes 1, 3 and 4, the EL spectra are cated with identical structures and their performances com-
comparable to the solution-state PL spectra while the EL spec- pared with an equivalent FIrpic device. The device containing
trum for 6 displays no sign of the dual emission present in the the carbazole complex 4 showed superior performance com-
PL spectra of 6 in polar solvents. The EL spectra for the pared to the FIrpic device. To the best of our knowledge, the
devices containing 2 and 5 are significantly broadened com- devices containing complexes 5 and 6 are the first devices
pared to the solution PL spectra, suggesting that the bipyridyl based on dual-emissive iridium complexes but they did not
ligands in these systems are responsible for the broadening. display dual emissions under operation. The device containing
However, the broadening of the EL band for 5 is not in accord 6 performed similarly to that containing FIrpic. There remains
with the dual emission bands present in the PL spectra of 5 in considerable scope for harnessing dual-emissive complexes in
polar solvents. The absence of dual emission may relate to PhOLEDs.
reduced rotational freedom of the complexes in the emissive
layer, in agreement with the observations in the thin film
studies above.
Experimental section
Materials, synthesis, and characterization
The device of complex 4 performed the best, outperforming
those of FIrpic and complex 1 in terms of EQE and brightness;
however the device emission was less blue (λELmax 484 nm for
General procedures. All commercially available chemicals
4 vs. 473 nm for FIrpic and 477 nm for 1). This improved per- were used without further purification unless stated otherwise.
formance may be explained by the steric bulkiness and solubi- Reactions requiring an inert atmosphere were performed
lity enhancement afforded by the carbazole units, which under a blanket of argon gas, which was dried over a phos-
reduce concentration quenching as explained elsewhere for phorus pentoxide column. Anhydrous solvents were dried
the mesityl groups in 1 compared to FIrpic.21 The devices of through an HPLC column on an Innovative Technology Inc.
the carbazole complexes 5 and 6 also showed improved per- solvent purification system. Column chromatography was per-
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formed using 40–60 μm mesh silica gel. Analytical TLC was where subscripts ‘x’ and ‘ref’ denote the material being
performed on plates pre-coated with silica gel (Merck, silica measured and the reference, respectively. Φ represents the
gel 60F254) and visualised using UV light (254, 315, 365 nm). PLQY, Grad is the gradient from the plot of integrated fluo-
NMR spectra were recorded on Bruker Avance 400 MHz, Varian rescence intensity vs. absorbance, and η is the refractive index
Mercury 200 and 400 MHz, Varian Inova 500 MHz or Varian of the solvent.
VNMRS 600 and 700 MHz spectrometers. 1H and 13C chemical
Solutions of the complexes in degassed solvent [<10−5 M]
shifts are referenced to tetramethylsilane [TMS, Si(CH3)4] at were used for decay measurements. The sample was excited by
0.00 ppm, 19F chemical shifts are referenced externally to the output of a pulse laser diode which produced a 1 kHz train
BF3·Et2O at 0.0 ppm. Melting points were determined in open of pulses of 20 ns duration at 405 nm. The luminescence was
ended capillaries using a Stuart Scientific SMP3 melting point collected at 90° and focused onto the entrance slit of a mono-
apparatus at a ramping rate of 1 °C min−1. They are reported chromator (Bethan TM 300 V). The emission was detected by a
to the nearest 0.1 °C. ESI and MALDI mass spectra were photon counting PMT and the arrival times of photons at the
recorded on a Thermo-Finnigan LTQ FT (7.0 T magnet) detector were determined using a multichannel scaler. Time-
spectrometer. ASAP mass spectra were recorded on a Waters resolved phosphorescence spectra and decay curves were
Xevo QTOF spectrometer. GCMS spectra were recorded on a recorded using nanosecond gated luminescence and lifetime
Thermo-Finnigan Trace GCMS (EI and CI ion sources). measurements (from 1 ns to 1 s) using either third harmonics
Elemental analyses were obtained on an Exeter Analytical Inc. of a high energy pulsed Nd:YAG laser emitting at 355 nm
CE-440 elemental analyser. Where solvent mixtures are men- (EKSPLA) or a N2 laser emitting at 337 nm. Emission was
tioned any percentage/ratio is by volume.
focused onto a spectrograph and detected on a sensitive gated
iCCD camera (Stanford Computer Optics) having sub-nano-
second resolution.
Electrochemistry
All optical analyses for 9–11 were carried out in quartz cuv-
ettes with a path length of 1 cm. Absorbance spectra were
measured on a Cary 5000 UV-Vis-NIR spectrometer with Cary
WinUV Scan software. Emission spectra were recorded on a
Jobin Yvon Fluorolog-3 luminescence spectrometer with a CCD
detector using FluorEssence software. Photoluminescence
quantum yields (PLQYs) were measured using a calibrated
Quanta-φ integrating sphere coupled with a Jobin Yvon
FluoroLog-3 spectrometer and PMT detector (0.5 s integration
time) and analysed using FluorEssence software. Time-
resolved measurements (TCSPC, time-correlated single-photon
counting) were performed on a Horiba Deltaflex system with
EzTime software.
Cyclic voltammetry (CV) measurements were recorded at a
scan rate of 100 mV s−1 at room temperature using an air-tight
single-compartment three-electrode cell equipped with a Pt
working electrode (1.2 mm surface diameter), Pt wire counter
electrode and Pt wire pseudo-reference electrode. The cell was
connected to a computer-controlled Autolab PG-STAT 30
potentiostat using GPES software. The solutions contained the
compound (1 mg mL−1) and n-Bu4NPF6 (0.1 M) as the support-
ing electrolyte in dichloromethane (CH2Cl2). All potentials
were determined with the ferrocene/ferrocenium couple (FcH/
FcH+) as an internal reference at E1/2 = 0.0 V.
Solution photophysics
Thin films and devices
Solution state photophysical data of the complexes 1–6 were
obtained using freshly prepared solutions in the solvent speci-
fied. UV-vis absorption measurements were measured using a
UV-3600 double beam spectrophotometer (Shimadzu).
Baseline correction was achieved by reference to pure solvent
in the same cuvette. Absorption measurements were obtained
using quartz cuvettes with a path length of 1 cm.
Emission and lifetime measurements were taken using
thoroughly degassed solutions achieved by three freeze–
pump–thaw cycles, and obtained using a quartz cuvette with a
path length of 1 cm. The solutions had absorbance below 0.10
to minimise inner filter effects. Emission spectra of complexes
1–6 were recorded on a Horiba Jobin Yvon SpexFluoromax 3
Spectrometer or a Horiba Jobin Yvon SPEX Fluorolog 3-22
spectrofluorometer. Solution PLQYs were recorded in degassed
solvent, and determined using the relative method using
quinine sulfate (ΦPL = 0.546 in 0.5 M H2SO4) as the reference.
The PLQYs are computed according to the following equation:
Details of thin film and device fabrication are included in the
ESI.†
Computational studies
All calculations were run using the Gaussian09 software
package.39 Analysis of the molecular orbital contributions was
conducted with GaussSum.40 Calculations on complexes 2–6
and ligands 7–11 were carried out using the B3LYP41,42 func-
tional with the LanL2DZ43–46 pseudopotential for Ir and the 3-
21G* basis set for N, C, O, F and H.47,48 The solvent effect
(solvent = chloroform) was applied within the self-consistent
reaction field (SCRF) theory using the solvation model density
(SMD) keyword that performs a polarised continuum model
(PCM)49,50 calculation with the use of the solvation model of
Truhlar and co-workers.51 All S0 optimised geometries of the
most stable conformers were true minima based on no imagin-
ary frequencies being found. Electronic structure and TD-DFT
calculations were generated from the optimised geometries at
B3LYP/LANL2DZ:3-21G*.
ꢀ
ꢁ
2
Gradx
Gradref ηref
ηx
Φx ¼ Φref
:
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Synthesis
and water was added. The precipitate was collected, dried and
purified by column chromatography (hexane : EtOAc 2 : 1, then
a second column, CH2Cl2 : EtOAc 5 : 1), to give 2 as a pale
yellow solid (0.708 g, 46%); Anal. Calcd for 2·0.2(CH2Cl2) Anal.
Calcd for C44.2H34.4Cl0.4F4IrN5O2: C, 55.88; H, 3.65; N, 7.37.
Found: C, 55.63; H, 3.66; N, 7.28; δH (400 MHz; CDCl3; Me4Si)
8.83 (1H, d, J 5.8 HA6), 8.42 (1H, d, J 7.7, HE3), 8.12 (m, HB3),
8.07 (1H, m, HA3) 8.07 (1H, m, HE4), 7.89 (1H, dd, J 5.4, 0.5
2-(2,6-Difluoro-3-pyridyl)-4-(2,4,6-trimethylphenyl)pyridine 7.
2-Chloro-4-(2,4,6-trimethylphenyl)pyridine, 12 (1.50 g, 6.47 mmol),
2,6-difluoropyridyl-3-MIDA boronate, 13 (2.10 g, 7.77 mmol),
tris(dibenzylideneacetone)dipalladium(0) Pd2(dba)3 (0.089 g,
0.097 mmol) and PCy3 (0.065 g, 0.233 mmol) were placed
under an argon atmosphere. Degassed aqueous 1.27 M K3PO4
(16.2 ml, 48.6 mmol) and 1,4-dioxane (80 ml) were added with
stirring to the reaction mixture. The reaction mixture was
stirred at 60 °C for 60 h and monitored by TLC. After cooling
to room temperature the 1,4-dioxane was removed in vacuo.
Ethyl acetate (150 ml) was added, and the mixture was trans-
ferred to a separating funnel and washed with brine (3 ×
100 ml). The organic layer was then dried over MgSO4, filtered
and the solvent removed in vacuo. The residue was purified by
column chromatography (4 : 1 hexane/ethyl acetate) followed
by recrystallisation from methanol, to give 7 as a white solid
(0.69 g, 34%); 74.5–75.9 °C; Anal. Calcd for C19H16F2N2: C,
73.53; H, 5.20; N, 9.03. Found: C, 73.70; H, 5.09; N, 9.12; δH
(400 MHz; CDCl3; Me4Si) 8.96–8.65 (2H, m), 7.71 (1H, d, J 1.5),
7.18 (1H, dd, J 5.0, 1.5), 7.03 (1H, dd, J 8.2, 3.0), 7.00 (2H, s),
2.37 (3H, s), 2.06 (6H, s); δC (125 MHz; CDCl3; Me4Si) 164.8
(dd, J 244.0, 13.6), 163.5 (dd, J 246.3, 14.7), 151.9, 151.0, 148.5,
145.0 (d, J 4.4), 138.9, 138.0, 137.2, 128.1, 120.8 (dd, J 26.2,
5.7), 118.7, 114.3, 107.7 (dd, J 35.5, 5.2), 24.7, 18.1; m/z (ES+)
311.3 (M + H)+.
H
E6), 7.58 (1H, ddd, J 7.2, 5.4, 1.5, HE5), 7.49 (1H, d, J 5.8 HB6),
7.18 (1H, dd, J 5.8, 1.6, HA5), 7.04 (1H, s, HF3/5), 7.01 (2H, s,
HF3/5 + HG3/5), 6.98 (1H, s, CG3/5), 6.95 (1H, dd, J 5.9, 1.8 Hz,
H
B5), 5.81 (1H, t, J 1.7, HC5), 5.55 (1H, t, J 1.7, HD5), 2.34 (6H, s,
HG8 + HF8), 2.13 (3H, s, HF7/9), 2.10 (3H, s, HG7/9), 2.08 (3H, s,
G7/9), 1.95 (3H, s, HF7/9); δF (376 MHz; CDCl3; Me4Si) −67.73
H
(1F, d, J 9.3), −68.26 (1F, d, J 9.4 Hz), −69.30 (1F, d, J 9.3),
−70.01 (1F, d, J 9.4); δC (125 MHz, CDCl3; Me4Si) 172.38 (CE1),
170.38 (d, J 6.0, CD1), 169.86 (d, J 6.0, CC1), 163.59 (d, J 10.1,
C
B2), 162.17 (d, J 10.1, CA2), 161.13 (dd, J 253.4, 15.5, CC3/4)
160.58 (dd, J 252.5, 15.5, CD3/4), 157.66 (dd, J 254.2, 16.7,
C3/4), 157.43 (dd, J 254.2, 16.2, CD3/4), 153.49 (CA4), 153.55
,
C
(CB4), 151.26 (CE2), 148.67 (CA6), 148.31 (CE6), 147.97 (CB6),
139.21 (CE4), 138.66 (CF/G4), 138.61 (CF/G4), 135.23 (CG2/6),
134.99 (CF2/6), 134.71 (CG2/6), 134.55 (CG1 + CF2/6), 134.52 (CF1),
129.02 (CE3), 128.92 (CE5), 128.88(CF3/5), 128.79 (CG3/5), 128.63
(CF3/5 + CG3/5), 125.00 (CA5), 124.99 (CD + CC2), 124.96 (d, J 16.9,
C
C
B3), 124.76 (CB5), 124.43 (d, J 16.9, CA3) 109.57 (dd, J 29.6, 4.3,
C5) 109.26 (dd, J 30.2, 4.0, CD5), 21.3 (CF8 + CG8), 20.83 (CG7/9),
20.56 (CG7/9 + CF7 + CF9); MS (MALDI+): m/z = 933.2 (M+,
100%). Single crystals of 2·1.5C6H14 for X-ray analysis were
grown by slow evaporation of solvent from a solution of 2 in
CH2Cl2–hexane.
Iridium complex 2
2-(3-Cyano-2,4-difluorophenyl)-4-(2,4,6-trimethylphenyl)pyri-
dine 8. 2-Chloro-4-(2,4,6-trimethylphenyl)pyridine, 12 (1.50 g,
6.47 mmol), 3-cyano-2,4-difluorophenyl MIDA boronate, 14
(2.17 g, 7.78 mmol), palladium(II) acetate (0.073 g, 0.33 mmol)
and 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl SPhos
(0.266 g, 0.65 mmol) were placed under an argon atmosphere.
Degassed aqueous 3 M K3PO4 (16.2 ml, 48.6 mmol) and 1,4-
dioxane (80 ml) were added with stirring to the reaction
mixture. The reaction mixture was stirred at 90 °C for 60 h and
monitored by TLC. After this time, more 14 (0.181 g,
0.65 mmol) was added and the reaction stirred at 90 °C for a
further 6 h. After cooling to room temperature the 1,4-dioxane
was removed by rotary evaporation. Ethyl acetate (150 ml) was
added before transferring the mixture to a separating funnel
and washing with brine (3 × 100 ml). The organic layer was
then dried over MgSO4, filtered and the solvent removed in
A mixture of 2-(2,6-difluoro-3-pyridyl)-4-(2,4,6-trimethylphenyl) vacuo. The residue was purified by column chromatography
pyridine 7 (1.20 g, 3.88 mmol), IrCl3·3H2O (0.58 g, 1.65 mmol), (silica, 4 : 1 hexane/ethyl acetate), and the product-containing
2-ethoxyethanol (32 ml) and water (12 ml) was heated to fractions were combined and dried in vacuo. The crude
110 °C overnight under an argon atmosphere. The resulting product was recrystallised from methanol (5 ml) giving 8 as an
yellow precipitate was collected by filtration and washed off-white powder (1.10 g, 51%); m.p. 117–118 °C (from MeOH);
sequentially with water (100 ml) and a mixture of ethanol and Anal. Calc. For C21H16F2N2; C, 75.43; H, 4.82; N, 8.38; Found:
acetone (1 : 1 v/v 80 ml). Picolinic acid (0.95 g, 7.73 mmol) and C, 75.13; H, 4.90; N, 8.39; δH (400 MHz; CDCl3; Me4Si) 8.80
2-ethoxyethanol (20 ml) were added to the precipitate, and the (1H, d, J 5.6), 8.45 (1H, dt, J 8.8, 6.4), 7.63 (1H, s), 7.21–7.25
mixture was heated to 110 °C for 16 h. The solution was cooled (1H, m), 7.19 (1H, dd, J 4.8, 1.6), 7.00 (2H, s), 2.37 (3H, s), 2.06
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(6H, s); δF (376 MHz; CDCl3) −102.9 to −103.0 (1F, m), −107.1 (CA6), 148.43 (CE6), 148.09 (CB6), 139.52 (CE4), 138.94 (CF/G4),
to −107.2 (1F, m); δC (100 MHz; CDCl3; Me4Si) 164.5–164.6 (wk 138.89 (CF/G4), 135.28 (CG2/6), 135.00 (CF2/6), 134.75 (CG2/6),
m), 161.8–162.1 (wk m), 159.3–159.5 (wk m), 150.7, 150.5 (d, J 134.63 (CF2/6), 134.47 (CF/G1), 134.45 (CF/G1), 129.58 (CC/D2),
2.3), 150.2, 137.9, 137.1 (dd, J 5.1 and 9.8), 135.7, 135.1, 128.5, 129.56 (CC/D2), 129.25 (CE3), 129.18 (CE5), 129.06 (CF3/5), 128.99
125.4 (d, J 9.5), 124.9–124.7 (m), 124.6, 112.6 (dd, J 9.1, 3.9), (7.01 CG3/5), 128.85 (CF3/5 + CG3/5), 125.77 (CA5), 125.63 (CB5),
109.2, 21.1, 20.6; MS (ES+): m/z = 335.3 (M + H+, 100%).
125.56 (d, J CB3), 125.10 (d, J, CA3), 115.53 (d, J 15.4, CC6),
115.17 (d, J 15.9, CD6), 110.47 (CC/D7), 110.44 (CC/D7), 86.20 (t,
J 20.1, CD4), 85.85 (t, J 20.9, CC4), 21.17 (CF8 + CG8), 20.92
(CG7/9), 20.66 (CF7 + CF9 + CG7/9); MS (MALDI+): m/z = 981.9
(M + H+, 100%), 980.9 (84.0), 979.9 (49.6), 982.9 (37.3), 978.9
(29.5), 983.9 (5.7). Single crystals of 3·4CDCl3 for X-ray analysis
were grown by slow evaporation of solvent from an NMR
sample of 3 in CDCl3.
Iridium complex 3
9-(2-Chloropyridin-4-yl)-2,7-dimethoxy-9H-carbazole 16. 2,7-
Dimethoxycarbazole 15 (3.16 g, 13.90 mmol) and 4-iodo-2-
chloropyridine (3.61 g, 13.91 mmol) were dissolved in 10 ml of
dry DMF. The reaction mixture was degassed by bubbling
argon for 15 min, followed by addition of CuI (0.77 g,
4.04 mmol), 1,10-phenanthroline (1.43 g, 7.93 mmol) and
K2CO3 (3.84 g, 27.83 mmol). The reaction mixture was heated
at 120 °C for 3 days. The solution was cooled and water was
added. The precipitate was collected, dried and purified by
column chromatography (CH2Cl2) to give 16 (4.51 g, 96%) as a
white solid; m.p. 109.3–110.9 °C; δH (400 MHz; CDCl3; Me4Si)
8.62 (1H, dd, J 5.4, 0.6), 7.88 (2H, dd, J 8.6, 0.5), 7.63 (1H, dd,
J 1.9, 0.6), 7.52 (1H, dd, J 5.4, 1.9), 6.98 (2H, d, J 2.2), 6.93 (2H,
A mixture of 2-(3-cyano-2,4-difluorophenyl)-4-(2,4,6-trimethyl- dd, J 8.5, 2.2), 3.87 (6H, s); δC (101 MHz; DMSO-d6; Me4Si)
phenyl)pyridine 8 (1.277 g, 3.81 mmol), IrCl3·3H2O (0.58 g, 158.65, 158.00, 152.43, 152.28, 147.51, 140.59, 121.04, 120.45,
1.63 mmol), 2-ethoxyethanol (32 ml) and water (12 ml) was 117.89, 110.03, 95.23, 55.97; MS (ASAP+): m/z 338.1 (M+,
heated to 110 °C overnight under an argon atmosphere. The 100%).
resulting yellow precipitate was collected by filtration and
9-(2-Chloropyridin-4-yl)-9H-carbazole-2,7-diol
17.
9-(2-
washed sequentially with water (100 ml) and a mixture of Chloropyridin-4-yl)-2,7-dimethoxy-9H-carbazole 16 (4.51 g,
water/methanol (1 : 1 v/v). Picolinic acid (0.94 g, 7.64 mmol) 13.31 mmol) was dissolved in dry CH2Cl2 (150 ml) and the
and 2-ethoxyethanol (20 ml) were added to the precipitate, and solution was cooled to 0 °C under an argon atmosphere. BBr3
the mixture was heated to 120 °C for 18 h. The solution was (20.01 g, 79.87 mmol) was slowly added over 10 min. After 1 h,
cooled and water was added. The precipitate was collected, the reaction was stopped by addition of water (40 ml). The pre-
dried and purified by column chromatography (firstly cipitate was collected, dried and recrystallised from ethanol to
CH2Cl2 : EtOAc 4 : 1, then another column using 1 : 1 give 17 as a white solid (3.00 g, 72%); m.p. 289.0–290.5 °C; δH
CH2Cl2 : EtOAc) followed by recrystallisation to give 3 as a pale (400 MHz; DMSO-d6; Me4Si) 9.53 (2H, br s), 8.65 (1H, d, J 5.4),
yellow powder (384 mg, 21%); Anal. Calcd for 3·0.2(CH2Cl2) 7.85 (1H, d, J 1.7), 7.83 (2H, d, J 8.4), 7.74 (1H, dd, J 5.4, 1.9),
Anal. Calcd for C48.2H34.4Cl0.4F4IrN5O2 C, 58.01; H, 3.47; N, 6.89 (2H, d, J 2.0), 6.73 (2H, dd, J 8.4, 2.1); δC (151 MHz;
7.02. Found: C, 58.26; H, 3.67; N, 6.85; δH (500 MHz; CDCl3; DMSO-d6; Me4Si) 156.33, 152.23, 152.11, 147.81, 140.42,
Me4Si) 8.83 (1H, d, J 5.5, HA6), 8.46 (1H, d, J 7.8, HE3), 8.16 120.65, 120.61, 120.06, 117.03, 110.80, 96.48; MS (ASAP+): m/z
(1H, m, HB3), 8.11 (1H, t, J 7.7, HA3), 8.09 (1H, dd, J HE4), 7.87 310.1 (M+, 100%).
(1H, d, J 4.5, HE6), 7.61 (1H, t, J 6.5, HE5), 7.49 (1H, d, J 6.0,
9-(2-Chloropyridin-4-yl)-2,7-bis(hexyloxy)-9H-carbazole
18.
H
B6), 7.23 (1H, dd, J 6.0, 2.0, HA5), 7.04 (1H, br s, HF3/5), 7.01 9-(2-Chloropyridin-4-yl)-9H-carbazole-2,7-diol 17 (2.46 g,
(2H, s, HF3/5 + HG3/5), 6.99 (1H, dd, J, HB5), 6.99 (1H, s, HG3/5), 7.9 mmol) and K2CO3 (3.28 g, 23.7 mmol) were dissolved in
6.00 (1H, d, J 8.5, HC6), 5.72 (1H, d, J 8.5, HD6), 2.38 (6H, s, HF8 DMSO (80 ml) and the solution was stirred at RT for 2 h.
+ HG8), 2.16 (3H, s, HF7/9), 2.11 (3H, s, HG7/9), 2.09 (3H, s, 1-Bromohexane (3.32 ml, 23.7 mmol) was slowly added over
H
G7/9), 1.99 (3H, s, HF7/9); δF (376 MHz; CDCl3; Me4Si) −102.41 10 min. The reaction mixture was stirred at RT overnight. The
(1F, d, J 3.9), −103.19 (1F, d, J 3.5), −105.21 (1F, d, J 4.0), reaction was stopped by an addition of water (50 ml). The pre-
−105.85 (1F, d, J 3.7); δC (151 MHz; CDCl3; Me4Si) 172.48 (CE7), cipitate was collected, dried and purified by column chromato-
163.80 (d, J 6.9, CB2), 162.64 (dd, J 268.3, 4.2, CC3/5), 162.39 (d, graphy (CH2Cl2) to give 18 (2.83 g, 75%) as a white solid;
J 6.7, CA2), 162.27 (dd, J 268.3, 4.2, CD3/5), 161.55 (d, J 7.2, CD1), m.p. 176.1–177.5 °C; δH (400 MHz; CDCl3; Me4Si) 8.61 (1H, dd,
160.90 (d, J 7.2, CC1), 160.17 (dd, J, CC3/5), 160.07 (dd, J 271.1, J 5.4, 0.6), 7.86 (2H, d, J 8.5), 7.61 (1H, dd, J 1.9, 0.6), 7.51 (1H,
4.5, CD3/5), 153.99 (CA4), 153.94 (CB4), 151.30 (CE2), 148.68 dd, J 5.4, 1.8), 6.87–7.00 (4H, m), 4.00 (4H, t, J 6.5), 1.81 (4H,
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dq, J 8.0, 6.6), 1.55 (3H, s), 1.28–1.42 (9H, m), 0.91 (6H, m); δC purified by column chromatography (CH2Cl2/EtOAc 20 : 1) to
(176 MHz; CDCl3; Me4Si) 158.08, 153.18, 151.27, 147.86, give 4 (0.23 g, 55%) as a yellow solid; Anal. Calc. For
140.56, 120.73, 120.32, 119.22, 118.19, 109.64, 95.59, 68.66, C76H78F4N5O6Ir; C, 64.03; H, 5.51; N, 4.91; Found: C, 64.04; H,
31.59, 29.30, 25.74, 22.57, 14.00; MS (ASAP+): m/z 478.2 (M+, 5.45; N, 4.77; δH (400 MHz; CDCl3; Me4Si) 8.94 (1H, d, J 6.4,
100%).
3-(4-(2,7-Bis(hexyloxy)-9H-carbazol-9-yl)pyridin-2-yl)-2,6-difluor-
H
H
A6), 8.64 (1H, m, HB3), 8.57 (1H, m, HA3), 8.47 (1H, d, J 7.8,
E3), 8.07 (1H, t, J 7.5 HE4), 7.98 (1H, d, J 5.0, HE6), 7.89 (2H, d,
obenzene 9. (2-Chloropyridin-4-yl)-2,7-bis(hexyloxy)-9H-carba- J 8.5, HF5/G5) 7.87 (2H, d, J 8.5, HF5/G5), 7.62–7.52 (3H, m, HB6
+
zole 18 (1.20 g, 2.51 mmol) and 2,4-difluorophenylboronic acid A5 + HE5), 7.31 (1H, d, J 5.9, HB5), 7.17 (2H, d, J, 2.1, HG2) 7.13
H
19 (0.66 g, 4.18 mmol) were dissolved in 1,4-dioxane (20 ml), (2H, d, J, 2.1, HF2), 6.95 (4H, dd, J 8.6, 2.1, HF4 + HG4), 6.55
and the reaction mixture was degassed by bubbling argon for (1H, dd, J 12.0, 9.0, HC4), 6.46 (1H, dd, J 12.0, 9.0, HD4), 6.08
15 min. Pd(PPh3)4 (0.05 g, 0.04 mmol) and degassed aqueous (1H, dd, J 8.4, 2.3 HC6), 5.82 (1H, dd, J 8.6, 2.3 HD6), 4.04 (8H,
2 M K2CO3 (5.2 ml, 10.4 mmol) were added, and the reaction q, J 6.2, HF7 + HG7), 1.83 (8H, p, J 6.6, HF8 + HG8), 1.49 (8H, m,
mixture was heated at 90 °C for 18 h. The solution was cooled HF9 + HG9), 1.35 (16H, m, HF10 + HG10 + HF11 + HG11),
and water was added. The precipitate was collected, dried and 0.94–0.86 (12H, m, HF12 + HG12); δF (564 MHz; CDCl3; Me4Si)
purified by column chromatography (CH2Cl2) to give 9 (1.10 g, −105.41 to −105.66 (1F, m), −106.23 to −106.51 (1F, m),
79%) as a white solid; Anal. Calc. for C35H38N2F2O2; C, 75.51; −109.52 to −109.78 (1F, m), −110.29 to −110.57 (1F, m); δC
H, 6.88; N, 5.03; Found: C, 75.50; H, 6.89; N, 4.91; δH (151 MHz; CDCl3; Me4Si) 172.98 (CE7), 167.57 (d, J 6.8, CB2),
(700 MHz; CDCl3; Me4Si) 8.92 (1H, d, J 5.2), 8.14 (1H, dd, 166.05 (d, J 6.8, CA2), 164.00 (dd, 257.72, 12.5, CC5), 163.68 (dd,
J 15.6, 8.5), 8.05 (1H, t, J 2.1), 7.87 (2H, d, J 8.5), 7.55 (1H, dd, J 256.3, 12.5, CD5), 161.77 (dd, J 259.1, 12.6, CC/D3), 161.72 (dd,
J 5.4, 1.9), 7.12–7.03 (3H, m), 7.00–6.88 (3H, m), 4.01 (4H, t, J 259.4, 12.6, CC/D3), 158.35 (CF/G3), 158.32 (CF/G3), 153.12 (d,
J 6.6), 1.88–1.76 (4H, m), 1.48 (4H, dd, J 14.5, 7.0), 1.39–1.31 J 6.9, CC/D1), 151.87 (CE2), 151.68 (d, J 6.9, CC/D1), 150.08 (CA6),
(8H, m), 0.92 (6H, t, J 6.6); δF (658 MHz; CDCl3; Me4Si) 149.24 (CB6), 148.72 (CE6), 147.85 (CA/B4), 147.81 (CA/B4), 140.49
−108.15, −113.3; δC (176 MHz; CDCl3; Me4Si) 163.73 (dd, (CF/G1), 140.48 (CF/G1), 138.81 (CE4), 129.05 (CE3), 128.93 (CE5),
J 252.0, 12.2), 160.89 (dd, J 252.4, 12.0), 158.18, 154.58 (d, 128.27 (CD2), 128.07 (CC2), 120.56 (CF/G5), 120.48, (CF/G5),
J 1.96), 151.66, 146.15, 140.90, 132.40 (dd, J 9.7, 4.2), 123.41 119.17 (d, J 20.5, CB3), 118.72 (CF/G6), 118.63 (CF/G6), 118.49
(dd, J 11.3, 3.7), 121.13 (d, J 9.3), 120.40, 119.04, 118.19, 112.46 (CA5), 118.43 (d, J 20.5, CA3) 118.34 (CA5), 115.17 (d, J 16.9, CC6),
(dd, J 21.2, 3.5), 109.98, 104.06 (dd, J 26.67, 25.60), 95.44, 114.91 (d, J 16.9, CD6), 110.50 (CF/G4), 110.21 (CF/G4), 98.58 (t,
68.68, 31.74, 29.47, 25.90, 22.76, 14.18; MS (ASAP+): m/z 556.3 J 26.8, CD4), 98.22 (t, J 26.8, CC4), 96.17 (CF2), 96.03 (CG2), 68.93
(M+, 100%).
(CF/G7), 68.89 (CF/G7), 31.74 (CF7 + CG7), 31.72 (CF10 + CG10
CF11 + CG11), 29.46 (CF8 + CG8), 25.90 (CF9 + CG9), 22.73 (CF12
G12); MS (MALDI+): m/z = 1425.4 (M+, 100%).
9-(2′,6′-Difluoro-[2,3′-bipyridin]-4-yl)-2,7-bis(hexyloxy)-9H-car-
/
+
C
Iridium complex 4
bazole 10. 9-(2-Chloropyridin-4-yl)-2,7-bis(hexyloxy)-9H-carba-
zole 18 (0.80 g, 1.67 mmol), MIDA ester 13 (0.68 g, 2.50 mmol)
and SPhos (0.11 g, 0.13 mmol) were dissolved in 1,4-dioxane
(20 ml) and the reaction mixture was degassed by bubbling
argon for 15 min, before Pd(OAc)2 (30 mg, 0.13 mmol) was
added. Degassed aqueous 1.5 M K3PO4 (4 ml, 6.0 mmol) was
added and the reaction mixture was heated to 60 °C for 18 h.
The solution was cooled and the solvent was removed in vacuo.
The crude material was dissolved in CH2Cl2, which was
washed with water before the solvent was removed. The crude
material was purified by column chromatography (CH2Cl2) to
give 9-(2′,6′-difluoro-[2,3′-bipyridin]-4-yl)-2,7-bis(hexyloxy)-9H-
carbazole 10 (0.81 g, 87%) as a white solid; Anal. Calc. for
C34H37N3F2O2; C, 73.23; H, 6.69; N, 7.53; Found: C, 72.96; H,
6.64; N, 7.46; δH (400 MHz; CDCl3; Me4Si) 8.92 (1H, dd, J 5.2,
0.7), 8.78 (1H, dt, J 9.7, 8.1), 8.10–8.16 (1H, m), 7.88 (2H, d,
J 8.6), 7.60 (1H, dd, J 5.3, 2.0), 7.08 (2H, d, J 2.2), 7.05 (1H, dd,
A mixture of 3-(4-(2,7-bis(hexyloxy)-9H-carbazol-9-yl)pyridin-2- J 8.2, 3.0, 0.8), 6.92 (2H, dd, J 8.6, 2.2), 4.01 (4H, t, J 6.5), 1.81
yl)-2,6-difluorobenzene 9 (0.36 g, 0.66 mmol), IrCl3·3H2O (4H, dt, J 14.3, 6.7), 1.42–1.54 (4H, m), 1.22–1.40 (8H, m),
(0.11 mg, 0.31 mmol) and 2-ethoxyethanol (10 ml) was heated 0.86–0.94 (6H, m); δF (376 MHz; CDCl3; Me4Si) −66.83 (ddd,
to 120 °C overnight. Picolinic acid (0.10 g, 0.81 mmol) and J 10.5, 7.6, 3.0), −69.87 (1F, t, J 10.0); δC (151 MHz; CDCl3;
sodium carbonate (0.1 mg, 0.01 mmol) were added and the Me4Si) 161.65 (dd, J 250.2, 14.6), 158.72 (dd, J 250.2, 14.2),
mixture was heated to 120 °C for 2 h. The solution was cooled 158.23, 152.81, 151.67, 146.45, 146.14, 140.65, 120.65 (d,
and water was added. The precipitate was collected, dried and J 10.3), 120.30, 119.46, 118.73 (d, J 23.8), 118.12, 109.94, 107.20
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(d, J 34.3), 95.41, 68.70, 31.75, 29.49, 25.92, 22.75, 14.17; MS (CF10/G10/F11/G11), 29.48 (CF8/G8), 29.45 (CF8/G8), 25.92 (CF9/G9),
(ASAP+): m/z 557.3 (M+, 100%).
22.73 (CF10/G10/F11/G11), 22.72 (CF10/G10/F11/G11), 14.16 (CF12
C
+
G12); HRMS (FTMS + ESI): calcd for [C74H76F4191IrN7O6 + H]:
1426.5477. Found: 1426.5470.
3-(4-(2,7-Bis(hexyloxy)-9H-carbazol-9-yl)pyridin-2-yl)-2,6-
Ir complex 5
difluorobenzonitrile 11. 9-(2-Chloropyridin-4-yl)-2,7-bis(hexy-
loxy)-9H-carbazole 18 (1.00 g, 2.09 mmol), MIDA ester 14
(0.92 g, 3.13 mmol) and SPhos (137 mg, 0.33 mmol) were dis-
solved in 1,4-dioxane (20 ml) and the reaction mixture was
degassed by bubbling argon for 15 min, before Pd(OAc)2
(37 mg, 0.16 mmol) was added. Degassed aqueous 2.1 M
K3PO4 (4 ml, 8.4 mmol) was added and the reaction mixture
was heated to 60 °C for 72 h. The solution was cooled and the
solvent was removed in vacuo. The crude material was dis-
solved in CH2Cl2, which was washed with water before the
solvent was removed. The crude material was purified by
column chromatography (CH2Cl2) to give 11 (1.01 g, 83%) as a
white solid; m.p. 126.1–127.9 °C; Anal. Calc. For C36H37N3F2O2;
C, 74.33; H, 6.41; N, 7.22; Found: C, 73.71; H, 6.34; N, 7.07; δH
(400 MHz; CDCl3; Me4Si) 8.93 (1H, dd, J 5.3, 0.7), 8.45 (1H, td,
J 8.9, 6.4), 8.07–8.03 (1H, m), 7.88 (2H, d, J 8.5), 7.63 (1H, dd,
J 5.3, 2.0), 7.25 (1H, ddd, J 9.0, 7.7, 1.2), 7.07 (2H, d, J 2.1), 6.93
A mixture of 10 (270 mg, 0.48 mmol) and IrCl3·3H2O (81 mg, (2H, dd, J 8.5, 2.2), 4.02 (4H, t, J 6.6), 1.82 (4H, dq, J 8.7, 6.6),
0.23 mmol) in diglyme (10 ml) was heated to 130 °C overnight 1.42–1.58 (4H, m), 1.27–1.42 (8H, m), 0.84–0.99 (6H, m); δF
under argon. Picolinic acid (57 mg, 0.46 mmol) was added and (376 MHz; CDCl3; Me4Si) −101.89 (1F, ddd, J 8.0, 6.4, 1.8),
the mixture was heated to 130 °C for 8 h. The reaction was −108.04 (1F, dq, J 8.7, 1.9); δC (178 MHz; CDCl3; Me4Si) 163.51
cooled, the solvent removed in vacuo and the residue was puri- (dd, J 265.0, 3.8), 160.7 (dd, J 263.8, 4.2), 158.27, 152.39 (d,
fied by column chromatography (4% EtOAc in CH2Cl2) to leave J 1.8), 152.05, 146.65, 140.80, 137.21 (dd, J 9.9, 4.8), 124.44 (dd,
5
as a yellow solid (110 mg, 33%); Anal. Calc. for J 10.0, 3.9), 121.16 (d, J 9.2), 120.53, 119.94, 118.34, 113.05 (dd,
C74H76F4N7O6Ir; C, 62.26; H, 5.37; N, 6.87; Found: C, 62.17; H, J 19.1, 4.0), 110.02, 109.06, 95.51, 93.30 (dd, J 20.5, 19.5), 68.78,
5.33; N, 6.88; δH (600 MHz; CDCl3; Me4Si) 8.95 (1H, d, J 6.3, 31.76, 29.50, 25.91, 22.75, 14.19; HRMS (FTMS + ESI): calcd for
H
A6), 8.68 (1H, t, J 2.6, HB3), 8.62 (1H, t, J 2.3, HA3), 8.50 (1H, [C36H37N3F2O2 + H]+: 582.2932. Found: 582.2931.
dd, J 7.6, 1.5, HE3), 8.14 (1H, td, J 7.8, 1.6, HE4), 7.99 (1H, dd,
J 5.5, 1.5, HE6), 7.88 (2H, d, J 8.5, HF5/G5), 7.87 (2H, d, J 8.5,
Ir complex 6
H
F5/G5), 7.69–7.65 (2H, m, HA5 + HE5), 7.57 (1H, d, J 6.3, HB6),
7.45 (1H, dd, J 6.3, 2.5, HB5), 7.18 (2H, d, J 2.1, HG2), 7.15 (2H,
d, J 2.1, HF2), 6.96 (4H, dd, J 8.6, 2.0, HF5 + HG5), 6.11 (t, J 1.8,
H
C5), 5.84 (d, J 1.9, HD5), 4.04 (8H, q, J 6.6, HF7 + HG7),
1.86–1.78 (8H, m, HF8 + HG8), 1.53–1.46 (8H, m, HF9 + HG9),
1.39–1.30 (16H, m, HF10 + HG10 + HF11 + HG11), 0.90 (12H, td,
J 6.4, 5.8, 2.5, HF12 + HG12); δF (376 MHz; CDCl3; Me4Si) −67.83
(1F, dt, J 9.1, 2.1), −68.29 (1F, dd, J 9.1, 2.4), −68.63 (1F, dt,
J 9.2, 2.3), −68.96 (1F, dd, J 9.1, 2.4); δC (151 MHz; CDCl3;
Me4Si) 172.60 (CE7), 170.62 (d, J 5.9, CD1), 170.18 (d, J 6.0, CC1),
165.30 (d, J 10.1, CB2), 163.87 (d, J 10.0, CA2), 161.67 (dd,
J 253.7, 15.9, CC3/4), 161.05 (dd, J 253.63, 15.4, CD3/4), 158.45
(CF/G3), 158.42 (CF/G3), 158.24 (dd, J 253.6, 16.5, CC3/4), 157.81
(dd, J 250.1, 16.9, CD3/4), 151.29 (CE2), 150.20 (CA6), 149.47
(CB6), 148.79 (CA4), 148.70 (CB4), 148.55 (CE6), 140.22 (CF/G1),
140.20 (CF/G1), 139.63 (CE4), 129.43 (CE3/5), 129.41 (CE3/5),
125.06 (dd, J 15.8, 3.7, CD2), 124.96 (dd, J 16.2, 3.7, CC2), 120.69
(CF/G5), 120.62 (CF/G5), 119.20 (d, J 18.5, CB3), 119.05 (CA5),
118.96 (CB5), 118.96 (CF6) 118.87 (CG6), 118.59 (d, J 17.3, CA3), A mixture of 11 (300 mg, 0.52 mmol) and IrCl3·3H2O (87 mg,
110.64 (CF/G4), 110.33 (CF/G4), 110.30 (dd, J 28.8, 3.9, CC5), 0.25 mmol) in 2-ethoxyethanol (5 ml) was heated to 110 °C
110.00 (dd, J 29.5, 3.9, CD5), 96.40 (CF2), 96.20 (CG2), 68.98 overnight under argon. Picolinic acid (106 mg, 0.86 mmol)
(CF7/G7), 68.94 (CF7/G7), 31.74 (CF10/G10/F11/G11), 31.73 and Na2CO3 (26 mg, 0.25 mmol) were added and the mixture
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was heated to 110 °C for 3 h. The reaction was cooled, the
solvent removed in vacuo and water (20 ml) and CH2Cl2
Acknowledgements
(20 ml) were added. The layers were separated and the EPSRC grant EP/K0394/23/1 is acknowledged for funding
aqueous layer was extracted with further CH2Cl2 (2 × 20 ml). equipment used in the Department of Chemistry, Durham
The organic phases were combined, dried over MgSO4, filtered University.
and the solvent removed. The residue was purified by column
chromatography (4% EtOAc in CH2Cl2) to leave 6 as a yellow
solid (196 mg, 54%); Anal. Calcd for 6·2(CH2Cl2)
C80H80Cl4F4IrN7O6, C, 58.39; H, 4.90; N, 5.96. Found: C, 58.58;
H, 4.86; N, 6.01; δH (600 MHz; CDCl3; Me4Si) 8.90 (1H, d, J 6.4,
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