Highly efficient phosphorescence from cyclometallated iridium(III) compounds: Improved syntheses of picolinate complexes and quantum chemical studies of their electronic structures

Article abstract of DOI:10.1016/j.ica.2019.119040

We report a new method to make heteroleptic cyclometallated iridium(III) complexes that employs 1,2-dimethoxyethane (DME) instead of the commonly used 2-ethoxyethanol for the addition of ancillary ligands to chloro-bridged dimeric iridium species. Thus, p

Full text of DOI:10.1016/j.ica.2019.119040

Accepted Manuscript
Highly Efficient Phosphorescence From Cyclometallated Iridium(III) Com-
pounds: Improved Syntheses of Picolinate Complexes and Quantum Chemical
Studies of Their Electronic Structures
Robert D. Sanner, Nerine J. Cherepy, H. Paul Martinez, Hung Q. Pham, Victor
G. Young Jr.
PII:
S0020-1693(19)30743-1
https://doi.org/10.1016/j.ica.2019.119040
119040
DOI:
Article Number:
Reference:
ICA 119040
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
22 May 2019
20 July 2019
23 July 2019
Please cite this article as: R.D. Sanner, N.J. Cherepy, H. Paul Martinez, H.Q. Pham, V.G. Young Jr., Highly Efficient
Phosphorescence From Cyclometallated Iridium(III) Compounds: Improved Syntheses of Picolinate Complexes
and Quantum Chemical Studies of Their Electronic Structures, Inorganica Chimica Acta (2019), doi: https://doi.org/
1
0.1016/j.ica.2019.119040
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Highly Efficient Phosphorescence From Cyclometallated Iridium(III)
Compounds: Improved Syntheses of Picolinate Complexes and Quantum
Chemical Studies of Their Electronic Structures
†
†
†
‡
Robert D. Sanner,* Nerine J. Cherepy , H. Paul Martinez, Hung Q. Pham, and Victor
G. Young, Jr.
‡
†
Lawrence Livermore National Laboratory, Livermore, CA 94550, United States
Department of Chemistry, University of Minnesota, Minneapolis, MN 55455, United States
‡
ABSTRACT: We report a new method to make heteroleptic cyclometallated
iridium(III) complexes that employs 1,2-dimethoxyethane (DME) instead of the
commonly used 2-ethoxyethanol for the addition of ancillary ligands to chloro-
bridged dimeric iridium species. Thus, picolinic acid was quickly and cleanly added
to [(F ppy) Ir(Cl)] (where F ppy = 2-(4’,6’-difluorophenyl)pyridinato)) with base
2
2
2
2
under DME reflux to afford (F ppy) Ir(picolinate) (FIrpic) in excellent yield. The
2
2
high purity of the products obviates the need for further purification, an
improvement over the common route in which column chromatography is required.
We prepared eleven picolinate complexes by this route, eight of which were
characterized by single crystal x-ray diffraction. The complexes possess the same
distorted octahedral geometry with two bidentate phenylpyridine ligands and one
bidentate 2-picolinate ligand. All of the compounds exhibited efficient
phosphorescence with colors ranging from blue to orange; photophysical
measurements revealed emission quantum yields as high as 0.92, while most
surpassed 0.5. Time-dependent density functional theory calculations, coupled with
the use of natural transition orbitals (NTOs), allowed a detailed interpretation of the
electronic structures for the complexes. The nature of the acceptor orbital for the
lowest-energy triplet state NTO was found to be an important predictor for the
emission spectra of FIrpic and its congeners.
Keywords:
Photoluminescence
Phosphorescent iridium complex
Blue emission
DFT calculations
OLED
FIrpic synthesis
1

INTRODUCTION
Phosphorescent cyclometallated iridium(III) compounds have been
2
-6
7-10
investigated for a variety of applications including solar cells, sensors,
1
1, 12
13-17
bioimaging,
and scintillators.
However, their most widespread use stems
from their electrophosphorescence. Research in this area has focused on light-
1
8, 19
20, 21
emitting electrochemical cells,
perhaps most importantly, organic light-emitting diodes (OLED’s).
spin-orbit coupling induced by the iridium atom allows for mixing of singlet and
electrogenerated chemiluminescence
and,
2
2-30
The strong
1
, 31, 32
triplet excited states through efficient intersystem crossing.
As a result,
phosphorescence quantum yields are enhanced beyond that achievable with
3
3
fluorescent emitters. These cyclometallated iridium(III) complexes may be
classified based on their associated ligands. Thus, homoleptic compounds such as
3
4
35
Ir(ppy)3 (where ppy = 2-phenylpyridinato) or Ir(F ppy) (where F ppy = 2-(4’,6’-
2
3
2
difluorophenyl)pyridinato)) have identical ligands. This is contrasted with
3
6
heteroleptic compounds such as (F ppy) Ir(pic) (where pic = picolinate or
2
2
3
7
pyridine-2-carboxylate), (ppy) Ir(ppz) (where ppz = 1-phenylpyrazolyl), or
F ppy)(ppy)Ir(acac) (where acac = acetylacetonate) that have at least two
2
3
8
(
2
different ligands. The cyclometallated ligands contain a (C^N) core, for example ppy
or F ppy, and are distinguished from the ancillary ligands such as picolinate or
2
acetylacetonate. The heteroleptic compounds that seem to have received the most
study are the bis(phenylpyridinato)iridium(III) picolinates, exemplified by the
3
9, 40
parent compounds (ppy) Ir(pic)
FIrpic.
and (F ppy) Ir(pic), commonly referred to as
2
2 2
3
6, 41
1, 42
43-49
They have benefitted from several spectroscopic
and theoretical
studies. These complexes are typically prepared via a two-step process. First, the
cyclometallating ligand is reacted with IrCl · x H O following the example of
3
2
5
0
51
Nonoyama or Sprouse to form a chloro-bridged dimeric iridium compound, e.g.
Next, the ancillary ligand is added by reacting the iridium dimer
with picolinic acid in refluxing 2-ethoxyethanol and base (usually Na CO ).
5
1, 52
[
(ppy) IrCl] .
2
2
4
0, 53-56
2
3
5
7
Thompson has prepared FIrpic by using refluxing 1,2-dichloroethane as solvent
5
8
and Baranoff used tetrabutylammonium hydroxide as base in refluxing
dichloromethane. After the second step it is necessary to perform additional
purification, usually culminating in column chromatography. As part of our
1
6, 59
synthesis program for plastic scintillators
we have investigated blue-emitting
6
0
iridium complexes. We have now expanded that effort to include longer
wavelength emitters and have examined alternate methods to prepare
cyclometallated iridium complexes. In particular, we find that refluxing 1,2-
dimethoxyethane in the presence of sodium carbonate makes an excellent reaction
medium for addition of the ancillary ligand. Yields equal to or better than those
reported in previous procedures are obtained and no additional purification steps
(
such as column chromatography) are required. We are examining the scope of this
reaction and report herein our results with picolinates as the ancillary ligand.
Compounds were characterized by NMR and optical spectroscopy, x-ray
crystallography, and photophysical measurements. Time-dependent density
functional theory (TD-DFT) calculations were performed on the complexes and
applied to the interpretation of absorption and emission spectra.
2

RESULTS AND DISCUSSION
Synthesis. The reaction to prepare heteroleptic iridium complexes
Z ppy) Ir(pic-X,Y) using 1,2-dimethoxyethane at reflux is shown in Scheme 1,
(
2
2
where Z = H or F and X,Y are various substituents on the picolinate ligand, including
OH, F, CF , and F . Reaction times are typically 6-9 hr and workup consists of simple
3
2
filtration and washing; yields range from 80-95%. An identification guide to
compounds 1-11 prepared in this work is given in Chart 1.
Scheme 1. Synthesis of iridium(III) picolinate complexes.
Chart 1. Heteroleptic iridium(III) picolinates prepared in this study.
3

5
1, 52
Compounds 1-5 employed [(ppy) IrCl]
as the iridium source while 6-10 used
2
2
5
4, 61
[
(F ppy) IrCl] .
For compound 11 it was necessary to synthesize the xylyl-
2 2 2
F2ppy ligand and dimeric iridium species; this procedure is shown in Scheme 2.
Scheme 2. Synthesis of dimeric iridium complex C.
The ligand (compound B) was prepared via two Suzuki cross-coupling reactions;
mixing the ligand with IrCl · x H O in refluxing 2-methoxyethanol:water gave the
3
2
5
0
39,
iridium dimer (compound C) by the usual Nonoyama procedure. Compounds 1,
4
0
2, 53 36, 54, 55, 58
56, 58
55
13
2,
6,
7,
8, and 10 have been previously prepared, usually by
mixing the iridium dimer with a picolinic acid derivative in refluxing 2-
ethoxyethanol and base; purification is accomplished by column chromatography.
In our reactions, column chromatography was only required in the case of
compound 11 and this was due to a small (~1%) impurity that remained from the
synthesis of the ligand B (xylyl-F ppy).
2
An NMR comparison of the FIrpic obtained by our DME method and the
1
19
ethoxyethanol method is shown in Fig. 1 ( H, aromatic region) and Fig. 2 ( F). Note
the higher purity of the crude product obtained in DME as illustrated in the bottom
traces of both H and F NMR spectra.
1
19
4

1
Figure 1. H NMR spectra of crude FIrpic prepared in ethoxyethanol (top) and dimethoxyethane (bottom).
Figure 2. 19F NMR spectra of crude FIrpic prepared in ethoxyethanol (top) and dimethoxyethane (bottom).
5

We believe that the gentler conditions of DME reflux (85° C) compared to
ethoxyethanol (134° C) are at least partly responsible for this difference. There did
not seem to be any yield penalty for this procedure as all starting material was
consumed and the desired product was cleanly obtained. We find that this reaction
proceeds smoothly with both (ppy) Ir and (F ppy) Ir cyclometallates and picolinic
2
2
2
acid derivatives having hydroxy, fluoro, difluoro, or trifluoromethyl functional
groups. Although we have only run this reaction with a maximum 2 g of dimeric
iridium starting material, scale-up should be feasible. In fact, the ability to omit
column chromatography would be most beneficial at larger scales.
Crystal Structure Determinations. The molecular structure of compounds
-5 and 7-11 have been confirmed by X-ray crystallography and ORTEP diagrams of
3
these complexes are shown in Figs. 3-10; crystal and structure refinement data are
provided in Tables S1-S8 in the Supporting Information. All the complexes exhibit
the same distorted octahedral geometry with two bidentate phenylpyridine ligands
(
coordinated through the pyridine nitrogen atom and a phenyl carbon atom) and
one bidentate pyridine-2-carboxylate ligand, also known as 2-picolinate
coordinated through the pyridine nitrogen atom and the carboxylate oxygen atom).
(
The two iridium-bound nitrogen atoms of the phenylpyridine ligands are trans to
each other while the phenyl carbon atoms bound to the iridium are cis. The two
ligated atoms in the picolinate ligand are then trans to the iridium-bound phenyl
carbon atoms of the phenylpyridine ligands. The trans effect of the phenyl groups is
most clearly seen when comparing Ir-N bond distances. Thus, the Ir-N (picolinate)
bond is on average 0.1 Å longer than the Ir-N (phenylpyridine) bond in the same
molecule due to its trans disposition to the phenyl group. Although there is no such
intramolecular comparison available for the picolinate Ir-O bond (which is also
trans to a phenyl group), we note that the mean Ir-O bond length in these eight
molecules is 2.16(1) Å. This compares with the shorter mean value of 2.09 Å
6
2
reported in the Cambridge Crystallographic Database for an Ir-O bond, again
illustrating the trans effect of the phenyl group in these molecules. The C-Ir-N “bite
angle” for the phenylpyridine ligand averages 80.7(3)° for these complexes while
the C-Ir-O angle for the picolinate ligand is somewhat smaller at 76.8(5)°. The
phenyl and pyridine rings in each phenylpyridine ligand are slightly twisted with
respect to each other across the C-C bond linking the two rings. The dihedral angle
between best planes for the two rings is typically in the range of 3 - 6°, although two
of the complexes show larger twist angles. In 8, one of the twist angles is 11.3°;
examination of a packing diagram shows a close intermolecular contact between the
fluorine atom on the picolinate ligand and a ring carbon on the phenyl group of the
phenylpyridine ligand. One of the twist angles in 9 is 11.0°; the packing diagram
shows a close intermolecular contact between two fluorine atoms, each located on
the phenyl group of a phenylpyridine ligand in adjacent molecules.
6

Figure 3. The molecular structure of compound 3 with displacement ellipsoids drawn at the 50%
probability level. Hydrogen atoms have been removed for clarity. Selected bond distances (Å)
and angles (°): Ir1-C1 1.995(3), Ir1-C12 2.002(3), Ir1-N1 2.034(3), Ir1-N2 2.048(3), Ir1-N3
2
.144(3), Ir1-O1 2.159(3), C1-Ir1-N1 80.72(13), C12-Ir1-N2 80.78(15), O1-Ir1-N3 77.19(10).
Figure 4. The molecular structure of compound 4 with displacement ellipsoids drawn at the
5
0% probability level. Hydrogen atoms have been removed for clarity. Selected bond distances
(
Å) and angles (°): Ir1-C1 1.994(5), Ir1-C12 2.006(4), Ir1-N1 2.037(4), Ir1-N2 2.044(4), Ir1-N3
2
.155(4), Ir1-O1 2.166(4), C1-Ir1-N1 80.73(19), C12-Ir1-N2 80.5(2), O1-Ir1-N3 76.83(15).
7

Figure 5. The molecular structure of compound 5 with displacement ellipsoids drawn at the 50%
probability level. Hydrogen atoms have been removed for clarity. Selected bond distances (Å)
and angles (°): Ir1-C1 2.010(9), Ir1-C12 2.010(9), Ir1-N1 2.069(8), Ir1-N2 2.046(7), Ir1-N3
2
.156(7), Ir1-O1 2.172(7), C1-Ir1-N1 80.4(3), C12-Ir1-N2 81.6(3), O1-Ir1-N3 75.5(2).
8

Figure 6. The molecular structure of compound 7a with displacement ellipsoids drawn at the
0% probability level. Hydrogen atoms and dichloromethane solvent have been omitted for
5
clarity. The hydrogen-bonding interaction is shown by the dashed line. Two molecules are
found in the asymmetric unit; only molecule A is shown in the figure. Selected bond distances
(
Å) and angles (°): Ir1A-C1A 1.998(4), Ir1A-C12A 1.988(4), Ir1A-N1A 2.047(4), Ir1A-N2A
2
8
.031(4), Ir1A-N3A 2.148(4), Ir1A-O1A 2.179(3), C1A-Ir1A-N1A 80.55(16), C12A-Ir1A-N2A
0.95(17), O1A-Ir1A-N3A 77.03(12).
9

Figure 7. The molecular structure of compound 8a with displacement ellipsoids drawn at the 50%
probability level. Hydrogen atoms and solvate molecules have been omitted for clarity. Two
molecules are found in the asymmetric unit; only molecule A is shown in the figure. Selected bond
distances (Å) and angles (°): Ir1A-C1A 2.005(6), Ir1A-C12A 1.999(5), Ir1A-N1A 2.037(5), Ir1A-N2A
2
.053(5), Ir1A-N3A 2.124(4), Ir1A-O1A 2.151(4), C1A-Ir1A-N1A 80.7(2), C12A-Ir1A-N2A 80.7(2),
O1A-Ir1A-N3A 77.01(16).
Figure 8. The molecular structure of compound 9 with displacement ellipsoids drawn at the 50%
probability level. Hydrogen atoms and water solvent have been omitted for clarity. Selected bond
distances (Å) and angles (°): Ir1-C1 2.008(2), Ir1-C12 1.981(2), Ir1-N1 2.053(2), Ir1-N2 2.038(2),
Ir1-N3 2.134(2), Ir1-O1 2.159(2), C1-Ir1-N1 80.36(7), C12-Ir1-N2 80.83(7), O1-Ir1-N3 76.67(6).
1
0

Figure 9. The molecular structure of compound 10 with displacement ellipsoids drawn at the
0% probability level. Hydrogen atoms and dichloromethane solvent have been omitted for
clarity. Selected bond distances (Å) and angles (°): Ir1-C1 1.998(5), Ir1-C12 1.993(5), Ir1-N1
5
2
8
.057(4), Ir1-N2 2.020(4), Ir1-N3 2.136(4), Ir1-O1 2.143(3), C1-Ir1-N1 80.86(19), C12-Ir1-N2
1.05(19), O1-Ir1-N3 76.85(15).
1
1

Figure 10. The molecular structure of compound 11 with displacement ellipsoids drawn at the
0% probability level. Hydrogen atoms and water solvent have been omitted for clarity. Selected
bond distances (Å) and angles (°): Ir1-C1 2.009(32), Ir1-C20 1.987(4), Ir1-N1 2.039(3), Ir1-N2
5
2
7
.033(3), Ir1-N3 2.134(3), Ir1-O1 2.161(3), C1-Ir1-N1 80.37(13), C20-Ir1-N2 80.64(12), O1-Ir1-N3
6.78(11).
1
2

The molecular structures of all the complexes were successfully solved,
although there were special features of some, which will now be discussed.
Compounds 3 and 4. These compounds were found to be isostructural.
Compound 5. This compound was recrystallized from a mixture of dichloromethane
and methanol but specimens desolvated rapidly while viewing under the
microscope at room temperature. One specimen was successfully mounted using a
cold transfer from the microscope stage to the diffractometer. The crystal structure
revealed large channels which dichloromethane or methanol could fill in a highly
disordered manner (Fig. S4 in Supporting Information). Neither solvent could be
modeled with peaks in the difference Fourier since the highest F peak in the map
-
3
63
3
was only 3 e /Å . PLATON/VOID was used to calculate a void volume of 1046 Å
(
6
4
33.8% of unit cell volume). PLATON/SQUEEZE was used to correct the
diffraction data for the effects of the disordered solvent by effectively removing it
from the problem; it was determined that the unit cell had disordered atoms
-
-
contributing 522 e . Since dichloromethane contributes 42 e per molecule and Z=4,
this is consistent with approximately three dichloromethane solvent molecules per
iridium complex (although some disordered methanol could also be present in the
void spaces). Please note that the density, absorption coefficient, and F000 are
known to be incorrect since the exact cell contents are unknown. The best estimate
would be to include 12 dichloromethanes/unit cell to calculate these otherwise
unknown quantities.
Compound 7. Dichloromethane solvent was again found in the structure but in
well-ordered positions. There are two iridium complexes and one dichloromethane
molecule per asymmetric unit. Of special note in this complex is the presence of
intramolecular hydrogen bonding between the 3-hydroxy group on the pyridine
ring of the picolinate and the carbonyl oxygen on the same ligand (dotted line in Fig.
6
1
). Typical bond lengths are found for the OH···O=C grouping: H3···O2 averages
.79 Å for the two molecules in the asymmetric unit, while O2-O3 is 2.54 Å. The
same sort of hydrogen bonding was found in the previously reported crystal
structure of the nonfluorinated ring analog, (ppy) Ir(3-hydroxypicolinate) (our
2
6
5
compound 2). In that case, the OH···O=C grouping showed an H···O distance of
.828 Å.
1
Compound 8. The crystal was a twin by non-merohedry and the masses of the twin
individuals refined to 0.81:0.19. The twin law corresponds to a rotation of 180°
about the crystallographic a axis (see CIF file for the matrix used to convert hkl data).
The asymmetric unit contains two iridium complexes, one methanol solvent, one
water solvent, and one site that is a compositional disorder of methanol (0.55
occupancy) and dichloromethane (0.45 occupancy) (Fig. S9). There is a hydrogen
bonding network in the structure (Fig. S10). A hydrogen bond exists between the
ordered methanol molecule and the carbonyl in the picolinate ligand (CH OH···O=C,
3
with H···O of 1.87 Å, O-O is 2.71 Å). Another hydrogen bond is found between the
solvent water and the carbonyl group in the picolinate ligand of the other molecule
in the asymmetric unit (HOH···O=C, with H···O of 1.93 Å, O-O is 2.77 Å). A third
hydrogen bond exists between the hydrogen on a water molecule and the oxygen on
an ordered methanol molecule (HOH···OCH , with H···O of 1.94 Å, O-O is 2.78 Å). A
3
final hydrogen bond exists between the oxygen of the water molecule and the
1
3

hydrogen on the compositionally disordered methanol (HO···HOCH , with H···O of
3
2
.02 Å, O-O is 2.85 Å).
Compound 9. This structure was found to be a partial hydrate: PLATON/SQUEEZE
was used to find that the water content corresponds to slightly greater than a
hemihydrate with 0.54 H O/Ir. Two hydrogen bonds involving the water molecule
2
were found in the structure (Fig. S12). The first, stronger, bond exists between a
water hydrogen atom and the carbonyl carbon in the picolinate ligand (HOH···O=C,
with H···O of 1.87 Å, O-O is 2.71 Å). The second, weaker, bond is between the other
hydrogen atom of water and a fluorine atom in the CF group (HOH···F-C, with H···F
3
of 2.36 Å, O-F is 3.12 Å). This allowed the hydrogen atoms of water to be placed
along the OH···O and OH···F vectors of the hydrogen bonds with an O-H distance of
0
.84 Å. These H atoms were then refined as riding on the O atom in the water
molecule.
Compound 10. Dichloromethane solvent was found in a 1:1 ratio with the iridium
complex. There was a 89:11positional disorder of the dichloromethane with the
disordered pair occupying closely adjacent positions in the cell (Fig. S14).
Compound 11. The most notable feature of this structure is the twist (dihedral)
angle between the planes of the pyridine ring and substituent xylyl ring in the
phenyl(4-xylylpyridine) ligand. There is a considerable difference in this
measurement: 6.1(2)° vs. 32.5(2)° for the two ligands in the molecule. Examination
of the packing diagram shows the larger twist angle may be due to a steric
interaction between a methyl group on the xylyl substituent and a fluorine atom on
an adjacent molecule. Furthermore, this compound exists as a dihydrate with
extensive hydrogen bonding (Fig. S16). The water molecules form a hydrogen bond
set with two additional water molecules from another asymmetric unit related
through an inversion center. Each water molecule has one fully occupied oxygen
atom, one fully occupied hydrogen atom, and one hydrogen atom that must be split
over two positions with each having 0.5 occupancy. Each of the “fully occupied”
hydrogen atoms is involved in hydrogen bonding with oxygen atoms in the iridium
complex. Thus, a hydrogen bond with the alkoxy oxygen of the picolinate ligand
(
HOH···O-C, with H···O of 2.14 Å, O-O is 2.93 Å) and a hydrogen bond with the
carbonyl oxygen of the picolinate ligand (HOH···O=C, with H···O of 1.97 Å, O-O is
.77 Å).
2
1
4

Spectroscopy and Photophysical Properties. The absorption spectra
above 350 nm of complexes 2-5 in the (ppy) Ir(pic) series are shown in the left half
2
of Fig. 11 (complete spectra in Fig. S17 in Supporting Information).
1
0
0
0
0
0
.0
.8
.6
.4
.2
.0
1
2
3
4
5
2
3
4
5
3
50
400
450
500
550
450
500
550
600
650
700
wavelength (nm)
wavelength (nm)
2
Figure 11. Absorption (left) and emission (right) spectra of (ppy) Ir(pic) series (0.1 wt% in PMMA discs).
In addition to intense ligand-centered π-π* transitions below 350 nm, three
common spectral features are bands ~400 and 440 nm of nearly equal intensity
1
typically assigned as MLCT (d  *) and a much weaker absorption at 485 nm
3
usually assigned to MLCT between the singlet ground state and the lowest triplet
5
3, 58, 65
state (S  T ).
The emission spectra of 1-5 are given in Fig. 11 (right) and,
0
1
except in one case, are fairly uniform. Compounds 1-3, and 5 show emission bands
at ~500 and 525 nm (2 is blue-shifted by 5 nm and 5 is red-shifted by 5 nm from
these values). Compound 4 exhibits very broad emission that begins around 480
nm and extends into the orange, with maximum at 560 nm.
The absorption spectra of complexes 7-11 in the FIrpic series are shown in
Fig. 12 (left). The two spectral features found in all the compounds are an
1
1
0
0
.5
.0
.5
.0
6
7
8
9
10
1
7
8
9
1
1
0
1
1
4
50
500
550
600
650
700
3
50
400
450
500
550
wavelength (nm)
wavelength (nm)
Figure 12. Absorption (left) and emission (right) spectra of FIrpic series (0.1 wt% in PMMA discs).
1
5

1
absorption at 380 nm (400 nm in 11) conventionally assigned to MLCT (d  *)
and a much weaker absorption at ~460 nm (470 nm in 11) generally assigned to
3
42, 58
MLCT between the singlet ground state and the lowest triplet state (S  T ).
0
1
The emission spectra of 6-11 are given in Fig. 12 (right) and the complexes under
blacklight illumination are shown in Fig. 13. The emission spectra show more
variation than the absorption spectra for the series. In general, the emission bands
of the FIrpic series are blue-shifted about 30 nm compared to the (ppy) Ir(pic)
2
series. Compounds 6, 7, 8, and 10 are nearly identical, with emission at 466 and
4
92 nm. The lower wavelength band is more intense except for 10 in which the
higher wavelength band is stronger; this gives 10 more of a blue-green emission as
shown in Fig. 13. (Fig. 11 shows this shift of intensity was also found in the
analogous difluoro compound 5 in the (ppy) Irpic series.). Compound 11 is red-
2
shifted by about 25 nm and compound 9 exhibits very broad emission, with maxima
ranging from 470 to 540 nm.
6
(FIrpic)
7
8
9
10
11
Figure 13. FIrpic series (0.1% complex in 1 mm thick PMMA disc) under 400 nm illumination.
The photophysical properties of the complexes are given in Table 1. The
F2ppy complexes exhibit higher emission quantum yields than their ppy analogs, e.g.
FIrpic > (ppy) Ir(pic). The compounds with hydroxy-substituted ligands, 2 and 7,
2
show enhanced quantum yields compared to the parent compounds, 1 and 6. This
6
5
was previously observed by Yi et al. for 7. The compounds with monofluorinated
picolinates, 3 and 8, show larger quantum yields than their difluorinated analogs, 5
and 10. The trifluoromethyl compounds, 4 and 9, are the weakest emitters in the
group and show broad, red-shifted emission. Compound 11, which has a xylyl group
on the pyridine ring, has Φ = 0.66. This is somewhat less than the value of 0.92
6
6
reported for the mesityl analog. The emission lifetimes (τ ) of the molecules in
em
the FIrpic series are longer than their counterparts in the (ppy) Ir(pic) series. The
2
hydroxy-substituted compound 7 displays the highest quantum efficiency (92%)
and longest lifetime (2.69 μs) of the complexes under study here. This behavior was
also found previously when examining this compound in a group of hydroxy- and
6
5
methoxy-substituted iridium cyclometallates. Finally, Compound 7 showed the
5
-1
slowest nonradiative rate constant (0.30 x 10 s ) in our group while the
trifluoromethyl-substituted compounds 4 and 9 exhibited the fastest at 9.4 and 7.2 x
5
-1
1
0 s , respectively.
1
6

Table 1. Photophysical properties of the iridium complexes.
Compounda
λ
em (nm)
Φ
b
τ
em (μs)
1.26
1.80
1.67
0.86
1.01
1.46
2.69
1.72
1.09
1.19
1.36
k
r
x 10 (s )
3.97
5
-1
k
nr x 10 (s )
3.97
5
-1
em
1
2
3
4
5
6
7
8
9
501, 525
496, 520
499, 523
560 (br)
509, 532
467, 492
465, 492
466, 492
0.50
0.69
0.52
0.19
0.23
0.89
0.92
0.60
0.22
0.46
0.66
3.83
3.11
2.21
2.28
6.10
3.42
3.49
2.02
1.72
2.87
9.42
7.62
0.75
0.30
2.33
7.16
470, 530 (br)
468, 495, 525 (sh)
490, 515
1
1
0
1
3.87
4.85
4.54
2.50
a
b
1
Measured in 0.1% PMMA discs. Relative to FIrpic with Φ = 0.89 ; values are ±20%
TD-DFT Calculations. Time-dependent density functional theory (TD-DFT)
calculations were performed on the (ppy) Irpic series (1-5) and FIrpic series (6-11)
2
of compounds in order to gain insight into the electronic structure of the lowest
energy excited states. Since excitation energies are strongly dependent on the
6
7
choice of the exchange-correlation functional used in TD-DFT calculations, we
compared two different functionals: B3LYP and CAM-B3LYP. We also tested the
effect of the Ir basis set on the predicted excitation energies by comparing two
different basis sets: (i) the Stuttgart/Dresden relativistically corrected effective core
potential (ECP) along with its [6s5p3d] valence basis, (ii) the Los Alamos relativistic
ECP along with its [3s3p2d] valence basis. Both ECPs were used to replace 60 core
electrons of Ir. In all cases we used the triple-ζ basis set def2-TZVP for the ligands.
Our results (shown in Tables S9 and S10 in the Supporting Information) reveal that
CAM-B3LYP overestimated the excitation energies while B3LYP gave excellent
agreement with the measured values. The effect of the iridium basis set choice was
negligible: SDD (36 basis functions) and LANL2DZ (22 basis functions) gave only
slightly different excitation energies. Our results are consistent with the previous
6
8
functional benchmark on Ir(III) complexes. Hence, the combination of the B3LYP
functional with the def2-TZVP (ligand)/LANL2DZ (Ir) basis set was utilized for the
calculations in the following discussion.
The six lowest energy singlet (S -S ) and triplet (T -T ) transitions are given
1
6
1
6
in Tables S11 (1-5) and S12 (6-11). Based on oscillator strength calculations, the
band near 435 nm in 1-5 is assigned to either the S  S (1-2) or S  S (3-5)
0
1
0
2
transition. The higher energy band near 400 nm in the (ppy) Irpic series
2
corresponds to the S  S transition, except for compound 4 which has a better fit
0
4
to S  S . As mentioned in the spectroscopy discussion above, the band near 485
0
5
nm in 1-5 is typically assigned to the lowest energy triplet transition S  T . Our
0
1
calculations in Table S11 underestimate the energy of this transition by approx. 0.1
eV. For the FIrpic series given in Table S12, much better agreement between
experiment and theory (typically < 0.05 ev) was found for the S  T absorption
0
1
1
7

band near 460 nm. Assignment of the low energy singlets in 6-11 was not as
straightforward since these bands are poorly resolved in the compounds. A band
near 380 nm corresponds to the S  S (compounds 8-10) or S  S (6, 7, 11)
0
4
0
5
transition, based on oscillator strength calculations. No other lower energy spectral
features can be definitively assigned for the FIrpic series until reaching the T band
1
at 460 nm.
6
9
We have computed natural transition orbitals (NTOs) for S -S and T -T
1
6
1
2
states for all compounds in the FIrpic series (6-11) and provide full details for these
in Tables S13-S25, including the description of the NTOs in terms of molecular
orbitals. We also present molecular orbital energy level diagrams and contour plots
for complexes 6-11 in Tables S26-32 although we will primarily utilize NTOs in the
following discussion. The use of these NTOs provides a simple qualitative
description of the electronic transitions for these complexes. Orbitals for the S -S
1
3
states are given in Table 2 for the representative compounds 6, 8, and 11. We find
that the orbitals show remarkable similarity for 6 and 7. Thus, for the S state,
1
donation from the Ir d-orbital to the phenylpyridine ligands occurs (ML CT) as
ppy
well as ligand-ligand donation between the phenylpyridine groups (L L CT). The
ppy ppy
acceptor is mainly localized on one of the phenylpyridines. The S state involves the
2
same donor orbitals but now the acceptor group is localized on the picolinate ligand
instead of the phenylpyridine ligands, giving this ML CT and L L CT character.
pic
ppy pic
Both S and S can be described mainly as a combination of HOMO  LUMO and
1
2
HOMO  LUMO+1 using molecular orbital theory; they differ in the phase of the
configuration mixing. The S state is very similar to S , with MLCT and LLCT
3
1
involving the phenylpyridine ligands. In this case the acceptor is localized on the
other phenylpyridine ligand than that involved in S . This can be described as
1
mainly HOMO  LUMO+2. Now, the NTOs for the fluorinated compounds 8-10 are
also very similar. Essentially, the composition of the S and S states from 6-7 is
1
2
unchanged in 8-10 but their energy ordering is inverted. That means S can be
1
classified as having ML CT and L L CT character while S can be classified as
pic
ppy pic
2
having ML CT and L L CT character. S for 8-10 is unchanged from the picture
ppy
ppy ppy
3
in 6-7, ML CT and L L CT. In terms of molecular orbitals, S is mainly HOMO 
ppy
ppy ppy
1
LUMO, S is HOMO  LUMO+1 and S is HOMO  LUMO+2 for 8-10. The NTOs for
2
3
1
1 are more complex due to the presence of the xylyl group on the pyridine in the
phenylpyridine ligand. As shown in Table 2, the donor state is the same for S -S :
1
3
the Ir d-orbital and the phenyl group in both phenylpyridine ligands are involved.
There is no contribution from the xylylpyridine group on these ligands. For the S1
state, the acceptor consists predominantly of the entire phenyl-xylylpyridine unit
for one ligand with minimal involvement of the other phenylpyridine ligand. This
can be classified as ML CT and L L CT in character. The S state is similar,
ppy
ppy ppy
2
except the acceptor is now localized on the other phenyl-xylylpyridine ligand. For S3,
the acceptor is localized solely on the picolinate ligand so this transition can be
characterized as ML CT and L L CT character. When viewed from the molecular
pic
ppy pic
orbital standpoint, S is mainly HOMO  LUMO, S is HOMO  LUMO+1 and S is
1
2
3
HOMO  LUMO+2 for 11.
1
8

Table 2. Natural Transition Orbitals (NTOs) for Low Energy Singlet States of Compounds 6, 8 and 11.
Sn
Donor
Acceptor
Sn
Donor
Acceptor
S1
S1
S2
S3
S2
S1
S2
S3
S3
1
9

The NTOs for the lowest energy triplet state (T ) calculated at the ground
1
state (S ) geometry are shown in Table 3. In the case of 10, both T and T NTOs are
0
1
2
given since the states are nearly degenerate (0.01 eV difference). We find that 6-8
exhibit very similar orbitals with donation from the Ir d-orbital to the
phenylpyridine ligands (ML CT) as well as ligand-ligand donation between the
ppy
phenylpyridine groups (L L CT). For 6 and 7 this can be described as a
ppy ppy
combination of HOMO  LUMO and HOMO  LUMO+1. It is predominantly HOMO

LUMO+1 for 8. The donor orbitals for 9 and 10 are similar, involving the Ir d-
orbital and the phenylpyridine ligands but the acceptor orbitals are very different.
Thus, the trifluoromethyl compound 9 utilizes the picolinate ligand as its
predominant acceptor and can be classified as ML CT and L L CT. The difluoro-
pic
ppy pic
substituted complex 10 has phenylpyridine and picolinate ligands both involved as
acceptors. The main difference between the nearly degenerate T and T states of
1
2
1
0 is the participation of both phenylpyridine ligands as acceptors in T but only
1
one ligand in T . These transitions can be classified as ML CT and ML CT
2
ppy
pic
(
involving both picolinate and phenylpyridine acceptor ligands) as well as L L CT
ppy pic
and L L CT. The T transition in 9 as well as T and T in 10 can be described as
ppy ppy
1
1
2
a combination of HOMO  LUMO and HOMO  LUMO+1. Finally, we consider the
xylylpyridine compound 11. The donor state involves the Ir d-orbital and
phenylpyridine ligands but no contribution from the xylyl group. The acceptor
involves predominantly one phenylpyridine ligand with its associated xylyl group.
This can be classified as ML CT and L L CT with charge transfer extending to
ppy
ppy ppy
the xylyl group; it is predominantly a HOMO  LUMO transition. This involvement
of the xylyl fragment is not surprising given the nearly coplanar configuration of the
pyridine and xylyl groups in the x-ray structure discussed above (6° dihedral angle
between the two planes for one of the phenyl-xylylpyridine ligands). This extension
of -conjugation into the xylyl group results in a red shift of ~10 nm in the T band
1
compared to the other compounds. Note that this shift was not found in the mesityl
6
6
analog, presumably due to the nearly orthogonal disposition of the mesityl and
7
0
pyridine rings found in the x-ray structure of this compound.
2
0

Table 3. Natural Transition Orbitals (NTOs) for Low Energy Triplet States of Compounds 6 – 11.
Tn
T1
Donor
Acceptor
Tn
T1
Donor
Acceptor
T1
T2
T1
T1
T1
2
1

Phosphorescence from cyclometallated iridium complexes is believed to
1
, 41, 43, 48
originate from the lowest energy triplet state
so we can use the information
gleaned from the T NTOs to better understand the emission spectra shown in
1
Figure 12. The T acceptor orbitals for these complexes can be divided into three
1
types: Type 1 has the acceptor located on the phenylpyridine ligands (compounds
6
-8 and 11); Type 2 has the acceptor located on the picolinate ligand (compound 9);
Type 3 is located on both the picolinate and phenylpyridine ligands (compound 10).
The Type 1 spectra for 6-8 are nearly identical with narrow emission bands in the
blue while that for 11 has a similar shape but with a 25 nm bathochromic shift into
the green due to the extension of -conjugation into the xylyl group. The Type 2
spectrum of 9 is very broad, ranging far into the visible giving rise to yellow-orange
emission. Finally, the Type 3 spectrum of 10 is broader than that of Type 1 but
much narrower than the Type 2 spectrum of 9. Its extension farther into the visible
than the blue Type 1 compounds gives it a blue-green emission.
CONCLUSIONS
In an effort to improve the synthesis of cyclometallated iridium complexes
we examined other solvents as an alternative to the glycol ethers typically used for
ancillary ligand addition. In particular, we found that 1,2-dimethoxyethane at reflux
with excess picolinic acid and base makes a reaction medium that is superior to the
usual refluxing 2-ethoxyethanol for addition to chloro-bridged dimeric iridium
compounds to prepare the picolinate complexes. This reaction proceeds quickly in
high yield and requires no product purification, a marked improvement over the
usual procedure which uses column chromatography. The ability to omit
chromatographic purification will be especially beneficial in large scale reactions.
We employed this new synthesis to prepare eleven picolinate complexes, five of
which are reported here for the first time. X-ray diffraction studies were carried out
on eight of the compounds to determine their molecular structures. All the
complexes exhibit the same distorted octahedral geometry with two bidentate
phenylpyridine ligands and one bidentate 2-picolinate ligand. The iridium-bound
nitrogen atoms of the two phenylpyridine ligands are trans to each other while the
two ligated atoms in the picolinate ligand (pyridine nitrogen and carboxylate
oxygen) are trans to the iridium-bound phenyl carbon atoms of the phenylpyridine
ligands. All of the compounds were emissive, with colors ranging from blue to
orange. Photophysical measurements showed them to be efficient, having emission
quantum yields greater than 50% in most cases. Measured emission lifetimes were
typically 1-2 μs. Time-dependent density functional theory calculations, coupled
with the use of natural transition orbitals, allowed a detailed interpretation of the
absorption and emission spectra for the complexes. We found it useful to study the
T1 NTOs for the FIrpic series to understand the phosphorescence colors for these
complexes. Thus, compounds with acceptor orbitals located on the phenylpyridine
ligands (Type 1) show narrow spectra with blue emission (6-8), picolinate-localized
acceptor orbitals (Type 2) show very broad yellow-orange emission (9), and
acceptor orbitals on both phenylpyridine and picolinate (Type 3) have somewhat
broadened blue-green emission (10). Compound 11 is a Type 1 complex with a
2
2

shift of emission into the green due to the extension of -conjugation into the xylyl
group. The success we have enjoyed with the synthesis of picolinates using this
modification of the conventional route has encouraged us to examine other ancillary
ligands. Our studies with acetylacetonates are currently in progress.
2
3

EXPERIMENTAL SECTION
General Information. All compounds were synthesized in a dry nitrogen
atmosphere, unless otherwise specified. The solvents and commercially available
starting materials were of the highest purity available and used as received. Most
organic compounds were purchased from TCI America and IrCl · x H 0 was
3
2
purchased from Strem Chemicals. Silica column chromatography was done with
silica gel 60 (particle size 40-63 m) from EMD Chemicals. Microanalysis was
performed by Galbraith Laboratories, Knoxville, TN. NMR spectra were recorded on
a Bruker Avance III 600 MHz spectrometer.
Photophysical and optical spectroscopy measurements. Specimens for
absorption and emission measurements were prepared by polymerizing 0.1%
solutions of the compounds in methyl methacrylate. This provided 14 mm diam
cylinders which were cut and polished to yield ~ 1 mm thick x 14 mm diam discs.
Optical absorption spectra were obtained with a Thermo Evolution 220 UV-visible
spectrometer. Emission spectra were measured using 425 nm excitation on a
Thermo Lumina luminescence spectrometer employing backscatter geometry,
excitation and emission slits of 1 nm, a signal averaging time of 0.2 s, and a scan rate
of 300 nm/minute. Quantum yields were estimated by sensitivity correcting the
emission spectra for the PMT and grating efficiency as a function of wavelength,
then normalizing the integrated emission spectra to the optical density of each
sample at the excitation wavelength, 425 nm. To estimate the quantum yields of the
compounds, their integral light yields were standardized relative to FIrpic, which
1
has a reported value of 0.89 in PMMA. Phosphorescence lifetime measurements
were acquired using a flashlamp-pumped Nd:YAG laser at 266 nm with 20 ns pulses.
Luminescence was collected with a monochromator, set to the emission wavelength
maximum for each compound, coupled to an R928 Hamamatsu PMT and read out by
an oscilloscope. For each sample, 10 traces were acquired and averaged to generate
the decay curves, which were then fit in Igor Pro, for all decays, to single
exponentials to obtain the phosphorescence lifetimes.
X-ray crystallography. Suitable crystals for single crystal diffraction studies on
compounds 3-5 and 7-11 were obtained by slow evaporation of solvent from
dichloromethane/methanol solutions. Data were collected on a Bruker-AXS VENTURE
diffractometer with a MoKα microfocus source (k = 0.71073 Å) with a PHOTON-II
7
1
(CPAD) detector. Unit cell constants were determined initially with APEX3 software.
Final unit cell constants were calculated on sets of strong reflections selected from the
7
1
integration of all data with SAINT. Multi-scan scaling and absorption correction were
applied with SADABS or TWINABS based on the Laue class determined for each crystal
7
1
72
structure. The crystal structures were solved by direct-methods using SHELXT-2014.
7
3
Final least-squares refinements were completed with SHELXL-2014. All non-
hydrogen atoms were refined with anisotropic displacements. Hydrogen atoms were
placed as riding atoms at calculated positions with isotropic displacements relative to
respective host atoms. Specimen 5 exhibited the effects of disordered lattice solvent.
These diffraction data were treated with PLATON/SQUEEZE to correct the diffraction
2
4

data for the effects.64 Specimen 8 was determined to be a twin by non-merohedry. CIF
data is available from the Cambridge Crystallographic Data Centre with deposit numbers:
1
873880 (8), 1873881 (4), 1873882 (7), 1873883 (9), 1873884 (3), 1873885 (11),
1
873886 (5), 1873887 (10). These data can be obtained free of charge via
www.ccdc.cam.ac.uk/data_request/cif.
5
1, 52
54, 61
Synthesis. [(ppy) IrCl]
and [(dfppy) IrCl]
2
were prepared by the literature
2
2
2
methods.
2
-chloro-4-(3,5-dimethylphenyl)pyridine (Compound A). A 250 mL round-
bottom flask was charged with 5.5 g (23 mmol) 2-chloro-4-iodopyridine, 4.0 g (27
mmol) 3,5-dimethylphenylboronic acid, and 31 mL (62 mmol) 2M aqueous
potassium carbonate in 40 mL 1,2-dimethoxyethane. The mixture was purged with
argon and 664 mg (0.575 mmol) tetrakis(triphenylphosphine) palladium (0) was
added. The reaction was brought to reflux and heated for 21 hr under an argon
atmosphere. After cooling to room temperature, the reaction mixture was poured
into a 250 mL separatory funnel. The aqueous layer was extracted with 3 x 50 mL
ethyl acetate. The combined organic layers were extracted with 2 x 100 mL water
and 2 x 100 mL brine and dried over magnesium sulfate. The solvent was removed
on a vacuum line to yield 3.5 g of oily material. This was used without further
1
purification for the next step (preparation of compound B.) H NMR (600MHz,
CDCl ) (ppm): 8.41 (d, J = 5.2 Hz, 1H), 7.54 (d, J = 1.3 Hz, 1H), 7.42 (dd, J = 5.2, 1.6 Hz,
3
1
H), 7.23 (s, 2H), 7.12 (s, 1H), 2.41 (s, 6H).
2
-(2,4-difluorophenyl)-4-(3,5-dimethylphenyl)pyridine (Compound B). A 250
mL round-bottom flask was charged with 8.7 g (40 mmol) 2-chloro-4-(3,5-
dimethylphenyl)pyridine (A from above), 8.2 g (52 mmol) 2,4-
difluorophenylboronic acid, and 56 mL (112 mmol) 2M aqueous potassium
carbonate in 75 mL 1,2-dimethoxyethane. The mixture was purged with argon and
9
25 mg (0.80 mmol) tetrakis(triphenylphosphine) palladium (0) was added. The
reaction was brought to reflux and heated for 19.5 hr under an argon atmosphere.
After cooling to room temperature, the reaction mixture was poured into a 250 mL
separatory funnel. The aqueous layer was extracted with 3 x 50 mL ethyl acetate.
The combined organic layers were extracted with 2 x 100 mL water and 2 x 100 mL
brine and dried over magnesium sulfate. The solvent was removed on a rotovap
and the residue was chromatographed on silica using ethyl acetate/hexane as eluent.
Finally, the solvent was removed on a vacuum line to yield 9.7 g (82%) of off-white
1
solid. H NMR (600MHz, CDCl ) (ppm): 8.75 (d, J = 5.1 Hz, 1H), 8.05 (q, J = 8.7 Hz,
3
1
1
H), 7.96 (s, 1H), 7.48 (d, J = 5.1 Hz, 1H), 7.31 (s, 2H), 7.13 (s, 1H), 7.05 (t, J = 8.3 Hz,
1
9
H), 6.96 (t, J = 10.0 Hz, 1H), 2.43 (s, 6H). F NMR (565 MHz, CDCl ) (ppm): -109.24
3
(
quintet, J = 7.8 Hz, 1F), -112.55 (q, J = 9.4 Hz, 1F).
Bis{bis[2-(2,4-difluorophenyl)-4-(3,5-dimethylphenyl)pyridinato](-
chloro)iridium(III)} (Compound C). A 300 mL round-bottom flask was charged
with 4.00 g (13.5 mmol) 2-(2,4-difluorophenyl)-4-(3,5-dimethylphenyl)pyridine (B
2
5

from above) in 112 mL methoxyethanol and 37 mL water. The mixture was purged
with nitrogen and 1.8 g (5.1 mmol) IrCl · x H O was added. The reaction was
3
2
brought to reflux and heated for 20.5 hr under a nitrogen atmosphere. After cooling
to room temperature, the reaction was filtered through a glass frit. The solids were
washed with four portions of methanol and dried under vacuum to yield 3.71 g of
1
yellow product (90%). H NMR (600MHz, CDCl ) (ppm): 9.17 (d, J = 5.8 Hz, 4H),
3
8
5
=
.55 (s, 4H), 7.26 (s, 8H), 7.16 (s, 4H), 7.00 (d, J = 5.9 Hz, 4H), 6.40 (t, J = 10.5 Hz, 4H),
1
9
.49 (d, J = 8.9 Hz, 4H), 2.36 (s, 24H). F NMR (565 MHz, CDCl ) (ppm): -108.07 (q, J
3
9.3 Hz, 4F), -110.23 (t, J = 11.1 Hz, 4F).
(
ppy) Ir(picolinate) (Compound 1). A 50 mL round-bottom flask was charged
2
with 1.03 g (9.70 mmol) sodium carbonate and 0.48 g (3.9 mmol) pyridine-2-
carboxylic acid in 30 ml 1,2-dimethoxyethane. The mixture was purged with
nitrogen and 1.04 g (0.97mmol) [(ppy) IrCl] was added. The reaction was brought
2
2
to reflux and heated for 6.5 hr under a nitrogen atmosphere. After cooling to room
temperature, the reaction was filtered through a glass frit. The solids were washed
with three portions of water and two portions of methanol and dried under vacuum
1
to yield 1.13 g of yellow product (94%). H NMR results were identical with those
4
0
previously reported.
(
ppy) Ir(3-hydroxypicolinate) (Compound 2). A 50 mL round-bottom flask was
2
charged with 1.0 g (9.4 mmol) sodium carbonate and 0.52 g (3.7 mmol) 3-
hydroxypyridine-2-carboxylic acid in 30 ml 1,2-dimethoxyethane. The mixture was
purged with nitrogen and 1.0 g (0.93 mmol) [(ppy) IrCl] was added. The reaction
2
2
was brought to reflux and heated for 9 hr under a nitrogen atmosphere. After
cooling to room temperature, the reaction was filtered through a glass frit. Due to
filtration problems with a subsequent water wash, an aqueous suspension of the
solids from the frit were transferred to a separatory funnel and extracted with three
portions of dichloromethane. The organic phase was dried over magnesium sulfate
and pumped to dryness on a vacuum line to yield 1.13 g of yellow product (95%).
1
2
H NMR results were identical with those previously reported.
(
ppy) Ir(5-fluoropicolinate) (Compound 3). Procedure as for compound 1, with
2
5
-fluoropyridine-2-carboxylic acid as ligand (91% yield). Anal. Calcd for
1
IrC H N O F: C, 52.49; H, 2.99; N, 6.56. Found: C, 52.22; H, 2.91; N, 6.47%. H
2
8
19
3 2
NMR (600MHz, CDCl ) (ppm): 8.78 (d, J = 5.6 Hz, 1H), 8.37 (m, 1H), 7.91 (d, J = 8.1
3
Hz, 1H), 7.87 (d, J = 8.1 Hz, 1H), 7.75 (m, 2H), 7.62 (m, 4H), 7.50 (d, J = 5.6 Hz, 1H),
7
6
.16 (t, J = 6.6 Hz, 1H), 6.97 (m, 2H), 6.88 (t, J = 7.4 Hz, 1H), 6.83 (t, J = 7.4 Hz, 1H),
.77 (t, J = 7.4 Hz, 1H), 6.42 (d, J = 7.6 Hz, 1H), 6.18 (d, J = 7.6 Hz, 1H). 19F NMR (565
MHz, CDCl ) (ppm): -118.40 (t, J = 6.2 Hz, 1F).
3
(
ppy) Ir[5-(trifluoromethyl)-picolinate] (Compound 4). Procedure as for
2
compound 1, with 5-trifluoromethylpyridine-2-carboxylic acid as ligand (92% yield).
Anal. Calcd for IrC H N O F : C, 50.43; H, 2.77; N, 6.08. Found: C, 49.86; H, 2.55;
N, 5.94%. H NMR (600MHz, CDCl ) (ppm): 8.76 (d, J = 5.7 Hz, 1H), 8.48 (d, J = 8.2
2
9
19
3 2 3
1
3
Hz, 1H), 8.14 (d, J = 8.2 Hz, 1H), 7.99 (s, 1H), 7.93 (d, J = 8.2 Hz, 1H), 7.88 (d, J = 8.2
2
6

Hz, 1H), 7.76 (t, J = 7.8 Hz, 2H,), 7.64 (d, J = 7.7 Hz, 1H), 7.61 (d, J = 7.7 Hz, 1H), 7.45
(
d, J = 5.7 Hz, 1H), 7.18 (m, 1H), 6.98 (m, 2H), 6.90 (t, J = 7.4 Hz, 1H), 6.85 (t, J = 7.4
1
9
Hz, 1H), 6.78 (t, J = 7.4 Hz, 1H), 6.43 (d, J = 7.6 Hz, 1H), 6.17 (d, J = 7.6 Hz, 1H).
F
NMR (565 MHz, CDCl ) (ppm): -62.69 (s, 3F).
3
(
ppy) Ir(3,5-difluoropicolinate) (Compound 5). Procedure as for compound 1,
2
with 3,5-difluoropyridine-2-carboxylic acid as ligand (81% yield). Anal. Calcd for
IrC H N O F : C, 51.06; H, 2.75; N, 6.38. Found: C, 49.41; H, 2.66; N, 6.13%. H
1
2
8
18
3 2 2
NMR (600MHz, CDCl ) (ppm): 8.80 (d, J = 5.7Hz, 1H), 7.93 (d, J = 8.2 Hz, 1H), 7.89 (d,
3
J = 8.2 Hz, 1H), 7.78 (m, 2H), 7.64 (d, J = 7.8 Hz, 1H), 7.60 (d, J = 7.8 Hz, 2H,), 7.56 (d, J
=
2.2 Hz, 1H), 7.54 (d, J = 5.7 Hz, 1H), 7.42 (t, J = 8.4 Hz, 1H), 7.21 (t, J = 7.2 Hz, 1H),
.02 (t, J = 7.2 Hz, 1H), 6.97 (t, J = 7.0 Hz, 1H), 6.89 (t, J = 7.0 Hz, 1H), 6.84 (t, J = 7.4
7
1
9
Hz, 1H), 6.77 (t, J = 7.4 Hz, 1H), 6.40 (d, J = 7.6 Hz, 1H), 6.13 (d, J = 7.6 Hz, 1H).
F
NMR (565 MHz, CDCl ) (ppm): -109.12 (dd, J = 12.5, 8.9 Hz, 1F), -114.32 (dd, J =
3
1
2.5, 7.9 Hz, 1F).
FIrpic (Compound 6). A 100 mL round-bottom flask was charged with 1.75 g (16.5
mmol) sodium carbonate and 0.81 g (6.6 mmol) pyridine-2-carboxylic acid in 53 ml
1
,2-dimethoxyethane. The mixture was purged with nitrogen and 2.00 g (1.64
mmol)[(dfppy) IrCl] was added. The reaction was brought to reflux and heated for
2
2
9
hr under a nitrogen atmosphere. The reaction was then chilled in an ice-water
bath prior to filtration through a glass frit. The solids were washed with three
portions of water and three portions of methanol and dried under vacuum. This
yielded 2.08 g yellow product (91%). H and F NMR results were identical with
1
19
5
5
those previously reported.
(
F ppy) Ir(3-hydroxypicolinate) (Compound 7). A 50 mL round-bottom flask
2
2
was charged with 0.87 g (8.2 mmol) sodium carbonate and 0.46 g (3.3 mmol) 3-
hydroxypyridine-2-carboxylic acid in 25 ml 1,2-dimethoxyethane. The mixture was
purged with nitrogen and 1.00 g (0.82 mmol) [(dfppy) IrCl] was added. The
2
2
reaction was brought to reflux and heated for 8 hr under a nitrogen atmosphere.
After cooling to room temperature, the reaction was filtered through a glass frit.
The solids were washed with three portions of water and two portions of ice-cold
1
methanol and dried under vacuum to yield 1.08 g of yellow product (92%). H NMR
5
6
19
results were identical with those previously reported. The F spectrum is
1
9
reported here for the first time: F NMR (565 MHz, CDCl ) (ppm): -107.01 (q, J =
3
9
.4 Hz, 1F), -107.77 (q, J = 9.4 Hz, 1F), -109.76 (t, J = 11.4 Hz, 1F), -110.16 (t, J = 11.5
Hz, 1F).
(
F ppy) Ir(5-fluoropicolinate) (Compound 8). Procedure as for compound 6,
2 2
with 5-fluoropyridine-2-carboxylic acid as ligand (first crop yield 72%, overall yield
9
1
19
55
3%). H and F NMR results were identical with those previously reported.
(
F ppy) Ir[5-(trifluoromethyl)picolinate] (Compound 9). A 50 mL round-
2
2
bottom flask was charged with 0.87 g (8.2 mmol) sodium carbonate and 0.52 g (3.3
mmol) 5-trifluoromethylpyridine-2-carboxylic acid in 25 ml 1,2-dimethoxyethane.
2
7

The mixture was purged with nitrogen and 1.00 g (0.82 mmol) [(dfppy) IrCl] was
2
2
added. The reaction was brought to reflux and heated for 7 hr under a nitrogen
atmosphere. The reaction was cooled to room temperature and filtered through a
glass frit. The filtrate was taken to dryness on a rotovap and washed with three
portions of water and one portion of ice-cold methanol and dried under vacuum.
This yielded 1.12 g of orange-yellow product (89%). Anal. Calcd for IrC H N O F :
2
9
15
3 2 7
1
C, 45.67; H, 1.98; N, 5.51. Found: C, 45.08; H, 2.17; N, 5.29%. H NMR (600MHz,
CDCl ) (ppm): 8.71 (d, J = 5.6 Hz, 1H), 8.50 (d, J = 8.1 Hz, 1H), 8.32 (d, J = 8.6 Hz, 1H),
3
8
.28 (d, J = 8.5 Hz, 1H), 8.21 (d, J = 8.1 Hz, 1H), 8.01 (s, 1H), 7.82 (t, J = 7.9 Hz, 2H),
.41 (d, J = 5.6 Hz, 1H), 7.23 (t, J = 6.6 Hz, 1H), 7.04 (t, J = 6.6 Hz, 1H), 6.52 (t, J = 10.0
7
1
9
Hz, 1H), 6.43 (t, J = 10.1 Hz, 1H), 5.85 (d, J = 8.4 Hz, 1H), 5.53 (d, J = 8.5 Hz, 1H).
F
NMR (565 MHz, CDCl ) (ppm): -62.57 (s, 3H), -106.34 (q, J = 9.5 Hz, 1F), -107.53 (q,
3
J = 9.5 Hz, 1F), -109.20 (t, J = 11.5 Hz, 1F), -110.06 (t, J = 11.5 Hz, 1F).
(
F ppy) Ir(3,5-difluoropicolinate) (Compound 10). A 50 mL round-bottom flask
2 2
was charged with 0.87 g (8.2 mmol) sodium carbonate and 0.52 g (3.3 mmol) 3,5-
difluoropyridine-2-carboxylic acid in 25 ml 1,2-dimethoxyethane. The mixture was
purged with nitrogen and 1.00 g (0.82 mmol) [(dfppy) IrCl] was added. The
2
2
reaction was brought to reflux and heated for 10 hr under a nitrogen atmosphere.
The reaction was then chilled in an ice-water bath prior to filtration through a glass
frit. The solids were washed with three portions of water and three portions of
methanol and dried under vacuum. This yielded 0.98 g of yellow product (82%).
Anal. Calcd for IrC H N O F : C, 46.03; H, 1.93; N, 5.75. Found: C, 45.75; H, 1.93;
2
8
14
3 2 6
1
3
N, 5.37%. A previous report of this compound did not provide NMR spectra; we
provide ours herein. H NMR (600MHz, CDCl ) (ppm): 8.77 (d, J = 5.6 Hz, 1H), 8.34
1
3
(
(
(
d, J = 8.2 Hz, 1H), 8.30 (d, J = 8.2 Hz, 1H), 7.85 (t, J = 7.7 Hz, 2H), 7.57 (s, 1H), 7.50
m, 2H), 7.27 (t, J = 6.6 Hz, 1H), 7.08 (t, J = 6.6 Hz, 1H), 6.53 (t, J = 10.7 Hz, 1H), 6.44
t, J = 10.7 Hz, 1H), 5.83 (d, J = 8.5 Hz, 1H), 5.51 (d, J = 8.7 Hz, 1H). F NMR (565
1
9
MHz, CDCl ) (ppm): -106.39 (q, J = 9.4 Hz, 1F), -107.52 (q, J = 9.4 Hz, 1F), -108.19
3
(
1
dd, J = 12.9, 9.0 Hz, 1F), -109.12 (t, J = 11.5 Hz, 1F), -110.07 (t, J = 11.5 Hz, 1F), -
12.93 (dd, J = 13.0, 7.8 Hz, 1F).
Bis[2-(2,4-difluorophenyl)-4-(3,5-dimethylphenyl)pyridinato]iridium(III)
picolinate (Compound 11). A 100 mL round-bottom flask was charged with 1.68 g
(
5
15.9 mmol) sodium carbonate and 0.78 g (6.4 mmol) pyridine-2-carboxylic acid in
0 ml 1,2-dimethoxyethane. The mixture was purged with nitrogen and 2.60 g (1.59
mmol) bis{bis[2-(2,4-difluorophenyl)-4-(3,5-dimethylphenyl)pyridinato](-
chloro)iridium(III)} (compound C, above) was added. The reaction was brought to
reflux and heated for 9 hr under a nitrogen atmosphere. The reaction was then
chilled in an ice-water bath prior to filtration through a glass frit. The solids were
washed with three portions of water and one portion of ice-cold methanol. This
material was chromatographed on silica using dichloromethane/ethyl acetate as
eluent. Solvent was removed on a vacuum line to yield 2.6 g of yellow product
(
90%). Anal. Calcd for IrC H N O F : C, 58.53; H, 3.57; N, 4.65. Found: C, 58.87;
44 32 3 2 4
1
H, 3.30; N, 4.56%. H NMR (600MHz, CDCl ) (ppm): 8.76 (d, J = 6.2 Hz, 1H), 8.52 (s,
3
1
H), 8.46 (s, 1H), 8.39 (d, J = 7.9 Hz, 1H), 7.98 (t, J = 7.7 Hz, 1H), 7.86 (d, J = 5.3 Hz,
2
8

1
H), 7.47 (t, J = 6.5 Hz, 1H), 7.43 (d, J = 5.9 Hz, 1H), 7.39 (d, J = 6.0 Hz, 1H), 7.34 (s,
H), 7.32 (s, 2H), 7.18 (d, J = 6.1 Hz, 1H), 7.15 (s, 2H), 6.53 (t, J = 10.7 Hz, 1H), 6.45 (t,
2
1
9
J = 10.7 Hz, 1H), 5.97 (d, J = 8.6 Hz, 1H), 5.73 (d, J = 8.6 Hz, 1H), 2.45 (s, 12H).
F
NMR (565 MHz, CDCl ) (ppm): -107.42 (q, J = 9.3 Hz, 1F), -108.27 (q, J = 9.3 Hz, 1F), -
3
1
09.69 (t, J = 11.2 Hz, 1F), -110.24 (t, J = 11.3 Hz, 1F).
TD-DFT Calculations. The ground-state geometries (S ) of all the complexes were
0
7
4-76
optimized by means of Kohn-Sham density functional theory (KS-DFT)
M06-L functional with the triple-ζ basis set def2-TZVP
SDD basis set for Ir. No imaginary mode was found in the frequency calculations,
validating the local minimum nature of the optimized structures. To compute the
vertical excitation energies, time-dependent DFT (TD-DFT)
using the
7
7
78, 79
for the ligands and the
8
0
8
1-83
calculations were
carried out for the optimized S geometries using three different combinations of
0
8
4
exchange-correlation functional and basis set: 1) CAM-B3LYP functional with the
def2-TZVP basis set for the ligands and the SDD basis set for Ir; 2) CAM-B3LYP
functional with the def2-TZVP basis set for the ligands and the double-ζ basis set
8
5-87
88-90
LANL2DZ
for Ir; 3) B3LYP
functional with the def2-TZVP basis set for the
ligands and LANL2DZ for Ir. Six low-lying singlet and six low-lying triplet excited
states of the complexes were calculated using these three approaches and the
results are presented in the Supporting Information, along with experimental data.
6
9
Natural transition orbitals (NTOs) were calculated using the B3LYP functional
with the def2-TZVP basis set for the ligands and LANL2DZ for Ir. All the calculations
9
1
were performed with the Gaussian 09 (revision D.01) program.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge:
Synthetic procedures (compounds 3-5 and 8)
X-ray diffraction data and figures (compounds 3-5 and 7-11)
UV-Visible spectra (compounds 1-11)
TD-DFT calculations (vertical transition energies for compounds 1-11,
natural transition orbitals for 6-11, molecular orbital energy levels for 6-11,
and molecular orbital contour plots for 6-11).
1
9
1
F spectra (compounds 3-5, 7, 9-11, B, and C) and H NMR spectra
compounds 3-5, 9-11, and A-C)
(
Accession Codes
CCDC 1873880-1873887 contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
2
9