Highly luminescent tridentate NC*N platinum(II) complexes featured in fused five-six-membered metallacycle and diminishing concentration quenching

Article abstract of DOI:10.1021/ic200794b

A series of cyclometalating ligands, N-phenyl-N-(3-(pyridin-2-yl)phenyl) pyridin-2-amine (L1), N-(3-(1H-pyrazol-1-yl)phenyl)-N-phenylpyridin-2-amine (L2), N-phenyl-N-(3-(quinolin-2-yl)phenyl)pyridin-2-amine (L3), N-phenyl-N-(3-(pyridin-2-yl)phenyl)quinolin-2-amine (L4), N-(3-(isoquinolin-1- yl)phenyl)-N-phenylpyridin-2-amine (L5), and N-phenyl-N-(3-(pyridin-2-yl)phenyl) isoquinolin-1-amine (L6), were synthesized, which reacted with K ₂PtCl₄ in glacial acetic acid to produce NC*N-coordinated platinum(II) complexes featured in a fused five-six-membered metallacycle, 1-6, respectively. The structures of 1, 3, 4, and 6 were determined by single crystal X-ray crystallography. The square geometries of the complexes are improved when compared with those of the N^C^N-coordinated complexes as the bite angles for the platinum in N^C*N-coordinated complexes 1, 3, and 4 are increased. The Pt-C bonds (1.94-1.95 A) are shorter than those of C^N^N-coordinated platinum complexes but longer than those found for N^C^N-coordinated platinum complexes. With the increase of the steric interaction, the distortion of the molecules from a planar coordination geometry becomes more and more severe from 1 to 3 to 4 and 6, and in 6, the N-phenyl ring has to stand up on the coordination sphere to minimize the steric interaction with the N-isoquinolyl ring. The photophysical properties of the complexes were studied, and their absorption and emission spectra were interpreted by relating to the structural features revealed by the X-ray crystal structures and the orbital characters predicted by DFT calculations. All complexes are emissive in fluid at room temperature, and the quantum yields (up to 0.65) are comparable to those of highly emissive N^C^N-coordinated platinum complexes. Self-quenching was not observed in the concentration range of 10^-6 to 10^-4 M. Large rigidochromic shifts for the emissions of 2, 4, and 6 upon cooling from room temperature to rigid glass (77 K) were observed. Two different triplet states that control the emissions were proposed to account for the photophysical properties of 6.

Full text of DOI:10.1021/ic200794b

ARTICLE
pubs.acs.org/IC
Highly Luminescent Tridentate N∧C*N Platinum(II) Complexes
Featured in Fused FiveꢀSix-Membered Metallacycle and
Diminishing Concentration Quenching
Dileep A. K. Vezzu,† Deepak Ravindranathan,† Alexander W. Garner,† Libero Bartolotti,† Meredith E. Smith,†
Paul D. Boyle,‡ and Shouquan Huo*,†
†Department of Chemistry, East Carolina University, Greenville, North Carolina 27858, United States
‡Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695, United States
S Supporting Information
b
ABSTRACT: A series of cyclometalating ligands, N-phenyl-
N-(3-(pyridin-2-yl)phenyl)pyridin-2-amine (L1), N-(3-(1H-
pyrazol-1-yl)phenyl)-N-phenylpyridin-2-amine (L2), N-phenyl-
N-(3-(quinolin-2-yl)phenyl)pyridin-2-amine (L3), N-phenyl-
N-(3-(pyridin-2-yl)phenyl)quinolin-2-amine (L4), N-(3-(iso-
quinolin-1-yl)phenyl)-N-phenylpyridin-2-amine (L5), and
N-phenyl-N-(3-(pyridin-2-yl)phenyl)isoquinolin-1-amine (L6),
were synthesized, which reacted with K2PtCl4 in glacial acetic
acid to produce N∧C*N-coordinated platinum(II) complexes featured in a fused fiveꢀsix-membered metallacycle, 1ꢀ6, respectively.
The structures of 1, 3, 4, and 6 were determined by single crystal X-ray crystallography. The square geometries of the complexes are
improved when compared with those of the N∧C∧N-coordinated complexes as the bite angles for the platinum in N∧C*N-coordinated
complexes 1, 3, and 4 are increased. The PtꢀC bonds (1.94ꢀ1.95 Å) are shorter than those of C∧N∧N-coordinated platinum
complexes but longer than those found for N∧C∧N-coordinated platinum complexes. With the increase of the steric interaction, the
distortion of the molecules from a planar coordination geometry becomes more and more severe from 1 to 3 to 4 and 6, and in 6, the
N-phenyl ring has to stand up on the coordination sphere to minimize the steric interaction with the N-isoquinolyl ring.
The photophysical properties of the complexes were studied, and their absorption and emission spectra were interpreted by relating
to the structural features revealed by the X-ray crystal structures and the orbital characters predicted by DFT calculations. All complexes
are emissive in fluid at room temperature, and the quantum yields (up to 0.65) are comparable to those of highly emissive N∧C∧N-
coordinated platinum complexes. Self-quenching was not observed in the concentration range of 10ꢀ6 to 10ꢀ4 M. Large rigidochromic
shifts for the emissionsof 2, 4, and6uponcoolingfromroomtemperaturetorigidglass(77K) were observed. Twodifferent triplet states
that control the emissions were proposed to account for the photophysical properties of 6.
’ INTRODUCTION
room-temperature phosphorescence emitted from this com-
pound was not recognized until its photophysical properties
were studied by Williams et al.,6 and the use of this compound as
an efficient triplet dopant in OLED devices was reported by Huo
et al.7 in 2003. Since then, the research on this important class of
cyclometalated platinum complexes has been expanded signifi-
cantly by Williams’ and other research groups focusing on photo-
physical properties8 and application in OLED devices.9 More
recently, the use of N∧C∧N platinum complexes in noninvasive
imaging and mapping of living cells3b and as labeling agents was
also reported.3e
The square planar geometry of the platinum complexes
bearing a conjugated ligand usually displays interesting photo-
physical and photochemical properties resulted from the axial
PtꢀPt or πꢀπ interactions. Cross-quenching and self-quenching
(concentration quenching),6,8a,8b,10 which are often accompanied
The design and synthesis of luminescent cyclometalated
platinum complexes, particularly those that can emit intense
phosphorescent light at ambient temperatures in the visible
region, has been a major focus in the recent research of
coordination chemistry of platinum. The major driving force
can be attributed to a number of applications demonstrated by
those phosphorescent materials in the areas of OLEDs (organic
light emitting diode),1 chemical sensing,2 biological labeling
and imaging,3 and photocatalysis.4 Luminescent efficiency is
one of the key factors controlling the utility of the luminescent
materials. Among various types of phosphorescent cyclometa-
lated platinum complexes, those based on 1,3-dipyridylbenzene
and its analogues have attracted a great deal of attention in recent
years. This is due to very high phosphorescence efficiencies
exhibited by this class of complexes, described as tridentate
N∧C∧N-coordinated platinum complexes. The cyclometalated
platinum complex based on 1,3-dipyridylbenzene was first re-
ported by Cꢀardenas et al.5 in 1999. However, the highly efficient
Received: April 18, 2011
Published: August 02, 2011
r
2011 American Chemical Society
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by the formation of excimers or exciplexes or aggregation and the
switch of emissive excited states, have been frequently observed.
While both photophysically and photochemically interesting,
such behavior undermines some of the important applications
in which high efficiency and consistence of the emission from the
complex are required. For instance, the concentration depen-
dence of either the luminescent efficiency or the emission hue
from the emitter would be undesirable for its use as a triplet
dopant in an OLED device. Strategies such as introducing bulky
substituents have been employed to minimize the concentration
quenching.11
In our continued efforts to discover and develop highly
efficient phosphorescent materials, we have recently reported
tetradentate C∧N*N∧C and N∧C*C∧N-coordinated biscyclo-
metalated12 and tridentate C∧N*N-coordinated cyclometalated13
platinum complexes, where N∧C or C∧N and C*N or N*C denote
a five- and six-membered chelation with the platinum, respectively.
These complexes have a common feature of a fused fiveꢀ
six-membered metallacycle and have demonstrated very high
photoluminescence quantum yields. The use of the tetradentate
C∧N*N∧C platinum complex as a highly efficient triplet emitter in
OLED devices has also been demonstrated.12a As indicated by their
X-ray crystal structures, the introduction of the fused fiveꢀ
six-membered metallacycle14 can rectify the distorted square
geometry displayed by the tridentate cyclometalated platinum
complexes with a more strained fused fiveꢀfive-membered metal-
lacycle, such as the complexes based on the C∧N∧N10d,15 and
N∧C∧N6,8 types of cyclometalating ligands. The higher quantum
yield of C∧N*N platinum complexes compared to those of
C∧N∧N platinum complexes suggested that the rectified geometry
might be beneficial to the emission efficiency as the improved
square planar geometry may maximize the strength of the ligand
field and minimize the nonradiative metal-centered transitions.
Williams et al. recently reported a modification on the N∧C∧N-
coordinated platinum complexes by preparing the tridentate
cyclometalating ligand that coordinates to the platinum to form a
fused sixꢀsix-membered metallacycle (N*C*N)PtCl16 (Chart 1).
The geometry of the platinum complex optimized by DFT
calculations showed a more optimal bite angle at the metal (close
to 180°); however the complex exhibited a very low quantum yield
(ϕ = 0.016)16 compared to that of the N∧C∧N-coordinated com-
plex Pt(dpyb)Cl6 (ϕ = 0.60). The deleterious effect of this
geometric modification has not been well understood because of
the complexity of the factors that could influence the emission
efficiency. Nonetheless, this is an important attempt to improve the
photophysical properties through changing the coordination ring
size of N∧C∧N-coordinated platinum complexes. It is desirable to
apply our fiveꢀsix-membered metallacycle strategy to preparing
the N∧C*N-coordinated platinum complexes and to investigate
their photophysical properties (Chart 1). It can be anticipated
that the complexes should be readily engineered on A, B, and C
rings to tune their photophysical properties. Herein, we report a
series of new tridentate N∧C*N-coordinated platinum complexes.
The complexes were highly emissive either in fluid or in solid
states and showed diminishing concentration quenching typically
associated with square planar platinum complexes.
’ RESULTS AND DISCUSSION
Synthesis. The N∧C*N-coordinated platinum complexes
studied in this report are shown in Chart 2. The syntheses of
the ligands are shown in Scheme 1. The synthetic strategy
designed to prepare the N∧C*N ligands L1ꢀL6 exemplifies
an efficient combination of the CꢀN bond cross-coupling
(HartwigꢀBuchwald protocol),17 the Negishi coupling,18 and
the Suzuki coupling19 to introduce different A, B, and C rings. L1
and L4 were prepared similarly by two consecutive palladium
catalyzed aminations of an appropriate heteroaromatic halide
with an aniline and subsequent Negishi coupling with a 2-pyridyl
zinc reagent. The pyridyl zinc reagent used in the Negishi
couplings was generated in situ by the lithiumꢀbromine ex-
change of 2-bromopyridine with n-butyllithium followed by
treatment with zinc chloride. L3 and L5 could be prepared in a
similar way to the preparation of L1 by Negishi coupling of the
same intermediate N-(3-bromophenyl)-N-phenylpyridin-2-
amine with the corresponding 2-quinolyl and 1-isoquinolyl zinc
reagents, respectively; however, the preparation of the zinc
reagent may require the use of expensive Rieke’s highly reactive
zinc. Alternatively, L3 and L5 were prepared through a chemo-
selective Suzuki coupling of 3-chlorophenylboronic acid with
2-chloroquinoline and 1-chloroisoquinoline, respectively, fol-
lowed by two consecutive CꢀN bond formation reactions with
aniline and 2-bromopyridine, respectively. It should be men-
tioned that, in the second step of preparation of L3 and L5,
Chart 1. Structural Formulas of N∧C∧N, N*C*N, and Pro-
posed N∧C*N-Coordinated Platinum Complexes
Chart 2. Structural Formulas of N∧C*N-Coordinated Platinum Complexes 1ꢀ6
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Scheme 1. Synthesis of N∧C*N Cyclometalating Ligands L1ꢀL6a
a Reagents and conditions: (a) Pd(dba)2 (2%), DPPF (2%), NaOtBu (1.2 equiv), toluene, reflux. (b) Pd(PPh3)4 (5%), THF, 50 °C. (c) CuI (5%), trans-
N,N0-dimethylcyclohexanediamine (20%), K2CO3 (2.1 equiv), toluene, reflux. (d) Pd(OAc)2 (2%), PPh3 (8%), DME, 2 M K2CO3 (aq), reflux. (e)
Pd(dba)2 (2%), PtBu3 (4%), NaOtBu (1.2 equiv), toluene, reflux.
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Figure 1. ORTEP drawing of 1, 3, 4, and 6 showing the labeling scheme of the atoms. Ellipsoids are at the 50% probability level, and hydrogen atoms
were omitted in 1 for clarity or were drawn with arbitrary radii in 3, 4, and 6.
N-phenylpyridin-2-amine could be used instead of aniline to
shorten the synthesis to two steps; however, we found that the
reaction did not proceed under the conditions used. The ligand
L6 was prepared in a similar way to the preparation of L3 and L5.
The product yield for each step was generally high. Considering
the availability of a large number of aromatic and heteroaromatic
halides and amines that can be used in these reactions, the use
of a combination of straightforward CꢀN and CꢀC bond
couplings should allow rapid construction of a library of reason-
able size to optimize the photophysical and other properties of
the materials for a particular application.
Complexation of ligands L1ꢀL6 with K2PtCl4 proceeded
smoothly in boiling glacial acetic acid, giving the complexes
1ꢀ6, respectively, in good yields. The complexes were purified
readily by column chromatography and recrystallization.
Structural Characterization of the Complexes. All
ligands and complexes are adequately characterized by proton
and carbon-13 NMR spectroscopy, mass spectrometry, and
elemental analysis. To elucidate the structure of the proposed
N∧C*N-coordinated platinum complexes, the single crystal
structures of compounds 1, 3, 4, and 6 were determined by
X-ray diffraction studies. The crystal data and structure refine-
ment details for 1, 3, 4, and 6 are provided in Table S1 (see the
Supporting Information). The structures of 1, 3, 4, and 6 are
shown in Figure 1, and selected bond lengths and angles are listed
in Table 1.
There are two independent molecules in the unit cell of
complex 1. They have very similar geometry with one being
slightly more coplanar around the platinum coordination sphere
than the other. The largest deviations from the coordination
plane that are made up of all atoms except for the unmetalated
N-phenyl ring is 0.38 Å and 0.33 Å by the chlorine in molecule A
and by the amino nitrogen in molecule B, respectively. The
N-phenyl ring is nearly perpendicular to the coordination plane
with dihedral angles of 89.1° and 86.9° for the molecules A and B,
respectively. In complex 3, the presence of the 2-quinolyl group
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Table 1. Selected Bond Lengths (Å) and Angles (deg) for 1, 3, 4, and 6
complex 1
complex 3
complex 4
compound 6
Pt(1)ꢀC(7A)
Pt(1)ꢀN(1A)
Pt(1)ꢀN(3)
Pt(1)ꢀCl(1A)
1.949(3)
2.031(2)
2.023(2)
Pt(1)ꢀC(11)
Pt(1)ꢀN(1)
Pt(1)ꢀN(3)
1.9526(17) Pt(1)ꢀC(11)
2.0296(15) Pt(1)ꢀN(1)
2.0544(15) Pt(1)ꢀN(3)
1.9407(19) Pt(1)ꢀC(11)
1.9447(12)
2.0261(11)
2.0316(11)
2.4180(3)
1.4116(16)
1.4420(16)
1.4160(17)
80.79(5)
2.0223(17) Pt(1)ꢀN(1)
2.0257(16) Pt(1)ꢀN(3)
2.4395(7) Pt(1)ꢀCl(1)
2.4346(5)
1.389(2)
1.428(2)
1.445(2)
91.47(7)
81.76(6)
170.04(7)
Pt(1)ꢀCl(1)
N(2)ꢀC(12)
N(2)ꢀC(10)
N(2)ꢀC(21)
2.4211(5)
1.375(3)
1.440(3)
1.453(2)
81.68(8)
89.79(7)
169.70(6)
Pt(1)ꢀCl(1)
N(2A)ꢀC(5A)
1.383(4)
1.419(3)
1.448(4)
92.10(10)
81.61(10)
N(2)ꢀC(5)
N(2)ꢀC(6)
N(2)ꢀC(21)
C(11)ꢀPt(1)ꢀN(1)
C(11)ꢀPt(1)ꢀN(3)
N(1)ꢀPt(1)ꢀN(3)
C(11)ꢀPt(1)ꢀCl(1) 164.07(6)
N(1)ꢀPt(1)ꢀCl(1)
N(3)ꢀPt(1)ꢀCl(1)
N(2)ꢀC(12)
N(2A)ꢀC(6A)
N(2)ꢀC(10)
N(2)ꢀC(21)
N(2A)ꢀC(17A)
C(7A)ꢀPt(1)ꢀN(1A)
C(7A)ꢀPt(1)ꢀN(3A)
C(11)ꢀPt(1)ꢀN(1)
C(11)ꢀPt(1)ꢀN(3)
N(1)ꢀPt(1)ꢀN(3)
C(11)ꢀPt(1)ꢀN(1)
C(11)ꢀPt(1)ꢀN(3)
N(1)ꢀPt(1)ꢀN(3)
89.74(5)
N(1A)ꢀPt(1)ꢀN(3A) 172.93(8)
C(7A)ꢀPt(1)ꢀCl(1A) 171.25(8)
163.87(5)
C(11)ꢀPt(1)ꢀCl(1) 169.67(6)
C(11)ꢀPt(1)ꢀCl(1) 174.56(4)
N(1A)ꢀPt(1)ꢀCl(1A)
N(3A)ꢀPt(1)ꢀCl(1A)
95.32(6)
91.22(7)
92.82(5)
95.67(5)
N(1)ꢀPt(1)ꢀCl(1)
N(3)ꢀPt(1)ꢀCl(1)
94.19(5)
95.16(5)
N(1)ꢀPt(1)ꢀCl(1)
N(3)ꢀPt(1)ꢀCl(1)
95.90(3)
94.44(3)
causes significant distortion of the planar coordination geometry,
mainly by the steric repulsion between the chlorine and the 8-H
of the quinoline moiety. As a result, although the fused fiveꢀsix-
membered metallacycle (Pt(1)N(1)C(5)N(2)C(6)C(11)C-
(10)C(12)N(3)) maintains nearly planar geometry, the PtꢀCl
bond bends significantly away from the plane with a distance of
0.95 Å between the chlorine and the plane, while the quinolyl
ring is twisted from the plane toward the other direction to
minimize the steric interaction with the chlorine. The dihedral
angle between the plane and the uncyclometalated N-phenyl ring
is 85.4°.
In complex 4, where the N-(2-pyridyl) group in 1 is replaced
with the 2-quinolyl group, a further distortion in planar geometry
of the fiveꢀsix-membered metallacycle was observed. The
platinum-centered coordination maintains an approximate pla-
nar geometry only with four donor atoms and the phenylpyridine
moiety, with the carbon donor and the chlorine deviating from
the plane by 0.41 and 0.24 Å, respectively. The amino nitrogen in
the six-membered metallacycle has a distance of 0.56 Å from the
plane. The N-quinolyl ring is remarkably twisted relative to the
plane with a dihedral angle of 42.1°. The dihedral angle between
the N-phenyl ring and the coordination plane is 84.5°.
When the N-quinoline in 4 is replaced with a 1-isoquinolyl
group, more distortion was observed in 6. The platinum forms a
coplanar geometry only with the phenylpyridine moiety and the
chlorine. The nitrogen donor from the isoquinoline has a
distance of 0.83 Å, while the amino nitrogen has a distance of
0.31 Å to the coordination plane. The dihedral angle between the
isoquinolyl ring and the coordination plane is 47.87°. Compared
with 4, a drastic geometry change to molecule 6 occurs with the
N-phenyl ring. The N-phenyl group, squeezed by the isoquinolyl
group, stands nearly straight up from the coordination sphere. In
complexes 1, 3, and 4, the amino nitrogen N(2) adopts a trigonal
planar geometry, and the sum of the three angles around the
nitrogen is 360°. The deviations of the nitrogen from the trigonal
plane composed of the three carbons are negligible (0.02ꢀ
0.04 Å). However, the nitrogen in 6 leans slightly to a trigonal
pyramidal geometry with the nitrogen being 0.195 Å from the
carbon trigonal plane.
platinum complexes13,15 (about 1.98 Å) but longer than those
of N∧C∧N-coordinated platinum complexes6,8 (about 1.90 Å).
Second, in 1, 3, and 4, the amino nitrogen forms the strongest
bond with the carbon of the N-heteroaromatic ring and the
weakest bond with the carbon of the N-phenyl ring. This may be
attributed to the strong donorꢀacceptor conjugation between
the nitrogen lone pair and the electron-deficient heteroaromatic
ring. The conjugation between the nitrogen and the N-phenyl
ring is disrupted because of the orthogonal relationship between
the lone pair (p orbital) and the π orbitals of the phenyl ring. In 6,
the amino nitrogen forms stronger bonds with both the carbon
(C12) of the N-heteroaromatic ring and the carbon (C21) of the
N-phenyl ring because of the geometry change to the amine
nitrogen and N-phenyl ring. Considering the trigonal plane of the
three carbons attached to the nitrogen, the N-phenyl ring has a
much smaller dihedral angle of 21.93 Å compared to those
(67ꢀ68°) formed by the isoquinolyl and the pyridylphenyl rings
with the trigonal plane, indicating a better conjugation between
the nitrogen and the N-phenyl ring. Finally, compared to the
N∧C∧N-coordinated platinum complexes where the NꢀPtꢀN
bond angles are typically in the range of 160ꢀ161°, the square
geometry was improved to some extent in complexes 1, 3, 4, and
6, but 3, 4, and 6 are significantly deviated from the ideal planar
geometry.
A weak πꢀπ stacking was observed in the crystal packing of 1,
3, and 6, but not 4. The distances for the πꢀπ contact are
3.596, 3.571, and 3.537 Å for 1, 3, and 6, respectively, as shown in
Figure S1 (see the Supporting Information). There is no PtꢀPt
interaction detected in the crystal packing.
DFT Calculations. Density functional theory (DFT) calcula-
tions were performed on compounds 1ꢀ6 to examine the
molecular orbital character of the complexes. The optimized
ground state geometries of 1, 3, 4, and 6 compare satisfactorily to
those determined by the X-ray crystallography. The selected
molecular orbital energies and the contribution of platinum to
the MOs are provided in Table S2 (see the Supporting In-
formation), and the Cartesian coordinates for optimized geome-
tries of 1ꢀ6 are listed in Table S3 (see the Supporting
Information). The orbital density for the HOMOs and LUMOs
is depicted in Figure 2. The HOMOs of all six complexes
are localized mainly on the platinum metal (27ꢀ38%) with
significant contribution from the amine nitrogen. The rest of
the HOMO is spread over the cyclometalated benzene ring.
From the selected bond lengths and angles in Table 1, several
points can be noted. First, the PtꢀC bond lengths in three
complexes are very similar (1.94ꢀ1.95 Å) and are shorter than
those reported for the C∧N∧N- or C∧N*N-coordinated
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Figure 2. Calculated orbital density for the LUMOs (top) and HOMOs (bottom) of 1ꢀ6.
Table 2. Photophysical Data for Complexes 1ꢀ6
298 Ka
77 Kb
λem/nm
λabs/nm (ε ꢁ 10ꢀ3 Mꢀ1 cmꢀ1
)
λem/nm
ϕc
τ/μsd
kre
knr
τ/μs solid state λem/nm (τ/μs)f
a
e
1
2
3
4
5
6
315 (15.4), 351(9.93), 420 (2.50), 435 (2.32)
275 (29.0), 342 (3.79), 379 (4.87),396 (4.80)
275 (18.3), 323 (7.28), 367 (7.65), 382 (8.49), 461(0.67)
298(22.3), 343(15.1), 439 (3.13), 454 (3.11)
278 (32.6),317 (17.2),370 (15.2),384 (17.2), 469 (1.76)
356 (9.91)
506
467
595
569
609
597
0.65
8.2
0.5
4.6
1.6
2.0
3.0
79.3 42.7
493, 531
13.3
16.2
13.9
12.2
10.2
42
540 (7.1)
0.038
0.39
76 1924 432, 458
466 (8.9), 526 (9.8)
609 (8.2)
84.8 133
81.3 544
570, 613
525
0.13
546 (8.2), 612 (10.4)
640 (9.8), 670 (9.4)
531 (12.9), 570(11.7)
0.028
14
486
594, 644
492, 529
0.019
6.3 325
a Measurements were carried out in a solution of dichloromethane. b Measurements were carried out in a solution of 2-methyltetrahydrofuran.
c Quantum yields were measured in deoxygenated dichloromethane. For 1 and 2, a deoxygenated solution of Pt(dpyb)Cl in dichloromethane (ϕ = 0.6)
was used as the reference; for 3, 4, and 5, a solution of Ru(bpy)3Cl2 in water (ϕ = 0.028) as the reference; for 6, a solution of quinine sulfate in
0.1 N H2SO4 (ϕ = 0.55) as the reference. d Measured in deoxygenated dichloromethane. e kr and knr are the radiative and nonradiative decay rate constant
estimated from the quantum yield and lifetime and were reported as 103 sꢀ1 f Solid state studies were measured with pure powder samples at 298 K.
The LUMOs of 1, 3, and 5 are mainly localized on the
cyclometalated phenylpyridine, phenylquinoline, and phenyliso-
quinoline ring, respectively, being more concentrated in the
nitrogen-containing ring in 3 and 5. The LUMOs of 2 and 4
are markedly different from those of 1 and 3. The LUMO of 2 is
more concentrated in the N-pyridyl ring than the pyrazolyl ring,
while the LUMO of 4 is more spread over both the N-quinolyl
and the pyridyl rings. This indicated that the phenylpyridine
and quinoline have similar electron-accepting abilities while the
pyrazole is a poorer acceptor, as expected.8b,12 The contribution
from the cyclometalated benzene ring is less significant. The
LUMO of 6 is completely localized in the isoquinolyl ring.
Photophysical Properties. The photophysical data obtained
for all complexes are listed in Table 2, which include absorptions,
emissions at room temperature and 77 K, solid state emissions at
room temperature, lifetimes of the excited states, quantum yields
at room temperature, and radiative and nonradiative decay rate
constants. The absorption, fluorescence, and phosphorescence emis-
sion spectra of ligands L1ꢀL6 are provided in Figures S2ꢀS4 (see
the Supporting Information). The emission spectra in the solid state
are shown in Figure S5 (see the Supporting Information).
Absorption. The absorption spectra of structurally related
complexes 1, 2, 3, and 5 are shown in Figure 3. These complexes
differ only in the A ring, namely, pyridyl, pyrazolyl, quinolyl, and
isoquinolyl in 1, 2, 3, and 5, respectively. The assignment of the
absorption spectrum of 1 can be made by analogy with other
cyclometalated platinum complexes. High energy bands with a
larger molar absorption coefficient (over 10 000 Mꢀ1 cmꢀ1) can
1
be assigned as ligand-based πꢀπ* transitions, while the low
energy, weaker absorptions in the range of 380ꢀ460 nm that
were not present in the absorption spectrum of the correspond-
ing ligand can be assigned as charge transfer bands. The lowest
charge transfer bands may be assigned as mixed MLCT/LLCT/
ILCT transitions based on the HOMO and LUMO characters of
the complexes. When the A ring is changed from pyridyl in 1 to
the pyrazolyl ring in 2, both the 1πꢀπ* and the charge transfer
absorptions of 2 are shifted to higher energy. On the other hand,
when the conjugations are extended as the result of introducing
the quinolyl and the isoquinolyl rings in 3 and 5, respectively, the
absorptions are shifted to longer wavelengths, as expected. The lower
energy 1πꢀπ* and the charge transfer absorptions of 5 are slightly
red-shifted compared to those of 3. The solvent effect was found to
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to increase electron density on the platinum and raise the
HOMO energy, while electron-donating to the isoquinolyl ring
would destabilize the LUMO.
Emission. All complexes are emissive in fluid at ambient
temperature and the emission spectra of 1ꢀ6 at 298 K are shown
in Figure 5. Lifetimes of the emissions are in the microsecond
regime, indicating that they are phosphorescent emissions.
Complex 1 emitted strongly green light in dichloromethane
with a quantum yield of 0.65, which is comparable to that of
N∧C∧N-coordinated complex Pt(dpyb)Cl (ϕ 0.60),6 one of the
brightest phosphorescent emitters based on the cyclometalated
platinum complexes. The lifetime (8.2 μs) is close to that of
emission from Pt(dpyb)Cl (7.2 μs);6 therefore, they displayed
similar radiative and nonradiative decay rate constants and
likely have similar emissive states, namely, ligand-centered triplet
excited state. There are two main differences in emission
property between 1 and Pt(dpyb)Cl. One is the band shape of
the emission, and the other is the concentration quenching. The
emission spectrum of 1 is less structured with an increased
vibrational band resulting from the 1 to 0 transition, which is
probably due to the less rigid geometry compared with Pt-
(dpyb)Cl. The other difference is in self-quenching caused by
excimer formation. A concentration series in the range of 10ꢀ6 to
10ꢀ4 M was studied for 1 by monitoring the lifetime of the
emission. The results showed that the lifetime remained un-
changed with the concentration, indicating the absence of the
self-quenching caused by either excimer formation or ground
state molecular aggregation observed in N∧C∧N-coordinated
platinum complexes.6,8b This can be explained by the geometric
feature of the N∧C*N-coordinated platinum complexes in which
the N-phenyl ring adopts a perpendicular orientation relative to
the coordination sphere, and the cyclometalating ligand is
twisted from an ideal planar geometry, which prohibited an
intermolecular πꢀπ or nꢀπ interaction in solution, although
the weak πꢀπ stacking was observed in the solid state.
Figure 3. Absorption spectra of 1, 2, 3, and 5 recorded in CH2Cl2 at
298 K.
Figure 4. Absorption spectra of 1, 4, and 6 in CH2Cl2 at 298 K.
be moderate on the lowest absorption bands with a 10ꢀ20 nm
hypsochromic shift as the solvent was changed from toluene to
acetonitrile (Tables S4, S5, S6, and S8, Supporting Information).
The absorption spectra of 1, 4, and 6 are shown in Figure 4 for
comparison. The low-energy 1πꢀπ* transitions in 1, 4, and 6 are
very similar to each other in both the energy and the band shape,
suggesting that these transitions originate from the cyclometa-
lated phenylpyridine ring, which is the common feature shared by
the three complexes. Compared to the lowest charge transfer
bands of 1, those of 4 are shifted to lower energy, while those of 6
seem to be shifted to slightly higher energy. Given the fact that
the absorption spectra of 3, 4, and 5 are shifted to lower energy
relative to those of 1 because of extended conjugation, the blue-
shift of the lowest-energy absorptions of 6 was noteworthy. As
discussed earlier in regard to the X-ray structure of 6, the electron
delocalization through participation of the amine nitrogen is
disrupted due to geometric distortion; therefore, the band gap
is increased. The relative energy level of lowest absorptions of
1ꢀ6 correlates very well with the calculated band gaps of the
compounds (Table S2, Supporting Information). The DFT
calculations also predicted a more stabilized HOMO for 6
when compared to the other compounds and a lower LUMO
than that of 4, which is consistent with the absence of electron
donation from the amine nitrogen to the isoquinolyl and the
pyridylphenyl rings through the conjugation. Since the HOMO
is localized on the platinum, amine nitrogen, and the phenyl ring
of the phenylpyridine moiety and the LUMO is localized on the
isoquinolyl ring, an electron-donating effect would be expected
Compounds 3 and 5 emit orange and red light as the result of
extended conjugation, with quantum yields of 0.39 and 0.028,
respectively. The fast radiative decay and the symmetrical broad
emission band observed for 3 suggested that the emissive states
might be more in MLCT character compared with those of 5 that
displayed a structured emission spectrum. The decreasing quan-
tum yield in the order of 1, 3, and 5 seems to follow the energy
gap law;20 however, the much higher quantum yield of 3 compared
with that of 5 is quite remarkable considering a very small energy
difference (0.048 eV) between the emissions of 3 and 5. Taking a
further look at the radiative decay constants, it is clear that the lower
quantum yield of 5 is also due to the slower radiative decay of the
excited state, which is likely attributed to the less MLCT mixing.
Compound 2 emits blue light and displayed a structureless
spectrum. The quantum yield was low. The estimated lifetime
was 0.5 μs. An analysis of decay rate constants suggested that the
excited state has fast radiative rate constant close to that of
complex 1 but much faster nonradiative decay. The faster
nonradiative decay may be attributed to the MC states that
become closer to the emissive states as the energy of the emission
increased compared to that of 1.
Compound 4 emitted bright yellow light and displayed a
smooth and symmetrical broad band. The excited state of this
compound has a fast radiative decay, indicating significant
MLCT character in the emissive state. The emission spectrum
of 6 displayed an interesting feature with a high-energy low
intensity emission that is apparently different from the major
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low-energy broad emission band. Observations from several
experiments do not support the formation of an excimer or
ground state aggregates. First, no concentration quenching was
observed for the emission of this complex within a concentration
range of 10ꢀ6 to 10ꢀ4 M. Second, the band shape of the
absorption spectra of the complex remained the same. Finally,
the emission spectrum, particularly the relative intensity of high-
energy and low-energy emission, did not change with the
concentration. The interaction with the solvent can also be
excluded because the low-energy emission is independent of
the solvents. It is likely that the emissions are attributed to two
different excited states. The fact that the normalized excitation
spectra monitored at both emissions were found to be identical
(Figure S6, Supporting Information) also favors this dual-
emission assignment. Since the high-energy emission appears
coincidently with the emission of 1, considering the common
feature of 1 and 6, the emission could be assigned to the state
localized on the cyclometalated phenylpyridine moiety. The low-
energy emission could be assigned to a lower (the lowest) triplet
state that must experience significant geometrical change to
maximize the conjugation of the fiveꢀsix-membered metalla-
cycle through the amine nitrogen, which is disrupted in the
ground state as revealed by both X-ray structure and DFT
optimization. Another possibility is that there might be a con-
formational isomerization21 in solution, the major isomer being
the one with maximized conjugation similar to the geometry of 4,
the minor one being similar to the crystal structure of 6 where
the N-phenyl ring stands straight up on the platinum coordina-
tion sphere. However, this argument is not supported by the
blue-shifted absorption spectrum of 6 and the proton NMR
spectrum that only displays one set of proton signals in deuter-
ated dichloromethane.
Figure 5. Emission spectra of 1ꢀ6 in CH2Cl2 at 298 K.
It should be mentioned that in no case of the N∧C*N-
coordinated platinum complexes investigated here was a con-
centration quenching (self-quenching) of emission observed in
solution with the concentration range of 10ꢀ6 to 10ꢀ4 M, since
the lifetimes remained constant (Table S10, Supporting Informa-
tion) and the relative emission intensity showed an approxi-
mately linear relationship with the concentration (Figures
S7ꢀS12, Supporting Information). At higher concentrations,
the self-quenching may exist, particularly in the solution of 1 and
3, as the lifetimes became shorter (Table S10, Supporting
Information), which is probably due to the molecular aggrega-
tion as revealed by the X-ray crystallographic studies discussed
above, but the change is much less significant than that observed
for the N∧C∧N-coordinated complex Pt(dpyb)Cl (Table S10,
Supporting Information). In addition to possible self-quenching,
the significant deviation of the emission intensity at higher
concentrations from the linear dependence in the concentration
range of 10ꢀ6 to 10ꢀ4 M (Figures S7ꢀS12, Supporting Infor-
mation) may also be attributed to the instrumental limitation of
power output in the excitation of concentrated sample solutions.
The absence of concentration quenching can be advantageous in
terms of certain applications such as OLEDs, where the phos-
phorescent emitters are usually doped into the host at a relatively
high concentration.
Figure 6. Emission spectra of 1ꢀ6 at 77 K in a 2-MeTHF glass.
(S = I1ꢀ0/I0ꢀ0 = 0.5ꢀ0.6) are similar to those observed for
C∧N*N-coordinated complexes reported recently.13 Complex 4
displayed a less structured emission with a shoulder, and the
HuangꢀRhys ratio seems to be higher, indicating a more
geometric displacement in the excited state. All emissions
showed a hypsochromic shift compared with those in fluid, but
the rigidochromic effect varied substantially. The hypsochromic
shifts for 1ꢀ5 are calculated to be 521, 1734, 737, 1473, and
414 cmꢀ1, respectively. A large rigidochromic effect has been
related to the CT transitions, which typically results in the reverse
of the dipole moment in the excited states.22 It is noteworthy that
1, 3, and 5 showed the least rigidochromic effect, while 2 and 4
showed larger rigidochromic shifts.
Complex 6 showed an unusually large hypsochromic shift with
a 105 nm (3574 cmꢀ1) difference between the major emissions
in the fluid and the rigid matrix. The highly structured spectrum
in the rigid glass was almost superimposable with that of 1, which
suggests that the emission of 6 might be from a localized state in
the cyclometalated phenylpyridine moiety as discussed earlier.
The lifetime of the emission in frozen glass is 42 μs, which is
significantly longer than that of the emission of 1 (13.3 μs) and
suggests more predominance of a LC state. The low-energy
emission observed in fluid for 6 seemed to disappear completely,
likely because the significant geometric change to form the low-
energy state could not be achieved in the rigid matrix. The large
rigidochromic shift of 2 can be explained similarly. The emission
(432, 458 nm) in rigid glass can be attributed to the triplet state
localized on the cyclometalated phenylpyrazole moiety because it
The emission spectra of 1ꢀ6 at 77 K are shown in Figure 6.
The highly structured spectra indicate a predominant ligand-
centered transition. The vibrational progression was calcu-
lated to be 1451, 1314, 1230, 1307, and 1422 for 1ꢀ3, 5, and
6, respectively. The HuangꢀRhys ratios estimated from the
peak intensities of the vibrational bands for 1ꢀ3, 5, and 6
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is very similar in both shape and energy to the emission (430,
460 nm) from the pyrazole-derived N∧C∧N-coordinated plati-
num complex reported by Williams et al.8b In fluid, the emission
can be attributed to a primarily MLCT state. The emission of 4 in
rigid glass can be assigned as a mixed LC and MLCT in character,
most likely because the energies of the LC (localized on the
cyclometalated phenylpyridine) and the MLCT states are closer
to each other when compared to those of complex 2 or 6. To
generalize, there may be two different triplet states controlling
the emissions of 2, 4, and 6 in fluid and a rigid matrix, the lower
state being a charge transfer state and the higher state being a LC
state localized on the cyclometalated phenylpyridine or phenyl-
pyrazole ring. When the two states are well separated in energy
(complex 6), the emissions from both states appeared simulta-
neously in fluid, but only the emission from the localized LC state
can be observed in rigid glass, since the geometric change to
maximize conjugation particularly involving the amine nitrogen
could not be achieved in rigid glass. When the two states are
separated reasonably in energy (complex 2), the emissions from
both states are mixed in fluid or rigid glass but with more MLCT
character in fluid and more LC character in rigid glass. When the
two states are close in energy (complex 4), the emissions in fluid
and rigid glass are more similar and can be assigned as a mixed LC
and CT state. The trends shown by the rigidochromic shifts
(3574, 1734, and 1473 cmꢀ1 for 6, 2, and 4, respectively) and
the lifetimes (42, 16.2, and 12.2 μs for 6, 2, and 4, respectively) of
the emissions in the frozen glass also support these assignments.
(3.16 g, 20 mmol), sodium tert-butoxide (2.31 g, 24 mmol), Pd(dba)2
(0.46 g, 0.8 mmol), DPPF (1,10-bis(diphenylphosphino)ferrocene,
0.44 g, 0.8 mmol), aniline (2.73 mL, 30 mmol), and anhydrous toluene
(75 mL). The mixture was refluxed for 24 h. After cooling to room
temperature, 50 mL of ethyl acetate was added, and the mixture was
stirred for a while. The precipitate formed was filtered, and the filtrate
was evaporated. The crude mixture was purified by chromatography
on silica gel with pure dichloromethane first to remove excess aniline
and then a mixture of dichloromethane and ethyl acetate (v/v = 10:1)
and recrystallization from hexane and dichloromethane to provide white
crystals, 2.16 g, yield 89%.
Preparation of N-(3-bromophenyl)-N-phenylpyridin-2-
amine. This compound was prepared from N-phenylpyridin-2-amine
and 1,3-dibromobenzene following general procedure A described
above and purified by chromatography on silica gel with a mixture of
dichloromethane and ethyl acetate (v/v = 10:1) to give white powder,
1.16 g, 45%. 1H NMR (300 MHz, CDCl3): δ 8.25 (dd, J = 8.5 Hz, 2 Hz,
1H), 7.49ꢀ7.43 (m, 1H), 7.36ꢀ7.29 (m, 3H), 7.22ꢀ7.06 (m, 6H),
6.823 (t, J = 10 Hz, 1H), 6.75 (d, J = 9.5 Hz, 1H). 13C NMR (75 MHz,
CDCl3): δ 158.63, 148.38, 147.52, 145.58, 137.48, 130.33, 129.64,
128.41, 126.98, 126.63, 125.19, 124.11, 122.67, 116.85, 114.33.
MS, m/z calcd for C17H13N2Br: 325.04 (M + H+). Found: 325.05
(M + H+).
Preparation of Ligand L1. To a 50 mL, three-necked dry, argon-
flushed flask were charged pyridylzinc bromide (0.6 M in THF, 12 mL,
5 mmol), N-(3-bromophenyl)-N-phenylpyridin-2-amine (1.14 g, 3.5 mmol),
Pd(PPh3)4 (203 mg, 0.17 mmol), and 5 mL of THF. The reaction mixture
was refluxed for 6 h. After cooling to room temperature, the reaction mixture
was quenched by water and extracted with ethyl acetate. The combined
organic phases were washed with water and brine, dried over MgSO4, filtered,
and evaporated. The crude product was purified by chromatography on silica
gel with a mixture of dichloromethane and ethyl acetate (v/v = 5:1) to give a
white solid, 1.0 g, yield 88%. 1H NMR (500 MHz, CDCl3): δ 8.64 (d, J =
5Hz, 1H),8.24(d,J=5Hz, 1H),7.83(s, 1H),7.76(d,J= 8 Hz, 1H), 7.70 (t,
J = 8 Hz, 1H), 7.63 (d, J = 7 Hz, 1H), 7.46ꢀ7.40 (m, 2H), 7.32 (t, J = 8 Hz,
2H), 7.23ꢀ7.18 (m, 4H), 7.13 (t, J = 7 Hz, 1H), 6.80ꢀ6.77 (m, 2H). 13C
NMR (75 MHz, CDCl3): δ 158.97, 156.96, 149.52, 148.25, 146.57, 145.94,
140.74, 137.36, 136.72, 129.78, 129.39, 126.91, 126.28, 124.81, 124.57,
123.21, 122.18, 120.70, 116.21, 113.95. MS, m/z calcd for C22H17N3 (M +
H+): 324.1. Found: 324.1. Anal. Calcd for C22H17N3: C, 81.71; H, 5.30; N,
12.99. Found: C, 81.49; H, 5.23; N, 12.78.
’ CONCLUSIONS
A series of N∧C*N-coordinated cyclometalated platinum
complexes have been synthesized. The syntheses of the cyclo-
metalating ligands were achieved effectively through a combina-
tion of powerful palladium catalyzed CꢀN and CꢀC bond
formation based on the HartwigꢀBuchwald protocol and the
Negishi or the Suzuki reaction. The structural characteristics of
the ligands allow easy tuning of emission properties. Therefore,
by engineering the different parts, namely the A, B, or C ring in
the ligand molecule, emissions from blue to red have been
achieved. The structural variations on the N∧C*N-coordinated
platinum complexes lead to interesting photophysical properties.
The photoluminescence quantum efficiencies of the new com-
plexes are comparable to those of highly emissive N∧C∧N-
coordinated platinum complexes,8e which renders them as bright
phosphorescent materials for various applications in the future.
Preparation of Complex 1. General Procedure B. To a 100 mL
dry, argon-flushed flask were charged ligand L1 (323 mg, 1 mmol),
K2PtCl4 (415.5 mg, 1 mmol), and glacial acetic acid (50 mL). The
mixture was degassed and refluxed under argon for 18 h. After cooling to
room temperature, the precipitates were collected by filtration and
washed with methanol and dried in the air. The crude material was
purified through flash chromatography on silica gel with a mixture of
dichloromethane and methanol (v/v = 10:1). The compound was further
recrystallized from dichloromethane and methanol to give a yellow solid,
387 mg, yield 70%. 1H NMR (500 MHz, CDCl3): δ 10.28 (dd, J = 7 Hz, 2
Hz, 3JPtꢀH =25 Hz, 1H), 9.95 (dd, J = 6 Hz, 1 Hz, 3JPtꢀH =25.5 Hz, 1H),
7.86 (td, J = 8 Hz, 1.5 Hz, 1H), 7.74ꢀ7.67 (m, 3H), 7.61ꢀ7.58 (m, 1H),
7.49ꢀ7.46 (m, 1H), 7.34ꢀ7.32 (m, 2H), 7.29 (d, J = 8 Hz, 1H),
7.25ꢀ7.22 (m, 1H), 6.98 (t, J = 8 Hz, 1H), 6.65 (td, J = 7 Hz, 1.5 Hz,
1H), 6.42 (d, J = 9.5 Hz, 1H), 6.19 (d, J = 9 Hz, 1H). 13C NMR (75 MHz,
CDCl3): δ 166.76, 153.65, 152.54, 150.03, 145.46, 142.87, 139.10, 138.39,
136.69, 131.89, 130.86, 129.55, 124.26, 122.79, 120.21, 119.29, 119.06,
116.63, 114.93. MS, m/z calcd for C22H16N3PtCl (M ꢀ Clꢀ): 517.1.
’ EXPERIMENTAL SECTION
Synthesis. All reactions involving moisture- or oxygen-sensitive
organometallic complexes were carried out under a nitrogen atmosphere
and anhydrous conditions. Tetrahydrofuran (THF) and 2-methyltetra-
hydrofuran were distilled from sodium and benzophenone under
nitrogen before use. All other anhydrous solvents were purchased from
Aldrich Chemical Co. and were used as received. All other reagents were
purchased from chemical companies and were used as received. Mass
spectra were measured on a Waters spectrometer. NMR spectra were
measured on a Mercury VX 300 or a Varian 500 spectrometer. Spectra
were taken in CDCl3 or CD2Cl2 using tetramethylsilane as a standard for
1H NMR chemical shifts and the solvent peak (CDCl3, 77.0 ppm; CD2-
Cl2, 53.8 ppm) as a standard for 13C NMR chemical shifts. Elemental
analyses were performed at Atlantic Microlab, Inc. Norcross, Georgia.
Preparation of N-Phenylpyridin-2-amine.23 General Proce-
dure A. To a 250 mL dry, argon-flushed flask were charged 2-bromopyridine
Found: 517.1. Anal. Calcd for C22H16N3PtCl 0.25CH2Cl2: C, 46.55; H,
3
2.90; N, 7.32. Found: C, 46.44; H, 2.75; N, 7.39.
Preparation of Ligand L2. To a 50 mL dry, argon-flushed flask
were charged N-(3-bromophenyl)-N-phenylpyridin-2-amine (789 mg,
2.4 mmol), pyrazole (248 mg, 3.6 mmol), potassium carbonate (705 mg,
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5.1 mmol), copper iodide (48 mg, 0.25 mmol), trans-N,N0-dimethylcy-
clohexanediamine (95 μL, 0.6 mmol), and toluene (10 mL). The
mixture was refluxed for 5 days. After cooling to room temperature, the
reaction mixture was transferred into a separatory funnel, and the organic
layer was separated and retained. The aqueous phase was extracted with
ethyl acetate. The combined organic layers were washed with water and
brine and dried over MgSO4. Filtration and evaporation produced a dark
brown solid, which was purified by chromatography on silica gel with
hexane and ethyl acetate (v/v = 3:1) and recrystallization from hexane and
dichloromethane to provide L2 as white crystals, 660 mg, yield 87%.
1H NMR (500 MHz, CDCl3): δ 8.25 (dd, J = 4.5 Hz, 2 Hz, 1H), 7.83
(d, J = 2.5 Hz, 1H), 7.67 (d, J = 1.5 Hz, 1H), 7.54 (t, J = 2.5 Hz, 1H),
7.49ꢀ7.46 (m, 1H), 7.42 (d, J = 7 Hz, 1H), 7.38ꢀ7.32 (m, 3H), 7.21 (d,
J = 7 Hz, 2H), 7.16 (t, J = 7.5 Hz, 1H), 7.06 (d, J = 7.5 Hz, 1H), 6.83ꢀ6.79
(m, 2H), 6.41 (t, J = 2.5 Hz, 1H). 13C NMR (75 MHz, CDCl3): δ 158.54,
148.09, 147.07, 145.54, 141.15, 141.03, 137.73, 130.19, 129.65, 126.90,
126.53, 125.16, 123.75, 116.67, 115.09, 114.33, 107.57. MS, m/z calcd
for C20H16N4 (M + H+): 313.1. Found: 313.1. Anal. Calcd for C20H16N4:
C, 76.90; H, 5.16; N, 17.94. Found: C, 76.71; H, 5.07; N, 17.91.
7.53ꢀ7.49 (m, 1H), 7.39 (t, J = 8 Hz, 1H), 7.30ꢀ7.27 (m, 2H), 7.19 (dd,
J = 8 Hz, 2 Hz, 1H), 7.13 (d, J = 7 Hz, 2H), 6.95(t, J = 7.5 Hz, 1H), 5.89
(s, 1H). 13C NMR (75 MHz, CDCl3): δ 157.20, 148.07, 143.75, 143.01,
140.82, 136.80, 129.72, 129.68, 129.60, 129.37, 127.42, 127.23, 126.30,
121.14, 120.20, 118.39, 118.03, 117.06. MS, m/z calcd for C21H16N2:
297.14 (M + H+). Found: 297.15 (M + H+).
Preparation of Ligand L3. This compound was prepared follow-
ing general procedure A, yielding an off-white solid, yield 37%. 1H NMR
(500 MHz, CDCl3): δ 8.27ꢀ8.26 (m, 1H), 8.18 (d, J = 8.5 Hz, 1H), 8.15
(d, J = 8 Hz, 1H), 7.97ꢀ7.95 (m, 2H), 7.81 (d, J = 7.5 Hz, 1H), 7.78 (d,
J = 8.5 Hz, 1H), 7.71 (t, J = 8.5 Hz, 1H), 7.53ꢀ7.46 (m, 3H), 7.34 (t, J = 8
Hz, 2H), 7.28ꢀ7.25 (m, 3H), 7.15 (t, J = 7.5 Hz, 1H), 6.85ꢀ6.80 (m,
2H). 13C NMR (75 MHz, CDCl3): δ 158.77, 156.82, 148.02, 147.83,
146.50, 145.79, 140.83, 137.64, 137.06, 129.99, 129.83, 129.51, 127.43,
127.34, 127.21, 126.47, 126.36, 125.46, 124.79, 124.13, 119.21, 116.27,
114.09. MS, m/z calcd for C26H19N3 (M + H+): 374.2. Found: 374.2.
Anal. Calcd for C26H19N3: C, 83.62; H, 5.13; N, 11.25. Found: C, 83.38;
H, 5.10; N, 11.19.
Preparation of Complex 3. This complex was prepared following
1
Preparation of Complex 2. This complex was prepared following
general procedure B, yielding a pale yellow color powder, 280 mg, 95%
general procedure B, yielding red color crystals, 73% yield. H NMR
(500 MHz, CD2Cl2): δ 10.33 (dd, J = 6.5 Hz, 2 Hz, 3JPtꢀH =21 Hz, 1H),
9.50 (d, J = 8.5 Hz, 1H), 8.34 (d, J = 8.5 Hz, 1H), 7.87 (d, J = 8.5 Hz, 1H),
7.82 (dd, J = 8 Hz, 1.5 Hz, 1H), 7.76ꢀ7.67 (m, 3H), 7.61ꢀ7.57 (m, 2H),
7.52ꢀ7.49 (m, 1H), 7.44 (d, J = 7.5 Hz, 1H), 7.39ꢀ7.37 (m, 2H) 7.05 (t,
J = 8.5 Hz, 1H), 6.73(td, J = 7.5 Hz, 1.5 Hz, 1H), 6.45 (dd, J = 7.5 Hz,
1 Hz, 1H), 6.26 (dd, J = 8.5 Hz, 1 Hz, 1H). 13C NMR (75 MHz,
CD2Cl2): δ 152.45, 139.73, 136.63, 134.19, 131.63, 130.62, 129.35,
129.34, 127.35, 127.09, 124.03, 120.87, 120.15, 116.67, 115.88, 114.62,
101.92 (only partial carbon signals were observed because of poor
solubility). MS, m/z calcd for C26H18N3PtCl (M ꢀ Clꢀ): 567.1. Found:
567.1. Anal. Calcd for C26H18N3PtCl: C, 51.79; H, 3.01; N, 6.97. Found:
C, 51.62; H, 3.01; N, 6.84.
1
yield. H NMR (500 MHz, CDCl3): δ 10.26 (dd, J = 7 Hz, 2 Hz,
3JPtꢀH =19.5 Hz, 1H), 8.38 (d, J = 2.5 Hz, 1H), 7.95 (d, J = 2.5 Hz, 1H),
7.68 (t, J = 8 Hz, 2H), 7.58 (t, J = 7.5 Hz, 1H), 7.46ꢀ7.43 (m, 1H), 7.29
(d, J = 7.5 Hz, 2H), 6.95ꢀ6.89 (m, 2H), 6.67 (t, J = 7 Hz, 1H), 6.56 (t, J =
2.5 Hz, 1H), 6.35 (d, J = 9 Hz, 1H), 5.94 (d, J = 8 Hz, 1H). 13C NMR (75
MHz, CDCl3): δ 196.88, 152.69, 149.27, 143.88, 142.38, 141.74, 138.86,
136.30, 131.62, 130.38, 129.26, 126.47, 124.11, 116.21, 115.32, 115.07,
106.71, 105.65. MS, m/z calcd for C20H15N4PtCl (M ꢀ Clꢀ): 506.1.
Found: 506.1. Anal. Calcd for C20H15N4PtCl: C, 44.33; H, 2.79; N,
10.34. Found: C, 43.95; H, 2.72; N, 10.27.
Preparation of 2-(3-Chlorophenyl)quinoline.24 General
Procedure C. To a 50 mL dry, argon-flushed flask were charged
2-chloroquinoline (785 mg, 4.8 mmol), 3-chlorophenylboronic acid
(625 mg, 4 mmol), triphenylphosphine (90 mg, 0.32 mmol), and DME
(12 mL). A homogeneous solution was formed. To this solution was
added 2 M K2CO3 (5 mL, 10 mmol). After the mixture was purged with
argon, Pd(OAc)2 (17.9 mg, 0.08 mmol) was added. The mixture was
refluxed for 19 h. After cooling to room temperature, 25 mL of ethyl
acetate was added and the mixture stirred for a while. The precipitate
formed was filtered, and the filtrate was transferred into a separatory
funnel. The organic layer was separated and retained. The aqueous
phase was extracted with ethyl acetate. The combined organic layers
were washed with water and brine and dried over MgSO4. Filtration
and evaporation produced a dark brown oil, which was purified by
chromatography on silica gel with a mixture of hexane and ethyl acetate
(v/v = 4:1) and recrystallization from hexane and dichloromethane to
provide white powder, 910 mg, yield 95%.
Preparation of N-Phenyl-3-(quinolin-2-yl)aniline. General
Procedure D. To a 25 mL dry, argon-flushed flask were charged
2-(3-chlorophenyl)quinoline (719 mg, 3 mmol), aniline (419 mg,
4.5 mmol), sodium tert-butoxide (432 mg, 4.5 mmol), Pd(dba)2 (86 mg,
0.15 mmol), tri-tert-butyl phosphine (1.0 M in toluene, 0.12 mL,
0.12 mmol), and toluene (10 mL). The reaction mixture was refluxed
for 12 h and then cooled to room temperature. After cooling to room
temperature, the reaction mixture was transferred into a separatory
funnel, and the organic layer was separated and retained. The aqueous
phase was extracted with ethyl acetate (3 ꢁ 25 mL). The combined
organic layers were washed with water and brine and dried over MgSO4.
Filtration and evaporation produced a dark brown liquid, which was
purified by chromatography on silica gel with dichloromethane and ethyl
acetate (v/v = 50:1), yielding a dark brown oil, 660 mg, 87%. 1H NMR
(500 MHz, CDCl3): δ 8.20ꢀ8.15 (m, 2H), 7.88 (t, J = 2 Hz, 1H),
7.83ꢀ7.80 (m, 2H), 7.73ꢀ7.69 (m, 1H), 7.65 (d, J = 7 Hz, 1H),
Preparation of N-Phenylquinolin-2-amine.25 This com-
pound was prepared following general procedure A, yielding white
crystals, 1.47 g and yield 67%.
Preparation of N-(3-Bromophenyl)-N-phenylquinolin-2-
amine. This compound was prepared following general procedure A,
1
yielding a white powder, yield 51%. H NMR (500 MHz, CDCl3): δ
7.89 (d, J = 9 Hz, 1H), 7.72 (d, J = 8.5 Hz, 1H), 7.65 (d, J = 7.5 Hz, 1H),
7.56 (td, J = 8 Hz, 1.5 Hz, 1H), 7.40ꢀ7.33 (m, 4H), 7.26ꢀ7.21 (m, 4H),
7.18ꢀ7.17 (m, 2H), 6.89 (d, J = 9 Hz, 1H). 13C NMR (75 MHz,
CDCl3): δ 156.75, 147.26, 147.11, 145.16, 137.43, 130.23, 129.68,
129.62, 128.70, 127.67, 127.21, 127.15, 127.05, 125.58, 124.83, 124.43,
124.19, 122.54, 115.29. MS, m/z calcd for C21H15N2Br: 374.04. Found:
374.04.
Preparation of Ligand L4. To a 50 mL, three-necked dry, argon-
flushed flask was charged n-BuLi (1.6 M in hexanes, 3 mL, 4.8 mmol),
and this was cooled to ꢀ78 °C. To this, a solution of 2-bromopyridine
(0.4 mL, 4 mmol) in 2 mL of ether was added dropwise. After stirring for
30 min, the reaction mixture was warmed to 0 °C, and zinc chloride solu-
tion (1.0 M in diethyl ether, 4 mL, 4 mmol) was added dropwise. The
mixture was then warmed to room temperature. N-(3-Bromophenyl)-
N-phenylquinolin-2-amine (375 mg, 1 mmol), Pd(PPh3)4 (57.5 mg,
0.05 mmol), and 3 mL of tetrahydrofuran were added, and the reaction
mixture was refluxed for 15 h. After cooling, the reaction mixture was
quenched by a solution of EDTA (1.5 g) and Na2CO3 (1.2 g) in 10 mL
of water and extracted with ethyl acetate (3 ꢁ 10 mL). The combined
organic phases were washed with water and brine, dried over MgSO4,
filtered, and evaporated. The crude product was purified by chroma-
tography on silica gel with a mixture of hexane and ethyl acetate
1
(v/v = 2:1) to give a solid, 350 mg, yield 94%. H NMR (500 MHz,
CDCl3): δ 8.64 (dd, J = 5 Hz, 1 Hz, 1H), 7.90ꢀ7.82 (m, 3H), 7.72ꢀ7.68
(m, 2H), 7.64 (d, J = 6 Hz, 2H), 7.54 (t, J = 7.5 Hz, 1H), 7.45 (d, J = 8 Hz,
1H), 7.37ꢀ7.33 (m, 2H), 7.31ꢀ7.25 (m, 4H), 7.21ꢀ7.17 (m, 2H),
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ARTICLE
6.96 (d, J = 9 Hz, 1H). 13C NMR (75 MHz, CDCl3): δ 196.85, 156.83,
149.40, 147.05, 146.12, 145.48, 140.50, 137.43, 136.98, 129.83, 129.60,
129.42, 127.39, 127.26, 127.13, 126.65, 125.13, 125.03, 124.62, 123.93,
123.65, 122.29, 120.83, 115.30. MS, m/z calcd for C26H19N3 (M + H+):
374.2. Found: 374.2. Anal. Calcd for C26H19N3: C, 83.62; H, 5.13;
N, 11.25. Found: C, 83.36; H, 5.11; N, 11.12.
Preparation of Complex 4. This complex was prepared following
general procedure B, yielding yellow color crystals, 70% yield. 1H NMR
(500 MHz, CD2Cl2): δ 9.79 (dd, J = 6.5 Hz, 1 Hz, 3JPtꢀH =20.5 Hz, 1H),
8.99 (d, J = 9 Hz, 1H), 7.19 (td, J = 8 Hz, 1.5 Hz, 1H), 7.83 (d, J = 9 Hz,
1H), 7.75 (d, J = 8 Hz, 1H), 7.69ꢀ7.65 (m, 2H), 7.63ꢀ7.56 (m, 3H),
7.39ꢀ7.28 (m, 5H), 6.98 (dd, J = 8 Hz, 7.5 Hz, 1H), 6.58 (d, J = 9.5 Hz,
1H), 6.29 (dd, J = 8.5 Hz, 1 Hz, 1H). 13C NMR (75 MHz, CD2Cl2): δ
153.29, 151.67, 141.83, 138.97, 137.16, 137.17, 133.42, 131.56, 130.77,
129.78, 128.36, 126.04, 125.12, 124.14, 122.91, 120.26, 120.03, 119.21,
116.27, 102.16, 90.23 (only partial carbon signals were observed because
of poor solubility). MS, m/z calcd for C26H18N3PtCl (M ꢀ Clꢀ): 567.1.
Found: 567.1. Anal. Calcd for C26H18N3PtCl: C, 51.79; H, 3.01; N, 6.97.
Found: C, 51.66; H, 2.87; N, 6.91.
Preparation of N-Phenyl-3-(pyridine-2-yl)aniline. This com-
pound was prepared following general procedure D, yielding a brown oil,
1
yield 61%. H NMR (300 MHz, CDCl3): δ 8.67 (d, J = 7.5 Hz, 1H),
7.77ꢀ7.70 (m, 3H), 7.52ꢀ7.48 (m, 1H), 7.38ꢀ7.20 (m, 5H), 7.17ꢀ
7.09 (m, 3H), 6.94 (t, J = 12 Hz, 1H). 13C NMR (75 MHz, CDCl3): δ
157.36, 149.60, 143.73, 143.05, 140.72, 136.70, 129.67, 129.39, 122.17,
121.18, 120.62, 119.54, 118.10, 118.04, 116.42. MS, m/z calcd for
C17H14N2: 247.12 (M + H+). Found 247.16 (M + H+).
Preparation of Ligand L6. This compound was prepared follow-
1
ing general procedure A, yielding a white solid, yield 97%. H NMR
(500 MHz, CDCl3): δ 8.62 (d, J = 4.5 Hz, 1H), 8.32 (d, J = 6 Hz, 1H),
7.95 (d, J = 9 Hz, 1H), 7.80 (d, J = 8 Hz, 1H), 7.69ꢀ7.65 (m, 3H),
7.59ꢀ7.55 (m, 2H), 7.47 (d, J = 5.5 Hz, 1H), 7.34 (t, J = 8 Hz, 2H), 7.25
(t, J = 8 Hz, 2H), 7.19ꢀ7.16 (m, 1H), 7.06ꢀ7.02 (m, 4H). 13C NMR
(75 MHz, CDCl3): δ 157.90, 57.11, 149.46, 148.66, 148.13, 142.02,
140.61, 138.85, 136.64, 129.99, 129.65, 129.30, 127.06, 126.97, 126.44,
124.57, 124.44, 123.79, 123.20, 122.30, 122.09, 121.96, 120.72, 118.54.
MS, m/z calcd for C26H19N3 (M + H+): 374.2. Found: 374.2. Anal.
Calcd for C26H19N3 (0.025CH2Cl2): C, 83.23; H, 5.11; N, 11.19.
3
Preparation of 1-(3-Chlorophenyl)isoquinoline.26 This
compound was prepared from 1-isochloroquinoline (790 mg, 4.8 mmol)
and 3-chlorophenylboronic acid (625 mg, 4 mmol) according to general
procedure C, yielding a white crystalline powder, 900 mg, yield 94%.
Preparation of 3-(Isoquinolin-1-yl)-N-phenylaniline. This
compound was prepared from 1-(3-chlorophenyl)isoquinoline (530 mg,
2.25 mmol) and aniline (628 mg, 6.75 mmol) according to general
Found: C, 83.09; H, 5.06; N, 11.08.
Preparation of Complex 6. This complex was prepared following
1
general procedure B, yielding yellow colored crystals, 74% yield. H
NMR (500 MHz, CD2Cl2): δ 9.83(d, J = 6.5 Hz, 3JPtꢀH =20 Hz, 1H),
9.68ꢀ9.66 (m, 1H), 8.61 (dd, J = 8.5 Hz, 1 Hz, 1H), 7.93ꢀ7.88 (m, 2H),
7.84 (td, J = 8 Hz, 1.0 Hz, 1H), 7.72 (d, J = 8.5 Hz, 1H), 7.66ꢀ7.60 (m,
3H), 7.48 (d, J = 7.5 Hz, 1H), 7.30 (t, J = 8.0 Hz, 1H), 7.25ꢀ7.22 (m,
1H), 7.12ꢀ7.09 (m, 2H), 6.91ꢀ6.88 (m, 1H), 6.79ꢀ6.78 (m, 2H). 13C
NMR (75 MHz, CD2Cl2): δ 166.81, 156.73, 152.35, 149.54, 146.61,
144.24, 141.58, 139.53, 138.17, 134.28, 132.84, 129.60, 129.52, 128.27,
128.20, 127.50, 124.10, 122.96, 122.75, 121.91, 121.39, 119.21, 119.03.
MS, m/z calcd for C26H18N3PtCl (M ꢀ Clꢀ): 567.1. Found: 567.1.
1
procedure D, yielding off-white crystals, 547 mg, yield 58%. H NMR
(500 MHz, CDCl3): δ 8.59 (d, J = 5.5 Hz, 1H), 8.16 (d, J = 8.5 Hz, 1H),
7.87 (d, J = 8 Hz, 1H), 7.68 (t, J = 8 Hz, 1H), 7.63 (d, J = 5.5 Hz, 1H),
7.54 (td, J = 7.5 Hz, 1 Hz, 1H), 7.41ꢀ7.35 (m, 2H), 7.27ꢀ7.24 (m, 2H),
7.22ꢀ7.20 (m, 2H), 7.12 (d, J = 7.5 Hz, 2H), 6.92 (t, J = 7.5 Hz, 7 Hz,
1H), 5.90 (s, 1H). 13C NMR (75 MHz, CDCl3): δ 160.59, 143.41,
142.82, 141.91, 140.53, 136.82, 130.07, 129.32, 129.17, 127.64, 127.15,
126.91, 126.65, 122.46, 121.20, 119.98, 119.01, 118.18, 117.52. MS, m/z
calcd for C21H16N2: 297.14 (M + H+). Found: 297.16 (M + H+).
Preparation of Ligand L5. This compound was prepared follow-
ing general procedure A, yielding an off-white solid, yield 92%. 1H NMR
(500 MHz, CDCl3): δ 8.57 (d, J = 5.5 Hz, 1H), 8.28ꢀ8.26 (m, 1H), 8.16
(d, J = 9 Hz, 1H), 7.85 (d, J = 8 Hz, 1H), 7.67 (t, J = 7.5 Hz, 1H), 7.62 (d,
J = 5.5 Hz, 1H), 7.53ꢀ7.50 (m, 2H), 7.48ꢀ7.43 (m, 3H), 7.33 (t, J = 8
Hz, 2H), 7.29ꢀ7.25 (m, 3H), 7.14 (td, J = 7.5 Hz, 1 Hz, 1H), 6.84 (d, J =
8 Hz, 1H), 6.79 (dd, J = 7 Hz, 5 Hz, 1H). 13C NMR (75 MHz, CDCl3): δ
160.05, 158.91, 148.24, 145.91, 145.88, 141.95, 140.29, 137.37, 136.82,
130.03, 129.50, 129.45, 127.64, 127.51, 127.14, 126.89, 126.58, 126.52,
125.78, 125.73, 124.73, 120.02, 116.42, 114.20. MS, m/z calcd for
C26H19N3 (M+H+): 374.2. Found: 374.2. Anal. Calcd for C26H19N3:
C, 83.62; H, 5.13; N, 11.25. Found: C, 83.36; H, 5.10; N, 11.24.
Preparation of Complex 5. This complex was prepared following
general procedure B, yielding reddish brown colored crystals, 110 mg,
73% yield. 1H NMR (500 MHz, CD2Cl2): δ 10.14 (dd, J = 6.5 Hz, 2 Hz,
3JPtꢀH =19 Hz, 1H), 9.82 (d, J = 7 Hz, 1H), 8.77 (d, J = 9 Hz, 1H), 7.92
(d, J = 9 Hz, 1H), 7.81ꢀ7.75 (m, 2H), 7.72ꢀ7.69 (m, 3H), 7.62ꢀ7.57
(m, 2H), 7.50ꢀ7.47 (m, 1H), 7.38 (d, J = 7.5 Hz, 2H), 7.05 (t, J = 8 Hz,
1H), 6.68 (td, J = 7 Hz, 1.5 Hz, 1H), 6.46 (d, J = 9 Hz, 1H), 6.27 (d, J =
8.5 Hz, 1H). 13C NMR (75 MHz, CD2Cl2): δ 153.54, 143.59, 142.89,
138.05, 136.87, 134.34, 132.03, 131.87, 13.99, 129.57, 128.72, 127.76,
125.70, 124.0, 120.26, 116.68, 115.15, 102.17. MS, m/z calcd for
C26H18N3PtCl (M ꢀ Clꢀ): 567.1. Found: 567.1. Anal. Calcd for
Anal. Calcd for C26H18N3PtCl (0.45CH2Cl2): C, 49.55; H, 2.97; N,
3
6.55. Found: C, 49.88; H, 2.87; N, 6.53.
DFT Calculations. Electronic structure calculations were per-
formed on complexes 1ꢀ6 using DMol3,27 a numerical based density
functional computer program.28,29 The orbitals for each atom in the
molecule are represented by a double numerical plus double polarization
basis set that was developed in our laboratory. For platinum, there
were both f and g polarization functions. For all calculations, we used
the BeckeꢀTsunedaꢀHirao exchange-correlation energy-density funct-
ional,30,31 a 20 Bohr cutoff, and a fine integration grid. The SCF
convergence was set to 1.0 ꢁ 10ꢀ8, and the geometry was considered
converged when the gradient was less than 5.0 ꢁ 10ꢀ4 hartree/Bohr.
Relativity is introduced into the calculations with the scattering theoretic
approach for all electron scalar relativistic corrections introduced by
Delley.32 The solvation model COSMO33 was used to simulate the
solvent effect of dichloromethane (with a dielectric constant of 9.08) in
the geometric optimization.
Photophysical Experiments. Absorption spectra were recorded
using a Shimadzu 2445 UV/vis spectrophotometer, using 1-cm-
path-length quartz cuvettes. The steady state emission spectra were
measured using a PTI QM-4CW system, and an excitation source with a
spectral bandpass of 2 nm was used. Quantum yields were measured
using a comparative method at room temperature in a dichloromethane
solution. The solution was deoxygenated by purging it with argon gas for
20 min. A long-necked 1 cm quartz cuvette was used for measurements.
The cuvette was cooled with a dry iceꢀacetone bath to prevent solvent
loss. The optical density of both sample and reference solutions was
maintained below 0.1 AU at and above the excitation wavelength. For 1
and 2, a deoxygenated solution of Pt(dpyb)Cl6 in dichloromethane
(ϕ = 0.6) was used as the reference; for 3, 4, and 5, Ru(bpy)3Cl234 (ϕ =
0.028 in H2O) as the reference; and for 6, a solution of quinine sulfate35
in 0.1 N H2SO4 (ϕ = 0.55) was used as the reference. Emission spectra in
a frozen glass were recorded in 2-MeTHF at 77 K. Solid state emission
C26H18N3PtCl (0.1CH2Cl2): C, 51.27; H, 3.00; N, 6.87. Found:
3
C, 51.18; H, 2.94; N, 6.70.
Preparation of 2-(3-Chlorophenyl)pyridine.26 This com-
pound was prepared from 2-bromopyridine (948 mg, 6 mmol) and
3-chlorophenylboronic acid (780 mg, 5 mmol) according to general
procedure C, yielding a colorless oil, 710 mg, yield 75%.
8271
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Inorganic Chemistry
ARTICLE
spectra were recorded at room temperature using a powder sample
holder. Phosphorescence lifetime measurements were performed on the
same fluorimeter equipped with a variable high rep rate pulsed xenon
source for excitation and were limited to lifetimes >0.4 μs. Delayed
phosphorescent emission spectra of the ligands were measured using a
gated analog detector with an R928 red extended PMT in 2-MeTHF at
77 K. The radiative and nonradiative rate constants were calculated from
the luminescent quantum yield (ϕ) and lifetime (τ) of the phosphor-
escent complex according to eqs 1 and 2, respectively:
(b) Williams, J. A. G.; Develay, S. D.; Rochester, D. L.; Murphy, L. Coord.
Chem. Rev. 2008, 252, 2596–2611. (c) Xiang, H.-F.; Lai, S.-W.; Lai, P. T.;
Che, C.-M. Phosphorescent platinum(II) materials for OLED applica-
tions. In Highly efficient OLEDs with phosphorescent materials; Yersin, H.,
Ed.; Wiley-VCH: Weiheim, Germany, 2008.
(2) (a) Ma, Y.-G.; Cheung, T.-C.; Che, C.-M.; Shen, J.-C. Thin Solid
Films 1998, 333, 224–227. (b) Evans, R. C.; Douglas, P.; Williams,
J. A. G.; Rochester, D. L. J. Fluorescence 2006, 16, 201–206. (c) Thomas,
S. W., III; Venkatesan, K.; Muller, P.; Swager, T. M. J. Am. Chem. Soc.
2006, 128, 16641–16648. (d) P, K.-M.; Lai, S.-W.; Lu, W.; Zhu, N.; Che,
C.-M. Eur. J. Inorg. Chem. 2003, 42, 2749–2752. (e) Lano€e, P.-H.; Fillaut,
J.-L.; Toupet, L.; Williams, J. A. G.; Le Bozec, H.; Guerchais, V. Chem.
Commun. 2008, 4333–4335. (f) Wong, K.-H.; Chan, M. C.-W.; Che,
C.-M. Chem.—Eur. J. 1999, 5, 2845–2849. (g) Koo, C.-K.; Ho, Y.-M.;
Chow, C.-F.; Lam, M. H.-W.; Lau, T.-C.; Wong, W.-Y. Inorg. Chem.
2007, 46, 3603–3612.
(3) (a) Siu, P. K.-M.; Ma, D.-L.; Che, C.-M. Chem. Commun.
2005, 1025–1027. (b) Botchway, S. W.; Charnley, M.; Haycock, J. W.;
Parker, A. W.; Rochester, D. L.; Weinstein, J. A.; Williams, J. A. G. Proc.
Natl. Acad. Sci. U.S.A. 2008, 105, 16071–16076. (c) Ma, D.-L.; Che,
C.-M.; Yan, S.-C. J. Am. Chem. Soc. 2009, 131, 1835–1846. (d) Wu, P.;
Wong, E.L.-M.; Ma, D.-L.; Tong, G. S.-M.; Ng, K.-M.; Che, C.-M. Chem.
—Eur. J. 2009, 15, 3652–3656. (e) Wieczorek, B.; Lemcke, B.; Dijkstra,
H. P.; Egmond, M. R.; Gebbink, R. J. M. K.; van Koten, G. Eur. J. Inorg.
Chem. 2010, 49, 1929–1938.
(4) Feng, K.; Zhang, R. Y.; Wu, L.-Z.; Tu, B.; Peng, M.-L.; Zhang,
L.-P.; Zhao, D.; Tung, C.-H. J. Am. Chem. Soc. 2006, 128, 14685–14690.
(5) Cꢀardenas, D. J.; Echavarren, A. M.; Ramírez de Arellano, M. C.
Organometallics 1999, 18, 3337–3341.
kr ¼ ϕτꢀ1
ð1Þ
knr ¼ krðϕꢀ1 ꢀ 1Þ
ð2Þ
where kr and knr are the radiative and nonradiative rate constants,
respectively.
X-Ray Crystallography. Data Collection and Processing. The
crystals were prepared using solvent diffusion method. The sample was
mounted on a nylon loop with a small amount of Paratone N oil. All
X-ray measurements were made on a Bruker-Nonius Kappa Axis X8
Apex2 diffractometer at a temperature of 110 or 294 K. The data
collection strategy was a number of ω and j scans. The frame
integration was performed using SAINT.36 The resulting raw data were
scaled and absorption corrected using a multiscan averaging of symme-
try equivalent data using SADABS.37 During the data collection on
complex 1, there was excessive ice buildup around the crystal. An
attempt to clear the ice from around the crystal led to the crystal being
lost. This resulted in average redundancies between 2.7 and 6.9 for the
data set, which is lower than the redundancies normally obtained. The
structure was solved by direct methods using the XS program.38 All non-
hydrogen atoms were obtained from the initial solution. The hydrogen
atoms were introduced at idealized positions and were allowed to ride on
the parent atom. The structural model was fit to the data using full matrix
least-squares based on F2. The calculated structure factors included
corrections for anomalous dispersion from the usual tabulation. The
structure was refined using the XL program from SHELXTL;39 graphic
plots were produced using the NRCVAX crystallographic program suite.
(6) Williams, J. A. G.; Beeby, A.; Davies, E. S.; Weinstein, J. A.;
Wilson, C. Inorg. Chem. 2003, 42, 8609–8611.
(7) Huo, S.; Deaton, J. C.; Sowinski, A. F. U.S. Patent 7,029,766,
April 18, 2006 (the patent application was filed in 2003), p 24.
(8) (a) Farley, S. J.; Rochester, D. L.; Thompson, A. L.; Howard,
J. A. K.; Williams, J. A. G. Inorg. Chem. 2005, 44, 9690–9703.
(b) Develay, S.; Blackburn, O.; Thompson, A. L.; Williams, J. A. G.
Inorg. Chem. 2008, 47, 11129–11142. (c) Rochester, D. L.; Develay, S.;
Zꢀaliꢁs, S.; Williams, J. A. G. Dalton Trans. 2009, 1728–1714. (d) Rausch,
A. F.; Murphy, L.; Williams, J. A. G.; Yersin, H. Inorg. Chem. 2009,
48, 11407–11414. (e) Wang, Z.; Turner, E.; Mahoney, V.; Madakuni, S.;
Groy, T.; Li, J. Inorg. Chem. 2010, 49, 11276–11286.
’ ASSOCIATED CONTENT
(9) (a) Sotoyama, W.; Satoh, T.; Sawatani, N.; Inoue, H. Appl. Phys.
Lett. 2005, 86 (153505), 1–3. (b) Cocchi, M.; Virgili, D.; Rochester,
D. L.; Williams, J. A. G. Adv. Funct. Mater. 2007, 17, 285–289.
(c) Cocchi, M.; Virgili, D.; Rochester, D. L.; Williams, J. A. G.;
Kalinowski, J. Appl. Phys. Lett. 2007, 90 (163508), 1–3.
(10) (a) Connick, W. B.; Gray, H. B. J. Am. Chem. Soc. 1997,
119, 11620–11627. (b) Pettijohn, C. N.; Jochnowitz, E. B.; Chuong,
B.; Nagle, J. K.; Vogler, A. Coord. Chem. Rev. 1998, 171, 85. (c) Connick,
W. B.; Geiger, D.; Eisenberg, R. Inorg. Chem. 1999, 38, 3264. (d) Lai,
S. -W.; Chan, M. C. W.; Cheung, T.-C.; Peng, S.-M.; Che, C.-M. Inorg.
Chem. 1999, 38, 4046–4055. (e) Crites Tears, D. K.; McMillin, D. R.
Coord. Chem. Rev. 2001, 211, 195–205. (f) Yam, V. W.-W.; Wong,
K. M. C.; Zhu, N. Y. J. Am. Chem. Soc. 2002, 124, 6506–6507. (g) Ma, B.;
Djurovich, P. I.; Thompson, M. E. Coord. Chem. Rev. 2005, 249,
1501–1510.
(11) (a) Chang, S.-Y.; Kavitha, J.; Hung, J.-Y.; Chi, Y.; Cheng, Y.-M.;
Li, E. Y.; Chou, P. T.; Lee, G. H.; Carty, A. J. Inorg. Chem. 2007,
46, 7064–7074. (b) Lu, W.; Mi, B.-X.; Chan, M. C. W.; Hui, Z.; Che,
C.-M.; Zhu, N.; Lee, S. T. J. Am. Chem. Soc. 2004, 126, 4958–4971.
(12) (a) Vezzu, D. A. K.; Deaton, J. C.; Jones, J. S.; Bartolotti, L.;
Harris, C. F.; Marchetti, A. P.; Kondakova, M.; Pike, R. D.; Huo, S. Inorg.
Chem. 2010, 49, 5107–5119. For other reports on tetradentate
biscyclometalated platinum complexes, see: (b) Feng, K.; Zuniga, C.;
Zhang, Y.-D.; Kim, D.; Barlow, S.; Marder, S. R.; Bredas, J. L.; Weck, M.
Macromolecules 2009, 42, 6855–6864.
S
Supporting Information. Crystallographic data in CIF
b
format for 1, 3, 4, and 6. The crystal data and structure refine-
ment details for 1, 3, 4, and 6. DFT calculation results. Photo-
physical data. Proton NMR spectra of the ligands and the com-
plexes. This material is available free of charge via the Internet at
http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: huos@ecu.edu.
’ ACKNOWLEDGMENT
We thank East Carolina University for financial support. S.H.
thanks the financial support from the Research Corporation for
Science Advancement through Cottrell College Science Award.
P.D.B. thanks the Department of Chemistry of North Carolina
State University and the State of North Carolina for funding the
purchase of the Apex2 diffractometer.
’ REFERENCES
(1) For recent reviews on OLED applications, see: (a) Evans, R. C.;
Douglas, P.; Winscom, C. J. Coord. Chem. Rev. 2006, 250, 2093–2126.
(13) Ravindranathan, D.; Vezzu, D. A. K.; Bartolotti, L.; Boyle, P. D.;
Huo, S. Inorg. Chem. 2010, 49, 8922–8928.
8272
dx.doi.org/10.1021/ic200794b |Inorg. Chem. 2011, 50, 8261–8273

Inorganic Chemistry
ARTICLE
(14) Hu, Y.-Z.; Wilson, M. H.; Zong, R.; Bonnefous, C.; McMillin,
D. R.; Thummel, R. P. Dalton Trans. 2005, 354–358.
(15) (a) Constable, E. C.; Henney, R. P. G.; Leese, T. A.; Tocher,
D. A. J. Chem. Soc., Chem., Commun. 1990, 513–515. (b) Cheung, T.-C.;
Cheung, K.-K.; Peng, S.-M.; Che, C.-M. J. Chem. Soc, Chem., Dalton
Trans. 1996, 1645–1651. (c) Neve, F.; Crispini, A.; Campagna, S. Inorg.
Chem. 1997, 36, 6150–6156. (d) Hofmann, A.; Dahlenburg, L.; van
Eldik, R. Inorg. Chem. 2003, 42, 6528–6538.
(16) (a) Garner, K. L.; Parkes, L. F.; Piper, J. D.; Williams, J. A. G.
Inorg. Chem. 2010, 49, 476–487. For other related sixꢀsix-membered
metallacycles, see: (b) Song, D.; Wu, Q.; Hook, A.; Kozin, I.; Wang, S.
Organometallics 2001, 20, 4683–4689. (c) Abrahamsson, M.; J€ager, M.;
€
Kumar, R. J.; Osterman, T.; Eriksson, L.; Persson, P.; Becker, H.-C.;
Johansson, O.; Hammarstr€om, L. J. Am. Chem. Soc. 2006, 128, 12616
€
12617. (d) Abrahamsson, M.; J€ager, M.; Kumar, R. J.; Osterman, T.;
Persson, P.; Becker, H.-C.; Johansson, O.; Hammarstr€om, L. J. Am.
Chem. Soc. 2008, 130, 15533–15542.
(17) Hartwig, J. Palladium-catalyzed amination of aryl halides and
related reactions. In Handbook of Organopalladium Chemistry for Organic
Synthesis; Negishi, E., Ed.; John Wiley & Sons: New York, 2002.
(18) Negishi, E. Overview of the Negishi Protocol with Zn, Al, Zr,
and Related Metals. In Handbook of Organopalladium Chemistry for
Organic Synthesis; Negishi, E., Ed.; John Wiley & Sons: New York, 2002.
(19) Suzuki, A. Overview of Suzuki Protocol with B. In Handbook of
Organopalladium Chemistry for Organic Synthesis; Negishi, E., Ed.; John
Wiley & Sons: New York, 2002.
(20) Kober, E. M.; Caspar, J. V.; Lumpkin, R. S.; Meyer, T. J. J. Phys.
Chem. 1986, 90, 3722–3734.
(21) Yin, B.; Niemeyer, F.; Williams, J. A. G.; Jiang, J.; Boucekkine,
A.; Toupet, L.; Le Bozec, H.; Guerchais, V. Inorg. Chem. 2006, 45, 8584–
8596.
(22) Lees, A. J. Comments Inorg. Chem. 1995, 17, 319–346.
(23) Katritzky, A. R.; Huang, T.-B.; Voronkov, M. V. J. Org. Chem.
2001, 66, 1043–1045.
(24) Su, W.; Yu, J.; Zheng, B. L. Synlett. 2010, 8, 1281–1284.
(25) Park, S. E.; Kang, B. S.; Jung, J. K.; Won, E. J.; Lee, G. S.; Yoon,
J. Y. Synthesis 2009, 5, 815–823.
(26) Mongin, F.; Rebstock, S. A.; Trecourt, F.; Queguiner., G.;
Marsias., F. J. Org. Chem. 2004, 69 (20), 6766–6771.
(27) DMol3; Accelrys Inc.: San Diego, CA, 2010.
(28) (a) Delley, B. J. Chem. Phys. 1990, 92, 508–517. (b) Delley, B.
J. Chem. Phys. 2000, 113, 7756–7764.
(29) Delley, B. DMol a Standard Tool for Density Functional
Calculations: Review and Advances. In Modern Density Functional
Theory: A Tool for Chemistry; Seminario, J. M., Politzer, P., Ed.; Elsevier
Science Publishing: Amsterdam, 1995; Vol. 2.
(30) Becke, A. D. J. Chem. Phys. 1988, 88, 2547–2553.
(31) Tsuneda, T; Suzumura, T; Hirao, K. J. Chem. Phys. 1999, 110,
10664–10678.
(32) Delley, B. Int. J. Quantum Chem. 1998, 69, 423–433.
(33) Klamt, A.; Schuurmann, G. J. Chem. Soc. Perkin Trans. 2. 1993,
799–805.
(34) Nakamaru, K. Bull. Chem. Soc. Jpn. 1982, 55, 2697–2705.
(35) Meech, S. R.; Phillips, D. J. Photochem. 1983, 23, 193–217.
(36) SAINT, version 2009.9, Bruker-Nonius: Madison, WI, 2009.
(37) SADABS, version 2009.9, Bruker-Nonius: Madison, WI, 2009
(38) XS, version 2009.9, Bruker-AXS: Madison, WI, 2009.
(39) XL, version 2009.9, Bruker-AXS: Madison, WI, 2009
8273
dx.doi.org/10.1021/ic200794b |Inorg. Chem. 2011, 50, 8261–8273