Enhancing phosphorescence and electrophosphorescence efficiency of cyclometalated Pt(II) compounds with triarylboron

Article abstract of DOI:10.1002/adfm.201000904

A synthetic strategy for the preparation of cyclometalated platinum(II) acetylacetonate (acac) complexes functionalized with triarylboron is achieved. This method is used to synthesize a series of triarylboron-functionalized phosphorescent Pt(acac) compou

Full text of DOI:10.1002/adfm.201000904

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Enhancing Phosphorescence and Electrophosphorescence
Efficiency of Cyclometalated Pt(II) Compounds with
Triarylboron
By Zachary M. Hudson, Christina Sun, Michael G. Helander, Hazem Amarne,
Zheng-Hong Lu, and Suning Wang*
stabilization of radical anions by the Lewis
acidic boron atom, making them par-
ticularly attractive for use as bifunctional
A synthetic strategy for the preparation of cyclometalated platinum(II) acety-
lacetonate (acac) complexes functionalized with triarylboron is achieved. This
method is used to synthesize a series of triarylboron-functionalized phospho-
rescent Pt(acac) compounds, which are characterized by NMR spectroscopy,
X-ray crystallography, and theoretical calculations. These complexes exhibit
a range of bright phosphorescent colors spanning the green to red region of
the visible spectrum (λmax = ∼520–650 nm) in solution and the solid state.
Functionalization with a triarylboron group leads to significant enhancement
in quantum yield for several of these complexes relative to the non-borylated
Pt(II) parent chromophores, which may be attributed to the increased mixing
of 1MLCT and 3LC states. The phosphorescent enhancement, electron trans-
port capabilities, and steric bulkiness offered by the triarylboron group can
be used to significantly enhance the performance of electrophosphorescent
devices based on Pt(II) emitters. A high efficiency green electrophosphores-
cent device is fabricated with a maximum external quantum efficiency of 8.9%,
luminance efficiency of 34.5 cd A−1 , and power efficiency of 29.8 lm W−1 ,
giving significantly improved performance over control devices in which the
Pt(II) emitter lacks the boron functionality.
active layers for organic light-emitting
diodes (OLEDs).[4]
We have also recently demonstrated
that the electron-accepting ability of the
triarylboron group can be used to greatly
enhance phosphorescence in triarylboron
complexes of Pt(II) and Cu(I), including
the highest solid-state quantum efficiency
for a Cu(I) complex known in literature.[6]
This enhancement may be achieved by
increased mixing of the 1MLCT state in
the 3LC-based excited state of the com-
plex,[6,7] that provides a faster rate of radia-
tive decay due to increased participation
of the metal atom in the excited state, and
thus the possibility of a higher phospho-
rescent quantum yield (ΦP). Triarylboron-
containing metal complexes are thus
promising candidates for use in elec-
trophosphorescent devices due to this
enhancement in emission brightness. Fur-
1. Introduction
thermore, metal chelation has been shown recently to greatly
enhance the electron-accepting ability of the triarylboron group
on the chelate backbone,[6] which should improve the electron-
transporting properties of the boron center. Since organic elec-
troluminescent (EL) devices typically show electron mobilities
1 to 2 orders of magnitude lower than hole mobilities, orga-
nometallic triarylboranes have the potential to greatly improve
device efficiency when used as emitters in OLEDs due to
improved carrier balance and charge recombination.[8] Finally,
the bulky triarylboron group has been shown to reduce inter-
molecular aggregation and promote the formation of amor-
phous films,[4] reducing excimer formation and nonradiative
energy transfer in optoelectronic devices.
Triarylboron compounds have recently emerged as an attractive
and versatile class of optoelectronic materials. By harnessing
the electron-accepting nature of the boron center, researchers
have successfully developed highly selective and sensitive
chemical sensors,[1–3] bright photo- and electroluminescent
materials,[4] and compounds with impressive nonlinear optical
properties[5] based on triarylboranes. Furthermore, these com-
pounds can act as efficient electron-transport materials due to
∗
[ ] Z. M. Hudson, C. Sun, H. Amarne, Prof. S. Wang
Department of Chemistry
Despite these considerable advantages and the intense
research activity directed towards phosphorescent emitters
for OLEDs in recent years,[9] only a single example has been
reported of a device based on a triarylboron-containing elec-
trophosphorescent material, an Ir(III) complex.[10] In con-
trast to cyclometalated Ir(III) compounds, which have been
extensively studied and produced many highly efficient Ir(III)
electroluminescent devices,[9] cyclometalated Pt(II) complexes
Queen’s University
90 Bader Lane, Kingston, Ontario, Canada K7L 3N6
E-mail: suning.wang@chem.queensu.ca
M. G. Helander, Prof. Z.-H. Lu
Department of Materials Science and Engineering
University of Toronto
184 College Street, Toronto, Ontario, Canada M5S 3E4
DOI: 10.1002/adfm.201000904
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have only found limited use in OLEDs due to their weaker
emission and the tendency to produce excimer emission
as a result of their square planar geometry.[11] We therefore
decided to examine the impact of triarylboron on a range of
N,C-cyclometalated Pt(II) compounds. Through our investi-
gation, we have found that the triarylboron moiety is capable
of significantly enhancing the quantum efficiency and elec-
tron-transporting properties of these Pt(II) complexes, which
in turn can be used to significantly enhance the brightness,
efficiency, and electron mobility of EL devices based on Pt(II)
electrophosphors.
because of their poor stability at high temperature in solution.
We have therefore developed an alternative strategy based on
the method of Crespo and co-workers,[13] involving the reac-
tion of 1 equivalent of ligand with PtCl(DMSO)(acac) in the
presence of NaOAc in refluxing methanol. The resulting Pt(II)
complexes can then be purified by column chromatography and
isolated in high purity. Though overall yields were often low due
to incomplete reaction, this procedure is a versatile method for
the synthesis of cyclometalated Pt(II) complexes requiring mild
temperatures. Furthermore, the previously reported cyclometa-
lation methods[12,13] employ excess ligand, giving yields with
respect to the ligand that are quite low, a situation best avoided
if the cyclometalating ligands themselves are of value.
All complexes have been fully characterized by NMR and
elemental analyses. Furthermore, crystal structures of all
complexes except Pt-BNppy have been obtained by single-
crystal X-ray diffraction analyses, which provide insight on
intermolecular interactions in the solid state and can be used as
starting points for theoretical investigations of their electronic
structures.
2. Synthesis and Molecular Design
To study the impact of boryl substitution on cyclometalated
complexes of Pt(II), a series of N,C-chelate ligands with well-
documented photophysical properties were selected and func-
tionalized with a dimesitylboron (BMes2) group. The ancillary
ligand selected for the Pt(II) complexes is the acetylacetonato
(acac) chelate ligand. This design offers significantly improved
solution and solid-state stability over previously reported
triarylboron-containing N,C-chelate platinum complexes, which
typically contain phenyl, SMe2, or DMSO ancillary ligands.[6c–e]
In addition, the acetylacetonate ligand does not have a low lying
triplet state, thus minimizing its interference with phospho-
rescent emission.[7,11,12] In addition, the acetylacetonate ligand
can improve the rigidity of the complexes, compared to the
non-chelating SMe2, phenyl, or DMSO ancillary ligands, thus
decreasing the loss of energy via vibrational radiationless decay.
Finally, this design facilitates direct comparison with the non-
boronfunctionalizedN,C-chelate-Pt(acac)phosphors, whichhave
been extensively investigated by Thompson and co-workers.[12a]
The π skeletons of the cyclometalates were selected to exem-
plify both a range of colors and functionalization, including
electron donating and withdrawing groups, heteroatoms, and
constitutional isomers. Due to the improved electron-accepting
ability of triarylboron centers attached to the π skeleton via a
pyridine ring,[6e] the majority of these materials were prepared
with the boron center on the pyridine site. The N,C-chelate lig-
ands BppyA and BppyB were obtained by previously published
procedures.[6e] All other N,C-chelate ligands are novel and were
prepared first by Suzuki coupling of 2,5-dibromopyridine with
the appropriate boronic acids to produce the bromo intermedi-
ates, as shown in Scheme 1, which proceed in good yields with
excellent selectivity for the 2-position of the pyridine ring under
mild conditions. Subsequent treatment of the bromo intermedi-
ates with n-BuLi, followed by the addition of Mes2BF gives the
target ligands also in good yields, although lower temperatures
(–100 °C) are necessary for the benzofuryl and benzothienyl
species to minimize deprotonation and subsequent formation
of four-coordinate boron side products.
3. Crystal Structures
The structures of Pt-BppyA, Pt-BppyB, Pt-Bdfp, Pt-Bmeop, and
Pt-Bbtp are shown in Figure 1. The Pt(II) center in all complexes
has a typical square planar geometry with similar Pt–C, Pt–N,
and Pt–O bond lengths. The two Pt–O bonds in each complex
show considerable difference–the one trans to the Pt–C bond
is significantly longer (2.08 Å on average) than the one trans to
the Pt–N bond (2.00 Å on average), owing to the greater trans
effect exerted by the carbanion ligand. Pt-Bdfp forms a stacked
dimer in the crystal lattice with a Pt···Pt separation distance
of 3.404(1) Å (Figure 1). Similar short Pt···Pt distances have
been well documented in literature.[14] A similar dimer is also
observed for Pt-Bbtp that has a Pt···Pt separation distance of
3.692(1) Å. The crystals of Pt-Bbzf and Pt-Bbtp are isomorphous
with similar unit cell parameters and the same space group
(P-1). However, the quality of all crystal structural data we have
obtained for Pt-Bbzf is poor, as the molecule shows two-site
disordering with approximate occupancies of 65% and 35% for
each site (see Supporting Information). Nonetheless, the crystal
data revealed that Pt-Bbzf has the same structural features as
that of Pt-Bbtp, forming a similar dimer in the crystal lattice.
Notably, no significant intermolecular stacking interactions
are evident for Pt-BppyA, Pt-BppyB, and Pt-Bmeop in the solid
state, and thus these compounds are likely to be less prone to
excimer emission in the solid state that can significantly shift
emission energy and reduce emission efficiency.
4. Photophysical and Electrochemical Properties
The synthesis of cyclometalated complexes of PtII(acac) is well
documented in literature, typically involving heating 2–3 equiv-
alents of the N,C-chelate ligand in the presence of K2PtCl4 to
form first the chloride-bridged dinuclear species, then cleavage
of the dimer at high temperature (≥80°C) with Na(acac) to form
the desired complex.[12] This method, however, is unsuitable for
the pyridine-functionalized BMes2 ligands shown in Scheme 1
4.1. Ligands
The new ligands are all luminescent in solution and the solid
state (Table 1). In the absence of a metal atom, these boron-
containing cyclometalating ligands all exhibit relatively strong,
broad absorption bands above 325 nm. This can be attributed
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B(OH)2
B(OH)2
B(OH)2
B(OH)2
Bpin
F
F
O
Br
O
S
MeO
N
Pd(PPh3)4
Br
K2CO3
THF/H2O, 55oC
N
Br
N
Br
N
Br
Br
N
Br
N
N
F
F
S
MeO
N
1. n-BuLi
2. FBMes2
THF/Et2O
-78oC
B
B
B
B
B
B
B
N
N
N
N
N
N
F
F
N
O
S
MeO
N
BppyA
BppyB
Bdfp
Bmeop
Bbzf
Bbtp
BNppy
Cl
O
DMSO
O
NaOAc
MeOH, reflux
B
B
B
B
B
B
B
N
N
N
O
N
N
N
O
Pt
O
O
O
O
O
O
O
O
O
O
O
Pt
Pt
F
F
O
N
O
S
MeO
N
Pt-BppyA
Pt-BppyB
Pt-Bdfp
Pt-Bmeop
Pt-Bbzf
Pt-Bbtp
Pt-BNppy
Scheme 1. Synthesis of ligands and complexes.
to charge-transfer to boron from the pendant mesityl groups,
and is common in compounds containing the dimesitylboron
moiety without strong external donors. This is supported by the
emission spectra of the ligands, which show nearly identical
emission maxima (406–422 nm) despite substantial variation
in the electronic nature of the π-skeleton to which the boron
group is attached (Figure 2) .
The BNppy ligand, which also contains a diphenylamine
donor group, is an exception to this trend. This compound
shows red shifted absorption and emission bands that are
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Figure 1. Crystal structures of the Pt(II) complexes.
highly sensitive to solvent polarity, due to donor-acceptor
charge transfer from nitrogen to boron. This results in a
highly polarized excited state which emits light with near-unit
quantum efficiency, similar to examples of donor-acceptor
triarylboranes previously reported by us and others.[2,4,6] By
varying the polarity of the solvent, the emission of this compound
in solution is tunable through the blue-violet (λmax = 432 nm
in hexanes) to yellow (λmax = 534 in MeOH) region of the vis-
ible spectrum (see Supporting Information). It is interesting to
note that the 5-methoxy substituent in Bmeop does not have
the same effect, presumably due to its weaker donor strength
or the improved electronic communication offered by the para
geometry in BNppy.
These ligands all show reversible reduction waves in their
cyclic voltammetry diagrams attributable to reduction of the
boron center, and some electronic effects are apparent. Bdfp
has the most positive reduction potential among the phenylpy-
ridines (−1.98 V relative to FeCp0/+, see Supporting Informa-
tion for complete CV diagrams), rendered the strongest elec-
tron acceptor by the electron-withdrawing fluorine atoms.
Bbtp and Bbzf undergo reduction at −1.93 V, consistent with
the smaller HOMO-LUMO gap imparted by more extensive
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T a b le 1 . Ligand photophysical properties.
Absorbance, λ [nm], ε [104 cm−1
233 (1.88), 329 (2.34)
M
−1 ] [a]
Emission λmax [nm] [a]
ΦF [b]
Ligand
BppyA
BppyB
Bdfp
E1/2red [mV] [c]
−2.12
HOMO [eV] [d] LUMO [EV] [D]
411
409
424
405
408
413
510
0.16
0.01
0.07
0.42
0.63
0.39
0.94
−5.99
−3.01
−6.11
−5.90
−5.84
−6.00
−5.41
−2.68
−2.64
−2.82
−2.87
−2.87
−2.70
−2.72
232 (2.12), 327 (2.57)
−2.16
232 (1.74), 289 (1.57), 323 (1.68)
233 (1.96), 355 (2.02), 367 (1.91)
233 (2.13), 358 (3.93), 366 (3.91)
232 (2.08), 335 (2.40)
−1.98
Bbtp
−1.93
Bbzf
−1.93
Bmeop
BNppy
−2.10
232 (2.39), 301 (2.14), 401 (3.24)
−2.08
[a] Measured in CH2Cl2 at 1 × 10−5 M, [b] Fluorescence quantum efficiency, measured in CH2Cl2 relative to anthracene (Φ = 0.36)[15] All QYs are 5%. [c] In DMF relative to
FeCp0/+. [d] Determined using the reduction potential and optical energy gap.
conjugation apparent from the absorption spectra. BNppy and
Bmeop undergo reduction at ca. 150 mV lower potentials, an
anticipated consequence of functionalization of the π system
with electron donor groups. In addition, BNppy also undergoes
quasi-reversible oxidation at +0.58 mV due to oxidation of the
diphenylamine moiety.
4.2. Complexes
Functionalization of the N,C-chelate ligands with Pt(acac) gives
rise to low-energy absorption bands in the UV-vis spectra of all
complexes. This transition is particularly intense in the case of
Pt-Bbtp, Pt-Bbzf, and Pt-BNppy, attributable to a primarily LC
transition in these molecules (ε ≈ 20 000–40 000) that appears to
completely overshadow the MLCT transition band (Figure 3a),
while this transition may be considered as MLCT in nature for
the nonborylated Pt(II) ppy derivatives.[12a] The lowest energy
absorption bands are red shifted by 15–40 nm and have higher
molar absorptivities (by a factor of ca. 1.5–4) relative to the cor-
responding non-borylated Pt(II) complexes reported in litera-
ture.[12] Pt-BNppy, however, shows a particularly large red shift
of 53 nm, due to the availability of a low-energy ligand-based
charge transfer pathway from diphenylamine to the boron
moiety. All complexes are emissive under UV irradiation at
room temperature in solid state and in solution (Figure 3a and
3b, for solid state emission spectra see Supporting Information)
with good color tunability from green to red.
TheseborylatedPt(II)complexesshowbright,oxygen-sensitive
phosphorescence, with impressive quantum efficiencies ranging
from 0.06–0.98 in degassed CH2Cl2 relative to Ir(ppy)3 (Table 2).
Pt-BppyA in particular has an emission efficiency on par with
that of Ir(ppy)3, making it among the brightest reported Pt(II)
emitters. Compared to that of Pt(ppy)(acac), the emission
energy of Pt-BppyA is about 50 nm red shifted and its quantum
efficiency is about 3 times brighter, demonstrating the effect
of phosphorescence enhancement by the BMes2 center. Fur-
thermore, when doped into a PMMA matrix at 10% by weight,
these complexes are similarly bright with only minor changes
in emission profile and lifetime. Consistent with the trends
observed in solution, Pt-BppyA has the highest quantum effi-
ciency in the solid state (0.57), making it an attractive candidate
for use in OLEDs. As pure solids, the complexes display similar
PL spectra as those in solution, with the exception of Pt-Bdfp.
The emission profile of Pt-Bdfp is red shifted by 100 nm in the
pure solid due to the close Pt-Pt stacking observed in the crystal
structure, a phenomenon that has been frequently observed
Figure 2. a) Absorption and b) normalized emission spectra of the
boron-functionalized ligands at 1 × 10−5 M in CH2Cl2.
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The phosphorescence in these complexes is attributed to a
mixture of 3LC-1MLCT character,[7] with the relative amount
of MLCT character increasing from green to red. The emis-
sion spectra of Pt-BppyA, Pt-BppyB and Pt-Bdfp show broad
vibrational features, indicative of substantial mixing with a 3LC
state, while Pt-Bmeop and Pt-BNppy show featureless emission
bands. Pt-Bbtp and Pt-Bbzf are the most weakly emissive of the
series, and show dual emission bands (a high energy peak at
525 nm and a low energy peak at 648 nm or 654 nm) with sim-
ilar excitation profiles. In both cases, the higher energy peak is
insensitive to the presence of O2 and may thus be attributed to
emission from a singlet state. Similar dual emission for these
two compounds were also observed in doped PMMA films (see
Supporting Information). The high energy band in Pt-Bbzf is
particularly pronounced in solution, giving rise to a pinkish-red
emission color for this complex in solution and red emission as
a doped film.
Several important observations can be made from com-
parison with previously reported analogous non-borylated
molecules. It is clear that the presence of the boron center
strongly promotes phosphorescence, producing large increases
in the quantum yield of the complex in some cases. While
enhancement in charge-transfer by triarylboron has also been
observed in systems containing other metals[3b–e,10] such as
Ir(III) and Re(I), the enhancement in ΦP appears particularly
pronounced for the N,C-chelate Pt(acac) phosphors. Although
the enhancement of a MLCT transition by an electron deficient
triarylboron unit is frequently observed, it does not necessarily
guarantee the enhancement of phosphorescence efficiency of
the complexes,[17] as observed in 5,5′-(BMes2)2–2,2′-bipy Pt(II)
complexes which are very weak emitters.[6a,b] However, a large
increase in quantum yield was recently reported for N,C-chelate
Pt(acac) complexes of N-(2′-pyridyl)-7-azaindole, functionalized
by a BMes2 unit.[6c,d] Thus, it appears that the triarylboron unit
is most effective in enhancing phosphorescence of N,C-chelate
Pt(II) complexes.
This phosphorescent enhancement is considerably more
effective when the boron center is added to a pyridine site on
the phenylpyridine chelate, rather than the phenyl ring. Com-
parison of constitutional isomers Pt-BppyA and Pt-BppyB shows
that the quantum efficiency of the pyridine-functionalized
isomer is significantly higher than that of the phenyl-function-
alized compound, which may be associated with the greater
MLCT promoted by the synergistic coupling of the boron
center with an electron-accepting pyridine ring. It is also note-
worthy that functionalization with triarylboron does not sig-
nificantly alter the HOMO level of these complexes, indicating
that changes in the LUMO are primarily responsible for the
changes in emission behavior.[12a] Of all the compounds in this
series, the greatest phosphorescent enhancement is exhibited
by Pt-BNppy, in which the quantum efficiency is increased
more than tenfold relative to the analogous complex lacking
the boron moiety.[18] It is clear from the long decay lifetime of
Pt-BNppy (67 μs) that the emission in this case occurs from a
3LC excited state involving intramolecular charge transfer from
the amino donor to the boron acceptor. Such phosphorescence
enhancement via intramolecular charge transfer has been pre-
viously demonstrated in Os(II) complexes.[19] Thus, both intra-
ligand donor-acceptor charge transfer and the MLCT transition
Figure 3. a) Absorption and b) normalized emission spectra of all com-
plexes at 298K at 1 × 10−5 M in CH2Cl2. λEX = 470 nm for Pt-Bbtp and
Pt-Bbzf, and 365 nm for all others. c) Photographs showing the colors
of Pt(II) complexes in CH2Cl2 at ∼10−5 M (top) and in PMMA at 10 wt%
on quartz substrates (bottom) under UV irradiation. From left to right:
Pt-BppyA, Pt-Bdfp, Pt-BppyB, Pt-Bmeop, Pt-BNppy, Pt-Bbtp, Pt-Bbzf.
in Pt(II) complexes.[14] In contrast, doped PMMA films of this
compound emit green light similar to that from solution upon
UV irradiation (see Supporting Information).
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T a b le 2 . Photophysical properties of Pt complexes.
Absorption, λmax [nm], ε [104 Cm−1 −1 ] [a]
M
Complex
Emission, 298K Solution [a]/ Solid [b]
max [nm] P [μs] [f]
Emission, 77K [d]
E1/2red [V] [e]
λ
τ
Φ
P [c]
λ
max [nm]
515
τ
P [μs]
10.2
12.7
16.3
13.6
8.9
Pt-BppyA
Pt-BppyB
Pt-Bdfp
231 (1.64), 255 (1.22), 304 (1.22),339 (1.55), 426 (0.43)
230 (2.04), 250 (2.12), 293 (1.52), 340 (1.94), 421 (0.34)
213 (1.64), 244 (1.44), 293 (1.19), 334 (1.45), 425 (0.36)
239 (2.30), 273 (1.98), 350 (2.48), 461sh (1.67), 483 (2.10)
231 (3.19), 287 (1.79), 349 (2.60), 459sh (1.37), 481 (1.83)
231 (2.85), 257 (2.08), 289 (1.99), 337 (2.33), 463 (0.61)
241 (2.28), 257 (2.25), 287sh (2.22), 302 (2.43), 474 (3.81)
527/526
538/536
9.5/8.6
10.2/11.0
7.9/8.5
0.98/0.57
0.77/0.38
0.56/0.32
0.12/0.03
0.06/0.02
0.46/0.27
0.79/0.42
−1.84
−2.02
−1.71
−1.77
−1.76
−1.83
−1.86
530
530/527
517
Pt-Bbtp
525, 648/535, 648
525, 654/519, 658
598/590
14.5/13.0
9.5/10.9
14.1/13.2
67.4/30.1
650
Pt-Bbzf
651
Pt-Bmeop
Pt-BNppy
576
18.6
105
596/588
592
[a] Measured in CH2Cl2 at 1 × 10−5 M, [b] Doped into PMMA at 10 wt%. [c] Phosphorescence quantum efficiency measured in CH2Cl2, relative to Ir(ppy)3 = 1. Though the
quantum yield of Ir(ppy)3 has traditionally been cited as Φ = 0.40, recent and detailed studies have indicated that this value is likely much higher (Φ ≈ 0.97).[16] We there-
fore use a reference value of 1 for simplicity. Solid state quantum yields were measured using an integration sphere. All QYs are 5%. [d] In frozen CH2Cl2 glass. [e] In DMF
relative to FeCp0/+. [f] Triplet band only. The decay lifetime of the singlet emission band from Pt-Bbtp and Pt-Bbzf were not determined due to instrument limitations.
promoted by the BMes2 unit are likely the key factors in phos-
phorescence enhancement of these Pt(acac) complexes. Similar
phenomena have also been observed in donor-acceptor func-
tionalized 2,2′-bipyridyl Pt(II) complexes.[6b,f ]
bandgap or emission color, attributable to the competing induc-
tively withdrawing and π-donating effects of the fluorine atoms
in the 4- and 5- positions, respectively. It is also possible to
reduce the bandgap and emission energies of these complexes
by increasing the conjugation length of the π-system, as in the
case of Pt-Bbzf and Pt-Bbtp. It is interesting to note that there
is little difference between the sulphur-containing Pt-Bbtp and
the oxygen-containing Pt-Bbzf in reduction potentials, emission
maxima, frontier orbital energy levels, and optical bandgaps,
despite the pronounced differences in electronegativity of these
two atoms.
To further explain the photophysical properties of these mate-
rials, we have examined their electronic structures in detail using
TD-DFT calculations[20] and Mulliken population analysis. We
note that the S0 → S1 transitions arise predominantly from the
HOMO and LUMO with reasonable oscillator strengths (Table 3) .
Hence, our discussion will focus on these orbitals (Figure 4) .
The trends in the calculated and observed energy gaps are in rea-
sonable agreement, with Pt-BNppy having the smallest optical
energy gap in both cases. Pt-BppyB has the largest HOMO-
LUMO gap of the series, due primarily to the high LUMO level
in this molecule caused by substitution of the borane on a phenyl
rather than the more electronegative pyridine ring.
Due to the stabilization of the radical anion by the triaryl-
boron center, these compounds all undergo highly reversible
reduction at −1.7 to −2.0 V relative to FeCp0/+ (see Supporting
Information). The complexes functionalized with the boryl
group on the pyridine ring have reduction potentials 0.47 to
0.66 V more positive than the corresponding non-borylated
Pt(II) analogues,[12a] demonstrating a significant enhancement
in the electron-accepting abilities of these molecules. Though
the effect is less pronounced, the phenyl-substituted Pt-BppyB
still undergoes reversible reduction at 0.37 V more positive
potential than its non-borylated parent complex. These results
thus demonstrate that the triarylboron center is capable of
enhancing not only the phosphorescence but also the electron-
accepting ability of cyclometalated complexes of Pt(II).
5. Electronic Structures and Theoretical
Calculations
The frontier molecular orbitals of the non-borylated platinum
phenylpyridines and derivative complexes have been described
previously in literature,[12] and it is known that the HOMO in
such systems has significant electron density on the 5-position
of the phenyl ring, while the phenyl 4- and 6-positions make
significant contributions to the LUMO. As described by
Thompson and others these electronic features can be used to
predictably control the optical band gaps in these systems.[7,12a]
In the borylated complexes, we observed that substitution
of the phenyl 5-position with an electron-donating methoxy
group raises the HOMO level of the molecule, producing a
72 nm red shift in the emission maximum and changing the
luminescence color of the complex from green (Pt-BppyA) to
orange (Pt-Bmeop). Furthermore, substitution of both HOMO
and LUMO sites with fluorine atoms in Pt-Bdfp improves the
electron accepting ability of the complex relative to Pt-BppyA
(ΔE = 130 mV) without significantly altering either the optical
T a b le 3 . Experimental HOMO-LUMO energy and DFT Calculation
Results.
Complex HOMO
(eV) [a]
LUMO
(eV) [b]
%Pt in
HOMO
%B in
LUMO
% H → L in S0 → S1 Oscil-
S0 → S1 lator Strength
Pt-BppyA
Pt-BppyB
Pt-Bbtp
33
33
16
17
31
26
1
29
18
23
23
27
29
28
91
83
85
82
91
92
88
0.101
0.054
0.283
0.413
0.078
0.079
0.651
−5.51
−5.45
−5.34
−5.40
−5.66
−5.32
−5.27
−2.96
−2.78
−3.03
−3.04
−3.09
−2.97
−2.94
Pt-Bbzf
Pt-Bdfp
Pt-Bmeop
Pt-BNppy
[a] Calculated using the LUMO level and the optical energy gap. [b] Calculated
using the reduction potential relative to the ferrocene HOMO level (–4.80 eV).
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Figure 4. Molecular orbital diagrams for the LUMO (top) and HOMO (bottom) for each Pt(II) complex with calculated orbital energy levels. Isocontour
value = 0.03.
As anticipated, the LUMOs of these molecules include large
contributions from the BMes2 group, and in particular the
6. Electroluminescence
Complex Pt-BppyA was selected for evaluation of performance
in electroluminescent devices due to its high phosphorescence
efficiency and good electron accepting ability. Because of the
relatively long decay lifetime, these Pt(II) complexes are better
used as doped emissive layers to prevent exciton quenching
by triplet-triplet annihilation. To optimize EL performance,
we first prepared multilayer devices on ITO-coated glass sub-
strates using N,N′-di-[(1-naphthalenyl)-N,N′-diphenyl]-(1,1′-
biphenyl)-4,4′-diamine (NPB) as the hole transport layer (HTL),
4,4′-N,N′-dicarbazolebiphenyl (CBP) as the host material, and
1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBI) as the
electron-transport layer (ETL), as shown in Figure 5, varying the
doping concentration from 10% to 30%. The EL spectra of these
devices (A-D) are shown in Figure 5, while their luminance–
current density–voltage (L–V–J) characteristics as well as current
and power efficiencies are provided as supporting information.
Though the efficiency of these initial devices was relatively poor,
several important observations can be made from these data. The
most efficient device was achieved with a doping concentration
of 15% Pt-BppyA by weight in the active layer, giving peak cur-
rent and power efficiencies of 5.31 cd A−1 and 5.21 lm W−1 , and
green electroluminescence with CIE coordinates of (0.35, 0.61).
boron atom itself (Table 3). While the Pt(II) center makes a
significant contribution to the HOMO of Pt-BppyA, Pt-BppyB,
Pt-Bdfp, and Pt-Bmeop (26%–33%), its involvement is lower for
Pt-Bbtp and Pt-Bbzf (16% and 17%), and negligible for BNppy
(1%), which instead has a large contribution from the –NPh2
group to the HOMO level. This is consistent with UV-visible
spectral data, which suggest that the lowest energy excited
states in these molecules possess greater LC character. It there-
fore appears that the triarylboron group is most effective in
enhancing the phosphorescence of cyclometalated Pt(II) com-
1
plexes in systems in which the LC states are high in energy
1
relative to the MLCT state, allowing efficient mixing between
the 1MLCT and 3LC states,[7a] which may be responsible for the
high phosphorescence efficiency of some of the complexes. It
should be noted that the boron center also promotes efficient
phosphorescence in Pt-BNppy, due not to an enhancement in
metal-to-ligand charge transfer, but rather the introduction of
3
a highly favorable donor-acceptor LC state. To firmly establish
the exact role of the triarylboron unit in the phosphorescence
enhancement of N,C-chelate Pt(II) complexes, however, more
detailed theoretical and photophysical work are necessary and
will be carried out in due course.
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Figure 5. EL device structures A–D and their EL spectra.
The EL spectra of devices A to C match very well with the PL
spectrum of Pt-BppyA. Excimer emission is observed at doping
levels above 20%, resulting in a broad EL profile and a reduc-
tion in device efficiency. This is likely a result of the use of a
square-planar Pt(II) complex as the electrophosphor, as these
molecules tend to have strong intermolecular interactions in
the solid state. It can also be seen that as the doping concentra-
tion increases, the driving voltage decreases, indicating that the
dopant is indeed effective at transporting charge. In addition,
a very small emission peak from NPB at 442 nm can be seen
at higher doping levels, indicating that the recombination zone
moves toward the anode as the dopant concentration increases.
This led us to suggest that the device may be hole-deficient. To
address this, similar devices were fabricated with the addition
of a WO3 hole-injection layer, which has been shown to improve
the injection of holes into NPB.[21] However, this had almost no
effect on device performance, indicating that the devices were
not in fact hole-deficient.
The HOMO level of Pt-BppyA was then measured directly
using UV photoelectron spectroscopy (UPS, see Supporting
Information) using a 3 nm thick layer of material deposited
on highly-oriented pyrolytic graphite (HOPG) in situ. The
UPS measured HOMO level of Pt-BppyA, 5.66 eV, matches
well with that obtained from CV and absorption spectra. This
energy level is significantly lower than that of NPB (5.40 eV)
and the well known triplet emitter Ir(ppy)3 (5.40 eV, measured
by the authors), suggesting that the energetic barrier to direct
charge injection from NPB to the dopant may be limiting
device performance. Build-up of NPB+ radical cations at the
hole transport-active layer interface provides a means by which
excitons in the active layer can be quenched by nonradiative
decay. It has recently been shown that incorporation of a thin
layer of non-doped CBP between these two layers can move
the recombination zone away from NPB and reduce charge
buildup at the NPB interface, thus reducing nonradiative
quenching.[22]
device E (ITO/NPB (45 nm)/CBP (5 nm)/15% Pt-BppyA:CBP
(15 nm)/TPBI (30 nm)/LiF (1 nm)/Al (100 nm)), which
gives peak current and power efficiencies of 34.5 cd A−1 and
29.8 lm W−1 , the highest of any OLED using a triarylboron-based
emitter reported in literature and among the brightest Pt(II)
electrophosphorescent devices. In addition, this new device
gave a maximum luminance of 31 510 cd m−2 at only 9.8 V,
as shown in Figure 6 and 7.
To clearly isolate the impact of the boron center, a control
device F was fabricated with a structure identical to device E,
but with Pt(ppy)(acac), which lacks the triarylboron group,
replacing Pt-BppyA in the active layer. UPS measurements indi-
cated that Pt(ppy)(acac) has a HOMO energy of 5.64 eV, very
similar to that of Pt-BppyA, and thus that the benefit afforded
through the use of the CBP buffer layer should be similar. The
EL efficiencies of device F are considerably lower, showing
maximum current and power efficiencies of 14.1 cd A−1 and
11.7 lm W−1 , with a maximum luminance of 4823 cd m−2
(Figure 6). The maximum external quantum efficiency of this
device is also lower, 6.9% at only 1 cd A−1 versus 8.9% at
100 cd A−1 for the Pt-BppyA based device. Furthermore, the EL
spectrum of the control device shows broad white electrolumi-
nescence with substantial emission in the UV region from TPBI,
with CIE coordinates of (0.30, 0.33) at low luminance. This can
be clearly attributed to excimer formation, which becomes domi-
nant even in dilute doped films in this case. This illustrates
the desirable film-forming properties provided by the bulky
boron center, which reduces aggregation and excimer forma-
tion in devices based on Pt-BppyA. In addition, the emission
from TPBI indicates that the recombination zone in device F
has moved significantly toward the cathode, consistent with
the substantially lower electron mobility of the active layer in
the control device. Previous studies on electrophosphorescent
N,C-chelate Pt(acac) compounds have focused mainly on com-
plexes of 2-(4,′6′-difluorophenyl)pyridine (FPt). OLEDs based on
FPt often do not have good color purity due to excimer emis-
sion, although efficient white OLEDs have been achieved using
this molecule.[11] In contrast, the Pt-BppyA device has not only a
high color purity, but also a high efficiency. In fact, the current
and power efficiencies of these Pt-BppyA devices were found
to be comparable to those of reference devices fabricated using
Based on this consideration, a new set of devices with a 15 nm
thick 15% Pt-BppyA:CBP active layer were fabricated, with a 5 nm
CBP layer between the active layer and HTL. The improvement
in device efficiency afforded by this simple structural modifi-
cation was truly impressive, as shown by the performance of
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500
104
103
102
101
100
10-1
Pt-BppyA
Pt(ppy)(acac)
1.0
0.8
0.6
0.4
0.2
0.0
Pt-BppyA
Pt(ppy)(acac)
400
300
200
100
0
400
500
600
700
800
0
2
4
6
8
10
Voltage (V)
Wavelength (nm)
40
35
30
25
20
15
10
5
35
30
25
20
15
10
5
Pt-BppyA
Pt(ppy)(acac)
Pt-BppyA
Pt(ppy)(acac)
0
0
100
101
102
103
104
100
101
102
103
104
Luminance (cd/m²)
Luminance (cd/m²)
Figure 6. L–V–J diagrams, current and power efficiency versus luminance characteristics, and EL profiles at 9V for device E (Pt-BppyA) and F
(Pt(ppy)(acac)).
enhance electron mobility in organic EL devices. The superior
performance of the electroluminescent device E relative to that
of device F can thus be attributed in part to the improved elec-
tron transport due to the boron center.
7. Conclusions
Herein we have described the first synthesis of N,C-cyclomet-
alated Pt(acac) complexes bearing the triarylboron functional
group, and have applied this strategy to a range of chromophores,
giving complexes with good color tunability and high phospho-
rescence quantum yields. The photophysical and electrochem-
Figure 7. Left: photo of the Pt-BppyA-based device E, operating at 9 V.
Right: Photo of a single pixel of device E.
ical properties of these complexes have been studied in detail,
and show excellent agreement with theoretical predictions.
Ir(ppy)3 as the emissive material, which is a
well known and extensively studied efficient
green emitter[7] (see Supporting Information).
To more thoroughly examine the electron-
transporting ability afforded by the triaryl-
boron group, we fabricated single-carrier
devices G and H (Figure 8) designed to trans-
port electrons only.[22] Pt-BppyA and Pt(ppy)
(acac) doped at 10 wt% into CBP were used
as the active layer in the two devices, respec-
tively. As shown in Figure 8, the Pt-BppyA
device G has a current density 3–4 orders of
magnitude higher than that of the Pt(ppy)
(acac) device H, establishing unambiguously
that the triarylboron center indeed can greatly device G (Pt-BppyA) and device H (Pt(ppy)(acac)). Right: the device structure.
Figure 8. Left: plots of current density as a function of average electric field for the electron-only
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pressure of 10−10 Torr. Additional details regarding device fabrication,
characterization and UPS measurements have been described
elsewhere.[26a,27]
Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no. CCDC-
776137 – 776142.
General Synthesis of Brominated Intermediates: To a 250 mL Schlenk
flask with stir bar and condenser was added boronic acid (5.6 mmol),
2,5-dibromopyridine (5.6 mmol), Pd(PPh3)4 (0.17 mmol), K2CO3
(28 mmol), and 120 mL degassed THF:H2O (1:1). The mixture was heated
to 55 °C under N2 and allowed to stir overnight, after which the THF was
evaporated in vacuo and the aqueous layer extracted with CH2Cl2. The
combined organic layers were dried with MgSO4, concentrated, and the
residue purified by column chromatography on silica (hexanes:CH2Cl2
eluent) to produce the desired brominated ligand.
These data support that the triarylboron moiety promotes
increased participation of the MLCT state in the lowest energy
emission pathway and greatly enhances phosphorescence
efficiency for some of the Pt(II) complexes. We have further
demonstrated that the electron-accepting properties and the
steric bulkiness of this boron functionality can be harnessed
to significantly enhance the brightness, efficiency and electron
mobility of electroluminescent devices based on Pt(II) phos-
phors, as highly efficient EL devices based on Pt-BppyA have
been achieved. This work highlights the potential offered by
triarylboron complexes for optoelectronic applications, and sug-
gests that further studies based on these compounds may lead
to significant improvements in electrophosphorescent device
performance.
Brbtp: (Yield: 82%). 1H NMR (600 MHz, CDCl3): δ 8.67 (d, J =
2.3 Hz, 1H, pyridine), 7.88–7.78 (m, 4H), 7.67 (d, J = 8.3 Hz, 1H,
thianaphthene), 7.36 (t, J = 6.4 Hz, 1H, thianapthene), 7.35 (t, J = 6.1 Hz,
1H, thianapthene) ppm; 13C NMR (100 MHz, CDCl3): δ 151.1, 150.7,
143.5, 140.7, 140.4, 139.2, 125.4, 124.7, 124.2, 122.6, 121.8, 120.7, 119.4
ppm; HRMS calc’d for C13H8BrNS [M]+: 288.9561, found 288.9561.
Brbzf: (Yield 56%). 1H NMR (400 MHz, CD2Cl2): δ 8.73 (d, J = 2.4 Hz,
1H, pyridine), 7.97 (dd, J = 8.4 Hz, J = 2.4 Hz, 1H, pyridine), 7.83 (d, J =
8.4 Hz, pyridine), 7.69 (d, J = 7.6 Hz, benzofuran), 7.58 (d, J = 8.0 Hz, 1H,
benzofuran), 7.47 (s, 1H, benzofuran), 7.39 (td, J = 7.2 Hz, J = 1.2 Hz,
1H, benzofuran), 7.30 (td, J = 7.6 Hz, J = 0.8 Hz, 1H, benzofuran)
ppm; 13C NMR (100 MHz, CD2Cl2): δ 155.7, 154.8, 151.3, 147.9, 139.6,
129.0, 125.7, 123.6, 122.1, 120.9, 119.9, 111.7, 105.5. HRMS calc’d for
C13H9NOBr [M+H]+: 273.9867, found 273.9875.
8. Experimental Section
General Experimental Information: All reactions were carried out under
a nitrogen atmosphere. Reagents were purchased from Aldrich chemical
company and used without further purification. Thin-layer and flash
chromatography were performed on silica gel. 1H and 13C NMR spectra
were recorded on Bruker Avance 400, 500 or 600 MHz spectrometers.
Deuterated solvents were purchased from Cambridge Isotopes and
used without further drying. Excitation and emission spectra were
recoded using a Photon Technologies International QuantaMaster
Model 2 spectrometer and are corrected for detector sensitivity. UV/
Visible spectra were recorded using an Ocean Optics CHEMUSB4
absorbance spectrophotometer. Cyclic voltammetry experiments were
performed using a BAS CV-50W analyzer with a scan rate of 0.2–
1.0 V s−1 using 1 mg sample in 0.5 mL dry DMF. The electrochemical
cell was a standard three-compartment cell composed of a Pt working
electrode, a Pt auxiliary electrode, and an Ag/AgCl reference electrode.
Brmeop: (Yield 73%). 1H NMR (600 MHz, CDCl3) δ 8.73 (d, J =
2.4 Hz, 1H, pyridine), 7.87 (dd, J = 8.5 Hz, J = 2.4 Hz, 1H, pyridine), 7.61
(d, J = 8.5 Hz, 1H, pyridine), 7.55 (t, J = 1.9 Hz, 1H, phenyl), 7.50 (d, J =
7.1 Hz, 1H, phenyl), 7.37 (t, J = 7.9 Hz, 1H, phenyl), 6.98 (dd, J = 8.2 Hz,
J = 2.5 Hz, 1H, phenyl), 3.88 (s, 3H, methoxy) ppm; 13C NMR (125 MHz,
CDCl3) δ 160.1, 155.6, 150.6, 139.6, 139.2, 129.8, 121.7, 119.4, 119.1,
115.3, 111.9, 55.3 ppm; HRMS calc’d for C12H10BrNO [M]+: 262.9946,
found 262.9925.
CV measurements were carried out at room temperature with 0.1
M
tetrabutylammonium hexafluorophosphate (TBAP) as the supporting
electrolyte, with ferrocene/ferrocenium as internal standard (E° = 0.55 V).
Elemental analyses were performed by Canadian Microanalytical Service
Ltd., Delta, British Columbia. Crystal structures were obtained at 180 K
using a Bruker AXS Apex II X-ray diffractometer (50 kV, 30 mA, Mo
Kα radiation). Molecular orbital and molecular geometry calculations
were performed using the Gaussian 03 program suite[20] using crystal
structures as the starting point for geometry optimizations where
possible. Calculations were performed at the B3LYP level of theory
using LAN2LDZ as the basis set for Pt, and 6–31G∗ for all other
atoms. The syntheses of BppyA, BppyB,[6e] p-(diphenylamino)phenyl
pinacolborane,[23] and PtCl(acac)(DMSO)[24] have been reported
previously.
EL Device Fabrication: Devices were fabricated in a Kurt J. Lesker
LUMINOS cluster tool with a base pressure of ∼10−8 Torr without
breaking vacuum. The ITO anode is commercially patterned and
coated on glass substrates 50 × 50 mm2 with a sheet resistance
less than 15 Ω sq-1.!!! Substrates were ultrasonically cleaned with a
standard regiment of Alconox, acetone, and methanol followed by
UV ozone treatment for 15 min. The active area for all devices was
2 mm2. The film thicknesses were monitored by a calibrated quartz
crystal microbalance and were further verified for single-carrier
devices using capacitance-voltage measurements (Agilent 4294A).
Current–voltage (I–V) characteristics were measured using a HP4140B
picoammeter in ambient air. Luminance measurements and EL spectra
were taken using a Minolta LS-110 luminance meter and an Ocean
Optics USB200 spectrometer with bare fiber, respectively. The external
quantum efficiency of EL devices was calculated following the standard
procedure.[25] After deposition, single carrier devices were transferred
to a homebuilt variable temperature cryostat for measurement at 298K.
UPS measurements were performed using a PHI 5500 MultiTechnique
Brdfp: (Yield 88%). 1H NMR (400 MHz, C6D6): δ 8.59 (d, J = 1.90 Hz,
1H, pyridine), 7.79 (tt, J = 7.9 Hz, J = 1.7 Hz, 1H, phenyl), 7.18 (dd,
J = 8.5 Hz, J = 1.5 Hz, 1H, pyridine), 7.11(dd, J = 8.5 Hz, J = 2.4 Hz,
1H, pyridine), 6.63 (m, 2H, phenyl) ppm; 13C NMR (100 MHz, C6D6):
δ 151.5, 151.0, 149.0, 138.9, 128.7, 125.8, 125.4, 124.3, 124.26, 120.3,
117.6 ppm; 19F NMR (376 MHz, C6D6): δ −139.3 (ddd, J = 19.5 Hz,
J = 9.8 Hz, J = 4.6 Hz), −143.5 (td, J = 19.5 Hz, J = 6.9 Hz) ppm; HRMS
calc’d for C11H6BrF2N [M+]: 268.9652, found 268.9641.
BrNppy: (Yield 89%). 1H NMR (600 MHz, CDCl3): δ 8.67 (d, J = 2.4 Hz,
1H, pyridine), 7.82 (d, J = 8.4 Hz, 2H, p-Ph), 7.81 (dd, J = 8.5 Hz, J =
2.4 Hz, 1H, pyridine), 7.55 (d, J = 8.5 Hz, 1H, pyridine), 7.27 (t, J =
7.7 Hz, 4H, N-Ph) 7.13 (d, J = 7.7 Hz, 4H, N-Ph), 7.12 (d, J = 8.3 Hz, 2H,
p-Ph), 7.05 (t, J = 7.8 Hz, 2H, N-Ph) ppm; 13C NMR (125 MHz, CDCl3): δ
155.4, 150.5, 149.0, 147.3, 139.1, 131.6, 129.3, 127.5, 124.9, 123.4, 122.8,
120.8, 118.3 ppm; HRMS calc’d for C23H17BrN2 [M+]: 400.0575, found
400.0580.
General Procedure for the Synthesis of N,C-Chelate Ligands: To a 250 mL
Schlenk flask with stir bar was added Brbtp (3.5 mmol) and 80 mL dry
THF. The mixture was cooled to −78°C under N2 and allowed to stir for
30 min, at which point n-BuLi (3.85 mmol, 1.6 M in hexanes) was added
dropwise. The mixture was stirred for 40 min, then FBMes2 (3.9 mmol)
in 20 mL THF was added dropwise via cannula. The mixture was stirred
1 h at −78 °C, then allowed to warm slowly to room temperature and
stirred overnight. The mixture was then concentrated and the residue
partitioned between CH2Cl2 and water. The aqueous layer was extracted
twice with CH2Cl2, and the combined organic layers were dried with
MgSO4, concentrated, and purified by column chromatography on
silica (hexanes:CH2Cl2 eluent) to afford the desired borylated ligand. A
reaction temperature of −100°C was used for the preparation of Bdfp,
Bbtp, and Bbzf.
system, with attached organic deposition chamber with
a base
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Bbtp: (Yield 63%). 1H NMR (500 MHz, CDCl3): δ 8.66 (s, 1H, pyridine),
7.93 (s, br, 1H, thianaphthene), 7.89–7.85 (m, 1H, thianaphthene), 7.84–
7.79 (m, 2H, thianaphthene/pyridine), 7.77 (d, J = 7.9 Hz, pyridine), 7.37
(t, J = 3.6 Hz, 1H, thianaphthene), 7.35 (t, J = 3.6 Hz, 1H, thianaphthene),
2.32 (s, 6H, mesityl), 2.05 (s, 12H, mesityl) ppm.13C NMR (125 MHz,
CDCl3) δ 157.3, 154.7, 144.8, 144.2, 141.2, 140.7, 140.4, 139.3, 138.9,
128.41, 128.36, 125.4, 124.6, 124.3, 122.6, 122.4, 118.9, 23.5, 21.2 ppm.
HRMS calc’d for C31H30BNS [M]+: 459.2192, found 459.2201.
Pt-Bbtp: (Yield 43%). 1H NMR (600 MHz, C6D6): δ 9.38 (s, 1H,
pyridine), 9.37 (d, J = 8.0 Hz, 1H, thianaphthene), 7.73 (d, J = 7.8 Hz,
1H, pyridine), 7.46 (d, J = 7.9 Hz, 1H, pyridine), 7.42 (t, J = 8.0 Hz, 1H,
thianaphthene), 7.21 (t, J = 8.0 Hz, 1H, thianaphthene), 6.81 (s, 4H,
mesityl), 6.81 (d, J = 8.0 Hz, 1H, thianaphthene), 5.13 (s, 1H, acac),
2.20 (s, 6H, mesityl), 2.09 (s, 12H, mesityl), 1.64 (s, 3H, acac), 1.51 (s,
3H, acac) ppm. 13C NMR (150 MHz, C6D6): δ 185.2, 183.7, 167.5, 156.2,
147.2, 146.5, 146.0, 144.2, 141.1, 140.8, 139.2, 138.6, 128.9, 128.3, 127.6,
126.7, 124.5, 122.9, 117.6, 102.6, 27.3, 26.2, 23.8, 21.2 ppm. Anal. calc’d. for
C36H36BNO2PtS: C 57.45, H 4.82, N 1.86, found C 57.29, H 4.68, N 1.86.
Pt-Bbzf: (Yield 15%). 11H NMR (600 MHz, CD2Cl2): δ 8.92 (s, 1H,
pyridine), 8.07 (d, J = 7.8 Hz, 1H, pyridine), 7.85 (d, J = 7.9 Hz, 1H,
pyridine), 7.48 (d, J = 8.2 Hz, 1H, benzofuran), 7.39 (t, J = 8.2 Hz,
1H, benzofuran), 7.36 (d, J = 8.0 Hz, 1H, benzofuran), 7.27 (t, J =
7.4 Hz, 1H, benzofuran), 6.92 (s, 4H, mesityl), 5.54 (s, 1H, acac), 2.34
(s, 6H, mesityl), 2.14 (s, 12H, mesityl), 2.05 (s, 3H, acac), 1.72 (s, 3H,
acac) ppm. 13C NMR (100 MHz, C6D6): δ 184.8, 183.8, 160.2, 158.9,
158.2, 157.1, 147.4, 141.0, 140.8, 139.2, 134.5, 134.2, 128.9, 127.0,
125.3, 124.6, 123.3, 115.9, 111.8, 102.5, 27.3, 26.2, 23.8, 21.2 ppm. Anal.
calc’d. for C36H36BNO3Pt: C 58.70, H 4.93, N 1.90, found: C 57.27, H
4.72, N 1.82 (The low carbon content may be caused by the presence of
CH2Cl2 solvent molecules in the crystal lattice. Calc’d for 0.2 CH2Cl2 per
molecule: C 57.70, H, 4.87, N, 1.86).
Bbzf: (Yield 31%). 1H NMR (600 MHz, CDCl3): δ 8.70 (s, 1H, pyridine),
7.87 (d, J = 7.9 Hz, 1H, benzofuran), 7.86 (d, J = 7.9 Hz, 1H, benzofuran),
7.66 (d, J = 8.1 Hz, 1H, pyridine), 7.56 (d, J = 8.1 Hz, 1H, pyridine), 7.53
(s, 1H, benzofuran), 7.34 (t, J = 7.5 Hz, 1H, benzofuran), 7.26 (t, J =
7.6 Hz, 1H, benzofuran), 6.84 (s, 4H, mesityl), 2.31 (s, 6H, mesityl),
2.04 (s, 12H, mesityl) ppm. 13C NMR (100 MHz, CDCl3): δ 157.3, 155.5,
155.1, 151.2, 144.4, 140.8, 140.7, 139.3, 139.1, 128.7, 128.4, 125.6, 123.3,
121.9, 119.1, 111.5, 106.4, 23.5, 21.2 ppm. HRMS calc’d for C31H31BNO
[M+H]+: 444.2500, found 444.2521.
Bmeop: (Yield 58%).1H NMR (600 MHz, CDCl3) δ 8.81 (s, 1H,
pyridine), 7.89 (d, J = 7.9 Hz, 1H, phenyl), 7.79 (s, 1H, phenyl), 7.78 (d, J =
8.0 Hz, 1H, pyridine), 7.69 (d, J = 7.7 Hz, 1H, phenyl), 7.41 (t, J = 7.9 Hz,
1H, phenyl), 7.03 (d, J = 8.0 Hz, 1H, pyridine), 6.90 (s, 4H, mesityl), 3.91
(s, 3H, methoxy), 2.36 (s, 6H, mesityl), 2.12 (s, 12H, mesityl) ppm. 13C
NMR (150 MHz, CDCl3) δ 160.0, 159.1, 156.9, 144.4, 140.8, 140.6, 140.1,
139.0, 138.2, 129.6, 128.3, 119.9, 119.5, 115.8, 112.0, 55.2, 23.4, 21.1
ppm. HRMS calc’d for C30H33BNO [M+H]+: 434.2655, found 434.2661.
Bdfp: (Yield 66%). 1H NMR (500 MHz, C6D6): δ 9.90 (s, 1H, pyridine),
8.12 (dd, J = 8.0 Hz, J = 6.5 Hz, 1H, phenyl), 7.70 (d, J = 7.9 Hz, 1H,
pyridine), 7.66 (dd, J = 7.9 Hz, J = 1.7 Hz, 1H, pyridine), 6.77 (s, 4H,
mesityl), 6.65 (multiplet, 2H, phenyl), 2.19 (s, 6H, mesityl), 2.06 (s, 12 H,
mesityl) ppm. 13C NMR (125 MHz, C6D6): δ 157.3, 154.8, 151.7, 148.7,
144.3, 141.4, 140.9, 139.5, 139.4, 129.6, 129.0, 126.3, 124.3, 124.2, 117.8,
23.7, 21.3 ppm. 19F NMR (376 MHz, C6D6): δ −139.4 (ddd, J = 20.7 Hz,
J = 9.2 Hz, J = 4.6 Hz), −142.8 (dt, J = 20.7 Hz, J = 6.9 Hz) ppm. HRMS
calc’d for C29H28BF2N [M+]: 439.2283, found 439.2263.
Pt-Bmeop: (Yield 23%).1H NMR (400 MHz, CD2Cl2): δ 9.00 (d, sat,
J = 1.5 Hz, JPt-H = 40.0 Hz, 1H, pyridine), 7.90 (dd, J = 8.1 Hz, J =
1.5 Hz, 1H, pyridine), 7.60 (d, J = 8.1 Hz, 1H, pyridine), 7.43 (d, J = 8.4 Hz,
1H, phenyl), 7.12 (d, J = 2.6 Hz, 1H, phenyl), 6.94–6.89 (m, 5H, mesityl/
phenyl), 5.44 (s, 1H, acac), 3.85 (s, 3H, methoxy), 2.33 (s, 6H, mesityl),
2.11 (s, 12H, mesityl), 1.97 (s, 3H, acac), 1.67 (s, 3H, acac) ppm. 13C
NMR (125 MHz, C6D6): δ 185.3, 183.9, 171.4, 157.7, 156.2, 146.0, 145.2,
141.1, 140.8, 139.4, 133.2, 132.7, 129.0, 117.8, 117.1, 110.2, 109.8, 102.6,
55.0, 27.6, 27.0, 23.9, 21.3 ppm. Anal. calc’d. for C35H38BNO3Pt: C 57.86,
H 5.27, N 1.93, found: C 57.86, H 5.07, N 1.92.
Pt-Bdfp: (Yield 16%). 1H NMR (600 MHz, C6D6): δ 9.46 (s, 1H,
pyridine), 7.76 (dd, 1H, J = 8.2 Hz, J = 4.9 Hz, phenyl), 7.61, (d, 1H,
J = 8.1 Hz, pyridine), 7.45 (d, 1H, J = 8.1, pyridine), 7.02 (dt, J = 10.5 Hz,
J = 8.2 Hz, 1H, phenyl) 6.79 (s, 4H, mesityl), 5.02 (s, 1H, acac), 2.19 (s,
6H, mesityl), 2.02 (s, 12H, mesityl), 1.64 (s, 3H, acac), 1.51 (s, 3H, acac)
ppm. 13C NMR (150 MHz, CDCl3): δ 185.7, 184.3, 155.8, 149.4, 147.7,
146.6, 141.1, 140.6, 139.6, 137.2, 137.0, 133.6, 129.0, 126.4, 122.5, 118.3,
114.5, 102.6, 27.4, 26.9, 23.8, 21.2. 19F NMR (376 MHz, C6D6): δ −142.4
(dd, J = 19.5 Hz, J = 8.1 Hz), −147.6 (ddd, J = 19.5 Hz, J = 10.4 Hz, J =
4.6 Hz) ppm. Anal. calc’d. for C34H34BF2NO2Pt: C 55.75, H 4.68, N 1.91,
found: C 55.15, H 4.70, N 1.83.
BNppy: (Yield 77%). 1H NMR (600 MHz, CD2Cl2): δ 8.66 (d, J = 1.9 Hz,
1H, pyridine), 8.02 (d, J = 8.8 Hz, 2H, p-Ph), 7.79 (dd, J = 8.0 Hz, J =
1.9 Hz, 1H, pyridine), 7.73 (d, J = 8.0 Hz, 1H, pyridine), 7.33 (t, J =
7.6 Hz, 4H, N-Ph), 7.17 (d, J = 7.7 Hz, 4H, N-Ph), 7.13 (d, J = 8.8 Hz,
2H, p-Ph), 7.11 (t, J = 7.4 Hz, 2H, N-Ph), 6.89 (s, 4H, mesityl), 2.34 (s,
6H, mesityl), 2.07 (s, 12H, mesityl) ppm. 13C NMR (150 MHz, CD2Cl2): δ
159.0, 157.3, 149.4, 147.4, 144.4, 141.1, 140.8, 139.1, 137.4, 132.2, 129.4,
128.4, 128.0, 125.1, 123.6, 122.4, 118.8, 23.3, 21.0 ppm. HRMS calc’d for
C41H39BrN2 [M+]: 570.3206, found 570.3234.
General Procedure for the Preparation of Cyclometalated Pt Complexes:
To a 100 mL Schlenk flask with stir bar and condenser was added N,C-
chelate ligand (0.17 mmol), PtCl(DMSO)(acac) (0.17 mmol), and NaOAc
(0.17 mmol) in 25 mL degassed MeOH. The mixture was heated at
reflux for two days, concentrated, then purified on silica (hexanes:CH2Cl2
eluent) to afford the desired cyclometalated Pt complex.
1
Pt-BNppy: (Yield 20%). H NMR (400 MHz, CD2Cl2): δ 8.90 (d, sat,
J = 1.6 Hz, JPt-H = 37.1 Hz, 1H, pyridine), 7.81 (dd, J = 8.1 Hz, J = 1.6 Hz,
1H, pyridine), 7.47 (d, J = 8.1 Hz, 1H, pyridine), 7.39 (d, J = 8.5 Hz, 1H,
phenyl), 7.34 (t, J = 7.4 Hz, 4H, N-Ph), 7.21 (d, J = 7.4 Hz, 4H, N-Ph),
7.12 (t, J = 7.3 Hz, 2H, N-Ph), 7.08 (d, J = 2.4 Hz, 1H, phenyl), 6.91 (s,
4H, mesityl), 6.75 (dd, J = 8.5 Hz, J = 2.4 Hz, 1H, phenyl), 5.37 (s, 1H,
acac), 2.33 (s, 6H, mesityl), 2.12 (s, 12H, mesityl), 1.70 (s, 3H, acac),
1.66 (s, 3H, acac) ppm.13C NMR (100 MHz, CD2Cl2): δ 186.0, 183.8,
169.8, 155.9, 149.3, 147.2, 146.0, 142.6, 140.8, 139.2, 137.3, 135.1, 129.3,
128.4, 125.8, 125.1, 123.8, 122.3, 116.9, 116.8, 101.9, 27.4, 26.7, 23.4,
21.0 ppm. Anal. calc’d. for C46H45BN2O2Pt: C 63.96, H 5.25, N 3.24,
found: C 64.19, H 5.32, N 3.03.
1
Pt-BppyA: (Yield 22%). H NMR (400 MHz, CD2Cl2): δ 9.02 (d, sat, J =
1.4 Hz, JPt-H = 39.9 Hz, 1H, pyridine), 7.91 (dd, J = 8.1 Hz, J = 1.4 Hz, 1H,
pyridine), 7.64 (d, J = 8.0 Hz, 1H, pyridine), 7.58–7.52 (m, 2H, phenyl), 7.21
(t, J = 7.4 Hz, 1H, phenyl), 7.12 (t, J = 7.6 Hz, 1H, phenyl), 6.92 (s, 4H,
mesityl), 5.45 (s, 1H, acac), 2.34 (s, 6H, mesityl), 2.11 (s, 12H, mesityl), 1.99
(s, 3H, acac), 1.69 (s, 3H, acac) ppm. 13C NMR (150 MHz, C6D6): δ 185.5,
184.1, 171.5, 156.2, 146.0, 144.8, 143.2, 141.1, 139.4, 136.6, 132.1, 130.5,
129.0, 124.5, 123.7, 117.8, 102.5, 27.6, 27.0, 23.8, 21.2 ppm. Anal. calc’d. for
C34H36BNO2Pt: C 58.63, H 5.21, N 2.01, found: C 58.32, H 5.62, N 1.86.
Pt-BppyB: (Yield 22%).1H NMR (400 MHz, CD2Cl2): δ 9.01 (d, sat,
J = 5.7 Hz, JPt-H = 38.5 Hz, 1H, pyridine), 7.88 (t, J = 7.9 Hz, 1H, pyridine),
7.72 (d, J = 7.9 Hz, 1H, pyridine), 7.63 (s, sat, JPt-H = 35.5 Hz, 1H,
phenyl), 7.45 (d, J = 7.6 Hz, 1H, phenyl), 7.23 (d, J = 7.7 Hz, 1H, phenyl),
7.20(dd, J = 7.9 Hz, J = 5.7 Hz, 1H, pyridine), 6.87 (s, 4H, mesityl),
5.46 (s, 1H, acac), 2.32 (s, 6H, mesityl), 2.10 (s, 12H, mesityl), 2.01 (s, 3H,
acac), 1.73 (s, 3H, acac) ppm. 13C NMR (100 MHz, CD2Cl2): δ 186.0, 184.1,
167.7, 148.0, 147.6, 146.3, 142.2, 140.7, 138.7, 138.41, 138.35, 138.1, 131.8,
128.0, 122.1, 119.3, 102.1, 28.1, 26.4, 23.3, 20.9 ppm. Anal. calc’d. for
C34H36BNO2Pt: C 58.63, H 5.21, N 2.01, found: C 58.50, H 5.26, N 2.00.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
We thank the Natural Sciences and Engineering Research Council for
financial support. We are also grateful to Professor Steven Holdcroft and
©
wileyonlinelibrary.com
Adv. Funct. Mater. 2010, 20, 3426–3439
2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
3437

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Dr. Jaclyn Brusso at Simon Fraser University for the determination of
solid state quantum efficiencies.
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