Syntheses, structures, and luminescent properties of dipyridylamine- functionalized anthracene and its complexes

Article abstract of DOI:10.1021/ic201757r

A novel multidentate ligand with 2,2′-dipyridylamine functionalities, 1,8-bis[4-(2,2′-dipyridylamino)phenylacetylenyl]anthracene (1), has been synthesized through a double Sonogashira coupling reaction and characterized by NMR spectroscopic, elemental, and X-ray diffraction analyses. Compound 1 can bind to either one metal center as a tetradentate ligand or two metal centers as a double-bidentate ligand. In the double-bidentate mode, the distance between the two metal centers may vary significantly. Compound 1 displays bright blue luminescence in the solid state and in solution with a quantum efficiency of 64% relative to 9,10-diphenylanthracene. While the dirhodium complex of 1 shows no luminescence, the two zinc complexes of 1 display blue luminescence with quantum efficiencies slightly lower than that of 1. Organic light-emitting devices (OLEDs) using 1 as the emitter show a maximum current efficiency of 7 cd/A.

Full text of DOI:10.1021/ic201757r

Article
pubs.acs.org/IC
Syntheses, Structures, and Luminescent Properties of
Dipyridylamine-Functionalized Anthracene and Its Complexes
Runyu Tan,† Zhi-Bin Wang,‡ Yu Li,† Daniel J. Kozera,† Zheng-Hong Lu,‡ and Datong Song*,†
†Davenport Chemical Research Laboratories, Department of Chemistry, University of Toronto, 80 St. George Street, Toronto,
Ontario, Canada M5S 3H6
‡Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, Ontario, Canada M5S 3E4
S
* Supporting Information
ABSTRACT: A novel multidentate ligand with 2,2′-dipyridylamine functionalities, 1,8-bis[4-(2,2′-dipyridylamino)-
phenylacetylenyl]anthracene (1), has been synthesized through a double Sonogashira coupling reaction and characterized by
NMR spectroscopic, elemental, and X-ray diffraction analyses. Compound 1 can bind to either one metal center as a tetradentate
ligand or two metal centers as a double-bidentate ligand. In the double-bidentate mode, the distance between the two metal
centers may vary significantly. Compound 1 displays bright blue luminescence in the solid state and in solution with a quantum
efficiency of 64% relative to 9,10-diphenylanthracene. While the dirhodium complex of 1 shows no luminescence, the two zinc
complexes of 1 display blue luminescence with quantum efficiencies slightly lower than that of 1. Organic light-emitting devices
(OLEDs) using 1 as the emitter show a maximum current efficiency of 7 cd/A.
separation between two potential binding sites. To achieve the
desired degree of flexibility of the binucleating ligand, instead of
tethering two metal binding groups directly onto a rigid
anthracene moiety,19−30 we install them onto a U-shaped linker
that consists of two phenylacetylene moieties attached to the
1,8-positions of an anthracene unit. We reason that by
increasing the length of the linker a certain degree of flexibility
could be realized. We chose 2,2′-dipyridylamine (DPA) as the
metal binding unit in our ligand design for its versatile metal
binding modes. Furthermore, DPA-functionalized ligands and
metal complexes have been found to be highly luminescent and
hence have been used as luminescent sensors and in
OLEDs.31,32 For example, the Ye group has reported a
tetrakis(dipyridylamine)-functionalized zinc porphyrin ligand
that can sense Cu2+ selectively by fluorescence quenching upon
binding of Cu2+ through the DPA moieties.31 Wang and co-
workers have studied DPA-containing molecules exten-
sively.33−39 They reported a series of linear and starburst-
shaped molecules that utilize DPA moieties to accommodate
INTRODUCTION
■
Because of their photophysical properties, luminescent organic
compounds have found use in many fields such as sensing,1−7
imaging,8−10 and solid-state lighting.11−13 Luminescent organic
compounds with metal binding ability are even more
interesting, because metal binding would improve the rigidity
of the molecule and in turn reduce the luminescence quenching
caused by thermal vibration. In addition, metal binding may
change the stability of the molecule. Moreover, heavy metals
such as Pt and Ir would facilitate intersystem crossing and
therefore make phosphorescence emission practically useful in
organic light-emitting devices (OLEDs).14−18 Our group is
interested in luminescent organic molecules with versatile metal
binding modes, because different metal binding modes are
associated with various symmetries and orbital energy levels of
the molecule and affect the luminescent properties. This should
allow us to investigate the photophysical properties of various
metal complexes of the organic ligand and to gain an
understanding of how the ligand geometry change enforced
by the metal center would alter the photophysical properties.
Our recent ligand design incorporates two luminescent metal
binding units and a luminescent spacer to provide the required
Received: August 12, 2011
Published: June 11, 2012
© 2012 American Chemical Society
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Scheme 1. Synthesis of Ligand 1
different metals. In these molecules, phenyl, silole, or triazine
groups are used as linkers. Some of these compounds are
promising candidates as emitters or electron transport materials
in OLEDs. In this paper, we report our effort to synthesize a U-
shaped ligand with DPA functional groups and the study of its
versatile coordination behavior caused by the less rigid linker
group as well as the luminescent properties of such a ligand and
its metal complexes.
RESULTS AND DISCUSSION
■
Synthesis of the Ligand 1. Ligand 1 can be synthesized in
good yield through a Sonogashira coupling reaction of 1,8-
dibromoanthracene and 4-(2,2′-dipyridylamino)-
phenylacetylene using PdCl2(PPh3)2/CuI as catalyst and Et3N
as solvent (Scheme 1).40 Alternatively, 1 can be synthesized via
a multicomponent one-pot reaction from 1,8-dibromoanthra-
cene, (trimethylsilyl)acetylene, and 4-(2,2′-dipyridylamino)-
Figure 1. Molecular structure of 1 with thermal ellipsoids plotted at
the 50% probability level. Hydrogen atoms are omitted for clarity.
phenyl bromide under similar conditions. H and 13C NMR
1
spectra of 1 indicated a symmetric structure in solution with
only one set of DPA resonance peaks. The solid-state structure
of 1 was unambiguously confirmed by X-ray crystallography. As
shown in Figure 1, the two phenylethynyl linkers are linear and
parallel to each other.
Coordination Chemistry of 1. One of the vital features of
compound 1 is that two DPA moieties are juxtaposed by the U-
shaped linker group with the separation distance of two tertiary
amine nitrogen atoms being ∼5 Å. As a result, they could
potentially accommodate two metals in close proximity. The
distances between the two metal centers may vary with different
auxiliary ligands as well as the coordination geometry of the
metal center. When 1 is treated with 2 equiv of [Rh(COD)-
(CH3CN)2]BF4 in THF (Scheme 2, left), the quantitative
formation of the product 2a can be observed. The solid-state
structure of 2a was confirmed by X-ray crystallography. As
shown in Figure 3, 2a consists of two Rh(COD) moieties per
ligand 1. Each rhodium center adopts a square-planar geometry
and is coordinated with two pyridine nitrogen donor atoms of
the DPA moiety and two CC double bonds of COD in a cis,cis
fashion. To accommodate this geometry, the dihedral angles
between the two pyridine rings within one DPA moiety are
58.44 and 67.92°, respectively. The two phenylethynyl linkers
deviate slightly from a linear geometry and bend away from
each other, creating a very large Rh−Rh distance (12.306(4)
Å).
The ground-state geometry of 1 was fully optimized using
the crystal structure as the starting geometry. The diagrams of
the frontier orbitals and their energy levels are shown in Figure
2. No symmetry restraint was imposed on the molecule, and
the optimized structure is slightly unsymmetrical, in contrast to
the symmetrical NMR spectrum, as a result of free rotation in
solution. Consequently, the MOs have slightly uneven
contribution from the two branches of the molecule. As
shown in Figure 2, the main contributor to HOMO-1 (−0.207
82 hartree) is the filled p orbital of the tertiary nitrogen of DPA,
the HOMO (−0.199 29 hartree) has significant contributions
from the p orbital of the tertiary nitrogen of DPA and the π
orbital of anthracene and phenylethynyl moieties, the LUMO
(−0.090 29 hartree) has mainly the π* character of the
anthracene moiety, and the LUMO+1 (−0.065 56 hartree)
shows the π* character of the U-shaped spacer.
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Figure 2. HOMO-1 (top left), HOMO (top right), LUMO (bottom left), and LUMO+1 (bottom right) diagrams of compound 1.
Scheme 2. Synthesis of 2
We next sought to explore the reactivity of ligand 1 toward
metals with other coordination geometries. When 1 was treated
with 2 equiv of ZnCl2 in THF (Scheme 2, top right),
quantitative formation of the new species 2b was observed in
both 1H and 13C NMR spectra. Although the 1H resonances of
2b shifted appreciably compared to those of 1, the 13C
resonances are similar to those of 1. X-ray crystallography
showed that 2b is a dinuclear zinc complex. It crystallized in the
orthorhombic space group Pnna and has a crystallographically
imposed 2-fold symmetry. As shown in Figure 4, each zinc
center adopts a tetrahedral geometry, with two pyridine
nitrogen atoms within one DPA group and two chlorides
occupying the four coordination sites. The dihedral angle
between the two pyridine rings within one DPA is 25.54°,
which is much smaller than those in 2a. There are π−π stacking
interactions between two of the pyridine rings that are close to
the C2 axis with a short contact distance of ∼3.47 Å. The
distance between the two metal centers (7.723 Å) is much
shorter than that in 2a. Interestingly, molecules of 2b stack
along the b axis in the crystal lattice with large 1-D solvent
channels in between (Figure 5). The framework is held
together by the weak intermolecular hydrogen-bonding
interactions between the chlorides and aromatic protons as
well as the weak intermolecular head-to-edge interactions
between the phenyl C−H bonds and the anthracene moiety
next to it. The solvent molecules in the channels were not fully
located, which, however, appeared to be unimportant, since the
same framework can be obtained by crystallizing 2b in different
solvents such as DCM and THF/CH3CN (see 2b′ in the
Supporting Information). The persistence of this framework
with extraordinarily large channels opens up a possibility of
utilizing this material for sensing applications and size-selective
catalysis.
To shorten the distance between the two Zn(II) centers, we
sought bridging anionic ligands to tie the two metal centers
together. Inspired by the Zn(II)-containing phosphotriesterase
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zinc center adopts an octahedral geometry, with four pyridine
nitrogen atoms occupying four coordination sites and two
triflate ligands occupying the remaining two in a cis fashion.
The dihedral angle between the two pyridine rings of the same
DPA moiety is 41.54°, much larger than that in 2b. The
distance between the two amino nitrogen atoms is 4.474(5) Å,
drastically shorter than that in 2a (8.190(5) Å) or 2b (6.501(4)
Å), demonstrating the flexibility of the U-shaped linker group.
In fact, the distance between the two amino nitrogen atoms in
2c is even shorter than that in the free ligand 1 (5.020(3) Å):
i.e., the two branches of the U-shaped linker are bending inward
in 2c, in contrast to the outward bending conformation in 2a,b.
Alternatively, 2c can be synthesized by treating 1 with 1 equiv
1
of Zn(OTf)2. Interestingly, the H NMR spectrum of the 1:2
mixture of 1 and Zn(OTf)2 is identical with that of 2c and no
further change was observed with addition of an excess amount
of Zn(OTf)2. Even the slow addition of ligand 1 solution into a
Zn(OTf)2 solution only produced 2c without forming any
dinuclear metal complexes, in contrast to the literature
examples of triflate-bridged dizinc complexes.41,42
Photophysical Properties. The UV−vis spectra of 1 in
various solvents show similar shapes: two intense absorption
bands in the UV region at 250−280 and 280−370 nm and a
weaker vibrational progression band in the region of 370−450
nm (Figure 7). The band at 280−370 nm could be assigned to
π−π* and n−-π* electronic transitions of the phenylalkynyl
and dipyridylamine groups.43 The bands at 250−280 and 370−
450 nm are characteristic for the anthracene moiety.44 In
methanol, while the characteristic anthracene bands remain in
place, the band at 280−370 nm split into a peak at 282 nm and
a shoulder at 310 nm. Such a split could be attributed to the
stabilization of the tertiary nitrogen lone pair through hydrogen
bonding with MeOH, which shifts the n−π* band to the higher
energy region. On irradiation with UV light, 1 emits bright blue
light in solution with a quantum efficiency of 0.65 relative to
9,10-diphenylanthracene. While the lowest energy absorption
band of 1 in various solvents shifts from short to long
wavelength according to the sequence MeOH < CH3CN <
THF < DCM ≈ DMF < DMSO, the emission band of 1 in
these solvents shifts from short to long wavelength according to
the slightly different sequence MeOH < DCM ≈ THF <
CH3CN ≈ DMF < DMSO (note the position change of
CH3CN in the series). This difference is not yet fully
understood. The emission band shift of 1 appears to
correspond to the polarity of the solvent: i.e. a red shift with
increasing solvent polarity in aprotic solvents (Figure 8),
indicating a polarized excited state.45,46 In methanol, the
emission band of 1 exhibits a blue shift compared to those in
dichloromethane and THF, which are less polar than
methanol.47 This shift is presumably due to the stabilization
of the tertiary amine nitrogen lone pairs, a contributor of the
HOMOs, through hydrogen-bonding interactions with the
solvent molecules.48 While 2a does not exhibit noticeable
emission in solution, the emission spectrum of 2b in DCM is
very similar to that of 1 in the same solvent (Figure 9). The
emission spectrum of 2c in DCM features two maxima at 430
and 457 nm, similar to that of 1 in hexanes. Compounds 2b,c in
DCM show photoluminescence quantum efficiencies of 0.57
and 0.54 (relative to 9,10-diphenylanthracene), respectively,
lower than that of the free ligand 1.
Figure 3. Molecular structure of 2a with thermal ellipsoids plotted at
the 50% probability level. All hydrogen atoms and BF4 counterions
are omitted for clarity.
−
Figure 4. Molecular structure of 2b with thermal ellipsoids plotted at
the 50% probability level. All hydrogen atoms are omitted for clarity.
whose active site comprises two Zn2+ ions bridged by
carboxylate ligands with a short metal−metal distance, we
tried to introduce acetates and triflates into the construction of
1
dizinc complexes. H and 13C NMR spectra of the 1:2 mixture
of 1 and Zn(OAc)2 are very similar to those of the free ligand,
suggesting that 1 does not bind to Zn(OAc)2 very well.
Attempts to crystallize the reaction mixture of 1 and Zn(OAc)2
always resulted in the isolation of free ligand 1. However, when
1 was treated with 2 equiv of Zn(OTf)2, significant chemical
1
shift changes were observed in both the H and 13C NMR
spectra in comparison to those of the free ligand. Recrystalliza-
tion of the reaction mixture yielded pale yellow crystals which
are suitable for X-ray crystallographic analyses. Instead of a
dizinc complex, the mononuclear zinc complex 2c was
obtained, despite the fact that 2 equiv of Zn(OTf)2 was used
(Scheme 2, bottom right). As shown in Figure 6, the molecule
2c has a crystallographically imposed C2 symmetry and each
Electroluminescent Properties of 1. The bright blue
luminescence of 1 in the solid state prompted us to explore its
electroluminescent properties. We fabricated OLEDs using 1 as
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Figure 5. Space-filling model showing channels in the lattice of 2b along the b axis. All solvents are removed for clarity.
Figure 6. Molecular structure of 2c with thermal ellipsoids plotted at the 50% probability level. All hydrogen atoms are omitted for clarity.
Figure 7. Absorption spectra of compound 1 in various solvents (∼10−5 M).
emitter with the device structure shown schematically in Figure
10, where 4,4′-bis(carbazol-9-yl)biphenyl (CBP) and 2,2′,2″-
(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole) (TPBi)
are selected as the hole transport layer (HTL) and electron
transport layer (ETL), respectively. The emitter is either a neat
film of 1 or 1 doped in different host molecules: i.e., N,N′-
diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (α-
NPD), CBP, and TPBi. It has been demonstrated that CBP
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Figure 8. Emission spectra of compound 1 in various solvents (∼10−5 M) using 400 nm excitation wavelength.
Figure 9. Emission spectra of compounds 2b,c in dichloromethane (∼10−5 M) using 400 nm excitation wavelength.
and TPBi can reduce the accumulation of carriers at different
organic/organic interfaces (such as the HTL/emission layer
(EML) and EML/ETL) and thus enhance the device
performance.49−51 The OLED device performances of 1
doped in different hosts with 1 wt % doping concentration as
well as a neat film of 1 as EML (indicated as neat film) are
summarized in Figure 11. Figure 11a shows the EL spectrum of
different devices and the PL spectrum of 1 in the solid state.
The emission band of the PL spectrum has a maximum at 478
nm, while the emission bands of EL spectra depend on the host
molecules. When TPBi is used as the host in the EML, there is
also a shoulder at 399 nm in the EL spectrum as a result of the
emission from TPBi (see the PL spectrum of TPBi from Figure
11f).
The benefit of using a guest−host system is that the charge
transport can be separated from the emission process.52 Figure
11f shows the solid-state PL spectrum of different hosts in
comparison with the absorption spectrum of 1 that is shown in
Figure 3. The considerable overlap of the PL emission
spectrum of CBP and TPBi with the absorption spectrum of
1 suggests effective Forster and/or Dexter energy transfer from
̈
the host to the dopant: e.g., from the singlet level of TPBi to
the single level of 1. The greatly decreased overlap of the PL
spectrum of α-NPD with the absorption spectrum of 1 is in
good agreement with the lower efficiency of the α-NPD device:
i.e., the energy transfer between the α-NPD and 1 is not as
effective. Although the PL spectra of TPBi and CBP have a
similar overlap with the absorption spectrum of 1, both the
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Figure 10. (a) Schematic diagram of the trilayer OLED structure with the emission zone (neat 1, 1 doped with CBP, or 1 doped with TPBi)
sandwiched between CBP and TPBi. (b) Structures of α-NPD, CBP, and TPBi.
current efficiency and external quantum efficiency (EQE) of the
TPBi device are higher than those of the CBP device over a
broad range of luminance (Figure 11b,c). This may be
attributed to the difference of the electrical properties (i.e.,
mobility and energy level alignment at organic/organic
interface) between the 1-doped TPBi and 1-doped CBP,
which can be seen from the significantly lower turn-on voltage
(>10 V at 10 mA/cm2) of the TPBi device in comparison to
that of the CBP device (see Figure 11d,e).
As mentioned above, in the TPBi device emission from TPBi
was observed, which indicates that there is some loss of exciton
in the device with a TPBi host due to the leakage current. To
reduce the leakage current and the emission from TPBi, we also
fabricated devices with higher doping concentrations of 1 into
TPBi, i.e., 5 and 10 wt %. The current efficiency, power
efficiency, EQE, and EL spectra of the devices with different
doping concentrations are shown in Figure 12. Among the
three doping concentrations, a higher doping concentration
gives higher current efficiency, reaching ∼7 cd/A at 1 cd/m2.
However, there is no significant improvement in the EQE when
the doping concentration is increased from 5% to 10%. The
highest EQE at 1000 cd/m2 (i.e., ∼1.5%), a typical brightness
for display applications, was achieved with 5% doping and the
corresponding current efficiency and power efficiency were 2.2
cd/A and 1.2 lm/W, respectively. The peak EQE value of this
device was as high as ∼4.0% at low luminance (1 cd/m2), which
is among the highest EQE values for fluorescent blue OLEDs
reported in the literature.53 Also, as the doping concentration
increases, less emission from TPBi can be observed. The shape
of the EL spectrum at higher doping concentration is similar to
that of the PL spectrum of 1.
at low luminance. Such a current efficiency is much higher than
those of known OLEDs with DPA-derivative-based emitters in
the literature.33,36 The external quantum efficiency of our
device is among the best of the blue fluorescent OLEDs
reported in the literature.
EXPERIMENTAL SECTION
■
General Considerations. All preparations and manipulations
were performed under nitrogen using standard Schlenk techniques or
in a nitrogen atmosphere glovebox from MBraun. Unless otherwise
stated, all reagents were purchased from commercial sources and used
without further purification. 1,8-Dibromoanthracene,54 (4-(2,2′-
dipyridylamino)phenyl)acetylene,55 and [Rh(COD)(CH3CN)2]BF4
56
were synthesized according to literature procedures. 1H, 13C{1H}, and
19F spectra were recorded on a Varian 400 or a Bruker Avance 400
spectrometer. Chemical shifts were referenced relative to the solvent’s
residual signals but are reported relative to Me4Si. The UV−vis spectra
were measured using an Agilent 8453 UV−visible spectrophotometer.
The solution photoluminescence (PL) spectra were measured using a
JY HORIBA Fluorolog-3 spectrofluorometer or a Perkin-Elmer LS-
50B luminescence spectrophotometer, while the solid-state PL spectra
were measured using a Perkin-Elmer LS55 fluorescence spectrometer.
Elemental analyses were performed on a PE 2400 C/H/N/S analyzer
at the Analest of our Chemistry Department.
Synthesis of 1,8-Bis[4-(2, 2′-dipyridylamino)-
phenylacetylenyl]anthracene (1). To a mixture of (4-(2,2′-
dipyridylamino)phenyl)acetylene (466 mg, 1.69 mmol), 1,8-dibro-
moanthracene (264 mg, 0.787 mmol), Pd(PPh3)4 (91 mg, 0.08
mmol), and CuI (15 mg, 0.08 mmol), was added 20 mL of degassed
Et3N. The mixture was then refluxed for 24 h. The resulting yellow
suspension was cooled to ambient temperature, and the solvent was
removed under reduced pressure. The residue was subjected to silica
gel column chromatography using THF/hexanes (1/1 volume ratio)
as eluent to yield the product as a yellow powder (71% yield).
Alternative method: to a mixture of 4-(2,2′-dipyridylamino)phenyl
bromide (639 mg, 1.96 mmol), 1,8-dibromoanthracene (264 mg,
0.787 mmol), Pd(PPh3)4 (91 mg, 0.08 mmol), and CuI (15 mg, 0.08
mmol) was added a mixture of degassed Et3N (20 mL) and
Me3SiCCH (0.28 mL, 1.96 mmol). The resulting mixture was then
refluxed for 48 h. The workup procedure was the same as above (20%
CONCLUSION
■
In conclusion, a novel U-shaped multidentate ligand has been
designed and synthesized. Due to the flexibility of the ligand,
this ligand can act either as a double-bidentate ligand, bringing
two metals in close proximity, or as a tetradentate ligand,
coordinating to one metal via four nitrogen donor atoms.
Compound 1 and its zinc complexes 2b,c display bright blue
luminescence with high PL quantum efficiencies. The
application of 1 as a blue emitter in OLED with current
efficiency as high as 7 cd/A has been successfully demonstrated
1
yield). H NMR (CDCl3, 400 MHz, 25 °C): δ 9.60 (s, 1H), 8.47 (s,
1H), 8.26 (d, J = 4.0 Hz, 4H), 8.02 (d, J = 4.0 Hz, 2H), 7.81 (d, J = 8.0
Hz, 2H), 7.63 (d, J = 4.0 Hz, 4H), 7.50−7.46 (m, 6H), 7.04 (d, J = 8.0
Hz, 4H), 6.91 (d, J = 12.0 Hz, 4H), 6.88 (dd, J = 8.0 Hz, J = 4.0 Hz,
4H). 13C{1H} NMR (CDCl3, 100 MHz, 25 °C): δ 171.0, 157.6, 148.5,
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Figure 11. (a) Normalized EL spectra, (b) current efficiency as a function of luminance, (c) current−voltage characteristics (IV), and (d)
luminance−voltage characteristics (LV) of OLED devices with 1 in different hosts as EML. The performance of pure 1 film as the EML is also shown
and indicated as the neat film. (f) Solid-state PL spectra of different hosts in comparison with the absorption spectrum of 1 that is shown in Figure 3.
145.0, 137.6, 133.1, 131.6, 131.4, 130.7, 128.8, 126.7, 125.2, 124.1,
121.7, 120.1, 118.5, 117.1, 94.77, 87.94. Anal. Calcd for
C50H32N6·1/3CHCl3: C, 79.68; H, 4.62; N, 11.07. Found: C, 79.90;
H, 4.31; N, 11.11.
94.20, 88.18, 85.43 (d, JRh−C = 123 Hz), 30.05 (two carbon atoms of
the anthracene moieties were not observed due to poor solubility of
the sample). Anal. Calcd for C66H56B2F8N6Rh2·1/4CH2Cl2: C, 59.20;
H, 4.88; N, 6.46. Found: C, 59.62; H, 4.27; N, 6.30.
Synthesis of [Rh2(1)(COD)2](BF4)2 (2a). A mixture of 1 (7.2 mg,
0.01 mmol) and [Rh(COD)(CH3CN)2]BF4 (7.6 mg, 0.02 mmol) was
dissolved in 4 mL of CH2Cl2, and the solution was stirred for 2 h. The
solvent was removed in vacuo, and the residue was recrytallized in
dichloromethane/hexanes to yield the product as a pale yellow
Synthesis of Zn2(1)Cl4 (2b). To a mixture of 1 (71.7 mg, 0.1
mmol) and ZnCl2 (27.3 mg, 0.2 mmol) was added 5 mL of Et2O, and
the suspension was stirred overnight at ambient temperature. The
product was collected by vacuum filtration and dried in vacuo (95%
1
yield). H NMR (CDCl3, 400 MHz, 25 °C): δ 9.61 (s, 1H), 8.48 (s,
1
crystalline solid (90% yield). H NMR (CD2Cl2, 400 MHz, 25 °C): δ
1H), 8.26 (d, J = 4.0 Hz, 4H), 8.02 (d, J = 4.0 Hz, 2H), 7.81 (d, J = 4.0
Hz, 2H), 7.63 (d, J = 4.0 Hz, 4H), 7.47−7.26 (m, 6H), 7.04 (d, J = 8.0
Hz, 4H), 6.98 (br, 2H), 6.94 (d, J = 8.0 Hz, 2H), 6.89−6.86 (m, 4H).
13C{1H} NMR (CDCl3, 100 MHz, 25 °C): δ 157.7, 148.6, 145.1,
137.6, 133.1, 131.6, 131.4, 130.8, 128.9, 127.6, 126.6, 125.2, 124.1,
121.6, 120.0, 118.6, 117.2, 94.84, 87.99. Anal. Calcd for
9.44 (s, 1H), 8.47 (s, 1H), 8.38 (d, J = 4.0 Hz, 4H), 8.13−8.09 (m,
4H), 8.00 (d, J = 8.8 Hz, 2H), 7.81−7.78 (m, 6H), 7.67 (d, J = 6.8 Hz,
4H), 7.56−7.52 (m, 4H), 7.47−7.43 (m, 2H), 6.69 (d, J = 8.8 Hz,
4H), 3.99 (br, 8H), 2.10 (br, 8H), 1.77−1.72 (m, 8H). 13C{1H} NMR
(CD2Cl2, 100 MHz, 25 °C): δ 151.1, 146.4, 142.5, 133.4, 131.5,
130.93, 129.1, 127.8, 126.8, 125.9, 125.3, 123.4, 121.2, 117.6, 115.3,
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for 2 h at ambient temperature. The solvent was then removed in
vacuo, and the residue was recrytallized in dichloromethane/hexanes
to afford the product as an orange-yellow crystalline solid (85% yield).
1H NMR (CDCl3 + CD3OD, 400 MHz, 25 °C): δ 9.54 (s, 1H), 8.50
(s, 1H), 8.23 (d, J = 4.0 Hz, 4H), 8.05 (d, J = 4.0 Hz, 2H), 7.81 (dd, J
= 6.8 Hz, J = 0.8 Hz, 2H), 7.65−7.63 (m, 8H), 7.49 (dd, J = 8.4 Hz, J =
6.8 Hz, 2H), 7.05−6.95 (m, 12H). 13C{1H} NMR (CDCl3 + CD3OD,
100 MHz, 25 °C): δ 158.7, 147.5, 143.7, 138.7, 132.9, 131.2, 131.0,
130.6, 128.8, 127.4, 125.8, 124.9, 124.7, 120.8, 120.4, 119.9 (q, JC−F
=
316 Hz), 119.2, 117.6, 93.87, 88.02. Anal. Calcd for
C50H32F6N6O6S2Zn·CH2Cl2: C, 54.66; H, 2.86; N, 7.22. Found: C,
54.64; H, 3.24; N, 7.16.
X-ray Diffraction Analyses. X-ray-quality crystals of 1 were
obtained by top-layering a chloroform solution of 1 with hexanes,
those of 2a were obtained from a THF/DCM solution of 2a, those of
2b were obtained by vapor diffusion of pentane into a CH2Cl2 solution
of 2b, those of 2b′ were obtained from a THF/CH3CN solution of 2b,
and those of 2c were obtained by top-layering a DCM solution of 2c
with hexanes. All crystals were mounted on the tip of a MiTeGen
MicroMount, and the single-crystal X-ray diffraction data were
collected on a Bruker Kappa Apex II diffractometer. All data were
collected with graphite-monochromated Mo Kα radiation (λ = 0.710
73 Å) at 150 K controlled by an Oxford Cryostream 700 series low-
temperature system. The diffraction data were processed with the
Bruker Apex 2 software package.57 All structures were solved by direct
methods and refined using SHELXTL V7.00.58 Compound 1
crystallized in the monoclinic space group P21/c with one molecule
per asymmetric unit. 2a crystallized in the triclinic space group P1 with
̅
one molecule per asymmetric unit. 2b crystallized in the orthorhombic
space group Pnna with half a molecule per asymmetric unit. 2c
crystallized in the monoclinic space group C2/c with half a molecule
per asymmetric unit. Half a molecule of disordered dichloromethane
was located in the crystal lattice of 2b. The residual diffuse electron
density of disordered and unidentified solvent molecules in the lattices
of 2a,b,b′,c were removed with the SQUEEZE function of PLATON,59
and their contributions were not included in the formula. Elemental
analysis of 2a suggested that the removed electron densities may
originate from THF molecules. All non-hydrogen atoms were refined
anisotropically, except for the disordered portions. In all structures
hydrogen atoms bonded to carbon atoms were included in calculated
positions and treated as riding atoms. The crystallographic data are
summarized in Table 1, while selected bond lengths and angles are
given in Table 2.
Figure 12. Current efficiency and power efficiency (top) and EQE of
OLED devices with different doping concentrations of 1 in TPBi as
EML (bottom). The inset gives the corresponding normalized EL
spectra.
C50H32N6Zn2Cl4·2/3CH2Cl2: C, 58.18; H, 3.21; N, 8.03. Found: C,
58.66; H, 2.68, N, 7.46.
Synthesis of Zn(1)(OTf)2 (2c). To a solution of 1 (21.5 mg, 0.03
mmol, in 3 mL of CH2Cl2) was added a solution of Zn(OTf)2 (11.2
mg, 0.03 mmol, in 5 mL of CH3OH). The mixed solution was stirred
Table 1. Crystallographic Data
1
2a
2b·1/2CH2Cl2
2c
formula
fw
C50H32N6
716.82
150(2)
P21/c
C67H58B2Cl2F8N6Rh2
1397.53
C50.5H33Cl5N6Zn2
C52H32F6N6O6S2Zn
1031.82
1080.33
T (K)
space group
a (Å)
150(2)
150(2)
150(2)
P1
̅
Pnna
C2/c
20.3101(9)
9.0336(3)
20.0894(9)
90
10.3248(5)
18.4630(10)
14.6487(4)
b (Å)
18.3669(9)
9.1420(5)
19.4576(6)
c (Å)
19.8936(11)
35.166(2)
16.5977(6)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
109.469(2)
90
90
99.057(2)
90
100.819(2)
90
108.5820(10)
102.057(2)
90
90
3639.9(3)
4
3340.1(3)
5935.6(6)
4484.2(2)
2
4
4
Dc (g cm−3
μ (mm−1
)
1.308
1.390
1.155
1.600
)
0.078
0.640
1.067
0.728
no. of rflns collcd
no. of indep rflns
GOF on F2
30 520
8292
55 337
27 067
20 002
15 138
6732
5151
0.958
1.028
0.947
1.052
R (I > 2σ(I))
R (all data)
R1 = 0.0593, wR2 = 0.1087
R1 = 0.1592, wR2 = 0.1389
R1 = 0.0504, wR2 = 0.1147
R1 = 0.0848, wR2 = 0.1246
R1 = 0.0673, wR2 = 0.1528
R1 = 0.1431, wR2 = 0.1767
R1 = 0.0512, wR2 = 0.1336
R1 = 0.0751, wR2 = 0.1472
7047
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Inorganic Chemistry
Article
of 15 Ω/□ was commercially patterned on a glass substrate with a
thickness of 1.1 mm. The ITO glass substrates were treated with a
standard process: i.e., ultrasonic cleaning in Alconox, acetone, and
methanol for 15 min, respectively, followed by a 15 min UV ozone
treatment. After the UV ozone process, substrates were quickly loaded
into the vacuum. MoO3, CBP, EML, CBP, TPBi, LiF, and Al were
sequentially deposited in different chambers without breaking the
vacuum, where the EML is the emission layer that is a neat film of
either 1 or 1 doped into different host molecules, i.e., α-NPD, CBP,
and TPBi. The active area of all the devices was hence 2 mm.28
Current−voltage (IV) characteristics were measured using an
HP4140B pA meter. Luminance measurements were measured by a
Minolta LS-110 luminance meter. EL spectra were measured by a USB
2000 miniature fiber optic spectrometer. All the measurements were
conducted in ambient air. The EQE and power efficiency are
calculated assuming a Lambertian emission pattern.
Table 2. Selected Bond Lengths (Å) and Angles (deg)
Ligand 1
C(1)−C(15)−C(16)
C(15)−C(16)−C(17)
178.3(2)
177.5(2)
C(34)−C(33)−C(11)
C(33)−C(34)−C(35)
176.3(2)
178.9(3)
Complex 2a
Rh(1)−N(2)
Rh(1)−N(3)
Rh(1)−C(51)
N(3)−Rh(1)−C(52)
N(3)−Rh(1)−N(2)
2.111(3)
2.105(3)
2.153(4)
Rh(1)−C(52)
Rh(1)−C(55)
Rh(1)−C(56)
2.109(4)
2.126(4)
2.120(4)
95.02(13)
37.82(16)
90.80(13) N(3)−Rh(1)−C(51)
84.87(10) C(52)−Rh(1)−
C(51)
C(52)−Rh(1)−N(2)
N(3)−Rh(1)−C(56)
152.41(15) N(2)−Rh(1)−C(51)
169.69(14)
80.34(16)
161.2(2)
C(56)−Rh(1)−
C(51)
C(52)−Rh(1)−
96.28(17) C(55)−Rh(1)−
90.08(16)
C(56)
C(51)
ASSOCIATED CONTENT
* Supporting Information
CIF files giving crystallographic data for 1 and 2a−c and figures
and tables giving the crystal structure of 2b′, details of the DFT
calculations, the input structure of 1 in Z matrix for geometry
optimization, and the atomic coordinates of optimized 1 in
Cartesian coordinates. This material is available free of charge
via the Internet at http://pubs.acs.org.
■
N(2)−Rh(1)−C(56)
N(3)−Rh(1)−C(55)
96.45(14) C(16)−C(15)−C(1)
175.8(4)
174.6(4)
S
161.32(19) C(15)−C(16)−
C(17)
C(52)−Rh(1)−
82.24(16) C(34)−C(33)−
174.7(4)
176.1(4)
C(55)
C(11)
N(2)−Rh(1)−C(55)
93.28(14) C(33)−C(34)−
C(35)
C(56)−Rh(1)−
37.5(2)
C(55)
Complex 2b
AUTHOR INFORMATION
Corresponding Author
*E-mail: dsong@chem.utoronto.ca.
Notes
■
Zn(1)−N(2)
Zn(1)−N(3)
N(2)−Zn(1)−N(3)
N(2)−Zn(1)−Cl(1)
N(3)−Zn(1)−Cl(1)
N(2)−Zn(1)−Cl(2)
2.009(4)
Zn(1)−Cl(1)
2.2108(13)
2.2141(13)
112.29(11)
114.40(5)
177.2(6)
2.014(4)
Zn(1)−Cl(2)
89.12(15)
113.52(11)
111.54(11)
113.42(11)
N(3)−Zn(1)−Cl(2)
Cl(1)−Zn(1)−Cl(2)
C(10)−C(9)−C(1)
The authors declare no competing financial interest.
C(9)−C(10)−C(11)
174.6(6)
a
ACKNOWLEDGMENTS
Complex 2c
■
Zn(1)−N(1)
Zn(1)−N(1)#1
Zn(1)−O(3)
2.112(2)
2.112(2)
2.136(2)
Zn(1)−O(3)#1
Zn(1)−N(2)#1
Zn(1)−N(2)
2.136(2)
2.140(3)
2.140(3)
89.81(10)
This research was supported by grants to D.S. and Z.-H.L. from
the Natural Science and Engineering Research Council
(NSERC) of Canada, the Canadian Foundation for Innovation,
the Ontario Research Fund, and the ERA program of Ontario.
R.T. is grateful for a postgraduate scholarship from the OGS
program of Ontario. D.J.K. is grateful for financial support from
the NSERC USRA program.
N(1)−Zn(1)−N(1)
98.62(14) O(3)#1−Zn(1)−
N(2)#1
87.39(10) N(1)−Zn(1)−N(2)
#1
N(1)−Zn(1)−O(3)
95.24(10)
83.72(10)
N(1)#1−Zn(1)−
171.53(10) N(1)#1−Zn(1)−
O(3)
N(2)
N(1)−Zn(1)−O(3)
#1
N(1)#1−Zn(1)−
O(3)#1
O(3)−Zn(1)−O(3)
#1
N(1)−Zn(1)−N(2)
#1
171.53(10) O(3)−Zn(1)−N(2)
89.81(10)
91.34(10)
178.41(14)
175.6(3)
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