Phosphorescent cuprous complexes with N,O ligands - Synthesis, photoluminescence, and electroluminescence

Article abstract of DOI:10.1002/ejic.201000377

Six heteroleptic cuprous complexes, [L¹Cu(PPh₃) ₂](BF₄) (1a), [L¹Cu(DPEphos)](BF₄) (1b), [L²Cu(PPh₃)₂](BF₄) (2a), [L²Cu-(DPEphos)](BF<

Full text of DOI:10.1002/ejic.201000377

FULL PAPER
DOI: 10.1002/ejic.201000377
Phosphorescent Cuprous Complexes with N,O Ligands – Synthesis,
Photoluminescence, and Electroluminescence
Wei Sun,[a,b] Qisheng Zhang,[c] Li Qin,[b,c] Yanxiang Cheng,*[a] Zhiyuan Xie,[a]
Canzhong Lu,*[c] and Lixiang Wang[a]
Keywords: Copper / N,O ligands / Phosphane ligands / Phosphorescence / Electroluminescence
Six heteroleptic cuprous complexes, [L1Cu(PPh3)2](BF4) (1a),
[L1Cu(DPEphos)](BF4) (1b), [L2Cu(PPh3)2](BF4) (2a), [L2Cu-
(DPEphos)](BF4) (2b), [L3Cu(PPh3)2](BF4) (3a), and [L3Cu-
(DPEphos)](BF4) (3b) {L1 = diphenyl(2-pyridyl)phosphane ox-
ide, L2 = diphenyl(8-quinolyl)phosphane oxide, L3 = di-
phenyl(2-pyridylmethyl)phosphane oxide, DPEphos = bis[2-
(diphenylphosphanyl)phenyl] ether}, were prepared and
fully characterized. The electronic absorption spectra and
quantum chemical calculations indicate that the lowest ex-
cited states of these complexes can be assigned to the metal-
to-ligand charge transfer (MLCT) transition. In poly(methyl
methacrylate) (PMMA) films, these complexes exhibit blue-
green to orange emissions with long lifetimes ranging from
7.5 to 28.6 µs. With wide energy-band gaps of 3.50 and
3.28 eV, complexes 3a and 3b emit efficiently in 20 wt.-%
PMMA films with photoluminescence quantum efficiencies
of 0.69 and 0.72, and emission maxima at 477 nm and
495 nm, respectively. Electroluminescent devices were fabri-
cated with these N,O-based CuI complexes as emitters. The
best device performance, with a peak current efficiency of
4.9 cd/A, was obtained for 3b.
and co-workers reported the first example of a highly emis-
sive mononuclear cuprous complex, [Cu(dbp)(DPEphos)]+
(dbp = 2,9-di-n-butyl-1,10-phenanthroline), with an impres-
sive quantum efficiency of 0.16[6] (0.26[3d]) in CH2Cl2 solu-
tion and 0.69[3a] in an PMMA film. Recently, a series of
CuI complexes combining two bis(phosphane) ligands
([Cu(P,P)2]+) was also found to exhibit strong emission
bands in both solid state and organic light-emitting diodes
(OLEDs).[7]
Over the past few years, increasing attention has also
been paid to luminescent CuI complexes based on asym-
metric N,P ligands. These complexes display some unexpec-
ted properties perhaps due to the asymmetric electronic
character of their ligands. Recently, Peter et al. reported
several dinuclear and mononuclear CuI complexes sup-
ported by [P,N,P]– {bis[2-(diisobutylphosphanyl)phenyl]-
amide}[8] and [P,N]– (amidophosphane) ligands[9] with un-
usually high quantum efficiencies, in the range of 0.16–0.70,
in solution. More recently, our group and Tsukuda et al.
reported a series of phosphorescent homo- and heteroleptic
CuI complexes with asymmetric N,P ligands of 8-(diphenyl-
phosphanyl)quinoline (dppq) and 2-methyl-8-(diphenyl-
phosphanyl)quinoline.[10,11] The CuI complexes based on
these iminophosphane ligands exhibit higher electro- and
photochemical stability than those based on traditional di-
imine or diphosphane ligands.[11]
Introduction
Extensive efforts have been focused on N-heterocyclic
CuI complexes for replacing phosphorescent transition
metal complexes based on ruthenium or other noble metal
ions in chemical sensors,[1] probes of biological systems,[2]
and energy-conversion devices[3] due to their advantages
such as having abundant resources, low cost, and nontoxic
properties. However, these tetrahedral cuprous complexes
always undergo a significant geometry change going from
the ground to excited state corresponding to a change from
d10 to d9 as a result of MLCT transitions. The distortion of
the excited state narrows the energy gap and increases the
nonradiative decay of these CuI complexes.[4] Compared to
classical [Cu(N,N)2]+ systems, mixed-ligand systems involv-
ing bulky phosphanes ([Cu(N,N)(P,P)]+) exhibit improved
emission properties, because the bulky and strong π-acidic
phosphane ligands will sterically inhibit the excited-state
distortion as well as enhance the energy level of the excited
states by stabilizing of the CuI species.[5] In 2002, McMillin
[a] State Key Laboratory of Polymer Physics and Chemistry,
Changchun Institute of Applied Chemistry, Chinese Academy
of Sciences,
Changchun 130022, P. R. China
E-mail: yanxiang@ciac.jl.cn
czlu@fjirsm.ac.cn
[b] The Graduate School, Chinese Academy of Sciences,
Beijing 100039, P. R. China
In the course of our studies on cuprous complexes with
N,P ligands, we isolated an unexpected phosphorescent
complex containing the oxidized N,P ligand, diphenyl(2-
pyridyl)phosphane oxide. To the best of our knowledge, cu-
View this journal online at
[c] State Key Laboratory of Structural Chemistry, Fujian Institute
of Research on the Structure of Matter, Chinese Academy of
Sciences,
Fuzhou 350002, P. R. China
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W. Sun, Q. Zhang, L. Qin, Y. Cheng, Z. Xie, C. Lu, L. Wang
FULL PAPER
prous complexes containing phosphane oxide coordinating region for 3a and 3b indicate a higher electron density rela-
ligands are few, and their luminescent properties have never tive to 1a and 1b, which is attributed to the introduction of
been reported.[12] The unexpected finding motivated us to an electron-donating methylene unit.
systematically explore the effects of the electronic character
In the course of our studies on cuprous complexes with
of the ligands on the photophysical properties of cuprous N,P ligands, we noticed that significant ligand exchange or
complexes. Herein, we report the synthesis of phosphores- redistribution reactions sometimes occur. For instance, the
cent cuprous complexes containing phosphane oxide coor- homoleptic species [Cu(dppq)2](BF4) has been observed in
dinating ligands, and the applications of these complexes in CDCl3 solution alongside [Cu(dppq)(PPh3)2](BF4) in a ra-
1
OLEDs.
tio of 0.07:1, according to H NMR spectra. However, sig-
nals for the homoleptic species have not been found in the
1H NMR spectra of these N,O-based complexes probably
due to their less crowded coordination environment.
Results and Discussion
Synthesis and Characterization
Description of the Structures
We synthesized six mixed-ligand CuI complexes of the
type [Cu(N,O)(P,P)](BF4), where N,O is diphenyl(2-pyr-
The X-ray crystal structures of all N,O complexes have
idyl)phosphane oxide (L1), diphenyl(8-quinolyl)phosphane been determined. Selected bond lengths and angles are
oxide (L2) or diphenyl(2-pyridylmethyl)phosphane oxide listed in Table 1, and views of the structures of the com-
(L3), and P,P is DPEphos or a pair of PPh3 ligands. The plexes showing the atom numbering appear in Figures 1, 2,
structures of the complexes are shown in Scheme 1. Com- 3, 4, 5, and 6.
plex 1a was first obtained as a byproduct when we at-
The central copper atoms in all of the complexes are sur-
tempted to prepare the N,P CuI complex. In the following rounded by one O and one N atom from the N,O ligands
studies, all complexes were directly synthesized from the ox- and two P atoms from phosphane ligands in a distorted
idized N,P ligands (N,O), in which ligand L2 was easily syn- tetrahedral geometry. The metallacycles consisting of the
thesized by the reaction of 8-(diphenylphosphanyl)quin- Cu, O, N, P, and one or two C atoms of the N,O ligands
oline with excess H2O2 in tetrahydrofuran (thf) at room are found in either a half-chair or a boat conformation. The
temperature. The mixed-ligand complexes were obtained former is found in complexs 1a and 1b where the O atoms
from two displacement reactions of [Cu(CH3CN)4](BF4). are out of the Cu–N–C–P near-plane. The latter conforma-
Crystals of the complexes were obtained through slow con- tion is seen in 2a and 2b, where the N and P atoms are out
centration and diffusion of solvents in moderate yields of the Cu–O–C–C near-plane, and in 3a and 3b, where the
ranging from 47.2 to 86.6%, and characterized by 1H Cu and sp3 C atoms are out of the O–P–N–C(sp2) plane.[13]
NMR, 31P NMR spectroscopy, and elemental analysis.
There are two independent molecules of 1a in the asym-
Significant upfield shifts are observed for the signal of metric unit of the crystal lattice. The largest deviations from
the α-H atom of the pyridine or quinoline ring in all com- ideal tetrahedral geometry (109.4°) are seen in the N–Cu–O
plexes compared to those of the free ligands in the 1H bond angles [83.98(11)° for 1a and 86.36(9)° for 1b] due to
NMR spectra, implying electron donation from the Cu ion the rigidity of L1. With PPh3 as the auxiliary ligand, 1a has
and the phosphane auxiliary ligands to the N,O ligands. For a larger P–Cu–P bond angle and longer Cu–N and Cu–P
instance, 1a and 1b exhibit signals at δ = 8.44 and 8.27 ppm, bonds than 1b, which has a DPEphos auxiliary ligand, im-
whereas L1 displays a signal at δ = 8.83 ppm. In comparison plying more steric congestion in 1a. Similar changes in the
with [Cu(dppq)(DPEphos)]+,[11] 2b has almost the same sig- P–Cu–P bond angle and the Cu–N and Cu–P bond lengths
nal for the α-H atom, but signals for other protons of the have also been found in other complexes described here and
quinoline ring are shifted downfield due to the lower elec- in [Cu(N,N)(P,P)]+ systems reported previously.[6,14,15] The
tron-donating ability of –OPPh2 to the adjacent quinoline sum of the internal angles of the five-membered metall-
ring than that of –PPh2. Additionally, signals in the upfield acycles of Cu–O–P(1)–C(5)–N and Cu–O–P(1)–C(1)–N are
Scheme 1. Molecular structures of the CuI complexes.
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Phosphorescent Cuprous Complexes with N,O Ligands
Table 1. Selected bond lengths [Å] and angles [°] for 1a, 1b, 2a, 2b, 3a, and 3b.
1a
1b
2a
2b
3a
3b
Cu–N
Cu–O
Cu–P(2)
Cu–P(3)
2.059(3)
2.199(2)
2.044(3)
2.171(2)
2.2120(9)
2.2611(9)
86.36(9)
130.02(8)
109.68(6)
106.92(8)
104.64(6)
113.46(3)
534.98
2.146(3)
2.105(2)
2.2364(9)
2.2906(9)
94.46(9)
116.04(8)
115.16(6)
103.17(7)
95.51(6)
126.39(3)
689.04
2.129(3)
2.117(2)
2.2376(9)
2.2787(9)
97.22(10)
120.17(8)
114.47(7)
103.77(8)
102.59(7)
115.74(3)
686.46
2.113(3)
2.148(2)
2.2734(9)
2.2595(9)
96.98(10)
106.47(8)
104.36(7)
108.07(8)
110.38(7)
126.58(4)
688.83
2.065(2)
2.230(2)
2.2466(7)
2.2657(7)
93.22(8)
116.39(6)
116.50(5)
118.14(6)
94.19(5)
114.22(2)
675.01
2.2621(10)
2.2390(10)
83.98(11)
114.01(8)
99.59(7)
121.34(8)
113.77(7)
116.71(4)
537.07
O–Cu–N
N–Cu–P(2)
O–Cu–P(2)
N–Cu–P(3)
O–Cu–P(3)
P(2)–Cu–P(3)
Σ metallacycle
Figure 1. Crystal structure of the cation of 1a with thermal ellipsoids at 30% probability. Solvent molecules, the anion, and H atoms are
omitted for clarity.
Figure 2. Crystal structure of the cation of 1b with thermal ellip-
Figure 3. Crystal structure of the cation of 2a with thermal ellip-
soids at 30% probability. Solvent molecules, the anion, and H
soids at 30% probability. The anion and H atoms are omitted for
atoms are omitted for clarity.
clarity.
537.07 and 534.98° for 1a and 1b, respectively, which are
slightly smaller than the value for a regular pentagon (540°), than that in the [Cu(dppq)(DPEphos)]+ cation.[11] However,
indicating the near coplanarity of the metallacycles. the average Cu–P bond for 2b (2.258 Å) is 0.017 Å shorter
The Cu–N bond for 2b [2.129(3) Å] is 0.043 Å longer
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Figure 6. Crystal structure of the cation of 3b with thermal ellip-
soids at 30% probability. Solvent molecules, the anion, and H
atoms are omitted for clarity.
Figure 4. Crystal structure of the cation of 2b with thermal ellip-
soids at 30% probability. Solvent molecules, the anion, and H
atoms are omitted for clarity.
closer to the ideal tetrahedral value of 109.4° than that of
1b. Furthermore, cuprous complexes based on L3 show
larger P–Cu–P bond angles and longer bonds than those in
L1-based complexes, suggesting that the coordination
sphere of the central copper atoms is more congested for
the complexes based on L3. For example, the P–Cu–P bond
angle for 3a (126.58°) is 9.87° larger than that in 1a. The
Cu–N bond length in 3a is 2.113(3) Å, which is 0.054 Å
longer than that in 1a, and the average Cu–P bond length
in 3a is 2.267 Å, which is 0.0159 Å longer than that in 1a.
The sums of the internal angles of the Cu–N–C(5)–C(6)–
P(1)–O six-membered metallacycles are 688.83 and 675.01°
for 3a and 3b, respectively, which are markedly different
from the value of a regular hexagon (720°).
Photophysical Properties
The electronic absorption spectra of the CuI complexes
in CH2Cl2 are shown in Figure 7. The intense UV absorp-
tion bands at 256–259 nm for 1a, 1b, 3a, and 3b and 267–
274 nm for 2a and 2b are ascribed to the π-π* absorption
bands of the N,O ligands. In addition to the high-energy
absorption bands, weak, broad, low-energy shoulder bands
are observed at around 355 nm for 1a and 1b, and around
Figure 5. Crystal structure of the cation of 3a with thermal ellip-
soids at 30% probability. Solvent molecules, the anion, and H
atoms are omitted for clarity.
than that in the analogous N,P complex, indicating that the 385 nm for 2a and 2b, in agreement with the yellow color
N,O ligand is sterically less crowded than the corresponding of these four complexes. These low-lying bands are attrib-
N,P ligand. The sum of the internal angles of the metallacy- uted to the MLCT transitions involving the N-heterocyclic
cle Cu–N–C(9)–C(8)–P(1)–O is 689.04 and 686.46° for com- unit and the CuI ion, which are always observed in diimine
plexes 2a and 2b, respectively, indicating significant distor- (N,N) and iminophosphane (N,P) CuI complexes.[3f,6,11]
tion of the six-membered metallacycles.
However, the MLCT band was not detected in the colorless
Complexes based on L3 tend towards ideal tetrahedral complexes 3a and 3b. To rationalize the feature qualita-
geometry compared to the complexes based on L1. For ex- tively, DFT calculations were performed on 3b by using 6-
ample, the N–Cu–O bond angle of 3b (93.22°) is 6.85° 31+G** coupled to the LanL2DZ basis set. As shown in
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Phosphorescent Cuprous Complexes with N,O Ligands
and thus makes it easier to be reduced. The introduction of
the electron-donating methylene group between the pyr-
idine ring and the –OPPh2 group[16] increases the electron
density of the pyridine ring and enhances the energy-band
gaps from 3.06 and 2.93 eV for 1a and 1b to 3.50 and
3.28 eV for 3a and 3b, respectively. According to the DFT
calculations, 3b shows a significantly higher LUMO energy
level (–0.14685 Hartree) and a close HOMO energy level
(–0.28709 Hartree) relative to those of [Cu(NN)(PP)]+ sys-
tems [e.g. the analogous 2-(2Ј-pyridyl)benzimidazolylben-
zene complex[15]].
In degassed CH2Cl2, complexes 3a and 3b emit with
maxima at 556 and 558 nm, respectively, while emission
maxima of 589 and 581 nm are observed for 1a and 1b,
respectively (Table 2). The blueshift of the emission maxima
is associated with the introduction of the electron-donating
methylene unit to the pyridine rings in 3a and 3b. Mean-
while, the quantum efficiencies (φ) and lifetimes (τ) increase
from 0.0005 (1.12 µs) and 0.0005 (1.05 µs) for 1a and 1b to
0.037 (2.15 µs) and 0.023 (1.71 µs) for 3a and 3b, respec-
tively, due to the enlarged energy gap that decreases the
nonradiative rate constant of the CuI complexes (energy-
gap law). In addition, the complexes comprising the PPh3
auxiliary ligand (1a and 3a) have longer lifetimes and higher
quantum efficiencies relative to the complexes with the
DPEphos auxiliary ligand (1b and 3b), which is different to
observations in classical mixed-ligand (phenanthroline)CuI
complexes[6] and consistent with a previous report of bi-
quinoline systems.[3f] Emissions for 2a and 2b in degassed
CH2Cl2 are too weak to be detected, owing to the narrow
energy-band gaps that increase the nonradiative pathways.
The photophysical data in PMMA films with concentra-
Figure 7. UV/Vis spectra of 1–6 in CH2Cl2 (c ≈ 10–5 ); inset: UV/
Vis spectra in the low energy band.
Figure 8, the electron density in the highest occupied molec-
ular orbital (HOMO) is mainly associated with the CuI cen-
ter and the Cu–P σ-bonding orbital, whereas that of the
lowest unoccupied molecular orbital (LUMO) is localized
on the π-antibonding orbital of the pyridine ring. This im-
plies that the lowest excited state of the complex 3b is also
attributed to the MLCT transition. The undetectable
MLCT band for 3b may be obscured by the strong π-π*
absorption band nearby.
The energy-band gaps, estimated by the edge of the ab-
sorption bands, increase in the series [L3Cu(PP)]+
Ͼ
[L1Cu(PP)]+ Ͼ [L2Cu(PP)]+ (Figure 7), relating to the π-
electron-accepting ability of the N-heterocycle on the N,O
ligands. The energy-band gap of 2.56 eV for 2b is narrower
than that of [Cu(dppq)(DPEphos)]+ (2.93 eV),[11] because
the incorporation of the electron-withdrawing –OPPh2 tions of 20 wt.-% are listed in Table 2. In a rigid matrix,
group[16] decreases the electron density of the quinoline ring the CuI complexes showed emission blueshifts of tens of
Figure 8. Calculated electron density of the HOMO (left) and LUMO (right) for 3b.
Table 2. Photophysical performance of the cuprous complexes.
Complex
Solution (in degassed CH2Cl2)
Film (20 wt.-% in PMMA)
λ [nm]
Abs. [nm][a], (lgε)
λ [nm]
τ [µs][b]
Φ [%]
τ [µs][c]
Φ [%]
1a
1b
2a
2b
3a
3b
258 (4.5), 347 (3.2)
256 (4.4), 358 (3.4)
267 (4.5), 375 (2.9)
274 (4.4), 395 (3.0)
259 (4.5)
589
581
1.12
0.05
0.05
521
527
565
573
477
495
8.3
7.5
28.6
14.9
24.6
18.6
11.8
12.7
6.4
6.4
69.3
71.9
1.05
[d]
[d]
556
558
2.15
1.71
3.70
2.26
258 (4.3)
[a] c ≈ 10–5  in CH2Cl2. [b] Fitted by single exponential. [c] Fitted by two exponentials, a pre-exponential weighted average lifetime
(τave) was used and calculated by the equation τave = Σ(Aiτi/ΣAi), where Ai is the pre-exponential for the lifetime τi. [d] Too weak to be
detected.
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W. Sun, Q. Zhang, L. Qin, Y. Cheng, Z. Xie, C. Lu, L. Wang
Contrary to those of [Cu(N,N)(P,P)]+ systems,[3a,3f] the
FULL PAPER
nanometers (54–79 nm), much higher quantum efficiencies
and longer lifetimes (up to 28.6 µs) relative to the liquid electroluminescent (EL) spectra of the complexes based on
phase.[3f,11] The quantum efficiencies of 0.69 for 3a and 0.72 L2 or L3 have large redshifts (≈ 50 nm) in PVK compared
for 3b are amongst the highest found for cuprous complex- to their photoluminescent (PL) spectra in PMMA films, as
es[3a,3f,17] and significantly higher than those of 1a, 1b, 2a, shown in Figure 10. The reason for this is not very clear
and 2b. Furthermore, an absence of concentration quench- but could be related to the flexible six-membered ring of
ing was observed in the complexes based on L3. For exam- (N–C–C–P–O–Cu), which may vibrate under the electric
ple, 3b has an efficiency of 0.71 and an emission maximum field and cause a decrease in the excited-state energy.[17] Al-
of 501 nm in its neat film, similar to those in 20 wt.-% though the complexes with the PPh3 auxiliary ligand have
PMMA film. This may be associated with the bulky phos- almost the same quantum efficiencies in PMMA film com-
phane auxiliary ligand and –OPPh2 that can effectively pared to the complexes based on DPEphos, the devices
separate the π-electron acceptors (i.e. N-heterocycles) from based on the former displayed lower performances. A sim-
each other and therefore avoid the nonradiative intermo- ilar result has been observed previously by our group and
lecular energy transfer.
has been ascribed to the ligand dissociation reactions in
solutions.[3f] It is likely that an undetectable ligand-dissoci-
ation reaction still occurs in these mixed-ligand systems in
CH2Cl2.
Electrophosphorescent Properties Characterization
Multilayer OLEDs with the configuration of indium tin
oxide/poly(3,4-ethylenedioxythiophene)/emitting
layer
(≈ 50 nm)/bathocuproine (BCP) (20 nm)/Alq3 (40 nm)/LiF
(1 nm)/Al (≈ 100 nm) were fabricated to evaluate the elec-
trophosphorescent properties of the cuprous complexes, as
shown in Figure 9. The host materials utilized here include
poly(9-vinylcarbazole) (PVK) that can match the phospho-
rescent materials with high energy-band gaps[3a,18] and
3,6-bis(carbazol-9-yl)-N-[4-(carbazol-9-yl)phenyl]carbazole
(TCCz) that is suitable for phosphorescent materials with
low energy-band gaps.[3f,19] The performance data of the
OLEDs are listed in Table 3.
Table 3. Turn-on voltage (VT), current efficiency (ηc), maximum
brightness (Bmax), and emission wavelength (λmax) of the OLEDs.
Figure 10. EL and PL spectra of 3b.
[a]
[b]
Emitting
layer
VT
ηc
ηc
Bmax
λmax
[V]
[cd/A] [cd/A] [cd/m2]
[nm]
With TCCz as the host material, the device performance
of the complexes 1b and 2b are significantly improved in
comparison with those with PVK. For instance, the current
efficiency at 1.0 mA/cm2 and the maximum brightness for
1b increases from 0.72 to 0.95 cd/A and from 403 to
1502 cd/m2, respectively. The improved performance of the
devices based on TCCz may be attributed to the improved
distribution of the cuprous complexes in TCCz than in
PVK.[3f] The blueshifted EL spectra give further evidence
for the lower aggregation level of the emitter in TCCz.
PVK:1a
PVK:1b
PVK:2a
PVK:2b
PVK:3a
PVK:3b
8.7
6.1
9.3
7.9
9.3
7.7
0.39
0.72
0.32
0.63
0.33
0.84
0.95
1.57
0.29
4.9
0.30
0.55
0.22
0.42
0.23
0.58
0.84
1.08
0.26
1.7
211 (19.3 V)
403 (13 V)
535
548
620
628
522
540
541
612
609
542
124 (20.9 V)
119 (16.7 V)
124 (18.9 V)
370 (14.9 V)
1502 (13.5 V)
846 (15.9 V)
508 (18.1 V)
164 (12 V)
TCCz:1b 6.1
TCCz:2b 8.5
TCCz:3b 8.7
3b
7.9
[a] Measured at 1 mA/cm2. [b] Measured at 10 mA/cm2.
Figure 9. Device architecture (left) and molecular structures of the OLED materials (right).
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Phosphorescent Cuprous Complexes with N,O Ligands
background-corrected by subtracting the spectrum obtained using
a blank substrate, and subsequently corrected for the wavelength
sensitivity of the fluorimeter and the spectra response of the
sphere.[25] The film PL quantum efficiency was determined accord-
ing to the method outlined by de Mello.[26] The luminescence-decay
measurements were performed with the time-correlated single-pho-
ton counting (TCSPC) upgrade on the FluoroMax-4 spectrometer
with a FluoroHub module. The lifetimes of solution samples were
measured by TCSPC mode in conjunction with a nanoLED pulsed
source (372 nm). The lifetimes of the PMMA film samples were
However, TCCz is not a suitable host material for 3b. As
shown in Figure 10, the device based on a TCCz:3b emit-
ting layer exhibited multiple emissions with the maximum
at 609 nm, which is not from 3b but probably from the exci-
plexes. DFT calculations reveal that 3b has a relatively high
LUMO level, while the LUMO level of TCCz is estimated
to be 0.45 eV lower than that of PVK, judging from the
cyclic voltammetry and absorption edge data. It may make
the cuprous complex a less than an ideal center for electron
direct-trapping in TCCz. In fact, the low current efficiency measured by multi-channel scaling mode in conjunction with a
(0.8 cd/A at 1.0 mA/cm2) and the impurities seen in the EL
spectraLED pulsed source (373 nm). Signals were collected with
a FluoroHub module and analyzed by the DAS6 Decay Analysis
software (HORIBA Jobin–Yvon).
spectrum (Figure 10) suggest that 3b has poor ability for
charge capture even in PVK. For comparison, pure 3b was
used as the emitting layer in this device configuration. Un-
surprisingly, the undoped device achieved an improved cur-
rent efficiency of 4.9 cd/A at 1.0 mA/cm2 with an EL spec-
trum almost identical to the PL spectrum of 3b in CH2Cl2.
We believe the EL performance of this complex can be fur-
ther improved by optimizing the device configurations.
Synthesis of the Ligand and the Cuprous Complexes
Synthesis of Diphenyl(8-quinolyl)phosphane Oxide (L2): To 8-(di-
phenylphosphanyl)quinoline (0.60 g, 1.92 mmol) in thf (12 mL)
was added an excess of 30% H2O2 at room temperature. The reac-
tion mixture was stirred for 0.5 h. The solution was poured into
water (ca. 30 mL) and extracted into CH2Cl2. The organic extract
was dried with sodium sulfate, filtered, and concentrated to afford
a yellow solid, which was purified by column chromatography to
give L2. Yield: 0.45 g (71.4%). 1H NMR (300 MHz, CDCl3,
298 K): δ = 7.36–7.50 (m, 7 H, Ar and quin-H3), 7.66 (m, 1 H,
Conclusions
3
We report the synthesis and characterization of six
mixed-ligand CuI complexes based on three N,O ligands.
All of the complexes are easily prepared and stable in air.
Similar to other mixed-ligands CuI complexes, they show
the characteristic MLCT transition demonstrated by the
electronic absorption spectra and DFT calculations. Their
emissive colors depend on the electron-accepting ability of
quin-H6), 7.80–7.87 (m, 4 H, Ar), 8.05 (d, JH,H = 8.1 Hz, 1 H,
3
3
quin-H5), 8.19 (d, JH,H = 8.4 Hz, 1 H, quin-H4), 8.40 (dd, JH,H
3
= 8.1 Hz, 1 H, quin-H7), 8.75 (dd, JH,H = 4.2 Hz, 1 H, quin-H2)
ppm.
Synthesis of [Cu(L1)(PPh3)2](BF4) (1a): Under nitrogen,
[Cu(CH3CN)4](BF4) (0.157 g, 0.5 mmol) and PPh3 (0.263 g,
1.0 mmol) were dissolved in CH2Cl2 (8 mL) and stirred for 1 h. L1
the N-heterocyclic unit in the N,O ligands. High PL effi- (0.139 g, 0.5 mmol) was added to the solution, and the mixture was
stirred for 5 h. The solution was filtered, and the solvents were
removed. The same procedure was applied in the synthesis of the
complexes 1b, 2a, 2b, 3a, and 3b. Recrystallization of the residue
from CH2Cl2 and methanol (MeOH) gave yellow-green crystals of
ciencies of about 0.70, without concentration quenching,
were observed in these complexes (3a and 3b) based on the
ligand diphenyl(2-pyridylmethyl)phosphane oxide with a
high π* level, implying that the cuprous complexes contain-
ing coordinated oxygen atoms are as effective phosphores-
cent emitters as the classical heteroleptic [Cu(N,N)(P,P)]+
systems.
1
1a. Yield: 0.27 g (56.7%). H NMR (300 MHz, CDCl3, 298 K): δ
= 7.09–7.18 (m, 26 H, Ar), 7.27–7.36 (m, 12 H, Ar), 7.55 (m, 2 H,
Ar), 7.70 (m, 1 H, Py-H5), 7.82 (m, 1 H, Py-H4), 8.29 (m, 1 H, Py-
H3), 8.44 (m, 1 H, Py-H6) ppm. 31P NMR: δ = –34.25 (s, PPh3),
0.69 (s, PO) ppm. C53H44BCuF4NOP3·0.2CH2Cl2 (970.0): calcd. C
65.79, H 4.61, N 1.44; found C 65.85, H 4.32, N 1.48.
Experimental Section
Synthesis of [Cu(L1)(DPEphos)](BF4) (1b): Recrystallization of the
residue from CH2Cl2 and MeOH gave yellow-green crystals of 1b.
Yield: 0.28 g (57.9%). 1H NMR (300 MHz, CDCl3, 298 K): δ =
General Considerations: The compounds [Cu(CH3CN)4](BF4),[20]
diphenyl(2-pyridyl)phosphane oxide (L1),[21] diphenyl(2-pyridyl-
methyl)phosphane oxide (L3),[22] and 8-(diphenylphosphanyl)quin-
oline[23] were synthesized according to literature procedures. All
other chemicals were of reagent grade and used without further
purification. All solvents were dried and distilled by standard meth-
ods. 1H NMR, with TMS as internal reference, and 31P NMR spec-
tra, with 85% H3PO4 as external reference were measured with a
Bruker AV300 NMR spectrometer at room temperature. Elemental
analyses were performed with a BioRad elemental analysis system.
The UV/Vis and PL spectra were measured at room temperature
with Perkin–Elmer Lambda 45 UV/Vis and Horiba Jobin–Yvon
FluoroMax-4 spectrometers, respectively. The solution PL quan-
tum efficiencies were measured and calculated by a relative method
using [Ru(bpy)3](PF6)2 (Φ = 0.042 in degassed water) as the stan-
dard.[24] The film samples were prepared by spin-coating a mixture
of the CuI complex (20 wt.-%) and PMMA (80 wt.-%) in CH2Cl2
3
6.72 (m, 2 H, Ar), 6.96 (t, JH,H = 7.5 Hz, 6 H, Ar), 7.05 (m, 6 H,
Ar), 7.16–7.35 (m, 22 H, Ar), 7.49 (m, 3 H, Py-H5 and Ar), 7.81
3
3
(t, JH,H = 6.6 Hz, 1 H, Py-H4), 8.20 (d, JH,H = 4.8 Hz, 1 H, Py-
H3), 8.27 (m, 1 H, Py-H6) ppm. 31P NMR: δ = –48.00 (s,
DPEphos), 0.91 (s, PO) ppm. C53H42BCuF4NO2P3 (967.2): calcd.
C 65.75, H 4.37, N 1.45; found C 65.94, H 4.00, N 1.44.
Synthesis of [Cu(L2)(PPh3)2](BF4) (2a): Recrystallization of the res-
idue from MeOH gave yellow crystals of 2a. Yield: 0.30 g (61.2%).
1H NMR (300 MHz, CDCl3, 298 K): δ = 6.97–7.41 (m, 40 H, Ar),
7.51 (m, 2 H, quin-H3 and H6), 7.64 (t, 3JH,H = 6.3 Hz, 1 H, quin-
3
H5), 8.38 (d, JH,H = 7.5 Hz, 1 H, quin-H4), 8.59 (m, 2 H, quin-
H2 and H7) ppm. 31P NMR: δ = –34.97 (s, PPh3), 6.28 (s, PO)
ppm. C57H46BCuF4NOP3 (1003.2): calcd. C 68.17, H 4.61, N 1.39;
found C 67.77, H 4.61, N 1.53.
onto a quartz glass slide. The spectra were measured with the Fluo- Synthesis of [Cu(L2)(DPEphos)](BF4) (2b): Recrystallization of the
roMax-4 spectrometer equipped with an integrating sphere and residue from MeOH gave yellow crystals of 2b. Yield: 0.24 g
Eur. J. Inorg. Chem. 2010, 4009–4017
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4015

W. Sun, Q. Zhang, L. Qin, Y. Cheng, Z. Xie, C. Lu, L. Wang
FULL PAPER
Table 4. Crystallographic data for compounds 1a, 1b, 2a, 2b, 3a, and 3b.
1a
1b
2a
2b
3a
3b
Empirical formula C109H93B2Cl7Cu2F8N2O2P6
C56H48BCuF4NO3P3
1002.19
triclinic
C57H46BCuF4NOP3
1004.21
triclinic
C58.5H50BCuF4NO3.5P3
1066.26
triclinic
C55H50BCuF4NO2P3
1000.22
monoclinic
P21/c
12.8052(10)
22.1640(13)
17.9279(11)
90
95.555(5)
90
C55H48BCuF4NO3P3
Formula mass
Crystal system
Space group
a [Å]
b [Å]
c [Å]
2197.52
monoclinic
C2/c
57.114(3)
12.7707(6)
27.2789(12)
90
1014.20
orthorhombic
Pna21
33.5515(14)
9.2554(4)
15.6499(7)
90
90
90
4859.8(4)
4
1.386
¯
P1
¯
P1
¯
P1
12.7999(8)
14.0967(8)
14.3565(8)
72.3360(10)
75.0550(10)
88.6640(10)
2380.6(2)
2
12.3447(9)
13.1441(10)
16.4044(13)
73.6520(10)
83.6310(10)
72.6630(10)
2437.1(3)
2
12.2697(8)
14.1003(9)
15.6564(10)
103.0970(10)
97.4870(10)
93.7190(10)
2603.2(3)
2
α [°]
β [°]
γ [°]
V [Å3]
Z
91.1270(10)
90
19892.9(15)
8
5064.3(6)
4
1.312
Dcalcd. [gcm–3
]
1.467
1.398
1.368
1.360
Abs. coefficient
[mm–1
0.780
0.621
0.604
0.573
0.582
0.609
]
Final R indices
[IϾ2σ(I)]:
R1, wR2
R indices (all
data):
0.0576, 0.1156
0.0545, 0.1549
0.0505, 0.1285
0.0581, 0.1580
0.0647, 0.1813
0.0346, 0.0809
R1, wR2
GOF
0.1048, 0.1277
0.997
0.0713, 0.1642
1.003
0.0635, 0.1384
1.015
0.0761, 0.1724
1.015
0.0894, 0.2069
1.057
0.0384, 0.0830
1.016
(47.2%). 1H NMR (300 MHz, CDCl3, 298 K): δ = 6.64–7.31 (m,
supplementary crystallographic data for complexes 1a, 1b, 3b, 3a,
2b, and 2a, respectively. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via http://
www.ccdc.cam.ac.uk/data request/cif.
3
38 H, Ar), 7.49 (td, JH,H = 7.2 Hz, 2 H, quin-H3 and H6), 7.62
(m, 1 H, quin-H5), 8.37 (d, 3JH,H = 7.5 Hz, 1 H, quin-H4), 8.47 (d,
3
3JH,H = 8.4 Hz, 1 H, quin-H7), 8.58 (d, JH,H = 8.4 Hz, 1 H, quin-
H2) ppm. 31P NMR: δ = –48.29 (s, DPEphos), 6.78 (s, PO) ppm.
C57H44BCuF4NO2P3 (1017.2): calcd. C 67.23, H 4.36, N 1.38;
found C 66.96, H 4.36, N 1.24.
Density Functional Calculations: DFT calculations were performed
by using the GAUSSIAN 03 software package[29] using a spin-re-
stricted formalism at the B3LYP level. 6-31+G** was used to opti-
mize the molecular geometry as a basis set for all elements, and
Los Alamos ECP plus DZ (LANL2DZ) was used additionally for
Cu. The HOMO and LUMO energies were determined by using
minimized singlet geometries to approximate the ground states.
Synthesis of [Cu(L3)(PPh3)2](BF4) (3a): Recrystallization of the res-
idue from MeOH gave colorless crystals of 3a. Yield: 0.35 g
1
2
(72.3%). H NMR (300 MHz, CDCl3, 298 K): δ = 3.75 (d, JH,H
= –13.8 Hz, 2 H, CH2), 6.83 (m, 1 H, Py-H3), 7.09–7.14 (m, 24 H,
Ar), 7.31–7.46 (m, 12 H, Ar), 7.61–7.72 (m, 5 H, Ar and Py-H5),
3
3
7.89 (d, JH,H = 7.8 Hz, 1 H, Py-H4), 7.98 (d, JH,H = 4.8 Hz, 1 H,
Py-H6) ppm. 31P NMR: δ = –2.51 (s, PPh3), 36.42 (s, PO) ppm.
C54H46BCuF4NOP3·CH3OH (999.2): calcd. C 66.04, H 5.04, N
1.40; found C 65.84, H 4.82, N 1.24.
Acknowledgments
This work was supported by the National Natural Science Founda-
tion of China (Nos. 20874098 and 50772113), the Natural Science
Foundation of Fujian Province (No. 2007F3116), the Science Fund
for Creative Research Groups (No. 20621401), and the 973 Project
(2009CB623600).
Synthesis of [Cu(L3)(DPEphos)](BF4) (3b): Recrystallization of the
residue from MeOH gave colorless crystals of 3b. Yield: 0.30 g
1
2
(61.2%). H NMR (300 MHz, CDCl3, 298 K): δ = 3.77 (d, JH,H
= –13.8 Hz, 2 H, CH2), 6.77 (m, 3 H, Py-H3 and Ar), 6.91–7.02
3
(m, 5 H, Ar), 7.18–7.49 (m, 31 H, Ar), 7.69 (t, JH,H = 7.5 Hz, 1
3
3
H, Py-H5), 7.82 (d, JH,H = 7.5 Hz, 1 H, Py-H4), 8.02 (d, JH,H
=
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Received: April 5, 2010
Published Online: July 9, 2010
Eur. J. Inorg. Chem. 2010, 4009–4017
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4017