Generation of blue light-emitting zinc complexes by band-gap control of the oxazolylphenolate ligand system: Syntheses, characterizations, and organic light emitting device applications of 4-coordinated bis(2-oxazolylphenolate) zinc(II) complexes

Article abstract of DOI:10.1021/ic702491j

Color-tunable Zn(II) complexes of the type Zn(N,O-OPh^OxZArX) ₂ (5), where the ligand consists of an oxazolylphenolate ion connected at the 4-position by a 2,4-substituted aryl functional group with X = NMe₂ a, OMe b, Ph c,

Full text of DOI:10.1021/ic702491j

Inorg. Chem. 2008, 47, 5666-5676
Generation of Blue Light-Emitting Zinc Complexes by Band-Gap Control
of the Oxazolylphenolate Ligand System: Syntheses, Characterizations,
and Organic Light Emitting Device Applications of 4-Coordinated
Bis(2-oxazolylphenolate) Zinc(II) Complexes
Ho-Jin Son, Won-Sik Han, Ji-Yun Chun, Byoung-Kook Kang, Soon-Nam Kwon, Jaejung Ko,*
Su Jung Han, Chongmok Lee, Sung Joo Kim, and Sang Ook Kang*
Department of Materials Chemistry, Korea UniVersity, 208 Seochang, Chochiwon, Chung-nam
339-700, South Korea, Department of Chemistry, Ewha Womans UniVersity, Seoul 120-750, South
Korea, and Department of Materials Science and Engineering, Columbia UniVersity, New York 10027
Received December 24, 2007
Color-tunable Zn(II) complexes of the type Zn(N,O-OPhOxZArX)2 (5), where the ligand consists of an oxazolylphenolate
ion connected at the 4-position by a 2,4-substituted aryl functional group with X ) NMe2 a, OMe b, Ph c, Cl d,
F2 e, and CN f, were prepared. X-ray structural studies of 5a, 5b, and 5e showed that a zinc atom was positioned
in a distorted tetrahedral coordination environment created by two oxazolylphenolate ligands with N,O-chelation.
Hammet plots of absorption and emission maxima, respectively, in UV and photoluminescence (PL) spectra with
respect to electron-donating and electron-withdrawing groups of the substituents indicate a direct correlation between
the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) band gaps and
electronic alterations at the ligand sites. A similar correlation was also observed for the reduction and oxidation
potentials in cyclic voltammograms (CVs). A gradual increase in the HOMO-LUMO band gap is seen from electron-
donating to electron-withdrawing functional groups, NMe2 < OMe < Ph < Cl < F2 < CN. An emission peak with a
maximum at 455 nm was achieved when the most electron-withdrawing group (cyano) was applied to the
oxazolylphenolate ligand system. Density-functional theory (DFT) calculations on the HOMOs and LUMOs for this
series lead to a conclusion similar to that arrived at from a blue-shift trend observed in UV data and trends in the
CVs. The 4-coordinated zinc complex (5c) was shown to be a potential blue-emitting material, exhibiting a maximum
efficiency of 1720 cd/m2 at 17 V with 0.3 cd/A in a multilayered device structure of ITO/NPB/5c/BCP/Alq3/LiF/Al.
On the basis of the low HOMO level of this series, 5a was tested as a hole-transporting material; this resulted in
the successful fabrication of a multilayered device of ITO/5a/DPVBI/Alq3/LiF/Al with an efficiency of 7000 cd/m2 at
13 V with 2.0 cd/A.
Introduction
focused on small organic molecules and polymers. However,
for the successful fabrication of full-color OLEDs, issues
related to efficiency and lifetime of blue emitting materials
need to be resolved. Major research on blue luminescent
materials has been carried out mainly using aromatic organic
molecules3 and organic polymers.4 Blue EL materials derived
from organometallic complexes are rare and limited to late
transition-metal complexes (Ir,5 Pt,6 Os7) and main group
metal complexes8,9 based on hydroquinoline-type ligands.
For this reason, new types of organometallic EL materials
utilizing main group metals (Al,10 Be,11 Cu,12 Zn13) with
N,O- and N,N-chelate ligands have been actively studied.
Since the discovery of organic light emitting devices
(OLEDs) by C. W. Tang1 and J. H. Burroughes,2 unrelenting
efforts have been made to develop highly efficient electrolu-
minescent (EL) materials. In particular, methods to construct
blue light-emitting materials with large band gaps have long
been sought; studies aimed at producing such materials have
* To whom correspondence should be addressed. E-mail: sangok@
korea.ac.kr. Tel: +82-41-860-1334. Fax: +82-41-867-5396.
(1) Tang, C. W.; VanSlyke, S. A. Appl. Phys. Lett. 1987, 51, 913.
(2) Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.;
Mackay, K.; Friend, R. H.; Burns, P. L.; Homes, A. B. Nature 1990,
347, 539.
5666 Inorganic Chemistry, Vol. 47, No. 13, 2008
10.1021/ic702491j CCC: $40.75  2008 American Chemical Society
Published on Web 06/11/2008

Blue Light-Emitting Zinc Complexes
Among them, zinc complexes have received much attention
because of their many advantageous EL properties, such as
electron transporting ability, light emitting efficiency, high
thermal stability, ease of sublimation, and great diversity of
tunable electronic properties resulting from ligand
substitution.13l–n,14 Because the electronic structure of metal
chelate luminescent materials is determined by the coordina-
tion of a ligand, the coordination geometry as well as the
highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO) contributions from
the ligand need to be examined. Indeed, the coordination
mode of the ligand relates to the photophysical properties
of the resulting metal complexes, and the bulkiness of the
ligand alters the bonding around the metal center; a bulky
ligand tends to form monomeric species while less bulky
ligands encourage the formation of dimeric or trimeric metal
complexes. Furthermore, modification of the chelating ligand
in Alq3 and Bq (q: hydroquinoline) with electron-donating
or electron-withdrawing groups proves to be an effective
method for the tuning of the optical properties of Alq38 and
Bq.9b However, until recently very few studies have been
performed on the systematic tuning of the luminescence of
zinc complexes. In an effort to investigate the efficacy of
the substituent effect and its possible use in color tuning in
zinc(II) complexes, a series of electron-rich and electron-
poor oxazolylphenol ligands was prepared, and the resulting
4-coordinated Zn(oxazolylphenolate)2 complexes were in-
vestigated for their electronic and photophysical properties.
Here, we report the full details of the syntheses and
characterizations of various electron-donating and electron-
withdrawing aryl-substituted Zn oxazolylphenolate com-
plexes (5). The photophysical and electrochemical properties
of these Zn complexes were estimated by means of UV and
photoluminescence (PL) spectroscopy, as well as cyclic
voltammetry (CV). The corresponding EL properties for 5a
and 5c were studied through device fabrication by applying
them respectively as hole-transporting and emitting materials
in multilayer devices, depending on the HOMO and LUMO
energy levels. In addition, theoretical calculations were
performed to account for the change in the electronic
structure as a result of the inductive and mesomeric effects
on aryl substituents (ArX), as shown in Chart 1.
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Son et al.
Chart 1. Zn Complexes Containing Electron-Donating/Withdrawing
Groups (5)
and angles are presented in Tables 1 and 2, respectively.
The dimethyl units on the oxazolyl group provide steric
protection against further metal coordination from nearby
zinc atoms. In general, most anhydrous zinc complexes with
a hydroxyquinolinate ligand exist as tetramers13a,c,e,h or
hexamers13g because the ligand has a planar structure
ensuring there are no bulky substituents near the nitrogen
and oxygen atoms to interfere with metal coordination. The
zinc(II) ion in each complex of 5a, 5b, and 5e is sym-
metrically coordinated to two N,O-chelate ligands with an
NfZn-O conformation. Therefore, all four structures adopt
a pseudotetrahedral geometry different from that found in
tetrameric zinc complexes, a distorted trigonal bipyramidal
geometry. The Zn-O and Zn-N lengths are in the range of
1.906-1.921 Å and 1.975-1.988 Å, implying the presence
of regular σ and dative bonding, respectively (Table 2). When
compared with the bond lengths of tetrameric zinc complexes
of Zn-O (1.962-2.058 Å) and Zn-N (2.095-2.170 Å),
these values are shorter because of the effective coordination
by the N,O-chelating oxazolylphenolate ligand (4). This again
reflects the preference for 4-coordination by the oxazolylphe-
nolate ligand system studied in this work. It is noteworthy
that the Zn-O bond length in a series varies depending on
the electron-donating and electron-withdrawing substituents:
the bond length decreases from 1.9203(14) Å for 5a to
1.906(4) Å for 5e. The angles around a zinc atom deviate
substantially from the tetrahedral values, exhibiting bond
angles of 120.4(2)-124.39(7)° and 114.7(3)-116.96(6)° for
N-Zn-N and O-Zn-O, respectively. One special feature
common to all three structures is that intermolecular π-π
interactions are discernible in the crystal packings, especially
in the aryl periphery. Shorter intermolecular distances of
3.665-3.745 Å were found in aryl-aryl stacking regions of
5a, 5b, and 5e, which is typical of aromatic-aromatic face-
to-face π-π stacking.16 Figure 4 shows a molecular packing
view of 5a, 5b, and 5e. Such an increase in intermolecular
interaction can be suggested as an origin of the high carrier
mobility in EL devices.
Oxazolyl-4-bromophenol (1) was prepared from the corre-
sponding aminoalcohol and carboxylic acid in moderate
yields, using a previously developed synthesis protocol.15
Subsequent protection of the phenolic oxygen atom was
carried out by reacting 1 with benzyl chloride in the presence
of base. A series of Suzuki-type cross-coupling reactions
were successfully performed to yield the desired ox-
azolylphenolate ligands (3) with suitable handling of electron-
donating and electron-withdrawing functional groups in the
para position. The final oxazolylphenol ligands (4) were
obtained using a hydrogenolytic deprotection procedure, as
shown in Scheme 1.
Zn(II) complexes of Zn(N,O-OPhOxZArX)2 were obtained
by reacting 2 equiv of ligand 4 with Zn(OAc)2 in ethanol
(Scheme 1). In all cases, products were isolated from the
reaction solution by slow recrystallization. After recrystal-
lization, filtration followed by washing with cold ethanol
resulted in the production of crude products in moderate
yields. The formation of metal complex 5 was confirmed by
means of high-resolution mass spectrometry and elemental
analyses. All Zn(II) complexes showed the expected signals
1
in the H and 13C NMR spectra, confirming the ligand
coordination (see Experimental Section).
X-ray Structural Studies on Zn(N, O-OPhOxZArX)2,
5a, 5b, and 5e. Structural studies on 5a, 5b, and 5e showed
that the zinc atom resides in a tetrahedral coordination site
as a monomeric entity. Oak Ridge Thermal Ellipsoid Plot
(ORTEP) structures of 5a, 5b, and 5e are shown in Figures
1–3, and X-ray structural parameters, selected bond lengths,
Photophysical Properties. The UV-visible absorption
and fluorescence spectra of the ligand-functionalized Zn
complexes (5) are summarized in Table 3 and Figures 5–7).
Scheme 1. Preparation of Zn Complexes (5)
5668 Inorganic Chemistry, Vol. 47, No. 13, 2008

Blue Light-Emitting Zinc Complexes
Figure 1. ORTEP drawing (30% probability for thermal ellipsoids) of 5a. Hydrogen atoms are omitted for clarity.
Figure 2. ORTEP drawing (30% probability for thermal ellipsoids) of 5b. Hydrogen atoms are omitted for clarity.
Figure 3. ORTEP drawing (30% probability for thermal ellipsoids) of 5e. Hydrogen atoms are omitted for clarity.
Table 1. Crystal Data and Structure Refinement for 5a, 5b, and 5ea b
,
5a
5b
5e
C34H28F4N2O4Zn
empirical formula
formula weight
C38H42N4O4Zn
684.13
C36H36N2O6Zn·CH2Cl2
742.96
669.95
temperature
233(2) K
233(2) K
233(2) K
wavelength
crystal system, space group
unit cell dimensions
0.71073 Å
triclinic, P1
0.71073 Å
triclinic, P1
0.71073 Å
monoclinic, P2/c
j
j
a ) 7.645(2) Å, R ) 73.477(4)°
b ) 12.213(3) Å, ꢀ ) 79.463(4)°
c ) 19.148(4) Å, γ ) 88.053(4)°
1684.9(6) Å3
a ) 7.589(2) Å, R ) 76.161(5)°
b ) 13.137(3) Å, ꢀ ) 80.499(5)°
c ) 19.121(4) Å, γ ) 75.500(4)°
1780.6(7) Å3
a ) 15.244(2) Å, R ) 90°
b ) 6.6431(7) Å, ꢀ ) 103.071(2)°
c ) 15.110(2) Å, γ ) 90°
1490.5(3) Å3
volume
Z, calculated density
reflections collected/unique
final R indices [I > 2σ(I)]
R indices (all data)
2, 1.348 mg/m3
2, 1.386 mg/m3
2, 1.488 mg/m3
23308/8409 [R(int) ) 0.0239]
R1 ) 0.0373, wR2 ) 0.1037
R1 ) 0.0517, wR2 ) 0.1158
24442/8785 [R(int) ) 0.0412]
R1 ) 0.0440, wR2 ) 0.1086
R1 ) 0.0831, wR2 ) 0.1339
14657/3704 [R(int) ) 0.1063]
R1 ) 0.0637, wR2 ) 0.1562
R1 ) 0.1692, wR2 ) 0.2269
a R1 ) ∑||Fo| - |Fc|| (based on reflections with Fo2 > 2σF2). b wR2 ) [∑[w(Fo2 - Fc )2]/∑[w(Fo )2]]1/2; w ) 1/[σ2(Fo ) + (0.095P)2]; P ) [max(Fo , 0)
2
2
2
2
2
2
+ 2Fc ]/3 (also with Fo > 2σF2).
In this series, we observed a correlation between the photo-
physical properties and the electronic nature of the attached
substituents. A systematic blue-shift on both the absorption
and emission spectra is observed on going from electron-
donating to electron-withdrawing substituents of the modula-
tor group. This, in turn, provides evidence of an electronic
communication between the oxazolylphenolate fluorophores
and the appended moieties. It is noteworthy that compound
5f does not follow the trend in the series. Photophysical
properties of 5a-f shown in Table 3 reveal that the fluores-
cence quantum yield correlates with the electronic nature of
the ligands. For the complexes bearing electron-withdrawing
substituents, the quantum yield was increased, whereas the
electron-rich moiety resulted in a decrease in the emission
Inorganic Chemistry, Vol. 47, No. 13, 2008 5669

Son et al.
Table 2. Selected Bond Lengths and Angles of 5a, 5b, and 5e
When an electrochemistry of the free ligand 4a was carried
out in CH3CN, one reversible oxidation peak and one
irreversible reduction peak were discernible in the corre-
sponding CV (see Supporting Information, Figure S4a). The
peak separation of the oxidation waves due to ligand 4a in
the CV of 5a is more pronounced on changing the solvent
from CH3CN to CH2Cl2/CH3CN (V/V ) 4/1), which might
be ascribed to electronic communication between the two
ligand centers as a result of significant charge delocalization
(Figure 9).17
structure parametera
5a
5b
5e
Zn-O(1)
1.920(1)
1.920(1)
1.987(2)
1.988(2)
116.96(6)
124.39(7)
111.34(7)
94.91(6)
116.08(6)
94.81(6)
22.2(3)
1.921(2)
1.920(2)
1.977(2)
1.975(2)
115.30(8)
123.91(9)
115.18(8)
95.42(8)
113.85(8)
94.70(8)
33.2(4)
1.906(4)
1.906(4)
1.975(4)
1.975(4)
114.7(3)
120.4(2)
117.2(2)
94.6(2)
Zn-O(2)
Zn-N(1)
Zn-N(2)
O(1)-Zn-O(2)
N(1)-Zn-N(2)
N(1)-Zn-O(2)
O(1)-Zn-N(1)
O(1)-Zn-N(2)
N(2)-Zn-O(2)
dihedral angleb
117.2(2)
94.6(2)
47.3(8)
The Eox and Ered values are known to be related to the
HOMO and LUMO energy levels, respectively. The HOMO
and LUMO energy levels for the Zn(II) complexes (5) shown
in Table 4 were calculated based on the relationship HOMO/
LUMO (eV) ) -e(Eox/Ered (V vs SCE) + 4.74 V).18 The
HOMO and LUMO energy levels of 5 were estimated to be
about -5.89 to about -5.28 eV and about -2.27 to about
-2.57 eV, respectively. Overall, the HOMO levels decrease
systematically on going from electron-rich to electron-poor
substituents, whereas the LUMO levels are less sensitive to
ligand variation, with a deviation of ∼∆ 0.3 eV. This result
correlates well with the blue shift in the UV spectra (Figure
12). Plots of the absorption maximum wavenumber Vabs and
a Bond lengths are reported in angstroms and bond angles in degrees.
b C(9)-C(10)-C(12)-C(17) for 5a, C(3)-C(4)-C(7)-C(8) for 5b, and
C(4)-C(5)-C(7)-C(8) for 5e.
quantum yield. This correlates well with the energy-gap law,
suggesting a uniform nature of photophysical behavior in
the series of complexes.
X-ray crystallographic structure determinations for 5a, 5b,
and 5e suggest that there is a higher degree of coplanarity
for the electron-donating derivatives than for the electron-
withdrawing compound. In particular, compound 5e displays
a 47.4° dihedral angle between the planes of phenol and the
phenyl groups, whereas the dihedral angles for 5a and 5b are
22.2 and 32.2°, respectively. This may provide additional
information on a blue-shift trend of the electron-poor systems
found in both UV and fluorescence spectra. It is worthy of note
that the crystal packing geometries of 5a, 5b, and 5e show
strong intermolecular π-π stacking between the modulator
phenyl rings. This relates to an enhanced red-shifted trend for
the film fluorescent spectra found in Table 3.
Electrochemistry. The electrochemical properties of zinc
complexes containing two oxazolylphenolate ligands (5) were
investigated by cyclic voltammetry (CV). The CV results
are summarized in Table 4 using CH3CN containing 0.1 M
tetrabutylammonium hexafluorophosphate (TBAPF6) with a
scan rate of 0.1 V s-1, and are also shown in Supporting
Information, Figure S4. The potential values of the first redox
wave in the scan of both the positive (Eox) and negative (Ered)
directions are included in Table 4, along with some multiple
redox waves.
It is notable that characteristic redox properties are
discernible with respect to electron-donating and electron-
withdrawing substituents at the 2,4-position of the aryl
substituent ring. The CVs of 5a and 5b show two oxidation
waves in the positive potential range because electron-
donating substituents provide electrons to the compound upon
oxidation, which in turn stabilize the radical cation (Sup-
porting Information, Figure S4a,b). The CVs of 5e and 5f
exhibit one or two reversible reduction waves in the negative
potential range because electron-poor substituents can ac-
commodate electrons upon reduction to form stable anion
radicals (Supporting Information, Figure S4e,f). These
explanations are strongly supported by Hammett plots of the
Eox and Ered values versus σ values of the substituents, where
a good linear relationship is observed based on the electron-
donating/withdrawing substituents on the arylphenolate ring
(Figure 8).
emission maximum wavenumber Vem versus ∆E () Eox
-
Ered) showed a direct correlation between HOMO-LUMO
band gaps and electronic alteration from the ligand sites
(Figure 10). A linear relationship was obtained between Vabs
and ∆E (Vabs × 104 ) 1.764 + 0.303∆E) except for 5f, and
the linearity for Vem showed a relatively high slope (Vem
×
104 ) -0.606 + 0.896∆E). The origin of the discrepancy
of the band gap of 5f between from absorption spectrum
and from electrochemistry is uncertain at this moment.
However, it is noticeable that the absorption spectrum of 5f
has a shoulder peak at 370 nm unlike other 5 compounds.
Theoretical Studies of Zn Complexes (5). To investigate
the nature of the electronic structure, quantum chemical
calculations of a series of Zn complexes (5) using density-
functional theory (DFT) as implemented in the DMol3
package were carried out.19 The HOMO-LUMO levels of
5 were calculated using double numerical plus d-functions
(DND), and the geometries were optimized under the same
conditions. No atom was omitted from the detailed study of
the bond lengths and angles of the optimized structure.
Previous work on Zn(II) chelate [Zn(L)2]n complexes (n )
1 or 2) has shown that the electron density of the HOMO is
localized mainly on the phenoxide ring while the LUMO is
localized on the heterocyclic ring.13a,e,h A similar result is
observed in our calculation: the HOMO orbitals of Zn(Oxa)2
(15) Hoveyda, H. R.; Karunaratne, V.; Rettig, S. J.; Orvig, C. Inorg. Chem.
1992, 31, 5408.
(16) Roesky, H. W.; Andruh, M. Coord. Chem. ReV. 2003, 236, 91.
(17) Barrie`re, F.; Geiger, W. E. J. Am. Chem. Soc. 2006, 128, 3980.
(18) Bard, A. J. ; Faulkner, L. R. In Electrochemical Methods: Funda-
mentals and Applications, 2nd ed.; John Wiley & Sons, Inc.: 2001; p
54.
(19) (a) Delley, B. J. Chem. Phys. 1990, 92, 508. (b) Delley, B. J. Chem.
Phys. 2000, 113, 7756.
(20) (a) SMART and SAINT; Bruker Analytical X-ray Division: Madison,
WI, 2002. (b) Sheldrick, G. M. SHELXTL-PLUS Software Package;
Bruker Analytical X-ray Division: Madison, WI, 2002.
5670 Inorganic Chemistry, Vol. 47, No. 13, 2008

Blue Light-Emitting Zinc Complexes
Figure 4. Packing diagram showing the intermolecular π-π interaction of 5a (a), 5b (b), and 5e (c).
Table 3. UV-vis, Photoluminescence Spectra, And Thermal Data for 5
UV-vis (nm)
PL (nm)
compounds solutiona filmb solutiona filmb Φf (%)c Mp (°C)
5a
5b
5c
5d
5e
5f
372
369
363
362
357
326
382
374
369
367
360
327
482
440
428
423
420
416
486
465
463
462
449
455
2
11
8
10
16
12
334
340
327
355
324
368
a In chloroform. b In thin solid film. c Relative to 9,10-diphenylanthracene
in chloroform at ambient temperature.
are distributed over a phenoxide and substituted aryl rings,
whereas the LUMO orbitals are located on phenoxide and
oxazolyl rings (see Supporting Information, Figure S5). From
these data, HOMO and LUMO energies are assumed to be
dominated by orbitals originating from the 2-(5-aryl-2-
hydroxyphenyl)oxazoline ligands in all cases where the
contributions of core metal Zn(II) are almost negligible. In
addition, there was a smooth decrease in both HOMO and
LUMO energy levels of the six model compounds, showing
a similar result with relatively constant LUMO levels
obtained in the CV experiments (Figure 11).
Figure 5. UV-vis absorption spectra of 5 in chloroform.
Fabrication of OLED Devices. On the basis of the
HOMO and LUMO energy levels obtained by CV, 5c was
selected as a reference to compare the results reported in a
similar study.13g,h,k Devices for the emitting and electron-
transporting layer were fabricated with the structure ITO/
Inorganic Chemistry, Vol. 47, No. 13, 2008 5671

Son et al.
7000 cd/cm2 at 13 V and a maximum current efficiency of
2.0 cd/A at 3 mA/cm2, showing the potential of 5a as a hole-
transporting material.
Conclusion
To carry out a systematic study of Zn(II) complexes, we
prepared metal chelating complexes based on new types of
ligand systems. The structures of monomeric Zn(II) com-
plexes [Zn(L)2] were characterized by X-ray analyses. This
showed that ligand bulkiness is closely related to intermo-
lecular interaction. From photophysical and electrochemical
studies, we found that the band gap and HOMO/LUMO
levels of the prepared Zn(II) complexes can be efficiently
controlled by electron-donating and -withdrawing substituents
on the ligands. In particular, fabrication of devices using 5c
and 5a showed the potential of these compounds as a blue
luminescent material and a hole-transporting material, re-
spectively. This method offers a powerful tool for the
preparation of electroluminescent material using a metal
complex with a chelating ligand.
Figure 6. PL spectra of 5 in chloroform.
Experimental Section
General Procedures. All manipulations were performed under
a dry nitrogen (or argon) atmosphere using standard Schlenk
techniques. Tetrahydrofuran (THF) was freshly distilled over
1
potassium benzophenone. H and 13C spectra were recorded on a
Varian Unity Inova AS600 spectrometer operating at 599.80 and
150.83 MHz, respectively. All proton and carbon chemical shifts
were measured relative to internal residual benzene from the lock
solvent (99.9% CDCl3) and then referenced to Me4Si (0.00 ppm).
Elemental analyses were performed with a Carlo Erba Instruments
CHNS-O EA 1108 analyzer. High Resolution Tandem Mass
Spectrometry (Jeol LTD JMS-HX 110/110A) was performed by
the Korean Basic Science Institute (Seoul). Absorption and pho-
toluminescence spectra were recorded on a SHIMADZU UV-
3101PC UV-vis-NIR scanning spectrophotometer and a VARIAN
Cary Eclipse fluorescence spectrophotometer, respectively. The
fluorescence quantum yields in chloroform using 9,10-diphenylan-
thracene as a standard were determined by the dilution method.
CV experiments were carried out in CH3CN or CH2Cl2/CH3CN
(V/V ) 4/1) mixed solution containing electro-active compounds
and 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF6, or
0.1 M tetrabutylammonium tetrafluoroborate (TBABF4)) at room
temperature using a BAS 100B electrochemical analyzer. A glassy
carbon disk (Φ ) 3 mm, or platinum disk (Φ ) 1.6 mm)), platinum
wire, and Ag|AgNO3 (0.1 M) were used as the working, counter,
and reference electrodes, respectively. All potential values were
calibrated versus the ferrocene/ferrocenium (Fc|Fc+) redox couple,
and then corrected to the saturated calomel electrode (SCE) on the
basis of an Fc|Fc+ redox potential of 0.38 V versus SCE. Zinc(II)
acetate, 2-amino-2-methyl-1-propanol, 5-bromo salicylic acid, and
palladium(II) acetate were purchased from Aldrich. Materials (5)
were purified by train sublimator (DOV Sublimation system model-
DOV1200) prior to device fabrication. ITO-coated glass (20 Ω/sq)
was first cleaned by conventional procedures. Under an inert
atmosphere in a fabrication chamber, the sample was exposed to
UV/ozone treatment. Then, organic and metal layers were deposited
thermally onto the ITO surface at a rate of 1∼2 Å/s at a pressure
of about 4 × 10-6 Torr. Typical devices were fabricated with NPB
or 5a as the hole-transporting layer (HTL, 50 nm), 5c or DPVBI
Figure 7. PL spectra of 5 in a solid film.
NPB/5c/LiF/Al (Table 5). However, the brightness and
efficiency turned out to be relatively poor, indicating the
difficulty of electron injection from the cathode. For this
reason, the device structure ITO/NPB/5c/Alq3/LiF/Al using
Alq3 as an electron-transporting layer was tested. As shown
in Supporting Information, Figure S6, the device showed
improved efficiency and brightness. However, the EL peak
showed interference from the Alq3 color that demonstrated
the recombination of holes and electrons in the Alq3 layer
due to the low HOMO level of 5c (Supporting Information,
Figure S7). To solve this problem, 2,9-dimethyl-4,7-diphe-
nylphenanthroline (BCP) was inserted into the device as a
hole-blocking layer. As expected, the EL peak of the device
(ITO/NPB/5c/BCP/Alq3/LiF/Al) showed agreement with the
film PL of 5c that proved exciton formation in the 5c layer,
displaying a maximum brightness of 1720 cd/cm2 at 17 V
and a current efficiency of 0.3 cd/A at 2 mA/cm2. In addition,
we found that 5a can be applied as a hole transporting layer
(HTL) on the basis of the preliminary HOMO/LUMO levels
determined by CV (Figure 12). Because 5a has two reversible
oxidation peaks in the CV, a hole from the anode can be
stabilized in these two electronic states. Accordingly, a device
was fabricated with the structure ITO/5a/DPVBI/Alq3/LiF/
Al and another device of structure ITO/NPB/DPVBI/Alq3/
LiF/Al was fabricated as a reference. As shown in Figure
13, the former device displayed a maximum brightness of
5672 Inorganic Chemistry, Vol. 47, No. 13, 2008

Blue Light-Emitting Zinc Complexes
Table 4. Cyclic Voltammetric Data and Theoretical Data of Zn Complexesa
oxidation [V]b
reduction [V]b
Epc1 (Epc2
[eV]
e
compound
Epa1 (Epa2
)
Epc1 (Epc2
)
Epa1 (Epa2
)
)
Eg
HOMOd
LUMOd
5a
5b
5c
5d
5e
5f
+0.57 (+0.84)
+0.98 (+1.32)
+1.07
+0.51 (+0.79)
c
c
-2.50
-2.31
-2.31
-2.24
-2.29
3.01
3.20
3.33
3.27
3.37
3.32
-5.28
-5.68
-5.78
-5.80
-5.85
-5.89
-2.27
-2.48
-2.45
-2.53
-2.48
-2.57
+0.89
c
c
c
c
-2.26
c
-2.24
c (-2.36)
+1.09
+1.14
+1.18
-2.21 (-2.45)
a CVs were recorded at room temperature in CH3CN/0.1 M TBAPF6. b Eox and Ered are represented as Epa and Epc (V vs SCE). c It is hard to measure this
value because of the lack of reversibility. d HOMO and LUMO levels were determined using the following equations: EHOMO (eV) ) -e(Eox + 4.74), ELUMO
(eV) ) -e(Ered + 4.74). e Eg ) LUMO - HOMO.
Figure 8. Plots of reduction (open circle, dashed line) and oxidation (closed
circle, solid line) peak potentials as a function of the σp values of para-
substituents on the phenyl groups of 5.
Figure 10. Plots of absorption and emission wavenumbers of Zn complexes
(5) as a function of the ∆E () Epa1 - Epc1) values.
chromatography using hexane/benzene (V/V ) 1/1) as an eluent to
give a pale yellow oil 1 (2.70 g, 50%). 1H NMR (CDCl3): δ 12.22
(s, 1H, -OH), 7.79 (d, 1H, Ph, J ) 2.0 Hz), 7.34 (dd, 1H, Ph, J )
9.3, 2.0 Hz), 6.77 (d, 2H, Ph, 3JH-H ) 9.0 Hz), 4.18 (s, 2H, -CH2-
), 1.36 (s, 6H, -CH3). 13C NMR (CDCl3): δ 169.23, 167.48, 138.30,
131.99, 126.12, 110.46, 105.15, 78.13 (-CH2-), 66.84, 28.44 (-CH3).
Anal. Calcd for C11H12BrNO2: C, 48.91; H, 4.48. Found: C, 48.76;
H, 4.45.
Synthesis of 4,4-Dimethyl-2-(5-bromo-2-benzyloxyphenyl)ox-
azoline (2). A mixture of 2-(5-bromo-2-hydroxyphenyl)oxazoline
(1), K2CO3 (4.15 g, 30 mmol), and benzyl chloride (2.31 mL, 20
mmol) was dissolved in CH3CN (100 mL) and refluxed for 12 h
under nitrogen. After cooling to room temperature, methylene
chloride was poured into the reaction mixture, and the solution was
filtered through Celite. The volatile solvent was removed under
reduced pressure, and the residue was purified by silica gel column
chromatography using ethylacetate/hexane (V/V ) 1/5) as an eluent
Figure 9. Cyclic voltammograms of 0.5 mM 5a (solid line) and 4a (dashed
line). The peaks were examined at a platinum electrode (Φ ) 1.6 mm) in
4:1 (V/V) CH2Cl2/CH3CN solution containing 0.1 M TBABF4 with V ) 0.1
V s-1
.
1
to give 2 (2.88 g, 80%) as a white powder. TLC, Rf ) 0.7. H
NMR (CDCl3): δ 7.85 (d, 1H, Ph, J ) 2.4 Hz), 7.43-7.30 (m,
as the emitting layer (EML, 40 nm), and Alq3 (10 nm) as the
electron-transporting layer (ETL). LiF (0.5 nm) and Al (100 nm)
were deposited as the cathode. The deposited film thickness was
measured by a Tencor P-2 long scan profiler. The characteristics
of the OLED device were measured using a Photoresearch PR650
spectrometer and a Keithley 306 source measure unit.
Preparation of 4,4-Dimethyl-2-(5-bromo-2-hydroxypheny-
l)oxazoline (1). To a stirred solution of 5-bromo salicylic acid (4.34
g, 20 mmol) was added 2-amino-2-methyl-1-propanol (2.48 g, 20
mmol), PPh3 (15.74 g, 3 equiv), and NEt3 (8.32 mL, 3 equiv) in
CH2Cl2 (100.0 mL), CCl4 (19.30 mL, 10 equiv) dropwise via
cannula at 0 °C for 8 h. The resulting solution was stirred at 50 °C
for 12 h, after which the reaction mixture was cooled to room
temperature and then dried under reduced pressure to give a pale
yellow oil. The resulting residue was purified by silica gel column
3
5H, Ph), 7.28 (d, 1H, Ph, J ) 7.2 Hz), 6.84 (d, 1H, Ph, JH-H
)
9.0 Hz), 5.11 (s, 2H, benzyl), 4.07 (s, 2H, -CH2-), 1.38 (s, 6H,
-CH3). 13C NMR (CDCl3): δ 164.06, 160.03, 135.45, 135.21,
133.81, 129.02, 128.51, 128.44, 126.80, 115.53, 114.56, 79.12
(-CH2-), 71.78, 70.89, 28.45 (-CH3). Anal. Calcd for C18H18BrNO2:
C, 60.01; H, 5.04. Found: C, 60.07; H, 5.06.
Suzuki Coupling and Deprotection of the Benzyl Derivative
by Hydrogenation. Synthesis of 4,4-Dimethyl-2-[5-(4-dimethy-
laminophenyl)-2-hydroxyphenyl]oxazoline (4a). 2-(5-Bromo-2-
benzyloxyphenyl)oxazoline (3.6 g, 10 mmol), 4-dimethylaminophe-
nylboronic acid (1.65 g, 10 mmol), K3PO4 (6.37 g, 30 mmol),
palladium(II) acetate (0.13 g, 5 mol%), and tris(2-methoxyphe-
nyl)phosphine (0.53 g, 15 mol%) were added to a two-phase mixture
of dimethoxyethane (40 mL) and water (10 mL). The resulting
Inorganic Chemistry, Vol. 47, No. 13, 2008 5673

Son et al.
Figure 11. HOMO and LUMO energy levels (left) and orbital diagram (right) of 5 obtained by DMol3 calculations.
Figure 12. HOMO-LUMO levels of 5 estimated from cyclic voltammo-
grams.
mixture was stirred under N2 at 60 °C for 3 h. The mixture was
hydrolyzed with water. The organic layer was extracted with CH2Cl2
(3 × 30 mL) and dried over magnesium sulfate. The solvent was
removed under reduced pressure, and the residue was purified by
silica gel column chromatography using benzene/hexane (1:1) as
an eluent. 3a was obtained as a pale yellow oil (2.00 g, 50%). The
prepared benzyl-derivative 3a with 10% Pd/C catalyst (1.0 g) was
dissolved in 30 mL of THF/EtOH (1:1), and then, the mixture was
shaken for 5 h under a hydrogen atmosphere (60 psi) at room
temperature. The mixture was filtered through Celite to remove
insoluble catalyst and dried under reduced pressure. The residue
was purified by silica gel column chromatography using ethylac-
etate/hexane (V/V ) 1/10) as an eluent to give 4a as a yellow powder
1
(1.35 g, 87%). H NMR (CDCl3): δ 12.14 (s, 1H, -OH), 7.82 (d,
1H, Ph, 4JH-H ) 2.4 Hz), 7.57 (dd, 1H, Ph, 3JH-H ) 8.4 Hz,4JH-H
) 2 Hz), 7.45 (d, 2H, Ph, 3JH-H ) 8.8 Hz), 7.03 (d, 1H, Ph, 3JH-H
) 8.4 Hz), 6.79 (d, 2H, Ph, 3JH-H ) 8.8 Hz), 4.11 (s, 2H, -CH2-),
2.98 (s, 6H, -NCH3), 1.41 (s, 6H, -CH3). 13C NMR (CDCl3): δ
163.71, 158.52, 149.76, 135.97, 132.11, 131.37, 127.34, 125.39,
117.07, 113.06, 111.14, 78.60 (-CH2-), 67.41, 40.95 (-NCH3), 28.85
(-CH3). HRMS(FAB) calcd for C19H22N2O2: 310.1681. Found:
310.1695 [M]+. Anal. Calcd for C19H22N2O2: C, 73.52; H, 7.14.
Found: C, 73.48; H, 7.12.
Figure 13. (a) I-V curve (current density vs voltage) and (b) L-V curve
(luminance vs voltage) of ITO/NPB or 5a/DPVBI/Alq3/LiF/Al device.
163.60, 158.98, 158.86, 133.12, 131.68, 131.65, 127.78, 125.93,
117.19, 114.36, 111.20, 78.64 (-CH2-), 67.45, 55.62 (-OCH3), 28.83
(-CH3). HRMS(FAB) calcd for C18H19NO3: 297.1365. Found:
297.1378 [M]+. Anal. Calcd for C18H19NO3: C, 72.71; H, 6.44.
Found: C, 72.67; H, 6.43.
Synthesis of 4,4-Dimethyl-2-[5-(4-methoxyphenyl)-2-hydroxy-
phenyl]oxazoline (4b). A procedure analogous to the preparation
of 4a was used but starting from 4-methoxyphenylboronic acid (1.52
g, 10 mmol). 4b was obtained as a yellow, crystalline powder.
Yield: 60% (1.78 g) based on 2-(5-bromo-2-benzyloxyphenyl)ox-
azoline. 1H NMR (CDCl3): δ 12.18 (s, 1H, -OH), 7.82 (d, 1H, Ph,
Synthesis of 4,4-Dimethyl-2-[5-phenyl-2-hydroxyphenyl]ox-
azoline (4c). A procedure analogous to the preparation of 4a was
used but starting from phenyl boronic acid (1.22 g, 10 mmol). 4c
was obtained as a white powder. Yield: 75.6% (2.02 g) based on
2-(5-bromo-2-benzyloxyphenyl)oxazoline. 1H NMR (CDCl3): δ
4
4JH-H ) 2.4 Hz), 7.56 (dd, 1H, Ph,3JH-H ) 8.4 Hz, JH-H ) 2.4
3
3
Hz), 7.48 (d, 2H, Ph, JH-H ) 8.8 Hz), 7.05 (d, 1H, Ph, JH-H
)
3
4
8.4 Hz), 6.95 (d, 2H, Ph, JH-H ) 8.8 Hz), 4.11 (s, 2H, -CH2-),
12.22 (s, 1H, -OH), 7.88 (d, 1H, Ph, JH-H ) 2.4 Hz), 7.58 (dd,
4
3
3.84 (s, 3H, -OCH3), 1.41 (s, 6H, -CH3). 13C NMR (CDCl3): δ
1H, Ph,3JH-H ) 8.4 Hz, JH-H ) 2.4 Hz), 7.53 (d, 2H, Ph, JH-H
5674 Inorganic Chemistry, Vol. 47, No. 13, 2008

Blue Light-Emitting Zinc Complexes
Table 5. EL Spectral Data and Performance Characteristics of Devices
current
efficiency (cd/A)
luminance
(cd/m2)
max current
efficiency (cd/A)
max luminance
(cd/m2)
device
λmax (nm)a
voltage (V)
ITO/NPB/5c/LiF/Al
431
7.6b
0.015b
0.01c
0.7b
23b
127c
173b
1142c
27b
0.02
0.8
0.3
2.0
3.5
225
12.1c
7.4b
ITO/NPB/5c/Alq3/LiF/Al
428, 525
430
3300
1720
7000
13700
9.5c
0.5c
ITO/NPB/5c/BCP/Alq3/LiF/Al
ITO/5a/DPVBI/Alq3/LiF/Al
ITO/NPB/DPVBI/Alq3/LiF/Al
7.0b
0.24b
0.21c
1.8b
11.4c
7.5b
376c
180b
1650c
330b
3537c
446
10.4c
7.2b
1.9c
446
3.3b
10.1c
2.7c
a Determined from the EL spectra. @10 mA/cm2. @100 mA/cm2.
b
c
) 7.2 Hz), 7.38 (t, 2H, Ph, 3JH-H ) 7.6 Hz), 7.27 (t, 1H, Ph, 3JH-H
) 7.2 Hz), 7.06 (d, 1H, Ph, 3JH-H ) 8.4 Hz), 4.06 (s, 2H, -CH2-),
1.37 (s, 6H, -CH3). 13C NMR (CDCl3): δ 163.64, 159.54, 140.48,
132.08, 131.97, 128.99, 127.00, 126.80, 126.49, 117.34, 111.34,
78.67 (-CH2-), 67.50, 28.86 (-CH3). HRMS(FAB) calcd for
C17H17NO2: 267.1259. Found: 268.1343 [M + H]+. Anal. Calcd
for C17H17NO2: C, 76.38; H, 6.41. Found: C, 76.35; H, 6.39.
Synthesis of 4,4-Dimethyl-2-[5-(4-chlorophenyl)-2-hydroxy-
phenyl]oxazoline (4d). A procedure analogous to the preparation
of 4a was used, but starting from 4-chlorophenyl boronic acid (1.56
g, 10 mmol). 4d was obtained as a white, crystalline powder. Yield:
41% (1.24 g) based on 2-(5-bromo-2-benzyloxyphenyl)oxazoline.
Preparation of the Zinc Complexes. Synthesis of Zinc(II)
Bis{4,4-dimethyl-2-[5-(4-dimethylaminophenyl)-2-hydroxyphe-
nyl]oxazolate} (5a). A solution of zinc acetate (0.183 g, 1 mmol)
in EtOH (5.0 mL) was added dropwise to a solution of 4a (0.620
g, 2 mmol) in EtOH (20.0 mL). After stirring at room temperature
for 12 h, a white precipitate was filtered and washed with EtOH (2
× 5 mL). The washed product was recrystallized in CH2Cl2-hexane
to give 5a as a yellow, fine crystal. Yield: 87% (0.59 g). 1H NMR
3
(CDCl3): δ 7.88 (s, 2H, Ph), 7.55 (dd, 2H, Ph, JH-H ) 8.4 Hz,
3
4JH-H ) 2.4 Hz), 7.44 (d, 4H, Ph, JH-H ) 8.4 Hz), 6.92 (d, 2H,
Ph, 3JH-H ) 9 Hz), 6.78 (d, 4H, Ph, 3JH-H ) 8.4 Hz), 4.17 (s, 4H,
-CH2-), 2.96 (s, 12H, -NCH3), 1.39 (s, 12H, -CH3). 13C NMR
(CDCl3): δ 168.41, 149.35, 133.76, 127.33, 127.20, 126.92, 125.23,
123.63, 113.21, 109.00, 105.00, 78.02 (-CH2-), 66.67, 40.96
(-NCH3), 28.57 (-CH3). HRMS(FAB) calcd for C38H42N4O4Zn:
682.2498. Found: 682.2474 [M]+. Anal. Calcd for C38H42N4O4Zn:
C, 66.71; H, 6.19. Found: C, 66.69; H, 6.17.
1H NMR (CDCl3): δ 12.16 (s, 1H, -OH), 7.93 (d, 1H, Ph, 4JH-H
)
4
2.4 Hz), 7.54 (dd, 1H, Ph,3JH-H ) 8.8 Hz, JH-H ) 2.4 Hz), 7.44
3
3
(d, 2H, Ph, JH-H ) 8.4 Hz), 7.36 (d, 2H, Ph, JH-H ) 8.4 Hz),
7.01 (d, 1H, Ph, 3JH-H ) 8.8 Hz), 4.06 (s, 2H, -CH2-), 1.37 (s, 6H,
-CH3). 13C NMR (CDCl3): δ 170.11, 160.86, 140.14, 133.60,
132.63, 129.14, 128.16, 127.38, 124.37, 119.20, 117.03, 114.51,
71.01 (-CH2-), 51.34, 30.40 (-CH3). HRMS(FAB) calcd for
C17H16ClNO2: 301.0870. Found: 301.0856 [M]+. Anal. Calcd for
C17H16ClNO2: C, 67.66; H, 5.34. Found: C, 67.68; H, 5.33.
Synthesis of 4,4-Dimethyl-2-[5-(2,4-fluorophenyl)-2-hydrox-
yphenyl]oxazoline (4e). A procedure analogous to the preparation
of 4a was used, but starting from 2,4-fluorophenyl boronic acid
(1.58 g, 10 mmol). 4e was obtained as a white powder. Yield: 64%
Synthesis of Zinc(II) Bis{4,4-dimethyl-2-[5-(4-methoxyphe-
nyl)-2-hydroxyphenyl]oxazolate} (5b). A procedure analogous to
the preparation of 5a was used but starting from 4b (0.59 g, 2
mmol). 5b was obtained as a yellow crystal. Yield: 79% (0.52 g).
4
1H NMR (CDCl3): δ 7.91 (d, 2H, Ph, JH-H ) 2.4 Hz), 7.55 (dd,
2H, Ph, 3JH-H ) 8.4 Hz, 4JH-H ) 2.8 Hz), 7.47 (d, 4H, Ph, 3JH-H
3
) 8.8 Hz), 6.93 (d, 4H, Ph, JH-H ) 8.8 Hz), 6.93 (d, 2H, Ph,
3JH-H ) 10 Hz), 4.18 (s, 4H, -CH2-), 3.82 (s, 6H, -OCH3), 1.40 (s,
12H, -CH3). 13C NMR (CDCl3): δ 169.64, 168.30, 158.35, 133.92,
133.69, 127.79, 127.30, 126.75, 123.76, 114.28, 109.07, 78.13
(-CH2-), 66.82, 55.62 (-OCH3), 28.73 (-CH3). HRMS(FAB) calcd
for C36H36N2O6Zn: 656.1865. Found: 656.1868 [M]+. Anal. Calcd
for C36H36N2O6Zn: C, 65.70; H, 5.51. Found: C, 65.48; H, 5.43.
Synthesis of Zinc(II) Bis{4,4-dimethyl-2-[5-phenyl-2-hydroxy-
phenyl]oxazolate} (5c). A procedure analogous to the preparation
of 5a was used but starting from 4c (0.53 g, 2 mmol). 5c was
obtained as a white powder. Yield: 83% (0.50 g). 1H NMR (CDCl3):
δ 7.98 (d, 2H, Ph, 4JH-H ) 2.4 Hz), 7.61 (dd, 2H, Ph, 3JH-H ) 8.6
(1.94 g) based on 2-(5-bromo-2-benzyloxyphenyl)oxazoline. 1H
5
NMR (CDCl3): δ 12.31 (s, 1H, -OH), 7.78 (dd, 1H, Ph, JH-F
)
1.0 Hz), 7.51 (ddd, 1H, Ph, 5JH-F ) 1.0 Hz), 7.37 (d, 2H, Ph, 3JH-H
) 8.4 Hz), 7.07 (d, 1H, Ph, JH-H ) 8.8 Hz), 6.96-6.86 (m, 2H,
3
Ph), 4.12 (s, 2H, -CH2-), 1.41 (s, 6H, -CH3). 13C NMR (CDCl3): δ
163.39, 159.60, 133.81, 131.23, 128.38, 125.53, 121.98, 117.08,
111.59, 104.51, 78.68 (-CH2-), 67.49, 28.82 (-CH3). HRMS(FAB)
calcd for C17H15F2NO2: 303.1071. Found: 304.1161 [M + H]+.
Anal. Calcd for C17H15F2NO2: C, 67.32; H, 4.98. Found: C, 67.24;
H, 4.95.
4
3
Synthesis of 4,4-Dimethyl-2-[5-(4-cyanophenyl)-2-hydroxy-
phenyl]oxazoline (4f). A procedure analogous to the preparation
of 4a was used, but starting from 4-cyanophenyl boronic acid (1.47
g, 10 mmol). 4f was obtained as a white, crystalline powder. Yield:
42% (1.23 g) based on 2-(5-bromo-2-benzyloxyphenyl)oxazoline.
Hz, JH-H ) 2.8 Hz), 7.56 (d, 4H, Ph, JH-H ) 7.2 Hz), 7.39 (t,
3
3
4H, Ph, JH-H ) 8.0 Hz), 7.25 (t, 2H, Ph, JH-H ) 7.6 Hz), 6.96
(d, 2H, Ph, JH-H ) 8.8 Hz), 4.06 (s, 2H, -CH2-), 1.37 (s, 6H,
3
-CH3). 13C NMR (CDCl3): δ 170.06, 168.31, 140.93, 134.13,
128.82, 128.41, 126.99, 126.27, 126.20, 123.85, 109.14, 78.15
(-CH2-), 66.85, 28.75 (-CH3). HRMS(FAB) calcd for
C34H32N2O4Zn: 596.1654. Found: 596.1679 [M]+. Anal. Calcd for
C34H32N2O4Zn: C, 68.29; H, 5.39. Found: C, 68.21; H, 5.38.
Synthesis of Zinc(II) Bis{4,4-dimethyl-2-[5-(4-chlorophenyl)-
2-hydroxyphenyl]oxazolate} (5d). A procedure analogous to the
preparation of 5a was used, but starting from 4d (0.60 g, 2 mmol).
5d was obtained as a white powder. Yield: 86% (0.57 g). 1H NMR
3
1H NMR (CDCl3): δ 12.40 (s, 1H, -OH), 7.70 (dd, 2H, Ph, JH-H
4
3
) 8.4 Hz, JH-H ) 2.0 Hz), 7.65 (dd, 2H, Ph, JH-H ) 8.8 Hz,
4JH-H ) 2.0 Hz), 7.62 (dd, 1H, Ph, JH-H ) 8.4 Hz, JH-H ) 2.0
Hz), 7.11 (d, 1H, Ph, JH-H ) 8.8 Hz), 4.14 (s, 2H, -CH2-), 1.43
3
4
3
(s, 6H, -CH3). 13C NMR (CDCl3): δ 163.24, 160.52, 144.83, 132.77,
131.92, 129.67, 127.15, 126.77, 119.20, 117.75, 111.61, 110.43,
78.76 (-CH2-), 67.60, 28.80 (-CH3). HRMS(FAB) calcd for
C18H16N2O2: 292.1212. Found: 293.1297 [M + H]+. Anal. Calcd
for C18H16N2O2: C, 73.95; H, 5.52. Found: C, 73.93; H, 5.51.
4
(CDCl3): δ 7.94 (d, 2H, Ph, JH-H ) 2.4 Hz), 7.55 (dd, 2H, Ph,
4
3
3JH-H ) 8.4 Hz, JH-H ) 2.4 Hz), 7.47 (d, 4H, Ph, JH-H ) 8.4
Inorganic Chemistry, Vol. 47, No. 13, 2008 5675

Son et al.
3
3
Hz), 7.34 (d, 4H, Ph, JH-H ) 8.4 Hz), 6.95 (d, 2H, Ph, JH-H
)
the diffractometer. Preliminary examination and data collection were
performed using a Bruker SMART CCD detector system single-
crystal X-ray diffractometer equipped with a sealed-tube X-ray
source (40 kV × 50 mA) using graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å). Preliminary unit cell constants were
determined from a set of 45 narrow-frame (0.3° in ω) scans. The
double-pass method of scanning was used to exclude any noise.
The collected frames were integrated using an orientation matrix
determined from the narrow-frame scans. The SMART software
package was used for data collection, and SAINT was used for
frame integration.20a Final cell constants were determined by a
global refinement of xyz centroids of reflections harvested from the
entire data set. Structure solution and refinement were carried out
using the SHELXTL-PLUS software package.20b Detailed informa-
tion is listed in Table 1.
8.8 Hz), 4.21 (s, 4H, -CH2-), 1.42 (s, 12H, -CH3). 13C NMR
(CDCl3): δ 170.69, 168.16, 139.35, 133.86, 132.09, 128.92, 128.37,
127.47, 125.98, 123.95, 109.85, 78.20 (-CH2-), 66.91, 28.69 (-CH3).
HRMS(FAB) calcd for C34H30Cl2N2O4Zn: 664.0874. Found: 665.0935
[M + H]+. Anal. Calcd for C34H30Cl2N2O4Zn: C, 61.23; H, 4.53.
Found: C, 61.17; H, 4.49.
Synthesis of Zinc(II) Bis{4,4-dimethyl-2-[5-(2,4-fluorophenyl)-
2-hydroxyphenyl]oxazolate} (5e). A procedure analogous to the
preparation of 5a was used, but starting from 4e (0.61 g, 2 mmol).
5e was obtained as a white crystal. Yield: 89% (0.60 g). 1H NMR
3
(CDCl3): δ 7.87 (s, 2H, Ph), 7.48 (d, 2H, Ph, JH-H ) 8.4 Hz),
6.98 (d, 2H, Ph, JH-H ) 8.8 Hz), 7.68-7.59 (m, 10H, Ph), 6.98
(d, 2H, Ph, JH-H ) 8.8 Hz), 4.24 (s, 4H, -CH2-), 1.44 (s, 12H,
3
3
-CH3). 13C NMR (CDCl3): δ 170.99, 168.06, 145.21, 133.77,
132.80, 132.69, 129.16, 126.46, 124.80, 124.31, 119.48, 109.43,
78.24 (-CH2-), 67.01, 28.71 (-CH3). (FAB) calcd for
C34H28F4N2O4Zn: 668.1277. Found: 668.1251 [M]+. Anal. Calcd
for C34H28F4N2O4Zn: C, 60.95; H, 4.21. Found: C, 60.67; H, 4.17.
Synthesis of Zinc(II) Bis{4,4-dimethyl-2-[5-(4-cyanophenyl)-
2-hydroxyphenyl]oxazolate} (5f). A procedure analogous to the
preparation of 5a was used, but starting from 4f (0.58 g, 2 mmol).
5f was obtained as a white powder. Yield: 91% (0.59 g). 1H NMR
(CDCl3): δ 8.02 (d, 2H, Ph, 4JH-H ) 2.4 Hz), 7.68-7.59 (m, 10H,
Ph), 6.98 (d, 2H, Ph, 3JH-H ) 8.8 Hz), 4.24 (s, 4H, -CH2-), 1.44 (s,
12H, -CH3). 13C NMR (CDCl3): δ 170.99, 168.06, 145.21, 133.77,
132.80, 132.69, 129.16, 126.46, 124.80, 124.31, 119.48, 109.43, 78.24
(-CH2-), 67.01, 28.71 (-CH3). HRMS(FAB) calcd for C36H30N4O4Zn:
646.1559. Found: 647.1626 [M + H]+. Anal. Calcd for C36H30N4O4Zn:
C, 66.72; H, 4.67. Found: C, 66.68; H, 4.65.
Acknowledgment. This work was supported by a grant
(R02-2004-000-10095-0) from the Basic Research Program
of the Korea Science and Engineering Foundation and a
Korea University Grant of year 2003.
Supporting Information Available: 1H and 13C NMR spectro-
scopic data for 5, cyclic voltammograms, UV-vis, and PL
spectrums for 4 and 5, orbital diagrams of 5 obtained by DMol3
calculation, and EL properties of OLED devices using 5c as an
emitting layer (PDF); cif files for three crystal structures (5a, 5b,
and 5e). This material is available free of charge via the Internet at
http://pubs.acs.org.
Crystal Structure Determination. Crystals of 5a, 5b, and 5e
were obtained from CH2Cl2/hexane (V/V ) 2/1) and mounted on
IC702491J
5676 Inorganic Chemistry, Vol. 47, No. 13, 2008