U.S. patent application number 12/438873 was filed with the patent office on 2010-01-21 for methods for producing materials with photo and electroluminescence properties and systems using such materials..
This patent application is currently assigned to THE UNIVERSITY OF AKRON. Invention is credited to Charles N. Moorefield, George R. Newkome.
Application Number | 20100013382 12/438873 |
Document ID | / |
Family ID | 39107146 |
Filed Date | 2010-01-21 |
United States Patent
Application |
20100013382 |
Kind Code |
A1 |
Newkome; George R. ; et
al. |
January 21, 2010 |
METHODS FOR PRODUCING MATERIALS WITH PHOTO AND ELECTROLUMINESCENCE
PROPERTIES AND SYSTEMS USING SUCH MATERIALS.
Abstract
The invention is directed to a method of preparing polymeric
metallomacrocycles having measurable photo- and electroluminescence
properties and devices using such materials. In an embodiment an
O-hexyl-3,5-bis(terpyridine)phenol ligand has been synthesized and
transformed into a hexagonal Zn(II)-metallomacrocycle by a facile
self-assembly procedure capitalizing on
terpyridine-Zn(II)-terpyridine connectivity. The material is usable
in an OLED device based on the photo- and electro-luminescence
characteristics thereof.
Inventors: |
Newkome; George R.; (Medina,
OH) ; Moorefield; Charles N.; (Akron, OH) |
Correspondence
Address: |
HAHN LOESER & PARKS, LLP
One GOJO Plaza, Suite 300
AKRON
OH
44311-1076
US
|
Assignee: |
THE UNIVERSITY OF AKRON
Akron
OH
|
Family ID: |
39107146 |
Appl. No.: |
12/438873 |
Filed: |
August 24, 2007 |
PCT Filed: |
August 24, 2007 |
PCT NO: |
PCT/US07/76719 |
371 Date: |
February 25, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60823574 |
Aug 25, 2006 |
|
|
|
Current U.S.
Class: |
313/504 ; 257/98;
257/E21.158; 438/29; 546/10 |
Current CPC
Class: |
H01L 51/009 20130101;
H01L 51/0092 20130101; C09K 2211/188 20130101; H01L 51/5012
20130101; C09K 2211/1029 20130101; C09K 11/06 20130101; H01L
51/0081 20130101; H01L 51/0037 20130101 |
Class at
Publication: |
313/504 ; 438/29;
546/10; 257/98; 257/E21.158 |
International
Class: |
H01J 1/62 20060101
H01J001/62; H01L 51/56 20060101 H01L051/56; C07F 15/00 20060101
C07F015/00 |
Goverment Interests
GRANT REFERENCE
[0001] The research carried out in connection with this invention
was supported in part by a grant from the National Science
Foundation (DMR-0401780, CHE-0420987, INT-0405242), the Air Force
Office of Scientific Research (F49620-02-1-0428,02), and the Ohio
Board of Regents for financial support. The Government has certain
rights in the invention.
Claims
1. A method of preparing a metallomacrocycle, the method comprising
the steps of: reacting a plurality of phenol-modified compounds
with at least one metal complex to form a self-assembled
complex.
2. The method of claim 1 where the phenol-modified compound is
O-hexyl-3,5-bis(terpyridine)phenol.
3. The method of claim 1 where the at least one metal complex
includes a transition metal.
4. The method of claim 3 where the at least one metal complex is
Zn(BF.sub.4).sub.2.4H.sub.2O.
5. The method of claim 1 where the metallomacrocycle exhibits
photoluminescent properties.
6. The method of claim 1 where the metallomacrocycle exhibits
electroluminescent properties.
7. The method of claim 1 where the assembled complex is a hexameric
metal complex.
8. A metallomacrocycle comprising: a transition
metal-terpyridinyl-based complex with alkyl side chains, wherein
the complex exhibits measurable photoluminescent and
electroluminescent properties.
9. The metallomacrocycle of claim 8 where the transition metal is
zinc.
10. The metallomacrocycle of claim 8 where the complex is a
hexamer.
11. A method of preparing an electroluminescent device, the method
comprising the steps of: depositing a mixture containing at least a
metallomacrocycle onto an indium tin oxide glass sheet; metallizing
a cathode to facilitate the deposition of a layer of a metal halide
compound and a layer of conductive metal.
12. The method of claim 11, further comprising the step of blending
the metallomacrocycle with at least one other dye.
13. The method of claim 12, further comprising the step of using at
least one color filter to form one of a red-green-blue (RGB)
emission.
14. The method of claim 11, wherein the mixture is spin-coated onto
the indium tin oxide glass sheet.
15. The method of claim 11, wherein the electroluminescent device
is a light emitting diode.
16. The method of claim 11, wherein the electroluminescent device
is an organic light emitting diode.
17. The metallomacrocycle of claim 8, wherein the metallomacrocycle
is deposited on a screen to create a graphical color display.
18. The metallomacrocycle of claim 17, wherein the graphical color
display is used ins systems selected from the group consisting of a
television screen, a computer display, a portable system screen,
and advertising and information board applications.
19. A light emitting diode device comprising the metallomacrocycle
of claim 8.
20. An organic light emitting diode device comprising the
metallomacrocycle of claim 8.
Description
TECHNICAL FIELD
[0002] The present invention relates to the preparation of
materials having photo and/or electroluminescence properties, and
more particularly to polymeric metallomacrocycles having measurable
photo- and electroluminescence properties and devices using such
materials.
BACKGROUND OF THE INVENTION
[0003] The design of highly ordered supramolecular structures has
attracted considerable interest in that the self-assembly of
specifically tailored monomers possessing appropriate ligand
directivity underpins the generation of novel and utilitarian
supramolecular complexes with two- and three-dimensional nano- and
macro-structures. Owing to their electronic and steric versatility,
aromatic N-heterocycles continue to play a prominent role as
classical ligands in coordination compounds, bridging ligands in
binuclear derivatives, and building blocks for supramacromolecular
assemblies. As a result of the connectivity of these
polyheteroaromatics by transition metals, they also provide
platforms for .pi.-back-bonding and thus an opportunity for
electron-delocalization and transport as related to photon capture
associated with light-energy conversion. More specifically,
examples of self-assembled constructs have been reported based on
the formation of stable transition metal complexes from tailored
macromolecules. These types of transition metal complexes have also
been applied to electroluminescence (EL) devices, since the fine
tuning of the light-emitting properties can be achieved by
structural modifications of the ligand or by using different
transition metals. Light-emitting properties of some materials,
which are composed of polymeric Rh(I) and Ru(II) bipyridine or
Zn(II) terpyridine complexes, have also been reported.
[0004] One type of EL device is known as an organic light-emitting
diode (OLED). An OLED is a thin-film light-emitting diode in which
the emissive layer is an organic compound. OLED technology may be
used to form picture elements in display devices. These devices
could be much less costly to fabricate than traditional LCD
displays. When the emissive electroluminescent layer is polymeric,
varying amounts of OLEDs can be deposited in rows and columns on a
screen using simple "printing" methods to create a graphical color
display, for use as television screens, computer displays, portable
system screens, and in advertising and information board
applications to name a few.
[0005] An OLED works on the principle of electroluminescence. The
key to the operation of an OLED is an organic luminophore. An
exciton, which consists of a bound, excited electron and hole pair,
is generated inside the emissive layer. When the exciton's electron
and hole combine, a photon can be emitted. An exciton can be in one
of two states, singlet or triplet. Only one in four excitons is a
singlet. The materials currently employed in the emissive layer are
typically fluorophors, which can only emit light when a singlet
exciton forms, which reduces the OLED's efficiency. By
incorporating transition metals into a small-molecule OLED, the
triplet and singlet states can be mixed by spin-orbit coupling,
which leads to emission from the triplet state.
[0006] It would be advantageous to provide a method of
self-assembly of hexameric metallomacrocycles wherein the
self-assembly process occurs by at least one metal-mediated moiety.
It would also be advantageous to provide a method of self-assembly
of hexameric metallomacrocycles, wherein the self-assembly process
provides self-assembled structures having measurable photo- and
electroluminescence properties and may be used in a light-emitting
diode device.
SUMMARY OF THE INVENTION
[0007] According to the present invention, there is provided a
method of preparing polymeric metallomacrocycles having measurable
photo- and electroluminescence properties and devices using such
materials. Other advantages and characteristics of the present
invention are described in more detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic representation of the self-assembly of
a metallomacrocycle of the present invention;
[0009] FIG. 2 is a UV/Vis and photoluminescence spectra of a
metallomacrocycle of the present invention;
[0010] FIG. 3A is a schematic diagram of the energy levels for OLED
device components of the present invention, wherein PEDOT, BCzVBi,
BCP, and Alq.sub.3 represent poly(3,4-ethylenedioxythiophene),
4,4'-[bis(9-ethyl-3-carbazovinylene]-1,1'-biphenyl,
2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, and
tris(8-hydroxyquinoline)aluminum, respectively;
[0011] FIG. 3B is an electroluminescence spectra OLED device of the
present invention at 10 mA/cm.sup.2 (I), 50 mA/cm.sup.2 (II), and
100 mA/cm.sup.2 (III) current density, respectively; EL emission
image (inset); and
[0012] FIG. 4 is a current-voltage (circle) and brightness-voltage
(triangle) measurements of the OLED device of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0013] Generally, the present invention provides a method of
preparing self-assembly of hexameric metallomacrocycles, wherein
the self-assembly process provides self-assembled structures having
measurable photo- and electroluminescence properties and may be
used in a light-emitting diode device. In a first embodiment, as
will be described in relation to FIGS. 1 and 2, the self-assembly
of hexameric metallomacrocycles, more specifically, this embodiment
relates to the self-assembly of O-hexyl-3,5-bis(terpyridine)phenol
ligand that has been synthesized and transformed into a hexagonal
Zn(II)-metallomacrocycle by a facile self-assembly procedure
capitalizing on terpyridine-Zn(II)-terpyridine connectivity.
[0014] Chemicals utilized in preparing the hexameric
metallomacrocycles of the present invention were commercially
purchased and used without further purification. Thin layer
chromatography (TLC) was conducted on flexible sheets precoated
with Al.sub.2O.sub.3 (IB-F) or SiO.sub.2 (IB2-F) and visualized by
UV light. Column chromatography was conducted using basic
Al.sub.2O.sub.3, Brockman Activity I (60-325 mesh) or SiO.sub.2
(60-200 mesh).
[0015] The initial O-hexyl-3,5-bis(terpyridine)phenol (1) was
constructed from O-benzyl-3,5-diformylphenol by treatment with
2-acetylpyridine under standard conditions, followed by a
Williamson synthesis with n-hexyl bromide. In particular, a mixture
of 3,5-di(terpyridine)phenol (210 mg, 380 .mu.mol) and
K.sub.2CO.sub.3 (26 mg, 190 .mu.mol) in MeCN (60 ml) was stirred at
25.degree. C. for 30 min, then n-hexyl bromide (68 mg, 420 .mu.mol)
was added. The resultant suspension was refluxed for 10 h under
N.sub.2. The solvent was removed in vacuo to give a pale yellow
oily residue, which was dissolved in CHCl.sub.3, washed with water,
and dried (MgSO.sub.4) to afford a light yellow oil. This crude
material was column chromatographed (Al.sub.2O.sub.3) eluting with
CHCl.sub.3, to give 1 (75%) as a white powder, which was
subsequently recrystallized from a CH.sub.2Cl.sub.2/hexane
mixture.
[0016] The structure was confirmed by .sup.1H NMR, which showed a
triplet at 4.17 ppm (OCH.sub.2) as well as peaks at 7.36 ppm (dd,
5,5''-tpyH), 8.70 (d, 3,3''-tpyH), 8.79 (s, 3',5'-tpyH), and 8.75
ppm (d, 6,6''-tpyH) attributed to the terpyridinyl moieties and the
presence of the definitive number and position of the other peaks
in the .sup.13C NMR; a mass peak (ESI-MS) appearing at m/z 641.5
amu (M.sup.++H, 100%) further confirmed the structure. .sup.1H and
.sup.13C NMR spectra were recorded on a 300 NMR MHz spectrometer.
Mass spectra were obtained on an Electrospray Ion Trap mass
spectrometer (ESI-MS).
[0017] Treatment of bisterpyridine 1, as seen in FIG. 1, with one
equivalent of Zn(BF.sub.4).sub.2.4H.sub.2O in MeCN for 12 h at
75.degree. C. resulted in the self-assembled hexameric complex
[Zn.sub.6(1).sub.6(BF.sub.4).sub.12] (2; FIG. 1). In particular,
O-Hexyl-bisterpyridine (1; 30 mg) was dissolved in MeCN (20 ml),
following a solution of Zn(BF.sub.4).sub.2.4H.sub.2O (one
equivalent) in MeOH (10 ml) was slowly drop-wise at 26.degree. C.,
the pale yellow solution was refluxed overnight. After
precipitation from diethyl ether, a yellow powder was collected
(>75%).
[0018] The .sup.1H NMR spectrum of 2 revealed two sharp singlets at
8.01 (2,6-ArH) and 8.55 ppm (3-ArH). These sharp peaks demonstrate
the presence of a single homogenous environment for all such
groups; this is in contrast to the broadened or multiple signals
that is expected for linear oligomers. The observed upfield shift
for the doublet at 7.94 ppm (6,6''-tpyHs; .DELTA..delta.=-0.81) and
downfield shift for the singlet at 9.25 ppm (3',5'-tpyHs;
.DELTA..delta.=0.46), when compared to the absorptions for the
uncomplexed starting material, also confirm the symmetry associated
with macrocyclization. Lastly, the hexagonal motif was established
(ESI-MS) by the definitive signals for multiple-charged entities
ranging from the +5 to +7 charge states derived from the loss of
(BF.sub.4.sup.-).sub.n.
[0019] The UV/Vis absorption and photoluminescence (PL) spectra of
this Zn(II)-hexamer is shown in FIG. 2. UV/Vis absorption spectrum
was obtained on Hewlett-Packard UV/Vis spectrophotometer, and is
shown at 10. Photoluminescence (PL) spectra were obtained using a
Perkin-Elmer LS55 luminescence spectrometer, with the PL spectra
under THF solution at 12 and film at 14. The EL spectrum and
brightness of the device were measured with a PR650 Spectra Scan
under 25.degree. C. The electrochemical experiments reported in
this work were performed using a BAS Epsilon potentiostat. The
major absorption bands at .lamda..sub.max=326 and 368 nm
originating from intra-ligand charge transfer (.sup.1ILCT) are
observed without metal-ligand charge transfer (MLCT) peaks; the
MLCT of Zn(II) metal to terpyridine can be excluded. The PL in a
THF solution at 25.degree. C. shows a blue emission [Commission
Internationale de l'Eclairage (CIE) coordinates: x=0.17, y=0.18] at
.lamda..sub.max=463 nm. The PL in a solid film (thickness: 100 nm)
is nearly identical (CIE coordinates: x=0.20, y=0.23) to that in
THF solution. This implies that there is no noticeable effect of
the charged complexes on the emission wavelength. Using charged
iridium complexes, large (up to 80 nm) shifts in the emission
spectra have been observed when changing from solution to solid
film. This leads to the conclusion that the PL of Zn(II)-hexamer is
less sensitive to its medium than the tris-chelated charged iridium
complexes.
[0020] In order to test the photo- and electroluminescent
properties of the metallomacrocycles of the present invention, an
LED device was prepared. In particular, the electroluminescent
device was prepared on indium tin oxide (ITO) glass (sheet
resistance: 20 .OMEGA./sq), which was cleaned sequentially with a
detergent solution, deionized water, ethanol, and acetone.
Poly(3,4-ethylenedioxythiophene) (PEDOT, 40 nm),
N,N'-diphenyl-N,N'-di(1-naphthyl)-1,1'-biphenyl-4,4'-diamine
(.alpha.-NPD, 20 nm), and Zn(II)-hexamer 2 were blended with 4 wt.
% of 4,4'-[bis(9-ethyl-3-carbazovinylene]-1,1'-biphenyl (BCzVBi, 30
nm), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP, 20 nm),
and tris(8-hydroxyquinoline)aluminum (Alq.sub.3, 20 nm) that was
deposited on the ITO glass in a standard spin-coating manner.
Metallization of the cathode was conducted at 7.times.10.sup.-7
Torr to deposit 1 nm of LiF and 100 nm of A1.
[0021] The cyclic voltammogram of this Zn(II)-hexamer coated on ITO
glass was measured in a conventional three-electrode cell
configuration with a Pt gauze counter electrode, a Ag/Ag.sup.+
reference electrode, and a 0.1 M tetrabutylammonium
hexafluorophosphate (TBAPF.sub.6), as the electrolyte, in DMF. The
Zn(II)-hexamer exhibited only terpyridinyl-centered reduction
couples, which are reversible one-electron couples for successive
reduction of the two coordinated terpyridinyl centers at -1.66 and
-1.85 V, respectively. As expected, there are no metal-centered
redox processes because the d-shell of the Zn(II) metal ion in the
complex is completely filled. Hence, the highest occupied molecular
orbital (HOMO: -5.8 eV) and lowest occupied molecular orbital
(LUMO: -2.3 eV) levels are estimated by their reduction potentials
and optical band gaps. The energy gap between the HOMO and LUMO
level of Zn(II)-hexamer is 3.5 eV.
[0022] The thermal stability of this Zn(II)-hexamer was studied by
thermogravimetric analysis (TGA) which showed the decomposition
temperature to be 405.degree. C. under a nitrogen atmosphere. This
material possesses good thermal stability supporting its
suitability for electronic device applications.
[0023] This Zn(II)-hexamer was fabricated into an
electroluminescent device with the following configuration:
ITO/PEDOT/NPD/Zn(II)-hexamer:BCzVBi/BCP/Alq.sub.3/LiF/Al. FIG. 3A
schematically depicts the relative HOMO and LUMO energies of the
OLED device components, where PEDOT, BCzVBI, BCP, and Alq.sub.3
represent poly(3,4-ethylenedioxythiophene),
4,4'-[bis(9-ethyl-3-carbazovinylene]-1,1'-biphenyl,
2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, and
tris(8-hydroxyquinoline)aluminum, respectively. The
electroluminescence (EL) spectrum of this LED device at a bias
voltage of 6.9 V shows an emission with peak maxima at 515 nm, as
seen in FIG. 3B, at 10 mA/cm.sup.2 current density as shown at 20,
at 50 mA/cm.sup.2 current density as shown at 22, and 100
mA/cm.sup.2 current density as shown at 24, respectively. There is
also shown the EL emission image as an inset in FIG. 3B. At all
forward-applied bias-voltages, only a green emission at
.lamda..sub.max=515 nm was realized. These EL spectral results
confirmed that the Zn(II)-hexamer functioned as an
electron-transport material in the LED device. The current
density-voltage-luminance (I-V-B) characteristics curve is shown in
FIG. 4, with the current-voltage measurements of the OLED device
shown at 30, and brightness-voltage measurements of the OLED device
shown at 32, according to an example of the present invention. The
turn-on voltage is .about.4 V and the device has a maximum
efficiency of 0.16 cd/A. The maximum luminance of 39 cd/cm.sup.2
was obtained under a driving voltage of 7.6 V. The emission color
of the device is green (CIE coordinate: x=0.28, y=0.48).
[0024] The Zn(II)-terpyridinyl-based hexagonal metallomacrocycle
having long alkyl chains to enhance the solubility was readily
synthesized by Zn(II)-mediated self-assembly and shown to possess
fluorescence, good thermal structural stability, and organic
solubility. A green light emission under forward bias potential was
obtained in an OLED made from this Zn(II)-hexamer, with an image of
the EL emission shown inset in FIG. 3B. By blending this material
with other dyes, the invention contemplates the preparation of
white-light EL devices that can be used to achieve red-green-blue
(RGB) emission by color-filtering technology,
[0025] To illustrate the invention, it is shown and described with
respect to specific embodiments. This is not intended as a
limitation, and other modifications or variations in the specific
form shown and described will be apparent to those skilled in the
art. The embodiments were chosen and described in order to best
explain the principles of the invention and practical applications
to thereby enable a person skilled in the art to best utilize the
invention and various embodiments with various modifications as are
suited to the particular use are contemplated.
* * * * *