For Immediate Release
Until now, the aluminum tris (8-hydroxyquinoline) (Alq3) material
which is used as the emission and electron transport layer in organic
light-emitting diodes had to be deposited under high vacuum conditions,
which requires costly equipment. Attaching it to a polymer backbone allows
the material to be applied using solution processes simple spin-coating
methods already widely used for applying thin films of materials.
Beyond the implications for less costly and more flexible flat panel
displays and similar devices, the new technique demonstrates that small
molecules with interesting properties can be self-assembled onto standard
polymer backbones. Using this "Lego-like" approach could have
applications to other materials that are easier to process in polymeric
"This could have a significant impact for industry because it would
make the manufacture of organic light-emitting diodes much easier,"
Weck, an assistant professor in Georgia Tech's School
of Chemistry and Biochemistry. "You can do this on a lab bench
without million-dollar equipment. Being able to spin coat these organic
systems could allow production of large surfaces suitable for displays."
Details of the work were presented March 27th at the 225th American Chemical
Society National Meeting in New Orleans, LA. Sponsored by the National
Science Foundation and the Office
of Naval Research, the research has also been published in the journal
Because they are based on polymers, organic light-emitting diodes produced
with the new technique could offer another significant advantage
physical flexibility. That would allow production of displays that are
less prone to damage and that can operate in shapes and forms not possible
with current technology.
Using the polymer poly(norbornene) as a backbone, Weck and graduate student
Amy Meyers designed a functional monomer containing Alq3, also
known as aluminum tris (8-hydroxyquinoline). The Alq3 was covalently
bonded to the poly(norbornene) backbone, which was selected because it
can be polymerized by ring-opening metathesis, a method that tolerates
many functional groups.
Though the prototype material shows great potential, Weck cautions that
much work remains to be done before the new material finds its way into
laptop computers and other display systems.
"From a scientific standpoint, this is a milestone, but there is
a lot of optimization and evaluation that must be done," he said.
"We've shown that we can change the polymer backbone and that we
can change the connection of our Alq3 to the polymer."
Though the pure polymer has limited solubility, the researchers hope
to improve that as part of an on-going optimization process. The optical
properties of the new material appear equivalent to the conventionally-produced
material, but the details are still under study. Weck believes the trade-offs
between easier processing and optical performance will ultimately be positive.
As part of optimizing the chemistry, Weck and Meyers are adjusting the
chemistry to provide emissions of different colors that would be necessary
if the material is to be used in flat-panel displays. The material's yellow-green
luminescence can be shifted with chemical additions or introduction of
optically inactive spacer molecules.
"We want to produce a polymer system that would provide whatever
color was needed," Weck said. "The goal would be to create a
'Lego-like' system in which you put different components together to get
the output you need. We would provide a polymer backbone with an aluminum
center, and then add more units to shift the wavelength."
The Georgia Tech researchers are working with scientists at the University
of Arizona to assess how well the new material would work in OLEDs. If
long-term testing shows the new polymer has the desired stability and
other properties, it could help open up new applications for OLEDs.
"One of the issues that has held back the market is this vacuum
deposition requirement," said Weck. "Most polymeric LEDs are
difficult to make and optimize. Our system would be straightforward and
could be very interesting to industry."
Earlier efforts to improve the processing properties of Alq3
have involved mixing it with or doping it into a polymer. Neither of those
strategies has worked well.
The Alq3 system is the first demonstration of a technique
Weck hopes will allow his research group to build many new types of polymers
using modular scaffolds programmed to attract building blocks of small
molecules. Weak and easily reversed chemical interactions would self-assemble
those molecules to form complex structures with predictable physical and
In the natural world, self-assembly techniques produce thousands of varied
life forms -- bacteria to human beings -- based on a relatively small
set of amino acids and nucleosides combined in different ways. By emulating
this natural system, he hopes to simplify the synthesis of new materials
for light-emitting diodes, optical storage materials, biosensors, drug-delivery
materials and other applications.
"The goal is to simplify the synthesis of designer polymers via self-assembly using combinatorial chemistry," Weck explained. "Our group is taking design lessons from Nature by incorporating into one system several of these weak interactions to get a degree of complexity that is difficult to achieve otherwise. We believe we now have the basic proof of principle to show that we will be able to address this problem."
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WRITER: John Toon