new class of organic materials developed at Northwestern University
boasts a very attractive but elusive property: ferroelectricity. The
crystalline materials also have a great memory, which could be very
useful in computer and cellphone memory applications, including cloud
team of organic chemists discovered they could create very long
crystals with desirable properties using just two small organic
molecules that are extremely attracted to each other. The attraction
between the two molecules causes them to self assemble into an ordered
network—order that is needed for a material to be ferroelectric.
starting compounds are simple and inexpensive, making the lightweight
materials scalable and very promising for technology applications. In
contrast, conventional ferroelectric materials—special varieties of
polymers and ceramics—are complex and expensive to produce. The
Northwestern materials can be made quickly and are very versatile.
addition to computer memory, the discovery of the Northwestern
materials could potentially improve sensing devices, solar energy
systems and nanoelectronics. The study will be published Aug. 23 by the
work will serve as a guide for designing these materials and using
ferroelectricity in new ways,” said Samuel I. Stupp, Board of Trustees
Professor of Chemistry, Materials Science and Engineering, and Medicine.
He is a senior author of the paper. “Our molecular design enables us to
invent a nearly infinite library of ferroelectric materials.”
materials exhibit spontaneous electric polarization (making one side of
the material positive and the opposite side negative) that can be
reversed by the application of an electric field (from a battery, for
example). These two possible orientations make the materials attractive
to researchers developing computer memory because one orientation could
correspond to a 1 and the other to a 0. (Computer memory stores
information in 1’s and 0’s.)
material’s behavior is complex, but the superstructure is simple,” said
Sir Fraser Stoddart, Board of Trustees Professor of Chemistry in the
Weinberg College of Arts and Sciences at Northwestern. He also is a
senior author. “It is the superstructure that gives the material its
two first authors of the paper are Alok Tayi, a former graduate student
in Stupp’s lab and now a postdoctoral fellow at Harvard University, and
Alexander Shveyd, a former graduate student in Stoddart’s lab and now a
postdoctoral fellow at the University of Rochester.
new supramolecular materials derive their properties from the specific
interaction, repeated over and over again between two small alternating
organic molecules, not from the molecules themselves. The two
complementary molecules interact electronically and so strongly that
they come close together and form very long crystals. This highly
ordered 3-D network is based on hydrogen bonds.
particular, the materials could help address the very expensive upkeep
of cloud computing. Facebook, Google, Web-based email and other services
are stored in the cloud and rely on volatile memory. When the power is
turned off, volatile memory forgets the information it’s holding. So the
power has to be kept on.
new ferroelectric materials could be developed into non-volatile
memory. With this type of memory, if the power is turned off, the
information is retained. If the cloud and electronic devices operated on
non-volatile memory, $6 billion in electricity costs would be saved in
the U.S. annually, the researchers said.
non-volatile computer memories are not based on ferroelectrics. But
ferroelectric memories promise to consume less power, last longer and
capture data faster than conventional non-volatile memories.
so often happens in science, serendipity played a role in this
discovery of super long crystals. Shveyd was trying to make boxlike
molecular rings, but this outcome was never observed. Instead, he
stumbled upon the interesting crystals.
discovery effectively opened up a Pandora’s box,” Stoddart said. “Alex
started working with Alok in Stupp’s group, and the two of them took
advantage of the interactions between the two building blocks. They
optimized the design so they could grow very long crystals with
interaction between the molecules is very strong—almost like a key in a
lock,” Shveyd said. “They fit very well together. This interaction
produces ferroelectricity, which, to our great surprise, happened at
type of interaction between two molecules previously had been found to
give rise to ferroelectricity in three other materials but only below
liquid nitrogen temperatures. The new materials developed at
Northwestern include additional interactions that enable this property
to occur for the first time at room temperature and above.
new material is all about electron exchange between two small
molecules. One molecule is the donor of electrons (red), and the other
is the acceptor of electrons (blue). The red and blue molecules are
arranged in a mixed stack, and one type alternates with the other.
Within that network, each molecule partners with a neighbor and
exchanges electrons. Then an electric field is applied, prompting the
molecules to switch partners, like dancers on a dance floor. This switch
of partners produces ferroelectricity.
research team developed a library of 10 complexes with this
architecture. Three are reported in the Nature paper. The crystals are
based on complexes between a pyromellitic diimide-acceptor and donors
that are derivatives of naphthalene, pyrene and tetrathiafulvalene.
simplicity of our system demonstrates how self-assembly can endow
materials with novel functions,” Tayi said. “We hope our work motivates
chemists and engineers to explore ferroelectricity in organic
Source: Northwestern University