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Molecular electronics got a boost with the discovery of a new
class of liquid crystalline materials that has potential use in
electronic devices such as light emitting diodes (LED), solar
cells, optical switches and transistors.
The new molecules are called supramolecular helical dendrimers.
The molecules making up liquid crystal are based on highly branched
polymers called dendrimers that assemble themselves into arrays
of semiconducting columns, each with a structure reminiscent of
DNA. The high degree of molecules' abilities to organize leads
to efficient transport of electrical signals.
Kenneth Singer, Case Western Reserve University professor of
physics; Virgil Percec, University of Pennsylvania professor of
macromolecular chemistry; and a team of researchers described
these dendrimers, their structures and properties in the September
26th Nature article, "Self-organization of supramolecular
helical dendrimers into complex electronic materials."
Interest in organic materials as electronic materials has grown
rapidly with the introduction of electronic displays made from
luminescent organic crystals and polymers. Highly organized fluids,
such as those described in the Nature article, combine
the important properties of efficient electrical transport with
the ability to easily and cheaply produce devices.
These new materials represent a significant advance in that they
allow unprecedented flexibility in the design of materials to
be custom-tailored in order to precisely match the electronic
function needed, according to Singer.
"The dedrimers are very robust at driving self-assembly of arrays
of columns, seeming to almost grow themselves into electronic
devices," he said. "This property enables the self-organization
of nearly any electronically active molecule, even ones that would
never be expected to organize in such an ordered array.
"This concept might enable a new generation of low-cost, light-weight
and easier to produce electronic devices," added Singer, whose
lab conducted the measurements of the electrical properties of
the dendrimers.
Over the past five years, Singer collaborated with Percec, who
is a pioneer in dendrimers and was responsible for advancing the
material concept. Dendrimers are molecules with branched tails
of hydrocarbons and fluorocarbons. These tails link to the electronically
functional molecules and force them to stack like poker chips
in a column, enhancing their electronic interactions. The columns
then self-organize into an ordered array.
"This concept is particularly exciting since one can imagine
the same material forming a device made from a single molecular
column up to a gigantic array of columns the size of computer
screens," Singer said.
The research by Singer and Percec, who was a former faculty member
in macromolecular science at CWRU, has the support of a grant
from the U.S. Air Force's Office for Scientific Research.
Other collaborators are Irina Shiyanovskaya from CWRU's physics
department; Martin Glodde, T.K. Bera, and Y. Miura from Penn's
chemistry department; V.S. K. Balagurusamy and Paul A. Heiney
from Penn's department of physics and astronomy; A. Rapp and H.
W. Spiess from the Max Planck Institute for Polymer Research in
Germany; and S. D. Hudson and H. Duan from the National Institute
of Standards and Technology in Maryland.
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