-- The future of high-speed electronics might very
well be defined by linking together small, "electrically
jumpy" molecules called chromophores. According
to researchers at the University of Pennsylvania
and St. Josephs University, electrical charges can
zip along chains of linked chromophores faster than
any electrical charge yet observed in organic semiconductors,
beating the previous benchmark in this regard by
a factor of three. Their findings suggest the
use of chromophore-based circuitry that could create
nano-sized electronic components for numerous applications. Their
findings are presented in the current issue of the
Journal of the American Chemical Society.
In chemistry, a chromophore is any molecule or part
of a molecule responsible for its color. Light
hitting a chromophore excites an electron, which
then emits light of a particular color.
"Here we have created chains of chromophores that
are primed to move charge," said Michael J. Therien,
a professor in Penn's Department of Chemistry and
lead researcher in the project. "When a charge
is introduced to an array of chromophores linked
closely together, it enables electrons to quickly
hop from one chromophore to the next."
A charge can travel down a chain of chromophores
at a rate of about 10 million times a second, which
means that these chromophore arrays can do anything
that organic semiconductors currently do, only much
Penn researchers Kimihiro Susumu and Paul Frail
built chromophore circuits that could, for example,
serve as the functional elements in disposable plastic
electronics, radio frequency identification tags,
electronic drivers for active-matrix liquid crystal
displays and organic light-emitting diodes as well
as for lightweight solar cells.
Therien and his colleagues have found that the key
to creating materials that allow electrons to move
so quickly and freely is to build structures that
feature long chromophores and short linkers between
"This arrangement of linked chromophores leads to
small structural changes when holes (positive charges)
and electrons (negative charges) are introduced into
these structures and these physical changes help
propagate the charge," said Paul Angiolillo of St.
Josephs University, co-author of the study. "The
introduction of these structural changes is actually
a new idea in the design of conducting and semi-conducting
The semiconductor industry is well aware of potential
barriers to creating faster and faster electronics. In
terms of circuitry, size directly relates to speed.
Currently, circuits based on semiconductors have
shrunk to dimensions just below 100 nanometers, or
one hundred billionths of a meter, across. Chromophores
may represent the first relatively easy-to-use materials
that function on the nanoscale.
"In order to move significantly past the 100-nano
barrier in electronics, we need to develop nano structures
that let electrons move, as they do through wires
and semiconductors," Therien said. "Our work
also shows for the first time that molecular conductive
elements can be produced on a 10-nanometer length
scale, providing an important functional element
for nanoscale circuitry."
This research was supported by the Department of
Energy and the National Science Foundation