Fluorescence image
of self-assembled TAT crystalline nanowires. Inset shows
a structural
schematic of the TAT crystal packing geometry and direction of charge
separation.
A new property
discovered in the organic semiconductor molecule could lead to more efficient
and cost-effective
materials for use in cell phone and laptop displays, among other applications. Courtesy
UMass Amherst/Mike Barnes
(February 25, 2016) Chemists
and polymer scientists collaborating at the University of Massachusetts Amherst
report in Nature Communications this week that they have for the first time
identified an unexpected property in an organic semiconductor molecule that
could lead to more efficient and cost-effective materials for use in cell phone
and laptop displays, for example, and in opto-electronic devices such as
lasers, light-emitting diodes and fiber optic communications.
Physical chemist Michael Barnes and polymer scientist
Alejandro Briseño, with doctoral students Sarah Marques, Hilary Thompson,
Nicholas Colella and postdoctoral researcher Joelle Labastide, discovered the
property, directional intrinsic charge separation, in crystalline nanowires of
an organic semiconductor known as 7,8,15,16-tetraazaterrylene (TAT).
The researchers saw not only efficient separation of charges
in TAT, but a very specific directionality that Barnes says “is quite useful.
It adds control, so we’re not at the mercy of random movement, which is
inefficient. Our paper describes an aspect of the nanoscopic physics within
individual crystals, a structure that will make it easier to use this molecule
for new applications such as in devices that use polarized light input for
optical switching. We and others will immediately exploit this directionality.”
He adds, “Observing the intrinsic charge separation doesn’t
happen in polymers, so far as we know it only happens in this family of small
organic molecule crystalline assemblies or nanowires. In terms of application
we are now exploring ways to arrange the crystals in a uniform pattern and from
there we can turn things on or off depending on optical polarization, for
example.”