Processing, Morphology and Physical Properties of Functionalized Pentacenes

1
Processing, Morphology and Physical Properties of
Functionalized Pentacenes Jihua Chen1, Chee Keong
Tee2, Kaitlin Gallup1,3, Chelsea Haughn1,3, John
Anthony6, and David C. Martin1,3,4 1Macromolecula
r Science and Engineering Center, 2Dept of
Electrical Engineering and Computer Science,
3Department of Materials Science and
Engineering, 4Department of Biomedical
Engineering, 5Dept of Aerospace Engineering, The
University of Michigan at Ann Arbor 6Department
of Chemistry, The University of Kentucky
Abstract With their enormous structural
variability and potential ease of fabrication,
organic electronic semiconductors have attracted
significant commercial and scientific interest in
the recent years. Of these, Pentacene has been
extensively investigated as the active
semiconducting materials in thin-film
transistors, for application in flexible displays
and other electronic devices. While pentacene
exhibits one of the highest reported hole
mobility values (1 cm2/Vs), it is not very
soluble in organic solvents, which limits its use
in low-cost solution-based fabrication processes.
Also, pentacene molecules are known to
adopt a herringbone molecular arrangement in thin
films even at the best deposition conditions.
This mode of packing limits the tuning of p-p
interaction, and hence the charge mobility.
We are investigating the variations in
microstructure and physical properties of a
family of functionalized pentacenes of interest
for making organic electronic devices such as
thin film transistors. These pentacenes have
been modified with alkyl acetylene or alkyl silyl
groups with systematic variations in the alkyl
spacer length. This modification disrupts the
herringbone packing seen in neat pentacene,
promoting face-to-face arrangements between the
acene rings and providing for solubility in a
variety of convenient solvents. Thin films can
be readily formed by solution casting from
toluene and other organic solvents. We have
investigated the structure and properties of the
functionalized pentances using hot stage optical
microscopy, differential scanning calorimetry,
transmission electron microscopy, and electron
diffraction. The materials show regular
variations in their thermal behavior and
macroscopic properties as the chemistry of the
side-group substituent changes.
Acknowledgements The authors would like to thank
the NSF for financial support. TEM studies were
conducted at the Electron Microbeam Analysis
Laboratory at the University of Michigan at Ann
Arbor, with patient assistance from the lab
managers, Dr. Carl Henderson, Dr. John Mansfield,
and Dr. Kai Sun. Transistor characterizations
were performed in the DC testing lab of the Solid
State Electronics Lab (SSEL) at the University of
Michigan.