Control of Molecular Orientation in Organic Semiconductors Using Weak Iodine–Iodine Interactions

Controlling
the molecular orientation of materials is a key issue
for improving the performance of organic semiconductor devices. Herein,
we demonstrate the structure–property relationships of iodinated
and noniodinated molecules based on an asymmetric thienoacene framework.
The noniodinated molecule formed an antiparallel slip-stack structure
with small orbital overlap between molecules. In contrast, the iodinated
molecule formed a head-to-head layered-herringbone structure, and
as a result, the transfer integrals became larger and the hole mobility
increased significantly compared with the noniodinated material. The
iodinated molecule was made into a stable and solution-processable
p-type organic semiconductor with a mobility of 2.2 cm2 V–1 s–1, which was 2 orders
of magnitude higher than that of the noniodinated molecule. This study
reveals that controlling molecular orientations using iodine–iodine
interactions is a promising strategy for accelerating the development
of organic semiconductor materials.