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Understanding the Role of Bulky Side Chains on Polymorphism of BTBT-Based Organic Semiconductors
journal contribution
posted on 2020-02-20, 12:38 authored by Hyunjoong Chung, Shanwen Chen, Bijal Patel, Guillaume Garbay, Yves H. Geerts, Ying DiaoPolymorphism
plays a major role in organic electronics, since even the slightest
change in packing can modulate electronic properties. Controlling
and accessing polymorphs of organic semiconductors are critical, but
they are usually discovered by serendipity. A clear understanding
of the molecular origin of polymorphism is essential, but system-specific
studies are largely prevalent, each system presenting a unique challenge.
In this work, we conduct a systematic study of five organic semiconductors
with the absence or presence of various bulky side chains. We discover
polymorphs only in three out of five systems in their bulk single-crystal
forms. The three systems that exhibit polymorphism all contain side
chains on both ends of the core. We resolve the crystal structures
and analyze key parameters for changes in the packing environment
such as density, intermolecular distance, and short contacts. These
parameters indicate that the added bulky side chains loosen the molecular
packing and that, as the side chains get bulkier, the effect is stronger.
Thus, the bulky side chains create a packing environment more favorable
for polymorphism. This proposes a generalizable molecular design rule
for triggering polymorphs in organic semiconductors.