Crystal Engineering-Based Approach to Introduce Mechanical Compliance in a Series of Highly Luminescent Substituted Distyrylbenzenes

Mechanically compliant adaptive molecular crystals have
recently
attracted considerable attention because of their distinctive properties
and potential applications across various fields. Nonetheless, the
fundamental understanding and practical use of these materials are
in the early stages of development. Integrating such mechanical compliance,
such as flexibility and self-healing properties, into functional organic
crystals is a promising area of research that can enhance their practical
applications and durability in optoelectronics, sensors, and other
technologies. This study presents a comprehensive analysis of the
mechanical and photophysical properties of cyano-substituted distyrylbenzene
derivatives, specifically, α-PDN-1, α-PDN-2, α-PDN-3,
and polymorphic α-PDN-4. These compounds are characterized by
their unique “twist elasticity,” resulting from changes
in torsional coordinates due to substituent effects. While isostructural
α-PDN-1, α-PDN-2, and α-PDN-3 exhibit a brittle
nature, the α-PDN-4 polymorph stands out due to its mechanical
compliance. Our structure and mechano-optical investigation reveal
that the isostructural compounds maintain similar conformational rigidity
and packing arrangements, leading to brittle mechanical behavior.
In contrast, α-PDN-4’s distinct structural and mechanical
properties highlight the influence of substituents on molecular packing
and mechanical compliance. This study underscores the potential of
cyano-substituted distyrylbenzenes in the development of mechanically
adaptive optical materials, paving the way for future applications
in flexible optoelectronic devices.