Advancements in π-conjugated polymers: harnessing cycloalkyl straps for high-performance π-conjugated materials

Abstract

Pendant alkyl chains are widely used to successfully obtain a wide variety of soluble linear 1D π-conjugated polymers. Over the past several decades, a wide variety of π-conjugated polymers have been synthesized to realize the desired properties and improve the performance of organic electronic devices. However, this strategy is not suitable for generating soluble 2D-π-conjugated materials, including ladder polymers, nanoribbons, and 2D-π-conjugated polymers, due to strong van der Waals interactions between the ribbons and sheets. The drive to synthesize higher dimensional polymers and to enhance polymers' properties has spurred the exploration of a novel direction in materials chemistry—the synthesis of unconventional monomers and polymers. The Gavvalapalli research group has developed and used cycloalkyl straps containing aryl building blocks for the synthesis of conjugated polymers. These cycloalkyl straps, positioned either above or below the π-conjugation plane, have been shown to directly control the π–π interactions between the polymer chains. We have demonstrated that π-face masking cycloalkyl straps hinder interchain π–π interactions. The first part of this review article highlights the use of cycloalkyl straps for the synthesis of higher dimensional π-conjugated polymers. In this section, we discuss the synthesis of 2D-H-mers, dispersible hyperbranched π-conjugated polymers, and conjugated porous polymers without the pendant solubilizing chains. The second part of the feature article highlights how the cycloalkyl straps can be used to gain control over polymer–acceptor interactions, including the interaction strength and the location of the acceptor along the polymer backbone. We conclude the article with the future outlook on cycloalkyl strap-containing building blocks in the world of conjugated polymers.