Conjugated ladder polymers: Advances from syntheses to applications

The bigger pictureOver the past century, the vast majority of polymers synthesized and studied by humanity were single stranded. Research on multi-stranded polymers, such as ladder polymers, presents a compelling challenge for chemists. Although ladder polymer chemistry is nascent compared with that of traditional polymers, it has seen significant advancements in recent decades. Among these multi-stranded polymers, conjugated ladder polymers (CLPs) are particularly noteworthy, thanks to their distinct electronic structures that contribute to unique electronic, optical, and magnetic properties. These properties, along with CLPs' extraordinary stability, could address challenges in various cutting-edge application fields; e.g., bioelectronic devices, wearable electronics, and sustainable energy storage. Future research should focus on developing new sustainable synthetic methods, applying large-area processing techniques, and enhancing the integrated functions of these polymers.SummaryConjugated ladder polymers (CLPs) represent a fascinating class of macromolecules characterized by their multi-stranded, π-conjugated structures with uninterrupted fused rings forming the backbone. Their unique constitution presents synthetic challenges that extend beyond those associated with conventional conjugated polymers. The synthesis of CLPs is typically achieved through one-pot annulative ladder polymerization or a two-step process involving polymerization followed by post-polymerization cyclization. Over the past decade, numerous innovative synthetic techniques and novel CLP structures have emerged. The distinctive architectures of these CLPs endow them with exceptional properties and robustness that are often unmatched by conventional non-ladder polymers. Significant progress has been made in the application of CLPs in various domains, such as organic semiconductors, active materials in organic electrochemical transistors, and organic thermoelectric devices. Despite these advances, the field continues to face a series of chemical and engineering challenges that must be overcome to fully harness the potential of CLPs as a highly promising class of functional organic materials.Graphical abstract