Unusual Cross-conjugation in Cyclic Dipeptide-based Building Blocks for Donor-Acceptor Semiconducting Conjugated Polymers

Cross conjugation, though prevalent in many organic compounds, is typically considered less effective for electron delocalization compared to linear conjugation. Consequently, it is rarely used as the backbone structure for semiconducting conjugated polymers. In this study, we designed and synthesized a novel building block, TIDP, which features a central cyclic dipeptide with cross conjugation characteristics. Strong intramolecular hydrogen bonding interactions confer TIDP with a highly rigid and coplanar conformation. Importantly, theoretical calculations reveal that π electrons are well delocalized across the entire structure, despite its low aromaticity. Conjugated polymers incorporating TIDP exhibit high charge carrier mobilities, demonstrating the effective π electron delocalization of this innovative building block. Our findings show that with rational design, cross conjugation can achieve effective π electron delocalization, providing a valuable approach for developing high-performance conjugated polymers for organic electronic materials.