Two Regioisomeric Ladder Polymers with a Fully Conjugated or Cross-Conjugated Polyacene-Type Skeleton

Two regioisomeric ladder polymers with a fully conjugated or cross-conjugated polyacene-type skeleton have been made by combining transition-metal-catalyzed aryl-aryl coupling and dehydrating post-polymerization cyclization. The regioisomeric variation results from a simple change in the monomers’ substitution pattern and gives rise to a fully conjugated PAL 1 and a cross-conjugated PAL 2. The fully soluble ladder polymers represent small-width graphene nanoribbons (GNRs) that can be investigated on the single-chain level. Density functional theory (DFT) calculations show different geometrical atomic arrangements along the fully annelated main chains and an appreciably lower HOMO-LUMO gap for the fully conjugated PAL 1. PAL 1 likewise exhibits increased on-chain charge carrier mobilities compared with PAL 2, as derived from ultrafast photoconductivity measurements using optical pump-terahertz (THz) probe (OPTP) spectroscopy.