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.