Development of semiconducting polymers based on a novel heteropolycyclic aromatic framework

The choice of appropriate building blocks and the development of new donor and acceptor units are essential for the creation of high-performance donor-acceptor (D-A)-type semiconducting polymers. In addition, the introduction of π-extended aromatic frameworks into polymer main chains is a useful strategy to facilitate dense π-π stacking structures with long-range order in the solid-state, thereby enabling efficient carrier transport in organic electronics. However, such highly π-extended aromatic frameworks have rarely been reported due to the need for multiple steps. This focus review describes the synthesis and characterization of D-A polymers based on three π-extended heteropolycyclic aromatic frameworks, using phenanthro[1,2-b:8,7-b’]dithiophene (PDT) as a weak donor and alkoxy-substituted anthra[1,2‑c:5,6‑c’]bis([1,2,5]thiadiazole) (ATz) and vinylene-bridged 5,6-difluorobenzo[c][1,2,5]thiadiazole (FBTzE) as new thiadiazole-based acceptor units. In addition, their applications to organic electronic devices, such as organic field-effect transistors (OFETs) and organic photovoltaic cells (OPVs), and the detailed relationship between the thin-film structure and device performance in OFETs and OPVs were investigated. These results indicate that these novel π-extended heteropolycyclic aromatic frameworks may serve as building units for the development of wide-bandgap p-type semiconducting polymers for nonfullerene solar cells and low-bandgap n-type semiconducting polymers for OFETs and OPVs.