Unlike naphthalene diimides, perylene diimides, and other classes of n-type conjugated polymers with numerous derivatives that enable understanding of structure–property relationships, the electronic structure and properties have not been reported for any derivative of ladder poly­(benzimidazobenzophenanthroline) (BBL). Herein, we report the synthesis and properties of BBL-P, a phenazine derivative of BBL. In acid solution, BBL-P has a broad absorption spectrum with a lowest energy absorption peak at 840 nm due to protonation-enhanced intramolecular charge transfer. Compared to BBL, BBL-P thin films have decreased crystallinity with face-on molecular orientations on substrates, resulting in a substantially decreased field-effect electron mobility of 1.2 × 10–4 cm2/V s. BBL-P films have excellent mechanical properties exemplified by a Young modulus of 11 GPa. The results demonstrate that BBL-P is a promising n-type semiconducting polymer and provide new insights into the effects of backbone structure on electronic structure, thin film microstructure, and charge transport properties of conjugated ladder polymers.

Improving carrier mobility, redox stability, blend morphology, and photovoltaic performance while elucidating structure–property relationships remains an important design goal for nonfullerene electron acceptors (NFAs) for organic solar cells. Although numerous NFAs have been created from rylene diimide electron-deficient building blocks, they have shown far inferior photovoltaic properties compared to benchmark fused-ring electron acceptors (FREAs) such as ITIC. Herein we show that new bis­(naphthalene-imide)­arylenelidenes (BNIAs), incorporating rylene-imide end-capping groups via methine bridges in donor–acceptor architectures, are endowed with enhanced electrochemical redox stability, high carrier mobilities, and high photovoltaic performance. Pairing of those BNIAs that are also FREAs, NIDT and NIBT, respectively, with donor polymer PBDB-T produced 10.0–10.8% efficient photovoltaic devices, which are comparable to benchmark ITIC devices. Blends of FREAs NIDT and NIBT and those of non-FREA NITV were found to have similar electron mobilities, demonstrating that the much higher photovoltaic efficiency of NIDT and NIBT devices does not originate from enhanced charge transport but from differences in blend morphology and blend photophysics. The results demonstrate that incorporating rylene imides into molecular architectures through the methine-bridged donor–acceptor coupling motif is a promising design strategy toward more efficient and electrochemically rugged materials for organic solar cells.