Using pyrrolizine-fused bipolar PAHs as a new strategy towards efficient red and NIR emissive dyes

We report the synthesis and characterization of the first pyrrolizine-embedded PAH systems. The bipolar core, based on a naphthalimide and indole fusion, was successfully synthesized through a one-pot cascade of Suzuki/Boc deprotection/Buchwald–Hartwig transformations. A facile post-functionalization of the unoccupied β-position of the heterocycle with aromatic amines as donor subunits led to a set of donor–acceptor architecture-based dyes. Effective narrowing of the HOMO–LUMO gap, along with its tuning by changing donor strength together with stabilization of π conjugation within the pyrrolizine–NMI core, provided a route to near-infrared (NIR) emission not only in solution (∼740 nm) but also in the solid-state (∼700 nm).