Highly emissive fused diarylmaleimides synthesized by a cascade reaction of selective bromination and visible-light-driven cyclization

Abstract A simple strategy for constructing fused diarylmaleimides (FAMs) under mild condition is presented through a cascade reaction involving a selective bromination with NBS and a visible-light-driven cyclization under 18 W of LED. Compared with traditional oxidation method, the cascade reaction does not use any oxidant, metal-based catalyst, and ultraviolet rays. According to the strategy, a series of symmetrical and asymmetrical FAMs with different aromatic rings are obtained in high yield up to 96%. Most of FAMs exhibit blue-shifted emission and higher luminescent efficiency (Φf up to 84%) in solution than their open-ring counterparts for the large π-conjugated systems weakening intramolecular charge transfer. Unexpectedly, the fused rings with nearly coplanar do not quench the solid-state fluorescence of FAMs, due to the heteroatoms and peripheral substituents inhibiting molecules forming H-aggregation-like tight packing, resulting in decent quantum yield in solid. Particularly, FAM with indolo [2,3-a] pyrrolo [3,4-c] carbazoles (B3IM-BHc) has unique pores in the crystal structure, which imposes it huge potential as smart florescent material and switch.