Site-selective nitrogen insertion in double helicenes and dibenzo-terrylenes

Abstract Polycyclic aromatic hydrocarbons, particularly light-absorbing and light-emitting rylenes, are central to optoelectronic devices, sensors, displays and bioimaging, yet small structural changes can strongly alter their performance. A key challenge is to place heteroatoms at chosen positions in large aromatic frameworks and understand how this controls structure and function. Here we show two modular synthetic strategies that position nitrogen atoms precisely in double aza-helicenes and aza-terrylenes. These complementary routes provide site-selective nitrogen incorporation and give, for the first time, systematically varied isomeric pairs with identical compositions but distinct topologies. This molecular control reveals clear structure–property relationships: nitrogen relocation predictably tunes absorption and emission, while the fully planarized diazabenzo-fused terrylene outperforms its positional isomer. Acid treatment further increases its photoluminescence quantum yield to 82%, highlighting potential for acid-responsive bioimaging. Single-crystal X-ray diffraction shows that small changes in nitrogen atom placement also alter packing motifs and chiral self-assembly. Together, these findings establish a framework for designing nitrogen-containing aromatic molecules with atom-placement-controlled optical, electronic, and self-assembly properties.