Regioselective heteroatom embedded ullazine framework: synthesis, structure–property relationships, and applications in organic electronics

Ullazine, a 16π-electron nitrogen-embedded polycyclic aromatic hydrocarbon, has emerged as a promising platform for organic electronics, combining intrinsic donor-acceptor character and highly tunable optoelectronic properties to deliver exceptional performance in dye-sensitized solar cells and organic photovoltaics. Recent advances have further expanded the functional space of ullazine derivatives through site-selective incorporation of additional heteroatoms, affording fine-tuning of frontier orbital energies, absorption/emission profiles, and charge-transport characteristics. This review systematically categorizes synthetic methodologies for aza-ullazines by substitution positions (C1/C2, C2'/C9', C4/C8, C5/C7, C6), discussing key synthetic strategies including Rh(III)-catalyzed C-H activation, Cu-mediated arylation/photocyclization, 1,3-dipolar cycloaddition, microwave-assisted cyclization, and BN/BO/BS isosteric replacement. Driven by the continuous evolution of heteroatom embedding strategies to afford interesting photophysical properties, ullazine-based π-systems are emerging as versatile building blocks for next-generation organic semiconductors.