Herz chemistry and its applications in small-molecule functional materials science: achievements, challenges, and prospects

This review discusses the achievements of Herz chemistry over its first century, together with challenges and prospects. The discussion focuses on the synthesis, structure, and reactivity of various closed- and open-shell chalcogen-nitrogen π-heterocyclic species. The latter are derivatives of the (het)areno-fused 1,2,3-dichalcogenazole ring system with S, Se, and less often Te, chalcogens in various spin and charge states encompassing cations, radicals, bipolar ions, and quinoid antiaromatics/diradicaloids. They are important for fundamental chemistry and materials science, specifically for the design and synthesis of metal-free conductive, magnetic, and optoelectronic materials. The potential for further extension of Herz chemistry to other non-transition elements is also considered. A comparative analysis of Herz species and their 1,3,2-isomers (Wolmershäuser species) is provided. The bibliography includes 344 references.