Azoimidazolium Salts as a Platform for Persistent Neutral Aminyl Radicals and Mesoionic Carbene Au(I) Complexes as Cell‐Permeable Fluorophores

Strategic electronic matching between imidazolium precursors and aryldiazonium salts enables the synthesis of azoimidazolium derivatives via an operationally simple, base-promoted protocol that circumvents the need for column chromatography. The resulting azoimidazolium scaffolds serve as precursors of highly persistent neutral aminyl radicals, which exhibit remarkable stability with negligible decay after 3 weeks in the solid state. Furthermore, these salts were successfully employed as a versatile platform to access novel Au(I)-mesoionic carbene (MIC) complexes. When evaluated in living human glioblastoma A172 cells, these Au(I)-MIC acted as efficient, cell-permeable fluorophores with an unprecedented substituent-governed, dual-channel readout spanning from the green to the red region, governed by donor strength of the peripheral substituents.