Aggregation-induced emission-active azines for chemosensing applications: a five-year update

Azines are an important class of compounds that display solvent-dependent fluorescence emission depending upon the substituents in the aromatic scaffolds. They are affordable, easy to synthesize, stable, and well-suited for numerous applications. Unlike most other AIE fluorophores, aromatic units of AIE-active azine derivatives are bridged by rotatable N–N bonds rather than C–C bonds. Their derivatives have been widely used in pharmaceuticals, drug delivery, organometallics, optoelectronics, dyes, etc., and most importantly in several sensing applications. This comprehensive review encapsulates the recent developments in the field of AIE-active azine molecules and their applications as chemosensors in the detection of various analytes. The review discusses the different chemosensing strategies involved in the detection of metal ions (Cu²⁺, Zn²⁺, Al³⁺, Fe³⁺, Cr³⁺, Hg²⁺, UO₂²⁺, etc.), anions (F⁻, CN⁻, ClO⁻, ONOO⁻, HSO₃⁻), small molecules (thiols, hydrazine, hydrogen peroxide), and bio-analytes (protamine/heparin, HSA/BSA, neuraminidase, β-lactamase, β-galactosidase, etc.) with a focus on the development in the last five years. The review also highlights the advancements in azine-based systems for their use in imaging, supramolecular host–guest recognitions, AIE polymers, COFs/MOFs, etc.