A dual‑site reactive ratiometric fluorescent probe for spermine and spermidine discrimination with visualizable sensing.

The bioamines spermine and spermidine, which are structurally similar and often coexist in complex matrices, still pose substantial challenges for achieving efficient detection of one another. To address this, a novel coumarin-based fluorescent probe, DX-Cl-CN has been developed. By introducing a chlorine atom and a vinylene-linked dicyanopropene motif as two dual reactive sites, the probe enables specific, differential responses toward spermine and spermidine across various bioamines. In DMSO, its maximum emission wavelength reaches 598 nm. Increasing solvent polarity induces a red shift in emission due to excited-state stabilization and enhanced molecular planarity. When interacting with spermine or spermidine, the probe exhibits a distinctive two-stage blue shift in fluorescence emission: its emission peak first shifts from 598 to 550 nm, then further to 486 nm. Ratiometric fluorescence analysis based on I550/I486 exhibits excellent linearity. Nanofibrous thin films prepared via electrospinning enable naked-eye visualization to discriminate among gaseous biogenic amines. Theoretical calculations revealed a two-step reaction mechanism in which the DX‑Cl‑CN first undergoes a Michael addition to the primary amine of spermine or spermidine, via the vinyl-dicyanide double bond, followed by intramolecular cyclization induced by the secondary amine via chlorine displacement. DX-Cl-N offers dual-application potential in solution and solid-state film systems, providing a new strategy for rapid, visual detection of spermine and spermidine in complex environments.