Evolving a high-performance bio-imaging tool derived from a compact fluorophore as well as creating a reaction-based fluorescent probe for precise determination of Ag+

Commonly, emission of red-region fluorescence is inherently in need of substantial conjugating segments and fused rings, which inescapably burdens fluorescent molecules in their size and molecular weight, impairing their membrane permeability and biocompatibility. Herein, a novel dicyanocoumarin 2-(7-(N,N-diethylamino)-4-(trifluoromethyl)–2H-chromen-2-ylidene)malononitrile (CouMal) has been evolved from traditional coumarin core for the first time. Without enlarged π-conjugation system, the low-molecular-weight CouMal unexpectedly possesses red-region fluorescence both in the solid and solution states with considerable brightness. Based on its compact structure and long-wavelength emission, the CouMal exhibits great cytomembrane penetrability and reduced cytotoxicity, enabling its promising application for intracellular imaging and in vivo imaging. Innovatively, enlightened by the flexible synthetic procedure of CouMal, a reaction-based sensing system named TC-Mal-Et3N, has been freshly designed for the precise detection of silver ion (Ag+). The limit of detection of this sensing system is as low as 60.9 nM. This Ag+-triggered composite probe also exhibits superb selectivity and short reaction time, which has been applied for the accurate quantification of both Ag+ and silver nanoparticles (AgNPs) in real-world representative samples.