Fluorescent 5H‐Pyrano[3,2‐c]chromenes: Synthesis, Photophysical Properties and Sensing of Nucleophilic Anions

We report the development of a convenient organocatalytic method for the synthesis of 5H‐pyrano[3,2‐c]chromenes from chromone‐containing acrylates and ethyl cyanoacetate. The synthesis is characterized by simple conditions (ethanol, basic catalysis) and good yields (up to 90 %). The synthesized pyrano[3,2‐c]chromenes are a promising new class of fluorescent compounds. They have intense fluorescence in the yellow‐green region of the spectrum (495–554 nm) with high quantum yields (up to 72 %) and exhibit large Stokes shifts (3514–5856 cm−1). We have demonstrated the possible application of the obtained pyrano[3,2‐c]chromenes as selective “turn‐off” sensors for nucleophilic anions, such as cyanide, sulfide and sulfite. Tricyclic heterocycles such as 5H‐pyrano[3,2‐c]chromenes have intense fluorescence in the yellow‐green range and are analogues of 7‐aminocoumarin dyes. The studied pyranochromenes can be used as selective chemosensors for nucleophilic anions. These heterocycles can be conveniently prepared by the tandem reaction of electron‐deficient 3‐vinylchromones with ethyl cyanoacetate.