Synthesis of 7-(diethylamino)-chromene-fused quinolines and 7-(diethylamino)-4-amino-3-formyl-coumarin derivatives, structural elucidation, and photophysical properties

Abstract

A series of 7-(diethylamino)-coumarin-based heterocycles have been designed and synthesized through the reaction of 7-diethylamino-4-chloro-3-formylcoumarins with arylamines by a one-pot acid-catalysed synthesis. By tuning the reaction time and temperature, this reaction provides a pathway to either fused coumarin–quinoline scaffolds (3, 4_meta, 4_para, 6, and 7) or unfused 7-diethylamino-4-amino-3-formyl-coumarins (8–12), all in moderate to good yields (58–87%). The fused derivatives (3–7) display unusual photophysical behavior in a wide range of solvents, whereas the unfused systems (8–12) are essentially non-emissive. The photophysical studies of fluorophores 3–7 exhibit dual absorption bands centered around 350 nm and 420 nm, while the emission shows pronounced solvent dependence, with high fluorescence efficiency (Φ = 0.62–0.82) and large Stokes shifts (>2000 cm⁻¹). All compounds are fully characterized, and X-ray quality crystals of compounds 4_para and 9_ortho are also reported.