Novel ESIPT fluorescent benzazolyl-4-quinolones: Synthesis, spectroscopic characterization and photophysical properties

Two, novel, benzazolyl-quinolone heterocycles, fluorescent by virtue of intramolecular proton transfer mechanism in the excited state (ESIPT), were obtained using the Gould-Jacobs reaction. The intramolecular cyclization step in the preparation of the anilinomethylene malonate derivatives was carried out using polyphosphoric acid, heat transfer fluids (Dowtherm A Fluid, mineral oil and diphenyl ether) as well as tandem methodology, at temperatures ranging from 180 °C to 250 °C. Tandem methodology provided better yields and lower by-product formation. The synthesized quinolones were characterized using elemental analysis, IR, 13C and 1H NMR spectroscopy. Photophysical behaviour was studied using UV–Vis and steady-state fluorescence, both in solution and in solid state. The quinolones were fluorescent in solution in the orange-red region (500–800 nm), under UV radiation, and displayed a large Stokes shift (165–194 nm).