Design, synthesis, characterization and fluorescence property evaluation of dehydroacetic acid-based chalcones

In this study, we decided to synthesize some new chalcone-type dyes derived from dehydroacetic acid (DHA) by the condensation of 4-amino-substituted benzaldehyde with DHA under the base-catalyzed condition and investigate their ability for rearrangement in acidic condition. For this purpose, initially we prepared the 4-aminobenzaldehyde derivatives via nucleophilic aromatic substitution reaction of 4-fluorobenzaldehyde with variety of amines in the presence of K2CO3 as base in DMF. The Knoevenagel condensation of DHA with 4-aminobenzaldehyde derivatives results in the desired compounds. In continuation, Fries rearrangement applied on DHA-chalcone compounds results in characterization of new pyranilidene-type derivatives. The optical responses of new dyes containing UV–Vis absorption and fluorescence spectroscopy were measured in dichloromethane (ET = 40 kcal/mol). Pyranilidene derivatives show low λmax values in comparison with chalcones, and molecule with strong dipole, in polar solvents, shows the bathochromic shift due to more stabilization of excited state in compared with ground state of molecule. Large stocks shifts were obtained for synthesized compounds.