Synthesis of new Schiff bases based on formyl derivatives of xanthenes

Abstract

New Schiff bases were synthesized by the reaction of tetracyclic formyl derivatives of xanthenes with aromatic amines in the presence of a vapor of acetic acid drops. The structures of these compounds were investigated by FTIR, NMR spectroscopies and massspectrometric technique. Formyl xanthenes showed absorption and emission in the range of 424-435 nm and 524-559 nm, respectively, in solvents with different polarities. Initial formyl xanthenes were characterized by a suficiently high Stokes shift of 100-130 nm and a moderate fluorescence quantum yield. The prepared Schiff bases exhibit no fluorescence, with the exception of two products with antranilic acid. These compounds show weakly structured absorption spectra with maxima at 527 nm and 532 nm. Luminescence maxima were found in the range of 582 and 598 nm; as a result, the prepared compounds are characterized by low fluorescence quantum yields in the range of 0.01-0.02 in acetonitrile solution and the Stokes shift of 55 nm and 65 nm.