Trifluoromethyl-substituted 2,8-diaryl-imidazo[1,2-a][1,8]naphthyridines: Synthesis, remarkable optical emission, and redox and thermal properties

Abstract

A novel series of thirteen examples of 2,8-diaryl-4-(trifluoromethyl)imidazo[1,2-a][1,8]naphthyridines (6) was synthesized at 21–96% yields, in which 2,8-diaryl = C6H5, 4-BrC6H4, 4-OMeC6H4, 4-CF3C6H4, and 2-naphtyl by intermolecular and regioselective [3+2] cyclocondensation reaction of a series of selected 7-aryl-2-amino-5-(trifluoromethyl)-[1,8]naphthyridines (3) with 1-aryl-2-bromo-ethanones (5). Aromatic amines 3 and bromo ethanones 5 were obtained by previously reported methods, which reacted 2,6-diamino-pyridine (2) with 4-aryl-4-methoxy-1,1,1-trifluorobut-3-en-2-ones (1) to obtain 3 and some acetophenones 4 with elemental bromo to synthesize 5. All new compounds 6 were fully characterized by 1H-, 13C, 19F NMR and IR spectroscopy, SC-XRD, and HRMS methods. The optical and electrochemical properties of the derivatives were determined by UV–Vis, steady-state and time-resolved fluorescence emission (solution and solid state), TD-DFT calculations, and redox potential and discussed, indicating a dependence of the substitution position in the heterocyclic core. In addition, the TGA experiments showed that compounds 6 presented good thermal stability at the 150–300 °C range.