An expeditious synthesis of 6,7-dihydrodibenzo[b,j][4,7] phenanthroline derivatives as fluorescent materials

A rapid and efficient method has been developed for the synthesis of 13,14-dimethyl-6,7-dihydrodibenzo[b,j][4,7]phenanthroline derivatives (3a–d) through the Friedländer condensation of 2-aminoarylketone with 1,4-cyclohexanedione under solvent-free conditions using p-toluenesulphonic acid. The synthetic utility of compounds 3a, 3b, and 3c was demonstrated by synthesizing compounds 6a–kvia Suzuki coupling, 8 by Buchwald–Hartwig amination, and 9a–bvia NBS bromination. Significantly, the emission band corresponding to the π–π* electronic transition of compounds 3a, 6a, 6d, 6f, and 8 showed a redshift with increasing polarity of the solvents. Molar extinction coefficient (ε), Stoke's shift (Δ[italic small upsilon, Greek, macron]), and quantum yield (Φ(f)) were calculated for all these compounds.