Emission Properties of 1,10-phenanthroline Derivatives Induced by Protonation of a Nitrogen Atom

Abstract This study presents new monoprotonated 1,10-phenanthroline derivatives that possess remarkable emission properties. We have prepared the monoprotonated compounds, [LH]PF6, by the reaction of L (L = mphen, dmphen, tmphen, NO2phen, bquin and dmdpphen) with concentrated HCl in water. Abbreviations used here are mphen = 5-methyl-1, 10-phenanthroline, dmphen = 2,9-dimethyl -1, 10-phenanthroline, tmphen = 3, 4, 7, 8-tetramethyl-1,10-phenanthroline, NO2phen = 5-nitro-1,10-phenanthroline, bquin = benzquinoline, dpphen = 4,7-diphenyl-1,10-phenanthroline and dmdpphen = 2, 9-dimethyl 4,7-diphenyl-1,10-phenanthroline. Density functional theory was used to investigate the ground and the excited singlet states in these derivatives. The attachment of one proton to the nitrogen atom leads to ionic characters of compounds. In the case of [dmdpphenH]PF6, hydrogen bond between the hydrogen atom in a methyl group and the adjacent F atom in PF6− anion increased molecular rigidity, resulted in a strong red-shifted emission (Φ = 0.197).