6-Arylamino-2,2′-bipyridine Push-Pull Fluorophores: Solvent-Free Synthesis and Photophysical Studies

This work describes a solvent-free approach towards push-pull fluorophores based on 5-aryl-2,2'-bipyridines bearing the residues of various anilines at the alpha-position of the edge pyridine cycle. We have also studied the possibility of varying (het)aromatic-substituents at C5 position of the resulted 2,2'-bipyridines as well as the substituents in the aniline residues. The structures of products were confirmed based on the H-1 and (CNMR)-C-13 spectroscopic data, mass spectrometry, elemental analysis and X-ray diffraction analysis. The photophysical features of the synthesized compounds have been investigated. The fluorescence emission of two key compounds was studied in solvents by varying polarities. It was demonstrated that an increase in the solvent polarity led to an increase in the Stokes shift. The linear dependence of the Stokes shift of the fluorophores on the increasing of the solvent nature was demonstrated by using the Lippert-Mataga plot. The fluorescence quenching response of the fluorophores towards metal cations was also demonstrated.