Tuning Fluorescence Properties Of 22-bipyridine Using Metal Cations

The steady state absorption, fluorescence excitation and emission spectra of 2,2’-bipyridine have been studied in polar solvents. Absorption spectra are almost independent of solvent polarity. The dependence of fluorescence emission on excitation wavelength was observed in acetonitrile and p-dioxane but independent of excitation energy in tetrahydrofuran. Addition of metal ion and varying pH of the solution shifted the absorption band to the red-edge and intensity change was observed in fluorescence excitation spectra. Corresponding excitation bands of the metal free conformers were compared to the stable conformers of metal-chelated and protonated 2,2’-bipyridine.rnStudy of the rotational profile of 2,2’-bipyridine at DFT/B3LYP/STO-3G level shows two energy minima corresponding to two conformations of different energy, cis/trans structures, with barrier to rotation greater than the room temperature thermal energy.rnIt is shown that distributions of energetically different conformers of the molecule (cis/trans) in the ground state are responsible for the dual fluorescence behavior of the systems.

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