Tuning Fluorescence Properties Of 2 2- Biquinoline Using Metal Cation

The steady state absorption, fluorescence excitation and emission spectra of 2, 2′- biquinolinernhave been studied in polar and non-polar solvents. Absorption spectra are almost independent ofrnsolvent polarity. The dependence of fluorescence emission on excitation wavelength wasrnobserved in acetonitrile, dichloromethane and p-dioxane but independent of excitation energy inrncyclohexane. Addition of metal ion and varying pH of the solution shifted the absorption andrnexcitation band to the red-edge. Corresponding excitation bands of the metal free conformersrnwere compared to the stable conformers of metal-chelated and protonated 2,2′- biquinoline.rnStudy of the rotational profile of 2, 2′- biquinoline at semi-empirical of INDO methods showsrntwo energy minima corresponding to two conformations of different energy, cis/trans structures,rnwith barrier to rotation comparable for trans to the room temperature thermal energy but less forrncis conformer. It is shown that distributions of energetically different conformers of the moleculern(cis/trans) in the ground state are responsible for the dual fluorescence behavior of the systems

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