Study of Conformers of 6,6'-Dimethyl-2,2'-bipyridine in the Ground and Excited States

UV absorption, luminescence, and luminescence-excitation spectra of the trans and metal-free cis conformers of 6,6'-dimethyl-2,2'-bipyridine (6,6'-Me₂bpy) and its Zn²⁺ complex have been observed in 2-propanol and 2-propanol-water mixtures at 77 K. The stable conformation of 6,6'-Me₂bpy in the ground state depends on the composition of the mixture at 77 K and the conformation remains unchanged upon photoexcitation. The lowest excited sing let energy is sensitive to the coordination to Zn²⁺, while the fluorescence lifetime is sensitive to both the conformation change of 6,6'-Me₂bpy and to the coordination to Zn²⁺.