U V 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'-Mezbpy in the ground state depends on the composition of the mixture at 77 K and the conformation remains unchanged upon photoexcitation. The lowest excited singlet energy is sensitive to the coordination to Zn2+, while the fluorescence