Lifetime heterogeneity of DNA-bound dppz complexes originates from distinct intercalation geometries determined by complex-complex interactions.

Despite the extensive interest in structurally explaining the photophysics of DNA-bound [Ru(phen)2dppz]2+ and [Ru(bpy)2dppz]2+, the origin of the two distinct emission lifetimes of the pure enantiomers when intercalated into DNA has remained elusive. In this report, we have combined a photophysical characterization with a detailed isothermal titration calorimetry study to investigate the binding of the pure Δ and Λ enantiomers of both complexes with [poly(dAdT)]2. We find that a binding model with two different binding geometries, proposed to be symmetric and canted intercalation from the minor groove, as recently reported in high-resolution X-ray structures, is required to appropriately explain the data. By assigning the long emission lifetime to the canted binding geometry, we can simultaneously fit both calorimetric data and the binding-density-dependent changes in the relative abundance of the two emission lifetimes using the same binding model. We find that all complex–complex interactions are slight...