The influence of loops on the binding of the [Ru(phen) 2 dppz] 2+ light-switch compound to i-motif DNA structures revealed by time-resolved spectroscopy.

Ultrafast time resolved infrared (TRIR) is used to report on the binding site of the "light-switch" complex [Ru(phen) ₂ (dppz)] ²⁺ 1 to i-motif structures in solution. Detailed information is provided due to perturbation of the local base vibrations by a 'Stark-like' effect which is used to establish the contribution of thymine base loop interactions to the binding site of 1 in this increasingly relevant DNA structure.