A luminescent europium hairpin for DNA photosensing in the visible, based on trimetallic bis-intercalators

Luminescence monitoring of DNA intercalator complexes is important for assessing their localisation and targeting: We report herein a luminescent hetero-trimetallic complex with europium as a luminescent reporter and two attached platinum acetylide terpyridyl units as the DNA recognition units. The ligand, based on a bisamide derivative of diethylenetriaminepentaacetic acid functionalized with two ethynyl groups, provides a backbone to anchor two platinum terpyridyl units, Pt-tpy, leading to the hairpin-shaped heterometallic complex 1. We also prepared a related mono-nuclear platinum complex 2 to compare its intercalation properties with 1. Linear dichroism, UV-visible and melting experiments show the ability of both complexes to interact with calf thymus DNA, with linear dichroism confirming intercalation and demonstrating the expected greater DNA stiffening by the bis-intercalator 1. Importantly, the tri-metallic complex 1 shows a three-fold enhancement in europium luminescence upon addition of calf thymus DNA; other mono-intercalator lanthanide designs have commonly shown a decrease in emission on binding. The ability of the complex to monitor DNA interactions gives the potential use as a luminescence switch in sensing experiments and highlights the design of heterometallic bis-intercalator complexes as an effective approach for DNA-responsive sensitisation of a lanthanide luminescence signal.