Synthetic approaches to combining sensing and sensitizing in a single luminescent agent

We are exploring and developing potential luminescent agents that can combine either a sensing or imaging function with a tumour killing capability. NIR emitting lanthanide complexes have demonstrated both sensing and PDT potential. Our recent efforts have focused combining these features in a single molecule in the form of cyclen based lanthanide complexes. Here we report the synthesis and photophysical characterization of two near IR-emitting complexes and a study of their interactions with DNA as a test substrate. The synthesis exploits our recently developed methodology to regioselectively incorporate up to three different substituents into a cyclen (1,4,7,10-tetraazacyclododecane) macrocycle.[1,2] The presence of two organic and a lanthanide chromophore results in Stokes shifts of > 20 000 cm−1. The lanthanides are sensitised by rhodamine, which in turn is excited by energy transfer from a coumarin 2 moiety in one mode. The three lumophores function as an energy transfer cascade spanning the UV-visible-near IR region of the spectrum, resulting in the large Stokes shifts when the coumarin is excited. Double stranded DNA selectively switches one of the two energy transfer processes off, illustrating a potential means by which a switching between two functions could be achieved by substrate binding such as a protein or cellular target