Temperature dependent luminescence of europium/cyanine FRET pairs

The temperature dependence of light emission from three europium complexes has been examined in detail between 293 and 318 K in aqueous buffered solution. Each complex undergoes temperature dependent sensitised emission <i>via</i> an integral chromophore that possesses an ICT state, to which thermally activated reverse energy transfer occurs. In the presence of an energy matched FRET acceptor, emission from the Eu donor and the near-IR cyanine dye show different temperature variations of emission lifetime and intensity, paving the way for the development of optical temperature probes. The examples studied include an intramolecular europium-dye conjugate and FRET pairs based on Eu and cyanine dye conjugates of Vismodegib, the competitive antagonist for the Smoothened receptor in the Hedgehog signalling pathway. This study paves the way for the development of targeted optical temperature probes.