Luminescent Thermometers: From a Library of Europium(III) β-Diketonates to a General Model for Predicting the Thermometric Behaviour of Europium-Based Coordination Systems

A new model with the aim to predict the temperature dependence of europium emission in coordination systems is presented. The model has been developed from a library of Eu3+ complexes of general formula EuL3A2, where L is a β-diketone, and A is an ancillary ligand. Three possible deactivation channels have been considered: two competitive metal-related terms describing the primary deactivation channels, i. e. back energy transfer and multiphonon quenching, and a third ligand-related term to describe non-radiative deactivation of the antenna triplet. As many parameters as possible are taken from measurable chemical-physical properties, such as ligand triplet and multiphonon quenching energies. The other parameters have been deduced from selected EuL3A2 compounds and used as one-size-fits-all values. The model proved to be very effective in describing the interplay between back energy transfer and multiphonon deactivation channels. Finally, the model has been implemented in a freeware standalone MATLAB application. Users need to input only the energy of the sensitizer triplet level and choose the coordinated quencher, if present. It simulates the range of applicability of the molecular thermometers and the shape of the thermometric sensitivity curve Sr employing as thermometric parameter either emission intensity or lifetime.