Indium complex with task-specific ionic liquid ligands: Ligand to ligand charge transfer in the excited state investigation and reliable DFT predictions

The work describes the use of ionophilic indium complex bearing a task-specific ionic liquid as the ligand with hydrophilic chlorides. The new luminescent complex was designed to be completely water-soluble aiming at cell-imaging application. The indium derivative was also characterized by single-crystal X-ray analysis and the molecular arrangement could be compared in the condensed phase with aqueous solutions. An alternative methodology had to be employed to an accurate analysis of the photophysical properties determined by DFT calculations to describe the experimental results. The complex stabilizes from the excited state through a charge transfer process which was depicted as a ligand-to-ligand transfer (from a chlorine atom to the imidazolium ring) as indicated by the theoretical investigation. EPR experiments could be conducted at −196 °C to evaluate the charge transfer process and it proved to be in accordance with the predicted result from DFT calculations. The luminescent properties of the complex allowed it to be used as a bioprobe during cell-imaging experiments with several live cells lineages.