Supramolecular Assembly of Water-Soluble Platinum(II) Complexes: From Emission Modulation to Cell Imaging in Specific...

The control of self-organized metal complexes presents advantages regarding the modulation of luminescence through dynamic assembly, rendering them promising for bioimaging. Herein, we demonstrate a strategy towards a series of amphiphilic Pt(II) complexes featuring bis-cyclometalated ligands as tetradentate luminophores, which exhibit enhanced water solubility and tuneable self-assembly properties. The resulting nanostructures can be precisely controlled by adjusting concentration and solvent composition, yielding switchable luminescence from red (i. e., excimer-based) to green (i. e., monomer-centred) and reversible (dis-)assembly of the aggregates. Cytotoxicity assays confirmed the innocuous nature of these luminophores at concentrations below 10 μM, while cellular uptake studies demonstrated effective internalization in both living and fixed cells. Using photoluminescence lifetime imaging micro(spectro)scopy, we determined that the complexes localized preferentially within lysosomes of living cells, while accumulating in the nuclei of fixed cells, with differences in photophysical behavior depending on whether the species were monomeric or excimeric in nature. These new findings provide insights into the systematic design of water-soluble Pt(II)-based luminophores with photophysical properties controlled by supramolecular interactions, underlining their potential for use in cellular imaging and diagnostics.