Luminescent 1,8-Naphthalimide-Derived ReI Complexes: Syntheses, Spectroscopy, X-ray Structure and Preliminary Bioimaging in Fission Yeast Cells

A series of picolyl-functionalised, fluorescent 1,8-naphthalimide ligands (L) have been synthesised and coordinated to Re-I to form luminescent cationic complexes of the general form fac-[Re(phen)(CO)(3)(L)]BF4. The complexes were characterised by using a range of spectroscopic and analytical techniques. One example of a complex was also characterised in the solid-state by using single-crystal X-ray diffraction, revealing a distorted octahedral coordination sphere at Re-I and Re-C/Re-N bond lengths within the expected ranges. All ligands were shown to be fluorescent, with the 4-amino derivatives showing intramolecular charge transfer in the visible region (511-534 nm). The complexes generally showed a mixture of ligand-centred and/or (MLCT)-M-3 emission depending upon the nature of the coordinated 1,8-naphthalimide ligand. For selected complexes, confocal fluorescence microscopy was undertaken by using fission yeast cells (Schizosaccharomyces pombe) and showed that the structure of the 1,8-naphthalimide ligand influences the uptake and localisation of the rhenium complex.