In this chapter, the fundamentals in regard to the use of transition metal complexes (TMCs) as luminescent probes will be presented. These metal complexes (MCs) between organic ligands and transition metal cations present many interesting properties that make them very suitable for a number of biomedical applications. First, a brief introduction to TMCs and their photophysics and photochemistry will be provided. Then, some particular applications of selected transition metals (TMs) in the field of fluorescence microscopy will be presented on a case-per-case basis. The relevant role played by lanthanide elements and their complexes in fluorescence microscopy, especially time-resolved, will be introduced. Some uses of actinide MCs will be presented as well.
Keywords: Actinide, d-d transitions, Denticity, f-f transitions, Lanthanide, Ligand, Ligand-to-metal charge transfer, Luminescence, Macrocycle, Metal-t- -ligand charge transfer, Time-resolved fluorescence microscopy, Transition metal, Transition metal complex.