Luminescent dinuclear rhenium(I) complexes containing bridging 1,2-diazine ligands: Photophysical properties and application

In this contribution we provide an overview of the preparation and of the properties of different classes of luminescent dinuclear tricarbonyl rhenium(I) complexes of general formula [Re2(μ-X)2(CO)6(μ-1,2-diazine)] (X = halide, hydride, alkoxide, and thiolate). Their electrochemical and photophysical properties in solution are presented, as well as combined density functional (DFT) and time-dependent density functional (TDDFT) studies of their geometry, relative stability and electronic structure. The relationships between the structure and the emission properties of the complexes are discussed in detail, showing a modulation effect of the bridging ancillary ligands as well as of the diazine substituents on energy, lifetime and quantum yield of the emission. Photoluminescent quantum yields (Φ) up to 0.53 have been measured in fluid solution for the dichloro complexes containing diazines bearing alkyl groups in both the β positions, designed to optimize all the parameters responsible for the radiative decay. The photophysical properties in the solid state are also briefly presented, showing in some cases an increase of the emission intensity, discussed in terms of restriction of intramolecular roto-vibrational motions. These properties, together with their good processability and high stability, allowed the successful use of some of these complexes as a phosphorescent dopant in OLEDs. The good performances of OLED devices prepared both by solution- and vacuum-processing are reported. The preliminary work exploring the potential of these complexes as luminescent labels for bioimaging is also presented.

► Binding a 1,2-diazine to a Re2(μ-X)2(CO)6 core affords new highly luminescent complexes.
► Quantum yields up to 0.53 are measured in fluid solution at room temperature.
► Much stronger emission in solid than in solution is sometimes observed.
► Highly performing OLEDs can be prepared using these complexes as phosphorescent dopants.
► Staining of cytoplasm and nucleus with different colours is observed upon cellular uptake.