Synthesis, Characterization, Absorption Spectra, and Luminescence Properties of Multinuclear Species Made of Ru(II) and Ir(III) Chromophores

A series of new mixed-metal Ru(II)-Ir(III) trinuclear complexes have been prepared and characterized, together with their mononuclear parents and a series of closely related dinuclear and trinuclear homometallic Ru(II) and Ir(III) species, and their absorption spectra and luminescence properties (both at 77 K in rigid matrix and at room temperature in fluid solution) have been studied. The absorption spectra and luminescence properties of the Ru(II) species and subunits are dominated by metal-to-ligand charge-transfer (MLCT) transitions and excited states, whereas ligand centered (LC) transitions and excited states govern the spectroscopic and photophysical properties of most of the Ir(III) species here studied, with MLCT states playing an important role when cyclometalated Ir(III) subunits are present. Each metal-based subunit retains in the multinuclear arrays its own spectroscopic properties, but in the case of the mixed Ru-Ir species an efficient, additional decay channel is opened for the excited states involving the Ir-centered subunits, that is, photoinduced energy transfer to the lower-lying MLCT state(s) involving the Ru centers.