Synthesis and Photophysical Properties of Iridium(III) Bisterpyridine and Its Homologues:  a Family of Complexes with a Long-Lived Excited State

A new synthetic procedure has been developed which makes possible the preparation of IrLL‘³⁺ complexes (L, L‘ = terpyridine derivative) in good yields. In a first step, IrLCl₃ is obtained under relatively mild conditions as an intermediate. Subsequent reaction with L‘ (a few minutes in refluxing ethylene glycol) affords IrLL‘³⁺. The electrochemical behavior and ground- and excited-state spectroscopic properties of four IrLL‘³⁺ complexes in nitrile solvents are reported. The X-ray structure of one of these complexes is also described. The complexes have been designed keeping in mind their incorporation in linearly arranged multicomponent arrays, according to a templating strategy based on the assembly of tpy-type ligands by the Ir(III) center. The complexes feature a high-lying level for the luminescent excited state (>2.5 eV), with a satisfactory room-temperature luminescence intensity (φ_em ≈ 10^-2) and lifetime on the microsecond time scale. These favorable properties indicate that the Ir(III)-tpy center will not be the final recipient of the energy-harvesting processes in multipartite systems built around them. Temperature-dependent studies of the luminescence properties in the 95−298 K range indicate that the higher-lying levels of these complexes are not efficient pathways for deactivation of the luminescent states. For these reasons, it is concluded that the studied Ir-tpy-type complexes are well suited (i) to play the role of photoactive center and to gather photo- and electroactive units or (ii) to act as electron relays in linearly arranged multicomponent arrays.