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 (φem ≈ 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.