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 prepa ration of IrLL'3+ complexes (L, L' = terpyridine derivative) in good yields . In a first step, IrLCl3 is obtained under relatively mild conditions as a n intermediate. Subsequent reaction with L' (a few minutes in refluxing eth ylene glycol) affords IrLL'3+. The electrochemical behavior and ground- and excited-state spectroscopic properties of four IrLL'3+ complexes in nitril e solvents are reported. The X-ray structure of one of these complexes is a lso described. The complexes have been designed keeping in mind their incor poration in linearly arranged multicomponent arrays, according to a templat ing strategy based on the assembly of tpy-type ligands by the Ir(III) cente r. The complexes feature a high-lying level for the luminescent excited sta te (>2.5 eV), with a satisfactory room-temperature luminescence intensity ( phi(em) approximate to 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 sys tems built around them. Temperature-dependent studies of the luminescence p roperties in the 95-298 K range indicate that the higher-lying levels of th ese complexes are not efficient pathways for deactivation of the luminescen t states. For these reasons, it is concluded that the studied Ir-tpy-type c omplexes 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.