Mono- and Dinuclear Cationic Iridium(III) Complexes Bearing a 2,5-Dipyridylpyrazine (2,5-dpp) Ligand

The
synthesis, X-ray structures, photophysical, and electrochemical characterization
of mono- (1) and dinuclear (2) cationic
iridium­(III) complexes bearing a 2,5-dipyridylpyrazine (2,5-dpp) ancillary
ligand are reported. Upon the complexation of a first equivalent of
iridium, the photoluminescence shifts markedly into the deep red
(λem = 710 nm, ΦPL = 0.9%) compared
to other cationic iridium complexes such as [Ir­(ppy)2(bpy)]­PF6. With the coordination of a second equivalent of iridium,
room temperature luminescence is completely quenched. Both 1 and 2 are luminescent at low temperatures but with
distinct excited state decay kinetics; the emission of 2 is significantly red-shifted compared to 1. Emission
both at 298 and 77 K results from a mixed charge-transfer state. Density
functional theory (DFT) calculations and electrochemical behavior
point to an electronic communication between the two iridium complexes.