Bis-cyclometallated iridium(III) complexes bearing pyridineimine and salicylimine ancillary ligands : synthesis, characterization and applications

Two stable diastereomeric atropisomers of a cyclometallated iridium complex containing a pyrene functionalized pyridineimine ligand have been isolated. These are the first fully characterized examples of metal containing atropisomers in which the rotational axis is not between two chelating atoms. The atropisomers can be converted thermally via a rocking motion of the pyrene moiety. A new mechanism for enhanced phosphorescence emission in the solid state (EPESS) in cyclometallated Ir complexes with the general formula [Ir(C^N)₂(N^O)] involving distortion of the six-membered chelate ring of the ancillary ligand is proposed. Photophysical and computational studies show that neither π-stacking nor restricted rotation cause the observed EPESS in these complexes and that ligand distortions in the triplet excited state are responsible for EPESS. Bis-cyclometallated Ir(III) complexes with the general formula Ir(ppz)₂(N^XPyrene) where X = N or O are shown. Modifications on the ancillary ligand containing pyrene drastically affect the emission lifetimes observed (2 μs to 104 μs). Extended emission lifetimes in these complexes compared to model complexes result from reversible electronic energy transfer or the observation of pyrene (³LC) phosphorescence. A combination of steady state and time-resolved spectroscopic techniques are used to observe reversible electronic energy transfer between the cyclometallated iridium core and the pyrene moiety in the complexes [Ir(ppz)₂(N^NPyrene)][PF₆]. Replacing the N^NPyrene ligand with an N^OPyrene ligand results in long-lived pyrene phosphorescence. Reversible electronic energy transfer as well as 3pyrene emission is observed and characterized in a PMMA film.Science, Faculty ofChemistry, Department ofGraduat