d → f Energy Transfer in a Series of IrIII/EuIII Dyads: Energy-Transfer Mechanisms and White-Light Emission

An extensive series of blue-luminescent iridium(III) complexes has been prepared containing two phenylpyridine-type ligands and one ligand containing two pyrazolylpyridine units, of which one is bound to IrIII and the second is pendant. Attachment of {Ln(hfac)3} (Ln = Eu, Gd; hfac = anion of 1,1,1,5,5,5,-hexafluoropentanedione) to the second coordination site affords IrIII/LnIII dyads. Crystallographic analysis of several mononuclear iridium(III) complexes and one IrIII/EuIII dyad reveals that in most cases the complexes can adopt a folded conformation involving aromatic π stacking between a phenylpyridine ligand and the bis(pyrazolylpyridine) ligand, but in one series, based on CF3-substituted phenylpyridine ligands coordinated to IrIII, the steric bulk of the CF3 group prevents this and a quite different and more open conformation arises. Quantum mechanical calculations well reproduce these two types of “folded” and “open” conformations. In the IrIII/EuIII dyads, Ir → Eu energy transfer occurs with vary...