Emission studies of hetero-bischelated iridium(III)–diimine complexes

Abstract

Two mixed-ligand complexes, cis-[Ir(bipy)(HDPA)Cl 2]Cl and cis-[Ir(phen)(HDPA)Cl 2]Cl (where bipy=2,2′-bipyridine, phen=1,10-phenanthroline, and HDPA=2,2′-dipyridylamine), have been synthesized and characterized. Both complexes show spin-allowed π–π* bands in the UV region. Besides, spin-allowed and spin-forbidden charge transfer bands are also observed in the vicinity of 24.8 and 19.5 kK, respectively. The magnitude of the polarization, P, in the excitation polarization spectra obtained for the two complexes indicate that both luminophores behave as linear oscillator corresponding to the symmetry lower than C 2 v of the two complexes. The emission spectra of both cis-[Ir(bipy)(HDPA)Cl 2] + in neutral and cis-[Ir(phen)(HDPA)Cl 2] + in slightly acidified EtOH–MeOH solvent (4:1 v/v) at 77 K, exhibit 3MLCT phosphorescence at 16–22 kK with lifetimes near 18 μs and a single vibration progression of 1240 and 1300 cm −1, respectively. The property that the emission energy becomes smaller while the polarity of solvent increases is consistent with the orbital nature of 3MLCT state. The emission energies of both complexes are nearly constant in acidic EtOH–MeOH solvent and are 3.1–3.3 kK smaller in basic solvent than that in the neutral one. The emissions of both complexes in the basic case are assigned as 3MLCT emission caused by the complexes of deprotonated form, cis-Ir(bipy)(DPA)Cl 2 and cis-Ir(phen)(DPA)Cl 2, with lifetimes of approximately 19 μs.