Photoluminescence of Cyclometalated Iridium Complexes in Poly(methyl methacrylate) Films

In this work, we describe the emission properties of 12 heteroleptic bis-cyclometalated iridium complexes immobilized in poly(methyl methacrylate) (PMMA) thin films. The compounds chosen for this study span a range of emission colors covering the visible spectrum and fall into three categories with electronically diverse ancillary ligands—four cationic bis(aryl isocyanide) complexes, four with chelating bis(acyclic diaminocarbene) (bis-ADC) ancillary ligands which can exist in two protonation states, and four neutral compounds with monoanionic, strongly π donating β-ketoiminate (acNac) and β-diketiminate (NacNac) ancillary ligands. Included in this suite of compounds are five new compounds, one with two aryl isocyanide ancillary ligands, two with bis-ADC ancillary ligands, and one each with acNac and NacNac; their syntheses are described, and crystal structures of three are presented. The bulk of the work presented here describes the emission spectra of all 12 compounds, comparing spectral features in solution to those in thin PMMA films (2 wt % of the respective iridium complex). The emission wavelengths and spectral profiles do not change substantially in PMMA films, but in most cases there are dramatic (2-fold to more than 10-fold) increases in photoluminescence quantum yields, with many of the compounds approaching unity quantum yield in PMMA. The increases in quantum yield come from a combination of larger radiative rates and smaller nonradiative rates in the thin film samples, with significant differences between the members of this series of compounds.