Efficient Phosphorescence from Naphthalenebenzimidizole‐Coordinated Iridium(III) Chromophores

The electronic structure and photophysical properties of two phosphorescent iridium(III) cyclometalated complexes are presented. The molecules were synthesized by cyclometalating the ligand 1,8‐naphthalenebenzimidizole (NBI), to an iridium(III) metal center. Two NBI ligands were covalently attached along with a 1,10‐phenanthroline (phen) ligand producing the [Ir(NBI)2(phen)](PF6) complex and three NBI ligands were used to prepare the corresponding tris‐cyclometalate fac‐Ir(NBI)3. The optical properties of these new IrIII molecules were investigated using DFT calculations, photoluminescence spectroscopy, and transient absorption spectroscopy. The molecules at the heart of this study were found to contain long‐lived ligand‐localized triplet excited states on the NBI species, featuring energies suitable for bimolecular photochemical reactions. Both iridium(III) chromophores possess excellent light absorptivity in the visible region of the spectrum with high photoluminescence quantum efficiencies approaching 30 %. Two phosphorescent iridium(III) complexes demonstrate that cyclometalation of the rigid naphthalenebenzimidizole (NBI) ligand onto Ir can impart desirable photophysical properties to the complex, such as visible light absorptivity and high photoluminescence quantum yields. The molecules were investigated using DFT calculations, photoluminescence spectroscopy, and transient absorption spectroscopy.