Iridium Complexes Based on 1H-imidazo[4,5-f][1,10]Phenanthroline Ligand: Photophysical Properties and Light-Emitting Electrochemical Cells Characterization

Cyclometallated Ir(III) complexes are extensively used in luminescent devices such as Light-Emitting Electrochemical Cells (LECs) due to their high stability and also high luminescence quantum yields. To increase the promising complexes for LEC applications, efforts are focused on the design of molecules with specific ligands that can modulate the emission color as well as the nature of the excited state from which radiative decays occur. In this context, this work presents a study of the luminescent properties of two new Ir(III) complexes containing a ligand derived from 1H-imidazo[4, 5-f][1,10]phenanthroline (dmbip). This study, complemented by theoretical DFT calculations and electrochemical characterizations, shows that, in solution, both Ir(III) complexes exhibit the same emission energy as that of the free dmbip ligand. However, in the solid state, the complexes exhibit phosphorescent emission with a marked red shift of nearly 100 nm relative to their performance in solution. This unusual behavior is due to the presence of a luminescent 3ILCT excited state in the solid state, whose population is favored by the heavy metal center. Furthermore, these complexes were characterized in LEC devices and displayed the same emission profile identified in solid-state photoluminescence.