Electronic structure and luminescence properties of unique complexes: cyclometalated iridium(iii) chelated by o-carboranyl-pyridine ligands

Abstract

Carboranes are showing promise as phosphorescent materials because of their excellent properties. Until now, very few investigations have been focused on the use of o-carborane itself as a chelating unit. In order to effectively enhance the phosphorescence quantum efficiency of complexes supported by the chelating ligand o-carborane, this work focuses on a series of complexes bearing cyclometalating ligands with π-conjugation in different positions and of different degrees to explore the properties of the molecules. Density functional theory and time-dependent density functional theory were used to calculate the electronic configurations, emission wavelengths, and the radiative and nonradiative decay processes. The calculated results confirm that the emission peaks of complexes 2 and 3a have a larger blue shift compared with that of complex 1. The introduction of π-conjugation in the cyclometalating ligands gives rise to an increase in the radiative rate constants for the designed complexes 2 and 3. Complex 5 has better structural rigidity, and more difficult to achieve thermally activated nonradiative photodeactivation processes, which is expected to be a better phosphorescent material with a higher phosphorescence quantum efficiency. So far, there has been no theoretical study that systematically focuses on cyclometalating iridium(III) complexes with o-carborane as a chelating ligand. Our research suggests new ideal candidates for the further synthesis of effective blue phosphorescent Ir(III) complexes which are supported by the chelating ligand o-carborane.