Theoretical investigation of the influence of heterocycles on the radiative and non-radiative decay processes of iridium(iii) complexes

Abstract

By means of density functional theory and time-dependent density functional theory, the radiative and non-radiative decay processes of a series of iridium(III) complexes are investigated to explore the role of N-heterocyclic moieties in chelating ligands. In this investigation, the emission properties and phosphorescent quantum yields are explored with the aid of emission wavelengths, natural transition orbitals (NTO), spin–orbit coupling (SOC) matrix elements, radiative decay rate constants and photodeactivation mechanisms. The calculated results indicate that different five-member N-heterocyclic moieties in chelating ligands can cause an obvious effect on the emission wavelengths of iridium(III) complexes. For the five-member N-heterocyclic moieties in chelating ligands, the O and S substituents in N-heterocyclic moieties could realize the very low radiative decay constants because of the low ³MLCT character in the emission state. Moreover, the N atom substituent is beneficial for facilitating the radiative decay process and substituents at the ortho- and meta-position can lead to a larger ³MLCT character compared to that of the N substituent at the para-position in the case of six-member N-heterocyclic moieties. Furthermore, the various five-member N-heterocyclic moieties can tune the energy barriers between the ³ES and ³MC excited states, which is beneficial for controlling the temperature-dependent decay processes. Therefore, according to our investigation, choosing suitable N-heterocyclic moieties in the chelating ligand is beneficial for obtaining phosphorescent emitters with high efficiencies.