A theoretical analysis of the effects of electron-withdrawing substitutions on electronic structures and phosphorescent efficiency of a series of Ir(III) complexes with 2-phenylpyridine ligands

Abstract

A density functional theory and time-dependent density functional theory approaches were used to understand the structure–property relationships of a series of Ir(III) complexes Ir(x-NHC)(y-ppy)2 [where NHC = 2,3-dihydro-1-methyl-3-phenyl-1H-imidazole, ppy = 2-phenylpyridine, x = Cl, y = H (1a); x = Cl, y = Cl (1a-Cl); x = Cl, y = F (1a-F); x = Cl, y = CN (1a-CN); x = Cl, y = CF3 (1a-CF 3 ); x = F, y = CF3 (2-CF 3 )]. The investigations on the electronic structures in the ground and lowest triplet excited states, the frontier molecular orbitals, the absorption and emission spectra, as well as charge injection and transport of these Ir complexes provided a good understanding of the structure–property relationships. Furthermore, the full details of the metal character in the phosphorescent spectra(3MLCT %), triplet energy (E T1), the singlet–triplet splitting energy (ΔE S1–Tn), 3MLCT–3MC energy gap, as well as d orbitals splitting revealed that quantum yield was effectively enhanced by introducing CN and CF3 groups on the ppy ligands. The designed complexes 1-CN, 1-CF 3 , and 2-CF 3 are expected to be highly efficient phosphorescent materials in organic light-emitting diodes.