A complete evaluation from theoretical aspect on the phosphorescent efficiency improvement through ancillary ligands modifications of a blue Ir(III) complex

Abstract

Abstract Five blue-emitting cationic Ir(III) materials with the form [ I r ( C ∧ N ) 2 ( N ∧ N ) ] + , where C ∧ N = 2-(2,4-difluorophenyl)pyridine (dfppy) cyclometalating ligands, and N ∧ N = biimidazole-type ancillary ligands, are investigated through a comprehensive theoretical scheme. Experimental researches concentrating on decorations of ancillary ligand, revealed that complex with 1,1′-CH3-2,2′-biimidazole (dMebiim) ancillary ligand is a non-emissive material due to the detrimental twisting of dMebiim resulting from steric hindrance of the methyl groups. When getting rid of methyl substituents that becomes the complex with a 1,1′-H-2,2′-biimidazole ancillary ligand, the quantum efficiency has been lifted to a large extent. Further rigidifying the biimidazole-type ancillary ligands, complex with an ortho-xylyl-tethered biimidzole ancillary ligand (1) was synthesized and has a higher quantum yield. From experimental aspect, the approaches employed in quantum efficiency enhancement is mainly concentrate on geometrical control through chelate effect. However, from theoretical aspect, we are not confined the strategies to rigidify the biimidazole ligand by divers chelates. In this study, our comprehensive theoretical scheme is firstly employed on the synthesized complex 1. Results show that the calculated radiative ( k r )and non-radiative ( k n r ) decay rates are consistence with the experimental findings. And further vibrational analysis clarified its nuclear behaviors during electronic transitions. Based on such vibrational analysis, it is found that substituting on the flanks of biimidzole can also effectively avoid detrimental twist. Therefore, in this study, we provide several new designed Ir(III) materials with substituent groups on the flanks of biimidzole, with the consideration of electron-withdrawing or -donating characters of the substituent groups. And Ir(III) materials with better performance are predicted from theoretical aspect.