Highly efficient iridium(iii) phosphors with a 2-(4-benzylphenyl)pyridine-type ligand and their high-performance organic light-emitting diodes

Abstract

A series of new cyclometalated iridium(III) complexes containing a methyl or a trifluoromethyl substituted 2-(4-benzylphenyl)pyridine molecular framework have been synthesized and characterized. All these complexes are amorphous and possess excellent thermal stabilities. Arising from the propensity of the tetrahedral geometry of the CH₂ moiety in the benzyl group, this could make the metal complexes less crystalline, attain more morphologically stable thin-film formation and reduce the triplet–triplet annihilation process, especially in the solid state. The optical, electrochemical, and photo- and electrophosphorescence traits of these iridium(III) phosphors have been studied in terms of the electronic nature of the pyridyl ring substituents. Electrophosphorescent organic light-emitting diodes (OLEDs) with attractive device performance can be fabricated based on these materials. The best electroluminescent (EL) performance can be obtained with a maximum current efficiency (η_L) of 76.3 cd A⁻¹, a maximum power efficiency (η_P) of 51.1 lm W⁻¹, a maximum external quantum efficiency (η_ext) of 21.4% and a pure green CIE color coordinates of (0.27, 0.64). The present work provides a simple way to enhance the OLED performance by simply modifying the molecular design of the benchmark emitters, which show great potential for application in multicolor displays.