Versatile phosphorescent color tuning of highly efficient borylated iridium(iii) cyclometalates by manipulating the electron-accepting capacity of the dimesitylboron group

Abstract

Several phosphorescent Ir^III ppy-type complexes (ppy = 2-phenylpyridine anion) bearing dimesitylboron (B(Mes)₂) units have been designed and some of them have been newly prepared. By changing the substitution positions with different electronic characters that can manipulate the electron-accepting ability of the attached B(Mes)₂ moieties, the direction of the metal-to-ligand charge transfer (MLCT) process for these Ir^III complexes can be either retained or shifted, which can provide a new strategy toward phosphorescent color tuning. Through computational studies, shifting the substitution position of the B(Mes)₂ moiety on the organic ligand, some electronic features, such as the electron injection/electron transporting (EI/ET) properties and charge transport balance, can also be conferred to the phosphorescent Ir^III complexes to give excellent electroluminescent (EL) characteristics. Highly efficient red phosphorescent bis(5-(dimesitylboryl)-2-phenylpyridinato)iridium(acetylacetonate) (Ir-B-1) based on the above notion shows a very good compatibility with the choice of host materials which can furnish maximum current efficiency (η_L) of 22.2 cd A⁻¹, external quantum efficiency (η_ext) of 14.7% and power efficiency (η_P) of 21.4 lm W⁻¹ for the devices constructed with the conventional host materials. So, these exciting results will not only provide both the systematic guidelines for the phosphorescent color variation on the Ir^III complexes with B(Mes)₂ units as well as a deeper insight into the conventional color-tuning approach on ppy-type Ir^III complexes, but also offer a simple outlet to afford unique electronic features to these phosphorescent emitters to show admirable EL performance.