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

Abstract

Several phosphorescent IrIII 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 IrIII 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 IrIII 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 (ηL) of 22.2 cd A−1, external quantum efficiency (ηext) of 14.7% and power efficiency (ηP) 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 IrIII complexes with B(Mes)2 units as well as a deeper insight into the conventional color-tuning approach on ppy-type IrIII complexes, but also offer a simple outlet to afford unique electronic features to these phosphorescent emitters to show admirable EL performance.