Iridium(III) Blue Phosphors with Carbene-Based Chromophoric Chelate

Description

Organic light-emitting diodes (OLEDs) dominate the high-end market for flat-panel monitors. Their advantages include low power consumption, good color saturation, and versatile form factor, particularly in making displays for smartphones and various handheld electronic devices. Since 2015, almost all major smartphone companies (i.e., Samsung, Apple, Sony, Huawei, etc.) have used OLED panels in their flagship products. Thus, with their high performance and power efficiency, OLED displays have gained a reputation as top-of-the-range products. Moreover, the materials, particularly the emitters, are undergoing continual development to improve performance. In contrast to the outstanding progress in long-wavelength emitters, however, there is an urgent demand for more efficient and durable blue-emitting materials, particularly those capable of harvesting both singlet and triplet excitons via thermally activated delay fluorescence (TADF) or phosphorescence, respectively. However, despite extensive studies, the color chromaticity, efficiency, and stability of blue-light emitters have failed to progress substantially. This opens up an opportunity for alternative materials to construct suitable blue emitters. To this end, we believe that Ir(III)-based emitters that bear carbene cyclometalate(s) are the best candidates for efficient and durable blue emitters, due to their more destabilized lowest unoccupied molecular orbitals (LUMOs) in comparison to other chelating designs. In turn, the greater Ir-C bond strength destabilizes the metal-centered (MC) dd excited states and reduces the unwanted quenching caused by thermal population of these MC dd states. As a result, this class of emitting materials should undergo fast intersystem crossing induced by both the iridium metal atom and intra-ligand charge transfer (CT) transition. They will also exhibit increased radiative decay and shortened lifetime to the sub-microsecond region and, ultimately, give rise to OLED devices with longer operational lifetimes.