Structure-Dependent Pyrene[4,5-d]imidazole-Based Deep Blue-Emitters with High-Performance OLEDs

Hybridized local and charge-transfer (HLCT) excited-state emitters have garnered significant attention due to their ability to efficiently utilize triplet excitons. Pyreno[4,5-d]imidazole (PyI) is considered an outstanding building block for constructing HLCT blue emitters. To understand the influence of the substituent position, the electronic effect, and the steric effect of the PyI substituents on the optical behavior and the electronic transition in the excited state, herein, a set of L-shaped and V-shaped PyI-based blue emitters has been designed and synthesized. The L-shaped compounds exhibit HLCT-dominated characteristics, which demonstrate better electroluminescence properties, while the V-shaped compounds are primarily LE-dominated with a relatively narrower full width at half-maximum (FWHM, <60 nm) in their EL spectra. The L-shaped PyI-based HLCT blue emitters achieve a maximum brightness (L_max) of 11060 cd m^-2 and maximum external quantum efficiency (η_ext) of 4.77% in the OLED devices, with significantly reduced efficiency roll-off. Thus, this work provides detailed examples demonstrating how the substitution positions on the PyI core can significantly influence the emission behavior and OLED properties of HLCT materials. Moreover, this work offers a valuable synthetic strategy for the preparation of high-performance HLCT materials that can efficiently harness triplet excitons in OLED devices.