Regional Isomerization Effect on Excited-State Dynamics Toward High-Performance Deep-Blue Electroluminescent Materials

Advancing deep-blue organic emitters with high exciton utilization efficiency, exceptional color purity, and suppressed efficiency roll-off remains a critical challenge for next-generation organic light-emitting diodes (OLEDs). Herein, two deep-blue emitters, BPIP-2TPA and RPIP-2TPA, designed through a regional isomerization strategy based on this developed helical phenanthroimidazo[1,2-f]phenanthridine (PIP) core. Regional isomerization not only regulates the charge transfer components to achieve color tuning in the saturated blue region, but also reveals the subtle differences it causes in the high-energy excited states through dynamic spectroscopy and theoretical calculations. This results in distinct electroluminescent behavior: RPIP-2TPA exhibits stable performance with no significant efficiency variation between devices with doped and non-doped emissive layers, whereas BPIP-2TPA exhibits notable changes upon device engineering. Notably, BPIP-2TPA-based OLED furnishes excellent EQE of 11.02% at a practical brightness of 1000 cd m⁻² with CIE coordinates of (0.154, 0.043), representing the best performance among hot-exciton-based blue OLEDs. This work demonstrates that regional isomerization, which leads to tuning device performance, may arise from changes in electrogenerated exciton dissipation pathways, and that the PIP core is a promising building block for high-efficiency, low-roll-off deep-blue OLEDs.