Ultra-Narrowband Helical Emitter with Frontier Orbital Confinement for Stable Deep-Blue Hybrid-Tandem Organic Light-emitting Diodes

Achieving efficient and stable deep-blue organic light-emitting diodes (OLEDs) with high color purity remains challenging, primarily due to the scarcity of blue emitters that simultaneously exhibit ultra-narrowband emission and high operational stability. Herein, we present a multiple-resonance emitter featuring a highly-twisted helical configuration with spatially-confined frontier molecular orbitals, thereby decoupling radiative transitions from structural distortion while mitigating spectral broadening from carbon–hydrogen bond repulsion and molecular aggregation. A sharp emission peaking at 460 nm with a full-width at half-maximum (FWHM) of only 12 nm is obtained in solution, which challenges the conventional belief that a twisted molecular skeleton compromises color purity. Remarkably, this emitter delivers cutting-edge performance with nearly identical spectra across emitting systems of varying polarity, enabling the realization of a unicolor hybrid-tandem OLED design that integrates complementary exciton-harvesting mechanisms to overcome the efficiency-lifetime trade-off inherent in conventional homogeneous tandem devices, while maintaining spectral uniformity. The targeted device concurrently achieves an external quantum efficiency of 39.7%, a lifetime of 539 hours to 90% of 1,000 cd·m⁻², a FWHM of 14 nm, and a chromaticity y-coordinate of 0.10. We further show that the stacking sequence of emitting units induces a twofold lifetime variation, which mainly arises from differences in outcoupling efficiency and photoelectric co-aging. This co-engineering strategy constitutes a substantial advance toward commercially viable ultrapure-blue OLED displays.