Modulating electronic confinement and structural distortion of multiple resonance emitters enables high-performance ultrapure blue OLED

Developing deep-blue emitters with high color purity is crucial for the advancement of ultrahigh-definition display technology based on organic light-emitting diodes (OLEDs). Since most emitters are empirically designed, establishing a feasible design strategy for developing ultrapure blue emitters with narrowband characteristics remains an urgent and challenging goal. Here, we subtly construct four blue emitters with multiple resonance (MR) effect and provide an in-depth understanding for the nature of narrowband emission from the perspective of electronic confinement and structural distortion combined with actual molecular structures. A novel and feasible molecular design strategy is proposed based on the “flexible locking-ring” concept, enabling effective narrowing main peak while retaining bluer emission. More impressively, a simple sensitizer-free OLED based on SAC2MN2B with the “flexible locking-ring” design achieves one of state-of-the-art device performance with a maximum external quantum efficiency of 19.80 %, and a pure deep-blue emission peaking at 448 nm with small full-width at half-maximum (FWHM) of 25 nm and CIE coordinates of (0.147, 0.061). This work successfully achieves high-performance OLED with high color purity and provides a feasible and promising design strategy for developing organic emitters with ultrapure blue emission.