Next-generation blue OLED emitters: efficiency, color purity, and the road to BT.2020

Next-generation ultrahigh-definition (UHD) displays demand blue organic light-emitting diodes (OLEDs) that can achieve high efficiency, long operational stability, and the stringent color purity required by the BT.2020 standard. Although thermally activated delayed fluorescence (TADF) and phosphorescent emitters enable full exciton utilization, conventional donor-acceptor TADF systems typically exhibit broad emission spectra arising from long-range charge-transfer character, ultimately limiting their color purity. Multiple-resonance (MR) TADF materials deliver intrinsically narrowband emission through short-range charge-transfer transitions induced by orthogonally arranged resonance atoms. In this comprehensive material review, we describe molecular design strategies for high-performance blue MR-TADF emitters, emphasizing boron-nitrogen-, carbonyl-nitrogen-, and indolocarbazole-based molecular frameworks. We discuss how structural engineering such as π-extension, peripheral shielding, spiro-locking, carbonyl incorporation, and heteroatom modulation assists in precisely controlling HOMO-LUMO distributions, suppressing vibronic coupling, and enhancing reverse intersystem crossing to achieve narrow emission bandwidths (