Ultrapure green organic light-emitting diodes based on highly distorted fused π-conjugated molecular design

Organic light-emitting diode (OLED) technology is promising for ultrahigh-definition displays and other applications, but further improvements in efficiency and colour purity are desired. Here, we designed and synthesized an ultrapure green emitter called DBTN-2, which is organoboron based and features a highly distorted fused π-conjugated molecular design. This design concept substantially reduces the relaxation energy between the geometries of the excited and ground states, leading to a full-width at half-maximum emission of only 20 nm. Furthermore, the different excitation characters of the singlet and triplet states enhance the spin–orbit couplings leading to highly efficient operation. The introduction of the multiple carbazole moieties gives rise to a charge-resonance-type excitation feature of the triplet states, thus resulting in a high density of the triplet states and a rate of reverse intersystem crossing (k_RISC) as fast as 1.7 × 10⁵ s⁻¹. An ultrapure green OLED exploiting DBTN-2 as an emitter without optimized cavity effects and colour filters operated with Commission Internationale de l’Eclairage coordinates of (0.19, 0.74), satisfying the requirement for a commercial green OLED display. Moreover, in combination with a photoluminescence quantum yield of near 100% and a strong horizontal dipole orientation in the doped film, an excellent external quantum efficiency of 35.2% with suppressed efficiency roll-off is simultaneously obtained.