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 pi-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 x 10(5) 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.