Improving performance of thermally activated delayed fluorescence emitter by extending its LUMO distribution

Abstract

An optimized compound 9-(9,9-dimethylacridin-10(9H)-yl)-6H-benzo[c]ch-romen-6-one (MAB) was designed and synthesized based on our previously reported TADF emitter 6-(9,9-dimethylacridin-10(9H)-yl)-3-methyl-1H-isochromen-1-one (MAC) to further improve the performance of thermally activated delayed fluorescence (TADF) emitters. With the additional phenyl in coumarin-contained plane, MAB possesses an extended distribution of the lowest unoccupied molecular orbitals (LUMO), and thus realizes reduced electron exchange between the frontier molecular orbitals and a stretched molecular dipole moment compared with MAC. MAB based organic light-emitting diode (OLED) exhibits a remarkable maximum external quantum efficiency (EQE) of 21.7%, which is much better than the maximum EQE of MAC-based OLED with a value of 12.8%. Our work proves that extending the distribution of LUMO is a simple but effective method to improve the efficiency of TADF emitter.

Rational design of perfectly oriented thermally activated delayed fluorescence emitter for efficient red electroluminescence

“…6d). The PhNAI-PMSBA-based device achieved outstanding EL performance with maximum current efficiency (η c ) of 34.3 cd A −1 , a maximum power efficiency (η p ) of 35.9 lm W −1 and a maximum η ext of 22.3% ( Fig. 6e and Table 2).…”

“…S7). The delayed fluorescence lifetime (τ d ) of PhNAI-PMSBA was fitted as short as 2.7 µs (Table 1 and Table S4), indicative of its effective RISC process [35,36]. Moreover, PhNAI-PMSBA exhibited PL quantum yield (Φ PL ) and radiative rate constant (k r,S ) comparable to PhNAI-MFAC in the mCPCN host (Φ PL = 55% and 61%, and k r,S = 0.90 × 10 7 and 1.74 × 10 7 s −1 , respectively).…”

Accelerating PLQY and RISC rates in deep-blue TADF materials with the acridin-9(10H)-one acceptor by tuning the peripheral groups on carbazole donors

“…1,3,[7][8][9]11,13 For example, there have been many reports on highly efficient pure and deep-blue TADF-OLEDs using carbonyl-containing emitters. 1,13,[17][18][19] The carbonyl group employs sp 2 hybridization, in which the electronic transition from the n orbital to the orthogonally overlapped p* orbital is beneficial for a small DE ST . 13,20 However, because the TADF molecules emit light from the charge transfer (CT) state, TADF molecules based on the widely used benzophenone acceptor usually show a broad emission profile with a relatively large full width at half maximum (FWHM) due to the low rigidity or planarity of benzophenone, having a negative influence on the color purity of the emitters.…”