Efficient donor–acceptor emitter based nonsymmetrical connection for organic emitting diodes with improving exciton utilization

Abstract

New strategy is developed to construct efficient blue emissive materials using unsymmetrical connection with identical phenanthrimidazole groups leads to donor–acceptor (D–A) architecture.

Efficient M-shaped blue emitters having a high conjugation extent with improved roll-off efficiency

“…In continuation of our research using the HLCT-emissive state strategy, 10 we report M-shaped blue emissive materials with the HLCT emissive state, namely 4′-(( E )-2-(1-(4-(diphenylamino)phenyl)-1 H -phenanthro[9,10- d ]imidazol-2-yl)vinyl)- N -(4′-(( E )-2-(1-(4-(diphenylamino)phenyl)-1 H -phenanthro[9,10- d ]imidazol-2-yl)vinyl)-[1,1′-biphenyl]-4-yl)- N -phenyl-[1,1′-biphenyl]-4-amine (TPA–2SPPITPA). The non-doped BOLEDs based on TPA–2SPPITPA/TPA–2PPITPA show a maximum EQE of 6.13/5.82% with small efficiency roll-off (1.63/3.0%), CE of 5.92/5.43 cd A −1 , power efficiency (PE) of 5.15/4.98 lm W −1 and CIE of (0.15, 0.07)/(0.15, 0.07).…”

“…Third-generation organic emitters, namely thermally activated delayed fluorescence (TADF) 8 and hybridized local and charge-transfer (HLCT) 9,10 excited-state emitters, which render 100% exciton utilization efficiency (EUE) while avoiding noble metals, have been considered as potential candidates. The long exciton lifetime of TADF emitters (D–A molecules with small splitting energy) tends to cause serious efficiency roll-off under high current due to triplet–triplet annihilation (TTA), whereas short exciton lifetimes of HLCT emitters are beneficial to suppress exciton annihilation and thus improve efficiency roll-off.…”

“…More importantly, the RISC in HLCT materials can be very fast, which can enable their applications in the more simply fabricated non-doped OLED. 9,10 Thus, tuning the excited state of D–A emitters is a promising strategy to enhance the exciton utilization efficiency (EUE) and PL efficiency ( η PL ).…”

Doped and non-doped blue organic light-emitting diodes based on AIEgens with high exciton utilization efficiency and external quantum efficiency

“…S3 & S4). The large ΔE T1 -T2 between T 1 and T 2 states of NSPI-DVP (1.19 eV) and CNSPI-DVP (1.60 eV) assisted the fast RISC by the restriction of internal conversion, called hot-exciton mechanism and ΔE T1-T2 of CNSPI-DVP is larger than NSPI-DVP due to cyano group (Figure 4 & Figure S3) [20][21][22][23] [k r s/f (10 8 s -1 ) -1.21/2.41: k nr s/f (10 8 s -1 ) -1.07/2.37 and CNSPI-DVP (k r s/f (10 8 s -1 ) -1.90/2.51: k nr s/f (10 8 s -1 ) -1.65/2.45]. The increase of k r and decrease of k nr of CNSPI-DVP and NSPI-DVP is in line with the aim of our design strategy.…”

“…Phenanthroimidazoles with C2 substitution developed effective conjugation and results in deep blue emission, whereas N1 substitution does not affect the optical properties significantly because of perpendicular configuration [15][16][17][18][19]. Though C2 and N1 substituted 3 phenanthroimidazoles have been studied widely, C6 and C9 substituted phenanthrimidazole derivatives have not been analysed broadly [20,21]. Recently, our research group reported C6 /C9 as well as C5/C10 substituted phenanthrimidazole derivatives (D-A) with excellent efficiency and low roll-off efficiency [22][23][24][25].…”