Highly efficient electron-transporting benzimidazole derivatives of xPBIPO with phosphine oxide joints were constructed to investigate the determinants for efficiency reduction.

Ternary donor (D)-acceptor (A)-acceptor (A) molecules are commonly considered as low triplet (T 1 ) energy systems for specific applications. In this work, this preoccupation was redressed by a triangleshaped D-A-A molecule PCImbPO with peculiarly high triplet energy of 3.0 eV. Profiting from the enhanced D-A electronic coupling, electron injecting and transporting ability of PCImbPO was 10 dramatically improved with negligible influences on its highest occupied molecular orbital (HOMO) characteristic. Its particular T 1 configuration adjustment further gives rise to the separated frontier MO and T 1 locations, beneficial to suppress quenching effects. By utilizing PCImbPO as host in blue phosphorescent organic light-emitting diodes (PHOLEDs) and thermally activated delayed fluorescence devices, the impressively high external quantum efficiency beyond 22 and 12% were achieved, 15 respectively. This work established a new understanding of high-energy-gap complicated D-A systems. 65 III), ternary D-A system is almost ideal as host materials with the independent highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and T 1 locations, which is conducive to suppressing polarization-induced exciton decomposition (PIED) 51 and triplet-polaron quenching (TPQ) 70 effects. 52-53 Recently, we reported a D-A-D host with a structure of two carbazole donors linked by a phenylphosphine oxide acceptor, which endowed its FIrpic-based blue PHOLEDs with favorable performance owing to its unique dynamically adaptive electrical characteristic. 54 Nevertheless, a more in-depth 75 This journal is © The Royal Society of Chemistry [year]90 CDCl 3 , 400 MHz): δ = 8.19-8.22 (d, J = 7.6 Hz, 2H), 7.77-7.79 (d, J = 8.8 Hz, 2H), 7.41-7.51 (m, 6H), 7.35-7.38 ppm (t, J = 6.8 Hz, 2H); LDI-TOF: m/z (%): 321 (100) [M + ]; elemental analysis (%) for C 18 H

The charge flux balance and interfacial optimization are two core concerns when simplifying blue thermally activated delayed fluorescence (TADF) diodes, which reflects the more stringent demand on carrier transporting materials (CTM) as the embodiment of the contradiction between charge transportation and quenching suppression with the opposite requirement on intermolecular interactions. Herein, phenylbenzimidazole (PBI) was used as the core substituted with two diphenylphosphine oxide (DPPO) groups to form six dual-encapsulated charge−exciton separation (CES)-type electron transporting materials (ETM) with the collective name of xyPBIDPO. Through tuning the substitution positions of DPPO group, its two functions of resonance and steric effects were integrated and optimized to enhance charged moiety encapsulation without cost of reducing electroactivity. As the result, among xyPBIDPO, mmPBIDPO successfully realizes the balance of favorable electrical performance and interfacial interaction suppressions in virtue of its doubled mesa-substitution structure and roughly symmetrical configuration, rendering the good electron affinity of 2.8 eV, the high electron mobility by the level of 10 −6 cm 2 V −1 s −1 and effective PBI-core encapsulation. Consequently, mmPBIDPO was used to extremely simplify the blue TADF devices with the state-of-the-art performance from trilayer and quadruple-layer configurations, such as the maximum external quantum efficiency (EQE) beyond 20% and improved efficiency stability. This work not only established a solid example of CEStype ETM for high-performance simple structured blue TADF devices but also provided the direction of developing this kind of materials in the future.