Rational design of pyridine-containing emissive materials for high performance deep-blue organic light-emitting diodes with CIEy ∼0.06

Charge balance does matter for emission materials to obtain high-performance organic light-emitting diodes (OLEDs), and it is well-known that the electron-transporting ability is inferior to the hole-transporting for the majority of organic emitting materials, especially for blue-emitting compounds. Hence, systematically investigating the effect of the electron-withdrawing group on fluorophore is of vital importance. In this study, we designed and synthesized two deep-blue phenanthro[9,10-d]imidazole (PI) based materials named DPy-PPI and DmPy-PPI by using pyridine-containing groups as electron acceptor as well as adjusting the conjugation length. The photophysical, theoretical, thermal and electrochemical properties of the compounds were investigated systematically, and the relationship between the conjugation length of substituent groups on phenanthroimidazole and the EL performance was clarified. Both of them exhibited good thermal stability and high photoluminescence quantum yields. Non-doped devices based on DPy-PPI and DmPy-PPI as emitter achieved deep-blue emissions with the Commission Internationale de L'Eclairage (CIE) index of (0.14, 0.06) and (0.15, 0.08) and high external quantum efficiencies (EQE(max)) of 4.24% and 3.74%, respectively. Meanwhile, using DPy-PPI and DmPy-PPI as the host materials, yellow-orange phosphorescent organic light-emitting diodes (PHOLEDs) were fabricated with EQE(max), CEmax and PEmax of 20.55%, 63.86 cd/A, 37.08 lm/W and 18.14%, 55.84 cd/A, 32.47 lm/W, respectively. Furthermore, the red PHO-LEDs were also constructed using DPy-PPI and DmPyPPI as the host with EQE max , CE max and PE max of 14.53%, 17.04 cd/A, 18.51 lm/W and 16.62%, 23.58 cd/A, 21.16 lm/W, respectively. And we believe this work can provide some insight suggestions for scientific researchers to design deep-blue emitting materials.

Automated summary

Charge balance is crucial for high-performance organic light-emitting diodes (OLEDs), with the electron-transporting ability usually inferior to hole-transporting ability for most organic emitting materials, especially blue-emitting compounds. This study systematically investigates the effect of electron-withdrawing groups on fluorophores, designing and synthesizing two deep-blue phenanthro[9,10-d]imidazole (PI) based materials named DPy-PPI and DmPy-PPI. The compounds exhibit good thermal stability, high photoluminescence quantum yields, and achieve deep-blue emissions with high external quantum efficiencies in non-doped devices. Additionally, yellow-orange and red phosphorescent OLEDs with high EQE and luminance were fabricated using DPy-PPI and DmPy-PPI as host materials.