Phenoxazine and phenothiazine embedded Multi-Resonance emitters for highly efficient Pure-Red OLEDs with improved color purity

Multi-resonance (MR) emitters based on boron-nitrogen doped polycyclic aromatic hydrocarbons are the cuttingedge light-emitting materials for organic light-emitting diodes (OLEDs) due to their high photoluminescence quantum yield and narrowband emission spectra. Among all the widely-reported MR molecules, emitters showing pure-red emission are the least developed. The difficulty in designing pure-red MR emitters lies in the limit of the weak charge transfer nature of the MR framework, as well as the large molecular weight which may bring difficulty in vacuum sublimation process. Herein, through introducing the strong electron donating phenoxazine and phenothiazine moiety into the double-boron-based MR molecular skeleton, two novel MR emitters namely PXZBNO and PTZBNO were designed and synthesized. These two emitters exhibited pure-red emission with emission maxima up to 627 nm, small full-width at half-maximum (FWHM) of 45 nm. Red OLEDs based on PTZBNO demonstrated very high maximum external quantum efficiency (EQEmax) of 34.5%, together with very small efficiency roll-off. Meanwhile, PXZBNO-based purity pure-red OLEDs exhibited high color purity with color coordinates of (0.69, 0.31), which is approaching BT. 2020 standard.

Automated summary

Multi-resonance (MR) emitters based on boron-nitrogen doped polycyclic aromatic hydrocarbons are advanced materials for organic light-emitting diodes (OLEDs) with high photoluminescence quantum yield and narrowband emission spectra. However, the development of pure-red MR emitters has been challenging due to weak charge transfer and large molecular weight. This study successfully designed and synthesized two novel MR emitters, PXZBNO and PTZBNO, by introducing strong electron donating moieties. These emitters exhibited pure-red emission, high efficiency, and color purity, making them promising for OLED applications.