Efficient nondoped Deep-Blue electrofluorescence benefiting from structural hindrance and regular C-H···π stacking

Abstract

Developing a high-performance nondoped deep-blue luminescent material that meets the substantial demand of high-definition organic light-emitting diodes (OLEDs) is significant and challenging. Herein, two highly efficient bar-like pure-blue and deep-blue materials, namely, PIPMePBO and PIPDMePBO, respectively, are designed and synthesized. Rigid planar phenanthroimidazole (PI) and benzoxazole (PBO) moieties are linked to construct a conjugated structure for a regulated aggregation pattern in both single crystals and evaporation films. This approach helps enhance and balance their carrier mobilities for excellent, stable OLED efficiency. Furthermore, different numbers of steric hindrance methyl groups are added to the π-conjugated bridge. This not only avoids potential conjugation quenching and aggregation redshift but also benefits the excited-state constructions for the regulation of blue purity. Results show that the double-methyl-substituted PIPDMePBO, with a moderate charge-transfer excited state, shows nondoped deep-blue electroluminescence with Commission Internationale de l’Eclairage coordinates of (0.156, 0.048). Its maximum luminescence is 12212 cd m−2. Remarkably, the nondoped OLED based on PIPDMePBO exhibits an excellent external quantum efficiency of 8.0%, with an efficiency roll-off of only approximately 12%, even at 10000 cd m−2. These findings are among the best for nondoped deep-blue fluorescent OLEDs with similar light colors.