Abstract: High-performance deep-blue emitters that meet the BT. 2020 standard proposed by the International Telecommunication Union (ITU) for organic light-emitting diodes (OLEDs) remain highly limited. In this work, four deep-blue emitters, PP1M, PP2M, PP3M, and PP4M, are designed and synthesized by connecting methyl-substituted biphenyl groups with classical hot exciton building block of phenanthreneimidazole. The introduction of methyl groups contributes to increase the molecular torsion angle and widen the energy gaps for the four compounds. Through appropriate modulation of substitution site, PP3M achieves the highest photoluminescence quantum yield of 85.3% in neat film. As a result, the PP3M-based device exhibits deep-blue light with external quantum efficiency of 7.2% and suppressed efficiency roll-off. The device also shows a small full width at half maximum of 53 nm and the CIE coordinates locate at (0.16, 0.04), meeting well with the BT. 2020 standard. The high exciton utilization efficiency is primarily ascribed to the hot exciton pathway. This study provides a reliable insight for the design of efficient deep-blue OLEDs with high color purity.

Key words: Organic light-emitting diodes; Deep-blue; Hybridized local and charge transfer, External quantum efficiency, Phenanthro[9,10]imidazole