Rational molecular design of multifunctional blue material based on phenanthroimidazole derivatives.

High-performance deep-blue emitters with EQEs over 5% are still scarce in OLEDs. In this work, by introducing the [1,2,4] triazolo [1,5-a] pyridine (TP) unit to the N1 position of phenanthroimidazole, two luminescent materials, PTPTPA and PTPBTPA were obtained. Based on systematic photophysical analysis, we found that the TP block is suitable for constructing HLCT emitters. Its moderate electron withdrawing ability and rigid planar structure can enhance the CT component while ensuring the color purity. In addition, compared with PTPTPA, the increased phenyl ring of PTPBPTA not only increases the oscillator strength, but also shortens the stokes shift. TDDFT calculations point to facile RISC processes in PTPBTPA from high-lying triplet states to the singlet excited state. PTPBTPA presents impressive performances when serving as non-doped device (EQE max = 7.11%, CIE: (0.15, 0.09)), as well as a high-performance host for yellow and red PhOLEDs. By doping yellow (PPYBA) and red (BTPG) phosphorescent dye into PTPBTPA, a white OLED with a high EQE of 23.85% was achieved. The successful design of PTPBTPA not only provides an optimization choice for OLED emitters, but also demonstrates the empirical rules for the design of multifunctional deep-blue emitters.