Highly efficient and stable pure blue nondoped organic light-emitting diodes at high luminance based on phenanthroimidazole-pyrene derivative enabled by triplei-triplet annihilation

• Three naphthalene, pyrene and anthracene-substituted phenanthroimidazole derivatives are developed, respectively.
• Pyrene and anthracene-containing derivatives exhibit TTA characteristics.
• The nondoped OLED of 2 demonstrates a stable pure blue emission (CIE (0.15, 0.14)) and a maximum luminance of 54300 cd m-2.
• The EQE reaches 5.11% and maintains EQE over 5% at luminance of 300∼3000 cd m-2.

To promote the application of organic light emitting diodes (OLEDs) in various areas, achieving high performance blue OLEDs with outstanding efficiencies at high luminance is still desired. Herein, we focus on realizing stable and highly efficient pure blue OLED capable of harvesting triplets via triplet-triplet annihilation (TTA). Three fused polycyclic aromatic substituents, naphthalene, pyrene and anthracene, are selected to construct phenanthroimidazole-functionalized molecules (1–3), among which pyrene and anthracene comprised ones display TTA characteristics in electroluminescence devices. High photoluminescence quantum efficiency of 57% is found in the neat film of emitter 2 from judicious molecular design. The nondoped OLED of 2 exhibits pure blue emission with CIE coordinates of (0.15, 0.14) and demonstrates a maximum external quantum efficiency (EQE) of 5.11%, stable EQE over 5% at luminance of 300–3000 cd m-2, EQE of 4.76% at an ultra-bright luminance of 10000 cd m-2 and a maximum luminance of 54300 cd m-2. Such great device performance are responsible for the appreciable TTA contribution substantially.

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