Efficient deep blue (CIE ∼0.08) fluorophore-based benzimidazole with hybridized local and charge transfer (HLCT) excited state for OLEDs

다국어 초록 (Multilingual Abstract)

Development of efficient deep blue fluorophore with Commission Internationale de l’Eclairage(CIE)y value <0.1 is of great importance for display technology. Herein, we designed and synthesizeda thermally stable deep blue emissive material 3-(2-(4-(1-phenyl-1H-benzo[d]imidazol-2-yl)-[1,1:4,1-terphenyl]-4-yl)-1H-phenanthro[9,10-d]imidazol-1-yl)benzonitrile (MCNPIBI) by integratingmoderate donor and acceptor, namely, phenanthroimidazole (PI) and benzimidazole withcyanophenyl (-CN) group at N1 position of the PI to tune the CT component in the excited states.
The systematic theoretical and photophysical study reveals the MCNPIBI with hybridized local andcharge transfer (HLCT) excited states. Time-dependent density functional theory (TD-DFT) calculationsuggests that the reverse intersystem crossing (RISC) process in MCNPIBI occurs from high-lyingtriplet states to a singlet state. Furthermore, the synthesized deep blue emissive materials wereemployed as dopants in multilayer organic light emitting diode (OLED) devices, thus resulting indeep-blue electroluminescence (EL) with an emission wavelength of 447nm and CIE coordinates of(0.15, 0.08), which are close to the standard values for blue emitters, as suggested by NTSC (0.14, 0.08).
The OLED device displays a maximum current efficiency of 2.78 cd A−1, a maximum power efficiencyof 1.94 lmW−1, and a maximum external quantum efficiency of 3.69%, respectively. In addition, theOLED device has a low turn in voltage of 3.8 V.

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