An Aromatic Imine Group Enhances the Electro-Luminescence Efficiency and Color Purity of Blue Emitter for Organic Light Emitting Diodes

摘要

DPBP-EPY has the same structure with DPBP-EIF, one of blue-light-emitting materials, except their cores, in which the former has two imine groups, but the latter has only carbon-containing groups. The electro-optical properties modulated by the adoption of the different core structures were systematically examined. It was confirmed that the maximum values in the UV-visible and PL spectra of DPBP-EPY were about 19-46 nm red-shifted from those of DPBP-EIF due to the electron-withdrawing effect of the imine groups whether in solution or in solid. In addition, in case of DPBP-EPY where imine group is substituted, LUMO level of DPBP-EPY decreased while HOME level did not show any significant change. Furthermore, the results of the non-doped OLED device built with these two materials for an emitting layer indicated that DPBP-EPY needed about 2 V lower operation-voltage, and produced higher quantum yield than DPBP-EIF. In particular, it was shown that DPBP-EPY emitted purer and deeper blue-light with CIE coordinate (0.157, 0.131) than DPBP-EIF with CIE coordinate is (0.179, 0.191).