Acquiring High‐Performance Deep‐Blue OLED Emitters through an Unexpected Blueshift Color‐Tuning Effect Induced by Electron‐Donating ‐OMe Substituents

Abstract A series of blue‐emissive 7‐(diphenylamino)‐4‐phenoxycoumarin derivatives bearing ‐CF 3 , ‐OMe, or ‐N(Me) 2 substituents on the phenoxy subunit were synthesized. Although both the ‐CF 3 and ‐N(Me) 2 modifications were found to trigger redshifted fluorescence, the ‐OMe substitution was demonstrated to exert an unexpected blueshift color‐tuning effect toward the deep‐blue region. The reason is that the moderate electron‐donating ‐OMe group can endow coumarins with unaltered HOMO but elevated LUMO energy levels. Moreover, the ‐OMe substitution was found to be beneficial to the thermal stability of these coumarins. Therefore, the trimethoxy‐substituted objective compound can act as a high‐performance deep‐blue organic light‐emitting diode (OLED) emitter, and OLED based on it emits deep‐blue light with CIE coordinates of (0.148, 0.084), maximum luminance of 7800 cd m −2 , and maximum external quantum efficiency of 5.1 %. These results not only shed light on the molecular design strategy for high‐performance deep‐blue OLED emitters through color‐tuning, but also show the perspective of coumarin derivatives as deep‐blue OLED emitters.