Spiro[fluorene-9,9ʹ-xanthene] based deep-blue emitter and the hidden electroplex for solution-processed non-doped white organic light-emitting devices

A deep-blue fluorescent emitter with an A − D − A-skeleton, named pTRASX, constructed from two diphenyltriazine acceptors and one spiro[fluorene-9,9ʹ-xanthene] (SFX) donor, was deliberately designed and synthesized. The blocking effect of O-atom in xanthene moiety of SFX and the rigid A − D − A-skeleton endow a deep-blue emission at 410 nm with a photoluminescence quantum yield of 43% in solid film. The solution-processed non-doped white organic light-emitting diode (OLED) was demonstrated by merging the emission of pTRASX and its electroplex. Based on the intermolecular through-space charge-transfer, the electroplex mechanism resulted in the non-doped white OLED with the wide spectral range from 400 to 800 nm, the color coordinate of (0.33, 0.27), the high color rendering index of 85, and the external quantum efficiency of 0.49%. The electro- and photo-luminance measurements clarify that the electroplex emission originates from the intermolecular interaction between pTRASX and the adjacent electron transporting layer, ranging from ca. 540 to 800 nm. This study illustrates that the rational molecular design cooperated with the innovative electroluminescent mechanism blazes a trail for simple solution-processed and metal-free blue and white OLED.