Achieving a stable dual-emission emitter with the asymmetric D-A-D’ structure

In this work, a novel dual-emission compound (PTZ-CO-PNA) with the asymmetric D-A-D’ structure was designed and synthesized, in which one side of carbonyl benzene was directly connected to phenothiazine unit, and the other side was N-phenyl-2-naphthylamine moiety. In the monomolecular state, PTZ-CO-PNA exhibited a single emission originated from the mixed charge transfer state and local excited state. In the different aggregation state (crystal, ground powder, thermally treated solid), PTZ-CO-PNA displayed a stable dual emission located at about 435 and 523 nm with the CIE coordinates of (0.27, 0.39), (0.28, 0.40), (0.29, 0.42) and (0.31, 0.42), respectively, closed to the white light emission. Importantly, both emissions in crystal exhibited long lifetimes (>50 ms) and the quantum yield was 10%. Moreover, in the crystal, PTZ-CO-PNA had relatively tight stacking with the intermolecular interaction of the C–H … π, S … π and π … π bonds and exhibited a large steric hindrance between phenothiazine unit and carbonyl benzene. The above-mentioned results proved that the dual emissions were derived from the monomolecular and aggregation states in the solid. Finally, PTZ-CO-PNA as the emitter could be used to prepare the near-white OLED that the doped device showed a greenish-white light emission with a CIE coordinate of (0.260, 0.326). [Display omitted] •A dual emission compound PTZ-CO-PNA with a twisted and asymmetrically D-A-D′ structure was synthesized.•The compound exhibited relatively stable dual emissions at 441 and 523 nm in the different aggregate states.•PTZ-CO-PNA exhibited a greenish-white light emission with a CIE coordinate of (0.260, 0.326) in the doped OLED.