Regulation of fluorescent color and efficiency by molecular symmetry engineering of triphenylamine-based red emitters and their applications

Fine tuning the energy gaps of red emitters and promoting the fluorescence efficiencies are especially highly desired considering their specific applications. Herein, by varying the molecular symmetry from D-A-D to D-A structures, the red fluorescent emitters with triphenylamine (TPA) donor and 2,3-dicyanopyrazino phenanthrene (DCPP) acceptor realized increased fluorescence quantum yield (Φ_PL) from 2TPA-DCPP to TPA-DCPP due to the decreased non-radiative paths. Moreover, fine control of the emitting color from orange to red and then to deep-red was achieved depending on the intermolecular packing patterns of TPA-DCPP in the aggregation state. Taking the advantages, TPA-DCPP-based OLED exhibited red emission (λ = 640 nm, CIE coordinate of (0.62, 0.38)) with an excellent maximum EQE of 8.30%. The TPA-DCPP@F-127 nanoparticles showed deep-red emission (λ = 684 nm) and were successfully used for cellular imaging of Hela cells. Our results demonstrated that “the simpler, the better” strategy may be feasible to construct D-A structured red emitters with high efficiencies for diverse applications.