Efficient full-colour organic light-emitting diodes based on donor–acceptor electroluminescent materials with a reduced singlet–triplet splitting energy gap

A series of efficient blue-emitting materials, namely, Cz-DPVI, Cz-DMPVI, Cz-DEPVI and TPA-DEPVI, possessing a donor–acceptor architecture with dual carrier transport properties and small singlet–triplet splitting is reported. These compounds exhibit excellent thermal properties with a very high glass-transition temperature (T(g)), and thus, a stable uniform thin film was formed during device fabrication. Among the weak donor compounds, specifically, Cz-DPVI, Cz-DMPVI and Cz-DEPVI, the Cz-DEPVI-based device showed the maximum efficiencies (L: 13 955 cd m(−2), η(ex): 4.90%, η(c): 6.0 cd A(−1), and η(p): 5.4 lm W(−1)) with CIE coordinates of (0.15, 0.06) at 2.8 V. The electroluminescent efficiencies of Cz-DEPVI were higher than that of the strong donor TPA-DEPVI-based device (L: 13 856 cd m(−2), η(ex): 4.70%, η(c): 5.7 cd A(−1), and η(p): 5.2 lm W(−1)). Furthermore, these blue emissive materials were used as hosts to construct efficient green and red phosphorescent OLEDs. The green device based on Cz-DEPVI:Ir(ppy)(3) exhibited the maximum L of 8891 cd m(−2), η(ex) of 19.3%, η(c) of 27.9 cd A(−1) and η(p) of 33.4 lm W(−1) with CIE coordinates of (0.31, 0.60) and the red device based on Cz-DEPVI:Ir(MQ)(2)(acac) exhibited the maximum L of 40 565 cd m(−2), η(ex) of 19.9%, η(c) of 26.0 cd A(−1) and η(p) of 27.0 lm W(−1) with CIE coordinates of (0.64, 0.37).