Design, synthesis, and electroluminescence of red TADF dyes based on cyanophenanthrene

Two rigid electron-deficient cyanophenanthrene frameworks with limited π-conjugation, phenanthrene-9-carbonitrile (CNP) and phenanthrene-9,10-dicarbonitrile (DCNP), are employed as the electron acceptors to construct thermally activated delayed fluorescence (TADF) dyes. The new TADF emitters exhibit long-wavelength emission without strong long-range π-π stacking or interchromophore coupling, as supported by the photophysical and crystallographic results. These unique features are suitable to construct red organic light-emitting diodes (OLEDs). An OLED based on CNP-TPXZ showed an orange-red emission with a peak at 586 nm and a maximum EQE of 8.4%, while that of DCNP-DPXZ exhibited red emission at 614 and a maximum EQE of 6.6%. These results demonstrate that DCNP and CNP are potential electron acceptors for the development of red TADF emitters and OLEDs.