Multichromophore Molecular Design for Thermally Activated Delayed-Fluorescence Emitters with Near-Unity Photoluminescence Quantum Yields.

Three multichromophore thermally activated delayed fluorescence (TADF) molecules, , , and , were synthesized and characterized. These molecules were designed by connecting the TADF moiety 4,5-di(9-carbazol-9-yl)phthalonitrile () to different positions of a central benzene ring scaffold. Three highly soluble emitters all exhibited near-quantitative photoluminescence quantum yields (Φ) in toluene. High Φs were also achieved in doped films, 59 and 70% for and in 10 wt % DPEPO doped film, respectively, and 54% for in 20 wt % doped CBP films. The rate constant of reverse intersystem crossing () for and in DPEPO films reached 1.1 × 10 and 0.7 × 10 s, respectively, and for in the CBP film reached 1.7 × 10 s. A solution-processed organic light-emitting diode based on exhibited a sky-blue emission with CIE coordinates of (0.22, 0.44) and achieved a maximum external quantum efficiency of 7.1%.