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

Three multichromophore thermally activated delayed fluorescence (TADF) molecules, p-di2CzPN, m-di2CzPN, and 1,3,5-tri2CzPN, were synthesized and characterized. These molecules were designed by connecting the TADF moiety 4,5-di(9H-carbazol-9-yl)phthalonitrile (2CzPN) to different positions of a central benzene ring scaffold. Three highly soluble emitters all exhibited near quantitative photoluminescence quantum yields (_PL) in toluene. High _PLs were also achieved in doped films, 59% and 70% for p-di2CzPN and m-di2CzPN in 10 wt% DPEPO doped films, respectively, and 54% for 1,3,5-tri2CzPN in 20 wt% doped CBP film. The rate constant of reverse intersystem crossing (k_RISC) for p-di2CzPN and m-di2CzPN in DPEPO films reached 1.1 × 10⁵ s⁻¹ and 0.7 × 10⁵ s⁻¹, respectively, and k_RISC for 1,3,5-tri2CzPN in CBP film reached 1.7 × 10⁵ s⁻¹. A solution-processed organic light-emitting diode based on 1,3,5-tri2CzPN exhibited a sky-blue emission with CIE coordinate of (0.22, 0.44), and achieved a maximum external quantum efficiency of 7.1%.