Two mononuclear cuprous complexes [Cu(PNNA)(POP)]-BF4 (1) and [Cu(PNNA)(Xantphos)]BF4 (2) (PNNA = 9,9-dimethyl-10-(6-(3-phenyl-1H-pyrazol-l-yl)pyridin-3-yl)-9,10-dihydroacridine, POP = bis[2-(dipenylphosphilo)phenyl]ether, Xantphos =4,5-bis-(diphenylphosphino)-9,9-dimethylxanthene), with intense bluish-green luminescence based On a new diimine ligand were designed and synthesized. Their strucrural, electrochemical, and photophysical properties were characterized by single-crystal X-ray analysis, cyclic voltammetry, temperature dependence, of spectroscopy, time-dependent emission spectroscopy, etc. The complexes exhibit high photoluminescence quantum yields in doped films (up to 74.6%) at room temperature. Thermally activated delayed fluorescence based on intraligand charge transfer was observed by grafting a strong electron-donor moiety, 9,9-dimethylacridan, on the diimine ligand, which is supported by the density functional theory calculations on two complexes. Highly efficient solution processed OLEDs based on these two complexes were fabricated, among which the electroluminescent device rising 2 as dopant shows a peak external quantum efficiency of 7.42%, a peak current efficiency of 20.24 cd/A, and a maximum brightness of 5579 cd/m(2).