Highly Efficient Cuprous Complexes with Thermally Activated Delayed Fluorescence for Solution-Processed Organic Light-Emitting Devices

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-1-yl)­pyridin-3-yl)-9,10-dihydroacridine,
POP = bis­[2-(dipenylphosphino)­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 structural, 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 using 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/m2.