Cu(I) and Ag(I) Complexes with a New Type of Rigid Tridentate N,P,P-Ligand for Thermally Activated Delayed Fluorescence and OLEDs with High External Quantum Efficiency

Neutral Cu(I) and Ag(I) complexes with a new rigid tridentate N,P,P ligand (dmpzpp, 3,5-dimethyl-1-(2-((2-(di-o-tolyl)-phosphanyl) (o-tolyI)-phosphanyl)phenyl)-1H-pyrazole), giving Cu-(dmpzpp)Cl 6, Cu(dmpzpp)Br 7, Cu(dmpzpp)I 8, Cu(dmpzpp)SPh 9, and Ag(dmpzpp)I 10 with SPh = thiophenylato, were prepared and their crystal structures, TD-DFT electronic structures, and phosphorescence and thermally activated delayed fluorescence (TADF) properties were studied in detail. The photoluminescence quantum yields Phi(PL) of neat powder materials lie between 70 and 90% with emission colors from blue to yellow. Compound 9, with bulky ligands showing 0,, = 90%, was used for detailed emission studies from T = 1.7 to 300 K. Up to T approximate to 70 K, 9 shows only long-lived phosphorescence with a radiative decay time of T-1 of tau(r)(phos) = 1 ms because of weak spin-orbit coupling. Accordingly, the zerofield splittings of T-1 in three substates are S-0 rate of 1.1 x 10(7) s(-1) (91 ns). For fabrication of OLED devices, we applied sublimable 8 and 9 using cohost device structures. For example, with a concentration of 2 wt % of 8, a green-emitting OLED showing CIE coordinates of (0.33; 0.52), a high external quantum efficiency of up to EQE = 16.4%, and a high luminance of almost 10,000 cd m(-2) could be fabricated. Strategies for designing compounds giving higher EQE are presented