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

Abstract

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-tolyl)-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 ΦPL of neat powder materials lie between 70 and 90% with emission colors from blue to yellow. Compound 9, with bulky ligands showing ΦPL = 90%, was used for detailed emission studies from T = 1.7 to 300 K. Up to T ≈ 70 K, 9 shows only long-lived phosphorescence with a radiative decay time of T 1 of τr(phos) = 1 ms because of weak spin–orbit coupling. Accordingly, the zero-field splittings of T 1 in three substates are < 1 cm–1 (0.1 meV). Individual decay times of 2400, 2250, and 292 μs are estimated. Presumably, the phosphorescence is essentially induced by spin–vibronic mechanisms. Up to T = 300 K, the radiative decay time decreases by more than two orders of magnitude to τr(TADF) = 5.6 μs because of the TADF effect. This short decay time is determined by the small gap of ΔE(S1–T1) = 600 cm–1 (74 meV) and the fast radiative S1 → S0 rate of 1.1 × 107 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.

Diversity of Luminescent Metal Complexes in OLEDs: Beyond Traditional Precious Metals

“…In addition to the four-coordinate cationic Cu(I) and Ag(I) complexes, four-coordinate neutral Cu(I) and Ag(I) complexes also have been investigated to a large extent. Many chelating ligands, such as bidentate NN/PP [15] and NP (Figure 1, Cu7-Cu9), [16] as well as tridentate PPP (Figure 1, Cu10-Cu12) [17] and PPN (Figure 1, Cu13-Cu16 and Ag2) [18] ligands have been developed. Bräse et al conducted a vast study about fourcoordinate neutral Cu(I) based on NP chelating ligands.…”

Crystalline Metal‐Organic Materials with Thermally Activated Delayed Fluorescence

“…In 8e), showing high TADF performance. [56] Due to the rigid tridentate ligand, the distortions in the excited states were severely restrained giving high emission QYs. For complex Cu(dmpzpp)SPh, it displayed an emission QY of 90% at 300 K, and upon cooling to 77 K, only QY of 70% could be detected, indicating the TADF process was inhibited.…”

“…Reproduced with permission. [56] Copyright 2020, American Chemical Society. 11a) [PP = 1,2-bis(diphenylphosphino)benzene and PS = 2-diphenylphosphinobenzenethiolate], having TADF-related emission in the solid-state at room temperature.…”

“…f) The absorption spectrum in CHCl 3 , emission spectra in the solid-state, doped into PMMA film and in DCM at different temperature (top) and decay lifetimes at disparate temperatures and the fitted line (red) based on Equation (1) of complex Cu(dmpzpp)SPh. Reproduced with permission [56]. Copyright 2020, American Chemical Society.…”

Synthesis of Pyrazoles through [3+2] Cyclization of Nitrile Imines with Cinnamaldehydes Followed by Air Oxidation

“…Ibrutinib, with a fused pyrazole, is a small molecular inhibitor of Bruton's tyrosine kinase (BTK) with antineoplastic activity, used to treat mantle cell lymphoma, chronic lymphocytic leukemia and small 0lymphocytic lymphoma, et al [5] . In addition, some pyrazoles are also applied to prepare polymer materials and supermolecules [6] . Consequently, devising straightforward synthetic strategies to access such scaffolds remains in the focus of research interest [7] .…”