N-doping is an effective way to increase the electron conductivity of organic semiconductors and achieve ohmic cathode contacts in organic electronics. To avoid the use of difficult-to-handle highly reactive n-dopants, air-stable precursors are widely used nowadays, which could decompose to release reactive species in a subtractive way though always with unwanted and even harmful byproducts during processing. Here, we show that air-stable metals, such as copper, silver and gold, could release free electrons readily in the presence of chelating ligands, as the irreversible coordination reaction between metal ions and the ligands would push the equilibrium between metals and metal ions to the forward direction. By using a well-designed multi-functional electron transport material with a strong nucleophilic quality, 4,7-dimethoxy-1,10-phenanthroline (p-MeO-Phen), silver could function as an n-dopant stronger than cesium and could be used to fabricate organic light-emitting diodes with higher performance than the cesium-doped control device.
The development of efficient non‐doped organic light‐emitting diodes (OLEDs) is highly desired but very challenging because of a severe aggregation‐caused quenching effect. Herein, we present a heptagonal diimide acceptor (BPI), which can restrict excessive intramolecular rotation and inhibit close intermolecular π–π stacking due to well‐balanced rigidity and rotatability of heptagonal structure. The BPI‐based luminogen (DMAC‐BPI) shows significant aggregation‐induced delayed florescence with an extremely high photoluminescence quantum yield (95.8 %) of the neat film, and the corresponding non‐doped OLEDs exhibit outstanding electroluminescence performance with maximum external quantum efficiency as high as 24.7 % and remarkably low efficiency roll‐off as low as 1.0 % at 1000 cd m−2, which represents the state‐of‐the‐art performance for non‐doped OLEDs. In addition, the synthetic route to DMAC‐BPI is greatly streamlined and simplified through oxidative Ar−H/Ar−H homo‐coupling reaction.
Scheme1.Synthesis of lipids 1a and 1b.Reagents and conditions: a) Cystamine, triethylamine;b)N a -Boc-l-histidine or N a ,N e -di-Boc-l-lysine, HOBt, EDC·HCl, N,N-diisopropylethylamine (DIEA); c) CF 3 COOH, CH 2 Cl 2 .
The development of a rational strategy
to achieve the complete
regioselectivity and the capability to switch regioselectivity is
an appealing, yet challenging, puzzle in transition-metal-catalyzed
oxidative Ar–H/Ar–H cross-coupling. Disclosed herein
is an iridium-catalyzed C2/C4 regioselective C–H heteroarylation
of indoles with the help of a pivaloyl group at the C3 position. The
judicious choice of the catalytic systems allows the C2-heteroarylation
of indole via a concerted metalation–deprotonation (CMD) process
and the C4-heteroarylation via a trimolecular electrophilic substitution
(SE3) pathway. The oxidants Cu(OAc)2·H2O and Ag2O are demonstrated to play a vital role
in the C2/C4 regioselectivity. In this Article, a heteroaryl–Ir(III)–heteroaryl
complex prior to reductive elimination is successfully isolated and
characterized, which represents the first example of capturing the
bis(hetero)aryl metallic intermediate in oxidative Ar–H/Ar–H
cross-coupling. The regiodivergent heteroarylation of indoles developed
herein provides an opportunity to rapidly assemble diverse C4- and
C2-heteroarylated indoles.
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