Lighting Silver(I) Complexes for Solution-Processed Organic Light-Emitting Diodes and Biological Applications via Thermally Activated Delayed Fluorescence

Abstract

Luminescent coinage metal complexes have shown promising applications as electroluminescent emitters, photocatalysts/photosensitizers, and bioimaging/theranostic agents, rendering them attractive alternatives to transition metal complexes based on iridium, ruthenium, and platinum that have extremely low earth abundance. In comparison to the widely studied Au­(I) and Cu­(I) complexes, Ag­(I) complexes have seldom been explored in this field because of their inferior emission properties. Herein, we report a novel series of [Ag­(N^N)­(P^P)]­PF6 complexes exhibiting highly efficient thermally activated delayed fluorescence by using easily accessible neutral diamine ligands and commercially available ancillary diphosphine chelates. The photoluminescence quantum yields (PLQYs) of the Ag­(I) emitters are ≤0.62 in doped films. The high PLQY with a large delayed fluorescence ratio enabled the fabrication of solution-processed organic light-emitting diodes (OLEDs) with a high maximum external quantum efficiency of 8.76%, among the highest values for Ag­(I) emitter-based OLEDs. With superior emission properties and an excited state lifetime in the microsecond regime, together with its potent cytotoxicity, the selected Ag­(I) complex has been used for simultaneous cell imaging and anticancer treatment in human liver carcinoma HepG2 cells, revealing the potential of luminescent Ag­(I) complexes for biological applications such as theranostics.

Solution-Processed OLEDs Based on Thermally Activated Delayed Fluorescence Copper(I) Complexes with Intraligand Charge-Transfer Excited State

“…As depicted in Figure 3b and Figure S2 (Supplementary Materials), the HOMOs in all complexes predominantly localize on the donor (PXZ or DMAC) and the LUMOs are distributed over the PyPI moiety. Previously, similar ILCT character of the lowest excited states have been shown for Ag(I) complexes based on ligands DMAC-PyPI and PXZ-PyPI [31].…”

“…The strong temperature independence of emission lifetimes reveals the large variation of radiative decay rate with temperature changes, which is determined by the emitting state nature. Thus, the emissions for 1-4 at room temperature are assigned to TADF, as that for Ag(I) analogues with the same ligands [31]. Notably, prompt fluorescence was not observed in the transient photoluminescent studies of each complex.…”

“…In the literature, it has been shown that the TADF can also be achieved from intraligand charge-transfer excited state in Pd(II), W(VI), and Au(III) complexes supported by tetradentate ligands [28][29][30]. Likewise, this concept has recently been demonstrated on Cu(I) and Ag(I) complexes using simple TADF-inactive donor-acceptor type ligands (Figure 1f) [19,31,32]. The coordination with metal ion was found to affect the relative energy levels of lowest lying singlet and triplet excited states of the ligand, thus switching on the ligand-based TADF.…”

“…The syntheses of the diimine ligands, 2-(5-(9,9-dimethylacridin-10(9H)-yl)pyridin-2yl)-1-phenyl-1H-phenanthro [9,10-d]imidazole (DMAC-PyPI) and 10-(6-(1-phenyl-1Hphenanthro [9,10-d]imidazol-2-yl)pyridin-3-yl)-10H-phenoxazine (PXZ-PyPI), have been described elsewhere [31]. As depicted in Scheme 1, all four cuprous complexes were prepared using a typical method and obtained as crystals in high yields of 77%-84%.…”

“…Since the emission lifetime is also a crucial factor in determining the device performances, complex 3 was studied for comparison in view of its moderate PLQY but a beneficial short emission lifetime. The device structure of ITO/PEDOT:PSS (50 nm)/OTPD (4 nm)/PYD2: emitter (60 nm)/DPEPO (10 nm)/TPBi (40 nm)/LiF (1.2 nm)/Al (100 nm) was designed according to that for similar Ag(I) complexes [31]. The energy level diagrams and chemical structures of the organic materials are shown in Figure 5a,b.…”