Novel Series of Mononuclear Aluminum Complexes for High‐Performance Solution‐Processed Organic Light‐Emitting Devices

Abstract

Light metal complexes, such as lithium (Li), sodium (Na), magnesium (Mg), and aluminum (Al) complexes, are attractive candidates for the fabrication of thermally activated delayed fluorescent (TADF) materials. Nevertheless, mononuclear Al complexes with delayed fluorescence have not been developed so far. In this study, we successfully developed a novel series of highly luminescent Al complexes with two phenylacridine‐modified asymmetric acetylacetonate‐type ligands. These complexes exhibit high photoluminescence quantum yields (PLQYs) of up to 79 % in the solid state with a short delayed fluorescence lifetime of approximately 4 μs. Solution‐processed organic light‐emitting devices (OLEDs) using these Al complexes exhibit excellent performance with an external quantum efficiency of 17.5 % at 100 cd m−2. This is the best performance in light metal‐based TADF OLEDs reported so far. The results are expected to guide the advancement of the next‐generation solid‐state lighting technology.

Bluish-green-to-green thermally activated delayed fluorescent emitters based on β-diketone derivatives exhibiting a horizontal emission dipole orientation ratio of 88% and an external quantum efficiency of nearly 25%

“…Furthermore, in 2021, Sasabe and Kido designed two variations of green β-diketone-based TADF emitters to act as the ligand for an Al complex. 20 These emitters revealed PLQY values up to 38% and an EQE of 9.1% in solution-based OLEDs; however, when employed as the ligands, the corresponding Al complex exhibited a PLQY of 92% and an EQE of 17.5% in solution-based OLEDs. Recently, they further advanced a yellow emissive Al complex named Al(DMACPDO) 3 , achieving PLQY close to 100% and an EQE of 18% in a solution-based OLED.…”

“…Among the aromatic ketone derivatives, only a handful of bdiketone and b-triketone-based TADF emitters have been reported in the green-to-orange region to date. [18][19][20][21] Unlike typical aromatic ketone derivatives, b-diketone and btriketone undergo transformation to the enol form via ketoenol tautomerism, a characteristic anticipated to unveil singular photofunctionalities such as excited-state intramolecular proton transfer (ESIPT) 18,19 and the utilization of the ligand in metal complexes. 20,21 In 2018, Yang et al developed two variations of ESIPT emitters based on b-diketone derivatives.…”

“…[18][19][20][21] Unlike typical aromatic ketone derivatives, b-diketone and btriketone undergo transformation to the enol form via ketoenol tautomerism, a characteristic anticipated to unveil singular photofunctionalities such as excited-state intramolecular proton transfer (ESIPT) 18,19 and the utilization of the ligand in metal complexes. 20,21 In 2018, Yang et al developed two variations of ESIPT emitters based on b-diketone derivatives. 18 These emitters demonstrated green-to-yellow emission and relatively high PLQY of up to 86% in the film state, accompanied by a short t d below 2 ms.…”