Carbene-Metal-Amide Materials Design: Tailoring π-Extended Amides for High-Performance Organic Light-Emitting Diodes.

Area of Science:

• Materials Science
• Organic Chemistry
• Photophysics
• Organic Electronics

Background:

• Development of efficient emitters for organic light-emitting diodes (OLEDs) is crucial for advanced display and lighting technologies.
• Carbene-metal-amide (CMA) complexes offer a promising platform for designing novel optoelectronic materials.
• Thermally activated delayed fluorescence (TADF) emitters are desirable for achieving high internal quantum efficiencies in OLEDs.

Purpose of the Study:

• To synthesize and characterize novel gold-centered carbene-metal-amide (CMA) complexes utilizing benzofuroindole (BFI) and benzothioindole (BTI) ligands.
• To investigate the photophysical properties, including emission characteristics and TADF mechanisms, of the synthesized CMA complexes.
• To fabricate and evaluate the performance of sky-blue OLED devices incorporating these novel CMA emitters.

Main Methods:

• Synthesis of gold-centered CMA complexes with BFI and BTI amide donor ligands and bicyclic(alkyl)amino carbene (BiC)Au(I) moiety.
• Photoluminescence spectroscopy (steady-state and transient) to analyze emission spectra, quantum yields, and excited-state lifetimes.
• Fabrication and characterization of host-guest and host-free OLED devices, including electroluminescence measurements and external quantum efficiency determination.
• Theoretical investigations including DFT calculations for charge-transfer states and spin-orbit coupling analysis.

Main Results:

• High-yield synthesis of CMA complexes featuring rigid BFI and BTI ligands.
• Sky-blue emission observed at 501 and 511 nm with unity quantum yields, characteristic of thermally activated delayed fluorescence (TADF).
• Short excited-state lifetimes (473 ns) and fast radiative rates (2 × 10^6 s^-1) attributed to efficient charge transfer (CT) states.
• OLED devices achieved electroluminescence around 490 nm with external quantum efficiencies up to 23% and CIE coordinates (0.19; 0.32).
• Superior performance and stability in neat (host-free) OLEDs correlated with the presence of a sulfur atom in the ligand.

Conclusions:

• The synthesized CMA complexes are efficient sky-blue emitters with TADF properties suitable for OLED applications.
• The electron-donating nature of oxygen and sulfur atoms in the ligands significantly impacts photoluminescence.
• Host-free OLED devices incorporating sulfur-containing CMA complexes demonstrate high performance and stability, paving the way for simplified OLED architectures.