Conformational Engineering of Two-Coordinate Gold(I) Complexes: Regulation of Excited-State Dynamics for Efficient...

Area of Science:

• Organometallic Chemistry
• Photophysics
• Materials Science

Background:

• Carbene-Au-amide (CMA) complexes exhibit delayed fluorescence (DF) via ligand-to-ligand charge transfer (LLCT).
• A coplanar donor-acceptor (D-A) conformation was previously thought crucial for efficient radiative decay in DF.
• The precise geometric factors governing the excited-state mechanism in CMA complexes remained unclear.

Purpose of the Study:

• To investigate the role of geometric conformation in the excited-state mechanism of Carbene-Au-amide (CMA) complexes.
• To develop new CMA complexes with restricted D-A rotation to enforce a twisted conformation.
• To understand how twisted D-A geometry influences delayed fluorescence (DF) properties and organic light-emitting diode (OLED) performance.

Main Methods:

• Synthesis of novel carbene-Au-carbazolate complexes with bulky aromatic substituents.
• X-ray crystallography to determine ground-state molecular geometry.
• Photophysical measurements (quantum yields, lifetimes) and theoretical calculations (DFT, TDDFT) to analyze excited-state dynamics.

Main Results:

• The new complexes adopted a highly twisted D-A orientation in crystal structures.
• Twisted conformation reduced the singlet-triplet energy gap (ΔE_ST), accelerating reverse intersystem crossing (RISC).
• Achieved comparable or improved DF quantum yields (up to 94%) and short lifetimes (sub-microseconds) in twisted complexes.
• OLEDs based on these complexes demonstrated high performance with minimal efficiency roll-off.

Conclusions:

• A twisted D-A conformation is key to efficient delayed fluorescence in CMA complexes, not a planar conformation or dynamic bond rotation.
• The study elucidates the excited-state mechanism, highlighting faster RISC rates in twisted structures.
• These findings provide a new design strategy for high-performance organic light-emitting diodes (OLEDs) utilizing delayed fluorescence.