π-Extended Ligands in Two-Coordinate Coinage Metal Complexes

Area of Science:

• Materials Science
• Photonic Applications
• Organic Electronics

Background:

• Two-coordinate carbene-metal-amide (cMa) complexes (M = Cu, Ag, Au) are efficient luminescent materials.
• Their utility stems from fast radiative rates via thermally activated delayed fluorescence (TADF) driven by interligand charge transfer (ICT).

Purpose of the Study:

• To investigate factors influencing radiative rates in cMa complexes.
• To understand parameters controlling the radiative TADF process.
• To design cMa derivatives with tailored photophysical properties.

Main Methods:

• Synthesis of a series of cMa derivatives.
• Photoluminescence efficiency (Φ_PL) and radiative rate (k_r) measurements.
• Temperature-dependent luminescence studies and theoretical calculations.

Main Results:

• Blue-emissive cMa complexes with high Φ_PL (> 0.95) and fast k_r (4 × 10⁶ s^-1) were achieved by extending π-systems.
• Increased hole-electron separation in the ICT excited state primarily affects the singlet-triplet energy gap (ΔE_ST).
• The radiative rate for the singlet state remained relatively constant.

Conclusions:

• Selective π-system extension is key for optimizing cMa complexes for photonic applications.
• Hole-electron separation is a critical parameter for tuning ΔE_ST and thus TADF properties.
• This work provides a framework for designing cMa derivatives with tunable radiative rates and excited-state lifetimes.