Competition between the heavy atom effect and vibronic coupling in donor-bridge-acceptor organometallics

Area of Science:

• Photochemistry and Photophysics
• Inorganic Chemistry
• Quantum Dynamics

Background:

• Donor-bridge-acceptor carbene metal-amides are promising functional materials.
• Understanding excited state dynamics, particularly intersystem crossing (ISC), is crucial for optimizing their performance.
• Coinage metals (Cu, Ag, Au) offer tunable electronic properties.

Purpose of the Study:

• To investigate the excited state properties and ISC dynamics of Cu, Ag, and Au carbene metal-amides.
• To elucidate the competing direct and indirect ISC pathways.
• To correlate ISC mechanisms with molecular functional properties.

Main Methods:

• Quantum dynamics simulations were employed to model ISC rates.
• Photophysical characterization experiments supported the simulation results.
• Analysis focused on the interplay between direct (1CT/3CT) and indirect (via 3LE states) ISC pathways.

Main Results:

• Simulated ISC rates closely matched experimental observations.
• A competition between direct ISC (1CT to 3CT) and indirect ISC (involving a 3LE state) was identified.
• The importance of the indirect pathway increases with decreasing metal size (Au > Ag > Cu) due to lower 3LE state energies.

Conclusions:

• Indirect ISC pathways, especially for lighter coinage metals, can significantly slow down the overall ISC rate when direct pathways are efficient.
• The energy of the locally excited triplet (3LE) state is a critical factor in determining the dominant ISC mechanism.
• These findings provide crucial mechanistic insights for designing next-generation high-performance carbene metal-amide materials.