Aggregation-Enhanced Thermally Activated Delayed Fluorescence Efficiency for Two-Coordinate Carbene-Metal-Amide...

Area of Science:

• Materials Science
• Physical Chemistry
• Computational Chemistry

Background:

• Two-coordinate carbene-metal-amide complexes are recognized for their potential in organic light-emitting diodes (OLEDs) due to their thermally activated delayed fluorescence (TADF) properties.
• Understanding the photophysical mechanisms governing TADF in these complexes is crucial for optimizing their performance.

Purpose of the Study:

• To elucidate the mechanism behind the high TADF efficiency in two-coordinate carbene-metal-amide complexes.
• To investigate the influence of aggregation on photophysical properties and excited-state decay rates.

Main Methods:

• Combined quantum mechanics/molecular mechanics (QM/MM) approaches for electronic structure calculations.
• Thermal vibration correlation function formalism to determine excited-state decay rates.
• Comparative analysis of complexes in solution and aggregated phases.

Main Results:

• Aggregation significantly enhances intersystem crossing (ISC) and reverse intersystem crossing (rISC) by 2-4 orders of magnitude.
• Increased metal contribution to frontier molecular orbitals enhances spin-orbit coupling between singlet (S₁) and triplet (T₁) states.
• Lowered reaction barriers for ISC and rISC in aggregated phases are attributed to a reduced energy gap (ΔE_ST) and altered reorganization energy.

Conclusions:

• Aggregation-induced changes in electronic structure and dynamics are key to achieving highly efficient TADF in these metal complexes.
• The findings provide a mechanistic explanation for the observed high TADF quantum efficiency.
• Proposed pump-probe time-resolved infrared spectroscopy can experimentally validate the proposed mechanism.