Tetrahedral Cu(I) Complexes for Thermally Activated Delayed Fluorescence: A Density Functional Benchmark Study with...

Area of Science:

• Organometallic Chemistry
• Materials Science
• Computational Chemistry

Background:

• Tetrahedral Cu(I) complexes are key organometallic thermally activated delayed fluorescence (TADF) emitters.
• Their d¹⁰ electronic structure leads to (pseudo)Jahn-Teller distortions in excited states, causing geometry changes.
• Isolated molecule models struggle to capture the solid-state environment's influence on these distortions.

Purpose of the Study:

• To compare the accuracy of isolated molecule models versus quantum mechanics/molecular mechanics (QM/MM) crystal models for Cu(I) TADF emitters.
• To investigate the effect of computational models on predicting excited-state geometries and fluorescence energies.
• To evaluate five common density functionals in these modeling approaches.

Main Methods:

• Computational study of 56 experimentally known tetrahedral Cu(I) TADF emitters.
• Comparison between isolated single molecule models and QM/MM crystal models.
• Utilized five commonly employed density functionals for calculations.

Main Results:

• Minor differences were found in ground-state geometries and excitation energies between the models.
• Significant deviations were observed in excited-state geometries and predicted fluorescence energies.
• QM/MM models, providing increased rigidity, showed reduced geometry flattening due to the (pseudo)Jahn-Teller effect, leading to blue-shifted fluorescence.

Conclusions:

• The surrounding solid-state environment critically influences the excited-state properties of Cu(I) TADF emitters.
• QM/MM crystal models provide a more realistic representation of these systems than isolated molecule models.
• Accurate prediction of TADF properties requires considering the solid-state effects, especially for geometry-dependent phenomena.