Photoluminescence in Square-Planar Ni(II) Complexes: A Study of Electronic Structure and Quantum Dynamics

Area of Science:

• Photochemistry
• Coordination Chemistry
• Quantum Chemistry

Background:

• Photoluminescent Nickel(II) complexes are rare but possess significant applications, particularly with spin-switch mechanisms.
• Understanding fluorescence and quenching mechanisms is crucial for designing novel functional materials.

Purpose of the Study:

• To investigate the photorelaxation dynamics and fluorescence mechanisms in two related Ni(II) square-planar complexes.
• To elucidate the role of structural modifications, specifically CF3 substitution, on excited-state dynamics and photoluminescence.

Main Methods:

• Utilized the multiconfiguration time-dependent Hartree (MCTDH) method.
• Calculated potential energy surfaces for 11 electronic states.
• Employed multiconfiguration wave function-based methods along 12 normal modes.

Main Results:

• In the methyl-substituted complex, singlet-state internal conversion dominates, leading to fluorescence.
• In the CF3-substituted complex, altered d-orbital splitting reduces metal-ligand mixing and enhances spin-orbit coupling effects.
• The CF3 substitution promotes intersystem crossing, suppressing fluorescence.

Conclusions:

• The study highlights the delicate balance between internal conversion and intersystem crossing in dictating photoluminescence in Ni(II) complexes.
• Electron-withdrawing groups like CF3 can effectively tune photophysical properties by influencing excited-state pathways.