Computational Approach to Phosphor-Sensitized Fluorescence Based on Monomer Transition Densities

Area of Science:

• Quantum Chemistry
• Photochemistry
• Spectroscopy

Background:

• Excitation energy transfer (EET) is crucial in photochemistry.
• Spin multiplicity-altering EET, like triplet-singlet transfer, is challenging to model.
• Accurate theoretical methods are needed to understand these processes.

Purpose of the Study:

• To extend the monomer transition density approach for spin multiplicity-altering EET.
• To develop a computationally feasible method for triplet-singlet coupling.
• To validate the approach with a model system.

Main Methods:

• Utilized complex-valued wave functions from DFT-based multireference spin-orbit coupling configuration interaction.
• Generated one-particle transition density matrices for donor and acceptor molecules.
• Contracted density matrices with two-electron integrals, leveraging symmetry relations.

Main Results:

• Developed a computationally feasible method for triplet-singlet coupling calculations.
• Applied the method to a platinum complex (AG97) and fluorescein (FITC) system.
• Estimated a Förster radius of approximately 35 Å for the model system.
• Found minimal error from the dipole approximation for separations near and beyond the Förster radius.

Conclusions:

• The extended monomer transition density approach is effective for spin multiplicity-altering EET.
• The method provides accurate estimations for Förster radius and coupling.
• This work facilitates theoretical studies of complex photochemical processes.