Modeling Triplet Excited-State Energy Transfer (TEET) via Multistate Density Functional Theory with Nonorthogonal...

Area of Science:

• Computational chemistry
• Quantum chemistry
• Theoretical chemistry

Background:

• Triplet excited-state energy transfer (TEET) is crucial in photochemistry and photophysics.
• Accurate theoretical methods are needed to describe TEET processes.
• Existing methods may lack transparency or a unified framework for different transfer types.

Purpose of the Study:

• To present a novel computational protocol for TEET.
• To enable a unified description of Dexter and Förster energy transfer.
• To provide a chemically intuitive understanding of TEET.

Main Methods:

• Multistate density functional theory with nonorthogonal state interaction (MSDFT-NOSI).
• Block-localized excitation via occupation-constrained orbital optimization.
• Generalized diabatic-at-construction (GDAC) transformation for diabatization.

Main Results:

• MSDFT-NOSI generates fragment-localized singlet and triplet configurations.
• GDAC transformation yields well-defined diabatic states and electronic couplings.
• The method reproduces TDDFT-quality excitation energies for propenal excimer.
• A transparent picture of the TEET process is achieved.

Conclusions:

• MSDFT-NOSI/GDAC is a practical and insightful method for studying TEET.
• The protocol is applicable to molecular complexes and photocatalytic systems.
• This work advances the theoretical understanding of triplet energy transfer.