Fragment-Based Configuration Interaction: Toward a Unifying Description of Biexcitonic Processes in Molecular...

Area of Science:

• Quantum Chemistry
• Photophysics
• Materials Science

Background:

• Biexcitonic states are central to singlet fission and exciton annihilation processes.
• A unified understanding of competing multiexcitonic processes within a shared electronic manifold is lacking.

Purpose of the Study:

• To develop a conceptual framework for systematically constructing diabatic Hamiltonians for biexcitonic systems.
• To provide first-principles access to biexciton formation, separation, and transport.

Main Methods:

• Fragment-based configuration interaction (CI) approach.
• SymbolicCI for analytic Hamiltonian matrix elements.
• NOCI-F for calculating couplings.
• Coupling diabatic Hamiltonians to quantum dynamics simulations.

Main Results:

• Charge-transfer (CT) configurations act as electronic gateways bridging excitonic manifolds.
• CT-mediated relaxation pathways compete with conventional annihilation.
• LECT admixture stabilizes a "biexcimer" in H-type aggregates.

Conclusions:

• The developed framework enables a systematic study of multiexcitonic photophysics.
• Charge-transfer states play a critical role in mediating energy transfer and relaxation pathways.
• This work bridges electronic-structure and quantum dynamics for predictive photophysical understanding.