A Qualitative Approach for Predicting Enhanced Intersystem Crossing in Chromophore-Radical Systems.

Area of Science:

• Photochemistry
• Quantum Chemistry
• Molecular Physics

Background:

• Enhanced Intersystem Crossing (EISC) is crucial for population transfer between singlet and triplet states in chromophore-radical (C-R) systems.
• Understanding EISC is key to controlling photophysical processes in organic molecules.

Purpose of the Study:

• To estimate the likelihood of EISC in organic C-R molecules using theoretical methods.
• To investigate the relationship between molecular structure and EISC efficiency.

Main Methods:

• First-order perturbation theory was employed to estimate EISC likelihood.
• Heisenberg-Dirac-Van Vleck Hamiltonian was used to calculate exchange coupling constants.
• CASSCF/QD-NEVPT2 calculations provided excited state wave functions and energies.

Main Results:

• The first-order mixing coefficient (κ) was found to depend on the difference in pairwise exchange interactions.
• Calculated exchange coupling constants correlate with EISC likelihood.
• Theoretical predictions align well with experimental transient absorption spectroscopy data.

Conclusions:

• The developed theoretical framework accurately predicts EISC likelihood in C-R systems.
• This approach provides valuable insights into controlling photophysical properties of organic molecules.