Dynamic Solvent Effect on Ultrafast Charge Recombination Kinetics in Excited Donor-Acceptor Complexes

Area of Science:

• Physical Chemistry
• Chemical Kinetics
• Photochemistry

Background:

• Photoexcited donor-acceptor complexes undergo charge recombination (CR) in polar solvents.
• The dynamic solvent effect (DSE) significantly influences CR kinetics.
• Understanding these effects is crucial for controlling charge transfer reactions.

Purpose of the Study:

• To investigate the manifestation of DSE on CR kinetics in polar solvents.
• To analyze ultrafast charge transfer reactions in both nonequilibrium and thermal regimes.
• To elucidate the role of solvent and intramolecular vibrational modes.

Main Methods:

• Utilized the multichannel stochastic model.
• Incorporated solvent reorganization and intramolecular vibrational mode relaxation.
• Described non-Markovian solvent dynamics using two relaxation modes.

Main Results:

• Identified key differences between thermal and nonequilibrium regimes regarding DSE strength and electronic coupling.
• Observed that DSE is strong for weak exergonicity in thermal reactions but reversed in nonequilibrium reactions.
• Found that increased electronic coupling decreases DSE in nonequilibrium transfer and increases it in thermal reactions.

Conclusions:

• The dynamic solvent effect exhibits contrasting behaviors in thermal and nonequilibrium charge transfer.
• Electronic coupling and reorganization energy critically modulate DSE magnitude and reaction kinetics.
• The two-staged regime is prominent when reorganization energy exceeds the CR free-energy gap.