Journal
JOURNAL OF PHYSICAL CHEMISTRY C
Volume 122, Issue 21, Pages 11288-11299Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpcc.8b02697
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Funding
- Department of Energy (DOE)-Basic Energy Sciences through the Chemical Sciences Geosciences and Biosciences Division [DE-SC0016501]
- National Science Foundation [CHE-1464477]
- NSF [1531814]
- Extreme Science and Engineering Discovery Environment (XSEDE) [TG-CHE160043]
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We investigated the charge-transfer dynamics between distinctive excited states of a carotenoid-porphyrin-C-60 molecular triad in tetrahydrofuran solvent. Our approach combines all-atom molecular dynamics simulations with an explicit solvent and electronic-state-specific force fields with a recently proposed hierarchy of approximations based on the linearized semiclassical method. The validity of the second-order cumulant approximation, which leads to a Marcus-like expression for the rate constants, was established by comparing the rate constants calculated with and without resorting to this approximation. We calculated the rate constants between the porphyrin-localized pi pi* state, porphyrin-to-C-60 charge-transfer state, and carotenoid-to-C-60 charge-separated state for the bent and linearly extended conformations. In agreement with our earlier finding, the charge separation was found to occur via a two-step mechanism, where the second step is switched on by the bent-to-linear conformational change. By comparing the rate constants calculated for a flexible and a rigid triad molecule, while allowing the solvent molecules to fluctuate, we showed that the charge-transfer process is driven by the solvent, rather than by the triad's intramolecular degrees of freedom. We further calculated the triad's amide I stretch frequency distributions and found them to be highly sensitive to the electronic state, thereby demonstrating the possibility of monitoring charge-transfer dynamics in this system via UV-vis/IR pump-probe spectroscopy.
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