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Many emerging light-harvesting systems for solar-energy capture depend on absorption of light by molecular dyes and subsequent electron transfer to metal-oxide semiconductors. However, the inhomoge- neous electron-transfer process is often misunderstood when analogies from bimolecular electron transfer are used to explain experimental trends. Here, we develop and apply a theoretical methodology that correctly incorporates the semiconductor density of states and the system reorganization energies to explain observed trends in a series of molecular sensitizers. The effects of chalcogen and bridge substitution on the electron transfer in rhodamine− TiO2 complexes are theoretically investigated by combining density functional theory (DFT)/time-dependent DFT calculations and Fermi’s golden rule for the rate constant. It is shown that all dyes exhibit τeT < 4 ps. Dyes with thiophene bridges exhibit shorter τeT (∼1 ps) than dyes with phenylene bridges (∼4 ps). When the planes of the dye core and bridge are fixed at coplanarity, the dye−TiO2 coupling strength is found to increase by a factor of ∼2 when compared with the Franck− Condon geometry. However, the donor energy level of coplanar dyes falls significantly below the TiO2 conduction band edge so that, despite enhanced coupling, electron transfer is slowed to ∼20 ps. Similar results appear for the excited triplet states of these dyes, showing that the intersystem crossing to low energy triplet states can increase electron-transfer time constants to 60−240 ps. These results are compared to the results of previous photocatalytic hydrogen generation and dye-sensitized solar cell experiments.
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Large Scale Exact Quantum Dynamics Calculations: Using phase space to truncate the basis effectively
The laws of physics that apply at the molecular scale are the laws of quantum mechanics. Whereas quantum electronic structure calculations are now routine for the most part, “quantum dynamics” calculations of nuclear motion are still plagued with the “curse of dimensionality.” Similar challenges may apply to the emerging field of electron dynamics. In this article, the role of recent phase- space (PS) based methods is reviewed—both individually in comparison with each other, and also collectively as an avenue for lifting the above “curse.” In addition: (a) the oldest such PS method is revamped, in order to render it suitable for extremely high accuracy applications; (b) a new PS method designed for electron dynamics is applied to a calculation of the He atom—performed in full quantum dimensionality, and treating electron correlation exactly.
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- PAR ID:
- 10066323
- Date Published:
- Journal Name:
- Advances in chemical physics
- Volume:
- 163
- ISSN:
- 0065-2385
- Page Range / eLocation ID:
- 245-271
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
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