Generalised Marcus theory for multi-molecular delocalised charge transfer

Taylor, Natasha B.; Kassal, Ivan

doi:10.1039/c8sc00053k

Cited by 30 publications

(38 citation statements)

References 35 publications

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“…Indeed, DFT calculations show that the electronic coupling and hence the transfer rate dramatically drop when the molecules are slightly further apart than in the equilibrium conformation (see discussion below). The slightly slower onset of HT in the other samples (1:1 blend and bilayer, 0.8 and 0.9 ps) can be explained by a less precise determination of the fastest time constant due to its low weight (14% and 17%), by a different molecular conformation between the donor and acceptor (we expect better coupling when m-ITIC is surrounded by J61 in the dispersed system) 48 , or by the influence of different molecular aggregation on the CT rate 10,49 . Nevertheless, the intrinsic time scale for HT remains surprisingly fast (<1 ps) no matter what phase morphology is present, in sharp contrast to previous observations (HT in ≈about 10 ps), where the influence of exciton diffusion was not accounted for 15,16,26,29 .…”

Section: Resultsmentioning

confidence: 91%

Sub-picosecond charge-transfer at near-zero driving force in polymer:non-fullerene acceptor blends and bilayers

et al. 2020

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Organic photovoltaics based on non-fullerene acceptors (NFAs) show record efficiency of 16 to 17% and increased photovoltage owing to the low driving force for interfacial chargetransfer. However, the low driving force potentially slows down charge generation, leading to a tradeoff between voltage and current. Here, we disentangle the intrinsic charge-transfer rates from morphology-dependent exciton diffusion for a series of polymer:NFA systems. Moreover, we establish the influence of the interfacial energetics on the electron and hole transfer rates separately. We demonstrate that charge-transfer timescales remain at a few hundred femtoseconds even at near-zero driving force, which is consistent with the rates predicted by Marcus theory in the normal region, at moderate electronic coupling and at low re-organization energy. Thus, in the design of highly efficient devices, the energy offset at the donor:acceptor interface can be minimized without jeopardizing the charge-transfer rate and without concerns about a current-voltage tradeoff.

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Section: Resultsmentioning

confidence: 91%

Sub-picosecond charge-transfer at near-zero driving force in polymer:non-fullerene acceptor blends and bilayers

et al. 2020

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“…First, we consider the diabatic limit. Just as describing EET in delocalised systems requires gFRET, diabatic CT in delocalised systems is described using our recently described generalised Marcus theory (gMT), 33 which predicts a CT rate of…”

Section: Dimerism Diminishes Charge Transfer (Ct) From the Special Pairmentioning

confidence: 99%

Why are photosynthetic reaction centres dimeric?

Taylor

Kassal

2019

Chem. Sci.

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Section: Dimerism Diminishes Charge Transfer (Ct) From the Special Pairmentioning

confidence: 99%

Section: Dimerism Diminishes Charge Transfer (Ct) From the Special Pairmentioning

confidence: 99%

“…Like gFRET, gMT allows for supertransfer through constructively interfering pathways 110 . However, it is more sensitive to geometry than gFRET because CT is mediated by wavefunction overlaps, which decay exponentially with distance 110 . In modern systems, the X 0 molecule that is more distant from the acceptor is so far away that its CT coupling to X A would be negligible compared with the nearer X 0 .…”

Section: Dimerism Diminishes Charge Transfer (Ct) From the Special Pairmentioning

confidence: 99%

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Theory of delocalised charge transfer

Taylor¹

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Charge transfer in molecular systems occurs between molecules, atoms, or ions, collectively called sites. Theories of charge transfer are fundamental to understanding both natural molecular systems, such as photosynthesis, and artificial molecular systems, such as organic semiconductors or inorganic coordination complexes. Charge transfer in many of these systems is, however, complicated by the existence of delocalisation, where the coupling between sites causes the charge's wavefunction to extend over multiple sites, to the point where it becomes meaningless to describe the charge as occupying any particular site.While quantum-chemical computational techniques exist to calculate charge transfer rates between these delocalised states, they can be computationally expensive (scaling up to exponentially with system size), are inflexible (that is, any change to the system requires a complete recalculation), and offer limited qualitative insight as to how the rate of charge transfer will change with various system properties.To overcome these limitations, this thesis presents a general theory of charge transfer between delocalised molecular states, generalised Marcus theory. Generalised Marcus theory is computationally cheap, flexible, and expressed in closed form. The closed-form nature of generalised Marcus theory allows for qualitative understanding of how charge transfer between delocalised molecular states is affected by changing the charge-transfer properties of the constituent molecules. Importantly, generalised Marcus theory leads to a number of predictions: supertransfer, or the enhancement of charge transfer through the constructive interference of delocalised charge transfer pathways; reorganisation energy suppression, where the environmental impact on charge transfer is somewhat mitigated by delocalisation; and the possibility of energetic tuning, where tuning energy offsets or reorganisation energies can allow significant enhancement to the charge transfer rate.This thesis applies generalised Marcus theory to a system in which delocalised charge transfer occurs, the photosynthetic reaction centre, a dimeric pigment-protein complex consisting of two monomeric branches. The reaction centre in photosynthetic organisms accepts excitons from an antenna system and outputs electrons, serving to convert solar energy into chemical energy. Importantly, excitons are transferred to a delocalised state where the two monomeric branches meet, a pair of molecules called the special pair, and charge separation occurs from this delocalised state. Many organisms only use a single monomeric branch for charge transfer, which raises an open question in biology: why is the reaction centre dimeric?This thesis compares the modern dimeric reaction centre, with delocalised exciton and charge transfer occurring at the special pair, to a model of the ancestral monomeric reaction centre, which lacks one half of the special pair and consequently does not experience exciton or charge delocalisation.By using Sumi's generalised Förster th...

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Generalised Marcus theory for multi-molecular delocalised charge transfer

Abstract: Transfer of charges delocalised over multiple molecules can be described using the properties of the component molecules.

Cited by 30 publications

References 35 publications

Sub-picosecond charge-transfer at near-zero driving force in polymer:non-fullerene acceptor blends and bilayers

Sub-picosecond charge-transfer at near-zero driving force in polymer:non-fullerene acceptor blends and bilayers

Why are photosynthetic reaction centres dimeric?

Theory of delocalised charge transfer

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Generalised Marcus theory for multi-molecular delocalised charge transfer

Abstract: Transfer of charges delocalised over multiple molecules can be described using the properties of the component molecules.

Cited by 30 publications

References 35 publications

Sub-picosecond charge-transfer at near-zero driving force in polymer:non-fullerene acceptor blends and bilayers

Sub-picosecond charge-transfer at near-zero driving force in polymer:non-fullerene acceptor blends and bilayers

Why are photosynthetic reaction centres dimeric?

Theory of delocalised charge transfer​​​​​​​

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Theory of delocalised charge transfer