Real-Time Observation of the Formation of Excited Radical Ions in Bimolecular Photoinduced Charge Separation: Absence of the Marcus Inverted Region Explained

Koch, Marius; Rosspeintner, Arnulf; Adamczyk, Katrin; Lang, Bernhard Felix; Dreyer, J.; Nibbering, Erik T. J.; Vauthey, Eric

doi:10.1021/ja403481v

Cited by 56 publications

(81 citation statements)

References 64 publications

(36 reference statements)

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“…It is fair to conclude that those push–pull‐based electron acceptors, which are endowed with highly polarized CN bonds, favor vibrational interactions with electrons. These open a channel of vibration‐assisted electron tunneling in the Marcus inverted region and explain the acceleration of charge recombination processes . Please note that the vibrational quantum

ℏ ω

is taken as 2200 cm −1 corresponding to CN stretching vibrations …”

Section: Resultsmentioning

confidence: 99%

Porphyrin Donor and Tunable Push–Pull Acceptor Conjugates—Experimental Investigation of Marcus Theory

Reekie

Sekita

Urner

et al. 2017

Chemistry A European J

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We report on a series of electron donor-acceptor conjugates incorporating a Zn -porphyrin-based electron donor and a variety of non-conjugated rigid linkers connecting to push-pull chromophores as electron acceptors. The electron acceptors comprize multicyanobutadienes or extended tetracyanoquinodimethane analogues with first reduction potentials ranging from -1.67 to -0.23 V vs. Fc /Fc in CH Cl , which are accessible through a final-step cycloaddition-retroelectrocyclization (CA-RE) reaction. Characterization of the conjugates includes electrochemistry, spectroelectrochemistry, DFT calculations, and photophysical measurements in a range of solvents. The collected data allows for the construction of multiple Marcus curves that consider electron-acceptor strength, linker length, and solvent, with data points extending well into the inverted region. The enhancement of electron-vibration couplings, resulting from the rigid spacers and, in particular, multicyano-groups in the conformationally highly fixed push-pull acceptor chromophores affects the charge-recombination kinetics in the inverted region drastically.

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ℏ ω

is taken as 2200 cm −1 corresponding to CN stretching vibrations …”

Section: Resultsmentioning

confidence: 99%

Porphyrin Donor and Tunable Push–Pull Acceptor Conjugates—Experimental Investigation of Marcus Theory

Reekie

Sekita

Urner

et al. 2017

Chemistry A European J

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“…However, strong evidence of the formation of excited ions has recently been obtained by measuring, using transient IR absorption spectroscopy, how the energy dissipated upon ultrafast CS and CR is redistributed into the vibrational modes of the reaction partners. 96 For moderately exergonic reactions, both donor and acceptor were found to be vibrationally hot, pointing to an even energy redistribution. For highly exergonic reactions, on the other hand, asymmetric energy redistribution with a very hot donor and a relatively much colder acceptor was observed.…”

Section: Excited Ionsmentioning

confidence: 98%

“…85, 95 We could recently show, using ultrafast Vis-pump IR-probe spectroscopy in collaboration with the Nibbering group, that excited radical ions can indeed be generated upon photoinduced bimolecular CS reactions. 96 The distance dependence of the ET reaction probability has also been invoked to explain the apparent absence of the Marcus inverted region. 67,97,98 Mataga and co-workers, and more recently, our group have measured the dynamics of bimolecular fluorescence quenching with ps-to fstime resolution and, in collaboration with Angulo, have used a diffusion-reaction equation approach combined with Marcus theory to extract the intrinsic electron transfer rate, k 0 = k CS .…”

Section: Driving-force Dependencementioning

confidence: 99%

Bimolecular photoinduced electron transfer reactions in liquids under the gaze of ultrafast spectroscopy

Rosspeintner

Vauthey

2014

Phys. Chem. Chem. Phys.

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Because of their key role in many areas of science and technology, bimolecular photoinduced electron transfer reactions have been intensively studied over the past five decades. Despite this, several important questions, such as the absence of the Marcus inverted region or the structure of the primary reaction product, have only recently been solved while others still remain unanswered. Ultrafast spectroscopy has proven to be extremely powerful to monitor the entire electron transfer process and to access, with the help of state-of-the-art theoretical models of diffusion-assisted reactions, crucial information like e.g. the intrinsic charge separation dynamics beyond the diffusion limit. Additionally, extension of these experimental techniques to other spectral regions than the UV-visible, such as the infrared, has given a totally new insight into the nature, the structure and the dynamics of the key reaction intermediates, like exciplexes and ions pairs. In this perspective, we highlight these recent progresses and discuss several aspects that still need to be addressed before a thorough understanding of these processes can be attained.

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“…It is interesting to note that our result coincides with recent measurements of inter-and intra-molecular photoinduced charge transfer reactions in molecular systems that show ET rates that are independent of the driving force in the inverted region. 44, 45 …”

Section: Resultsmentioning

confidence: 99%

Heterogeneous Electron-Transfer Dynamics through Dipole-Bridge Groups

Nieto-Pescador

Abraham

et al. 2015

J. Phys. Chem. C

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Heterogeneous electron transfer (HET) between photoexcited molecules and colloidal TiO2 has been investigated for a set of Zn-porphyrin chromophores attached to the semiconductor via linkers that allow to change level alignment by 200 meV by reorientation of the dipole moment. These unique dye molecules have been studied by femtosecond transient absorption spectroscopy in solution and adsorbed on the TiO2 colloidal film in vacuum. In solution energy transfer from the excited chromophore to the dipole group has been identified as a slow relaxation pathway competing with S2-S1 internal conversion. On the film heterogeneous electron transfer occurred in 80 fs, much faster compared to all intramolecular pathways. Despite a difference of 200 meV in level alignment of the excited state with respect to the semiconductor conduction band, identical electron transfer times were measured for different linkers. The measurements are compared to a quantum-mechanical model that accounts for electronic-vibronic coupling and finite band width for the acceptor states. We conclude that HET occurs into a distribution of transition states that differs from regular surface states or bridge mediated states.

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Real-Time Observation of the Formation of Excited Radical Ions in Bimolecular Photoinduced Charge Separation: Absence of the Marcus Inverted Region Explained

Cited by 56 publications

References 64 publications

Porphyrin Donor and Tunable Push–Pull Acceptor Conjugates—Experimental Investigation of Marcus Theory

Porphyrin Donor and Tunable Push–Pull Acceptor Conjugates—Experimental Investigation of Marcus Theory

Bimolecular photoinduced electron transfer reactions in liquids under the gaze of ultrafast spectroscopy

Heterogeneous Electron-Transfer Dynamics through Dipole-Bridge Groups

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