Test of theoretical models for ultrafast heterogeneous electron transfer with femtosecond two-photon photoemission data

Gundlach, Lars; Letzig, T.; Willig, F.

doi:10.1007/s12039-009-0068-x

Cited by 22 publications

(37 citation statements)

References 45 publications

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“…As a benchmark dye, we use perylenecarboxylic acid, which provides fast electron injection into TiO 2 and has been a subject of several experimental and theoretical studies of charge transfer rates. [34][35][36]39,44,45 The injection times calculated using this molecule's LUMO energy (À2.37 eV according to our DFT B3LYP calculations) as the injection energy are presented in the third column of Table 2 for all computed adsorption geometries. The injection times for the most stable configuration on each surface are plotted in Fig.…”

Section: Charge Injectionmentioning

confidence: 99%

“…All of these surfaces have been observed in anatase particles used in DSSC, 1,32 (101) is the dominant surface, but there are also synthetic routes to produce (001) and (100) surfaces in large amounts. [10][11][12][13][14][15][16][17] With these surfaces, we use the same dye -perylenecarboxylic acid, which is a common model system for time-resolved experimental studies of charge injection 34,35,45 and which shows a fast injection time according to experiments 34,35,45 and calculations. 36,39,42,43 We outline our computational setup and the procedure to calculate injection times in Section 2.…”

Section: Introductionmentioning

confidence: 99%

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How TiO2 crystallographic surfaces influence charge injection rates from a chemisorbed dye sensitiser

Martsinovich

Troisi

2012

Phys. Chem. Chem. Phys.

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High-energy metal oxide surfaces are considered to be promising for applications involving surface-adsorbate electron transfer, such as photocatalysis and dye-sensitised solar cells. Here, we compare the efficiency of electron injection into different TiO(2) anatase surfaces. We model the adsorption of a carboxylic acid (formic acid) on anatase (101), (001), (100), (110) and (103) surfaces using density functional theory calculations, and calculate electron injection times from a model dye into these surfaces. We find that the different positions of the conduction band edge of these surfaces determine the rate of electron injection (which is faster for the surfaces with lower-lying conduction band, among them the most stable (101) surface). However, if the dye's injection energy is enforced to be at a fixed energy deep inside each surface's conduction band, then several anatase surfaces, such as the synthetically achievable (001) surface, show rates of injection comparable or faster than the (101) surface. Moreover, because of their higher-lying conduction bands, these minority surfaces are likely to offer higher open-circuit voltages in dye-sensitised solar cells. Therefore, synthetically accessible high-energy anatase surfaces, such as (001)-oriented nanostructures, may be promising candidates for use in dye-sensitised solar cells.

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Section: Charge Injectionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

How TiO2 crystallographic surfaces influence charge injection rates from a chemisorbed dye sensitiser

Martsinovich

Troisi

2012

Phys. Chem. Chem. Phys.

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“…35 On the basis of ultraviolet photoemission spectroscopy and twophoton photoemission, Gundlach et al reported a vibrational excited ionized perylene dye along with a broad energy distribution of electrons injected to the TiO 2 . 44,45 In contrast to these investigations, wave packets in real time at distinct probe wavelengths are measured in our study. The results allows to unambiguously trace the source of the observed vibrational modes.…”

Section: ■ Results and Discussionmentioning

confidence: 97%

Beyond Vibrationally Mediated Electron Transfer: Coherent Phenomena Induced by Ultrafast Charge Separation

Huber

Dworak

Moser³

et al. 2016

J. Phys. Chem. C

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Wave packet propagation succeeding electron transfer (ET) from alizarin dye molecules into the nanocrystalline TiO 2 semiconductor has been studied by ultrafast transient absorption spectroscopy. Because of the ultrafast time scale of the ET reaction of about 6 fs, the system shows substantial differences to molecular ET systems. We show that the ET process is not mediated by molecular vibrations, and therefore classical ET theories lose their applicability. Here the ET reaction itself prepares a vibrational wave packet and not the electromagnetic excitation by the laser pulse. Furthermore, the generation of phonons during polaron formation in the TiO 2 lattice is observed in real time for this system. The presented investigations enable an unambiguous assignment of the involved photoinduced mechanisms and can contribute to a corresponding extension of molecular ET theories to ultrafast ET systems like alizarin/TiO 2 . ■ INTRODUCTIONMolecular electron transfer (ET) belongs to the most important and ubiquitously encountered processes in the fields of chemistry and biology. The standard theoretical treatment for molecular ET was developed by Marcus 1,2 providing a correlation of the difference in Gibb's free energy (ΔG) between donor and acceptor, the curvature of the potential energy surfaces (PES), and the reorganization energy (λ). Within the framework of this nonadiabatic theory, ET rates of many systems were predicted quite well. Further quantum mechanical extensions by theories of Hopfield 3 and Jortner 4 were then even able to further extend the scope of theoretical ET models. All of these ET theories are based on the assumption that the energies of the donor and the acceptor states are matched by energy fluctuations caused by the surrounding solvent acting as thermal bath. In a standard photoinduced ET reaction a bimolecular donor (D)−acceptor (A) system is excited from the ground state DA into the Franck−Condon region of a higher electronic state DA* (Figure 1a). In a classical view the system can subsequently propagate along the PES of the electronic configuration DA*, approximated as one-dimensional parabola. Energy conservation allows the electronic transition between the states DA* and D + A − only at the intersection of the two PESs. In the picture of electronic quantum dots the propagation of the system on the PES of the state DA* leads to a periodic modulation of the electronic energy level of the donor (Figure 1a, inset) corresponding to the potential energy in the PES picture. In the configuration where the energies of donor and acceptor levels match (i.e., exactly at the crossing point of the DA* and the D + A − parabolas), ET can occur as a tunneling process with a certain probability, depending on the electronic coupling matrix element between the state DA* and the charge-separated state D + A − . Based on this microscopic view of ET, macroscopic rates can be calculated by assuming a thermal occupation of the energy eigenstates of the DA* potential. Thus, within the Marcus picture, t...

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“…Molecular model systems that are designed to satisfy the experimental requirements as well as the computational capabilities are essential for investigating new concepts in IET. Perylene-based sensitizers have proven to be well suited for ultrafast spectroscopic investigations of IET while still being accessible to combined nonadiabatic quantum mechanics/molecular mechanics (QM/MM) simulations. ,− …”

Section: Introductionmentioning

confidence: 99%

Conformational and Binding Effects on Interfacial Electron Transfer from Dual-Linker Sensitizers

et al. 2021

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Interfacial electron transfer (IET) between novel dual-linker perylenes and TiO 2 was investigated by ultrafast spectroscopy and nonadiabatic quantum mechanics/molecular mechanics (QM/MM) simulations. The influence of the number of linkers (one vs two) and their substitution position (ortho vs peri) on IET was investigated. Perylene sensitizers derivatized with two acrylic acid linkers in the peri position, pDtBuPe-(C 2 H 2 COOH) 2 (bis-peri), and in the ortho position, oDtBuPe-(C 2 H 2 COOH) 2 (bis-ortho), were compared to their single-linker counterparts: pDtBuPeC 2 H 2 COOH (peri) and oDtBu-PeC 2 H 2 COOH (ortho). MM simulations of the bis-peri and bisortho sensitizers predicted that, in both cases, only one linker binds covalently to the {101} surface of anatase TiO 2 , while the second one binds weakly via vdW or hydrogen-bonding interactions. Results from QM/MM simulations corroborated experimental injection times for all compounds, thereby supporting single-linker binding to the surface for the dual-linker sensitizers. The study showed that, surprisingly, IET from bis-peri was significantly slower than that from peri. Theory attributes this behavior to small conformational changes caused by steric interactions. The degrees of freedom that are most strongly correlated with variations in IET times were identified by principal component analysis. Comparison between bis-ortho and ortho showed, as expected, that the dual-linker sensitizer injects faster than the single-linker variant. However, the influence of the substitution position on IET was much smaller than expected based on the difference in the static electronic structure. Finally, the strong effect of conformational changes on IET was also observed experimentally in modulations of IET due to coupling to vibrational modes, in excellent agreement with the QM/MM simulations. This study shows that small conformational changes and vibrational coupling can have a significant influence on IET even on the femtosecond time scale. The addition of linkers that differ in bonding strength and serve different functions opens up new avenues for controlling IET dynamics.

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Test of theoretical models for ultrafast heterogeneous electron transfer with femtosecond two-photon photoemission data

Cited by 22 publications

References 45 publications

How TiO2 crystallographic surfaces influence charge injection rates from a chemisorbed dye sensitiser

How TiO2 crystallographic surfaces influence charge injection rates from a chemisorbed dye sensitiser

Beyond Vibrationally Mediated Electron Transfer: Coherent Phenomena Induced by Ultrafast Charge Separation

Conformational and Binding Effects on Interfacial Electron Transfer from Dual-Linker Sensitizers

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