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Dive into the research topics where Yizhu Liu is active.

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Featured researches published by Yizhu Liu.


Nature Chemistry | 2015

Iron sensitizer converts light to electrons with 92% yield

Tobias Harlang; Yizhu Liu; Olga Gordivska; Lisa A. Fredin; Carlito S. Ponseca; Ping Huang; Pavel Chábera; Kasper Skov Kjær; Helena Mateos; Jens Uhlig; Reiner Lomoth; Reine Wallenberg; Stenbjörn Styring; Petter Persson; Villy Sundström; Kenneth Wärnmark

Solar energy conversion in photovoltaics or photocatalysis involves light harvesting, or sensitization, of a semiconductor or catalyst as a first step. Rare elements are frequently used for this purpose, but they are obviously not ideal for large-scale implementation. Great efforts have been made to replace the widely used ruthenium with more abundant analogues like iron, but without much success due to the very short-lived excited states of the resulting iron complexes. Here, we describe the development of an iron-nitrogen-heterocyclic-carbene sensitizer with an excited-state lifetime that is nearly a thousand-fold longer than that of traditional iron polypyridyl complexes. By the use of electron paramagnetic resonance, transient absorption spectroscopy, transient terahertz spectroscopy and quantum chemical calculations, we show that the iron complex generates photoelectrons in the conduction band of titanium dioxide with a quantum yield of 92% from the (3)MLCT (metal-to-ligand charge transfer) state. These results open up possibilities to develop solar energy-converting materials based on abundant elements.


Chemical Communications | 2013

Towards longer-lived metal-to-ligand charge transfer states of iron(ii) complexes: an N-heterocyclic carbene approach.

Yizhu Liu; Tobias Harlang; Sophie E. Canton; Pavel Chabera; Karina Suarez-Alcantara; André Fleckhaus; Dimali A. Vithanage; Erik Göransson; Alice Corani; Reiner Lomoth; Villy Sundström; Kenneth Wärnmark

A 9 ps (3)MLCT lifetime was achieved by a Fe(II) complex based on C(NHC)^N(py)^C(NHC) pincer ligands. This is the longest known so far for any kind of complexes of this abundant metal, and increased by almost two orders of magnitude compared to the reference Fe(II) bis-terpyridine complex.


Nature Communications | 2015

Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses.

Sophie E. Canton; Kasper Skov Kjær; György Vankó; Tim Brandt van Driel; Shin-ichi Adachi; Amélie Bordage; Christian Bressler; Pavel Chabera; Morten Christensen; Asmus Ougaard Dohn; Andreas Galler; Wojciech Gawelda; David J. Gosztola; Kristoffer Haldrup; Tobias Harlang; Yizhu Liu; Klaus B. Møller; Zoltán Németh; Shunsuke Nozawa; Mátyás Pápai; Tokushi Sato; Takahiro Sato; Karina Suarez-Alcantara; Tadashi Togashi; Kensuke Tono; Jens Uhlig; Dimali A. Vithanage; Kenneth Wärnmark; Makina Yabashi; Jianxin Zhang

Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectroscopy with ultrafast X-ray emission spectroscopy and diffuse X-ray scattering at the SACLA facility to track the non-equilibrated electronic and structural dynamics within a bimetallic donor–acceptor complex that contains an optically dark centre. Exploiting the 100-fold increase in temporal resolution as compared with storage ring facilities, these measurements constitute the first X-ray-based visualization of a non-equilibrated intramolecular electron transfer process over large interatomic distances. Experimental and theoretical results establish that mediation through electronically excited molecular states is a key mechanistic feature. The present study demonstrates the extensive potential of femtosecond X-ray techniques as diagnostics of non-adiabatic electron transfer processes in synthetic and biological systems, and some directions for future studies, are outlined.


Nature | 2017

A low-spin Fe( iii ) complex with 100-ps ligand-to-metal charge transfer photoluminescence

Pavel Chabera; Yizhu Liu; Om Prakash; Erling Thyrhaug; Amal El Nahhas; Alireza Honarfar; Sofia Essén; Lisa A. Fredin; Tobias Harlang; Kasper Skov Kjær; Karsten Handrup; Fredric Ericson; Hideyuki Tatsuno; Kelsey M. Morgan; Joachim Schnadt; Lennart Häggström; Tore Ericsson; Adam Sobkowiak; Sven Lidin; Ping Huang; Stenbjörn Styring; Jens Uhlig; Jesper Bendix; Reiner Lomoth; Villy Sundström; Petter Persson; Kenneth Wärnmark

Transition-metal complexes are used as photosensitizers, in light-emitting diodes, for biosensing and in photocatalysis. A key feature in these applications is excitation from the ground state to a charge-transfer state; the long charge-transfer-state lifetimes typical for complexes of ruthenium and other precious metals are often essential to ensure high performance. There is much interest in replacing these scarce elements with Earth-abundant metals, with iron and copper being particularly attractive owing to their low cost and non-toxicity. But despite the exploration of innovative molecular designs, it remains a formidable scientific challenge to access Earth-abundant transition-metal complexes with long-lived charge-transfer excited states. No known iron complexes are considered photoluminescent at room temperature, and their rapid excited-state deactivation precludes their use as photosensitizers. Here we present the iron complex [Fe(btz)3]3+ (where btz is 3,3′-dimethyl-1,1′-bis(p-tolyl)-4,4′-bis(1,2,3-triazol-5-ylidene)), and show that the superior σ-donor and π-acceptor electron properties of the ligand stabilize the excited state sufficiently to realize a long charge-transfer lifetime of 100 picoseconds (ps) and room-temperature photoluminescence. This species is a low-spin Fe(iii) d5 complex, and emission occurs from a long-lived doublet ligand-to-metal charge-transfer (2LMCT) state that is rarely seen for transition-metal complexes. The absence of intersystem crossing, which often gives rise to large excited-state energy losses in transition-metal complexes, enables the observation of spin-allowed emission directly to the ground state and could be exploited as an increased driving force in photochemical reactions on surfaces. These findings suggest that appropriate design strategies can deliver new iron-based materials for use as light emitters and photosensitizers.


Journal of Physical Chemistry Letters | 2013

Toward Highlighting the Ultrafast Electron Transfer Dynamics at the Optically Dark Sites of Photocatalysts

Sophie E. Canton; Xiaoyi Zhang; Jianxin Zhang; Tim Brandt van Driel; Kasper S. Kjaer; Kristoffer Haldrup; Pavel Chabera; Tobias Harlang; Karina Suarez-Alcantara; Yizhu Liu; Jorge Perez; Amélie Bordage; Mátyás Pápai; Gyoergy Vanko; G. Jennings; Charles Kurtz; Mauro Rovezzi; Pieter Glatzel; Grigory Smolentsev; Jens Uhlig; Asmus Ougaard Dohn; Morten Christensen; Andreas Galler; Wojciech Gawelda; Christian Bressler; Henrik T. Lemke; Klaus Braagaard Møller; Martin Meedom Nielsen; Reiner Lomoth; Kenneth Wärnmark

Building a detailed understanding of the structure-function relationship is a crucial step in the optimization of molecular photocatalysts employed in water splitting schemes. The optically dark nature of their active sites usually prevents a complete mapping of the photoinduced dynamics. In this work, transient X-ray absorption spectroscopy highlights the electronic and geometric changes that affect such a center in a bimetallic model complex. Upon selective excitation of the ruthenium chromophore, the cobalt moiety is reduced through intramolecular electron transfer and undergoes a spin flip accompanied by an average bond elongation of 0.20 ± 0.03 Å. The analysis is supported by simulations based on density functional theory structures (B3LYP*/TZVP) and FEFF 9.0 multiple scattering calculations. More generally, these results exemplify the large potential of the technique for tracking elusive intermediates that impart unique functionalities in photochemical devices.


Structural Dynamics | 2017

Ligand manipulation of charge transfer excited state relaxation and spin crossover in [Fe(2,2′-bipyridine)2(CN)2]

Kasper Skov Kjær; Wenkai Zhang; Roberto Alonso-Mori; Uwe Bergmann; Matthieu Chollet; Ryan G. Hadt; Robert W. Hartsock; Tobias Harlang; Thomas Kroll; K. Kubicek; Henrik T. Lemke; Huiyang W. Liang; Yizhu Liu; Martin Meedom Nielsen; Edward I. Solomon; Dimosthenis Sokaras; Tim Brandt van Driel; Tsu Chien Weng; Diling Zhu; Petter Persson; Kenneth Wärnmark; Villy Sundström; Kelly J. Gaffney

We have used femtosecond resolution UV-visible and Kβ x-ray emission spectroscopy to characterize the electronic excited state dynamics of [Fe(bpy)2(CN)2], where bpy=2,2′-bipyridine, initiated by metal-to-ligand charge transfer (MLCT) excitation. The excited-state absorption in the transient UV-visible spectra, associated with the 2,2′-bipyridine radical anion, provides a robust marker for the MLCT excited state, while the transient Kβ x-ray emission spectra provide a clear measure of intermediate and high spin metal-centered excited states. From these measurements, we conclude that the MLCT state of [Fe(bpy)2(CN)2] undergoes ultrafast spin crossover to a metal-centered quintet excited state through a short lived metal-centered triplet transient species. These measurements of [Fe(bpy)2(CN)2] complement prior measurement performed on [Fe(bpy)3]2+ and [Fe(bpy)(CN)4]2− in dimethylsulfoxide solution and help complete the chemical series [Fe(bpy)N(CN)6–2N]2N-4, where N = 1–3. The measurements confirm that simple ligand modifications can significantly change the relaxation pathways and excited state lifetimes and support the further investigation of light harvesting and photocatalytic applications of 3d transition metal complexes.


Faraday Discussions | 2015

Watching the dynamics of electrons and atoms at work in solar energy conversion.

Sophie E. Canton; Xiaoyi Zhang; Yizhu Liu; Jianxin Zhang; Mátyás Pápai; Alice Corani; Amanda L. Smeigh; Grigory Smolentsev; K. Attenkofer; G. Jennings; Charles Kurtz; Fei Li; Tobias Harlang; Dimali A. Vithanage; Pavel Chabera; Amélie Bordage; Licheng Sun; Sascha Ott; Kenneth Wärnmark; Villy Sundström

The photochemical reactions performed by transition metal complexes have been proposed as viable routes towards solar energy conversion and storage into other forms that can be conveniently used in our everyday applications. In order to develop efficient materials, it is necessary to identify, characterize and optimize the elementary steps of the entire process on the atomic scale. To this end, we have studied the photoinduced electronic and structural dynamics in two heterobimetallic ruthenium-cobalt dyads, which belong to the large family of donor-bridge-acceptor systems. Using a combination of ultrafast optical and X-ray absorption spectroscopies, we can clock the light-driven electron transfer processes with element and spin sensitivity. In addition, the changes in local structure around the two metal centers are monitored. These experiments show that the nature of the connecting bridge is decisive for controlling the forward and the backward electron transfer rates, a result supported by quantum chemistry calculations. More generally, this work illustrates how ultrafast optical and X-ray techniques can disentangle the influence of spin, electronic and nuclear factors on the intramolecular electron transfer process. Finally, some implications for further improving the design of bridged sensitizer-catalysts utilizing the presented methodology are outlined.


Accounts of Chemical Research | 2016

Fe N-Heterocyclic Carbene Complexes as Promising Photosensitizers

Yizhu Liu; Petter Persson; Villy Sundström; Kenneth Wärnmark


Chemistry: A European Journal | 2015

A Heteroleptic Ferrous Complex with Mesoionic Bis(1,2,3-triazol-5-ylidene) Ligands: Taming the MLCT Excited State of Iron(II).

Yizhu Liu; Kasper Skov Kjær; Lisa A. Fredin; Pavel Chabera; Tobias Harlang; Sophie E. Canton; Sven Lidin; Jianxin Zhang; Reiner Lomoth; Karl-Erik Bergquist; Petter Persson; Kenneth Wärnmark; Villy Sundström


Journal of Physical Chemistry C | 2014

Probing the Anisotropic Distortion of Photoexcited Spin Crossover Complexes with Picosecond X-ray Absorption Spectroscopy

Sophie E. Canton; Xiaoyi Zhang; Latevi Max Lawson Daku; Amanda L. Smeigh; Jianxin Zhang; Yizhu Liu; Carl-Johan Wallentin; Klaus Attenkofer; G. Jennings; Charles Kurtz; David J. Gosztola; Kenneth Wärnmark; Andreas Hauser; Villy Sundström

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Kasper Skov Kjær

SLAC National Accelerator Laboratory

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Jianxin Zhang

Tianjin Polytechnic University

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