Photo-Induced Spin-State Conversion in Solvated Transition Metal Complexes Probed via Time-Resolved Soft X-ray Spectroscopy

Huse, Nils,Kim, Tae Kyu,Jamula, Lindsey,McCusker, James K.,de Groot, Frank M. F.,Schoenlein, Robert W. American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.19

<P>Solution-phase photoinduced low-spin to high-spin conversion in the Fe<SUP>II</SUP> polypyridyl complex [Fe(tren(py)<SUB>3</SUB>)]<SUP>2+</SUP> (where tren(py)<SUB>3</SUB> is tris(2-pyridylmethyliminoethyl)amine) has been studied via picosecond soft X-ray spectroscopy. Following <SUP>1</SUP>A<SUB>1</SUB> → <SUP>1</SUP>MLCT (metal-to-ligand charge transfer) excitation at 560 nm, changes in the iron L<SUB>2</SUB>- and L<SUB>3</SUB>-edges were observed concomitant with formation of the transient high-spin <SUP>5</SUP>T<SUB>2</SUB> state. Charge-transfer multiplet calculations coupled with data acquired on low-spin and high-spin model complexes revealed a reduction in ligand field splitting of ∼1 eV in the high-spin state relative to the singlet ground state. A significant reduction in orbital overlap between the central Fe-3d and the ligand N-2p orbitals was directly observed, consistent with the expected ca. 0.2 Å increase in Fe−N bond length upon formation of the high-spin state. The overall occupancy of the Fe-3d orbitals remains constant upon spin crossover, suggesting that the reduction in σ-donation is compensated by significant attenuation of π-back-bonding in the metal−ligand interactions. These results demonstrate the feasibility and unique potential of time-resolved soft X-ray absorption spectroscopy to study ultrafast reactions in the liquid phase by directly probing the valence orbitals of first-row metals as well as lighter elements during the course of photochemical transformations.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2010/jacsat.2010.132.issue-19/ja101381a/production/images/medium/ja-2010-01381a_0007.gif'></P>

Major pathways by which climate may force marine fish populations

Ottersen, G.,Kim, S.,Huse, G.,Polovina, J.J.,Stenseth, N.Chr. Elsevier 2010 Journal of marine systems Vol.79 No.3

Climate may affect marine fish populations through many different pathways, operating at a variety of temporal and spatial scales. Climate impacts may work their way bottom up through the food web or affect higher trophic levels more directly. In this review we try to disentangle and summarize some of the current knowledge made available through the rapidly increasing literature on the topic, with particular emphasis on the work within the Global Ocean Ecosystems Dynamics (GLOBEC) programme. We first consider different classification schemes and hypotheses relating climate through physical features of the ocean to population patterns. The response of a population or community to climate may be linear or non-linear, direct or indirect. The hypotheses may be classified according to the form of physical features in operation as being related to mixing, advection or temperature. The bulk of the paper is devoted to a region-by-region presentation and discussion of examples relating climate variability to marine fish populations. It is slanted towards the North Atlantic and North Pacific, but the tropical Pacific is also covered. By means of different categorization methods we compare climate responses between ecosystems. We conclude that the use of such classification schemes allows for a more precise description of the various ecosystems particular properties and facilitates inter-regional comparison.

Element-Specific Characterization of Transient Electronic Structure of Solvated Fe(II) Complexes with Time-Resolved Soft X-ray Absorption Spectroscopy

Hong, Kiryong,Cho, Hana,Schoenlein, Robert W.,Kim, Tae Kyu,Huse, Nils American Chemical Society 2015 Accounts of chemical research Vol.48 No.11

<title>Conspectus</title><P>Polypyridyl transition-metal complexes are an intriguing class of compounds due to the relatively facile chemical designs and variations in ligand-field strengths that allow for spin-state changes and hence electronic configurations in response to external perturbations such as pressure and light. Light-activated spin-conversion complexes have possible applications in a variety of molecular-based devices, and ultrafast excited-state evolution in these complexes is of fundamental interest for understanding of the origins of spin-state conversion in metal complexes. Knowledge of the interplay of structure and valence charge distributions is important to understand which degrees of freedom drive spin-conversion and which respond in a favorable (or unfavorable) manner.</P><P>To track the response of the constituent components, various types of time-resolved X-ray probe methods have been utilized for a broad range of chemical and biological systems relevant to catalysis, solar energy conversions, and functional molecular devices. In particular, transient soft X-ray spectroscopy of solvated molecules can offer complementary information on the detailed electronic structures and valence charge distributions of photoinduced intermediate species: First-row transition-metal L-edges consist of 2p–3d transitions, which directly probe the unoccupied valence density of states and feature lifetime broadening in the range of 100 meV, making them sensitive spectral probes of metal–ligand interactions.</P><P>In this Account, we present some of our recent progress in employing picosecond and femtosecond soft X-ray pulses from synchrotron sources to investigate element specific valence charge distributions and spin-state evolutions in Fe(II) polypyridyl complexes via core-level transitions. Our results on transient L-edge spectroscopy of Fe(II) complexes clearly show that the reduction in σ-donation is compensated by significant attenuation of π-backbonding upon spin-crossover. This underscores the important information contained in transient metal L-edge spectroscopy on changes in the 3d orbitals including oxidation states, orbital symmetries, and covalency, which largely define the chemistry of these complexes. In addition, ligand K-edge spectroscopy reveals the “ligand view” of the valence charge density by probing 1s–2p core-level transitions at the K-edge of light elements such as nitrogen, carbon, and oxygen. In the case of Fe(II) spin-conversion complexes, additional details of the metal–ligand interactions can be obtained by this type of X-ray spectroscopy. With new initiatives in and construction of X-ray free-electron laser sources, we expect time-resolved soft X-ray spectroscopy to pave a new way to study electronic and molecular dynamics of functional materials, thereby answering many interesting scientific questions in inorganic chemistry and material science.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/achre4/2015/achre4.2015.48.issue-11/acs.accounts.5b00154/production/images/medium/ar-2015-00154n_0006.gif'></P>

Modifications of structural, optical and electrical properties of nanocrystalline bismuth sulphide by using swift heavy ions

R.R. Ahire,Abhay A. Sagade,S.D. Chavhan,V. Huse,F. Singh,D.K. Avasthi,D.M. Phase,Ramphal Sharma 한국물리학회 2009 Current Applied Physics Vol.9 No.3

Modified chemical bath deposited (MCBD) bismuth sulphide (Bi2S3) thin films’ structural, optical and electrical properties are engineered separately by annealing in air for 1 h at 300 ℃ and irradiating with 100 MeV Au swift heavy ions (SHI) at 5 × 1012 ions/㎠ fluence. It is observed that the band gap of the films gets red shifted after annealing and irradiation from pristine (as deposited) films. In addition, there is an increase in the grain size of the films due to both annealing and irradiation, leading to the decrease in resistivity and increase in thermoemf of the films. These results were explained in the light of thermal spike model. Modified chemical bath deposited (MCBD) bismuth sulphide (Bi2S3) thin films’ structural, optical and electrical properties are engineered separately by annealing in air for 1 h at 300 ℃ and irradiating with 100 MeV Au swift heavy ions (SHI) at 5 × 1012 ions/㎠ fluence. It is observed that the band gap of the films gets red shifted after annealing and irradiation from pristine (as deposited) films. In addition, there is an increase in the grain size of the films due to both annealing and irradiation, leading to the decrease in resistivity and increase in thermoemf of the films. These results were explained in the light of thermal spike model.

Structural studies of Mn doped ZnO nanoparticles

B.N. Dole,V.D. Mote,V.R. Huse,Y. Purushotham,M.K. Lande,K. M. Jadhav,S.S. Shah 한국물리학회 2011 Current Applied Physics Vol.11 No.3

Mn substituted ZnO nanoparticles with compositional formula Zn_(1-x)Mn_xO where x = 0.00, 0.04 and 0.08were synthesized by sol-gel route. All the samples sintered at 650 ℃ for 12 h in a furnace followed by furnace cooling up to room temperature. X-ray diffraction (XRD) studies shows the presence of hexagonal crystal structure as same as parent compound (ZnO) in all samples. The lattice parameters ‘a’ and ‘c’were determined from XRD data and found that they increase linearly with the Mn content, which suggests that doped Mn ions go to Zn sites. Grain size, X-ray density and Atomic packing fraction (APF)were evaluated using XRD data and found that grain size increases while X-ray density and Atomic packing fraction (APF) decreases with dopant concentration increases. The functional groups and chemical interactions of Mn substituted Zinc oxide samples were also determined at various peaks using FTIR data and observed the presence of function groups in the samples. Results of such an investigation presented in this paper.

Tracking reaction dynamics in solution by pump–probe X-ray absorption spectroscopy and X-ray liquidography (solution scattering)

Kim, Jeongho,Kim, Kyung Hwan,Oang, Key Young,Lee, Jae Hyuk,Hong, Kiryong,Cho, Hana,Huse, Nils,Schoenlein, Robert W.,Kim, Tae Kyu,Ihee, Hyotcherl The Royal Society of Chemistry 2016 Chemical communications Vol.52 No.19

<P>Characterization of transient molecular structures formed during chemical and biological processes is essential for understanding their mechanisms and functions. Over the last decade, time-resolved X-ray liquidography (TRXL) and time-resolved X-ray absorption spectroscopy (TRXAS) have emerged as powerful techniques for molecular and electronic structural analysis of photoinduced reactions in the solution phase. Both techniques make use of a pump-probe scheme that consists of (1) an optical pump pulse to initiate a photoinduced process and (2) an X-ray probe pulse to monitor changes in the molecular structure as a function of time delay between pump and probe pulses. TRXL is sensitive to changes in the global molecular structure and therefore can be used to elucidate structural changes of reacting solute molecules as well as the collective response of solvent molecules. On the other hand, TRXAS can be used to probe changes in both local geometrical and electronic structures of specific X-ray-absorbing atoms due to the element-specific nature of core-level transitions. These techniques are complementary to each other and a combination of the two methods will enhance the capability of accurately obtaining structural changes induced by photoexcitation. Here we review the principles of TRXL and TRXAS and present recent application examples of the two methods for studying chemical and biological processes in solution. Furthermore, we briefly discuss the prospect of using X-ray free electron lasers for the two techniques, which will allow us to keep track of structural dynamics on femtosecond time scales in various solution-phase molecular reactions.</P>

Electronic and Molecular Structure of the Transient Radical Photocatalyst Mn(CO)₅ and Its Parent Compound Mn₂(CO)₁₀

Cho, Hana,Hong, Kiryong,Strader, Matthew L.,Lee, Jae Hyuk,Schoenlein, Robert W.,Huse, Nils,Kim, Tae Kyu American Chemical Society 2016 Inorganic Chemistry Vol.55 No.12

<P>We present a time-resolved X-ray spectroscopic study of the structural and electronic rearrangements of the photocatalyst Mn-2(CO)(10) upon photodeavage of the metal-metal bond. Our study of the manganese K-edge fine structure reveals details of both the molecular structure and valence charge distribution of the photodissociated radical product. Transient X-ray absorption spectra of the formation of the Mn(CO)(5) radical demonstrate surprisingly small structural modifications between the parent molecule and the resulting two identical manganese monomers. Small modifications of the local valence charge distribution are decisive for the catalytic activity of the radical product. The spectral changes reflect altered hybridization of metal-3d, metal-4p, and ligand-2p orbitals, particularly loss of interligand interaction, accompanied by the necessary spin transition due to radical formation. The spectral changes in the manganese pre- and main-edge region are well-reproduced by time-dependent density functional theory and ab initio multiple scattering calculations.</P>

UV-Photochemistry of the Disulfide Bond: Evolution of Early Photoproducts from Picosecond X-ray Absorption Spectroscopy at the Sulfur K-Edge

Ochmann, Miguel,Hussain, Abid,von Ahnen, Inga,Cordones, Amy A.,Hong, Kiryong,Lee, Jae Hyuk,Ma, Rory,Adamczyk, Katrin,Kim, Tae Kyu,Schoenlein, Robert W.,Vendrell, Oriol,Huse, Nils American Chemical Society 2018 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.140 No.21

<P>We have investigated dimethyl disulfide as the basic moiety for understanding the photochemistry of disulfide bonds, which are central to a broad range of biochemical processes. Picosecond time-resolved X-ray absorption spectroscopy at the sulfur K-edge provides unique element-specific insight into the photochemistry of the disulfide bond initiated by 267 nm femtosecond pulses. We observe a broad but distinct transient induced absorption spectrum which recovers on at least two time scales in the nanosecond range. We employed RASSCF electronic structure calculations to simulate the sulfur-1s transitions of multiple possible chemical species, and identified the methylthiyl and methylperthiyl radicals as the primary reaction products. In addition, we identify disulfur and the CH<SUB>2</SUB>S thione as the secondary reaction products of the perthiyl radical that are most likely to explain the observed spectral and kinetic signatures of our experiment. Our study underscores the importance of elemental specificity and the potential of time-resolved X-ray spectroscopy to identify short-lived reaction products in complex reaction schemes that underlie the rich photochemistry of disulfide systems.</P> [FIG OMISSION]</BR>

Ligand-field symmetry effects in Fe(<small>II</small>) polypyridyl compounds probed by transient X-ray absorption spectroscopy

Cho, Hana,Strader, Matthew L.,Hong, Kiryong,Jamula, Lindsey,Gullikson, Eric M.,Kim, Tae Kyu,de Groot, Frank M. F.,McCusker, James K.,Schoenlein, Robert W.,Huse, Nils The Royal Society of Chemistry 2012 Faraday discussions Vol.157 No.-

<P>Ultrafast excited-state evolution in polypyridyl Fe(<SMALL>II</SMALL>) complexes is of fundamental interest for understanding the origins of the sub-ps spin-state changes that occur upon photoexcitation of this class of compounds as well as for the potential impact such ultrafast dynamics have on incorporation of these compounds in solar energy conversion schemes or switchable optical storage technologies. We have demonstrated that ground-state and, more importantly, ultrafast time-resolved X-ray absorption methods can offer unique insights into the interplay between electronic and geometric structure that underpins the photo-induced dynamics of this class of compounds. The present contribution examines in greater detail how the symmetry of the ligand field surrounding the metal ion can be probed using these X-ray techniques. In particular, we show that steady-state K-edge spectroscopy of the nearest-neighbour nitrogen atoms reveals the characteristic chemical environment of the respective ligands and suggests an interesting target for future charge-transfer femtosecond and attosecond spectroscopy in the X-ray water window.</P>

Light-Induced Radical Formation and Isomerization of an Aromatic Thiol in Solution Followed by Time-Resolved X-ray Absorption Spectroscopy at the Sulfur K-Edge

Ochmann, Miguel,von Ahnen, Inga,Cordones, Amy A.,Hussain, Abid,Lee, Jae Hyuk,Hong, Kiryong,Adamczyk, Katrin,Vendrell, Oriol,Kim, Tae Kyu,Schoenlein, Robert W.,Huse, Nils American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.13

<P>We applied time-resolved sulfur-1s absorption spectroscopy to a model aromatic thiol system as a promising method for tracking chemical reactions in solution. Sulfur-1s absorption spectroscopy allows tracking multiple sulfur species with a time resolution of similar to 70 ps at synchrotron radiation facilities. Experimental transient spectra combined with high-level electronic structure theory allow identification of a radical and two thione isomers, which are generated upon illumination with 267 nm radiation. Moreover, the regioselectivity of the thione isomerization is explained by the resulting radical frontier orbitals. This work demonstrates the usefulness and potential of time-resolved sulfur-1s absorption spectroscopy for tracking multiple chemical reaction pathways and transient products of sulfur-containing molecules in solution.</P>