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RISS 인기검색어
- 검색키워드
- 저자 : Jamula, Lindsey L. (검색결과 3 건)
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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>
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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>
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Britz, Alexander,Gawelda, Wojciech,Assefa, Tadesse A.,Jamula, Lindsey L.,Yarranton, Jonathan T.,Galler, Andreas,Khakhulin, Dmitry,Diez, Michael,Harder, Manuel,Doumy, Gilles,March, Anne Marie,Bajno American Chemical Society 2019 Inorganic chemistry Vol.58 No.14
<P>We have employed a range of ultrafast X-ray spectroscopies in an effort to characterize the lowest energy excited state of [Fe(dcpp)<SUB>2</SUB>]<SUP>2+</SUP> (where dcpp is 2,6-(dicarboxypyridyl)pyridine). This compound exhibits an unusually short excited-state lifetime for a low-spin Fe(II) polypyridyl complex of 270 ps in a room-temperature fluid solution, raising questions as to whether the ligand-field strength of dcpp had pushed this system beyond the <SUP>5</SUP>T<SUB>2</SUB>/<SUP>3</SUP>T<SUB>1</SUB> crossing point and stabilizing the latter as the lowest energy excited state. Kα and Kβ X-ray emission spectroscopies have been used to unambiguously determine the quintet spin multiplicity of the long-lived excited state, thereby establishing the <SUP>5</SUP>T<SUB>2</SUB> state as the lowest energy excited state of this compound. Geometric changes associated with the photoinduced ligand-field state conversion have also been monitored with extended X-ray absorption fine structure. The data show the typical average Fe-ligand bond length elongation of ∼0.18 Å for a <SUP>5</SUP>T<SUB>2</SUB> state and suggest a high anisotropy of the primary coordination sphere around the metal center in the excited <SUP>5</SUP>T<SUB>2</SUB> state, in stark contrast to the nearly perfect octahedral symmetry that characterizes the low-spin <SUP>1</SUP>A<SUB>1</SUB> ground state structure. This study illustrates how the application of time-resolved X-ray techniques can provide insights into the electronic structures of molecules-in particular, transition metal complexes-that are difficult if not impossible to obtain by other means.</P><P>Time-resolved X-ray emission and absorption spectroscopies have been used to probe the excited-state electronic and geometric structure of an Fe(II) polypyridyl complex. Analysis of the data revealed that the lowest energy excited state is high-spin (<I>S</I> = 2) in character. This determination had not been possible using other experimental techniques (e.g., time-resolved optical spectroscopy), demonstrating the potential for ultrafast X-ray methods to address scientific questions that are difficult to resolve by other means.</P> [FIG OMISSION]</BR>
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