Excited State Spectroscopic Methods

Chem 529 <> Excited State Spectroscopic Methods

Electronic Absorption Spectroscopy

File:2009W2-C529-S031a.pdf

Typically called "UV/Vis" spectroscopy, electronic absorption spectroscopy is a technique which probes electronically excited states using unpolarized or linearly polarized photons. The selection rules are straight-forward and are dominated by the electric dipole mechanism.

Literature examples from inorganic chemistry

"Photoinduced electron flow in a self-assembling supramolecular extension cable", B. Ferrer, G. Rogez, A. Credi, R. Ballardini, M. T. Gandolfi, V. Balzani, Y. Liu, H. R. Tseng, and J. F. Stoddart PNAS, 2006, 103, 49, 18411-18416, doi:10.1073/pnas.0606459103.

UV/vis absorption and luminescence spectroscopy are used to monitor pseudo-rotaxane type threading between molecular species. Electron-transfer kinetics are also monitored between the molecules of the system, using absorption spectroscopy at 398 nm.Lwence

"Combined NMR and UV/Vis Spectroscopy in the Solution State: Study of the Geometries of Strong OHO Hydrogen Bonds of Phenols with Carboxylic Acids", Peter M. Tolstoy, Benjamin Koeppe, Gleb S. Denisov, and Hans-Heinrich Limbach Angew. Chem. Int. Ed., 2009, 48, 5745-5747, doi:10.1002/anie.200806181.

A new probe head for simultaneous NMR and UV/Vis spectroscopic measurements is designed. ¹H NMR and UV/Vis spectra of an intermolecular hydrogen-bonded complex are measured simultaneously in CD₂Cl₂ at 175 K. Aided by the ¹H NMR spectra, the sample concentration can be adjusted so that the desired complex is the exclusive form of the phenol present. The UV/Vis spectra allow the approximate position of the bridging proton to be found.CuilingXu

"Old Molecules, New Concepts: [Ru(bpy)3]2+ as a Molecular Encoder-Decoder", P. Ceroni, G. Bergamini, V. Balzani Angew. Chem. Int. Ed., 2009, 48, 1-4, doi:10.1002/anie.200904764.

The potential for use of [Ru(bpy)3]2+ and its derivatives as a molecular encoder-decoder is discussed. The significant differences between the absorption and emission properties of [Ru(bpy)3]2+ and its oxidized [Ru(bpy)3]3+ and reduced [Ru(bpy)3]+ forms allows for four different input functions which can be translated into two different output functions or vice versa. This system could therefore be used in 4-to-2 encoder or 2-to-4 decoder applications. (AshleeJHowarth)

Circular Dichroism Spectroscopy

File:2009W2-C529-S031b.pdf

Literature examples from inorganic chemistry

"A Facile Circular Dichroism Protocol for Rapid Determination of Enantiomeric Excess and Concentration of Chiral Primary Amines", S. Nieto, J.M. Dragna, and E.V. Anslyn, Chem. Eur. J., 2010, 16, 227-232, doi:10.1002/chem.200902650.

This article reports the use of circular dichroism coupled with other instrumental and computational equipment to determine the enantiomeric excess and concentration of chiral primary amines. The authors note that this would be extremely useful for rapid screening for asymmetric catalysts for amination, as well alpha-chiral primary amines are crucial to the chemical and pharmaceutical companies. One drawback of this method is the need to derivatized the amine into an imine, but this processes is quantitative and does not require extra purification. A CD spectrum is then taken on the imine and after data processing, the %ee and concentration can be determined. JackyYim

"Surface Plasmon Coupled Circular Dichroism of Au Nanoparticles on Peptide Nanotubes", J. George, and K. G. Thomas, J. Am. Chem. Soc., 2010, 132(8), 2502-3, doi: 10.1021/ja908574j.

This paper explores the in situ growth of Au nanoparticles on D- and L- isomers of diphenylalanine peptide nanotubes and their chiral properties. Circular dichroism spectroscopy showed that gold nanoparticle bunches on D- and L- isomers of diphenylalanine peptide nanotubes produce signals with symmetrical mirror images at the gold surface plasmon frequency. It is believed that the Au nanoparticles are asymmetrically organized as bunches on the peptide nanotube, however the possibility of the chiral arrangement of atoms in a nanoparticle cannot be ruled out. SusanVickers

"Circularly Polarized Luminescence and Circular Dichroism from Si-Si Bonded Network Polymers", S. Fukao, M. Fujiki, Macromolecules, 2009, 42, 8062-8067, doi:10.1021/ma901427v.

This paper examines three new Si-Si bonded network polymers which have a chiral alkyl side group. These polymers are examined using both circularly polarized luminescence and circular dichroism. All three polymers show CD spectra, however only one shows CPL spectra. This indicates a largely different interactions due to the differences in the chiral alkyl side group. AmberJuilfs

"Nucleotide-Catalyzed Conversion of Racemic Zeolite-Type Zincophosphate into Enantioenriched Crystals", J. Zhang, S. Chen, X. Bu. Angew. Chem. Int. Ed. 2009, 48, 6049-6051, doi:10.1002/anie.200903001

The asymmetric crystallization of a zeolite-type material using a nucleotide has been demonstrated in this paper. The nucleotide serves as a chirality-induction agent to induce chirality. Addition of the nucleotide (-)ump gives rise to the enantioenriched form of the material, where the material is initially racemic. Solid-state CD spectroscopy reflects the newly-formed chirality of the crystal. ReneeMan

Magnetic Circular Dichroism Spectroscopy

File:2009W2-C529-S031c.pdf

Literature examples from inorganic chemistry

"Synthesis of an optically active poly(aryleneethynylene) bearing galvinoxyl residues and its chiroptical and magnetic properties." T. Kaneko et al. Synthetic Metals. 2009, 159, 864-867. doi:10.1016/j.synthmet.2009.01.042

This paper describes the synthesis of a new chiral conjugated polyradical species which displays weak antiferromagnetic properties. Magnetic circular dichroism shows that there are Faraday effects present in the spectrum of the polyradical, suggesting that the magnetic interactions are independent of the polymer stereo regularity and higher order structure.Kimosten

"Probing the Magnetic Properties of Three Interconvertible Redox States of a Single-Molecule Magnet with Magnetic Circular Dichroism Spectroscopy." M. Gonidec et al. J. Am. Chem. Soc. 2010, 132, 1756-1757. [http://dx.doi.org/10.1021/ja9095895 doi:10.1021/ja9095895

This paper uses MCD to examine the magnetic behaviours of anionic, neutral, and cationic forms of a terbium complex. Each state has different responses to magnetization. In dilute solutions at low temperatures, the complex has single-molecule magnetic behaviour. AlexandraAnderson

."Spectroscopic Studies and Electronic Structure Description of the High Potential Type 1 Copper Site in Fungal Laccase: Insight into the Effect of the Axial Ligand." Amy E. Palmer, David W. Randall, Feng Xu, Edward I. Solomon. J. Am. Chem. Soc. 1999, 121, 7138-7149. doi:110.1021/ja991087v

This paper compares fungal laccase copper metalloproteins with plastocyanin using techniques such as MCD, CD, EPR, and UV/Vis absorption. Changes in oxidation state of the Cu centers are made in order to evalute their coordination modes and redox chemistry.//EricPrice

Photoelectron Spectroscopy

File:2009W2-C529-S031d.pdf

Literature examples from inorganic chemistry

"Electroactie mesoporous tantalum oxide catalysts for nitrogen activat oin and ammonia synthesis", C. Yue, M. Trudeau, and D. Antonelli, Chem. Comm., 2006, 1918-1920, doi:10.1039/b517415e.

Mesoporous Tantalum oxides doped with ruthenium and barium are synthesized exposed to dinitrogen. The system found in this paper has an unexpectedly low activation energy for the conversion of N₂ to ammonia. Photo-electron spectroscopy is used to study the oxidation state of the Ru, and Ta present in the catalyst in an attempt to elucidate where catalytic activity is occurring. It is thought that the Ta(II) / Ta(IV) redox couple is responsible for N₂ reduction.TrumanWambach

"Grafting Oligothiophenes on Surfaces by Diazonium Electroreduction: A Step toward Ultrathin Junction with Well-Defined Metal/Oligomer Interface", V. Stockhausen, J. Ghilane, P. Martin, G. Trippé-Allard, H. Randriamahazaka, J.-C. Lacroix, J. Am. Chem. Soc., 2009, 131, 14920-14927. doi:10.1021/ja9047009.

Electrode materials (glassy carbon, gold, and platinum) are functionalized with a terthiophene unit by electrochemical reduction of 2-terthiophenyldiazonium cation. X-ray photoelectron spectroscopy is used to confirm the covalent attachment of terthiophene and indicates a thickness of <10 nm for the organic layer. BrianSahli

Core Electronic Spectroscopies

File:2009W2-C529-S032.pdf

Literature examples from inorganic chemistry

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"In Situ Time-Resolved XAFS Study on the Formation Mechanism of Cu Nanoparticles Using Poly(N-vinyl-2-pyrrolidone) as a Capping Agent", S. Nishimura, A. Takagaki, S. Maenosono, K. Ebitani Langmuir, 2010, 26(6), 4473-4479. doi: 10.1021/la904248z

XAFS along with TEM, XRD, UV-vis spectroscopy and an indicator method is used to determine the role of the capping agent poly(N-vinyl-2-pyrrolidone) (PVP) in the formation of Cu nanoparticles. The reduction of Cu(II)acetate to Cu(0) is monitored with and without PVP using the aforementioned techniques. It is shown that PVP may be essential for the formation of Cu nanoparticles due to it's role in the formation of a stable Cu(I) intermediate. (AshleeJHowarth)

"In situ X-ray investigations on AgIn/SiO2 hydrogenation catalysts", F. Haass, M. Bron, H. Fuess, P. Claus, Applied Catalysis A: General, 2007, 318, 9-16. doi: 10.1016/j.apcata.2006.10.031

The authors use x-ray absorption (both XANES and EXAFS) to learn about the in situ structure of heterogeneous Ag and AgIn on SiO2 hydrogenation catalysts. The authors are interested in why these catalysts have selectivity for reducing the aldehyde over double bond in acrolein and use the XANES analysis to show that In has an oxidized state that influences binding of acrolein in some way. They also use EXAFS analysis of Ag to investigate the coverage of acrolein on these catalysts to make some conclusions about catalytic activity. Kimosten

"Structure and Orientation of the Mn₄Ca Cluster in Plant Photosystem II Membranes studied by Polarized Range-extended X-ray Absorption Spectroscopy", Y. Pushkar, J. Yano, P. Glatzel, J. Messinger, A. Lewis, K. Sauer, U. Bergmann and V. Yachandra. J. Bio. Chem., 2007, 282(10), 7198-7208. doi: 10.1074/jbc.M610505200

Structural data of the Mn₄Ca Cluster of the spinach PS II Membrane is looked at more fully. Previously the fine structure of the cluster has been disrupted by the presence of iron in the photosystem. Using a higher resolution spectrometer, the fine structure range was extended beyond the onset of the iron absorption edge. By doing this, the fine structure was more clear and a refinement of the known structure was able to be done . AmberJuilfs

"An activity and XANES study of Mn-promoted, Fe-based Fischer-Tropsch catalysts", A. Campos N. Lohitharn, A. Roy, E. Lotero, J. G. Goodwin Jr., and J. J. Spivey Appl. Catal., A, 2010, 375, 12-16, doi:10.1016/j.apcata.2009.11.015.

Iron-based Fischer-Tropsch catalysis is examined with respect to the ratio of Fe:Mn. Studies were completed on 100:0, 95:5, and 80:20 Fe:Mn in catalysis. XANES was used to study the variance of oxidation state of Fe and Mn dependent on this ratio, as well as to gain insight into composition and bonding.Lwence

"Heme-Copper-Dioxygen Complexes: Toward Understanding Ligand-Environmental Effects on the Coordination Geometry, Electronic Structure, and Reactivity", X. Halime, M.T. Kieber-Emmons, M.F. Qayyum, B. Mondal, T. Gandhi, S.C. Piui, E.E. chufan, A.A.N. Arjeant, K.O. Hodgson, B. Hedman, E.I. Solomon, K.D. Karlin. Inorg. Chem. 2010, 49, 3629-3645. doi:10.1021/ic9020993

Various Fe, Cu systems designed to model heme-copper active sites are synthesized. The effect of various ligands on Cu is explored using a variety of spectroscopic techniques, including EXAFS. The binding mode of oxygen as a function of Cu ligands is explored. TrumanWambach

"A Reactive Oxide Overlayer on Rhodium Nanoparticles during CO Oxidation and Its Size Dependence Studied by In Situ Ambient-Pressure X-ray Photoelectron Spectroscopy", Michael E. Grass, Yawen Zhang, Derek R. Butcher, Jeong Y. Park, Yimin Li, Hendrik Bluhm, Kaitlin M. Bratlie, Tianfu Zhang, and Gabor A. Somorjai Angew. Chem. Int. Ed, 2008, 47, 8893-8896, doi:10.1002/anie.200803574.

The authors used in situ synchrotron ambient pressure X-ray photoelectron spectroscopy to exam the oxidation state of the surface of the rhodium nanoparticles (NPs) during CO oxidation in an O₂ atmosphere. 2 nm NPs oxidize to a larger extent than 7 nm NPs during reaction at 150-200 °C, which correlates with a fivefold increase in turnover frequency for the smaller nanoparticles.CuilingXu

"Heterogeneous Catalysts for Hydroamination Reactions: Structure-Activity Relationship", Penzien, J. Haeßner, C. Jentys, A. Köhler, K. Müller, T.E., J. Catal., 2004, 221, 302-312, doi:10.1016/S0021-9517(03)00283-5.

This article reports the use of ion-exchanged zeolite BEA, particularly Cu/H-BEA and Zn/H-BEA, for hydroamination reaction. X-ray absorption studies of the Cu/H-BEA were used to determine the oxidation state and local environment of the Cu ion. XANES showed that the catalytically active Cu(II)/H-BEA sample generates Cu(I) in-situ after activation. From EXAFS the local environment was found such that there were 3 closer oxygen neighbors and 3 further neighbors. Similar studies were done for Zn/H-BEA but XANES was inconclusive and an oxidation state was not found but EXAFS found that there were 4 oxygen neighbors slightly closer to the Zn ion and 2 which were slightly further from the Zn ion.JackyYim

"The structural determination of endohedral metallofullerene Gd@C82 by XANES{", L. Liu, B. Gao, W. Chu, D. Chen, T. Hu, C. Wang, L. Dunsch, A. Marcelli, Y. Luob, Z. Wu, Chem. Commun., 2008, 4, 474-476. doi:10.1039/b714603e.

The structure of the metallofullerene Gd@82 was determined using XANES. Several structural models of the complex were constructed and their XANES spectra were predicted. The experimental spectra of the metallofullerene was then compared to the predictions to determine agreement. AlexandraAnderson

"EXAFS study of oxide precursors of the high active Co-Mo hydrotreating catalysts: Effect of drying conditions", G. A. Bukhtiyarova, O. V. Klimov, D. I. Kochubey, A. S. Noskov, A. V. Pashigreva, Nucl. Instrum. Meth., 2009, 603, 119-21, doi:v10.1016/j.nima.2008.12.173.

The paper uses EXAFS to study bimetallic hydrodesulfurization catalysts prepared from bimetallic Co-Mo complexes and dried at different temperatures. A radial distribution function (RDF) curve depicting the Mo local surrounding in catalysts dried at different temperatures. Upon drying at high temperatures (>220 °C), alteration of the RDF curves indicates the formation of inactive components and so suggests that to achieve active hydrodesulfurization, catalysts drying temperatures should be kept below this. SusanVickers

"The Interaction of Bromide Ions with Graphitic Materials", A. Mehta,E. J. Nelson, S. M. Webb, J. K. Holt, Adv. Mater., 2009, 21, 102-106, doi:10.1002/adma.200801602

The coordination of bromide ions onto graphene materials is explored in this paper. The X-ray absorption spectra of a RbBr solution, compared to that of a rinsed graphitic material, has different features that shows presence of Br on the material. From the EXAFS signal, the local structure of Br ions at the graphitic interface was examined. ReneeMan

"Identifying the Minimal Copper- and Zinc-binding Site Sequence in Amyloid-beta Peptides", Velia Minicozzi, Francesco Stellato, Massimiliano Comai, Mauro Dalla Serra, Cristina Potrich, Wolfram Meyer-Klaucke, and Silvia Morante, J. Biol. Chem., 2008, 283, 10784-10792, doi:10.1074/jbc.M707109200.

This paper discusses the coordination environment of copper and zinc with amyloid-beta peptide. Using XANES as a qualitative view of changes in geometry between complexes, and EXAFS as a more quantitative look at the exact coordinating ligands. Binding models from the literature were used to model the binding mode of copper(II) and create simulated data to fit with the experimental results. A model of 3 histidines and 1 tyrosine fit best with experimental data; however a model with the tyrosine replaced with the n-terminus was only a marginally worse fit. EricPrice

"Octahedral Monodithiolene Complexes of Iron: Characterization of S,S'-Coordinated Dithiolate(1-)π Radical Monoanions: A Spectroscopic Density Functional Theoretical Investigation", Carsten Milsmann, Goutam Kumar Patra, Eckhard Bill, Thomas Weyhermüller, Serena DeBeer George, and Karl Wieghardt, Inorg. Chem., 2009, 48, 7430-7445, DOI: 10.1021/ic900936p.

In this report a series of Fe complexes were prepared and their electronic structures were probed using a variety of techniques. In particular the redox pair [Fe(cyclam)(dithiolate)]^{+, +2} was studied to determine if the dithioate ligand was acting as a non-innocent redox partner. To study this system by K-edge Fe XAS the authors first assign [Fe(cyclam)(Et2dtc)]²⁺ to be a reference for an Fe(III) LS atom in a octahedral cis-N₄S₂ coordination environment. By comparing [Fe(cyclam)(tdt)]⁺ and [Fe(cyclam)(tdt)]²⁺ to [Fe(cyclam)(Et2dtc)]²⁺ it was determined that both species contained a LS Fe(III) core indicating that the redox process is predominately ligand centered. To further investigate the non-innocent behavior of the ligand K-edge S XAS spectra were recorded for [Fe(cyclam)(tdt)]⁺ and [Fe(cyclam)(tdt)]²⁺ which confirms the conclusion that the oxidation is ligand centered. The authors support this conclusion with EPR and Maussbouer spectroscopy and the XAS data is compared with DFT calculations. FraserPick 15:19, 23 March 2011 (PDT)

"Structural Investigation of Lanthanoid Coordination: a Combined XANES and Molecular Dynamics Study", Paola D’Angelo, Andrea Zitolo, Valentina Migliorati, Giordano Mancini, Ingmar Persson, and Giovanni Chillemi, Inorg. Chem., 2009, 48, 10239-10249, [1].

This paper discusses the use of XANES in probing the coordination geometry of three lanthanoid(III) ions (Yb, Nd, Gd) in aqueous solution. The quantitative analysis of the XANES spectra has been done at the K and the L³ edge. Furthermore the XANES spectra were computed using molecular dynamics (MD) simulations. DineshAluthge

"Complexing Mechanism of the Lanthanide Cations Eu3+, Gd3+, and Tb3+ with 1,4,7,10-Tetrakis(carboxymethyl)-1,4,7,10-tetraazacyclododecane (dota)—Characterization of Three Successive Complexing Phases: Study of the Thermodynamic and Structural Properties of the Complexes by Potentiometry, Luminescence Spectroscopy, and EXAFS", Juliette Moreau, Emmanuel Guillon, Jean-Claude Pierrard, Jean Rimbault, Marc Port, and Michel Aplincourt, Chem. Eur. J., 2004, 10, 5218 – 5232, [2].

Complexation of the lanthanides Eu3+, Gd3+, and Tb3+ with 1,4,7,10-tetrakis(carboxymethyl)- 1,4,7,10-tetraazacyclododecane (dota) has been studied in solution by using potentiometry, luminescence spectrometry, and EXAFS. The immediate complexes would change into final complexes via intermediate complexes. Through EXAFS, the authors discovered what happen to the complexes in the next several weeks after the immediate complexes are formed. The numbers and bond lengths of Ln-O(OC), Ln-O(H2) and Ln-N bonds have been studied. Taking the Gd as the example, the appearance of a new nitrogen contribution, and the decrease in the Gd- O contributions relative to previous complex indicate the Gd-N bonds forms and some Gd-O bonds are broken. After the EXAFS, the authors concluded that the numbers of Ln-O(OC), Ln-O(H2) and Ln-N bonds change from 4,5,0 respectively to 4,3,2, finally resulting in 4,1,4 respectively with some changes of bond lengths. ZhengyuChen

"X-ray Absorption Spectroscopic Studies of Chromium Nitroso Complexes. Crystal and Molecular Structure of (Ph₄P)₃[Cr(NO)(NCS)₅]·2.4(CH₃)₂CO", Aviva Levina, Peter Turner, and Peter A. Lay, Inorg. Chem., 2003, 42, 5392-5398. doi:10.1021/ic0340480

The authors used XAS to determine the oxidation state of Cr in Cr-NO complexes, which had been unclear previously due to conflicting experimental data. By comparing the pre- and near-edge features of XAS spectra of the nitrosyl and reference complexes, they determined that the most likely formulation is Cr(III)-NO^-. They found that the onset of the edge was only slightly different from the reference Cr(III) compounds. In addition, the lowered symmetry of the nitrosyl complexes relative to the references gives rise to a pre-edge peak representing a 1s -> 3d transition. A shoulder before the main edge is also observed; the authors attribute this to the pi-acidity of the ligand, which permits p and d orbital mixing. This shoulder can therefore provide a direct measurement of pi-bonding in coordination complexes. CatherineChow

"In Situ XANES of an Iron Porphyrin Irreversibly Adsorbed on an Electrode Surface", Sunghyun Kim, In Tae Bae, Marnita Sandifer, Philip N. Ross,Roger Carr, Joseph Woicik, Mark R. Antonio, and Daniel A. Scherson, J. Am. Chem. SOC., 1991, 113, 9063-9066, [3].

The authors absorbed (p-oxo)bis[iron meso-tetrakis(4-methoxyphenyl)porphyrin] (FeTMPP)2O onto the a high area carbon substrate, Black Pearl (BP), as a function of applied potential. They measured the in situ XANES spectra of different complexes which changed with the electric potential. They found that the the iron in the original complex retains its μ-oxo character when it is in oxidized state, while the complex changes into a four-coordinate square-planar FeTMPP without axial ligation after reduction. And the in situ XANES indicated that the redox process is reversible. ZhengyuChen

"Water Influences on the Copper Active Site in Hemocyanin", Daniel Panzer, Christian Beck, Michaela Hahn, Jochen Maul, Gerd Schonhense, Heinz Decker, and Emad F. Aziz, J. Phys. Chem. Lett., 2010, 1, 1642-1647. [4]

The authors investigated the electronic structure of the active copper sites in hemocyanin via L-edge X-ray absorption spectroscopy under physiological conditions. Using soft XAS at the L_2;3-edge (2p_1/2;3/2 to 3d transitions) particularities of the oxidation/valence charges of the copper could be investigated in detail. A comparison of deoxygentaed and oxygenated states suggest that the copper sites do not simply switch between Cu(I) and Cu(II), but instead may interact with water molecules in the deoxygenated state that can keep the copper sites partially oxidized. The role of water could not have been revealed without the use of L-edge spectroscopy. CaterinaRamogida

"X-ray absorption spectroscopy of manganese, cobalt, copper and zinc inorganic salts of tetrathiafulvalene and bis(ethylenedithio)tetrathiafulvalene", V. Briois, R. M. Lequan, M. Lequan, C. Cartier, G. Van der Laan, A. Michalowicz, M. Verdaguer, Chem. Mater., 1992, 4(2), 484-493. [5]

The authors used K-edge X-ray absorption spectroscopy to investigate transition metal ions in a series of powdered materials: (TTF)₁₄(MCl₄)₄, BEDT-TTF(MCl₄)_0.3-0.4, and (TTF)₆(MnC1₃)₃(MnCl₂)₃^.13H₂O. The stereochemistry around the absorbing metal centers is proposed in comparison to model compounds using XANES, and insight into their electronic structures is obtained. Additionally, the bond lengths around each are determined using EXAFS and subsequent calculations. Joanna De Witt

"Visualizing Interfacial Charge Transfer in Ru-Dye-Sensitized TiO₂ Nanoparticles Using X-ray Transient Absorption Spectroscopy", Zhang, X.; Smolentsev, G.; Guo, J.; Attenkofer, K.; Kurtz, C.; Jennings, G.; Lockard, J. V.; Stickrath, A. B.; Chen, L. X. J. Phys. Chem. Lett., 2011, 2, 628. [6]

In this article, XTA (X-ray transient absorption) spectroscopy[7] was employed to study the transient charge separation process in the dye-sensitized solar cell (DSSC) in which Ru(dcbpy)₂(NCS)₂ dye was deposited onto TiO₂ nanoparticles. When laser was shone onto the DSSC, electrons were injected from Ru dye into TiO₂ particles. Comparing with computational simulation, the average Ru-NCS bond length then reduced by 0.06 Å, while average length of Ru-N(dcbpy) bonds almost unchanged.[8] The author attributed the change in bond-order and steric hindrance between two types of ligands to their structural response in the charge separation. YangCao