Femtosecond Absorption Spectroscopy of Transition Metal Charge-Transfer Complexes

McCusker, James K.

doi:10.1021/ar030111d

Cited by 399 publications

(413 citation statements)

References 30 publications

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“…The observed rise of vibrational features caused by the triplet state, together with the extremely low fluorescence quantum yield, suggests that rapid (<30-fs) solvent relaxation occurs that renders the singlet and triplet states nearly degenerate immediately after absorption of a photon and thereby catalyzes the extremely fast intersystem crossing to the triplet state (26,29). Thus, intersystem crossing is gated by rapid solvent relaxation.…”

Section: +mentioning

confidence: 99%

Femtosecond Stimulated Raman Spectroscopy

Kukura

Yoon²,

Mathies³

2006

Anal. Chem.

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R aman spectroscopy is a powerful analytical technique for revealing vibrational structure. It is widely used in biology, chemistry, and studies of molecular reaction dynamics (1-3). One of the technique's greatest advantages is that a single spectrum contains a wealth of vibrational structural information about the sample. The large number of well-resolved vibrational bands provides unique information analogous to a human fingerprint, and the technique is very sensitive to molecular structure. Changes in bond lengths of as little as 0.01 Å can produce clear differences in the vibrational spectrum. This specificity and sensitivity make Raman an excellent tool for trace analysis and for studies of chemically induced structural changes.Although a wide variety of Raman techniques have been developed over the years and applied to analytical problems, significant room for improvement still exists. FT Raman methods are often used in industrial applications to avoid background fluorescence-via intense laser radiation in the NIR-and to exploit the FT multiplex advantage. Clinical applications of FT Raman range from identification of cancerous tissues to microscopic imaging (4). However, it can suffer from weak resonance enhancement and intense Rayleigh scattering caused by the noise distribution of the FT (5). In surface-enhanced Raman spectroscopy, spectra of molecules adsorbed to roughened metallic surfaces or nanostructures can be taken with extreme sensitivity; however, the technique relies on the not-easily-controlled interaction of the metallic substrates with the analyte (6). Raman imaging has recently been advanced through the use of nonlinear Raman techniques, in particular coherent anti-stokes Raman scattering (CARS), which has been used, for example, to monitor biological processes in real time (7,8). Despite these advances, limitations exist that prevent these methods from exploiting the full potential of Raman scattering. We asked: Can an analytical resonance Raman technique be developed that can produce high-S/N spectra that are immune to background fluorescence, with short data-acquisition times?Time-resolved vibrational spectroscopies are also extensively used in structural studies of dynamics of chemical and biological reactions. The earliest (<50-fs) events in photochemical and photophysical processes are best studied by resonance Raman intensity analysis, an extremely powerful technique that can provide detailed excited-state structural information (9, 10). Spontaneous time-resolved resonance A new approach for obtaining vibrational Raman spectra and for studying chemical reaction dynamics. 9 4 A N A LY T I C A L C H E M I S T R Y / S E P T E M B E R 1 , 2 0 0 6Raman spectroscopy is limited to the picosecond time domain because of the transform limit; this prevents the technique from being applied to chemical reactions that occur on the order of 10 f s-1 ps. This limitation has recently been overcome by the availability of femtosecond pulses in the IR. As a consequence, pump-probe approaches for measu...

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Section: +mentioning

confidence: 99%

Femtosecond Stimulated Raman Spectroscopy

Kukura

Yoon²,

Mathies³

2006

Anal. Chem.

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“…Tools sensitive to the electronic structure and the spin state, which can also be utilized on the femtosecond (fs) to nanosecond (ns) time scales, can shed light on the yet unknown details of the relevant intermediate steps involved in the spin-state switching process. Previously, fs laser spectroscopy has been used for this purpose, which have delivered a rich picture of the ultrafast events taking place on the first few hundred fs [4,5,6,7,8]. These tools are, however, rather insensitive to the changes in the spin state next to the concomitant geometric structure changes.…”

Section: Introductionmentioning

confidence: 99%

Spin-state studies with XES and RIXS: From static to ultrafast

Vankó

Bordage

Glatzel

et al. 2013

Journal of Electron Spectroscopy and Related Phenomena

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We report on extending hard X-ray emission spectroscopy (XES) together with resonant inelastic X-ray scattering (RIXS) to study ultrafast phenomena in a pump-probe scheme at MHz repetition rates. The investigated system consists of low-spin (LS) Fe II complex compounds, where optical pulses induce a spinstate transition to their ≈ nanosecond-lived high-spin (HS) state. Time-resolved XES clearly reflects the spinstate variations with very high signal-to-noise ratio, in agreement with HS-LS difference spectra measured via thermally induced spin crossover, and reference HS-LS systems in static experiments. 1s2p RIXS, measured at the Fe 1s pre-edge region shows variations after laser excitation, which are consistent with the formation of the HS state. Our results demonstrate that now X-ray spectroscopy experiments with overall rather weak signals, such as RIXS, can be reliably exploited to study chemical and physical transformations on ultrafast time scales.

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“…Nevertheless, there are often significant limitations of electronic and vibrational spectroscopies: the sometimes broad, nondescript nature of electronic spectra and the inherent vibrational complexity of large molecular frameworks can make interpretation of time-resolved optical and infrared and/or Raman data challenging. This is a common situation in the spectroscopy of transition metal-containing systems, 7 wherein the density of both electronic and vibrational states can render mechanistic questions concerning photo-induced dynamics difficult to resolve.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2010

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Solution-phase photo-induced low-spin to high-spin conversion in the Fe II polypyridyl complex [Fe(tren(py) 3 )] 2+ (where tren(py) 3 is tris(2-pyridylmethylimino-ethyl)amine) has been studied via picosecond soft x-ray spectroscopy. Following 1 A 1 → 1 MLCT (metal-to-ligand charge transfer) excitation at 560 nm, changes in the iron L 2 and L 3 edges were observed concomitant with formation of the transient high-spin 5 T 2 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.

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Femtosecond Absorption Spectroscopy of Transition Metal Charge-Transfer Complexes

Cited by 399 publications

References 30 publications

Femtosecond Stimulated Raman Spectroscopy

Femtosecond Stimulated Raman Spectroscopy

Spin-state studies with XES and RIXS: From static to ultrafast

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

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