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Michael W. George - One of the best experts on this subject based on the ideXlab platform.

  • New insights into the photochemistry of [CpFe(CO)2]2 using picosecond through microsecond Time-Resolved Infrared Spectroscopy (TRIR)
    Polyhedron, 2014
    Co-Authors: Christopher M. Brookes, Xue-zhong Sun, Justin P. Lomont, Son C. Nguyen, Charles B. Harris, James A. Calladine, Michael W. George
    Abstract:

    Abstract Picosecond to microsecond Time-Resolved Infrared Spectroscopy (TRIR) has been used to investigate the photochemistry of [CpFe(CO) 2 ] 2 . The early-time TRIR spectra are dominated by vibrationally hot transient species and this leads to spectra with broad featureless bands. The majority (84%) of the well characterized Cp 2 Fe 2 (μ-CO) 3 , with a band at 1824 cm −1 , grows in on a timescale (15–20 ps) similar to the cooling rate of many of the ν (CO) bands, and this arises from presumably the initially formed species, [CpFe(CO)(μ-CO) 2 FeCp] of which we were unable to find clear evidence. However, Cp 2 Fe 2 (μ-CO) 3 is formed by two different processes and under CO the remaining slower formation (16%) occurs at the same rate (46 ± 2 ns) as a transient band at 1908 cm −1 decays. The 1908 cm −1 had been previously observed in an earlier study but its identity remained unclear. We find that this 1908 cm −1 intermediate has no corresponding bridging ν (CO) band and is formed by a 1-photon process. This band is assigned to a dicarbonyl-loss photoproduct, [CpFe(CO)] 2 and is a rare example of double CO loss occurring following a single-photon excitation in the condensed phase.

  • High-pressure-low-temperature cryostat designed for use with fourier transform Infrared spectrometers and Time-Resolved Infrared Spectroscopy.
    Applied spectroscopy, 2014
    Co-Authors: James A. Calladine, Ashley Love, Peter A. Fields, Richard Wilson, Michael W. George
    Abstract:

    The design for a new high-pressure-low-temperature Infrared (IR) cell for performing experiments using conventional Fourier transform Infrared or fast laser-based Time-Resolved Infrared Spectroscopy, in a range of solvents, is described. The design builds upon a commercially available compressor and cold end (Polycold PCC® and CryoTiger®), which enables almost vibration-free operation, ideal for use with sensitive instrumentation. The design of our cell and cryostat allows for the study of systems at temperatures from 77 to 310 K and at pressures up to 250 bar. The CaF2 windows pass light from the mid-IR to the ultraviolet (UV), enabling a number of experiments to be performed, such as Raman, UV-visible absorption Spectroscopy, and Time-Resolved techniques where sample excitation/probing using continuous wave or pulsed lasers is required. We demonstrate the capabilities of this cell by detailing two different applications: (i) the reactivity of a range of Group V-VII organometallic alkane complexes using Time-Resolved Spectroscopy on the millisecond timescale and (ii) the gas-to-liquid phase transition of CO2 at low temperature, which is applicable to measurements associated with transportation issues related to carbon capture and storage.

  • Photochemistry of (η6-anisole)Cr(CO)3 and (η6-thioanisole)Cr(CO)3: evidence for a photoinduced haptotropic shift of the thioanisole ligand, a picosecond Time-Resolved Infrared Spectroscopy and density functional theory investigation.
    The journal of physical chemistry. A, 2012
    Co-Authors: Ian P. Clark, Michael W. George, Gregory M. Greetham, Conor Long, Jennifer C. Manton, Emma C. Harvey, Hazel Mcardle, Mary T. Pryce
    Abstract:

    The photochemistry of (η(6)-anisole)Cr(CO)(3) and (η(6)-thioanisole)Cr(CO)(3) was investigated by picosecond Time-Resolved Infrared Spectroscopy in n-heptane solution at 298 K. Two independent excited states are populated following 400 nm excitation of each of these complexes. An excited state with some metal-to-CO charge-transfer character is responsible for the CO-loss process, which is slow compared to CO-loss from Cr(CO)(6). Observed first order rate constants of 1.8 × 10(10) s(-1) and 2.5 × 10(10) s(-1) were obtained for the anisole and thioanisole complexes, respectively. The second excited state has metal-to-arene charge transfer character and results in a haptotropic shift of the thioanisole ligand. DFT calculations characterized the excited states involved and the nature of the haptotropic shift intermediate observed for the thioanisole species.

  • Photochemistry of (η6-Arene)Cr(CO)3(Arene = Methylbenzoate, Naphthalene, or Phenanthrene) inn-Heptane Solution: Population of Two Excited States Following 400 nm Excitation As Detected by Picosecond Time-Resolved Infrared Spectroscopy
    The journal of physical chemistry. A, 2011
    Co-Authors: Ian P. Clark, Michael W. George, Gregory M. Greetham, Conor Long, Jennifer C. Manton, Emma C. Harvey, Mary T. Pryce
    Abstract:

    The photochemistry of (η6-methylbenzoate)Cr(CO)3, (η6-naphthalene)Cr(CO)3, and (η6-phenanthrene)Cr(CO)3 in n-heptane solution was investigated by picosecond Time-Resolved Infrared Spectroscopy (TRIR). The observation of two transient IR features in the organic carbonyl region at 1681 and 1724 cm−1 following 400 nm excitation of (η6-methylbenzoate)Cr(CO)3 confirms formation of two excited states which are classified as metal-to-arene charge transfer (MACT) and metal-to-CO charge transfer (MCCT), respectively. Time-dependent density functional theory calculations have been used to support these assignments. Population of the MCCT excited state results in a slow (150 ps) expulsion of one CO ligand. Excitation of (η6-naphthalene)Cr(CO)3 or (η6-phenanthrene)Cr(CO)3 at either 400 or 345 nm produced two excited states: the MCCT state results in CO loss, while the MACT excited state results in a change to the coordination mode of the polyaromatic ligands before relaxing to the parent complex. A comparison of the ...

  • Monitoring the effect of ultrafast deactivation of the electronic excited states of DNA bases and polynucleotides following 267 nm laser excitation using picosecond Time-Resolved Infrared Spectroscopy.
    Chemical communications (Cambridge England), 2005
    Co-Authors: Marina K. Kuimova, Michael W. George, Xue-zhong Sun, David C. Grills, Michael Towrie, John Kelly, Joanne Dyer, Pavel Matousek, Anthony W. Parker, Aine M. Whelan
    Abstract:

    In this paper we demonstrate the use of picosecond Time-Resolved Infrared Spectroscopy (ps-TRIR) to monitor the early structural dynamics of DNA bases and polydeoxynucleotides following UV excitation in solution.

Matthew S. Platz - One of the best experts on this subject based on the ideXlab platform.

Hiro-o Hamaguchi - One of the best experts on this subject based on the ideXlab platform.

  • Triplet quantum chain process in the photoisomerization of 9-cis retinal as revealed by nanosecond Time-Resolved Infrared Spectroscopy
    Journal of Molecular Structure, 2010
    Co-Authors: Tetsuro Yuzawa, Hiro-o Hamaguchi
    Abstract:

    Abstract The mechanism of the photoisomerization of 9- cis retinal has been studied by nanosecond Time-Resolved Infrared Spectroscopy. A cyclohexane solution of 9- cis retinal was photoexcited at 349 nm and the subsequent photodynamics were traced. A singular value decomposition (SVD) analysis of the Time-Resolved Infrared data shows that there are two distinct isomerization pathways. One is the triplet pathway that takes place in the picosecond time regime from 9- cis to all- trans . The other involves the energy transfer between the all- trans triplet state and the 9- cis ground state with the resultant 9- cis triplet state subsequently reproducing the all- trans by fast isomerization on the triplet potential surface . This quantum chain process occurs in the microsecond time regime.

  • Solvent-dependent intra- and intermolecular vibrational energy transfer of W(CO) 6 probed with sub-picosecond Time-Resolved Infrared Spectroscopy
    Chemical Physics Letters, 2005
    Co-Authors: Motohiro Banno, Koichi Iwata, Shin Sato, Hiro-o Hamaguchi
    Abstract:

    Abstract Solvent-dependent intra- and intermolecular vibrational energy transfer from the triply degenerate CO stretch mode of W(CO) 6 is observed in nine alkanes (C n H 2 n  + 2 , n  = 5–13) with single-color sub-picosecond Time-Resolved Infrared Spectroscopy. In all the solvents, the vibrational relaxation process is well characterized by three time constants: τ 1 ( τ 2 (3–13 ps) and τ 3 (124–160 ps). The solvent dependence of τ 2 and τ 3 cannot be explained by the macroscopic properties of the solvent. In particular, the longest time constant τ 3 shows the minimum value of 124 ps in decane among the nine alkanes. The rate of the vibrational energy relaxation is a sensitive measure of the microscopic environments.

  • MECHANISM OF THE PHOTOCHEMICAL REACTION BETWEEN ANTHRACENE AND CARBON TETRACHLORIDE STUDIED BY Time-Resolved Infrared Spectroscopy
    Journal of Molecular Structure, 1997
    Co-Authors: Koichi Iwata, Hiro-o Hamaguchi
    Abstract:

    Abstract The photochemical reaction between anthracene and carbon tetrachloride has been studied by Time-Resolved Infrared Spectroscopy. A strong transient Infrared band observed at 896 cm −1 was assigned to the trichloromethyl (CCl 3 ) radical. A few other transient Infrared bands showing the same temporal behavior as that of CCl 3 were assigned to the anthracene-Cl adduct. The participation of these two radicals as reaction intermediates is thus confirmed. A singular value decomposition (SVD) analysis shows that they further react with each other to form the final product, following second-order kinetics. Comparison of the finger print region of the Infrared spectra strongly supports the previously proposed idea that the final product is the 9-chloro-10-trichloro adduct of anthracene.

  • Nanosecond Time-Resolved Infrared Spectroscopy distinguishes two K species in the bacteriorhodopsin photocycle
    Biophysical journal, 1995
    Co-Authors: Jun Sasaki, Tetsuro Yuzawa, Hideki Kandori, Akio Maeda, Hiro-o Hamaguchi
    Abstract:

    The photochemical reaction process of bacteriorhodopsin in the nanosecond time range (-120–860 ns) was measured in the 1400–900 cm-1 region with an improved time resolved dispersive-type Infrared spectrometer. The system is equipped with a newly developed detection unit whose instrumental response to a 5-ns laser pulse has a full width of the half-maximum of 60 ns. It provides highly accurate data that enabled us to extract a kinetic process one order of magnitude faster than the instrumental response. The spectral changes in the 1400–900 cm-1 region were analyzed by singular value decomposition and resolved into three components. These components were separated by fitting with 10- and 1000-ns exponential functions and a step function, which were convoluted with the instrumental response function. The components with decay time constants of 10 and 1000 ns are named K and KL, respectively, on the basis of previous visible Spectroscopy. The spectral shapes of K and KL are distinguishable by their hydrogen-out-of-plane (HOOP) modes, at 958 and 984 cm-1, respectively. The former corresponds to the K intermediate recorded at 77 K and the latter to a K-like photoproduct at 135 K. On the basis of published data, these bands are assigned to the 15-HOOP mode, indicating that the K and KL differ in a twist around the C14-C15 bond.

  • Nanosecond Time-Resolved Infrared Spectroscopy with a Dispersive Scanning Spectrometer
    Applied Spectroscopy, 1994
    Co-Authors: Tetsuro Yuzawa, Michael W. George, Chihiro Kato, Hiro-o Hamaguchi
    Abstract:

    A nanosecond Time-Resolved Infrared spectroscopic system based on a dispersive scanning spectrometer has been constructed. This is an advanced version of a similar system reported in a previous paper; the time resolution has been improved from 1 μs to 50 ns and the sensitivity from 10-4 in intensity changes to 10-6. These have been achieved by the use of a high-temperature ceramic Infrared light source, a photovoltaic MCT detector, and a low-noise, wide-band preamplifier developed specifically for the present purpose. Time-Resolved Infrared spectra of a few samples of photochemical and photobiological interests are presented to show the capability of the system. The origin of the thermal artifacts, which have been found to hamper the Time-Resolved Infrared measurements seriously, is shown to be due to the transient reflectance change induced by a small temperature jump. The future prospect of Time-Resolved Infrared Spectroscopy is discussed with reference to other methods including Infrared laser Spectroscopy and Fourier transform Infrared Spectroscopy.

Gregory M. Greetham - One of the best experts on this subject based on the ideXlab platform.

  • Photochemical or electrochemical bond breaking – exploring the chemistry of (μ2-alkyne)Co2(CO)6 complexes using Time-Resolved Infrared Spectroscopy, spectro-electrochemical and density functional methods
    Dalton transactions (Cambridge England : 2003), 2019
    Co-Authors: Jennifer C. Manton, Ian P. Clark, Gregory M. Greetham, Conor Long, Florian J R Cerpentier, Emma C. Harvey, Mary T. Pryce
    Abstract:

    The photochemistry of (μ2-CRCR')Co2(CO)6 complexes (R = pyrenyl, R' = H; R = pyrenyl, R' = ferrocenyl; R = ferrocenyl, R = H) was investigated by ps-Time-Resolved Infrared Spectroscopy at room temperature in dichloromethane solution. The main focus of these studies was to determine the primary photoprocess relevant to the light assisted Pauson-Khand reaction. These studies were supported by spectro-electrochemical investigations and density functional calculations which suggest that the primary process to initiate the Pauson-Khand reaction involves a homolytic cleavage of the Co-Co bond forming a high-spin diradical species and not CO-loss as previously thought.

  • Monitoring Base Specific Dynamics during Melting of DNA-Ligand Complexes Using Temperature-Jump Time-Resolved Infrared Spectroscopy
    The journal of physical chemistry. B, 2019
    Co-Authors: Robby Fritzsch, Michael Towrie, Ian P. Clark, Anthony W. Parker, Gregory M. Greetham, Lucy Minnes, Neil T. Hunt
    Abstract:

    Ultrafast Time-Resolved Infrared Spectroscopy employing nanosecond temperature-jump initiation has been used to study the melting of double-stranded (ds)DNA oligomers in the presence and absence of minor groove-binding ligand Hoechst 33258. Ligand binding to ds(5′-GCAAATTTCC-3′), which binds Hoechst 33258 in the central A-tract region with nanomolar affinity, causes a dramatic increase in the timescales for strand melting from 30 to ∼250 μs. Ligand binding also suppresses premelting disruption of the dsDNA structure, which takes place on 100 ns timescales and includes end-fraying. In contrast, ligand binding to the ds(5′-GCATATATCC-3′) sequence, which exhibits an order of magnitude lower affinity for Hoechst 33258 than the A-tract motif, leads to an increase by only a factor of 5 in melting timescales and reduced suppression of premelting sequence perturbation and end-fraying. These results demonstrate a dynamic impact of the minor groove ligand on the dsDNA structure that correlates with binding strength...

  • Variation in LOV Photoreceptor Activation Dynamics Probed by Time-Resolved Infrared Spectroscopy.
    Biochemistry, 2018
    Co-Authors: James N. Iuliano, Agnieszka A. Gil, Sergey P. Laptenok, Christopher R. Hall, Jinnette Tolentino Collado, Andras Lukacs, Safaa A. Hag Ahmed, Jenna Abyad, Taraneh Daryaee, Gregory M. Greetham
    Abstract:

    The light, oxygen, voltage (LOV) domain proteins are blue light photoreceptors that utilize a noncovalently bound flavin mononucleotide (FMN) cofactor as the chromophore. The modular nature of these proteins has led to their wide adoption in the emerging fields of optogenetics and optobiology, where the LOV domain has been fused to a variety of output domains leading to novel light-controlled applications. In this work, we extend our studies of the subpicosecond to several hundred microsecond transient Infrared Spectroscopy of the isolated LOV domain AsLOV2 to three full-length photoreceptors in which the LOV domain is fused to an output domain: the LOV-STAS protein, YtvA, the LOV-HTH transcription factor, EL222, and the LOV-histidine kinase, LovK. Despite differences in tertiary structure, the overall pathway leading to cysteine adduct formation from the FMN triplet state is highly conserved, although there are slight variations in rate. However, significant differences are observed in the vibrational spectra and kinetics after adduct formation, which are directly linked to the specific output function of the LOV domain. While the rate of adduct formation varies by only 3.6-fold among the proteins, the subsequent large-scale structural changes in the full-length LOV photoreceptors occur over the micro- to submillisecond time scales and vary by orders of magnitude depending on the different output function of each LOV domain.

  • Next generation ultrafast Time-Resolved Infrared Spectroscopy at the central laser facility
    2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO Europe-EQEC), 2017
    Co-Authors: Gregory M. Greetham, Igor V. Sazanovich, Ian P. Clark, Paul M. Donaldson, Michael Towrie
    Abstract:

    Time-Resolved Spectroscopy developments are presented focussing on ultrafast IR laser techniques probing molecular dynamics. These developments at the ULTRA laboratory focus on improving sensitivity, expanding data collection parameters and widening application to a diverse array of samples. The techniques presented apply high repetition rate lasers, 1-100 kHz, based on cryo-cooled, titanium sapphire, ytterbium (Yb:KGW) and an ytterbium-pumped optical parametric chirped pulse (OPCPA) amplifiers. The outputs are used directly in experiments or via wavelength conversion devices in the ultraviolet to Infrared (200-16000 nm).

  • Photochemistry of (η6-anisole)Cr(CO)3 and (η6-thioanisole)Cr(CO)3: evidence for a photoinduced haptotropic shift of the thioanisole ligand, a picosecond Time-Resolved Infrared Spectroscopy and density functional theory investigation.
    The journal of physical chemistry. A, 2012
    Co-Authors: Ian P. Clark, Michael W. George, Gregory M. Greetham, Conor Long, Jennifer C. Manton, Emma C. Harvey, Hazel Mcardle, Mary T. Pryce
    Abstract:

    The photochemistry of (η(6)-anisole)Cr(CO)(3) and (η(6)-thioanisole)Cr(CO)(3) was investigated by picosecond Time-Resolved Infrared Spectroscopy in n-heptane solution at 298 K. Two independent excited states are populated following 400 nm excitation of each of these complexes. An excited state with some metal-to-CO charge-transfer character is responsible for the CO-loss process, which is slow compared to CO-loss from Cr(CO)(6). Observed first order rate constants of 1.8 × 10(10) s(-1) and 2.5 × 10(10) s(-1) were obtained for the anisole and thioanisole complexes, respectively. The second excited state has metal-to-arene charge transfer character and results in a haptotropic shift of the thioanisole ligand. DFT calculations characterized the excited states involved and the nature of the haptotropic shift intermediate observed for the thioanisole species.

Plinio Innocenzi - One of the best experts on this subject based on the ideXlab platform.

  • Structural Evolution during Evaporation of a 3-Glycidoxypropyltrimethoxysilane Film Studied in Situ by Time Resolved Infrared Spectroscopy
    The journal of physical chemistry. A, 2011
    Co-Authors: Plinio Innocenzi, Masahide Takahashi, Massimo Piccinini, Cristiana Figus, Luca Malfatti
    Abstract:

    Time resolved Infrared Spectroscopy has been applied to study in situ the evaporation process of a 3-glycidoxypropyltrimethoxysilane hybrid sol by casting a droplet on a ZnSe substrate; the analysis has been performed in the middle-Infrared range and in the near-Infrared range. The experiment has allowed following the structural changes induced by water evaporation and the formation of ordered structures within the cast film; the CH 2 scissoring bands have been used as a fingerprint for the disorder to order transition of the hybrid. The experiment has been done using both a fresh sol and an aged sol which produce respectively an amorphous material and a crystalline hybrid material. The analysis has shown that the epoxy groups do not react during the evaporation while the silica structure shows only a slight condensation and an increase in open cage-like species. At the end of evaporation the hybrid has a “soft-like” state which allows structural rearrangements to self-order.

  • Evaporation-Induced Crystallization of Pluronic F127 Studied in Situ by Time-Resolved Infrared Spectroscopy
    The journal of physical chemistry. A, 2010
    Co-Authors: Plinio Innocenzi, Luca Malfatti, Massimo Piccinini, Augusto Marcelli
    Abstract:

    Rapid scan Time-Resolved Infrared Spectroscopy has been used to study in situ the crystallization induced by evaporation in an aqueous solution of a triblock copolymer, Pluronic F127. A droplet of the solution was cast on a silicon substrate and the evaporation followed by an Infrared microscope in transmission mode. The evaporation rate of water, in the last stage of the process, has been shown to be correlated to the changes in the block copolymer; four different stages can be distinguished. The block copolymer passes from an amorphous micellar state in water to a partially crystallized phase in well-defined stages of the evaporation; the complete change from amorphous to crystalline state of Pluronic F127 is observed only after all water is evaporated.

  • Water evaporation studied by in situ Time-Resolved Infrared Spectroscopy.
    The journal of physical chemistry. A, 2009
    Co-Authors: Plinio Innocenzi, Luca Malfatti, Massimo Piccinini, Augusto Marcelli, David Grosso
    Abstract:

    Evaporation of water is a fundamental and ubiquitous process that is on the ground of different types of nanoscience phenomena such as evaporation induced self-assembly. Even if water evaporation is a very basic phenomenon, there is still a lack of experiments that give a direct insight of the process. In situ application of rapid scan Time-Resolved Infrared Spectroscopy to an evaporating droplet has allowed monitoring the process at different relative humidity conditions. The experiments have been performed in the near-Infrared range using water and deuterated water. The water evaporation appears as a continuous process that is not affected by changes of relative humidity in the external environment. This result, however, is affected by the impossibility to discriminate the contribution of the adsorbed water. The same experiment repeated with a deuterated water droplet has allowed, instead, a direct observation of the contribution during the evaporation process from water in the external environment. The Time-Resolved analysis has shown that at higher relative humidity the water adsorption is enhanced and that this process is time delayed with respect to the beginning of the evaporation process.

  • Evaporation of Ethanol and Ethanol−Water Mixtures Studied by Time-Resolved Infrared Spectroscopy
    The journal of physical chemistry. A, 2008
    Co-Authors: Plinio Innocenzi, Tongjit Kidchob, Luca Malfatti, Stefano Costacurta, Massimo Piccinini, Augusto Marcelli
    Abstract:

    The knowledge of the physics and the chemistry behind the evaporation of solvents is very important for the development of several technologies, especially in the fabrication of thin films from liquid phase and the organization of nanostructures by evaporation-induced self-assembly. Ethanol, in particular, is one of the most common solvents in sol-gel and evaporation-induced self-assembly processing of thin films, and a detailed understanding of its role during these processes is of fundamental importance. Rapid scan Time-Resolved Infrared Spectroscopy has been applied to study in situ the evaporation of ethanol and ethanol-water droplets on a ZnSe substrate. Whereas the evaporation rate of ethanol remains constant during the process, water is adsorbed by the ethanol droplet from the external environment and evaporates in three stages that are characterized by different evaporation rates. The adsorption and evaporation process of water in an ethanol droplet has been observed to follow a complex behavior: due to this reason, it has been analyzed by two-dimensional Infrared correlation. Three different components in the water bending band have been resolved.

  • In-situ study of sol–gel processing by Time-Resolved Infrared Spectroscopy
    Journal of Sol-Gel Science and Technology, 2008
    Co-Authors: Plinio Innocenzi, Tongjit Kidchob, Luca Malfatti, Stefano Costacurta, Masahide Takahashi, Massimo Piccinini, Augusto Marcelli
    Abstract:

    Sol–gel processing of thin films involves time dependent phenomena which are basically driven by solvent evaporation. An example is evaporation induced self-assembly that is used to prepare mesoporous ordered films through self-organization of templating micelles. The possibility to follow in situ as a function of time the evolution of the system can give a better knowledge of the process and the physics and chemistry beneath. Time-Resolved Infrared techniques have been applied to different sol–gel systems to study time-dependent phenomena, in particular rapid scan time resolved Infrared Spectroscopy has been used to monitor in situ the process and as a tool to design the sol–gel synthesis.