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Michael Towrie

Publications and source records attributed to Michael Towrie.

At least 19 recordsLinked to original sources
PubMed2007

Formation of the early photoproduct lumi-R of cyanobacterial phytochrome cph1 observed by ultrafast mid-infrared spectroscopy.

The photoreactions of the Pr ground state of cyanobacterial phytochrome Cph1 from Synechocystis PCC 6803 have been investigated by picosecond time-resolved mid-infrared spectroscopy at ambient temperature. With femtosecond excitation of the Pr state at 640 nm, the photoisomerized Lumi-R product state is generated with kinetics and associated difference spectra indicative of vibrational cooling with tau(1) = 3 ps time constant and excited state decay with tau(1) = 3 ps, tau(2) = 14 ps, and tau(3) = 134 ps time constants. The Lumi-R state is characterized by downshifted absorption of three C=C modes assigned to C(15)=C(16), C(4)=C(6), and a delocalized C=C mode, in addition to the downshifted C(19)=O mode. The Lumi-R minus Pr difference spectrum is indicative of global restructuring of the chromophore on the ultrafast timescale, which is discussed in light of C(15) Z/E photoisomerization in addition to changes near C(5), which could be low bond order torsional angle changes.

Bacterial Proteins↗
PubMed2006

Electronic structure and excited states of rhenium(I) amido and phosphido carbonyl-bipyridine complexes studied by picosecond time-resolved IR spectroscopy and DFT calculations.

UV-vis absorption and picosecond time-resolved IR (TRIR) spectra of amido and phosphido complexes fac-[Re(ER2)(CO)3(bpy)] (ER2 = NHPh, NTol2, PPh2, bpy = 2,2'-bipyridine, Tol = 4-methylphenyl) were investigated in conjunction with DFT and TD-DFT calculations in order to understand their ground-state electronic structure, low-lying electronic transitions and excited-state character and dynamics. The HOMO is localized at the amido/phosphido ligand. Amide and phosphide ligands are sigma-bonded to Re, the pi interaction being negligible. Absorption spectra show a weak band at low energies (1.7-2.1 eV) that arises from essentially pure ER(2) --> bpy ligand-to-ligand charge transfer (LLCT). The lowest excited state is the corresponding triplet, (3)LLCT. Low triplet energies and large distortions diminish the excited-state lifetimes to 85 and 270 ps for NHPh and NTol(2), respectively, and to ca. 30 ps for PPh2. nu(CO) vibrations undergo only very small ( bpy MLCT character, is a unique feature of the amido/phoshido complexes, whose lowest excited state can be viewed as containing a highly unusual aminyl/phosphinyl radical-cationic ligand. For comparison, the amino and phosphino complexes fac-[Re(NHPh(2))(CO)3(bpy)]+ and fac-[Re(PPh3)(CO)3(bpy)]+ are shown to have the usual Re --> bpy (3)MLCT lowest excited states, characterized by upshifted nu(CO) bands.

Journal Article↗
PubMed2006

Ultrafast charge separation in a photoreactive rhenium-appended porphyrin assembly monitored by picosecond transient infrared spectroscopy.

Rhenium(bipyridine)(tricarbonyl)(picoline) units have been linked covalently to tetraphenylmetalloporphyrins of magnesium and zinc via an amide bond between the bipyridine and one phenyl substituent of the porphyrin. The resulting complexes, abbreviated as [Re(CO)(3)(Pic)Bpy-MgTPP][OTf] and [Re(CO)(3)(Pic)Bpy-ZnTPP][OTf], exhibit no signs of electronic interaction between the Re(CO)(3)(bpy) units and the metalloporphyrin units in their ground states. However, emission spectroscopy reveals solvent-dependent quenching of porphyrin emission on irradiation into the long-wavelength absorption bands localized on the porphyrin. The characteristics of the excited states have been probed by picosecond time-resolved absorption (TRVIS) spectroscopy and time-resolved infrared (TRIR) spectroscopy in nitrile solvents. The presence of the charge-separated state involving electron transfer from MgTPP or ZnTPP to Re(bpy) is signaled in the TRIR spectra by a low-frequency shift in the nu(CO) bands of the Re(CO)(3) moiety similar to that observed by spectroelectrochemical reduction. Long-wavelength excitation of [Re(CO)(3)(Pic)Bpy-MTPP][OTf] results in characteristic TRVIS spectra of the S(1) state of the porphyrin that decay with a time constant of 17 ps (M = Mg) or 24 ps (M = Zn). The IR bands of the CS state appear on a time scale of less than 1 ps (Mg) or ca. 5 ps (Zn) and decay giving way to a vibrationally excited (i.e., hot) ground state via back electron transfer. The IR bands of the precursors recover with a time constant of 35 ps (Mg) or 55 ps (Zn). The short lifetimes of the charge-transfer states carry implications for the mechanism of reaction in the presence of triethylamine.

Journal Article↗
PubMed2006

Excited-state dynamics of structurally characterized [ReI(CO)3(phen)(HisX)]+ (X = 83, 109) Pseudomonas aeruginosa azurins in aqueous solution.

The triplet metal-to-ligand charge transfer ((3)MLCT) dynamics of two structurally characterized Re(I)(CO)(3)(phen)(HisX)-modified (phen = 1,10-phenanthroline; X = 83, 109) Pseudomonas aeruginosa azurins have been investigated by picosecond time-resolved infrared (TRIR) spectroscopy in aqueous (D(2)O) solution. The (3)MLCT relaxation dynamics exhibited by the two Re(I)-azurins are very different from those of the sensitizer [Re(I)(CO)(3)(phen)(im)](+) (im = imidazole). Whereas the Re(I)(CO)(3) intramolecular vibrational relaxation in Re(I)(CO)(3)(phen)(HisX)Az (4 ps) is similar to that of [Re(I)(CO)(3)(phen)(im)](+) (2 ps), the medium relaxation is much slower ( approximately 250 vs 9.5 ps); the 250-ps relaxation is attributable to reorientation of D(2)O molecules as well as structural reorganization of the rhenium chromophore and nearby polar amino acids in each of the modified proteins.

Azurin↗
PubMed2006

Monitoring the direct and indirect damage of DNA bases and polynucleotides by using time-resolved infrared spectroscopy.

The nucleotide 5'-dGMP and polynucleotide poly(dGdC).poly(dGdC) have been irradiated by using a 200-fs, 200-nm laser pulses and spectrally characterized by using time-resolved infrared spectroscopy. Under the experimental conditions, 200-nm excitation generates both electronic excited states and radical cations through photoionization; the former decay rapidly to vibrationally hot ground state. By using infrared signatures we have been able to follow these processes, and at time scales of >1 ns we observe an infrared marker band at 1,702 cm(-1) within both 5'-dGMP and the polynucleotide assigned to a photoionized product of guanine. This transient has also been reproduced through indirect chemistry through the reaction with photogenerated carbonate radical with 5'-dGMP. The ability to use time-resolved infrared spectroscopy in this way paves the way for developing solution-phase studies to investigate both direct and indirect radiation chemistry of DNA.

DNA↗
PubMed2005

Photoelectron spectroscopy of S1 toluene: II. Intramolecular dynamics of selected vibrational levels in S1 toluene studied by nanosecond and picosecond time-resolved photoelectron spectroscopies.

We present results which suggest that the photophysics of S(1) toluene is significantly more complicated than that of the related molecules p-fluorotoluene or p-difluorobenzene. We have measured a range of photoelectron spectra for a number of S(1) internal energies, on different time scales and at different temperatures, in an attempt to unravel the competing processes, but the final conclusion remains outstanding.

Journal Article↗
PubMed2005

Picosecond time-resolved infrared spectroscopic investigation into electron localisation in the excited states of Re(i) polypyridyl complexes with bridging ligands.

Mono- and binuclear complexes of (Re(CO)3Cl) with dipyrido[2,3-a:3',2'-c]-6,7-dimethylphenazine (ppbMe2) were synthesised and their photophysical properties probed using picosecond time-resolved infrared spectroscopy (TRIR). Excitation of these complexes in solution at 400 nm produces short-lived excited states. The IR spectrum of the excited state of the mononuclear [Re(CO)3Cl(ppbMe2)] have nu(CO) bands shifted to higher wavenumber relative to those of the ground state. This is consistent with formation of a (3)MLCT excited state. The IR spectrum of the excited state of the bimetallic [(Re(CO)3Cl)2(micro-ppbMe2)] shows the formation of two distinct groups of nu(CO) bands. This is interpreted as the formation of two distinct Re sites arising from a localised MLCT state with formally oxidised Re centre and a formally reduced bridging ligand. The nu(CO) bands of the adjacent Re centre are affected by the reduction of the bridging ligand. On the IR timescale the excited state structure is best formulated as [Cl(CO)3Re(II)(micro-ppbMe2 *-)Re(I)(CO)3Cl].

Electrons↗
PubMed2005

New members of the [Ru(diimine)(CN)(4)](2-) family: structural, electrochemical and photophysical properties.

A series of complexes of the type K(2)[Ru(NN)(CN)(4)] has been prepared, in which NN is a diimine ligand, and were investigated for both their structural and photophysical properties. The ligands used (and the abbreviations for the resulting complexes) are 3-(2-pyridyl)pyrazole (Ru-pypz), 2,2'-bipyrimidine (Ru-bpym), 5,5'-dimethyl-2,2'-bipyridine (Ru-dmb), 1-ethyl-2-(2-pyridyl)benzimidazole (Ru-pbe), bidentate 2,2':6',2'''-terpyridine (Ru-tpy). The known complexes with = 2,2'-bipyridine (Ru-bpy) and 1,10-phenathroline (Ru-phen) were also included in this work. A series of crystallographic studies showed that the [Ru(NN)(CN)(4)](2-) complex anions form a range of elaborate coordination networks when crystallised with either K(+) or Ln(3+) cations. The K(+) salts are characterised by a combination of near-linear Ru-CN-K bridges, with the cyanides coordinating to K(+) in the usual 'end-on' mode, and unusual side-on pi-type coordination of cyanide ligands to K(+) ions. With Ln(3+) cations in contrast only Ru-CN-Ln near-linear bridges occurred, affording 1-dimensional helical or diamondoid chains, and 2-dimensional sheets constituted from linked metallamacrocyclic rings. All of the K(2)[Ru(CN)(4)] complexes show a reversible Ru(II)/Ru(III) couple (ca.+0.9 V vs. Ag/AgCl in water), the exception being Ru-tpy whose oxidation is completely irreversible. Luminescence studies in water showed the presence of (3)MLCT-based emission in all cases apart from Ru-bpym with lifetimes of tens/hundreds of nanoseconds. Time-resolved infrared studies showed that in the (3)MLCT excited state the principal C-N stretching vibration shifts to positive energy by ca. 50 cm(-1) as a consequence of the transient oxidation of the metal centre to Ru(III) and the reduction in back-bonding to the cyanide ligands; measurement of transient decay rates allowed measurements of (3)MLCT lifetimes for those complexes which could not be characterised by luminescence spectroscopy. A few complexes were also examined in different solvents (MeCN, dmf) and showed much weaker emission and shorter excited-state lifetimes in these solvents compared to water.

Journal Article↗
PubMed2005

Structural events in the photocycle of green fluorescent protein.

Picosecond time-resolved mid-infrared absorption changes of the wild type green fluorescent protein from Aequorea victoria are reported on structural events during the photocycle. Concomitant with rapid H/D transfer following excitation of the neutral A state at 400 nm, a transient signal at 1721/1711 cm(-1) (H/D) developed belonging to protonated glutamate 222, which was definitively assigned using the E222D mutant from the altered proton-transfer kinetics to aspartate in addition to the altered band position and intensity in the spectra. A transient at 1697 cm(-1), assigned to a structural perturbation of glutamine 69, had a H/D kinetic isotope effect of >32, showing the conformational dynamics to be sensitive to the active site H/D vibrations. The kinetic data up to 2 ns after excitation in the 1250-1800 cm(-1) region in D2O provided 10 and 75 ps time constants for the excited-state deuteron transfer and the associated A1* - A1 and A2* - A2 difference spectra and showed the radiative intermediate I state vibrations and the transient accumulation of the long-lived ground-state intermediate I2. Assignments of chromophore modes for the A1, A2, and I2 ground states are proposed on the basis of published model compound studies (Esposito, A. P.; Schellenberg, P.; Parson, W. W.; Reid, P. J. J. Mol. Struct. 2001, 569, 25 and He, X.; Bell, A. F.; Tonge, P. J. J. Phys. Chem. B 2002, 106, 6056). Tentative assignments for the singlet-state intermediates A1*, A2*, and I* are discussed. An unexpected and unassigned band that may be a C=C chromophore vibration was observed in the ground state (1665 cm(-1)) as well as in all photocycle intermediates. Optical dumping of the transient I population was achieved using an additional 532 nm pulse and the directly obtained I2 - I* difference spectrum was highly similar to the I2 - I* photocycle spectrum. The pump-dump-probe spectrum differed from the pump-probe photocycle difference spectrum with respect to the intensity of the phenol 1 mode at 1578 cm(-1), suggesting stronger delocalization of the negative charge onto the phenolic ring of the anionic chromophore in the dumped I2 state. Indication for structural heterogeneity of the chromophore, Glu 222, and the chromophore environment was found in the two parallel proton-transfer reactions and their distinct associated ground- and intermediate-state vibrations. Vibrational spectral markers at 1695 cm(-1) assigned to Gln 69, at 1631 cm(-1) belonging to a C=C mode, and at 1354 cm(-1) belonging to a phenolate vibration further indicated the I2 and I* states to be unrelaxed.

Glutamine↗
PubMed2005

Excited states of nitro-polypyridine metal complexes and their ultrafast decay. Time-resolved IR Absorption, spectroelectrochemistry, and TD-DFT calculations of fac-[Re(Cl)(CO)3(5-nitro-1,10-phenanthroline)].

The lowest absorption band of fac-[Re(Cl)(CO)3(5-NO2-phen)] encompasses two close-lying MLCT transitions. The lower one is directed to LUMO, which is heavily localized on the NO2 group. The UV-vis absorption spectrum is well accounted for by TD-DFT (G03/PBEPBE1/CPCM), provided that the solvent, MeCN, is included in the calculations. Near-UV excitation of fac-[Re(Cl)(CO)3(5-NO2-phen)] populates a triplet metal to ligand charge-transfer excited state, 3MLCT, that was characterized by picosecond time-resolved IR spectroscopy. Large positive shifts of the nu(CO) bands upon excitation (+70 cm(-1) for the A'1 band) signify a very large charge separation between the Re(Cl)(CO)3 unit and the 5-NO2-phen ligand. Details of the excited-state character are revealed by TD-DFT calculated changes of electron density distribution. Experimental excited-state nu(CO) wavenumbers agree well with those calculated by DFT. The 3MLCT state decays with a ca. 10 ps lifetime (in MeCN) into another transient species, that was identified by TRIR and TD-DFT calculations as an intraligand 3npi excited state, whereby the electron density is excited from the NO2 oxygen lone pairs to the pi system of 5-NO2-phen. This state is short-lived, decaying to the ground state with a approximately 30 ps lifetime. The presence of an npi state seems to be the main factor responsible for the lack of emission and the very short lifetimes of 3MLCT states seen in all d6-metal complexes of nitro-polypyridyl ligands. Localization of the excited electron density in the lowest 3MLCT states parallels localization of the extra electron in the reduced state that is characterized by a very small negative shift of the nu(CO) IR bands (-6 cm(-1) for A'1) but a large downward shift of the nu(s)(NO2) IR band. The Re-Cl bond is unusually stable toward reduction, whereas the Cl ligand is readily substituted upon oxidation.

Journal Article↗
PubMed2005

Ultrafast and low barrier motions in the photoreactions of the green fluorescent protein.

Green fluorescent protein (GFP) fluoresces efficiently under blue excitation despite major electrostatic rearrangements resulting from photoionization of the chromophore and neutralization of Glu-222. A competing phototransformation process, which ionizes the chromophore and decarboxylates Glu-222, mimics the electrostatic and structural changes in the fluorescence photocycle. Structural and spectroscopic analysis of the cryogenically stabilized photoproduct at 100 K and a structurally annealed intermediate of the phototransformed protein at 170 K reveals distinct structural relaxations involving protein, chromophore, solvent, and photogenerated CO2. Strong structural changes of the 100 K photoproduct after decarboxylation appear exclusively within 15 angstroms of the chromophore and include the electrostatically driven perturbations of Gln-69, Cys-70, and water molecules in an H-bonding network connecting the chromophore. X-ray crystallography to 1.85 angstroms resolution and static and picosecond time-resolved IR spectroscopy identify structural mechanisms common to phototransformation and to the fluorescence photocycle. In particular, the appearance of a 1697 cm(-1) (+) difference band in both photocycle and phototransformation intermediates is a spectroscopic signature for the structural perturbation of Gln-69. This is taken as evidence for an electrostatically driven dynamic response that is common to both photoreaction pathways. The interactions between the chromophore and the perturbed residues and solvent are decreased or removed in the T203H single and T203H/Q69L double mutants, resulting in a strong reduction of the fluorescence quantum yield. This suggests that the electrostatic response to the transient formation of a buried charge in the wild type is important for the bright fluorescence.

Bacterial Proteins↗
PubMed2005

Ligand-to-diimine/metal-to-diimine charge-transfer excited states of [Re(NCS)(CO)3(alpha-diimine)] (alpha-diimine = 2,2'-bipyridine, di-iPr-N,N-1,4-diazabutadiene). A spectroscopic and computational study.

Two new complexes fac-[Re(NCS)(CO)3(N,N)] (N,N = 2,2'-bipyridine (bpy), di-iPr-N,N-1,4-diazabutadiene (iPr-DAB)) were synthesized and their molecular structures determined by X-ray diffraction. UV-vis absorption, resonance Raman, emission, and picosecond time-resolved IR spectra were measured experimentally and calculated with TD-DFT. A good agreement between experimental and calculated ground- and excited-state spectra is obtained, but only if the solvent (MeCN) is included into calculations and excited state structures are fully optimized at the TD-DFT level. The lowest excited states of the bpy and iPr-DAB complexes are assigned by TD-DFT as 3aA' by comparison of calculated and experimental IR spectra. Excited-state lifetimes of 23 ns and ca. 625 ps were determined for the bpy and DAB complex, respectively, in a fluid solution at room temperature. Biexponential emission decay (1.3, 2.7 micros) observed for [Re(NCS)(CO)3(bpy)] in a 77 K glass indicates the presence of two unequilibrated emissive states. Low-lying electronic transitions and excited states of both complexes have a mixed NCS --> N,N ligand-to-ligand and Re --> N,N metal-to-ligand charge-transfer character (LLCT/MLCT). It originates in mixing between Re d(pi) and NCS pi characters in high-lying occupied MOs. Experimentally, the LLCT/MLCT mixing in the lowest excited state is manifested by shifting the nu(CO) and nu(NC) IR bands to higher and lower wavenumbers, respectively, upon excitation. Resonant enhancement of both nu(CO) and nu(NC) Raman bands indicates that the same LLCT/MLCT character mixing occurs in the lowest allowed electronic transition.

2,2'-Dipyridyl↗
PubMed2005

Pt(II) mono-carbonyl complexes of a cyclometallating 2-(2'-thienyl)-(pyridinato-C,3N') ligand: nature and dynamics of the lowest excited state of the chloro- and thiolato-complexes.

The synthesis of a cyclometallated Pt(II) thiolate carbonyl complex Pt(thpy)(CO)(mts), (thpy = 2-(2'-thienyl)-pyridinate, mts = methylthiosalicylate) is reported. A combination of emission and time-resolved infrared (TRIR) techniques revealed for both Pt(thpy)(CO)(mts) and its chloride analogue Pt(thpy)(CO)Cl the predominant intra 2-(2'-thienyl)-pyridinate 3pi pi* character of the lowest electronic excited state. The unusually short lifetime (780 ps) of the intraligand 3pi pi* lowest excited state of Pt(thpy)(CO)(mts) indicates that this electronic state is influenced by another close-lying excited state, probably charge-transfer in origin.

Journal Article↗
PubMed2005

Ultrafast excited-state dynamics preceding a ligand trans-cis isomerization of fac-[Re(Cl)(CO)3(t-4-styrylpyridine)2] and fac-[Re(t-4-styrylpyridine)(CO)3(2,2'-bipyridine)]+.

UV-vis absorption and resonance Raman spectra of the complexes fac-[Re(Cl)(CO)3(stpy)2] and fac-[Re(stpy)(CO)3(bpy)]+ (stpy = t-4-styrylpyridine, bpy = 2,2'-bipyridine) show that their lowest absorption bands are dominated by stpy-localized intraligand (IL) pi pi* transitions. For the latter complex a Re --> bpy transition contributes to the low-energy part of the absorption band. Optical population of the 1IL excited state of fac-[Re(Cl)(CO)3(stpy)2] is followed by an intersystem crossing (< or =0.9 ps) to an 3IL state with the original planar trans geometry of the stpy ligand. This state undergoes a approximately 90 degrees rotation around the stpy C=C bond with a 11 ps time constant. An electronically excited species with an approximately perpendicular orientation of the phenyl and pyridine rings of the stpy ligand is formed. Conversion to the ground state and isomerization occurs in the nanosecond range. Intraligand excited states of fac-[Re(stpy)(CO)3(bpy)]+ show the same behavior. Moreover, it was found that the planar reactive 3IL excited state is rapidly and efficiently populated after optical excitation into the Re --> bpy 1MLCT excited state. A 1MLCT --> 3MLCT intersystem crossing takes place first with a time constant of 0.23 ps followed by an intramolecular energy transfer from the ReI(CO)3(bpy) chromophore to a stpy-localized 3IL state with a 3.5 ps time constant. The fast rate ensures complete conversion. Coordination of the stpy ligand to the ReI center thus switches the ligand trans-cis isomerization mechanism from singlet to triplet (intramolecular sensitization) and, in the case of fac-[Re(stpy)(CO)3(bpy)]+, opens an indirect pathway for population of the reactive 3IL excited state via MLCT states.

Isomerism↗
PubMed2005

Observation of excited-state proton transfer in green fluorescent protein using ultrafast vibrational spectroscopy.

The photodynamics of wtGFP have been studied by ultrafast time-resolved infrared spectroscopy (TIR). In addition to the expected bleaching and transient infrared absorption of bands associated with the chromophore, we observe the dynamics of the proton relay reaction in the protein. Protonation of a protein carboxylate group occurs on the tens of picoseconds time scale following photoexcitation. Comparison with data for mutant GFPs, in which excited-state proton transfer has been disabled, supports the assignment of the carboxylate to the side chain of E222, a component of the hydrogen bonding network that links the two ends of the chromophore. The TIR data show that the rate-limiting step in the proton relay is deprotonation of the chromophore.

Green Fluorescent Proteins↗
PubMed2005

Redox control of light-induced charge separation in a transition metal cluster: photochemistry of a methyl viologen-substituted [Os3(CO)10(alpha-diimine)] cluster.

(Sub)picosecond transient absorption (TA) and time-resolved infrared (TRIR) spectra of the cluster [Os3(CO)10-(AcPy-MV)]2+ (the dication AcPy-MV = AcPy-MV2+ = [2-pyridylacetimine-N-(2-(1'-methyl-4,4'-bipyridine-1,1'-diium-1-yl)ethyl)](PF6)2) (1(2+)) reveal that photoinduced electron transfer to the electron-accepting 4,4'-bipyridine-1,1'-diium (MV2+) moiety competes with the fast relaxation of the initially populated sigmapi excited state of the cluster to the ground state and/or cleavage of an Os-Os bond. The TA spectra of cluster 1(2+) in acetone, obtained by irradiation into its lowest-energy absorption band, show the characteristic absorptions of the one-electron-reduced MV*+ unit at 400 and 615 nm, in accordance with population of a charge-separated (CS) state in which a cluster-core electron has been transferred to the lowest pi orbital of the remote MV2+ unit. This assignment is confirmed by picosecond TRIR spectra that show a large shift of the pilot highest-frequency nu(CO) band of 1(2+) by ca. +40 cm(-1), reflecting the photooxidation of the cluster core. The CS state is populated via fast (4.2 x 10(11) s(-1)) and efficient (88%) oxidative quenching of the optically populated sigmapi excited state and decays biexponentially with lifetimes of 38 and 166 ps (1.2:1 ratio) with a complete regeneration of the parent cluster. About 12% of the cluster molecules in the sigmapi excited state form long-lived open-core biradicals. In strongly coordinating acetonitrile, however, the cluster core-to-MV2+ electron transfer in cluster 1(2+) results in the irreversible formation of secondary photoproducts with a photooxidized cluster core. The photochemical behavior of the [Os3(CO)10(alpha-diimine-MV)]2+ (donor-acceptor) dyad can be controlled by an externally applied electronic bias. Electrochemical one-electron reduction of the MV2+ moiety prior to the irradiation reduces its electron-accepting character to such an extent that the photoinduced electron transfer to MV(*+) is no longer feasible. Instead, the irradiation of reduced cluster 1(*+) results in the reversible formation of an open-core zwitterion, the ultimate photoproduct also observed upon irradiation of related nonsubstituted clusters [Os3(CO)10(alpha-diimine)] in strongly coordinating solvents such as acetonitrile.

Journal Article↗
PubMed2005

A high-sensitivity femtosecond to microsecond time-resolved infrared vibrational spectrometer.

We describe an apparatus that provides, for the first time, a seamless bridge between femtosecond and microsecond time-resolved Raman and infrared vibrational spectroscopy. The laser system comprises an actively Q-switched sub-nanosecond pulsed kilohertz laser electronically synchronized to an ultrafast titanium sapphire regenerative amplifier to within 0.2 ns. The ultrafast amplifier provides the stable probe light source enabling high-sensitivity infrared vibrational spectroscopy of transients. Time-resolved infrared spectra of the excited-state relaxation dynamics of metal carbonyl compounds are presented to illustrate the capability of the apparatus, and transient data is resolved from 1 picosecond to over 100 microseconds. The results are compared to conventional nanosecond Fourier transform infrared (FT-IR) and laser based flash photolysis time-resolved infrared technology.

Computer Systems↗