Bio


I am a Staff Scientist at SLAC National Accelerator Laboratory. I received my master's degree in Chemistry from University of Karlsruhe, Germany, in 2009. In 2012, I finished my PhD degree in Physical Chemistry at Karlsruhe Institute of Technology, Germany. After a postdoctoral stay at Karlsruhe Institute of Technology, I joined the Gühr research group at SLAC National Accelerator Laboratory in 2013. I have been working in my current role as PI of the Excited States in Isolated Molecules group within the Stanford PULSE Institute since 2016.

Education & Certifications


  • Dipl. Chem., Karlsruhe University, Chemistry (2009)
  • Dr. rer. nat., Karlsruhe Institute of Technology, Physical Chemistry (2012)

Professional Interests


I am interested in ultrafast photoinduced dynamics of organic molecules. Ultrafast photoinduced dynamics involve correlated electronic and nuclear motion in the vicinity of conical intersections between different electronic states. To understand in detail, what drives a molecule like cyclohexadiene to undergo an electrocyclic reaction within less than 100 femtoseconds after absorption of an ultraviolet photon or a nucleobase like thymine to instead dissipate the absorbed energy into heat on the same timescale, direct access to the electronic and nuclear dynamics on the timescale of those processes is required. To achieve this, I combine femtosecond time-resolved gas phase VUV and soft x-ray spectroscopy to investigate ultrafast changes in the electronic structure with electron diffraction to obtain exclusive access to the correlated dynamics of the nuclear wavepacket.

Professional Affiliations and Activities


  • Principal Investigator of the Excited States in Isolate Molecules group, Stanford PULSE Institute (2016 - Present)

All Publications


  • Site-specific interrogation of an ionic chiral fragment during photolysis using an X-ray free-electron laser COMMUNICATIONS CHEMISTRY Ilchen, M., Schmidt, P., Novikovskiy, N. M., Hartmann, G., Rupprecht, P., Coffee, R. N., Ehresmann, A., Galler, A., Hartmann, N., Helml, W., Huang, Z., Inhester, L., Lutman, A. A., MacArthur, J. P., Maxwell, T., Meyer, M., Music, V., Nuhn, H., Osipov, T., Ray, D., Wolf, T. A., Bari, S., Walter, P., Li, Z., Moeller, S., Knie, A., Demekhin, P. V. 2021; 4 (1)
  • Direct observation of ultrafast hydrogen bond strengthening in liquid water. Nature Yang, J., Dettori, R., Nunes, J. P., List, N. H., Biasin, E., Centurion, M., Chen, Z., Cordones, A. A., Deponte, D. P., Heinz, T. F., Kozina, M. E., Ledbetter, K., Lin, M., Lindenberg, A. M., Mo, M., Nilsson, A., Shen, X., Wolf, T. J., Donadio, D., Gaffney, K. J., Martinez, T. J., Wang, X. 2021; 596 (7873): 531-535

    Abstract

    Water is one of the most important, yet least understood, liquids in nature. Many anomalous properties of liquid water originate from its well-connected hydrogen bond network1, including unusually efficient vibrational energy redistribution and relaxation2. An accurate description of the ultrafast vibrational motion of water molecules is essential for understanding the nature of hydrogen bonds and many solution-phase chemical reactions. Most existing knowledge of vibrational relaxation in water is built upon ultrafast spectroscopy experiments2-7. However, these experiments cannot directly resolve the motion of the atomic positions and require difficult translation of spectral dynamics into hydrogen bond dynamics. Here, we measure the ultrafast structural response to the excitation of the OH stretching vibration in liquid water with femtosecond temporal and atomic spatial resolution using liquid ultrafast electron scattering. We observed a transient hydrogen bond contraction of roughly 0.04A on a timescale of 80 femtoseconds, followed by a thermalization on a timescale of approximately 1 picosecond. Molecular dynamics simulations reveal the need to treat the distribution of the shared proton in the hydrogen bond quantum mechanically to capture the structural dynamics on femtosecond timescales. Our experiment and simulations unveil the intermolecular character of the water vibration preceding the relaxation of the OH stretch.

    View details for DOI 10.1038/s41586-021-03793-9

    View details for PubMedID 34433948

  • Transient resonant Auger-Meitner spectra of photoexcited thymine. Faraday discussions Wolf, T. J., Paul, A. C., Folkestad, S. D., Myhre, R. H., Cryan, J. P., Berrah, N., Bucksbaum, P. H., Coriani, S., Coslovich, G., Feifel, R., Martinez, T. J., Moeller, S. P., Mucke, M., Obaid, R., Plekan, O., Squibb, R. J., Koch, H., Guhr, M. 2021

    Abstract

    We present the first investigation of excited state dynamics by resonant Auger-Meitner spectroscopy (also known as resonant Auger spectroscopy) using the nucleobase thymine as an example. Thymine is photoexcited in the UV and probed with X-ray photon energies at and below the oxygen K-edge. After initial photoexcitation to a pipi* excited state, thymine is known to undergo internal conversion to an npi* excited state with a strong resonance at the oxygen K-edge, red-shifted from the ground state pi* resonances of thymine (see our previous study Wolf, et al., Nat. Commun., 2017, 8, 29). We resolve and compare the Auger-Meitner electron spectra associated both with the excited state and ground state resonances, and distinguish participator and spectator decay contributions. Furthermore, we observe simultaneously with the decay of the npi* state signatures the appearance of additional resonant Auger-Meitner contributions at photon energies between the npi* state and the ground state resonances. We assign these contributions to population transfer from the npi* state to a pipi* triplet state via intersystem crossing on the picosecond timescale based on simulations of the X-ray absorption spectra in the vibrationally hot triplet state. Moreover, we identify signatures from the initially excited pipi* singlet state which we have not observed in our previous study.

    View details for DOI 10.1039/d0fd00112k

    View details for PubMedID 33566045

  • Electron-ion coincidence measurements of molecular dynamics with intense X-ray pulses. Scientific reports Li, X., Inhester, L., Osipov, T., Boll, R., Coffee, R., Cryan, J., Gatton, A., Gorkhover, T., Hartman, G., Ilchen, M., Knie, A., Lin, M., Minitti, M. P., Weninger, C., Wolf, T. J., Son, S., Santra, R., Rolles, D., Rudenko, A., Walter, P. 2021; 11 (1): 505

    Abstract

    Molecules can sequentially absorb multiple photons when irradiated by an intense X-ray pulse from a free-electron laser. If the time delay between two photoabsorption events can be determined, this enables pump-probe experiments with a single X-ray pulse, where the absorption of the first photon induces electronic and nuclear dynamics that are probed by the absorption of the second photon. Here we show a realization of such a single-pulse X-ray pump-probe scheme on N[Formula: see text] molecules, using the X-ray induced dissociation process as an internal clock that is read out via coincident detection of photoelectrons and fragment ions. By coincidence analysis of the kinetic energies of the ionic fragments and photoelectrons, the transition from a bound molecular dication to two isolated atomic ions is observed through the energy shift of the inner-shell electrons. Via ab-initio simulations, we are able to map characteristic features in the kinetic energy release and photoelectron spectrum to specific delay times between photoabsorptions. In contrast to previous studies where nuclear motions were typically revealed by measuring ion kinetics, our work shows that inner-shell photoelectron energies can also be sensitive probes of nuclear dynamics, which adds one more dimension to the study of light-matter interactions with X-ray pulses.

    View details for DOI 10.1038/s41598-020-79818-6

    View details for PubMedID 33436816

  • Structure retrieval in liquid-phase electron scattering. Physical chemistry chemical physics : PCCP Yang, J., Nunes, J. P., Ledbetter, K., Biasin, E., Centurion, M., Chen, Z., Cordones, A. A., Crissman, C., Deponte, D. P., Glenzer, S. H., Lin, M., Mo, M., Rankine, C. D., Shen, X., Wolf, T. J., Wang, X. 2020

    Abstract

    Electron scattering on liquid samples has been enabled recently by the development of ultrathin liquid sheet technologies. The data treatment of liquid-phase electron scattering has been mostly reliant on methodologies developed for gas electron diffraction, in which theoretical inputs and empirical fittings are often needed to account for the atomic form factor and remove the inelastic scattering background. In this work, we present an alternative data treatment method that is able to retrieve the radial distribution of all the charged particle pairs without the need of either theoretical inputs or empirical fittings. The merits of this new method are illustrated through the retrieval of real-space molecular structure from experimental electron scattering patterns of liquid water, carbon tetrachloride, chloroform, and dichloromethane.

    View details for DOI 10.1039/d0cp06045c

    View details for PubMedID 33367391

  • Spectroscopic and Structural Probing of Excited-State Molecular Dynamics with Time-Resolved Photoelectron Spectroscopy and Ultrafast Electron Diffraction PHYSICAL REVIEW X Liu, Y., Horton, S. L., Yang, J., Nunes, J. F., Shen, X., Wolfe, T. A., Forbes, R., Cheng, C., Moore, B., Centurion, M., Hegazy, K., Li, R., Lin, M., Stolow, A., Hockett, P., Rozgonyi, T., Marquetande, P., Wang, X., Weinacht, T. 2020; 10 (2)
  • Liquid-phase mega-electron-volt ultrafast electron diffraction STRUCTURAL DYNAMICS-US Nunes, J. F., Ledbetter, K., Lin, M., Kozina, M., DePonte, D. P., Biasin, E., Centurion, M., Crissman, C. J., Dunning, M., Guillet, S., Jobe, K., Liu, Y., Mo, M., Shen, X., Sublett, R., Weathersby, S., Yoneda, C., Wolf, T. A., Yang, J., Cordones, A. A., Wang, X. J. 2020; 7 (2): 024301

    Abstract

    The conversion of light into usable chemical and mechanical energy is pivotal to several biological and chemical processes, many of which occur in solution. To understand the structure-function relationships mediating these processes, a technique with high spatial and temporal resolutions is required. Here, we report on the design and commissioning of a liquid-phase mega-electron-volt (MeV) ultrafast electron diffraction instrument for the study of structural dynamics in solution. Limitations posed by the shallow penetration depth of electrons and the resulting information loss due to multiple scattering and the technical challenge of delivering liquids to vacuum were overcome through the use of MeV electrons and a gas-accelerated thin liquid sheet jet. To demonstrate the capabilities of this instrument, the structure of water and its network were resolved up to the 3 rd hydration shell with a spatial resolution of 0.6 Å; preliminary time-resolved experiments demonstrated a temporal resolution of 200 fs.

    View details for DOI 10.1063/1.5144518

    View details for Web of Science ID 000531214100001

    View details for PubMedID 32161776

    View details for PubMedCentralID PMC7062553

  • Intermolecular Coulombic Decay in Endohedral Fullerene at the 4d→4f Resonance. Physical review letters Obaid, R. n., Xiong, H. n., Augustin, S. n., Schnorr, K. n., Ablikim, U. n., Battistoni, A. n., Wolf, T. J., Bilodeau, R. C., Osipov, T. n., Gokhberg, K. n., Rolles, D. n., LaForge, A. C., Berrah, N. n. 2020; 124 (11): 113002

    Abstract

    Intermolecular processes offer unique decay mechanisms for complex systems to internally relax. Here, we report the observation of an intermolecular Coulombic decay channel in an endohedral fullerene, a holmium nitride complex (Ho_{3}N) embedded within a C_{80} fullerene, between neighboring holmium ions, and between the holmium complex and the carbon cage. By measuring the ions and the electrons in coincidence after XUV photoabsorption, we can isolate the different decay channels, which are found to be more prevalent relative to intra-atomic Auger decay.

    View details for DOI 10.1103/PhysRevLett.124.113002

    View details for PubMedID 32242685

  • Simultaneous observation of nuclear and electronic dynamics by ultrafast electron diffraction. Science (New York, N.Y.) Yang, J. n., Zhu, X. n., F Nunes, J. P., Yu, J. K., Parrish, R. M., Wolf, T. J., Centurion, M. n., Gühr, M. n., Li, R. n., Liu, Y. n., Moore, B. n., Niebuhr, M. n., Park, S. n., Shen, X. n., Weathersby, S. n., Weinacht, T. n., Martinez, T. J., Wang, X. n. 2020; 368 (6493): 885–89

    Abstract

    Simultaneous observation of nuclear and electronic motion is crucial for a complete understanding of molecular dynamics in excited electronic states. It is challenging for a single experiment to independently follow both electronic and nuclear dynamics at the same time. Here we show that ultrafast electron diffraction can be used to simultaneously record both electronic and nuclear dynamics in isolated pyridine molecules, naturally disentangling the two components. Electronic state changes (S1→S0 internal conversion) were reflected by a strong transient signal in small-angle inelastic scattering, and nuclear structural changes (ring puckering) were monitored by large-angle elastic diffraction. Supported by ab initio nonadiabatic molecular dynamics and diffraction simulations, our experiment provides a clear view of the interplay between electronic and nuclear dynamics of the photoexcited pyridine molecule.

    View details for DOI 10.1126/science.abb2235

    View details for PubMedID 32439793

  • Tunable isolated attosecond X-ray pulses with gigawatt peak power from a free-electron laser NATURE PHOTONICS Duris, J., Li, S., Driver, T., Champenois, E. G., MacArthur, J. P., Lutman, A. A., Zhang, Z., Rosenberger, P., Aldrich, J. W., Coffee, R., Coslovich, G., Decker, F., Glownia, J. M., Hartmann, G., Helml, W., Kamalov, A., Knurr, J., Krzywinski, J., Lin, M., Nantel, M., Natan, A., O'Neal, J., Shivaram, N., Walter, P., Wang, A., Welch, J. J., Wolf, T. A., Xu, J. Z., Kling, M. F., Bucksbaum, P. H., Zholents, A., Huang, Z., Cryan, J. P., Marinelli, A., Marangos, J. P. 2020; 14 (1): 30-+
  • Attosecond transient absorption spooktroscopy: a ghost imaging approach to ultrafast absorption spectroscopy. Physical chemistry chemical physics : PCCP Driver, T., Li, S., Champenois, E. G., Duris, J., Ratner, D., Lane, T. J., Rosenberger, P., Al-Haddad, A., Averbukh, V., Barnard, T., Berrah, N., Bostedt, C., Bucksbaum, P. H., Coffee, R., DiMauro, L. F., Fang, L., Garratt, D., Gatton, A., Guo, Z., Hartmann, G., Haxton, D., Helml, W., Huang, Z., LaForge, A., Kamalov, A., Kling, M. F., Knurr, J., Lin, M., Lutman, A. A., MacArthur, J. P., Marangos, J. P., Nantel, M., Natan, A., Obaid, R., O'Neal, J. T., Shivaram, N. H., Schori, A., Walter, P., Li Wang, A., Wolf, T. J., Marinelli, A., Cryan, J. P. 2019

    Abstract

    The recent demonstration of isolated attosecond pulses from an X-ray free-electron laser (XFEL) opens the possibility for probing ultrafast electron dynamics at X-ray wavelengths. An established experimental method for probing ultrafast dynamics is X-ray transient absorption spectroscopy, where the X-ray absorption spectrum is measured by scanning the central photon energy and recording the resultant photoproducts. The spectral bandwidth inherent to attosecond pulses is wide compared to the resonant features typically probed, which generally precludes the application of this technique in the attosecond regime. In this paper we propose and demonstrate a new technique to conduct transient absorption spectroscopy with broad bandwidth attosecond pulses with the aid of ghost imaging, recovering sub-bandwidth resolution in photoproduct-based absorption measurements.

    View details for DOI 10.1039/c9cp03951a

    View details for PubMedID 31793561

  • Femtosecond-resolved observation of the fragmentation of buckminsterfullerene following X-ray multiphoton ionization NATURE PHYSICS Berrah, N., Sanchez-Gonzalez, A., Jurek, Z., Obaid, R., Xiong, H., Squibb, R. J., Osipov, T., Lutman, A., Fang, L., Barillot, T., Bozek, J. D., Cryan, J., Wolf, T. A., Rolles, D., Coffee, R., Schnorr, K., Augustin, S., Fukuzawa, H., Motomura, K., Niebuhr, N., Frasinski, L. J., Feifel, R., Schulz, C. P., Toyota, K., Son, S., Ueda, K., Pfeifer, T., Marangos, J. P., Santra, R. 2019; 15 (12): 1279-+
  • Spectroscopic Signature of Chemical Bond Dissociation Revealed by Calculated Core-Electron Spectra. The journal of physical chemistry letters Inhester, L., Li, Z., Zhu, X., Medvedev, N., Wolf, T. J. 2019: 6536–44

    Abstract

    The advent of ultrashort soft X-ray pulse sources permits the use of established gas-phase spectroscopy methods to investigate ultrafast photochemistry in isolated molecules with element and site specificity. In the present study, we simulate excited-state wavepacket dynamics of a prototypical process, the ultrafast photodissociation of methyl iodide. Using the simulation, we calculate time-dependent excited-state carbon edge photoelectron and Auger electron spectra. We observe distinct signatures in both types of spectra and show their direct connection to C-I bond dissociation and charge rearrangement processes in the molecule. We demonstrate at the CH3I molecule that the observed signatures allow us to map the time-dependent dynamics of ultrafast photoinduced bond breaking with unprecedented detail.

    View details for DOI 10.1021/acs.jpclett.9b02370

    View details for PubMedID 31589459

  • Femtosecond gas-phase mega-electron-volt ultrafast electron diffraction. Structural dynamics (Melville, N.Y.) Shen, X., Nunes, J. P., Yang, J., Jobe, R. K., Li, R. K., Lin, M., Moore, B., Niebuhr, M., Weathersby, S. P., Wolf, T. J., Yoneda, C., Guehr, M., Centurion, M., Wang, X. J. 2019; 6 (5): 054305

    Abstract

    The development of ultrafast gas electron diffraction with nonrelativistic electrons has enabled the determination of molecular structures with atomic spatial resolution. It has, however, been challenging to break the picosecond temporal resolution barrier and achieve the goal that has long been envisioned-making space- and-time resolved molecular movies of chemical reaction in the gas-phase. Recently, an ultrafast electron diffraction (UED) apparatus using mega-electron-volt (MeV) electrons was developed at the SLAC National Accelerator Laboratory for imaging ultrafast structural dynamics of molecules in the gas phase. The SLAC gas-phase MeV UED has achieved 65 fs root mean square temporal resolution, 0.63A spatial resolution, and 0.22A-1 reciprocal-space resolution. Such high spatial-temporal resolution has enabled the capturing of real-time molecular movies of fundamental photochemical mechanisms, such as chemical bond breaking, ring opening, and a nuclear wave packet crossing a conical intersection. In this paper, the design that enables the high spatial-temporal resolution of the SLAC gas phase MeV UED is presented. The compact design of the differential pump section of the SLAC gas phase MeV UED realized five orders-of-magnitude vacuum isolation between the electron source and gas sample chamber. The spatial resolution, temporal resolution, and long-term stability of the apparatus are systematically characterized.

    View details for DOI 10.1063/1.5120864

    View details for PubMedID 31649964

  • Diffractive imaging of dissociation and ground-state dynamics in a complex molecule PHYSICAL REVIEW A Wilkin, K. J., Parrish, R. M., Yang, J., Wolf, T. A., Nunes, J. F., Guehr, M., Li, R., Shen, X., Zheng, Q., Wang, X., Martinez, T. J., Centurion, M. 2019; 100 (2)
  • The photochemical ring-opening of 1,3-cyclohexadiene imaged by ultrafast electron diffraction NATURE CHEMISTRY Wolf, T. A., Sanchez, D. M., Yang, J., Parrish, R. M., Nunes, J. F., Centurion, M., Coffee, R., Cryan, J. P., Guehr, M., Hegazy, K., Kirrander, A., Li, R. K., Ruddock, J., Shen, X., Vecchione, T., Weathersby, S. P., Weber, P. M., Wilkin, K., Yong, H., Zheng, Q., Wang, X. J., Minitti, M. P., Martinez, T. J. 2019; 11 (6): 504–9
  • Photochemical pathways in nucleobases measured with an X-ray FEL. Philosophical transactions. Series A, Mathematical, physical, and engineering sciences Wolf, T. J., Guhr, M. 2019; 377 (2145): 20170473

    Abstract

    The conversion of light energy into other molecular energetic degrees of freedom is often dominated by ultrafast, non-adiabatic processes. Femtosecond spectroscopy with optical pulses has helped in shaping our understanding of crucial processes in molecular energy-conversion. The advent of new, ultrashort and bright X-ray free electron laser sources opens the possibility to use X-ray-typical element and site sensitivity for ultrafast molecular research. We present two types of spectroscopy, ultrafast Auger and ultrafast X-ray absorption spectroscopy, and discuss their sensitivity to molecular processes. While Auger spectroscopy is able to monitor bond distance changes in the vicinity of an X-ray created core hole, near-edge absorption spectroscopy can deliver high-fidelity information on non-adiabatic transitions involving lone-pair orbitals. We demonstrate these features on the example of the UV-excited nucleobase thymine, investigated at the oxygen K-edge. We find a C-O bond elongation in the Auger data in addition to pipi*/ npi* non-adiabatic transition in X-ray near-edge absorption. We compare the results from both methods and draw a conclusive scenario of non-adiabatic molecular relaxation after UV excitation. This article is part of the theme issue 'Measurement of ultrafast electronic and structural dynamics with X-rays'.

    View details for DOI 10.1098/rsta.2017.0473

    View details for PubMedID 30929626

  • Observation of Ultrafast Intersystem Crossing in Thymine by Extreme Ultraviolet Time-Resolved Photoelectron Spectroscopy. The journal of physical chemistry. A Wolf, T. J., Parrish, R. M., Myhre, R. H., Martínez, T. J., Koch, H. n., Gühr, M. n. 2019

    Abstract

    We studied the photoinduced ultrafast relaxation dynamics of the nucleobase thymine using gas-phase time-resolved photoelectron spectroscopy. By employing extreme ultraviolet pulses from high harmonic generation for photoionization, we substantially extend our spectral observation window with respect to previous studies. This enables us to follow relaxation of the excited state population all the way to low-lying electronic states including the ground state. In thymine, we observe relaxation from the optically bright 1ππ* state of thymine to a dark 1nπ* state within 80 ± 30 fs. The 1nπ* state relaxes further within 3.5 ± 0.3 ps to a low-lying electronic state. By comparison with quantum chemical simulations, we can unambiguously assign its spectroscopic signature to the 3ππ* state. Hence, our study draws a comprehensive picture of the relaxation mechanism of thymine including ultrafast intersystem crossing to the triplet manifold.

    View details for DOI 10.1021/acs.jpca.9b05573

    View details for PubMedID 31319031

  • Photo-ionization and fragmentation of Sc3N@C80 following excitation above the Sc K-edge. The Journal of chemical physics Obaid, R. n., Schnorr, K. n., Wolf, T. J., Takanashi, T. n., Kling, N. G., Kooser, K. n., Nagaya, K. n., Wada, S. I., Fang, L. n., Augustin, S. n., You, D. n., Campbell, E. E., Fukuzawa, H. n., Schulz, C. P., Ueda, K. n., Lablanquie, P. n., Pfeifer, T. n., Kukk, E. n., Berrah, N. n. 2019; 151 (10): 104308

    Abstract

    We have investigated the ionization and fragmentation of a metallo-endohedral fullerene, Sc3N@C80, using ultrashort (10 fs) x-ray pulses. Following selective ionization of a Sc (1s) electron (hν = 4.55 keV), an Auger cascade leads predominantly to either a vibrationally cold multiply charged parent molecule or multifragmentation of the carbon cage following a phase transition. In contrast to previous studies, no intermediate regime of C2 evaporation from the carbon cage is observed. A time-delayed, hard x-ray pulse (hν = 5.0 keV) was used to attempt to probe the electron transfer dynamics between the encapsulated Sc species and the carbon cage. A small but significant change in the intensity of Sc-containing fragment ions and coincidence counts for a delay of 100 fs compared to 0 fs, as well as an increase in the yield of small carbon fragment ions, may be indicative of incomplete charge transfer from the carbon cage on the sub-100 fs time scale.

    View details for DOI 10.1063/1.5110297

    View details for PubMedID 31521092

  • Generation and Characterization of Attosecond Pulses from an X-ray Free-electron Laser Li, S., Rosenberger, P., Champenois, E. G., Driver, T., Bucksbaum, P. H., Coffee, R., Gatton, A., Hartmann, G., Helml, W., Huang, Z., Knurr, J., Kling, M. F., Lin, M., MacArthur, J. P., Maxwell, T. J., Nantel, M., Natan, A., Oneal, J. T., Shivaram, N. H., Walter, P., Wolf, T. A., Cryan, J. P., Marinelli, A., IEEE IEEE. 2019
  • A tilted pulse-front setup for femtosecond transient grating spectroscopy in highly non-collinear geometries JOURNAL OF OPTICS Battistoni, A., Durr, H. A., Guehr, M., Wolf, T. A. 2018; 20 (9)
  • Normal and resonant Auger spectroscopy of isocyanic acid, HNCO JOURNAL OF CHEMICAL PHYSICS Holzmeier, F., Wolf, T. A., Gienger, C., Wagner, Bozek, J., Nandi, S., Nicolas, C., Fischer, Guehr, M., Fink, R. F. 2018; 149 (3): 034308

    Abstract

    In this paper, we investigate HNCO by resonant and nonresonant Auger electron spectroscopy at the K-edges of carbon, nitrogen, and oxygen, employing soft X-ray synchrotron radiation. In comparison with the isosteric but linear CO2 molecule, spectra of the bent HNCO molecule are similar but more complex due to its reduced symmetry, wherein the degeneracy of the π-orbitals is lifted. Resonant Auger electron spectra are presented at different photon energies over the first core-excited 1s → 10a' resonance. All Auger electron spectra are assigned based on ab initio configuration interaction computations combined with the one-center approximation for Auger intensities and moment theory to consider vibrational motion. The calculated spectra were scaled by a newly introduced energy scaling factor, and generally, good agreement is found between experiment and theory for normal as well as resonant Auger electron spectra. A comparison of resonant Auger spectra with nonresonant Auger structures shows a slight broadening as well as a shift of the former spectra between -8 and -9 eV due to the spectating electron. Since HNCO is a small molecule and contains the four most abundant atoms of organic molecules, the reported Auger electron decay spectra will provide a benchmark for further theoretical approaches in the computation of core electron spectra.

    View details for DOI 10.1063/1.5030621

    View details for Web of Science ID 000439428400024

    View details for PubMedID 30037265

  • Fragmentation of endohedral fullerene Ho3N@C-80 in an intense femtosecond near-infrared laser field PHYSICAL REVIEW A Xiong, H., Fang, L., Osipov, T., Kling, N. G., Wolf, T. A., Sistrunk, E., Obaid, R., Guehr, M., Berrah, N. 2018; 97 (2)
  • A theoretical and experimental benchmark study of core-excited states in nitrogen JOURNAL OF CHEMICAL PHYSICS Myhre, R. H., Wolf, T. A., Cheng, L., Nandi, S., Coriani, S., Guhr, M., Koch, H. 2018; 148 (6): 064106

    Abstract

    The high resolution near edge X-ray absorption fine structure spectrum of nitrogen displays the vibrational structure of the core-excited states. This makes nitrogen well suited for assessing the accuracy of different electronic structure methods for core excitations. We report high resolution experimental measurements performed at the SOLEIL synchrotron facility. These are compared with theoretical spectra calculated using coupled cluster theory and algebraic diagrammatic construction theory. The coupled cluster singles and doubles with perturbative triples model known as CC3 is shown to accurately reproduce the experimental excitation energies as well as the spacing of the vibrational transitions. The computational results are also shown to be systematically improved within the coupled cluster hierarchy, with the coupled cluster singles, doubles, triples, and quadruples method faithfully reproducing the experimental vibrational structure.

    View details for DOI 10.1063/1.5011148

    View details for Web of Science ID 000425299800006

    View details for PubMedID 29448773

  • Time-resolved photoelectron spectroscopy of nitrobenzene and its aldehydes CHEMICAL PHYSICS LETTERS Schalk, O., Townsend, D., Wolf, T. A., Holland, D. P., Boguslavskiy, A. E., Szori, M., Stolow, A. 2018; 691: 379–87
  • Imaging CF3I conical intersection and photodissociation dynamics with ultrafast electron diffraction Science Yang, J., Zhu, X., Wolf, T. J., Li, Z., Nunes, J. F., Coffee, R., Cryan, J. P., Gühr, M., Hegazy, K., Heinz, T. F., Jobe, K., Li, R., Shen, X., Veccione, T., Weathersby, S., Wilkin, K. J., Yoneda, C., Zheng, Q., Martinez, T. J., Centurion, M., Wang, X. 2018; 361 (6397): 64-67

    View details for DOI 10.1126/science.aat0049

  • Soft-x-ray-induced ionization and fragmentation dynamics of Sc3N@C-80 investigated using an ion-ion-coincidence momentum-imaging technique PHYSICAL REVIEW A Xiong, H., Obaid, R., Fang, L., Bomme, C., Kling, N. G., Ablikim, U., Petrovic, V., Liekhus-Schmaltz, C. E., Li, H., Bilodeau, R. C., Wolf, T., Osipov, T., Rolles, D., Berrah, N. 2017; 96 (3)
  • Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra APPLIED SCIENCES-BASEL Wolf, T. A., Holzmeier, F., Wagner, I., Berrah, N., Bostedt, C., Bozek, J., Bucksbaum, P., Coffee, R., Cryan, J., Farrell, J., Feifel, R., Martinez, T. J., McFarland, B., Mucke, M., Nandi, S., Tarantelli, F., Fischer, I., Guhr, M. 2017; 7 (7)

    View details for DOI 10.3390/app7070681

    View details for Web of Science ID 000407700400038

  • Probing ultrafast pi pi*/n pi* internal conversion in organic chromophores via K-edge resonant absorption NATURE COMMUNICATIONS Wolf, T. A., Myhre, R. H., Cryan, J. P., Coriani, S., Squibb, R. J., Battistoni, A., Berrah, N., Bostedt, C., Bucksbaum, P., Coslovich, G., Feifel, R., Gaffney, K. J., Grilj, J., Martinez, T. J., Miyabe, S., Moeller, S. P., Mucke, M., Natan, A., Obaid, R., Osipov, T., Plekan, O., Wang, S., Koch, H., Guehr, M. 2017; 8: 29

    Abstract

    Many photoinduced processes including photosynthesis and human vision happen in organic molecules and involve coupled femtosecond dynamics of nuclei and electrons. Organic molecules with heteroatoms often possess an important excited-state relaxation channel from an optically allowed ππ* to a dark nπ* state. The ππ*/nπ* internal conversion is difficult to investigate, as most spectroscopic methods are not exclusively sensitive to changes in the excited-state electronic structure. Here, we report achieving the required sensitivity by exploiting the element and site specificity of near-edge soft X-ray absorption spectroscopy. As a hole forms in the n orbital during ππ*/nπ* internal conversion, the absorption spectrum at the heteroatom K-edge exhibits an additional resonance. We demonstrate the concept using the nucleobase thymine at the oxygen K-edge, and unambiguously show that ππ*/nπ* internal conversion takes place within (60 ± 30) fs. High-level-coupled cluster calculations confirm the method's impressive electronic structure sensitivity for excited-state investigations.Many photo-induced processes such as photosynthesis occur in organic molecules, but their femtosecond excited-state dynamics are difficult to track. Here, the authors exploit the element and site selectivity of soft X-ray absorption to sensitively follow the ultrafast ππ*/nπ* electronic relaxation of hetero-organic molecules.

    View details for PubMedID 28642477

  • Emitter-site-selective photoelectron circular dichroism of trifluoromethyloxirane PHYSICAL REVIEW A Ilchen, M., Hartmann, G., Rupprecht, P., Artemyev, A. N., Coffee, R. N., Li, Z., Ohldag, H., Ogasawara, H., Osipov, T., Ray, D., Schmidt, P., Wolf, T. A., Ehresmann, A., Moeller, S., Knie, A., Demekhin, P. V. 2017; 95 (5)
  • The Role of Super-Atom Molecular Orbitals in Doped Fullerenes in a Femtosecond Intense Laser Field SCIENTIFIC REPORTS Xiong, H., Mignolet, B., Fang, L., Osipov, T., Wolf, T. J., Sistrunk, E., Guehr, M., Remacle, F., Berrah, N. 2017; 7

    Abstract

    The interaction of gas phase endohedral fullerene Ho3N@C80 with intense (0.1-5 × 10(14) W/cm(2)), short (30 fs), 800 nm laser pulses was investigated. The power law dependence of Ho3N@C80(q+), q = 1-2, was found to be different from that of C60. Time-dependent density functional theory computations revealed different light-induced ionization mechanisms. Unlike in C60, in doped fullerenes, the breaking of the cage spherical symmetry makes super atomic molecular orbital (SAMO) states optically active. Theoretical calculations suggest that the fast ionization of the SAMO states in Ho3N@C80 is responsible for the n = 3 power law for singly charged parent molecules at intensities lower than 1.2 × 10(14) W/cm(2).

    View details for DOI 10.1038/s41598-017-00124-9

    View details for Web of Science ID 000396868900003

    View details for PubMedID 28273922

  • Gas Phase Photochemistry Probed by Free Electron Lasers X-Ray Free Electron Lasers: Applications in Materials, Chemistry and Biology Wolf, T. J., Gühr, M. Royal Society of Chemistry. 2017; 1: 173–186
  • Auger electron and photoabsorption spectra of glycine in the vicinity of the oxygen K-edge measured with an X-FEL JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS Sanchez-Gonzalez, A., Barillot, T. R., Squibb, R. J., Kolorenc, P., Agaker, M., Averbukh, V., Bearpark, M. J., Bostedt, C., Bozek, J. D., Bruce, S., Montero, S. C., Coffee, R. N., Cooper, B., Cryan, J. P., Dong, M., Eland, J. H., Fang, L., Fukuzawa, H., Guehr, M., Ilchen, M., Johnsson, A. S., Liekhus-S, C., Marinelli, A., Maxwell, T., Motomura, K., Mucke, M., Natan, A., Osipov, T., Ostlin, C., Pernpointner, M., Petrovic, V. S., ROBB, M. A., Sathe, C., Simpson, E. R., Underwood, J. G., Vacher, M., Walke, D. J., Wolf, T. J., Zhaunerchyk, V., Rubensson, J., Berrah, N., Bucksbaum, P. H., Ueda, K., Feifel, R., Frasinski, L. J., Marangos, J. P. 2015; 48 (23)
  • Ultrafast Dynamics of o-Nitrophenol: An Experimental and Theoretical Study JOURNAL OF PHYSICAL CHEMISTRY A Ernst, H. A., Wolf, T. J., Schalk, O., Gonzalez-Garcia, N., Boguslavskiy, A. E., Stolow, A., Olzmann, M., Unterreiner, A. 2015; 119 (35): 9225-9235

    Abstract

    The photolysis of o-nitrophenol (o-NP), a typical push-pull molecule, is of current interest in atmospheric chemistry as a possible source of nitrous acid (HONO). To characterize the largely unknown photolysis mechanism, the dynamics of the lowest lying excited singlet state (S1) of o-NP was investigated by means of femtosecond transient absorption spectroscopy in solution, time-resolved photoelectron spectroscopy (TRPES) in the gas phase and quantum chemical calculations. Evidence of the unstable aci-nitro isomer is provided both in the liquid and in the gas phase. Our results indicate that the S1 state displays strong charge transfer character, which triggers excited state proton transfer from the OH to the NO2 group as evidenced by a temporal shift of 20 fs of the onset of the photoelectron spectrum. The proton transfer itself is found to be coupled to an out-of-plane rotation of the newly formed HONO group, finally leading to a conical intersection between S1 and the ground state S0. In solution, return to S0 within 0.2-0.3 ps was monitored by stimulated emission. As a competitive relaxation channel, ultrafast intersystem crossing to the upper triplet manifold on a subpicosecond time scale occurs both in solution and in the gas phase. Due to the ultrafast singlet dynamics, we conclude that the much discussed HONO split-off is likely to take place in the triplet manifold.

    View details for DOI 10.1021/acs.jpca.5b04900

    View details for Web of Science ID 000360947700004

    View details for PubMedID 26266823

  • Understanding the modulation mechanism in resonance-enhanced multiphoton probing of molecular dynamics PHYSICAL REVIEW A Koch, M., Wolf, T. J., Guehr, M. 2015; 91 (3)
  • Direct Comparison of Multi-photon and EUV Single-Photon Probing of Molecular Relaxation Processes Wolf, T. A., Koch, M., Sistrunk, E., Grilj, J., Guehr, M., Yamanouchi, Cundiff, S., DeVivieRiedle, R., KuwataGonokami, M., DiMauro, L. SPRINGER-VERLAG BERLIN. 2015: 48–51
  • Time-Resolved Photoelectron Spectroscopy and Ab Initio Multiple Spawning Studies of Hexamethylcyclopentadiene Wolf, T. A., Kuhlman, T. S., Schalk, O., Martinez, T. J., Moller, K. B., Stolow, A., Unterreiner, A., Yamanouchi, Cundiff, S., DeVivieRiedle, R., KuwataGonokami, M., DiMauro, L. SPRINGER-VERLAG BERLIN. 2015: 184–87
  • Femtosecond photoelectron and photoion spectrometer with vacuum ultraviolet probe pulses JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA Koch, M., Wolf, T. J., Grilj, J., Sistrunk, E., Guehr, M. 2014; 197: 22-29
  • Studying the polymerization initiation efficiency of acetophenone-type initiators via PLP-ESI-MS and femtosecond spectroscopy POLYMER CHEMISTRY Frick, E., Ernst, H. A., Voll, D., Wolf, T. J., Unterreiner, A., Barner-Kowollik, C. 2014; 5 (17): 5053-5068

    View details for DOI 10.1039/c4py00418c

    View details for Web of Science ID 000340581200023

  • Hexamethylcyclopentadiene: time-resolved photoelectron spectroscopy and ab initio multiple spawning simulations. Physical chemistry chemical physics Wolf, T. J., Kuhlman, T. S., Schalk, O., Martínez, T. J., Møller, K. B., Stolow, A., Unterreiner, A. 2014; 16 (23): 11770-11779

    Abstract

    Progress in our understanding of ultrafast light-induced processes in molecules is best achieved through a close combination of experimental and theoretical approaches. Direct comparison is obtained if theory is able to directly reproduce experimental observables. Here, we present a joint approach comparing time-resolved photoelectron spectroscopy (TRPES) with ab initio multiple spawning (AIMS) simulations on the MS-MR-CASPT2 level of theory. We disentangle the relationship between two phenomena that dominate the immediate molecular response upon light absorption: a spectrally dependent delay of the photoelectron signal and an induction time prior to excited state depopulation in dynamics simulations. As a benchmark molecule, we have chosen hexamethylcyclopentadiene, which shows an unprecedentedly large spectral delay of (310 ± 20) fs in TRPES experiments. For the dynamics simulations, methyl groups were replaced by "hydrogen atoms" having mass 15 and TRPES spectra were calculated. These showed an induction time of (108 ± 10) fs which could directly be assigned to progress along a torsional mode leading to the intersection seam with the molecular ground state. In a stepladder-type approach, the close connection between the two phenomena could be elucidated, allowing for a comparison with other polyenes and supporting the general validity of this finding for their excited state dynamics. Thus, the combination of TRPES and AIMS proves to be a powerful tool for a thorough understanding of ultrafast excited state dynamics in polyenes.

    View details for DOI 10.1039/c4cp00977k

    View details for PubMedID 24817114

  • Synthesis and Application of Photolithographically Patternable Deep Blue Emitting Poly(3,6-Dimethoxy-9,9-dialkylsilafluorene)s ACS APPLIED MATERIALS & INTERFACES McDowell, J., Maier-Flaig, F., Wolf, T. A., Unterreiner, A., Lemmer, U., Ozin, G. 2014; 6 (1): 83–93

    Abstract

    Poly(silafluorene)s (PSFs) are promising light-emitting materials with brilliant solid-state blue luminescence, high quantum efficiency, excellent solubility, and improved thermal and chemical stability. PSFs are reported to have high electron affinity and conductivity originating from σ*-π* conjugation between the σ*-antibonding orbital of the exocyclic Si-C bond and the π* antibonding orbital of the butadiene fragment, a promising characteristic for improved charge carrier balance in OLEDs. In this paper, we present a protocol for photopatterning derivatives of poly(3,6-dimethoxy-9,9-dialkylsilafluorenes) with resolutions exceeding 10 μm. The procedure begins by converting polymers (Mn = 50-55 kg/mol, PDI = 1.8) with cyclohexenyl and norbornenyl containing side chains to their respective epoxides using the Prilezhaev reaction and m-chloroperoxybenzoic acid (m-CPBA). Using the I-line (365 nm) of a Karl Suss MA6 mask aligner, a 1 s UV light exposure of the photoacid generator (PAG) bis(4-tert-butylphenyl)iodonium hexafluoro-phosphate (DtBPI-PF6) generates sufficient protons to catalyze epoxide ring-opening and form a bridging network of covalent C-O bonds which renders the material insoluble in developing solvents such as toluene or THF. The resultant cross-linked material possess characteristic blue photoluminescence with solid state quantum yields >80%. Polymer films have excellent transparency (with a measured Eg ≈ 3.0 eV). Energy levels determined using cyclic voltammetry were -5.7 and -2.7 eV for HOMO and LUMO, respectively. Additionally, several device applications are demonstrated which incorporate cross-linked films. These include examples of solid state lasing in the region of 420-450 nm from cross-linked films on second order corrugated silica substrates (Λ = 200 nm). OLEDs were also prepared with a cross-linked emitting layer as part of a trilayer device which we report to have a maximum external quantum efficiency of 3.2% at 33 mA/cm(2) and a stable blue-violet emission with an electroluminescence maximum at 410 nm. Photopatternable PSF epoxides are also shown to be efficient hosts for Förster energy transfer and we provide examples of pattern layers incorporating small molecule emitters which emit in both the red and green while blue emission of the host is effectively suppressed.

    View details for DOI 10.1021/am4025406

    View details for Web of Science ID 000329586300014

    View details for PubMedID 24024545

  • Three-dimensional multi-photon direct laser writing with variable repetition rate OPTICS EXPRESS Fischer, J., Mueller, J. B., Kaschke, J., Wolf, T. A., Unterreiner, A., Wegener, M. 2013; 21 (22): 26244–60

    Abstract

    We perform multi-photon direct laser writing as a function of laser repetition rate over many orders of magnitude and otherwise unchanged experimental conditions. These new data serve as basis for investigating the influence of different proposed mechanisms involved in the photopolymerization: two-photon absorption, photoionization, avalanche ionization and heat accumulation. We find different non-linearities for high and low repetition rates consistent with different initiation processes being involved. The scaling of the resulting linewidths, however, is neither expected nor found to depend on repetition rate or non-linearity.

    View details for DOI 10.1364/OE.21.026244

    View details for Web of Science ID 000327007800084

    View details for PubMedID 24216849

  • Fluorescence Quenching over Short Range in a Donor-DNA-Acceptor System CHEMPHYSCHEM Ehrenschwender, T., Liang, Y., Unterreiner, A., Wagenknecht, H., Wolf, T. J. 2013; 14 (6): 1197-1204

    Abstract

    A new donor-DNA-acceptor system has been synthesized containing Nile red-modified 2'-deoxyuridine as charge donor and 6-N,N-dimethylaminopyrene-modified 2'-deoxyuridine as acceptor to investigate the charge transfer in DNA duplexes using fluorescence spectroscopy and time-resolved femtosecond pump-probe techniques. Fluorescence quenching experiments revealed that the quenching efficiency of Nile red depends on two components: 1) the presence of a charge acceptor and 2) the number of intervening CG and AT base pairs between donor and acceptor. Surprisingly, the quenching efficiency of two base pairs (73% for CG and the same for AT) is higher than that for one base pair (68% for CG and 37% for AT), while at a separation of three base pairs less than 10% quenching is observed. A comparison with the results of time-resolved measurements revealed a correlation between quenching efficiency and the first ultrafast time constant suggesting that quenching proceeds via a charge transfer from the donor to the acceptor. All transients are satisfactorily described with two decays: a rapid charge transfer with 600 fs (∼10(12) s(-1)) that depends strongly and in a non-linear fashion on the distance between donor and acceptor, and a slower time constant of a few picoseconds (∼10(11) s(-1)) with weak distance dependence. A third time constant on a nanosecond time scale represents the fluorescence lifetime of the donor molecule. According to these results and time-dependent density functional theory (TDDFT) calculations a combination of single-step superexchange and multistep hopping mechanisms can be proposed for this short-range charge transfer. Furthermore, significantly less quenching efficiency and slower charge transfer rates at very short distances indicate that the direct interaction between donor and acceptor leads to a local structural distortion of DNA duplexes which may provide some uncertainty in identifying the charge transfer rates in short-range systems.

    View details for DOI 10.1002/cphc.201200924

    View details for Web of Science ID 000317393000015

    View details for PubMedID 23532955

  • Electron tunneling from electronically excited states of isolated bisdisulizole-derived trianion chromophores following UV absorption PHYSICAL CHEMISTRY CHEMICAL PHYSICS Winghart, M., Yang, J., Kuehn, M., Unterreiner, A., Wolf, T. J., Dau, P. D., Liu, H., Huang, D., Klopper, W., Wang, L., Kappes, M. M. 2013; 15 (18): 6726-6736

    Abstract

    Photoelectron spectra of isolated [M-BDSZ](3-) (BDSZ = bisdisulizole, M = H, Li, Na, K, Cs) triply charged anions exhibit a dominant constant electron kinetic energy (KE) detachment feature, independent of detachment wavelengths over a wide UV range. Photoelectron imaging spectroscopy shows that this constant KE feature displays an angular distribution consistent with delayed rather than direct electron emission. Time-resolved pump-probe (388 nm/775 nm) two-colour photoelectron spectroscopy reveals that the constant KE feature results from two simultaneously populated excited states, which decay at different rates. The faster of the two rates is essentially the same for all the [M-BDSZ](3-) species, regardless of M. The slower process is associated with lifetimes ranging from several picoseconds to tens of picoseconds. The lighter the alkali cation is, the longer the lifetime of this state. Quantum chemical calculations indicate that the two decaying states are in fact the two lowest singlet excited states of the trianions. Each of the two corresponding photoexcitations is associated with significant charge transfer. However, electron density is transferred from different ends of the roughly chain-like molecule to its aromatic center. The energy (and therefore the decay rate) of the longer-lived excited state is found to be influenced by polarization effects due to the proximal alkali cation complexed to that end of the molecule. Systematic M-dependent geometry changes, mainly due to the size of the alkali cation, lead to M-dependent shifts in transition energies. At the constant pump wavelength this leads to different amounts of vibrational energy in the respective excited state, contributing to the variations in decay rates. The current experiments and calculations confirm excited state electron tunneling detachment (ESETD) to be the mechanism responsible for the observed constant KE feature. The ESETD phenomenon may be quite common for isolated multiply charged anions, which are strong fluorophores in the condensed phase - making ESETD useful for studies of the transient response of such species after electronic excitation.

    View details for DOI 10.1039/c3cp50497b

    View details for Web of Science ID 000317866300017

    View details for PubMedID 23549163

  • The interplay of different relaxation channels in the excited state dynamics of photoinitiators 18th International Conference on Ultrafast Phenomena Wolf, T. J., Fischer, J., Voll, D., Wegener, M., Barner-Kowollik, C., Unterreiner, A. E D P SCIENCES. 2013
  • Ultrafast photoinduced dynamics of halogenated cyclopentadienes: observation of geminate charge-transfer complexes in solution PHYSICAL CHEMISTRY CHEMICAL PHYSICS Wolf, T. J., Schalk, O., RADLOFF, R., Wu, G., Lang, P., Stolow, A., Unterreiner, A. 2013; 15 (18): 6673-6683

    Abstract

    The photoinduced dynamics of the fully halogenated cyclopentadienes C5Cl6 and C5Br6 have been investigated in solution and gas phase by femtosecond time-resolved spectroscopy. Both in solution and in gas phase, homolytic dissociation into a halogen radical and a C5X5 (X = Cl, Br) radical was observed. In liquid phase, solvent-dependent formation of charge transfer complexes between geminate radicals was observed for the first time. These complexes were found to be surprisingly stable and offered the opportunity to follow the dynamics of specific radical pairs. In the case of C5Cl6 in trichloroethanol, a reaction of the chlorine radical with molecules from the solvent cage was observed.

    View details for DOI 10.1039/c3cp44295k

    View details for Web of Science ID 000317866300011

    View details for PubMedID 23443649

  • Resonant tunneling through the repulsive Coulomb barrier of a quadruply charged molecular anion PHYSICAL REVIEW A Phuong Diem Dau, P. D., Liu, H., Yang, J., Winghart, M., Wolf, T. J., Unterreiner, A., Weis, P., Miao, Y., Ning, C., Kappes, M. M., Wang, L. 2012; 85 (6)
  • Elucidating the Early Steps in Photoinitiated Radical Polymerization via Femtosecond Pump-Probe Experiments and DFT Calculations MACROMOLECULES Wolf, T. J., Voll, D., Barner-Kowollik, C., Unterreiner, A. 2012; 45 (5): 2257-2266

    View details for DOI 10.1021/ma202673q

    View details for Web of Science ID 000301397800010

  • Novel Lanthanide-Based Polymeric Chains and Corresponding Ultrafast Dynamics in Solution INORGANIC CHEMISTRY Thielemann, D. T., Klinger, M., Wolf, T. J., Lan, Y., Wernsdorfer, W., Busse, M., Roesky, P. W., Unterreiner, A., Powell, A. K., Junk, P. C., Deacon, G. B. 2011; 50 (23): 11990-12000

    Abstract

    Two types of structurally related one-dimensional coordination polymers were prepared by reacting lanthanide trichloride hydrates [LnCl(3)·(H(2)O)(m)] with dibenzoylmethane (Ph(2)acacH) and a base. Using cesium carbonate (Cs(2)CO(3)) and praseodymium, neodymium, samarium, or dysprosium salts yielded [Cs{Ln(Ph(2)acac)(4)}](n) (Ln = Pr (1), Nd (2), Sm (3), Dy (4)) in considerable yields. Reaction of potassium tert-butoxide (KOtBu) and the neodymium salt [NdCl(3)·(H(2)O)(6)] with Ph(2)acacH resulted in [K{Nd(Ph(2)acac)(4)}](n) (5). All polymers exhibit a heterobimetallic backbone composed of alternating lanthanide and alkali metal atoms which are bridged by the Ph(2)acac ligands in a linear fashion. ESI-MS investigations on DMF solutions of 1-5 revealed a dissociation of all the five compounds upon dissolution, irrespective of the individual lanthanide and alkali metal present. Temporal profiles of changes in optical density were acquired performing pump/probe experiments with DMF solutions of 1-5 via femtosecond laser spectroscopy, highlighting a lanthanide-specific relaxation dynamic. The corresponding relaxation times ranging from seven picoseconds to a few hundred picoseconds are strongly dependent on the central lanthanide atom, indicating an intramolecular energy transfer from ligands to lanthanides. This interpretation also demands efficient intersystem crossing within one to two picoseconds from the S(1) to T(1) level of the ligands. Magnetic studies show that [Cs{Dy(Ph(2)acac)(4)}](n) (4) has slow relaxation of the magnetization arising from the single Dy(3+) ions and can be described as a single-ion single molecule magnet (SMM). Below 0.5 K, hysteresis loops of the magnetization are observed, which show weak single chain magnet (SCM) behavior.

    View details for DOI 10.1021/ic201157m

    View details for Web of Science ID 000297274600020

    View details for PubMedID 22066577

  • Pump–probe spectroscopy on photoinitiators for stimulated-emission-depletion optical lithography Optics Letters Wolf, T. J., Fischer, J., Wegener, M., Unterreiner, A. 2011; 36 (3188): 3188–90

    Abstract

    We report on femtosecond pump-probe experiments on two different photoinitiators in solution. These two molecules have recently appeared as attractive candidates for far-field optical lithography based on stimulated-emission-depletion (STED) inspired approaches aiming at beating Abbe's diffraction limit. For the case of 7-diethylamino-3-thenoylcoumarin (DETC), we find that stimulated emission clearly dominates over excited-state absorption, whereas the opposite holds true for the case of isopropylthioxanthone. We argue that it is desirable that stimulated emission dominates over excited-state absorption as depletion mechanism in STED photoresists. Thus, DETC is an attractive corresponding photoinitiator.

    View details for DOI 10.1364/OL.36.003188