Introduction: Ultrafast Processes in Chemistry - Chemical Reviews

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Editorial pubs.acs.org/CR

Introduction: Ultrafast Processes in Chemistry

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mechanics. Application of ab initio quantum molecular dynamics to systems of increasing structural complexity and the extension of classical molecular dynamics to large hydrated biomolecular systems in a time range up to microseconds represent other key developments. The increasing relevance of X-ray spectroscopy and structure-sensitive methods is reflected in novel theoretical concepts and methods for describing the nonlinear response connected with elementary excitations in this spectral range. This thematic issue provides an overview of recent developments and results, covering a broad range of ultrafast processes in chemistry. It is organized in four interconnected topical areas, • the structural dynamics and fluctuating interactions of molecular systems in their electronic ground state, with contributions by P. Hamm,1 T. Tahara,2 D. Laage,3 and M. Zanni et al.;4 • atto- to femtosecond processes in electronically excited states, discussed by M. Nisoli5 • photoinduced chemical processes in organic molecules, biological chromophores, and light harvesting systems with articles by E. Vauthey6 and V. Sundström et al.;7 and • ultrafast structural dynamics as mapped by time-resolved X-ray methods and electron diffraction, with contributions by M. Chergui8 and R. J. D. Miller et al.9

ltrafast science has a truly interdisciplinary and strong impact on modern physics, chemistry, and biology. Elementary electronic, atomic, and molecular motions and excitations in a time range from tens of attoseconds to several picoseconds are key topics which have been studied by the combination of time-resolved nonlinear spectroscopy with indepth theory and simulations. In chemistry, this approach has generated a wealth of knowledge on molecular processes, basic chemical events, and the mechanisms and interactions governing them. The 2004 thematic issue of Chemical Reviews, which was edited by M. Dantus and A. Zewail, represents an impressive collection of articles documenting the early development of the field and its particular potential. Recent progress in the field has initiated a number of developments with a strong impact on current research. The time resolution of ultrafast experiments has been pushed to the 100 attosecond domain by a systematic improvement of highharmonic sources. The spectral range in which intense ultrashort pulses are available now extends from the farinfrared or terahertz range up to hard X-rays. In the extended ultraviolet, soft and hard X-ray range, lasers and laser-driven sources have been complemented by accelerator-based free electron lasers, providing an unprecedented photon flux at sub50-fs pulse durations. Beyond photon sources, femtosecond electron pulses from laser-driven generation schemes find increasing application in probing transient molecular structures. Two-dimensional (2D) nonlinear spectroscopy in a range from far-infrared to X-ray wavelengths has developed into a key method for studying couplings between electronic and/or vibrational excitations and for elucidating interactions between molecules and their fluctuating environment in condensed phases. Applications include chemical processes in biomolecules and molecular systems at surfaces. Time-resolved X-ray absorption, Raman, and photoelectron spectroscopies have strongly benefitted from the novel short-wavelength sources and now address photoinduced chemical dynamics in great detail. The manifold of spectroscopic approaches has been complemented by ultrafast structure research based on timeresolved X-ray and electron diffraction methods. In contrast to optical spectroscopy, which probes the dielectric function of the system under study, diffraction techniques provide spatially resolved electron distributions or charge density maps from which the positions of atoms or molecular subunits can be inferred with a resolution of a fraction of a chemical bond length. This direct probing of transient structure allows for following chemical reactions, charge transport, phonon propagation, and other elementary processes in space and time. In combination with spectroscopy and theory, “molecular movies” are in reach now, and recent work demonstrates their strong potential for new insight. Recent progress in theory includes the treatment of coupled electron and nuclear dynamics in complex molecules, as well as detailed microscopic descriptions of elementary chemical processes by hybrid quantum mechanics and molecular © 2017 American Chemical Society

The collection of articles addresses new experimental and theoretical methods as well as a broad range of outstanding results. I would like to thank the Editor, Professor Joachim Heberle, for his encouragement, helpful discussions, and a continuous strong support of this endeavor which has benefitted decisively from his and his team’s dedication and efforts. I hope that this thematic issue will be most helpful for sharing our current insight with a broad audience and for developing new ideas and collaborations in the wider community.

Thomas Elsaesser

Max-Born-Institute and Humboldt University

AUTHOR INFORMATION Notes

Views expressed in this editorial are those of the author and not necessarily the views of the ACS. Special Issue: Ultrafast Processes in Chemistry Published: August 23, 2017 10621

DOI: 10.1021/acs.chemrev.7b00226 Chem. Rev. 2017, 117, 10621−10622

Chemical Reviews

Editorial

Biography

Thomas Elsaesser is a director at the Max-Born-Institute for Nonlinear Optics and Short-Pulse Spectroscopy, Berlin, Germany, and holds a joint appointment as a professor for experimental physics with Humboldt University, Berlin. Ultrafast processes in condensed matter represent his main area of research. Thomas Elsaesser received a Dr. rer. nat. degree from the Technical University of Munich in 1986 and worked there as a research associate until 1993. In 1990, he spent a postdoc period at AT&T Bell Laboratories, Holmdel, NJ. He finished his habilitation at the TU Munich in 1991 and joined the newly established Max-Born-Institute in 1993.

REFERENCES (1) Kraack, J. P.; Hamm, P. Surface-Sensitive and Surface-Specific Ultrafast Two-Dimensional Vibrational Spectroscopy. Chem. Rev. 2017, DOI: 10.1021/acs.chemrev.6b00437. (2) Nihonyanagi, S.; Yamaguchi, S.; Tahara, T. Ultrafast Dynamics at Water Interfaces Studied by Vibrational Sum-Frequency Generation Spectroscopy. Chem. Rev. 2017, DOI: 10.1021/acs.chemrev.6b00728. (3) Laage, D.; Elsaesser, T.; Hynes, J. T. Water Dynamics in the Hydration Shells of Biomolecules. Chem. Rev. 2017, DOI: 10.1021/ acs.chemrev.6b00765. (4) Ghosh, A.; Ostrander, J. S.; Zanni, M. T. Watching Proteins Wiggle: Mapping Structures with Two-Dimensional Infrared Spectroscopy. Chem. Rev. 2017, DOI: 10.1021/acs.chemrev.6b00582. (5) Nisoli, M.; Decleva, P.; Calegari, F.; Palacios, A.; Martín, F. Attosecond Electron Dynamics in Molecules. Chem. Rev. 2017, DOI: 10.1021/acs.chemrev.6b00453. (6) Kumpulainen, T.; Lang, B.; Rosspeintner, A.; Vauthey, E. Ultrafast Elementary Photochemical Processes of Organic Molecules in Liquid Solution. Chem. Rev. 2017, DOI: 10.1021/acs.chemrev.6b00491. (7) Ponseca, C. S., Jr.; Chábera, P.; Uhlig, J.; Persson, P.; Sundström, V. Ultrafast Electron Dynamics in Solar Energy Conversion. Chem. Rev. 2017, DOI: 10.1021/acs.chemrev.6b00807. (8) Chergui, M.; Collet, E. Photoinduced Structural Dynamics of Molecular Systems Mapped by Time-Resolved X-ray Methods. Chem. Rev. 2017, DOI: 10.1021/acs.chemrev.6b00831. (9) Ischenko, A. A.; Weber, P. M.; Miller, R. J. D. Capturing Chemistry in Action with Electrons: Realization of Atomically Resolved Reaction Dynamics. Chem. Rev. 2017, DOI: 10.1021/ acs.chemrev.6b00770.

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DOI: 10.1021/acs.chemrev.7b00226 Chem. Rev. 2017, 117, 10621−10622