Dalton Transactions EDITORIAL
Spectroscopy of inorganic excited states Cite this: Dalton Trans., 2014, 43, 17565
Julia A. Weinstein
DOI: 10.1039/c4dt90185a www.rsc.org/dalton
Understanding fundamental processes that drive light-induced molecular changes continues to be the focus of research uniting time and chemistry. The advent of ultrafast laser technology provides the tools to both selectively activate specific events, and probe induced changes through the eyes of spectroscopy, yielding unique insights into relating structure and function. The rich field of light-induced science has its roots in the early observations of the effect that sunlight had on colored objects many millennia ago, leading to the beginning of modern photochemistry in Ciamician’s laboratory in Bologna, progressing to the revolutionary developments of flash photolysis by Porter and Norrish, and further through laser-based methods into femtochemistry and the work of Zewail. The continuous technological development of ever faster, precise, and diverse time-resolved methods of interrogation keep redefining our understanding of light–matter interactions and its timescales. This themed issue of Dalton Transactions highlights the scope and breadth of developments in ultrafast photochemistry in metal-containing molecules and assemblies thereof – the “inorganic excited state toolbox”. The content of the issue illustrates how diversified and sophisticated the field of time-resolved spectroscopy in the context of inorganic excited states has become: the methods Department of Chemistry, University of Sheffield, S3 7HF, UK. E-mail: julia.weinstein@sheffield.ac.uk; Tel: +44 (0)114 222 9408
This journal is © The Royal Society of Chemistry 2014
presented cover decades of timescales, from femtoseconds to seconds, the length scales from small molecules to oligomers, and energies from a few tens of wavenumbers to several electron Volts. Accordingly, the papers presented cover an extremely diverse range of science, from detailed insights into the structure of excited states inferred from Raman spectroscopy, to photoreactivity of metal carbonyls and polyazides, photoisomerism, organic/inorganic hybrid emissive species, photophysics of DNA intercalators and direct observation of evolution of spin-states. Representative examples of applications of photoactive metal complexes – which span a range of coordination centres across the entire periodic table – include conjugated oligomers and polymers as potential optical power limiting materials, oxidation catalysts, triplet photosensitizers for photoredox reactions, or light-activated drugs. The success in elucidating lightinduced chemical dynamics often relies on our ability to identify transient species involved. Spectroelectrochemical studies of electrochemically generated radical species using UV, visible, IR, Raman or EPR spectroscopies of electrochemically generated radical and/or ions are invaluable tools in this regard, and the interplay between photochemistry and electrochemistry has been demonstrated in several contributions. Intertwined with the experimental progress, enormous advances in theoretical and computational approaches to
electronic structure and dynamics of inorganic excited states are illustrated by several papers, including the work describing direct incorporation of Spin– Orbit Coupling in TD-DFT calculations which finally permits investigation of ultrafast (femto-picosecond) intersystem crossing, and high precision calculations of resonance Raman spectra of metalcontaining species. Of particular interest is the fact that the drastic advances in individual methods made it feasible to combine optical excitation with other types of interrogation techniques – such as X-ray absorption and diffraction, electron diffraction, and magneto-optical methods. The power of combining ultrafast laser excitation with X-ray interrogation methods is illustrated in the example of X-ray transient absorption study of interfacial electron injection from an excited state of Cu(I) diimine complexes to a TiO2 nanoparticle. In this experiment, a laser pulse creates the excited state of the diimine complex, and an X-ray pulse probes the structural changes of the complex during the electron injection at different time delays after the photoexcitation, building a “molecular movie” in real time. An exciting emerging direction in method development is that of transient multidimensional infrared spectroscopy, T-2DIR, which permits direct study of vibronic coupling and energy dissipation pathways of non-equilibrated, electronically excited states – so far, there are only few examples of application of T-2DIR to inorganic systems, but the
Dalton Trans., 2014, 43, 17565–17566 | 17565
Editorial
potential of such studies is clearly enormous. Whilst it is impossible to cover all aspects of the field in any single collection, the trends evident from the papers published herein reflect broader trends in the field. Two particularly prominent current features are that most of the experimental contributions include calculations at various levels of complexity,
17566 | Dalton Trans., 2014, 43, 17565–17566
Dalton Transactions
and that the majority of the work now combines several interrogation methods as a matter of course. Bringing together the great diversity of excited states, the ultrafast initiation of the transformations, the extremely sensitive detection technologies, and novel theoretical methods – the fascinating world of “inorganic excited states” is developing ever faster.
I would like to thank all the authors for their enthusiasm, time and effort in supporting this issue – the contributions of over 180 scientists from 21 different countries all over the world is the best testimony to how fascinating, important and exciting this field of science is. I am most grateful to colleagues at the Dalton Transactions editorial office for making this issue possible.
This journal is © The Royal Society of Chemistry 2014
Copyright of Dalton Transactions: An International Journal of Inorganic Chemistry is the property of Royal Society of Chemistry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
Spectroscopy of inorganic excited states Cite this: Dalton Trans., 2014, 43, 17565
Julia A. Weinstein
DOI: 10.1039/c4dt90185a www.rsc.org/dalton
Understanding fundamental processes that drive light-induced molecular changes continues to be the focus of research uniting time and chemistry. The advent of ultrafast laser technology provides the tools to both selectively activate specific events, and probe induced changes through the eyes of spectroscopy, yielding unique insights into relating structure and function. The rich field of light-induced science has its roots in the early observations of the effect that sunlight had on colored objects many millennia ago, leading to the beginning of modern photochemistry in Ciamician’s laboratory in Bologna, progressing to the revolutionary developments of flash photolysis by Porter and Norrish, and further through laser-based methods into femtochemistry and the work of Zewail. The continuous technological development of ever faster, precise, and diverse time-resolved methods of interrogation keep redefining our understanding of light–matter interactions and its timescales. This themed issue of Dalton Transactions highlights the scope and breadth of developments in ultrafast photochemistry in metal-containing molecules and assemblies thereof – the “inorganic excited state toolbox”. The content of the issue illustrates how diversified and sophisticated the field of time-resolved spectroscopy in the context of inorganic excited states has become: the methods Department of Chemistry, University of Sheffield, S3 7HF, UK. E-mail: julia.weinstein@sheffield.ac.uk; Tel: +44 (0)114 222 9408
This journal is © The Royal Society of Chemistry 2014
presented cover decades of timescales, from femtoseconds to seconds, the length scales from small molecules to oligomers, and energies from a few tens of wavenumbers to several electron Volts. Accordingly, the papers presented cover an extremely diverse range of science, from detailed insights into the structure of excited states inferred from Raman spectroscopy, to photoreactivity of metal carbonyls and polyazides, photoisomerism, organic/inorganic hybrid emissive species, photophysics of DNA intercalators and direct observation of evolution of spin-states. Representative examples of applications of photoactive metal complexes – which span a range of coordination centres across the entire periodic table – include conjugated oligomers and polymers as potential optical power limiting materials, oxidation catalysts, triplet photosensitizers for photoredox reactions, or light-activated drugs. The success in elucidating lightinduced chemical dynamics often relies on our ability to identify transient species involved. Spectroelectrochemical studies of electrochemically generated radical species using UV, visible, IR, Raman or EPR spectroscopies of electrochemically generated radical and/or ions are invaluable tools in this regard, and the interplay between photochemistry and electrochemistry has been demonstrated in several contributions. Intertwined with the experimental progress, enormous advances in theoretical and computational approaches to
electronic structure and dynamics of inorganic excited states are illustrated by several papers, including the work describing direct incorporation of Spin– Orbit Coupling in TD-DFT calculations which finally permits investigation of ultrafast (femto-picosecond) intersystem crossing, and high precision calculations of resonance Raman spectra of metalcontaining species. Of particular interest is the fact that the drastic advances in individual methods made it feasible to combine optical excitation with other types of interrogation techniques – such as X-ray absorption and diffraction, electron diffraction, and magneto-optical methods. The power of combining ultrafast laser excitation with X-ray interrogation methods is illustrated in the example of X-ray transient absorption study of interfacial electron injection from an excited state of Cu(I) diimine complexes to a TiO2 nanoparticle. In this experiment, a laser pulse creates the excited state of the diimine complex, and an X-ray pulse probes the structural changes of the complex during the electron injection at different time delays after the photoexcitation, building a “molecular movie” in real time. An exciting emerging direction in method development is that of transient multidimensional infrared spectroscopy, T-2DIR, which permits direct study of vibronic coupling and energy dissipation pathways of non-equilibrated, electronically excited states – so far, there are only few examples of application of T-2DIR to inorganic systems, but the
Dalton Trans., 2014, 43, 17565–17566 | 17565
Editorial
potential of such studies is clearly enormous. Whilst it is impossible to cover all aspects of the field in any single collection, the trends evident from the papers published herein reflect broader trends in the field. Two particularly prominent current features are that most of the experimental contributions include calculations at various levels of complexity,
17566 | Dalton Trans., 2014, 43, 17565–17566
Dalton Transactions
and that the majority of the work now combines several interrogation methods as a matter of course. Bringing together the great diversity of excited states, the ultrafast initiation of the transformations, the extremely sensitive detection technologies, and novel theoretical methods – the fascinating world of “inorganic excited states” is developing ever faster.
I would like to thank all the authors for their enthusiasm, time and effort in supporting this issue – the contributions of over 180 scientists from 21 different countries all over the world is the best testimony to how fascinating, important and exciting this field of science is. I am most grateful to colleagues at the Dalton Transactions editorial office for making this issue possible.
This journal is © The Royal Society of Chemistry 2014
Copyright of Dalton Transactions: An International Journal of Inorganic Chemistry is the property of Royal Society of Chemistry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
